***Your Christmas Day Forecast***

First and foremost, a very merry Christmas to everyone. I've decided to provide a small weather forecast, not only for the anticipated Fire on Ice fireworks display taking place tonight, but also for any plans that may be in place for the day in its entirety. The weather is cooperative in general, but it's chilly. Here is what to typically expect for Christmas day:

Temperature/Humidity

Temperatures are again going to be chilly and below seasonal at -6 to -7 C during the afternoon hours with a slight windchill factor of -8 to -10 C. By early-mid evening, I am anticipating temperatures to fall to -8 to -9 C with continued light winds generating a windchill of -11 to -13 C. Moisture levels are very low.

Precipitation

Not much to report in this section. However, a weak disturbance South of the border will bring us some cloudy periods during the early evening through to Boxing day. For the day itself, skies are expected to be mostly sunny with a few mid to high level clouds.

Wind

Yet again, winds are expected to be very light in nature at speeds anywhere between 7-9 km/h during the day. With the strong area of high pressure to the West, directional tendencies are generally out from NNW early in the day, but then transitioning over variably from between the North to NNE by the time the fireworks are set to begin. I also believe that winds will slightly decrease during the evening to between 4-7 km/h (periods of calm conditions are also possible). Consequently, smoke should predominantly be blowing very slowly away (if the very light winds are present at the time) from spectators who are stationed either SW or SSW relative to the firing site. Some brief moments of smoke buildup could also develop, but not extensively as moisture levels are very low - this is more of an issue during the Summer.

That's what we should generally expect as far as the weather is concerned for Christmas day. To sum it up, calm conditions to very light NNW to later NNE winds along with chilly temperatures. Cloudy periods will later move in following dusk. So, dress warm and enjoy the day to the fullest!
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With respect to the Nor'easter that I referred to previously, it is still projected to rapidly intensify, enough that it will earn itself the title of "weather bomb" - that is, a low pressure area whose central pressure has dropped at least 24 millibars (mb) within a 24-hour time frame. This storm will unleash heavy rains and near-hurricane force winds following Boxing day in the maritimes and eventually Newfoundland - this is particularly devastating as the Atlantic provinces are still recovering from the impacts of the recent Nor'easter. The weather system seems to also be traveling closely along to Atlantic seaboard, so we will also likely receive some gusty northwesterly winds here in southern Quebec Monday into early Tuesday assuming that the storm maintains its current course. Northwesterly winds in SW Ontario from this storm would mean ongoing snowsquall activity along the southeastern shores of Lake Huron. In addition, because we will be on the back end of the system, the storm will maintain temperatures below seasonal for the first half of the holiday week. I will keep an eye on the track of the system as well, as it could potentially result in some decent snowfall if it moves closer along the eastern seaboard - at this point, that is not the case (as mentioned in the previous post), but it's still something to monitor in future model runs.

Merry Christmas and happy holidays!

Trav.

Just one small update with respect to the winds for the fireworks tonight. Speeds are still projected to be very light to occasionally calm early this evening, but I am detecting a possible shift in direction locally from the WSW by roughly 7-9:00 p.m before North to NNE tendencies take place. If present, this would cause smoke to blow slowly towards some spectators. If there is no shift, expect the light winds from the NNE. Everything else holds constant, as described in the above post.

And I did forget to mention previously that there is the possibility of a Winter storm for late New Year's Eve into New Year's Day. We'll continue to track that storm as the week progresses.

Trav.

Following a week of relatively chilly weather, above seasonal conditions are making their debut to end 2010 and to bring in 2011. Two areas of low pressure (including a Colorado Low) are advancing northeast towards eastern Canada and are expected to bring with them a variety of precipitation. Originally, the Colorado Low was the Winter storm that I had initially mentioned since several days now in the above post, but due to its current rapid northerly track, this storm is no longer expected to deliver significant snowfall here in southern Quebec. Instead, we will see a variety of precipitation, but most of it will likely be in the form of a cold rain. As we are only concerned with New Year’s Eve to New Year’s Day, here is what to generally expect in terms of weather in southern Quebec for the festivities and, of course, the fireworks:

Your New Year’s Forecast:

Temperature/Humidity

Temperatures will continue to be well above seasonal for New Year’s Eve into New Year’s Day with values holding steady from 3-5 C, including for the evening-overnight period. Moisture levels are elevated, so although it is relatively mild, the dampness of the air would invite a more piercing-like cold whenever encountering the light winds. The light winds would therefore be enough to generate a slight windchill factor of 1 to 0 C. Patches of fog could develop early New Year’s Eve as dewpoint levels rise to near to slightly above freezing.

Precipitation

Being in the warm sector of air associated with these low pressure systems, the unsettled atmosphere will bring mainly cloudy conditions throughout New Year’s Eve and New Year’s Day along with occasional periods of a cold light drizzle to light rains – for Friday, the probability of precipitation (P.O.P.) is 70% during the early morning hours, followed by mostly cloudy skies (40% P.O.P.) for the afternoon and then a return to periods of light drizzle to light rain for the evening-overnight (70%) - probabilities will rise to 80% for most of Saturday. The overhead cloud cover will also play a role in keeping temperatures fairly constant from Friday through to early Sunday morning. A brief period of light wet flurries as well as freezing drizzle (be cautious with that) are also possible tonight (Thursday) into early New Year’s Eve before a transition to drizzle and light rain showers during the morning hours.

Wind

Winds are once again light in nature and, due to the warm airmass, are from the SSW to eventually South by late evening. Wind speeds range from 7-11 km/h through the day. As such, smoke from the fireworks display should be blowing mostly towards your right (if looking SW). I understand from STL that spectators tend to be stationed farther away from the firing site for this event as compared to the displays associated with the Fire on Ice. Still, try to avoid the North to North-northeast sections, if possible.

That’s the way the weather should behave. In summary, mostly cloudy conditions with periods of drizzle to light rains accompanied by relatively light winds from the SSW for Friday evening. If heading to the fireworks, bring an umbrella, or a hooded jacket, just in case. Temperatures will progressively decline through Sunday and the rain will briefly transition over to a rain-snow mix to straight snow as that cold front slices through. Temperature values will therefore be at their highest for the day Sunday early in the morning before a gradual return to more seasonal to slightly below seasonal standards - this will prompt sudden freeze conditions late Sunday, so be wary of that as icy surfaces quickly take form.

I wish everyone a safe and happy new year.

EDIT: Last weather report for 2010! What a year this was as far as weather and natural disasters are concerned!

Trav.

Thanks Travis ! Happy New Year !

I'm now heading to the Old Port to prepare tonight's display with FAE's crew. I'll film it as usual, but I'm less familiar with the Jacques-Cartier Place vantage point so I don't really know what will come out of this...

For the final display of the Fire on Ice event being held tonight, the weather is looking to be a little chilly and unsettled. Over the last number of days, a chain of weak disturbances (clippers) rapidly tracked from West to East (courtesy of a fairly zonal jet stream), bringing with them ongoing periods of snowfall. This pattern is expected to continue for today and early Sunday due to an upper level low, which is supporting the development of a Nor'easter that is moving up the Atlantic towards the maritimes and Newfoundland. With the atmospheric setup, here is what to generally expect for this evening:

Temperature/Humidity

Temperatures are expected to be somewhat chilly but above seasonal for the day and into the evening-overnight at -4 to -5 C. Considering the winds, the windchill factor generated would be between -9 to -12 C. Moisture levels are relatively low, and the relative humidity is 70-80% (closer to 85% during the day).

Precipitation

With the instability associated with the strong (and large) upper level low, mostly overcasted conditions will prevail for today and the first half of Sunday along with on and off periods of flurries to light snow (amounts are up to 5 cm by mid-way Sunday). A little more sunshine should appear gradually for later Sunday, but the gusty winds from the Nor'easter will keep temperatures down.

Wind

The developing Nor'easter will be directing the general wind flow for eastern Canada for the weekend and into Monday. As such, winds are typically borderline light to moderate for this evening at 12-16 km/h and coming out from the North to NNE - this would be ideal as smoke would be blowing towards the water and, therefore, directly away (if looking to the SW-SSW) from the audience. This also makes things a little comfortable as the winds would be blowing from behind you (again if looking SW-SSW).

That's the way the weather should behave. To summarize, cool temperatures, possible periods of flurries to light snow under mostly light-moderate wind speeds. Be sure to dress accordingly. Strong areas of Arctic high pressure will eventually bring fair weather, though will also drop temperatures down to seasonal to below seasonal (well below seasonal out West) for the coming week across much of North America, so be sure to dress warm!

So, I guess this is it until Summer - that is unless major weather events are set to take place here in Montreal.

Enjoy the final display for all those in attendance!

Trav.

Just cautioning that dangerously cold weather is expected to settle into much of eastern Canada for this weekend and the start of the work week as a strong area of Arctic high pressure presses southeastward. This shot of intense cold air could send temperatures down to as low as -18 to -20 C (generated windchill factor between -24 to -28 C with the light winds) for daytime highs accompanied by overnight lows that are not too far away from the -30 C threshold (windchill factor of -32 to -37 depending on wind speed), particularly for both Sunday and Monday night. Temperatures will gradually rise closer to seasonal standards around mid way into the work week and onwards as a weak clipper system from the West moves in and brings some snow. The degree of cold forecasted for this weekend was last seen in January 2009, which was one of the coldest Januaries on record.

If you must be outdoors for whatever reason, please try and mininmize your exposure time to the cold. It is in times like these that I need to be situated far South or reflect upon the nice hot days of Summer 2010:

http://i18.photobucket.com/albums/b132/Rain12/CIMG3434.jpg

Spring officially arrives in 58 days, 20 hours and 42 minutes.

Trav.

In addition to the above, there is the possibility of a potential major snowstorm (our second) by late Wednesday into Thursday. An area of low pressure will eventually be developing over the Gulf of Mexico and strengthen into the next Nor'easter as the week progresses. Right now, the amount of snow we receive is a matter of storm track. For the history of this season, the path that most Nor'easters took were generally North, and then northeast once reaching the maritimes, which led to smaller amounts of snow here in southern Quebec and larger quantities over many parts of Atlantic Canada. Unlike most previous Atlantic storms, however, this time there may be a strong area of high pressure over the North Atlantic that could prevent the storm from migrating too much to the northeast as it travels northward, which is elevating our chances of sharing this system - current model projections seem to be illustrating this, as they are keeping the storm farther inland along the eastern seaboard before a possible shift to the North-northeast. Because we would be on the back end of the system, this would be a snow event along with gusty North-northeasterlies. The weak clipper system I mentioned above will also merge with this storm.

As there is still plenty of time for this Nor'easter to shift its course, there are, of course, no guarantees that we will in fact see large snowfall - it is, therefore, important to continue to monitor the system for the next few days. If the storm maintains its projected trajectory, it could lead to significant snowfall here in southern Quebec and eastern Ontario (potentially in excess of 20 cm). If there is even a slight shift to the Northeast, then this would result in much less snowfall totals. Assuming it adheres to its current path, you will hear more about the storm in the coming days.

Temperatures are warming up significantly into the work week towards more seasonal standards due to, again, a weak clipper passing through, which could provide a little snow Monday night into Tuesday. Until then, dress very warmly if heading outdoors, and, if possible, try to minimize your exposure to this cold, Arctic airmass.

Trav.

As it turned out since over the last few days, the Nor'easter mentioned above did in fact shift more to the northeast (due to that area of high pressure over the North Atlantic weakening) and, consequently, left us with minimal snow accumulations here in southern Quebec but considerably larger amounts across many parts of the U.S northeast (roughly 50 cm in New York City) and Atlantic Canada, along with hurricane force wind gusts in parts of the maritimes.

I do have my eyes on yet another prospective storm system that may become an important weather player to start off February 2011, although this time this doesn't appear to be a Nor'easter. Currently, the models are detecting an area of low pressure to be eventually developing in the southern U.S Midwest (right now, it looks to be originating in Texas). For some technical details, there seems to be ideal upper level support for this intensifying surface low, as there is a progressively deepening trough to the West. Additionally, an intense area of Arctic high pressure over northwestern Canada could assist in enhancing the circulation of this system with the injection of cold air on its western and northwestern flanks. The divergence zone associated with the trough in the polar jet stream also seems to be flowing northward towards southern Ontario and southern Quebec, which would allow the system to travel in this direction after intensification.

The storm is, of course, a longshot, and the track still needs to be monitored over the coming days, but it appears that this system could be fairly moisture-rich if it continues developing in the manner that the models are projecting. If anything, this would be an event for late Tuesday into Wednesday for southern Quebec and southern Ontario. Could be a messy way to start off February 2011, but again, it is important to monitor the evolution and trajectory of this next potentially large storm system. When the models are later in agreement, it would then become easier to assess snowfall amounts providing that it comes to the system having an impact.

Trav.

The storm that I had outlined in the post above several days ago is expected to affect much of the eastern portion of North America. Because of the intensity and track associated with this powerful area of low pressure, large amounts of snow are possible from SW Ontario stretching all the way to Nova Scotia. For us here in southern Quebec, I am anticipating a minimum of 15 cm worth of snow and a maximum of 18-20 cm from today (Tuesday, February 1st) to the early morning of Thursday due to the speed and trajectory of the center of low pressure. As mentioned previously above, the storm is moisture-rich in its warm sector, so this is also contributing to potentially larger amounts of snowfall.

What we will be experiencing through today is an initial pulse of moisture associated with the principal low. This preliminary wave of energy will deliver periods of snow this afternoon before the main storm system itself advances, which will provide the bulk of snow across Ontario and Quebec through Wednesday, starting early near sunrise. Because of the storm track, the heaviest bands of snow will be located into SW Ontario and New York (and eventually Nova Scotia) - these regions could see locally in excess of 35 cm of snow. Even though we are avoiding the strongest areas of the system, the total amount of snow that we receive could still be enough to be considered significant and, therefore, may prompt Winter storm/snowfall advisories within the next 12 hours or so in southern Quebec (they already have in Ontario). Also, please note that the winds will be sustained at 33-37 km/h (gusts occasionally close to 48-51 km/h) from the NE for Wednesday, so expect blowing and drifting snow as well as near-zero visibility. Temperatures are close to -10 to -11 C for Wednesday, so the snow should be powdery in texture.

In the U.S, this storm is bringing terrible weather conditions, with heavy snow to the North and enduring periods of freezing rain along a narrow band farther South into the Midwest and the eastern U.S. Into the southern U.S, this is all rain, and even severe thunderstorms and tornadoes are possible in these areas. This gives you an idea as to the scope of this storm system and its dynamics!

I am watching yet another potential storm system that may affect the eastern U.S and eastern Canada later this weekend, so we'll have to keep an eye on that one. If anything, I don't think this prospective storm will deliver the same sort of punch as this upcoming one, although it's still a possibility in the later numerical model outputs. Luckily, temperatures are dramatically rising across much of the country (Montreal included) to seasonal to above seasonal standards later on in the week and onwards.

And it is with great, great delight that I can say that January has concluded! With luck, the groundhogs will provide us with some good news tomorrow for Groundhog Day.

EDIT: Given the moisture content associated with this storm system and after reviewing some of the newer model runs, it is actually possible to see locally as much as 22-25 cm by Thursday morning here across southern Quebec. Texas lows tend to carry massive amounts of moisture with them within their warm sectors, generating copious snows on their northern peripheries. The center of the low is also closely passing to our South.

The latest satellite (infrared) imagery of this storm system:

http://aviationweather.gov/adds/satellite/displaySat.php?region=US&isi ngle=single&itype=irbw

Notice the defined comma-like structure of the system - this indicates powerful cyclogenesis. The bright white signatures on this image represent the highest cloud tops (strong convection) - this is shown by that elongated bright cloud cluster that extends from the North to South, which roughly depicts the position of the cold front. Here, heavy rains and strong thunderstorms are taking place, especially farther South into Mississippi. To the North, the West-East extent of cloud curvature illustrates where all of the snow is located - this tends to be along and ahead of the warm front as well as wrapping around the back end of the system.

Trav.

I just wanted to briefly bring to your attention another Winter storm (an end-February storm) that will have some influence on eastern Canada overnight Sunday through to early Tuesday. A large and defined trough of low pressure over the western U.S will likely be fostering the development of a surface low just to the East, which appears to be an intense Colorado Low. Projections have the storm developing late Saturday and intensifying early Sunday in the Great Plains of the U.S. The rate of intensification may warrant "weather bomb" status through Sunday - the models don't seem to be detecting this in the strictest sense, but the total reduction in central surface pressure within a 24-hour period wouldn't be too far off of meeting the criteria regardless.

Despite the massive system, I am not entirely convinced that this is going to be a complete snow event as of yet, simply because of the storm trajectory - the models are in good agreement that the center of the low will be tracking North-northeastward (NNE) along the jet stream after strengthening. Consequently, although precipitation would likely start off as heavy snowfall overnight Sunday into early Monday (could be a fair load of snow), it would quickly transition over to mixed precipitation (perhaps some patchy freezing rain and ice pellets) and eventually rain through Monday before a rapid change back to snow Monday evening - hence "Winter storm". Due to the intense circulation of the system, there will be a great deal of moisture associated with it, and so an abundance of all types of precipitation, principally with respect to the rain and snow. The powerful circulation also means strong winds (gusts potentially near 75-80 km/h at times), first from the South to SSW for most of Monday and then gradually shifting from the North to NNW to WNW from Monday night into early Tuesday morning. Temperatures will drop off fast on Tuesday.

In the meantime, an area of low pressure will be skimming us to our South for Friday (tomorrow). Earlier simulations, as I had mentioned to Enkil previously, had the center of the low to be staying a fair deal South - however, recent projections are suggesting the center being stationed a little more to the North, which could result in larger amounts of snow here in southern Quebec (closer to 10-12 cm). There is also a good amount of moisture with this system, and so local amounts could actually be higher near 15-17 cm by overnight Friday. East of Montreal, amounts are nearly double. Note that winds will also be gusty at times, especially during the afternoon period - winds are sustained at 24-35 km/h during the afternoon, with gusts occasionally attaining 50-53 km/h, so expect blowing and drifting snow. Snow should start lightly not too long after sunrise and pick up during the afternoon hours. This storm is also responsible for severe thunderstorms and potentially tornadoes in the U.S South and southern midwest today (we're heading into that time of year again).

In short, it's a sloppy next week and a half with one system after the next - this pattern is responsible for our overall near-seasonal temperature distribution over the next while.

This Winter has been the contrast from last year's across most of the country, eh?

Trav.

After following this potential Winter storm, which consisted of a series of systems, for several days now, it turns out that my predictions mostly came into fruition concerning the evolution and, to some extent, the timing of these systems. I was vigilantly monitoring the trajectory of the last of the two systems, simply because the added snows from this storm could result in larger accumulations by Monday afternoon. As this system is traveling close enough westward as it heads NNE, total snow accumulations could be as much as 20 cm (likely closer to 15 cm - on top of the snow that we received this morning after the rain transitioned) by Monday afternoon (worst case scenario is 23-25 cm *note that this is more prevalent for areas East of Montreal). Watch also for gusty northerly to NNE winds overnight tonight (Sunday) into the early morning hours of Monday - winds are sustained at 27-31 km/h and gusts are as much as 43-48 km/h for this timeframe.

I am now focused on the next storm system (a Colorado Low) that could begin to have some influence starting Wednesday night through to Friday. As I mentioned briefly to Enkil, this storm will likely produce a mixed bag of precipitation, much like these last series of systems. However, snow amounts could be significant before a transition to ice pellets/ freezing rain and rain. Winds will also likely be gusty, first from the ESE to SE and later from the NNW to NW as the system departs by the very end of the week. We'll continue to track this system.

For those of you who are Facebook users, you are more than welcome to visit my profile that I have there. I rarely use Facebook, but I found it to be a neat way to post coverage on major storm systems (or significant weather events) whenever they threaten Montreal and surrounding areas. As such, I post notes on my profile if I detect a prospective storm over the short and long term that could have some impact. If you are interested, I invite you to check out my updates whenever storms are possible - I am not exactly certain how Facebook operates, but I think listed friends receive notifications when someone posts something? I can also continue to post coverage here, if you want me to, but then I feel that I would be bombarding the Montreal fireworks forum with weather!

My profile:

http://www.facebook.com/profile.php?id=738801345

Alternatively, you may also follow me on my YouTube channel:

http://www.youtube.com/user/Rain1290?feature=mhum

Edit: Oh yes, I am happy to say that we will soon be putting the clocks one hour forward. This will take place next Sunday, March 13th.

Trav.

Winter storm/snowfall potential (March 9th-10th)

As mentioned in my last post three days ago, the next storm system, a Colorado Low, is expected to have an impact in much of eastern Canada starting tonight (March 9th) through to the weekend - the prolonged effect of this unstable weather is for reasons that I will explain shortly. The forecast is a little tricky for us here in southern Quebec, but unlike southern Ontario, the amount of snow that we receive from this storm could be significant from tonight stretching into later tomorrow (Thursday) before a transition to ice pellets/patchy freezing rain and then to rain by late afternoon Thursday into Friday. Total snow accumulations could be up to 15-20 cm at this point in time, although higher amounts of snow (potentially near a foot) are possible depending on how long the transition to a mix takes. Luckily, most of this snow should melt in the following days as temperatures rise to as much as 5 C along with the rainfall.

The principal reason for the enduring instability from tonight through to the weekend is simply because there is another system coming in from the West, an Alberta Clipper, that will begin to have some impact through Saturday. However, this upcoming first system, the Colorado Low (which is soon merging with a separate low from the South), will be stalled because of strong blocking high pressure over the North Atlantic, causing the system to linger for a little while longer. Furthermore, this will give the approaching Alberta Clipper the chance to fuse with it by the weekend, creating one large storm. Fortunately, the ongoing effect of these two systems could keep temperatures above seasonal later this week into the weekend (maintaining mostly rainfall for Saturday), but as the resultant low finally makes its departure later Sunday, the rain may change back over to some accumulating snow for early to mid Sunday. There may also be a change to snow late Friday to early Saturday before on and off periods of rain return later Saturday. Temperatures quickly drop off through Sunday and into Monday, and the sun returns for Monday, although temperatures are once again below seasonal. Winds also remain fairly gusty but shifting direction from SW to NNW for Sunday and early Monday. Winds should be gusting mostly from the ESE to SE from Thursday to early Friday but becoming easterly for later Friday and SSE to southerly for Saturday.

That's the way the weather seems to be behaving for the next little while - essentially back and forth with precipitation but generally mild. If snow amounts are expected to reach the estimated values that I had specified above by Thursday afternoon, then you will see Winter storm (because of possible freezing rain and ice pellets following the snow)/snowfall advisories popping up in the near future.

As far as accumulations with the previous snowfall are concerned, if you include the 4.4 cm that fell after the rain changed over to snow Sunday morning (March 5th) and then the wave of snow from the last system Sunday night into the first half of Monday, then it is about 19-20 cm. I will verify the official figures later on. Actual snow depth on the surface is roughly 25 cm (locally higher) here in Montreal as of the early morning of March 8th.

*I am currently monitoring a prospective storm, another Colorado Low, that "may" have an influence in time for next weekend, just before Spring officially arrives. We'll see what turns up with this.

Trav.

Here is my personal weather outlook and corresponding analysis for Spring-Summer 2011, specifically for eastern Canada and focused on the Montreal area. This outlook can also be found on my Facebook homepage, but I had also wanted to share it here. The introduction emphasizes the average weather patterns that were observed this past Winter, which is followed by the Spring-Summer 2011 outlook. Towards the end, you will find some statistics that broadly define what was previously described in the introduction.

*A near-average temperature and average to above average precipitation trend is possible for the Spring-Summer period in much of eastern Canada this year (more details below).

After the typical Winter season of 2010-2011 and Spring’s refusal to commence appropriately, many are curious as to what sort of weather patterns could be awaiting for the Spring to Summer 2011 period. For those of you who recall my prediction for this past Winter, I predicted a typical end-Fall to Winter season - that is, a Winter showing average to slightly below average temperatures and average to above average snowfall. This outlook did not necessarily imply a harsh Winter season by any means but rather a more Winter-like one. As compared to the previous Winter of 2009-2010, which was directed by strong El Nino conditions, it turned out that Winter 2011 was, as expected, quite the sharp contrast, where we had seen temperatures closer to average and snowfall that was well above the seasonal mean. For a closer examination and comparative analysis of Winter 2009-2010 versus Winter 2010-2011 for Montreal, please refer to the compiled statistics below following my personal “Spring-Summer outlook” section.

For this past season, we had markedly seen an increase in bitterly cold episodes (especially towards the end of January where consecutive overnight lows reached near -30 C), while major snowfall episodes (characterized as near 15 cm or more of accumulating snow) also showed a defined increase from last year. Individually, many days, most notably in February, had appreciable snowfall. If we consider each of the Winter months in terms of monthly maximum and minimum temperatures (all monthly max and min temperatures averaged), values have been slightly above average (relative to 1971-2000 climatology). However, average daily maximums by themselves were conversely normal to slightly below normal. Therefore, the overall slightly above average temperature trend was attributed to the generally above average daily minimum temperatures, which was enough to offset the pattern exhibited by the daily maximums. At the very end, this was more of a Canadian-like Winter.

The borderline moderate-strong La Nina that had been in place was the basis of my predictions for this past Winter. La Nina conditions, again, are observed when sea-surface temperatures (SSTs) in the eastern and central equatorial Pacific decline to below average values (negative anomalies) to certain thresholds and last for at least seven consecutive months. As represented in the ENSO (El Nino Southern Oscillation) models, this La Nina phase, however, has been rapidly dwindling through the Winter season, to the point where slightly above normal values (positive anomalies) have surfaced in the extreme eastern equatorial Pacific through February - this suggests that we could see a continued gradual weakening of La Nina during the Spring until near-neutral, though still slightly negative, conditions are present by this Summer. This rapid warming that had taken place in February was likely partly due to a strong Kelvin wave (as suggested by NOAA), which is a fast and enormous (large North-South extent) eastward propagating wave of warm water that travels along the equator from the western Pacific. The Kelvin wave seems to have been triggered by recent activity associated with the MJO (Madden Julian Oscillation), which is the common mechanism that generates these waves. In either case, a waning La Nina transitioning to near-neutral conditions is likely going to have at least some effect on our weather this Spring and Summer. Despite this current weakening, though, it is to my belief that La Nina’s influence will continue to have a grasp on the Spring to Summer period this year. As such, this is what I think could occur as far as temperature and precipitation are concerned:

Spring-Summer 2011 outlook

Temperature

In general, I don’t believe that both Spring and Summer 2011 will be as warm as what we had witnessed last year in 2010. Given the average jet stream configurations associated with the oceanic temperature patterns in the eastern and central equatorial Pacific, a weakening La Nina tends to produce a Spring that has average to slightly below average temperatures (in terms of average monthly daily maximums) for April to most of June. From the end of June through to August, it is with a fair likelihood that monthly temperatures could follow similar average tendencies, though a potentially warm August (under the assumption that a developing El Nino forms later in the Summer) is possible. This overall average temperature pattern suggests fewer heat waves and a reduction in days reaching 30 C or more as compared to Spring-Summer 2010, likely because of a more southerly-bound subtropical jet stream towards eastern Canada. I hope that my temperature assessment is largely incorrect, so that we receive a very warm Summer!

Precipitation

Predicting precipitation is always much more of a challenging task than it is for temperature for any given year. Previous years that entailed a transition from La Nina to near-neutral conditions in time for the Spring-Summer period have expressed considerable variability in rainfall from one year to another, especially for the Summer. That said, Spring precipitation has a tendency to be average to above average running from April to June, and it is possible that Spring 2011 could follow a similar pattern – this is, in part, because of the current moisture-rich soil surface (after a fairly snowy Winter) contributing to an increase in evaporation, and, therefore, an increased probability for enhanced precipitation. Thunderstorms may also contribute to the potentially above average rainfall mid-way to later in the season. It is equally probable that Summer 2011 could trace this trend, though more closer to average. Precipitation abundance is largely governed by the track of the jet stream, but if the subtropical jet stream maintains La Nina-like configurations and remains strong (and, therefore, more variable), it could signify a slight increase in severe weather in southern Ontario, southern Quebec and the U.S northeast because of increased directional and speed wind shear (winds that change in direction and speed with increasing altitude) in these regions, particularly from the end of June spanning towards mid August. Depending on the number of thunderstorms received, this could mean significantly more or less monthly rainfall at a local scale, simply because of the stochastic nature of thunderstorms.

Closing comments

To briefly synthesize the above, given the average atmospheric setup in response to a weakening La Nina, overall, we could see an average to below average temperature regime for Spring 2011, while precipitation follows an average to above average pathway. Summer 2011 could display monthly temperatures and rainfall that are about average, though monthly temperatures (in terms of daytime highs) could, at times, be slightly below average. Going a little further, some of the models are currently indicating that the equatorial Pacific could maintain ENSO-neutral conditions to even possibly weak El Nino configurations by the end of Summer. If neutral conditions are observed by that point in time, we can expect an average to slightly above average Atlantic and eastern Pacific hurricane season. Alternatively, if El Nino conditions develop and persist, then this activity would be below average with respect to total named storms. Kelvin waves, especially strong Kelvin waves, are believed to sometimes initiate an El Nino event following the warming in the eastern equatorial Pacific directly caused by the waves, so if an El Nino, even if weak in nature, does in fact form by late Summer and persists thereafter, it could signal a more forgiving end-Fall to Winter period (2011-2012), or, at the very least, for the duration of the first half of the Winter. All that said, large uncertainties exist in the models as to the overall status of the equatorial Pacific SST anomalies beyond Summer 2011, so it is still clearly something that needs to be closely monitored in the coming months.

I believe that there will be a fairly active tornado season in the U.S Midwest and southeast from April to June and for the northeast from later June to August. Tornado activity has already taken an unusually early active start this year in the U.S. Both El Nino and La Nina do not generate tornadoes themselves, but they can shift their overall geographic distribution because of differences in the average location of the jet stream when they are present. However, recent studies have suggested that La Nina years have a tendency of promoting more active and enduring tornado seasons, though these findings are inconclusive, principally because of the relatively short and inconsistent climate data records currently available to work with.
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Here are some statistics that I've tabulated to summarize a little of what was described above. The figures essentially serve to make a comparative analysis between Winter 2009-2010 and Winter 2010-2011 in order to see the contrast between the two very different seasons – you will see that, with the exception of December, these two seasons virtually mirrored each other. Particularly noticeable is how much degrees centigrade warmer January-March 2010 was as compared to January-March 2011. “Actual” temperature and precipitation values are compared for each month for the 2009-2010 and 2010-2011 seasons – that is, relevant figures for both seasons are separated by a “/” (read as 2009/2010 values for December and 2010/2011 values for the following months where applicable) for a given attribute for each respective month. Note that March has an extra figure that I threw in (represented by a “*”) showing the number of days reaching 10 C or more for the month in 2010 and 2011. “Normal” monthly values are reflected upon 1971-2000 climatology for the Montreal area.

December (2009 vs. 2010):
Normal December snowfall: 48.3 cm
Actual snowfall: 56.4 cm/70.6 cm
Monthly normal temperature (all daily maximums and minimums averaged): -6.3 C
Actual monthly average temperature (all daily maximums and minimums averaged): -5.4 C/-5.8 C
Monthly normal daily maximum: -2.2 C
Actual monthly average daily maximum: -2.1 C/-2.7 C
Normal average monthly snow depth: 8 cm
Actual average monthly snow depth: 10.5 cm/ 7.5 cm
Highest snow depth: 18 cm/13 cm
Number of days with a daily maximum at or above 0 C: 14/8
Highest daily maximum temperature: 8.1 C/12.6 C
Coldest daily minimum: -18.7 C/-21.6 C

January (2010 vs. 2011):
Normal January snowfall: 44.8 cm
Actual snowfall: 52.5 cm/33.0 cm
Monthly normal temperature (all daily maximums and minimums averaged): -10.4 C
Actual monthly average temperature (all daily maximums and minimums averaged): -6.4 C/-9.5 C
Monthly normal daily maximum: -5.7 C
Actual monthly average daily maximum: -3.2 C/-6.1 C
Normal average monthly snow depth: 15 cm
Actual average monthly snow depth: 10.5 cm/ 5.6 cm
Highest snow depth: 19 cm/9 cm
Number of days at or above 0 C: 10/3
Highest daily maximum temperature: 8.4 C/8.4 C
Coldest daily minimum: -21.4 C/-27.9 C

February (2010 vs. 2011):
Normal February snowfall: 43.3 cm
Actual snowfall: 47.8 cm/76.4 cm
Monthly normal temperature (all daily maximums and minimums averaged): -8.4 C
Actual monthly average temperature (all daily maximums and minimums averaged): -4.7 C/-7.6 C
Monthly normal daily maximum: -3.9 C
Actual monthly average daily maximum: -1.9 C/-3.2 C
Normal average monthly snow depth: 18 cm
Actual average monthly snow depth: 3.2 cm/19.1 cm
Highest snow depth: 8 cm/32 cm
Number of days at or above 0 C: 14/8
Highest daily maximum temperature: 4.6 C/9.6 C
Coldest daily minimum: -15.7 C/-19.0 C

March (2010 vs. 2011):
Normal March snowfall: 36 cm
Actual snowfall: 3.6 cm/43.2 cm
Monthly normal temperature (all daily maximums and minimums averaged): -2.3 C
Actual monthly average temperature (all daily maximums and minimums averaged): 3.3 C/-2.0 C
Monthly normal daily maximum: 2.2 C
Actual monthly average daily maximum: 7.8 C/2.5 C
Normal average monthly snow depth: 13 cm
Actual average monthly snow depth: 0.2 cm/7.3 cm
Highest snow depth: 2 cm/29 cm
Number of days at or above 0 C: 30/24
*Number of days at or above 10 C: 11/1
Highest daily maximum temperature: 15.7 C/11.2 C
Coldest daily minimum: -10.2 C/-20.4 C

Trav.