Wednesday, 29 May 2013

Yet Another Rainstorm

     A major slow-moving Colorado Low is poised to slam parts of southern Manitoba with excessive rainfall Thursday through to early Saturday. This system looks strangely similar to the major 4-day long storm of 2 weekends ago. However, there are a few small differences. The deformation boundary is expected to reach a bit further north and west this time. What this essentially means is that the heavy rains will reach a bit further west and north. Some of the areas that saw little to no rain last time will likely see high amounts this time. The storm is also expected to be a little shorter; lasting 2-3 days instead of 4. But that wont necessarily mean lower rainfall amounts. It will have an ample amount of time to pump in lots of moisture from the deep southern US. The flow of moisture can be seen in the map below.

Precipitable water map from the NAM model for Thursday afternoon showing the flow of moisture straight from the southern US

     Rain, heavy at times, is expected to move into southern Manitoba in the morning tomorrow. It will likely begin to rain in Winnipeg sometime in the morning. However, there is still a little uncertainty in the timing as some models are not bringing it until late afternoon and others early morning. We'll have to wait and see right now.

     Winds will be strong from the east/northeast at 40 km/h with gusts as high as 60 km/h at times. This will create upsloping near the escarpment and Riding Mountains which will give those areas higher rainfall amounts. A general 15-40 mm is expected throughout the day Thursday generally along and south of the Riding Mountains and from the southern Interlake southwards, with as much as 40-50 mm possible along the escarpment and Riding Mountains. 15-30 mm is expected for the Winnipeg region.

     There will be the potential for thunderstorms tomorrow as well. The best risk will remain south of the border, however scattered embedded thunderstorms are still likely close to the US border. Areas to the north of the border will have a smaller chance. I don't think we'll see storms here in Winnipeg, but just remember that the potential is there. Any storm activity will give locally enhanced rainfall amounts.

     On Friday, much of the same. Rain and wind will be the story with an additional 15-30 mm possible, with higher amounts locally along the escarpment. A few embedded storms will be possible in southeastern Manitoba.

     Conditions will improve on Saturday. Scattered showers are still expected in the early morning for southeastern portions of the province before things begin to clear out in the afternoon or evening.

     In total for the entire storm, a general 20-60 mm can be expected in southern Manitoba with locally higher amounts of 75 mm + possible along the escarpment. Here's my personal forecast for some select communities (updated at 11 am May 30):

     Note that amounts in Gimli and Dauphin will be highly dependant on the location of the deformation boundary. Dauphin may get more than forecast if the boundary is further north, but they may get little to nothing if it sets up further south. This is highly visible on the models this morning with a predicted range of 2 mm (NAM) to 94 mm (GFS) for Dauphin. This is a similar situation that Winnipeg experienced during the last storm 2 weekends ago when we were often right on the edge of the heavier rainfall.

Saturday, 25 May 2013

Winnipeg's Thunderstorm Drought

     We are now witnessing another side effect of the extended winter we had in April.

     Due to our late spring, it has been a very slow start to the thunderstorm season across southern Manitoba. We are now May 25, and we have yet to receive a single thunderstorm in Winnipeg. In addition, across all of southern Manitoba, only 7 thunderstorm days have occured so far.

     In Winnipeg, the beginning of our thunderstorm season this year is already a month behind. The 1981-2010 normal date to get our first thunderstorm is April 26!

    As of today, May 25, we have already reached 5th latest start to the thunderstorm season on record. Only 3 times since 1953 have we not received our first storm until June (1958, 1992 and 1995). (Note: this was determined with data from the airport only, therefore this is not representative of southern Manitoba as a whole). We'll have to wait and see in the next few days if we can manage to break this curse and not have to wait until June. It's a depressing thought!

     Here's a graph illustrating the beginning of the thunderstorm season in Winnipeg per year since 1953. The years that I added are the top 5 latest and top 5 earliest.
     Just a side note: as you may have noticed, there's been a lot of ups and downs the last few years. 2010's thunderstorm season had the 5th earliest start on record, 2011's had the 4th latest, 2012's was the earliest and now this year is among the top 5 latest. Call it the thunderstorm variety of weather whiplash if u will :P

     Today also marks the 274th consecutive day without a thunderstorm. So far, this is the second longest ''thunderstorm drought''. We will need to have no storms for the next 12 days to at least tie for longest:

     I'll update all these stats in the May summary next Saturday - that is if we manage to get a storm before then!

_ _ _ _ _
An important note on where I got all these stats:
From 1953-1972 and 1978-1981 I used Environment Canada hourly data from Winnipeg Int'l... As a result, in this period the data is not as precise. This is because a storm may have occured in between hourly observations that got missed.
From 1973-1977 and 1982-present I used a METAR archive courtesy of wunderground. This ensures that no thunderstorm was missed in this period because this archive includes observations in between hourly observations. And yes, I was watchful of potentially erroneous obs and I did have to eliminate a couple that I found were erroneous.

Friday, 24 May 2013

Unsettled For the Next Several Days

     Precipitation forecasts are looking tricky for the next week as multiple areas of disorganised showers and storms are expected across the Prairies as multiple weak disturbances track along the jet stream. This will be accompanied by increasing moisture and lots of cloud cover with brief periods of sunshine.

     For tonight, a line of showers is expected to materialise across Manitoba along the low-level jet. This is expected to affect Winnipeg by sometime this evening then continue overnight and end sometime Saturday morning. 2-5 mm of rainfall is possible with locally higher amounts under any heavier bands. The low-level jet (llj) is expected to weaken as it moves east also dissipating the rainfall, therefore areas east of Lake Winnipeg may not even get a drop of rain tonight.

Anticipated rainfall amounts for tonight by the GEM regional model

     On Sunday, some showers and storms will be possible, especially in western areas of the province and along the US border.

     Beyond that, I wont go into much detail due to the uncertainty. At least a small chance of scattered showers and storms looks possible almost every day next week. Some models have also been hinting at a more organised system south of the border to end the week for a few runs now. It's too early to say just how this will impact Manitoba.

     Something you will notice in the next several days is the increased humidity as dewpoints rise into the low teens. Overnight lows will be quite mild, likely remaining in the teens, thanks to both the increased humidity and increased cloud cover.

Tuesday, 21 May 2013

4-Day Long Storm Summarised

     We can finally say goodbye to this low pressure system that has plagued us since last Friday. Due to uncertainty about where convection would form south of the border and also uncertainty in the exact position of the deformation boundary, this was a particularly difficult system to predict for the Winnipeg area. In fact, at times the boundary cut the city in half, which is the reason why amounts were highest in southern sections.

     The following map summarises rainfall totals from midnight Saturday to 5 am this morning across southern Manitoba, using data from Environment Canada and Cocorahs. I encourage you to click the map to enlarge; I apologize for the poor sizing.
Click to enlarge. Data from Environment Canada and Cocorahs

    The full Environment Canada summary can be seen here.

     The heavy rains in the southwestern RRV east of the escarpment has created flooding problems according to Global Winnipeg.

     And here's rainfall amounts in the Winnipeg area for the same period. Note the large difference from north to south in the city. Again you may have to click to enlarge, sorry about that.

Data from robsobs, gorilla weather, cocorahs and Envinronment Canada

     We will thankfully see some sunshine today; much welcomed. The sun will remain for Wednesday and Thursday with highs reaching the high teens, and perhaps 20°C on Wednesday. Normal high for this time of year is around 19°C to 20°C (1981-2010 normals)

     Looking for a warmup? There are hints that we may see a warmup to start the work week next week, but it's still a ways off to confirm how warm it could get. At this point, no prolonged warmups are to be seen with long-range models maintaining the idea of near normal temperatures for the next few weeks.

     The system this weekend spawned deadly tornadoes south of the border over the past 2 days. Dozens were killed in the southern subarbs of Oklahoma City yesterday as a very large and very strong tornado hit the populated area. Article about this here.

Sunday, 19 May 2013

Hold On to Your Umbrellas!

     Well, it appears we may have finally gotten a better hold on what this system will bring to southern Manitoba over the next few days (fingures crossed there's no more flip flopping!).

     It is looking very wet and fairly windy for the next 3 days. We may not see any major improvement until Wednesday!

     Rain will begin to push in to Winnipeg soon as seen in the radar image directly below. This will be giving way to a rainy afternoon and evening today. The rain could be heavy at times. 5-15 mm is expected in Winnipeg today alone, but locally higher amounts are possible.

You can find this radar on The Weather Network

     Tomorrow will continue the tradition of rainy May long weekends with yet another rainy day. And it will likely be a SOAKER. Drenching rains are expected for much of the day. Isolated thunderstorms are possible in southern Manitoba, but the risk is generally small.

     20-40 mm of rainfall is expected in the Winnipeg area tomorrow (that's for the entire 24-hour day). However, even higher amounts could fall IF we end up under some heavier bands for a prolonged period of time. Localized overland flooding could become a concern in some areas if these higher amounts verify. Amounts will drop steadily as you go northwards.

     Even as we get back to work on Tuesday, rain will still be possible. Although it wont be nearly as bad on Tuesday than on Monday, scattered showers are expected across southern Manitoba. An additional 2-5 mm could fall in some areas.

     Rain wont be the only story however. Strong winds are expected today through to Wednesday. They will be east/northeasterly on each of these days. The windiest day will be Monday when gusts to 60 or 70 km/h are possible. Hold on to your hats and umbrellas tomorrow!

     Conditions will finally improve by Wednesday with sunnier and more seasonal temperatures to finish the week thanks to a building ridge of high pressure over the Prairies. At this time, highly above normal temperatures are not expected.

Wednesday, 15 May 2013

''Weather Whiplash'' The Story of May So Far

     The central continent as a whole has had very extreme weather in the last couple weeks. The battle between winter and summer has been much more intense than we are used to. There is a term for this: weather whiplash. Unofficially, this term describes the extreme and sudden turn from one extreme to the next (drought to flood or summer to winter or vice versa). Here's a brief discussion of the extremes we have felt so far.

     Although we may not want to remember, the month of May began with very chilly conditions and even snowfall. Areas west of Lake Manitoba started the month with an intense snowstorm which dumped in excess of 30 cm in some areas. After the storm, record cold temperatures were felt in some areas. Dauphin dropped to -15.4°C on May 2, breaking the old record of -11.7°C in 1966. That also made it the coldest temperature ever recorded in May in the city, smashing the old record of -12.2°C on May 1, 1958 and May 7, 1907. Records began in 1890 there (however there is a lot of missing data).

     A seperate system, dubbed Winter Storm Achilles, brought record snowfall south of the border from May 1-3. Parts of Iowa, Minnesota and Wisconsin were pummeled with more than 20 cm. All-time May snowfall records were broken in Minnesota (45 cm in Blooming Prairie), Wisconsin (43 cm in Rice Lake), Iowa (30 cm in Chariton) and Missouri (15 cm in Warrensburg). In addition, Arkansas received the first May snowfall in state history with 5-10 cm in the northwestern part of the state. The storm also dumped copious amounts of snowfall in northern Ontario. 10 cm fell in Geraldton and 5-10 cm in Thunder Bay.

Image source Jeff Masters. Amounts in INCHES

     Only days later, a dramatic shift to summer-like weather took place here in southern Manitoba as temperatures rose to the mid twenties on May 6-7. However, it was brief. Well below normal weather settled back a few days later as we went back down the temperature roller coaster.

     Highs struggled to reach 10°C on May 11, then bottomed out on the morning of the 12th. Winnipeg dipped to -7.3°C, not quite breaking the old record of -10.0°C in 1918. At the same time, record high temperatures were being seen in the BC Interior as temperatures exceeded 30°C. In northern Ontario, a snowstorm pummeled the region with over 30 cm in spots. Chapleau recorded 32 cm while Timmins got 26 cm.

     Only a day later, we got slapped with mid-summer-like temperatures in Manitoba with highs in the high twenties and low thirties in some instances. Winnipeg's high of 27.5°C was almost 35 degrees warmer than it was the morning before! Gretna reached a record high 31.9°C, a full 36.5 degrees hotter than the previous morning! It was a similar story south of the border with some areas challenging their record for greatest 1-day warmup. Aberdeen, South Dakota reached 33.3°C May 13, a 39°C warmup from the previous morning low of -5.6°C.

     It was even hotter yesterday south of the border. According to Jeff Masters, temperatures reached highs never seen this early in the year. Sioux City, Iowa hit 41°C yesterday, the hottest temperature ever in May. This is just 2 weeks following its first ever snowfall in May on May 1! Perhaps most extraordinary was in Omaha, Nebraska. After tying for the coldest temperature for so late in the season on May 12 (0°C) they reached the hottest temperature for so early in the season just 2 days later with a high of 38°C! Hard to find a better example of weather whiplash than that...

     Back here at home, enjoy today and tomorrow's mild  and generally pleasant conditions. A rainy weekend may be in the cards. I'll try to have a post about it on Friday.