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.

20 comments:

  1. There's still incredible uncertainty about this weekend's system when it comes to TIMING. NAM/GFS/GEM/ECMWF all have their own plans for Winnipeg.

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  2. For tomorrow, it doesn't look like it will an all-day rain for Winnipeg. Most of the rain is expected to weaken and dissipate as it moves east where air is expected to be drier. Scattered showers would be a better term for the city. I'm expecting 1-3 mm.

    For the weekend, best chance for rain will be Sunday and Monday, and thunderstorms will be possible. Saturday is the day that is most uncertain for me right now. GEM brings in abundant rains, but GFS, ECMWF and NAM bring in only light amounts and even keep us with a bit of sunshine in the afternoon. Right now I'm leaning towards the drier solution for Saturday, but that could change. I'll be watching it closely.

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  3. ECMWF (european model) maintains that Sunday and Monday will be the wettest days of the weekend in its afternoon update today. In fact, it has raised amounts to 40-50 mm for those 2 days and then points at an additional 10-15 mm for Tuesday. GEM global has now turned to a similar forecast, except bringing even more rain; around 70 mm from Sunday to Tuesday, with only a few mm on Saturday morning.

    Definitely an interesting system unfolding...

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  4. I've put a new poll up! I am asking how much rain do you think we will get from 12 AM Saturday through to the end of the day Tuesday. You will have until 12 AM Saturday to answer.
    Good luck and thank you for participating!

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  5. Thunderstorm potential looks quite good as well, thunderstorms are likely almost every night just 1km south of the border from saturday night to monday night. Anything that is south of the border could travel north into our region giving the oppurtunity for mutiple convective chances it has to go somewhere, and the border won't stop them from moving. What is your thoughts?

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  6. Yeah I agree, we may see some storms drift northwards here this weekend, however it's difficult to pinpoint just exactly when that would occur right now. If I had to pick the timeframe that has the best risk it would be sometime in the Saturday night and Sunday timeframe. At this point, it appears that it is around that time that the bulk of the moisture begins to stream northwards into our area (but then again not all models are agreeing).

    Rainfall is of concern with this system. There's going to be a heck of a lot of moisture to work with thanks to how slowly the system is expected to move. The strong southerly winds ahead of it will have ample amount of time to pump in plenty of moisture from the Gulf. Question right now is just if most of the moisture stays south of the border or not? That's something that is uncertain right now.

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  7. Thank's JJ, I'll likely have an update on this storm system up on my blog tomorrow evening. I cannot wait to share my thoughts with others.

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  8. Well now some of today's models have switched again with heaviest rains on Saturday and the bulk of the rain staying to our south on Sunday and Monday. Crazy.. I wouldn't be surprised to see another switcheover again later today or tomorrow. NAM however is persistent with heaviest rains Sunday/Monday. Preparing forecasts now, will update later this morning.

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  9. Rain has materialised to our south with a good band coming in. Looks like a wet afternoon and evening for us. Bulk of it will take at least an hour to get here.

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  10. Consensus for tomorrow is now a drenching rain in the afternoon and evening or so. 15-30 mm looks like a good range right now based on what I'm seeing. Still not 100% certain on amounts though given the convective nature of this precipitation.

    Thunderstorms will be possible, however the BEST risk for them will be to our south and east. Severe storms are expected in North Dakota. Depending on how far north the warm front moves, the potential is there for a few strong storms to reach southeastern Manitoba. At this point, it doesn't look like these particular ones will reach Winnipeg.

    Wildcard still remains to be Sunday through Tuesday. Models are struggling to determine how far north the rain shield will reach. NAM brings in an awfully scary 80 mm of rain on Monday alone, while GEM, ECMWF and GFS bring little to nothing (keep it all to our south).

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  11. 2-3 mm with today's rain.. 2.1 mm at my place. This will seem extremely minor by tomorrow.

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  12. Still looks like a rainy afternoon and evening for us here today. Amounts are uncertain, but consensus right now looks like 15-30 mm. We'll have to see if the area of rain to our southwest can maintain its strength or even strengthen or not. If it weakens, look for lesser amounts.

    As for thunderstorms, I maintain my thought that the best risk will be south and east of the city today. We may see a few embedded rumbles here and there however, but it doesn't look very impressive for us here. Warm front looks to remain south of the border after all, which will keep instability low in our area. Areas along the International border and in the southeastern corner of Manitoba will have the best risk.

    Forecasts will be updated soon.

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  13. Forecasts updated...

    As for rain Sunday and Monday, more and more it looks like the bulk will stay to our south. Areas south of the Trans-Canada may see some steady rains on Monday, but along the TC and northwards it looks mainly dry right now and that includes Winnipeg. This could still change so I'll be sure to keep you updated.

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  14. Rain struggling to move north today. I'm changing my predicted amounts today in Winnipeg to 5-15 mm.

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  15. I was just starting to make a new post about what looks like a dry Sunday and Monday for Winnipeg. However, the afternoon update of the GEM regional brings back the rain into the Winnipeg area on Monday with significant accumulations... As a result, it is still not certain how far north the rain will track Monday. My gut feeling is that the bulk will stay south of Winnipeg, but we'll see. I'll hold off on a new post until things are more certain.

    As for today, only 2-3 mm has fallen so far in Wpg.

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  16. Now the GFS give 50 mm Monday....

    I cannot remember the last time there has been this much flip flopping among ALL the models! A forecaster's nightmare!

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  17. Mike (St.James,Winnipeg)May 18, 2013 11:00 pm

    I posted an update on my blog, might get storms in a few places....

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  18. Looking like we will get a soaking rain tomorrow. Rain and thunderstorms currently in North Dakota pushing slowly north, almost touching the US Border now. Updating forecasts now, update on timing and amounts coming later this morning.

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  19. Rain seems to be pushing north even faster than models were indicating. If this trend continues, rain could begin as early as this afternoon in Winnipeg.

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  20. Could someone tell me what the poll results that they are seeing in my poll please?
    I don't know why, but it says 0 poll respondants for me :( Something wrong with my computer or something.

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