There was much excitement and anticipation when the polar vortex was disrupted and led to a sudden stratospheric warming event back in mid February.
I’ve gone into detail about how the polar vortex (both the stratospheric (high up, beyond 40,000 feet) and tropospheric (lower atmosphere, where we live up to 40,000 feet) impact our weather (I suggest looking back at some of those in-depth articles if you’re a true weather geek) but in summary: a strong polar vortex means the coldest air stays ‘locked up’ spinning rapidly at the pole but a weak vortex, or a disrupted one, slows down or even reverses it’s spin and falls apart or is displaced. When the vortex is knocked off its rocker or broken apart, the impacts often are felt in our lower (troposphere) atmosphere.
Here’s an animation of the stratospheric polar vortex this winter from start to its demise:
Often, disturbing the sleeping giant that is the polar vortex means cold is unleashed into Europe or Asia or interior North America into the east coast. This blast of cold can help lead to some big snowstorms if timed right. Meteorologists in the northeast, who have been lacking snow this winter, got excited for the possibility. It turns out Minnesota into just the interior most portions of New England got socked with snow and our recent cold.
Kudos to the Climate Prediction Center for their long range forecast trying to capture this. We don’t always know where that cold will set up. Here was their week 3-4 prediction for March 11-24 that was issued February 24:
Here is what happened:
The main ‘error’ was that the cold was concentrated more central rather than spreading fully into the northeast, which accounted for the ‘snow belt’ being farther west and south as well.
Here’s another way of looking at it. If we compare the 30 day period leading up to the polar vortex disruption and compare it to the most recent 30 days after the fact, you see a BIG difference in temperatures and snowfall in Minnesota.
Of course this whole winter has been a whopper for snowfall, but recall that after the big storm in early January we were really in quite the lull for about 6 weeks. The change in the polar vortex likely at least contributed to the shift that brought back the active pattern we’ve now seen overall for a month in addition to the chill.
Alright, now all that is behind us, right? Probably, at least the worst of it. At this point in the season the polar vortex will not regain traction, there’s sun reaching all corners of the arctic rapidly more and more each day. The key to developing and maintaining the stratospheric polar vortex especially is the lack of sunlight mid Autumn through winter. Now, even the north pole has more daylight than night. Here’s a look at the long range GFS (American) model which goes out 16 days. While just looking at the colors may be difficult to decipher much, the average temperature in the northern hemisphere warms 10 degrees F over the next two weeks. That’s progress and the areas of cold are shrinking and becoming less cold.
The effects of all of the above however have led to a very slow, sluggish start to spring. One way to measure this (besides the unusual amounts of snow pack this late in the season) is looking at the first 50 degree day.
Of course that first 50 is late for everyone, and may not be in the reliable forecast range’s (5-7 days) sight. Here’s a look at the American (GFS) and European models. The American model goes out 16 days (on top) and the European goes out 10 days (bottom):
Before you get overly excited about the American model’s 60s and 70s, know that it has had some notoriously erroneous forecasts the last several months, so take it with a wheelbarrow’s worth of grains of salt. The bigger point is that the models are showing a warming trend, at least modestly, with a real shot at 50 by next weekend.
If we don’t hit 50 by next weekend, this will be one of only 9% of years where we didn’t reach 50 before April! The latest 50 degree reading in 22 years (2001)! Let’s hope we don’t go for the latest ever, which was April 17, 1962.
Besides our general sanity, the effect of the slow spring and tons of late season moisture has increased the probabilities dramatically of major flooding this spring. Major flooding is likely on the Red River (Fargo), Mississippi (Aitkin, Hastings, Redwing) and St. Croix (Stillwater). The probabilities range from 3 to 8 times higher than an average spring.
You want your normal gradual thaw in March, something we didn’t get this year. You especially NEED that gradual thaw when you have as much snow and water locked up in the snowpack as we do this year. We’re increasing the chances of a rapid melt since, as you head into April, that’s more inevitable, combined with precipitation.
(Above: liquid equivalent water in the snow pack)
In addition to a bad temperature trend scenario, precipitation hasn’t been working in our favor as far as the flood situation goes either. We’re especially watching a late week ‘April fools?’ storm next week. Whether it’s snow or rain doesn’t matter so much. The amount of liquid equivalent precipitation is what matters, especially if the American model’s doomsday scenario of a rapid warm up occurs after the fact.
Computer models from the last couple days have looked very bleak, dumping one inch or more of water on Minnesota in a widespread fashion, these are from Thursday night into early Friday.
Model runs during the day Friday (March 24) have shifted the precipitation overall more south and east, but some models keep it north and we still have a week to go. Needless to say, despite your inclination: hope for a cool, dry start to April… warm weather will come, we just need it to have better timing this year. Of course, Minnesota weather rarely does what we want does it?
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