Big changes are in the works over the next few weeks. As noted in the story earlier this week, the arctic circulation recently experienced a major Sudden Stratospheric Warming Event (SSWE). The result so far has been to split the polar vortex into pieces causing the development of western trough and a southwest-northeast storm track across the country into Wisconsin and the Great Lakes.
Forecast models continue to showing strong signals for this pattern. This is an interesting time because this pattern completely contrasts the winter we've had thus far, which has been colder and drier than average. Late February/early March is usually a very chaotic time for Wisconsin Weather. This is related to the collapse/end phase of winter and our first steps towards spring. We still have to work out the details but the big picture is at the very least exciting and interesting.
Five Day Forecast
Not much happening today and Friday. A quick hitting system could bring a dash of snow or light mix Saturday. Blah blah blah. All eyes on the long range.
Winter Storm is Coming
The first in what could become a series of storms, models develop an elongated baroclinic zone into the Great Lakes late this weekend into early next week Feb 19-21. Two or more bundles of energy will traverse northeast along this zone and produce precipitation across Wisconsin. This will mean snow, freezing rain/ice, and some rain and/or thunder early next week. This event will take place on multiple days (long duration) which reduces the overall impact I believe.
Most models (GFS, EC) continue to show potential for cold air at the surface and warm air in the low to mid levels(see picture below). With a very sharp and strong polar front located just to the north this is very easy to believe. Ice is rarely an issue for Wisconsin because we typically experience mature low pressure systems which have well organized temperature profiles. With young, developing systems like this you are susceptible to ice storms. Ice was the one thing that stood out about this event and I will continue to watch. The Canadian model was warmer and stronger so we'll see.
So much can change in terms of location, timing, and amounts so PLEASE don't take the image above as a literal forecast. Please don't etch this in stone. Instead think of it as "wherever these pieces come together, this is likely to happen". If the boundary trends south then expect more snow across Wisconsin.
I am less concerned about severe weather or heavy rain right now in Wisconsin. If models trend stronger & more north (like the Canadian) then maybe. The 2/15 12Z GFS was a good in-between with ensembles and other models in consideration.
Late February into Early March
Expect the storms to continue. This pattern is likely to continue in some form or flavor for 2-3 weeks beyond the Mon-Weds system. I predict systems will become more mature as we approach March 1st. We still haven't had a major snowstorm south of HWY 29 in Wisconsin yet this winter.
- We haven't seen a pattern like this yet in the 2017-18 Winter. Hold onto your butts...
- Very broad and deep western trough develops at times. -PNA to very -PNA anticipated!
- STILL trying to understand what upper level mechanism drives snowstorms through southern Wisconsin as opposed to the north where they typically go. Without any blocking the low pressure systems go awol into northeast Canada. Storm systems entering the country pretty far north in Washington state. I should have this figured out pretty soon.
- Moving into -PNA/-AO relationship which is good for storms. New research shows this is the most active and stormy configuration for Wisconsin during February disproving my previous ideology that -PNA/+AO was the best relationship.
- We haven't seen ANY episodes of -NAO or blocking in the northern Atlantic. There is a good chance this will change before February ends. Starting to think -NAO is important to our southern Wisconsin snowstorm trends.