A strong low pressure system will have a major impact on Wisconsin weather starting Friday morning (late Thursday night) and potentially lasting through Sunday. Plenty of uncertainty remains with regards to where, when, and what but the big picture is filled with stormy weather. Forecast models are showing potential for heavy snow and rain both Friday night and again on Sunday so we need to keep our eyes on it. We are also monitoring a system for Wednesday night this week.
FRIDAY - SATURDAY MORNING
On Friday morning, a band of warm air advection will kick off rain across Wisconsin. Rain will change to snow in the north. Heavy snow is probable but there is disagreement between models on exactly where. To the south heavy rain and thunderstorms are likely to develop during Friday or Friday night. There might even be freezing rain smashed in there somewhere.
We are monitoring the potential for severe weather which looks to be focused on Iowa Friday night. The surface warm front is forecast to stall along the WI/IL border remaining capped with little/no daytime forcing. Plenty of clouds too. GFS only showing up to 800 j/kg MUCAPE in southern Wisconsin fading fast after dark. The elevated warm front will intensify Friday night kicking off a ribbon of rain and storms, some which could produce be heavy rain across the south. Elevated hail storms are very common this time of year but I'm not convinced t-storms will be capable of severe, yet. Rainfall may exceed 2" in spots across the southeast.
As for the heavy snow, the main event is most likely to setup across Minnesota and northern Wisconsin Friday night into Saturday morning. It is too early to get specific about snow totals. This is an area that is very familiar with snow by now. I expect snow totals to exceed 12" *somewhere* in northern Wisconsin, if not by Saturday then definitely by Sunday.
More details to come on all of this.
TWO PART SYSTEM?
There are two things that makes this forecast challenging; storm life cycle and storm duration. This might ultimately end with splitting the storm into two parts for communication sake.
On Saturday AM the low will occlude and begin to weaken. However the upper level trough is reinvigorated Sunday taking on a negative tilt and strengthening a new low to the east. This is currently forecast to bring a second round of snow/rain to Wisconsin Sunday. There will be decay in precipitation Saturday, perhaps to scattered showers or drizzle but it will remain at the very least cloudy and gloomy. Not a good weekend weather-wise.
The Sunday forecast is the biggest question mark right now. The worst case scenario is another batch of accumulating heavy snow for central or northern Wisconsin. It's also possible that the storm ends up slightly further to the east and nothing happens. Things could get interesting if the EC model is correct suggesting a blizzard on Sunday?!? Other models are less enthusiastic, and perhaps the safest thing to say is that snow chances continue almost into Monday. Stay tuned to future forecasts as details become clearer!
The long term forecast for mid/late April continues to show below average temperatures.
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WIWXGROUP/" class="fb-xfbml-parse-ignore">Wisconsin Weather
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April 30, 1996