Wisconsin Weather

OLD - Weekend Winter Storm Discussion

Hey Everyone! Was originally going to post as "free content" but decided to limit to members only because I went deep into some stuff. I may open this up to everyone on Friday.

WISCONSIN - beginning Saturday an intense low pressure system will track from Colorado to through southern Wisconsin into Michigan. The storm will intensify as it passes through, potentially reaching sub-980mb strength northeast of Wisconsin. By Saturday night a narrow but heavy band of snow will develop (changing over from rain/freezing rain) somewhere over northern, potentially west-central Wisconsin. Rain will fall on central and southern Wisconsin. On Sunday, the pressure gradient tightens as the system moves away resulting in the development of strong westerly winds.

We are no stranger to winter storms in Wisconsin, especially lately. The storm this weekend will be more intense than average with multiple hazards statewide. I break the storm down in great detail below. Please know that as the exact storm track changes, so does the exact location of some of these hazards. We are still working on exactly how the details will break out. This my best guess right now.

STORM TIMING

The storm will occur in three main phases:

LEADER PRECIP - The first phase is during the morning/mid-day on Saturday as leader slug of generally scattered precipitation falls across Wisconsin. Snow, Sleet, Freezing rain, and rain all possible. There will be some ice accumulation with this. A lull and warm up is expected Saturday afternoon. The main precipitation event begins around or after 6PM Saturday.

NAM Saturday afternoon scattered freezing rain.
NAM Saturday afternoon scattered freezing rain.

MAIN EVENT- On Saturday night the warm front moves up near Green Bay switching any mix over to rain for locations south. As the low pressure arrives heavy precipitation in the form of rain or freezing rain will break out roughly from La Crosse to Green Bay/Iron Mountain. A changeover to heavy snow will occur overnight into Sunday along or north of that line while a dry slot slices across southern Wisconsin.

EC Sat PM changeover
EC Sat PM changeover

SUNDAY - By mid-Sunday morning, the storm is already exiting towards the northeast with wrap around precipitation in progress. Westerly wind gusts are increasing blowing the snow around possibly causing tree damage or power outages.

SUN AM wrap around. Wind increasing from the west.
SUN AM wrap around. Wind increasing from the west.

IMPACTS & HAZARDS

1. Heavy Snow Band

Latest models show a narrow but heavy band of snow accumulation from southeast Minnesota through northern Wisconsin. I expect 6-12" of heavy, wet snow within this band with lighter accumulations on the northern edge. Unfortunately given how narrow the band could be (two-three counties wide?) I cannot know exactly where. I suspect it will fall roughly somewhere along a line from Rochester(MN) to Eau Claire to Kewneenaw Bay/Marquette (MI)? Totally subject to change.

NAM snowfall prediction. See how narrow that band is.
NAM snowfall prediction. See how narrow that band is.

Snow may fall in central/east-central Wisconsin during the day Sunday as the storm wraps up and pulls away but these accumulations would be relatively minor. Blowing and drifting snow on Sunday in northern Wisconsin. Lake effect in upper Michigan.

2. Freezing Rain and Ice Accumulation

My biggest concern is where or if freezing rain will occur? This is the hardest question to answer. Let me explain in detail:

GFS freezing rain prediction. Freezing rain forecasts are delicate and subject to change.
GFS freezing rain prediction from an earlier model run. Freezing rain forecasts are delicate and subject to change.

Multiple forecast models show the potential for around 0.5" of ice accumulation over northeast or central Wisconsin. Not speculation - pure output. If it is that much we will have problems. The thermal profile Saturday has two important characteristics; a thin layer of barely below freezing air near the surface and a period of a heavy (convective?) precipitation at the peak of the event. During the day might be the best time for ice in central Wisconsin? The only thing we don't have is a stationary boundary/reinforcing cold front and surface temps are only "kind of" cold. This makes me worried that the warm front will sneak further north and turn everything to rain, before going straight to snow via top-down cooling. Need to wait for details to clear up regarding this threat.

Any ice accumulation could lead to power outages Sunday as wind gusts increase (please see wind section below). The best case would be for more sleet to develop or warm front to sneak further north. Keep an eye on it.

3. Rain May lead to Localized Flooding & Ponding

Hopefully the least impactful hazard and it applies mostly southern and central Wisconsin. Rainfall amounts from 0.5" to 1.5", perhaps a rumble of thunder. The combination of snow cover and frozen ground could prevent rain from soaking into the ground. Rain becomes runoff which leads to standing water, localized flooding, and ponding in low lying areas. Be on alert if you plan to travel Saturday night as puddles can sneak up on you while driving. You can help by making sure your city storm drains are clear of snow/debris.

4. Very Strong Westerly Wind on Sunday

More problems arise Sunday as westerly winds gusts increase to around or exceeding 50 MPH develop over portions of Wisconsin. The EC model is showing gusts up to 60 MPH in spots!

EC wind gust prediction for Sunday. From windy.com
EC wind gust prediction for Sunday. From windy.com

The strongest gusts would likely be in elevated/exposed areas such as the Niagara escarpment in eastern Wisconsin, Washington Island. Also southern Wisconsin and upper Michigan (lower MI as well) as the storm pulls away. Any locations receiving ice accumulation Saturday night will be at risk for tree damage and power outages on Sunday.

This is because the weight of the ice pulls down limbs/branches causing them to break in the bouncing caused by the wind. I will be watching this very closely. Sunday could be "blizzard-like" in northern Wisconsin. I hesitate to call it a blizzard overall because wind gusts Saturday night will be in the 20-30 MPH range.

Lastly, a flash freeze will occur Sunday into Monday as a strong cold front arrives. With the flash freeze, blowing snow, and wind...travel hazards may extend into Monday morning so give yourself extra time.

Be Prepared - That's It

It's Wisconsin. Winter happens. This will be a major storm for Wisconsin. Everyone will be impacted in some way. I'm watching northeast Wisconsin the closest. We share this information (for free) so you can be prepared and plan ahead. If we waited for 100% model agreement it might be too late; the time to take action is now. Better safe than sorry. That's it. Next update on Friday! Stay tuned!

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