SAT 11:15 PM - No changes.
SAT 3:15 PM - Just shifted the snowfall map eastward a bit. No other changes or details to add.
FRI 2:00PM - 12z EC/NAM are the favored models on this update. I've disregarded the GFS for now because it's an outlier...not saying the other models won't trend east later. GFS ensemble mean was pretty far east so needless to say agreement could be better. I've kept confidence level = LOW. In most situations I would start going down the major storm route in terms of verbiage. Will leave that for Saturday and hammer it then if things do indeed pan out the way the EC/NAM show today. See details and maps below.
HEAVY SNOW - Yesterday I was on the conservative end as much as I'd like to stay there, I respect the agreement between EC/NAM on high end amounts potentially exceeding 12" in a narrow band now across northern WI. I hedged it by going 8-13". Please note that the track has been trending west and I tried to hedge that way SLIGHTLY. I noticed that the NAM has surface temperatures in the low to mid 40's over southern WI SAT/SUN so I think it will be really hard for accumulation down there throughout the event; but perhaps some accum on grassy/elevated surfaces Mon AM on the wrap around before ending.
13-18" in upper Michigan includes lake effect snow throughout the period leading up to the storm...and the storm itself.
HEAVY RAIN/T-STORMS - Big model disagreement in the handling of convective t-storm elements across southern Wisconsin Saturday night, mainly Sunday PM. The question of presence and ability to produce heavy rains. EC is non-existent and driest with 0.4-0.75" QPF south. Rest of the models much wetter including NAM/GFS up to 2.0". Given my skepticism toward the way GFS might be handling it...I maintained the previous forecast of 0.75-1.5". Confidence is very low. As for t-storms....with the surface warm sector likely remained well off to the south...the threat for t-storms in general will remain low. The EC does open the door. Just not feeling it right now. If anything small hail would be possible but that feels like a stretch.
Wind Gusts to 45 MPH on Monday - Wind gusts will be on the weak side Saturday thru Sunday. Monday will be the windy day, especially southeast. I sided with the 12GFS wind forecast vs. the 00EC (windy.com hadn't updated yet). The EC was really windy and want to avoid the worst case. There is room to increase the wind gust forecast on future forecast. I'm comfortable where this stands.
Travel Hazard/Power Outage Hazards- I bumped up to moderate risk in portions of the Great Lakes regions for the event for TRAVEL. The biggest problems may come from the wind on Monday. Just something to consider.
Next Update - by Saturday mid-afternoon.
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FRI 8:15AM - some divergence in progs over the last 24 hours with EC trending back west and 06zGFS being an outlier. No changes right now. Full update this afternoon following the arrival of 12Z models.
THU 10:30 AM - Still waiting on full 12z suite so forecast is based on overnight runs. I thought agreement was good enough to start pulling some levers. The positive news is that models currently focus the primary snowfall on Sunday night/early Monday AM so overall impact should be less than if it were mid-day. This system has the look of a strengthening low going pole-ward over Michigan. This tends to bring about heavy snow, nasty weather on the wrap around. Keeping recent history of model performance in mind this winter with other societal issues...staying away from worst case scenarios. This forecast hour recently has been a back breaker with general agreement then diverging solutions.
WEDS 4/8 8:45 PM - Models today continue to show winter storm potential Sunday night into Monday. Feel like we're at a critical point were things tend to diverge so will wait for tomorrow's model runs. 12EC was a nudge further east actually. I adjusted the snowfall map for location....will take a shot at snow amounts soon.
WEDS 4/8 8:45 AM - A winter storm is possible Sunday into Monday AM in Wisconsin. Confidence is low.
There are differences between the GFS (colder) & EC(warmer). I'm leaning more toward the EC warmer solution with lighter snow accumulations mainly north and northwest WI. The GFS appears too aggressive/dynamic. Model consistency could be better thus overall confidence is once again LOW. Not out of the question a stronger, colder system will materialize but at this stage not going there yet.
Regarding rainfall amounts, models are not in agreement but some do show an inch or more for portions of WI. That may also depend on exact precipitation type/thermal profile. Recent storms started snowier...then trended warmer with time. Either way not choosing a bias just watching how this aspect evolves. This time of year we kind of expect soaking heavy rain so not too concerned right now.
GFS/EC agree on taking the surface low center south & east of WI which should reduce t-storm potential. Many details to be resolved. Stay tuned!
Next update THU AM.
JP