Monday/Tuesday Storm Latest

Update 4 a.m.
The entire viewing area has been upgraded to a Winter Storm Warning.

Update 10:50 p.m.
I'm about to head out for the night. The Weather Service offices are going to hold off on Winter Storm Warnings until later tonight, after they've done additional analysis. An additional thing that's being looked at is how long the blowing snow will be a problem after the snow itself stops falling.

Meteorologist Adam Painter will have all the latest during 13News Today.

Update 9:50 p.m.
Enough of the GFS model run has come in... it nudges the low track a touch farther north than its previous run. However, based on what it and the NAM have both been doing, I'm going to stick with my going forecast. Tune in to the news shortly and I'll give a complete rundown of the storm.

Update 8:15 p.m.
The latest run of the NAM computer model nudges the low track a smidge farther south. Now to wait for the GFS to come in to see how it compares...

Update 7:15 p.m.
The energy that will go into the development of the low pressure has come onshore. Upper-air observations are being ingested into the models, which will help them get a better idea of what may occur. I've been scouring for more data to peruse and based what I've seen so far, am sticking with my snowfall map from earlier this afternoon. Based on some "ensemble" data, as it's called, it would appear the heaviest snowfall amounts will be in the neighborhood of I-88. Ensemble data puts together a bunch of different tweaks made to a model and puts them together, which is a helpful tool.

In any event, I'll be anxiously awaiting tonight's model runs. One will be in sometime during the 8 o'clock hour, and the other will be coming down the pike closer to 10.

Update 4:45 p.m.
I decided to see how close we've gotten to the snowiest winter record. Our snowiest December-February period was 63.4" in 1978-1979. We're sitting at 58.9" right now. My too-many-to-want-to-remember semesters of calculus tells me that an additional 4.5" will tie the record. It looks to me like the record will most likely go down in the next 36 hours.

Update 3:50 p.m.

I've put together a snowfall forecast map with my current thinking. I'm forecasting 3-6" amounts across the entire area. South of the Illinois/Wisconsin border down to around I-80, I believe there will be quite a few locations picking up at least 6". The important thing to remember with the snowfall map is this: if the low tracks farther north, the snowfall bands will shift northward and probably decrease a bit due to a later changeover to snow. If the low tracks farther south, then the snowfall bands will shift southward. I'll update this map this evening after I've gotten additional new information.

Update 2:15 p.m.
Above are the counties under the Winter Storm Watch. It includes the entire viewing area. It goes into effect midday Monday and lasts through midday Tuesday.

Sunday Morning Update
A Winter Storm Watch in effect for all of Northern Illinois and Southern Wisconsin for a combination of freezing rain, sleet, and snow Monday evening. Snow is expected to accumulate at least a few inches, but a combination of different types of precipitation will likely make roadways very slick late Monday into Tuesday. A Winter Storm Watch is issued when wintry weather is expected to have serious impact on travel. We will post more detailed forecast later this afternoon along with a snowfall forecast map.

Update 10:30 p.m.
The latest model runs have come in... and they're becoming in better agreement on a southern track. I'm becoming more sold on it, but still want to hedge slightly to the north of their advertised tracks. As far as the impact on us... right now, my thinking is that the initial rain/snow line will be close to the Illinois/Wisconsin border. I wouldn't be surprised if I trim Monday's forecast high when I come into work tomorrow... especially based on the recent and now-consistent trends.

Original Post
The sunshine was a sight to see today. The good thing is that tomorrow will be another quiet day!

Our attention is turning to a system that's going to push through the area on Monday. Just like pretty much every other low this winter, the track being predicted by the models is wavering. Current trends have been pushing the storm track a bit farther south again, which would lead to an earlier change from rain to snow. However, the low has tended to track a bit northwest of the predicted path. While I do have some confidence in going with a somewhat southern track, I'm leery about going too far south just quite yet; I want to see additional model runs that indicate it... and I'm waiting for the energy that'll spawn the low to actually make it onshore so the observing networks can sample it better.

As it stands now, it does appear we'll have mostly rain at the onset, but a changeover to snow will happen sometime Monday afternoon. Another piece of energy is expected to swing around behind the low and help give some more lift with the wraparound snow. Tomorrow, I'll have a much better idea of how I believe it'll all play out... but in the meantime, it certainly looks like a messy start to the workweek with rain, accumulating snow, and chilly northwest winds.