In fact, with temperatures hovering between 29 and 35, depending on your location, we could see the full gamut of winter pre-slopitation Monday and Monday night, including freezing rain, rain, sleet and snow. Oh, and a shit-ton of wind.
Officially, the National Weather Service has posted a Winter Storm Watch for all 72 Wisconsin counties. But the nature of the storm will be very different from north to south.
Here's the scoop:
The same intense low pressure creating extreme blizzard conditions right now in parts of New Mexico and Texas will push northeastward toward central Illinois overnight tonight. Normally, this kind of "panhandle hook" track (explained here) would put much of Wisconsin in a heavy snow area. But with El Nino's influence, this low will be so strong that it will wrap warmer air all the way over to the northwest side of the low. With that warm air aloft, precipitation then starts as rain, and ends up falling to the surface either as sleet or ice, depending on the surface temperature.
Here's how the National Weather Service sees the map shaping up for 6am Monday (and remember, you can click on any image to enlarge):
That orange color represents freezing rain. You'll see the low positioned in extreme southwestern Missouri. What happens after that depends completely on where the low goes from there. A track toward Rockford or Chicago keeps us in relatively "warm" space, meaning that rain and sleet are more likely. A track toward Detroit puts us in a colder position, meaning more snow and freezing rain.
The GFS weather model, which forecasters rely on to predict the position of pressure systems, seems to split the difference between those tracks -- maybe just east of Chicago, but just west of Detroit. These two images show the 12-hour advance of the low...
In all winter storms, pinpointing the track of the low is the key to accurate forecasting. But in this storm, low track is even more important, because temperatures will hover right around the freezing mark. That means that two areas only 10 or 20 miles apart, with only a 1-2 degree temperature difference, could see completely different types of precipitation at the same time.
In fact, the only thing really certain about this storm is wind. As the low gets closer during the day tomorrow, look for east/northeast winds to gust as high as 35-45 MPH. This wind forecast shows lower Lake Michigan taking the brunt of the strongest winds:
Wind and ice, as all Wisconsinites know, is a terrible combination if you want to drive somewhere. And an extra word of caution about that driving thing -- you may step out of your house and office, and driving conditions will seem fine. But 5 miles down the road could be a completely different story. If you are on Twitter, and you absolutely have to drive Monday or Monday night, keep your Twitter feed on Madison Traffic, 511 Wisconsin and Ready Wisconsin for timely updates on weather, traffic and crashes.
If ice accumulates to more than a tenth of an inch -- which is likely in parts of South-Central and Southwestern Wisconsin, power outages and downed trees are also a distinct possibility. So today is the day to get prepared for that eventuality. Ice of a quarter inch or more is considered an extreme ice storm, and that can't be ruled out in some locations.
Mateo Earth models show New Glarus right in the sleet/ice (yellow) band for a lengthy period of time. Here's 1:00pm Monday and 1:00am Tuesday:
Okay, I'm sure that's a lot more than you wanted to know about freezing rain. What about the snow?
We can be pretty sure that snow amounts will be lowest in the far Southeastern part of the state, and highest in the Northwest. Some locations won't see any snow at all. In the New Glarus and Madison areas, I think we see 2-4 inches as the low passes to the east on Monday night. That's not much, unless there's a layer of ice and sleet underneath it.
So here's my official New Glarus forecast, subject to change as I watch the low progress today:
Monday: Sleet and freezing rain starting mid-morning, changing to all rain for a brief time in the early afternoon, and changing back to sleet and freezing rain around sunset. Total sleet and ice accumulation about 0.15 inches. High 33. Strong east wind of 15-25 MPH becoming northeast late in the day, with gusts up to 40 MPH.
Monday night: Sleet turning to snow in the evening, accumulating 2-4 inches before diminishing late. Winds remaining strong and gusty from the northeast, creating blowing and drifting snow. Low 29.
If you're traveling to the north or northwest Monday or Tuesday, look for snow totals as high as 8-14 inches toward the Eau Claire area.
FYI, there is another chance of light snow on Wednesday, as a weaker system approaches from the west. Late this week, we'll see our coldest temperatures of the season, with highs only getting into the teens in most places.
I'll take your questions both here and on Facebook! And remember, you heard about this storm on Rippeology before anyone else was talking about it. First post was last Tuesday morning on Facebook. Just sayin'.
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