LIVING ON THE EDGE (active weather ahead)...
A Winter Weather Advisory continues in effect for the northwest third of the region through Tuesday for what looks like a minimal freezing rain set-up. Wintry weather in the form of light ice accumulations is expected, especially on elevated surfaces as colder air works its way in as the morning progresses. Areas of hazardous travel are also a threat (but not a certainty) with the greatest chances NW of line from Cedar Rapids to to just SE of Dubuque. The southeast 2/3rds of my area will see little in the way of icing if things go as planned. We're living on the edge of this system.
Following a mild day Monday with highs in the upper 30s north to the upper 50s south, moisture has increased along a nearly stationary boundary just south of I-80. Along it a battle has been going on since Monday between cold air advection to the north and warm air advection in the south. That's tightened the front even more and through Tuesday morning a significant range of temperatures is expected until a surface low draws colder air into all of the region by noon. The HRRR at 8:00 AM Tuesday shows a 36 degree spread from 17 in Decorah to 53 in Galesburg. Areas of fog and drizzle are also likely by then, especially near the boundary of the two air masses.
As low pressure gets organized Tuesday morning, forcing increases for showers and perhaps even a few thunderstorms. Most of the measurable precipitation from the system is expected in this early morning window when the low cuts southeast of the Quad Cities. Amounts of 1/4 inch or so are possible, perhaps a little higher if in fact some thunderstorms can get going in the southeast half. The EURO is bullish on that idea. Here's what the EURO and GFS show for total precipitation from the event. There's really not much in the NW where the freezing rain threat is indicated which should limit the impacts of the ice.
The EURO
The GFS
As far as ice accrual is concerned, the window for that begins around daybreak in the far northwest NW of a line from near Cedar Rapids to Dubuque. As the low lifts NE colder air makes progress further into my counties in east-central Iowa and far NW Illinois by mid-morning, particularly NW of a line from Iowa City to Savannah. Little if any ice is expected southeast of that line. Ice totals of up to 1/10 of an inch are possible in the far NW but in general amounts should be less than that. Overall, ice accumulations appear manageable but in spots could create some difficult travel off to the northwest. These are freezing rain totals indicated by the EURO, GFS, and HRRR.
The EURO
The GFS
The HRRR
Elsewhere, the majority of of the precipitation falls as rain until the tail end of the system when a brief transition to freezing rain or a light snow mix is possible. It's not expected to cause anything in the way of problems here. The only place that might see any snow accumulations would again be the far northwest (Cedar Rapids to Dubuque) where a dusting of snow is a possibility. Most models don't even indicate more than a trace.
Thursday afternoon, strong cold air advection envelops the area as the low moves east allowing the front to sweep southeast. In doing so strong NW winds will overspread the Midwest sending temperatures crashing. Lows Tuesday night will sink into the single digits, quite impressive without snow cover. As you can see below, readings in the south will be about 40 degrees colder than those 24hrs earlier Monday night.
Wednesday will be a cold but dry day with highs remaining in the low to mid 20s in most areas. Wind chills to start will around 5 below to 5 above. They will improve significantly in the afternoon as winds back off and readings warm.
With plenty of cold air in place the next system coming out of the southwest will be a snow producer on late Thursday, especially Thursday night. There are still some phasing differences to resolve and in recent runs the GFS and EURO have come in a bit higher with available moisture and snow totals. With the cold readings snow ratios will be at least 15 to 1 meaning this will be a fluffy snow with the potential to accumulate 1-3 inches (perhaps 4 in a few spots) if new data verifies. Here's what both the models indicate for totals by Friday morning. These are not forecasts, just raw model output.
The EURO
The GFS
No matter how you slice it, after a couple mild spring-like days in most of my area, winter is alive and well and there will be no disputing that fact Tuesday night through the weekend. I'm out for now, roll weather...TS
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