SLIP SLIDING AWAY...
ICE STORM WARNING EC IOWA
Significant ice accumulations of 1/4 to 1/2 inch
WINTER WEATHER ADVISORIES ELSEWHERE
Mixed precipitation (Freezing rain, rain, sleet, some snow)
A late fall storm is bringing mixed precipitation and freezing rain that will continue to spread NE across the region Saturday morning. Initially, freezing rain (perhaps a brief period of snow north) is expected. Eventually, a transition to rain follows as thermal profiles aloft warm slightly above freezing from south to north in the afternoon. The speed of the change over will play a critical role in the amount of icing that occurs. Additionally, precipitation is substantially heavier SW of the Quad Cities in Iowa than further NE in Illinois where the system weakens and encounters drier air, again increasing chances of higher ice accumulations in Iowa.
The bottom line is this all makes for a difficult forecast, as a couple of hours more (or less) of freezing temperatures could significantly alter the amount of icing. Either way, it does not take more than a glaze to create hazardous travel conditions and many locations will have a period of ice accretion and poor travel conditions, especially with the cold surface conditions we've recently experienced. At this juncture, it appears the greatest ice accumulations will be found in EC and parts of SE Iowa.
As far as total precipitation is concerned, here's what models are indicating the area will have to draw from regarding the system. You will note there is quite a bit of variance from west to east in terms of amounts, with a very sharp decrease to what falls in NW Illinois.
The EURO
The GFS
The 3k NAM
The HRRR
THE 10K GEM
Now to the ice potential. Ice storm warnings have been extended a bit further west and south by the NWS. The epicenter for greatest ice accumulation is concentrated from roughly Cedar Rapids and Iowa City south towards Washington in Iowa. In this area ice accumulations of up to .25" are likely with some totals pushing .40"+. For those outside the ice storm warning, advisories are in effect for ice totals that could range from a glaze to .20".
Freezing rain, (perhaps a bit of sleet and snow mixed to begin) will be ongoing at daybreak in the south and then spread into the rest of the area during the morning hours of Saturday. At the same time, warmer air at the surface and aloft continues to slowly advance northward, changing the freezing rain to rain for most locations south of I-80 by noon.
Further north, the transition to rain will slowly advance northward, reaching HWY 30 by mid-afternoon and HWY 20 by evening. Overall, roads and icing conditions will improve in the south by noon and will do so in the north towards evening as temperatures step above freezing. Here's what models are currently suggesting for ice accumulations.
The EURO
The GFS
The 3k NAM
The HRRR
The 10k GEM
Snow does not appear to be much of a factor with this event locally due to warm air aloft. Soundings do support the possibility of a brief period of snow Saturday morning in my northwest counties before flipping to freezing rain and finally rain to end late day and evening. Here, up to an inch is possible in a few spots. NE Iowa has a better chance of seeing up to 2 inches. Here's the latest projections for snow totals.
The EURO
The GFS
THE 3k NAM
The HRRR
The 10K GEM
Temperatures at 5:00pm Saturday look like this on the HRRR. By that time, all locations south of HWY 20 are projected to be above freezing. Travel conditions should be significantly better by then, after a rough period in the morning and early afternoon.
Saturday night light showers and drizzle will gradually come to an end with near steady temperatures. Sunday, while dry, will be cloudy and mild with plenty of lingering low level moisture. Highs should range from the upper 30s to low 40s. By then, any ice or snow that accumulates Saturday will be nothing more than a memory. Have a great weekend and be extra careful on the roads until the icing threat has passed. Roll weather...TS
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