Rockford Scanner®: Update Forecast From the NWS, Chance of A Winter Storm This Weekend

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216 PM CST Fri Nov 23 2018

Including the cities of Rockford, Belvidere, Woodstock, Oregon,
Dixon, and DeKalb
216 PM CST Fri Nov 23 2018


* WHAT…Heavy snow possible. Total snow accumulations in excess
of 6 inches possible. Winds could gust as high as 35 mph.

* WHERE…Portions of north central and northeast Illinois.

* WHEN…From Sunday morning through Sunday evening.

* ADDITIONAL DETAILS…Travel could be very difficult. Snow
covered roads and significantly reduced visibility are possible.


A Winter Storm Watch means there is potential for significant
snow, sleet or ice accumulations that may impact travel. Continue
to monitor the latest forecasts.

Update from the NWS

Through Saturday…

Concerns center on a period of generally lighter rain this evening
into the overnight hours.

A broad upper trough extends through the nation’s heartland this
afternoon. High pressure to our east ahead of this system is
leading to a period of breezy southeast winds. The strongest
forcing and better moisture will pass by to our south, but the
trough axis will drive an area of rain through the area tonight.
We could start to see some spotter rain fall out of the mid to
higher cloud deck in the evening, though confidence is higher in
the more organized rain shield spreading through the area late
evening into the overnight hours. Some areas may see a few tenths
of an inch of rain.

The rain will taper to drizzle with some lingering low level
clouds into Saturday morning. Certainly some areas will clear out
behind the system, and with mild west southwest winds in place,
temperatures will again top out in the 40s northwest to the 50s
across Chicago and points south and east.



209 PM CST

Sunday through Friday…

Winter storm system will be the primary concern during the long
term forecast period. Several inches of accumulating snowfall
expected across portions of northern Illinois, though details in
precise placement and timing still remain in flux. From 24 hours
ago, guidance has had a pronounced southward shift in the surface
low track, bringing more favorable conditions for accumulating
snowfall farther south across the forecast area, including the
Chicago metro area. Upper wave that will be responsible for the
late weekend snow is still over the northern Pacific and may be
sampled by the 00Z RAOB network this evening, though more likely
sampled by the 12Z launch tomorrow. Guidance should hopefully have
a better handle on the details in the next 24 hours as a result.

What we know… Strong upper level disturbance over the northern
Pacific is progged to move over the Pacific Northwest this evening
and tonight and dig into the southern/central Great Plains early
on Sunday. Surface low will deepen in response lifting from
Missouri early Sunday morning across the Midwest Sunday evening.
Warm advection wing will overspread the region early in the day
Sunday allowing the column to saturate and for precipitation to
eventually reach the surface. P-type details will still have to be
worked out, but precip may start off as rainfall in some areas
before transitioning over to snow for the remainder of the event.
There will likely be a swath of heavy snow left of the surface low
track. Confidence is highest in accumulating snow over far north
and northwest Illinois and diminishes farther south.

Details that still need to be worked out… Surface low track is
the main area of uncertainty. While there has been a pronounced
southward shift from yesterday’s guidance, the latest suite of 12Z
guidance still has important inter-model differences that will
impact the location of heaviest snow. Meso-scale banding will be a
concern within the axis of heaviest snow. Guidance indicates a
corridor of strong f-gen which will help enhance snow totals for
some locations. In addition, lapse rates above 700/600mb remain
steep at times and could help to promote a deep vertical response
to forcing. SREF/GEFS plumes really highlight the uncertainty well
showing a broad range of no snow to over a foot of snowfall in
some members.

Bottom line… A winter storm appears likely somewhere across
eastern Iowa, northern Illinois, and southern Wisconsin, though
details in the placement of the heaviest snow remains low within
50- 100 miles. Rain/Snow line is favored to set up over the CWA,
but again confidence is low within 50-100 miles. Either way,
travel impacts Sunday are likely, and may potentially become
significant for some locations.

Monday through Thursday… Slow moving upper low over the Great
Lakes will keep the local area locked into a colder but primarily
dry pattern through most of the upcoming week. Surface ridge axis
will extend from the Canadian Prairies into the lower Mississippi
Valley Monday through Wednesday keeping us under colder northwest
flow. May have to keep an eye out for some lower amplitude
clippers that could bring some snow into the CWA or nearby, but
primarily expect dry weather to prevail. The ridge will gradually
shift east to the midwest Thursday. Another southwest low may
impact the region late in the week.




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