and KLOT nice update from Ricky
UPDATE...
1015 PM CST
There have been no changes made to the going Winter Storm Warnings
and Winter Weather Advisories. However, based off conditions in
the pre-dawn hours, the midnight shift may give consideration to
converting some of the warnings over to a Winter Weather Advisory.
This is because snowfall rates aside from lake enhancement near
Lake Michigan are expected to be mainly light and occasionally
moderate on Tuesday. The main message tonight remains hazardous
travel due to a variety of winter hazards, snow covered roads,
reduced visibility and at least patchy blowing snow in the north
due to 30-40 mph northeast wind gusts, and freezing rain and
drizzle south. Have overall lowered storm total snowfall a bit to
only locally to 6+" inland and highest amounts near Lake Michigan
in Illinois at 6-8", maybe a few spots coming in just above 8"+.
These changes were reflected in the updated WSW text product.
The evolution of our winter system is quite different from just a
few days ago, as double or triple barreled weaker low pressure is
analyzed from southwest MO to western KY, instead of a stronger
low lifting northeast of the Ohio River. Forcing is being driven
by weakening, but still certainly sufficient large scale forcing
from 500 mb short-wave, along with mesoscale f-gen (thermal
gradient) driven forcing at the lower and mid-levels, plus also
augmented by convective processes by very steep lapse rates aloft.
Trends have been a challenge this evening, as we`ve been fighting
pockets of dry air aloft. Most notably, dry air centered around
850 mb was driven into far northern Illinois and southern
Wisconsin earlier, which guidance did a fairly poor job of
capturing. That dry air finally lost out as snow banding finally
pushed north. There`s been some good f-gen driven banding amidst
the dry air issues, so reports of nearing 2" have trickled in
centered near I-88 and just south. More convective elements have
been streaming northward out of central Illinois thanks to
aforementioned very steep mid and upper lapse rates sampled by
DVN RAOB. The dry air at 500 mb and above is allowing for
convection to help fill in some of the dry pockets where snow has
been more prevalent and this should be the case north of I-80 for
a decent chunk of the overnight.
850 mb warm nose appears it made inroads into our far southern CWA
near and south of US-24, while to the north of that varied precip
types have been from pockets of saturation amidst some 700 mb
drying and above described convection that has brought reports of
snow and sleet. This dry layer at 700 mb will shift northward
overnight, causing a loss of cloud ice in the DGZ and introducing
a concern for some freezing drizzle from I-80 and south into
Tuesday morning. It appears that for areas to the north of that up
to around I-88 corridor, saturation depth will be to just cold
enough at -9 to -11C to keep snow as primary p-type. Steady
generally light to moderate snow rates with briefly heavier snow
will occur until about 3 or 4 AM, and then expecting the lake
enhancement to take hold along the Illinois shore. On Tuesday, the
500 mb and 700 mb circulations will slowly translate across the
area, keeping lighter snow going and resulting in light additional
accumulations of 1-2/1-3", but higher near lake in IL at up to
2-5". The midnight shift will assess transition to lake effect
snow Tuesday night, which should last into Wednesday and add
additional accumulations for affected areas.
Castro
