Area Forecast Discussion
Issued by NWS Central Illinois
FXUS63 KILX 070904
Area Forecast Discussion
National Weather Service Lincoln IL
304 AM CST Fri Mar 7 2014
ISSUED 304 AM CST Fri Mar 7 2014
SHORT TERM...Today through Sunday
Surface ridge axis lingering over the CWA early this morning.
Under clear skies and light winds radiational cooling has dropped
temps near dewpoints in low/mid 20s and allowed light fog in a 2-5
mile range to form. A peek out the front window shows this has
deposited a thick layer of frost on cars in the parking lot.
Upstream, a cold front and unorganized low pressure complex
stretched from northern MN back into central NEB.
As this front shifts SE towards NW IL by this evening, warm
advection ahead of it will bring the warmest readings of the week
with widespread upper 40s/lower 50s highs, and even some mid 50s
in the far south and southwest. Exception will be where thicker
snowpack resides over the far northern CWA where highs will be
limited to the mid 40s. Precip chances increase especially after
midnight over the NW, where a zone of post-frontal frontogenetic
forcing and lift in the entrance region of a 90 kt jet over the
Great Lakes, initially produces a mix until evaporative cooling
and low level cold advection transitions to a clean snow
changeover after 09Z. A couple models show a corridor of
maximized lift over the far NW CWA where 0.10-0.15 QPF is
possible, which would translate to around an inch of wet snow
mainly north of PIA. As boundary layer temps rise through the
morning under increased mid level cold advection, a rain/snow mix
looks likely for the central CWA to near I-72, with rain to the
south. Where snow does fall surface temperatures above freezing
will prevent any accumulation. QPF for these areas looks to be
under a tenth of an inch. Any remaining precip quickly exits SE IL
by early evening, as incoming surface ridge from the northwest
dries things out.
This ridge sinks south of the region on Sunday, with return
flow/warm advection rebounding readings back up closer to normal.
LONG TERM...Monday through Thursday
By late in the weekend and early next week a strong branch of the
northern jet along the Canadian border temporarily flattens the
mid level flow over the central US allowing Pacific air to bathe
the region on Monday. Southwest flow on the warm side of a clipper
passing through the northern Great Lakes will draw the Plains
thermal ridge up into the area, with 850 mb temps getting up to
around +10C for the first time in quite a while. This should yield
widespread upper 50s/lower 60s highs.
A cold front trailing south from the above mentioned clipper
shifts into the region on Tuesday, while more significant energy
drops into a developing central Rockies trough. As expected at
this range models show a large spread in location/strength of
possible phasing of northern and southern streams for a
potentially significant precip event in the central US for
midweek. ECMWF continues to be most aggressive in phasing and
tapping cold air off Arctic high north of Lake Superior for a
potential late winter storm over parts of the Midwest or Ohio
Valley. Of note, 00Z GFS/GEM have backed off on this possibility
which leads to higher uncertainty for this portion of the forecast.
Consensus chance pops for rain/snow seem prudent at this point.
Beyond this potential system, the upper air pattern reverts to a
familiar ridge/west trough/east configuration which places the
area back into a cooler northwest flow regime through Thursday.
This may be short-lived though as some signs of zonal flow
becoming established to our west by the end of next week.
ISSUED 1152 PM CST Thu Mar 6 2014
Southerly flow is still expected to develop across the central
Illinois terminals late tonight into early Friday. However, winds
have mostly died off across the area right now. The light winds
have combined with mostly clear skies and low temp/dew point
spreads to produce patchy fog. This may continue to be a problem
through the night, but confidence in how thick the fog will be
low. However, the latest HRRR model runs suggest patchy dense fog
is not out of the question. That being said, do not have enough
confidence to include the thicker fog at this time. Aside from the
fog, VFR conditions should prevail. A cold front is expected reach
KPIA, KBMI, and KSPI by the Friday evening, resulting in a wind
shift to the northwest and thicker VFR cigs.