Area Forecast Discussion
Issued by NWS Central Illinois
FXUS63 KILX 071749
Area Forecast Discussion
National Weather Service Lincoln IL
1149 AM CST Fri Mar 7 2014
ISSUED 1037 AM CST Fri Mar 7 2014
Southerly winds are bringing warmer air into central Illinois this
morning, with 16z/10am temperatures running about 15 degrees
warmer than 24 hours ago. Given rate of morning temp rise and
continued sunshine/southerly flow, afternoon highs will reach the
50s across most of the area. The exception will be across the far
northern KILX CWA from the Peoria area northward where a
significant snow cover will likely keep readings in the middle to
upper 40s. Current forecast has a good handle on things, so no
update is needed at this time.
ISSUED 1149 AM CST Fri Mar 7 2014
Main aviation challenge will be the approach of a cold front and
the potential for MVFR ceilings and light precip tonight into
Saturday morning. Front currently extends from central Wisconsin
across Iowa into far northern Kansas. Models are in good agreement
with timing of FROPA tonight, with wind shift from southerly to
northwesterly occurring at KPIA by 03z, then further east at KCMI
by around 10z. Upstream obs show very little precip associated
with the front: however, MVFR ceilings are noted along and behind
the boundary. NAM forecast soundings remain rather dry overall,
but do suggest lower ceilings behind the front. Have therefore
lowered ceilings into the MVFR category and introduced VCSH at
the terminals between 09z and 12z.
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.