Area Forecast Discussion
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FXUS63 KILX 040851

Area Forecast Discussion
251 AM CST Wed Mar 4 2015

.SHORT TERM...(Today)

2am surface analysis indicates the cold front has shifted south of
the Ohio River with another surge of Arctic air spilling southeast
into our area. Quite a range in temperatures across the Midwest
early this morning with single digits readings common over parts of
north central Iowa, while over far southeast Illinois, temperatures
will in the mid to upper 30s. The aforementioned cold front will
be located south of the Ohio River Valley over the next 24 hours
with models indicating a rather tight baroclinic zone along either
side of the boundary with several weak surface waves moving east
along the thermal gradient producing periodic precip chances to the
north which will include parts of the I-70 corridor through early

Forecast soundings suggest some precip-type issues for the first few
hours just after dawn before a deep enough cold layer settles in
from the northwest changing any wintry mix over to snow. Latest 06z
NAM-WRF soundings over southeast IL are a bit slower in breaking
down the elevated warm layer seen between the 850 and 750 mb layer.
This should continue to result in some melting of the ice crystals
before refreezing again as it falls through a rather deep low level
cold layer. This should result in some rain mixing with sleet, with
the possibility for a brief period of freezing rain this morning
before the precip changes over to snow by mid morning. Models
indicating we may see a brief lull in the precip later this morning
before the next wave of deep layer forcing accompanied by some
enhanced lift associated with the entrance region of a jet max at
300 mb moves across the area this afternoon into this evening. This
should produce a steady snowfall mainly south of I-70 with a tight
gradient in snowfall amounts with our counties in the far southeast
sections of the forecast area seeing around 3 to 4 inches, with
higher totals further south.

For the rest of central through east central Illinois, much colder
air will continue to push southeast into the area during the day
with not much response in temperatures. Guidance values look
reasonable across the north and central sections today with
afternoon temperatures not rising much with upper teens to low
20s common by mid-afternoon, while to the southeast, we should see
morning highs in the upper 20s to lower 30s, with the the mercury
slowly falling thru the day.


.LONG TERM...(Tonight through Tuesday)

Have made little change to the snow chances south of I-70 tonight,
mainly concentrating them through the evening with an additional
half to 1.5 inches along the highway 50 corridor. The other concern
for tonight is with the wind chills across the northwest. Deepening
upper trough currently dropping into the upper Mississippi Valley,
and will swing through Illinois with 850 mb temperatures around -18C
by Thursday morning. Late-season winter storm over the Ohio Valley
won`t be in a big hurry to leave, so winds will stay up some as an
area of high pressure moves southeast from the Dakotas. Clearing
line will advance southeast through the night, with the northwest
CWA mostly clear the longest, allowing temperatures to drop below
zero. Wind chills around -15 currently expected late tonight and
early Thursday from Galesburg to Toulon. As the -15 area has been
fluctuating in size recently, will hold off on a headline due to the
uncertainty in coverage area and borderline conditions.

The unseasonably cold air will continue into early Friday, but the
upper pattern after that is continuing to favor a steady and welcome
warming trend. Temperatures will reach the 40s this weekend, and an
increasing area of 50s is not far behind for early next week. While
some disturbances will move through the upper Midwest, flow from the
Gulf will be cut off due to a persistent surface high over the
Tennessee Valley and mid-Atlantic regions. This will result in a dry
passage of these disturbances.


.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)

MVFR ceilings temporarily cleared at the central Illinois
terminals this evening: however, another patch of lower clouds is
noted on 05z satellite imagery along/west of the Illinois River.
These clouds will spread eastward over the next couple of hours
before clearing out once again later tonight. Latest HRRR suggests
MVFR ceilings will depart KPIA by 09z, then further east to KCMI
by around 13z. Even when the lower clouds exit, a mid-level cloud
deck at 12000-15000ft will remain as low pressure tracks along a
frontal boundary draped along the Ohio River. Any associated
precip will remain south of the central Illinois terminals,
although overcast conditions will persist through the entire 06z
TAF period. Northwesterly winds will gust to between 15 and 20kt
tonight through Wednesday afternoon before subsiding to less than
10kt by Wednesday evening.


WINTER WEATHER ADVISORY from 6 AM this morning to 6 PM CST this
evening FOR ILZ071>073.



LONG TERM...Geelhart
AVIATION...Barnes is the U.S. government's official web portal to all federal, state and local government web resources and services.