Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 041640
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1040 AM CST Wed Mar 4 2015

.UPDATE...
ISSUED AT 1040 AM CST WED MAR 4 2015

Skies have become mostly cloudy to cloudy and will remain that way
as the next wave moves across southern Illinois today. Current
forecast of light snow in the southeast still look good, and
current grids has a good handle on this. Did make some minor
tweaks to the sky cover grids for cloudier conditions in the
northwest. Remainder of forecast looks good, but will still be
sending an update shortly.

&&

.SHORT TERM...(Today)
ISSUED AT 250 AM CST WED MAR 4 2015

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
were 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
tonight.

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)
ISSUED AT 250 AM CST WED MAR 4 2015

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 12Z TAFS through 12Z Thursday morning)
ISSUED AT 505 AM CST WED MAR 4 2015

A band of MVFR cigs continues to track east across the forecast
area this morning but should push east of CMI and DEC by 13z
with VFR conditions for the remainder of the period. Another
Arctic high was located to our northwest and will bring in
gusty northwest winds along with much colder and drier air
into the region over the next 12 to 24 hours. A weather system
over the Southern Plains this morning is expected to bring
snow to areas along and south of I-70 today into this evening
missing our TAF sites, but close enough to bring some mid and
high level cloud cover during the day and into early this eve.
Surface winds will be out of the northwest to north at 12 to
17 kts with a few gusts around 22 kts at times into the
afternoon, before we see winds begin to diminish after 00z.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY until 6 PM CST this evening FOR
ILZ071>073.

&&

$$

UPDATE...Auten
SHORT TERM...Smith
LONG TERM...Geelhart
AVIATION...Smith





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