Area Forecast Discussion
Issued by NWS Central Illinois

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000
FXUS63 KILX 180309
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
909 PM CST Wed Dec 17 2014

.UPDATE...
ISSUED AT 909 PM CST WED DEC 17 2014

Have already made one adjustment to cloud cover since it is not
clearing as fast as originally expected. Will be making another
adjustment for the same thing with high clouds advecting in from
the southwest. Pcpn is moving across MO and still expected to
arrive in western IL in the morning. Forecast still has good
handle on this. Most of forecast looks fine, but will be updating
to reflect current cloud trends. Update coming shortly.

&&

.SHORT TERM...(Tonight)
ISSUED AT 245 PM CST WED DEC 17 2014

19z/1pm satellite imagery continues to show overcast conditions
across much of central Illinois: however, the clouds are beginning
to erode northwest of the Illinois River.  While HRRR guidance has
not been particularly useful in the short-term, satellite trends
suggest skies will partially clear across all but the far E/NE KILX
CWA by early evening.  After a period of mostly clear skies early
tonight, clouds will once again begin increasing in advance of the
next storm system, which is currently evident on water vapor imagery
over west Texas.  Quite a bit of precip and even some thunder is
occurring ahead of this wave over Oklahoma/Texas: however, it is
expected to weaken as it lifts northeastward into the region on
Thursday.  It will also be coming into a dry airmass beneath a
prevailing surface ridge axis.  Forecast soundings show gradual
moistening from the top-down later tonight, but the lowest levels
below 850mb will remain quite dry through 12z.  As a result, have
maintained a dry forecast through the overnight hours.  Due to the
initially clear skies and low dewpoints, have gone a couple of
degrees below MAV guidance for lows tonight, with readings dropping
into the teens and lower 20s.

&&

.LONG TERM...(Thursday through Wednesday)
ISSUED AT 245 PM CST WED DEC 17 2014

Upper flow will be zonal for next few days, with weak waves moving
east through flow. Moisture channel data and upper air shows initial
wave to affect region over NM this morning. This system to
continue tracking to the northeast, pushing some overrunning pcpn
into MO and southern 1/2 of IL for late tonight into Thursday. Weak
vort lobe and isentropic lift to be enough to move the light snow
into southern 1/2 of CWA in the morning, but wave moving fast enough
to only affect the morning. Mainly less than half inch.

Next wave to move into region for Friday night and Saturday morning
and the area of lift with this one is farther south, mainly over
southeast cwa. Again, some light snow possible.

Upper flow starts to change on late in weekend and by Monday, flow
is northwest. Digging upper trough over Great Lakes with upper low
closing off by Monday night. This will bring some initial pcpn into
the region ahead of cold front that moves through Tuesday.
Temperatures however, are only cold enough for possible mixture
until post frontal on Tuesday night and Wednesday. Therefore no snow
accumulation. However by Tues night to Wed, only minor vort lobes
rotating around the closed upper low in the cold air, so chance of
light snow accumulations only.

&&

.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
ISSUED AT 536 PM CST WED DEC 17 2014

Some clearing has occurred at PIA and SPI, but clouds still remain
at BMI, DEC, and CMI. Question is that now that the sun is gone,
when will clouds push further east, clearing at the last three TAF
sites, or will it even clear there at all. All models continue to
clear lower clouds so will scatter the low clouds out later this
evening at those sites. However, all sites will be covered with
cirrus overnight. By morning, mid clouds around 8-12kft will move
into the area in advance of the next weather system. Based on the
movement of the system, very light snow will begin at SPI around
15z with cigs around 3.5kft, with vis around 5sm. The other 4
sites will not see any snow, but cigs will drop to 4-6kft. The
system will dissipate as it moves into the area, which will
improve conditions by late afternoon at all sites. Lower clouds
will diminish and then broken cirrus will be left at all sites.
Winds will be light and variable through the period.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...Auten
SHORT TERM...Barnes
LONG TERM...Goetsch
AVIATION...Auten






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