Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 222052

Area Forecast Discussion
252 PM CST Sat Nov 22 2014

.SHORT TERM...(Tonight)

Weakening 1031 mb high pressure drifting off eastern NC shore while
strong and deepening 985 mb low moving east into sw Sasketchewan.
This was giving a tight pressure gradient over central and southeast IL
this afternoon with very breezy ssw winds 12 to 22 mph and gusts of
25 to 30 mph. SSW winds advecting in much milder and more moist air
from western Gulf of Mexico with temperatures in the mid 50s to lower 60s
(warmest sw areas with Mount Carmel airport at 64F) and dewpoints in
the middle to upper 40s. Cloudy skies across much of central IL with
some breaks in clouds se of I-70 in southeast IL. Isolated light
rain showers over eastern IL this afternoon while showers more
numerous over sw IL from I-64 south into southern MO along and se of
I-44 where a few thunderstorm were a few hours ago. Mid level
moisture spreads northward tonight across areas se of the IL river
and this to increase chances of light rain showers though rainfall
amounts will be light due to weak lift/forcing. Also have patchy
drizzle with lower clouds over IL river valley tonight and areas of
fog overnight (currently getting fog over parts of nw IL and se IA).
Went a few degrees above similar MET/MAV guidance for lows tonight
in the mid to upper 40s due to cloud cover and southerly winds of
10-15 mph and gusts to 20 mph especially this evening.


.LONG TERM...(Sunday through Saturday)

The vigorous short wave, lifting out of the southern plains will
phase with a northern stream system tomorrow; The related surface
system will strengthen over the CWA and lift northeast east tomorrow
night through Monday. The associated cold front with this system
will move through the area Monday night and bring the return to
colder air in the region for the beginning of the coming week. This
system is the main challenge with this forecast package this
afternoon. The resulting weather with this system will be for mostly
rain across the whole area tomorrow with the possibility of isolated
thunderstorms in southeastern IL, along and south of I-70, for
tomorrow afternoon through tomorrow evening. The dynamics of this
system do not look very strong, so severe storms are not expected in
southeast Illinois tomorrow afternoon or evening. Areas across the
north will see the areas of fog continuing through tomorrow and
tomorrow night. The fog will dissipate in the north once the low
pressure area moves northeast and the cold front moves through the
area, tomorrow night. The colder air that moves in Sunday night and
Monday, as the system deepens and moves northeast, will bring a
change to the p-type, resulting in rain mixing with snow in the west
Sunday night, and then becoming all snow by Monday. Snowfall
accumulations will be a half inch or less; since the pcpn will be
ending as the system moves northeast.

Temps will remain warm tomorrow but then fall from tomorrow night
through Monday night. Temps on Monday will be steady or slowly
falling in the afternoon, with the 24hr highs likely being around
midnight tomorrow night, and lows late Monday evening.

The remainder of the forecast period, through Saturday, will be
relatively dry. However, the models are bringing in a weak clipper
system Wed through Thur, that will bring a chance of snow to the
northern third of the CWA. Models are fairly consistent with the
location of the track of the low pressure area, but differ on
timing. So will still with a blend of the two models and keep the
chance of snow Wed and Wed night, as with previous forecast; and
then have a chance in the northeast parts for Thur to accommodate
the slower timing of the ECMWF.

Temps will warm some on Wed, ahead of the clipper system, but then
turn cold again after the system moves through and colder air
advects into the region again.


.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)

MVFR ceilings at PIA and BMI most of this morning (just lifted to
VFR at PIA) while VFR ceilings along I-72 at midday. Meanwhile
isolated to scattered showers had shifted se of the central IL
airports at late morning. HRRR shows MVFR ceilings 2-3k ft
possible at times over central IL this afternoon especially at PIA
and BMI, and this model shifts these lower ceilings along with fog
further north of central IL this evening. Was more pestimistic
with keeping MVFR ceilings and vsbys around tonight and even lower
IFR ceilings at PIA and BMI Sunday morning. Rain showers to become
more likely later this evening/overnight with best chances
shifting into IL river valley by PIA late tonight and Sunday
morning. Breezy ssw winds 12-17 kts with gusts 18-25 kts into this
evening to veer sse Sunday morning and still gust again to 18-23
kts. Kept LLWS in TAFs again tonight until mid morning Sunday
with 2k ft sw winds of 40 kts.




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