Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 252057

Area Forecast Discussion
257 PM CST Tue Nov 25 2014

.SHORT TERM...(Tonight)

Persistent back of stratocumulus has finally started showing a
significant clearing trend over the last few hours. As of mid
afternoon, most areas west of a Galesburg to Effingham line were
mostly clear, and the remainder of the CWA should clear out by 6 pm
or so.

Quiet conditions expected overnight, with winds starting to become
southeast as high pressure that is currently overhead exits the
area. Clipper system currently dropping southeast from the Dakotas
will spread mid and high clouds into the western portions of the CWA
through the night, while the east remains relatively clear. With the
increase in clouds and winds, much of the forecast area will likely
see fairly steady temperatures overnight, with lows in the 20s.


.LONG TERM...(Wednesday through Tuesday)

Main concern this forecast package will be the location of the pcpn
tomorrow as a clipper system moves through the area. NAM/GFS/ECMWF
models are very similar with timing and track of the surface
low/clipper system moving through the area tomorrow. However the
Canadian is slower and little further east than the others, so it
will be the odd model out for this package. Pcpn will move into the
area beginning tomorrow morning and slowly spread eastward during
the day while the whole area of pcpn moves southeast. It is very
possible that the northwest areas of the CWA may not see any pcpn
tomorrow, but will still have a chance pops for tomorrow afternoon.
Likely pops will be in the west through the period, as this will be
closest to the track of the low, which should be southeast along the
IL/MO border. All the models hold some light pcpn back tomorrow
evening so will keep slight chance and chance pops in the
east/southeast counties during the evening. The big issue with this
system will be the temp profile as it moves through. Warmer air will
advect northward just ahead of the clipper system, so p-type could
be in the form of rain over the southern parts of the CWA. During
the morning, a mix of rain and snow will be possible in the
southeast 9 counties. By afternoon, this rain and snow area will
drift northward as temp rise. So, the rain and snow area will be
across the central part of the area tomorrow afternoon, with all
snow in the north and all rain in the southeast/south. The mix type
of pcpn will also limit the amount of snowfall accumulation. Higher
accumulations will be limited to the western areas, closer to the
track of the low. A half inch or more can be expected along and west
of a Galesburg to Springfield line through tomorrow evening.

Past this system, dry weather is expected through the rest of the
week and into the first part of the weekend. The pattern will also
become more zonal through the rest of the week, which will allow
temperatures to gradually warm through the period and into the
weekend. The coolest temps will be on Thursday and then gradually
warm into the 50s for Saturday.

During the latter part of the weekend, a dry cold front will drop
through the area. This front will not become active until after it
gets through most of the cwa because the a large high pressure area
will have the moisture blocked off from the gulf. So when the front
does become active, the pcpn chances will be confined to the
southeast third of the CWA. Pcpn type during the period will
dependent on time of day, so for simplicity, will have a chance of
rain showers Sunday and chance of snow Sunday night.

After the warm day on Sat, temps will slightly cool for Sun and
Monday. Then temps will warm back into the 40s and 50s for Tuesday.


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

Main forecast concern is with the timing of the MVFR conditions
this afternoon. All TAF sites currently with ceilings at or below
2000 feet. Clearing line advancing eastward from far western
Illinois, with AWIPS timing tool showing it reaching KSPI around
20Z, but not reaching KCMI until toward 00-01Z. Once skies clear,
VFR conditions are on tap the remainder of the forecast period.
There will be lowering ceilings late Wednesday morning ahead of a
fast moving storm system, but any MVFR conditions would likely be
after 18Z. Westerly winds this afternoon will become light and
variable for a time early this evening, before a southeast flow
sets up and persists the remainder of the forecast period.




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