Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 220751

Area Forecast Discussion
251 AM CDT Wed Oct 22 2014

.SHORT TERM...(Today)

A sprawling ridge of high pressure extends from the high pressure
center over northeast Ontario into the southern Plains. The current
position of the ridge cuts across west-central Illinois. This
surface ridge, and driving upper ridge, will slowly drift east today
across the forecast area. The associated air mass is quite dry and
cloud cover today should be minimal at best. Our main concern is how
warm it will get today. Most of the guidance has today`s high
temperatures cooler than yesterday. Have a hard time seeing how this
would occur as full sun and a dry air mass should promote rapid
warming from the cool starting temperatures. Also, in the western
portion of the forecast area, low level WAA/return flow on the back
side of the surface ridge is expected to begin later today. So, plan
to boost forecast highs a few degrees above the model consensus,
which results in temperatures similar to yesterday. It should be
noted that the guidance was too cool yesterday too.


.LONG TERM...(Tonight through Tuesday)

Early morning water vapor imagery showing two upper waves of
interest, one across Montana and another extending from Wyoming
southwest into New Mexico. The evening models continue to try and
unify this into a single wave mid week over the Plains. Large upper
low currently just west of Washington DC only makes slow eastward
progress the next couple days, so the models have been trending a
bit slower with the progression of the incoming wave. As to how much
of the rain makes it over here, the NAM continues to be more of the
odd model out with the rain largely limited to near the Great Lakes
by afternoon. GFS, ECMWF and Canadian models are more wet, but
largely keep the rain across the west half of the CWA during the day
and quickly lifting the area northeast in the evening. Forecast
soundings for Champaign are still fairly dry below 600 mb through
the afternoon except off the Canadian model, so will keep the rain
our of the forecast for the southeast third of CWA during the day.
Mentionable rain in the worded forecasts Thursday evening will just
be in areas from Bloomington to Danville.

Focus into the weekend is with the warming temperatures, as upper
ridge builds just east of the Rockies. 850 mb temperatures progged
to reach the 15C range off both the GFS and ECMWF models by late
Sunday afternoon, and will maintain highs in the upper 60s to mid
70s for the weekend, with the warmest highs occurring into Monday.

Next item of concern is with a digging wave across the Plains early
next week. The longer range models are not really in agreement with
this feature beyond Monday evening, as the ECMWF digs the wave much
further south before arriving in Illinois on Tuesday. Consequently,
its surface storm development is much wetter and slower. The GFS
focuses most of the wave across the upper Mississippi Valley by
Tuesday afternoon with more of a split upper flow developing, and
most of its precipitation is closer to the surface low which lifts
northeast toward Lake Superior. Have introduced some rain chances
for Tuesday as even the GFS solution would produce at least some
scattered showers, but will limit them to around 30% at this time.


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

Areas of MVFR cigs will continue to affect KPRG-KCMI-KBMI
northward until 12z. Otherwise, mostly clear skies expected for
the next 24 hours as a 500 mb ridge axis approaches from the
west. Surface high pressure settling over Illinois will bring
light winds veering from northeasterly to southeasterly over the
next 24 hours. Low level moisture indicates fog possible
overnight, however persistent light winds should keep fog thin,
generally no worse than MVFR visibility. Therefore, have continued
temporary MVFR fog from 10Z-12Z in TAFS.




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