Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 280457
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1157 PM CDT Wed Aug 27 2014

.UPDATE...
ISSUED AT 905 PM CDT WED AUG 27 2014

Main surface front has settled south of the forecast area this
evening, and currently lies west/east across the southern tip of
Illinois. Still some convection in the vicinity of this boundary,
some of which is clipping our southeast Illinois counties, but
these showers/storms appear to be, and should continue, to exhibit
a strong diurnal component and fade with time. Attention turns to
an impulse ejecting northeast across the central Plains from the
strong upper low over the Rockies. This disturbance is expected to
help push the western extent of the surface boundary to our south
back northward, especially on Thursday.

Many of the latest forecast models have been trending drier
through the night, and this seems reasonable. Given the fading
diurnal instability, the fact that no significant surface boundary
and/or upper level disturbance will be moving through, and low
level jet forcing is apt to remain closer to the ejecting Plains
wave, do not expect much in the way of rainfall for the rest of
the night.

An earlier update tweaked PoPs down through the night, and plan to
make further downward adjustments. Otherwise, no significant
forecast changes appear necessary at this time.

&&

.SHORT TERM...(This evening through Thursday)
ISSUED AT 310 PM CDT WED AUG 27 2014

Surface pattern is a little weak behind a now almost stationary
front over the central portions of the state. Warm weather and
humid conditions still in place and remnants of a decaying MCS
working into the forecast area with the front providing focus for
the system. One thunderstorm in the Jacksonville producing a lot of
lightning and heavy rainfall. Models have varying solutions for the
progression of the boundary through the region and forecast
collaboration is resulting in a drier forecast than prev.
Concerned that the front is initializing too far south...but will
back off the pops for now.  Either way activity should recede
somewhat in the overnight hours as current convection is getting
more than a little support from diurnal heat.  Once the sun sets,
the convective element reduces enough to allow the cooler air to
help progress the boundary to the south.  The low then lifts just
west of the Miss River Valley and brings the boundary back northward
as a warm front again, returning the chances for showers and
thunderstorms to the forecast area Thursday.

&&

.LONG TERM...(Thursday night through Wednesday)
ISSUED AT 310 PM CDT WED AUG 27 2014

The upper level ridge will be over the area again, but not as steep
as early this week. On the surface, southerly winds will bring the
return of moisture and warmer temperatures for Friday. The
associated surface front will be well northwest of the area, which
will slowly move east and southeast into the area for Friday night
through the weekend. As the front gets into the area, the chance of
thunderstorms will become likely, first in the northwest on Friday
night, then the whole area on Saturday, and then likely in the east
Saturday night. The chance of showers and thunderstorms will
continue through the rest of the weekend, but not as high as Fri
through Sat.

After the weekend system moves east, another system will be
approaching from the west and this will keep a chance of pcpn in
some portion of the CWA through the rest of the weekend and into the
first part of next week. This system should move out of the area by
Tue night, so Wed currently looks to be dry forecast. However, with
the flow being very zonal and multiple boundaries will be in and
around the area through the period, the timing of pcpn chances will
likely vary from day to day.

Temps will warm a tad for Fri and Sat, but not as warm as what they
have been earlier this week. Then normal temps are expected for the
remainder of the forecast period. However, with pcpn on and off
through the period as well, humid/muggy conditions will likely
continue.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
ISSUED AT 1157 PM CDT WED AUG 27 2014

Quiet aviation weather conditions expected to prevail for the most
part across the central Illinois terminals. Weak high pressure has
built across the area, with the main frontal boundary stalled
across the southern tip of Illinois. A storm complex is getting
going across the central Plains and lifting to the northeast. While
this specific complex should miss the terminals, the disturbance
driving it will help lift the frontal boundary over southern
Illinois back to the north. This should eventually bring a risk of
thunderstorms back to the area by Thursday afternoon, but
confidence is too low to go above a VCTS mention at this time.

&&

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

$$

UPDATE...BAK
SHORT TERM...HJS
LONG TERM...AUTEN
AVIATION...BAK





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