Area Forecast Discussion
Issued by NWS Central Illinois

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000
FXUS63 KILX 211741
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1241 PM CDT Thu Aug 21 2014

.UPDATE...
ISSUED AT 1015 AM CDT THU AUG 21 2014

15z/10am surface analysis shows warm front extending from northern
Iowa to southern Lake Michigan. Numerous showers and thunderstorms
have been tracking along this boundary early this morning, mainly
impacting locations along/north of the I-80 corridor. This is a
bit further north than previously forecast, thanks to the upper
ridge building across the region. 12z NAM keeps central Illinois
dry throughout the day, then develops nocturnal convection as far
south as the I-72 corridor late tonight. NAM was too aggressive
with the southward extent of precip last night, so am skeptical
of its latest solution. HRRR is also dry through the day, and
does not develop any convection across the area through 03z this
evening. Based on latest satellite/radar trends and NAM/HRRR data,
have trimmed PoPs today and tonight. Will maintain slight chance
for showers/thunder across the far N and E CWA through the
morning, then will go with dry conditions across the board this
afternoon. Have also reduced PoPs for tonight, focusing highest
chances across the north from the Peoria and Bloomington areas
northward after midnight. With a good deal of sunshine and
southwesterly winds, afternoon highs will reach the upper 80s and
lower 90s.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 342 AM CDT THU AUG 21 2014

Warm front has lifted north through most of the area and based on
surface observations, looks to be just north of I-74 at this point.
Believe the front will continue to lift north through the day,
resulting in the whole CWA being in the warm sector for the end of
the week. However, the mid level ridge will be somewhat flat and any
disturbance or wave that moves along the top of the ridge could
result in precip dropping into the northern and northeastern part of
the CWA. So chance pops will continue to be warranted over parts of
the CWA today and tonight. Pops will be less during the daytime
hours but then increase over the northeastern half of the CWA for
the overnight hours, tonight. Temperatures will be warm today, but
cloud cover could keep afternoon highs from getting too high, though
still expecting highs around 90 today. Lows tonight will be similar
to now, just about 1-2 degrees warmer.

&&

.LONG TERM...(Friday through Wednesday)
ISSUED AT 342 AM CDT THU AUG 21 2014

Summer heat continues through the remains of the weekend.  Hot and
humid conditions lending to an isolated thunderstorm threat through
the weekend, particularly towards the NE as waves push over the
upper ridge building into the Midwest. Models shifting with each
issuance as to the actual increased threat with the erosion of the
ridging to the NE.  Heat and humidity has been more consistent,
though even that has seen some shifts, starting to retract some of
the eastward creep of the 850 mb temps.  Not pulling back too much
in the way of guidance just yet and temps Fri-Sun still in the 90s,
heat indices over 100F.  Issuance of a Heat Advisory covered
above...however, should the dwpts materialize, or see the temps
respond as expected behind this mornings warm front today... will
rethink the issuance of a Heat Advisory for the weekend as these
temps are not only well above normal, but more impactful after such
a mild summer so far. Into the extended, day 6/just into day 8,
models have gone back to a divergence in solutions as the GFS is
more progressive with the next upper trof moving a cold front
through with storms and cooler temps in the wake...while the 00Z
ECMWF is now cutting off the low over the NW, extending the ridges
hold over the region.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
ISSUED AT 1241 PM CDT THU AUG 21 2014

Scattered convection continues to track along a nearly stationary
frontal boundary draped across far northern Illinois/southern
Wisconsin early this afternoon. This activity will remain north of
the central Illinois terminals through this evening. Main aviation
question will be when/where additional nocturnal convection will
develop later tonight. Once again the NAM seems too aggressive in
driving precip southward into the area tonight, while the HRRR is
completely dry through 04z. Prefer a compromise solution as seen
on the latest Rapid Refresh model, which features a cluster of
showers/storms developing across eastern Iowa by around midnight,
then tracking E/SE across north-central Illinois overnight. Based
on this model, have introduced VCTS at the I-74 terminals between
07z and 09z. Further south, have gone completely dry at both KSPI
and KDEC through the night. Once any early morning convection
clears the area, dry weather is anticipated after 14z.

&&

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

$$

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






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