Area Forecast Discussion
Issued by NWS Central Illinois

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152
FXUS63 KILX 231147
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
647 AM CDT SAT JUL 23 2016

.SHORT TERM...(Today and tonight)
ISSUED AT 327 AM CDT Sat Jul 23 2016

Light winds, clear skies, and a muggy boundary layer will
lead to fog in various locations early this morning. Locally dense
fog has already developed along the Wabash River in our southeast
counties, with lighter fog now also developing west of the Illinois
river near Galesburg. HRRR is pointing toward additional dense fog
west of Peoria as well. For now, will continue to handle the smaller
areas of dense fog with a Special Weather Statement instead of Dense
Fog Advisory, and evaluate trends in the next hour or two.

As for convective potential today, the main surface front is
expected to remain stalled out north of our counties, from northern
Lower Michigan across the northern Plains. The 850mb low level jet
will remain focus west of IL in the Nebraska, Dakotas, Minnesota
area through tonight, then rotate to the northeast toward Wisconsin
and Michigan on Sunday. A weak shortwave in the 500mb flow is
triggering some storms in SW Iowa early this morning, and those
storms are expected to progress east into northern IL. The NSSL-WRF
is indicating the southwestern flank of that convection will
eventually affect our northern counties later this afternoon and
evening. ARW-east and NMM-east both show storms developing this
afternoon east of I-57 as well. Will keep slight chance PoPs in
north and east, with a narrow area of chance PoPs north of Peoria
late this afternoon and evening where more consensus for storms is
confined at this point.

We should see more sunshine today that yesterday, with mainly cirrus
in our southern counties this morning and increasing ACCAS in our
northern counties this afternoon. Prolonged sunshine should help our
area see high temps reach 91 to 94 today. Plenty of surface moisture
will be available to push dewpoints into the mid to upper 70s, which
will support heat indices of 105-110F this afternoon. No changes
will be done to the heat headlines with this forecast update.

Better potential for storms tonight looks to come after midnight
north of I-74, as a nocturnal MCS affects northern IL, closer to the
focus of the 850mb LLJ. We increased PoPs after midnight to low
chance across the north, with a narrow area of slight chances
bordering that to the south. Another muggy night is in store, as
lows remain in the mid 70s and dewpoints stay in low 70s. Patchy fog
will be possible after midnight Saturday night, especially in low
lying areas and river valleys.

.LONG TERM...(Sunday through Friday)
ISSUED AT 327 AM CDT Sat Jul 23 2016

Upper level ridge weakening as a wave moves across southern
Canada...eventually into the Great Lakes, dragging a cold front with
the surface system later Sun night/into Monday morning.  Overall,
the forecast remains dominated with low pops in a summertime
pattern.

Hot and muggy continuing into Sunday as the frontal passage is
delayed again in the 00z run of the models. Showers and thunderstorm
chances increasing for Sunday night and may have to increase the
pops if the trend continues. Precip settling southward by Monday
afternoon as the front loses momentum.  But a cooler airmass moving
into the region will drop temps at least through Thursday back into
more seasonable 80s.  However, beyond midweek, the western thermal
ridge continues to grow, eventually amplifying flow enough to bring
back the more northwesterly flow aloft.  Under this regime, the
series of short waves over the ridge returns, bringing precip back
to dominate the end of the week.

&&

.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 647 AM CDT Sat Jul 23 2016

Patchy MVFR fog across central IL has only affected the CMI
terminal so far this morning. Trends show that the other sites may
remain VFR as mixing develops, so have only included fog in CMI
for a couple hours. The remainder of this TAF period should be VFR
at all TAF sites, with thunderstorm chances generally remaining
north of our forecast area. PIA will be closest to the complex of
storms that will progress across eastern Iowa and into northern
IL. Depending on how far south the flanking line becomes active,
PIA and BMI may see a nearby storm early this afternoon. Have
included a VCTS only in PIA and BMI, but the short range high
resolution models are mainly showing storms remaining north of the
terminal sites.

Clouds will be minimal over the next 24 hours, depending on the
coverage of storms to our north. Winds will remain southerly at
less than 10kt throughout this TAF period, under a weak pressure
gradient.

&&

.ILX Watches/Warnings/Advisories...
Excessive Heat Warning until 7 PM CDT Sunday for ILZ040>057-
061>063-066>068-071>073.

Excessive Heat Warning until 7 PM CDT this evening for
ILZ027>031-036>038.

&&

$$

SHORT TERM...Shimon
LONG TERM...HJS
AVIATION...Shimon



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