Area Forecast Discussion
Issued by NWS Central Illinois

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519
FXUS63 KILX 231756
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1256 PM CDT SAT JUL 23 2016

.UPDATE...
Issued at 1045 AM CDT Sat Jul 23 2016

Forecast looks on track today and main update was to remove the
morning fog wording in southeast IL. A hot and humid day unfolding
with highs 90-95F with partly sunny skies. Dewpoints in the mid
to upper 70s to give peak afternoon heat index readings of
100-110F this afternoon until 7 pm this evening. Updated the NPW
product to keep the excessive heat warning going through 7 pm
across CWA, and across central and southeast CWA through 7 pm
Sunday. May need to extend the heat warning for northern CWA into
Sunday afternoon as well, and that will be addressed with the
afternoon forecast package. MCS over northern IA, southeast MN and
sw WI is tracking east and will mostly stay north of central IL
today. Have isolated showers and thunderstorms this afternoon
especially north of I-74. SPC has marginal risk of severe storms
north of Peoria late this afternoon and into tonight for
convection developing on southern outflow boundary of MCS moving
toward the IL river valley after 00Z/7 pm this evening.

&&

.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 18Z TAFS through 18Z Sunday afternoon)
Issued at 1255 PM CDT Sat Jul 23 2016

Latest forecast models show more low level moisture and cumulus
clouds over eastern IL this afternoon, which support the broken
ceilings of 2.5-4k ft from CMI eastward. Some broken cirrus
clouds as well especially from I-74 north from MCS over northern
IA, sw WI and se MN that is tracking east. A band of convection
over western IA from I-35 west is projected to track east into the
IL river valley after 00Z, reaching PIA by sunset and BMI by 03Z
as it weakens later this evening. Added VCSH for this convection
and may need to add TS this afternoon especially at PIA. Models
keep more widespread convection north of central IL especially
over WI through Sunday morning. Have light fog/haze from 09-14Z
with vsbys 3-6 miles as more widespread fog with vsbys under 2
miles stays over southeast IL again. SSW winds of 4-8 kts this
afternoon become light SSE after sunset, and SSW 7-11 kts after
14Z Sunday.

&&

.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.

&&

$$

UPDATE...07
SHORT TERM...Shimon
LONG TERM...HJS
AVIATION...07



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