Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 251758

Area Forecast Discussion
National Weather Service Lincoln IL
1258 PM CDT SUN SEP 25 2016

Issued at 1040 AM CDT Sun Sep 25 2016

Updated the forecast about an hour ago to remove the patchy fog
wording this morning. Also updated to lower pops over western CWA
this morning as much of area still mostly sunny and dry at 1030
am. HRRR model appears to be too quick develop convection over
central and western CWA late this morning and slowed this down by
a few hours. Otherwise one more warm and rather humid summerlike
day expected over central and southeast IL, with highs mostly in
the 80s, ranging from lower 80s over far nw CWA by Galesburg, to
near 90F far southeast CWA by Lawrenceville. Late morning surface
map shows a cold front over central IA and western MO while a
prefrontal trof was pushing east near the MS river. Aloft an upper
level ridge was over the OH/TN river valleys. Patchy fog lifted
during mid morning leaving mostly sunny skies across CWA.
Temperatures warmed up into the upper 70s and lower 80s while
dewpoints ranged from 65-72F with southerly winds 5-15 mph.

Models continue to push cold front east into the IL river valley
late this afternoon, and through central and eastern IL during
this evening. Models agree with scattered convection developing
across much of CWA during the afternoon and continuing this
evening especially east of the IL river. SPC day1 outlook has a
marginal risk of severe storms for 5% risk of damaging wind gusts
this afternoon until sunset/7 pm along and east of a Peoria to
Springfield line and north of I-70. CAPES increase to 1-2k J/kg
east of the IL river during this afternoon into mid evening and
highest over southeast IL where some models have CAPES peaking a
bit above 2k J/kg. The 0-6km bulk shear is weak over central and
southeast IL today, less then 30 kts east of the IL river this
afternoon and only increase above 30 kts behind the front nw CWA
late this afternoon.


.SHORT TERM...(Today and tonight)
ISSUED AT 322 AM CDT Sun Sep 25 2016

CWA is now caught right in between the surface ridge to the east and
the cold front approaching from the west. Short-term model trend has
to slow the onset of precip into the CWA. Based on radar trends and
surface analysis, looks like precip will not arrive until this
morning; so, will have just slight chance of precip over the western
part of the CWA this morning and then increase pops to chance
northwest of the Illinois river before noon. Precip will spread east
through the CWA during the afternoon and into and then continuing
into the evening hours. Precip will gradually come to an end, from
west to east, behind the front after midnight. POPs will be in the
chance category ahead and behind the front, with likely along the
front as it moves east through the CWA. Precip type should be
showers and storms, mainly in the afternoon and evening, but
isolated thunderstorms will continue into the overnight hours

Temps will once again be very warm across parts of the CWA, mainly
looking at the mid to upper 80s east of the Illinois river and
toward the IN border. Overnight lows will be cooler than the last
several days, with mid to upper 50s common, except in the southeast
parts of the CWA where lower 60s is likely.

.LONG TERM...(Monday through Saturday)
ISSUED AT 322 AM CDT Sun Sep 25 2016

Main focus for the longer range period will be the evolution of the
current upper low spinning over North Dakota. Models remain in good
agreement in this evolving into a fairly strong upper low over Lake
Superior by midday Monday, with the low only slowly weakening with
time as it wobbles across much of the Midwest. The latter week still
shows some discrepancies with the track of this low. The ECMWF
drifts it back north from the Tennessee Valley and it still is
present over northern Ohio by late Sunday, while the GFS lifts it
into New England on Friday. The former scenario would suggest some
late week showers as the associated surface low drifts north out of
Kentucky, while the latter scenario pretty much keeps us high and
dry aside for a few potential lake-effect showers over the far
northeast CWA on Thursday. With the uncertainty and what likely
would be spotty coverage at best, will continue to keep the forecast
dry for the time being.

A gradual moderation of the air mass should result in temperatures
climbing a degree or two each day this week, but the overall dry
conditions should result in a nice diurnal swing each day. Lows in
the 40s are likely Monday and Tuesday nights, and perhaps
Wednesday night as well if the ECMWF pans out.

The deepening of the low will result in rather breezy conditions
Monday and Tuesday afternoons, with some wind gusts of 25-30 mph
across the northern CWA.


.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1258 PM CDT Sun Sep 25 2016

Isolated showers and thunderstorms developed in past hour east of
the IL river to along I-55 and nearing SPI and BMI. The hi-res
models continue to develop scattered convection this afternoon
across central IL and carried showers along with VCTS into mid
evening. A prefrontal trof was moving east into western IL while
cold front was pushing into eastern IA and central MO early this
afternoon. Models push the cold front east toward the IL river by
late afternoon and pass I-57 during mid evening. Still have
chances of showers with upper level trof behind the cold front
tonight and have showers ending at PIA by 07Z and at DEC and CMI
between 10-12Z. Cloud bases are mostly VFR but could get down to
MVFR with convection. Breezy SSW winds 10-15 kts and gusts 15-20
kts this afternoon to turn WNW behind cold front this evening and
gradually diminish to around 10 kts by overnight. Then winds gust
back to 15-20 kts by 15Z Monday with scattered cumulus clouds.


.ILX Watches/Warnings/Advisories...



LONG TERM...Geelhart
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