Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 281739

Area Forecast Discussion
National Weather Service Lincoln IL
1239 PM CDT THU JUL 28 2016

Issued at 1050 AM CDT Thu Jul 28 2016

Forecast overall looks good today and will continue chances of
scattered showers and thunderstorms this afternoon across central
and southeast IL. Another warm and humid day in the mid 80s with
dewpoints in the lower 70s, giving peak heat index readings by mid
afternoon around 90F.

Isolated showers and thunderstorms are occurring east of the IL
river with a few new cells recently develpiing near east Peoria
and Petersburg. Had some isolated flooding near Farmer City around
7 am where up to 2.20 inches of rain fell in about a half hour
prior to 645 am. 12Z KILX UA sounding shows precipitable water
value near 1.70 inches and wind fields fairly weak, so this
supports pockets of heavy rains from slow moving isolated
thunderstorms. A weak cold front was just east of the IL river and
is forecast to track into eastern IL during this afternoon. Most
forecast models show isolated to scattered convection this
afternoon east of the IL river, with greater coverage from I-55
east as weak front moves into eastern IL and interacts very
unstable airmass. LAPS capes are currently 1200-2200 J/kg at 10 am
and are highest in western CWA. Models show CAPES may come up a
bit higher especially over eastern IL. SPC day1 outlook just has
general risk of thunderstorms today and tonight over IL with
Marginal risk central and southern CWA from Canton and Bloomington
south on Friday.


.SHORT TERM...(Today and tonight)
ISSUED AT 344 AM CDT Thu Jul 28 2016

Our forecast area remains between a couple of frontal boundaries. A
stationary front is lingering across southern IL, with a cold front
approaching from eastern Iowa and SW Wisconsin. The convective
initiation prior to the cold front arriving will be random and more
difficult to pin-point. Steering flow and the mid-levels is weak, so
storm motions have been slow and locally heavy rain has occurred
with any storms that have developed. High resolution models are
pointing toward an increase in storm coverage this afternoon mainly
tied to the arrival of the cold front from the northwest. Prior to
that, storms chances appear higher in our SE counties, due to
proximity to shortwaves moving along the stationary front across
southern IL. Active showers/storms near our western counties appear
poised to drift into our area early this morning. Therefore, have
trended an increase in PoPs today starting in the western and
southern portions of the CWA, then advanced the increasing PoPs east-
northeast this afternoon.

The timing of the cold frontal passage is difficult to discern in
the models, but based on surface wind projections, it looks to reach
I-55 by Noon, and push southeast of our counties by 6 pm. Will start
to decrease PoPs this evening from west to east, with only slight
chance PoPs in all counties after midnight.

Satellite images show we should see a period of sunshine this
morning before convection becomes more widespread and clouds thicken
and increase. We should see enough sun to support high temps
approaching the mid 80s in all areas. Lows tonight should remain on
the mild side, dropping close to minimum dewpoints in the mid to
upper 60s. Light fog will once again be expected late tonight.

.LONG TERM...(Friday through Wednesday)
ISSUED AT 344 AM CDT Thu Jul 28 2016

Weak open wave aloft will keep shower and thunderstorm threat in the
region through Friday/into early Saturday morning, providing some
minimal lift to an already unstable airmass. Once the system moves
to the east a bit, showers will become more widely spread, but
likely linger through Saturday. Less so on Sunday, and more confined
to the southern tier of Illinois. High pressure ridge builds into
the eastern half of the CONUS, although its influence looks somewhat
weak this far west of the ridge axis. Monday  maintaining some
consistency with small disturbance moving into the region with
another round of precip, particularly to the south. Though forecast
for Tuesday had a drying trend previously, still have to concede the
potential mesoscale influences over a warm and moist airmass will
keep the shower and thunderstorm threat in place over a large part
of the Midwest through the forecast period.

Temps trending slightly cooler through the first half of the weekend
with the more northwesterly flow and the precip influence.  850mb
temps not moderating quite as much, and holes/breaks in the cloud
cover for the next couple days could result in some isolated warmer
temps.  After the first half of the weekend, the building heat in the
western half of the CONUS begins to shift, putting another warming
trend in place for Central Illinois for next week.


.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1240 PM CDT Thu Jul 28 2016

Scattered thunderstorms have been quickly developing over central
IL at midday in warm and moist tropical airmass as temps have
risen into the low to mid 80s and dewpoints in the low to mid 70s.
CAPES at midday were 1600-2600 j/kg over central IL and highest
west of I-57. A frontal boundary just east of the IL river will
push southeast into eastern IL during the afternoon and continue
to develop scattered thunderstorms along and ahead of it. A
thunderstorms already affecting SPI while another TS was just
southeast of PIA and moving southeast. Thunderstorms will track to
near DEC in next hour and possibley to BMI and CMI in about an
hour or 2. Have VSTS at all TAF sites this afternoon with tempo
groups of MVFR conditions with thunderstorms this afternoon
especially southeast of IL river. Have added fog with MVFR vsbys
to TAF sites overnight until mid morning Friday with vsbys
possibly getting down to 1-2 miles from 09-13Z especially at CMI.
Winds to stay fairly light next 24 hours, trending nw direction
behind the front and staying less than 10 kts, and light winds


.ILX Watches/Warnings/Advisories...



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