Area Forecast Discussion
Issued by NWS Central Illinois

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS63 KILX 221752
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1252 PM CDT Fri Aug 22 2014

.UPDATE...
ISSUED AT 1038 AM CDT FRI AUG 22 2014

Large cluster of thunderstorms that developed along an outflow
boundary late last night continues to diminish as it pushes
eastward across central Illinois this morning. 1530z radar imagery
shows showers with a few embedded thunderstorms along/north of a
Beardstown...to Decatur...to Paris line. High-res models suggest a
continued weakening trend, with little or no precip remaining by
mid-afternoon. Have adjusted PoPs to go categorical along/north of
I-72 for the next couple of hours, followed by a decrease to just
slight chance this afternoon. Have also lowered high temperatures
by a few degrees across the central and northern zones where
widespread clouds/rain have kept readings cooler than previously
expected. Visible satellite imagery shows plenty of breaks
developing upstream across Iowa, so have only dropped highs into
the upper 80s. Further south where the rain has not occurred this
morning, have maintained highs in the lower 90s.

&&

.SHORT TERM...(Today and tonight)
ISSUED AT 325 AM CDT FRI AUG 22 2014

07z/2am surface analysis shows a stationary front extending from
west to east across northern Illinois. A 35kt LLJ has helped trigger
a line of convection just south of that front. Those storms will
affect our northern counties early this morning, with locally heavy
rainfall rates possible. Areas near Midway airport last night picked
up 3" in 30 minutes. There most likely will be a break in the
rainfall for at least a few hours later this morning and early this
afternoon, before the next shortwave over Iowa works its way into
IL. Precipitable water values up near 2" will continue through the
day, so any convection that redevelops this afternoon into evening
will have the potential to produce very heavy rainfall. Coverage may
not be too extensive during the day, so slight chance and low chance
PoPs were used for areas north of I-72 after 7 am.

The HRRR/NAM/GFS/ECMWF all show an enhanced opportunity for storms
either later this afternoon or this evening as an MCS develops to
our west and rolls across N IL. With timing still in question, we
did not ramp up to likely PoPs in any one area even this evening and
overnight. The main theme does seem to be that the northern half of
the KILX CWA will be the main target area for storms over the next
24-36 hours.

High temps today will once again climb into the upper 80s to low
90s, with dewpoints already in the mid 70s and likely to climb into
the upper 70s in some areas. Heat index readings will likely climb
to around 105 in southern areas. We can not rule out the possible
need to expand the heat advisory northward. Precip and cloud cover
across the north should keep their heat index readings below
advisory levels in general.

&&

.LONG TERM...(Saturday through Thursday)
ISSUED AT 325 AM CDT FRI AUG 22 2014

Main issue through the extended remains the extreme heat for this
time of year through the weekend and into the first portion of next
week.  Models still having issues with the ultimate breaking down of
the ridge, resulting in a potential extension to the heat wave
should the trend continue. Hot daytime highs into the 90s and
dewpoints into the mid 70s resulting in heat indices over 100F for
several days on end.  Scattered chances exist as long as the
boundary remains close to the FA...and will be the only chance for
brief cool downs.  But as the high builds into the region, the
general subsidence will be hard to overcome, so the forecast for
Saturday night through Sunday night is dry for now...with some
slight chances coming back for Monday...but the models struggling
with the solutions in the mid range with the timing of a vigorous
wave to erode the ridge. GFS still far more aggressive, amplified,
and fast with the passage of the upper trof/sfc front Tues night
into Wednesday.  ECMWF starting to close the gap and has abandoned
the closed low of 24 hrs ago... but is still signif weaker,
resulting in a developing baroclinic zone at the sfc as the wave
fizzles in parallel flow and provides a focus for a longer duration
potential for precip. Model blends now through the mid/end of next
week results in more widespread chances.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
ISSUED AT 1252 PM CDT FRI AUG 22 2014

Remnant of morning convective complex persists across north-central
Illinois early this afternoon, with light rain currently being
reported at KPIA, KBMI, and KCMI. Based on radar trends, think the
rain will diminish and come to an end over the next couple of
hours, followed by generally dry weather this afternoon/evening.
Will have to watch for isolated shower/storm development across
northern Missouri that could spread eastward this afternoon, but
think areal coverage will remain low enough to leave out of TAFs.
Main aviation concern will once again be nocturnal convection
firing along the northern periphery of upper ridge centered over
the southern CONUS. Models have varying solutions as to the exact
placement and track of the storm complex, but general consensus
develops it over northern Missouri/southern Iowa this evening,
then pushes it E/SE across central Illinois late tonight into
Saturday morning. Will include -RA and VCTS at all terminals
between 07z and 14z accordingly.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
HEAT ADVISORY until 7 PM CDT Monday FOR ILZ042-047>054-056-
061>063-066>068-071>073.

&&

$$

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






USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.