Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 181740
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1240 PM CDT Mon Aug 18 2014

.UPDATE...
ISSUED AT 1005 AM CDT MON AUG 18 2014

Dense fog that formed overnight has largely lifted as of 10 am,
though stratus and some lower visibilities linger mainly across
the east central and southeast CWA. Had to make some adjustments
to the hourly temperatures for the next few hours due to the
lingering clouds, but have left the highs alone for now.

Have removed the small rain chances across the east and northwest
counties for this afternoon. Latest model guidance shows the
development to our northwest this afternoon will more likely drop
into our area during the evening. Across the eastern CWA, the
lingering frontal boundary was located in far southern Illinois,
with the focus for any development more likely in that area as a
shortwave pushes southeast out of Missouri.

&&

.SHORT TERM...(Today and tonight)
ISSUED AT 323 AM CDT MON AUG 18 2014

Low pressure area that produced the rain in southeastern IL
yesterday has moved little more east while a brief, weak area of
ridging slides across the region today. Though the low is southeast
of the area, it could still bring some pcpn to the east and
southeastern parts of the CWA tomorrow afternoon. At the same time,
a cold front will approach the area from the northwest and bring a
chance of showers and thunderstorms to areas northwest of the
Illinois river this afternoon and into this evening. As the front
moves southeast, the chances of pcpn will increase and spread
southeast tonight.

Temperatures will be moderated by the cloud cover over the area
today and through tonight.

&&

.LONG TERM...(Tuesday through Sunday)
ISSUED AT 323 AM CDT MON AUG 18 2014

Tuesday, the new wave dipping into the Great Lakes will spread
chances for rain and thunderstorms across Central Illinois for the
day on Tuesday, mostly diminishing west to east through the evening
until a developing baroclinic zone starts to build from NW to SE
along the southwestern portions of the state and into IA.  Same
boundary will have little reflection at the sfc with very weak flow
and an open pressure pattern, but thermal gradient is better
represented in the mid levels.  Boundary will provide a weak focus
for waves moving through the region as the boundary lifts to the NE
through the area for Wed/Wed night.  Though Wed is lacking signif
pop for now, the timing of the progression is better for early
evening and into the overnight on Wednesday night/shifting to the
northeast for Thurs. Position of the boundary or the remnants
thereof will be where the majority of the precip lands in this time
frame.  Ample sfc based instability in the form of hot and humid
conditions as the ridge over the southwest opens and spreads signif
heat into the Midwest.  850 mb temps in the 19-25C range from
Wednesday through Sunday will drive the temps into the upper 80s
then into the lower 90s with heat indices in the upper
90s/approaching 100.  A far more summer time pattern than much of
the season so far, and well above normal for this time of year...with
breaks from the heat provided by any thunderstorms that have the
chance to form.  Upper winds not really enough to cultivate too much
in the way of an extended severe weather threat at this point, but
that could change in the shorter range as the days wear on.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
ISSUED AT 1226 PM CDT MON AUG 18 2014

Lowest ceilings/visibilities have lifted from the earlier fog, but
rapid diurnal development resulting in MVFR ceilings at midday,
This will continue for a couple more hours before ceilings lift
above 3000 feet.

Main concern later in the period is with convective potential
overnight with a storm system moving through the upper Mississippi
Valley. Most of the 12Z models form a line of convection across
Iowa this evening as an upper wave drops southeast, but weaken the
line as it crosses the Mississippi River. Have included a PROB30
group at KPIA and KBMI to address potential MVFR visibilities with
the storms moving through northern Illinois, but currently feel
potential further south is still too uncertain to go more than the
existing VCTS.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...GEELHART
SHORT TERM...AUTEN
LONG TERM...HJS
AVIATION...GEELHART






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