Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 291949

Area Forecast Discussion
National Weather Service Lincoln IL
249 PM CDT MON AUG 29 2016

.SHORT TERM...(This evening through Tuesday)
ISSUED AT 248 PM CDT Mon Aug 29 2016

19z/2pm water vapor imagery shows upper high centered over southwest
Indiana...with fetch of deep moisture flowing around the high from
the Gulf of Mexico N/NW into Missouri/Iowa and western Illinois.
Scattered diurnal thunderstorms have developed within the moisture
plume, primarily along/west of the I-55 corridor.  As has been the
case over the past few days, steering currents aloft are quite weak
and the storms are very slow-moving.  As a result, heavy rainfall
and localized flash flooding will be possible across the western
half of the KILX CWA through the afternoon into the early evening.
Once the sun sets and instability wanes, the storms will gradually
dissipate by mid to late evening.  Have therefore included chance
PoPs everywhere along/west of I-55 this evening...dropping down to
just slight chance overnight.

Rain chances will become more focused during the day Tuesday as a
cold front currently over the Northern Plains approaches from the
west.  Have therefore increased PoPs to high chance across all but
the far E/SE CWA.  Given precipitable water values of 2 to 2.5, any
storms that develop will once again be capable of producing
torrential downpours and localized flash flooding.  High
temperatures will range from the lower 80s northwest of the
Illinois around 90 degrees south of I-70.


.LONG TERM...(Tuesday night through Monday)
ISSUED AT 248 PM CDT Mon Aug 29 2016

A weak slow moving upper level trough will be moving through the
Midwest Tuesday evening promoting scattered showers and
thunderstorms across especially northwestern portions of the central
and southeast IL forecast area through the night. With weak sfc-6km
shear values less than 20 kts and widespread cloud cover, severe
thunderstorm risk is minimal. Localized heavy rainfall will be a
risk as storm motion should remain very slow along with a slow moving
upper feature.

For Wednesday...Models have continued a trend of deepening a trough
farther westward into the Midwest and pushing a substantial cold
front southward through the region including central IL. Initially,
this will bring another focus for scattered thunderstorms. Although
timing differences continue, the consensus of 12Z models today bring
the associated rainfall to an end during the afternoon in the
northern parts of the forecast area north of I-74, while areas to
the south should see an end to precipitation by evening. Wednesday
south of I-70. A downtrend in temperature will begin Wednesday
starting with lows Wednesday morning upper 60s to around 70 in the
warm, humid, and cloudy air mass ahead of the front...followed by
highs ranging from around 80 along I-74 to as high as 85 south of
I-70. Lows Wednesday night should drop into the upper 50s to lower
60s as dewpoints drop into the 50s, down from the humid 70s prior to
the frontal passage.

Thursday through the weekend...dry conditions can be expected as the
cool and dry air mass slowly moderates through the period and high
pressure develops over the Great Lakes Region. Expect highs in the
upper 70s Thursday gradually rising to the mid 80s by Monday.
Dewpoints should be in the 50s to lower 60s through Saturday,
increasing to the 60s to around 70 by Monday.

As troughing slowly works its way eastward into the central U.S.
and a frontal zone develops in the Plains...chances for
precipitation look to start again northwest of the Illinois River on
Labor Day.


.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1253 PM CDT Mon Aug 29 2016

Robust Cu field with high MVFR/low VFR bases has developed
along/west of I-55 early this afternoon. Based on persistence
forecast from the past couple of days, will include a period of
MVFR ceilings at KBMI through 20z before ceilings rise to between
3500 and 4000ft. Elsewhere around central Illinois, will introduce
VFR ceilings and VCTS over the next couple of hours. HRRR seems to
have a good handle on the current situation, suggesting scattered
convection will mainly be confined to the western half of the CWA
this afternoon/early evening. Will hold off on any TEMPO thunder
groups until convective trends at specific terminals become better
defined. Once diurnal storms dissipate by 01/02z, mostly clear
conditions will be noted tonight, with patchy fog forming toward
dawn Tuesday. Have lowered visbys to between 4 and 5 miles after
09z accordingly.


.ILX Watches/Warnings/Advisories...


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