Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 020907

Area Forecast Discussion
407 AM CDT Tue Sep 2 2014

.SHORT TERM...(Today and tonight)

Surface cold front moving into central Illinois early this morning
with light shower activity along the front from around Peoria to
Pontiac. Heavy rainfall and thunderstorms affecting areas from
around I-72 southward with the activity gradually shifting into far
southern Illinois along a corridor of high precipitable water around
2 inches with a strong low level jet and convergence.  Radar
indicates  a swath of around 4-5 inches of rain has fallen this
evening from just south of Effingham to Robinson. Current radar
indicates scattered rainfall rates in excess of 1 inch per hour are
now confined to Jasper, Crawford, Richland, and Lawrence counties
and areas to the south and east...and trending southeastward. A
number of flash flood warnings as well as a flash flood watch and a
flood advisory continue in this area. This activity should continue
through around 7 a.m. with lingering showers and thunderstorms
continuing to subside through the afternoon as the system
responsible moves eastward.

Cool and dry conditions expected tonight as dry air and subsidence
moves over central Illinois in the post frontal environment.


.LONG TERM...(Wednesday through Monday)

The frontal boundary is expected to return north as a warm front in
Missouri and western IL during Wednesday. The 00Z model guidance has
trended a bit quicker with a short wave moving out of MO into IL Wed
afternoon and into IN Wed evening. Best chances of convection still
apears to be over sw IL into MO where better 850 mb low level jet
will be and more moisture transport. Confined pops to areas from
I-74 sw on Wed. Warmer and more humid air starting to return back to
central/se IL with highs in the mid to upper 80s and dewpoints
elevating into the upper 60s and lower 70s Wed afternoon and
highest in sw counties.

Have 20-30% chance of showers and thunderstorms over northern
counties by IL river valley Wed night mainly after midnight as the
instability axis, thermal ridge, and nose of the 850mb LLJ advance
toward northwest IL. Thu still appears to be the warmest day this
week with highs in the upper 80s and lower 90s and dewpoints in the
low to mid 70s with breezy sw winds and well entrenched in the warm
sector. Peak afternoon heat indices may reach into the upper 90s to
around 100F on Thu. Most areas should be dry Thu with just isolated
convection near the Wabash river Thu afternoon.

Low pressure deepening ne from the northern plains to north of the
Great Lakes will drag a cold front into the IL river valley early
Friday morning and into southern Illinois by Friday evening. Have
20-30% chance of showers and thunderstorms after midnight Thu night
over the IL river valley. Then a good chance of showers and
thunderstorms spreading se across central/se IL during the day
Friday and continue Friday night. Still a very warm and humid day
Friday with highs in the 80s and dewpoints in the upper 60s to mid
70s, with southeast IL near 90F southeast of I-70. Lingered chances
of showers and thunderstorms Saturday south of I-72, with
diminishing chances in southeast IL during Saturday afternoon as
frontal boundary pushes se into TN river valley.

A significant airmass change will follow that frontal passage, as a
1024 mb Canadian high pressure builds southeast into the western
Great Lakes. Less humid air along with cooler highs Sunday and
Monday in the 70s, with lows Saturday and Sunday night in the 50s.
This will be the coolest air since mid August to visit central IL,
the last time we had below normal temperatures.


.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)

A band of showers and thunderstorms will continue to brush past
KSPI, KDEC, and KCMI for the next several hours, but KPIA and KBMI
should be largely dry. Conditions will likely degrade to MVFR as the
rains continue and/or as fog develops in the case of KPIA/KBMI.
Quieter weather and VFR conditions will prevail for most of the
daytime hours Tuesday and into the evening as drier air filters
into the area behind a cold front.


FLASH FLOOD WATCH until 7 AM CDT this morning FOR ILZ056-057-



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