Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 011959

Area Forecast Discussion
259 PM CDT Wed Oct 1 2014

.SHORT TERM...(Tonight)

Scattered showers and thunderstorms in west central IL will become
more numerous overnight as several ingredients come together. At the
surface a warm front extended from NW Missouri into south central
Illinois. This boundary, along with a shortwave trough lifting to
the northeast and plenty of upper level divergence will keep the
showers and isolated thunderstorms going from west central into
central Illinois this evening. Relatively drier air in eastern IL
will initially keep the eastward extent of the precipitation limited
to west of I-55 much of this evening.

The warm front will slowly continue to lift to the northeast
tonight, remaining the focus for additional convection to develop.
An increasing low level jet intersecting the front and higher low
level moisture levels in much of the forecast area will result in
widespread showers and thunderstorms in central IL toward midnight,
and eastern IL toward daybreak. Rainfall totals around 0.50-1.00
inch are possible overnight, with the highest amounts anticipated
along and west of the IL river valley.


.LONG TERM...(Thursday through Wednesday)

Models are very consistent with the cold front refiring tomorrow
afternoon west of the area and then storms moving into the area late
tomorrow afternoon through tomorrow evening. Should be sufficient
moisture tomorrow ahead of the front to produce instabilities around
1500 J/kg. Models also forecasting strong low level winds and decent
wind shear. So storms are expected to become severe in the CWA,
mainly during evening hours. Agree with SPC with the slight risk
across the area tomorrow with the threat of large hail in the west
and damaging winds throughout the CWA after the storms become more
linear. In addition to the threat of severe weather, heavy rainfall
is also possible through tomorrow night west of I-55 where 1.75 to
over 2 inches is possible and just over 1.25 is possible in the
southeast parts of the CWA. Once the front moves through the area
cooler air will move into the area. However, the area will remain
controlled by an upper level trough. This will bring several chances
of scattered showers Friday and Friday night. The upper level trough
will remain over the area, but dry weather is expected for the first
part of the weekend.

The upper level trough will still be in control of some of the area
for the later part of the weekend and into the beginning of next
week. This will bring another shot of scattered showers to the area
for Sun through Mon night. However, the chances will be low enough
so that pops will just be slight chances; which means it will be in
the grids, but not in the worded forecast. A warm frontal system
will push into the area the beginning of next week, so will have
higher chances of pcpn for Mon night in the southeast only. As the
upper level flow becomes more zonal for middle of next week, dry
weather will return.

Temps will be warm one more day, tomorrow, and then cooler, below
normal temps are expected over the weekend and through most of next
week. By middle of the week, temps begin a slow trend of warming.


.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)

Increasing clouds and potential for showers and thunderstorms can
be expected in parts of central Illinois this afternoon, and
across all of central and eastern IL tonight.

Satellite and radar indicated that convection from NE Missouri and
SE Iowa continues to advance east-northeast, but weaken gradually.
Scattered showers can be expected along the IL river valley early
this afternoon, and toward the I-55 corridor just before dusk.
This activity will continue to weaken as it encounters dry air in
the mid-lower levels.

A slow moving warm front, which extended from western IA into
southeast MO around midday will slowly advance through central IL
tonight. The NAM, SREF, HRRR and RAP models are all in fairly good
agreement that an increasing southwesterly low level jet will
intersect this boundary and result in widespread showers and
elevated thunderstorms between 06-10z in west central IL, and
09-15z in eastern IL. This will result in MVFR visibility, but
have decided to hold off on MVFR ceilings for now until confidence
is greater in low level moisture fields.

Am expecting a break in the convection during much of the post
dawn hours in west central IL and by late morning in eastern IL as
the warm front continues to lift northeast and put the region in
the warm sector. Could see the beginnings of the next round of
scattered convection, ahead of a cold front, in western IL late
Thursday morning, but the best chances will be later Thursday




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