Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 030424

Area Forecast Discussion
National Weather Service Lincoln IL
1124 PM CDT MON MAY 2 2016

Issued at 900 PM CDT Mon May 2 2016

The upper shortwave departing to the east along with the arrival
of dry air from near Lake Michigan has allowed clouds to clear out
in our northeast counties early this evening. Farther NW of
Peoria and Galesburg where diurnal cumulus were more prevalent,
clouds are also decreasing in coverage in general. HRRR output
remains very optimistic that clearing with push quickly east
across our forecast area by sunrise Tuesday. Have sped up the
clearing in the forecast for tonight. Will monitor trends closely,
as night-time clearing can be more troublesome than daytime
clearing trends, due to subsidence inversions and decoupling of
low level winds.

Spotty showers or sprinkles will still be possible in any cloud
cover as the surface trough slowly drifts south toward southern
IL. Will keep isolated rain chances going in the south, with
diminishing coverage from NW to SE the rest of the night.

Have trimmed a degree or two from the overnight lows to account
for possible earlier clearing. Lower 40s appear likely in
locations north of I-72, especially in a areas where clearing has
already developed this evening. Lows should bottom out in the
upper 40s southeast of I-70 where clouds linger the longest.

Updated forecast info is already available.


.SHORT TERM...(Tonight)
ISSUED AT 313 PM CDT Mon May 2 2016

Main short-term forecast concern will be timing of potential
clearing tonight.  While the main surface boundary has dropped south
of the Ohio River, a trailing upper trough extending from Wisconsin
southwestward to Kansas has provided enough synoptic lift to produce
widespread overcast conditions today.  Visible satellite loops show
the low cloud cover pivoting southward on the back side of a subtle
upper wave currently over central Illinois.  As this feature tracks
further eastward, think clouds will gradually dissipate/clear the
Illinois River Valley this evening.  Due to trajectory of cloud
cover and relatively light flow, clouds will likely hold throughout
the entire night along/east of the I-57 corridor.  May see a few
isolated light showers this evening: however, most locations will
remain dry.  Overnight low temperatures will range from the lower
40s northwest of the Illinois River where clearing will occur around 50 degrees far southeast around Robinson and

.LONG TERM...(Tuesday through Monday)
ISSUED AT 313 PM CDT Mon May 2 2016

Cyclonic flow will continue over the area through Wed. A lull in the
pcpn chances will be seen Tuesday as CWA will be in between troughs
rotating through the area. However, will still keep a slight chance
of showers in the east and southeast Tuesday due to a 500mb trough
moving south through the area...just without any surface reflection.
A bigger and more dominate trough will drop into the area Tue night
through Wed. Pcpn will start in the north Tue evening and then move
south through the area the remainder of the night and then in the
east on Wed. Isolated thunder will also be possible given greater
lapse rates due to cold 500mb temps moving over the area in
association with the upper level low. The pcpn will move off to the
east Wed night, which will allow high pressure to build into the
region with dry weather and slowly warming temps for Thur through
Fri. This surface high pressure ridge will get flattened by the end
of the week as another frontal system drops into the area for the
weekend. With warm and moist air being advected into the area Friday
and Saturday, will be plenty of instability for thunderstorms along
and ahead of the front Sat night through Monday. The front does seem
to hang around the area through the weekend since there will be an
upper level low just east of the US and another one over the
southwest US.

Temps will remain below normal most of the week, but begin to warm
back up as the high pressure that builds in Thursday moves off to
the east, bringing back southerly winds. The warmer temps will
continue through the weekend and into the beginning of next week.


.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1124 PM CDT Mon May 2 2016

The clearing line has advanced south late this evening, with no
ceiling anymore at PIA, BMI and CMI. VFR ceilings remain at SPI
and DEC at 7-8K FT, but even those ceilings should erode shortly
after 06z as the upper shortwave shifts east of the region and
drier air continues to work in from the north. Scattered cumulus
will develop by mid morning and may periodically go broken with
bases remaining above MVFR levels through afternoon. A sprinkle or
two can not be ruled out during the flare-up of cumulus during the
day, but most areas will remain dry.

Winds will become light and variable tonight as a weak high
pressure ridge shifts into Illinois overnight. Winds tomorrow will
veer to the WNW and climb to 10-13 kts by mid-afternoon on Tuesday,
ahead of a cold front approaching from the north. Winds will
weaken below 10kt Tue eve as they back to the west-southwest.

Rain showers could develop near the northern terminals of PIA,
BMI, and CMI late in this TAF period, but the better chances will
hold off until after 06z Tuesday night.


.ILX Watches/Warnings/Advisories...


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