Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 251955

Area Forecast Discussion
National Weather Service Lincoln IL
255 PM CDT WED MAY 25 2016

.SHORT TERM...(Tonight)
ISSUED AT 253 PM CDT Wed May 25 2016

A weak shortwave lifting northeast across central IL this
afternoon and exiting IL by sunset, will be accompanied by a band
of showers and thunderstorms. So far this afternoon most of the
convection has been north of I-80 and west of I-39 and another
narrow band southeast of Springfield to Evansville. More
widespread convection was over western KY/TN. Forecast models
continue to develop scattered showers/thunderstorms over central
and eastern IL through early evening with widespread coverage over
northern and southern IL. More convection possible by late
tonight/early Thu morning with next weak disturbance moving into
IL. CAPES are 1-2K J/kg late this afternoon/early evening and
highest in nw CWA. 0-6km Bulk Shear is 20-30 kts and highest in
western CWA, so fairly weak organization of thunderstorms expected
rest of today. The surface dewpoints fairly moist in low to mid
60s over central/southeast IL though moisture is fairly shallow
over CWA with 850 mb dewpoints of 6-8C with deeper moisture in AR
and sw MO. SPC has marginal risk of severe storms late
afternoon/early evening over IL, with best risk west of IL where
slight risk in eastern KS. SSW breezes 10-20 mph and gusts 20-30
mph this afternoon to diminish to 5-10 mph after sunset. Mild lows
overnight in the mid to upper 60s.


.LONG TERM...(Thursday through Wednesday)
ISSUED AT 253 PM CDT Wed May 25 2016

A persistent summer-like pattern will continue throughout the
extended forecast. The main movement in the upper level pressure
pattern will be the progression of the 300 mb low from southern
Arizona Thursday morning to central Nebraska by Friday evening, and
eventually becoming an open wave over Iowa on Saturday reaching
Wisconsin on Sunday. The Bermuda High off the East Coast will hold
firm across the southeast states during that time, limiting the
eastward progression of the western US trough. At the surface, all
frontal boundaries will remain in the northern and central Plains.
Therefore, triggers for afternoon and evening convection will be
more difficult to pinpoint. The one period that appears to have more
agreement in widespread coverage of showers/storms looks to be
late Thursday night but especially Friday as a weak surface wave
progresses up through eastern Iowa and far western Illinois.
Instability parameters look marginal for severe storms, with deep
layer shear at 25 kts and MUCAPES of 1500 to 2500 J/kg. If we get
a break in the clouds for increased insolation, we could see more
of the area utilize the higher MUCAPE values.

For now, have concentrated the only likely PoPs of the extended
forecast in Knox county Thursday night and all but the far
eastern counties on Friday.

Beyond that, we went with lower trends in storm chances for the last
half of the holiday weekend, with just slight chance PoPs for a
majority of our forecast area Sunday night, Memorial Day, and Monday
night. That is in response to upper level ridging and a weak
surface high that passes over Illinois per the ECMWF and GFS.
There will be spotty showers/storms that bubble up in the summer-
time airmass during the afternoon/eve, but coverage and intensity
appear very limited at this point. Better chances start again
Tuesday through Wednesday as the next upper level wave makes its
way toward Illinois from the SW states.

The warmest day of the next week looks to be Thursday, with highs in
the mid to upper 80s. Friday and Saturday may only reach the low 80s
due to increased precip and cloud cover. Highs will creep toward the
mid 80s on Sunday and Memorial Day due to a bit more sunshine.
Dewpoints will remain the mid to upper 60s through Sunday, making
for uncomfortable conditions for at least the first 2/3rds of the
holiday weekend. Dewpoints dip to the lower 60s for Memorial Day
through Wednesday, which still can feel muggy with highs in the
low 80s.


.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1258 PM CDT Wed May 25 2016

A weak short wave from eastern IA into sw IL early this afternoon
will northeast across central IL during this afternoon, reaching
the IL/IN border by 00Z/7 pm. A band of showers and a few
thunderstorms has recently developed along this feature ne of St
Louis and will continue to develop as it lifts ne toward SPI
around 19-1930Z, PIA and DEC by 20Z and BMI and CMI 21-2130Z.
Have included VCTS from mid afternoon into early evening for this
feature and may need tempo groups if activity gets more
widespread. Models showing more convection moving in from the WSW
by 12Z/Thu and diminishing by midday Thu. Have reintroduced VCTS
starting between 11-13Z Thu. Southerly winds prevailing over IL
next 24 hours with 1006 mb low pressure over ne SD and 1025 mb
high pressure off the southeast Atlantic coast. Breezy south winds
this afternoon of 10-15 kts and gusts to around 20 kts, then
diminish to 5-9 kts after sunset. South winds to pick back up a
bit during Thu morning to 8-14 kts.


.ILX Watches/Warnings/Advisories...


LONG TERM...Shimon
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