Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 280502

Area Forecast Discussion
National Weather Service Lincoln IL
1202 AM CDT SAT MAY 28 2016

Issued at 857 PM CDT Fri May 27 2016

Made minor adjustments to the forecast based on current convective
trends. The HRRR has a fairly decent handle on the departing
convection in eastern IL and the showers/isolated thunderstorms in
western/central IL. The water vapor satellite loop shows
additional weak shortwaves poised to move NNE toward the mid-MS
valley, which will provide some upper support.

The 00z ILX sounding indicated plenty of deep moisture with
precipitable water around 1.70 inches. Short range models
including the HRRR and RAP point to a continuation of low level
moisture transport overnight. All of this leads to periods of
showers through much of Saturday morning. Low instability levels
and the lack of a low level focusing mechanism should keep
thunderstorms very isolated. The latest forecast update reflects
this change.


.SHORT TERM...(Tonight)
ISSUED AT 256 PM CDT Fri May 27 2016

One weak short wave lifting NNE over northeast IL has scattered
showers and isolated thunderstorms north of CWA. The next short wave
upstream over southeast MO, northeast AR and southern tip of IL is
developing showers and scattered thunderstorms NNE into southern IL
from I-64 south at mid afternoon. 561 dm 500 mb low over far eastern
CO will track into northeast Nebraska by 12Z/7 am Saturday. The
short wave in southeast MO will lift NNE across central IL during
this evening and spread scattered showers and thunderstorms NNE
across the area this evening. Another short wave scheduled to arrive
over central/western IL by early Saturday morning and likely to
bring more showers and scattered thunderstorms. Widespread cloud
cover has limited instablity over central and southeast IL and 0-6
km bulk shear has been weakening during the day. So SPC only has
marginal risk of severe storms late this afternoon and evening over
parts of Knox, Stark and Schuyler counties, while slight risk
remains further west over central/eastern KS, central OK and
southeast Nebraska. Moist dewpoints in the mid to upper 60s over
central IL and around 70F in southeast IL to bring another mild
night with lows 65 to 70F. Breezy south winds 10-20 mph and gusts
20-30 mph to diminish to around 10 mph after sunset.

.LONG TERM...(Saturday through Friday)
ISSUED AT 256 PM CDT Fri May 27 2016

Unsettled weather remains the name of the game across central and
southeast Illinois over the next week. While it certainly will not
be raining all the time, picking periods with zero risk of
showers/storms is proving difficult. However, despite the
uncertainty with respect to precipitation, expect temperatures to
largely remain in the 80s for daily highs and in the 60s for
daily lows.

Initially our main focus remains on the upper-level low that is
currently centered over far eastern Colorado. Pieces of energy
streaming northeast to the east of this circulation will be the
primary driver of our PoPs into Sunday, along with diurnal effects.
The remnants of this upper low finally push north/east of the
forecast area by Sunday, potentially allowing for a mostly rain free
period from later Sunday into Monday.

Then, attention turns to some northern stream energy that will dive
into the plains around the middle of the week. The models are
handling this system quite differently, which makes forecasting the
associated rainfall threat difficult. The spread exists both inter
and intra model with considerable spread in the spaghetti plots. The
operational ECMWF and Canadian models are more progressive, keeping
the main rain threat Wednesday into Thursday. The operational GFS
develops a larger cut-off upper low, and is much slower moving the
system out of the area. This solution would keep a rain risk in
through the end of the forecast period, and may require a downward
adjustment to temperatures as well.


.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1159 PM CDT Fri May 27 2016

Scattered showers can be expected overnight into early Saturday
morning at central and eastern IL TAF sites. MVFR ceilings are
expected to accompany the showers, particularly at PIA and BMI
where lower clouds and rainfall have prevailed already this
evening. Could see a brief period of MVFR ceilings at CMI, but
will hold off for now as the best low level moisture flow will be
to the west.

Many of the short range models are showing a break in the rain
potential by mid-late Saturday morning. However, similar to today,
an increase in south-southwest winds are expected as the cloud
heights rise and mixing maximizes.

The latest NAM is pointing to the best instability, lift and
potential for scattered t-storms in NW and northern IL, so only
west with VCTS for PIA and kept the convection out of the rest of
central IL for now.


.ILX Watches/Warnings/Advisories...


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