Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 261155
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
655 AM CDT FRI AUG 26 2016

.SHORT TERM...(Today and tonight)
ISSUED AT 304 AM CDT Fri Aug 26 2016

A stationary frontal boundary appears oriented roughly along I-70
early this morning, with scattered showers and storms north of the
front between I-70 and Peoria. The storms are progressing into a
more stable airmass, per SPC mesoanalysis graphics, however shear
values of 35kts will be present ahead of the storms. We still expect
coverage and intensity of the storms to gradually diminish as we
head into the daylight hours. The better instability will continue
south of the stationary front, where little convection is occurring
at the moment. Patchy fog is expected around sunrise across the
area, with widespread dewpoint depressions 2F or less.

The front is projected to make a slow shift northward later today
and tonight, with more favorable instability and shear parameters
expanding as far north as I-74 by 00z/7pm. The high res models point
toward storms expanding in coverage from SW to NE this afternoon,
which seems reasonable based on the projected frontal progression.
The GFS/NAM/GEM/ECMWF all point toward an MCS impacting NW Illinois,
including our northwest counties later tonight as well, so ramped up
PoPs to likely after midnight NW of the IL river.

There should be enough of a break in the rain today that periods of
sun will push high temps into the upper 80s S of I-70, with around
80 toward Galesburg. Dewpoints are expected to climb into the upper
60s to low 70s by tonight, which will set the stage for muggy low
temps in the same range.

.LONG TERM...(Saturday through Thursday)
ISSUED AT 304 AM CDT Fri Aug 26 2016

Upper trough currently digging over Montana/Idaho to eject eastward
this weekend. Convective complex that is progged to form over Iowa
and northern Missouri this evening will push eastward overnight and
Saturday morning. High-resolution model guidance shows some breaks
in the rain during the afternoon, with another round of convection
forming over west central Illinois by late afternoon and lifting
northeast as the wave passes through.

The upper level pattern will undergo some transition this weekend,
as the persistent high over the southeast U.S. forms more of an east-
west axis which will push the main storm track closer to the
Canadian border early next week. The longer range models show some
amplification of the high east of the Rockies by Tuesday, edging
eastward as the week progresses. This will keep the trend of warm
and humid weather much of the upcoming week. The main question will
be how far south any shortwaves in the storm track can penetrate the
high. The ECMWF solution is generally on the drier side and trends
toward some diurnal, scattered activity, while the GFS remains quite
wet through the period. Leaned more toward the drier solution with
PoP`s generally around the 30-35% range early in the week, before
transitioning toward slight chances midweek with a surface high
trying to build southward into the Mississippi Valley.

&&

.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 655 AM CDT Fri Aug 26 2016

Fog formation around sunrise has been mainly in low lying areas,
and the terminal sites have remained VFR, most likely due to
plenty of mid and high clouds streaming across central Illinois.

A few lingering showers early this morning should remain confined
to the northwestern terminals near PIA and BMI. Additional chances
for showers and storms today look low, with an isolated shower or
storm possible. However, prevailing conditions should be dry with
VFR clouds through early evening.

High resolution models have widely varying solutions for tonight,
with some bringing storms into central IL from SW to NE as early
as 23z/6pm. Another keeps primarily dry conditions through the
night. The overall consensus shows an MCS developing in N Missouri
tonight and progressing into NW Illinois after midnight. Have
opted to introduce thunder after midnight at all terminals,
especially since we expect likely precip at least across the
northern terminals by Saturday morning.

Winds will continue to prevail less than 10kt thru this forecast
period. Wind directions should start out easterly, then become
southeast this evening.

&&

.ILX Watches/Warnings/Advisories...
NONE.
&&

$$

SHORT TERM...Shimon
LONG TERM...Geelhart
AVIATION...Shimon


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