Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 260805
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
305 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 06Z TAFS through 06Z Friday night)
Issued at 1100 PM CDT Thu Aug 25 2016

Little overall change in thinking from previous discussion. The
main concern overnight will be with the threat for fog and MVFR/
local IFR vsbys and cigs. Satellite data continues to show quite
a bit of mid and high level clouds across the forecast area
which may tend to limit the fog coverage overnight. Another wave
of showers and storms was located north of STL and was tracking
northeast and may affect the SPI and DEC terminals during the
early morning hours. The low levels of the atmosphere are
saturated and despite a weak cool frontal passage across the TAF
sites this evening, little in the way of drying is expected.
This will bring parts of the area the threat for fog and lower
cigs into the mid morning hours before VFR conditions return for
the afternoon hours. Winds will continue to be a non-factor thru
this forecast period with a light northerly flow tonight of 5kts
or less, and a easterly flow at 5 to 10 kts on Friday.


&&

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

$$

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



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