Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 261749
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1249 PM CDT FRI AUG 26 2016

.UPDATE...
Issued at 1022 AM CDT Fri Aug 26 2016

15z/10am surface analysis shows stationary frontal boundary
extending from southern Indiana W/SW into the Ozarks. A couple
clusters of showers and thunderstorms are currently ongoing well
north of the boundary...one between Peoria and Bloomington and
another near Quincy. These storms are tracking E/NE and will
mainly impact locations along/north of a Jacksonville to
Bloomington line over the next few hours. Additional showers are
developing upstream across central/southwest Missouri, and am
expecting those to arrive by mid to late afternoon. Based on radar
trends and 12z NAM/HRRR forecast, have gone with scattered showers
and thunderstorms along/north of a Jacksonville to Bloomington
line...with only isolated storms further east and south. Have
updated sky cover as well to go with more sunshine along/east of
I-57 through at least early afternoon. High temperatures will
range from the upper 70s to around 80 degrees across the Illinois
River Valley where clouds and showers will be most prevalent...to
around 90 degrees south of I-70 where sunshine will persist the
longest.

&&

.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 18Z TAFS through 18Z Saturday afternoon)
Issued at 1249 PM CDT Fri Aug 26 2016

Widespread mid-level cloud cover will continue to blanket the area
through the afternoon. Latest satellite/radar trends suggest most
of the convection will develop closer to the stationary frontal
boundary across southeast Illinois...with only isolated showers
further north at the central Illinois terminals. Will only carry
VCSH accordingly.

Main aviation question will be timing/extent of convection later
tonight into Saturday morning, as front begins to return
northward. Model solutions vary, with the Rapid Refresh showing
widespread showers/thunder developing along/west of I-55 as early
as this evening, while the NAM/GFS tend to keep the majority of
the precip further west across Iowa/Missouri until after midnight.
Based on current radar trends, have sided with the NAM/GFS
consensus here. As a result, have introduced predominant rain
showers with VCTS at KPIA by 07z...then further east to KCMI by
09z. At this time, will maintain low VFR ceilings during the
precip, but have reduced visbys down to around 4 miles.

&&

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

$$

UPDATE...Barnes
SHORT TERM...Shimon
LONG TERM...Geelhart
AVIATION...Barnes


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