Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 280302
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
902 PM CST Sun Nov 27 2016

.UPDATE...
Issued at 902 PM CST Sun Nov 27 2016

Initial wave of rain has progressed eastward slightly ahead of
model projections, and there appears to be a back edge of the rain
approaching from across Missouri ahead of previous forecasts as
well. The faster pace may be partly due to the intense low and mid
level winds out of the southwest that have developed this
evening. Winds 1-2K ft above the ground are up to 40-50kts based
on VWP plots from the ILX radar. Surface winds have sustained up
around 20 mph with gusts over 30 mph at times. HRRR and RAP
updates are showing the faster progression of the first wave of
rain, so we have followed suit in the PoP and weather grids for
the next 12-18 hours.

Thunder has not materialized in Illinois, nor Missouri for that
matter, so we removed any mention of storms from the rest of the
night.

Low temps will be help warmer due to blanket of clouds, periodic
rains, and strong ground level winds. Forecast lows are not much
below current air temps, so expect relatively steady temps
overnight.

Updated forecast info is already available.

&&

.SHORT TERM...(This evening through Monday)
ISSUED AT 230 PM CST Sun Nov 27 2016

Early afternoon surface map shows surface low organizing across
northwest Kansas, as the upper low takes shape over eastern parts of
Montana and Wyoming. The earlier stratus continues to lift
northeastward and the southern half of the forecast area is mainly
seeing mid and high level clouds at this point. A few showers have
grazed the western CWA as of late, but the more organized
precipitation is steadily advancing across southern Iowa and
northern Missouri and should reach the middle Illinois River Valley
by late afternoon.

Morning model suite continues to indicate a rapid intensification of
the surface low as it lifts into eastern South Dakota this evening,
before it begins to occlude later Monday over eastern North Dakota.
Showers will continue to steadily advance across the forecast area
this evening and have gone with categorical PoP`s at most locations
tonight. Have added some isolated thunder mention as well. The
initial dry slot behind this band of showers will spread across the
western CWA late tonight, and rain chances will be somewhat minimal
for a time over a large area west of I-55 early Monday. The higher
PoP`s for the afternoon still look good though, as a wave ejects
northeast out of the Desert Southwest and sends another surge of
moisture northward ahead of the cold front. Precipitable water
values approach 1.1-1.2 inches south of I-70, which will help with
some healthy rain totals near an inch during the daytime.

The mild temperatures -- lows in the lower 40s and highs in the
lower 50s -- will be offset by wind gusts of 30-35 mph at times over
central Illinois overnight and Monday.

.LONG TERM...(Monday night through Sunday)
ISSUED AT 230 PM CST Sun Nov 27 2016

The main cold front associated with the weather system moving
through the area, will quickly move through the remainder of the CWA
Monday evening. As it does, most areas will see an end to the precip
by midnight, with just a chance of precip in the eastern parts of
the CWA. Dry weather is then expected behind this front. However,
central IL will remain in a cyclonic flow pattern through most of
the week, with the associated surface low slowly moving east
northeast across the Great Lakes region. The models do develop a
secondary surface low that moves across northern IL; but, since
there will also be another weather system in the southern Miss
valley at the same time, moisture will be limited for the northern
system in our area. So, for Tue night, when this moves through, dry
weather is still expected over most of the CWA, with a slight chance
of precip in southeast IL from the southern system. The upper level
low will finally move into eastern Canada toward the end of the
week, bringing a change in the pattern for the weekend. The
resulting pattern seems to be one with a split flow as an upper
level low sets up in the southwest US and a northwest flow pattern
sets up over the norther US and Great Lakes region. This should keep
things somewhat quite over the area, but the ECMWF brings a weather
system across Illinois for Sunday. Since this is the first run with
that and the GFS is dry, pops for Sunday will only be slight chance
for now.

Colder air will lag behind the weather system Mon night so high
temps Tuesday will still be above normal, reaching the 55 to 60
degree range. Given the pattern, the colder air does not really make
into the CWA until Wed night. So, Wed highs will be slightly above
normal for end of November. Normal to slightly below normal temps
can then be expected Thur through next weekend.

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 603 PM CST Sun Nov 27 2016

Rain has already reached SPI and PIA and will overspread the
remainder of the TAF sites by 03z. VFR clouds ahead of the rain
will drop to MVFR a couple of hours after rain onset. Periods of
light to moderate rain are expected this evening. Radar images
upstream indicate we will see breaks in the rain after the first
2-3 hours of steady rain at the onset. A warm front will lift
northeast through Illinois later this evening, prompting a
lowering of ceilings to IFR and possible MVFR fog development at
all terminals tomorrow morning. Cloud heights and visibility in
fog are projected to drop even further tomorrow afternoon, with
1-2SM BR and OVC004 become widespread.

South winds will increase this evening and remain strong the
remainder of this TAF period, in response to a tightening pressure
gradient and LLJ winds mixing to the surface. We are expecting
sustained winds of 18-20kt with gusts over 30kt at times.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

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



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