Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 140311
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
911 PM CST Wed Dec 13 2017

.UPDATE...
Issued at 910 PM CST Wed Dec 13 2017

The 995mb surface low will continue to weaken and pull away to the
east of Illinois the rest of the night. The low has reached NW
Ohio as of 9 pm. However, trailing energy behind the low is
combining with low level moisture to produce scattered flurries
this evening. Strong winds from this afternoon and early evening
will continue to diminish as pressure rises weaken and the
pressure gradient becomes less compact. Therefore, the Wind
Advisory was allowed to expire at 9 pm. Some clearing in the
clouds could develop after midnight, and satellite loops show
holes in the cloud shield developing in northern Illinois already.

Low temps will occur at sunrise, once winds weaken and the cold
air plummets into the area. Most areas should see the low to mid
20s.

The updates this evening were to add flurries and adjust cloud
cover to expected trends. The remainder of the forecast looked on
track.

&&

.SHORT TERM...(This evening through Thursday)
ISSUED AT 308 PM CST Wed Dec 13 2017

A 992 mb low is centered near Milwaukee this afternoon and a cold
front trailing from the low southwestward through roughly the I-55
corridor, pushing southeastward. Brisk winds were gusting up to 40
mph well ahead of the front, with a short lull in winds until behind
the cold front where gusts to around 45 mph are prevalent, with the
winds shifted to WNW. Expecting the strongest winds to push east to
the IN border by around sunset, then winds will begin to taper off a
few hours after sunset across central IL as the parent low moves
rapidly east and the strongest winds aloft and surface pressure
gradients shift east. A wind advisory remains in effect until 9 p.m.
for most of central Illinois except for Richland, Lawrence, and
Crawford Counties. Light showers can also be expected along the
front this afternoon, with little or no measurable precipitation.
Overnight, winds will gradually decrease as a high pressure ridge
approaches from the west. Winds will end up light WNW only around 5
mph during the day Thursday as a result of the ridge. Expect lows
tonight back down to the low to mid 20s as cold post-frontal air
moves back in from the northwest, with highs Thursday only in the
low to mid 30s.

.LONG TERM...(Thursday night through Wednesday)
ISSUED AT 308 PM CST Wed Dec 13 2017

The next weather system will arrive early Friday morning as a
shortwave trough arrives from the northwest. Models produce only
scattered and very light precipitation with this feature, however it
will likely be able to produce some flurries north of I-70. After
this, the pattern begins to shift as the large-scale eastern
trough/western ridge move east with ridging and southerly flow
developing into the central U.S. bringing warmer temperatures
reaching the 40s in central IL through early next week. A
disturbance embedded in the southwesterly flow aloft will provide a
chance of rain Sunday, potentially beginning as light snow early
Sunday morning. After that, models disagree on timing and track of
precipitation, however general trends in the pattern suggest
precipitation gravitating toward the southeast U.S. early next week
as the west coast ridge and eastern trough re-establish.

&&

.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 600 PM CST Wed Dec 13 2017

A deep surface low just east of Chicago will continue to pull away
to the east this evening. An expansive area of MVFR clouds are
expected to rotate through central Illinois behind the low. HRRR
is optimistically showing ceilings improving to VFR toward 06z,
but confidence on that is low. HRRR is also showing clearing in N
Illinois expanding toward our I-74 TAF sites after midnight. PIREPs
are showing the cloud thickness to be about 2,000 feet, which is
thick enough to reduce the chances of the cloud layer thinning out
overnight. Have kept MVFR conditions through 06z, but may need to
extend later.

Strong W-NW winds will continue this evening. Mixing heights will
lower after 03z, which will help gusts diminish by midnight. By
sunrise, the pressure gradient and height rises will weaken enough
for sustained winds below 10kt.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Wind Advisory until 9 PM CST this evening for ILZ027>031-036>038-
040>057-061>063-066-067-071.

&&

$$

UPDATE...Shimon
SHORT TERM...37
LONG TERM...37
AVIATION...Shimon



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