Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 212124
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
324 PM CST Sun Jan 21 2018

.SHORT TERM...(This evening through Monday)
ISSUED AT 250 PM CST Sun Jan 21 2018
A deep trough and upper low over the southern High Plains this
afternoon will be the main issue for the forecast through tonight
and Monday. A warm front stretching out into the Midwest today has
brought significant moisture and very warm temperatures up into
Central IL. Persistent fog along the boundary continued into the
early evening hours to the north...as well as east central and
southeastern portions of the state. Moisture to the east and
southeast not properly handled in most of the models early...and
now models are having issue with the much warmer sfc temps that
are starting to erode the southern edge of the more limited
visibilities. Later tonight, precip develops along and ahead of a
cold frontal feature as the low further occludes and moves into
the Central Plains. Precip moves into the forecast area mainly
later tonight and into tomorrow morning. Although the instability
is somewhat limited in the early hours, there is still some
assistance offered by a LLJ, particularly in the southern half of
the state. Strong winds will be the main threat with the early
storms. Gusts in the overnight hours remain high mainly for just
that issue, even with only moderate tightening of the pressure
gradient...it won`t take much to pull some of those winds down
with a shower. Some isolated thunder will remain possible through
the overnight hours.

As for Monday, a significant dry slot has been consistent in
models for tomorrow into the early afternoon. In the past few
runs, NAM/4km WRF have been developing scattered thunderstorms in
the expansive dry slot. With lingering surface moisture, cooler
air moving in aloft, the lapse rates increase considerably in that
environment...with instability parameters less than impressive.
Any thunderstorms that do develop in that environment will have a
vertical assist from the proximity of the low, as well as offering
some shear to help with potential for mini/low topped supercells.
Threat for any severe weather will end quite quickly in the early
evening as the low moves into the Great Lakes.

&&

.LONG TERM...(Monday night through Sunday)
ISSUED AT 250 PM CST Sun Jan 21 2018
Cold air moving into the region behind the low will result in
potential for light snow for late Monday night...but little more
than a dusting on already wet ground will limit accumulations.
Forecast settles into a northwesterly flow regime with
temperatures closer to seasonal normals. 12Z runs of ECMWF and GFS
both pointing to a wave moving through aloft on Tues night/Wed
morning, but so far the wave is moisture starved aloft and sliding
over a surface high...producing zero qpf. Behind that wave, high
pressure ridge slips eastward, starting another warm advection
pattern through the end of the week. Highs are back to the low 50s
by Friday. A developing storm system in the desert SW will push
moisture and precip chances northeast into the Midwest to start
the weekend. Another rainy Saturday shaping up so far...warmer but
rainy.


&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1120 AM CST Sun Jan 21 2018

Not much of a change in the overall forecast, but continuing the
fog/VLIFR in a few TAFs at least through 20Z. Models inconsistent
in handling improvement in the vis but CMI BMI the most likely to
see a continuation of the poor conditions. HRRR tries to improve
the vis slightly late this afternoon, only to reestablish LIFR
conditions. As is, TAFs may be far too optimistic, but the
clearing to the SW for SPI and DEC is more than currently picked
up by models as well. Trying to balance between the two, with
southern flow pushing warmer temps into the region. A lot will
ride on this afternoons crossover temps with regards to the
overnight vis. In addition, developing showers with isolated
thunder possible after 06z in the TAFs.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory until 4 PM CST this afternoon for ILZ038-
043>046-053>057-061>063-066-067-071-072.

&&

$$

SHORT TERM...HJS
LONG TERM...HJS
AVIATION...HJS


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