Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 201717

Area Forecast Discussion
National Weather Service Lincoln IL
1117 AM CST Sat Jan 20 2018

Issued at 944 AM CST Sat Jan 20 2018

Low cloud deck has been quickly pushing east across the central
and northern CWA this morning, just starting to move into Decatur
and Bloomington as of 9:30 am. AWIPS time-of-arrival tool has it
reaching Danville and Paris a little after 11 am. HRRR model
suggests the southeast CWA should remain out of this cloud deck
until early afternoon, when additional low clouds currently in the
southern tip of Illinois begin to arrive. Once the clouds arrive,
forecast soundings suggest little improvement through tonight,
though some thinning of the cloud deck is currently seen over
northern Missouri. So far, no drizzle was being reported at
stations across Missouri, though some of the high-res models hint
at some development by mid afternoon over our area.

Recent updates mainly adjusted the sky trends, with some more
minor adjustments to the temperature and weather trends.


.SHORT TERM...(Today and tonight)
ISSUED AT 320 AM CST Sat Jan 20 2018

The pressure gradient between a 1026mb high centered over Georgia
and a 1004mb low developing in the lee of the Rockies across
eastern Colorado continues to provide a mild southerly flow to
central Illinois this morning. 08z/2am temperatures are generally
in the lower to middle 30s, with a few readings near 40 degrees
across the far W/SW KILX CWA. Other than a blanket of high/thin
clouds, skies are currently mostly clear. Latest IR satellite
imagery shows lower clouds poised to the south/southwest...with
clouds across eastern Kansas and far western Missouri rapidly
spreading N/NE over the past couple of hours. Its this area of
cloudiness that will eventually spread/develop further
northeastward into central Illinois later this morning. NAM
925-850mb layer RH progs suggest pronounced moistening and thus
rapidly increasing clouds between 15z and 18z. HRRR had indicated
an even faster increase in clouds: however, latest runs have
backed off just a bit and look more like the NAM. End result will
be a partly sunny start to the morning followed by overcast
conditions across the board by midday. As increasing amounts of
boundary layer moisture flow northward, fog and drizzle will
develop across the southwest this afternoon...then will spread
across the entire area tonight. High temperatures this afternoon
will be in the middle to upper 40s. Lows tonight will remain in
the middle to upper 30s.

.LONG TERM...(Sunday through Friday)
ISSUED AT 320 AM CST Sat Jan 20 2018

Based on only shallow boundary layer moisture profiles, opted to
remove shower chances for Sunday in favor of continued
fog/drizzle throughout the day. Despite the dreary conditions,
temperatures will rise into the upper 40s and lower 50s.

A vigorous short-wave trough evident on latest water vapor imagery
over central California will track across the Rockies over the
next 24 hours, resulting in surface cyclogenesis in the Plains.
00z Jan 20 models are in good agreement concerning the track of
the low from central Kansas 00z northeast Iowa by 00z
Tue. As the low and its associated cold front slowly approach from
the west, a band of deep-layer moisture flowing northward from the
Gulf of Mexico will provide the fuel for widespread showers Sunday
night into Monday morning. NAM MUCAPE values increase to
200-400J/kg, suggesting the potential for isolated thunderstorms
as well. After a band of early morning showers/thunder, the dry
slot associated with the system will work into central Illinois
toward midday Monday through the afternoon...resulting in a lull
in precip chances.

Once the low tracks into the southern Great Lakes Monday night,
wrap around moisture will bring an increased chance for precip.
Enough cold air will get drawn into the region to support a change
over from rain to snow Monday night into Tuesday morning. Due to
expected light QPF and the progressive nature of the system, only
minor snow accumulations of a couple tenths of an inch are
anticipated. After that, mild and dry weather will be on tap for
much of next week...before the next storm system brings rain
chances by Friday night into Saturday.


.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1117 AM CST Sat Jan 20 2018

MVFR cloud deck has overspread all of the TAF sites as of late
morning. Some thinning seen in satellite imagery across far west
central Illinois, but clouds likely to remain at least broken
through the afternoon. Reports along the northern edge of the
cloud shield are showing some ceilings below 1,000 feet now, and
will mention continue to mention IFR conditions from KPIA-KCMI by
around mid afternoon or so. Latest HRRR and LAMP guidance suggests
KSPI may hold off on the IFR ceilings until about mid evening.
Once these low ceilings arrive, they likely will remain in place
through the end of the forecast period. Visibility-wise, several
guidance sources support fog developing over east central Illinois
this evening, though the extent of dense fog outside of KCMI is
more questionable. For now, will only mention the lowest
visibilities there, with mainly 1SM elsewhere.




LONG TERM...Barnes
AVIATION...Geelhart is the U.S. government's official web portal to all federal, state and local government web resources and services.