Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 200920
AFDILX

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

.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 Mon...to 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 06Z TAFS through 06Z Saturday night)
Issued at 1144 PM CST Fri Jan 19 2018

LLWS conditions will continue through 14z, with a strong southwest
LLJ across central IL. Southwest speed maxima has climbed between
50-55KT in the 1500-2000FT layer, affecting all our terminal
sites. The LLJ weakens Saturday morning, as MVFR and IFR clouds
rapidly advance from SW to NE across the area. Cloud heights look
to drop directly to 1200FT around 14z, with IFR to 800FT mixed in
with the initial push of clouds. While mixing will diminish
somewhat with the stratus layer arrival, sustained winds look to
maintain in the 10-14KT range from the S-SW. Any IFR conditions
that do develop in the morning, should improve up to MVFR during
the afternoon as steady warm air advection flows increase the
LCL`s. Slight chances of rain look to begin Saturday evening, in
the broad warm advection pattern. Any rainfall amounts during the
last 6 hours of this TAF period will be very light, so only VCSH
was included at this point. MVFR fog could begin to develop as
winds weaken tomorrow evening.


&&

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

$$

SHORT TERM...Barnes
LONG TERM...Barnes
AVIATION...Shimon



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