Area Forecast Discussion
Issued by NWS Central Illinois

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000
FXUS63 KILX 210144
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
844 PM CDT Fri Oct 20 2017

.UPDATE...
Issued at 835 PM CDT Fri Oct 20 2017

High level clouds continue to stream northward ahead of a weak
upper level wave noted on the water vapor loop over Oklahoma
and Arkansas this evening. The 00z ILX sounding continues to show
a very dry air mass in place, especially in the low and mid
levels of the atmosphere this evening with the Springfield, Mo.
sounding showing better moisture above 850 mb. The latest surface
map indicating a tighter pressure gradient across the region this
evening with our southerly winds expected to hold up through most
of the night. That will set the table for a windy and mild day on
Saturday ahead of our next weather maker which will push across
the central Plains during the day and inch closer to our area,
but not until late tomorrow night or more likely on Sunday bringing
the threat for showers and thunderstorms to the area. Until then,
the pleasant weather will continue.

Updated the sky grids to reflect more cloud cover across the area
with a denser cirrus shield streaming northward into central
Illinois. Bumped wind gusts up some during the day on Saturday
ahead of the next weather system based on the latest forecast
soundings. We should have the updated zone forecast out by 9 PM.

&&

.SHORT TERM...(This evening through Saturday)
ISSUED AT 300 PM CDT Fri Oct 20 2017

20Z/3 pm surface analysis shows 1025 mb high pressure along the
OH/WV border and ridging from the eastern Great Lakes to AL/GA.
Sunshine filtering through cirrus clouds over central IL along
with south breezes was giving warm temps in the 75-80F range, with
mid 70s in sw/west central IL where thicker cirrus clouds.
Surface high pressure ridge to drift east off the Atlantic coast
Saturday while strong upper level ridge remains over the Atlantic
States. Dry weather to continue through Saturday as mid/high
clouds continue to increase from the SSW ahead of a short wave
trof in Texas and nw Gulf of Mexico. Milder lows tonight in the
lower 50s in eastern IL and upper 50s from Peoria and Springfield
west. Another warm day in the upper 70s to near 80F on Saturday.

.LONG TERM...(Saturday night through Friday)
ISSUED AT 300 PM CDT Fri Oct 20 2017

A strong cold front to track east into nw IL by 12Z/7 am Sunday
and sweep through IL during the day Sunday. Have 20-30% chances of
showers and thunderstorms over the IL river valley Sat evening,
then spread 50-80% pops of showers and chances of thunderstorms
eastward across CWA during overnight Sat night. SPC day2 outlook
has a marginal risk of severe thunderstorms Sat night from
Galesburg to Rushville west while slight risk of severe storms is
west of IL. Continued 50-80% chance of showers and isolated
thunderstorms on Sunday, with thunder chances mainly Sunday
morning. Mild lows Sat night in the lower 60s, except upper 50s by
Galesburg where cold front passes through by dawn Sunday. Cooler
highs Sunday range from lower 60s by Galesburg to the mid 70s
along the Wabash river.

Forecast models continue to develop at 570 dm 500 mb cutoff low
over the AR ozarks by sunset Sunday and tracks into the southern
TN river valley by sunset Monday. ECMWF and GEM models keeps a
fair amount of qpf east of the IL river Sunday night and Monday
while GFS is further east with qpf in eastern IL Sunday night and
east of IL on Monday. Leaned toward the wetter ECMWF and GEM
models for Sunday night and Monday. Seasonable highs Monday of
64-68F.

A strong upper level trof digs sse into IL later Monday night and
Tuesday and continues chances of showers in eastern IL Monday
night and across most of CWA on Tue as colder air ushers in. Highs
Tue range from the lower 50s nw of the IL river, to around 60F by
Lawrenceville. Clouds to decrease from west to east during Tue
night. Lows Tue night of 35-40F and could be some patchy frost
late nw of IL river if nw winds decrease enough. Highs Wed only in
the low to mid 50s despite partly to mostly sunny skies as strong
upper level trof shifts east of IL. Lows Wed night in the lower
40s, except upper 30s in eastern IL. Some upper level ridging
into IL Wed night and into the Ohio river valley Thu to moderate
temps into low to mid 60s for highs Thu. Next chance of showers
arrives overnight Thu night and Friday of next week as another
cold front moves through the area. This will be followed by colder
lows in the mid to upper 30s next Fri night and risk of frost
again.

&&

.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 640 PM CDT Fri Oct 20 2017

VFR conditions are expected this forecast period. The main concern
will be with low level wind shear later tonight at PIA and SPI,
and gusty southerly winds across most of our area tomorrow. The
latest soundings and time height cross sections indicate a band of
40-45 kt winds from the south at 1500-2000 ft AGL after 05z at
both PIA and SPI so will add LLWS to the SPI group for this
forecast issuance. After 14z, winds should mix out with most areas
seeing southerly flow at 12 to 20 kts with a few gusts around 25
kts at times, especially during the late morning and afternoon
hours. Other than some cirrus, no MVFR or lower clouds are
expected over the area through 00z Sun.


&&

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

$$

UPDATE...Smith
SHORT TERM...07
LONG TERM...07
AVIATION...Smith


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