Area Forecast Discussion
Issued by NWS Central Illinois

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064
FXUS63 KILX 210417
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1117 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 06Z TAFS through 06Z Saturday night)
Issued at 1110 PM CDT Fri Oct 20 2017

VFR conditions are expected through this forecast period. Two
concerns this period include LLWS late tonight for PIA and
SPI, and then timing of showers and thunderstorms into our
western TAF sites late tomorrow evening or overnight. ILX VAD
wind profile indicating 35 kts at 1500-2000 ft AGL and models
continue to suggest areas from SPI to PIA have the higher
probabilities for seeing LLWS overnight so will continue to
hold with the current forecasts for those areas. Quite a bit
of cirrus around the area overnight which may tend to thin for
a short period of time Saturday morning before more VFR clouds
moving in during the afternoon and evening.

Showers and storms should develop tomorrow afternoon west of I-35
along a slow moving cold front and those should consolidate into
a line of storms which will translate east towards the Mississippi
River by Midnight in a weakening state. It still appears SPI and
PIA may see some showers move in after 04z with areas to the east
not seeing the rain until late Saturday night or Sunday morning.
southerly winds of 10 to 15 kts can be expected tonight with
south winds increasing to 15 to 20 kts on Saturday with gusts
around 25 kts at times by late morning into the afternoon hours.
A south wind of 12 to 17 kts can be expected Saturday evening.

&&

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

$$

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



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