Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 192336

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
636 PM CDT Mon Mar 19 2018

.SHORT TERM...  (Through Late Tuesday Afternoon)
Issued at 335 PM CDT Mon Mar 19 2018

Low pressure is moving quickly east along the Missouri/Arkansas
border this afternoon.  A broad area of rain is wrapping around the
low in the cold sector across much of central and eastern Missouri
as well as southwest Illinois.  This area of rain will clear from
west to east this evening and into the overnight hours as the low
continues east into the Ohio/Tennessee Valley. Some deformation
zone sprinkles or possibly some drizzle will continue to linger
into the daylight hours of Tuesday morning...primarily along and
southeast of the I-44 corridor in Missouri and south of I-64 in
Illinois. This precipitation may be enhanced a bit as a secondary
shortwave dives southeast through the Mississippi Valley into the
base of the longwave trof between 12-15Z Tuesday. Temperatures
aloft are marginal for any frozen precip, but there might be a few
flakes mixed in with the light rain in southeast Missouri early
Tuesday morning as the trof amplifies. Expect temperatures to stay
below seasonal normals tonight and tomorrow with abundant cloud
cover in the wake of the low.


.LONG TERM...  (Tuesday Night through Next Monday)
Issued at 335 PM CDT Mon Mar 19 2018

The global models from Tuesday night into the weekend show the large
scale flow shifting east and deamplifying.  The large upper low that
will be over Ohio Valley on Tuesday night will move off the East
Coast by late week at the same time that the upper ridge over the
West Coast moves east into the central CONUS. The GFS/ECMWF/Canadian
all show northwesterly upper flow setting up over Missouri and
Illinois through Friday before the upper ridge deamplifies as it
moves across the area Friday night into Saturday. It still looks
like we should expect dry weather Tuesday night into Wednesday
night as a surface high moves across Missouri and Illinois. There
will be a chance of showers Wednesday night into Thursday as
shortwave trough moves southeast across the region. A better
chance for showers and a few thunderstorms will be Friday into
Saturday when a surface low and a warm front develops across
Missouri and Illinois, and then again Sunday into Monday when a
cold front moves across the area. There is increased model
uncertainty over the weekend concerning location and timing of
fronts which decreases the confidence in this part of the
forecast. However I am confident that there will be precipitation
sometime during the 4 day period.

Temperatures are expected to be near normal mid to late week.  Over
the weekend, temperatures will likely be near normal, though it will
be dependent on the location of the front.  Best chance for above
normal temperatures will be Saturday when current model runs are
suggesting that the warm front will move northward into the area.



.AVIATION...  (For the 00z TAFs through 00z Tuesday Evening)
Issued at 623 PM CDT Mon Mar 19 2018

Sfc low will continue to move east tonight. As it does, ongoing
rain will gradually end from west to east. Have added some mention
of light fog overnight as well at COU. With winds expected to be
a little lighter, would expect visbys to drop. With at least some
mixing thru the night, have kept visbys in the MVFR range. With
stronger mixing persisting longer at SUS/CPS, believe any fog will
struggle to develop this far north. Otherwise, expect cigs to
improve late tonight into Tues morning as the low pulls east and
drier air filters into the region. Winds will increase with gusts
during the morning hours.

SPECIFICS FOR KSTL: Ongoing rain will slowly move east out of the
area. Cigs are uncertain with a wide range if cigs across the
region. Still believe that MVFR cigs will dominate tonight, tho it
may be low MVFR thru the evening hours. Otherwise, winds will
increase again Tues morning with gusts to around 20 kts.





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