Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 140545

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1245 AM CDT Wed Mar 14 2018

Issued at 842 PM CDT Tue Mar 13 2018

Quiet night ahead as a surface RIDGE slides around and to the
south of our region and just some thin high clouds passing
overhead. As winds diminish, temperatures are expected to drop
into the 20s late.

Nearly full sunshine is anticipated on Wednesday, and with winds
becoming southwest and gusty by afternoon, should see a healthy
temp rise during the day. The higher MAV MOS numbers look like a
good first guess, and if gusty SW winds come to fruition,
realized max temps will probably be even higher as many locations
west of the MS river make a run on 60F.



.SHORT TERM...  (Through Late Wednesday Afternoon)
Issued at 320 PM CDT Tue Mar 13 2018

Surface ridge to move off to the south tonight allowing winds to
back to the west to southwest by Wednesday morning. In the meantime,
light winds and clear skies will allow temps to drop into the low to
mid 20s tonight.

On Wednesday, winds to pickup from the southwest with highs warming
up into the upper 40s to upper 50s.


.LONG TERM...  (Wednesday Night through Next Tuesday)
Issued at 320 PM CDT Tue Mar 13 2018

By Wednesday night, next system to approach from the north. Frontal
boundary will slowly sink south, stalling out across far southern
Missouri by Thursday night.

In the meantime, dry and milder weather in store with increasing
clouds as front moves in. Lows Wednesday night will be in the 30s.
Temps on Thursday will depend on where the frontal boundary is, but
for now have highs on Thursday in the low 50s far north to the upper
60s far south.

Thursday night first in a series of shortwaves to slide along
stalled boundary. Will see showers develop and spread eastward. With
surface temps approaching freezing in portions of northeast Missouri
and west central/southwestern Illinois, will see mixed precipitation
towards daybreak on Friday. Little or no snow or ice accumulation is
expected at this time.

As surface low tracks along boundary will see best chances of
showers and a few storms Friday through Friday night, before system
weakens and shifts east during the day on Saturday. With the
increasing chances of rain, clouds and frontal boundary south of
forecast area, temps will be cooler with highs only in the 40s on
Friday. A little snow to mix in then change over to all snow late
Friday night through Saturday morning for portions of the area before
tapering off. Depending on depth of colder air and ground temps,
could see some light accumulations, mainly over northeast Missouri
and portions of west central and southwest Illinois by Saturday

Warmer temps to return by Sunday as upper ridge builds in. However,
another round of showers and a few storms is expected late Sunday
night through Monday night as next system over Central Plains
slides east into region. As precipitation tapers off late Monday
night into Tuesday, could see rain become mixed with snow before
tapering off.



.AVIATION...  (For the 06z TAFs through 06z Wednesday Night)
Issued at 1226 AM CDT Wed Mar 14 2018

VFR and dry conditions will persist through Wednesday night. High
pressure over southeast Nebraska will continue to move south
during the period away from the region. Northwest winds will
switch to the southwest after sunrise Wednesday morning. Breezy
southwest winds will likely impact KCOU and KUIN on Wednesday
afternoon but will likely weaken after sunset. A southwesterly
LLJ will develop over the region with LLWS developing on Wednesday
night at or about 1500ft AGL over all the terminals at or around
04z at 40kts.

SPECIFICS FOR KSTL: VFR and dry conditions expected at the
terminal through Wednesday night. Northwest winds will switch to
the southwest after sunrise morning but remain light through
Wednesday night. A southwesterly LLJ will develop over the
terminal on Wednesday night with LLWS around 04z at or around



Issued at 320 PM CDT Tue Mar 13 2018

Relative humidities to drop below 30 percent Wednesday afternoon
with a majority of forecast area having RH values between 20 and
25 percent. Also, winds to pickup from the southwest, especially
over portions of northeast Missouri and west central Illinois.
As for fuel moisture values, they have dipped below 10 percent as of
20z today, so feel we will see heightened fire danger for this area
Wednesday afternoon. Will add mention to HWO and sit rep.





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