Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 182045
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
345 PM CDT Wed Apr 18 2018

.SHORT TERM...  (Through Late Thursday Afternoon)
Issued at 310 PM CDT Wed Apr 18 2018

A cold front extending from a surface low over southwest IN
southwest through southeastern MO will continue moving
southeastward. Strong and gusty west-northwest surface winds will
continue late this afternoon and early this evening, but then
begin to gradually diminish later this evening and overnight as a
strong surface ridge over the northern Plains builds southeastward
into MO. Will continue the Wind Advisory for central MO and
southwest IL until 7 PM with sustained speeds of 20 to 35 mph and
gusts as high as 45 mph. Unseasonably cold temperatures can be
expected tonight and Thursday. It appears that the winds will be
too high and there will be too much cloudiness for much frost
late tonight and early Thursday morning. The clouds will gradually
clear out from north-northwest to south-southeast on Thursday.

GKS

.LONG TERM...  (Thursday Night through Next Wednesday)
Issued at 310 PM CDT Wed Apr 18 2018

Good radiational cooling can be expected Thursday night near the
surface ridge axis due to a light surface wind, a clear sky, and
low surface dew points for April. These conditions will lead to
frost formation late Thursday night with lows in the lower to
middle 30s. May eventually need to issue a Frost Advisory for late
Thursday night and early Friday morning where the growing season
has begun. Warmer conditions can be expected by Friday afternoon
with upper level ridging over the central US, and as surface winds
become east-southeasterly on the backside of the retreating
surface ridge. An upper level low and associated surface low will
pass well south of our area this weekend. Showers may move into
parts of southeast MO Saturday night on the northern fringes of
the precipitation shield, then into southwestern IL on Sunday. Due
to the slow movement of the upper level low, showers may linger
across parts of southeast MO and southwest IL Sunday night and
Monday. An upper level trough and associated cold front may bring
a quick shot of showers to much of the area in the Tuesday to
Wednesday time frame. The quicker operational GFS model has the
system moving through on Tuesday, while the less progressive
ECMWF model favors Wednesday. With these timing differences will
keep the pops on the low side.

GKS

&&

.AVIATION...  (For the 18z TAFs through 18z Thursday Afternoon)
Issued at 1119 AM CDT Wed Apr 18 2018

Surface low just northeast of STL with a cold front extending
southwest through the St Louis metro area late this morning.
Strong and gusty west-northwesterly surface winds will occur after
fropa. These winds will gradually diminish later this evening and
overnight as the surface pressure gradient relaxes. MVFR cigs
have already advected into UIN and post frontal low level
cloudiness will move into COU and the St Louis metro area this
afternoon, with the cloud ceiling dropping into the MVFR category
tonight.

SPECIFICS FOR KSTL: Surface low just northeast of STL with a cold
front extending southwest through the St Louis metro area late
this morning. Strong and gusty west-northwesterly surface winds
will occur after fropa. These winds will gradually diminish later
this evening and overnight as the surface pressure gradient
relaxes. MVFR cigs have already advected into UIN and post frontal
low level cloudiness will move into STL afternoon, with the cloud
ceiling dropping into the MVFR category tonight. These clouds
will scatter out by early Thursday afternoon.

GKS

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Wind Advisory until 7 PM CDT this evening for Audrain MO-Boone
     MO-Callaway MO-Cole MO-Franklin MO-Gasconade MO-Jefferson
     MO-Lincoln MO-Moniteau MO-Montgomery MO-Osage MO-Pike MO-
     Saint Charles MO-Saint Louis City MO-Saint Louis MO-Warren
     MO.

IL...Wind Advisory until 7 PM CDT this evening for Bond IL-Calhoun IL-
     Clinton IL-Fayette IL-Greene IL-Jersey IL-Macoupin IL-
     Madison IL-Marion IL-Monroe IL-Montgomery IL-Saint Clair IL-
     Washington IL.

&&

$$

WFO LSX



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