Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 180450
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1150 PM CDT Mon Apr 17 2017

.SHORT TERM...  (Through Late Tuesday Afternoon)
Issued at 312 PM CDT Mon Apr 17 2017

Weak high pressure is trying to build across the the area this
afternoon.  Most of the lower clouds and showers have moved
southeast of the area with just a few lingering showers over
southeast Missouri and central Illinois.  These remaining showers
should be out of our CWFA by 00Z.  Expect dry weather to prevail
tonight and for most of Tuesday...with a slight chance of
thunderstorms late Tuesday afternoon over northeast Missouri ahead
of the next upstream cold front.  Above normal temperatures continue
with tonight`s lows in the upper 40s and low to mid 50s and highs
tomorrow in the mid 70s.

Carney

.LONG TERM...  (Tuesday Night through Next Monday)
Issued at 312 PM CDT Mon Apr 17 2017

Front to our south will undergo frontolysis on Tuesday night as the
surface temperatures gradient relaxes.  Focus then turns northward
as a shortwave trough moves across the Upper Midwest on Tuesday, and
its attendant cold front drops into southern Iowa by late Tuesday
night. Still appears there will be enough low level moisture
convergence ahead of the front to keep a chance of showers and
thunderstorm across northeast Missouri and west central Illinois.
There is some indication that showers and thunderstorms may move
southeast into south central Illinois on Wednesday morning.  Still
looks like GFS/ECMWF will keep this front quasi-stationary to the
north of the area on Wednesday.  Forecast soundings indicate that
most of the warm sector will have a cap during the day, so any
scattered shower and thunderstorm development will be confined north
of I-70 in the afternoon.

By Wednesday night and Thursday a deeper trough will move across the
central CONUS causing a cold front to move from the Central Plains
on Wednesday into MO/IL on Thursday.  Showers and thunderstorms that
develop along the front during the day on Wednesday will possibly
move into central and northeast Missouri and west central Illinois
on Wednesday night.  A few of these will possibly be strong to
severe given the marginally strong instability and shear available.
By Thursday, the cold front will move southeast across the area, and
additional thunderstorms will be able to develop during the day
ahead of the front.

The front will move south of the area by Friday, but next closed low
is already beginning to move out of the southwest CONUS.  Recent
runs of the GFS and ECMWF show the track of the surface low south of
the the CWA.  Consequently the warm sector will likely also stay to
our south.  It will looks like showers and some thunderstorms will
move back into the area as soon as late Friday and continue into
Sunday as the upper low move move across the area.  Monday looks dry
at this point as a weak ridge moves into the area behind the exiting
closed low.

Temperatures on Wednesday and Thursday ahead of the front still look
warm with 850mb temperatures of 10-15C.  Temperatures will cool down
Friday into the weekend to near or below normal as the closed low
passes over the area with clouds and rain.

Britt

&&

.AVIATION...  (For the 06z TAFs through 06z Tuesday Night)
Issued at 1143 PM CDT Mon Apr 17 2017

VFR through the period with occasional mid/high clouds. Winds will
gradually veer and become southerly to southwesterly by the end of
the valid TAF period. There is a slim possibility that isolated to
scattered SHRA/TSRA may affect KUIN during the last 6 hours of the
TAF period due to an approaching cold front, but confidence was
too low to include in the 18/06z TAF for KUIN.

Kanofsky

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&

$$

WFO LSX



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