Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 302050
AFDLSX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
350 PM CDT Mon Mar 30 2015

.SHORT TERM:  (Through Late Tonight)
Issued at 350 PM CDT Mon Mar 30 2015

South to southwest flow will prevail tonight ahead of a weak cold
front which will move through Tuesday.  Dry atmosphere will provide
a mostly clear sky...with perhaps a few cirrus clouds.  Temperatures
look to stay near or just above climatological normals due to the
warm southwest winds.  Used a blend of guidance for lows, but leaned
toward some of the warmer members of the ensemble.

Carney

.LONG TERM:  (Tuesday through Next Monday)
Issued at 350 PM CDT Mon Mar 30 2015

The forecast over this period can be broken down into three
segments, all primarily based off the upper flow pattern.

Through Tuesday night, a northwest flow will prevail over our
region, delivering quiet wx, thanks to dry air and little in the way
of any forcing mechanisms.  A weak cold front will move thru during
the day on Tuesday, but both the associated WAA ahead of it, and its
expected position when it might be able to gain some leverage from
the heating of the day for some surface based convection are not
favorable for any mention of pcpn at this time.  Have continued the
dry forecast from the previous package.

The air following the cold front will not be much different than the
one ahead of it, and so despite NW winds for much of Tuesday for
most areas, temps are expected to follow persistence or a bit above.

The upper flow will then back to the W-SW by late Wednesday and
continue into Friday night, signalling a more active wx pattern to
close the work week.  The old front from Tuesday will be buckling
northward as a warm front on Wednesday, but the timing looks to be a
bit slower than it did 24hrs ago.  Given the significant increase of
moisture thru the column that will accompany this warm front, its
delay will still mean worth a small PoP mention for the afternoon
and evening but over a more western area than 24hrs ago.

More significant forcing will move in late Wednesday night and
continue into Thursday evening as a stronger cold front than the one
on Tuesday drops down and will result in periods of showers and
thunderstorms.  Another shot of forcing, mostly frontogenetical and
post-frontal, will then move in on Friday providing mostly rain with
any thunder confined to southern MO and IL.

A warm day is expected for Wednesday, and potentially into Thursday
depending on the exact timing of the rain and front, with much
cooler temps than expected on Friday behind the front with rain.

A period of quieter wx is then expected for the weekend with NW flow
restored by Saturday morning and drier air moving in.  Temps will be
quick to rebound, after a cool Saturday, towards normal on Sunday as
surface winds turn from the south.

Southwest upper flow could occur already by Monday next week with
the normal accompanying rain chances, but some model disagreement on
timing here so went conservative with PoPs and leaned towards climo
values.

TES

&&

.AVIATION:  (For the 18z TAFs through 18z Tuesday Afternoon)
Issued at 1245 PM CDT Mon Mar 30 2015

VFR flight conditions will prevail through Tuesday. Prevailing
southwest flow will turn to the west and then north-northwest on
Tuesday morning as a weak cold front moves through the area.
Marginal low level wind shear conditions are possible overnight
tonight, but have opted not to mention in the TAFs at this time as
model guidance sometimes overestimates low level winds.

Specifics for KSTL:

VFR flight conditions will prevail through Tuesday. Prevailing
southwest flow will turn to the west overnight and then north-
northwest as a weak cold front passes through the terminal around
13-14Z. Marginal low level wind shear conditions are possible
overnight tonight, but have opted not to mention in the KSTL TAF
at this time as model guidance sometimes overestimates low level
winds.

Carney

&&

.LSX WATCHES/WARNINGS/ADVISORIES:
MO...NONE.
IL...NONE.
&&

$$

WFO LSX




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