Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 172010
AFDLSX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
310 PM CDT Thu Apr 17 2014

.SHORT TERM:  (Through Late Tonight)
Issued at 306 PM CDT Thu Apr 17 2014

Despite cold front moving through region, front is weakening and
moisture is lacking so any precipitation will be very light in
nature. So just have slight chance of showers for portions of west
central/southwestern IL tonight. Otherwise, partly to mostly cloudy
skies to begin scattering out late tonight. Not a lot of caa with
this system, so lows will be in the mid 30s to mid 40s.

Byrd

.LONG TERM:  (Friday through Next Thursday)
Issued at 306 PM CDT Thu Apr 17 2014

Should have a clearing sky from northwest to southeast on Friday as
the surface ridge builds into the area behind the weakening cold
front, and as the upper level trough shifts east of our area.
Tranquil and warmer weather heading into the weekend as an upper
level ridge moves into the area on Saturday behind the upper level
trough/low.  Above normal high temperatures expected on Saturday and
Sunday as southerly surface/low level flow returns.  Low level
moisture and instability will increase over our area Saturday night
and Sunday due to the persistent southerly flow ahead of a slow
moving shortwave over the central Plains.  Scattered showers and a
few thundestorms will likely develop Sunday afternoon across MO, west
of STL.  Showers and a few storms should overspread our area Sunday
night and continue on Monday as this weakening shortwave/upper level
trough moves slowly eastward through the region, while a relatively
weak cold front moves slowly southeastward through our area on
Monday and Monday evening. The precipitation threat should shift
southeast of our forecast area by late Monday night as the upper
level trough shifts east of the region and a surface ridge
builds southeastward into the area behind the cold front.  Only
slight and short lived cooling is expected behind the cold front,
with pronounced warming expected Tuesday night and Wednesday as an
upper level ridge moves eastward into the region and southerly low
level flow returns and strengthens.  The GFS model increases the 850
mb temperatures to 12-16 degrees C by Wednesday night over our
forecast area, whle the ECMWF is not quite as warm.  The GFS model
brings convection into northeast MO and west central IL Wednesday
and Wednesday night due to strong low-mid level warm air advection
ahead of "ridge runner" type shortwaves.  There does seem to be some
convectve feedback in the GFS model at this time leading to
overamplified vort maxes and potentially too much convection
depicted by the model, although the ECMWF also has some qpf
extending south into this area as well.

GKS

&&

.AVIATION:  (For the 18z TAFs through 18z Friday Afternoon)
Issued at 1249 PM CDT Thu Apr 17 2014

Weak cold front is making very slow progress to the south today.
It has moved through KUIN and KCOU, but is stalled over metro
area as of 17z. Mvfr cigs at KUIN have scattered out. Otherwise,
mid and high clouds prevail over region. As low level moisture
increases, just a bit, will see low end vfr cigs develop north of
frontal boundary late this afternoon and early this evening.
Shower activity will be very sparse so did not add mention to tafs
at this time. Otherwise, southwest winds to veer to the northwest
to north behind the boundary, but remain rather light. Later
tonight cigs to scatter out and winds become light and variable.
Winds will pickup just a bit from the northeast on Friday as
frontal boundary washes out and surface ridge builds in.

Specifics for KSTL:
Weak cold front is making very slow progress to the south today.
It has stalled over metro area as of 17z. Mid and high clouds
prevail over region. As low level moisture increases, just a bit,
will see low end vfr cigs develop north of frontal boundary after
03z Friday. Shower activity will be very sparse so did not add mention
to taf at this time. Otherwise, southwest winds to veer to the
north behind the boundary, but remain rather light. By 09z Friday
cigs to scatter out and winds become light and variable. Winds
will pickup just a bit from the northeast by 19z Friday as
frontal boundary washes out and surface ridge builds in.

Byrd

&&

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

$$

WFO LSX






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