Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 130900
AFDLSX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
400 AM CDT Sun Jul 13 2014

.SHORT TERM: (Through Tonight)
Issued at 340 AM CDT Sun Jul 13 2014

(Today and tonight)

Showers and thunderstorms currently ongoing over northeast and
central Missouri and southwest Illinois are part of a larger band
of storms stretching from northern Indiana to eastern Kansas ahead
of an approaching cold front. Storms have been slow to progress
south due to warm temperatures aloft, and high resolution model
guidance indicates that while the activity should continue its
slow southward progression, it will gradually weaken through the
morning hours. The aforementioned cold front will move south
across the forecast area today and tonight, and given the moist,
unstable airmass in place ahead of it, particularly over the
southern half of the CWA, scattered convection should redevelop
this afternoon. Given CAPE values expected to range from 1500-2500
J/kg, as well as 0-6km bulk shear 25-30kt, organized convection is
possible, particularly over the southern half of the forecast
area. The SPC has placed portions of southeast Missouri as well as
southern Illinois in a slight risk for severe weather this
afternoon and tonight, with damaging winds being the primary
threat. Precipitable water values ahead of the front are around
2.00-2.25 inches as well, so very heavy rain is also possible with
any storms that develop. Temperatures today will range from the
mid 80s over northern portions of the forecast area to the low to
mid 90s south, as the thermal ridge is suppressed southward ahead
of the approaching front. As the front continues to move south
tonight, low temperatures in the wake of the front will be a bit
cooler than the last few nights, ranging from the mid 60s north to
low 70s over southeast Missouri and southern Illinois as well as
in the St. Louis metro area.

JP

.LONG TERM:  (Monday through Saturday)
Issued at 340 AM CDT Sun Jul 13 2014

Temperatures Monday will be a bit cooler, with upper 70s over the
far northern forecast area, and mid to upper 80s elsewhere. A
second cold front will move across the area on Monday, and given
modest recovery of the atmosphere in the wake of Sunday`s front,
models indicate CAPE values Monday afternoon around 1500 J/kg.
There is a slight risk of severe weather Monday for southeast
Missouri and southern Illinois, where widespread height falls and
increasing cyclonic flow could once again support organized
convection, with damaging winds the primary threat. The chance of
showers and thunderstorms will persist until the front moves south
of the area Monday night.

Strong cold air advection in the wake of Monday`s front will mark
a distinct change for Tuesday, with 850mb temperatures expected to
range from 7-10C, which translates to highs in the low to mid 70s
across the area. Temperatures will struggle to make it out of the
70s Wednesday as high pressure continues to build into the region,
though a moderating trend is expected by the start of the weekend,
with highs in the low to mid 80s expected Saturday. Much of the
extended should remain dry, though the GFS and ECMWF both indicate
a shortwave moving through the area Friday/Friday night. However,
given model discrepancies, have left the forecast dry for now.

JP

&&

.AVIATION:  (For the 06z TAFs through 06z Sunday Night)
Issued at 1123 PM CDT Sat Jul 12 2014

Fcst remains focused on precip and clouds assoc with a cold front.
Front currently stretches from nthrn IL SW thru SE IA into NW MO
and on into KS. Earlier convection struggled to maintain intensity
as it moved east and has since all but dssptd. A new band of
SHRA/TSTMs has dvlpd in the past couple of hrs along the cold
front across sthrn IA...nthrn MO and SE NEB. This activity should
push SE thru the night. Models have the precip dssptng between 8Z-
11Z as it moves away from better upper level support...into warmer
mid level temps and during a climatologically unfavorable time for
convection to exist. Have MVFR VSBYs at KUIN and KCOU as this band
passes thru overnight. Not confident at all that it will hold
together long enough to affect the STL metro area terminals so
have a few hrs of VCSH to address the threat. Beyond that...the
front is fcst to be just south of the STL metro sites by early
aftn when convective dvlpmnt should begin. Think that the front
should be far enough south by that time that precip and/or TSTMs
should not be a problem...but due to uncertainties in the exact
placement of the front left the going VCTS in place until there is better
confidence that convection will not be an issue for the metro area.

Specifics for KSTL:

Dssptng band of SHRAs possibly affecting the terminal around 12Z with
addntl TSTMs possible during the aftn. Otherwise expect a VFR fcst with
winds aob 10kts.

2%

&&

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

$$

WFO LSX





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