Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 140446
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
1146 PM CDT Sun Jul 13 2014

.UPDATE:
Issued at 925 PM CDT Sun Jul 13 2014

Wavy frontal boundary stretches from southwest OK through southern
MO/IL into the Ohio Valley this evening. A very moist and moderately
unstable air mass spans both sides of the boundary with PWs around
1.80 inches and SBCAPE averaging around 1500 j/kg. Lift associated
with a 25 kt westerly LLJ and an upstream weak short wave trof
from western MO into southeast KS, continues to generate clusters
of showers and thunderstorms spanning both sides of the front. The
greatest increase in organization and coverage during the last
hour or so has been across southwest Missouri. This trend is
expected to continue through at least the remainder of the evening
as the boundary oozes southward with likely pops across the
eastern Ozarks into far southwest IL. Severe threat looks pretty
isolated with heavy downpours a greater concern. The more formidable
cold front will drop south to near the IA/MO border by 12z with a
threat of isolated showers and thunderstorms immediately ahead of
it.

Glass

&&

.SHORT TERM:  (Through Late Tonight)
Issued at 313 PM CDT Sun Jul 13 2014

Cold front has moved to a Effingham to St. Louis metro to Rolla
line at 20Z. Atmosphere is moderately unstable with MLCAPEs around
1000-1500 J/kg with an effective sheer of 35 kts. Still some
potential for a few severe thunderstorms capable of producing
primarily damaging winds with some large hail through the evening
hours given the amount of instability and shear in the SPC slight
risk area. Scattered thunderstorms have been developing over the
past couple of hours, primarily behind the front. A series of vort
maxes will continue to move across the area through early evening
per the RAP which will provide some modest ascent, but some
increase in overall coverage of thunderstorms should occur during
this evening over the southern and eastern parts the CWA when a
modest increase in 925-850mb moisture convergence occurs. This is
depicted well on the HRRR and NSSL-WRF simulated reflectivity.
These storms will shift south of the CWA overnight, though there
will be a slight chance of storms late tonight over northeast
Missouri and west central Illinois as a secondary cold front moves
south out of Iowa.

Britt

.LONG TERM:  (Monday through Next Sunday)
Issued at 313 PM CDT Sun Jul 13 2014

(Monday through Wednesday)

The aforementioned secondary cold front will move southward through
the CWA during the day Monday as a stronger shortwave pivots
through the area. Expect additional scattered thunderstorms to
develop along front tomorrow because of this. There will be the
risk of a few severe thunderstorms along and ahead of the front
given forecast MLCAPE values of 1000-1500 J/kg and deep layer near
40kts. Storms will move out of the area by early Monday evening.

Monday should be out last warm day with 850mb temperatures between
14-18C. These temperatures will fall to between 8-12C on Tuesday
and Wednesday which should keep highs only in the lower to middle
70s. Lows on Tuesday morning look like they will fall into the
middle 50s in most areas because of decent radiational cooling and
dewpoints in the low 50s. Tuesday and Wednesday still look dry as we
will lie under subsidence in northwesterly flow aloft.

(Thursday through next Sunday)

GFS and ECMWF are still in relatively good agreement in showing that
the deep upper low that will be centered over the Great Lakes at
midweek will lift into eastern Canada on Thursday.  At the same
time, another weaker upper low will be digging in behind it.
Expect a dry Thursday with the surface high bringing drier air
from the east with highs near 80 given the 850mb temperatures
around 12C. The GFS and ECMWF are in decent agreement on Friday
and Saturday that most of the precipitation associated with the
upper trough will stay to the south, so will keep the forecast
dry. Shower and thunderstorm chances will increase by next Sunday
as both models show a warm front moving northeast through the
area. 850mb temperatures will climb into the 17-19C range which
favor temperatures in the middle to upper 80s.

Britt

&&

.AVIATION:  (For the 06z TAFs through 06z Monday Night)
Issued at 1131 PM CDT Sun Jul 13 2014

Existing precip should be east of the terminals by 6Z. This precip
is expected aid in fog formation overnight. The light winds and
recent rainfall will combine with a moist air mass to allow fog to
form late tonight after the clouds begin to clear. If the clouds
clear out sooner than expected...then the fog could be more dense
than currently expected. Any fog that forms should dsspt quickly
after sunrise. Attention then turns to a secondary cold front that
will drop through the region on Monday. There a some very isld
cells along the front as of 0430Z. Models indicate fairly decent
coverage along the bndry by aftn. Given uncertainty in coverage...
have held onto the VC groups during the late morning into the
aftn. Other than early morning fog...terminals have a VFR fcst for
the remainder of the prd with winds aob 12kts.

Specifics for KSTL:

Sctrd TSTMs from this evng should be east of the terminal by 6Z.
There may be some high end MVFR fog that forms prior to sunrise
due to recent rainfall...light winds and a moist air mass. A
secondary cold front pushes thru during the aftn bringing another
chance for TSTMs. Given uncertainties with coverage...opted to
hold onto the VCTS group. Other than the possible MVFR fog early
Monday morning...the remainder of the fcst should be VFR with
winds aob 12kts.

2%

&&

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

$$

WFO LSX





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