Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 240830
AFDLSX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
330 AM CDT Thu Apr 24 2014

.SHORT TERM: (Today through Friday
Issued at 329 AM CDT Thu Apr 24 2014

Strong upper level trof is moving east through the Great Plains
this morning. The surface reflection of this trof extends from
eastern Nebraska/Kansas southwest into western Texas. Looks like
good moisture surging ahead of the trof with upper 50s to mid 60s
dewpoints all the way up into eastern Kansas. All short-range
guidance has slowed the eastward progression of this system today,
and thereby also slowing down the precipitation associated with
it. This should allow for a warmer day than previously forecast.
Have bumped up temperatures toward warmer MAV guidance for today.
Should see little but spotty showers across most of the area this
morning, but with increasing chances of precipitation by 18-20Z.
Additional heating of course mean more instability than previously
forecast as well, and the NAM is forecasting a narrow corridor of
1200+ J/Kg MUCAPE ahead of the front this afternoon along and
south of the I-70 corridor. With deep layer shear in excess of 40
kts it does look like some severe storms will be possible.
Convective mode is somewhat indeterminate with shear strong enough
for supercells, but instability probably lacking a bit. I kind of
like the latest run of the HRRR which as a broken line of storms
moving across the area this afternoon, tho with a bit more
instability the convection could easily be more discrete
initially. Front now looks to be into central Missouri by around
00Z, along the Mississippi River by 03-04Z, and through Salem
Illinois by about 06Z. Have adjusted PoPs for this slower
progression through tonight.

Temperatures on Friday are still somewhat in question.  A relatively
mild Pacific airmass will build in behind the front on Friday.
850mb temps don`t really fall off that much and are 10-12C by 00Z
Saturday.  This would suggest mid to upper 70s which makes MOS
numbers a bit too cool across most of the area.  Bumped up a bit
over MOS to compensate.

Carney

.LONG TERM:  (Thursday through Next Wednesday)
Issued at 329 PM CDT Wed Apr 23 2014

(Thursday through Saturday)

Main focus for Thurs will be precip chances. Not much change from
the prev forecast other than slowing timing down a bit. Some
questions remain regarding exactly how precip on Thurs will play
out. Believe that the morning hours will be similar to what is
occurring now. Expect precip to intensify during the afternoon and
into the evening along and just ahead of the cdfnt, if enuf heating
can occur. Am becoming more concerned of an isod TSRA becoming
strong to severe, mainly across portions of central MO. However,
this is highly conditional on the amount of heating that can occur
during the day. Will therefore not mention for now and allow the
night shift to reevaluate.

Beyond Thurs, the remainder of the period shud be dry. Did keep low
chance POPs for Sat as a wrmfnt lifts thru the region due to
uncertainty. However, with height rises over the area and better
forcing across KS and wrn MO, believe bulk of precip will remain W
of the CWA.

The focus quickly turns to temps for Fri and Sat. Differences among
mdls leads to a lot of uncertainty for these days. Given the past
couple of warm up events, will trend twd the GFS/local WRF solns.
These solns strong SW to W flow at the sfc with the thermal ridge
pushing into the region. This, coupled with deep mixing, shud allow
temps to reach the 80s for Fri. Sat shud be a little cooler as a
weak cdfnt drops swd across the region, but still a warm day.

(Sunday through Wednesday)

While specifics may differ among mdl solns, general trends are in
fairly good agreement thru the extd period. Mdls suggest an initial
surge of TSRA will push thru the region on Sun thru Mon as a large
low system approaches the area. This system has a threat of severe
weather for much of the CWA. As this system is still 5 plus days
out, time will not be spent discussing details that are likely to
change many times by the end of this weekend.

By Mon night, a S/W associated with the upper low progd to be over
the nrn Atlantic, will approach the upper low over the MO region.
After a brief Fujiwhara interaction, these two low centers are progd
to combine forming one large low system. Mdls differ regarding
placement of this interaction, which will be vital to determining
where precip will occur associated with this low. If the interaction
is further E, the low shud eject precip ewd out of the region, per
the GFS soln. If it is further W, per the ECMWF, precip shud linger
for at least a while.

Regardless, both solns suggest much colder temps will remain locked
in place thru the remainder of next week. Will take a closer look at
temps for Wed and beyond tomorrow, but going forecast of mid 50s may
have too much of an influence on climo and need to be lowered with
future updates.


Tilly

&&

.AVIATION:  (For the 06z TAFs through 06z Thursday Night)
Issued at 1155 PM CDT Wed Apr 23 2014

VFR flight conditions/mid-high clouds will persist overnight with modest
southeast surface winds. A southerly LLJ has developed and is broader
than originally anticipated, and now have marginal LLWS conditions
at all TAF sites. Precipitation timing is still a tough call on
Thursday, but overall the trend and timing is slower than previous
forecasts. Expecting shra and possibly a few rumbles of thunder to
impact KCOU-KUIN in the 16-18z time frame with this activity
weakening as it moves east. Better potential for organized showers
and thunderstorms at all TAFS sites will be on Thursday afternoon/evening
along and ahead of a cold front where I have conditions lowering
to MVFR.

Specifics for KSTL:

VFR flight conditions/mid-high clouds will persist overnight with modest
southeast surface winds. A southerly LLJ has developed and is broader
than originally anticipated, and local radar VWPs suggest marginal LLWS
conditions through 14-15z. Best potential for organized showers
and thunderstorms at KSTL will be between 22-02z on Thursday
afternoon/evening along and ahead of a cold front where I have
conditions lowering to MVFR.

Glass

&&

.PRELIMINARY POINT TEMPS/POPS:
Saint Louis     73  50  78  55 /  80  80   0  10
Quincy          68  47  76  51 /  80  80   0  10
Columbia        71  46  78  51 /  80  70   0  10
Jefferson City  72  48  79  50 /  80  80   0  10
Salem           74  49  76  51 /  70  80   0  10
Farmington      75  49  77  49 /  80  80   0  10

&&

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

$$

WFO LSX






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