Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 240903

403 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.


.LONG TERM: (Saturday through Wednesday)
Issued at 403 AM CDT Thu Apr 24 2014

Guidance continues to come into better agreement for the weekend.
The secondary front which was forecast to sweep all the way
through Missouri into Arkansas earlier in the week is now only
going to get to southern Iowa according to the model collective.
Still showing a good low level baroclinic zone stretching from
southwest Missouri up into Iowa Saturday through Sunday with a
southwest low level jet ramping up to 40-50kts flowing
perpendicular to the thermal gradient. All models print out some
light precip in response to this on Saturday, primarily over
central and western Missouri but I wouldn`t be surprised to see it
a bit further north/northeast as well if this verifies.
Temperatures will be highly dependent on how much sunshine we end
up getting, but I leaned heavily on the warmer MAV numbers.

Strong warm advection continues ahead of the ginormous trof which
will be moving over the Rockies Saturday night, and it looks like
there could be some nocturnal convection as a a result...mostly
across northern sections of the CWFA.  The trof moves into the Great
Plains on Sunday and closes off while also becoming negatively
tilted.  The resulting wound up, slow moving storm system will draw
abundant moisture into the Mid-Mississippi Valley from the Gulf
producing at least a couple of rounds of showers and thunderstorms
Sunday into Monday night before the associated cold front comes
through and drier air works into the area.  Temperatures should stay
seasonably mild through the Monday with highs near normal.

Tuesday and Wednesday the storm system moves slowly overhead and
then on into the Ohio Valley.  Models print out widespread precip
over the area as cold air aloft moves in with the cut off low.
Heaviest amounts look to be across northern Missouri and southern
Iowa associated with the deformation zone.  While this makes sense
conceptually, still not sure I totally believe the medium range
models as this is a highly anomalous pattern for late April/early.
Stuck relatively close to guidance though as the mass fields on the
GFS and ECMWF are in very good agreement considering strength of
this system and its anomalous nature.



.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.



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




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