Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 190847

Area Forecast Discussion
National Weather Service Saint Louis MO
347 AM CDT Sun Mar 19 2017

.SHORT TERM...  (Through Late Tonight)
Issued at 340 AM CDT Sun Mar 19 2017

High pressure over Illinois will continue moving east today and a
developing trof of low pressure over the Great Plains will move into
the Midwest.  Low level moisture convergence is producing isolated
showers over southwest missouri at this time...and expect this
isolated convection to spread east this morning as the 850mb ridge
axis moves east of the Mississippi River.  Short range guidance is
hinting that coverage could get as high as 30-40% this afternoon
over central Missouri when isentropic lift and moisture convergence
is greatest, and convection allowing models support this as well.

Should see convection weaken during the late afternoon to early
evening as the low level jet refocuses further north over Iowa.
Model guidance is mixed on placement and amount of precip tonight.
The GFS is the furthest west with the bulk of the precip in our area
falling along and west of the Mississippi...and it`s also the
fastest in developing precip this evening.  ECMWF puts almost all of
the QPF over Illinois and also has all of the precip after midnight.
The NAM is very similar to the ECMWF but does have some precip west
of the Mississippi overnight.  The NSSL and NCEP WRF have little or
no precip over our area all night.  So...without a good consensus,
have 30-50 PoPs across the area tonight with the higher end of the
range across Illinois.  Guidance is consistent in showing MUCAPE in
excess of 1500 J/Kg (albeit in different locations) tonight.  This
instability combined with 30-40kts of deep layer shear should be
sufficient for elevated severe thunderstorms with the primary threat
being large hail.


.LONG TERM...  (Monday through Saturday)
Issued at 340 AM CDT Sun Mar 19 2017

Scattered thunderstorms will likely be ongoing early on Monday
morning, particularly over the eastern half of the CWA.  This is
where both the NAM/GFS are showing decent low level moisture
convergence occurring under modest mid level ascent associated with
a weak shortwave trough moving across the Missouri and Illinois.
This storms will move east early in the day as the forcing moves off
to the east.  A cold front will move slowly southeast across the
area during the day, and forecast MLCAPES will increase above 1000
J/kg during the afternoon along and south of I-70.  However,
forecast soundings are showing a significant inversion in the low
levels which will limit just isolated showers and thunderstorms over
southeast Missouri.  Favor the warmer NAM MOS temperatures on Monday
for highs which has temperatures climbing into the 70s which is
supported by 850mb temperatures in the 10-15C range.

Then much like previous runs, the GFS and ECMWF has the front
dropping to the south of Missouri and Illinois on Tuesday and
Wednesday.  Even though the front will be south of the area on
Monday night into Tuesday night, will keep a chance of showers going
over the area.  Still looks like a low level jet will transport
enough low level moisture into the area as a series of weak vort
maxes move across the region in west northwesterly flow aloft. There
will be a brief break in the rain on Wednesday, chances will
increase again Wednesday night into next Saturday.  This will occur
as low level flow turn out of the southwest and transports more
moisture into the area in response to an upper trough approaching
from the west.  Temperatures will be near normal at midweek, but
then climb back above normal at the end of the week as a warm front
moves north in response with the approach of the upper trough.  By
Friday and Saturday, expect a chance of showers and thunderstorms
over the area with highs in the 60s and 70s.



.AVIATION...  (For the 06z TAFs through 06z Sunday Night)
Issued at 1146 PM CDT Sat Mar 18 2017

SPECIFICS FOR KCOU, KUIN: VFR for the first 0-6 hours at KUIN, but
there is greater uncertainty at KCOU towards the end of the first
6 hours. Increasing VFR clouds are expected at both TAF sites
after 09z ahead of a developing warm front, but KCOU is far
enough west that scattered rain showers could briefly lower
conditions to MVFR if a shower happens to move directly over the
terminal. Southeasterly to southerly winds will increase to around
10 kts after 14z due to the tightening pressure gradient.

SPECIFICS FOR KSTL, KSUS, KCPS: VFR for the first 0-6 hours. Winds
will continue to veer overnight with the passage of a surface
ridge axis. Winds will increase after 12z due to a tightening
pressure gradient. Expect increasing VFR clouds after 09z ahead of
a developing warm front. Rain is likely just beyond the end of the
24-hr TAF period.





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