Area Forecast Discussion
Issued by NWS St. Louis, MO

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828
FXUS63 KLSX 192039
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
339 PM CDT Fri May 19 2017

.SHORT TERM...  (Through Late Saturday Afternoon)
Issued at 338 PM CDT Fri May 19 2017

New tornado watch has just been issued for much of central and parts
of east central Missouri along the quasi-stationary front.  Latest
GOES-16 imagery is showing cloud streets ahead of a QLCS over
southwest Missouri.  This is south of the stationary front that
extends front south of Kansas City and Columbia to north of St.
Louis.  The atmosphere has destabilized to the south of the warm
front with MLCAPES now between 500-2000 J/kg.  Deep layer shear is
also sufficient for severe storms including supercells and organized
multi-cells including the QLCS.  Runs of the CAMS have been showing
one QLCS moving across the CWA this evening and another moving
across the CWA late tonight.  There will the potential for all
hazards with these storms.  There could also be some locally heavy
rainfall across the area.

Showers and thunderstorms will begin to move out of the area on
Saturday from west to east as a cold front begins to move across the
area.


Britt


.LONG TERM...  (Saturday Night through Next Friday)
Issued at 338 PM CDT Fri May 19 2017

(Saturday Night - Wednesday Night)

Cold front will exit the CWA early on Saturday night from west to
east. Along and ahead of the front, there will exist at least a
chance of showers and thunderstorms. Severity is highly unknown as
atmosphere may be overworked and stabilized ahead of the actual cold
front due to antecedent convection. Severe threat regardless
would likely be confined to the evening hours.

Story behind the front continues to be the much cooler airmass which
will quickly filter into the mid-Mississippi Valley beginning after
the frontal passage. Below to much below normal temperatures will
likely be the rule through at least Wednesday night as longwave
trough amplifies overhead, and pivots southeastward toward the area
by Tuesday night/Wednesday. A prolonged chance of showers appears
possible beginning Monday night through Wednesday, with a closed low
forming at midlevels. Cannot rule out a few thunderstorms on Monday
and Tuesday, particularly during peak heating.

Coolest temperatures will likely be on Wednesday as 850-hPa
temperatures drop below +5C. Look for highs in the low to mid 60s
for most locations. Coldest night will likely be Wednesday Night
with lows in the mid to upper 40s.


(Thursday - Next Friday)

A quick moderation in temperatures is likely to end the work week
along with drier conditions as midlevel shortwave ridge moves toward
the bi-state region. Highs by Friday look to be back to just below
normal.


Gosselin


&&

.AVIATION...  (For the 18z TAFs through 18z Saturday Afternoon)
Issued at 1236 PM CDT Fri May 19 2017

Scattered thunderstorms are expected to redevelop along and south
of a stationary front this afternoon that currently extends from
south of KCOU to north of KSTL. MVFR and some IFR ceilings will
slowly lift during the afternoon hours. There will be a better
chance of thunderstorms toward 00Z when a more organized band of
thunderstorms moves across the area. A second area of
thunderstorms is expect to move across the area between 08-12Z
affecting all of the terminals. Any thunderstorms will have the
potential to produce MVFR/IFR conditionals and brief gusty winds.
MVFR/some IFR conditions are expect late tonight and early on
Saturday morning before they improve on during the day on
Saturday.

SPECIFICS FOR KSTL: There will be the threat for thunderstorms to
redevelop late this afternoon and early this evening. The best
chance for thunderstorms will be early this evening and again
overnight. Any thunderstorms will have the potential to produce
MVFR/IFR conditionals and brief gusty winds. MVFR/some IFR
conditions are expect late tonight and early on Saturday morning
before they improve on during the day on Saturday.  Any
thunderstorms will have the potential to produce MVFR/IFR
conditionals and brief gusty winds. MVFR/some IFR conditions are
expect late tonight and early on Saturday morning before they
improve on during the day on Saturday. Current southwest winds is
expected to turn to the north this afternoon.



Britt

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&

$$

WFO LSX



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