Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 200024

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
724 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


.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



.AVIATION...  (For the 00z TAFs through 00z Saturday Evening)
Issued at 723 PM CDT Fri May 19 2017

Thunderstorms are still the main impact at the terminals over the
next 12 hours. Line of storms will move across the St. Louis
terminals between 01-04Z bringing MVFR/IFR and gusty winds. It
still appears that there will be an additional complex of storms
affect all of the sites between 07-12Z tonight with the same
conditions. After this line moves through, MVFR and IFR ceilings
will linger through Saturday morning before improving to VFR by
Saturday afternoon.

SPECIFICS FOR KSTL: Thunderstorms will continue to be the main
impact over the next 12 hours. Line of storms will affect the
terminal between 01-03Z. Additional storms will affect the
terminal between 09-12Z late tonight. Any storms will have the
potential to produce MVFR/IFR conditions as well as gusty winds.
After this line moves through, MVFR ceilings will linger through
Saturday morning before improving to VFR by Saturday afternoon.





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