Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 292018
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
318 PM CDT FRI APR 29 2016

.SHORT TERM...  (Through Late Tonight)
Issued at 315 PM CDT Fri Apr 29 2016

Will show an increase in showers and thunderstorms this afternoon
this evening as low level moisture convergence begins to increase
over the area.  Will keep categorical PoPs over the entire area
overnight as low level moisture increases on the nose of a 40kt low
level jet.  This will occur under increasing mid-upper ascent of
large upper low now entering southern Plains. Severe weather
threat tonight will be limited by the lack of instability, but
moisture will be plentiful with increasing PWATs around 1.5 by
12Z. Widespread lows in the 50s still look good and are close to
MOS guidance.

Britt

.LONG TERM...  (Saturday through Next Friday)
Issued at 315 PM CDT Fri Apr 29 2016

(Saturday through Monday)

Main concern will continue to be the potential for severe storms on
Saturday and Saturday evening.  Widespread showers and thunderstorms
should be ongoing during the early morning hours as there will still
be some strong low level moisture convergence underlying the mid
level ascent.  This will allow for the widespread showers and
thunderstorms to end from southwest to northeast during the late
morning and early afternoon hours.  Still have some concern about
redevelopment of thunderstorms along and south of I-70 during the
afternoon and evening hours.  Latest run of the GFS is farther north
of the surface low which matches better with the more consistent
ECMWF and NAM.  Will continue to show chance PoPS for thunderstorms
during the afternoon and evening.  Model MUCAPES are in the 1000-
2000 J/kg range with deep layer that supports supercells.
Hodographs in the warm sector suggests a sheared environment that
would favor multicells with a damaging wind potential.  However,
could not rule out a brief tornado potential along the warm front.
Severe potential should end toward late evening once the cold front
moves east of the CWA.

Shower chances will continue into Sunday as the upper low passes
through the area.

(Tuesday through Friday)

GFS and ECMWF continues to show highly amplified upper flow over
North America next week with a deep trough over the eastern CONUS
and a ridge over the Rocky Mountains.  This will result in northerly
upper flow aloft through the period that is cutoff from a supply of
Gulf Moisture, so will keep forecast mainly dry for now.  GFS and
ECMWF does show a cold front that moves across the area from the
north on Wednesday night.  850mb temperatures look cooler today than
previous runs, which support temperatures closer to normal as we go
into early May.

Britt

&&

.AVIATION...  (For the 18z TAFs through 18z Saturday Afternoon)
Issued at 1245 PM CDT Fri Apr 29 2016

Specifics for KCOU: Mid/high clouds will persist ahead of an
approaching disturbance. SHRA/TSRA develop after 03z and persist
through the overnight hours, accompanied by MVFR cigs. Conditions
may fall to IFR at times.

Specifics for KUIN: KUIN is far enough north that MVFR cigs are
expected to persist for at least the next few hours and possibly
longer. Thereafter, mid/high clouds will continue to increase
ahead of an approaching disturbance. SHRA/TSRA develop after 06z
and persist into the morning hours, accompanied by MVFR cigs.
Conditions may fall to IFR at times.

Specifics for KSTL, KSUS, KCPS: A brief period of MVFR cigs is
ongoing at TAF issuance at KSTL but should improve quickly based
on recent obs at KSUS and KCPS. Mid/high clouds will persist ahead
of an approaching disturbance. SHRA/TSRA develop after 06z and
persist into the morning hours, accompanied by MVFR cigs.
Conditions may fall to IFR at times. Beyond the end of the 24hr
TAF pd, a second round of scattered thunderstorms is possible at
St. Louis metro area terminals after 30/21z.

Kanofsky

&&

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

$$

WFO LSX



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