Area Forecast Discussion
Issued by NWS St. Louis, MO

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000
FXUS63 KLSX 260244
AFDLSX

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE ST LOUIS MO
944 PM CDT Mon May 25 2015

.UPDATE:
Issued at 927 PM CDT Mon May 25 2015

An extensive MCS which originated this afternoon across the
southern Plains continues to push eastward into the lower MS
Valley this evening. Large scale ascent associated with the
upstream shortwave trof, ponounced southerly lower trop flow of
moist unstable air, and system relative convergence is helping
maintain the line from AR into Eastern TX, however radar has begun
to show decreasing convective organization on the northern periphery
which is moving more northeastward into MO. This may result in a
diminished severe threat for southern MO. However, the southerly
LLJ is forecast to ramp up and veer later tonight and this combined
with large scale ascent associated with the progressive shortwave
trof and an apparent newd moving MCV presently in NW AR should
maintain a shield of northeast moving showers and thunderstorms.

Glass

&&

.SHORT TERM: (Tonight through Thursday)
Issued at 236 PM CDT Mon May 25 2015

Expect quiet weather to continue for any remaining holiday
festivities this evening, with the anticipation that the northern
portion of the aforementioned MCS, likely in a decaying phase,
will be entering our southwestern counties shortly after midnight.
Large scale ascent with the shortwave should initiate additional
convection further north as well with the entire area moving
northeast through the remainder of the CWA through daybreak on
Tuesday. Not sure how much redevelopment will be able to occur
Tuesday afternoon in the wake of the morning rain. Have lowered
PoPs from west to east Tuesday afternoon.

Have chance PoPs continuing Tuesday night through Thursday as a
series of weaker shortwaves are forecast to impact the area as the
upper level pattern temporarily becomes a little more zonal.

CVKING

.LONG TERM: (Next Weekend)
Issued at 236 PM CDT Mon May 25 2015

Thunderstorm chances will steadily increase as the upper trough will
deepen again to our west by the end of the work week and actually
progress east into the middle Mississippi River Valley by the end of
the weekend. Temperatures will remain near normal for the end of May.

CVKING

&&

.AVIATION:  (For the 00z TAFs through 00z Tuesday Evening)
Issued at 636 PM CDT Mon May 25 2015

Primary concern for tonight is the large thunderstorm complex
currently moving northeast out of Oklahoma into northwest
Arkansas. The upper level disturbance associated with the storms
will move over our area after 05-06Z tonight. Am fairly certain
there will be rain and thunderstorms associated with the
disturbance as it moves across the area, but am less certain about
the strength, and areal coverage in thunderstorms. This
uncertainty is the primary reason the TAFs have prevailing showers
with vicinity thunder. Will continue to monitor the convection as
it moves into Missouri later this evening and adjust TAFs as
needed. Otherwise...expect VFR flight conditions ahead of the
rain, with ceilings falling to MVFR after the rain begins. If
storms can stay strong through the night, IFR visibility in
intermittent heavy rain is possible. Forecast for Tuesday is
uncertain as well, as warm moist and unstable air will persist
behind the early morning rain. Current thinking is that widely
scattered to scattered thunderstorms will be possible, mainly east
of the Mississippi River...but this could change depending on what
happens with the storms tonight.

Specifics for KSTL:

VFR flight conditions are expected to prevail at Lambert at least
through the evening and for a few hours after 06Z.  Primary
concern for tonight is the large thunderstorm complex currently
moving northeast out of Oklahoma into northwest Arkansas. The
upper level disturbance associated with the storms will move over
our area after 05-06Z tonight. Am fairly certain there will be
rain and thunderstorms associated with the disturbance, but am
less certain about the strength, and areal coverage in
thunderstorms. This uncertainty is the primary reason the Lambert
TAF has prevailing showers with vicinity thunder. Will continue
to monitor the convection as it moves into Missouri later this
evening and adjust TAFs as needed. If storms can stay strong
through the night, IFR visibility in intermittent heavy rain is
possible. Forecast for Tuesday is uncertain as well, as warm moist
and unstable air will persist behind the early morning rain.
Current thinking is that widely scattered to scattered
thunderstorms will be possible, mainly east of the Mississippi
River...but this could change depending on what happens with the
storms tonight.

Carney

&&

.LSX WATCHES/WARNINGS/ADVISORIES:
MO...NONE.
IL...NONE.
&&

$$

WFO LSX





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