Area Forecast Discussion
Issued by NWS St. Louis, MO

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

000
FXUS63 KLSX 291721
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
1221 PM CDT Fri Aug 29 2014

.SHORT TERM:  (Through Sunday night)
Issued at 326 AM CDT Fri Aug 29 2014

The primary forecast concern over the next 7 days is precipitation
chances.

An upper trough axis is forecast to move across the area
today/tomorrow accompanied by SH/TS. A surface low moving into
the Great Lakes will drag a cold front into MO/IL on Sat, but the
temperature gradient is forecast to be fairly weak and this looks
like more of a gentle wind shift line rather than a true exchange
of air masses. Even so, models show a secondary vort max clipping
the northern CWA on Sat and the wind shift line might act as a
focus for SH/TS development. It doesn`t look like solid rain for
the whole weekend, but it`s tough to rule out scattered SH/TS in
almost any forecast period because isentropic ascent starts to
increase ahead of the next trough almost as soon as the Fri/Sat
trough moves away from the area. The most likely time period for
mostly dry weather across most of the LSX CWA appears to be from
late Sat night through late Sun morning.

Kanofsky

.LONG TERM: (Monday through Thursday)
Issued at 326 AM CDT Fri Aug 29 2014

Precipitation chances increase again on Mon/Mon night ahead of an
approaching longwave trough. With several embedded vorticity
maxima moving through the base of the broad trough, scattered
SH/TS will be possible across MO/IL through Tue as a cold front
sinks towards the MO/IA border. The best opportunity for
precipitation appears to be on Mon morning as the nocturnal LLJ
veers and becomes focused across the CWA. The temperature gradient
is forecast to be stronger with this front compared to the
previous one, but models still show that the synoptic front never
makes it very far into MO before it is lifted back northward as a
warm front. Broad upper troughing then gives way to quasizonal
flow by Tue night followed by weak upper ridging towards the end
of the week.

Temperatures look seasonally warm, although there is more
uncertainty with temps on days when precipitation is expected.
If recent model runs are correct with the expansion of the upper
high over the southeastern CONUS, then expect a warming trend for
late next week.

Kanofsky

&&

.AVIATION:  (For the 18z TAFs through 18z Saturday Afternoon)
Issued at 1205 PM CDT Fri Aug 29 2014

Focus over the next 24-30 hours will be on the chances of showers
and thunderstorms affecting the terminals. Band of showers and
thunderstorms ahead of a midlevel impulse is expected to translate
slowly eastward across the area through the day/night. Did my best
to time this area with convection first affecting KCOU this
afternoon...and rest of terminals by early evening. Broken line of
activity may weaken a bit and break up later on tonight as
stronger forcing for ascent translates north and east.
Precipitation should move off to the east of terminals by late
tonight though cannot rule out lingering showers or perhaps a
storm really anytime as associated cold front stalls out and never
really makes it through the area. Winds will veer to the southwest
and eventually to the west/southwest at KCOU and KUIN behind
boundary.


Specifics for KSTL:

Focus over the next 24-30 hours will be on the chances of showers
and thunderstorms affecting Lambert Field. Band of showers and
thunderstorms ahead of a midlevel impulse is expected to translate
slowly eastward across the area through the day/night. Showers
with embedded thunder possible is likely late this evening into
the early overnight period with visibilities possibly dipping into
MVFR or even IFR in heavier activity. Precipitation should move
off to the east of terminal by late tonight though cannot rule
out lingering showers or perhaps a storm really anytime as
associated cold front stalls out and never really makes it through
the area. Slightly better chance of showers and storms may
redevelop during the day tomorrow...especially along/in vicinity
of old cold front. Winds will remain out of the south and veer
to the southwest tomorrow afternoon.

Gosselin

&&

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

$$

WFO LSX





USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.