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

FXUS63 KLSX 272059

Area Forecast Discussion
National Weather Service Saint Louis MO
359 PM CDT WED APR 27 2016

.SHORT TERM...  (Through Late Tonight)
Issued at 332 PM CDT Wed Apr 27 2016

The air mass has recovered in the wake of the morning storms. The
combination of increasing moisture and heating along with
overspreading steeper mid level lapse rates has produced SBCAPE
from 1500-2000+ j/kg south of the warm front. The warm front was
drapped from the surface low in southeast NE through northeast MO
and into south central IL. Satellite imagery shows a rather
extensive cu field and right now we sit and wait. A couple of
scenarios are possible from the current obs and CAMs. One is that
soley the broken line of storms in northeast KS/northwest MO will
continue to develop southward some and thing swing northeast
across portions of northern MO as the short wave trof located
across eastern KS rotates northeast this evening. Another scenario
is a combination of the aforementioned evolution, and additionally
scattered more discrete storms will form from central thru
northeast MO between 21-23z as large scale ascent associated with
the short wave overspreads the area. Primary zone will again be
the north of I-70 with more isolated development further south.
Threats are primarily large hail and some tornado potential across
northeast MO where surface winds are locally backed enhancing the
low level shear. Believe all of the activity should have exited
the area by 06-07z as the upper low/trof lifts northeast and the
surface cold front advances across the area.


.LONG TERM...  (Thursday through Next Wednesday)
Issued at 332 PM CDT Wed Apr 27 2016

Deep westerly flow in the wake of the front will result in good
drying and tranquil weather Thursday with weak high pressure
dominating Thursday night.

Things begin to get busy again Friday into the weekend, and especially
Friday night into Saturday night. There are model differences with
the position and speed of the upper low/trof and associated surface
system. At this time the GFS looks too far south and have more
closely followed the ECMWF and NAM.

The approach of the next deep upstream upper trof and retreating
high pressure will allow for an initial short wave to impact the
area as early as late Friday afternoon at which time low level
moisture return will begin to get underway. I have some low pops
from central into southeast MO. This scenario is most likely to
really get underway on Friday night with widespread showers and
thunderstorms in response to the southerly LLJ and large scale
ascent with the short wave. The thunderstorm threat will remain
high Saturday into Saturday night with the advancing upper trof
and attendant cold front moving across the region. A broad,
unstable and significantly sheared warm sector in advance of the
front would suggest severe weather potential as well.



.AVIATION...  (For the 18z TAFs through 18z Thursday Afternoon)
Issued at 1235 PM CDT Wed Apr 27 2016

North-south oriented isolated-scattered showers and weak
thunderstorms is expected to move east of KUIN and metro terminals
by 1900 UTC. Another round of at least scattered thunderstorms is
expected to develop by late afternoon. Development may be east of
KCOU but is expected to be west of the metro terminals as well as
KUIN. Atmosphere should destabilize enough to cause some storms to
be strong/severe with large hail and damaging winds possible with
stronger thunderstorms in addition to heavy rain/IFR visbys. By
mid- late evening...thunderstorms are expected to move off to the
east of the terminals with VFR conditions expected into Thursday
afternoon. Only exception could be at KUIN as some high-end MVFR
ceilings are possible by mid morning on Thursday. Winds will
initially be southeast early this afternoon before turning out of
the west/southwest behind the frontal passage later on tonight.

Specifics for KSTL:

Isolated-scattered showers/weak storms expected to quickly move
to the east of the terminal early this afternoon. Partially
clearing sky to the west will advect in within the next 1-2 hours
and help destabilize the atmosphere. Scattered thunderstorms are
expected to develop to the west of the terminal by mid afternoon
with storms possibly affecting the terminal between late afternoon
and early evening. Stronger thunderstorms will be capable of
producing large hail and damaging winds as well as heavy rain/IFR
visbys. Threat of storms should exit by mid-late evening...with
VFR conditions in its wake. Winds will turn from the southeast
early this afternoon to the west/southwest behind a frontal
boundary late tonight/early Thursday morning.





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