Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 280528

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1228 AM CDT THU APR 28 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
draped 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 06z TAFs through 06z Thursday Night)
Issued at 1213 AM CDT Thu Apr 28 2016

Thunderstorms are clearing the area to the east at this time. Any
storms will be capable of producing gusty wind, hail and IFR
conditions in heavy rain. To the west of the storms, expect VFR
flight conditions to prevail across most of the area for the rest
of the night. There is some fog developing over northeast
Missouri...which could spread into west central Illinois...however
am not very confident in how low to go. Regardless, fog threat
should be done by 12-13Z as drier air moves into the area. Some
MVFR ceilings likely across northeast MO and west central IL
Thursday as well...though some guidance has the clouds above 3,000

Specifics for KSTL:

VFR flight conditions are expected at Lambert through Thursday.





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