Area Forecast Discussion
Issued by NWS St. Louis, MO
FXUS63 KLSX 192356
AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
656 PM CDT Sun Apr 19 2015
.SHORT TERM: (Through Tonight)
Issued at 344 PM CDT Sun Apr 19 2015
Main rain shield that developed in response to the low pressure
system to our southeast will continue to slowly lift northeast late
this afternoon and into this evening. Meanwhile, scattered
convection will continue to develop in its wake ahead of the main
upper level trof and cold front. Believe much of the convection is
diurnally driven and will dissipate late in the evening, with only a
few showers remaining after midnight. Threat of any severe weather
should stay south of the CWA where better instability resides.
.LONG TERM: (Monday through Next Sunday)
Issued at 344 PM CDT Sun Apr 19 2015
(Monday through Wednesday)
Focus finally turns to temps thru the period.
Have kept slight chance PoPs Mon morning across nern/ern portions of
the CWA as the system continues to pull out of the region. Some of
the explicit mdls suggest isod SHRA developing during the afternoon
hours. However, given the lack of precip behind the trof currently
across the Plains, believe mdls are simply showing CU developing.
Have therefore kept much of the day dry.
Next chance for RA is then Tues afternoon thru Wed with mdls
continuing to show a s/w rounding the base of the upper low. Mdls
continue to differ in placement and timing for this s/w. Have kept
similar PoPs going for this period until mdls come into better
Temps for Mon will be difficult with questions about cloud cover.
Expect CU to develop behind this trof. Based on latest sat trends,
wud expect more cloud cover than mdls are currently expecting.
However, am trending twd a more cloud free soln, and therefore
slightly warmer, for now. Temps shud moderate slightly with the
thermal ridge building into the area on Tues, but then CAA again on
Wed as a back door cdfnt pushes thru the area again.
(Thursday through Sunday)
Mdl differences continue thru the extd with the GFS/GEM a more zonal
soln and the ECMWF more amplified. Have therefore kept PoPs on the
low end except for periods where mdls were in better agreement
despite differences in setup.
Largely kept temp trends going as well twd a compromise given the
uncertainty in solns.
.AVIATION: (For the 00z TAFs through 00z Monday Evening)
Issued at 632 PM CDT Sun Apr 19 2015
Specifics for KCOU, KUIN: An area of scattered SHRA/TSRA was
approaching KCOU at TAF issuance while a separate area of SHRA was
moving away from KUIN. Scattered SHRA/TSRA are possible at KCOU
for the next few hours because the decrease in clouds during the
late afternoon was contributing to slightly greater instability.
West to southwest winds will become northwesterly after a cold
front moves through the region overnight. Winds are expected to
increase behind the front and gust to around 30kts. Fog is
possible tonight during a brief window ahead of the cold front in
any locations where clouds clear out near or shortly after sunset.
Upstream observations suggest that MVFR ceilings will persist for
several hours after fropa.
Specifics for KSTL, KSUS, KCPS: Although isolated SHRA/TSRA are
possible tonight, there is little instability left near the St.
Louis metro area after the rain showers all day, thus there is no
mention of precip in the 00z TAFs attm. West to southwest winds
will become northwesterly after a cold front moves through the
region overnight. Winds are expected to increase behind the front
and gust to around 30kts. Winds will decrease after sunset on
Monday. Fog is possible tonight during a brief window ahead of the
cold front in any locations where clouds clear out near or shortly
after sunset. Upstream observations suggest that MVFR ceilings
will persist for several hours after fropa.