Area Forecast Discussion
Issued by NWS St. Louis, MO
FXUS63 KLSX 250447
AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
1147 PM CDT Thu Apr 24 2014
.SHORT TERM: (Through Late Tonight)
Issued at 234 PM CDT Thu Apr 24 2014
Main focus through tonight will be cold front and associated risk for
showers and thunderstorms. Degree of instability is still a concern and
a source of uncertainty. Dewpoints have really struggled to climb so
far today due to persistent southeasterly surface flow. Winds are expected
to veer to the south/southwest as a subtle warm front lifts north to near
the I-70 corridor by 0000 UTC this evening. This should allow sfc dewpoints
to at least climb into the 50s across the southern half of the area. That
being said...instability is likely to be on the marginal side for severe
thunderstorms...on the order of several hundred J/kg. Wind shear will be
supportive however of organized convection over the southern CWA with
40+ knots of 0-6 km shear just downstream of approaching shortwave trough.
Regardless of the severity of storms tonight...believe widespread showers
and thunderstorms will affect the entire CWA due to very strong forcing for
ascent aloft via DCPVA ahead of vort max and jet coupling. This strong
upper-level support may help overcome the lack of instability and may
lead to more strong/severe storms with damaging straight-line winds being
the primary threat. Frontal timing and associated ending to precipitation
is even more delayed than this time yesterday...with frontal timing just
after 0000 UTC likely along the Mississippi River including the St. Louis
metropolitan area and around 0400 UTC for KSLO/K3LF.
Skies will quickly clear overnight tonight with northwesterly winds gradually
lightening up a bit. Look for lows in the 40s to near 50 degrees across the
area and went with a consensus of guidance for mins tonight.
.LONG TERM: (Friday through Next Thursday)
Issued at 240 PM CDT Thu Apr 24 2014
With sfc ridge building into the region on Fri, have continued
warm trend aoa MOS thru Sat.
Mdls remain in relatively good agreement regarding the system
approaching the area on Sun into Mon. A lot can change by Sun and
will not focus much on details, but Sun and/or Mon will have a
potential for svr wx. Timing differs among mdl guidance, but GFS
suggests main threat will be Sun, while the ECMWF suggests the
threat continuing into Mon.
For Tues and beyond, large upper low will remain anchored over the
region thru much of the week. Will need to keep an eye on temps
during this time as going forecast may be too cold. While this
period shud be cooler, expect cloud to become bkn during the
morning and into afternoon allowing low topped convection to occur.
For now, will trend near a guidance compromise.
.AVIATION: (For the 06z TAFs through 06z Friday Night)
Issued at 1141 PM CDT Thu Apr 24 2014
The cold front will pass through the St. Louis metro area between
05-06Z accompanied by MVFR and occasionally IFR cigs, light rain
and gusty nw winds. Clearing has just occurred at KCOU and should
occur around 07Z at KUIN and the St. Louis terminals between
09-10z. Thereafter VFR flight conditions/clear skies will
dominate with surface winds backing from northwesterly early
Friday morning to southwesterly by Friday afternoon.
Specifics for KSTL:
The cold front will pass through the terminal between 05-06Z
accompanied by a period of MVFR and occasionally IFR cigs, light
rain and gusty nw winds. Clearing should occur around 09z. Thereafter
VFR flight conditions/clear skies will dominate with surface
winds backing from northwesterly early Friday morning to
southwesterly on Friday afternoon.