Area Forecast Discussion
Issued by NWS St. Louis, MO
FXUS63 KLSX 190911
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
411 AM CDT Tue Aug 19 2014
.SHORT TERM: (Through Tonight)
Issued at 251 AM CDT Tue Aug 19 2014
Main focus thru this period will be precip chances.
A weak cdfnt continues to approach the area this morning. A weak
sfc low along the fnt is located over nern KS which is no doubt
helping the ongoing convection. Mdls are not handling the ongoing
convection well and therefore have lower confidence in the going
forecast. However, the ECMWF and local WRF seem to have the best
handle currently. Believe storms will dissipate as they approach
central MO later this morning, but some question remains as to how
far E the storms will travel before doing so. With the fnt
lingering in the region, anticipate another round of storms
developing later today. The main question is timing. Have
therefore kept Low chance PoPs thru much of the day, but after
this morning, focused PoPs for late this afternoon. An approaching
mid level wave may help erode the cap sooner. Regardless, ample
insolation today combined with dewpoints reaching the low 70s shud
allow for MLCAPE in the 2 to 3k J/kg range. This trof will also be
responsible for a small area of enhanced shear along the fnt.
These storms shud shift ewd early this evening. However, as the
LLJ increases tonight, more storms will be possible.
With questions in timing and location of convection, made only
minor changes to the prev forecast for temps today and tonight. In
general, trended twd the cooler guidance for nrn and ern portions
of the CWA while trending warmer across western, southern and
central portions of the CWA.
.LONG TERM: (Wednesday through Monday)
Issued at 338 AM CDT Tue Aug 19 2014
Focus thru this period will be temps thru the period.
Mdls pull the sfc fnt NE of the area tomorrow evening. Can not
rule out isod to sct storms as this fnt lifts newd. Beyond
tomorrow night, chances for precip are nearly non-existent until
next week, but more on that later.
The GEM is currently the only mdl that does not build the upper
ridge into the region. Have therefore ignored the GEM for this
forecast package and trended twd an overall compromise of the
remaining guidance. Thurs still appears to be the start of the
warmest day and continued with a persistence forecast thru the
weekend. The rainfall late last week and over the weekend will
help boost evapotranspiration boosting the dewpoints well into the
Mdl solns begin to diverge late this weekend as the upper low over
the CA coast finally ejects into the Plains. The GFS suggests the
upper ridge will break down sooner than the ECMWF. Regardless, the
ECMWF also breaks down the ridge by Mon which may allow for the
sfc fnt to approach close enuf for storms to impact at least the
nrn portions of the CWA late Sun and thru Mon. With mdls in
agreement of the ridge breaking down by Mon, have slightly cooler
temps for Mon and will not extend the going headline beyond Sun.
Areas beyond the current watch may eventually need some sort of
heat headline due to a combination of temps in the 90s and high
dewpoints. Will hold off with additional headlines for now.
.AVIATION: (For the 06z TAFs through 06z Tuesday Night)
Issued at 1053 PM CDT Mon Aug 18 2014
A complex of thunderstorms may develop and drop southeastward
through west central and southwest MO late tonight, possibly
impacting or at least grazing COU. There may also be more
scattered showers/storms moving through UIN area late tonight
ahead of a weak surface trough dropping southeastward through
northwest MO and southeast IA. Will include VCSH or VCTS in the
UIN and COU tafs late tonight/early Tuesday morning. Should be
mid-high level warm air advection cloudiness along with convective
debris cloudiness late tonight/Tuesday morning. Should also be
scattered diurnal cumulus clouds again late Tuesday morning and
afternoon. Mainly a light sly surface wind late tonight, then
gradually strengthening on Tuesday and veering around to a w-swly
direction by late Tuesday afternoon. There will be fog late
tonight/early Tuesday morning in SUS and CPS.
Specifics for KSTL: Mid-high level clouds late tonight and
Tuesday morning. Weakening convection may impact STL Tuesday
morning, but will leave the STL taf dry for now as the better
chance of showers/storms should be north and west of STL late
tonight and west-southwest of STL Tuesday morning. Scattered
diurnal cumulus clouds should develop again late Tuesday morning
and afternoon. Light sly surface winds late tonight, then veering
around to a swly direction Tuesday and increasing to about 10-12 kts
Tuesday afternoon. The wind will become light again Tuesday night.
.PRELIMINARY POINT TEMPS/POPS:
Saint Louis 91 74 95 76 / 30 40 20 20
Quincy 88 68 92 71 / 30 30 20 30
Columbia 93 71 96 73 / 40 40 20 10
Jefferson City 94 72 97 73 / 40 40 20 10
Salem 87 69 91 74 / 30 30 20 30
Farmington 91 71 94 73 / 30 30 20 10
MO...EXCESSIVE HEAT WATCH from Wednesday afternoon through Sunday
evening FOR St. Louis City MO-St. Louis MO.
IL...EXCESSIVE HEAT WATCH from Wednesday afternoon through Sunday
evening FOR Madison IL-St. Clair IL.