Area Forecast Discussion
Issued by NWS St. Louis, MO

Home | Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary On
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 46 47 48 49 50
000
FXUS63 KLSX 191741
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
1241 PM 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.

Tilly

.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
70s.

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.

Tilly
&&

.AVIATION:  (For the 18z TAFs through 18z Wednesday Afternoon)
Issued at 1241 PM CDT Tue Aug 19 2014

Showers and thunderstorms have moved east of taf sites, but could
still see some redevelopment as front moves through. Confidence is
low on coverage and timing, so kept tafs dry for now. Otherwise,
south to southwest winds to become westerly behind boundary. Then
winds to become light and variable this evening, before picking
back up from the southwest on Wednesday. Some models indicating
activity firing north of frontal boundary as it lifts back north
through region later tonight. But once again confidence on timing
and coverage hard to pin down, so kept tafs dry.

Specifics for KSTL:
Showers and thunderstorms have moved east of metro area, but could
still see some redevelopment as front moves through. Confidence is
low on coverage and timing, so kept taf dry for now. Otherwise,
south to southwest winds to become westerly behind boundary after
20z Tuesday. Then winds to become light and variable by 01z Wednesday,
before picking back up from the southwest 17z Wednesday. Some models
indicating activity firing north of frontal boundary as it lifts
back north through region later tonight. But once again confidence
on timing and coverage hard to pin down, so kept taf dry.

Byrd
&&

.LSX WATCHES/WARNINGS/ADVISORIES:
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.

&&

$$
WFO LSX




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