Area Forecast Discussion
Issued by NWS St. Louis, MO

Home | Current Version | Previous Version | Text Only | 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
FXUS63 KLSX 201749

1249 PM CDT Wed Aug 20 2014

Issued at 1119 AM CDT Wed Aug 20 2014

Clouds and precip blanketing the eastern portion of the CWFA have
made for a challenging temperature forecast this morning. Have
updated to go cooler from around Quincy down southeast to
Litchfield/Salem areas. Heat advisory across Greene, Jersey,
Macoupin, and perhaps Bond and Marion counties will likely be a
bust today. However, hate to cancel the advisory in these areas
given the possibility that we could still clear out and heat up
significantly this afternoon. Additionally, the advisory still
looks pretty good for Thursday through Sunday in those areas. Will
just hang onto it for the time being. Short range guidance
continues to hint at some isolated storms bubbling up this
afternoon due to diurnal heating. Outflow boundaries from this
morning`s storms may provide enough focus to allow these isolated
storms to form, so will also hang on to slight chance PoPs.



.SHORT TERM:  (Through Tonight)
Issued at 240 AM CDT Wed Aug 20 2014

Main focus thru the period will be PoPs, which will influence
temps today and therefore, also headlines.

There is still some uncertainty regarding heat headlines thru the
weekend, but will go ahead and issue a Heat Advisory for portions
of central and ern MO and SW IL. This expansion is due to expected
heat index values of 100+ for at least 4 days. However, values of
105+ degrees may be possible across the adv area, especially Thurs
and Fri. This adv may need to be expanded to include counties not
currently in the adv. However, since criteria is not expected to
be reached today, will handle that area tomorrow.

Dewpoints are the main question as portions of central and SE MO
have been mixing out well the past few days. These are the areas
that have seen the least rainfall lately and generally mix out
well during the day. Have therefore kept the ern Ozarks out of the
adv for now.

As for PoPs...the HRRR, local 4km WRF and the 4km NSSL WRF seem
to be handling the current convection fairly well. Have therefore
tailored PoPs for the remainder of today and into tonight twd
those solns. In general, ongoing storms over IA and far NE MO shud
move sewd impacting mainly the nrn portions of the CWA this
morning. Mdls suggest storms developing this afternoon over the
ern Ozarks or along the MS Rvr, but these shud remain isod. For
tonight, storms shud remain focused along the fnt and where 850mb
convergence is greatest. Believe the best chances will remain NE
of the CWA, but have kept slight chance PoPs along the nern
counties due to uncertainty.

A lot of questions remain regarding temps today due to possible
convection. However, have trended above the cooler MOS, but stayed
below the warmer MOS. Overall, this verified fairly well
yesterday. Temps for tonight are a little more complex as mixing
shud be greater across central MO. However, have trended above the
warmer MOS due to swly winds thru the night.

.LONG TERM:  (Tonight through Tuesday)
Issued at 338 AM CDT Wed Aug 20 2014

Focus thru the period will be temps and the ongoing heat

Much of the questions regarding dewpoints and headlines continues
thru the weekend as mentioned above and will therefore not dwell
on the uncertainties here. Dewpoints across the ern Ozarks and
perhaps into central MO are expected to mix out during the
afternoon. The rainfall over the past few days shud help drive up
dewpoints across NE MO and much of SW IL. Overall not much change
to the prev forecast as it appears to be on track.

The GEM continues to be an outlier especially beyond Sat and have
therefore trended twd the other guidance. The local WRF and to
some degree the NAM also trend away from a GFS/ECMWF compromise
for Fri and beyond and have therefore trended away from these
solns as well.

The main changes from yesterday are how this heat event comes to
an end. The GFS/ECMWF now suggest the upper ridge, while weaker,
will remain in place into Tues. However, both mdls prog cooler
850mb and 700mb temps which shud still result in cooler temps as
well as an increase in precip chances. These precip chances will
be mainly afternoon pulse TSRA as a s/w approaches the region from
the SE.


.AVIATION:  (For the 18z TAFs through 18z Thursday Afternoon)
Issued at 1239 PM CDT Wed Aug 20 2014

Tricky aviation forecast this afternoon...primarily along and east
of the Mississippi. Outflow boundary from this morning`s
thunderstorms over Illinois is approaching the STL Metro area at
this time. Wind will shift to a northeasterly direction as the
boundary passes. This will cause a runway swap for the Metro
terminals. Expect outflow boundary to stall over eastern Missouri
at some point, tho exactly where is uncertain. Next problem will
be the probability that thunderstorms will form along the boundary
this afternoon. At this time, expect there will be isolated storms
along the boundary, however am not confident enough there will be
great enough coverage to include in TAFs at this time. Any storms
that do form should dissipate within an hour or two of sunset this
evening. There will be another chance for storms overnight
tonight, primarily over central Illinois as the low level jet
pushes more warm/moist air into the region. Expect VFR flight
conditions through the period outside of thunderstorms.

Specifics for KSTL:



MO...HEAT ADVISORY until 7 PM CDT Sunday FOR Audrain MO-Boone MO-
     Callaway MO-Cole MO-Franklin MO-Gasconade MO-Jefferson MO-
     Lincoln MO-Madison MO-Moniteau MO-Montgomery MO-Osage MO-
     St. Charles MO-St. Francois MO-Ste. Genevieve MO-Warren MO.

     EXCESSIVE HEAT WARNING until 7 PM CDT Sunday FOR St. Louis City
     MO-St. Louis MO.

IL...HEAT ADVISORY until 7 PM CDT Sunday FOR Bond IL-Calhoun IL-
     Clinton IL-Greene IL-Jersey IL-Macoupin IL-Marion IL-Monroe
     IL-Randolph IL-Washington IL.

     EXCESSIVE HEAT WARNING until 7 PM CDT Sunday FOR Madison IL-St.
     Clair IL.



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