Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion...updated aviation 
National Weather Service St Louis MO
646 am CDT Wed Aug 20 2014

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 Illinois. 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 southeast 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 Iowa and far NE MO shud
move sewd impacting mainly the nrn portions of the County Warning Area 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 Illinois. 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/European model (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/European model (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 thunderstorms and rain as a S/W approaches the region from
the southeast.


Aviation: (for the 12z tafs through 12z Thursday morning)
issued at 640 am CDT Wed Aug 20 2014

Visual flight rules expected for all taf sites except KUIN.
Scattered morning thunderstorms there should end by noon however.
Otherwise all taf sites will see relatively light southwest winds
today, with some VFR clouds moving in overnight, but no rain is

Specifics for kstl: visual flight rules expected through this taf
period. Southwest winds around 10 mph today will continue tonight
as a deck of VFR clouds moves in.



Preliminary point temperatures/pops:
Saint Louis 95 75 96 77 / 30 10 5 10
Quincy 89 71 93 73 / 50 20 10 10
Columbia 94 73 96 74 / 20 10 5 10
Jefferson City 94 73 97 74 / 10 10 5 10
Salem 90 72 92 73 / 20 20 10 10
Farmington 94 70 95 72 / 20 10 5 5


Lsx watches/warnings/advisories:
MO...heat advisory from 1 PM this afternoon to 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 from 1 PM this afternoon to 7 PM CDT
Sunday for St. Louis city MO-St. Louis MO.

Illinois...heat advisory from 1 PM this afternoon to 7 PM CDT Sunday for
Bond Illinois-Calhoun Illinois-Clinton Illinois-Greene Illinois-Jersey Illinois-Macoupin
Illinois-Marion Illinois-Monroe Illinois-Randolph Illinois-Washington Illinois.

Excessive heat warning from 1 PM this afternoon to 7 PM CDT
Sunday for Madison IL-St. Clair Illinois.



Weather forecast office lsx

National Weather Service Glossary of Abbreviations