Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 310244
AFDLSX

Area Forecast Discussion...Updated
National Weather Service Saint Louis MO
944 PM CDT SAT JUL 30 2016

.UPDATE...
Issued at 926 PM CDT Sat Jul 30 2016

A quick update to clean up the rest of tonight. With some
instability across the srn portions of the CWA and an approaching
s/w, believe an isod storm may still develop overnight. Otherwise,
the focus will be across the Plains with the development of an MCS
expected to approach the wrn portions of the CWA after sunrise
thru the morning hours.

&&

.SHORT TERM...  (Through Late Sunday Afternoon)
Issued at 330 PM CDT Sat Jul 30 2016

A weak trof of low pressure is oriented east-west over the area.
It`s difficult to discern exactly where the trof is, but from wind
direction and dewpoint gradient it looks like it`s across southeast
Missouri, just south of Farmington.  Daytime heating combined with a
shortwave aloft has allowed a fairly extensive cu field to develop
over the area.  Could see an isolated shower or storm before sunset,
but any convection that develops should dissipate quickly after 01Z.
Some low clouds/fog possible again tonight.  Ensemble guidance is
particularly bullish over west central and parts of southwest
Illinois as is the operational MOS guidance.  There`s been some
mixing and drying today, so am not sure about the fog potential. Did
mention fog in the Quincy TAF, but will hold off on mention in the
public forecasts for now and pass on fog ideas to evening shift.

Next item of interest is potential for thunderstorms on Sunday. Mass
fields on the GFS, NAM, and ECMWF point more to thunderstorms over
western/southwestern Missouri as a weakening MCS moves moves into
the state from the Great Plains.  Low level riding over eastern
Missouri and Illinois will likely keep the precipitation to our
west, but models do move the MCV from this dying system over our
area in the afternoon which could allow some convection to build in
spite of the ridging.  Think the chance PoPs in the going forecast
look good, and only made small tweaks to blend with neighboring
offices.

Carney

.LONG TERM...  (Sunday Night through Next Saturday)
Issued at 330 PM CDT Sat Jul 30 2016

(Sunday Night - Monday)

H500 heights will begin to rise overhead as an upper level RIDGE to
our southwest builds.  At the surface, the frontal boundary that
has been to our south for quite some time will buckle
northeastward and move thru our region during this period as a
warm front.  The combination of NW flow aloft streaming upper
level disturbances as in previous periods and low level focus
provided by the warm front will give us decent rain chances,
especially for northeast MO and areas near the MS river.

Lurking just to the southwest of these decent rain chances will be
plenty of heat that will be ready to fill the void as the better
rain chances steadily slide eastward.  Depending on exactly how the
rain evolves and how fast it exits to the east on Monday, we may need
heat related headlines in some parts of our region.  One area that
is being looked at closely for this are sections of central MO.
Currently, it looks like the rain and clouds will linger long enough
elsewhere to keep the heat away.  Leaned towards the higher MET MOS
values for central MO for max temps Monday, while going with a MOS
blend elsewhere.

(Tuesday - Friday)

Upper RIDGE expected to dominate our region for this period.  At
some point late in the week, a TROF will try to develop over eastern
North America and should tilt the mid level flow enough from the NW
to allow a surface cold front down into our region.  Current
indications are that this will not be until Saturday.

In the meantime, looks like rain chances will be small during this
period with somewhat better chances during the diurnally favorable
afternoon and early evening as much of the better organized and
higher rain chances should be further to the north and northeast.

With the surface front moving to our north by Tuesday and remaining
there thru Friday afternoon, high heat and humidity is expected to
make a return for much of our region, with max temps in the 90s
and heat index values peaking from 100 to 110 each day.  Heat
headlines are looking increasingly likely during this period and will
be specifically addressed as we get a bit closer.  In the meantime,
this will be highlighted in outlook-type products.

(Next Saturday)

Most models agree on mid and upper flow being sufficiently from the
NW to allow a cold front into a good part of our region this period
and will bring into significant doubt on whether the high heat and
humidity will continue from earlier in the week, either from the
cooler air filtering south or the higher rain chances.

TES

&&

.AVIATION...  (For the 00z TAFs through 00z Sunday Evening)
Issued at 615 PM CDT Sat Jul 30 2016

Predominantly VFR and dry thru the period. However, latest
guidance suggests fog may develop again impacting UIN late
tonight into Sun morning. Have kept visbys in the MVFR range for
now, but if trends continue, IFR conditions are possible during
that time as well. COU may be impacted by TSRA, mainly Sun
afternoon. However, chances are too low attm. region appears to
have dried out enuf that fog shud not be a problem at STL/SUS/CPS
tonight. Otherwise, winds will be light and vrb gradually becoming
sly to sely on Sun as a wrmfnt approaches the region, but
remaining light.

Tilly

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&

$$

WFO LSX


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