Area Forecast Discussion
Issued by NWS St. Louis, MO

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156
FXUS63 KLSX 302030
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
330 PM CDT SAT JUL 30 2016

.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 18z TAFs through 18z Sunday Afternoon)
Issued at 1239 PM CDT Sat Jul 30 2016

A weak trof of low pressure over the area is producing scattered
to broken clouds with primarily VFR bases across the area. There
are still some pockets of MVFR across parts of northern MO/west
central IL...but those clouds should continue to rise. There may
be some isolated showers or thunderstorms this afternoon across
parts of the area...most likely along and south of I-70. Any
storms that do form should dissipate quickly after 00-01Z. VFR
conditions should prevail otherwise. There continues to be some
concern for fog and low stratus tonight. The best chances look to
be over west central and parts of central Illinois.

SPECIFICS FOR KSTL:

Cumulus with VFR bases are expected to prevail this afternoon.
There`s a chance there could be some isolated showers or
thunderstorms in the vicinity of the terminal through about
00Z...but chance is only about 15-20% so I did not mention it the
TAF. VFR conditions are expected tonight.

Carney

&&

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

$$

WFO LSX



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