Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 200545
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1145 PM CST Sun Nov 19 2017

.SHORT TERM...  (Through Late Monday Afternoon)
Issued at 109 PM CST Sun Nov 19 2017

No significant weather is expected through late Monday afternoon.
Initially northwest winds will become westerly to southwesterly
after a surface high pressure center has moved from the southern
plains into the southeastern CONUS. The change in wind direction
will bring a warmer air mass back into MO/IL, and highs on Monday
are expected to be in the mid-50s to lower 60s.

Kanofsky

.LONG TERM...  (Monday Night through Next Sunday)
Issued at 109 PM CST Sun Nov 19 2017

Although a couple of PV anomalies will move across the region over
the next several days, it will be difficult to produce widespread
precipitation due to a dry air mass. At best, some of the upper
disturbances may produce increased mid/high clouds.

Temperature swings are expected over the next several days due to
frontal passages, but no widespread precipitation is expected at
this time due to limited moisture. The first of these fronts will
be a cold front which is expected to move across MO/IL on Monday
night and Tuesday. Models solutions indicate that the colder air
lags the initial wind shift/pressure trough. Depending on the
speed of the colder air, some parts of MO/IL could experience
falling temperatures during the day on Tuesday. The tightening
pressure gradient and stronger wind speeds aloft will also bring
windy conditions to the region. Lows on Tuesday night will
probably be in the 20s within the post-frontal air mass, which
will be nearly 20 degrees cooler compared to the previous night. A
surface high pressure center settles across the region for
Wed/Thu before the influence of a developing low pressure system
over Canada brings a warmer air mass back into the region on
Friday ahead of another cold front which is forecast to move
through the region on Fri night/Sat.

Kanofsky

&&

.AVIATION...  (For the 06z TAFs through 06z Monday Night)
Issued at 1134 PM CST Sun Nov 19 2017

The latest data continues to support much of the previous
forecast. VFR flight conditions will persist through the period
with bouts of high clouds streaming across the area. The main
element of concern will remain wind. South surface winds have
slowly begun to increase across parts of central MO late this
evening, and will remain light but also increase a bit into
eastern MO and western IL. LLWS remains a concern overnight until
about mid-morning on Monday. A southwesterly LLJ based near 1,000
feet AGL has already developed across eastern KS into northwest
MO. This LLJ will shift east-southeast overnight bringing LLWS
conditions, and the southeast fringe of the jet now looks like it
will move into western sections of the St. Louis metro during the
predawn hours. After 15z, vertical mixing should bring an end to
the LLWS and increasing and gusty S-SW surface winds will
commence and last into the afternoon.

SPECIFICS FOR KSTL:

VFR flight conditions will persist through the period with bouts
of high clouds streaming across the area. The main element of
concern will remain wind and now LLWS. A southwesterly LLJ based
near 1,000 feet AGL has already developed across eastern KS into
northwest MO. This LLJ will shift east-southeast overnight
bringing LLWS conditions as the southeast fringe of the jet moves
into the area during the predawn hours. After 15z, vertical
mixing should bring an end to the LLWS, and increasing and gusty
S-SW surface winds will commence and last into the afternoon.

Glass

&&

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

$$

WFO LSX



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