Area Forecast Discussion
Issued by NWS St. Louis, MO

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
FXUS63 KLSX 020335

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1035 PM CDT Sat Oct 1 2022

.SHORT TERM...  (Through Late Sunday Night)
Issued at 239 PM CDT Sat Oct 1 2022

High surface pressure and ridging aloft across the central CONUS
continue to dominate our sensible weather. The ridge is buttressed
by two upper-level lows: one in the intermountain West that has
moved only minimally over the last 24 hours and the other over the
Southeast US associated with PTC Ian. While the low to the west of
the Mid-Mississippi Valley will eventually move downstream, a noted
lack of steering flow aloft will keep the current weather pattern in
place through the weekend. Near-normal temperatures, mostly sunny
skies, and no rain will make for a phenomenal weekend.


.LONG TERM...  (Monday through Next Saturday)
Issued at 239 PM CDT Sat Oct 1 2022

Starting Monday, the polar jet aloft will slowly seep south from
northern Canada as a longwave trough amplifies. The jet will begin
to interact with the upper-level low over the intermountain West,
allowing a more progressive flow pattern to develop. The low will
approach the Mid-Mississippi Valley at a snail`s pace, however,
which will make for continued sunny, tranquil weather until the
middle of the week. By Wednesday, the trough will finally be close
enough to the region to affect our weather. Winds will veer out of
the south as the system approaches on Wednesday, likely sending
temperatures into the upper 70s/low 80s (slightly above average).

Attention then turns to the approaching cold front and the increased
potential for light rain associated with that feature. Some
deterministic guidance depicts a slightly more amplified mid-level
trough than previous runs, which would lend more forcing to the
marginally-higher, though still limited, precipitable water
available for rain. Ensemble cluster analysis supports the slightly
more amplified solution as well. As a result, ensemble
probabilities of measurable rain are higher (50-60%) north of I-70
on Thursday morning/early afternoon, where the combination of
stronger forcing and higher PWATs exists. However, the
probabilities of higher totals (0.1" or higher) drop off to around
10% at the most. In short, while the chances of rain are higher,
showers will be widely-scattered at best and those who see rain
will likely not see much of it.

Behind the front, deep northwest flow aloft will allow several
rounds of shortwave impulses to enter the region. While very
limited available moisture looks to preclude much in the way of
precipitation going into next weekend, the story will turn to the
potential for frost. There remains some uncertainty about exactly
how cold the airmass will be, though ensembles agree that 850mb
temperatures going into next weekend will be upwards of 10C below
normal. That being said, they also uniformly paint us on the
periphery of the coldest air, which will stay further east across
the Great Lakes. This scenario is illustrated well in the Climate
Prediction Center`s latest 6-10 Day Temperature Outlook. The
coldest night of the period still looks to be Friday night into
Saturday morning, when temperatures drop into the 30s across the
region. A widespread freeze appears unlikely, though some
solutions bring temperatures around 32F, but many areas are
poised to see frost.


.AVIATION...  (For the 06z TAFs through 06z Sunday Night)
Issued at 1034 PM CDT Sat Oct 1 2022

No major changes to this set of TAFs. Surface ridge axis remains
overhead. So with clear skies, light winds, and cold air expect
radiational fog will develop in the river valleys towards
daybreak. Visibilities at KSUS and KCPS will drop down to MVFR at
times, then fog will lift and scatter out by 13z Sunday.
Otherwise, VFR flight conditions through the forecast period with
winds picking up from the east to northeast around 5 to 10 kts by
the afternoon.



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