231
FXUS63 KLSX 080342
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1042 PM CDT Sat Sep 7 2024

.KEY MESSAGES...

- Cool, below normal high temperatures on Sunday will warm up to above
  normal temperatures by mid week.

- Beneficial rainfall is unlikely through the period.


&&

.SHORT TERM...  (Through Late Sunday Night)
Issued at 246 PM CDT Sat Sep 7 2024

Latest water vapor imagery shows the region in northwesterly flow
aloft with an upper-level low over the eastern Great Lakes and an
upper-level ridge over the western CONUS. At the surface, high
pressure is present across the region with the center over the Upper
Mississippi River Valley. Northwesterly flow aloft and the center of
the high to our north is helping establish northerly CAA into the
CWA. This CAA regime is keeping temperatures in the upper 60s - low
70s and dewpoints in the mid 30s to low 40s today.

The surface high center will make its way over the CWA overnight.
So, with little to no cloud cover and light winds, sufficient
radiational cooling will result in low temperatures to drop in the
40s. It is not out of the realm of possibilities that low-lying and
more sheltered locations could see temperatures in the 30s. The
forecasted lows temperatures at two of our climate locations (Quincy
and Columbia) are within a few degrees of record lows for September
8th.

Overnight river valley fog cannot be ruled out due to cool
temperatures, relatively warm river water, clear skies, and light
winds. However, current ensemble guidance soundings are showing that
the airmass is much too dry so I have not included any river valley
fog at this time.

By Sunday, the low-level high will dominate over the region with
light winds and sunny skies. Temperatures on Sunday will be a few
degrees warmer than today as CAA will no longer be present.

MMG/Pfahler

&&

.LONG TERM...  (Monday through Next Saturday)
Issued at 246 PM CDT Sat Sep 7 2024

Ensemble guidance is in consensus that the Western CONUS upper-level
ridge will expand eastwards starting Monday. At the same time, the
low-level high will also begin pushing east out of the region,
reintroducing low-level southerly flow. This will be the beginning
of our warm up for the upcoming week. Despite this southerly flow,
moisture will remain limited within region with the low-level high
extending into the Mid- and Lower-Mississippi River Valley. The
southerly flow, abundant sunshine, and a lack of deep moisture, high
temperatures are forecast to be near normal (low 80s) on Monday and
increase to around 10 degrees above normal (mid 80s-low 90s) by
Wednesday. Confidence in these temperatures is relatively high with
less than a 5 degree spread between the NBM 25th and 75th
percentiles Monday through Wednesday.

Guidance begins to differ for the second half of the work week as
some deterministic guidances indicate the remnants of a tropical
disturbance, currently in the western Gulf of Mexico, to track up
the Mississippi River Valley, leading to a slight uptick in low to
mid level moisture. Some guidance is hinting that this could be the
next shot at rainfall, however rain will be very conditional on the
evolution of the tropical disturbance. Should the remnants of the
system make it into our region, the current forecast reflected low
rain chances (15% across southeast Missouri and southwest Illinois)
and this is supported with less than 30% of ensemble guidance
members indicating measurable rain (0.01 inch) towards the end of
the week. The primary "impacts" will likely be increased cloud
cover. How much cloud cover we do see will have an impact on how
warm temperatures get. This is reflect in the NBM interquartile
range with a 7+ degree temperature spread.

MMG/Pfahler

&&

.AVIATION...  (For the 06z TAFs through 06z Sunday Night)
Issued at 1041 PM CDT Sat Sep 7 2024

Calm winds tonight will not increase much on Sunday, likely
staying light and variable through the day under a clear sky.
There is at least a little bit better chance of river valley fog
Sunday night into Monday morning.

Kimble

&&

.CLIMATE...
Issued at 309 AM CDT Fri Sep 6 2024

RECORD LOWS ON 9/8

SITE | RECORD
KSTL | 42 (1986)
KUIN | 40 (1986)
KCOU | 43 (1986)


&&

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

$$

WFO LSX