Area Forecast Discussion
Issued by NWS St. Louis, MO

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818
FXUS63 KLSX 161919
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
219 PM CDT Fri Aug 16 2024

.KEY MESSAGES...

- A few chances for isolated, weak showers and thunderstorms across
portions of the area through tomorrow afternoon, but the majority of
the area will be dry.

- Sunday and beyond will be largely dry with below normal
temperatures.



&&

.SHORT TERM...  (Through Late Saturday Night)
Issued at 219 PM CDT Fri Aug 16 2024

A weak cold front is slowly making its way southeastward through the
forecast area, with little modification to our sensible weather
behind the front. Meanwhile, aloft a trough is churning over the
Great Lakes region, with a ridge centered over New Mexico/west-
Texas, leaving the mid-Mississippi Valley in northwesterly flow.
Despite the weak moisture convergence along the front, a small mid-
level disturbance moving across the region has a 20% chance of
generating a few showers or isolated thunderstorm along and south of
the front through the early evening. The weakness of the synoptic
features increases confidence that if anything does develop, it will
be short lived.

Tonight, an MCS (ongoing across central Kansas) will strengthen and
organize, sliding into southwest Missouri overnight along the
northwesterly Corfidi vectors. While this area of showers and
thunderstorms is expected to stay largely outside of our forecast
area, I cannot rule out portions of our central Missouri counties
getting clipped by a few showers and isolated thunderstorms
overnight.

As this MCS passes by, a secondary cold front will start sliding
through the forecast area tomorrow morning. While forcing for ascent
aloft and at the surface will be weak, I cannot rule out a weak
diurnal shower or thunderstorm across southeast Missouri and
southern Illinois ahead of the front during the afternoon. This
airmass south of the front will be moist and unstable with 1000-2000
J/kg of MLCAPE during the afternoon, favorable for thunderstorm
development if enough lift can force one. The secondary front will
usher in the expected shift in sensible weather, bringing seasonally
cool and dry conditions back to the region.


MRM

&&

.LONG TERM...  (Sunday through Next Friday)
Issued at 219 PM CDT Fri Aug 16 2024

The mid-level trough will end the weekend over the Great Lakes
region, but shift eastward through the first half of next week. At
the same time the ridge over the southern Rockies will expand. The
resulting northwest flow over the mid-Mississippi Valley, combined
with a large surface high, will advect a cooler, drier airmass into
the region through much of next week. 850mb temperatures will drop
about 5-6 degrees with the post-frontal airmass from where they are
now. Confidence is high in this occurrence, with the ensemble spread
in 850 mb temperatures only 1-2 degrees into next week. Surface
temperatures will respond in kind, topping out about 5 degrees below
average for this time of year through mid-week.

Into the second half of next week the surface the high will shift
east, throwing the region back into southerly surface flow. This
will start a gentle warming trend that we will see through the
remainder of the period.

MRM

&&

.AVIATION...  (For the 18z TAFs through 18z Saturday Afternoon)
Issued at 1219 PM CDT Fri Aug 16 2024

Dry and VFR flight conditions will continue through the TAF
period, expect for a short period of VCSH at the mid-Missouri
terminals tonight. There is a 20% chance for showers along the
northern edge of a complex of thunderstorms moving through SW
Missouri that could impact the terminals (KCOU, KJEF). Confidence
isn`t yet high enough to include more than a VCSH at this point.

A cold front will move through the terminals tomorrow, turning
winds to the northwest.

MRM

&&

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

$$

WFO LSX