340
FXUS63 KLSX 092246
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
546 PM CDT Tue Jul 9 2024

.KEY MESSAGES...

- Rain chances will diminish from southwest to northeast through
  this evening. Additional rainfall amounts of roughly 1-3" are expected
  mainly over eastern Missouri and southwestern Illinois with
  locally higher amounts possible.

- The threat for strong to severe thunderstorms mainly capable of tornadoes
  is low across portions of far southwestern Illinois and far
  southeastern Missouri, but the more favorable conditions for
  this threat is expected to remain southeast of the CWA.

- Relatively calmer weather along with cooler temperatures will
  persist Wednesday through the early weekend before temperatures
  warm above normal by the end of the weekend into early next
  week.


&&

.SHORT TERM...  (Through Late Wednesday Night)
Issued at 246 PM CDT Tue Jul 9 2024

The remnants of Beryl continue to move through the region, with the
center of the system currently over the Missouri Bootheel. North of
the center, a widespread shield of light to moderate rainfall is
occurring across much of the CWA. Rainfall rates have generally been
0.25-0.5"/hour, with mainly nuisance flooding and ponding on roadways
occurring in addition to rises on area creeks and streams. As we get
further into the afternoon, there is a low chance (20-30%) that the
atmosphere destabilizes enough to produce convective elements
through early this evening within the broader rain shield that yield
higher rainfall rates and a threat of flash flooding. Therefore,
there are no plans to adjust the current Flood Watch.

On the note of convection, there remains a threat of strong to
severe storms mainly capable of tornadoes over the far eastern-
southeastern extent of our CWA. However, given the track of the post-
tropical low, climatology and the currently expected parameter space
favors that this threat will remain to the east-southeast of the
CWA.

This evening and tonight, Beryl`s remnants will push east-
northeastward, with rain exiting the area through late tonight/early
tomorrow morning. As the system begins departing the CWA, guidance
consensus is that mid to low-level winds will increase, with some
mixing down to the surface. This is expected to produce gusts up to
around 35 mph this evening mainly along and east of the Mississippi
River. Fog also can`t be ruled out tonight, mainly across portions
of central Missouri where clearing may occur prior to sunrise
tomorrow morning.

Tomorrow, Beryl`s remnants will continue northeastward and merge
with an upper-level trough. A shortwave rounding the backside of
this trough will move through the Midwest during the afternoon and
evening, providing enough forcing to produce widely scattered
convection mainly north of I-70. The airmass over this portion of
the CWA will be quite unstable, with MUCAPE forecast to reach
roughly 2,000 J/kg. However, deep-layer shear will be weak, with
values topping out around 20 kts. Given the amount of instability,
small hail can`t be ruled out in the strongest cores, but a
relatively high melting layer and lack of shear should limit storm
strength and hail size.

Elmore

&&

.LONG TERM...  (Thursday through Next Tuesday)
Issued at 246 PM CDT Tue Jul 9 2024

At the beginning of the period, guidance consensus is that the
upper-level trough will be gradually moving eastward, placing the
Middle Mississippi Valley beneath northwesterly flow. Deterministic
guidance shows a subtle shortwave digging equatorward on the
backside of this trough through the Midwest. Given the deep
northwesterly flow in place over the region, robust moisture return
prior to the passage of this shortwave is not expected. Even so,
guidance consensus is that there will be just enough to produce a
low chance (30%) of rain, with ensembles focusing this rain mainly
somewhere along and north of I-70 during the afternoon.

For Friday and Saturday, additional rounds of rain are possible as a
ridge expands eastward across the CONUS and into the Middle
Mississippi Valley, prompting a warm front to move through the
region amidst passing weak shortwaves along the periphery of the
ridge. However, the signal for rain remains weak among guidance,
prompting a low chance (20%) for rain Friday and Saturday afternoon.

As the ridge builds in further on Sunday and early next workweek,
warm air will advect into the region via southerly to southwesterly
low-level flow. In turn, 850 mb temperatures top out in the mid-20s
degrees C per ensemble consensus. Climatologically, this favors
surface temperatures in the mid to upper 90s assuming deep mixing,
and these hot surface temperatures are within the 25th-75th
percentile of ensemble guidance. How hot the region stays toward the
middle of next week is uncertain, as guidance is split on the
southward progression of a trough digging equatorward somewhere over
the eastern CONUS. If the trough is able to dig further south,
temperatures will cool to some degree compared to earlier in the
week, but if the ridge holds out over the region, temperatures will
remain as warm into the middle of next week as they are for earlier
in the week.

Elmore

&&

.AVIATION...  (For the 00z TAFs through 00z Wednesday Evening)
Issued at 540 PM CDT Tue Jul 9 2024

There are a few items of interest in the 00Z TAF cycle. First,
lingering stratiform rain is gradually diminishing this evening,
but light rain may intermittently impact local terminals during
the first few hours of the period. A few embedded convective cells
may also linger into the evening, but are expected to diminish by
morning. Heavier bursts of rain are possible within these cells,
but confidence is low that they will directly impact local
terminals.

Some patchy fog may also develop in a few areas overnight and
early tomorrow morning, particularly in central MO and possibly
UIN where lighter winds are expected. More persistent northerly
winds at STL/SUS/CPS will likely limit fog development, but if
winds weaken faster than anticipated, fog will be possible here as
well.

VFR conditions are expected during the day tomorrow, but a
scattered to broken field of cumulus clouds is expected. A few
showers and weak thunderstorms will also be possible at UIN late
in the afternoon.

BRC


&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Flood Watch until 4 AM CDT Wednesday for Jefferson MO-Lincoln MO-
     Saint Charles MO-Saint Louis City MO-Saint Louis MO-Sainte
     Genevieve MO.

     Flood Watch until 10 PM CDT this evening for Audrain MO-Boone MO-
     Callaway MO-Cole MO-Crawford MO-Franklin MO-Gasconade MO-
     Iron MO-Madison MO-Moniteau MO-Montgomery MO-Osage MO-
     Reynolds MO-Saint Francois MO-Warren MO-Washington MO.

IL...Flood Watch until 4 AM CDT Wednesday for Bond IL-Calhoun IL-
     Clinton IL-Fayette IL-Greene IL-Jersey IL-Macoupin IL-
     Madison IL-Marion IL-Monroe IL-Montgomery IL-Randolph IL-
     Saint Clair IL-Washington IL.

&&

$$

WFO LSX