014
FXUS63 KLSX 180338
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1038 PM CDT Wed Jul 17 2024

.KEY MESSAGES...

- Dry weather along with well-below normal temperatures is forecast
  through Saturday.

- Temperatures are expected to moderate slightly heading into next
  week. Rain chances also return, but at this time look to be
  focused in the afternoon/early evening each day and largely
  unorganized (not widespread, low chance for heavy rainfall/flash
  flooding and severe weather).


&&

.SHORT TERM...  (Through Late Thursday Night)
Issued at 205 PM CDT Wed Jul 17 2024

Isolated to scattered showers continue along the cold front. A few
lightning strikes are also expected over parts of southeast
Missouri through the late afternoon hours given 1000+ J/kg of CAPE.
This boundary is progressing to the southeast, and is expected to
clear the CWA just before dusk early this evening. Further to the
northwest, there is a dewpoint gradient with an uptick in
northerly surface winds. This lower humidity and cooler air mass
will infiltrate the remainder of the area through early overnight.

The strength of this incoming air mass is certainly notable for
mid/late July. The surface anticyclone (1022+ hPa) over the Upper
Midwest on Thursday is above the 99th percentile of climatology.
In terms of 850-hPa temperatures (+9 to +12C), those values are
forecast to be below the 2nd percentile. This impressively cool
air mass will first enter northern sections of the area tonight,
with lows in the mid 50s (~10 degrees below normal). Further
southeast, lows in the low to mid 60s are expected. Thursday`s
highs are expected to be in the upper 70s to near 80 degrees or
about 10 degrees below normal across the entire area. Thursday
night`s lows should be cooler than tonight in most locations, with
more widespread mid to upper 50s forecast.

Gosselin
&&

.LONG TERM...  (Friday through Next Wednesday)
Issued at 205 PM CDT Wed Jul 17 2024

(Friday - Saturday)

There is very little change in the synoptic pattern heading into
early this weekend as the strong surface high very slowly moves
eastward. Dry weather along with below normal temperatures are
expected to continue, though temperatures should moderate
slightly.

(Saturday Night - Next Wednesday)

Ensemble guidance is in good agreement that a midlevel shortwave
trough will move southward out of the northern Plains Saturday
night. This feature is then expected to become cutoff from the mean
flow across southeast Canada and become quasi-stationary. The mid-
Mississippi Valley is forecast to be downstream/east of this cutoff
low, with areas of vorticity pinwheeling northeast around
the eastern periphery of the midlevel anticyclone. This pattern
should mean a return of shower and thunderstorm chances to the
area. At this early juncture, chances will likely be at least
partially influenced by daytime heating/when instability is
maximized. Deterministic guidance at this time are not showing a
strong low-level jet any of the nights. In addition, wind shear
and instability do not look particularly high nor does precipitable
water values (only slightly above normal). This all indicates
likely unorganized, weaker convection that should not be a high
threat for severe weather nor heavy rainfall/flash flooding. Due
to the increase in cloud cover and rain chances, daytime high
temperatures should stay below normal (in the 80s) though
nighttime readings should moderate back into the 60s to near 70
degrees (very close to seasonal normals).

Gosselin
&&

.AVIATION...  (For the 06z TAFs through 06z Thursday Night)
Issued at 1037 PM CDT Wed Jul 17 2024

VFR flight conditions through the forecast period. Otherwise, will
see a few diurnal cu during the late morning through afternoon
hours. Light north winds will veer to the northeast by mid morning
on Thursday.

On another note, still confident that there will be some river
valley fog in parts of southeast Missouri, but well south of the
any terminals.

Byrd
&&

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

$$
WFO LSX