401
FXUS63 KLSX 141129
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
629 AM CDT Fri Jun 14 2024

.KEY MESSAGES...

- Above average temperatures are expected through next week with
  Sunday and Monday the warmest days as peak heat index values
  reach the upper 90s to 105 F. Although confidence in heat index
  values reaching dangerous levels is low, care should still be
  taken since this period will be the first wave of summer-like
  heat.

- There are multiple opportunities with low (20 to 40 percent)
  chances of showers and thunderstorms, especially mid-next week.


&&

.SHORT TERM...  (Through Late Saturday Afternoon)
Issued at 344 AM CDT Fri Jun 14 2024

Multiple weakening clusters of showers and thunderstorms skirting
central and southeastern MO will gradually dissipate early this
morning as expanding cold pools and nocturnal cooling decrease
instability in the absence of any strong forcing. The increasingly
diffuse cold front originally responsible for these showers and
thunderstorms will push southward through the CWA this morning as
well. Although this front is anticipated to be south of the CWA by
this afternoon and large-scale forcing within upper-level
northwesterly flow will be negligible, CAMs indicate diurnally aided
instability behind the front supporting a stray shower or
thunderstorm during the afternoon across southeastern MO. Low-level
CAA behind the front will be weak with high temperatures again
reaching the upper 80s to low-90s F with infiltration of drier
air/lower dewpoints a more noticeable change along and north of I-70.

On Saturday, most short-term models depict weakening showers and
thunderstorms across western MO tracking eastward during the morning
and early afternoon while dissipating as a LLJ weakens and they
outrun richer instability to the west. The latest HREF has highest
probabilities of showers and thunderstorms to the west of the CWA
but these probabilities reach around 20 percent across central and
northeastern MO. Cloud debris from those showers and thunderstorms
could have some impact on Saturday`s high temperatures; however, a
decrease in these clouds through the day and onset of low-level WAA
are expected to provide temperatures similar to today.

Pfahler

&&

.LONG TERM...  (Saturday Night through Thursday)
Issued at 344 AM CDT Fri Jun 14 2024

Late Saturday through the beginning of next week, global models are
in good agreement that an anomalous upper-level ridge will blossom
across the eastern CONUS, downstream of longwave troughing across
the western CONUS. This upper-level wave pattern will leave the
central CONUS, under the influence of weak, persistent southerly
flow through much of the troposphere with a summer-like pattern in
the CWA characterized by widespread temperatures in the 90s F (most
days), increasing dewpoints/humidity, and chances of showers and
thunderstorms at times. The NBM portrays the warmest, furthest above
average temperatures of the period on Sunday and Monday owing to
those days favored to have the least cloud cover, lowest probability
of precip, and strongest southerly flow. The combination of
temperatures well into the 90s F and increasing humidity will
support peak afternoon heat index values reaching the upper 90s to
105 F. Although confidence is not high that heat index values will
reach dangerous thresholds, care should still be taken, especially
for vulnerable individuals, since this period will be the first wave
of summer-like heat across the CWA. Late Monday onward, a series of
low-amplitude mid-level shortwave troughs/potential MCVs are progged
to drift northward in the aforementioned southerly flow, increasing
the chance of showers and thunderstorms at times. It is impossible
to glean further details of these features at this juncture, but
associated showers/thunderstorms and cloud cover introduce some
uncertainty in daily temperature forecasts after Monday. This
uncertainty is encapsulated by NBM interquartile temperature ranges
increasing to 5 to 8 F. With the 25th percentile remaining above
average, however, confidence in above average temperatures
persisting is still high.

Pfahler

&&

.AVIATION...  (For the 12z TAFs through 12z Saturday Morning)
Issued at 629 AM CDT Fri Jun 14 2024

A patch of IFR or MVFR stratus across central and northeastern MO
could briefly impact KCOU this morning. Otherwise, dry and VFR
flight conditions will prevail through the vast majority of the TAF
period along with light northerly winds today, becoming easterly or
variable tonight.

Pfahler

&&

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

$$

WFO LSX