749
FXUS63 KLSX 061944
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
244 PM CDT Sat Jul 6 2024

.KEY MESSAGES...

- Above normal temperatures will return on Sunday along with a
  chance of primarily afternoon thunderstorms across parts of
  central and northeast Missouri and west-central Illinois.

- Shower and thunderstorm chances will increase and expand to the
  entire CWA Sunday Night through Tuesday, with the greatest
  chances (40-60 percent) Sunday night and Monday.

- Depending on the track, the remnants of tropical cyclone Beryl
  could bring rain to parts of southeast Missouri and southern
  Illinois Wednesday and Wednesday night.

&&

.SHORT TERM...  (Through Late Sunday Afternoon)
Issued at 227 PM CDT Sat Jul 6 2024

A few pinhead showers/sprinkles have developed across northeast MO
and west-central IL. These are shallow and high-based and aren`t
expected to amount to much and overall will individually be rather
short-lived this afternoon.

All in all it appears we should have a rather quiet weather night
with lower than normal dew points/humidity for early July.
Surface high pressure presently centered in southwest MO will
slowly retreat eastward. An MCS is expected to organized across
the Plains and move east into northwest MO and southwest IA later
tonight. Presently it looks like sufficient low-level moisture
return and instability will not be available on the backside side
of the retreating high to sustain it as it moves towards north-central
MO and thus weakening and dissipation is anticipated.

The residual boundary, and a vort max or a left-over MCV is expected
to be the catalyst for our first chance of showers and thunderstorms
on Sunday. This should mainly be across central and northeast MO
and west-central IL on Sunday afternoon, and will be aided by the
return of low-level southerly flow in the wake of the retreating
high and the accompanying WAA, moisture transport and instability.
Otherwise Sunday should be the warmest day for the upcoming week
(above normal temps) due to the southerly flow and warmer temps
aloft.

Glass

&&

.LONG TERM...  (Sunday Night through Next Saturday)
Issued at 227 PM CDT Sat Jul 6 2024

More active weather will ensue Sunday Night into the first half
of the upcoming week.

While there are some subtle differences in vort max positions in the
model guidance, the overall trend remains the same, with the
positively-tilted upper trof slowly progressing eastward into the
mid-upper MS Valley Monday-Monday night. A series of vort maxes
within the southwest flow ahead of the trof, lift via the
southwesterly LLJ, and frontal forcing associated with the advancing
cold front will result in scattered-numerous showers and
thunderstorms impacting mainly central and northeast MO and west-
central IL late Sunday night. This overnight activity could persist
and slowly move eastward through the day on Monday, or weaken early
in the morning with new development ensuing in the afternoon along
the boundary capitalizing on diurnal heating/instability.

There remains some uncertainty with the longevity and footprint of
precipitation/POPs Tuesday into Wednesday. The slowly progressive
upper trof will weaken and move across the mid-upper MS Valley
Tuesday into early Wednesday, eventually becoming absorbed into the
southern extent of an upper trof centered in eastern Canada. Besides
the initial cold front passage late Monday Night, there are less
well-defined signals of a second boundary/cold front moving across
the area on Tuesday associated with the upper trof axis and it`s
passage. This later boundary and trof would support a continue
threat of showers and thunderstorms across primarily the
southeast half of the CWA on Tuesday, peaking in the afternoon
with diurnal heating/instability.

IF we see any impacts from the remnants of TC Beryl, at this time
they look to be mainly across southeast parts of the CWA. The
recurving remnants of Beryl are forecast to track from east TX
across the lower MS Valley late Tuesday through Wednesday Night.
The mean track of the superensemble would have the remnant low
passing near the bootheel, however the track spread is such that
it could be further north or south. The current forecasted
impacts would be a slug of mid-high level tropical moisture and
attendant rainfall across SE MO/SRN IL including parts of the
southern CWA. We continue to have a sizable footprint of POPs
Tuesday, and the new forecast has a bit larger footprint Tuesday
Night-Wednesday night centered through SE MO and SRN IL to account
for the potential for Beryl. The current guidance from the 100
member LREF suggests the greatest threat of attendant excessive rainfall
appears to be south of the CWA.

Ensemble guidance continues to show that during the later half of
the upcoming week there will be a weakness in the mid-upper flow
across the central U.S. with strong upper ridges centered in the
western Atlantic and Intermountain West. This weakness could be
the reflection of a weak upper trof dropping southeastward from
the Plains or just an area of relatively lower heights with an
embedded weak upper low. Either way there is no strong signal for
organized precipitation, but perhaps some isolated diurnal
activity. There shouldn`t be any extreme temperatures Tuesday
through Friday. Tuesday and Wednesday look like the "coolest" days
with largely below normal temps with highs Thursday-Friday within
a few degrees of normal, and the NBM max temperature distribution
continues to show a very small IQR. Greater summer heat could
return by next weekend as there are some signals that by next
weekend the western ridge may attempt to build into the mid MS
Valley.

Glass

&&

.AVIATION...  (For the 18z TAFs through 18z Sunday Afternoon)
Issued at 1215 PM CDT Sat Jul 6 2024

VFR flight conditions are expected through the forecast period.
Diurnal cumulus clouds are expected this afternoon with some high
clouds late tonight.

Glass

&&

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

$$

WFO LSX