842
FXUS63 KLSX 051944
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
244 PM CDT Fri Jul 5 2024

.KEY MESSAGES...

- Near to slightly above average temperatures are forecast this
  weekend with lower humidity.

- The chance of showers and thunderstorms will return on Sunday
  afternoon and continue through Tuesday, with the greatest
  chances Sunday night and Monday.

- High temperatures will hover near normal much of next week.

&&

.SHORT TEthe RM...  (Through Late Saturday Night)
Issued at 230 PM CDT Fri Jul 5 2024

We will have a respite from the active weather we experienced
earlier this week as we head into the weekend. The upper low/trof
currently extending through the upper-mid MS Valley will
gradually weaken and depart east-northeast into southeast Canada
and the Othe hio Valley over the next 36 hours. As a result, weak
post-frontal surface high pressure will dominate the region
resulting in tranquil, less humid, and slightly cooler
temperatures compared to earlier this week.

Increasing broad longwave trofing across the central U.S. heading
into Sunday night will be the harbinger of a return to a bit more
active pattern. The first sign of this is the potential for residual
showers associated with a decaying Plains MCS to move into NE MO
late Saturday night. I`m not super excited about the potential and
we have no POPs at this time, but we`ll need to keep an eye on
the development of weak low-level WAA and moisture return
attendant with the eastern periphery of a southwesterly LLJ on the
backside of the retreating anticyclone.

&&

.LONG TERM...  (Sunday through Next Friday)
Issued at 230 PM CDT Fri Jul 5 2024

Renewed deepening of the upper trof across he Plains Sunday-
Sunday night will result in backing mid-upper flow and allow for
embedded vort maxes to begin impacting the area. The accompanying
retreat of the lower tropospheric anticyclone will bring a
decided return of low-level southerly flow and accompanying
WAA/warmer temperatures, along with increasing moisture/instability.
I`m not sure we will see much activity during the daylight
Sunday, as other than the possibility of a residual convective
boundary across central/northeast MO, there are a lack of forcing
mechanisms. However on Sunday night, the threat of showers and
thunderstorms should increase significantly across the western CWA
associated with a lead vort max within the southwest flow aloft,
an advancing cold front across western MO, and forcing/moisture
transport via a southwesterly LLJ.

The slowly progressive positively-tilted upper trof will advance
from the Plains into the mid-upper MS Valley Monday into Tuesday.
The combination of ascent associated with a series of vort maxes in
the southwest flow ahead of the trof axis and the advancing cold
front itself interacting with a warm, moist and unstable air mass
should bring scattered-widespread showers and thunderstorms
Monday into Monday night.

There is general agreement in the evolution of the large scale
pattern Tuesday through Wednesday with the ensemble means and
cluster analysis of the LREF depicting broad upper trofing from
eastern Canada southeastwarthe d into the mid MS Valley and a
strong upper high centered over the Intermountain West. However
there are some subtleties which could impact the forecast, namely
the speed of the frontal progression through the area on Tuesday
and the longevity of attendant precipitation chances. The other
item is the remnants of TC Beryl. The superensemble mean track and
greatest clustering keeps the curving track of Beryl south of the
bootheel around midweek with mainly increasing mid-high level
moisture within the southwest flow aloft impacting SEMO and SRN
IL. The result is a larger footprint of POPs across the southeast
half of the CWA Tuesday and low POPs the confined to far southeast
MO and southern IL Tuesday night-Wednesday.

During the later part of next week the central U.S. is dominated by
very weak mid-upper flow sandwiched between ridges centered in the
western Atlantic and Intermountain West. While not resolved well in
the ensembles, there are signs in the deterministic solutions of
an upper low floating around somewhere within the aforementioned
weakness in the flow across the central U.S.. Models typically
have low skill with these types of features in this kind of flow
regime, and if present it could end up bringing low precipitation
chances.

Otherwise, following the Tuesday cold fropa, forecast temperatures
are forecast to hover within a few degrees of normal, so no
extremes. Confidence in this is greater than average with the NBM
max temperature distribution showing a small interquartile range
Tuesday-Friday.

Glass

&&

.AVIATION...  (For the 18z TAFs through 18z Saturday Afternoon)
Issued at 1150 AM CDT Fri Jul 5 2024

VFR flight conditions are expected through the forecast period.
Diurnal cumulus is expected this afternoon with scattered high
clouds tonight. Northwest surface winds will gust to 20+ kts this
afternoon and diminish early this evening.

Glass

&&

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

$$

WFO LSX