381
FXUS63 KLSX 081110
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
610 AM CDT Mon Jul 8 2024

.KEY MESSAGES...

- The main concern over the next 2+ days is on impacts associated
  with the remnants of Tropical Cyclone Beryl. The track and
  associated heavy rainfall (2-4") has shifted back slightly to
  the southeast. The heaviest axis is most likely across southeast
  Missouri and southwest Illinois. A flood watch has been issued
  for these locations beginning late tonight lasting through
  Tuesday night.

- Main impacts include the potential for heavy rainfall and flash
  flooding. Concern for aggravated mainstem river flooding on the
  Mississippi and Missouri Rivers has lessened given the shift to
  the southeast.

- Scattered thunderstorms are expected this afternoon and evening
  near a cold front. A few of the stronger storms will be capable
  of producing gusty winds in southeast Missouri and southwest
  Illinois.


&&

.SHORT TERM... (Through Tuesday Night)
Issued at 347 AM CDT Mon Jul 8 2024


(Through This Evening)

An ill-defined cold front is currently located across far western
Missouri northward into Iowa and Minnesota. This boundary is
forecast to slowly move eastward today and serve as a focusing
mechanism for the development of scattered showers and thunderstorms
late this morning through the early evening hours. The latest HREF
shows a 50-60% probability of at least 1000 J/kg of SBCAPE
collocated with 25-30+ knots of deep-layer shear in parts of
southeast Missouri and southwest Illinois. A few of these storms may
become strong to severe this afternoon/early evening, with damaging
winds via wet microbursts the main threat. Heavy, efficient
downpours are also expected with precipitable water values of 1.75-
2.00" (~95th percentile of climatology).


(Late Tonight - Tuesday Night)

A decrease in convective coverage is forecast by late this evening
as instability wanes. This loss of instability also should close the
window on any potential for strong to severe thunderstorms.

Attention will then turn to the remnants of Tropical Cyclone Beryl.
By late tonight, Beryl is expected to track into far southwest
Arkansas per the National Hurricane Center. Widespread rain showers
are expected to develop in the wee hours of the morning on Tuesday
as strong low-level moisture advection enters southeast Missouri.
Broad mid/upper level forcing for ascent is expected to increase
on Tuesday as a longwave trough approaches from the west and
divergence increases beneath the right-entrance region of a jet
streak across the Upper Midwest. This enhanced divergence actually
will stop the weakening post-tropical cyclone and may even lead
to some weak cyclogenesis. The aforementioned mid/upper level
forcing for ascent should act to broaden the precipitation shield
further northwest into parts of central and northeast Missouri as
well as west-central Illinois. However, the heavier rainfall rates
should stay beneath the axis of strong low-level moisture
advection which remains just downstream of the track of the
850-hPa cyclone. The track of the low-level cyclone has shifted
gradually southeast with each successive model suite over the past
24 hours. This may be at least in part due to a further east
track close to the Texas shoreline denoted by last night`s
discussion from the National Hurricane Center. The most likely
track of Beryl`s remnants is now through the bootheel of Missouri.
If this holds, Tropical Storm Claudette (1979) would remain the
only storm to pass through the CWA within the month of July.
However, this track likely will be close and any deviation to the
northwest could clip the far southeastern CWA.

Given that the storm should gain more and more extratropical
characteristics (interaction with frontal boundary, etc.) as it heads
northeastward, the orientation of the heavier rainfall amounts
should shift poleward of the track of the surface low. This puts the
most likely axis of heaviest rainfall totals (2-4") through parts
of southeast Missouri and southwest Illinois. I wouldn`t be
surprised to see some isolated totals of 4-5+" within the heavier
axis given the infusion of deep, tropical moisture (efficiency) and
a lengthy duration of steady rain expected (~18 hours). The
probability-matched mean from the HREF, which only ran through 0Z
Wednesday, already had some 2.50-3.00+" totals with another 3-6+
hours of rainfall across parts of the area. Given this heavy
rainfall threat and the potential for flash flooding, went ahead and
issued a flood watch for parts of southeast Missouri and southwest
Illinois. The threat is more conditional a bit further northwest
(including parts of east-central Missouri into south-central
Illinois). The shift of the track to the southeast has dropped
rainfall totals a bit in these regions, and the gradient on the
northwestern edge in reality likely will be tighter than currently
forecast. These locations are very saturated though, so any shift
back to the northwest could cause hydrological problems. If that
shift were to occur back to the northwest, then the flood watch
would need to be expanded. For this initial issuance however,
focused on the areas where there was the most confidence in
significant (2-4") rainfall totals.

Another potential concern is for isolated tornadoes. This threat is
more likely to our southeast given the track of the system, but a
shift back to the northwest could put parts of south-central
Illinois in play for Tuesday afternoon.

Temperatures on Tuesday will be quite cool for early/mid July given
the widespread clouds and persistent rainfall. Coolest values are
expected to be in parts of southeast Missouri where low 70s are
forecast. Locations in northeast Missouri and west-central Illinois
should be the warmest, with highs nearing the 80 degree mark.


Gosselin

&&

.LONG TERM... (Wednesday through Sunday)
Issued at 347 AM CDT Mon Jul 8 2024

(Wednesday - Sunday)

Seasonably cool conditions are forecast on Wednesday as the remnants
of Beryl move off into the Ohio Valley/lower Great Lakes. A cloudy
start to the day for some is expected to transition to more sunshine
by the afternoon. High temperatures in the low to mid 80s are
expected.

Model guidance is hinting at a weak midlevel shortwave approaching
from the northwest. This feature could bring some low chances of
showers and thunderstorms (likely diurnally driven) to portions of
the area. While nearly all members from the grand ensemble have this
feature, there is some discrepancies with the strength and placement
Thursday-Friday. A stronger, further southwest placement would
likely yield higher coverage of showers and thunderstorms each
afternoon/evening along with cooler temperatures. A weaker, further
northeast location of the midlevel shortwave in terms of sensible
weather impacts likely would lead to dry conditions along with
temperatures warming back to near or slightly above normal.

Ensemble guidance is in good agreement that mid/upper level ridging
in the intermountain west will begin to move eastward into the
central Plains. This is expected to result in dry weather along with
above normal temperatures next weekend (highs in the 90s).

GOSSELIN

&&

.AVIATION...  (For the 12z TAFs through 12z Tuesday Morning)
Issued at 605 AM CDT Mon Jul 8 2024

Isolated to scattered showers along with a few thunderstorms are
the concern through this evening. Activity has weakened overall
the past few hours with not much in the way of lightning.
Therefore, elected to go with a VCSH instead of a VCTS at
terminals for this morning. Better chances of thunder exist this
afternoon/early evening for the metro terminals. More widespread
rain and a few rumbles of thunder associated with the remnants of
Tropical Cyclone Beryl will begin to move north in central
Missouri early Tuesday morning followed by metro St. Louis
terminals.

Gosselin

&&

.HYDROLOGY...
Issued at 354 AM CDT Mon Jul 8 2024

Isolated flash flooding is possible in parts of southeast Missouri
and southwest Illinois late tonight through Tuesday night due to
persistent and efficient rainfall rates. Antecedent conditions are
not as favorable as further northwest as these locations largely
missed out on the heavier rainfall earlier this month. However,
there may be at least pockets of very heavy tropical rainfall that
overwhelms 3 or 6-hour flash flood guidance (2-3" and 3-4+"
respectively).

In addition to the potential flash flood threat in parts of
southeast Missouri and southwest Illinois late tonight through
Tuesday night, river flooding is also a concern. If the heavier axis
of rainfall does end up in these locations, both the mainstem
Missouri and Mississippi Rivers likely will not be impacted too
much. Any subsequent crest on the Missouri River is very likely
(>90%) to be below the previous crest on the latest HEFS guidance.
For the Mississippi River, most of the river is at or very near
crest. Some points may see their crests come up slightly, but not
significantly unless the track of the heavier rainfall axis were to
end up further northwest than currently forecast. The exception may
be Chester, which has a ~20% chance of moderate flooding over the
next week.

Basins that are most likely to be more directly impacted by the
remnants of Beryl include the Meramec, Big, Bourbeuse, and Black
River basins. Probabilities for minor flooding on the Meramec and
its tributaries are not particularly high due to slightly below
normal flows. However, if the heavy axis of rainfall sets up over
any of these basins, minor flooding odds would increase sharply. The
Black River at Annapolis has the best chance of seeing minor
flooding given the placement of the heavier rainfall axis.

Gosselin


&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Flood Watch from late tonight through Wednesday morning for
     Crawford MO-Iron MO-Jefferson MO-Madison MO-Reynolds MO-
     Saint Francois MO-Sainte Genevieve MO-Washington MO.

IL...Flood Watch from late tonight through Wednesday morning for Bond
     IL-Clinton IL-Fayette IL-Marion IL-Monroe IL-Randolph IL-
     Saint Clair IL-Washington IL.

&&

$$

WFO LSX