250
FXUS63 KLSX 151121
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
621 AM CDT Thu Aug 15 2024

.KEY MESSAGES...

- After some morning thunderstorms, hot and humid conditions
  overspread the region today with heat index values above 100
  degrees.

- Additional thunderstorms, some severe, are expected to develop
  late this afternoon and this evening ahead of an approaching
  cold front. Damaging winds and large hail are the primary
  threats although locally heavy rain is also possible.

- Our stretch of wet weather ends with the cold front tonight as
  drier conditions are expected this weekend and into next week.
  Temperatures will be near normal for this time of year.


&&

.SHORT TERM...  (Through Late Friday Afternoon)
Issued at 239 AM CDT Thu Aug 15 2024

An area of thunderstorms continues early this morning mainly along
an axis from southeast Kansas into eastern Iowa and northwest
Illinois. This is primarily due to moist advection in a low level
jet centered around 850MB. This jet weakens as it shifts east this
morning and convective activity likely decreases in coverage as
well. With sun today we`ll warm into the upper 80s to low 90s with
dewpoints climbing into the low to mid 70s. Heat index values push
above 100 degrees but likely stay near or below 105, keeping us just
below Heat Advisory.

With the heat and humidity today, we`ll see much more instability
than we`ve seen in recent weeks. SBCape of 3000 or more is likely by
late this afternoon just as mid level flow increases around the base
of a trough to our north. While the instability and shear parameters
will be in place for strong to severe thunderstorms, primarily in
the form of supercells or convective clusters, the uncertainty
primarily centers on the trigger for thunderstorm initiation.
There`s not a clear forcing mechanism to trigger storms in the warm
sector this afternoon, however outflow boundaries from this
morning`s convection could do the trick. Latest CAMs are more
pessimistic on the afternoon convection, but I wouldn`t rule it
out at this stage. If storms don`t get going in the warm sector by
late this afternoon, better forcing will be able to focus along
the advancing cold front this evening. More recent CAMs have hit
this possibility a little harder, stretching the threat window a
bit later in the evening, possibly until a little after midnight.
The primary threats with thunderstorms this afternoon and evening
will be damaging winds and large hail, although a tornado cannot
be ruled out in areas where low level shear can maximize.

The cold front makes good progress through the area overnight
tonight, exiting our forecast area during the morning on Friday.
This will bring drier air into the region and shift the focus for
thunderstorms to the southeast for Friday, likely keeping our area
dry. Temperatures behind the front will actually be fairly similar
to today, in the low 90s, as plenty of sun will act on the drier air
mass to warm things up.

Kimble

&&

.LONG TERM...  (Friday Night through Wednesday)
Issued at 239 AM CDT Thu Aug 15 2024

Ridging develops over the Rockies this weekend while troughing
winding up over the Great Lakes is slow to progress eastward. The
combination will put us in a northwesterly flow aloft which is
generally a dry and somewhat cool pattern. As the trough does
finally begin to push east early next week it will allow a flow of
cooler and drier air out of the north behind it. This will lead to
some pleasant late summer weather with temperatures only warming
into the low 80s with low humidity. Nighttime temperatures drop well
into the 60s, and perhaps the 50s.

Kimble

&&

.AVIATION...  (For the 12z TAFs through 12z Friday Morning)
Issued at 621 AM CDT Thu Aug 15 2024

Early morning thunderstorms are most likely in the St Louis metro
over the next few hours. We should see a break in the activity
lasting through much of the day with light to moderate SSW winds.
Additional thunderstorms are expected this afternoon, although
there`s considerable uncertainty on where and when. Current
thinking is that afternoon storms develop south of all terminals,
but thunderstorms developing over northern Missouri may impact all
terminals in the evening or into the early overnight. Strong winds
are possible with thunderstorms this afternoon and evening.

Kimble

&&

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

$$

WFO LSX