659
FXUS63 KLSX 161058
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
558 AM CDT Thu May 16 2024

.KEY MESSAGES...

- Showers and a few thunderstorms will fade over the area this morning.
  Additional showers and thunderstorms are possible this
  afternoon and evening with isolated hail and gusty winds.

- Locally heavy rainfall could lead to localized nuisance flooding
  over extreme southern section of the forecast area Friday.

- Temperatures will begin to warm this weekend and further into
  next week, becoming 10-15 degrees above normal. Next week`s
  warmth could be accompanied by another period of active weather.


&&

.SHORT TERM...  (Through Late Friday Afternoon)
Issued at 344 AM CDT Thu May 16 2024

Regional satellite imagery shows a broad area of cloud cover over
eastern Kansas and Oklahoma, streaming eastward into Missouri early
this morning. Widespread rainfall and embedded thunderstorms can be
seen over southwest Missouri, progressing almost due east. At far
east fringes of this activity are isolated showers.

Showers running ahead of the broader, more persistent rainfall have
had little ground truth with radar trends showing them falling apart
with eastward movement. Model soundings suggest that there may be
enough dry air in the 700-850mb layer to inhibit at least the
lighter activity from reaching the ground. Meanwhile, mid-level
moisture is expected to continues advance northeast through the
morning as rainfall moves into central and eastern Missouri. The
main question then will be how long this area of rainfall hold
together.

Latest SPC mesoanalysis shows what thunderstorms do remain are riding
along the northern fringes of MLCAPE that horseshoes from central
Oklahoma into southwest Missouri and central Arkansas. This area of
CAPE has greatly decreased in magnitude and area over the last
several hours with essentially no CAPE over southeast Missouri.
Additionally, mid-level lapse rates drop to 5.5-6C further east of
the complex, which should lead to continued weakening through the
morning as it approaches the Mississippi River. Though the area may
not entirely collapse, scattered remnants will cross the CWA through
early afternoon.

All this leads to even great reservation with regard to severe
thunderstorm potential given debris clouds that remain overhead. RAP
guidance shows a mid-level vort reaching the Mississippi River
around 19z this afternoon and approaching I-57 in southern Illinois
by 23z. Simultaneously, MLCAPE only recovers to 500-1000 J/kg at any
given location underneath the vort max. HREF guidance suggest only a
30-40% probability of reading 1000 J/kg and essentially 0% for
reaching 2000 J/kg with that value being the absolute maximum
possible and even that is localized. Shear values still only look to
reach 30 knots at best. Model soundings don`t give much more
excitement with long, thin CAPE profiles and deep saturation, both
of which would not favor hail and gusty winds. All-in-all, while the
severe threat isn`t zero, it`s not high either. If a strong storm
develops, the window is extremely short (2pm-6pm) and has spatial
limitations, too (far southeast MO and southwest IL).

Activity today will play into Friday`s rainfall potential as cooler
air is reinforces further south. A more vigorous surface low moves
east out of Oklahoma underneath the left exit region of the upper
jet and ahead of the upper level trough. While this provides plenty
of support over a broad pool of high moisture content and leads to
widespread rainfall along and south of I-70, the potential for
locally heavy rain from thunderstorms has shifted slightly further
south and further limits the spatial area previously concerning
localized flood potential. Given the 14-30 day precipitation amounts
have reached 150% to locally 300% of normal values, saturated ground
layer would offer opportunity for nuisance flooding if locally heavy
rain materialized over far southeast Missouri and southwest Illinois
Friday.


Maples

&&

.LONG TERM...  (Friday Night through Wednesday)
Issued at 344 AM CDT Thu May 16 2024

(Friday Night through Thursday)

The theme continues to be a trend toward warmer than normal
temperatures beginning this weekend. Weekend warmth of 5-10 degrees
above normal could inch to as much as 15 degrees above normal into
the first half of next week. Signals show next week`s warmth could
be accompanied by yet another period of active weather, which could
have a play on temperatures, pending placement and timing of
precipitation.

A pronounced upper level trough will be gradually exiting to the
east late Friday into early Saturday. A weak boundary/surface trough
extending through the mid-Mississippi Valley will gradually become
overtopped by an amplifying upper level ridge from the west later in
the day Saturday. Surface high pressure begins to build in from the
northern Plains, but may not occur quick enough to spare the region
of isolated showers, especially over southeast sections of the CWA.
A thunderstorm cannot be ruled out, but MLCAPE values peak between
500-1000 J/kg with weak bulk shear of 10-20 knots. Anything that
develops will likely be slow-moving, relatively short-lived and fade
after peak heating. Surface high pressure and upper ridging then
take over to provide dry and warm conditions Sunday with
temperatures running 5-10 degrees above normal through the weekend.

Surface/mid-level ridging extending from north to south down the
Atlantic seaboard will result in southerly return flow at the
surface with strengthening southwesterly mid-level flow. Strong warm
air advection Monday will boost temperatures even further with the
potential that some areas could approach 90 degrees Monday and
Tuesday. NBM spreads remain tightly clustered through Monday (5
degrees or less) with a little more spread introduced Tuesday.
Beyond that, the gap continues to widen. The main culprit to the
diverging solutions is the handling of broad upper trough that
traversed the northern CONUS and shortwaves that eject northeast at
the base of the trough. Where these features track, their surface
inflections, and boundaries, will factor into precipitation chances
and temperature trends. GEFS mean heights show very little spread,
through Tuesday, placing us comfortably under the upper ridge and
within the warm sector, while quickly spreading out Wednesday
beyond. Additionally, CIPS analog threat guidance shows 70%
probability for warmer than normal temperatures through days 6-8,
but also signal potential for an increasingly wet pattern toward the
end of the same period. Warm and mainly dry conditions have the
potential to be tempered by an increasingly more active pattern next
week.


Maples

&&

.AVIATION...  (For the 12z TAFs through 12z Friday Morning)
Issued at 549 AM CDT Thu May 16 2024

A complex of weakening showers and thunderstorms are progressing
eastward across central Missouri this morning. Embedded stronger
thunderstorms continue to decay, but not before produced brief
reductions to visibility down to around 3SM and locally gusty
winds. The weakening continue is expected to continue through the
morning as it approaches the central Missouri terminal in the next
1-2 hours and will be considerably weaker as it approaches the
metro terminals. KUIN is at the northern fringes, where scattered
showers and maybe a thunderstorm will be possible. Overall, VFR
conditions are expected to continue until more persistent rainfall
arrives and results largely in MVFR visibilities and cloud bases.

Additional thunderstorms are possible this afternoon into this
evening. However, the best potential for more impactful weather
will be just south of the metro terminals, where a strong storm or
two is possible. Outside of this, locally heavy downpours,
lightning and MVFR visibilities and cloud bases will be the main
impact around metro terminals in a general window between 18z-00z.
Widespread precipitation will be focused south of the terminals
with the northern fringes of the precipitation field skimming the
metro area. A remnant boundary could linger through the area
resulting in MVFR/IFR fog potential late tonight into Friday from
central MO through west-central IL.


Maples

&&

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

$$

WFO LSX