356
FXUS63 KLSX 120409
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1109 PM CDT Sat May 11 2024

.KEY MESSAGES...

- Sunday will end the weekend dry and warm with temperatures climbing
  into the low 80s for much of the area.

- A period of showers and thunderstorms will kick off the work
  week lasting late Sunday night through Tuesday. There is high
  confidence (70 to 90%) in widespread rainfall values of 0.5
  inches or greater.

- There will be another opportunity for showers and thunderstorms
  late next week..


&&

.SHORT TERM...  (Through Late Sunday Night)
Issued at 221 PM CDT Sat May 11 2024

Tonight, ridging extending from the mid-levels to the surface will
keep our sensible weather calm and quiet. At the surface, the high
pressure center sliding east across the southeast CONUS will cause
light winds and clear skies in the bi-state. This will result in
radiational cooling conditions for the area tonight, with locations
south of I-70 (upper 40s) actually forecast to be a few degrees
cooler than locations to the north (low 50s) due to their proximity
to the high.

In the mid-levels, our next closed low will be entering the
central Plains Sunday afternoon with lobes of vorticity riding
into Missouri ahead of it. This feature will push low-level
ridging out of the area, and winds will shift to southerly behind
it. This will result in warm air advection and an increase in
temperatures on Sunday with widespread low 80s expected. By late
Sunday afternoon, the system will still be well within the Plains,
but an area of low to mid- level moisture advection and the first
vorticity lobes will be approaching the area from the west. This
weak upper level lift will result in the slight chance of isolated
to widely scattered convection, mainly possible in northeast and
central Missouri where moisture, lift, and instability will be
greater. Severe weather is not expected as instability values will
remain at or below 500-750 J/kg through the afternoon and
effective shear will be meager with 15-20 kts within the area of
interest. Overall, weak lift, instability, and shear will make it
difficult for updrafts to grow upscale or organize. Convection is
expected to dissipate as the sun sets, leaving a few hours of dry
weather before the real rain arrives.

Jaja

&&

.LONG TERM...  (Monday through Next Saturday)
Issued at 221 PM CDT Sat May 11 2024

We`ll begin to feel the influence of the mid-level closed low early
Monday morning as a wing of warm advection rain overtakes the CWA
ahead of a deepening surface cyclone. This slow moving system will
crawl through the Mid-Mississippi Valley, providing widespread
rainfall into Tuesday night as rain wraps back into our area within
the deformation zone. Ensembles continue to support widespread 0.5"
rainfall totals with 70-90% of members depicting 0.5" or greater of
total accumulated precipitation by Tuesday night. The probability
of accumulating 1" of rain by this point is on par with previous
forecasts, landing in the 50-60% range. Confidence remains low in
the potential for severe weather on Monday. The best environment
for severe weather will be well to our south, with instability and
shear decreasing to the north. How far north is yet to be seen,
but both deterministic and ensemble guidance keep the highest
values south of I-70. Otherwise, ongoing rain and cloudiness will
keep the diurnal temperature change small on Monday and Tuesday.
While lows both mornings will be above average (upper 50s to 60),
afternoon highs will be below average (upper 60s to low 70s) with
temperatures only changing about 10 degrees.

Low to mid-level ridging will follow the early week system, yielding
reasonably high confidence in a dry day Wednesday. The return of
sunshine will help temperatures bounce back to near average, with a
gradual warming trend evident in the NBM interquartile range despite
growing spread.

This uncertainty translates to the precipitation forecast as well.
Deterministic guidance is consistent in depicting multiple
shortwaves passing through the region late next week with another
chance at rain and thunderstorms Thursday and Friday. However,
differences in the characteristics of the pattern and features
create too much uncertainty to draw any solid conclusions at this
time.

Jaja

&&

.AVIATION...  (For the 06z TAFs through 06z Sunday Night)
Issued at 1109 PM CDT Sat May 11 2024

Dry and VFR flight conditions are likely to persist through Sunday
evening at all terminals. The chance of isolated to scattered
showers and a few thunderstorms begins to increase late Sunday
afternoon, but higher confidence in coverage and impacts to
terminals is not present until just beyond the TAF period.

Pfahler

&&

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

$$

WFO LSX