FXUS63 KLSX 112317
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
617 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 00z TAFs through 00z Sunday Evening)
Issued at 616 PM CDT Sat May 11 2024

Winds diminish quickly this evening under a clear sky. Some higher
clouds spill in tomorrow but conditions remain VFR. Winds become
more southerly tomorrow but remain light.

Kimble

&&

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

$$

WFO LSX