901
FXUS63 KLSX 150839
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
339 AM CDT Sat Jun 15 2024

.KEY MESSAGES...

- Temperatures are expected to remain above average through next
  week. Summer-like heat will be most pronounced on Sunday and
  Monday with peak afternoon heat index values in the upper 90s to
  105 F.

- There is a low (20 to 40 percent) chance of showers and
  thunderstorms at times, primarily Monday onward and during each
  afternoon.


&&

.SHORT TERM...  (Through Late Tonight)
Issued at 328 AM CDT Sat Jun 15 2024

An upper-level ridge will shift from the Mississippi River Valley to
the Ohio Valley today, providing mostly dry conditions. In addition
to a weakening MCS this morning passing well west/northwest of the
CWA in the Central Plains, isolated to scattered showers and
thunderstorms are anticipated to develop this afternoon near a weak
warm front from west-central MO into southern MO. Instability should
decrease with northeastward extent from this front into the CWA,
with CAMs only indicating an isolated shower or weakening
thunderstorm reaching central MO this afternoon. Upper-level cloud
debris from any of these showers and thunderstorms is expected to be
thin and transient, allowing insolation to accompany the onset of
southerly low-level WAA and support high temperatures similar or
slightly warmer than yesterday and in the upper 80s to low-90s F.

Pfahler

&&

.LONG TERM...  (Sunday through Friday)
Issued at 328 AM CDT Sat Jun 15 2024

Sunday through Monday, the upper-level ridge will amplify and expand
over the eastern CONUS with deep, weak southerly flow becoming
established throughout the troposphere in the lower to mid-
Mississippi River Valley at the ridge`s western periphery. As a
result, a period of summer-like heat is anticipated, especially on
Sunday and Monday when ensemble model guidance depict the warmest
850-hPa temperatures above the 90th climatological percentile. Model
guidance and the overall pattern (e.g., southwesterly component of
low-level flow possibly downsloped off the Ozark Plateau) support
the warmest temperatures occurring on Sunday with high temperatures
in the low to upper 90s F, approaching daily records (see CLIMATE
section). Moisture/dewpoints will also be increasing, yielding
afternoon heat index values of 100 to 105 F in many locations.
Although these values are just below hazardous thresholds, extra
care should be taken since Sunday will be the hottest day of the
year so far. As the axis of the upper-level ridge shifts northeast
after Sunday, model guidance is in agreement that 850-hPa
temperatures will cool slightly (1 to 2C)as low-level flow backs
to the southeast. In addition, a series of mid-level
perturbations/potential MCVs is progged to accentuate diurnal
showers and thunderstorms Monday onward, communicated by low
chances (20 to 40 percent) of showers and thunderstorms peaking
during each afternoon. The exact impact of showers/thunderstorms
and associated clouds on temperatures is unclear and captured by
NBM temperature interquartile ranges spanning 5 to 8 F during that
time. However, the vast majority of the ensemble model 850-hPa
temperature distribution remains above average, increasing
confidence in temperatures enduring above average across most of
the CWA.

Pfahler

&&

.AVIATION...  (For the 06z TAFs through 06z Saturday Night)
Issued at 1035 PM CDT Fri Jun 14 2024

Under weak southerly winds and high surface pressure, VFR
conditions will persist through the valid TAF period. There is a
very low (10%) chance for isolated convection in central and
northeast Missouri Saturday afternoon, but confidence is far to
low to mention in the KCOU/KJEF TAFs.

MRB

&&

.CLIMATE...
Issued at 328 AM CDT Sat Jun 15 2024

Daily High Temperature Records:
                 |=== June 16 ==|=== June 17 ==|
St. Louis (KSTL) | 100 F (1952) |  99 F (1944) |
Columbia  (KCOU) |  99 F (2006) | 100 F (1936) |
Quincy    (KUIN) | 102 F (1936) | 103 F (1918) |

&&

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

$$

WFO LSX