879
FXUS63 KLSX 191915
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
215 PM CDT Fri Jul 19 2024

.KEY MESSAGES...

- Mild mid-summer temperatures continue through Sunday with
  seasonally low humidity.

- Humidity increases Monday and Tuesday along with chances for
  showers and thunderstorms.

&&

.SHORT TERM...  (Through Late Saturday Night)
Issued at 215 PM CDT Fri Jul 19 2024

Surface high pressure remains centered near our area with mild
mid-summer temperatures and low humidity. Afternoon cumulus will
dissipate this evening leading to another night with efficient
radiational cooling. Some thunderstorms upstream in South Dakota
and Nebraska may send some high level cloudiness toward our area
overnight which could limit the cooling a little bit. But in areas
where it remains clear, another pleasant summer night in the 50s
is expected, with urban areas warmer. Patchy fog is likely mainly
in the Ozark river valleys. Saturday will be pretty similar today
with light winds and mild temperatures. Humidity gradually creeps
up, though, so temperatures Saturday night won`t be quite as cool.

Kimble

&&

.LONG TERM...  (Sunday through Next Friday)
Issued at 215 PM CDT Fri Jul 19 2024

Upper ridging remains parked over the western US, even backing up
toward the West Coast a bit next week. Broad troughing will
persist downstream across the central and eastern US, though where
the subtle shortwave impulses within this trough exist will be a
key in determining rain chances next week. Moisture returns from
the Gulf of Mexico bringing dewpoints back up to near 70 or higher
for Monday and Tuesday. While temperatures remain somewhat mild,
the humidity will be noticeable compared to this weekend. With
that added moisture we`ll see the return of instability and the
chance for showers and thunderstorms. It`s likely that there will
be one or more shortwave troughs embedded in the flow that will
serve as a focus for showers and thunderstorms Monday and Tuesday,
though where they will be is still highly uncertain. Our rain
chances are highest on these days as it is more likely that the
trough axis will be nearby. Thunderstorm chances are greatest in
the afternoon and evening when instability should maximize. The
severe weather threat with these storms should be low considering
a remarkable lack of shear. While we are climatologically toward
the time of year when flash flooding is a greater concern, total
moisture content does not look high enough to warrant this concern
especially in the absence of a forcing mechanism to trigger storm
training. PWAT is expected to peak around 1.5 inches, much lower
than what was seen last week.

As the shortwave trough moves east, a weak cold front moves south
in its wake. Another deeper trough drops into the western Great
Lakes behind it with another cold front associated with it. While
we do maintain low PoPs Wednesday through the end of the week, the
forcing for more widespread showers and storms looks pretty weak
at this point leading to the lower confidence in those
precipitation chances.

Kimble

&&

.AVIATION...  (For the 18z TAFs through 18z Saturday Afternoon)
Issued at 1220 PM CDT Fri Jul 19 2024

Primary aviation impact for most locations is diurnal cumulus
otherwise winds are very light and often variable. It is possible
that fog develops in the river valleys tonight, with this threat
greatest at SUS. If this occurs it will be for just a few hour
window near 12Z.

Kimble

&&

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

$$

WFO LSX