165
FXUS63 KLSX 260308
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1008 PM CDT Fri Apr 25 2025

.KEY MESSAGES...

-Scattered showers and thunderstorms are expected along a cold front
this afternoon into early evening, and again Saturday night into
Sunday.

-Monday will be the warmest day of the week with highs in the 80s.

-There is a 15-30% chance for strong to severe thunderstorms
 across the forecast area Monday and Tuesday.


&&

.SHORT TERM...  (Through Late Saturday Night)
Issued at 155 PM CDT Fri Apr 25 2025

Scattered showers and thunderstorms are expected to continue ahead
of and along the advancing cold front that currently runs from
southwest Missouri through the St. Louis metro into central
Illinois. Weak shear will keep thunderstorms sub-severe, though I
cannot rule out a storm or two briefly producing small hail.

Behind the front cold air advection will be offset by a mostly sunny
to partly cloud sky, keeping Saturday`s temperatures near normal.
Aloft, a mid-level shortwave will be located near southwest Missouri
during the afternoon, sliding east into the overnight hours.
Showers, and perhaps a rumble of thunder, move south of I-70
overnight.

Delia

&&

.LONG TERM...  (Sunday through Next Friday)
Issued at 155 PM CDT Fri Apr 25 2025

This first wave of showers will exit the forecast area during the
early morning on Sunday with the mid-level shortwave. At the same
time an elevated warm front will push into the forecast area along
the newly reestablished southwesterly low-level flow, resulting in
showers mainly south of I-70 during the day. Sunday won`t be a wash
out though, with at most a 40% chance of exceeding 0.1" of rain
mainly south of I-70 in Missouri.The addition of thicker cloud cover
will offset the warm air advection along the southwesterly low-level
flow, and temperatures on Sunday will be similar to Saturday.

Zooming back out, the mid-level flow Sunday afternoon will be
characterized by a ridge moving through the mid-Mississippi Valley
and a strong trough/low over the western CONUS.  Overnight into
Monday the trough will become a split stream system and the northern
stream trough will move into the Intermountain West with numerous
vorticity maxima moving through the flow into the Upper Midwest. A
surface low will form across the Dakotas in response on Monday,
trailing a cold front through the central Plains. Across the mid-
Mississippi Valley low-level southerly flow will push temperatures
into the 80s across the region.

Meanwhile, a 300 mb jet entrance, mid-level vort maxes, and
strengthening low-level jet will combine to produce widespread lift
in the vicinity of the surface low and cold front across the Upper
Midwest. Strong to severe thunderstorms are expected along and near
this feature Monday, as SBCAPE pushes 1500-2500 J/kg in the warm
sector which stretches down into the mid-Mississippi Valley (with
similar MUCAPE values). Despite the presence of a low-level warm
nose and modest cap, strong lift aloft and an abundance of elevated
instability will make elevated storms preferred, with surface based
storms possible if the cap is able to erode or if the lift is able
to overcome the cap. The best chance for severe thunderstorms on
Monday will be across the Upper Midwest into Iowa and northwestern
Missouri, closest to the cold front and surface low. However, I
cannot rule out a few strong to severe thunderstorms forming in our
forecast area ahead of the front as it approaches the area Monday
evening and, to a lesser extent, overnight.

The cold front is not currently projected to enter the forecast area
until daytime Tuesday as the surface low and the northern stream mid-
level trough swing into the Great Lakes region. Severe thunderstorm
chances on Tuesday hinge on the timing of the frontal passage and
instability rebounding in the warm sector ahead of the front. If the
front is slower to enter the forecast area, instability will be able
to build over a larger portion of the forecast area and result in a
larger risk for strong to severe thunderstorms. If the front moves
into the forecast area sooner, then a smaller area will rebuild the
necessarily instability and see the threat for strong to severe
thunderstorms. The current SPC 15% threat remains appropriate at
this time. All hazards remain on the table for both days.

Beyond this system the pattern remains active across the mid-
Mississippi Valley. The southern stream trough eventually kicks out
of the Four Corners region by mid-week, translating into the mid-
Mississippi Valley and bringing another chance for showers and
thunderstorms to the forecast area during the second half of the
work week.

Delia

&&

.AVIATION...  (For the 06z TAFs through 06z Saturday Night)
Issued at 1005 PM CDT Fri Apr 25 2025

Widespread stratus continues to expand and move south into the
area. Ceilings have generally been around 2000 feet AGL, though
may tend to dip below 2000 feet overnight at KCOU and KUIN in
particular. The stratus should advect out of the area from north
to south on Saturday, with VFR conditions areawide favored by
early afternoon. Northerly winds overnight are forecast to slowly
veer to the northeast and then eventually east during the day on
Saturday.

Gosselin

&&

.CLIMATE...
Issued at 218 AM CDT Wed Apr 23 2025

Unseasonably warm temperatures are expected on Monday, nearing
daily records for late April. Here are the daily record highs
for April 28.

LOCATION        RECORD
ST LOUIS    92 set in 1970
COLUMBIA    88 set in 1970
QUINCY      88 set in 1970


&&

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

$$

WFO LSX