Hazelwood, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

066
FXUS63 KLSX 171943
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
243 PM CDT Thu Apr 17 2025

.KEY MESSAGES...

-There is a threat for elevated strong to severe thunderstorms on
 Friday night, Saturday, and Sunday. Large hail and damaging winds
 will be the main threat with these storms.

-On Sunday, concern is increasing that we`ll see even stronger
 thunderstorms capable of producing tornadoes along with large
 hail and damaging winds.

-A flood watch has been issued for areas along and south of
 Interstate 70, where up to 5" of rain is possible through Sunday
 night.

&&

.SHORT TERM...  (Through Late Friday Night)
Issued at 201 PM CDT Thu Apr 17 2025

The central portion of the country is now between upper level
ridging over the eastern CONUS and an amplified trough extending
from northern Manitoba into the eastern Pacific. Water vapor
imagery reveals that the trough is punctuated by shortwaves over
central Saskatchewan, the northern Great Basin, and off the coast
of southern California. The trough will slide eastward through
this period with the northernmost shortwave diving south, reaching
the upper Great Lakes by Saturday morning. At the surface, a low
currently over western Kansas will zip to the northeast through
Friday morning before a cold front driven by the above shortwave
drops southeast into the Mid-Mississippi Valley tomorrow evening.

Before the arrival of the front, deep layer flow will remain out of
the southwest across the region. This will result in strong warm air
advection in the low levels, leading to the development of a stout
capping inversion ahead of the front. The cap is expected to largely
keep a lid on any surface based convection along the leading edge of
the front tomorrow afternoon. Precipitation chances should gradually
tick up, mostly behind the front, beginning in the late afternoon as
the low level jet intensifies. Instability will already be decreasing
by the time convection gets going, but MUCAPE is expected to
remain around 1,000 J/kg across our south through the evening
hours. This instability coupled with effective deep layer shear
around 40kts will support the development of at least a few
elevated strong to severe storms. The primary threat with these
storms will be large hail and perhaps damaging winds if they can
punch through the low level inversion. Despite the cap, there are
a few high-res models that develop a surface-based storm or two
along the front. If this were to occur, winds would be a greater
threat than with the elevated storms. Given the low chances for
surface based convection, and the fact the surface winds are
expected to be southwesterly, tomorrow`s tornado threat is quite
low.

BSH

&&

.LONG TERM...  (Saturday through Next Thursday)
Issued at 201 PM CDT Thu Apr 17 2025

On Saturday, The upper level trough will continue to slide east,
with a series of embedded impulses ejecting downstream toward the
Mid-Mississippi Valley. These shortwaves will ride atop Friday`s
cold front, which will be stalled somewhere across southern
Missouri and Illinois by Saturday morning, resulting in multiple
rounds of rainfall across the area. LREF mean MUCAPE ranges from
around 100 J/kg in northern MO/central IL to 1000 J/kg in southern
MO/IL. The higher instability in the south will again overlap
with effective deep layer shear around 40kts, which would support
the development of isolated strong/severe elevated thunderstorms
capable of producing hail to 1". More concerning is the potential
for multiple rounds of efficient rainfall over the same locations.
By Saturday evening, mean LREF QPF exceeds 1.5" along the I-44
corridor, and this will be the start of the flash flood threat
that will extend into Sunday.

By Sunday, guidance is in strong consensus that a sharp, negatively
tilted shortwave will eject eastward out of the deep western
CONUS trough. This wave will drive a surface low somewhere across
the Mid-Mississippi Valley, though guidance differs on the
depth/intensity of this disturbance. Roughly 50% of 00z LREF
members favor a relatively weaker wave with a weaker surface low
tracking through our forecast area. Should this scenario pan out,
it`s unlikely that we would see much instability with roots in the
boundary layer, though MUCAPE should again push to 500-1000 J/kg.
This elevated instability, coupled with deep layer shear in
excess of 50kts, would set the stage for at least a few strong to
perhaps severe storms capable of producing large hail.

The other 50% of LREF membership favors a stronger wave, with a
deeper and more northerly surface low. This low track would put much
of the CWA in the warm sector, pushing dewpoints into the 60s and
MLCAPE to near 1000 J/kg. Deep layer shear in this scenario would
again be in excess of 50kts, with a large component of the shear
vectors perpendicular to the cold front attendant to the surface
low. This would support the development of strong to severe discrete
thunderstorms. With 0-1km near expected to be near 30kts, these
storms would be capable of producing tornadoes along with large
hail and damaging winds.

LREF mean QPF shows another 1.5" of QPF along and just north of
the I-44 corridor from Saturday night through Sunday, putting
storm total amounts near 4" in some areas. Amounts are likely to
be even higher than that in locations that see multiple convective
core pass the area, pushing closer to the 90th percentile (5").
With high confidence in all this rain, we`re gone ahead and raised
a flood watch for the southern 2/3rds of the forecast area, where
we`re expecting at least some flash flooding as well as widespread
minor to perhaps moderate river flooding.

BSH

&&

.AVIATION...  (For the 18z TAFs through 18z Friday Afternoon)
Issued at 1213 PM CDT Thu Apr 17 2025

Rain has moved out of the area, leaving mostly clear skies and
gusty southerly winds in its wake. Winds will remain elevated
through the afternoon before tailing off slightly overnight. Winds
just of the deck will remain rather strong through the night, but
with elevated surface winds, I don`t think we`ll quite meet LLWS
criteria. Winds will again be gusty tomorrow before a cold front
moves into the area in the afternoon. Showers and storms are
expected along and behind this front, though precipitation isn`t
expected to reach the terminals until after the TAF period.

BSH

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Flood Watch from Friday evening through Sunday evening for
     Audrain MO-Boone MO-Callaway MO-Cole MO-Crawford MO-
     Franklin MO-Gasconade MO-Iron MO-Jefferson MO-Lincoln MO-
     Madison MO-Moniteau MO-Montgomery MO-Osage MO-Pike MO-
     Reynolds MO-Saint Charles MO-Saint Francois MO-Saint Louis
     City MO-Saint Louis MO-Sainte Genevieve MO-Warren MO-
     Washington MO.

IL...Flood Watch from Friday evening through Sunday evening for Bond
     IL-Calhoun IL-Clinton IL-Fayette IL-Greene IL-Jersey IL-
     Macoupin IL-Madison IL-Marion IL-Monroe IL-Montgomery IL-
     Randolph IL-Saint Clair IL-Washington IL.

&&

$$

WFO LSX