284
FXUS63 KLSX 072242
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
542 PM CDT Mon Apr 7 2025

.KEY MESSAGES...

- A widespread freeze will impact sensitive vegetation tonight
  with the entire region falling below freezing. Those outside of
  either the Mississippi River Valley and metropolitan areas are
  at risk of a hard freeze (less than 28 degrees).

- Cool temperatures moderate by mid-week, when a few chances (30-
  50%) for light rain and a rumble of thunder also return.


&&

.SHORT TERM...  (Through Late Tuesday Night)
Issued at 138 PM CDT Mon Apr 7 2025

A dry cold front is traversing the region per surface observations,
forced by a mid-level shortwave amidst stronger northwest flow
aloft. Behind it, cool and gusty conditions will spread south
through the afternoon and evening. With surface high pressure
building through the late evening, winds are forecast to weaken
under clear skies. These favorable conditions for radiative
cooling, combined with the colder airmass itself, will lead to
temperatures falling a few degrees further than last night`s lows.
The entire region remains heavily favored (80-90% chance) to cool
below freezing, which will threaten any tender vegetation. The
greatest impacts are expected in exposed areas away from the major
river valleys and metropolitan areas, where a hard freeze (less
than 28 degrees) is forecast.

The surface high quickly exits tomorrow from west to east, veering
winds gradually out of the south and establishing a weak warm air
advection regime. While temperatures will still be abnomally-cold
tomorrow, in parts of Illinois by as much as 15 degrees, this will
be the last of the cool air for a few days at least. Another weak
shortwave develops in the central Plains late Tuesday afternoon and
tracks east with the flow becoming quasi-zonal with time. The wave
will allow for weak cyclogenesis as it crosses over our region.
Depending on the wave`s strength, we have a threat for isolated to
scattered showers early Wednesday morning along a developing warm
front. Between weak shear and limited moisture, any thunderstorms
that manage to develop would be fairly meager.

MRB

&&

.LONG TERM...  (Wednesday through Next Monday)
Issued at 138 PM CDT Mon Apr 7 2025

The threat for showers and a few non-severe thunderstorms continues
into Wednesday as the surface low tracks through the region. Most of
the activity will be confined to the vicinity of the low and a weak
cold front that trails behind it, keeping the highest rain chances
in northern Missouri and western Illinois. Wednesday will also see a
notable warmup, with most very likely (80-90% chance) seeing a 10-15
degree rise in high temperatures compared to the day before. The
cold front drops through the region during the evening Wednesday,
but cooler air lags behind it. Most ensemble and deterministic
guidance does have a reinforcing cold front dive through the
northwest flow aloft to spark renewed shower/weak thunderstorm
activity for most of the region on Thursday. While daytime highs
will be similar to Wednesday, this front will have a more
noticeable impact on temperatures Thursday night into Friday. The
NBM interquartile range is fairly narrow for Friday`s highs (5-7
degrees depending on the location) and far below the potential
high temperatures Thursday. A freeze is not likely (less than 20%
chance) but a frost can`t be ruled out late Friday into Saturday
morning in exposed, low-lying parts outside of urban areas.

This secondary shot of cooler air will be short-lived, with the
surface high again quickly scooting east and bringing warmer
southerly flow to the region for the weekend. While rain chances
look very low (less than 15%) until early next week, there are a few
ensemble members that threaten some light rain Sunday amidst a wing
of warm air advection.

MRB

&&

.AVIATION...  (For the 00z TAFs through 00z Tuesday Evening)
Issued at 541 PM CDT Mon Apr 7 2025

Dry and VFR flight conditions will continue through the end of the
forecast period. Northerly winds will become light and variable
overnight and into the day tomorrow as a surface high moves across
the area. Winds will pick up from the south late in the period.

Delia

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Freeze Warning from midnight tonight to 9 AM CDT Tuesday for
     Audrain MO-Boone MO-Callaway MO-Cole MO-Crawford MO-
     Franklin MO-Gasconade MO-Iron MO-Jefferson MO-Knox MO-Lewis
     MO-Lincoln MO-Madison MO-Marion MO-Moniteau MO-Monroe MO-
     Montgomery MO-Osage MO-Pike MO-Ralls MO-Reynolds MO-Saint
     Charles MO-Saint Francois MO-Saint Louis City MO-Saint
     Louis MO-Sainte Genevieve MO-Shelby MO-Warren MO-Washington
     MO.

IL...Freeze Warning from midnight tonight to 9 AM CDT Tuesday for
     Adams IL-Bond IL-Brown IL-Calhoun IL-Clinton IL-Fayette IL-
     Greene IL-Jersey IL-Macoupin IL-Madison IL-Marion IL-Monroe
     IL-Montgomery IL-Pike IL-Randolph IL-Saint Clair IL-
     Washington IL.

&&

$$

WFO LSX