Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 271949
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
249 PM CDT Wed Mar 27 2024

.KEY MESSAGES...

- Some locations will see sub-freezing temperatures tonight for
  the last time until at least early next week. A widespread hard
  freeze is not expected.

- Thursday will kick off our warming trend. Expect temperatures in
  at least the 60s and 70s from tomorrow through Monday.

- The chance of showers and thunderstorms re-enters the forecast
  on Friday night. There is the potential for strong to severe
  thunderstorms Sunday and Monday.


&&

.SHORT TERM...  (Through Late Thursday Night)
Issued at 247 PM CDT Wed Mar 27 2024

Surface high pressure continues to spill into the region this
afternoon providing us with a tranquil, sunny spring day. Tonight,
near calm winds will work in tandem with clear skies to produce
radiational cooling conditions. The dry airmass overhead will
promote cooling as well, supporting another forecast of around
freezing lows. The probability of a hard freeze (<28 degrees) begins
to diminish, however, given the timing of the surface high`s
passage. The will happen near midnight, and the best radiational
cooling conditions will occur near the same time. In the very early
morning hours, winds will gradually be increasing, decreasing the
effectiveness of the cooling with time. MOS guidance, which tends to
do well with radiational cooling setups, keeps temperatures around
the region largely above 29 degrees with the exception of sites in
low-lying areas and HREF probabilities of <28 degrees are <20%
areawide. With all of this in mind, a widespread hard freeze appears
to be unlikely with only localized instances of these conditions
expected.

Low to mid-level ridging will slide east on Thursday, leaving the
Mid-Mississippi Valley in deep ridging with southwest flow in the
low-levels. New found warm air advection will kick off our
warming trend with afternoon highs in the 60s - a 10 to 15 degree
jump from today. Tomorrow will be another dry day with slightly
higher winds under the influence of daytime mixing.

Jaja

&&

.LONG TERM...  (Friday through Next Wednesday)
Issued at 247 PM CDT Wed Mar 27 2024

Friday will be very warm and dry as southwest flow continues to pump
warm air into the region. This flow will introduce Gulf moisture
into the region as well, which will continue to increase before a
cold front washes it away early next week. Until the frontal
passage, we`re looking at a more active pattern setting up with
increasingly more warmth and moisture to fuel thunderstorms.

The first round of precipitation is expected Friday night as a mid-
level shortwave passes through the Midwest. There is a chance (40-
50%) of showers and thunderstorms largely north of I-70, but meager
upper level forcing and instability dampen the potential for
anything strong to severe. An attendant cold front will stall east-
to-west over the forecast area, though its exact location is still
yet to be seen. Between Saturday and Monday, the front will serve to
create a stark temperature gradient of up to 15 degrees from the
north side of the front to the south side. Locations north of the
front may struggle to reach 65, whereas locations to the south could
reach 80.

Precipitation chances increase again on Sunday after a very warm and
largely dry Saturday. By this point, a deep mid-level trough will be
moving onto the west coast with ridging in the eastern two-thirds of
the CONUS. A surface low pressure system will be deepening on the
Front Range, intensifying the pull of warm air and moisture into the
central CONUS. Deterministic guidance does show significant capping
within the warm sector on Sunday, but there`s still enough
uncertainty to keep the possibility of strong warm advection
thunderstorms on the table. Elevated thunderstorms triggering off
the surface boundary are possible as well.

A shortwave will eject into the Mid-Mississippi Valley from the
western mid-level trough on Monday. With increased instability, a
now advancing front, and increased upper level support, the
potential for strong to severe thunderstorms will increase. There`s
a wide spread in ensemble and deterministic guidance regarding how
unstable we are able to become on Monday. However, high confidence
in above average temperatures and moisture combined with a favorable
setup for severe weather yield enough confidence to mention the
potential.

Jaja

&&

.AVIATION...  (For the 18z TAFs through 18z Thursday Afternoon)
Issued at 1214 PM CDT Wed Mar 27 2024

VFR flight conditions are expected to prevail through Thursday.
Northwest flow will become light and variable later this
afternoon and evening, and them turn back to the southwest
Thursday morning as high pressure moves from the eastern Plains
into the Lower Mississippi Valley

Carney

&&

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

$$

WFO LSX


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