604
FXUS63 KLSX 221130
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
530 AM CST Fri Nov 22 2024

.KEY MESSAGES...

- Seasonably cold conditions will continue through tonight before
  temperatures warm back up above normal by Sunday. A cold front
  moves through on Monday, cooling temperatures below normal for
  the remainder of the week.

- An active pattern brings increasing chances of precipitation
  around the Thanksgiving holiday. Rain continues to be the most
  likely precipitation type.


&&

.SHORT TERM...  (Through Late Saturday Afternoon)
Issued at 259 AM CST Fri Nov 22 2024

Broad cyclonic rotation over the eastern U.S. is resulting in
northwesterly flow across the Midwest and seasonably cool
conditions this morning. A mid-level stratus deck has been huddled
over the region overnight, slowly inching to the southwest over
the last several hours. Surface observations show the coldest
temperatures at the top of the 09z hour were in the mid-30s over
central Missouri where skies remained clear longer. Clouds have
kept temperatures 5-7 degrees warmer to the east and will likely
be prevented from falling too much further.

The shallow, low level saturated layer of about 1.5-2k feet deep
is centered round 2k feet, signaling much of the day will be
spent under some degree of low clouds. The western edges are where
breaks are more likely in the later part of the day. Much of this
won`t be motivated to move out until ridging to the west nudges
eastward late tonight into Saturday. While it keep conditions
chilly today with highs in the 40s, winds will be far less of an
issue. Light winds and partial clearing will allow temperatures to
drop a few degrees cooler tonight with lows ranging from the
mid-20s to low-30s. Saturday sees a bit of an uptick, however, as
return flow rounds the departing surface ridge. Highs return to
the 50s.

Maples

&&

.LONG TERM...  (Saturday Night through Thursday)
Issued at 259 AM CST Fri Nov 22 2024

Ridging over the southeastern U.S. and troughing over the central
Plains will work in tandem to strengthen deep, southwesterly flow
over the Mid-Mississippi Valley Saturday night into Sunday. Warm air
advection is expected to push temperatures back above November norms
(upper 40s/low-50s) with LREF ensembles showing 60-90% probabilities
for highs exceeding 60 degrees along and west of the Mississippi
River. Probabilities (<10%) drop off quite a bit when approaching
the 65 degree threshold, suggest most locations will end up in this
range Sunday afternoon.

The trough to the west gives rise to a surface low that has shown a
varying degree of deepening somewhere between the Mid-Mississippi
Valley into the Great Lakes Region. This continues to result in an
increasing spread in temperatures heading into Monday thanks to
differences in strength and speed. One minor, promising sign is in
the latest 00z LREF spreads showing a slight decrease not only
between the 25th/75th percentile ranges, but also showing a
narrowing in the geographic coverage in such spreads. Though still
rather large (8-10 degrees or so), this trend is in the right
direction. Precipitation will be highly reliant on timing as the
system only becomes better organized as it move northeast late
Monday. Saturation in the lowest 5,000 feet will be aided by
convergence along the front that is departed from better
mid/upper forcing well to the north. Even then, while a majority
of ECM/GFS ensembles show precipitation, all but three members
show less than 0.10" of an inch near STL with about one-third of
the members near 0.10" near Salem, IL.

Though spread decreases Tuesday, this signals higher confidence in a
dry, seasonably cold forecast with highs back in the 40s. Focus
shifts to the midweek period with holiday travel coming into view.
Global guidance is coming into better alignment with the general
synoptic pattern. However, finer details remain uncertain as zonal
upper flow introduces additional shortwaves into the central U.S.
with a north-south temperature gradient. These systems, while
progressive and relatively weak, do have southern tracks with
colder air moving in at the end of the period. While daytime
temperatures currently favor rainfall as a predominant
precipitation type, a handful of ensemble members show the
potential for snowfall in the later half of the week. What has
been notable is a persistent signal to what could be the year`s
first real intrusion of very cold air from the north-central U.S.
sometime late next week.


Maples

&&

.AVIATION...  (For the 12z TAFs through 12z Saturday Morning)
Issued at 530 AM CST Fri Nov 22 2024

A near-solid blanket of MVFR stratus continue to affect the region
this morning. It was initially expected to last through morning
before lifting to VFR. However, latest guidance has been more
pessimistic and delayed improvement by a few hours. Considering
the cool, northwesterly flow, stratus may be slower to erode with
guidance showing a shallow saturated layer centered around 2k feet
through at least early afternoon. VFR conditions are expected one
skies scatter out.

Maples

&&

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

$$

WFO LSX