423
FXUS63 KLSX 101757
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1157 AM CST Sun Nov 10 2024

.KEY MESSAGES...

- Patchy fog remains possible early this morning, but visibilities
  are improving and this is not expected to last much beyond
  sunrise.

- Most of the week is likely to be dry, with the next opportunity
  for rain expected Wednesday and Wednesday night. While some rain
  is likely (60 to 80% chance over 24 hours), amounts are expected
  to be generally light and thunderstorm chances are minimal.


&&

.SHORT TERM...  (Through Late Monday Afternoon)
Issued at 314 AM CST Sun Nov 10 2024

While rain is winding down across the region, low clouds and fog
continue to impact much of eastern Missouri and western Illinois as
low level moisture lingers ahead of an approaching Pacific front.
While dense fog has not been common as of 2:30 am, there have been a
few observations of visibilities of between 1/4 and 1 mile, most
notably in central/southeast Missouri. Visibilities have also
fluctuated quite a bit over time, with clearing skies often leading
to quick drops in visibilities as fog intensifies near the surface.

However, low clouds are slowly eroding along their western edge as
southwesterly winds advance eastward, and this trend is expected to
continue through the morning. This will likely limit fog formation
to a brief window, and skies should be mostly clear by the
afternoon. The lone exception to this may be across northern
Missouri and west-central Illinois, where wraparound moisture and
resultant cloud cover may clip our northern areas this afternoon as
the upper low drifts through Iowa.

During the day today, breezy southwesterlies will settle into the
area, which will help temperatures to rebound quickly from
yesterday`s values thanks in part to downslope warming in the lee of
the Ozarks. As such, expect afternoon values mostly ranging from 60
to 70 degrees, with the warmest values across the Ozarks and
southwest Illinois. Winds will weaken overnight tonight, and as such
temperatures should cool efficiently and settle into the upper 30s
to low 40s. This may also yield another round of patchy fog in
river valleys thanks to lingering low level moisture.

On Monday, a zonal flow pattern will become established aloft, and
surface high pressure will approach the area behind a very weak cold
front. While this will likely cool temperatures a bit on Tuesday,
mild temperatures will persist tomorrow with afternoon readings
climbing once again into the 60s. Mostly sunny skies can also be
expected, resulting in a pleasant start to the work week.

BRC

&&

.LONG TERM...  (Monday Night through Saturday)
Issued at 314 AM CST Sun Nov 10 2024

As we begin the extended period Tuesday, the previously discussed
weak cold front will sink south of the area along with surface high
pressure. Latest ensemble guidance has cooled surface temperatures a
bit Tuesday behind this boundary, although there seems to be at
least some increasing ensemble spread among members. Still, the
trend is clear, and it is increasingly likely that temperatures
Tuesday will be about 5 to 10 degrees cooler than Monday thanks to
this boundary. Dry conditions are also expected to persist as well.

By Wednesday, attention turns to the approach of a progressive
trough from the west, which has been a persistent feature in
ensemble guidance over the past few days. However, while past
forecasts exhibited a great deal of spread among ensemble members,
there has been an increase in agreement regarding the timing and
strength of this wave in recent model runs. Likewise, confidence is
growing that this wave will quickly move through and drive a modest
cold front through the Mid-Mississippi Valley region sometime
between Wednesday afternoon and Thursday morning. This also remains
our next best opportunity for precipitation, as both the LREF and
NBM maintain around a 70 to 80% chance of at least some
precipitation falling along this boundary. However, given that this
wave will be rather progressive, there will only be a limited amount
of time for quality moisture return to occur, and instability
projections in the warm sector continue to trend lower and lower.
As such, rain amounts are likely to be generally light, and some
areas may miss out completely. Meanwhile, the potential for
thunderstorms also appears to be diminishing, although a stray
strike of lighting or two can`t be completely ruled out.

After this brief period of showers, a broad ridge of high pressure
is once again expected to gradually build back into the lower and
middle Mississippi Valley over the latter half of the work week, and
precipitation chances will diminish. This is likely to result in a
modest warming trend over the latter half the week as well, although
another passing shortwave to our north may slow this warming down
slightly. Otherwise, there are early indications that an active jet
stream pattern may resume over the weekend, but confidence remains
low regarding potential impacts at this time.

BRC

&&

.AVIATION...  (For the 18z TAFs through 18z Monday Afternoon)
Issued at 1150 AM CST Sun Nov 10 2024

VFR conditions are expected to persist at most site with exception
to terminals located near rivers and adjacent valleys (KSUS, KJEF
and KCPS). Initially, gusty southwest flow will impact all
terminals through the afternoon hours with winds expected to
subside this evening. As surface flow become light and variable,
fog is likely to develop over milder rivers and larger streams.
Additionally, recent rainfall has added moisture to the surface
soil, which will support fog in low lying valleys, especially
those adjacent to rivers. MVFR visibilities are forecast at the
aforementioned TAF site above. A brief period of IFR cannot be
entirely ruled out if denser fog is carried into one of these
terminals through the early morning hours.

Maples

&&

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

$$

WFO LSX