Mehlville, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

031
FXUS63 KLSX 241128
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
528 AM CST Sun Nov 24 2024

.KEY MESSAGES...

- Temperatures will run about 10 degrees above normal today (60s)
  before cooling near or slightly below normal behind Monday`s
  cold front.

- There is a chance (15-30%) of rain over parts of the area late
  tonight into Monday along the cold front. Additional chances of
  precipitation exist from mid to late week mainly favoring rain,
  possibly mixing with snow at times Wednesday night into
  Thursday morning.

- Arctic air will spill southward late on Thanksgiving Day,
  leading to what is likely (80-90% probability) to be a prolonged
  period of well-below normal temperatures (about 20 degrees below
  normal).


&&

.SHORT TERM...  (Through Late Monday Afternoon)
Issued at 320 AM CST Sun Nov 24 2024

Nighttime microphysics show mainly high clouds streaming overhead as
a warm front advances to the northeast of the of the forecast area.
Surface analysis shows southeasterly winds along and east of the
Mississippi River turning out of the south over central Missouri.
Further to the west, high clouds erode with mainly clear skies over
the central Plains. While much of the day will have some degree of
cloud cover, the area of clearing over the Plains is expected to
work eastward through the day today, resulting in partly to mostly
sunny conditions. RAP/GFS/NAM all show a shallow, strong inversion
that will limit mixing depth under 2k feet in Illinois. Mixing
deepens westward over central Missouri, but still remains around 3k
feet. The environment likely limits much potential in overachieving
forecast highs, which are already in the low to mid-60s. That being
said, winds along are in 20-30 knots or so near the top of the
boundary layer, resulting in southerly gusts of 20-30 mph from late
morning through early this evening.

A strong cold front is expected to move in from the northwest late
this evening and progress through the region through early Monday
afternoon. Timing has been fairly consistent over the last couple of
forecast cycles. Rain chances are low (15-30%) and what falls is
likely to be light with HREF probabilities show a narrow range even
between the 1st-99th percentiles (0.00"-0.07") where the range is
widest over southeast Missouri and southwest Illinois. In addition
to moisture depth being limited, LREF stats suggest what fall will
be very light. Temperatures during the day Monday may briefly
stagnate during peak heating, but overall trends will be downward
with 30s/40s moving in from the northwest Monday evening.


Maples

&&

.LONG TERM...  (Monday Night through Saturday)
Issued at 320 AM CST Sun Nov 24 2024

The cold front will push southeast into the Ohio and Tennessee
Valleys Monday night. Surface high pressure begins to build in from
the central Plains underneath quasi-zonal flow aloft. This will
secure a dry forecast Monday night through late Tuesday night.
Though it will be much cooler with lows in the 20s (Tue AM) and 30s
(Wed AM) and highs in the 40s (Tue), these temperatures are near or
slightly below normal.

A progressive shortwave is still providing challenges Wednesday into
Thanksgiving Day as ensembles remain dispersed with a couple of
trends to point out in the latest 00z suite. Each of the ensembles
(Canadian/GFS/ECMWF) are similar in the sense that roughly half of
the members are producing some magnitude of light snowfall generally
from the central sections of the CWA (I-70) northward. Another
notable trend is that the number of members producing more than a
couple of inches of snow are trending downward, even as few as there
were in past ensemble suites.

If taking the ensemble members at face value, it mutes additional
details that favor less in the way of accumulations, especially as
you work north to south through Missouri and Illinois. LREF
probabilities for 6-hourly snowfall accumulations of 0.1" land along
and north of I-70. At 1" or more, these probabilities have been
trending lower over the past couple of forecast cycles.
Probabilities now peak around 25% along and north of Hwy 36/I-72,
roughly from Kirksville, MO through Quincy, IL. The question is how
much moisture will extend that far north, for how long, and whether
surface temperatures will support accumulation. While each of the
deterministic models have something different on track, timing and
northward extend of precipitation, surface temperatures remain
marginal or too warm. While there is a north-south gradient to the
temperature pattern, the lack of organization makes this a simpler
east-west progressive scenario with limited residence time.
Locations that mix with or change to snow are likely to be brief and
will not have the advantage of being preceded by a prolonged period
of sub-freezing surfaces. Additionally, some of the deterministic
soundings are or nearly saturated and do not show much potential for
wet bulbing, which would otherwise effectively cool the air below
the cloud base.

Speaking of sub-freezing surfaces... The real story may end up being
the arctic cold that moves in late Thanksgiving Day and stretches
through the following weekend. Signals have been consistent and have
grown stronger over the last several days. This is likely to be our
first prolonged period of well-below normal cold sourced from Canada
following the Thanksgiving holiday. There is a wide spread in NBM
and LREF temperature data, but despite this, even the upper quartile
shows widespread 30s for highs and lows in the teens (about 20
degrees below normal) from November 29th through December 2nd as
a large upper trough practically swallows the eastern 2/3rds of
North America, places us in northwest flow and even supports a
clipper pattern that brings an occasional flurry or light snow
toward the end of the period.


Maples

&&

.AVIATION...  (For the 12z TAFs through 12z Monday Morning)
Issued at 528 AM CST Sun Nov 24 2024

VFR conditions are expected to persist today. Southerly gusts are
expected to develop during the daylight hours and subside after
sunset. A cold front will approach from the northwest this evening
with low chances (15-30%) for a light shower as the front moves
southeast through early afternoon Monday. Guidance has been
consistent with MVFR ceilings along and behind the front tonight
into Monday. Some of the more pessimistic data suggests some IFR,
but the spread and persistence of IFR is uncertain. Therefore,
MVFR is favored. Guidance also highlights low level wind shear
(directional) potential along the front, but potential lands in
the later portion of the TAF, which can be fine tuned in later
updates.

Maples

&&

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

$$

WFO LSX