Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 162322
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
622 PM CDT Sat Mar 16 2024

.KEY MESSAGES...

- Behind this evening`s cold front, gradually colder and colder
  air will infiltrate the area. A brief period of well-below
  normal temperatures (10-15 degrees) is forecast Sunday night
  and Monday. Subfreezing lows are forecast both Sunday and Monday
  nights, with the coldest night Sunday night for a majority of
  the area.

- Temperatures are forecast to quickly moderate back above normal
  by Tuesday and remain that way through the end of the week. Dry
  weather is forecast through Wednesday, with the next chance of
  rain Wednesday night into Thursday.


&&

.SHORT TERM...  (Through Late Sunday Afternoon)
Issued at 223 PM CDT Sat Mar 16 2024

A surface cold front is currently moving across northeast Missouri
and west-central Illinois late this afternoon. This front will move
through the remaining portion of the CWA by mid evening, with winds
veering from the west to the northwest. No shower activity is
anticipated with this front this far southwest, with stronger low-
level convergence and mid/upper level forcing for ascent staying
well off to our east/northeast closer to the Great Lakes/Ohio
Valley. Some increase in midlevel cloud cover is expected, along
with decreasing temperatures. Lows tonight are forecast to drop back
into the 30s, or right around normal for the date.


Low-level cold air advection continues on Sunday with 850-hPa
temperatures falling below -5C for most of the area by Sunday
afternoon. There will be at least some sunshine, though some cirrus
is expected beneath the right-entrance region of an upper-level jet
streak. In addition, soundings show some cumulus development by
afternoon. The increasingly strong March sunshine and deep mixing
should help temperatures climb into the 40s to low 50s for most
locations. This would be slightly below normal for mid March.

Gosselin
&&

.LONG TERM...  (Sunday Night through Next Saturday)
Issued at 223 PM CDT Sat Mar 16 2024

(Sunday Night - Monday Night)

Gradually colder air will continue to infiltrate the bi-state area
Sunday night as 850-hPa temperatures drop to around -10C. That would
be at about the 5th percentile of climatology. The incoming surface
high in the Plains (~1030 hPa) is also seasonably strong, above the
90th percentile. These factors lead credence to the expectation for
a (short) period of well-below normal (10-15 degrees) temperatures
starting Sunday night. Lows Sunday night/Monday morning are forecast
to drop into the 20s areawide, with the possible exception of the
urban heat island of St. Louis (~30F). The only reason lows will not
be several degrees colder is because northwest winds should stay up
around 5-10 mph with the surface anticyclone around 1200 UTC Monday
located across the mid-Missouri Valley.

The coldest daytime temperatures will be on Monday as the surface
high slides into southwest Missouri. Highs in the low to mid 40s are
forecast areawide.

Monday night is not expected to be as cold as Sunday night due to
the surface high very quickly sliding into the lower Mississippi
Valley. Temperatures should cool sharply after dusk given a clear
sky and light/variable winds, but increasing return flow overnight
should lead to warming temperatures late night. Lows are forecast to
be in the upper 20s to near 30 degrees, with these lows likely
coming around midnight or slightly after.

(Tuesday - Wednesday)

Continued dry weather is forecast into the middle of the work week.
After a cool start Tuesday morning, a rapid warmup is forecast by
afternoon as strong low-level warm air advection builds eastward
into the area. A cold front is expected to move through sometime
late Tuesday, but how far west the relatively cooler air reaches is
a question mark. The spread between the NBM`s 25th/75th percentile
increases quite a bit (~10F) beginning with Tuesday night`s lows and
continues into Wednesday with respect to high temperatures. At least
a slight cooldown is forecast by Wednesday, with highs back close to
normal (mid 50s to low 60s).

(Wednesday Night - Next Saturday)

Forecast uncertainty continues to be high for the remainder of the
extended. While ensemble guidance agrees fairly well with the
general synoptic pattern (quasi-zonal/weak northwest flow aloft),
there are some substantial differences with how strong/far north a
midlevel shortwave trough will be as it ejects out of the south-
central Plains. While this system does not look like much of a rain
maker (LREF probabilities for >=0.10" are only 20-30%), thicker
cloud cover would impact temperatures late this week. The spread
between the 25th/75th percentile high temperatures increase
Thursday/Friday, with differences at most locations on the order of
10-15 degrees. This spread roughly represents near normal
temperatures on the cool end to 10+ degrees above normal on the
higher end of the spectrum.

Gosselin
&&

.AVIATION...  (For the 00z TAFs through 00z Sunday Evening)
Issued at 621 PM CDT Sat Mar 16 2024

VFR flight conditions through the forecast period. Otherwise, the
main issue is the cold front which is currently sinking south
across the region as of 23z and has move through KUIN. The front
will move through TAF sites along I-70 corridor by 02z Sunday with
winds veering to the northwest and diminishing. Winds will pick
back up by mid morning on Sunday with gusts near 25kts at times.

BYRD
&&

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

$$
WFO LSX


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