Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 150808
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
308 AM CDT Fri Mar 15 2024

.KEY MESSAGES...

-Dry weather is expected through the weekend into early next week.

-Temperatures will be variable through the period with near to
 slightly above normal highs on today and Saturday, dropping to
 below normal behind a cold front Sunday and Monday. Above normal
 temperatures will return by mid-week.


&&

.SHORT TERM...  (Through Late Saturday Afternoon)
Issued at 306 AM CDT Fri Mar 15 2024

Cooler and drier air will continue filtering into the Mid-
Mississippi Valley today. The sky will clear slowly from northwest
to southeast, and most of the area should be sunny to mostly
sunny by early this afternoon. Parts of southeast Missouri may not
see much sunshine until later in the day though. The cold
advection on north- northeast flow combined with the clouds will
produce a colder day with highs between 10-20 degrees lower than
Thursday`s. While there may be a stray early morning shower in
southeast Missouri (<10% chance), today will be a start of a dry
period which will likely last at least until the middle of next
week.

Another vigorous short wave trough will dig from
Saskatchewan/Manitoba into the Upper Midwest and Great Lakes Region
tonight into Saturday.  The surface reflection will skirt the
northern Great Lakes across Ontario.  The trailing cold front will
dip into Iowa and far northern Missouri Saturday afternoon. Most of
Missouri as well as central/southern Illinois should stay south of
the front on Saturday.  Westerly flow across these locations along
with plenty of increasingly strong mid-March sunshine will allow
temperatures to warm back up to well above normal in the mid to
upper 60s...perhaps even low 70s across parts of southeast Missouri

Carney

&&

.LONG TERM...  (Saturday Night through Thursday)
Issued at 306 AM CDT Fri Mar 15 2024

The weekend warmup will be short-lived as another strong vortmax
dives south on the western edge of the wave over Ontario, and digs
into the Midwest Saturday night. This vortmax will try to briefly
phase with a closed low over the southwest U.S. as it continues
digging into the Mid-Mississippi Valley Sunday. It will
ultimately greatly amplify the long wave pattern Sunday night into
Monday, developing into a long wave trough over the eastern U.S.
and a strong ridge over the west. The brief phasing then continued
digging Sunday and Sunday night will shove the surface cold front
through the area Saturday night and strong cold advection will
push temperatures back below normal on Sunday and Monday. In fact,
current indications are that temperatures will fall into the mid
20s to around 30 Sunday night/Monday morning as a Canadian high
settles across the Plains and Midwest in the wake of the front,
and highs will struggle into the 40s on Monday. As an aside, all
guidance members are showing a distinct lack of low level moisture
for the front to work with Saturday night, so it should pass
through the area with no precip.

Forecast uncertainty increases out beyond Monday as the eastern
trough moves off into the Atlantic and the flow aloft attenuates,
becoming almost zonal by late Wednesday into Thursday.  This
attenuation develops into a split-flow pattern aloft and the
southern jet stream picks up the aforementioned closed low over the
southwest U.S.  The low opens up into a wave and moves into the
southern Plains on Thursday.  Deterministic GFS and ECMWF handle the
timing and amplitude of the wave somewhat differently as it moves
into the Plains.  The LREF is showing 4 clusters in the Tuesday-
Thursday time frame, and unsurprisingly given the deterministic
solutions, uncertainty in both the amplitude and timing of the
retreating long wave to the east, and the approaching short wave
from the west.  This is leading to wide temperature ranges between
the upper and lower quartiles in the LREF from Tuesday through
Thursday...as much as 15 degrees on Wednesday and Thursday.
Regardless, the quasi-zonal flow should allow temperatures to warm
up.  The latest NBM temperatures are mainly in the low to mid 60s
for highs and mid 30s to mid 40s for Wednesday and Thursday which is
near to slightly above normal.  I can`t argue with these temps given
the uncertainty and lack of any strong signal in either the
deterministic or ensemble guidance.

Carney

&&

.AVIATION...  (For the 06z TAFs through 06z Friday Night)
Issued at 1100 PM CDT Thu Mar 14 2024

Post-frontal stratus producing MVFR flight conditions has moved
into northern/central MO and west-central IL impacting KUIN, KCOU,
and KJEF. The stratus will continue to spread southward
overnight. A gradual north to south clearing and return to VFR
flight conditions will occur on Friday morning.

Glass

&&

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

$$

WFO LSX


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