Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 260231

Area Forecast Discussion...Updated
National Weather Service Saint Louis MO
931 PM CDT Tue Oct 25 2016

Issued at 925 PM CDT Tue Oct 25 2016

Area of showers oriented northwest to southeast has pushed off to
the east of the CWA. This area is associated with a region of
850-hPa moisture convergence north and east of the sfc warm
frontal boundary. Have reduced PoPs this evening as area of
forcing responsible for this activity has begun to push out of the
CWA. Attention will then turn to the approaching cold front where
prefrontal showers and a few thunderstorms are expected. Frontal
timing looks a bit slower than previous guidance so slowed the
southeastward progress of higher PoPs late tonight and early
Wednesday. major changes to the going forecast. A
mild night looks to be on tap with light southeasterly sfc winds
under a partly to mostly cloudy sky.



.SHORT TERM...  (Through Late Wednesday Afternoon)
Issued at 340 PM CDT Tue Oct 25 2016

Widely scattered showers and a few storms were moving through
parts of central and northeast MO this afternoon along and north of
a weak, subtle warm front and in an area of low-mid level warm air
advection.  This activity should continue to move eastward into
parts of west central and southwest IL by late afternoon/early this
evening, and then should shift east-northeast of our forecast area
by late evening.  Warmer conditions can be expected tonight compared
to the previous night due to higher surface dew points along with
stronger southeast surface winds and south-southwesterly low level
winds. Lows tonight will be at least 5 to 10 degrees above normal
for late October with the warmest lows in central MO.  More
significant rain is expected very late tonight and Wednesday morning
across northeast and central MO and west central IL, and across the
rest of the area Wednesday afternoon as a shortwave approaches the
region along with its associated cold front.  The models were
depicting good upper level divergence over our area on Wednesday
ahead of the upper level trough.  Will include likely pops over most
of the forecast area on Wednesday.  Despite cloud cover and
precipitation the high temperatures should continue to be above


.LONG TERM...  (Wednesday Night through Next Tuesday)
Issued at 340 PM CDT Tue Oct 25 2016

Thursday night thru Tuesday

This period will feature a dry pattern with aoa avg temps. The upper
pattern will transition from NW flow in the wake of the mid-week
trough to more zonal flow by the wknd as a significant short wave
gets ejected from the base of the West Coast trough Friday night and
flattens the ridge as it works E thru the wknd.

The trough axis should pass thru the CWA Wed evng bringing an end to
the precip Wed night. This is a little bit of a slower solution than
yesterday so have retained decent PoPs Wed evng...esp across the
ern portion of the CWA...and then a sliver of slight chance PoPs
along the common CWA border with PAH. This is to account for any
lingering SHRAs along the bndry as it exits the FA between 06Z-
09Z. Since this system was of Pacific origin and did not tap into
any true cold air...Wed night low`s should be relatively mild with
lows in the mid 40s N to low 50s S considering this is a post
frontal air mass towards the end of Oct. A weak SFC ridge will
build into the area on Thu. This should be the coolest day of the
fcst prd with highs near normal in the 60s. High pressure will
quickly slide E by Thu evng allowing return flow to commence Thu
night. Fri looks like a warm day with 850mb temps in the mid
teens C. It doesn`t look quite as good of a set up as it did
yesterday because the short wave that was progged to pass NE of
the FA Fri night has deamplified considerably over the past 24 hrs
and isn`t anything more than a weak vort max attm. Therefore...
the flow ahead of the short wave and attendant cold front has
veered from a more favorable SW orientation to more SSW. Plus the
850mb thermal ridge was fcst to be centered across the CWA on Fri
but isn`t as far S with the 12Z runs this mrng. That being
said...Fri still looks quite warm with widespread 70s with near
80 possible along the I70 corridor from the STL metro to cntrl
MO...with low 80s possible across cntrl MO. Now that there is no
FROPA fcst for Fri night...sthrly flow will continue thru Sat
producing yet another warm day with highs in the 70s...and
possibly warmer.

The West Coast energy approaches the region Sat night. The ECMWF is
much more robust with this feature than the GFS...and hence about
6hrs slower. The ECMWF drives a cold front thru the CWA Sun
aftn/evng while the GFS solution stalls the front across the CWA Sun
aftn/evng and then basically washes it out Sun night. If the ECMWF
solution verifies then there may be a bit of a cool down from Fri
and Sat highs but temps should continue to be aoa normal. Regardless
of the moisture results in a dry FROPA. Another
weak SFC ridge slides thru Sun night with return flow already in
place by Mon mrng.

A low amplitude transient upper level ridge will quickly move thru
Sun night with the flow turning more SWrly by Mon as the energy
assoc with the West Coast trough works into the cntrl CONUS. Deep
sthrly flow will remain in place thru Mon with mid/upper teen C
850mb temps...which means Mon should be another warm day with
widespread highs in the 70s...if not warmer. The energy assoc with
the West Coast trough approaches Mon night/Tue with the GFS about
6-12 hrs faster than the ECMWF. The main brunt of this feature is
fcst to pass well N of the FA but the short wave will drag a cold
front into the CWA Tue/Tue night. Depending on FROPA timing...Tue
could be yet another day with above avg temps. Models do not
depict much QPF with FROPA so the dry conditions are fcst to



.AVIATION...  (For the 00z TAFs through 00z Wednesday Evening)
Issued at 626 PM CDT Tue Oct 25 2016

VFR conditions within light southeasterly flow will continue
during the overnight hours tonight. A cold front will approach
from the northwest on Wednesday bringing a likely round of showers
and embedded thunderstorms. Ceilings behind this front should also
lower into the MVFR range along with a wind shift to the


VFR conditions expected tonight and Wednesday morning along with
light southeasterly winds. A round of showers and possibly a few
thunderstorms is likely on Wednesday afternoon associated with a
cold frontal passage. Behind the front...winds will shift to the
west/northwest with ceilings dropping down to around 3000 feet
Wednesday evening.





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