Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 251105

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
505 AM CST Sat Nov 25 2017

.SHORT TERM...  (Through Late Tonight)
Issued at 304 AM CST Sat Nov 25 2017

The cold front has moved through the CWA and stretched across
southern IL and southeast MO early this morning, with high clouds
skirting the area to the north. These clouds will clear to the
southeast through daybreak. Another day of mild - above average
temperatures is expected today, although no records like yesterday.
Surface high pressure will build eastward into the area from the
Plains throughout the day with low levels dominated by weak CAA.
Despite the weak CAA, the post-frontal air mass isn`t all that cold
and there will be abundant sunshine today. These considerations
along with upstream temperatures yesterday would support raising the
previous high temperature forecast from 2-4 degrees across the

The surface high will then dominate tonight as the center/axis
slides into the mid MS Valley from the Plains. A few high clouds
will move into the area late tonight associated with a migratory
short-wave in the northwest flow aloft, however these won`t be much
of an issue. Given the dry air mass and good radiational cooling
conditions, the lows tonight will likely be a tad lower than MOS and
the previous forecast.


.LONG TERM...  (Sunday through Friday)
Issued at 304 AM CST Sat Nov 25 2017

High amplitude/slow moving pattern over the CONUS will begin
shifting to a more zonal pattern by early next week. This will
shunt the surface high eastward to the Mid-Atlantic Region by
Monday night and Tuesday allowing for increasing southerly flow
over the Mississippi Valley ahead of the next system. What this
translates to in sensible weather for our area is warming
temperatures for Sunday and Monday...probably not record highs as
happened yesterday, but certainly temperatures well above normal
for late November.

Quasi-zonal flow aloft will bring at least three shortwaves through
the Midwest Tuesday through Friday.  Most of the energy from the
first wave will be focused north of our forecast area across the
Northern Plains and Upper Midwest on Tuesday.  However, guidance is
very consistently showing this wave pushing a cold front southeast
from the Northern Plains into Missouri on Tuesday.  Between the
GFS/ECMWF/Canadian the GFS is the only mode that`s printing out
precip in the vicinity of the front over our area on Tuesday.
Regardless, there should be increasing clouds over the area and the
front is forecast to make it through at least the northern 1/3 of
our forecast area on Tuesday which will lead to overall cooler
temperatures than Sunday and Monday.

The aforementioned upper trof which will be responsible for
Tuesday`s cold front fractures over the Rocky Mountains late
Tuesday, leaving a fairly wound up little southern wave which
moves into the East-Central Plains between 06Z-12Z Wednesday. This
southern wave forces low level cyclogenesis on the baroclinic
zone left by Tuesday`s front and the resulting surface low tracks
east across the Mississippi Valley on Wednesday and Wednesday
night. The 25/00Z ECMWF made quite a jump from the 24/12Z run and
is now much closer to the GFS solution with the shortwave moving
across Arkansas rather than further north across northern
Missouri. There is also more precip associated with the system on
Wednesday and Wednesday night...although it is mostly south of our
forecast area unfortunately. This does make sense though given
the ridge axis from the high over the Mid-Atlantic will still be
laid out east-west just north of the Gulf Coast therefore blocking
deep moisture return into the Mid-Mississippi Valley. That being
said, still think low PoPs over much of the area Wednesday into
Wednesday night is reasonable given the run- to-run inconsistencies
in the models.

The third upper trof in the series sweeps into the Midwest on
Thursday.  This trof re-amplifies the pattern over the CONUS and
pushes another cold front through the area.  Once again, there is a
question of how much moisture there will be available for the system
to work with, but the front should be through our forecast area by
00Z Friday according to both the ECMWF and GFS.  Canadian is slower,
but is the outlier with a much less amplified trof and slower
surface front.  Temperatures from Wednesday through Friday continue
to look very mild as none of these systems really taps any of the
truly cold air lurking up in Canada though we should cool down to
near normal on Friday behind the cold front.



.AVIATION...  (For the 12z TAFs through 12z Sunday Morning)
Issued at 505 AM CST Sat Nov 25 2017

VFR flight conditions will prevail through the forecast period.


VFR flight conditions will prevail through the forecast period.



Saint Louis     61  36  62  44 /   0   0   0   0
Quincy          56  31  58  40 /   0   0   0   0
Columbia        61  34  62  42 /   0   0   0   0
Jefferson City  62  33  62  42 /   0   0   0   0
Salem           58  32  55  40 /   0   0   0   0
Farmington      61  33  62  38 /   0   0   0   0




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