Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 181907

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
207 PM CDT TUE OCT 18 2016

.SHORT TERM...  (Through Late Tonight)
Issued at 335 AM CDT Tue Oct 18 2016

Our region remains sandwiched between a strong RIDGE over the south-
central and southeastern CONUS, and streams of Pacific upper level
disturbances tracking to our north in a west-southwest flow.  At the
surface, the tight pressure gradient that had resulted in a windy
day on Monday is slowly losing its grip over our region as a cold
front nears, with occasional gusts to 25-30 mph still going on.  A
surface cold front extends from south-central IA thru northwestern MO
and into southeastern KS and has only recently begun to develop
clouds just ahead of it.  Temperatures remain very mild for this
time of year with readings in the lower to mid 70s areawide.

The surface cold front is expected to reach the STL metro area
during the afternoon hours and should continue to push southeastward
into far southern IL and southeastern MO this evening and south of
our forecast area during the pre-dawn hours of Wednesday.

A decent bubble of moisture is expected to follow ahead of the front
and will result in enough instability to support thunder, but what
should prevent any pcpn until the afternoon is a cap, and even then,
it is not readily apparent that enough lift will exist to result in
widespread pcpn during the afternoon or evening.  It is enough to
justify a low PoP in the forecast for this afternoon and this
evening for areas along and just ahead of the front.  Heading into
the late night tonight, despite the front now expected to
be south of the area, broadscale lift is expected to increase thanks
to an approaching strong shortwave, and may be able to induce rain
further north towards the I-70 corridor region by daybreak.

The cold front is expected to make it thru UIN and COU/JEF by early
afternoon and will limit any warmup, but STL metro and areas to the
southeast will be limited by what should be an increasing cloud
field ahead of the front and a weaker sun angle in late October but
will be offset somewhat by the very warm start to the day.  Not
expecting any record maxes to be threatened at UIN or COU, but
have forecasted values within a few degrees of the record at STL.
For further details on records for today, please consult the CLIMATE
section below.


.LONG TERM...  (Wednesday through Monday)
Issued at 335 AM CDT Tue Oct 18 2016

Precipitation chances will ramp up on Wednesday into Wednesday
night as a deepening upper level trough approaches from the Plains
and induces a surface wave along the nearly stationary front across
extreme southern portions of MO and IL.  The front will shift
slightly northward ahead of the surface wave.  Low-mid level warm
air advection will increase over the front ahead of the upper level
trough and weak surface low/wave.  Much of the precipitation across
our forecast area will be north of the surface front and along or
south of the 850 mb front.  The highest QPF and best coverage of
thunderstorms will likely occur across southeast MO and southwest IL
where the most favorable low level moisture and low-mid level
instability will exist.  Showers will continue across southeast MO
and southwest IL Thursday morning, but should shift southeast of the
forecast area Thursday afternoon as the deepening surface low and
trailing cold front shift well southeast of our forecast area and
the deep upper level trough moves eastward through the central US.
Much cooler temperatures can be expected Thursday and Thursday night
as we get into northwesterly upper level flow behind the upper level
trough and a strong surface ridge builds into the region behind the
cold front.  The 850 mb temperature should drop down to around 2-3
degrees C in STL by 12Z Friday. Low temperatures Thursday night
while only being 5 degrees below normal will feel much colder after
the current stretch of unseasonably warm weather.  A gradual warming
trend can be expected this weekend as upper level heights rise as an
upper level ridge approaches from the Plains.  Any precipitation
should remain north of our forecast area.  A cold front will sag
southward through our region Sunday night and Monday, but it appears
that the colder air will remain northeast of the forecast area in
the Great Lakes region.



.AVIATION...  (For the 18z TAFs through 18z Wednesday Afternoon)
Issued at 1237 PM CDT Tue Oct 18 2016

Front continues to push SE thru the region. Winds will become nwly
behind the fnt, then nly later this evening thru overnight. This
fnt will remain over SE MO into srn IL thru the remainder of the
period. However, showers with some TS are expected to spread nwd,
mainly during the afternoon hours. The best chances are at
KSTL/KSUS/KCPS during the late afternoon hours.



Issued at 245 AM CDT Mon Oct 17 2016

Unseasonably warm conditions are expected to persist through
Tuesday and may approach record territory. The following lists
record high temperatures and record high minimum temperatures for
St. Louis, Columbia and Quincy during these times.

St. LouisColumbiaQuincy

Tuesday High:87/195386/195387/1924
10/18High Low:68/198564/197166/1938




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