Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 160159

Area Forecast Discussion...Updated
National Weather Service Saint Louis MO
859 PM CDT Sun Oct 15 2017

Issued at 857 PM CDT Sun Oct 15 2017

Low clouds are moving east and will soon move out of the eastern
part of the CWA. That will leave just clear skies across the area.
Winds have already begun to diminish over the area as high
pressure currently centered over the Central Plains builds into
the area. With clear skies and light winds overnight, it will be
quite cool as drier air continues to advect into the area. Going
lows appear to have a good handle on the situation. There may be
some patchy frost in sheltered areas where lows drop into the
middle 30s. Otherwise, can`t rule out that there will be steam fog
in the river valleys, but forecast soundings are very dry in the
lower atmosphere, so any fog will remain confined to near the
water source.



.SHORT TERM...  (Through Late Monday Afternoon)
Issued at 321 PM CDT Sun Oct 15 2017

Cumulus cloud field, mainly across west central and southwest IL
this afternoon will dissipate or shift east-southeast of our
forecast area early this evening as the deep surface low and
trailing cold front pull further east-southeast of the region, while
a strong surface ridge over the Plains builds eastward into MO.
Strong and gusty northwesterly surface winds will also diminish this
evening.  With a clear sky, light surface wind, surface dew points
dropping into the 30s, and 850 mb temperatures of only about 2 to 4
degrees C late tonight we will see good radiational cooling and
likely the coldest lows of the Fall season so far.  Although these
lows will only be 5 to 10 degrees below normal for mid October, they
will feel colder owing to the recent unseasonably warm weather we
just experienced.  There may be light, patchy frost in the colder
locations late tonight and early Monday morning.  Sunny conditions
can be expected on Monday as the surface ridge moves eastward
through our area with relatively cool conditions continuing with
northwesterly upper level flow.


.LONG TERM...  (Monday Night through Next Sunday)
Issued at 321 PM CDT Sun Oct 15 2017

The synoptic pattern at the start of the long term period will
feature northwest flow over much of the Midwest in the wake of a
trough sliding through the eastern CONUS. This northwest flow will
be fairly short-lived, as the flow deamplifies and then eventually
turns southwesterly as yet another ridge builds across the Southeast.

As far as sensible weather goes, it will be a very benign week.  A
sprawling surface ridge will influence the region for much of the
week.  The coolest night will be Monday night, as this ridge settles
into portions of southwest IL/southeast MO.  The combination of
light winds/mostly clear skies should allow for ideal radiational
cooling conditions.  Have gone below guidance for temps as a result,
which could allow for a few isolated instances of frost over the
eastern Ozarks as temperatures dip into the 30s.

Otherwise, the surface ridge will slowly shift east through the
period. This will result in a warming trend through the upcoming
week.  After highs in the upper 60s/low 70s Tuesday, they will
gradually warm each day until they are near 80 degrees once again
next weekend.

The next chance for precipitation will not come until the end of
next weekend as a cold front approaches the area.  There are still
substantial timing differences with this system, but have favored
the GFS/ECMWF over the fast outlier GEM solution.



.AVIATION...  (For the 00z TAFs through 00z Monday Evening)
Issued at 559 PM CDT Sun Oct 15 2017

Dry and VFR conditions are expected through the period. Northwest
winds are expected to diminish this evening as high pressure
builds into the area. There is a some risk of river fog tonight,
but it is too low at this point to add to the KSUS and KCPS TAFs
at this point.


Dry and VFR conditions are expect through the period. Northwest
winds are expected to diminish this evening.





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