Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 091118

618 AM CDT Wed Jul 9 2014

.SHORT TERM:  (Through Late This Afternoon)
Issued at 425 AM CDT Wed Jul 9 2014

A secondary boundary is forecast to move south of the area today.
Weak high pressure beneath northwest flow aloft should maintain
slightly cooler and drier weather across the LSX CWA today.


.LONG TERM:  (Tonight through Tuesday)
Issued at 425 AM CDT Wed Jul 9 2014

Unseasonably cool low temperatures expected tonight with nwly upper
level flow and a surface ridge extending from the Great Lakes region
southwest into eastern MO.  The 850 mb temperatures are forecast to
be about 12-15 degrees C across the forecast area.  The next chance
for convection will occur late Thursday night and Friday due to
relatively strong 850 mb warm air advection, theta e advection and
moisture convergence across the northern portion of the forecast
area on the nose of a swly low level jet and ahead of a nw flow
shortwave.  The models also depict significant upper level
divergence ahead of this shortwave.  A warming trend will begin
Thursday night and Friday as southerly return flow on the backside
of the surface ridge, shifting east of the area, brings warmer and
more humid air into the region.  Warm conditions can be expected for
the weekend as a mid-upper level ridge tries to build northeastward
into southwest MO.  Convection is possible across the northern and
eastern portion of the forecast area as shortwaves move east
southeastward over the mid-upper level ridge.  The ECMWF model
brings a weak cold front southward through our area already on
Sunday, while the GFS model is a little slower not bringing the
front through our area until Sunday night.  There should be at least
slight cooling behind this front with the mid-upper level ridge
getting suppressed southward as an upper level trough deepens over
the Great Lakes region.  The ECMWF model brings a second stronger
cold front southward through our forecast area Monday night as a
strong shortwave moves through the Great Lakes region.  The GFS
model is not as deep with the upper level trough over the Great
Lakes region and does not bring the cold front through our area
until Tuesday.  There should be at least scattered convection along
this front along with much cooler air behind it, especially if the
ECMWF model is the correct solution.  Due to the model timing
differences and inconsistencies will keep the pops low over most of
the area for Monday through Tuesday, but will lower the highs for
Tuesday below seasonal values.



.AVIATION:  (For the 12z TAFs through 12z Thursday Morning)
Issued at 614 AM CDT Wed Jul 9 2014

An extremely brief period of MVFR fog is possible before 14z,
especially at KSUS due to its proximity to the river, but area
METARs suggest that this is becoming less likely now that the sun
is up, and no flight restrictions are mentioned in the 12z TAFs.
Expect VFR conditions due to high pressure moving across the area.

Specifics for KSTL: VFR due to high pressure moving across the
area. Winds will gradually veer with time.





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