Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 241722

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1222 PM CDT Mon Jul 24 2017

.SHORT TERM...  (Through Late Tonight)
Issued at 235 AM CDT Mon Jul 24 2017

Northwest flow aloft prevails over our region early this morning and
this favorable setup for surface frontal intrusion did not
disappoint, with the main front already through and a TROF located
near I-70 that was popping isolated to scattered TSRA earlier
tonight.  Otherwise, skies were mostly clear with temps slipping
into the 60s north of the TROF and in a few spots in the Ozark
valleys, with 70s elsewhere.

Heights aloft will already be building overhead later today and into
tonight and so will essentially close the window for surface fronts
and TROFs to easily move thru our region.  While the main synoptic
front is successfully through, the TROF may not fare as well, with
the latest models now placing it over southern MO and far southern
IL when the favorable flow to the south ceases.  While it is
possible the TROF may still pop a random and isolated shower or
storm during the morning hours, it is more probable that it will do
so during peak heating in the afternoon over the eastern Ozarks and
far southern IL and the activity that does develop will likely carry
thru into much of the evening.  Have added low PoPs for most of the
eastern Ozarks and far southern IL for this afternoon and most of

With abundant sunshine for our region today with a diurnal cumulus
cloud field forming and NE surface flow, stayed close to MOS temps
which looked reasonable but leaned towards the higher numbers.  All
in all, a seasonable late July day with less humidity than the past
week with peak temps from the mid 80s in the north to around 90 for
most areas near and south of I-70.

Most areas should see clear skies again tonight save southeast MO
and far southern IL where, depending on how persistent the
convection is along the old TROF boundary, may keep those areas
mostly cloudy.  Should see widespread min temps in the 60s thanks to
this clear skies and light wind setup for most areas, with higher
values in the STL heat island.


.LONG TERM...  (Tuesday through Sunday)
Issued at 235 AM CDT Mon Jul 24 2017

A progressive upper level trof centered through the northeastern
U.S. will maintain a retreating surface high through the Great Lakes
region on Tuesday. This surface high will have a strong influence on
Tuesday resulting in a quasi-stationary surface front draped
across southern MO into the western TN Valley. A few showers and
thunderstorms will be possible in the vicinity of the frontal
boundary across southeast MO and southern IL, especially during
the afternoon and early evening. Temperatures should be rather

Wednesday looks like the hottest day of the week and potentially
another short-lived period of dangerous levels of heat. The southern
Plains upper high will retrograde slightly in response to the
beginning of large scale amplification and a short wave trof moving
through the mid-upper MS valley region. Despite the slight
retrogression of the upper high, the low levels will be marked by
the return of south to southwesterly flow and rising lower
tropospheric temps as the warm front retreats back to the
north/northeast. Highs should be well into the 90s with peak
afternoon heat index values from 103-110. The models vary some on
the strength and position of the short wave and associated cold
front moving through the mid/upper MS Valley into the OH Valley in
the late Wednesday-Thursday time frame. The NAM is the big outlier
and appears too strong and a bit too fast. The GFS and ECMWF are
fairly close bringing the cold front into northern MO/central IL
late Wednesday night into early Thursday morning and through the
entire CWA by late Thursday evening. The front should be accompanied
by showers and thunderstorms as it progresses through the area.

Surface high pressure and much cooler and drier air will then
dominate from Friday through next weekend as large scale
amplification proceeds and an upper trof sharpens over the eastern



.AVIATION...  (For the 18z TAFs through 18z Tuesday Afternoon)
Issued at 1217 PM CDT Mon Jul 24 2017

VFR through the period with diurnal cumulus and occasional
cirrus. Northwesterly to northeasterly winds will gradually veer
and become southeasterly by the end of the valid TAF period.
Isolated SHRA/TSRA may develop after 24/20z, but any
precipitation is expected to remain south of the terminals.





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