Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 150444

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1144 PM CDT Thu Sep 14 2017

.SHORT TERM...  (Through Late Friday Afternoon)
Issued at 312 PM CDT Thu Sep 14 2017

With upper ridge overhead and south winds at surface, will have
dry and warmer weather for the last part of the work week. Skies to
remain clear tonight through Friday. So, lows will be in the upper
50s to mid 60s tonight with highs on Friday between 85 and 90
degrees, about 10 degrees above normal for this time of year. As for
any possible fog late tonight, should not be a problem as there was
plenty of mixing during the day today to dry out the lower levels.


.LONG TERM...  (Friday Night through Next Thursday)
Issued at 312 PM CDT Thu Sep 14 2017

The remainder of the seven day forecast period will be marked by
above average temperatures and periodic thunderstorm chances.

Heights aloft will be on the rise Friday night into Saturday as the
upper ridge builds through the mid MS Valley in response to a
migratory upper trof moving from the Great Basin/Northern Rockies
into the northern and central Plains region. This along with veering
south-southwesterly lower tropospheric flow will contribute to
tranquil but seasonably warm conditions. As the upper trof moves
across the upper MS Valley Saturday night it will result in weak
height falls aloft across northern parts of the CWA, and will be
the impetus for a cold front advancing into northern sections of
the CWA. Increasing low level moisture and instability will aid in
scattered shower and thunderstorm development/maintenance along
and ahead of the front Saturday night/Sunday morning. I guess if
there is any question, it is just how far south this front will
sag into the CWA through Sunday night. Given the lack of strong
post-frontal high pressure and southwest flow aloft, I tend to
lean towards a solution which largely keeps the front north of
I-70, and then retreats the front back northward and out of the
CWA by early Monday evening. I would think that the highest
precipitation chances then would reside along and north of the
front however the ECMWF is quite bullish with extensive QPF well

From Tuesday into Thursday there is a good amount of variance in
model solutions that lead to lower than normal confidence. One thing
that can be said is that above average temps should persist through
the week. Low confidence revolves around two things - the ECMWF
seems to want to generate QPF every period, and also the GFS is more
progressive than the ECMWF with the large scale western trof and mid-
week lead short wave. At this point the forecast reflects the
anticipated seasonably warm temps, along with POPS in numerous
forecast periods.



.AVIATION...  (For the 06z TAFs through 06z Friday Night)
Issued at 1144 PM CDT Thu Sep 14 2017

VFR conditions, dry wx, and light SE-S surface winds will prevail
at the TAF sites thru the valid period. Crossover temps are too
low for much fog formation tonight except in areas SE of the STL
metro area and have no fog going at the TAF sites in this set.





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