Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 182328

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
628 PM CDT SUN SEP 18 2016

.SHORT TERM...  (Through Late Monday Afternoon)
Issued at 316 PM CDT Sun Sep 18 2016

Isolated showers and thunderstorms occurring over the Ozarks will
move east of the CWA late this afternoon/early this evening.
Still expect tonight and Monday to be dry as the upper level
trough that is currently moving across the Midwest will move off
to the east this evening, allowing an upper ridge to build over
the area tomorrow. Expect another night of fog development with
mostly clear skies as and light winds as the surface ridge lingers
over the area. Expect the greatest fog potential will once again
be near the river valleys. Fog should once again dissipate by mid
morning on Monday with sunshine and southwest winds.

Stayed close to going lows tonight as temperatures will likely be
cooler than guidance over the eastern Ozarks.  With upper ridge
building in and southwest surface winds, highs still look like they
will be at or above the warmest MOS temperatures for highs.


.LONG TERM...  (Monday Night through Next Sunday)
Issued at 316 PM CDT Sun Sep 18 2016

(Monday Night - Tuesday)

Weak cold front will be approaching the northwestern portion of the
CWA by late Monday evening. Isolated showers and thunderstorms still
appear possible along this boundary...but better chances are well to
the northeast of the CWA where better upper-air support will reside.
Quite possible that no convection is generated further to the
southwest across the CWA Monday night due to strong capping
inversion aloft but did leave isolated wording in for late evening
hours until about midnight for northern sections of the forecast
area for now. Any storms that do form should dissipate overnight
with loss of instability. Mild temperatures are expected ahead of
this front for Monday night. Increase in cloud cover should also
help keep temperatures from dropping too much. Leaned more toward
warmer MET MOS numbers for lows which yielded most areas between
65-70 degrees. Exception is portions of the St. Louis
metropolitan area where lows should be in the low 70s due to the
urban heat island effect.

Cold front will continue to move slowly southward on Tuesday and
largely wash out. Main impact will be to increase sky cover as
chances of any showers and storms still appear too low to have
mentionable PoPs at this time. Temperatures will once again be
well above normal for mid to late September. Exactly how warm is a
bit tricky however as there could be enough impacts from cloud
cover to mitigate the diurnal rise in temperatures. For now did
not make much of an adjustment from previous forecast and went
with highs ranging from the mid 80s to near 90 degrees but could
foresee a scenario where cloud cover is thick and prevalent
enough to cause these forecast highs being a couple of degrees too

(Wednesday - Next Sunday)

Late summer weather pattern to persist through the rest of the
work week and likely into at least early next weekend. Evolution
of the closed low moving eastward out of the northern Rockies will
likely be problematic for models over the next few days (at
least). But still believe that the arrival of that system and its
associated cold front will likely be at least another 12-24 hours
delayed than what is modeled. Have therefore boosted temperatures
on Saturday as well as lowered PoPs on Saturday and Saturday night
compared to previous forecast. Expect persistence high (85-90F)
and low (65-70+F) temperatures Wednesday through Saturday. Next
chance of showers and thunderstorms will be timed with the arrival
of the aforementioned cold front...most likely sometime late next
weekend...if not early the following week. Cooler temperatures
will also be likely behind this front.



.AVIATION...  (For the 00z TAFs through 00z Monday Evening)
Issued at 623 PM CDT Sun Sep 18 2016

VFR through the period except for fog in river valleys overnight.
Similar to the last few nights, conditions remain favorable for
fog, and vsbys should fall to IFR after 06z and remain there for a
few hours. Fog will begin to mix out after sunrise and VFR
conditions are expected thereafter. Winds will remain AOB 10 kts
through the period.





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