Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 190000

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
700 PM CDT Mon Sep 18 2017

.SHORT TERM...  (Through Late Tuesday Afternoon)
Issued at 322 PM CDT Mon Sep 18 2017

Showers and thunderstorms have developed in advance of the warm
front and short wave. This trend should continue into the early
evening and then dissipate. Some fog possible overnight but have
questions of whether it will be widespread enough. Front gradually
lifts north Tuesday morning bringing in a light south to southwest
wind and above normal temperatures. Current forecast high
temperatures for Tuesday are above guidance so have left them.
Tuesday looks to be dry as high pressure begins to build into the


.LONG TERM...  (Tuesday Night through Next Monday)
Issued at 322 PM CDT Mon Sep 18 2017

Anomalous ridging is expected to continue to strengthen over the mid-
Mississippi Valley and Great Lakes through the end of the work week.
This will help continue the trend of well-above normal temperatures
through the extended portion of the forecast period. Warmest
period appears to be on Wednesday and Thursday with low-level
thermal ridge overhead. Quite humid air also looks to be in place
(dewpoints near 70 degrees) during this time period so it will
feel even warmer than actual air temperatures. Current expectation
is for highs on Wednesday and Thursday to be in the low to mid
90s, with peak heat index values generally of 95-100 degrees each
afternoon. Some weakening of the upper-level anticyclone should
take place beginning this weekend as it drifts eastward. This will
allow slightly "cooler" air to move into the area, but still
expecting highs well into the 80s which is still about 5-10
degrees above normal.

Precipitation chances look to be generally below normal given the
mid/upper level flow pattern. Best chances of showers and
thunderstorms currently look to be on Wednesday night across
portions of northeast Missouri in proximity to a frontal boundary
and next Monday across portions of central Missouri as another
front approaches from the west.



.AVIATION...  (For the 00z TAFs through 00z Tuesday Evening)
Issued at 643 PM CDT Mon Sep 18 2017

An area of showers and thunderstorms was moving through the taf
sites early this evening ahead of an upper level disturbance. This
precipitation should shift east of COU shortly after 00Z early this
evening, but will continue in UIN and the St Louis metro area
until 02-03Z later this evening. Partial clearing can be expected
later tonight with at least patchy fog developing due to light
surface winds, high surface dew points, and recent rainfall. This
fog will dissipate by late Tuesday morning with surface winds
becoming south-southeasterly.

SPECIFICS FOR KSTL: An area of showers and a few thunderstorms
was moving into the STL area early this evening ahead of an upper
level disturbance. This precipitation will continue until 02-03Z
later this evening. Partial clearing can be expected late tonight
with light surface winds. The light surface wind will become
south-southeasterly Tuesday afternoon, increasing to only about
6 kts.





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