Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 192018

Area Forecast Discussion
National Weather Service Saint Louis MO
318 PM CDT MON SEP 19 2016

.SHORT TERM...  (Through Late Tuesday Afternoon)
Issued at 315 PM CDT Mon Sep 19 2016

Weak vort max currently moving across Iowa will move slowly east
southeastward into west central Illinois later this evening.  This
will cause a cold front currently over central Iowa to move into
northeast Missouri toward midnight.  Instability along the front
will be waning with the loss of daytime heating, and convergence will
be relatively weak, so have kept with just a slight chance of
showers and thunderstorms late this evening and overnight across
northeast Missouri and west central Illinois.  This goes along well
with latest runs of the HRRR and NSSL WRF which are showing isolated
storms developing over the northern part of the CWA during this same
time period.  Still expect tomorrow to be dry as the upper ridge
continues to build over the area.

Do think there will be some additional fog development tonight as
the winds will be light, and all but the northern CWA will see
mainly clear skies.   Like the past few nights, worst of the fog
will be near the river valleys.

Coolest temperatures will be over southeast Missouri and south
central Illinois where winds will be the lightest and skies will be
the clearest in the retreating surface ridge axis.  Agreeable MOS
lows look reasonable.  Went at or above MOS tomorrow with highs
given the expected mostly sunny skies and mixing into the 900-850mb


.LONG TERM...  (Tuesday Night through Next Monday)
Issued at 315 PM CDT Mon Sep 19 2016

(Tuesday Night - Friday Night)

Two features will largely dominate the sensible weather across the
mid-Mississippi Valley heading into early next week: 1) surface
ridge nearly anchored across the northeastern United States
southwestward into the lower Ohio Valley and 2) mid/upper level
ridge overhead. Both of these features will help promote plenty of
clear skies and above normal temperatures. The area will also be by
and large precipitation free as any chance of widespread shower and
thunderstorm activity look very small. Dewpoints will be in the
mid 60s to near 70 degrees each day so it will even feel a bit
hotter than the forecast highs of roughly 85-90 degrees each
afternoon. Warmest days of this forecast period appear to be on
Wednesday and Friday where highs in the upper 80s to near 90 degrees
are expected. Nighttime lows will initially start off fairly
seasonable on Tuesday night and even Wednesday night due to the
clear skies and sfc ridge near the area. Dropped minimum
temperatures a few degrees in the eastern Ozarks each of these
nights from previous forecast. Lows are expected to moderate a
few degrees by Thursday night and Friday night...mainly due to
slightly increased southerly surface flow.

(Saturday - Next Monday)

Backdoor cold front will try and push southwestward into the CWA on
Saturday. Slightly cooler temperatures are likely compared to Friday
due to an increase in cloud cover predominantly. Still lots of
uncertainty heading toward late this weekend and early next week.
Evolution of closed low in the Rockies continues to cause problems
in the medium range. Latest guidance suggests a portion of the
closed low hanging out in the desert southwest with a portion
ejecting out into the northern Plains on Saturday night/Sunday. This
portion should send a cold front down toward our way either on
Sunday or Monday. Continue to lean toward the slower end of the
guidance envelope. Temperatures on Saturday and Sunday continue to
look warmer than 24-48 hours ago with the highest PoPs now on Sunday
night coincident with the expected frontal timing...though would not
be surprised if it is yet delayed another 12 hours.



.AVIATION...  (For the 18z TAFs through 18z Tuesday Afternoon)
Issued at 1254 PM CDT Mon Sep 19 2016

Dry and VFR conditions are expected through this evening. A front
will move into the area overnight which may produce isolated
showers and thunderstorms over west central Illinois. Do not have
enough confidence at this point to put this chance in the KUIN
TAF. Otherwise, expect there to be redevelopment of fog again late
tonight and early Tuesday, mainly along river valleys. Have placed
IFR visibilities at KSUS and KCPS between 08-13Z. Fog should
diminish by mid morning on Tuesday. Winds should be mainly light
through the period.

SPECIFICS FOR KSTL: Expect mainly dry and VFR conditions through
the period with light winds.





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