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Area forecast discussion...updated aviation 
National Weather Service St Louis MO
1154 PM CDT Tue Sep 23 2014

issued at 939 PM CDT Tue Sep 23 2014

Forecast on track, and only thing to really tweak was sky cover,
with more clouds than originally anticipated. Believe this is
temporary, especially for areas for stl Metro and south and east,
with some clearing expected later tonight.



Short term: (through late tonight)
issued at 333 PM CDT Tue Sep 23 2014

Upper-level low and attendant trough axis currently across the
Dakotas is forecast to slowly move eastward overnight tonight. Not
much impact is expected for our County warning forecast area other than an increase in
clouds for portions of central and northeastern Missouri. Showers
with embedded thunder should stay to the west of the area in close
proximity to aforementioned trough. For lows tonight...started
with this morning's observed mins as a baseline and added a few
degrees due to airmass modification. Leaned a bit warmer across
the northwestern third of the area due to expected clouds.
Conversely...leaned toward cooler guidance for Eastern Ozarks and
portions of southwest Illinois due to light winds near sfc ridge
and a mostly clear sky. All in all...another pleasant early fall
night looks to be in store for the bi-state region with lows
ranging from the mid 40s to the mid 50s.


Long term: (wednesday through next tuesday)
issued at 333 PM CDT Tue Sep 23 2014

(wednesday - saturday)

Mid/upper level pattern through at least the start of this upcoming
weekend looks nebulous/chaotic. Short to medium range guidance agree
that at least a portion of the trough across the northern plains will
halt its eastward progression sometime Wednesday or Wednesday night
and begin to retrograde southwestward. Impacts of this feature will still
likely be minor and in the form of increasing clouds. However...would not
be surprised if a few showers is kicked up by the remnant midlevel low/
shear axis. Models are fairly bearish on precipitation..but some do have
a few hundreths of an inch over random 6-hr blocks of time. Conceptually...
a few widely scattered/isolated showers does make sense beneath cooler
midlevel temps aloft. However...with low-level ridging remaining entrenched
across the area collocated with very dry air...still maintaining a dry
forecast through Saturday at this time. Main theme in the Wednesday through
Saturday forecast period will be seasonably warm temperatures day/night
with highs in the upper 70s/low 80s and overnight lows in the 50s to low
60s...or around 5 degrees above normal for late September.

(Sunday - tuesday)

GFS/European model (ecmwf) models diverge fairly quickly late this weekend with how to
handle cutoff low/shear axis. The GFS actually moves the low southeastward
on Sunday and phases it with a low across southeast Texas. The European model (ecmwf)
on the other hand retrogrades the low westward toward the mid-Missouri
Valley and brings the system northward from Texas much faster and
further northward when compared with the GFS. Needless to say...quite
a bit of uncertainty in the extended. If system does indeed stream
northward out of Texas...chances of showers and a few storms will return
to at least portions of the region...most likely across southeast Missouri
and southwest Illinois. However...outside of that particular system...
rain chances will remain very low. Temperatures will remain mild for late
September and continue to be above normal.



Aviation: (for the 06z tafs through 06z Wednesday night)
issued at 1152 PM CDT Tue Sep 23 2014

VFR conditions and light southeast surface winds will prevail for much of
the valid time at the taf sites. Only exception is some fog
expected in the River Valley locations with air to water temp
differences becoming in excess of 20 degrees at sus and cps. This
will likely spawn another round of steam fog, just a matter of
whether or not it can expand sufficiently into the airports
nearby. Maintained MVFR visibility forecast currently at sus and cps as
presence of clouds very close to the area may interfere enough to
prevent the required cooldown for steam fog.

Specifics for kstl: VFR and light southeast surface winds thru the



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