Area Forecast Discussion
Issued by NWS St. Louis, MO

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590
FXUS63 KLSX 232354
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
654 PM CDT MON MAY 23 2016

.SHORT TERM... (Through Tuesday Afternoon)
Issued at 305 PM CDT Mon May 23 2016

Surface ridge centered over eastern Missouri will drift east tonight
and Monday allowing the wind to turn to the south across the area by
Monday morning.  Expect another relatively cool night due to light
wind and clear sky providing good radiational cooling conditions.
Don`t expect dewpoint temperatures to really begin rising until
after 12Z Monday so think lows will drop to near dewpoint
temperatures in the low to mid 50s across most of the area.

Southerly flow on the western periphery of the ridge on Monday will
begin moistening up the boundary layer...as well as begin warm
advection over the region in earnest.  With 850mb temps approaching
the mid teens MOS highs in the mid 80s look very reasonable.  Still
some question whether or not there`s a chance for storms in central
MO.  Latest run of the NCEP 4km WRF model has a broken line of
storms approaching the area (tho not quite) into our CWFA) by 00Z.
NSSL WRF also has a broken line of convection which is weakening as
it approaches the western fringes of our CWFA late Monday afternoon.
The The latest NAM has backed precip chances further west...and the
GFS has been pretty consistently dry over our area for Monday
afternoon.  Given how close it looks like thunderstorms might get, I
think I`ll keep a low chance/slight chance area going late Monday
afternoon in central and northeast Missouri

Carney

.LONG TERM...  (Tuesday Night through Next Monday)
Issued at 305 PM CDT Mon May 23 2016

A rather persistent pattern of southwest flow aloft and southerly
flow at the surface can be expected thru early next week.

The southwest flow aloft will carry with it a series of imbedded
disturbances picked up or ejected from the main system that will
lodge in the southwestern CONUS for much of this week.  These
disturbances will be acting on what will be a very moist and
unstable column this week.  Although there will be the lack of
synoptic scale fronts to work off of at the surface, the initial
rounds of convection tonight and Tuesday, along with anticipated
subsequent rounds, should create sufficient mesoscale boundaries to
effectively act as initiators of convection, especially during the
daytime.  At night, our area should additionally be downstream from
where the low level jet sets of the MCS of the night where this
feature could either move in late night or during the following
morning.  All of this is very general, and given the overall
situation, it will be very hard to nail down specifics after the
next round, which is set for later tonight and Tuesday, with each
subsequent round heavily dependent on the exact outcome of the one
preceding it.

The days with the highest levels of instability continue to be from
late Tuesday night thru Wednesday and into Thursday.  This will
primarily couple with shear that will be at marginal levels.  It
will be during this period that there will be an elevated threat for
severe thunderstorms.

The main system in the southwestern CONUS does not fully exit and
move thru our region until Saturday.

After this, there is little overall change in the pattern, if
anything, it just looks less organized than it did before.

Above average temps can be expected each day, with maxes mainly in
the 80s and mins in the 60s.

TES
&&

.AVIATION...  (For the 00z TAFs through 00z Tuesday Evening)
Issued at 645 PM CDT Mon May 23 2016

MCV over southwestern MO trying to make its way into forecast area
this evening, but activity with it seems to be waning. For now
kept vcts mention at KCOU from 03z to 06z Tue then vicinity
showers from 06z to 12z Tue, with rest of taf sites dry til
daybreak on Tuesday. For metro area and KUIN just have vicinity
shower mention during the day on Tuesday. Otherwise, VFR
conditions to prevail out side of activity with south winds.

Specifics for KSTL:
MCV over southwestern MO trying to make its way into forecast area
this evening, but activity with it seems to be waning. For now
kept KSTL dry til 13z Tuesday, then have vicinity showers. Could
see a break from 18z Tuesday through 06z Wednesday as activity is
hard to pin down, so kept taf dry through this period. Otherwise,
VFR conditions to prevail out side of activity with south winds.

Byrd
&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&

$$
WFO LSX



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