Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 232007

Area Forecast Discussion
National Weather Service Saint Louis MO
307 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 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


.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.



.AVIATION...  (For the 18z TAFs through 18z Tuesday Afternoon)
Issued at 1247 PM CDT Mon May 23 2016

VFR flight conditions are expected to prevail at least through the
remainder of the afternoon...and likely through the evening and
overnight hours as well. Expect scattered showers and
thunderstorms to try to move into central Missouri during the
early evening, but it looks like they will be dissipating as they
do so. Rain chances continue to overspread the area tonight with
isolated to scattered showers and thunderstorms possible across
most of the area by tomorrow morning. Again...VFR conditions are
expected to prevail...but any heavier shower or storm could easily
bring visibility down to 2-3 miles or less.

Specifics for KSTL:

VFR conditions are expected to prevail at Lambert through the
period. Scattered showers are likely to be in the vicinity of the
terminal Tuesday morning, though timing and intensity are
uncertain at this time. Could see some thunderstorms as well.
Think shower activity will diminish through early afternoon. If a
shower or storm hits the terminal directly it could briefly drop
visibility to 2-3 miles or less.





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