Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 200456

1156 PM CDT Tue May 19 2015

.SHORT TERM:  (Through Late Tonight)
Issued at 322 PM CDT Tue May 19 2015

Shortwave over Colorado will move east across the central Plains
tonight.  Resulting low level wave will develop and move along the
850mb baroclinic zone tonight into early Wednesday morning.  Strong
low level jet ahead of the low level circulation will be pointing
directly at the baroclinic zone out over the eastern Plains and into
western Missouri late tonight.  Expect there to be plenty of rain
west of our area tonight, approaching the Columbia/Jefferson City
areas toward 12Z Wednesday as the wave moves into eastern Kansas.
Don`t think there will be much more than some light rain or
sprinkles, but probably enough to get the ground wet.  MOS
temperatures for tonight in the upper 40s to low 50s look reasonable.


.LONG TERM:  (Wednesday through Next Tuesday)
Issued at 322 PM CDT Tue May 19 2015

(Wednesday through Friday)

Still looks like tomorrow will be cool with showers as upper trough
now over the southwest CONUS moves northeast and shears out as it
moves into confluent flow over the the Midwest.  The GFS still looks
have a bit too much gridscale feedback with this system while the
ECMWF looks like it has better continuity the past 24 hours, so have
followed it.  There is still quite a bit of ascent with the trough
along with low level moisture convergence ahead of it which warrants
categorical PoPs.  Some limited ascent will linger over the
southeast half of the CWA into Wednesday evening before subsidence
sets in over the area behind the trough for Thursday.  An upper
ridge will be building into the region from the west on Friday which
will continue to keep the area dry.

Still expect cooler than normal weather during this period because
of the cool, dry northerly winds.  This will be particularly
noticeably tomorrow with the rain when highs will be around 15
degrees below normal. There will be some moderation thereafter as
high pressure moves over the area and sunshine returns to the
area. A compromise on MOS guidance looks reasonable the next few

(Saturday through next Tuesday)

ECMWF/GFS/UKMET look in a little better agreement today with the
timing of the upper ridge axis that will not move across the area
until Saturday now.  This means that scattered showers and
thunderstorms will likely be delayed until Saturday afternoon over
mainly Missouri now.  The global models are also in better agreement
that upper low over southwestern CONUS will open up and lift
northeastward over the holiday weekend which will allow for an a
series of vort maxes to move over the area with an open Gulf.  Will
likely see a few rounds of showers and thunderstorms over the
weekend that will be timed out by the aforementioned vort maxes and
low level moisture convergence.  Will keep high chance or likely
pops until the upper trough passes through the area on Tuesday.
Temperatures over the weekend will warm up back closer to normal
despite the rain chances because of the surge of warm, moist air
from the south and +15C 850mb temperatures.



.AVIATION:  (For the 06z TAFs through 06z Wednesday Night)
Issued at 1155 PM CDT Tue May 19 2015

Deteriorating conditions are expected beginning late tonight and
continuing into Wednesday morning from west to east across our
region as first rain, then lower CIGs move in. At some point, we
should see IFR conditions at COU, with STL metro continuing to be
on the threshold, but have expanded IFR mention into SUS and STL
with this issuance. Otherwise, low-end MVFR will be the rule for
much of Wednesday. Prefer the faster timing presented with the
18z/00z GFS model run, which brings rain in fast and is consistent
by and large with the lifting mechanisms present in these systems.
We should still see a bit of drizzle at the tail-end of the main
area of rain and this will move in about the same time as the
lower CIGs. Otherwise, NE surface winds will prevail for much of
this period.

Specifics for KSTL: Faster rain timing still on track and have
now added IFR into the mix by afternoon. Unknown how fast low
clouds will move out, though, with several solutions possible.
Have continued to go with a slightly optimistic approach for
improvement in the evening but kept the non-VFR conditions all
night. Should still see some drizzle to accompany the IFR CIGs
during the afternoon.





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