Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 170511

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1211 AM CDT Mon Apr 17 2017

.SHORT TERM...  (Through Late Monday Afternoon)
Issued at 334 PM CDT Sun Apr 16 2017

Primary concern for tonight and Monday is thunderstorm chances.
Guidance is showing another complex of thunderstorms tonight,
developing somewhere between Oklahoma City and Springfield Missouri.
This obviously covers a lot of real estate...and the key for precip
chances in our area will be how far north the storms develop.  The
RAP mass fields support a more solution to the high sliding in
across northern Missouri, and this fits my conceptual model of how
this might evolve better than most other guidance. However, most of
the convection allowing models like the HRRR, and WRF develop the
thunderstorms further north which affect most areas along and south
of I-70.  Can`t ignore the CAMs in good conscience, so have kept
mention of storms in along and south of I-70 after midnight and into
Monday morning with likely PoPs across the eastern Ozarks by around
12Z.  Think any lingering showers or storms should be exiting the
area by late afternoon.  Temperatures will once again be very
dependent on where precipitation falls...but am leaning once again
toward the warmer MAV guidance.


.LONG TERM...  (Monday Night through Next Sunday)
Issued at 334 PM CDT Sun Apr 16 2017

Still looks like an active week as global models are showing a
transition from quasi-zonal upper flow at mid-week to more
amplified flow by next weekend. ECMWF/GFS/Canadian still show two
shortwave troughs moving across the area during the workweek. As
is often the case with zonal flow, there are slight differences in
the timing and strength of the shortwaves today compared to
yesterday. Consequently have low confidence in the timing of
precipitation from midweek on.

It now appears that the first shortwave will stay north of the area
on Tuesday causing the attendant cold front only to move as far
south as northern Missouri and central Illinois.  Then the next
shortwave will move into the Midwest by Wednesday night and Thursday
which will help push that front southeast through the area on
Thursday. It does appear that we will spend more time in the warm
sector in between the the two storm systems.

Monday night into Tuesday looks mostly dry as a shortwave ridge
moves across the area.  Then the chance of showers and thunderstorms
will be mainly concentrated over the northern half of the CWA
Tuesday into Wednesday night close to where the cold front will be
stalled.  Still have a chance of showers and thunderstorms going
across the entire area on Thursday as the cold front moves through.

The global models have come into better agreement next weekend in
showing a large upper low moving out of the southwest CONUS into the
the Midwest by next weekend.  There is still some uncertainty with
the exact track of the surface low with this storm system, but it
does appear that we will get showers and some thunderstorms with
this system.

Temperatures this week will continue to be above normal in the warm
sector with 850mb temperatures in the 10-15C range.  Then near or
just below normal temperatures will move into the area behind the
cold front.



.AVIATION...  (For the 06z TAFs through 06z Monday Night)
Issued at 1208 AM CDT Mon Apr 17 2017

Scattered to isolated SHRA/TSRA on the northern edge of a
thunderstorm complex may clip KCOU and KSTL/KSUS/KCPS overnight
during the first 0-6 hours. Otherwise, VFR conditions are
expected at the terminals. Initially northerly to northeasterly
winds will continue to veer and become easterly to southeasterly
by the end of the valid TAF period.





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