Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 211157

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
657 AM CDT Fri Apr 21 2017

.SHORT TERM...  (Through Late Tonight)
Issued at 355 AM CDT Fri Apr 21 2017

Shortwave over Rocky Mountains will close off and move east into the
Great Plains today and tonight.  Low level cyclogenesis is already
occurring over the eastern Rockies and southerly flow is bringing
moisture out of the Gulf into the eastern Plains and the Mississippi
Valley.  The a 20-30kt low level jet pointed at the baroclinic zone
over southern Missouri is providing lift for widespread showers and
a few thunderstorms across much of southwest Missouri into parts of
southeast Missouri.  The baroclinic zone will lift slowly northward
today and the low level jet will increase this evening and overnight
as the shortwave moves over Missouri and the low level system moves
along the Missouri/Arkansas border.  Highest chances for precip will
be along and south of I-70 through the period.  Should be enough
instability through the day today for isolated to widely scattered
thunderstorms across southeast Missouri as well, but instability
falls of tonight so have only general rain showers in the forecast
after 00Z.  Current total QPF through 12Z Saturday is 1.5 to 2
inches across the eastern Ozarks.  There could be some localized
water issues with this much QPF...but flash flood guidance values
are 2 inches or more, so don`t see a need for any watch products
right now.  Temperatures will be cooler than in recent days in the
upper 50s to low 60s today and in the 40s tonight.


.LONG TERM...  (Saturday through Thursday)
Issued at 355 AM CDT Fri Apr 21 2017

Still appears that rain will continue through the first half of the
weekend as the GFS/NAM/ECWMF all show the upper low moving from
southwest Missouri at 12Z Saturday morning into western Tennessee by
12Z Saturday.  Models continue to show concentrated low level
moisture convergence underneath strong mid-level ascent along and
south of I-70 on Saturday morning warranting likely PoPs.
Thereafter, the low level jet will veer eastward and the upper
level ascent will begin to wane causing the precipitation to
slowly end from west to east on Saturday night.

Sunday and Monday both still look dry as a ridge moves in quickly
behind the upper trough.   Then the upper flow becomes more
progressive by the middle of next week with the GFS/ECMWF/Canadian
all showing a shortwave trough moving through the upper Midwest.
This brings an attendant cold front across Missouri and Illinois
by Tuesday night and Wednesday night. The global models show a
couple of additional shortwaves moving through at midweek which
will help hold up the front over the area before a deeper trough
builds into the western CONUS by late in the week.

Temperatures will begin to warm back up on Sunday as the upper low
moves off to the east. Temperatures will be above normal most of
next week as 850mb temperatures hover mainly between 10-15C.



.AVIATION...  (For the 12z TAFs through 12z Saturday Morning)
Issued at 641 AM CDT Fri Apr 21 2017

Area of rain over the Ozarks stretching into parts of east central
Missouri and southwest Illinois will continue moving east this
morning. There may be some patchy MVFR in the rain over the
Ozarks, but the majority of this area is VFR and will remain VFR
through the day. More rain will overspread the area primarily
along and south of I-70. Lowering ceilings and possibly visibility
will accompany the rain with MVFR ceilings over the Ozarks
building north to the I-70 corridor before sunrise. There`s some
chance ceilings could drop below 1000 feet south of I-70 before
12Z...though confidence is low at this time.


Area of rain south of the terminal should stay south this
morning. Can`t rule out a sprinkle or two though, but don`t expect
any impacts to operations. Next round of rain will likely move in
during the evening with VFR conditions continuing to
prevail...probably through most of the night. Think ceilings will
eventually fall to MVFR near daybreak Saturday and stay down
through 18Z.





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