Area Forecast Discussion
Issued by NWS St. Louis, MO

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290
FXUS63 KLSX 210903
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
403 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.

Carney

.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.

Britt

&&

.AVIATION...  (For the 06z TAFs through 06z Friday Night)
Issued at 1151 PM CDT Thu Apr 20 2017

High pressure will settle into the region tonight as the cold
front continues to move southward into AR and TN. VFR flight
conditions are expected at the terminals overnight and through the
day on Friday with mid and high clouds spreading across the region
overnight and into Friday morning and gradually lowering VFR cigs
on Friday afternoon. Still some question on the northern extent
of any precipitation on Friday. Most of it will be centered across
southern MO. I can`t rule out a few showers at KCOU or the St.
Louis terminals in the afternoon, but confidence is not high and
any such occurrence will still result in VFR flight conditions.
Rain will gradually spread north on Friday night and impact all
the terminals except KUIN.

SPECIFICS FOR KSTL:

High pressure will settle into the region tonight. VFR flight
conditions are expected and through the day on Friday with mid
and high clouds spreading across the region overnight and into
Friday morning and gradually lowering VFR cigs on Friday
afternoon. Still some question on the northern extent of any
precipitation on Friday. Most of it will be centered across
southern MO. I can`t rule out a few showers at KSTL, but
confidence is not high and any such occurrence will still result
in VFR flight conditions. Rain will gradually spread north on
Friday night and become continuous.

Glass

&&

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

$$

WFO LSX



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