Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 211814
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
114 PM CDT Sat Apr 21 2018

.SHORT TERM...  (Through Late Tonight)
Issued at 317 AM CDT Sat Apr 21 2018

Large closed upper low over New Mexico/Colorado will drift east
into the Great Plains through today and this evening.  GOES-16 low
and mid level water vapor imagery is showing strong upglide in the
warm conveyor belt region of the system over the Plains this
morning...and radar has a broad area of light to moderate rain
across Kansas stretching south into Oklahoma and north Texas. Expect
this area of upglide and rain to migrate slowly east today and
tonight ahead of the low.  Short range models are in fairly decent
agreement that the surface reflection of the low will pass through
east Texas into Arkansas late today into tonight...although there is
some question on speed and precise location of the low.  Regardless,
low level flow over Missouri and Illinois will remain easterly today
and turn to the northeast tonight as the low moves into Arkansas.
The easterly/northeasterly wind will be constantly advecting dry air
in at the low levels from high pressure centered over the Ohio
Valley and Great Lakes region.  Forecast soundings show a very
persistent dry layer below 10,000 ft today and into this evening
across the entire area.  This should really limit any chances of
precip today to perhaps a few sprinkles.  Eventually though the
column should moisten up late this evening and overnight from west
to east for rain to reach the ground.  Best chances for rain will be
along and south of the I-70 corridor in Missouri and into southwest
Illinois...primarily after 06Z.  Highs today should be similar to
Friday`s readings even with more extensive cloud cover since we`ll
be starting out the morning a little warmer.  Lows Sunday morning
will likely be the warmest we`ve seen in almost a week due to
extensive cloud cover and some milder air being drawn northward into
the low pressure system from the lower Mississippi Valley.

Carney

.LONG TERM...  (Sunday through Friday)
Issued at 317 AM CDT Sat Apr 21 2018

A closed upper level low and corresponding surface feature will be
situated over the Ark-La-Tex Region early Sunday morning. 700mb mean
flow out of the south/southeast will draw moisture northward from
the gulf and into Southern Illinois/Missouri during the day Sunday.
Though rain will initially have some trouble overcoming dry air,
chances for showers will increase as smaller vort features rotate
around the parent system with its overall eastward progress. Best
potential for measurable precipitation is likely to stay focused
south of Interstate 70. Showers will become more scattered in nature
on the northern fringe of the system.

The eastward progress of the low could slow or temporarily stall
over the Tennessee Valley Monday, as it fights a strengthening
surface high positioned just off the New England seaboard. Showers
could linger through the first half of Monday, especially over
southern Illinois, before exiting Tuesday morning.

A brief dry period is forecast for Tuesday, before couple more upper
wave features drop southeast through the Midwest over the midweek
period. The first will be a weaker upper level shortwave that brings
a cold front through during the day Wednesday with a round of
showers. Much of the day Thursday is dry before a colder air if
reinforced by yet another front late Thursday into Friday. The
eastern trough becomes more amplified and pronounced late in the
week.

Temperatures through the period will likely stay near or below
normal in northwest flow.

Maples
&&

.AVIATION...  (For the 18z TAFs through 18z Sunday Afternoon)
Issued at 112 PM CDT Sat Apr 21 2018

VFR conditions through forecast period, except for KCOU, where
cigs will dip down to MVFR with onset of showers after 10z Sunday.
Otherwise, majority of pcpcn to remain just south of taf sites for
now and winds to persist from the east.

SPECIFICS FOR KSTL:
VFR conditions through forecast period even when pcpn approaches
from the south. Otherwise, majority of pcpcn to remain just south
of taf sites for now and winds to persist from the east.

Byrd
&&

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

$$
WFO LSX



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