Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 242312
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
612 PM CDT Thu May 24 2018

.SHORT TERM...  (Through Friday Night)
Issued at 350 PM CDT Thu May 24 2018

Surface high pressure and upper ridging will gradually move east
late today into Friday. A north-south oriented boundary exists on
the western periphery of the high, clearly evident on visible
satellite imagery, in the form of diurnal cu and mid-level bkn
ceilings through central Missouri. Expect a few widely scattered
showers or isolated thunderstorm through sunset with little
support for anything sustained. Most will stay dry, especially
along and east of the Mississippi River.

A complex of thunderstorms is expected around a shortwave feature
that will push through the central plains and southwest Missouri
overnight. While precipitation chances edge eastward into the CWA,
much of the support for organized convection will be over south
and southeast Missouri Friday afternoon. The inhibiting factor
could be any remnant showers/cloud cover during the morning hours,
limiting with short recovery time for afternoon instability.
Chances decrease further north and east of St. Louis. While
the airmass is unstable, shear is unimpressive, suggesting we
could see diurnally driven pulse showers/storms that wane through
the evening hours.

Late Friday, a troughing extends well south and west from an
upper level low. Another shortwave feature over Iowa likely places
the main focus for thunderstorms from central Iowa through
central Missouri. Plenty of instability builds ahead of the system
over central and northeast Missouri with CAPE values around 3000
J/kg, while shear is somewhat marginal at 25 kts. May see storms
produce some hail or gusty winds, but late day timing may keep
overall severe threat low.

Maples

.LONG TERM...  (Saturday through Next Thursday)
Issued at 350 PM CDT Thu May 24 2018

The main story in the long term will be above normal temperatures
and limited chances for thunderstorms over the Memorial Day
weekend.

The boundary that drops in from the north late Friday is expected
to wash out in the region through early Saturday. Surface
dewpoints well into the 60s, possibly near 70 in some cases, could
make the weekend feel pretty sticky. While not a lot of support
exists for thunderstorms, cannot rule out an isolated afternoon
storm, especially south and east of the St. Louis Metro.

The real key to the extended period will be in relation to the
tropical system over the gulf. Upper ridging develops and tries to
build in from the southwest through Monday, as surface high
pressure likely keeps us dry. The last few runs in model guidance
have wobbled a bit with track/timing. However, solutions have come
into somewhat better agreement in holding the system just far
enough south to not be a hindrance for Memorial Day.

The surface high that keeps us dry Monday moves east for the
midweek period. The ECM keep a formidable closed upper low and
tracks it over the Tennessee Valley, while the GFS is somewhat
weaker, slower and further south with the system. Temperature
will remain above normal through at least Tuesday, possible
challenging some record highs. Depending on the exact track of the
low, temps may be tamed somewhat through midweek...back into the
80s.

Maples

&&

.AVIATION...  (For the 00z TAFs through 00z Friday Evening)
Issued at 551 PM CDT Thu May 24 2018

A surface ridge centered over the Ohio Valley region southwest
into southeastern MO early this evening. Isolated showers/storms
may impact COU early this evening. Diurnal cumulus clouds will
dissipate later this evening due to lose of daytime heating.
Mainly just high level cloudiness later this evening and
overnight. An appproaching upper level disturbance may bring
scattered showers and storms to COU as early as Friday morning,
but elsewhere the better chance of showers and storms should be
during Friday afternoon and early evening when instability will
be maximized. A light southeast surface wind can be expected
tonight with a south-southwest wind on Friday.

SPECIFICS FOR KSTL: A surface ridge centered over the Ohio Valley
region southwest into southeastern MO early this evening.
Diurnal cumulus clouds will dissipate later this evening due to
lose of daytime heating. Mainly just high level cloudiness later
this evening and overnight. An appproaching upper level
disturbance and diurnal instability should lead to scattered
showers and storms Friday afternoon and early evening. A light
southeast surface wind can be expected tonight with a south-
southwest wind on Friday.

GKS

&&

.PRELIMINARY POINT TEMPS/POPS...
Saint Louis     71  87  70  91 /  10  30  20  20
Quincy          68  85  68  90 /  10  30  30  20
Columbia        67  85  67  89 /  20  30  30  20
Jefferson City  68  86  67  89 /  20  30  20  20
Salem           65  84  67  89 /   5  20  20  20
Farmington      66  83  65  88 /  10  40  20  20

&&

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

$$

WFO LSX



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