Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 172252
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
552 PM CDT Thu May 17 2018

.SHORT TERM...  (Through Late Friday Afternoon)
Issued at 308 PM CDT Thu May 17 2018

Focus thru the period will be PoPs. MCV evident in sat image over
wrn MO with another further south into AR will continue to impact
the area thru Fri. With the trof stretching thru the region, these
MCVs will have a Fujiwhara effect with a s/w moving precip back
northwestward into the area late tonight and Fri morning.

Mdls differ exactly where the precip will be in the morning, but
best chances shud be over the ern half of the CWA where the s/w is
tracking nwd. After sunrise, believe a band of TSRA will develop
along the wrn flank of the upper low where insolation is possible.
The 18z NAM just arriving suggests a more ern soln, but will need
to continue to monitor trends. Wherever the lower-res mdls wud
suggest periods of heavy rain possible thru the early morning
hours. If the more wrn soln verifies, going temps for tomorrow are
too high. While I have trended further west slightly, have not
moved PoPs as far west as the NAM soln.

The upper trof will slowly pull newd out of the area Fri afternoon
and evening as the main trof ejects into the Plains. Some precip
shud linger into Fri evening across ern portions of the CWA, but
the threat of precip shud shift east fairly quickly.

Tilly

.LONG TERM...  (Friday Night through Next Thursday)
Issued at 354 PM CDT Thu May 17 2018

Mdls are in fairly good agreement with a wrmfnt lifting north
through the area Sat morning. With fairly good moisture
convergence associated with this fnt, believe a round of storms is
possible Sat morning across far wrn portions of the CWA. This
threat shud diminish thru the morning, but return across much of
the CWA during the afternoon hours with peak heating. Mdls keep
the warm sector capped, tho differ on placement of the wrmfnt
during the afternoon hours. Have kept some low PoPs during the
afternoon to account for possible isod storms.

Also have slightly higher PoPs for Sun night into Mon as a weak
cdfnt pushes thru the area that shud provide a focus for storm
development. However, mdls disagree with location of best forcing
with this as well.

With 500mb heights in the 582dam range, and a sfc boundary across
the region thru much of the forecast period, have generally
trended warm with numerous period of lower PoPs.

Tilly

&&

.AVIATION...  (For the 00z TAFs through 00z Friday Evening)
Issued at 525 PM CDT Thu May 17 2018

It appears that most of the showers and storms will be just south
of COU and the St Louis metro area this evening, although may
need to include at least VCSH until 01Z early this evening at
these taf sites depending on the latest radar trends. Some of the
model guidance does lift convection back into the St Louis metro
area late tonight and early Friday morning, associated with an
upper level disturbance. Will include VCTS for this time period.
At least MVFR cloud ceilings are also likely at the taf sites
Friday morning, with ceilings possibly as low as 1000 feet in the
St Louis metro area. The cloud ceiling should gradually rise
during the afternoon, with a redevelopment of convection possible
in the St Louis metro area. A persistent east-northeasterly
surface wind can be expected through the period with surface
ridging extending from the Great Lakes region southwest into
northeastern MO.

SPECIFICS FOR KSTL: It appears that most of the showers and storms
will be just south of STL this evening, although may need to
include at least VCSH until 01Z early this evening in the STL taf
depending on the latest radar trends. Some of the model guidance
does lift convection back into the STL area late tonight and
early Friday morning, associated with an upper level disturbance.
Will include VCTS for this time period. At least MVFR cloud
ceilings are also likely at STL Friday morning, with ceilings
possibly as low as 1000 feet. The cloud ceiling should gradually
rise during the afternoon, with a redevelopment of convection
possible. This convection should shift east of STL by early Friday
evening. A persistent east-northeasterly surface wind can be
expected through the period with surface ridging extending from
the Great Lakes region southwest into northeastern MO.

GKS

&&

.PRELIMINARY POINT TEMPS/POPS...
Saint Louis     64  79  64  88 /  40  40  10  20
Quincy          60  76  60  83 /  10  20   5  10
Columbia        59  79  61  85 /  50  30   5  20
Jefferson City  59  80  61  87 /  60  30   5  20
Salem           64  76  62  85 /  50  50  30  20
Farmington      60  75  59  86 /  60  40  10  20

&&

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

$$

WFO LSX



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