Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 280419
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
1119 PM CDT Mon Oct 27 2014

.UPDATE:
Issued at 910 PM CDT Mon Oct 27 2014

A gradual uptick in convection has occurred over the past few
hours near and ahead of the cold front from central MO into SE KS.
OOz UA data as well as the latest hi-res solutions strongly
suggest that this increase in coverage should accelerate late
this evening and overnight as large scale ascent increases with
approach of upstream shortwave, along with some additional
increase in moisture due to the southwest flow ahead of the front.
Believe the trend in going forecast...which indicates PoPs heading
into the categorical range after 06z from the Ozarks through the
STL metro area...still looks pretty good.  Still working on
specifics, but primary change will be to try to sharpen the
northern gradient of the PoPs along and north of a MBY-UIN line;
however, will continue some low PoPs after fropa as there is some
very light rain associated with the shortwave as far back as
northern KS attm.

Truett

&&

.SHORT TERM:  (Through Late Tonight)
Issued at 259 PM CDT Mon Oct 27 2014

The ongoing area of elevated showers and thunderstorms across west
central MO is located within the pre-frontal warm conveyor belt
and along the northern fringe of the low-level wind max. Mid level
lapse rates are rather steep and there is just enough MUCAPE at
200-300 j/kg to support thunder. Present indications are these
should spread northeast ahead of the advancing cold front through
the remainder of the afternoon and into the early evening. The
coverage of precipitation is expected to ramp up this evening both
ahead and behind the advancing cold front as the upper trof now
centered through the Plains progresses eastward producing increasing
large scale ascent. CAMs suggest the majority of the precipitation
will be in the form of showers/rain but that the coverage of
embedded thunderstorms will increase as well. Hard not to believe
them given the current amount of thunder with such meager instability.

Glass

.LONG TERM:  (Tuesday through Next Monday)
Issued at 259 PM CDT Mon Oct 27 2014

The cold front should be located on the fringes of the CWA across
southeast MO and southwest IL at 12z Tuesday with the precipitation
threat generally confined to the first half of the morning in the
vicinity of the frontal zone. Thereafter the main story will be
much cooler temperatures than today - more seasonable - as cooler
and drier advects into the region in the wake of the front. Low-
mid clouds will clear to the southeast rather quickly during the
morning with some increase in high clouds during the afternoon
across the southern half of MO into IL. Seasonably cool temperatures
are expected Tuesday night into Wednesday as high pressure builds
into and then dominates the area.

Impacts of the next system should begin late Wednesday night as
mid clouds spread into the area within the developing low level
warm advection regime ahead of a northwest flow short-wave. This
trof and the associated cold front will move across the area on
Thursday accompanied by decent mid level moisture and sufficient
lift for at least isolated showers. The cold air in the wake of
this front is more formidable with a 1030+ mb surface high, and
will produce a short-lived bout of the coolest weather thus far
this fall Friday-Saturday. Early indications are a light freeze
and frost may occur overnight Friday into early Saturday morning.

A highly amplified flow regime will be in place at the start of the
upcoming weekend with deep trofs in the vicinity of both coasts
and an upper ridge through the Plains. Despite the amplitude, this
flow will be progessive with the upper ridge pushing through the
mid MS Valley and into the OH/TN valley Saturday night into Sunday
resulting in seasonably warmer temperatures Sunday and Monday. Eventually
the the western trof and associated frontal system will progress
into the area late Monday-Tuesday bringing the next good chance of
precipitation.

Glass

&&

.AVIATION:  (For the 06z TAFs through 06z Tuesday Night)
Issued at 1051 PM CDT Mon Oct 27 2014

Cold front extending from a surface low over southwestern WI
southwest to just west of UIN and COU will move southeastward
through the taf sites late tonight. A sw to ne band of showers
with embedded thunderstorms will continue along the front. Most
of the showers/storms should shift southeast of UIN and COU by
06Z tonight, with the precipitation moving northeastward along
the front through the St Louis metro area between 06Z and 10Z late
tonight. The cloud ceiling will also lower late tonight in the
St Louis metro area as the lower levels of the atmosphere
continue to saturate, possibly briefly into the MVFR catagory. The
swly surface wind will veer around to a nwly direction late
tonight after fropa. The clouds will clear out early Tuesday
morning as a surface ridge builds southeastward into the area
behind the cold front.

Specifics for KSTL: Showers and a few thunderstorms will move into
the STL area overnight. Will include a 4 hour window of
prevailing showers in the STL taf from 06Z to 10Z late tonight
with at least VCTS as well. The cloud ceiling will lower late
tonight, possibly briefly into the MVFR catagory. The swly surface
wind will veer around to a nwly direction late tonight after
fropa. The clouds will clear out early Tuesday morning with w-nwly
winds on Tuesday, becoming light Tuesday night.

GKS

&&

.LSX WATCHES/WARNINGS/ADVISORIES:
MO...NONE.
IL...NONE.
&&

$$

WFO LSX






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