Area Forecast Discussion
Issued by NWS St. Louis, MO

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000
FXUS63 KLSX 271716
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
1216 PM CDT Fri Mar 27 2015

.UPDATE:
Issued at 739 AM CDT Fri Mar 27 2015

Added likely PoPs with a bit of QPF and a tenth of an inch of snow
across SE MO and extrm SW IL for a few hrs this mrng. Getting reports
of several tenths of an inch accums on elevated and grassy sfcs.

&&

.SHORT TERM:  (Through Late This Afternoon)
Issued at 331 AM CDT Fri Mar 27 2015

A potent northwest flow short wave has been generating an area of
light rain across western MO since late last night. This is far
removed from our CWA however there is some very light precipitation
now showing up in mid MO. Current projections would have this
across parts of the southern CWA after 12z and at this time I just
have a mention of sprinkles and flurries. It is moving rather
quickly due to the digging wave so anything that does occur is
expected to exit by 14z or so. Otherwise we should see alot of
clouds this morning and even into the early afternoon as low level
CAA continues, with a trend towards more cumuliform clouds as the
afternoon progresses. Once again a cold day with below average
temperatures for late March.

Glass

.LONG TERM:  (Tonight through Thursday)
Issued at 331 AM CDT Fri Mar 27 2015

Yet another robust short wave trof in the northwest flow will dig
southeastward thru the mid MS Valley late this evening into
Saturday morning. This wave looks even more potent than the
present one. The combination of large scale forcing/lift with the
short wave, strong low-mid level frontogenesis and low level WAA
will result in a band of snowfall. The center of this band looks
like it should be just west of the CWA, however snow will impact
portions of central and southeast MO. Since most of it will fall
at night, this will help the accumulation potential and presently
have amounts less than an inch. Saturday should be the last day of
the well below average temperatures.

Heights aloft begin to rise on Saturday night with the departure
of the eastern U.S. trof and surface high pressure retreats
allowing for low level WAA to get underway. Rather strong WAA
persists on Sunday ahead of the next cold front and this should
bring a rebound in temperatures back closer to normal. The WAA
associated lift along with ascent due to the migrating shortwave
will bring an area of pre-frontal showers on Sunday into Sunday
evening ahead of the advancing cold front.

Temperatures moderate back to above average next week as the
overall flow aloft decrease in amplitude and gains a more zonal
component. While there are some timing issues in the deterministic
models, another shortwave and attendant cold front will bring a
threat of showers and thunderstorms in the Wed/Wed Night time frame.

Glass

&&

.AVIATION:  (For the 18z TAFs through 18z Saturday Afternoon)
Issued at 1150 AM CDT Fri Mar 27 2015

Diurnally enhanced cumulus field will continue early this
afternoon, but should eventually dissipate later this afternoon as
subsidence increases as the surface ridge over the northern
Plains builds southeastward into MO. There may be
flurries/sprinkles or even light snow/rain showers early this
afternoon in the St Louis metro area. An upper level disturbance
will drop southeastward into the area tonight. Mid level clouds
are expected ahead of it with at least a brief period of light
snow, MVFR cigs and MVFR/IFR vsbys at COU late tonight/early
Saturday morning in a narrow snow band which will impact central
MO. Precipitation should remain west of UIN, STL, SUS and CPS.
N-nely surface wind will veer around to an e-sely direction late
tonight as the surface ridge shifts southeastward into the Great
Lakes region.

Specifics for KSTL: Sprinkles or flurries early this afternoon
from a stratocumulus deck. These clouds will dissipate late this
afternoon with mid level clouds advecting southeastward into STL
late tonight. The mid level clouds will advect southeast of STL
Saturday afternoon. Nly surface wind will become light this
evening and veer around to an ely direction by late tonight, then
to an e-sely direction Saturday morning.

GKS

&&

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

$$

WFO LSX





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