Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 242038
AFDLSX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
338 PM CDT Fri Apr 24 2015

.SHORT TERM:  (Through Late Tonight)
Issued at 334 PM CDT Fri Apr 24 2015

Clouds and mild temperatures blanket the area late this afternoon
and we`ve seen very little precipitation thus far. The main forecast
issue tonight will be the precipitation chance/trends. Present
indications are two main areas to watch. The first is an area of
origination in south central and southeast MO this evening. The
guidance is in relatively good agreement showing a perturbation in
the southwest flow aloft will track northeast out of OK across the
aforementioned region. The latest water vapor imagery suggests the
presence of 2 upstream perturbations. This disturbance combined with
with strong moisture convergence/lift via an intensifying and
veering LLJ should result in an area of showers and thunderstorms
over the southeast third of the CWA. The second region of interest
is much further west. The short wave trof currently getting ready to
move into the central and southern High Plains combined with lift
via a secondary branch of the southerly LLJ should result in the
development of strong-severe thunderstorms along and east of the
dryline in KS over the next 2-4 hours. This initially scattered
convection should grow upscale into a convective system across
eastern KS this evening which will migrate eastward ahead of the
advancing surface low, and impact areas along/north of I-70
overnight into Saturday morning.

Glass

.LONG TERM:  (Saturday through Next Friday)
Issued at 334 PM CDT Fri Apr 24 2015

By 12z Saturday morning, strengthening surface low will be over
northwestern MO. Will see overnight activity sliding north and east
of forecast area as dry slot wraps around low with a brief break in
activity, mainly for St. Louis metro and areas to the south and east
through midday. Then for afternoon hours, possibility of severe
weather and location of it will depend on location of surface low,
frontal boundary and how much the atmosphere recovers from morning
activity. Reintroduced thunderstorms for all locations as there is
enough instability, at the surface and aloft and decent low level
jet for storms to develop even north of track of surface low. For
now best chances of severe weather will be over east central and
southeast Missouri as well as southern Illinois as surface low
slides east southeast Saturday afternoon. Models showing CAPE
between 1000-2500 J/kg, decent lapse rates and shear, with supercell
development possible and main severe threats being large hail,
damaging winds, and isolated tornadoes. SPC has placed this area in
a slight risk with an area of enhanced risk southeast of STL metro
area. Highs will vary from the low 60s far north to the mid 70s far
south.

System to exit region Saturday night with lingering showers tapering
off from north to south. Cooler air to slowly filter in with lows in
the low 40s far north to the low 50s far south.

Below normal temps and gradual clearing expected on Sunday as
surface ridge builds in. Beyond that, temperatures to slowly
moderate through the work week, with a shortwave sliding through
region on Wednesday with some scattered showers possible.

Byrd
&&

.AVIATION:  (For the 18z TAFs through 18z Saturday Afternoon)
Issued at 1238 PM CDT Fri Apr 24 2015

Multi-layered clouds are occurring across the region at midday with
all sites VFR at this time. A large area of MVFR cigs will advance
into central MO/KCOU later this afternoon, gradually overspreading
the other terminals later this evening. Main precipitation through
mid-evening will be spotty showers with little if any impact. A
better threat of showers and thunderstorms will exist during the
later part of the evening into the overnight hours and this will
be possible in 2 modes. The first being showers and thunderstorms
which originate in southeast MO and push northeast and then a large
region of showers and thunderstorms which develops in KS late this
afternoon/this evening and moves east-northeast. Flight conditions
will deteriorate overnight with IFR developing and lasting into the
morning hours.

Specifics for KSTL:

VFR flight conditions are expected until later this evening. Any
precipitation during this time period should be sprinkles or
spotty short-lived showers with little if any impact.

Later this evening a better threat of showers and thunderstorms
will exist and it will coincide with the arrival of MVFR cigs.
Showers and possibly thunderstorms which originate in southeast MO
will move northeast potentially impacting the terminal after
03-04z. Following this first batch, a large region of showers and
thunderstorms which develops in KS late this afternoon/this
evening may move into KSTL after 09z. Flight conditions will
deteriorate overnight with IFR developing and lasting into Saturday
morning. An additional threat of thunderstorms may unfold after
19-20z Saturday however due to the uncertainty will refrain from
mentioning in the current TAF.

Glass
&&

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

$$
WFO LSX




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