Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 250445
AFDLSX

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE ST LOUIS MO
1145 PM CDT Tue Mar 24 2015

.UPDATE:
Issued at 1145 PM CDT Tue Mar 24 2015

Updated the forecast earlier to allow severe thunderstorm watch to
expire for central MO. Showers and thunderstorms moving quickly
to the east and should be east of Mississippi River by midnight.
As for temperatures, could still see temps rise a little bit in
warm sector as surface low, currently between STL and UIN, lifts
northeast towards great lakes region. Otherwise, lows will be
in the mid 30s to mid 40s. Will send out one last update before
midnight to freshen wording.

Byrd
&&

.SHORT TERM:  (Through Late Tonight)
Issued at 356 PM CDT Tue Mar 24 2015

Convective initiation has commenced within the last 45 minutes across
southeastern KS ahead of the surface low/warm front intersection
and south along the dryline as large scale ascent associated with
the potent short wave trof currently in central KS spreads across
that region. All the short term guidance and CAM show an upswing
in convection through 00z as the surface low tracks east-northeast
into central MO. Present indications are the surface low will
track just north of St. Louis and into central IL by 06z, with the
warm front lifting northward in the process allowing a narrow
wedge of instability to advance into mainly central/southern parts
of the area. While showers and thunderstorms will spread across
the bulk of the area due to strong large scale ascent with the
short wave, the severe threat will primarily be limited to just
north of the warm front and into the warm sector. This will be
greatest in central MO this evening, and despite the lifting warm
front, the instability will diminish with eastward extent limiting
the severe weather potential over far eastern MO and into IL. All
the showers and storms should exit the area by 07z or so as the
surface low moves quickly towards the Great Lakes and cold front
advances.

Glass

.LONG TERM:  (Wednesday through Next Tuesday)
Issued at 336 PM CDT Tue Mar 24 2015

The next active period will unfold during the later part of
Wednesday afternoon and especially Wednesday night. The cold front
will be stationary across southern IL to near the MO/AR border at
12z and will once again lift northward during the day into
southeast MO with convective development expected in the vicinity
of the front mid-late afternoon. Shear and instability suggests
the potential for organized severe storms across the southeast
third of the CWA from late afternoon into the evening. Significant
large scale forcing and mid level frontogenetical forcing on
Wednesday night will also contribute to extensive precipitation
within the cool air well to the north of the front, with the LLJ
promoting extensive thunderstorms along and ahead of the front and
for a 100 mile or so wide corridor on the cool side of the front.
There is a decent threat of some heavy rainfall within this area
across southeast Missouri and southern IL due to persistent
thunderstorms and high convective rainfall rates and thus I have
issued a flash flood watch for Wednesday night.

Some lingering rain may impact portions of east central and southeast
MO and southern IL on Thursday morning, otherwise the main story
will be much cool weather from Thursday into Saturday with well
below average temperatures. A northwest flow short wave may even
bring some precipitation to central and southeast sections of the
MO Friday night into Saturday, some of which could be snow.

A warm-up is on tap beginning on Sunday. Despite another cold
front passage on Sunday night, temperatures Sunday into early next
week look at least average for late March.

Glass
&&

.AVIATION:  (For the 06z TAFs through 06z Wednesday Night)
Issued at 1145 PM CDT Tue Mar 24 2015

Showers and thunderstorms to be east of taf sites by 06z
Wednesday. So main issue will be cigs across region as ifr sc deck
slides southeast overnight. Some breaks in overcast, but feel that
cigs will not scatter out til mid to late morning. Some patchy fog
possible as well, so kept mvfr vsby in tafs. During the day today
will see mid and high clouds before next system moves in during
the late afternoon and evening hours. KUIN to be on northern
fringes of precipitation so just have vcnty shower mention there
for now after 02z Thursday. KCOU should see storms move in by 01z
Thursday and STL metro area after 02Z Thursday with better chances
after 05z Thursday. As for winds through the forecast period, west
winds to veer to the northeast late in the day then back to the
north and pickup as system slides along frontal boundary that is
just south of I-70 corridor.

Specifics for KSTL:
Showers and thunderstorms to be east of metro by 06z Wednesday.
So main issue will be cigs across region as ifr sc deck slides
southeast overnight. Some breaks in overcast, but feel that cigs
will not scatter out til late morning. Some patchy fog possible
as well, so kept mvfr vsby in taf. During the day today will see
mid and high clouds before next system moves in during the late
afternoon and evening hours. STL metro area will see precipitation
move in by 02Z Thursday with better chances after 05z Thursday.
As for winds through the forecast period, west winds to veer to
the northeast late in the day then back to the north and pickup as
system slides along frontal boundary that is just south of I-70
corridor.

Byrd
&&

.LSX WATCHES/WARNINGS/ADVISORIES:
MO...FLASH FLOOD WATCH from Wednesday evening through late Wednesday
     night FOR Crawford MO-Iron MO-Jefferson MO-Madison MO-
     Reynolds MO-St. Francois MO-Ste. Genevieve MO-Washington MO.

IL...FLASH FLOOD WATCH from Wednesday evening through late Wednesday
     night FOR Clinton IL-Marion IL-Monroe IL-Randolph IL-St.
     Clair IL-Washington IL.

&&

$$
WFO LSX




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