Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 231143
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
643 AM CDT Wed Apr 23 2014

.SHORT TERM: (Today through Friday)
Issued at 342 AM CDT Wed Apr 23 2014

Surface ridge extending from Wisconsin south/southwest into the
Mid-Mississippi Valley and back into east Texas will move east today
ahead of developing low pressure over the Great Plains.  Increasing
southerly low level flow will result.  All short-range model
guidance develops an area of warm advection showers over the eastern
Plains and pushes it east northeast into northwest Missouri and Iowa
today.  Looks possible that the southeast edge of the showers could
clip our area, but low level air is pretty dry according to the NAM,
GFS, and RUC and the primary thrust of moisture return will be back
over western Missouri so have only introduced slight chance PoPs
over our northwest counties.  We should see highs pretty close to
what occurred yesterday even with the warm advection since we`ll be
starting out the day cooler than Tuesday morning.  The exception
will be central Missouri where morning lows should be a bit warmer
than areas further east.

The shortwave currently digging across the Rockies will move out
into the Great Plains tonight and the resulting cold front will move
into northwest Missouri around 12Z.  Still looks like showers and
thunderstorms will be ongoing along and ahead of the front as it
moves through the CWFA on Thursday.  Diurnal heating will likely be
limited due to cloud cover and advancing precip from the west, so
instability still looks relatively weak.  While there should be
enough CAPE for thunderstorms, widespread severe weather does not
look likely at this time.  Stuck closer to the warmer MAV guidance
for highs since morning lows will be around 50 across the area and
15-20 degrees of rise should be attainable in warm advection this
time of year regardless of cloud cover.

Guidance is in good agreement with pushing the front through the
entire area shortly after 00Z.  Still have some lingering precip
east of the Mississippi River Thursday evening as the front exits,
but dry after midnight.  Pacific high builds across the region
Friday morning.  As opposed to a colder Canadian airmass, the
Pacific ridge should produce temperatures near or slightly above
normal in the upper 40s to low 50s Friday morning.  West-southwest
flow develops Friday morning as the high scoots quickly into the
Tennessee Valley so expect temperatures to rebound into the mid and
upper 70s.

Carney

.LONG TERM:  (Saturday through Tuesday)
Issued at 342 AM CDT Wed Apr 23 2014

While the medium range guidance is coming into better agreement on
the overall synoptic pattern, the smaller scale is still unclear.
Generally, a secondary cold front will dip south across the Upper
Midwest driven south by the last vestiges of Thursday`s shortwave.
The front will stall somewhere across the Midwest on Saturday,
though models can`t make up their minds where.  GFS stalls the front
across south/southwest Missouri Saturday morning, while the ECMWF
stalls it out over northern Iowa.  The GEM is right about in the
middle stalling the front over northern Missouri.  All three models
have some low level baroclinicity over our area, whether it is the
primary baroclinic zone associated with the front (GFS/GEM) or a
secondary baroclinic zone left over from the Pacific airmass which
will be exiting to the east (EC).  Warm advection begins Saturday
morning with a 30+ kt low level jet pointed at this baroclinic zone
and all three models print out some light precip.  Have therefore
kept chance pops going in central Missouri, and would not be
surprised if subsequent shifts need to bump up pops a bit more
across the area if model trends become more consistent.

The front remains stalled somewhere between Springfield Missouri and
Davenport Iowa depending on which model you believe through Monday
as the longwave trof over the Pacific moves inland, and becomes
negatively tilted over the Rockies and Great Plains.  A strong
surface low develops as a result and it moves into the Mississippi
Valley Monday night into Tuesday.  The upper trof cuts off and
becomes stagnant while the surface low tracks across Missouri into
the Ohio Valley Tuesday.  Pattern is more reminiscent of late Fall
or Winter than mid to late Spring.  Unsure how likely this is to
happen, but this is at least the second run in a row that I`ve seen
do this.  Will have to wait and see, but right now it looks like a
cold/wet end to April.

Carney

&&

.AVIATION:  (For the 12z TAFs through 12z Thursday Morning)
Issued at 628 AM CDT Wed Apr 23 2014

VFR flight conditions will continue to prevail this forecast
period, with winds veering and becoming more southerly as the
surface ridge moves off to the east. The next system which will
impact the area is taking shape over the plains, and as it moves
east, area TAF sites will see winds increase to roughly 10-15KT by
late morning/early afternoon in response to a tightening pressure
gradient and increased southerly flow. The aforementioned pressure
gradient should also be enough to produce some gusts around
20-22KT beginning by late afternoon, mainly impacting KCOU and
KUIN. Only increasing midlevel clouds are expected through the
period, and while there is a chance for precipitation to move into
central and northeast Missouri late Wednesday night, exact timing
has yet to be pinned down, and as the onset would be in the last
few hours of the forecast period, have not included mention at
this time.

Specifics for KSTL:
VFR flight conditions will prevail through the forecast period,
with winds continuing to veer and become more southerly as the
surface ridge moves east and the next system to impact the area
takes shape over the plains. Expect winds to increase to about
12-14KT by early afternoon, remaining fairly steady overnight, and
become gusty Thursday morning as the surface pressure gradient
tightens ahead of the approaching system. Showers and
thunderstorms will move through the area on Thursday, though exact
timing for impact at KSTL has yet to be pinned down, and as it
would likely be within the last couple hours of the forecast
period, have not mentioned it in the TAF at this time. Prior to
the storms, expect a gradual increase in midlevel clouds
overspreading the area from west to east today/tonight.

JP

&&

.PRELIMINARY POINT TEMPS/POPS:
Saint Louis     69  52  72  52 /   5  10  80  30
Quincy          66  49  66  46 /  10  20  80  20
Columbia        72  53  70  47 /  10  30  80  10
Jefferson City  75  53  70  47 /  10  20  80  10
Salem           65  49  72  49 /   5   5  70  50
Farmington      69  48  73  47 /   5   5  80  30

&&

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

$$

WFO LSX






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