Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 120923
AFDLSX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
423 AM CDT Sat Apr 12 2014

.SHORT TERM:  (Through Late This Afternoon)
Issued at 422 AM CDT Sat Apr 12 2014

Warm front lifts northward through the region today as a developing
surface low over NE/SD shifts eastward into IA while a new surface
wave develops farther southwest along the cold front. Expect warm
temperatures today, an increase in low level moisture behind the
warm front, and breezy winds due to the tightening pressure gradient
ahead of the developing surface trough. BUFKIT profiles also show
stronger winds aloft mixing down to the surface, suggesting gusts
reaching 30-40 mph at times during the afternoon. Neither the
sustained wind speeds nor the wind gusts appear strong/widespread
enough to require wind headlines at this time. Can`t rule out
isolated thunderstorms late this afternoon, but BUFKIT soundings
show a decent cap between 800-700mb that will be tough to overcome
without additional forcing.

Kanofsky

.LONG TERM:  (Tonight through Friday)
Issued at 422 AM CDT Sat Apr 12 2014

(Tonight - Sunday night)

Only minor changes to going forecasts heading into the latter half
of the weekend, with increasing shower and thunderstorm chances the
main sensible weather concern.

The evolution of the precipitation threat later tonight and into
midday Sunday remains rather uncertain at this point.  All of the
00z guidance certainly suggests storm initiation late this afternoon
or early this evening along cold front over IA, which is reasonable
given the low level convergence and amount of instability that will
be available by late in the day.  However, after this point in time
trends become much more murky.  Outflow from the IA convection could
be a player in northern sections of our CWA as the night progresses,
but have also noticed that over the last 24 hours models are
suggesting a southward development or shift in the low level
convergence and 850mb theta-e advection to near the KC area during
the overnight hours, and if elevated storms do manage to form in
this area they would tend to propagate east across northern sections
of the CWA during the predawn hours.

Thunderstorm activity at least into early Sunday afternoon
will likely remain elevated in nature, as forecast soundings
continue to suggest very stout cap which should inhibit any surface
based convection.  However, by mid-late afternoon mid level cooling
with approaching shortwave and strong low level convergence along
the approaching cold front should break the cap, igniting
thunderstorms over northwest sections of the CWA.  Showers and
storms will then become widespread across the FA overnight as the
cold front and upper level dynamics work their way east.  It would
appear that there still may be a small window of opportunity for
severe convection late in the afternoon and during the early evening
hours while the max instability of the afternoon can be realized.
Certainly wind fields are supportive of potentially severe
convection, but exact extent of severe threat will likely be
determined by how much ams can destabilize during the afternoon.
However the initial storms develop, it would appear that they would
quickly morph into qlcs/line convection, with strong winds being the
greatest threat.

Have not made many changes to going temps at this time.  Tonight
should be relatively mild with some cloudiness and southerly winds
holding lows in the upper 50s to mid 60s.  Due to the large
uncertainty of cloud cover on Sunday have generally kept highs in
the 70s, which could be much too cool if cloud cover is not as great
as currently expected.  Temps will make a sharp drop Sunday night
with the passage of the cold front, and given the strength of the
cold air low temps in most areas will not occur until 13-15z Monday
morning.

(Monday-Monday Night)

The very cold air that begins its southward push Sunday night will
continue its surge across the mid-Mississippi Valley on Monday.
Every available piece of guidance indicates that Monday will be a
raw April day with unseasonably cold temperatures and strong
northwest winds, along with rain that will gradually diminish from
northwest to southeast during the day. Temperatures could fall most
of the day in many areas, and at most only expect a modest rebound
of the mercury from their mid-late morning readings.

The NAM seems to lock onto the northern stream shortwave and hangs
onto precipitation several hours longer heading into Monday night
than the other short range guidance.  Have leaned towards consensus
for now, essentially ending the rain threat over our far southeast
counties early Monday evening, followed by clearing skies and very
chilly overnight temps.   Still some uncertainty on extent of winds
and mixing that would limit frost potential, but in spite of the
winds the AMS is looking cold enough that sub-freezing temps are
looking very possible over northwest sections of the CWA.

(Tuesday - Friday)

No significant changes to going forecasts in the medium range, with
chilly weather continuing into Tuesday followed by a moderation in
temperatures during the latter half of the week.  Frost may be a
concern over southeast parts of the CWA on Tuesday morning beneath
the retreating surface ridge, but this should be the last morning of
this cold snap where temperatures will be a concern to agricultural
interests.   Next chance of rain appears to be around Friday with
the approach of the next front.

Truett

&&

.AVIATION:  (For the 00z TAFs through 00z Saturday Evening)
Issued at 615 PM CDT Fri Apr 11 2014

Winds will become sely this evening but expected to remain aob 8
kts. Winds will become sly, then sswly to swly Sat late morning
and thru the afternoon. Believe VFR conditions will continue thru
the period. Some concern moisture return will generate cigs near
MVFR, but believe cigs will remain in the low end of VFR, similar
to patch of clouds over ern OK.

Tilly

&&

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

$$

WFO LSX






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