000
FXUS63 KLSX 131139
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
639 AM CDT Thu Mar 13 2014

.SHORT TERM:  (Through Late This Afternoon)
Issued at 313 AM CDT Thu Mar 13 2014

The temperature roller coaster continues for the LSX CWA, and today
we will be on the uphill climb of the ride.  Center of the N-S
surface ridge currently centered over IL, with return flow already
setting up from the plains into the upper Mississippi Valley and
surface trofing and signals of surface warm front already showing up
along the mid-Missouri River Valley.

Initially, the increase of waa over the region should result in mid
level cloudiness. Next batch of waa-induced clouds are on the
increase across Iowa and are beginning to advect into northern
Missouri. As the mid level waa increases across the area this
morning this cloudiness should sweep southeast and primarily impact
areas along and east of the Mississippi River.  However, these
clouds should work their way east in the afternoon with the zone of
isentropic ascent.

At the same time, the surface warm front should make a dramatic ewd
surge.  Synoptically, this pattern (strong westerly component to
surface winds and lots of sunshine) is very favorable for a big warm
up, and this type of setup led to the taste of spring we experienced
earlier this week.  So far this spring guidance has been too
cool/too slow on our warmups, so have used bias corrected guidance
for highs...which is a few degrees warmer than going forecasts
along and west of the Mississippi River. Most areas along and
southwest of a Mexico-St Louis line will hit the 60s, with the
residual cool air over our far e counties limiting the warmup
there to the lower 50s.

Truett

.LONG TERM:  (Tonight through Wednesday)
Issued at 313 AM CDT Thu Mar 13 2014

Rapid temperature swings are common during the transition season,
and the past few days have been no exception. In fact, tonight`s
lows should be similar to yesterday`s highs.

A low pressure system moving through the Great Lakes will drag a
cold front through the area on Fri night. Very little if any
precipitation is expected with this feature.

Cutoff low over CA/NV begins to eject eastward late this week,
perhaps throwing off a couple of lead shortwaves that could
produce increased cloudiness. The remnants of the cutoff low are
expected to pass south of the area on Fri night and Sat.

Models are still having difficulty with the development of a new
cutoff low which forms over the Southwest, tracks nearly due south
into Mexico, and then retrogrades southwestward. GFS/ECMWF are in
broad agreement but the GEM is slightly farther east with the new
vort max as it crosses the Rockies and slower to depart the
previous cutoff low. Because of these two slight differences, the
GEM depicts sufficient interaction between the two features for
the new shortwave to remain progressive rather than cutting off as
shown in the GFS/ECMWF. Knowing that the models are sometimes too
quick to bring closed lows eastward, it is difficult to discount
any of these solutions out of hand. GFS/ECMWF also disagree on the
strength and placement of a vort max diving southeastward from
Canada on Sun. Precipitation is possible on Sat night and Sun, but
confidence in the specifics remains low due to poor model
agreement.

Kanofsky

&&

.AVIATION:  (For the 12z TAFs through 12z Friday Morning)
Issued at 640 AM CDT Thu Mar 13 2014

Outside of a few mid clouds along and east of the Mississippi
River early this morning, expecting nearly cloud-free skies across
the FA today and into the evening. Warm front over western
Missouri early today will sweep east this morning, producing southwest
winds in the 10-15kt range by mid afternoon.

Specifics for KSTL: Nearly ideal aviation conditions expected
today and into tonight, with no significant clouds and unlimited
visibilities throughout the period. With surface ridge shifting to
the east, expect winds to become southerly and begin a slow
increase over the next few hours, then veer to the southwest at
around 10kts this afternoon as aforementioned warm front surges
through the mid-Mississippi Valley.

Truett

&&

.FIRE WEATHER:
Issued at 313 AM CDT Thu Mar 13 2014

Increasing southwest winds and a fairly stout warmup should allow
for some fairly low humidity levels along and south of I-70.  In
spite of the fairly widespread precip Tuesday night and early
Wednesday, small fuels (such as dead grasses) are forecast to be
very dry this afternoon.  This combination of humidity, wind, and
dry vegetation will produce an elevated fire danger this afternoon,
and we will be issuing an SPS to highlight this threat.

Truett


&&

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

$$

WFO LSX