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000
FXUS63 KEAX 150258
AFDEAX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE KANSAS CITY/PLEASANT HILL MO
958 PM CDT Fri Jun 14 2013

.UPDATE...
Issued at 957 PM CDT FRI JUN 14 2013

Upscale growth of the storms across eastern Nebraska late this
afternoon and early this evening has resulted in a bow echo,
currently entering western Iowa. Currently the bow echo is moving
east of the highest axis of instability as it moves into the region
of western Iowa where thunderstorms have already been occurring.
However, this system has unfettered access to a decent moisture feed
on the southwest 850mb wind. So, while the storms are moving away
from the best moisture and instability, they are not leaving it
behind all together. This should allow the bow echo to maintain some
legs as it pushes farther east into Iowa overnight. Looking back into
Kansas and Missouri, water vapor imagery still shows the ridge axis
across the Plains affixed across the Missouri-Kansas border. This
brought enough of a cap to western Missouri to keep todays storms
limited to areas of north central and northeast Missouri. Current
expectations are that the bow echo moving into Iowa will rollover the
top of the ridge in western Iowa, allowing the southern end of the
storms to push into far north central Missouri later tonight. This
could bring severe weather, with the primary threats focused on large
hail and damaging winds.

Otherwise, will have to watch the southern end of the line of storms
which is still lingering back across southeast Nebraska. The south
side of these storms has slowed its movement as that segment of
storms has become parallel to the mean mid-level flow. This might
result in a cold pool with sufficient strength to develop a secondary
progressive line of storms, which might try to dive south southeast
along the Missouri river as the nocturnal jet gets going later
tonight. Confidence in this scenario is not great, so haven`t
retooled the forecast to account for this yet, but it can not be
ruled out either.


UPDATE Issued at 626 PM CDT FRI JUN 14 2013

Late afternoon thunderstorm activity occurring across Iowa and
sliding southeast into north central and northeast Missouri appears
to be fading in intensity, which has been expected as persistent storms
in that region have ultimately stabilized that region. However, regional
composite radar shows redevelopment back to the west -- southwest Iowa --
as southerly low to mid-level winds continue to feed unstable
air-parcels up and over a warm frontal boundary laying along the
Missouri River from Omaha south to Kansas City.

Expectations for this evening are for further development of storms
across southwest Iowa with possible back building development into
southeast Nebraska. MLCAPE values per SPC meso-analysis page of 2500+
J/KG look to be available in this region, and with models advertising a
850mb southwest low level jet quickly kicking up this evening as a
shortwave trough rotates northeast through the Dakotas this evening.
Effective shear values in this initiation area of Iowa remain rather
high at 50 knots. All this points to the continued potential for
severe thunderstorms this evening. However, with all that said there
is the problem of the cap. With the upper level ridge axis along the
Missouri-Kansas border there is lots of warm air aloft. 700mb
temperatures of 12C have advected in aloft along with a fairly dry
layer of air. So, while storms might be able to initiate in southeast
Nebraska and southwest Iowa, their ability to propagate south looks
somewhat limited, which is relevant as many of the meso-scale models
advertise the development of storms that then ride the effective
boundary from convection earlier in the day into far northern
Missouri. Have increased the POPs across the Iowa border region for
late this evening, highlighting the hours from 10 PM through 1 AM for
likely activity. Some sever threat form large hail and damaging wind
gusts would be possible with this evening activity.

&&

.SHORT TERM...(This Evening through Saturday Night)
Issued at 400 PM CDT FRI JUN 14 2013

Main concerns for the next 24 to 36 hours deals with convective
chances and potential for severe weather this evening and possibly
again tomorrow afternoon/evening.

The northern to northeastern portions of the forecast area is on the
edge of the cap and storms have persisted all day in this area. This
cluster of storms may have layed out an outflow boundary, which is
indistinct, but may run from northeastern MO through central MO. A
warm front should also be in the vicinity which will aid in
convergence and possible initiation as well as provide for extreme
instability with 70 degree dewpoints working northward in eastern
Kansas and western Missouri. The focus for all of this should be
across northwestern MO as several earlier short-range model runs as
well as the NAM initiate convection eastern Nebraska later this
afternoon and shifts it southward this evening and overnight.
Given the instability that has been able to build, which should be
on the order of 2000 to 3000 J/kg and possibly as high as 3000 to
4000 J/kg, and enough shear to lead to storm organization, if storms
can develop, they should become severe. All hazards are possible if
convection can initiate but should mainly be large hail and damaging
winds by this evening and overnight. There is also intensifying
isentropic lift in the 310K to 315K layer after 00Z across
northwestern MO and northeastern KS. This adds confidence to the
model precipitation forecast.

The focus will then shift to a weak upper disturbance lifting
northward from the Southern Plains. Much will depend on how
convection tonight and tomorrow morning plays out and given that part
of the forecast is uncertain, tomorrow`s forecast is very uncertain.
There is the potential for an extremely unstable airmass to be in
place across the forecast area, with CAPE values approaching 4000
J/kg possible. Modest westerly flow should support 0-6 KM shear
around 40 kts. This combination would be more than enough to produce
severe storms if we can get them to develop in the afternoon.
Supercell structures would also be possible but veered surface winds
should tend to limit helicity values and resultant tornado chances.
But very large hail and damaging winds would be possible in the
strongest storms.

Any convection that does form should drift southeastward and impact
the southern zones, mainly south of Interstate 70, through the rest
of the evening and overnight. The threat of severe weather would
diminish overnight but we could still large hail and damaging winds
as well as locally heavy rainfall that could lead to isolated
flooding.

.LONG TERM...(Sunday through Friday)
Issued at 400 PM CDT FRI JUN 14 2013

Sunday-Monday: While the weekend continues to offer the likelihood
of several rounds of organized convection via MCS
development/propagation the details in timing/location will be
lacking owing to mesoscale processes and where any left over
convective boundaries set up. Current model solutions suggest
Saturday nights MCS may be exiting the southern portion of the CWA
Sunday morning and given latest model trends this seems reasonable
so will adjust highest PoPs to Sunday morning. With a tropical type
of airmass in place and any residual boundary(ies) best to leave low
chance PoPs for the afternoon for the possibility of convection
redeveloping within a moderate instability/low shear environment.

A better bet for organized convection will enter the picture Sunday
night although the entire CWA may not be affected. A rather robust
shortwave is progged to strengthen and dive southeast through the
Northern Plains and Upper MS Valley Sunday/Sunday night. The zonal
flow from the Central Rockies through MO will veer in response with
any convective system tracking more nw-se as it exits the Central
High Plains. This makes placement/timing of Sunday nights convection
a bit more difficult. For now will focus the likely PoPs across our
southwestern counties. Convection is expected to exit the CWA from
northwest to southeast as a cold front sweeps the tropical airmass
out.

Temperatures on Sunday will be a challenge owing to convective cloud
debris and any lingering convection. Monday should see readings
closer to seasonal averages.

Tuesday-Wednesday: Canadian high pressure will build into the region
the northerly winds will bring in a welcomed drier and cooler
airmass with seasonal afternoon temperatures and pleasant overnight
readings.

Wednesday night-Friday: A large closed upper system pressing east
through the Northern and Central Rockies will initially bulge an
upper level ridge eastward. This will allow the next chance for
elevated warm advection generated convection to move into the region
Wednesday night. Low chance PoPs will remain through Thursday as a
more humid airmass arrives and allows the airmass to destabilize.
Temperatures will likely warm well into the 80s.

&&

.AVIATION...(For the 00Z TAFS through 00Z Saturday Evening)
Issued at 638 PM CDT FRI JUN 14 2013

VFR conditions are expected at the terminals over the next 24 hours,
however some thunderstorm activity will be percolating across the
region. Thunderstorms across southeast Nebraska and southwest Iowa
will persist well into the overnight hours. There is a chance that
some of that stormy activity could propagate towards the terminals
late this evening, though confidence in storms at any particular
terminal are rather low. Best timing has any vicinity storms
advertised between 10 PM and 1 AM. Otherwise, look for winds to
slowly veer around from the southeast Saturday to the southwest,
remaining steady with speeds above 10 knots through the day. Lastly,
the potential for thunderstorms will revisit the terminals late
Saturday afternoon, though the preferred timing for Saturday
convection is just beyond the end of this TAF cycle.


&&

.EAX WATCHES/WARNINGS/ADVISORIES...
KS...NONE.
MO...NONE.
&&

$$

UPDATE...Cutter
SHORT TERM...CDB
LONG TERM...MJ
AVIATION...Cutter