Area Forecast Discussion
Issued by NWS Kansas City/Pleasant Hill, MO

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000
FXUS63 KEAX 171143
AFDEAX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE KANSAS CITY/PLEASANT HILL MO
643 AM CDT Fri Apr 17 2015

.DISCUSSION...
Issued at 435 AM CDT FRI APR 17 2015

Today - Tonight:

Today will be a transition day. An upper ridge, now overhead, has
kept the KS/OK/TX Panhandle convection at bay since yesterday.
However, as the upper ridge nudges east this convection will be able
to edge closer and closer. This activity has been generated by weak
impulses ejecting from a cut-off upper low near the 4-corners area
and mid-level frontogenesis. This upper low has moved little over
the past 24 hours as it awaits its kicker which is just now crossing
into British Columbia. This latter feature is expected to strengthen
later today as upstream ridging sharpens and forces this shortwave
trough to dig southeast into the Northern Rockies...but not until
tomorrow. What this means is any convection reaching the CWA today
will weaken/fall apart as it moves away from the better upper
support.

Having said that there are some signals from the last couple runs of
the HRRR and to a lesser extent the 00z NAM that convection now
moving east through northern OK/south central KS could reach the far
western counties by around the noon hour. Regional radars show an
outflow boundary now expanding east from the KS convection with new
activity sprouting over north central OK. This activity is what the
HRRR picks up on and lifts northeast later this morning. So, will
slowly shift chance PoPs across the far western CWA today while
leaving the eastern half dry. Convective debris clouds will also
thin as they spread east today providing a thin veil of high clouds.
This shouldn`t hold back warming and expect temperatures to top out
in the middle and upper 70s.

The Southern Plateau closed low will gradually shift east tonight,
allowing new convection to push further east and become more
organized as it reaches the KS/MO state line towards sunrise. Will
handle this with a steady and gradual increase in PoPs through the
night.

Saturday - Sunday:

A very wet period with convection becoming numerous and likely
coming in waves as cells track nne while shifting slowly east. Model
precipitable water values 2 to 3 standard deviations are a cause for
concern. Steering winds in the 20kt area plus this moisture heighten
the threat of localized flooding. Have increased qpf and this may
even be underdone as its certainly feasible that some areas could
see up to 2 inches of rain through Saturday night. Extensive cloud
cover and rain-cooled air forces me to lower highs on both days and
won`t be surprised if they are lowered further in future
forecasts.

Modest MLCAPEs and 0-6km shear in the 20-30kt range are not likely
to support any severe threat on Saturday. Sunday may be a slightly
different story. By then the closed upper low will have opened up
and accelerated eastward. There is a chance we could  be rain free
Sunday morning with some partial sunshine. Should this occur more
robust afternoon convection could form within a marginally supportive
airmass featuring MLCAPEs of 1200-1400 J/kg but only 25-30kt 0-6 km
bulk shear.

Monday - Friday:

The shortwave trough which will act as the kicker to move the
current closed upper low near the 4-corners will have formed into a
well developed upper trough from the Upper MS Valley through the Mid
MO Valley early in this period. As the upper trough axis passes
through on Monday strong subsidence and cold air advection will
provide ample sunshine but below average temperatures through
Tuesday.

By mid week, an upper ridge axis will build east into the Central
Plains with warm air advection spreading east. The GFS is more
aggressive and faster than the ECMWF in pushing weak mid level
vorticity lobes through the ridge axis. These features will be
ejected from a broad upper trough that will works into the desert
southwest. Difficult to determine how soon any scattered convection
could work its way back into the region. For now will introduce some
low chance PoPs for late Wednesday into Thursday.

The current closed upper low now over northern Mexico is expected to
weaken as it lifts north-northeast through the Central Plains and
CWA. While there should be decent moisture lifted northward with
this feature minimal instability will limit amount of thunder. Given
that the operational models have been generating a similar solution
believe 30-40 PoPs are warranted for scattered convection.

Thursday - Sunday:

Roll of the dice as to how weather will evolve from Thursday through
Sunday. Not especially fond of the blended model approach of carpet
bombing chance PoPs in every period. The medium range models drop a
deep upper trough into the Desert Southwest and then cut it off.
Models typically are challenged significantly with these features
initially. They tend to lift them out too soon and too far east. Will
be interesting to see how this system is handled going forward.
Difficult trying to time any weak impulse ejected from this system
within the downstream southwesterly flow. For now will handle this
with low chance PoPs with above average temperatures.

&&

.AVIATION...(For the 12Z TAFS through 12Z Saturday Morning)
Issued at 639 AM CDT FRI APR 17 2015

Generally VFR conditions through this evening with a steady stream of
higher based clouds. Watching a band of showers and storms over north
central OK and south central KS that are starting to turn to the
northeast. Seeing signs this activity could lift through far eastern
KS and western MO but weaken during the afternoon hours. Rest of
northern and central MO should stay dry through the afternoon hours.
If current trends continue will likely need to amend forecast and
increase chances for thunder.

Should see a lull in activity this evening but another round of more
robust convection should form over KS tonight and reach far eastern
KS and western MO during the pre- dawn hours of Saturday morning.
Should see MVFR visibilities with this batch of showers and storms.

&&

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

$$

DISCUSSION...MJ
AVIATION...MJ





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