Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 251801
AFDTOP

AREA FORECAST DISCUSSION
National Weather Service Topeka KS
101 PM CDT WED MAY 25 2016

...Update to aviation forecast discussion...

.SHORT TERM...(Today and Tonight)
Issued at 415 AM CDT WED MAY 25 2016

At 4 AM Wednesday morning, a large thunderstorm complex continued to
progress east out of the area. A well-developed MCV was present in
northern parts of this storm complex over far SE Nebraska while a
wake low has developed on the back side. This wake low has been
producing gusts up to 50 mph and will continue to do so as it moves
east although it would seem likely to be near its peak intensity
right now. Additional convective showers and storms were developing
in the convergence zone into east central KS, but this area has been
well worked over and do not anticipate anything more than a few
pockets of heavy rain in this area. Another area of thunderstorms
has been persistently developing in association with the LLJ near
the KS/NE border in north central KS. This area of development is
likely to gradually push a weak cold pool a bit south with
development progressively into northern and northeast KS. However,
it will also be making its way into an area of lesser instability
with the effective convective overturning from early this morning,
and expect the storm development to be sub-severe and any associated
outflow likely not very strong.

As the day goes on, the forecast will once again be complex but
there are at least a few moderate confidence elements to grasp on to
in making the forecast. The first is the outflow incoming from the
north which should set up east to west across the area and then wash
out by mid to late afternoon...although some semblance of it may
remain through late day. The second feature of interest has been
consistently forecast by models over the past few days, and that is a
slightly veered flow owing to the passage of a rather strong short
wave early this morning. This veered flow will cause the dryline to
surge east with a dryline bulge into eastern KS. Most indications
are that this dryline bulge will focus into the local forecast area,
probably over the Flint Hills region just west of Emporia and south
of Manhattan. An area of surface low pressure is also expected to
develop into this area. So, as the afternoon progresses, expect
effective heating to lead to a rather unstable airmass across the
forecast area. This instability is likely to be capped for much of
the day though as those veered winds aloft will bring a slightly
stronger EML into the local area.

What this all leads to is a conditional forecast for severe
thunderstorms. The main question will be if the cap can be broken
with only nebulous large scale lifting mechanisms (and even some
potential for weak subsidence aloft), and only modest convergence
along the dryline. IF thunderstorms are able to develop, it would be
in a very unstable environment with effective shear in the 35-40 kt
range which would be more than sufficient for supercells. It also
seems that if storms develop they would remain relatively discrete
owing to the convective inhibition, and would probably not develop
until peak heating. Thus, any storms that are able to develop can be
expected to become severe with very large hail and locally damaging
winds possible. Veered low level winds are not particularly
supportive of tornadoes, but the potential of a weak remnant outflow
boundary along with localized backing depending on the strength of
the surface meso-low in central KS means there is at least some
tornado potential with any long-lived supercell structures. The best
chance for initiation would be along the nose of that dryline bulge
with storm motion being almost due east.

Later tonight, convective coverage is in question, and it may focus
an area of development over far northeast KS where the LLJ
convergence maximizes in an unstable airmass. If this occurs, could
see areas of heavy rain as well as a continued severe weather threat
through the overnight hours.

.LONG TERM...(Thursday through Tuesday)
Issued at 415 AM CDT WED MAY 25 2016

Main focus for the period in terms of severe weather chances reside
on Thursday afternoon and then on Friday afternoon as the open
trough axis lifts through the central plains.  Exact details on
location and timing of convection is still uncertain and dependent
on Wednesday night convection and how quickly it clears which
currently appears during the morning hours. With the system becoming
more negatively tilted during the afternoon on Thursday, winds aloft
are expected to increase while sfc winds back towards the south and
southeast as the sfc low stretches across central KS. The dryline is
the likely trigger for convection to fire in
central KS by late afternoon. These storms are expected to track
eastward towards north central KS during the evening. Second area
for possible convection is along the expected outflow boundary
draped over the area from previous convection. With ample moisture
and available CAPE in excess of 4000 J/KG, it will not take much
forcing to initiate development. By the evening, LLJ increases with
a cluster of storms to center around the warm front near the KS and
NE border. These storms are likely to impact much of the area as the
low level jet veers overnight. Main threats are large hail and
damaging winds. Tornadoes are possible as well,
especially with any discrete cells or in vicinity to a boundary
through early evening. Localized flash flooding is likely given
the excessive rainfall these past few days.

By Friday, upper level dynamics increases as the trough lifts over
central KS, becoming more stacked with the sfc low and attendant
dryline. The dryline is expected to shift east into the CWA,
creating another a decent chance for thunderstorms to develop in the
late afternoon and evening. Shear profiles are sufficient to once
again see all modes of severe weather with decent low level shear
profiles in the early evening near the sfc low over north central
KS.

Highlights for the weekend into mid next week do not change much
from previous forecasts. As upper trough exits northeast Saturday
afternoon, could see additional storms in afternoon. Severe weather
is unlikely as effective shear is pretty weak, less than 20 kts.
Similar scenario is likely from Sunday onward as broad
southwest troughing continues to bring disturbances into the area.
Flash Flooding and River Flooding threats are very high through the
weekend. Rainfall totals through the weekend range from 1-4 inches
or more through Sunday. With little change in airmass, scattered
thunderstorms are possible for each period until perhaps Wednesday
when a cool front may finally bring a relief from the rainfall.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday Afternoon)
Issued at 1257 PM CDT WED MAY 25 2016

Outflow boundary from earlier thunderstorms along the Kansas river
at noon time, very near TAF sites. Ceilings should rise to VFR
shortly, while winds could be variable for the next 2 or 3 hours,
particularly at TOP and FOE before the boundary moves back north.
Isolated thunderstorms developing over central KS late this
afternoon may move through or near TAF sites by early evening so
have VCTS for a few hours during that time. Later tonight, moist
airmass could allow fog to form.

&&

.TOP Watches/Warnings/Advisories...
NONE.
&&

$$

SHORT TERM...Barjenbruch
LONG TERM...Prieto
AVIATION...GDP



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