Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 291207
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
707 AM CDT Thu Jun 29 2017

...Update to aviation forecast discussion...

.SHORT TERM...(Today and tonight)
Issued at 422 AM CDT Thu Jun 29 2017

A complicated set up is in place at 08Z with overnight convection
along the KS/NE border in association with LLJ convergence
continuing to evolve into a more linear small scale MCS advancing
into the richer elevated theta-e axis.  Severe threat at this time
is low with a stable low level boundary layer and the LLJ beginning
to show some signs of weakening on VAD wind profiles. With that
said, some stronger winds may occur with some cells if strong
enough precipitation mixes down stronger winds aloft. The upper
pattern remains mainly zonal with embedded waves traversing the
area. Currently, another cluster of storms is forward propagating
into portions of western KS. This cluster of storms is expected to
enter northeastern KS near the 12-15Z time frame. This will
further complicate the mesoscale set up as currently a diffuse
outflow boundary is stretched along the I-70 corridor. The
synoptic boundary appears to be laid through southeastern NE back
through an inverted trough and leeside low over SE CO into SW KS
vicinity.

Into early this morning, expecting ongoing convection to continue
and taper off by mid to late morning over northeast KS as the LLJ
veers and weakens over the area.  Still some stronger updrafts could
persist with marginal shear and steep mid level lapse rates
contributing to pulsing nature.  As convection diminishes and moves
out of the area, clearing should take place with a weak mid level
cap in place.  Most guidance suggests that with strong
destabilization into the afternoon will likely take place as
southerly WAA continues to pool richer gulf moisture along and ahead
of the synoptic boundary.  As and impending shortwave approaches the
region, mid level lapse rates should steepen and put MLCAPE values
in the 3000-4000 J/kg range. A top of this instability, deep layer
shear values range from 35-50kts which suggests there will be
potential for any storms that develop to quickly rotate.  As
discrete cells mature, there is at least some potential for a
tornado threat to be in place early on into a portion of the evening
hours as SRH values should be between 100-150 m2/s2.  Minimizing
this threat is the fact that surface winds probably remain more
southerly to slightly southwesterly.   However, with the complicated
outflow set up from multiple previous storms over the area, there
could be an opportunity for some storms to ingest more favorable
baroclinic vorticity and stretch that into the updrafts.  Something
that will likely be watch carefully.  But, a large hail threat and
strong outflow wind threat still appears most likely outcome. Storms
should transition into a linear complex once again as the evening
progresses and eventually move out of the area.  Heavy rain is
expected also with these storms, so while the flash flood watch has
been passed at this time it won`t be entirely out of the question
that one or two flash flood warnings may be needed. Again, this will
likely be highly localized.

.LONG TERM...(Friday through Wednesday)
Issued at 422 AM CDT Thu Jun 29 2017

Friday through Friday night, the upper trough across the central
plains will will shift eastward into the mid MS river valley. The
surface front will push southeast of the CWA after 12Z. The heavier
rain and thunderstorms will move southeast along the front. There
may be a few isolated showers that redevelop under the H5 trough
axis Friday afternoon but these should end by 23Z. Highs will be
cooler in the lower 80s.

Saturday and Saturday night, the upper trough across the eastern
conus will amplify and cause the mid and upper level flow across the
plains to be from the northwest. At the surface a ridge of high
pressure will push southeast across eastern KS into southern MO and
AR. Highs will be in the mid 80s, with dewpoints in the mid to upper
50s.

Sunday through Wednesday, An upper level trough will move east
across the central rockies, then dig southeast and amplify across
the plains. Both he ECMWF and GFS are much slower digging this upper
trough across the eastern plains. Therefore, expect a chance for
showers and thunderstorms from Sunday afternoon through Wednesday
afternoon. I`m sure there will be some breaks in the rain chances
but 4th of July fire works shows may see at least the chance for
scattered showers and thunderstorms. Highs will be in the mid to
upper 80s.

Wednesday night through Thursday. The upper positive tile upper
trough will finally move southeast across the mid and lower MS river
valley. An upper level ridge will build east across the high plains.
Expect temperatures to warm into the lower to mid 90s on Thursday.

&&

.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 641 AM CDT Thu Jun 29 2017

For the 12Z TAFs, showers and storms should taper off within the
next couple hours before a period of relative calm into the noon
time frame before storms are expected to reform this afternoon.
Some storms could be severe. Have handled approximate time frames
with VCTS until confidence increases in exact timing and placement
of storms. Have VFR prevailing right now as only very short
periods of reduced CIG/VIS are expected.

&&

.TOP WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...Drake
LONG TERM...Gargan
AVIATION...Drake



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