Area Forecast Discussion
Issued by NWS Topeka, KS

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FXUS63 KTOP 280458
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
1158 PM CDT Tue Jun 27 2017

...Update to aviation forecast discussion...

.SHORT TERM...(This evening through Wednesday)
Issued at 342 PM CDT Tue Jun 27 2017

As of 20Z, a broad upper ridge was positioned across the eastern
half of the CONUS. Further west, a broad upper trough was across the
Northern Rockies. At the surface, deeper moisture continues to surge
north and westward across central Kansas. Isolated to scattered
thunderstorms continue to develop along the theta-e gradient in east
central Kansas. As we progress into the late afternoon and evening,
thunderstorm activity is expected to diminish. We then turn our
attention to the overnight hours. Thunderstorms are already
developing within the foothills of the Rockies in portions of
eastern WY and western NE. Upscale growth into an MCS is expected by
the evening hours. Given the zonal mid and upper flow, coupled with
the east to west progression of the trough, expected the bulk of
thunderstorm activity to remain north of the KS/NE border through
the overnight hours. However, any deviation to the south of due east
or a cold pool generation southeastward could result in the
potential for strong to severe thunderstorms after 06z for areas
north of I-70. Primary hazards with any storm includes large hail
and damaging winds.

Wednesday: Tomorrow`s thunderstorm potential remains uncertain. The
surface boundary stalls from west central KS into northern IA. A
strong LLJ overnight will continue to usher up upper 60s to near 70
degree dew points by tomorrow afternoon. Steep mid level lapse rates
will contribute to MLcape upwards of 3000-4000 J/KG. A secondary
weak shortwave within the zonal flow is expected to weaken the EML,
possibly enough for thunderstorm development after 21Z along the
KS/NE border. Given the large instability and effective bulk shear
40-50 knots, if thunderstorms develop, rotating updrafts can be
expected. Large hail and damaging winds will be the primary hazards.
The tornado threat is not zero, however the low level wind shear is
relatively unidirectional.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 342 PM CDT Tue Jun 27 2017

By Wednesday night, a mid-level shortwave and associated surface low
will be located in eastern Minnesota.  The cold front with this
feature will extend south and west into central Kansas by early
evening and storms may back build into the area near the surface
boundary.  As this front pushes eastward, storms will move into
northeastern Kansas later that evening and overnight.  Towards
central Kansas and east central Kansas, a cap is present which may
prevent storms from extending too far south and keeping the best
chances near north central Kansas and the Kansas/Nebraska boarder.
Shear on the order of 35 knots along with plentiful CAPE and steep
lapse rates will allow for strong to severe storms to develop with
large hail and damaging wind gusts being the main hazards.  Low
level parameters look limited except during the late afternoon/early
evening, and an isolated risk for a tornado cannot be ruled out.
These storms may continue into the overnight hours, but begin to
weaken into the early morning hours and move east out of the area.

On Thursday, a surface cold front is expected to move through the
area and another round of strong to severe storms will be possible
in the afternoon and evening.  Models have come into slightly better
agreement that a surface low will make its way across the area
Thursday afternoon with a cold front draping across the area
oriented from northeast to southwest by early evening.  Storms are
expected to develop along this front and move out of the area by
Friday morning.  Depending on exactly when storms initiate, low
level parameters become more favorable for tornados near 00Z
Thursday night.  If any storms begin as discrete supercells early in
the evening, an isolated tornado cannot be ruled out.  Overall, it
looks like storms will eventually form into a line or MCS.  Damaging
winds would be the main threat along with hail in this case.
Depending on how fast this frontal system moves, localized flooding
may also become an issue with the multiple days of rainfall
predicted.

A period of dry weather looks to finally come Friday through
Saturday with weekend temperatures topping out in the mid to upper
80s.  Models diverge a bit after Saturday night with storm chances
on and off again through the end of the period.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1154 PM CDT Tue Jun 27 2017

For the 06z TAFs, despite southerly winds remaining gusty near
20kt this evening and overnight, a strong 50-55kt low-level jet
will result in LLWS concerns overnight into Wednesday morning for
all the TAF sites. These LLWS concerns will diminish by Wednesday
morning as mixing increases after sunrise and surface winds
quickly increase, with gusts upwards of 24-26kts expected through
the afternoon. There is the potential for some scattered
thunderstorms to develop near the TAF sites after 09z. Have added
a TEMPO group for KMHK where confidence is higher for these
storms, but have kept just VCTS mentioned for KTOP/KFOE as models
show these storms breaking apart as they approach. Additional
thunderstorm development is possible across portions of north
central to northeast KS late afternoon into the evening. However,
confidence remains low amongst the models with regards to the
timing and coverage of any storms, so do not have a mention of it
in the TAFs at this time.

&&

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

$$

SHORT TERM...Baerg
LONG TERM...Heller
AVIATION...Hennecke


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