Area Forecast Discussion
Issued by NWS Hastings, NE

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FXUS63 KGID 210608

Area Forecast Discussion
National Weather Service Hastings NE
108 AM CDT Wed Jun 21 2017

.SHORT TERM...(This evening through Wednesday)
Issued at 244 PM CDT Tue Jun 20 2017

Plenty of instability has built across the local area this
afternoon as temperatures have met...and in some cases
exceeded...the previously forecast highs for the day. As the CAP
is eroding...we are starting to see some CU develop across the
area with the first couple of thunderstorms popping up on radar
just southwest of the local area. Expect continued thunderstorm
development to result in some chances for showers and
thunderstorms across the region...especially across north central
Kansas...where the CU field is more dense and the instability
greatest. If storms are able to develop and tap the energy in the
atmosphere...expect explosive development with decent mid to upper
level rotation...which will allow for large hail to around the
size of golf balls to become possible with the stronger storms.

Since the overall forcing across the local area is weak and
primarily diurnally driven...expect the aforementioned storms to
have trouble maintaining themselves by mid to late evening...which
barring any outflow initiated storms...should mean an end to
thunderstorm activity by late evening. The focus of additional
storm development will then shift to our northeast where forcing
from the LLJ should allow for additional shower and thunderstorm
development across northeastern Nebraska overnight...with the
local area remaining dry.

While there will likely be a severe storm or two across our Kansas
counties this afternoon or evening...things turn more interesting
for the entire forecast area tomorrow as a weak front from the
northwest makes its way across the local area near the time of
peak heating. With some adiabatic compression ahead of this
front...expect a very hot afternoon across the local area...with
heat index values likely nearing or exceeding 100 degrees. These
unseasonably hot temperatures will further help to destabilize the
atmosphere...which combined with modest shear values...will
likely help initiate additional severe thunderstorms across the
local area tomorrow.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 244 PM CDT Tue Jun 20 2017

Ongoing storms will likely be evident to start the extended
periods as the first cold front exits the local area. Expect a
stronger reinforcing cold front to move across the area Thursday
afternoon through Friday morning...providing additional chances
for showers and thunderstorms across the local area...and
potentially more severe weather as there will be ample moisture
and instability available for storm development. The one downfall
Thursday is the stronger CAP forecast to be in place across the
local area...but with strong forcing from the front...the
advertised slight risk of severe weather from the Storm Prediction
Center is more than justified.

Behind this relatively strong front for summer standards...expect
a significant cool down in temperatures for the weekend...with
highs Friday through Monday expected to be 5 to 10 degrees below
normal for late June. In addition...there will be multiple chances
for precipitation...with showers and possibly even an isolated
thunderstorm possible from time to time. That said...instability
is very limited over the severe weather is not
anticipated unless something changes.

High pressure will then nudge in from the west late in the
extended periods...with southerly flow returning in the low
levels of the atmosphere...which will mean a return to above
normal temperatures by the middle of next week.


.AVIATION...(For the 06Z KGRI/KEAR TAFS through 06Z Wednesday)
Issued at 108 AM CDT Wed Jun 21 2017

General overview:
Unless thunderstorms happen to get into the mix this
afternoon/evening and cause issues, confidence is pretty high in
VFR ceiling/visibility persisting through the period with only
limited mid-high clouds. Will now go into more element-specific
detail for those interested...

Precipitation/thunderstorm potential:
While confidence is fairly high that the first 12-17 hours of the
period should remain storm-free, have introduced a generic
"vicinity" (VCTS) mention to the final 7 hours late this
afternoon/evening to account for the possibility of vigorous
severe thunderstorm development in the general area (obviously
later issuances can refine details). Should any storms directly
impact the terminals, severe weather in the form of 50+kt gusts
and/or large hail are possible.

Surface winds and low level wind shear (LLWS):
Obviously not accounting for any impossible-to-resolve-yet
thunderstorm outflow effects, the vast majority of the period is
expected to feature a southerly wind component. The overall-
strongest speeds should slightly favor KGRI versus KEAR, and
should occur between 16-23Z with gust potential of 20+kt. Thanks
to a strengthening low level jet early this morning, have
maintained a formal mention of LLWS at both terminals through
either 12/13Z, as the shear magnitude between the surface and
roughly 1,000 ft. should reach or exceed 30kt.




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