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Forecast Discussion
NWS Omaha/Valley, NE

FXUS63 KOAX 191035

Area Forecast Discussion
National Weather Service Omaha/Valley NE
535 AM CDT Sat Aug 19 2017

.SHORT TERM...(Today through Monday)
Issued at 300 AM CDT Sat Aug 19 2017

A shortwave trough --evident in water vapor imagery-- over WY
early this morning will translate east-southeast into the NE
Sandhills this afternoon before moving through our area late
tonight into early Sunday. Forcing for ascent attendant to this
feature coupled with low-level convergence along an associated
surface trough will foster a band of storms to our west this
afternoon. A strengthening nocturnal LLJ along with DCVA related
to the shortwave trough should maintain a subset of these storms
across eastern NE/wrn IA tonight into early Sunday. While a strong
storm is possible, greater severe weather potential will remain
to our west this afternoon into evening. Abundant sunshine in
conjunction with low-level warm advection will support warmer
temperatures today with values ranging from lower 90s south to mid
to upper 80s north.

On Sunday, the afore-mentioned shortwave trough will continue
east of the area with rebounding mid-level heights in its wake.
However, model guidance is suggestive that a west-to-east-oriented
boundary will be situated across our area which could serve as a
focus for late afternoon or early evening storm development.
Increasing amounts of low-level heat and moisture will yield a
moderately unstable air mass late in the day and isolated severe
storms are possible. Afternoon temperatures will again be warm; in
the upper 80s to lower 90s.

A nocturnally strengthening LLJ will likely support an uptick in
thunderstorm coverage Sunday night, especially to the north of the
above-mentioned surface boundary where warm advection is enhanced.
Deterministic model guidance is somewhat dispersive on specifically
where that preferred corridor may be, though there is some
indication it will be to our north/northeast.

--Eclipse Weather Outlook--

On Monday, it appears that any early-day storms will move east of
the area prior to the time of the eclipse. However, the models
continue to indicate the potential for high-level cloudiness
associated with a weak perturbation moving into the central Plains
from the west/southwest. At this juncture, it is difficult to
determine the extent and opacity of any cloud cover. Simply put,
it seems quite likely that some degree of cloudiness will be
present at 1 PM CDT. Afternoon highs will be impacted by the
degree of clouds and the dip in incoming solar radiation
associated with the eclipse with readings in the mid to upper
80s. Heat index values will rise into the lower to mid 90s by late
afternoon. Precipitation chances during the time of the eclipse
currently appear low with a gradual increase thereafter.

.LONG TERM...(Monday night through Friday)
Issued at 300 AM CDT Sat Aug 19 2017

Latest medium-range guidance continues to advertise considerable
amplification of a mid-level trough over eastern North America
next week. This process will result in the movement of a notable
cool front through the forecast area Monday night into early
Tuesday. Strengthening mid-level flow and forcing for ascent
should yield one or multiple MCSs along the cool front with
isolated strong to marginally severe storms possible Monday
evening/night. Locally heavy rainfall will also be possible.

The front will usher in a cooler and drier Canadian air mass which
will linger across the mid-MO Valley through much of the upcoming
work week.


.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 535 AM CDT Sat Aug 19 2017

A surface high over central NE as of 10z will build east today
with winds gradually shifting to the southeast by this afternoon
or tonight. Thunderstorms are expected to develop to the west of
the area this afternoon before moving across portions of eastern
NE tonight. Confidence in timing and specific location of this
convection remains low, so we have only added a mention of VCTS at
all three TAF sites. A strengthening nocturnal LLJ could result in
LLWS criteria being met tonight with the highest probability of
this occurrence being at KLNK. Otherwise, expect prevailing VFR
conditions with increasing mid-level clouds tonight.





NWS OAX Office Area Forecast Discussion

Forecast Discussion
NWS Hastings, NE

FXUS63 KGID 190859

Area Forecast Discussion
National Weather Service Hastings NE
359 AM CDT Sat Aug 19 2017

.SHORT TERM...(Today and tonight)
Issued at 352 AM CDT Sat Aug 19 2017

Main issues will be chance of storms tonight and severe weather

Currently we have a clear sky under west/northwest upper level flow
as the shortwave ridge assuring us of dry weather slips east.  Water
vapor reveals an upstream low-amplitude shortwave trough over
western Wyoming heading this way.

By late afternoon, this wave could be essentially on our doorstep.
Steep low and mid-level lapse rates plus plenty of instability
should garner at least isolated thunderstorm activity over the High
Plains, with fairly widespread agreement between numerical models
that at least some parts of the CWA will have rain tonight as a
strong low-level jet is forecast to develop and 0-6 km bulk shear
will be somewhere in the 25 to 35 mph. This may be bode very well
for severe weather, with possible intense updrafts/downdrafts,
severe wind gusts, and large hail. Hanging my hat on the
increased low-level jet for a group of storms to increase and
expand in areal coverage, and I am generally going on the high
side of guidance to clearly above guidance for the chance of
precipitation tonight.

.LONG TERM...(Sunday through Friday)
Issued at 309 AM CDT Sat Aug 19 2017

The main concerns in the long-term portion of the forecast are:

1.) Potential for strong to severe storms on Sunday evening.
2.) Weather impacts for Eclipse Day...especially cloud cover
3.) Another round of thunderstorms Monday evening through the night

The daytime of Sunday should be dry and warm, with high temperatures
in the upper 80s to the mid 90s across Nebraska and the mid to upper
90s across Kansas. Heat index values may even reach the 100s across
north-central Kansas. A warm front will provide focus for scattered
thunderstorm development in the evening and overnight as a weak wave
pushes through the area and the low-level jet ramps up. Models have
trended this warm front farther south as compared to previous
forecast cycles. This gives me a bit more confidence that we will
see thunderstorms in central Nebraska and northern Kansas. The NAM
is quite bullish on high as 4500J/kg of MUCAPE
Sunday evening. The GFS is a bit more reasonable at 2500 to 3000
J/kg. Either way, we will probably have at least a few strong to
severe storms in the area during this timeframe.

I will cover Monday`s weather impacts more thoroughly below, but the
overall idea is that thunderstorms will clear out of the area by
morning and skies will gradually start to clear. Another wave will
start to encroach on the area starting around noon. This could
produce additional mid and high level cloud cover during the
afternoon, and will eventually lead to a good chance for
rain/thunderstorms Monday evening and overnight as a cold front
sweeps through the area. Given the strength of this front, there is a
threat for some strong to severe storms again Monday night.

After overnight activity clears out of the area, Tuesday marks the
beginning of a dry and relatively cool period for the forecast area
that will last at least through the daytime on Thursday.

Chances for thunderstorms return to the forecast area late Thursday
night into Friday, and will likely continue through Saturday as
models bring a potent upper low through the region.

.Eclipse...(Monday, August 21st around 1PM)

Precipitation & Thunderstorms:
There will be thunderstorms in the area Sunday night into early
Monday morning, and again Monday evening, but is very unlikely
that any of these will directly impact solar eclipse viewing.

To start the day, there may be lingering cloud cover from the
overnight storms. You shouldn`t panic if you wake up to overcast
skies, though. This will likely start to clear up during the
morning. The more concerning aspect is that areas of scattered mid
to high-level clouds will likely develop ahead of a shortwave
moving into the area.

Our forecast calls for partly cloudy conditions across the entire
area, with the highest sky cover (50 to 60%) for areas southeast of
the tri-cities (Hastings, Grand Island & Kearney). Overall, I think
that the farther northwest areas have a better chance of relatively
clear skies than areas to the east and southeast. Having said all of
this, please keep in mind that cloud forecasts are quite fickle in
nature and could still change substantially before Monday.

Temperatures & Winds:
Winds are still expected to be southwesterly at 10 to 20 MPH.
Temperatures should be in the upper 70s to mid 80s at 1PM,
eventually reaching the mid 80s to low 90s by late afternoon. With
the uncertainty of cloud cover and relatively strong winds, I
only decreased the 1PM temperature by around 4 degrees. It could
end up being a bigger temperature drop if skies end up being
clear, though.


.AVIATION...(For the 06Z KGRI/KEAR TAFS through 06Z Saturday)
Issued at 1154 PM CDT Fri Aug 18 2017

VFR conditions expected to prevail at KGRI/KEAR. Surface high
pressure will continue to slide overhead with southerly winds
returning by morning/afternoon Saturday. Skies will be mostly
clear with some clouds returning by afternoon/evening Saturday.
There is a chance for some thunderstorms in the evening hours, but
have left any mention out of the TAFs at this time due to lack of
confidence on timing and location.




SHORT TERM...Heinlein
LONG TERM...Mangels
AVIATION...Billings Wright

NWS GID Office Area Forecast Discussion