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000
FXUS63 KGID 191806
AFDGID

Area Forecast Discussion
National Weather Service Hastings NE
106 PM CDT Sat Aug 19 2017

.UPDATE...
Issued at 655 AM CDT Sat Aug 19 2017

Forecast still on track for this evening. Convection could develop
this afternoon and build east. Warm front and developing low-level
jet will likely maintain/increase coverage of storms.

&&

.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
possibility.

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 instability...as 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.

Clouds:
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 18Z KGRI/KEAR TAFS through 18Z Sunday)
Issued at 1252 PM CDT Sat Aug 19 2017

The primary aviation concern will center around the strong to
severe thunderstorms that will likely be tracking across the area
this evening as well as some strong low level wind shear this
evening through tonight. We`ll be making updates to the TAF
regarding the thunderstorm threat as storms develop later this
evening.

&&

.GID WATCHES/WARNINGS/ADVISORIES...
NE...None.
KS...None.
&&

$$

UPDATE...Heinlein
SHORT TERM...Heinlein
LONG TERM...Mangels
AVIATION...Wesely