Area Forecast Discussion
Issued by NWS Hastings, NE

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FXUS63 KGID 182324
AFDGID

Area Forecast Discussion
National Weather Service Hastings NE
624 PM CDT THU AUG 18 2016

.SHORT TERM...(This evening through Friday night)
Issued at 341 PM CDT Thu Aug 18 2016

For tonight, it looks quiet for the evening, but with an approaching
cold front, we could get a shot at some showers/thunderstorms late
tonight, especially toward dawn, and mainly in our northwest quarter
of the CWA. Most models indicate a dry situation for the tri-cities
for the entire night.

Friday could be a tricky day, as the results are highly dependent on
the timing of the expected cold front. A stout shortwave trough over
the northern plains will dive south southeast toward the Central
Plains on Friday as a strong cold front (by August standards) moves
through the CWA Friday. For now, the timing of the cold front is
expected to nearly bisect the CWA by 7 am, but slowing down somewhat
compared to the southeastward progression overnight. This is a bit
faster than originally though a day or two earlier, so this will
diminish the area of severe weather concern to be focused roughly in
the southeast half of the CWA, as well as cooling down high
temperatures a bit, although I still anticipate the sharper gradient
advertised by the NAM as opposed to the SuperBlend initialization,
considering the strength of this cold front. There are certainly some
model differences with the general upper level pattern, but the
early destabilization scenario in the warm sector has been a
repeated and consistent forecast from several models. We may need to
keep an eye on any possible nocturnal convection that may give us
some lingering convection from overnight as this may quell our
destabilization potential, and hence, our severe weather potential.

Bulk shear magnitude in the 0-6km level along and ahead of the front
at 18Z will be rather marginal as CAPE could be approaching 1000
J/kg. This may be enough to get some marginally severe weather going
as early as around 18Z, but a lot of this will rely on whether or
not we have some lingering convection from overnight that may cut
down on instability. As the aforementioned shortwave moves south
southeast and height falls occur, I expect the chance of severe
weather to increase along and ahead of the cold front toward 3pm or
4 pm and into the evening, but by then, the cold front will have
cleared much of our CWA. Even the 850 mb cold front will have made
it pretty far southeast by 00Z, and will generally relegate our
chance of severe weather to our southeastern half of the CWA by
evening, and could very well be focused in our southeastern quarter
by then. Shear will probably top out at near 30 kts along the cold
front with MLCape not likely getting past 1200 J/kg the way it looks
now, which would indicate a marginally severe situation. Considering
that the gradient of stronger shear aligns with the cold front, and
the fact that instability will be modest, I would expect primarily a
severe wind gust threat as a squall line develops, although we do
have a shot of getting some quarter size hail as well. Most of our
severe potential should fall between roughly 20Z and 04Z in our
southeastern half of the CWA. POPs will diminish quickly as
subsidence takes over and height rises ensue. Height rises are
strong enough to go with CONSRAW wind gusts for Friday night, which
puts us near 30 mph for some locations.

.LONG TERM...(Saturday through Thursday) Issued at 341 PM CDT Thu
Aug 18 2016

Subsidence should take over for Saturday, and I have kept us cleared
out, which is what the overnight forecast indicated. It will kind of
feel like fall. There is good agreement that we will have a chilly
night Saturday night, with perhaps lows in the upper 40s for some
locations in the far west/north.

As return flow ensues, expect a modest warm-up with a return of
shower/thunderstorm chances mid-week.

&&

.AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Friday evening)
Issued at 624 PM CDT Thu Aug 18 2016

TAFS are tricky tonight with a cold front entering from the
northwest through the next 12 hours bringing with it showers and
thunderstorms. Showers and thunderstorms will be possible from
early this morning through the day Friday. Have kept just VCTS for
this issuance, but do expect prevailing TSRA at some point during
the day tomorrow at both KGRI/KEAR. Winds will begin to flip from
the south to the north as the front moves through overnight into
early tomorrow. In addition to the wind shift/precip there will
also be the potential for low level wind shear at both terminals
through the overnight hours with a stronger low level jet. While
the TAFs are currently VFR, do expect some decreases in conditions
to MVFR or IFR at least at times with showers and thunderstorms
tomorrow.

&&

.GID Watches/Warnings/Advisories...
NE...None.
KS...None.
&&

$$

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



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