Area Forecast Discussion
Issued by NWS Hastings, NE

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FXUS63 KGID 180047
AFDGID

Area Forecast Discussion
National Weather Service Hastings NE
647 PM CST Fri Nov 17 2017

.SHORT TERM...(This evening through Saturday)
Issued at 227 PM CST Fri Nov 17 2017

Potentially Hazardous Weather: there is a low risk for a narrow
band of minor snow accum.

Aloft: 12Z upr-air/aircraft data and GOES derived winds showed
WSW flow over the Cntrl Plns with a fairly potent +tilt shortwave
trof from MT-ID-NV. This trof will cross the CWA tomorrow AM
followed by NW flow.

Surface: A cool front has been sagging S thru the CWA and was
near the Neb-KS border. This front will cont S and be near I-70 by
sunset. Wrn USA high pres will begin building in tonight and a
piece of this high will break off and emerge onto the Plns
tomorrow afternoon.

Rest of this afternoon: most locations now seeing m/sunny skies.
Temps svrl degs above normal for mid Nov.

Tonight: Becoming cldy. The incoming trof will have a strong
pulse of -divQ/strong upr-lvl forcing/ascent to supplement/
coincide with strong mid-lvl Fgen. As is typical in these
situations...the models are all over the place with their narrow
(1-2 county wide) bands of heavier QPF/precip...ranging from the
Sandhills to the Neb/KS state line.

In general...we will see bands of -RA develop. Wetbulb cooling
above the BL will lower the temp profile to or just below frzg.
That leaves the lowest roughly 1000-1800 ft of slightly above frzg
air for melting. We could see the rain mix with or briefly change
to snow over S-cntrl Neb...N and W of a line from Alma-Hastings-
Columbus. This is a very marginal situation (rain vs snow).

If snow does fall...current expectation is that its wet nature...
the warm ground...and light intensity will keep accum little or
none. However...it is possible that ascent could be strong enough
in a narrow band or two for snow to come down heavy enough to
briefly change completely over to snow for a couple hrs. That
would result in some cosmetic coating (up to 1"?)...primarily on
grassy areas.

Current belief is that the models with heavier QPF (0.25 to 0.5")
are overdone given the quick-hitting nature of this system.

Situations like this (small-scale...short in duration) are
notoriously difficult to fcst. It should be stated that while the
probability appears to be very low...it cannot be completely ruled
out that we see a narrow stripe of 1-2" of wet snow over part of
the CWA. It`s impossible to know where though the greatest chance
of this occurring would be where sfc/BL temps are coldest (N of a
line from Alma-Hastings-Columbus).

Lows will be in the 30s. NNW winds will increase to 15-25 kts
after midnight with gusts up to 30 kts at times.

Sat: The precip should be done by sunrise as the trof will be E
of the CWA. Clds will decrease in the AM with just a few stratocu
around in the afternoon. Windy with highs in the 40s...except near
50 over N-cntrl KS. NW winds 20-25 kts with gusts up to 35 kts.

.LONG TERM...(Saturday night through Friday)
Issued at 211 PM CST Fri Nov 17 2017

Potentially Hazardous Weather: Near critical fire wx conds are
possible over Rooks/Osborne/Mitchell Counties Sun.

Pattern: While there are model diff`s in amplitude...the longwaves
will feature a Wrn ridge/Ern trof over the CONUS. This means NW
flow over the Plns. This is a dry pattern and means a continuation
of the dryness we`ve seen since early Oct.

Temps: warmer than normal...except for Tue-Wed when temps will be
near normal behind a cold front that moves thru Mon night.

Fire Wx: fcst guidance maintained the possibility of near critical
conds over the far Srn fringe of the CWA. Winds are marginal
though.

Thxgvg Travel Wx: Looking very good Wed-Thu. Dry wx.

&&

.AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Saturday)
Issued at 647 PM CST Fri Nov 17 2017

General overview:
A fairly challenging period, with concerns for sub-VFR
ceiling/visibility and also precipitation during the first half,
and then fairly high confidence in VFR ceiling/visibility during
the second half but with relatively strong surface winds. Read on
for more element-specific details...

Ceiling/visibility/precipitation:
All concerns for sub-VFR ceiling/visibility are mainly
concentrated during the 07-12Z time frame. During this time,
expect rain showers to eventually mix with and possibly change
over to snow, with a light, wet coating possible. Will call for
MVFR ceiling and at least a brief period of visibility down to IFR
(assuming snow materializes), but stay tuned as things could
easily waver at least one category either side. By around 12Z,
expect a rapid return to VFR conditions as low clouds and
precipitation vacate to the east-southeast.

Winds:
Except for these first few hours and perhaps the very last few
hours late Saturday afternoon, the majority of the period will
feature modestly strong north-northwest winds with sustained
speeds commonly 15-25kt and gusts mainly 24-32kt. There are hints
of some marginal low level wind shear (LLWS) centered a few hours
either side of 15Z, but at this time expect surface winds to
remain elevated enough to keep the overall-shear magnitude at
least slightly below 30kt within the lowest 1-2 thousand
feet...and thus will refrain from a formal LLWS inclusion.

&&

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

$$

SHORT TERM...Kelley
LONG TERM...Kelley
AVIATION...Pfannkuch



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