Area Forecast Discussion
Issued by NWS Hastings, NE

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FXUS63 KGID 180534
AFDGID

Area Forecast Discussion
National Weather Service Hastings NE
1134 PM CST Fri Nov 17 2017

.UPDATE...
Issued at 958 PM CST Fri Nov 17 2017

A few notes regarding the overnight/next 12 hours or so:

1) Snow potential: If anything, legitimate snow accumulation
seems to be looking a touch less likely (not that we were
expecting much to begin with). Have officially kept a token 1 to
2 TENTHS of an inch (dusting) going for areas mainly near/north of
the Highway 6 corridor in Nebraska, but with low temperatures
expected to go no lower than 33-36 in most of this area, and even
then not getting this cold until well after midnight, the window
of opportunity for snow accumulation will be quite small. That
being said, will echo day shift discussion below and acknowledge
that some very localized banding thanks to strong mid-level
frontogenesis could perhaps put down a half-inch or slightly more,
but it`s still nearly impossible to "nail down" where this would
be, but perhaps favoring our far western counties if anything?

2) Rainfall: currently isolated to scattered showers will
continue increasing in coverage as the night wears on, while
gradually ending from north to south as forcing departs. Even so,
the vast majority of the CWA should see no more than 0.10-0.20" of
liquid at best. One minor change from the afternoon issuance was
to linger some small precip chances in our southeast zones for the
first hours of the "daytime" period (mainly 6-8 AM), as the back
edge precip looks just a touch slower to depart than previously.

3) Thunderstorms: Not very surprisingly, the strong frontogenetic
forcing has teamed with meager-but-non-zero elevated instability
to pop a few weak thunderstorms over the past few hours, mainly
within counties along the I-80 and Highway 6 corridors. Pondered
adding a formal thunderstorm mention to our standard forecast
products/Hazardous Weather Outlook, but given the relatively
limited coverage and expected low impact, have thus far opted to
handle with non-routine short term forecast products (text and
graphical). The majority of existing thunder activity is expected
to wane post-midnight.

&&

.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 06Z KGRI/KEAR TAFS through 06Z Saturday)
Issued at 1120 PM CST Fri Nov 17 2017

A band of rain showers will cross the terminals during the
overnight hours and a brief mix of rain and snow is possible
before the precipitation ends. North to northwest winds will be
strong and gusty through Saturday in a tight pressure gradient
behind a cold frontal boundary.

&&

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

&&

$$

UPDATE...Pfannkuch
SHORT TERM...Kelley
LONG TERM...Kelley
AVIATION...Fay


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