Area Forecast Discussion
Issued by NWS Hastings, NE

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000
FXUS63 KGID 291806
AFDGID

Area Forecast Discussion
National Weather Service Hastings NE
106 PM CDT Sat Apr 29 2017

.UPDATE...
Issued at 1108 AM CDT Sat Apr 29 2017

Solely regarding the rest of today (through around 7 PM):
Despite plentiful clouds, it`s become increasingly apparent that
our previously-advertised very high rain chances (PoPs) through at
least mid-late afternoon were probably overdone, especially for
counties near/north of Interstate 80. It still looks like rain
will gradually redevelop from south-to-north later this afternoon
into this evening, and have left some pretty decent PoPs in for
this time frame, but the way things stand now a lot of folks have
been/and will continue to be in for a drier majority-of-today than
earlier expected, as we reside in this "lull" before stronger
forcing arrives tonight into tomorrow.

Going largely hand-in-hand with these overall-drier daytime
expectations, bumped up high temps today a good 2-3 degrees all
areas, with mid to perhaps upper 40s a good bet northern half and
more so low 40s far south/southwest.

&&

.SHORT TERM...(Today and tonight)
Issued at 250 AM CDT Sat Apr 29 2017

Starting to see initial round of rainfall moving northeast into
north central Kansas in the right rear of the strong upper level
jet to the north, and ahead of the upper level low pressure about
ready to deepen significantly tonight and early Sunday. Expect
that of precipitation to move northeast. Rain showers will
gradually spread north across south central Nebraska by midday.
A smattering of rain/snow mix is possible again this morning
thought accumulations should not be a problem.

Another round of precipitation will start to take shape late
tonight and continue during the day Sunday. This will be the main
heavy precipitation as it wraps north/northwest while the low
deepens. Powerful lift will add in cooling column, along with
cooler lower atmospheric temperatures, to promote more mix and
change over to snow in the western/southwest forecast area.
Mixture could work as far east as Highway 281 late tonight but
the area along and west of a Holdrege to Phillipsburg line has the
best snow at any accumulation late tonight. A variety of winter
weather headlines will begin tonight. Pushed start times back
about 3 hours to 1 AM. Once snow does take hold by 4-5 AM, it
could be snowing very heavily with reduced visbility and strong
north winds. That trend will continue into Sunday.

Many areas could add another 0.50" to 1" by Sunday AM of moisture
to already plentiful rain totals. More precipitation will
continue through the day Sunday. South central Nebraska especially
was in need of this moisture and will definitely help the spring
moisture profile immensely.

.LONG TERM...(Sunday through Friday)
Issued at 250 AM CDT Sat Apr 29 2017

Primary forecast concern in the long term continues to lie in the
first 24 hrs, through the day Sunday and into the first part of
Monday.

At 12Z Sunday, precipitation is expected to be well under way.
Models are in pretty good agreement with the placement of the upper
level low, generally over south central KS. At the surface, the main
low also sits to the south-southeast, keeping winds north-
northeasterly. Through the daytime hours, model agreement with the
timing/track of the low remains pretty good, the 00Z NAM is just a
touch slower. By 00Z Monday, the low is expected to shift
northeastward to the northeastern quadrant of KS, then continuing
its trek Sunday night and ending up over central portions of Iowa by
sunrise Monday. In general terms, there hasn`t been a huge change in
the story, with the CWA sitting on the northwest side of the track
of the low, leaves the area in the deformation zone/favorable area
of stronger frontogenetical forcing. The big questions have been
exactly where the main banding sets up, and with lower level/surface
temperatures. The western half/third of the CWA continues to be the
area under the biggest threat of accumulating snowfall, which
matched up well with the inherited Winter Storm Watch. Things
working in favor of accumulating snowfall...plenty of moisture to
work with, strong forcing, could at times being falling at a hefty
rate. Things working against even higher amounts...it`s the end of
April. Ground temps are warm. Low level/sfc temps, while supportive
of snow across the west, are hovering in close proximity of the
freezing mark. Another big question mark that still lingers is how
sharp of a west-east gradient there will be between accumulating
snow over to all liquid. There are still some model differences with
where exactly that transition will ultimately set up. Accompanying
the snowfall will be strong northerly winds, thanks to a tight
pressure gradient and mixing of stronger wind aloft. Sustained
speeds of 25-30 MPH and gusts near 45 MPH not out of the question,
especially across the western half of the CWA.

Changes made to the forecast...made a slight westward adjustment to
the axis of heavier snow amounts. Also made some adjustments to
amounts more into the 4-6" range and isolated higher in the SW,
meshing well with neighbors and WPC. As far as headline changes go,
after collab with neighbors, upgraded the southwestern portion of
the watch to a winter storm warning or advisory, these areas will be
impacted earlier on than others. Kept the rest of the watch as is
for now. These amounts are certainly not set in stone. Expect
further adjustments from the day shift today. Be sure to stay
updated to the latest forecasts.

Precipitation will be gradually tapering off to an end from SW to NE
Sunday night into Monday morning, though there continue to be some
model differences with exactly when things end. Once activity moves
out, the rest of the day Monday is dry. Breezy northwest winds
remain, but models do show highs climbing back into the 50s. Take
those highs with a grain of salt, especially in the west, as
whatever snow does fall may have a greater/less impact.

With the weekend system on our door step, little time was spent
making any notable adjustments to the forecast for Tuesday through
Friday. Models are in pretty good agreement at 12Z Tuesday, showing
northwesterly flow in place, with the main upper level now moving
into Ontario. Another shortwave disturbance continues to be shown by
models to slide southeast out of the Rockies into the region,
bringing chances for precipitation Tues/Wed. PoPs remain on the
lower side, still some timing/location details to be worked out in
the models. Forecast highs both days are in the lower 60s.

Dry conditions remain in the forecast for Thursday and Friday, with
more amplified ridging building over the western CONUS and sliding
east through the Plains. Should see highs back up near 70 for both
days.

&&

.AVIATION...(For the 18Z KGRI/KEAR TAFS through 18Z Sunday afternoon)
Issued at 106 PM CDT Sat Apr 29 2017

Not much time today to go into much detail, but needless to say
this is a rather complex forecast, especially with regard to a
possible transition to accumulating/blowing snow late tonight
into the day Sunday (favoring KEAR more than KGRI). The majority
of the period should feature MVFR/IFR ceiling, with any of the
current VFR right away this afternoon not lasting more than 3-5
more hours. Again, confidence is quite low on the timing of a
transition to rain to snow or a rain/snow mix, not to mention
actual accumulation. As it currently stands, we are calling for a
wet/slushy accumulation to around 2 inches at KEAR during the
latter half of the period, with little if any at KGRI. As usual,
confidence is reasonably higher in wind trends: Direction will
gradually transition to more true-northerly from the current
north-northeast, and speed/intensity will gradually pick up with
time. In short, this means that gust potential of generally
25-30kt this afternoon will increase closer to 35kt (if not
higher) by late in the period.

&&

.GID WATCHES/WARNINGS/ADVISORIES...
NE...Winter Storm Warning from 1 AM Sunday to 6 AM CDT Monday for
     NEZ072-073-082-083.

     Winter Storm Watch from late tonight through late Sunday night
     for NEZ039-040-046-047-060-061-074-084.

KS...Winter Storm Warning from 1 AM Sunday to 6 AM CDT Monday for
     KSZ005.

     Winter Weather Advisory from 1 AM Sunday to 6 AM CDT Monday for
     KSZ017.

&&

$$

UPDATE...Pfannkuch
SHORT TERM...NOAA/NWS/Moritz
LONG TERM...ADP
AVIATION...Pfannkuch


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