Area Forecast Discussion
Issued by NWS Hastings, NE

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FXUS63 KGID 271120

Area Forecast Discussion
National Weather Service Hastings NE
620 AM CDT Thu Apr 27 2017

.SHORT TERM...(Today and tonight)
Issued at 359 AM CDT Thu Apr 27 2017

Quiet conditions in place early this morning, with satellite and
upper air data showing the CWA sitting between upper level
disturbances, one moving into the Midwest region and the other
moving through the Rockies. Been a few returns showing up on radar
off to our west, but over the past hr have waned some while
moving closer to the CWA. Outside of the far west and east fringes
of the CWA having a few clouds, skies have been clear. At the
surface, light and variable winds remain in place thanks to a high
pressure ridge axis extending through the Plains and right
through the heart of the CWA.

The main focus through the short term period today/tonight
continues to revolve around the above mentioned upper level
disturbance currently off to the west, and the accompanying
precipitation chances. The majority (if not all) of the CWA looks
to be dry though the morning hours. Kept some small shower chances
in later this morning, a few models still try developing some
isolated activity. This afternoon, models are in pretty good
agreement showing this disturbance moving into western portions of
the Plains. As we get into the evening/overnight hours, the
disturbance will swing mainly north, rotating around a deepening
area of low pressure over the WY/CO border. The area of increased
mid level frontogenetical forcing will be the driving force behind
our precipitation chances. While PoPs will be on the increase
this afternoon, the better chances shown by recent model runs come
after 21Z across the southwestern third/half of the CWA. Precip
is expected to expand in coverage with the main band shifting
north overnight, but there are some model differences with just
how far north it gets before 12Z Friday, and current forecast is a
touch on the slower side of things. Debated inserting any thunder
mention at all, but the NAM shows the potential for a few rumbles
late this afternoon/early evening, as do SREF probs. Decided to
throw in a slight chance mention across NC KS. Kept precipitation
type as liquid through the overnight hours, while lows in far
north and western areas may get into the mid/upper 30s, temps
aloft look to remain above freezing as well...better chances for a
RA/SN mix or just SN should remain outside of the CWA.

At the surface, the ridge axis will gradually push off to the
east, with winds turning to the southeast for much of the day
today, and eventually more easterly as low pressure deepens to our
south- southwest. Speeds through the short term period for most
look to top out in the 10-15 MPH range. Didn`t make any notable
changes to high temperatures for today, with the forecast calling
for mid 50s.

.LONG TERM...(Friday through Wednesday)
Issued at 359 AM CDT Thu Apr 27 2017

The main story this forecast period is the increasing and high
likelihood of widespread precipitation a couple of different times
through Sunday night, with the potential for snow, especially late
Saturday night through Sunday night.

Friday through Monday. First, high temperatures will be below
normal through the period, and could be as much as 30 degrees
below normal Sunday. There will be some rebound Monday but still
below normal for May Day.

On Friday, we walk into the day with a fairly large band of light
rain ongoing. The precipitation is associated with a weakening
mid/upper level wave pivoting its wave across the area. Initially
frontogenetic in nature, the system weakens and becomes
frontolytic aloft by late in the day. That results in the rain
area starting to diminish by late morning and continuing the trend
in the afternoon. Weak surface low and boundary in Kansas could
spark a couple of afternoon showers in southern areas but that
shouldn`t be too widespread as the upper system weakens and more
of an open wave. Despite this daytime diminishing precipitation
trend with time, additional rainfall during the day averaging on
the 0.20" to 0.40" range is likely, with the heavier amounts
favoring south central Nebraska north of Highway 6/34 and west of
Highway 281.

Friday night should bring a temporary break to precipitation as we
await the influence of the main weekend storm system.
Precipitation chances are lower, but north central Kansas could
start to see more steady precipitation toward dawn Saturday. The
trend of a gradual feed of moisture and precipitation ahead of an
upper level low will continue all day Saturday. Far northern parts
of the forecast will be the last for precipitation Saturday and
may be dry much of the day, while north central Kansas could
easily see rain showers on/off all day.

Frankly, the main show and most intriguing part of the forecast is
late Saturday night, Sunday and Sunday night. All models are in
agreement with a rapidly deepening upper level low pressure
expected to move from the Texas panhandle to south of Des Monies
by Monday morning. 200+ decameter height falls with this system
thanks to a strong potential vorticity intrusion and 120-140KT
H250 jet wrapping around it. This will be a very potent system for
the region.

A few things stand out. One is the the wind by Sunday afternoon.
H850 winds of 50-60KTS are forecast and will likely see 25-35 mph
surface winds from the north by afternoon. Have increased wind
speeds Sunday.

Temperatures will also be very chilly and in the "record low high"
range Sunday for some locations. Lowered high temperatures Sunday
to the upper 30s some areas, and it may not be that warm.

Finally, precipitation looks plentiful, especially if the strong
deformation axis verifies as advertised Sunday and Sunday night.
After the initial rainfall Thursday night and Friday, the GFS,
ECMWF and Canadian are all very similar with heavy precipitation
Sunday and Sunday night. For the 48 hour period of Saturday 7 am
through Monday 7 am, additional precipitation ranges from 0.50" to
2.50+", with most of the area in the 1.50" to 2.50" range. There
will likely be spots in the forecast area, and it could be
several, which pick up 2 to 3 inches of moisture during the next 4

With the precipitation and temperatures expected, snowfall comes
into play. Surface wet bulb and H850 temperatures suggest a high
likelihood of snow late Saturday through Sunday night.
Accumulation is on the table though its hard to say just how
much will accumulate right now. Stay tuned, but it could be a very
wintry scene for parts of the forecast area Sunday and Sunday
night. The system should be pulling out Monday. Right now we have
the forecast dry, but that might be a bit optimistic. Though
warmer Monday, its still chilly and likely breezy for a time.

Tuesday and Wednesday...the Central Plains region remains in
cyclonic flow in the wake of the large upper level low pressure.
Such a northwest flow will keep small chance for precipitation in
the forecast, especially later Tuesday and Wednesday. Though
warmer, I wouldn`t expect an big warming trend. Current forecast
of lower 60s could be on the high side if clouds are more
widespread and precipitation develops.

Though a bit beyond this forecast cycle, its worth noting an upper
level ridge appears likely late next week. So at least for a few
days, probably Thursday through Saturday (May 4-6), dry weather
and moderating temperatures appear in store for most of the
central High Plains.


.AVIATION...(For the 12Z KGRI/KEAR TAFS through 12Z Friday morning)
Issued at 613 AM CDT Thu Apr 27 2017

VFR conditions forecast through much of this TAF period, with
deteriorating conditions later tonight as precipitation chances
increase. There continue to be some minor differences between
models with the timing of the heaviest precip, but there will be
at least a chance for rain starting mid afternoon today. The best
chances look to come closer to midnight and through the end of the
TAF period, where models also show the potential for ceilings
lowering into MVFR/IFR criteria. Winds this morning will remain
light/variable thanks to sfc high pressure ridge axis in the area,
but will be turning southeasterly then easterly through the end of
the period as the ridge slides east and low pressure deepens to
our southwest.


NE...Frost Advisory until 9 AM CDT this morning for NEZ060>064-

     Freeze Warning until 9 AM CDT this morning for NEZ039>041-

KS...Frost Advisory until 9 AM CDT this morning for KSZ005>007-



LONG TERM...Moritz
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