Area Forecast Discussion
Issued by NWS Hastings, NE

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984
FXUS63 KGID 240544
AFDGID

Area Forecast Discussion
National Weather Service Hastings NE
1244 AM CDT SAT SEP 24 2016

.SHORT TERM...(This evening through Monday daytime)
Issued at 352 PM CDT Fri Sep 23 2016

Forecast highlights/overview of these next 72 hours:
Very generally, we undergo a noticeable transition from "summer"
to fall these next few days, with this transition marked by at
least a marginal threat for a few strong to severe thunderstorms
from late tonight through Saturday evening. Although SPC Day
1/Day 2 severe outlooks only highlight our western counties (Day
1 tonight) and eastern counties (Day 2 Saturday) in official
Marginal Risk areas, we have chosen to broadbrush nearly the
entire CWA with a low-end severe threat in our own local forecast
products such as the Hazardous Weather Outlook (HWOGID),
especially for tonight (Day 1). Temperature-wise, Saturday marks
the "transition day" between the near-90 degree heat of today and
noticeably cooler highs only around 70 on Sunday. Speaking of
cooler temperatures, we are going to have to keep a close eye on
low temperature trends for both Sunday night and Monday night just
in case especially our typically-coldest counties (such as Valley,
Dawson) start trending into frost-supportive readings in the
mid-30s. Due to inherent uncertainty this far out in time, our
latest official forecast does not quite support lows this cold,
but it wouldn`t be the first time that nights such as these
trended several degrees colder as they get closer in time.

Taking a look at current conditions as of 3 PM:
Other than dewpoints mixing out a bit lower into the 50s than
anticipated in most areas, today has largely turned out as
expected and has been more "straightforward" than yesterday.
Unlike yesterday, high temperatures across the CWA today will be
much more uniform, mainly in the 89-92 range, under sunny to
mostly sunny skies with only a smattering of fair weather cumulus
here or there. As expected, it`s been quite breezy (some might
call it windy) this afternoon, with sustained southerly speeds
generally 15-25 MPH and gusts 25-35 MPH. These strong breezes are
a result of a tightening pressure gradient in response to a
steadily-deepening surface low currently centered over northeast
CO at a magnitude of roughly 998 millibars. As a result, the front
that bisected the CWA 24 hours ago has flown well off to our north
as a warm front. In the mid-upper levels, water vapor satellite
and short term model data clearly show a gradual strengthening of
south-southwest flow aloft into the Central Plains, as a large
scale trough with a powerful, closed low is churning slowly east-
northeast through the UT/WY/CO border area. With little forcing
yet into our area and very little instability, a nearly
"guaranteed" forecast continues into this evening under
considerable sunshine.

Now looking ahead forecast-wise through the next 6 night/day
periods...

This evening/tonight:
The paramount concern is the possibility for a few strong to
perhaps marginally severe thunderstorms between midnight and
sunrise. In the meantime, for those with outdoor activities this
evening it should be dry/storm-free, and we only indicate the
slightest chance of a storm in a few extreme western counties
before midnight, before storm chances/PoPs increase into the
30-50 percent range across the entire CWA after midnight. In the
mid-upper levels, the center of the big low/vort max to our west
will pivot across WY during the night, as large-scale forcing and
mid-upper wind fields strengthen into the Central Plains. Although
the typically-favored nose of the strong southerly low level jet
(evident at 850 mb) is aimed well to our north tonight, most
models agree that at least isolated to scattered shower/storm
activity should blossom late tonight as upper forcing increases
from the west. Although SPC only highlights some of our western
counties in a formal Marginal Risk for severe storms tonight, the
presence of elevated CAPE potentially increasing up to around 1500
J/kg in the 850-700 mb layer over most of the CWA makes it hard to
completely rule out a rogue, marginally severe storm mainly with
quarter size hail potential almost anywhere in the CWA. In other
departments, a deck of lower stratus clouds is expected to
overtake much of the CWA late tonight, which along with steady
breezes averaging sustained 10-20 MPH will result in yet another
unseasonably mild night with low temps aimed into the mid-upper
60s most areas.

Saturday daytime/night:
The main focus remains on the potential for a few strong to severe
storms, which although cannot be ruled out at almost any point
into the evening hours, would appear most favored along the
passing cold front within the eastern half of the CWA during the
afternoon/early evening. In the big picture of the mid-upper
levels, models such as NAM/GFS are in pretty darn good agreement
in shifting the primary mid level low/vort max from central WY at
daybreak to the eastern ND area by Saturday night`s end.
Meanwhile, the large-scale trough shifting east across the Central
CONUS will start to stall out a bit as the parent low breaks away
to the northeast. At the surface, the main surface low will spend
most of the day well to our north over ND, while a trailing
north-south oriented cold front slowly slides through our CWA from
west-to-east, marked by a shift from breezy south winds ahead of
it to somewhat lighter west-southwest winds behind it. During the
morning, much of the CWA will probably see a continuation of
isolated/scattered convection from the late night hours, some of
which could still be strong to marginally severe. However, the
"main event", should one occur, will likely hold off until the
afternoon/early evening hours as the front slowly presses into
counties along/east of the Highway 281 corridor, where mixed-layer
CAPE of at least 1000-2000 J/kg is likely in the presence of
fairly strong deep-layer shear around 40kt. Various higher-res
models suggest that a broken line of storms will develop
along/near the front, with individual storms moving northeast with
the mean flow. The main threats with any severe storms will be
hail/wind, as fairly weak low level and a fairly uni-directional
deep shear field shear does not appear all that favorable for
tornadoes. Most lingering storms should gradually depart our
eastern/southeast zones during the evening, and have only small
PoPs lingering past midnight in far southeast counties. If
confidence was higher in widespread coverage, would have raised
afternoon PoPs into "likely" 60+ percentages, but because this
activity could remain more scattered in nature have capped PoPs at
50 percent at this time. Temperature-wise, don`t have a great feel
for highs as effects of cloud cover and a gradual invasion of
cooler air from the west will play a role, but stuck close to
previous forecast with highs aimed 79-83.

Sunday/Sunday night:
By sunrise, any risk for rain/storms will be long-gone off to our
east and south, paving the way for a very fall-like day. In the
mid-upper levels, the main trough axis shifts through the area,
shifting flow to northwesterly with time and ushering in a deep,
dry airmass with little cloud cover expect for possibly some
lingering high level cirrus during the day. At the surface,
northwest breezes will be noticeable as deep-mixing promotes
sustained 15-20 MPH and gusts up to around 30 MPH. In a noticeably
cooler post-frontal airmass, highs are only aimed 70-73 although
this is just a "tick" higher than previous forecast. Surface high
pressure continues moving in Sunday night, but still expect 5-10
MPH speeds. As mentioned in the opener, will have to keep a close
eye on low temps here, as they could trend colder. For now though,
already opted to lower 2-3 degrees from previous forecast, now
aimed low-mid 40s most areas but colder upper 40s far north/west-
central.

Monday daytime:
Very similar to Sunday, except with somewhat lighter breezes
averaging sustained 10-15 MPH for the most part out of the
northwest. Otherwise, deep, dry northwesterly flow continues
aloft making for a sun-filled and dry day. High temps are expected
to be very much like Sunday`s, and have most of the CWA aimed
69-72.

.LONG TERM...(Monday night through Friday)
Issued at 352 PM CDT Fri Sep 23 2016

The long term period starts of Monday night with models in good
agreement showing amplified northwesterly flow aloft across the
region, set up between low pressure spinning  over the western Great
Lakes and high pressure over much of the western CONUS. Going
through Tuesday and Wednesday, that upper level ridging continues to
push east onto the Central Plains, with flow eventually
transitioning to the southwest as the main ridge axis slides east of
the CWA. With no disturbance affecting the area through this time
frame, the forecast remains dry. At the surface, high pressure
continue to affect the area through the day on Tuesday, though it`s
starting to push further east. Light winds starting off the period
turn more southerly through the day. Winds remain southerly through
Wednesday, picking up a bit in speed as low pressure starts to
become better organized over CO. Still expecting pleasant
temperatures, with lower 70s for Tuesday and mid-upper 70s for
Wednesday.

Thursday and Friday, precipitation chances work their way back into
the forecast. With the southwesterly flow now in place across the
area, models are in decent agreement showing a shortwave disturbance
sliding out of the Desert SW and eventually through the Plains.
Models are in pretty good agreement with the general track, bringing
it through our area, but have some slight differences with timing.
At this point forecast has 20-30%, until those finer details can be
ironed out. Mid-upper 70s expected for highs both Thurs-Fri.

&&

.AVIATION...(For the 06Z KGRI/KEAR TAFS through 06Z Saturday night)
Issued at 1230 AM CDT Sat Sep 24 2016

Prevailing VFR conditions are expected through the period...albeit
there will be a prolonged period where thunderstorms will be
possible across both terminals as a cold front progresses across
the local area during the early morning through afternoon hours
today. Ahead of this front...expect increasing mid level clouds
with occasionally gusty southerly winds and some LLWS as latest
VWP still indicating upwards of 45KTS about 1KFT above the
surface. As this front makes its way across the local
area...expect significant mid level cloud cover with potentially
some MVFR CIGS or VSBYS at either terminal if they are affected by
a thunderstorm. Expect slow clearing late in the afternoon as the
front progresses further eastward...with winds shifting westerly.

&&

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

$$

SHORT TERM...Pfannkuch
LONG TERM...ADP
AVIATION...Rossi



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