Area Forecast Discussion
Issued by NWS Hastings, NE

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FXUS63 KGID 091758

National Weather Service Hastings NE
1258 PM CDT Fri Jun 9 2023

...Aviation Update...

.DISCUSSION...(Today through Thursday)
Issued at 516 AM CDT Fri Jun 9 2023


* Although not technically reflected in latest SPC Day 1/2
  outlooks (mainly due to rather weak deep layer wind shear), here
  at the local level we feel there is a reasonable probability
  that several strong and even few marginally-severe storms will
  probably develop during the afternoon-evening hours BOTH today
  and Saturday almost anywhere in the outlook area. This
  forecaster would not be one bit surprised to see later SPC
  outlooks introduce or re-introduce Marginal Risk (level 1 of 5)
  severe categories to at least some (much?) of our coverage area
  (CWA) in later issuances depending on model trends.

* Although a few spotty showers/sprinkles could perhaps linger
  into the first part of the daytime hours Sunday, Sunday daytime-
  night is an overall high-confidence DRY period, and is in fact
  the only part of the 7-day forecast to feature almost
  "guaranteed" dry conditions for the entire CWA.

* Although MOST of our CWA probably stays dry/storm-free Mon-Mon
  night as well, the Mon-Thurs time frame again becomes "littered"
  with a variety of fairly low-confidence rain chances (PoPs) for
  at least parts of the area. Although more instances of at least
  strong to marginally-severe storms cannot be ruled out, none of
  this time frame currently looks particularly concerning for a
  more widespread/organized severe threat, and agree with SPC in
  opting against any formal severe outlook on their latest Day 4-8

* Temperature-wise: Today appears to mark the last in our recent
  stretch of modestly above-average heat (by early June
  standards), with one more day of upper 80s-low 90s forecast.
  Highs will start to ease downward slightly Saturday, with a more
  noticeable cool-down (and also a drier/less humid airmass)
  arriving Sunday which is the overall-coolest day of the 7-day
  forecast with highs only mid-upper 70s. A gradual warm-up kicks
  back in for next week, but overall not as seasonably-hot as what
  we`ve seen lately.

 (including all further discussion of Days 3-7 Sun-Thurs):

- General overview of the large scale upper air surface weather
  pattern/precipitation trends:

This is this forecaster`s first shift back after a few days off,
and although the upper air pattern is still a bit "off kilter" by
early-mid June standards, at least storms are no longer moving
east-to-west as they were a few days back (so at least some sense
of "normalcy" has returned). That being said, an overall "blocky"
upper air pattern remains in place, with most of our weather
through the next week being driven by unusually subtle and or/weak
disturbances (more typical of later in the summer season), and an
overall lack of seasonably-strong deep layer wind shear
(particularly of the 30+ knot variety) tending to keep any truly
widespread/more significant severe storm episodes at bay. For the
most part, the latest ECMWF/GFS solutions are in reasonable
agreement on the upper air basics through the next 7
short: 1) we start off today-tonight in a weak/blocky flow regime
with the Central Plains sandwiched between larger scale/broad lows
both well to our west and east...2) Sat-Sat night a shortwave
trough drops down the backside of a shortwave trough/closed low
dropping south toward the Great Lakes, which in turn drives a
seasonably-decent surface cold front southward across our
area...3) Sunday-Monday (especially Sunday) the majority of our
CWA likely stays dry as we remain in a somewhat cooler/drier
post-frontal regime at the surface, while aloft we remain "in
between" forcing at somewhat of an Omega block pattern sets up
over the central CONUS with upper level ridging centered to our
north and upper lows on either side over both the Desert Southwest
and Great Lakes regions...4) Tues-Thurs the blocking pattern
gradually breaks down and allows relatively weak/mainly quasi-
zonal (west-to-east) flow aloft to overspread our region, bringing
back rain/thunderstorm chances, but to what degree being a bit in
question as models currently depict fairly low amplitude shortwave
troughs, with stronger upper flow/deep layer shear focusing to our
south over the Southern Plains. Thus, while the Tues-Thurs time
frame currently carries various rain/thunderstorm chances, there
is a good reason why actual chances/PoPs on any given day/night
are currently held mainly no more than 20-40 percent.


Following some spotty/isolated strong to severe storms during the
peak heating of the day on Thursday (including a downburst near
Davenport in Thayer County with an unofficial measured 76 MPH
gust), the later evening-overnight hours has been quiet/dry across
the vast majority of the CWA, with only a few spotty sprinkles
noted mainly within the southwest half of the area within a
weak/subtle zone of mid-level convergence. Flow aloft is
weak/disorganized with stronger northerly flow well to our east
and stronger south-southwesterly flow well to our west. At the
surface, a rather weak/non-descript regime is in place, with pre-
dawn breezes over most of the CWA averaging roughly 3-9 MPH from
an east to southeast direction. Some very spotty/light fog has
been picked up by area airport sensors so far mainly at
Kearney/Hastings, but nothing truly widespread/impactful at least
SO FAR. Overnight low temps are on track to bottom out 61-66
across most of the CWA.

- EARLY THIS MORNING (through around 9 AM):
Although a few spotty sprinkles/weak showers could continue to
develop mainly within some of our central/southwest counties, the
main thing to watch through around 8-9 AM will be the possibility
of at least localized pockets of more concentrated fog, with the
latest HRRR at least weakly hinting that spotty, maybe even dense
fog could briefly plague some of our especially central counties.
Will monitor obs closely and do have some limited, generic "patchy
fog" in the official forecast for a central counties through 9 AM,
but unless/until fog becomes more of an issue will refrain from
highlighting more formally (including in the Hazardous Weather

MOST of our CWA should get through at least 3 PM dry. That being
said, subtle forcing/lift within the aforementioned weak mid level
convergence zone could easily keep at least spotty sprinkles (and
MAYBE even a few weak thunderstorms) in play this morning into
early this afternoon, so at least have a generic "slight chance of
sprinkles" mentioned CWA-wide through that time. Then, once the
peak heating/diurnal cycle kicks into gear mainly near/after 3 PM,
scattered to eventually perhaps fairly numerous thunderstorms will
blossom across the CWA, with individual storms/storm clusters
slowly drifting east or southeast with time. Much like Thursday,
instability will be fairly decent with mixed-layer CAPE commonly
1500-2500 J/kg, but deep layer shear will be seasonably-weak at
20KT or less. However, unlike Thursday, this afternoon-tonight
will feature a bit more (albeit weak) upper forcing, as various
models depict a low amplitude shortwave trough slowly traversing
the area from west-to-east, along with a seasonably-weak (but
evident) 20-30 KT south-southwesterly low level jet helping to
sustain or possibly regenerate new storms/storm clusters well into
the night. As already touched on in the Key Messages above, and
after seeing a few storms reach severe levels on Thursday, feel
that a broad Marginal Risk of severe could probably be justified
by SPC on later Day 1 outlook updates (similar to what the
previous Day 2 outlook depicted for our area), with the main time
frame for possible spotty severe storms focused 3 PM-Midnight.
Certainly cannot rule out some isolated damaging winds, with large
hail a lesser threat. While pockets of heavy rain of 1-2" are
likely on almost a "random" basis (and 2+" bullseyes certainly
possible), the OVERALL dry last 3-4 days should allow most places
to handle this overall-welcomed rainfall. Prior to thunderstorm
outflow likely coming into play and "messing up" the
prevailing/background wind fields, breezes today will generally
average 10-15 MPH out of the south-southeast. High temps for today
were changed little from previous, generally aimed 87-91 most
areas. Lows tonight also changed little, with similar values to
this morning...mainly low-mid 60s.

For only being 24-36 hours away, will readily admit that there is
at least some modest uncertainty in how Saturday plays out, as
models continue to vary regarding EXACTLY how fast a seasonably-
decent cold front passes southward through our CWA (generally
speaking though, there has been a touch of a slowing trend in most
00Z/06Z models). Generally speaking, the leading edge of the shift
to northerly/northwesterly breezes should be about halfway through
the CWA by early-mid afternoon, then clearing through our
southern/KS zones at some point in the evening. While certainly
not guaranteed dry, MOST of the CWA will probably be dry between
sunrise and early afternoon as we reside "in between" forcing from
the departing Fri night wave and the incoming disturbance dropping
in from the north that is helping to drive the cold front through.
Like today, and as supported by modeled reflectivity progs from
higher-res models (such as 06Z HRRR), a few strong to possibly
(probably?) marginally-severe storms look to be a decent bet
especially 3-10 PM, and would not be surprised to see SPC
introduce a Marginal Risk to especially southern parts of our CWA
in later outlooks. Instability values look to be similar today
(mixed-layer CAPE generally 1500-2500 J/kg), and although still
fairly weak by mid-June standards, deep layer shear will probably
be slightly stronger (at least 20-25 KT), helping to drive at
least a localized damaging winds/hail threat along the front,
along with perhaps more localized heavy rain. As instability
starts to wane/decrease southward with time later in the evening-
overnight, the severe storm threat should wane in turn, but weaker
storms/general showers will likely continue through much of the
night as steady northerly post-frontal breezes (gusting 20-25 MPH)
become established. Temperature-wise, highs Saturday are expected
to average 5+ degrees cooler than today (mainly low-mid 80s), with
lows Saturday night at least slightly cooler than tonight most
areas (mainly upper 50s-low 60s).


.AVIATION...(For the 18Z KGRI/KEAR TAFS through 18Z Saturday)
Issued at 1257 PM CDT Fri Jun 9 2023

The primary concern for the terminals will be widely scattered
thunderstorms this afternoon and evening. Some may linger into the
overnight hours before a brief lull and another shot Saturday.
Activity is expected to develop around 21z this afternoon and may
impact the terminals at any point in the late afternoon hours and
that is indicated with a tempo group. Generally thunderstorm
activity is expected to develop west of the terminals and slowly
slide eastward, but the airmass/pulse nature of these storms will
be challenging to identify where they will develop or move. Into
the evening hours, the low level jet will develop and help to fuel
some of the thunderstorm activity. Similar to this morning, fog
is possible in the early morning hours as abundant low level
moisture and light flow are present.




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