341
FXUS63 KGID 211151
AFDGID

Area Forecast Discussion
National Weather Service Hastings NE
651 AM CDT Sat Sep 21 2024

...Aviation Update...

.KEY MESSAGES...

- A seasonably-strong cold front arrives today (marked by rather
  gusty north winds), but despite this most areas will see one
  more day of above-average warmth...especially the southeast
  1/3 of our coverage area (CWA) where upper 80s to around 90
  are likely.

- Although very spotty showers/storms are possible during the
  daytime today (mainly this afternoon and mainly in KS), it`s
  increasingly-clear that MOST of our CWA will get through
  sunset dry, with higher/more widespread chances for
  rain/embedded thunder arriving later this evening-overnight
  (overall severe threat low).

- While at least portions of some counties especially
  along/south of the KS border are still expected to pick up
  1-2" of rain this weekend, expected total rainfall (QPF) for
  MOST of our CWA continues to trend down, with especially
  counties along/north of I-80 now looking at less than 0.50"
  (and our far north around Ord/Greeley unfortunately struggling
  to see 0.10"). Suspect more folks will be disappointed than
  pleased across our CWA as a whole.

- Once the last showers depart Sunday afternoon-evening, the
  Mon-Fri time frame currently features a dry forecast.

- Temperature-wise: lovers of early-fall weather (highs mainly
  70s/lows mainly 40s-50s) should really enjoy next week! Sun
  night should be overall-coolest with parts of especially
  Valley/Sherman/Dawson counties possibly dropping into the
  upper 30s.

&&

.DISCUSSION...
Issued at 507 AM CDT Sat Sep 21 2024

-- PRIMARY CHANGES WITH THIS 7-DAY FORECAST VERSUS THE PREVIOUS
 ONE ISSUED FRI AFTERNOON:

- Chances for measurable rain (PoPs) have continued to nudge
  downward for the daytime today, with especially our Nebraska
  CWA expected to remain largely dry until at least sunset. None
  of our CWA features "likely" (60+%) PoPs until later evening.

- As hit on above, total weekend rain totals (QPF) continue to
  trend down especially for the northern half of our area (most
  places 0.50" at most), and while our south half should see
  more overall, anything in excess of 1.50" will likely be a
  very localized exception. Minimal concern for anything more
  than very minor/nuisance flooding at worst.

- As touched on above, low temps for Sun night have have trended
  down very slightly, and IF they trend down much more some
  patchy frost could MAYBE even come into play for a few of our
  far north-northwest counties (currently not in official
  forecast).

- High temps for especially Sun-Wed have trended up a few
  degrees. However, Sunday is clearly still the coolest day of
  the next week with at least spotty lingering rain/widespread
  clouds holding highs down mainly a few degrees either side of
  60 most places.


-- 7-DAY FORECAST CHRONOLOGICAL DETAILS:

- UP-FRONT ADMIN NOTE: now that our roughly 30-hours of various
  comms issues (due to a fiber cut) are behind us, it`s back to
  "business as usual"...one more big thanks to OAX for helping
  us out with product issuance, radar watch, etc.!

- CURRENT/RECENT WEATHER SCENE AS OF 4 AM:
Following a brief flare-up of spotty storms in our far southeast
zones Friday evening (including a radar-indicated marginally-
severe storm in Mitchell County KS), the remainder of the
overnight has been quiet/dry and unseasonably warm. In the big
picture of the mid-upper levels, we reside under broad
southwesterly flow...downstream from a strong/large scale closed
low currently churning across the CA/AZ border. At the surface,
weak low pressure is centered over the NE/CO/KS border area,
with a weak boundary extending off to its northeast separating
modest southerly breezes and warmer/humid air (over our CWA)
from the leading edge of a strong cold front that is currently
diving southeastward through northwest NE. Just within mainly
the last hour, some high-based showers/perhaps a thunderstorm
have developed just outside the extreme southeast corner of our
CWA within a zone of low-mid level warm air/moisture advection.
overnight low temps are on track to range from around 60 far
northwest...to mid-upper 60s central...to upper 60s-low 70s
southeast. Early morning dewpoints have risen into the low-mid
60s most places.


- TODAY-EARLY EVENING (through around sunset/9 PM):
In the mid-upper levels, the aforementioned strong upper low
over the Desert will trudge northeast...centered over the Four
Corners by sunset. Meanwhile, lower amplitude disturbances out
ahead of it will stream into the Central Plains from the
southwest, providing the necessary lift for at least spotty
showers/thunderstorms as the day wears on (especially in our
south). That being said, higher-res models (HRRR/NAMNest)
clearly show that any showers/storms this morning should mainly
favor our extreme southeast counties, with at least scattered
activity eventually becoming a bit more widespread toward late
afternoon-early evening especially near/south of the KS border.
At the surface, the cold front is clearly the "story of the
day", with its passage marked by an abrupt transition to
northerly winds generally sustained 15-25 MPH/gusts 25-35 MPH.
The leading edge of this front will enter our far northwest
shortly after sunrise, be roughly halfway through our CWA by
Noon, and then slow a bit as it finally reaches our extreme
southeast CWA by late afternoon-early evening. Although not
likely, there appears to be a brief window for a strong to
marginally-severe storm to develop along/just behind this front
mainly between 5-8 PM and mainly in our far southeast KS
counties (Osborne/Mitchell/Jewell), with latest RAP depicting
around 1500 J/kg mixed-layer CAPE/around 30KT of deep layer
shear. Interestingly, SPC has not included this portion of our
CWA in its initial Day 1 Marginal Risk area, but should it be
expanded in later issuances it might include this area. Overall
though, the vast majority of our CWA is not expected to have any
severe threat. Last but not least, both high temperatures and
hourly temperature trends will be a bit tricky today given the
cold frontal passage and a gradual increase in clouds this
afternoon...with a good 15-degree difference/gradient expected
across our CWA. Leaned heavily on a multi-model blend, which if
anything nudged highs up 1-2 degrees from previous, but ranging
from only mid 70s far northwest, to upper 70s-low 80s central
(Tri Cities area), to upper 80s-around 90 southeast where the
front arrives last (especially Hebron to Beloit areas).


- LATER THIS EVENING-OVERNIGHT (post-sunset/after 9 PM):
While any possible/brief severe storm threat in our far
southeast should be on the wane, chances for increasingly-
widespread showers with embedded thunderstorms (a few possibly
strong enough to produce small hail) will expand northward to
include the majority of our CWA...in response to increasing mid-
level convergence (especially around 700 millibars) out ahead of
the main/parent upper low that will still be out to our west
over CO through the night. As already hit on above, while most
all of our CWA should see at least minimal rain, the most
concentrated heavier showers/downpours will surely favor our
south more than our north...as increasingly-dry low level air
with surface dewpoints falling into the 40s will help to "eat
away" at the northern edges of steady rain. Also at the surface,
steady north-northeast breezes at least 10-15 MPH with gusts
around 20+ MPH will persist overnight. Low temps were actually
nudged up very slightly given the expectation of widespread
clouds, with most of the CWA aimed fairly uniformly between
51-55.


- SUNDAY DAYTIME-NIGHT:
Over the course of these 24 hours, the main upper low initially
over CO will gradually track east-northeast over the heart of
our CWA, opening up/weakening slightly as it does so. However,
forcing will remain sufficient for scattered to numerous showers
and perhaps a few weak thunderstorms especially during the
morning-mid afternoon hours, with activity becoming increasingly
spotty during the late afternoon-evening while also departing
from west-to-east with the upper wave. At the surface, it will
remain a bit breezy through the day with northerly sustained
speeds generally 10-15 MPH/gusts 15-20 MPH. Under cloudy/mostly
cloudy skies, high temperatures will easily be the coolest of
the next many days, with highs currently aimed mainly a few
degrees either side of 60 (warmest north where rain/showers
should be least prevalent and clouds not as deep).

Sunday night, skies should slowly/gradually clear from
northwest-to-southeast, and winds will become very light as
surface high pressure moves in. There are still some question
marks regarding exactly how fast clouds vacate, but assuming
they do vacate efficiently, this is on track to be a
legitimately cool night for late-September, and have lows aimed
from upper 30s far north/west central (Ord/Gothenburg areas), to
low-mid 40s central (Tri Cities) to mid-upper 40s southeast. As
already hit on, IF temps trend a few degrees colder in our
north/west-central Nebraska zones, then at least limited/patchy
frost COULD come into play, but this is still considered a low
probability scenario.


- MONDAY-TUESDAY:
Various models are in agreement that at least the vast majority
of our CWA remains dry, as we initially reside in the wake of
the departing weekend system, before another disturbance drops
down into our region out of the north-northwest. There are hints
that especially some western counties could see some light
showers/sprinkles mainly Tues AM from this second wave, but am
okay letting our CWA-wide dry forecast ride for now. Overall,
these look like two seasonably pleasant days. High temps have
trended up generally 1-4 degrees from previous for both days,
with Monday now aimed mainly 67-70 and Tuesday low-mid 70s.
Overnight lows will also nudge upward...mainly mid 40s Mon night
and mid-upper 40s Tues night.


- WEDNESDAY-FRIDAY:
At least for now, our forecast remains dry CWA-wide, with
overall-high confidence in seasonably-pleasant high temps mid-
upper 70s and lows a few degrees either side of 50. That being
said, latest ECMWF/GFS really start to diverge with their
depiction of the upper air pattern in the wake of Tuesday`s
disturbance. In short, the ECMWF cuts off a very slow moving
low pressure system somewhere between north TX and southern KS,
while the GFS keeps any possible closed upper low well to our
east with more prominent upper ridging over our region. Either
way though, both primary models currently favor mainly (if not
completely) dry conditions.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 651 AM CDT Sat Sep 21 2024

For KGRI/KEAR Airports:
- Ceiling/visibility/precipitation/thunderstorm potential:
High confidence in VFR ceiling/visibility through the vast
majority of the period, with the primary possible "catch" being
the possibility of intermittent sub-VFR visibility in passing
showers/non-severe thunderstorms this evening- overnight.
Speaking of this thunderstorm potential, given it is still
beyond the first 12 hours have elected to maintain a more
generic "vicinity thunderstorm" (VCTS) starting 02Z...and will
defer to later forecasts to introduce TEMPO/prevailing groups as
needed. As for clouds, especially this morning will remain
mostly clear, with a gradual increase in mid-high clouds then
taking hold through this afternoon-evening. While some scattered
lower clouds around 3-4K ft. are certainly possible during
overnight convection, ceiling should primarily remain at-or-
above 6K ft.

- Winds:
Along with evening-overnight convection, the passage of a
seasonably-strong cold front is the other "main story" aviation-wise.
Following a few hours of fairly light/variable direction
breezes right away this morning, the main frontal surge and
associated north winds will arrive between 15-17Z, with
sustained speeds commonly around 20KT/gusts 25-30KT in its wake.
Winds this evening-overnight will remain out of the north, but
speeds will back off a bit...more so sustained 10-15KT/gusts
15-20KT.

&&

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

&&

$$

DISCUSSION...Pfannkuch
AVIATION...Pfannkuch