569
FXUS63 KGID 221155
AFDGID

Area Forecast Discussion
National Weather Service Hastings NE
655 AM CDT Sun Sep 22 2024

...Aviation Update...

.KEY MESSAGES...

- While this weekend`s "rain event" will surely end up being a
  disappointing dud for the vast majority of our coverage area
  (CWA) with MOST places unlikely to exceed 0.10-0.20" (instead
  of the widespread 1-3" potential it appeared to carry a few
  days ago!), there was already one "surprising stripe" with
  embedded 0.25-0.75+" amounts overnight, so this thing can`t be
  totally written off yet for all.

- Once the rain from this system departs tonight, the vast
  majority of the next 7 days appear dry, although there are
  hints of least spotty rain chances centered on Tuesday and
  perhaps toward next weekend (although the latter is of very
  low confidence).

- A few of our far northern/northwest counties (especially
  Valley/western Dawson) could actually flirt with brief/patchy
  frost potential very late tonight/early Mon AM as temps could
  drop into the upper 30s, but current thinking it should
  remain JUST warm enough to keep frost at bay.

- Temperature-wise, this next week will feature what most folks
  will probably consider a pretty darn pleasant/comfortable
  stretch of early fall weather, with daily high temps mainly
  70s and overnight lows mainly 40s/50s.

- That being said, medium range models are currently exhibiting
  an unusually large spread (high uncertainty) in both the upper
  air/low level pattern for especially Thurs onward...with at
  least some chance that Thurs-Sat end up being warmer than
  currently forecast.

&&

.DISCUSSION...
Issued at 526 AM CDT Sun Sep 22 2024

-- PRIMARY CHANGES/UNCERTAINTIES/WEAKNESSES WITH THIS 7-DAY
 FORECAST PACKAGE:

- Unfortunately, expected cumulative weekend rainfall amounts
  (QPF) have continued to "free fall" after peaking as high as
  1-3" just a few days ago (this forecaster honestly can`t
  remember the last time a larger scale rain event fizzled this
  drastically). It now appears that MOST places will be lucky
  to pick up more than 0.10-0.20" (if hardly a drop in several
  counties especially north of I-80). That being said, as
  mentioned above we will likely continue to see some very
  narrow/localized bands that "overachieve" the dwindling
  expectations and give some lucky folks at least 0.25-0.75".

- Although not a "high impact" uncertainty, by far the biggest
  uncertainty apparent over the next 7 days are temperature
  trends for Thurs-Sat. Will hit on this more below, but in
  short our official forecast falls more in line with the cooler
  ECMWF solution (highs in the 70s), while the GFS suggests a
  more marked warm-up with highs climbing back well into the 80s
  to maybe even around 90. These trends bear watching, as this
  is a pretty notable spread even by Day 5-7 standards.

- A bit closer in time, one of the possible weaknesses with our
  going official forecast is a lack of at least a low-end rain
  chance in most areas for late Mon night into Tuesday daytime,
  and it`s quite possible that later forecasts will at least
  need to expand/introduce some small chances/PoPs.


-- 7-DAY FORECAST CHRONOLOGICAL DETAILS:

- CURRENT/RECENT WEATHER SCENE AS OF 4 AM:
In the big picture of the mid-upper levels, water vapor
satellite and short term model data clearly reveal a fairly
strong low pressure system centered over CO, with various
smaller pieces of energy streaming out ahead of this main low
and extending over our CWA and points east. Meanwhile at the
surface, the seasonably-strong cold front that passed through
yesterday is now well south into OK/TX, with breezy (but not
overly-strong) north winds in place over our CWA (sustained
speeds mainly 10-15 MPH/gusts 15-20+ MPH). While a good chunk of
our CWA (especially KS zones and also several counties north of
I-80) have had a dry/mostly dry night, in contrast, many places
within counties especially along the I-80 and Hwy 6 corridors
(along with Polk County north of I-80) have seen the development
of scattered to numerous rain showers...with this generally
west-southeast to east-northeast oriented swath of precip
apparently tied to a zone of concentrated mid level
convergence/saturation (somewhat evident at 700 millibars). As
of this writing, the main "rain winners" overnight have been
within a roughly 10-15 mile band extending roughly from
Holdrege-Kearney-Grand Island-Osceola...with some personal
weather stations in this band (along with Grand Island airport)
reporting at least 0.25-0.75". Overnight low temps are on track
to bottom out somewhere in the 50s most all areas...ranging from
low 50s north to upper 50s southeast.


- TODAY (daylight hours):
Although amounts will not be nearly what was once anticipated
for most areas, today still features decent chances for
scattered to numerous showers...particularly for counties south
of I-80 and into our KS zones. In the mid-upper levels, the
aforementioned "parent" upper low currently over CO will
gradually slide eastward to over the heart of our CWA by late
afternoon/early evening, but likely in a somewhat weakening
phase at it "shears out" somewhat (this weakening trend, along
with the invasion of drier air from the north with dewpoints
mainly only 40s are the basic/primary reasons for the overall
"rain event" falling short). Leaning on higher-res shorter term
models such as HRRR/NAMnest, it`s quite clear that the vast
majority of scattered to numerous rain showers today will focus
within counties south of I-80 down into KS...within the main mid
level convergence/lift zone associated with the upper wave. MOST
places will likely receive no more than 0.10-0.20" of rain, BUT
as evidenced by what`s already happened tonight there could be
localized/luckier exceptions that could continue to sneak into
at least 0.25-0.75" territory. Unfortunately for most areas
near/especially north of I-80 (except for those limited places
that already saw rain overnight), little to no rain is
anticipated. As for the rain itself, have characterized it as
simply "showers" in the official forecast, as while a very rogue
rumble or two of thunder is not out of the question, convective
instability appears quite meager and unworthy of a formal
thunder mention.

In other departments today, temperature-wise there is ZERO doubt
that this will be coolest day of these next 7, BUT high temps
continue to nudge slightly upward given the expectation of rain
showers to diminish in coverage through the mid-late afternoon
hours, along with possibly some limited/filtered sunshine
breaking through especially in our far northern counties. The
net result is highs aimed mainly low-mid 60s south to more
solidly mid 60s north. North winds will gradually/slowly ease as
the day wears on, but most of the day will generally feature
10-15 MPH with occasional gusts 15-20.


-THIS EVENING-OVERNIGHT (sunset onward):
It will take most of the night to actually get the heart of the
upper level low east of our CWA as it slowly passes overhead.
That being said, mid level saturation/lift will be on a steady
decrease. Although most models suggest it will be an almost
totally dry night (especially post-midnight), especially the
ECMWF hints at some "sneaky" lingering showers (at least
sprinkles if not spotty measurable rain) especially in some of
our eastern counties overnight, and thus have lingered/expanded some
slight Pops (20% chances) well into the night.

Really, the biggest question mark overnight involves how
efficiently/quickly clouds clear and thus how chilly temps can
manage to get. While would not be surprised to see clouds linger
a bit stubbornly especially in our southern/eastern zones with
the upper wave still passing overhead, most models are fairly
insistent that especially our northwest half will clear pretty
efficiently post-midnight. This clearing, in the presence of
very light winds thanks to dominant surface high pressure, will
likely set the stage for the coolest night our CWA has seen so
far this late summer/early fall. Currently have lows for most of
the CWA aimed from low-mid 40s northwest to mid-upper 40s
southeast. HOWEVER, especially parts of
Valley/Greeley/Sherman/western Dawson counties could perhaps
drop into the upper 30s (currently have as cold as 37-39). This
puts these areas perilously close to possible frost formation,
but current thinking is that they will remain "safe" by a few
degrees, especially given the expected very limited time
duration of temps under 40. Something to watch though.


- MONDAY-MON NIGHT:
The daytime hours appear very seasonably-pleasant, as skies will
be sunny/mostly sunny as we reside "in between" the
aforementioned departing system and another one dropping in from
the north through the Dakotas. Breezes will start out very
light, but gradually pick up a bit from the south in the
afternoon, albeit only around 10 MPH and gusts mainly under 15
MPH. High temps were raised a decent 3-4 degrees from previous
forecast, as despite the chilly start to the morning afternoon
readings should reach 71-73.

Monday night, high confidence that most of the night stays dry
(especially pre-midnight). However, especially the latest
NAM/ECMWF suggest that we may need to add a chance for light
showers/sprinkles to the late-night hours as the aforementioned
disturbance drops down from the north. Temp-wise, it will not
be quite as chilly as tonight, with lows aimed mainly 46-49.


- TUESDAY-TUES NIGHT:
In suit with the preceding Monday night paragraph, it`s starting
to look like later forecasts very well might need to
increase/expand at least slight rain chances into especially
Tues AM, as the upper wave dropping down from the north appears
to be fairly potent. Amounts would likely be minimal (no more
than a few hundredths), but again the potential is seemingly
increasing. This wave will also send another weak cold front
across the area, flipping breezes to northerly. That being said,
temps are actually expected to be slightly warmer than
Monday...most of the CWA aimed 74-77. Lows Tues night again
mainly mid-upper 40s.


- WEDNESDAY-WED NIGHT:
High confidence in our going dry forecast here, as the Tuesday
disturbance departs to our southeast/east. Thus another
seasonably-pleasant day with highs mid-upper 70s and lows upper
40s to around 50.


- THURSDAY-SATURDAY:
Honestly, this is where things get unusually uncertain in the
model world. While confidence is reasonably high that most of
our CWA will remain dry most of this time (especially Thurs),
our official forecast features some small rain chances mainly in
our eastern counties Fri-Sat, which is a nod toward the latest
ECMWF solution. In short, the 00Z ECMWF solution shows a quasi-
stationary/cutoff upper low generally centered over MO/AR
throughout this time frame, with our CWA perhaps catching some
showers along its western periphery Fri-Sat. The ECMWF also
supports our going forecast high temps in the mid-upper 70s.
However, in start contrast, the 00Z GFS solution does NOT cut
off an upper low just to our east, but instead moves it well
east and allows widespread ridging to dominate the
Central/Southern Plains. Although not reflected in our current
forecast, IF this scenario plays out, then Thurs-Sat could
easily trend 10-15 degrees warmer than currently advertised
(more 80s to possibly near-90). So plenty of uncertainty here on
the large-scale pattern and the ultimate evolution of any larger
scale trough/low over the central/eastern United
States...perhaps also influenced by possible tropical
development in the Gulf.

&&

.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
Issued at 655 AM CDT Sun Sep 22 2024

For KGRI/KEAR Airports:
- Ceiling/visibility/precipitation:
High confidence in VFR ceiling/visibility throughout, with the
only possible "catch" being the possibility of brief MVFR
visibility at some point these first 12 hours IF a steadier rain
shower happens to pass through. Speaking of which, although
KGRI/KEAR will likely remain just north of the primary area of
scattered/numerous rain showers in southern NE today, felt
enough potential still exists to maintain a basic vicinity
shower (VCSH) inclusion through 00Z (lesser chance of rain
beyond that, albeit probably not truly zero chance until closer
to 03Z). As for ceiling, today into this evening will likely
feature a mid-level VFR ceiling mainly 7-10K ft., with
scattering/clearing increasingly likely as the night wears on.

- Winds:
The overall-strongest northerly breezes of the period will focus
these first 9 hours through around 21Z (sustained around
10-12KT/gusts up to around 17KT). Thereafter, speeds will
decrease to under 5KT this-evening overnight with a somewhat
variable direction, but probably favoring some semblance of
westerly.

&&

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

&&

$$

DISCUSSION...Pfannkuch
AVIATION...Pfannkuch