Damaging Winds in Nebraska, September 7, 2023

AREA FORECAST DISCUSSION
National Weather Service Hastings NE
722 PM CDT Thu Sep 7 2023

...Aviation Update...

.DISCUSSION...(This evening through Thursday)
Issued at 450 PM CDT Thu Sep 7 2023

Key Messages:

* Poor air quality will continue to impact the region for about
  another 24 hours, or so.

* There is a Marginal Risk for a few severe thunderstorms this
  evening into early overnight, mainly north of the Tri-Cities.

* A stronger storm system will bring better and more widespread
  rain and thunderstorm chances this weekend into early next week.
  Once again, there is a Marginal Risk for a few severe
  thunderstorms with the initial cold front Saturday afternoon and
  evening.

* Expect much cooler and more fall-like temperatures for the brunt
  of next week.

Forecast Details:
It's been a fairly quiet and warm day across the area thus far,
though once again on the smokey/hazy side. Visibility has been
reduced to 4-5sm in spots, even this aftn despite better mixing,
and PM 2.5 levels remain in the "Unhealthy" category per the NDOT
sensor near GI. 12Z HRRR backed off of bringing any significant
relief to the area today or tonight as it appears any push of
cleaner air remains W of the area this aftn, and any tstm
development remains fairly spotty/limited tonight. Thus, after
collaboration with surrounding offices and NDEE, the Air Quality
Alert has been extended into Fri aftn. Hopefully by then
additional mixing and incr deep layer flow will be enough to see
improving conditions at the surface.

Tstm chcs will be on the incr this eve, at least for N portions of
the CWA, as a quick moving disturbance slides through the area.
Tstm chcs look to stem from two main areas/regimes:
1)southward extension/development of WAA-driven activity currently
running from around Sioux Falls to Norfolk and 2)within field of
agitated CU in hot/deeply mixed environment over NW Sandhills. The
former area could pose a risk anytime within next few hrs, with
the later area probably not affecting far NW zones until after
~01Z per latest HRRR trends. There remains a Marginal Risk of
severe per SPC, though the areal coverage has decr compared to
earlier outlooks. Deep layer shear is strong thanks to veering in
low to mid levels and decent H5 speed max, but instability is
certainly lacking given dew points only in the 50s. Latest CAMs
suggest main window being 01Z to 05Z and limited to areas mainly N
of the Tri-Cities. Marginally severe hail would probably be the
main threat, though gusty winds can't be ruled out.

Quiet, but warm, conditions are expected Fri into Fri night with
aftn high temps ranging from mid 80s to low 90s. Should be great
early-fall conditions for area football games Fri eve as temps
fall back from the low 80s around 7PM to upper 60s to 70s by 10PM
amidst light winds and improving air quality.

Pattern becomes more active this weekend as a decent trough moves
into the Great Lakes region and forces a cold front into central
Plains. The initial arrival of the sfc front looks to be into NW
zones at some point Sat aftn-eve and perhaps provide enough
forcing for scat sfc based tstms. Models are somewhat mixed with
this potential as low level moisture again looks to be lacking.
Areas ahead of the front will see warm conditions once again, and
gut feeling is that magnitude of mixing combined with decent sfc
convergence invof low pressure/triple point somewhere near/just W
of far W CWA, will indeed be enough to spark some sct tstms after
21Z. Deep layer shear should be sufficient for svr activity given
substantial veering with height and at least modest H7-H5 wrly
flow ~30kt, with overall instability again being potential
limiting factor. Some models suggest a potentially narrow tongue
of enhanced low level moisture immediately ahead of/SE of
aforementioned triple point, which if it indeed pans out could
lead to a few hr window for somewhat enhanced svr threat over far
W/NW zones, but confidence on these details is still limited.

None of the models barrel the front through the area Sat night and
instead keep a nearly stationary boundary draped across at least
portions of the CWA through the remainder of the weekend. Thus,
would expect iso-scat tstms to continue and/or redevelop off and
on Sun into Sun night. Models have even lesser instability on Sun
due to incr poor mid level lapse rates - so anything more than
iso/marginal svr threat appears unlikely at this time. Models
suggest overall-greatest shwr/tstm chcs/coverage should come Sun
aftn into Sun night, esp. for areas W and S of Tri-Cities, as
additional upper level support in the form of coupled upper jet,
deep layer frontogenesis, and mid level height falls overspread
the area. Am a bit concerned models are over-doing the the NE
extent of pcpn (which would include the Tri-Cities N and E) as
sometimes these types of events tend to "hug" the higher terrain
further W and low level dry air filters in from the NE.
Nonetheless, looks to be the best rain chcs most of the CWA has
seen in quite some time.

Should see gradual drying trend on Mon as upper trough continues
to dig through N Plains/Upper MS Valley and force the front even
further S/SE. Other than perhaps a return of Canadian smoke (???),
the biggest story next week will be the much cooler and more
fall-like temperatures with highs in the upper 60s-70s and lows in
the upper 40s-50s (possibly even low 40s(!) Tue AM for mainly
areas like LXN to ODX) expected each day. Assuming smoke doesn't
become a significant issue in the cool Nrly flow, should see
prolonged period of excellent conditions for outdoor activities
next week.

&&

.AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Saturday)
Issued at 721 PM CDT Thu Sep 7 2023

- General overview:
High confidence in VFR ceiling throughout the period and and
rain/thunderstorm-free conditions through at least the vast
majority of the period. That leaves the following primary 3
concerns: 1) reduced visibility from Canadian wildfire smoke
(MVFR probable through much of the period)...2) at least a brief
window- of- opportunity for a passing thunderstorm this evening
(especially at KGRI), which could yield gusty outflow winds and
perhaps small hail...3) Even if no thunderstorms directly affect
KGRI/KEAR and remain off to the north (currently deemed the most
favorable scenario), there are increasing signs that an outflow
boundary could arrive later this evening and "disrupt" the
prevailing wind field with a few hours of more northerly winds.

- Wildfire-smoke related visibility details:
Although KEAR is starting off high-end VFR, based on nearby obs
and best-available model data (honestly this is more of a "best
guess" given that models are struggling in this unusual smoke
regime), expect MVFR to prevail through most of the first 18 hours
of the period at both sites. Have indicated a return to low-end
VFR for the final 6 hours Friday afternoon as gradual improvement
in low-level smoke concentration continues...but again this is not
an overly-high confidence situation.

- Thunderstorm details:
Although some of the latest/usually-reliable short-term model data
keep any isolated/scattered thunderstorm activity this evening at
least 30-50 miles north of KGRI/KEAR, it appears that it could be
just enough of a "close call" for KGRI that decided to introduce
a generic "vicinity thunderstorm" (VCTS) 03-06Z, with KEAR looking
"safer" and thus have kept VCTS out for now. IF any storms do
directly impact especially KGRI, gusty outflow winds of 30+KT and
perhaps small hail cannot be ruled out.

- Winds:
Aside from any possible thunderstorm outflow-related influences,
winds should not be a significant concern, with the vast majority
of the period likely to feature sustained speeds near-to-below
10KT out of a southeasterly or easterly direction. However, there
are signs that especially the 04-06Z time frame this evening
could feature the arrival of a convective outflow boundary that
could abruptly shifts winds to some variation of northerly, with
at least brief gusts of 20+KT possible. This is currently not
reflected in 00Z TAFs, but will monitor upstream obs/trends for
possible amendments.

&&

.GID WATCHES/WARNINGS/ADVISORIES...
NE...NONE.
KS...NONE.
&&

DISCUSSION...Thies
AVIATION...Pfannkuch

Hazardous Weather Outlook...UPDATED
National Weather Service Hastings NE
758 PM CDT Thu Sep 7 2023

NEZ039>041-046>049-060>064-072>077-082>087-090100-
Valley-Greeley-Nance-Sherman-Howard-Merrick-Polk-Dawson-Buffalo-
Hall-Hamilton-York-Gosper-Phelps-Kearney-Adams-Clay-Fillmore-
Furnas-Harlan-Franklin-Webster-Nuckolls-Thayer-
758 PM CDT Thu Sep 7 2023

This Hazardous Weather Outlook is for south central Nebraska.

.DAY ONE...Tonight.

Through at least part of the overnight hours, isolated to
scattered thunderstorm activity is possible within primarily the
northeast half of the area, or mainly north/east of a line from
roughly Ravenna, to Hastings, to Hebron. The majority of storms
will be weak. However, through around 1 AM, there is a Marginal
Risk that a few strong to marginally-severe storms could occur,
capable of producing mainly gusty winds of 50 to 60 MPH and
perhaps fairly small hail up to around nickel size.

In addition to any thunderstorms overnight, areas of smoke from
Canadian wildfires will continues to cause reduced visibility and
poor air quality, and an Air Quality Alert issued by the Nebraska
Department of Environment and Energy remains in effect for the
entire area. Please refer to the Air Quality Alert statement for
more details.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday.

Through at least a portion of Friday daytime, poor air quality
due to Canadian wildfire smoke will continue, and an Air Quality
Alert issued by the Nebraska Department of Environment and Energy
remains in effect for the entire area through 3 PM Friday. Please
refer to the Air Quality Alert statement for more details.

Between Saturday and Monday, there will be periodic chances for
thunderstorms across the area, with the overall highest chances
focused Saturday night into Sunday and Sunday night. Widespread
severe weather is unlikely, but there is a Marginal Risk for a
few strong to severe thunderstorms Saturday afternoon and evening,
mainly within the northwest half of the area.

.SPOTTER INFORMATION STATEMENT...

Spotters are encouraged to report any hail or wind gusts of 50 MPH
or higher that might occur this evening.

&&

More information may be obtained at the following web page:
   https://www.weather.gov/hastings

KSZ005>007-017>019-090100-
Phillips-Smith-Jewell-Rooks-Osborne-Mitchell-
758 PM CDT Thu Sep 7 2023

This Hazardous Weather Outlook is for portions of north central
Kansas.

.DAY ONE...Overnight.

The probability for widespread hazardous weather is low.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday.

Between Saturday and Monday, there will be periodic chances for
thunderstorms across the area, with the overall highest chances
focused Saturday night into Sunday and Sunday night. Widespread
severe weather is unlikely, but there is a Marginal Risk for a
few strong to severe thunderstorms Saturday afternoon and evening,
mainly for areas west of Highway 281.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will not be needed through tonight.

&&

More information may be obtained at the following web page:
   https://www.weather.gov/hastings

Pfannkuch