Special Weather Statement, NWS North Platte, NE

Area Forecast Discussion
National Weather Service North Platte NE
720 PM CDT Wed Oct 11 2023

...Aviation Update...

.SYNOPSIS...
Issued at 300 PM CDT Wed Oct 11 2023

Key Messages:

- An anomalous storm system will begin to impact the area
  tonight, continuing through Friday bringing strong winds, heavy
  rainfall, strong to severe storms, and wintry precipitation.

- Calm, seasonable weather through weekend and early next week.

Recent GOES-16 WV and RAP 500-mb analysis showed a cut off low
pressure system centered on the Ontario/Quebec border with a
trough extending south across the northeastern CONUS. Further west
of this feature, a deep low pressure system was centered over the
state of Washington with a negatively tilted trough extending
southeast across the Great Basin. A rapidly decaying ridge was
noted across the northern Plains between the two low pressure
systems. All of these features combined has resulted in
southwesterly flow aloft across western and north central
Nebraska. At the surface, low pressure was apparent across eastern
Colorado with a weak warm front extending across northern Kansas
and a stationary front on the lee side of the Rockies, extending
into the Nebraska Panhandle. At 3P CT, temperatures ranged from
69 degrees at O'Neill to 74 degrees at Imperial.

&&

.SHORT TERM...(This evening through Friday)
Issued at 300 PM CDT Wed Oct 11 2023

The main concern in the short-term period surrounds the significant
fall system that will begin to impact the area tonight, continuing
through Friday. With multiple weather hazards expected, make sure
to continue the forecast for the most up to date information.

The focus for tonight revolves around the potential for strong to
severe storms capable of producing large hail, gusty winds, and
locally heavy rainfall for portions of central and north central
Nebraska. The aforementioned surface low will continue to deepen and
push eastward along the Nebraska/Kansas border tonight with a warm
from lifting northward across the area. As this occurs, widespread
thunderstorm development is expected along and ahead of the
frontal boundary. On the eastern periphery of the intensifying
cyclone, a 30-50kts LLJ combined with 1,000+ J/kg MUCAPE and
30-40kts 0-6km Bulk Shear will create an environment that will be
supportive of isolated to scattered strong to severe storms
capable of producing large hail and gusty winds. This round of
convection will be isolated to widely scattered due to continued
mid-level WAA creating a cap thus lowering forecaster confidence.
The greatest severe threat timing is from 9P to 3A CT across
central and north central Nebraska with general thunderstorms
expected to continue beyond 3A CT for all of western and north
central Nebraska.

As we head into Thursday afternoon, focus quickly shifts to a
potentially more impactful second round of strong to severe
thunderstorms expected to effect portions of central and north
central Nebraska. Though some discrepancies amongst model
solutions exist on exact location, the previously mentioned
surface low will push northeast into north central Nebraska
Thursday afternoon with a triple point and sharpening warm front
just ahead of the low. The southerly LLJ quickly increases to
40-50kts combined with steepening mid-level lapse rates (8+ C/km)
due to cooling aloft, modest destabilization (MLCAPE ~1,500+ J/kg)
and increasing 0-6km Bulk Shear (40kts+) will create an
environment supportive of organized thunderstorm development. The
main threat is large hail, but severe wind and a couple of
tornadoes are also possible. The greatest tornado threat lies
across portions of central and north central Nebraska where the
low-level shear will become enhanced near the triple point and
locally backed winds are expected. This is in line with similar
thinking of the previous shift and SPC's westward expansion of the
Slight Risk of Severe Thunderstorms. This will need to be closely
monitored as we head into the near-term and details become more
fine scale. Initiation is expected by early-afternoon with the
severe threat increasing after 1P CT and the threat exiting the
forecast area around 8P CT. Make sure to take the necessary
precautions to prepare for this event by having an emergency kit
ready and multiple way to receive warning information (weather
radio, TV, cell phone, radio, etc.).

Heading into Thursday night and Friday we begin to shift focus to
strong winds across all of western and north central Nebraska and
possibly the first taste of winter across northwest Nebraska. As the
surface low begins to exit northeast out of the area Thursday night
into Friday, the SPG will tighten on the backside of the departing
system. Though wind gusts have trended down somewhat from the
inherited forecast, it will be a gusty and chilly day across
western and north central Nebraska. With high temperatures in the
40s and northerly wind gusts of 50+ mph, wind chill values will
struggle to climb out of the 30s. Combining these conditions with
continued precipitation on Friday, it will be quite the gloomy
fall day for the area. Make sure to store or secure loose items
such as holiday decoration and patio furniture before these strong
winds encompass the area late Thursday into Friday.

On the backside of the departing system, wraparound precipitation
will develop with deep forcing for ascent occurring and dynamic
cooling aloft. Model guidance continues to hint at the snow
potential for northwestern Nebraska, however, forecast confidence
continues to remain low on a complete transition to snow. Any snow
that does fall will be heavy and wet with accumulations nearing
an inch or two possible. Further east towards Highway 83, some
locations may see a rain/snow mix with no accumulations expected.
The primary concern with this period of winter weather is the
potential for reduced visibilities as the strong winds combine
with the precipitation, especially in the Friday morning commute
timeframe.

In regards to storm total precipitation amounts for this system,
we are beginning to see a more northward trend in the QPF
amounts. A swath of 1-2"+ total are expected through Friday
afternoon for areas north of Highway 2, with amounts tapering off
to the south. This is highlighted by the EFI (Extreme Forecast
Index) for QPF which is continuing to suggest increased confidence
of an anomalous event, such that the SoT (Shift of Tails) is
greater than 2 across portions of the northern Sandhills. As usual
with thunderstorms, locally higher amounts will be possible and
could lead to localized flooding.

.LONG TERM...(Friday night through Wednesday)
Issued at 300 PM CDT Wed Oct 11 2023

As the surface low moves out of the area, wrap around precipitation
remains in the area early Saturday morning, but mostly clears out by
Noon. The upper level trough moves further east as well, settling
western and north central Nebraska under upper-level convergence.
Guidance is pointing to a fairly short lived Omega block setting up
at 500-mb over the region this weekend. As the Omega block
collapses, the area remains along an upper level ridge on Monday.
There is a bit of uncertainty with the amplitude of the trough/ridge
pattern, but in general the area stays under or just to the north of
the upper-level jet stream, which will contribute to keeping
temperatures this weekend and early next week feeling more like fall
weather.

As the upper pattern continues to evolve, a shortwave trough begins
to develop over Montana on Tuesday, though there is disagreement on
timing of the set up, with the European solutions being quicker and
more aggressive compared to GEFS solutions. This is further
reinforced in cluster analysis for next Wednesday, with the more
heavily weighted European solutions progressing the shortwave over
western and north central Nebraska, indicating potential for
precipitation. Solutions more heavily influenced by the GEFS and
Canadian ensembles are a bit slower with the progression and
intensity of this shortwave, and are less optimistic on
precipitation. Either way, this will merit watching as further
ensemble runs may give a better idea on timing and potential for
precipitation.

&&

.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 711 PM CDT Wed Oct 11 2023

Conditions are expected to deteriorate across all of western and
north central Nebraska later tonight and into Thursday. A strong
storm system will bring widespread IFR and MVFR ceilings and
precipitation to the area starting tonight. Southwest into
central Nebraska will be the last to see the lower ceilings
arrive, likely not until Thursday afternoon. Winds will also be
gusty, over 30 kts at times, especially across northern Nebraska.

&&

.LBF WATCHES/WARNINGS/ADVISORIES...
High Wind Watch from Thursday evening through Friday evening for
NEZ004>010-022>029-035>038-056>059-069>071-094.

&&

SYNOPSIS...Viken
SHORT TERM...Viken
LONG TERM...Richie/Viken
AVIATION...Taylor

Hazardous Weather Outlook
National Weather Service North Platte NE
322 PM CDT Wed Oct 11 2023

NEZ004>010-022>029-035>038-056>059-069>071-094-122030-
Sheridan-Eastern Cherry-Keya Paha-Boyd-Brown-Rock-Holt-Garden-Grant-
Hooker-Thomas-Blaine-Loup-Garfield-Wheeler-Arthur-McPherson-Logan-
Custer-Deuel-Keith-Perkins-Lincoln-Chase-Hayes-Frontier-
Western Cherry-
322 PM CDT Wed Oct 11 2023 /222 PM MDT Wed Oct 11 2023/

This Hazardous Weather Outlook is for portions of western and north
central Nebraska.

.DAY ONE...Tonight.

A few thunderstorms will be capable of large hail and gusty winds
late this evening and overnight for parts of central and north
central Nebraska. The main area of concern is generally north of a
line from Tryon to Ansley and east of a line from Tryon to Cody. The
greatest threat for severe storms is between 9 PM and 3 AM CDT.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday.

A powerful storm system continues to present multiple hazards to the
forecast area Thursday through Friday.

Additional strong to severe storms are possible on Thursday, with a
threat for a brief tornado, large hail, and strong winds. The
primary threat area will be across central and north central
Nebraska, mainly east of a Curtis, to Tryon, to Valentine line.

Prolonged rain will be possible across the Sandhills and north
central Nebraska Thursday into Friday, including the potential for 1
to 3 inches. Locally higher amounts are possible along the South
Dakota and Nebraska border.

Colder air arriving Thursday night into early Friday may result in a
wintry mix of rain and snow. The main threat for a wintry mix is west
of a line from Cody to Big Springs. Snow accumulations of up to an
inch are possible, mainly over the Pine Ridge of northern Sheridan
County.

Northerly winds gusting 50 to 60 MPH Thursday night through Friday
afternoon across the area, will produce strong crosswinds on east to
west routes. Winds combined with precipitation and cold temperatures
may be hazardous to young livestock.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed Thursday afternoon over portions of
central Nebraska, mainly east and south of a line from Arnold, to
Dunning, to Bassett and O'Neill.

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