Severe Thunderstorm Warning 271, NWS North Platte, NE

Area Forecast Discussion...UPDATED
National Weather Service North Platte NE
625 PM CDT Thu Aug 3 2023

...Aviation Update...

.SYNOPSIS...
Issued at 324 PM CDT Thu Aug 3 2023

Key Messages:

- Severe storms possible tonight with damaging winds, large hail and
  heavy rain possible.

- Marginal risk for severe storms Friday afternoon/evening.

- Another threat for severe storms Saturday afternoon/evening
  mainly over eastern and and southeastern portions of the
  forecast area.

H5 analysis this morning had high pressure anchored over the
Arklatex with a ridge extending north into the Ozarks and
southeastern Kansas. Further west, a closed area of low pressure was
located over eastern Idaho. Downstream of this feature, a weaker
shortwave trough extended from central Nebraska into northern
Kansas. Both of these features were south of a northern stream ridge
which extended from south central Canada, north into eastern
portions of the NW Territories of Canada. Another feature of note
this morning was a weak shortwave off the coast of northern
California. At the surface, a quasi-stationary front extended from
the northern Texas Panhandle, east-northeast into far southern
Kansas and the central Ozarks. This afternoon, a weak surface trough
extended from the western Panhandle into far southwestern Nebraska.
Skies were partly to mostly cloudy across western and north central
Nebraska this afternoon. Temperatures as of 2 AM CDT, ranged from 79
degrees at Gordon to 85 degrees at Imperial.

&&

.SHORT TERM...(This evening through Friday night)
Issued at 324 PM CDT Thu Aug 3 2023

The threat for severe storms and possibly heavy rain tonight are
the main forecast concerns. Late this afternoon, a lead shortwave,
associated with the closed low over eastern Idaho, will cross
northern Colorado and southern Wyoming. Thunderstorms are expected
to initiate along the I25 corridor from eastern Wyoming to Denver
around 20z this afternoon. Activity will approach the western
border of the forecast area around 23z this evening, hitting the
highway 83 corridor in the 02z to 04z time frame. The latest HRRR
runs this morning along with support from the 4KM NAM and NAM12
solns have slowed down the onset of thunderstorms tonight. Taking
these solns into account, keeps storms out of the forecast area
through 23z this evening. Activity crosses into the eastern
panhandle around 00z, then hits the highway 83 corridor around 03z
this evening. With the later expected timing, went ahead and made
adjustments to this afternoon's forecast and slowed down the
progression of storms tonight. With respect to the threat for
severe storms tonight, two main modes/hazards are expected. First,
there will be a threat for large hail, mainly west of highway 61
early this evening as there is a threat for more discrete storms
in these areas. Mid level lapse rates along with SB CAPE of
1500+J/KG, straight hodographs and effective bulk shear of 30 KTS
will be enough to support this threat. Second, as the evening
progresses, these storms are expected to congeal into a line as
they approach the highway 83 corridor. The latest NAM12 soln this
morning is indicating a nice area of downdraft CAPE in excess of
1000j/kg across southwestern Nebraska and northwestern KS this
evening which would facilitate strong winds. The HRRR runs this
morning, along with the 12z-4km NAM soln is also indicating some
bowing structures with their forecast reflectivity products later
this evening. These signatures are most prolific from far SW
Nebraska into northern Kansas. Another concern for tonight's
forecast is the threat for flood potential across portions of
southwestern Nebraska. Locations across Frontier, Hayes and
portions of Lincoln county, saw rainfall amounts of 2 to as much
as 5 inches of rainfall last night. The heaviest rainfall was from
eastern Hayes, into Frontier county. This was on top of heavy
rain which also occurred Tuesday night from far eastern Hayes into
Frontier county. With the heavy rain in these areas over the past
couple of nights, am concerned with flash flooding potential
tonight. Forecast PWAT's are between 1.25 and 1.5 inches early
this evening in SW Nebraska, so plenty of moisture is available
for heavy rain. With this in mind and after conversing with
emergency management, will hoist a flood watch for Hayes and
Frontier counties for tonight through Friday morning. There still
is the potential for 1 to 2 inches of rainfall in these areas,
although storm motion should be faster tonight compared to last
night. On Friday the upper level low will track into northwestern
South Dakota. Showers and thunderstorms from the overnight will
gradually lift east of the forecast area by mid morning in the
eastern forecast area. Slightly drier air aloft will try to push
into the area Friday, however, southerly low level winds will
allow boundary layer air to remain in place across the area. PWATS
Friday afternoon will be around 1.25 inches. Slightly less than
tonight's but still enough moisture to support precipitation and
thunderstorm development Friday afternoon/night. With afternoon
heating and destabilization ahead of a shortwave rotating around
the southern periphery of the upper level low, thunderstorms will
develop Friday afternoon over the higher terrain of eastern
Wyoming, western Nebraska and northeastern Colorado. Aided by a
weak frontal passage, storms will track east into the evening and
nighttime hours. Storm coverage Friday night is expected to be
less than tonight's as low level moisture is not as robust. Severe
storms will remain in play Friday night as surface to 6 KM shear
remains in the 30 to 35 KT range.

.LONG TERM...(Saturday through Thursday)
Issued at 324 PM CDT Thu Aug 3 2023

A second, stronger cold front will be forced through the forecast
area Saturday. Showers and thunderstorms will fire INVOF this
feature Saturday afternoon and evening. As was the case overnight,
this feature is faster compared to yesterdays model runs. That
being said the severe threat appears to be south and east of the
forecast area. Northwesterly flow aloft will develop early next
week and persist through midweek. The pattern will amplify
somewhat with a trough developing across the upper midwest into
the Ohio Valley. High pressure, currently over the Arklatex, will
drift west into northern Mexico and the southwestern CONUS midweek
amplifying a ridge across the western third of the CONUS. The
northwesterly flow will be fairly active with periodic
disturbances bringing daily precipitation chances to the Central
Plains. Temperatures will be below normal in the extended periods
with highs in the 70s Sunday and Monday, transitioning to 70s to
lower 80s Tuesday, Wednesday and Thursday.

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 624 PM CDT Thu Aug 3 2023

Thunderstorms on the CO/WY high Plains this evening are expected
to move east through wrn and ncntl Nebraska overnight. Storm
activity is expected to become more numerous across wrn Nebraska
as it develops into a north-south line of storms. This process
should be underway by 02z-03z this evening. It is worth noting
this forecast may not verify. Storms could remain mostly isolated
as they move east overnight. Whatever develops should exit ncntl
Nebraska by 12z-15z Friday morning.

An area of MVFR/IFR ceilings are expected to develop across wrn
and ncntl Nebraska 09z-15z Friday morning affecting areas south of
highway 20. VFR/local MVFR should be widespread by 18z.

Isolated thunderstorms are possible west of highway 61 Friday
afternoon; from about 21z onward.

&&

.LBF WATCHES/WARNINGS/ADVISORIES...
Flood Watch through Friday morning for NEZ070-071.

&&

SYNOPSIS...Buttler
SHORT TERM...Buttler
LONG TERM...Buttler
AVIATION...CDC

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Special Weather Statement
National Weather Service North Platte NE
752 PM MDT Thu Aug 3 2023

NEZ022-056-040230-
Deuel NE-Garden NE-
752 PM MDT Thu Aug 3 2023

...Strong thunderstorms will impact portions of southwestern Garden
and Deuel Counties through 830 PM MDT...

At 751 PM MDT, Doppler radar was tracking strong thunderstorms along
a line extending from 10 miles southwest of Lisco to near Lodgepole
to 6 miles north of Twin Buttes. Movement was east at 30 mph.

HAZARD...Wind gusts of 50 to 55 mph and penny size hail.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects. Minor damage to outdoor objects is
         possible.

Locations impacted include...
Chappell, Oshkosh, Lewellen, Ash Hollow State Historical Park, Mount
Vernon, Intersection of Highway 27 and 9 Mile Road, Bluewater
Battlefield State Historical Park and Windlass Hill.

This includes the following highways...
 Highway 92 near mile marker 115.
 Interstate 80 in Nebraska between mile markers 78 and 100.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

A Severe Thunderstorm Watch remains in effect until 900 PM MDT for
the Panhandle of Nebraska.

&&

LAT...LON 4146 10215 4122 10210 4100 10220 4100 10261
      4139 10261 4140 10264 4145 10264
TIME...MOT...LOC 0151Z 265DEG 27KT 4136 10271 4118 10264 4101 10277

MAX HAIL SIZE...0.75 IN
MAX WIND GUST...55 MPH

Brown

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