Severe Thunderstorm Warning 349, NWS North Platte, NE

Area Forecast Discussion
National Weather Service North Platte NE
622 PM CDT Thu Sep 21 2023

...Aviation discussion...

.SYNOPSIS...
Issued at 215 PM CDT Thu Sep 21 2023

Key Messages:

Severe potential tonight though Friday night. In addition expect
locally heavy rainfall to occur, with highest chances for this
occurring across northern Nebraska.

A cold front moves through the area Saturday with northwest winds
developing.

Mainly dry weather is expected Sunday into the middle of next week.
Temperatures should mostly be near normal during this time.

&&

.SHORT TERM...(This evening through Friday night)
Issued at 215 PM CDT Thu Sep 21 2023

Potent upper level low pressure is located across across the Pacific
Northwest this afternoon. Diffluent flow aloft coupled with mid-
level WAA has contributed to training/redeveloping convection across
northern NE. Locally heavy rainfall has already occurred with 2-3"
recorded in a few spots. Continued scattered redevelopment is
expected to continue across northern NE well into the evening
tonight...as mid-level WAA continues and upper level forcing
gradually increases.

As far as the severe aspect goes, it is a bit complicated. An
earlier MCS across northeast NE contributed to an outflow boundary
that extends from near Holdrege to North Platte. A surface low is
located across far northeast CO. A dryline/steep low-level lapse
rates have pushed eastward into northwest KS south of the low where
temperatures have warmed to near 90. Consecutive runs of the HRRR
develop convection on the nose of the steeper low-level lapse rates
across northwest KS/far SW Neb. As the convection develops it will
push east-northeastward into moist backed southeast low-level flow.
Any activity that develops should quickly become supercellular. Very
steep mid-level lapse rates will contribute to a large hail threat.
Tornado threat is also there, as the backed southeast low-level flow
will result in curved hodographs and effective SRH locally up to 300
m2/s2. Will have to monitor the location of the stalled outflow
boundary which could locally enhance the tornado threat. Convection
will likely increase further into the mid-evening hours across
portions of the Sandhills central/north central NE as the low-level
jet increases. This activity would be more elevated in nature but
could still pose a hail threat.

Confidence in the overall evolution convection/severe is low on
Friday. Parts of northern into central will likely see an overcast
stratus deck for much of the day. Still mid-level WAA will continue
and elevated convection will certainly be possible amid favorable
forcing aloft. A surface low will remain anchored across far
southwest NE, with steep low-level lapse rates again nosing into
this area. This could certainly be an area for initiation, with an
unstable and highly sheared environment located downstream. A marked
increase in convection is expected Friday evening as the better
dynamics overspread the Northern Plains as the upper low approaches.
Northern NE will be located nearer the better dynamics/forcing and
thus the higher pops will be located across this area...decreasing
to the south.

.LONG TERM...(Saturday through Thursday)
Issued at 215 PM CDT Thu Sep 21 2023

A vertically stacked (weakening) upper low should be located across
SD Saturday. A cold front will swing southeastward across the area
as the surface low migrates across SD. The focus for severe will
shift east of the area along the cold front during afternoon. Breezy
northwest winds should overspread our area of western and north
central Nebraska. The continued weakening upper low will remain
anchored across the SD vicinity though early next week. An isolated
shower could occur across far northern NE during this time, but will
be located in the drier sector of the upper low. Temperatures will
generally average near normal during this timeframe. Upper level
ridging may try to nose into the area mid-week ahead of developing
upper level troughing across the western CONUS.

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 617 PM CDT Thu Sep 21 2023

Ongoing convection will continue to affect TAF sites, especially
KLBF, through the first part of the valid period. Expect
stratus/fog will bloom overnight, with some additional shower and
thunderstorm development overnight as the low level jet
amplifies. Fog/stratus will persist into Friday morning before
dissipating by the afternoon. Additional convection will develop
Friday afternoon but with low confidence in location/timing will
not mention so late in the period and allow later guidance a
chance to refine the forecast.

Strong, erratic wind gusts are possible near any thunderstorms.

&&

.LBF WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

SYNOPSIS...Taylor
SHORT TERM...Taylor
LONG TERM...Taylor
AVIATION...MBS

Hazardous Weather Outlook
National Weather Service North Platte NE
324 PM CDT Thu Sep 21 2023

NEZ004>010-022>029-035>038-056>059-069>071-094-222030-
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-
324 PM CDT Thu Sep 21 2023 /224 PM MDT Thu Sep 21 2023/

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

.DAY ONE...This afternoon and tonight.

Thunderstorms tonight may be capable of producing very large hail,
damaging winds, locally heavy rain, and even a tornado or two. The
greatest threat of flooding lies across far north central Nebraska,
generally along and north of Highway 20 from Valentine to O'Neill.
The higher potential for a tornado or two would be across southwest
Nebraska.

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

Strong to severe thunderstorms will be possible Friday evening and
night. The main threats are damaging winds, large hail and possibly
an isolated tornado.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed this evening.

Taylor

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