-- Discussion containing changed information from previous version are highlighted. --
519
FXUS63 KLBF 251037
AFDLBF

Area Forecast Discussion
National Weather Service North Platte NE
537 AM CDT Sat May 25 2024

.KEY MESSAGES...

-  Strong to severe thunderstorms are possible across much of
   western and north central Nebraska this evening.

-  Additional showers and thunderstorms are expected Sunday,
   though the threat for severe weather appears low at this
   time.

-  A brief lull in precipitation is on tap for Memorial Day,
   before a more active weather regime and a potential return of
   severe weather middle to late week.

&&

.SHORT TERM /THROUGH SUNDAY NIGHT/...
Issued at 345 AM CDT Sat May 25 2024

Currently, temperatures have fallen into the 40s to low 50s across
the area, with scattered high clouds streaming in aloft from the
west. Winds have begun to transition southerly, in response to
increasing lee cyclogenesis across eastern Colorado. Aloft, broad
zonal flow was noted, with an upper low centered over southeastern
Manitoba. Another shortwave trough was moving eastward into the
Intermountain West.

For today, the primary concern will be the threat for strong to
severe thunderstorms, in association with the aforementioned
shortwave trough and associated surface low, progged to eject
eastward out of Colorado into western Kansas this evening. As
surface cyclogenesis persists into this afternoon, a warm front
is expected to lift northward through the southern and central
Plains, reaching potentially as far north as south central
Nebraska late this evening. Current dewpoints across western and
north central Nebraska sit in the upper 30s to low 40s, with
50F+ dewpoints as far north as northern Oklahoma and 60F+
dewpoints locked south of the Red River. This lends some
uncertainty to the exact nature of any severe threat today, and
trends in moisture return bear watching as we head into this
afternoon. As southerly flow strengthens this afternoon,
dewpoints are progged to rise out of the 40s into the lower 50s
by early evening. Wind gusts of 30-35 miles per hour are
anticipated across the entire area this afternoon from the
south. More "just in time" moisture of ~55F dewpoints may reach
as far north as areas south of I-80 and east of HWY 83. The
limited boundary layer moisture will hold instability back,
though ample cold air aloft and steep lapse rates in the mid-
levels will overcome this enough to promote some threat for
strong/severe storms.

By 3-4 PM CDT, high based convection should begin to initiate across
the high terrain of WY, as the surface low ejects eastward into far
western Kansas, dragging an associated cold front into the
Panhandle. High-res guidance continues to come into better agreement
with the handling of this convection, with at least a broken line of
convection ahead of the front translating quickly from west to east
across the area. This should approach the HWY 83 corridor
around 6-8 PM CDT and then begin to exit into eastern Nebraska
by 10-11 PM CDT. Forecast soundings ahead of the frontal
boundary are characterized by ample deep layer shear, with
rather long and largely straight hodographs with height. This,
along with the steep lapse rates aloft, would at least support
some hail threat locally. However, the expected more strongly
forced linear storm mode would likely hinder this threat
somewhat. That said, will have to watch the southern most storm
on the line for a higher threat for hail, especially
considering this portion of the line segment would have the
richest boundary layer moisture/instability to work with. The
most prevalent threat for much of the area looks to come in the
form of damaging winds. High LCLs and deep inverted-v low level
thermodynamic profiles suggest ample sub-cloud layer
evaporation, and the potential for acceleration of downdrafts.
In fact, some high-res guidance paints the potential for
localized gusts approaching as high as 70mph in the fast moving
line this evening. Any tornado threat looks to be limited to the
southern end of the line, where the deeper moisture reaches
(likely areas near/south of I-80 and east of HWY 83). This would
also likely be tied to the low level jet strengthening
near/after sunset, though boundary layer stabilization after
dark does add additional uncertainty.

The surface cold front clears the area by Midnight Sunday, with
at least a brief period of increasing cold advection in its
wake. This will lead to highs ~5-10F cooler tomorrow than today.
Additionally, scattered shower and thunderstorm development is
expected into Sunday afternoon, in response to another shortwave
quickly moving through the area immediately behind Saturday`s
shortwave trough. Some instability remains across the area
Sunday afternoon, though weak deep layer shear should keep any
threat for strong to severe storms low. Any showers/thunderstorms
look to quickly exit the area Sunday evening, as the shortwave
begins to exit the area and subsidence increases aloft.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
Issued at 345 AM CDT Sat May 25 2024

Next week looks to begin quieter, as upper ridging begins to amplify
across the central Plains on Memorial Day. In fact, the holiday looks
to be a pleasant weather day, with highs in the low to middle
70s and sunny skies, though winds will be breezy from the
northwest.

The brief lull in the active regime looks to come to an end by
midweek, as upper troughing establishes over the Intermountain West
by Wednesday. This leads to strengthening and broad west-southwest
flow aloft across the Plains. Low-level flow looks to remain
persistent southerly, with guidance indicating the best
moisture return of the season into Thursday (low/mid-60
dewpoints). This looks to lead to a multi-day threat for severe
thunderstorms, potentially beginning as early as Tuesday and
persisting until a cold front arrives sometime Friday. Longer
range deterministic/ensemble guidance is already hinting at
daily convection rolling eastward off the higher terrain,
reaching the area in the late afternoon/evening hours. The
overlap of strong, deep layer wind fields and ample instability
(especially Thursday) suggest a favorable background environment
for supercellular convection across western Nebraska Wed-
Thursday. This is also supported by pattern recognition of past
severe weather episodes for western Nebraska. Mesoscale details
will likely drive the threat each day, though this will need to
be monitored closely for an increasing threat for (significant?)
severe weather in the middle part of next week.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
-- Changed Discussion --
Issued at 535 AM CDT Sat May 25 2024

No changes to previous reasoning as low level wind shear will
continue for an hour or two after daybreak with a low level jet
dissipating over central Nebraska. Otherwise, expect VFR
conditions with light winds at the surface through early this
morning. There may be a few sprinkles around from some mid
clouds but looking at observations under current radar echoes do
not see much in the way of any precipitation reaching the
ground so will maintain dry conditions and amend if necessary.
Winds will become gusty as diurnal heating mixes the boundary
layer this morning with gusts to 30kt at KLBF but a bit lower at
KVTN. Expect widely scattered showers and thunderstorms to
develop late in the day and will use VCTS for a couple of hours
toward 00Z before returning to dry VFR conditions by the end of
the valid period. Probabilities for some low clouds and fog are
quite high across northern/eastern Nebraska so will include at
KVTN toward the end of the valid period where confidence is
high, but keep out of KLBF where confidence is not yet high
enough.
-- End Changed Discussion --

&&

.LBF WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

SHORT TERM...Brown
LONG TERM...Brown
AVIATION...MBS