-- Discussion containing changed information from previous version are highlighted. --
146
FXUS63 KLBF 272333
AFDLBF

Area Forecast Discussion
National Weather Service North Platte NE
633 PM CDT Thu Jun 27 2024

.KEY MESSAGES...

- Severe thunderstorm potential this evening and again tomorrow
evening, consisting of significant hail/wind, tornado, and flash
flooding risk

- Virtually daily thunderstorm chances through mid next week,
although weekend potential is mainly limited to the panhandle

- Up and down temperatures over the next week, although
  generally warm tomorrow, mild Saturday, and hot Monday with
  values pushing advisory criteria in the south

&&

.SYNOPSIS...
Issued at 349 PM CDT Thu Jun 27 2024

A couple low pressure centers along the High Plains are the focus
this afternoon, one being just north of the Black Hills and the
other near the southern CO/KS line. A trough connects the two,
stretching across the panhandle, while a warm front extends
southeast from the Black Hills low toward the Neb stretch of the
Missouri R. Mixed cloudiness has accompanied gusty south winds
across the CWA today that have pushed dew points well into the 60s
and air temps into the 80s. Upper levels indicate a substantial
shortwave incoming from the northern Rockies and quasi-zonal
flow.

&&

.SHORT TERM /THROUGH FRIDAY/...
Issued at 349 PM CDT Thu Jun 27 2024

This evening into tonight... Convective initiation and evolution are
the main challenges through tonight as thunderstorms are expected to
roll through portions of the forecast area, likely resulting in
severe wind and/or hail. Initiation should occur mid afternoon invof
the surface trough in the panhandle, then spread east through the
evening and early nighttime hours. Convective parameters support
supercellular mode early on, per SPC RAP mesoanalysis and 19z LBF
RAOB. The wind profile features low level veering becoming straight
higher up, suggestive of splitting cells and an evolution toward
mixed convective mode. Of note, deep layer shear is almost marginal
given the setup (0-6km bulk of 35-40 kts), although trends show it
is increasing this afternoon. Instability is ample though, around
2000j/kg MLCAPE, and fairly steep mid-level lapse rates around 7-7.5
C/km. The CAPE profile is also rather fat in the -10 to -30C hail
growth zone. Considering these factors, agree with SPC for
significant severe outlooks (2" hail, 75mph winds). As for
tornadoes, the greater low level / LCL-LFC moisture and SRH are
farther east away from the forcing and where clusters or bowing
segments are anticipated versus initial supercells. If one were to
occur, the most favorable corridor would be somewhere Hwy 61 to Hwy
83 ahead of the surface trough and before more mixed/linear
evolution takes over. General CAMs consensus highlights the 21-03z
timeframe for most activity in the west and 00-06z toward north
central Neb. Will also need to monitor the hydrology situation as
H85 vectors indicate (and sfc dew points near 70F) strong
convergence and advection across the area. Estimated PWAT values
exceed 1.5 in central Neb where storm coverage may be more
widespread as the event wears on, especially as the low level jet
strengthens. Forecast storm motion of 20-25 kts may help limit the
overall widespread threat of flash flooding, and it will be more
concentrated toward locations that have received recent rainfall.
Overnight, low level flow switches to north/northwest behind the
boundary and followup cool front, which will help kick out most of
the thunder activity and reset the atmosphere at least temporarily.

Tomorrow and tomorrow night... A surface high briefly fills into the
northern Plains during the day, then gives way to another surface
low that parks over Colorado. Another surface trough may extend
northward into the panhandle later in the day to help serve as
additional focus or lift, while another potent shortwave approaches
and an upper trough brushes the northern reaches of the region. The
tail end of the 100kt H3 jet streak dips into the northern Sandhills
later in the day. A repeat performance is possible in terms of
convection developing in the panhandle and growing upscale as it
spreads east through the evening. The greatest concern generally
lies in the southern CWA invof the surface low where a ribbon of
greater instability intersects with deeper shear and steep lapse
rates. The tornado threat appears more uncertain with the setup, but
severe hail and wind are definitely on the table. As for max temps,
blended in some warmer guidance as the trend has increased slightly.
Advection at H85 will be nearly negligible (00z to 00z) despite the
northerly flow to start the day, so leaned toward 80s north and
lower 90s south. These values are still below the median of the NBM
envelope, so later forecast may need adjusted up further. Another
punch of relatively drier air arrives behind the action overnight,
and temps may actually touch 50F along the Pine Ridge.

&&

.LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/...
Issued at 349 PM CDT Thu Jun 27 2024

A heat dome builds over the Southern US over the weekend and expands
to start the workweek, with the H5 ridge axis bisecting the
Sandhills late Sunday into Monday. While a dip in max temps is
expected Saturday under a northern Plains surface high, a rebound
into the 90s and possibly 100F (south) is anticipated for Monday.
The southern three counties approach heat headline criteria, so this
trend will need watched going forward. After the upper ridge, flow
becomes southwesterly and eventually quasi-zonal. When combined with
various surface boundaries and frontal passages, the active
thunderstorm pattern will likely resume Monday and continue through
at least Wednesday. An outside chance of thunder exists in the
meantime, mainly for the panhandle where higher terrain activity may
survive. The greater potential for widespread storms comes Monday
and Tuesday, and SPC highlights north central for severe.

&&

.AVIATION /00Z TAFS THROUGH 00Z FRIDAY/...
-- Changed Discussion --
Issued at 618 PM CDT Thu Jun 27 2024

Thunderstorms continue to attempt to develop across the
Sandhills and southwest Nebraska this evening. At this time, LBF
has the greatest potential of seeing thunderstorm activity,
generally 01Z to 03Z. Gusty, erratic winds and brief reductions
in visibility will be possible within any thunderstorms. Confidence
on VTN seeing impacts from thunderstorm activity is meager.
Will heavily rely on radar and satellite trends for future
amendments and inclusions should they be needed. Outside of
thunderstorms, southerly winds will veer towards the north
behind a cold frontal passage tonight. These northerly winds may
become breezy along and behind the front with gusts up to
25kts.
-- End Changed Discussion --

&&

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

&&

$$

SYNOPSIS...DS
SHORT TERM...DS
LONG TERM...DS
AVIATION...Viken