757
FXUS63 KLBF 170824
AFDLBF

Area Forecast Discussion
National Weather Service North Platte NE
324 AM CDT Tue Jun 17 2025

.KEY MESSAGES...

- The threat for severe weather continues with a Slight Risk
  (level 2 of 5) across southwest Nebraska on Tuesday.

- The threat for heavy rain remains through late Tuesday with
  0.75-1.50" of new rainfall, the heaviest of which will likely
  occur across southwest Nebraska.

- Heat remains a concern for Friday and Saturday as forecast
  heat indices reach the triple digits each day for portions of
  southwest and central Nebraska.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 324 AM CDT Tue Jun 17 2025

Strong to severe thunderstorms remain the main concern for the short
term forecast period. Early this morning, scattered rain and
thunderstorms stretched from southwest Wyoming into southwest
Nebraska. Much of this activity was driven by moist upslope flow
interacting with topography across the higher terrain. The
background environment remained strongly unstable with MUCAPE values
of roughly 2000-3000 j/kg rooted in the h7 to h8 layer. This
easterly low level flow beneath westerly h5 flow was proving to
create a strongly sheared environment with 0-6km BWD values of 50+
knots. Indeed, storms have remained fairly intense with multiple
warnings being issued across the Nebraska Panhandle including golf
ball hail reported in Scottsbluff around 0630z (130am CDT). Believe
this severe threat may persist through daybreak but remain largely
isolated in nature.

For Tuesday...believe a few rounds of rain and thunderstorms appear
probable today. As surface low pressure deepens over eastern
Colorado, an inverted surface trough extending north and east
through the Sandhills will serve as the focus for renewed deep
convection development. Eventually this wind shift line will lift
north and west and as it does, convergence along it will ramp up and
lead to more expansive rain and thunderstorm development. Within
moderate mid-level flow out of the west-northwest, rain and
thunderstorm progression will be west to east fairly quickly.
Through mid and late morning, the first wave of rain and
thunderstorms will sweep through. This round will favor southwest
Nebraska and it`s here where PoPs area highest with "Likely"
categories (up to 75%). Believe this will quickly exit by midday to
the east. NAM Nest output closely matches this thinking.
Particularly concerning from this sole NWP guidance is the damaging
winds it advertises. While storms are likely to be elevated, they
are likely to ride an instability gradient with modest theta-e
advection within a reasonably strong LLJ. As always, it`s hard to
realize some of these stronger nocturnal wind gusts to the surface
but will need to closely monitor going forward. Forecast highs
across the region are difficult at best due to the expected cloud
cover in addition to the precipitation through the day. Leaned
heavily on MET/ECS guidance with a slight blend to higher resolution
output from HREF/HRRR/RAP. This introduced a slight cooldown with
highs generally holding onto the 70s and perhaps struggling to climb
out of the upper 60s over the western Sandhills. Even with this in
mind, the environment will once again prime for a second round of
rain and thunderstorms in the late afternoon and evening. Winds will
likely back to the northeast as a cool front crashes south across
eastern Colorado. This will likely maintain upper 50s to lower 60s
dew points across the whole of the area. Instability will remain
modest as the area remains on the northeast periphery of the more
pronounced EML to the southwest. With cooler temperatures but steep
lapse rates remaining in place, instability should remain more muted
though HREF still suggests 90-100% potential for surface based CAPE
(SBCAPE) to exceed 1000 j/kg. Once again, orographic forcing will
lead to scattered thunderstorms with expected prorogation to be east-
southeast. This may carry much of the greatest severe threat to our
southwest, an idea illustrated by the latest SPC Day 1 Outlook which
keeps higher probabilities confined to eastern Colorado and western
Kansas. Can`t rule out a few stronger wind gusts and isolated
instances of severe hail, but believe the threat will be rather
limited compared to Monday events. The HRRR is much more bullish on
its output, largely due to better recovery from morning activity and
increased afternoon instability. In either outcome, shear will
remain supportive of organized convection so the lingering question
is magnitude of instability. Will need to monitor this trend closely
going forward. Given continued anomalous moisture within the
environment, heavy rain will likely accompany this round of
convection again. When factoring in all rain and thunderstorms from
the day, widespread 0.75-1.50" of rainfall is likely and locally
heavier amounts exceeding 2.00" cannot be ruled out. HREF ensemble
max values suggest even higher amounts in highly localized areas.
Believe these are well overdone given fairly quick storm motions
expected with probability matched-mean values more representative of
forecaster thoughts. Precipitation quickly winds down late Tuesday
night into early Wednesday and most if not all activity should
depart the area to the east by daybreak. Will see lows a touch
cooler for the area with all 50s forecast and even a few locations
threatening the upper 40s in the west.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
Issued at 324 AM CDT Tue Jun 17 2025

Wednesday through Sunday...well advertised warm-up remains likely
for much of the region. Trough axis will shift east through the day
and height rises will overspread the area through the daytime
Wednesday. This will continue right into Thursday as amplifying
ridge reaches the Continental Divide by early Friday. Ridge axis
appears likely to settle over western Nebraska Friday morning and
this will coincide with fairly impressive temperatures aloft as h7
and h85 values near NAEFS climatological max values. The ECWMF
Extreme Forecast Index (EFI) continues to show Friday and Saturday
as the days to watch as values peak around 0.6-0.8 and Shift of
Tails (SoT) reach 0-1. NBM MaxT probabilities of > 100F continue to
exceed 70% for much of the area and even exceed 90% for all of the
forecast area south of Interstate 80. Ensemble mean values for
afternoon highs, from both the GEFS/EPS, show expansive 100F+ and
where those aren`t prevalent middle to upper 90s. While the heat
alone is concern enough, the question becomes how muggy it gets and
it`s implications on forecast heat index values. NBM probabilities
of > 60F dew points remains largely confined to areas east of
Highway 83 and nearly 100% for the Highway 281 corridor. This lends
fairly high confidence in heat indices reaching Heat Advisory
criteria (100F or greater) for our far east zones but decreasing
confidence with westward extent. The going forecast has Heat
Advisory criteria heat indices generally near and east of a line
from Imperial through Broken Bow through Butte. Believe there will
be a need for Advisory issuance with later forecasts but will hold
off for now as we`re talking day 4. While similar conditions are
likely Saturday, Sunday is somewhat uncertain. Ridge breakdown will
begin early next week but southwesterly flow will support warm
temperatures off the surface lingering. As a few disturbances within
the mid-level flow eject over the northern Plains, a surface low
will take shape and drag a cool front south into western Nebraska.
Timing of this front appears to favor the daytime on Sunday but
intense heat remains probable ahead of the feature so timing will be
everything. NBM inner-quartile values show an increasing spread with
10th percentile values even suggesting middle 80s. For now, the
going forecast calls for upper 80s northwest to upper 90s southeast
but enough low-level moisture scouring to preclude heat advisory
conditions. Will need to watch this potential closely.

Monday and beyond...longwave troughing will reside in the west with
broad upper-level ridging to the east. This will prolong
southwesterly flow ahead of approaching disturbance. Both the
EPS/GEFS show a return to anomalous moisture quality by early Monday
and with multiple perturbations within the flow, increased rain and
thunderstorm potential. In fact, periods of Likely categories of
PoPs (> 55%) exist late Sunday through Tuesday. Both the EPS/GEFS
show increased probabilities focusing on Tuesday for much of the
area along a stalled frontal boundary. Will keep an eye on this
timeframe as background conditions support the threat for not only
some heavy rain potential but also some threat for severe
weather.

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 1140 PM CDT Mon Jun 16 2025

Thunderstorms will persist into Wednesday morning and afternoon,
with MVFR visibilities and gusty, erratic winds expected inside
thunderstorms. Some low stratus development is possible across
western and southwest Nebraska towards sunrise leading to MVFR
CIGs, though confidence in this is low. CIGS should rise in any
stratus that does develop back to VFR into Wednesday afternoon.

Winds remain east-northeast outside of thunderstorms, at 10 to
15kts.

&&

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

&&

$$

SHORT TERM...NMJ
LONG TERM...NMJ
AVIATION...Brown