367
FXUS63 KLBF 261143
AFDLBF

Area Forecast Discussion
National Weather Service North Platte NE
643 AM CDT Wed Jun 26 2024

.KEY MESSAGES...

- Threat for strong to severe thunderstorms continues with a
  Slight Risk (level 2 of 5) across the area each day Wednesday
  and Thursday, and a Marginal Risk (level 1 of 5) for Friday.

- Outside of severe chances, recurring rain and thunderstorms
  will pose a threat of locally heavy rain and at least a low-
  end risk of flooding for portions of western and north central
  Nebraska.

- Temperatures will generally favor near to below normal values
  for the end of the week into the upcoming weekend before
  warming early next week.

&&

.SHORT TERM /THROUGH THURSDAY/...
Issued at 423 AM CDT Wed Jun 26 2024

Northerly low-level flow has established itself across the area as
surface boundary that was responsible for Tuesday`s convection has
cleared the state and currently is tracking into Kansas. Surface
high pressure across the far Northern Plains will encroach on the
area but will remain north of the area. This should keep the cooler
temperatures bottled up to areas north of Interstate 90. As this
high pressure translates east, low-level flow will veer to easterly
and eventually to southeasterly across much of western Nebraska.
This will occur as mid-level height falls begin in earnest later
today with an approaching upper trough into the Pacific Northwest.
The result will be a flattening of mid-level flow and developing
surface low pressure across the central and northern Rockies. With
increasing southeasterly flow along the Front Range, orographic lift
coincident with improving upper-level dynamics will again promote
afternoon and evening thunderstorm potential for much of the region.
Afternoon highs will range from the lower 80s along the NE/SD border
to low 90s across far southwest Nebraska. The expected southeasterly
flow will favor modest moisture recovery with various short-term
solutions depicting a return to upper 50s to middle 60s for much of
the local forecast area by late afternoon. With mean h5-h7 flow
largely out of the southwest, persistence is expected with regards
to steep lapse rates or roughly 7-8 degC/km. Overtop adequate low-
level moisture, instability should quickly build this afternoon with
MLCAPE values climbing into the 1000-2000 j/kg range. The
southeasterly surface flow and almost due westerly h5 flow will
combine to yield sufficient deep layer shear for updraft
organization as 0-6km BWD values reach 40-50 knots. Capping should
preclude more widespread coverage, at least initially. This cap
should be overcome in closer proximity to the Front Range for
reasons previously mentioned, however, with thunderstorm chances
arriving in the local area as early as late afternoon but likely
holding off until the evening. Forecast soundings show limited
directional shear early on with long straight hodographs. This would
favor splitting supercells with large hail begin the greatest
concern. Eventually, with merging cold pools within deeply inverted-
v profiles, will likely see a transition to more damaging winds in
the evening. This is also supported by 1000+ j/kg DCAPE and 0-3km
delta theta-e values approaching -25 degC. Even with increasing flow
off the surface leading to large, looping hodographs in the evening,
the lack of appreciable instability with meager lapse rates arriving
should preclude any long lasting severe threat as well as any
tornado threat. Latest HREF guidance indicates the greatest signal
for more robust thunderstorm activity to be located across southeast
Wyoming into the Nebraska Panhandle between 06/26 23z and 06/27 05z
(or 6pm to Midnight CDT Wednesday). Subsequent runs of individual
CAMS echo this idea fairly well. The latest Storm Prediction Center
(SPC) outlook for Wednesday shows a Slight Risk (level 2 of 5)
stretching along an Ellsworth to Palisade line and points west. A
Marginal Risk (level 1 of 5) buffer extends from Merriman to Halsey
to Oconto and west. In general agreement with this placement though
will need to be mindful of potential northward expansion with
subsequent updates. Increased capping and decreased instability with
eastward progression should allow the severe threat to wane quickly
through the evening, especially with the lack of more appreciable
theta-e advection in the low/mid-level. Lows tonight, under mostly
cloudy skies with scattered rain and thunderstorms, should only
reach the 60s which will be around 5 to 10 degrees above normal for
late June.

&&

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
Issued at 423 AM CDT Wed Jun 26 2024

Thursday...Fairly notable uncertainties exist regarding Thursday
across the region. Northern stream disturbance will continue to dive
southeast out of the Pacific Northwest, bringing continued strong
upper-level dynamics supporting additional rain and thunderstorm
chances across the area. Deepening surface low across southeast
Montana will promote strong southerly flow through much of the day
as the area becomes wedged between the surface low and developing
lee trough and stagnant high pressure anchored near Lake Michigan.
This strong southerly flow will support continued WAA and low-level
moisture advection. Various NWP solutions depict low-level fog
within the moisture advection with a transition to stratus that
lingers through much of the day. Latest HREF guidance does suggest
mostly cloudy conditions in the morning but a gradual waning of
cloud cover probabilities through the afternoon. Given fairly high
disparity between various solutions, NBM percentile spreads for
daytime highs remain large given only 24 to 36 hours out. For now,
utilized a mix of NBM 50th Percentile and CONSRaw guidance plus bias
correction. This lowered forecast highs slightly in the area with
middle 70s in our northeast and upper 80s to low 90s in our west to
far southwest. This generally lines up with Tuesday evening MAV
guidance and roughly averages out the MET/ECS guidance, the former
suggesting more widespread 70s and the latter showing more
widespread 80s to middle 90s. Given discrepancies in forecast highs,
this will play a role in magnitude of instability during the
afternoon. With continued modest h5 flow overtop nearly southerly
low-level flow, deep layer shear will again be supportive of
organized convection, but with spreads in HREF members of 750-1200
j/kg of SBCAPE questions remain about magnitude of severe threat.
Latest SPC outlook highlights the entire forecast area in a Slight
Risk (level 2 of 5) and believe the ceiling of this setup, should
the higher instability values be realized, would more than support
it. This would include the threat of large hail, damaging wind
gusts, and a tornado or two possible as the evening LLJ increases
markedly which will elongate hodographs within decreasing LCLs. Will
need to closely monitor this potential with subsequent forecasts.
Storms, regardless of severe or not, will be occurring in an
anomalously moist environment with forecast soundings depicting deep
saturation with skinny CAPE profiles and deep warm cloud layers.
While storms will likely remain somewhat progressive with
anticipated storm motions around 20 to 30 knots should offset a more
widespread flooding concern, recent heavy rainfall in the past 14
days will make a few areas more susceptible to a flooding risk as
QPF values range from 0.50-1.00" with locally higher amounts
possible. Latest Weather Prediction Center Excessive Rainfall
Outlook highlights much of our eastern zones in a Marginal Risk
(level 1 of 4) with a Slight Risk (level 2 of 4) clipping
Frontier/Custer Counties. Trends will be monitored with later
forecasts to hone in on where the heavier QPF is likely to set up.

Friday and beyond...trough axis will slide through the northern and
central plains during the day on Friday, though discrepancies remain
between deterministic solutions. The northern stream system will
drop a cool front south through the area with timing of frontal
passage favoring sometime early morning through early afternoon.
Even with this relatively unfavorable timing, moisture pooling
within northeasterly flow behind this front should allow for another
day of moderate instability underneath a belt of enhanced mid-level
flow. This will support another severe weather threat with the
latest outlook from the SPC highlighting much of the area in a
Marginal Risk (level 1 of 5). The greatest severe threat will likely
reside in the warm sector which will be well south and east of the
local area, however, believe enough of a local threat exists that
have no qualms with SPC thinking. Temperatures will again range from
the lower 80s to lower 90s north to south. For the following
weekend, expect steady westerly to quasi-northwesterly flow to
remain established across the central and northern plains. Upper-
level ridging will strengthen across the southern Plains with
increasing heights aloft locally. Continued southerly low-level flow
should support at least another low-level moisture to feed modest
instability which would allow low-end precipitation chances to
continue daily. It isn`t until early next week around Monday or
Tuesday that a larger system departs the Pacific Northwest and
ejects onto the central and northern Plains. Overall agreement is
fairly good on timing and placement of greatest upper-level
features. This points to cooler temperatures and increased
precipitation chances to our north with some questions of how far
south these extend. For now, believe the inherited forecast hedging
the higher side of the forecast envelope with temperatures is the
way to go. While precipitation chances will be prevalent, day to day
predictability outside of Monday and Tuesday will be fairly limited
confidence wise.

&&

.AVIATION /12Z TAFS THROUGH 12Z THURSDAY/...
Issued at 642 AM CDT Wed Jun 26 2024

Mostly quiet aviation conditions are expected over the next day with
the exception of some isolated thunderstorms possible during the
evening across portions of the Panhandle and southwest Nebraska.
Confidence remains low in development and location, however, KLBF
has the best chance to see some scattered convection during the late
afternoon and evening hours. Storms should come to an end by late
evening, however, ceilings remain at or below 5000 feet through 12Z
Thursday.

&&

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

&&

$$

SHORT TERM...NMJ
LONG TERM...NMJ
AVIATION...Kulik