023
FXUS63 KLBF 031944
AFDLBF

Area Forecast Discussion
National Weather Service North Platte NE
244 PM CDT Fri May 3 2024

.KEY MESSAGES...

- Strong to severe thunderstorm development is expected Friday afternoon
  and evening with damaging wind gusts and locally heavy
  rainfall the main concerns.

- Another episode of severe weather appear increasingly likely
  for Monday, but confidence in impacts in the local area is
  low at this time.

- Cooler temperatures are likely for Day 5 (Tuesday) and beyond.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 243 PM CDT Fri May 3 2024

Immediate concern focuses on the threat for severe thunderstorms
this afternoon and evening across much of western Nebraska.

As of 19z, convection was developing along a stationary boundary
draped from the southern Panhandle into north central Nebraska or
roughly just north of a SNY to just south of a VTN line. Ahead of
this feature, strong southerly flow was driving low-level
convergence in immediate proximity to the boundary. Moisture in the
warm sector is marginal at best with dew points reading the upper
30s to low 40s as air temperatures read the upper 60s to lower 70s
south of Highway 2. This will greatly limit instability with MLCAPE
values only progged to approach 1000 j/kg for areas south of Highway
23. Further north, values will likely remain 750 j/kg or less with
rapid decrease with northward extent. Even so, forcing should be
fairly strong with the frontal boundary progressing through the
area. At the same time, flow aloft remains fairly strong with h5
flow exceeding 40 knots. With southerly surface flow, this is
producing moderate 0-6km BWD values of 40 to 50 knots. Forecast
soundings show inverted-v profiles ahead of the main line of
convection but with a lack of drier air aloft, max theta-e values
are marginal only falling to around minus 10 degC. At the same time,
DCAPE values are on the lower end as well with most locations
reporting values of less than 750 j/kg. That said, flow off the
surface immediately following the frontal boundary will respond
accordingly as a strengthening cold pool drives this south quickly
this evening. These elevated winds will likely be efficiently mixed
to the surface by the convection. This will support at least a
concern for isolated damaging wind gusts in the local area. While
hail cannot be ruled out, believe this threat is fairly low given
lack of greater instability aloft.

As forcing translates east along the boundary, increasing moist
advection will help increase coverage of thunderstorms on approach
to southwest and eventually central Nebraska later this evening.
Coverage should blossom as a result with a growing concern of
locally heavy rain. While PWATs remain low, less than 0.75", rain
rates exceeding 0.50"/hour with potential for training storms should
lead to a smaller area of QPF likely exceeding 1.00" from
southeastern Lincoln/Frontier Counties up through central Nebraska
to include southern Custer County. These areas have recently seen
fairly heavy rainfall events as departures from normal values exceed
150% and even approaching 300% for some of these locations. This has
helped drive county based Flash Flood Guidance to around 1.5"/2.0"
for the 1 hour/3 hour values respectively. Latest HREF guidance
shows Probability Matched Mean values of 3 hour QPF exceeding 1.25"
for many of the mentioned areas and even peaking around 2.0". This
suggests some hydrology concerns so this will need monitored as the
evening progresses. Believe incoming dry air behind the front and
the main source of lift should clear the area by Midnight Friday
night though lingering stratiform precipitation could last into the
early morning hours Saturday. This later departure of clouds and
precipitation should help keep overnight lows across our east on the
milder side with its implications on any frost threat covered at the
start of the long term discussion below.

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
Issued at 243 PM CDT Fri May 3 2024

Saturday and Sunday...Departing trough to the northeast will allow
mid-level heights to rise as shortwave ridging builds in its wake.
This will promote dry conditions for Saturday as surface high
pressure settles through the area. Forecast lows for Saturday
morning do not line up with latest guidance on vulnerable vegetation
therefore thinking no frost headlines are needed at this time.
Supporting this thought is steady northerly winds with potential for
lingering low stratus across our eastern zones. Admittedly, the
residual cloud cover behind a progressive cool front tends to be
overstated in NWP guidance. Even with the more pessimistic guidance
though we see steady enough flow in the low-levels to prevent full
boundary layer decoupling with surface winds remaining in the 10 to
15 mph range through sunrise. Further west where the setup for
radiational cooling will be more favorable, lows will again fall
below the freezing mark. That said, the areas remain outside the
latest guidance for susceptible vegetation therefore no Frost or
Freeze headlines are expected. All that said, lows will range from
the upper 20s west to upper 30s east. Daytime highs will climb into
the low to middle 60s with light and variable winds generally 15 mph
or less through the daytime. Ridge breakdown begins Sunday as the
next shortwave trough approaches the central Rockies late in the
day. With developing surface low to the west and departing high
pressure to the east, a west to east pressure gradient will compress
locally and help drive some increasing southerly winds late Saturday
into early Sunday. This will promote increasing moisture advection
into the area. This will also favor a fairly stubborn low stratus
deck across our western zones that may struggle to clear out until
later in the day. As a result, cool temperatures will remain
stubborn with afternoon highs remaining in the low to middle 60s.
Winds will be on the stronger side for areas west of Highway 61
where gusts may climb into the 35 to 45 mph range with 25 to 35
generally expected elsewhere. Can`t rule out a few light rain
showers west of Highway 83 in the area of greatest moisture
advection but given the general lack of convergence and limited WAA,
believe this potential is fairly low with minimal if any impacts
expected.

Monday...A well advertised storm system will traverse the Plains,
bringing with it the potential for a fairly robust severe weather
episode across the region. Low-level southerly flow will persist
early into the day helping increase surface moisture as a dryline
tightens from western South Dakota down through western Texas.
Aloft, the aforementioned shortwave disturbance will begin to take a
negative tilt as it ejects onto the Plains early in the day. A
concentrated area of significant height falls in concert with
strengthening upper-level divergence will help foster the
development of an elongated area of low pressure stretching from
southern Colorado up through eastern Montana. Within the plume of
richer low-level moisture, the combination of mild afternoon highs
and steep mid-level lapse rates will lead to increasing instability
within a strongly sheared environment. For now, greatest confidence
in severe weather remains east and southeast of the local area where
all hazards will be possible. Closer to the local area, expecting
the greatest threat to favor large hail and damaging wind gusts.
That said, the progressive cold front overtaking the dryline will
encounter modest instability in our eastern zones so the prospect
for severe weather affecting the local area cannot be ruled out. The
latest SPC Day 5 severe weather outlook highlights areas east of
Highway 83 in the 15% probability, or the equivalent of a Slight
Risk (level 2 of 5). For now, have no qualms with this but impacts
from morning rain and thunderstorms within the strong WAA within the
warm sector and how this affects the afternoon environment will need
to be closely monitored. Behind the boundary within the drier
airmass invading the area, strong CAA will support windy conditions
with gusts nearing the 35 to 45 mph range out of the west.
Temperatures will likely falter as a result but this looks to be
late enough in the day that afternoon highs will still reasonably
reach the upper 50s to lower upper 60s across the area.

Tuesday and beyond...mid-level heights will be quick to fill in
early Tuesday as a cutoff low at h5 takes shape across the northern
High Plains. This feature will likely remain fairly stagnant through
the middle of the upcoming week with a slight cooling trend in
temperatures expected for the later half of the forecast period.
Latest ECMWF Extreme Forecast Index (EFI) guidance hints at a
continuation of strong winds from Monday into Tuesday. Another cool
front will traverse the area by late Tuesday into Wednesday,
bringing about a more noteable drop in temperatures. Some low-end
PoPs will also dot the forecast, favoring areas north of Interstate
80. For now, confidence is greatest in precipitation Thursday
afternoon and evening. Higher percentile values from the NBM suggest
the potential for wetting rains but variances in deterministic and
other ensemble guidance limits confidence in this occuring thus far.
Temperatures will favor below normal values through the time frame
which will include overnight lows falling to near the freezing mark.
This would line up with frost/freeze climatological median dates so
potential need for headlines next week cannot be ruled out.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 1220 PM CDT Fri May 3 2024

Strong south winds continue this afternoon for terminals south
of Highway 2. A cold front will then slide through the area this
afternoon and evening, with a line of thunderstorms expected to
develop along this boundary. Gusty, erratic winds and MVFR
visibilities can be expected with the passage of these storms.
Additionally MVFR ceilings are expected to develop in the wake
of the cold front/thunderstorms, and will persist into early
tomorrow morning. Clouds will quickly clear from west to east
by late tomorrow morning, with VFR expected through the end of
the valid period.

&&

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

&&

$$

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