332
FXUS63 KLBF 191141
AFDLBF

Area Forecast Discussion
National Weather Service North Platte NE
641 AM CDT Sun May 19 2024

.KEY MESSAGES...

- The Storm Prediction Center has maintained a Slight Risk
  (level 2 of 5) for western Nebraska Sunday, mainly for areas
  west of Highway 83 with large hail and damaging winds the main
  concerns.

- Additional strong to severe thunderstorms are possible on
  Monday though the main concern is likely to be the threat of
  heavy rain Monday night into Tuesday.

- Cooler temperatures arrive around the middle of the week. Confidence
  in seeing a frost or freeze event remains low.

- A return to normal temperatures with active weather is
  expected for the latter half of the upcoming week.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 407 AM CDT Sun May 19 2024

Early morning radar and satellite analysis depict a broad area of
moderate to heavy rainfall lifting north and east out of western
Kansas into far southwest and south central Nebraska. This activity
is largely being driven by a modest shortwave ejecting ahead of
larger scale troughing taking shape across the western CONUS. DCVA
and WAA in the low-levels are helping provide broad ascent across
the local area. Though instability declines quickly with northward
extent, non-zero MUCAPE values and values reaching as high as 1000-
1500 j/kg have reached the Nebraska/Kansas border and will continue
to translate north through the morning. This should allow for a
continuation of rain and thunderstorm chances this morning. Given
the magnitude of instability and deep-layer shear exceeding 35
knots, cannot completely rule out stronger storms capable of at
least small hail during the late morning, mainly for areas east of
Highway 83. Lift is expected to wane by early afternoon as the main
shortwave departs to the north and east. This should lead to an
appreciable break during the day with dry conditions likely for at
least the majority of the early afternoon.

Residual cloud cover as well as rain will likely hamper diurnal
temperatures during the day. NWP model spread for high temperatures
today vary widely for central Nebraska with discrepancies nearing 10
degF. Higher resolution guidance is more bullish on afternoon high
temperatures. This is largely due to quicker departure of
rain/clouds as well as continued strong southerly flow in the lower
levels which will support advection of warmer air into the area.
Afternoon dew points will steadily climb with many locations
climbing into the middle to upper 50s and even a few locations
potentially seeing values in the lower 60s. While confidence is
fairly limited for the immediate short range, the going forecast
calls for afternoon highs in the middle 70s to middle 80s east to
west. With the expected overlap of greatest surface temperatures and
greatest low-level moisture, moderate instability will develop as
west-southwesterly flow aloft will advect a stout EML over the
region. This will yield moderate to strong instability immediately
east of a sharpening dryline that will stretch from the Black Hills
south into far northeast Colorado. With adequate deep layer shear
already in place, organized severe convection is appearing more
likely. The latest SPC Day 1 Outlook has expanded the pre-existing
Slight Risk (level 2 of 5) north and east with the coverage now
including most if not all locations between the Highway 385 and
Highway 83 corridors. Forecast soundings, while depicting fairly
strong capping that will need to be overcome, show long/straight
hodographs above 1km with the majority of the instability located
within and above the hail growth zone. With non-zero SCP values and
moderate storm relative inflow at the surface, believe hail up to
golf ball size will be possible with discrete convection early on.
Gradually, upscale growth due to merging cold pools in an area of
1000+ j/kg DCAPE and delta theta-e values falling below -20 degC
should support more of a damaging wind threat. This will likely
persist into the evening as rich theta-e air continues to be
advected into what will likely be a maturing MCS. Only when this
system begins to encounter recycled air originating from strong
convection across Kansas will a weakening trend become likely. This
will generally be around Midnight with the majority of activity
likely having exited the local area by then. Precipitation amounts
from this activity will be fairly variable. While a few localized
areas may see 1.00" or more, most locations will likely remain in
the 0.25-0.50" range.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
Issued at 407 AM CDT Sun May 19 2024

Monday and Tuesday...Largely expect Monday to begin fairly quiet as
the area is caught between the smaller scale system departing to the
east and approaching large scale trough from the west. Deepening
trough to the west will begin to approach the central CONUS by early
morning Monday. Height falls are unlikely to increase markedly until
the latter half of the day though which should limit the arrival of
the greatest rain chances. Opted to decrease PoPs during the day as
a result. This was done by blending in SREF/HREF PoPs. As a result,
only Slight Chance PoPs (< 20%) exist for the early afternoon with
only a slight increase of up to 35% (Chance category) expected by
late afternoon for the eastern Panhandle. PoPs will maximize Monday
evening into early Tuesday as the main PV anomaly overspreads the
area. An attendant surface low lifting southwest to northeast across
central Kansas will help promote strong lift within a anomalously
moist environment where PWATs will likely exceed 1.00" in the pre-
convective environment. PoPs overnight Monday into Tuesday will
likely near 100% for most locations in the local forecast area, as
confidence remains high in a noteworthy rainfall event. The ECMWF
Extreme Forecast Index (EFI) continues to highlight this with values
exceeding 0.8 and Shift of Tails values of 0-2, suggesting the
extreme values of the ensemble suite exceed the 90th percentile in
the model climatology. Both EPS and GEFS ensemble products show
increased probabilities of exceeding 1.00" total QPF for Monday
night through Tuesday afternoon with the EPS the more bullish
solution of the two. The 24-hour mean values from both ensemble
suites exceed 1.00" in the maxima with the EPS nearing 1.75" for
mean QPF. Deterministic solutions show widespread 1.00-2.00"
rainfall with localized amounts closer to 3.50". It`s important to
note that unlike typical convective heavy rainfall scenarios, these
amounts are being achieved in closer to 6 hour timeframe versus
shorter periods. This should limit, but not negate, the threat for
flash flooding. As the main trough aloft lifts north and east into
the upper Mississippi Valley, precipitation will wind down and
likely end by late in the day Tuesday. The PoPs inherited from the
NBM maintain Slight Chance and Chance categories right through
Tuesday evening and into Wednesday but deterministic solutions
suggest there should be a notable break for the latter half of the
daytime Tuesday so expecting these to be cleaned up with later
forecasts. Temperatures will be trending cooler with a values
falling into the 60s to low 70s Monday and 50s-60s by Tuesday.

A fairly active pattern will persist through the middle of next week
as a stalled out upper-low allows smaller scale disturbances to
pivot through the area. While day-to-day predictability remains
fairly low confidence for now, ensemble signals point to Friday into
early Saturday as the next appreciable chance in the local area.
This will be attributed to a stronger cold front expected to dive
south through the area. For now, precipitation chances will favor
eastern Nebraska with decreasing probabilities as one goes west.
That said, finer details like timing and placement of key features
are unlikely to be confidently located until we`re closer to 48-72
hours out so expect the forecast to waver somewhat in the coming
days. Ahead of this, temperatures will recover to seasonable values
for Thursday and possibly Friday before falling once again in the
wake of the front. The exact magnitude of cold air moving in remains
to be seen but a brief cooldown is likely and the current forecast
highs for Friday and Saturday include temperatures falling to around
10 degrees below normal.

&&

.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
Issued at 640 AM CDT Sun May 19 2024

Showers and thunderstorms will develop and move into southwest
Nebraska over the next few hours. While a break in active weather is
expected by late morning into the early afternoon, skies will remain
mostly cloudy. Another round of stronger storms will then develop
across the Panhandle and push eastward into the evening. Large hail
and strong gusts will be the main threats as well as reductions in
visibility due to intense falling rain. In addition to strong gusts
in thunderstorms, gusts up to 25 knots are possible throughout the
day in advance of the next disturbance arriving this evening. As
thunderstorms come to an end, skies try to scatter out by late
evening with ceilings rising back to near 10 kft.

&&

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

&&

$$

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