662
FXUS63 KLBF 172050
AFDLBF

Area Forecast Discussion
National Weather Service North Platte NE
350 PM CDT Fri May 17 2024

.KEY MESSAGES...

- Fairly warm and dry to begin the weekend, then storms overspread
the area late Saturday and persist through at least Tuesday

- Severe weather possible Sunday (hail and wind main threats), then
significant rainfall possible Monday into Tuesday

- Relatively big cooldown for Tuesday before temperatures
  rebound to seasonable levels for the rest of the week

&&

.SYNOPSIS...
Issued at 349 PM CDT Fri May 17 2024

Quasi-zonal flow aloft is the regime for Nebraska today as an upper
low swings through the southern Plains and a more significant trough
digs into the Inland Northwest. At the surface, a low centered near
the MT/ND border pulls not only a cold front back toward the Great
Basin but also a subtle trough down the Hwy 83 corridor. Somewhat
gusty southerly winds exist in central Nebraska this afternoon and
slightly warmer breezy west winds in the panhandle and western
Sandhills. Some of the warmest air of the season (outside a short
spell in mid-April) is the story for today as highs approach 90
across the area.

&&

.SHORT TERM /THROUGH SATURDAY NIGHT/...
Issued at 349 PM CDT Fri May 17 2024

This evening into tonight... The aforementioned cool front quickly
drops south through the Plains, approaching our northern border by
06z and nearly exits our south/east borders by 12z. Introduced a
schc PoP (<20%) for the northwest half of the CWA, roughly OGA-ANW
and points west with its passage. A potent mid-level shortwave
accompanies the surface front, adding to the deep layer forcing. Low
level moisture will be the main limiting factor, partly told by
afternoon dew point depressions around 40F. A ribbon of moisture at
H5-7 and the strong forcing may be able to overcome the dry layer in
spots. Used the more aggressive CAMS solutions (mainly HRRR) for
coverage and timing should isolated showers develop. Otherwise, most
of the CWA should experience a rapid wind shift to northwesterly
overnight and newly arriving cool air, especially in the panhandle.
Forecast min temps range from mid 40s near the Pine Ridge to around
50 along Hwy 83 to mid 50s central Neb.

Tomorrow and tomorrow night... The Dakotas take the brunt of the
northern US trough, keeping Nebraska in quasi-zonal flow aloft.
Toward the surface, high pressure briefly settles into the Sandhills
in the wake of the cool front. Northerly low level flow starts the
day, then transitions to south/southeasterly return flow by sunset.
Notable cold air advection occurs at H85 with 24 hr temp changes of
around -8C. With forecast sounding suggesting a mixed layer to H7,
max temps should generally range in the 70s across the area (lower
to the north, upper south). Depending on the timing of the returning
south winds and continued sunshine, the western and southern
portions of the CWA may be a tad cool. The higher end of the NBM
envelope (75%ile) suggests lower 80s. Going into the evening, and
especially nighttime hours, low level moisture advection kicks into
high gear. Dew points in the 30s are replaced by the 40s and even
lower 50s (far south). Strong isentropic upglide is noted around 300-
305K, corresponding with a warm front lifting north. Scattered
showers and storms should develop in the southern panhandle or
northeast CO after sunset and spread into the Sandhills overnight.
The increasing cloud cover and persistent south/southeast winds
should hold min temps in the lower/mid 50s.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
Issued at 349 PM CDT Fri May 17 2024

The active synoptic pattern for next week is still on track with one
large upper trough is quickly replaced by another. Details for
Sunday have grown a bit fuzzier regarding the severe potential for
western Nebraska, seeming to shift away from a greater tornado
threat to more of hail and wind. Convective mode and location may be
messy due to existing morning precip as well. A couple trains of
thought... a more pessimistic route involving increased cloud cover
through midday and stabilization, or breaks of sunshine later on to
help redevelopment along several little boundaries. Overall, still
think the risk of severe exists even with quite a large spread in
parameters or precip coverage in model guidance. Forecast soundings
suggest drier air in the low levels Sunday afternoon, showing more
of an inverted-V profile at times, versus more of a loaded gun with
yesterday`s guidance. Deep layer shear appears slightly weaker
overall, but veering still occurs in the first 3km, encouraging
supercells at onset. The mid/upper levels grow more unidirectional
and hodographs take on a longer profile at 6+ km, which is more
indicative of large hail. Abundant CAPE, including in the hail
growth zone, still appears likely east of Hwy 83, along with very
steep mid-level lapse rates of 8+ C/km. A cool front Sunday night
clears out whatever convection occurs, also leaving a lull in action
early Monday. The next wave of precip arrives later Monday and
continues into Tuesday as the Western US upper trough digs further
into the Four Corners. A deep surface low cuts up the central Plains
while broad southwesterly flow aloft is supported by a stout H3 jet.
This wave does not appear as conducive for severe storms (for
western Nebraska), as the brunt of the energy is shifted toward
eastern half of the state. Deep layer shear will be plentiful with 0-
6km values of 50+ kts, but instability is limited and lapse rates go
back below 7 C/km. However, the risk of heavy rainfall will need to
be monitored. NAEFS ensembles suggest PWAT values around 90%ile of
climo, and the NBM envelope and WPC guidance suggest widespread 1"+
amounts. Most of the activity wanes on Tuesday, but low end chances
continue through the end of the week. As for temps, highs begin to
take a hit on Monday in the northwest and Tuesday for everywhere,
when forecast values range form mid 50s (northwest) to around 70F
(far south). Milder air arrives again Wednesday as low level flow
transitions to southerly and helps push highs into the 70s. The risk
of frost appears low at this time, but will need to watch Wednesday
morning as some min temps brush the upper 30s in the panhandle.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 1226 PM CDT Fri May 17 2024

VFR conditions are expected to continue through tomorrow afternoon
across western and north central Nebraska. Forecast soundings
suggest strong mixing will be possible this afternoon and again
tomorrow morning, which will lead to periods of gusty winds. Skies
will remain relatively clear, though passing high clouds will be
possible. Winds will shift overnight from westerly to northerly
following the passage of a cold front across the region.

&&

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

&&

$$

SYNOPSIS...Snively
SHORT TERM...Snively
LONG TERM...Snively
AVIATION...Richie