-- Discussion containing changed information from previous version are highlighted. --
942
FXUS63 KLBF 211143
AFDLBF

Area Forecast Discussion
National Weather Service North Platte NE
643 AM CDT Sat Sep 21 2024

.KEY MESSAGES...

- A frontal boundary tracking through the area will bring strong northerly
  winds gusting 40 to 50 mph with the strongest speeds expected
  across portions of the Sandhills.

- Precipitation potential continues to trend down for much of
  the area this weekend with the latest forecast suggesting
  less than 0.50" of total rain in the forecast area.

- Still monitoring the potential for at least patchy frost
  Monday morning with probabilities of around 50-60% along and
  west of Highway 61.

- Outside of a low-end chance Monday Night, the extended
  forecast will largely be dry with temperatures returning to
  above normal values.

&&

.SHORT TERM /THROUGH SUNDAY NIGHT/...
Issued at 415 AM CDT Sat Sep 21 2024

Morning satellite analysis depicts broad mid-level ridging centered
over the Southern Plains. Longwave troughing with an associated h5
cutoff low continues to drift across the Desert Southwest and this
is the system that will encroach on the area over the weekend. To
the north, broad troughing continues to track west to east invof the
Canadian border with extended weak troughing ahead of it across the
northern Great Lakes.

Early morning rain and thunderstorms continue across far north
central Nebraska. This is being driven in large part by modest warm
air advection within the broad southwesterly low-level flow. With
the focus shifting up into South Dakota, convection has become more
disorganized. The background environment shows modest elevated
instability along with strong speed shear aloft. This has allowed a
few cells to strengthen and be capable of small hail and frequent
lightning. This threat appears to be diminishing though with loss of
forcing for ascent. Scattered showers and weak thunderstorms are
likely to linger through sunrise though before exiting to the east.
Behind this activity, a pronounced cold front is diving south
through the area. This is the attendant cold front from the system
near the Canadian border. As of 0825z, the front is approaching the
Pine Ridge. Strong CAA behind this system will bring strong
northerly winds to much of the area today. Upstream observations
show widespread gusts across western South Dakota in the 30 to 40
mph range. This boundary is likely to hit with a "wall of wind" as
once winds veer to the northwest, gusts should rapidly increase into
said speed range. Beyond sunrise, mixing heights should increase
just enough to tap into strong h85 flow. This will likely lead to a
notable increase locally to around 40 to 50 mph. Given the expected
northerly component, am a bit concerned about the crosswind factor
on area roads, notably I-80. The cooler air invading will lead to a
much different day from 24 hours prior with daytime temps tumbling
15 to 25 degrees across the region. This translates to highs only in
the upper 60s to middle 70s. Later today as the southwest upper-
level low ejects across the Rockies, southerly flow in the mid-
levels will increase as an elevated warm front takes shape.
Increasing fgen around h7 will lead to increasing precipitation
chances across the southwest. Recent trends remain unchanged with
the overall thinking of this system. Invading dry air and weaker
upper-level dynamics have effectively removed many from the prospect
of seeing rain at all and limited rain amounts for those who will
still see some. Latest ensemble guidance, most notably the NBM,
shows probabilities of > 0.25" limited to slightly better than a
50/50 potential south of Interstate 80 whereas areas to the north
are likely to struggle seeing much in the way of measureable rain.
Modest Canadian high pressure will inch in from the north by late
Saturday and bring with it rather dry air. This is easily denoted by
sub-0.50" PWATs and h7 humidity dropping to 30% or less. PoPs have
again been decreased as a result with manual manipulation to tighten
the gradient. This has produced a probability of precipitation
gradient of nearly 3-5% for each 10 miles north to south with dry
conditions now likely for almost all locations north of an Alliance
to Chambers line and "Likely" PoPs limited to the Highway 23
corridor and points south. These values may not be low enough as
HREF probabilities suggest even lower confidence and lower QPF than
what is currently forecast. All this to say, many if not all
locations may see less than a tenth of an inch from what once
appeared like a promising storm system. The event peak still looks
to occur early Sunday but with greatest mesoscale lift to the south,
the PV anomaly shearing out, and invading dry air...prospects look
bleak. Dry air should fully overspread the area by late Sunday which
will bring a swift end to the short threat of rain and weak
thunderstorms. Temperatures for Sunday have moderated some as a
result of decreased cloud cover. Current forecast calls for upper
60s along the South Dakota border and upper 50s south of Interstate
80 for Sunday. The dry air and clearing skies as high pressure works
in will allow for a good radiational cooling setup. Probabilities of
falling below 36 degF Sunday night have crept up in NBM guidance
with greater than a 50/50 shot of seeing this occur. Will hold off
on any mention of frost for now as surface high pressure may have
settled south by the overnight period which would support increasing
southwesterly winds and milder temperatures so stay tuned.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
Issued at 415 AM CDT Sat Sep 21 2024

Monday...As the departing storm system weakens and phases back into
the flow aloft, and southeastward diving system will track into the
Northern Plains. This will drop another cool front into the area
Monday. Moisture will be quite scant other than the incoming Pacific
airmass. As such, precipitation prospects appear quite limited. Have
maintained the inherited Slight Chance (< 25%) categories for areas
west of Highway 61 but confidence in these values is low. We should
see highs range from the upper 70s to upper 60s northwest to
southeast.

Tuesday and beyond...amplified ridging to the west will move into
the Great Basin and eventually onto the Plains. This will favor
moderating temperatures while keeping any precipitation chances next
to nil. Highs look to become more seasonable by Tuesday but begin
climbing to above normal values by Wednesday. For the late week, NWP
guidance is in agreement pegging a h5 cutoff disturbance that`ll
likely drift through the central and eastern CONUS. The same NWP
guidance varies on placement of these feature, however, and this
casts the extended forecast in doubt somewhat. How this affects the
large dome of ridging across the Central CONUS along with timing of
the next northern stream trough remains somewhat uncertain. Overall
thinking is any upper-level system remaining clear of the forecast
area through the end of the period. This maintains dry conditions
and the warming temperatures. Latest CPC outlooks suggest the same
with above normal temperatures and drier than normal precipitation
both favored.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
-- Changed Discussion --
Issued at 626 AM CDT Sat Sep 21 2024

VFR conditions will prevail over the next 24 hours. Winds will
be strong this morning and afternoon out of the north, sustained
at 20 to 30 kts with gust up to 45 kts. Winds will diminish this
evening to around 5 to 10 kts out of the north. There is an
isolated chance of showers and thunderstorms tonight into
Sunday, generally south of a line from North Platte to Broken
Bow.
-- End Changed Discussion --

&&

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

&&

$$

SHORT TERM...NMJ
LONG TERM...NMJ
AVIATION...Gomez