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000
FXUS63 KLBF 132003
AFDLBF

Area Forecast Discussion
National Weather Service North Platte NE
303 PM CDT Sat Apr 13 2024

.KEY MESSAGES...

- Well above normal temperatures continue for Sunday and Monday.

- A strong storm system will arrive Monday and Tuesday bringing
  the threat for critical fire weather, strong to severe
  thunderstorms, and strong synoptic winds for the 48 hour
  period. Later forecasts may require Fire and/or Wind
  headlines.

- Turning much cooler for late week with well below normal
  temperatures likely and sub-freezing overnight temperatures
  expected.

&&

.SHORT TERM /THROUGH SUNDAY NIGHT/...
Issued at 301 PM CDT Sat Apr 13 2024

Tranquil weather continues this weekend as temperatures climb to
well above normal values Saturday and again Sunday. Latest
observations for Saturday as of 1930z show widespread 80s and a
select few making a run at the 90 degF mark. This is occurring even
as a weak shortwave tracks through the area. This feature is fairly
subtle but is leading to increasing clouds and the prospect of even
an isolated light shower this afternoon and early evening. As mixing
increases in the boundary layer, a plume of mid-level moisture will
overspread the area. This moisture is focused around h5 or roughly
4km aloft. With weak lift and little in the way to suggest a
thunderstorm threat other than modest lapse rates, believe the
prospects of seeing measurable precipitation any one location to be
quite limited. Surface relative humidity values are generally in the
10-20% range and extend upwards towards the anticipated cloud bases.
The threat for liquid falling into a dry airmass at the surface will
introduce the threat for some gusty erratic winds.

For Sunday...expecting similar conditions across the area with the
exception of slightly cooler temperatures and no threat of
precipitation. As surface high pressure moves into the northern
Plains, a backdoor cool front will enter north central Nebraska.
This will allow h85 temperatures to drop 4-8 degC. Easterly flow
tends to be unfavorable for temperatures to overachieve so will
hedge closer to what NBM output gives which is about a 1-3 degF drop
across the board compared to Saturday. This yields highs in the low
80s across north central Nebraska to middle 80s for the far
southwest. With dry air in place, expecting afternoon humidity
minimums to once again fall into the 15 to 25 percent range.
Limiting overall concern and thus precluding headlines at this time
will be weak winds of less than 20 mph.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
Issued at 301 PM CDT Sat Apr 13 2024

A fairly busy day is expected across the whole of the Plains as a
negative tilt trough and associated strong surface low take aim on
the region.

Aloft, h5 low is progged to translate west to east across southern
Utah into western Colorado. Ridge breakdown will begin in earnest as
h5 height falls of reasonable magnitude overspread the central and
southern High Plains by the afternoon. A dryline will sharpen from
west central Kansas south through northwest Texas with continued
south to southeast low-level flow continuing to usher in greater low-
level moisture to portions of Nebraska. By midday Monday, a sub-995
hPa surface low is expected to take shape in the vicinity of
northeast Colorado to the Nebraska Panhandle. Deterministic
solutions vary by approximately 150 miles regarding center of
surface low. This will have fairly large implications on important
surface features such as how far west dryline sets up and
timing/placement of mid-level dry air surge which will act to
inhibit rain/thunderstorm potential and only increase fire weather
concerns. Even with ensemble guidance, individual members of
respective suites vary by closer to 200 miles with EPS/GEFS mean
output differing by around 100 miles by early evening Monday. All
this to say, uncertainty lingers even less than 60 hours out.
Generally speaking, the NAM solution is most bullish on moisture
advection into the area while the GFS is more pessimistic. This
translates to a greater severe weather threat versus greater fire
weather threat respectively. With the ECMWF somewhere in the middle
but a closer lean to the GFS solution, starting to think fire
weather concerns will trump all else in the local forecast area for
Monday. As the surface low begins to track east late in the day, dry
mid-level air emanating from the Desert Southwest will overspread
much of the area. This will help to not only effectively cap the
environment, preventing widespread rain and thunderstorms from
developing initially, but also promote deeper mixing which will
bolster afternoon highs and drive humidity values down. Flow aloft
is strong as rapid response from deepening surface low will aid the
formation of h85 and h7 lows and tight height gradients will promote
kinematic response. With the anticipation of fairly deep mixing,
surface wind gusts will be fairly strong. NBM probabilities of
exceeding 34 knot gusts range from near 50 percent across the
Sandhills to as high as 95% over much of southwest and central
Nebraska. These values line up fairly well with forecast h7 winds
which look to approach 40 knots on the eastern periphery of the
surface low. With the deep mixing and incoming dry air aloft,
surface humidity values are expected to tank with single digit
values not completely ruled out particularly south of Interstate 80
and west of Highway 83. Should confidence in this occurring continue
to increase, Fire Weather headlines are likely to be needed with
subsequent forecasts. Given the threat is for Period 4, will forgo
anything at this time. With the slug of dry air, confidence in
precipitation chances is low. In fact, both the EPS/GEFS solutions
suggest less than a 10% chance of seeing 0.10" or greater of QPF for
the entire day Monday across the southwest and Sandhills. With that
in mind, believe PoPs may be a bit overzealous and will plan to at
least cap mention to Chance categories for the mentioned areas.
While the SPC has introduced a Slight Risk to our eastern zones (level
2 of 5), lingering low confidence in placement of surface
features including signals for most convection to stay east
should support a more Marginal outlook with later forecasts.

Tuesday...expecting the surface low to have moved to the eastern
portions of Nebraska by late morning with the flip to northerly
winds in the local area. The western periphery of surface lows tends
to be the favored setup for significant wind gusts across western
Nebraska and this event does not appear to be an exception to that
rule. By this point, the system will be fairly vertically stacked as
GFS/ECMWF suggests the h5 low to be directly overtop the surface
low. With h85 and h7 flow pushing 40 to 50 knots and unidirectional
flow to the surface, efficient momentum transfer will allow wind
gusts to easily reach the surface. Latest SREF probabilities show 50-
60% probabilities of seeing surface winds exceeding 25 knots
sustained for areas west of Highway 83. At the same time, NBM
probabilities of seeing peak gusts for the day exceeding 48 knots
climbing above 50% for the same areas. Later forecasts may require
High Wind headlines. Precipitation potential appears to be
decreasing somewhat in the past 24 hours. Recent probabilistic
guidance has backed off on the earlier thought of widespread wetting
rains. Gradually, an eastward shift has been noted with
probabilities of exceeding 0.10" for Tuesday now focusing east of
Highway 83 and even closer to Highway 281 and points east. Similar
trends have occurred with deterministic solutions and so things are
starting to look a bit unfavorable for widespread appreciable
rainfall. While some locations will likely see it still (central
Nebraska), the main focus trending east is unfavorable for the
western half of the CWA. The latest storm total QPF reflects this
eastward shift with 0.75" or greater east of Highway 183 and less
than a quarter of an inch west of Highway 97 for Monday afternoon
through early Wednesday morning. This essentially mirrors the NBM
probabilities of > 0.50" in the previous 48 hours ending Wednesday
morning with greater and less than 50% for east and west
respectively. Upper-level forcing will be quick to depart to the
east as mid-level heights build in rapidly. While some precipitation
may linger beyond Midnight Tuesday night, most if not all activity
will have ended prior to dawn Wednesday.

Wednesday and Beyond...upper-level troughing remains in place across
the Great Lakes with modest zonal/northwest flow locally. Another
upper-level disturbance will track west to east across southern
Canada with a progressive cold front then expected to track through
the area. This will herald the start of a period of cooler weather
as Canadian high pressure settles south and east into the northern
Rockies. Long range guidance is in good agreement in depicting
anomalously cool temperatures arriving by Thursday with both NAEFS
and ENS guidance suggesting h85 temperatures fall below the 10th
percentile and approach sub-zero values. Adding to this, NBM
probabilities of seeing overnight lows below 32 are fairly high:
exceeding 50% west of Highway 83 for Thursday morning, exceeding 70%
for all locations in the forecast area for Friday morning, and
increasing further to 80% or greater for all locations Saturday
morning, with decreasing probabilities by Sunday. Likewise,
climatological high temperatures for late week are in the low 60s
for the area. NBM probabilities of seeing daytime highs above 60
degF peak around 40% for south of Highway 23 Thursday but fail to
reach 25% anywhere in the region for Friday and Saturday. With
encroaching high pressure, enough mid-level lift will materialize to
produce some Chance PoPs (< 50%). This would likely fall mainly as
rain though some overnight snow can`t be ruled out. For now, any
prospects of winter impacts appear low.

Behind the now departing surface high pressure on Saturday,
temperatures should slowly moderate for early next week with daytime
highs expected to return to the 60s and even some low 70s. Though
NBM percentile spreads remain high, 25th percentile values show near
seasonable values for early the following week suggesting near to
above normal temperatures likely favored for the time frame.
Confidence in day-to-day predictability beyond Day 7 wanes quickly
as notable discrepancies exist between both deterministic and
ensemble solutions. With anticipated positive height anomalies
across the western CONUS, the pattern would suggest a return to near
or above normal temperatures but day-to-day predictability of
precipitation chances is difficult at best.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1215 PM CDT Sat Apr 13 2024

VFR conditions will persist through Sunday morning across
western and north central Nebraska. Scattered to broken high
cloudiness will continue today, followed by mainly SKC tonight
through Sunday morning. Light west to northwest winds this
afternoon and evening become light northeasterly Sunday
morning.

&&

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

&&

$$

SHORT TERM...NMJ
LONG TERM...NMJ
AVIATION...Roberg