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000
FXUS63 KLBF 230905
AFDLBF

Area Forecast Discussion
National Weather Service North Platte NE
405 AM CDT Tue Apr 23 2024

.KEY MESSAGES...

- Breezy at times today and again on Wednesday with isolated
  showers possible across portions of the area each night.

- Seasonal temperatures continue through the week with highs generally
  in the 60s to lower 70s, trending cooler for Saturday and
  Sunday.

- Unsettled weather conditions likely for Thursday into the
  weekend with multiple rounds of rain showers and
  thunderstorms. Widespread accumulating rain is likely (>70%
  chance for total rainfall of 0.50" or more) across western and
  north central Nebraska during this timeframe.

- A Marginal Risk (1/5) for isolated strong to severe
  thunderstorms capable of producing large hail and severe wind
  gusts exists across much of the area for Thursday. The severe
  threat for Friday into this weekend remains uncertain at this
  time.

&&

.SYNOPSIS...
Issued at 400 AM CDT Tue Apr 23 2024

Recent GOES-16 WV imagery and RAP 500-mb analysis showed a deep
trough of low pressure centered over the Hudson Bay with a northern
stream shortwave cantered near North Dakota/Canada border, tracking
southeast into the Upper Midwest and Upper Great Lakes. An upper-
level low pressure system was centered over the Pacific,
approximately 600 miles off the California coast. At the
surface, low pressure was noted over the Upper Midwest/Great
Lakes region with an attendant cold front extending southwest
into the Iowa/Missouri/Nebraska/Kansas borders to another area
of low pressure located over southwest Kansas. Surface high
pressure across the northern Rockies was beginning to nudge
into the northern Plains. The previously mentioned upper-level
shortwave and convergence behind the surface cold front has
provided a focus for light rain showers and isolated
thunderstorms across portions of the state. The bulk of the
activity occurred to the south and east of the forecast area
earlier tonight with even some small hail reported over
Beatrice in southeast Nebraska. While early morning radar shows
some returns across portions of the local area, believe a lot of
this is in the form of virga given drier air moving southward.
Any rain that is reaching the ground will be very light and
quick hitting through around sunrise.

&&

.SHORT TERM /THROUGH WEDNESDAY NIGHT/...
Issued at 400 AM CDT Tue Apr 23 2024

Today and Tonight...Generally dry and quiet conditions are expected
during the day today, though breezy at times due to a tightened
surface pressure gradient (SPG). Northwest winds gusting 15 to 25
mph will be common for most locations with the strongest gusts up to
35 mph expected across north central Nebraska where the SPG is more
compact. These breezy winds will quickly diminish heading into the
evening as the SPG relaxes and surface high pressure takes hold over
the area. Daytime temperatures will be a few degrees cooler than
yesterday,though still in the seasonal range, generally in the 60s.
An upper-level shortwave over the Idaho Panhandle/western Montana
will continue southeast into portions of the northern Plains today,
providing another quick-hitting chance for precipitation tonight for
the southern Panhandle/southwest Nebraska. Confidence continues to
remain rather low on the potential for precipitation due limited
moisture and weak forcing across the area. Temperatures tonight will
fall into the mid 30s to low 40s with winds veering towards the
south on the backside of the departing surface high pressure.

Wednesday and Wednesday Night...Upper-level ridging will build back
into the central CONUS with the upper-level low continuing to deepen
off the coast of California. High temperature warm back into the at
to slightly above normal range in the mid 60s to lower 70s. The SPG
will tighten again between developing surface low pressure systems
to the west and strong surface high pressure holding strong over the
Great Lakes and Mississippi Valley. South-southeasterly winds will
strengthen during the day as a result with wind gusts of 15 to 25
mph for most locations, though the strongest gusts up to 35 mph will
be felt for areas west of Highway 83. As the upper-level trough
begins to move further inland across southern California Wednesday
afternoon/evening, lee-cyclogenesis will begin to organize across
far southeast Colorado, driven by mid-level height falls and upper-
level divergence under the left exit region of the 250mb jet streak.
At the same time, a weak leading shortwave will eject eastward out
of the central Rockies into the area, with a strong (40kts+)
southerly low-level jet (LLJ) ramping up over the northern Plains.
Not only will the LLJ support continued breezy winds through the
night, it will also provide a focus for another round of isolated to
scattered precipitation chances early Wednesday evening into the
overnight as warm air and moisture begins to advect across the area.
Not much in the way of moisture return quite yet with dew points
generally in the 40s, lowering overall forecaster confidence on
precipitation during this period.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
Issued at 400 AM CDT Tue Apr 23 2024

The flow aloft will transition to southwesterly on Thursday as the
the first of two upper-level trough tracks into the Four Corners
region. As the southern California upper-level trough
approaches the Front Range late Thursday afternoon, the lee
cyclone will deepen even further across southeast Colorado,
moving northeastward toward northeast Kansas and southwest
Nebraska by Friday morning. Continued low-level southeasterly
flow will support modest moisture return across the area,
highlighted by both the NAEFS and ENS ensembles, suggesting that
the mean PWAT will meet or exceed the 90th percentile. An
attendant warm front will move northward across the central
Plains during the day with some thunderstorm development
possible near and to the cool side of the effective warm front
during the afternoon/evening. While deep layer shear will be
rather weak, steep mid-level lapse rates (8+ C/km) and
increasing instability (MLCAPE ~500-1,500+ J/kg) will create an
environment supportive of isolated thunderstorm development
capable of producing large hail. A lot can change from now to
Thursday, so will need to closely monitor the severe threat as
we head into the near-term and details become more fine scale.

With the first upper-level low moving northeast across Nebraska into
Minnesota on Friday, another upper-level shortwave will develop
across the Desert Southwest, pushing into the central Plains
Saturday evening into Sunday. While this second system will be
similar to the first, it appears the track of the surface low will
be further to the south and east of us. Despite this, the system
will provide another optimal shot at widespread precipitation across
western and north central Nebraska. There will certainly be some
breaks in the precipitation during this period, though there
continues to be quite a bit of spread amongst models on exact timing
of each of the individual disturbances. Although questions remain,
confidence continues to grow on the potential for widespread wetting
rain Thursday into the weekend. NBM Probabilities indicate an
overwhelming 90% chance or greater for 72 hour 0.25"+ liquid
equivalent precipitation across all of western and north central
Nebraska. When looking at the potential for 1.0"+, probabilities
become a lot more sporadic, though generally a 30 to 60% chance
exists across the area. When looking at the ECMWF EFI (Extreme
Forecast Index), it has begun to suggest increased confidence of an
anomalous event on Friday into Saturday, such that the SoT (Shift of
Tails) is greater than 0 across portions of the Panhandle into the
Sandhills. While the severe threat remains uncertain beyond
Thursday, thunderstorms are entirely possible which would result in
locally higher rain rates and amounts.

Precipitation will begin to taper off late Sunday as the second
system continues northeastward into the Upper Midwest. Ensemble and
deterministic model solutions are in general agreement that
upper-level ridging will reestablish itself across the central
CONUS at the beginning of next week. This will bring the return
of above normal temperatures in the 70s.

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 1220 AM CDT Tue Apr 23 2024

An upper level trough of low pressure will spread high level
cloudiness across western and north central Nebraska overnight.
Expect broken ceilings ranging from 10000 to 15000 FT AGL
through daybreak on Tuesday. Skies will then scatter out by mid
morning with ceilings increasing to 25000 FT AGL. Winds will be
northerly and may become gusty at the KVTN terminal mid morning
Tuesday. Gusts up to 30 KTS are possible through the late
afternoon hours.

&&

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

&&

$$

SYNOPSIS...Viken
SHORT TERM...Viken
LONG TERM...Viken
AVIATION...Buttler