901
FXUS63 KLBF 101136
AFDLBF

Area Forecast Discussion
National Weather Service North Platte NE
636 AM CDT Sat Aug 10 2024

.KEY MESSAGES...

- Cloudy and cooler again for Saturday with afternoon highs 5 to
  15 degrees below normal.

- Multiple rounds of rain and thunderstorms are expected over
  the next 48 hours, primarily late tonight into early Sunday
  morning and again Sunday afternoon and evening. Strong to
  severe thunderstorms are possible with each round of
  thunderstorms.

- Temperatures look to return to climatological values early
  next week with continued southerly flow supporting daily rain
  and thunderstorm chances.

&&

.SHORT TERM /THROUGH SUNDAY NIGHT/...
Issued at 340 AM CDT Sat Aug 10 2024

Morning satellite analysis shows broad troughing across the Great
Lakes region as low-amplitude ridging settles across the Great
Basin. A fairly notable plume of sub-tropical moisture was crossing
the central and southern Rockies where low-level fog and scattered
rain and thunderstorms are noted as of 0730z. Surface high pressure
situated across northwest Kansas will continue to settle east and
lead to increasing southerly flow later in the day.

Saturday...Low-stratus remains prevalent across the area as surface
high pressure maintains local influence. Areas of fog have been
noted across far northeast Colorado but this activity should remain
south and west of the local area. As the central high pressure
continues to drift east, southerly flow will overspread the area.
Modest WAA will support continued cloud cover for the bulk of the
daytime which should help keep temperatures on the cooler side.
Forecast soundings indicate stratus layer will be shallow, around 1
to perhaps 2km thick. With modest if any lift in the layer and a
fairly strong inversion located immediately above this, believe
precipitation prospects for the daytime are fairly low. This idea is
supported by most NWP guidance including HREF and deterministic
NAM/GFS/RAP solutions. Capped inherited PoPs at 16% with timing
closely resembling SREF output. Again, expectation is for most if
not all locations to remain dry. Regarding temperatures, confidence
remains fairly low in magnitude of warming today. Latest statistical
guidance ranges from 70 degF (MET), to 76 degF (ECS), up to 80 degF
(MAV) for LBF. NBM percentile values reflect this split with 25th
and 75th percentile values exhibiting a 9 degF split. Though skies
will likely limit insolation greatly today, the modest WAA with the
increasing southerly flow suggests at least a limited warm up across
the area. Went ahead and utilized a CONSRaw/NBM 50th blend which
closely lines up with latest short-term guidance. This paints low
70s near and just north of the I-80 corridor to near 80 along the
Nebraska/South Dakota border and far southwest Nebraska. Attention
quickly turns to the threat of convection as early as late afternoon
in our western zones but more likely arriving in the mid to late
evening hours from the west. Southeasterly surface flow interacting
with the Laramie Range will lead to afternoon thunderstorm
development. While strong mid-level flow will support adequate deep-
layer shear for storm organization, limited low-level moisture will
hamper instability magnitude as MUCAPE values appear limited to
around 1000 j/kg in our far western zones. The greatest overlap of
low-level moisture tongue and mid-level lapse rates will form a
northwest to southeast instability axis stretching from near
Chugwater, WY down through Yuma, CO. This will likely reinforce a
northwest to southeast storm motion which should steer most activity
around the area. Far southwest Nebraska will still be in the area of
concern for strong to briefly severe thunderstorms and it is here
where the Storm Prediction Center maintains a Marginal Risk (level 1
of 5). The main concern would be damaging wind gusts, however,
storms are likely to lose intensity quickly as they outrun the
greatest instability. While anomalous moisture will remain in place,
quick storm motion and weakening convective elements should preclude
a greater heavy rain threat. Even so, a few locations may still
manage to see over a quarter inch of rainfall.

Sunday...surface high pressure continues to slowly track east,
further away from the local area. This will support south to
southeasterly flow locally. Broad easterly flow across Kansas will
inhibit WAA and moisture advection, at least initially, across the
local area. Later in the day, low-level moisture advection will
increase with model guidance suggesting surface dew points climbing
into the upper 50s to low 60s. Temperatures at h85 will remain
fairly stagnant from Saturday, so little in the way of a warm up is
expected. Afternoon highs, again under partly to mostly cloudy
skies, will likely remain in the 70s and 80s. A warm front will
sharpen across our northwest zones late in the day as a shortwave
approaches from the west. With continued strong mid-level flow,
deep layer shear will once again be favorable for storm organization
and the threat for strong to severe thunderstorms. The greatest
overlap of shear and instability will favor invof this warm front
and immediately north where more easterly surface flow will elongate
hodographs. Even so, forecast shear profiles show limited low-level
curvature outside a 20 mile buffer from the main surface boundary
and limited low-level lapse rates which inhibits both SBCAPE and
3CAPE values. Above 1km, hodographs are fairly long and straight
which generally support splitting supercells and a greater threat
for large hail and damaging winds as opposed to tornadoes. Even so,
non-negligible overlap of surface vorticity along the boundary in a
localized pool of richer moisture suggest the threat for a brief
tornado cannot be ruled out. The latest SPC Day 2 outlook highlights
most of western Nebraska in a Marginal Risk (level 1 of 5) for
Sunday. Generally have no qualms with this, however, latest hi-res
guidance have indicated more scattered coverage with fairly high
concentration of moderate updraft helicity tracks. Should this idea
continue, wouldn`t be surprised to see a necessary upgrade to the
Severe Weather Outlook. As mentioned before, low-level moisture will
increase in the warm sector. Though instability response to this
appears fairly limited, increasing moisture quality suggests a
greater threat for locally heavy rain. HREF probability-matched mean
values for the 24 hour period ending Sunday evening suggests
rainfall amounts exceeding a half inch for much of north central
Nebraska and even some locations approaching 2.0" total rain for the
day. This generally matches individual NAM Nest/RAP/HRRR output with
multiple swaths of 1-2". This partly explains the latest Day 2
Excessive Rainfall Outlook which highlights these areas in a
Marginal Risk. While the threat for Flash Flooding appears limited,
locally heavy rain could introduce low-land flooding so this threat
will need monitored with subsequent forecasts. Precipitation chances
should diminish late Sunday into early Monday as the main shortwave
trough clears the area and heights begin to build immediately behind
the mid-level disturbance.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
Issued at 340 AM CDT Sat Aug 10 2024

Overall, a fairly active pattern will remain in place for the first
half of next week. Upstream ridging will amplify slightly, with the
ridge axis approaching the area by early Monday. This ridge axis
looks to settle into the area by late Monday. This support warming
temperatures with highs returning to the upper 70s to low 80s for
Monday and climbing further into the middle 80s to lower 90s by
Wednesday and Thursday. Even with increasing mid-level heights, rain
and thunderstorm chances will persist as southeasterly surface flow
drives rain and thunderstorms off the mountains to the west with a
track moving through western Nebraska. Ensemble guidance varies on
more precise timing next week, but near daily chances will exist.
Utilizing the NBM 90th percentile values, the main windows appear to
be late Monday into early Tuesday and again to a lesser degree late
Tuesday into early Wednesday. This output closely aligns with the
latest EPS solution with locally heavy rainfall amounts suggested by
this modest suite. Temperatures will continue to increase with NBM
25th and 75th percentile values settling low 80s to near 90 degF
respectively each day Tuesday through the following weekend. This
suggests limited concerns for excessive heat but a quick return to
more seasonable values in the extended periods. Latest Climate
Prediction Center outlooks for the 6-10 and 8-14 day periods both
favor above normal temperatures but a flip from above normal
precipitation to below normal precipitation. This looks to coincide
with a return to amplified ridging along the spine of the Rockies
around the middle of the month.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 631 AM CDT Sat Aug 10 2024

The main aviation concern will be some lowering of clouds across the
region. Across southwest Nebraska, ceilings will remain below
5000 feet Saturday night. Clouds will be above 5000 feet across
northern Nebraska, but will remain overcast through the entire
TAF period. There is also some concern of some fog development
across southwest Nebraska tonight. Confidence remains too low to
put into the forecast, but it is something to watch over the
next few forecast cycles.


&&

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

&&

$$

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