846
FXUS63 KLBF 110900
AFDLBF

Area Forecast Discussion
National Weather Service North Platte NE
400 AM CDT Sun Aug 11 2024

.KEY MESSAGES...

- Strong to severe thunderstorms are again possible today with
  large hail, damaging winds, locally heavy rain, and a tornado
  or two possible.

- Near-daily rain and thunderstorm chances will persist through
  the extended forecast as temperatures look to return to normal
  by the middle of the week.

- The recurring rain and thunderstorm chances may allow for
  appreciable rain amounts for some.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 358 AM CDT Sun Aug 11 2024

Modest northwest flow once again has entrenched itself across much
of the central Plains. This is as deep troughing continues to drift
into southeast Canada and broad ridging remains in place across much
of the southern half of CONUS. Morning satellite analysis depicts
another slug of mid-level moisture slowly departing the central
Rockies and tracking onto the High Plains over much of Nebraska,
Kansas, and portions of Oklahoma. Observations show fairly
widespread low-stratus moving into southwest Nebraska. This is
coincident with some isolated light rain and patchy fog, both of
which should prevail through sunrise mainly for areas along and
south of Highway 2.

For Sunday...expect this plume of moisture to continue to be shunted
east in the moderately strong mid-level flow. As it does, a modest
increase in WAA both at h85 and h7 should support reinvigorated
showers with a few embedded weak thunderstorms. While the majority
of this activity will wane after sunrise, areas of north central
Nebraska could see new development as forcing for ascent increases
along and ahead of a subtle h7 warm front. HREF ensemble mean
guidance picks up on this with a splattering of light QPF between
12-18z. Recent runs of the HRRR have shown a notable trend
towards this outcome, so will keep Slight Chance (< 20%) PoPs to
cover this. Reasoning for capping at such a low value is dry
low-level air necessary to overcome. NWP forecast soundings
depict cloud bases nearing 3km and limited convective elements
owing to poor mid-level lapse rates. After morning showers
depart around midday, expecting a decent break before the next
wave of thunderstorms arrives from the northwest. Recent
performance of NWP guidance on high temperatures has been poor,
and little evidence exists to suggest we`ll break the mold
today. Surface high pressure will maintain an influence locally
as it remains situated just east of here. Though broad southerly
flow will develop, advection will remain modest and favor the
early part of the day before tapering off. With stubborn cloud
cover and h85 temperatures continuing to remain on the cooler
side of climatology, expecting another well below-normal day for
much of the area. Many locations may struggle to reach 70 degF
and all locations are likely to remain below 80 degF. Values
such as these are roughly 10-15 degF below normal for early to
mid August. Confidence continues to increase with respect to the
development of strong to severe thunderstorms across central
and southern South Dakota, quickly tracking southeast into the
local area. Given previously mentioned cooler temperatures,
instability values will be fairly limited. Even so, near steady
to slightly increasing low- level moisture with steep lapse
rates overhead should support modest instability, favoring our
western zones. As a mid-level speed max remains centered along
and near the I-80 corridor, deep layer shear will be strong with
southerly surface flow quickly veering to just north of due
west around h7. This limits greatest curvature in forecast
hodographs to the lowest 2km with mainly speed shear above that.
Latest CAMs output, particularly consecutive runs of the HRRR,
advertise a plethora of semi-discrete supercells developing near
the I-90 corridor of South Dakota and quickly tracking south
and east. HREF output showcases high neighborhood probabilities
of updraft helicity values exceeding 75 m2/s2 with multiple
swaths depicted in paintball output, including in a second area
centered around the Cheyenne Ridge across the southern
Panhandle. This suggests not only supercellular storm structure
but also the potential for extended life storms. While the
tornado potential appears somewhat limited, its hard to
completely rule one out with expected storm mode and a surface
boundary draped in the area. Fortunately, storm motion versus
boundary orientation may preclude greater concerns. Otherwise,
the main concerns will be large hail approaching golf ball size
and damaging wind gusts of 70 mph. Storms will eventually cross
the boundary into more stable air and this should lead to a
fairly rapid weakening with southeastward extent. Even so,
locally heavy rain will remain a threat. Latest QPF values top
out near 1.0" for north central Nebraska. This generally lines
up with the HREF probability-matched mean output but do believe
a few locations may top 1.5" before all is said and done.
Precipitation should depart the area to the east by sunrise
Monday.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
Issued at 358 AM CDT Sun Aug 11 2024

Overall thinking for the extended forecast hasn`t changed much in
the past 24 hours. Ridging will build north into the Great Basin
early in the week with the ridge axis expected to push onto the High
Plains by late morning into Tuesday. With the lack of any
appreciable disturbance tracking around the northern periphery of
the main high pressure, little will be done to scour out local
moisture. With steady south to southeasterly flow through the
forecast period, rain and thunderstorm chances will return daily as
convection fires off the Front Range and tracks east to east-
southeast into the local area. Latest NBM probabilities suggest
Monday night into Tuesday and again Tuesday night into Wednesday as
the favored periods for appreciable rainfall at this time. In both
instances, the greatest probabilities focus across southwest
Nebraska which lines up well with some of the greatest Drought
intensities in the area. Overall, total QPF through next week may
surpass 0.50" for many and 2.0" for some. This is highly dependent
on placement of thunderstorms so continue to check back for more
precise details. Temperatures, as ridging arrives around the middle
of the week, will moderate through that time but then look to
resemble a persistence forecast thereafter. This means a return to
80s for all and possibly low 90s for some. These values are right
near climatology for mid-August.

&&

.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 104 AM CDT Sun Aug 11 2024

Isolated rain showers will continue to move into southwest Nebraska
and the Sandhills over the next several hours. Some of these showers
could have an embedded thunderstorm or two, but should not be
severe. Regardless, reduced visibilities due to falling rain as well
as erratic winds may be possible. A brief break returns by mid
morning before a better chance of stronger storms arrives by late
afternoon and into the evening. These storms could become severe
with large hail along with strong, erratic winds and heavy rainfall
all being possible.

&&

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

&&

$$

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