602
FXUS63 KLBF 141854
AFDLBF

Area Forecast Discussion
National Weather Service North Platte NE
154 PM CDT Wed Aug 14 2024

.KEY MESSAGES...

- A Marginal Risk (level 1 of 5) is in place for Wednesday
  across much of western and central Nebraska.

- A cool front will drop south into the area later this
  afternoon, bringing the threat for thunderstorms as well as a
  slight cooldown for Thursday.

- Daily rain and thunderstorm chances continue through the
  upcoming weekend, however, PoPs remain limited to 35% or less
  any one day.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 350 AM CDT Wed Aug 14 2024

Morning satellite analysis shows a plume of high cirrus over the
eastern half of the forecast area. This is originating from
thunderstorm activity that moved through the area late Tuesday night
and early this morning. Satellite imagery shows little to suggest
deep convection is expected to redevelop in the area this morning.
At the same time, radar shows broad spin across central Nebraska
likely associated with an MCV tracking out of the area. Modest lift
on the northern periphery of this feature was leading to an increase
of scattered showers and weak convection for north central Nebraska.

For Wednesday...mid-level PV anomaly continues to shift east through
the area. Height falls are maximized in close proximity to this
feature and these are expected to wane through the late morning
hours. Weak low pressure will develop across southwest South Dakota.
This is largely driven by enhanced h5 flow ejecting across the
central Rockies. This will drive a cool front south into the area
with broad downsloping winds pinching a warm sector east into
central and eventually eastern Nebraska. This warm sector will be
denoted by surface dew points in the upper 60s to low 70s. While the
area will be lacking a strong EML, cooling mid-level temperatures
should foster some modest lapse rates. As afternoon highs climb into
the mid to upper 80s, moderate instability is expected to develop
with MLCAPE values likely climbing into the 2000-3000 j/kg range.
This will largely be confined to the warm sector east of Highway 83,
at least initially, as dry air to the west limit both LI and
instability values. Low-level convergence on the leading edge of the
approaching cool front will be enough to lead to at least isolated
thunderstorms across north central Nebraska. Tuesday evening HREF
output shows this potential well with NAM Nest being the most
aggressive individual ensemble member. Of interest, recent runs of
the HRRR are fairly pessimistic to this potential likely due to
strong capping in place and not as strong low-level convergence.
Given some limited confidence, will limit PoPs to around 45% (Chance
category). Given modest deep-layer shear, multicells are the likely
storm mode and with most instability being confined to the mid-
levels, isolated instances of large hail and damaging wind gusts are
the main concerns. This thinking largely lines up with the latest
SPC outlook however, confidence quickly wanes with westward extent.
Here, the decision was made to decrease PoPs and introduce a dry
forecast for portions of the western Sandhills into southwest
Nebraska. This is largely due to a significant lack of low-level
moisture and as a result, much weaker instability. Forcing will
largely come via the cool front but in these areas, convergence is
much weaker and dry air is quick to overspread the area. In fact,
most synoptic scale NWP solutions depict mid-level humidity dropping
below 50%. And while HREF probabilities show thunderstorms likely
forming off the higher terrain, an unfavorable environment with weak
shear and limited instability suggest activity won`t be able to
reach our western zones easily. The most bullish solutions, the NAM
Nest and FV3, limit any activity extending east of Highway 61 so
have maintained a small area of 15-20% (Slight Chance) PoPs to
account for this. Storms will quickly die though and with convection
likely having exited central Nebraska by then, mostly dry conditions
are expected for Wednesday night into early Thursday.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
Issued at 350 AM CDT Wed Aug 14 2024

Thursday...Deeper troughing will settle into the Northern Plains by
early Thursday. This will lead to broad height falls across central
and eastern Nebraska. The main surface low will remain well north of
the area and drying air advecting in northwesterly surface flow will
greatly inhibit any rain or thunderstorm chances. Temperatures will
be slightly cooler than what was seen Wednesday as h85 temperatures
will see modest cooldown from 24 hours prior. Highs will generally
be in the low to middle 80s and outside of an isolated shower or
weak thunderstorm along the Highway 20 corridor, dry conditions are
expected.

Friday through early next week...southern Plains ridging will build
through the period as h5 heights climb to around 595 dam. The ridge
axis will still along the Rocky Mountains, leaving the area in
northwesterly flow. NBM probabilities of measurable precipitation
are quite muted with < 40% outlook for seeing greater than 0.01" of
liquid any day through the weekend. Meanwhile, the EPS and GEFS
solutions are not as dire but they too are limited in their optimism
of noteworthy rainfall. Heights continue to build in as the high
pressure aloft extends its influence into the central and southern
Plains. Sometime late Monday into early Tuesday, a shortwave will
round the ridge and bring about the best potential for rain and
thunderstorms to the area. Latest NBM guidance shows PoPs reaching
around 35% late Monday evening into Tuesday morning. This closely
coincides with EPS thinking that shows western Nebraska seeing 40 to
60% probabilities of precipitation exceeding 0.10". Higher
percentile values show a widespread wetting rain event, but median
values show a much less impressive signal. So uncertainties remain
and folks should continue to check later forecasts for more details.
Overall, temperatures will peak in the upper 80s to lower 90s as
highlighted by 25th and 75th percentile values. It is interesting to
note that 90th percentile values are much warmer with mid to upper
90s being advertised. This is likely being driven by the GFS and its
ensemble suite and discounted as a bias issue. Overall thinking is
middle ground between GEFS and EPS for day-to-day temperatures is
more realistic and thus produces the middle 80s to low 90s in the
extended period.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 122 PM CDT Wed Aug 14 2024

VFR conditions will prevail across all of western and north
central Nebraska through tonight into Thursday morning. Isolated
thunderstorms cannot be ruled out this afternoon and evening,
but widespread activity is not expected. Winds will gradually
shift to the northwest at 5-15 kts.

&&

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

&&

$$

SHORT TERM...NJ
LONG TERM...NJ
AVIATION...Taylor