000
FXUS63 KLBF 260932
AFDLBF

Area Forecast Discussion
National Weather Service North Platte NE
432 AM CDT Fri Apr 26 2024

.KEY MESSAGES...

- Threat for heavy rain and possibly some severe thunderstorms continues
  Friday across portions of western and central Nebraska. A
  Marginal Risk for severe weather exists for areas east of
  Highway 183.

- After a lull in activity late Friday into early Saturday,
  round 2 begins to move into the area late Saturday into
  Sunday with renewed potential for locally heavy rain.

- Fairly active weather continues through the upcoming week with recurring
  chances for rain and thunderstorms.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 431 AM CDT Fri Apr 26 2024

Widespread rainfall with embedded convection continues across much
of the northern Sandhills through central Nebraska. Latest radar
estimates of rainfall as of 08z (3am CDT) have ranged from around a
half inch for all locations south of an Alliance to Ainsworth line
to fairly widespread 1.00" south of Interstate 80 and even a few
locations topping 2.00" in the area. Keep in mind, these are radar
estimates so we`ll wait to validate with ground truth later this
morning. Morning observations show developing surface low to the
south with an inverted surface trough extending north into western
South Dakota. Downstream of this feature, broad warm air advection
is helping to drive persistent rain and thunderstorms from central
Nebraska eastward through the Missouri valley. Satellite analysis
shows the broad shield of dry air wrapping around the southern
periphery of the main h5 low and this is helping to erode the rain
shield across the area.

Regarding the severe threat Friday...the surface low is progged to
lift north and east through the morning hours, placing it in our
eastern zones around midday Friday. Placement of this central low
will have large implications on today`s thunderstorm potential.
Ahead of this feature, southeasterly low-level flow will continue to
advect moisture into the central circulation. A narrow plume of 60+
degF dew points will extend from north central Nebraska south and
east through the southern Plains. While many locations behind the
passing low will remain on the cooler side with northerly flow,
clouds, and precipitation, the immediate vicinity of this moisture
tongue will see all the ingredients come together for another threat
for severe weather: steep lapse rates aloft overtop adequate surface
moisture and heating, allowing instability to build. In close
proximity to a deep h5 low, kinematics will certainly not be lacking
as h5 flow ranges from 50 to 70 knots allowing surface to h5 BWD
values to exceed 30 knots and even approach 50 knots for eastern
Nebraska. Initiation looks to be tied to the h85 front meeting the
surface warm front. Timing of this appears to be somewhat tricky but
recent runs of various hi-res guidance, notably the 06z HRRR and NAM
Nest, suggest this occurs around or shortly after midday in our
north central Nebraska zones. Forecast soundings show modest
clockwise curvature within the narrow warm sector with abundant 0-
3km shear as SRH values climb to around 150-250 m2/s2. With 0-3 CAPE
values exceeding 200 j/kg in a few spots and fairly widespread 1000+
j/kg of MLCAPE values, am growing somewhat concerned about the
prospect for rotating storms amid a low LCL environment capable of a
tornado or two. To emphasize, this is all contingent of placement of
surface low around midday today. The latest SPC outlook highlights
areas east of Highway 183 in the Marginal Risk (1 of 5) with the
Slight Risk (2 of 5) immediately east of the forecast area in
Boone/Antelope Counties. Should the timing of the surface low and
richer low-level moisture line up just right, as the HRRR is
advertising, I believe an upgrade to Slight Risk with a further
northwest expansion of the greater tornado threat will be warranted.
Higher confidence exists in the threat for large hail and damaging
winds. All forecast parameters are lining up with local research on
large hail events in the county warning area...h7-h5 lapse rates of
7.5-8 degC, MLCAPE of 1000-1500 j/kg, and SHIP values exceeding 2.
Limiting confidence is fairly weak inflow and limited upper-level
BWD values as flow is generally uniform in the 2-7km layer. With
storms likely surface based in a localized area, efficient downward
mixing of stronger winds is anticipated which highlights the
damaging wind gust potential. Though DCAPE values look to remain
below 1000 j/kg in the local area, fairly significant delta theta-e
values (-20 to even -30 degC) are enough to increase concern.

On the backside of the tracking low pressure, mid-level convergence
will increase which will lead to the development of a north to south
oriented precipitation shield near if not just west of the Highway
61 corridor. While precipitable water values will remain fairly
modest, slow movement of moderate intensity rain and thunderstorms
should lead to localized areas of heavy rainfall again through
midday. Values will likely range from 0.25-0.75" but short term
guidance hints at a few locations potentially seeing 1"+. This will
occur in a span of about 6 hours, so no flooding is anticipated.
This area of convergence will gradually wane, following the surface
low north through the afternoon. As the low lifts north,
precipitation chances will follow and decrease through the latter
half of the day. Save for areas north of Highway 2 overnight Friday
into Saturday, many locations will see a notable break ahead of the
second round expected to come Saturday. Daytime highs Friday will
range from middle 50s across the Sandhills to middle 60s south and
east. Lows tonight will only fall into the low to middle 40s under
partly to mostly cloudy skies and with a steady northwest
breeze.

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
Issued at 431 AM CDT Fri Apr 26 2024

Saturday and Sunday...Round 2 of rainfall will arrive during the
daytime Saturday. Recent trends have been to slow arrival time
slightly, so PoPs have been decreased for the daytime hours with
peak values arriving during the evening hours. This is tied to a
slowing of the h5 low ejection and greatest mid-level height falls
which will favor the overnight hours in the local area. Though
modest decreases in PWATs are expected between system 1 and system
2, easterly to northeasterly flow on the back side of the departing
system will help sustain moisture with Gulf Moisture streaming north
into a stalled warm front stretching from northwest Kansas into
eastern Nebraska. It`s this boundary that should keep the threat for
severe weather south and east of the forecast area but any wavering
in placement of this boundary may reintroduce the threat closer to
home so stay tuned. Even so, steep mid-level lapse rates may yield a
strong storm or two locally though shear appears to be significant
enough that storms may have a hard time persisting. The SPC
maintains a Marginal Risk (level 1 of 5) across our southern 5
counties. Should any storm threat materialize, it would be elevated
in nature and likely only pose a threat of hail. Will need to
monitor trends regarding this threat with later forecasts. Daytime
highs will range from the upper 40s in the north to middle 60s in
the south. As forcing increases in the evening, precipitation will
again become fairly widespread for Saturday night into Sunday. Have
fairly widespread Likely and Definite categories (55%+ and 75%+
respectively) with potential for another 0.50-1.00" of QPF. Even
lower percentile values from the NBM suggest another round of
wetting rains, so confidence is fairly high in moderate to heavy
rainfall amounts. Of course, being convective in nature, locally
higher amounts are possible. Though Flash Flooding appears unlikely,
antecedent wet grounds from the first round of rain may creep this
concern up just slightly. More concerning would be low-land flooding
in localized areas with the expected rainfall amounts. Precipitation
looks to depart the area late in the day Sunday, with dry conditions
returning for much of the area by Sunday evening. Even with rain
ending, clouds will linger and cooler air will remain in place. This
should hold temperatures to well below normal values as highs only
reach the 40s and 50s.

Monday and beyond...as system 2 continues to lift north into
southern Canada on Monday, mid-level heights will fill in and a more
zonal patter will become established. This will favor moderating
temperatures early in the week. Multiple northern stream
disturbances will track west to east out of the Pacific Northwest
and onto the Northern Plains which will remain north but drop
frontal boundaries into the region. This will allow for recurring
low-end potential for additional rain and thunderstorms. PoPs in the
extended are generally limited to Slight Chance or Chance (35% or
less) so confidence in finer details is low in any individual event
at this time. NBM temperature guidance shows temperatures recovering
to the 70s by Tuesday and likely lingering through the following
weekend but with probabilities of seeing > 0.01" QPF no greater than
a 50/50 shot any day, the threat for any additional noteworthy rain
events appears quite low.

&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 1051 PM CDT Thu Apr 25 2024

A storm system crossing the area will bring widespread
SHWRS/TSTMS and IFR/MVFR ceilings to much of the area through
Friday midday. Winds will shift to the north-northwest and
become gusty by Friday afternoon. Overall conditions will begin
to improve late Friday afternoon onward.

&&

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

&&

$$

SHORT TERM...NMJ
LONG TERM...NMJ
AVIATION...Taylor