172
FXUS63 KLBF 162031
AFDLBF

Area Forecast Discussion
National Weather Service North Platte NE
331 PM CDT Sun Jun 16 2024

.KEY MESSAGES...

- Isolated to scattered severe thunderstorms possible across
  much of western and north central Nebraska this evening and
  tonight. Primary hazards include damaging wind, large hail,
  and perhaps an isolated tornado(es).

- Another round of severe weather will be possible late Monday
  with the potential for damaging winds and large hail.

- Near daily shower and thunderstorm chances continue across the
  area each day through the rest of the week into the weekend.
  The severe threat remains uncertain at this time.

&&

.SYNOPSIS...
Issued at 330 PM CDT Sun Jun 16 2024

Recent GOES-16 WV and RAP 500-mb analysis showed a ridge of high
pressure situated across the southeast US, extending northward into
the Great Lakes region. Multiple upper-level shortwave troughs were
traversing along the upstreams of the ridge across the southern
Plains into the western Great Lakes. Just to the west-southwest of
this feature, a positively-tilted upper level trough was centered
over the Washington/Oregon border. An upper-level trough of low
pressure was swinging northeastward across Manitoba. Surface low
pressure associated with this system is gradually shifting eastward
into northern Manitoba, while an attendant cold front extends
southwest across the Upper Midwest, stalling across southwest
Nebraska. A dry line extends southward from a surface low
located to the lee of the Rockies across eastern Colorado. These
boundaries will have to be monitored very closely as we head
into the evening as they will provide a focus for potential
storm initiation this evening and tonight. In fact, recent
satellite imagery is starting to show the first bubbling cumulus
across northwest Colorado. As of 3 PM CT, temperatures ranged
from 71 degrees at Ainsworth to 85 degrees at Imperial.

&&

.SHORT TERM /THROUGH MONDAY NIGHT/...
Issued at 330 PM CDT Sun Jun 16 2024

This evening and tonight...Although it has been a fairly quiet
Father`s Day under mostly clear skies, attention turns to the
potential for isolated to scattered severe thunderstorms for two
portions of the forecast area...

1) areas along and south of I-80

High temperatures have begun to rise into the 80s along and south of
the aforementioned front across southwest Nebraska. Combined
with increasing dew points into the upper 60s, nearing the low
70s for some locations, ample instability (MLCAPE 2,000 to
3,000+ J/kg) has set up across this area. Pre-convective low to
mid-level lapse rates have steepened across this area (7.5 to
8.5+ C/km) with strong 0-6km Bulk Shear (of 40 to 50 kts)
creating a rather robust environment supporting a threat for
large hail, damaging winds, and perhaps an isolated tornado(es).
The biggest question that remains is, will convection be able
to initiate along this boundary given the strength of the CAP?
Our special 20Z UA launch shows a strong CAP in place here at
LBF. However, a subtle shortwave looks to progress
northeastward in the mean flow aloft, combined with increased
surface convergence along the front, could be enough to get
robust multicells and perhaps marginal supercells to develop
across southwest Nebraska. This is a highly conditional and
somewhat low confidence, but a potentially high impact
scenario. Will be monitoring for storm initiation between 4 and
7 PM CT.

2) areas along and north of I-80

As we head into tonight, a low level jet (LLJ) will start to
strengthen and nose into the region. Upper-level forcing will
strengthen as well with increasing frontogenetical forcing and
isentropic lift in an easterly upslope flow regime. There
continues to be a strong signal for robust elevated convection
to develop across portions of the Sandhills into northern
Nebraska, north of the front. This activity will grow upscale as
storms move east/northeastward through the overnight hours into
South Dakota, exiting across the Nebraska/South Dakota border
by 09Z. Forecast soundings exhibit elevated instability with
substantial MUCAPE (2,000 to 3,000 J/km). Large hail will be the
primary concern with the elevated convection, though isolated
damaging wind gusts cannot be rules out.

Monday and Monday Night... The aforementioned stalled cold
front will slowly lift northward as a warm front through the
day on Monday. Instability will increase yet again as the low-
level wind field amplifies Monday afternoon with strong winds
of 30 to 40 miles per hour across southwest into central and
north central Nebraska. Ample instability (MLCAPE 3,500+ J/km)
and continued impressive 0-6km Bulk Shear (of 40 to 50 kts) sets
up across much of the area, especially for areas along and east
of Highway 83. The dry line should aid in overcoming the CAP
late in the day with the potential of thunderstorms developing
across the southern Panhandle and southwest Nebraska. These
storms may grow upscale as they move east/northeast into Monday
evening. Primary concerns will be large hail and damaging wind
gusts. However, an isolated tornado(es) threat exists for areas
along and north of Highway 20. Outside of the convective threat,
daytime highs will warm into the 80s across northwest Nebraska
to upper 90s across southwest Nebraska, some locations may near
the 100 degree mark.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
Issued at 330 PM CDT Sun Jun 16 2024

Tuesday and Wednesday... The flow aloft at the start of the
long term period will be defined by a high amplitude ridge
across the eastern US and a trough across the western US. A
cold front will advance across the area through the day on
Tuesday, stalling just to our east, eventually building back
into the region through midweek. This front will continue to
provide focus for thunderstorm development Tuesday night into
Wednesday. At this time it appears the strongest forcing and
corridor of greatest instability will reside to the east of the
forecast area. Though the severe risk appears limited for our
area, will need to monitor the potential for heavy rainfall for
portions of southwest and north central Nebraska Tuesday night
into Wednesday. Precipitable water values appear to meet or
exceed the 90th percentile during this time as highlighted by
both the NAEFS and ENS ensemble guidance. This is supported by
WPC`s Day 3 Excessive Rainfall Outlook (ERO) outlooking the
previously mentioned areas under a Marginal to Slight Risk for
Excessive Rainfall. Persistent cloud cover and precipitation
will lead to a nice cool down with Tuesday`s highs in the 70s
and 80s to the 60s on Wednesday.

Thursday and beyond... The midweek cool down will be short-lived
as temperatures warm back into the 80s as the upper-level ridge
retrogrades westward into the weekend. Continued southwesterly
flow aloft with additional northern stream disturbances tracking
across the area will keep the extended forecast in an active
pattern. While day-to-day predictability is low and the severe
risk remains uncertain, recurring afternoon and evening
thunderstorm chances will exist each day for the latter end of
the week into the weekend.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1233 PM CDT Sun Jun 16 2024

VFR conditions are expected to prevail through early this
evening at the KLBF and KVTN terminals. Thunderstorms may
develop south and east of the KLBF terminal by 23Z. Have
included a PROB30 until 03Z. Overnight, increasing low stratus
will lead to MVFR/IFR CIGs across northern Nebraska, along with
increasing showers and thunderstorms. Timing and placement of
thunderstorms still remains somewhat uncertain, though
prevailing -TSRA included at KVTN from 06Z until 11Z. Winds
remain from the north and northeast with gusts to 20KT, before
shifting easterly into this evening, at around 10 to 20kts.

&&

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

&&

$$

SYNOPSIS...Viken
SHORT TERM...Viken
LONG TERM...Viken
AVIATION...Roberg