FXUS63 KLBF 060908

Area Forecast Discussion
National Weather Service North Platte NE
408 AM CDT Sat Jun 6 2020

.SHORT TERM...(Today through Sunday)
Issued at 407 AM CDT Sat Jun 6 2020

Short term concerns revolve around the potential for severe weather
both Saturday and Sunday across portions of western and north
central Nebraska. Large-scale pattern shows large scale ridging
across the southern plains caught between departing troughing in the
east and stronger troughing to the west. Highly amplified flow
across the across the Rockies will slowly shift east through the day
Saturday as a disturbance lifts up out of the desert southwest and
into the central Rockies today which will be the impetus for
thunderstorm development late this afternoon and evening. Prior to
that, strong southerly flow in the lowest levels will increase in
response to approaching mid-level wave. This will lead to strong
winds developing this afternoon as h7 and h85 winds 2 to 3 standard
deviations above climatology overspread much of the central plains.
Looking at morning RAP forecast soundings, these increased winds
with good insolation will allow the boundary layer to mix to a depth
of 3-4km. With the winds in this layer largely unidirectional and
generally south-southwest to north-northeast, momentum transfers
will be efficient during the daytime. As a result, winds will likely
climb into the 20-30 mph sustained range with gusts up to 50 mph
possible...the strongest of these generally across the Sandhills
into southwest Nebraska. Temperatures will be very warm today as h85
temperatures approach 30 degrees celsius which may be record
territory for LBF on a 07/00z sounding. Given these very anomalous
temperatures and winds being favorable for mixing, have boosted
temperatures slightly with all locations climbing into the 90s and a
few spots potentially touching triple digits. Cloud cover may slow
things down a bit if it ends up being thicker than forecast, but
confidence is high in most locations reaching the mid 90s at least.
What will be limited today is the overlap of the heat and humidity
and though a few locations may see heat indices reach the low 100s,
all locations should fall short of Heat Advisory criteria.

Attention quickly turns to the western half of the CWA where the SPC
has highlights in the SWO Day 1 for Slight and Enhanced risks for
severe weather. Thinking the bulk of the daytime will be dry across
the area given such warm mid-level temperatures. Stronger forcing
for ascent will arrive towards the late afternoon and evening as
stronger DCVA arrives with a few shortwaves rotating around the
eastern periphery of the parent trough. Divergence aloft and mid-
level convergence will increase in response and coupled with h5
height falls should lead to storm development along and just east of
the I-25 corridor in closer proximity to where the developing
surface low will form. Given general south to north winds through
much of the profile, storm track will be southwest to northeast.
This lines up with the mean wind flow and 0-3km and 0-6km BWD
vectors. As storms track west of the area, outflow may creep east
into the local area and provide the focus for additional
thunderstorm development. Morning RAP guidance suggests a sharp
drop-off of instability as you go west to east with the highest
values generally along and west of a Valentine to Hayes Center line
with a relative minimum closer to Highway 83 then another slight
increase further east towards Highway 281. With this in mind,
thinking the greatest potential for severe weather will remain
across the western Sandhills into portions of the southern Panhandle
and southwest Nebraska. Deep layer shear will be strong with 0-6km
BWD values of 40-50 knots and MUCAPE values of around 3000 j/kg.
Given the orientation of the surface trough and shear vectors,
storms are expected to go upscale fairly quick and with such strong
flow aloft, damaging winds will be the greatest threat with
potentially a significant gust or two possible. Steep lapse rates
will also be in place and hail will also be possible but given
relatively low SB-LI values, lack of higher normalized CAPE, and high
freezing/WBZ levels, believe this threat is lower. Thinking tornado
potential is fairly low as well given high LCLs and lack of
curvature in forecast hodographs. Will have to watch for the
potential for back-building thunderstorms during the evening as the
low-level jet kicks in. Though we`ve been fairly dry lately,
training storms may lead to localized areas see heavy rainfall
though flooding is not anticipated at this time. Trough axis clears
the area to the north by late this evening and we should expect to
see storms wind down around or shortly before Midnight tonight.

Residual outflow/frontal boundary will split the CWA late tonight
and make for a stark contrast in overnight lows. With the stronger
flow from the low-level jet across the east, will see lows remain in
the 70s with values in the 50s and 60s further west. Precisely where
this boundary sets up is difficult to pin down but initial thoughts
are near a North Platte to Ainsworth line. This frontal boundary
will drift slowly back to the west and set up the area for a second
round of strong to severe thunderstorms across the local area on
Sunday as another disturbance moves through the area during the
afternoon and a developing surface low sets up across northeast
Colorado and rides the boundary to the north up through Nebraska
into South Dakota. SPC highlights portions of western Nebraska in a
SWO Day 2 Slight risk with most locations in general thunder or a
Marginal risk. With continued warmth off the surface, capping should
hold out until boundary layer mixing erodes the lingering inhibition
and allows storms to develop. Continued strong flow aloft will allow
strong deep-layer shear to be in place and with daytime heating,
strong instability should once again develop. Initially, storms will
be predominantly large hail and damaging wind producers given steep
lapse rates and largely linear hodographs with limited tornado
potential again due to elevated LCLs and limited SRH. High
temperatures on Sunday will once again climb into the 90s for most
if not all locations making for yet another hot day this weekend.

.LONG TERM...(Sunday night through Friday)
Issued at 407 AM CDT Sat Jun 6 2020

Beginning 12z Monday. The big wild card in the extended forecast is
the evolution of the Gulf of Mexico tropical system. While local
impacts from it are unlikely, its influence on the upper patter and
progression of the troughing across the western CONUS will be
something to watch. For now, models are in fairly good agreement
that another disturbance will move into the area on Monday with a
surface boundary associated with a surface low across the Canadian
prairies moving into the area. This should lead to another period of
scattered rain and thunderstorms across much of western Nebraska but
also herald in a much cooler stretch of days this week with the last
of the 90s being swept out and highs only reaching the 70s and 80s
for much of the upcoming week. The threat for strong to severe
storms will continue on Monday along this boundary though the
greatest overlap of shear and instability may reside along or just
east of the eastern row of counties. This will be a very fluid
situation with some shifting of the focal point likely in the coming
days. This trough and frontal boundary should sweep out much of the
humidity and any threat from the tropical system leading to a
stretch of benign weather for Tuesday and beyond. Temperatures will
be much closer to normal for early June standards and precipitation
chances will be limited with shortwave ridging building in through
the week and surface high pressure expected to setup along the Gulf
Coast. With dew points forecast to be in the 30s and 40s and highs
in the 70s and 80s, it`ll feel more like spring than summer.


.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1247 AM CDT Sat Jun 6 2020

Thunderstorms and increasing winds remain the primary aviation
weather threats for western and north central Nebraska. Isolated
storms are ongoing early this morning north of KOGA, but latest
guidance suggests these dying off before 08z. Otherwise attention
turns to winds after 12z, greater than 30kts are possible in the
afternoon. We are watching for the prospects for severe weather
starting late afternoon. Gusty wind and large hail remain the
primary threats to western Nebraska.




SHORT TERM...Jurgensen
LONG TERM...Jurgensen

NWS LBF Office Area Forecast Discussion