Severe Thunderstorm Warning 2, NWS Omaha, NE

Area Forecast Discussion
National Weather Service Omaha/Valley NE
148 PM CDT Sat Apr 6 2024

.KEY MESSAGES...

- A powerful storm system will bring strong southeasterly winds
  to the region this afternoon into the evening with gusts of
  45-55 mph expected. The strong winds will contribute to
  extreme wildfire conditions this afternoon.

- A fast-moving band of showers and thunderstorms (100% chance
  of development) will move through the area this evening with
  widespread measurable rainfall expected. Some severe weather
  is possible (10- 20% chance within 25 miles of a point).

- Dry weather returns Monday into Tuesday, with scattered to
  broken clouds forecasted for eclipse watchers locally.

&&

.DISCUSSION...
Issued at 147 PM CDT Sat Apr 6 2024

.TODAY...

A strong upper level low pushing east off of the rockies has spun up
a lee cyclone over northeast CO overnight. The low is deepening and
taking on a negative tilt as it makes its way towards the Nebraska
panhandle and brings us an eventful day of weather concerns
including strong winds, extreme fire danger, and the potential for
severe thunderstorms. The low has helped to push a cold/occluded
front across the NE/KS border and draping down into central OK.

The deepening low has prompted a tightening pressure gradient,
bringing strong winds to the entire region. This will continue to
support a strong nocturnal southerly low-level jet through the day
which in addition to deep diurnal mixing will bring sustained
southeasterly winds of 30 to 35 mph with gusts of 45 to 55 mph
possible. As of 1:30 PM, gusts over 40 mph have already been
observed in the area. This has prompted a High Wind Warning to be
issued for the strongest winds in the western half of our CWA until
10 PM tonight with a Wind Advisory in place for the remaining
counties.

Fire danger concerns remain extreme today. Despite minimum relative
humidity values remaining in the 30 to 40 percent range ahead of the
front, very strong winds and dry fuels will lead to rapid fire
development today. This has prompted a Red Flag Warning to be issued
for the entire CWA into the afternoon and evening. Fire weather
concerns will remain until this evenings line of thunderstorms and
rain showers moves through.

The potential for severe weather moves into the area late this
afternoon into the evening in the wake of the frontal passage.
Plentiful deep layer sheer is present across the area (0-6 km shear
of 60-70+ kts). Instability will be the limiting factor in this
event with dewpoints struggling to break above 50 degrees. A narrow
corridor or MUCAPE values from 250 to just above 500 J/kg will drape
from southern NE into northern KS ahead of the front. Regardless,
strong forcing for ascent associated with the low pressure system
will prompt convective initiation in South Central NE and North
Central KS this afternoon before pushing east. There is potential
for the development of a few low-topped supercells before a linear
storm mode takes over. The best potential for severe weather will be
from 6 pm to 9 pm west of a line from Columbus to Nebraska City, NE.
The primary hazard will be strong winds with gusts over 60 mph
possible. The HRRR has consistently shown a signal for wind gusts
over 50 kts (approx. 58 mph) working their way into southeastern NE
and some areas of far southwestern IA. Large hail (1" or greater)
will be possible with some of the more isolated strong updrafts
thanks to steep (7-7.5 degree/km) mid level lapse rates. While it is
not the primary hazard, a brief tornado or two can't be ruled out as
0-1 km shear values of 20 to 30 kts are complimented with modest low-
level SRH values.

Convection will weaken into the evening as convective inhibition
takes over in eastern NE and western IA. An overperformance in
instability in this area could lead to the severe threat creeping a
little further into eastern NE than expected. However, the entire
area is expected to see this fast-moving band of showers and
thunderstorms pass through with measurable precipitation. A quick
0.25 to 0.50" is expected.

.SUNDAY...

The deep low pressure system is expected to track east across
Nebraska and into northwest Iowa through Sunday, bringing more
precipitation chances along its path.  The best chance of seeing
measurable rainfall will be late Sunday morning into the afternoon.
A strong gradient in PoPs is present across the CWA with values of
60 to 80 percent present toward the NE/SD border and values dropping
off to 10 to 15 percent by the NE/KS border. Steep 700-500 mb lapse
rates of 6 to 7 degrees/km will be present coinciding with very cold
air aloft. This brings the potential for a rumble or two of thunder
as well as funnel development due to the cold air aloft. A brief
period of hail (non-severe) is also possible. Weekend rain totals
remain between 0.60 to 0.75" north of Interstate 80 with values
dropping towards 0.35 to 0.45" south of Interstate 80.

.MONDAY THROUGH FRIDAY...

The upper level low is expected to fill and move northeast towards
the Great Lakes region during the first half of the week. This will
bring southwesterly flow aloft and high temperatures in the upper 50
to mid 60s through mid-week. Cloud cover in response to the
departing low pressure system may impact eclipse viewing on Monday.
The NBM is expecting a strong gradient of cloud cover across the
CWA. The NBM is projecting the southern half of our CWA to have the
best chance of clear skies with the northernmost counties of our CWA
only displaying a 30-40% chance of seeing cloud cover less than 50%
(scattered to broken clouds) during the partial eclipse viewing.

High temperatures are expected in the 70s and potentially the 80s by
the end of the week as upper level ridging builds into the region.
Our next chance of precipitation will be Wednesday night into
Thursday morning as an upper level trough slides to our southeast.
PoPs remain low (15 to 20 percent) and contained to our southeastern
counties at this time.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1200 PM CDT Sat Apr 6 2024

VFR conditions will prevail with strong southeasterly winds
expected throughout the forecast period. Winds will increase to
their peak of 30-35 kts with gusts of 40-55 kts possible this
afternoon and evening. Winds will be improved (yet still
strong) tomorrow with gusts of 25-30 kts likely.

A line of showers and thunderstorms will develop to the
southwest around 5pm this evening before pushing east through
the late evening. This line is expected to impact KOFK and KLNK
around 00-03Z and KOMA from 01-04Z. Storms are expected to
weaken as they move east with thunderstorm potential in question
by the time they reach KOMA. Ceiling may decrease to FL040 with
this passage. Additional light rain is expected to move into
KOFK towards the end of the forecast period.

&&

.OAX WATCHES/WARNINGS/ADVISORIES...
NE...Wind Advisory until 10 PM CDT this evening for NEZ015-034-045-
     052-053-067-068-090>093.
     Red Flag Warning until 8 PM CDT this evening for NEZ011-012-
     015>018-030>034-042>045-050>053-065>068-078-088>093.
     High Wind Warning until 10 PM CDT this evening for NEZ011-012-
     016>018-030>033-042>044-050-051-065-066-078-088-089.
IA...Wind Advisory until 10 PM CDT this evening for IAZ043-055-056-
     069-079-080-090-091.
     Red Flag Warning until 9 PM CDT this evening for IAZ043-055-
     056-069-079-080-090-091.

&&

DISCUSSION...Wood
AVIATION...Wood

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