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979
FXUS63 KOAX 242040
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
340 PM CDT Mon Jun 24 2024

.KEY MESSAGES...

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- Flooding is expected to continue along the Missouri River this
  week. See the Hydrology section for more details.

- Hot temperatures are expected to continue tomorrow, with a
  heat advisory in effect for heat indices as high as 105
  degrees.

- A stray thunderstorm or two will be possible (~20 percent
  chance) later this evening. Scattered strong to severe
  thunderstorms will be possible (40-60 percent chance) tomorrow
  afternoon and tomorrow night.

- Scattered thunderstorms will return to the region Thursday
  night into Friday. Some locations may see up to an inch of
  additional rain heading into next weekend. A few storms may be
  strong to severe.
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&&

.DISCUSSION...
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Issued at 233 PM CDT Mon Jun 24 2024

...This Afternoon and Tonight...

Temperatures in the mid to upper 90s are widespread across
eastern Nebraska and southwestern Iowa. Some locations along the
I-80 corridor have hit 100 degrees today, or will do so the next
couple of hours. With dew points well into the 70s, heat indices
have been on the order of 105 to 115 degrees. Further to the
northwest, a weak cold front will slowly push its way south and
east across our area into the overnight hours. Isolated showers
are expected to develop along this front, particularly near and
north of US Highway 20. Due to very warm temperatures aloft, the
chances of thunderstorm development along this front are much
lower, on the order of 15 to 20 percent. Nonetheless, surface
temperatures are expected to be within a few degrees of the
convective temperature, keeping a couple thunderstorms later
this evening, likely after 5PM, within the realm of possibility.
If thunderstorms are able to develop, they will pose a risk for
strong gusty winds and small hail. The greatest chance for a
thunderstorm or two will be north of US Highway 30, but can`t be
rules out as far south as the I-80 corridor.

...Tomorrow and Wednesday...

To our northwest, a weakening surface low pressure will slowly
move southeast into the central Plains, likely tracking through
western and southern Nebraska tomorrow afternoon. East of this
surface low, a quasi-stationary surface boundary is expected to
drape across east-central Nebraska into western Iowa. Surface
moisture is expected to pool along this boundary, resulting in
an instability axis paralleling the front. Surface dewpoints as
high as the mid 70s will yield MLCAPE potentially exceeding 4000
J/kg. Aloft, a subtle shortwave is expected to eject out into
the central/northern High Plains by midday. As such,
thunderstorm development is expected near and northeast of the
intersection of the surface front and the low-pressure center.
Thunderstorms that are able to develop should quickly strengthen as
they ride the instability axis to the east-southeast through
eastern Nebraska and into western Iowa. Bulk shear potentially
in excess of 40 knots and storm motions paralleling the boundary
will favor bowing segments capable of damaging straight line
winds, large hail, and a brief spin up tornado. CAMs show an
erosion of the capping inversion sometime between 5 and 7 PM,
however warm temperatures in the mid-levels still yield some
uncertainty as to whether updrafts will be able to persist and
strengthen through the evening hours. There is also some
uncertainty with regards to how far north this surface boundary
will set up. Nonetheless, even if early storm development is
sparse in nature, upscale growth and increased coverage of
convection is expected heading into tomorrow night, with storms
likely moving east and south of the region by 1 AM. Hot and
humid conditions south of the surface front will bring heat
indices of 100 to 105 in the afternoon. As such, a heat advisory
has been issued, primarily for locations south of I-80.

Warm and mild weather returns to the region on Wednesday, with
afternoon highs in the upper 80s, approaching 90 across the
region and clear skies. Wednesday night, there will be the
potential (30 to 40 percent chance) for decaying storms out west
to make it into portions of eastern Nebraska. The greatest
chances for rain will be north of US Highway 30 and west of Us
Highway 77. The timing for these storms would be after midnight.

...Thursday Through Sunday...

By Thursday, the next upper-level disturbance is expected to
approach our region from the west. A trough over the northern
Rockies on Thursday should eject out into the northern Plains by
Friday. Height falls overspreading the Great Plains in advance
of this disturbance will provide enough lift for widely
scattered showers and thunderstorms (30 to 50 percent chance of
rain) to develop across the region. Moisture return from the
south will allow PWATs to potential reach 2 inches. This in
conjunction with tall and skinny instability profiles will
allow any convection that can develop across our area Thursday
afternoon into Thursday night to be efficient rain producers.
Some locations Thursday may see over half an inch of rain. Some
thunderstorms may be on the stronger side, however with the
strongest forcing for ascent lagging further west and the
surface cold front still in the northern Plains, severe
potential appears low at this time.

On Friday, the main piece of upper-level energy will approach
and move over our area. At the surface, a cold front will push
south and east across the region during the afternoon hours.
Ahead of this front, moderate stabilization of the airmass is
expected, with SBCAPE on the order of 2000 to 3000 J/kg. Bulk
shear is also expected to increase throughout the day on Friday,
with shear magnitudes as great as 50 knots possible. Scattered
thunderstorms are expected to develop along this boundary and
persist into the overnight hours. Uncertainties in the exact
timing of the upper-level disturbance, timing of the surface
front, storm motions, the strength of the capping inversion,
etc. preclude any further or more detailed discussion on exact
timing and threats associated with these storms. However
stronger storms appear possible, with a severe thunderstorm or
two not out of the question.

After Friday, and through the rest of the forecast period,
ridging is expected over the central CONUS, bringing several
days of dry weather across our region. Afternoon highs next
weekend will likely range from the mid 70s to the low 80s before
we begin to warm back into the upper 80s/lower 90s by next week.
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&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1200 PM CDT Mon Jun 24 2024

Gusty southerly winds across the region between 15 and 20 knots
will prevail through 00Z. A weak cold front will slowly move
northwest to southeast across the region, with winds veering to
prevail out of the southwest behind it. The timing of frontal
passage will be between 00Z and 09Z. There is a low chance of
isolated to widely scattered thunderstorms developing along this
front, however uncertainty is high at this time. As such have
left out of the TAFs for now. If thunderstorms develop, timing
would be between 22Z and 03Z north of I-80 (KOFK), and between
02 and 12Z along and south of I-80 (KLNK and KOMA). If storms
develop, there will be the potential for wind gusts up to 50
knots.

&&

.HYDROLOGY...
Issued at 105 PM CDT Sun Jun 23 2024

A number of forecast changes occurred for the Missouri, Platte
and Little Sioux Rivers during the morning round of updates.
Water flow from Missouri River tributaries down stream of Gavins
Point dam remain in major flood, with minor impacts beginning
along the Missouri River between Sioux City and Decatur. Minor
to moderate flooding is expected to occur along the Missouri
between today and next weekend, with a 5-25% chance of flood
levels reaching major stages downstream of Plattsmouth due to
additional water flow from the Platte River. The Platte
currently is flooding between Leshara and Ashland, with minor
flooding expected from Louisville to the confluence with the
Missouri tonight into early Monday. Minor to moderate flooding
is anticipated along the Little Sioux River Monday and Tuesday,
with historic crest levels being reached in northwest Iowa. Flooding
is abating along Ponca Creek to its confluence with the
Missouri in Knox County.

&&

.OAX WATCHES/WARNINGS/ADVISORIES...
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NE...Excessive Heat Warning until 8 PM CDT this evening for NEZ015-
     018-033-034-044-045-051>053-066>068.
     Heat Advisory until 8 PM CDT this evening for NEZ011-012-016-
     017-030>032-042-043-050-065-078-088>093.
     Heat Advisory from 1 PM to 7 PM CDT Tuesday for NEZ051>053-
     066>068-088>093.
IA...Excessive Heat Warning until 8 PM CDT this evening for IAZ043-
     055-069-079.
     Heat Advisory until 8 PM CDT this evening for IAZ056-080-090-
     091.
     Heat Advisory from 1 PM to 7 PM CDT Tuesday for IAZ069-079-080-
     090-091.
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&&

$$

DISCUSSION...Darrah
AVIATION...Darrah
HYDROLOGY...Fortin