660
FXUS63 KOAX 252049
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
349 PM CDT Tue Jun 25 2024

.KEY MESSAGES...

- Moderate flood stage is ongoing or expected to begin along the
  Missouri River the next day or two, and lasting through the
  end of the week. See the hydrology section for more details.

- Heat indices as high as 107 are expected this afternoon across
  portions of southeast Nebraska and southwest Iowa.

- Scattered strong to severe thunderstorms are expected to
  develop from northeast Nebraska into southwest Iowa. The
  primary risk will be hail, some of which may be as large as
  baseballs. Damaging winds and a tornado or two will also be
  possible.

- Another storm system Thursday into Friday will bring several
  rounds of thunderstorms, some of which may be strong, and
  heavy rain to the forecast area.

&&

.DISCUSSION...
Issued at 213 PM CDT Tue Jun 25 2024

     This Afternoon and Tonight...

This afternoon, high temperatures in the 90s with dew points in
the 70s in most locations have resulted in heat indices ranging
from 100 to 108. As such, a heat advisory has been issued for
portions of southeast Nebraska and southwest Iowa through 7 PM
this evening.

The primary concern for impactful weather this evening heading
into tonight will be the potential for scattered strong to
severe thunderstorms to develop from northeast Nebraska into
southwest Iowa.

At the surface, a frontal zone extends from central Nebraska
into southern Iowa. Along and north of this front, moisture
pooling at the surface has helped increase dewpoints several
degrees, resulting in MLCAPE ranging from 3000 to 4000 J/kg.
Aloft, a low-amplitude shortwave is expected to traverse the
northern Plains northwest so southeast. As this wave ejects out
over the region, bulk shear this evening could be as high as 50
knots in northeast Nebraska, and 30-35 knots as far south as the
I-80 corridor. This shear profile in conjunction with extreme
destabilization of the boundary layer will result in the
potential for scattered strong to severe thunderstorms to
develop as early as 5 PM this evening. There is little agreement
as to where exactly convection will initiate. General model
trends suggest the potential for several areas/rounds of
thunderstorms this evening. Wherever storms develop, they are
expected to begin supercellular in nature, and grow upscale
quickly as they traverse east-southeast along the surface
instability axis. Though all modes of severe weather will be
possible, large hail appears to be the primary threat,
particularly early on during the evening hours. With extreme
instability in place, hail up to the size of baseballs will be
possible. Storm motions in general parallel the surface
boundary/instability axis. As such, fairly quick upscale growth
into bowing segments or an MCS is likely, transitioning from a
hail threat to more of a damaging wind threat. Convection will
last into the overnight hours, with storms exiting the region to
the south and east by 2 or 3 AM. With the tendency for
thunderstorms to potentially train over the same area, there
will also be a risk for flooding. Some locations may see up to
an inch of rain, though depending on storm coverage and tracks,
could locally be higher.

     Wednesday through Friday...

Wednesday is expected to be a pleasant day, with clear skies and
afternoon highs in the 80s. Dewpoints in the low to mid 60s will
also help keep heat indices much lower than what they have been
the last couple of days.

By early Thursday morning, troughing is expected over the
western CONUS with a low-amplitude short wave ejecting out into
the central Plains. This will bring the potential for rain
Thursday (30 to 50 percent chance). No severe weather is
expected Thursday during the day. Diurnally driven convection
over the terrain in the High Plains will initiate another round
of storms that will move east across the Plains overnight
Thursday night. The timing for these storms would be after
midnight, with small hail and gusty winds possible. Scattered
showers and thunderstorms may linger through the morning hours
on Friday, bringing some uncertainty as to how much
destabilization can occur before a cold front sweeps through the
region Friday evening. Regardless, strong forcing for ascent as
the primary piece of upper level energy moves across the
northern Plains and the Midwest and dew points well into the 70s
ahead of the surface front will create an environment favorable
for strong to potentially severe thunderstorms. Exact timing and
hazard details will become more clear as the week progresses.

     Saturday through Monday...

Medium range guidance suggests that upper-level pattern heading
into this weekend and the beginning of next week will favor
additional chances for showers and thunderstorms. Divergence
amongst model solutions remains too high to pin down any given
day for greatest threat, or if any of these days may see strong
to severe thunderstorms. Temperature wise, highs this weekend
should be in the 80s, with the region warming back up into the
90s by the end of the forecast period with heat indices across
southeast Nebraska and southwest Iowa potentially returning into
the 100s.

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1156 AM CDT Tue Jun 25 2024

A weak surface front is draped across east-central Nebraska into
southern Iowa. Areas north of this front (KOFK, KOMA) will see
winds prevailing out of the east-southeast. Areas south (KLNK)
will see wind prevailing out of the south/southwest. This
boundary should remain relatively stationary until thunderstorms
develop along it later this evening. After 21Z, scattered strong
to severe thunderstorms are expected to develop in northeast
Nebraska and move east-southeast across the region. Most likely
timing for thunderstorms at KOFK and KOMA have been included in
a TEMPO group, with the lower probability but still possible
time frame for convection in a -SHRA FM group. There is still
substantial uncertainty as to how far south convection will
move, so have left precip out of KLNK TAFs for now. Wind gusts
up to 60 knots and hail up to the size of baseballs will be
possible in the strongest storms (most likely northeast Nebraska
into southwest Iowa, KOFK and KOMA). Thunderstorms should move
south and east of the forecast area by 06Z.

&&

.HYDROLOGY...
Issued at 328 PM CDT Tue Jun 25 2024

...The Little Sioux River...

Minor flood stage was reached on the Little Sioux at the Turin
gauge just after 7 PM Monday evening. A levee breach further
upstream last night is showing a potential early and lower crest
downstream than originally thought. Current observations show
the river cresting at just over 27 feet this evening, with some
signal that waters at the gauge site might begin to start
dropping as early as tonight. Current forecasts have the Little
Sioux at Turin dropping below flood stage by Thursday afternoon.

...The Missouri River...

The Missouri River at the Decatur gauge has topped out at 37.42
feet. While water levels may rise to 38 before dropping, the
river is expected to remain in minor flood stage for the
duration of the flooding event. This northern stretch of the
Missouri may drop below flood stage as early as late Wednesday
night. Further south, moderate flood stage is either ongoing or
expected to begin later this week, as water levels at all river
gauges from Blair south continue to rise. River levels at Omaha
should crest Thursday afternoon. Current guidance has this crest
at 35.4 feet. Trends in gauge data suggest this crest may lag a
little later however, potentially featuring a slightly lower yet
prolonged crest on Friday. Regardless, moderate flood stage is
expected to begin in Omaha on the Missouri as early as Wednesday
morning and last through Saturday night.

The Missouri River crest will take several days to work its way
down the Nebraska-Iowa and Nebraska-Missouri border. The
Missouri River at Rulo should crest in moderate flood stage
Saturday Night, and drop below flood stage by next Tuesday
morning.

Additional information can be found at water.noaa.gov

&&

.OAX WATCHES/WARNINGS/ADVISORIES...
NE...Heat Advisory until 7 PM CDT this evening for NEZ045-051>053-
     066>068-088>093.
IA...Heat Advisory until 7 PM CDT this evening for IAZ055-069-079-
     080-090-091.

&&

$$

DISCUSSION...Darrah
AVIATION...Darrah
HYDROLOGY...McCoy