871
FXUS63 KOAX 230506
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
1206 AM CDT Sun Jun 23 2024

.KEY MESSAGES...

- Flooding of the Missouri River tributaries in southeast South
  Dakota and northwest Iowa will lead to increased water flow
  into the Missouri River downstream of Sioux City. Flood
  warnings are in effect along the Missouri from Decatur to Rulo
  beginning early next week.

- There is less than a 5% chance of severe thunderstorm
  development in southeast Nebraska through early evening, with
  damaging winds the primary hazards.

- The hottest temperatures so far this year are expected Monday
  and possibly Tuesday, with heat index readings of 100 to 110.

- There will be additional storm chances next week, with
  occasional severe weather and heavy rainfall possible,
  particularly on Tuesday and Friday.

&&

.DISCUSSION...
Issued at 358 PM CDT Sat Jun 22 2024

Quasi-zonal flow prevails across the northern plains this
afternoon, with a short wave feature moving eastward into the
Great Lakes region. An attendant frontal boundary is slowing
moving through the forecast area, so far only marked by a
wind shift and slightly cooler temperatures. Diabatic heating
will allow SB/MUCAPE to increase into the 1500-2500 J/kg range
by late afternoon with bulk shear 30-35kt. Diabatic forcing
combined with weak large scale forcing and low level convergence
may be sufficient to develop isolated thunderstorms late this
afternoon, generally south and east of Harlan IA to Omaha-
Council Bluffs to Pawnee City line. Given bulk shear values on
the low side, it may be difficult to storms to sustain updrafts,
thus any storm that reaches severe limits may collapse producing
isolated damaging wind gusts. The front is expected to move
south of the forecast area early this evening, effectively
ending the severe weather threat. The rest of the evening will
be characterized by clearing skies and light northwest winds,
with temperatures falling into the 60s.

Sunday through Tuesday:

Upper level riding amplifies as aforementioned short wave
feature carves a long wave trough across the eastern U.S.
bisecting southern tier H5 dome. The sensible weather effect
across the forecast area is a dramatic increase in temperatures,
especially Monday. Temperatures on Sunday will be about 5
degrees above normal, with upper 80s and lower 90s expected, and
heat indicies in the mid 90s. Monday will be the sizzler of the
week, with high temperatures in the upper 90s to lower 100s and
heat indicies 100 to 110. There still is some spread in the
forecast guidance, with half the at least one of the ensemble
clusters indicating less ridging. 75+% confidence in heat
headlines being issued in the next 24 hours. Tuesday, the signal
is a little mixed. A vortex moving across the central Canadian
provinces has a slight reflection in the form of a diffuse upper
level disturbance that moves across the central plains Monday
night into Tuesday, dragging another weak cold front across the
region. Synoptic models and medium range ensemble clusters
indicate the development of a MCS that will move across the
area, mainly affecting northeast Nebraska and western Iowa.
Convective cloud debris and cooling from the passage of the
front may impact the level of warming, except for southeast
Nebraska and southwest Iowa. Still, NBM 25-75% temperatures near
or above 90 in most locations. Redevelopment of storms along the
front later in the afternoon appears possible, which could
further limit temperatures. Rainfall amounts do not appear
excessive at this time, with model QPF a quarter inch or less,
thus would not expect flooding situation to be exacerbated.
However, precipitable water values will be in the 75% of
climatology, thus isolated heavy rainfall may be possible.

Wednesday Through Saturday:

A relatively quiet weather day on Wednesday, with slightly above
average temperatures and no precipitation expected. A large
scale trough develops across the western U.S. coast Thursday,
with medium range deterministic and ensembles ejecting systems
quickly eastward Friday and Saturday across the northern U.S.
and southern central Canada. One or more convective complexes
will affect the area, with the possibility of severe weather and
heavy rainfall, with the grand ensemble indicating a 20 to 40%
probability of sufficient CAPE and shear for severe weather on
Friday. Temperatures will trend slightly above average Wednesday
through Friday, with more seasonable temperatures on Saturday.
Similarly the probability of 1 inch or greater rainfall
occurring somewhere across the region is 30 to 50%. The
additional rainfall could delay the recession of the Missouri
river if realized.

&&

.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 1203 AM CDT Sun Jun 23 2024

Latest runs of the short-term models suggest that fog chances
are decreasing at KOMA, but have elected to keep them in with
the expected slight winds, and potential for it to still by
patchy. Aside from the fog chances, winds have slackened and
will become calm to somewhat variable in not from the northwest,
and will return southwesterly tomorrow morning and turn
southeasterly while staying light.

&&

.HYDROLOGY...
Issued at 358 PM CDT Sat Jun 22 2024

Flood warnings have been posted along the Missouri River
downstream from Sioux City to Rulo. The successive river
forecasts during the past 24-36 hours have lagged the onset of
flooding and crests, forecasts are tracking with observations
more closely. This will be the first time since 2020 that the
Missouri has been in flood along its entire reach in the HSA.
Additionally flooding is occurring along Ponca Creak from its
headwaters to Verdel, with some indications that the river could
re-crest again based on the National Water Model. River levels
also are above action stage along the Platte between Schuyler
and North Bend, Loup upstream of Columbus and Clear Creek.
Fortunately there will be no precipitation in the short-term to
affect rivers in the next 24-48 hours, but precipitation Tuesday
and onward could impact the recession of the Missouri, and cause
other area rivers to rise from Wednesday onward.

&&

.OAX WATCHES/WARNINGS/ADVISORIES...
NE...None.
IA...None.

&&

$$

DISCUSSION...Fortin
AVIATION...Petersen
HYDROLOGY...Fortin