-- Discussion containing changed information from previous version are highlighted. --
810
FXUS63 KOAX 221748
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
1248 PM CDT Sat Jun 22 2024

.KEY MESSAGES...

- Widespread flooding to our north will eventually feed water
  into the Missouri River. A flood watch is in effect for the
  Missouri, and flooding appears increasingly likely by next
  week.

- If storms can develop this afternoon, they may become severe
  with large hail and isolated damaging winds the primary
  hazards.

- Monday into Tuesday may become quite hot, 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 Thursday into Friday.

&&

.DISCUSSION...
Issued at 340 AM CDT Sat Jun 22 2024

Current Scenario...
Showers with a few embedded thunderstorms have been generally
decreasing in coverage and intensity since 2 AM, but do continue
to drop moderate rain in parts of east central NE as we approach
4 AM. Rainfall estimates suggest that 3-4 inches or so have
fallen in parts of western Butler County, while OLU measured
2.72" through 3:40 AM. The outflow from this system has pushed
well south of the ongoing convection while the LLJ has veered
slightly and lifted its most convergent region to the northeast,
disassociated with the low level outflow boundary and amidst
weakening instability. All of this suggests that current
activity will continue to diminish and lift to the east
northeast over the next couple of hours. It is also worth noting
that a healthy elevated supercell produced intense winds in the
North Platte area this past hour, but is pushing into an
increasingly hostile environment with eastward extent, and
appears likely to dissipate prior to reaching the OAX forecast
area. The flood watch for northeast Nebraska (not including the
Missouri River Watch) has been cancelled.

A Note On River Flooding...
Another round of heavy rain fell over the already flooded areas
of southeast SD and northwest IA into southern MN. The James,
Vermillion, Big Sioux, Floyd, and Little Sioux Rivers all of
forecast points in major flood stage with several already
exceeding or forecast to exceed record flood stage. All of this
water is headed into the Missouri River below Gavins Point Dam,
and thus uncontrolled by the system of dams. The timing of flow in
these relatively flat river basins is complex, and observations
are of key importance in modeling downstream flows. This is
likely to cause flooding along the Missouri for several days.
Current forecasts indicate that the river will not reach flood
stage at or below Decatur until at least Monday, and the crest
will not reach the Omaha area until June 28 or 29. Given the
extent of upstream flooding, and the amount of additional rain
on Friday night, it appears very likely that the Missouri will
reach flood stage, and anticipate upgrading the existing watch
to a warning with the issuance of the morning Missouri River
Mainstem forecast. Even still, there will be some level of
uncertainty with the specific forecast magnitude until the water
from those upstream rivers gets closer to...or into...the
Missouri and flows are observed.

We should also note that the Ponca Creek at Verdel is in
Moderate flood stage this morning, but forecast to improve over
the coming day. The Elkhorn upstream of Norfolk had quite a bit
of rain fall around Oneill in the past 48 hours, and is
currently forecast to reach action stage, but will be monitoring
closely for flood potential.

Storm Potential Today...
The effective cold front is located just northwest of the
forecast area early Saturday morning, but a short wave trough
moving across western SD will progress steadily east over the
course of the day and push the cold front southeast in its wake.
By noon, the front should be approaching I-80 and by 6 PM should
be southeast of the forecast area. Forecast soundings in the
warm sector are initially capped, but show some cooling of the
cap as the front approaches, perhaps eroding inhibition enough
to allow early afternoon convection along the front. One
ingredient that seems to be largely missing in this equation is
that boundary layer convergence along the front is pretty weak,
and most CAMs are rather limited in convective initiation...
keeping storms weak or non-existent until later in the day and
only in far southeastern parts of the forecast area. However,
with that in mind, there is a fair potential for earlier
initiation along the front so long as the cap does effectively
erode, and if convergence or other boundary layer lifting
mechanisms are sufficient to support it. If sustained updrafts
develop, deep layer shear would likely be sufficient for right
moving supercells to organize, with some potential for hail and
damaging wind. As it stands, the threat is low, and hinges on
whether or not sustained updrafts will exist in our forecast
area.

Middle to Long Term Period...
Sunday will be mainly dry, although a small chance for a late
day storm west as southerly flow returns on the back side of
high pressure. Upper level ridging builds in for Monday, and
lingers into Tuesday with hot conditions expected. The near-
surface airmass will also be quite humid, and heat index values
are likely to exceed 100...possibly coming close to 110. While
precip chances are quite low, this could be a sneaky chance for
isolated severe storms late Monday, and again late Tuesday as a
short wave trough over the Northern Plains drops a front into
the area. Model agreement is then quite good regarding a strong
Northern Plains short wave trough moving through Thursday into
Friday, possibly bringing a decent setup for severe weather and
heavy rainfall.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
-- Changed Discussion --
Issued at 1248 PM CDT Sat Jun 22 2024

MVFR ceilings at FL020-025 will linger until 19z-20z at KOFK,
with diurnal mixing and frontal passage leading to VFR ceiling
FL040, and gradually becoming scattered. VFR conditions will
prevail at KLNK and KOMA with SCT to BKN clouds at FL040-060.
Front moving across the forecast area will cause southwest to
westerly winds 10 to 20 with gusts up to 25kt to veer to a
northwesterly direction between 20z and 22z. Any remaining low
clouds will dissipate by 00z-01z with northwest winds slackening
below 10kts, then becoming light and variable after 08z. There
is a 15 to 25% probability of MVFR visibilities 3SM to 5SM
developing 10z-12z, but will leave out for now.
-- End Changed Discussion --



&&

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

&&

$$

DISCUSSION...Barjenbruch
AVIATION...Fortin