260
FXUS63 KOAX 071742
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
1242 PM CDT Fri Jun 7 2024

.KEY MESSAGES...

- Severe thunderstorms will develop (95% chance) in northern
  Nebraska by mid to late afternoon, and move across parts of
  eastern Nebraska and southwest Iowa through mid evening.

- The strongest storms may produce areas of significant
  damaging wind and hail, flash flooding, and a lesser-but-non-
  zero chance for a tornado. The greatest potential for
  significant severe weather is southwest of a line from
  Niobrara to Norfolk to Omaha to Clarinda.

- There is another chance for showers or a storm late Saturday,
  and a lesser chance on Sunday, with mostly dry conditions
  after that through the first half of the week.

- The large scale weather pattern becomes increasingly
  favorable for a few rounds of strong to severe storms late
  next week into the weekend.

&&

.DISCUSSION...
Issued at 414 AM CDT Fri Jun 7 2024

Early Friday morning, conditions were quite comfortable across
eastern NE and western IA. Temperatures were in the 50s and a few
low 60s with light winds under high pressure. Most of the area will
wake up to a calm, pleasant morning. Our benign early weather will
not be a good indicator of what is to come late this afternoon and
evening in the form of strong to severe storms.

A long wave ridge axis from the Four Corners into Montana this
morning has a strong upper jet and embedded short wave trough
running over the ridge across the Rockies this morning. At the
surface, pressure falls are ongoing this morning with the deepening
surface low over eastern WY. Showers and a few storms have developed
in the warm advection wing into southwest SD, and this activity will
move east this morning, bringing showers and perhaps a storm across
northeast NE. Looking farther south, there is a pool of decent
boundary layer moisture as far north as extreme southwest KS. As the
surface low continues to deepen, that moisture will be drawn north
into north central NE by mid afternoon and an effective warm front
will lift north into the local forecast area where it will orient
itself from northwest to southeast by this afternoon.

Thunderstorm development is likely in north central Nebraska by mid
afternoon. One thing that we`ll need to watch closely is just how
far north these storms will develop and how far north the boundary
layer moisture and surface based instability will extend around the
time of initiation. It would seem that the longer that
convection is delayed, the farther north that the warm sector
will extend, and the farther north and east that severe storm
potential will extend. Wherever these storms do initiate, the
warm sector in central NE will be characterized by 1000-2000
J/kg of MLCAPE. Farther east, the MLCAPE decreases sharply but
still expect around 1000 J/kg to extend into a good portion of
the forecast area and probably even extend into southwest Iowa.
Those most unstable parcels should also be unstable enough that
a healthy cold pool could lift into the LFC and support forward
propagation...especially with westward extend in the forecast
area. Deep layer wind shear is impressive in the near storm
environment with some turning of winds in the low levels and an
elongated hodograph through the mid and upper levels of the
storm. So while CAPE is not particularly impressive, the shear
profiles will strongly favor storm organization and intensity.
This all favors an initial supercell storm mode transitioning
toward forward propagating systems and probably with wind-
driven hail being a concern during that transition period. So,
initial hazards will be smaller pockets of intense wind and
potential for some very large hail. This will transition toward
wind-driven hail especially in large RFD regions of storms...and
eventually toward a predominantly damaging wind and marginally
severe hail hazard. The forward propagating Corfidi vectors are
in the 70-90 kt range over southeast NE, and this alone suggest
that significant wind gusts greater than 80 mph are possible
assuming that this storm mode develops. There is also a non-zero
tornado potential, especially in southeast Nebraska in the
early evening hours where low level directional and speed shear
will be maximized compared to the areas farther northeast. The
peak severe weather time frame appears to be between 6 and 11 PM
in the local forecast area, but again will need to watch
initiation time to our west very closely...and a farther-north
initiation would cause more of our area to be under the gun. As
it stands, locations near/southwest of a line from Niobrara to
Norfolk to Omaha to Clarinda seem to stand the best chance for
severe weather.

There is also potential for some heavy rain and flash flooding,
despite the fast storm motion. Any flooding would be tied to
training storms near the frontal boundary draped across the area,
especially as the storm motion is pretty parallel to that boundary.
If the whole front lights up in advance of the severe storms and
these initial cells track along the front, then some areas could see
isolated 3+ inch amounts of rain. This isn`t a guarantee, but a
possibility.

Northwest flow persists through the weekend with another short wave
trough passage on Saturday bringing a chance for showers and storms,
although these should not be strong. There is perhaps another lower
chance for showers Sunday evening, but after that see a good chance
for mostly dry weather through the first part of the week with highs
in the 70s...and 80s by Wednesday.

The upper air pattern flips by late in the week with a high
likelihood of a large scale trough building into the western CONUS
and a series of short wave troughs ejecting into the Plains.
Boundary layer moisture will increase and this is a favorable setup
for increasing potential for rounds of severe weather by next
weekend into the following week. Most model guidance keeps the heart
of the jet stream north of the local area, but embedded waves of
enhanced mid/upper winds will drive severe potential. There is
plenty of time to watch this unfold, but certainly appears to be a
signal for an active weather period.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 1233 PM CDT Fri Jun 7 2024

VFR conditions expected through this afternoon with winds out of
the southeast. Storms are expected to develop later this
afternoon over north-central Nebraska and track southeast across
eastern Nebraska this evening. Cigs with storms should stay VFR,
but winds could get as high as 70+ kt on the leading edge of the
strongest storms out of the northwest. Large hail and tornadoes
are also possible. Once storms move through, winds will return
back to the southeast for a period until the front moves through
around 09 - 12Z, when winds shift to northwesterly. This front
will also bring in a 50-60% chance of MVFR cigs around 1500 ft,
but possibly as low as 700 ft (20% chance). MVFR cigs should
break up and lift around 16-18Z on Saturday.

&&

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

&&

$$

DISCUSSION...Barjenbruch
AVIATION...McCoy