137
FXUS63 KOAX 190902
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
402 AM CDT Thu Sep 19 2024

.KEY MESSAGES...

- A few strong to isolated severe storms will be possible (5-15%
  chance) this afternoon and evening in far southeast NE and far
  southwest IA. Damaging winds and hail will be the primary
  threats, but a tornado cannot be ruled out.

- Widespread rainfall will begin Friday night and continue
  through the weekend. The heaviest rainfall is expected
  Saturday night into Sunday (60 to 90%). Rainfall totals of 1.5
  to 3" inches are expected

- Above average temperatures (highs in the 80s/low 90s) are
  expected to continue through Friday. Temperatures will cool
  this weekend into next week with highs in the 60s and 70s.

&&

.DISCUSSION...
Issued at 402 AM CDT Thu Sep 19 2024

Early this morning analysis showed a cutoff low spinning along
the ND/Saskatchewan border with an attendant surface cold front
stretching southward across the Dakotas and southwest into NE.
Meanwhile, another cutoff low was spinning just off the CA coast
and will play a large role in our weather heading into the
weekend. Over the forecast area, spotty showers and storms were
pushing east- northeast as low level moisture transport was
becoming quite strong. A few of these storms could produce some
hail and gusty winds early this morning, but for the most part,
not expecting anything too impactful. These storms should come
to an end/push east by mid to late morning and give way to
another warm and mostly sunny day. That said, the aforementioned
cold front will be sliding southeast through the area and will
lead to a bit of a high temperature gradient with mid 80s in
northeast NE and lower to mid 90s in southeast NE and far
southwest IA. Those areas that warm up ahead of the front will
also see dewpoints in the mid 60s to lower 70s, good for
1500-2000+ J/kg of SBCAPE per the HREF mean. As the front pushes
in late this afternoon/this evening, expect more shower and
storm development in far southeast NE/southwest IA. The
strongest deep layer shear looks to largely remain behind the
front, but still could see upwards of 35 kts of 0-6 km shear,
certainly good enough for some degree of storm organization. In
addition, model soundings show steep low level lapse rates,
indicating decent potential for some gusty to potentially
damaging winds with any of these storms. The big question will
be how far west or east they develop, as slower front
progression would suggest more of our area could see a strong to
severe storm threat, while a faster progression would push the
threat to our east. As it stands, the storm threat looks to push
to our east by around 10 PM.

Attention then turns to more widespread shower and storm
chances Friday evening through the weekend and into Monday as
the aforementioned western cutoff low approaches and a surface
low spins up east of the Rockies and eventually tracks through
the area. Most of Friday should be dry with a decent amount of
sunshine, allowing temperatures once again to top out in the 80s
to lower 90s. By the evening, a warm front will advance
northward into the area and low level moisture transport ahead
of the deepening low looks to ramp up and point into the area,
leading to at least spotty shower and storm development. Trends
over the last several days have been toward later development
with current consensus suggesting 10 PM, or potentially even
later. That said, there`s still about a 15% chance prior to
that, so definitely something to keep an eye on if you plan on
being outdoors Friday night.

At least spotty showers and storms look to continue through the
day Saturday, though with the trough and low remaining to our
west, coverage may end up being a little bit less than
previously expected, at least through the morning and early
afternoon. Instead, will likely have to wait until mid to late
afternoon/evening for more widespread development when we should
start to see much stronger forcing as the low inches closer and
a cold front slides in from the north. If we end up seeing
lesser storm coverage during the day, we could build a little
more instability and yield a small severe weather threat, but
overall confidence is rather low on how that would pan out.

Widespread precip will continue during much of the day Sunday
as the low passes through. While there remains some spread on
track of the low and in turn location of the band of heaviest
precip, overall consensus suggests the low will remain just to
our south, keeping us out of the warm sector and largely
eliminating any severe weather chances we may have for Sunday.
Still, with this strong of a system, it`s worth keeping an eye
on trends, as a slight shift north could give us a few stronger
to isolated severe storms in southern portions of the forecast
area. Regarding rain amounts, there will be plenty of moisture
to work with NAEFS guidance indicating precipitable water values
in the 1.25-1.75" range, good for the 90th to 99th percentile
of climatology for this time of year. Current forecast calls for
a a pretty widespread band of 1.5" to 3" of rain Sunday night
across the area, though slightly lower amounts are expected for
areas just north of Norfolk. Some locally higher amounts of 3"
to 4+" will also be possible, with guidance favoring these
totals in areas near and south of Interstate 80 (10-20% chance).
While rain will probably be heavy at times, given how dry most
of us have been, we can likely handle that amount of rain,
especially with the longer duration expected. Still, can`t
completely rule out some localized flooding in a few spots.
Finally, just want to further emphasize the track differences
between models, as even just a small shift could lead to 1-2"
reduction in forecast rainfall. I`m just glad this isn`t a snow
forecast!

Some spotty lighter precip could linger into Monday and Tuesday
behind the departing low as we remain under the influence of
cyclonic flow aloft and we see another cold front pass through
sometime Tuesday. Temperatures will also be much cooler and
fall- like starting Sunday, with highs in the 60s and 70s
through the remainder of the forecast period.

&&

.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 1119 PM CDT Wed Sep 18 2024

Scattered showers are developing west of KLNK, and these could
impact this location 06-08z, and could impact KOMA 08-10z.
Otherwise, VFR conditions with winds the primary concern. LLWS
at KLNK/KOMA 08-13z with winds at 2000` from around 190-200 at
35-40 knots. Southerly winds do become northwest through the
period.

&&

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

&&

$$

DISCUSSION...CA
AVIATION...DeWald