221
FXUS63 KOAX 192023
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
323 PM CDT Sun May 19 2024

.KEY MESSAGES...

- A line of severe thunderstorms may impact portions of
  southeast Nebraska this evening or early tonight. Straight
  line winds appear to be the greatest risk at this time.

- Several additional rounds of strong to severe thunderstorms
  will be possible Monday evening into Tuesday afternoon. All
  modes of severe weather will be possible including flash
  flooding.

- Additional rounds of thunderstorms will be possible beginning
  Thursday night. Timing and potential for severe weather is
  unclear at this time.

&&

.DISCUSSION...
Issued at 1258 PM CDT Sun May 19 2024

...Today and Tonight...

Widespread cloud cover and light rain will continue to shrink
and move east through the rest of the afternoon. There is
already clearing for much of the area west of US-77. To the
south in Kansas, less cloud cover has helped to destabilize the
atmosphere, yielding MLCAPE up to 3000 J/kg across portions of
southwest Kansas. Between our area and the more unstable airmass
to the south, a residual outflow boundary extends across north-
central Kansas before turning north into western Nebraska. The
general consensus amongst short term guidance is to lift this
boundary north into southern Nebraska by 5 PM this evening, and
to continue lifting it north through the early overnight hours.
The severe risk today will almost exclusively be south of this
boundary. An area of thunderstorms that has persisted in south-
central Nebraska is expected to track through east-central
Nebraska this evening. These storms will pose a low end wind and
hail threat. Being north of the aforementioned boundary, the
tornado threat with these storms will be near zero. There is
potential for the main complex of storms in Kansas to build
north into southeast Nebraska later this evening. The threat in
this area is more uncertain, as CAMs are still in disagreement
with how to develop these storms as they move east. Nonetheless,
if the north side of this complex can build north into southeast
Nebraska, it will pose a risk for all modes of severe weather.
The highest threat should these storms build north would likely
remain south of Highway 2, though stronger storms will be
possible as far north as I-80. All storms should dissipate
and/or move east of the region by midnight.

...Tomorrow through Tuesday Night...

With the approach of the primary upper-level disturbance from
out west, surface cyclogenesis is expected in northwest
Oklahoma/southwest Kansas tomorrow afternoon. Arcing northeast
out of the developing surface low will be a warm front. This
should extend somewhere across eastern Nebraska and western
Iowa by tomorrow afternoon. Moisture return at the surface is
more confident for tomorrow afternoon across eastern Nebraska
and southwest Iowa, with dewpoints well into the 60s. A capping
inversion is expected to be in place across the warm sector,
though SREF and GFS signal the cap might weaken substantially by
7 PM tomorrow evening. General consensus amongst short term
guidance is to develop a few isolated strong to severe
thunderstorms by the early overnight hours tomorrow night, with
coverage and intensity increasing as the main upper-level
disturbance ejects out into the central Plains. With the
development of a low-level jet expected, bulk shear increasing
to somewhere between 40 and 50 knots, and CAPE ranging from 1500
to 2500 J/kg, all modes of severe weather will be possible.
Though it is unclear whether the severe potential lasts through
the entire night tomorrow night, showers and thunderstorms are
expected to be ongoing into Tuesday morning.

By Tuesday morning, the surface low is expected to be somewhere
in the vicinity of south-central Nebraska, tracking quickly to
the northeast over the course of the day. A cold front will
extend to the southwest from the low-pressure. The airmass ahead
of this front is expected to destabilize quickly, with surface
based CAPE likely exceeding 2000 J/kg by noon. HREF suggests the
0-1km SRH will range somewhere between 100 and 200 m2/s2 Tuesday
morning. With a jet streak rotating up the downwind side of the
trough, bulk shear values will be on the order of 50 to 60+
knots. This setup favors early convection to develop along the
cold front by late morning, with strengthening into the
afternoon hours. Once storms become severe, all modes of severe
weather will be possible. This front should be fairly
progressive, with most model solutions having the front east of
our area into central Iowa and Missouri by 5 PM.



...Wednesday through Saturday Night...

A high pressure system is expected to build into the central
Plains on Wednesday, bringing a beautiful day across the region
with highs in the low 70s, dewpoints in the 40s and mostly
clear skies.

Beginning Thursday night, a series of shortwaves coinciding with
moisture return from the south will bring several chances for
showers and thunderstorms. Timing and strength of these
disturbances and the amount of moisture return at the surface is
too uncertain at this time to discuss exact timing and potential
for any stronger convection.


&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1156 AM CDT Sun May 19 2024

Easterly winds will veer to become south/southeasterly with the
passage of a warm front this afternoon/evening. There is a
chance (20 to 30%) of isolated strong to severe storms across
southeast Nebraska between 21Z and 00Z. This activity should
stay south of TAF sites. A second more widespread round of
thunderstorms will move through southeast Nebraska into
southwest Iowa (KLNK and KOMA) sometime between 02Z and 06Z.
These storms, particularly in Nebraska, will pose a threat for
damaging straight-line winds. Will likely include TEMPO group
for these thunderstorms in subsequent TAF issuance. All rain
should move east of TAF sites by 10Z tomorrow morning.

&&

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

&&

$$

DISCUSSION...Darrah
AVIATION...Darrah