112
FXUS63 KOAX 300354
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
1054 PM CDT Mon Apr 29 2024

.KEY MESSAGES...

- An active weather pattern will continue into the weekend.

- Showers and storms return Tuesday afternoon, with a 15-30%
  chance of severe storms. Large hail and damaging winds are
  the primary threats, but tornadoes cannot be ruled out.

- Storms redevelop Wednesday and linger into Thursday, with
  potential for a few severe storms and flash flooding.

&&

.DISCUSSION...
Issued at 322 PM CDT Mon Apr 29 2024

.Tuesday and Tuesday night:

A shortwave trough currently over the Pacific Northwest will
progress east into the northern Plains and mid MO Valley Tuesday
in tandem with mid/upper-level wind maxima situated on the
immediate equatorward side of that feature. Increasing zonal
flow across the central Rockies will allow for the eastward
advection of an elevated mixed-layer into the mid MO Valley,
atop a moistening boundary layer, characterized by dewpoints in
the 50s to low 60s. Those differential advections will yield a
moderately unstable air mass by afternoon ahead of a cold front,
which will push through the area during the afternoon and
evening hours. High temperatures will largely be in the 70s,
though some low 80s will be possible.

Forcing for ascent attendant to the midlevel wave coupled with
convergence along the front will foster scattered thunderstorm
development by early to mid-afternoon, initially along the NE-SD
border. Subsequent storm development appears likely southward
along the front in eastern NE during the mid to late afternoon
with that activity spreading into western IA during the late
afternoon into early evening hours.

A largely perpendicular orientation of the deep-layer shear
vector to the initiating boundary would suggest the potential
for more discrete storm modes. However, a relatively fast
boundary motion may keep storms within the zone of frontal
forcing, which would support the potential for upscale growth
into the line. These contradictory signals are apparent in
latest CAM data which offer various scenarios with regard to
convective coverage and predominant storm type. Should a
discrete or semi-discrete storm mode persist for a period of
time, the anticipated environment would support supercells
capable of very large hail up to 2-3" in diameter as the
predominant severe weather hazard. In the event storms
transition fairly quickly to a line, maximum hail size would be
limited (perhaps up to golf-ball size) with an increased risk
for corridors of damaging wind gusts of 60-70+ mph. The tornado
threat in either of these scenarios is complicated by initially
higher cloud bases and the potential for organized cold pool
development (especially in the linear scenario) that may precede
strengthening low-level shear during the late afternoon/early
evening time period. In short, a couple tornadoes are possible,
but the threat is considerably lower than this past Friday.

The progressive nature of the storms is expected to limit
flooding potential with the activity shifting east of the area
by midnight (12 AM Wednesday).

.Wednesday and Wednesday night:

The surface front that moves through the area tomorrow is
expected to stall across northern KS Wednesday in response to a
deepening surface low over eastern CO/western KS. Temperatures
will be cooler than those on Tuesday with highs in the mid 60s
to low 70s. The low is expected to develop into north-central
KS Wednesday night with the boundary attempting to lift into
southeast NE as a warm front. Aloft, another shortwave trough is
forecast to progress from the Great Basin into central Rockies,
which will contribute the development of a 40-50+ kt low-level
jet (LLJ) across the southern and central Plains Wednesday
night.

Thunderstorms are expected to develop during the afternoon and
evening hours along the surface boundary over northern KS. And
similar to this past Saturday`s setup, the extent of storm
development along that boundary will dictate how far north it
will move Wednesday evening/night. At the least, latest model
data suggest that storms will become widespread to the north of
the boundary and along the LLJ axis Wednesday night, especially
along and south of I-80 with an associated flash flood risk.
However, should the warm front lift north into parts of southeast
NE, then there would be an associated risk for all severe
hazards, including flash flooding.

.Thursday:

The above-mentioned surface low is forecast to rapidly develop
through eastern NE/western IA Thursday morning, reaching north-
central IA by midday. Meanwhile, a trailing cold front will move
through the area with the boundary exiting our area by mid to
late afternoon. Scattered showers and thunderstorms are likely
to be ongoing Thursday morning ahead of the surface low and
associated front. It remains uncertain whether sufficient
afternoon destabilization can occur along the surface front in
southeast NE and southwest IA to support a strong to severe
storm threat.

Highs on Thursday will largely be in the 60s with some low 70s
possible ahead of the front in southeast NE and southwest IA.

Friday through the weekend:

The 12z global models indicate another shortwave trough and
associated frontal system moving through the region Saturday,
supporting a chance of showers and thunderstorms. Severe weather
potential remains uncertain at this time as available
moisture/instability appears somewhat limited.

High temperatures will be in the 60s and 70s during this time
frame.

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 1042 PM CDT Mon Apr 29 2024

VFR conditions are expected at all TAF sites through 11Z. After
11Z, isolated to widely scattered showers and thunderstorms may
develop across southeast Nebraska (KLNK and KOMA). As such have
included a TEMPO group for this morning convection. Morning
convection should weaken and move east of the region by 15Z. After
19Z, an additional round of thunderstorms, some of which may be
severe, will develop across northeast Nebraska and expand
southeastward through 04Z. Thunderstorm conditions are not
expected to last long enough to be prevailing, so will
necessitate the inclusion of a TEMPO group in the next TAF
issuance.

&&

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

&&

$$

DISCUSSION...Mead
AVIATION...Darrah