000
FXUS63 KOAX 250825
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
325 AM CDT Thu Apr 25 2024

.KEY MESSAGES...

- Several rounds of showers and thunderstorms are expected,
  beginning tonight and continuing through Sunday.

- Severe weather appears likely (>80% chance), especially
  during the afternoon and evening hours on Friday, Saturday,
  and perhaps Sunday.

- Flash flooding is also a concern due to the potential for
  repeated thunderstorm activity over the same areas.

&&

.DISCUSSION...
Issued at 316 AM CDT Thu Apr 25 2024

.Today and tonight:

Warm/moist advection occurring along a 40-50 kt nocturnal low-
level jet has supported widely scattered shower and thunderstorm
development from western NE into eastern KS early this morning.
And, latest CAM output suggests that an elevated thunderstorm
complex will evolve prior to daybreak across portions of
western and central NE with parts of southeast NE being affected
by those storms later this morning. An interesting signal that
has been consistently shown over several runs of the HRRR is a
corridor of 40-50+ kt wind gusts overspreading southeast NE
later this morning, on the northeast flank of the more intense
storms tracking from south-central NE into northeast KS. It`s
not readily apparent what mechanism in the model is driving the
strong winds, but we will be on the lookout for their
development.

The early-day storms will move to the south of the area by
afternoon with the models indicating only weak reflectivity
structures across the area within a persistent warm advection
regime. Highs today will be limited by widespread cloud cover
with readings in the low to mid 60s.

By this evening, increasing height falls/forcing for ascent
downstream from a vigorous midlevel trough emerging into the
central and southern High Plains will support the development of
thunderstorms over northwest KS into south-central NE. That
thunderstorm complex is expected to increase in areal coverage
while spreading northeast into our area from late evening into
the overnight hours. The storms will be elevated to the north of
a warm front lifting though KS with forecast soundings
suggesting the potential for severe hail with the strongest
updrafts. In addition, the potential will exist for localized
flooding in areas of regenerative/training storms.


.Friday and Friday night:

The 00z global models remain in good agreement in suggesting
that a vertically stacked, but progressive low pressure system
will move into central NE by midday Friday before reaching northeast
NE by early evening. Meanwhile, an associated warm front will
lift north through eastern NE and western IA during the day
as a Pacific front advances into eastern NE during the
afternoon. Latest model data suggest the Pacific front will
serve as the focus for severe thunderstorm development during
the afternoon and evening hours.

Showers and thunderstorms may be ongoing Friday morning;
however, the northward advection of the system dry slot should
allow for cloud breaks and resultant air mass destabilization by
afternoon ahead of a Pacific front approaching the area from
the west. Forecast soundings within the destabilizing warm
sector exhibit steep lapse rates through a deep layer (owing to
cold temperatures attendant to the midlevel low), supporting the
potential for moderate instability amidst a kinematic
environment favorable for organized storm modes, including
supercells. The primary hazard will be large hail, potentially
up to 2-3" in diameter.

Multi-model consensus indicates the strongest low-level shear
developing from far eastern NE into western IA from late
afternoon into evening where tornadoes (including one or two of
EF-2+ intensity) are most probable. Tornado potential will
extend into northeast NE along the arcing Pacific front/frontal
occlusion where a favorable overlap of low-level CAPE and
vertical vorticity will reside.

The afternoon/evening storms are expected to advance to the
northeast of the area Friday night in conjunction with the low
pressure system moving into southern MN.

High temperatures will range from 60s north where clouds and
areas of precipitation could linger to 70s near the KS and MO
borders where breaks in the clouds are expected.


.Saturday and Saturday night:

The surface front trailing the lead low pressure system over the
upper MS Valley will bisect the area Saturday with that feature
extending southwest to a deepening surface low over western KS.
It still appears that we will see a break in shower and
thunderstorm chances Saturday morning into early afternoon with
high temperatures ranging from 60s in northeast NE to lower 80s
in far southeast NE.

Later Saturday afternoon into Saturday night, another significant
shortwave trough will pivot across the southern into central
Plains, supporting the deepening of the surface low over KS and
the northward movement of the surface boundary through our area.
Thunderstorms are expected to develop by late afternoon into
evening, along and south of the surface front within an
environment favorable for organized storm modes with all severe
weather hazards possible.

Showers and thunderstorms are likely to continue Saturday night
into Sunday morning with an increased risk for flash flooding
owing to greater runoff potential.


.Sunday and Sunday night:

The 00z global models suggest that this second low pressure
system will take a similar track to the the Friday system with a
cold front moving into eastern NE during the afternoon hours. It
appears that the attending midlevel dry slot will overspread
far eastern NE and western IA during the afternoon hours,
allowing for at least modest air mass destabilization to occur.
As such, the potential will exist for a few severe storms during
the afternoon and evening hours with the primary hazard being
large hail.

The forecast will indicate Sunday`s highs ranging from 50s in
northeast NE to 70s in southeast NE and southwest IA.

.Early next Week:

A quasi-zonal midlevel pattern is forecast to develop early next
week with some model differences in the timing and amplitude of
embedded shortwave troughs moving through that pattern. Guidance
suggests that a cold front will move through the area Tuesday
with low shower and thunderstorm chances Tuesday into Tuesday
night.

Highs in the 60s Monday are expected to warm into the 70s to
lower 80s ahead of the front Tuesday.

&&

.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 1141 PM CDT Wed Apr 24 2024

Widespread cloud cover and spotty showers are currently ongoing
across the region. With some showers not reaching the ground and
spotty coverage of convection, have opted to keep rain out of
TAFs for tonight except at KLNK. Highest rain chances will be
along and south of Highway 34 after 12Z. Ceilings will steadily
lower over the course of the TAF period with IFR ceilings
expected at all TAF sites by the end of the forecast period.
Moderate to heavy icing will be possible between 13000 and 19000
feet from 09Z to 18Z across all of eastern Nebraska and western
Iowa.

&&

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

&&

$$

DISCUSSION...Mead
AVIATION...Darrah

NWS OAX Office Area Forecast Discussion