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223
FXUS63 KOAX 290845
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
345 AM CDT Wed May 29 2024

.KEY MESSAGES...

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- Widespread rain showers and thunderstorms are expected to
  develop across the region tomorrow morning and persist
  through Friday morning. Some of these storms may contain heavy
  rain, small hail and gusty winds.

- There will be daily chances for rain/thunderstorms starting
  tomorrow and lasting through Tuesday.

- There is increasing potential for strong to severe storms
  during the Sunday-Monday time frame.
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&&

.DISCUSSION...
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Issued at 205 AM CDT Wed May 29 2024

...Today and Tonight...

Ridging over the central CONUS will continue to keep
precipitation out of our area for the day today. At the
surface, winds are expected to become south/southeasterly
initiating the return of gulf moisture back into the region.
Dewpoints by the end of today should rise into the 50s.
Temperatures will also be on the rise, with temperatures around
80 degrees this afternoon and lows tonight around 60 degrees.

...Tomorrow through Saturday Night...

A longwave trough in the Pacific Northwest is expected to move
into the Northern Rockies by tomorrow morning. Further south,
several weak low-amplitude shortwaves are expected to eject out
into the central Plains. Surface moisture should continue to
increase, with dewpoints across central Nebraska returning into
the low 60s by tomorrow afternoon. On the west side of this
tongue of surface moisture, a weak cold front is expected to
slowly move east and stall out in western Nebraska and central
South Dakota. By tomorrow morning, forcing for ascent associated
with PVA from the aforementioned shortwaves will help
convection start to develop across central Nebraska along and
east of the surface front. This will be aided by mesoscale
forcing at the exit region of the low-level jet. These initial
storms will be west of our area. By noon tomorrow, scattered
showers and thunderstorms are expected to move into portions of
eastern Nebraska, with the highest chances of rain north of
US-30 and west of US-77. Marginal instability will be in place
Thursday afternoon, most likely for areas west of US-77. Here,
MUCAPE will be as high as 1000 J/kg. This will bring a low end
risk for hail up to the size of quarters and gusty winds with
the stronger thunderstorms. Forecast soundings also show high
relative humidities through the depth of the troposphere with
tall skinny CAPE profiles. This in conjunction with slow storm
motions and PWAT ranging from 1 to 1.5 inches will bring the
concern for heavy rain and isolated pockets of flash flooding,
primarily across central and eastern Nebraska. The highest risk
for flooding will be south of I-80 where the highest PWAT values
will be, and west of US-77 where storms are expected to persist
the longest. Storms Thursday afternoon are expected to last
through the overnight hours and into Friday morning as they
slowly move east. By Friday morning, storms will be decreasing
in coverage and strength as they move into western Iowa.
Convection should largely be south and east of the region by
Friday afternoon, with a low chance (20 to 30 percent) of an
isolate shower or thunderstorm south of I-80 and east of US-75.

There will be very low chances for rain (15 to 25 percent) west
of US-77 Saturday night as afternoon storms coming off the high
terrain in the central High Plain move into eastern Nebraska
from the west. These storms will be weakening as they move into
our area, and will struggle to persist past 1 AM in the morning.

...Sunday through Tuesday...

There is increasing signal for more widespread chances of
thunderstorms Sunday and Monday. While there are still
substantial uncertainties with regards to timing, several key
factors are becoming more clear. First, general consensus
amongst models is to have a low pressure develop in the northern
High Plains and track east-northeast across the northern Plains
and the Upper Midwest. Extending south and west from the
pressure center, a cold front will move southeast across the
northern and central Plains. Ahead of this front, southerly
winds are expected to transport surface dew points in the 60s
and near 70 degree as far north as the South Dakota/North Dakota
border by Sunday evening. At the same time aloft, this system
will be supported by longwave troughing over the western CONUS with
its axis likely in the vicinity of the Rockies. The front is
expected to stall out across the central Plains before it
transitions to a warm front and recedes north in advance of the
next storm system.

What this means for us here in eastern Nebraska and western
Iowa, is we will see the potential for scattered thunderstorms
to develop Sunday afternoon/evening across northeast Nebraska
and eastern South Dakota. These storms would then move to the
east/southeast through the evening and early overnight hours,
with highest rain chances (50 to 60 percent) north of I-80.
Wherever the front stalls out, there will be a second potential
for isolated to scattered thunderstorms Monday afternoon as
well, though the exact placement of this risk is more uncertain
at this time. With dew points in the upper 60s and afternoon
temperatures in the upper 70s/low 80s both afternoons, surface-
based CAPE may well exceed 3000 J/kg east and south of the front.
Furthermore, bulk shear will be on the order of 30 to 40 knots,
particularly for locations north of I-80. Assuming these
details hold true, the environment will be favorable for strong
to severe thunderstorms both afternoons. Uncertainty is high
enough at this time to preclude any further discussion on
regions with highest severe risk and favored mode of severe
weather.

These forecast details will likely be changed/adjusted in the
coming days. With this being said, the main point I want to get
across for this section of the AFD is to keep your eye on the
forecast for Sunday and Monday for an emerging risk for
potential severe weather.

After this, model solutions diverge so it is hard to pinpoint
any specific storm location and associated potential for storms.
In general, the synoptic pattern favors continued rounds of
showers and thunderstorms during the middle and end of next
week.
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&&

.AVIATION /06Z TAFS THROUGH 06Z THURSDAY/...
Issued at 1159 PM CDT Tue May 28 2024

VFR conditions will continue through the TAF period. Winds will
shift to southeasterly by Wednesday morning. Expect winds to
increase to 12g20kt by Wednesday afternoon, then calm back down
to around 10 to 12 kt by Wednesday evening.

&&

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

&&

$$

DISCUSSION...Darrah
AVIATION...McCoy