Flash Flooding and Hail in Nebraska, July 4, 2023

Area Forecast Discussion
National Weather Service Omaha/Valley NE
313 PM CDT Tue Jul 4 2023

...Updated Forecast Discussion...

.DISCUSSION...
Issued at 249 PM CDT Tue Jul 4 2023

Key Messages:

 - Severe storms across the area this evening with damaging winds
   the primary hazards. Locally large hail is possible as well,
   and there is a very small non-zero chance for a tornado.

 - Showers and a few thunderstorms continue through Wednesday
   morning.

 - Much cooler temperatures for the work week with highs in the
   70s and lows in the 50s.

Convection is deepening as of 3 PM this Independence Day
afternoon. Convergence has increased and deepened over the past
couple hours from Boone and Antelope counties east along an
outflow boundary in far southern Pierce, Wayne, and Thurston
counties. Expect initial updrafts to organize into supercell
structures, particularly along that outflow boundary where
horizontal vorticiaty is maximized. Instability is substantial
with very little inhibition, and while deep layer shear is not
particularly strong, there does appear to be enough turning with
height and enough length to the hodograph to favor development of
mid level mesocyclones at least early on in the life cycle.
However, over time, expect the convection to become more strongly
forced by the advancing cold front and the development of rather
strong outflow due to a fairly dry sub-cloud layer over much of
the forecast area. Thus, there will be a risk for severe wind
gusts and larger hail early on in the event as well as a non-zero
chance for a tornado in the vicinity of the outflow boundary. That
will transition to mainly an outflow driven severe wind hazard
with embedded areas of hail as we get later into the evening. It
will be interesting to see how/where the outflow is able to
support deep convection as the low level shear vectors are not
particularly favorable and it would seem there is a good chance
for outflow to run out ahead of the convection this evening. This
would promote some surprising winds well before storms arrive but
would also favor near-severe or sub-severe wind speeds in any
scenarios where the outflow gets way ahead of the convection.
Another thing to watch will be the slightly more organized MCS
progged to move east near the KS/NE border late this evening. This
MCS should be a bit more organized but will have to interact with
any surging outflow and convection from our local convection.
Where it all converges this could lead to a zone of relatively
greater severe wind potential across far southern NE but will see
how the evening plays out.

Showers and embedded storms will continue into the morning hours
Wednesday but the big difference for tomorrow will be the influx
of cooler temperatures. Really the next several days will be quite
pleasant with highs in the 70s and lows in the 50s through the
work week...and climbing back into the 80s for the weekend. There
are a few low-end chances for rain with the best chance looking to
come Friday into Friday night and largely focused in the southern
part of the forecast area.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1227 PM CDT Tue Jul 4 2023

Main focus is on convective timing and tried to give the most
likely 2 hour window at all TAF sites. When storms pass through,
some locations will approach 50 kt winds or stronger with the
storms but unsure on exact locations relative to TAF sites at this
time. After the initial line of storms, will be periods of showers
or perhaps embedded TS for several hours before precip moves out
and some lower MVFR or perhaps even IFR ceilings build in. Some
uncertainty regarding cloud base height, but LNK seems to have
best chance for IFR.

&&

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

DISCUSSION...Barjenbruch
AVIATION...Barjenbruch

Hazardous Weather Outlook
National Weather Service Omaha/Valley NE
315 PM CDT Tue Jul 4 2023

IAZ043-055-056-069-079-080-090-091-NEZ011-012-015>018-030>034-
042>045-050>053-065>068-078-088>093-051015-
Monona-Harrison-Shelby-Pottawattamie-Mills-Montgomery-Fremont-
Page-Knox-Cedar-Thurston-Antelope-Pierce-Wayne-Boone-Madison-
Stanton-Cuming-Burt-Platte-Colfax-Dodge-Washington-Butler-
Saunders-Douglas-Sarpy-Seward-Lancaster-Cass-Otoe-Saline-
Jefferson-Gage-Johnson-Nemaha-Pawnee-Richardson-
315 PM CDT Tue Jul 4 2023

This Hazardous Weather Outlook is for portions of southwest
Iowa...west central Iowa...east central Nebraska...northeast
Nebraska and southeast Nebraska.

.DAY ONE...Tuesday Afternoon Through Wednesday

Strong to severe thunderstorms are will continue to develop across
northeast Nebraska through early evening, eventually becoming
widespread and marching southeast across the entire forecast area.

Through 8 PM the primary hazards with the most intense storms
will be isolated wind gusts up to 80 mph and isolated areas with
hail up to 2 inches in diameter. There is also a very small chance
for a tornado. After 8 PM through the very early morning hours,
the primary hazards will be broad swaths of 60 to 70 mph damaging
winds and isolated areas with hail up to 1.5 inches in diameter.
Pockets of heavy rainfall are also expected with localized flash
flooding possible.

.DAYS TWO THROUGH SEVEN...Wednesday night through Tuesday

The probability for widespread Hazardous Weather is low.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed for some areas late this
afternoon through the evening.