Hail and Damaging Winds in Nebraska, September 1, 2018

Area Forecast Discussion
National Weather Service Omaha/Valley NE
608 PM CDT Sat Sep 1 2018

.SHORT TERM...(Tonight through Tuesday)
Issued at 351 PM CDT Sat Sep 1 2018

The main forecast problems during the forecast period is
severe weather and heavy rain.

A surface cold front extending from north central Iowa to south
central Nebraska is forecast to move little during the forecast
period. Along and south of surface front surface dewpoints are in
the lower 70s. ML CAPE values are at 17Z between 500 and 2000
J/Kg. This will increase to around 3000 J/Kg with continued
surface heating south of the front over southeast Nebraska.
Forecast 0-6 KM bulk shear over southeast Nebraska is expected to
be between 35-40 kts, which is sufficient for a severe
thunderstorm development.

Water vapor imagery indicate upper short wave lifting out northeast
out of near the KS/CO border. This wave is expected to enhance
convective development across northern Kansas and south central
Nebraska. HRRR models indicate a complex of storms reaching the
southwestern portion part of the OAX CWA by 00Z and then moving
northeast to near LNK and BIE between 01-02Z and to OMA by 03Z.
Main hazards will be larger hail and damaging winds with After
that wave goes through, convection lingers on through the night.

This lingering convection brings up the possibility of flash
flooding. PW values from model soundings in eastern Nebraska and
western Iowa are forecast to be 1.5 to 1.8 inches,which is high
for this time of year. Planning on doing a flash flood watch to
cover southwest Iowa and several counties in southeast Nebraska.

Depending on what happens tonight, a flash flood watch is a
distinct possibility for Sunday or Monday as more waves of
thunderstorms move across the area due to the surface front
stalling out across southeast Nebraska and western Iowa. Models
bring in another wave of storms mainly Sunday night and again on
Monday.

Front lifts northward Monday night into Tuesday with
thunderstorms again possible during the day.

.LONG TERM...(Tuesday night through Saturday)
Issued at 351 PM CDT Sat Sep 1 2018

Tuesday night, another round of storms is forecast to move into
the area as the front moves southward This activity and continue
into Wednesday. After Wednesday, front moves into Kansas and
Missouri. But, thunderstorm activity may linger on and off through
Sunday over southeast parts of Nebraska.

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 553 PM CDT Sat Sep 1 2018

Thunderstorms activity is expected to develop at all TAF sites
this evening. LNK and OMA will see the storm potential increase
from 01-03z at LNK and OFK and 02-04z at OMA. Some of these
storms tonight have the potently to be strong to severe,
particularly over southeast Nebraska impacting LNK and OMA.
Scattered storms are expected to continue overnight with off and
on rain chances through Sunday.

&&

.OAX WATCHES/WARNINGS/ADVISORIES...
NE...Flash Flood Watch through Sunday morning for NEZ045-050>053-
     065>068-078-088-089.

IA...Flash Flood Watch through Sunday morning for IAZ055-056-069-079-
     080.

&&

SHORT TERM...Smith
LONG TERM...Smith
AVIATION...HB

Hazardous Weather Outlook
National Weather Service Omaha/Valley NE
458 PM CDT Sat Sep 1 2018

IAZ043-055-056-069-079-080-090-091-NEZ011-012-015>018-030>034-
042>045-050>053-065>068-078-088>093-021200-
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-
458 PM CDT Sat Sep 1 2018

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

.DAY ONE...Tonight and Sunday

Severe thunderstorms are expected through much of the evening,
especially along and south of Interstate 80. The best timing for
severe weather will from around 6 to 7 pm, through about 3 to 5
am. A few storms could approach severe limits with winds 60 mph
or higher, hail of 1 to 2 inches in diameter, and 1 to 2 inches
of rain. Those with outdoor plans this evening should remain
weather aware and be ready to implement a severe weather plan at a
moments notice.

There could be flash flooding tonight, especially if several
rounds of storms move over the same locations.

Minor flooding will continue along the Missouri River upstream of
Lewis and Clark Lake in northwest Knox county.

.DAYS TWO THROUGH SEVEN...Sunday night through Saturday

Scattered thunderstorms remain in the forecast for Sunday through
Monday. Some strong storms and areas of locally heavy rain will be
possible, especially from late Sunday afternoon into Monday
morning. Some flash flooding could develop. Total rainfall
through Monday could reach 3 to 5 inches in some spots across east
central Nebraska and western Iowa.

The weather pattern should remain active through at least mid
week, with a continued chance for thunderstorms just about every
day.

Minor flooding will continue along the Missouri River upstream of
Lewis and Clark Lake in northwest Knox county. With the expected
heavy rains through the remainder of the Labor Day weekend,
additional river flooding could develop.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed in some areas tonight, primarily
across southeast Nebraska and southwest Iowa.

Pearson