Flash Flooding and Flooding in Nebraska, June 18 to 20, 2020

Area Forecast Discussion
National Weather Service Omaha/Valley NE
628 AM CDT Thu Jun 18 2020

...Updated Aviation Forecast Discussion...

.DISCUSSION...
Issued at 335 AM CDT Thu Jun 18 2020

Today and Tomorrow:
Currently in north central Nebraska, there are ongoing
thunderstorms and heavy rain. The rain is associated with a cold
front that is expected to move through the forecast area today.
The cold front is expected to move into Knox County (the far
northwest extent of Omaha's warning area) by 7 am. This is a slow
moving front and is not expected to be felt in Omaha until 6 pm.

That ongoing precipitation isn't expected to have much impact this
morning. It's likely it will dissipate, before regaining
strengthen in the early afternoon. However, it wouldn't be
surprising to have a some light rain in the Albion, Norfolk,
Neligh, and Crofton areas. The slow moving front will allow for
plenty of daytime heating for the southern half of the forecast
area. The SPC has issued a marginal severe risk covering eastern
Nebraska and western Iowa. Day time heating will see that surface
based CAPE will reach 1500 to 2500 J/kg across the area. The lack
of deep layer sheer though should keep the risk to isolated storms
with strong, potentially damaging, wind gusts as the most likely
threat.

The other potential hazard will be heavy rain. Precipitable
water will increase with strong moisture advection ahead of the
cold front. This increase in precipitable water, slow movement of
the front, and potential for storm training could lead to some
high rain amounts across the area. By time the rain ends Friday
night, a few spots could be over 2 inches of rain. Confidence is
low in a specific area as it's difficult to pinpoint locations due
to the nature of convective storm development.

High temperatures Friday are expected to top out in the 75 to 80
degree range. And if we're lucky (if you don't enjoy 90 degree
temperatures I suppose), 90 degrees won't be seen for the next 7
days or so. There will be another chance for rain Friday
afternoon and evening as a weak shortwave is expected to move
across the area. The best chance for rain will be along the
Nebraska/Kansas border.

Saturday:
Water vapor imagery currently shows another upper level trough
developing over the West Coast. That trough will likely continue
to move south, reaching the Four Corner's area before the
southwesterly flow ejects it over the plains. It should strengthen
as it moves across Nebraska and will provide another good chance
for rain. These cumulative rain events could result in 2 to 4
inches of much needed rain for the area. Hopefully it'll be spread
far enough apart over time that flooding concerns will be
minimized. Though, river levels are likely to rise in response to
the rain.

Sunday through Wednesday:
Extended range guidance indicates there will be a couple more chances
for rain Sunday night and Monday. At this time, it's too far out
to mention specifics. Northwest flow will dominate the area though
so expect temperatures to be near normal for the extended period.

&&

.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 622 AM CDT Thu Jun 18 2020

Scattered thunderstorms in northeast Nebraska this morning may
affect KOFK for a couple hours with brief MVFR cigs/vsbys through
mid morning. Cold front sliding southeast will reach KOFK by 17Z,
then KOMA and KLNK by 22Z or so. Thunderstorms are forecast along
and just behind the front, affecting KOFK through mid afternoon
before sliding off to the southeast. As front slows in southeast
Nebraska this afternoon and evening, continued development of
showers and thunderstorms behind cold front will likely affect
KLNK and KOMA through the end of the TAF period. However the
strongest storms are forecast between 00Z and 06Z when IFR
cigs/vsbys are likely. Strong outflow winds are possible as well.

&&

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

DISCUSSION...Fajman
AVIATION...Dergan

Hazardous Weather Outlook
National Weather Service Omaha/Valley NE
411 AM CDT Thu Jun 18 2020

IAZ043-055-056-069-079-080-090-091-NEZ011-012-015>018-030>034-
042>045-050>053-065>068-078-088>093-190915-
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-
411 AM CDT Thu Jun 18 2020

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

.DAY ONE...Today and Tonight

There is a marginal risk for severe weather today. A cold front
will slowly move through the area leading to rain, and possibly
some isolated strong storms. Heavy rain, strong winds, and small
hail are the most likely threats. The time frame for severe
weather will be from 1 PM to 8 PM.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday

There are several chances for rain through the weekend which
could lead to elevated stream levels and a risk for flooding.

.SPOTTER INFORMATION STATEMENT...