Flash Flood Warning 14, NWS Omaha, NE

Area Forecast Discussion
National Weather Service Omaha/Valley NE
1233 PM CDT Wed Jul 29 2020

...Updated Aviation Forecast Discussion...

.SYNOPSIS...
Issued at 336 AM CDT Wed Jul 29 2020

Widespread rain showers are expected across the area today and
tomorrow. This will be a slow moving system that will lead to more
rain over southeast Nebraska. High soil moisture and elevated
rivers in that area will leave it vulnerable to flash flooding
over the next 48 hours.

&&

.DISCUSSION...
Issued at 336 AM CDT Wed Jul 29 2020

Today and Tomorrow:
Water vapor imagery shows a deepening trough over the northern
Rockies. That upper level disturbance is expected to slowly move
southeast across Nebraska providing a broad area of lift leading
to widespread showers across the forecast area. The system will be
moving into a fairly unstable airmass with forecast soundings
showing that instability should top 2000 J/kg. The instability
will be mitigated by a lack of shear and weak lapse rates which
will largely limit any severe weather threats. The increased
instability will likely lead to pockets of heavier rainfall in
some places. Rain is expected to begin in the mid morning along
the KS/NE border and move northward. The best chances for rain
will generally be south of the Platte River. Though, there is some
large model spread in precipitation and there is a chance some
heavier rain does make it into northeast Nebraska.

While the upper level disturbance is moving from the northern
Rockies into Nebraska, a surface low will develop and move across
Kansas. It will help bring more moisture into the area.
Precipitable water (PW) values are expected to increase to close
to 2 inches. The increased PW should help the 2 day rainfall
totals range from 1 to 3 inches. Again, most of the rain should
fall south of the Platte River. There could be some locally higher
amounts in places where stronger convection takes place.
Southeast Nebraska will be vulnerable to flash flooding due to the
increased moisture, the slow speed of the system, and the heavy
rain that fell on Sunday. Rain is likely to come to an end across
the area Thursday afternoon.

Friday through Tuesday:
Temperatures in the longer range are expected to be about 5 to 10
degrees below normal as an amplified upper level pattern builds
over North America. A trough is expected to move south from the
Hudson Bay area and strengthen over the East Coast. At the same
time, a ridge will build over the West Coast and reach peak
strength on Monday. This will leave the central portion of the
country in northwest flow (more north northwest) and will keep
temperatures well below normal for much of the country. The
extended range should also be mostly dry except for a slight
chance on Saturday. The ECMWF/Euro/Canadian are all in good
agreement on precipitation. Any precipitation would be on the
lighter side without any severe weather threats.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1223 PM CDT Wed Jul 29 2020

Precipitation has already begun to overspread southeast Nebraska,
with scattered showers and storms reaching near the KLNK TAF site
and will likely reach the KOMA site between 18 and 19z. Ceilings
are largely VFR, but areas with precipitation have been dipping
into MVFR or very near it. Winds are generally from the southeast,
but will switch to northeasterly around sunset, with wind speeds
expected to stay light through the TAF period. A few thunderstorms
will be possible this afternoon/evening along a front near the
NE/SD border, but the convective allowing models are not
consistent with placement or development in general, so any TSRA
mentions are left out of KOFK's TAF at this time.

&&

.OAX WATCHES/WARNINGS/ADVISORIES...
NE...Flash Flood Watch through late tonight for NEZ088-089-092-093.

IA...None.
&&

SYNOPSIS...Fajman
DISCUSSION...Fajman
AVIATION...Petersen

Hazardous Weather Outlook
National Weather Service Omaha/Valley NE
1120 AM CDT Wed Jul 29 2020

IAZ043-055-056-069-079-080-090-091-NEZ011-012-015>018-030>034-
042>045-050>053-065>068-078-088>093-300630-
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-
1120 AM CDT Wed Jul 29 2020

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

.DAY ONE...This Afternoon and Tonight

Scattered showers and storms are expected today through tonight,
especially south of the Platte River. Southeast Nebraska is
especially vulnerable to flash flooding today and tonight due to
high rainfall forecast, high soil moisture, and elevated river
levels.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday

Rain will continue into Thursday and come to an end in the
afternoon. This will be a long duration event and areas receiving
high amounts of rain will be vulnerable to flooding.

.SPOTTER INFORMATION STATEMENT...

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
151 PM CDT WED JUL 29 2020

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0148 PM     HEAVY RAIN       HICKMAN                 40.62N 96.63W
07/29/2020  M2.73 INCH       LANCASTER          NE   PUBLIC

            PWS STATION KNEHICKM7. STILL RAINING.

&&