Flash Flood Watch 5, NWS Omaha, NE

Area Forecast Discussion
National Weather Service Omaha/Valley NE
654 PM CDT THU AUG 11 2016

.SHORT TERM...(tonight through Sunday)
Issued at 303 PM CDT Thu Aug 11 2016

The 12z upper-air analysis revealed a mid to upper-level low
over Saskatchewan with a trailing trough across the Interior
West. These data and current water vapor imagery suggest the
presence of a weak perturbation tracking across South Dakota and
Nebraska, ahead of the primary, western U.S. trough. At the
surface, a cold front stretched from eastern South Dakota to
central Nebraska as of 20z, with an outflow boundary gradually
becoming poorer defined as it lifts north through eastern Nebraska
and western Iowa.

Thunderstorms are beginning to increase in both coverage and
intensity ahead of the cold front from northeast Nebraska into
southeast South Dakota and northwest Iowa owing to persistent
low-level warm advection and increasing height falls attendant to
the NE/SD disturbance mentioned above. This activity is likely
still elevated, and rooted above a cap situated at the base of an
elevated-mixed layer. However with time, continued heating of the
warm sector coupled with low-level uplift along the front should
foster surface-based storms amidst an environment characterized by
mlCAPE of 2000-3000+ j/kg and 30-40 kt of effective bulk shear.
As such, isolated severe storms are possible as highlighted by the
current day 1 convective outlook from the SPC. While locally
damaging wind gusts and heavy rainfall appear to be the primary
hazards, a conditional threat for large hail and possibly a brief
tornado exists, contingent on the evolution of supercell storm
modes.

Showers and thunderstorms will likely persist tonight both along
and in the wake of the surface cold front as it continues
southeast across the area. While localized flooding is possible,
uncertainty in specifically where the band of heaviest rain will
set up coupled with relatively dry antecedent conditions precludes
us from considering a flash flood watch at this juncture.

Some of these showers and storms could linger into Friday,
especially across portions of southeast Nebraska and southwest
Iowa. We will see a slightly cooler and perhaps a bit drier air
mass filter into the area behind the cold front with highs on
Friday in the lower to mid 80s.

This weekend, we will remain in northwest flow aloft with a
surface ridge axis gradually building through the lower Missouri
Valley. This pattern should yield dry conditions with high
temperatures in the mid 80s and cooler overnight lows (compared to
recent nights) in the lower to mid 60s.

.LONG TERM...(Sunday night through Thursday)
Issued at 303 PM CDT Thu Aug 11 2016

Latest medium-range guidance suggests that a quasi-zonal belt of
polar westerlies will reside along the U.S.-Canadian border
through early next week with some amplification to the pattern by
the middle to latter part of the week. It appears that
precipitation chances will remain low through the extended period
with highs generally in the 80s.

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 641 PM CDT Thu Aug 11 2016

Rather complicated fcst with TSRA spread across the region...thus
confidence is quite low. At any rate...latest trends in addition
to model guidance suggest a low probability of anymore convection
making a direct hit at KOFK the rest of this evening.
However...rogue TSRA outflow may well spark something over NERN
Neb. For now will just go with VCTS this evening until situation
becomes a bit more clear. As for KOMA/KLNK...radar trends indicate
a line forming just to the west of both terminals. In
addition...another complex over n-cntrl KS was making a push to
the NE. The bottom line is that occasional convection is likely at
both TAF site during the evening hours. TSRA activity should be
exiting EWD sometime after midnight.

&&

.OAX Watches/Warnings/Advisories...
NE...Heat Advisory until 8 PM CDT this evening for NEZ051>053-066>068-
     078-088>093.

IA...Heat Advisory until 8 PM CDT this evening for IAZ056-069-079-080-
     090-091.

&&

SHORT TERM...Mead
LONG TERM...Mead
AVIATION...DEE

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SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE OMAHA/VALLEY NEBRASKA
807 PM CDT THU AUG 11 2016

IAZ069-NEZ045-051>053-067-120145-
POTTAWATTAMIE IA-DOUGLAS NE-CASS NE-WASHINGTON NE-SAUNDERS NE-
SARPY NE-
807 PM CDT THU AUG 11 2016

...SIGNIFICANT WEATHER ADVISORY FOR SOUTHWESTERN POTTAWATTAMIE...
EASTERN DOUGLAS...NORTHWESTERN CASS...SOUTHEASTERN WASHINGTON...SARPY
AND SOUTHEASTERN SAUNDERS COUNTIES UNTIL 845 PM CDT...

AT 804 PM CDT...DOPPLER RADAR WAS TRACKING STRONG THUNDERSTORMS ALONG
A LINE EXTENDING FROM 6 MILES SOUTHEAST OF FORT CALHOUN TO 3 MILES
NORTHEAST OF ASHLAND. MOVEMENT WAS NORTHEAST AT 30 MPH.

SMALL HAIL...HEAVY RAIN AND WINDS OF AROUND 40 MPH WILL BE POSSIBLE
WITH THESE STORMS. A RAINFALL AMOUNT OF 0.91 INCHES HAS ALREADY BEEN
REPORTED NEAR 164TH AND PACIFIC AS OF 800 PM CDT.

LOCATIONS IMPACTED INCLUDE...
OMAHA...COUNCIL BLUFFS...BELLEVUE...PAPILLION...LA VISTA...RALSTON...

PRECAUTIONARY/PREPAREDNESS ACTIONS...

HEAVY RAIN IS OCCURRING WITH THESE STORMS...AND MAY LEAD TO
LOCALIZED FLOODING. DO NOT DRIVE YOUR VEHICLE THROUGH FLOODED
ROADWAYS.

&&

A SEVERE THUNDERSTORM WATCH REMAINS IN EFFECT UNTIL 1100 PM CDT FOR
SOUTHWESTERN IOWA...AND SOUTHEASTERN AND EAST CENTRAL NEBRASKA.

LAT...LON 4143 9560 4100 9605 4101 9645 4143 9605
TIME...MOT...LOC 0104Z 245DEG 27KT 4141 9590 4107 9632

MILLER

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE OMAHA/VALLEY NEBRASKA
814 PM CDT THU AUG 11 2016

IAZ056-069-079-080-NEZ053-120145-
SHELBY IA-MILLS IA-POTTAWATTAMIE IA-MONTGOMERY IA-SARPY NE-
814 PM CDT THU AUG 11 2016

...SIGNIFICANT WEATHER ADVISORY FOR NORTHWESTERN MONTGOMERY...
SOUTHEASTERN SHELBY...MILLS...EASTERN POTTAWATTAMIE AND EASTERN SARPY
COUNTIES UNTIL 845 PM CDT...

AT 813 PM CDT...DOPPLER RADAR WAS TRACKING STRONG THUNDERSTORMS ALONG
A LINE EXTENDING FROM NEAR WALNUT TO 6 MILES SOUTHWEST OF TREYNOR.
MOVEMENT WAS EAST AT 40 MPH.

WIND GUSTS OF UP TO AROUND 50 MPH WILL BE POSSIBLE WITH THESE
STORMS...AND THE OUTFLOW MAY BE WELL AHEAD OF THE RAIN.

LOCATIONS IMPACTED INCLUDE...
GLENWOOD...HARLAN...OAKLAND...AVOCA...MALVERN...TREYNOR...CARSON...
WALNUT...SHELBY...MACEDONIA...SILVER CITY...HANCOCK...HENDERSON...
HASTINGS...FARM CREEK PUBLIC WILDLIFE AREA...
NISHNA BEND RECREATION AREA...BOTNA BEND PARK...OLD TOWN PARK...
ELK HORN CREEK RECREATION AREA AND PRAIRIE ROSE STATE PARK.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

THESE STORMS MAY INTENSIFY...SO BE CERTAIN TO MONITOR LOCAL RADIO
STATIONS AND AVAILABLE TELEVISION STATIONS FOR ADDITIONAL INFORMATION
AND POSSIBLE WARNINGS FROM THE NATIONAL WEATHER SERVICE.

&&

A SEVERE THUNDERSTORM WATCH REMAINS IN EFFECT UNTIL 1100 PM CDT FOR
SOUTHWESTERN IOWA...AND EAST CENTRAL NEBRASKA.

LAT...LON 4150 9516 4124 9516 4092 9566 4109 9587
      4178 9520 4169 9509 4160 9509 4160 9504
      4150 9504
TIME...MOT...LOC 0113Z 258DEG 33KT 4148 9519 4118 9572

MILLER

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE OMAHA/VALLEY NEBRASKA
824 PM CDT THU AUG 11 2016

NEZ065-066-078-120200-
SEWARD NE-LANCASTER NE-SALINE NE-
824 PM CDT THU AUG 11 2016

...SIGNIFICANT WEATHER ADVISORY FOR SOUTHEASTERN SEWARD...
NORTHEASTERN SALINE AND SOUTHWESTERN LANCASTER COUNTIES UNTIL 900 PM
CDT...

AT 824 PM CDT...DOPPLER RADAR WAS TRACKING A STRONG THUNDERSTORM 7
MILES SOUTHEAST OF PLEASANT DALE...OR 11 MILES SOUTHWEST OF
LINCOLN... MOVING EAST AT 35 MPH.

WIND GUSTS OF 45 TO 55 MPH WILL BE POSSIBLE WITH THIS STORM.

LOCATIONS IMPACTED INCLUDE...
LINCOLN...PLEASANT DALE...ROCA...DENTON...CONESTOGA STATE RECREATION
AREA...PAWNEE STATE RECREATION AREA AND WALNUT CREEK RECREATION AREA.

THIS INCLUDES THE FOLLOWING HIGHWAYS...
 HIGHWAY 2 IN NEBRASKA NEAR MILE MARKER 466.
 HIGHWAY 77 IN NEBRASKA BETWEEN MILEMARKERS 51 AND 71...AND NEAR
MILEMARKER 77.
 INTERSTATE 80 IN NEBRASKA BETWEEN MILE MARKERS 388 AND 405.

A SEVERE THUNDERSTORM WATCH REMAINS IN EFFECT UNTIL 1100 PM CDT FOR
SOUTHEASTERN NEBRASKA.

LAT...LON 4062 9693 4083 9698 4092 9663 4067 9657
TIME...MOT...LOC 0124Z 257DEG 32KT 4071 9685

MEAD