August 19th Tornadoes and Wind Damage

Tornadoes:

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Tornado - West of Almeria, Nebraska Loup County Date August 19, 2017 Time (Local) 7:40 pm - 8:15 pm EF Rating 2 Est. Peak Winds 120 mph Path Length 8.1 Miles, discontinuous Max Width 840 Yards Injuries/Deaths 0/0 Summary: A thunderstorm underwent rapid intensification as it entered into a very favorable storm environment. There were several circulations during the life cycle of the storm as it moved near Almeria. Eyewitnesses saw 5 tornadoes out of this storm. We were able to discern 4 different tracks. The fifth touchdown may have been in an open field. There were also several areas of straight line wind damage either from the very strong rear flank downdraft with this storm, or from the strong inflow into the storm as it intensified. The storm eventually became less organized as it moved south of Almeria and became outflow dominant. The damage continued, however as it moved into Custer County and the rear flank downdraft intensified again just northwest of Sargent. Track Map Downloadable KMZ File

The Enhanced Fujita (EF) Scale classifies tornadoes into the following categories:

EF0 Weak 65-85 mph	EF1 Moderate 86-110 mph	EF2 Significant 111-135 mph	EF3 Severe 136-165 mph	EF4 Extreme 166-200 mph	EF5 Catastrophic 200+ mph

Photos & Video:

Video of One of the Tornadoes West of Almeria as it Developed (Ann Wurst)	Flipped Camper onto a truck near Sargent due to a very strong rear flank downdraft wrapping around the storm (NWS)	Wooden missile from destroyed Shed 400 yards away (NWS)

Image from drone that flew over Dunbar Ranch SW of Almeria     (Janet Sanders)	Image from drone that flew over Dunbar Ranch SW of Almeria     (Janet Sanders)	Image from drone that flew over Dunbar Ranch SW of Almeria     (Janet Sanders)	Piece of corrugated metal roof driven into a post from their corral, just under ground level        (Paul Dunbar)

Twisted Tree in Wind Break outside Dunbar Ranch (NWS)	Stripped Wind Break outside the Dunbar Ranch (NWS)	Paneling located underneath attic access panel on the interior wall of the room sucked off of the wall by tornado (NWS)	Corrugated metal roof from a shed 60 yards away impaled by a tree. (NWS)

Remnants of a shed with trees in the background stripped of bark  (NWS)	Remnants of a shed (NWS)	Corrugated metal crumpled into a wad by the tornado (NWS)	Remnants of sheds scattered into the field behind the Dunbar Ranch (NWS)

New hole in the eve of the roof from flying debris. TV antenna ripped off roof at Dunbar Ranch (NWS)	Tipped Windmill at Dunbar Ranch (NWS)	Quonset Hut lifted, turned almost 90 degrees and crumpled by tornado (furthest northeastern track) (NWS)	Partial roof loss on newer Wardcraft Home. Roof trusses were attached to the walls with hurricane straps. (NWS)

Radar:

7:40 PM - First tornado touchdown near the Blaine County Line	7:56 PM - Just after 2nd and 3rd touchdown	8:07 PM - Tornadic Circulation has barely moved	8:17 PM - Inflow into the storm was strong enough to flip pivots east of Almeria at around this time

8:27 PM - The flanking line was showing quite a bit of buoyancy (towering CU) at this time indicating that the storm was still likely maintaining a very strong updraft	9:06 PM - The storm became outflow dominant at this time and became unfavorable for additional tornado development. However, the outflow winds and rear flank downdraft were very strong, approaching 90 mph. These winds blew into Custer County and flipped a 5th wheel, crushing a pickup truck and damaging an outbuilding.	0.5 degree Radar Reflectivity Loop. The loop begins at 7:35 PM and ends at 9:06 PM

7:40 PM - First tornado touchdown near the Blaine County Line	7:56 PM - Just after 2nd and 3rd touchdown	8:07 PM - Tornadic Circulation has barely moved	8:17 PM - Inflow into the storm was strong enough to flip pivots east of Almeria at around this time

8:27 PM - The flanking line was showing quite a bit of buoyancy (towering CU) at this time indicating that the storm was still likely maintaining a very strong updraft	9:06 PM - The storm became outflow dominant at this time and became unfavorable for additional tornado development. However, the outflow winds and rear flank downdraft were very strong, approaching 90 mph. These winds blew into Custer County and flipped a 5th wheel, crushing a pickup truck and damaging an outbuilding.	0.5 degree Radar Storm Relative Velocity Loop. The loop begins at 7:35 PM and ends at 9:06 PM

Storm Reports

Click Here to see all Storm Reports from August 19th: 
http://www.spc.noaa.gov/climo/reports/170819_prt_rpts.html



...NWS DAMAGE SURVEY FOR 08/19/2017 TORNADO EVENT...

.UPDATE...Updated the paths and times on some of the
tornado tracks.

.OVERVIEW...The atmosphere was primed for thunderstorms
on Saturday, August 19th but there was only one large storm
that took advantage of it. This storm produced 4 distinct
tornado tracks and there were two significant areas of
straight line wind damage. One area in Almeria was likely
due to strong inflow into the storm, and the other, northwest
of Sargent was likely due to a very strong rear flank
downdraft. There is also evidence in the radar data and in
the survey of possibly two tornadoes on the ground at once,
one was likely anticyclonic.

.TORNADO #1...

Rating:                 EF-0
Estimated peak wind:    65 mph
Path length /Statute/:  0.1 miles
Path width /Maximum/:   10 yards
Fatalities:             0
Injuries:               0

Start date:             08/19/2017
Start time:             7:40 pm CDT
Start location:         10 miles Northwest of Almeria

End date:               08/19/2017
End time:               7:41 pm CDT
End Location:           10 miles Northwest of Almeria

SURVEY_SUMMARY: There was likely a brief touchdown near the
Blaine County line, supported by a debris signature on radar.
This path will be updated after surveyed by the EM.

.TORNADO #2...

Updated time

Rating:                 EF-1
Estimated peak wind:    105 mph
Path length /Statute/:  2.3 miles
Path width /Maximum/:   840 yards
Fatalities:             0
Injuries:               0

Start date:             08/19/2017
Start time:             7:48 pm CDT
Start location:         5.5 miles Northwest of Almeria

End date:               08/19/2017
End time:               8:03 pm CDT
End Location:           3.8 miles Northwest of Almeria

SURVEY_SUMMARY: This path began with the partial loss of a roof on
a well-built Ward Craft home. The trusses were anchored with hurricane
clips. The owner stated that the wind was at least over 60 mph for
40 minutes so some of this damage may have been from straight line wind
preceding the tornado. The tree line just east of the home was not
significantly damaged but the damage path carried far to the south with
debris from the roof, a lot of tree damage, and some snapped wooden
power poles.

.TORNADO #3...

Updated path length and width

Rating:                 EF-1
Estimated peak wind:    100 mph
Path length /Statute/:  1 mile
Path width /Maximum/:   180 yards
Fatalities:             0
Injuries:               0

Start date:             08/19/2017
Start time:             7:48 pm CDT
Start location:         5.3 miles Northwest of Almeria

End date:               08/19/2017
End time:               7:50 pm CDT
End Location:           3.3 miles Northwest of Almeria

SURVEY_SUMMARY: This damage path included snapped wooden power poles,
and widespread tree damage with entire trees leaning over but not
fully uprooted and large branches broken. There was also a large
corrugated metal Quonset hut that was twisted about 90 degrees and
collapsed inward.

.TORNADO #4...

Rating:                 EF-2
Estimated peak wind:    120 mph
Path length /Statute/:  0.65 miles
Path width /Maximum/:   540 yards
Fatalities:             0
Injuries:               0

Start date:             08/19/2017
Start time:             8:14 pm CDT
Start location:         2.82 miles West of Almeria

End date:               08/19/2017
End time:               8:17 pm CDT
End Location:           3.52 miles West-Southwest of Almeria

SURVEY_SUMMARY: The damage here was to a 100 year old shelter belt
and recently vacated homestead with several outbuildings. All outbuildings
were completely destroyed but were in various stages of decay. Some had
cement foundations and the walls were straight nailed to a bottom plate
that was bolted into the foundation. Other sheds were wooden and covered
in corrugated sheet metal. This sheet metal and missiles from the wooden
parts of the shed were found almost one half mile away in the shelter
belt. The property also had a boat on a trailer. The boat was missing for
the most part but parts of a boat were seen by the Emergency Manager in
a nearby field less than one mile away. Many of the trees were debarked
and twisted in the shelter belt with only the larger branches remaining.
Most of the trees were soft wood, most were healthy. The home had some
damage to the roof and there was evidence of a missile from one of the
sheds penetrating the attic. Some faux wood paneling in the home was
sucked off of the wall near the access to the attic.

EF SCALE: The Enhanced Fujita Scale classifies
tornadoes into the following categories.

EF0...Weak......65 to 85 mph
EF1...Weak......86 tO 110 mph
EF2...Strong....111 To 135 mph
EF3...Strong....136 to 165 mph
EF4...Violent...166 To 200 mph
EF5...Violent...>200 mph

.THUNDERSTORM WIND IN AND EAST OF ALMERIA...

Peak wind Estimated:    88 mph
Path length /Statute/:  0.25 miles
Path width /Maximum/:   300 yards
Fatalities:             0
Injuries:               0

Start date:             08/19/2017
Start time:             8:15 pm CDT
Start location:         Almeria, NE

End date:               08/19/2017
End time:               8:20 pm CDT
End location:           0.25 miles East of Almeria

SURVEY_SUMMARY: Strong inflow winds into the storm, estimated
near 90 mph by radar and evidenced in the damage, likely caused
a pivot to flip and caused some significant tree damage in and
near the town of Almeria.

.THUNDERSTORM WIND NEAR SARGENT...

Peak wind Estimated:    85 mph
Path length /Statute/:  0.1 miles
Path width /Maximum/:   10 yards
Fatalities:             0
Injuries:               0

Start date:             08/19/2017
Start time:             9:07 pm CDT
Start location:         Northwest of Sargent

End date:               08/19/2017
End time:               9:15 pm CDT
End location:           Northwest of Sargent

SURVEY_SUMMARY: A fifth wheel was blown over into a truck and a structure
by strong winds in the rear flank downdraft portion of the storm as it
came out of Loup County. Winds were between 80 and 90 mph based on radar
estimates and the nature of the damage. This portion will likely be updated
as we receive more information on the location and extent of the damage.

NOTE:
The information in this statement is PRELIMINARY and subject to
change pending final review of the events and publication in
NWS Storm Data.

Environment

Click images to expand

The morning forecast highlighted the chance for thunderstorms on the 19th and through the weekend leading up to the Solar Eclipse. Primary hazards were expected to be strong wind and hail. The tornado probability was less than 2%	Day 1 Thunderstorm Outlook from the Storm Prediction Center had much of central Nebraska in a Slight Risk for severe thunderstorms. Loup County and the town of Almeria were on the northern edge of this area.	The afternoon surface analysis showed a stationary front in eastern Nebraska and a trough moving into western Nebraska. Aloft, a short wave disturbance moved out of Wyoming and into the Panhandle. This disturbance was expected to provide some broad lift needed to generate thunderstorms in the afternoon and evening.

The morning technical discussion from the Storm Prediction Center in Norman highlighted the likelihood of thunderstorms in Nebraska. There was going to be some moisture moving into the area (which acts as gasoline for thunderstorms) and once the sun started heating the surface in the afternoon, there would be a significant amount of instability, a necessity for thunderstorm development as well. The dry line moving in from the west would provide lift, or a focus for thunderstorms. Another necessary ingredient, wind shear, would encourage some more organized storms but the lower level wind shear looked too weak to be considered favorable for tornado development.	As the day went on, it looked like there would be two specific areas of development, one cluster would develop around Ogallala and head eastward, and the other would develop up toward Mullen and head east through the evening. Both clusters looked like more of a straight line wind threat with some possible supercells toward the beginning of the event. As it turned out, the southern area, the one that looked more favorable for thunderstorms earlier in the day ended up not sustaining the storms that moved into it. This left all of the energy available in the atmosphere ready for the northern storms to take advantage of.	Mesoscale Discussion 1534 NWS Storm Prediction Center Norman OK 0756 PM CDT Sat Aug 19 2017 Areas affected...Portions of NE and northern KS Concerning...Severe Thunderstorm Watch 458... Valid 200056Z - 200200Z The severe weather threat for Severe Thunderstorm Watch 458 continues. SUMMARY...A cluster of storms across north-central NE will continue to pose an isolated large hail and damaging wind threat, while other storms have struggled to intensify across western portions of WW 458. DISCUSSION...Recent water vapor satellite imagery depicts a low-amplitude shortwave trough with embedded vorticity maximum moving eastward over NE this evening. At the surface, a lee trough/dryline extends southward from a weak surface low over central SD across western NE into eastern CO. Multiple attempts at convective initiation have occurred along the axis of the lee trough across western NE and northwestern KS over the past several hours, with none of them being successful in sustaining organized thunderstorms. The airmass across much of NE and northern KS remains very unstable as of 0050Z, with the 00Z sounding from North Platte NE indicating MLCAPE around 2800 J/kg. Low and mid-level flow remains generally modest, but does veer with height, and this veering is the primary contributor to about 25-35 kt of effective bulk shear. A south-southwesterly low-level jet is expected to undergo some strengthening this evening to around 30-35 kt, which may allow for the small cluster of ongoing convection in north-central NE (with dominant supercell in Loup County NE) to persist. Isolated large to very large hail and damaging winds will be the main threat with this activity as it moves generally east-southeastward. Current low-level radar velocity trends also suggest a very near-term threat for a tornado, as effective SRH becomes maximized with the modestly strengthening low-level jet. With time, increasing convective inhibition should lessen the possibility for a tornado. If current radar trends continue, western portions of WW 458 could be canceled early.

Near-storm environment

As the storm in Blaine and Loup Counties moved eastward, it encountered a much more favorable environment. There was a sharp gradient of increasing instability. There was also a sharp increase in the "SigTor" (Significant Tornado) parameter, an index that takes instability and rotation in the atmosphere into account, combining the elements into one index.

In all the images below, the black dotted line shows where the surface boundary is, and the yellow oval shows the area with the most favored environment for rapid storm intensification.

This figure shows the surface map at the time the thunderstorm underwent rapid intensification. Notice how the winds to the west of the line and the winds toward the east of the line are going in opposite directions. This shows an area of strong convergence, which would provide a source for lift.	The red lines in this image show areas of increasing instability. Where the lines are close together, that implies a sharp gradient, which would explain why the storm intensified so rapidly as it moved to the east.	The red and orange lines in this image show the Significant Tornado Parameter. Note the sharp increase from west to east. This indicates that the storm was moving into an environment that was favorable for tornadoes at this time (around 7:00pm CDT)

GOES 16 Satellite Data

Data is preliminary and non-operational

Some "agitated cumulus" began showing up on the satellite at around 5:00pm that afternoon.	By 6pm, there was storm development both in the expected area in southwest Nebraska and in the more favorable area in north central Nebraska.	This image is just 20 minutes after the middle image, you can see how quickly the storm grew once it approached the better instability, moisture, and spin in the atmosphere. It only grew larger from here. (but these are visible satellite images and we began to lose daylight)