11/23/10 DISC: CA

[Jason Harris]

Who would have predicted this? Only tornado today in El Dorado Hills CA:
--
TORNADO SURVEY RESULTS...
THE WEATHER SERVICE HAS CONCLUDED ITS SURVEY OF THE TORNADO THAT
DEVELOPED THIS AFTERNOON AT 117 PM ABOUT 4 MILES SOUTH OF EL DORADO
HILLS NEAR LATROBE. THE TORNADO WAS RATED ON THE ENHANCED FUJITA
SCALE AS AN EF1. THE ENHANCED FUJITA SCALE TAKES INTO ACCOUNT THE
TYPE OF CONSTRUCTION A STRUCTURE HAS AND VEGETATION. BASED ON
WITNESS REPORTS AND DAMAGE... ONCE THE TORNADO FORMED IT MOVED TO
THE EAST FOR ABOUT 2 MILES BEFORE DISSIPATING. THE TORNADO FORMED ON
A HILLSIDE AND BROKE A TELEPHONE POLE... THEN MOVED JUST TO THE
NORTH SIDE OF A COMMERCIAL BUILDING RESULTING IN ROOF DAMAGE ON THE
SOUTH SIDE CAUSED BY THE STORM INFLOW. THE TORNADO CONTINUED TO
TRAVEL TO THE EAST WHERE IT MOVED A WATER TANK SEVERAL INCHES AND
DAMAGED NUMEROUS TREES. ONE TREE WAS SNAPPED NEAR THE TOP AND SOME
OTHERS WERE TOPPLED.

 

[Dann Cianca]

I just reviewed the reflectivity and velocity data from that time period and nothing screamed "supercellular". It looked like the storm formed on a boundary. Most of the sites to the north had northerly winds and sites to the south, southerly. Barring the possibility of a min-supe, I'd say it was a non-supercell tornado. Here is a pic from a local news site:

There is another photo of a tornado in a slide show here:

http://www.news10.net/news/article.aspx?storyid=107823&provider=top&catid=188

... but it doesn't look to be of the same event.

 

[Jason Harris]

met mentions hook echok, witnesses mention two separate funnel clouds, with second leading to tornadic damage:

http://www.kcra.com/video/25899584/detail.html

there are other videos too, like this
but some repetition
http://www.kcra.com/video/25899584/detail.html

ups driver has some witness observations and cellphone pic, nickle-sized hail mentioned too
http://www.kcra.com/video/25900910/detail.html
http://www.kcra.com/weather/25897829/detail.html

 

[R R Smith]

Here's the rest of the damage assessment report:

The damage assessment conducted by the NWS Sacramento office concluded that at approximately 1:17 pm an EF1 tornado developed near the town of Latrobe in El Dorado County, which is about four miles south of El Dorado Hills. The maximum wind speed of the tornado was estimated at 100 mph with a damage path of two miles. No injuries or fatalities have been reported. There was damage to the roof of one commercial building, a single power pole, a water tank, and to numerous trees. The estimated cost to repair the roof damage is $1,000. The water tank has not been in use for several years and received no physical damage.

Witness reports were crucial to the conclusion of the damage assessment as there was not a great deal of damage from which to distinguish between tornadic, downburst, or straight line winds. Notable was that the damage occurred along a roughly straight line which is more typical of a tornado, while scattered damage is more typical of downburst or straight line winds. Witnesses repeatedly mentioned seeing evidence of a circulation on the ground and of debris rising from the ground though the visual nature of the circulation only briefly reached to the ground for some witnesses while never reaching for others..

The conclusion of an EF1 designation was based primarily upon the damage caused to the oak trees in the damage path. A hardwood tree with a snapped trunk is estimated to range between 93 and 134 mph. In this case, the wind speed was graded at the lower end of the scale due to the large number of leaves still attached to the portions of the tree that had been broken off (increased friction) and due to the snapped portion being high on the tree rather than in the sturdier lower portion. There were also some ponderosa pine trees that were toppled, but this has a lower wind speed value on the damage scale. The roof damage to the commercial building was to two corrugated tin panels in which the lip of the panels were buffeted by the strong storm inflow. The wood overhang over the building entrance that was near the site of the roof damage is more sturdily built and had lifted during the event but not broken. The only damage that could not yet be evaluated for wind speed strength is the water tank. The solidly built metal tank is located at the top of a hill and was moved several inches during the event but more information is needed to determine what wind speed was needed to do so.

Likewise the damage path is preliminary as the eastern extent could not be definitively determined prior to night fall. The western extent is defined just east of the commercial building as witnesses described watching the tornado develop in that area.

Radar images indicate thunderstorms over the general location at the time of the event. Two Significant Weather Advisories (SPSSTO) were issued concerning the thunderstorms and funnel clouds, including one issued near the approximate time of the event. Review of the radar images at the time and after the event was reported shows a possible indication of rotation in the area on the velocity data but not for a length of time or of a sufficient size to definitively distinguish it from others. Reflectivity data also show possible signatures of circulation and it was in large part due to these reflectivity and velocity signatures that the SPS products were issued. The data will be archived for future review and training.

 

[Dann Cianca]

Interesting photos on the site... and of the damage assessment. The UPS driver's phone pic definitely makes it look more supercellular with the lowering around it. Could have been a mini-supe! The radar data that I was looking at wasn't all that high in resolution.

 

[Marcus Diaz]

Here's the radar grabs I got from NCDC. Not sure if the reflectivity and volicity grab is lined up correctly on time (I used the exact time) but maybe a mini-sup might explain it.

 

[joel ewing]

Sacramento Tornado??

met mentions hook echok, witnesses mention two separate funnel clouds, with second leading to tornadic damage:

http://www.kcra.com/video/25899584/detail.html

there are other videos too, like this
but some repetition
http://www.kcra.com/video/25899584/detail.html

ups driver has some witness observations and cellphone pic, nickle-sized hail mentioned too
http://www.kcra.com/video/25900910/detail.html
http://www.kcra.com/weather/25897829/detail.html

Early in this thread and in the first slide-show (not the vid) I immediately spotter two separate funnels. There's the obvious one, with the second one beginning to protrude out of the upper right-hand corner area. You'll see it...it's dark. It's there. There is another photo of the exact same shot..but the darker 2nd funnel is either cropped out or the lighting isn't allowing it to be seen.
Also, there is a photo that shows the base of some sort of circulation embedded within what looks like a line. One of the funnel cloud shots in the video shows the top half of what I feel is a pretty darn healthy tornado....especially for that area of the country. I'm actually surprised that they don't seem to get more funnel / quick touchdowns around there each year. Being from Arizona, I've asked several people from the Sac area over the years if they get occasional tornadoes, and they all scratch their heads...try to remember...and ultimately say no. I guess if you want funnels / tornadoes in central California...your action area is around Fresno and thereabouts.

 

[Dann Cianca]

Here's the radar grabs I got from NCDC. Not sure if the reflectivity and volicity grab is lined up correctly on time (I used the exact time) but maybe a mini-sup might explain it.

Don't suppose you have a non-smoothed version of that velocity data. Also, on an off-topic note, how do you smooth data in the NOAA Weather & Climate Toolkit?

 

[R R Smith]

Tornadoes do occur in the Sacramento Valley - more common (common being a relative term) to the north of Sacramento around the Chico area. John Monteverdi (San Francisco State University) has authored and coauthored several papers about tornadic setups in California.

Here's a link to check out: http://tornado.sfsu.edu/geosciences/tornadochase/Research.html

 

[cdcollura]

Good day all,

John Monteverdi (San Francisco State University) has authored and coauthored several papers about tornadic setups in California.

Here's a link to check out: http://tornado.sfsu.edu/geosciences/tornadochase/Research.html

Many of these links are dead ;-(

 

[GPhillips]

Perhaps a better radar depiction of the storm at the time of the tornado. Looks like one of those tiny supercells they sometimes get out in the Sacramento Valley.

Image has 0.5 Ref upper left, 0.5 SRV upper right, 0.9 SRV lower left, 1.4 SRV lower right.

 

[R R Smith]

Bummer... here's a link to a paper off Chuck Doswell's website (Chuck coauthored with Monteverdi):

Shear Parameter Thresholds for Forecasting Tornadic Thunderstorms in Northern and Central California
http://www.flame.org/~cdoswell/publications/monteverdietal_03.pdf

Also try California Tornado and Thunderstorm Resources Site:

http://ggweather.com/tornado.htm

 

[Marcus Diaz]

Don't suppose you have a non-smoothed version of that velocity data. Also, on an off-topic note, how do you smooth data in the NOAA Weather & Climate Toolkit?

Data>Layer Selector>Data Layers>Smoothing (the grabs above are at a 5)

 

[Andy Jackson]

good link

Here's a couple of good pages on the Natomas funnels/tornadoes of 2005:
link 1

another video (I've never seen until now):
link 2

 

[Toni Scholz]

I live in El Dorado Hills and am not happy about being 45 minutes north of this when it happened....there is a small radar anomaly that shows up in Marcus' reflectivity screen shot though. We have a huge radio transmission tower nearby that can been seen by the highway line intersecting it (in about a 6:30 clock position from the map lettering "El Dorado Hills").