Posted on 11/10/2002 2:01:45 PM PST by Lucas1
Apparently a number of towns have been hit hard by tornadoes this afternoon. Maybe people can post information from their local areas? One report had FOUR TORNADOES moving into Van Wert, Ohio.
AT 329 PM EST...LAW ENFORCEMENT AND EMERGENCY MANAGEMENT REPORTED FOUR SEPARATE TORNADOES JUST WEST AND SOUTHWEST OF THE CITY OF VAN WERT...MOVING NORTHEAST AT 40 MPH. VAN WERT RESIDENTS SHOULD REMAIN IN THEIR BASEMENTS OR INTERIOR CLOSETS...AWAY FROM WINDOWS. PEOPLE NORTHEAST OF THE CITY OF VAN WERT SHOULD TAKE SHELTER NOW AS WELL!
Later reports from Emergency Management indicate that the town was hit by the tornado and there is severe damage. Injuries and fatalities are being reported.
http://www.spc.noaa.gov/climo/reports/today.html
Some tornado watches carry extra weight
The Storm prediction Center in Norman, OK and formerly the Severe Local Storms Unit (SELS) in Kansas City, MO, have had the responsibility of forecasting tornadoes over the 48 contiguous U.S. states since SELS was established in 1953. The vehicle for providing tornado forecasts to the users (public, media, emergency preparedness, etc.) is the tornado watch.
But tornado intensities vary widely, dependent on the meteorological conditions in which they form. A small percentage of tornadoes result in the greatest threat to life and property. These are generally considered to be those rated F3 to F5 on the Fujita tornado intensity scale. Usually, but not always, these intense tornadoes occur in association with supercell thunderstorms that develop in particularly evident synoptic environments.
The primary means of alerting users to the perceived threat of these tornadoes has been the tornado watch, which remained for many years the same for all tornado situations. Thus, the need arose for a mechanism to provide an awareness of the SPC/SELS concern for potentially intense tornado conditions.
The option to include "enhanced" language in the public text of the tornado watch was added in 1982. The goal was to heighten awareness to the threat of the more violent tornadoes. Within the description of the tornado watch, a line contained text that states "this is a particularly dangerous situation (PDS) with the possibility of very damaging tornadoes."
The operational philosophy over the years has been to reserve these PDS tornado watches for primarily the "tornado outbreak" situations in which widespread damaging tornadoes are predicted. Over the 16 years the PDS option has been available, there has been no evaluation of the forecasting skill associated with these PDS watches. With the plans for the future of tornado forecasting expected to include enhanced resolution with regard to expected tornado intensities, it is apparent that an evaluation of the skills of the PDS Tornado Watch is needed.
This study will provide insight as to increase in forecast skill levels over the 16 year period. It will also provide an assessment where we are in pursuit of identifying those "particularly dangerous tornado situations."
The distribution of PDS watches and total PDS watch days over the same period show a rather even distribution through the spring months (March through June) with a secondary peak in November related to the maxima noted in tornado occurrence. In fact, the actual number of PDS watches issued peaks in April, with May the least of the four spring months . May is climatologically the time of peak intense tornado occurrence.
A possible explanation for this discrepancy between intense tornado occurrence and PDS watch issuance is the philosophy that has been established when considering issuance of PDS watches. Over the years, SPC/SELS has focused on the "tornado outbreak" environments. These are days when the Convective Outlooks use the "High Risk" terminology (July, 1993), and there is considerable skill shown in identifying an area of intense tornado development at the outlook level. However, where within the High Risk outlook area the intense tornadoes will occur is frequently difficult to determine. Intense tornadoes are more difficult to determine. Intense tornadoes are more difficult to isolate on early spring days when systems are moving rapidly, thus more PDS watches are typically required during an early spring High Risk day.
During the 14 year period between 1982 and 1995, only 557 intense tornadoes occurred in the U.S. The annual total varies greatly from only 15 in 1987 to as many as 65 in 1982 and 62 in 1983.
Beginning about 1988, there was a noticeable increase in the number of PDS watches issued . Prior to 1988, there were never more than 11 issued in any one year. From 1988 to 1995, between 21 to as many as 42 in 1992 were issued. The most recent two years up to 1997 has again seen a noticeable decrease in PDS watches issued; 12 in 1996 and a low five through September of 1997.
One of the verification statistics used by forecasters in SPC to determine which situation requires a PDS Watch is the probability of detection (POD). Prior to 1988, the POD of intense tornadoes in PDS watches was generally less than 10%. Since that time, there has been a tremendous increase in the understanding and diagnosis of the tornadic supercell and the environment in which it forms.
A rapid increase in POD commenced in 1988 reaching a high of 75% in 1991 where 36 PDS watches were issued. This not only reflects the experience of the SPC forecasters, but also indicates an increase in the understanding of tornadic supercell formation. A rapid increase in availability of observed and forecast wind information through the WSR-88Ds, profilers, and model soundings bolstered this understanding. The VWP (VAD Wind Profile) from the WSR-88D has greatly enhanced operational availability of real-time wind data.
By John E. Hales, Jr., Storm Prediction Center
I helped with Skywarn and EMA communications this afternoon - it was a wild time!
Stay safe, all you WV,PA, and VA FReepers - it'll be a long night.
Tony
That's ok - I'll pass it along to him! :-)
Stay safe, fellow Freepers! It promises to be a *busy* night...
Thanks for the heads up. My sister in Indianapolis came through okay. Looks like our turn. Headed for the weather channel.
Terrible damage in Van Wert, also in Tennessee, incl Clarksville, which is adjacernt to Ft Campbell, KY. Spoke with my aunt in SW Indiana, and she said there were a couple of tornadoes reported nearby.
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