The Wednesday, 18 November, Supplemental file from the course website gives a review of the year's tornado activity to date. The 2009 tornado season has been about normal in activity so far. Spring is typically the most active tornado season with April to June the months of greatest numbers and severity of tornado occurrence. June (268 confirmed tornadoes) was the most active month versus May in 2008. February this year was the deadliest month with 9 fatalities while April and May each had 6. The death toll for the year (so far) is 22, significantly under the most recent 3-year average of 91 and many fewer than last year's 126. And, November (at this writing) has had only one tornado, a decided relief comparable to September's low value of 10. October experienced a more normal 69.
The NOAA Storm Prediction Center (SPC) is one of NOAA's National Centers for Environmental Prediction. Their website is at http://www.spc.noaa.gov/. The SPC provides severe thunderstorm and tornado watches for the contiguous U.S. (The warning of an actual impending or occurring event is issued by the local National Weather Service office.) We will examine a tornado event from the October activity and then the last tornado report as of this writing.
Image 1 is composite image from the Louisville, KY National Weather Service office displaying the damage path of the October 9, 2009 tornado through western Casey County located southeast of Louisville, on the left and the storm relative velocity image at 1838Z 9 OCT 2009, locally 2:38 p.m. EDT on the right. That day there were 13 tornadoes, 164 reports of wind damage and 2 reports of hail damage to SPC. A strong frontal system was crossing the south-central portion of the country. One tornado earlier in the day caused a fatality in Mississippi. The "vital statistics" associated with the Casey County tornado are:
| Begin time: | 2:36 PM |
| End time: | 2:38 PM |
| EF scale rating: | 2 |
| Path length: | 1.50 mi. |
| Path width: | 1/8 mi. |
From the Image 1 track map, the Casey County tornado moved toward the [(south-southeast)(south-southwest)(east-northeast)(north-northwest)]. North is at the top of the image. The thunderstorms that spawned this and similar tornadoes that day traveled with the northeasterly-directed upper-level winds (not shown).
Based on the EF category determination for this tornado, use the enhanced Fujita scale on page 11B-8 of the Applications section of the Weather Studies Investigations Manual's investigation 11B to find the approximate wind speeds. The table showed wind speeds could have ranged from 110 to [(124)(137)(146)] mph.
From the distance traveled as determined from the damage track and the times on the ground, this tornado was moving at about [(10)(45)(80)] mph. (Hint: For a distance of one mile traveled in one minute, the speed would be 60 mph.)
This event is fairly typical of the directions and speeds of tornadoes experienced in the U.S. The brief time of contact with the ground is also reasonable although the EF-2 intensity is greater than the majority.
The right radial velocity view in Image 1 displays the tornadic vortex signature (TVS) of red and green colors adjacent to each other east of Clementsville (labelled on map), the location of the tornadic thunderstorm cell at that time. The radar site is located off the display to the northwest (top left). Recall from Investigation 7B that red denotes Doppler velocities away from the radar site and green is toward. Draw a short arrow away from the radar site across the bright red section of the pixels of the lightest red rectangle. Also draw a short arrow toward the radar site across the bright green portion. These represent the radial velocities away and toward the radar's location. Your pattern of arrows suggests a circulation that is [(clockwise)(counterclockwise)].
The report of the Casey County, Kentucky tornado can be found at http://www.crh.noaa.gov/lmk/?n=october_9th_2009 as the first link. The page includes several other tornadoes on that day as well as wind damage cases. There are many photos of the destruction around the area from these events.
The last (at this writing) tornado event in the U.S. occurred in Lincoln City, Oregon on 6 November. In fact, this has been the only tornado experienced in November in the country! This event was unusual in several respects. Of course, November is rather late in the year for tornadoes anywhere. Also, thunderstorms are fairly infrequent along the West Coast of the U.S. at any time. Tornadoes are rare in the states west of the Rocky Mountains as can be seen from the national distribution map in the AMS Weather Studies text. Nonetheless, at 9:37 p.m. PST on the 6th of November, a tornado touched down near Lincoln City, on the coast of Oregon from an isolated thunderstorm cell. Image 2 is the combination of the lowest level reflectivity (left) and storm relative radial velocity (right) displays adapted from the Portland, OR NWS Doppler radar at 0537Z when the tornado was north of Lincoln City.
From the Image 2 reflectivity display, the Oregon coast is the irregular line basically bisecting the image from top to bottom with the Pacific Ocean to the west (left) and land to the east. The cell is seen with the most intense precipitation displayed using white pixels. This location of most intense rainfall is located just [(offshore)(onshore)]. The "hook echo" often seen with tornado reflectivities in the center of the U.S. cannot be readily noted here. The storm circulation appears here as a slight curvature of the reddest hues. This curved reflectivity at the southern edge of the storm would likely be the mesocyclone location. Possibly, the local winds at the ocean-land boundary were involved in the sudden development of rotation in this thunderstorm.
The right radial velocity view in Image 2 displays the tornadic vortex signature (TVS) of red and green colors adjacent to each other north of Lincoln City near the coast. The location of the radar site is to the upper right (northeast) off the image. The location of the red-green shading differences [(is)(is not)] at the same relative position at the south side of the thunderstorm cell's most intense precipitation.
Draw a short arrow away from the radar site across the center of the red section. Also draw a short arrow toward the radar site across the bright green portion. These represent the radial velocities away and toward the radar's location. Your pattern of arrows suggests a circulation that is [(clockwise)(counterclockwise)].
The tornado on November 6th was only packing 65-85 mph winds making it an EF-0 rating. Even so, eleven homes and three cars were damaged. The report of the Lincoln City, OR tornado is at http://www.wrh.noaa.gov/pqr/paststorms/20091106/lc_tornado.php. The webpage also provides several radar loops of reflectivities and relative velocities from the Portland office on this storm system progression. Of particular note is the original view of 4 panels (link "Radar at time of tornado") from which the Image 2 views were taken. The upper right panel shows the base relative velocity while lower right panel is the storm relative velocity. Comparison of the two images shows the difficulty of spotting tornadic circulations in marginal cases. This highlights the need for training of radar meteorologists in detecting severe weather. Additional details can be found in the Portland Channel 12 TV story, http://www.kptv.com/weather/21552066/detail.html.
On the SPC page using the link of "Storm Reports", you can check out past storms that have affected your area. Another good example of tornadic activity displayed in Doppler imagery is that in the Investigation 11B, "Applications" section.
Record your responses to items in CWS Activities 11A and 11B on the
CWS Answer Form for transmission to your course
mentor.
Instructions for Communications with Mentor:
After completing this week's applications, transmit the following work to your
LIT mentor by Monday, 23 November 2009, or as coordinated with your mentor:
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