That whistling generated as the wind passes over wires indicates a wind velocity of 25-31 MPH, a “strong breeze.”
The movement of air masses, wind, is described and defined by several scales. The velocity is described numerically in MPH, KPH, and knots. It is also described in terms relating to degree of storminess. A force number unique to the Beaufort Scale links a number to a graphic flag used to chart winds by meteorologists. These arrow/flag markers are used to denote wind direction as well as velocity. Newspaper weather maps sometimes still have them for local reports but such maps are becoming less common in newspapers.
At 0745 Monday 25 October I heard the wind in the wires. By 0835, a seemingly solid wall of wind and water tore through N.E. Tennessee, downing trees, dropping lines, and damaging many homes. The gust reached 36 mph in our sheltered valley location with a large tree screening the wind somewhat from our anemometer. That gust left us with downed branches and downed power lines. It also split the large Bradford Pear that once screened the anemometer and the N.E. corner of the house from extreme winds.
Sustained winds from the same storm, still strongly present Tuesday 26 October, dropped one third of the tree on our roof and back deck Tuesday morning. It took until Thursday to find someone to remove the tree. We were far luckier than most people who lost trees to this storm. We had no damage to our home.
Wind speed on the 1946 Beaufort scale is based on the empirical formula:
v = 0.836 B3/2 m/s
where v is the equivalent wind speed at 10 meters above the sea surface and B is Beaufort scale number. For example, B = 9.5 is related to 24.5 m/s which is equal to the lower limit of "10 Beaufort". Using this formula the highest winds in hurricanes would be 23 in the scale.
Today, hurricane force winds are sometimes described as Beaufort scale 12 through 16, very roughly related to the respective category speeds of the Saffir-Simpson Hurricane Scale, by which actual hurricanes are measured, where Category 1 is equivalent to Beaufort 12. However, the extended Beaufort numbers above 13 do not match the Saffir-Simpson Scale. Category 1 tornadoes on the Fujita and TORRO scales also begin roughly at the end of level 12 of the Beaufort scale but are indeed independent scales.
Note that wave heights in the scale are for conditions in the open ocean, not along the shore.
Beaufort Wind Scale
Developed in 1805 by Sir Francis Beaufort of England
The storm system that pushed through North East Tennessee on Monday 25 October and Tuesday 26 October was a monster storm. It apparently displayed the lowest barometric pressure ever recorded in the continental U.S. excluding tornado and hurricane pressures. The adjusted sea level pressure was 28.20 inHg, 954.9mb. Average sea-level pressure is 101.325 kPa (1013.25 mbar, or hPa) or 29.921 inches of mercury (inHg) or 760 millimeters (mmHg)
The storm that did so much damage, which stretched from Georgia into Canada, was stronger, more intense, and exhibited lower barometric pressure than the storm, which sank the Edmund Fitzgerald, November 10, 1975.
For satellite imagery of this storm and a more scholarly discussion of storm and wind forces see the link below, Weather Underground.
http://www.wunderground.com/blog/JeffMasters/comment.html?entrynum=1674
“The wind in the wires made a tattletale sound
And a wave broke over the railing
And every man knew, as the Captain did, too,
T'was the witch of November come stealing.
The dawn came late and the breakfast had to wait
When the gales of November came slashing
When afternoon came it was freezing rain
In the face of a hurricane West Wind…
The legend lives on from the Chippewa on down
Of the big lake they call Gitche Gumee
Superior, they say, never gives up her dead
When the gales of November come early”
There were some fatalities attributed to this storm, many tornadoes, and lots of line wind damage. The upper curve contained blizzard conditions due to the high winds spiraling inward to the low center. The bottom curve had 80-degree temperatures and tornadoes.
The lyrics included are appropriate. The wind we dealt with was recorded as a “strong breeze” (force 6) here but as a “whole gale” or “Storm” (force 10) at the official sites. With the tree now down, our recorded winds will be much more in agreement with the official values.
The gales of November came early this year.
No comments:
Post a Comment