Edward W. Ferguson

The Tornado Season of 1985

Abstract A review of tornado activity in the United States during 1985 is presented. Annual statistics are compared with both recent and long-term values. Month-by-month highlights of tornado events are summarized. Meteorology patterns associated with three noteworthy tornado outbreaks are examined.

The Tornado Season of 1983

Abstract Tornado events of 1983 are reviewed. Significant and interesting aspects of the 931 reported tornadoes are noted. Synoptic patterns associated with four noteworthy tornado days are examined.

Tornado 1982: A Near-Record Year

Abstract The tornado events of 1982 are reviewed. Significant and interesting aspects of the 1047 reported storms are noted. The synoptic patterns associated with four major tornado days are examined.

PICTURE OF THE MONTH: Satellite View of a Lake-Effect Snowstorm

The lake effect on snowfall has been of great interest to meteorologists for many years. Earlier work by Sheridan (1941) and Wiggin (1950) showed that cold arctic air flowing across relatively warm open water such as Lakes Erie and Ontario picks up vast amounts of moisture and heat. This is most pronounced during the early winter months when there is a large air-lake temperature difference. Heating of the lowest layer of arctic air produces convection that can result in heavy snowfall to the lee of the lakes. Later, a group of scientists under the direction of Dr. George McVehil made a study (McVehil et al. 1967) on the lake effect and agreed with these earlier ideas, but further concluded that initial air mass stability, height, and strength of air inversions and large-scale vorticity are important factors in determining the extent of lake-induced snow. Lavoie (1968) tested several of these ideas in his model of mesoscale lake-effect storms, found good agreement with earlier results, and observed that the most intense band of convergence was created when the average wind direction below 850 mb was 250°-280” with little shear but with large vertical gradient. He did, however, have diaculty explaining the strong vertical motions associated with the most severe storms of this type. Jiusto et al. (1970) made an extensive investigation of this type of snowstorm, with strong emphasis on determining what mechanism controlled the intensity and amount of snowfall to the lee of lakes. Conclusions drawn from this study supported earlier work, but added a t least one important new idea. Jiusto found that a severe snowstorm occurred when there was an upper level shortwave trough located west of the heavy snow area. This shortwave trough was so positioned that there was positive vorticity advection (on an isentropic surface) east of the trough over the lake area where other criteria had been met and conditions were ripe for heavy snowfall. The satellite pictures in figures 1A and 1B show the band of clouds, @ to @, associated with a severe snowstorm to the lee of Lake Erie on Nov. 23, 1970. The cloud band appears to form near the central portion of the lake. The winds were moderately strong from the west-southwest as cold arctic air moved across the relatively warm lake. A rapidly moving front passed Buffalo, N.Y., during the evening of November 22 and was located just off the east coast (fig. 2) by the time the satellite picture was taken at 0941 EST on November 23. The clouds associated with a portion of this front extend northeast from point @ in figure 1A. At 0700 EST on November 23, the National Meteorological Center (NMC) FIGURE 1.-(A) ESSA 8 APT photograph at 0941 EST on Nov. 23, 1970; (B) an enlargement of the area enclosed by the dashed line in (A).

The Tornado Season of 1986

Abstract A review of tornado activity in the United States during 1986 is presented. Annual statistics are compared with both recent and long-term values. Month-by-month highlights of tornado events are summarized. Meteorological patterns associated with four noteworthy tornado outbreaks are examined.

The Tornado Season of 1984

Abstract Tornado events of 1984 are reviewed. Significant and interesting aspects of the 907 reported tornadoes are noted. Synoptic patterns associated with four noteworthy tornado days are examined.

Comments on “The Unnamed Atlantic Tropical Storms of 1970”

I read Spiegler’s (1971) article with special interest as we in the Applications Group of the National Environmental Satellite Service have attempted, for the past several years, to gain a better undertsanding of this type storm. Our interest was stimulated by the fact that the cloud pattern and distribution as observed in satellite data was much the same as that produced by intense hurricanes but on a much smaller scale. The most obvious question was whether surface winds generated by a system of this type were of hurricane force. Our approach to answering this question was to request from the US. Coast Guard the name and location of all ships in the vicinity of the storm. This information was then relayed to the Port Meteorological Office in New York City. Walter Stoddard or William Winkert of that office contacted the ships and told them of our interest in the weather conditions that they encountered. The ship’s log was either mailed to them or, if the ship docked in New York, they yent aboard the ship, copied pertinent weather information from the log, and checked the instruments for exposure ancl measuring accuracy. Aug. 18, 1970, \vas one day on which we exercised this procedure. This was5 also the last day included in Spieglers’ discussion of unnamed storm number 1. The first Applications Technology Satellite (ATS 3) picture of the day, taken a t 1311 GRIT, located the storm near 40°N and 62OW. Subsequent pictures showed the system to be moving northeastward a t about 40 k t until around 1900 GMT when it took on a more northerly track and increased in speed of forward motion, Two ships are known to have passed near the storm on this day. The Mosengen (LKZI) passed close to the center around 1400 GRIT (fig. 1) and observed 105-kt north winds for a 15to 20-min period and a minimum pressure of 988 mb. This pressure, if it is indeed the central pressure, is 13 mb lower than that observed by ship Hotel at 0310 GRIT. This represents an average deepening of slightly more than 1 mb/hr and agrees with Spiegler’s computation of pressure change for the 9-hr period preceding 0300 GRIT. Note in figure 1, that the ship was less than 60 n.mi. from the center of the storm at 1500 GMT, but the surface wind had decreased to 50 kt. This supports Spiegler’s conclusion that the strong winds are limited to ‘‘a very small area near the center.”

PICTURE OF THE MONTH: Snowstorm in the Central Plains

The ESSA 8 APT picture shown in figure 1 was taken on a day when 3 to 5 in. of snow fell over a portion of Kansas. Smaller amounts were observed in parts of Texas, Oklahoma, and Nebraska. By the time this picture was taken (1500 GMT), a lom-level southerly flow from the Gulf of Mexico had produced a vast area of stratus and fog from Texas to Kansas. These low clouds can be seen in figure 1 and are easily identified by the sharp western edge and smooth upper surface of the cloud mass. The weather depiction chart for 1600 GMT is presented in figure 2A. Note that low clouds cover much of Kansas, while middle clouds are reported over the northeast part of the State. Another feature of interest in the satellite picture is the area of middle and high clouds that forms a vortical pattern over northern Oklahoma and Kansas. Shadows and highlights produced by the low sun angle give a three-dimensional effect to the clouds in this area. This system is associated with a vorticity maximum that was centered in northeast Colorado at 1200 GMT (fig. 2B). Before this vorticity maximum moved into the area covered by low stable clouds, little or no precipitation was