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Edward W. Ferguson, Frederick P. Ostby, Preston W. Leftwich Jr., William E. Carle, Steven F. Corfidi, Richard G. Cundy, and William D. Hirt

months after the first tornado of 1983.3. Noteworthy tornado outbreaks Analysis of relative positions of atmospheric featuresis essential to severe local storm prediction (Miller,1972). As documented by Ferguson et al. (1983),numerous studies have related various parameters,such as vertical wind shear, atmospheric stability,low-level jets, and temperature and moisture gradients,to tornado development. Such important parametersand their relative distributions are depicted on composite charts for

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Lixion A. Avila, Richard J. Pasch, and Jiann-Gwo Jiing

for 1996 reveals that the tropical waves were well marked in the wind field and were accompanied by sharp cyclonic low- to middle-level wind shifts. In particular, note the strong wave that crossed Dakar on 19 August 1996, preceded by a strong 20 m s −1 middle-level easterly jet and a distinct low-level cyclonic wind shift. The time section for Trinidad, also in Fig. 1 , shows that the wind shift associated with the waves at that location was a little less marked. This resulted from the fact

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J. Korshover and J. K. Angell

becoming stationary over the Southeast after moving sluggishly eastwardacross the cenU~l United States. Southward displacement of the 500 mb jet, as well as a west-east coldfront through the center of the country, limited thenorthward extension of the area of stagnation. The second episode was similar in nature. Stagnation during 17-21 July was slightly northeastTABLE 1. Cases of stagnation in the eastern United States during 1985. Duration

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Edward W. Ferguson, Frederick P. Ostby, and Preston W. Leftwich Jr.

three noteworthy tornado outbreaks that occurred during theyear. Also, a composite chart, depicting the relativepositions of some key meteorological fields, is shownfor each outbreak. Outbreaks of 5 April and 31 May were associatedwith strongly baroclinic environments characterized bywell-defined jet streams and intensifying synoptic-scalesystems. Although the mesoscale structure and evolution of these two cases were different, both were representative of dynamically-forced springtime severelocal

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Edward W. Ferguson, Frederick P. Ostby, Preston W. Leftwich Jr., and John E. Hales Jr.

Index.......... Surface Dew Point 50 kPa Tem[~er&ture......... Existing Squall Line~ ~urface Boundary~ Surface Dry Line... ~ ~ 70 kPa Dr3t Intrusion~ 50 kPa JetFIG. 5. Composite chart depicting significant synoptic features for 0600 CST 28 March 1984.a level of 85 kPa) as high as 30 m s-~ were observedat Waycross, Georgia, and a polar jet of 75 m s-~ atupper levels was approaching from

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Edward W. Ferguson, Frederick P. Ostby, and Preston W. Leftwich Jr.

regions of southern Texas. At850 hPa a southerly jet flowed from the MississippiDelta northeastward to southern Tennessee. Maximumwind speed in this jet was observed to be 33 m s-~ atNashville, Tennessee. A cold trough at 500 hPa extended from Arkansas southeastward across Mississippito southern Alabama. This feature, together with warm,moist low-level air, produced unstable conditions.Values of Lifted Index (Prosser and Foster 1966) were-8 at Jackson, Mississippi and Centerville, Alabama

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Edward N. Rappaport

satellite pictures and reconnaissance aircraft data suggest that Claudette retained 30–40-kt winds from 13 to 16 July. During that period, Claudette initially moved northward, but then was accelerated toward the east by the flow ahead of an approaching frontal system. On 14 July, this environment was sampled by Global Positioning System (GPS) dropsondes deployed from the NOAA G-IV jet making its inaugural flight in support of tropical cyclone operations ( Fig. 4 ). This high-altitude aircraft is

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Neil L. Frank and Gilbert Clark

Atlantic) of which 58maintained their identity while traversing the Caribbea'n. The eight disturbances that formed over theCaribbean added to the number from the Antillesresulted in 66 seedlings entering Central America. One unusual aspect of the 1976 season was th~ earlyappearance of a well-defined African wave that movedby I)akar on 15 May. The first African system of theseason does not~enerally occur until late May or earlyJune when the easterly subtropical jet becomes established across tropical

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winds dropped to 60m.p.h. Prior to this time, a jet maximum at high levelshad worked around peninsular Florida, and by evening ofthe 8th it was located from the central Bahamas toBermuda. It was this wind fieldwhichinfluenced thestorm to make a turn to the north during the 9th and 10th.There were times when the jet appeared to be in a favor-ableposition for an increased divergent field over thestorm. The analysis delineating the jet maximum a tthis high level may have been in error due to lack of

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NEIL L. FRANK

the east, andApril 1970 Neil L. Frank 31 3concluded they probably form over the mountains of eastAfrica. This conclusion is in agreement with Thompson(1965) who states that moving perturbations play no partin the weather of east Africa.African waves are a summertime phenomena. Duringthe past 3 yr, the first wave occurred in June and the lastin October. This suggests they may be related to thestrong subtropical easterly jet stream that dominates theupper troposphere of west Africa during the summer

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