October 1966 Julian W. Posey 61 9 THE WEATHER AND CIRCULATION OF JULY 1966 A Month With An Extensive Heat Wave JULIAN W. POSEY Weather Bureau, Environmental Science Services Administration, Washington, D.C. 1. HIGHLIGHTS July was also marked by intensifying drought in the Northeast. Figure 1 illustrates how drought conditions One of the predominant features of the weather during varied from the beginning to the end of July in the North- July was an extended heat wave that began in the northern east and adjacent areas. In the Ohio Valley some sec- Mississippi Valley and the Northeast during June [l]. tions, such as eas t-central Indiana, had increasing drought In July the hot weather gradually intensified as it spread conditions, while in Ohio a large area shifted from mild southward and southwestward. Reports from 42 major drought to adequate moisture or even slightly met condi- Weather Bureau stations from the Rocky AIountains to tions. The severest drought developed in the Washing- the Atlantic Coast indicated record high temperatures ton, D.C. area and immediately northward through Mary- during the month. Many of these localities reported the land into Pennsylvania. Both the heat and the lack of largest number of days with maximum temperatures rainfall contributed to the critical condition. Washington above either 90" F. or 100" F. ever experienced there. D.C. had only 0.93 in. of a normal 4.15 in. of rain during Tables 1 and 2 list some of the details. The peak of the July, n-hile Harrisburg, Pa. had only 0.81 inches of a usual 3.51 in. During May, June, and July, Harrisburg heat wave occurred from the 10th through the 16th when received only 1.86 in., their lowest precipitation for any an average of about 397,000 square miles in the eastern consecutive three months of record. Some areas in the two-thirds of the Nation had temperatures that exceeded Northeast did receive at least temporary drought relief 100" F. On the 11th approximately 527,000 square miles during the month. Albany, N.Y., received 3.88 in. of of the country had temperatures above the 100" mark. rainfall which was slightly more than the July normal and was the heaviest July amount since 1961. Buffalo, N.Y. reported 4.92 in. which was 2.35 in. above normal. TABLE1.-Record high temperatures established or equaled during Drier than normal weather in parts of the Great Plains, July 1966 Rocky Mountain States, and some areas west of the Rockies also persisted. Flagstaff, Ariz., Mount Shasta, Cjty Temperature Date Type of Record Calif., Casper and Sheridan, Wyo., and Reno, Nev., all - i(.F.)( ~ - reported six or more consecutive months with below Hartford, Conn.. .................... 3 All time maximum. Concord, N.H ........................ 3 Do. normal precipitation. ,4t Wendover, Utah, general LaGuardis Field, N.Y ............... 3 Do. Allentown, Pa ........................ 3 Do. showers on the last day of the month broke a prolonged Harrisburg, Pa ....................... 3 Do. Huron, S. Dak ....................... 10 Do., dry spell. Concordin, Kans. reported another month Philadelphia, Pa. .................... 3 July Maximum. Reading, Pa .......................... 3 Do. with deficient rainfall which contributed to the less than Little Rock, Ark ..................... 10 Daily maximum. '103 14 Do. half of normal precipitation there so far in 1966. Kansas Wilmington, Del- .................... 102 3 Do. 102 4 Do. City, Mo. reported the driest July of record. Rome, Ga ............................ 9 Do. 12 Do. 101 13 Do. TABLE2.-Duration of heat wave in July 1966 Lansing, Mich ........................ 99 3 Do. Valentinc, Nebr. ..................... 10 Do. Newark, N.J- ........................ 3 Do. Temperaturc Number Central Park, N.Y ...................j 3 Do. City (" F.) equalec of Days 101 13 Do. or exceeded Harrisburg Pa ....................... 104 4 Do. Elkins, W. ba........................ 2 Do. Casper, Wyo ......................... 7 Do. Hartford, Conn ............................................. 90 16 16 Do. Washington, D.C ........................................... 90 20 30 Do. Central Park, N.Y .......................................... 90 9 Sheridan, Wyo ....................... 16 Do. Greensboro, N.C.. .......................................... 90 20 30 Do. Oklahoma City, Okla ....................................... 100 21 Pueblo, Colo ......................... 102 5 Do. Philadelphia, Pa. ........................................... 100 3 101 17 Do. Cheyenne, Wyo ............................................. 90 18 1 Memphis, Tenn-.. .......................................... 100 6 *Equaled previous record. Unauthenticated | Downloaded 09/27/21 01:42 AM UTC 620 MONTHLY WEATHER REVIEW Vol. 94, No. 10 DROUGHT SEVERITY (Palmer Index) \ CHARACTER OF RECENT WEATHER i More than 4.00 Extremely Wet \ 3.00 to 4.00 Very Wet \ CHARACTER OF I I 2.00 to 3.00 Moderately Wet I INDEX NUMBER RECENT WEATHER i 1.00 to 2.00 Slightly Ret \ Near Normal More than 4.00 Extremely Wet 1.00 to -1.00 ! i 3.00 to 4.00 Very Wet I \ c----------- i ~ :-\ - 1.00 to -2.00 Mild Drought \ ,~____--.--A ,__-_.__. 2.00 to 3.00 kloderatelv Wet -2.00 to -3.00 Moderate Drough' 1.00 to 2.00 Slightly ket \-3.00 to -4.00 Severe Drought 1.00 to -1.00 Near Normal Less than-4.00 Extreme Drought -1.00 to -2.00 Mild Drought -2.00 to -3.00 Moderate Drought Based on preliminary weekly data -3.00 to -4.00 Severe Drought for climatological divisions. Less than -4.00 Extreme Drought Based on Preliminary weekly data for climatological divisions. FIGURE1.-Palmer drought index for eastern United States (A) July 1, 1966, (B) July 29, 1966 (from [4]). 2. MEAN CIRCULATION were considerably stronger than normal, as evidenced by Over the western half of the Northern Hemisphere the the anomalous flow along the 40th parallel in that area 700-mb. flow in July was much more meridional than (fig. 3). The basic pattern over the eastern Pacific, across l normal (figs. 2 and 3). ii ridge orer North America with a trough along each coast is the usual July pattern, but North America, and over the dtlantic was similar to the this year (fig. 2) (as in other summer drought years) the three-season average circulation for the 1952-54 summers ridge over the United States was displaced eastward from (fig. 4) that Namias [2] related to drought. Compare the its normal Rocky Mountain location, resulting in a posi- location of the three major positive anomaly centers over tive anomaly somewhere over the eastern two-thirds of the eastern Pacific, North America, and the Atlantic in the country. figures 3 and 4. Namias demonstrated in an earlier The Atlantic anticyclone was more than 10' north of article [3] that the presence of two of these positive its normal July position and unusually strong. Anoma- centers implies the third. lously strong northerly flow east of this intense anticyclone 3. TEMPERATURE and the resulting deep trough downstream gave unusually cool weather to much of Europe. Figure 5 shows that to Most of the Nation from the Rocky Mountains east- the east of the deep European trough the main polar ward had temperatures considerably above normal for 11-esterlies were again deflected north of their usual July July (fig. 6). This extensive area of warmth is consistent position. However, over Asia and most of the Pacific the with the ridge over the Midwest and the associated area major westerlies were slightly south of their normal of positive height anomaly centered over the Northern position. Wind speeds over the western half of the Pacific Plains (figs. 2 and 3). The temperature anomaly for the Unauthenticated | Downloaded 09/27/21 01:42 AM UTC October 1966 Julian W. Posey 62 1 FIGURE2.--Mean 700-mb. contours (tens of feet), July 1966. A typical heat wave and drought pattern. FIGURE3.-Departure of mean 700-mb. heights from normal FIGURE4.-Mean 700-mb. contours (solid) and departure of 700- (tens of feet), JU~V1966. The strong Dositivc anomaly in the ,- -- mb. heights from normal (dashed) (both in tens of feet). for three Atlantic was the most intense anomaly in the hemisphere. summers 1952-54 (from [2]). Unauthenticated | Downloaded 09/27/21 01:42 AM UTC 622 MONTHLY WEATHER REVIEW Vol. 94, No, 10 I <’5-7-.., TEMPERATURE DEPARTURE (OF) from 30-YEAR MEAN FIGURE6.-Surface temperature departure from normal (OF.), July 1966 (from [4]). FIGURE5.-Mean 700-mb. isotachs (meters per second), July 1966. Solid arrows indicate principal axes of maximum wind speed and dashed lines the normal. drought summers 1952-54 mentioned earlier (fig. 7) was extremely similar to the pattern of this July. Below nor- mal temperatures in the Southeast were associated with the below normal 700-mb. heights in that section. In the Far West a deep trough along the coast (fig. 2) a1- lowed frequent incursions of cool maritime air that I resulted in below normal temperatures west of the Rockies. FIGURE7.-Average temperature departures from normal (OF.) for three summers (June, July, and August) of 1952-54 (from [2]). 4. PRECIPITATION This July there were some very great contrasts in the precipitation amounts at nearby stations. Raleigh, N.C., had only 0.91 in. of rain for the driest July since 1953, with these anomalously large July rainfall totals many but Wilmington, N.C., reported 15.12 in., the largest parts of Oregon and nearby areas were still unusually dry. JUIYtotal in 96 years of record. Omaha, Nebr., received At Pendleton, Oreg., where 0.79 in. fell (0.57 in. above 4.70 in., while only 0.89 in. fell at Kansas City, Mo. just, normal), the April through July rainfall was the lowest to the south. Oak Ridge, Tenn., had less than half its of record. normal rainfall, but nearby I<noxville received 5.44 in., Again a comparison can be made with one of the which mas more than normal. Charleston, W. Va. had a drought patterns presented in [2].