November 1964 Julian W. Posey 53 5 THE WEATHER AND CIRCULATION OF AUGUST 1964 An Unusually Cool Month JULIAN W. POSEY Extended Forecast Division, National Meteorological Center, U.S. Weather Bureau, Washington, D.C. 1, WEATHER HIGHLIGHTS deep polar Low.” He further stated that negative height anomalies had dominated the polar region Strong cooling was one of the outstanding features of 1L . during every month of 1964. .” In contrast, a August’s weather, although some of the more southerly feature of the 700-mb. circulation for August (fig. 1) was parts of the United States remained warmer than normal; a ridge orer the poliir basin with a High center near where this was in contrast to July when, “w:irm and generally the polar Low is normally loctited. Heights of the 700-mb. dry conditions prevailed in most of the Kation” [I]. In surface over the Arctic in August were significttntly some sections of the country the lingering dry conditions above normal (fig. 2). A maximum positive value of were alleviated, but in other areas the shortage of reinfall 250 ft. was centered in almost the same position RS the became more critical. large 500-ft. negative anomaly of the previous month; Large sections of the Southern Plains reported rain the dramatic change pattern shown in figure 3 rcsulted. which brought welcome relief froin extended dryness. Strong anticyclonic activity was also present at sea level Heavy rain in the last two weeks of August in most of in the high latitudes (fig. 4). The positive sea level Minneso ta and parts of Wisconsin also brought relief pressure anonialy covered itbout the same area as the to the Upper Mississippi Valley, where the Mississippi upper-level positive departures, with a maxiniuiii value Rirer Iiad reached an all-time low rate of ice-free flow of 10 nib. centered over Greenland. at McGregor, Iowa. Outside the polar region changes of the mean circula- The surnmer-long drought in portions of the Middle tion froni July were less pronounced. While the high Atlantic States continued. Washington, D.C., Baltimore, latitude flow exhibited a strong blocking pattern in Md., and Wilmington, Del., all with less than half normal August, the mid-latitude winds were quite zond, par- rainfull, reported the driest summer of record in more ticularly in the western portion of the Northern Hemi- than 60 yr. After having almost twice nornial rainfall sphere. A band of negative 700-mb. height anomaly in July, Trenton, N.J., and nearby areas returned to the (fig. 2) almost encircled the globe to the south of the large drought conditions of early summer with only one-tenth positive anonialy over the Arctic. This band of negative normal rainfall in August. New York, N.Y., with 0.24 anomaly was associated with a slightly southward dis- in., reported the driest August since 1869; Philadelphia, placement of the westerlies (fig. 5A), and, since the sub- Pa., with 0.49 in., had the second driest August since 1896. tropical Highs were stronger than normal, the speed of Many other sections of the I’r’ortheast reported fair the westerlies was faster than nornial over the United amounts of rainfall in August but continued in great States and adjacent oceans (fig. 5B). Major long-wave need of more rain because of the long-period deficiency. troughs were located very close to the west and east Another major feature of August weather was hurricane coasts of the United States (fig. 1) near their usuitl posi- Cleo which swept northward through Florida, Georgia, tions; however the east coast trough had a negative tilt and the Carolinas; first estimates of damage were placed into an abnormally depressed Low along the eastern shore near $200 million. Details of this storm are discussed of Hudson Bay. Two other mean cyclonic vortices in section 6. were in positions displaccd froin their usual higher latitude locations in August-one between Iceland and Scnndi- 2. MEAN CIRCULATION navia, and the other over northeastern Siberia. The only A sudden change occurred in the circulation of the major mean Low that was near its normal location was Northern Hemisphere early in August. Andrews [I] the one along the north ccntral coast of Siberia. noted during his discussion of the weather and circulation 3. TEMPERATURE for July of this year that “The most unusual feature of the 700-inb. circulation for July was the extremely The warm air that was associated with the strong ridge Unauthenticated | Downloaded 09/30/21 02:29 PM UTC 536 MONTHLY WEATHER REVIEW Vol. 92, No. 11 FIGUREl.-Menn 700-mb. contours (tens of ft.) draw-n at intervals of 100 ft. for August 1964. Aiiticycloiiic flow was obscrvcd over the polar basin for the first month this year. over central North America in July [l] wris replaced during August by very cool air acconipanying the large shift in the liemispheric circulation. In the upper Mississippi Valley and Northern Plains, where some of the relatively warmest air was observed in July, large negative temperature anoilinlies were recorded in August (fig. 6). After initially hot weather over much of the Nation, the coolness beciime very persistent, relenting only in the Northeast in the final week of August. Some- what warmer than usual weather did continue all ol tlic month, however, in southern Texas, Arizona, and Florida. The intensity md persistency of the cool air gave many sections the coolest August in the past 50 years. Table 1 lists severid of the cooler stations. Portlsncl, Maine, with 92 years of temperature observations, re- ported the coolest August of record. The anomaly FIGURE2.--Mean 700-1nb. height departures from normal for August 1964 at intervals of 50 ft., with centers labeled in tens of patterns of surface temperature (fig. 6) and of 700-nib. feet and thc zcro isopleth heavy. A blocking pattcrn was present height (fig. 2) corresponded closely. The relntively at high latitudes. wannest area, located in western Teses, was associated Unauthenticated | Downloaded 09/30/21 02:29 PM UTC November 1964 Julian W. Posey 537 FIGURE3.--i\iIean 700-mb. height change (tens of ft.) for July to FIGURE4.-hilean sea lcvel isobars (solid) and departures from nor- August 1964. Extremely large height rises over the polar region mal (dotted), both in millibars, for August 1964. Outstanding were associated with the cool weather in the United States. feature is the large positive anomaly over the Arctic. with southerly anomalous flow and height values that in one day and 350,000 acres of range burned in north- were near normal; an objective method for specifying eastern Nevada this season, and Reno reported several the surface temperature from the mean 700-nib. height large and numerous small range fires. pattern [2] indicated the largest positive temperature Hurricane Cleo was responsible for most of the continued anomdies should be expected in this section. heavy rains in southeastern United States. The monthly totals were much less than those of July in the Southeast 4. PRECIPITATION but were still above normal in many sections. With the collapse of the strong ridge over North 5. WEEKLY EVOLUTION America during July, t,lie resulting more frequent and more intense cyclonic activity during August brought Although the salient feature of August weather was precipitation to areas that were fairly dry in July. How- coolness dominating most of the United States, the ever, the distribution of rainfall was extremely varied plnnetnry waves of the iniddle latitudes were not stagnant. (fig. 7), and nearby contrasts were frequent. Just south Slow retrogression was apparent from week to week. of drought-stricken Washington at Richmond, Va., 9.88 A temperature cycle was noticeable also, as conditions in. fell; 4.18 in. was reported at Willinnisport, Pa., a chnged from warm over much of the western two-thirds little more than 100 mi. from Philadelphia which had of the Nation and cool in the East the first week to very only 0.49 in.; and more than 6 in. of rain occurred in cool for this season 017er most of the country the second coastal Texas not far from Corpus Christi, which had week. Then small areas of the East begnn to liave near only 0.50 in. Billings, Mont., reported the wettest August in 30 years; yet Cheyenne, Wyo. had only 18 percent of normal rainfall. Cheyenne had received less TABLEI .--Extreme low mean temperature for August recorded in 1964 than half normal precipitation since the beginning of avcragc years since 1964, the driest first 8 months in the century. The pre- Station cipihtion contrast was also present in Oregon; some observctl sections in the eastern part of the State recorded up to Rockford, Ill ............................... 66.9 -5. 6 49 four times the normal rainfall, while Yendleton again l’ortlantl, Maine............................ GG. 1 -5.7 02 13osto11, Mass............................... 68.4 -5.3 GI reported below normal min and had received only 8.49 Worcester, Mass ............................ G3.4 -4.9 ti3 Missonla, hlont..--.- ...................... 60.8 -4.0 68 in. in the last 12 months-the driest September to August Concord, N.I-I..------ ...................... 62. 7 -4.7 G1 Ilismnrck, N. Dak .......................... 64.8 -4. 5 40 period since 1890. l’rovidcncc, R.1............................ 66.6 -3. Y 59 \I‘alla Walla, Wash......................... 69. 7 -4.1 62 The dryness in sonie parts of the West resulted in Ynkirna, Wash ............................. 62.8 -5.8 53 frequent range fires. In Nevada, Elko reported 30 fires - Unauthenticated | Downloaded 09/30/21 02:29 PM UTC 538 MONTHLY WEATHERIREVIEW Vol. 92, No. 11 FIGURE6.-Depnrture of average surfacc tcmperatiire from normal (OF.) for August 1964 (from [3]).