Julian W. Posey 53 5

THE WEATHER AND CIRCULATION OF

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 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 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 , , tions; however the east coast trough had a negative tilt and the ; 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

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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, , 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

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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 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 -

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FIGURE6.-Depnrture of average surfacc tcmperatiire from normal (OF.) for August 1964 (from [3]). An unusually cool August followed a warm July in most sections.

FIGURE7.-Percentage of normal precipitation for August 1964 FIGURE5.-(A) Mean isotachs at 700-mb. and (B) deparature from (from [3]). A highly variable precipitation pattern was observed. monthly normal wind speed (both in m./sec.) for August 1964. Solid arrows in (A) indicate the primary axes of the maximum wind, dashed line the normal. Low that had been over the polar basin moved southward into eastern as rapid anticyclogenesis occurred over the Arctic (fig. 9A). 700-nib. heights were 800 it. normal temperatures the third week, and during the final above normal where only a short while before a very large week strong warming in the Northeast contrasted with negative height anomaly had prevailed. An unusually the coolest weather of the month in the west coast States. cold mass of air, perhaps the coldest air niass to enter During the first week of August the deep polar Low the United States during the second week of August in that had persisted for several months [I] began to weaken the past 100 years, spread southward from the Arctic and shift southward; at the same time, the ridge over during this week and covered most of the United States North America moved westward and strengthened (fig. east of the Rocky Mountains. Negative tenipersture SA). These events, resulting in two surges of cool air anomalies for the week were as much as 15" (fig. 9B). horn Canada into eastern United States during the week, The surface weather map at 1200 Gh4T gave the temperature pattern shown in figure 8B. The showed about 2500 mi. of almost direct northerly wind precipitation for the first several days of August continued from northern Texas to north of Hudson Bay. There generally light (fig. SC), but heavy rain fell in frontal were 36 stations from North Dakotii to New showers and thunderstorms over scattered areas eastward that observed record niiniinum temperatures during the from the Rocky Mountains. The very heavy rain in week. Table 2 lists some of these stations, and shows coastal Texas was caused by tropical storm Abby t,hat the length of the record of many to be more than 90 years. moved inland and dissipated rapidly. Again, as in the previous week, precipitation in the vicinity In the second week of August the deep upper-level of fronts produced the heavier rain (fig. 9C).

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FIGURE8.-(A) 700-mb. contours (solid) and height departures FIGURE9.-(A) 700-mb. contours (solid) and height departures from normal (dotted), both in tens of feet, for -8, 1964. from normal (dotted), both in tens of feet, for -15, (E) Surface tempcratiire departure from normal (OF.) and (C) 1964. (B) Surfitce temperature departure from normal (OF.) total precipitation (in.) for the week ending , 1064 and (C) total precipitation (in.) for the week ending , (from [3]). 1964 (from [3]).

Retrogression continued during the third week as the consequence, another cool air iniws that was guided south- western ridge nioved off the Pacific Coast and a mean ward by the northerly flow in eastern Canada affected trough became established in the Midwest (fig. 10A). many eastern States, while the strong Pacific ridge At the same time a blocking High moved into Canada deployed cold air farther west (fig. 10B). Precipitation directly north of the trough over the Plains. As a was heaviest this week just east of the mean trough in

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FIGURE10.-(A) 700-nib. contours (solid) and height departures FIGURE11.-(A) 700-mb. contours (solid) and height departures from normal (dottcd), both in tens of feet, for -22, from normal (dotted), both in tcns of feet, for -29, 1964. (B) Surface temperature dcparture from normal (OF.) 1964. (13) Surface temperature departure from normal (OF.) and (C) total precipitation (in.) for the wcek ending , and (C) total precipitation (in.) for the meek cnding , 1964 (from [3]). 1964 (from [3]). the Plains (fig. 10C) and was more closely associated with The ridge that had moved off the west coast the week surface cyclones, instead of being niainly frontal. Heavy before retrogressed further in the final week of August, rain did occur in parts of Montana and North Dakota, while the subtropical High in the Atlantic moved toward as cyclonic systems moved from the west into the inean the Southeast (fig. 11A). Concurrently, the 700-mb. trough. Low that had been over Labrador moved westward to

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November 1964 Julian W. Posey 541 TABLEZ.---Xtalions establishing daily record inininei~intempe~alzires the western Pacific, where six disturbances reached in Augzist 1964 tropical storm intensity. One of these storms, typhoon Minimum Length of Helen, which was just south of Jap:in on , moved Selected stations temperature Date record (" F.) (yr.) through the Yellow Sea into . The second typhoon I-- I-- of the month, Ida, del-eloped east of the Philippines and \Vaterloo, Iowa ...... 41 14 68 Dodge City, Kans ...... 55 12 89 moved westward across Luzon, then passed very closely I,ouisville, Ky..- ...... 49 13 92 Boston, Mass ...... 52 15 92 south of Hoiig Rong and into southern China. Between I)etroit, Rfich ...... 48 14 93 Ihlutli, Minn ...... 36 14 90 August 11 and 15 four tropical storms formed in rapid Springfield, &!to ...... 4s 12 iG North l'latte, Nebr ...... 38 12 89 succession east of the Philippines and south of Japiin. New York, N.Y ...... 54 14 95 Bismarck, N. Dak ...... 33 12 89 Two of these dissipated shortly after forming. The Clcvclaiid, ...... 40 14 93 Philadelphia, Pa...... 53 1G 93 remaining two developed typhoon intensity and slowly Huron, S. Ihk...... 3ti 13 82 Nnshvillc, Tcnn ...... 54 13 93 rotated around each other in the fashion typical of nearby Norfolk, Va...---- ...... 55 15 93 1'arkcrsl)ura. W. Va ...... 47 15 iti cyclonic vortices until the older and larger storni, Kathy, Madison, Wis ...... 37 14 107 engulfed the other. Kathy moved across southern into the Sea of Japan, then eastwnrd across Japan near the 40th parallel, finally becoming extratropical about . Hudson Bay and combined with tlie trough over the Plains, as the ridge in Canada weakened and also shifted One tropical storm detected in the eiistern Pacific westward. Negative 700-nib. height departures over netw 15' N., 110' W. on the 19th drifted slowly north- central United States became larger as the mean trough westward and lost its identity after the 23d. in the Plains and Upper Mississippi Valley was almost Three tropical storms were observed in the Atlantic and stationary for a few days. However, conditions were the Gulf of . Only one of these storins, Cleo, becoming suitable for the retrogression of this trough, reached hurricane strength. The other two were short tis the relatively shi~llowbut intense trough shown in lived. figure 11A along tlie western coast of Ctinudii was moving Hurricane Abby formed in the near southward arid deepening. A five-day mean chart the Texas shore, nioved inland, and caused the heavy centered on the last dtiy of August (not shown) revealed r:Lins in Texas mentioned before; 110 major wind damage rctrogression of the main trough to near tlie west coast. was attributed to Abby. Brenda formed just west of As would be expected with the push of' the Atlantic Bermuda and nioved across the island with sustained ridge to near the east coast, above normd temperatures wind speeds of 39 kt. and gusts to 56 kt. A tornado were observed in the Middle Atlantic States and the with measured wind speeds of SO kt. formed within Northeast for the first time in August (fig. 11B). The Brenda and damaged several aircraft. arca of warm air which had been in and neur Texas during Cleo, the storm that was most important for the the three previous weeks expanded somewlint, and above United States mainlnnd, was detected about nornial temperature was again observed iill along the 1000 mi. east of the . After rettching coast of the Gulf ol Mexico. The Far West averaged hurricane strength, this storm passed over , cooler than nornial this week for the first time in August. F.W.I., during the afternoon of the 22d, then moved Migratory storms ngiLin brought heavy precipitation to ncross the northern Caribbean, tiflecting the Virgin niuch of Montana and parts of Wyoming and Idaho in Jsltinds, , and . Cleo passed the liist week of August (fig. 11C). Snow was reported in northeast of Jitmiticit on the 24th and over west of the mountains of Montnnn and Wyoniing in both of the Santiago on the 25th. The center of the 10- to 16-mi.- liist two weeks of the month. At the Medicine Wheel diameter eye crossed the northeastern section of Ranger Station near Sheridan, WJ~O.,19 in. of snow fell on the morning of the 27th. With the center remaining on the 21st, and snow was reported in the htontana inland 10 to 20 mi., the storm niored north about 300 mi. mountains on tlie 19th. A more general snow until it passed briefly over the ocean around Jacksonville deposited 12 in. of snow on U.S. Highway 14 in the on the 28th and liiid its final landftill in Georgia the stiiiie Wyoniing mountains. A trailing front froin a storm day. This hurriciine then weakened, advanced north- moving eastward through Canada and two subsequent ward through the Ctirolinas, and returned to the Atlitntic storms, which both inoved from eastern Colorado across Ocean between Norfolk and Cape Hiitterns on the the Great Lakes, produced the heary rainfall in parts of morning of September 1. The storm again attained the Eastern Plains and the Mississippi Valley the last hurricane intensity at sea, but as it passed east of week of August. Hurricane Cleo caused the very heavy Newfoundland on the 4th, it lost its tropical features. rains in the Southeast. Major wind damage from Cleo was confined to a narrow strip along the Florid21 cotist from Mitiini to Melbourne. 6. TROPICAL STORMS Conservative estimates placed damage in Florida slightly Most tropical storm activity during August was in under $12 0,000,000. From Georgia nor thwtird , damage

Unauthenticated | Downloaded 09/30/21 02:29 PM UTC 542 MONTHLY WEATHER REVIEW Vcl. 92, No. 11 was mostly attributable to local flooding. Several tor- REFERENCES nadoes imbedded in Cleo’s circulation caused wind 1. J. F. Andrcws, “Thc Wcather and Circulation of - drmiages estimated at almost $400,000 in the Carolinas. A Warm Month Associated with Rctrogrcssion,” Monthly Weather Review, vol. 92, No. 10, Oct. 1964, pp. 477-482. Rainfall amounts were heaviest just before the storm 2. W. H. Klein, “Spccificntion of Monthly Mcnn Surface Tempern- returned to sea near Norfolk. At the Black Bay Wildlife ture from 700-mb. Hcights,” Journal of Applied Meteorology, Refuge, 25 mi. southeast of the Norfolk airport, 14.09 in. v01. 1, NO.2, Junc 1962, pp. 154-156. of rain fell during the passage of the hurricane, and at 3. U.S. Wenthcr Burcau, WeekZy Weather and Crop Bulletin, Norfolk the storm total was 10.40 in. Not all these National Summary, vol. LI, Nos. 32, 33, 34, 35, 36, , 17, 24, 31, niid Scptcmbcr 7, 1964. heavier amounts are reflected in figure 7 for two reasons: The bulletin from which figure 7 was obtained is based on preliminary telegraphic reports, and some of the toto1 rainfdl attributed to Cleo occurred after the end of August.

Publications by Weather Bureau Authors (Continued from p. 522)

J. C. Purvis, “Lightning Fatalities in South CarolintL,” S. F. Singer, “What Determines the Lifetime of Trapped Civil Defense Agency, Aug. 1964. Protons?,” pp. 681-689 of Space fiesearch IV, Pro- R. H. Simpson (with J. S. Mnlkus), “Note on the Poten- ceedings of the Fourth International Space Science tialities of Cumulonimbus and Hurricane Seeding Symposium, Warsaw, June 4-10, 1963 (P. Muller, Experiments,” Journal of Applied A4eteoroloyy, vol. editor), North-Holland Publishing Co. , Amsterdam , 3, No. 4, Aug. 1964, pp. 470-475. 1964.

U 5 GOVERNMENT PRINTING OFFICE:1964

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