MONTHLY WEATHER REVIEW 229 THE WEATHER AND CIRCULATION OF JUNE 1960 A Hot Dry Month in the Southwest CHARLES M. WOFFINDEN Extended Forecast Section, U.S. Weather Bureau. Washington, D.C. 1. INTRODUCTION the Washington-Oregon coast in conjunctionwith this change) led to a temperature reversal in the West from In the southwestern United States the mont'h of June a relatively cool May to a June heat wave. The small- 1960 was one of the hottest and driest ever experienced, amplitude westerly flow across the northern tier of States even in that normally hotand dry region. Numerous favored the progression of several daily cyclones roughly new records forhigh temperature, amount of sunshine, along a zonal course across thecountry (see tracks in andrainfall deficit were established from California to Chart X of [2]). Some of these storms passed sufficiently Texas. Thehot spot of thenation was Yuma, Ariz., close to the Gulf of Mexico to draw in a supply of moisture where the monthly average of 92.3' F. was the highest and produce heavy rainfall over much of the East. ever recorded there for June, and the maximum temper- Over northernCanada a system of largeramplitude ature, which averaged 108.8' F. for the period, exceeded prevailed with a ridge of a blocking type in the far north- 100' each day and reached 115' on several occasions. By west and a vigorous low centerover the Davis Strait. contrastthe East was cool andwet, following a trend The blocking ridgeaccounted for the largest departure which characterized May as well as the spring season as from normal (+240 ft.) observed on the mean map for the a whole. The associatedcirculation patternfeatured month. Blocking was also activeduring the previous westerlies flowing across the northern United States with month [l], though centered mainly in the Maritime Prov- atrough of broad cyclonic curvature in the East. The inces of Canadain that instance.A vestige thereof first tropicalstorm of the season,though small and of continued intoJune and was reflected in the anomaly onlymoderate intensity, brought flood rainsto south- center of + 120 ft. off the Newfoundland coast. However, eastern Texas. the principalseat of blocking migratednorthwestward 2. THE MEAN CIRCULATION early in Juneand became well entrenchednorthward from Hudson Bay. The mean circulation pattern at 700 mb. for June 1960 Over Eurasia departures from normal were remarkably (fig. 1) was dominated by anarrow band of relatively small, even for a June map, andtrough and ridge positions fast westerlies- extendingin an unbroken sweep around agreed well withtheir normal locations. Height de- theNorthern Hemisphere. As aresult of the small partures were generally positive and the flow difluent over amplitude of theplanetary waves, thelatitude of the Europe, reflecting the retrogression of a weak blocking axis of maximum westerlies (fig. 2) varied less than 10' ridge which was activemainly over Russia during the along itsentire course from Japan across the Western first half-monthand over theBritish Isles during the Hemisphere to the British Isles. The accompanying snb- latter half. tropical Highs over both oceans were similarly zonal in naturewith centersnear their normal locations. As a 3. TROPICALSTORM ACTIVITY consequence, departures from normalheight in those areas were quite small. Broad cyclonic curvature characterized The fisttropical storm of the season moved ashore just the central Pacific trough and its downstream counterpart south of Corpus Christi, Tex. during the early morning of over theUnited States. The wavelength between these June 24 and proceeded to movevery slowly north- two systems was long by summertimestandards and northeastward across eastern Texas during the next two appearsto have been sustained bythe stronger than days. The attendant prolonged period of torrential rains, normalwesterly circulation (fig. 2). Thus,the trough which resultedin severe flood conditions along most normally active along the United States west coast was streams in southeastern Texas. was described by Dunham entirely absent at middle latitudes, andpositive departures 131. from normal dominated the whole region. In this respect, While tropical storms are not frequent over the Gulf of the June pattern differed sharply from that of May when Mexico during June, they have occurred on several occa- thetrough was very vigorous [ 11. The filling of this, sions, and some, such as Beulah in 1959, Audrey in 1957, trough (anomalous 700-mb. heights rose over 300 ft. off and Alice in 1954, havereached hurricane proportions. Unauthenticated | Downloaded 10/01/21 09:54 AM UTC 230 MONTHLYREVIEW WEATHER JUNE1960 FIGURE1.-Mean 700-mb. contours (solid) and height departures from normal (dotted), both in tens of feet, for June 1960. Blocking over northern Canada and a more southerly than normal band of westerlies with broad cyclonic curvature composed the principal circula- tion features over North America. A number of these have developed in a manner described ner, and a series of &day mean maps has been chosen to by Riehl [4], in which: (A) awesterly trough of large illustrate this evolution (fig. 3). amplitudeextends well intothe Tropics, and (B) the Figure 3A represents the 700-mb. 5-day mean flow southern portion shears from the parent trough and retro- pattern for June 14-18. A deep full-latitudetrough ex- grades. , Oftentimes the tropical portions of the sheared tended from northeastern Canada through the subtropical waves are observed to weaken as they pass to the south ridge into the Gulf of Mexico. In fact, this trough and the of the subtropical anticyclone and subsequently to rein- one in the Atlantic were the only trough systems in the tensify upon emergence on the southwestern side of the Western Hemisphere which were able to penetrate appre- High. An example of thissequence was described by ciably into the Tropics. Elsewhere the subtropical anti- Green [5] in terms of 5-day mean maps. The storm which cyclonic belt was well developed with little or no meridio- occurred this June developed in a closely analogous man- nal exchange between the westerly andtrade wind Unauthenticated | Downloaded 10/01/21 09:54 AM UTC JUNE 1960 REVIEWWEATHER MONTHLY 23 1 FIGURE2.-(A) Mean 700-mb. isotachsand (B) theirdeparture from monthly normal wind speed (both in meters per second) for June 1960. Solid arrowsin (A) indicate axes of primary westwind maxima. The westerlieswere stronger than normal overmost of theWestern Hemisphere and of relativelysmall amplitude. FIGURE3.-Five-day mean 700-mb. contours (solid) andheight departures from normal (dotted), both in tens of feet, for (A) systems. In this respect the flow of this 5-day period June 14-18, (B) June 18-22, and (C) June 23-27, 1960. The closely resembled that of the month as a whole (fig. l), deep trough in the Mississippi Valley on (A) assumed a strong positive tilt on (B) and sheared on (C) as the southern portion asindeed was the case withmost other circulation retrograded to central Texas. elements including the blocking High over northwestern Canada. During the ensuing period (fig. 3B), the United States south. During this phase, as the subtropical ridge bridged trough showed atendency to shear, as it continued to across to the north, the sea level tropicalstorm center make eastward progress in the north but stalled in the became weak and poorly defined so that it was difficult to Unauthenticated | Downloaded 10/01/21 09:54 AM UTC 232 REVIEW WEATHER MONTHLY JUNE1960 FIGURE4.-Departure of average temperature from normal (OF.) FIGURE5.-Departure of average temperature from normal (OF.) for June 1960. The June pattern showed unusual warmth in the for spring(March-May) 1960. (From [SI). Withthe exception West and cool weatherin the East with the exception of the of Texasand the Northwest, the spring pathern persisted into Northeast.(From [SI). June. trace across the central Gulf of Mexico. However,dur- Warm air occupied most of the West, but the region of ing the following period (fig. 3C) it regained its intensity most intense heatextended from California across Arizona and became a well organized storm upon entry into the and New Mexico into West Texas. This region, normally continent,then retrograded and recurved northward hot and arid anyway, experienced one of the worst heat througheastern Texas. The effect, asfar as the 5-day waves of record as maximumtemperatures soared well over mean map (fig. 3C) was concerned, was retrogression of the looo F. mark on numerous occasions. California was the sheared off southern part of the meantrough into the first to suffer the searing heat, and on June 2 maxima Mexico and southern Texas. reached 107O to establish a new all time record at Oakland One other interesting aspect of the circulation during Airport and102' to seta new June record at San Francisco. this series (fig. 3) was the tendency of trough systems in Highest maxima were reached in the interior thefollowing themid-latitude westerlies to be independent of those day with representative readings of109O at Bakersfield, at lower latitudes. This is often the case when the flow 108O at Red Bluff, and 107' at Sacramento. is strongly zonal, and has been noted on a number of pre- The heatwave subsequently spread eastward to include vious occasions. As an example, the depression centered in Arizona aboutmid-month and the Texas-New Mexico the Gulf of Alaska on the initial chart of the series (fig. region thereafter.At Yuma, Ariz., the maximumtem- 3A), moved rapidly eastward and joined briefly with the perature climbed above looo each day of the month and trough off Lower California on the mean map for June went on up to a torrid115O on foursuccessive days from the 16-20 (not shown), only to sever this connection on the 19th through the 22d. Winslow, Ariz. posted a new high mean map 2 days later and advance rapidly into Canada for June of 103' on the 19th; while El Paso,Tex., ex- to the position shown in figure 3B.