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MARCH 1959 MONTHLY WEATHER REVIEW 111 il THE WEATHER AND CIRCULATION OF MARCH 1959 Record Cold in Alaska But Mild Temperatures in the Remainder of the United States CARLOS R. DUNN Extended Forecust Sectlon. U.S. Weather Bureau, Washington, D.C. 1. INTRODUCTION l'ositions (indicated by arrowheads on heavy dashed lines in fig. 2). The departures from normal of circu1:holl and leu- ' In Eurasia the mean winds were generally weak. Re- perature for March 1059 were rather small over most of sidual blocking over Europe, which was associated with the cont,iguous United States. Westerly flow, silnilar to n split jet stream, produced a large area of subnormal the normal [6], prevailedin the mid-troposphere, and wind over central Europe but supernormal wind to the maritime polar airmasses, with their moderating, spring- nort,h and south. One jet stream axis was depressed and time effects, dominated the weather.However, the pre- flowed across northern Africa ; the other was displaced cipitation was more abnormal. There were periodically north of the normal position, producing wind speeds up heavy rain and snow falls as vigorous Lows developed in to 9 m.p.s. above normal between Scandinavia and Spitz- the Southwest and moved across eastern United States. bergen. There were no organizedjet streams at the Some regions received 200-300 percent of their normal 700-mb. level over Asia. precipitation. Returning to the30-day mean circulationover the oceans In sharp contrast to the nlild weather ill the contiguous (fig. 1),we note that the troughs as well as the primary States was the bitter cold throughout the Stateof Alwka. wind maxima were displaced eastward from their normal Long-period Alaskanrecords were broken, andthe positions. This eastwardshift of the Asiatic coastal reported mean temperatures were more typical of micl- trough resulted in above normal heights and abnormally minter than earlyspring. For example, the monthly anticyclonic conditions over Japan and eastern Siberia. mean temperature at Barrow was a frigid 27" below F. The cyclonic areas were also displaced eastward, produc- zero. ing significant negative anomalies in the central Pacific Meanwhile, the Hawaiian Islantls hadunnsually war~n? Ocean and Alaska. n record dry weather. Honolulu, for example, reported The largest anomalies were in northern latitudes,where high mean temperatureand lit,tle precipitation. There the 700-mb. heights were far enough above normal to re- were just 6 days with measurable rai~lf:rll, and tlle total sult in a High over Kamchatka, the approximatelocation for was the month only 7 percent of normal. of the normal Low, and also far enough below normal to produce a trough over Alaska, near the position of the 2. THIRTY-DAY MEAN CIRCULATION normalridge. This anomaloussituation affected the The monthly mean circulation at 700 mb. for Marc11 downstream pattern, so that the trough normally found 1959 consisted of a large-amplitude, three-wave pattern over eastern Canada was displaced approximately 25" of in high latitudes and n smaller-amplitude, four-wave pat- longitudeeastward to southernGreenland, reducing tern in middle latitudes (fig. 1). These two vave trains heights in that areato 510 feet below normal, the largest were approximately 180" out of phase. Only the trough anomaly in the Northern Hemisphere. in Eurasia extended continuously across all latitudes, and In retrospect, it appears that theblock over Europe and even it had a marked slope from northeast to southwest. the unusually strong trough in western Siberia, through Associated with these truncated, out-of-phase troughs and tlle flux of vorticity, molded the well-marked wave train ridges were several confluence zones with accon~panying downstream. In addition, the eastward displacement of strong winds. The most prominent ones were in the At- waves was favoredbystronger-than-normal polar lantic andeastern Pacific, where theheight anon~alies westerlies. (fig. 1) indicatestronger-than-norlrlal westerly geo- In the United States 700-mb. height departures from strophic winds. In fact, wind speed maxima were located normal were snlall (fig. 1). Over the western States posi- in bot,h of these regions, and mean spwls ~1-emore tIm11 tive anomalies were associated with the flat ridge along 8 m.p.s. above normal (fig. 2). The ce~rterin the Atlantic the coast. In the eastern States therewere weak negative was a primary wind maximum, but the one in the eastern anomalies over a broad band, typicalof a flatmean trough. Pacific was essentially just an eastward extension of a The latter feature suggests that cyclonic activity during larger primary wind maximum located in mid-ocean. All March was uniformly distributed over the eastern two- of these wind speed maxima were dl east, of their normal thirds of t,he United States. Unauthenticated | Downloaded 09/25/21 05:26 PM UTC 112 REVIEW WEATHER MONTHLY MARCH 1959 FIGURE1.-Mean 700-mb. contours (solid) and height departures from nornlal (dotted), bothin tens of feet, for Mmvh 1959. Mean ridge in the western and trough in the eastern United States were assoc.iatetl with stormy \\.rather vast of the western niassif. Abnormally deep trough brought cold weather to Alaska. Unauthenticated | Downloaded 09/25/21 05:26 PM UTC MARCIX 1959 MONTHLY WEATHER REVIEW 113 FIGURE3.-Difference between monthly mean 700-mb. height anom- aly for February and March 1959 (March minus February) in tens of feet.Largest falls were over Great Britain. Changes inmany areas have striking resemblance to 700-mb. height anomalies for March (fig. 1). 700-mb. 5-day mean troughs and ridges (fig. 4) and by their relationship to the 30-day mean chart (fig. 1). The bands of high frequency of troughs and ridges were nar- row, indicating a small variation inthe longitudinal psi- tion of thetroughs and ridges.One except,ion is the eastern United States, where the 5-day mean troughswere rather uniformly distributed from the Mississippi Valley to the AtlanticCoast. It is particularly noteworthy that the positions of the 5-day mean troughsand ridges clusteredaround their respective 30-day mean troughs and ridges. This means that the 30-day mean accurately portrayed the predomi- nant circulation regime of March and was not merely the average of several heterogeneous, short-lived circulations. The 30-day mean flow of small amplitude across North America was accompanied by zonaltrajectories of the FIGURE2.-(A) Mean 700-mb. isotachs and (B) departures from Highs for March (Chart IX in [4] ) . The continental monthly normalwind speeds, both in meters per second, for polar a.nticyclones, whichformed in western Canada, March 1959. Solidarrows in (A) indicateprincipal axes of maximum winds, and dashed arrows their normal March posi- glanced east-southeastward and remained almost entirely tions. Regionswith wind speeds greater than 15 1n.p.s. and in Canada. They affected only the northeastern United anomalies greaterthan 5 m.p.s. are stippled.Principal wind States where the monthly me'an thickness (fig. 5) and maxima werelocated over the Oceans east of theirnormal surface temperatures (fig. 7)averaged below normal. The positions. remainder of the United States was dominated by mari- time Pacific air masses, which also moved eastward across 4. RECURRENT CIRCULATIONAND WEATHER the country. A few anticyclonic centers had trajectories The 5-day mean flow patterns during March resembled from the Pacific through the Northwest, but many of the each other andwere quite similar to the30-day mean flow. Highs first appeared over the Plains and Central States This isillustrated by thegeographical frequencies of nnd subsequently moved eastward into the AtlanticOcean. Unauthenticated | Downloaded 09/25/21 05:26 PM UTC FIGURE5,"Departure from monthly normal of the mean thick- ness (700-1000 mb.)for March 1959 intens of feet. Isoline interval is 50 feet. Below normalvalues are stippled. Pattern over the United States bears a striking resemblance to the sur- facetemperature anomalies (fig. 7). Extremenegative de- partures over Alaska were associated with record cold weather. normal for the northern areas of the United States. This was particularly true for Montana and the Dakotas,where in March continental polarair masses are requiredto pro- duce subnormal thickness, However, the same maritime Pacific air masses produced below normal thickness in the southernStates (fig. 5). The same was generallytrue for the accompanyingsur- face temperatures (fig. 7),but this month an exception existed in the Far Northwest where subnormal surface temperatures were associated with above normal 30-day mean t,hicknesses. The coolest weather here occurred dur- ing the second and fourth weeks [7],when there was a strong flow of abnormally cold air from the Arctic and Alaska (fig. 5) into the Northwest. These air masses had a short and rapid trajectory0~7er the ocean, thus minimiz- ing the diabatic heating,so that the airwas still cool when it reached the northwestern United States. During the fourth week t'he cooling vas further enhanced by cyclonic flow aloft. Along the California coast the weather was unusually FIGURE4.-Percent of the time that (A) troughs and (B) ridges warm. Both San Francisco and San Diego, which have on 5-day mean 700-mb. charts were located within 10" longitude long periods of reaord, reported new high mean tempera- intervals at latitudes from20" N. to 70" N. for March 1959. The tures for March. Furthermore,temperatures averaged data were adjusted to an equivalent basis with 10" at GO" X. asthe unit. Isoline interval is 20 percent.Areas with fre- above normal every day of the month at San Diego and quency greaterthan 20 percentare stippled; zero areas are were belov normal only one day out of the month at Sa11 hatched.Note high frequency of troughsand ridges 1le:Ir the Francisco.Previously, se.veral authors [l, 31 of this locations of the30-day mean troughs and ridges, respectively series of articles have related the persistently above nor- (fig.

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