The Weather and Circulation of January 1965
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April 1965 James F. Andrews 269 THEWEATHER AND CIRCULATION OF JANUARY 1965 Mild in the West and Cold in the East JAMES F. ANDREWS Extended Forecast Division, National Meteorological Center, U.S. Weather Bureau, Washington, D.C. 1. MEAN CIRCULATION 2. TEMPERATURE A ma.rked decrease of oceanic blocking in January was The depa,rtureof average temperature from normal for accompanied by a sharp increase in the zonal index. In January (fig. 4) shows a well-defined gradient of tempera- the Pacific the strong blocking ridge and area of positive ture anomaly from central Montana southeastward to the 700-mb. height anomaly, which was over the Bering Sea central Gulf States. Temperatures to the east were below inDecember [I], movednorthward in January. This normal,and to the west they were well abovenormd. blocking was associated with the High over the Arctic Greatestdepartures were observed across the Northern Ocean on the mean 700-mb.Circulation for January (fig. 1) GreatPlains. This was one of thewarmest Januarys and its related area of positive height anomaly (fig. 2). everobserved inWyoming and southwestern Montanu The mid-Pacific westerlies also were displaced northward where temperatures averaged up to 10" F. abo\7e normd. (from December) but were still southof their normal posi- Portions of the Great Basin also had near-record warmth, tion for January (fig. 3). At sea level the Aleutian Low produced in part by a deficiency of snow. and nccompanyingprincipal storm tracks were slightly The patternof temperature anomttly was well related to south of their expected positions in January. theconcurrent circulation. The degree of cold inthe The westerlies also shifted northward over the eastern eastern hnlf of the United States during the cold season Pacific and western North America. Herewesterly cy- is closely dependentupon the ttmplitude of the ridge- clonic flow in December was replacedby moreanticyclonic troughsystem over North America. Temperature de- flow in January, and a ridge slightly stronger than normal partures from normal of 2' to 4' F. in the East are in wasobserved over western North America. Cyclonic general agreement with the position and intensity of the flow prevailed over eastern North America and the western700-mb. ridge in western North America (figs. 1 and 2). Athn ttic, the northern portion of this broad trough being Thenorthwesterly flow inmid-continent transported deeper than the southern portion, partly as a result of the cold Canadianair masses southeastward from a source strong blocking High in the Arctic. region that has beenunusually cold thiswinter. Mild Only a remnmt of the December blocking pattern in maritime air dominated the West which was under the theAtlmtic remuined inJanuary. This appeared as a influence of a ridge and westerly flow from the Pacific. ridge over eastern Greenland where 700-mb. heights were onlyslightly above normal. Some of December'sstrong 3. PRECIPITATION blocking WRVe also appears to have retrograded to merge withthe Arctic High. Weakening of Atlanticblocking Except for the Great Basin mostof the West had above accompanied the return to a more nearly normal circula- normalprecipitation in Januq~(fig. 5). Some of this tion across the Atlantic and the principal jet axis at 700 w.ns related to storms moving ILCI'OSS the Northwest from mb. was close to its expected position (fig. 3). As in the the Pacific. Upslopeconditions contributed to pre- Pacific, there was nn increase and northward displacement cipitntionin theRocky hiIount,ain States,with over- of the principal storminess and the Icelandic Low was onlyrunning of cold Polar air by warm moist Pacific air also slightly south of its usual location. a, factor. The circulation across Europe and Asia (figs. 1 and 2) It was very dry in the Rio Grande Valley where the was moremeridional with respect to normal. A trough anomalous flow \vas northerlyand principal storminess with below normd 700-nib. heights was the principal fea- passed north of thearea. Dry weather also prevailed ture in Europe and the Mediterranean where the weather fromthe eastern Dakotas to Wisconsin. This area lay in Jtmuary was cold and wet. Another deep trough with between t,wo primarystorm tracks, one of which wns a pronounced negntive tilt was observed in north central north of the region andthe other to the south. The Siberia betweenthe Arctic High anda stronger tha,n normal southern track was associated with a band of above nor- ridge over eastern Russia. malprecipitation from t,he MiddleMississippi Valley Unauthenticated | Downloaded 10/01/21 06:17 AM UTC 270 MONTHLY WEATHERREVIEW Vol. 93, No. 4 FIGUHE2.--Dcparture of mean 700-mb.heights from normal (tens FIGURE3,”Nean 7OO-mb. isotachs (meters per second) for Janu- of feet) for Janu:wy 19G5. Heightclepartures in the United ary 1965. The primary axis of maxi~numwest wind was close Statesand concurrent surface temperature anomaly wcrc closely to itsusual position over much of thc Northern Hemisphere. related. Unauthenticated | Downloaded 10/01/21 06:17 AM UTC April 1965 James F. Andrews 271 through t.he Northeast, although portionsof New England were dry. The Concord, N.H., areahad its driest Jtinuilry in 95 years. A rntller varirLble precipitationpattern was observed in the South, but amounts were generally close to normal. This is in accotd with the weak nnomalous flow and posi- tion of the mean trough (figs. 1 and 2). 4. WEEKLY EVOLUTION 'I%e circultLtion early io the monthconsisted of a trough along the Pacific comt and one in the western Atlantic, with rather fltLt flow :xrossNorth America (fig. 6-4). This westerly flow pattern brought the warmest weather of Janunry to the NjLtion during the meek ending on the 10th (fig. 6B). hhsimumtemperature departures of FIculta 4,"l)cparturc of :Lvcr:lgc surf:lce tcmpcratnre from normal 9' I?. were observed in portions of the Rocky Mountain nncl CentralStates. 'J.'he outstanding exception to the (OF.) for J:munry 1065. (From [2].) mild we;lt,her was in prts of Montana and the Dakotas 25O where averagetemperatures were as much as F. I PERCENTAGEPRECIPITATION OF NORMAL I below normal.Extreme cold had prevailedin this area :tnd in weste~mCtLnda since mid-December. T-IerLvy precipitation fell in the Pacific Northwest duringthe first week (fig. 6C)in association withthe deepcoastal trough. A disturbancemoving into the Grerlt Basin spread moderate to heavy amountsof rain or snow across the Soutllmest. This system combined with a southeastwardmoving strong cold frontto produce most of theheavy band of precipitationfrom eastern Texas to the Middle Atlantic States. Several days of un- usu&lnrarmth, in \vhich dailytemperature departures from nota~nlexceeded 20' P. fromthe Sout,hern Plains to the Sortheast, preceded the arrid of the cold front whose passage brought a new temperature regime to the Enst. FIGUIUC5.-I'crccntngc of normal precipitation for JiLnuary I OG5. Marked amplificationin the second week produced :L (From [2].) simple wnve pattern which featured a strong ridge over western Xorth Americaflanked by deeperthan normal troughs in the mid-P>wific andenstern North America averagingubout hdf nn inch.Much of thisoccurred (fig. 78).Northwesterly -How overmid-Xorth America late in the week as two storms,one moving southeast,- resulted in n sh:Lrp contrast in average temperature for ward ncross the Central Plains and the otheroff the south the week with the strongest anomaly gradient across the Atlnnticcowt, combined to spread a blanket of snow NorthernStates (fig. 7B). Repeatedoutbreaks of from Illinois to the east coast mcl southmard to South Arct.ic airkept temperatures well below normalin the Carolina and Georgia. eastern half of the Nation while mild Pacific air associated Shearing of the long-wave troughs accompanied an in- withthe upper-level ridgedominated the West. An creasein westerly flow during the third week (fig. SA). exa.mple of extreme cold WLS the"42' F. recorded at This occurred as the mid-Pacific trough weakened and the InternntiondFalls, Minn., on t,he14th, the lowest high-latitudeportion moved into the Gulf of Alaska. tempertltureobserved there in 25 years.The coldest The increase in the Pacific westerlies and shorteningof the weatherreached southern Florida near the end of the wavelength downstrem1 was accompanied by progression week when temperaturesin the 30's were reported at and some de-amplification of the higher-ltititude flow over Miami. North America.Retrogression of thetrough inthe l'recipitntion was generally light west of the Mississippi Southeast was relttted to adjustment of the low-latitude inassociation with the large-amplitude northerly flow wavelength, a compensation for the loss of the trough west pattern which prevniled (fig. 7C). Amounts were mostly of Bnja Cdifornia (fig. 7A). less thnn 0.25 in. across the Borthern States, while little Flattening of the flow over the United States during the if my precipitlltion fell in the Sout,hwest. Heavier pre- third week (fig. SA) brought warmer weather to the eastern cipitatiou fell in and ewtof the mean trough with amounts hdf of the Nation (fig. SB), although temperatures con- Unauthenticated | Downloaded 10/01/21 06:17 AM UTC 272 REVIEWWEATHER MONTHLY Vol. 93, No. 4 c , \ \ \ \ / \ \ L I .l, :DEPARTURE OF AVERAGETEMPERATURE FROMNORMAL (OF) 1 FIGURE6.-(A) Mean 700-mb. contours (tens of feet) for January FIGURE7.-(A) Mean 700-mb. contours (tens of feet) for January 5-9, 1965. (U) Surfacetemperature departure from normal 12-16, 1965. (B) Surfacetemperature departure from normal (OF.) and (C) totalprecipitation (in.) for January 4-10, 1965 (“F.) and (C) total precipitation (in.) forJanuary 11-17, 1965 (from [2]). (from [a]). Unauthenticated | Downloaded 10/01/21 06:17 AM UTC ~ ~~ ~ April 1965 James F Andrews 273 ~:1.'?.'6.~ DEPARTUREOF AVERAGE IEMPERATURE FROM NORMAL PFI FIGURE8.-(A) Mean 700-mb. contours (tens of fcet) for January FIGURE9.-(A) &lean 700-mb. contours (tens of feet) for January 19-23,1965.