A Study of the Type "B" Weather Situations Citation Tiemann, Cordes Fredrich and Miller, Joseph Alfred, Jr. (1941) A Study of the Type "B" Weather Situations. Master's thesis, California Institute of Technology. doi:10.7907/rkrn-q242. https://resolver.caltech.edu/CaltechTHESIS:01282025-185619009 Abstract No abstract. Item Type: Thesis (Master's thesis) Subject Keywords: (Meteorology) Degree Grantor: California Institute of Technology Division: Engineering and Applied Science Major Option: Meteorology Thesis Availability: Public (worldwide access) Research Advisor(s): Krick, Irving Parkhurst Thesis Committee: Unknown, Unknown Defense Date: 1 February 1941 Record Number: CaltechTHESIS:01282025-185619009 Persistent URL: https://resolver.caltech.edu/CaltechTHESIS:01282025-185619009 DOI: 10.7907/rkrn-q242 Default Usage Policy: No commercial reproduction, distribution, display or performance rights in this work are provided. ID Code: 16962 Collection: CaltechTHESIS Deposited By: Benjamin Perez Deposited On: 30 Jan 2025 18:58 Last Modified: 30 Jan 2025 18:58 Thesis Files PDF - Final Version See Usage Policy. 27MB Repository Staff Only: item control page

A STUDY OF THE TYPE 11 Bt1 WEATHER SITUATIONS Thesis by Cordes F. Tiemann Captain United States Army, Air Corps. and Joseph A. Miller Jr. Captain United States Army, Air Corps. In Partial Fulfillment of the Requirements for the Degree of Master of Science in Meteorology California Institute of Technology Pasadena, California 1941 BIBLIOGRAPHY 1. Lectures and Notes on Type Weather Situations by Dr. Irving P. Krick . 2. Plates 1 to 13 inclusive by Dr. Irving P. Krick. 3. Synoptic Weather Sharts, California Institute of Technology. 4. Weather Bureau Meteorology Bulletins. INTRODUCTION The purpose of this thesis is to study and classify the daily synoptic weather charts and to develop a system of type weather situations which may be used as aids to long range forecasting. Special emphasis will be placed upon the synoptic charts for the year 19 39. As a result of this research, we hope to become more familiar with the types as originally defined by Dr. Irving P. Krick, Meteorological Department, California Institute of Technology, to check thoroughly type tt B", to develop additional "B" types and phases where they seem necessary, and to satisfy ourselves that our f inal types, phases, and anomalies are the best that we can find. METHOD FOR CLASSIFICATION Any system of classification of daily synoptic weather charts is satisfactory provided the boundaries are clearly defined and the types check with actual conditions. There is, however, a necessity for uniformity in classification of weather situations in order that all meteorologists may have a standard plan in their study and use of these classifications as aids to forecasting. In order to mainta j_ n uniformity and continuity, we have chosen the types, phases, boundaries, criteria, and anomalies as defined by Dr. Krick. The boundaries, types, and phases are shown on Plates 1 - 13. The criteria and anomalies are as follows: Type "A" Criteria: Wedge extends from cold high in Alaska southward over North Pacific. coast of British Columbia. in east. Anomalies: Trough along the Generally polar high (winter situation). Wet on west coast and cold especially in Southern California. Generally cold in east. (winter situation). Type "B" Criteria: Semi-permanent Pacific hi gh about 30-130. Semi-permanent Basin high in northern part. Sys- tems enter continent by way of British Columbia. Regenerate with Foen winds east of Rocky Mountains. Occasionally well developed systems have formed by the time trough reaches Great Lakes and New England regions. Gulf systems seldom form or occasionally every six days. There is generally a high in the southeast oriented NESW. Anomalies: Dry in most of west, espec i ally southwest. Warm with large diurnal range. Dry in southeast and warm except in mid-winter with large diurnal range. Active at Great Lakes, eastern Canada, and New England. Acti ve at east coast. Foehn winds east of Rockies from Montana northward. Type "C" Criteria: Systems mowing in from Pacific south of latitude 35 or 4 0. Break down wedge over Sou- thern California. Systems move across south. Good Gulf waves form with heavy precipitation. Generally cold in east wi th snow far south. Anomalies: Wet Southern California and southwest. Warm in wi nter. Wet Gulf, southern Mississippi and Ohio, and southern At lantic states. rall y cold in winter or fluctuating. Gene- Occasion- ally type "Btt in north. Typ e "E" Criteria: Systems moving into continent in Northern California, Oregon, and Washington. Low pressure centers occur in Basin area, only when wedges are weak and to the south. Low forms east of Rockies affecting central part of country with secondary Gulf wave producing heavy :precipitation. Anomalies: Wet Great Basin and warm in winter. Affects more of North Basin than type "C''. Wet southern Great -Plains, Gulf, and southern Mississippi and Ohio, central and south Atlantic, east Great Lakes, and New England. temperatures. Fluctuating Cold southeast. CLASSIFICATION AND STUDY OF SYNOPTIC CHARTS With the aid of these criteria, the daily 05:00 AM PST synoptic weather charts of the California Institute of Technology for the year 1939 were classified as shown in Plates 14 and 15. It was noted that at times it was neces- sary to combine two types in order to completely eXJ.)lain the sttue.tion. We feel that the "BCtt type combination is a true type and that it persists for a period of time. Types ttEC" and "BE" were used at times to show the transition between "E" and "C" and between the types "B" and "E". Type "B" was always followed by type "E" or some combination. The greatest periods o:f uninterrupted type "B" were from W.La.y 2 to June 13, from July 19 to August 10, and from September 2 to September 23. The longest :period when not any " B" types were present was from November 6 to December 20. Yearly a nd seasonal type percentages for the year 19 ::'9 are shown on Plate 16. Type "B" persisted for 180 days and therefore accounted for 49 .4% of the weather. Type "E", which persisted for 151 days, was next in importance. Type "Btt predominated in all seasons except Autumn, during which season tY.Pe "E" prevailed. Type "B" persisted for 70% of Summer and only 35% of Autumn. In order to obtain more representative data, the years 19 38 and 1 940 were considered. The periods of per- sistence of type "Btt in 19 38 and 1939 compare favorably. However, in 1940, type "B" persisted from June 14 to August 30, a period of 77 days, which is approximately two and one half times as long as any · period observed in the other two years. See Plate 17. The total number of days that type "B" persisted for these years was as follows: 1938 ...................... 181 days. 1939 ...................... 1 80 days. 19 40 ...................... 220 day s. It is evj_dent f rom this that type "B" is the most persistent and there f ore probe.bly the most i mp ortant type. The seasonal percentages, as shown on Plate 18, check favorably except in Autumn of 1940, when more than 90% of the weather was type "B". This i s almost three times as great as the 19 ~9 percentage. In the Winter of the same year, we found type "B" only 12% of the time which is about one third of the 19 39 :percentage. The percentages for the other t wo seasons compare favorably. DEVELOPivlliNT OF THE "B" T:fPE Using Dr. Krick's types and phases in our classif ication of the 19 39 synoptic charts, it was necessary to make interpolations to obtain the daily synoptic situations and allow f or seasonal variations. Therefore, we divided type "B" into se a sons each with sufficient phases to cover the daily variations for one complete cycle. We feel that the diff erent seasons overlap, with boundar i es quite variable, and for convenience divided the year into the following seasons: Winter (February 15 - June 15) Summer {June 15 - September 15) Autumn (September 15 - February 15) ~e studied the type "B" daily synoptic charts and plotted the trajectories of the centers of low pressure in an ef f ort to determine the number of phases necessary for each of these seasons. The :positions and trajectories of these cyclones were obtained f rom the Monthly Weather Review Bulletin. See Plates 19, 20, and 21. An Examina- tion of these plates shows that when we consider a cycle e qual to one wave length, or approximately the distance across the United States, the following number of phases are necessary for each season: Wi nter . ..................... 6 SulllDl.er . ........•.•.••••• 9 Autumn . ..•••............ 6 A limitation must be placed upon the amount of detail shown on these types, thus preventing the ty~es from becoming too complicated and inflexible. We have put into our t~es some details which take care of the more frequent unusual weather situations. to fail completely. At times our types may seem This is partly true, but upon closer examination it will be found that the predominant features of the t~e do exist. An analysis of the daily synoptic charts, accelerations, decele~ations, shifts of the streamlines, polar outbreaks, etc., are some of the factors that complicate the typing of the weather charts in accordance with a set t ype of daily phases. Type "B" has certain outstanding features. The Paci- fic ant i cyclone is oriented with its axis NE-SW or E-W, forming a wedge which prevents frontal systems from entering the continent farther south than Washington and Oregon. There is generally an extension of this high inland. A series of occlusions move across the northern periphery of this high and enter the continent in Alaska and western Canada. These systems cross the mountains as upper fronts and regenerate on the east side by the interaction of the Pc and Pp air masses. The Bermuda high extends inland in the southeastern part of the country and brings Tg air onshore. Type "B" may be considered as a fair weather type, especially in the Southwest and in the Southeast. SUIVJJ.IER "B" TYPE (Plates 22 - 30) This type cons i sts of nine phases. Occlusions enter the continent in British Columbia and Alaska producing precip i tation as far south as Washington and Oregon. They cross the mountains as upper fronts and regenerate east of the Rockies in Alberta. This is an inactive wave due to the small temperature difference between the Pc and Pp air masses and to the dryness of the Pp air after having crossed the Rockies. This wave deepens southwest of Hudson's Bay from the interaction of the cold moist air from the Bay with the warm air f rom the continent. It then moves north- eastward out through Hudson Strait and into Baffin Bay. About every sixth day Tg moving inward forms a wave in the south central states. This wave produces precipitation as it moves northeastward toward the Great Lakes and out the st~ Lawrence Valley. The Southwest, the Great Basin, and the Southeast are dry and warm. The extension of the Pacific high inland is conducive to the formation of a thermal low in Southern California which inducts sea air onshore, and subse quent radiation at ni ght tends to form fog or stratus. AUTUNlN "B" TYPE {Plates 31 - 36) A series of occlusions move into British Columbia around the periphery of the Pacific high producing showers along the west coast north of the state of Wa shington. These occl usions cr oss t he mountains as upper f ronts and regenerate in Alberta. The new wave moves either southeast or east depend i ng upon the presence of a polar outbreak. The eastward moving system has very little effect on the weather of the United States and passes off the map. The southeastward moving system deepens west of the Great Lakes, when supp lied with warm air, and swings around and out the St. Lawrence Valley. The movement and trajectory of this system are variable depend i ng on the presence and i ntensity of a polar outbreak. An additional sy stem of waves forms of f the coast of Florida around the periphery of the high. This system of waves f ollows the eastern coastline and dee pens as it moves northward producing precip itation all along the east coa st. Sometimes these waves give the typi- cal "Northeaster " for the New England States as t he Ta air is drawn around the low and i nteracts with the Pc air of the continent. With an intense polar outbreak, a wave is somet imes generated in the southwestern part of the country between the Pp and the Tg or Tp air masses. WI NTER "B" TYPE (Plates 37 - 42) This type is very similar to the Autumn type with the following excepti ons. The Pc and Tg or the Pc and RPc f ront i s f arther south due to the more intense polar outbreaks of thi s season. Waves f orm along this f ront and dee pen as they move northeastward :producing li ght to mode- rate precipitation in the New England States. The system of waves found in the Autumn type off the co ast of Florida is displaced eastward off the map and does not affect the eastern part of the country. CONCLUS I ONS Type "B" , since it is common throughout the year, must be very complex to meet vary i ng cond i ti ons. During the years of 19 38 , 19 39, and 1940, it was more prevalent than a ny other type and we feel that it is t he predominant type of weather for any year. This type does not give any v i olent or unusual weather on the west coa st, however, as explained in the tYJ?es for the seasons, it often develops frontal systems in the southwestern states, south central states, along the western side of the Appalachian Mountains, and along the east coast. Normally it is expected t hat the occluded systems wi ll proceed across the map at rather high latitudes :producing relatively small amounts of :precipi tat i on, but polar outbreaks and other periodical variat i ons cause more southerly trajectories of these s ystems and tend to destroy the regularity of their movement. Ni ne phases were developed for the Summer type when warm moist systems move slower. We observed that often during a "B" type, the Pacif ic h igh takes the shape of a "J" with the we dge extending f ar northward, and an occlusion moves eastward across this wedge. As the wedge weakens more, the occlusion moves southeastward a nd produces a "BE" comb ination. This is merely a transitional type which lasts for a period of one to three days. The western end of the Paci f ic high increases in :pressure, spreads out northward and eastward, and returns to a "B" t y:pe regime. If the Pacific high re- mains oriented E- W and displaced southward without the increase of pressure and the extension northward, this "BEtt combi nation reverts to type "E". It was noted also tbat this type generally persi sted for shorter periods of time in Autumn and Winter than in Summer, but it almost alway s :pe rsisted for three days or some multiple thereof. We feel that this study has caused us to become more familiar with the type weather situations, that it will aid us in forecasting, and that our types do check favorably with the daily ty:pe "B" synoptic charts. LISTING OF ALL TYPES FOR THE YEAR 1939 11 TYPE Dat e Started Feb. 2 Da te Ended Feb. Days Persisted 9 8 TYPE Jan. 8 Jan. 21 Feb. 15 Feb. 20 Mar. 14 Mar. 28 Apr. 5 Apr. 14 May 11 May 23 June 18 June 30 July 9 July 19 Aug. 14 Sept 2 Oct. 1 Oct. 8 Oct. 19 Oct. 27 Dec.. 20 A 11 Jan. 19 Jan. 23 Feb. 17 Mar. 4 Mar. 22 Apr. 1 Apr. 10 Apr. 16 May l~•= ' June 13 June 26 July 2 July 12 Aug. 10 Aug. 23 Sept 23 Oct. 4 Oct. 15 Oct. 23 Nov. 6 Dec. 21 11 Days since Last occured Went Into - - - - -- - - -- ? E ? BC E BE-BC BE-E B!f 12 3 3 13 9 5 6 3 3 22 9 3 4 23 10 22 3 8 5 11 2 1 22 2 E E 9 5 3 3 24 9 4 3 6 E E E E E E E E E 6 3 9 BC E E 7 3 3 E E 3 43 BC TYPE "BC" Jan. 20 Feb. 19 4 May Sept 24 Dec. 22 Jan. 20 Feb. 19 8 May Sept 30 Dec. 24 1 1 5 7 3 B B ? 29 74 138 82 B B E PLATE: 14 LISTING OF ALL TYPES FOR 'I'HE YEAR 1 939 TYPE Date Started J an. 1 J an. 24 Feb. 10 Mar. 7 Mar. 23 Apr. 2 Apr. 11 Apr. 17 May 14 June 14 June 27 July 3 July 13 Aug. 11 Aug. 24 Oct. 5 Oct. 16 Oct. 24 Nov. 7 Dec. 25 Date Ended Jan. Fe b . Feb. Mar. Mar. Apr. Apr. 7 1 11 13 26 4 13 3 M:?Y May 22 June 17 June 29 July 8 July 18 Aug. 13 ~le.:gt 1 Oct. 7 Oct. 18 Oct. 26 Dec. 19 Dec. 31 !IE II Days Persisted - Days since Last occured I ·went Into ' 7 ? B 9 16 8 23 9 6 6 3 10 22 9 3 4 23 10 33 8 5 11 5 EB B EB B B BC B B B B B B B B B B BC ? 2 7 4 3 3 17 9 4 3 6 6 3 9 3 3 3 43 'fl A TYPE l~BE li Feb. 12 Feb. 18 Mar. 5 Mar. 27 Feb. 14 Feb. 18 Mar. 6 Mar. 27 3 ? B 1 2 1 3 14 20 BC E B May May 10 2 ? B 9 PLATE: 15 TYPE PERCEN'I'AGES FOR 1939 Type ']_l ype Typ e Type Ty pe Type 11 B c n !! Ell l! BEi l 11 -- ....... .. .. .... . . . . .. •• 2 .18'.5 .... . . . . 40 . ..... .. .. .. ....... ... .. ... . 4941.40 4 .6 5 .......... .. ....................• l.9Q 0.52 . .. . . . . . ............ ...... . . .... ....... EC II A II !!Bil 11 ---- - - • • • • • • • • • . . . • • 8 day s ...... 180 day s •• .. 17 day s . . . . . . . ... 151 d ays • • • • .... 7 days .. . ... . . . . . •• 2 days • • •••• • SEASIDNAL PERCEN'r AGES .!IN'l'E-q : ( Dec • 21 to Mar. 21 ) Type ll A l l Type nB" 'l'y pe 11 BC 11 Ty pe IIE!I Typ e 11 BE II Type ,i EC 1' 8 days .. . . . . • • • • • • • 8.90% • •• . . . ...... .. .. .... d a ys . . . . . ... .• •...••••• 39 43. 30 •••• •• •• . . . . . . . . . . . . days . . . . 5 5.55 • •••••• ••• • • • .. .... • • • .. 32 days .. . . . . . . ........ 35 . 60 .. . ... .... .••. .. ...... .. .. 60 day s • • ..... . . ... ..... 6.65 . . . . . . . .. . . days o.oo SPRI ,G : Mar. 21 to June 21 ) Type !I A l Type !! B U Typ e 17 BC" Type nE rr Type 1:BE II Type " E C II ..• • •• 440 days • • ...... .... ..... 0.00% days • • ..• • • • ..... .... 47.80 •••• •••• • • • • • • • ... ... .... • • 4 5.42 . . days .... 5 • • • • •••• • • • • • .. days 39 •••••• • • • • • • • •• 2 .41 ••• ••••••••• . . . . 1 ..... .. . .. . 1.09 . . . . . day . . . . •• • . . . . . . . . . . .. • • • 3 days •• •• ........... ••• • •• 3.27 S Ul·.ilvt1iR : June 21 to Sept 21 ) • • • • • • • • •• •••• •••• •••••••.. • • • ....... .. 65(J) days 0.00% ••••••• ...... • •• days ••• ......... .... 70.70 d ays ••• .. • •• • • • • • ... o.oo .. ...... . 270 days . . . . . •••• ....... ... • 29.30 0 days •••••• • • ...... • • o.oo .. . . ... 0 days • • • • • • • . ........ o.oo Type 11 An • • • • •• • • Type rrB u • • • • • • • • • • • • • Type 11 BC II . • • • • • • • •• . .. . Type llE If • • Type 11 BE ~· •• •••• • • • • • •• Type HEC" • • . . . . . ••• AU'.I'UHN: Type Type ']_lype Type Type Type A II '' Brr • Sept 21 to Dec. 21 ) 0 days ... • • • 0.00% •••••••••• ••••••• . . . ... .. 32 days ••• .. . . . . ... . . • • 35.10 ,iBc u 7 days • • . . . • • •••• .. . .. 7.70 • • ...... . . . . . .. days ••••• .. ... . . . . . . 57.20 . . 52 • • • • •• •••• • • • !' BE" •••• ... • • . . . . . . 0 days ..... •• • • ....... o.oo "EC rr • • • . . . . . . • •• • • • 0 days •••• • • • . . ....... o.oo II ••••••••••••••• 11E 1t PLATE: 16 ' "B II TYPES FOR THE YEARS 1938 AND 1940 1940 Date Started Jan. 14 Mar. 1 Apr. 18 Apr. 30 May 5 June 4 June 14 Sept 19 Nov. 27 Date Ended ,Days Persisted ,Days since Last occured Jan. 1'1 Mar. 7 Apr. 18 May 1 May 28 June 11 Aug. 30 Sept 22 Dec. 8 4 7 11 2 24 8 77 4 12 ? E 43 31 11 3 6 2 19 65 EC C E E E E E BC-C ? E E E E E E E E E E E E E E E Went In~o l.938 Jan. 3 Jan. 20 Feb. 21 Mar. 24 Apr. 6 Apr. 20 1 May May 31 Sept 9 Sept 24 Oct. 3 Oct. 12 Nov. 2 Dec. 5 Dec. 22 Jan. 12 Jan. 27 Feb. 27 Apr. 2 Apr. 14 Apr. 22 May 18 Aug. 23 Sept 16 Sept 30 Oct. 8 Oct. 28 Nov. 27 Dec. 11 Dec. 27 10 8 7 10 9 3 18 24 8 7 6 17 26 7 7 7 25 6 3 5 8 12 16 7 2 3 4 7 10 PLATE: 17 1938, 1939, 1940 11 B11 TYPE SEASONAL PERCENTAGES WINTER: ( Dec. 21 to Mar. 21 ) ... . . . .. . .. . . . . . . . . . . . . . . . 32 days • • • • • • • • • • • • • • • • • • • • • • 35.55% 1938 . . . . . . . . . . 39 days • • • • • • • • • • • • • • • • • • • • • • 43.30 1939 , . . . . . . . . . . . ••••• 12.20 1940 • • • • • • • • • • • • • • • • • • • 11 days . ... . .. SPRING: ( Mar. 21 to June 21 ) ... ... . . ..... 1938 • • • • • • • • • • • • • • • • • • • 61 days ••••• • • • ••••••••• 66.41% . . . . . . . . . 44 days • • • • • • • • • • • • • • • • • • • • • • 47.80 1939 . . . . . . . . . . . . . . 58.69 1940 • • • • • • • • • • • • • • • • • • • 53 days .. .. . . . . .. SUMl'lER: ( June 21 to Sept 21 ) ... .... .. .. .... .. .. .. .. 70.70 78.02% . . . .. . .. .. . . . . . . . 80.22 1938 • • • • • • • • • • • • • • • • • • • 71 days • • • • • • • • • • . 65 days • • • • • • • • • . 1939 • • • • • • . . . • • • • • • • • • • • • • 73 days • •• . . . 1940 .. .. . . . ........ AU'l'lTIJN : ( Sept 21 to Dec. 21 ) 1938 • • • • • • • • • • • • • • • • • • • filfp days • • • • • 0 • • • • • • • • • • • • • • • • 15.60% 35.10 1939 • • • • • • • • • • • • • • • • • • • 32 days • • • . . . . . . . • • . 91.21 . 1940 • • • • • • • • . . . . . . 83 days ••••• . . .. . . ......... . . ........ ..... PLATE: 18