Forecasting Santa Ana Winds Citation Fox, Elmer Joseph (1944) Forecasting Santa Ana Winds. Master's thesis, California Institute of Technology. doi:10.7907/ame5-7042. https://resolver.caltech.edu/CaltechTHESIS:05052025-165318444 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): Unknown, Unknown Thesis Committee: Unknown, Unknown Defense Date: 2 January 1944 Record Number: CaltechTHESIS:05052025-165318444 Persistent URL: https://resolver.caltech.edu/CaltechTHESIS:05052025-165318444 DOI: 10.7907/ame5-7042 Default Usage Policy: No commercial reproduction, distribution, display or performance rights in this work are provided. ID Code: 17200 Collection: CaltechTHESIS Deposited By: Benjamin Perez Deposited On: 06 May 2025 00:09 Last Modified: 06 May 2025 00:18 Thesis Files PDF - Final Version See Usage Policy. 28MB Repository Staff Only: item control page

FORECAS'l'ING SAN'l'A ANA Y, INDS Thesis by Elmer J. Fox In PBrtial Fulfillment of the Requirements for the Degree of Master of Science in Meteorology, California Institute of Technology, Pasadena, California, 1944. -1 ... No definfte irrefutable _conclusions can be set forth for the . absolutely, infallable forecasti~g of Santa Ana winds from the results of · the rather meti.ger htv.~stig at ion conducted by the author.· 'I'o set forth adiquate if1~-Aexible rules to cover every case wo1.11.d require an analysis . O:f" many such vyinds over a long period of time. But from ; a perusal of the accompanying 37-charts, covering the 3-hourly teiliperatures, dewpoints,- wind directions end v, ind velocities fo r two such occur "ences, and the re.ob s for t~o nearby stations fqr one period, we may arrive at a fe~ facts whi ch see n ingly would app ly in every case. From these few conclusions, by studying the sccompanying cherts, and by extending the investigation to other incidents of like nature, undoubtedly an accur~te basis can be established for for ece8ting within a matter of hours or even mi nutes the approach and occurrenc e of Senta Ana wi nds . As everyone knows, Santa Ana v inds are c?used pri~ arily b) a buildup of atmospheric pressure over the Gre 2 t Easin~ r:nd \'ihenthis pressure is great enough the air is naturally forced through the mountain pas s es into the valleys to the ~est ward --provi ded of course that there is the necessary ne ga tive p ressure gradient in those valleys. The Los An§eles Basin bears t h e brunt of this onslaugh t of high pressure ,¼inds because, while normally the center of the Thermal Low :i,.'s in southern Nevada, a buildup of p ressure in the Great tiasii forces the center of that Low to migrate ~est~Ard. In this ~ay the pattern is arrange d for the outflov1 of air from the Ba~in into a space which now h s s lov. e r g.t1;;!-QS£heric pressure, though ore: inarily it 111ould shov! co ns iderably ~t'es§tire. As n usual occurrenGe, the pressure gredient botw~en Burbank or l◄ 'ield and Las Vegas ranges betveen tv, o Ed1 G six mill:1.'cars~ , with the lov, er pressure being of cou:r-:se. at Las Veg ns. .Curing Ma y _and J·une in the periods of foggy 1.·.eather thj_s cJifferentiBl r.-isy even reach ten mill ibars or mofe. How~ver, ~hen sant e Ana vinds occur it is notec that a very s1ig ht w.se of pressure 2t Les Ve ga s or· Kingston above that at Burbenk or.Mines Field is enough-to start the eir pouring through the mountain pas!:'es into the Los Angeles Easin. A pressure differential in this direction of o~ly one to two millib e rs is all that is required to bri ng vinds of Beaufort • Force six to nine in the va ll eys. i\Hnes As v,;a s st 2, ted a Love, the Therms 1 Low is centered over the Los Ange les Besin at this time instead of close to the A~izbnaNevada -C alifornia boundary. As a result, it is observed_ ,that on the afternoon of t he day preceding the ~trong ~ind~, ibnormsllv high te mp eratures prevail throughout the Los Angeles •Ba 's .in. • The " dew point continues fairly steady and relatively high through the peri od of maximum temperature. Then it is obs e rved that from tv·o to six·hours after the highest temp e rature is reached the dew point begins to dro~ sharply, and continu es a do~nv~rd trend unti l six to n1ne hour•s before the high winds subside, from wh:tch· the trend ·is gredually upn:i rd, with a surge up,ard as soon as ligh ter vdnds prevai l. '!'he strong ' v:'inds arr·i ve from. six 'to nine hours after the dew point begins to,fall, plaoing their ap pearan ce apl)r>oxi aa tely twelve hours after the time of maxit1um tempera.ture , Ens.t of the pflsscs, hhv, evor, it is noted that the great wind increase is begun shortly after the mexi num temperature 1s reached. At Xingston t he ~_ina fnrco b~~nmes high from one to three hours aft-er th e rnGx :ir!m m t empera tur e :!. s re~ched, and r. t Las Vegas the vdnos rise fro m tll.re o to six hours s"fter the t cn::pc rntnr o b·eginas to decline. ,, '':)- It o.p p ci-lr!1 th£1t the l-i igh w:!.r:d~ reach the lov:er pnrts of the Loi' ,~:-i.gcles bn:~ 1n about tv, olve hc- :1. rs nftor t.hoy beg :ln blO\dng nt Lincston, Dm1 About nin·: hni rs nfter Urnir increof o nt Las V0 g [~s. r1_ h~:-- sec rn. to ::· eu ch the:: :r .hi cJ10s t ve loc.1 t 1 e f1 1 n the 1 01, e:r p nrU on of the .Snn .b'or ~1 r,nc1n Ve, ll0y. D[:l<ersf1 eld E:ind Sr.in Dicgn ap f.:en r to ~,o· ··s 1 t np toc1 o t ,t h e nortl: c rn nn 0 rio u U,orn pc ri.r:o t o r of the h:t gh v,iod 8ren, be:i ng les8 nffecloc1 b: ext re mes of tem.porc:>t:ure ·~1nd d t >Vi po 1 n t , e s v, o l J fl s b : high \', 1 nch . 1 . Dur1nr; the pn.~.sngc of the )jgh 1,· :tnd8, h1 [-~.h er thnn r;or:,;1:;11 :t q m1,c r0.t 11 res provn.tl, b1Jt vdtl,o ut extre1ne ''. tuximum~ or· t:... n.1mums ·occurring. 'l'o conc'lude," tho fo11cw-1ng basic. rcqu:!.r·oments rre necesf'.nry for the occurrence of ~.[rn ta Ann 'i·, ind s, r1ml th Air pi'e ~ ence should first be ~scerta1nod in tho preperulion of n f n r s cv s t nf these 1. High atmospheric buildup o~er the Grcrt DAB1n. 2. Thefmhl Low over the Los Ahgeles Easin a rea .. ....,. Pressvre g raf.icnt of one to tv, 0 m:tllibf1rs froi"i! I.. r-Js Vogr1s or Kingston to Eurbank or Minos Field. ,1~ t:xtremely high maxi:-r.um t elllpera tures in the Los Angele~ Lesln ·on.the efternoori before the high winds becin. b. Falling dev. points fro m h··o to six hours r, fter tirnc o f t maxl-num temperature.s G.nd fro m six to nine hours· before , high v, inc: s begin. 6. :txtremely low \";-values in 'THOb et Hirth Island_ for tv; ent;yf' n,1r hqurs before high winds begin end during the passage of the strong ~inds:• slso relatively low ~-values end subsidence J-• indicated in roobs at Oakland: C.J.T. Meteorology 5-2;.s-44