January 1962.CER62HR3.Includes bibliographical references

Riehl, Herbert, 1915-

Schleusener, Richard A.

English

Riehl, Herbert, 1915-, author

Schleusener, Richard A., author

Department of Atmospheric Science, Colorado State University, publisher

Mountain Scholar (Digital Collections of Colorado and Wyoming)

On Identification of Hail-Bearing Clouds from Satellite Photographs By H. Riehl and R.A. Schleusener Department of Atmospheric Science Colorado State University Fort Collins, Colorado January 1962 CER62HR3 ATMOSPHERIC SCIENCE TECHNICAL PAP R January 196'2 NUMBER 27 On Identification of fiaU ... Bearing Clouds From Satellit~ Photographs by H. Riehl and R, A. Schleusener Departm nt of Atmospheric Science Colorado State University Fort Collins, Colorado CER62HR3 On Identification of Hail-Bearing Clouds From Satellite Photographs by H. Riehl and R. A. Schleusener Colorado State University Introduction: Meteorological satellites of the TIROS series have permitted observations of cloud patterns over large areas. The forthcoming NIMBUS series will afford even better observations of cloud patterns and other meteorological parameters. For maximum uti1~zation of such information, u..."1derstanding is needed in the physical interpretation of satellite data. Re-garding possible relation between cloud arrangements and associated severe weather, a study was made of eight cases during the summer of 1960. Re-sults may assist operational, use of the NIMBUS series data. Hypothesis: Much observational and theoretical work has suggested frequent existence of band or "street" arrangements of convective clouds, with a connection between such structure and severe weather. Kuettner (1) has given an excellent discussion of this subject. In view of these observations, - 2 -a limited sample of satellite photos from TIROS I has been analyzed in a test of the following hypothesis: Hail occurrence should be correlated with the occurrence of convective clouds in well-ordered streets. Such streets suggest concentration of low-level mass convergence into narrow elongated zones~ hence also concentration of water vapor, condensation and production of water available for hail formation. Procedure: Satellite photographs were analyzed and maps of cloud photo-graphs were prepared for eleven TIROS I photographs from eight days in 1960 (see Table 1). Table I. Dates and times of TIROS I photographs analyzed in pilot study of the relation between cloud streets and hail. Date Time 1960 GMT Orbit 16 May 20: 55: 34 659 16 May 20: 54: 35 659 18 May 20: 53: 31 688 23 May 19:55:21 760 25 May 23: 21 : 30 791 28 May 22: 26: 21 834 28 May 22: 27: 21 834 30 May 22: 22: 41 863 5 June 20:32:50 949 6 June 19: 39: 52 963 6 June 19: 38: 22 963 - 3 -For each of the dates listed in this table, the publication "Storm Data" (2) was examined for state reports of damaging hail equal to or greate:r than "category 4" (dollar damage $5,000-$50,000). Whenever hail of this cate .. gory was reported, a "hail day" was considered to have occurred in the given state. This type of "verification" was made for each state for which the cloud structure was available from the satellite photographs. It was then com-pared with a "forecast" of hail occurrence for each of the same states, based on the cloud-street hypotheses stated above. The synoptic situations were completely unknown to the forecaster. Table II. Contingency table for "Forecasts" of hail occurrence~ based on the hypothesis that hail occurs in well-defined cloud streets only. (Verification for individual states from "Storm Data"). Yes Yes 10 Observed No 8 18 Per cent correct: Per cent skill sco:re: Forecast 83 50 No 6 59 65 16 67 83 - 4 -Results~ The results of this pilot study (see Table II) indicate that the hy-pothesis deserves further study. The preliminary results. illustrated in figs. 1-4. appear encouraging" But it is recognized that the following fac-tors creat~ uncertainties: (1) The satellite photos provide only a snapshot of the clouds at one or two instances for a given day. Hence the pattern that existed at the time of the photo may not be representative at the time of severe weather. (2) On some occasions there may have beer. extensive cirrus shields which obscured organization of cumulus clouds below. (3) The evolution of cloud systems may be as important as the in-stantaneous cloud pattern with respect to type and intensity of severe weather. (4) The data on hail extent and intensity in "Storm Data" is at best an estimate of hail occurrence. In many CB.ses. this statistic n:-.I.ay not furnish an accurate account of the exact extent and in-tensity of a storm. With these reservations it may be possible to incorporate satellite data into operational forecasts of convective severe weather, if the skill score shown in Table II is in fact representative of the degree of correlation between or-ganization of clouds into well-ordered streets and hail occurrence. Conclusions: (1) Results from this study indicate a skill score of 50 per cent in "forecasting" the occurrence of hail damage equal to or greater - 5 -than $51 000-$50, 000 in a given state from observations of well-defined cloud streets in one or two TIROS I cloud photographs. (2) Further study is required to determine the validity of the hy-pothesis of correlation between cloud streets and hail. (3) If the hypothesis is valid, it can be operationally useful for short-range weather forecasts from satellite observations. Acknowledgements: This research was performed under contracts between the National Science Foundation and the United States Weather Bureau with Colorado State University. Special acknowledgement is due to the Satellite Section of the Weather Bureau which provided the photos requested, and to Mr. R. W. Hayman, Colorado State University, under whose supervision the photographic analysis and mapping was performed. References: (1) Kuetiner, J.. The Band Structure of the Atmosphere. Tellus, II, 267-295, 1959. (2) Storm Data. U. S. Department of Commerce. Weather Bureau. Government Printing Office. Washington. D. C. - 6 -16 May 1960 2156 GMT Fig. 1. TIROS I cloud map~ 16 May 1960, 2156 GMT. SSP and PP indicate sub-satellite and principal pOints. respectively. Shading points toward cloudy area. 16 May 1960 Fig. 2. Hail "forecast" verification by states, 16 May 1960 (from two photos). Y denotes yes; N, no. Scheme: forecast/observed. / I / - 7 -r ;;~;'19s0 ( 1440 GMT ; Fig. 3. TIROS I cloud map, 6 June 1960, 1440 GMT. /1-........ .. I : --... ..... __ I ) -"-r / \ % ; 'N ' , ! X '-....;---- -.r-·----, 1.....-.!4 / N .-: N : I -.-J /( L YN I , L N ,'--.. _ I , . -. \ IN ·-r·- __ .L N/. " I y,; I -, /N . L N / ~ f---- .. J., r' '-'-.... IN: N ) : r---·----·J YN : I ~ I ;--.:::;-----•• ~ Z Ni~ i:~ \1 ". : N I L __ N i '-. L : --"--'''i., .. -..... ,---":,,,,-.. _--J ~ \, N/ \ ! /N ) I-----J.--l....;::,.---.....;" /""-. . - \ ~-'-.""'" 6 JUNE 1960 \. '-. Fig. 4, Hail "forecas(' verification, 6 June 1960. 

On identification of hail-bearing clouds from satellite photographs

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On identification of hail-bearing clouds from satellite photographs

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