418 BULLETIN AMERICAN METEOROLOGICAL SOCIETY

Forecasting Summertime Shower Activity at Grand Junction, Colorado

WOODROW W. DICKEY

U. S. Weather Bureau

ABSTRACT

Due to the lack of a dense network of reporting stations in the Grand Junction, Colorado area and the inadequate representation of shower activity by observations of at a single rain gage, certain arbitrary criteria were set up to define a "shower" day at Grand Junction. Relationships of a number of meteorological variables to shower activity were determined and the four variables which showed the strongest relationships were combined graphically to form an objective forecast aid for determining the probability of shower activity at Grand Junction during the 18-hour period 1130MST to 0530MST. Tests on independent data confirm the relationship found in the developmental data.

INTRODUCTION accuracy equal to those that have been issued in the past. HIS study was initiated with the objec- tive of providing one of a number of DEFINITION OF A SHOWER DAY AT objective aids for forecasting various T GRAND JUNCTION weather elements in the Grand Junction, Colorado area. Specifically it was aimed at forecasting Summertime shower activity even in a rela- July and August shower activity during the pe- tively small area is not adequately represented by riod 1130MST to 0530MST the following morn- observation of rain at a single rain gage. Lack- ing, the forecast to be based on data available no ing a dense network of reporting stations in the later than 0530MST of the forecast morning. Grand Junction area, an attempt was made to Since the aid was to be used for the generalized obtain a more representative picture of shower weather forecast which is normally released to activity by inspecting the remarks entered on the the public, no attempt was made to pinpoint the WBAN Form 1130's and setting up certain arbi- trary criteria for deciding if the day were a forecast with respect to time, and a deliberate "shower day" or not. The criteria for a shower attempt was made to keep the procedure as sim- day decided upon are as follows: ple as possible. As it turned out the least com- plicated variables tested showed the strongest 1. Observed at the station, in- relationship to shower activity. cluding traces. The graphical techniques used to relate the 2. Thunder heard at the station, but no pre- variables to the element to be forecast have been cipitation recorded. explained in great detail in numerous papers on 3. Showers in sight, but no precipitation re- objective forecast aids in recent years, so will not corded at the station (for example: RW SE be dwelt upon here. One advantage of the graph- Quad, or RW west, etc.). ical techniques which might well be stressed again, Remarks of towering cumulus or cumulonimbus however, is that they usually not only result in in certain quadrants or all quadrants, and obser- a fairly accurate yes or no forecast, but in addition vations of virga or distant were not indicate the reliability of the forecast. Or in other considered as shower activity in the immediate words a probability statement can, if desired, be vicinity of Grand Junction. These criteria re- attached to the categorical forecast. An addi- sulted in 133 days being designated as shower tional value of objective aids in a local forecast days during the 248 days of the 8 months of office is that if for some unforeseen reason a new July and August 1947-1950 inclusive, which com- forecaster must be sent to the station on short prised the developmental data upon which the notice, forecasts of this particular weather ele- study was based. The shower days were dis- ment can be made by the new forecaster with an tributed according to the above criteria as follows:

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1. Precipitation observed at the station: Measurable precipitation (.01 inch or more) 33 days Trace of precipitation 50 days 2. Thunder heard at the station but no pre- cipitation 14 days 3. Showers in sight 36 days

Total 133 days

VARIABLES INVESTIGATED A number of meteorological variables which have been found useful in the problem of shower and forecasting were investigated to determine their relationships to shower activity in the Grand Junction area. These variables included: 1. Upper air moisture, both at the station and "upstream" 2. Surface moisture, both at the station and "upstream" 3. Measures of instability 4. Height of convective condensation level and FIG. 1. Graph for determining "upstream" radiosonde height of freezing level station.

Upper Air Moisture labeled with the "upstream" station to be used when the point determined by the 700 mb height In a similar study to this one for Salt Lake differences falls in that sector. At the reference City, Williams [ 1 ] found that the minimum station thus determined, the 2000M sounding was spread between the curve and the inspected and the minimum spread between the dew point curve in the 700-500 mb layer at an temperature and dew point curves in the 700-500 upstream radiosonde station showed a useful cor- mb layer tabulated. TABLE 1 shows the relation- relation with showers at Salt Lake City. Wil- ship of this minimum spread to the frequency of liams picked the upstream station by noting the occurrence of subsequent shower activity at Grand direction at 12,000 feet over Salt Lake City Junction. (For brevity the minimum difference and then going directly upstream and selecting between the temperature and dew point tempera- the closest raob station. A slightly more gen- ture has been called "Minimum Dew Point eralized method of selection was used in this study Spread.") The minimum spread in the 700-500 partly because it was felt a single wind over the mb layer at Grand Junction itself was also tabu- station would not necessarily indicate the general upper air flow and partly because sufficient wind TABLE 1 data at the 12,000 foot level were not readily RELATIONSHIP OF MINIMUM DEW POINT SPREAD IN THE available. This method consisted of determining LAYER 700-500 MB AT 2000M AT AN UPSTREAM REFER- a direction of flow by obtaining a measure of the ENCE STATION TO THE FREQUENCY OF OCCURRENCE E-W and N-S components of the height gra- OF SHOWERS AT GRAND JUNCTION. dient at 700 mbs over the plateau area from the Class intervals of minimum No. of Frequency of 2000M (0300Z) chart. Height differences were Total cases dew point spread shower cases occurrence of obtained between Ely, Nevada and Denver, Colo- °C showers % rado (ELY minus DEN) for a measure of the E-W component, and between Lander, Wyoming 0-2 20 16 80 3-4 54 42 78 and the average of Phoenix and Albuquerque, 5-6 36 21 58 New Mexico (LND minus AVG) for the N-S 7-8 20 11 55 component. These differences were used as co- 9-10 22 9 41 11-12 25 ordinates of a graph as shown in FIGURE 1, where 9 36 >12 71 25 35 the graph is divided into sectors with each sector

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TABLE 8 TABLE 3

RELATIONSHIP OF MINIMUM DEW POINT SPREAD IN THE RELATIONSHIP OF 0530M DEW POINT AT GRAND JUNCTION LAYER 700-500 MB AT 2000M AT GRAND JUNCTION TO TO FREQUENCY OF OCCURRENCE OF SHOWERS AT GRAND FREQUENCY OF OCCURRENCE OF SHOWERS AT GRAND JUNCTION. JUNCTION.

Class intervals of Frequency of Total casse No. of Class intervals dew point °F occurrence of Frequency of shower cases of minimum No. of showers % Total cases occurrence of dew point spread shower cases showers % °c >55 21 19 90 51-55 46 35 76 0-2 40 35 88 46-50 49 31 63 3-4 72 45 63 41-45 44 25 57 5-6 54 30 56 36-40 49 16 33 7-8 34 15 44 31-35 21 5 24 9-10 22 4 18 <31 18 2 11 11-12 18 2 11 >12 18 2 11 activity in this region is associated with high surface dew points and since the dew point tem- lated and the relationship to subsequent shower perature is more representative of the moisture activity is shown in TABLE 2. Surprisingly, the content of the air than the random occurrence relationship of the Grand Junction spread appears of showers, the 0530M dew points at three sta- to be stronger than the spread "upstream." tions to the southwest of Grand Junction were It might be argued that the method of selecting tabulated. These stations were Milford and the reference station does not depict the right Blanding, Utah, and Grand Canyon, Arizona. source of moisture in many cases, which is un- The average of these three dew point tempera- doubtedly true. However, due to the wide sepa- tures was then related to subsequent shower ac- ration of the reference stations geographically, tivity at Grand Junction as shown in TABLE 4. there would be very few differences in the refer- This variable showTs the strongest relationship to ence stations selected regardless of the method shower activity of any tested. used to select them. A limited check on two months data using the 700 mb wind at Grand Measures of Instability Junction, the 500 mb wind, and following the 500 mb contour through Grand Junction up- In a study of September at stream to select the reference station showed that Denver, Colorado, Tillotson [2] found a fairly all methods used picked the same reference sta- strong relationship between thunderstorms at tion around 90 percent of the time. The results Denver and the difference between the surface depicted in TABLE 1, therefore, are probably dew point and the 500 mb temperature. At- representative of results to be expected from any tempts to use this variable at Grand Junction in scheme for selecting upstream stations. July and August were unsatisfactory. TABLE 5 shows the relationship between the difference of the 0530M dew point and the 2000M, 500 mb Surface Moisture temperature at Grand Junction and subsequent Early morning surface dew point over the plateau region show a very strong rela- TABLE 4 tionship to afternoon and evening shower activ- RELATIONSHIP OF AVERAGE DEW POINT AT MILFORD, ity. The air over this region during the summer BLANDING AND GRAND CANYON (0530M) TO FREQUENCY months is almost always conditionally unstable OF OCCURRENCE OF SHOWERS AT GRAND JUNCTION. and if sufficient moisture is present in the lowest Class intervals Frequency of layers it becomes convectively unstable. The No. of of average dew Total cases occurrence of shower cases relationship of the 0530MST surface dew point point °F showers % temperature at Grand Junction to subsequent >55 8 8 100 TABLE shower activity is shown in 3. 51-55 35 32 91 From the experience of forecasters in this 46-50 59 45 76 region it has been noted that shower activity 41-45 39 23 59 in the Grand Junction region is generally pre- 36-40 40 18 45 31-35 34 5 15 ceded by shower activity to the south and south- <31 33 2 6 west the previous day or evening. Since shower

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TABLE 5 The difference between the 0530M surface dew

RELATIONSHIP OF DIFFERENCE BETWEEN THE 0530M point and the 0800M, 500 mb temperature the SURFACE DEW POINT AND THE 2000M 500 MB TEM- same morning was also obtained. The relation- PERATURE AT GRAND JUNCTION TO THE FREQUENCY ship of this difference to shower activity is shown OF OCCURRENCE OF SHOWERS AT GRAND JUNCTION. in TABLE 6. This relationship is not a great TABLE Class intervals deal better than that shown in 5. Since Ferquency of of diff. of sfc. dew No. of Total cases occurrence of the difference between the 500 mb temperature at point and 500 shower cases showers % mb temp. °F 0530M and 0800M is probably considerably smaller than the error which would be made in >36 24 17 71 33-36 49 37 76 trying to estimate the 0530M, 500 mb tempera- 29-32 36 22 61 ture from the 2000M, 500 mb chart of the pre- 25-28 41 26 63 vious evening, it would be to no avail to make 21-24 44 18 41 such estimates to try to make use of this variable. 17-20 20 8 40 <17 34 5 15 A modified version of Showalter's stability index devised by Means [3] in which the early morning surface dew point and the expected shower activity at Grand Junction. While a maximum temperature for the day are used to definite relationship exists, it is not as pronounced compute the temperature a parcel of air would as when the dew point is used alone (TABLE 3). attain at 500 mb if lifted to that level, was also A test of the 500 mb temperature alone shows a tested. In this test the observed maximum tem- very weak relationship between this temperature perature was utilized. The index is the number and the occurrence of showers, but in the opposite obtained by subtracting the lifted temperature sense that would be expected from stability con- from the observed 500 mb temperature, with nega- siderations. That is, the warmer the 2000M, 500 tive numbers indicating instability, and positive mb temperature, the greater the likelihood of numbers stability. The correction for the height showers the following day. The difference be- of the station above mean sea level recommended tween the surface dew point and the 500 mb by Means was made. TABLE 7 shows the results temperature, therefore, shows a less strong rela- of the test of this index. While a relationship tionship to shower activity than the surface dew does exist, it is not too strong. point alone. Actually, the sum of the two tem- Legg [4] and Tillotson [2] found a useful peratures shows a stronger relationship than the relationship between the difference in "height" difference, but no better than the surface dew of the convective condensation level and the point alone. The variability of the 500 mb tem- freezing level to thunderstorm activity in their perature at Grand Junction is small during July studies for Denver. This variable shows an even and August, ranging generally from — 5 to — 12° more marked relationship to shower activity at Celsius (23 to 10°F), so that most of the vari- Grand Junction, possibly because of the more ability in the difference, or sum, is contained in liberal definition of a shower day used in this the surface dew point which ranged from as low study and because of the marked relationship be- as 15°F into the 60s.

TABLE 7 TABLE 6 RELATIONSHIP OF STABILITY INDEX (MEANS) TO THE RELATIONSHIP OF DIFFERENCE BETWEEN THE 0530M FREQUENCY OF OCCURRENCE OF SHOWERS AT GRAND SURFACE DEW POINT AND THE 0800M 500 MB TEMP- JUNCTION. PERATURE AT GRAND JUNCTION TO THE FREQUENCY OF OCCURRENCE OF SHOWERS AT GRAND JUNCTION. Frequency of No. of Stability index Total cases occurrence of shower cases showers % Class intervals Frequency of of diff. of sfc. dew No. of Total cases occurrence of shower cases point and 500 showers % mb temp. °F <-4 60 32 53 -4 24 16 67 >36 39 30 77 -3 44 28 64 33-36 40 26 65 .-2 45 29 64 29-32 43 33 77 -1 29 11 38 25-28 36 18 50 0 26 10 38 21-24 43 17 40 1 '5 2 40 17-20 21 7 33 -2 6 3 50 <17 26 2 8 >2 9 •2 22

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TABLE 8 surface dew point was plotted on the 2000M

RELATIONSHIP OF DIFFERENCE IN HEIGHT OF CONVECTIVE sounding of the previous evening. The mixing CONDENSATION LEVEL (CCL) AND FREEZING LEVEL ratio line through this point was then followed (FL) TO FREQUENCY OF OCCURRENCE OF SHOWERS upward until it intersected the temperature curve. AT GRAND JUNCTION. This point of intersection is the convective con- densation level. The freezing level was taken Class intervals Frequency of No. of of difference Total cases occurrence of shower cases directly from the sounding. The at CCL-FL(MBS) showers % which the two levels occurred were recorded and <-50 34 4 12 the "height" difference between them was ex- -26 -50 34 11 32 pressed as the difference in . TABLE 8 -1 -25 42 20 48 shows that a fairly strong relationship exists be- 0 24 44 27 61 tween this difference and subsequent shower ac- 25 49 25 17 68 50 99 45 33 73 tivity at Grand Junction. It is emphasized again, 100 149 19 16 84 however, that a great deal of this relationship is >149 5 5 100 the result of the moisture measurement used to compute the CCL. tween surface moisture and shower activity al- ready noted in TABLE 4. In computing the con- COMBINATION OF VARIABLES vective condensation level for this study the Despite the relative weakness of some of the 0530M surface dew point temperature was used relationships discussed above, all of the variables in conjunction with the 2000M sounding of the were tested in joint relationships to shower activ- previous evening. On a pseudo-adiabatic chart ity. Four were finally selected as yielding the a given dew point temperature and pressure de- best results, to which the remaining variables termines a mixing ratio line. To determine the convective condensation level used here the 0530M

FIG. 2. Joint relationship between the 0530M surface dew point temperature at Grand Junction and the aver- FIG. 3. Joint relationship between the minimum dew age of the surface dew point temperatures at Milford, point spread in the 700-500 mb layer and the height Grand Canyon and Blanding to the frequency of occur- difference CCL minus FL at 2000M to the frequency of rence of showers at Grand Junction during the period occurrence of showers at Grand Junction during period 1130-0530M. 1130-0530M the following afternoon and night.

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TABLE III

PERCENT FREQUENCIES OF OCCURRENCE OF SHOWERS AT GRAND JUNCTION IN THE AREAS OR CATEGORIES DE- LINEATED ON FIGURES 2, 3 AND 4. (Developmental Data, July and August 1947-50 incl.)

Category number

I II in IV V % % % % %

Figure 2 5 22 63 79 93 Figure 3 11 38 53 67 91 Figure 4 11 31 70 83 100

probability of showers in the three highest cate- gories as a result of relating all four variables jointly to the occurrence of showers. The vari- ables and charts were tested on 6 months of in- FIG. 4. Joint relationship between Category Numbers dependent data (July and August 1951, 1952, taken from FIGURES 2 and 3 and the frequency of occur- rence of showers at Grand Junction. (Denominator of and 1954). TABLE 10 is similar to TABLE 9 fraction is total cases, numerator is number of shower showing the frequency of occurrence of showers cases.) in the various categories from FIGURES 2, 3 and 4. The final frequencies from FIGURE 4 compare seemed to add nothing. These four were (1) quite closely with those in the developmental data 0530M surface dew point temperature at Grand except in category V where the percentage Junction, (2) average of surface dew point tem- dropped to 83. TABLE 11 shows the percentages peratures (0S30M) at Milford, Grand Canyon resulting when all 14 months of data are com- and Blanding, (3) minimum dew point spread bined. in 700-500 mb layer (2000M) at Grand Junction, TABLE 10 and (4) height difference (in mbs) between the PERCENT FREQUENCIES OF OCCURRENCE OF SHOWERS AT convective condensation level and the freezing GRAND JUNCTION IN THE AREAS OR CATEGORIES DE- level at Grand Junction (2000M). These four LINEATED ON FIGURES 2, 3 AND 4. (Test Data, July variables were combined graphically and related and August 1951, 52 and 54.) jointly to the frequency of occurrence of showers at Grand Junction, as shown in FIGURES 2, 3 and Category number 4. A cross in FIGURES 2 and 3 represents a I II HI IV V "shower" day and a dot represents a "no shower" % % % % % day. In FIGURE 4 the denominators of the frac- tions are the total number of cases with the Figure 2 6 24 48 74 84 Figure 3 16 26 67 65 80 indicated combination of category numbers from Figure 4 15 27 67 76 83 FIGURES 2 and 3 and the numerators are the number of shower days. FIGURE 4 is the final forecasting chart with showers being forecast if TABLE 11 the case falls above the solid line and no showers PERCENT FREQUENCIES OF OCCURRENCE OF SHOWERS AT being forecast if the case falls below the solid GRAND JUNCTION IN THE AREAS OR CATEGORIES DE- line. In addition to the categorical forecast of LINEATED ON FIGURES 2, 3 AND 4. (Developmental "showers" or "no showers" a probability, or and Test Data combined.) confidence, statement may be attached to the fore- cast depending upon which category the case Category number falls in. l II in IV V % % % % % RESULTS AND TEST Figure 2 5 23 59 77 88 TABLE 9 is a comparison of the per cent fre- Figure 3 13 33 57 66 86 quencies in the areas or categories delineated on Figure 4 13 30 69 80 91 FIGURES 2, 3 and 4, showing the increase in the

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The results of "forecasts" based on the line dominating for days. A persistence forecast of of separation in FIGURE 4 for the 8 months of showers, or no showers, even for a point, such developmental data are summarized in TABLE as Grand Junction, will therefore show consider- 12(a). The skill score is based on the marginal able skill above chance. TABLE 12(d) shows the totals of the contingency table. TABLE 12(b) is results of the persistence forecast for Grand Junc- a similar summary of forecasts made from the tion for the 14 months involved in this study. 6 months of test data. The skill score and per- The persistence forecast consists merely of: if cent correct fall off somewhat, but no more than showers occurred during the period 1130-0530M might be expected. TABLE 12(C) summarizes "yesterday and last night," showers are forecast the forecasts for all 14 months. for "this afternoon and tonight." When any weather phenomenon occurs more than 50 percent of the days during a month or CONCLUSIONS series of months, it is important to test whether The aid for forecasting shower activity in the the forecasting procedure developed is really fore- Grand Junction area developed in this study casting or whether it is merely reflecting the tendency of the phenomenon to recur over a shows considerable skill in selecting on a cate- series of days. Changes of air masses over the gorical "yes" or "no" basis, the days on which Plateau and Great Basin region are usually rather showers will occur. More important, it shows a slow during the summer months, so that once the consistent ability to state, within rather broad area is covered by a moist air mass scattered to limits, the probability of showers during the spe- numerous showers are a daily occurrence for cific forecast period. Many of the "errors," es- quite a number of days. Conversely when the pecially those in the higher frequency categories area is covered by a dry air mass only isolated from FIGURE 4, can be attributed to the well showers at most will occur, with clear skies pre- known randomness of shower activity over an

TABLE 12 CONTINGENCY TABLES OF FORECAST VS OBSERVED SHOWERS AT GRAND JUNCTION, COLORADO.

Forecasts Forecasts

Shwrs. No shwrs. Total Shwrs. No shwrs. Total T3 <>D Shwrs. 115 18 133 1 Shwrs. 78 16 94 u u cu

Skill Score: .67 Skill Score: .56 Percent correct: 83 % Percent correct: 78% (a) Forecasts made from developmental data, July (b) Forecasts made from test data, July and August and August 1947-50 incl. 1951, 52, 54.

Forecasts Forecasts

Shwrs. No shwrs. Total Shwrs. No shwrs. Total

1 Shwrs. 193 34 227 1 Shwrs. 151 76 227 u u CD

Skill Score: .62 Skill Score: .30 Percent correct 81% Percent correct: 65% (c) Forecasts from developmental and test data (d) Persistence forecasts for developmental and combined. test.

Unauthenticated | Downloaded 09/26/21 01:53 PM UTC VOL. 37, No. 8, OCTOBER, 1956 425 area. A check of the reports of cooperative sta- lower layers is such a predominate factor in the tions west of the divide in Colorado on these occurrence of showers in this region that the days shows that in most of the "error" cases in "triggering" mechanism is relatively unimportant. categories III, IV, and V numerous showers Some of the factors not incorporated into the occurred over western Colorado, but none hap- system, such as stability criteria and measures pended to occur in the immediate vicinity of of and cold aloft which Grand Junction. On the other hand the "errors" might indicate changes in stability, are undoubt- in the lower frequency categories (I and II) edly related to the intensity of the showers or must be attributed primarily to the failure of the thunderstorms, and in individual cases may be rigid system of fixed upstream stations to catch the controlling factor in the actual occurrence. an influx of moisture into the Grand Junction However, the frequency of occurrence of showers, area. For instance there are times when moisture regardless of their intensity, with which this moves into the region from a more southerly or study was concerned seems to be so predomi- southeasterly direction over New Mexico, and nately associated with the amount of surface infrequently sufficient moisture for shower activ- moisture that more complex variables add little ity will move into the area from the northwest. when all cases are considered. It will be noted that all shower days were con- sidered, and no attempt was made to stratify REFERENCES according to the "triggering" mechanism which [1] Williams, Philip, Jr. "An Objective Method of might be responsible for the release of the in- Forecasting Summer Precipitation at Salt Lake stability. Thermal convection and orographic City, Utah." Monthly Weather Review, August lifting are by far the predominate "trigger" mech- 1950. [2] Tillotson, Kenneth C. "An Objective Aid for Fore- anisms, as the results of this study, which is casting September Thunderstorms at Denver, based mainly on moisture variables, would indi- Colorado." Monthly Weather Review, February cate. A number of high level, "dry" thunder- 1951. [3] Means, Lynn L. "Stability Index Computation storms are undoubtedly released by frontal lift- Graph for Surface Data." Manuscript, WBO- ing or upper trough action, which this aid may Chicago, July 1952. or may not catch. Such storms are partially [4] Legg, E. M. "A Study of the Position of the 0° C. Isotherm and the Convective Condensation Level accounted for by the use of the upper air moisture in Connection with Thunderstorms at Denver, variable. The availability of moisture in the Colorado." Manuscript, WBO-Denver, 1948.

Early in 1958 the Raytheon Manufacturing Company NEWS AND NOTES of Waltham, Mass., is scheduled to begin delivery of 31 new type long range sets especially designed to meet Weather Bureau requirements. These sets will go to selected coastal stations for hurricane detection and to USWB Radar Installations selected inland stations for tornado tracking. The U. S. Weather Bureau announced the installation of a third high-powered radar station capable of detect- Napier Shaw Memorial Prize ing and tracking storms over an area of 200,000 square The first award of the Napier Shaw Memorial Prize miles. This latest set, located at Nantucket, Mass., is was made by the Royal Meteorological Society on 20 also equipped to transmit storm photos immediately by June 1956 to Dr. Norman A. Phillips of the Institute radio from Nantucket to the hurricane forecast center for Advanced Study, Princeton. at Boston. The Napier Shaw Prize is granted for an original Similar powerful radar sets had already been installed essay on and the topic chosen for the first at San Juan, Puerto Rico, in July 1956 and on Cape competition was "The Energetics of the General Circu- Hatteras, North Carolina, in August 1955. lation." Dr. Phillips' paper was entitled "The General In addition the Weather Bureau now has in operation Circulation: A Numerical Experiment." The paper shorter range radar equipment at 42 other stations gives the results of a remarkable experiment in numeri- throughout the United States. Stations on the Atlantic cal calculation based on mathematical equations describ- coast with this type of radar include Boston, Mass.; ing the large scale movements of the . Dr. Charleston, South Carolina; Miami, Florida. Gulf radar Phillips was present at the meeting of the Society and stations include Tampa, Florida; Lake Charles, Baton answered questions during the discussion which followed Rouge and Burrwood, Louisiana; Port Arthur, Houston, presentation of the paper. There was general agreement Galveston and Brownsville, Texas. Swan Island in the that Dr. Phillips had achieved his aim of explaining the Carribbean is also equipped for radar storm detection. main features of the circulation of the atmosphere.

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