About the USGS Data
 

Each variable is shown in a large table with one row for each year's data.  Every row is divided into 12 boxes, one per month. When several measurements were made in a single month, they are shown in chronological order, from top to bottom. The averages were computed as follows:  First, the values in each box were averaged to produce a single value per box.  Next, the 12 columns of the table were averaged to get typical monthly values of the variable.  These 12 monthly values were averaged to get the overall average and to determine what fraction of the annual average came from each particular month.  These monthly weights were then used to correct for missing data in the 5-year averages.  Entries recorded as "less than X" were calculated as being X/2. Most of the standard measurements were taken on the days and at approximately the times shown in the following table. (For example, the first measurements were made at approximately 11:15 AM on October 24, 1980.)

Measurement Dates and Times

Year	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
1980										24 1115	18 1500	18 1020
1981	15 1345	11 1000	11 1010	16 1045	14 1015	18 1015	10 1110	5 1000	4 1045	23 1050	18 1145	15 1040
1982	20 1250	11 1010	17 1040	16 1210	11 1200	17 1030	16 1130	10 1010	2 920	20 950	17 1230	16 1030
1983	12 1220		2 1000	12 1030	20 1345	16 1015	18 1235	11 1025	3 1300	25 1025	18 1030	19 1110 28
1984	26 1155		15 1000	17 1110	21 1136	21 1130	11 1130	15 1218	5 1053	23 1045	14 1036	19 1645
1985	16 1000		11 1050	16 955	16 1130	19 900	9 925  9	14 915	4 925	23 1200	19 1145	16 1100
1986	22 1120		11 1415	16 1310	15 1240	18 1231	10 1030	15 1300	6 1130	24 1050	14 1120	17 1145
1987	14 1130		13 1300	23 1145	15 1040	18 1030	8 1215	12 1120	2 1245	20 1310	13 1420	17 1300
1988	21 1200		10 1345	13 1030 26 1212	11 1100 24 1203	15 1300 28 1200	12 1325 26 1245	9 930 23 1245	6 855	3 1210 18 900	10 1245	14 1405
1989	25 1455	7 1350 22 1355	15 1330 28 1350	10 1230 25 1240	9 1250 31 1140	13 1325 27 1205	11 1010 25 1215	7 1215 22 1035	6 1400 19 1045	18 1250	20 1110	12 1245
1990	10 1500 18 1545	6 1230 21 1200	15 1100 26 1245	9 1230 24 1110	8 1240 23 1105	13 1225 26 950	10 1350 24 1535	7 1230 21 1210	4 1510 18 1510	2 1410 24 1225	5 1300 21 1315	4 1145 17 1210
1991	14 1420		19 1430	12 1100		12 1320	12 945	15 1045	9 1040	25 1015	12 1200	16 1115
1992	13 1220		6 1220	21 1020	7 1105	15 1120	7 1245	14 1045	9 1120	14 1145 20 1640		10 1030
1993		9 1015	17 1030 26 1045	8 1025 12 1130 22 1015 29 1140	3 1130 10 1130 21 1000 26 1200	2 1100  8 1200 15 1045 21 1041 28 1000	12 1030 19 1130 26 1130	10 1200 26 940 31 1200	7 1300 15 1000 15 1005 20 1200 27 950	4 1200 13 1200 19 1100 25 1105	8 1045 22 1200	7 1015  7 1200
1994	13 1145	1 1130  7 1020	14 1100 21 1120 29 1220	7 1000 12 1030 19 1045 25 1100	4 800 10 955 17 1045 25 1130 31 1130	7 1045  7 1530 14 800 22 1045 28 1330	6 1050 12 935 19 1200 26 1130	2 1130  9 1115 10 925 16 1100 22 1245 30 1030	8 1030	14 945	21 1215	7 1045
1995	25 1110	13 1130	20 1215	6 1100	23 1030	27 945	12 1215 27 1015	14 1020	26 1030	31 1140
1996	18 1050	21 945		24 945		18 930	8 930	7 1300	20 915	24 930		5 1030
1997		3 1115		7 945	15 1015 28 920	10 930	8 915  8 1030 23 945	14 1030 14 1045 26 930	10 1100 10 1130 11 1000 11 1015 25 1000