Benson Lake Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Benson Lake Observatory clear sky chart from 2005-11-05 to 2017-10-06.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.
Observation TypeMinimum conditions for hour to be usableOut of hours
Clear of CloudsTransparencySeeingSky Brightness
Planetary:50%(no limit)Average(no limit)Nighttime Hours
Deep Sky:70%Average(no limit)5.9Nighttime Hours
CCD Imaging:70%Below AveragePoor(no limit)Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

PlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
Night
32%
16204
15%
47049
7%
16159
39%
16159
21%
32284

By Month

MonthDays of MonthPlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
January1st to 15thNight
20%
900
11%
2506
3%
895
27%
895
15%
1862
January16th to endNight
17%
960
13%
2688
2%
960
26%
960
16%
2023
February1st to 15thNight
18%
858
14%
2312
3%
855
27%
855
18%
1678
February16th to endNight
24%
631
14%
1893
7%
631
30%
631
15%
1382
March1st to 15thNight
26%
720
16%
2160
8%
720
33%
720
20%
1429
March16th to endNight
31%
625
18%
2014
12%
625
40%
625
20%
1366
April1st to 15thNight
26%
539
14%
1797
6%
539
36%
539
18%
1250
April16th to endNight
30%
540
16%
1685
8%
540
39%
540
20%
1168
May1st to 15thNight
29%
540
13%
1498
6%
540
35%
540
20%
1083
May16th to endNight
37%
562
13%
1498
5%
561
44%
561
28%
1013
June1st to 15thNight
43%
540
10%
1440
4%
540
47%
540
26%
974
June16th to endNight
45%
540
11%
1440
5%
540
48%
540
29%
946
July1st to 15thNight
56%
510
14%
1360
8%
510
59%
510
40%
805
July16th to endNight
54%
564
16%
1417
8%
531
59%
531
42%
822
August1st to 15thNight
54%
539
21%
1455
12%
536
61%
536
37%
892
August16th to endNight
53%
573
19%
1883
16%
573
59%
573
28%
1130
September1st to 15thNight
53%
540
23%
1800
20%
540
61%
540
34%
1011
September16th to endNight
43%
711
18%
1974
12%
711
49%
711
31%
1247
October1st to 15thNight
33%
684
20%
1989
11%
684
41%
684
24%
1302
October16th to endNight
27%
704
12%
2272
5%
704
35%
704
15%
1618
November1st to 15thNight
26%
700
18%
2276
9%
700
37%
700
19%
1530
November16th to endNight
26%
864
14%
2484
6%
864
34%
864
15%
1826
December1st to 15thNight
17%
900
11%
2520
2%
900
25%
900
16%
1860
December16th to endNight
19%
960
13%
2688
3%
960
28%
960
14%
2067

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

Occurrence of each ForecastData
Points
Cloud CoverDay
14%7%36%6%35%5%5%7%34%
48160
Night
14%8%36%5%34446%38%
47217
Cloud CoverDay
14%8%36%6%35%45%7%34%
48169
Night
14%8%36%5%34446%38%
47222
TransparencyDay
48%6%13%20%9%
47846
Night
45%6%13%22%10%1
47049
SeeingDay
17%12%31%22%10%4
6195
Night
18%9%33%27%9%
16205

By Month

Percentage Cloud Cover NE (2006-)
Color Meanings:
Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
12%11%5%7%6%46%35%7%28%
1432
16th to endDay
13%12%6%8%7%3435%5%26%
1536
February1st to 15thDay
10%11%47%6%35%5%47%34%
1549
16th to endDay
14%11%39%6%35%5%45%31%
1580
March1st to 15thDay
12%10%37%6%345%5%5%33%
1790
16th to endDay
17%9%48%7%35%445%30%
2220
April1st to 15thDay
17%11%45%6%245%45%31%
2151
16th to endDay
20%9%25%5%35%45%6%32%
2274
May1st to 15thDay
17%7%37%7%45%445%33%
2451
16th to endDay
11%6%26%6%35%5%6%7%38%
2617
June1st to 15thDay
14%6%36%5%36%447%37%
2520
16th to endDay
11%5%36%6%45%5%6%10%34%
2520
July1st to 15thDay
7%5%25%5%46%6%6%9%40%
2520
16th to endDay
8%325%6%35%6%6%8%41%
2655
August1st to 15thDay
8%4246%46%6%6%8%40%
2496
16th to endDay
15%425%5%245%49%40%
2318
September1st to 15thDay
11%426%6%25%5%48%42%
2154
16th to endDay
11%435%7%45%5%6%8%36%
1980
October1st to 15thDay
19%6%25%42345%7%36%
1767
16th to endDay
21%10%47%5%45%44427%
1599
November1st to 15thDay
14%9%37%5%345%5%6%34%
1582
16th to endDay
16%11%47%5%35%5%6%8%25%
1473
December1st to 15thDay
16%12%46%5%24435%32%
1440
16th to endDay
20%12%5%8%7%3444423%
1536
January1st to 15thNight
15%10%47%6%35%445%31%
2506
16th to endNight
11%11%5%9%7%3445%6%28%
2688
February1st to 15thNight
11%11%47%6%34246%36%
2310
16th to endNight
12%13%5%9%6%34445%32%
1893
March1st to 15thNight
13%7%46%42444442%
2147
16th to endNight
14%8%36%435%445%38%
2014
April1st to 15thNight
20%7%36%424446%35%
1797
16th to endNight
19%7%27%44435%6%35%
1685
May1st to 15thNight
18%6%36%5%2445%6%34%
1498
16th to endNight
11%435%435%45%8%42%
1496
June1st to 15thNight
11%7%35%5%445%5%5%42%
1440
16th to endNight
11%6%25%5%25%46%7%43%
1440
July1st to 15thNight
8%21332435%8%54%
1440
16th to endNight
7%32342345%9%53%
1513
August1st to 15thNight
7%324435%5%6%8%49%
1464
16th to endNight
10%5%245%24447%48%
1883
September1st to 15thNight
8%424323446%54%
1800
16th to endNight
13%42442345%8%46%
1974
October1st to 15thNight
15%6%25%43335%6%43%
1989
16th to endNight
19%8%36%434447%31%
2272
November1st to 15thNight
16%8%26%434446%37%
2276
16th to endNight
16%9%46%5%45%5%5%6%31%
2484
December1st to 15thNight
16%11%46%5%23445%33%
2520
16th to endNight
18%14%5%7%5%23335%28%
2688

Percentage Cloud Cover SE (2006-)
Color Meanings:
Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
13%11%48%6%45%36%5%28%
1432
16th to endDay
13%13%5%9%7%3445%5%25%
1536
February1st to 15thDay
10%12%37%6%25%447%33%
1549
16th to endDay
13%12%48%6%35%446%30%
1580
March1st to 15thDay
12%11%47%7%35%5%45%32%
1800
16th to endDay
17%10%38%6%35%435%30%
2219
April1st to 15thDay
17%10%5%6%425%5%45%31%
2151
16th to endDay
20%8%25%5%245%5%5%32%
2274
May1st to 15thDay
18%6%37%7%45%445%32%
2451
16th to endDay
12%6%25%6%35%5%5%7%39%
2617
June1st to 15thDay
15%5%35%6%35%447%38%
2520
16th to endDay
12%5%26%7%46%5%6%8%34%
2520
July1st to 15thDay
8%425%5%47%5%6%10%40%
2520
16th to endDay
8%425%6%35%6%6%8%41%
2655
August1st to 15thDay
8%425%5%46%5%6%10%40%
2496
16th to endDay
15%425%4245%5%7%42%
2318
September1st to 15thDay
11%427%5%35%45%8%42%
2154
16th to endDay
11%436%7%35%5%6%8%36%
1980
October1st to 15thDay
18%6%26%42345%7%36%
1767
16th to endDay
22%10%36%6%45%345%27%
1599
November1st to 15thDay
14%9%46%5%345%46%34%
1582
16th to endDay
16%11%5%7%5%36%46%7%25%
1473
December1st to 15thDay
16%12%47%5%24335%32%
1440
16th to endDay
20%12%5%9%6%3443423%
1536
January1st to 15thNight
15%11%47%6%35%445%30%
2506
16th to endNight
11%12%5%8%7%4445%6%28%
2688
February1st to 15thNight
11%11%47%6%24346%35%
2303
16th to endNight
12%13%6%8%6%33445%32%
1893
March1st to 15thNight
13%7%46%5%24335%42%
2160
16th to endNight
14%8%36%434446%38%
2014
April1st to 15thNight
20%7%36%424446%34%
1797
16th to endNight
19%6%36%5%35%346%35%
1685
May1st to 15thNight
19%7%36%6%3445%6%33%
1497
16th to endNight
12%5%15%4345%5%8%42%
1496
June1st to 15thNight
12%6%25%5%44446%42%
1440
16th to endNight
12%435%4245%6%8%42%
1440
July1st to 15thNight
8%31332445%8%53%
1440
16th to endNight
7%21333345%9%53%
1513
August1st to 15thNight
6%3145%245%6%7%50%
1464
16th to endNight
11%5%235%33446%49%
1883
September1st to 15thNight
8%42442345%6%53%
1800
16th to endNight
13%42442435%8%46%
1974
October1st to 15thNight
15%6%35%43435%6%42%
1989
16th to endNight
19%9%35%6%34447%31%
2272
November1st to 15thNight
16%8%35%5%34447%36%
2276
16th to endNight
16%9%46%5%35%5%47%30%
2484
December1st to 15thNight
16%12%46%5%24435%33%
2520
16th to endNight
18%13%6%7%5%33335%28%
2688

Transparency (when cloud cover <= 30%)
Color Meanings:
Too cloudy to forecast Poor Below Average Average Above average Transparent
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
55%6%11%17%8%
1433
16th to endDay
58%416%14%6%
1536
February1st to 15thDay
49%5%16%19%7%
1551
16th to endDay
55%6%12%18%7%
1580
March1st to 15thDay
52%6%12%19%8%1
1800
16th to endDay
55%5%13%17%6%1
2220
April1st to 15thDay
52%6%11%19%9%
2151
16th to endDay
51%6%10%17%12%1
2274
May1st to 15thDay
52%5%10%18%10%1
2451
16th to endDay
42%7%12%22%12%1
2621
June1st to 15thDay
44%6%13%22%12%
2520
16th to endDay
44%8%16%18%10%
2520
July1st to 15thDay
36%8%15%25%12%1
2371
16th to endDay
37%8%15%21%15%1
2488
August1st to 15thDay
38%7%15%25%11%1
2481
16th to endDay
39%7%15%22%12%
2318
September1st to 15thDay
39%7%14%27%10%
2154
16th to endDay
42%6%18%25%6%
1980
October1st to 15thDay
45%6%14%24%8%
1767
16th to endDay
59%6%10%17%5%
1599
November1st to 15thDay
49%6%11%20%11%
1582
16th to endDay
56%9%14%14%5%
1473
December1st to 15thDay
54%6%11%20%7%
1440
16th to endDay
63%5%11%14%4
1536
January1st to 15thNight
54%6%12%18%7%
2506
16th to endNight
55%6%11%19%7%
2688
February1st to 15thNight
51%5%12%19%9%2
2312
16th to endNight
54%5%13%17%7%
1893
March1st to 15thNight
44%5%13%23%12%1
2160
16th to endNight
46%5%12%23%10%1
2014
April1st to 15thNight
50%410%19%12%2
1797
16th to endNight
49%411%19%12%2
1685
May1st to 15thNight
48%7%11%20%10%1
1498
16th to endNight
39%7%14%23%14%
1498
June1st to 15thNight
42%5%13%22%15%
1440
16th to endNight
37%7%15%25%11%1
1440
July1st to 15thNight
27%7%14%31%17%1
1360
16th to endNight
25%7%20%27%15%2
1417
August1st to 15thNight
30%7%14%30%15%1
1455
16th to endNight
35%6%13%25%15%3
1883
September1st to 15thNight
30%6%14%33%15%
1800
16th to endNight
35%6%17%30%8%
1974
October1st to 15thNight
41%5%13%27%9%1
1989
16th to endNight
52%6%14%18%7%
2272
November1st to 15thNight
47%5%13%22%11%
2276
16th to endNight
52%7%14%18%6%
2484
December1st to 15thNight
52%6%15%18%7%
2520
16th to endNight
58%5%12%16%6%
2688

Seeing (when cloud cover <= 80%)
Color Meanings:
Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
21%13%42%18%4
90
16th to endDay
30%9%36%16%6%1
96
February1st to 15thDay
21%27%41%6%21
90
16th to endDay
23%16%41%13%31
81
March1st to 15thDay
18%23%35%17%31
90
16th to endDay
27%13%25%22%9%1
243
April1st to 15thDay
24%12%30%21%9%
270
16th to endDay
29%12%28%17%9%3
270
May1st to 15thDay
22%21%29%15%8%2
408
16th to endDay
18%15%35%18%6%4
517
June1st to 15thDay
17%15%33%20%9%2
495
16th to endDay
13%13%33%25%9%3
495
July1st to 15thDay
10%9%32%29%12%5%
475
16th to endDay
8%8%36%25%13%7%
515
August1st to 15thDay
12%6%27%28%15%8%
469
16th to endDay
20%5%22%25%18%7%
332
September1st to 15thDay
12%6%22%30%19%9%
315
16th to endDay
11%9%31%27%15%4
314
October1st to 15thDay
22%14%27%21%13%1
168
16th to endDay
29%20%31%16%2
96
November1st to 15thDay
7%18%40%21%8%3
90
16th to endDay
30%17%23%20%8%
90
December1st to 15thDay
23%16%44%10%41
90
16th to endDay
31%23%35%9%
96
January1st to 15thNight
20%12%38%22%4
900
16th to endNight
18%11%42%20%6%
960
February1st to 15thNight
18%13%39%22%6%
858
16th to endNight
19%13%33%27%5%
631
March1st to 15thNight
17%14%35%24%7%
720
16th to endNight
18%10%33%28%7%1
625
April1st to 15thNight
23%11%32%26%5%
539
16th to endNight
23%8%32%26%7%
540
May1st to 15thNight
22%10%33%26%6%
540
16th to endNight
15%6%35%31%9%1
563
June1st to 15thNight
17%7%26%36%12%
540
16th to endNight
14%431%37%11%
540
July1st to 15thNight
8%425%45%16%
510
16th to endNight
9%329%39%17%
564
August1st to 15thNight
9%28%38%21%2
539
16th to endNight
12%424%36%19%1
573
September1st to 15thNight
10%5%26%31%21%5%
540
16th to endNight
16%6%29%28%18%1
711
October1st to 15thNight
18%10%32%24%13%
684
16th to endNight
24%10%31%23%9%
704
November1st to 15thNight
20%10%36%23%7%
700
16th to endNight
21%13%31%25%6%
864
December1st to 15thNight
23%13%38%18%4
900
16th to endNight
25%9%35%23%5%1
960
Page generated at 2017-10-07 13:07:55. Version ac04

Copyright 2017 A. Danko


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