Joseph P. Strogen Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Joseph P. Strogen Observatory clear sky chart from 2005-11-05 to 2017-12-20.

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
36%
16220
23%
48100
13%
16173
46%
16173
28%
29712

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
19%
900
20%
2360
6%
895
31%
895
23%
1590
January16th to endNight
21%
960
23%
2496
6%
960
33%
960
26%
1657
February1st to 15thNight
18%
880
17%
2288
4%
876
27%
876
22%
1579
February16th to endNight
17%
657
21%
1919
4%
657
30%
657
22%
1241
March1st to 15thNight
24%
546
20%
1986
10%
546
36%
546
18%
1270
March16th to endNight
21%
576
14%
2103
8%
576
31%
576
16%
1446
April1st to 15thNight
26%
539
22%
1797
11%
539
42%
539
27%
1028
April16th to endNight
27%
540
20%
1800
11%
540
41%
540
22%
1132
May1st to 15thNight
40%
540
19%
1662
13%
540
49%
540
25%
1091
May16th to endNight
42%
563
21%
1535
14%
561
49%
561
29%
1006
June1st to 15thNight
59%
540
20%
1440
13%
540
63%
540
39%
865
June16th to endNight
58%
540
26%
1440
15%
540
65%
540
48%
797
July1st to 15thNight
62%
510
18%
1416
14%
510
65%
510
38%
833
July16th to endNight
70%
564
24%
1594
24%
531
75%
531
42%
863
August1st to 15thNight
72%
539
25%
1610
28%
536
74%
536
41%
881
August16th to endNight
72%
573
26%
1901
31%
573
75%
573
40%
991
September1st to 15thNight
62%
540
27%
1800
28%
540
65%
540
33%
1014
September16th to endNight
59%
595
32%
1973
25%
595
68%
595
37%
1040
October1st to 15thNight
46%
720
28%
2160
19%
720
52%
720
35%
1234
October16th to endNight
33%
768
29%
2304
15%
768
47%
768
33%
1321
November1st to 15thNight
33%
760
29%
2365
15%
760
47%
760
29%
1364
November16th to endNight
25%
911
25%
2666
11%
911
38%
911
26%
1669
December1st to 15thNight
22%
975
18%
2730
6%
975
33%
975
22%
1850
December16th to endNight
18%
984
19%
2755
5%
984
29%
984
19%
1950

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
13%6%25%42445%7%42%
48730
Night
12%6%24423346%47%
48290
TransparencyDay
40%6%11%23%15%2
48425
Night
37%5%11%25%17%3
48100
SeeingDay
15%9%27%27%16%3
6146
Night
17%10%31%26%12%1
16220

By Month

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
12%7%26%414346%44%
1577
16th to endDay
12%9%36%42445%6%42%
1728
February1st to 15thDay
12%9%47%6%2435%5%37%
1575
16th to endDay
13%10%45%424445%39%
1555
March1st to 15thDay
16%9%45%5%33446%37%
1980
16th to endDay
21%10%45%5%23445%32%
2117
April1st to 15thDay
15%7%245%34346%42%
2151
16th to endDay
20%8%36%42345%5%33%
2160
May1st to 15thDay
19%5%25%5%25%447%36%
2286
16th to endDay
14%5%25%6%36%45%7%37%
2577
June1st to 15thDay
9%5%25%435%5%5%8%43%
2520
16th to endDay
6%2135%25%5%6%10%48%
2520
July1st to 15thDay
10%425%436%6%6%9%40%
2456
16th to endDay
6%325%6%36%6%7%9%43%
2466
August1st to 15thDay
8%325%5%36%6%7%9%41%
2340
16th to endDay
8%4244445%6%8%47%
2298
September1st to 15thDay
13%5%245%3345%7%44%
2160
16th to endDay
10%414435%45%7%47%
1971
October1st to 15thDay
16%5%1431332452%
1800
16th to endDay
13%5%13323345%53%
1920
November1st to 15thDay
13%6%23423345%50%
1823
16th to endDay
16%6%34312336%47%
1622
December1st to 15thDay
14%9%36%324445%41%
1560
16th to endDay
14%11%46%424336%38%
1568
January1st to 15thNight
14%7%25%5%23445%43%
2360
16th to endNight
11%8%46%423345%45%
2496
February1st to 15thNight
12%10%47%423446%39%
2278
16th to endNight
13%8%35%423446%44%
1919
March1st to 15thNight
16%8%34433335%42%
1986
16th to endNight
21%7%3443435%5%35%
2103
April1st to 15thNight
11%6%2332435%7%50%
1797
16th to endNight
16%5%24424446%42%
1800
May1st to 15thNight
16%5%25%42445%5%43%
1661
16th to endNight
12%5%3342435%7%44%
1533
June1st to 15thNight
5%314425%5%6%8%50%
1440
16th to endNight
5%2122345%6%11%55%
1440
July1st to 15thNight
8%4133245%6%8%50%
1501
16th to endNight
5%31343446%9%53%
1702
August1st to 15thNight
5%3243245%5%8%55%
1620
16th to endNight
5%31332445%8%56%
1901
September1st to 15thNight
13%413323338%52%
1800
16th to endNight
9%31332336%7%55%
1973
October1st to 15thNight
12%413323346%53%
2160
16th to endNight
14%41342223455%
2304
November1st to 15thNight
13%5%24323336%53%
2365
16th to endNight
14%7%3432224449%
2666
December1st to 15thNight
16%8%35%423345%41%
2730
16th to endNight
16%10%37%42333438%
2755

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
41%410%24%19%
1578
16th to endDay
41%5%12%26%11%1
1728
February1st to 15thDay
48%5%13%22%10%
1576
16th to endDay
47%49%24%13%1
1555
March1st to 15thDay
48%49%20%13%3
1980
16th to endDay
54%5%11%18%9%
2119
April1st to 15thDay
42%5%10%21%17%2
2151
16th to endDay
51%411%18%12%1
2160
May1st to 15thDay
46%7%11%21%12%
2286
16th to endDay
45%8%11%20%12%1
2581
June1st to 15thDay
36%8%12%24%16%1
2520
16th to endDay
28%7%16%29%16%2
2520
July1st to 15thDay
38%7%13%23%12%2
2312
16th to endDay
33%8%14%27%13%2
2311
August1st to 15thDay
35%7%15%24%15%1
2326
16th to endDay
33%7%11%22%19%5%
2298
September1st to 15thDay
38%6%10%22%18%4
2160
16th to endDay
33%6%11%28%16%3
1971
October1st to 15thDay
36%47%24%20%5%
1800
16th to endDay
33%48%28%20%4
1920
November1st to 15thDay
37%39%24%19%5%
1823
16th to endDay
39%47%27%19%
1622
December1st to 15thDay
43%5%11%24%13%
1560
16th to endDay
49%411%20%11%2
1568
January1st to 15thNight
43%411%23%16%1
2360
16th to endNight
40%413%24%16%1
2496
February1st to 15thNight
45%410%24%13%1
2288
16th to endNight
41%411%24%16%1
1919
March1st to 15thNight
45%47%22%16%2
1986
16th to endNight
50%5%10%21%11%
2103
April1st to 15thNight
33%5%12%26%18%4
1797
16th to endNight
41%5%11%25%13%2
1800
May1st to 15thNight
40%7%10%21%18%1
1662
16th to endNight
38%6%13%25%12%3
1535
June1st to 15thNight
29%7%14%27%19%2
1440
16th to endNight
22%6%16%29%21%4
1440
July1st to 15thNight
30%5%14%28%16%3
1416
16th to endNight
24%7%13%35%18%1
1594
August1st to 15thNight
25%6%13%33%18%2
1610
16th to endNight
24%6%13%27%21%6%
1901
September1st to 15thNight
32%49%24%23%5%
1800
16th to endNight
28%410%28%25%2
1973
October1st to 15thNight
31%410%24%23%6%
2160
16th to endNight
32%38%26%23%5%
2304
November1st to 15thNight
33%39%25%20%6%
2365
16th to endNight
39%47%27%19%2
2666
December1st to 15thNight
45%411%22%14%1
2730
16th to endNight
50%411%17%12%3
2755

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
31%21%35%12%
90
16th to endDay
22%31%33%9%3
96
February1st to 15thDay
16%27%43%10%2
90
16th to endDay
30%24%33%8%2
81
March1st to 15thDay
28%20%40%10%1
90
16th to endDay
31%18%33%16%
103
April1st to 15thDay
20%14%35%22%5%
270
16th to endDay
28%10%34%17%9%
270
May1st to 15thDay
20%15%34%19%8%1
423
16th to endDay
17%10%38%22%8%3
517
June1st to 15thDay
10%427%33%18%4
495
16th to endDay
10%5%30%35%13%4
495
July1st to 15thDay
14%319%38%20%3
475
16th to endDay
7%215%30%36%6%
515
August1st to 15thDay
10%116%35%30%5%
493
16th to endDay
12%115%33%27%9%
338
September1st to 15thDay
11%5%15%32%28%7%
315
16th to endDay
10%423%34%21%6%
198
October1st to 15thDay
20%11%31%28%8%
135
16th to endDay
15%15%40%24%4
144
November1st to 15thDay
21%8%31%26%7%3
135
16th to endDay
30%17%30%17%3
135
December1st to 15thDay
15%26%37%12%42
135
16th to endDay
25%24%37%10%1
108
January1st to 15thNight
21%18%38%17%4
900
16th to endNight
17%19%38%21%2
960
February1st to 15thNight
20%17%39%20%2
880
16th to endNight
22%16%39%18%2
657
March1st to 15thNight
23%15%33%23%3
546
16th to endNight
26%10%38%20%4
576
April1st to 15thNight
17%14%39%22%5%
539
16th to endNight
20%9%38%23%7%
540
May1st to 15thNight
17%6%32%34%8%1
540
16th to endNight
15%6%30%29%17%1
563
June1st to 15thNight
7%324%41%22%1
540
16th to endNight
5%130%39%19%3
540
July1st to 15thNight
12%17%39%26%3
510
16th to endNight
7%13%38%36%3
564
August1st to 15thNight
8%11%40%35%2
539
16th to endNight
6%15%42%29%5%
573
September1st to 15thNight
15%214%33%29%4
540
16th to endNight
10%420%33%26%5%
595
October1st to 15thNight
14%7%29%27%18%2
720
16th to endNight
18%11%34%26%8%
768
November1st to 15thNight
18%13%33%25%9%
760
16th to endNight
21%16%34%21%6%
911
December1st to 15thNight
24%16%34%19%5%
975
16th to endNight
24%14%38%19%2
984
Page generated at 2017-12-21 06:04:54. Version ac04

Copyright 2017 A. Danko


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