Saint John's University Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Saint John's University Observatory clear sky chart from 2005-11-06 to 2024-01-12.

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%
24882
17%
74488
9%
24824
43%
24824
24%
49087

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 10thNight
27%
950
13%
2837
5%
946
35%
946
19%
1995
January11th to 20thNight
25%
908
11%
2494
6%
908
30%
908
17%
1869
January21st to endNight
23%
990
14%
2574
5%
990
30%
990
17%
1946
February1st to 10thNight
27%
900
15%
2340
3%
900
35%
900
24%
1617
February11th to 20thNight
29%
879
18%
2274
6%
875
36%
875
26%
1532
February21st to endNight
30%
740
17%
1924
5%
740
38%
740
23%
1366
March1st to 10thNight
32%
550
15%
1990
9%
550
40%
550
20%
1298
March11th to 20thNight
29%
540
20%
1980
11%
540
41%
540
21%
1231
March21st to endNight
32%
594
16%
2178
13%
594
40%
594
17%
1475
April1st to 10thNight
27%
540
16%
1818
9%
540
39%
540
21%
1191
April11th to 20thNight
33%
533
20%
1688
16%
533
43%
533
20%
1147
April21st to endNight
33%
540
17%
1620
12%
540
41%
540
21%
1120
May1st to 10thNight
34%
540
16%
1562
8%
540
40%
540
26%
1033
May11th to 20thNight
40%
531
18%
1417
7%
531
45%
531
27%
949
May21st to endNight
46%
584
15%
1552
6%
582
50%
582
33%
990
June1st to 10thNight
51%
540
15%
1395
5%
540
54%
540
38%
864
June11th to 20thNight
45%
540
17%
1260
6%
540
50%
540
41%
806
June21st to endNight
53%
540
17%
1260
7%
540
56%
540
43%
786
July1st to 10thNight
64%
525
19%
1225
8%
525
66%
525
56%
692
July11th to 20thNight
59%
522
22%
1311
9%
522
62%
522
51%
731
July21st to endNight
63%
591
22%
1553
12%
558
66%
558
50%
819
August1st to 10thNight
64%
537
22%
1601
17%
534
67%
534
40%
902
August11th to 20thNight
61%
534
23%
1600
21%
534
68%
534
37%
906
August21st to endNight
58%
594
26%
1836
24%
594
65%
594
42%
965
September1st to 10thNight
55%
540
22%
1800
21%
540
62%
540
38%
941
September11th to 20thNight
48%
540
24%
1888
20%
540
58%
540
34%
1017
September21st to endNight
39%
566
25%
2006
16%
566
53%
566
31%
1108
October1st to 10thNight
37%
720
22%
2160
13%
720
44%
720
30%
1312
October11th to 20thNight
30%
720
23%
2160
11%
720
39%
720
25%
1374
October21st to endNight
29%
792
19%
2376
9%
792
38%
792
21%
1595
November1st to 10thNight
34%
925
20%
2573
9%
925
42%
925
26%
1669
November11th to 20thNight
27%
950
17%
2660
6%
950
36%
950
19%
1901
November21st to endNight
27%
950
16%
2660
7%
950
35%
950
23%
1780
December1st to 10thNight
28%
950
12%
2660
4%
950
34%
950
19%
1921
December11th to 20thNight
21%
949
12%
3205
4%
949
29%
949
13%
2332
December21st to endNight
20%
1038
7%
5051
4%
1026
27%
1026
7%
3907

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%8%47%6%35%5%5%7%38%
74907
Night
12%8%47%6%3445%7%40%
74819
TransparencyDay
46%414%25%11%1
74602
Night
44%414%25%12%2
74645
SeeingDay
16%10%31%27%13%3
14863
Night
15%9%32%32%11%1
24890

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 10thDay
8%11%5%8%9%6%6%6%5%7%30%
1328
11th to 20thDay
10%13%6%12%10%5%5%5%5%6%24%
1486
21st to endDay
9%12%5%13%8%48%5%7%8%20%
1782
February1st to 10thDay
8%11%6%7%8%5%5%5%47%35%
1620
11th to 20thDay
8%9%5%10%9%45%47%7%33%
1574
21st to endDay
10%12%410%9%35%5%5%7%30%
1336
March1st to 10thDay
12%12%5%7%7%45%5%5%6%33%
1980
11th to 20thDay
14%8%47%435%5%5%8%37%
1980
21st to endDay
18%12%48%5%3445%7%30%
2178
April1st to 10thDay
17%9%47%5%3445%7%34%
2142
11th to 20thDay
18%13%47%5%35%437%31%
2220
21st to endDay
22%9%46%5%2445%5%32%
2340
May1st to 10thDay
18%9%37%6%35%5%5%6%35%
2398
11th to 20thDay
16%7%46%5%35%5%5%7%37%
2479
21st to endDay
14%6%36%5%35%5%5%8%38%
2725
June1st to 10thDay
12%5%35%4345%6%8%45%
2560
11th to 20thDay
13%5%36%6%445%6%9%39%
2700
21st to endDay
9%425%6%36%5%7%11%41%
2700
July1st to 10thDay
5%315%5%35%5%7%10%50%
2700
11th to 20thDay
8%4245%35%5%6%9%51%
2604
21st to endDay
5%324435%7%7%10%50%
2671
August1st to 10thDay
8%5%36%6%35%6%7%9%43%
2328
11th to 20thDay
12%5%25%5%45%46%9%44%
2301
21st to endDay
10%5%25%43345%8%52%
2520
September1st to 10thDay
9%435%43445%9%50%
2160
11th to 20thDay
11%5%25%6%35%5%6%8%45%
2070
21st to endDay
15%6%35%4245%5%7%44%
1936
October1st to 10thDay
18%8%26%4245%5%7%41%
1800
11th to 20thDay
14%10%47%5%35%45%6%39%
1800
21st to endDay
17%10%47%5%34447%37%
1976
November1st to 10thDay
14%11%36%6%3446%5%37%
1504
11th to 20thDay
9%12%7%11%7%45%447%29%
1520
21st to endDay
13%10%47%6%35%5%5%7%35%
1520
December1st to 10thDay
9%12%5%9%9%5%5%6%5%6%28%
1520
11th to 20thDay
10%14%6%11%7%35%45%7%28%
1918
21st to endDay
22%14%5%14%6%24335%20%
2531
January1st to 10thNight
7%8%6%10%8%45%5%6%8%32%
2837
11th to 20thNight
10%13%7%9%7%46%6%6%6%27%
2494
21st to endNight
10%13%6%9%7%45%5%6%7%26%
2574
February1st to 10thNight
5%11%5%8%7%35%5%6%8%35%
2340
11th to 20thNight
6%9%5%9%6%35%5%5%9%40%
2273
21st to endNight
12%10%47%7%46%5%5%6%34%
1924
March1st to 10thNight
12%10%47%5%45%5%5%8%36%
1990
11th to 20thNight
11%10%47%5%35%346%41%
1980
21st to endNight
17%9%48%5%3445%6%34%
2178
April1st to 10thNight
14%10%46%6%34346%39%
1818
11th to 20thNight
18%10%46%5%2445%6%36%
1688
21st to endNight
19%9%47%43445%6%36%
1620
May1st to 10thNight
14%9%36%43445%7%40%
1562
11th to 20thNight
15%6%25%6%35%446%43%
1416
21st to endNight
13%425%5%245%6%8%45%
1551
June1st to 10thNight
10%4244346%6%8%48%
1395
11th to 20thNight
8%5%25%5%346%6%8%49%
1260
21st to endNight
8%3345%25%45%8%53%
1260
July1st to 10thNight
231342447%10%59%
1260
11th to 20thNight
7%41333335%9%60%
1354
21st to endNight
4224325%5%6%7%60%
1644
August1st to 10thNight
7%425%5%235%6%8%52%
1611
11th to 20thNight
11%5%2433445%6%55%
1600
21st to endNight
8%32432445%7%58%
1836
September1st to 10thNight
8%325%4235%5%8%54%
1800
11th to 20thNight
10%5%14434446%55%
1888
21st to endNight
13%5%2442446%6%51%
2006
October1st to 10thNight
15%6%25%5%3445%6%47%
2160
11th to 20thNight
15%9%36%42345%6%43%
2160
21st to endNight
17%9%37%433447%37%
2376
November1st to 10thNight
12%8%36%6%345%6%7%40%
2573
11th to 20thNight
13%10%6%10%6%345%46%34%
2660
21st to endNight
12%8%47%6%3445%7%40%
2660
December1st to 10thNight
9%10%6%10%8%45%46%7%31%
2660
11th to 20thNight
10%12%5%10%8%45%6%5%6%28%
3279
21st to endNight
21%14%6%11%7%34445%21%
5132

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 10thDay
53%6%15%20%7%
1329
11th to 20thDay
61%412%15%8%
1486
21st to endDay
61%5%12%15%7%
1782
February1st to 10thDay
51%313%23%9%1
1620
11th to 20thDay
51%5%12%24%7%1
1583
21st to endDay
55%49%20%11%1
1336
March1st to 10thDay
53%414%20%8%1
1980
11th to 20thDay
48%414%24%9%1
1980
21st to endDay
56%411%22%7%
2178
April1st to 10thDay
49%312%21%13%1
2142
11th to 20thDay
55%49%19%11%1
2220
21st to endDay
55%311%20%10%1
2340
May1st to 10thDay
50%6%12%20%11%1
2398
11th to 20thDay
46%412%25%12%1
2483
21st to endDay
44%5%12%26%11%2
2725
June1st to 10thDay
38%415%30%11%1
2560
11th to 20thDay
42%6%15%22%14%1
2700
21st to endDay
35%5%19%28%10%2
2700
July1st to 10thDay
28%5%17%32%17%1
2626
11th to 20thDay
30%5%15%29%17%3
2524
21st to endDay
28%6%17%31%16%2
2523
August1st to 10thDay
38%5%15%29%11%3
2314
11th to 20thDay
37%5%17%30%10%1
2301
21st to endDay
31%314%34%16%2
2520
September1st to 10thDay
32%414%36%13%
2160
11th to 20thDay
37%5%18%32%9%1
2070
21st to endDay
40%412%34%9%1
1936
October1st to 10thDay
42%414%27%12%
1800
11th to 20thDay
47%312%25%11%2
1800
21st to endDay
49%313%26%9%
1976
November1st to 10thDay
48%412%21%13%3
1504
11th to 20thDay
55%312%19%10%1
1520
21st to endDay
49%416%23%7%2
1520
December1st to 10thDay
57%415%18%6%
1520
11th to 20thDay
57%317%19%4
1915
21st to endDay
68%29%14%6%
2531
January1st to 10thNight
51%5%12%21%10%1
2837
11th to 20thNight
56%5%14%16%8%1
2494
21st to endNight
56%412%19%8%1
2574
February1st to 10thNight
47%314%23%11%2
2340
11th to 20thNight
42%5%15%24%12%2
2274
21st to endNight
49%411%21%13%2
1924
March1st to 10thNight
47%416%23%9%
1990
11th to 20thNight
45%314%24%14%1
1980
21st to endNight
51%411%24%8%2
2178
April1st to 10thNight
47%310%25%13%1
1818
11th to 20thNight
51%37%22%15%2
1688
21st to endNight
50%49%23%13%2
1620
May1st to 10thNight
43%413%25%14%1
1562
11th to 20thNight
42%5%11%24%15%2
1417
21st to endNight
36%5%16%23%17%3
1552
June1st to 10thNight
32%5%17%30%14%2
1395
11th to 20thNight
32%5%17%28%15%3
1260
21st to endNight
29%5%17%29%17%3
1260
July1st to 10thNight
20%419%35%20%1
1225
11th to 20thNight
23%415%37%17%5%
1311
21st to endNight
21%5%16%37%16%5%
1553
August1st to 10thNight
30%416%33%13%4
1601
11th to 20thNight
31%418%32%15%1
1600
21st to endNight
25%5%14%33%20%4
1836
September1st to 10thNight
27%5%17%34%17%1
1800
11th to 20thNight
31%416%32%17%
1888
21st to endNight
34%313%35%15%1
2006
October1st to 10thNight
38%310%32%15%2
2160
11th to 20thNight
42%311%28%13%2
2160
21st to endNight
48%313%25%11%
2376
November1st to 10thNight
42%314%25%13%2
2573
11th to 20thNight
52%413%20%11%1
2660
21st to endNight
44%418%25%7%2
2660
December1st to 10thNight
54%316%21%7%
2660
11th to 20thNight
56%414%18%6%2
3281
21st to endNight
67%310%16%5%
5132

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 10thDay
15%11%29%30%13%1
270
11th to 20thDay
16%11%33%34%6%
243
21st to endDay
14%8%42%22%12%2
264
February1st to 10thDay
15%17%44%23%2
240
11th to 20thDay
15%19%39%21%6%
240
21st to endDay
19%12%39%28%3
198
March1st to 10thDay
18%14%38%23%6%2
240
11th to 20thDay
22%10%33%23%10%2
240
21st to endDay
25%13%26%22%12%2
264
April1st to 10thDay
28%15%29%22%7%
402
11th to 20thDay
27%14%25%22%10%1
498
21st to endDay
25%12%32%19%10%2
600
May1st to 10thDay
21%12%33%24%8%2
603
11th to 20thDay
20%10%31%25%11%3
625
21st to endDay
18%7%29%30%12%3
679
June1st to 10thDay
11%7%26%31%21%3
630
11th to 20thDay
15%8%33%30%13%1
630
21st to endDay
12%7%32%28%16%4
630
July1st to 10thDay
8%325%35%20%9%
621
11th to 20thDay
10%6%29%30%20%6%
618
21st to endDay
8%5%24%36%23%5%
684
August1st to 10thDay
8%424%34%25%5%
626
11th to 20thDay
13%6%23%29%24%6%
615
21st to endDay
11%6%24%33%21%4
639
September1st to 10thDay
13%5%30%33%16%3
450
11th to 20thDay
11%429%33%18%4
360
21st to endDay
20%12%31%23%10%3
270
October1st to 10thDay
20%9%33%21%12%5%
270
11th to 20thDay
15%19%35%21%8%1
270
21st to endDay
20%19%37%17%6%1
297
November1st to 10thDay
23%14%29%26%6%2
270
11th to 20thDay
14%19%43%21%2
270
21st to endDay
21%14%39%21%6%
270
December1st to 10thDay
15%11%43%22%8%1
270
11th to 20thDay
19%16%38%23%4
270
21st to endDay
30%12%34%21%31
297
January1st to 10thNight
10%12%37%30%9%2
950
11th to 20thNight
17%9%36%28%8%1
908
21st to endNight
17%12%36%28%7%
990
February1st to 10thNight
10%12%40%29%8%1
900
11th to 20thNight
12%13%39%28%7%1
879
21st to endNight
17%11%32%31%8%1
740
March1st to 10thNight
16%10%37%27%9%1
550
11th to 20thNight
17%9%40%27%6%1
540
21st to endNight
22%9%31%25%11%2
594
April1st to 10thNight
19%10%38%26%6%
540
11th to 20thNight
22%12%28%29%8%
533
21st to endNight
22%8%31%29%8%2
540
May1st to 10thNight
17%9%35%29%8%1
540
11th to 20thNight
16%8%30%33%12%1
531
21st to endNight
15%6%27%38%14%1
584
June1st to 10thNight
13%426%40%16%1
540
11th to 20thNight
11%433%42%10%
540
21st to endNight
9%5%27%43%15%1
540
July1st to 10thNight
3223%44%25%1
525
11th to 20thNight
7%426%46%16%1
522
21st to endNight
4324%46%20%2
591
August1st to 10thNight
9%218%48%22%1
537
11th to 20thNight
12%318%40%24%3
534
21st to endNight
9%424%38%24%1
594
September1st to 10thNight
10%426%39%18%2
540
11th to 20thNight
11%6%30%32%19%1
540
21st to endNight
14%10%33%29%13%2
566
October1st to 10thNight
16%8%35%29%11%1
720
11th to 20thNight
20%10%33%29%7%1
720
21st to endNight
23%13%30%27%7%
792
November1st to 10thNight
16%11%32%31%9%1
925
11th to 20thNight
18%13%35%26%8%1
950
21st to endNight
17%14%38%25%7%
950
December1st to 10thNight
14%12%35%30%8%1
950
11th to 20thNight
19%9%38%28%6%1
950
21st to endNight
24%11%33%26%5%1
1045
Page generated at 2024-01-09 06:14:41. Version ac07

Copyright 2024 Attilla Danko


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