Ritchie Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ritchie Observatory clear sky chart from 2005-11-06 to 2024-02-15.

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
41%
22632
10%
80492
10%
22537
44%
22537
14%
59084

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
25%
842
6%
4710
6%
816
27%
816
4%
4049
January11th to 20thNight
31%
759
15%
4343
7%
748
33%
748
6%
3140
January21st to endNight
32%
829
4%
4765
7%
814
35%
814
6%
4041
February1st to 10thNight
27%
760
7%
2470
5%
760
31%
760
9%
1984
February11th to 20thNight
33%
718
9%
2331
7%
718
37%
718
12%
1790
February21st to endNight
30%
592
10%
1875
8%
592
34%
592
12%
1444
March1st to 10thNight
35%
720
10%
2103
8%
720
38%
720
15%
1620
March11th to 20thNight
33%
720
12%
1980
8%
720
36%
720
16%
1508
March21st to endNight
31%
792
6%
2116
3%
792
32%
792
12%
1727
April1st to 10thNight
36%
720
8%
1800
4%
720
37%
720
16%
1416
April11th to 20thNight
38%
672
11%
1740
5%
672
40%
672
19%
1326
April21st to endNight
40%
509
10%
1589
7%
509
43%
509
16%
1176
May1st to 10thNight
43%
360
12%
1440
16%
360
46%
360
16%
953
May11th to 20thNight
55%
354
12%
1416
17%
354
58%
354
18%
918
May21st to endNight
48%
388
7%
1552
12%
388
49%
388
14%
1101
June1st to 10thNight
47%
360
5%
1365
6%
360
48%
360
16%
911
June11th to 20thNight
41%
360
4%
1260
4%
360
42%
360
14%
914
June21st to endNight
58%
360
10%
1260
10%
360
61%
360
26%
759
July1st to 10thNight
65%
350
12%
1225
14%
350
66%
350
31%
676
July11th to 20thNight
71%
348
18%
1303
26%
348
74%
348
37%
641
July21st to endNight
78%
394
21%
1488
34%
372
81%
372
44%
644
August1st to 10thNight
72%
410
20%
1476
26%
408
73%
408
36%
742
August11th to 20thNight
77%
534
25%
1602
23%
534
79%
534
47%
830
August21st to endNight
65%
688
22%
1876
17%
688
66%
688
35%
1131
September1st to 10thNight
65%
720
21%
1800
13%
720
67%
720
44%
1080
September11th to 20thNight
57%
720
19%
1800
12%
720
58%
720
29%
1244
September21st to endNight
52%
720
18%
2058
15%
720
54%
720
25%
1377
October1st to 10thNight
49%
720
12%
2160
11%
720
51%
720
23%
1473
October11th to 20thNight
45%
720
13%
2160
12%
720
48%
720
19%
1549
October21st to endNight
38%
792
12%
2474
10%
792
42%
792
16%
1812
November1st to 10thNight
31%
740
8%
2562
8%
740
34%
740
11%
1993
November11th to 20thNight
28%
760
9%
2660
7%
760
32%
760
11%
2054
November21st to endNight
31%
760
7%
2660
5%
760
34%
760
10%
2063
December1st to 10thNight
35%
760
10%
2660
9%
760
37%
760
11%
2061
December11th to 20thNight
22%
759
3%
3256
3%
759
23%
759
5%
2694
December21st to endNight
21%
922
4%
5157
3%
903
25%
903
4%
4243

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
17%9%48%7%45%5%5%7%30%
78193
Night
18%10%48%7%45%5%5%6%30%
80812
TransparencyDay
53%7%16%17%7%1
77909
Night
55%7%14%17%7%1
80676
SeeingDay
19%10%20%26%19%6%
14108
Night
22%9%18%29%19%3
22673

By Month

Percentage Cloud Cover NW (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
28%13%5%10%8%45%5%5%5%12%
2219
11th to 20thDay
22%10%5%9%7%35%45%7%23%
2466
21st to endDay
31%13%5%10%7%36%445%12%
2894
February1st to 10thDay
22%12%48%10%5%6%7%6%6%15%
1710
11th to 20thDay
19%13%5%8%7%45%6%6%7%20%
1612
21st to endDay
16%12%6%8%7%45%5%6%6%24%
1381
March1st to 10thDay
18%11%49%8%46%5%6%7%21%
1854
11th to 20thDay
22%11%49%8%46%5%6%7%19%
1980
21st to endDay
19%10%5%8%10%5%7%6%6%7%17%
2240
April1st to 10thDay
19%12%48%7%5%6%6%6%7%20%
2160
11th to 20thDay
17%11%5%7%8%46%5%6%7%25%
2166
21st to endDay
16%9%49%8%46%7%6%7%26%
2369
May1st to 10thDay
13%8%48%7%46%6%5%7%32%
2520
11th to 20thDay
15%7%47%7%46%5%6%6%31%
2477
21st to endDay
20%9%48%7%46%5%5%6%26%
2723
June1st to 10thDay
16%9%47%7%45%6%6%7%28%
2591
11th to 20thDay
18%10%5%9%8%5%7%6%6%7%20%
2700
21st to endDay
12%7%37%6%35%5%6%8%39%
2700
July1st to 10thDay
9%6%37%5%435%46%48%
2700
11th to 20thDay
8%425%5%345%6%8%49%
2614
21st to endDay
7%42332335%7%59%
2741
August1st to 10thDay
8%5%25%4345%5%7%52%
2453
11th to 20thDay
7%5%234245%6%8%54%
2298
21st to endDay
10%6%36%5%3445%8%45%
2480
September1st to 10thDay
9%6%35%5%3345%7%51%
2160
11th to 20thDay
10%7%38%6%45%5%5%7%40%
2160
21st to endDay
13%9%36%6%345%5%7%39%
1900
October1st to 10thDay
15%9%37%6%45%6%6%7%33%
1800
11th to 20thDay
16%10%48%7%5%5%5%6%8%28%
1800
21st to endDay
21%10%48%8%46%5%5%8%22%
1882
November1st to 10thDay
24%10%49%7%45%6%5%7%18%
1516
11th to 20thDay
25%11%48%7%45%446%23%
1520
21st to endDay
24%12%49%8%35%45%7%20%
1520
December1st to 10thDay
22%11%47%7%45%5%47%23%
1520
11th to 20thDay
25%11%6%13%10%46%5%36%12%
1925
21st to endDay
22%12%6%13%10%5%6%6%5%5%12%
2442
January1st to 10thNight
28%13%5%10%9%46%5%5%413%
4726
11th to 20thNight
23%11%48%6%3445%8%25%
4414
21st to endNight
28%13%410%7%45%5%5%6%12%
4765
February1st to 10thNight
21%12%5%9%7%45%5%47%21%
2470
11th to 20thNight
17%13%48%7%45%5%5%6%26%
2329
21st to endNight
18%12%5%9%6%45%46%7%24%
1875
March1st to 10thNight
18%10%47%6%46%6%6%7%27%
2103
11th to 20thNight
20%10%36%6%35%5%6%8%28%
1979
21st to endNight
18%12%48%8%5%6%5%6%7%22%
2116
April1st to 10thNight
18%9%37%7%47%6%6%7%26%
1800
11th to 20thNight
16%8%37%7%45%5%5%8%32%
1740
21st to endNight
16%10%47%6%45%5%6%7%30%
1589
May1st to 10thNight
14%7%47%6%46%45%6%38%
1440
11th to 20thNight
11%6%47%7%5%6%5%6%8%36%
1416
21st to endNight
12%9%39%7%45%5%6%7%33%
1552
June1st to 10thNight
15%7%46%7%45%46%7%35%
1365
11th to 20thNight
18%8%37%7%46%45%7%29%
1260
21st to endNight
8%6%25%7%4445%8%47%
1260
July1st to 10thNight
7%6%35%425%446%55%
1260
11th to 20thNight
5%42342445%6%62%
1345
21st to endNight
5%21442245%5%66%
1576
August1st to 10thNight
5%425%5%34248%60%
1484
11th to 20thNight
4324413348%64%
1602
21st to endNight
9%435%5%3445%6%52%
1876
September1st to 10thNight
6%4145%345%46%58%
1800
11th to 20thNight
11%7%45%5%35%5%5%6%44%
1800
21st to endNight
13%8%36%6%445%5%6%42%
2058
October1st to 10thNight
13%8%37%7%345%5%7%40%
2160
11th to 20thNight
18%8%37%6%445%6%6%34%
2160
21st to endNight
19%8%37%6%445%6%8%31%
2474
November1st to 10thNight
24%9%47%7%45%5%5%6%25%
2562
11th to 20thNight
22%10%48%7%35%5%5%6%25%
2660
21st to endNight
21%10%5%9%8%45%5%6%7%21%
2660
December1st to 10thNight
22%12%48%6%3445%7%25%
2660
11th to 20thNight
22%12%6%11%8%45%5%6%5%16%
3280
21st to endNight
23%15%5%11%9%46%5%5%413%
5196

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
75%5%8%9%2
2219
11th to 20thDay
63%6%11%15%31
2490
21st to endDay
76%5%10%6%2
2894
February1st to 10thDay
68%9%11%7%41
1710
11th to 20thDay
65%8%11%10%6%
1621
21st to endDay
61%7%12%13%6%
1381
March1st to 10thDay
62%7%13%14%3
1854
11th to 20thDay
64%7%12%13%31
1980
21st to endDay
65%8%13%13%1
2240
April1st to 10thDay
61%8%17%13%2
2160
11th to 20thDay
55%7%14%16%6%1
2166
21st to endDay
55%7%17%15%5%1
2369
May1st to 10thDay
48%7%19%18%7%1
2520
11th to 20thDay
48%8%20%19%5%
2480
21st to endDay
55%7%20%15%4
2724
June1st to 10thDay
49%7%23%14%5%1
2591
11th to 20thDay
56%8%20%13%3
2700
21st to endDay
40%6%25%20%8%2
2700
July1st to 10thDay
35%6%17%26%13%3
2626
11th to 20thDay
28%6%19%29%15%2
2533
21st to endDay
23%416%37%17%3
2589
August1st to 10thDay
29%6%21%28%14%3
2436
11th to 20thDay
27%6%21%29%14%3
2298
21st to endDay
36%6%17%29%10%1
2480
September1st to 10thDay
33%5%18%26%13%5%
2160
11th to 20thDay
43%6%15%18%15%2
2160
21st to endDay
44%7%17%19%10%2
1900
October1st to 10thDay
49%6%16%22%7%
1800
11th to 20thDay
55%7%16%17%5%1
1800
21st to endDay
62%6%12%13%8%
1882
November1st to 10thDay
66%7%12%11%4
1516
11th to 20thDay
64%7%10%12%6%2
1520
21st to endDay
65%7%9%12%7%
1520
December1st to 10thDay
62%7%10%13%7%
1520
11th to 20thDay
74%6%10%8%21
1928
21st to endDay
72%8%12%7%2
2442
January1st to 10thNight
75%6%8%8%2
4726
11th to 20thNight
58%8%9%21%31
4452
21st to endNight
74%5%10%8%2
4765
February1st to 10thNight
65%7%12%11%5%
2470
11th to 20thNight
59%8%13%13%6%1
2331
21st to endNight
60%7%13%14%6%
1875
March1st to 10thNight
57%7%14%17%5%
2103
11th to 20thNight
55%8%15%17%41
1980
21st to endNight
62%8%16%12%1
2116
April1st to 10thNight
56%9%17%15%3
1800
11th to 20thNight
53%8%15%15%7%1
1740
21st to endNight
54%7%15%16%7%1
1589
May1st to 10thNight
48%7%16%19%9%1
1440
11th to 20thNight
45%8%20%18%8%1
1416
21st to endNight
51%10%17%18%4
1552
June1st to 10thNight
49%6%20%19%5%1
1365
11th to 20thNight
54%7%21%15%3
1260
21st to endNight
39%5%25%21%8%3
1260
July1st to 10thNight
32%6%17%28%12%5%
1225
11th to 20thNight
25%5%17%34%16%3
1303
21st to endNight
18%6%13%36%21%6%
1488
August1st to 10thNight
27%5%16%29%20%4
1476
11th to 20thNight
21%6%21%29%19%4
1602
21st to endNight
33%5%16%30%14%1
1876
September1st to 10thNight
28%6%18%28%16%5%
1800
11th to 20thNight
42%6%12%19%16%5%
1800
21st to endNight
43%6%13%25%11%1
2058
October1st to 10thNight
45%7%14%25%9%
2160
11th to 20thNight
51%7%16%19%8%
2160
21st to endNight
53%7%13%18%9%
2474
November1st to 10thNight
61%7%13%14%41
2562
11th to 20thNight
62%6%12%11%6%2
2660
21st to endNight
62%6%12%12%7%1
2660
December1st to 10thNight
62%7%11%14%7%
2660
11th to 20thNight
70%7%13%7%3
3276
21st to endNight
72%5%11%9%3
5196

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
36%13%17%17%13%4
180
11th to 20thDay
31%14%20%16%13%5%
180
21st to endDay
32%15%24%18%9%3
259
February1st to 10thDay
34%14%18%22%9%3
370
11th to 20thDay
32%17%22%19%9%2
348
21st to endDay
25%17%26%19%11%2
302
March1st to 10thDay
25%17%27%20%9%2
420
11th to 20thDay
29%13%22%19%12%5%
420
21st to endDay
26%14%27%23%9%2
462
April1st to 10thDay
27%15%21%22%10%4
420
11th to 20thDay
20%14%30%19%10%6%
412
21st to endDay
20%11%28%26%13%1
420
May1st to 10thDay
12%10%24%35%15%4
423
11th to 20thDay
19%6%19%29%19%8%
448
21st to endDay
18%7%18%28%20%9%
485
June1st to 10thDay
19%9%21%26%19%6%
521
11th to 20thDay
20%8%19%30%20%3
630
21st to endDay
11%5%22%33%22%7%
630
July1st to 10thDay
10%5%16%33%27%10%
621
11th to 20thDay
7%414%33%33%9%
532
21st to endDay
6%38%30%40%13%
487
August1st to 10thDay
7%311%30%36%13%
447
11th to 20thDay
6%39%31%37%14%
437
21st to endDay
13%5%20%32%22%8%
495
September1st to 10thDay
12%6%23%35%21%4
450
11th to 20thDay
14%8%19%28%24%7%
450
21st to endDay
16%12%21%28%18%4
450
October1st to 10thDay
20%10%21%23%18%8%
450
11th to 20thDay
24%9%20%28%16%5%
450
21st to endDay
28%15%19%21%13%4
397
November1st to 10thDay
30%14%23%22%9%2
194
11th to 20thDay
32%15%19%18%10%6%
180
21st to endDay
31%12%23%16%11%9%
180
December1st to 10thDay
30%14%21%15%14%6%
180
11th to 20thDay
31%18%27%13%9%1
180
21st to endDay
30%15%22%23%9%2
198
January1st to 10thNight
37%13%16%18%14%2
850
11th to 20thNight
32%11%15%23%17%2
769
21st to endNight
29%9%20%27%14%3
836
February1st to 10thNight
29%14%20%24%12%2
760
11th to 20thNight
25%11%21%28%14%2
722
21st to endNight
26%14%19%28%12%2
592
March1st to 10thNight
24%13%20%28%13%2
720
11th to 20thNight
25%12%22%26%13%2
720
21st to endNight
24%11%23%29%10%2
792
April1st to 10thNight
23%8%23%29%16%2
720
11th to 20thNight
20%11%21%29%16%3
672
21st to endNight
22%7%22%33%13%2
509
May1st to 10thNight
15%11%21%34%17%2
360
11th to 20thNight
14%5%17%35%25%4
354
21st to endNight
17%413%38%24%4
389
June1st to 10thNight
19%6%18%33%21%3
360
11th to 20thNight
17%11%20%33%17%3
360
21st to endNight
10%5%18%39%26%3
360
July1st to 10thNight
7%313%35%37%4
350
11th to 20thNight
8%212%41%32%5%
348
21st to endNight
6%37%38%42%5%
394
August1st to 10thNight
8%28%33%39%11%
410
11th to 20thNight
6%19%31%45%9%
534
21st to endNight
11%313%34%34%5%
688
September1st to 10thNight
9%216%38%29%5%
720
11th to 20thNight
14%7%12%28%34%6%
720
21st to endNight
18%7%15%35%22%4
720
October1st to 10thNight
15%6%20%30%25%5%
720
11th to 20thNight
22%10%16%28%21%3
720
21st to endNight
26%10%20%27%16%2
792
November1st to 10thNight
30%11%20%28%10%
740
11th to 20thNight
27%12%24%21%14%1
760
21st to endNight
28%10%21%24%15%3
760
December1st to 10thNight
28%12%14%30%15%1
760
11th to 20thNight
30%14%21%23%11%2
760
21st to endNight
34%14%21%21%9%1
932
Page generated at 2024-02-12 03:35:36. Version ac07

Copyright 2024 Attilla Danko


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