Observe the Heavens Astronomy Camp
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observe the Heavens Astronomy Camp clear sky chart from 2005-11-06 to 2024-01-14.

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
53%
22851
15%
74978
14%
22813
56%
22813
21%
50426

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
26%
759
7%
2646
5%
756
30%
756
8%
2202
January11th to 20thNight
30%
734
6%
2568
5%
734
33%
734
8%
2129
January21st to endNight
36%
792
7%
2772
6%
792
39%
792
9%
2231
February1st to 10thNight
41%
720
10%
2498
9%
720
45%
720
14%
1845
February11th to 20thNight
45%
703
13%
2210
9%
700
50%
700
18%
1587
February21st to endNight
52%
592
17%
1776
15%
592
57%
592
23%
1205
March1st to 10thNight
51%
720
14%
2160
14%
720
54%
720
21%
1509
March11th to 20thNight
47%
720
16%
2119
13%
720
51%
720
23%
1481
March21st to endNight
48%
792
13%
1980
7%
792
49%
792
23%
1447
April1st to 10thNight
55%
720
15%
1800
6%
720
58%
720
27%
1246
April11th to 20thNight
51%
672
18%
1740
11%
672
54%
672
26%
1196
April21st to endNight
55%
527
18%
1607
14%
527
58%
527
27%
999
May1st to 10thNight
60%
360
20%
1440
24%
360
67%
360
26%
781
May11th to 20thNight
68%
354
18%
1416
30%
354
70%
354
27%
783
May21st to endNight
62%
389
11%
1552
17%
388
64%
388
21%
942
June1st to 10thNight
66%
360
10%
1278
13%
360
67%
360
27%
763
June11th to 20thNight
65%
360
10%
1260
10%
360
66%
360
28%
731
June21st to endNight
74%
360
16%
1260
16%
360
75%
360
41%
618
July1st to 10thNight
81%
350
15%
1400
19%
350
83%
350
47%
577
July11th to 20thNight
82%
348
21%
1392
34%
348
86%
348
53%
537
July21st to endNight
88%
394
30%
1488
48%
372
93%
372
70%
477
August1st to 10thNight
84%
358
29%
1424
43%
356
87%
356
53%
552
August11th to 20thNight
83%
410
34%
1478
39%
410
84%
410
54%
608
August21st to endNight
79%
769
33%
1957
23%
769
81%
769
61%
1001
September1st to 10thNight
78%
720
32%
1800
18%
720
81%
720
60%
934
September11th to 20thNight
72%
720
28%
1869
19%
720
74%
720
42%
1108
September21st to endNight
68%
720
27%
1980
23%
720
71%
720
42%
1119
October1st to 10thNight
65%
720
21%
2096
20%
720
67%
720
34%
1239
October11th to 20thNight
59%
720
21%
2241
19%
720
64%
720
30%
1373
October21st to endNight
53%
792
18%
2574
17%
792
58%
792
23%
1702
November1st to 10thNight
47%
740
11%
2405
10%
740
50%
740
15%
1750
November11th to 20thNight
40%
760
10%
2626
7%
760
44%
760
13%
1953
November21st to endNight
37%
840
8%
2740
7%
840
39%
840
12%
2135
December1st to 10thNight
37%
950
10%
2850
7%
950
40%
950
13%
2263
December11th to 20thNight
29%
950
3%
3507
3%
949
30%
949
6%
3095
December21st to endNight
28%
956
5%
5069
5%
950
31%
950
5%
4308

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
9%8%37%6%45%5%6%7%40%
74585
Night
11%10%47%6%35%5%6%7%37%
75180
TransparencyDay
43%6%12%21%15%4
74287
Night
46%6%11%19%13%4
74996
SeeingDay
14%9%23%29%19%7%
13608
Night
16%413%38%25%4
22866

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
20%18%7%11%7%5%5%35%5%14%
1519
11th to 20thDay
17%13%6%13%8%5%7%5%45%16%
1464
21st to endDay
15%16%5%13%9%46%45%7%18%
1584
February1st to 10thDay
12%12%49%9%5%6%5%5%8%24%
1461
11th to 20thDay
11%13%36%7%35%6%7%8%29%
1638
21st to endDay
12%12%5%8%6%45%6%6%7%29%
1480
March1st to 10thDay
12%12%36%6%46%6%7%9%29%
1800
11th to 20thDay
12%11%47%5%36%5%5%10%31%
1837
21st to endDay
12%11%5%9%8%46%6%7%7%25%
2376
April1st to 10thDay
11%10%47%8%47%7%8%9%26%
2160
11th to 20thDay
9%8%38%7%47%5%6%8%34%
2171
21st to endDay
9%6%48%7%47%6%6%9%35%
2351
May1st to 10thDay
5%8%48%6%45%5%6%9%42%
2520
11th to 20thDay
8%6%37%6%46%7%7%9%36%
2477
21st to endDay
9%7%48%6%46%6%7%9%33%
2723
June1st to 10thDay
13%6%46%6%45%5%6%7%38%
2678
11th to 20thDay
10%6%47%8%47%5%7%8%35%
2700
21st to endDay
5%325%435%5%5%8%54%
2695
July1st to 10thDay
32234345%5%7%62%
2520
11th to 20thDay
3323424347%67%
2520
21st to endDay
2212223345%75%
2741
August1st to 10thDay
331442345%7%64%
2507
11th to 20thDay
4213233448%66%
2420
21st to endDay
3424435%45%7%59%
2397
September1st to 10thDay
33133235%5%6%65%
2160
11th to 20thDay
5%4246%36%6%6%7%51%
2090
21st to endDay
7%5%25%5%45%46%7%50%
1980
October1st to 10thDay
8%6%38%5%345%6%7%45%
1862
11th to 20thDay
9%6%26%6%45%5%7%8%42%
1718
21st to endDay
15%10%46%6%26%6%5%6%34%
1782
November1st to 10thDay
16%12%47%7%45%5%6%7%27%
1674
11th to 20thDay
15%13%5%9%8%45%436%28%
1552
21st to endDay
14%18%6%9%8%45%5%45%21%
1418
December1st to 10thDay
12%15%7%11%8%47%5%6%5%21%
1330
11th to 20thDay
20%22%7%11%6%45%45%410%
1682
21st to endDay
13%20%8%12%11%45%5%5%5%13%
2598
January1st to 10thNight
22%17%6%11%7%35%445%16%
2646
11th to 20thNight
18%15%7%12%8%46%446%16%
2568
21st to endNight
13%18%7%10%8%5%5%45%6%19%
2772
February1st to 10thNight
11%15%5%9%7%35%5%6%7%27%
2498
11th to 20thNight
9%12%48%7%45%6%7%6%31%
2208
21st to endNight
9%9%47%6%35%6%7%8%35%
1776
March1st to 10thNight
11%10%47%8%46%5%6%8%33%
2160
11th to 20thNight
12%9%47%6%46%6%47%36%
2119
21st to endNight
9%9%5%7%8%46%6%6%10%31%
1980
April1st to 10thNight
8%7%38%7%46%6%7%8%36%
1800
11th to 20thNight
7%8%48%8%5%6%5%5%7%40%
1740
21st to endNight
5%7%46%7%45%5%7%8%41%
1607
May1st to 10thNight
6%5%27%7%36%5%6%9%45%
1440
11th to 20thNight
7%5%25%5%46%5%7%10%44%
1416
21st to endNight
8%7%47%6%35%5%7%10%38%
1552
June1st to 10thNight
8%6%35%5%45%6%8%9%42%
1278
11th to 20thNight
6%5%25%6%46%6%8%9%42%
1260
21st to endNight
34235%35%45%8%58%
1260
July1st to 10thNight
211333436%8%65%
1440
11th to 20thNight
2112323447%70%
1440
21st to endNight
111212346%79%
1576
August1st to 10thNight
3312322336%73%
1432
11th to 20thNight
221332346%7%68%
1478
21st to endNight
221242346%7%67%
1957
September1st to 10thNight
31133235%5%9%65%
1800
11th to 20thNight
6%425%435%5%7%7%54%
1869
21st to endNight
7%42443437%7%54%
1980
October1st to 10thNight
9%5%25%5%3445%7%50%
2096
11th to 20thNight
9%6%37%5%345%6%7%46%
2241
21st to endNight
14%8%25%5%35%6%6%7%39%
2574
November1st to 10thNight
17%9%47%6%35%6%7%8%28%
2405
11th to 20thNight
16%12%5%7%6%46%6%6%5%28%
2626
21st to endNight
16%13%6%10%7%45%45%5%24%
2740
December1st to 10thNight
13%14%5%10%8%45%5%6%6%23%
2850
11th to 20thNight
19%22%8%11%9%35%44412%
3510
21st to endNight
17%21%6%10%9%5%5%6%5%412%
5086

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
72%8%8%7%5%
1519
11th to 20thDay
70%7%10%9%21
1464
21st to endDay
68%6%9%12%5%
1584
February1st to 10thDay
57%8%15%12%7%1
1461
11th to 20thDay
51%8%16%17%8%
1647
21st to endDay
53%8%13%16%10%1
1480
March1st to 10thDay
51%7%18%16%7%1
1800
11th to 20thDay
49%8%14%20%8%
1837
21st to endDay
56%7%17%14%5%1
2376
April1st to 10thDay
52%7%14%19%7%1
2160
11th to 20thDay
45%6%15%21%11%2
2171
21st to endDay
44%7%12%24%9%3
2351
May1st to 10thDay
38%5%13%29%14%2
2520
11th to 20thDay
41%6%15%25%12%1
2480
21st to endDay
44%6%14%23%11%1
2724
June1st to 10thDay
44%5%10%21%15%5%
2678
11th to 20thDay
45%7%10%22%14%4
2700
21st to endDay
28%5%12%27%22%6%
2695
July1st to 10thDay
21%5%8%25%27%15%
2451
11th to 20thDay
18%37%22%31%18%
2445
21st to endDay
12%3322%39%20%
2589
August1st to 10thDay
19%5%8%25%30%14%
2490
11th to 20thDay
17%39%27%35%8%
2420
21st to endDay
24%49%29%28%5%
2397
September1st to 10thDay
20%49%31%28%8%
2160
11th to 20thDay
31%5%12%24%22%5%
2090
21st to endDay
33%5%18%28%12%4
1980
October1st to 10thDay
38%7%14%29%12%1
1862
11th to 20thDay
39%8%16%27%10%
1718
21st to endDay
48%8%15%21%8%1
1782
November1st to 10thDay
56%9%12%16%6%1
1674
11th to 20thDay
59%7%13%14%5%2
1552
21st to endDay
64%8%11%12%4
1418
December1st to 10thDay
64%7%11%12%5%
1330
11th to 20thDay
75%8%8%6%3
1684
21st to endDay
69%13%8%7%4
2598
January1st to 10thNight
69%7%9%9%5%
2646
11th to 20thNight
69%7%11%10%31
2568
21st to endNight
66%6%12%10%41
2772
February1st to 10thNight
55%8%15%13%7%2
2498
11th to 20thNight
50%8%15%18%8%
2210
21st to endNight
44%8%15%20%12%1
1776
March1st to 10thNight
48%6%16%21%8%1
2160
11th to 20thNight
48%5%13%22%11%1
2120
21st to endNight
47%8%16%19%9%1
1980
April1st to 10thNight
44%5%14%25%11%1
1800
11th to 20thNight
45%5%10%23%16%2
1740
21st to endNight
39%5%12%25%16%3
1607
May1st to 10thNight
35%410%30%17%3
1440
11th to 20thNight
33%7%13%29%15%4
1416
21st to endNight
40%7%11%28%12%1
1552
June1st to 10thNight
36%7%9%24%18%6%
1278
11th to 20thNight
34%7%13%23%18%5%
1260
21st to endNight
24%5%10%28%25%8%
1260
July1st to 10thNight
16%5%7%22%32%18%
1400
11th to 20thNight
14%48%23%28%23%
1392
21st to endNight
7%2420%38%29%
1488
August1st to 10thNight
15%37%21%32%23%
1424
11th to 20thNight
16%38%25%40%9%
1478
21st to endNight
16%310%27%33%10%
1957
September1st to 10thNight
17%48%30%30%13%
1800
11th to 20thNight
28%6%10%24%24%8%
1869
21st to endNight
29%314%32%15%6%
1980
October1st to 10thNight
34%413%32%16%1
2096
11th to 20thNight
36%6%16%27%14%1
2241
21st to endNight
43%8%14%25%10%1
2574
November1st to 10thNight
53%8%17%15%7%1
2405
11th to 20thNight
55%9%15%13%6%2
2626
21st to endNight
61%7%13%13%6%
2740
December1st to 10thNight
61%8%11%17%3
2850
11th to 20thNight
74%8%8%7%3
3507
21st to endNight
70%10%7%8%5%
5086

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
30%6%17%29%14%4
180
11th to 20thDay
30%318%25%19%5%
166
21st to endDay
27%6%17%32%14%4
176
February1st to 10thDay
17%7%27%37%12%1
181
11th to 20thDay
18%9%22%31%16%3
363
21st to endDay
17%9%25%31%16%3
346
March1st to 10thDay
18%15%27%24%11%5%
420
11th to 20thDay
20%10%19%26%19%5%
420
21st to endDay
19%13%25%28%11%4
462
April1st to 10thDay
20%11%27%26%11%5%
420
11th to 20thDay
15%20%28%21%11%5%
412
21st to endDay
15%15%24%26%15%5%
420
May1st to 10thDay
11%12%28%28%17%5%
423
11th to 20thDay
15%8%25%26%20%6%
448
21st to endDay
13%9%21%26%20%10%
485
June1st to 10thDay
15%11%19%28%21%6%
608
11th to 20thDay
12%10%25%29%19%5%
630
21st to endDay
5%7%19%32%28%9%
625
July1st to 10thDay
5%6%26%36%22%5%
446
11th to 20thDay
5%10%24%33%20%7%
444
21st to endDay
27%24%33%22%11%
487
August1st to 10thDay
7%6%15%36%26%12%
447
11th to 20thDay
5%419%30%28%14%
437
21st to endDay
6%7%25%26%23%13%
495
September1st to 10thDay
8%6%26%26%25%9%
450
11th to 20thDay
8%9%19%32%24%8%
450
21st to endDay
10%11%26%28%18%8%
450
October1st to 10thDay
11%10%22%29%21%6%
450
11th to 20thDay
16%7%18%34%18%7%
368
21st to endDay
21%8%22%31%15%3
297
November1st to 10thDay
22%7%21%29%21%1
270
11th to 20thDay
24%8%18%27%20%4
194
21st to endDay
23%7%14%34%19%4
180
December1st to 10thDay
24%5%21%22%21%7%
180
11th to 20thDay
24%7%24%29%12%3
180
21st to endDay
26%7%15%37%12%3
198
January1st to 10thNight
31%5%18%28%16%2
760
11th to 20thNight
28%413%35%16%3
734
21st to endNight
24%411%40%19%3
792
February1st to 10thNight
21%417%41%14%2
720
11th to 20thNight
16%5%19%38%20%2
704
21st to endNight
14%417%41%20%4
592
March1st to 10thNight
16%415%40%22%2
720
11th to 20thNight
18%418%33%24%2
720
21st to endNight
15%419%40%18%4
792
April1st to 10thNight
13%5%12%40%26%4
720
11th to 20thNight
11%5%18%42%21%3
672
21st to endNight
9%5%19%42%23%3
527
May1st to 10thNight
8%6%14%41%26%5%
360
11th to 20thNight
10%38%35%37%6%
354
21st to endNight
12%5%8%36%33%7%
389
June1st to 10thNight
11%111%44%30%3
360
11th to 20thNight
7%313%45%28%3
360
21st to endNight
5%29%41%39%4
360
July1st to 10thNight
327%37%46%5%
350
11th to 20thNight
319%49%36%2
348
21st to endNight
127%39%46%6%
394
August1st to 10thNight
415%31%49%10%
358
11th to 20thNight
216%33%46%10%
410
21st to endNight
439%39%41%6%
769
September1st to 10thNight
3112%41%35%7%
720
11th to 20thNight
7%38%33%39%10%
720
21st to endNight
11%39%40%32%5%
720
October1st to 10thNight
13%210%39%32%4
720
11th to 20thNight
13%5%13%38%28%5%
720
21st to endNight
19%315%42%19%4
792
November1st to 10thNight
24%411%45%16%1
740
11th to 20thNight
24%5%18%34%17%3
760
21st to endNight
24%414%34%20%3
840
December1st to 10thNight
22%5%14%39%17%3
950
11th to 20thNight
28%6%13%37%15%2
950
21st to endNight
29%5%13%40%12%1
969
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