Hawk's Hollow Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hawk's Hollow Observatory 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
35%
24630
14%
74711
10%
24573
40%
24573
18%
54118

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
17%
950
7%
2648
3%
946
21%
946
8%
2274
January11th to 20thNight
17%
920
5%
2575
3%
920
19%
920
8%
2217
January21st to endNight
20%
990
4%
2772
2%
990
22%
990
8%
2413
February1st to 10thNight
17%
756
7%
2304
3%
756
20%
756
8%
1941
February11th to 20thNight
20%
700
11%
2099
6%
700
25%
700
11%
1672
February21st to endNight
18%
592
10%
1776
3%
592
25%
592
12%
1386
March1st to 10thNight
28%
720
15%
2160
9%
720
33%
720
19%
1541
March11th to 20thNight
33%
720
21%
2044
10%
720
41%
720
25%
1372
March21st to endNight
32%
718
16%
2104
10%
718
38%
718
21%
1488
April1st to 10thNight
30%
540
13%
1800
9%
540
37%
540
18%
1234
April11th to 20thNight
32%
533
19%
1731
11%
533
42%
533
20%
1167
April21st to endNight
36%
540
18%
1620
9%
540
43%
540
24%
1084
May1st to 10thNight
36%
540
14%
1620
8%
540
40%
540
21%
1116
May11th to 20thNight
40%
531
18%
1580
11%
531
47%
531
25%
1044
May21st to endNight
49%
583
14%
1552
9%
582
53%
582
28%
1044
June1st to 10thNight
53%
540
16%
1440
11%
540
57%
540
34%
907
June11th to 20thNight
51%
540
16%
1440
12%
540
54%
540
33%
910
June21st to endNight
57%
540
17%
1440
11%
540
60%
540
33%
908
July1st to 10thNight
67%
525
17%
1400
13%
525
69%
525
42%
817
July11th to 20thNight
65%
522
20%
1392
16%
522
68%
522
40%
823
July21st to endNight
65%
591
22%
1487
18%
558
68%
558
38%
896
August1st to 10thNight
66%
537
21%
1566
16%
534
68%
534
37%
898
August11th to 20thNight
65%
534
23%
1598
19%
534
69%
534
35%
925
August21st to endNight
63%
594
23%
1956
21%
594
67%
594
32%
1129
September1st to 10thNight
60%
544
22%
1804
20%
544
64%
544
29%
1063
September11th to 20thNight
61%
720
28%
1980
22%
720
64%
720
38%
1181
September21st to endNight
50%
720
21%
1980
16%
720
52%
720
30%
1293
October1st to 10thNight
50%
720
23%
1980
18%
720
53%
720
30%
1286
October11th to 20thNight
32%
720
13%
2206
8%
720
39%
720
17%
1575
October21st to endNight
26%
792
14%
2574
9%
792
34%
792
15%
1869
November1st to 10thNight
33%
740
18%
2406
15%
740
39%
740
19%
1648
November11th to 20thNight
23%
760
12%
2470
7%
760
29%
760
12%
1907
November21st to endNight
25%
760
11%
2470
7%
760
29%
760
12%
1914
December1st to 10thNight
14%
908
5%
2618
2%
908
16%
908
7%
2254
December11th to 20thNight
17%
950
5%
3257
2%
948
20%
948
7%
2778
December21st to endNight
11%
1040
3%
4862
1%
1026
16%
1026
4%
4144

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%10%47%6%35%5%5%7%34%
74846
Night
15%11%5%8%6%3445%6%32%
74937
TransparencyDay
49%6%12%20%11%1
74547
Night
52%6%11%19%10%1
74757
SeeingDay
17%12%29%24%13%5%
14651
Night
19%9%28%31%12%1
24639

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
15%15%6%13%12%5%6%445%15%
1517
11th to 20thDay
15%18%10%12%10%45%5%46%11%
1464
21st to endDay
15%20%10%14%11%45%42311%
1584
February1st to 10thDay
12%15%8%13%12%5%5%5%4415%
1651
11th to 20thDay
14%13%7%13%10%5%5%445%20%
1748
21st to endDay
16%14%8%11%6%45%5%5%5%21%
1480
March1st to 10thDay
14%11%49%7%5%5%5%5%8%27%
1800
11th to 20thDay
12%10%47%7%345%5%7%35%
1915
21st to endDay
18%11%46%7%345%47%31%
2268
April1st to 10thDay
19%12%5%6%6%3445%7%30%
2160
11th to 20thDay
17%10%36%43446%6%36%
2177
21st to endDay
17%9%37%6%45%5%47%35%
2340
May1st to 10thDay
16%8%36%6%35%5%5%8%36%
2340
11th to 20thDay
18%7%37%434448%38%
2310
21st to endDay
12%6%345%45%5%5%8%43%
2725
June1st to 10thDay
10%6%25%5%36%5%5%9%44%
2520
11th to 20thDay
11%5%35%5%3445%8%48%
2520
21st to endDay
11%5%35%5%345%6%11%42%
2520
July1st to 10thDay
6%4235%25%6%7%9%50%
2520
11th to 20thDay
9%5%25%4246%7%8%47%
2520
21st to endDay
8%4245%345%6%11%46%
2743
August1st to 10thDay
9%425%5%345%8%11%44%
2363
11th to 20thDay
10%426%5%45%5%6%9%45%
2303
21st to endDay
10%5%26%5%345%7%9%45%
2397
September1st to 10thDay
11%6%36%435%5%6%7%43%
2138
11th to 20thDay
11%5%25%5%25%5%6%9%46%
1980
21st to endDay
12%6%36%7%35%45%8%41%
1980
October1st to 10thDay
16%8%26%6%34445%42%
1980
11th to 20thDay
22%10%48%6%46%5%5%7%25%
1750
21st to endDay
24%11%38%7%45%446%23%
1782
November1st to 10thDay
13%11%37%5%35%5%5%8%36%
1672
11th to 20thDay
16%17%7%9%7%45%45%6%22%
1710
21st to endDay
21%15%6%9%5%34447%22%
1710
December1st to 10thDay
14%21%10%14%7%5%4345%14%
1558
11th to 20thDay
14%19%10%14%8%46%445%13%
1918
21st to endDay
21%24%8%11%8%4433410%
2783
January1st to 10thNight
16%15%8%13%10%45%44415%
2648
11th to 20thNight
17%17%9%12%8%45%44416%
2575
21st to endNight
15%16%10%12%10%46%445%13%
2772
February1st to 10thNight
14%17%8%13%11%45%445%17%
2304
11th to 20thNight
13%15%6%12%8%45%5%45%23%
2098
21st to endNight
17%15%5%9%7%45%5%45%25%
1776
March1st to 10thNight
15%9%47%6%4445%7%33%
2160
11th to 20thNight
12%9%45%6%35%35%7%41%
2044
21st to endNight
19%8%47%6%3445%7%34%
2104
April1st to 10thNight
15%11%47%5%35%5%5%7%35%
1800
11th to 20thNight
20%8%35%5%245%5%6%37%
1731
21st to endNight
17%9%45%5%335%5%7%38%
1620
May1st to 10thNight
16%8%37%6%445%5%6%36%
1620
11th to 20thNight
19%6%25%4345%5%7%40%
1579
21st to endNight
11%6%46%6%45%5%5%8%41%
1551
June1st to 10thNight
11%4345%345%5%9%46%
1440
11th to 20thNight
9%5%35%5%3447%9%44%
1440
21st to endNight
9%4245%36%6%6%9%45%
1440
July1st to 10thNight
6%326%5%245%7%8%54%
1440
11th to 20thNight
7%32443447%9%51%
1440
21st to endNight
6%425%5%35%45%8%53%
1575
August1st to 10thNight
8%5%25%425%5%6%9%50%
1575
11th to 20thNight
9%425%4246%7%8%50%
1598
21st to endNight
9%5%25%5%3445%7%50%
1956
September1st to 10thNight
9%6%26%4345%5%7%49%
1804
11th to 20thNight
11%4245%3345%6%53%
1980
21st to endNight
13%7%35%6%3445%7%45%
1980
October1st to 10thNight
18%6%24434447%46%
1980
11th to 20thNight
22%10%47%6%3335%5%33%
2206
21st to endNight
24%10%36%43345%6%31%
2574
November1st to 10thNight
15%11%47%5%3445%6%37%
2406
11th to 20thNight
16%16%6%9%6%345%6%7%22%
2470
21st to endNight
19%15%6%8%5%34447%24%
2470
December1st to 10thNight
16%21%9%12%7%34445%14%
2618
11th to 20thNight
16%18%9%12%8%34445%16%
3279
21st to endNight
26%21%7%9%6%3444412%
4884

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
71%7%10%9%2
1518
11th to 20thDay
74%7%11%6%2
1464
21st to endDay
79%46%7%4
1584
February1st to 10thDay
72%5%8%12%2
1651
11th to 20thDay
66%6%9%13%7%
1758
21st to endDay
64%6%11%13%5%
1480
March1st to 10thDay
55%6%14%18%7%1
1800
11th to 20thDay
48%6%14%20%11%2
1915
21st to endDay
54%5%12%20%8%1
2268
April1st to 10thDay
54%6%10%19%10%1
2160
11th to 20thDay
47%5%11%21%13%2
2177
21st to endDay
48%6%12%17%14%2
2340
May1st to 10thDay
46%6%13%23%11%1
2340
11th to 20thDay
44%5%12%21%14%3
2314
21st to endDay
38%7%14%25%15%1
2725
June1st to 10thDay
35%7%13%27%16%2
2520
11th to 20thDay
35%6%13%24%20%2
2520
21st to endDay
35%7%16%22%18%2
2520
July1st to 10thDay
28%6%14%30%17%4
2451
11th to 20thDay
32%7%14%27%18%3
2445
21st to endDay
31%7%14%25%20%3
2591
August1st to 10thDay
33%7%15%31%13%2
2348
11th to 20thDay
34%7%15%27%14%2
2303
21st to endDay
33%6%15%26%17%3
2397
September1st to 10thDay
38%6%15%25%13%3
2138
11th to 20thDay
34%6%13%32%14%1
1980
21st to endDay
40%6%13%24%16%
1980
October1st to 10thDay
45%5%9%26%13%1
1980
11th to 20thDay
58%7%13%15%7%
1750
21st to endDay
62%6%12%14%6%1
1782
November1st to 10thDay
47%8%12%21%12%1
1672
11th to 20thDay
64%6%10%15%5%1
1710
21st to endDay
63%6%13%13%4
1710
December1st to 10thDay
75%6%8%9%2
1558
11th to 20thDay
74%6%10%9%1
1915
21st to endDay
79%5%7%8%1
2783
January1st to 10thNight
72%6%9%10%3
2648
11th to 20thNight
73%6%9%8%4
2575
21st to endNight
73%7%10%6%3
2772
February1st to 10thNight
71%5%8%12%4
2304
11th to 20thNight
64%5%8%16%6%
2099
21st to endNight
61%6%11%15%6%1
1776
March1st to 10thNight
50%6%13%22%8%1
2160
11th to 20thNight
44%5%12%23%13%3
2044
21st to endNight
50%5%11%22%10%2
2104
April1st to 10thNight
49%6%11%21%13%1
1800
11th to 20thNight
47%5%8%17%18%4
1731
21st to endNight
45%5%12%19%16%4
1620
May1st to 10thNight
48%6%12%20%12%2
1620
11th to 20thNight
43%6%11%20%18%3
1580
21st to endNight
41%7%12%23%15%2
1552
June1st to 10thNight
35%6%10%29%17%3
1440
11th to 20thNight
35%7%13%24%19%2
1440
21st to endNight
34%8%15%25%15%3
1440
July1st to 10thNight
27%6%14%28%19%5%
1400
11th to 20thNight
28%7%15%29%20%2
1392
21st to endNight
30%7%13%26%21%4
1487
August1st to 10thNight
29%7%16%31%16%2
1566
11th to 20thNight
29%8%14%31%17%2
1598
21st to endNight
33%6%10%27%21%3
1956
September1st to 10thNight
33%8%12%26%18%3
1804
11th to 20thNight
31%5%11%33%18%2
1980
21st to endNight
39%7%13%27%14%1
1980
October1st to 10thNight
39%6%9%27%17%2
1980
11th to 20thNight
53%5%12%19%10%
2206
21st to endNight
54%6%12%18%9%
2574
November1st to 10thNight
48%6%10%23%12%1
2406
11th to 20thNight
60%7%12%15%6%1
2470
21st to endNight
61%7%14%15%3
2470
December1st to 10thNight
73%6%8%9%4
2618
11th to 20thNight
71%7%11%8%3
3281
21st to endNight
76%5%10%7%2
4884

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
20%17%32%24%5%2
270
11th to 20thDay
24%13%40%17%4
249
21st to endDay
27%14%33%21%5%1
264
February1st to 10thDay
20%27%30%20%2
240
11th to 20thDay
20%21%37%18%3
240
21st to endDay
26%27%35%10%21
198
March1st to 10thDay
21%25%39%11%4
240
11th to 20thDay
21%14%30%25%10%1
355
21st to endDay
28%15%29%20%7%2
462
April1st to 10thDay
27%12%31%23%6%1
420
11th to 20thDay
25%18%26%21%6%4
412
21st to endDay
23%13%31%19%11%2
420
May1st to 10thDay
22%14%30%22%9%3
423
11th to 20thDay
17%11%29%23%15%4
456
21st to endDay
15%9%26%29%15%6%
679
June1st to 10thDay
11%7%34%29%13%5%
630
11th to 20thDay
13%9%27%32%14%5%
630
21st to endDay
12%8%32%30%13%5%
630
July1st to 10thDay
7%425%31%23%10%
621
11th to 20thDay
10%6%25%32%19%8%
618
21st to endDay
10%430%32%18%7%
684
August1st to 10thDay
10%321%27%24%16%
482
11th to 20thDay
11%5%18%28%26%12%
439
21st to endDay
12%421%30%24%10%
495
September1st to 10thDay
15%422%30%19%9%
450
11th to 20thDay
9%420%29%26%12%
450
21st to endDay
15%12%20%25%20%9%
450
October1st to 10thDay
16%13%25%24%17%4
450
11th to 20thDay
23%17%30%24%5%
350
21st to endDay
31%13%38%10%42
297
November1st to 10thDay
21%15%32%23%7%1
270
11th to 20thDay
21%23%36%15%6%
270
21st to endDay
26%14%43%13%4
270
December1st to 10thDay
26%23%29%14%7%1
270
11th to 20thDay
20%21%38%16%5%
270
21st to endDay
25%24%34%14%4
297
January1st to 10thNight
21%15%32%24%7%1
950
11th to 20thNight
26%11%32%25%6%1
920
21st to endNight
22%9%31%33%5%
990
February1st to 10thNight
22%11%37%26%4
756
11th to 20thNight
21%13%35%25%6%
703
21st to endNight
25%13%39%20%4
592
March1st to 10thNight
19%10%35%27%8%1
720
11th to 20thNight
17%12%33%29%8%1
720
21st to endNight
21%10%30%29%8%1
718
April1st to 10thNight
19%9%34%30%7%
540
11th to 20thNight
23%8%33%28%7%1
533
21st to endNight
21%9%30%31%8%1
540
May1st to 10thNight
18%6%31%35%9%1
540
11th to 20thNight
21%5%28%34%12%
531
21st to endNight
14%424%36%21%2
584
June1st to 10thNight
11%425%41%18%
540
11th to 20thNight
12%427%40%17%
540
21st to endNight
11%322%42%20%1
540
July1st to 10thNight
7%215%43%30%2
525
11th to 20thNight
7%417%44%25%2
522
21st to endNight
8%118%45%28%1
591
August1st to 10thNight
9%214%45%28%2
537
11th to 20thNight
11%213%43%27%5%
534
21st to endNight
10%315%40%28%3
594
September1st to 10thNight
11%417%41%23%5%
544
11th to 20thNight
12%5%17%36%26%4
720
21st to endNight
14%8%22%31%21%4
720
October1st to 10thNight
19%6%21%34%18%1
720
11th to 20thNight
27%11%24%27%9%1
720
21st to endNight
30%9%30%23%7%
792
November1st to 10thNight
21%11%30%29%10%
740
11th to 20thNight
24%14%32%23%6%1
760
21st to endNight
26%11%31%28%5%
760
December1st to 10thNight
27%13%31%23%6%
908
11th to 20thNight
25%13%35%23%4
950
21st to endNight
31%10%36%20%2
1045
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