Headlands International Dark Sky Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Headlands International Dark Sky Park clear sky chart from 2005-11-05 to 2017-10-16.

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
29%
15753
11%
47162
6%
15707
34%
15707
14%
35196

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
15%
900
4%
2506
1%
895
18%
895
5%
2200
January16th to endNight
15%
960
7%
2688
2%
960
19%
960
8%
2262
February1st to 15thNight
16%
753
7%
2315
3%
750
20%
750
8%
1836
February16th to endNight
26%
631
10%
1893
5%
631
31%
631
10%
1517
March1st to 15thNight
27%
720
15%
2121
7%
720
33%
720
18%
1506
March16th to endNight
32%
747
17%
2091
10%
747
40%
747
19%
1450
April1st to 15thNight
28%
539
14%
1767
9%
539
35%
539
16%
1238
April16th to endNight
30%
540
17%
1620
6%
540
40%
540
18%
1094
May1st to 15thNight
31%
540
12%
1620
7%
540
36%
540
17%
1144
May16th to endNight
39%
506
15%
1443
8%
504
47%
504
26%
923
June1st to 15thNight
37%
360
12%
1260
7%
360
44%
360
18%
801
June16th to endNight
46%
360
11%
1260
9%
360
51%
360
21%
773
July1st to 15thNight
52%
450
13%
1300
9%
450
54%
450
29%
796
July16th to endNight
48%
564
14%
1417
9%
531
55%
531
30%
894
August1st to 15thNight
56%
539
18%
1557
14%
536
60%
536
33%
906
August16th to endNight
52%
573
17%
1747
11%
573
58%
573
28%
1050
September1st to 15thNight
47%
616
15%
1876
11%
616
51%
616
24%
1195
September16th to endNight
48%
717
16%
1980
12%
717
51%
717
26%
1336
October1st to 15thNight
35%
720
14%
2055
9%
720
39%
720
18%
1477
October16th to endNight
22%
708
7%
2297
4%
708
27%
708
8%
1868
November1st to 15thNight
22%
700
13%
2276
10%
700
27%
700
11%
1742
November16th to endNight
13%
750
5%
2505
3%
750
16%
750
5%
2168
December1st to 15thNight
8%
900
2%
2700
1%
900
9%
900
3%
2461
December16th to endNight
10%
960
4%
2868
1%
960
13%
960
4%
2559

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%9%36%5%3445%6%34%
48256
Night
16%11%5%7%6%34445%29%
47330
Cloud CoverDay
14%9%47%5%3445%6%34%
48265
Night
15%11%48%6%34446%29%
47335
TransparencyDay
49%7%12%20%9%
47942
Night
55%6%12%16%7%
47162
SeeingDay
17%16%26%25%11%3
6118
Night
18%21%23%24%10%1
15753

By Month

Percentage Cloud Cover NE (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
15%16%6%15%11%46%5%3310%
1432
16th to endDay
13%14%7%13%10%5%5%44415%
1536
February1st to 15thDay
12%13%6%9%6%45%5%5%6%24%
1542
16th to endDay
12%11%410%8%45%45%7%24%
1580
March1st to 15thDay
12%10%47%7%33446%35%
1829
16th to endDay
13%8%36%5%2436%6%38%
2144
April1st to 15thDay
19%8%45%42445%7%32%
2181
16th to endDay
15%8%36%5%3445%6%35%
2340
May1st to 15thDay
15%7%45%5%34446%39%
2331
16th to endDay
12%6%244245%5%7%43%
2666
June1st to 15thDay
13%5%25%5%25%5%7%8%38%
2700
16th to endDay
13%5%25%5%35%5%5%8%40%
2700
July1st to 15thDay
9%5%2432445%7%49%
2577
16th to endDay
9%42441346%7%50%
2655
August1st to 15thDay
10%4143245%5%8%49%
2394
16th to endDay
12%42442346%7%47%
2453
September1st to 15thDay
15%5%25%3345%5%7%42%
2071
16th to endDay
14%5%245%245%5%9%41%
1980
October1st to 15thDay
21%9%35%5%33446%31%
1905
16th to endDay
24%13%48%7%345%5%5%17%
1593
November1st to 15thDay
19%13%5%7%6%34447%22%
1582
16th to endDay
20%20%8%11%7%4333312%
1452
December1st to 15thDay
19%18%11%14%10%333239%
1260
16th to endDay
20%20%7%12%8%3433411%
1353
January1st to 15thNight
17%15%8%12%9%46%33413%
2506
16th to endNight
15%12%7%11%10%5%6%345%16%
2688
February1st to 15thNight
10%14%7%9%8%46%5%5%6%21%
2313
16th to endNight
13%13%5%8%10%45%5%5%5%23%
1893
March1st to 15thNight
13%8%48%6%33445%37%
2108
16th to endNight
13%9%36%425%45%5%38%
2091
April1st to 15thNight
19%8%35%5%3445%6%32%
1767
16th to endNight
15%9%35%435%445%39%
1620
May1st to 15thNight
15%8%37%6%35%45%6%34%
1620
16th to endNight
11%6%25%42445%7%45%
1441
June1st to 15thNight
13%5%25%435%5%49%39%
1260
16th to endNight
12%5%245%345%6%9%40%
1260
July1st to 15thNight
9%5%25%5%245%5%6%46%
1380
16th to endNight
9%435%42445%7%48%
1513
August1st to 15thNight
6%4145%34448%52%
1566
16th to endNight
11%42442435%6%50%
1747
September1st to 15thNight
14%5%26%433346%45%
1876
16th to endNight
16%7%25%423446%41%
1980
October1st to 15thNight
20%8%36%5%23446%35%
2055
16th to endNight
25%12%47%6%35%435%20%
2297
November1st to 15thNight
20%14%47%5%24446%24%
2276
16th to endNight
23%19%7%10%6%3433412%
2505
December1st to 15thNight
19%20%8%12%11%3433310%
2700
16th to endNight
20%19%9%11%9%3433311%
2868

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
15%16%7%14%11%48%4339%
1432
16th to endDay
11%15%8%12%11%45%445%14%
1536
February1st to 15thDay
12%14%6%11%5%5%5%45%7%22%
1542
16th to endDay
12%12%5%9%9%45%5%5%7%23%
1580
March1st to 15thDay
11%10%47%7%3445%6%33%
1839
16th to endDay
13%8%36%5%34447%37%
2143
April1st to 15thDay
19%9%35%43445%7%32%
2181
16th to endDay
15%8%36%6%3445%7%35%
2340
May1st to 15thDay
14%7%36%5%34446%39%
2331
16th to endDay
11%6%3442445%7%43%
2666
June1st to 15thDay
12%5%25%5%35%5%6%8%39%
2700
16th to endDay
13%6%245%35%45%8%41%
2700
July1st to 15thDay
10%42443445%7%49%
2577
16th to endDay
9%425%32445%8%49%
2655
August1st to 15thDay
9%4244245%6%7%49%
2394
16th to endDay
12%5%15%33446%7%46%
2453
September1st to 15thDay
15%5%244345%47%41%
2071
16th to endDay
14%5%25%425%45%8%40%
1980
October1st to 15thDay
21%9%36%5%33346%31%
1905
16th to endDay
24%14%48%7%45%445%16%
1593
November1st to 15thDay
18%15%5%7%6%35%5%5%6%22%
1582
16th to endDay
20%19%8%12%7%45%33311%
1452
December1st to 15thDay
17%20%11%15%10%333248%
1260
16th to endDay
20%19%7%14%9%334339%
1353
January1st to 15thNight
17%15%7%12%10%5%5%43413%
2506
16th to endNight
14%13%6%13%11%45%346%16%
2688
February1st to 15thNight
11%14%7%9%9%37%5%45%21%
2306
16th to endNight
13%12%5%9%9%46%45%6%21%
1893
March1st to 15thNight
13%9%48%5%34445%36%
2121
16th to endNight
13%9%36%435%5%46%37%
2091
April1st to 15thNight
20%8%35%5%335%5%6%32%
1767
16th to endNight
15%8%35%5%2445%5%39%
1620
May1st to 15thNight
14%8%47%6%45%45%6%33%
1619
16th to endNight
11%7%235%2435%8%45%
1441
June1st to 15thNight
14%5%25%435%46%9%38%
1260
16th to endNight
11%5%35%435%5%6%9%40%
1260
July1st to 15thNight
9%5%25%5%35%45%6%47%
1380
16th to endNight
7%5%25%425%45%8%48%
1513
August1st to 15thNight
6%415%43435%8%52%
1566
16th to endNight
9%6%24423446%50%
1747
September1st to 15thNight
14%5%26%423446%45%
1876
16th to endNight
16%6%25%434448%40%
1980
October1st to 15thNight
20%7%36%5%33247%33%
2055
16th to endNight
25%12%47%6%35%45%5%19%
2297
November1st to 15thNight
19%15%47%5%24446%24%
2276
16th to endNight
21%18%7%11%7%3433313%
2505
December1st to 15thNight
18%19%8%14%10%442339%
2700
16th to endNight
19%19%9%13%8%3433311%
2868

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
77%8%6%5%1
1433
16th to endDay
71%7%9%8%2
1536
February1st to 15thDay
62%7%13%11%5%
1544
16th to endDay
60%6%12%15%5%
1580
March1st to 15thDay
51%6%13%19%8%1
1839
16th to endDay
46%6%13%22%8%1
2144
April1st to 15thDay
50%6%10%20%10%
2181
16th to endDay
47%5%11%17%15%2
2340
May1st to 15thDay
45%6%11%21%11%3
2331
16th to endDay
40%7%13%25%12%1
2670
June1st to 15thDay
40%8%13%25%11%1
2700
16th to endDay
41%7%16%22%11%1
2700
July1st to 15thDay
33%6%14%30%13%1
2428
16th to endDay
34%7%13%27%15%
2488
August1st to 15thDay
32%8%15%29%12%
2379
16th to endDay
35%7%18%26%10%1
2453
September1st to 15thDay
41%7%15%26%9%
2071
16th to endDay
40%7%17%27%7%
1980
October1st to 15thDay
53%7%10%21%8%
1905
16th to endDay
68%8%12%7%3
1593
November1st to 15thDay
60%7%12%14%5%
1582
16th to endDay
77%7%8%5%1
1452
December1st to 15thDay
81%5%6%5%1
1260
16th to endDay
79%5%8%5%1
1353
January1st to 15thNight
73%7%9%6%1
2506
16th to endNight
68%6%11%9%3
2688
February1st to 15thNight
62%7%12%12%3
2315
16th to endNight
63%7%11%13%4
1893
March1st to 15thNight
49%5%12%21%9%
2121
16th to endNight
46%5%13%20%12%1
2091
April1st to 15thNight
50%5%9%22%11%1
1767
16th to endNight
45%6%11%18%15%2
1620
May1st to 15thNight
50%6%10%17%11%3
1620
16th to endNight
37%6%12%26%14%2
1443
June1st to 15thNight
40%8%12%21%16%
1260
16th to endNight
38%6%15%26%10%1
1260
July1st to 15thNight
34%6%12%27%17%2
1300
16th to endNight
34%7%15%24%17%
1417
August1st to 15thNight
30%6%17%32%12%1
1557
16th to endNight
33%7%19%25%12%1
1747
September1st to 15thNight
39%6%14%25%12%
1876
16th to endNight
41%6%16%26%8%
1980
October1st to 15thNight
50%6%11%21%8%
2055
16th to endNight
64%8%11%11%3
2297
November1st to 15thNight
58%7%12%15%5%
2276
16th to endNight
73%7%10%6%2
2505
December1st to 15thNight
80%6%7%4
2700
16th to endNight
77%5%7%6%1
2868

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
20%15%42%17%4
90
16th to endDay
25%12%29%28%41
96
February1st to 15thDay
22%21%37%14%4
90
16th to endDay
22%17%33%23%3
81
March1st to 15thDay
16%19%29%21%13%
129
16th to endDay
22%16%22%25%9%3
288
April1st to 15thDay
22%19%22%20%13%1
270
16th to endDay
20%21%28%16%10%3
270
May1st to 15thDay
17%22%26%20%10%3
288
16th to endDay
14%19%28%25%9%3
512
June1st to 15thDay
15%18%30%26%7%1
495
16th to endDay
17%16%24%27%11%2
495
July1st to 15thDay
12%13%28%26%15%4
475
16th to endDay
10%17%23%29%12%6%
515
August1st to 15thDay
11%8%21%33%16%8%
367
16th to endDay
18%9%20%25%21%4
332
September1st to 15thDay
13%9%18%25%21%11%
315
16th to endDay
13%11%22%29%16%6%
314
October1st to 15thDay
23%12%29%23%10%
315
16th to endDay
31%10%33%22%3
99
November1st to 15thDay
18%18%27%24%7%2
90
16th to endDay
20%20%35%20%1
67
December1st to 15thDay
25%26%36%8%3
60
16th to endDay
33%30%30%4
65
January1st to 15thNight
19%29%23%20%6%
900
16th to endNight
16%26%28%22%4
960
February1st to 15thNight
16%26%29%22%4
753
16th to endNight
17%21%25%27%7%
631
March1st to 15thNight
15%24%26%24%8%
720
16th to endNight
16%22%22%27%9%
747
April1st to 15thNight
19%22%24%25%7%
539
16th to endNight
17%23%25%20%11%
540
May1st to 15thNight
16%20%24%26%11%
540
16th to endNight
12%20%23%27%14%1
506
June1st to 15thNight
15%19%22%32%9%
360
16th to endNight
13%19%15%32%17%1
360
July1st to 15thNight
10%13%17%34%18%3
450
16th to endNight
10%17%17%32%18%3
564
August1st to 15thNight
9%10%17%33%25%3
539
16th to endNight
10%12%19%34%21%2
573
September1st to 15thNight
15%11%21%26%19%5%
616
16th to endNight
17%12%16%30%17%5%
717
October1st to 15thNight
22%15%21%26%12%1
720
16th to endNight
31%19%21%22%5%
708
November1st to 15thNight
22%24%25%19%7%
700
16th to endNight
26%29%24%15%3
750
December1st to 15thNight
25%32%26%11%3
900
16th to endNight
24%27%26%15%31
960
Page generated at 2017-10-17 16:35:20. Version ac04

Copyright 2017 A. Danko


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