Highlands Wilderness Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Highlands Wilderness Observatory clear sky chart from 2005-11-05 to 2017-09-16.

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%
14711
13%
46716
8%
14679
36%
14679
16%
33260

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
11%
719
7%
2506
3%
716
16%
716
5%
2052
January16th to endNight
18%
768
11%
2527
6%
768
25%
768
10%
1988
February1st to 15thNight
14%
701
10%
2287
3%
701
23%
701
9%
1806
February16th to endNight
19%
631
13%
2024
4%
631
30%
631
12%
1505
March1st to 15thNight
19%
720
14%
1995
6%
720
26%
720
14%
1489
March16th to endNight
28%
768
20%
2109
10%
768
36%
768
23%
1431
April1st to 15thNight
22%
718
14%
1796
5%
718
27%
718
19%
1361
April16th to endNight
29%
579
19%
1659
8%
579
37%
579
22%
1129
May1st to 15thNight
36%
432
17%
1512
12%
432
45%
432
20%
976
May16th to endNight
39%
375
15%
1497
11%
374
51%
374
22%
872
June1st to 15thNight
38%
360
10%
1440
9%
360
48%
360
18%
896
June16th to endNight
45%
360
11%
1323
12%
360
50%
360
22%
831
July1st to 15thNight
53%
340
15%
1327
20%
340
58%
340
31%
704
July16th to endNight
54%
415
16%
1454
16%
390
60%
390
29%
826
August1st to 15thNight
58%
539
15%
1609
11%
536
61%
536
33%
957
August16th to endNight
53%
636
19%
1782
10%
636
58%
636
35%
1082
September1st to 15thNight
45%
720
17%
1800
8%
720
49%
720
32%
1196
September16th to endNight
47%
658
21%
1835
14%
658
52%
658
29%
1199
October1st to 15thNight
34%
660
16%
1980
11%
660
41%
660
18%
1415
October16th to endNight
18%
704
11%
2112
4%
704
27%
704
11%
1641
November1st to 15thNight
28%
700
17%
2414
14%
700
35%
700
16%
1672
November16th to endNight
21%
720
10%
2520
5%
720
27%
720
10%
1935
December1st to 15thNight
12%
720
6%
2520
2%
720
16%
720
6%
2079
December16th to endNight
11%
768
8%
2688
2%
768
18%
768
6%
2218

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
18%10%47%5%34446%30%
48014
Night
17%10%46%5%34446%31%
46890
Cloud CoverDay
17%10%46%5%34446%30%
48024
Night
17%10%47%5%34446%31%
46895
TransparencyDay
53%410%19%10%1
47706
Night
53%411%19%10%
46716
SeeingDay
23%11%29%21%9%4
5481
Night
23%11%28%24%10%1
14715

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
20%15%7%9%6%3434420%
1432
16th to endDay
13%17%9%11%7%3343420%
1695
February1st to 15thDay
14%15%6%14%8%35%33320%
1575
16th to endDay
15%16%6%10%6%4434422%
1448
March1st to 15thDay
15%13%5%6%6%45%445%26%
1954
16th to endDay
15%10%45%5%34435%36%
2115
April1st to 15thDay
23%11%35%42434431%
2152
16th to endDay
21%9%3442334438%
2310
May1st to 15thDay
19%7%37%5%35%446%32%
2437
16th to endDay
15%5%25%445%45%8%36%
2618
June1st to 15thDay
21%6%36%5%34448%29%
2520
16th to endDay
17%6%35%5%35%5%6%8%32%
2628
July1st to 15thDay
13%5%245%35%5%5%9%37%
2547
16th to endDay
11%6%36%6%46%6%5%8%34%
2612
August1st to 15thDay
13%6%26%6%35%5%6%7%35%
2340
16th to endDay
13%5%26%5%35%5%6%8%37%
2407
September1st to 15thDay
18%6%25%433447%39%
2160
16th to endDay
17%7%34433346%40%
1796
October1st to 15thDay
23%8%27%5%34446%29%
1650
16th to endDay
31%11%36%5%33445%21%
1760
November1st to 15thDay
19%10%37%6%4435%5%31%
1442
16th to endDay
24%15%5%8%5%3345%417%
1440
December1st to 15thDay
19%23%7%9%5%2344415%
1440
16th to endDay
20%20%8%9%5%2433317%
1536
January1st to 15thNight
20%18%6%9%8%3433417%
2506
16th to endNight
14%15%8%11%7%34345%21%
2527
February1st to 15thNight
13%14%6%12%6%45%5%45%20%
2285
16th to endNight
16%13%5%7%6%35%445%26%
2024
March1st to 15thNight
17%12%46%6%33445%30%
1983
16th to endNight
15%8%46%5%23345%41%
2109
April1st to 15thNight
21%11%36%434345%31%
1796
16th to endNight
16%8%36%423446%38%
1659
May1st to 15thNight
18%5%25%5%25%446%37%
1512
16th to endNight
12%4345%35%46%7%42%
1495
June1st to 15thNight
16%7%14435%46%7%36%
1440
16th to endNight
13%5%25%445%46%8%39%
1323
July1st to 15thNight
8%41443446%7%49%
1407
16th to endNight
10%5%13425%45%8%46%
1553
August1st to 15thNight
9%424435%47%8%45%
1620
16th to endNight
9%5%145%25%45%7%49%
1782
September1st to 15thNight
15%5%25%5%1345%6%44%
1800
16th to endNight
16%6%245%33345%45%
1835
October1st to 15thNight
19%9%36%5%2435%6%32%
1980
16th to endNight
25%11%47%5%33345%24%
2112
November1st to 15thNight
19%8%35%5%34446%33%
2414
16th to endNight
23%12%46%5%35%446%22%
2520
December1st to 15thNight
22%19%6%8%6%34445%15%
2520
16th to endNight
22%18%8%10%5%33335%16%
2688

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
19%16%6%9%6%3434420%
1432
16th to endDay
13%16%9%11%7%3343420%
1695
February1st to 15thDay
14%15%7%13%9%35%33419%
1575
16th to endDay
15%16%6%9%6%4434422%
1448
March1st to 15thDay
16%12%5%7%6%45%445%26%
1965
16th to endDay
15%10%36%5%25%345%36%
2114
April1st to 15thDay
23%11%35%424445%31%
2152
16th to endDay
21%8%34423345%38%
2310
May1st to 15thDay
19%8%36%5%34446%32%
2437
16th to endDay
15%6%25%5%35%45%8%37%
2618
June1st to 15thDay
21%6%36%5%3445%8%29%
2520
16th to endDay
16%6%35%5%35%5%6%9%32%
2628
July1st to 15thDay
12%5%25%5%35%5%6%9%37%
2547
16th to endDay
11%6%35%7%46%6%5%8%34%
2612
August1st to 15thDay
12%6%36%6%35%5%6%7%35%
2340
16th to endDay
12%6%26%435%5%6%9%36%
2407
September1st to 15thDay
17%5%35%5%23447%39%
2160
16th to endDay
16%8%25%434347%40%
1796
October1st to 15thDay
22%8%36%6%33445%30%
1650
16th to endDay
30%11%35%5%24445%21%
1760
November1st to 15thDay
18%10%26%7%34445%31%
1442
16th to endDay
23%16%5%8%6%3445%418%
1440
December1st to 15thDay
20%22%7%10%5%2344415%
1440
16th to endDay
21%19%8%9%6%2433317%
1536
January1st to 15thNight
20%17%7%9%8%4433317%
2506
16th to endNight
14%15%7%11%7%34345%21%
2527
February1st to 15thNight
13%14%6%11%7%35%5%45%20%
2278
16th to endNight
16%13%48%6%35%45%5%26%
2024
March1st to 15thNight
18%11%46%6%34445%30%
1995
16th to endNight
14%8%46%5%23345%40%
2109
April1st to 15thNight
21%11%46%434345%31%
1796
16th to endNight
16%8%26%5%23446%38%
1659
May1st to 15thNight
17%6%35%5%25%346%38%
1512
16th to endNight
11%5%34445%5%5%7%42%
1495
June1st to 15thNight
16%7%24435%46%7%36%
1440
16th to endNight
12%5%25%5%35%46%8%40%
1323
July1st to 15thNight
8%4235%3446%6%49%
1407
16th to endNight
10%423336%46%8%46%
1553
August1st to 15thNight
8%4245%25%46%9%45%
1620
16th to endNight
8%424435%5%5%7%49%
1782
September1st to 15thNight
15%5%26%42345%7%43%
1800
16th to endNight
16%6%24423445%45%
1835
October1st to 15thNight
19%9%26%6%33446%32%
1980
16th to endNight
26%11%37%6%33345%24%
2112
November1st to 15thNight
19%8%35%5%3445%7%32%
2414
16th to endNight
23%11%46%6%35%45%5%22%
2520
December1st to 15thNight
21%19%6%8%5%24445%15%
2520
16th to endNight
22%18%7%10%5%23335%16%
2688

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
66%410%11%6%
1433
16th to endDay
67%38%9%9%1
1695
February1st to 15thDay
70%37%14%3
1577
16th to endDay
64%28%12%10%
1448
March1st to 15thDay
58%412%16%6%1
1965
16th to endDay
49%47%19%15%3
2115
April1st to 15thDay
55%37%18%12%1
2152
16th to endDay
48%37%23%14%2
2310
May1st to 15thDay
52%39%19%13%1
2437
16th to endDay
44%6%11%21%14%1
2622
June1st to 15thDay
52%49%22%10%
2520
16th to endDay
47%5%13%20%11%
2628
July1st to 15thDay
39%5%12%28%13%1
2398
16th to endDay
45%6%12%24%9%
2448
August1st to 15thDay
46%6%13%21%11%1
2327
16th to endDay
42%6%11%28%10%
2407
September1st to 15thDay
45%412%26%10%
2160
16th to endDay
45%411%28%9%
1796
October1st to 15thDay
55%49%19%10%
1650
16th to endDay
65%410%12%6%
1760
November1st to 15thDay
53%5%13%18%7%1
1442
16th to endDay
67%5%9%10%41
1440
December1st to 15thDay
72%410%9%3
1440
16th to endDay
72%36%11%5%
1536
January1st to 15thNight
71%38%10%41
2506
16th to endNight
65%48%13%7%
2527
February1st to 15thNight
65%49%15%5%
2287
16th to endNight
58%410%18%7%
2024
March1st to 15thNight
55%5%10%18%9%
1995
16th to endNight
46%29%21%16%2
2109
April1st to 15thNight
56%36%19%12%1
1796
16th to endNight
45%49%20%18%2
1659
May1st to 15thNight
46%310%19%15%3
1512
16th to endNight
39%5%12%25%15%1
1497
June1st to 15thNight
44%5%11%22%15%
1440
16th to endNight
41%6%13%23%14%
1323
July1st to 15thNight
30%5%11%30%21%
1327
16th to endNight
35%413%30%15%
1454
August1st to 15thNight
32%6%20%26%13%
1609
16th to endNight
33%5%16%29%14%
1782
September1st to 15thNight
39%416%26%11%1
1800
16th to endNight
40%410%32%10%
1835
October1st to 15thNight
52%410%20%11%
1980
16th to endNight
62%410%14%7%
2112
November1st to 15thNight
50%5%13%19%9%
2414
16th to endNight
62%5%13%13%4
2520
December1st to 15thNight
71%410%10%3
2520
16th to endNight
71%38%10%5%
2688

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
28%20%35%10%6%
60
16th to endDay
32%7%42%13%21
91
February1st to 15thDay
33%25%36%4
90
16th to endDay
34%12%38%14%
107
March1st to 15thDay
26%14%32%22%3
270
16th to endDay
25%15%32%16%8%1
288
April1st to 15thDay
29%16%25%20%5%1
270
16th to endDay
26%14%28%15%11%3
270
May1st to 15thDay
32%8%22%21%8%6%
288
16th to endDay
19%13%33%18%10%3
331
June1st to 15thDay
26%9%30%24%6%2
315
16th to endDay
19%9%32%25%10%2
423
July1st to 15thDay
13%7%30%25%13%8%
332
16th to endDay
9%9%31%28%15%7%
326
August1st to 15thDay
15%427%26%15%10%
313
16th to endDay
17%8%21%26%15%11%
332
September1st to 15thDay
15%7%24%23%16%11%
315
16th to endDay
19%9%23%23%15%8%
254
October1st to 15thDay
21%12%29%21%12%3
255
16th to endDay
37%13%26%19%2
272
November1st to 15thDay
22%12%31%26%5%2
95
16th to endDay
45%8%35%10%1
60
December1st to 15thDay
31%21%23%21%1
60
16th to endDay
40%34%21%11
64
January1st to 15thNight
32%18%29%13%5%
720
16th to endNight
23%14%32%22%6%1
768
February1st to 15thNight
22%19%35%18%3
704
16th to endNight
25%16%32%19%5%
631
March1st to 15thNight
26%16%32%20%3
720
16th to endNight
22%12%31%21%11%1
768
April1st to 15thNight
28%14%30%20%5%
718
16th to endNight
22%12%31%21%10%1
579
May1st to 15thNight
22%428%26%15%2
432
16th to endNight
15%333%34%12%
375
June1st to 15thNight
20%8%25%35%10%
360
16th to endNight
15%5%26%38%13%
360
July1st to 15thNight
8%326%39%21%
340
16th to endNight
11%325%39%21%
415
August1st to 15thNight
10%317%37%25%4
539
16th to endNight
11%424%29%26%2
636
September1st to 15thNight
17%5%26%26%19%5%
720
16th to endNight
19%5%20%31%19%3
658
October1st to 15thNight
24%10%24%25%13%1
660
16th to endNight
31%13%27%20%5%
704
November1st to 15thNight
25%11%29%23%9%1
700
16th to endNight
32%10%29%20%6%
720
December1st to 15thNight
34%19%29%13%4
720
16th to endNight
33%13%33%16%2
768
Page generated at 2017-09-16 17:06:59. Version ac04

Copyright 2017 A. Danko


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