Heavens View Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Heavens View Observatory clear sky chart from 2005-11-05 to 2017-09-18.

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
36%
15648
16%
46886
10%
15608
42%
15608
21%
32209

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
16%
898
11%
2506
4%
895
22%
895
13%
1979
January16th to endNight
21%
861
10%
2589
4%
861
26%
861
12%
2020
February1st to 15thNight
17%
701
10%
2269
3%
701
25%
701
11%
1732
February16th to endNight
22%
631
15%
1893
6%
631
32%
631
15%
1390
March1st to 15thNight
25%
720
15%
2075
9%
720
31%
720
18%
1486
March16th to endNight
33%
768
19%
2112
10%
768
40%
768
22%
1480
April1st to 15thNight
26%
590
14%
1806
8%
590
33%
590
19%
1262
April16th to endNight
34%
540
21%
1620
8%
540
45%
540
26%
1033
May1st to 15thNight
37%
540
15%
1620
9%
540
44%
540
23%
1084
May16th to endNight
51%
562
16%
1672
12%
561
56%
561
31%
1014
June1st to 15thNight
55%
402
17%
1302
15%
402
61%
402
29%
761
June16th to endNight
55%
423
17%
1323
15%
423
61%
423
32%
787
July1st to 15thNight
63%
510
17%
1360
14%
510
65%
510
41%
801
July16th to endNight
67%
564
19%
1498
15%
531
70%
531
41%
847
August1st to 15thNight
66%
539
20%
1609
16%
536
69%
536
36%
945
August16th to endNight
62%
573
23%
1728
17%
573
68%
573
37%
985
September1st to 15thNight
59%
669
24%
1929
19%
669
62%
669
35%
1137
September16th to endNight
58%
669
23%
1848
18%
669
61%
669
34%
1138
October1st to 15thNight
44%
660
20%
1901
15%
660
50%
660
28%
1242
October16th to endNight
24%
704
14%
2205
7%
704
33%
704
15%
1595
November1st to 15thNight
34%
700
21%
2276
16%
700
42%
700
22%
1461
November16th to endNight
23%
720
14%
2418
9%
720
31%
720
15%
1739
December1st to 15thNight
16%
744
9%
2544
3%
744
22%
744
10%
1958
December16th to endNight
14%
960
7%
2783
1%
960
19%
960
9%
2333

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%47%6%35%5%5%7%32%
47888
Night
15%9%46%5%34446%35%
47064
Cloud CoverDay
13%9%47%6%35%5%5%7%32%
47898
Night
14%9%46%5%34446%35%
47068
TransparencyDay
50%411%20%11%1
47584
Night
48%411%22%12%1
46886
SeeingDay
16%7%26%24%16%7%
5839
Night
18%8%28%29%12%1
15654

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
16%15%7%12%7%345%35%17%
1432
16th to endDay
14%19%8%12%9%4445%314%
1635
February1st to 15thDay
14%15%6%10%10%46%5%5%5%16%
1593
16th to endDay
12%14%7%11%8%35%5%4421%
1580
March1st to 15thDay
16%11%49%6%44446%27%
1873
16th to endDay
17%11%5%8%7%4433429%
2112
April1st to 15thDay
19%11%46%5%2445%6%30%
2151
16th to endDay
16%8%36%5%2435%7%36%
2340
May1st to 15thDay
19%7%35%5%3445%6%33%
2331
16th to endDay
14%6%25%5%35%45%8%38%
2440
June1st to 15thDay
11%5%25%5%35%5%6%8%39%
2652
16th to endDay
9%5%36%6%36%6%7%9%35%
2632
July1st to 15thDay
7%425%5%35%6%6%8%42%
2520
16th to endDay
8%5%25%6%46%7%7%9%36%
2565
August1st to 15thDay
9%5%26%6%45%6%7%8%37%
2340
16th to endDay
12%5%25%5%35%6%5%8%39%
2471
September1st to 15thDay
13%5%25%435%46%9%40%
2019
16th to endDay
14%425%435%5%5%9%38%
1837
October1st to 15thDay
15%7%36%5%34446%37%
1727
16th to endDay
21%9%46%5%34436%30%
1667
November1st to 15thDay
14%8%37%5%345%5%6%35%
1582
16th to endDay
16%14%5%8%6%3445%6%25%
1539
December1st to 15thDay
15%14%8%11%7%35%345%21%
1413
16th to endDay
19%17%8%11%5%2334418%
1437
January1st to 15thNight
21%13%5%7%7%3444323%
2506
16th to endNight
12%14%7%10%8%45%445%22%
2589
February1st to 15thNight
14%14%5%8%7%45%5%3426%
2267
16th to endNight
14%12%49%8%35%345%28%
1893
March1st to 15thNight
17%11%47%5%24345%33%
2063
16th to endNight
16%8%46%5%25%446%35%
2112
April1st to 15thNight
19%8%36%433446%33%
1806
16th to endNight
15%6%25%5%2346%7%40%
1620
May1st to 15thNight
17%6%35%5%25%35%8%36%
1620
16th to endNight
12%42443445%7%45%
1670
June1st to 15thNight
9%425%425%5%6%10%43%
1302
16th to endNight
8%5%25%4235%6%8%45%
1323
July1st to 15thNight
7%3235%34348%53%
1440
16th to endNight
5%3143345%7%11%50%
1601
August1st to 15thNight
6%3136%36%6%6%8%47%
1620
16th to endNight
10%424423347%51%
1728
September1st to 15thNight
11%42442345%6%50%
1929
16th to endNight
10%5%25%43445%6%46%
1848
October1st to 15thNight
15%6%35%5%23446%41%
1901
16th to endNight
21%7%37%6%34445%30%
2205
November1st to 15thNight
14%8%35%5%245%5%5%38%
2276
16th to endNight
20%12%5%6%5%24447%26%
2418
December1st to 15thNight
19%13%7%10%5%24345%23%
2544
16th to endNight
20%16%7%10%6%3443416%
2783

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
16%15%6%12%6%44445%16%
1432
16th to endDay
14%19%8%12%8%5%444314%
1635
February1st to 15thDay
14%15%6%11%9%46%45%5%16%
1593
16th to endDay
12%14%7%11%9%3445%421%
1580
March1st to 15thDay
16%11%49%6%44445%27%
1884
16th to endDay
16%11%5%9%6%4433429%
2111
April1st to 15thDay
19%10%46%424446%30%
2151
16th to endDay
15%8%36%5%3335%7%36%
2340
May1st to 15thDay
18%8%45%5%34446%33%
2331
16th to endDay
14%6%25%5%2445%8%38%
2440
June1st to 15thDay
10%5%36%5%35%5%6%8%38%
2652
16th to endDay
9%5%26%6%46%6%7%9%35%
2632
July1st to 15thDay
7%425%5%45%6%7%8%42%
2520
16th to endDay
7%5%25%7%46%7%7%9%36%
2565
August1st to 15thDay
9%5%35%7%46%6%7%8%36%
2340
16th to endDay
11%6%25%5%35%6%5%8%38%
2471
September1st to 15thDay
12%5%25%435%45%9%39%
2019
16th to endDay
14%425%435%5%6%9%38%
1837
October1st to 15thDay
14%7%36%5%34447%37%
1727
16th to endDay
21%9%46%5%34446%30%
1667
November1st to 15thDay
14%7%47%6%345%5%6%34%
1582
16th to endDay
15%14%5%7%6%34446%25%
1539
December1st to 15thDay
15%14%8%11%6%34345%21%
1413
16th to endDay
19%17%8%11%6%2434418%
1437
January1st to 15thNight
21%13%5%7%6%3444422%
2506
16th to endNight
12%13%7%10%8%45%445%21%
2589
February1st to 15thNight
14%14%5%8%7%45%44426%
2260
16th to endNight
14%11%49%8%35%345%27%
1893
March1st to 15thNight
17%11%47%434435%33%
2075
16th to endNight
16%8%36%5%35%447%34%
2112
April1st to 15thNight
19%9%35%5%33447%33%
1806
16th to endNight
14%7%25%5%2446%6%40%
1620
May1st to 15thNight
17%6%36%425%45%7%36%
1619
16th to endNight
11%5%2443445%7%45%
1670
June1st to 15thNight
9%425%425%5%6%10%43%
1302
16th to endNight
9%425%5%2446%8%45%
1323
July1st to 15thNight
7%3235%34348%52%
1440
16th to endNight
5%3143335%6%11%50%
1601
August1st to 15thNight
5%3145%45%6%6%8%47%
1620
16th to endNight
9%424423347%51%
1728
September1st to 15thNight
11%325%42435%6%49%
1929
16th to endNight
10%6%25%5%2445%6%46%
1848
October1st to 15thNight
15%6%36%5%33446%41%
1901
16th to endNight
20%8%36%6%35%445%29%
2205
November1st to 15thNight
14%8%35%5%345%5%5%39%
2276
16th to endNight
19%11%5%6%5%34447%26%
2418
December1st to 15thNight
19%13%7%10%5%24345%23%
2544
16th to endNight
20%16%7%10%6%3443416%
2783

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
68%310%12%5%
1433
16th to endDay
72%38%10%4
1635
February1st to 15thDay
67%5%7%13%6%
1595
16th to endDay
64%48%14%7%1
1580
March1st to 15thDay
58%411%17%7%
1884
16th to endDay
57%410%18%8%1
2112
April1st to 15thDay
53%48%21%10%
2151
16th to endDay
47%314%17%14%2
2340
May1st to 15thDay
51%311%20%10%2
2331
16th to endDay
43%312%24%13%2
2444
June1st to 15thDay
40%5%13%24%14%1
2652
16th to endDay
41%6%12%21%16%
2632
July1st to 15thDay
36%410%27%19%2
2371
16th to endDay
39%7%13%21%15%2
2405
August1st to 15thDay
41%5%12%25%12%1
2327
16th to endDay
40%6%9%26%14%1
2471
September1st to 15thDay
40%5%13%27%12%1
2019
16th to endDay
40%411%31%11%
1837
October1st to 15thDay
45%411%23%13%1
1727
16th to endDay
54%414%18%6%
1667
November1st to 15thDay
48%410%24%10%1
1582
16th to endDay
58%411%17%6%
1539
December1st to 15thDay
64%412%15%3
1413
16th to endDay
69%312%9%4
1437
January1st to 15thNight
63%39%14%8%
2506
16th to endNight
62%412%15%4
2589
February1st to 15thNight
60%5%9%15%8%
2269
16th to endNight
57%310%19%8%
1893
March1st to 15thNight
53%310%20%11%1
2075
16th to endNight
49%310%23%10%1
2112
April1st to 15thNight
51%310%20%13%
1806
16th to endNight
41%411%21%17%3
1620
May1st to 15thNight
46%411%22%12%2
1620
16th to endNight
36%413%25%15%4
1672
June1st to 15thNight
34%6%12%29%16%1
1302
16th to endNight
35%414%25%18%1
1323
July1st to 15thNight
30%38%31%23%2
1360
16th to endNight
27%5%17%26%20%2
1498
August1st to 15thNight
30%6%13%32%14%2
1609
16th to endNight
31%313%31%17%2
1728
September1st to 15thNight
33%411%30%19%1
1929
16th to endNight
35%411%31%16%
1848
October1st to 15thNight
42%411%23%18%1
1901
16th to endNight
54%411%21%6%
2205
November1st to 15thNight
43%412%24%13%1
2276
16th to endNight
56%313%20%6%
2418
December1st to 15thNight
63%311%14%5%
2544
16th to endNight
69%5%9%10%4
2783

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
18%17%48%13%1
90
16th to endDay
29%6%44%16%3
96
February1st to 15thDay
23%17%43%14%1
90
16th to endDay
18%16%40%19%4
81
March1st to 15thDay
29%10%29%23%6%
174
16th to endDay
23%9%32%22%9%2
288
April1st to 15thDay
21%12%30%24%9%2
270
16th to endDay
22%7%31%21%12%5%
270
May1st to 15thDay
25%6%25%26%11%4
288
16th to endDay
17%8%25%26%16%7%
340
June1st to 15thDay
13%6%31%27%18%3
495
16th to endDay
11%6%31%26%17%5%
495
July1st to 15thDay
11%420%32%21%9%
475
16th to endDay
8%322%32%22%10%
425
August1st to 15thDay
11%115%28%23%19%
313
16th to endDay
14%5%15%23%21%19%
332
September1st to 15thDay
12%419%20%25%18%
315
16th to endDay
16%413%23%29%12%
262
October1st to 15thDay
16%6%23%26%19%7%
255
16th to endDay
25%11%34%21%6%1
179
November1st to 15thDay
10%17%32%23%13%3
90
16th to endDay
23%20%36%14%5%
77
December1st to 15thDay
21%18%40%16%3
60
16th to endDay
21%27%40%10%
79
January1st to 15thNight
26%12%35%20%41
900
16th to endNight
17%12%35%28%5%
861
February1st to 15thNight
21%15%36%22%3
704
16th to endNight
22%12%31%27%5%
631
March1st to 15thNight
22%10%33%25%7%
720
16th to endNight
18%9%31%28%10%1
768
April1st to 15thNight
22%11%32%27%5%1
590
16th to endNight
18%7%34%29%8%2
540
May1st to 15thNight
20%429%33%10%1
540
16th to endNight
14%322%40%16%2
563
June1st to 15thNight
11%223%47%13%
402
16th to endNight
10%223%43%18%1
423
July1st to 15thNight
10%118%39%26%4
510
16th to endNight
5%215%49%23%3
564
August1st to 15thNight
7%116%42%27%5%
539
16th to endNight
11%215%34%30%5%
573
September1st to 15thNight
13%416%33%25%7%
669
16th to endNight
13%416%32%28%4
669
October1st to 15thNight
20%5%22%31%17%2
660
16th to endNight
24%11%32%25%5%
704
November1st to 15thNight
18%10%30%25%14%1
700
16th to endNight
24%15%30%21%7%
720
December1st to 15thNight
24%14%35%21%4
744
16th to endNight
28%12%36%19%2
960
Page generated at 2017-09-19 07:32:26. Version ac04

Copyright 2017 A. Danko


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