This page made possible by the sponsorship of: Jerry Spevak.

Heartwood Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Heartwood Observatory clear sky chart from 2005-11-05 to 2017-09-10.

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%
14745
13%
46685
8%
14711
35%
14711
16%
33207

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
8%
2503
2%
716
19%
716
6%
2012
January16th to endNight
17%
768
10%
2496
4%
768
24%
768
8%
1993
February1st to 15thNight
14%
701
9%
2287
4%
701
21%
701
9%
1804
February16th to endNight
16%
631
12%
2024
4%
631
26%
631
11%
1515
March1st to 15thNight
17%
720
14%
1980
4%
720
25%
720
14%
1484
March16th to endNight
26%
768
20%
2112
9%
768
35%
768
23%
1422
April1st to 15thNight
22%
718
15%
1808
5%
718
27%
718
19%
1337
April16th to endNight
29%
569
19%
1649
8%
569
37%
569
24%
1109
May1st to 15thNight
39%
465
16%
1545
11%
465
47%
465
21%
1023
May16th to endNight
38%
374
16%
1497
13%
374
49%
374
24%
845
June1st to 15thNight
39%
360
11%
1440
11%
360
48%
360
19%
881
June16th to endNight
46%
360
12%
1333
14%
360
51%
360
24%
797
July1st to 15thNight
57%
340
16%
1333
21%
340
63%
340
31%
708
July16th to endNight
52%
455
16%
1491
14%
427
58%
427
29%
867
August1st to 15thNight
57%
539
17%
1609
11%
536
62%
536
35%
942
August16th to endNight
54%
629
21%
1775
11%
629
59%
629
33%
1088
September1st to 15thNight
46%
700
17%
1750
8%
700
50%
700
32%
1165
September16th to endNight
49%
657
20%
1839
14%
657
52%
657
29%
1188
October1st to 15thNight
32%
660
16%
1980
11%
660
38%
660
19%
1395
October16th to endNight
18%
704
11%
2112
4%
704
27%
704
11%
1642
November1st to 15thNight
27%
700
17%
2394
15%
700
34%
700
15%
1669
November16th to endNight
20%
720
10%
2520
6%
720
26%
720
9%
1966
December1st to 15thNight
10%
720
5%
2520
1%
720
15%
720
6%
2102
December16th to endNight
10%
768
6%
2688
1%
768
16%
768
5%
2253

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
15%9%47%6%35%45%6%31%
47924
Night
14%9%47%6%34446%32%
46862
Cloud CoverDay
15%9%37%6%35%45%7%31%
47934
Night
15%9%47%6%34446%32%
46867
TransparencyDay
51%6%11%18%10%
47619
Night
51%6%11%19%10%
46685
SeeingDay
19%13%30%21%10%4
5436
Night
20%13%30%24%9%1
14750

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%13%6%11%7%45%445%20%
1433
16th to endDay
12%14%7%12%8%45%45%5%18%
1728
February1st to 15thDay
12%16%6%12%8%45%5%45%20%
1575
16th to endDay
16%13%6%10%8%35%34423%
1444
March1st to 15thDay
14%11%48%7%35%45%5%29%
1969
16th to endDay
14%9%445%44436%38%
2112
April1st to 15thDay
20%9%36%5%34445%31%
2140
16th to endDay
16%9%35%5%23347%38%
2322
May1st to 15thDay
15%7%36%5%35%5%47%35%
2406
16th to endDay
13%6%245%35%46%7%40%
2618
June1st to 15thDay
17%6%25%4345%6%7%34%
2520
16th to endDay
13%5%25%6%35%5%7%9%35%
2618
July1st to 15thDay
9%425%5%36%5%6%8%41%
2538
16th to endDay
9%5%26%6%46%5%7%10%35%
2573
August1st to 15thDay
9%5%35%6%345%7%9%37%
2340
16th to endDay
11%6%15%435%5%6%8%39%
2414
September1st to 15thDay
16%5%25%435%45%7%37%
2098
16th to endDay
15%5%36%5%34346%41%
1789
October1st to 15thDay
19%9%36%6%44445%31%
1650
16th to endDay
26%12%48%5%3444421%
1760
November1st to 15thDay
14%11%5%7%6%4345%6%29%
1461
16th to endDay
17%14%5%8%7%36%5%5%5%19%
1440
December1st to 15thDay
16%17%7%11%8%345%5%5%15%
1440
16th to endDay
18%15%7%11%7%35%5%46%13%
1536
January1st to 15thNight
17%15%6%9%8%5%4445%17%
2503
16th to endNight
14%14%6%10%9%36%45%5%18%
2496
February1st to 15thNight
12%14%6%10%8%46%5%4420%
2285
16th to endNight
13%11%5%9%8%45%445%26%
2024
March1st to 15thNight
16%11%5%7%6%3434432%
1968
16th to endNight
14%8%45%5%23445%41%
2112
April1st to 15thNight
19%9%45%5%34346%33%
1808
16th to endNight
14%7%36%5%23447%39%
1649
May1st to 15thNight
16%5%25%5%3346%7%37%
1545
16th to endNight
11%4243345%6%7%46%
1495
June1st to 15thNight
14%5%25%5%3445%8%39%
1440
16th to endNight
10%6%25%425%46%8%42%
1333
July1st to 15thNight
6%325%424447%52%
1413
16th to endNight
8%425%5%245%6%9%46%
1593
August1st to 15thNight
6%4245%346%5%8%49%
1620
16th to endNight
7%5%15%5%2445%6%49%
1775
September1st to 15thNight
14%6%35%433347%43%
1750
16th to endNight
13%7%25%333336%45%
1839
October1st to 15thNight
17%7%36%5%345%36%35%
1980
16th to endNight
22%10%48%5%34447%23%
2112
November1st to 15thNight
17%9%37%43435%6%32%
2394
16th to endNight
19%12%5%8%7%35%5%5%6%21%
2520
December1st to 15thNight
18%15%6%10%7%45%5%45%16%
2520
16th to endNight
19%14%7%12%8%345%4414%
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
16%13%6%10%7%445%45%20%
1433
16th to endDay
13%13%7%12%8%45%45%5%18%
1728
February1st to 15thDay
12%14%7%11%8%45%45%420%
1575
16th to endDay
15%14%5%10%7%3443424%
1444
March1st to 15thDay
14%10%48%7%35%445%29%
1980
16th to endDay
15%9%445%44346%38%
2111
April1st to 15thDay
20%9%36%5%24345%31%
2140
16th to endDay
17%8%35%5%22447%38%
2322
May1st to 15thDay
16%7%36%6%345%47%34%
2406
16th to endDay
13%6%245%35%5%5%7%40%
2618
June1st to 15thDay
17%7%25%435%46%7%34%
2520
16th to endDay
13%5%35%5%25%6%6%9%35%
2618
July1st to 15thDay
9%5%25%5%36%6%6%8%40%
2538
16th to endDay
9%5%36%5%37%5%7%10%34%
2573
August1st to 15thDay
9%6%25%7%35%5%6%9%37%
2340
16th to endDay
12%6%25%435%6%7%8%39%
2414
September1st to 15thDay
17%6%25%5%35%45%7%36%
2098
16th to endDay
15%6%26%5%34446%41%
1789
October1st to 15thDay
20%9%36%6%34445%31%
1650
16th to endDay
25%13%47%6%3444422%
1760
November1st to 15thDay
15%11%46%7%2445%6%30%
1461
16th to endDay
17%15%5%9%6%45%5%5%5%19%
1440
December1st to 15thDay
17%17%5%11%8%4445%5%15%
1440
16th to endDay
19%15%7%10%6%35%446%14%
1536
January1st to 15thNight
16%15%6%9%8%35%445%18%
2503
16th to endNight
14%14%7%10%8%45%5%5%5%19%
2496
February1st to 15thNight
12%14%7%9%8%5%6%445%21%
2278
16th to endNight
13%11%5%10%8%45%5%45%26%
2024
March1st to 15thNight
16%11%5%7%7%3434432%
1980
16th to endNight
13%8%35%423445%42%
2112
April1st to 15thNight
19%9%36%5%34346%33%
1808
16th to endNight
14%8%36%5%325%47%39%
1649
May1st to 15thNight
16%5%26%5%345%5%8%37%
1545
16th to endNight
11%4243245%7%7%46%
1495
June1st to 15thNight
14%5%245%35%45%8%40%
1440
16th to endNight
10%6%25%5%25%45%8%43%
1333
July1st to 15thNight
6%315%42445%7%52%
1413
16th to endNight
8%4245%346%6%8%46%
1593
August1st to 15thNight
6%4145%245%6%8%49%
1620
16th to endNight
7%425%5%3445%7%49%
1775
September1st to 15thNight
14%6%3442435%7%43%
1750
16th to endNight
13%6%35%324436%45%
1839
October1st to 15thNight
18%7%26%5%345%45%36%
1980
16th to endNight
22%10%48%5%35%446%24%
2112
November1st to 15thNight
17%9%36%43445%7%33%
2394
16th to endNight
19%12%5%8%6%35%5%46%21%
2520
December1st to 15thNight
18%15%6%10%8%45%5%4417%
2520
16th to endNight
19%13%7%12%7%345%45%15%
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
65%5%10%12%5%
1434
16th to endDay
66%5%8%10%7%
1728
February1st to 15thDay
66%5%8%14%4
1577
16th to endDay
63%410%13%7%
1444
March1st to 15thDay
58%5%12%16%6%
1980
16th to endDay
49%49%17%17%2
2112
April1st to 15thDay
55%5%8%18%11%
2140
16th to endDay
45%5%10%20%15%1
2322
May1st to 15thDay
49%6%10%19%13%
2406
16th to endDay
42%7%12%21%13%1
2622
June1st to 15thDay
47%6%13%21%11%
2520
16th to endDay
44%6%15%20%12%
2618
July1st to 15thDay
38%7%12%24%15%1
2389
16th to endDay
43%8%12%22%10%1
2412
August1st to 15thDay
42%8%14%20%12%1
2327
16th to endDay
40%8%13%25%11%1
2414
September1st to 15thDay
45%6%13%23%9%
2098
16th to endDay
44%7%11%27%9%
1789
October1st to 15thDay
54%5%10%18%9%
1650
16th to endDay
65%412%12%5%
1760
November1st to 15thDay
54%6%13%16%8%1
1461
16th to endDay
65%7%11%10%4
1440
December1st to 15thDay
69%7%13%8%1
1440
16th to endDay
70%7%8%10%2
1536
January1st to 15thNight
67%5%9%10%5%1
2503
16th to endNight
64%6%8%13%5%
2496
February1st to 15thNight
64%5%9%15%5%
2287
16th to endNight
58%5%11%17%7%
2024
March1st to 15thNight
56%411%19%7%
1980
16th to endNight
44%410%21%16%1
2112
April1st to 15thNight
51%49%19%14%
1808
16th to endNight
43%5%10%18%18%2
1649
May1st to 15thNight
45%6%10%20%15%2
1545
16th to endNight
35%7%13%26%15%2
1497
June1st to 15thNight
42%5%12%23%15%
1440
16th to endNight
38%6%14%24%15%
1333
July1st to 15thNight
29%6%10%30%22%1
1333
16th to endNight
33%7%12%29%15%1
1491
August1st to 15thNight
30%7%19%27%14%
1609
16th to endNight
33%6%13%29%16%1
1775
September1st to 15thNight
38%5%16%25%13%
1750
16th to endNight
39%5%10%30%13%
1839
October1st to 15thNight
49%6%11%20%12%
1980
16th to endNight
59%7%11%13%7%
2112
November1st to 15thNight
50%6%12%17%11%1
2394
16th to endNight
61%7%13%12%4
2520
December1st to 15thNight
68%7%10%10%2
2520
16th to endNight
71%6%9%9%3
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
18%37%26%16%1
61
16th to endDay
31%18%37%10%2
96
February1st to 15thDay
21%36%36%5%
90
16th to endDay
29%24%36%7%2
97
March1st to 15thDay
24%22%31%18%4
270
16th to endDay
25%16%31%18%6%2
288
April1st to 15thDay
26%16%34%14%7%1
270
16th to endDay
19%18%28%19%9%4
270
May1st to 15thDay
24%11%27%22%9%5%
288
16th to endDay
17%12%36%20%9%3
331
June1st to 15thDay
24%10%27%28%8%
315
16th to endDay
15%8%37%24%9%3
413
July1st to 15thDay
13%6%28%27%17%7%
323
16th to endDay
9%8%30%30%12%7%
326
August1st to 15thDay
10%8%25%26%16%12%
313
16th to endDay
17%5%24%24%16%12%
332
September1st to 15thDay
12%5%29%23%17%11%
294
16th to endDay
18%6%23%28%15%8%
254
October1st to 15thDay
21%10%34%18%10%4
255
16th to endDay
32%16%30%16%4
272
November1st to 15thDay
20%13%34%22%7%2
94
16th to endDay
31%25%28%15%
60
December1st to 15thDay
21%38%25%10%5%
60
16th to endDay
32%39%28%
64
January1st to 15thNight
25%22%31%14%4
720
16th to endNight
22%16%32%22%5%
768
February1st to 15thNight
21%19%36%19%2
704
16th to endNight
21%20%35%17%3
631
March1st to 15thNight
23%20%33%18%3
720
16th to endNight
18%13%36%22%7%1
768
April1st to 15thNight
24%16%32%22%4
718
16th to endNight
18%13%32%25%9%
569
May1st to 15thNight
19%6%28%30%11%2
465
16th to endNight
13%5%35%29%14%1
375
June1st to 15thNight
14%10%28%33%12%
360
16th to endNight
11%5%31%39%12%
360
July1st to 15thNight
8%326%43%17%1
340
16th to endNight
9%327%37%21%
455
August1st to 15thNight
8%322%37%25%2
539
16th to endNight
9%425%33%23%3
629
September1st to 15thNight
18%5%24%28%19%4
700
16th to endNight
17%5%22%32%18%3
657
October1st to 15thNight
23%9%30%23%11%1
660
16th to endNight
27%18%30%17%5%
704
November1st to 15thNight
23%14%29%23%8%1
700
16th to endNight
26%16%28%21%6%
720
December1st to 15thNight
27%20%33%13%3
720
16th to endNight
28%17%35%15%2
768
Page generated at 2017-09-11 19:35:20. Version ac04

Copyright 2017 A. Danko


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