3 Herons Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the 3 Herons Observatory clear sky chart from 2005-11-05 to 2017-09-24.

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
30%
14732
11%
46913
8%
14701
34%
14701
14%
35302

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
17%
720
7%
2506
5%
716
20%
716
6%
2092
January16th to endNight
17%
768
7%
2688
4%
768
22%
768
7%
2190
February1st to 15thNight
16%
704
6%
2283
3%
701
20%
701
6%
1949
February16th to endNight
21%
631
10%
1893
6%
631
27%
631
9%
1537
March1st to 15thNight
23%
720
13%
2160
8%
720
29%
720
12%
1667
March16th to endNight
27%
768
17%
2006
8%
768
33%
768
16%
1515
April1st to 15thNight
24%
718
14%
1796
5%
718
29%
718
16%
1404
April16th to endNight
29%
607
15%
1687
6%
607
35%
607
18%
1211
May1st to 15thNight
32%
453
16%
1533
12%
453
39%
453
18%
1038
May16th to endNight
39%
374
11%
1497
12%
374
45%
374
15%
1010
June1st to 15thNight
33%
360
9%
1440
9%
360
40%
360
12%
1034
June16th to endNight
49%
360
8%
1440
12%
360
53%
360
18%
937
July1st to 15thNight
51%
340
10%
1360
15%
340
54%
340
20%
852
July16th to endNight
57%
376
12%
1418
16%
354
60%
354
20%
878
August1st to 15thNight
52%
407
13%
1478
12%
405
54%
405
22%
924
August16th to endNight
55%
741
19%
1887
11%
741
57%
741
33%
1230
September1st to 15thNight
49%
720
13%
1815
8%
720
50%
720
29%
1249
September16th to endNight
49%
693
22%
1913
16%
693
52%
693
31%
1212
October1st to 15thNight
34%
660
16%
1906
10%
660
40%
660
17%
1392
October16th to endNight
23%
704
8%
2272
5%
704
28%
704
10%
1806
November1st to 15thNight
28%
700
15%
2277
12%
700
33%
700
13%
1715
November16th to endNight
21%
720
11%
2450
9%
720
25%
720
9%
1931
December1st to 15thNight
15%
720
4%
2520
2%
720
18%
720
4%
2170
December16th to endNight
12%
768
5%
2688
3%
768
14%
768
4%
2359

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
19%11%47%6%34446%27%
48023
Night
18%12%5%8%6%34445%27%
47083
Cloud CoverDay
17%11%48%6%35%45%6%27%
48033
Night
16%11%5%8%6%34445%27%
47088
TransparencyDay
57%410%18%8%
47711
Night
59%310%17%7%
46913
SeeingDay
26%13%25%20%11%3
5698
Night
25%13%22%26%10%1
14733

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%14%7%13%10%46%5%35%12%
1432
16th to endDay
11%14%7%11%10%36%5%5%5%16%
1536
February1st to 15thDay
11%15%7%15%11%5%6%43315%
1576
16th to endDay
11%16%7%13%10%5%433318%
1580
March1st to 15thDay
15%17%8%8%7%3444422%
1790
16th to endDay
18%14%6%8%6%2323429%
2214
April1st to 15thDay
20%15%47%5%23345%28%
2152
16th to endDay
21%10%36%5%33445%32%
2272
May1st to 15thDay
22%9%46%5%24446%29%
2429
16th to endDay
20%8%36%5%25%6%5%7%28%
2618
June1st to 15thDay
30%6%25%5%3445%6%25%
2520
16th to endDay
21%6%26%5%35%5%6%8%28%
2520
July1st to 15thDay
16%5%25%6%35%5%6%8%32%
2520
16th to endDay
16%5%35%6%36%6%6%8%29%
2654
August1st to 15thDay
18%9%36%5%36%5%5%7%28%
2460
16th to endDay
14%6%345%35%5%5%8%37%
2313
September1st to 15thDay
22%7%14313345%39%
2144
16th to endDay
16%6%14433347%43%
1906
October1st to 15thDay
24%9%37%5%24445%27%
1722
16th to endDay
25%17%45%5%4334321%
1599
November1st to 15thDay
17%17%46%5%35%345%26%
1581
16th to endDay
17%16%6%9%5%35%435%22%
1509
December1st to 15thDay
20%19%8%9%7%3323416%
1440
16th to endDay
20%18%9%14%7%35%32311%
1536
January1st to 15thNight
14%17%7%13%9%46%44413%
2506
16th to endNight
12%16%7%12%8%47%43417%
2688
February1st to 15thNight
13%14%8%17%11%5%5%33313%
2282
16th to endNight
12%16%6%12%9%35%44320%
1893
March1st to 15thNight
18%14%6%8%7%2433327%
2147
16th to endNight
16%14%7%9%42233332%
2006
April1st to 15thNight
22%12%5%8%43433427%
1796
16th to endNight
22%8%35%5%23345%35%
1687
May1st to 15thNight
21%9%36%323347%33%
1533
16th to endNight
20%7%35%435%5%48%32%
1495
June1st to 15thNight
29%6%25%5%24447%26%
1440
16th to endNight
19%6%244246%6%8%33%
1440
July1st to 15thNight
16%5%15%445%6%6%9%34%
1440
16th to endNight
14%4345%36%5%6%8%36%
1514
August1st to 15thNight
14%6%36%5%2445%9%37%
1488
16th to endNight
13%6%3432445%6%44%
1887
September1st to 15thNight
19%5%25%414446%41%
1815
16th to endNight
18%5%13323347%45%
1913
October1st to 15thNight
23%9%36%5%24335%32%
1906
16th to endNight
29%14%26%5%3333421%
2272
November1st to 15thNight
20%15%46%5%24345%26%
2277
16th to endNight
18%15%6%11%6%2433323%
2450
December1st to 15thNight
21%20%8%10%7%3433313%
2520
16th to endNight
18%21%9%12%8%3432311%
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
14%12%7%15%10%47%5%3413%
1432
16th to endDay
11%12%7%11%10%5%6%5%5%5%17%
1536
February1st to 15thDay
10%13%8%14%11%6%6%35%315%
1576
16th to endDay
11%15%7%13%10%6%443318%
1580
March1st to 15thDay
14%15%7%10%7%35%44421%
1800
16th to endDay
17%12%5%10%7%2323429%
2214
April1st to 15thDay
19%14%5%7%5%34245%28%
2152
16th to endDay
20%9%37%5%34345%32%
2272
May1st to 15thDay
21%10%46%5%24445%29%
2429
16th to endDay
19%8%36%5%25%5%6%7%28%
2618
June1st to 15thDay
28%8%25%5%2445%6%24%
2520
16th to endDay
20%7%36%6%345%5%8%28%
2520
July1st to 15thDay
15%6%35%6%35%5%6%7%32%
2520
16th to endDay
16%6%36%5%46%6%6%8%28%
2654
August1st to 15thDay
17%8%37%5%45%5%6%7%28%
2460
16th to endDay
13%7%346%25%5%6%7%36%
2313
September1st to 15thDay
20%7%34423346%39%
2144
16th to endDay
14%8%24424447%42%
1906
October1st to 15thDay
22%10%36%6%2445%428%
1722
16th to endDay
22%19%47%5%3433422%
1599
November1st to 15thDay
16%15%5%6%6%34345%26%
1581
16th to endDay
16%15%7%10%5%34445%22%
1509
December1st to 15thDay
17%18%9%11%8%3433416%
1440
16th to endDay
19%17%9%13%7%35%42311%
1536
January1st to 15thNight
13%13%6%14%10%46%5%5%414%
2506
16th to endNight
10%14%7%12%9%5%7%5%45%17%
2688
February1st to 15thNight
11%13%7%16%12%6%6%44313%
2275
16th to endNight
12%13%6%12%10%35%5%4420%
1893
March1st to 15thNight
16%13%5%9%8%35%33327%
2160
16th to endNight
14%12%6%10%6%2332432%
2005
April1st to 15thNight
19%12%5%8%5%3344427%
1796
16th to endNight
20%9%25%5%3344435%
1687
May1st to 15thNight
20%9%35%423347%34%
1533
16th to endNight
19%7%35%426%5%5%7%32%
1495
June1st to 15thNight
26%8%25%5%34447%27%
1440
16th to endNight
18%6%25%3346%6%8%34%
1440
July1st to 15thNight
15%5%16%5%26%5%6%9%34%
1440
16th to endNight
13%5%25%436%6%6%7%38%
1514
August1st to 15thNight
13%7%35%43445%8%37%
1488
16th to endNight
13%6%3433345%7%44%
1887
September1st to 15thNight
17%6%25%414445%41%
1815
16th to endNight
17%5%23313346%46%
1913
October1st to 15thNight
21%9%37%5%34335%32%
1906
16th to endNight
26%14%47%5%2434422%
2272
November1st to 15thNight
16%15%5%6%6%34445%27%
2277
16th to endNight
16%14%7%11%8%3333323%
2450
December1st to 15thNight
19%17%9%11%8%35%42313%
2520
16th to endNight
15%20%9%12%9%36%33311%
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
75%36%10%3
1433
16th to endDay
67%411%11%4
1536
February1st to 15thDay
73%35%13%2
1579
16th to endDay
70%37%9%7%1
1580
March1st to 15thDay
66%39%13%5%1
1800
16th to endDay
60%37%15%11%1
2214
April1st to 15thDay
59%37%17%10%1
2152
16th to endDay
54%48%19%10%3
2272
May1st to 15thDay
55%47%20%11%
2429
16th to endDay
52%7%10%20%8%1
2622
June1st to 15thDay
58%5%10%17%7%
2520
16th to endDay
52%5%12%20%8%
2520
July1st to 15thDay
45%7%14%23%8%
2371
16th to endDay
49%5%14%22%6%
2487
August1st to 15thDay
52%5%15%19%6%
2446
16th to endDay
42%5%13%26%11%
2313
September1st to 15thDay
46%39%27%11%
2144
16th to endDay
41%412%27%12%1
1906
October1st to 15thDay
57%411%18%8%
1722
16th to endDay
67%39%13%5%
1599
November1st to 15thDay
60%310%16%7%1
1581
16th to endDay
65%49%12%7%
1509
December1st to 15thDay
72%49%10%2
1440
16th to endDay
80%35%5%4
1536
January1st to 15thNight
73%39%8%3
2506
16th to endNight
70%47%11%5%
2688
February1st to 15thNight
75%36%11%3
2283
16th to endNight
68%37%11%7%
1893
March1st to 15thNight
62%38%17%6%1
2160
16th to endNight
57%27%16%13%2
2006
April1st to 15thNight
60%26%17%11%
1796
16th to endNight
51%48%18%14%2
1687
May1st to 15thNight
51%37%20%16%1
1533
16th to endNight
50%6%12%20%9%1
1497
June1st to 15thNight
57%411%18%7%
1440
16th to endNight
45%6%13%23%9%
1440
July1st to 15thNight
41%8%15%25%8%
1360
16th to endNight
42%6%16%23%10%
1418
August1st to 15thNight
43%420%22%8%
1478
16th to endNight
38%416%28%12%
1887
September1st to 15thNight
43%413%28%9%
1815
16th to endNight
39%313%30%12%1
1913
October1st to 15thNight
55%310%21%9%
1906
16th to endNight
66%39%14%5%
2272
November1st to 15thNight
59%410%15%7%2
2277
16th to endNight
66%38%14%5%
2450
December1st to 15thNight
77%37%10%1
2520
16th to endNight
79%37%7%2
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
16%33%23%20%6%
60
16th to endDay
32%23%23%20%
64
February1st to 15thDay
23%29%30%12%4
124
16th to endDay
25%17%30%18%6%
239
March1st to 15thDay
30%18%24%23%3
270
16th to endDay
26%18%26%14%11%2
288
April1st to 15thDay
33%13%24%20%7%1
270
16th to endDay
28%17%24%15%10%4
270
May1st to 15thDay
34%11%27%12%9%4
288
16th to endDay
25%16%27%22%6%1
331
June1st to 15thDay
36%10%25%17%9%
315
16th to endDay
22%14%29%23%9%
315
July1st to 15thDay
21%9%27%27%10%3
305
16th to endDay
16%7%32%27%12%3
326
August1st to 15thDay
23%9%24%24%12%4
313
16th to endDay
20%8%18%22%20%9%
332
September1st to 15thDay
22%6%21%19%19%10%
315
16th to endDay
15%9%20%20%19%13%
287
October1st to 15thDay
25%10%20%20%18%4
255
16th to endDay
39%14%18%20%7%
243
November1st to 15thDay
28%12%20%25%11%1
235
16th to endDay
29%18%25%14%10%
129
December1st to 15thDay
31%13%33%20%1
60
16th to endDay
39%21%32%6%
64
January1st to 15thNight
23%19%29%24%3
720
16th to endNight
23%17%30%23%4
768
February1st to 15thNight
20%19%33%24%3
704
16th to endNight
21%20%27%25%5%
631
March1st to 15thNight
29%15%25%25%4
720
16th to endNight
26%16%24%21%9%1
768
April1st to 15thNight
30%15%23%24%6%
718
16th to endNight
27%14%23%23%10%
607
May1st to 15thNight
26%12%24%22%12%1
453
16th to endNight
21%8%24%33%10%1
375
June1st to 15thNight
31%6%19%26%14%1
360
16th to endNight
20%5%18%40%13%
360
July1st to 15thNight
12%321%36%23%2
340
16th to endNight
14%317%46%18%
376
August1st to 15thNight
19%414%37%22%1
407
16th to endNight
17%415%33%26%3
741
September1st to 15thNight
22%6%15%34%19%2
720
16th to endNight
21%5%18%25%22%5%
693
October1st to 15thNight
28%11%16%26%14%1
660
16th to endNight
37%12%20%21%7%
704
November1st to 15thNight
28%13%22%24%8%1
700
16th to endNight
30%16%23%17%10%1
720
December1st to 15thNight
32%20%23%18%4
720
16th to endNight
28%20%27%19%3
768
Page generated at 2017-09-25 09:02:20. Version ac04

Copyright 2017 A. Danko


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