Holiday
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Holiday clear sky chart from 2005-11-05 to 2017-09-20.

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
64%
15839
20%
46995
18%
15800
67%
15800
30%
29398

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
49%
716
19%
2327
15%
716
56%
716
24%
1469
January16th to endNight
49%
768
23%
2385
18%
768
55%
768
27%
1488
February1st to 15thNight
52%
701
24%
2103
19%
698
58%
698
33%
1254
February16th to endNight
50%
631
24%
1876
15%
631
58%
631
31%
1139
March1st to 15thNight
56%
720
28%
1980
19%
720
63%
720
39%
1170
March16th to endNight
61%
768
27%
2112
21%
768
65%
768
39%
1233
April1st to 15thNight
68%
718
23%
1976
19%
718
70%
718
43%
1112
April16th to endNight
66%
678
27%
1853
20%
678
69%
678
41%
1076
May1st to 15thNight
78%
539
26%
1619
22%
539
80%
539
44%
862
May16th to endNight
78%
561
24%
1682
21%
561
79%
561
39%
964
June1st to 15thNight
71%
540
13%
1620
12%
540
71%
540
26%
1093
June16th to endNight
77%
540
10%
1620
9%
540
77%
540
25%
1103
July1st to 15thNight
75%
510
7%
1530
7%
510
75%
510
22%
1092
July16th to endNight
77%
564
7%
1595
6%
531
78%
531
22%
1135
August1st to 15thNight
79%
539
5%
1691
5%
536
79%
536
23%
1161
August16th to endNight
71%
677
9%
2014
10%
677
71%
677
21%
1438
September1st to 15thNight
67%
720
7%
1980
7%
720
67%
720
18%
1483
September16th to endNight
66%
677
15%
1870
14%
677
67%
677
23%
1327
October1st to 15thNight
73%
660
27%
1834
27%
660
74%
660
35%
1129
October16th to endNight
62%
704
27%
2112
27%
704
66%
704
34%
1249
November1st to 15thNight
66%
700
30%
2101
30%
700
69%
700
38%
1192
November16th to endNight
57%
720
28%
2279
24%
720
65%
720
34%
1315
December1st to 15thNight
58%
720
25%
2340
25%
720
61%
720
29%
1408
December16th to endNight
58%
768
23%
2496
23%
768
62%
768
29%
1506

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
8%425%5%36%6%7%9%39%
47823
Night
7%425%5%35%5%6%9%44%
47204
TransparencyDay
37%10%15%17%14%5%
47524
Night
34%9%16%20%15%5%
47007
SeeingDay
8%19%21%29%28%
5706
Night
9%214%31%30%11%
15849

By Month

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
11%6%25%425%47%10%39%
1611
16th to endDay
10%6%233235%6%5%48%
1838
February1st to 15thDay
13%5%25%42345%6%46%
1750
16th to endDay
7%42443435%7%51%
1595
March1st to 15thDay
6%32343345%8%53%
1980
16th to endDay
7%4245%245%5%7%51%
2111
April1st to 15thDay
6%315%5%35%5%7%9%47%
1972
16th to endDay
6%2145%2445%8%53%
2115
May1st to 15thDay
5%31322446%8%56%
2331
16th to endDay
6%3246%36%5%8%10%42%
2431
June1st to 15thDay
10%426%5%46%7%9%11%30%
2340
16th to endDay
5%5%36%6%47%8%9%12%28%
2340
July1st to 15thDay
6%5%37%7%48%10%11%11%23%
2340
16th to endDay
6%427%7%5%10%10%10%11%21%
2465
August1st to 15thDay
7%426%8%5%9%10%9%13%22%
2253
16th to endDay
9%5%27%8%48%7%9%10%24%
2175
September1st to 15thDay
9%5%37%7%47%8%10%10%23%
1980
16th to endDay
9%6%27%7%5%7%8%8%10%26%
1859
October1st to 15thDay
6%425%5%46%5%7%8%42%
1794
16th to endDay
8%415%6%2445%8%48%
1760
November1st to 15thDay
6%414335%5%5%7%52%
1757
16th to endDay
8%325%5%245%6%8%47%
1678
December1st to 15thDay
9%5%36%425%45%8%43%
1620
16th to endDay
6%425%5%345%7%9%45%
1728
January1st to 15thNight
11%6%36%325%5%5%8%39%
2327
16th to endNight
12%5%25%43446%8%42%
2385
February1st to 15thNight
10%7%1432335%6%49%
2103
16th to endNight
8%5%36%424348%47%
1876
March1st to 15thNight
5%425%434447%53%
1980
16th to endNight
7%3143245%5%6%55%
2112
April1st to 15thNight
6%21432446%10%52%
1976
16th to endNight
6%2145%24447%55%
1853
May1st to 15thNight
431342345%9%56%
1619
16th to endNight
4224425%47%9%52%
1682
June1st to 15thNight
10%425%6%35%5%6%10%38%
1620
16th to endNight
5%426%5%37%6%9%14%35%
1620
July1st to 15thNight
5%416%6%36%8%10%14%32%
1620
16th to endNight
4425%6%5%7%8%9%13%30%
1703
August1st to 15thNight
43146%5%6%8%10%15%31%
1702
16th to endNight
7%5%25%6%46%7%7%11%33%
2014
September1st to 15thNight
7%5%36%7%47%8%8%11%27%
1980
16th to endNight
8%6%36%6%46%5%8%10%32%
1870
October1st to 15thNight
6%4235%345%6%9%48%
1834
16th to endNight
8%6%25%42435%7%49%
2112
November1st to 15thNight
6%323425%45%7%53%
2101
16th to endNight
7%425%33446%8%48%
2279
December1st to 15thNight
10%424425%5%5%9%45%
2340
16th to endNight
7%5%26%5%345%6%8%44%
2496

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
38%7%10%20%18%5%
1612
16th to endDay
34%6%8%18%25%7%
1838
February1st to 15thDay
37%48%14%21%13%
1752
16th to endDay
30%6%13%16%22%11%
1595
March1st to 15thDay
27%5%13%25%21%7%
1980
16th to endDay
30%7%10%22%20%8%
2112
April1st to 15thDay
30%8%13%17%22%6%
1972
16th to endDay
27%6%11%22%24%6%
2115
May1st to 15thDay
24%7%14%26%19%7%
2331
16th to endDay
33%10%13%23%16%2
2435
June1st to 15thDay
42%14%17%20%5%
2340
16th to endDay
42%17%20%15%3
2340
July1st to 15thDay
47%18%24%8%1
2201
16th to endDay
47%19%20%10%1
2310
August1st to 15thDay
45%20%25%8%
2240
16th to endDay
48%17%20%12%
2175
September1st to 15thDay
48%17%20%10%3
1980
16th to endDay
47%13%14%16%6%1
1859
October1st to 15thDay
36%9%11%16%16%10%
1794
16th to endDay
32%5%9%15%23%11%
1760
November1st to 15thDay
28%5%9%24%22%8%
1757
16th to endDay
32%7%11%18%19%11%
1678
December1st to 15thDay
37%6%12%20%18%4
1620
16th to endDay
33%5%13%20%19%6%
1728
January1st to 15thNight
39%7%11%20%16%3
2327
16th to endNight
38%5%9%17%20%7%
2385
February1st to 15thNight
34%49%17%22%12%
2112
16th to endNight
35%5%13%16%22%7%
1876
March1st to 15thNight
29%5%11%27%18%7%
1980
16th to endNight
27%7%10%26%19%8%
2112
April1st to 15thNight
26%5%17%23%22%5%
1976
16th to endNight
28%5%11%25%23%5%
1853
May1st to 15thNight
23%5%14%29%18%6%
1620
16th to endNight
25%9%19%25%17%3
1684
June1st to 15thNight
38%11%21%21%6%
1620
16th to endNight
35%15%24%19%5%
1620
July1st to 15thNight
37%17%32%10%2
1530
16th to endNight
36%18%30%12%1
1595
August1st to 15thNight
34%18%35%10%
1691
16th to endNight
40%15%26%15%1
2014
September1st to 15thNight
45%15%23%12%2
1980
16th to endNight
42%12%18%18%6%2
1870
October1st to 15thNight
30%9%12%19%20%8%
1834
16th to endNight
34%49%17%25%9%
2112
November1st to 15thNight
28%6%9%22%24%8%
2101
16th to endNight
31%6%10%22%17%12%
2279
December1st to 15thNight
35%6%11%25%15%4
2340
16th to endNight
35%7%13%20%17%6%
2496

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
11%328%28%21%6%
90
16th to endDay
14%11%26%28%17%2
96
February1st to 15thDay
8%7%26%22%24%10%
90
16th to endDay
5%5%30%37%18%3
96
March1st to 15thDay
7%322%42%19%3
270
16th to endDay
9%219%32%30%5%
288
April1st to 15thDay
6%220%31%32%6%
270
16th to endDay
6%12%28%39%12%
270
May1st to 15thDay
6%11%28%32%19%
288
16th to endDay
7%416%36%35%
331
June1st to 15thDay
13%229%30%40%
315
16th to endDay
4117%28%55%
315
July1st to 15thDay
5%1420%68%
305
16th to endDay
11%19%24%52%
326
August1st to 15thDay
8%12424%58%
313
16th to endDay
10%28%26%51%
332
September1st to 15thDay
13%212%31%39%
315
16th to endDay
12%39%40%33%
270
October1st to 15thDay
8%18%25%42%14%
255
16th to endDay
11%11%33%30%11%
272
November1st to 15thDay
5%212%35%33%10%
265
16th to endDay
8%212%39%31%6%
148
December1st to 15thDay
8%125%42%22%
90
16th to endDay
5%310%31%39%10%
96
January1st to 15thNight
14%5%22%34%22%1
720
16th to endNight
14%426%34%19%
768
February1st to 15thNight
12%425%40%17%
704
16th to endNight
9%427%42%14%
631
March1st to 15thNight
7%325%46%17%
720
16th to endNight
8%222%43%20%1
768
April1st to 15thNight
6%216%45%25%2
718
16th to endNight
7%217%41%29%
678
May1st to 15thNight
48%43%35%5%
540
16th to endNight
5%8%33%40%11%
563
June1st to 15thNight
12%1419%43%18%
540
16th to endNight
5%211%42%37%
540
July1st to 15thNight
7%15%38%45%
510
16th to endNight
5%27%38%45%
564
August1st to 15thNight
6%26%41%43%
539
16th to endNight
8%312%42%32%
677
September1st to 15thNight
10%5%16%42%25%
720
16th to endNight
10%15%21%48%13%
677
October1st to 15thNight
8%9%32%40%7%
660
16th to endNight
11%215%32%34%3
704
November1st to 15thNight
6%117%43%27%4
700
16th to endNight
8%323%40%22%1
720
December1st to 15thNight
11%321%37%25%
720
16th to endNight
9%319%37%27%1
768
Page generated at 2017-09-21 07:18:11. Version ac04

Copyright 2017 A. Danko


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