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 2018-11-30.

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
65%
17448
21%
51767
18%
17409
68%
17409
30%
32304

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
48%
776
19%
2522
15%
776
55%
776
25%
1592
January16th to endNight
49%
832
24%
2584
20%
832
55%
832
27%
1606
February1st to 15thNight
53%
761
23%
2283
18%
758
59%
758
32%
1383
February16th to endNight
52%
683
25%
2031
17%
683
60%
683
33%
1214
March1st to 15thNight
56%
780
28%
2145
19%
780
63%
780
39%
1259
March16th to endNight
62%
832
28%
2288
21%
832
66%
832
41%
1309
April1st to 15thNight
67%
778
23%
2141
19%
778
69%
778
42%
1216
April16th to endNight
66%
726
27%
1983
20%
726
69%
726
42%
1142
May1st to 15thNight
77%
584
26%
1754
23%
584
79%
584
43%
945
May16th to endNight
76%
609
22%
1826
19%
609
77%
609
35%
1083
June1st to 15thNight
72%
585
14%
1755
12%
585
72%
585
26%
1170
June16th to endNight
77%
585
9%
1755
8%
585
77%
585
24%
1205
July1st to 15thNight
76%
555
7%
1665
6%
555
76%
555
23%
1183
July16th to endNight
75%
612
6%
1739
6%
579
76%
579
20%
1255
August1st to 15thNight
79%
575
5%
1801
6%
572
79%
572
22%
1242
August16th to endNight
70%
734
9%
2183
10%
734
70%
734
20%
1574
September1st to 15thNight
68%
780
7%
2145
7%
780
68%
780
18%
1605
September16th to endNight
68%
777
16%
2145
16%
777
69%
777
24%
1498
October1st to 15thNight
72%
780
27%
2168
27%
780
74%
780
34%
1334
October16th to endNight
63%
832
28%
2496
28%
832
67%
832
35%
1446
November1st to 15thNight
67%
820
28%
2461
28%
820
71%
820
38%
1390
November16th to endNight
58%
840
28%
2658
25%
840
66%
840
34%
1532
December1st to 15thNight
59%
780
25%
2535
24%
780
63%
780
30%
1505
December16th to endNight
60%
832
23%
2704
24%
832
64%
832
29%
1616

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
7%425%5%35%6%7%9%40%
52517
Night
7%425%5%35%5%6%9%44%
51976
TransparencyDay
36%11%15%17%14%5%
52218
Night
33%9%16%20%15%5%
51779
SeeingDay
8%110%21%30%27%
7317
Night
8%214%31%31%11%
17458

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%
1746
16th to endDay
9%6%243235%6%5%48%
1991
February1st to 15thDay
13%5%25%42345%7%45%
1900
16th to endDay
7%41442445%7%52%
1726
March1st to 15thDay
6%32342345%8%54%
2145
16th to endDay
7%4234235%5%7%52%
2287
April1st to 15thDay
6%315%435%5%7%9%48%
2137
16th to endDay
6%2145%2445%8%54%
2261
May1st to 15thDay
6%31332446%8%55%
2526
16th to endDay
8%3246%36%5%8%10%40%
2639
June1st to 15thDay
9%426%5%46%8%9%11%30%
2535
16th to endDay
5%5%36%6%47%9%9%13%28%
2535
July1st to 15thDay
6%5%27%7%48%10%11%12%23%
2535
16th to endDay
7%5%27%8%5%9%10%10%11%21%
2673
August1st to 15thDay
7%427%7%5%9%10%9%13%23%
2396
16th to endDay
9%5%27%8%49%7%9%10%25%
2357
September1st to 15thDay
8%437%7%48%8%10%10%24%
2145
16th to endDay
8%6%27%7%46%8%8%10%28%
2145
October1st to 15thDay
5%426%6%46%6%7%8%40%
2120
16th to endDay
7%415%6%2435%8%50%
2080
November1st to 15thDay
6%4144345%5%7%52%
2057
16th to endDay
8%325%5%3446%7%47%
1954
December1st to 15thDay
8%5%36%43445%8%44%
1755
16th to endDay
6%425%5%3446%9%46%
1872
January1st to 15thNight
11%6%35%335%5%5%8%39%
2522
16th to endNight
12%5%25%43446%8%42%
2584
February1st to 15thNight
10%7%1432445%6%48%
2283
16th to endNight
7%5%35%423348%48%
2031
March1st to 15thNight
5%425%434447%54%
2145
16th to endNight
6%31432445%7%56%
2288
April1st to 15thNight
6%22442446%9%51%
2141
16th to endNight
6%2145%24447%56%
1983
May1st to 15thNight
5%31342345%9%56%
1754
16th to endNight
5%324425%47%10%49%
1826
June1st to 15thNight
9%425%5%35%5%6%11%39%
1755
16th to endNight
5%416%5%37%7%9%14%34%
1755
July1st to 15thNight
5%416%6%36%8%10%14%32%
1755
16th to endNight
45%25%6%5%7%8%9%13%29%
1847
August1st to 15thNight
44147%46%8%10%15%31%
1812
16th to endNight
7%6%25%6%47%7%8%11%32%
2183
September1st to 15thNight
7%436%7%47%8%8%11%28%
2145
16th to endNight
7%5%26%7%46%6%8%11%33%
2145
October1st to 15thNight
5%4245%345%6%9%48%
2168
16th to endNight
7%5%25%42435%7%50%
2496
November1st to 15thNight
5%31342445%7%54%
2461
16th to endNight
7%425%43445%8%48%
2658
December1st to 15thNight
9%424425%5%5%9%46%
2535
16th to endNight
7%5%25%5%345%6%8%45%
2704

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%11%19%18%4
1747
16th to endDay
34%6%8%18%24%7%
1991
February1st to 15thDay
37%5%9%14%19%12%
1902
16th to endDay
29%6%13%16%23%10%
1726
March1st to 15thDay
26%5%13%24%21%9%
2145
16th to endDay
29%7%10%22%21%8%
2288
April1st to 15thDay
29%9%13%18%22%6%
2137
16th to endDay
27%6%12%22%25%6%
2261
May1st to 15thDay
26%7%13%24%20%7%
2526
16th to endDay
35%10%13%21%15%2
2643
June1st to 15thDay
41%14%18%20%4
2535
16th to endDay
41%17%22%14%3
2535
July1st to 15thDay
46%19%25%7%1
2396
16th to endDay
47%20%20%10%1
2518
August1st to 15thDay
44%20%25%8%
2383
16th to endDay
47%18%21%12%
2357
September1st to 15thDay
47%18%21%10%3
2145
16th to endDay
44%13%15%19%5%1
2145
October1st to 15thDay
37%9%11%17%15%8%
2120
16th to endDay
31%5%9%16%23%12%
2080
November1st to 15thDay
28%6%11%24%21%7%
2057
16th to endDay
32%7%10%20%19%10%
1954
December1st to 15thDay
36%6%12%22%17%4
1755
16th to endDay
33%5%13%21%18%6%
1872
January1st to 15thNight
39%7%11%20%17%3
2522
16th to endNight
38%5%9%17%21%7%
2584
February1st to 15thNight
34%5%11%16%21%11%
2292
16th to endNight
33%5%12%16%23%7%
2031
March1st to 15thNight
29%5%11%25%19%8%
2145
16th to endNight
26%6%11%27%19%8%
2288
April1st to 15thNight
26%5%17%23%21%5%
2141
16th to endNight
27%5%12%25%24%5%
1983
May1st to 15thNight
24%5%14%28%19%6%
1755
16th to endNight
27%10%19%23%15%2
1828
June1st to 15thNight
36%11%22%22%6%
1755
16th to endNight
35%16%25%18%4
1755
July1st to 15thNight
36%17%33%9%2
1665
16th to endNight
37%19%29%12%1
1739
August1st to 15thNight
34%19%34%10%
1801
16th to endNight
40%16%25%15%1
2183
September1st to 15thNight
44%16%24%11%2
2145
16th to endNight
40%12%19%20%6%2
2145
October1st to 15thNight
29%10%12%21%18%7%
2168
16th to endNight
32%410%18%25%9%
2496
November1st to 15thNight
28%6%11%22%23%7%
2461
16th to endNight
31%6%9%22%18%10%
2658
December1st to 15thNight
34%6%11%26%16%4
2535
16th to endNight
34%7%13%21%16%6%
2704

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
12%5%28%30%17%4
135
16th to endDay
13%9%23%36%15%1
144
February1st to 15thDay
6%5%22%28%27%9%
135
16th to endDay
3322%33%25%11%
136
March1st to 15thDay
6%428%40%18%2
330
16th to endDay
9%219%34%29%4
352
April1st to 15thDay
5%219%31%33%6%
330
16th to endDay
5%13%31%37%10%
319
May1st to 15thDay
8%11%28%34%16%
348
16th to endDay
11%5%16%34%31%
395
June1st to 15thDay
12%129%32%40%
375
16th to endDay
5%116%28%56%
375
July1st to 15thDay
5%1421%67%
365
16th to endDay
11%210%26%48%
390
August1st to 15thDay
8%115%25%57%
358
16th to endDay
9%27%25%54%
396
September1st to 15thDay
11%212%32%40%
375
16th to endDay
10%28%39%37%
374
October1st to 15thDay
7%19%24%42%14%
375
16th to endDay
10%112%34%30%12%
400
November1st to 15thDay
4211%33%37%10%
385
16th to endDay
7%214%38%31%4
246
December1st to 15thDay
6%426%36%22%2
135
16th to endDay
329%34%40%10%
144
January1st to 15thNight
14%5%23%33%21%1
780
16th to endNight
14%426%36%18%
832
February1st to 15thNight
12%424%40%18%
764
16th to endNight
9%425%41%18%
683
March1st to 15thNight
7%226%45%17%
780
16th to endNight
7%223%42%21%1
832
April1st to 15thNight
6%216%45%26%2
778
16th to endNight
7%218%42%28%
726
May1st to 15thNight
5%8%43%35%5%
585
16th to endNight
6%8%33%39%11%
611
June1st to 15thNight
11%1418%43%20%
585
16th to endNight
5%110%41%40%
585
July1st to 15thNight
7%15%38%46%
555
16th to endNight
5%38%37%45%
612
August1st to 15thNight
6%25%42%42%
575
16th to endNight
8%311%42%33%
734
September1st to 15thNight
9%5%15%43%25%
780
16th to endNight
9%15%19%49%16%
777
October1st to 15thNight
8%9%31%42%7%
780
16th to endNight
10%215%33%34%3
832
November1st to 15thNight
6%116%41%29%4
820
16th to endNight
8%222%42%22%1
840
December1st to 15thNight
10%321%37%27%1
780
16th to endNight
8%318%37%29%1
832
Page generated at 2018-12-01 11:35:33. Version ac04

Copyright 2018 A. Danko


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