Hazard
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hazard clear sky chart from 2005-11-05 to 2017-10-06.

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
42%
15603
19%
47131
14%
15560
48%
15560
23%
31133

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
19%
720
15%
2327
8%
716
28%
716
13%
1720
January16th to endNight
20%
768
17%
2496
8%
768
31%
768
14%
1791
February1st to 15thNight
19%
704
14%
2181
4%
701
28%
701
15%
1576
February16th to endNight
16%
631
16%
1893
7%
631
25%
631
14%
1415
March1st to 15thNight
25%
720
18%
2043
10%
720
32%
720
18%
1465
March16th to endNight
30%
768
14%
2112
8%
768
35%
768
19%
1517
April1st to 15thNight
33%
658
20%
1916
10%
658
43%
658
24%
1229
April16th to endNight
37%
540
21%
1623
10%
540
46%
540
24%
1058
May1st to 15thNight
39%
539
15%
1620
8%
539
44%
539
21%
1108
May16th to endNight
58%
561
18%
1683
13%
561
62%
561
27%
1072
June1st to 15thNight
65%
540
16%
1620
13%
540
68%
540
34%
959
June16th to endNight
66%
540
17%
1620
17%
540
68%
540
32%
982
July1st to 15thNight
61%
510
11%
1530
10%
510
62%
510
26%
1000
July16th to endNight
71%
564
17%
1595
16%
531
73%
531
33%
961
August1st to 15thNight
73%
539
21%
1609
20%
536
73%
536
35%
963
August16th to endNight
71%
573
24%
1803
24%
573
72%
573
33%
1051
September1st to 15thNight
62%
715
23%
1975
20%
715
63%
715
33%
1232
September16th to endNight
60%
717
27%
1980
23%
717
63%
717
33%
1238
October1st to 15thNight
54%
684
30%
1944
27%
684
59%
684
35%
1151
October16th to endNight
41%
704
27%
2112
21%
704
50%
704
28%
1324
November1st to 15thNight
44%
700
28%
2273
23%
700
54%
700
30%
1321
November16th to endNight
35%
720
24%
2340
16%
720
47%
720
23%
1480
December1st to 15thNight
29%
720
14%
2340
11%
720
34%
720
14%
1702
December16th to endNight
24%
768
17%
2496
9%
768
35%
768
13%
1818

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%7%36%5%35%45%7%36%
48061
Night
15%7%35%42445%7%39%
47329
TransparencyDay
47%5%10%20%13%2
47762
Night
44%410%21%15%3
47132
SeeingDay
20%9%20%21%17%10%
5462
Night
19%9%21%27%18%3
15606

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
19%11%5%10%6%23335%28%
1611
16th to endDay
17%13%5%6%423335%34%
1728
February1st to 15thDay
16%13%6%7%423345%30%
1678
16th to endDay
17%11%49%5%34446%27%
1580
March1st to 15thDay
21%10%4442425%5%34%
1917
16th to endDay
19%8%46%6%34346%32%
2111
April1st to 15thDay
16%5%25%5%2445%7%40%
2042
16th to endDay
18%5%25%5%34447%37%
2336
May1st to 15thDay
18%7%37%7%36%5%47%29%
2331
16th to endDay
14%5%25%6%35%5%6%7%36%
2431
June1st to 15thDay
9%426%6%47%7%6%9%36%
2340
16th to endDay
9%425%6%45%6%7%9%37%
2340
July1st to 15thDay
14%5%25%6%46%5%6%8%32%
2340
16th to endDay
12%5%36%7%46%6%6%8%31%
2465
August1st to 15thDay
11%6%25%7%47%6%7%9%31%
2340
16th to endDay
11%425%5%46%6%6%10%35%
2387
September1st to 15thDay
17%5%245%35%5%5%6%37%
1980
16th to endDay
16%5%26%423335%45%
1980
October1st to 15thDay
13%424423345%50%
1814
16th to endDay
20%6%14413245%45%
1760
November1st to 15thDay
13%6%24423446%47%
1582
16th to endDay
17%9%34224345%42%
1620
December1st to 15thDay
21%9%36%5%24445%32%
1620
16th to endDay
19%11%37%43445%6%29%
1728
January1st to 15thNight
18%11%5%9%5%3443429%
2327
16th to endNight
18%12%5%7%5%2333432%
2496
February1st to 15thNight
17%10%5%7%5%34346%31%
2172
16th to endNight
19%13%46%43445%5%27%
1893
March1st to 15thNight
18%11%36%425%336%33%
2043
16th to endNight
17%8%35%6%25%447%32%
2112
April1st to 15thNight
15%6%2443435%7%42%
1916
16th to endNight
15%6%245%25%5%6%7%40%
1623
May1st to 15thNight
17%6%35%5%235%5%9%34%
1619
16th to endNight
9%4245%45%5%7%9%40%
1682
June1st to 15thNight
7%3135%346%8%10%45%
1620
16th to endNight
7%3244245%7%11%43%
1620
July1st to 15thNight
11%5%25%5%35%6%6%9%38%
1620
16th to endNight
7%225%6%46%6%6%10%41%
1703
August1st to 15thNight
9%415%4345%7%9%46%
1620
16th to endNight
8%324425%6%7%9%45%
1803
September1st to 15thNight
12%425%32346%9%43%
1975
16th to endNight
11%5%25%5%24445%49%
1980
October1st to 15thNight
14%41431235%6%52%
1944
16th to endNight
17%6%23423345%45%
2112
November1st to 15thNight
16%6%14312236%50%
2273
16th to endNight
16%7%24323446%43%
2340
December1st to 15thNight
21%11%47%42445%5%29%
2340
16th to endNight
22%11%46%5%23337%29%
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
59%27%17%11%1
1612
16th to endDay
53%28%23%10%1
1728
February1st to 15thDay
56%36%20%10%1
1680
16th to endDay
58%29%19%9%1
1580
March1st to 15thDay
52%29%19%12%2
1917
16th to endDay
52%49%22%10%
2112
April1st to 15thDay
41%311%23%15%3
2042
16th to endDay
46%48%22%13%4
2336
May1st to 15thDay
54%5%11%16%9%1
2331
16th to endDay
44%7%13%23%9%2
2435
June1st to 15thDay
42%7%13%20%13%1
2340
16th to endDay
40%8%12%16%19%2
2340
July1st to 15thDay
47%7%12%16%14%1
2201
16th to endDay
44%8%13%19%11%2
2310
August1st to 15thDay
45%8%13%19%11%
2327
16th to endDay
42%7%13%21%13%1
2387
September1st to 15thDay
45%5%10%19%14%4
1980
16th to endDay
41%39%21%21%2
1980
October1st to 15thDay
36%39%23%21%4
1814
16th to endDay
43%26%24%18%3
1760
November1st to 15thDay
37%37%23%22%5%
1582
16th to endDay
44%25%24%20%2
1620
December1st to 15thDay
53%29%20%11%2
1620
16th to endDay
56%311%17%8%1
1728
January1st to 15thNight
59%27%14%12%2
2327
16th to endNight
56%27%20%10%2
2496
February1st to 15thNight
54%49%19%10%1
2181
16th to endNight
58%39%18%8%1
1893
March1st to 15thNight
52%38%19%13%2
2043
16th to endNight
51%410%22%10%
2112
April1st to 15thNight
41%49%23%16%4
1916
16th to endNight
42%5%10%22%13%5%
1623
May1st to 15thNight
46%6%14%18%11%2
1620
16th to endNight
37%8%14%23%13%2
1684
June1st to 15thNight
30%7%21%23%15%1
1620
16th to endNight
32%8%16%23%15%3
1620
July1st to 15thNight
40%7%15%19%13%3
1530
16th to endNight
32%7%19%24%13%2
1595
August1st to 15thNight
32%5%17%23%18%1
1609
16th to endNight
31%6%14%27%16%2
1803
September1st to 15thNight
35%5%13%23%16%5%
1975
16th to endNight
35%5%8%21%26%2
1980
October1st to 15thNight
32%48%26%21%6%
1944
16th to endNight
41%25%25%20%4
2112
November1st to 15thNight
37%25%21%25%7%
2273
16th to endNight
42%36%25%18%3
2340
December1st to 15thNight
56%39%16%10%3
2340
16th to endNight
57%39%16%11%1
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
30%31%23%10%32
90
16th to endDay
37%27%23%7%4
96
February1st to 15thDay
34%25%30%6%21
90
16th to endDay
29%19%35%13%1
81
March1st to 15thDay
27%16%33%17%4
207
16th to endDay
22%16%28%21%10%1
288
April1st to 15thDay
22%12%26%23%10%2
270
16th to endDay
24%10%24%21%14%5%
270
May1st to 15thDay
25%14%23%18%10%7%
288
16th to endDay
18%5%22%22%17%14%
331
June1st to 15thDay
8%5%16%25%28%13%
315
16th to endDay
9%6%27%20%22%12%
315
July1st to 15thDay
20%420%27%9%17%
305
16th to endDay
13%210%25%26%22%
326
August1st to 15thDay
16%211%24%26%17%
313
16th to endDay
15%111%26%25%19%
332
September1st to 15thDay
20%210%20%29%17%
315
16th to endDay
17%5%11%24%27%14%
314
October1st to 15thDay
16%6%19%21%24%11%
278
16th to endDay
21%10%23%23%17%3
272
November1st to 15thDay
24%7%24%22%16%4
90
16th to endDay
33%11%28%18%5%2
90
December1st to 15thDay
30%17%30%15%5%1
90
16th to endDay
35%20%29%11%3
96
January1st to 15thNight
29%18%29%17%5%
720
16th to endNight
27%19%29%22%1
768
February1st to 15thNight
26%18%31%22%1
704
16th to endNight
30%18%31%16%2
631
March1st to 15thNight
26%14%29%23%5%
720
16th to endNight
21%14%26%25%10%1
768
April1st to 15thNight
21%14%28%26%8%
658
16th to endNight
18%8%30%27%13%1
540
May1st to 15thNight
20%7%25%29%15%1
540
16th to endNight
10%319%34%25%7%
563
June1st to 15thNight
9%214%34%33%5%
540
16th to endNight
8%113%36%34%5%
540
July1st to 15thNight
15%111%32%34%4
510
16th to endNight
9%17%29%41%10%
564
August1st to 15thNight
10%17%33%40%7%
539
16th to endNight
11%8%28%41%9%
573
September1st to 15thNight
15%211%28%35%6%
715
16th to endNight
13%314%29%32%6%
717
October1st to 15thNight
16%5%17%29%25%5%
684
16th to endNight
21%8%23%27%16%1
704
November1st to 15thNight
20%9%21%28%17%3
700
16th to endNight
22%14%23%27%12%
720
December1st to 15thNight
27%16%22%25%7%
720
16th to endNight
28%17%24%25%4
768
Page generated at 2017-10-07 14:07:54. Version ac04

Copyright 2017 A. Danko


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