KW Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the KW Observatory clear sky chart from 2005-11-05 to 2017-09-18.

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
39%
14819
14%
46911
10%
14783
44%
14783
20%
32389

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
18%
718
8%
2479
3%
716
25%
716
9%
1939
January16th to endNight
22%
768
10%
2496
5%
768
29%
768
12%
1925
February1st to 15thNight
20%
701
9%
2287
3%
701
28%
701
11%
1732
February16th to endNight
27%
631
12%
2017
6%
631
34%
631
15%
1475
March1st to 15thNight
25%
720
13%
1980
6%
720
31%
720
17%
1481
March16th to endNight
35%
768
20%
2112
12%
768
42%
768
25%
1432
April1st to 15thNight
33%
718
15%
1817
6%
718
38%
718
23%
1320
April16th to endNight
45%
565
20%
1645
10%
565
52%
565
28%
1070
May1st to 15thNight
50%
486
17%
1566
12%
486
56%
486
24%
1015
May16th to endNight
54%
374
17%
1497
17%
374
61%
374
25%
840
June1st to 15thNight
52%
360
12%
1440
13%
360
59%
360
22%
837
June16th to endNight
58%
360
13%
1440
19%
360
62%
360
24%
836
July1st to 15thNight
70%
340
16%
1360
25%
340
73%
340
34%
687
July16th to endNight
67%
483
16%
1516
17%
452
68%
452
32%
861
August1st to 15thNight
70%
539
17%
1609
14%
536
72%
536
36%
943
August16th to endNight
68%
627
24%
1773
16%
627
71%
627
37%
1038
September1st to 15thNight
59%
720
20%
1806
10%
720
63%
720
35%
1167
September16th to endNight
59%
669
21%
1873
16%
669
61%
669
33%
1162
October1st to 15thNight
44%
660
17%
1980
16%
660
48%
660
22%
1361
October16th to endNight
28%
704
12%
2112
6%
704
35%
704
16%
1588
November1st to 15thNight
39%
700
18%
2378
16%
700
45%
700
20%
1594
November16th to endNight
30%
720
10%
2520
8%
720
35%
720
13%
1872
December1st to 15thNight
19%
720
7%
2520
4%
720
22%
720
10%
1996
December16th to endNight
16%
768
6%
2688
2%
768
21%
768
8%
2218

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%8%36%6%35%5%5%7%32%
47885
Night
15%8%36%5%3445%6%35%
47091
Cloud CoverDay
14%7%36%6%35%5%5%7%33%
47895
Night
15%7%36%5%35%45%6%35%
47095
TransparencyDay
47%8%13%19%9%
47583
Night
47%7%13%20%10%1
46911
SeeingDay
17%422%29%18%7%
5351
Night
18%6%27%30%14%1
14825

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
18%11%5%9%6%36%45%6%23%
1459
16th to endDay
13%13%6%11%9%46%5%5%5%17%
1728
February1st to 15thDay
14%14%5%11%8%45%435%21%
1575
16th to endDay
17%12%5%8%5%345%45%26%
1455
March1st to 15thDay
16%9%48%8%345%5%6%27%
1969
16th to endDay
16%9%36%6%35%445%34%
2112
April1st to 15thDay
20%9%46%43345%6%30%
2131
16th to endDay
17%7%35%424445%38%
2325
May1st to 15thDay
15%7%36%5%345%5%7%35%
2384
16th to endDay
11%5%25%6%345%5%8%40%
2618
June1st to 15thDay
15%5%25%5%345%6%9%36%
2520
16th to endDay
13%4246%35%5%7%9%36%
2520
July1st to 15thDay
8%425%447%6%7%8%40%
2520
16th to endDay
9%5%26%6%46%6%7%9%35%
2544
August1st to 15thDay
8%5%26%6%446%6%9%39%
2340
16th to endDay
10%5%25%435%6%6%9%39%
2417
September1st to 15thDay
15%5%244345%5%6%41%
2152
16th to endDay
13%6%36%5%25%447%40%
1812
October1st to 15thDay
18%7%45%5%345%5%5%34%
1650
16th to endDay
24%9%37%6%245%5%6%22%
1760
November1st to 15thDay
14%9%37%6%335%5%8%32%
1478
16th to endDay
18%12%5%8%5%4446%7%22%
1440
December1st to 15thDay
20%11%7%10%6%36%5%5%6%17%
1440
16th to endDay
20%13%7%8%7%35%5%5%6%17%
1536
January1st to 15thNight
20%14%48%6%3445%5%21%
2479
16th to endNight
14%12%6%8%7%36%5%46%24%
2496
February1st to 15thNight
14%13%6%9%6%345%5%5%25%
2285
16th to endNight
14%10%48%7%345%5%5%29%
2017
March1st to 15thNight
18%8%48%7%34435%32%
1968
16th to endNight
15%8%36%42333443%
2112
April1st to 15thNight
18%7%26%5%34446%35%
1817
16th to endNight
12%6%36%5%2335%6%43%
1645
May1st to 15thNight
15%4246%345%5%7%39%
1566
16th to endNight
12%4243335%5%6%48%
1495
June1st to 15thNight
13%5%24445%35%10%41%
1440
16th to endNight
10%5%15%5%35%46%9%42%
1440
July1st to 15thNight
5%21342445%7%56%
1440
16th to endNight
7%3144345%6%8%49%
1621
August1st to 15thNight
6%31442446%9%50%
1620
16th to endNight
8%41343445%6%53%
1773
September1st to 15thNight
11%324325%45%7%48%
1806
16th to endNight
12%41442345%7%48%
1873
October1st to 15thNight
18%6%26%433347%38%
1980
16th to endNight
20%8%46%6%35%446%28%
2112
November1st to 15thNight
16%6%35%5%35%45%5%36%
2378
16th to endNight
21%9%45%5%45%45%7%26%
2520
December1st to 15thNight
20%13%5%7%5%45%45%6%21%
2520
16th to endNight
21%13%5%9%7%45%45%6%17%
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
18%10%5%9%6%35%45%6%24%
1459
16th to endDay
13%13%6%11%8%46%5%5%6%17%
1728
February1st to 15thDay
13%14%5%11%8%45%45%5%21%
1575
16th to endDay
17%10%5%8%6%345%45%27%
1455
March1st to 15thDay
16%8%49%8%35%5%5%5%28%
1980
16th to endDay
16%7%36%6%3445%5%36%
2111
April1st to 15thDay
20%8%37%42445%7%30%
2131
16th to endDay
17%8%25%5%24446%38%
2325
May1st to 15thDay
14%7%27%6%35%45%8%34%
2384
16th to endDay
11%5%35%5%35%5%6%8%40%
2618
June1st to 15thDay
15%5%25%5%345%7%8%36%
2520
16th to endDay
12%4245%36%6%7%10%36%
2520
July1st to 15thDay
7%425%5%37%6%6%9%40%
2520
16th to endDay
9%5%25%6%36%6%7%9%36%
2544
August1st to 15thDay
8%5%36%6%45%5%6%9%39%
2340
16th to endDay
10%5%245%35%5%6%8%40%
2417
September1st to 15thDay
15%5%25%43445%6%42%
2152
16th to endDay
13%5%36%5%25%448%40%
1812
October1st to 15thDay
18%7%35%6%245%5%6%33%
1650
16th to endDay
23%10%37%6%345%5%6%23%
1760
November1st to 15thDay
13%8%37%6%35%46%8%31%
1478
16th to endDay
17%10%6%8%6%35%5%6%7%23%
1440
December1st to 15thDay
18%12%6%10%7%35%46%6%18%
1440
16th to endDay
20%11%5%9%6%45%5%5%7%17%
1536
January1st to 15thNight
20%13%48%6%2445%5%22%
2479
16th to endNight
14%11%6%9%7%46%45%5%24%
2496
February1st to 15thNight
14%14%5%8%6%35%5%5%5%25%
2278
16th to endNight
15%10%38%7%3445%6%29%
2017
March1st to 15thNight
18%8%5%8%6%35%345%31%
1980
16th to endNight
15%7%36%5%2433443%
2112
April1st to 15thNight
19%6%25%6%35%346%35%
1817
16th to endNight
12%6%35%5%2435%6%43%
1645
May1st to 15thNight
14%435%435%5%5%7%38%
1565
16th to endNight
12%32432445%8%48%
1495
June1st to 15thNight
13%5%24425%45%9%41%
1440
16th to endNight
11%5%245%25%5%6%7%43%
1440
July1st to 15thNight
5%2233245%5%8%54%
1440
16th to endNight
7%314425%46%8%48%
1621
August1st to 15thNight
6%415%3245%6%9%50%
1620
16th to endNight
8%314325%45%6%53%
1773
September1st to 15thNight
11%42342446%7%47%
1806
16th to endNight
12%414424446%49%
1873
October1st to 15thNight
17%6%36%5%2435%6%38%
1980
16th to endNight
21%8%46%6%35%45%5%28%
2112
November1st to 15thNight
16%6%26%436%5%5%6%36%
2378
16th to endNight
20%9%45%5%35%5%6%6%26%
2520
December1st to 15thNight
20%13%5%6%6%25%45%5%23%
2520
16th to endNight
21%11%6%8%8%35%5%5%6%17%
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
60%8%13%12%4
1460
16th to endDay
65%8%10%10%3
1728
February1st to 15thDay
64%6%12%14%1
1577
16th to endDay
56%8%13%14%6%
1455
March1st to 15thDay
55%7%12%16%7%
1980
16th to endDay
48%6%10%18%13%1
2112
April1st to 15thDay
53%5%11%18%11%
2131
16th to endDay
46%5%11%19%14%2
2325
May1st to 15thDay
46%6%10%22%13%
2384
16th to endDay
38%8%14%21%14%2
2622
June1st to 15thDay
41%8%13%23%12%
2520
16th to endDay
38%9%16%22%12%
2520
July1st to 15thDay
34%9%14%24%16%1
2371
16th to endDay
40%9%15%22%10%1
2386
August1st to 15thDay
37%10%16%20%14%1
2327
16th to endDay
36%8%15%26%11%1
2417
September1st to 15thDay
39%9%15%23%11%
2152
16th to endDay
41%6%13%28%9%
1812
October1st to 15thDay
48%6%12%21%8%1
1650
16th to endDay
59%8%14%13%4
1760
November1st to 15thDay
47%10%15%18%7%1
1478
16th to endDay
57%10%14%13%4
1440
December1st to 15thDay
64%9%15%9%1
1440
16th to endDay
65%9%12%10%2
1536
January1st to 15thNight
61%7%12%12%4
2479
16th to endNight
59%7%15%13%3
2496
February1st to 15thNight
59%6%13%16%3
2287
16th to endNight
55%5%15%16%6%
2017
March1st to 15thNight
55%412%20%5%
1980
16th to endNight
45%410%21%16%2
2112
April1st to 15thNight
49%5%10%18%14%
1817
16th to endNight
39%6%11%22%16%3
1645
May1st to 15thNight
41%7%11%22%14%2
1566
16th to endNight
34%7%14%25%15%3
1497
June1st to 15thNight
39%6%13%24%15%1
1440
16th to endNight
37%6%12%24%18%
1440
July1st to 15thNight
26%6%12%27%24%2
1360
16th to endNight
30%7%15%25%17%3
1516
August1st to 15thNight
29%8%18%28%13%1
1609
16th to endNight
29%6%13%32%16%1
1773
September1st to 15thNight
33%8%14%27%15%1
1806
16th to endNight
34%7%13%31%13%
1873
October1st to 15thNight
45%7%12%22%12%
1980
16th to endNight
55%7%12%17%6%
2112
November1st to 15thNight
45%7%13%20%12%1
2378
16th to endNight
55%7%16%15%4
2520
December1st to 15thNight
61%9%13%12%3
2520
16th to endNight
65%9%12%9%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
12%20%41%13%10%1
65
16th to endDay
31%13%31%22%1
96
February1st to 15thDay
25%6%50%16%1
90
16th to endDay
20%11%38%25%3
93
March1st to 15thDay
22%10%32%25%8%
270
16th to endDay
22%430%29%10%2
288
April1st to 15thDay
23%430%31%8%1
270
16th to endDay
19%6%29%25%13%5%
270
May1st to 15thDay
18%421%28%19%9%
288
16th to endDay
13%321%34%21%5%
331
June1st to 15thDay
19%216%35%23%2
315
16th to endDay
13%218%34%25%5%
315
July1st to 15thDay
11%11%35%30%10%
305
16th to endDay
11%16%35%26%10%
326
August1st to 15thDay
8%14%31%30%15%
313
16th to endDay
14%212%23%28%19%
332
September1st to 15thDay
12%213%28%25%17%
315
16th to endDay
16%314%31%19%14%
262
October1st to 15thDay
19%324%27%18%6%
255
16th to endDay
26%6%30%26%9%
272
November1st to 15thDay
11%9%20%39%15%3
96
16th to endDay
23%13%26%25%10%1
60
December1st to 15thDay
16%11%43%20%6%1
60
16th to endDay
25%17%45%12%
64
January1st to 15thNight
27%12%34%19%5%
720
16th to endNight
19%8%36%28%6%
768
February1st to 15thNight
20%11%38%24%4
704
16th to endNight
19%9%35%29%7%
631
March1st to 15thNight
22%8%36%26%6%
720
16th to endNight
19%6%31%29%12%1
768
April1st to 15thNight
20%6%32%32%7%
718
16th to endNight
15%5%29%35%12%2
565
May1st to 15thNight
17%222%33%20%2
486
16th to endNight
11%124%38%22%1
375
June1st to 15thNight
15%123%37%21%1
360
16th to endNight
12%118%42%24%
360
July1st to 15thNight
6%14%47%28%2
340
16th to endNight
8%113%45%28%3
483
August1st to 15thNight
8%10%43%33%4
539
16th to endNight
9%212%37%33%4
627
September1st to 15thNight
13%219%30%27%7%
720
16th to endNight
15%215%31%29%5%
669
October1st to 15thNight
19%6%23%28%19%2
660
16th to endNight
25%5%32%28%6%
704
November1st to 15thNight
18%6%29%29%14%1
700
16th to endNight
25%9%27%27%9%1
720
December1st to 15thNight
28%9%35%21%4
720
16th to endNight
26%8%38%22%3
768
Page generated at 2017-09-19 07:32:31. Version ac04

Copyright 2017 A. Danko


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