Douglas
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Douglas clear sky chart from 2005-11-05 to 2017-12-02.

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
55%
16004
22%
47836
16%
15962
61%
15962
29%
29738

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
35%
717
22%
2327
10%
716
50%
716
24%
1430
January16th to endNight
38%
768
23%
2460
14%
768
49%
768
26%
1499
February1st to 15thNight
40%
704
24%
2108
13%
699
52%
699
29%
1294
February16th to endNight
39%
631
26%
1893
14%
631
51%
631
30%
1149
March1st to 15thNight
46%
720
27%
1995
15%
720
56%
720
36%
1189
March16th to endNight
45%
768
23%
2112
13%
768
53%
768
35%
1262
April1st to 15thNight
47%
718
25%
1976
17%
718
54%
718
36%
1176
April16th to endNight
57%
591
29%
1725
21%
591
64%
591
41%
952
May1st to 15thNight
59%
539
25%
1619
16%
539
66%
539
36%
954
May16th to endNight
70%
561
20%
1682
17%
561
72%
561
33%
1025
June1st to 15thNight
69%
540
13%
1620
10%
540
70%
540
26%
1083
June16th to endNight
76%
540
13%
1620
12%
540
77%
540
24%
1114
July1st to 15thNight
73%
510
13%
1530
12%
510
74%
510
25%
1039
July16th to endNight
75%
564
11%
1595
11%
531
75%
531
25%
1083
August1st to 15thNight
74%
539
11%
1609
10%
536
75%
536
22%
1140
August16th to endNight
65%
633
13%
1965
13%
633
65%
633
19%
1419
September1st to 15thNight
64%
720
14%
1980
13%
720
64%
720
22%
1399
September16th to endNight
59%
717
20%
1980
18%
717
62%
717
26%
1346
October1st to 15thNight
60%
720
28%
2022
25%
720
65%
720
35%
1210
October16th to endNight
58%
768
34%
2304
31%
768
65%
768
40%
1253
November1st to 15thNight
57%
760
30%
2318
26%
760
65%
760
38%
1283
November16th to endNight
48%
780
29%
2535
21%
780
61%
780
34%
1410
December1st to 15thNight
42%
728
23%
2365
17%
728
50%
728
27%
1438
December16th to endNight
43%
768
23%
2496
19%
768
51%
768
23%
1591

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
10%5%25%5%35%5%5%7%41%
48599
Night
9%5%24435%5%5%8%45%
48040
TransparencyDay
39%7%11%17%16%6%
48300
Night
35%7%12%18%17%9%
47843
SeeingDay
11%314%22%26%20%
5855
Night
12%420%33%25%4
16010

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
12%6%25%43436%8%42%
1611
16th to endDay
13%5%26%323446%46%
1761
February1st to 15thDay
14%6%25%5%24345%45%
1750
16th to endDay
15%6%14324335%49%
1580
March1st to 15thDay
10%5%14424446%51%
1964
16th to endDay
11%6%24424445%47%
2111
April1st to 15thDay
10%424425%446%48%
1972
16th to endDay
8%32433445%7%51%
2242
May1st to 15thDay
7%224436%45%9%49%
2331
16th to endDay
8%5%25%5%45%6%6%8%41%
2431
June1st to 15thDay
9%425%6%37%7%7%9%35%
2340
16th to endDay
5%426%7%48%8%8%11%32%
2340
July1st to 15thDay
6%5%26%6%6%8%7%9%11%28%
2340
16th to endDay
8%5%36%7%5%8%8%8%9%28%
2465
August1st to 15thDay
10%6%37%9%5%8%8%7%10%22%
2340
16th to endDay
12%7%36%7%5%8%6%6%8%26%
2221
September1st to 15thDay
9%6%37%7%5%7%6%6%8%30%
1980
16th to endDay
14%6%26%6%35%5%6%7%33%
1980
October1st to 15thDay
13%424423336%50%
1937
16th to endDay
8%324423345%58%
1920
November1st to 15thDay
7%423323445%58%
1868
16th to endDay
11%414423335%55%
1755
December1st to 15thDay
14%6%25%4335%46%44%
1632
16th to endDay
16%7%35%5%24446%39%
1728
January1st to 15thNight
11%6%25%5%245%5%7%43%
2327
16th to endNight
13%5%34325%445%46%
2460
February1st to 15thNight
13%5%24424345%48%
2103
16th to endNight
11%5%24324346%49%
1893
March1st to 15thNight
9%323424448%51%
1995
16th to endNight
10%424413436%53%
2112
April1st to 15thNight
9%424425%347%52%
1976
16th to endNight
6%3123245%5%8%55%
1725
May1st to 15thNight
6%414435%35%9%51%
1619
16th to endNight
5%425%5%36%6%6%9%45%
1682
June1st to 15thNight
8%425%6%36%6%9%13%33%
1620
16th to endNight
6%425%447%8%9%12%33%
1620
July1st to 15thNight
4436%7%46%7%9%12%32%
1620
16th to endNight
5%436%5%48%6%8%13%32%
1703
August1st to 15thNight
7%415%6%47%7%10%14%28%
1620
16th to endNight
9%6%35%6%48%7%7%10%29%
1965
September1st to 15thNight
10%5%36%5%45%5%7%10%33%
1980
16th to endNight
11%7%26%5%35%5%5%8%37%
1980
October1st to 15thNight
12%414323346%51%
2022
16th to endNight
8%42432233459%
2304
November1st to 15thNight
9%413323337%55%
2318
16th to endNight
10%413333436%53%
2535
December1st to 15thNight
12%5%35%424446%45%
2365
16th to endNight
14%7%25%5%24445%41%
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
39%49%17%18%11%
1612
16th to endDay
39%46%16%22%11%
1761
February1st to 15thDay
41%45%13%22%12%
1752
16th to endDay
37%36%15%25%11%
1580
March1st to 15thDay
33%48%20%22%10%
1964
16th to endDay
36%6%10%17%20%8%
2112
April1st to 15thDay
36%5%7%20%21%9%
1972
16th to endDay
31%410%22%20%9%
2242
May1st to 15thDay
31%6%12%22%20%7%
2331
16th to endDay
38%6%14%22%14%3
2435
June1st to 15thDay
42%9%15%21%9%
2340
16th to endDay
41%11%16%18%9%1
2340
July1st to 15thDay
44%14%20%15%4
2201
16th to endDay
45%13%20%16%3
2310
August1st to 15thDay
51%12%19%12%3
2327
16th to endDay
51%11%16%13%5%
2221
September1st to 15thDay
48%11%13%13%12%1
1980
16th to endDay
47%7%10%16%13%3
1980
October1st to 15thDay
35%5%9%18%21%10%
1937
16th to endDay
29%35%17%28%16%
1920
November1st to 15thDay
27%47%20%24%14%
1868
16th to endDay
32%37%17%25%14%
1755
December1st to 15thDay
40%5%9%18%17%8%
1632
16th to endDay
44%39%19%13%8%
1728
January1st to 15thNight
39%48%15%21%10%
2327
16th to endNight
38%47%13%23%11%
2460
February1st to 15thNight
37%46%14%21%15%
2112
16th to endNight
36%47%15%20%15%
1893
March1st to 15thNight
31%5%11%20%20%11%
1995
16th to endNight
31%5%10%18%22%11%
2112
April1st to 15thNight
31%5%8%21%21%12%
1976
16th to endNight
26%5%13%22%21%11%
1725
May1st to 15thNight
29%7%12%21%18%10%
1620
16th to endNight
32%8%15%25%14%4
1684
June1st to 15thNight
36%12%20%19%9%1
1620
16th to endNight
37%14%19%18%8%1
1620
July1st to 15thNight
37%13%22%20%5%
1530
16th to endNight
37%13%25%18%5%
1595
August1st to 15thNight
39%15%25%15%4
1609
16th to endNight
44%13%19%15%41
1965
September1st to 15thNight
43%11%16%13%12%2
1980
16th to endNight
42%8%14%17%13%4
1980
October1st to 15thNight
33%410%20%18%12%
2022
16th to endNight
28%27%16%25%19%
2304
November1st to 15thNight
29%47%19%25%14%
2318
16th to endNight
31%49%16%22%15%
2535
December1st to 15thNight
39%412%18%17%8%
2365
16th to endNight
42%5%8%20%14%8%
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
12%12%34%18%12%10%
90
16th to endDay
12%17%39%17%11%1
96
February1st to 15thDay
11%22%31%24%10%1
90
16th to endDay
12%7%40%29%9%
81
March1st to 15thDay
11%7%29%33%16%1
254
16th to endDay
12%5%27%28%20%4
288
April1st to 15thDay
12%9%20%27%22%7%
270
16th to endDay
8%118%28%25%17%
270
May1st to 15thDay
8%6%16%30%24%13%
288
16th to endDay
8%37%18%32%30%
331
June1st to 15thDay
14%6%16%29%32%
315
16th to endDay
9%316%31%37%
315
July1st to 15thDay
5%213%29%47%
305
16th to endDay
9%411%34%39%
326
August1st to 15thDay
11%16%13%34%31%
313
16th to endDay
12%5%15%23%43%
332
September1st to 15thDay
15%17%19%31%24%
315
16th to endDay
18%8%17%34%20%
314
October1st to 15thDay
17%115%26%27%11%
315
16th to endDay
9%419%30%30%6%
336
November1st to 15thDay
12%218%32%27%6%
286
16th to endDay
5%6%21%36%22%8%
135
December1st to 15thDay
15%8%26%27%15%5%
94
16th to endDay
23%7%18%30%14%5%
96
January1st to 15thNight
13%11%32%30%10%
720
16th to endNight
15%9%33%33%8%
768
February1st to 15thNight
16%8%30%37%7%
704
16th to endNight
13%8%35%38%3
631
March1st to 15thNight
11%7%30%40%10%
720
16th to endNight
11%8%30%33%15%
768
April1st to 15thNight
10%7%30%34%15%
718
16th to endNight
8%425%37%24%
591
May1st to 15thNight
8%124%40%22%1
540
16th to endNight
7%111%36%38%4
563
June1st to 15thNight
10%16%34%40%7%
540
16th to endNight
7%5%31%43%11%
540
July1st to 15thNight
7%428%42%16%
510
16th to endNight
6%1326%51%11%
564
August1st to 15thNight
10%225%48%11%
539
16th to endNight
13%15%24%39%15%
633
September1st to 15thNight
12%17%29%40%9%
720
16th to endNight
15%12%31%35%3
717
October1st to 15thNight
15%116%32%30%3
720
16th to endNight
10%421%35%27%2
768
November1st to 15thNight
11%421%38%21%2
760
16th to endNight
12%5%29%33%17%1
780
December1st to 15thNight
14%7%28%31%16%1
728
16th to endNight
17%5%25%34%16%
768
Page generated at 2017-12-03 11:16:38. Version ac04

Copyright 2017 A. Danko


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