Birdland Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Birdland Observatory clear sky chart from 2005-11-05 to 2017-09-24.

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
35%
16115
17%
46948
9%
16069
43%
16069
25%
30922

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
25%
900
13%
2506
5%
895
31%
895
18%
1823
January16th to endNight
20%
960
13%
2553
4%
960
27%
960
17%
1928
February1st to 15thNight
24%
879
14%
2288
4%
875
31%
875
22%
1655
February16th to endNight
27%
723
17%
1985
6%
723
35%
723
22%
1375
March1st to 15thNight
31%
603
16%
2043
10%
603
38%
603
21%
1297
March16th to endNight
34%
576
15%
2079
11%
576
42%
576
19%
1388
April1st to 15thNight
30%
539
17%
1797
11%
539
40%
539
22%
1177
April16th to endNight
30%
540
17%
1716
11%
540
40%
540
19%
1182
May1st to 15thNight
32%
540
16%
1484
7%
540
39%
540
26%
1002
May16th to endNight
41%
562
16%
1497
6%
561
47%
561
31%
974
June1st to 15thNight
47%
540
14%
1440
6%
540
50%
540
33%
914
June16th to endNight
53%
540
17%
1440
6%
540
58%
540
44%
837
July1st to 15thNight
61%
510
16%
1360
7%
510
64%
510
50%
733
July16th to endNight
68%
564
24%
1423
15%
531
71%
531
50%
778
August1st to 15thNight
63%
539
22%
1610
20%
536
67%
536
37%
921
August16th to endNight
54%
573
22%
1824
21%
573
61%
573
36%
1026
September1st to 15thNight
59%
540
25%
1800
23%
540
67%
540
37%
951
September16th to endNight
45%
579
22%
1898
15%
579
55%
579
32%
1072
October1st to 15thNight
38%
660
25%
1980
15%
660
46%
660
31%
1179
October16th to endNight
35%
704
18%
2137
10%
704
43%
704
24%
1397
November1st to 15thNight
30%
784
22%
2360
10%
784
42%
784
27%
1471
November16th to endNight
25%
900
15%
2520
7%
900
32%
900
19%
1793
December1st to 15thNight
20%
900
11%
2520
3%
900
27%
900
16%
1883
December16th to endNight
19%
960
12%
2688
4%
960
26%
960
12%
2166

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
14%8%36%5%3445%7%36%
47988
Night
12%8%36%5%24446%40%
47118
Cloud CoverDay
26%7%25%423346%31%
47999
Night
24%7%25%423345%35%
47122
Cloud CoverDay
14%8%36%5%3445%7%36%
47997
Night
12%8%36%5%24446%40%
47122
TransparencyDay
46%313%23%10%
47675
Night
44%313%24%12%1
46949
SeeingDay
17%7%28%28%13%4
6129
Night
16%8%31%30%11%1
16117

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
10%9%7%8%8%46%448%25%
1432
16th to endDay
11%14%6%11%8%4446%6%22%
1671
February1st to 15thDay
9%12%6%9%7%35%6%6%6%27%
1575
16th to endDay
14%10%47%5%34446%32%
1488
March1st to 15thDay
15%10%47%5%3435%5%35%
1915
16th to endDay
19%9%46%5%3445%6%29%
2145
April1st to 15thDay
18%11%37%5%23346%33%
2151
16th to endDay
22%12%35%423345%29%
2241
May1st to 15thDay
20%8%35%5%35%45%6%30%
2466
16th to endDay
15%5%26%5%25%45%7%38%
2617
June1st to 15thDay
14%5%35%5%3445%7%40%
2520
16th to endDay
11%6%25%5%35%46%8%40%
2520
July1st to 15thDay
6%3245%35%46%8%48%
2520
16th to endDay
7%424435%5%6%10%44%
2646
August1st to 15thDay
8%425%5%35%5%7%9%41%
2340
16th to endDay
12%5%235%35%46%8%43%
2378
September1st to 15thDay
11%4245%335%6%7%45%
2160
16th to endDay
14%7%3443435%7%41%
1908
October1st to 15thDay
15%7%25%323335%47%
1650
16th to endDay
18%10%35%422345%38%
1734
November1st to 15thDay
11%8%46%42345%6%40%
1495
16th to endDay
13%10%5%8%5%24346%35%
1440
December1st to 15thDay
16%10%6%7%7%445%45%26%
1440
16th to endDay
20%15%8%9%7%3422421%
1536
January1st to 15thNight
11%9%5%8%8%46%45%6%31%
2506
16th to endNight
11%12%5%9%7%45%5%5%6%26%
2553
February1st to 15thNight
8%12%6%8%6%24335%36%
2285
16th to endNight
10%9%47%6%35%446%37%
1985
March1st to 15thNight
12%11%35%423346%40%
2031
16th to endNight
16%8%46%5%2445%7%34%
2079
April1st to 15thNight
18%8%35%423346%37%
1797
16th to endNight
23%10%25%324245%35%
1716
May1st to 15thNight
20%5%25%32435%5%41%
1484
16th to endNight
13%5%25%5%2446%7%42%
1496
June1st to 15thNight
10%3246%3446%9%44%
1440
16th to endNight
6%3145%1445%7%54%
1440
July1st to 15thNight
331242446%9%57%
1440
16th to endNight
5%143235%6%9%56%
1519
August1st to 15thNight
5%4145%345%5%7%51%
1620
16th to endNight
11%413423335%54%
1824
September1st to 15thNight
9%423324345%56%
1800
16th to endNight
11%5%2442325%7%50%
1898
October1st to 15thNight
15%5%2431335%5%49%
1980
16th to endNight
16%8%25%423446%40%
2137
November1st to 15thNight
11%8%25%424446%44%
2360
16th to endNight
14%10%47%6%34446%33%
2520
December1st to 15thNight
14%12%5%7%8%35%446%28%
2520
16th to endNight
17%16%5%9%6%35%33423%
2688

Percentage Cloud Cover SW (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
24%7%5%7%7%45%347%22%
1432
16th to endDay
26%12%5%9%7%3335%417%
1671
February1st to 15thDay
23%11%47%6%2345%5%24%
1575
16th to endDay
26%9%46%5%33335%28%
1488
March1st to 15thDay
28%7%36%42324431%
1926
16th to endDay
31%8%35%423345%25%
2145
April1st to 15thDay
31%8%26%5%22335%27%
2151
16th to endDay
35%12%25%323235%22%
2241
May1st to 15thDay
32%7%25%5%24345%25%
2466
16th to endDay
30%5%15%423345%31%
2617
June1st to 15thDay
29%425%423346%32%
2520
16th to endDay
26%5%15%5%3345%5%33%
2520
July1st to 15thDay
22%31442445%6%39%
2520
16th to endDay
23%42442445%8%36%
2646
August1st to 15thDay
16%4145%35%5%6%8%38%
2340
16th to endDay
17%5%1342446%7%41%
2378
September1st to 15thDay
17%4145%3345%7%43%
2160
16th to endDay
20%6%2443435%6%39%
1908
October1st to 15thDay
23%6%1432232443%
1650
16th to endDay
25%9%25%42234435%
1734
November1st to 15thDay
23%7%36%322345%36%
1495
16th to endDay
28%8%36%5%22235%32%
1440
December1st to 15thDay
30%9%47%6%3343421%
1440
16th to endDay
31%13%6%8%6%2322318%
1536
January1st to 15thNight
24%7%37%7%34345%27%
2506
16th to endNight
26%11%38%5%3345%5%21%
2553
February1st to 15thNight
22%11%47%5%2332432%
2278
16th to endNight
23%7%36%6%24335%32%
1985
March1st to 15thNight
25%9%25%423335%35%
2043
16th to endNight
29%7%25%423345%30%
2079
April1st to 15thNight
31%6%24322345%32%
1797
16th to endNight
36%9%1432323428%
1716
May1st to 15thNight
34%41422224435%
1483
16th to endNight
28%5%14423346%34%
1496
June1st to 15thNight
25%3245%33347%35%
1440
16th to endNight
22%314412346%45%
1440
July1st to 15thNight
19%2232345%7%47%
1440
16th to endNight
20%1322345%7%48%
1519
August1st to 15thNight
13%314434446%47%
1620
16th to endNight
17%312423335%52%
1824
September1st to 15thNight
15%313323345%52%
1800
16th to endNight
18%5%14323247%47%
1898
October1st to 15thNight
22%5%23312245%45%
1980
16th to endNight
24%7%15%423336%37%
2137
November1st to 15thNight
23%7%14413335%40%
2360
16th to endNight
27%8%36%5%23335%30%
2520
December1st to 15thNight
29%11%37%6%24335%23%
2520
16th to endNight
30%13%48%5%3322419%
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
9%9%7%8%8%46%45%8%25%
1432
16th to endDay
11%14%6%11%8%4446%6%22%
1671
February1st to 15thDay
9%12%7%8%7%35%6%6%6%27%
1575
16th to endDay
14%10%46%5%34446%32%
1488
March1st to 15thDay
15%10%47%5%2425%5%34%
1926
16th to endDay
20%10%36%43445%6%29%
2143
April1st to 15thDay
18%11%37%5%23346%33%
2151
16th to endDay
22%12%35%433345%29%
2241
May1st to 15thDay
20%8%36%5%35%45%7%30%
2466
16th to endDay
15%5%36%5%35%45%6%38%
2617
June1st to 15thDay
14%5%35%5%25%45%7%40%
2520
16th to endDay
11%5%25%5%3446%8%40%
2520
July1st to 15thDay
6%3145%35%46%8%48%
2520
16th to endDay
8%4245%35%5%6%10%44%
2646
August1st to 15thDay
8%425%5%35%5%7%9%41%
2340
16th to endDay
12%5%24435%45%8%43%
2378
September1st to 15thDay
12%4245%3346%7%45%
2160
16th to endDay
14%6%3442435%6%41%
1908
October1st to 15thDay
15%7%25%323335%47%
1650
16th to endDay
18%10%35%422345%38%
1734
November1st to 15thDay
11%8%5%6%5%2335%6%40%
1495
16th to endDay
13%10%48%5%23446%35%
1440
December1st to 15thDay
16%10%5%8%8%445%45%26%
1440
16th to endDay
20%15%7%9%6%3432421%
1536
January1st to 15thNight
11%9%5%8%8%36%45%6%31%
2506
16th to endNight
12%11%5%9%7%45%5%5%6%26%
2553
February1st to 15thNight
7%13%5%9%6%34335%36%
2278
16th to endNight
11%9%47%6%35%446%37%
1985
March1st to 15thNight
12%11%35%433446%40%
2043
16th to endNight
16%8%46%5%2445%7%34%
2079
April1st to 15thNight
18%8%35%424346%37%
1797
16th to endNight
23%10%35%324336%35%
1716
May1st to 15thNight
20%5%25%424346%41%
1483
16th to endNight
12%5%25%5%2445%7%42%
1496
June1st to 15thNight
10%325%5%3445%9%44%
1440
16th to endNight
7%3145%1445%8%54%
1440
July1st to 15thNight
331342446%9%57%
1440
16th to endNight
5%1143235%6%9%57%
1519
August1st to 15thNight
5%415%5%35%5%5%7%51%
1620
16th to endNight
11%423423435%54%
1824
September1st to 15thNight
9%413324346%56%
1800
16th to endNight
11%5%25%42325%7%50%
1898
October1st to 15thNight
15%5%24313346%49%
1980
16th to endNight
16%8%25%424346%40%
2137
November1st to 15thNight
12%8%25%424447%44%
2360
16th to endNight
15%10%47%6%34447%33%
2520
December1st to 15thNight
14%12%5%8%7%34446%28%
2520
16th to endNight
18%15%5%9%6%35%33423%
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
58%312%16%9%
1433
16th to endDay
61%314%14%5%
1671
February1st to 15thDay
55%314%18%7%
1576
16th to endDay
53%311%23%7%
1488
March1st to 15thDay
51%315%21%8%
1926
16th to endDay
54%314%22%4
2145
April1st to 15thDay
52%211%21%9%1
2151
16th to endDay
57%213%18%7%1
2241
May1st to 15thDay
53%314%21%7%
2466
16th to endDay
44%312%23%13%1
2621
June1st to 15thDay
42%413%26%11%
2520
16th to endDay
40%414%27%12%1
2520
July1st to 15thDay
32%5%16%29%14%1
2371
16th to endDay
33%6%15%27%15%1
2479
August1st to 15thDay
36%5%14%31%11%1
2326
16th to endDay
37%415%28%13%1
2378
September1st to 15thDay
36%414%32%13%
2160
16th to endDay
41%313%31%8%
1908
October1st to 15thDay
40%211%28%15%
1650
16th to endDay
49%214%25%8%
1734
November1st to 15thDay
44%313%22%14%1
1495
16th to endDay
50%419%16%7%
1440
December1st to 15thDay
59%5%13%15%5%
1440
16th to endDay
68%39%13%4
1536
January1st to 15thNight
53%311%21%8%
2506
16th to endNight
56%313%17%6%
2553
February1st to 15thNight
51%313%22%8%
2288
16th to endNight
47%312%25%9%1
1985
March1st to 15thNight
44%314%24%11%1
2043
16th to endNight
49%315%23%6%1
2079
April1st to 15thNight
47%29%24%13%2
1797
16th to endNight
51%210%19%13%2
1716
May1st to 15thNight
44%412%24%13%1
1484
16th to endNight
39%413%25%16%
1498
June1st to 15thNight
35%5%14%28%13%1
1440
16th to endNight
27%415%30%18%3
1440
July1st to 15thNight
22%416%37%17%2
1360
16th to endNight
21%5%17%32%18%4
1423
August1st to 15thNight
30%5%12%30%17%2
1610
16th to endNight
32%314%29%16%3
1824
September1st to 15thNight
28%311%33%22%
1800
16th to endNight
34%214%31%16%
1898
October1st to 15thNight
37%210%30%16%2
1980
16th to endNight
44%313%23%13%1
2137
November1st to 15thNight
40%312%24%17%1
2360
16th to endNight
51%314%21%7%1
2520
December1st to 15thNight
57%413%19%6%
2520
16th to endNight
65%310%13%5%
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
18%10%36%27%5%1
90
16th to endDay
28%9%34%23%31
96
February1st to 15thDay
14%17%38%26%2
90
16th to endDay
24%11%29%28%6%
81
March1st to 15thDay
27%7%35%23%5%
90
16th to endDay
33%8%30%19%43
129
April1st to 15thDay
25%9%30%24%10%
270
16th to endDay
31%11%26%21%8%
351
May1st to 15thDay
22%13%31%22%8%2
468
16th to endDay
19%7%30%24%14%3
517
June1st to 15thDay
14%8%29%30%13%3
495
16th to endDay
13%8%32%25%15%4
495
July1st to 15thDay
6%426%33%17%11%
475
16th to endDay
8%425%34%19%6%
515
August1st to 15thDay
9%220%37%22%7%
493
16th to endDay
17%318%32%19%8%
418
September1st to 15thDay
12%324%33%19%7%
315
16th to endDay
16%5%29%30%15%3
189
October1st to 15thDay
6%7%30%32%16%6%
90
16th to endDay
27%11%25%25%11%
96
November1st to 15thDay
48%36%36%10%3
90
16th to endDay
35%10%33%16%4
90
December1st to 15thDay
20%12%34%32%1
90
16th to endDay
36%18%33%9%2
96
January1st to 15thNight
15%13%37%25%7%1
900
16th to endNight
18%10%40%25%5%
960
February1st to 15thNight
14%12%38%25%6%1
880
16th to endNight
15%12%38%24%8%
723
March1st to 15thNight
18%12%32%27%7%1
603
16th to endNight
18%8%30%29%11%1
576
April1st to 15thNight
22%9%33%28%6%
539
16th to endNight
29%5%28%27%8%
540
May1st to 15thNight
22%7%33%28%6%1
540
16th to endNight
14%6%29%35%12%1
563
June1st to 15thNight
12%428%38%15%
540
16th to endNight
8%229%44%14%
540
July1st to 15thNight
5%225%37%26%2
510
16th to endNight
5%217%50%21%2
564
August1st to 15thNight
7%118%41%28%3
539
16th to endNight
12%322%34%23%3
573
September1st to 15thNight
12%121%37%19%6%
540
16th to endNight
12%7%28%30%18%1
579
October1st to 15thNight
17%7%31%28%12%1
660
16th to endNight
20%9%27%32%9%
704
November1st to 15thNight
16%11%36%25%9%
784
16th to endNight
18%13%35%22%9%
900
December1st to 15thNight
20%11%37%23%6%
900
16th to endNight
25%10%31%23%8%
960
Page generated at 2017-09-25 08:02:27. Version ac04

Copyright 2017 A. Danko


Birdland Observatory Clear Sky Chart | Charts Home