Baker Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Baker Observatory clear sky chart from 2005-11-05 to 2017-09-21.

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
38%
15810
23%
46987
13%
15763
48%
15763
30%
28639

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
20%
900
22%
2327
6%
895
32%
895
25%
1538
January16th to endNight
20%
960
25%
2496
7%
960
32%
960
28%
1623
February1st to 15thNight
18%
880
18%
2288
3%
876
28%
876
25%
1539
February16th to endNight
17%
647
23%
1909
4%
647
31%
647
25%
1200
March1st to 15thNight
23%
540
21%
1980
10%
540
36%
540
19%
1245
March16th to endNight
25%
576
15%
2112
10%
576
33%
576
17%
1410
April1st to 15thNight
30%
539
22%
1806
11%
539
47%
539
29%
1022
April16th to endNight
27%
540
20%
1800
11%
540
43%
540
25%
1126
May1st to 15thNight
38%
540
20%
1653
15%
540
47%
540
25%
1059
May16th to endNight
45%
563
19%
1592
14%
561
52%
561
29%
1032
June1st to 15thNight
62%
540
20%
1440
15%
540
66%
540
43%
829
June16th to endNight
65%
540
26%
1440
18%
540
70%
540
49%
790
July1st to 15thNight
68%
510
17%
1484
16%
510
70%
510
38%
869
July16th to endNight
77%
564
25%
1594
25%
531
81%
531
45%
841
August1st to 15thNight
76%
539
24%
1610
28%
536
77%
536
39%
914
August16th to endNight
74%
573
27%
1895
31%
573
77%
573
39%
998
September1st to 15thNight
65%
540
27%
1800
28%
540
69%
540
32%
1021
September16th to endNight
59%
549
30%
1883
24%
549
68%
549
34%
1015
October1st to 15thNight
47%
660
30%
1980
21%
660
55%
660
37%
1124
October16th to endNight
37%
704
28%
2112
14%
704
50%
704
35%
1196
November1st to 15thNight
35%
700
31%
2133
15%
700
50%
700
35%
1196
November16th to endNight
26%
846
24%
2466
10%
846
39%
846
28%
1519
December1st to 15thNight
23%
900
19%
2520
6%
900
34%
900
24%
1692
December16th to endNight
19%
960
21%
2667
6%
960
31%
960
21%
1841

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
12%6%25%5%2445%7%42%
47859
Night
11%5%24423347%48%
47182
TransparencyDay
40%5%11%23%15%2
47559
Night
36%411%25%18%3
46987
SeeingDay
14%7%24%28%19%4
5850
Night
15%9%31%28%12%1
15810

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
13%7%245%13435%47%
1611
16th to endDay
11%6%46%5%14346%44%
1728
February1st to 15thDay
11%10%36%5%2445%5%38%
1575
16th to endDay
11%11%45%425%5%46%38%
1572
March1st to 15thDay
14%9%45%5%24436%38%
1980
16th to endDay
20%9%35%5%25%445%32%
2110
April1st to 15thDay
13%8%26%424346%43%
2142
16th to endDay
17%9%36%5%245%46%34%
2160
May1st to 15thDay
19%5%25%425%45%6%37%
2296
16th to endDay
12%5%25%6%35%5%6%7%38%
2520
June1st to 15thDay
9%425%425%47%10%44%
2520
16th to endDay
5%313435%6%6%10%49%
2520
July1st to 15thDay
10%4245%35%5%6%9%40%
2382
16th to endDay
6%4245%36%6%8%9%41%
2466
August1st to 15thDay
7%425%5%46%5%6%9%42%
2340
16th to endDay
7%425%5%36%5%6%7%44%
2306
September1st to 15thDay
13%5%2443345%7%45%
2160
16th to endDay
9%6%25%6%245%46%46%
1854
October1st to 15thDay
13%6%2433343452%
1650
16th to endDay
11%5%24413346%52%
1760
November1st to 15thDay
11%6%24413326%54%
1722
16th to endDay
15%7%34323236%47%
1491
December1st to 15thDay
15%8%35%5%1345%7%39%
1440
16th to endDay
13%11%47%423346%38%
1554
January1st to 15thNight
13%6%35%423346%45%
2327
16th to endNight
9%7%46%433446%47%
2496
February1st to 15thNight
12%8%36%423436%43%
2278
16th to endNight
11%7%25%424347%45%
1909
March1st to 15thNight
16%8%36%42424443%
1980
16th to endNight
17%8%35%5%24436%38%
2112
April1st to 15thNight
10%5%2222445%7%51%
1806
16th to endNight
15%6%245%24447%42%
1800
May1st to 15thNight
13%435%5%2345%6%45%
1652
16th to endNight
12%5%24425%36%8%45%
1590
June1st to 15thNight
6%32332445%10%53%
1440
16th to endNight
421233335%9%60%
1440
July1st to 15thNight
6%3234445%7%8%50%
1574
16th to endNight
33133235%7%11%54%
1702
August1st to 15thNight
5%2135%2446%8%54%
1620
16th to endNight
5%31442345%8%56%
1895
September1st to 15thNight
10%414423347%52%
1800
16th to endNight
9%21443435%7%54%
1883
October1st to 15thNight
11%313313346%56%
1980
16th to endNight
13%413312345%55%
2112
November1st to 15thNight
9%5%23222446%56%
2133
16th to endNight
13%7%24323346%49%
2466
December1st to 15thNight
17%6%35%423448%40%
2520
16th to endNight
13%10%36%424345%39%
2667

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
40%310%24%18%2
1612
16th to endDay
41%411%26%12%2
1728
February1st to 15thDay
46%412%23%12%1
1576
16th to endDay
46%49%22%13%3
1572
March1st to 15thDay
47%48%20%14%3
1980
16th to endDay
53%5%10%18%10%1
2112
April1st to 15thDay
43%313%21%17%1
2142
16th to endDay
51%5%10%19%10%2
2160
May1st to 15thDay
47%5%11%21%12%
2296
16th to endDay
44%8%14%20%11%
2524
June1st to 15thDay
35%6%13%27%16%1
2520
16th to endDay
28%7%16%29%15%2
2520
July1st to 15thDay
39%7%13%25%12%2
2243
16th to endDay
33%8%15%26%13%1
2311
August1st to 15thDay
37%7%14%23%16%
2326
16th to endDay
37%5%11%21%17%6%
2306
September1st to 15thDay
38%6%9%22%16%5%
2160
16th to endDay
38%48%27%17%3
1854
October1st to 15thDay
36%48%25%20%5%
1650
16th to endDay
34%38%29%19%6%
1760
November1st to 15thDay
34%38%27%20%6%
1722
16th to endDay
40%38%21%23%1
1491
December1st to 15thDay
44%5%11%23%13%1
1440
16th to endDay
48%310%20%13%2
1554
January1st to 15thNight
41%310%24%18%1
2327
16th to endNight
39%311%26%16%2
2496
February1st to 15thNight
42%411%25%14%1
2288
16th to endNight
40%311%25%17%2
1909
March1st to 15thNight
45%38%21%16%4
1980
16th to endNight
48%5%9%22%12%1
2112
April1st to 15thNight
32%413%25%19%4
1806
16th to endNight
41%412%25%14%2
1800
May1st to 15thNight
40%5%10%24%17%1
1653
16th to endNight
38%7%16%24%11%2
1592
June1st to 15thNight
26%5%16%29%20%1
1440
16th to endNight
21%5%15%31%21%3
1440
July1st to 15thNight
29%6%14%28%16%3
1484
16th to endNight
21%7%15%36%18%
1594
August1st to 15thNight
27%6%13%32%18%1
1610
16th to endNight
25%6%13%26%21%6%
1895
September1st to 15thNight
33%49%26%20%5%
1800
16th to endNight
30%49%27%25%3
1883
October1st to 15thNight
30%49%24%25%6%
1980
16th to endNight
32%29%28%20%6%
2112
November1st to 15thNight
30%48%27%22%7%
2133
16th to endNight
38%37%25%21%3
2466
December1st to 15thNight
44%411%21%16%
2520
16th to endNight
47%411%19%13%3
2667

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
25%21%40%11%2
90
16th to endDay
13%34%35%12%4
96
February1st to 15thDay
12%24%50%10%3
90
16th to endDay
19%25%34%17%2
81
March1st to 15thDay
24%18%40%15%1
90
16th to endDay
21%20%37%15%4
96
April1st to 15thDay
14%18%34%26%4
261
16th to endDay
23%12%35%16%10%1
270
May1st to 15thDay
20%8%35%23%10%1
433
16th to endDay
19%7%33%25%11%3
517
June1st to 15thDay
10%419%35%24%6%
495
16th to endDay
8%126%40%18%4
495
July1st to 15thDay
13%214%38%26%4
475
16th to endDay
8%8%31%37%12%
515
August1st to 15thDay
10%10%36%34%7%
493
16th to endDay
10%111%34%33%7%
346
September1st to 15thDay
13%112%29%34%8%
315
16th to endDay
15%127%23%23%8%
140
October1st to 15thDay
11%7%34%28%11%6%
90
16th to endDay
11%8%29%41%7%2
96
November1st to 15thDay
8%11%22%36%18%2
90
16th to endDay
28%27%24%13%41
90
December1st to 15thDay
20%17%38%14%44
90
16th to endDay
19%25%40%11%3
96
January1st to 15thNight
19%20%38%17%5%
900
16th to endNight
15%18%43%19%3
960
February1st to 15thNight
17%16%44%19%1
880
16th to endNight
17%17%44%18%2
647
March1st to 15thNight
22%12%39%22%4
540
16th to endNight
22%12%35%23%6%
576
April1st to 15thNight
15%12%38%27%5%
539
16th to endNight
19%8%40%24%6%
540
May1st to 15thNight
15%6%33%33%10%
540
16th to endNight
15%330%33%15%1
563
June1st to 15thNight
7%221%44%22%1
540
16th to endNight
5%122%44%24%1
540
July1st to 15thNight
7%17%45%25%3
510
16th to endNight
49%42%39%4
564
August1st to 15thNight
7%7%42%36%4
539
16th to endNight
8%11%44%29%5%
573
September1st to 15thNight
12%113%35%34%2
540
16th to endNight
11%219%38%23%4
549
October1st to 15thNight
13%5%31%28%17%3
660
16th to endNight
17%8%32%29%10%
704
November1st to 15thNight
13%10%37%27%10%
700
16th to endNight
18%14%38%19%7%
846
December1st to 15thNight
22%14%37%21%3
900
16th to endNight
21%14%40%20%2
960
Page generated at 2017-09-22 06:35:29. Version ac04

Copyright 2017 A. Danko


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