Battlefield Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Battlefield Observatory clear sky chart from 2005-11-05 to 2017-08-12.

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
43%
15334
20%
46538
13%
15298
51%
15298
26%
29603

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
28%
716
21%
2383
9%
716
44%
716
20%
1493
January16th to endNight
23%
768
22%
2496
9%
768
39%
768
22%
1577
February1st to 15thNight
24%
701
19%
2246
10%
701
38%
701
23%
1408
February16th to endNight
23%
631
26%
1893
11%
631
41%
631
27%
1134
March1st to 15thNight
30%
720
21%
2028
10%
720
42%
720
27%
1299
March16th to endNight
31%
768
19%
2067
10%
768
39%
768
26%
1401
April1st to 15thNight
33%
718
20%
1796
7%
718
41%
718
31%
1198
April16th to endNight
42%
720
19%
1800
8%
720
46%
720
32%
1197
May1st to 15thNight
40%
690
14%
1770
7%
690
43%
690
26%
1239
May16th to endNight
63%
376
18%
1499
19%
376
66%
376
25%
865
June1st to 15thNight
65%
360
15%
1440
19%
360
67%
360
23%
861
June16th to endNight
67%
360
15%
1440
19%
360
70%
360
22%
855
July1st to 15thNight
69%
363
13%
1383
15%
363
70%
363
22%
846
July16th to endNight
70%
564
16%
1595
14%
531
73%
531
31%
999
August1st to 15thNight
65%
590
14%
1638
10%
587
66%
587
28%
1105
August16th to endNight
62%
700
16%
1750
10%
700
63%
700
27%
1220
September1st to 15thNight
64%
660
24%
1650
17%
660
66%
660
31%
1110
September16th to endNight
48%
657
16%
1788
13%
657
51%
657
24%
1266
October1st to 15thNight
51%
660
24%
1980
21%
660
58%
660
27%
1268
October16th to endNight
44%
704
30%
2112
21%
704
57%
704
31%
1251
November1st to 15thNight
42%
700
22%
2215
15%
700
52%
700
27%
1337
November16th to endNight
40%
720
23%
2361
18%
720
49%
720
25%
1422
December1st to 15thNight
34%
720
19%
2520
12%
720
46%
720
20%
1585
December16th to endNight
30%
768
23%
2688
13%
768
45%
768
22%
1667

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
13%5%245%245%5%7%41%
47420
Night
13%5%25%42445%7%44%
46724
Cloud CoverDay
13%5%25%5%3445%7%41%
47430
Night
13%5%25%42445%7%44%
46728
TransparencyDay
40%7%12%21%15%2
47124
Night
39%6%12%21%16%3
46538
SeeingDay
16%6%23%26%20%6%
5710
Night
16%7%26%32%15%1
15342

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
16%6%33424445%44%
1552
16th to endDay
15%6%332245%46%44%
1728
February1st to 15thDay
14%7%26%423346%44%
1614
16th to endDay
14%5%244235%5%7%43%
1580
March1st to 15thDay
14%5%24323346%49%
1918
16th to endDay
18%5%24324445%43%
2157
April1st to 15thDay
12%5%23422347%50%
2152
16th to endDay
13%5%15%5%2445%6%45%
2160
May1st to 15thDay
15%5%25%4245%6%7%39%
2192
16th to endDay
12%425%5%245%6%8%42%
2614
June1st to 15thDay
10%424426%6%7%9%41%
2520
16th to endDay
7%5%25%5%36%6%7%11%37%
2520
July1st to 15thDay
8%325%6%36%7%8%11%36%
2492
16th to endDay
7%5%346%37%6%8%11%34%
2465
August1st to 15thDay
10%6%25%7%46%6%7%9%33%
2214
16th to endDay
10%7%26%7%36%6%7%9%31%
2100
September1st to 15thDay
13%5%25%6%35%5%5%9%38%
1980
16th to endDay
21%7%36%6%25%45%6%30%
1840
October1st to 15thDay
18%7%24424336%43%
1650
16th to endDay
11%424423435%51%
1760
November1st to 15thDay
17%5%2431334446%
1640
16th to endDay
14%41442435%5%50%
1596
December1st to 15thDay
14%7%235%25%35%7%43%
1440
16th to endDay
19%6%25%324345%42%
1536
January1st to 15thNight
13%6%25%42445%7%43%
2383
16th to endNight
17%6%24424336%44%
2496
February1st to 15thNight
17%6%14423345%44%
2245
16th to endNight
12%6%24423345%49%
1893
March1st to 15thNight
14%414424446%47%
2016
16th to endNight
18%5%25%434445%42%
2067
April1st to 15thNight
11%6%25%43445%8%44%
1796
16th to endNight
16%5%2342335%7%46%
1800
May1st to 15thNight
14%6%25%43445%7%40%
1770
16th to endNight
10%5%134235%5%8%47%
1497
June1st to 15thNight
9%4245%35%5%7%10%40%
1440
16th to endNight
5%325%5%35%7%7%9%43%
1440
July1st to 15thNight
6%425%6%35%7%6%12%38%
1465
16th to endNight
8%4245%35%5%8%10%40%
1703
August1st to 15thNight
8%426%6%35%5%6%11%38%
1649
16th to endNight
10%6%26%5%35%5%6%10%37%
1750
September1st to 15thNight
11%5%25%5%3445%8%43%
1650
16th to endNight
18%7%36%5%24447%36%
1788
October1st to 15thNight
16%5%24324435%46%
1980
16th to endNight
13%414323446%52%
2112
November1st to 15thNight
15%5%24322447%48%
2215
16th to endNight
15%424423446%47%
2361
December1st to 15thNight
14%6%25%434346%42%
2520
16th to endNight
17%6%24413346%43%
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
16%6%243235%45%44%
1552
16th to endDay
15%6%24224446%45%
1728
February1st to 15thDay
14%7%24423445%44%
1614
16th to endDay
13%5%25%4245%48%42%
1580
March1st to 15thDay
14%5%23323345%49%
1929
16th to endDay
18%5%24325%445%43%
2156
April1st to 15thDay
12%424432346%51%
2152
16th to endDay
13%425%5%2435%6%45%
2160
May1st to 15thDay
15%5%25%425%5%5%8%39%
2192
16th to endDay
12%425%5%35%5%5%8%42%
2614
June1st to 15thDay
10%414426%6%7%9%40%
2520
16th to endDay
8%5%25%6%46%6%7%12%36%
2520
July1st to 15thDay
8%325%6%36%7%8%10%36%
2492
16th to endDay
7%5%26%7%46%6%8%12%33%
2465
August1st to 15thDay
11%5%36%7%36%6%7%9%33%
2214
16th to endDay
11%7%36%6%46%6%6%10%30%
2100
September1st to 15thDay
13%5%25%5%346%6%8%37%
1980
16th to endDay
22%7%26%6%35%35%6%29%
1840
October1st to 15thDay
19%6%24423345%42%
1650
16th to endDay
11%425%423336%52%
1760
November1st to 15thDay
18%5%24323435%46%
1640
16th to endDay
14%324423345%50%
1596
December1st to 15thDay
14%6%25%43435%6%44%
1440
16th to endDay
19%6%24413445%42%
1536
January1st to 15thNight
13%6%244245%5%7%42%
2383
16th to endNight
17%5%35%434336%44%
2496
February1st to 15thNight
17%6%24323445%44%
2238
16th to endNight
12%6%24423346%49%
1893
March1st to 15thNight
14%414424346%47%
2028
16th to endNight
18%5%25%324345%42%
2067
April1st to 15thNight
11%6%25%42445%7%45%
1796
16th to endNight
17%414423347%46%
1800
May1st to 15thNight
15%6%25%5%35%45%7%39%
1769
16th to endNight
10%5%144245%5%8%47%
1497
June1st to 15thNight
8%4344345%7%10%41%
1440
16th to endNight
6%335%5%35%6%7%9%43%
1440
July1st to 15thNight
7%425%5%36%6%7%11%38%
1465
16th to endNight
7%5%245%346%9%9%40%
1703
August1st to 15thNight
8%5%26%5%346%6%9%39%
1649
16th to endNight
10%5%26%6%35%47%9%37%
1750
September1st to 15thNight
12%425%5%25%35%8%44%
1650
16th to endNight
18%5%36%5%24346%36%
1788
October1st to 15thNight
16%5%24334435%46%
1980
16th to endNight
13%414323345%52%
2112
November1st to 15thNight
16%5%14313347%48%
2215
16th to endNight
15%414423445%47%
2361
December1st to 15thNight
14%6%35%5%3435%6%42%
2520
16th to endNight
17%6%24424346%44%
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
41%5%10%21%18%3
1553
16th to endDay
40%49%23%17%4
1728
February1st to 15thDay
41%48%23%17%4
1617
16th to endDay
37%6%11%22%17%3
1580
March1st to 15thDay
37%5%10%22%18%4
1929
16th to endDay
42%5%10%19%17%3
2157
April1st to 15thDay
35%411%24%19%4
2152
16th to endDay
38%6%11%18%18%6%
2160
May1st to 15thDay
42%7%14%21%12%1
2192
16th to endDay
38%8%14%24%13%1
2618
June1st to 15thDay
34%10%16%23%13%
2520
16th to endDay
37%9%17%20%13%2
2520
July1st to 15thDay
36%13%16%21%10%1
2345
16th to endDay
37%10%17%21%11%1
2310
August1st to 15thDay
42%10%14%19%11%
2201
16th to endDay
45%9%14%16%11%2
2100
September1st to 15thDay
42%8%11%17%15%2
1980
16th to endDay
52%6%10%15%14%
1840
October1st to 15thDay
44%47%22%18%2
1650
16th to endDay
34%5%7%25%21%4
1760
November1st to 15thDay
41%411%19%18%4
1640
16th to endDay
36%411%24%18%4
1596
December1st to 15thDay
41%5%12%20%15%3
1440
16th to endDay
44%410%22%13%3
1536
January1st to 15thNight
39%6%11%20%17%4
2383
16th to endNight
42%410%21%17%4
2496
February1st to 15thNight
41%47%23%19%4
2246
16th to endNight
36%310%25%18%5%
1893
March1st to 15thNight
38%6%11%23%16%4
2028
16th to endNight
43%5%10%20%17%3
2067
April1st to 15thNight
37%6%12%19%20%3
1796
16th to endNight
38%5%10%20%19%5%
1800
May1st to 15thNight
42%8%13%23%10%1
1770
16th to endNight
32%11%17%24%13%2
1499
June1st to 15thNight
36%9%16%25%11%1
1440
16th to endNight
34%11%18%19%14%1
1440
July1st to 15thNight
35%12%19%21%10%1
1383
16th to endNight
31%11%18%24%11%1
1595
August1st to 15thNight
38%9%18%20%11%
1638
16th to endNight
41%8%14%22%10%1
1750
September1st to 15thNight
39%7%14%20%15%3
1650
16th to endNight
47%6%11%15%17%1
1788
October1st to 15thNight
40%5%9%22%18%3
1980
16th to endNight
33%5%8%25%22%5%
2112
November1st to 15thNight
37%5%11%18%22%4
2215
16th to endNight
37%5%8%24%17%6%
2361
December1st to 15thNight
42%5%12%19%16%3
2520
16th to endNight
41%412%21%15%4
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
22%18%38%17%2
80
16th to endDay
17%25%35%18%3
96
February1st to 15thDay
20%18%41%15%4
130
16th to endDay
12%13%42%26%4
239
March1st to 15thDay
12%14%38%25%8%1
270
16th to endDay
17%10%31%29%7%2
288
April1st to 15thDay
14%12%32%23%13%3
270
16th to endDay
18%7%25%28%17%3
270
May1st to 15thDay
23%5%36%20%12%2
288
16th to endDay
16%418%26%25%9%
331
June1st to 15thDay
15%316%27%28%8%
315
16th to endDay
11%120%33%27%4
315
July1st to 15thDay
11%9%34%35%8%
305
16th to endDay
8%8%31%35%14%
326
August1st to 15thDay
11%9%34%29%14%
297
16th to endDay
14%6%26%34%17%
268
September1st to 15thDay
16%211%26%22%20%
255
16th to endDay
28%214%21%24%8%
254
October1st to 15thDay
25%321%25%19%5%
255
16th to endDay
13%7%27%26%19%5%
272
November1st to 15thDay
20%5%30%23%14%5%
246
16th to endDay
16%14%24%23%19%2
216
December1st to 15thDay
20%13%35%16%11%3
60
16th to endDay
25%14%31%23%6%
64
January1st to 15thNight
16%15%33%26%7%
720
16th to endNight
19%13%39%25%2
768
February1st to 15thNight
20%13%38%25%2
704
16th to endNight
14%16%41%22%3
631
March1st to 15thNight
16%10%37%27%7%
720
16th to endNight
20%7%35%27%8%
768
April1st to 15thNight
15%8%38%27%9%
718
16th to endNight
19%5%30%34%9%1
720
May1st to 15thNight
17%5%30%36%9%
690
16th to endNight
12%215%43%23%2
377
June1st to 15thNight
7%216%43%24%4
360
16th to endNight
7%16%46%27%1
360
July1st to 15thNight
8%11%46%29%2
363
16th to endNight
8%110%41%33%4
564
August1st to 15thNight
9%110%41%32%4
590
16th to endNight
12%18%38%35%4
700
September1st to 15thNight
14%10%38%30%6%
660
16th to endNight
21%214%31%27%1
657
October1st to 15thNight
18%419%32%22%2
660
16th to endNight
16%9%26%28%15%2
704
November1st to 15thNight
17%7%27%30%15%2
700
16th to endNight
16%10%29%28%14%1
720
December1st to 15thNight
18%10%31%27%11%
720
16th to endNight
20%9%34%29%6%
768
Page generated at 2017-08-13 14:16:17. Version ac04

Copyright 2017 A. Danko


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