Borderline Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Borderline Observatory clear sky chart from 2005-11-05 to

2017-09-12
.

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
25%
14836
17%
46781
7%
14804
37%
14804
16%
30583

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
15%
720
19%
2506
6%
716
31%
716
12%
1656
January16th to endNight
13%
768
17%
2685
4%
768
30%
768
10%
1764
February1st to 15thNight
10%
704
14%
2213
1%
701
25%
701
10%
1526
February16th to endNight
14%
631
20%
1893
6%
631
32%
631
12%
1270
March1st to 15thNight
14%
720
17%
2160
5%
720
28%
720
11%
1474
March16th to endNight
20%
768
22%
2006
6%
768
33%
768
16%
1337
April1st to 15thNight
16%
718
16%
1796
2%
718
24%
718
16%
1269
April16th to endNight
22%
635
18%
1715
3%
635
32%
635
17%
1173
May1st to 15thNight
21%
503
16%
1583
5%
503
32%
503
14%
1084
May16th to endNight
27%
375
13%
1497
8%
374
38%
374
13%
972
June1st to 15thNight
28%
360
12%
1440
9%
360
39%
360
14%
935
June16th to endNight
36%
360
11%
1440
10%
360
47%
360
19%
870
July1st to 15thNight
45%
340
12%
1360
14%
340
52%
340
21%
788
July16th to endNight
44%
376
16%
1418
15%
354
56%
354
23%
800
August1st to 15thNight
45%
458
16%
1529
10%
456
52%
456
26%
895
August16th to endNight
48%
764
20%
1910
9%
764
52%
764
32%
1224
September1st to 15thNight
40%
707
20%
1786
8%
707
46%
707
30%
1148
September16th to endNight
45%
657
25%
1815
15%
657
53%
657
32%
1099
October1st to 15thNight
29%
660
20%
1895
11%
660
39%
660
19%
1275
October16th to endNight
21%
704
15%
2255
4%
704
34%
704
15%
1507
November1st to 15thNight
24%
700
21%
2277
10%
700
39%
700
17%
1452
November16th to endNight
20%
720
19%
2394
7%
720
34%
720
14%
1545
December1st to 15thNight
17%
720
14%
2520
4%
720
30%
720
10%
1707
December16th to endNight
13%
768
17%
2688
4%
768
28%
768
9%
1813

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
16%6%35%5%35%5%5%7%34%
47887
Night
15%6%245%3445%7%39%
46951
Cloud CoverDay
16%6%25%5%35%5%5%7%35%
47897
Night
15%6%2443445%7%40%
46956
TransparencyDay
46%6%12%20%12%1
47575
Night
42%6%13%22%12%1
46781
SeeingDay
21%22%24%18%9%3
5746
Night
19%27%23%20%8%
14836

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
12%7%36%6%47%6%6%7%31%
1432
16th to endDay
11%8%36%6%36%5%6%8%32%
1539
February1st to 15thDay
11%8%38%7%5%6%6%7%6%28%
1647
16th to endDay
14%9%36%7%25%5%6%5%32%
1580
March1st to 15thDay
16%9%35%6%35%5%5%8%30%
1790
16th to endDay
15%7%36%434446%39%
2217
April1st to 15thDay
17%7%46%5%35%446%33%
2152
16th to endDay
14%7%26%5%345%5%6%36%
2244
May1st to 15thDay
24%7%36%5%3435%5%30%
2379
16th to endDay
19%5%36%42445%7%36%
2618
June1st to 15thDay
24%5%245%35%5%6%7%29%
2520
16th to endDay
16%7%26%6%45%5%6%9%30%
2520
July1st to 15thDay
13%436%6%36%6%6%9%33%
2520
16th to endDay
13%5%35%5%35%5%6%8%35%
2654
August1st to 15thDay
13%5%35%5%46%5%9%7%33%
2404
16th to endDay
12%4245%35%6%6%8%39%
2292
September1st to 15thDay
14%5%245%46%45%7%39%
2093
16th to endDay
14%5%23323346%47%
1815
October1st to 15thDay
22%6%25%5%3444436%
1734
16th to endDay
17%6%26%5%45%5%6%7%31%
1617
November1st to 15thDay
15%7%24434447%40%
1581
16th to endDay
17%6%25%5%24445%38%
1563
December1st to 15thDay
16%8%46%6%46%447%31%
1440
16th to endDay
16%10%36%6%35%5%7%6%28%
1536
January1st to 15thNight
14%7%35%5%25%5%6%6%37%
2506
16th to endNight
10%7%46%5%45%5%6%7%35%
2685
February1st to 15thNight
11%8%46%6%37%45%7%33%
2212
16th to endNight
12%10%245%25%5%48%36%
1893
March1st to 15thNight
15%7%25%5%35%6%5%6%35%
2147
16th to endNight
13%5%25%5%35%46%6%42%
2006
April1st to 15thNight
16%7%35%5%25%45%8%36%
1796
16th to endNight
18%5%25%42345%6%40%
1715
May1st to 15thNight
20%7%26%5%25%347%34%
1583
16th to endNight
18%5%346%245%5%9%34%
1495
June1st to 15thNight
22%424333448%38%
1440
16th to endNight
15%4243245%48%43%
1440
July1st to 15thNight
12%4235%35%46%10%42%
1440
16th to endNight
12%4244245%5%8%45%
1514
August1st to 15thNight
11%5%1342446%9%47%
1539
16th to endNight
14%41333346%7%45%
1910
September1st to 15thNight
14%4234235%5%7%46%
1786
16th to endNight
13%413323346%52%
1815
October1st to 15thNight
20%6%23424345%42%
1895
16th to endNight
17%6%25%4345%6%8%35%
2255
November1st to 15thNight
14%7%25%425%346%42%
2277
16th to endNight
16%6%25%5%345%5%7%37%
2394
December1st to 15thNight
17%7%35%6%35%5%6%7%33%
2520
16th to endNight
17%8%35%5%245%6%8%31%
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
12%7%36%7%36%6%6%6%33%
1432
16th to endDay
12%8%36%5%446%6%8%35%
1539
February1st to 15thDay
12%7%38%7%47%5%6%6%29%
1647
16th to endDay
15%8%36%6%35%46%5%34%
1580
March1st to 15thDay
17%8%35%6%345%5%7%31%
1800
16th to endDay
15%6%36%5%2445%5%40%
2217
April1st to 15thDay
17%7%36%5%3445%6%35%
2152
16th to endDay
14%6%26%5%245%5%6%38%
2244
May1st to 15thDay
23%7%25%6%3445%5%30%
2379
16th to endDay
19%5%25%5%3445%7%36%
2618
June1st to 15thDay
23%5%25%5%245%5%7%30%
2520
16th to endDay
16%5%25%6%36%5%6%8%31%
2520
July1st to 15thDay
12%5%35%6%36%6%6%8%34%
2520
16th to endDay
13%5%245%35%6%6%8%36%
2654
August1st to 15thDay
13%5%26%5%46%47%9%33%
2404
16th to endDay
12%4245%445%6%9%40%
2292
September1st to 15thDay
15%325%5%25%5%5%7%40%
2093
16th to endDay
14%5%14423346%48%
1815
October1st to 15thDay
21%6%245%33445%36%
1734
16th to endDay
17%7%26%5%4446%6%34%
1617
November1st to 15thDay
15%6%34424447%41%
1581
16th to endDay
17%6%35%42444440%
1563
December1st to 15thDay
16%7%46%7%36%347%32%
1440
16th to endDay
17%10%36%5%35%5%5%8%29%
1536
January1st to 15thNight
14%7%26%5%3445%7%38%
2506
16th to endNight
11%7%36%6%35%5%6%7%36%
2685
February1st to 15thNight
11%7%36%6%36%6%5%6%36%
2205
16th to endNight
13%9%245%345%47%38%
1893
March1st to 15thNight
16%7%25%5%35%5%6%6%36%
2160
16th to endNight
14%5%244245%5%6%43%
2005
April1st to 15thNight
15%7%345%25%45%8%36%
1796
16th to endNight
18%6%2443335%6%40%
1715
May1st to 15thNight
20%6%26%5%3435%6%34%
1583
16th to endNight
18%5%25%5%3445%9%36%
1495
June1st to 15thNight
22%42433435%6%38%
1440
16th to endNight
15%413325%5%5%7%44%
1440
July1st to 15thNight
11%4235%25%5%5%9%43%
1440
16th to endNight
11%42343446%9%45%
1514
August1st to 15thNight
10%5%1442437%9%47%
1539
16th to endNight
14%41333346%7%46%
1910
September1st to 15thNight
14%31342435%8%47%
1786
16th to endNight
14%314213347%52%
1815
October1st to 15thNight
21%5%14323436%42%
1895
16th to endNight
18%6%144345%48%37%
2255
November1st to 15thNight
15%6%24324446%43%
2277
16th to endNight
16%6%245%4445%6%40%
2394
December1st to 15thNight
17%7%2443445%8%35%
2520
16th to endNight
18%8%344245%6%9%33%
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
48%7%11%21%9%1
1433
16th to endDay
45%6%15%22%9%1
1539
February1st to 15thDay
52%6%13%17%9%
1650
16th to endDay
49%6%11%17%13%1
1580
March1st to 15thDay
50%5%13%16%12%1
1800
16th to endDay
45%5%10%18%16%4
2217
April1st to 15thDay
48%5%11%20%12%2
2152
16th to endDay
45%6%9%20%15%3
2244
May1st to 15thDay
53%5%7%19%12%1
2379
16th to endDay
46%7%13%19%11%1
2622
June1st to 15thDay
52%6%12%18%9%
2520
16th to endDay
47%8%13%18%11%
2520
July1st to 15thDay
44%8%11%22%12%
2371
16th to endDay
41%6%15%23%12%
2487
August1st to 15thDay
43%8%14%22%9%1
2390
16th to endDay
37%6%14%26%14%1
2292
September1st to 15thDay
41%5%11%24%15%
2093
16th to endDay
36%49%26%20%2
1815
October1st to 15thDay
48%5%10%22%10%2
1734
16th to endDay
48%6%13%18%10%2
1617
November1st to 15thDay
42%5%15%21%13%1
1581
16th to endDay
44%5%13%21%13%2
1563
December1st to 15thDay
52%5%14%17%10%
1440
16th to endDay
52%7%14%17%8%
1536
January1st to 15thNight
44%7%12%21%11%2
2506
16th to endNight
44%7%12%20%12%2
2685
February1st to 15thNight
47%7%15%18%10%
2213
16th to endNight
45%5%11%23%11%2
1893
March1st to 15thNight
46%6%11%22%11%1
2160
16th to endNight
39%6%12%18%16%5%
2006
April1st to 15thNight
44%6%12%19%15%1
1796
16th to endNight
44%6%9%21%15%3
1715
May1st to 15thNight
49%310%19%14%1
1583
16th to endNight
44%7%14%20%11%1
1497
June1st to 15thNight
46%6%14%22%8%
1440
16th to endNight
36%10%16%24%12%
1440
July1st to 15thNight
34%9%15%27%13%
1360
16th to endNight
33%8%16%29%11%1
1418
August1st to 15thNight
32%7%17%27%13%
1529
16th to endNight
34%6%14%30%14%
1910
September1st to 15thNight
34%7%13%25%18%
1786
16th to endNight
33%410%28%22%1
1815
October1st to 15thNight
44%412%20%14%3
1895
16th to endNight
44%6%16%22%9%
2255
November1st to 15thNight
41%5%12%21%16%2
2277
16th to endNight
44%5%14%22%11%1
2394
December1st to 15thNight
47%6%16%20%8%
2520
16th to endNight
47%7%13%22%9%
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
26%28%26%10%8%
60
16th to endDay
32%24%27%10%4
65
February1st to 15thDay
27%34%24%11%2
163
16th to endDay
18%33%28%15%4
239
March1st to 15thDay
31%30%20%15%2
270
16th to endDay
24%32%22%11%5%2
288
April1st to 15thDay
25%30%23%11%8%1
270
16th to endDay
20%25%27%15%6%4
270
May1st to 15thDay
31%25%20%13%5%3
288
16th to endDay
19%24%27%19%7%1
331
June1st to 15thDay
24%21%26%18%7%
315
16th to endDay
15%24%27%18%12%1
315
July1st to 15thDay
16%12%29%24%15%1
305
16th to endDay
14%16%30%24%11%2
326
August1st to 15thDay
14%13%24%24%15%7%
313
16th to endDay
10%11%19%28%15%13%
332
September1st to 15thDay
17%14%20%20%17%10%
299
16th to endDay
17%12%23%16%16%12%
254
October1st to 15thDay
21%18%18%21%15%3
255
16th to endDay
25%22%23%20%8%
246
November1st to 15thDay
21%26%22%19%8%2
235
16th to endDay
27%28%20%13%7%2
183
December1st to 15thDay
26%25%25%16%5%1
60
16th to endDay
35%31%23%9%
64
January1st to 15thNight
18%35%27%15%2
720
16th to endNight
18%36%26%16%1
768
February1st to 15thNight
18%34%29%15%1
704
16th to endNight
20%35%25%16%1
631
March1st to 15thNight
24%34%22%15%2
720
16th to endNight
19%33%22%18%5%
768
April1st to 15thNight
20%33%25%16%3
718
16th to endNight
20%31%23%16%8%
635
May1st to 15thNight
21%27%24%19%7%
503
16th to endNight
19%24%24%21%9%1
375
June1st to 15thNight
20%24%23%23%8%
360
16th to endNight
13%20%24%29%11%
360
July1st to 15thNight
12%16%19%39%12%
340
16th to endNight
10%19%20%32%16%
376
August1st to 15thNight
11%12%22%33%18%1
458
16th to endNight
13%11%19%29%21%3
764
September1st to 15thNight
14%15%23%25%18%1
707
16th to endNight
15%15%17%26%19%5%
657
October1st to 15thNight
26%20%19%22%10%1
660
16th to endNight
21%25%25%21%5%
704
November1st to 15thNight
18%29%24%19%7%1
700
16th to endNight
20%30%23%17%6%1
720
December1st to 15thNight
24%32%23%14%5%
720
16th to endNight
26%35%22%13%2
768
Page generated at 2017-09-13 07:39:03. Version ac04

Copyright 2017 A. Danko


Borderline Observatory Clear Sky Chart | Charts Home