Brooklin Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Brooklin Observatory clear sky chart from 2005-11-05 to 2018-01-20.

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%
15393
15%
48472
6%
15358
35%
15358
15%
33429

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
14%
780
16%
2716
4%
776
28%
776
9%
1855
January16th to endNight
10%
788
13%
2717
2%
788
24%
788
8%
1960
February1st to 15thNight
12%
703
12%
2283
2%
701
24%
701
9%
1671
February16th to endNight
15%
631
17%
1893
3%
631
32%
631
14%
1324
March1st to 15thNight
16%
720
16%
2085
4%
720
28%
720
14%
1509
March16th to endNight
21%
768
18%
2112
7%
768
31%
768
17%
1458
April1st to 15thNight
18%
669
17%
1769
4%
669
26%
669
17%
1278
April16th to endNight
27%
540
13%
1620
4%
540
35%
540
16%
1148
May1st to 15thNight
26%
540
12%
1620
6%
540
32%
540
15%
1188
May16th to endNight
26%
479
11%
1547
8%
478
32%
478
13%
1137
June1st to 15thNight
33%
360
9%
1260
8%
360
38%
360
12%
942
June16th to endNight
34%
360
9%
1260
8%
360
40%
360
15%
857
July1st to 15thNight
42%
340
9%
1311
14%
340
44%
340
16%
844
July16th to endNight
35%
406
10%
1446
9%
382
43%
382
14%
996
August1st to 15thNight
44%
539
11%
1608
7%
535
46%
535
20%
1105
August16th to endNight
50%
573
19%
1719
11%
573
54%
573
25%
1085
September1st to 15thNight
44%
717
17%
1923
9%
717
49%
717
31%
1215
September16th to endNight
42%
717
26%
1980
13%
717
51%
717
31%
1195
October1st to 15thNight
33%
720
19%
2077
9%
720
42%
720
22%
1371
October16th to endNight
21%
768
18%
2430
7%
768
34%
768
18%
1626
November1st to 15thNight
27%
760
18%
2472
10%
760
38%
760
17%
1629
November16th to endNight
18%
815
17%
2686
5%
815
33%
815
12%
1807
December1st to 15thNight
13%
825
13%
2841
3%
825
26%
825
10%
2029
December16th to endNight
10%
875
14%
3097
2%
875
26%
875
9%
2200

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
19%6%2442345%7%38%
49040
Night
20%7%35%424446%36%
48647
TransparencyDay
46%5%12%21%12%1
48733
Night
49%5%11%20%12%1
48472
SeeingDay
22%18%27%21%8%1
6794
Night
21%24%24%20%8%1
15394

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
17%7%35%5%2335%8%36%
1552
16th to endDay
18%8%2442435%8%36%
1609
February1st to 15thDay
16%10%26%5%2445%7%32%
1578
16th to endDay
13%8%46%5%35%45%6%34%
1580
March1st to 15thDay
20%8%34435%346%35%
1864
16th to endDay
17%7%245%24447%40%
2112
April1st to 15thDay
21%7%245%23346%38%
2176
16th to endDay
19%7%35%424246%37%
2340
May1st to 15thDay
25%6%25%5%2345%6%31%
2332
16th to endDay
23%6%3442335%7%33%
2575
June1st to 15thDay
25%7%35%5%3445%5%29%
2700
16th to endDay
23%6%345%23447%33%
2700
July1st to 15thDay
16%5%1442446%8%40%
2565
16th to endDay
16%6%2442446%9%36%
2609
August1st to 15thDay
15%5%25%4345%6%7%40%
2340
16th to endDay
12%41443345%7%47%
2483
September1st to 15thDay
12%5%13423448%49%
2033
16th to endDay
15%5%23312346%50%
1980
October1st to 15thDay
18%424433345%44%
1881
16th to endDay
20%6%34333345%41%
1791
November1st to 15thDay
20%7%25%323446%39%
1716
16th to endDay
20%7%25%423445%38%
1602
December1st to 15thDay
25%7%24423446%33%
1446
16th to endDay
23%10%24424346%32%
1476
January1st to 15thNight
16%8%36%43345%8%36%
2716
16th to endNight
16%11%35%5%3446%9%29%
2717
February1st to 15thNight
15%9%36%5%35%447%31%
2282
16th to endNight
15%8%36%5%3435%5%37%
1893
March1st to 15thNight
20%10%36%42345%5%32%
2073
16th to endNight
17%6%35%5%24346%39%
2112
April1st to 15thNight
22%9%345%33445%34%
1769
16th to endNight
23%8%35%423337%34%
1620
May1st to 15thNight
24%8%35%5%2345%7%29%
1620
16th to endNight
26%9%35%5%24446%28%
1545
June1st to 15thNight
29%8%25%4245%47%25%
1260
16th to endNight
22%9%25%424447%33%
1260
July1st to 15thNight
19%7%25%425%46%8%33%
1391
16th to endNight
19%8%345%35%5%5%7%30%
1544
August1st to 15thNight
17%6%25%5%245%5%8%35%
1620
16th to endNight
15%5%24425%45%8%42%
1719
September1st to 15thNight
17%41432335%6%46%
1923
16th to endNight
15%5%12324336%51%
1980
October1st to 15thNight
20%6%33323445%42%
2077
16th to endNight
21%7%25%323335%39%
2430
November1st to 15thNight
18%6%25%434446%39%
2472
16th to endNight
19%7%235%24445%39%
2686
December1st to 15thNight
24%7%34424346%34%
2841
16th to endNight
23%8%34423347%33%
3097

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
49%7%11%18%11%1
1553
16th to endDay
49%5%12%21%9%
1609
February1st to 15thDay
52%5%14%17%9%
1581
16th to endDay
48%6%12%18%11%2
1580
March1st to 15thDay
51%412%18%11%1
1875
16th to endDay
41%6%11%18%18%4
2112
April1st to 15thDay
45%38%22%17%2
2176
16th to endDay
46%410%20%13%3
2340
May1st to 15thDay
51%5%8%19%13%2
2332
16th to endDay
50%5%12%20%9%1
2579
June1st to 15thDay
55%6%9%18%8%1
2700
16th to endDay
49%6%10%19%12%1
2700
July1st to 15thDay
42%6%15%24%11%
2416
16th to endDay
43%7%15%22%9%
2445
August1st to 15thDay
42%6%14%26%10%
2327
16th to endDay
34%6%14%26%17%
2483
September1st to 15thDay
34%5%12%26%18%1
2033
16th to endDay
36%49%27%20%1
1980
October1st to 15thDay
40%411%27%14%1
1881
16th to endDay
45%411%25%12%
1791
November1st to 15thDay
45%5%12%22%12%
1716
16th to endDay
48%5%13%19%12%1
1602
December1st to 15thDay
52%5%13%20%8%
1446
16th to endDay
54%5%9%17%11%
1476
January1st to 15thNight
48%7%12%21%9%1
2716
16th to endNight
53%7%11%18%8%
2717
February1st to 15thNight
54%6%11%17%8%
2283
16th to endNight
48%6%10%20%12%2
1893
March1st to 15thNight
52%48%18%11%2
2085
16th to endNight
46%410%17%17%2
2112
April1st to 15thNight
52%38%16%15%2
1769
16th to endNight
52%49%16%13%3
1620
May1st to 15thNight
54%5%8%15%14%1
1620
16th to endNight
55%6%8%19%9%
1547
June1st to 15thNight
58%5%10%16%6%2
1260
16th to endNight
50%412%20%11%
1260
July1st to 15thNight
45%6%15%20%11%
1311
16th to endNight
50%7%13%20%6%1
1446
August1st to 15thNight
46%6%15%21%10%
1608
16th to endNight
39%5%12%24%16%
1719
September1st to 15thNight
36%5%14%26%16%1
1923
16th to endNight
35%28%30%20%1
1980
October1st to 15thNight
43%49%24%15%1
2077
16th to endNight
47%311%24%12%
2430
November1st to 15thNight
46%413%21%13%
2472
16th to endNight
48%412%20%12%1
2686
December1st to 15thNight
54%5%11%19%9%
2841
16th to endNight
53%5%10%19%10%
3097

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%32%33%14%1
90
16th to endDay
22%25%35%15%
110
February1st to 15thDay
20%32%31%12%3
237
16th to endDay
16%26%35%16%4
239
March1st to 15thDay
22%30%28%14%3
270
16th to endDay
23%27%28%14%41
288
April1st to 15thDay
25%21%28%18%41
270
16th to endDay
22%18%37%12%6%2
270
May1st to 15thDay
28%18%25%18%6%2
288
16th to endDay
26%17%28%19%7%
382
June1st to 15thDay
23%14%24%28%8%
495
16th to endDay
27%14%24%22%10%1
495
July1st to 15thDay
20%10%24%29%13%1
350
16th to endDay
18%11%23%31%13%1
326
August1st to 15thDay
17%8%23%30%17%1
313
16th to endDay
15%7%23%31%17%4
332
September1st to 15thDay
18%8%25%31%13%2
315
16th to endDay
18%9%26%24%14%6%
314
October1st to 15thDay
18%15%25%26%12%2
290
16th to endDay
26%16%34%16%5%
288
November1st to 15thDay
21%24%21%23%6%2
280
16th to endDay
22%30%25%13%6%1
285
December1st to 15thDay
26%23%30%16%3
171
16th to endDay
31%33%25%10%
96
January1st to 15thNight
17%38%26%15%2
780
16th to endNight
18%35%30%12%2
788
February1st to 15thNight
19%34%30%13%2
704
16th to endNight
19%32%28%14%4
631
March1st to 15thNight
23%29%25%16%4
720
16th to endNight
17%28%27%17%7%
768
April1st to 15thNight
23%23%30%16%5%
669
16th to endNight
22%21%22%23%7%1
540
May1st to 15thNight
23%18%25%21%9%1
540
16th to endNight
25%19%21%23%9%1
479
June1st to 15thNight
24%19%17%27%9%1
360
16th to endNight
24%17%16%26%13%1
360
July1st to 15thNight
22%14%13%33%14%1
340
16th to endNight
20%17%16%27%16%1
406
August1st to 15thNight
21%12%13%30%20%1
539
16th to endNight
17%8%15%31%24%1
573
September1st to 15thNight
16%10%22%30%17%2
717
16th to endNight
18%12%22%27%15%4
717
October1st to 15thNight
22%15%22%24%11%2
720
16th to endNight
21%22%30%17%8%
768
November1st to 15thNight
17%25%23%22%9%1
760
16th to endNight
20%32%24%14%7%
815
December1st to 15thNight
28%30%23%13%3
825
16th to endNight
25%33%26%11%2
875
Page generated at 2018-01-21 12:19:33. Version ac04

Copyright 2018 A. Danko


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