Crow's Nest Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Crow's Nest Observatory clear sky chart from 2005-11-05 to 2017-10-16.

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
29%
14944
16%
47361
8%
14913
39%
14913
18%
31823

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
16%
720
17%
2506
6%
716
30%
716
13%
1659
January16th to endNight
13%
768
16%
2688
3%
768
29%
768
12%
1829
February1st to 15thNight
16%
702
13%
2240
4%
701
27%
701
12%
1605
February16th to endNight
19%
631
17%
1893
5%
631
34%
631
16%
1319
March1st to 15thNight
17%
720
15%
2118
5%
720
29%
720
14%
1516
March16th to endNight
25%
768
20%
2086
8%
768
35%
768
20%
1396
April1st to 15thNight
22%
709
18%
1787
4%
709
30%
709
21%
1269
April16th to endNight
30%
540
17%
1620
6%
540
38%
540
20%
1115
May1st to 15thNight
32%
540
14%
1620
7%
540
39%
540
17%
1143
May16th to endNight
29%
436
11%
1558
10%
435
33%
435
12%
1133
June1st to 15thNight
34%
360
9%
1440
9%
360
40%
360
11%
1033
June16th to endNight
44%
360
9%
1440
12%
360
48%
360
16%
917
July1st to 15thNight
52%
340
10%
1360
16%
340
54%
340
17%
848
July16th to endNight
49%
376
13%
1418
15%
354
56%
354
18%
896
August1st to 15thNight
52%
530
14%
1600
11%
527
55%
527
24%
1050
August16th to endNight
57%
632
21%
1778
12%
632
61%
632
30%
1121
September1st to 15thNight
50%
720
18%
1896
11%
720
55%
720
31%
1225
September16th to endNight
47%
717
26%
1980
15%
717
56%
717
34%
1180
October1st to 15thNight
37%
720
20%
2040
10%
720
46%
720
24%
1334
October16th to endNight
26%
708
18%
2276
8%
708
38%
708
20%
1502
November1st to 15thNight
29%
700
20%
2277
12%
700
41%
700
20%
1474
November16th to endNight
22%
722
18%
2352
6%
722
35%
722
15%
1557
December1st to 15thNight
16%
750
14%
2661
3%
750
29%
750
13%
1830
December16th to endNight
14%
775
15%
2727
3%
775
28%
775
12%
1872

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
18%6%24424447%40%
48056
Night
18%7%2442445%6%38%
47532
Cloud CoverDay
17%6%2442445%7%40%
48066
Night
18%7%2442445%7%38%
47537
TransparencyDay
43%5%12%22%14%1
47745
Night
46%5%11%21%13%1
47361
SeeingDay
20%13%25%25%11%2
6032
Night
19%20%24%23%10%1
14946

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
15%7%345%3445%6%39%
1432
16th to endDay
17%7%33325%448%40%
1536
February1st to 15thDay
17%9%25%5%25%45%6%35%
1618
16th to endDay
13%9%35%5%35%446%36%
1580
March1st to 15thDay
20%8%26%423346%37%
1832
16th to endDay
16%7%25%423335%43%
2136
April1st to 15thDay
19%5%2442345%7%40%
2161
16th to endDay
19%5%145%2435%6%40%
2340
May1st to 15thDay
25%6%35%5%23446%32%
2332
16th to endDay
22%5%2443445%7%35%
2565
June1st to 15thDay
27%5%24323446%34%
2520
16th to endDay
20%425%5%2445%7%36%
2520
July1st to 15thDay
13%5%245%35%5%6%9%37%
2520
16th to endDay
13%5%145%35%6%7%9%39%
2648
August1st to 15thDay
12%4244245%5%9%42%
2340
16th to endDay
11%313425%45%8%48%
2423
September1st to 15thDay
14%413423447%49%
2064
16th to endDay
13%5%23313336%52%
1980
October1st to 15thDay
18%6%24423335%44%
1920
16th to endDay
20%6%24424345%41%
1613
November1st to 15thDay
20%6%23322445%44%
1581
16th to endDay
21%6%2431233445%
1605
December1st to 15thDay
23%5%34425%345%37%
1296
16th to endDay
23%10%25%323436%34%
1494
January1st to 15thNight
15%8%25%42445%7%39%
2506
16th to endNight
16%10%34423447%37%
2688
February1st to 15thNight
14%8%36%6%35%5%5%5%33%
2239
16th to endNight
16%9%34425%35%5%38%
1893
March1st to 15thNight
20%8%26%5%33346%34%
2105
16th to endNight
17%6%24422346%44%
2086
April1st to 15thNight
20%7%245%24445%37%
1787
16th to endNight
22%5%25%5%23446%36%
1620
May1st to 15thNight
21%7%34425%5%5%7%31%
1620
16th to endNight
24%9%35%424446%28%
1556
June1st to 15thNight
25%7%35%5%35%45%5%29%
1440
16th to endNight
21%5%14325%45%8%35%
1440
July1st to 15thNight
16%5%245%26%5%6%7%36%
1440
16th to endNight
14%6%25%5%445%6%9%34%
1514
August1st to 15thNight
14%6%24435%5%6%8%38%
1611
16th to endNight
13%41343445%7%46%
1778
September1st to 15thNight
15%5%23423445%48%
1896
16th to endNight
12%5%23313336%53%
1980
October1st to 15thNight
19%5%2442445%6%42%
2040
16th to endNight
21%6%25%32335%5%39%
2276
November1st to 15thNight
18%6%244235%4443%
2277
16th to endNight
18%6%245%24446%41%
2352
December1st to 15thNight
22%8%24423345%36%
2661
16th to endNight
22%9%24323347%36%
2727

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%34435%26%8%37%
1432
16th to endDay
17%8%3432345%6%38%
1536
February1st to 15thDay
18%7%345%3445%7%33%
1618
16th to endDay
14%9%35%5%25%45%5%37%
1580
March1st to 15thDay
20%8%25%5%23447%36%
1842
16th to endDay
15%7%25%423346%44%
2136
April1st to 15thDay
18%5%23423448%42%
2161
16th to endDay
19%5%24424446%41%
2340
May1st to 15thDay
23%6%36%423446%33%
2332
16th to endDay
21%6%2442445%7%34%
2565
June1st to 15thDay
26%6%23323446%35%
2520
16th to endDay
20%5%2442445%7%37%
2520
July1st to 15thDay
13%6%245%35%5%6%10%38%
2520
16th to endDay
12%5%245%45%5%6%9%39%
2648
August1st to 15thDay
11%5%244245%6%10%42%
2340
16th to endDay
11%3134245%6%8%48%
2423
September1st to 15thDay
13%41441335%6%50%
2064
16th to endDay
13%6%14222346%51%
1980
October1st to 15thDay
17%7%14323335%45%
1920
16th to endDay
19%7%25%324346%41%
1613
November1st to 15thDay
19%7%23312445%43%
1581
16th to endDay
20%7%24412335%44%
1605
December1st to 15thDay
22%7%25%434346%36%
1296
16th to endDay
23%11%34323346%33%
1494
January1st to 15thNight
15%8%244345%6%8%35%
2506
16th to endNight
17%10%35%43336%6%34%
2688
February1st to 15thNight
15%8%35%7%35%5%5%7%32%
2232
16th to endNight
16%9%34435%35%6%36%
1893
March1st to 15thNight
21%9%25%5%33446%33%
2118
16th to endNight
18%6%33323346%42%
2085
April1st to 15thNight
20%7%24424446%37%
1787
16th to endNight
22%6%35%423446%36%
1620
May1st to 15thNight
21%6%344245%6%7%32%
1620
16th to endNight
24%8%35%5%23446%29%
1556
June1st to 15thNight
25%7%25%425%45%6%29%
1440
16th to endNight
20%42432445%9%36%
1440
July1st to 15thNight
15%5%15%437%5%6%8%36%
1440
16th to endNight
13%6%25%435%5%7%10%35%
1514
August1st to 15thNight
12%5%35%435%5%5%8%39%
1611
16th to endNight
13%423325%45%7%46%
1778
September1st to 15thNight
14%5%24324446%48%
1896
16th to endNight
13%6%13222436%52%
1980
October1st to 15thNight
18%5%1432445%6%42%
2040
16th to endNight
20%6%24424445%40%
2276
November1st to 15thNight
18%6%24424445%42%
2277
16th to endNight
18%6%25%434447%39%
2352
December1st to 15thNight
23%8%24423345%35%
2661
16th to endNight
23%9%2442335%7%34%
2727

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
44%6%12%22%11%1
1433
16th to endDay
44%6%14%22%11%
1536
February1st to 15thDay
49%6%14%18%10%
1621
16th to endDay
47%413%20%12%2
1580
March1st to 15thDay
49%413%18%11%2
1842
16th to endDay
42%39%20%19%4
2136
April1st to 15thDay
41%411%22%17%3
2161
16th to endDay
43%6%9%22%15%3
2340
May1st to 15thDay
51%49%16%15%1
2332
16th to endDay
48%6%12%18%12%1
2569
June1st to 15thDay
50%5%12%20%9%
2520
16th to endDay
45%7%10%23%12%1
2520
July1st to 15thDay
38%6%15%27%11%
2371
16th to endDay
38%8%16%23%12%1
2481
August1st to 15thDay
36%8%17%25%11%
2327
16th to endDay
31%6%16%26%17%1
2423
September1st to 15thDay
34%5%11%26%20%1
2064
16th to endDay
34%5%9%27%22%1
1980
October1st to 15thDay
41%410%24%15%2
1920
16th to endDay
43%412%24%13%
1613
November1st to 15thDay
42%5%14%22%14%1
1581
16th to endDay
44%414%19%15%1
1605
December1st to 15thDay
49%6%12%19%11%
1296
16th to endDay
52%7%10%17%11%1
1494
January1st to 15thNight
45%7%12%22%10%1
2506
16th to endNight
49%6%10%20%11%1
2688
February1st to 15thNight
52%5%11%18%10%
2240
16th to endNight
49%5%11%20%10%2
1893
March1st to 15thNight
52%48%18%13%2
2118
16th to endNight
42%410%18%19%4
2086
April1st to 15thNight
47%47%18%18%3
1787
16th to endNight
48%410%20%13%3
1620
May1st to 15thNight
48%7%11%16%14%2
1620
16th to endNight
55%6%10%16%9%1
1558
June1st to 15thNight
54%8%10%17%8%1
1440
16th to endNight
45%5%15%20%12%
1440
July1st to 15thNight
42%6%16%22%10%
1360
16th to endNight
42%7%14%24%9%
1418
August1st to 15thNight
40%7%15%24%11%
1600
16th to endNight
35%7%11%28%16%
1778
September1st to 15thNight
37%5%10%29%16%1
1896
16th to endNight
32%410%31%20%1
1980
October1st to 15thNight
41%5%10%25%15%2
2040
16th to endNight
45%411%24%13%1
2276
November1st to 15thNight
44%5%12%22%14%1
2277
16th to endNight
45%5%13%20%13%1
2352
December1st to 15thNight
51%5%12%21%9%
2661
16th to endNight
50%5%12%19%10%
2727

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
15%25%31%25%3
60
16th to endDay
20%18%35%23%1
64
February1st to 15thDay
21%21%35%18%2
239
16th to endDay
19%17%33%23%5%
239
March1st to 15thDay
24%23%31%16%3
270
16th to endDay
18%24%31%18%41
288
April1st to 15thDay
22%20%24%22%8%
270
16th to endDay
21%14%32%21%8%1
270
May1st to 15thDay
30%14%25%18%8%3
288
16th to endDay
24%11%27%27%8%1
331
June1st to 15thDay
24%10%22%31%10%
315
16th to endDay
21%11%25%30%9%1
315
July1st to 15thDay
17%7%17%38%16%3
305
16th to endDay
13%10%15%36%20%3
326
August1st to 15thDay
15%6%22%30%22%3
313
16th to endDay
14%6%17%31%22%7%
332
September1st to 15thDay
15%7%23%27%19%6%
315
16th to endDay
17%8%21%27%17%7%
314
October1st to 15thDay
22%11%20%26%14%5%
300
16th to endDay
23%12%31%24%7%
243
November1st to 15thDay
22%17%26%21%9%2
235
16th to endDay
22%24%27%17%6%1
240
December1st to 15thDay
29%16%33%14%6%
96
16th to endDay
34%17%31%15%1
64
January1st to 15thNight
15%32%32%16%3
720
16th to endNight
20%30%30%15%3
768
February1st to 15thNight
17%30%29%19%3
704
16th to endNight
20%25%31%18%4
631
March1st to 15thNight
24%25%28%16%4
720
16th to endNight
19%25%26%20%7%
768
April1st to 15thNight
20%22%30%19%6%
709
16th to endNight
19%18%25%23%10%1
540
May1st to 15thNight
20%18%22%24%12%2
540
16th to endNight
26%19%17%24%9%1
436
June1st to 15thNight
21%19%15%28%14%1
360
16th to endNight
21%17%10%35%13%1
360
July1st to 15thNight
17%12%9%36%21%1
340
16th to endNight
16%17%11%32%21%1
376
August1st to 15thNight
15%9%11%38%22%2
530
16th to endNight
13%9%12%34%25%5%
632
September1st to 15thNight
16%9%17%29%23%3
720
16th to endNight
16%9%20%26%20%5%
717
October1st to 15thNight
21%12%22%26%14%2
720
16th to endNight
22%16%30%23%6%1
708
November1st to 15thNight
18%19%28%23%8%1
700
16th to endNight
16%27%28%17%8%
722
December1st to 15thNight
25%24%29%15%4
750
16th to endNight
26%28%28%14%2
775
Page generated at 2017-10-17 16:35:26. Version ac04

Copyright 2017 A. Danko


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