Blythewood
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Blythewood clear sky chart from 2005-11-06 to 2024-01-11.

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
46%
24315
22%
74345
14%
24260
54%
24260
26%
46687

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 10thNight
29%
759
23%
2459
9%
757
46%
757
23%
1496
January11th to 20thNight
31%
724
23%
2352
11%
724
46%
724
23%
1444
January21st to endNight
27%
792
27%
2574
14%
792
44%
792
24%
1555
February1st to 10thNight
32%
720
21%
2336
12%
720
44%
720
23%
1455
February11th to 20thNight
21%
702
22%
2098
9%
699
35%
699
23%
1363
February21st to endNight
28%
592
25%
1718
11%
592
42%
592
24%
1098
March1st to 10thNight
33%
720
27%
1980
13%
720
45%
720
31%
1232
March11th to 20thNight
28%
720
21%
1980
10%
720
38%
720
26%
1300
March21st to endNight
31%
792
21%
2178
8%
792
42%
792
26%
1422
April1st to 10thNight
36%
720
24%
1980
11%
720
47%
720
32%
1187
April11th to 20thNight
39%
711
24%
1793
10%
711
48%
711
35%
1118
April21st to endNight
43%
629
29%
1709
14%
629
52%
629
38%
992
May1st to 10thNight
45%
540
21%
1620
11%
540
52%
540
33%
943
May11th to 20thNight
47%
531
15%
1593
8%
531
52%
531
24%
1070
May21st to endNight
63%
582
19%
1744
15%
582
66%
582
29%
1110
June1st to 10thNight
57%
540
15%
1620
12%
540
58%
540
23%
1101
June11th to 20thNight
62%
540
14%
1620
11%
540
64%
540
26%
1071
June21st to endNight
63%
540
14%
1620
11%
540
64%
540
24%
1094
July1st to 10thNight
65%
525
12%
1575
10%
525
65%
525
23%
1085
July11th to 20thNight
70%
522
11%
1566
9%
522
71%
522
24%
1066
July21st to endNight
68%
591
13%
1672
11%
558
70%
558
24%
1153
August1st to 10thNight
64%
537
11%
1600
11%
534
64%
534
22%
1127
August11th to 20thNight
62%
534
14%
1598
11%
534
63%
534
22%
1113
August21st to endNight
59%
751
14%
1939
10%
751
59%
751
24%
1390
September1st to 10thNight
68%
720
19%
1971
15%
720
69%
720
29%
1286
September11th to 20thNight
59%
720
20%
1980
17%
720
61%
720
27%
1334
September21st to endNight
56%
720
19%
1980
15%
720
60%
720
26%
1338
October1st to 10thNight
52%
720
26%
2083
23%
720
58%
720
33%
1240
October11th to 20thNight
49%
720
30%
2160
25%
720
59%
720
33%
1239
October21st to endNight
51%
792
32%
2376
24%
792
63%
792
35%
1353
November1st to 10thNight
48%
740
29%
2221
22%
740
58%
740
35%
1258
November11th to 20thNight
41%
760
28%
2379
19%
760
53%
760
31%
1373
November21st to endNight
45%
760
26%
2470
20%
760
54%
760
29%
1441
December1st to 10thNight
37%
760
23%
2470
13%
760
50%
760
21%
1602
December11th to 20thNight
40%
759
28%
2921
20%
758
51%
758
24%
1651
December21st to endNight
32%
830
16%
4410
15%
817
43%
817
13%
2587

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%5%25%5%35%5%6%8%43%
74914
Night
13%6%25%5%345%5%7%44%
74796
TransparencyDay
38%7%12%20%18%5%
74637
Night
38%7%11%19%19%6%
74592
SeeingDay
15%10%24%24%19%8%
14189
Night
15%8%24%31%19%2
24326

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 10thDay
16%6%25%43445%6%45%
1706
11th to 20thDay
16%7%35%5%34445%44%
1620
21st to endDay
17%6%34423445%47%
1782
February1st to 10thDay
15%6%35%5%36%45%7%41%
1622
11th to 20thDay
21%5%24324346%45%
1748
21st to endDay
20%7%35%5%3335%6%41%
1538
March1st to 10thDay
14%5%24424345%53%
1980
11th to 20thDay
16%5%35%5%35%5%5%7%41%
1980
21st to endDay
15%6%35%6%345%6%7%42%
2178
April1st to 10thDay
10%325%5%25%5%6%7%50%
1980
11th to 20thDay
10%5%35%5%35%5%6%7%47%
2116
21st to endDay
9%4344345%5%8%51%
2265
May1st to 10thDay
7%5%25%5%345%6%8%48%
2340
11th to 20thDay
12%5%35%5%36%5%7%7%41%
2301
21st to endDay
10%5%36%6%47%5%6%9%38%
2531
June1st to 10thDay
9%6%26%7%36%6%7%11%36%
2340
11th to 20thDay
8%425%5%37%6%8%11%41%
2340
21st to endDay
6%425%6%47%6%8%12%39%
2340
July1st to 10thDay
9%5%36%8%47%7%8%12%33%
2340
11th to 20thDay
7%5%37%7%5%7%7%9%12%32%
2340
21st to endDay
6%5%36%7%5%8%7%10%12%31%
2547
August1st to 10thDay
9%6%37%7%47%7%8%12%30%
2327
11th to 20thDay
14%6%26%7%46%7%8%11%29%
2303
21st to endDay
12%6%36%7%46%7%9%10%29%
2399
September1st to 10thDay
8%5%27%6%46%5%7%10%41%
1984
11th to 20thDay
12%6%36%6%35%6%6%7%41%
1980
21st to endDay
16%6%26%5%3445%6%42%
1980
October1st to 10thDay
15%5%24433446%50%
1877
11th to 20thDay
11%5%15%433345%57%
1800
21st to endDay
12%5%2432433457%
1980
November1st to 10thDay
12%6%23423345%56%
1857
11th to 20thDay
14%5%25%313436%54%
1796
21st to endDay
14%5%25%5%23446%50%
1710
December1st to 10thDay
19%7%35%5%345%5%6%39%
1710
11th to 20thDay
16%424423346%51%
2153
21st to endDay
20%7%34334446%44%
3124
January1st to 10thNight
17%6%35%333335%48%
2459
11th to 20thNight
15%6%25%5%3445%6%45%
2352
21st to endNight
17%6%34423445%48%
2574
February1st to 10thNight
18%5%245%3445%6%44%
2336
11th to 20thNight
19%6%25%5%34446%44%
2098
21st to endNight
16%6%26%435%45%7%44%
1718
March1st to 10thNight
14%6%24424446%50%
1980
11th to 20thNight
16%5%245%4445%6%44%
1980
21st to endNight
13%6%245%346%5%8%43%
2178
April1st to 10thNight
11%5%2432445%7%52%
1980
11th to 20thNight
12%42443445%6%52%
1793
21st to endNight
10%4245%2345%8%53%
1709
May1st to 10thNight
8%5%245%345%7%8%48%
1620
11th to 20thNight
11%5%36%5%5%6%5%7%9%38%
1592
21st to endNight
9%435%5%45%6%8%9%43%
1744
June1st to 10thNight
12%6%35%6%46%6%9%10%33%
1620
11th to 20thNight
9%5%25%6%46%6%9%10%37%
1620
21st to endNight
7%5%35%6%47%8%9%12%34%
1620
July1st to 10thNight
7%6%36%7%47%8%8%11%33%
1620
11th to 20thNight
7%6%247%46%7%9%11%35%
1620
21st to endNight
5%5%37%7%5%6%8%8%12%34%
1771
August1st to 10thNight
9%427%8%46%7%8%12%32%
1611
11th to 20thNight
11%7%37%7%45%6%8%11%32%
1598
21st to endNight
10%6%47%8%45%6%8%11%31%
1939
September1st to 10thNight
8%5%35%6%46%6%6%11%40%
1971
11th to 20thNight
12%6%26%6%45%5%6%7%40%
1980
21st to endNight
16%7%346%3445%5%43%
1980
October1st to 10thNight
13%6%25%42335%6%52%
2083
11th to 20thNight
13%5%2442235%6%53%
2160
21st to endNight
10%5%23423445%56%
2376
November1st to 10thNight
12%6%24323345%56%
2221
11th to 20thNight
14%5%34433345%54%
2379
21st to endNight
14%43443446%7%47%
2470
December1st to 10thNight
18%7%25%5%34445%43%
2470
11th to 20thNight
17%5%24423335%52%
3042
21st to endNight
20%6%25%434446%41%
4532

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 10thDay
40%5%9%18%22%6%
1707
11th to 20thDay
42%5%8%16%22%6%
1620
21st to endDay
39%35%21%25%7%
1782
February1st to 10thDay
42%5%10%20%18%6%
1622
11th to 20thDay
42%5%5%19%25%5%
1758
21st to endDay
45%47%16%19%9%
1538
March1st to 10thDay
35%47%21%23%10%
1980
11th to 20thDay
42%6%10%18%17%7%
1980
21st to endDay
42%6%10%18%20%4
2178
April1st to 10thDay
32%6%11%19%27%6%
1980
11th to 20thDay
35%6%10%20%19%10%
2116
21st to endDay
30%6%10%25%23%5%
2265
May1st to 10thDay
33%7%14%22%20%4
2340
11th to 20thDay
40%8%14%18%18%2
2305
21st to endDay
40%9%13%22%15%1
2531
June1st to 10thDay
40%9%15%24%10%2
2340
11th to 20thDay
34%10%17%26%12%2
2340
21st to endDay
35%11%18%20%14%2
2340
July1st to 10thDay
38%13%20%16%10%2
2275
11th to 20thDay
40%14%21%18%6%2
2271
21st to endDay
39%13%20%20%8%1
2405
August1st to 10thDay
43%11%18%19%8%1
2314
11th to 20thDay
46%13%16%16%9%1
2303
21st to endDay
43%13%17%17%8%2
2399
September1st to 10thDay
37%9%13%18%19%4
1984
11th to 20thDay
39%9%11%16%21%4
1980
21st to endDay
42%5%8%21%16%7%
1980
October1st to 10thDay
35%48%20%25%7%
1877
11th to 20thDay
31%48%24%25%8%
1800
21st to endDay
31%46%18%29%11%
1980
November1st to 10thDay
32%47%18%28%12%
1857
11th to 20thDay
33%47%21%25%10%
1796
21st to endDay
37%48%19%23%9%
1710
December1st to 10thDay
45%6%9%19%17%5%
1710
11th to 20thDay
35%37%21%23%10%
2150
21st to endDay
42%47%22%23%3
3124
January1st to 10thNight
40%48%18%24%7%
2459
11th to 20thNight
40%5%9%17%22%7%
2352
21st to endNight
40%3420%25%8%
2574
February1st to 10thNight
41%48%18%19%9%
2336
11th to 20thNight
42%5%7%17%21%7%
2099
21st to endNight
40%410%17%19%9%
1718
March1st to 10thNight
36%48%16%23%12%
1980
11th to 20thNight
41%5%11%16%21%7%
1980
21st to endNight
38%7%11%19%19%5%
2178
April1st to 10thNight
32%5%11%19%23%9%
1980
11th to 20thNight
32%6%10%20%22%11%
1793
21st to endNight
29%5%11%27%23%5%
1709
May1st to 10thNight
31%6%14%23%20%5%
1620
11th to 20thNight
40%10%14%19%16%1
1593
21st to endNight
33%11%13%24%15%3
1745
June1st to 10thNight
41%11%17%19%11%1
1620
11th to 20thNight
37%11%17%22%10%2
1620
21st to endNight
37%14%18%18%11%2
1620
July1st to 10thNight
41%12%21%14%10%3
1575
11th to 20thNight
38%13%23%18%7%2
1566
21st to endNight
38%14%21%18%9%1
1672
August1st to 10thNight
42%13%21%18%6%1
1600
11th to 20thNight
43%11%21%16%8%1
1598
21st to endNight
44%10%18%18%8%2
1939
September1st to 10thNight
36%10%16%19%15%5%
1971
11th to 20thNight
41%7%12%17%19%3
1980
21st to endNight
42%7%11%17%18%5%
1980
October1st to 10thNight
34%5%9%19%27%6%
2083
11th to 20thNight
32%5%8%22%23%10%
2160
21st to endNight
30%5%6%19%27%13%
2376
November1st to 10thNight
31%48%15%27%14%
2221
11th to 20thNight
34%47%17%25%13%
2379
21st to endNight
35%48%19%24%9%
2470
December1st to 10thNight
44%5%8%18%18%6%
2470
11th to 20thNight
36%37%18%25%10%
3044
21st to endNight
44%47%20%21%4
4532

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 10thDay
20%24%41%12%3
270
11th to 20thDay
20%20%37%20%4
240
21st to endDay
21%28%37%12%3
264
February1st to 10thDay
19%25%38%14%4
240
11th to 20thDay
35%17%40%6%2
240
21st to endDay
27%21%33%14%5%
256
March1st to 10thDay
19%16%36%22%6%
420
11th to 20thDay
20%19%39%16%41
420
21st to endDay
19%16%36%19%8%1
462
April1st to 10thDay
19%17%34%19%11%
420
11th to 20thDay
13%17%29%24%14%4
412
21st to endDay
14%11%29%26%15%4
420
May1st to 10thDay
10%13%36%22%15%4
423
11th to 20thDay
16%6%21%29%20%8%
447
21st to endDay
14%416%27%25%13%
485
June1st to 10thDay
12%419%29%27%10%
450
11th to 20thDay
9%6%18%24%26%15%
450
21st to endDay
9%316%32%27%13%
450
July1st to 10thDay
9%29%26%31%24%
445
11th to 20thDay
9%212%28%33%16%
444
21st to endDay
7%210%35%33%14%
488
August1st to 10thDay
13%5%14%22%31%15%
446
11th to 20thDay
15%49%27%29%16%
439
21st to endDay
13%212%28%30%15%
495
September1st to 10thDay
10%310%31%33%13%
450
11th to 20thDay
15%413%27%30%12%
450
21st to endDay
18%5%17%27%26%8%
450
October1st to 10thDay
17%6%20%28%20%9%
450
11th to 20thDay
11%9%24%28%21%7%
450
21st to endDay
14%7%28%29%17%5%
495
November1st to 10thDay
17%9%28%26%16%5%
455
11th to 20thDay
19%14%32%26%8%1
356
21st to endDay
12%15%37%25%9%2
270
December1st to 10thDay
27%13%38%17%4
270
11th to 20thDay
22%13%38%19%6%2
270
21st to endDay
27%16%34%16%5%2
297
January1st to 10thNight
21%14%31%27%7%
760
11th to 20thNight
21%11%31%30%6%
724
21st to endNight
20%14%35%27%4
792
February1st to 10thNight
20%13%32%31%4
720
11th to 20thNight
22%14%39%23%2
703
21st to endNight
19%16%33%28%5%
592
March1st to 10thNight
17%11%36%31%5%
720
11th to 20thNight
19%12%36%24%8%
720
21st to endNight
15%14%35%27%8%
792
April1st to 10thNight
15%14%32%30%8%
720
11th to 20thNight
13%13%32%29%14%
711
21st to endNight
14%7%31%35%12%
629
May1st to 10thNight
10%8%31%38%13%
540
11th to 20thNight
13%330%34%18%2
531
21st to endNight
9%315%36%34%3
584
June1st to 10thNight
13%314%39%26%5%
540
11th to 20thNight
10%314%32%32%8%
540
21st to endNight
9%214%38%30%6%
540
July1st to 10thNight
10%19%38%34%8%
525
11th to 20thNight
10%17%35%39%8%
522
21st to endNight
7%210%36%40%6%
591
August1st to 10thNight
11%29%31%39%7%
537
11th to 20thNight
14%38%31%38%6%
534
21st to endNight
12%112%30%38%7%
751
September1st to 10thNight
10%210%31%41%6%
720
11th to 20thNight
14%214%30%36%4
720
21st to endNight
20%412%35%26%3
720
October1st to 10thNight
16%5%20%29%26%4
720
11th to 20thNight
15%7%22%31%22%2
720
21st to endNight
13%8%24%31%22%2
792
November1st to 10thNight
15%7%25%32%18%3
740
11th to 20thNight
16%11%28%31%12%1
760
21st to endNight
15%8%27%34%15%1
760
December1st to 10thNight
19%12%27%32%9%1
760
11th to 20thNight
20%9%25%34%11%1
760
21st to endNight
25%13%25%28%9%
836
Page generated at 2024-01-08 11:14:19. Version ac07

Copyright 2024 Attilla Danko


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