Site "M"
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Site "M" clear sky chart from 2005-11-05 to 2018-10-27.

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
40%
17395
20%
51258
13%
17349
47%
17349
27%
32830

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
25%
975
17%
2716
7%
970
32%
970
22%
1882
January16th to endNight
21%
1040
16%
2743
4%
1040
29%
1040
19%
1989
February1st to 15thNight
25%
913
13%
2441
4%
910
31%
910
20%
1756
February16th to endNight
25%
683
20%
2049
8%
683
35%
683
22%
1350
March1st to 15thNight
28%
735
18%
2295
9%
735
37%
735
21%
1536
March16th to endNight
28%
624
15%
2191
9%
624
36%
624
16%
1521
April1st to 15thNight
30%
584
19%
1947
12%
584
42%
584
22%
1230
April16th to endNight
37%
579
19%
1928
15%
579
45%
579
23%
1241
May1st to 15thNight
41%
585
18%
1729
12%
585
47%
585
25%
1159
May16th to endNight
53%
611
19%
1625
12%
609
58%
609
32%
1063
June1st to 15thNight
62%
585
20%
1560
14%
585
65%
585
42%
923
June16th to endNight
55%
585
20%
1560
12%
585
60%
585
37%
958
July1st to 15thNight
70%
555
20%
1480
15%
555
71%
555
41%
881
July16th to endNight
73%
612
26%
1565
21%
579
76%
579
46%
883
August1st to 15thNight
78%
575
24%
1773
26%
572
79%
572
42%
933
August16th to endNight
71%
621
22%
2070
25%
621
75%
621
36%
1133
September1st to 15thNight
65%
585
30%
1950
33%
585
68%
585
36%
1059
September16th to endNight
62%
725
31%
2093
23%
725
67%
725
38%
1201
October1st to 15thNight
47%
780
26%
2327
18%
780
54%
780
32%
1408
October16th to endNight
34%
816
25%
2496
15%
816
45%
816
30%
1475
November1st to 15thNight
34%
760
25%
2471
15%
760
46%
760
29%
1428
November16th to endNight
29%
852
22%
2607
12%
852
41%
852
26%
1633
December1st to 15thNight
24%
975
14%
2730
6%
975
31%
975
20%
1942
December16th to endNight
19%
1040
13%
2912
4%
1040
27%
1040
14%
2246

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%7%35%5%35%45%7%39%
52300
Night
12%7%35%424446%43%
51429
Cloud CoverDay
12%7%35%5%3445%7%39%
52308
Night
13%7%35%424446%43%
51434
TransparencyDay
43%5%12%23%13%2
51988
Night
41%411%23%15%2
51259
SeeingDay
14%6%23%28%19%7%
7409
Night
16%7%28%31%13%1
17395

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
13%12%5%10%6%35%445%28%
1552
16th to endDay
12%13%5%8%6%34345%31%
1830
February1st to 15thDay
13%11%5%8%6%35%436%31%
1749
16th to endDay
13%10%48%6%35%347%32%
1710
March1st to 15thDay
14%11%46%6%3445%5%34%
1996
16th to endDay
17%10%47%5%35%45%7%28%
2385
April1st to 15thDay
17%7%36%5%25%445%37%
2331
16th to endDay
17%6%36%5%35%45%6%35%
2307
May1st to 15thDay
18%6%25%5%35%46%7%33%
2549
16th to endDay
13%5%35%6%35%47%8%37%
2841
June1st to 15thDay
8%426%426%5%7%8%44%
2730
16th to endDay
8%425%6%35%5%5%9%43%
2730
July1st to 15thDay
6%3145%45%6%6%9%46%
2730
16th to endDay
5%324425%6%7%11%44%
2856
August1st to 15thDay
6%415%5%35%6%6%9%43%
2430
16th to endDay
8%4245%35%5%5%8%45%
2484
September1st to 15thDay
12%424424437%48%
2340
16th to endDay
7%6%245%3445%7%48%
2183
October1st to 15thDay
16%6%245%23345%43%
1960
16th to endDay
15%7%23423336%46%
1985
November1st to 15thDay
16%5%25%32445%6%44%
1717
16th to endDay
15%8%5%6%5%13245%41%
1681
December1st to 15thDay
16%11%46%6%33446%31%
1560
16th to endDay
17%12%6%6%5%25%5%46%27%
1664
January1st to 15thNight
13%8%46%6%34445%37%
2716
16th to endNight
12%11%5%7%6%34445%33%
2743
February1st to 15thNight
15%10%46%6%24345%35%
2439
16th to endNight
15%9%36%323346%40%
2049
March1st to 15thNight
16%8%44424345%40%
2282
16th to endNight
17%10%45%5%25%347%32%
2191
April1st to 15thNight
13%7%25%434447%40%
1947
16th to endNight
18%7%25%424446%40%
1928
May1st to 15thNight
15%5%35%42446%7%38%
1729
16th to endNight
8%6%26%425%5%6%9%43%
1624
June1st to 15thNight
8%41442345%8%51%
1560
16th to endNight
6%5%15%43347%8%48%
1560
July1st to 15thNight
5%3245%3445%9%51%
1560
16th to endNight
422342447%10%54%
1662
August1st to 15thNight
422332445%9%56%
1783
16th to endNight
7%2234245%5%8%53%
2070
September1st to 15thNight
11%413322345%55%
1950
16th to endNight
6%5%2342445%8%52%
2093
October1st to 15thNight
13%424424347%48%
2327
16th to endNight
14%5%2431335%450%
2496
November1st to 15thNight
11%7%25%423245%50%
2471
16th to endNight
15%6%24423446%44%
2607
December1st to 15thNight
19%10%36%424345%35%
2730
16th to endNight
19%12%49%6%35%33427%
2912

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
13%12%5%10%7%35%445%28%
1552
16th to endDay
12%13%5%8%6%34335%31%
1830
February1st to 15thDay
13%11%6%7%6%35%446%31%
1749
16th to endDay
13%10%48%6%35%347%33%
1710
March1st to 15thDay
14%11%46%6%3445%5%34%
2006
16th to endDay
17%10%48%5%25%45%7%29%
2383
April1st to 15thDay
17%7%35%5%25%445%37%
2331
16th to endDay
17%7%26%5%345%5%6%35%
2307
May1st to 15thDay
19%6%35%5%35%5%5%7%33%
2549
16th to endDay
13%5%35%5%35%46%8%37%
2841
June1st to 15thDay
8%426%326%5%7%8%44%
2730
16th to endDay
8%425%5%35%5%5%8%43%
2730
July1st to 15thDay
6%4245%35%6%6%9%46%
2730
16th to endDay
6%314425%6%7%10%45%
2856
August1st to 15thDay
7%325%5%35%6%6%9%43%
2430
16th to endDay
8%4245%35%5%5%8%45%
2484
September1st to 15thDay
12%414434446%49%
2340
16th to endDay
7%5%245%3345%7%49%
2183
October1st to 15thDay
17%5%25%423445%43%
1960
16th to endDay
16%7%23422336%46%
1985
November1st to 15thDay
16%5%2441445%6%44%
1717
16th to endDay
15%8%47%412245%41%
1681
December1st to 15thDay
16%11%46%5%3345%7%31%
1560
16th to endDay
17%11%5%7%5%25%5%5%5%27%
1664
January1st to 15thNight
13%9%37%5%34445%37%
2716
16th to endNight
13%11%5%7%6%34445%34%
2743
February1st to 15thNight
15%10%46%6%24345%35%
2432
16th to endNight
16%9%26%423346%40%
2049
March1st to 15thNight
16%8%35%5%23345%39%
2295
16th to endNight
17%10%36%5%34447%32%
2191
April1st to 15thNight
13%7%25%43445%6%41%
1947
16th to endNight
17%7%24424446%40%
1928
May1st to 15thNight
16%5%345%25%46%8%38%
1728
16th to endNight
9%5%25%5%245%6%8%43%
1624
June1st to 15thNight
8%4144235%5%8%52%
1560
16th to endNight
6%5%15%5%3346%8%48%
1560
July1st to 15thNight
5%3245%3445%9%51%
1560
16th to endNight
421332447%10%54%
1662
August1st to 15thNight
421332446%9%56%
1783
16th to endNight
7%22342445%8%52%
2070
September1st to 15thNight
11%413323345%55%
1950
16th to endNight
6%5%24424448%52%
2093
October1st to 15thNight
13%424424347%48%
2327
16th to endNight
14%5%2432325%450%
2496
November1st to 15thNight
11%7%25%422245%50%
2471
16th to endNight
15%6%24423446%44%
2607
December1st to 15thNight
19%10%36%424345%35%
2730
16th to endNight
18%12%49%6%3433428%
2912

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
58%38%18%11%
1553
16th to endDay
55%413%19%7%
1830
February1st to 15thDay
54%413%20%5%
1751
16th to endDay
51%5%12%20%10%
1710
March1st to 15thDay
51%413%21%7%
2006
16th to endDay
54%5%13%19%6%1
2385
April1st to 15thDay
48%410%23%11%1
2331
16th to endDay
47%5%11%20%12%1
2307
May1st to 15thDay
48%6%13%20%9%
2549
16th to endDay
42%7%13%18%15%2
2845
June1st to 15thDay
34%7%13%25%16%2
2730
16th to endDay
36%7%12%23%16%3
2730
July1st to 15thDay
32%7%13%27%13%4
2581
16th to endDay
29%8%16%30%14%
2690
August1st to 15thDay
33%8%13%27%15%1
2416
16th to endDay
34%7%11%25%17%4
2484
September1st to 15thDay
35%5%7%23%19%7%
2340
16th to endDay
33%49%29%20%2
2183
October1st to 15thDay
41%410%23%17%2
1960
16th to endDay
39%310%25%18%2
1985
November1st to 15thDay
40%311%22%18%3
1717
16th to endDay
45%312%26%11%
1681
December1st to 15thDay
52%415%18%9%
1560
16th to endDay
57%411%18%7%
1664
January1st to 15thNight
47%411%21%13%
2716
16th to endNight
52%313%20%9%
2743
February1st to 15thNight
52%313%18%10%2
2441
16th to endNight
45%313%24%11%1
2049
March1st to 15thNight
46%49%23%13%2
2295
16th to endNight
52%411%21%8%1
2191
April1st to 15thNight
42%410%25%14%2
1947
16th to endNight
44%410%20%15%4
1928
May1st to 15thNight
43%6%13%21%15%
1729
16th to endNight
37%6%14%19%18%3
1626
June1st to 15thNight
28%5%14%26%20%3
1560
16th to endNight
32%6%13%24%20%4
1560
July1st to 15thNight
30%412%29%17%5%
1480
16th to endNight
24%5%14%31%20%2
1565
August1st to 15thNight
23%6%13%31%21%3
1773
16th to endNight
27%7%11%27%20%5%
2070
September1st to 15thNight
31%28%25%22%8%
1950
16th to endNight
29%410%25%25%4
2093
October1st to 15thNight
35%49%24%20%5%
2327
16th to endNight
36%38%26%22%2
2496
November1st to 15thNight
36%311%24%18%5%
2471
16th to endNight
40%311%27%16%
2607
December1st to 15thNight
51%314%18%10%
2730
16th to endNight
60%410%16%7%1
2912

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
24%13%37%15%8%
135
16th to endDay
7%20%41%25%5%
144
February1st to 15thDay
23%16%33%21%5%
135
16th to endDay
22%16%33%21%5%
120
March1st to 15thDay
27%11%40%18%1
135
16th to endDay
29%13%29%18%8%1
241
April1st to 15thDay
20%11%32%25%9%
330
16th to endDay
18%6%28%29%14%2
319
May1st to 15thDay
18%12%27%26%12%1
413
16th to endDay
16%5%28%24%15%8%
597
June1st to 15thDay
9%320%33%25%7%
570
16th to endDay
10%425%32%19%7%
570
July1st to 15thDay
10%114%32%25%14%
550
16th to endDay
8%113%35%30%10%
595
August1st to 15thDay
7%110%35%30%13%
493
16th to endDay
10%114%27%35%10%
396
September1st to 15thDay
14%112%27%29%13%
375
16th to endDay
8%6%15%27%30%12%
374
October1st to 15thDay
22%6%21%33%11%4
190
16th to endDay
21%9%31%30%6%1
178
November1st to 15thDay
9%8%34%21%15%11%
135
16th to endDay
32%8%33%18%6%
135
December1st to 15thDay
14%21%33%20%8%2
135
16th to endDay
25%13%48%11%2
144
January1st to 15thNight
18%13%38%23%5%
975
16th to endNight
20%13%36%26%3
1040
February1st to 15thNight
20%12%34%28%4
913
16th to endNight
21%11%35%27%2
683
March1st to 15thNight
22%9%35%28%4
735
16th to endNight
23%9%33%25%7%
624
April1st to 15thNight
17%13%35%27%7%
584
16th to endNight
22%6%30%30%10%
579
May1st to 15thNight
20%5%28%33%10%1
585
16th to endNight
9%325%37%19%3
611
June1st to 15thNight
11%218%48%18%1
585
16th to endNight
10%224%39%21%1
585
July1st to 15thNight
6%212%42%33%3
555
16th to endNight
5%13%41%36%3
612
August1st to 15thNight
6%6%46%33%5%
575
16th to endNight
7%12%34%40%3
621
September1st to 15thNight
12%312%35%31%5%
585
16th to endNight
9%5%17%34%28%5%
725
October1st to 15thNight
15%5%27%32%17%1
780
16th to endNight
18%9%34%27%10%
816
November1st to 15thNight
14%10%36%28%9%
760
16th to endNight
20%9%37%25%6%
852
December1st to 15thNight
24%10%36%23%5%
975
16th to endNight
25%11%35%24%3
1040
Page generated at 2018-10-28 07:41:06. Version ac04

Copyright 2018 A. Danko


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