NAA
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the NAA clear sky chart from 2005-11-05 to 2017-09-18.

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
39%
15961
19%
46853
11%
15919
46%
15919
25%
30695

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
22%
900
15%
2506
4%
895
31%
895
19%
1795
January16th to endNight
23%
960
13%
2635
5%
960
30%
960
17%
1975
February1st to 15thNight
23%
803
14%
2214
4%
803
30%
803
20%
1576
February16th to endNight
29%
631
19%
1893
8%
631
39%
631
19%
1300
March1st to 15thNight
29%
720
15%
2160
9%
720
34%
720
19%
1498
March16th to endNight
29%
609
15%
2007
10%
609
37%
609
20%
1362
April1st to 15thNight
30%
539
16%
1797
11%
539
40%
539
21%
1191
April16th to endNight
35%
540
19%
1752
12%
540
44%
540
23%
1147
May1st to 15thNight
35%
540
17%
1590
8%
540
43%
540
24%
1059
May16th to endNight
53%
562
19%
1498
11%
561
58%
561
34%
941
June1st to 15thNight
54%
540
17%
1440
11%
540
57%
540
38%
875
June16th to endNight
51%
540
18%
1440
10%
540
55%
540
33%
927
July1st to 15thNight
64%
510
18%
1360
12%
510
67%
510
40%
811
July16th to endNight
73%
564
24%
1417
18%
531
76%
531
46%
798
August1st to 15thNight
78%
539
22%
1590
22%
536
79%
536
43%
881
August16th to endNight
68%
573
23%
1910
23%
573
72%
573
37%
1023
September1st to 15thNight
65%
540
29%
1800
29%
540
70%
540
38%
935
September16th to endNight
60%
663
27%
1842
20%
663
64%
663
37%
1100
October1st to 15thNight
51%
660
29%
1909
21%
660
58%
660
36%
1107
October16th to endNight
32%
704
20%
2225
12%
704
42%
704
23%
1416
November1st to 15thNight
34%
700
24%
2276
17%
700
45%
700
25%
1379
November16th to endNight
29%
764
18%
2384
10%
764
38%
764
21%
1580
December1st to 15thNight
24%
900
13%
2520
5%
900
30%
900
18%
1855
December16th to endNight
19%
960
11%
2688
3%
960
26%
960
12%
2164

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
14%7%35%5%3445%7%37%
47949
Night
14%7%35%424346%40%
47021
Cloud CoverDay
14%7%36%5%3445%7%37%
47958
Night
14%7%35%424446%40%
47026
TransparencyDay
45%312%23%12%1
47635
Night
44%311%23%14%2
46853
SeeingDay
15%5%24%26%19%7%
5973
Night
18%7%27%32%13%1
15965

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%13%5%9%5%35%446%26%
1432
16th to endDay
15%14%6%9%6%34435%25%
1587
February1st to 15thDay
16%13%5%6%5%35%445%29%
1645
16th to endDay
16%9%47%6%33345%33%
1580
March1st to 15thDay
17%10%37%5%3445%6%31%
1790
16th to endDay
18%8%46%5%35%448%29%
2227
April1st to 15thDay
18%10%45%5%2435%6%32%
2151
16th to endDay
20%7%25%5%34347%35%
2208
May1st to 15thDay
19%8%36%5%4446%7%29%
2360
16th to endDay
15%6%25%4345%6%7%38%
2617
June1st to 15thDay
11%5%25%5%345%5%7%44%
2520
16th to endDay
9%5%35%6%35%6%6%9%38%
2520
July1st to 15thDay
8%3135%35%5%6%9%46%
2520
16th to endDay
6%4245%36%6%6%9%43%
2655
August1st to 15thDay
6%426%5%345%6%10%43%
2357
16th to endDay
10%3245%35%6%6%9%42%
2292
September1st to 15thDay
12%313434446%50%
2153
16th to endDay
8%435%5%2446%8%45%
1837
October1st to 15thDay
15%5%25%324447%43%
1719
16th to endDay
17%7%26%6%33347%38%
1646
November1st to 15thDay
13%7%35%42435%6%42%
1582
16th to endDay
19%8%47%424435%35%
1575
December1st to 15thDay
19%11%47%5%35%436%28%
1440
16th to endDay
23%13%5%7%424436%22%
1536
January1st to 15thNight
16%11%47%423436%34%
2506
16th to endNight
13%12%7%8%6%24346%28%
2635
February1st to 15thNight
15%12%5%6%423336%35%
2212
16th to endNight
16%9%47%5%24345%36%
1893
March1st to 15thNight
17%11%36%43434437%
2147
16th to endNight
16%10%36%5%2446%5%33%
2007
April1st to 15thNight
17%8%45%424346%37%
1797
16th to endNight
19%7%25%333446%38%
1752
May1st to 15thNight
18%5%26%42445%8%36%
1590
16th to endNight
10%41443446%10%44%
1496
June1st to 15thNight
11%415%33345%6%50%
1440
16th to endNight
8%4345%45%5%6%9%42%
1440
July1st to 15thNight
6%415%43445%7%52%
1440
16th to endNight
5%213425%47%9%52%
1513
August1st to 15thNight
33243345%6%9%53%
1599
16th to endNight
10%41331435%9%51%
1910
September1st to 15thNight
10%313213347%58%
1800
16th to endNight
7%425%434448%50%
1842
October1st to 15thNight
12%5%23332347%51%
1909
16th to endNight
19%7%24422345%42%
2225
November1st to 15thNight
14%7%2442344447%
2276
16th to endNight
19%7%35%423337%38%
2384
December1st to 15thNight
21%9%46%5%34345%31%
2520
16th to endNight
24%13%49%6%3433422%
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
14%12%6%8%5%36%346%26%
1432
16th to endDay
15%14%6%8%7%345%36%24%
1587
February1st to 15thDay
16%13%5%7%5%35%445%28%
1645
16th to endDay
17%10%48%5%23445%33%
1580
March1st to 15thDay
17%10%47%5%25%446%30%
1800
16th to endDay
18%9%45%6%35%45%7%30%
2226
April1st to 15thDay
19%9%46%42345%6%32%
2151
16th to endDay
20%6%35%5%33446%35%
2208
May1st to 15thDay
20%8%36%6%345%5%7%30%
2360
16th to endDay
15%5%25%4245%5%7%39%
2617
June1st to 15thDay
11%5%245%35%45%7%44%
2520
16th to endDay
9%5%25%5%46%6%7%9%37%
2520
July1st to 15thDay
8%3235%35%5%6%9%46%
2520
16th to endDay
6%4245%36%6%6%8%43%
2655
August1st to 15thDay
6%425%5%45%5%6%10%42%
2357
16th to endDay
10%415%436%5%6%9%42%
2292
September1st to 15thDay
11%413435%447%49%
2153
16th to endDay
8%5%26%43346%8%46%
1837
October1st to 15thDay
14%5%25%5%24447%43%
1719
16th to endDay
17%6%36%5%23448%37%
1646
November1st to 15thDay
14%8%34424346%42%
1582
16th to endDay
18%9%37%424346%34%
1575
December1st to 15thDay
19%11%46%5%35%446%28%
1440
16th to endDay
23%13%6%6%5%35%436%22%
1536
January1st to 15thNight
16%10%47%5%23445%34%
2506
16th to endNight
13%11%7%9%6%23446%28%
2635
February1st to 15thNight
15%12%6%6%424335%35%
2205
16th to endNight
15%9%47%5%24345%36%
1893
March1st to 15thNight
17%11%45%5%24335%36%
2160
16th to endNight
17%8%46%5%3446%5%33%
2007
April1st to 15thNight
17%7%45%5%23446%38%
1797
16th to endNight
20%6%25%33335%7%38%
1752
May1st to 15thNight
18%5%25%33345%9%35%
1589
16th to endNight
10%4244346%6%9%44%
1496
June1st to 15thNight
12%325%32445%5%50%
1440
16th to endNight
9%435%6%26%5%5%9%42%
1440
July1st to 15thNight
6%3145%35%45%7%51%
1440
16th to endNight
5%313325%5%7%9%52%
1513
August1st to 15thNight
43144245%5%9%52%
1599
16th to endNight
10%31332345%9%51%
1910
September1st to 15thNight
11%213313347%57%
1800
16th to endNight
7%314435%45%7%50%
1842
October1st to 15thNight
13%423323347%50%
1909
16th to endNight
20%7%34322245%42%
2225
November1st to 15thNight
13%6%25%5%23345%47%
2276
16th to endNight
19%6%45%5%24246%38%
2384
December1st to 15thNight
21%9%47%5%3433432%
2520
16th to endNight
24%13%5%9%6%3423422%
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
59%312%15%9%
1433
16th to endDay
61%312%15%7%
1587
February1st to 15thDay
57%311%17%7%1
1647
16th to endDay
52%313%22%6%1
1580
March1st to 15thDay
54%313%21%6%
1800
16th to endDay
52%414%21%5%1
2227
April1st to 15thDay
52%310%22%11%
2151
16th to endDay
49%214%17%11%3
2208
May1st to 15thDay
52%312%23%7%
2360
16th to endDay
43%412%22%15%2
2621
June1st to 15thDay
38%410%27%17%1
2520
16th to endDay
41%5%12%22%16%1
2520
July1st to 15thDay
33%414%28%16%2
2371
16th to endDay
33%5%17%26%14%2
2488
August1st to 15thDay
34%414%28%16%1
2342
16th to endDay
35%5%12%26%17%3
2292
September1st to 15thDay
35%39%26%20%5%
2153
16th to endDay
34%310%30%19%2
1837
October1st to 15thDay
40%310%28%15%1
1719
16th to endDay
46%213%24%10%2
1646
November1st to 15thDay
43%210%25%15%2
1582
16th to endDay
51%212%24%8%
1575
December1st to 15thDay
58%113%18%7%
1440
16th to endDay
65%210%12%7%
1536
January1st to 15thNight
52%312%19%11%
2506
16th to endNight
57%314%16%8%
2635
February1st to 15thNight
52%211%22%9%1
2214
16th to endNight
50%311%23%9%1
1893
March1st to 15thNight
51%212%20%10%2
2160
16th to endNight
50%214%20%9%1
2007
April1st to 15thNight
47%29%22%15%2
1797
16th to endNight
46%210%22%12%4
1752
May1st to 15thNight
45%312%25%12%
1590
16th to endNight
34%5%14%22%19%2
1498
June1st to 15thNight
33%312%27%19%3
1440
16th to endNight
36%5%13%21%18%3
1440
July1st to 15thNight
31%312%27%21%2
1360
16th to endNight
25%415%29%19%4
1417
August1st to 15thNight
26%5%16%30%19%2
1590
16th to endNight
29%412%29%19%4
1910
September1st to 15thNight
28%39%28%26%4
1800
16th to endNight
32%49%29%20%3
1842
October1st to 15thNight
32%210%28%22%2
1909
16th to endNight
44%210%25%15%1
2225
November1st to 15thNight
40%38%25%17%4
2276
16th to endNight
47%212%24%11%
2384
December1st to 15thNight
56%211%21%8%
2520
16th to endNight
66%29%14%6%
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
25%5%35%23%10%
90
16th to endDay
18%8%34%28%10%
96
February1st to 15thDay
17%17%43%18%2
90
16th to endDay
20%7%33%22%16%
81
March1st to 15thDay
34%14%27%16%6%
90
16th to endDay
28%8%28%20%11%2
234
April1st to 15thDay
22%10%29%24%10%1
270
16th to endDay
23%8%23%28%11%5%
270
May1st to 15thDay
22%8%26%26%12%4
317
16th to endDay
17%7%29%22%18%5%
517
June1st to 15thDay
12%424%32%20%5%
495
16th to endDay
12%5%30%28%17%6%
495
July1st to 15thDay
11%321%28%24%11%
475
16th to endDay
7%220%30%27%12%
515
August1st to 15thDay
7%212%31%28%17%
408
16th to endDay
11%212%26%31%15%
332
September1st to 15thDay
11%212%30%32%10%
315
16th to endDay
10%218%30%29%8%
262
October1st to 15thDay
13%5%23%26%25%6%
159
16th to endDay
21%7%35%26%9%
96
November1st to 15thDay
7%8%26%31%16%8%
90
16th to endDay
43%5%27%13%8%1
90
December1st to 15thDay
22%12%31%24%8%1
90
16th to endDay
28%15%45%7%21
96
January1st to 15thNight
23%11%36%23%6%
900
16th to endNight
19%11%32%32%4
960
February1st to 15thNight
21%9%35%28%4
806
16th to endNight
21%9%32%29%6%
631
March1st to 15thNight
22%11%30%28%6%
720
16th to endNight
20%9%34%25%9%1
609
April1st to 15thNight
20%10%34%28%6%
539
16th to endNight
23%5%31%29%9%
540
May1st to 15thNight
23%332%29%10%
540
16th to endNight
12%424%41%16%
563
June1st to 15thNight
14%223%44%15%
540
16th to endNight
9%324%42%19%1
540
July1st to 15thNight
9%116%42%27%2
510
16th to endNight
6%111%45%31%4
564
August1st to 15thNight
36%49%33%5%
539
16th to endNight
10%212%37%33%3
573
September1st to 15thNight
11%215%36%29%5%
540
16th to endNight
9%317%37%28%3
663
October1st to 15thNight
15%5%21%35%19%1
660
16th to endNight
23%8%29%28%9%
704
November1st to 15thNight
16%10%32%27%12%1
700
16th to endNight
22%10%30%27%8%
764
December1st to 15thNight
26%10%30%25%7%
900
16th to endNight
29%9%31%24%4
960
Page generated at 2017-09-19 06:32:29. Version ac04

Copyright 2017 A. Danko


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