Greenwood
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Greenwood clear sky chart from 2005-11-06 to 2024-03-28.

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
19%
23796
10%
80846
4%
23669
25%
23669
10%
62314

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
7%
839
6%
4722
2%
817
12%
817
2%
3898
January11th to 20thNight
8%
795
6%
4238
1%
772
13%
772
2%
3645
January21st to endNight
10%
833
4%
4515
2%
814
15%
814
3%
3661
February1st to 10thNight
9%
760
5%
2470
2%
760
14%
760
4%
2132
February11th to 20thNight
8%
743
7%
2406
1%
740
15%
740
5%
2035
February21st to endNight
14%
628
9%
1994
1%
628
22%
628
9%
1553
March1st to 10thNight
11%
760
11%
2106
4%
760
19%
760
9%
1699
March11th to 20thNight
15%
760
10%
2090
3%
760
21%
760
11%
1661
March21st to endNight
14%
821
12%
2256
3%
821
23%
821
12%
1746
April1st to 10thNight
12%
586
10%
1846
3%
586
20%
586
9%
1427
April11th to 20thNight
16%
534
15%
1652
6%
534
26%
534
14%
1185
April21st to endNight
18%
540
13%
1620
4%
540
25%
540
13%
1217
May1st to 10thNight
21%
540
12%
1616
5%
540
27%
540
14%
1208
May11th to 20thNight
22%
532
14%
1417
5%
532
30%
532
19%
1039
May21st to endNight
20%
583
11%
1551
3%
582
27%
582
18%
1143
June1st to 10thNight
22%
500
9%
1400
4%
500
27%
500
17%
1039
June11th to 20thNight
27%
360
12%
1260
7%
360
35%
360
15%
884
June21st to endNight
25%
360
9%
1260
5%
360
31%
360
14%
905
July1st to 10thNight
28%
350
10%
1225
5%
350
36%
350
19%
810
July11th to 20thNight
32%
437
9%
1307
6%
437
36%
437
20%
916
July21st to endNight
37%
590
11%
1613
7%
558
39%
558
21%
1152
August1st to 10thNight
37%
538
14%
1600
10%
534
40%
534
24%
1060
August11th to 20thNight
36%
532
12%
1596
7%
532
40%
532
18%
1130
August21st to endNight
38%
594
17%
1840
9%
594
45%
594
26%
1169
September1st to 10thNight
37%
540
18%
1800
11%
540
46%
540
23%
1136
September11th to 20thNight
32%
662
20%
1922
12%
662
40%
662
26%
1234
September21st to endNight
28%
720
20%
2002
9%
720
37%
720
22%
1377
October1st to 10thNight
30%
720
17%
2160
9%
720
37%
720
21%
1460
October11th to 20thNight
22%
720
15%
2160
6%
720
31%
720
17%
1523
October21st to endNight
17%
792
13%
2385
5%
792
25%
792
11%
1814
November1st to 10thNight
17%
798
12%
2528
5%
798
24%
798
11%
1895
November11th to 20thNight
15%
850
10%
2660
6%
850
20%
850
8%
2137
November21st to endNight
14%
850
6%
2660
2%
850
18%
850
8%
2166
December1st to 10thNight
8%
850
5%
2660
1%
850
13%
850
5%
2304
December11th to 20thNight
7%
850
5%
3239
1%
849
10%
849
3%
2829
December21st to endNight
9%
929
4%
5070
2%
907
14%
907
2%
4125

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%12%5%8%6%34446%29%
78794
Night
19%13%5%10%7%34445%25%
81192
TransparencyDay
57%6%10%17%9%1
78496
Night
61%6%10%16%7%1
81025
SeeingDay
27%21%31%16%5%1
16015
Night
26%19%31%19%5%
23817

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 10thDay
15%20%7%12%14%4423415%
2207
11th to 20thDay
16%18%8%23%9%443339%
2672
21st to endDay
17%15%8%14%11%5%433416%
3124
February1st to 10thDay
18%16%8%13%13%5%433413%
1710
11th to 20thDay
16%16%7%13%12%6%433416%
1663
21st to endDay
11%14%8%10%8%44345%28%
1456
March1st to 10thDay
15%19%7%10%8%4433421%
2068
11th to 20thDay
13%15%7%10%8%35%33429%
2090
21st to endDay
17%17%6%10%6%3332430%
2255
April1st to 10thDay
23%15%5%7%43345%5%26%
2114
11th to 20thDay
20%12%35%433447%36%
2254
21st to endDay
22%13%35%6%34446%30%
2340
May1st to 10thDay
24%12%47%5%3445%6%27%
2344
11th to 20thDay
22%9%35%424346%37%
2478
21st to endDay
20%10%35%5%3445%7%34%
2724
June1st to 10thDay
25%8%35%5%35%5%6%6%29%
2574
11th to 20thDay
22%7%36%5%345%5%7%35%
2700
21st to endDay
22%9%46%6%45%45%6%29%
2700
July1st to 10thDay
17%7%25%4345%6%8%40%
2700
11th to 20thDay
17%7%35%4345%7%8%37%
2588
21st to endDay
18%7%36%6%35%6%6%7%32%
2607
August1st to 10thDay
16%6%35%5%35%5%6%7%39%
2327
11th to 20thDay
16%6%26%5%45%5%6%7%38%
2304
21st to endDay
15%6%35%43435%7%47%
2516
September1st to 10thDay
18%5%245%2435%7%45%
2160
11th to 20thDay
17%7%35%5%33435%45%
2034
21st to endDay
20%7%25%423346%44%
1958
October1st to 10thDay
20%8%25%5%2345%7%39%
1800
11th to 20thDay
21%10%36%5%24448%34%
1800
21st to endDay
22%14%36%6%33445%29%
1967
November1st to 10thDay
22%13%47%6%34436%28%
1549
11th to 20thDay
19%17%8%9%7%34435%22%
1520
21st to endDay
19%20%7%11%5%34435%18%
1520
December1st to 10thDay
23%20%8%14%6%3333414%
1520
11th to 20thDay
25%18%7%14%10%3443211%
1906
21st to endDay
22%18%10%14%9%2333312%
2545
January1st to 10thNight
15%16%9%18%11%4333315%
4748
11th to 20thNight
16%18%8%19%9%3434412%
4271
21st to endNight
17%13%7%14%13%4445%5%15%
4532
February1st to 10thNight
18%16%8%14%11%4433414%
2470
11th to 20thNight
18%14%6%13%12%4444416%
2403
21st to endNight
12%14%8%11%8%45%445%26%
1994
March1st to 10thNight
16%17%5%9%9%3444423%
2097
11th to 20thNight
16%14%8%10%7%45%345%24%
2089
21st to endNight
19%14%7%8%6%3333330%
2256
April1st to 10thNight
24%16%36%6%4443426%
1846
11th to 20thNight
22%12%45%433447%32%
1652
21st to endNight
23%14%35%6%34346%29%
1620
May1st to 10thNight
22%11%47%5%345%46%29%
1616
11th to 20thNight
25%8%35%5%3445%6%32%
1416
21st to endNight
18%10%47%5%2445%7%33%
1550
June1st to 10thNight
27%7%35%446%46%8%28%
1400
11th to 20thNight
22%7%36%6%35%336%34%
1260
21st to endNight
21%8%35%6%445%5%8%30%
1260
July1st to 10thNight
16%6%46%4346%6%9%36%
1260
11th to 20thNight
15%7%36%6%46%6%7%9%31%
1350
21st to endNight
17%8%36%6%36%6%6%9%32%
1707
August1st to 10thNight
16%8%25%5%3446%8%41%
1612
11th to 20thNight
18%8%25%6%446%6%8%32%
1596
21st to endNight
15%6%35%6%3445%8%42%
1840
September1st to 10thNight
15%6%345%345%6%7%43%
1800
11th to 20thNight
19%7%25%42335%6%44%
1922
21st to endNight
17%7%25%4245%6%7%40%
2002
October1st to 10thNight
19%6%35%5%3445%6%40%
2160
11th to 20thNight
18%10%36%5%35%5%47%34%
2160
21st to endNight
27%12%47%424345%28%
2385
November1st to 10thNight
22%13%47%6%34445%29%
2528
11th to 20thNight
18%19%7%9%6%34345%21%
2660
21st to endNight
19%20%7%9%6%34345%21%
2660
December1st to 10thNight
23%19%8%13%6%2433414%
2660
11th to 20thNight
22%17%8%15%9%3332314%
3293
21st to endNight
25%19%8%11%6%2333318%
5117

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
72%6%14%7%1
2208
11th to 20thDay
79%5%6%8%2
2672
21st to endDay
71%5%11%10%3
3124
February1st to 10thDay
77%47%8%4
1710
11th to 20thDay
73%6%8%8%4
1671
21st to endDay
60%5%10%17%8%1
1456
March1st to 10thDay
68%37%14%6%1
2072
11th to 20thDay
60%5%10%14%9%1
2090
21st to endDay
61%46%17%10%2
2255
April1st to 10thDay
63%5%7%13%11%2
2114
11th to 20thDay
51%6%8%20%13%2
2254
21st to endDay
56%5%10%16%10%2
2340
May1st to 10thDay
59%5%9%17%9%2
2344
11th to 20thDay
49%6%9%22%13%1
2482
21st to endDay
53%6%11%21%9%1
2724
June1st to 10thDay
56%6%9%20%8%
2574
11th to 20thDay
50%6%13%18%12%1
2700
21st to endDay
57%7%9%16%10%1
2700
July1st to 10thDay
43%9%15%20%12%1
2625
11th to 20thDay
44%9%14%22%10%1
2508
21st to endDay
51%9%11%21%7%1
2461
August1st to 10thDay
44%9%13%22%11%
2314
11th to 20thDay
45%9%15%21%11%
2304
21st to endDay
38%6%13%27%14%1
2516
September1st to 10thDay
40%7%13%25%14%2
2160
11th to 20thDay
43%5%11%24%16%1
2034
21st to endDay
42%410%25%17%1
1958
October1st to 10thDay
45%5%11%26%12%
1800
11th to 20thDay
51%6%13%22%7%
1800
21st to endDay
59%5%8%17%9%1
1967
November1st to 10thDay
60%6%9%16%8%1
1549
11th to 20thDay
65%6%11%13%41
1520
21st to endDay
71%7%10%10%2
1520
December1st to 10thDay
77%48%8%3
1520
11th to 20thDay
78%6%6%7%3
1905
21st to endDay
77%5%10%6%2
2545
January1st to 10thNight
73%6%9%11%1
4748
11th to 20thNight
75%7%8%8%3
4271
21st to endNight
71%6%10%11%2
4532
February1st to 10thNight
75%5%8%7%41
2470
11th to 20thNight
72%6%8%10%41
2406
21st to endNight
61%7%10%13%8%1
1994
March1st to 10thNight
65%49%13%7%1
2106
11th to 20thNight
62%6%10%12%9%1
2090
21st to endNight
60%5%9%16%9%2
2256
April1st to 10thNight
62%49%11%10%3
1846
11th to 20thNight
53%5%9%18%13%1
1652
21st to endNight
58%5%9%16%12%1
1620
May1st to 10thNight
56%6%10%18%9%1
1616
11th to 20thNight
51%7%10%23%9%1
1417
21st to endNight
50%8%14%19%8%1
1551
June1st to 10thNight
53%6%13%21%6%
1400
11th to 20thNight
52%6%10%22%9%1
1260
21st to endNight
53%9%11%18%9%1
1260
July1st to 10thNight
43%10%17%21%8%
1225
11th to 20thNight
47%8%18%18%9%
1307
21st to endNight
46%9%16%20%8%1
1613
August1st to 10thNight
40%9%13%28%10%
1600
11th to 20thNight
47%10%17%19%7%
1596
21st to endNight
40%6%16%28%11%
1840
September1st to 10thNight
39%8%11%29%12%1
1800
11th to 20thNight
41%412%27%15%1
1922
21st to endNight
43%8%9%24%14%1
2002
October1st to 10thNight
45%7%11%23%13%1
2160
11th to 20thNight
49%7%13%24%7%
2160
21st to endNight
59%5%10%15%10%1
2385
November1st to 10thNight
57%7%11%17%8%
2528
11th to 20thNight
66%6%10%13%5%1
2660
21st to endNight
66%6%14%11%2
2660
December1st to 10thNight
75%5%8%9%2
2660
11th to 20thNight
76%5%7%9%2
3295
21st to endNight
72%5%8%12%2
5117

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
33%31%26%10%
180
11th to 20thDay
36%26%25%11%2
356
21st to endDay
24%27%37%11%1
407
February1st to 10thDay
30%27%29%12%11
370
11th to 20thDay
32%31%26%9%2
366
21st to endDay
23%31%32%12%3
328
March1st to 10thDay
30%27%31%10%2
460
11th to 20thDay
27%31%28%11%3
460
21st to endDay
32%27%26%11%3
490
April1st to 10thDay
38%26%26%6%3
420
11th to 20thDay
29%30%27%11%2
412
21st to endDay
29%21%29%15%5%
420
May1st to 10thDay
31%25%31%11%3
427
11th to 20thDay
28%20%28%19%5%1
624
21st to endDay
29%18%33%16%31
680
June1st to 10thDay
33%15%30%17%6%
630
11th to 20thDay
24%16%33%20%6%1
630
21st to endDay
24%15%33%21%6%1
630
July1st to 10thDay
21%11%38%22%8%1
620
11th to 20thDay
20%9%37%24%10%
618
21st to endDay
21%10%35%25%7%1
547
August1st to 10thDay
14%9%41%27%9%
446
11th to 20thDay
21%12%33%23%10%1
439
21st to endDay
19%15%28%27%9%2
495
September1st to 10thDay
18%13%36%24%8%1
450
11th to 20thDay
24%15%32%18%8%2
450
21st to endDay
21%21%29%19%9%2
439
October1st to 10thDay
24%16%28%20%8%3
360
11th to 20thDay
27%21%28%16%6%2
360
21st to endDay
29%26%24%16%41
396
November1st to 10thDay
28%22%32%14%31
365
11th to 20thDay
35%23%25%11%41
370
21st to endDay
31%26%33%7%2
370
December1st to 10thDay
34%27%27%10%2
370
11th to 20thDay
39%31%21%8%1
370
21st to endDay
32%30%30%6%11
260
January1st to 10thNight
29%26%31%13%1
850
11th to 20thNight
31%26%28%13%3
796
21st to endNight
23%27%33%14%3
836
February1st to 10thNight
31%26%27%14%1
760
11th to 20thNight
31%28%27%12%2
743
21st to endNight
21%25%34%17%2
628
March1st to 10thNight
27%25%32%14%2
760
11th to 20thNight
24%23%32%16%4
760
21st to endNight
26%23%32%14%4
821
April1st to 10thNight
35%21%27%14%2
586
11th to 20thNight
26%24%31%17%3
534
21st to endNight
28%19%30%20%4
540
May1st to 10thNight
28%15%32%20%41
540
11th to 20thNight
28%13%33%23%3
532
21st to endNight
22%12%42%19%4
583
June1st to 10thNight
29%11%34%21%5%
500
11th to 20thNight
24%10%33%26%5%1
360
21st to endNight
22%8%37%25%6%1
360
July1st to 10thNight
18%5%43%28%6%
350
11th to 20thNight
16%11%36%27%10%
437
21st to endNight
18%8%31%37%6%
590
August1st to 10thNight
18%8%32%34%7%
538
11th to 20thNight
18%9%30%32%11%1
532
21st to endNight
18%7%32%30%12%1
594
September1st to 10thNight
18%9%32%31%9%1
540
11th to 20thNight
22%12%29%26%10%1
662
21st to endNight
20%14%34%23%9%1
720
October1st to 10thNight
21%12%32%26%8%1
720
11th to 20thNight
24%17%33%19%6%2
720
21st to endNight
34%21%25%17%3
792
November1st to 10thNight
32%17%28%17%5%1
798
11th to 20thNight
27%27%26%15%4
850
21st to endNight
31%24%27%16%3
850
December1st to 10thNight
33%22%31%12%2
850
11th to 20thNight
32%29%27%10%2
850
21st to endNight
33%25%27%13%2
935
Page generated at 2024-03-25 00:36:59. Version ac07

Copyright © 2024 Attilla Danko.


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