Greenwood
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Greenwood clear sky chart from 2005-11-05 to 2018-02-22.

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%
15697
10%
48761
4%
15652
25%
15652
11%
37816

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
8%
822
5%
2840
1%
818
12%
818
4%
2463
January16th to endNight
9%
832
5%
2704
1%
832
13%
832
5%
2338
February1st to 15thNight
9%
764
4%
2481
1%
761
13%
761
3%
2201
February16th to endNight
13%
659
7%
2110
1%
659
20%
659
6%
1743
March1st to 15thNight
14%
720
11%
1991
4%
720
22%
720
11%
1582
March16th to endNight
15%
768
11%
2112
4%
768
22%
768
12%
1643
April1st to 15thNight
15%
569
11%
1802
4%
569
23%
569
10%
1376
April16th to endNight
21%
540
14%
1620
6%
540
28%
540
16%
1172
May1st to 15thNight
22%
540
9%
1557
5%
540
26%
540
13%
1197
May16th to endNight
21%
561
10%
1496
2%
560
28%
560
17%
1137
June1st to 15thNight
23%
453
7%
1353
3%
453
27%
453
13%
1035
June16th to endNight
25%
360
9%
1260
3%
360
32%
360
14%
905
July1st to 15thNight
33%
341
10%
1191
7%
341
38%
341
22%
761
July16th to endNight
35%
565
9%
1501
6%
532
36%
532
20%
1099
August1st to 15thNight
39%
539
13%
1608
10%
535
41%
535
22%
1107
August16th to endNight
38%
573
17%
1758
9%
573
44%
573
25%
1125
September1st to 15thNight
31%
561
17%
1821
10%
561
40%
561
23%
1164
September16th to endNight
33%
717
21%
1995
11%
717
41%
717
25%
1319
October1st to 15thNight
27%
720
16%
2160
8%
720
33%
720
19%
1492
October16th to endNight
18%
768
13%
2311
5%
768
26%
768
13%
1716
November1st to 15thNight
20%
795
10%
2620
7%
795
25%
795
10%
2025
November16th to endNight
17%
825
8%
2730
4%
825
21%
825
8%
2209
December1st to 15thNight
8%
825
5%
2730
1%
825
13%
825
4%
2343
December16th to endNight
7%
880
4%
3010
1%
880
11%
880
2%
2664

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%11%47%6%34345%29%
49486
Night
19%12%5%8%7%34345%25%
48931
TransparencyDay
58%5%10%16%8%
49174
Night
60%5%10%15%6%
48761
SeeingDay
26%18%30%17%6%
7703
Night
25%18%30%19%5%
15697

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%19%8%12%11%5%433411%
1423
16th to endDay
15%15%8%11%11%5%6%43412%
1872
February1st to 15thDay
17%15%7%14%14%5%432310%
1710
16th to endDay
12%16%8%12%8%3423423%
1507
March1st to 15thDay
14%15%6%10%8%45%32424%
1957
16th to endDay
15%15%7%9%6%2332429%
2112
April1st to 15thDay
19%14%46%434445%29%
2144
16th to endDay
22%10%25%423335%34%
2340
May1st to 15thDay
25%10%36%424345%28%
2395
16th to endDay
23%10%35%5%34346%29%
2618
June1st to 15thDay
27%8%35%42445%6%27%
2616
16th to endDay
21%7%46%6%345%5%6%29%
2700
July1st to 15thDay
16%6%244245%5%8%40%
2685
16th to endDay
19%8%36%5%345%5%6%31%
2561
August1st to 15thDay
18%6%25%5%3445%6%39%
2340
16th to endDay
14%5%24423347%47%
2444
September1st to 15thDay
18%5%245%13345%43%
2136
16th to endDay
18%6%14422346%45%
1965
October1st to 15thDay
20%8%24413346%39%
1800
16th to endDay
22%12%36%5%23436%28%
1911
November1st to 15thDay
21%14%5%7%6%345%35%24%
1567
16th to endDay
21%17%7%10%5%3433418%
1560
December1st to 15thDay
23%17%8%14%7%3332311%
1560
16th to endDay
22%18%8%14%11%2333210%
1563
January1st to 15thNight
16%17%8%13%11%4333413%
2840
16th to endNight
16%14%6%13%12%45%34313%
2704
February1st to 15thNight
18%15%7%14%13%4433411%
2480
16th to endNight
15%15%7%11%8%25%43420%
2110
March1st to 15thNight
17%13%5%8%8%3434425%
1979
16th to endNight
18%15%7%7%6%2333428%
2112
April1st to 15thNight
23%14%36%434435%26%
1802
16th to endNight
22%10%345%23336%32%
1620
May1st to 15thNight
25%9%36%5%345%45%26%
1557
16th to endNight
21%8%46%5%2445%7%29%
1494
June1st to 15thNight
28%7%35%435%446%25%
1353
16th to endNight
20%7%35%6%445%48%30%
1260
July1st to 15thNight
13%5%444245%7%9%37%
1261
16th to endNight
16%8%36%5%35%6%6%9%28%
1604
August1st to 15thNight
20%7%15%5%2345%6%36%
1620
16th to endNight
13%6%25%5%345%48%41%
1758
September1st to 15thNight
17%6%2442345%7%41%
1821
16th to endNight
16%5%25%42335%6%44%
1995
October1st to 15thNight
18%6%35%5%24346%37%
2160
16th to endNight
23%10%36%424335%30%
2311
November1st to 15thNight
21%14%47%5%34445%25%
2620
16th to endNight
19%18%6%8%6%3423421%
2730
December1st to 15thNight
22%16%8%12%7%2433414%
2730
16th to endNight
23%18%9%12%9%3332311%
3010

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
77%49%7%
1424
16th to endDay
76%5%6%8%3
1872
February1st to 15thDay
79%5%6%5%2
1713
16th to endDay
66%5%9%13%4
1507
March1st to 15thDay
65%28%13%8%
1968
16th to endDay
59%47%17%8%1
2112
April1st to 15thDay
59%47%13%12%1
2144
16th to endDay
53%5%9%17%13%1
2340
May1st to 15thDay
58%5%7%17%9%1
2395
16th to endDay
56%6%10%19%6%
2622
June1st to 15thDay
58%5%9%16%7%1
2616
16th to endDay
56%6%10%16%9%
2700
July1st to 15thDay
41%8%14%21%12%
2527
16th to endDay
52%7%11%20%7%
2401
August1st to 15thDay
47%7%12%19%11%
2327
16th to endDay
37%6%14%27%13%
2444
September1st to 15thDay
43%5%12%23%13%1
2136
16th to endDay
40%310%26%16%1
1965
October1st to 15thDay
46%411%26%11%
1800
16th to endDay
57%5%9%20%6%
1911
November1st to 15thDay
63%6%10%12%6%
1567
16th to endDay
70%5%10%10%2
1560
December1st to 15thDay
79%47%7%1
1560
16th to endDay
80%47%5%2
1563
January1st to 15thNight
75%5%8%8%1
2840
16th to endNight
76%47%9%1
2704
February1st to 15thNight
78%47%6%2
2481
16th to endNight
67%7%9%9%5%
2110
March1st to 15thNight
63%49%14%6%1
1991
16th to endNight
60%48%16%9%
2112
April1st to 15thNight
60%48%13%10%2
1802
16th to endNight
54%49%16%14%
1620
May1st to 15thNight
57%7%10%17%6%
1557
16th to endNight
52%8%13%18%6%1
1496
June1st to 15thNight
58%6%11%18%4
1353
16th to endNight
52%8%11%19%7%
1260
July1st to 15thNight
39%10%18%21%9%
1191
16th to endNight
48%8%15%20%5%
1501
August1st to 15thNight
45%7%13%24%9%
1608
16th to endNight
39%6%16%26%9%
1758
September1st to 15thNight
41%6%10%29%11%1
1821
16th to endNight
41%5%11%25%15%
1995
October1st to 15thNight
47%6%11%22%11%
2160
16th to endNight
56%5%10%19%8%
2311
November1st to 15thNight
61%5%11%14%6%
2620
16th to endNight
66%5%12%11%3
2730
December1st to 15thNight
74%5%8%9%1
2730
16th to endNight
78%5%6%7%2
3010

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
26%32%28%11%
145
16th to endDay
27%26%33%10%
304
February1st to 15thDay
26%28%30%13%1
281
16th to endDay
22%27%29%14%5%
237
March1st to 15thDay
22%32%29%11%4
270
16th to endDay
27%26%26%13%5%1
288
April1st to 15thDay
26%28%28%11%4
270
16th to endDay
23%23%31%14%5%
270
May1st to 15thDay
31%18%30%13%5%1
351
16th to endDay
32%16%29%16%4
519
June1st to 15thDay
32%14%29%17%5%
495
16th to endDay
25%13%35%17%6%1
495
July1st to 15thDay
20%8%36%23%10%1
475
16th to endDay
25%6%32%24%10%
422
August1st to 15thDay
22%8%32%26%9%1
313
16th to endDay
21%9%30%25%12%1
332
September1st to 15thDay
22%10%38%19%9%
315
16th to endDay
21%12%29%23%10%2
310
October1st to 15thDay
26%13%28%20%7%4
270
16th to endDay
29%27%20%16%5%
288
November1st to 15thDay
28%20%25%18%5%2
280
16th to endDay
31%22%30%10%5%
285
December1st to 15thDay
33%31%22%10%1
285
16th to endDay
29%34%25%8%1
203
January1st to 15thNight
25%27%32%12%1
822
16th to endNight
26%26%30%13%2
832
February1st to 15thNight
29%25%29%14%1
764
16th to endNight
25%26%29%15%3
659
March1st to 15thNight
24%23%32%16%3
720
16th to endNight
24%22%32%14%5%
768
April1st to 15thNight
32%19%28%16%3
569
16th to endNight
27%15%31%22%2
540
May1st to 15thNight
30%12%30%21%5%
540
16th to endNight
24%11%38%20%3
561
June1st to 15thNight
30%9%32%22%5%
453
16th to endNight
21%7%38%24%6%1
360
July1st to 15thNight
14%5%42%28%8%
341
16th to endNight
18%7%31%35%7%
565
August1st to 15thNight
22%6%26%34%10%
539
16th to endNight
15%7%34%30%11%1
573
September1st to 15thNight
22%8%33%26%8%
561
16th to endNight
18%11%32%27%8%1
717
October1st to 15thNight
23%13%32%22%7%1
720
16th to endNight
30%20%27%17%4
768
November1st to 15thNight
28%18%26%18%6%1
795
16th to endNight
27%23%27%17%4
825
December1st to 15thNight
32%24%28%12%1
825
16th to endNight
32%27%26%9%2
880
Page generated at 2018-02-23 12:21:35. Version ac04

Copyright 2018 A. Danko


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