Robert W. Woodruff Scout Reservation
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Robert W. Woodruff Scout Reservation clear sky chart from 2005-11-06 to 2024-01-12.

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%
23826
20%
74459
14%
23770
53%
23770
23%
48281

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
22%
760
18%
2459
9%
757
35%
757
16%
1668
January11th to 20thNight
25%
727
18%
2360
10%
727
37%
727
15%
1646
January21st to endNight
23%
792
23%
2542
10%
792
38%
792
19%
1682
February1st to 10thNight
29%
720
21%
2160
11%
720
39%
720
21%
1439
February11th to 20thNight
19%
702
17%
2098
5%
699
31%
699
15%
1487
February21st to endNight
18%
592
19%
1776
7%
592
29%
592
15%
1276
March1st to 10thNight
26%
720
22%
2106
11%
720
35%
720
22%
1378
March11th to 20thNight
28%
720
18%
1980
8%
720
35%
720
21%
1375
March21st to endNight
31%
792
17%
2178
8%
792
38%
792
22%
1497
April1st to 10thNight
38%
680
23%
1940
14%
680
47%
680
28%
1198
April11th to 20thNight
39%
533
24%
1775
16%
533
52%
533
27%
1047
April21st to endNight
48%
540
26%
1630
18%
540
55%
540
31%
998
May1st to 10thNight
48%
540
17%
1620
10%
540
54%
540
28%
1015
May11th to 20thNight
55%
531
15%
1593
10%
531
58%
531
24%
1066
May21st to endNight
68%
582
17%
1744
14%
582
69%
582
29%
1100
June1st to 10thNight
65%
540
15%
1620
12%
540
66%
540
24%
1085
June11th to 20thNight
74%
540
13%
1620
11%
540
75%
540
34%
980
June21st to endNight
75%
540
15%
1620
13%
540
77%
540
31%
1014
July1st to 10thNight
69%
525
12%
1575
12%
525
70%
525
23%
1077
July11th to 20thNight
73%
522
11%
1566
11%
522
73%
522
27%
1020
July21st to endNight
75%
591
14%
1672
13%
558
75%
558
25%
1130
August1st to 10thNight
72%
537
13%
1600
12%
534
73%
534
25%
1072
August11th to 20thNight
72%
534
17%
1688
17%
534
72%
534
24%
1123
August21st to endNight
65%
594
17%
1980
19%
594
66%
594
23%
1311
September1st to 10thNight
64%
691
17%
1951
16%
691
64%
691
27%
1294
September11th to 20thNight
60%
720
20%
1980
16%
720
62%
720
26%
1341
September21st to endNight
63%
720
26%
1980
22%
720
66%
720
34%
1230
October1st to 10thNight
57%
720
30%
1980
23%
720
63%
720
38%
1168
October11th to 20thNight
47%
720
27%
2096
20%
720
55%
720
31%
1271
October21st to endNight
49%
792
31%
2376
24%
792
59%
792
33%
1386
November1st to 10thNight
50%
740
27%
2404
23%
740
58%
740
32%
1364
November11th to 20thNight
42%
760
26%
2470
19%
760
52%
760
26%
1456
November21st to endNight
38%
760
23%
2470
17%
760
48%
760
23%
1556
December1st to 10thNight
31%
760
19%
2470
12%
760
40%
760
16%
1727
December11th to 20thNight
33%
759
22%
2950
16%
758
43%
758
17%
1898
December21st to endNight
28%
830
13%
4430
11%
817
37%
817
9%
2906

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
11%7%36%6%46%6%6%8%37%
74866
Night
11%7%36%5%35%5%6%8%42%
74861
TransparencyDay
43%8%11%18%16%4
74589
Night
40%8%12%19%17%4
74657
SeeingDay
17%13%22%21%17%10%
13735
Night
16%11%21%28%20%4
23836

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
13%9%46%6%3445%6%39%
1706
11th to 20thDay
14%11%49%5%35%45%6%36%
1629
21st to endDay
12%9%47%5%345%45%42%
1812
February1st to 10thDay
15%11%5%7%6%34446%35%
1800
11th to 20thDay
16%9%5%8%425%35%7%34%
1748
21st to endDay
19%9%47%5%44445%36%
1480
March1st to 10thDay
12%8%45%425%5%6%9%40%
1853
11th to 20thDay
16%9%36%6%35%5%5%6%36%
1980
21st to endDay
12%10%47%5%35%5%5%7%37%
2178
April1st to 10thDay
10%7%26%5%45%6%6%7%42%
2034
11th to 20thDay
12%7%36%6%3446%6%43%
2134
21st to endDay
10%7%26%6%45%5%5%7%43%
2330
May1st to 10thDay
11%6%36%5%46%5%5%7%41%
2340
11th to 20thDay
12%7%47%7%46%6%6%7%34%
2301
21st to endDay
8%6%36%7%47%7%7%9%36%
2531
June1st to 10thDay
9%6%37%7%48%7%8%10%31%
2340
11th to 20thDay
5%5%36%7%5%7%8%8%10%37%
2340
21st to endDay
7%6%36%7%5%7%6%8%11%34%
2340
July1st to 10thDay
8%7%39%8%5%8%8%8%9%26%
2340
11th to 20thDay
10%5%36%8%7%9%9%8%10%25%
2340
21st to endDay
7%7%37%10%6%8%9%8%9%26%
2547
August1st to 10thDay
9%5%37%9%5%8%8%9%12%26%
2327
11th to 20thDay
10%6%47%7%5%6%7%7%10%29%
2209
21st to endDay
12%7%37%9%5%7%7%6%8%28%
2376
September1st to 10thDay
10%7%38%7%45%6%6%8%36%
1990
11th to 20thDay
13%7%26%6%45%6%7%8%36%
1980
21st to endDay
12%5%25%6%345%6%8%43%
1980
October1st to 10thDay
10%425%5%3445%5%52%
1980
11th to 20thDay
11%7%24325%45%6%52%
1863
21st to endDay
11%7%24424345%53%
1979
November1st to 10thDay
10%5%25%33435%6%56%
1672
11th to 20thDay
10%6%35%4345%5%7%49%
1710
21st to endDay
12%8%346%245%5%7%44%
1710
December1st to 10thDay
16%9%48%6%35%5%5%6%34%
1710
11th to 20thDay
12%9%5%7%5%35%45%5%39%
2153
21st to endDay
13%11%6%6%6%345%5%8%32%
3124
January1st to 10thNight
14%9%48%5%45%445%37%
2459
11th to 20thNight
13%11%48%6%345%5%6%33%
2360
21st to endNight
13%9%47%6%35%44441%
2542
February1st to 10thNight
13%9%46%5%35%45%6%40%
2160
11th to 20thNight
18%9%48%5%25%45%436%
2098
21st to endNight
17%10%48%5%35%6%45%33%
1776
March1st to 10thNight
11%9%36%5%35%45%6%44%
2106
11th to 20thNight
14%8%36%6%3446%7%38%
1980
21st to endNight
12%9%46%6%3445%6%40%
2178
April1st to 10thNight
10%5%24435%46%8%48%
1940
11th to 20thNight
10%6%36%434448%48%
1775
21st to endNight
10%6%345%3435%7%49%
1630
May1st to 10thNight
9%7%25%435%5%6%9%45%
1620
11th to 20thNight
10%5%36%5%45%6%7%9%40%
1592
21st to endNight
6%5%25%5%35%7%7%12%42%
1744
June1st to 10thNight
6%5%36%6%47%7%7%13%36%
1620
11th to 20thNight
4215%5%46%7%9%13%46%
1620
21st to endNight
5%335%446%7%7%11%46%
1620
July1st to 10thNight
9%5%36%7%46%7%9%10%35%
1620
11th to 20thNight
6%5%25%6%36%7%8%13%39%
1620
21st to endNight
6%435%6%47%8%9%13%35%
1771
August1st to 10thNight
7%5%347%46%7%8%12%38%
1611
11th to 20thNight
7%5%26%6%47%5%7%10%41%
1688
21st to endNight
10%6%36%6%45%6%6%10%37%
1980
September1st to 10thNight
8%6%36%6%45%6%6%9%41%
1951
11th to 20thNight
10%6%36%6%35%5%6%8%42%
1980
21st to endNight
7%5%26%435%5%6%7%50%
1980
October1st to 10thNight
10%5%23323446%58%
1980
11th to 20thNight
11%5%25%5%33446%51%
2096
21st to endNight
10%7%24424445%53%
2376
November1st to 10thNight
11%6%24334446%53%
2404
11th to 20thNight
12%8%34433345%50%
2470
21st to endNight
12%8%26%6%345%5%7%43%
2470
December1st to 10thNight
16%8%46%6%45%5%5%7%33%
2470
11th to 20thNight
12%12%47%433446%41%
3042
21st to endNight
13%11%5%8%6%46%5%5%9%29%
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
45%6%8%17%20%4
1707
11th to 20thDay
50%47%16%19%4
1629
21st to endDay
44%5%7%20%19%5%
1812
February1st to 10thDay
51%47%18%17%4
1800
11th to 20thDay
50%6%6%16%17%4
1758
21st to endDay
51%48%12%19%6%
1480
March1st to 10thDay
41%6%9%16%21%8%
1853
11th to 20thDay
48%6%12%14%15%5%
1980
21st to endDay
46%7%11%20%14%2
2178
April1st to 10thDay
39%7%11%21%18%4
2034
11th to 20thDay
41%6%8%18%23%5%
2134
21st to endDay
38%6%12%26%15%2
2330
May1st to 10thDay
41%7%13%21%15%3
2340
11th to 20thDay
47%10%13%18%11%1
2305
21st to endDay
41%11%14%20%13%1
2531
June1st to 10thDay
44%12%16%19%7%1
2340
11th to 20thDay
38%12%17%20%11%1
2340
21st to endDay
41%11%17%18%11%2
2340
July1st to 10thDay
48%13%17%15%6%1
2275
11th to 20thDay
47%14%17%11%8%2
2271
21st to endDay
47%15%17%15%7%
2405
August1st to 10thDay
45%15%17%17%5%
2314
11th to 20thDay
46%13%15%15%9%1
2209
21st to endDay
51%12%13%15%8%2
2376
September1st to 10thDay
44%10%12%16%14%4
1990
11th to 20thDay
44%9%12%17%16%2
1980
21st to endDay
39%6%13%16%20%6%
1980
October1st to 10thDay
34%7%10%16%27%6%
1980
11th to 20thDay
34%6%9%22%21%9%
1863
21st to endDay
34%46%21%25%9%
1979
November1st to 10thDay
30%49%14%32%10%
1672
11th to 20thDay
34%5%8%19%25%9%
1710
21st to endDay
41%5%7%16%25%5%
1710
December1st to 10thDay
51%5%7%17%16%4
1710
11th to 20thDay
45%6%8%13%23%6%
2150
21st to endDay
47%7%8%20%15%3
3124
January1st to 10thNight
49%5%7%16%18%4
2459
11th to 20thNight
50%7%9%14%16%4
2360
21st to endNight
46%5%6%18%21%4
2542
February1st to 10thNight
45%5%9%18%19%4
2160
11th to 20thNight
51%5%6%16%18%4
2099
21st to endNight
51%7%7%15%15%5%
1776
March1st to 10thNight
43%5%8%16%20%8%
2106
11th to 20thNight
44%7%11%18%16%4
1980
21st to endNight
45%6%11%22%15%2
2178
April1st to 10thNight
35%6%12%21%22%4
1940
11th to 20thNight
36%5%10%22%21%7%
1775
21st to endNight
35%6%12%29%16%2
1630
May1st to 10thNight
35%9%15%23%17%2
1620
11th to 20thNight
38%12%17%22%11%1
1593
21st to endNight
31%13%17%27%10%2
1745
June1st to 10thNight
37%14%18%22%8%1
1620
11th to 20thNight
26%14%25%25%9%1
1620
21st to endNight
31%12%20%21%13%3
1620
July1st to 10thNight
40%12%19%19%8%1
1575
11th to 20thNight
33%15%27%15%8%3
1566
21st to endNight
35%16%22%19%7%1
1672
August1st to 10thNight
35%15%22%22%6%
1600
11th to 20thNight
37%13%18%17%13%1
1688
21st to endNight
41%10%19%20%8%2
1980
September1st to 10thNight
37%11%17%17%13%4
1951
11th to 20thNight
38%11%13%19%18%
1980
21st to endNight
32%8%12%22%20%6%
1980
October1st to 10thNight
29%6%11%19%28%6%
1980
11th to 20thNight
35%5%10%21%21%8%
2096
21st to endNight
33%5%6%21%27%9%
2376
November1st to 10thNight
32%5%7%21%25%9%
2404
11th to 20thNight
37%47%19%24%10%
2470
21st to endNight
41%5%7%21%21%5%
2470
December1st to 10thNight
50%6%8%15%15%4
2470
11th to 20thNight
44%6%7%13%25%5%
3044
21st to endNight
51%5%8%18%15%2
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
27%26%34%10%3
270
11th to 20thDay
27%27%28%14%5%
243
21st to endDay
21%38%26%11%3
264
February1st to 10thDay
28%26%34%10%2
240
11th to 20thDay
35%33%26%5%1
240
21st to endDay
37%27%27%8%1
198
March1st to 10thDay
24%19%35%14%7%
293
11th to 20thDay
26%21%25%20%7%1
420
21st to endDay
23%24%27%18%7%1
462
April1st to 10thDay
21%16%26%22%11%2
420
11th to 20thDay
16%21%28%20%14%2
412
21st to endDay
20%15%24%23%14%4
420
May1st to 10thDay
16%17%29%20%12%6%
423
11th to 20thDay
13%9%26%26%16%11%
447
21st to endDay
10%7%21%27%21%14%
485
June1st to 10thDay
11%420%28%22%14%
450
11th to 20thDay
8%5%18%25%25%20%
450
21st to endDay
10%424%25%20%18%
450
July1st to 10thDay
10%410%24%28%23%
445
11th to 20thDay
8%310%26%27%25%
444
21st to endDay
9%310%24%27%27%
488
August1st to 10thDay
12%416%22%22%23%
446
11th to 20thDay
12%414%20%28%22%
439
21st to endDay
15%313%18%29%23%
495
September1st to 10thDay
9%414%24%32%17%
450
11th to 20thDay
14%6%14%20%32%14%
450
21st to endDay
12%7%16%26%30%10%
450
October1st to 10thDay
14%7%21%29%21%9%
450
11th to 20thDay
16%12%25%25%18%4
450
21st to endDay
16%14%24%26%17%3
494
November1st to 10thDay
16%14%31%24%11%3
270
11th to 20thDay
20%18%37%19%6%
270
21st to endDay
15%19%39%19%7%1
270
December1st to 10thDay
30%24%25%17%31
270
11th to 20thDay
23%19%33%19%6%1
270
21st to endDay
24%27%29%14%6%1
297
January1st to 10thNight
24%20%30%20%6%
760
11th to 20thNight
24%19%27%23%7%
727
21st to endNight
19%21%33%25%3
792
February1st to 10thNight
22%16%29%28%5%
720
11th to 20thNight
26%21%30%21%2
703
21st to endNight
27%22%29%19%3
592
March1st to 10thNight
19%20%33%24%4
720
11th to 20thNight
20%18%30%23%8%1
720
21st to endNight
19%15%30%27%9%
792
April1st to 10thNight
16%15%27%30%10%1
680
11th to 20thNight
15%14%26%30%14%2
533
21st to endNight
12%9%26%34%18%1
540
May1st to 10thNight
11%11%24%34%18%1
540
11th to 20thNight
11%7%20%32%24%5%
531
21st to endNight
8%313%33%35%8%
584
June1st to 10thNight
7%213%34%37%5%
540
11th to 20thNight
4311%32%36%14%
540
21st to endNight
5%29%33%41%10%
540
July1st to 10thNight
10%25%25%49%9%
525
11th to 20thNight
8%28%21%46%15%
522
21st to endNight
5%26%23%49%15%
591
August1st to 10thNight
9%27%25%43%15%
537
11th to 20thNight
9%27%30%43%10%
534
21st to endNight
13%28%24%43%11%
594
September1st to 10thNight
10%211%27%40%10%
691
11th to 20thNight
13%311%29%38%5%
720
21st to endNight
11%315%35%33%4
720
October1st to 10thNight
12%7%20%30%25%7%
720
11th to 20thNight
14%9%23%32%21%2
720
21st to endNight
15%11%20%35%17%2
792
November1st to 10thNight
15%9%21%33%19%3
740
11th to 20thNight
17%14%24%31%13%2
760
21st to endNight
18%16%23%29%13%1
760
December1st to 10thNight
24%16%25%27%8%1
760
11th to 20thNight
22%14%26%29%8%1
760
21st to endNight
24%17%26%27%6%
836
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