C&O Canal National Historical Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the C&O Canal National Historical Park clear sky chart from 2005-11-05 to 2017-04-25.

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
34%
14792
20%
45648
10%
14754
45%
14754
20%
29094

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
19%
717
18%
2398
8%
716
33%
716
13%
1598
January16th to endNight
17%
768
19%
2496
5%
768
34%
768
15%
1629
February1st to 15thNight
21%
702
19%
2287
6%
701
37%
701
16%
1432
February16th to endNight
16%
631
20%
1949
5%
631
33%
631
14%
1288
March1st to 15thNight
22%
720
20%
1980
8%
720
35%
720
18%
1323
March16th to endNight
20%
768
20%
2111
7%
768
31%
768
18%
1420
April1st to 15thNight
22%
718
17%
1796
5%
718
29%
718
21%
1251
April16th to endNight
35%
685
19%
1735
5%
685
43%
685
23%
1159
May1st to 15thNight
31%
495
18%
1485
9%
495
39%
495
17%
1028
May16th to endNight
42%
347
18%
1374
14%
347
53%
347
18%
820
June1st to 15thNight
43%
330
20%
1320
17%
330
53%
330
20%
759
June16th to endNight
53%
330
17%
1320
16%
330
61%
330
24%
730
July1st to 15thNight
53%
318
13%
1248
14%
318
56%
318
18%
766
July16th to endNight
59%
522
14%
1469
9%
489
68%
489
33%
860
August1st to 15thNight
56%
494
20%
1474
13%
491
61%
491
29%
896
August16th to endNight
62%
658
20%
1708
13%
658
64%
658
34%
1084
September1st to 15thNight
55%
660
25%
1650
15%
660
59%
660
33%
1070
September16th to endNight
48%
657
22%
1829
16%
657
54%
657
26%
1191
October1st to 15thNight
42%
660
23%
1980
18%
660
52%
660
26%
1255
October16th to endNight
36%
704
27%
2112
13%
704
53%
704
29%
1241
November1st to 15thNight
35%
700
25%
2199
16%
700
47%
700
24%
1314
November16th to endNight
29%
720
20%
2520
10%
720
44%
720
15%
1566
December1st to 15thNight
23%
720
16%
2520
6%
720
37%
720
12%
1663
December16th to endNight
20%
768
19%
2688
7%
768
35%
768
13%
1751

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%5%25%5%35%5%5%7%39%
45983
Night
14%5%2442445%7%42%
45831
Cloud CoverDay
14%5%25%5%35%5%5%7%39%
45993
Night
14%5%2442445%7%42%
45835
TransparencyDay
42%6%12%21%15%2
45685
Night
40%6%12%23%15%2
45648
SeeingDay
18%18%18%20%16%7%
5024
Night
15%24%21%25%12%1
14798

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
14%5%46%6%36%5%5%8%34%
1537
16th to endDay
14%9%26%6%2445%6%36%
1728
February1st to 15thDay
14%7%47%6%35%246%36%
1575
16th to endDay
12%7%48%6%44346%38%
1524
March1st to 15thDay
15%7%35%5%25%445%40%
1969
16th to endDay
17%7%26%4245%5%7%35%
2112
April1st to 15thDay
15%426%5%3446%7%38%
2152
16th to endDay
18%5%24424445%42%
2124
May1st to 15thDay
19%5%24435%6%6%8%33%
2136
16th to endDay
14%5%25%5%35%46%7%38%
2389
June1st to 15thDay
13%3144346%6%11%39%
2310
16th to endDay
9%425%5%35%5%6%10%41%
2310
July1st to 15thDay
9%425%6%46%6%7%8%38%
2299
16th to endDay
8%325%6%36%7%7%10%38%
2283
August1st to 15thDay
10%4146%36%7%8%10%36%
2145
16th to endDay
10%424335%5%6%8%44%
2129
September1st to 15thDay
14%5%14424347%46%
1980
16th to endDay
16%5%25%42445%6%40%
1800
October1st to 15thDay
19%41341345%6%44%
1650
16th to endDay
15%415%5%2345%6%44%
1760
November1st to 15thDay
14%5%23424445%48%
1655
16th to endDay
20%6%25%324446%38%
1440
December1st to 15thDay
17%6%35%5%345%6%7%33%
1440
16th to endDay
17%7%26%6%25%5%6%5%34%
1536
January1st to 15thNight
16%7%36%42445%6%36%
2398
16th to endNight
15%8%36%42445%8%36%
2496
February1st to 15thNight
14%6%245%2445%7%41%
2285
16th to endNight
11%8%35%6%35%46%6%37%
1949
March1st to 15thNight
17%5%235%3445%6%40%
1968
16th to endNight
16%6%35%434346%41%
2111
April1st to 15thNight
15%6%35%5%245%6%6%38%
1796
16th to endNight
15%4234245%47%44%
1735
May1st to 15thNight
19%5%35%425%448%36%
1485
16th to endNight
13%4135%25%45%7%45%
1372
June1st to 15thNight
11%4244245%6%10%44%
1320
16th to endNight
9%3245%3347%10%45%
1320
July1st to 15thNight
9%415%5%35%47%10%41%
1328
16th to endNight
5%3145%35%6%7%11%45%
1577
August1st to 15thNight
8%325%5%345%6%9%45%
1485
16th to endNight
11%313425%45%6%49%
1708
September1st to 15thNight
13%3244245%5%7%47%
1650
16th to endNight
15%6%24334446%45%
1829
October1st to 15thNight
18%42442345%5%44%
1980
16th to endNight
14%313323447%50%
2112
November1st to 15thNight
13%6%34413346%48%
2199
16th to endNight
16%5%24425%45%7%40%
2520
December1st to 15thNight
17%6%35%5%25%5%5%6%35%
2520
16th to endNight
17%6%35%5%245%5%8%36%
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%5%35%6%35%5%5%8%34%
1537
16th to endDay
14%8%36%5%34447%36%
1728
February1st to 15thDay
13%7%37%6%45%346%36%
1575
16th to endDay
12%7%48%5%34346%38%
1524
March1st to 15thDay
15%7%25%5%25%446%40%
1980
16th to endDay
17%7%245%25%5%5%6%36%
2111
April1st to 15thDay
15%5%25%5%345%6%7%39%
2152
16th to endDay
18%5%25%434445%42%
2124
May1st to 15thDay
18%5%24435%5%6%8%33%
2136
16th to endDay
15%5%26%5%35%5%5%7%39%
2389
June1st to 15thDay
12%3245%25%6%6%11%40%
2310
16th to endDay
9%335%5%25%6%6%9%41%
2310
July1st to 15thDay
9%5%25%6%45%5%7%9%38%
2299
16th to endDay
7%425%6%36%6%7%10%38%
2283
August1st to 15thDay
10%415%6%36%7%7%9%36%
2145
16th to endDay
10%425%335%46%8%44%
2129
September1st to 15thDay
14%5%1343445%6%46%
1980
16th to endDay
15%5%25%42446%7%39%
1800
October1st to 15thDay
19%41342335%7%44%
1650
16th to endDay
15%4245%2445%6%45%
1760
November1st to 15thDay
13%5%23424346%48%
1655
16th to endDay
19%5%25%325%346%39%
1440
December1st to 15thDay
18%6%345%246%5%7%33%
1440
16th to endDay
16%7%35%6%25%45%6%34%
1536
January1st to 15thNight
16%7%36%43445%6%37%
2398
16th to endNight
15%7%45%5%2445%7%37%
2496
February1st to 15thNight
14%7%25%42445%7%42%
2278
16th to endNight
11%8%35%6%35%45%6%38%
1949
March1st to 15thNight
17%5%234345%5%6%40%
1980
16th to endNight
15%6%35%424347%41%
2111
April1st to 15thNight
14%6%35%5%245%6%6%39%
1796
16th to endNight
15%423425%5%5%7%44%
1735
May1st to 15thNight
18%5%35%5%2445%8%35%
1484
16th to endNight
12%6%145%35%45%8%44%
1372
June1st to 15thNight
10%4235%345%6%9%44%
1320
16th to endNight
8%3245%3347%11%44%
1320
July1st to 15thNight
10%425%5%35%5%7%9%41%
1328
16th to endNight
5%2245%35%6%8%10%45%
1577
August1st to 15thNight
8%325%5%346%5%10%45%
1485
16th to endNight
11%3135%2445%7%48%
1708
September1st to 15thNight
12%323425%46%6%46%
1650
16th to endNight
15%6%24334436%44%
1829
October1st to 15thNight
18%424423446%44%
1980
16th to endNight
14%413323347%50%
2112
November1st to 15thNight
13%6%24423336%48%
2199
16th to endNight
16%5%34425%5%5%6%40%
2520
December1st to 15thNight
16%6%35%5%35%5%5%6%36%
2520
16th to endNight
16%5%35%4245%5%7%37%
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
45%6%12%21%12%1
1538
16th to endDay
46%412%22%11%2
1728
February1st to 15thDay
49%411%21%11%2
1577
16th to endDay
47%412%24%11%1
1524
March1st to 15thDay
44%5%10%22%14%1
1980
16th to endDay
47%5%11%18%14%2
2112
April1st to 15thDay
42%6%11%18%17%2
2152
16th to endDay
43%47%20%18%5%
2124
May1st to 15thDay
46%7%12%19%13%
2136
16th to endDay
43%5%13%21%12%2
2393
June1st to 15thDay
36%8%15%23%14%1
2310
16th to endDay
37%8%15%21%15%1
2310
July1st to 15thDay
40%9%12%20%14%3
2151
16th to endDay
36%9%14%20%16%2
2128
August1st to 15thDay
40%8%13%22%14%
2132
16th to endDay
35%7%12%26%14%2
2129
September1st to 15thDay
37%6%12%19%22%2
1980
16th to endDay
43%5%7%22%19%1
1800
October1st to 15thDay
41%410%25%15%2
1650
16th to endDay
38%5%11%26%17%1
1760
November1st to 15thDay
36%412%21%20%5%
1655
16th to endDay
44%5%10%24%14%1
1440
December1st to 15thDay
45%7%15%20%9%1
1440
16th to endDay
49%6%11%21%10%
1536
January1st to 15thNight
45%6%11%18%14%3
2398
16th to endNight
45%413%23%11%1
2496
February1st to 15thNight
40%5%13%23%13%2
2287
16th to endNight
44%5%11%23%13%1
1949
March1st to 15thNight
42%5%12%26%11%1
1980
16th to endNight
43%411%22%15%1
2111
April1st to 15thNight
43%5%10%21%15%3
1796
16th to endNight
39%5%9%21%17%6%
1735
May1st to 15thNight
45%7%8%22%13%1
1485
16th to endNight
37%7%14%23%15%2
1374
June1st to 15thNight
35%7%12%27%16%1
1320
16th to endNight
31%7%15%26%16%1
1320
July1st to 15thNight
37%10%13%19%13%4
1248
16th to endNight
27%9%19%23%17%2
1469
August1st to 15thNight
33%7%14%24%18%1
1474
16th to endNight
33%6%12%24%20%3
1708
September1st to 15thNight
34%7%13%20%22%2
1650
16th to endNight
40%5%8%22%20%3
1829
October1st to 15thNight
40%49%25%18%2
1980
16th to endNight
32%49%30%20%1
2112
November1st to 15thNight
36%48%24%19%6%
2199
16th to endNight
41%5%10%22%17%2
2520
December1st to 15thNight
46%6%12%22%11%
2520
16th to endNight
43%7%14%22%10%1
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
27%33%22%10%6%
77
16th to endDay
33%28%25%10%3
96
February1st to 15thDay
30%28%30%10%1
90
16th to endDay
21%28%25%22%2
177
March1st to 15thDay
20%28%19%26%4
270
16th to endDay
22%27%24%16%5%2
288
April1st to 15thDay
16%25%25%19%10%2
270
16th to endDay
24%19%19%13%15%8%
250
May1st to 15thDay
25%24%16%16%11%6%
228
16th to endDay
17%17%11%19%25%8%
267
June1st to 15thDay
16%18%20%18%20%7%
255
16th to endDay
10%16%23%27%16%5%
255
July1st to 15thDay
13%11%22%20%22%9%
245
16th to endDay
7%12%12%30%24%13%
270
August1st to 15thDay
14%8%16%19%27%13%
253
16th to endDay
8%8%8%24%30%19%
268
September1st to 15thDay
14%11%13%16%25%19%
255
16th to endDay
20%8%12%23%23%10%
254
October1st to 15thDay
23%10%13%24%22%6%
255
16th to endDay
14%19%26%22%14%1
272
November1st to 15thDay
16%19%20%20%19%3
245
16th to endDay
28%15%20%26%6%3
60
December1st to 15thDay
23%25%21%13%13%3
60
16th to endDay
26%15%32%21%3
64
January1st to 15thNight
18%31%24%21%3
720
16th to endNight
17%31%27%21%1
768
February1st to 15thNight
16%31%25%24%1
704
16th to endNight
16%35%28%17%2
631
March1st to 15thNight
19%29%25%21%4
720
16th to endNight
16%29%28%19%5%
768
April1st to 15thNight
16%30%29%20%4
718
16th to endNight
16%26%18%26%11%
685
May1st to 15thNight
20%23%18%24%13%
495
16th to endNight
14%22%14%29%17%1
348
June1st to 15thNight
9%21%21%25%21%1
330
16th to endNight
6%18%14%39%20%
330
July1st to 15thNight
10%14%12%31%28%1
318
16th to endNight
5%18%10%31%29%3
522
August1st to 15thNight
11%11%11%37%26%2
494
16th to endNight
11%10%8%35%28%5%
658
September1st to 15thNight
11%11%14%29%30%3
660
16th to endNight
17%12%14%25%26%2
657
October1st to 15thNight
19%13%17%28%18%2
660
16th to endNight
14%19%26%29%10%
704
November1st to 15thNight
13%23%22%27%12%1
700
16th to endNight
16%32%19%24%7%
720
December1st to 15thNight
18%29%23%22%6%
720
16th to endNight
18%30%25%23%2
768
Page generated at 2017-04-26 17:21:47. Version ac04

Copyright 2017 A. Danko


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