George Washington National Forest Helicopter Landing Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the George Washington National Forest Helicopter Landing Site clear sky chart from 2005-11-05 to 2017-09-17.

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
40%
15370
20%
46949
12%
15334
49%
15334
25%
29702

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
23%
716
21%
2327
9%
716
38%
716
17%
1479
January16th to endNight
19%
768
20%
2496
6%
768
36%
768
20%
1565
February1st to 15thNight
22%
701
20%
2287
7%
701
37%
701
21%
1401
February16th to endNight
21%
631
21%
1916
7%
631
35%
631
19%
1253
March1st to 15thNight
25%
720
20%
1980
10%
720
35%
720
24%
1289
March16th to endNight
26%
768
17%
2112
8%
768
33%
768
23%
1394
April1st to 15thNight
28%
718
17%
1832
6%
718
35%
718
25%
1221
April16th to endNight
40%
670
20%
1750
9%
670
46%
670
31%
1139
May1st to 15thNight
41%
540
15%
1620
8%
540
47%
540
22%
1112
May16th to endNight
52%
489
16%
1612
12%
489
57%
489
27%
1016
June1st to 15thNight
61%
360
17%
1440
18%
360
68%
360
24%
847
June16th to endNight
62%
360
19%
1440
19%
360
69%
360
25%
819
July1st to 15thNight
60%
476
12%
1496
11%
476
61%
476
26%
967
July16th to endNight
73%
564
16%
1595
14%
531
76%
531
37%
942
August1st to 15thNight
68%
539
18%
1609
14%
536
70%
536
30%
1033
August16th to endNight
63%
693
19%
1839
14%
693
65%
693
31%
1218
September1st to 15thNight
59%
720
24%
1815
15%
720
62%
720
35%
1164
September16th to endNight
51%
665
21%
1859
17%
665
54%
665
27%
1229
October1st to 15thNight
47%
660
23%
1980
20%
660
54%
660
27%
1257
October16th to endNight
37%
704
27%
2112
15%
704
52%
704
31%
1234
November1st to 15thNight
44%
700
26%
2134
19%
700
54%
700
30%
1269
November16th to endNight
35%
720
20%
2520
12%
720
47%
720
21%
1533
December1st to 15thNight
28%
720
17%
2520
9%
720
39%
720
18%
1629
December16th to endNight
26%
768
20%
2658
10%
768
41%
768
18%
1692

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
13%6%36%5%35%45%7%36%
47797
Night
12%6%25%5%345%5%7%42%
47142
Cloud CoverDay
13%6%36%5%35%5%5%7%36%
47807
Night
12%6%25%5%345%5%7%42%
47146
TransparencyDay
43%6%12%20%14%2
47508
Night
38%6%13%23%15%2
46949
SeeingDay
17%10%22%24%17%8%
5573
Night
15%10%25%31%14%1
15379

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
11%7%38%5%45%6%5%6%36%
1611
16th to endDay
12%7%36%6%3445%5%39%
1728
February1st to 15thDay
10%9%38%6%4445%6%35%
1575
16th to endDay
10%8%47%5%25%45%5%40%
1552
March1st to 15thDay
14%8%36%334436%40%
1969
16th to endDay
15%9%35%5%36%445%36%
2112
April1st to 15thDay
11%7%35%5%3345%6%42%
2114
16th to endDay
17%5%25%5%3435%6%39%
2220
May1st to 15thDay
19%6%36%6%35%446%31%
2331
16th to endDay
14%5%27%5%46%5%6%7%33%
2501
June1st to 15thDay
12%425%6%36%5%6%9%36%
2520
16th to endDay
10%5%25%7%47%6%7%9%34%
2520
July1st to 15thDay
13%5%37%6%48%5%7%7%29%
2370
16th to endDay
9%436%8%48%7%7%8%30%
2465
August1st to 15thDay
10%6%47%7%46%6%6%9%29%
2340
16th to endDay
12%6%27%8%46%5%7%8%30%
2351
September1st to 15thDay
13%6%36%5%35%446%39%
2142
16th to endDay
19%6%26%5%3445%7%34%
1805
October1st to 15thDay
19%6%24425%34442%
1650
16th to endDay
13%6%25%43345%5%44%
1760
November1st to 15thDay
11%6%2432335%5%50%
1718
16th to endDay
15%7%35%424446%41%
1440
December1st to 15thDay
13%7%25%5%25%46%6%39%
1440
16th to endDay
15%7%36%5%3436%7%34%
1563
January1st to 15thNight
12%6%25%5%345%5%7%39%
2327
16th to endNight
12%8%35%44445%7%39%
2496
February1st to 15thNight
10%7%25%5%25%5%6%6%41%
2285
16th to endNight
9%7%26%6%35%6%7%7%36%
1916
March1st to 15thNight
13%6%25%425%5%6%8%40%
1968
16th to endNight
13%8%25%43445%7%40%
2112
April1st to 15thNight
10%6%36%5%35%447%42%
1832
16th to endNight
14%5%1442346%8%43%
1750
May1st to 15thNight
15%6%26%4345%5%6%37%
1620
16th to endNight
13%5%2442446%9%42%
1610
June1st to 15thNight
8%4235%26%5%8%8%44%
1440
16th to endNight
6%425%5%345%6%10%46%
1440
July1st to 15thNight
10%6%24435%5%6%9%40%
1586
16th to endNight
43245%36%6%7%12%43%
1703
August1st to 15thNight
8%5%245%35%5%6%8%43%
1620
16th to endNight
10%4245%35%6%6%9%42%
1839
September1st to 15thNight
11%4245%3335%7%47%
1815
16th to endNight
17%5%24424446%42%
1859
October1st to 15thNight
17%3135%34346%44%
1980
16th to endNight
12%4244235%5%7%48%
2112
November1st to 15thNight
12%6%24423445%48%
2134
16th to endNight
13%5%25%5%3445%7%42%
2520
December1st to 15thNight
13%7%36%6%35%5%46%37%
2520
16th to endNight
12%7%35%6%345%6%8%36%
2658

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
11%7%37%6%35%5%5%5%36%
1611
16th to endDay
12%8%36%5%3445%5%40%
1728
February1st to 15thDay
10%9%38%5%4446%6%36%
1575
16th to endDay
11%8%47%5%35%45%5%40%
1552
March1st to 15thDay
14%7%35%5%34446%40%
1980
16th to endDay
16%8%35%5%35%445%35%
2111
April1st to 15thDay
12%7%35%5%34346%43%
2114
16th to endDay
17%5%25%43445%6%39%
2220
May1st to 15thDay
20%7%26%6%26%346%31%
2331
16th to endDay
15%5%27%6%46%6%5%8%32%
2501
June1st to 15thDay
12%435%5%35%6%6%9%36%
2520
16th to endDay
10%5%25%7%47%6%6%9%34%
2520
July1st to 15thDay
13%5%37%6%47%7%6%7%29%
2370
16th to endDay
9%5%37%7%5%6%7%7%8%30%
2465
August1st to 15thDay
11%7%37%7%46%6%5%9%29%
2340
16th to endDay
13%6%37%8%46%5%5%8%30%
2351
September1st to 15thDay
13%6%36%5%3445%6%39%
2142
16th to endDay
19%5%35%5%345%5%7%33%
1805
October1st to 15thDay
19%6%245%2434441%
1650
16th to endDay
14%5%34424445%44%
1760
November1st to 15thDay
11%6%24423345%51%
1718
16th to endDay
15%7%25%424446%41%
1440
December1st to 15thDay
14%6%245%3446%6%39%
1440
16th to endDay
15%8%26%5%3445%7%35%
1563
January1st to 15thNight
12%7%25%5%345%5%7%40%
2327
16th to endNight
12%8%345%35%45%7%39%
2496
February1st to 15thNight
10%7%25%5%26%5%5%6%42%
2278
16th to endNight
9%7%36%5%35%6%7%7%37%
1916
March1st to 15thNight
13%6%24425%5%6%7%40%
1980
16th to endNight
14%7%3443445%6%41%
2112
April1st to 15thNight
10%6%35%6%3445%7%42%
1832
16th to endNight
14%42442436%8%43%
1750
May1st to 15thNight
15%6%36%5%245%47%37%
1619
16th to endNight
13%5%1442445%9%42%
1610
June1st to 15thNight
9%4135%36%5%7%8%44%
1440
16th to endNight
7%335%4345%6%9%46%
1440
July1st to 15thNight
10%5%245%35%6%6%9%40%
1586
16th to endNight
5%225%435%6%7%12%44%
1703
August1st to 15thNight
7%6%15%6%35%6%5%8%43%
1620
16th to endNight
10%4246%445%6%9%41%
1839
September1st to 15thNight
11%5%15%44435%7%47%
1815
16th to endNight
17%5%244245%45%43%
1859
October1st to 15thNight
17%3245%34346%45%
1980
16th to endNight
12%41442345%6%49%
2112
November1st to 15thNight
12%5%24424346%49%
2134
16th to endNight
14%5%25%334446%43%
2520
December1st to 15thNight
13%6%36%6%35%5%5%6%38%
2520
16th to endNight
12%7%35%5%345%6%7%37%
2658

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%5%12%19%14%2
1612
16th to endDay
43%412%21%14%3
1728
February1st to 15thDay
44%6%12%19%15%2
1577
16th to endDay
42%413%24%12%2
1552
March1st to 15thDay
43%5%10%23%13%3
1980
16th to endDay
46%6%12%18%13%3
2112
April1st to 15thDay
39%5%11%21%17%4
2114
16th to endDay
42%5%10%19%16%4
2220
May1st to 15thDay
50%7%11%17%11%1
2331
16th to endDay
46%8%13%20%8%1
2505
June1st to 15thDay
40%10%15%21%12%1
2520
16th to endDay
41%9%15%18%13%1
2520
July1st to 15thDay
47%9%11%16%11%2
2231
16th to endDay
44%9%13%18%12%1
2310
August1st to 15thDay
47%7%13%18%11%
2327
16th to endDay
48%8%13%20%9%
2351
September1st to 15thDay
42%5%12%18%18%2
2142
16th to endDay
47%6%7%21%15%1
1805
October1st to 15thDay
43%410%23%13%4
1650
16th to endDay
38%5%8%24%19%4
1760
November1st to 15thDay
34%310%22%22%6%
1718
16th to endDay
42%410%22%17%2
1440
December1st to 15thDay
42%6%12%21%13%4
1440
16th to endDay
45%5%12%21%12%1
1563
January1st to 15thNight
40%7%12%18%17%4
2327
16th to endNight
41%5%12%24%14%2
2496
February1st to 15thNight
38%5%13%24%16%2
2287
16th to endNight
40%7%13%23%13%1
1916
March1st to 15thNight
38%6%13%27%11%2
1980
16th to endNight
41%6%15%21%13%1
2112
April1st to 15thNight
39%6%12%23%16%3
1832
16th to endNight
36%6%14%20%17%4
1750
May1st to 15thNight
45%7%13%19%11%1
1620
16th to endNight
37%8%17%24%10%1
1612
June1st to 15thNight
33%10%15%25%13%
1440
16th to endNight
31%10%15%23%16%1
1440
July1st to 15thNight
37%9%17%20%11%3
1496
16th to endNight
27%9%21%26%14%
1595
August1st to 15thNight
36%8%16%22%15%
1609
16th to endNight
37%7%15%26%10%1
1839
September1st to 15thNight
34%6%15%20%19%2
1815
16th to endNight
41%5%10%22%18%1
1859
October1st to 15thNight
40%410%25%16%1
1980
16th to endNight
33%412%26%20%2
2112
November1st to 15thNight
34%49%21%21%8%
2134
16th to endNight
39%5%11%23%17%3
2520
December1st to 15thNight
43%6%11%20%14%2
2520
16th to endNight
42%6%14%22%12%2
2658

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
16%30%33%13%5%1
90
16th to endDay
29%32%22%12%3
96
February1st to 15thDay
17%38%37%5%
90
16th to endDay
20%20%36%18%4
148
March1st to 15thDay
19%20%27%27%5%
270
16th to endDay
15%17%32%23%8%2
288
April1st to 15thDay
14%20%23%25%14%1
270
16th to endDay
23%7%24%22%15%5%
270
May1st to 15thDay
21%17%23%19%11%6%
288
16th to endDay
21%5%22%21%18%10%
331
June1st to 15thDay
13%7%22%25%21%9%
315
16th to endDay
14%6%27%27%15%7%
315
July1st to 15thDay
15%322%33%18%6%
305
16th to endDay
10%19%32%29%16%
326
August1st to 15thDay
15%216%25%23%15%
313
16th to endDay
14%110%24%27%22%
332
September1st to 15thDay
15%5%17%20%22%19%
315
16th to endDay
23%319%22%22%9%
259
October1st to 15thDay
22%417%25%23%6%
255
16th to endDay
13%15%26%28%14%2
272
November1st to 15thDay
19%7%22%28%18%3
236
16th to endDay
25%15%26%21%10%1
60
December1st to 15thDay
20%21%30%16%8%3
60
16th to endDay
26%23%36%13%1
69
January1st to 15thNight
18%20%32%23%5%
720
16th to endNight
17%15%41%23%
768
February1st to 15thNight
17%18%36%25%1
704
16th to endNight
17%20%36%23%1
631
March1st to 15thNight
18%16%35%25%4
720
16th to endNight
19%14%33%23%7%1
768
April1st to 15thNight
14%21%31%26%6%
718
16th to endNight
17%11%24%32%14%
670
May1st to 15thNight
17%7%26%32%14%1
540
16th to endNight
15%220%35%22%3
491
June1st to 15thNight
8%219%40%26%1
360
16th to endNight
7%117%53%18%1
360
July1st to 15thNight
13%114%38%30%2
476
16th to endNight
5%110%37%37%7%
564
August1st to 15thNight
10%110%42%32%2
539
16th to endNight
13%10%37%34%3
693
September1st to 15thNight
14%216%32%29%4
720
16th to endNight
19%316%30%25%3
665
October1st to 15thNight
19%6%19%30%19%3
660
16th to endNight
15%11%30%29%12%1
704
November1st to 15thNight
15%11%22%35%13%2
700
16th to endNight
17%16%26%26%11%1
720
December1st to 15thNight
16%15%32%29%5%
720
16th to endNight
16%15%33%32%2
768
Page generated at 2017-09-18 08:38:28. Version ac04

Copyright 2017 A. Danko


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