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 2018-10-08.

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%
16740
20%
51125
12%
16704
49%
16704
25%
32388

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
24%
776
21%
2522
9%
776
39%
776
18%
1583
January16th to endNight
20%
832
21%
2704
7%
832
37%
832
21%
1689
February1st to 15thNight
21%
761
19%
2482
7%
761
36%
761
20%
1549
February16th to endNight
20%
683
20%
2074
7%
683
35%
683
19%
1368
March1st to 15thNight
24%
780
21%
2145
10%
780
35%
780
25%
1378
March16th to endNight
25%
832
17%
2288
8%
832
33%
832
22%
1520
April1st to 15thNight
27%
778
17%
1985
5%
778
34%
778
25%
1335
April16th to endNight
39%
717
19%
1873
9%
717
45%
717
30%
1223
May1st to 15thNight
45%
585
15%
1755
9%
585
50%
585
23%
1181
May16th to endNight
53%
531
15%
1750
12%
531
57%
531
25%
1128
June1st to 15thNight
61%
390
17%
1560
18%
390
67%
390
23%
922
June16th to endNight
63%
390
19%
1560
20%
390
69%
390
25%
887
July1st to 15thNight
62%
518
13%
1628
12%
518
64%
518
28%
1030
July16th to endNight
71%
612
16%
1739
13%
579
75%
579
35%
1046
August1st to 15thNight
68%
575
18%
1715
14%
572
70%
572
30%
1102
August16th to endNight
65%
751
18%
1993
13%
751
66%
751
31%
1318
September1st to 15thNight
58%
780
23%
1966
15%
780
61%
780
33%
1286
September16th to endNight
52%
777
22%
2171
18%
777
55%
777
27%
1436
October1st to 15thNight
49%
752
21%
2255
19%
752
56%
752
27%
1435
October16th to endNight
37%
768
28%
2304
17%
768
52%
768
31%
1344
November1st to 15thNight
45%
760
25%
2317
19%
760
54%
760
29%
1403
November16th to endNight
35%
780
22%
2730
14%
780
49%
780
23%
1621
December1st to 15thNight
28%
780
17%
2730
9%
780
39%
780
17%
1773
December16th to endNight
27%
832
20%
2879
10%
832
42%
832
19%
1831

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%6%36%5%35%45%7%36%
51982
Night
12%6%25%5%345%5%7%41%
51318
Cloud CoverDay
14%6%36%5%35%5%5%7%36%
51992
Night
12%6%25%5%345%5%7%42%
51322
TransparencyDay
43%6%12%20%14%2
51693
Night
38%6%13%23%15%2
51125
SeeingDay
18%10%22%23%16%7%
6946
Night
15%10%25%30%15%1
16749

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
10%7%38%6%35%6%5%6%36%
1746
16th to endDay
12%7%36%6%2435%5%40%
1872
February1st to 15thDay
11%9%38%5%3345%6%35%
1710
16th to endDay
12%8%47%5%25%445%39%
1680
March1st to 15thDay
14%7%36%434436%40%
2134
16th to endDay
16%9%35%5%36%445%35%
2288
April1st to 15thDay
11%8%35%5%33446%42%
2291
16th to endDay
17%5%25%5%3435%6%39%
2373
May1st to 15thDay
19%6%36%6%36%45%6%32%
2526
16th to endDay
15%6%27%6%46%5%6%7%32%
2715
June1st to 15thDay
13%5%25%5%36%5%6%9%36%
2730
16th to endDay
10%5%25%6%47%6%7%9%33%
2730
July1st to 15thDay
12%5%27%5%48%5%7%8%31%
2568
16th to endDay
11%5%36%8%48%6%7%8%29%
2673
August1st to 15thDay
11%6%36%7%46%6%7%9%29%
2487
16th to endDay
12%6%27%8%46%5%7%8%30%
2548
September1st to 15thDay
15%6%36%5%34446%38%
2321
16th to endDay
19%6%26%6%3445%7%34%
2117
October1st to 15thDay
18%6%24425%345%41%
1875
16th to endDay
13%6%2443345%5%46%
1920
November1st to 15thDay
12%6%35%32335%5%48%
1865
16th to endDay
14%6%35%424446%43%
1560
December1st to 15thDay
13%7%25%5%35%46%6%38%
1560
16th to endDay
14%7%36%6%3436%7%35%
1693
January1st to 15thNight
11%6%25%4345%5%8%41%
2522
16th to endNight
12%8%35%445%45%7%39%
2704
February1st to 15thNight
11%7%25%5%36%5%6%6%40%
2480
16th to endNight
10%7%26%5%35%6%7%7%36%
2074
March1st to 15thNight
13%6%25%4245%6%8%40%
2133
16th to endNight
14%8%35%43445%7%39%
2288
April1st to 15thNight
10%6%36%6%35%5%47%40%
1985
16th to endNight
15%5%15%42345%8%43%
1873
May1st to 15thNight
15%6%26%4345%5%6%39%
1755
16th to endNight
14%6%2442446%9%40%
1748
June1st to 15thNight
9%4235%26%5%8%8%43%
1560
16th to endNight
7%425%5%345%6%10%46%
1560
July1st to 15thNight
9%5%24435%5%6%10%42%
1718
16th to endNight
5%3245%36%6%8%11%42%
1847
August1st to 15thNight
8%5%25%5%35%5%6%8%43%
1726
16th to endNight
9%4245%35%6%6%8%41%
1993
September1st to 15thNight
13%5%2443335%7%45%
1966
16th to endNight
17%5%24424446%43%
2171
October1st to 15thNight
17%3245%3445%6%43%
2255
16th to endNight
12%4144235%5%7%48%
2304
November1st to 15thNight
12%6%25%423445%47%
2317
16th to endNight
13%5%2443445%7%44%
2730
December1st to 15thNight
12%7%37%5%35%5%46%37%
2730
16th to endNight
12%7%35%6%345%6%8%36%
2879

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%
1746
16th to endDay
12%8%36%5%3435%5%41%
1872
February1st to 15thDay
11%9%38%5%4446%6%35%
1710
16th to endDay
13%8%47%5%3445%5%38%
1680
March1st to 15thDay
14%7%35%5%34446%41%
2145
16th to endDay
16%8%35%5%35%445%35%
2287
April1st to 15thDay
12%7%35%5%34346%42%
2291
16th to endDay
17%5%25%434446%39%
2373
May1st to 15thDay
19%6%26%6%26%45%6%32%
2526
16th to endDay
16%5%27%6%46%5%5%8%31%
2715
June1st to 15thDay
13%335%5%45%6%6%9%36%
2730
16th to endDay
10%5%25%7%47%6%7%9%33%
2730
July1st to 15thDay
12%5%37%6%47%7%6%8%31%
2568
16th to endDay
11%5%37%7%5%6%7%7%8%29%
2673
August1st to 15thDay
11%7%37%7%46%6%6%9%29%
2487
16th to endDay
12%6%37%8%46%5%5%8%31%
2548
September1st to 15thDay
15%6%36%5%3445%6%38%
2321
16th to endDay
20%5%35%5%3445%7%34%
2117
October1st to 15thDay
19%6%24424345%41%
1875
16th to endDay
13%5%34424445%46%
1920
November1st to 15thDay
12%7%24423346%48%
1865
16th to endDay
15%7%25%424446%44%
1560
December1st to 15thDay
14%7%25%5%35%45%6%39%
1560
16th to endDay
14%8%27%6%3445%7%35%
1693
January1st to 15thNight
12%6%25%5%345%5%7%42%
2522
16th to endNight
12%8%345%35%45%6%40%
2704
February1st to 15thNight
10%7%25%5%36%5%6%6%40%
2473
16th to endNight
10%7%26%5%35%6%6%7%36%
2074
March1st to 15thNight
13%5%244345%6%7%42%
2145
16th to endNight
14%8%3442445%6%40%
2288
April1st to 15thNight
10%6%35%6%35%5%5%7%40%
1985
16th to endNight
15%42442436%8%43%
1873
May1st to 15thNight
15%6%26%5%245%47%39%
1754
16th to endNight
14%6%15%42445%9%41%
1748
June1st to 15thNight
10%4145%35%5%7%8%43%
1560
16th to endNight
7%335%4345%6%9%46%
1560
July1st to 15thNight
9%5%244345%6%9%42%
1718
16th to endNight
5%325%445%6%7%11%43%
1847
August1st to 15thNight
7%6%15%6%25%6%6%8%43%
1726
16th to endNight
10%4246%445%6%9%41%
1993
September1st to 15thNight
13%5%2443435%6%46%
1966
16th to endNight
18%5%244235%45%43%
2171
October1st to 15thNight
17%324434446%43%
2255
16th to endNight
12%41442345%6%49%
2304
November1st to 15thNight
12%6%24424445%48%
2317
16th to endNight
13%5%24334446%44%
2730
December1st to 15thNight
12%7%36%5%35%5%46%38%
2730
16th to endNight
12%7%35%5%345%5%7%37%
2879

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
44%5%12%19%15%3
1747
16th to endDay
43%412%21%15%3
1872
February1st to 15thDay
45%6%11%19%14%2
1712
16th to endDay
44%412%23%12%2
1680
March1st to 15thDay
43%5%10%23%14%3
2145
16th to endDay
46%6%12%17%14%2
2288
April1st to 15thDay
40%5%10%21%17%4
2291
16th to endDay
42%5%10%19%16%5%
2373
May1st to 15thDay
48%7%13%17%10%1
2526
16th to endDay
48%8%13%19%8%1
2719
June1st to 15thDay
40%10%14%21%12%1
2730
16th to endDay
41%9%15%19%12%1
2730
July1st to 15thDay
44%9%11%18%12%2
2429
16th to endDay
46%9%12%17%12%1
2518
August1st to 15thDay
47%8%14%18%11%
2474
16th to endDay
47%8%13%19%9%
2548
September1st to 15thDay
44%5%12%18%17%2
2321
16th to endDay
47%5%7%22%14%1
2117
October1st to 15thDay
42%411%22%13%4
1875
16th to endDay
36%5%8%25%20%3
1920
November1st to 15thDay
35%410%21%21%6%
1865
16th to endDay
39%410%24%18%2
1560
December1st to 15thDay
43%5%12%20%13%3
1560
16th to endDay
45%5%12%22%11%1
1693
January1st to 15thNight
39%7%12%18%18%4
2522
16th to endNight
40%5%12%24%15%2
2704
February1st to 15thNight
38%6%13%23%15%2
2482
16th to endNight
41%7%13%22%12%2
2074
March1st to 15thNight
37%6%12%27%12%3
2145
16th to endNight
41%6%15%20%14%1
2288
April1st to 15thNight
40%5%12%22%15%3
1985
16th to endNight
36%6%14%20%17%4
1873
May1st to 15thNight
43%7%14%20%11%2
1755
16th to endNight
39%8%17%23%10%1
1750
June1st to 15thNight
33%11%16%24%13%
1560
16th to endNight
31%10%15%23%17%1
1560
July1st to 15thNight
35%9%17%21%11%3
1628
16th to endNight
28%9%20%25%14%
1739
August1st to 15thNight
36%8%17%22%14%
1715
16th to endNight
37%7%16%26%10%1
1993
September1st to 15thNight
36%6%16%19%18%2
1966
16th to endNight
41%5%10%24%16%1
2171
October1st to 15thNight
40%5%12%24%16%1
2255
16th to endNight
32%411%27%21%2
2304
November1st to 15thNight
35%49%22%19%7%
2317
16th to endNight
37%5%11%23%19%3
2730
December1st to 15thNight
44%6%11%20%14%2
2730
16th to endNight
42%6%14%22%12%2
2879

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%31%34%12%5%
135
16th to endDay
26%30%24%16%2
144
February1st to 15thDay
22%36%35%5%
135
16th to endDay
25%19%34%15%4
193
March1st to 15thDay
20%23%28%23%4
330
16th to endDay
17%18%32%22%7%2
352
April1st to 15thDay
16%22%25%22%11%1
330
16th to endDay
23%10%25%21%14%4
319
May1st to 15thDay
20%14%23%22%12%5%
348
16th to endDay
24%421%22%18%9%
395
June1st to 15thDay
14%7%21%26%20%8%
375
16th to endDay
13%5%26%29%16%8%
375
July1st to 15thDay
13%319%32%20%10%
365
16th to endDay
12%212%30%27%14%
390
August1st to 15thDay
16%215%24%24%16%
358
16th to endDay
13%110%26%26%21%
396
September1st to 15thDay
20%414%18%21%19%
375
16th to endDay
25%317%23%21%9%
374
October1st to 15thDay
21%314%28%24%7%
345
16th to endDay
12%16%26%27%14%2
336
November1st to 15thDay
20%7%24%29%16%3
293
16th to endDay
18%16%28%23%11%1
90
December1st to 15thDay
20%20%32%17%7%2
90
16th to endDay
23%24%38%11%1
103
January1st to 15thNight
18%20%32%23%5%
780
16th to endNight
17%15%41%24%1
832
February1st to 15thNight
17%17%37%25%1
764
16th to endNight
18%20%36%22%1
683
March1st to 15thNight
17%17%35%25%3
780
16th to endNight
19%14%34%23%6%
832
April1st to 15thNight
14%20%32%25%5%
778
16th to endNight
18%11%25%31%13%
717
May1st to 15thNight
16%6%25%33%16%1
585
16th to endNight
17%219%36%22%3
533
June1st to 15thNight
9%218%39%28%1
390
16th to endNight
7%116%52%20%1
390
July1st to 15thNight
12%113%36%31%4
518
16th to endNight
6%110%37%37%7%
612
August1st to 15thNight
10%110%41%32%3
575
16th to endNight
12%10%35%35%4
751
September1st to 15thNight
16%215%30%29%6%
780
16th to endNight
19%315%30%26%3
777
October1st to 15thNight
19%6%18%30%21%3
752
16th to endNight
15%11%30%28%13%1
768
November1st to 15thNight
15%11%22%35%12%2
760
16th to endNight
17%16%26%28%11%1
780
December1st to 15thNight
16%14%33%28%6%
780
16th to endNight
16%14%34%32%2
832
Page generated at 2018-10-09 10:39:17. Version ac04

Copyright 2018 A. Danko


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