Great Basin National Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Great Basin National Park clear sky chart from 2005-11-05 to 2017-08-12.

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
58%
15233
26%
46218
21%
15196
65%
15196
39%
25024

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
57%
716
22%
2327
18%
716
63%
716
37%
1246
January16th to endNight
56%
768
25%
2496
24%
768
62%
768
32%
1418
February1st to 15thNight
55%
697
22%
2181
20%
697
61%
697
35%
1224
February16th to endNight
50%
632
22%
1895
20%
632
57%
632
34%
1110
March1st to 15thNight
52%
720
26%
2084
18%
720
63%
720
39%
1157
March16th to endNight
48%
768
24%
2112
14%
768
56%
768
37%
1229
April1st to 15thNight
44%
719
22%
1844
9%
719
51%
719
34%
1146
April16th to endNight
48%
561
29%
1641
15%
561
59%
561
39%
878
May1st to 15thNight
52%
540
25%
1619
16%
539
59%
539
38%
892
May16th to endNight
52%
561
21%
1685
16%
561
56%
561
32%
967
June1st to 15thNight
53%
516
24%
1596
19%
516
61%
516
40%
814
June16th to endNight
70%
360
32%
1440
35%
360
81%
360
52%
555
July1st to 15thNight
74%
369
21%
1389
23%
369
78%
369
32%
726
July16th to endNight
64%
564
21%
1593
19%
531
65%
531
33%
917
August1st to 15thNight
67%
527
29%
1575
21%
524
72%
524
44%
810
August16th to endNight
74%
627
34%
1677
23%
627
77%
627
52%
871
September1st to 15thNight
72%
660
33%
1769
23%
660
77%
660
51%
943
September16th to endNight
72%
656
38%
1815
29%
656
78%
656
58%
874
October1st to 15thNight
64%
660
33%
1846
24%
660
71%
660
46%
993
October16th to endNight
64%
704
33%
2183
27%
704
72%
704
43%
1095
November1st to 15thNight
64%
700
31%
2275
28%
700
71%
700
44%
1114
November16th to endNight
59%
720
31%
2340
28%
720
67%
720
42%
1167
December1st to 15thNight
52%
720
20%
2340
16%
720
59%
720
32%
1328
December16th to endNight
45%
768
22%
2496
17%
768
53%
768
26%
1550

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
342443445%7%55%
47749
Night
231342445%7%57%
46405
TransparencyDay
26%7%10%19%21%14%
47437
Night
24%7%11%22%22%12%
46219
SeeingDay
6%16%32%28%12%2
5357
Night
46%24%34%23%6%
15246

By Month

Percentage Cloud Cover SW (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
1425%6%445%49%51%
1611
16th to endDay
26%344245%6%7%51%
1728
February1st to 15thDay
27%243245%7%9%48%
1679
16th to endDay
16%335%2446%9%50%
1579
March1st to 15thDay
1435%5%3446%7%53%
1875
16th to endDay
35%345%35%5%6%7%48%
2112
April1st to 15thDay
26%25%5%446%6%7%48%
2101
16th to endDay
35%2443445%7%53%
2319
May1st to 15thDay
34135%36%5%6%6%53%
2331
16th to endDay
45%246%26%5%6%9%45%
2429
June1st to 15thDay
23235%25%5%5%7%56%
2358
16th to endDay
21231333472%
2520
July1st to 15thDay
4315%5%35%5%6%5%52%
2484
16th to endDay
5%3245%45%5%5%7%49%
2467
August1st to 15thDay
2314434445%61%
2290
16th to endDay
221334345%6%61%
2171
September1st to 15thDay
331332333466%
1860
16th to endDay
123312235%73%
1815
October1st to 15thDay
3414425%46%7%56%
1782
16th to endDay
231232435%5%64%
1686
November1st to 15thDay
1313335%45%8%58%
1584
16th to endDay
2213235%5%5%8%59%
1620
December1st to 15thDay
1435%42337%10%50%
1620
16th to endDay
25%36%6%36%6%7%9%41%
1728
January1st to 15thNight
132342445%9%58%
2327
16th to endNight
25%245%3346%9%52%
2496
February1st to 15thNight
2324435%45%9%54%
2170
16th to endNight
1434436%5%6%9%51%
1895
March1st to 15thNight
142343445%6%59%
2084
16th to endNight
23144246%7%9%53%
2112
April1st to 15thNight
3323436%5%6%8%51%
1844
16th to endNight
43123245%5%9%56%
1641
May1st to 15thNight
43144245%5%6%56%
1619
16th to endNight
6%41443345%8%52%
1684
June1st to 15thNight
3323433346%61%
1596
16th to endNight
123312245%71%
1440
July1st to 15thNight
2315%5%35%5%6%6%54%
1471
16th to endNight
43145%46%5%5%8%49%
1701
August1st to 15thNight
22133346%6%7%57%
1584
16th to endNight
32242445%6%64%
1677
September1st to 15thNight
421331343466%
1769
16th to endNight
221121223473%
1815
October1st to 15thNight
5%313223446%62%
1846
16th to endNight
221322345%6%64%
2183
November1st to 15thNight
141331335%6%64%
2275
16th to endNight
22232446%8%61%
2340
December1st to 15thNight
1424425%5%6%9%53%
2340
16th to endNight
1436%6%46%5%8%9%43%
2496

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
29%8%20%26%13%1
1612
16th to endDay
29%10%18%20%13%6%
1728
February1st to 15thDay
30%9%17%22%14%5%
1679
16th to endDay
29%8%14%25%19%2
1579
March1st to 15thDay
28%7%12%32%15%4
1875
16th to endDay
32%7%13%28%12%5%
2112
April1st to 15thDay
32%7%11%24%17%5%
2101
16th to endDay
27%7%9%22%27%4
2319
May1st to 15thDay
26%7%9%19%28%8%
2331
16th to endDay
32%9%9%15%26%6%
2432
June1st to 15thDay
23%5%7%14%31%16%
2358
16th to endDay
14%348%24%44%
2520
July1st to 15thDay
30%6%6%8%14%34%
2338
16th to endDay
30%8%8%9%14%28%
2312
August1st to 15thDay
22%5%6%10%19%36%
2275
16th to endDay
21%6%6%11%23%30%
2171
September1st to 15thDay
21%5%5%9%27%29%
1860
16th to endDay
15%3417%33%24%
1815
October1st to 15thDay
25%5%10%21%30%7%
1782
16th to endDay
20%5%7%25%34%5%
1686
November1st to 15thDay
22%8%13%26%23%6%
1584
16th to endDay
22%8%10%30%21%5%
1620
December1st to 15thDay
28%10%17%30%11%1
1620
16th to endDay
35%11%18%20%13%1
1728
January1st to 15thNight
23%8%20%27%15%3
2327
16th to endNight
27%9%15%24%16%6%
2496
February1st to 15thNight
26%8%17%27%15%4
2181
16th to endNight
29%8%16%23%19%2
1895
March1st to 15thNight
25%5%13%30%19%4
2084
16th to endNight
25%9%14%30%16%4
2112
April1st to 15thNight
28%9%12%25%19%4
1844
16th to endNight
21%8%13%25%27%4
1641
May1st to 15thNight
25%7%7%23%28%6%
1620
16th to endNight
30%6%11%18%25%6%
1685
June1st to 15thNight
23%5%6%14%32%18%
1596
16th to endNight
14%339%24%43%
1440
July1st to 15thNight
28%6%5%8%16%33%
1389
16th to endNight
31%6%7%13%13%26%
1593
August1st to 15thNight
21%6%9%12%17%32%
1575
16th to endNight
17%6%6%12%22%33%
1677
September1st to 15thNight
20%47%10%26%30%
1769
16th to endNight
14%46%16%33%25%
1815
October1st to 15thNight
22%5%7%21%34%7%
1846
16th to endNight
19%7%7%24%35%5%
2183
November1st to 15thNight
20%6%11%30%22%8%
2275
16th to endNight
19%8%11%30%25%5%
2340
December1st to 15thNight
26%11%17%28%13%2
2340
16th to endNight
33%11%14%24%13%2
2496

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
5%15%26%34%14%3
90
16th to endDay
7%14%21%22%22%10%
96
February1st to 15thDay
7%12%29%27%18%4
194
16th to endDay
6%25%39%21%6%
238
March1st to 15thDay
422%33%21%13%3
270
16th to endDay
10%22%39%20%5%
288
April1st to 15thDay
6%31%30%20%7%2
269
16th to endDay
10%36%27%20%4
270
May1st to 15thDay
7%22%34%26%6%1
288
16th to endDay
8%20%25%29%14%2
330
June1st to 15thDay
6%19%36%26%10%
315
16th to endDay
211%33%32%17%2
315
July1st to 15thDay
6%6%30%38%15%2
305
16th to endDay
6%6%32%39%12%1
327
August1st to 15thDay
38%37%38%10%2
300
16th to endDay
48%28%38%16%3
268
September1st to 15thDay
5%12%38%30%10%2
255
16th to endDay
414%28%29%20%2
255
October1st to 15thDay
418%36%25%10%4
222
16th to endDay
11%13%33%29%11%1
96
November1st to 15thDay
11%8%11%27%28%12%
90
16th to endDay
5%16%37%30%7%2
90
December1st to 15thDay
115%46%27%7%1
90
16th to endDay
6%11%32%27%17%5%
96
January1st to 15thNight
36%26%32%21%9%
720
16th to endNight
5%6%24%32%21%8%
768
February1st to 15thNight
35%27%38%17%6%
704
16th to endNight
37%31%36%17%3
632
March1st to 15thNight
48%27%34%20%4
720
16th to endNight
311%31%32%18%2
768
April1st to 15thNight
5%15%29%27%16%3
719
16th to endNight
6%12%28%31%18%2
561
May1st to 15thNight
7%6%29%34%19%2
540
16th to endNight
8%9%22%28%25%4
563
June1st to 15thNight
6%11%24%33%20%3
516
16th to endNight
1222%42%27%3
360
July1st to 15thNight
410%42%37%4
369
16th to endNight
6%217%38%30%4
564
August1st to 15thNight
4120%45%26%2
527
16th to endNight
4114%36%35%7%
627
September1st to 15thNight
3312%36%32%11%
660
16th to endNight
35%14%25%34%16%
656
October1st to 15thNight
6%6%19%34%23%9%
660
16th to endNight
45%20%31%28%9%
704
November1st to 15thNight
36%21%32%26%10%
700
16th to endNight
46%25%30%22%9%
720
December1st to 15thNight
45%30%35%16%6%
720
16th to endNight
28%34%32%17%3
768
Page generated at 2017-08-13 11:16:25. Version ac04

Copyright 2017 A. Danko


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