Las Vegas
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Las Vegas 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
74%
15746
38%
46569
31%
15709
81%
15709
61%
20648

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
73%
717
35%
2327
32%
716
81%
716
54%
1038
January16th to endNight
69%
768
38%
2469
33%
768
79%
768
48%
1165
February1st to 15thNight
71%
697
36%
2112
31%
697
80%
697
53%
1001
February16th to endNight
62%
632
38%
1895
35%
632
71%
632
49%
947
March1st to 15thNight
65%
720
37%
2103
30%
720
76%
720
60%
940
March16th to endNight
67%
768
40%
2112
28%
768
78%
768
61%
978
April1st to 15thNight
56%
719
36%
1820
16%
719
67%
719
59%
888
April16th to endNight
64%
627
43%
1707
21%
627
76%
627
66%
754
May1st to 15thNight
68%
539
37%
1619
25%
539
75%
539
67%
664
May16th to endNight
63%
561
36%
1685
24%
561
71%
561
62%
708
June1st to 15thNight
70%
540
33%
1620
26%
540
75%
540
73%
626
June16th to endNight
80%
540
35%
1620
31%
540
84%
540
81%
602
July1st to 15thNight
87%
510
30%
1530
28%
510
87%
510
63%
678
July16th to endNight
88%
564
34%
1593
30%
531
88%
531
59%
725
August1st to 15thNight
85%
556
39%
1604
30%
553
87%
553
65%
712
August16th to endNight
88%
700
41%
1750
28%
700
89%
700
73%
837
September1st to 15thNight
86%
660
40%
1760
31%
660
89%
660
70%
805
September16th to endNight
85%
656
47%
1815
40%
656
90%
656
80%
740
October1st to 15thNight
76%
660
43%
1815
35%
660
83%
660
65%
834
October16th to endNight
76%
704
44%
2162
39%
704
84%
704
66%
882
November1st to 15thNight
79%
700
40%
2275
38%
700
88%
700
68%
898
November16th to endNight
78%
720
43%
2340
43%
720
84%
720
64%
944
December1st to 15thNight
75%
720
37%
2340
36%
720
81%
720
53%
1054
December16th to endNight
64%
768
35%
2496
31%
768
73%
768
44%
1228

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
111212235%75%
47408
Night
211212235%75%
46764
TransparencyDay
12%2414%27%36%
47103
Night
13%2415%27%37%
46570
SeeingDay
38%20%35%23%8%
5505
Night
2415%38%33%5%
15759

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
221212226%73%
1611
16th to endDay
32232234469%
1754
February1st to 15thDay
1111213347%70%
1751
16th to endDay
3112223446%67%
1579
March1st to 15thDay
111112237%74%
1857
16th to endDay
111121235%7%70%
2112
April1st to 15thDay
121212346%72%
2125
16th to endDay
11111223479%
2253
May1st to 15thDay
112236%79%
2331
16th to endDay
111111235%78%
2429
June1st to 15thDay
1112385%
2340
16th to endDay
111388%
2340
July1st to 15thDay
1112314345%69%
2340
16th to endDay
211242445%8%62%
2467
August1st to 15thDay
211212335%74%
2259
16th to endDay
211212346%74%
2100
September1st to 15thDay
12112235%77%
1870
16th to endDay
111112484%
1815
October1st to 15thDay
221221222476%
1815
16th to endDay
1111223480%
1708
November1st to 15thDay
1111111335%77%
1584
16th to endDay
212111335%77%
1620
December1st to 15thDay
3212313246%67%
1620
16th to endDay
3313212346%66%
1728
January1st to 15thNight
222222435%71%
2327
16th to endNight
421223345%67%
2469
February1st to 15thNight
222222246%70%
2101
16th to endNight
431122335%6%65%
1895
March1st to 15thNight
111121235%7%71%
2103
16th to endNight
111113246%75%
2112
April1st to 15thNight
211112236%75%
1820
16th to endNight
112236%79%
1707
May1st to 15thNight
1111246%78%
1619
16th to endNight
11121214478%
1684
June1st to 15thNight
11113483%
1620
16th to endNight
1212387%
1620
July1st to 15thNight
112222346%70%
1620
16th to endNight
21231346%8%65%
1701
August1st to 15thNight
11211233474%
1613
16th to endNight
11211246%78%
1750
September1st to 15thNight
1111123478%
1760
16th to endNight
11112287%
1815
October1st to 15thNight
211111225%77%
1815
16th to endNight
11111113480%
2162
November1st to 15thNight
111111235%79%
2275
16th to endNight
112112125%79%
2340
December1st to 15thNight
421213349%67%
2340
16th to endNight
5%313313346%65%
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
13%29%29%36%7%
1612
16th to endDay
19%47%26%30%11%
1754
February1st to 15thDay
16%38%23%32%16%
1751
16th to endDay
19%37%19%33%16%
1579
March1st to 15thDay
11%2420%39%21%
1857
16th to endDay
14%26%21%34%20%
2112
April1st to 15thDay
14%3415%31%30%
2125
16th to endDay
10%2213%33%37%
2253
May1st to 15thDay
8%1314%28%42%
2331
16th to endDay
9%138%31%45%
2432
June1st to 15thDay
6%17%16%66%
2340
16th to endDay
411311%78%
2340
July1st to 15thDay
17%346%16%52%
2201
16th to endDay
17%46%11%21%38%
2312
August1st to 15thDay
12%2210%20%51%
2244
16th to endDay
12%2210%20%51%
2100
September1st to 15thDay
11%248%17%55%
1870
16th to endDay
7%216%25%57%
1815
October1st to 15thDay
14%1311%29%39%
1815
16th to endDay
9%1313%36%35%
1708
November1st to 15thDay
11%25%18%39%22%
1584
16th to endDay
11%35%22%36%20%
1620
December1st to 15thDay
18%311%25%32%8%
1620
16th to endDay
20%6%12%27%24%9%
1728
January1st to 15thNight
16%26%25%35%13%
2327
16th to endNight
20%36%23%28%19%
2469
February1st to 15thNight
17%37%20%29%21%
2112
16th to endNight
21%3318%34%18%
1895
March1st to 15thNight
12%35%16%37%24%
2103
16th to endNight
13%2418%35%25%
2112
April1st to 15thNight
13%25%14%32%31%
1820
16th to endNight
9%2113%29%43%
1707
May1st to 15thNight
9%2212%28%44%
1620
16th to endNight
10%2210%24%50%
1685
June1st to 15thNight
7%117%15%66%
1620
16th to endNight
5%1310%78%
1620
July1st to 15thNight
12%338%15%56%
1530
16th to endNight
15%25%12%21%42%
1593
August1st to 15thNight
12%327%18%56%
1604
16th to endNight
9%339%19%55%
1750
September1st to 15thNight
10%249%15%57%
1760
16th to endNight
5%117%20%63%
1815
October1st to 15thNight
12%2310%26%45%
1815
16th to endNight
10%2311%24%47%
2162
November1st to 15thNight
10%2217%37%29%
2275
16th to endNight
12%1417%32%32%
2340
December1st to 15thNight
17%37%24%33%13%
2340
16th to endNight
22%49%26%26%10%
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
16%6%17%41%16%1
90
16th to endDay
7%7%16%30%27%10%
122
February1st to 15thDay
47%17%34%25%9%
266
16th to endDay
5%16%24%31%18%3
238
March1st to 15thDay
5%14%20%30%21%7%
270
16th to endDay
5%14%26%33%16%3
288
April1st to 15thDay
7%17%29%22%15%7%
269
16th to endDay
5%20%29%30%11%2
270
May1st to 15thDay
210%30%32%18%5%
288
16th to endDay
49%24%34%21%6%
330
June1st to 15thDay
25%26%39%20%4
315
16th to endDay
5%18%35%26%14%
315
July1st to 15thDay
1211%43%29%11%
305
16th to endDay
318%42%33%11%
327
August1st to 15thDay
3219%39%25%10%
300
16th to endDay
412%38%32%10%
268
September1st to 15thDay
2318%43%25%7%
255
16th to endDay
15%16%31%33%10%
255
October1st to 15thDay
27%21%40%18%10%
255
16th to endDay
6%18%33%34%6%
113
November1st to 15thDay
2214%26%37%16%
90
16th to endDay
7%14%45%27%4
90
December1st to 15thDay
35%13%41%30%6%
90
16th to endDay
9%417%39%26%3
96
January1st to 15thNight
2316%40%29%7%
720
16th to endNight
5%416%40%27%5%
768
February1st to 15thNight
2218%45%26%4
704
16th to endNight
46%22%42%21%2
632
March1st to 15thNight
15%22%38%25%4
720
16th to endNight
27%20%39%25%4
768
April1st to 15thNight
312%25%31%21%4
719
16th to endNight
9%23%39%21%5%
627
May1st to 15thNight
25%22%39%27%3
540
16th to endNight
9%22%32%31%3
563
June1st to 15thNight
1422%41%27%1
540
16th to endNight
215%44%32%4
540
July1st to 15thNight
15%41%44%6%
510
16th to endNight
21335%54%3
564
August1st to 15thNight
16%38%48%3
556
16th to endNight
16%27%52%12%
700
September1st to 15thNight
26%32%46%10%
660
16th to endNight
110%33%43%11%
656
October1st to 15thNight
3315%39%32%6%
660
16th to endNight
2314%32%38%9%
704
November1st to 15thNight
1115%35%39%7%
700
16th to endNight
1313%41%32%7%
720
December1st to 15thNight
6%113%41%31%5%
720
16th to endNight
6%5%18%36%28%4
768
Page generated at 2017-08-13 11:16:38. Version ac04

Copyright 2017 A. Danko


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