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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 2018-02-22.

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%
16525
39%
48913
32%
16488
81%
16488
62%
21645

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%
777
34%
2522
32%
776
81%
776
53%
1138
January16th to endNight
70%
832
38%
2675
34%
832
80%
832
50%
1244
February1st to 15thNight
72%
757
37%
2292
32%
757
81%
757
54%
1075
February16th to endNight
62%
660
39%
1979
36%
660
72%
660
49%
978
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%
571
39%
1643
29%
568
87%
568
65%
729
August16th to endNight
88%
764
43%
1910
30%
764
89%
764
72%
918
September1st to 15thNight
86%
720
38%
1920
30%
720
89%
720
68%
893
September16th to endNight
85%
716
49%
1980
41%
716
91%
716
81%
805
October1st to 15thNight
77%
720
42%
1980
34%
720
83%
720
67%
898
October16th to endNight
77%
768
45%
2359
41%
768
85%
768
67%
963
November1st to 15thNight
79%
760
39%
2470
37%
760
87%
760
67%
986
November16th to endNight
78%
780
44%
2535
44%
780
84%
780
64%
1021
December1st to 15thNight
75%
780
37%
2535
36%
780
81%
780
56%
1118
December16th to endNight
66%
832
36%
2704
32%
832
74%
832
45%
1316

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%
49344
Night
211212235%74%
49108
TransparencyDay
12%2415%27%36%
49039
Night
13%2415%27%37%
48914
SeeingDay
37%19%35%25%9%
6177
Night
2315%37%34%6%
16538

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
221212236%73%
1746
16th to endDay
322322345%69%
1900
February1st to 15thDay
1111213347%70%
1901
16th to endDay
3112323446%67%
1641
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%
2306
16th to endDay
211212346%74%
2292
September1st to 15thDay
12212235%75%
2040
16th to endDay
111112484%
1980
October1st to 15thDay
21211222478%
1980
16th to endDay
1111223481%
1863
November1st to 15thDay
1111111335%76%
1719
16th to endDay
111111235%77%
1755
December1st to 15thDay
3212213246%69%
1755
16th to endDay
3213212346%66%
1872
January1st to 15thNight
222222446%69%
2522
16th to endNight
421213345%68%
2675
February1st to 15thNight
222222245%71%
2281
16th to endNight
431223346%66%
1979
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
12211233475%
1652
16th to endNight
11211246%77%
1910
September1st to 15thNight
111212345%76%
1920
16th to endNight
11112287%
1980
October1st to 15thNight
21121122478%
1980
16th to endNight
11111113480%
2359
November1st to 15thNight
111112235%79%
2470
16th to endNight
112112125%79%
2535
December1st to 15thNight
321212348%68%
2535
16th to endNight
5%212313346%65%
2704

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
14%29%31%35%7%
1747
16th to endDay
18%48%26%31%10%
1900
February1st to 15thDay
16%38%22%32%16%
1901
16th to endDay
19%37%18%32%19%
1641
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%
2291
16th to endDay
12%2210%20%51%
2292
September1st to 15thDay
11%249%18%53%
2040
16th to endDay
7%215%28%55%
1980
October1st to 15thDay
13%1310%27%43%
1980
16th to endDay
9%1312%35%37%
1863
November1st to 15thDay
11%25%17%40%21%
1719
16th to endDay
11%3423%36%20%
1755
December1st to 15thDay
17%310%24%30%13%
1755
16th to endDay
19%6%11%27%25%9%
1872
January1st to 15thNight
17%36%25%34%12%
2522
16th to endNight
19%36%23%29%18%
2675
February1st to 15thNight
17%36%19%30%21%
2292
16th to endNight
20%2317%34%20%
1979
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%227%18%56%
1643
16th to endNight
10%338%20%55%
1910
September1st to 15thNight
11%3410%17%53%
1920
16th to endNight
5%116%22%61%
1980
October1st to 15thNight
11%229%25%48%
1980
16th to endNight
10%2310%23%49%
2359
November1st to 15thNight
10%2217%38%27%
2470
16th to endNight
11%1417%34%31%
2535
December1st to 15thNight
16%37%22%32%18%
2535
16th to endNight
21%49%26%27%11%
2704

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
14%414%37%23%5%
135
16th to endDay
6%5%15%27%31%12%
172
February1st to 15thDay
48%17%32%26%10%
326
16th to endDay
5%16%23%32%19%3
264
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%40%24%10%
315
16th to endDay
410%35%33%15%
332
September1st to 15thDay
2216%39%29%9%
315
16th to endDay
15%15%34%31%11%
315
October1st to 15thDay
15%23%40%19%9%
315
16th to endDay
15%13%30%34%14%
162
November1st to 15thDay
2217%31%34%11%
135
16th to endDay
8%11%34%38%5%
135
December1st to 15thDay
26%15%32%31%11%
135
16th to endDay
6%415%34%31%8%
144
January1st to 15thNight
2315%40%30%7%
780
16th to endNight
5%415%39%29%5%
832
February1st to 15thNight
2217%44%26%5%
764
16th to endNight
46%22%41%22%2
660
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
571
16th to endNight
15%26%52%13%
764
September1st to 15thNight
26%32%47%10%
720
16th to endNight
110%33%43%10%
716
October1st to 15thNight
2314%40%32%5%
720
16th to endNight
2313%31%39%10%
768
November1st to 15thNight
1115%36%38%6%
760
16th to endNight
1313%40%34%6%
780
December1st to 15thNight
6%114%41%32%4
780
16th to endNight
5%5%17%36%29%4
832
Page generated at 2018-02-23 08:21:38. Version ac04

Copyright 2018 A. Danko


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