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Joshua Tree Astronomy Arts Theater
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Joshua Tree Astronomy Arts Theater clear sky chart from 2005-11-05 to 2018-01-12.

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
75%
16564
41%
48405
33%
16523
82%
16523
66%
20555

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
70%
763
35%
2471
31%
760
78%
760
51%
1107
January16th to endNight
65%
768
42%
2367
33%
768
78%
768
52%
1082
February1st to 15thNight
68%
699
40%
2108
33%
698
79%
698
58%
929
February16th to endNight
63%
632
41%
1895
36%
632
75%
632
52%
888
March1st to 15thNight
65%
720
38%
2136
32%
720
77%
720
60%
925
March16th to endNight
66%
768
41%
2079
28%
768
77%
768
61%
960
April1st to 15thNight
56%
719
39%
1799
17%
719
69%
719
64%
855
April16th to endNight
65%
705
44%
1785
22%
705
76%
705
75%
785
May1st to 15thNight
71%
539
44%
1619
30%
539
78%
539
78%
600
May16th to endNight
68%
562
41%
1685
28%
561
74%
561
76%
648
June1st to 15thNight
78%
540
35%
1620
28%
540
82%
540
80%
603
June16th to endNight
82%
540
38%
1620
32%
540
84%
540
81%
608
July1st to 15thNight
88%
510
33%
1530
29%
510
89%
510
72%
620
July16th to endNight
87%
564
37%
1593
32%
531
87%
531
63%
707
August1st to 15thNight
91%
695
39%
1769
26%
692
92%
692
79%
798
August16th to endNight
91%
764
46%
1910
31%
764
92%
764
81%
856
September1st to 15thNight
90%
720
40%
1893
32%
720
92%
720
76%
830
September16th to endNight
89%
716
51%
1980
44%
716
93%
716
87%
767
October1st to 15thNight
79%
720
45%
1980
37%
720
87%
720
76%
831
October16th to endNight
83%
768
48%
2322
45%
768
90%
768
75%
901
November1st to 15thNight
78%
760
40%
2470
37%
760
88%
760
70%
945
November16th to endNight
78%
780
45%
2535
45%
780
85%
780
64%
1003
December1st to 15thNight
70%
780
38%
2535
33%
780
80%
780
55%
1086
December16th to endNight
64%
832
40%
2704
34%
832
75%
832
48%
1221

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%76%
48929
Night
111112235%77%
48604
TransparencyDay
11%1214%28%41%
48624
Night
10%1315%29%39%
48410
SeeingDay
39%20%34%23%7%
6192
Night
25%14%33%35%10%
16572

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
2313213336%68%
1710
16th to endDay
3112312437%67%
1854
February1st to 15thDay
1211213346%71%
1751
16th to endDay
112313348%67%
1579
March1st to 15thDay
11111347%75%
1824
16th to endDay
111212336%76%
2142
April1st to 15thDay
11222346%74%
2149
16th to endDay
11125%83%
2175
May1st to 15thDay
111112483%
2331
16th to endDay
1123483%
2429
June1st to 15thDay
122485%
2340
16th to endDay
11111288%
2340
July1st to 15thDay
2112212336%73%
2340
16th to endDay
111232435%6%67%
2467
August1st to 15thDay
11221123477%
2179
16th to endDay
111112345%75%
2292
September1st to 15thDay
11111224478%
2067
16th to endDay
111112287%
1980
October1st to 15thDay
111123481%
1980
16th to endDay
121213482%
1899
November1st to 15thDay
11121234476%
1719
16th to endDay
1111113337%73%
1755
December1st to 15thDay
1212223248%68%
1755
16th to endDay
2223223246%67%
1872
January1st to 15thNight
1212223448%66%
2471
16th to endNight
2112212346%69%
2367
February1st to 15thNight
2112212335%73%
2101
16th to endNight
21122346%7%66%
1895
March1st to 15thNight
1111112337%73%
2136
16th to endNight
11213236%75%
2079
April1st to 15thNight
1221233477%
1799
16th to endNight
11235%83%
1785
May1st to 15thNight
11225%85%
1619
16th to endNight
111112485%
1684
June1st to 15thNight
122387%
1620
16th to endNight
1111289%
1620
July1st to 15thNight
111112235%78%
1620
16th to endNight
112123245%73%
1701
August1st to 15thNight
1111122482%
1778
16th to endNight
111113482%
1910
September1st to 15thNight
1111235%81%
1893
16th to endNight
12191%
1980
October1st to 15thNight
112225%82%
1980
16th to endNight
111113483%
2322
November1st to 15thNight
112335%79%
2470
16th to endNight
211112236%76%
2535
December1st to 15thNight
211221235%7%68%
2535
16th to endNight
2212313346%67%
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
18%25%20%34%19%
1711
16th to endDay
18%1420%31%22%
1854
February1st to 15thDay
15%15%18%32%27%
1751
16th to endDay
16%25%20%35%19%
1579
March1st to 15thDay
9%2220%33%31%
1824
16th to endDay
11%1322%34%25%
2142
April1st to 15thDay
11%1314%37%30%
2149
16th to endDay
7%116%34%39%
2175
May1st to 15thDay
7%1110%34%45%
2331
16th to endDay
6%1110%31%47%
2432
June1st to 15thDay
5%17%19%65%
2340
16th to endDay
6%29%79%
2340
July1st to 15thDay
13%118%20%53%
2201
16th to endDay
17%2413%24%36%
2312
August1st to 15thDay
10%1110%22%53%
2164
16th to endDay
11%2210%23%49%
2292
September1st to 15thDay
11%2310%21%51%
2067
16th to endDay
6%15%26%59%
1980
October1st to 15thDay
8%119%30%47%
1980
16th to endDay
8%1310%28%48%
1899
November1st to 15thDay
12%1316%34%32%
1719
16th to endDay
12%1317%32%32%
1755
December1st to 15thDay
16%25%23%27%24%
1755
16th to endDay
20%27%24%27%18%
1872
January1st to 15thNight
18%2420%31%22%
2471
16th to endNight
17%2422%26%26%
2367
February1st to 15thNight
15%1319%31%29%
2112
16th to endNight
16%3322%32%21%
1895
March1st to 15thNight
12%2319%33%28%
2136
16th to endNight
12%2418%36%25%
2079
April1st to 15thNight
11%15%16%36%28%
1799
16th to endNight
5%1215%35%39%
1785
May1st to 15thNight
41214%35%41%
1620
16th to endNight
6%214%36%39%
1685
June1st to 15thNight
5%119%20%62%
1620
16th to endNight
5%5%12%75%
1620
July1st to 15thNight
9%118%19%59%
1530
16th to endNight
14%2415%26%36%
1593
August1st to 15thNight
7%1111%25%52%
1769
16th to endNight
7%110%27%52%
1910
September1st to 15thNight
7%249%21%53%
1893
16th to endNight
46%26%62%
1980
October1st to 15thNight
7%1210%32%46%
1980
16th to endNight
7%1310%25%52%
2322
November1st to 15thNight
9%1314%37%33%
2470
16th to endNight
11%1216%33%34%
2535
December1st to 15thNight
15%27%18%29%27%
2535
16th to endNight
18%28%21%29%20%
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
9%9%17%39%21%1
123
16th to endDay
419%23%33%15%3
222
February1st to 15thDay
5%15%23%32%20%3
266
16th to endDay
10%22%24%25%15%
238
March1st to 15thDay
6%17%21%30%21%3
270
16th to endDay
7%15%25%30%17%3
288
April1st to 15thDay
9%21%24%24%17%4
269
16th to endDay
6%21%29%24%12%5%
270
May1st to 15thDay
412%25%34%18%5%
288
16th to endDay
110%24%36%19%6%
330
June1st to 15thDay
17%26%32%25%7%
315
16th to endDay
1323%32%25%13%
315
July1st to 15thDay
1113%39%32%12%
305
16th to endDay
2112%40%26%16%
327
August1st to 15thDay
2214%47%19%13%
315
16th to endDay
1110%40%26%18%
332
September1st to 15thDay
2216%44%27%6%
315
16th to endDay
19%18%35%27%6%
315
October1st to 15thDay
19%27%35%22%3
315
16th to endDay
26%18%28%34%10%
225
November1st to 15thDay
8%15%33%32%8%
135
16th to endDay
211%19%28%28%9%
135
December1st to 15thDay
410%16%28%36%4
135
16th to endDay
7%10%18%27%30%5%
144
January1st to 15thNight
36%14%38%27%9%
764
16th to endNight
47%16%35%27%8%
768
February1st to 15thNight
26%16%36%27%9%
704
16th to endNight
38%21%37%21%7%
632
March1st to 15thNight
28%19%35%27%7%
720
16th to endNight
110%17%35%27%8%
768
April1st to 15thNight
111%25%28%26%5%
719
16th to endNight
9%22%34%26%6%
705
May1st to 15thNight
16%19%34%34%4
540
16th to endNight
5%23%32%32%5%
563
June1st to 15thNight
317%42%33%3
540
16th to endNight
113%41%36%6%
540
July1st to 15thNight
15%33%50%8%
510
16th to endNight
2428%56%7%
564
August1st to 15thNight
1427%52%14%
695
16th to endNight
1319%53%22%
764
September1st to 15thNight
427%51%15%
720
16th to endNight
116%31%44%14%
716
October1st to 15thNight
1313%35%35%10%
720
16th to endNight
39%29%39%17%
768
November1st to 15thNight
215%33%35%12%
760
16th to endNight
35%10%32%34%14%
780
December1st to 15thNight
45%15%38%28%8%
780
16th to endNight
5%8%16%35%26%7%
832
Page generated at 2018-01-12 19:01:36. Version ac04

Copyright 2018 A. Danko


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