Scripps Ranch Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Scripps Ranch Observatory clear sky chart from 2005-11-05 to 2017-09-19.

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
73%
16276
29%
46998
28%
16232
74%
16232
44%
25755

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
71%
717
29%
2311
30%
716
75%
716
42%
1202
January16th to endNight
68%
768
33%
2304
32%
768
72%
768
39%
1289
February1st to 15thNight
72%
698
32%
2106
34%
698
75%
698
43%
1125
February16th to endNight
61%
632
26%
1895
30%
632
62%
632
31%
1163
March1st to 15thNight
69%
720
27%
2160
31%
720
71%
720
40%
1194
March16th to endNight
71%
768
25%
2035
24%
768
72%
768
41%
1213
April1st to 15thNight
66%
719
25%
1799
18%
719
67%
719
41%
1106
April16th to endNight
70%
720
27%
1800
18%
720
70%
720
45%
1080
May1st to 15thNight
67%
593
25%
1673
18%
593
67%
593
38%
1015
May16th to endNight
64%
561
22%
1685
18%
561
65%
561
34%
1048
June1st to 15thNight
66%
540
20%
1620
17%
540
66%
540
37%
979
June16th to endNight
83%
540
29%
1620
26%
540
83%
540
57%
773
July1st to 15thNight
81%
510
22%
1530
19%
510
81%
510
46%
815
July16th to endNight
78%
646
25%
1669
19%
607
78%
607
44%
951
August1st to 15thNight
78%
717
29%
1790
19%
713
79%
713
55%
969
August16th to endNight
83%
764
35%
1910
25%
764
83%
764
60%
1010
September1st to 15thNight
82%
720
32%
1869
27%
720
83%
720
56%
981
September16th to endNight
84%
671
41%
1856
40%
671
84%
671
61%
880
October1st to 15thNight
77%
660
33%
1815
33%
660
79%
660
49%
964
October16th to endNight
75%
704
35%
2100
37%
704
76%
704
45%
1092
November1st to 15thNight
79%
700
32%
2275
38%
700
80%
700
49%
1076
November16th to endNight
77%
720
32%
2340
37%
720
78%
720
43%
1179
December1st to 15thNight
67%
720
31%
2340
34%
720
68%
720
36%
1274
December16th to endNight
65%
768
31%
2496
31%
768
69%
768
36%
1377

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
5%413313347%61%
47803
Night
6%6%24323347%55%
47206
TransparencyDay
22%26%17%25%24%
47506
Night
27%37%16%22%23%
47005
SeeingDay
7%5%23%41%18%4
5946
Night
8%16%30%40%12%
16288

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
8%414323345%58%
1626
16th to endDay
10%5%24313336%55%
1920
February1st to 15thDay
8%314313437%58%
1751
16th to endDay
11%5%25%42445%7%45%
1579
March1st to 15thDay
6%413323449%55%
1800
16th to endDay
5%323323448%56%
2185
April1st to 15thDay
7%5%23324447%55%
2149
16th to endDay
5%313112247%65%
2160
May1st to 15thDay
6%5%23322337%59%
2277
16th to endDay
46%13312147%62%
2429
June1st to 15thDay
5%7%23323226%60%
2340
16th to endDay
1313112225%73%
2340
July1st to 15thDay
35%23314446%61%
2340
16th to endDay
331321336%8%61%
2382
August1st to 15thDay
1313113225%72%
2160
16th to endDay
1212212346%70%
2292
September1st to 15thDay
133213336%69%
2090
16th to endDay
2212122235%72%
1849
October1st to 15thDay
4423423446%60%
1815
16th to endDay
6%312212235%68%
1767
November1st to 15thDay
5%213313346%63%
1584
16th to endDay
6%313322347%61%
1620
December1st to 15thDay
8%313333449%53%
1620
16th to endDay
11%314324337%53%
1728
January1st to 15thNight
7%314423446%58%
2311
16th to endNight
10%424322247%55%
2304
February1st to 15thNight
8%314322346%58%
2101
16th to endNight
12%5%35%5%2434446%
1895
March1st to 15thNight
8%5%24313448%52%
2160
16th to endNight
7%6%2332445%7%50%
2035
April1st to 15thNight
10%7%24322248%51%
1799
16th to endNight
8%7%14312346%56%
1800
May1st to 15thNight
7%10%44322249%46%
1673
16th to endNight
10%11%35%323338%44%
1684
June1st to 15thNight
5%12%46%5%2335%9%41%
1620
16th to endNight
16%3431335%8%57%
1620
July1st to 15thNight
38%243135%5%9%50%
1620
16th to endNight
36%25%4245%5%8%50%
1783
August1st to 15thNight
26%3432335%10%54%
1800
16th to endNight
25%14212248%62%
1910
September1st to 15thNight
2423433347%61%
1869
16th to endNight
3412112238%68%
1856
October1st to 15thNight
4423323347%61%
1815
16th to endNight
7%5%13223236%61%
2100
November1st to 15thNight
4323213335%65%
2275
16th to endNight
5%414424347%58%
2340
December1st to 15thNight
9%425%423347%52%
2340
16th to endNight
12%413312345%55%
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
28%26%12%22%27%
1627
16th to endDay
30%38%14%14%29%
1920
February1st to 15thDay
26%36%14%22%26%
1751
16th to endDay
36%48%14%23%12%
1579
March1st to 15thDay
26%27%19%21%21%
1800
16th to endDay
26%48%25%19%14%
2185
April1st to 15thDay
29%38%23%25%10%
2149
16th to endDay
20%38%24%24%19%
2160
May1st to 15thDay
25%27%21%25%16%
2277
16th to endDay
24%27%24%31%10%
2432
June1st to 15thDay
25%15%17%29%20%
2340
16th to endDay
13%137%29%45%
2340
July1st to 15thDay
20%35%13%26%31%
2201
16th to endDay
18%411%23%28%13%
2234
August1st to 15thDay
15%2318%34%26%
2146
16th to endDay
14%2415%35%28%
2292
September1st to 15thDay
15%3312%34%30%
2090
16th to endDay
13%2312%35%33%
1849
October1st to 15thDay
24%25%17%24%24%
1815
16th to endDay
20%1412%22%37%
1767
November1st to 15thDay
21%27%16%17%35%
1584
16th to endDay
23%26%15%18%33%
1620
December1st to 15thDay
28%310%15%16%25%
1620
16th to endDay
32%38%16%22%17%
1728
January1st to 15thNight
26%36%13%20%29%
2311
16th to endNight
30%38%11%14%31%
2304
February1st to 15thNight
26%37%15%20%27%
2112
16th to endNight
38%36%13%21%15%
1895
March1st to 15thNight
30%28%18%17%22%
2160
16th to endNight
29%5%10%19%20%14%
2035
April1st to 15thNight
33%28%24%20%11%
1799
16th to endNight
29%37%21%20%18%
1800
May1st to 15thNight
34%39%19%16%16%
1674
16th to endNight
36%38%22%16%11%
1685
June1st to 15thNight
34%29%15%23%13%
1620
16th to endNight
19%311%28%36%
1620
July1st to 15thNight
25%26%12%26%26%
1530
16th to endNight
25%5%9%23%25%9%
1669
August1st to 15thNight
22%25%21%31%17%
1790
16th to endNight
18%25%13%33%26%
1910
September1st to 15thNight
20%25%12%31%27%
1869
16th to endNight
16%1212%35%31%
1856
October1st to 15thNight
23%36%19%24%23%
1815
16th to endNight
26%2311%20%35%
2100
November1st to 15thNight
21%26%16%15%37%
2275
16th to endNight
25%36%16%16%32%
2340
December1st to 15thNight
31%37%15%18%24%
2340
16th to endNight
30%49%14%18%21%
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
22%221%36%16%
105
16th to endDay
13%9%29%36%7%2
288
February1st to 15thDay
8%6%31%38%14%1
266
16th to endDay
12%12%35%28%9%1
238
March1st to 15thDay
8%10%29%34%12%4
270
16th to endDay
410%30%38%11%4
288
April1st to 15thDay
8%10%37%29%9%3
269
16th to endDay
413%38%31%7%3
270
May1st to 15thDay
12%8%30%36%10%2
288
16th to endDay
9%7%30%36%15%1
330
June1st to 15thDay
5%224%46%18%2
315
16th to endDay
114%48%26%7%
315
July1st to 15thDay
5%9%46%31%6%
305
16th to endDay
5%347%33%10%
327
August1st to 15thDay
310%53%26%5%
315
16th to endDay
26%55%29%6%
332
September1st to 15thDay
3120%53%16%4
315
16th to endDay
4222%51%13%4
268
October1st to 15thDay
46%40%34%12%1
255
16th to endDay
10%127%38%18%4
221
November1st to 15thDay
25%17%30%32%12%
90
16th to endDay
6%8%21%36%24%2
90
December1st to 15thDay
4314%38%32%6%
90
16th to endDay
17%317%37%21%2
96
January1st to 15thNight
7%110%38%29%12%
720
16th to endNight
12%29%37%29%8%
768
February1st to 15thNight
9%27%35%34%9%
704
16th to endNight
14%29%42%25%5%
632
March1st to 15thNight
10%37%40%31%6%
720
16th to endNight
9%27%35%36%7%
768
April1st to 15thNight
11%39%39%29%6%
719
16th to endNight
10%28%36%32%9%
720
May1st to 15thNight
9%18%34%37%7%
594
16th to endNight
11%29%32%40%4
563
June1st to 15thNight
8%8%39%38%4
540
16th to endNight
2228%59%6%
540
July1st to 15thNight
4214%65%12%
510
16th to endNight
4211%60%21%
646
August1st to 15thNight
4114%59%18%
717
16th to endNight
319%56%29%
764
September1st to 15thNight
4117%58%17%
720
16th to endNight
4326%48%16%
671
October1st to 15thNight
5%15%35%41%9%
660
16th to endNight
9%16%29%33%19%
704
November1st to 15thNight
6%15%34%37%14%
700
16th to endNight
6%6%33%35%17%
720
December1st to 15thNight
10%110%35%29%11%
720
16th to endNight
14%210%34%27%10%
768
Page generated at 2017-09-20 01:49:55. Version ac04

Copyright 2017 A. Danko


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