This page made possible by the sponsorship of: Mark Hanning-Lee.

Irvine Regional Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Irvine Regional Park clear sky chart from 2005-11-05 to 2018-04-23.

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
77%
16825
34%
49226
31%
16781
80%
16781
49%
25097

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%
776
30%
2496
30%
776
74%
776
40%
1297
January16th to endNight
65%
832
35%
2496
30%
832
72%
832
40%
1349
February1st to 15thNight
72%
757
35%
2283
34%
757
77%
757
47%
1170
February16th to endNight
66%
684
30%
2051
32%
684
68%
684
35%
1195
March1st to 15thNight
72%
780
29%
2340
31%
780
75%
780
41%
1255
March16th to endNight
75%
832
29%
2184
25%
832
77%
832
46%
1236
April1st to 15thNight
72%
779
29%
1949
20%
779
74%
779
46%
1152
April16th to endNight
77%
744
32%
1860
20%
744
79%
744
53%
1010
May1st to 15thNight
76%
605
29%
1685
21%
605
77%
605
48%
910
May16th to endNight
80%
561
28%
1685
23%
561
80%
561
49%
858
June1st to 15thNight
80%
540
25%
1620
23%
540
80%
540
46%
871
June16th to endNight
90%
360
37%
1440
44%
360
90%
360
57%
526
July1st to 15thNight
87%
360
32%
1380
37%
360
87%
360
51%
563
July16th to endNight
87%
658
31%
1680
24%
618
87%
618
55%
872
August1st to 15thNight
86%
717
35%
1790
22%
713
86%
713
65%
893
August16th to endNight
90%
764
41%
1910
28%
764
90%
764
69%
929
September1st to 15thNight
87%
720
38%
1842
31%
720
87%
720
64%
916
September16th to endNight
88%
716
45%
1980
44%
716
89%
716
68%
887
October1st to 15thNight
83%
720
36%
1980
35%
720
84%
720
59%
965
October16th to endNight
79%
768
41%
2331
43%
768
81%
768
51%
1126
November1st to 15thNight
80%
760
34%
2470
36%
760
84%
760
51%
1138
November16th to endNight
77%
780
37%
2535
40%
780
80%
780
45%
1247
December1st to 15thNight
70%
780
33%
2535
33%
780
75%
780
39%
1302
December16th to endNight
62%
832
34%
2704
30%
832
70%
832
37%
1430

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%312212346%65%
50270
Night
5%413323347%62%
49429
TransparencyDay
20%25%18%27%26%
49966
Night
22%25%16%24%27%
49236
SeeingDay
6%7%20%37%20%7%
6743
Night
6%2431%41%13%
16839

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%5%22312346%59%
1769
16th to endDay
10%413312335%58%
2080
February1st to 15thDay
7%312312345%63%
1901
16th to endDay
11%5%24313346%52%
1709
March1st to 15thDay
6%3122235%6%7%56%
1950
16th to endDay
431242345%9%56%
2388
April1st to 15thDay
5%313324347%59%
2329
16th to endDay
5%312211227%68%
2214
May1st to 15thDay
4413312347%63%
2262
16th to endDay
4413312347%62%
2429
June1st to 15thDay
6%6%13212249%60%
2340
16th to endDay
11111222479%
2514
July1st to 15thDay
2312213446%68%
2496
16th to endDay
2212222336%69%
2369
August1st to 15thDay
11111235%78%
2160
16th to endDay
11121234476%
2292
September1st to 15thDay
112112235%77%
2117
16th to endDay
211112235%78%
1980
October1st to 15thDay
5%213212346%66%
1980
16th to endDay
4312212245%69%
1890
November1st to 15thDay
4312322245%67%
1719
16th to endDay
4313323347%62%
1755
December1st to 15thDay
6%312324449%57%
1755
16th to endDay
10%413223336%57%
1872
January1st to 15thNight
7%41322335%7%57%
2496
16th to endNight
9%423313335%59%
2496
February1st to 15thNight
7%314212336%62%
2281
16th to endNight
12%5%14314435%53%
2051
March1st to 15thNight
6%41232245%9%55%
2340
16th to endNight
5%423324448%56%
2184
April1st to 15thNight
6%5%33312448%56%
1949
16th to endNight
4412323345%65%
1860
May1st to 15thNight
36%23322348%59%
1685
16th to endNight
25%23212349%60%
1684
June1st to 15thNight
35%23423449%56%
1620
16th to endNight
13112133310%67%
1440
July1st to 15thNight
15%12322349%62%
1461
16th to endNight
331233446%9%59%
1795
August1st to 15thNight
232212346%69%
1800
16th to endNight
211213236%73%
1910
September1st to 15thNight
2212222235%71%
1842
16th to endNight
23111225%76%
1980
October1st to 15thNight
2212212336%69%
1980
16th to endNight
3314313236%67%
2331
November1st to 15thNight
3313212335%68%
2470
16th to endNight
5%313323346%63%
2535
December1st to 15thNight
7%324323346%58%
2535
16th to endNight
11%413213335%59%
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
27%26%15%23%24%
1770
16th to endDay
29%26%15%17%28%
2080
February1st to 15thDay
24%2315%26%27%
1901
16th to endDay
33%2420%26%11%
1709
March1st to 15thDay
25%38%21%20%20%
1950
16th to endDay
24%410%25%21%13%
2388
April1st to 15thDay
26%37%26%22%13%
2329
16th to endDay
19%29%23%28%17%
2214
May1st to 15thDay
22%27%22%27%16%
2262
16th to endDay
21%26%31%27%9%
2432
June1st to 15thDay
22%25%16%35%17%
2340
16th to endDay
9%128%31%46%
2514
July1st to 15thDay
15%3311%28%38%
2349
16th to endDay
16%26%22%32%20%
2222
August1st to 15thDay
10%1113%38%34%
2146
16th to endDay
11%2112%37%34%
2292
September1st to 15thDay
11%2311%34%36%
2117
16th to endDay
10%2115%35%35%
1980
October1st to 15thDay
19%2319%26%27%
1980
16th to endDay
19%2314%20%39%
1890
November1st to 15thDay
20%25%17%21%31%
1719
16th to endDay
22%3413%22%32%
1755
December1st to 15thDay
24%39%16%17%28%
1755
16th to endDay
29%36%17%20%22%
1872
January1st to 15thNight
27%26%13%21%28%
2496
16th to endNight
28%26%15%15%31%
2496
February1st to 15thNight
25%15%16%21%29%
2292
16th to endNight
33%3415%24%18%
2051
March1st to 15thNight
27%36%20%21%21%
2340
16th to endNight
26%39%20%23%16%
2184
April1st to 15thNight
28%28%24%21%15%
1949
16th to endNight
21%37%23%23%20%
1860
May1st to 15thNight
23%39%22%22%17%
1686
16th to endNight
22%39%27%24%12%
1685
June1st to 15thNight
23%5%7%16%28%18%
1620
16th to endNight
13%229%29%43%
1440
July1st to 15thNight
17%2211%30%36%
1380
16th to endNight
18%45%22%27%21%
1680
August1st to 15thNight
13%3114%37%29%
1790
16th to endNight
11%2111%33%38%
1910
September1st to 15thNight
14%2310%32%35%
1842
16th to endNight
12%1112%34%37%
1980
October1st to 15thNight
17%2417%32%26%
1980
16th to endNight
20%2211%21%41%
2331
November1st to 15thNight
20%15%16%20%34%
2470
16th to endNight
23%2414%20%34%
2535
December1st to 15thNight
26%26%14%19%28%
2535
16th to endNight
28%27%13%24%22%
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
22%5%14%28%25%3
158
16th to endDay
12%11%23%31%15%4
352
February1st to 15thDay
8%8%25%34%16%6%
326
16th to endDay
13%15%26%30%13%1
290
March1st to 15thDay
9%15%26%26%17%3
330
16th to endDay
7%10%31%34%13%2
352
April1st to 15thDay
5%13%35%28%11%4
329
16th to endDay
215%42%28%7%4
288
May1st to 15thDay
9%10%28%35%11%4
288
16th to endDay
8%6%27%36%15%5%
330
June1st to 15thDay
6%323%38%21%6%
315
16th to endDay
12%46%26%13%
315
July1st to 15thDay
38%42%33%12%
305
16th to endDay
31343%34%13%
327
August1st to 15thDay
118%48%29%9%
315
16th to endDay
16%46%31%14%
332
September1st to 15thDay
214%55%18%7%
315
16th to endDay
2419%44%20%7%
315
October1st to 15thDay
35%25%41%17%6%
315
16th to endDay
6%418%37%22%10%
297
November1st to 15thDay
5%8%11%33%25%15%
135
16th to endDay
6%9%17%28%21%15%
135
December1st to 15thDay
410%14%26%34%8%
135
16th to endDay
9%10%13%31%27%8%
144
January1st to 15thNight
9%37%40%27%11%
780
16th to endNight
11%49%35%29%9%
832
February1st to 15thNight
7%37%38%30%12%
764
16th to endNight
14%36%40%27%7%
684
March1st to 15thNight
8%37%41%31%8%
780
16th to endNight
5%3441%36%9%
832
April1st to 15thNight
8%26%41%35%6%
779
16th to endNight
5%4440%35%10%
744
May1st to 15thNight
5%26%35%41%8%
606
16th to endNight
316%36%43%7%
563
June1st to 15thNight
32435%47%6%
540
16th to endNight
122%65%9%
360
July1st to 15thNight
2110%67%17%
360
16th to endNight
311%63%20%
658
August1st to 15thNight
1113%62%20%
717
16th to endNight
110%61%26%
764
September1st to 15thNight
318%54%22%
720
16th to endNight
3126%49%17%
716
October1st to 15thNight
41337%40%12%
720
16th to endNight
5%1429%37%21%
768
November1st to 15thNight
45%36%37%15%
760
16th to endNight
7%16%32%36%15%
780
December1st to 15thNight
9%36%37%32%10%
780
16th to endNight
11%7%9%32%29%9%
832
Page generated at 2018-04-24 07:03:04. Version ac04

Copyright 2018 A. Danko


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