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Griffin Ranch
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Griffin Ranch clear sky chart from 2005-11-05 to 2017-09-10.

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
70%
15485
34%
46821
29%
15446
76%
15446
49%
23086

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
62%
718
30%
2327
26%
716
71%
716
41%
1175
January16th to endNight
57%
768
34%
2496
29%
768
68%
768
39%
1286
February1st to 15thNight
64%
701
33%
2244
30%
700
75%
700
48%
1080
February16th to endNight
59%
632
37%
1836
31%
632
67%
632
42%
992
March1st to 15thNight
64%
720
39%
1980
29%
720
73%
720
54%
1000
March16th to endNight
68%
768
37%
2112
27%
768
76%
768
56%
1037
April1st to 15thNight
65%
662
33%
1921
23%
662
74%
662
50%
944
April16th to endNight
68%
540
42%
1770
35%
540
79%
540
63%
698
May1st to 15thNight
71%
539
38%
1619
30%
539
78%
539
62%
701
May16th to endNight
74%
561
39%
1684
31%
561
79%
561
68%
698
June1st to 15thNight
81%
540
34%
1620
30%
540
82%
540
67%
688
June16th to endNight
86%
540
32%
1620
29%
540
86%
540
63%
711
July1st to 15thNight
79%
510
19%
1530
17%
510
79%
510
37%
868
July16th to endNight
77%
564
18%
1593
16%
531
77%
531
28%
1004
August1st to 15thNight
80%
539
23%
1611
21%
536
80%
536
38%
908
August16th to endNight
81%
573
28%
1845
30%
573
81%
573
37%
1007
September1st to 15thNight
76%
682
30%
1907
27%
682
77%
682
43%
1080
September16th to endNight
78%
656
39%
1815
29%
656
82%
656
60%
872
October1st to 15thNight
73%
660
38%
1930
30%
660
78%
660
58%
892
October16th to endNight
77%
704
43%
2112
34%
704
84%
704
65%
911
November1st to 15thNight
75%
700
41%
2100
33%
700
81%
700
60%
938
November16th to endNight
65%
720
39%
2313
33%
720
74%
720
49%
1082
December1st to 15thNight
66%
720
36%
2340
33%
720
73%
720
44%
1164
December16th to endNight
60%
768
33%
2496
30%
768
67%
768
36%
1350

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
4213323446%62%
47802
Night
4213323346%63%
47017
TransparencyDay
21%36%14%28%26%
47497
Night
21%35%15%27%27%
46823
SeeingDay
8%10%28%33%15%3
5329
Night
6%214%38%32%5%
15493

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
6%314223435%61%
1611
16th to endDay
10%312213346%59%
1728
February1st to 15thDay
46%23312346%61%
1616
16th to endDay
8%5%23323346%56%
1636
March1st to 15thDay
6%313323346%62%
1980
16th to endDay
421331233467%
2112
April1st to 15thDay
2212223347%66%
2026
16th to endDay
3111212235%74%
2187
May1st to 15thDay
1111223246%72%
2331
16th to endDay
32121223474%
2429
June1st to 15thDay
111113335%76%
2340
16th to endDay
11213345%74%
2340
July1st to 15thDay
4314435%6%7%8%49%
2340
16th to endDay
5%325%6%36%7%9%13%35%
2467
August1st to 15thDay
5%315%5%35%6%7%9%45%
2340
16th to endDay
5%314436%6%6%8%50%
2357
September1st to 15thDay
5%3143345%6%8%52%
1937
16th to endDay
311113346%71%
1815
October1st to 15thDay
3112213245%70%
1699
16th to endDay
111211233475%
1760
November1st to 15thDay
222212336%69%
1759
16th to endDay
431332223468%
1644
December1st to 15thDay
8%423313335%58%
1620
16th to endDay
9%6%23313336%56%
1728
January1st to 15thNight
6%42331335%460%
2327
16th to endNight
10%313323345%59%
2496
February1st to 15thNight
5%5%22212246%64%
2233
16th to endNight
7%413423447%56%
1836
March1st to 15thNight
6%312312245%66%
1980
16th to endNight
4212213336%68%
2112
April1st to 15thNight
4213214346%64%
1921
16th to endNight
11122235%77%
1770
May1st to 15thNight
112212446%72%
1619
16th to endNight
21111112479%
1684
June1st to 15thNight
212112225%77%
1620
16th to endNight
11231234473%
1620
July1st to 15thNight
3224435%7%7%11%47%
1620
16th to endNight
5%3245%37%8%9%12%36%
1701
August1st to 15thNight
2324445%5%8%9%49%
1620
16th to endNight
2324436%6%7%10%48%
1845
September1st to 15thNight
43243345%6%8%52%
1907
16th to endNight
221232223472%
1815
October1st to 15thNight
311231313472%
1930
16th to endNight
111221122378%
2112
November1st to 15thNight
3113212245%71%
2100
16th to endNight
431331223468%
2313
December1st to 15thNight
9%32323336%61%
2340
16th to endNight
10%424323336%54%
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
25%36%15%32%16%
1612
16th to endDay
25%2418%30%18%
1728
February1st to 15thDay
23%25%16%27%23%
1616
16th to endDay
28%2318%28%17%
1636
March1st to 15thDay
23%1210%36%25%
1980
16th to endDay
21%2311%39%21%
2112
April1st to 15thDay
16%2316%35%25%
2026
16th to endDay
13%1212%33%35%
2187
May1st to 15thDay
13%1312%31%36%
2331
16th to endDay
14%239%30%39%
2432
June1st to 15thDay
10%126%24%53%
2340
16th to endDay
11%247%19%54%
2340
July1st to 15thDay
27%7%13%16%14%21%
2201
16th to endDay
32%9%21%22%10%2
2312
August1st to 15thDay
31%6%9%19%17%15%
2325
16th to endDay
28%6%10%20%24%9%
2357
September1st to 15thDay
26%5%9%18%23%16%
1937
16th to endDay
14%2410%37%31%
1815
October1st to 15thDay
16%25%13%28%33%
1699
16th to endDay
12%25%10%34%34%
1760
November1st to 15thDay
15%1217%35%26%
1759
16th to endDay
20%1314%30%29%
1644
December1st to 15thDay
27%26%19%27%16%
1620
16th to endDay
29%36%23%28%8%
1728
January1st to 15thNight
25%35%15%31%19%
2327
16th to endNight
27%25%16%30%18%
2496
February1st to 15thNight
22%16%18%25%25%
2244
16th to endNight
27%2217%29%19%
1836
March1st to 15thNight
19%1311%34%29%
1980
16th to endNight
18%1413%38%23%
2112
April1st to 15thNight
20%2214%35%25%
1921
16th to endNight
10%2312%32%39%
1770
May1st to 15thNight
12%2412%33%35%
1620
16th to endNight
10%1311%30%42%
1685
June1st to 15thNight
12%125%18%60%
1620
16th to endNight
13%236%18%56%
1620
July1st to 15thNight
26%8%14%15%13%21%
1530
16th to endNight
32%12%18%23%9%3
1593
August1st to 15thNight
27%7%13%19%15%16%
1611
16th to endNight
27%6%14%20%19%12%
1845
September1st to 15thNight
26%5%10%22%17%16%
1907
16th to endNight
16%2310%32%34%
1815
October1st to 15thNight
17%15%12%29%33%
1930
16th to endNight
13%1412%28%40%
2112
November1st to 15thNight
15%1314%35%30%
2100
16th to endNight
20%1312%27%33%
2313
December1st to 15thNight
24%25%18%29%19%
2340
16th to endNight
30%26%20%29%9%
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
21%7%35%23%10%2
90
16th to endDay
16%328%27%18%6%
96
February1st to 15thDay
7%10%27%34%18%1
131
16th to endDay
15%21%34%20%6%
238
March1st to 15thDay
8%21%34%19%11%4
270
16th to endDay
9%22%31%23%10%2
288
April1st to 15thDay
11%20%36%22%7%2
269
16th to endDay
11%27%36%18%5%1
270
May1st to 15thDay
7%20%38%24%6%1
288
16th to endDay
416%38%29%9%1
330
June1st to 15thDay
314%35%31%12%2
315
16th to endDay
331%44%14%5%
315
July1st to 15thDay
4121%51%16%4
305
16th to endDay
6%111%45%21%12%
327
August1st to 15thDay
5%15%45%26%7%
315
16th to endDay
4115%43%29%5%
332
September1st to 15thDay
10%325%38%19%3
294
16th to endDay
9%6%28%33%18%2
255
October1st to 15thDay
28%25%42%15%6%
139
16th to endDay
5%127%35%29%2
96
November1st to 15thDay
410%21%36%23%4
90
16th to endDay
10%13%31%36%8%
90
December1st to 15thDay
10%317%45%21%2
90
16th to endDay
21%9%25%29%13%1
96
January1st to 15thNight
10%318%44%19%3
720
16th to endNight
13%5%18%36%23%2
768
February1st to 15thNight
8%416%44%23%2
704
16th to endNight
10%420%43%19%1
632
March1st to 15thNight
7%419%41%24%3
720
16th to endNight
5%317%40%29%3
768
April1st to 15thNight
5%6%17%45%23%1
662
16th to endNight
17%20%42%24%4
540
May1st to 15thNight
2417%42%27%4
540
16th to endNight
3315%39%34%3
563
June1st to 15thNight
310%42%39%3
540
16th to endNight
15%35%51%4
540
July1st to 15thNight
5%425%57%6%
510
16th to endNight
6%418%54%15%
564
August1st to 15thNight
3318%56%17%
539
16th to endNight
2422%55%14%
573
September1st to 15thNight
5%6%29%48%9%
682
16th to endNight
3112%36%37%9%
656
October1st to 15thNight
4214%40%32%5%
660
16th to endNight
2113%42%31%7%
704
November1st to 15thNight
4214%44%29%4
700
16th to endNight
7%319%39%27%3
720
December1st to 15thNight
11%215%43%26%1
720
16th to endNight
13%315%46%19%2
768
Page generated at 2017-09-11 16:35:26. Version ac04

Copyright 2017 A. Danko


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