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Gilbert Rotary Centennial Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Gilbert Rotary Centennial Observatory clear sky chart from 2005-11-05 to 2019-05-11.

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
80%
17863
38%
53623
35%
17825
83%
17825
56%
25133

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
76%
838
34%
2717
36%
836
79%
836
45%
1336
January16th to endNight
74%
896
36%
2912
37%
896
79%
896
44%
1447
February1st to 15thNight
73%
819
36%
2554
37%
819
78%
819
52%
1209
February16th to endNight
70%
736
36%
2187
36%
736
74%
736
45%
1146
March1st to 15thNight
75%
840
42%
2310
36%
840
80%
840
59%
1126
March16th to endNight
80%
896
39%
2464
32%
896
85%
896
64%
1164
April1st to 15thNight
75%
824
37%
2293
27%
824
81%
824
59%
1106
April16th to endNight
75%
624
44%
1971
38%
624
83%
624
70%
780
May1st to 15thNight
78%
616
43%
1849
36%
616
83%
616
69%
766
May16th to endNight
82%
609
41%
1828
33%
609
87%
609
75%
722
June1st to 15thNight
89%
585
37%
1755
33%
585
89%
585
73%
715
June16th to endNight
92%
585
35%
1755
31%
585
92%
585
75%
701
July1st to 15thNight
85%
555
25%
1665
20%
555
85%
555
48%
843
July16th to endNight
84%
612
28%
1737
24%
579
85%
579
43%
952
August1st to 15thNight
85%
575
32%
1719
28%
572
85%
572
47%
877
August16th to endNight
85%
689
32%
2025
31%
689
85%
689
46%
1076
September1st to 15thNight
82%
780
36%
2145
32%
780
84%
780
57%
1081
September16th to endNight
85%
776
43%
2145
35%
776
88%
776
68%
975
October1st to 15thNight
81%
780
41%
2239
35%
780
84%
780
62%
1033
October16th to endNight
86%
832
45%
2496
41%
832
89%
832
69%
1045
November1st to 15thNight
84%
820
44%
2485
42%
820
87%
820
64%
1085
November16th to endNight
81%
840
40%
2730
41%
840
84%
840
56%
1193
December1st to 15thNight
75%
840
39%
2730
41%
840
78%
840
48%
1288
December16th to endNight
74%
896
38%
2912
40%
896
77%
896
44%
1467

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
3212213346%69%
54230
Night
3212213346%68%
53821
TransparencyDay
16%2312%25%39%
53925
Night
17%2311%23%41%
53627
SeeingDay
4211%28%35%18%
7585
Night
418%41%39%4
17873

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%323322335%63%
1881
16th to endDay
6%213312236%65%
2016
February1st to 15thDay
5%313312236%65%
1964
16th to endDay
7%323323247%60%
1857
March1st to 15thDay
4212323345%65%
2310
16th to endDay
3212223245%69%
2464
April1st to 15thDay
212213337%70%
2314
16th to endDay
21111125%80%
2590
May1st to 15thDay
111112235%79%
2658
16th to endDay
21111122382%
2637
June1st to 15thDay
1111112482%
2535
16th to endDay
1111222383%
2535
July1st to 15thDay
21144245%6%7%59%
2535
16th to endDay
4314435%7%7%11%46%
2675
August1st to 15thDay
231232447%10%56%
2485
16th to endDay
22342447%9%59%
2526
September1st to 15thDay
3212322437%66%
2145
16th to endDay
2111222381%
2145
October1st to 15thDay
311212325%74%
2051
16th to endDay
111212235%78%
2080
November1st to 15thDay
112212235%76%
2031
16th to endDay
4213212225%71%
1890
December1st to 15thDay
6%34323336%60%
1890
16th to endDay
5%414313346%61%
2016
January1st to 15thNight
6%313314446%61%
2717
16th to endNight
8%21332333464%
2912
February1st to 15thNight
5%313222336%66%
2545
16th to endNight
7%312323336%60%
2187
March1st to 15thNight
4212112347%67%
2310
16th to endNight
3112212236%71%
2464
April1st to 15thNight
3112212436%69%
2293
16th to endNight
21111122480%
1971
May1st to 15thNight
112112236%76%
1849
16th to endNight
211111384%
1828
June1st to 15thNight
1112225%80%
1755
16th to endNight
111113482%
1755
July1st to 15thNight
1213425%5%6%11%55%
1755
16th to endNight
3213435%6%9%13%45%
1845
August1st to 15thNight
12133245%8%9%55%
1728
16th to endNight
11145%35%6%6%9%53%
2025
September1st to 15thNight
221242335%8%63%
2145
16th to endNight
11121224477%
2145
October1st to 15thNight
3212212135%74%
2239
16th to endNight
111211123379%
2496
November1st to 15thNight
1112212235%75%
2485
16th to endNight
311231223471%
2730
December1st to 15thNight
6%213312346%63%
2730
16th to endNight
7%313323335%61%
2912

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
24%2414%28%25%
1882
16th to endDay
21%1315%26%30%
2016
February1st to 15thDay
21%1315%28%28%
1964
16th to endDay
24%2215%31%24%
1857
March1st to 15thDay
20%210%29%36%
2310
16th to endDay
18%119%33%35%
2464
April1st to 15thDay
14%19%35%38%
2314
16th to endDay
9%117%24%55%
2590
May1st to 15thDay
9%118%24%54%
2658
16th to endDay
9%15%21%62%
2640
June1st to 15thDay
9%1215%70%
2535
16th to endDay
9%1311%74%
2535
July1st to 15thDay
21%47%15%18%32%
2396
16th to endDay
26%6%13%25%19%9%
2520
August1st to 15thDay
20%48%19%19%27%
2470
16th to endDay
20%46%19%26%23%
2526
September1st to 15thDay
18%3413%26%33%
2145
16th to endDay
10%16%28%53%
2145
October1st to 15thDay
14%229%25%46%
2051
16th to endDay
10%129%28%46%
2080
November1st to 15thDay
12%112%32%39%
2031
16th to endDay
17%1110%28%40%
1890
December1st to 15thDay
25%2316%27%23%
1890
16th to endDay
24%2421%29%16%
2016
January1st to 15thNight
24%2412%25%30%
2717
16th to endNight
25%2112%26%31%
2912
February1st to 15thNight
20%1413%25%34%
2556
16th to endNight
25%2113%27%29%
2187
March1st to 15thNight
17%2110%26%42%
2310
16th to endNight
15%118%31%41%
2464
April1st to 15thNight
16%27%28%43%
2293
16th to endNight
9%115%22%60%
1971
May1st to 15thNight
10%17%25%54%
1850
16th to endNight
8%16%16%66%
1829
June1st to 15thNight
9%1212%73%
1755
16th to endNight
8%1147%77%
1755
July1st to 15thNight
21%49%16%14%33%
1665
16th to endNight
23%6%11%23%21%12%
1737
August1st to 15thNight
21%5%7%19%16%29%
1719
16th to endNight
24%47%15%24%24%
2025
September1st to 15thNight
18%26%18%21%31%
2145
16th to endNight
11%25%22%56%
2145
October1st to 15thNight
14%219%23%49%
2239
16th to endNight
11%119%21%54%
2496
November1st to 15thNight
14%119%29%44%
2485
16th to endNight
17%1110%25%43%
2730
December1st to 15thNight
21%2216%26%29%
2730
16th to endNight
25%2316%30%21%
2912

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
16%26%32%33%8%
180
16th to endDay
437%34%35%14%
192
February1st to 15thDay
10%112%32%33%10%
299
16th to endDay
9%5%20%38%21%4
342
March1st to 15thDay
5%6%16%37%19%14%
390
16th to endDay
2418%32%28%12%
416
April1st to 15thDay
46%18%32%27%11%
389
16th to endDay
26%23%31%26%8%
378
May1st to 15thDay
2423%28%29%12%
389
16th to endDay
2215%36%34%10%
394
June1st to 15thDay
229%32%36%16%
375
16th to endDay
11323%45%24%
375
July1st to 15thDay
31220%46%26%
365
16th to endDay
3212%40%40%
391
August1st to 15thDay
2115%42%36%
359
16th to endDay
116%45%36%
396
September1st to 15thDay
47%22%41%23%
375
16th to endDay
4111%27%35%20%
375
October1st to 15thDay
6%114%30%33%13%
281
16th to endDay
26%22%42%25%
192
November1st to 15thDay
2111%33%41%11%
180
16th to endDay
6%17%27%42%14%
180
December1st to 15thDay
8%5%38%38%8%
180
16th to endDay
11%113%29%32%11%
192
January1st to 15thNight
7%17%51%28%3
840
16th to endNight
9%18%49%28%2
896
February1st to 15thNight
6%110%48%29%3
824
16th to endNight
10%112%50%24%1
736
March1st to 15thNight
5%112%51%25%4
840
16th to endNight
319%47%34%4
896
April1st to 15thNight
3213%49%29%1
824
16th to endNight
2117%47%26%3
624
May1st to 15thNight
1114%46%32%3
617
16th to endNight
211%45%36%3
611
June1st to 15thNight
11446%43%2
585
16th to endNight
1133%59%3
585
July1st to 15thNight
2326%57%8%
555
16th to endNight
31113%67%13%
612
August1st to 15thNight
2116%66%13%
575
16th to endNight
2217%65%12%
689
September1st to 15thNight
316%25%55%8%
780
16th to endNight
26%36%47%6%
776
October1st to 15thNight
49%45%38%2
780
16th to endNight
16%41%43%6%
832
November1st to 15thNight
26%50%35%4
820
16th to endNight
47%44%38%4
840
December1st to 15thNight
7%17%48%33%1
840
16th to endNight
8%18%48%29%4
896
Page generated at 2019-05-11 21:31:06. Version ac04

Copyright 2019 A. Danko


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