San Isabel Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the San Isabel Observatory clear sky chart from 2005-11-05 to 2017-09-22.

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
54%
15919
28%
46931
17%
15878
64%
15878
45%
24306

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
46%
891
32%
2500
17%
889
60%
889
56%
1182
January16th to endNight
50%
768
36%
2496
24%
768
66%
768
55%
1094
February1st to 15thNight
43%
699
27%
2262
15%
697
59%
697
46%
1095
February16th to endNight
42%
632
34%
1894
15%
632
62%
632
53%
913
March1st to 15thNight
47%
720
30%
2082
15%
720
59%
720
50%
1056
March16th to endNight
47%
699
29%
2043
15%
699
60%
699
45%
1069
April1st to 15thNight
42%
539
26%
1798
15%
539
57%
539
42%
869
April16th to endNight
42%
540
23%
1800
15%
540
56%
540
34%
991
May1st to 15thNight
46%
540
20%
1637
15%
540
54%
540
32%
970
May16th to endNight
54%
562
18%
1498
11%
561
62%
561
38%
889
June1st to 15thNight
62%
540
24%
1440
17%
540
68%
540
55%
726
June16th to endNight
73%
540
26%
1440
21%
540
76%
540
56%
721
July1st to 15thNight
73%
510
17%
1360
16%
510
74%
510
34%
851
July16th to endNight
72%
564
16%
1495
15%
531
73%
531
33%
901
August1st to 15thNight
71%
539
16%
1657
16%
536
72%
536
31%
984
August16th to endNight
72%
573
24%
1910
25%
573
74%
573
33%
1071
September1st to 15thNight
68%
540
25%
1800
24%
540
73%
540
33%
1000
September16th to endNight
63%
529
34%
1841
28%
529
73%
529
44%
888
October1st to 15thNight
55%
660
33%
1980
18%
660
66%
660
50%
989
October16th to endNight
58%
704
35%
2112
20%
704
70%
704
50%
1057
November1st to 15thNight
54%
870
35%
2270
18%
870
63%
870
58%
1142
November16th to endNight
51%
900
36%
2408
18%
900
63%
900
58%
1156
December1st to 15thNight
43%
900
25%
2520
11%
900
55%
900
53%
1254
December16th to endNight
42%
960
27%
2688
13%
960
54%
960
44%
1438

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
34244345%6%8%53%
47960
Night
232332345%8%60%
47111
TransparencyDay
28%5%14%26%20%5%
47642
Night
22%416%30%21%5%
46931
SeeingDay
9%7%23%32%20%7%
5822
Night
4429%42%16%1
15928

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
3123243410%63%
1450
16th to endDay
131432235%7%64%
1728
February1st to 15thDay
3244235%48%61%
1600
16th to endDay
324324449%61%
1580
March1st to 15thDay
14134245%6%7%58%
1875
16th to endDay
26%2443445%7%55%
2181
April1st to 15thDay
2414435%45%10%53%
2150
16th to endDay
47%35%5%35%5%7%6%46%
2160
May1st to 15thDay
5%7%25%5%36%5%6%8%41%
2310
16th to endDay
45%245%36%6%7%9%44%
2616
June1st to 15thDay
34244245%7%9%50%
2520
16th to endDay
3214435%6%6%7%55%
2520
July1st to 15thDay
7%426%6%46%7%6%7%40%
2520
16th to endDay
8%5%25%6%36%6%7%8%37%
2567
August1st to 15thDay
8%5%36%6%46%6%6%7%37%
2292
16th to endDay
7%4145%35%7%6%8%44%
2292
September1st to 15thDay
7%425%5%35%447%49%
2160
16th to endDay
3313423345%62%
1927
October1st to 15thDay
331342445%7%60%
1650
16th to endDay
2313323445%64%
1752
November1st to 15thDay
1212213246%70%
1583
16th to endDay
223212249%68%
1551
December1st to 15thDay
42441335%8%61%
1440
16th to endDay
2233235%6%8%60%
1536
January1st to 15thNight
21132235%8%68%
2500
16th to endNight
1213212336%71%
2496
February1st to 15thNight
324313348%62%
2252
16th to endNight
424313348%63%
1894
March1st to 15thNight
5%23213348%62%
2082
16th to endNight
2414313346%62%
2043
April1st to 15thNight
5%1332335%7%61%
1798
16th to endNight
5%6%34424346%54%
1800
May1st to 15thNight
7%8%35%423347%48%
1636
16th to endNight
6%5%2331345%9%52%
1497
June1st to 15thNight
321212225%10%65%
1440
16th to endNight
21222435%9%63%
1440
July1st to 15thNight
5%315%435%7%7%10%45%
1440
16th to endNight
6%325%435%6%7%10%43%
1598
August1st to 15thNight
6%414435%5%5%10%48%
1666
16th to endNight
6%4134245%7%9%49%
1910
September1st to 15thNight
5%4245%345%6%8%49%
1800
16th to endNight
3413323335%64%
1841
October1st to 15thNight
3212213446%65%
1980
16th to endNight
2423313446%64%
2112
November1st to 15thNight
212213246%70%
2270
16th to endNight
1312212238%69%
2408
December1st to 15thNight
323313348%65%
2520
16th to endNight
33432345%9%60%
2688

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%225%32%17%3
1451
16th to endDay
20%215%36%19%5%
1728
February1st to 15thDay
21%420%33%16%3
1601
16th to endDay
20%413%33%24%3
1580
March1st to 15thDay
22%316%30%23%3
1875
16th to endDay
26%413%31%18%3
2181
April1st to 15thDay
27%5%14%30%17%5%
2150
16th to endDay
35%413%26%17%3
2160
May1st to 15thDay
38%6%14%22%16%
2310
16th to endDay
33%6%16%24%14%4
2620
June1st to 15thDay
28%6%12%18%22%11%
2520
16th to endDay
24%6%8%22%25%11%
2520
July1st to 15thDay
38%8%12%16%14%8%
2371
16th to endDay
38%9%18%18%11%3
2407
August1st to 15thDay
41%8%14%14%13%6%
2277
16th to endDay
33%6%11%25%17%3
2292
September1st to 15thDay
33%411%20%20%8%
2160
16th to endDay
23%39%26%30%6%
1927
October1st to 15thDay
23%5%9%26%29%6%
1650
16th to endDay
21%39%28%30%6%
1752
November1st to 15thDay
15%412%29%26%11%
1583
16th to endDay
15%211%34%28%8%
1551
December1st to 15thDay
21%419%33%18%3
1440
16th to endDay
19%6%20%30%17%5%
1536
January1st to 15thNight
14%421%35%20%3
2500
16th to endNight
15%316%33%25%5%
2496
February1st to 15thNight
20%416%39%16%3
2262
16th to endNight
19%213%34%25%5%
1894
March1st to 15thNight
20%313%35%24%3
2082
16th to endNight
23%414%35%20%3
2043
April1st to 15thNight
22%314%33%20%5%
1798
16th to endNight
32%315%29%16%3
1800
May1st to 15thNight
35%416%26%15%2
1637
16th to endNight
27%8%19%25%14%4
1498
June1st to 15thNight
16%419%25%19%14%
1440
16th to endNight
16%5%14%26%23%13%
1440
July1st to 15thNight
31%9%17%20%13%7%
1360
16th to endNight
30%9%26%21%9%3
1495
August1st to 15thNight
31%9%18%19%15%5%
1657
16th to endNight
29%8%17%25%15%3
1910
September1st to 15thNight
30%6%15%22%16%9%
1800
16th to endNight
22%311%30%27%4
1841
October1st to 15thNight
18%5%11%28%28%7%
1980
16th to endNight
20%39%29%31%5%
2112
November1st to 15thNight
15%311%30%28%10%
2270
16th to endNight
15%212%34%27%7%
2408
December1st to 15thNight
17%323%32%19%2
2520
16th to endNight
21%6%19%30%18%3
2688

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
7%15%17%31%20%7%
90
16th to endDay
4121%46%21%4
96
February1st to 15thDay
318%24%43%8%1
90
16th to endDay
16%27%33%19%3
81
March1st to 15thDay
7%10%30%34%15%1
165
16th to endDay
8%14%39%26%10%
288
April1st to 15thDay
7%15%32%26%14%2
269
16th to endDay
15%17%32%23%8%1
270
May1st to 15thDay
10%8%24%38%14%3
379
16th to endDay
8%10%20%34%20%5%
517
June1st to 15thDay
6%8%23%31%21%7%
495
16th to endDay
3219%38%25%10%
495
July1st to 15thDay
12%112%31%30%11%
475
16th to endDay
11%210%30%33%11%
426
August1st to 15thDay
16%321%30%20%8%
315
16th to endDay
14%419%30%21%10%
332
September1st to 15thDay
12%428%28%18%7%
315
16th to endDay
7%6%23%32%16%12%
172
October1st to 15thDay
17%22%23%28%16%
90
16th to endDay
8%8%18%28%26%10%
96
November1st to 15thDay
36%16%28%28%15%
90
16th to endDay
414%33%37%8%1
90
December1st to 15thDay
317%35%36%6%
90
16th to endDay
16%31%50%8%3
96
January1st to 15thNight
6%38%39%11%2
894
16th to endNight
2437%44%9%1
768
February1st to 15thNight
1442%44%7%
704
16th to endNight
2444%42%7%
632
March1st to 15thNight
3439%42%9%
720
16th to endNight
47%36%45%6%
699
April1st to 15thNight
47%39%41%7%
539
16th to endNight
8%7%35%38%10%
540
May1st to 15thNight
10%5%27%43%13%1
540
16th to endNight
8%424%41%18%1
563
June1st to 15thNight
4224%45%19%3
540
16th to endNight
2117%46%29%1
540
July1st to 15thNight
7%16%38%40%4
510
16th to endNight
6%1432%49%4
564
August1st to 15thNight
9%17%38%40%2
539
16th to endNight
7%16%42%38%3
573
September1st to 15thNight
6%111%44%29%5%
540
16th to endNight
4221%45%23%3
529
October1st to 15thNight
4331%41%16%3
660
16th to endNight
3328%45%15%2
704
November1st to 15thNight
16%34%42%13%1
870
16th to endNight
36%35%44%10%1
900
December1st to 15thNight
15%41%43%6%
900
16th to endNight
16%41%40%9%
960
Page generated at 2017-09-23 04:43:47. Version ac04

Copyright 2017 A. Danko


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