Twin Creeks Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Twin Creeks Observatory clear sky chart from 2005-11-05 to 2017-10-31.

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
50%
15712
29%
47429
20%
15666
60%
15666
40%
25830

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
39%
898
29%
2327
13%
895
48%
895
39%
1364
January16th to endNight
36%
960
33%
2496
12%
960
48%
960
40%
1456
February1st to 15thNight
33%
728
28%
2131
12%
722
46%
722
34%
1224
February16th to endNight
24%
632
31%
1894
9%
632
42%
632
36%
1051
March1st to 15thNight
34%
540
28%
1980
16%
540
49%
540
27%
1115
March16th to endNight
36%
576
25%
2112
15%
576
51%
576
31%
1113
April1st to 15thNight
31%
539
26%
1977
14%
539
51%
539
32%
1008
April16th to endNight
35%
540
28%
1710
17%
540
51%
540
36%
949
May1st to 15thNight
36%
539
22%
1620
14%
539
50%
539
33%
959
May16th to endNight
51%
562
25%
1684
20%
561
61%
561
38%
944
June1st to 15thNight
71%
540
24%
1620
24%
540
77%
540
53%
789
June16th to endNight
73%
540
26%
1620
28%
540
76%
540
45%
869
July1st to 15thNight
78%
510
25%
1530
29%
510
80%
510
47%
796
July16th to endNight
87%
564
30%
1594
36%
531
88%
531
54%
771
August1st to 15thNight
90%
539
37%
1610
43%
536
90%
536
60%
735
August16th to endNight
79%
573
28%
1917
32%
573
80%
573
38%
1016
September1st to 15thNight
72%
540
23%
1980
27%
540
74%
540
34%
1053
September16th to endNight
72%
537
32%
1980
33%
537
77%
537
38%
999
October1st to 15thNight
64%
597
35%
2037
28%
597
71%
597
44%
995
October16th to endNight
53%
768
38%
2304
22%
768
64%
768
49%
1144
November1st to 15thNight
52%
730
31%
2130
18%
730
61%
730
44%
1143
November16th to endNight
41%
900
33%
2340
15%
900
51%
900
41%
1371
December1st to 15thNight
38%
900
31%
2340
14%
900
49%
900
38%
1426
December16th to endNight
37%
960
27%
2496
11%
960
47%
960
35%
1540

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
7%313323346%60%
48315
Night
7%312212336%64%
47630
Cloud CoverDay
9%424423447%52%
48313
Night
8%313313347%57%
47630
TransparencyDay
31%5%10%22%21%8%
48013
Night
27%410%22%23%11%
47435
SeeingDay
9%5%19%30%27%8%
5685
Night
10%6%28%35%17%1
15716

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
10%41331122363%
1611
16th to endDay
7%313212235%65%
1728
February1st to 15thDay
9%41431223461%
1735
16th to endDay
10%32321122464%
1580
March1st to 15thDay
15%5%1331332356%
1980
16th to endDay
6%414312235%63%
2112
April1st to 15thDay
7%313322346%61%
1971
16th to endDay
10%413322235%60%
2247
May1st to 15thDay
11%41432334456%
2331
16th to endDay
8%31442336%7%53%
2430
June1st to 15thDay
311342435%8%61%
2340
16th to endDay
3212323447%62%
2340
July1st to 15thDay
43133235%46%61%
2340
16th to endDay
22124335%5%9%59%
2466
August1st to 15thDay
21232446%8%62%
2340
16th to endDay
7%315%5%35%5%7%8%46%
2282
September1st to 15thDay
9%424424445%53%
1980
16th to endDay
7%31442345%6%56%
1980
October1st to 15thDay
7%213322345%62%
1909
16th to endDay
7%21221122371%
1919
November1st to 15thDay
8%41232233463%
1726
16th to endDay
10%3221222366%
1620
December1st to 15thDay
14%6%1331223456%
1620
16th to endDay
11%5%1342223458%
1728
January1st to 15thNight
10%42221123463%
2327
16th to endNight
8%21221223369%
2496
February1st to 15thNight
10%41331222364%
2126
16th to endNight
9%31222123466%
1894
March1st to 15thNight
12%42321224459%
1980
16th to endNight
5%312213235%66%
2112
April1st to 15thNight
5%312222245%65%
1977
16th to endNight
9%213212236%64%
1710
May1st to 15thNight
5%413312247%61%
1619
16th to endNight
5%2331335%7%62%
1683
June1st to 15thNight
2112212336%72%
1620
16th to endNight
111221335%8%69%
1620
July1st to 15thNight
222212249%67%
1620
16th to endNight
212212348%69%
1702
August1st to 15thNight
111212249%72%
1620
16th to endNight
5%31242446%9%55%
1917
September1st to 15thNight
8%31332345%6%57%
1980
16th to endNight
6%21332345%8%58%
1980
October1st to 15thNight
7%312212236%66%
2037
16th to endNight
7%1121213471%
2304
November1st to 15thNight
6%21331223468%
2130
16th to endNight
10%31321223464%
2340
December1st to 15thNight
11%41331232459%
2340
16th to endNight
9%413322335%59%
2496

Percentage Cloud Cover SE (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
12%5%1432233455%
1611
16th to endDay
12%413213336%56%
1728
February1st to 15thDay
12%42432223455%
1735
16th to endDay
14%423212325%55%
1580
March1st to 15thDay
15%5%24423445%47%
1980
16th to endDay
11%5%25%423336%51%
2110
April1st to 15thDay
9%32443345%7%52%
1971
16th to endDay
11%4145%23446%50%
2247
May1st to 15thDay
13%425%43445%5%45%
2331
16th to endDay
10%5%25%5%345%6%9%41%
2430
June1st to 15thDay
421443445%9%55%
2340
16th to endDay
6%3235%245%6%8%50%
2340
July1st to 15thDay
6%324435%6%5%8%49%
2340
16th to endDay
32135%35%6%7%10%49%
2466
August1st to 15thDay
2112325%5%6%9%58%
2340
16th to endDay
7%4245%35%6%7%9%42%
2282
September1st to 15thDay
10%424425%447%48%
1980
16th to endDay
8%3144235%5%7%53%
1980
October1st to 15thDay
8%21331345%6%58%
1909
16th to endDay
8%21221122469%
1919
November1st to 15thDay
9%414323336%57%
1726
16th to endDay
11%41331232460%
1620
December1st to 15thDay
14%5%24312236%52%
1620
16th to endDay
14%6%24323345%50%
1728
January1st to 15thNight
12%5%22212335%57%
2327
16th to endNight
12%313213345%59%
2496
February1st to 15thNight
12%42431223457%
2126
16th to endNight
12%422322245%57%
1894
March1st to 15thNight
13%5%24313445%50%
1980
16th to endNight
8%423324347%55%
2112
April1st to 15thNight
7%32332335%7%56%
1977
16th to endNight
11%323313247%55%
1710
May1st to 15thNight
9%5%2341435%8%50%
1619
16th to endNight
6%31342446%9%53%
1683
June1st to 15thNight
21322345%7%66%
1620
16th to endNight
321332445%10%58%
1620
July1st to 15thNight
421331335%12%57%
1620
16th to endNight
21232345%10%62%
1702
August1st to 15thNight
11121235%10%67%
1620
16th to endNight
5%3134345%6%10%51%
1917
September1st to 15thNight
10%32332345%7%52%
1980
16th to endNight
7%31332345%8%55%
1980
October1st to 15thNight
7%312212337%62%
2037
16th to endNight
8%2221223468%
2304
November1st to 15thNight
6%313313345%62%
2130
16th to endNight
11%413312335%59%
2340
December1st to 15thNight
12%414322435%54%
2340
16th to endNight
12%424413445%52%
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
33%36%20%26%10%
1612
16th to endDay
29%37%17%30%11%
1728
February1st to 15thDay
33%36%20%24%12%
1736
16th to endDay
33%35%20%23%14%
1580
March1st to 15thDay
39%5%6%16%22%9%
1980
16th to endDay
35%49%20%21%8%
2112
April1st to 15thDay
32%5%10%21%17%12%
1971
16th to endDay
34%6%8%19%23%7%
2247
May1st to 15thDay
39%6%9%16%19%8%
2331
16th to endDay
38%7%13%20%17%2
2434
June1st to 15thDay
25%7%13%27%21%4
2340
16th to endDay
30%5%12%25%20%4
2340
July1st to 15thDay
29%8%15%29%15%2
2201
16th to endDay
24%8%19%28%17%1
2311
August1st to 15thDay
19%8%14%30%24%3
2326
16th to endDay
33%8%16%25%13%2
2282
September1st to 15thDay
34%7%9%21%19%7%
1980
16th to endDay
29%5%9%23%22%9%
1980
October1st to 15thDay
26%5%11%22%19%15%
1909
16th to endDay
21%26%17%30%21%
1919
November1st to 15thDay
29%49%23%21%11%
1726
16th to endDay
30%25%17%29%16%
1620
December1st to 15thDay
36%38%20%24%7%
1620
16th to endDay
36%36%20%24%8%
1728
January1st to 15thNight
30%26%17%27%15%
2327
16th to endNight
29%37%17%26%17%
2496
February1st to 15thNight
32%36%14%25%17%
2136
16th to endNight
30%38%19%23%15%
1894
March1st to 15thNight
35%49%16%21%12%
1980
16th to endNight
29%5%11%20%25%6%
2112
April1st to 15thNight
27%5%10%21%19%15%
1977
16th to endNight
29%411%18%24%10%
1710
May1st to 15thNight
32%5%12%19%20%9%
1620
16th to endNight
26%6%17%24%20%4
1685
June1st to 15thNight
17%5%13%32%23%7%
1620
16th to endNight
22%7%12%27%24%5%
1620
July1st to 15thNight
20%6%14%36%17%4
1530
16th to endNight
14%7%20%34%20%3
1594
August1st to 15thNight
13%414%35%26%5%
1610
16th to endNight
25%6%14%31%17%4
1917
September1st to 15thNight
28%6%12%23%20%9%
1980
16th to endNight
25%5%10%21%24%12%
1980
October1st to 15thNight
22%411%25%18%17%
2037
16th to endNight
21%3417%29%24%
2304
November1st to 15thNight
25%37%23%25%14%
2130
16th to endNight
29%36%14%29%16%
2340
December1st to 15thNight
33%29%20%22%11%
2340
16th to endNight
33%48%20%21%11%
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
16%13%33%26%10%
90
16th to endDay
11%10%46%20%10%
96
February1st to 15thDay
6%12%40%36%4
90
16th to endDay
14%9%45%23%41
81
March1st to 15thDay
23%17%25%24%7%1
90
16th to endDay
5%8%41%26%17%1
96
April1st to 15thDay
8%18%30%25%16%
90
16th to endDay
12%12%38%24%10%1
357
May1st to 15thDay
16%8%38%26%7%2
468
16th to endDay
13%6%31%29%15%3
517
June1st to 15thDay
6%115%42%26%7%
495
16th to endDay
5%211%38%31%10%
495
July1st to 15thDay
5%9%37%37%10%
475
16th to endDay
2423%50%18%
515
August1st to 15thDay
3230%47%14%
493
16th to endDay
11%18%30%36%11%
322
September1st to 15thDay
15%20%40%32%
135
16th to endDay
8%1220%45%21%
135
October1st to 15thDay
210%37%34%15%
135
16th to endDay
11%5%22%26%26%6%
144
November1st to 15thDay
18%6%23%34%13%3
90
16th to endDay
22%17%28%21%6%3
90
December1st to 15thDay
24%431%23%15%1
90
16th to endDay
9%15%43%25%6%
96
January1st to 15thNight
14%10%32%34%8%
900
16th to endNight
14%9%36%31%7%
960
February1st to 15thNight
14%11%37%31%4
728
16th to endNight
13%12%48%23%2
632
March1st to 15thNight
16%9%38%30%5%
540
16th to endNight
10%10%41%31%6%
576
April1st to 15thNight
7%11%46%27%7%
539
16th to endNight
11%7%42%30%7%
540
May1st to 15thNight
9%7%41%34%6%1
540
16th to endNight
6%432%36%17%1
563
June1st to 15thNight
319%48%26%1
540
16th to endNight
315%45%31%2
540
July1st to 15thNight
5%9%48%35%1
510
16th to endNight
2443%45%4
564
August1st to 15thNight
1241%48%5%
539
16th to endNight
6%6%38%40%7%
573
September1st to 15thNight
10%9%37%38%3
540
16th to endNight
8%11%37%36%5%
537
October1st to 15thNight
10%120%38%25%3
597
16th to endNight
10%5%28%35%18%1
768
November1st to 15thNight
7%430%36%18%1
730
16th to endNight
13%8%34%30%11%1
900
December1st to 15thNight
15%7%34%33%7%
900
16th to endNight
15%8%34%33%6%
960
Page generated at 2017-11-01 16:23:34. Version ac04

Copyright 2017 A. Danko


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