Timber Rock Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Timber Rock Observatory clear sky chart from 2005-11-05 to 2018-01-20.

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%
16101
30%
48480
20%
16056
61%
16056
41%
25852

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
38%
972
32%
2522
13%
970
49%
970
41%
1453
January16th to endNight
39%
964
36%
2540
14%
964
53%
964
42%
1417
February1st to 15thNight
35%
704
30%
2106
13%
698
49%
698
37%
1141
February16th to endNight
27%
632
32%
1894
10%
632
44%
632
37%
1028
March1st to 15thNight
33%
572
28%
2012
15%
572
48%
572
29%
1113
March16th to endNight
32%
576
27%
2112
15%
576
50%
576
33%
1061
April1st to 15thNight
32%
539
26%
1977
13%
539
51%
539
34%
978
April16th to endNight
33%
540
29%
1692
16%
540
52%
540
38%
916
May1st to 15thNight
33%
540
24%
1620
13%
540
49%
540
33%
959
May16th to endNight
50%
562
26%
1684
19%
561
63%
561
41%
924
June1st to 15thNight
68%
540
24%
1620
22%
540
75%
540
54%
778
June16th to endNight
71%
540
28%
1620
30%
540
75%
540
48%
837
July1st to 15thNight
78%
510
26%
1530
28%
510
81%
510
49%
783
July16th to endNight
88%
564
33%
1594
39%
531
89%
531
56%
746
August1st to 15thNight
91%
539
37%
1610
42%
536
92%
536
60%
741
August16th to endNight
80%
573
28%
1950
34%
573
81%
573
39%
1009
September1st to 15thNight
75%
540
23%
1980
28%
540
77%
540
34%
1056
September16th to endNight
71%
537
33%
1980
33%
537
76%
537
37%
990
October1st to 15thNight
62%
564
35%
2004
30%
564
71%
564
44%
936
October16th to endNight
54%
768
37%
2304
21%
768
64%
768
50%
1129
November1st to 15thNight
50%
835
30%
2355
15%
835
60%
835
45%
1271
November16th to endNight
42%
975
36%
2535
16%
975
54%
975
45%
1423
December1st to 15thNight
41%
975
33%
2535
15%
975
52%
975
41%
1499
December16th to endNight
36%
1040
29%
2704
12%
1040
47%
1040
35%
1664

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%313323345%61%
49038
Night
6%312212346%65%
48682
Cloud CoverDay
8%424424446%54%
49036
Night
7%313323347%58%
48682
TransparencyDay
29%5%9%22%22%9%
48736
Night
25%49%22%24%13%
48487
SeeingDay
9%5%21%32%24%7%
5912
Night
9%6%30%36%16%1
16105

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%41321222465%
1746
16th to endDay
7%31222233468%
1797
February1st to 15thDay
7%32322233464%
1750
16th to endDay
9%41321225%66%
1580
March1st to 15thDay
13%5%2321233457%
1947
16th to endDay
6%31331223466%
2112
April1st to 15thDay
6%212222345%65%
1971
16th to endDay
8%31331234464%
2265
May1st to 15thDay
8%324322345%58%
2331
16th to endDay
8%3144235%5%7%53%
2430
June1st to 15thDay
3213323446%64%
2340
16th to endDay
3112323447%64%
2340
July1st to 15thDay
3214424436%61%
2340
16th to endDay
321232345%8%63%
2466
August1st to 15thDay
2124345%47%63%
2340
16th to endDay
6%4145%345%7%7%48%
2250
September1st to 15thDay
9%3143345%46%53%
1980
16th to endDay
8%313423436%56%
1980
October1st to 15thDay
6%21331334464%
1941
16th to endDay
6%31221123372%
1920
November1st to 15thDay
7%33323345%62%
1830
16th to endDay
8%31221222369%
1755
December1st to 15thDay
11%6%2421232358%
1755
16th to endDay
10%6%2332333455%
1872
January1st to 15thNight
8%413212135%65%
2522
16th to endNight
7%2221223469%
2540
February1st to 15thNight
9%32222213366%
2102
16th to endNight
8%212221235%67%
1894
March1st to 15thNight
12%412212335%59%
2012
16th to endNight
5%21221133469%
2112
April1st to 15thNight
5%213222245%67%
1977
16th to endNight
7%21321224467%
1692
May1st to 15thNight
5%413312346%61%
1619
16th to endNight
42221335%9%62%
1683
June1st to 15thNight
1121345%7%70%
1620
16th to endNight
111212247%72%
1620
July1st to 15thNight
312212449%66%
1620
16th to endNight
11121335%9%69%
1702
August1st to 15thNight
12212238%74%
1620
16th to endNight
431332446%9%55%
1950
September1st to 15thNight
7%314323447%57%
1980
16th to endNight
8%31332335%7%58%
1980
October1st to 15thNight
6%212112336%67%
2004
16th to endNight
5%21221223471%
2304
November1st to 15thNight
5%2332333467%
2355
16th to endNight
8%21321224465%
2535
December1st to 15thNight
10%41321223461%
2535
16th to endNight
8%5%24323335%57%
2704

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%2422223457%
1746
16th to endDay
11%412223345%59%
1797
February1st to 15thDay
9%424323345%56%
1750
16th to endDay
13%5%23211225%58%
1580
March1st to 15thDay
13%5%23314346%49%
1947
16th to endDay
10%5%24312245%55%
2110
April1st to 15thDay
8%32342345%6%56%
1971
16th to endDay
9%424413445%54%
2265
May1st to 15thDay
10%425%5%34446%47%
2331
16th to endDay
9%425%5%25%6%6%8%43%
2430
June1st to 15thDay
431443445%7%56%
2340
16th to endDay
7%2233345%5%9%51%
2340
July1st to 15thDay
5%325%5%35%5%48%48%
2340
16th to endDay
4213435%5%6%10%52%
2466
August1st to 15thDay
2112435%6%5%8%57%
2340
16th to endDay
6%4246%45%6%7%8%43%
2250
September1st to 15thDay
9%414435%5%47%47%
1980
16th to endDay
8%4244335%46%53%
1980
October1st to 15thDay
7%31332435%460%
1941
16th to endDay
6%31221223470%
1920
November1st to 15thDay
8%413323446%56%
1830
16th to endDay
9%31321223464%
1755
December1st to 15thDay
11%7%2421333453%
1755
16th to endDay
13%6%34323445%48%
1872
January1st to 15thNight
10%413212236%59%
2522
16th to endNight
10%313222346%59%
2540
February1st to 15thNight
9%5%23222235%60%
2102
16th to endNight
11%322222246%58%
1894
March1st to 15thNight
13%414223446%52%
2012
16th to endNight
7%423323447%58%
2112
April1st to 15thNight
6%324333346%58%
1977
16th to endNight
8%323313346%58%
1692
May1st to 15thNight
7%42442345%7%51%
1619
16th to endNight
6%32332446%10%53%
1683
June1st to 15thNight
211122446%8%65%
1620
16th to endNight
321241445%9%61%
1620
July1st to 15thNight
41123235%6%11%56%
1620
16th to endNight
21221347%12%61%
1702
August1st to 15thNight
1112313349%68%
1620
16th to endNight
5%3234245%6%10%52%
1950
September1st to 15thNight
8%31432345%8%52%
1980
16th to endNight
8%31332335%8%55%
1980
October1st to 15thNight
7%313112346%64%
2004
16th to endNight
6%21221223467%
2304
November1st to 15thNight
6%213323345%62%
2355
16th to endNight
9%313213235%61%
2535
December1st to 15thNight
10%5%23323345%55%
2535
16th to endNight
10%6%24423345%51%
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
31%26%19%28%10%
1747
16th to endDay
27%36%18%29%14%
1797
February1st to 15thDay
29%37%19%24%15%
1751
16th to endDay
30%25%19%25%16%
1580
March1st to 15thDay
35%48%15%24%11%
1947
16th to endDay
32%48%19%23%10%
2112
April1st to 15thDay
28%5%10%22%18%14%
1971
16th to endDay
31%5%8%19%24%11%
2265
May1st to 15thDay
37%5%9%18%18%10%
2331
16th to endDay
36%7%12%20%20%2
2434
June1st to 15thDay
25%5%13%26%24%5%
2340
16th to endDay
27%6%12%26%20%6%
2340
July1st to 15thDay
31%6%15%27%16%2
2201
16th to endDay
23%8%16%31%18%2
2311
August1st to 15thDay
21%6%13%31%21%3
2326
16th to endDay
32%8%13%25%15%2
2250
September1st to 15thDay
33%6%11%21%20%6%
1980
16th to endDay
30%410%19%24%10%
1980
October1st to 15thDay
25%5%9%22%21%14%
1941
16th to endDay
20%26%18%30%22%
1920
November1st to 15thDay
26%6%6%25%22%12%
1830
16th to endDay
25%35%19%28%18%
1755
December1st to 15thDay
34%26%19%25%11%
1755
16th to endDay
38%26%19%24%8%
1872
January1st to 15thNight
28%25%18%28%16%
2522
16th to endNight
26%35%17%29%18%
2540
February1st to 15thNight
28%27%13%27%19%
2112
16th to endNight
28%27%18%24%18%
1894
March1st to 15thNight
32%48%17%21%15%
2012
16th to endNight
26%5%12%20%26%8%
2112
April1st to 15thNight
26%49%22%20%17%
1977
16th to endNight
27%411%18%26%12%
1692
May1st to 15thNight
31%7%10%19%21%10%
1620
16th to endNight
24%6%18%22%21%5%
1685
June1st to 15thNight
15%5%14%33%22%7%
1620
16th to endNight
20%6%10%30%25%6%
1620
July1st to 15thNight
20%5%14%34%20%4
1530
16th to endNight
13%6%17%35%23%3
1594
August1st to 15thNight
13%5%12%33%29%6%
1610
16th to endNight
24%6%15%29%19%4
1950
September1st to 15thNight
28%6%11%22%22%8%
1980
16th to endNight
26%49%22%23%13%
1980
October1st to 15thNight
21%312%25%18%16%
2004
16th to endNight
20%25%15%30%24%
2304
November1st to 15thNight
23%47%24%23%16%
2355
16th to endNight
25%36%15%30%18%
2535
December1st to 15thNight
29%37%21%22%13%
2535
16th to endNight
34%37%18%23%12%
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
14%11%33%33%5%
135
16th to endDay
11%10%45%20%8%4
109
February1st to 15thDay
5%12%37%40%4
90
16th to endDay
16%8%45%24%4
81
March1st to 15thDay
20%12%33%26%7%
90
16th to endDay
7%10%30%36%13%2
96
April1st to 15thDay
6%16%36%26%13%
90
16th to endDay
12%14%42%22%8%
375
May1st to 15thDay
13%10%36%28%8%1
468
16th to endDay
12%436%29%14%2
517
June1st to 15thDay
4217%44%26%5%
495
16th to endDay
6%112%40%28%9%
495
July1st to 15thDay
5%17%42%34%9%
475
16th to endDay
35%28%45%16%
515
August1st to 15thDay
3331%45%16%
493
16th to endDay
12%16%38%28%13%
290
September1st to 15thDay
11115%48%31%
135
16th to endDay
13%222%40%21%
135
October1st to 15thDay
28%36%38%13%
135
16th to endDay
12%321%29%27%6%
144
November1st to 15thDay
16%332%29%12%5%
135
16th to endDay
14%15%26%27%12%3
135
December1st to 15thDay
14%7%34%33%8%2
135
16th to endDay
19%14%38%20%6%
144
January1st to 15thNight
13%9%34%34%8%
975
16th to endNight
12%9%36%32%8%
964
February1st to 15thNight
12%10%38%32%5%
704
16th to endNight
13%12%45%25%2
632
March1st to 15thNight
15%10%39%28%6%
572
16th to endNight
7%12%45%28%5%
576
April1st to 15thNight
7%11%46%28%5%
539
16th to endNight
8%9%46%28%6%
540
May1st to 15thNight
9%8%45%29%6%
540
16th to endNight
6%337%36%15%
563
June1st to 15thNight
2123%50%20%1
540
16th to endNight
3120%47%23%3
540
July1st to 15thNight
5%10%48%32%1
510
16th to endNight
3448%40%2
564
August1st to 15thNight
1242%48%3
539
16th to endNight
7%440%40%6%
573
September1st to 15thNight
8%8%42%36%3
540
16th to endNight
11%10%41%33%2
537
October1st to 15thNight
7%222%41%22%3
564
16th to endNight
8%5%28%37%17%1
768
November1st to 15thNight
7%433%36%16%1
835
16th to endNight
10%7%36%30%13%
975
December1st to 15thNight
13%7%34%36%7%
975
16th to endNight
14%9%36%30%8%
1040
Page generated at 2018-01-21 11:19:30. Version ac04

Copyright 2018 A. Danko


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