Twin Lakes Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Twin Lakes Observatory clear sky chart from 2005-11-05 to 2019-07-16.

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
46%
17907
22%
54247
15%
17864
55%
17864
27%
33911

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
24%
840
23%
2717
9%
836
41%
836
20%
1713
January16th to endNight
25%
896
25%
2863
11%
896
42%
896
21%
1793
February1st to 15thNight
29%
824
24%
2472
10%
821
43%
821
24%
1557
February16th to endNight
22%
735
22%
2205
7%
735
35%
735
21%
1451
March1st to 15thNight
27%
840
23%
2407
10%
840
39%
840
25%
1544
March16th to endNight
36%
896
20%
2464
11%
896
43%
896
28%
1567
April1st to 15thNight
41%
745
25%
2213
16%
745
51%
745
31%
1299
April16th to endNight
47%
624
25%
1960
16%
624
57%
624
32%
1136
May1st to 15thNight
53%
630
21%
1890
13%
630
59%
630
30%
1167
May16th to endNight
61%
657
20%
1971
13%
657
66%
657
29%
1237
June1st to 15thNight
69%
630
16%
1890
14%
630
70%
630
28%
1221
June16th to endNight
75%
630
16%
1890
13%
630
76%
630
32%
1156
July1st to 15thNight
67%
600
13%
1800
12%
600
68%
600
25%
1198
July16th to endNight
73%
615
15%
1748
12%
582
75%
582
26%
1137
August1st to 15thNight
69%
575
18%
1738
18%
572
69%
572
27%
1137
August16th to endNight
65%
621
17%
2070
19%
621
65%
621
22%
1385
September1st to 15thNight
62%
764
17%
2129
16%
764
63%
764
26%
1455
September16th to endNight
61%
777
24%
2145
19%
777
65%
777
30%
1374
October1st to 15thNight
54%
780
31%
2156
24%
780
61%
780
38%
1265
October16th to endNight
50%
832
33%
2496
24%
832
62%
832
36%
1386
November1st to 15thNight
48%
820
29%
2651
23%
820
58%
820
32%
1490
November16th to endNight
40%
840
27%
2730
18%
840
53%
840
29%
1554
December1st to 15thNight
30%
840
23%
2730
11%
840
45%
840
22%
1722
December16th to endNight
28%
896
19%
2912
12%
896
38%
896
18%
1967

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
14%5%25%5%35%5%5%7%40%
55063
Night
13%5%2442445%7%44%
54445
TransparencyDay
40%7%12%18%16%4
54764
Night
37%6%11%19%18%5%
54248
SeeingDay
16%8%20%22%20%11%
7764
Night
15%8%23%27%20%4
17909

By Month

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
19%6%24413346%42%
1881
16th to endDay
18%6%24423345%45%
2061
February1st to 15thDay
20%6%1431435%6%39%
2050
16th to endDay
22%5%25%423347%39%
1840
March1st to 15thDay
18%425%434446%41%
2212
16th to endDay
16%4245%34447%41%
2463
April1st to 15thDay
13%5%25%5%2445%7%43%
2406
16th to endDay
12%4144245%46%48%
2605
May1st to 15thDay
11%5%25%43445%8%44%
2721
16th to endDay
11%5%245%35%5%6%8%40%
2847
June1st to 15thDay
9%5%25%7%46%6%7%9%34%
2730
16th to endDay
6%3145%37%7%8%12%39%
2730
July1st to 15thDay
10%5%25%6%5%7%7%8%11%27%
2730
16th to endDay
8%436%7%5%9%8%7%10%28%
2676
August1st to 15thDay
10%5%247%37%6%8%10%31%
2461
16th to endDay
14%5%27%8%46%6%8%8%26%
2484
September1st to 15thDay
13%6%26%5%45%5%6%8%35%
2148
16th to endDay
15%5%145%2345%6%43%
2145
October1st to 15thDay
12%413323345%54%
2132
16th to endDay
12%5%1421223458%
2080
November1st to 15thDay
16%42331334451%
1865
16th to endDay
13%424324445%48%
1890
December1st to 15thDay
21%6%24413346%40%
1890
16th to endDay
28%6%24323345%35%
2016
January1st to 15thNight
19%5%24324345%43%
2717
16th to endNight
18%6%34433345%44%
2863
February1st to 15thNight
17%5%24323346%45%
2463
16th to endNight
20%425%42435%5%41%
2205
March1st to 15thNight
15%5%2442445%5%45%
2407
16th to endNight
12%6%2442345%6%46%
2464
April1st to 15thNight
12%5%1332445%7%49%
2213
16th to endNight
10%4144245%5%7%49%
1960
May1st to 15thNight
9%4245%35%5%6%7%46%
1889
16th to endNight
9%5%235%2445%8%46%
1970
June1st to 15thNight
6%425%5%35%7%8%11%38%
1890
16th to endNight
43245%36%6%9%11%43%
1890
July1st to 15thNight
8%426%6%37%6%7%10%36%
1890
16th to endNight
5%415%6%36%8%7%13%36%
1856
August1st to 15thNight
9%5%25%5%246%6%12%39%
1749
16th to endNight
11%5%246%45%6%7%10%35%
2070
September1st to 15thNight
10%426%5%46%5%6%9%38%
2129
16th to endNight
13%4144245%5%6%46%
2145
October1st to 15thNight
11%5%1331225%6%55%
2156
16th to endNight
10%323323345%57%
2496
November1st to 15thNight
14%422312336%53%
2651
16th to endNight
14%5%13322445%52%
2730
December1st to 15thNight
17%6%35%423336%42%
2730
16th to endNight
23%7%35%423346%35%
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
43%49%17%21%4
1882
16th to endDay
40%36%20%21%7%
2061
February1st to 15thDay
43%39%19%20%3
2052
16th to endDay
45%48%19%17%5%
1840
March1st to 15thDay
42%49%16%19%6%
2212
16th to endDay
41%5%11%20%16%3
2464
April1st to 15thDay
39%5%11%21%18%4
2406
16th to endDay
34%6%10%21%20%5%
2605
May1st to 15thDay
35%6%14%21%18%2
2721
16th to endDay
38%8%13%21%15%2
2851
June1st to 15thDay
40%11%19%19%8%1
2730
16th to endDay
31%12%18%24%11%1
2730
July1st to 15thDay
42%13%19%17%6%1
2591
16th to endDay
43%13%17%16%8%1
2521
August1st to 15thDay
42%12%17%17%8%1
2448
16th to endDay
50%10%15%14%8%
2484
September1st to 15thDay
43%10%14%15%13%2
2148
16th to endDay
40%5%11%18%19%4
2145
October1st to 15thDay
31%6%11%18%25%7%
2132
16th to endDay
30%36%18%29%11%
2080
November1st to 15thDay
35%37%16%29%8%
1865
16th to endDay
36%47%16%27%7%
1890
December1st to 15thDay
45%48%18%15%7%
1890
16th to endDay
52%39%15%13%4
2016
January1st to 15thNight
42%38%17%22%5%
2717
16th to endNight
42%35%19%22%6%
2863
February1st to 15thNight
40%47%20%19%7%
2472
16th to endNight
43%47%19%19%5%
2205
March1st to 15thNight
38%5%10%17%19%8%
2407
16th to endNight
37%5%10%22%20%4
2464
April1st to 15thNight
32%5%10%23%21%5%
2213
16th to endNight
32%5%10%22%20%8%
1960
May1st to 15thNight
35%7%14%21%18%2
1890
16th to endNight
34%9%12%24%15%3
1972
June1st to 15thNight
34%11%20%21%10%1
1890
16th to endNight
29%11%19%23%13%2
1890
July1st to 15thNight
38%11%20%19%8%1
1800
16th to endNight
33%14%21%19%9%2
1748
August1st to 15thNight
35%11%17%22%11%1
1738
16th to endNight
40%11%17%17%11%1
2070
September1st to 15thNight
40%9%14%17%14%3
2129
16th to endNight
35%8%11%21%17%5%
2145
October1st to 15thNight
30%412%18%26%7%
2156
16th to endNight
29%45%17%30%12%
2496
November1st to 15thNight
32%47%17%27%11%
2651
16th to endNight
33%47%19%26%9%
2730
December1st to 15thNight
43%39%19%17%6%
2730
16th to endNight
49%38%16%16%4
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
23%18%36%17%3
180
16th to endDay
16%29%36%14%21
192
February1st to 15thDay
27%25%28%14%3
180
16th to endDay
33%20%30%14%
159
March1st to 15thDay
22%23%29%18%4
292
16th to endDay
14%15%35%23%9%1
416
April1st to 15thDay
16%14%31%23%11%2
390
16th to endDay
16%6%25%26%20%3
379
May1st to 15thDay
12%7%26%25%18%10%
408
16th to endDay
16%415%26%23%14%
459
June1st to 15thDay
12%211%23%28%21%
435
16th to endDay
9%113%25%26%23%
435
July1st to 15thDay
9%17%23%32%24%
425
16th to endDay
9%8%19%36%25%
391
August1st to 15thDay
15%9%22%28%23%
358
16th to endDay
17%10%21%30%19%
396
September1st to 15thDay
14%310%23%29%17%
375
16th to endDay
16%213%27%28%12%
374
October1st to 15thDay
16%323%26%19%10%
375
16th to endDay
14%10%20%27%23%4
400
November1st to 15thDay
30%10%23%19%13%1
193
16th to endDay
9%17%32%25%12%3
180
December1st to 15thDay
31%17%28%18%3
180
16th to endDay
34%16%31%16%1
192
January1st to 15thNight
22%18%29%22%6%
840
16th to endNight
21%17%32%24%4
896
February1st to 15thNight
20%15%32%26%4
824
16th to endNight
21%16%36%22%3
735
March1st to 15thNight
17%15%36%24%5%
840
16th to endNight
15%12%29%29%12%
896
April1st to 15thNight
14%11%28%30%14%
745
16th to endNight
11%6%28%33%18%1
624
May1st to 15thNight
10%424%31%25%3
630
16th to endNight
13%115%28%33%7%
659
June1st to 15thNight
8%11%34%33%11%
630
16th to endNight
410%35%36%11%
630
July1st to 15thNight
10%7%22%45%12%
600
16th to endNight
5%16%24%49%13%
615
August1st to 15thNight
10%18%25%42%11%
575
16th to endNight
13%9%25%39%10%
621
September1st to 15thNight
13%110%27%37%9%
764
16th to endNight
15%115%33%31%2
777
October1st to 15thNight
13%422%28%23%7%
780
16th to endNight
12%7%25%30%21%3
832
November1st to 15thNight
16%7%24%29%20%2
820
16th to endNight
16%13%26%26%15%
840
December1st to 15thNight
21%12%30%25%9%
840
16th to endNight
26%12%29%25%5%
896
Page generated at 2019-07-17 08:53:06. Version ac04

Copyright 2019 A. Danko


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