Stake Lake Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Stake Lake Observatory clear sky chart from 2005-11-05 to 2017-09-18.

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
37%
14756
10%
46698
7%
14732
41%
14732
17%
32806

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
27%
746
5%
2686
4%
746
30%
746
8%
2151
January16th to endNight
34%
769
7%
2694
6%
769
37%
769
11%
2073
February1st to 15thNight
34%
697
8%
2369
6%
697
37%
697
12%
1793
February16th to endNight
38%
632
12%
1995
8%
632
44%
632
18%
1365
March1st to 15thNight
27%
720
10%
2139
4%
720
32%
720
13%
1571
March16th to endNight
29%
768
10%
2016
3%
768
34%
768
15%
1513
April1st to 15thNight
36%
719
10%
1799
4%
719
39%
719
18%
1353
April16th to endNight
33%
478
13%
1558
8%
478
41%
478
16%
1089
May1st to 15thNight
38%
359
11%
1440
15%
359
43%
359
16%
955
May16th to endNight
43%
374
5%
1496
6%
374
45%
374
15%
1025
June1st to 15thNight
37%
360
2%
1092
0%
360
38%
360
18%
756
June16th to endNight
35%
360
3%
1080
0%
360
35%
360
22%
713
July1st to 15thNight
54%
340
5%
1167
1%
340
54%
340
32%
632
July16th to endNight
60%
376
12%
1372
14%
354
66%
354
36%
659
August1st to 15thNight
68%
360
18%
1432
26%
358
72%
358
36%
690
August16th to endNight
51%
618
20%
1764
15%
618
56%
618
33%
1060
September1st to 15thNight
60%
720
20%
1800
10%
720
62%
720
41%
1069
September16th to endNight
47%
667
19%
1817
12%
667
51%
667
29%
1157
October1st to 15thNight
44%
660
15%
1980
12%
660
49%
660
24%
1284
October16th to endNight
34%
704
13%
2252
7%
704
42%
704
16%
1573
November1st to 15thNight
25%
700
10%
2425
7%
700
31%
700
11%
1804
November16th to endNight
27%
766
8%
2566
3%
766
32%
766
10%
2002
December1st to 15thNight
31%
903
9%
2719
6%
903
35%
903
12%
2109
December16th to endNight
25%
960
7%
3040
3%
960
29%
960
9%
2410

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
9%10%48%7%46%5%6%6%30%
48106
Night
7%10%48%7%46%5%6%7%32%
46854
Cloud CoverDay
8%9%48%7%46%5%6%7%31%
48106
Night
7%9%48%6%46%5%6%7%32%
46857
TransparencyDay
49%7%14%18%7%1
47766
Night
48%7%16%19%7%1
46698
SeeingDay
16%18%26%23%13%3
6268
Night
13%14%24%27%16%3
14769

By Month

Percentage Cloud Cover NW (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
5%11%413%11%5%8%7%6%6%19%
1253
16th to endDay
6%14%5%9%7%45%5%9%7%24%
1527
February1st to 15thDay
8%16%6%8%8%45%6%6%5%22%
1492
16th to endDay
414%6%9%9%35%6%6%6%25%
1478
March1st to 15thDay
5%14%6%11%9%5%7%6%6%6%19%
1818
16th to endDay
6%13%5%10%10%5%7%6%7%7%19%
2208
April1st to 15thDay
9%13%6%11%9%5%7%6%5%6%18%
2149
16th to endDay
9%15%5%10%9%36%6%5%6%20%
2401
May1st to 15thDay
10%12%5%8%7%45%5%5%6%27%
2511
16th to endDay
17%10%5%8%8%46%5%5%7%21%
2615
June1st to 15thDay
20%8%5%8%7%45%5%5%7%22%
2862
16th to endDay
14%7%48%7%46%5%5%6%28%
2880
July1st to 15thDay
7%426%5%35%5%6%8%44%
2720
16th to endDay
7%4245%3445%7%48%
2699
August1st to 15thDay
5%425%5%345%6%6%48%
2520
16th to endDay
7%5%27%5%35%5%6%7%43%
2435
September1st to 15thDay
9%6%25%43335%5%49%
2160
16th to endDay
14%6%36%6%45%5%5%7%34%
1865
October1st to 15thDay
10%8%46%6%36%45%7%36%
1650
16th to endDay
10%12%37%6%5%6%5%5%7%28%
1620
November1st to 15thDay
11%12%6%10%8%45%5%5%6%24%
1430
16th to endDay
6%15%5%8%8%5%5%7%7%6%22%
1380
December1st to 15thDay
5%12%7%12%7%5%6%6%5%6%25%
1239
16th to endDay
6%12%5%8%9%5%8%6%6%7%21%
1194
January1st to 15thNight
8%13%7%12%10%46%5%6%6%18%
2686
16th to endNight
6%12%5%11%8%47%5%7%8%22%
2694
February1st to 15thNight
8%15%6%10%7%35%5%6%6%24%
2357
16th to endNight
410%5%10%6%37%5%6%9%31%
1995
March1st to 15thNight
411%49%8%47%6%7%7%28%
2139
16th to endNight
310%49%9%48%6%7%8%26%
2012
April1st to 15thNight
410%49%9%5%6%6%6%7%29%
1799
16th to endNight
411%5%9%8%36%5%6%6%31%
1558
May1st to 15thNight
7%11%47%6%35%5%5%5%36%
1439
16th to endNight
13%7%38%7%35%6%6%8%29%
1496
June1st to 15thNight
14%5%37%7%345%8%8%30%
1092
16th to endNight
9%5%5%7%6%3446%6%39%
1080
July1st to 15thNight
6%324425%6%6%7%51%
1237
16th to endNight
6%3133245%6%7%55%
1467
August1st to 15thNight
5%31342436%7%56%
1440
16th to endNight
6%5%345%3445%8%47%
1764
September1st to 15thNight
6%41432435%6%55%
1800
16th to endNight
9%6%35%5%3345%8%44%
1817
October1st to 15thNight
8%8%37%6%35%45%7%40%
1980
16th to endNight
10%8%48%7%45%5%6%7%31%
2252
November1st to 15thNight
9%12%48%7%5%7%6%6%5%26%
2425
16th to endNight
8%14%7%9%9%46%5%5%6%22%
2566
December1st to 15thNight
5%13%7%10%7%5%6%5%6%5%24%
2719
16th to endNight
6%12%6%11%9%47%6%5%5%22%
3040

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
5%10%5%13%10%5%8%6%7%8%18%
1253
16th to endDay
6%12%5%9%8%46%5%7%8%24%
1527
February1st to 15thDay
7%16%6%8%7%45%6%5%6%23%
1492
16th to endDay
412%5%10%8%46%5%8%7%26%
1478
March1st to 15thDay
5%11%6%11%9%48%7%8%6%20%
1818
16th to endDay
5%11%5%10%9%5%7%6%7%8%20%
2208
April1st to 15thDay
7%13%6%10%10%47%7%6%6%19%
2149
16th to endDay
8%13%6%10%8%47%5%6%6%22%
2401
May1st to 15thDay
9%11%48%8%46%5%5%6%29%
2511
16th to endDay
15%11%38%7%45%6%7%6%22%
2615
June1st to 15thDay
17%8%38%7%36%6%6%7%23%
2862
16th to endDay
13%7%48%8%35%5%6%6%29%
2880
July1st to 15thDay
6%425%5%35%5%6%8%45%
2720
16th to endDay
6%4245%35%448%50%
2699
August1st to 15thDay
44245%45%5%6%6%49%
2520
16th to endDay
6%5%25%5%45%5%6%7%45%
2435
September1st to 15thDay
7%6%26%5%23346%50%
2160
16th to endDay
13%7%25%6%35%5%6%8%35%
1865
October1st to 15thDay
9%7%37%6%36%5%6%7%37%
1650
16th to endDay
10%11%48%7%36%5%7%7%27%
1620
November1st to 15thDay
10%10%6%9%8%46%6%5%7%25%
1430
16th to endDay
6%13%7%6%9%48%7%7%7%22%
1380
December1st to 15thDay
5%12%7%11%7%46%47%7%25%
1239
16th to endDay
6%10%410%9%5%9%6%6%7%22%
1194
January1st to 15thNight
8%14%7%11%9%5%7%5%6%8%16%
2685
16th to endNight
6%12%5%10%8%48%7%7%7%20%
2694
February1st to 15thNight
8%14%5%10%7%35%5%5%7%25%
2357
16th to endNight
49%49%7%36%46%8%33%
1995
March1st to 15thNight
410%49%8%46%6%7%8%29%
2139
16th to endNight
48%5%9%8%46%8%8%7%28%
2016
April1st to 15thNight
5%9%48%8%5%7%6%6%7%30%
1799
16th to endNight
5%9%410%6%46%5%7%7%31%
1558
May1st to 15thNight
7%10%48%5%46%5%5%5%36%
1439
16th to endNight
12%7%38%6%45%6%6%8%30%
1496
June1st to 15thNight
15%5%36%6%45%6%7%9%30%
1092
16th to endNight
9%6%37%7%35%46%6%38%
1080
July1st to 15thNight
5%323425%5%7%8%51%
1237
16th to endNight
5%21332446%8%55%
1467
August1st to 15thNight
5%31432446%9%55%
1440
16th to endNight
5%5%245%245%5%8%48%
1764
September1st to 15thNight
5%41442446%6%55%
1800
16th to endNight
8%6%35%5%2445%8%45%
1817
October1st to 15thNight
7%6%46%6%35%45%7%42%
1980
16th to endNight
10%8%28%7%445%6%8%33%
2252
November1st to 15thNight
9%10%5%9%7%46%6%6%5%27%
2425
16th to endNight
8%14%6%10%7%36%6%5%6%22%
2566
December1st to 15thNight
6%13%6%10%7%46%5%6%7%24%
2719
16th to endNight
6%14%6%10%8%5%7%6%6%5%22%
3040

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
60%11%15%10%2
1253
16th to endDay
54%7%18%14%31
1527
February1st to 15thDay
58%9%15%12%2
1492
16th to endDay
54%7%16%14%7%
1478
March1st to 15thDay
60%9%15%12%2
1818
16th to endDay
59%7%15%13%2
2208
April1st to 15thDay
62%8%10%14%3
2149
16th to endDay
57%8%14%13%5%
2401
May1st to 15thDay
53%6%12%17%9%
2511
16th to endDay
57%8%13%16%4
2619
June1st to 15thDay
57%7%11%14%7%1
2862
16th to endDay
51%7%12%17%9%
2880
July1st to 15thDay
33%7%13%23%18%3
2561
16th to endDay
31%6%12%29%16%2
2531
August1st to 15thDay
31%6%15%28%13%3
2503
16th to endDay
33%8%14%27%12%2
2435
September1st to 15thDay
35%413%28%16%1
2160
16th to endDay
45%8%13%21%8%2
1865
October1st to 15thDay
45%6%18%24%6%
1650
16th to endDay
52%9%19%15%3
1620
November1st to 15thDay
57%8%13%16%4
1430
16th to endDay
56%9%14%15%4
1380
December1st to 15thDay
55%11%15%14%3
1239
16th to endDay
58%9%15%13%3
1194
January1st to 15thNight
62%9%14%10%2
2686
16th to endNight
58%8%16%12%2
2694
February1st to 15thNight
56%7%15%14%4
2369
16th to endNight
47%6%19%18%7%
1995
March1st to 15thNight
50%9%17%17%4
2139
16th to endNight
50%9%18%17%3
2016
April1st to 15thNight
50%8%16%18%6%
1799
16th to endNight
48%7%16%21%5%
1558
May1st to 15thNight
45%8%12%19%12%1
1440
16th to endNight
50%6%18%17%6%
1496
June1st to 15thNight
47%6%14%22%6%1
1092
16th to endNight
42%6%18%21%10%1
1080
July1st to 15thNight
27%7%13%28%19%4
1167
16th to endNight
23%6%15%31%18%4
1372
August1st to 15thNight
25%5%18%28%18%4
1432
16th to endNight
32%6%16%26%15%2
1764
September1st to 15thNight
27%5%15%30%17%3
1800
16th to endNight
36%6%17%24%11%4
1817
October1st to 15thNight
40%6%18%25%9%
1980
16th to endNight
47%7%18%23%2
2252
November1st to 15thNight
54%8%15%14%5%
2425
16th to endNight
60%7%13%12%5%
2566
December1st to 15thNight
57%8%15%15%2
2719
16th to endNight
60%9%14%12%3
3040

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
5%320%28%26%16%
60
16th to endDay
6%21%28%26%14%3
64
February1st to 15thDay
17%21%26%23%7%2
152
16th to endDay
12%22%26%22%14%1
221
March1st to 15thDay
28%30%24%12%3
270
16th to endDay
20%30%31%12%4
288
April1st to 15thDay
21%21%31%15%8%1
269
16th to endDay
17%29%29%16%5%1
270
May1st to 15thDay
18%22%23%24%7%3
288
16th to endDay
19%16%18%22%18%4
330
June1st to 15thDay
20%15%22%24%14%2
657
16th to endDay
15%14%28%24%13%3
675
July1st to 15thDay
10%15%26%29%14%3
495
16th to endDay
10%9%27%33%14%4
368
August1st to 15thDay
6%8%22%31%23%7%
315
16th to endDay
9%15%29%28%14%3
332
September1st to 15thDay
13%17%23%22%19%3
315
16th to endDay
19%17%29%18%12%2
264
October1st to 15thDay
22%19%24%20%11%1
255
16th to endDay
15%15%18%31%18%1
132
November1st to 15thDay
20%25%35%14%4
64
16th to endDay
13%21%26%11%15%11%
60
December1st to 15thDay
8%30%20%11%23%6%
60
16th to endDay
12%18%32%18%10%6%
64
January1st to 15thNight
19%14%23%26%13%1
750
16th to endNight
12%12%27%29%16%2
769
February1st to 15thNight
15%14%18%34%14%2
704
16th to endNight
9%14%25%25%22%2
632
March1st to 15thNight
13%25%25%23%9%2
720
16th to endNight
11%22%28%22%11%3
768
April1st to 15thNight
12%16%24%26%16%3
719
16th to endNight
10%17%31%27%11%1
478
May1st to 15thNight
11%14%24%31%14%3
360
16th to endNight
15%8%23%25%24%3
375
June1st to 15thNight
15%12%25%29%13%3
360
16th to endNight
10%13%31%27%16%1
360
July1st to 15thNight
6%7%26%36%21%1
340
16th to endNight
7%322%39%24%3
376
August1st to 15thNight
8%315%30%35%8%
360
16th to endNight
9%8%22%29%24%4
618
September1st to 15thNight
9%8%16%26%30%9%
720
16th to endNight
12%14%20%24%22%5%
667
October1st to 15thNight
11%13%23%27%20%3
660
16th to endNight
16%15%26%22%16%3
704
November1st to 15thNight
18%20%28%24%7%
700
16th to endNight
16%18%23%25%12%3
766
December1st to 15thNight
14%15%26%28%13%1
903
16th to endNight
14%17%28%27%10%1
960
Page generated at 2017-09-19 04:32:27. Version ac04

Copyright 2017 A. Danko


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