Lalen Lake Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lalen Lake Observatory clear sky chart from 2005-11-05 to 2017-04-25.

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
40%
12797
8%
45645
6%
12769
42%
12769
13%
34008

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
43%
776
9%
3178
8%
776
45%
776
13%
2269
January16th to endNight
42%
805
12%
3105
10%
805
43%
805
14%
2234
February1st to 15thNight
42%
733
11%
2614
9%
730
44%
730
16%
1797
February16th to endNight
31%
596
9%
2149
7%
596
35%
596
12%
1589
March1st to 15thNight
41%
570
18%
2182
14%
570
50%
570
19%
1377
March16th to endNight
53%
587
14%
2005
15%
586
55%
586
21%
1326
April1st to 15thNight
38%
539
4%
1645
3%
539
38%
539
12%
1304
April16th to endNight
50%
525
1%
1378
1%
525
50%
525
20%
1029
May1st to 15thNight
47%
343
0%
1004
0%
343
47%
343
16%
761
May16th to endNight
50%
228
0%
844
0%
228
50%
228
17%
578
June1st to 15thNight
42%
165
0%
660
0%
165
42%
165
9%
520
June16th to endNight
47%
165
0%
660
0%
165
47%
165
8%
532
July1st to 15thNight
43%
155
0%
620
0%
155
43%
155
7%
510
July16th to endNight
37%
327
0%
886
0%
305
37%
305
9%
753
August1st to 15thNight
37%
350
0%
1059
0%
348
37%
348
9%
893
August16th to endNight
36%
525
1%
1400
0%
525
37%
525
10%
1187
September1st to 15thNight
34%
495
3%
1605
3%
495
34%
495
8%
1354
September16th to endNight
34%
499
5%
1798
5%
499
36%
499
10%
1423
October1st to 15thNight
42%
591
9%
2046
9%
591
43%
591
13%
1539
October16th to endNight
42%
736
8%
2447
6%
736
43%
736
13%
1840
November1st to 15thNight
37%
730
7%
2694
5%
730
39%
730
12%
2027
November16th to endNight
40%
750
15%
2997
13%
750
46%
750
14%
2062
December1st to 15thNight
38%
775
8%
3213
9%
775
40%
775
9%
2477
December16th to endNight
34%
832
6%
3456
5%
832
35%
832
8%
2627

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
20%11%47%6%35%45%6%26%
46076
Night
18%13%47%5%34445%27%
45745
TransparencyDay
56%8%16%12%4
45677
Night
57%7%13%14%6%1
45650
SeeingDay
22%5%17%27%21%6%
7771
Night
23%416%27%23%4
12804

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
15%15%5%7%6%3333431%
758
16th to endDay
13%16%6%7%6%4435%5%25%
1118
February1st to 15thDay
10%16%5%7%6%35%345%32%
1250
16th to endDay
9%17%5%8%7%44445%28%
1325
March1st to 15thDay
7%13%47%423335%43%
1778
16th to endDay
7%14%45%6%245%5%7%35%
2212
April1st to 15thDay
11%15%5%8%5%45%5%5%5%26%
2301
16th to endDay
9%11%37%7%35%6%7%7%28%
2470
May1st to 15thDay
16%12%38%6%35%45%5%26%
2617
16th to endDay
16%7%36%5%35%45%6%35%
2917
June1st to 15thDay
20%9%38%6%45%5%5%7%22%
2970
16th to endDay
19%7%46%7%35%6%6%8%22%
2970
July1st to 15thDay
24%8%46%6%47%5%5%6%19%
2970
16th to endDay
29%9%36%6%34446%20%
2907
August1st to 15thDay
35%7%36%5%35%445%17%
2563
16th to endDay
31%8%26%6%245%5%6%20%
2450
September1st to 15thDay
35%10%27%5%3443418%
2024
16th to endDay
31%10%37%5%2333423%
1830
October1st to 15thDay
28%9%46%4235%45%24%
1584
16th to endDay
19%11%46%335%45%6%28%
1425
November1st to 15thDay
12%17%5%9%6%35%5%4326%
1162
16th to endDay
16%15%4432344337%
963
December1st to 15thDay
17%16%5%7%5%3434426%
744
16th to endDay
11%18%6%8%7%35%5%46%20%
768
January1st to 15thNight
14%13%6%7%6%24445%30%
3178
16th to endNight
15%16%46%5%2445%5%27%
3105
February1st to 15thNight
10%15%5%7%424345%34%
2602
16th to endNight
13%16%5%8%7%44445%25%
2149
March1st to 15thNight
8%10%47%5%24345%41%
2182
16th to endNight
8%14%36%43445%7%37%
2005
April1st to 15thNight
13%17%6%9%7%44445%23%
1645
16th to endNight
10%12%46%6%45%5%5%7%30%
1378
May1st to 15thNight
14%9%6%7%6%26%5%47%27%
1003
16th to endNight
14%8%37%7%35%5%45%33%
843
June1st to 15thNight
21%11%48%5%35%45%5%25%
660
16th to endNight
20%7%5%8%5%445%6%9%21%
660
July1st to 15thNight
27%10%35%6%36%5%7%7%16%
660
16th to endNight
34%7%36%5%2345%6%19%
954
August1st to 15thNight
34%8%36%435%446%17%
1065
16th to endNight
33%8%36%6%33445%20%
1400
September1st to 15thNight
36%8%35%5%23445%18%
1605
16th to endNight
32%9%27%5%23345%23%
1798
October1st to 15thNight
29%10%36%5%22335%28%
2046
16th to endNight
20%11%47%5%3435%427%
2447
November1st to 15thNight
15%16%47%7%3445%5%25%
2694
16th to endNight
14%13%46%5%24445%33%
2997
December1st to 15thNight
19%15%48%5%34446%23%
3213
16th to endNight
11%16%6%9%6%45%5%45%23%
3456

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
54%10%8%13%8%4
758
16th to endDay
58%7%10%15%7%
1118
February1st to 15thDay
52%6%10%17%10%1
1250
16th to endDay
54%7%10%16%8%
1325
March1st to 15thDay
43%48%18%17%7%
1778
16th to endDay
46%8%14%17%11%1
2212
April1st to 15thDay
56%7%15%15%5%
2301
16th to endDay
49%10%16%18%3
2470
May1st to 15thDay
56%6%16%15%5%
2617
16th to endDay
46%6%18%23%4
2921
June1st to 15thDay
57%10%19%10%1
2970
16th to endDay
55%13%22%7%2
2970
July1st to 15thDay
62%12%20%4
2781
16th to endDay
63%9%20%6%
2712
August1st to 15thDay
67%9%17%5%
2544
16th to endDay
62%11%14%8%2
2450
September1st to 15thDay
68%9%13%7%1
2024
16th to endDay
63%7%14%11%2
1830
October1st to 15thDay
60%7%13%14%3
1584
16th to endDay
51%9%19%13%5%
1425
November1st to 15thDay
59%7%11%15%5%
1162
16th to endDay
50%5%11%18%11%1
963
December1st to 15thDay
60%9%12%9%7%
744
16th to endDay
61%6%13%12%4
768
January1st to 15thNight
54%6%12%14%7%4
3178
16th to endNight
54%7%12%17%7%
3105
February1st to 15thNight
50%6%9%19%10%3
2614
16th to endNight
57%6%11%15%8%
2149
March1st to 15thNight
44%5%7%16%18%7%
2182
16th to endNight
44%6%15%18%12%1
2010
April1st to 15thNight
63%5%13%13%3
1645
16th to endNight
51%7%19%15%5%
1378
May1st to 15thNight
56%6%14%18%4
1004
16th to endNight
48%7%17%22%3
844
June1st to 15thNight
61%10%16%11%1
660
16th to endNight
58%15%18%5%1
660
July1st to 15thNight
68%8%17%5%
620
16th to endNight
66%10%16%6%
886
August1st to 15thNight
66%10%16%6%
1059
16th to endNight
66%9%14%7%2
1400
September1st to 15thNight
67%9%12%8%1
1605
16th to endNight
63%6%13%12%3
1798
October1st to 15thNight
58%6%15%12%6%
2046
16th to endNight
57%6%15%12%6%
2447
November1st to 15thNight
58%7%13%16%4
2694
16th to endNight
51%6%10%19%10%1
2997
December1st to 15thNight
61%8%11%10%8%
3213
16th to endNight
61%8%12%13%4
3456

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
25%9%13%22%18%11%
72
16th to endDay
24%5%15%22%24%8%
224
February1st to 15thDay
16%321%24%17%16%
215
16th to endDay
18%7%28%27%11%6%
211
March1st to 15thDay
12%5%28%31%16%5%
240
16th to endDay
14%414%26%28%10%
425
April1st to 15thDay
14%7%21%25%24%6%
433
16th to endDay
14%8%18%31%25%2
425
May1st to 15thDay
19%7%20%27%21%2
393
16th to endDay
17%8%18%36%16%2
506
June1st to 15thDay
21%5%22%32%16%2
585
16th to endDay
17%5%16%29%24%6%
585
July1st to 15thDay
20%314%29%24%8%
555
16th to endDay
27%315%29%20%4
518
August1st to 15thDay
30%317%20%20%7%
419
16th to endDay
28%5%14%23%23%4
443
September1st to 15thDay
37%5%10%21%19%4
395
16th to endDay
34%313%18%18%11%
283
October1st to 15thDay
29%313%26%17%8%
225
16th to endDay
23%412%24%21%13%
240
November1st to 15thDay
24%221%23%14%13%
224
16th to endDay
20%6%12%23%22%13%
93
December1st to 15thDay
16%26%43%13%
30
16th to endDay
34%315%21%15%9%
32
January1st to 15thNight
20%6%15%29%23%5%
780
16th to endNight
22%419%31%18%4
805
February1st to 15thNight
14%5%24%32%19%3
734
16th to endNight
21%5%25%28%17%1
596
March1st to 15thNight
13%7%24%33%18%2
570
16th to endNight
15%5%12%27%31%6%
587
April1st to 15thNight
21%5%17%24%24%7%
539
16th to endNight
13%416%29%32%4
525
May1st to 15thNight
15%5%15%33%28%2
344
16th to endNight
15%314%33%32%
229
June1st to 15thNight
23%313%30%28%1
165
16th to endNight
18%312%34%27%3
165
July1st to 15thNight
34%26%20%32%3
155
16th to endNight
36%37%18%30%3
327
August1st to 15thNight
37%29%23%24%3
350
16th to endNight
36%310%20%24%5%
525
September1st to 15thNight
38%29%21%21%6%
495
16th to endNight
37%311%16%21%9%
499
October1st to 15thNight
32%29%24%25%5%
591
16th to endNight
24%414%25%27%4
736
November1st to 15thNight
22%419%30%18%5%
730
16th to endNight
21%6%18%27%22%3
750
December1st to 15thNight
25%5%16%25%18%8%
775
16th to endNight
17%5%23%26%20%6%
832
Page generated at 2017-04-26 13:21:45. Version ac04

Copyright 2017 A. Danko


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