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 2017-10-31.

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
40%
13255
7%
47055
6%
13227
42%
13227
12%
35228

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%
540
1%
1416
1%
540
50%
540
19%
1065
May1st to 15thNight
46%
374
0%
1095
0%
374
46%
374
16%
840
May16th to endNight
48%
249
0%
923
0%
249
48%
249
16%
641
June1st to 15thNight
41%
180
0%
720
0%
180
41%
180
8%
572
June16th to endNight
47%
180
0%
720
0%
180
47%
180
8%
584
July1st to 15thNight
45%
170
0%
680
0%
170
45%
170
7%
550
July16th to endNight
38%
353
0%
963
0%
331
37%
331
9%
820
August1st to 15thNight
37%
382
0%
1156
0%
380
37%
380
9%
976
August16th to endNight
34%
573
1%
1528
0%
573
35%
573
9%
1312
September1st to 15thNight
32%
540
3%
1752
3%
540
33%
540
7%
1495
September16th to endNight
34%
548
5%
1962
5%
548
36%
548
10%
1569
October1st to 15thNight
42%
657
9%
2232
9%
657
43%
657
13%
1698
October16th to endNight
41%
816
9%
2670
7%
816
43%
816
13%
2017
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%25%
48780
Night
18%13%47%5%34445%27%
47155
TransparencyDay
57%8%16%12%4
48381
Night
57%7%13%14%6%1
47060
SeeingDay
23%5%16%26%21%7%
8662
Night
23%416%26%23%5%
13262

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
10%11%48%7%45%6%7%7%27%
2544
May1st to 15thDay
16%12%48%6%45%45%5%26%
2856
16th to endDay
17%8%36%5%35%446%34%
3190
June1st to 15thDay
20%9%38%6%45%5%5%7%22%
3240
16th to endDay
19%8%47%7%36%6%6%8%21%
3240
July1st to 15thDay
23%8%47%6%47%5%5%6%20%
3240
16th to endDay
28%9%36%6%34446%20%
3138
August1st to 15thDay
34%8%36%6%35%446%17%
2796
16th to endDay
31%8%36%6%245%5%6%19%
2674
September1st to 15thDay
35%10%27%5%35%33417%
2207
16th to endDay
32%10%38%5%3333421%
1996
October1st to 15thDay
28%10%46%4235%45%23%
1728
16th to endDay
19%11%46%33445%6%28%
1552
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
12%12%46%6%45%5%5%7%29%
1416
May1st to 15thNight
14%9%6%8%6%26%6%47%26%
1094
16th to endNight
16%8%37%7%35%5%4432%
922
June1st to 15thNight
20%10%5%10%5%35%445%23%
720
16th to endNight
20%8%48%5%45%5%6%9%21%
720
July1st to 15thNight
26%9%35%6%47%5%6%7%16%
720
16th to endNight
33%8%47%5%2345%5%18%
1031
August1st to 15thNight
34%8%37%435%446%17%
1162
16th to endNight
34%9%36%5%33445%18%
1528
September1st to 15thNight
35%9%37%5%24445%17%
1752
16th to endNight
33%9%27%5%2334422%
1962
October1st to 15thNight
29%10%35%5%2233427%
2232
16th to endNight
21%12%47%5%34345%26%
2670
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
50%9%16%18%3
2544
May1st to 15thDay
56%6%15%15%5%
2856
16th to endDay
47%6%17%22%5%
3194
June1st to 15thDay
57%10%19%10%2
3240
16th to endDay
55%13%21%6%2
3240
July1st to 15thDay
60%12%21%4
3051
16th to endDay
63%10%20%5%
2943
August1st to 15thDay
66%9%18%5%
2777
16th to endDay
63%11%14%7%2
2674
September1st to 15thDay
69%9%13%6%1
2207
16th to endDay
64%7%14%10%2
1996
October1st to 15thDay
60%7%13%14%3
1728
16th to endDay
51%9%18%14%5%
1552
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
52%7%19%15%5%
1416
May1st to 15thNight
57%7%14%17%4
1095
16th to endNight
50%7%16%21%4
923
June1st to 15thNight
62%9%15%10%1
720
16th to endNight
59%15%17%6%1
720
July1st to 15thNight
66%8%19%5%
680
16th to endNight
66%10%16%6%
963
August1st to 15thNight
66%9%16%6%
1156
16th to endNight
68%8%13%7%2
1528
September1st to 15thNight
69%9%12%7%1
1752
16th to endNight
65%6%13%11%2
1962
October1st to 15thNight
59%6%14%13%6%
2232
16th to endNight
58%6%15%13%6%
2670
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
15%7%18%30%24%4
450
May1st to 15thDay
19%7%20%26%22%3
468
16th to endDay
19%8%19%33%16%2
592
June1st to 15thDay
21%5%21%31%17%3
675
16th to endDay
18%415%29%24%6%
675
July1st to 15thDay
20%214%29%25%8%
645
16th to endDay
28%213%27%22%5%
593
August1st to 15thDay
30%216%19%21%9%
494
16th to endDay
30%5%13%22%24%4
523
September1st to 15thDay
37%410%22%19%5%
457
16th to endDay
35%313%18%17%10%
333
October1st to 15thDay
32%312%26%17%8%
270
16th to endDay
26%311%23%22%13%
288
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
14%415%28%31%4
540
May1st to 15thNight
15%415%32%28%3
375
16th to endNight
17%314%32%31%
250
June1st to 15thNight
25%213%28%28%1
180
16th to endNight
18%311%35%27%2
180
July1st to 15thNight
34%25%21%32%3
170
16th to endNight
35%36%18%30%4
353
August1st to 15thNight
36%110%23%24%3
382
16th to endNight
38%310%19%23%4
573
September1st to 15thNight
39%39%21%20%6%
540
16th to endNight
38%311%18%20%8%
548
October1st to 15thNight
33%310%22%25%5%
657
16th to endNight
25%313%24%27%5%
816
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 2017-11-01 13:23:42. Version ac04

Copyright 2017 A. Danko


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