Lawrence Lake Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lawrence Lake Observatory clear sky chart from 2005-11-05 to 2017-09-20.

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
37%
15212
9%
46621
6%
15185
41%
15185
17%
33578

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
30%
914
6%
2796
3%
914
33%
914
11%
2200
January16th to endNight
24%
936
12%
2856
6%
936
31%
936
14%
2112
February1st to 15thNight
34%
701
9%
2460
7%
698
38%
698
14%
1782
February16th to endNight
39%
632
11%
2031
10%
632
43%
632
17%
1463
March1st to 15thNight
35%
720
13%
2121
8%
720
41%
720
18%
1560
March16th to endNight
35%
767
12%
2080
6%
767
38%
767
16%
1586
April1st to 15thNight
40%
592
14%
1672
8%
592
43%
592
21%
1187
April16th to endNight
35%
522
10%
1599
8%
522
38%
522
17%
1169
May1st to 15thNight
49%
359
5%
1260
4%
359
50%
359
23%
778
May16th to endNight
43%
374
0%
1309
0%
374
43%
374
17%
910
June1st to 15thNight
46%
360
0%
1128
0%
360
46%
360
17%
807
June16th to endNight
55%
360
0%
1080
0%
360
55%
360
22%
744
July1st to 15thNight
58%
340
0%
1029
0%
340
58%
340
29%
655
July16th to endNight
53%
376
0%
1239
0%
354
54%
354
23%
762
August1st to 15thNight
68%
360
4%
1350
6%
358
69%
358
23%
828
August16th to endNight
48%
554
11%
1700
9%
554
53%
554
24%
1117
September1st to 15thNight
53%
618
14%
1755
10%
618
55%
618
31%
1117
September16th to endNight
45%
675
17%
1869
9%
675
50%
675
30%
1203
October1st to 15thNight
37%
660
13%
1991
9%
660
42%
660
20%
1408
October16th to endNight
33%
727
11%
2311
7%
727
40%
727
16%
1653
November1st to 15thNight
27%
875
13%
2525
7%
875
33%
875
16%
1884
November16th to endNight
27%
900
8%
2700
3%
900
32%
900
13%
2087
December1st to 15thNight
27%
900
8%
2700
4%
900
30%
900
11%
2189
December16th to endNight
31%
990
10%
3060
4%
990
37%
990
12%
2377

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
12%9%47%7%46%5%6%7%28%
48256
Night
10%10%48%7%45%5%6%7%30%
46760
TransparencyDay
51%8%17%17%4
47896
Night
50%7%16%18%5%
46625
SeeingDay
16%9%27%26%14%4
6622
Night
14%7%28%32%15%2
15223

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
8%10%5%10%9%6%6%6%6%8%20%
1140
16th to endDay
7%13%5%12%8%25%446%28%
1377
February1st to 15thDay
6%12%410%7%47%5%6%8%26%
1400
16th to endDay
5%13%8%10%8%36%5%5%7%24%
1441
March1st to 15thDay
6%14%6%10%9%46%5%5%7%22%
1839
16th to endDay
11%10%7%9%7%47%5%5%7%21%
2141
April1st to 15thDay
11%13%6%7%6%45%5%5%7%26%
2275
16th to endDay
15%13%5%8%7%35%45%6%24%
2360
May1st to 15thDay
13%7%36%7%36%5%6%7%31%
2691
16th to endDay
17%8%25%7%45%5%5%7%30%
2802
June1st to 15thDay
18%9%37%7%45%45%7%24%
2830
16th to endDay
16%6%36%5%46%6%6%7%28%
2880
July1st to 15thDay
12%5%25%5%35%6%7%8%35%
2871
16th to endDay
10%5%26%6%37%6%6%10%32%
2846
August1st to 15thDay
12%5%26%5%36%6%7%9%34%
2601
16th to endDay
10%6%26%7%36%6%7%10%32%
2501
September1st to 15thDay
15%6%25%5%3445%7%37%
2202
16th to endDay
12%6%245%25%5%7%8%39%
1860
October1st to 15thDay
15%10%36%6%45%5%5%7%30%
1636
16th to endDay
11%13%5%7%8%35%45%5%29%
1549
November1st to 15thDay
11%10%6%8%6%45%45%6%29%
1333
16th to endDay
5%12%6%11%8%5%6%45%5%27%
1260
December1st to 15thDay
8%14%5%11%8%6%7%5%5%7%18%
1260
16th to endDay
310%8%14%10%5%8%7%6%6%18%
1161
January1st to 15thNight
8%12%6%10%8%5%6%7%6%6%21%
2796
16th to endNight
6%11%5%10%9%45%5%46%29%
2856
February1st to 15thNight
8%11%5%9%7%46%5%5%7%28%
2452
16th to endNight
6%11%6%8%8%36%6%6%7%28%
2031
March1st to 15thNight
9%10%5%7%7%46%6%6%7%27%
2121
16th to endNight
10%13%5%9%6%35%5%5%7%26%
2077
April1st to 15thNight
11%10%46%6%36%5%5%8%31%
1672
16th to endNight
13%13%47%6%345%5%7%28%
1599
May1st to 15thNight
12%5%35%435%6%7%9%37%
1259
16th to endNight
18%9%36%5%3445%7%30%
1309
June1st to 15thNight
13%6%47%6%46%7%7%9%26%
1128
16th to endNight
13%7%25%5%46%6%6%8%33%
1080
July1st to 15thNight
11%424435%5%5%12%40%
1089
16th to endNight
11%426%5%2445%10%40%
1323
August1st to 15thNight
8%4235%45%5%8%11%40%
1357
16th to endNight
12%5%36%5%345%6%7%39%
1700
September1st to 15thNight
11%6%245%235%6%8%43%
1755
16th to endNight
11%5%25%5%25%45%8%42%
1869
October1st to 15thNight
12%10%36%6%35%5%5%7%32%
1991
16th to endNight
10%11%47%5%35%5%6%6%30%
2311
November1st to 15thNight
11%12%5%9%6%35%45%6%29%
2525
16th to endNight
7%12%7%11%8%45%5%5%6%25%
2700
December1st to 15thNight
9%14%6%9%8%5%7%6%5%6%19%
2700
16th to endNight
5%11%5%12%9%5%7%5%6%7%22%
3060

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
57%9%18%10%4
1140
16th to endDay
57%5%11%17%6%1
1377
February1st to 15thDay
54%7%17%15%5%
1400
16th to endDay
57%5%18%14%4
1441
March1st to 15thDay
58%7%14%15%4
1839
16th to endDay
59%7%13%14%4
2142
April1st to 15thDay
55%6%14%16%6%
2275
16th to endDay
59%6%10%14%7%
2360
May1st to 15thDay
48%6%12%22%10%
2691
16th to endDay
51%6%11%20%8%
2807
June1st to 15thDay
58%7%14%16%3
2830
16th to endDay
51%9%15%17%4
2880
July1st to 15thDay
41%10%21%20%4
2702
16th to endDay
43%11%24%17%2
2667
August1st to 15thDay
42%11%28%15%1
2583
16th to endDay
43%10%25%16%3
2501
September1st to 15thDay
44%8%24%18%4
2202
16th to endDay
39%9%21%22%7%
1860
October1st to 15thDay
52%6%19%18%2
1636
16th to endDay
54%6%15%20%2
1549
November1st to 15thDay
52%6%18%16%4
1333
16th to endDay
56%8%15%14%3
1260
December1st to 15thDay
65%6%14%11%1
1260
16th to endDay
62%8%13%12%3
1161
January1st to 15thNight
58%9%15%12%3
2796
16th to endNight
53%7%16%14%6%1
2856
February1st to 15thNight
53%7%15%15%7%
2464
16th to endNight
52%6%16%18%6%
2031
March1st to 15thNight
52%7%15%18%6%
2121
16th to endNight
54%7%11%18%6%
2080
April1st to 15thNight
49%5%12%20%10%1
1672
16th to endNight
54%5%10%17%10%1
1599
May1st to 15thNight
40%6%12%25%13%1
1260
16th to endNight
51%6%11%20%9%1
1309
June1st to 15thNight
51%7%17%17%5%
1128
16th to endNight
44%8%17%22%5%
1080
July1st to 15thNight
35%9%23%26%4
1029
16th to endNight
37%8%24%25%3
1239
August1st to 15thNight
33%12%27%23%1
1350
16th to endNight
42%7%22%23%5%
1700
September1st to 15thNight
35%7%21%26%6%1
1755
16th to endNight
37%6%20%24%8%1
1869
October1st to 15thNight
49%6%15%23%4
1991
16th to endNight
50%8%17%20%3
2311
November1st to 15thNight
55%6%12%21%4
2525
16th to endNight
58%7%16%13%3
2700
December1st to 15thNight
63%8%13%12%2
2700
16th to endNight
58%8%14%14%3
3060

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
11%5%30%30%20%3
60
16th to endDay
17%143%25%7%4
64
February1st to 15thDay
15%10%41%26%33
60
16th to endDay
15%11%31%30%11%2
100
March1st to 15thDay
12%18%37%21%7%1
270
16th to endDay
16%13%36%22%9%1
288
April1st to 15thDay
14%17%36%23%7%
269
16th to endDay
26%14%31%17%9%1
272
May1st to 15thDay
15%11%22%30%14%4
468
16th to endDay
19%6%20%31%15%5%
517
June1st to 15thDay
20%8%26%26%14%3
625
16th to endDay
17%5%22%28%19%5%
675
July1st to 15thDay
12%426%32%21%2
636
16th to endDay
11%6%29%27%19%7%
515
August1st to 15thDay
13%6%18%28%22%11%
396
16th to endDay
12%11%35%28%11%
332
September1st to 15thDay
25%10%23%26%10%4
315
16th to endDay
20%10%34%19%11%2
272
October1st to 15thDay
29%9%26%19%12%3
131
16th to endDay
19%11%17%26%20%4
96
November1st to 15thDay
29%7%31%24%6%
77
16th to endDay
8%13%28%25%15%10%
60
December1st to 15thDay
16%8%25%28%15%6%
60
16th to endDay
7%7%32%28%14%9%
64
January1st to 15thNight
13%8%32%32%10%2
919
16th to endNight
11%14%36%28%8%1
936
February1st to 15thNight
13%8%28%33%14%1
704
16th to endNight
9%5%30%36%15%2
632
March1st to 15thNight
11%9%32%31%12%1
720
16th to endNight
14%7%30%28%16%1
768
April1st to 15thNight
15%6%28%33%13%1
592
16th to endNight
21%7%25%28%14%1
522
May1st to 15thNight
15%5%22%34%19%2
360
16th to endNight
23%320%32%18%1
375
June1st to 15thNight
15%5%21%33%20%3
360
16th to endNight
17%215%35%26%1
360
July1st to 15thNight
13%218%39%25%
340
16th to endNight
13%319%35%22%4
376
August1st to 15thNight
11%113%36%32%4
360
16th to endNight
14%323%37%19%1
554
September1st to 15thNight
13%420%37%22%2
618
16th to endNight
13%6%28%34%14%1
675
October1st to 15thNight
19%329%31%13%1
660
16th to endNight
18%9%26%31%12%1
727
November1st to 15thNight
17%9%34%27%8%2
875
16th to endNight
13%11%32%28%12%1
900
December1st to 15thNight
17%11%32%26%10%2
900
16th to endNight
11%7%31%30%15%3
990
Page generated at 2017-09-21 05:18:19. Version ac04

Copyright 2017 A. Danko


Lawrence Lake Observatory Clear Sky Chart | Charts Home