WYA Eastern Lassen Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the WYA Eastern Lassen Site clear sky chart from 2005-11-05 to 2017-09-19.

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
52%
15019
25%
46883
19%
14995
59%
14995
32%
25851

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
48%
716
18%
2506
16%
716
54%
716
22%
1484
January16th to endNight
47%
768
21%
2568
20%
768
52%
768
22%
1542
February1st to 15thNight
43%
700
17%
2263
17%
700
47%
700
21%
1417
February16th to endNight
44%
632
21%
1895
16%
632
51%
632
25%
1166
March1st to 15thNight
43%
720
14%
2121
12%
720
47%
720
24%
1379
March16th to endNight
39%
768
18%
2019
10%
768
46%
768
25%
1292
April1st to 15thNight
43%
719
19%
1799
9%
719
47%
719
28%
1207
April16th to endNight
45%
720
21%
1800
10%
720
49%
720
35%
1071
May1st to 15thNight
41%
471
24%
1551
14%
471
51%
471
30%
800
May16th to endNight
48%
374
19%
1496
17%
374
57%
374
24%
787
June1st to 15thNight
52%
360
22%
1440
23%
360
63%
360
30%
709
June16th to endNight
57%
360
30%
1440
30%
360
74%
360
43%
555
July1st to 15thNight
65%
340
30%
1360
34%
340
76%
340
54%
471
July16th to endNight
66%
376
38%
1416
40%
354
82%
354
54%
501
August1st to 15thNight
70%
568
34%
1642
23%
566
77%
566
55%
767
August16th to endNight
75%
764
43%
1910
22%
764
81%
764
68%
887
September1st to 15thNight
74%
720
40%
1800
25%
720
78%
720
65%
867
September16th to endNight
66%
671
40%
1809
28%
671
76%
671
55%
869
October1st to 15thNight
59%
660
31%
1973
27%
660
68%
660
44%
992
October16th to endNight
58%
704
29%
2159
24%
704
68%
704
38%
1124
November1st to 15thNight
55%
700
23%
2275
22%
700
61%
700
30%
1297
November16th to endNight
44%
720
18%
2433
16%
720
50%
720
26%
1365
December1st to 15thNight
43%
720
18%
2520
16%
720
49%
720
21%
1558
December16th to endNight
38%
768
19%
2688
16%
768
46%
768
18%
1744

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
342442445%7%55%
47951
Night
35%2442445%7%53%
47056
TransparencyDay
27%5%9%21%21%15%
47622
Night
28%5%11%22%19%12%
46884
SeeingDay
6%18%21%25%20%7%
5696
Night
5%20%15%31%22%5%
15029

By Month

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
38%48%7%36%5%6%9%36%
1432
16th to endDay
48%37%7%35%6%7%9%35%
1653
February1st to 15thDay
45%46%6%35%7%6%8%41%
1600
16th to endDay
37%37%6%35%6%5%10%39%
1579
March1st to 15thDay
48%48%6%35%5%6%7%37%
1836
16th to endDay
38%46%6%35%5%7%9%39%
2205
April1st to 15thDay
48%46%6%45%5%5%7%42%
2149
16th to endDay
5%6%3443346%7%50%
2160
May1st to 15thDay
2314313448%60%
2396
16th to endDay
6%7%25%5%34446%47%
2615
June1st to 15thDay
5%325%5%245%46%53%
2520
16th to endDay
21221222474%
2520
July1st to 15thDay
111212345%75%
2520
16th to endDay
11221233476%
2657
August1st to 15thDay
211221334471%
2306
16th to endDay
11121123480%
2292
September1st to 15thDay
1111233477%
2160
16th to endDay
2212312346%70%
1895
October1st to 15thDay
4313323337%62%
1656
16th to endDay
4425%5%3445%6%54%
1713
November1st to 15thDay
6%6%24426%6%6%7%45%
1584
16th to endDay
36%36%5%25%6%6%8%44%
1527
December1st to 15thDay
6%7%49%425%5%6%8%38%
1440
16th to endDay
5%10%37%8%35%6%6%9%32%
1536
January1st to 15thNight
5%8%35%5%35%47%8%41%
2506
16th to endNight
49%46%5%2445%7%44%
2568
February1st to 15thNight
48%38%6%45%6%7%8%38%
2252
16th to endNight
39%46%6%25%5%5%8%43%
1895
March1st to 15thNight
38%47%6%36%5%7%8%38%
2121
16th to endNight
48%35%6%34448%44%
2019
April1st to 15thNight
27%46%436%5%6%9%41%
1799
16th to endNight
5%5%2442345%7%55%
1800
May1st to 15thNight
441343445%6%57%
1551
16th to endNight
45%25%5%35%46%8%49%
1496
June1st to 15thNight
45%1332445%7%56%
1440
16th to endNight
111232323473%
1440
July1st to 15thNight
111112246%76%
1440
16th to endNight
1131223477%
1512
August1st to 15thNight
332212245%71%
1650
16th to endNight
11121212382%
1910
September1st to 15thNight
111112235%78%
1800
16th to endNight
222212335%73%
1809
October1st to 15thNight
4423313236%64%
1973
16th to endNight
341432445%6%58%
2159
November1st to 15thNight
6%4244245%8%8%47%
2275
16th to endNight
36%36%6%3446%8%46%
2433
December1st to 15thNight
6%7%38%6%35%46%8%40%
2520
16th to endNight
6%10%47%5%35%6%6%8%34%
2688

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
40%10%17%22%7%1
1432
16th to endDay
42%8%13%18%13%2
1653
February1st to 15thDay
34%9%17%24%11%3
1600
16th to endDay
37%6%17%26%10%1
1579
March1st to 15thDay
41%7%13%21%13%2
1836
16th to endDay
36%9%20%20%9%3
2205
April1st to 15thDay
37%6%13%24%15%1
2149
16th to endDay
30%413%32%16%2
2160
May1st to 15thDay
21%411%29%26%6%
2396
16th to endDay
35%310%26%19%4
2619
June1st to 15thDay
29%5%7%18%29%10%
2520
16th to endDay
14%2316%38%25%
2520
July1st to 15thDay
11%2211%26%46%
2371
16th to endDay
13%217%21%53%
2490
August1st to 15thDay
14%3111%24%43%
2289
16th to endDay
10%1112%32%41%
2292
September1st to 15thDay
11%1213%33%37%
2160
16th to endDay
15%25%24%31%20%
1895
October1st to 15thDay
23%37%29%27%8%
1656
16th to endDay
28%49%27%21%7%
1713
November1st to 15thDay
32%7%16%25%12%4
1584
16th to endDay
33%7%13%26%15%3
1527
December1st to 15thDay
41%8%14%25%10%
1440
16th to endDay
45%8%11%22%11%1
1536
January1st to 15thNight
35%6%17%25%11%1
2506
16th to endNight
37%5%12%21%15%6%
2568
February1st to 15thNight
37%7%16%20%14%3
2263
16th to endNight
36%6%15%27%11%2
1895
March1st to 15thNight
38%7%17%20%12%3
2121
16th to endNight
34%7%17%25%10%2
2019
April1st to 15thNight
36%7%14%26%12%1
1799
16th to endNight
28%415%31%16%3
1800
May1st to 15thNight
26%410%27%25%5%
1552
16th to endNight
31%414%28%15%4
1496
June1st to 15thNight
25%6%10%23%26%8%
1440
16th to endNight
16%15%16%36%23%
1440
July1st to 15thNight
10%2412%29%40%
1360
16th to endNight
11%229%25%49%
1416
August1st to 15thNight
15%2313%26%38%
1642
16th to endNight
9%1114%33%39%
1910
September1st to 15thNight
11%2311%30%41%
1800
16th to endNight
14%3424%30%23%
1809
October1st to 15thNight
22%28%28%26%11%
1973
16th to endNight
24%411%28%22%7%
2159
November1st to 15thNight
29%8%16%26%14%4
2275
16th to endNight
32%416%25%16%3
2433
December1st to 15thNight
38%7%14%25%13%
2520
16th to endNight
42%7%12%21%14%2
2688

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
15%16%18%26%18%5%
60
16th to endDay
9%19%16%24%20%9%
181
February1st to 15thDay
422%15%25%24%6%
241
16th to endDay
8%23%16%28%18%3
238
March1st to 15thDay
11%27%19%21%14%5%
270
16th to endDay
9%27%26%21%13%1
288
April1st to 15thDay
10%23%21%24%15%4
269
16th to endDay
10%30%22%17%12%7%
270
May1st to 15thDay
8%26%22%25%12%4
288
16th to endDay
10%18%16%21%20%12%
330
June1st to 15thDay
9%22%20%24%18%4
315
16th to endDay
320%22%24%20%9%
315
July1st to 15thDay
212%14%30%29%9%
305
16th to endDay
213%22%27%22%11%
327
August1st to 15thDay
49%20%29%24%11%
315
16th to endDay
19%21%29%21%15%
332
September1st to 15thDay
19%21%26%28%12%
315
16th to endDay
414%24%25%25%6%
268
October1st to 15thDay
7%18%23%26%21%3
255
16th to endDay
13%21%24%24%15%
225
November1st to 15thDay
46%20%22%33%13%
90
16th to endDay
6%17%33%28%9%5%
75
December1st to 15thDay
18%15%31%30%31
60
16th to endDay
6%420%23%42%3
64
January1st to 15thNight
6%21%11%29%24%6%
720
16th to endNight
7%21%12%29%20%7%
768
February1st to 15thNight
5%24%14%31%22%1
704
16th to endNight
6%24%15%32%16%4
632
March1st to 15thNight
7%25%18%25%16%6%
720
16th to endNight
6%27%19%27%16%2
768
April1st to 15thNight
326%19%29%17%3
719
16th to endNight
7%24%19%25%18%4
720
May1st to 15thNight
6%23%23%29%14%2
472
16th to endNight
422%16%28%24%4
375
June1st to 15thNight
420%18%31%21%3
360
16th to endNight
220%17%36%20%2
360
July1st to 15thNight
212%15%38%29%1
340
16th to endNight
218%10%44%23%1
376
August1st to 15thNight
6%9%10%40%28%4
568
16th to endNight
19%10%38%34%4
764
September1st to 15thNight
29%10%30%37%9%
720
16th to endNight
413%12%26%33%9%
671
October1st to 15thNight
5%14%15%30%24%8%
660
16th to endNight
5%14%15%30%24%9%
704
November1st to 15thNight
6%17%13%34%21%7%
700
16th to endNight
424%18%29%17%4
720
December1st to 15thNight
6%24%16%31%17%3
720
16th to endNight
9%23%19%29%16%2
768
Page generated at 2017-09-20 01:49:53. Version ac04

Copyright 2017 A. Danko


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