Lassen National Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lassen National Park clear sky chart from 2005-11-05 to 2017-08-12.

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
55%
14917
24%
46511
20%
14883
60%
14883
32%
26924

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
44%
718
18%
2506
14%
716
51%
716
23%
1560
January16th to endNight
41%
768
22%
2499
19%
768
47%
768
23%
1603
February1st to 15thNight
42%
698
17%
2288
15%
697
47%
697
20%
1514
February16th to endNight
42%
632
18%
1912
15%
632
48%
632
21%
1306
March1st to 15thNight
39%
720
11%
2058
9%
720
42%
720
18%
1478
March16th to endNight
38%
768
15%
2061
10%
768
42%
768
21%
1434
April1st to 15thNight
37%
719
16%
1799
7%
719
41%
719
22%
1289
April16th to endNight
48%
720
20%
1800
9%
720
53%
720
36%
1116
May1st to 15thNight
51%
478
23%
1558
17%
478
58%
478
36%
814
May16th to endNight
56%
374
17%
1496
18%
374
60%
374
26%
837
June1st to 15thNight
61%
360
22%
1440
26%
360
68%
360
33%
706
June16th to endNight
76%
360
30%
1440
42%
360
81%
360
48%
576
July1st to 15thNight
89%
340
31%
1360
44%
340
90%
340
67%
450
July16th to endNight
89%
453
39%
1487
42%
425
91%
425
71%
535
August1st to 15thNight
88%
526
38%
1575
32%
523
89%
523
65%
681
August16th to endNight
84%
695
41%
1745
27%
695
85%
695
76%
799
September1st to 15thNight
84%
660
44%
1650
29%
660
86%
660
77%
758
September16th to endNight
73%
656
39%
1789
32%
656
78%
656
61%
835
October1st to 15thNight
61%
660
29%
1980
26%
660
69%
660
43%
1009
October16th to endNight
59%
704
28%
2112
27%
704
65%
704
37%
1177
November1st to 15thNight
53%
700
21%
2267
20%
700
59%
700
26%
1403
November16th to endNight
45%
720
18%
2481
16%
720
51%
720
23%
1531
December1st to 15thNight
40%
720
17%
2520
13%
720
47%
720
18%
1657
December16th to endNight
34%
768
19%
2688
14%
768
42%
768
16%
1856

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
5%8%35%423345%53%
47472
Night
47%36%424446%50%
46690
TransparencyDay
32%38%19%22%13%
47150
Night
33%49%19%20%12%
46512
SeeingDay
15%17%29%24%10%2
5650
Night
10%11%16%29%25%5%
14927

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
49%5%8%7%46%447%36%
1432
16th to endDay
6%14%49%424445%38%
1722
February1st to 15thDay
5%13%47%6%35%5%5%6%36%
1576
16th to endDay
5%16%9%8%5%34347%32%
1562
March1st to 15thDay
5%17%7%9%6%35%336%30%
1900
16th to endDay
6%17%5%7%425%45%7%31%
2163
April1st to 15thDay
7%16%5%8%6%45%447%30%
2149
16th to endDay
6%10%35%42435%5%47%
2160
May1st to 15thDay
5%7%24423348%52%
2388
16th to endDay
10%11%35%5%23336%45%
2615
June1st to 15thDay
7%7%24424335%52%
2520
16th to endDay
22221223474%
2520
July1st to 15thDay
11121233377%
2520
16th to endDay
11111112383%
2578
August1st to 15thDay
11111223477%
2291
16th to endDay
11111213282%
2104
September1st to 15thDay
11121224476%
1980
16th to endDay
3312212338%67%
1839
October1st to 15thDay
6%424423236%59%
1650
16th to endDay
6%8%25%423347%51%
1760
November1st to 15thDay
8%7%25%6%45%45%8%40%
1591
16th to endDay
410%5%10%43445%6%40%
1476
December1st to 15thDay
6%11%410%5%35%5%5%5%34%
1440
16th to endDay
8%12%7%9%6%34445%32%
1536
January1st to 15thNight
49%49%5%35%45%7%39%
2506
16th to endNight
411%5%9%5%34446%39%
2499
February1st to 15thNight
5%10%5%8%8%35%5%5%7%34%
2276
16th to endNight
5%14%6%8%6%34447%34%
1912
March1st to 15thNight
5%13%6%10%7%35%5%5%7%29%
2058
16th to endNight
413%49%4445%6%7%34%
2061
April1st to 15thNight
5%14%6%7%7%44447%33%
1799
16th to endNight
5%9%45%42345%8%47%
1800
May1st to 15thNight
5%5%13424447%56%
1558
16th to endNight
6%7%35%5%34347%47%
1496
June1st to 15thNight
6%6%2341335%7%56%
1440
16th to endNight
222422223372%
1440
July1st to 15thNight
1221112381%
1440
16th to endNight
1111111284%
1589
August1st to 15thNight
11221222378%
1584
16th to endNight
11111122482%
1745
September1st to 15thNight
1111122483%
1650
16th to endNight
113212236%73%
1789
October1st to 15thNight
6%423313435%61%
1980
16th to endNight
35%15%43445%6%53%
2112
November1st to 15thNight
7%6%36%5%36%5%6%7%41%
2267
16th to endNight
48%5%8%5%3446%7%39%
2481
December1st to 15thNight
5%8%5%12%7%3445%7%35%
2520
16th to endNight
7%13%5%10%7%35%437%30%
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
43%5%10%20%15%4
1432
16th to endDay
46%5%6%17%14%10%
1722
February1st to 15thDay
44%412%19%15%3
1576
16th to endDay
52%311%21%9%1
1562
March1st to 15thDay
54%48%16%12%4
1900
16th to endDay
49%5%15%17%9%3
2163
April1st to 15thDay
51%410%19%13%
2149
16th to endDay
37%313%26%15%3
2160
May1st to 15thDay
28%311%29%21%4
2388
16th to endDay
40%310%25%16%3
2619
June1st to 15thDay
33%39%19%25%9%
2520
16th to endDay
14%2421%39%17%
2520
July1st to 15thDay
11%2412%33%35%
2371
16th to endDay
9%1212%27%46%
2417
August1st to 15thDay
11%2317%28%36%
2275
16th to endDay
9%1216%36%34%
2104
September1st to 15thDay
11%2312%37%32%
1980
16th to endDay
16%36%25%31%17%
1839
October1st to 15thDay
26%37%24%27%10%
1650
16th to endDay
32%410%20%22%10%
1760
November1st to 15thDay
39%412%21%13%8%
1591
16th to endDay
42%310%20%17%5%
1476
December1st to 15thDay
47%5%9%19%15%1
1440
16th to endDay
52%39%13%15%5%
1536
January1st to 15thNight
41%5%13%18%15%5%
2506
16th to endNight
44%38%15%16%11%
2499
February1st to 15thNight
45%5%10%18%14%5%
2288
16th to endNight
48%311%19%13%3
1912
March1st to 15thNight
51%5%12%13%11%5%
2058
16th to endNight
45%6%15%18%10%2
2061
April1st to 15thNight
48%5%12%22%9%1
1799
16th to endNight
32%416%27%16%3
1800
May1st to 15thNight
26%5%11%29%21%5%
1559
16th to endNight
35%414%26%14%3
1496
June1st to 15thNight
26%5%11%24%24%7%
1440
16th to endNight
17%25%20%37%16%
1440
July1st to 15thNight
9%1414%30%40%
1360
16th to endNight
8%1310%26%50%
1487
August1st to 15thNight
12%2215%30%36%
1575
16th to endNight
8%1215%34%35%
1745
September1st to 15thNight
8%1212%38%36%
1650
16th to endNight
14%27%24%31%19%
1789
October1st to 15thNight
23%27%25%27%12%
1980
16th to endNight
27%5%10%24%22%8%
2112
November1st to 15thNight
38%6%13%21%13%6%
2267
16th to endNight
40%5%10%21%16%6%
2481
December1st to 15thNight
47%48%17%18%3
2520
16th to endNight
52%37%12%17%5%
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
25%20%38%15%1
60
16th to endDay
22%20%26%17%12%
250
February1st to 15thDay
27%18%23%23%7%
236
16th to endDay
25%20%26%20%5%
235
March1st to 15thDay
30%25%22%12%7%1
270
16th to endDay
25%30%24%15%4
288
April1st to 15thDay
26%24%26%17%41
269
16th to endDay
22%24%31%15%5%
270
May1st to 15thDay
15%20%38%18%5%1
288
16th to endDay
23%12%25%22%11%3
330
June1st to 15thDay
18%15%29%22%10%1
315
16th to endDay
416%33%27%13%4
315
July1st to 15thDay
36%37%34%12%5%
305
16th to endDay
19%34%36%11%7%
327
August1st to 15thDay
39%34%34%8%10%
300
16th to endDay
111%38%30%13%4
268
September1st to 15thDay
211%30%36%16%2
255
16th to endDay
9%12%29%30%16%1
255
October1st to 15thDay
12%18%31%22%12%1
255
16th to endDay
22%19%26%23%8%
272
November1st to 15thDay
13%7%24%24%28%1
97
16th to endDay
9%33%25%21%7%3
66
December1st to 15thDay
28%30%23%15%3
60
16th to endDay
17%20%20%23%18%
64
January1st to 15thNight
11%12%23%32%15%4
720
16th to endNight
14%14%23%24%17%5%
768
February1st to 15thNight
15%16%17%31%16%2
704
16th to endNight
17%14%18%31%14%3
632
March1st to 15thNight
17%17%18%25%15%4
720
16th to endNight
15%21%18%24%16%2
768
April1st to 15thNight
13%17%22%30%14%1
719
16th to endNight
12%13%20%30%18%5%
720
May1st to 15thNight
9%8%24%31%21%3
479
16th to endNight
11%8%16%27%33%3
375
June1st to 15thNight
10%6%18%30%31%3
360
16th to endNight
35%10%35%42%3
360
July1st to 15thNight
1327%62%3
340
16th to endNight
15%30%55%7%
453
August1st to 15thNight
2328%55%9%
526
16th to endNight
118%39%42%5%
695
September1st to 15thNight
139%33%41%10%
660
16th to endNight
46%11%30%34%12%
656
October1st to 15thNight
9%9%14%31%28%6%
660
16th to endNight
9%10%15%27%27%8%
704
November1st to 15thNight
11%9%19%33%21%5%
700
16th to endNight
11%17%20%27%18%5%
720
December1st to 15thNight
13%15%22%26%16%4
720
16th to endNight
19%16%21%27%12%1
768
Page generated at 2017-08-13 11:16:22. Version ac04

Copyright 2017 A. Danko


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