Penn Valley
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Penn Valley clear sky chart from 2005-11-06 to 2024-01-14.

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
65%
23392
28%
74724
26%
23345
69%
23345
39%
40564

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 10thNight
49%
757
17%
2646
16%
756
52%
756
22%
1683
January11th to 20thNight
55%
734
22%
2440
20%
734
60%
734
26%
1500
January21st to endNight
52%
792
25%
2574
24%
792
57%
792
27%
1590
February1st to 10thNight
55%
720
26%
2340
24%
720
62%
720
30%
1381
February11th to 20thNight
51%
701
26%
2167
22%
700
59%
700
29%
1320
February21st to endNight
49%
592
25%
1776
23%
592
55%
592
30%
1096
March1st to 10thNight
42%
720
15%
2102
13%
720
47%
720
21%
1490
March11th to 20thNight
50%
720
22%
1980
17%
720
55%
720
30%
1292
March21st to endNight
48%
792
18%
2094
11%
792
53%
792
29%
1400
April1st to 10thNight
52%
720
22%
1800
11%
720
57%
720
32%
1202
April11th to 20thNight
55%
711
26%
1779
13%
711
60%
711
40%
1110
April21st to endNight
65%
720
26%
1800
12%
720
70%
720
48%
1031
May1st to 10thNight
59%
642
28%
1722
16%
642
65%
642
47%
944
May11th to 20thNight
68%
354
31%
1416
32%
354
73%
354
41%
620
May21st to endNight
67%
388
27%
1552
29%
388
74%
388
40%
690
June1st to 10thNight
71%
360
26%
1440
30%
360
78%
360
42%
634
June11th to 20thNight
77%
360
35%
1440
43%
360
84%
360
61%
505
June21st to endNight
83%
360
35%
1440
45%
360
88%
360
61%
508
July1st to 10thNight
90%
350
37%
1400
48%
350
93%
350
76%
426
July11th to 20thNight
90%
348
39%
1392
50%
348
91%
348
76%
421
July21st to endNight
88%
559
39%
1644
36%
528
89%
528
70%
658
August1st to 10thNight
86%
537
38%
1602
31%
534
88%
534
66%
691
August11th to 20thNight
90%
664
41%
1732
27%
664
92%
664
80%
756
August21st to endNight
91%
792
43%
1980
27%
792
92%
792
81%
892
September1st to 10thNight
89%
720
46%
1800
31%
720
90%
720
82%
804
September11th to 20thNight
82%
720
44%
1800
33%
720
84%
720
71%
864
September21st to endNight
78%
720
42%
2014
36%
720
85%
720
69%
900
October1st to 10thNight
74%
720
32%
2160
32%
720
80%
720
54%
1023
October11th to 20thNight
75%
720
39%
2160
42%
720
79%
720
54%
1023
October21st to endNight
72%
792
38%
2376
37%
792
78%
792
52%
1157
November1st to 10thNight
63%
740
28%
2373
29%
740
67%
740
36%
1324
November11th to 20thNight
63%
760
28%
2470
26%
760
70%
760
38%
1319
November21st to endNight
60%
760
27%
2617
27%
760
66%
760
33%
1429
December1st to 10thNight
54%
760
24%
2660
23%
760
59%
760
29%
1530
December11th to 20thNight
48%
760
19%
3223
21%
759
53%
759
16%
2243
December21st to endNight
44%
827
14%
4813
18%
817
52%
817
12%
3108

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
11%313323345%63%
74751
Night
14%413323345%58%
75020
TransparencyDay
25%38%18%24%21%
74464
Night
29%48%18%22%20%
74828
SeeingDay
11%7%20%31%26%6%
14003
Night
13%314%36%30%5%
23408

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 10thDay
27%6%25%324347%38%
1519
11th to 20thDay
19%5%14324436%49%
1590
21st to endDay
21%6%34313448%42%
1782
February1st to 10thDay
21%6%24223346%47%
1620
11th to 20thDay
19%6%23424447%46%
1679
21st to endDay
21%7%23323345%46%
1480
March1st to 10thDay
22%9%25%5%34447%36%
1854
11th to 20thDay
24%6%24323446%40%
1980
21st to endDay
21%7%2332346%7%42%
2260
April1st to 10thDay
19%6%2442345%6%45%
2160
11th to 20thDay
15%423322446%54%
2129
21st to endDay
10%42232435%6%59%
2160
May1st to 10thDay
8%314223337%63%
2234
11th to 20thDay
6%313324446%64%
2477
21st to endDay
7%323324446%62%
2723
June1st to 10thDay
7%322223448%63%
2520
11th to 20thDay
221221223480%
2520
21st to endDay
311111122383%
2520
July1st to 10thDay
1111122388%
2520
11th to 20thDay
11111122388%
2520
21st to endDay
111121223384%
2574
August1st to 10thDay
21111222483%
2328
11th to 20thDay
11111122486%
2169
21st to endDay
1111111192%
2376
September1st to 10thDay
211122488%
2160
11th to 20thDay
4212212335%76%
2160
21st to endDay
421111223379%
1942
October1st to 10thDay
6%212312445%70%
1800
11th to 20thDay
7%213223336%68%
1800
21st to endDay
9%31432334464%
1980
November1st to 10thDay
15%42432435%6%53%
1705
11th to 20thDay
16%31332445%6%51%
1710
21st to endDay
14%5%14423446%53%
1558
December1st to 10thDay
19%413314447%49%
1520
11th to 20thDay
32%8%35%423345%31%
1928
21st to endDay
18%7%25%5%35%5%6%7%37%
2794
January1st to 10thNight
24%6%2432335%7%40%
2646
11th to 20thNight
18%5%25%33435%6%46%
2440
21st to endNight
22%5%24324446%45%
2574
February1st to 10thNight
21%5%13323345%50%
2340
11th to 20thNight
16%6%143345%46%47%
2167
21st to endNight
21%6%23323345%48%
1776
March1st to 10thNight
25%8%35%424435%37%
2102
11th to 20thNight
22%6%23423348%42%
1980
21st to endNight
21%5%24324445%45%
2094
April1st to 10thNight
16%6%35%433447%47%
1800
11th to 20thNight
15%424313347%54%
1779
21st to endNight
10%32222335%6%62%
1800
May1st to 10thNight
9%5%13323346%63%
1722
11th to 20thNight
8%2132135%5%7%62%
1416
21st to endNight
7%313422447%63%
1552
June1st to 10thNight
7%312323346%67%
1440
11th to 20thNight
2112212235%78%
1440
21st to endNight
321222222382%
1440
July1st to 10thNight
1111221388%
1440
11th to 20thNight
11121111388%
1440
21st to endNight
121221232481%
1741
August1st to 10thNight
321222223379%
1611
11th to 20thNight
111111223384%
1732
21st to endNight
11211222287%
1980
September1st to 10thNight
211111211387%
1800
11th to 20thNight
5%212112235%78%
1800
21st to endNight
3111212235%78%
2014
October1st to 10thNight
7%21222333472%
2160
11th to 20thNight
7%21221234472%
2160
21st to endNight
9%312222346%67%
2376
November1st to 10thNight
16%5%1332235%6%54%
2373
11th to 20thNight
13%31441345%7%55%
2470
21st to endNight
14%423433335%55%
2617
December1st to 10thNight
22%413323346%50%
2660
11th to 20thNight
35%5%2432335%6%32%
3276
21st to endNight
22%7%36%6%35%45%6%35%
4862

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 10thDay
49%410%20%13%5%
1519
11th to 20thDay
38%48%18%16%15%
1590
21st to endDay
42%38%15%21%10%
1782
February1st to 10thDay
40%310%18%19%11%
1620
11th to 20thDay
38%410%18%23%8%
1688
21st to endDay
42%49%22%17%7%
1480
March1st to 10thDay
48%6%10%16%16%5%
1854
11th to 20thDay
45%310%21%16%5%
1980
21st to endDay
41%6%13%20%16%4
2260
April1st to 10thDay
39%5%12%23%17%4
2160
11th to 20thDay
31%5%12%24%22%7%
2132
21st to endDay
25%413%28%25%4
2160
May1st to 10thDay
22%410%26%29%9%
2234
11th to 20thDay
22%410%30%25%10%
2480
21st to endDay
22%5%14%31%21%6%
2724
June1st to 10thDay
21%311%24%27%13%
2520
11th to 20thDay
11%29%20%33%25%
2520
21st to endDay
9%2313%37%36%
2520
July1st to 10thDay
5%239%27%54%
2451
11th to 20thDay
6%1411%25%53%
2445
21st to endDay
8%227%25%56%
2431
August1st to 10thDay
9%2311%30%45%
2312
11th to 20thDay
6%129%35%46%
2169
21st to endDay
41111%36%46%
2376
September1st to 10thDay
5%128%27%57%
2160
11th to 20thDay
14%25%19%35%24%
2160
21st to endDay
12%25%19%32%30%
1942
October1st to 10thDay
18%36%20%27%26%
1800
11th to 20thDay
19%36%19%25%28%
1800
21st to endDay
24%46%18%25%23%
1980
November1st to 10thDay
32%5%7%20%22%14%
1705
11th to 20thDay
34%411%20%23%9%
1710
21st to endDay
32%49%19%23%13%
1558
December1st to 10thDay
37%48%20%20%11%
1520
11th to 20thDay
57%37%14%13%6%
1928
21st to endDay
45%5%14%20%12%4
2794
January1st to 10thNight
44%5%11%21%13%7%
2646
11th to 20thNight
40%5%9%13%17%16%
2440
21st to endNight
41%49%14%22%11%
2574
February1st to 10thNight
38%37%19%19%14%
2340
11th to 20thNight
37%5%7%20%22%9%
2169
21st to endNight
38%48%23%19%8%
1776
March1st to 10thNight
51%5%9%16%14%6%
2102
11th to 20thNight
41%49%20%19%7%
1980
21st to endNight
41%6%10%21%16%6%
2094
April1st to 10thNight
39%5%12%17%20%6%
1800
11th to 20thNight
32%5%12%23%19%10%
1779
21st to endNight
24%5%12%30%23%6%
1800
May1st to 10thNight
23%6%10%21%29%12%
1722
11th to 20thNight
21%412%30%22%12%
1416
21st to endNight
21%415%30%23%6%
1552
June1st to 10thNight
21%5%10%27%26%12%
1440
11th to 20thNight
11%28%20%32%27%
1440
21st to endNight
11%3312%32%40%
1440
July1st to 10thNight
6%2211%27%53%
1400
11th to 20thNight
6%1212%22%57%
1392
21st to endNight
9%228%21%57%
1644
August1st to 10thNight
12%2215%25%45%
1602
11th to 20thNight
7%2212%30%48%
1732
21st to endNight
7%2210%27%52%
1980
September1st to 10thNight
6%227%29%54%
1800
11th to 20thNight
12%26%16%39%25%
1800
21st to endNight
11%25%18%30%34%
2014
October1st to 10thNight
18%36%17%27%29%
2160
11th to 20thNight
18%3418%26%31%
2160
21st to endNight
20%35%20%26%26%
2376
November1st to 10thNight
31%49%20%18%17%
2373
11th to 20thNight
29%411%23%23%11%
2470
21st to endNight
32%37%19%21%16%
2617
December1st to 10thNight
37%49%19%18%14%
2660
11th to 20thNight
53%46%14%17%6%
3276
21st to endNight
51%5%11%16%12%5%
4862

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 10thDay
40%6%21%18%13%2
180
11th to 20thDay
26%7%17%28%18%5%
292
21st to endDay
21%7%21%25%20%6%
374
February1st to 10thDay
24%8%17%28%19%4
340
11th to 20thDay
20%13%23%27%14%3
383
21st to endDay
20%13%25%28%14%1
346
March1st to 10thDay
27%15%26%19%10%2
420
11th to 20thDay
27%10%23%21%15%3
420
21st to endDay
21%13%31%22%12%1
462
April1st to 10thDay
20%12%27%24%15%2
420
11th to 20thDay
18%14%27%25%13%4
412
21st to endDay
8%12%25%30%21%5%
420
May1st to 10thDay
9%12%30%26%19%4
423
11th to 20thDay
9%9%26%28%22%6%
448
21st to endDay
7%8%19%31%27%8%
485
June1st to 10thDay
5%9%20%31%28%7%
450
11th to 20thDay
38%21%37%25%5%
450
21st to endDay
2218%39%31%7%
450
July1st to 10thDay
1114%43%36%5%
446
11th to 20thDay
1110%41%40%7%
444
21st to endDay
111%41%38%8%
487
August1st to 10thDay
2212%42%35%7%
447
11th to 20thDay
115%36%38%10%
437
21st to endDay
1112%36%44%6%
495
September1st to 10thDay
2210%43%33%9%
450
11th to 20thDay
5%420%34%30%6%
450
21st to endDay
36%21%33%29%7%
450
October1st to 10thDay
39%22%28%28%9%
450
11th to 20thDay
6%7%16%30%32%10%
450
21st to endDay
11%7%17%29%28%8%
495
November1st to 10thDay
16%6%16%25%31%7%
301
11th to 20thDay
13%415%30%29%9%
270
21st to endDay
13%419%30%26%9%
198
December1st to 10thDay
22%8%16%26%21%8%
180
11th to 20thDay
22%6%22%23%17%10%
180
21st to endDay
23%9%19%27%19%3
198
January1st to 10thNight
24%5%16%28%22%6%
760
11th to 20thNight
19%415%38%20%3
734
21st to endNight
22%216%30%25%5%
792
February1st to 10thNight
21%315%35%23%3
720
11th to 20thNight
18%5%19%34%20%4
704
21st to endNight
23%5%19%36%16%2
592
March1st to 10thNight
24%7%18%29%19%3
720
11th to 20thNight
22%5%16%29%25%3
720
21st to endNight
20%5%21%32%21%1
792
April1st to 10thNight
17%419%37%20%3
720
11th to 20thNight
13%6%21%33%23%4
711
21st to endNight
9%418%37%27%5%
720
May1st to 10thNight
8%422%36%26%3
642
11th to 20thNight
7%317%36%35%2
354
21st to endNight
8%414%34%39%2
389
June1st to 10thNight
7%118%35%36%3
360
11th to 20thNight
2115%46%34%2
360
21st to endNight
319%44%39%3
360
July1st to 10thNight
6%46%45%3
350
11th to 20thNight
25%50%41%3
348
21st to endNight
15%37%50%6%
559
August1st to 10thNight
36%41%44%5%
537
11th to 20thNight
115%43%44%6%
664
21st to endNight
1441%50%4
792
September1st to 10thNight
27%36%49%6%
720
11th to 20thNight
4210%36%42%8%
720
21st to endNight
3215%36%36%9%
720
October1st to 10thNight
6%312%41%32%7%
720
11th to 20thNight
7%410%36%37%6%
720
21st to endNight
8%414%33%30%11%
792
November1st to 10thNight
15%413%30%30%8%
740
11th to 20thNight
12%214%39%27%5%
760
21st to endNight
14%316%38%25%6%
760
December1st to 10thNight
22%414%34%21%6%
760
11th to 20thNight
30%313%31%20%3
760
21st to endNight
25%419%32%19%2
836
Page generated at 2024-01-11 01:22:42. Version ac07

Copyright 2024 Attilla Danko


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