Penn Valley
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Penn Valley clear sky chart from 2005-11-05 to 2017-09-21.

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
67%
15209
28%
46915
25%
15172
70%
15172
40%
25490

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
60%
717
19%
2482
20%
716
63%
716
28%
1459
January16th to endNight
54%
768
25%
2496
23%
768
59%
768
27%
1539
February1st to 15thNight
57%
697
23%
2270
23%
696
62%
696
25%
1437
February16th to endNight
52%
632
25%
1895
22%
632
58%
632
27%
1213
March1st to 15thNight
51%
720
15%
2061
14%
720
54%
720
24%
1417
March16th to endNight
51%
768
20%
2055
14%
768
55%
768
29%
1363
April1st to 15thNight
53%
719
19%
1799
11%
719
55%
719
31%
1235
April16th to endNight
64%
720
25%
1800
13%
720
67%
720
43%
1074
May1st to 15thNight
66%
546
28%
1626
22%
546
70%
546
50%
797
May16th to endNight
71%
375
26%
1496
30%
374
74%
374
38%
682
June1st to 15thNight
73%
360
27%
1440
33%
360
79%
360
43%
622
June16th to endNight
86%
360
35%
1440
47%
360
89%
360
63%
495
July1st to 15thNight
94%
340
34%
1360
47%
340
95%
340
75%
418
July16th to endNight
92%
486
40%
1517
42%
455
92%
455
78%
534
August1st to 15thNight
90%
565
38%
1638
31%
562
90%
562
71%
695
August16th to endNight
94%
764
44%
1910
29%
764
95%
764
83%
844
September1st to 15thNight
90%
720
43%
1800
30%
720
91%
720
79%
811
September16th to endNight
83%
680
43%
1841
38%
680
86%
680
70%
841
October1st to 15thNight
71%
660
31%
1980
32%
660
76%
660
48%
996
October16th to endNight
73%
704
34%
2112
35%
704
77%
704
46%
1098
November1st to 15thNight
67%
700
27%
2256
27%
700
71%
700
38%
1225
November16th to endNight
60%
720
23%
2433
24%
720
64%
720
31%
1379
December1st to 15thNight
53%
720
21%
2520
20%
720
58%
720
24%
1544
December16th to endNight
46%
768
21%
2688
20%
768
52%
768
20%
1772

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%31221223462%
47946
Night
13%312212335%59%
47105
TransparencyDay
25%37%18%24%20%
47627
Night
28%37%18%22%19%
46924
SeeingDay
13%7%22%32%18%4
5864
Night
14%29%31%34%6%
15220

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
21%324224235%46%
1455
16th to endDay
23%6%23213336%44%
1728
February1st to 15thDay
22%6%14213236%45%
1585
16th to endDay
24%6%23213336%40%
1579
March1st to 15thDay
24%5%24424337%38%
1896
16th to endDay
21%6%2332235%7%40%
2167
April1st to 15thDay
21%5%2332245%5%42%
2149
16th to endDay
12%322213335%59%
2160
May1st to 15thDay
6%212113337%66%
2321
16th to endDay
7%313213335%61%
2615
June1st to 15thDay
7%312213236%64%
2520
16th to endDay
211122383%
2520
July1st to 15thDay
1112286%
2520
16th to endDay
11112287%
2545
August1st to 15thDay
111111285%
2313
16th to endDay
1111288%
2292
September1st to 15thDay
211122382%
2160
16th to endDay
42111113378%
1908
October1st to 15thDay
8%112212435%66%
1650
16th to endDay
11%313323335%59%
1760
November1st to 15thDay
12%31333335%6%51%
1603
16th to endDay
19%41432343449%
1524
December1st to 15thDay
23%5%23314345%42%
1440
16th to endDay
27%5%23323335%39%
1536
January1st to 15thNight
20%31322325%7%46%
2482
16th to endNight
22%41431333447%
2496
February1st to 15thNight
21%6%13324446%42%
2266
16th to endNight
23%413213445%45%
1895
March1st to 15thNight
24%5%23424337%38%
2061
16th to endNight
21%5%23323236%45%
2055
April1st to 15thNight
16%5%25%5%24437%42%
1799
16th to endNight
12%323222345%59%
1800
May1st to 15thNight
7%22212337%65%
1626
16th to endNight
7%2133225%46%61%
1496
June1st to 15thNight
6%312212135%68%
1440
16th to endNight
21111221381%
1440
July1st to 15thNight
1111387%
1440
16th to endNight
11111287%
1622
August1st to 15thNight
21111222281%
1647
16th to endNight
1123285%
1910
September1st to 15thNight
111222384%
1800
16th to endNight
21111223379%
1841
October1st to 15thNight
8%21221333466%
1980
16th to endNight
9%212213345%62%
2112
November1st to 15thNight
13%31321235%7%55%
2256
16th to endNight
15%413413336%51%
2433
December1st to 15thNight
25%312323345%44%
2520
16th to endNight
28%5%13223335%40%
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%39%19%18%7%
1455
16th to endDay
43%27%15%17%13%
1728
February1st to 15thDay
42%210%17%20%6%
1585
16th to endDay
45%49%25%12%3
1579
March1st to 15thDay
46%412%15%15%6%
1896
16th to endDay
43%5%13%17%15%4
2167
April1st to 15thDay
41%412%22%15%3
2149
16th to endDay
27%412%25%24%6%
2160
May1st to 15thDay
19%38%29%29%9%
2321
16th to endDay
24%411%29%21%7%
2619
June1st to 15thDay
22%29%20%22%21%
2520
16th to endDay
8%1314%37%34%
2520
July1st to 15thDay
5%138%28%52%
2371
16th to endDay
7%139%22%55%
2387
August1st to 15thDay
7%1210%31%46%
2297
16th to endDay
5%112%38%41%
2292
September1st to 15thDay
7%1311%33%41%
2160
16th to endDay
13%1422%32%25%
1908
October1st to 15thDay
19%36%25%26%17%
1650
16th to endDay
28%37%20%25%15%
1760
November1st to 15thDay
32%411%22%20%9%
1603
16th to endDay
37%48%20%21%6%
1524
December1st to 15thDay
43%38%17%21%4
1440
16th to endDay
47%47%15%17%6%
1536
January1st to 15thNight
36%410%19%17%10%
2482
16th to endNight
41%37%12%18%16%
2496
February1st to 15thNight
42%37%17%18%9%
2278
16th to endNight
40%48%23%17%4
1895
March1st to 15thNight
46%410%16%14%6%
2061
16th to endNight
41%5%9%20%17%6%
2055
April1st to 15thNight
41%5%12%19%14%6%
1799
16th to endNight
27%5%11%23%23%8%
1800
May1st to 15thNight
20%39%24%27%13%
1627
16th to endNight
22%413%31%19%8%
1496
June1st to 15thNight
20%39%22%23%20%
1440
16th to endNight
10%1414%30%37%
1440
July1st to 15thNight
6%128%26%54%
1360
16th to endNight
6%1210%20%58%
1517
August1st to 15thNight
10%1114%26%45%
1638
16th to endNight
5%1212%32%45%
1910
September1st to 15thNight
7%1310%36%40%
1800
16th to endNight
11%26%18%33%27%
1841
October1st to 15thNight
22%36%22%26%20%
1980
16th to endNight
23%35%21%27%17%
2112
November1st to 15thNight
28%412%23%19%11%
2256
16th to endNight
34%37%21%20%10%
2433
December1st to 15thNight
42%38%17%20%7%
2520
16th to endNight
47%46%13%18%8%
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
48%6%12%20%12%1
83
16th to endDay
30%6%18%25%14%5%
256
February1st to 15thDay
26%6%21%28%14%1
238
16th to endDay
28%13%21%23%13%
238
March1st to 15thDay
29%13%20%20%11%4
270
16th to endDay
25%15%25%21%11%1
288
April1st to 15thDay
26%14%28%20%8%1
269
16th to endDay
16%18%26%24%11%2
270
May1st to 15thDay
10%11%36%26%11%3
288
16th to endDay
11%10%20%29%21%6%
330
June1st to 15thDay
8%13%25%35%13%4
315
16th to endDay
2424%43%17%7%
315
July1st to 15thDay
117%52%20%7%
305
16th to endDay
120%47%22%7%
327
August1st to 15thDay
2118%45%26%6%
315
16th to endDay
120%40%29%8%
332
September1st to 15thDay
2218%44%25%6%
315
16th to endDay
47%25%32%25%4
276
October1st to 15thDay
7%11%23%32%19%5%
255
16th to endDay
16%5%23%31%22%
272
November1st to 15thDay
14%215%23%35%7%
109
16th to endDay
22%6%18%31%18%1
74
December1st to 15thDay
40%6%28%16%8%
60
16th to endDay
25%414%29%20%6%
64
January1st to 15thNight
20%38%35%25%6%
720
16th to endNight
24%29%31%25%5%
768
February1st to 15thNight
23%28%36%24%2
704
16th to endNight
24%5%12%30%22%4
632
March1st to 15thNight
23%5%10%30%26%4
720
16th to endNight
23%315%28%25%3
768
April1st to 15thNight
17%6%15%36%21%3
719
16th to endNight
13%5%12%33%27%7%
720
May1st to 15thNight
8%217%36%30%4
547
16th to endNight
8%39%30%44%3
375
June1st to 15thNight
6%212%30%43%4
360
16th to endNight
27%37%45%6%
360
July1st to 15thNight
127%63%6%
340
16th to endNight
1223%63%9%
486
August1st to 15thNight
3231%52%9%
565
16th to endNight
231%57%8%
764
September1st to 15thNight
2327%55%10%
720
16th to endNight
319%29%40%15%
680
October1st to 15thNight
8%310%33%34%9%
660
16th to endNight
11%29%29%34%11%
704
November1st to 15thNight
13%39%32%32%8%
700
16th to endNight
15%311%35%25%7%
720
December1st to 15thNight
26%48%33%22%5%
720
16th to endNight
29%313%30%20%2
768
Page generated at 2017-09-22 04:35:36. Version ac04

Copyright 2017 A. Danko


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