Putah Creek Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Putah Creek Observatory clear sky chart from 2005-11-05 to 2017-04-25.

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%
14870
29%
45638
24%
14829
71%
14829
41%
23929

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
55%
720
20%
2407
18%
716
60%
716
27%
1422
January16th to endNight
52%
768
27%
2496
22%
768
60%
768
28%
1475
February1st to 15thNight
52%
700
24%
2288
20%
699
60%
699
25%
1403
February16th to endNight
50%
632
25%
1922
17%
632
61%
632
28%
1163
March1st to 15thNight
52%
720
17%
2001
12%
720
56%
720
26%
1308
March16th to endNight
47%
768
22%
2094
13%
768
55%
768
31%
1300
April1st to 15thNight
48%
719
24%
1799
10%
719
56%
719
34%
1123
April16th to endNight
58%
700
26%
1750
12%
700
63%
700
47%
961
May1st to 15thNight
67%
524
31%
1514
21%
524
72%
524
56%
713
May16th to endNight
71%
342
27%
1368
27%
342
79%
342
52%
516
June1st to 15thNight
72%
330
30%
1320
33%
330
81%
330
47%
522
June16th to endNight
83%
330
35%
1320
44%
330
87%
330
62%
459
July1st to 15thNight
91%
322
37%
1252
47%
322
93%
322
74%
395
July16th to endNight
91%
522
38%
1467
35%
489
93%
489
78%
561
August1st to 15thNight
93%
493
42%
1476
36%
490
93%
490
76%
578
August16th to endNight
92%
692
42%
1742
27%
692
94%
692
78%
794
September1st to 15thNight
91%
660
45%
1650
31%
660
93%
660
81%
737
September16th to endNight
85%
656
43%
1806
39%
656
88%
656
69%
801
October1st to 15thNight
70%
660
34%
1980
31%
660
79%
660
52%
940
October16th to endNight
69%
704
35%
2112
33%
704
76%
704
47%
1068
November1st to 15thNight
64%
700
27%
2194
23%
700
71%
700
40%
1150
November16th to endNight
58%
720
25%
2472
25%
720
63%
720
32%
1340
December1st to 15thNight
51%
720
21%
2520
16%
720
60%
720
22%
1573
December16th to endNight
45%
768
22%
2688
17%
768
55%
768
23%
1627

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
7%313313345%62%
45997
Night
8%313323346%60%
45824
TransparencyDay
24%37%20%25%18%
45682
Night
25%38%20%24%17%
45639
SeeingDay
10%11%22%29%20%6%
5399
Night
9%6%12%31%32%6%
14876

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
15%6%35%413336%45%
1529
16th to endDay
15%5%24424347%44%
1728
February1st to 15thDay
15%425%42335%7%44%
1576
16th to endDay
16%6%25%43335%5%42%
1550
March1st to 15thDay
15%6%35%6%2346%7%37%
1956
16th to endDay
13%5%24425%45%6%43%
2130
April1st to 15thDay
14%5%24435%5%5%6%41%
2149
16th to endDay
5%313323447%60%
2098
May1st to 15thDay
422212348%67%
2103
16th to endDay
5%21331345%7%61%
2389
June1st to 15thDay
4212223435%66%
2310
16th to endDay
111222381%
2310
July1st to 15thDay
11112386%
2295
16th to endDay
112388%
2286
August1st to 15thDay
11123384%
2145
16th to endDay
112387%
2108
September1st to 15thDay
11112386%
1980
16th to endDay
211111235%77%
1821
October1st to 15thDay
5%32312235%67%
1650
16th to endDay
9%413212335%62%
1760
November1st to 15thDay
8%31342445%7%54%
1663
16th to endDay
11%424415%445%50%
1485
December1st to 15thDay
16%6%35%4235%2444%
1440
16th to endDay
19%7%34314346%40%
1536
January1st to 15thNight
14%5%234233410%44%
2407
16th to endNight
16%423313436%49%
2496
February1st to 15thNight
14%5%235%2446%6%43%
2276
16th to endNight
13%3134235%48%46%
1922
March1st to 15thNight
13%5%245%345%47%42%
2001
16th to endNight
12%5%2442335%6%49%
2094
April1st to 15thNight
9%424434447%50%
1799
16th to endNight
5%212213346%64%
1750
May1st to 15thNight
3112212349%67%
1514
16th to endNight
21121245%7%70%
1368
June1st to 15thNight
3112212235%72%
1320
16th to endNight
11121221381%
1320
July1st to 15thNight
11121187%
1333
16th to endNight
11111486%
1575
August1st to 15thNight
111111485%
1485
16th to endNight
111125%83%
1742
September1st to 15thNight
1112485%
1650
16th to endNight
11112226%79%
1806
October1st to 15thNight
4212213345%69%
1980
16th to endNight
6%212322348%62%
2112
November1st to 15thNight
7%32332336%8%56%
2194
16th to endNight
10%424323346%54%
2472
December1st to 15thNight
17%5%2443335%6%43%
2520
16th to endNight
17%5%24423346%44%
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
41%211%18%16%9%
1529
16th to endDay
41%47%13%21%11%
1728
February1st to 15thDay
41%47%19%22%4
1576
16th to endDay
43%49%24%13%4
1550
March1st to 15thDay
44%411%18%14%6%
1956
16th to endDay
40%413%19%18%4
2130
April1st to 15thDay
41%5%11%19%18%4
2149
16th to endDay
23%413%27%23%8%
2098
May1st to 15thDay
16%37%28%30%12%
2103
16th to endDay
20%313%31%21%9%
2393
June1st to 15thDay
20%49%23%24%18%
2310
16th to endDay
8%2317%38%28%
2310
July1st to 15thDay
6%2111%32%45%
2147
16th to endDay
5%1312%28%48%
2131
August1st to 15thDay
6%2113%37%39%
2129
16th to endDay
5%2114%41%35%
2108
September1st to 15thDay
6%2211%37%39%
1980
16th to endDay
11%2325%31%24%
1821
October1st to 15thDay
20%36%21%29%18%
1650
16th to endDay
25%25%25%27%12%
1760
November1st to 15thDay
28%5%10%29%17%8%
1663
16th to endDay
35%5%9%21%21%7%
1485
December1st to 15thDay
45%37%17%21%5%
1440
16th to endDay
44%38%18%17%7%
1536
January1st to 15thNight
37%410%21%15%9%
2407
16th to endNight
37%38%16%19%15%
2496
February1st to 15thNight
39%48%19%19%8%
2288
16th to endNight
35%5%11%25%18%3
1922
March1st to 15thNight
41%414%16%15%6%
2001
16th to endNight
36%312%22%17%7%
2094
April1st to 15thNight
33%313%24%17%6%
1799
16th to endNight
21%312%28%24%8%
1750
May1st to 15thNight
15%49%22%33%15%
1515
16th to endNight
13%313%38%22%9%
1368
June1st to 15thNight
16%29%24%28%18%
1320
16th to endNight
10%2217%36%31%
1320
July1st to 15thNight
7%19%31%49%
1252
16th to endNight
6%1211%24%53%
1467
August1st to 15thNight
7%111%33%45%
1476
16th to endNight
6%2112%39%37%
1742
September1st to 15thNight
6%119%37%43%
1650
16th to endNight
10%2221%33%29%
1806
October1st to 15thNight
17%37%22%28%20%
1980
16th to endNight
21%46%25%24%18%
2112
November1st to 15thNight
26%313%28%18%9%
2194
16th to endNight
32%39%22%23%9%
2472
December1st to 15thNight
41%5%7%17%19%7%
2520
16th to endNight
40%310%16%21%7%
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
26%13%19%27%12%
157
16th to endDay
16%16%22%25%14%5%
256
February1st to 15thDay
21%13%22%26%13%2
236
16th to endDay
19%15%25%19%17%3
233
March1st to 15thDay
21%19%20%19%14%5%
270
16th to endDay
16%21%26%21%11%2
288
April1st to 15thDay
16%25%25%18%10%2
269
16th to endDay
10%21%28%22%13%2
250
May1st to 15thDay
7%13%37%27%10%3
228
16th to endDay
6%13%24%25%22%7%
266
June1st to 15thDay
6%11%28%35%14%3
255
16th to endDay
7%27%38%19%6%
255
July1st to 15thDay
1213%46%27%7%
245
16th to endDay
115%43%30%8%
271
August1st to 15thDay
1217%41%29%7%
255
16th to endDay
117%37%29%13%
268
September1st to 15thDay
16%33%36%12%
255
16th to endDay
37%16%31%29%12%
255
October1st to 15thDay
7%14%19%31%18%9%
255
16th to endDay
13%11%22%29%19%4
272
November1st to 15thDay
9%11%17%20%33%8%
169
16th to endDay
14%14%23%26%17%1
67
December1st to 15thDay
30%21%13%26%6%1
60
16th to endDay
17%14%21%23%18%4
64
January1st to 15thNight
16%5%13%31%25%7%
720
16th to endNight
19%7%13%31%22%6%
768
February1st to 15thNight
16%8%12%33%24%4
704
16th to endNight
16%9%16%31%21%5%
632
March1st to 15thNight
15%9%15%28%26%5%
720
16th to endNight
15%10%21%28%22%2
768
April1st to 15thNight
10%12%20%31%21%3
719
16th to endNight
7%12%18%31%24%6%
700
May1st to 15thNight
4419%33%32%5%
525
16th to endNight
35%15%34%34%5%
343
June1st to 15thNight
37%11%37%37%1
330
16th to endNight
129%45%40%1
330
July1st to 15thNight
1430%58%4
322
16th to endNight
1224%61%10%
522
August1st to 15thNight
1329%55%9%
493
16th to endNight
1329%56%8%
692
September1st to 15thNight
1426%53%12%
660
16th to endNight
217%31%42%14%
656
October1st to 15thNight
5%5%11%33%32%10%
660
16th to endNight
8%312%30%33%11%
704
November1st to 15thNight
7%5%16%31%32%8%
700
16th to endNight
11%7%12%36%23%8%
720
December1st to 15thNight
19%7%12%32%21%6%
720
16th to endNight
19%11%14%32%20%1
768
Page generated at 2017-04-26 14:21:45. Version ac04

Copyright 2017 A. Danko


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