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 2017-10-31.

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%
15455
29%
47422
24%
15414
71%
15414
42%
24620

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%
720
27%
1800
12%
720
63%
720
47%
987
May1st to 15thNight
67%
572
30%
1652
20%
572
72%
572
56%
774
May16th to endNight
72%
374
30%
1496
31%
374
79%
374
53%
564
June1st to 15thNight
72%
360
29%
1440
31%
360
80%
360
48%
567
June16th to endNight
84%
360
37%
1440
48%
360
88%
360
64%
495
July1st to 15thNight
92%
353
35%
1373
45%
353
94%
353
76%
426
July16th to endNight
92%
564
40%
1593
37%
531
93%
531
80%
604
August1st to 15thNight
92%
538
40%
1611
34%
535
93%
535
75%
636
August16th to endNight
93%
755
44%
1901
29%
755
94%
755
79%
862
September1st to 15thNight
91%
720
43%
1800
30%
720
93%
720
79%
812
September16th to endNight
85%
716
45%
1971
41%
716
88%
716
71%
861
October1st to 15thNight
71%
720
33%
2160
30%
720
79%
720
54%
1002
October16th to endNight
71%
768
37%
2304
35%
768
78%
768
49%
1146
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%313313335%63%
48326
Night
8%312323346%61%
47608
TransparencyDay
23%37%20%25%19%
48011
Night
25%38%20%24%18%
47423
SeeingDay
9%11%21%29%22%6%
6147
Night
9%6%12%31%33%6%
15461

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
4313323447%60%
2160
May1st to 15thDay
322212347%68%
2295
16th to endDay
421331345%7%62%
2613
June1st to 15thDay
4212223435%66%
2520
16th to endDay
111222382%
2520
July1st to 15thDay
1112387%
2503
16th to endDay
111389%
2468
August1st to 15thDay
11123384%
2340
16th to endDay
112387%
2301
September1st to 15thDay
11112384%
2160
16th to endDay
211111235%77%
1986
October1st to 15thDay
422312235%69%
1800
16th to endDay
8%312212335%64%
1918
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%212313346%64%
1800
May1st to 15thNight
3112212348%68%
1652
16th to endNight
21121245%6%70%
1496
June1st to 15thNight
3212212235%72%
1440
16th to endNight
11121221382%
1440
July1st to 15thNight
11111188%
1454
16th to endNight
11111486%
1701
August1st to 15thNight
111111485%
1620
16th to endNight
111125%83%
1901
September1st to 15thNight
1111125%84%
1800
16th to endNight
11111225%80%
1971
October1st to 15thNight
321221234471%
2160
16th to endNight
6%22222347%63%
2304
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%26%23%8%
2160
May1st to 15thDay
16%37%29%31%11%
2295
16th to endDay
20%312%31%22%9%
2617
June1st to 15thDay
20%39%25%24%16%
2520
16th to endDay
8%2317%36%31%
2520
July1st to 15thDay
5%2110%31%47%
2355
16th to endDay
41311%26%52%
2313
August1st to 15thDay
6%2114%38%36%
2324
16th to endDay
42115%40%36%
2301
September1st to 15thDay
6%2313%35%38%
2160
16th to endDay
11%2426%32%22%
1986
October1st to 15thDay
19%25%20%28%23%
1800
16th to endDay
24%25%24%27%14%
1918
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%313%28%24%9%
1800
May1st to 15thNight
14%38%24%33%14%
1653
16th to endNight
13%313%36%23%9%
1496
June1st to 15thNight
16%29%25%29%17%
1440
16th to endNight
9%2216%34%33%
1440
July1st to 15thNight
6%18%31%51%
1373
16th to endNight
6%1210%22%56%
1593
August1st to 15thNight
7%211%35%43%
1611
16th to endNight
6%2112%38%38%
1901
September1st to 15thNight
7%1211%35%41%
1800
16th to endNight
9%1322%33%28%
1971
October1st to 15thNight
16%36%20%27%25%
2160
16th to endNight
20%36%23%24%20%
2304
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
11%21%28%22%13%2
270
May1st to 15thDay
6%15%34%27%12%3
288
16th to endDay
5%11%22%26%26%7%
330
June1st to 15thDay
6%11%25%35%16%4
315
16th to endDay
5%23%39%23%7%
315
July1st to 15thDay
1111%43%32%8%
305
16th to endDay
115%41%29%11%
327
August1st to 15thDay
1114%38%33%9%
315
16th to endDay
14%33%34%15%
332
September1st to 15thDay
16%35%35%10%
315
16th to endDay
28%19%30%28%10%
315
October1st to 15thDay
6%14%20%31%18%8%
315
16th to endDay
10%10%19%29%22%7%
336
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%23%6%
720
May1st to 15thNight
35%19%33%33%5%
573
16th to endNight
45%14%33%36%5%
375
June1st to 15thNight
37%11%37%37%1
360
16th to endNight
118%43%42%1
360
July1st to 15thNight
1328%60%4
353
16th to endNight
1225%60%10%
564
August1st to 15thNight
1328%56%10%
538
16th to endNight
1328%57%10%
755
September1st to 15thNight
11428%52%11%
720
16th to endNight
227%32%42%13%
716
October1st to 15thNight
5%5%12%34%32%9%
720
16th to endNight
8%311%29%35%11%
768
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 2017-11-01 14:23:33. Version ac04

Copyright 2017 A. Danko


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