Angwin
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Angwin clear sky chart from 2005-11-05 to 2017-09-10.

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%
15265
28%
46837
24%
15225
70%
15225
40%
24825

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%
719
19%
2398
18%
716
59%
716
26%
1440
January16th to endNight
54%
768
26%
2496
23%
768
61%
768
28%
1496
February1st to 15thNight
53%
699
23%
2288
20%
698
59%
698
23%
1438
February16th to endNight
50%
632
23%
1923
18%
632
59%
632
28%
1186
March1st to 15thNight
51%
720
16%
1998
12%
720
55%
720
26%
1329
March16th to endNight
46%
768
21%
2097
14%
768
53%
768
31%
1323
April1st to 15thNight
48%
719
24%
1799
10%
719
55%
719
32%
1139
April16th to endNight
58%
720
26%
1800
13%
720
63%
720
46%
996
May1st to 15thNight
65%
572
29%
1652
20%
572
69%
572
54%
791
May16th to endNight
72%
382
28%
1504
28%
382
80%
382
47%
612
June1st to 15thNight
70%
360
28%
1440
31%
360
78%
360
47%
580
June16th to endNight
85%
360
36%
1440
47%
360
89%
360
63%
503
July1st to 15thNight
91%
362
35%
1382
44%
362
93%
362
76%
438
July16th to endNight
92%
564
39%
1593
35%
531
93%
531
76%
616
August1st to 15thNight
91%
538
38%
1611
32%
535
91%
535
73%
643
August16th to endNight
92%
754
42%
1900
28%
754
93%
754
78%
862
September1st to 15thNight
90%
700
42%
1750
29%
700
92%
700
78%
794
September16th to endNight
84%
656
42%
1807
37%
656
87%
656
67%
819
October1st to 15thNight
70%
660
31%
1980
30%
660
78%
660
50%
962
October16th to endNight
71%
704
33%
2112
33%
704
76%
704
47%
1075
November1st to 15thNight
64%
700
27%
2187
23%
700
71%
700
39%
1163
November16th to endNight
59%
720
24%
2472
25%
720
63%
720
31%
1360
December1st to 15thNight
51%
720
20%
2520
17%
720
58%
720
21%
1597
December16th to endNight
47%
768
22%
2688
18%
768
55%
768
22%
1663

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%61%
47784
Night
8%313323346%59%
47024
TransparencyDay
25%38%20%25%16%
47470
Night
27%39%20%23%16%
46838
SeeingDay
10%10%21%31%20%5%
5956
Night
10%412%31%33%6%
15273

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
17%5%25%423335%45%
1537
16th to endDay
14%5%35%5%33436%43%
1728
February1st to 15thDay
16%5%25%434446%43%
1576
16th to endDay
17%6%35%5%33446%40%
1550
March1st to 15thDay
16%6%37%6%2445%7%35%
1959
16th to endDay
14%6%25%5%25%446%42%
2127
April1st to 15thDay
13%6%35%435%5%5%6%40%
2149
16th to endDay
5%323323446%59%
2160
May1st to 15thDay
422213347%65%
2295
16th to endDay
421432335%7%61%
2605
June1st to 15thDay
4213223346%64%
2520
16th to endDay
1111223481%
2520
July1st to 15thDay
1112385%
2493
16th to endDay
1112485%
2468
August1st to 15thDay
1111325%80%
2340
16th to endDay
1122484%
2301
September1st to 15thDay
111122482%
2097
16th to endDay
2112211326%74%
1819
October1st to 15thDay
6%213222236%65%
1650
16th to endDay
8%414312335%61%
1760
November1st to 15thDay
8%324324347%54%
1669
16th to endDay
12%5%24435%44449%
1485
December1st to 15thDay
16%8%35%5%2342443%
1440
16th to endDay
19%7%24424445%40%
1536
January1st to 15thNight
14%5%25%423448%43%
2398
16th to endNight
16%5%23324345%48%
2496
February1st to 15thNight
14%6%245%25%45%6%41%
2276
16th to endNight
14%424424448%45%
1923
March1st to 15thNight
14%5%25%5%345%46%41%
1998
16th to endNight
12%7%24422347%47%
2097
April1st to 15thNight
10%424425%35%7%49%
1799
16th to endNight
6%313213347%62%
1800
May1st to 15thNight
312313347%67%
1652
16th to endNight
2111223447%67%
1504
June1st to 15thNight
321221225%6%69%
1440
16th to endNight
1122122281%
1440
July1st to 15thNight
1111111386%
1464
16th to endNight
111236%80%
1701
August1st to 15thNight
1112236%78%
1620
16th to endNight
112246%78%
1900
September1st to 15thNight
1112226%81%
1750
16th to endNight
111222235%76%
1807
October1st to 15thNight
4313313345%66%
1980
16th to endNight
7%21322345%7%59%
2112
November1st to 15thNight
7%41332335%8%55%
2187
16th to endNight
9%5%25%333246%53%
2472
December1st to 15thNight
18%5%35%423346%41%
2520
16th to endNight
18%5%24413346%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
42%212%17%15%9%
1537
16th to endDay
43%37%13%20%12%
1728
February1st to 15thDay
42%47%18%21%4
1576
16th to endDay
45%311%23%13%4
1550
March1st to 15thDay
46%411%17%13%5%
1959
16th to endDay
42%5%12%19%16%3
2127
April1st to 15thDay
43%412%18%17%3
2149
16th to endDay
25%314%24%22%7%
2160
May1st to 15thDay
18%38%30%29%9%
2295
16th to endDay
22%314%30%20%8%
2609
June1st to 15thDay
21%411%24%23%14%
2520
16th to endDay
10%1419%37%26%
2520
July1st to 15thDay
7%1312%32%43%
2346
16th to endDay
6%15%12%27%46%
2313
August1st to 15thDay
8%1316%38%31%
2324
16th to endDay
7%319%38%30%
2301
September1st to 15thDay
8%1415%35%34%
2097
16th to endDay
13%15%25%31%22%
1819
October1st to 15thDay
22%28%21%28%17%
1650
16th to endDay
26%28%24%25%12%
1760
November1st to 15thDay
29%410%29%15%8%
1669
16th to endDay
38%39%20%20%7%
1485
December1st to 15thDay
46%37%17%21%4
1440
16th to endDay
45%5%8%17%16%7%
1536
January1st to 15thNight
38%411%20%15%9%
2398
16th to endNight
38%38%15%18%14%
2496
February1st to 15thNight
42%39%18%17%8%
2288
16th to endNight
38%412%23%17%3
1923
March1st to 15thNight
43%414%16%15%6%
1998
16th to endNight
37%411%21%18%6%
2097
April1st to 15thNight
34%413%23%17%6%
1799
16th to endNight
23%313%28%22%9%
1800
May1st to 15thNight
17%310%24%31%13%
1653
16th to endNight
15%414%34%21%9%
1504
June1st to 15thNight
16%310%26%26%16%
1440
16th to endNight
11%1317%35%30%
1440
July1st to 15thNight
6%111%32%46%
1382
16th to endNight
7%15%14%24%45%
1593
August1st to 15thNight
9%416%33%35%
1611
16th to endNight
8%5%18%34%32%
1900
September1st to 15thNight
7%1314%35%37%
1750
16th to endNight
12%1321%34%25%
1807
October1st to 15thNight
20%29%21%26%20%
1980
16th to endNight
23%29%23%23%16%
2112
November1st to 15thNight
26%413%28%16%9%
2187
16th to endNight
33%29%22%22%9%
2472
December1st to 15thNight
43%48%16%19%6%
2520
16th to endNight
42%310%15%20%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
31%9%18%29%10%
165
16th to endDay
16%16%21%25%16%4
256
February1st to 15thDay
23%10%25%22%16%1
236
16th to endDay
21%15%22%22%15%2
233
March1st to 15thDay
24%16%22%17%15%4
270
16th to endDay
21%16%27%21%11%1
288
April1st to 15thDay
20%20%26%20%9%2
269
16th to endDay
14%19%28%24%10%2
270
May1st to 15thDay
8%17%31%28%12%1
288
16th to endDay
6%11%22%32%22%5%
330
June1st to 15thDay
6%13%26%37%12%3
315
16th to endDay
2326%39%23%6%
315
July1st to 15thDay
1214%45%29%6%
305
16th to endDay
117%46%23%10%
327
August1st to 15thDay
2218%45%24%7%
315
16th to endDay
16%37%34%9%
332
September1st to 15thDay
1116%38%32%10%
294
16th to endDay
47%17%33%27%9%
255
October1st to 15thDay
8%12%23%29%18%7%
255
16th to endDay
15%8%22%30%20%3
272
November1st to 15thDay
9%9%16%21%35%7%
175
16th to endDay
13%13%22%29%19%1
67
December1st to 15thDay
33%20%16%21%6%1
60
16th to endDay
14%12%21%31%14%6%
64
January1st to 15thNight
17%412%33%25%7%
720
16th to endNight
20%5%13%30%23%6%
768
February1st to 15thNight
18%6%12%34%24%4
704
16th to endNight
16%7%17%31%21%4
632
March1st to 15thNight
16%7%15%29%26%4
720
16th to endNight
16%8%21%27%23%2
768
April1st to 15thNight
13%9%20%31%21%3
719
16th to endNight
7%11%17%30%25%6%
720
May1st to 15thNight
4320%31%34%5%
573
16th to endNight
35%14%33%36%6%
383
June1st to 15thNight
45%12%37%37%1
360
16th to endNight
118%43%41%3
360
July1st to 15thNight
1428%61%5%
362
16th to endNight
1328%55%11%
564
August1st to 15thNight
1328%55%9%
538
16th to endNight
331%55%8%
754
September1st to 15thNight
11430%52%10%
700
16th to endNight
227%31%41%14%
656
October1st to 15thNight
5%5%11%33%34%9%
660
16th to endNight
8%311%30%34%11%
704
November1st to 15thNight
8%316%31%32%7%
700
16th to endNight
12%6%12%35%24%8%
720
December1st to 15thNight
21%5%12%32%22%6%
720
16th to endNight
21%8%15%32%21%1
768
Page generated at 2017-09-11 16:35:23. Version ac04

Copyright 2017 A. Danko


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