This page made possible by the sponsorship of: A member of the Imperial Polk County Astronomical Society., Wayne Frey.

Wayne's Backyard Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Wayne's Backyard Observatory 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
59%
15934
20%
46867
16%
15893
64%
15893
29%
29674

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
44%
718
19%
2327
15%
716
53%
716
24%
1465
January16th to endNight
45%
768
25%
2439
18%
768
55%
768
29%
1458
February1st to 15thNight
47%
701
24%
2103
17%
698
55%
698
33%
1247
February16th to endNight
44%
631
25%
1827
14%
631
54%
631
33%
1084
March1st to 15thNight
50%
720
30%
1980
18%
720
61%
720
40%
1140
March16th to endNight
55%
768
26%
2112
19%
768
61%
768
40%
1218
April1st to 15thNight
59%
718
23%
1976
18%
718
63%
718
43%
1105
April16th to endNight
58%
720
27%
1847
17%
720
64%
720
44%
1072
May1st to 15thNight
68%
581
27%
1661
19%
581
73%
581
41%
922
May16th to endNight
73%
561
22%
1683
17%
561
75%
561
33%
1029
June1st to 15thNight
68%
540
11%
1620
10%
540
68%
540
22%
1162
June16th to endNight
71%
540
7%
1620
6%
540
71%
540
19%
1197
July1st to 15thNight
73%
510
6%
1530
5%
510
73%
510
19%
1174
July16th to endNight
75%
564
7%
1595
6%
531
75%
531
20%
1173
August1st to 15thNight
79%
539
5%
1609
5%
536
79%
536
24%
1124
August16th to endNight
66%
726
7%
2060
7%
726
66%
726
20%
1502
September1st to 15thNight
63%
700
7%
1925
6%
700
63%
700
18%
1448
September16th to endNight
56%
657
11%
1815
10%
657
57%
657
18%
1342
October1st to 15thNight
69%
660
25%
1875
25%
660
71%
660
32%
1176
October16th to endNight
58%
704
28%
2112
24%
704
65%
704
32%
1275
November1st to 15thNight
60%
700
30%
2101
27%
700
67%
700
38%
1181
November16th to endNight
52%
720
29%
2214
22%
720
62%
720
33%
1312
December1st to 15thNight
53%
720
26%
2340
23%
720
60%
720
29%
1395
December16th to endNight
55%
768
23%
2496
23%
768
60%
768
30%
1473

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
8%5%26%7%46%6%6%8%36%
47743
Night
7%5%25%5%35%5%6%9%43%
47075
TransparencyDay
43%8%13%15%13%5%
47444
Night
35%8%15%19%14%5%
46878
SeeingDay
8%212%21%25%29%
5785
Night
9%217%33%27%9%
15942

By Month

Percentage Cloud Cover SE (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
11%5%25%435%6%6%7%40%
1611
16th to endDay
10%435%4245%5%7%47%
1782
February1st to 15thDay
11%5%25%42446%7%44%
1750
16th to endDay
7%5%25%5%3445%7%47%
1646
March1st to 15thDay
6%315%5%25%45%8%51%
1980
16th to endDay
8%415%5%345%5%7%48%
2111
April1st to 15thDay
5%425%5%36%5%6%8%45%
1972
16th to endDay
6%4246%46%6%6%8%44%
2112
May1st to 15thDay
4415%5%36%6%6%8%47%
2296
16th to endDay
6%437%7%6%7%7%7%8%33%
2431
June1st to 15thDay
13%8%48%8%5%7%5%6%9%22%
2340
16th to endDay
9%6%38%10%5%9%7%7%9%22%
2340
July1st to 15thDay
9%5%38%10%6%8%7%8%8%21%
2340
16th to endDay
9%7%49%10%6%8%7%7%8%20%
2465
August1st to 15thDay
5%6%39%11%6%9%7%8%10%21%
2340
16th to endDay
11%7%38%9%6%7%7%6%9%21%
2126
September1st to 15thDay
10%6%39%10%6%7%7%7%9%21%
1923
16th to endDay
11%7%39%8%7%7%6%7%9%21%
1815
October1st to 15thDay
7%6%37%6%45%7%6%8%36%
1755
16th to endDay
9%5%25%5%35%5%47%44%
1760
November1st to 15thDay
4325%6%26%5%5%8%49%
1757
16th to endDay
6%6%25%6%45%5%48%44%
1743
December1st to 15thDay
9%6%35%5%25%5%7%7%41%
1620
16th to endDay
8%4245%45%6%6%8%44%
1728
January1st to 15thNight
9%6%26%6%25%45%8%41%
2327
16th to endNight
11%5%3442446%8%44%
2439
February1st to 15thNight
11%6%24323347%50%
2103
16th to endNight
7%42443445%7%49%
1827
March1st to 15thNight
5%31443435%7%54%
1980
16th to endNight
5%4144235%48%54%
2112
April1st to 15thNight
5%31442346%10%53%
1976
16th to endNight
5%32442446%7%55%
1847
May1st to 15thNight
332342445%8%56%
1661
16th to endNight
6%3136%25%6%6%10%46%
1682
June1st to 15thNight
9%6%36%6%46%5%7%10%33%
1620
16th to endNight
6%5%47%6%47%7%8%11%29%
1620
July1st to 15thNight
8%5%38%6%46%6%9%10%29%
1620
16th to endNight
5%435%7%48%8%9%11%28%
1703
August1st to 15thNight
2427%6%5%7%7%9%10%35%
1620
16th to endNight
9%5%26%6%47%7%7%11%30%
2060
September1st to 15thNight
7%6%37%8%46%7%8%12%28%
1925
16th to endNight
11%8%37%7%46%5%7%9%28%
1815
October1st to 15thNight
6%426%5%35%5%6%10%44%
1875
16th to endNight
9%5%25%42435%7%48%
2112
November1st to 15thNight
6%4245%24446%54%
2101
16th to endNight
8%425%5%345%5%7%47%
2214
December1st to 15thNight
9%435%5%3445%9%46%
2340
16th to endNight
6%425%5%345%6%8%45%
2496

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
39%7%8%19%19%6%
1612
16th to endDay
34%5%8%17%24%9%
1782
February1st to 15thDay
37%5%7%14%21%14%
1752
16th to endDay
35%5%10%15%22%10%
1646
March1st to 15thDay
30%410%23%21%8%
1980
16th to endDay
33%6%10%21%19%9%
2112
April1st to 15thDay
35%7%11%18%20%7%
1972
16th to endDay
34%7%10%16%21%8%
2112
May1st to 15thDay
32%8%12%19%18%8%
2296
16th to endDay
44%8%13%17%13%2
2435
June1st to 15thDay
55%9%14%16%4
2340
16th to endDay
55%10%19%11%2
2340
July1st to 15thDay
55%14%18%9%1
2201
16th to endDay
56%13%18%10%1
2310
August1st to 15thDay
51%13%25%8%
2327
16th to endDay
55%13%19%10%1
2126
September1st to 15thDay
55%13%17%10%2
1923
16th to endDay
55%11%15%9%6%1
1815
October1st to 15thDay
41%9%10%14%15%8%
1755
16th to endDay
37%5%9%13%21%11%
1760
November1st to 15thDay
31%6%7%22%22%9%
1757
16th to endDay
37%7%8%18%15%12%
1743
December1st to 15thDay
40%5%11%17%18%5%
1620
16th to endDay
35%6%13%18%17%7%
1728
January1st to 15thNight
40%5%10%20%16%6%
2327
16th to endNight
36%5%8%20%19%9%
2439
February1st to 15thNight
34%48%17%21%13%
2112
16th to endNight
32%5%13%17%22%7%
1827
March1st to 15thNight
27%5%10%27%20%7%
1980
16th to endNight
27%5%12%23%21%8%
2112
April1st to 15thNight
24%6%15%25%20%6%
1976
16th to endNight
25%5%14%24%21%7%
1847
May1st to 15thNight
25%6%15%24%19%7%
1662
16th to endNight
30%9%17%23%16%1
1684
June1st to 15thNight
45%10%20%19%4
1620
16th to endNight
44%14%20%16%3
1620
July1st to 15thNight
45%16%25%10%2
1530
16th to endNight
41%16%28%12%
1595
August1st to 15thNight
36%16%36%10%
1609
16th to endNight
44%14%27%12%1
2060
September1st to 15thNight
45%16%22%13%2
1925
16th to endNight
48%11%18%14%42
1815
October1st to 15thNight
34%7%12%20%17%6%
1875
16th to endNight
35%48%17%24%9%
2112
November1st to 15thNight
29%410%22%23%8%
2101
16th to endNight
34%49%20%18%12%
2214
December1st to 15thNight
35%6%12%24%14%7%
2340
16th to endNight
34%5%13%21%15%8%
2496

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
21%432%25%13%3
90
16th to endDay
16%14%29%21%16%1
96
February1st to 15thDay
414%27%27%17%7%
90
16th to endDay
9%6%38%31%12%
147
March1st to 15thDay
6%5%28%34%24%1
270
16th to endDay
11%421%28%28%5%
288
April1st to 15thDay
4424%29%26%10%
270
16th to endDay
7%210%30%32%16%
270
May1st to 15thDay
4212%26%32%21%
288
16th to endDay
5%16%19%29%36%
331
June1st to 15thDay
17%16%13%20%41%
315
16th to endDay
6%39%23%56%
315
July1st to 15thDay
6%2420%66%
305
16th to endDay
9%5%7%21%55%
326
August1st to 15thDay
6%1311%23%54%
313
16th to endDay
12%49%18%53%
332
September1st to 15thDay
11%15%11%24%45%
294
16th to endDay
12%39%31%41%
254
October1st to 15thDay
10%110%24%37%14%
255
16th to endDay
9%320%27%29%8%
272
November1st to 15thDay
4117%36%28%12%
265
16th to endDay
6%123%38%26%4
213
December1st to 15thDay
8%327%42%17%
90
16th to endDay
6%6%10%40%31%5%
96
January1st to 15thNight
10%6%27%35%17%1
720
16th to endNight
12%5%28%38%14%
768
February1st to 15thNight
13%5%27%39%12%1
704
16th to endNight
9%433%39%11%
631
March1st to 15thNight
6%5%30%41%13%
720
16th to endNight
7%427%42%17%1
768
April1st to 15thNight
6%223%46%20%
718
16th to endNight
6%323%44%21%
720
May1st to 15thNight
416%46%28%2
582
16th to endNight
6%10%34%40%8%
563
June1st to 15thNight
9%15%25%43%14%
540
16th to endNight
6%414%44%29%
540
July1st to 15thNight
10%28%44%33%
510
16th to endNight
5%110%44%37%
564
August1st to 15thNight
329%50%33%
539
16th to endNight
11%1417%39%26%
726
September1st to 15thNight
11%6%22%37%22%
700
16th to endNight
15%16%24%39%12%
657
October1st to 15thNight
9%8%38%36%6%
660
16th to endNight
12%217%32%30%4
704
November1st to 15thNight
7%221%41%24%4
700
16th to endNight
8%328%39%19%1
720
December1st to 15thNight
10%324%38%21%1
720
16th to endNight
7%323%41%21%2
768
Page generated at 2017-09-11 19:35:33. Version ac04

Copyright 2017 A. Danko


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