Bill's Doghouse Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bill's Doghouse Observatory clear sky chart from 2005-11-06 to 2024-01-27.

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
38%
24353
17%
74782
12%
24296
44%
24296
22%
51104

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 10thNight
20%
950
13%
2648
6%
946
27%
946
13%
2090
January11th to 20thNight
14%
950
11%
2660
5%
950
19%
950
12%
2142
January21st to endNight
19%
886
12%
2730
5%
886
26%
886
13%
2122
February1st to 10thNight
19%
720
11%
2195
6%
720
24%
720
14%
1670
February11th to 20thNight
21%
703
13%
2098
7%
699
28%
699
17%
1516
February21st to endNight
18%
592
14%
1776
5%
592
27%
592
15%
1323
March1st to 10thNight
24%
720
16%
2160
8%
720
31%
720
19%
1482
March11th to 20thNight
28%
720
17%
2021
8%
720
36%
720
23%
1395
March21st to endNight
26%
760
15%
2146
7%
760
34%
760
19%
1556
April1st to 10thNight
32%
540
18%
1800
11%
540
42%
540
21%
1178
April11th to 20thNight
36%
533
20%
1769
14%
533
44%
533
23%
1142
April21st to endNight
27%
540
17%
1620
7%
540
37%
540
22%
1133
May1st to 10thNight
30%
540
13%
1620
6%
540
35%
540
18%
1194
May11th to 20thNight
46%
531
16%
1593
11%
531
51%
531
24%
1074
May21st to endNight
56%
583
17%
1745
12%
582
60%
582
30%
1079
June1st to 10thNight
57%
540
18%
1445
14%
540
60%
540
35%
901
June11th to 20thNight
58%
540
21%
1440
14%
540
63%
540
35%
901
June21st to endNight
59%
540
20%
1440
14%
540
64%
540
35%
894
July1st to 10thNight
66%
525
17%
1400
14%
525
68%
525
33%
906
July11th to 20thNight
69%
522
21%
1392
16%
522
71%
522
40%
828
July21st to endNight
67%
591
22%
1609
19%
558
70%
558
38%
959
August1st to 10thNight
70%
537
21%
1600
19%
534
71%
534
36%
923
August11th to 20thNight
69%
534
23%
1642
21%
534
72%
534
34%
962
August21st to endNight
70%
594
22%
1980
22%
594
73%
594
36%
1088
September1st to 10thNight
64%
579
23%
1839
20%
579
68%
579
31%
1105
September11th to 20thNight
65%
720
30%
1980
24%
720
69%
720
40%
1156
September21st to endNight
55%
720
27%
1980
20%
720
59%
720
34%
1218
October1st to 10thNight
51%
720
26%
1980
19%
720
57%
720
37%
1183
October11th to 20thNight
37%
720
23%
2105
15%
720
45%
720
27%
1356
October21st to endNight
31%
792
20%
2574
14%
792
41%
792
22%
1697
November1st to 10thNight
38%
740
24%
2406
17%
740
49%
740
28%
1433
November11th to 20thNight
31%
760
22%
2470
13%
760
44%
760
21%
1608
November21st to endNight
30%
760
17%
2470
11%
760
38%
760
16%
1777
December1st to 10thNight
21%
760
12%
2470
7%
760
29%
760
15%
1849
December11th to 20thNight
24%
854
14%
3120
8%
853
31%
853
13%
2272
December21st to endNight
17%
1037
7%
4859
5%
1026
23%
1026
6%
3992

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
15%9%47%6%35%5%5%7%35%
75000
Night
15%9%47%5%3445%7%37%
75063
TransparencyDay
47%6%12%21%13%2
74710
Night
47%5%11%21%14%2
74874
SeeingDay
18%9%26%24%17%7%
14413
Night
19%8%28%29%14%2
24363

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 10thDay
18%13%6%9%8%5%5%5%5%6%21%
1517
11th to 20thDay
18%14%7%11%7%45%445%21%
1520
21st to endDay
16%17%7%11%6%45%5%5%5%19%
1766
February1st to 10thDay
19%14%7%9%7%35%44424%
1764
11th to 20thDay
16%11%5%11%7%45%446%26%
1748
21st to endDay
18%13%6%9%5%24345%30%
1480
March1st to 10thDay
18%11%5%7%7%35%35%6%31%
1800
11th to 20thDay
19%10%5%7%7%345%5%6%30%
1939
21st to endDay
23%12%5%8%5%35%5%5%6%25%
2225
April1st to 10thDay
15%11%47%6%3445%7%34%
2160
11th to 20thDay
18%9%36%425%5%5%6%37%
2138
21st to endDay
21%8%36%5%34447%34%
2340
May1st to 10thDay
19%9%46%6%35%5%5%7%33%
2340
11th to 20thDay
20%8%36%6%345%5%7%33%
2301
21st to endDay
10%5%36%7%46%6%7%10%35%
2531
June1st to 10thDay
11%6%25%6%35%6%6%8%41%
2510
11th to 20thDay
10%5%36%5%36%5%6%9%44%
2520
21st to endDay
10%5%25%5%35%6%7%9%41%
2520
July1st to 10thDay
11%5%26%5%46%6%7%10%38%
2520
11th to 20thDay
8%4245%35%5%8%11%45%
2520
21st to endDay
10%425%5%36%6%8%10%42%
2613
August1st to 10thDay
9%5%25%6%35%5%7%9%45%
2327
11th to 20thDay
10%5%25%6%46%6%8%10%38%
2255
21st to endDay
8%4345%36%5%7%10%46%
2376
September1st to 10thDay
12%6%36%445%45%7%45%
2102
11th to 20thDay
11%425%4345%7%9%46%
1980
21st to endDay
14%5%2443335%6%50%
1980
October1st to 10thDay
13%5%36%6%24437%48%
1980
11th to 20thDay
14%6%25%435%5%6%7%43%
1852
21st to endDay
21%11%36%5%3345%8%33%
1782
November1st to 10thDay
9%6%35%42445%6%51%
1672
11th to 20thDay
16%11%47%5%3335%6%35%
1710
21st to endDay
20%11%47%5%33347%32%
1710
December1st to 10thDay
20%14%6%10%6%43445%23%
1710
11th to 20thDay
15%16%7%10%5%35%445%27%
2009
21st to endDay
22%21%10%9%6%3433414%
2783
January1st to 10thNight
17%14%6%10%7%35%45%5%25%
2648
11th to 20thNight
18%15%6%11%8%44335%23%
2660
21st to endNight
18%13%6%10%8%45%445%25%
2730
February1st to 10thNight
21%11%6%9%6%4435%426%
2195
11th to 20thNight
15%11%5%9%7%3446%7%30%
2098
21st to endNight
19%12%5%8%6%33445%29%
1776
March1st to 10thNight
17%10%37%5%35%446%37%
2160
11th to 20thNight
15%11%35%6%3435%7%37%
2021
21st to endNight
22%10%47%5%3436%6%32%
2146
April1st to 10thNight
14%8%46%5%35%45%8%38%
1800
11th to 20thNight
16%8%36%5%3445%7%39%
1769
21st to endNight
17%8%46%6%25%5%5%6%35%
1620
May1st to 10thNight
18%9%47%6%35%5%5%6%31%
1620
11th to 20thNight
18%8%345%345%5%7%39%
1592
21st to endNight
9%5%25%6%35%5%6%11%43%
1744
June1st to 10thNight
10%5%246%35%45%7%49%
1445
11th to 20thNight
9%5%25%5%3445%10%48%
1440
21st to endNight
7%325%5%36%6%7%11%45%
1440
July1st to 10thNight
8%5%26%435%5%6%9%45%
1440
11th to 20thNight
7%4244345%5%9%52%
1440
21st to endNight
9%5%25%4345%6%8%50%
1704
August1st to 10thNight
8%414435%6%6%10%49%
1611
11th to 20thNight
6%435%6%35%5%6%8%49%
1642
21st to endNight
6%315%4345%6%9%53%
1980
September1st to 10thNight
11%6%25%43445%8%48%
1839
11th to 20thNight
9%32442445%8%54%
1980
21st to endNight
12%5%25%5%2445%7%50%
1980
October1st to 10thNight
10%425%43435%6%54%
1980
11th to 20thNight
17%7%35%434446%43%
2105
21st to endNight
18%7%35%5%34446%39%
2574
November1st to 10thNight
13%7%36%324446%48%
2406
11th to 20thNight
15%9%46%5%3445%7%38%
2470
21st to endNight
20%12%48%5%34445%31%
2470
December1st to 10thNight
18%12%5%9%7%3445%6%27%
2470
11th to 20thNight
19%13%6%8%6%34446%29%
3184
21st to endNight
23%18%7%9%6%44445%17%
4884

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 10thDay
63%48%16%8%
1518
11th to 20thDay
67%411%13%5%
1520
21st to endDay
66%5%10%14%41
1766
February1st to 10thDay
64%49%13%9%1
1764
11th to 20thDay
59%410%18%8%1
1758
21st to endDay
57%5%9%18%8%2
1480
March1st to 10thDay
55%5%9%21%10%
1800
11th to 20thDay
55%5%13%17%9%1
1939
21st to endDay
59%5%12%18%5%1
2225
April1st to 10thDay
50%6%12%20%13%1
2160
11th to 20thDay
47%5%12%22%11%3
2138
21st to endDay
50%6%12%20%10%3
2340
May1st to 10thDay
50%8%12%21%9%1
2340
11th to 20thDay
50%7%12%17%13%1
2305
21st to endDay
42%9%14%21%14%1
2531
June1st to 10thDay
39%7%12%25%15%3
2510
11th to 20thDay
36%7%12%25%18%2
2520
21st to endDay
37%9%16%20%15%4
2520
July1st to 10thDay
39%9%14%22%14%2
2451
11th to 20thDay
31%9%16%25%17%2
2445
21st to endDay
34%9%17%22%14%3
2468
August1st to 10thDay
34%8%14%29%13%2
2314
11th to 20thDay
37%9%15%24%14%1
2255
21st to endDay
31%9%13%24%16%7%
2376
September1st to 10thDay
39%6%11%22%17%5%
2102
11th to 20thDay
34%6%11%26%20%3
1980
21st to endDay
36%410%26%24%1
1980
October1st to 10thDay
38%5%10%24%21%3
1980
11th to 20thDay
38%5%10%25%18%2
1852
21st to endDay
51%310%21%12%1
1782
November1st to 10thDay
34%413%28%18%3
1672
11th to 20thDay
50%49%20%13%3
1710
21st to endDay
53%410%21%9%2
1710
December1st to 10thDay
63%410%15%7%
1710
11th to 20thDay
60%5%8%19%8%
2006
21st to endDay
74%5%7%9%5%
2783
January1st to 10thNight
61%5%6%17%9%
2648
11th to 20thNight
66%39%15%6%1
2660
21st to endNight
62%5%9%16%8%1
2730
February1st to 10thNight
61%411%16%7%1
2195
11th to 20thNight
54%5%12%17%11%1
2099
21st to endNight
57%5%10%16%9%2
1776
March1st to 10thNight
49%410%21%14%1
2160
11th to 20thNight
47%5%13%22%11%3
2021
21st to endNight
53%5%11%22%8%2
2146
April1st to 10thNight
44%6%10%25%13%2
1800
11th to 20thNight
44%5%10%20%17%5%
1769
21st to endNight
47%7%10%20%12%4
1620
May1st to 10thNight
53%7%10%19%8%3
1620
11th to 20thNight
44%7%13%21%13%2
1593
21st to endNight
34%9%17%23%13%4
1745
June1st to 10thNight
34%5%11%25%20%3
1445
11th to 20thNight
33%7%13%24%19%4
1440
21st to endNight
31%9%15%24%17%4
1440
July1st to 10thNight
35%8%14%21%16%6%
1400
11th to 20thNight
29%7%16%28%18%3
1392
21st to endNight
30%7%14%29%17%3
1609
August1st to 10thNight
28%8%17%28%17%2
1600
11th to 20thNight
31%7%14%27%19%1
1642
21st to endNight
28%7%15%23%22%5%
1980
September1st to 10thNight
35%6%12%22%18%7%
1839
11th to 20thNight
29%6%11%27%25%3
1980
21st to endNight
33%6%10%24%23%3
1980
October1st to 10thNight
31%6%11%26%23%3
1980
11th to 20thNight
42%49%24%20%1
2105
21st to endNight
46%49%23%15%2
2574
November1st to 10thNight
38%410%23%22%3
2406
11th to 20thNight
45%49%22%16%3
2470
21st to endNight
56%410%20%10%1
2470
December1st to 10thNight
58%5%9%17%10%1
2470
11th to 20thNight
57%49%20%10%1
3186
21st to endNight
70%5%9%11%5%
4884

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 10thDay
22%16%36%22%41
270
11th to 20thDay
24%19%34%17%6%
270
21st to endDay
30%15%32%18%41
282
February1st to 10thDay
30%14%37%16%3
240
11th to 20thDay
25%20%34%18%3
240
21st to endDay
26%17%39%16%3
198
March1st to 10thDay
21%21%38%18%3
240
11th to 20thDay
25%14%35%18%7%2
379
21st to endDay
31%13%30%18%7%
462
April1st to 10thDay
20%14%32%22%10%3
420
11th to 20thDay
21%13%30%21%11%4
412
21st to endDay
26%12%34%19%8%2
420
May1st to 10thDay
24%11%31%23%9%4
423
11th to 20thDay
20%7%32%21%15%6%
447
21st to endDay
15%325%25%18%14%
485
June1st to 10thDay
12%425%30%22%6%
620
11th to 20thDay
13%323%29%24%8%
630
21st to endDay
11%5%26%29%21%8%
630
July1st to 10thDay
12%214%26%26%19%
621
11th to 20thDay
8%319%32%23%15%
618
21st to endDay
11%315%26%30%15%
554
August1st to 10thDay
10%211%28%30%18%
446
11th to 20thDay
14%317%26%26%13%
439
21st to endDay
9%312%27%33%15%
495
September1st to 10thDay
12%418%24%31%12%
450
11th to 20thDay
12%113%28%31%16%
450
21st to endDay
16%8%18%23%24%11%
450
October1st to 10thDay
13%5%23%32%18%9%
450
11th to 20thDay
13%14%33%26%13%1
428
21st to endDay
31%11%34%21%3
297
November1st to 10thDay
15%12%32%24%13%4
270
11th to 20thDay
22%14%30%21%10%2
270
21st to endDay
26%9%39%22%4
270
December1st to 10thDay
19%19%38%17%7%1
270
11th to 20thDay
22%14%37%21%41
270
21st to endDay
28%17%35%15%4
297
January1st to 10thNight
24%13%34%23%5%
950
11th to 20thNight
26%13%37%19%3
950
21st to endNight
23%11%37%24%4
886
February1st to 10thNight
27%9%36%25%2
720
11th to 20thNight
21%14%38%24%2
703
21st to endNight
25%10%40%22%3
592
March1st to 10thNight
23%12%35%24%6%
720
11th to 20thNight
22%11%35%25%7%1
720
21st to endNight
25%9%33%26%6%1
760
April1st to 10thNight
16%11%36%29%7%1
540
11th to 20thNight
19%9%32%30%9%1
533
21st to endNight
22%6%39%22%10%1
540
May1st to 10thNight
21%8%34%27%9%1
540
11th to 20thNight
20%424%33%17%3
531
21st to endNight
10%421%38%25%2
584
June1st to 10thNight
11%322%41%23%
540
11th to 20thNight
11%419%41%23%2
540
21st to endNight
8%222%38%28%1
540
July1st to 10thNight
11%211%34%34%8%
525
11th to 20thNight
9%411%39%31%5%
522
21st to endNight
11%211%40%33%3
591
August1st to 10thNight
9%210%40%36%4
537
11th to 20thNight
7%311%40%34%6%
534
21st to endNight
7%312%34%38%6%
594
September1st to 10thNight
14%312%35%32%5%
579
11th to 20thNight
11%214%33%33%7%
720
21st to endNight
13%5%21%35%23%4
720
October1st to 10thNight
11%5%25%32%21%5%
720
11th to 20thNight
19%10%30%27%13%1
720
21st to endNight
22%9%34%25%9%
792
November1st to 10thNight
16%9%34%28%13%1
740
11th to 20thNight
18%14%31%28%7%1
760
21st to endNight
24%11%29%28%8%
760
December1st to 10thNight
24%11%36%23%5%
760
11th to 20thNight
26%7%35%26%5%1
855
21st to endNight
30%14%31%22%4
1045
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