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Carr Astronomical Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Carr Astronomical Observatory clear sky chart from 2005-11-05 to 2015-05-26.

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
30%
12146
10%
37809
7%
12111
34%
12111
13%
29185

By Month

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
JanuaryNight
12%
1343
2%
4235
1%
1343
13%
1343
3%
3871
FebruaryNight
17%
1104
5%
3555
1%
1104
21%
1104
7%
3009
MarchNight
28%
1240
14%
3427
8%
1240
33%
1240
17%
2574
AprilNight
32%
1028
16%
2862
8%
1028
36%
1028
20%
2068
MayNight
48%
723
15%
2524
14%
723
53%
723
23%
1578
JuneNight
50%
540
12%
1960
13%
540
55%
540
21%
1274
JulyNight
60%
630
15%
2011
16%
598
62%
598
29%
1174
AugustNight
58%
850
16%
2514
11%
847
61%
847
29%
1571
SeptemberNight
48%
1077
16%
2869
11%
1077
50%
1077
26%
1974
OctoberNight
27%
1116
10%
3359
7%
1116
32%
1116
12%
2646
NovemberNight
21%
1180
9%
4078
7%
1180
25%
1180
8%
3353
DecemberNight
9%
1315
1%
4415
0%
1315
10%
1315
2%
4093

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
14%10%48%7%35%45%7%28%
38441
Night
14%10%5%8%7%35%5%5%6%26%
37980
Cloud CoverDay
14%9%48%6%35%45%7%28%
38451
Night
14%10%5%8%7%35%5%5%6%27%
37984
TransparencyDay
55%7%11%16%8%
38131
Night
57%8%10%14%7%
37809
SeeingDay
16%7%23%28%17%6%
2614
Night
19%12%28%26%10%1
12155

By Month

Percentage Cloud Cover NE (2006-)
Color Meanings:
Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
MonthOccurrence of each ForecastData
Points
JanuaryDay
10%14%8%16%13%6%7%5%448%
2556
Night
12%14%7%13%12%5%7%5%5%5%8%
4235
FebruaryDay
13%15%8%13%11%5%7%44412%
2524
Night
11%12%6%12%10%5%7%5%6%6%16%
3553
MarchDay
10%11%5%9%7%35%45%6%29%
3381
Night
10%11%5%9%6%35%5%45%32%
3415
AprilDay
16%10%46%5%3435%7%33%
3732
Night
17%8%46%6%34346%34%
2862
MayDay
13%8%25%5%3446%7%38%
4064
Night
12%6%245%345%5%7%41%
2522
JuneDay
14%6%25%5%25%6%6%8%35%
3978
Night
12%5%25%5%26%6%5%8%38%
1960
JulyDay
10%5%25%5%35%47%9%37%
3937
Night
8%323425%46%9%49%
2187
AugustDay
11%5%26%6%35%5%6%8%38%
3603
Night
10%415%4345%5%8%46%
2525
SeptemberDay
20%6%35%5%3435%8%33%
3069
Night
17%5%243235%6%8%39%
2869
OctoberDay
23%12%46%7%35%45%5%21%
2777
Night
21%11%36%6%4445%6%25%
3359
NovemberDay
14%15%6%9%6%46%6%45%18%
2420
Night
16%14%6%8%6%35%5%5%6%19%
4078
DecemberDay
16%18%10%13%9%45%45%5%7%
2400
Night
17%16%9%14%8%46%5%5%47%
4415

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
MonthOccurrence of each ForecastData
Points
JanuaryDay
10%14%7%15%13%6%7%5%448%
2556
Night
12%14%7%13%12%5%7%5%5%5%8%
4235
FebruaryDay
13%15%8%13%11%5%6%44413%
2524
Night
11%12%6%12%10%5%6%5%6%6%16%
3546
MarchDay
10%10%5%9%7%45%45%6%30%
3391
Night
11%11%6%8%6%345%45%32%
3427
AprilDay
16%9%46%5%3435%7%33%
3732
Night
17%8%37%5%34346%34%
2862
MayDay
13%8%25%5%3445%7%38%
4064
Night
13%6%25%4345%5%7%41%
2521
JuneDay
14%5%25%5%25%6%6%8%36%
3978
Night
12%5%25%5%26%5%5%9%38%
1960
JulyDay
10%5%35%5%35%5%7%9%37%
3937
Night
8%2235%25%47%9%48%
2187
AugustDay
11%5%26%6%35%5%5%8%39%
3603
Night
10%4244345%5%7%46%
2525
SeptemberDay
20%6%35%5%3445%8%33%
3069
Night
17%5%2432446%8%39%
2869
OctoberDay
22%12%46%6%35%45%5%21%
2777
Night
21%11%35%6%35%45%6%25%
3359
NovemberDay
14%16%7%9%6%45%6%5%5%18%
2420
Night
16%14%6%9%5%35%5%6%6%20%
4078
DecemberDay
16%18%10%13%8%4445%5%8%
2400
Night
17%15%9%13%8%46%5%5%48%
4415

Transparency (when cloud cover <= 30%)
Color Meanings:
Too cloudy to forecast Poor Below Average Average Above average Transparent
MonthOccurrence of each ForecastData
Points
JanuaryDay
79%6%6%41
2557
Night
78%9%6%41
4235
FebruaryDay
75%5%7%7%3
2526
Night
69%8%9%8%3
3555
MarchDay
55%6%11%15%9%1
3392
Night
53%7%9%17%10%1
3427
AprilDay
51%5%9%20%12%1
3732
Night
52%49%17%15%
2862
MayDay
44%6%11%22%13%1
4068
Night
41%6%12%24%13%2
2524
JuneDay
44%8%14%20%11%
3978
Night
41%8%13%21%13%
1960
JulyDay
42%8%14%21%11%1
3622
Night
31%9%14%26%16%1
2011
AugustDay
42%8%15%21%11%1
3590
Night
35%7%15%25%14%
2514
SeptemberDay
50%6%12%22%6%1
3069
Night
41%9%14%26%8%
2869
OctoberDay
64%7%9%11%6%
2777
Night
59%8%10%13%7%
3359
NovemberDay
68%8%8%10%3
2420
Night
64%9%10%10%3
4078
DecemberDay
82%7%6%3
2400
Night
81%8%6%2
4415

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
MonthOccurrence of each ForecastData
Points
JanuaryNight
18%21%33%19%5%
1348
FebruaryNight
17%16%37%22%5%
1107
MarchDay
16%8%31%30%12%1
292
Night
16%12%34%25%9%1
1240
AprilDay
21%11%28%21%14%3
300
Night
22%10%29%27%10%
1028
MayDay
16%8%22%25%19%7%
350
Night
15%423%37%16%2
724
JuneDay
14%5%22%34%17%4
468
Night
14%422%36%20%
540
JulyDay
10%5%22%31%19%9%
392
Night
8%321%42%20%3
630
AugustDay
12%216%29%25%13%
277
Night
13%318%36%25%3
850
SeptemberDay
20%7%20%23%17%10%
269
Night
19%5%21%31%15%7%
1077
OctoberDay
25%14%25%24%9%1
266
Night
27%13%25%21%9%1
1116
NovemberNight
24%18%29%18%7%
1180
DecemberNight
24%21%34%15%2
1315
Page generated at 2015-05-27 12:02:43. Version ac04

Copyright 2015 A. Danko


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