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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 2015-07-24.

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
31%
12267
10%
38247
7%
12232
34%
12232
13%
29430

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%
733
15%
2564
14%
733
53%
733
23%
1608
JuneNight
50%
600
12%
2178
13%
600
54%
600
21%
1403
JulyNight
60%
681
15%
2191
17%
649
62%
649
30%
1260
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%
39296
Night
14%10%5%8%7%35%5%5%6%27%
38418
Cloud CoverDay
14%9%48%6%35%5%5%7%28%
39306
Night
14%10%5%8%7%35%5%5%6%27%
38422
TransparencyDay
55%7%11%16%8%
38986
Night
57%8%10%14%7%
38247
SeeingDay
17%7%23%28%17%6%
2886
Night
19%12%28%26%10%1
12276

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
14%8%25%5%2446%7%38%
4137
Night
13%6%245%345%5%7%41%
2562
JuneDay
15%6%25%5%25%6%6%8%35%
4420
Night
12%5%26%5%25%5%5%8%39%
2178
JulyDay
10%5%25%5%35%5%7%9%38%
4277
Night
8%323425%46%8%49%
2367
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%
4137
Night
13%6%25%5%345%5%7%41%
2561
JuneDay
15%5%26%5%25%6%6%8%35%
4420
Night
12%5%26%5%26%5%5%8%39%
2178
JulyDay
10%5%25%5%35%5%7%9%39%
4277
Night
8%2235%2446%9%49%
2367
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
45%6%11%22%13%1
4141
Night
41%6%12%24%13%1
2564
JuneDay
45%8%14%20%11%
4420
Night
41%8%12%22%13%
2178
JulyDay
41%8%14%22%12%1
3962
Night
30%8%14%26%17%1
2191
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%26%19%7%
371
Night
15%424%37%16%2
734
JuneDay
17%5%22%32%18%3
610
Night
15%422%38%19%1
600
JulyDay
10%5%21%32%20%10%
501
Night
8%321%42%21%3
681
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 2015-07-25 08:51:15. Version ac04

Copyright 2015 A. Danko


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