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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 2016-11-15.

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
32%
13958
10%
43452
8%
13923
35%
13923
14%
33027

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%
1478
3%
4661
1%
1478
14%
1478
3%
4225
FebruaryNight
17%
1220
5%
3927
2%
1220
21%
1220
7%
3324
MarchNight
29%
1364
14%
3769
8%
1364
34%
1364
17%
2825
AprilNight
33%
1131
16%
3148
8%
1131
37%
1131
20%
2258
MayNight
50%
807
15%
2824
15%
807
55%
807
24%
1749
JuneNight
51%
660
12%
2395
14%
660
56%
660
22%
1496
JulyNight
60%
775
15%
2498
16%
743
62%
743
31%
1426
AugustNight
60%
1036
17%
3066
12%
1033
62%
1033
30%
1905
SeptemberNight
52%
1317
17%
3507
11%
1317
54%
1317
28%
2363
OctoberNight
27%
1364
10%
4106
7%
1364
31%
1364
12%
3227
NovemberNight
22%
1360
10%
4695
8%
1360
26%
1360
9%
3765
DecemberNight
9%
1446
2%
4856
1%
1446
10%
1446
3%
4464

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%47%6%35%45%7%29%
44630
Night
14%10%48%7%35%5%5%6%28%
43623
Cloud CoverDay
14%9%47%6%35%5%5%7%29%
44640
Night
14%10%48%7%35%5%5%6%28%
43627
TransparencyDay
54%7%11%16%9%
44320
Night
56%8%10%15%8%
43452
SeeingDay
17%7%24%28%16%5%
4624
Night
19%12%28%26%11%1
13967

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%7%16%13%6%7%5%448%
2812
Night
11%14%7%14%12%5%7%5%5%5%8%
4661
FebruaryDay
13%15%8%13%10%5%6%5%4412%
2789
Night
11%13%6%12%11%5%7%5%5%6%15%
3925
MarchDay
11%11%5%9%7%35%45%6%29%
3721
Night
12%10%5%8%5%345%45%32%
3757
AprilDay
15%11%46%5%3435%6%33%
4107
Night
17%8%46%6%34346%34%
3148
MayDay
13%8%25%5%2445%7%38%
4559
Night
12%6%25%4345%5%7%42%
2822
JuneDay
14%6%25%5%35%6%6%9%36%
4862
Night
12%5%25%5%25%5%5%8%41%
2395
JulyDay
10%5%25%5%35%5%6%9%39%
4813
Night
8%323425%46%8%50%
2674
AugustDay
11%5%26%6%35%5%6%8%38%
4391
Night
9%415%4345%5%8%47%
3077
SeptemberDay
18%6%35%5%3445%8%35%
3751
Night
15%5%2432345%8%42%
3507
OctoberDay
22%13%46%7%3445%5%22%
3394
Night
20%12%36%6%345%46%26%
4106
NovemberDay
14%15%6%9%6%46%5%5%5%20%
2791
Night
16%13%5%8%6%35%5%6%6%22%
4695
DecemberDay
16%18%10%13%9%45%45%5%8%
2640
Night
16%15%9%13%8%46%5%5%48%
4856

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
9%14%7%15%13%6%7%5%448%
2812
Night
12%13%7%14%12%5%7%5%5%6%9%
4661
FebruaryDay
13%15%7%12%11%5%6%5%4413%
2789
Night
11%13%6%12%10%5%7%5%5%6%16%
3918
MarchDay
11%11%5%9%7%35%45%6%29%
3731
Night
12%11%6%8%6%345%45%32%
3769
AprilDay
16%10%46%5%2435%7%33%
4107
Night
17%8%37%5%34346%35%
3148
MayDay
13%8%25%42446%7%39%
4559
Night
12%6%25%4245%5%7%42%
2821
JuneDay
14%5%25%5%25%6%6%9%37%
4862
Night
12%5%25%5%25%5%5%8%41%
2395
JulyDay
10%425%5%35%5%6%9%40%
4813
Night
8%3235%2446%8%50%
2674
AugustDay
11%5%26%5%35%5%6%9%39%
4391
Night
9%4244345%5%7%47%
3077
SeptemberDay
18%6%25%5%3445%8%35%
3751
Night
15%5%2432446%7%42%
3507
OctoberDay
21%13%46%6%35%45%5%22%
3394
Night
21%12%35%6%345%5%6%25%
4106
NovemberDay
14%15%6%8%6%45%6%5%6%20%
2791
Night
16%13%5%8%5%35%5%6%6%22%
4695
DecemberDay
16%18%10%12%8%45%45%5%8%
2640
Night
17%15%9%13%8%46%5%5%48%
4856

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%5%1
2813
Night
77%9%7%41
4661
FebruaryDay
74%6%8%8%3
2791
Night
69%8%9%8%3
3927
MarchDay
56%6%11%15%10%1
3732
Night
53%7%9%17%10%1
3769
AprilDay
51%49%20%12%1
4107
Night
51%49%17%15%1
3148
MayDay
44%6%11%22%14%1
4563
Night
40%6%12%23%15%2
2824
JuneDay
42%7%14%21%13%
4862
Night
40%7%12%23%15%
2395
JulyDay
39%8%13%23%12%1
4498
Night
30%8%13%26%19%1
2498
AugustDay
41%8%15%21%11%
4378
Night
35%8%15%25%14%1
3066
SeptemberDay
48%6%12%23%7%
3751
Night
39%8%14%26%10%
3507
OctoberDay
63%7%10%11%6%
3394
Night
59%8%10%13%7%
4106
NovemberDay
66%7%10%10%4
2791
Night
62%9%11%11%41
4695
DecemberDay
81%7%6%3
2640
Night
80%8%7%3
4856

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
JanuaryDay
11%20%41%23%2
81
Night
18%21%34%19%5%
1483
FebruaryDay
29%12%37%19%
87
Night
18%16%36%23%4
1223
MarchDay
19%9%31%27%10%1
415
Night
18%12%33%25%9%1
1364
AprilDay
22%9%28%21%13%5%
420
Night
22%10%28%27%10%
1131
MayDay
17%6%22%26%20%6%
495
Night
15%323%37%17%2
808
JuneDay
16%5%23%32%19%3
752
Night
14%421%38%20%
660
JulyDay
9%422%35%19%8%
670
Night
7%321%42%22%3
775
AugustDay
12%218%32%23%11%
521
Night
12%217%36%26%3
1036
SeptemberDay
16%5%20%26%21%9%
509
Night
18%5%19%32%16%7%
1317
OctoberDay
27%14%25%22%8%1
511
Night
28%13%26%21%8%1
1364
NovemberDay
20%12%30%22%10%1
101
Night
23%17%30%19%8%
1360
DecemberDay
22%25%30%19%1
62
Night
24%21%35%16%2
1446
Page generated at 2016-11-16 12:29:37. Version ac04

Copyright 2016 A. Danko


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