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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 2016-01-22.

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%
12973
10%
40435
7%
12938
34%
12938
13%
31037

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%
1442
3%
4543
2%
1442
14%
1442
3%
4122
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%
702
15%
2254
16%
670
63%
670
31%
1287
AugustNight
59%
941
16%
2785
11%
938
61%
938
29%
1741
SeptemberNight
50%
1197
16%
3187
11%
1197
52%
1197
26%
2180
OctoberNight
27%
1240
10%
3732
7%
1240
31%
1240
12%
2937
NovemberNight
22%
1300
10%
4492
8%
1300
25%
1300
8%
3644
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%48%7%35%45%7%28%
41090
Night
14%10%5%8%7%35%5%5%6%27%
40606
Cloud CoverDay
14%9%48%6%35%5%5%7%28%
41100
Night
14%10%5%8%7%35%5%5%6%27%
40610
TransparencyDay
55%7%11%16%8%
40780
Night
57%8%10%14%8%
40435
SeeingDay
17%7%23%27%17%6%
3459
Night
19%12%28%26%11%1
12982

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%
2727
Night
12%14%7%14%12%5%7%5%5%5%8%
4543
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%47%9%39%
4375
Night
8%313425%46%8%50%
2430
AugustDay
11%5%26%6%35%5%6%8%38%
3991
Night
9%415%4345%5%8%46%
2796
SeptemberDay
19%6%35%5%3435%8%34%
3411
Night
16%5%243235%6%8%40%
3187
OctoberDay
22%13%46%7%35%45%6%21%
3086
Night
21%11%36%6%4445%6%26%
3732
NovemberDay
14%15%6%9%6%46%5%5%5%19%
2666
Night
16%13%6%8%6%35%5%5%6%21%
4492
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%16%13%6%7%5%448%
2727
Night
12%13%7%13%12%5%7%5%5%5%9%
4543
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%425%5%35%5%7%9%39%
4375
Night
8%22342447%9%50%
2430
AugustDay
11%5%26%6%35%5%6%8%39%
3991
Night
10%4244345%5%7%46%
2796
SeptemberDay
19%6%35%5%3445%8%34%
3411
Night
16%5%243245%6%7%40%
3187
OctoberDay
21%13%46%6%35%45%6%21%
3086
Night
21%11%35%6%345%5%6%25%
3732
NovemberDay
14%15%6%9%6%45%6%5%5%19%
2666
Night
16%13%6%8%5%35%5%6%6%21%
4492
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%41
2728
Night
77%9%7%41
4543
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
40%8%14%23%12%1
4060
Night
30%8%14%26%18%1
2254
AugustDay
41%8%15%21%11%
3978
Night
35%7%16%25%13%
2785
SeptemberDay
49%6%13%23%6%
3411
Night
40%9%14%25%9%
3187
OctoberDay
63%7%10%11%6%
3086
Night
59%8%10%13%7%
3732
NovemberDay
66%8%9%10%4
2666
Night
63%9%11%10%41
4492
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
7%15%50%21%5%
52
Night
18%21%34%19%5%
1447
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
9%421%32%21%10%
531
Night
7%321%41%22%3
702
AugustDay
13%216%32%22%12%
397
Night
12%218%36%26%3
941
SeptemberDay
19%6%19%22%22%10%
389
Night
18%5%20%31%16%7%
1197
OctoberDay
24%14%28%23%7%1
389
Night
27%13%26%21%8%1
1240
NovemberDay
19%19%25%22%12%
66
Night
23%18%29%19%8%
1300
DecemberDay
22%25%30%19%1
62
Night
24%21%35%16%2
1446
Page generated at 2016-01-23 06:47:45. Version ac04

Copyright 2016 A. Danko


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