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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 2014-06-18.

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%
10918
10%
34011
7%
10883
33%
10883
13%
26358

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
10%
1208
2%
3810
1%
1208
12%
1208
2%
3525
FebruaryNight
15%
992
4%
3195
1%
992
19%
992
6%
2732
MarchNight
29%
1116
15%
3084
9%
1116
34%
1116
17%
2332
AprilNight
31%
925
15%
2575
8%
925
35%
925
19%
1861
MayNight
48%
658
15%
2303
15%
658
53%
658
23%
1447
JuneNight
49%
514
12%
1870
14%
514
54%
514
20%
1225
JulyNight
61%
557
17%
1767
18%
525
63%
525
30%
1026
AugustNight
57%
755
17%
2233
12%
752
60%
752
30%
1397
SeptemberNight
48%
957
15%
2550
10%
957
50%
957
25%
1769
OctoberNight
27%
992
10%
2986
7%
992
31%
992
12%
2359
NovemberNight
22%
1060
10%
3664
8%
1060
25%
1060
8%
2993
DecemberNight
8%
1184
1%
3974
0%
1184
9%
1184
2%
3692

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%7%35%45%7%28%
34701
Night
14%10%5%8%7%35%5%5%6%26%
34182
Cloud CoverDay
14%10%48%6%35%45%7%28%
34711
Night
14%10%5%8%7%35%5%5%6%26%
34186
TransparencyDay
56%7%10%16%8%
34391
Night
58%8%10%14%7%
34011
SeeingDay
16%7%23%28%17%6%
2317
Night
19%12%29%26%10%1
10927

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%15%8%16%13%6%7%5%347%
2300
Night
13%14%7%14%12%5%7%5%5%5%7%
3810
FebruaryDay
13%16%9%13%11%5%6%44412%
2268
Night
11%12%6%12%10%5%7%5%6%6%15%
3193
MarchDay
11%11%5%9%7%45%45%6%29%
3042
Night
11%11%6%8%6%35%5%45%32%
3072
AprilDay
16%10%46%5%2435%7%32%
3359
Night
17%8%46%6%34346%34%
2575
MayDay
14%8%25%5%2446%7%38%
3716
Night
13%6%245%345%5%7%40%
2301
JuneDay
14%6%25%5%25%6%6%8%35%
3784
Night
12%5%25%5%26%6%5%8%38%
1870
JulyDay
11%5%25%5%36%47%10%37%
3499
Night
8%323425%47%9%48%
1943
AugustDay
12%5%26%6%35%45%8%39%
3203
Night
10%415%43445%7%47%
2244
SeptemberDay
20%6%35%5%3445%8%32%
2728
Night
17%5%243245%6%8%38%
2550
OctoberDay
23%12%46%7%35%445%22%
2468
Night
22%11%36%6%3445%6%25%
2986
NovemberDay
14%15%7%8%7%46%5%45%19%
2174
Night
16%14%6%8%6%35%5%5%6%20%
3664
DecemberDay
16%17%10%12%9%45%45%5%7%
2160
Night
17%15%9%13%8%46%5%5%47%
3974

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%15%8%16%13%6%7%5%447%
2300
Night
13%14%7%14%12%5%7%5%5%5%7%
3810
FebruaryDay
13%16%8%13%11%5%5%44412%
2268
Night
11%13%6%12%10%5%6%5%6%6%15%
3186
MarchDay
11%10%5%9%7%35%45%6%29%
3052
Night
11%11%6%8%6%345%45%32%
3084
AprilDay
17%9%45%5%2445%6%33%
3359
Night
17%8%46%5%24346%34%
2575
MayDay
14%8%25%5%2446%7%38%
3716
Night
13%6%25%4345%5%7%41%
2300
JuneDay
14%5%26%5%25%6%6%8%36%
3784
Night
12%5%25%5%26%5%5%8%38%
1870
JulyDay
10%5%25%5%35%5%7%9%37%
3499
Night
8%223425%47%9%48%
1943
AugustDay
11%5%26%6%35%45%8%39%
3203
Night
10%41443445%7%47%
2244
SeptemberDay
20%6%35%6%3445%8%32%
2728
Night
17%5%243245%6%8%38%
2550
OctoberDay
23%12%46%6%3445%5%22%
2468
Night
22%10%45%6%3445%6%25%
2986
NovemberDay
14%15%7%9%6%46%5%5%5%19%
2174
Night
17%14%6%9%5%35%5%6%6%21%
3664
DecemberDay
16%17%10%12%8%4445%5%8%
2160
Night
17%15%9%13%8%46%5%5%47%
3974

Transparency (when cloud cover <= 30%)
Color Meanings:
Too cloudy to forecast Poor Below Average Average Above average Transparent
MonthOccurrence of each ForecastData
Points
JanuaryDay
81%6%7%4
2301
Night
79%9%6%4
3810
FebruaryDay
76%6%7%7%2
2270
Night
70%8%10%8%2
3195
MarchDay
55%6%12%15%8%
3053
Night
54%7%10%18%9%
3084
AprilDay
51%5%9%20%11%1
3359
Night
51%49%17%15%
2575
MayDay
45%6%11%21%13%1
3720
Night
41%6%12%24%13%2
2303
JuneDay
44%8%13%20%11%
3784
Night
42%9%13%21%12%
1870
JulyDay
42%9%14%20%12%1
3184
Night
30%9%14%26%17%1
1767
AugustDay
42%7%13%21%12%1
3190
Night
36%7%14%26%15%1
2233
SeptemberDay
50%7%12%21%7%1
2728
Night
42%9%14%25%8%
2550
OctoberDay
64%6%9%11%6%
2468
Night
60%7%10%13%7%
2986
NovemberDay
68%7%9%10%4
2174
Night
64%9%10%11%31
3664
DecemberDay
81%8%6%3
2160
Night
81%8%6%2
3974

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
19%20%35%19%4
1213
FebruaryNight
18%17%37%21%4
995
MarchDay
17%7%29%31%12%1
263
Night
17%11%34%25%10%1
1116
AprilDay
22%11%27%21%13%2
270
Night
22%10%30%26%9%
925
MayDay
16%7%20%26%21%7%
274
Night
15%324%38%15%2
659
JuneDay
14%6%23%34%17%4
443
Night
14%423%36%20%
514
JulyDay
10%5%21%33%19%9%
346
Night
7%320%43%20%3
557
AugustDay
13%217%29%24%13%
246
Night
13%318%37%23%2
755
SeptemberDay
19%7%22%23%17%9%
239
Night
19%6%21%32%14%6%
957
OctoberDay
25%13%25%24%9%1
236
Night
28%13%25%21%9%1
992
NovemberNight
24%18%28%19%8%
1060
DecemberNight
24%21%34%16%2
1184
Page generated at 2014-06-18 17:01:34. Version ac04

Copyright 2014 A. Danko


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