Cape Cod Imaging Station
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cape Cod Imaging Station clear sky chart from 2005-11-05 to 2018-02-14.

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
34%
15579
16%
48734
9%
15542
42%
15542
19%
33267

By Month

MonthDays of 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
January1st to 15thNight
19%
780
15%
2716
5%
776
32%
776
15%
1866
January16th to endNight
15%
832
15%
2868
4%
832
30%
832
12%
2012
February1st to 15thNight
17%
760
14%
2359
3%
757
31%
757
14%
1691
February16th to endNight
21%
631
21%
1893
6%
631
39%
631
19%
1279
March1st to 15thNight
24%
720
16%
2121
8%
720
35%
720
19%
1499
March16th to endNight
27%
768
19%
2085
8%
768
37%
768
21%
1461
April1st to 15thNight
31%
718
17%
1796
5%
718
37%
718
24%
1280
April16th to endNight
36%
561
17%
1641
8%
561
41%
561
21%
1145
May1st to 15thNight
33%
540
14%
1620
8%
540
39%
540
20%
1156
May16th to endNight
40%
499
10%
1621
8%
498
43%
498
17%
1171
June1st to 15thNight
39%
360
10%
1440
12%
360
44%
360
13%
1017
June16th to endNight
55%
360
11%
1440
16%
360
57%
360
21%
883
July1st to 15thNight
53%
340
12%
1360
17%
340
56%
340
21%
833
July16th to endNight
53%
415
14%
1454
17%
390
54%
390
18%
956
August1st to 15thNight
61%
539
16%
1608
11%
535
63%
535
29%
1027
August16th to endNight
63%
679
21%
1825
14%
679
64%
679
32%
1183
September1st to 15thNight
54%
720
19%
1899
12%
720
57%
720
32%
1232
September16th to endNight
50%
717
23%
1980
17%
717
54%
717
29%
1302
October1st to 15thNight
39%
720
19%
2016
12%
720
46%
720
23%
1370
October16th to endNight
31%
768
17%
2460
10%
768
41%
768
20%
1641
November1st to 15thNight
34%
760
13%
2472
10%
760
40%
760
17%
1712
November16th to endNight
28%
780
19%
2535
9%
780
40%
780
19%
1640
December1st to 15thNight
21%
780
16%
2613
5%
780
33%
780
14%
1829
December16th to endNight
15%
832
16%
2912
4%
832
29%
832
12%
2082

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
17%7%25%42445%7%39%
49343
Night
17%8%35%5%2445%7%35%
48909
Cloud CoverDay
17%7%25%424447%38%
49353
Night
17%8%35%5%2445%7%35%
48914
TransparencyDay
45%5%11%22%13%1
49036
Night
48%410%21%13%1
48734
SeeingDay
21%5%24%28%15%3
6479
Night
21%9%27%27%12%1
15579

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
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
17%9%46%424447%34%
1552
16th to endDay
18%10%36%6%2345%5%34%
1706
February1st to 15thDay
19%8%45%6%34448%30%
1800
16th to endDay
15%8%36%5%24347%36%
1580
March1st to 15thDay
19%8%25%5%3335%8%33%
1829
16th to endDay
17%7%35%413446%40%
2137
April1st to 15thDay
18%7%3432335%6%41%
2152
16th to endDay
17%7%25%423346%42%
2318
May1st to 15thDay
24%7%35%423437%34%
2332
16th to endDay
14%7%25%42435%8%39%
2502
June1st to 15thDay
24%6%2442445%8%32%
2520
16th to endDay
13%5%245%3445%9%41%
2520
July1st to 15thDay
12%5%244245%5%8%43%
2520
16th to endDay
13%5%25%5%35%5%6%8%39%
2603
August1st to 15thDay
12%5%25%43345%8%44%
2340
16th to endDay
11%5%2442335%8%47%
2375
September1st to 15thDay
14%5%24434446%47%
2061
16th to endDay
16%6%15%413347%45%
1980
October1st to 15thDay
19%5%24423346%42%
1944
16th to endDay
16%5%36%423346%42%
1763
November1st to 15thDay
22%8%34422346%35%
1716
16th to endDay
16%8%245%235%5%7%38%
1755
December1st to 15thDay
19%7%47%5%34346%32%
1674
16th to endDay
22%13%37%433345%28%
1664
January1st to 15thNight
18%8%47%6%245%47%31%
2716
16th to endNight
19%11%37%5%24346%30%
2868
February1st to 15thNight
18%10%37%6%245%46%30%
2358
16th to endNight
15%9%36%5%33346%37%
1893
March1st to 15thNight
19%8%26%6%2345%7%33%
2108
16th to endNight
16%9%36%434346%37%
2085
April1st to 15thNight
19%10%34424445%37%
1796
16th to endNight
20%8%25%6%24345%36%
1641
May1st to 15thNight
20%9%46%424346%32%
1620
16th to endNight
18%9%36%425%5%5%6%31%
1619
June1st to 15thNight
23%9%35%43445%7%28%
1440
16th to endNight
17%6%25%31436%9%38%
1440
July1st to 15thNight
14%7%245%35%45%9%37%
1440
16th to endNight
13%6%37%5%35%6%7%7%33%
1553
August1st to 15thNight
8%6%25%425%6%7%8%41%
1620
16th to endNight
11%5%2442445%8%45%
1825
September1st to 15thNight
13%4245%2435%7%45%
1899
16th to endNight
13%7%25%423446%44%
1980
October1st to 15thNight
18%7%245%24345%40%
2016
16th to endNight
18%6%35%43345%7%37%
2460
November1st to 15thNight
20%7%35%5%34445%35%
2472
16th to endNight
16%7%25%5%2335%7%39%
2535
December1st to 15thNight
20%7%36%6%34346%31%
2613
16th to endNight
19%10%36%5%35%5%47%27%
2912

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
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
17%9%37%433347%35%
1552
16th to endDay
18%10%25%5%34445%33%
1706
February1st to 15thDay
19%8%35%6%35%45%7%30%
1800
16th to endDay
15%7%46%5%34446%36%
1580
March1st to 15thDay
19%8%35%5%3445%8%32%
1839
16th to endDay
18%7%35%424345%40%
2137
April1st to 15thDay
18%6%35%323446%40%
2152
16th to endDay
17%7%25%424346%41%
2318
May1st to 15thDay
24%7%25%5%23337%32%
2332
16th to endDay
15%7%25%434447%39%
2502
June1st to 15thDay
24%7%35%42445%7%31%
2520
16th to endDay
13%5%24435%45%9%40%
2520
July1st to 15thDay
12%6%145%25%45%8%42%
2520
16th to endDay
13%5%25%5%245%6%10%37%
2603
August1st to 15thDay
12%5%245%3435%8%43%
2340
16th to endDay
11%42442435%8%46%
2375
September1st to 15thDay
13%5%24424436%46%
2061
16th to endDay
16%7%2342335%7%44%
1980
October1st to 15thDay
19%5%24423346%41%
1944
16th to endDay
15%5%26%425%346%41%
1763
November1st to 15thDay
22%8%345%2335%5%35%
1716
16th to endDay
17%6%26%424448%37%
1755
December1st to 15thDay
18%8%5%6%5%35%337%32%
1674
16th to endDay
23%10%37%5%24336%28%
1664
January1st to 15thNight
17%8%36%6%34448%31%
2716
16th to endNight
19%10%37%43435%6%31%
2868
February1st to 15thNight
18%9%36%5%35%5%46%30%
2351
16th to endNight
14%9%36%5%34346%38%
1893
March1st to 15thNight
19%7%35%6%2445%6%33%
2121
16th to endNight
16%8%46%424445%37%
2084
April1st to 15thNight
19%11%35%41335%5%36%
1796
16th to endNight
20%7%26%6%24346%35%
1641
May1st to 15thNight
21%10%35%5%23346%33%
1620
16th to endNight
19%10%36%5%35%446%31%
1619
June1st to 15thNight
24%10%35%3235%5%6%28%
1440
16th to endNight
18%7%2432345%10%37%
1440
July1st to 15thNight
15%8%34434449%37%
1440
16th to endNight
13%6%46%5%36%6%6%7%33%
1553
August1st to 15thNight
9%6%24435%5%6%9%41%
1620
16th to endNight
12%6%244245%47%44%
1825
September1st to 15thNight
14%5%25%424448%44%
1899
16th to endNight
14%8%25%42335%6%43%
1980
October1st to 15thNight
19%7%245%24345%40%
2016
16th to endNight
18%6%245%245%5%6%37%
2460
November1st to 15thNight
19%7%35%5%2445%5%35%
2472
16th to endNight
17%6%25%42445%8%38%
2535
December1st to 15thNight
20%8%36%5%2435%6%32%
2613
16th to endNight
20%9%36%5%3446%7%28%
2912

Transparency (when cloud cover <= 30%)
Color Meanings:
Too cloudy to forecast Poor Below Average Average Above average Transparent
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
49%5%11%20%10%2
1553
16th to endDay
52%411%21%9%
1706
February1st to 15thDay
53%412%19%9%1
1803
16th to endDay
48%313%20%12%1
1580
March1st to 15thDay
50%414%21%8%1
1839
16th to endDay
46%310%22%14%2
2137
April1st to 15thDay
43%39%22%17%2
2152
16th to endDay
43%49%24%15%2
2318
May1st to 15thDay
52%5%7%17%13%2
2332
16th to endDay
43%6%13%22%11%1
2506
June1st to 15thDay
51%6%10%20%10%
2520
16th to endDay
40%5%14%22%15%
2520
July1st to 15thDay
38%6%14%24%14%1
2371
16th to endDay
39%6%15%23%12%2
2440
August1st to 15thDay
38%5%15%24%14%1
2327
16th to endDay
35%5%11%26%18%1
2375
September1st to 15thDay
38%5%9%22%21%1
2061
16th to endDay
39%5%8%25%18%2
1980
October1st to 15thDay
43%49%25%14%2
1944
16th to endDay
43%411%25%13%1
1763
November1st to 15thDay
50%412%19%10%1
1716
16th to endDay
45%5%13%22%11%1
1755
December1st to 15thDay
53%414%16%11%
1674
16th to endDay
58%311%18%6%
1664
January1st to 15thNight
51%413%19%10%
2716
16th to endNight
54%310%19%10%
2868
February1st to 15thNight
54%410%20%9%
2359
16th to endNight
48%310%23%13%1
1893
March1st to 15thNight
51%312%19%12%1
2121
16th to endNight
48%48%18%16%3
2085
April1st to 15thNight
49%28%20%15%2
1796
16th to endNight
50%48%19%13%3
1641
May1st to 15thNight
52%410%17%13%2
1620
16th to endNight
52%6%11%18%8%2
1621
June1st to 15thNight
54%6%9%17%11%
1440
16th to endNight
42%6%12%22%15%
1440
July1st to 15thNight
43%411%25%13%
1360
16th to endNight
46%7%11%25%7%2
1454
August1st to 15thNight
37%7%13%25%15%1
1608
16th to endNight
36%7%11%25%18%1
1825
September1st to 15thNight
38%5%10%26%17%1
1899
16th to endNight
41%46%21%24%1
1980
October1st to 15thNight
46%48%23%14%2
2016
16th to endNight
45%5%11%22%13%1
2460
November1st to 15thNight
50%5%11%19%12%1
2472
16th to endNight
44%412%23%12%2
2535
December1st to 15thNight
53%313%19%9%
2613
16th to endNight
55%411%18%9%
2912

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
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
17%13%42%18%7%
90
16th to endDay
26%16%31%22%2
138
February1st to 15thDay
27%11%34%23%1
301
16th to endDay
16%9%43%22%7%
239
March1st to 15thDay
23%12%34%24%5%
270
16th to endDay
22%12%33%23%7%
288
April1st to 15thDay
22%7%33%30%6%
270
16th to endDay
23%332%28%9%2
270
May1st to 15thDay
32%224%22%14%3
288
16th to endDay
21%120%36%17%2
331
June1st to 15thDay
27%217%31%19%1
315
16th to endDay
15%220%39%19%3
315
July1st to 15thDay
19%11%38%27%3
305
16th to endDay
12%212%38%28%5%
326
August1st to 15thDay
15%112%36%27%7%
313
16th to endDay
12%10%36%27%12%
332
September1st to 15thDay
17%121%30%21%7%
315
16th to endDay
25%218%23%17%13%
314
October1st to 15thDay
23%5%19%23%21%5%
306
16th to endDay
17%7%34%24%13%2
288
November1st to 15thDay
23%7%27%27%12%2
280
16th to endDay
19%14%27%27%11%1
285
December1st to 15thDay
22%10%34%25%8%
204
16th to endDay
29%16%36%14%3
96
January1st to 15thNight
22%16%37%19%3
780
16th to endNight
26%17%34%19%2
832
February1st to 15thNight
22%15%38%21%1
760
16th to endNight
19%16%37%22%3
631
March1st to 15thNight
23%11%34%23%6%
720
16th to endNight
21%13%31%23%9%
768
April1st to 15thNight
23%6%32%31%5%
718
16th to endNight
23%5%27%29%12%1
561
May1st to 15thNight
24%428%28%11%2
540
16th to endNight
23%421%35%14%1
499
June1st to 15thNight
28%5%18%31%15%1
360
16th to endNight
21%311%39%23%
360
July1st to 15thNight
20%116%40%21%
340
16th to endNight
16%113%38%27%1
415
August1st to 15thNight
11%16%43%25%2
539
16th to endNight
15%211%35%30%4
679
September1st to 15thNight
15%217%39%21%3
720
16th to endNight
18%5%16%28%24%6%
717
October1st to 15thNight
23%6%23%26%16%2
720
16th to endNight
23%10%30%24%9%1
768
November1st to 15thNight
23%10%25%25%13%1
760
16th to endNight
22%13%29%24%8%1
780
December1st to 15thNight
24%15%32%21%6%
780
16th to endNight
25%15%37%18%1
832
Page generated at 2018-02-15 10:58:43. Version ac04

Copyright 2018 A. Danko


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