Colebrook
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Colebrook clear sky chart from 2005-11-05 to 2017-12-04.

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
26%
15232
19%
47807
7%
15201
39%
15201
19%
30875

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
15%
720
20%
2506
7%
716
32%
716
13%
1599
January16th to endNight
13%
768
19%
2661
4%
768
33%
768
12%
1713
February1st to 15thNight
12%
704
16%
2208
3%
701
28%
701
12%
1486
February16th to endNight
15%
631
23%
1893
6%
631
36%
631
15%
1251
March1st to 15thNight
15%
720
17%
2160
5%
720
29%
720
15%
1442
March16th to endNight
19%
768
24%
2002
6%
768
32%
768
19%
1304
April1st to 15thNight
16%
718
16%
1796
2%
718
25%
718
18%
1301
April16th to endNight
22%
653
18%
1733
3%
653
32%
653
22%
1177
May1st to 15thNight
22%
513
17%
1593
6%
513
33%
513
17%
1094
May16th to endNight
32%
374
13%
1497
9%
374
41%
374
16%
957
June1st to 15thNight
31%
360
13%
1440
7%
360
45%
360
15%
921
June16th to endNight
43%
360
14%
1440
13%
360
53%
360
24%
828
July1st to 15thNight
45%
340
13%
1360
15%
340
52%
340
23%
791
July16th to endNight
48%
376
15%
1418
16%
354
54%
354
22%
843
August1st to 15thNight
48%
494
17%
1565
9%
492
55%
492
31%
916
August16th to endNight
51%
764
20%
1910
10%
764
54%
764
34%
1237
September1st to 15thNight
38%
720
21%
1815
9%
720
44%
720
32%
1170
September16th to endNight
48%
717
28%
1980
18%
717
55%
717
34%
1180
October1st to 15thNight
34%
720
21%
2070
12%
720
44%
720
24%
1341
October16th to endNight
23%
768
17%
2445
6%
768
38%
768
17%
1606
November1st to 15thNight
27%
760
20%
2472
8%
760
42%
760
19%
1574
November16th to endNight
23%
780
22%
2581
9%
780
39%
780
17%
1665
December1st to 15thNight
19%
736
16%
2574
4%
736
33%
736
13%
1676
December16th to endNight
13%
768
18%
2688
4%
768
30%
768
11%
1803

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
16%6%25%5%35%5%5%7%37%
48692
Night
16%6%2442445%6%40%
47977
Cloud CoverDay
16%6%25%5%35%5%5%7%37%
48702
Night
16%6%25%42445%7%40%
47982
TransparencyDay
45%5%11%22%13%1
48380
Night
43%412%23%14%1
47807
SeeingDay
20%17%27%19%9%3
6051
Night
21%18%28%22%7%
15233

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
15%6%25%436%5%6%6%37%
1432
16th to endDay
13%7%345%35%5%7%6%36%
1563
February1st to 15thDay
14%7%448%46%45%6%31%
1651
16th to endDay
15%8%36%5%45%5%36%36%
1580
March1st to 15thDay
16%7%37%5%3446%7%33%
1790
16th to endDay
16%8%25%424446%38%
2220
April1st to 15thDay
18%8%345%34445%37%
2152
16th to endDay
16%5%25%5%2435%7%39%
2226
May1st to 15thDay
23%7%344345%45%32%
2367
16th to endDay
18%5%245%3445%8%36%
2618
June1st to 15thDay
23%5%245%25%5%5%6%31%
2520
16th to endDay
16%5%25%5%35%5%6%9%33%
2520
July1st to 15thDay
12%5%26%6%36%5%6%7%36%
2520
16th to endDay
12%5%35%5%45%6%6%7%37%
2654
August1st to 15thDay
15%5%25%5%46%5%6%8%34%
2370
16th to endDay
12%5%15%6%25%5%5%8%40%
2292
September1st to 15thDay
13%5%25%5%35%5%46%41%
2144
16th to endDay
15%41432345%7%47%
1980
October1st to 15thDay
19%7%34424345%40%
1887
16th to endDay
17%6%25%5%34446%38%
1779
November1st to 15thDay
17%6%34425%35%8%39%
1716
16th to endDay
18%6%24424446%41%
1707
December1st to 15thDay
17%6%26%5%345%5%7%36%
1468
16th to endDay
18%9%35%5%35%5%6%7%30%
1536
January1st to 15thNight
16%7%345%3445%7%37%
2506
16th to endNight
14%8%35%435%45%6%38%
2661
February1st to 15thNight
13%8%45%5%345%6%6%36%
2207
16th to endNight
15%8%24435%445%40%
1893
March1st to 15thNight
17%7%245%3445%7%36%
2147
16th to endNight
16%6%25%32335%7%43%
2002
April1st to 15thNight
17%7%35%6%44445%35%
1796
16th to endNight
19%6%34433336%41%
1733
May1st to 15thNight
20%8%26%5%23446%36%
1593
16th to endNight
18%6%245%3446%7%36%
1495
June1st to 15thNight
22%5%25%42435%7%37%
1440
16th to endNight
15%42442346%9%42%
1440
July1st to 15thNight
13%4245%25%448%44%
1440
16th to endNight
12%335%5%35%6%5%8%41%
1514
August1st to 15thNight
12%42342345%8%47%
1575
16th to endNight
13%414335%45%7%46%
1910
September1st to 15thNight
15%425%423346%46%
1815
16th to endNight
12%5%23312346%52%
1980
October1st to 15thNight
17%6%24322346%43%
2070
16th to endNight
19%6%145%3435%6%39%
2445
November1st to 15thNight
16%7%34424345%42%
2472
16th to endNight
17%7%24425%445%40%
2581
December1st to 15thNight
19%6%2443446%7%34%
2574
16th to endNight
19%7%35%4345%5%6%34%
2688

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
14%6%25%5%25%6%6%6%37%
1432
16th to endDay
13%8%245%35%5%7%6%37%
1563
February1st to 15thDay
14%7%35%7%46%5%46%32%
1651
16th to endDay
15%8%36%5%35%5%36%37%
1580
March1st to 15thDay
17%7%26%5%445%5%8%33%
1800
16th to endDay
16%8%35%424446%39%
2220
April1st to 15thDay
17%8%344245%46%37%
2152
16th to endDay
16%6%25%42445%7%40%
2226
May1st to 15thDay
23%8%35%434445%32%
2367
16th to endDay
17%5%35%435%5%5%7%36%
2618
June1st to 15thDay
23%5%25%435%5%5%7%31%
2520
16th to endDay
15%5%25%5%345%7%9%33%
2520
July1st to 15thDay
12%6%25%6%36%6%6%8%36%
2520
16th to endDay
12%5%26%6%35%6%6%7%37%
2654
August1st to 15thDay
14%5%25%5%36%6%7%8%34%
2370
16th to endDay
12%5%245%45%5%5%8%40%
2292
September1st to 15thDay
13%5%25%445%5%5%5%42%
2144
16th to endDay
14%5%2432345%7%47%
1980
October1st to 15thDay
18%8%24423445%40%
1887
16th to endDay
17%5%25%5%34446%39%
1779
November1st to 15thDay
17%7%2432435%8%39%
1716
16th to endDay
17%6%24324437%42%
1707
December1st to 15thDay
16%6%26%5%25%45%7%35%
1468
16th to endDay
17%9%26%5%35%46%6%31%
1536
January1st to 15thNight
16%7%25%5%2445%7%38%
2506
16th to endNight
14%8%35%5%25%447%38%
2661
February1st to 15thNight
13%8%35%6%35%5%6%6%36%
2200
16th to endNight
14%8%345%35%346%40%
1893
March1st to 15thNight
17%7%25%5%2446%7%36%
2160
16th to endNight
15%6%25%323447%43%
2001
April1st to 15thNight
17%6%35%6%35%5%46%35%
1796
16th to endNight
18%6%345%23346%41%
1733
May1st to 15thNight
20%7%26%5%33346%36%
1593
16th to endNight
18%6%234245%5%7%36%
1495
June1st to 15thNight
21%6%25%32435%6%37%
1440
16th to endNight
15%42343336%10%42%
1440
July1st to 15thNight
12%325%336%45%8%44%
1440
16th to endNight
11%425%6%36%6%5%7%41%
1514
August1st to 15thNight
11%42442346%8%47%
1575
16th to endNight
13%414425%46%7%45%
1910
September1st to 15thNight
14%5%24414447%46%
1815
16th to endNight
12%5%2431335%7%51%
1980
October1st to 15thNight
17%6%25%313346%43%
2070
16th to endNight
19%5%245%34346%40%
2445
November1st to 15thNight
15%8%25%423446%42%
2472
16th to endNight
17%8%24424346%40%
2581
December1st to 15thNight
19%5%245%35%46%7%35%
2574
16th to endNight
19%7%25%4345%5%6%35%
2688

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
43%5%13%24%10%2
1433
16th to endDay
43%6%12%24%11%1
1563
February1st to 15thDay
50%412%19%11%
1654
16th to endDay
48%310%22%13%1
1580
March1st to 15thDay
48%313%21%10%2
1800
16th to endDay
45%39%20%16%4
2220
April1st to 15thDay
48%39%22%14%2
2152
16th to endDay
42%48%22%18%3
2226
May1st to 15thDay
52%47%20%11%2
2367
16th to endDay
45%7%12%20%13%1
2622
June1st to 15thDay
50%6%12%20%9%
2520
16th to endDay
44%7%13%21%12%
2520
July1st to 15thDay
44%6%10%22%14%1
2371
16th to endDay
42%5%16%20%12%1
2487
August1st to 15thDay
44%6%13%22%12%
2356
16th to endDay
40%5%9%26%17%
2292
September1st to 15thDay
41%5%10%23%17%1
2144
16th to endDay
36%38%25%25%1
1980
October1st to 15thDay
45%49%24%13%2
1887
16th to endDay
45%5%11%21%13%2
1779
November1st to 15thDay
43%412%21%15%1
1716
16th to endDay
42%311%24%15%1
1707
December1st to 15thDay
46%416%19%11%1
1468
16th to endDay
50%6%15%17%9%
1536
January1st to 15thNight
45%412%22%13%2
2506
16th to endNight
45%410%23%14%1
2661
February1st to 15thNight
46%413%20%12%1
2208
16th to endNight
44%39%24%14%2
1893
March1st to 15thNight
45%413%21%12%2
2160
16th to endNight
39%310%22%17%5%
2002
April1st to 15thNight
48%49%19%15%1
1796
16th to endNight
45%38%22%17%2
1733
May1st to 15thNight
50%39%19%14%2
1593
16th to endNight
44%7%17%18%11%1
1497
June1st to 15thNight
47%414%22%10%
1440
16th to endNight
37%416%27%13%
1440
July1st to 15thNight
37%5%13%28%12%
1360
16th to endNight
38%7%15%25%12%1
1418
August1st to 15thNight
33%6%17%27%13%1
1565
16th to endNight
36%5%12%28%16%
1910
September1st to 15thNight
37%413%24%18%
1815
16th to endNight
33%38%27%25%1
1980
October1st to 15thNight
42%311%22%17%2
2070
16th to endNight
45%413%24%12%
2445
November1st to 15thNight
43%411%20%17%3
2472
16th to endNight
44%412%24%13%1
2581
December1st to 15thNight
46%5%16%21%11%
2574
16th to endNight
47%5%11%22%11%
2688

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
18%38%26%13%3
60
16th to endDay
20%36%31%11%
69
February1st to 15thDay
20%37%31%9%1
167
16th to endDay
20%32%29%14%4
239
March1st to 15thDay
29%25%27%15%2
270
16th to endDay
24%29%26%11%5%2
288
April1st to 15thDay
25%23%28%14%6%1
270
16th to endDay
21%20%28%18%8%3
270
May1st to 15thDay
36%15%21%17%5%2
288
16th to endDay
20%16%31%19%9%2
331
June1st to 15thDay
25%13%28%21%10%1
315
16th to endDay
17%15%32%22%9%1
315
July1st to 15thDay
14%10%35%25%13%1
305
16th to endDay
14%7%33%27%13%3
326
August1st to 15thDay
15%9%23%28%14%7%
313
16th to endDay
12%7%25%26%18%9%
332
September1st to 15thDay
14%14%22%23%15%9%
315
16th to endDay
16%8%25%17%19%12%
314
October1st to 15thDay
20%9%27%22%15%4
315
16th to endDay
21%21%26%22%7%
301
November1st to 15thDay
24%17%25%22%8%2
280
16th to endDay
24%23%26%15%8%1
237
December1st to 15thDay
19%34%31%7%7%
67
16th to endDay
26%39%26%6%1
64
January1st to 15thNight
22%25%32%15%3
720
16th to endNight
22%27%30%17%1
768
February1st to 15thNight
22%26%32%17%1
704
16th to endNight
22%29%29%16%2
631
March1st to 15thNight
24%26%30%15%2
720
16th to endNight
22%28%26%16%4
768
April1st to 15thNight
21%22%36%15%4
718
16th to endNight
22%20%31%17%7%
653
May1st to 15thNight
24%17%30%20%6%
513
16th to endNight
20%10%31%28%8%
375
June1st to 15thNight
24%10%26%29%9%
360
16th to endNight
18%429%36%9%1
360
July1st to 15thNight
14%327%36%17%
340
16th to endNight
11%6%24%39%17%
376
August1st to 15thNight
15%426%36%14%1
494
16th to endNight
15%422%33%20%3
764
September1st to 15thNight
16%7%29%31%13%1
720
16th to endNight
16%7%23%26%20%5%
717
October1st to 15thNight
23%11%25%26%10%1
720
16th to endNight
23%21%27%22%5%
768
November1st to 15thNight
21%20%26%21%9%1
760
16th to endNight
23%20%28%20%6%1
780
December1st to 15thNight
25%23%29%16%4
736
16th to endNight
25%28%29%14%2
768
Page generated at 2017-12-05 10:18:58. Version ac04

Copyright 2017 A. Danko


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