Cambridge Narrows
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cambridge Narrows clear sky chart from 2005-11-05 to 2017-09-23.

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
22%
14870
14%
46819
5%
14828
31%
14828
15%
33476

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
14%
745
13%
2658
1%
741
29%
741
10%
1859
January16th to endNight
17%
768
16%
2574
4%
768
31%
768
13%
1771
February1st to 15thNight
16%
704
12%
2286
3%
701
28%
701
12%
1617
February16th to endNight
15%
631
12%
1992
3%
631
26%
631
11%
1493
March1st to 15thNight
15%
720
16%
2025
4%
720
27%
720
14%
1494
March16th to endNight
18%
768
16%
2112
5%
768
27%
768
15%
1561
April1st to 15thNight
18%
593
14%
1776
5%
593
26%
593
12%
1347
April16th to endNight
20%
540
15%
1620
6%
540
28%
540
16%
1166
May1st to 15thNight
22%
540
11%
1578
4%
540
27%
540
13%
1196
May16th to endNight
19%
543
10%
1478
2%
542
27%
542
14%
1141
June1st to 15thNight
22%
360
7%
1260
3%
360
27%
360
11%
948
June16th to endNight
27%
360
7%
1260
4%
360
33%
360
13%
926
July1st to 15thNight
36%
340
10%
1190
8%
340
43%
340
20%
799
July16th to endNight
29%
472
9%
1432
7%
442
34%
442
16%
1047
August1st to 15thNight
35%
539
10%
1608
8%
535
38%
535
20%
1132
August16th to endNight
36%
573
18%
1722
10%
573
42%
573
26%
1101
September1st to 15thNight
26%
602
15%
1862
7%
602
35%
602
20%
1258
September16th to endNight
37%
689
25%
1902
13%
689
46%
689
29%
1186
October1st to 15thNight
28%
660
20%
1969
8%
660
38%
660
21%
1335
October16th to endNight
19%
704
15%
2166
4%
704
29%
704
14%
1560
November1st to 15thNight
24%
719
14%
2390
7%
719
32%
719
15%
1680
November16th to endNight
23%
750
13%
2520
5%
750
32%
750
12%
1793
December1st to 15thNight
13%
750
13%
2559
3%
750
25%
750
9%
1905
December16th to endNight
11%
800
11%
2880
2%
800
23%
800
8%
2161

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
20%8%35%5%34446%33%
48095
Night
20%8%36%5%34446%32%
46987
TransparencyDay
52%5%11%19%10%1
47781
Night
52%5%10%19%10%
46819
SeeingDay
29%14%29%18%6%1
6953
Night
27%14%31%20%6%
14870

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%14%47%5%24345%33%
1280
16th to endDay
13%12%5%6%5%345%45%33%
1649
February1st to 15thDay
15%11%36%6%35%5%46%31%
1575
16th to endDay
15%12%5%7%5%35%445%30%
1479
March1st to 15thDay
17%12%6%8%5%2333431%
1924
16th to endDay
16%9%48%434336%34%
2112
April1st to 15thDay
21%11%45%5%34445%30%
2170
16th to endDay
24%9%24422346%35%
2340
May1st to 15thDay
25%8%36%5%24336%29%
2372
16th to endDay
22%7%36%5%34447%29%
2645
June1st to 15thDay
27%8%35%5%34445%26%
2700
16th to endDay
24%7%35%425%45%6%29%
2700
July1st to 15thDay
16%5%345%35%5%6%8%36%
2700
16th to endDay
17%6%26%5%36%6%6%8%30%
2622
August1st to 15thDay
18%5%25%5%25%5%5%7%34%
2340
16th to endDay
14%5%25%5%3445%7%42%
2480
September1st to 15thDay
16%5%2342445%6%43%
2097
16th to endDay
18%413312345%50%
1895
October1st to 15thDay
21%6%23412437%40%
1661
16th to endDay
22%7%46%5%33445%32%
1705
November1st to 15thDay
22%9%34433345%33%
1467
16th to endDay
21%9%46%5%34335%31%
1440
December1st to 15thDay
25%8%5%6%5%34346%27%
1398
16th to endDay
23%12%5%6%5%22347%25%
1344
January1st to 15thNight
16%9%37%5%2445%6%32%
2658
16th to endNight
15%10%35%6%35%446%33%
2574
February1st to 15thNight
16%10%36%5%35%45%6%31%
2285
16th to endNight
17%14%5%6%5%34445%29%
1992
March1st to 15thNight
19%11%46%424436%31%
2013
16th to endNight
17%10%47%6%24445%32%
2112
April1st to 15thNight
23%10%36%5%3434429%
1776
16th to endNight
24%7%26%425%346%32%
1620
May1st to 15thNight
25%7%36%5%2445%6%26%
1578
16th to endNight
21%8%36%5%35%45%6%27%
1476
June1st to 15thNight
29%6%36%5%34347%24%
1260
16th to endNight
22%7%46%5%25%45%6%29%
1260
July1st to 15thNight
14%5%346%45%5%8%8%34%
1260
16th to endNight
18%6%47%6%45%46%8%28%
1533
August1st to 15thNight
19%6%25%5%25%35%7%35%
1620
16th to endNight
13%6%2443446%7%43%
1722
September1st to 15thNight
20%6%2442345%7%38%
1862
16th to endNight
14%414423345%49%
1902
October1st to 15thNight
19%7%2442345%6%38%
1969
16th to endNight
23%8%35%424445%33%
2166
November1st to 15thNight
22%6%26%5%34346%33%
2390
16th to endNight
20%10%35%5%24335%33%
2520
December1st to 15thNight
25%9%37%5%24435%28%
2559
16th to endNight
26%11%45%5%3434426%
2880

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
53%314%17%8%1
1281
16th to endDay
53%38%20%13%
1649
February1st to 15thDay
53%412%19%7%1
1578
16th to endDay
56%411%17%8%1
1479
March1st to 15thDay
58%39%16%10%1
1935
16th to endDay
53%310%17%12%2
2112
April1st to 15thDay
57%47%14%12%2
2170
16th to endDay
52%39%17%13%3
2340
May1st to 15thDay
58%48%17%10%1
2372
16th to endDay
56%5%10%20%5%
2649
June1st to 15thDay
60%49%15%7%1
2700
16th to endDay
56%6%11%16%8%
2700
July1st to 15thDay
43%8%15%20%11%
2541
16th to endDay
51%7%14%19%7%
2461
August1st to 15thDay
50%6%12%22%8%
2327
16th to endDay
42%7%13%27%9%
2480
September1st to 15thDay
42%5%12%25%12%1
2097
16th to endDay
38%38%29%18%1
1895
October1st to 15thDay
46%311%26%11%
1661
16th to endDay
55%5%9%19%10%
1705
November1st to 15thDay
53%5%10%16%12%
1467
16th to endDay
55%414%15%9%
1440
December1st to 15thDay
60%5%11%18%4
1398
16th to endDay
59%410%15%9%
1344
January1st to 15thNight
51%6%13%18%8%1
2658
16th to endNight
50%411%22%10%
2574
February1st to 15thNight
52%5%12%18%11%
2286
16th to endNight
58%49%15%9%2
1992
March1st to 15thNight
54%48%19%11%2
2025
16th to endNight
54%47%18%13%1
2112
April1st to 15thNight
58%37%14%12%3
1776
16th to endNight
54%39%16%14%1
1620
May1st to 15thNight
57%5%9%17%8%1
1578
16th to endNight
57%5%12%16%7%
1478
June1st to 15thNight
62%310%17%41
1260
16th to endNight
56%5%10%17%9%
1260
July1st to 15thNight
45%7%15%22%8%
1190
16th to endNight
54%6%12%18%8%
1432
August1st to 15thNight
48%6%13%22%8%
1608
16th to endNight
39%6%15%28%9%
1722
September1st to 15thNight
45%6%9%25%12%
1862
16th to endNight
37%310%30%16%1
1902
October1st to 15thNight
46%49%25%12%
1969
16th to endNight
53%410%21%10%
2166
November1st to 15thNight
51%5%13%18%9%
2390
16th to endNight
54%5%13%17%8%
2520
December1st to 15thNight
59%49%20%5%
2559
16th to endNight
61%49%17%7%
2880

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
31%18%40%10%
60
16th to endDay
24%16%40%15%2
177
February1st to 15thDay
25%18%32%18%4
236
16th to endDay
27%23%27%16%4
222
March1st to 15thDay
29%22%28%14%31
270
16th to endDay
29%20%26%14%5%3
288
April1st to 15thDay
37%19%23%15%4
270
16th to endDay
33%15%27%14%6%1
270
May1st to 15thDay
36%16%26%12%6%1
328
16th to endDay
35%12%28%17%5%
519
June1st to 15thDay
36%13%27%17%4
495
16th to endDay
31%10%30%18%8%
495
July1st to 15thDay
24%9%31%20%12%1
475
16th to endDay
23%7%33%26%8%
401
August1st to 15thDay
23%9%33%24%5%2
313
16th to endDay
18%10%30%25%11%3
332
September1st to 15thDay
22%12%29%25%7%1
315
16th to endDay
20%13%29%19%11%4
283
October1st to 15thDay
30%11%23%19%10%4
227
16th to endDay
32%17%30%12%7%
240
November1st to 15thDay
31%12%28%16%8%2
235
16th to endDay
31%18%25%17%5%1
240
December1st to 15thDay
36%18%24%16%3
198
16th to endDay
45%28%18%7%
64
January1st to 15thNight
27%19%30%18%4
745
16th to endNight
26%18%33%17%4
768
February1st to 15thNight
24%18%35%18%3
704
16th to endNight
29%19%29%17%3
631
March1st to 15thNight
28%18%32%18%2
720
16th to endNight
25%18%32%17%5%
768
April1st to 15thNight
31%16%29%18%4
593
16th to endNight
29%13%33%17%5%
540
May1st to 15thNight
30%13%30%18%5%
540
16th to endNight
25%14%35%18%4
543
June1st to 15thNight
31%9%33%21%3
360
16th to endNight
27%8%30%27%5%
360
July1st to 15thNight
18%434%33%8%
340
16th to endNight
22%6%34%28%7%
472
August1st to 15thNight
22%5%28%29%12%
539
16th to endNight
16%8%34%30%10%
573
September1st to 15thNight
25%10%34%20%9%
602
16th to endNight
19%10%29%27%12%1
689
October1st to 15thNight
24%10%32%22%7%2
660
16th to endNight
31%17%28%17%4
704
November1st to 15thNight
26%16%28%17%9%1
719
16th to endNight
28%16%27%20%6%
750
December1st to 15thNight
33%18%29%14%3
750
16th to endNight
35%20%26%14%3
800
Page generated at 2017-09-24 10:15:46. Version ac04

Copyright 2017 A. Danko


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