Whitby
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Whitby clear sky chart from 2005-11-05 to 2017-12-01.

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
36%
15100
15%
47834
10%
15065
43%
15065
20%
32436

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%
719
10%
2500
3%
716
24%
716
10%
1928
January16th to endNight
22%
768
13%
2496
5%
768
31%
768
12%
1883
February1st to 15thNight
18%
702
11%
2287
3%
701
27%
701
12%
1727
February16th to endNight
24%
631
14%
2021
5%
631
34%
631
16%
1442
March1st to 15thNight
24%
720
14%
1980
7%
720
31%
720
17%
1470
March16th to endNight
32%
768
21%
2112
10%
768
41%
768
26%
1399
April1st to 15thNight
31%
718
16%
1803
6%
718
36%
718
23%
1299
April16th to endNight
38%
582
20%
1662
9%
582
45%
582
28%
1074
May1st to 15thNight
47%
465
16%
1545
12%
465
53%
465
23%
982
May16th to endNight
54%
374
17%
1497
18%
374
61%
374
28%
803
June1st to 15thNight
48%
360
12%
1440
13%
360
56%
360
21%
852
June16th to endNight
53%
360
11%
1440
16%
360
57%
360
25%
825
July1st to 15thNight
68%
340
16%
1360
24%
340
72%
340
34%
679
July16th to endNight
65%
458
17%
1494
18%
430
67%
430
33%
827
August1st to 15thNight
67%
539
17%
1609
14%
536
69%
536
38%
905
August16th to endNight
62%
639
23%
1785
14%
639
66%
639
37%
1050
September1st to 15thNight
55%
720
21%
1800
10%
720
60%
720
36%
1152
September16th to endNight
54%
717
24%
2004
17%
717
58%
717
33%
1228
October1st to 15thNight
42%
720
18%
2160
15%
720
47%
720
23%
1460
October16th to endNight
31%
768
14%
2304
8%
768
38%
768
17%
1658
November1st to 15thNight
35%
760
18%
2585
15%
760
43%
760
19%
1733
November16th to endNight
26%
780
11%
2730
7%
780
33%
780
13%
1981
December1st to 15thNight
17%
724
7%
2532
4%
724
21%
724
10%
1958
December16th to endNight
15%
768
7%
2688
2%
768
22%
768
9%
2121

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%7%36%5%35%5%5%7%34%
48588
Night
15%7%36%5%3445%6%36%
48011
Cloud CoverDay
14%7%36%5%35%46%7%35%
48598
Night
16%8%36%5%3445%6%36%
48016
TransparencyDay
47%5%14%21%10%1
48284
Night
47%413%21%11%1
47834
SeeingDay
17%6%25%27%16%6%
5611
Night
19%8%26%30%13%1
15104

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
18%13%48%6%33446%26%
1435
16th to endDay
14%13%6%10%7%5%6%5%46%19%
1728
February1st to 15thDay
14%12%5%11%7%5%6%45%5%22%
1575
16th to endDay
16%11%6%7%5%35%345%28%
1449
March1st to 15thDay
15%9%37%7%36%447%29%
1969
16th to endDay
16%8%35%5%24446%38%
2112
April1st to 15thDay
21%7%46%5%2445%6%31%
2143
16th to endDay
18%6%34434346%40%
2308
May1st to 15thDay
14%6%36%5%35%45%8%35%
2406
16th to endDay
11%5%246%25%5%6%8%41%
2618
June1st to 15thDay
15%5%25%5%35%5%7%8%35%
2520
16th to endDay
12%424436%5%7%10%38%
2520
July1st to 15thDay
8%3245%35%5%7%9%44%
2520
16th to endDay
9%5%245%35%6%8%9%38%
2571
August1st to 15thDay
8%425%5%35%5%7%9%41%
2340
16th to endDay
9%5%245%35%5%7%9%42%
2405
September1st to 15thDay
14%4145%345%6%6%42%
2160
16th to endDay
12%425%5%35%45%6%44%
1953
October1st to 15thDay
18%7%36%5%345%5%5%34%
1800
16th to endDay
22%8%46%6%345%46%26%
1920
November1st to 15thDay
16%8%37%7%4445%8%30%
1598
16th to endDay
19%9%38%7%3445%7%25%
1560
December1st to 15thDay
18%13%5%8%6%45%5%5%6%19%
1442
16th to endDay
20%12%6%9%7%35%446%19%
1536
January1st to 15thNight
21%13%48%5%25%445%23%
2500
16th to endNight
15%12%5%9%6%45%45%5%24%
2496
February1st to 15thNight
14%13%6%8%7%35%445%25%
2285
16th to endNight
15%9%38%6%4445%6%30%
2021
March1st to 15thNight
19%8%47%5%35%33432%
1968
16th to endNight
14%7%35%5%24335%43%
2112
April1st to 15thNight
19%6%25%5%24446%36%
1803
16th to endNight
12%7%245%2445%6%43%
1662
May1st to 15thNight
15%425%6%345%6%6%39%
1545
16th to endNight
12%3143245%5%7%49%
1495
June1st to 15thNight
12%425%435%5%6%8%40%
1440
16th to endNight
10%425%4345%6%9%42%
1440
July1st to 15thNight
5%3233245%5%7%55%
1440
16th to endNight
8%3234346%6%9%48%
1596
August1st to 15thNight
7%41442446%9%49%
1620
16th to endNight
7%325%434346%52%
1785
September1st to 15thNight
12%5%2342445%6%48%
1800
16th to endNight
13%425%42345%6%48%
2004
October1st to 15thNight
18%6%25%5%23446%38%
2160
16th to endNight
21%7%35%5%35%5%46%30%
2304
November1st to 15thNight
17%8%25%6%3445%6%35%
2585
16th to endNight
21%9%36%5%35%5%5%7%27%
2730
December1st to 15thNight
20%12%5%7%6%35%5%46%21%
2532
16th to endNight
22%12%5%9%5%35%45%6%18%
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
19%12%38%7%34446%25%
1435
16th to endDay
14%13%6%10%7%5%6%5%46%19%
1728
February1st to 15thDay
15%12%5%11%7%46%35%5%21%
1575
16th to endDay
16%11%5%7%6%35%346%29%
1449
March1st to 15thDay
16%9%37%6%35%45%6%29%
1980
16th to endDay
16%8%35%5%35%35%5%39%
2111
April1st to 15thDay
20%7%36%5%3445%7%30%
2143
16th to endDay
17%6%35%433446%40%
2308
May1st to 15thDay
14%7%26%5%35%46%7%36%
2406
16th to endDay
11%5%25%5%35%47%7%41%
2618
June1st to 15thDay
15%425%5%35%5%6%9%35%
2520
16th to endDay
12%424435%5%7%10%39%
2520
July1st to 15thDay
7%324435%5%7%9%44%
2520
16th to endDay
8%4145%35%6%7%10%40%
2571
August1st to 15thDay
7%425%436%6%6%8%42%
2340
16th to endDay
9%5%145%245%7%9%44%
2405
September1st to 15thDay
14%413435%5%6%7%42%
2160
16th to endDay
12%425%435%35%7%44%
1953
October1st to 15thDay
19%7%36%6%2445%5%35%
1800
16th to endDay
23%9%36%6%34445%27%
1920
November1st to 15thDay
16%7%38%6%445%5%7%30%
1598
16th to endDay
19%10%38%6%345%5%7%26%
1560
December1st to 15thDay
18%12%5%8%7%45%5%5%6%19%
1442
16th to endDay
21%12%5%9%6%35%446%19%
1536
January1st to 15thNight
21%13%5%7%5%34445%23%
2500
16th to endNight
15%12%5%9%7%35%5%5%5%23%
2496
February1st to 15thNight
15%13%6%8%7%3445%5%25%
2278
16th to endNight
16%9%28%6%445%46%30%
2021
March1st to 15thNight
20%8%47%5%34335%31%
1980
16th to endNight
14%7%35%5%33335%43%
2112
April1st to 15thNight
19%6%25%5%34446%36%
1803
16th to endNight
13%6%3442445%6%44%
1662
May1st to 15thNight
15%425%5%345%5%7%39%
1545
16th to endNight
11%3144235%5%7%49%
1495
June1st to 15thNight
12%425%5%45%5%5%8%40%
1440
16th to endNight
10%435%5%345%5%10%42%
1440
July1st to 15thNight
5%31433445%7%55%
1440
16th to endNight
9%3134346%6%9%48%
1596
August1st to 15thNight
7%4144245%6%9%49%
1620
16th to endNight
7%424424446%52%
1785
September1st to 15thNight
13%5%2332435%6%48%
1800
16th to endNight
13%42442335%6%48%
2004
October1st to 15thNight
18%6%26%5%23446%38%
2160
16th to endNight
22%7%35%5%35%5%46%31%
2304
November1st to 15thNight
17%7%25%6%3445%6%35%
2585
16th to endNight
22%9%35%5%35%5%5%6%27%
2730
December1st to 15thNight
20%13%5%7%5%45%45%6%22%
2532
16th to endNight
22%12%5%8%6%36%45%6%18%
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
60%413%15%6%
1436
16th to endDay
64%5%10%13%5%
1728
February1st to 15thDay
63%311%16%4
1577
16th to endDay
57%412%17%8%
1449
March1st to 15thDay
54%413%18%8%
1980
16th to endDay
47%310%19%16%2
2112
April1st to 15thDay
52%311%18%11%
2143
16th to endDay
45%311%22%14%2
2308
May1st to 15thDay
45%411%22%13%1
2406
16th to endDay
39%5%16%24%12%2
2622
June1st to 15thDay
44%6%13%23%12%
2520
16th to endDay
38%6%17%24%12%
2520
July1st to 15thDay
33%5%15%27%16%1
2371
16th to endDay
38%6%16%25%11%1
2411
August1st to 15thDay
36%7%17%23%13%1
2327
16th to endDay
35%5%16%29%11%1
2405
September1st to 15thDay
38%6%15%26%11%1
2160
16th to endDay
38%6%13%29%11%
1953
October1st to 15thDay
50%412%21%9%1
1800
16th to endDay
56%5%17%14%5%
1920
November1st to 15thDay
51%5%14%18%8%1
1598
16th to endDay
57%415%15%6%
1560
December1st to 15thDay
62%6%17%11%1
1442
16th to endDay
64%5%13%13%2
1536
January1st to 15thNight
62%411%14%6%
2500
16th to endNight
60%311%17%5%
2496
February1st to 15thNight
59%5%10%18%5%
2287
16th to endNight
53%413%19%7%
2021
March1st to 15thNight
56%311%20%7%
1980
16th to endNight
43%310%24%16%2
2112
April1st to 15thNight
48%49%19%15%1
1803
16th to endNight
40%411%21%18%3
1662
May1st to 15thNight
42%5%12%21%15%2
1545
16th to endNight
33%5%15%25%17%2
1497
June1st to 15thNight
39%6%11%25%16%1
1440
16th to endNight
37%5%14%24%16%1
1440
July1st to 15thNight
27%5%12%29%24%2
1360
16th to endNight
30%5%14%28%17%2
1494
August1st to 15thNight
29%5%20%29%13%1
1609
16th to endNight
31%413%33%16%1
1785
September1st to 15thNight
35%415%27%15%1
1800
16th to endNight
35%412%32%15%
2004
October1st to 15thNight
46%410%23%13%
2160
16th to endNight
53%415%18%7%
2304
November1st to 15thNight
48%413%20%12%1
2585
16th to endNight
55%5%16%15%6%
2730
December1st to 15thNight
62%5%14%14%3
2532
16th to endNight
65%5%13%11%3
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
19%18%37%16%6%1
61
16th to endDay
34%13%28%20%3
96
February1st to 15thDay
24%23%34%16%1
90
16th to endDay
20%15%41%17%4
105
March1st to 15thDay
24%13%32%22%7%
270
16th to endDay
22%6%35%23%9%1
288
April1st to 15thDay
20%8%33%27%9%1
270
16th to endDay
19%7%34%20%14%4
270
May1st to 15thDay
18%5%25%28%14%7%
288
16th to endDay
15%325%31%19%4
331
June1st to 15thDay
18%6%24%31%17%2
315
16th to endDay
15%220%36%19%5%
315
July1st to 15thDay
10%115%34%28%8%
305
16th to endDay
8%224%32%21%10%
326
August1st to 15thDay
11%114%32%25%14%
313
16th to endDay
14%314%25%24%18%
332
September1st to 15thDay
12%216%29%24%14%
315
16th to endDay
14%317%28%20%16%
314
October1st to 15thDay
20%5%24%28%15%5%
315
16th to endDay
25%13%26%23%10%
336
November1st to 15thDay
23%7%24%32%10%1
142
16th to endDay
18%12%42%17%7%1
90
December1st to 15thDay
18%13%40%16%8%3
60
16th to endDay
29%12%45%12%
64
January1st to 15thNight
27%15%33%17%4
720
16th to endNight
21%10%33%28%5%
768
February1st to 15thNight
20%13%38%22%4
704
16th to endNight
20%11%34%26%6%
631
March1st to 15thNight
25%11%31%27%4
720
16th to endNight
18%8%32%28%10%1
768
April1st to 15thNight
22%9%30%31%5%
718
16th to endNight
15%7%31%32%11%1
582
May1st to 15thNight
19%422%34%18%1
465
16th to endNight
13%322%38%21%1
375
June1st to 15thNight
14%5%23%38%17%
360
16th to endNight
10%320%43%21%
360
July1st to 15thNight
6%215%48%24%1
340
16th to endNight
9%115%42%27%2
458
August1st to 15thNight
8%112%44%29%4
539
16th to endNight
8%216%37%31%4
639
September1st to 15thNight
14%5%17%32%25%5%
720
16th to endNight
14%5%16%28%26%7%
717
October1st to 15thNight
22%5%23%30%16%2
720
16th to endNight
26%8%26%30%7%
768
November1st to 15thNight
22%7%26%29%11%2
760
16th to endNight
24%12%26%26%9%1
780
December1st to 15thNight
30%11%32%20%4
724
16th to endNight
27%10%36%21%3
768
Page generated at 2017-12-02 09:14:14. Version ac04

Copyright 2017 A. Danko


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