Whitby
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Whitby clear sky chart from 2005-11-06 to 2024-02-05.

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%
22861
14%
80389
10%
22774
42%
22774
18%
55092

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 10thNight
15%
752
9%
4410
5%
737
26%
737
6%
3176
January11th to 20thNight
16%
757
7%
4253
3%
740
23%
740
5%
3175
January21st to endNight
22%
828
8%
4524
6%
814
32%
814
8%
3365
February1st to 10thNight
17%
739
11%
2399
3%
739
27%
739
12%
1826
February11th to 20thNight
18%
701
13%
2275
4%
700
30%
700
13%
1671
February21st to endNight
20%
592
14%
1879
4%
592
31%
592
16%
1345
March1st to 10thNight
24%
720
17%
1980
8%
720
33%
720
20%
1408
March11th to 20thNight
22%
720
18%
1980
8%
720
32%
720
19%
1425
March21st to endNight
32%
792
20%
2178
9%
792
40%
792
24%
1478
April1st to 10thNight
27%
720
17%
1813
5%
720
34%
720
22%
1323
April11th to 20thNight
31%
686
18%
1750
7%
686
36%
686
24%
1236
April21st to endNight
33%
540
17%
1620
8%
540
41%
540
21%
1106
May1st to 10thNight
41%
518
15%
1598
10%
518
46%
518
23%
1044
May11th to 20thNight
43%
354
22%
1416
18%
354
56%
354
24%
795
May21st to endNight
58%
388
18%
1551
20%
388
65%
388
30%
813
June1st to 10thNight
48%
360
14%
1440
15%
360
59%
360
22%
848
June11th to 20thNight
47%
360
16%
1440
19%
360
56%
360
24%
808
June21st to endNight
52%
360
13%
1440
16%
360
59%
360
23%
831
July1st to 10thNight
64%
350
17%
1400
23%
350
69%
350
33%
701
July11th to 20thNight
61%
348
19%
1392
27%
348
65%
348
30%
738
July21st to endNight
64%
518
18%
1604
17%
490
67%
490
36%
900
August1st to 10thNight
64%
537
18%
1600
15%
534
66%
534
36%
914
August11th to 20thNight
67%
534
22%
1598
15%
534
71%
534
38%
902
August21st to endNight
55%
691
22%
1879
12%
691
59%
691
34%
1169
September1st to 10thNight
55%
720
18%
1800
8%
720
59%
720
35%
1167
September11th to 20thNight
56%
720
28%
1868
16%
720
62%
720
40%
1119
September21st to endNight
48%
720
21%
2038
16%
720
52%
720
28%
1317
October1st to 10thNight
42%
720
18%
2160
15%
720
48%
720
24%
1432
October11th to 20thNight
31%
720
14%
2160
9%
720
40%
720
18%
1549
October21st to endNight
28%
792
15%
2376
9%
792
35%
792
16%
1732
November1st to 10thNight
36%
740
20%
2476
15%
740
46%
740
21%
1608
November11th to 20thNight
27%
760
15%
2660
8%
760
37%
760
16%
1849
November21st to endNight
25%
760
10%
2660
7%
760
30%
760
13%
1934
December1st to 10thNight
18%
760
10%
2660
5%
760
24%
760
10%
2022
December11th to 20thNight
17%
759
8%
3249
3%
758
24%
758
8%
2461
December21st to endNight
13%
825
4%
4863
1%
817
21%
817
5%
3905

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
15%8%47%6%45%5%6%7%34%
78177
Night
16%9%47%6%35%5%5%7%34%
80672
TransparencyDay
48%6%14%21%10%1
77890
Night
50%5%13%20%11%1
80494
SeeingDay
20%10%29%25%12%4
13381
Night
20%9%28%30%12%1
22895

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 10thDay
17%13%38%7%34346%32%
2517
11th to 20thDay
11%17%7%14%9%45%5%45%19%
2686
21st to endDay
21%18%6%10%7%45%445%18%
3124
February1st to 10thDay
16%14%5%11%8%5%6%5%5%5%22%
1656
11th to 20thDay
13%13%7%11%6%45%45%6%27%
1573
21st to endDay
19%13%5%9%6%3444428%
1373
March1st to 10thDay
14%10%39%8%46%5%5%6%31%
1977
11th to 20thDay
15%11%5%7%6%35%446%34%
1980
21st to endDay
18%9%46%6%35%445%36%
2178
April1st to 10thDay
18%9%48%7%3446%7%30%
2146
11th to 20thDay
19%7%45%5%35%5%5%6%37%
2173
21st to endDay
20%8%36%5%45%45%6%35%
2340
May1st to 10thDay
15%8%47%5%35%5%5%8%34%
2361
11th to 20thDay
14%7%36%6%345%6%8%40%
2478
21st to endDay
11%5%25%6%35%5%6%8%44%
2725
June1st to 10thDay
15%5%36%5%45%5%7%8%37%
2520
11th to 20thDay
12%5%35%5%35%5%7%9%41%
2520
21st to endDay
13%5%345%36%5%6%10%41%
2520
July1st to 10thDay
8%425%5%35%5%7%10%47%
2520
11th to 20thDay
10%5%25%6%347%8%9%41%
2520
21st to endDay
8%5%25%6%5%6%7%8%10%38%
2618
August1st to 10thDay
7%5%25%6%46%6%8%10%41%
2327
11th to 20thDay
9%435%5%35%6%8%10%41%
2303
21st to endDay
10%6%35%5%36%5%7%9%42%
2458
September1st to 10thDay
13%425%5%35%5%6%7%44%
2160
11th to 20thDay
12%4244345%7%8%47%
2088
21st to endDay
13%5%36%6%35%5%6%7%40%
1922
October1st to 10thDay
17%8%25%6%45%6%5%6%35%
1800
11th to 20thDay
20%8%47%6%445%6%6%30%
1800
21st to endDay
23%10%48%6%45%5%46%25%
1980
November1st to 10thDay
15%8%38%7%45%45%8%33%
1596
11th to 20thDay
16%10%48%8%45%5%7%7%26%
1520
21st to endDay
21%10%48%7%35%45%8%25%
1520
December1st to 10thDay
18%13%5%9%8%5%6%6%5%7%18%
1520
11th to 20thDay
18%13%48%5%35%5%6%7%26%
1906
21st to endDay
29%14%5%11%7%45%43414%
2772
January1st to 10thNight
18%14%5%8%7%35%5%5%5%24%
4429
11th to 20thNight
16%12%411%10%5%5%6%5%6%21%
4271
21st to endNight
21%13%5%8%7%36%5%5%5%23%
4532
February1st to 10thNight
14%14%6%9%8%46%5%5%5%25%
2399
11th to 20thNight
16%12%5%8%7%45%45%6%28%
2273
21st to endNight
15%10%49%6%45%5%6%6%30%
1879
March1st to 10thNight
14%8%47%7%46%5%45%36%
1970
11th to 20thNight
17%10%5%7%6%3445%5%34%
1979
21st to endNight
16%8%35%6%35%446%40%
2178
April1st to 10thNight
19%9%45%6%345%5%7%34%
1813
11th to 20thNight
15%6%36%6%36%5%5%6%39%
1750
21st to endNight
17%8%36%6%35%5%6%7%35%
1620
May1st to 10thNight
17%6%346%345%6%6%39%
1598
11th to 20thNight
13%426%5%245%5%8%45%
1415
21st to endNight
10%415%4345%5%8%52%
1550
June1st to 10thNight
12%425%5%36%5%7%8%42%
1440
11th to 20thNight
8%437%5%45%6%5%9%45%
1440
21st to endNight
12%5%35%4445%6%9%43%
1440
July1st to 10thNight
5%424435%5%5%7%56%
1440
11th to 20thNight
10%4244345%6%8%49%
1440
21st to endNight
9%325%3346%6%9%49%
1698
August1st to 10thNight
8%4245%35%46%8%50%
1611
11th to 20thNight
7%425%5%345%6%9%51%
1598
21st to endNight
9%5%26%5%3445%8%48%
1879
September1st to 10thNight
10%5%345%35%5%6%7%46%
1800
11th to 20thNight
11%42343335%7%54%
1868
21st to endNight
16%5%36%5%3445%6%44%
2038
October1st to 10thNight
16%6%36%6%345%5%6%39%
2160
11th to 20thNight
20%8%36%6%35%5%5%6%32%
2160
21st to endNight
22%9%36%6%45%6%5%6%29%
2376
November1st to 10thNight
17%7%26%6%35%45%7%38%
2476
11th to 20thNight
17%9%36%6%5%5%6%6%7%30%
2660
21st to endNight
20%10%37%5%45%5%6%8%26%
2660
December1st to 10thNight
20%12%6%8%7%46%5%5%7%22%
2660
11th to 20thNight
16%15%49%6%45%5%6%6%22%
3288
21st to endNight
30%13%5%7%6%35%5%5%5%15%
4884

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 10thDay
55%420%12%8%1
2518
11th to 20thDay
68%412%11%5%
2686
21st to endDay
69%5%11%11%41
3124
February1st to 10thDay
64%411%15%5%1
1656
11th to 20thDay
58%5%10%18%8%1
1582
21st to endDay
58%5%11%18%8%
1373
March1st to 10thDay
52%6%13%18%11%1
1980
11th to 20thDay
52%411%18%13%2
1980
21st to endDay
50%49%18%16%3
2178
April1st to 10thDay
53%412%19%11%2
2146
11th to 20thDay
47%5%10%22%15%1
2173
21st to endDay
49%411%20%12%3
2340
May1st to 10thDay
48%410%21%14%2
2361
11th to 20thDay
41%5%12%26%14%2
2482
21st to endDay
37%5%18%25%12%2
2725
June1st to 10thDay
42%7%14%22%14%1
2520
11th to 20thDay
38%6%14%26%15%2
2520
21st to endDay
38%7%16%25%13%1
2520
July1st to 10thDay
32%6%14%28%19%2
2450
11th to 20thDay
35%7%16%30%11%1
2445
21st to endDay
38%7%18%24%12%1
2472
August1st to 10thDay
35%8%18%25%12%1
2314
11th to 20thDay
36%6%19%28%12%
2303
21st to endDay
37%7%15%29%12%1
2458
September1st to 10thDay
38%7%14%29%10%1
2160
11th to 20thDay
33%6%16%29%15%1
2088
21st to endDay
41%7%15%27%9%
1922
October1st to 10thDay
48%5%16%19%11%1
1800
11th to 20thDay
52%6%14%20%7%1
1800
21st to endDay
59%5%14%15%6%1
1980
November1st to 10thDay
49%6%14%21%9%1
1596
11th to 20thDay
55%6%14%15%9%1
1520
21st to endDay
58%416%17%4
1520
December1st to 10thDay
64%6%15%13%3
1520
11th to 20thDay
57%8%15%13%7%
1906
21st to endDay
73%5%9%10%3
2772
January1st to 10thNight
59%6%15%14%5%1
4429
11th to 20thNight
63%6%16%11%31
4271
21st to endNight
62%5%15%12%5%1
4532
February1st to 10thNight
60%5%11%18%5%1
2399
11th to 20thNight
57%5%10%18%9%1
2275
21st to endNight
53%5%13%20%8%1
1879
March1st to 10thNight
50%413%21%10%2
1980
11th to 20thNight
52%39%22%11%2
1980
21st to endNight
46%410%22%16%3
2178
April1st to 10thNight
51%48%22%14%1
1813
11th to 20thNight
46%5%10%19%17%2
1750
21st to endNight
48%5%11%20%14%2
1620
May1st to 10thNight
44%5%11%22%16%3
1598
11th to 20thNight
38%412%24%19%4
1416
21st to endNight
31%5%16%24%19%4
1551
June1st to 10thNight
38%7%11%26%16%2
1440
11th to 20thNight
36%5%12%22%22%2
1440
21st to endNight
37%6%14%26%16%1
1440
July1st to 10thNight
28%5%12%28%24%3
1400
11th to 20thNight
32%5%12%31%18%2
1392
21st to endNight
30%6%15%30%17%2
1604
August1st to 10thNight
31%5%20%29%14%2
1600
11th to 20thNight
30%5%17%33%14%1
1598
21st to endNight
35%5%13%30%16%1
1879
September1st to 10thNight
36%6%15%28%14%2
1800
11th to 20thNight
31%413%34%18%
1868
21st to endNight
41%5%12%29%13%1
2038
October1st to 10thNight
44%5%12%23%14%1
2160
11th to 20thNight
51%6%13%22%8%
2160
21st to endNight
54%5%13%16%10%
2376
November1st to 10thNight
46%413%24%13%1
2476
11th to 20thNight
52%5%15%17%10%1
2660
21st to endNight
55%7%18%16%4
2660
December1st to 10thNight
61%5%13%16%4
2660
11th to 20thNight
61%6%13%15%5%
3288
21st to endNight
70%5%14%8%3
4884

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 10thDay
24%17%32%19%7%1
180
11th to 20thDay
27%21%30%17%41
229
21st to endDay
30%16%34%15%41
297
February1st to 10thDay
28%24%31%13%3
252
11th to 20thDay
25%23%39%12%1
240
21st to endDay
33%20%33%13%1
235
March1st to 10thDay
24%16%36%19%6%
420
11th to 20thDay
24%16%34%20%6%
420
21st to endDay
31%10%31%20%8%1
462
April1st to 10thDay
20%14%37%22%6%1
420
11th to 20thDay
28%11%27%21%10%3
412
21st to endDay
26%13%34%17%8%2
420
May1st to 10thDay
24%8%29%24%9%6%
423
11th to 20thDay
17%7%28%30%14%4
447
21st to endDay
13%7%25%31%18%6%
485
June1st to 10thDay
16%7%32%30%13%2
450
11th to 20thDay
14%8%25%32%19%3
450
21st to endDay
17%428%32%14%5%
450
July1st to 10thDay
9%322%35%24%7%
445
11th to 20thDay
14%322%32%20%8%
444
21st to endDay
9%328%38%16%7%
488
August1st to 10thDay
11%222%33%20%12%
446
11th to 20thDay
13%320%29%27%8%
439
21st to endDay
13%5%22%31%18%11%
495
September1st to 10thDay
14%5%23%30%18%10%
450
11th to 20thDay
12%422%28%21%13%
450
21st to endDay
14%8%30%25%15%7%
450
October1st to 10thDay
22%9%25%24%15%6%
450
11th to 20thDay
22%14%32%23%7%1
450
21st to endDay
30%12%29%22%7%
495
November1st to 10thDay
23%16%26%25%9%1
269
11th to 20thDay
22%18%34%20%5%1
180
21st to endDay
29%13%37%16%41
180
December1st to 10thDay
24%14%34%20%5%2
180
11th to 20thDay
27%19%30%18%6%
180
21st to endDay
30%19%35%14%2
198
January1st to 10thNight
24%15%36%18%6%1
760
11th to 20thNight
28%14%31%22%41
760
21st to endNight
21%11%34%28%6%
836
February1st to 10thNight
22%15%38%22%3
739
11th to 20thNight
22%15%36%22%5%
703
21st to endNight
22%13%39%21%4
592
March1st to 10thNight
20%12%35%27%41
720
11th to 20thNight
23%12%34%25%5%1
720
21st to endNight
21%9%31%29%10%
792
April1st to 10thNight
25%11%31%28%6%
720
11th to 20thNight
18%11%33%27%9%1
686
21st to endNight
22%7%29%31%11%
540
May1st to 10thNight
22%425%30%17%2
518
11th to 20thNight
17%5%27%37%14%
354
21st to endNight
11%322%41%22%1
389
June1st to 10thNight
14%424%38%18%1
360
11th to 20thNight
11%5%24%40%19%1
360
21st to endNight
12%5%22%43%19%1
360
July1st to 10thNight
7%318%46%25%1
350
11th to 20thNight
13%218%41%25%1
348
21st to endNight
11%117%46%23%2
518
August1st to 10thNight
10%312%42%30%3
537
11th to 20thNight
8%113%42%31%5%
534
21st to endNight
12%320%38%25%3
691
September1st to 10thNight
12%5%19%37%22%5%
720
11th to 20thNight
14%419%32%25%6%
720
21st to endNight
18%7%19%32%21%4
720
October1st to 10thNight
20%5%26%29%19%2
720
11th to 20thNight
25%9%28%28%9%1
720
21st to endNight
29%7%28%30%5%1
792
November1st to 10thNight
23%9%25%31%11%1
740
11th to 20thNight
22%13%29%27%7%2
760
21st to endNight
25%11%30%26%7%
760
December1st to 10thNight
29%13%32%22%4
760
11th to 20thNight
23%13%36%23%4
760
21st to endNight
31%11%35%20%3
836
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