York Factory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the York Factory 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
40%
23941
6%
81137
5%
23864
42%
23864
12%
63766

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
38%
940
5%
5027
4%
926
40%
926
4%
4119
January11th to 20thNight
41%
935
3%
4960
5%
930
43%
930
6%
4126
January21st to endNight
40%
1040
5%
5199
7%
1023
43%
1023
7%
4154
February1st to 10thNight
50%
923
11%
2709
7%
923
52%
923
15%
2099
February11th to 20thNight
52%
874
12%
2311
8%
874
54%
874
20%
1742
February21st to endNight
54%
740
16%
1924
10%
740
56%
740
21%
1433
March1st to 10thNight
48%
770
12%
2210
9%
770
51%
770
18%
1659
March11th to 20thNight
47%
568
11%
2008
11%
568
51%
568
15%
1446
March21st to endNight
51%
594
17%
2070
19%
594
56%
594
18%
1429
April1st to 10thNight
47%
540
12%
1776
12%
540
50%
540
16%
1319
April11th to 20thNight
52%
533
13%
1539
9%
533
53%
533
20%
1103
April21st to endNight
51%
540
10%
1440
6%
540
52%
540
23%
1031
May1st to 10thNight
34%
540
2%
1389
2%
540
34%
540
15%
1111
May11th to 20thNight
36%
397
0%
1106
0%
397
36%
397
17%
860
May21st to endNight
34%
389
0%
1164
0%
388
34%
388
17%
871
June1st to 10thNight
48%
360
0%
1080
0%
360
48%
360
21%
763
June11th to 20thNight
50%
307
0%
1027
0%
307
50%
307
21%
693
June21st to endNight
55%
180
0%
900
0%
180
55%
180
13%
570
July1st to 10thNight
49%
337
0%
1037
0%
337
49%
337
17%
754
July11th to 20thNight
53%
348
0%
1044
0%
348
53%
348
21%
737
July21st to endNight
56%
511
0%
1227
0%
483
57%
483
24%
874
August1st to 10thNight
54%
537
2%
1264
2%
534
54%
534
26%
912
August11th to 20thNight
54%
534
7%
1422
6%
534
54%
534
21%
1030
August21st to endNight
47%
594
10%
1715
6%
594
49%
594
20%
1249
September1st to 10thNight
35%
540
6%
1768
5%
540
38%
540
11%
1362
September11th to 20thNight
36%
540
7%
1800
7%
540
38%
540
12%
1401
September21st to endNight
34%
651
9%
2051
6%
651
38%
651
13%
1581
October1st to 10thNight
24%
720
9%
2160
5%
720
27%
720
10%
1791
October11th to 20thNight
26%
720
7%
2247
6%
720
27%
720
7%
1899
October21st to endNight
22%
980
4%
2762
1%
980
24%
980
7%
2420
November1st to 10thNight
22%
925
5%
2595
2%
925
25%
925
7%
2294
November11th to 20thNight
27%
950
5%
2921
4%
950
29%
950
7%
2522
November21st to endNight
26%
950
4%
3040
2%
950
29%
950
7%
2577
December1st to 10thNight
34%
950
6%
3040
5%
950
36%
950
8%
2553
December11th to 20thNight
40%
949
8%
3716
6%
949
42%
949
8%
2977
December21st to endNight
38%
1035
5%
5489
8%
1026
41%
1026
6%
4305

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%11%5%9%8%46%6%6%7%24%
77421
Night
11%12%5%10%9%5%7%7%7%7%19%
81463
TransparencyDay
58%7%12%18%5%
77086
Night
62%7%11%15%4
81331
SeeingDay
17%420%30%21%7%
14776
Night
17%421%34%20%4
23987

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
5%9%5%16%15%7%9%8%7%6%11%
1899
11th to 20thDay
49%6%15%12%7%9%9%10%7%12%
2002
21st to endDay
9%14%6%13%10%5%7%10%8%6%12%
2442
February1st to 10thDay
27%413%12%6%10%11%9%8%17%
1346
11th to 20thDay
49%47%9%5%11%8%13%12%18%
1534
21st to endDay
49%5%8%9%7%9%9%13%9%19%
1332
March1st to 10thDay
6%10%5%10%8%5%10%8%9%10%18%
1748
11th to 20thDay
6%9%5%10%9%6%9%12%9%8%18%
1968
21st to endDay
6%8%49%9%6%11%9%7%7%25%
2286
April1st to 10thDay
9%11%5%9%9%7%10%8%7%6%20%
2182
11th to 20thDay
8%9%5%8%9%7%9%6%6%7%28%
2372
21st to endDay
6%8%410%10%6%6%6%6%7%30%
2520
May1st to 10thDay
16%14%5%12%10%44446%22%
2569
11th to 20thDay
16%11%7%12%7%35%45%6%24%
2788
21st to endDay
16%12%5%9%6%345%6%7%26%
3112
June1st to 10thDay
15%11%5%9%6%345%5%8%29%
2880
11th to 20thDay
15%6%35%5%45%6%6%8%37%
2925
21st to endDay
14%6%37%6%45%5%6%8%35%
3060
July1st to 10thDay
18%10%47%6%35%5%6%8%29%
2888
11th to 20thDay
14%8%36%6%35%5%6%9%36%
2880
21st to endDay
17%6%45%6%36%6%6%8%33%
3016
August1st to 10thDay
20%8%26%5%35%5%6%9%32%
2667
11th to 20thDay
20%7%36%6%345%5%7%33%
2479
21st to endDay
22%9%37%5%245%7%7%29%
2638
September1st to 10thDay
24%11%48%6%45%5%5%6%22%
2192
11th to 20thDay
23%13%48%6%45%45%7%21%
2160
21st to endDay
19%17%37%6%2445%6%27%
1886
October1st to 10thDay
22%18%5%8%6%35%445%20%
1800
11th to 20thDay
28%18%6%9%5%34435%13%
1713
21st to endDay
21%21%7%11%6%3334416%
1591
November1st to 10thDay
15%18%9%12%9%5%6%5%4413%
1482
11th to 20thDay
11%18%7%12%10%5%6%6%5%6%14%
1258
21st to endDay
8%19%10%12%9%5%9%8%7%6%9%
1140
December1st to 10thDay
7%16%7%14%11%5%8%6%9%7%9%
1140
11th to 20thDay
7%11%7%14%12%6%7%5%8%8%14%
1436
21st to endDay
6%15%9%12%9%5%9%8%7%6%15%
2090
January1st to 10thNight
410%5%13%15%8%11%11%8%6%8%
5057
11th to 20thNight
38%5%17%14%10%11%8%9%6%8%
4965
21st to endNight
10%16%7%11%11%5%7%8%9%7%9%
5225
February1st to 10thNight
47%410%11%8%12%12%11%8%14%
2709
11th to 20thNight
49%5%8%7%6%10%10%13%9%19%
2310
21st to endNight
5%10%6%8%7%5%9%11%12%10%17%
1924
March1st to 10thNight
7%9%49%10%6%8%9%10%9%20%
2199
11th to 20thNight
6%9%5%10%9%6%7%9%8%8%23%
2007
21st to endNight
6%9%47%7%6%9%9%7%8%27%
2070
April1st to 10thNight
9%11%49%9%5%9%7%7%6%24%
1776
11th to 20thNight
8%9%49%8%6%7%5%5%8%32%
1539
21st to endNight
7%9%48%8%5%5%5%6%6%36%
1440
May1st to 10thNight
18%14%5%11%9%24345%25%
1389
11th to 20thNight
17%11%7%11%7%35%446%26%
1106
21st to endNight
17%12%6%8%6%34348%28%
1164
June1st to 10thNight
17%8%47%6%45%5%5%8%33%
1080
11th to 20thNight
13%6%37%8%38%5%7%8%33%
1027
21st to endNight
10%9%47%6%47%5%5%7%35%
900
July1st to 10thNight
16%8%47%7%37%5%7%7%29%
1067
11th to 20thNight
15%8%47%5%36%6%5%7%34%
1080
21st to endNight
16%7%35%6%346%6%8%35%
1299
August1st to 10thNight
18%7%345%446%6%8%35%
1271
11th to 20thNight
17%6%37%5%45%6%7%8%33%
1422
21st to endNight
22%8%26%5%35%45%6%33%
1715
September1st to 10thNight
21%11%37%8%445%6%8%25%
1768
11th to 20thNight
23%10%36%7%46%5%6%7%25%
1800
21st to endNight
20%16%5%6%5%44445%29%
2051
October1st to 10thNight
25%17%5%8%5%245%45%19%
2160
11th to 20thNight
26%20%5%8%6%33345%17%
2247
21st to endNight
21%21%7%9%7%34335%15%
2762
November1st to 10thNight
14%19%8%14%8%5%6%5%5%5%12%
2595
11th to 20thNight
11%15%7%12%10%7%7%7%5%5%15%
2921
21st to endNight
9%17%8%14%10%46%7%6%7%12%
3040
December1st to 10thNight
6%14%8%13%11%5%8%8%11%7%9%
3040
11th to 20thNight
413%6%11%12%7%10%9%8%8%11%
3761
21st to endNight
5%12%8%12%10%7%11%7%7%6%16%
5577

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
71%5%12%11%1
1900
11th to 20thDay
65%8%11%14%2
2002
21st to endDay
66%5%9%12%8%
2442
February1st to 10thDay
57%6%11%21%5%
1346
11th to 20thDay
51%7%15%21%6%
1543
21st to endDay
53%7%10%19%12%
1332
March1st to 10thDay
56%7%11%21%41
1750
11th to 20thDay
59%6%12%16%7%
1968
21st to endDay
54%7%12%16%9%2
2286
April1st to 10thDay
62%7%7%18%6%
2182
11th to 20thDay
53%7%10%21%8%1
2372
21st to endDay
52%7%13%20%8%1
2520
May1st to 10thDay
64%5%9%17%4
2569
11th to 20thDay
60%6%9%18%7%
2792
21st to endDay
56%6%12%21%5%
3112
June1st to 10thDay
53%5%12%22%7%
2880
11th to 20thDay
42%7%13%28%10%1
2925
21st to endDay
45%8%12%26%8%
3060
July1st to 10thDay
52%9%13%21%5%
2809
11th to 20thDay
44%8%17%28%3
2793
21st to endDay
47%10%17%23%3
2848
August1st to 10thDay
49%8%18%21%4
2650
11th to 20thDay
50%9%18%20%3
2479
21st to endDay
53%8%17%18%3
2638
September1st to 10thDay
61%8%15%13%2
2192
11th to 20thDay
65%6%13%14%1
2160
21st to endDay
58%7%14%17%4
1886
October1st to 10thDay
68%6%10%13%2
1800
11th to 20thDay
74%8%9%8%1
1713
21st to endDay
74%6%8%8%3
1591
November1st to 10thDay
75%9%7%7%2
1482
11th to 20thDay
72%8%9%10%1
1258
21st to endDay
72%8%10%9%1
1140
December1st to 10thDay
71%6%8%12%3
1140
11th to 20thDay
66%6%9%16%3
1436
21st to endDay
67%6%8%15%4
2090
January1st to 10thNight
71%7%11%9%3
5057
11th to 20thNight
72%5%12%8%2
4965
21st to endNight
69%5%8%13%6%
5225
February1st to 10thNight
58%7%12%17%6%
2709
11th to 20thNight
53%7%14%20%6%
2311
21st to endNight
52%7%11%21%9%
1924
March1st to 10thNight
54%7%15%19%5%
2210
11th to 20thNight
54%7%12%20%7%
2008
21st to endNight
51%5%10%22%11%1
2070
April1st to 10thNight
56%6%9%20%9%
1776
11th to 20thNight
52%49%22%11%1
1539
21st to endNight
48%6%12%23%9%1
1440
May1st to 10thNight
63%47%21%4
1389
11th to 20thNight
61%49%17%9%1
1107
21st to endNight
55%6%10%23%5%
1164
June1st to 10thNight
49%6%9%26%10%
1080
11th to 20thNight
47%6%10%23%13%1
1027
21st to endNight
46%8%10%24%10%1
900
July1st to 10thNight
50%10%14%21%5%
1037
11th to 20thNight
47%8%16%25%5%
1044
21st to endNight
45%9%18%26%3
1227
August1st to 10thNight
43%10%20%23%4
1264
11th to 20thNight
46%10%17%23%4
1422
21st to endNight
51%7%16%21%4
1715
September1st to 10thNight
59%9%14%16%2
1768
11th to 20thNight
58%10%16%15%2
1800
21st to endNight
59%8%12%16%5%
2051
October1st to 10thNight
68%7%10%12%3
2160
11th to 20thNight
72%6%12%8%2
2247
21st to endNight
74%7%9%7%2
2762
November1st to 10thNight
75%7%9%8%1
2595
11th to 20thNight
71%9%9%10%1
2921
21st to endNight
70%8%12%10%1
3040
December1st to 10thNight
69%8%9%12%2
3040
11th to 20thNight
65%7%13%12%3
3760
21st to endNight
65%8%8%16%3
5577

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
7%129%35%22%5%
180
11th to 20thDay
6%327%38%22%4
211
21st to endDay
12%416%33%28%7%
297
February1st to 10thDay
5%419%39%29%5%
252
11th to 20thDay
9%121%45%22%2
240
21st to endDay
6%316%32%30%13%
198
March1st to 10thDay
9%117%34%23%16%
240
11th to 20thDay
8%423%31%22%13%
240
21st to endDay
7%421%30%26%11%
372
April1st to 10thDay
12%320%25%29%11%
442
11th to 20thDay
8%323%34%23%8%
590
21st to endDay
9%419%32%26%10%
600
May1st to 10thDay
18%6%19%30%20%7%
603
11th to 20thDay
17%6%28%30%16%4
625
21st to endDay
19%5%24%32%18%3
679
June1st to 10thDay
19%5%21%30%21%5%
630
11th to 20thDay
17%318%32%21%8%
630
21st to endDay
17%317%33%22%8%
630
July1st to 10thDay
22%214%30%24%6%
621
11th to 20thDay
17%414%34%25%7%
618
21st to endDay
19%5%15%30%21%10%
684
August1st to 10thDay
22%316%30%21%8%
626
11th to 20thDay
20%415%28%23%10%
615
21st to endDay
27%316%28%19%7%
693
September1st to 10thDay
30%6%22%26%13%3
482
11th to 20thDay
26%7%23%25%16%4
450
21st to endDay
29%324%28%13%3
306
October1st to 10thDay
21%6%26%28%16%3
270
11th to 20thDay
35%6%22%18%15%4
270
21st to endDay
24%7%26%22%18%3
297
November1st to 10thDay
17%7%27%29%15%6%
267
11th to 20thDay
17%7%29%32%12%2
180
21st to endDay
19%13%19%23%16%9%
180
December1st to 10thDay
15%424%34%21%2
180
11th to 20thDay
10%7%27%32%21%3
180
21st to endDay
6%6%19%33%29%8%
198
January1st to 10thNight
12%323%36%19%7%
950
11th to 20thNight
9%423%38%22%5%
950
21st to endNight
11%5%21%35%24%4
1045
February1st to 10thNight
6%422%37%27%3
923
11th to 20thNight
8%218%43%23%5%
879
21st to endNight
8%316%39%24%10%
740
March1st to 10thNight
12%219%34%28%5%
770
11th to 20thNight
11%5%22%37%22%4
568
21st to endNight
9%422%31%26%7%
594
April1st to 10thNight
13%319%34%25%5%
540
11th to 20thNight
11%320%36%24%5%
533
21st to endNight
9%5%20%38%24%4
540
May1st to 10thNight
25%420%30%18%3
540
11th to 20thNight
19%5%24%36%15%1
397
21st to endNight
22%325%34%15%1
389
June1st to 10thNight
18%319%39%18%3
360
11th to 20thNight
15%418%36%24%2
307
21st to endNight
14%117%44%22%2
180
July1st to 10thNight
20%116%37%24%2
337
11th to 20thNight
19%414%36%24%4
348
21st to endNight
20%312%31%28%6%
511
August1st to 10thNight
20%313%32%28%4
537
11th to 20thNight
19%315%34%26%3
534
21st to endNight
26%414%35%18%3
594
September1st to 10thNight
28%323%33%12%2
540
11th to 20thNight
29%5%22%26%16%2
540
21st to endNight
29%5%24%28%13%2
651
October1st to 10thNight
36%8%22%25%9%1
720
11th to 20thNight
37%6%18%24%13%3
720
21st to endNight
32%5%25%25%11%3
980
November1st to 10thNight
22%7%28%28%13%2
925
11th to 20thNight
17%5%30%31%14%2
950
21st to endNight
17%8%25%33%12%5%
950
December1st to 10thNight
12%429%36%17%3
950
11th to 20thNight
11%423%33%25%4
950
21st to endNight
11%322%36%21%7%
1045
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Copyright 2024 Attilla Danko


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