Rochester
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Rochester clear sky chart from 2005-11-05 to 2018-02-14.

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
29%
15443
12%
48845
8%
15411
35%
15411
15%
35545

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
10%
778
5%
2716
3%
776
14%
776
5%
2302
January16th to endNight
12%
832
7%
2730
3%
832
18%
832
6%
2276
February1st to 15thNight
8%
759
6%
2468
1%
757
15%
757
5%
2031
February16th to endNight
16%
631
8%
1979
4%
631
22%
631
9%
1579
March1st to 15thNight
19%
720
11%
2019
5%
720
25%
720
12%
1602
March16th to endNight
27%
768
15%
2087
7%
768
33%
768
19%
1539
April1st to 15thNight
24%
718
13%
1796
4%
718
29%
718
18%
1371
April16th to endNight
37%
649
18%
1729
9%
649
42%
649
27%
1172
May1st to 15thNight
43%
432
16%
1512
12%
432
49%
432
18%
1015
May16th to endNight
43%
374
16%
1497
15%
374
54%
374
24%
864
June1st to 15thNight
43%
360
14%
1440
14%
360
53%
360
19%
894
June16th to endNight
45%
360
12%
1440
14%
360
52%
360
21%
865
July1st to 15thNight
56%
340
15%
1360
20%
340
61%
340
28%
746
July16th to endNight
57%
421
16%
1460
16%
396
62%
396
30%
819
August1st to 15thNight
56%
539
16%
1609
10%
536
59%
536
33%
959
August16th to endNight
59%
685
22%
1831
13%
685
63%
685
36%
1117
September1st to 15thNight
50%
720
19%
1800
10%
720
53%
720
32%
1190
September16th to endNight
53%
717
23%
1983
18%
717
56%
717
30%
1277
October1st to 15thNight
35%
720
13%
2160
11%
720
39%
720
19%
1531
October16th to endNight
19%
768
10%
2310
4%
768
26%
768
13%
1768
November1st to 15thNight
26%
760
14%
2547
12%
760
31%
760
15%
1801
November16th to endNight
19%
780
10%
2730
7%
780
24%
780
10%
2069
December1st to 15thNight
11%
780
5%
2730
1%
780
16%
780
6%
2233
December16th to endNight
9%
832
4%
2912
1%
832
12%
832
4%
2525

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%9%47%6%35%45%6%31%
49235
Night
16%10%47%6%3445%6%30%
49019
Cloud CoverDay
15%9%47%6%35%5%5%6%29%
49245
Night
16%10%47%6%3445%6%29%
49024
TransparencyDay
52%6%12%18%9%
48927
Night
54%5%12%17%9%
48845
SeeingDay
19%13%28%22%11%4
5892
Night
21%14%27%23%10%1
15447

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%15%8%10%10%46%445%13%
1552
16th to endDay
12%15%8%13%10%5%6%445%13%
1846
February1st to 15thDay
16%14%8%12%9%45%5%3414%
1695
16th to endDay
17%12%5%12%9%35%45%5%16%
1494
March1st to 15thDay
16%14%6%10%8%46%435%20%
1927
16th to endDay
17%10%46%5%34347%32%
2136
April1st to 15thDay
19%10%36%5%3445%5%32%
2152
16th to endDay
17%9%2442445%6%38%
2241
May1st to 15thDay
15%7%25%5%35%5%5%7%35%
2439
16th to endDay
13%6%245%3445%8%40%
2618
June1st to 15thDay
18%6%25%5%35%45%6%36%
2520
16th to endDay
13%4145%345%6%9%40%
2520
July1st to 15thDay
10%425%435%5%6%8%43%
2520
16th to endDay
11%426%6%46%6%6%8%36%
2607
August1st to 15thDay
11%5%25%6%45%6%5%8%38%
2340
16th to endDay
14%5%25%5%345%5%8%39%
2357
September1st to 15thDay
18%4345%245%5%6%39%
2160
16th to endDay
15%5%25%434447%40%
1973
October1st to 15thDay
21%7%26%5%33436%33%
1800
16th to endDay
26%10%36%5%35%445%23%
1914
November1st to 15thDay
14%12%37%7%25%445%31%
1640
16th to endDay
19%15%38%6%36%45%6%21%
1560
December1st to 15thDay
18%15%7%10%8%24445%17%
1560
16th to endDay
20%18%8%12%6%3444312%
1664
January1st to 15thNight
18%15%7%11%9%4444414%
2716
16th to endNight
15%15%8%11%9%46%335%16%
2730
February1st to 15thNight
16%15%7%12%7%34445%17%
2466
16th to endNight
14%12%6%13%8%35%446%19%
1979
March1st to 15thNight
19%11%5%10%8%2444424%
2007
16th to endNight
16%10%47%5%3444434%
2087
April1st to 15thNight
20%10%35%6%3444431%
1796
16th to endNight
17%5%25%42345%8%40%
1729
May1st to 15thNight
17%5%25%5%3446%7%35%
1512
16th to endNight
11%42442435%8%46%
1495
June1st to 15thNight
15%6%24435%5%7%7%37%
1440
16th to endNight
11%5%25%5%26%5%5%9%40%
1440
July1st to 15thNight
8%4244435%5%8%48%
1440
16th to endNight
9%32433447%8%47%
1559
August1st to 15thNight
8%3245%2446%9%47%
1620
16th to endNight
9%3135%25%6%5%7%49%
1831
September1st to 15thNight
16%5%25%424347%44%
1800
16th to endNight
15%42432347%7%43%
1983
October1st to 15thNight
21%6%36%5%34446%34%
2160
16th to endNight
28%10%26%5%33346%24%
2310
November1st to 15thNight
18%10%36%5%345%5%5%31%
2547
16th to endNight
19%13%47%6%35%35%6%24%
2730
December1st to 15thNight
18%18%6%9%6%245%45%17%
2730
16th to endNight
22%18%6%10%7%45%34412%
2912

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
15%15%7%11%10%5%6%5%45%12%
1552
16th to endDay
11%15%8%14%11%5%5%5%45%12%
1846
February1st to 15thDay
16%14%9%13%9%46%5%3413%
1695
16th to endDay
17%13%5%12%9%35%45%5%16%
1494
March1st to 15thDay
16%15%6%10%8%45%44420%
1938
16th to endDay
16%10%5%6%5%34446%31%
2135
April1st to 15thDay
18%11%46%5%2445%5%31%
2152
16th to endDay
18%8%35%424446%37%
2241
May1st to 15thDay
15%8%25%5%35%46%7%34%
2439
16th to endDay
13%6%25%5%3446%8%38%
2618
June1st to 15thDay
17%7%25%435%5%5%7%35%
2520
16th to endDay
12%425%5%35%6%7%9%37%
2520
July1st to 15thDay
9%5%25%5%36%6%7%8%41%
2520
16th to endDay
11%436%6%46%6%7%9%33%
2607
August1st to 15thDay
10%5%26%6%36%6%6%9%36%
2340
16th to endDay
13%6%25%5%35%5%6%8%36%
2357
September1st to 15thDay
16%5%345%345%5%7%38%
2160
16th to endDay
14%6%36%43445%7%39%
1973
October1st to 15thDay
20%8%26%5%34446%33%
1800
16th to endDay
24%10%48%6%35%5%36%22%
1914
November1st to 15thDay
13%12%48%5%35%6%45%30%
1640
16th to endDay
19%13%5%8%6%36%45%6%20%
1560
December1st to 15thDay
17%15%8%12%7%3344417%
1560
16th to endDay
19%17%8%14%7%345%3411%
1664
January1st to 15thNight
17%16%7%11%9%45%5%4413%
2716
16th to endNight
14%16%7%12%9%5%6%345%15%
2730
February1st to 15thNight
15%16%6%13%8%45%445%17%
2459
16th to endNight
14%13%6%12%8%45%45%5%19%
1979
March1st to 15thNight
19%12%5%9%7%3434424%
2019
16th to endNight
17%9%47%5%34345%32%
2087
April1st to 15thNight
20%10%35%6%35%435%30%
1796
16th to endNight
16%6%25%42345%7%40%
1729
May1st to 15thNight
17%5%26%5%345%6%7%35%
1512
16th to endNight
10%5%25%4335%5%7%45%
1495
June1st to 15thNight
14%6%245%36%5%7%7%37%
1440
16th to endNight
10%6%26%425%5%6%8%40%
1440
July1st to 15thNight
6%5%26%42446%8%47%
1440
16th to endNight
8%4243245%7%8%46%
1559
August1st to 15thNight
8%3246%345%6%10%46%
1620
16th to endNight
9%313435%5%5%8%49%
1831
September1st to 15thNight
15%5%25%42345%7%43%
1800
16th to endNight
14%5%1432446%8%43%
1983
October1st to 15thNight
19%7%36%5%34446%33%
2160
16th to endNight
26%10%36%5%3335%6%24%
2310
November1st to 15thNight
17%10%36%6%3445%6%30%
2547
16th to endNight
19%13%48%5%35%45%6%23%
2730
December1st to 15thNight
17%17%6%9%6%36%446%16%
2730
16th to endNight
20%18%7%10%8%44445%11%
2912

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
73%5%9%9%2
1553
16th to endDay
73%6%11%6%1
1846
February1st to 15thDay
74%5%8%9%1
1697
16th to endDay
68%5%10%11%4
1494
March1st to 15thDay
67%410%13%4
1938
16th to endDay
53%5%10%19%9%
2136
April1st to 15thDay
54%411%17%10%1
2152
16th to endDay
46%5%7%20%17%2
2241
May1st to 15thDay
47%6%11%21%12%1
2439
16th to endDay
41%6%14%22%13%1
2622
June1st to 15thDay
47%6%11%21%12%
2520
16th to endDay
40%7%14%23%13%
2520
July1st to 15thDay
36%7%11%26%16%
2371
16th to endDay
43%8%15%21%10%
2443
August1st to 15thDay
41%7%16%20%12%
2327
16th to endDay
41%7%13%25%10%1
2357
September1st to 15thDay
43%6%12%24%11%
2160
16th to endDay
42%5%13%23%14%
1973
October1st to 15thDay
52%5%10%19%11%
1800
16th to endDay
61%6%15%13%2
1914
November1st to 15thDay
53%7%13%14%8%1
1640
16th to endDay
62%5%14%14%3
1560
December1st to 15thDay
69%412%10%1
1560
16th to endDay
76%5%9%5%2
1664
January1st to 15thNight
72%5%9%7%4
2716
16th to endNight
71%410%10%3
2730
February1st to 15thNight
69%410%11%3
2468
16th to endNight
66%312%12%4
1979
March1st to 15thNight
62%411%16%4
2019
16th to endNight
53%5%10%17%12%1
2087
April1st to 15thNight
55%5%9%18%10%1
1796
16th to endNight
42%5%10%21%15%3
1729
May1st to 15thNight
46%7%10%19%14%1
1512
16th to endNight
35%7%14%23%16%2
1497
June1st to 15thNight
42%6%13%24%12%
1440
16th to endNight
39%7%12%21%17%1
1440
July1st to 15thNight
33%5%15%25%19%1
1360
16th to endNight
31%7%16%28%14%2
1460
August1st to 15thNight
32%7%18%28%12%
1609
16th to endNight
31%7%13%32%14%1
1831
September1st to 15thNight
39%413%26%13%2
1800
16th to endNight
36%6%12%28%15%
1983
October1st to 15thNight
50%5%11%18%12%
2160
16th to endNight
58%5%15%13%4
2310
November1st to 15thNight
52%6%14%15%8%2
2547
16th to endNight
59%5%15%14%4
2730
December1st to 15thNight
68%5%13%10%2
2730
16th to endNight
75%6%9%6%2
2912

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
15%33%32%13%5%
90
16th to endDay
26%24%39%8%
138
February1st to 15thDay
22%40%29%7%
130
16th to endDay
24%21%39%13%1
153
March1st to 15thDay
22%26%25%18%5%
270
16th to endDay
24%15%35%17%5%2
288
April1st to 15thDay
25%20%30%15%5%1
270
16th to endDay
18%14%29%23%10%3
270
May1st to 15thDay
24%12%26%19%13%4
288
16th to endDay
15%10%33%24%12%3
331
June1st to 15thDay
22%6%30%27%11%1
315
16th to endDay
15%7%33%29%12%1
315
July1st to 15thDay
11%423%38%18%2
305
16th to endDay
11%7%27%31%18%3
326
August1st to 15thDay
12%226%33%15%9%
313
16th to endDay
15%5%17%29%20%12%
332
September1st to 15thDay
15%6%20%24%21%11%
315
16th to endDay
14%9%20%19%21%14%
314
October1st to 15thDay
25%7%27%18%14%6%
315
16th to endDay
30%17%28%18%5%
334
November1st to 15thDay
19%11%32%24%9%1
204
16th to endDay
25%26%26%17%3
90
December1st to 15thDay
18%32%24%18%41
90
16th to endDay
30%36%28%5%
96
January1st to 15thNight
27%23%32%13%2
780
16th to endNight
22%24%33%17%2
832
February1st to 15thNight
26%24%33%13%1
760
16th to endNight
23%22%31%19%2
631
March1st to 15thNight
26%20%29%20%3
720
16th to endNight
22%14%32%21%8%
768
April1st to 15thNight
25%15%30%24%3
718
16th to endNight
20%11%28%28%10%1
649
May1st to 15thNight
21%6%21%33%16%
432
16th to endNight
12%435%29%18%1
375
June1st to 15thNight
16%5%27%33%15%1
360
16th to endNight
14%430%36%13%
360
July1st to 15thNight
8%223%40%22%2
340
16th to endNight
9%224%38%22%3
421
August1st to 15thNight
9%225%36%22%4
539
16th to endNight
10%419%33%28%2
685
September1st to 15thNight
18%6%19%26%27%2
720
16th to endNight
16%8%17%24%25%8%
717
October1st to 15thNight
23%10%25%24%14%2
720
16th to endNight
33%13%28%20%3
768
November1st to 15thNight
23%14%31%20%9%1
760
16th to endNight
26%21%26%16%8%
780
December1st to 15thNight
28%24%28%14%2
780
16th to endNight
30%24%29%13%1
832
Page generated at 2018-02-15 10:58:48. Version ac04

Copyright 2018 A. Danko


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