This page made possible by the sponsorship of: Peter Zsenits.

Rochester
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Rochester clear sky chart from 2005-11-06 to 2024-01-31.

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
27%
22924
12%
75049
8%
22882
33%
22882
14%
54840

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
9%
758
6%
2649
3%
757
14%
757
5%
2215
January11th to 20thNight
12%
760
4%
2603
2%
760
15%
760
4%
2261
January21st to endNight
12%
835
7%
2711
3%
835
17%
835
6%
2292
February1st to 10thNight
8%
720
7%
2340
1%
720
16%
720
6%
1903
February11th to 20thNight
11%
702
8%
2275
2%
700
19%
700
7%
1844
February21st to endNight
13%
592
9%
1816
4%
592
20%
592
9%
1451
March1st to 10thNight
16%
720
11%
2039
5%
720
23%
720
11%
1600
March11th to 20thNight
19%
720
14%
1980
7%
720
26%
720
15%
1482
March21st to endNight
24%
792
15%
2141
6%
792
31%
792
18%
1597
April1st to 10thNight
19%
720
13%
1800
3%
720
25%
720
17%
1372
April11th to 20thNight
28%
711
14%
1775
5%
711
32%
711
21%
1307
April21st to endNight
32%
614
16%
1694
7%
614
37%
614
21%
1197
May1st to 10thNight
38%
468
14%
1548
10%
468
43%
468
17%
1072
May11th to 20thNight
40%
354
20%
1416
16%
354
51%
354
21%
843
May21st to endNight
43%
388
15%
1551
14%
388
53%
388
24%
874
June1st to 10thNight
40%
360
15%
1440
14%
360
52%
360
20%
883
June11th to 20thNight
44%
360
15%
1440
18%
360
52%
360
21%
837
June21st to endNight
45%
360
14%
1440
15%
360
53%
360
20%
880
July1st to 10thNight
58%
350
16%
1400
20%
350
63%
350
27%
770
July11th to 20thNight
52%
348
18%
1392
21%
348
59%
348
27%
777
July21st to endNight
53%
461
18%
1550
16%
436
59%
436
30%
890
August1st to 10thNight
54%
537
18%
1600
13%
534
58%
534
33%
956
August11th to 20thNight
55%
534
18%
1598
13%
534
57%
534
29%
1001
August21st to endNight
54%
761
20%
1949
10%
761
57%
761
35%
1240
September1st to 10thNight
48%
720
18%
1800
8%
720
52%
720
32%
1186
September11th to 20thNight
52%
720
24%
1800
15%
720
55%
720
35%
1178
September21st to endNight
44%
720
19%
2074
14%
720
48%
720
24%
1385
October1st to 10thNight
33%
720
13%
2160
10%
720
38%
720
19%
1530
October11th to 20thNight
23%
720
11%
2160
6%
720
30%
720
16%
1562
October21st to endNight
18%
792
13%
2384
5%
792
27%
792
13%
1833
November1st to 10thNight
26%
740
16%
2421
11%
740
34%
740
16%
1678
November11th to 20thNight
19%
760
13%
2660
9%
760
25%
760
12%
1918
November21st to endNight
16%
760
8%
2660
5%
760
22%
760
9%
2047
December1st to 10thNight
11%
760
5%
2660
2%
760
14%
760
6%
2168
December11th to 20thNight
11%
759
5%
3258
1%
759
16%
759
4%
2635
December21st to endNight
8%
828
3%
4865
0%
817
11%
817
2%
4176

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%10%47%6%45%5%5%7%31%
74856
Night
17%11%48%6%35%5%5%6%29%
75273
TransparencyDay
53%6%12%18%9%1
74565
Night
55%6%12%17%9%1
75098
SeeingDay
20%17%30%21%9%3
13490
Night
22%16%29%23%9%1
22937

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
13%16%9%11%10%5%7%5%5%5%13%
1517
11th to 20thDay
16%18%8%14%11%45%445%11%
1577
21st to endDay
14%16%8%13%13%6%6%445%11%
1872
February1st to 10thDay
18%15%7%13%8%45%6%46%14%
1620
11th to 20thDay
12%15%8%13%10%6%7%5%35%16%
1573
21st to endDay
21%13%413%9%35%46%5%17%
1440
March1st to 10thDay
14%12%6%11%8%5%6%5%45%22%
1914
11th to 20thDay
14%14%5%9%7%45%446%29%
1980
21st to endDay
19%11%5%7%6%3435%7%30%
2214
April1st to 10thDay
17%12%5%7%6%3445%6%31%
2160
11th to 20thDay
19%9%35%5%245%5%6%37%
2134
21st to endDay
21%10%36%6%3445%6%31%
2281
May1st to 10thDay
17%9%27%6%45%5%6%7%33%
2412
11th to 20thDay
16%7%35%5%45%5%5%7%39%
2478
21st to endDay
12%6%25%6%45%5%6%8%43%
2725
June1st to 10thDay
17%6%26%5%36%5%5%7%39%
2520
11th to 20thDay
13%5%25%5%45%5%7%10%40%
2520
21st to endDay
13%6%35%5%345%6%8%41%
2520
July1st to 10thDay
10%5%25%5%345%6%9%46%
2520
11th to 20thDay
12%5%35%6%46%6%7%9%39%
2520
21st to endDay
12%5%36%6%46%6%7%9%38%
2674
August1st to 10thDay
11%5%25%6%46%6%6%9%41%
2327
11th to 20thDay
10%6%37%7%45%7%7%9%35%
2303
21st to endDay
15%5%25%5%45%5%5%9%40%
2388
September1st to 10thDay
15%5%346%345%6%7%41%
2160
11th to 20thDay
16%5%245%345%5%7%43%
2160
21st to endDay
17%6%36%6%46%5%5%7%36%
1883
October1st to 10thDay
22%8%36%5%44446%34%
1800
11th to 20thDay
21%10%37%7%35%45%6%28%
1800
21st to endDay
28%11%37%7%35%5%45%23%
1972
November1st to 10thDay
15%11%38%8%35%5%5%5%32%
1654
11th to 20thDay
15%14%5%8%8%45%45%5%26%
1520
21st to endDay
20%16%49%6%46%5%5%6%20%
1520
December1st to 10thDay
20%18%9%10%8%3445%5%15%
1520
11th to 20thDay
19%17%8%14%8%35%44415%
1906
21st to endDay
27%20%7%12%6%3443410%
2772
January1st to 10thNight
17%17%7%11%9%5%5%44416%
2649
11th to 20thNight
17%17%8%14%9%4444413%
2603
21st to endNight
14%16%7%14%11%5%6%435%14%
2711
February1st to 10thNight
18%16%6%13%7%445%46%18%
2340
11th to 20thNight
15%12%7%12%9%47%45%6%19%
2273
21st to endNight
17%13%6%13%7%35%5%46%20%
1816
March1st to 10thNight
16%13%6%11%8%35%45%5%24%
2029
11th to 20thNight
17%12%48%7%35%445%31%
1979
21st to endNight
18%11%49%6%34445%33%
2141
April1st to 10thNight
19%13%46%7%34446%30%
1800
11th to 20thNight
18%8%36%5%35%5%5%6%35%
1775
21st to endNight
21%7%36%5%345%5%7%35%
1694
May1st to 10thNight
19%8%36%6%35%5%6%6%35%
1548
11th to 20thNight
13%6%26%6%345%7%8%42%
1415
21st to endNight
11%5%35%5%35%45%8%49%
1550
June1st to 10thNight
16%6%25%435%6%7%9%37%
1440
11th to 20thNight
12%6%25%5%45%5%6%8%42%
1440
21st to endNight
11%5%37%5%36%6%6%9%40%
1440
July1st to 10thNight
8%425%5%345%5%9%49%
1440
11th to 20thNight
11%5%24445%46%8%48%
1440
21st to endNight
11%5%2443448%9%46%
1641
August1st to 10thNight
9%435%5%35%5%6%9%47%
1611
11th to 20thNight
10%426%6%35%6%6%8%43%
1598
21st to endNight
9%4245%36%6%6%8%45%
1949
September1st to 10thNight
15%6%25%43445%8%44%
1800
11th to 20thNight
16%425%43445%6%46%
1800
21st to endNight
16%6%25%5%345%7%7%39%
2074
October1st to 10thNight
21%6%36%6%34446%35%
2160
11th to 20thNight
22%9%37%6%345%5%7%30%
2160
21st to endNight
29%10%37%5%3345%5%25%
2384
November1st to 10thNight
16%10%37%6%345%5%5%35%
2421
11th to 20thNight
16%11%48%6%45%5%6%6%28%
2660
21st to endNight
20%14%5%7%7%35%46%7%22%
2660
December1st to 10thNight
19%19%6%9%7%45%5%5%5%17%
2660
11th to 20thNight
18%17%7%11%7%35%445%18%
3288
21st to endNight
31%17%6%10%6%4445%410%
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
73%6%9%10%2
1518
11th to 20thDay
77%6%9%5%1
1577
21st to endDay
76%6%10%6%1
1872
February1st to 10thDay
73%5%10%10%2
1620
11th to 20thDay
72%5%8%11%3
1582
21st to endDay
70%5%10%10%5%
1440
March1st to 10thDay
64%6%11%14%31
1917
11th to 20thDay
58%6%10%16%10%1
1980
21st to endDay
56%6%8%18%10%2
2214
April1st to 10thDay
55%411%18%10%1
2160
11th to 20thDay
48%6%10%21%14%2
2134
21st to endDay
54%6%7%18%13%2
2281
May1st to 10thDay
50%6%10%20%12%2
2412
11th to 20thDay
44%7%11%23%13%2
2482
21st to endDay
39%6%15%24%14%1
2725
June1st to 10thDay
45%7%11%20%17%1
2520
11th to 20thDay
40%7%13%25%14%1
2520
21st to endDay
40%6%14%22%16%1
2520
July1st to 10thDay
35%7%12%28%15%2
2450
11th to 20thDay
39%8%15%25%12%
2445
21st to endDay
41%10%14%21%13%1
2524
August1st to 10thDay
38%8%17%24%13%1
2314
11th to 20thDay
43%9%14%24%9%1
2303
21st to endDay
41%7%13%26%10%2
2388
September1st to 10thDay
41%8%12%27%11%1
2160
11th to 20thDay
40%5%13%26%15%
2160
21st to endDay
47%6%12%22%12%1
1883
October1st to 10thDay
51%6%13%19%11%1
1800
11th to 20thDay
56%6%15%17%6%1
1800
21st to endDay
64%6%10%14%5%1
1972
November1st to 10thDay
53%7%11%18%9%2
1654
11th to 20thDay
60%6%14%14%6%1
1520
21st to endDay
65%5%15%13%2
1520
December1st to 10thDay
73%412%11%1
1520
11th to 20thDay
74%5%11%6%3
1906
21st to endDay
80%5%8%7%1
2772
January1st to 10thNight
72%5%10%9%4
2649
11th to 20thNight
75%6%10%7%2
2603
21st to endNight
73%410%9%4
2711
February1st to 10thNight
68%5%10%12%4
2340
11th to 20thNight
67%5%11%13%4
2275
21st to endNight
65%5%11%13%6%
1816
March1st to 10thNight
62%5%12%16%5%
2039
11th to 20thNight
56%5%11%20%8%1
1980
21st to endNight
55%5%9%18%12%2
2141
April1st to 10thNight
55%6%10%20%9%1
1800
11th to 20thNight
49%7%11%18%14%2
1775
21st to endNight
48%6%10%20%14%2
1694
May1st to 10thNight
49%7%9%18%15%2
1548
11th to 20thNight
39%7%13%23%15%3
1416
21st to endNight
34%8%16%22%19%2
1551
June1st to 10thNight
42%7%13%23%14%2
1440
11th to 20thNight
39%6%13%23%18%2
1440
21st to endNight
39%9%11%25%16%1
1440
July1st to 10thNight
33%6%14%25%19%3
1400
11th to 20thNight
35%5%13%30%15%2
1392
21st to endNight
32%7%16%28%14%2
1550
August1st to 10thNight
33%7%16%29%14%1
1600
11th to 20thNight
37%7%17%29%10%1
1598
21st to endNight
33%7%15%30%12%2
1949
September1st to 10thNight
38%6%15%28%12%2
1800
11th to 20thNight
38%413%28%16%1
1800
21st to endNight
41%7%14%25%12%1
2074
October1st to 10thNight
50%6%12%19%12%1
2160
11th to 20thNight
52%7%15%18%8%1
2160
21st to endNight
59%5%13%14%7%1
2384
November1st to 10thNight
49%7%13%19%10%2
2421
11th to 20thNight
55%6%16%15%7%1
2660
21st to endNight
60%7%16%14%3
2660
December1st to 10thNight
68%6%14%9%2
2660
11th to 20thNight
68%6%12%11%2
3288
21st to endNight
77%5%10%7%1
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
26%28%30%11%4
180
11th to 20thDay
25%29%35%9%1
207
21st to endDay
24%25%34%14%4
294
February1st to 10thDay
28%34%31%7%
240
11th to 20thDay
25%37%32%6%
240
21st to endDay
34%25%33%8%1
306
March1st to 10thDay
18%31%32%15%31
420
11th to 20thDay
25%25%31%15%31
420
21st to endDay
29%21%28%15%6%
462
April1st to 10thDay
23%25%30%16%5%1
420
11th to 20thDay
27%21%27%15%7%3
412
21st to endDay
24%21%32%17%6%1
420
May1st to 10thDay
26%15%30%18%8%3
423
11th to 20thDay
17%13%33%28%7%2
447
21st to endDay
14%13%31%25%13%4
485
June1st to 10thDay
16%12%37%26%8%1
450
11th to 20thDay
16%12%30%28%12%2
450
21st to endDay
12%12%36%27%11%1
450
July1st to 10thDay
11%8%25%35%18%4
445
11th to 20thDay
11%7%29%32%17%2
444
21st to endDay
10%9%36%32%11%2
488
August1st to 10thDay
10%7%26%34%17%6%
446
11th to 20thDay
13%8%25%31%17%7%
439
21st to endDay
12%9%27%31%14%6%
495
September1st to 10thDay
14%11%26%28%13%8%
450
11th to 20thDay
14%9%23%24%21%9%
450
21st to endDay
16%15%26%24%15%5%
450
October1st to 10thDay
24%13%26%18%14%4
450
11th to 20thDay
26%19%32%16%6%2
450
21st to endDay
32%19%29%17%3
491
November1st to 10thDay
22%18%31%20%8%1
348
11th to 20thDay
26%28%28%14%31
180
21st to endDay
30%22%36%10%2
180
December1st to 10thDay
31%24%29%12%31
180
11th to 20thDay
31%27%28%12%2
180
21st to endDay
29%30%31%9%11
198
January1st to 10thNight
27%24%32%13%3
760
11th to 20thNight
26%24%31%16%3
760
21st to endNight
21%24%35%17%3
835
February1st to 10thNight
27%26%32%14%1
720
11th to 20thNight
24%24%34%14%2
703
21st to endNight
27%22%33%16%2
592
March1st to 10thNight
26%19%34%18%4
720
11th to 20thNight
24%21%31%18%4
720
21st to endNight
23%15%33%21%7%1
792
April1st to 10thNight
24%17%36%20%3
720
11th to 20thNight
22%17%29%24%6%2
711
21st to endNight
23%12%28%27%8%1
614
May1st to 10thNight
24%8%25%28%14%1
468
11th to 20thNight
15%6%32%38%9%
354
21st to endNight
11%6%35%28%19%1
389
June1st to 10thNight
15%8%31%33%14%1
360
11th to 20thNight
15%8%28%32%18%1
360
21st to endNight
11%6%31%41%10%
360
July1st to 10thNight
7%323%45%19%3
350
11th to 20thNight
11%329%36%20%2
348
21st to endNight
12%325%40%17%3
461
August1st to 10thNight
10%226%38%21%3
537
11th to 20thNight
10%6%20%37%23%4
534
21st to endNight
10%6%24%35%23%2
761
September1st to 10thNight
17%7%23%28%23%3
720
11th to 20thNight
16%7%19%29%24%5%
720
21st to endNight
16%10%24%28%18%4
720
October1st to 10thNight
22%10%28%22%15%3
720
11th to 20thNight
24%18%30%20%6%1
720
21st to endNight
35%12%31%20%2
792
November1st to 10thNight
23%15%33%21%8%
740
11th to 20thNight
21%23%33%16%7%1
760
21st to endNight
28%22%29%17%5%
760
December1st to 10thNight
30%24%28%14%3
760
11th to 20thNight
25%28%29%16%21
760
21st to endNight
34%22%29%13%2
836
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