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 2017-08-12.

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
30%
14705
12%
46523
8%
14673
35%
14673
15%
33854

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%
718
6%
2506
3%
716
14%
716
5%
2114
January16th to endNight
12%
768
7%
2520
3%
768
17%
768
6%
2110
February1st to 15thNight
9%
703
6%
2287
1%
701
16%
701
6%
1877
February16th to endNight
16%
631
9%
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
34%
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
53%
374
24%
864
June1st to 15thNight
42%
360
14%
1440
14%
360
53%
360
19%
894
June16th to endNight
44%
360
12%
1440
14%
360
51%
360
21%
865
July1st to 15thNight
57%
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%
527
16%
1575
10%
524
60%
524
33%
933
August16th to endNight
59%
627
21%
1677
12%
627
62%
627
36%
1026
September1st to 15thNight
51%
660
20%
1650
10%
660
54%
660
32%
1089
September16th to endNight
51%
657
21%
1818
15%
657
54%
657
28%
1197
October1st to 15thNight
35%
660
14%
1980
11%
660
40%
660
18%
1409
October16th to endNight
19%
704
7%
2117
3%
704
25%
704
11%
1656
November1st to 15thNight
27%
700
15%
2346
13%
700
32%
700
15%
1639
November16th to endNight
19%
720
10%
2520
7%
720
23%
720
10%
1919
December1st to 15thNight
11%
720
5%
2520
1%
720
16%
720
6%
2078
December16th to endNight
9%
768
4%
2688
1%
768
12%
768
4%
2341

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%
47454
Night
17%10%47%6%3445%6%30%
46697
Cloud CoverDay
15%9%47%6%35%5%5%6%29%
47464
Night
16%10%47%6%3445%6%29%
46702
TransparencyDay
52%6%12%18%9%
47146
Night
54%5%12%17%9%
46523
SeeingDay
19%12%28%23%11%4
5322
Night
22%14%27%23%10%1
14709

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%11%10%45%445%12%
1432
16th to endDay
12%15%8%13%11%6%6%445%12%
1704
February1st to 15thDay
15%14%8%13%9%45%5%3414%
1575
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%
2288
16th to endDay
15%5%25%5%345%5%8%38%
2160
September1st to 15thDay
18%4345%245%5%6%39%
1980
16th to endDay
16%5%36%434447%39%
1809
October1st to 15thDay
21%8%26%5%33446%33%
1650
16th to endDay
27%10%36%5%35%445%22%
1755
November1st to 15thDay
13%12%37%7%25%5%45%32%
1511
16th to endDay
19%14%39%6%36%45%5%21%
1440
December1st to 15thDay
19%15%7%10%7%24445%17%
1440
16th to endDay
20%19%9%12%6%3444312%
1536
January1st to 15thNight
19%16%7%11%8%4444415%
2506
16th to endNight
15%15%8%12%9%45%335%15%
2520
February1st to 15thNight
15%15%7%12%7%34445%17%
2285
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%
1586
16th to endNight
10%3135%25%5%5%7%48%
1677
September1st to 15thNight
16%5%24434346%44%
1650
16th to endNight
16%5%25%3245%6%8%40%
1818
October1st to 15thNight
22%6%36%5%34436%33%
1980
16th to endNight
28%10%26%6%33346%22%
2117
November1st to 15thNight
18%9%36%5%345%5%6%31%
2346
16th to endNight
19%13%47%6%25%35%6%24%
2520
December1st to 15thNight
19%17%6%9%6%34445%17%
2520
16th to endNight
22%18%7%10%7%45%345%11%
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
15%16%7%12%10%45%5%45%12%
1432
16th to endDay
11%15%8%14%11%5%5%5%4411%
1704
February1st to 15thDay
15%14%9%13%9%46%5%3413%
1575
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%8%36%
2288
16th to endDay
14%6%25%5%345%6%9%36%
2160
September1st to 15thDay
17%5%345%245%5%7%38%
1980
16th to endDay
15%7%36%5%3445%7%38%
1809
October1st to 15thDay
20%8%26%5%34445%33%
1650
16th to endDay
25%11%48%5%35%5%36%21%
1755
November1st to 15thDay
13%12%47%5%35%5%46%31%
1511
16th to endDay
19%13%5%8%6%36%45%7%20%
1440
December1st to 15thDay
18%15%8%12%7%2344417%
1440
16th to endDay
19%18%8%14%7%345%3411%
1536
January1st to 15thNight
17%16%7%11%8%345%4414%
2506
16th to endNight
14%16%8%12%9%5%6%345%15%
2520
February1st to 15thNight
14%15%6%13%8%45%445%17%
2278
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%3445%9%47%
1586
16th to endNight
9%323435%5%5%8%48%
1677
September1st to 15thNight
15%5%25%423446%44%
1650
16th to endNight
15%5%15%32446%8%40%
1818
October1st to 15thNight
20%7%36%5%34446%33%
1980
16th to endNight
27%10%36%6%3335%6%22%
2117
November1st to 15thNight
17%10%36%5%3445%7%31%
2346
16th to endNight
19%13%5%8%6%35%45%5%23%
2520
December1st to 15thNight
18%17%7%9%6%36%445%16%
2520
16th to endNight
20%19%7%10%7%44445%10%
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
73%5%8%8%2
1433
16th to endDay
75%6%10%6%1
1704
February1st to 15thDay
74%5%8%10%1
1577
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%
2275
16th to endDay
41%7%12%26%10%1
2160
September1st to 15thDay
43%6%12%25%11%
1980
16th to endDay
44%5%12%22%14%
1809
October1st to 15thDay
52%5%11%19%11%
1650
16th to endDay
62%6%15%12%2
1755
November1st to 15thDay
52%7%13%15%9%1
1511
16th to endDay
63%5%14%13%3
1440
December1st to 15thDay
70%413%10%1
1440
16th to endDay
76%5%9%5%2
1536
January1st to 15thNight
72%5%9%7%4
2506
16th to endNight
71%410%10%3
2520
February1st to 15thNight
69%5%10%11%3
2287
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%29%12%
1575
16th to endNight
32%6%13%32%13%1
1677
September1st to 15thNight
39%413%28%12%1
1650
16th to endNight
39%6%11%27%13%
1818
October1st to 15thNight
51%5%11%18%12%
1980
16th to endNight
61%5%15%12%4
2117
November1st to 15thNight
50%6%14%15%9%2
2346
16th to endNight
60%5%14%13%4
2520
December1st to 15thNight
69%5%12%9%2
2520
16th to endNight
75%6%9%6%1
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
15%40%25%11%8%
60
16th to endDay
27%27%36%8%
92
February1st to 15thDay
20%43%26%10%
90
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
13%224%34%16%9%
297
16th to endDay
16%216%27%22%13%
268
September1st to 15thDay
16%5%17%26%19%13%
255
16th to endDay
17%8%23%21%18%11%
254
October1st to 15thDay
25%7%25%19%16%5%
255
16th to endDay
34%14%29%18%2
271
November1st to 15thDay
18%9%34%24%10%2
165
16th to endDay
25%20%28%21%5%
60
December1st to 15thDay
15%36%23%18%5%1
60
16th to endDay
32%32%31%3
64
January1st to 15thNight
27%23%31%13%3
720
16th to endNight
22%24%32%17%2
768
February1st to 15thNight
24%24%34%14%2
704
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%224%36%22%4
527
16th to endNight
11%419%33%28%3
627
September1st to 15thNight
18%6%18%26%26%2
660
16th to endNight
17%8%17%26%23%6%
657
October1st to 15thNight
23%10%24%23%14%2
660
16th to endNight
34%13%27%20%3
704
November1st to 15thNight
23%14%31%20%9%1
700
16th to endNight
26%20%26%16%8%
720
December1st to 15thNight
29%25%28%14%2
720
16th to endNight
30%24%29%14%1
768
Page generated at 2017-08-13 14:16:22. Version ac04

Copyright 2017 A. Danko


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