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 2024-11-04.

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 Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(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

By Month

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 Forecast	Data Points
Cloud Cover	Day	13% 9% 3 8% 5% 4 4 4 6% 7% 37%	101555
	Night	12% 9% 3 8% 5% 4 4 3 5% 6% 39%	97546
Transparency	Day	45% 6% 13% 24% 11% 1	105149
	Night	44% 5% 12% 24% 13% 2	102092
Seeing	Day	17% 11% 30% 26% 12% 4	15973
	Night	16% 10% 33% 30% 10% 1	25825

By Month

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
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	8% 16% 8% 20% 6% 5% 5% 4 4 5% 20%	2527
	11th to 20th	Day	7% 12% 5% 13% 9% 7% 6% 8% 10% 4 19%	2539
	21st to end	Day	12% 18% 8% 15% 6% 4 4 3 5% 5% 20%	3135
February	1st to 10th	Day	8% 12% 5% 11% 8% 6% 5% 5% 8% 6% 27%	1710
	11th to 20th	Day	10% 11% 4 10% 7% 6% 5% 3 6% 5% 32%	1664
	21st to end	Day	14% 11% 5% 9% 7% 4 4 3 5% 6% 31%	1520
March	1st to 10th	Day	14% 8% 3 7% 4 3 3 3 4 6% 45%	3305
	11th to 20th	Day	11% 9% 3 9% 4 4 4 3 5% 8% 40%	3480
	21st to end	Day	24% 13% 4 11% 5% 4 4 3 4 5% 23%	3902
April	1st to 10th	Day	18% 14% 4 8% 5% 4 4 3 5% 6% 31%	2280
	11th to 20th	Day	19% 14% 4 8% 4 4 3 3 4 5% 32%	2254
	21st to end	Day	21% 13% 3 6% 4 5% 3 3 5% 5% 30%	2405
May	1st to 10th	Day	19% 7% 3 6% 4 4 4 3 6% 7% 36%	4274
	11th to 20th	Day	13% 7% 2 6% 4 4 5% 4 6% 7% 41%	4399
	21st to end	Day	18% 7% 2 6% 5% 4 4 3 5% 7% 38%	4824
June	1st to 10th	Day	13% 5% 2 6% 4 4 4 3 6% 7% 46%	2660
	11th to 20th	Day	13% 7% 2 7% 5% 4 5% 4 6% 8% 39%	2660
	21st to end	Day	12% 7% 3 6% 5% 5% 5% 4 6% 8% 40%	2660
July	1st to 10th	Day	11% 5% 2 6% 6% 5% 6% 5% 7% 9% 37%	4440
	11th to 20th	Day	5% 3 1 4 4 3 5% 4 5% 8% 57%	4440
	21st to end	Day	7% 5% 2 6% 5% 5% 5% 4 7% 8% 44%	4768
August	1st to 10th	Day	12% 6% 2 6% 4 5% 5% 4 6% 8% 41%	4104
	11th to 20th	Day	12% 6% 2 6% 4 4 4 3 6% 8% 43%	4041
	21st to end	Day	8% 5% 2 6% 4 5% 5% 4 6% 8% 46%	4245
September	1st to 10th	Day	13% 6% 2 5% 4 4 4 4 5% 7% 47%	2280
	11th to 20th	Day	11% 6% 2 5% 4 3 4 4 6% 8% 48%	2280
	21st to end	Day	14% 7% 2 6% 4 4 5% 3 5% 8% 41%	1989
October	1st to 10th	Day	15% 7% 2 5% 4 3 4 3 5% 5% 46%	1900
	11th to 20th	Day	15% 10% 2 7% 4 4 4 3 4 7% 40%	1900
	21st to end	Day	19% 11% 3 6% 4 3 4 2 5% 6% 36%	2048
November	1st to 10th	Day	12% 10% 4 6% 4 3 4 4 5% 7% 41%	1661
	11th to 20th	Day	13% 13% 5% 11% 8% 4 3 3 5% 6% 28%	1520
	21st to end	Day	11% 12% 4 9% 5% 4 3 3 5% 6% 38%	1520
December	1st to 10th	Day	12% 12% 4 13% 8% 6% 6% 3 5% 5% 27%	1520
	11th to 20th	Day	10% 13% 6% 9% 6% 5% 4 4 6% 7% 28%	1918
	21st to end	Day	18% 17% 8% 17% 5% 4 4 3 3 4 17%	2783
January	1st to 10th	Night	10% 15% 8% 18% 6% 4 4 3 4 4 25%	4428
	11th to 20th	Night	8% 13% 6% 13% 8% 6% 6% 7% 9% 5% 20%	4428
	21st to end	Night	14% 17% 7% 12% 6% 5% 4 3 5% 5% 24%	4532
February	1st to 10th	Night	6% 15% 5% 9% 6% 6% 5% 3 5% 6% 33%	2470
	11th to 20th	Night	8% 10% 4 10% 6% 6% 5% 4 5% 6% 37%	2403
	21st to end	Night	13% 9% 4 9% 5% 5% 5% 4 4 5% 36%	1933
March	1st to 10th	Night	11% 8% 3 7% 3 3 3 3 5% 6% 46%	3578
	11th to 20th	Night	9% 8% 3 9% 5% 4 5% 4 5% 8% 40%	3480
	21st to end	Night	24% 12% 3 11% 4 3 3 2 3 5% 29%	3728
April	1st to 10th	Night	16% 11% 3 7% 4 3 4 4 5% 6% 37%	1900
	11th to 20th	Night	20% 11% 3 6% 4 3 4 3 5% 6% 36%	1875
	21st to end	Night	19% 10% 3 7% 4 4 4 3 4 5% 37%	1772
May	1st to 10th	Night	15% 7% 3 7% 4 4 4 3 5% 6% 42%	2617
	11th to 20th	Night	13% 5% 2 4 4 3 4 3 5% 7% 50%	2506
	21st to end	Night	13% 7% 3 7% 4 3 4 3 5% 7% 43%	2743
June	1st to 10th	Night	9% 4 2 6% 4 4 4 4 6% 9% 49%	1520
	11th to 20th	Night	11% 5% 2 6% 5% 5% 4 4 7% 8% 43%	1520
	21st to end	Night	9% 4 2 5% 4 3 4 3 5% 8% 53%	1520
July	1st to 10th	Night	10% 5% 2 5% 4 4 4 4 7% 9% 47%	2530
	11th to 20th	Night	3 4 1 4 3 4 4 4 6% 9% 59%	2530
	21st to end	Night	6% 3 1 5% 3 3 4 5% 6% 9% 56%	2779
August	1st to 10th	Night	11% 6% 2 6% 4 3 4 4 5% 6% 48%	2836
	11th to 20th	Night	13% 5% 1 5% 3 3 4 3 5% 6% 52%	2798
	21st to end	Night	10% 5% 2 7% 5% 4 4 3 5% 7% 50%	3411
September	1st to 10th	Night	9% 4 2 5% 3 3 3 4 5% 6% 57%	1900
	11th to 20th	Night	12% 4 2 5% 4 3 3 3 5% 7% 52%	1900
	21st to end	Night	12% 7% 2 4 3 3 3 3 5% 6% 53%	2169
October	1st to 10th	Night	13% 7% 2 6% 3 3 4 3 4 6% 50%	2280
	11th to 20th	Night	14% 8% 3 6% 4 4 4 4 5% 7% 43%	2280
	21st to end	Night	16% 10% 3 7% 4 4 4 4 5% 6% 38%	2548
November	1st to 10th	Night	12% 9% 3 6% 5% 4 4 3 4 6% 44%	2489
	11th to 20th	Night	12% 12% 5% 10% 5% 4 4 3 5% 5% 35%	2660
	21st to end	Night	13% 11% 4 9% 5% 4 3 3 4 6% 38%	2660
December	1st to 10th	Night	11% 13% 4 12% 7% 5% 5% 4 5% 6% 29%	2660
	11th to 20th	Night	11% 13% 4 12% 7% 5% 5% 4 5% 6% 28%	3279
	21st to end	Night	20% 15% 5% 14% 6% 4 4 3 5% 4 20%	4884

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	66% 5% 11% 13% 4	2528
	11th to 20th	Day	59% 8% 10% 16% 6%	2539
	21st to end	Day	65% 5% 12% 13% 4	3135
February	1st to 10th	Day	53% 6% 13% 17% 10% 1	1710
	11th to 20th	Day	52% 5% 11% 23% 7% 2	1673
	21st to end	Day	54% 4 11% 19% 10% 1	1520
March	1st to 10th	Day	41% 4 13% 26% 14% 1	3305
	11th to 20th	Day	41% 6% 10% 31% 10% 2	3480
	21st to end	Day	64% 6% 9% 15% 5% 1	3902
April	1st to 10th	Day	54% 5% 11% 19% 10% 1	2280
	11th to 20th	Day	54% 5% 10% 19% 11% 1	2254
	21st to end	Day	55% 7% 12% 17% 9% 1	2405
May	1st to 10th	Day	44% 6% 13% 23% 12% 1	4312
	11th to 20th	Day	37% 8% 12% 30% 12% 1	4403
	21st to end	Day	45% 6% 10% 25% 13% 1	4837
June	1st to 10th	Day	36% 7% 13% 29% 14% 1	2660
	11th to 20th	Day	41% 8% 14% 22% 15% 1	2660
	21st to end	Day	40% 7% 15% 25% 12% 2	2660
July	1st to 10th	Day	42% 5% 19% 24% 9% 1	4371
	11th to 20th	Day	26% 5% 15% 34% 19% 2	4365
	21st to end	Day	36% 6% 13% 28% 16% 1	4618
August	1st to 10th	Day	39% 6% 11% 29% 13% 2	4090
	11th to 20th	Day	39% 4 14% 32% 10%	4080
	21st to end	Day	35% 4 16% 29% 14% 1	4244
September	1st to 10th	Day	37% 6% 12% 29% 16% 1	2280
	11th to 20th	Day	34% 7% 17% 31% 11% 1	2280
	21st to end	Day	41% 5% 12% 30% 12% 1	1989
October	1st to 10th	Day	27% 3 7% 39% 23%	3160
	11th to 20th	Day	39% 3 14% 23% 19% 2	3140
	21st to end	Day	42% 3 13% 31% 10%	3350
November	1st to 10th	Day	42% 6% 14% 21% 15% 2	1661
	11th to 20th	Day	57% 6% 11% 16% 9% 1	1520
	21st to end	Day	48% 5% 18% 21% 7% 1	1520
December	1st to 10th	Day	58% 6% 14% 13% 8% 1	1520
	11th to 20th	Day	53% 7% 18% 15% 7%	1915
	21st to end	Day	72% 5% 7% 12% 3	2783
January	1st to 10th	Night	62% 4 9% 18% 6%	4428
	11th to 20th	Night	59% 6% 11% 16% 8%	4428
	21st to end	Night	62% 5% 10% 16% 7% 1	4532
February	1st to 10th	Night	52% 4 12% 21% 10% 2	2470
	11th to 20th	Night	47% 6% 12% 23% 10% 1	2404
	21st to end	Night	50% 5% 11% 21% 12% 2	1933
March	1st to 10th	Night	39% 5% 11% 30% 14% 1	3578
	11th to 20th	Night	39% 6% 10% 27% 16% 1	3480
	21st to end	Night	59% 4 8% 20% 7% 2	3728
April	1st to 10th	Night	47% 6% 9% 21% 14% 2	1900
	11th to 20th	Night	48% 5% 10% 19% 16% 2	1875
	21st to end	Night	48% 5% 10% 20% 14% 2	1772
May	1st to 10th	Night	42% 7% 11% 18% 22% 1	2643
	11th to 20th	Night	33% 6% 11% 27% 18% 5%	2507
	21st to end	Night	40% 7% 10% 27% 16% 1	2751
June	1st to 10th	Night	29% 9% 14% 30% 15% 2	1520
	11th to 20th	Night	37% 7% 13% 23% 17% 3	1520
	21st to end	Night	29% 7% 15% 30% 16% 3	1520
July	1st to 10th	Night	34% 4 21% 28% 12% 1	2490
	11th to 20th	Night	22% 5% 16% 38% 17% 2	2482
	21st to end	Night	25% 5% 18% 29% 20% 2	2691
August	1st to 10th	Night	37% 5% 12% 29% 15% 3	2826
	11th to 20th	Night	34% 4 14% 31% 15% 1	2825
	21st to end	Night	35% 4 17% 27% 15% 2	3411
September	1st to 10th	Night	28% 5% 11% 33% 21% 1	1900
	11th to 20th	Night	32% 5% 15% 31% 16% 1	1900
	21st to end	Night	32% 5% 13% 30% 19% 1	2169
October	1st to 10th	Night	26% 3 6% 35% 27% 3	3800
	11th to 20th	Night	30% 4 11% 29% 23% 3	3779
	21st to end	Night	46% 3 10% 26% 15% 1	4196
November	1st to 10th	Night	40% 5% 13% 23% 15% 2	2489
	11th to 20th	Night	51% 5% 12% 19% 11% 1	2660
	21st to end	Night	48% 5% 15% 23% 8% 1	2660
December	1st to 10th	Night	54% 5% 15% 18% 7% 1	2660
	11th to 20th	Night	56% 6% 12% 18% 7% 1	3281
	21st to end	Night	68% 5% 9% 13% 5%	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
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	13% 14% 39% 21% 10% 3	270
	11th to 20th	Day	19% 13% 39% 22% 5% 2	270
	21st to end	Day	14% 11% 38% 26% 9% 1	297
February	1st to 10th	Day	13% 17% 44% 19% 6% 1	270
	11th to 20th	Day	16% 21% 36% 23% 4 1	270
	21st to end	Day	20% 16% 39% 24% 2	225
March	1st to 10th	Day	18% 14% 42% 20% 6%	270
	11th to 20th	Day	23% 14% 34% 21% 7% 2	270
	21st to end	Day	28% 15% 27% 21% 6% 3	347
April	1st to 10th	Day	27% 14% 35% 17% 6%	460
	11th to 20th	Day	27% 19% 23% 22% 8% 1	452
	21st to end	Day	28% 14% 27% 23% 7% 2	585
May	1st to 10th	Day	21% 12% 35% 23% 8% 1	653
	11th to 20th	Day	20% 11% 28% 27% 10% 4	675
	21st to end	Day	19% 8% 27% 28% 14% 3	734
June	1st to 10th	Day	10% 9% 27% 31% 17% 5%	680
	11th to 20th	Day	15% 8% 34% 30% 11% 2	680
	21st to end	Day	14% 10% 29% 27% 15% 5%	680
July	1st to 10th	Day	8% 5% 23% 31% 23% 9%	671
	11th to 20th	Day	7% 7% 29% 30% 19% 8%	668
	21st to end	Day	7% 4 27% 37% 19% 6%	739
August	1st to 10th	Day	10% 5% 21% 34% 22% 7%	676
	11th to 20th	Day	14% 4 21% 32% 22% 7%	665
	21st to end	Day	10% 6% 26% 33% 18% 6%	578
September	1st to 10th	Day	16% 7% 26% 29% 15% 6%	490
	11th to 20th	Day	12% 7% 29% 30% 18% 5%	490
	21st to end	Day	14% 15% 30% 25% 13% 2	322
October	1st to 10th	Day	16% 14% 26% 26% 16% 3	300
	11th to 20th	Day	19% 17% 36% 22% 6%	300
	21st to end	Day	28% 16% 35% 14% 7% 2	330
November	1st to 10th	Day	17% 16% 36% 21% 8% 1	279
	11th to 20th	Day	18% 23% 37% 18% 4	270
	21st to end	Day	21% 13% 42% 19% 5%	270
December	1st to 10th	Day	16% 11% 40% 27% 6% 1	270
	11th to 20th	Day	17% 16% 38% 23% 6%	270
	21st to end	Day	28% 13% 40% 16% 2	297
January	1st to 10th	Night	14% 14% 39% 25% 7% 1	950
	11th to 20th	Night	18% 13% 38% 26% 5% 1	950
	21st to end	Night	18% 12% 36% 26% 7% 1	1045
February	1st to 10th	Night	13% 15% 41% 26% 5% 1	950
	11th to 20th	Night	14% 15% 41% 23% 6% 1	929
	21st to end	Night	18% 15% 34% 26% 6%	677
March	1st to 10th	Night	19% 13% 37% 24% 7% 1	670
	11th to 20th	Night	16% 13% 36% 29% 6%	570
	21st to end	Night	21% 9% 30% 27% 10% 2	627
April	1st to 10th	Night	20% 15% 35% 25% 5%	570
	11th to 20th	Night	26% 10% 30% 28% 6%	563
	21st to end	Night	26% 8% 34% 24% 8% 1	570
May	1st to 10th	Night	21% 9% 32% 30% 6% 1	570
	11th to 20th	Night	19% 6% 30% 33% 10% 1	561
	21st to end	Night	16% 7% 27% 37% 13% 1	617
June	1st to 10th	Night	11% 4 29% 41% 14% 1	570
	11th to 20th	Night	12% 5% 33% 38% 11%	570
	21st to end	Night	11% 4 26% 42% 17% 1	570
July	1st to 10th	Night	7% 2 23% 38% 29% 2	555
	11th to 20th	Night	5% 5% 25% 41% 23% 2	552
	21st to end	Night	5% 3 18% 50% 21% 3	624
August	1st to 10th	Night	8% 2 18% 47% 23% 2	567
	11th to 20th	Night	11% 4 20% 35% 27% 4	564
	21st to end	Night	9% 3 25% 39% 21% 2	627
September	1st to 10th	Night	11% 3 25% 39% 17% 4	570
	11th to 20th	Night	13% 3 31% 33% 16% 3	570
	21st to end	Night	13% 9% 31% 32% 14% 1	674
October	1st to 10th	Night	17% 7% 29% 33% 12% 1	760
	11th to 20th	Night	19% 12% 35% 27% 7% 1	760
	21st to end	Night	22% 11% 32% 28% 6%	836
November	1st to 10th	Night	17% 13% 36% 26% 7% 1	792
	11th to 20th	Night	16% 16% 39% 23% 6% 1	950
	21st to end	Night	17% 16% 37% 22% 7%	950
December	1st to 10th	Night	17% 11% 39% 25% 7% 1	950
	11th to 20th	Night	20% 11% 39% 22% 7% 1	950
	21st to end	Night	24% 14% 34% 22% 5%	1045

Page generated at 2024-11-01 21:47:30. Version ac07

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