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 2024-05-13.

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	16% 11% 4 9% 6% 5% 5% 4 5% 6% 30%	83527
	Night	17% 12% 4 9% 5% 4 4 4 5% 6% 28%	85964
Transparency	Day	54% 6% 12% 18% 9% 1	83236
	Night	56% 6% 12% 17% 8% 1	85789
Seeing	Day	20% 17% 30% 21% 9% 3	13879
	Night	22% 16% 29% 23% 9% 1	23324

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
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	14% 20% 8% 13% 7% 5% 5% 3 4 4 16%	2517
	11th to 20th	Day	12% 23% 9% 16% 9% 6% 4 3 4 5% 9%	2616
	21st to end	Day	20% 20% 8% 13% 9% 6% 5% 3 3 4 9%	3124
February	1st to 10th	Day	16% 17% 5% 13% 7% 6% 4 5% 4 6% 15%	1710
	11th to 20th	Day	12% 16% 7% 14% 9% 8% 5% 4 4 4 17%	1663
	21st to end	Day	20% 14% 3 13% 8% 5% 4 3 6% 6% 17%	1527
March	1st to 10th	Day	19% 13% 4 8% 6% 5% 4 3 4 5% 29%	3331
	11th to 20th	Day	10% 18% 4 9% 5% 5% 5% 3 5% 6% 29%	3480
	21st to end	Day	15% 12% 4 10% 5% 5% 4 4 6% 7% 29%	3878
April	1st to 10th	Day	18% 13% 4 8% 5% 4 3 3 5% 6% 31%	2280
	11th to 20th	Day	20% 10% 3 6% 4 4 4 4 5% 6% 36%	2254
	21st to end	Day	20% 12% 3 7% 5% 4 4 3 5% 6% 31%	2408
May	1st to 10th	Day	17% 9% 2 8% 5% 5% 4 4 6% 7% 33%	2546
	11th to 20th	Day	15% 8% 2 6% 4 5% 4 4 6% 7% 39%	2509
	21st to end	Day	12% 6% 2 6% 5% 4 5% 4 6% 8% 42%	2725
June	1st to 10th	Day	17% 7% 2 7% 5% 5% 5% 4 5% 6% 39%	2520
	11th to 20th	Day	13% 5% 2 5% 5% 5% 5% 4 7% 10% 39%	2520
	21st to end	Day	13% 6% 3 6% 5% 4 5% 4 6% 8% 41%	2520
July	1st to 10th	Day	10% 6% 2 5% 4 4 4 4 6% 8% 46%	2520
	11th to 20th	Day	12% 6% 2 6% 5% 5% 6% 5% 7% 9% 38%	2520
	21st to end	Day	12% 5% 2 7% 5% 5% 5% 5% 7% 9% 37%	2674
August	1st to 10th	Day	11% 5% 2 6% 5% 6% 6% 5% 6% 9% 41%	2327
	11th to 20th	Day	10% 6% 3 8% 6% 6% 6% 5% 7% 9% 35%	2303
	21st to end	Day	15% 5% 2 5% 4 5% 5% 3 5% 9% 40%	2388
September	1st to 10th	Day	15% 7% 2 5% 5% 4 4 4 6% 8% 41%	2160
	11th to 20th	Day	16% 5% 2 5% 4 5% 4 4 5% 7% 43%	2160
	21st to end	Day	17% 6% 2 7% 6% 5% 6% 4 5% 7% 36%	1883
October	1st to 10th	Day	21% 8% 3 7% 4 4 4 4 5% 6% 34%	1800
	11th to 20th	Day	21% 10% 3 9% 6% 4 4 3 5% 6% 28%	1800
	21st to end	Day	28% 12% 3 8% 6% 5% 4 4 4 5% 23%	1972
November	1st to 10th	Day	15% 12% 2 9% 7% 5% 5% 4 5% 5% 32%	1654
	11th to 20th	Day	14% 15% 5% 9% 6% 6% 5% 3 5% 6% 25%	1520
	21st to end	Day	20% 16% 4 9% 5% 4 6% 4 5% 7% 19%	1520
December	1st to 10th	Day	20% 19% 8% 12% 6% 5% 4 3 5% 5% 15%	1520
	11th to 20th	Day	19% 18% 7% 15% 7% 4 4 3 4 4 15%	1906
	21st to end	Day	26% 21% 6% 13% 5% 4 4 3 3 4 10%	2772
January	1st to 10th	Night	18% 21% 6% 13% 6% 5% 4 3 4 4 15%	4429
	11th to 20th	Night	12% 19% 9% 17% 8% 6% 4 3 5% 5% 12%	4344
	21st to end	Night	23% 21% 6% 13% 8% 5% 4 2 3 4 11%	4532
February	1st to 10th	Night	17% 17% 5% 13% 7% 5% 3 4 5% 5% 19%	2470
	11th to 20th	Night	14% 14% 6% 14% 7% 6% 5% 4 5% 6% 19%	2403
	21st to end	Night	16% 15% 5% 14% 7% 5% 4 4 4 6% 21%	1927
March	1st to 10th	Night	20% 12% 4 10% 6% 4 4 3 5% 4 30%	3505
	11th to 20th	Night	16% 18% 3 9% 5% 4 5% 4 5% 6% 25%	3479
	21st to end	Night	16% 10% 4 10% 5% 4 4 3 5% 5% 34%	3739
April	1st to 10th	Night	19% 13% 4 7% 6% 4 4 3 4 6% 30%	1900
	11th to 20th	Night	18% 9% 3 8% 5% 4 5% 4 5% 6% 34%	1875
	21st to end	Night	20% 7% 3 7% 4 3 4 3 6% 7% 35%	1788
May	1st to 10th	Night	19% 8% 3 8% 4 4 4 4 6% 6% 34%	1634
	11th to 20th	Night	13% 7% 2 6% 5% 3 4 4 7% 7% 41%	1439
	21st to end	Night	10% 5% 2 5% 4 4 4 4 6% 8% 48%	1550
June	1st to 10th	Night	15% 6% 2 5% 4 5% 5% 5% 7% 8% 37%	1440
	11th to 20th	Night	12% 6% 2 6% 5% 4 5% 4 6% 7% 42%	1440
	21st to end	Night	10% 6% 2 8% 4 5% 5% 5% 6% 9% 40%	1440
July	1st to 10th	Night	8% 5% 2 5% 5% 5% 4 4 6% 8% 49%	1440
	11th to 20th	Night	11% 6% 2 5% 4 5% 4 4 6% 7% 47%	1440
	21st to end	Night	11% 5% 2 5% 4 3 4 4 8% 8% 46%	1641
August	1st to 10th	Night	9% 4 2 6% 4 3 5% 4 6% 9% 47%	1611
	11th to 20th	Night	10% 4 2 7% 5% 4 5% 4 6% 8% 43%	1598
	21st to end	Night	9% 5% 2 5% 4 4 6% 5% 6% 8% 45%	1949
September	1st to 10th	Night	14% 6% 2 6% 4 4 4 3 5% 8% 44%	1800
	11th to 20th	Night	16% 5% 2 6% 3 3 4 3 6% 6% 46%	1800
	21st to end	Night	16% 7% 2 6% 4 4 4 4 7% 7% 39%	2074
October	1st to 10th	Night	21% 7% 3 7% 5% 4 4 4 4 6% 35%	2160
	11th to 20th	Night	22% 9% 3 7% 5% 5% 4 4 5% 7% 30%	2160
	21st to end	Night	29% 11% 3 8% 5% 4 3 3 5% 5% 25%	2384
November	1st to 10th	Night	16% 11% 2 8% 5% 5% 4 4 5% 5% 35%	2421
	11th to 20th	Night	15% 13% 3 9% 5% 5% 5% 4 6% 6% 28%	2660
	21st to end	Night	20% 14% 4 8% 6% 5% 4 3 6% 7% 22%	2660
December	1st to 10th	Night	18% 20% 6% 10% 6% 5% 5% 4 5% 5% 17%	2660
	11th to 20th	Night	18% 19% 7% 12% 6% 5% 5% 3 5% 5% 18%	3288
	21st to end	Night	30% 18% 6% 11% 5% 5% 4 3 5% 4 10%	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	73% 5% 11% 9% 2	2518
	11th to 20th	Day	76% 9% 9% 4 1	2616
	21st to end	Day	79% 5% 10% 4 1	3124
February	1st to 10th	Day	71% 5% 10% 11% 2	1710
	11th to 20th	Day	71% 6% 8% 11% 3	1672
	21st to end	Day	68% 5% 11% 11% 5%	1527
March	1st to 10th	Day	57% 6% 10% 21% 6%	3334
	11th to 20th	Day	55% 7% 15% 14% 8% 1	3480
	21st to end	Day	52% 8% 10% 22% 7% 1	3878
April	1st to 10th	Day	56% 4 10% 18% 10% 1	2280
	11th to 20th	Day	49% 6% 10% 20% 14% 2	2254
	21st to end	Day	54% 6% 8% 18% 13% 2	2408
May	1st to 10th	Day	50% 6% 10% 20% 12% 2	2546
	11th to 20th	Day	45% 7% 11% 22% 13% 2	2513
	21st to end	Day	39% 6% 15% 24% 14% 1	2725
June	1st to 10th	Day	45% 7% 11% 20% 17% 1	2520
	11th to 20th	Day	40% 7% 13% 25% 14% 1	2520
	21st to end	Day	40% 6% 14% 22% 16% 1	2520
July	1st to 10th	Day	35% 7% 12% 28% 15% 2	2450
	11th to 20th	Day	39% 8% 15% 25% 12%	2445
	21st to end	Day	41% 10% 14% 21% 13% 1	2524
August	1st to 10th	Day	38% 8% 17% 24% 13% 1	2314
	11th to 20th	Day	43% 9% 14% 24% 9% 1	2303
	21st to end	Day	41% 7% 13% 26% 10% 2	2388
September	1st to 10th	Day	41% 8% 12% 27% 11% 1	2160
	11th to 20th	Day	40% 5% 13% 26% 15%	2160
	21st to end	Day	47% 6% 12% 22% 12% 1	1883
October	1st to 10th	Day	51% 6% 13% 19% 11% 1	1800
	11th to 20th	Day	56% 6% 15% 17% 6% 1	1800
	21st to end	Day	64% 6% 10% 14% 5% 1	1972
November	1st to 10th	Day	53% 7% 11% 18% 9% 2	1654
	11th to 20th	Day	60% 6% 14% 14% 6% 1	1520
	21st to end	Day	65% 5% 15% 13% 2	1520
December	1st to 10th	Day	73% 4 12% 11% 1	1520
	11th to 20th	Day	74% 5% 11% 6% 3	1906
	21st to end	Day	80% 5% 8% 7% 1	2772
January	1st to 10th	Night	73% 6% 12% 7% 2	4429
	11th to 20th	Night	73% 9% 9% 6% 3	4344
	21st to end	Night	78% 4 9% 6% 2	4532
February	1st to 10th	Night	67% 5% 11% 14% 4	2470
	11th to 20th	Night	67% 5% 11% 13% 4	2405
	21st to end	Night	64% 5% 12% 13% 6%	1927
March	1st to 10th	Night	57% 5% 11% 22% 5%	3515
	11th to 20th	Night	60% 5% 14% 15% 6%	3480
	21st to end	Night	49% 7% 11% 22% 11% 1	3739
April	1st to 10th	Night	56% 6% 10% 19% 9% 1	1900
	11th to 20th	Night	49% 7% 11% 18% 14% 1	1875
	21st to end	Night	47% 6% 11% 20% 14% 2	1788
May	1st to 10th	Night	49% 7% 9% 18% 15% 2	1634
	11th to 20th	Night	39% 7% 14% 23% 14% 3	1440
	21st to end	Night	34% 8% 16% 22% 19% 2	1551
June	1st to 10th	Night	42% 7% 13% 23% 14% 2	1440
	11th to 20th	Night	39% 6% 13% 23% 18% 2	1440
	21st to end	Night	39% 9% 11% 25% 16% 1	1440
July	1st to 10th	Night	33% 6% 14% 25% 19% 3	1400
	11th to 20th	Night	35% 5% 13% 30% 15% 2	1392
	21st to end	Night	32% 7% 16% 28% 14% 2	1550
August	1st to 10th	Night	33% 7% 16% 29% 14% 1	1600
	11th to 20th	Night	37% 7% 17% 29% 10% 1	1598
	21st to end	Night	33% 7% 15% 30% 12% 2	1949
September	1st to 10th	Night	38% 6% 15% 28% 12% 2	1800
	11th to 20th	Night	38% 4 13% 28% 16% 1	1800
	21st to end	Night	41% 7% 14% 25% 12% 1	2074
October	1st to 10th	Night	50% 6% 12% 19% 12% 1	2160
	11th to 20th	Night	52% 7% 15% 18% 8% 1	2160
	21st to end	Night	59% 5% 13% 14% 7% 1	2384
November	1st to 10th	Night	49% 7% 13% 19% 10% 2	2421
	11th to 20th	Night	55% 6% 16% 15% 7% 1	2660
	21st to end	Night	60% 7% 16% 14% 3	2660
December	1st to 10th	Night	68% 6% 14% 9% 2	2660
	11th to 20th	Night	68% 6% 12% 11% 2	3288
	21st to end	Night	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
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	26% 28% 30% 11% 4	180
	11th to 20th	Day	25% 29% 35% 9% 1	207
	21st to end	Day	24% 25% 34% 14% 4	297
February	1st to 10th	Day	27% 31% 30% 10% 1	270
	11th to 20th	Day	24% 36% 33% 6% 1	270
	21st to end	Day	34% 24% 33% 9% 1	339
March	1st to 10th	Day	19% 30% 32% 16% 3 1	460
	11th to 20th	Day	26% 24% 32% 15% 3 1	460
	21st to end	Day	28% 22% 30% 14% 6%	506
April	1st to 10th	Day	25% 25% 30% 15% 5% 1	460
	11th to 20th	Day	28% 23% 27% 14% 6% 3	452
	21st to end	Day	23% 21% 32% 17% 6% 1	460
May	1st to 10th	Day	26% 14% 30% 19% 8% 3	463
	11th to 20th	Day	17% 12% 33% 29% 7% 2	456
	21st to end	Day	14% 13% 31% 25% 13% 4	485
June	1st to 10th	Day	16% 12% 37% 26% 8% 1	450
	11th to 20th	Day	16% 12% 30% 28% 12% 2	450
	21st to end	Day	12% 12% 36% 27% 11% 1	450
July	1st to 10th	Day	11% 8% 25% 35% 18% 4	445
	11th to 20th	Day	11% 7% 29% 32% 17% 2	444
	21st to end	Day	10% 9% 36% 32% 11% 2	488
August	1st to 10th	Day	10% 7% 26% 34% 17% 6%	446
	11th to 20th	Day	13% 8% 25% 31% 17% 7%	439
	21st to end	Day	12% 9% 27% 31% 14% 6%	495
September	1st to 10th	Day	14% 11% 26% 28% 13% 8%	450
	11th to 20th	Day	14% 9% 23% 24% 21% 9%	450
	21st to end	Day	16% 15% 26% 24% 15% 5%	450
October	1st to 10th	Day	24% 13% 26% 18% 14% 4	450
	11th to 20th	Day	26% 19% 32% 16% 6% 2	450
	21st to end	Day	32% 19% 29% 17% 3	491
November	1st to 10th	Day	22% 18% 31% 20% 8% 1	348
	11th to 20th	Day	26% 28% 28% 14% 3 1	180
	21st to end	Day	30% 22% 36% 10% 2	180
December	1st to 10th	Day	31% 24% 29% 12% 3 1	180
	11th to 20th	Day	31% 27% 28% 12% 2	180
	21st to end	Day	29% 30% 31% 9% 1 1	198
January	1st to 10th	Night	27% 24% 32% 13% 3	760
	11th to 20th	Night	26% 24% 31% 16% 3	760
	21st to end	Night	20% 24% 35% 17% 3	836
February	1st to 10th	Night	26% 26% 31% 16% 1	760
	11th to 20th	Night	24% 25% 35% 14% 2	743
	21st to end	Night	27% 23% 32% 17% 2	628
March	1st to 10th	Night	25% 19% 33% 19% 4	760
	11th to 20th	Night	25% 22% 31% 18% 4	760
	21st to end	Night	24% 16% 33% 20% 6%	836
April	1st to 10th	Night	24% 16% 36% 20% 3	760
	11th to 20th	Night	23% 17% 30% 23% 6% 1	751
	21st to end	Night	23% 13% 28% 27% 8% 1	648
May	1st to 10th	Night	24% 8% 25% 29% 14% 1	494
	11th to 20th	Night	15% 6% 32% 37% 9%	360
	21st to end	Night	11% 6% 35% 28% 19% 1	389
June	1st to 10th	Night	15% 8% 31% 33% 14% 1	360
	11th to 20th	Night	15% 8% 28% 32% 18% 1	360
	21st to end	Night	11% 6% 31% 41% 10%	360
July	1st to 10th	Night	7% 3 23% 45% 19% 3	350
	11th to 20th	Night	11% 3 29% 36% 20% 2	348
	21st to end	Night	12% 3 25% 40% 17% 3	461
August	1st to 10th	Night	10% 2 26% 38% 21% 3	537
	11th to 20th	Night	10% 6% 20% 37% 23% 4	534
	21st to end	Night	10% 6% 24% 35% 23% 2	761
September	1st to 10th	Night	17% 7% 23% 28% 23% 3	720
	11th to 20th	Night	16% 7% 19% 29% 24% 5%	720
	21st to end	Night	16% 10% 24% 28% 18% 4	720
October	1st to 10th	Night	22% 10% 28% 22% 15% 3	720
	11th to 20th	Night	24% 18% 30% 20% 6% 1	720
	21st to end	Night	35% 12% 31% 20% 2	792
November	1st to 10th	Night	23% 15% 33% 21% 8%	740
	11th to 20th	Night	21% 23% 33% 16% 7% 1	760
	21st to end	Night	28% 22% 29% 17% 5%	760
December	1st to 10th	Night	30% 24% 28% 14% 3	760
	11th to 20th	Night	25% 28% 29% 16% 2 1	760
	21st to end	Night	34% 22% 29% 13% 2	836

Page generated at 2024-05-10 12:39:04. Version ac07

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