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 2024-03-23.

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% 4 7% 6% 3 5% 5% 5% 7% 35%	78670
	Night	12% 9% 4 8% 6% 3 4 4 5% 6% 38%	81274
Transparency	Day	47% 7% 13% 22% 10% 1	78372
	Night	46% 6% 12% 22% 12% 1	81093
Seeing	Day	16% 10% 30% 27% 13% 4	14997
	Night	16% 10% 33% 30% 10% 1	25104

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% 15% 9% 18% 7% 3 5% 5% 4 5% 20%	2527
	11th to 20th	Day	7% 12% 5% 11% 11% 6% 6% 9% 10% 4 19%	2539
	21st to end	Day	12% 17% 8% 13% 8% 3 4 4 5% 6% 20%	3135
February	1st to 10th	Day	8% 11% 5% 9% 9% 5% 6% 5% 7% 7% 27%	1710
	11th to 20th	Day	11% 10% 5% 9% 7% 4 6% 5% 6% 5% 32%	1664
	21st to end	Day	14% 10% 6% 8% 8% 3 5% 4 5% 6% 31%	1520
March	1st to 10th	Day	13% 9% 6% 10% 6% 3 4 4 4 6% 34%	2007
	11th to 20th	Day	14% 11% 4 7% 5% 4 4 4 4 8% 34%	2090
	21st to end	Day	20% 12% 4 6% 6% 3 5% 5% 6% 6% 29%	2247
April	1st to 10th	Day	18% 13% 4 7% 5% 3 4 4 6% 6% 31%	2160
	11th to 20th	Day	19% 13% 4 7% 5% 3 3 4 4 5% 32%	2134
	21st to end	Day	22% 12% 4 6% 5% 3 4 4 5% 5% 30%	2278
May	1st to 10th	Day	18% 9% 3 7% 6% 4 5% 5% 6% 7% 30%	2448
	11th to 20th	Day	18% 8% 3 6% 5% 3 5% 5% 6% 7% 36%	2479
	21st to end	Day	16% 6% 3 6% 5% 3 5% 4 5% 8% 38%	2725
June	1st to 10th	Day	13% 4 2 5% 5% 3 5% 4 6% 8% 45%	2520
	11th to 20th	Day	12% 6% 2 6% 5% 3 5% 6% 5% 8% 41%	2520
	21st to end	Day	12% 6% 3 5% 5% 4 6% 5% 5% 9% 40%	2520
July	1st to 10th	Day	7% 4 2 5% 5% 3 6% 5% 5% 9% 48%	2520
	11th to 20th	Day	7% 5% 2 4 5% 2 5% 6% 5% 10% 49%	2520
	21st to end	Day	8% 4 2 4 5% 3 5% 5% 7% 9% 47%	2724
August	1st to 10th	Day	9% 4 2 6% 5% 4 5% 6% 8% 10% 42%	2328
	11th to 20th	Day	13% 6% 3 5% 5% 4 4 4 6% 9% 42%	2301
	21st to end	Day	9% 5% 2 5% 4 3 5% 5% 5% 8% 49%	2413
September	1st to 10th	Day	14% 6% 2 4 4 3 5% 5% 5% 7% 45%	2160
	11th to 20th	Day	11% 5% 2 4 5% 2 4 5% 6% 7% 48%	2160
	21st to end	Day	15% 7% 3 5% 5% 3 5% 4 5% 9% 40%	1885
October	1st to 10th	Day	16% 7% 2 5% 4 3 4 4 5% 5% 44%	1800
	11th to 20th	Day	16% 10% 3 6% 5% 3 4 4 4 7% 39%	1800
	21st to end	Day	19% 11% 4 6% 5% 2 3 3 5% 5% 36%	1941
November	1st to 10th	Day	11% 10% 4 6% 5% 2 4 5% 5% 7% 42%	1634
	11th to 20th	Day	14% 11% 6% 10% 9% 3 4 4 5% 6% 28%	1520
	21st to end	Day	12% 11% 5% 8% 6% 2 4 3 5% 6% 38%	1520
December	1st to 10th	Day	12% 11% 5% 10% 10% 5% 6% 5% 5% 5% 27%	1520
	11th to 20th	Day	11% 12% 7% 8% 6% 4 5% 5% 6% 7% 28%	1918
	21st to end	Day	19% 16% 9% 16% 7% 3 3 4 3 4 17%	2783
January	1st to 10th	Night	10% 14% 8% 16% 7% 3 4 4 4 4 25%	4428
	11th to 20th	Night	8% 13% 6% 11% 9% 5% 7% 8% 9% 5% 20%	4428
	21st to end	Night	14% 17% 7% 11% 6% 4 4 4 4 5% 24%	4532
February	1st to 10th	Night	6% 14% 6% 9% 7% 4 6% 4 5% 6% 33%	2470
	11th to 20th	Night	9% 9% 4 8% 7% 4 6% 4 5% 6% 38%	2403
	21st to end	Night	14% 9% 5% 8% 6% 4 5% 5% 4 6% 36%	1933
March	1st to 10th	Night	14% 10% 4 7% 5% 3 4 5% 5% 6% 39%	2190
	11th to 20th	Night	12% 9% 4 8% 6% 4 4 4 5% 7% 37%	2090
	21st to end	Night	18% 10% 3 7% 6% 3 5% 5% 5% 7% 33%	2152
April	1st to 10th	Night	16% 10% 4 6% 5% 2 4 5% 5% 6% 37%	1800
	11th to 20th	Night	21% 10% 3 6% 5% 2 4 3 4 6% 35%	1775
	21st to end	Night	20% 9% 4 6% 4 3 4 4 4 6% 37%	1679
May	1st to 10th	Night	18% 8% 3 6% 4 3 5% 4 4 6% 39%	1511
	11th to 20th	Night	17% 6% 2 4 4 3 4 5% 5% 9% 42%	1416
	21st to end	Night	14% 5% 3 6% 6% 3 4 5% 5% 9% 41%	1551
June	1st to 10th	Night	8% 3 2 5% 5% 3 4 5% 6% 9% 50%	1440
	11th to 20th	Night	11% 4 2 6% 6% 4 4 5% 6% 8% 44%	1440
	21st to end	Night	8% 3 2 4 4 2 4 4 5% 9% 54%	1440
July	1st to 10th	Night	5% 3 2 4 3 3 4 4 6% 9% 57%	1440
	11th to 20th	Night	4 4 1 4 4 3 4 5% 6% 8% 57%	1440
	21st to end	Night	6% 2 2 3 3 2 3 5% 5% 10% 59%	1591
August	1st to 10th	Night	6% 5% 2 4 5% 3 4 5% 6% 8% 51%	1611
	11th to 20th	Night	10% 5% 2 4 5% 3 4 4 5% 6% 53%	1600
	21st to end	Night	9% 3 2 5% 5% 3 4 4 5% 6% 55%	1941
September	1st to 10th	Night	9% 4 3 4 4 2 4 4 4 6% 56%	1800
	11th to 20th	Night	12% 4 2 5% 5% 2 3 3 5% 7% 52%	1800
	21st to end	Night	12% 6% 2 3 4 2 3 3 5% 7% 52%	2054
October	1st to 10th	Night	14% 7% 2 5% 4 2 4 4 4 6% 48%	2160
	11th to 20th	Night	15% 8% 3 5% 4 3 4 4 5% 7% 42%	2160
	21st to end	Night	17% 11% 3 6% 4 3 4 4 4 6% 38%	2413
November	1st to 10th	Night	12% 8% 3 6% 6% 2 4 4 4 7% 45%	2443
	11th to 20th	Night	12% 12% 6% 8% 6% 3 4 4 5% 5% 35%	2660
	21st to end	Night	14% 10% 4 8% 6% 3 4 4 4 6% 38%	2660
December	1st to 10th	Night	11% 12% 5% 10% 8% 4 5% 5% 5% 6% 30%	2660
	11th to 20th	Night	12% 13% 5% 10% 8% 4 5% 6% 4 6% 28%	3279
	21st to end	Night	21% 15% 6% 12% 8% 3 4 4 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	51% 5% 14% 20% 8% 1	2007
	11th to 20th	Day	49% 6% 12% 23% 10% 1	2090
	21st to end	Day	55% 7% 11% 20% 6% 1	2247
April	1st to 10th	Day	54% 4 12% 20% 9% 1	2160
	11th to 20th	Day	55% 5% 10% 19% 10% 1	2134
	21st to end	Day	55% 6% 12% 17% 8% 1	2278
May	1st to 10th	Day	51% 7% 14% 19% 8% 1	2448
	11th to 20th	Day	45% 8% 13% 22% 10% 1	2483
	21st to end	Day	45% 7% 12% 22% 13% 1	2725
June	1st to 10th	Day	36% 7% 13% 30% 13% 1	2520
	11th to 20th	Day	40% 8% 14% 22% 15% 1	2520
	21st to end	Day	40% 7% 15% 25% 11% 2	2520
July	1st to 10th	Day	31% 9% 16% 29% 14% 1	2451
	11th to 20th	Day	30% 9% 14% 27% 17% 3	2445
	21st to end	Day	30% 8% 16% 30% 13% 2	2573
August	1st to 10th	Day	34% 10% 15% 30% 10% 2	2314
	11th to 20th	Day	39% 7% 16% 26% 12% 1	2301
	21st to end	Day	32% 6% 14% 28% 18% 1	2413
September	1st to 10th	Day	38% 6% 12% 27% 15% 1	2160
	11th to 20th	Day	34% 7% 16% 31% 11% 1	2160
	21st to end	Day	42% 6% 12% 30% 10% 1	1885
October	1st to 10th	Day	41% 6% 11% 28% 14% 1	1800
	11th to 20th	Day	45% 5% 14% 22% 13% 1	1800
	21st to end	Day	50% 5% 12% 23% 10%	1941
November	1st to 10th	Day	42% 6% 13% 21% 15% 3	1634
	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	46% 6% 14% 24% 9% 1	2190
	11th to 20th	Night	46% 5% 12% 22% 13% 1	2090
	21st to end	Night	51% 5% 13% 21% 8% 2	2152
April	1st to 10th	Night	47% 6% 9% 21% 14% 2	1800
	11th to 20th	Night	50% 5% 10% 18% 14% 3	1775
	21st to end	Night	49% 5% 10% 20% 14% 2	1679
May	1st to 10th	Night	46% 6% 12% 21% 14% 1	1511
	11th to 20th	Night	39% 7% 15% 23% 13% 2	1417
	21st to end	Night	40% 7% 12% 24% 15% 1	1552
June	1st to 10th	Night	29% 9% 14% 30% 15% 2	1440
	11th to 20th	Night	37% 7% 13% 23% 17% 3	1440
	21st to end	Night	27% 8% 16% 31% 16% 3	1440
July	1st to 10th	Night	23% 6% 14% 37% 18% 2	1400
	11th to 20th	Night	23% 7% 16% 32% 18% 3	1392
	21st to end	Night	20% 7% 18% 33% 18% 4	1503
August	1st to 10th	Night	28% 7% 15% 30% 16% 3	1601
	11th to 20th	Night	32% 6% 15% 28% 17% 2	1600
	21st to end	Night	30% 6% 14% 28% 18% 4	1941
September	1st to 10th	Night	29% 5% 11% 32% 21% 1	1800
	11th to 20th	Night	32% 5% 15% 31% 17% 1	1800
	21st to end	Night	33% 5% 14% 30% 17% 1	2054
October	1st to 10th	Night	37% 5% 11% 30% 15% 2	2160
	11th to 20th	Night	41% 6% 13% 24% 16% 1	2160
	21st to end	Night	47% 5% 11% 22% 13% 1	2413
November	1st to 10th	Night	40% 5% 13% 24% 16% 2	2443
	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% 13% 34% 21% 7% 2	270
	21st to end	Day	27% 16% 26% 21% 6% 4	317
April	1st to 10th	Day	27% 14% 35% 18% 6%	420
	11th to 20th	Day	26% 19% 23% 22% 8% 1	412
	21st to end	Day	28% 13% 27% 23% 7% 2	538
May	1st to 10th	Day	21% 12% 35% 23% 8% 1	603
	11th to 20th	Day	21% 12% 27% 26% 10% 4	625
	21st to end	Day	19% 7% 27% 29% 15% 3	679
June	1st to 10th	Day	10% 9% 26% 32% 18% 6%	630
	11th to 20th	Day	15% 7% 33% 31% 12% 2	630
	21st to end	Day	13% 10% 29% 28% 16% 5%	630
July	1st to 10th	Day	7% 4 23% 32% 24% 10%	621
	11th to 20th	Day	8% 6% 29% 30% 19% 7%	618
	21st to end	Day	7% 4 27% 37% 19% 5%	684
August	1st to 10th	Day	9% 3 21% 36% 23% 8%	626
	11th to 20th	Day	14% 4 19% 32% 23% 8%	615
	21st to end	Day	10% 6% 25% 33% 19% 7%	532
September	1st to 10th	Day	17% 6% 26% 29% 15% 6%	450
	11th to 20th	Day	12% 7% 29% 30% 18% 5%	450
	21st to end	Day	15% 16% 30% 24% 12% 2	291
October	1st to 10th	Day	17% 12% 26% 26% 16% 4	270
	11th to 20th	Day	19% 17% 35% 22% 7%	270
	21st to end	Day	28% 15% 34% 14% 7% 2	297
November	1st to 10th	Day	17% 17% 36% 21% 8% 1	270
	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% 28% 11% 2	600
April	1st to 10th	Night	20% 14% 36% 24% 5%	540
	11th to 20th	Night	27% 9% 29% 28% 6%	533
	21st to end	Night	26% 7% 33% 24% 8% 1	540
May	1st to 10th	Night	22% 8% 32% 31% 6% 1	540
	11th to 20th	Night	20% 6% 30% 33% 10% 1	531
	21st to end	Night	16% 7% 26% 36% 14% 1	584
June	1st to 10th	Night	10% 4 28% 42% 15% 1	540
	11th to 20th	Night	12% 4 34% 38% 12%	540
	21st to end	Night	10% 3 25% 43% 18% 1	540
July	1st to 10th	Night	6% 2 22% 38% 30% 2	525
	11th to 20th	Night	5% 5% 25% 41% 22% 2	522
	21st to end	Night	5% 3 18% 51% 20% 3	591
August	1st to 10th	Night	7% 2 17% 47% 25% 2	537
	11th to 20th	Night	10% 4 20% 34% 28% 4	534
	21st to end	Night	9% 4 25% 38% 22% 3	594
September	1st to 10th	Night	12% 3 24% 40% 17% 5%	540
	11th to 20th	Night	13% 4 31% 33% 17% 3	540
	21st to end	Night	14% 9% 32% 31% 13% 1	638
October	1st to 10th	Night	17% 7% 30% 33% 13% 1	720
	11th to 20th	Night	20% 12% 33% 27% 7% 1	720
	21st to end	Night	22% 11% 32% 28% 7%	792
November	1st to 10th	Night	16% 13% 35% 27% 8% 1	777
	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 2024-03-19 22:31:07. Version ac07

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