Rochester Hills
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Rochester Hills clear sky chart from 2005-11-06 to 2025-10-04.

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	14% 9% 3 8% 5% 5% 5% 4 5% 7% 34%	125745
	Night	14% 10% 4 8% 5% 4 4 4 5% 6% 35%	123723
Transparency	Day	48% 5% 12% 21% 13% 1	129315
	Night	48% 5% 12% 21% 12% 1	128223
Seeing	Day	17% 12% 30% 23% 13% 5%	16616
	Night	19% 10% 29% 29% 12% 1	26241

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	11% 15% 7% 15% 6% 4 4 3 4 5% 25%	3617
	11th to 20th	Day	15% 14% 6% 16% 8% 10% 6% 4 4 5% 12%	3620
	21st to end	Day	21% 16% 6% 11% 6% 5% 5% 3 4 5% 16%	4439
February	1st to 10th	Day	13% 16% 4 13% 8% 6% 5% 4 5% 5% 22%	1800
	11th to 20th	Day	14% 14% 4 13% 7% 6% 5% 3 5% 6% 24%	1874
	21st to end	Day	14% 15% 4 10% 7% 5% 4 3 5% 7% 25%	1650
March	1st to 10th	Day	15% 12% 5% 10% 5% 4 4 3 4 6% 31%	4613
	11th to 20th	Day	12% 11% 4 8% 6% 5% 5% 3 5% 8% 33%	4980
	21st to end	Day	19% 14% 3 9% 5% 5% 4 3 4 5% 29%	5465
April	1st to 10th	Day	16% 12% 3 7% 5% 4 4 4 6% 6% 31%	2310
	11th to 20th	Day	16% 10% 3 7% 4 5% 4 4 5% 7% 34%	2551
	21st to end	Day	17% 9% 3 8% 4 4 4 3 6% 7% 35%	2600
May	1st to 10th	Day	19% 8% 3 7% 4 4 5% 3 5% 6% 35%	5862
	11th to 20th	Day	17% 8% 3 8% 5% 5% 5% 4 6% 7% 33%	5861
	21st to end	Day	14% 6% 2 7% 4 4 4 4 5% 7% 42%	6433
June	1st to 10th	Day	10% 6% 3 6% 6% 5% 4 4 6% 8% 41%	2913
	11th to 20th	Day	10% 5% 3 7% 4 5% 6% 5% 6% 8% 41%	3000
	21st to end	Day	9% 6% 2 7% 5% 5% 6% 5% 7% 9% 37%	2906
July	1st to 10th	Day	9% 5% 2 7% 5% 5% 6% 5% 7% 10% 39%	6360
	11th to 20th	Day	6% 5% 2 6% 4 5% 6% 5% 6% 9% 46%	6360
	21st to end	Day	8% 5% 2 6% 5% 5% 5% 4 6% 9% 45%	6497
August	1st to 10th	Day	12% 5% 2 6% 5% 5% 5% 4 6% 9% 41%	4234
	11th to 20th	Day	9% 5% 2 6% 5% 6% 5% 5% 8% 9% 39%	4174
	21st to end	Day	9% 6% 2 7% 6% 5% 6% 5% 7% 9% 39%	4657
September	1st to 10th	Day	11% 6% 3 6% 5% 5% 5% 4 6% 8% 41%	2250
	11th to 20th	Day	10% 6% 1 4 4 4 5% 4 6% 9% 47%	2200
	21st to end	Day	14% 7% 2 7% 6% 5% 5% 4 6% 8% 36%	2200
October	1st to 10th	Day	13% 6% 2 6% 5% 5% 4 5% 5% 6% 43%	2058
	11th to 20th	Day	17% 10% 3 6% 5% 5% 5% 4 4 7% 35%	1900
	21st to end	Day	19% 12% 3 7% 4 5% 5% 3 5% 6% 31%	1948
November	1st to 10th	Day	11% 10% 3 7% 5% 4 5% 4 6% 7% 38%	1762
	11th to 20th	Day	15% 12% 4 8% 6% 5% 6% 4 5% 6% 31%	1800
	21st to end	Day	17% 13% 5% 9% 5% 5% 4 4 4 5% 29%	1650
December	1st to 10th	Day	12% 14% 7% 12% 6% 5% 5% 4 5% 6% 24%	2600
	11th to 20th	Day	21% 19% 5% 9% 4 4 4 4 6% 5% 21%	2785
	21st to end	Day	25% 21% 7% 11% 5% 4 3 3 4 4 13%	3816
January	1st to 10th	Night	13% 13% 6% 11% 5% 5% 4 3 5% 5% 29%	6348
	11th to 20th	Night	11% 15% 6% 15% 8% 6% 6% 4 5% 6% 18%	6360
	21st to end	Night	17% 16% 7% 9% 5% 5% 5% 3 4 4 24%	6514
February	1st to 10th	Night	14% 16% 4 11% 8% 6% 5% 3 5% 5% 23%	2600
	11th to 20th	Night	13% 13% 5% 11% 7% 5% 5% 4 5% 6% 27%	2410
	21st to end	Night	18% 11% 3 9% 5% 4 4 3 5% 6% 29%	1980
March	1st to 10th	Night	15% 12% 3 8% 5% 4 4 4 5% 6% 35%	5240
	11th to 20th	Night	9% 8% 3 7% 5% 4 5% 4 5% 7% 42%	4980
	21st to end	Night	15% 9% 3 9% 5% 4 4 3 4 5% 38%	5467
April	1st to 10th	Night	17% 10% 3 6% 5% 4 5% 4 5% 6% 35%	2107
	11th to 20th	Night	18% 8% 3 6% 4 4 3 4 5% 7% 38%	1797
	21st to end	Night	16% 7% 2 6% 5% 4 4 4 5% 7% 41%	1800
May	1st to 10th	Night	21% 8% 3 7% 4 4 4 3 5% 6% 34%	4033
	11th to 20th	Night	18% 7% 2 7% 4 4 3 3 5% 7% 40%	4032
	21st to end	Night	14% 5% 2 5% 4 4 5% 3 5% 8% 45%	4421
June	1st to 10th	Night	11% 5% 2 6% 4 4 4 4 5% 7% 47%	1472
	11th to 20th	Night	9% 5% 2 7% 4 5% 5% 3 8% 8% 45%	1400
	21st to end	Night	8% 6% 2 6% 4 3 4 4 6% 7% 50%	1487
July	1st to 10th	Night	8% 4 2 5% 4 4 4 4 6% 10% 48%	3618
	11th to 20th	Night	9% 4 2 5% 4 4 4 4 5% 10% 49%	3617
	21st to end	Night	8% 4 2 5% 4 4 5% 4 6% 8% 49%	4355
August	1st to 10th	Night	10% 6% 2 5% 4 4 3 4 6% 8% 47%	2915
	11th to 20th	Night	9% 5% 2 6% 4 4 4 4 6% 7% 48%	2875
	21st to end	Night	9% 5% 2 6% 5% 5% 4 4 5% 7% 49%	3223
September	1st to 10th	Night	9% 6% 2 5% 4 4 4 4 6% 7% 49%	2130
	11th to 20th	Night	9% 5% 2 5% 3 3 3 3 4 8% 57%	2200
	21st to end	Night	15% 6% 3 6% 4 4 4 3 5% 7% 44%	2200
October	1st to 10th	Night	14% 6% 2 5% 3 3 3 4 5% 6% 47%	2188
	11th to 20th	Night	19% 9% 3 6% 5% 4 5% 3 5% 5% 37%	2280
	21st to end	Night	20% 9% 3 7% 4 5% 5% 4 5% 6% 32%	2646
November	1st to 10th	Night	13% 8% 2 6% 4 4 4 3 5% 7% 44%	2536
	11th to 20th	Night	15% 11% 3 8% 6% 5% 6% 5% 6% 6% 31%	2600
	21st to end	Night	18% 13% 3 8% 5% 4 4 4 5% 6% 28%	2746
December	1st to 10th	Night	12% 14% 5% 13% 6% 5% 5% 4 6% 7% 24%	4580
	11th to 20th	Night	15% 19% 6% 10% 7% 5% 4 3 4 6% 21%	5409
	21st to end	Night	27% 20% 6% 10% 4 3 4 3 3 4 16%	7157

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	60% 6% 11% 15% 7% 1	3618
	11th to 20th	Day	73% 5% 8% 7% 6% 1	3620
	21st to end	Day	70% 6% 11% 7% 5%	4439
February	1st to 10th	Day	63% 7% 9% 14% 7%	1800
	11th to 20th	Day	61% 5% 9% 16% 8% 1	1883
	21st to end	Day	59% 6% 11% 16% 7% 1	1650
March	1st to 10th	Day	55% 4 14% 17% 8% 2	4613
	11th to 20th	Day	49% 4 14% 22% 8% 2	4980
	21st to end	Day	57% 4 12% 15% 10% 1	5465
April	1st to 10th	Day	52% 5% 11% 19% 11% 1	2310
	11th to 20th	Day	48% 5% 11% 20% 13% 2	2551
	21st to end	Day	49% 5% 12% 18% 14% 2	2600
May	1st to 10th	Day	49% 5% 11% 19% 13% 4	5897
	11th to 20th	Day	48% 6% 12% 21% 12% 1	5865
	21st to end	Day	41% 5% 9% 21% 19% 4	6447
June	1st to 10th	Day	39% 6% 12% 26% 14% 2	2913
	11th to 20th	Day	39% 7% 13% 23% 16% 3	3000
	21st to end	Day	40% 8% 13% 22% 16% 2	2906
July	1st to 10th	Day	39% 5% 14% 25% 16% 2	6291
	11th to 20th	Day	33% 5% 15% 28% 18% 1	6285
	21st to end	Day	35% 5% 15% 22% 22% 1	6312
August	1st to 10th	Day	39% 6% 14% 25% 16% 1	4221
	11th to 20th	Day	37% 7% 11% 32% 10% 1	4213
	21st to end	Day	40% 5% 13% 28% 13% 1	4656
September	1st to 10th	Day	38% 7% 14% 26% 14% 2	2250
	11th to 20th	Day	32% 6% 13% 33% 16% 1	2200
	21st to end	Day	44% 6% 14% 23% 13%	2200
October	1st to 10th	Day	32% 5% 12% 31% 19% 1	3396
	11th to 20th	Day	40% 4 12% 25% 18%	3140
	21st to end	Day	46% 4 14% 23% 12% 1	3185
November	1st to 10th	Day	45% 6% 12% 24% 12% 1	1762
	11th to 20th	Day	53% 5% 12% 19% 10% 1	1800
	21st to end	Day	58% 5% 12% 18% 7% 1	1650
December	1st to 10th	Day	61% 4 17% 14% 5%	2600
	11th to 20th	Day	66% 4 11% 12% 7%	2781
	21st to end	Day	75% 5% 7% 8% 5%	3816
January	1st to 10th	Night	56% 5% 10% 19% 7% 2	6348
	11th to 20th	Night	65% 6% 11% 12% 6% 1	6360
	21st to end	Night	64% 4 10% 14% 8%	6514
February	1st to 10th	Night	62% 6% 10% 14% 7% 1	2600
	11th to 20th	Night	56% 7% 10% 17% 9% 1	2412
	21st to end	Night	54% 5% 12% 18% 9% 1	1980
March	1st to 10th	Night	50% 4 14% 21% 10% 1	5240
	11th to 20th	Night	41% 5% 15% 23% 15% 1	4980
	21st to end	Night	48% 4 11% 20% 15% 2	5467
April	1st to 10th	Night	49% 4 11% 20% 13% 2	2107
	11th to 20th	Night	44% 7% 11% 19% 18% 2	1797
	21st to end	Night	44% 5% 11% 20% 17% 3	1800
May	1st to 10th	Night	51% 4 10% 16% 14% 4	4060
	11th to 20th	Night	45% 5% 11% 26% 11% 2	4033
	21st to end	Night	37% 6% 12% 23% 17% 5%	4429
June	1st to 10th	Night	35% 5% 11% 27% 19% 2	1472
	11th to 20th	Night	35% 7% 14% 25% 18% 2	1400
	21st to end	Night	32% 7% 13% 26% 21% 1	1487
July	1st to 10th	Night	32% 4 15% 29% 16% 5%	3580
	11th to 20th	Night	32% 4 15% 30% 17% 2	3572
	21st to end	Night	32% 6% 15% 23% 23% 2	4227
August	1st to 10th	Night	35% 5% 14% 27% 17% 1	2904
	11th to 20th	Night	34% 6% 12% 35% 12% 2	2902
	21st to end	Night	34% 5% 13% 33% 14% 1	3223
September	1st to 10th	Night	34% 7% 13% 28% 16% 2	2130
	11th to 20th	Night	27% 5% 12% 33% 21% 2	2200
	21st to end	Night	40% 5% 12% 29% 13% 1	2200
October	1st to 10th	Night	26% 4 10% 32% 27% 1	3630
	11th to 20th	Night	43% 4 11% 23% 18%	3779
	21st to end	Night	42% 4 12% 28% 14% 1	4359
November	1st to 10th	Night	40% 6% 12% 26% 15% 1	2536
	11th to 20th	Night	51% 6% 13% 20% 9% 1	2600
	21st to end	Night	56% 5% 13% 19% 6%	2746
December	1st to 10th	Night	59% 5% 17% 15% 4	4580
	11th to 20th	Night	63% 6% 12% 13% 6% 1	5412
	21st to end	Night	73% 4 9% 8% 6%	7157

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	22% 21% 36% 15% 6%	300
	11th to 20th	Day	23% 19% 40% 14% 3 1	300
	21st to end	Day	25% 16% 39% 15% 4 1	330
February	1st to 10th	Day	23% 21% 38% 14% 3 1	300
	11th to 20th	Day	22% 21% 39% 16% 2	300
	21st to end	Day	21% 24% 41% 10% 2	249
March	1st to 10th	Day	25% 19% 37% 15% 3	355
	11th to 20th	Day	22% 16% 34% 21% 6% 1	500
	21st to end	Day	28% 15% 32% 19% 4 1	550
April	1st to 10th	Day	20% 18% 35% 19% 7% 1	500
	11th to 20th	Day	25% 20% 29% 14% 8% 5%	492
	21st to end	Day	24% 13% 30% 20% 9% 2	500
May	1st to 10th	Day	23% 13% 29% 21% 11% 3	503
	11th to 20th	Day	21% 12% 28% 23% 11% 6%	527
	21st to end	Day	15% 8% 26% 27% 17% 8%	573
June	1st to 10th	Day	12% 11% 31% 29% 13% 3	703
	11th to 20th	Day	11% 8% 33% 30% 15% 3	730
	21st to end	Day	12% 8% 31% 31% 14% 5%	730
July	1st to 10th	Day	7% 6% 25% 30% 21% 10%	721
	11th to 20th	Day	11% 7% 27% 31% 17% 8%	718
	21st to end	Day	8% 5% 25% 29% 23% 10%	610
August	1st to 10th	Day	10% 3 22% 27% 26% 12%	526
	11th to 20th	Day	12% 4 19% 31% 21% 13%	519
	21st to end	Day	10% 5% 22% 30% 20% 12%	583
September	1st to 10th	Day	12% 6% 26% 22% 22% 12%	530
	11th to 20th	Day	9% 3 18% 26% 28% 16%	530
	21st to end	Day	18% 8% 23% 24% 18% 8%	530
October	1st to 10th	Day	17% 10% 26% 21% 17% 9%	502
	11th to 20th	Day	22% 14% 30% 24% 7% 2	490
	21st to end	Day	27% 15% 37% 16% 5% 1	397
November	1st to 10th	Day	17% 19% 35% 20% 7% 2	300
	11th to 20th	Day	23% 21% 33% 15% 6% 1	300
	21st to end	Day	23% 20% 34% 19% 4	225
December	1st to 10th	Day	24% 19% 37% 14% 8%	200
	11th to 20th	Day	31% 21% 34% 13% 3 1	200
	21st to end	Day	27% 23% 32% 14% 3	293
January	1st to 10th	Night	22% 15% 36% 21% 5% 1	1000
	11th to 20th	Night	23% 15% 35% 22% 4 1	1000
	21st to end	Night	20% 13% 33% 28% 5%	891
February	1st to 10th	Night	22% 15% 37% 23% 3	800
	11th to 20th	Night	21% 16% 33% 26% 4	783
	21st to end	Night	23% 16% 39% 19% 2	660
March	1st to 10th	Night	20% 13% 35% 26% 6%	800
	11th to 20th	Night	17% 16% 38% 24% 5% 1	800
	21st to end	Night	22% 14% 31% 26% 7% 1	880
April	1st to 10th	Night	22% 14% 33% 27% 4	707
	11th to 20th	Night	22% 10% 33% 25% 8% 1	593
	21st to end	Night	20% 9% 31% 32% 9%	600
May	1st to 10th	Night	19% 8% 30% 33% 10% 1	600
	11th to 20th	Night	22% 6% 26% 30% 15% 1	591
	21st to end	Night	11% 3 25% 41% 18% 2	650
June	1st to 10th	Night	13% 6% 26% 40% 14%	450
	11th to 20th	Night	11% 4 25% 49% 11%	400
	21st to end	Night	11% 4 22% 45% 17% 1	487
July	1st to 10th	Night	8% 2 19% 42% 26% 4	585
	11th to 20th	Night	9% 4 19% 41% 25% 3	582
	21st to end	Night	6% 3 20% 47% 23% 2	657
August	1st to 10th	Night	9% 2 17% 37% 32% 3	597
	11th to 20th	Night	8% 2 20% 35% 31% 4	594
	21st to end	Night	10% 3 18% 36% 30% 3	660
September	1st to 10th	Night	13% 6% 19% 33% 25% 5%	730
	11th to 20th	Night	10% 4 16% 34% 31% 5%	800
	21st to end	Night	18% 5% 21% 30% 21% 5%	800
October	1st to 10th	Night	16% 8% 25% 31% 18% 3	773
	11th to 20th	Night	24% 11% 28% 26% 9% 2	760
	21st to end	Night	25% 12% 30% 27% 5%	836
November	1st to 10th	Night	18% 11% 31% 25% 13% 1	780
	11th to 20th	Night	21% 16% 31% 24% 7% 1	800
	21st to end	Night	25% 14% 33% 22% 6%	800
December	1st to 10th	Night	24% 13% 35% 21% 6%	800
	11th to 20th	Night	24% 14% 36% 23% 3	895
	21st to end	Night	30% 12% 33% 22% 3	1100

Page generated at 2025-10-01 01:39:05. Version ac07

Copyright © 2025 Attilla Danko.