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 2024-11-05.

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 6% 7% 34%	100999
	Night	15% 10% 4 8% 5% 4 4 4 5% 6% 36%	98015
Transparency	Day	47% 6% 12% 21% 12% 1	104613
	Night	47% 6% 12% 22% 12% 1	102541
Seeing	Day	17% 12% 30% 23% 13% 5%	15387
	Night	18% 10% 29% 29% 12% 1	25050

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	16% 17% 7% 11% 5% 4 5% 4 5% 5% 22%	2527
	11th to 20th	Day	16% 17% 6% 13% 8% 9% 7% 4 4 5% 12%	2530
	21st to end	Day	27% 19% 7% 10% 5% 4 4 3 4 4 13%	3097
February	1st to 10th	Day	13% 16% 4 13% 8% 6% 5% 4 5% 5% 22%	1710
	11th to 20th	Day	13% 14% 4 12% 7% 6% 5% 3 5% 6% 25%	1777
	21st to end	Day	14% 16% 4 10% 7% 4 4 3 5% 7% 26%	1570
March	1st to 10th	Day	18% 15% 5% 9% 5% 4 4 3 4 6% 27%	3211
	11th to 20th	Day	13% 11% 5% 9% 7% 5% 5% 3 5% 7% 31%	3480
	21st to end	Day	20% 12% 3 9% 5% 4 4 3 5% 5% 29%	3815
April	1st to 10th	Day	15% 13% 3 7% 5% 4 4 4 6% 6% 31%	2194
	11th to 20th	Day	17% 10% 3 7% 4 5% 4 4 5% 7% 34%	2422
	21st to end	Day	18% 9% 3 8% 5% 4 4 3 6% 7% 34%	2470
May	1st to 10th	Day	18% 7% 3 7% 4 4 5% 4 6% 6% 36%	4082
	11th to 20th	Day	17% 7% 3 7% 5% 4 4 4 6% 8% 34%	4081
	21st to end	Day	10% 6% 2 7% 4 4 5% 4 5% 8% 46%	4476
June	1st to 10th	Day	10% 5% 3 7% 6% 6% 5% 4 6% 8% 41%	2767
	11th to 20th	Day	10% 5% 2 7% 4 5% 6% 5% 6% 8% 42%	2850
	21st to end	Day	10% 6% 3 7% 5% 5% 6% 6% 8% 9% 36%	2761
July	1st to 10th	Day	10% 5% 2 8% 5% 5% 7% 5% 6% 9% 38%	4440
	11th to 20th	Day	7% 5% 2 5% 4 4 6% 5% 6% 10% 46%	4440
	21st to end	Day	7% 5% 3 6% 6% 6% 6% 5% 7% 9% 41%	4511
August	1st to 10th	Day	12% 5% 2 6% 5% 5% 5% 4 6% 9% 41%	4104
	11th to 20th	Day	9% 5% 2 6% 5% 6% 5% 5% 8% 9% 40%	4044
	21st to end	Day	9% 6% 2 7% 6% 5% 6% 5% 7% 9% 38%	4514
September	1st to 10th	Day	11% 6% 3 6% 5% 5% 5% 4 6% 8% 40%	2138
	11th to 20th	Day	10% 6% 1 4 4 4 5% 4 6% 9% 46%	2090
	21st to end	Day	15% 7% 2 7% 6% 5% 5% 4 6% 9% 35%	2090
October	1st to 10th	Day	13% 6% 2 6% 5% 4 4 5% 5% 6% 43%	2025
	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%	1708
	11th to 20th	Day	14% 12% 4 8% 6% 5% 5% 4 5% 6% 32%	1710
	21st to end	Day	18% 12% 5% 8% 5% 5% 4 4 4 5% 31%	1568
December	1st to 10th	Day	13% 16% 6% 12% 7% 5% 5% 4 5% 6% 22%	1520
	11th to 20th	Day	17% 15% 5% 9% 5% 4 5% 4 7% 6% 24%	1770
	21st to end	Day	25% 21% 7% 11% 5% 4 4 3 4 5% 11%	2659
January	1st to 10th	Night	16% 15% 6% 10% 5% 5% 4 3 4 5% 26%	4428
	11th to 20th	Night	14% 17% 7% 13% 7% 6% 6% 4 5% 6% 16%	4440
	21st to end	Night	23% 17% 8% 10% 5% 4 3 3 4 4 20%	4556
February	1st to 10th	Night	14% 16% 4 10% 8% 6% 5% 3 5% 5% 23%	2470
	11th to 20th	Night	12% 13% 5% 10% 7% 5% 5% 4 5% 6% 27%	2287
	21st to end	Night	19% 12% 3 9% 5% 4 4 3 5% 6% 29%	1884
March	1st to 10th	Night	15% 14% 4 8% 5% 3 3 3 4 5% 35%	3642
	11th to 20th	Night	9% 9% 3 6% 5% 5% 5% 4 5% 7% 42%	3480
	21st to end	Night	15% 9% 3 9% 5% 4 4 4 5% 5% 37%	3817
April	1st to 10th	Night	16% 10% 3 6% 5% 4 5% 4 5% 6% 36%	2002
	11th to 20th	Night	18% 8% 2 6% 4 4 3 4 5% 7% 38%	1706
	21st to end	Night	17% 8% 2 6% 5% 3 4 4 5% 7% 40%	1710
May	1st to 10th	Night	18% 8% 3 6% 4 3 4 4 5% 7% 38%	2813
	11th to 20th	Night	15% 6% 2 7% 4 4 4 3 5% 8% 42%	2812
	21st to end	Night	10% 5% 2 5% 4 4 5% 3 5% 8% 49%	3079
June	1st to 10th	Night	11% 5% 2 6% 4 4 4 4 5% 7% 47%	1399
	11th to 20th	Night	9% 5% 2 7% 4 5% 5% 3 8% 8% 45%	1330
	21st to end	Night	9% 6% 2 6% 4 3 4 4 7% 7% 49%	1412
July	1st to 10th	Night	9% 4 1 4 4 4 4 4 6% 11% 49%	2530
	11th to 20th	Night	9% 4 2 4 3 3 4 3 5% 9% 54%	2530
	21st to end	Night	6% 4 2 5% 4 5% 7% 5% 7% 9% 47%	3041
August	1st to 10th	Night	11% 6% 2 6% 4 4 3 3 6% 8% 47%	2825
	11th to 20th	Night	9% 5% 2 6% 4 4 4 4 6% 7% 48%	2785
	21st to end	Night	9% 5% 2 6% 5% 4 4 4 5% 7% 49%	3124
September	1st to 10th	Night	9% 6% 2 5% 4 4 4 3 6% 7% 48%	2023
	11th to 20th	Night	9% 5% 2 5% 3 3 4 3 4 8% 55%	2090
	21st to end	Night	15% 6% 3 6% 4 4 4 3 5% 7% 44%	2090
October	1st to 10th	Night	14% 7% 2 5% 3 3 3 4 5% 6% 47%	2154
	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%	2470
	11th to 20th	Night	16% 10% 3 7% 6% 4 5% 5% 6% 7% 31%	2470
	21st to end	Night	19% 13% 3 8% 4 4 4 4 5% 6% 29%	2608
December	1st to 10th	Night	17% 15% 5% 10% 5% 5% 5% 4 6% 6% 23%	2660
	11th to 20th	Night	14% 15% 5% 10% 6% 5% 5% 4 5% 6% 26%	3419
	21st to end	Night	28% 22% 6% 10% 4 3 4 3 3 4 13%	5003

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	62% 7% 11% 13% 6% 1	2528
	11th to 20th	Day	72% 7% 11% 7% 4	2530
	21st to end	Day	75% 7% 8% 6% 3 1	3097
February	1st to 10th	Day	63% 7% 9% 14% 7%	1710
	11th to 20th	Day	60% 5% 9% 16% 9% 1	1786
	21st to end	Day	58% 6% 11% 16% 7% 2	1570
March	1st to 10th	Day	59% 5% 12% 18% 5% 1	3211
	11th to 20th	Day	52% 6% 13% 20% 8% 2	3480
	21st to end	Day	57% 6% 12% 14% 9% 2	3815
April	1st to 10th	Day	51% 6% 12% 19% 12% 1	2194
	11th to 20th	Day	49% 5% 11% 20% 13% 2	2422
	21st to end	Day	50% 5% 13% 17% 14% 2	2470
May	1st to 10th	Day	46% 6% 12% 22% 11% 2	4120
	11th to 20th	Day	45% 8% 14% 22% 9% 1	4085
	21st to end	Day	36% 7% 11% 18% 23% 5%	4489
June	1st to 10th	Day	40% 6% 11% 26% 14% 2	2767
	11th to 20th	Day	38% 7% 13% 23% 16% 3	2850
	21st to end	Day	40% 8% 13% 22% 15% 2	2761
July	1st to 10th	Day	42% 5% 14% 21% 16% 2	4371
	11th to 20th	Day	31% 6% 14% 32% 15% 1	4365
	21st to end	Day	38% 6% 16% 16% 22% 2	4368
August	1st to 10th	Day	39% 6% 13% 25% 16% 1	4091
	11th to 20th	Day	37% 7% 11% 32% 11% 1	4083
	21st to end	Day	40% 5% 13% 27% 13% 1	4513
September	1st to 10th	Day	39% 7% 14% 24% 14% 2	2138
	11th to 20th	Day	32% 7% 12% 32% 16% 1	2090
	21st to end	Day	44% 6% 14% 23% 12%	2090
October	1st to 10th	Day	31% 5% 12% 31% 20% 1	3363
	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	44% 6% 13% 23% 12% 1	1708
	11th to 20th	Day	52% 5% 13% 19% 10% 1	1710
	21st to end	Day	56% 5% 12% 18% 7% 1	1568
December	1st to 10th	Day	63% 5% 10% 16% 5%	1520
	11th to 20th	Day	60% 6% 14% 15% 6%	1766
	21st to end	Day	75% 6% 9% 6% 3	2659
January	1st to 10th	Night	60% 6% 12% 15% 6% 1	4428
	11th to 20th	Night	68% 8% 11% 10% 4	4440
	21st to end	Night	69% 5% 9% 13% 3	4556
February	1st to 10th	Night	61% 7% 10% 14% 7% 1	2470
	11th to 20th	Night	55% 7% 10% 17% 9% 1	2289
	21st to end	Night	54% 6% 12% 18% 9% 1	1884
March	1st to 10th	Night	51% 4 13% 24% 7%	3642
	11th to 20th	Night	39% 7% 16% 19% 18% 1	3480
	21st to end	Night	48% 5% 11% 23% 12% 1	3817
April	1st to 10th	Night	48% 5% 11% 21% 13% 2	2002
	11th to 20th	Night	45% 7% 10% 19% 17% 2	1706
	21st to end	Night	44% 5% 11% 20% 17% 3	1710
May	1st to 10th	Night	45% 6% 11% 21% 14% 4	2840
	11th to 20th	Night	41% 6% 12% 27% 13% 2	2813
	21st to end	Night	32% 8% 12% 21% 21% 6%	3087
June	1st to 10th	Night	35% 5% 11% 28% 17% 2	1399
	11th to 20th	Night	35% 7% 14% 24% 19% 2	1330
	21st to end	Night	33% 7% 12% 26% 21% 1	1412
July	1st to 10th	Night	30% 4 13% 31% 15% 6%	2490
	11th to 20th	Night	29% 4 13% 34% 18% 2	2482
	21st to end	Night	31% 8% 18% 21% 20% 3	2944
August	1st to 10th	Night	36% 5% 14% 28% 16% 1	2814
	11th to 20th	Night	34% 6% 12% 35% 12% 2	2812
	21st to end	Night	34% 5% 13% 32% 14% 1	3124
September	1st to 10th	Night	34% 7% 13% 27% 17% 2	2023
	11th to 20th	Night	28% 5% 12% 32% 21% 2	2090
	21st to end	Night	40% 5% 11% 30% 13% 1	2090
October	1st to 10th	Night	26% 4 10% 32% 27% 1	3596
	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	2470
	11th to 20th	Night	50% 6% 14% 20% 9% 1	2470
	21st to end	Night	55% 5% 14% 19% 7%	2608
December	1st to 10th	Night	62% 7% 10% 15% 6%	2660
	11th to 20th	Night	57% 7% 14% 14% 7% 1	3422
	21st to end	Night	75% 5% 10% 7% 2	5003

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% 34% 15% 7%	270
	11th to 20th	Day	23% 18% 40% 15% 3 1	270
	21st to end	Day	26% 14% 39% 16% 4 1	297
February	1st to 10th	Day	23% 21% 38% 14% 3 1	270
	11th to 20th	Day	21% 20% 40% 17% 2	270
	21st to end	Day	20% 25% 42% 10% 3	225
March	1st to 10th	Day	25% 19% 35% 16% 4	322
	11th to 20th	Day	21% 15% 34% 22% 6% 1	460
	21st to end	Day	27% 15% 32% 20% 5% 1	506
April	1st to 10th	Day	17% 18% 36% 20% 8% 1	460
	11th to 20th	Day	25% 19% 28% 14% 8% 5%	452
	21st to end	Day	25% 13% 30% 19% 10% 2	460
May	1st to 10th	Day	23% 11% 29% 22% 11% 3	463
	11th to 20th	Day	20% 11% 28% 23% 12% 6%	487
	21st to end	Day	14% 6% 24% 29% 19% 8%	529
June	1st to 10th	Day	13% 11% 29% 30% 14% 4	654
	11th to 20th	Day	12% 8% 32% 31% 15% 3	680
	21st to end	Day	12% 8% 31% 30% 14% 4	680
July	1st to 10th	Day	7% 6% 24% 30% 22% 11%	671
	11th to 20th	Day	11% 6% 26% 31% 16% 9%	668
	21st to end	Day	8% 5% 25% 28% 24% 10%	564
August	1st to 10th	Day	10% 3 23% 25% 27% 12%	486
	11th to 20th	Day	11% 4 20% 30% 21% 14%	479
	21st to end	Day	11% 5% 22% 29% 21% 12%	539
September	1st to 10th	Day	12% 6% 26% 23% 22% 11%	490
	11th to 20th	Day	10% 3 20% 27% 26% 15%	490
	21st to end	Day	18% 9% 24% 23% 18% 8%	490
October	1st to 10th	Day	17% 10% 26% 21% 17% 9%	490
	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	16% 19% 35% 21% 8% 2	282
	11th to 20th	Day	20% 22% 34% 16% 7% 1	270
	21st to end	Day	23% 19% 35% 19% 4	203
December	1st to 10th	Day	23% 19% 37% 12% 8%	180
	11th to 20th	Day	28% 21% 35% 13% 3 1	180
	21st to end	Day	26% 24% 33% 14% 3	263
January	1st to 10th	Night	22% 15% 35% 22% 6% 1	950
	11th to 20th	Night	24% 15% 33% 23% 4 1	950
	21st to end	Night	20% 13% 33% 29% 6%	847
February	1st to 10th	Night	21% 14% 38% 23% 3	760
	11th to 20th	Night	21% 15% 33% 27% 4	743
	21st to end	Night	24% 16% 38% 20% 2	628
March	1st to 10th	Night	20% 13% 35% 27% 6%	760
	11th to 20th	Night	16% 16% 38% 25% 5% 1	760
	21st to end	Night	21% 13% 30% 27% 8% 1	836
April	1st to 10th	Night	21% 13% 33% 28% 4	672
	11th to 20th	Night	22% 10% 34% 25% 8% 1	563
	21st to end	Night	20% 8% 31% 31% 9%	570
May	1st to 10th	Night	18% 7% 30% 34% 10% 1	570
	11th to 20th	Night	22% 5% 25% 32% 15% 1	561
	21st to end	Night	10% 2 25% 41% 19% 2	617
June	1st to 10th	Night	13% 5% 26% 41% 15%	428
	11th to 20th	Night	11% 4 24% 50% 11%	380
	21st to end	Night	11% 3 22% 45% 18% 1	462
July	1st to 10th	Night	8% 2 20% 41% 26% 4	555
	11th to 20th	Night	9% 4 19% 40% 25% 3	552
	21st to end	Night	5% 3 20% 47% 23% 2	624
August	1st to 10th	Night	9% 2 18% 37% 31% 3	567
	11th to 20th	Night	8% 2 20% 35% 31% 4	564
	21st to end	Night	10% 3 18% 36% 31% 3	627
September	1st to 10th	Night	13% 6% 18% 34% 24% 5%	693
	11th to 20th	Night	11% 4 17% 34% 29% 5%	760
	21st to end	Night	18% 5% 21% 30% 21% 5%	760
October	1st to 10th	Night	16% 8% 25% 31% 17% 3	760
	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% 12% 31% 25% 14% 1	760
	11th to 20th	Night	21% 16% 31% 24% 7% 1	760
	21st to end	Night	25% 13% 33% 22% 6%	760
December	1st to 10th	Night	25% 12% 36% 21% 6%	760
	11th to 20th	Night	23% 14% 36% 23% 3	850
	21st to end	Night	30% 12% 33% 21% 3	1045

Page generated at 2024-11-03 02:11:17. Version ac07

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