Mill Ridge
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mill Ridge clear sky chart from 2005-11-06 to 2025-03-27.

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	10% 8% 4 8% 5% 5% 5% 4 6% 7% 35%	109472
	Night	10% 9% 4 9% 5% 5% 5% 4 6% 7% 36%	109886
Transparency	Day	42% 10% 12% 19% 13% 4	113227
	Night	42% 10% 12% 19% 14% 4	114270
Seeing	Day	20% 15% 25% 21% 13% 6%	15457
	Night	18% 13% 22% 29% 16% 3	25618

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% 12% 5% 13% 6% 5% 4 3 5% 6% 33%	4056
	11th to 20th	Day	7% 9% 7% 14% 4 5% 4 3 4 6% 37%	4060
	21st to end	Day	11% 13% 6% 8% 5% 4 4 4 4 5% 37%	4466
February	1st to 10th	Day	12% 10% 5% 10% 6% 5% 4 4 5% 7% 33%	1895
	11th to 20th	Day	13% 12% 6% 10% 6% 5% 5% 3 4 5% 31%	1948
	21st to end	Day	14% 12% 3 9% 3 4 4 3 6% 5% 36%	1650
March	1st to 10th	Day	16% 12% 5% 8% 4 5% 4 3 5% 5% 33%	3441
	11th to 20th	Day	10% 9% 3 7% 4 4 4 3 4 6% 46%	3590
	21st to end	Day	14% 10% 3 7% 5% 4 4 4 5% 7% 37%	3881
April	1st to 10th	Day	9% 10% 3 5% 5% 5% 4 5% 7% 9% 40%	2090
	11th to 20th	Day	14% 8% 2 6% 4 5% 4 4 5% 6% 40%	2294
	21st to end	Day	12% 8% 3 7% 5% 4 6% 4 6% 7% 39%	2470
May	1st to 10th	Day	12% 9% 4 9% 6% 6% 6% 4 6% 7% 31%	4082
	11th to 20th	Day	13% 10% 3 9% 6% 6% 6% 5% 7% 6% 28%	4081
	21st to end	Day	8% 7% 2 8% 5% 6% 7% 5% 8% 10% 34%	4476
June	1st to 10th	Day	10% 7% 2 7% 6% 7% 7% 6% 7% 9% 32%	2470
	11th to 20th	Day	6% 6% 3 9% 6% 7% 7% 6% 8% 10% 32%	2470
	21st to end	Day	9% 6% 3 7% 6% 7% 8% 5% 8% 9% 32%	2470
July	1st to 10th	Day	6% 6% 3 8% 7% 7% 7% 6% 8% 10% 33%	4120
	11th to 20th	Day	9% 6% 3 8% 7% 7% 7% 5% 8% 8% 32%	4120
	21st to end	Day	12% 10% 4 13% 9% 8% 7% 6% 7% 8% 16%	4466
August	1st to 10th	Day	10% 6% 3 8% 7% 6% 8% 6% 8% 11% 27%	4104
	11th to 20th	Day	7% 6% 3 8% 7% 6% 7% 6% 9% 10% 30%	4044
	21st to end	Day	6% 5% 2 6% 5% 5% 6% 4 6% 8% 46%	4198
September	1st to 10th	Day	9% 7% 3 9% 5% 5% 6% 4 7% 8% 37%	2090
	11th to 20th	Day	13% 8% 3 9% 6% 4 5% 4 5% 8% 35%	2090
	21st to end	Day	13% 7% 3 7% 4 5% 5% 5% 6% 7% 38%	2090
October	1st to 10th	Day	12% 6% 2 6% 4 4 4 4 5% 7% 46%	2066
	11th to 20th	Day	10% 8% 3 6% 4 3 3 4 5% 6% 49%	1900
	21st to end	Day	11% 8% 2 5% 3 3 4 3 5% 6% 49%	2090
November	1st to 10th	Day	9% 7% 2 5% 4 4 4 3 5% 6% 51%	1835
	11th to 20th	Day	9% 9% 2 7% 5% 4 4 3 6% 7% 45%	1800
	21st to end	Day	10% 10% 4 6% 4 4 4 3 6% 7% 43%	1800
December	1st to 10th	Day	9% 8% 3 9% 5% 4 4 5% 6% 7% 40%	2930
	11th to 20th	Day	10% 11% 5% 9% 5% 5% 6% 5% 7% 7% 30%	3373
	21st to end	Day	12% 9% 7% 8% 4 5% 5% 4 6% 7% 33%	4466
January	1st to 10th	Night	10% 10% 5% 16% 7% 5% 4 3 4 6% 28%	5889
	11th to 20th	Night	10% 9% 5% 14% 7% 6% 4 3 4 6% 31%	5900
	21st to end	Night	10% 12% 4 8% 5% 4 5% 4 5% 6% 37%	6490
February	1st to 10th	Night	11% 11% 4 9% 4 5% 4 4 7% 7% 35%	2502
	11th to 20th	Night	16% 12% 4 11% 5% 4 4 3 5% 5% 31%	2338
	21st to end	Night	13% 12% 4 9% 5% 5% 4 3 6% 6% 34%	1980
March	1st to 10th	Night	17% 15% 4 10% 6% 5% 5% 3 4 5% 27%	3631
	11th to 20th	Night	9% 9% 3 7% 4 4 4 4 5% 7% 44%	3590
	21st to end	Night	12% 8% 3 7% 5% 5% 4 4 6% 6% 40%	3890
April	1st to 10th	Night	10% 9% 3 6% 5% 4 4 4 6% 7% 41%	2090
	11th to 20th	Night	10% 10% 3 6% 4 4 3 4 4 8% 42%	1850
	21st to end	Night	10% 7% 3 7% 5% 4 4 5% 6% 6% 42%	1710
May	1st to 10th	Night	11% 11% 4 9% 6% 5% 5% 5% 6% 8% 31%	2813
	11th to 20th	Night	12% 11% 4 10% 5% 5% 5% 5% 7% 8% 29%	2812
	21st to end	Night	6% 8% 3 9% 6% 4 5% 5% 8% 10% 35%	3079
June	1st to 10th	Night	8% 6% 3 7% 6% 5% 6% 5% 9% 12% 34%	1710
	11th to 20th	Night	4 5% 2 7% 5% 6% 5% 5% 8% 14% 38%	1710
	21st to end	Night	7% 6% 3 6% 6% 6% 5% 4 8% 11% 39%	1710
July	1st to 10th	Night	7% 6% 3 8% 5% 6% 7% 6% 8% 12% 31%	2840
	11th to 20th	Night	6% 4 3 8% 6% 4 6% 5% 10% 12% 36%	2840
	21st to end	Night	9% 10% 5% 12% 8% 7% 7% 6% 8% 8% 20%	3087
August	1st to 10th	Night	6% 6% 3 9% 6% 6% 6% 6% 9% 12% 32%	2825
	11th to 20th	Night	7% 7% 3 10% 6% 5% 6% 4 8% 8% 35%	2785
	21st to end	Night	5% 4 2 6% 4 3 4 5% 8% 10% 47%	3422
September	1st to 10th	Night	9% 7% 2 8% 5% 5% 5% 5% 7% 8% 40%	2090
	11th to 20th	Night	12% 9% 4 8% 5% 5% 5% 4 6% 8% 36%	2090
	21st to end	Night	11% 7% 3 8% 5% 4 4 3 5% 6% 45%	2090
October	1st to 10th	Night	13% 7% 2 6% 4 3 4 3 4 7% 48%	2113
	11th to 20th	Night	11% 7% 2 6% 4 4 4 3 5% 5% 48%	2280
	21st to end	Night	9% 9% 2 6% 3 4 3 3 5% 6% 49%	2508
November	1st to 10th	Night	11% 7% 3 6% 4 4 4 4 5% 6% 47%	2460
	11th to 20th	Night	10% 10% 3 7% 4 3 4 3 5% 7% 44%	2600
	21st to end	Night	10% 11% 4 6% 4 3 3 4 5% 6% 45%	2600
December	1st to 10th	Night	9% 8% 4 12% 6% 5% 5% 4 5% 6% 37%	4250
	11th to 20th	Night	13% 11% 6% 13% 5% 4 4 3 5% 6% 30%	4822
	21st to end	Night	12% 9% 5% 11% 6% 5% 4 4 5% 8% 31%	6490

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	46% 8% 9% 20% 16% 2	4057
	11th to 20th	Day	44% 7% 7% 15% 24% 2	4060
	21st to end	Day	44% 7% 8% 19% 18% 3	4466
February	1st to 10th	Day	50% 7% 10% 15% 15% 3	1895
	11th to 20th	Day	54% 7% 9% 14% 14% 3	1958
	21st to end	Day	47% 7% 10% 15% 16% 6%	1650
March	1st to 10th	Day	47% 8% 9% 17% 14% 5%	3441
	11th to 20th	Day	38% 6% 9% 21% 17% 8%	3590
	21st to end	Day	44% 8% 9% 25% 11% 3	3881
April	1st to 10th	Day	39% 9% 12% 21% 17% 3	2090
	11th to 20th	Day	41% 9% 8% 18% 20% 4	2294
	21st to end	Day	42% 9% 12% 23% 12% 2	2470
May	1st to 10th	Day	47% 13% 12% 19% 8% 1	4120
	11th to 20th	Day	49% 13% 12% 20% 5% 1	4085
	21st to end	Day	37% 14% 15% 19% 13% 2	4489
June	1st to 10th	Day	43% 15% 17% 16% 8% 1	2470
	11th to 20th	Day	42% 15% 16% 15% 12% 1	2470
	21st to end	Day	43% 13% 14% 17% 11% 2	2470
July	1st to 10th	Day	41% 15% 17% 18% 8%	4055
	11th to 20th	Day	45% 13% 16% 19% 6% 1	4051
	21st to end	Day	63% 13% 11% 10% 4	4324
August	1st to 10th	Day	46% 15% 17% 19% 4	4091
	11th to 20th	Day	39% 14% 21% 16% 9% 1	4083
	21st to end	Day	33% 11% 14% 32% 9% 1	4198
September	1st to 10th	Day	42% 12% 12% 17% 14% 4	2090
	11th to 20th	Day	46% 9% 10% 18% 14% 1	2090
	21st to end	Day	44% 8% 13% 17% 14% 4	2090
October	1st to 10th	Day	28% 6% 9% 19% 26% 12%	3430
	11th to 20th	Day	26% 4 7% 25% 19% 19%	3140
	21st to end	Day	27% 6% 9% 26% 19% 13%	3428
November	1st to 10th	Day	34% 6% 9% 19% 25% 7%	1835
	11th to 20th	Day	37% 7% 7% 20% 23% 6%	1800
	21st to end	Day	40% 6% 9% 22% 19% 5%	1800
December	1st to 10th	Day	40% 9% 9% 17% 22% 3	2930
	11th to 20th	Day	49% 8% 10% 17% 14% 2	3370
	21st to end	Day	46% 8% 13% 21% 9% 2	4466
January	1st to 10th	Night	53% 7% 8% 15% 13% 2	5889
	11th to 20th	Night	50% 6% 7% 13% 19% 5%	5900
	21st to end	Night	43% 8% 8% 18% 21% 3	6490
February	1st to 10th	Night	46% 8% 11% 18% 15% 3	2502
	11th to 20th	Night	54% 6% 9% 16% 12% 4	2339
	21st to end	Night	49% 8% 9% 16% 14% 4	1980
March	1st to 10th	Night	54% 10% 10% 12% 12% 3	3631
	11th to 20th	Night	36% 8% 10% 22% 16% 8%	3590
	21st to end	Night	41% 9% 11% 23% 13% 3	3890
April	1st to 10th	Night	39% 8% 14% 21% 15% 3	2090
	11th to 20th	Night	40% 8% 10% 20% 19% 4	1850
	21st to end	Night	39% 9% 13% 26% 13% 1	1710
May	1st to 10th	Night	44% 13% 15% 21% 7% 1	2840
	11th to 20th	Night	45% 15% 14% 21% 5%	2813
	21st to end	Night	34% 17% 17% 23% 8% 1	3087
June	1st to 10th	Night	37% 14% 21% 18% 9%	1710
	11th to 20th	Night	33% 15% 22% 21% 9% 1	1710
	21st to end	Night	36% 12% 19% 19% 11% 2	1710
July	1st to 10th	Night	42% 15% 18% 19% 6%	2795
	11th to 20th	Night	35% 17% 23% 19% 4 1	2786
	21st to end	Night	57% 15% 13% 11% 4	2988
August	1st to 10th	Night	40% 15% 23% 18% 4	2814
	11th to 20th	Night	39% 15% 21% 17% 7%	2812
	21st to end	Night	29% 11% 19% 33% 9% 1	3422
September	1st to 10th	Night	40% 10% 15% 19% 13% 3	2090
	11th to 20th	Night	44% 10% 14% 16% 15% 1	2090
	21st to end	Night	39% 8% 12% 21% 17% 3	2090
October	1st to 10th	Night	31% 7% 12% 17% 22% 11%	3529
	11th to 20th	Night	25% 6% 8% 21% 23% 16%	3779
	21st to end	Night	30% 6% 6% 24% 20% 14%	4120
November	1st to 10th	Night	36% 8% 10% 19% 21% 6%	2460
	11th to 20th	Night	38% 6% 7% 21% 22% 6%	2600
	21st to end	Night	39% 7% 7% 25% 18% 4	2600
December	1st to 10th	Night	43% 10% 10% 16% 20% 2	4250
	11th to 20th	Night	55% 8% 8% 15% 12% 2	4824
	21st to end	Night	46% 10% 15% 17% 11% 1	6490

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	36% 28% 26% 9% 1	300
	11th to 20th	Day	41% 22% 25% 11% 1	300
	21st to end	Day	32% 30% 29% 7% 2	330
February	1st to 10th	Day	28% 29% 33% 9% 1	300
	11th to 20th	Day	42% 31% 21% 5%	300
	21st to end	Day	39% 27% 28% 5% 1	249
March	1st to 10th	Day	30% 23% 29% 12% 6%	430
	11th to 20th	Day	29% 26% 26% 14% 4 1	500
	21st to end	Day	28% 25% 27% 15% 4	530
April	1st to 10th	Day	25% 22% 26% 18% 8% 1	460
	11th to 20th	Day	22% 22% 25% 21% 9% 2	452
	21st to end	Day	21% 18% 27% 21% 10% 3	460
May	1st to 10th	Day	21% 17% 30% 17% 11% 5%	463
	11th to 20th	Day	18% 14% 25% 24% 12% 6%	487
	21st to end	Day	13% 11% 25% 26% 16% 9%	529
June	1st to 10th	Day	12% 9% 29% 26% 18% 7%	490
	11th to 20th	Day	8% 5% 27% 27% 24% 10%	490
	21st to end	Day	10% 10% 30% 25% 16% 10%	490
July	1st to 10th	Day	9% 5% 19% 29% 23% 15%	485
	11th to 20th	Day	9% 5% 16% 30% 24% 15%	484
	21st to end	Day	10% 5% 19% 27% 26% 13%	532
August	1st to 10th	Day	14% 8% 20% 24% 20% 13%	486
	11th to 20th	Day	11% 7% 21% 27% 23% 12%	479
	21st to end	Day	11% 3 15% 29% 25% 16%	539
September	1st to 10th	Day	9% 7% 17% 32% 25% 11%	490
	11th to 20th	Day	13% 8% 20% 24% 27% 9%	490
	21st to end	Day	19% 6% 21% 29% 20% 4	490
October	1st to 10th	Day	17% 8% 25% 26% 18% 6%	490
	11th to 20th	Day	16% 16% 24% 25% 17% 2	490
	21st to end	Day	19% 16% 24% 29% 11% 2	539
November	1st to 10th	Day	15% 20% 27% 26% 10% 2	373
	11th to 20th	Day	24% 21% 34% 17% 4	300
	21st to end	Day	24% 20% 34% 15% 6% 1	300
December	1st to 10th	Day	29% 28% 30% 10% 2	300
	11th to 20th	Day	26% 22% 32% 15% 5%	300
	21st to end	Day	27% 22% 35% 12% 3	330
January	1st to 10th	Night	27% 21% 27% 21% 4	800
	11th to 20th	Night	27% 20% 28% 21% 4	800
	21st to end	Night	22% 22% 33% 21% 2	880
February	1st to 10th	Night	22% 18% 30% 27% 4	800
	11th to 20th	Night	31% 22% 29% 16% 1	783
	21st to end	Night	27% 24% 31% 18% 1	660
March	1st to 10th	Night	23% 20% 30% 23% 4	800
	11th to 20th	Night	25% 19% 29% 20% 7% 1	800
	21st to end	Night	21% 18% 32% 23% 6%	863
April	1st to 10th	Night	22% 17% 28% 25% 8%	760
	11th to 20th	Night	19% 15% 27% 27% 10% 1	626
	21st to end	Night	15% 12% 25% 36% 11% 1	570
May	1st to 10th	Night	16% 12% 26% 28% 17% 1	570
	11th to 20th	Night	13% 8% 24% 34% 20% 2	561
	21st to end	Night	11% 4 15% 37% 30% 4	617
June	1st to 10th	Night	8% 4 16% 40% 28% 4	570
	11th to 20th	Night	6% 4 14% 36% 31% 8%	570
	21st to end	Night	9% 3 13% 38% 33% 4	570
July	1st to 10th	Night	12% 2 11% 31% 38% 6%	555
	11th to 20th	Night	9% 3 9% 30% 41% 8%	552
	21st to end	Night	8% 3 8% 32% 39% 10%	624
August	1st to 10th	Night	9% 2 9% 34% 41% 5%	567
	11th to 20th	Night	10% 5% 10% 34% 35% 5%	564
	21st to end	Night	11% 3 8% 33% 38% 7%	660
September	1st to 10th	Night	11% 5% 12% 33% 33% 6%	760
	11th to 20th	Night	15% 5% 15% 31% 29% 5%	760
	21st to end	Night	16% 5% 18% 33% 26% 3	760
October	1st to 10th	Night	16% 8% 19% 29% 23% 6%	760
	11th to 20th	Night	16% 12% 22% 32% 16% 2	760
	21st to end	Night	16% 15% 22% 33% 12% 2	836
November	1st to 10th	Night	17% 10% 21% 33% 15% 3	780
	11th to 20th	Night	20% 14% 25% 30% 10% 1	800
	21st to end	Night	19% 16% 24% 29% 11% 1	800
December	1st to 10th	Night	24% 18% 27% 26% 5%	800
	11th to 20th	Night	20% 18% 26% 29% 7% 1	800
	21st to end	Night	25% 18% 28% 26% 4	880

Page generated at 2025-03-24 09:04:27. Version ac07

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