Old Mill State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Old Mill State Park clear sky chart from 2005-11-06 to 2025-12-03.

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	11% 9% 3 9% 5% 5% 5% 4 6% 7% 35%	127366
	Night	9% 10% 4 10% 6% 5% 5% 4 6% 7% 33%	123586
Transparency	Day	46% 6% 15% 23% 9% 1	130815
	Night	49% 6% 13% 22% 9% 1	128222
Seeing	Day	14% 9% 31% 29% 14% 3	17672
	Night	14% 8% 33% 33% 11% 1	27597

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	4 11% 7% 17% 7% 7% 8% 6% 6% 8% 17%	3178
	11th to 20th	Day	4 10% 4 14% 11% 10% 11% 11% 9% 7% 11%	3244
	21st to end	Day	5% 15% 8% 18% 8% 6% 6% 4 6% 6% 17%	4022
February	1st to 10th	Day	8% 13% 6% 11% 7% 6% 7% 6% 7% 5% 23%	1800
	11th to 20th	Day	6% 11% 4 10% 9% 7% 9% 6% 8% 8% 23%	1754
	21st to end	Day	6% 10% 4 14% 9% 8% 7% 4 5% 8% 25%	1561
March	1st to 10th	Day	10% 9% 3 8% 8% 5% 5% 4 6% 8% 33%	4674
	11th to 20th	Day	8% 9% 5% 13% 10% 5% 5% 5% 6% 9% 25%	4980
	21st to end	Day	13% 16% 6% 10% 5% 5% 4 3 5% 6% 28%	5464
April	1st to 10th	Day	11% 14% 4 7% 5% 5% 4 4 5% 7% 33%	2392
	11th to 20th	Day	16% 11% 4 8% 5% 4 5% 3 5% 6% 32%	2572
	21st to end	Day	20% 9% 3 8% 5% 4 5% 3 5% 6% 33%	2600
May	1st to 10th	Day	14% 8% 2 5% 3 4 4 3 5% 7% 45%	6020
	11th to 20th	Day	16% 9% 2 6% 5% 5% 4 4 6% 8% 36%	6376
	21st to end	Day	14% 8% 2 6% 4 4 4 3 5% 7% 43%	7428
June	1st to 10th	Day	14% 6% 3 6% 5% 4 5% 4 7% 8% 39%	3000
	11th to 20th	Day	15% 6% 2 6% 4 4 5% 4 7% 9% 39%	3000
	21st to end	Day	12% 7% 3 7% 6% 5% 5% 5% 7% 8% 37%	3000
July	1st to 10th	Day	6% 4 2 5% 5% 5% 5% 4 8% 12% 44%	6799
	11th to 20th	Day	10% 6% 2 6% 4 5% 5% 4 6% 8% 46%	6800
	21st to end	Day	9% 5% 2 5% 4 4 5% 5% 7% 10% 44%	7230
August	1st to 10th	Day	10% 5% 2 5% 4 4 5% 4 6% 8% 48%	4247
	11th to 20th	Day	12% 5% 2 5% 3 4 4 4 6% 8% 46%	4171
	21st to end	Day	12% 5% 2 5% 4 3 4 3 5% 7% 51%	4675
September	1st to 10th	Day	12% 5% 2 5% 3 3 3 4 4 8% 49%	2458
	11th to 20th	Day	14% 5% 2 6% 4 5% 5% 4 6% 8% 42%	2200
	21st to end	Day	13% 6% 2 5% 3 4 4 3 6% 8% 45%	2200
October	1st to 10th	Day	16% 9% 3 7% 4 4 4 3 4 6% 40%	2025
	11th to 20th	Day	15% 12% 3 7% 4 5% 3 3 5% 6% 36%	2000
	21st to end	Day	14% 16% 5% 9% 5% 3 5% 4 5% 5% 29%	2005
November	1st to 10th	Day	12% 16% 5% 10% 6% 4 4 3 4 5% 31%	1694
	11th to 20th	Day	12% 14% 7% 14% 5% 5% 4 3 6% 4 28%	1680
	21st to end	Day	10% 16% 4 13% 9% 6% 5% 4 5% 4 24%	1676
December	1st to 10th	Day	10% 15% 5% 15% 9% 11% 5% 4 6% 6% 13%	2304
	11th to 20th	Day	9% 16% 7% 13% 6% 4 5% 5% 7% 7% 21%	2639
	21st to end	Day	11% 15% 6% 18% 9% 8% 6% 3 4 4 16%	3498
January	1st to 10th	Night	4 11% 5% 19% 8% 10% 7% 6% 8% 9% 15%	6787
	11th to 20th	Night	4 13% 5% 12% 10% 9% 9% 8% 8% 7% 13%	6644
	21st to end	Night	6% 16% 8% 15% 6% 5% 6% 4 6% 6% 21%	6954
February	1st to 10th	Night	8% 11% 5% 11% 7% 6% 8% 5% 6% 7% 26%	2600
	11th to 20th	Night	6% 10% 4 9% 6% 6% 7% 5% 7% 9% 30%	2533
	21st to end	Night	6% 11% 4 12% 8% 7% 5% 4 5% 7% 31%	2085
March	1st to 10th	Night	6% 9% 4 10% 7% 5% 5% 4 6% 8% 36%	5165
	11th to 20th	Night	8% 11% 4 10% 9% 5% 5% 4 6% 6% 31%	4979
	21st to end	Night	12% 15% 6% 12% 5% 5% 3 3 4 5% 30%	5467
April	1st to 10th	Night	12% 10% 3 7% 4 4 4 4 6% 7% 39%	2005
	11th to 20th	Night	14% 12% 4 8% 5% 4 4 3 6% 5% 36%	1779
	21st to end	Night	18% 8% 3 8% 4 4 4 4 3 6% 38%	1800
May	1st to 10th	Night	14% 7% 2 4 4 4 3 3 6% 6% 46%	3938
	11th to 20th	Night	15% 8% 2 6% 4 4 4 4 6% 7% 40%	3536
	21st to end	Night	13% 7% 2 6% 4 3 4 3 5% 7% 47%	3470
June	1st to 10th	Night	12% 4 1 5% 5% 3 5% 4 8% 8% 45%	1400
	11th to 20th	Night	12% 5% 2 4 4 5% 5% 4 7% 8% 45%	1400
	21st to end	Night	9% 5% 2 5% 4 4 5% 5% 8% 8% 45%	1400
July	1st to 10th	Night	7% 4 2 4 4 4 3 4 6% 10% 52%	3180
	11th to 20th	Night	5% 4 1 5% 4 4 4 4 6% 9% 55%	3180
	21st to end	Night	5% 5% 2 6% 4 4 5% 4 8% 11% 45%	3642
August	1st to 10th	Night	5% 4 2 6% 4 4 4 4 6% 8% 53%	2911
	11th to 20th	Night	11% 4 1 4 3 3 4 4 6% 9% 50%	2888
	21st to end	Night	10% 5% 2 6% 3 3 4 3 5% 7% 52%	3234
September	1st to 10th	Night	9% 4 1 4 3 3 4 3 6% 7% 56%	1937
	11th to 20th	Night	11% 6% 2 4 4 3 3 3 6% 8% 50%	2200
	21st to end	Night	14% 5% 2 4 4 4 4 4 5% 7% 48%	2200
October	1st to 10th	Night	16% 8% 2 7% 3 3 4 3 5% 7% 41%	2355
	11th to 20th	Night	16% 12% 3 6% 4 3 4 3 5% 6% 38%	2400
	21st to end	Night	16% 12% 3 7% 6% 5% 4 3 5% 7% 33%	2834
November	1st to 10th	Night	12% 13% 4 11% 6% 4 5% 4 5% 6% 32%	2824
	11th to 20th	Night	10% 16% 6% 13% 6% 4 5% 3 4 6% 28%	2940
	21st to end	Night	11% 13% 4 12% 8% 5% 5% 4 5% 6% 26%	2940
December	1st to 10th	Night	6% 14% 7% 15% 14% 9% 6% 5% 5% 5% 14%	4931
	11th to 20th	Night	8% 16% 5% 14% 9% 6% 5% 4 6% 6% 22%	5568
	21st to end	Night	13% 14% 6% 17% 9% 7% 5% 3 5% 5% 16%	7480

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% 6% 9% 16% 7%	3179
	11th to 20th	Day	66% 7% 9% 14% 4	3272
	21st to end	Day	67% 6% 11% 12% 4	4022
February	1st to 10th	Day	59% 6% 13% 15% 7%	1800
	11th to 20th	Day	54% 7% 12% 17% 8% 1	1763
	21st to end	Day	56% 8% 14% 15% 6% 1	1561
March	1st to 10th	Day	48% 5% 18% 17% 11% 1	4676
	11th to 20th	Day	53% 8% 15% 18% 6%	4980
	21st to end	Day	56% 5% 10% 22% 7%	5464
April	1st to 10th	Day	49% 7% 12% 22% 9% 1	2392
	11th to 20th	Day	52% 5% 13% 19% 10% 1	2572
	21st to end	Day	52% 6% 13% 20% 8% 1	2600
May	1st to 10th	Day	38% 5% 13% 26% 18% 1	6031
	11th to 20th	Day	44% 7% 11% 23% 14% 1	6380
	21st to end	Day	40% 6% 10% 27% 15% 3	7428
June	1st to 10th	Day	41% 7% 18% 25% 9%	3000
	11th to 20th	Day	40% 8% 18% 25% 9%	3000
	21st to end	Day	42% 9% 17% 24% 7% 1	3000
July	1st to 10th	Day	31% 8% 26% 30% 6%	6726
	11th to 20th	Day	35% 6% 21% 31% 7%	6719
	21st to end	Day	34% 8% 19% 29% 9%	7020
August	1st to 10th	Day	34% 7% 17% 28% 14% 1	4232
	11th to 20th	Day	35% 7% 17% 33% 7%	4210
	21st to end	Day	33% 5% 22% 32% 8%	4674
September	1st to 10th	Day	35% 5% 16% 32% 11%	2458
	11th to 20th	Day	40% 8% 19% 27% 6% 1	2200
	21st to end	Day	37% 7% 16% 33% 7%	2200
October	1st to 10th	Day	36% 4 14% 29% 16% 1	3298
	11th to 20th	Day	42% 4 10% 27% 17%	3240
	21st to end	Day	50% 5% 13% 25% 7%	3226
November	1st to 10th	Day	56% 6% 12% 18% 7% 1	1694
	11th to 20th	Day	61% 6% 12% 15% 6% 1	1680
	21st to end	Day	63% 8% 12% 12% 5%	1676
December	1st to 10th	Day	71% 7% 11% 9% 2	2304
	11th to 20th	Day	59% 5% 13% 14% 8%	2640
	21st to end	Day	72% 4 8% 12% 3	3498
January	1st to 10th	Night	63% 6% 10% 13% 8%	6787
	11th to 20th	Night	64% 6% 9% 15% 5%	6691
	21st to end	Night	62% 6% 12% 16% 5%	6954
February	1st to 10th	Night	55% 7% 13% 16% 8%	2600
	11th to 20th	Night	47% 7% 14% 20% 11%	2534
	21st to end	Night	53% 5% 12% 20% 9% 1	2085
March	1st to 10th	Night	45% 6% 17% 19% 10% 3	5176
	11th to 20th	Night	50% 6% 13% 18% 12%	4980
	21st to end	Night	56% 5% 9% 21% 8% 1	5467
April	1st to 10th	Night	43% 5% 12% 24% 14% 2	2005
	11th to 20th	Night	50% 5% 10% 20% 13% 2	1779
	21st to end	Night	48% 5% 10% 25% 10% 2	1800
May	1st to 10th	Night	36% 6% 13% 27% 18% 1	3947
	11th to 20th	Night	42% 7% 10% 23% 18% 2	3537
	21st to end	Night	37% 5% 10% 27% 18% 3	3470
June	1st to 10th	Night	34% 7% 20% 27% 11% 2	1400
	11th to 20th	Night	35% 9% 16% 27% 12% 2	1400
	21st to end	Night	33% 9% 19% 31% 7% 2	1400
July	1st to 10th	Night	28% 8% 24% 30% 9% 1	3145
	11th to 20th	Night	26% 5% 22% 38% 10%	3138
	21st to end	Night	31% 7% 23% 28% 9% 1	3538
August	1st to 10th	Night	27% 6% 16% 35% 14% 1	2902
	11th to 20th	Night	29% 7% 19% 33% 11% 1	2915
	21st to end	Night	32% 6% 20% 30% 12%	3234
September	1st to 10th	Night	28% 5% 17% 36% 13% 1	1937
	11th to 20th	Night	33% 6% 21% 29% 11% 1	2200
	21st to end	Night	36% 6% 13% 32% 13%	2200
October	1st to 10th	Night	35% 4 12% 34% 13% 2	3849
	11th to 20th	Night	42% 4 12% 29% 13%	3899
	21st to end	Night	48% 5% 11% 27% 9%	4572
November	1st to 10th	Night	54% 5% 13% 19% 8% 2	2824
	11th to 20th	Night	59% 5% 14% 15% 6% 1	2940
	21st to end	Night	58% 6% 16% 14% 6%	2940
December	1st to 10th	Night	72% 6% 11% 9% 2	4931
	11th to 20th	Night	62% 5% 11% 14% 7%	5566
	21st to end	Night	70% 5% 9% 12% 4	7480

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	10% 8% 36% 29% 13% 3	300
	11th to 20th	Day	12% 8% 34% 33% 12%	300
	21st to end	Day	13% 12% 32% 29% 10% 3	330
February	1st to 10th	Day	12% 14% 36% 30% 6% 2	300
	11th to 20th	Day	8% 15% 41% 22% 12% 2	300
	21st to end	Day	9% 7% 45% 31% 7% 1	249
March	1st to 10th	Day	13% 13% 30% 33% 9% 1	300
	11th to 20th	Day	14% 10% 35% 25% 13% 4	300
	21st to end	Day	14% 12% 32% 29% 10% 3	330
April	1st to 10th	Day	15% 12% 35% 27% 9% 2	492
	11th to 20th	Day	19% 13% 32% 26% 10% 1	690
	21st to end	Day	23% 10% 28% 27% 12% 1	700
May	1st to 10th	Day	18% 11% 29% 28% 11% 3	703
	11th to 20th	Day	18% 9% 32% 25% 13% 3	725
	21st to end	Day	18% 8% 26% 30% 15% 3	789
June	1st to 10th	Day	14% 9% 27% 30% 16% 4	730
	11th to 20th	Day	14% 12% 34% 26% 13% 2	730
	21st to end	Day	13% 9% 29% 30% 15% 5%	730
July	1st to 10th	Day	7% 5% 26% 33% 21% 8%	721
	11th to 20th	Day	12% 6% 30% 27% 20% 5%	718
	21st to end	Day	5% 4 27% 35% 21% 7%	794
August	1st to 10th	Day	8% 5% 23% 32% 27% 5%	726
	11th to 20th	Day	11% 6% 23% 31% 20% 9%	715
	21st to end	Day	12% 9% 26% 32% 18% 4	803
September	1st to 10th	Day	13% 9% 30% 29% 17% 3	588
	11th to 20th	Day	15% 11% 32% 29% 11% 2	330
	21st to end	Day	16% 8% 36% 27% 10% 3	330
October	1st to 10th	Day	18% 11% 28% 31% 10% 2	330
	11th to 20th	Day	18% 10% 38% 25% 8%	330
	21st to end	Day	23% 12% 33% 23% 8% 1	363
November	1st to 10th	Day	21% 13% 30% 28% 8% 1	330
	11th to 20th	Day	17% 15% 37% 25% 5% 1	330
	21st to end	Day	15% 14% 39% 24% 6% 1	330
December	1st to 10th	Day	16% 11% 32% 32% 7% 2	306
	11th to 20th	Day	17% 11% 35% 31% 5%	300
	21st to end	Day	17% 8% 34% 27% 11% 4	330
January	1st to 10th	Night	10% 9% 35% 31% 12% 2	1000
	11th to 20th	Night	14% 9% 37% 31% 9%	1000
	21st to end	Night	13% 9% 39% 30% 9%	1100
February	1st to 10th	Night	13% 9% 30% 35% 12% 1	1000
	11th to 20th	Night	12% 6% 38% 31% 11% 3	979
	21st to end	Night	11% 8% 37% 29% 13% 2	765
March	1st to 10th	Night	13% 9% 34% 31% 10% 2	719
	11th to 20th	Night	12% 6% 39% 33% 8% 1	600
	21st to end	Night	17% 9% 30% 29% 13% 2	660
April	1st to 10th	Night	17% 8% 35% 30% 9% 1	600
	11th to 20th	Night	18% 10% 32% 30% 9% 1	593
	21st to end	Night	21% 8% 26% 33% 12% 1	600
May	1st to 10th	Night	17% 8% 32% 34% 9% 1	600
	11th to 20th	Night	16% 9% 34% 30% 11%	591
	21st to end	Night	16% 6% 32% 34% 13%	650
June	1st to 10th	Night	13% 5% 29% 40% 13% 1	600
	11th to 20th	Night	14% 5% 33% 38% 11%	600
	21st to end	Night	10% 5% 28% 39% 18% 1	600
July	1st to 10th	Night	6% 2 24% 46% 20% 2	585
	11th to 20th	Night	5% 3 30% 44% 16% 1	582
	21st to end	Night	6% 3 23% 46% 21% 2	657
August	1st to 10th	Night	7% 3 20% 48% 21% 1	597
	11th to 20th	Night	9% 3 26% 38% 21% 3	594
	21st to end	Night	9% 4 28% 39% 18% 1	660
September	1st to 10th	Night	12% 4 29% 39% 14% 2	600
	11th to 20th	Night	14% 5% 34% 35% 13%	600
	21st to end	Night	16% 6% 34% 34% 10% 1	600
October	1st to 10th	Night	18% 9% 36% 29% 8%	755
	11th to 20th	Night	21% 10% 35% 28% 7%	800
	21st to end	Night	22% 9% 32% 30% 6% 1	1074
November	1st to 10th	Night	18% 10% 36% 28% 8%	1025
	11th to 20th	Night	17% 12% 33% 30% 8% 1	1050
	21st to end	Night	17% 12% 41% 24% 6% 1	1050
December	1st to 10th	Night	14% 10% 32% 33% 10%	1011
	11th to 20th	Night	17% 10% 35% 31% 6% 1	1000
	21st to end	Night	23% 8% 33% 25% 9% 1	1100

Page generated at 2025-11-30 00:00:53. Version ac07

Copyright © 2025 Attilla Danko.