Grafton Lakes State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Grafton Lakes State Park 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	16% 10% 4 9% 5% 4 4 4 5% 6% 32%	126491
	Night	17% 11% 4 10% 5% 4 4 3 5% 6% 31%	122885
Transparency	Day	52% 6% 12% 19% 10% 1	129982
	Night	54% 6% 12% 17% 10% 1	127481
Seeing	Day	24% 19% 27% 19% 8% 2	16011
	Night	23% 18% 27% 24% 7% 1	24990

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	11% 15% 7% 22% 6% 4 4 3 3 4 21%	3597
	11th to 20th	Day	13% 14% 6% 13% 7% 4 5% 4 5% 5% 23%	3570
	21st to end	Day	15% 16% 6% 9% 5% 5% 4 3 4 4 28%	4051
February	1st to 10th	Day	15% 15% 5% 11% 7% 4 5% 5% 6% 4 23%	1800
	11th to 20th	Day	13% 15% 6% 14% 8% 4 4 3 4 6% 24%	1938
	21st to end	Day	17% 16% 4 12% 6% 4 4 3 4 5% 27%	1650
March	1st to 10th	Day	19% 15% 6% 11% 5% 4 3 2 3 4 26%	4476
	11th to 20th	Day	14% 15% 4 10% 4 4 4 3 4 5% 34%	4692
	21st to end	Day	20% 11% 4 10% 5% 4 4 3 4 4 30%	5970
April	1st to 10th	Day	20% 14% 4 8% 5% 4 4 3 4 5% 32%	2400
	11th to 20th	Day	16% 11% 3 7% 5% 4 5% 3 5% 5% 35%	2374
	21st to end	Day	21% 11% 3 6% 5% 4 4 4 5% 6% 32%	2510
May	1st to 10th	Day	30% 11% 4 7% 4 3 4 3 5% 6% 22%	5950
	11th to 20th	Day	18% 11% 3 8% 5% 6% 5% 4 6% 6% 29%	6318
	21st to end	Day	20% 9% 3 7% 5% 4 4 4 6% 7% 31%	6949
June	1st to 10th	Day	18% 7% 3 6% 5% 5% 6% 4 7% 8% 31%	2800
	11th to 20th	Day	18% 7% 3 5% 5% 4 5% 5% 7% 8% 32%	2800
	21st to end	Day	18% 7% 3 7% 5% 4 6% 5% 6% 8% 33%	2800
July	1st to 10th	Day	11% 7% 3 8% 5% 5% 5% 5% 8% 9% 34%	6360
	11th to 20th	Day	9% 5% 2 7% 5% 6% 6% 5% 8% 10% 36%	6360
	21st to end	Day	14% 6% 2 7% 5% 4 5% 4 6% 7% 40%	6926
August	1st to 10th	Day	16% 8% 3 7% 5% 5% 5% 4 6% 8% 33%	4532
	11th to 20th	Day	13% 8% 3 8% 5% 4 5% 5% 7% 8% 34%	3883
	21st to end	Day	11% 6% 3 6% 4 5% 5% 4 7% 8% 40%	4312
September	1st to 10th	Day	14% 5% 1 5% 5% 4 6% 3 5% 7% 45%	2400
	11th to 20th	Day	14% 6% 2 4 3 3 4 3 5% 7% 48%	2294
	21st to end	Day	17% 7% 2 5% 3 4 4 4 6% 8% 41%	2200
October	1st to 10th	Day	21% 9% 3 6% 5% 4 4 3 5% 4 36%	2038
	11th to 20th	Day	16% 9% 3 7% 4 4 5% 3 6% 7% 38%	1891
	21st to end	Day	24% 11% 3 8% 4 4 4 3 5% 6% 29%	1881
November	1st to 10th	Day	14% 11% 2 7% 4 3 4 3 4 6% 42%	1761
	11th to 20th	Day	16% 13% 3 7% 4 4 4 3 4 5% 36%	1800
	21st to end	Day	19% 12% 4 8% 5% 4 5% 4 5% 5% 30%	1662
December	1st to 10th	Day	12% 18% 6% 12% 7% 5% 5% 3 4 5% 23%	2600
	11th to 20th	Day	17% 15% 5% 10% 4 4 3 3 4 5% 29%	2986
	21st to end	Day	17% 16% 6% 11% 4 4 4 3 4 5% 26%	3960
January	1st to 10th	Night	12% 15% 8% 20% 5% 4 3 2 3 4 23%	6349
	11th to 20th	Night	10% 15% 6% 19% 8% 5% 4 3 5% 5% 20%	6315
	21st to end	Night	16% 12% 4 11% 7% 6% 5% 4 5% 5% 25%	6904
February	1st to 10th	Night	15% 14% 4 12% 7% 5% 5% 4 5% 5% 24%	2600
	11th to 20th	Night	14% 13% 5% 12% 7% 6% 5% 4 5% 5% 24%	2346
	21st to end	Night	16% 16% 4 11% 5% 4 5% 3 4 6% 26%	1980
March	1st to 10th	Night	18% 10% 5% 11% 6% 4 4 4 5% 6% 26%	5364
	11th to 20th	Night	14% 15% 3 8% 5% 4 5% 3 5% 6% 32%	5250
	21st to end	Night	22% 15% 5% 11% 4 3 3 2 3 4 28%	4962
April	1st to 10th	Night	21% 13% 3 7% 5% 4 4 3 5% 6% 28%	2000
	11th to 20th	Night	19% 12% 3 7% 4 4 3 4 5% 6% 33%	1975
	21st to end	Night	20% 10% 3 7% 4 3 3 3 6% 6% 35%	1890
May	1st to 10th	Night	32% 11% 4 7% 4 4 4 3 4 5% 22%	4019
	11th to 20th	Night	18% 10% 3 9% 6% 5% 5% 4 6% 7% 28%	3575
	21st to end	Night	22% 9% 3 7% 5% 5% 4 3 5% 6% 30%	3926
June	1st to 10th	Night	21% 7% 2 6% 5% 5% 4 3 5% 7% 36%	1600
	11th to 20th	Night	18% 6% 2 6% 4 4 4 5% 6% 7% 39%	1600
	21st to end	Night	14% 6% 2 6% 4 4 6% 4 6% 8% 40%	1600
July	1st to 10th	Night	10% 7% 3 8% 6% 5% 5% 4 7% 9% 37%	3600
	11th to 20th	Night	12% 8% 3 9% 6% 5% 6% 5% 6% 7% 34%	3600
	21st to end	Night	11% 7% 3 7% 5% 4 4 3 5% 6% 46%	3926
August	1st to 10th	Night	21% 8% 3 7% 4 4 4 3 6% 7% 34%	2586
	11th to 20th	Night	14% 7% 3 8% 6% 6% 5% 4 6% 7% 36%	3160
	21st to end	Night	12% 6% 2 7% 4 4 4 4 6% 8% 43%	3586
September	1st to 10th	Night	16% 7% 3 6% 4 3 4 3 5% 6% 44%	2000
	11th to 20th	Night	15% 5% 1 4 3 4 3 2 4 7% 52%	2105
	21st to end	Night	16% 7% 2 7% 5% 4 4 3 5% 6% 43%	2200
October	1st to 10th	Night	21% 8% 3 6% 5% 4 4 4 4 5% 36%	2205
	11th to 20th	Night	16% 9% 2 6% 5% 4 4 4 5% 6% 38%	2289
	21st to end	Night	24% 10% 3 7% 4 4 4 3 6% 7% 29%	2717
November	1st to 10th	Night	15% 11% 3 7% 4 4 4 3 5% 4 40%	2537
	11th to 20th	Night	16% 12% 3 7% 5% 5% 5% 4 4 5% 34%	2600
	21st to end	Night	16% 14% 4 8% 5% 4 5% 4 4 5% 32%	2735
December	1st to 10th	Night	15% 17% 7% 14% 5% 5% 4 3 5% 5% 20%	4580
	11th to 20th	Night	21% 15% 5% 8% 5% 4 4 3 4 4 27%	5208
	21st to end	Night	19% 16% 6% 9% 5% 4 5% 3 4 4 25%	6996

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% 6% 9% 15% 4	3598
	11th to 20th	Day	62% 7% 9% 11% 10% 2	3600
	21st to end	Day	61% 4 8% 17% 10% 1	4051
February	1st to 10th	Day	61% 7% 12% 14% 6%	1800
	11th to 20th	Day	61% 6% 9% 15% 8% 1	1947
	21st to end	Day	60% 6% 10% 14% 9%	1650
March	1st to 10th	Day	62% 4 10% 12% 9% 3	4479
	11th to 20th	Day	51% 7% 15% 16% 7% 3	4692
	21st to end	Day	56% 5% 6% 12% 18% 2	5970
April	1st to 10th	Day	56% 5% 7% 20% 10% 2	2400
	11th to 20th	Day	50% 6% 11% 18% 14% 1	2374
	21st to end	Day	53% 6% 9% 18% 12% 3	2510
May	1st to 10th	Day	63% 6% 9% 14% 7% 1	5961
	11th to 20th	Day	54% 7% 14% 18% 7% 1	6322
	21st to end	Day	51% 7% 12% 21% 9% 1	6949
June	1st to 10th	Day	49% 8% 14% 19% 10%	2800
	11th to 20th	Day	48% 8% 13% 19% 11% 1	2800
	21st to end	Day	48% 9% 14% 19% 10%	2800
July	1st to 10th	Day	46% 6% 13% 23% 11%	6290
	11th to 20th	Day	42% 6% 16% 23% 12% 1	6285
	21st to end	Day	43% 5% 13% 28% 11%	6728
August	1st to 10th	Day	49% 7% 14% 21% 9%	4518
	11th to 20th	Day	46% 6% 16% 26% 6% 1	3920
	21st to end	Day	40% 6% 14% 30% 9% 1	4312
September	1st to 10th	Day	38% 7% 13% 27% 14% 1	2400
	11th to 20th	Day	36% 6% 11% 25% 21% 1	2294
	21st to end	Day	42% 7% 12% 25% 13% 2	2200
October	1st to 10th	Day	51% 4 8% 21% 14% 1	3363
	11th to 20th	Day	43% 5% 13% 23% 14% 3	3119
	21st to end	Day	42% 5% 13% 27% 11% 2	3081
November	1st to 10th	Day	43% 6% 15% 22% 12% 1	1761
	11th to 20th	Day	51% 6% 11% 17% 14% 2	1800
	21st to end	Day	54% 7% 16% 16% 6% 1	1662
December	1st to 10th	Day	64% 5% 12% 15% 4	2600
	11th to 20th	Day	58% 4 12% 16% 9%	2986
	21st to end	Day	60% 5% 8% 14% 10% 3	3960
January	1st to 10th	Night	66% 6% 10% 12% 6% 1	6349
	11th to 20th	Night	66% 6% 11% 10% 6% 1	6360
	21st to end	Night	60% 5% 10% 12% 12% 2	6904
February	1st to 10th	Night	61% 6% 12% 14% 6% 1	2600
	11th to 20th	Night	59% 8% 12% 13% 8% 1	2348
	21st to end	Night	59% 6% 12% 15% 7% 2	1980
March	1st to 10th	Night	58% 6% 10% 13% 12% 1	5374
	11th to 20th	Night	52% 6% 16% 16% 7% 2	5251
	21st to end	Night	61% 4 4 13% 15% 2	4962
April	1st to 10th	Night	56% 6% 11% 18% 9% 1	2000
	11th to 20th	Night	51% 6% 10% 18% 13% 1	1975
	21st to end	Night	49% 7% 11% 16% 14% 3	1890
May	1st to 10th	Night	63% 6% 10% 12% 8% 1	4025
	11th to 20th	Night	54% 8% 12% 17% 7% 1	3576
	21st to end	Night	54% 8% 10% 16% 11% 1	3927
June	1st to 10th	Night	47% 7% 12% 22% 11% 1	1600
	11th to 20th	Night	43% 8% 15% 23% 11%	1600
	21st to end	Night	41% 8% 15% 24% 12%	1600
July	1st to 10th	Night	43% 5% 16% 21% 14% 1	3560
	11th to 20th	Night	48% 6% 13% 20% 13% 1	3552
	21st to end	Night	39% 4 14% 31% 11% 1	3809
August	1st to 10th	Night	51% 6% 15% 21% 8%	2576
	11th to 20th	Night	46% 6% 18% 22% 8%	3189
	21st to end	Night	38% 5% 15% 31% 10% 1	3586
September	1st to 10th	Night	41% 5% 12% 26% 14% 1	2000
	11th to 20th	Night	34% 4 12% 29% 20% 1	2105
	21st to end	Night	42% 7% 10% 25% 15% 1	2200
October	1st to 10th	Night	52% 5% 10% 20% 11% 1	3660
	11th to 20th	Night	41% 5% 13% 21% 18% 2	3800
	21st to end	Night	44% 5% 13% 29% 9%	4467
November	1st to 10th	Night	45% 7% 12% 20% 14% 2	2537
	11th to 20th	Night	50% 7% 13% 16% 13% 2	2600
	21st to end	Night	54% 7% 15% 17% 6%	2735
December	1st to 10th	Night	67% 5% 10% 14% 3	4580
	11th to 20th	Night	59% 6% 12% 11% 12%	5208
	21st to end	Night	62% 6% 7% 11% 9% 4	6996

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	29% 32% 26% 11% 3	200
	11th to 20th	Day	33% 28% 28% 9% 2 1	200
	21st to end	Day	25% 30% 30% 10% 5%	240
February	1st to 10th	Day	34% 36% 25% 3 2	300
	11th to 20th	Day	32% 33% 23% 10% 1	486
	21st to end	Day	29% 29% 28% 12% 2	414
March	1st to 10th	Day	32% 24% 27% 15% 2	500
	11th to 20th	Day	30% 28% 27% 12% 3 1	500
	21st to end	Day	34% 27% 22% 11% 5% 1	550
April	1st to 10th	Day	37% 24% 22% 12% 5% 1	500
	11th to 20th	Day	32% 27% 24% 11% 5% 2	492
	21st to end	Day	30% 21% 30% 13% 4 2	500
May	1st to 10th	Day	33% 22% 25% 11% 7% 2	503
	11th to 20th	Day	23% 18% 33% 19% 5% 2	527
	21st to end	Day	20% 15% 30% 23% 8% 3	573
June	1st to 10th	Day	19% 15% 31% 25% 10% 1	530
	11th to 20th	Day	21% 14% 30% 24% 10% 1	530
	21st to end	Day	21% 16% 32% 21% 10% 1	530
July	1st to 10th	Day	14% 11% 33% 26% 13% 3	525
	11th to 20th	Day	12% 8% 33% 32% 12% 2	524
	21st to end	Day	15% 12% 36% 23% 12% 1	576
August	1st to 10th	Day	14% 10% 26% 32% 13% 5%	526
	11th to 20th	Day	17% 8% 29% 24% 15% 7%	519
	21st to end	Day	14% 14% 27% 26% 13% 6%	583
September	1st to 10th	Day	18% 11% 23% 26% 15% 7%	530
	11th to 20th	Day	15% 12% 23% 22% 16% 11%	530
	21st to end	Day	19% 13% 28% 22% 12% 6%	530
October	1st to 10th	Day	25% 14% 23% 21% 13% 4	502
	11th to 20th	Day	23% 18% 27% 20% 10% 2	485
	21st to end	Day	32% 16% 26% 19% 5% 1	429
November	1st to 10th	Day	24% 22% 24% 19% 10% 1	395
	11th to 20th	Day	26% 28% 26% 14% 6% 1	400
	21st to end	Day	31% 27% 24% 16% 2	262
December	1st to 10th	Day	30% 28% 29% 11% 3 1	200
	11th to 20th	Day	37% 25% 26% 11% 2	200
	21st to end	Day	30% 25% 30% 11% 3	220
January	1st to 10th	Night	24% 29% 31% 14% 2	800
	11th to 20th	Night	27% 25% 29% 17% 2	800
	21st to end	Night	21% 25% 33% 19% 2	880
February	1st to 10th	Night	25% 25% 33% 16% 1	800
	11th to 20th	Night	25% 27% 32% 15% 2	783
	21st to end	Night	29% 24% 27% 17% 2	660
March	1st to 10th	Night	28% 23% 30% 17% 2	800
	11th to 20th	Night	25% 28% 28% 16% 2	800
	21st to end	Night	29% 22% 26% 17% 6%	880
April	1st to 10th	Night	30% 21% 27% 20% 2	800
	11th to 20th	Night	27% 22% 26% 19% 6%	791
	21st to end	Night	26% 19% 29% 20% 5%	690
May	1st to 10th	Night	27% 17% 27% 22% 7%	591
	11th to 20th	Night	20% 13% 30% 32% 4 1	394
	21st to end	Night	17% 9% 28% 34% 11% 1	433
June	1st to 10th	Night	22% 8% 29% 30% 12%	400
	11th to 20th	Night	18% 9% 27% 37% 11%	400
	21st to end	Night	14% 8% 25% 42% 11% 1	400
July	1st to 10th	Night	14% 6% 23% 44% 13% 1	390
	11th to 20th	Night	15% 6% 22% 41% 16% 1	388
	21st to end	Night	14% 5% 23% 44% 13% 1	438
August	1st to 10th	Night	14% 2 20% 45% 18% 1	398
	11th to 20th	Night	16% 5% 22% 35% 19% 4	765
	21st to end	Night	15% 7% 23% 35% 19% 2	880
September	1st to 10th	Night	18% 8% 26% 31% 15% 2	800
	11th to 20th	Night	18% 8% 20% 30% 20% 5%	800
	21st to end	Night	19% 9% 26% 30% 14% 2	800
October	1st to 10th	Night	25% 10% 22% 29% 13% 1	773
	11th to 20th	Night	21% 14% 29% 28% 9%	760
	21st to end	Night	30% 17% 28% 22% 4	836
November	1st to 10th	Night	21% 20% 28% 23% 7%	780
	11th to 20th	Night	24% 21% 29% 19% 7% 1	800
	21st to end	Night	25% 23% 27% 20% 5% 1	800
December	1st to 10th	Night	28% 26% 27% 15% 4	800
	11th to 20th	Night	29% 23% 27% 18% 3	800
	21st to end	Night	28% 26% 28% 16% 2	880

Page generated at 2025-10-01 01:39:07. Version ac07

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