Hamilton Branch State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hamilton Branch State Park clear sky chart from 2005-11-06 to 2025-12-18.

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	12% 6% 2 6% 4 4 4 4 6% 8% 43%	127085
	Night	13% 6% 2 6% 4 4 4 4 6% 8% 44%	123959
Transparency	Day	23% 40% 8% 13% 12% 4	130796
	Night	23% 39% 7% 12% 14% 5%	128317
Seeing	Day	16% 9% 24% 25% 19% 7%	16671
	Night	15% 9% 23% 31% 19% 3	26727

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	15% 5% 2 4 3 3 3 3 5% 6% 51%	4056
	11th to 20th	Day	13% 5% 2 5% 3 3 2 2 3 5% 58%	4060
	21st to end	Day	17% 7% 2 6% 4 3 3 3 4 5% 45%	4466
February	1st to 10th	Day	15% 6% 2 6% 4 4 5% 4 6% 7% 40%	1920
	11th to 20th	Day	21% 8% 2 5% 3 3 3 3 4 6% 43%	1948
	21st to end	Day	17% 5% 2 7% 3 4 4 3 4 6% 44%	1650
March	1st to 10th	Day	20% 8% 3 8% 4 3 4 3 4 5% 40%	4925
	11th to 20th	Day	9% 4 2 4 3 3 4 3 5% 7% 55%	4980
	21st to end	Day	16% 6% 3 6% 5% 4 4 3 4 4 46%	5465
April	1st to 10th	Day	10% 5% 2 4 4 4 5% 4 5% 7% 50%	2200
	11th to 20th	Day	10% 5% 2 6% 4 4 4 3 6% 6% 49%	2299
	21st to end	Day	8% 5% 2 5% 4 4 5% 4 5% 8% 50%	2600
May	1st to 10th	Day	11% 6% 2 7% 4 4 5% 4 6% 10% 40%	5862
	11th to 20th	Day	17% 7% 3 7% 4 5% 5% 5% 7% 7% 32%	5861
	21st to end	Day	11% 6% 2 5% 4 5% 5% 4 6% 9% 43%	6433
June	1st to 10th	Day	9% 7% 2 6% 6% 5% 5% 5% 8% 11% 36%	2600
	11th to 20th	Day	6% 5% 1 6% 4 5% 6% 6% 8% 10% 44%	2600
	21st to end	Day	5% 4 2 5% 6% 6% 6% 6% 8% 12% 41%	2600
July	1st to 10th	Day	10% 6% 3 7% 6% 6% 7% 5% 9% 10% 31%	5900
	11th to 20th	Day	5% 4 2 5% 5% 5% 7% 6% 9% 16% 37%	5900
	21st to end	Day	8% 7% 3 7% 6% 6% 6% 6% 9% 13% 29%	6424
August	1st to 10th	Day	17% 7% 3 7% 6% 5% 6% 6% 7% 11% 26%	4234
	11th to 20th	Day	10% 5% 2 5% 4 5% 6% 5% 9% 12% 37%	4174
	21st to end	Day	6% 5% 2 5% 4 5% 4 4 6% 10% 49%	4201
September	1st to 10th	Day	8% 4 2 6% 5% 5% 6% 5% 7% 9% 43%	2200
	11th to 20th	Day	13% 6% 3 6% 5% 5% 4 3 6% 8% 42%	2200
	21st to end	Day	15% 7% 2 6% 4 4 4 3 6% 8% 42%	2200
October	1st to 10th	Day	12% 7% 2 6% 3 3 3 2 5% 6% 51%	2163
	11th to 20th	Day	12% 4 2 4 2 2 2 3 4 6% 60%	2000
	21st to end	Day	12% 5% 2 5% 3 4 3 2 3 4 57%	2200
November	1st to 10th	Day	14% 5% 2 6% 3 3 3 3 4 6% 52%	2057
	11th to 20th	Day	14% 5% 2 4 3 3 3 2 4 6% 55%	1895
	21st to end	Day	14% 4 2 5% 4 4 3 4 5% 7% 49%	1890
December	1st to 10th	Day	13% 6% 2 6% 4 4 3 3 5% 6% 47%	3020
	11th to 20th	Day	15% 6% 2 5% 4 4 4 3 5% 6% 46%	3436
	21st to end	Day	22% 6% 2 4 3 2 3 3 5% 6% 44%	4466
January	1st to 10th	Night	13% 4 2 5% 4 3 3 2 4 5% 56%	5889
	11th to 20th	Night	12% 6% 2 5% 3 3 4 3 6% 7% 49%	5900
	21st to end	Night	16% 8% 2 6% 4 3 4 3 4 4 46%	6490
February	1st to 10th	Night	16% 6% 2 5% 4 3 4 4 5% 6% 46%	2475
	11th to 20th	Night	20% 7% 2 6% 4 3 3 3 4 5% 44%	2338
	21st to end	Night	14% 6% 2 6% 3 4 4 4 5% 6% 46%	1980
March	1st to 10th	Night	19% 8% 3 6% 4 3 4 3 5% 6% 38%	4928
	11th to 20th	Night	9% 4 2 4 3 3 4 3 6% 7% 56%	4980
	21st to end	Night	15% 5% 2 5% 4 3 3 3 5% 6% 48%	5467
April	1st to 10th	Night	12% 5% 2 4 4 3 4 4 6% 7% 49%	2200
	11th to 20th	Night	11% 5% 2 4 4 3 3 3 4 7% 53%	2065
	21st to end	Night	8% 4 1 5% 4 4 4 4 6% 7% 52%	1800
May	1st to 10th	Night	11% 7% 3 8% 4 5% 5% 4 6% 10% 38%	4033
	11th to 20th	Night	19% 6% 2 5% 4 4 5% 5% 6% 10% 34%	4032
	21st to end	Night	11% 5% 2 5% 4 4 4 4 6% 10% 44%	4421
June	1st to 10th	Night	10% 7% 2 7% 4 6% 6% 5% 7% 12% 33%	1800
	11th to 20th	Night	7% 5% 2 6% 5% 6% 5% 4 7% 12% 40%	1800
	21st to end	Night	6% 5% 2 6% 5% 5% 7% 6% 10% 12% 35%	1800
July	1st to 10th	Night	13% 7% 3 10% 6% 6% 6% 5% 7% 10% 26%	4058
	11th to 20th	Night	6% 5% 2 7% 6% 5% 6% 7% 11% 16% 30%	4057
	21st to end	Night	11% 7% 3 9% 7% 6% 7% 6% 8% 12% 24%	4427
August	1st to 10th	Night	16% 7% 3 9% 6% 7% 7% 6% 8% 10% 22%	2915
	11th to 20th	Night	10% 5% 2 7% 5% 5% 5% 6% 8% 10% 36%	2875
	21st to end	Night	7% 4 2 5% 4 4 5% 5% 7% 10% 47%	3657
September	1st to 10th	Night	10% 5% 3 6% 5% 4 6% 4 8% 9% 41%	2200
	11th to 20th	Night	11% 7% 3 8% 5% 5% 5% 3 6% 7% 40%	2200
	21st to end	Night	15% 5% 2 6% 4 4 4 4 5% 7% 46%	2200
October	1st to 10th	Night	11% 6% 2 6% 3 3 4 3 5% 7% 51%	2235
	11th to 20th	Night	11% 4 2 5% 3 3 3 2 4 5% 59%	2400
	21st to end	Night	11% 4 1 4 4 4 3 2 3 5% 57%	2640
November	1st to 10th	Night	12% 5% 2 5% 4 3 3 3 5% 6% 54%	2461
	11th to 20th	Night	13% 6% 2 4 3 3 3 3 4 5% 53%	2722
	21st to end	Night	13% 4 2 4 4 4 4 4 5% 7% 50%	2730
December	1st to 10th	Night	15% 5% 2 5% 3 3 3 2 4 5% 53%	4380
	11th to 20th	Night	17% 6% 2 5% 3 3 3 3 5% 6% 46%	4914
	21st to end	Night	21% 6% 2 6% 4 3 3 3 5% 5% 42%	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	24% 27% 4 15% 24% 6%	4057
	11th to 20th	Day	20% 26% 2 14% 28% 8%	4060
	21st to end	Day	31% 28% 3 13% 16% 9%	4466
February	1st to 10th	Day	15% 63% 4 10% 6% 3	1920
	11th to 20th	Day	19% 61% 2 7% 8% 2	1958
	21st to end	Day	18% 62% 3 5% 8% 5%	1650
March	1st to 10th	Day	39% 30% 4 7% 14% 7%	4925
	11th to 20th	Day	17% 30% 4 12% 19% 18%	4980
	21st to end	Day	31% 29% 3 12% 18% 6%	5465
April	1st to 10th	Day	13% 63% 5% 7% 9% 3	2200
	11th to 20th	Day	15% 63% 4 8% 6% 3	2299
	21st to end	Day	14% 63% 5% 10% 8% 1	2600
May	1st to 10th	Day	29% 32% 12% 19% 7% 1	5897
	11th to 20th	Day	37% 31% 11% 13% 7%	5865
	21st to end	Day	27% 31% 10% 14% 17% 2	6447
June	1st to 10th	Day	16% 64% 7% 8% 4 2	2600
	11th to 20th	Day	10% 65% 9% 9% 7%	2600
	21st to end	Day	13% 64% 9% 10% 5% 1	2600
July	1st to 10th	Day	33% 32% 14% 18% 3	5835
	11th to 20th	Day	22% 35% 27% 15% 1	5831
	21st to end	Day	34% 33% 15% 14% 4	6240
August	1st to 10th	Day	37% 40% 12% 11% 1	4221
	11th to 20th	Day	19% 42% 11% 15% 11% 1	4213
	21st to end	Day	10% 39% 10% 23% 14% 3	4201
September	1st to 10th	Day	13% 60% 8% 9% 8% 2	2200
	11th to 20th	Day	18% 59% 5% 8% 8% 1	2200
	21st to end	Day	18% 59% 7% 9% 6% 1	2200
October	1st to 10th	Day	19% 37% 4 10% 22% 8%	3527
	11th to 20th	Day	7% 36% 2 10% 19% 27%	3240
	21st to end	Day	13% 36% 3 16% 23% 10%	3538
November	1st to 10th	Day	19% 54% 4 7% 11% 5%	2057
	11th to 20th	Day	16% 54% 4 10% 12% 4	1895
	21st to end	Day	15% 55% 4 10% 13% 3	1890
December	1st to 10th	Day	24% 35% 4 10% 21% 6%	3020
	11th to 20th	Day	25% 32% 7% 15% 15% 5%	3433
	21st to end	Day	31% 27% 6% 17% 18% 1	4466
January	1st to 10th	Night	22% 27% 3 14% 27% 6%	5889
	11th to 20th	Night	24% 27% 3 14% 26% 6%	5900
	21st to end	Night	30% 28% 3 10% 23% 6%	6490
February	1st to 10th	Night	13% 61% 4 10% 8% 3	2475
	11th to 20th	Night	20% 61% 3 7% 8% 2	2339
	21st to end	Night	16% 62% 3 5% 7% 6%	1980
March	1st to 10th	Night	37% 31% 6% 8% 16% 4	4928
	11th to 20th	Night	18% 29% 4 8% 23% 19%	4980
	21st to end	Night	27% 29% 4 13% 15% 11%	5467
April	1st to 10th	Night	15% 63% 4 7% 7% 4	2200
	11th to 20th	Night	15% 62% 4 8% 7% 4	2065
	21st to end	Night	12% 63% 5% 12% 7% 2	1800
May	1st to 10th	Night	29% 33% 12% 17% 7% 1	4060
	11th to 20th	Night	34% 31% 15% 12% 7%	4033
	21st to end	Night	24% 32% 10% 16% 17% 2	4429
June	1st to 10th	Night	17% 65% 7% 7% 3 1	1800
	11th to 20th	Night	12% 65% 9% 8% 6% 1	1800
	21st to end	Night	12% 65% 9% 9% 4	1800
July	1st to 10th	Night	38% 32% 16% 12% 2	4015
	11th to 20th	Night	26% 38% 24% 11% 1	4006
	21st to end	Night	41% 33% 13% 10% 3 1	4297
August	1st to 10th	Night	40% 41% 11% 7% 1	2904
	11th to 20th	Night	21% 43% 15% 14% 6% 1	2902
	21st to end	Night	12% 39% 11% 22% 14% 2	3657
September	1st to 10th	Night	14% 61% 7% 9% 7% 2	2200
	11th to 20th	Night	20% 59% 5% 8% 8% 1	2200
	21st to end	Night	17% 59% 7% 11% 6% 1	2200
October	1st to 10th	Night	19% 38% 6% 12% 21% 4	3651
	11th to 20th	Night	7% 35% 3 9% 18% 28%	3899
	21st to end	Night	12% 36% 3 14% 22% 14%	4252
November	1st to 10th	Night	19% 54% 3 7% 12% 4	2461
	11th to 20th	Night	16% 54% 3 8% 13% 6%	2722
	21st to end	Night	15% 55% 4 10% 12% 4	2730
December	1st to 10th	Night	23% 35% 3 9% 25% 5%	4380
	11th to 20th	Night	26% 32% 8% 13% 15% 6%	4916
	21st to end	Night	34% 27% 3 19% 16% 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	21% 20% 42% 15% 2	300
	11th to 20th	Day	24% 21% 33% 18% 3 1	300
	21st to end	Day	23% 25% 37% 11% 4 1	330
February	1st to 10th	Day	21% 17% 39% 19% 4	300
	11th to 20th	Day	37% 17% 30% 15% 1	300
	21st to end	Day	24% 18% 40% 14% 4	249
March	1st to 10th	Day	23% 17% 29% 21% 8% 1	490
	11th to 20th	Day	19% 15% 40% 20% 6%	500
	21st to end	Day	21% 16% 36% 18% 8%	550
April	1st to 10th	Day	19% 14% 31% 25% 10%	500
	11th to 20th	Day	14% 13% 33% 25% 14% 2	492
	21st to end	Day	12% 11% 29% 27% 17% 4	500
May	1st to 10th	Day	12% 12% 32% 26% 14% 4	503
	11th to 20th	Day	17% 6% 25% 29% 15% 9%	527
	21st to end	Day	17% 6% 19% 25% 22% 11%	573
June	1st to 10th	Day	11% 4 18% 30% 28% 9%	530
	11th to 20th	Day	6% 5% 18% 28% 28% 15%	530
	21st to end	Day	7% 3 14% 33% 31% 13%	530
July	1st to 10th	Day	7% 3 11% 25% 32% 22%	525
	11th to 20th	Day	7% 2 9% 27% 38% 18%	524
	21st to end	Day	5% 3 8% 31% 39% 14%	576
August	1st to 10th	Day	14% 5% 14% 27% 27% 14%	526
	11th to 20th	Day	11% 2 12% 25% 32% 17%	519
	21st to end	Day	12% 2 14% 27% 29% 16%	583
September	1st to 10th	Day	9% 2 14% 32% 31% 12%	530
	11th to 20th	Day	18% 3 12% 27% 28% 12%	530
	21st to end	Day	17% 6% 19% 26% 24% 9%	530
October	1st to 10th	Day	15% 6% 24% 30% 17% 8%	530
	11th to 20th	Day	12% 8% 22% 29% 22% 7%	530
	21st to end	Day	16% 8% 26% 26% 20% 4	583
November	1st to 10th	Day	21% 8% 25% 25% 16% 4	535
	11th to 20th	Day	19% 12% 41% 19% 7% 1	335
	21st to end	Day	13% 15% 35% 25% 11% 1	330
December	1st to 10th	Day	27% 16% 35% 18% 5% 1	330
	11th to 20th	Day	22% 16% 34% 20% 7% 1	321
	21st to end	Day	30% 15% 32% 16% 5% 3	330
January	1st to 10th	Night	22% 17% 31% 26% 5%	800
	11th to 20th	Night	19% 18% 30% 26% 7%	800
	21st to end	Night	21% 19% 35% 23% 3	880
February	1st to 10th	Night	18% 15% 31% 30% 6%	800
	11th to 20th	Night	24% 15% 34% 24% 3	783
	21st to end	Night	19% 18% 31% 28% 3	660
March	1st to 10th	Night	17% 15% 33% 30% 5%	800
	11th to 20th	Night	17% 13% 36% 27% 7% 1	800
	21st to end	Night	17% 15% 33% 27% 8%	880
April	1st to 10th	Night	15% 15% 33% 27% 10%	800
	11th to 20th	Night	14% 14% 27% 31% 13%	776
	21st to end	Night	9% 8% 28% 39% 16%	600
May	1st to 10th	Night	11% 9% 26% 38% 16% 1	600
	11th to 20th	Night	11% 5% 27% 35% 20% 2	591
	21st to end	Night	11% 3 14% 39% 28% 4	650
June	1st to 10th	Night	12% 4 17% 37% 27% 4	600
	11th to 20th	Night	7% 3 14% 35% 32% 9%	600
	21st to end	Night	8% 3 13% 35% 35% 7%	600
July	1st to 10th	Night	11% 3 9% 32% 36% 9%	585
	11th to 20th	Night	8% 2 6% 32% 45% 7%	582
	21st to end	Night	9% 2 10% 31% 41% 7%	657
August	1st to 10th	Night	13% 3 7% 34% 35% 8%	597
	11th to 20th	Night	11% 3 9% 32% 38% 6%	594
	21st to end	Night	11% 2 13% 33% 35% 6%	763
September	1st to 10th	Night	10% 4 11% 35% 35% 6%	800
	11th to 20th	Night	13% 4 14% 28% 38% 4	800
	21st to end	Night	16% 4 17% 31% 28% 4	800
October	1st to 10th	Night	13% 5% 20% 34% 24% 5%	800
	11th to 20th	Night	13% 7% 21% 34% 23% 3	800
	21st to end	Night	13% 9% 22% 32% 22% 2	880
November	1st to 10th	Night	13% 8% 26% 31% 19% 3	820
	11th to 20th	Night	16% 10% 30% 30% 12% 1	840
	21st to end	Night	16% 12% 28% 27% 16% 1	840
December	1st to 10th	Night	21% 14% 25% 31% 8% 1	840
	11th to 20th	Night	19% 11% 27% 30% 13% 1	829
	21st to end	Night	26% 13% 25% 28% 8%	880

Page generated at 2025-12-15 01:13:52. Version ac07

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