Randolph State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Randolph 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	10% 6% 3 6% 4 4 4 3 5% 7% 48%	126909
	Night	9% 6% 2 6% 4 4 4 3 5% 7% 51%	124357
Transparency	Day	35% 5% 11% 26% 20% 3	130573
	Night	32% 4 11% 26% 21% 4	128756
Seeing	Day	13% 10% 31% 29% 14% 3	17197
	Night	12% 9% 34% 33% 10% 1	27098

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	12% 9% 3 10% 4 5% 5% 4 6% 7% 35%	4077
	11th to 20th	Day	7% 10% 4 10% 5% 6% 5% 3 4 6% 42%	4080
	21st to end	Day	8% 11% 5% 9% 4 4 4 2 3 5% 45%	4488
February	1st to 10th	Day	10% 12% 3 8% 5% 4 4 3 5% 7% 39%	1800
	11th to 20th	Day	8% 9% 3 7% 4 4 5% 3 6% 8% 43%	1866
	21st to end	Day	7% 7% 3 7% 4 3 5% 3 5% 6% 50%	1650
March	1st to 10th	Day	10% 8% 2 5% 4 3 3 2 4 6% 55%	4847
	11th to 20th	Day	10% 7% 2 4 3 3 4 3 4 6% 55%	4980
	21st to end	Day	11% 8% 4 7% 5% 4 4 4 5% 6% 41%	5462
April	1st to 10th	Day	13% 6% 2 7% 4 3 3 3 5% 7% 47%	2210
	11th to 20th	Day	11% 7% 3 6% 4 5% 4 4 5% 6% 44%	2492
	21st to end	Day	19% 7% 2 7% 4 4 4 3 5% 7% 40%	2600
May	1st to 10th	Day	13% 8% 3 5% 4 3 3 3 5% 6% 47%	5862
	11th to 20th	Day	11% 6% 2 5% 4 3 4 3 5% 6% 52%	5862
	21st to end	Day	17% 7% 2 6% 4 5% 5% 4 6% 6% 39%	6434
June	1st to 10th	Day	7% 3 2 5% 3 4 4 4 5% 9% 55%	2600
	11th to 20th	Day	7% 4 2 5% 4 4 5% 5% 6% 8% 51%	2600
	21st to end	Day	6% 3 2 4 4 4 5% 4 7% 8% 54%	2600
July	1st to 10th	Day	8% 5% 2 5% 4 4 4 4 6% 8% 49%	5900
	11th to 20th	Day	7% 5% 3 6% 4 5% 5% 4 7% 9% 46%	5900
	21st to end	Day	6% 5% 2 6% 4 4 5% 4 6% 8% 50%	6422
August	1st to 10th	Day	7% 4 2 5% 4 4 4 3 6% 8% 52%	4234
	11th to 20th	Day	12% 5% 2 5% 5% 4 3 3 5% 6% 49%	4171
	21st to end	Day	5% 4 1 4 4 4 4 3 6% 9% 57%	4591
September	1st to 10th	Day	11% 4 2 4 3 2 4 3 5% 7% 55%	2245
	11th to 20th	Day	10% 4 2 5% 4 4 3 3 5% 7% 53%	2200
	21st to end	Day	10% 4 2 5% 3 3 4 4 4 5% 57%	2200
October	1st to 10th	Day	12% 4 2 5% 4 3 2 3 4 5% 55%	2085
	11th to 20th	Day	10% 4 2 4 3 3 3 2 4 5% 60%	2000
	21st to end	Day	13% 6% 2 5% 3 4 3 2 4 5% 53%	2200
November	1st to 10th	Day	8% 4 1 5% 3 4 3 4 5% 6% 58%	1893
	11th to 20th	Day	9% 7% 2 5% 3 3 3 3 4 5% 56%	1890
	21st to end	Day	13% 7% 3 4 3 2 3 3 5% 6% 51%	1890
December	1st to 10th	Day	5% 5% 2 5% 4 4 4 3 5% 7% 57%	2709
	11th to 20th	Day	7% 8% 3 7% 5% 3 3 3 4 6% 53%	3381
	21st to end	Day	16% 12% 5% 14% 4 4 4 3 4 5% 30%	4488
January	1st to 10th	Night	10% 9% 4 13% 5% 5% 4 3 5% 6% 36%	5888
	11th to 20th	Night	5% 7% 3 7% 4 5% 5% 4 5% 7% 48%	5900
	21st to end	Night	11% 10% 4 8% 3 3 3 2 4 5% 46%	6490
February	1st to 10th	Night	10% 10% 3 7% 5% 5% 4 4 5% 6% 42%	2600
	11th to 20th	Night	9% 8% 3 6% 5% 5% 5% 3 5% 7% 44%	2440
	21st to end	Night	8% 6% 2 7% 4 4 4 3 4 6% 53%	1980
March	1st to 10th	Night	10% 6% 2 4 2 3 3 2 4 6% 58%	5010
	11th to 20th	Night	7% 4 2 4 3 3 3 3 6% 8% 57%	4980
	21st to end	Night	12% 8% 3 6% 4 4 4 3 5% 7% 43%	5467
April	1st to 10th	Night	11% 6% 2 5% 4 3 3 3 5% 6% 52%	2190
	11th to 20th	Night	12% 7% 2 5% 4 4 3 2 5% 7% 47%	1853
	21st to end	Night	14% 7% 2 5% 4 4 4 3 6% 7% 44%	1800
May	1st to 10th	Night	15% 6% 2 6% 3 3 3 3 4 6% 49%	4053
	11th to 20th	Night	13% 5% 2 4 3 2 2 3 4 7% 55%	4053
	21st to end	Night	16% 5% 2 5% 3 3 3 3 5% 7% 48%	4443
June	1st to 10th	Night	5% 4 1 3 3 4 3 4 6% 10% 56%	1800
	11th to 20th	Night	6% 3 1 4 3 3 4 4 6% 10% 54%	1800
	21st to end	Night	6% 2 1 4 3 3 3 4 7% 10% 58%	1800
July	1st to 10th	Night	6% 4 2 6% 4 4 4 4 5% 8% 52%	4078
	11th to 20th	Night	4 4 2 5% 4 4 4 4 6% 10% 52%	4077
	21st to end	Night	7% 4 2 4 4 4 4 3 6% 9% 53%	4449
August	1st to 10th	Night	3 3 1 5% 3 3 4 4 6% 11% 57%	2926
	11th to 20th	Night	9% 5% 2 6% 5% 4 4 3 5% 7% 51%	2888
	21st to end	Night	6% 4 1 4 3 3 3 3 5% 8% 61%	3313
September	1st to 10th	Night	9% 3 2 4 2 3 3 3 5% 7% 60%	2150
	11th to 20th	Night	9% 3 2 5% 3 3 4 3 5% 6% 58%	2200
	21st to end	Night	8% 4 2 5% 4 3 3 3 4 6% 60%	2200
October	1st to 10th	Night	12% 5% 2 4 3 3 3 3 5% 6% 53%	2293
	11th to 20th	Night	11% 5% 1 4 3 3 3 2 4 5% 59%	2400
	21st to end	Night	11% 7% 2 5% 3 2 3 3 4 5% 55%	2640
November	1st to 10th	Night	7% 5% 1 5% 3 3 3 3 4 7% 59%	2621
	11th to 20th	Night	8% 5% 2 4 3 2 4 3 5% 6% 58%	2730
	21st to end	Night	12% 7% 2 4 4 3 3 3 4 6% 53%	2730
December	1st to 10th	Night	5% 5% 1 4 3 3 4 3 4 6% 62%	4673
	11th to 20th	Night	8% 6% 2 6% 3 3 4 3 5% 7% 51%	4952
	21st to end	Night	15% 13% 5% 10% 4 4 3 3 4 5% 36%	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	47% 7% 11% 22% 12% 1	4078
	11th to 20th	Day	45% 3 13% 20% 17% 3	4080
	21st to end	Day	44% 4 10% 24% 18% 2	4488
February	1st to 10th	Day	45% 5% 14% 22% 10% 4	1800
	11th to 20th	Day	40% 4 13% 26% 14% 4	1875
	21st to end	Day	34% 5% 10% 25% 21% 5%	1650
March	1st to 10th	Day	34% 3 8% 20% 26% 10%	4847
	11th to 20th	Day	31% 3 8% 22% 28% 7%	4980
	21st to end	Day	42% 6% 15% 28% 8% 1	5464
April	1st to 10th	Day	37% 4 12% 24% 19% 3	2210
	11th to 20th	Day	40% 6% 12% 24% 17% 2	2492
	21st to end	Day	45% 5% 11% 26% 13% 1	2600
May	1st to 10th	Day	38% 5% 10% 26% 19% 3	5900
	11th to 20th	Day	34% 4 10% 22% 24% 6%	5866
	21st to end	Day	43% 6% 11% 26% 14% 1	6447
June	1st to 10th	Day	27% 7% 15% 34% 16% 2	2600
	11th to 20th	Day	29% 6% 14% 28% 20% 3	2600
	21st to end	Day	26% 6% 15% 29% 19% 4	2600
July	1st to 10th	Day	32% 5% 11% 27% 22% 3	5836
	11th to 20th	Day	33% 7% 13% 26% 18% 3	5831
	21st to end	Day	29% 6% 13% 30% 20% 2	6240
August	1st to 10th	Day	30% 5% 14% 26% 20% 4	4220
	11th to 20th	Day	35% 5% 15% 25% 18% 2	4210
	21st to end	Day	25% 5% 15% 30% 18% 8%	4590
September	1st to 10th	Day	29% 5% 12% 27% 21% 7%	2245
	11th to 20th	Day	31% 4 11% 27% 24% 3	2200
	21st to end	Day	29% 4 9% 29% 26% 3	2200
October	1st to 10th	Day	22% 2 7% 19% 44% 6%	3397
	11th to 20th	Day	19% 2 8% 30% 32% 9%	3240
	21st to end	Day	30% 3 9% 25% 29% 4	3538
November	1st to 10th	Day	26% 5% 12% 30% 23% 5%	1893
	11th to 20th	Day	31% 3 9% 27% 26% 3	1890
	21st to end	Day	36% 3 12% 28% 20% 2	1890
December	1st to 10th	Day	29% 3 12% 37% 18% 1	2709
	11th to 20th	Day	34% 3 13% 36% 13% 1	3379
	21st to end	Day	57% 4 8% 22% 8% 1	4488
January	1st to 10th	Night	49% 5% 10% 24% 12% 1	5888
	11th to 20th	Night	36% 4 12% 24% 21% 3	5900
	21st to end	Night	43% 3 11% 19% 18% 7%	6490
February	1st to 10th	Night	43% 5% 12% 22% 16% 4	2600
	11th to 20th	Night	39% 4 12% 27% 15% 3	2441
	21st to end	Night	33% 4 9% 24% 22% 8%	1980
March	1st to 10th	Night	30% 3 7% 26% 29% 5%	5010
	11th to 20th	Night	26% 3 8% 20% 34% 9%	4980
	21st to end	Night	40% 5% 17% 27% 9% 2	5467
April	1st to 10th	Night	33% 4 12% 25% 23% 4	2190
	11th to 20th	Night	37% 5% 9% 26% 19% 3	1853
	21st to end	Night	39% 5% 12% 26% 17% 1	1800
May	1st to 10th	Night	36% 5% 10% 25% 21% 3	4080
	11th to 20th	Night	31% 3 10% 25% 24% 7%	4054
	21st to end	Night	36% 6% 14% 26% 18% 1	4452
June	1st to 10th	Night	24% 6% 17% 33% 19% 3	1800
	11th to 20th	Night	25% 6% 14% 32% 18% 5%	1800
	21st to end	Night	21% 6% 14% 33% 21% 5%	1800
July	1st to 10th	Night	29% 6% 13% 25% 22% 5%	4035
	11th to 20th	Night	27% 6% 14% 26% 25% 2	4026
	21st to end	Night	26% 5% 13% 32% 22% 2	4320
August	1st to 10th	Night	22% 5% 20% 26% 21% 7%	2916
	11th to 20th	Night	33% 5% 14% 26% 19% 2	2915
	21st to end	Night	22% 5% 15% 33% 20% 6%	3313
September	1st to 10th	Night	25% 4 12% 29% 23% 8%	2150
	11th to 20th	Night	28% 5% 11% 28% 25% 5%	2200
	21st to end	Night	26% 3 9% 26% 31% 5%	2200
October	1st to 10th	Night	22% 3 7% 18% 44% 6%	3748
	11th to 20th	Night	20% 3 6% 31% 29% 12%	3899
	21st to end	Night	28% 3 8% 28% 29% 4	4252
November	1st to 10th	Night	26% 3 10% 29% 25% 7%	2621
	11th to 20th	Night	27% 4 11% 31% 24% 4	2730
	21st to end	Night	34% 4 10% 28% 21% 3	2730
December	1st to 10th	Night	25% 4 15% 36% 19% 1	4673
	11th to 20th	Night	33% 4 13% 30% 18% 2	4953
	21st to end	Night	52% 4 9% 24% 10% 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	14% 15% 41% 20% 8% 1	300
	11th to 20th	Day	18% 18% 39% 21% 4	300
	21st to end	Day	10% 12% 47% 25% 5%	330
February	1st to 10th	Day	16% 20% 43% 17% 4	300
	11th to 20th	Day	16% 15% 46% 18% 5% 1	300
	21st to end	Day	12% 22% 43% 19% 3	249
March	1st to 10th	Day	17% 15% 44% 19% 4	300
	11th to 20th	Day	25% 14% 37% 17% 6% 1	300
	21st to end	Day	24% 19% 40% 13% 4	330
April	1st to 10th	Day	23% 18% 37% 19% 4	310
	11th to 20th	Day	18% 19% 37% 21% 5%	610
	21st to end	Day	22% 19% 31% 18% 8% 2	700
May	1st to 10th	Day	17% 13% 36% 24% 8% 2	703
	11th to 20th	Day	18% 11% 29% 27% 12% 2	725
	21st to end	Day	19% 7% 32% 26% 14% 2	789
June	1st to 10th	Day	6% 5% 24% 36% 23% 6%	730
	11th to 20th	Day	8% 5% 32% 35% 17% 3	730
	21st to end	Day	7% 6% 38% 35% 12% 2	730
July	1st to 10th	Day	9% 3 19% 36% 26% 6%	721
	11th to 20th	Day	6% 3 21% 40% 24% 7%	718
	21st to end	Day	7% 3 18% 40% 27% 5%	794
August	1st to 10th	Day	8% 2 21% 41% 25% 3	726
	11th to 20th	Day	8% 4 18% 45% 21% 4	715
	21st to end	Day	10% 3 19% 35% 27% 6%	758
September	1st to 10th	Day	11% 3 24% 41% 17% 4	375
	11th to 20th	Day	7% 5% 28% 39% 16% 5%	330
	21st to end	Day	15% 5% 31% 31% 15% 3	330
October	1st to 10th	Day	16% 10% 29% 29% 12% 4	330
	11th to 20th	Day	8% 17% 42% 24% 8% 1	330
	21st to end	Day	22% 15% 35% 20% 7% 1	363
November	1st to 10th	Day	15% 15% 41% 22% 6% 1	330
	11th to 20th	Day	16% 16% 38% 24% 6% 1	330
	21st to end	Day	23% 12% 37% 20% 7% 1	330
December	1st to 10th	Day	10% 12% 44% 25% 7% 2	330
	11th to 20th	Day	14% 17% 40% 21% 8%	321
	21st to end	Day	21% 16% 41% 19% 2	330
January	1st to 10th	Night	11% 13% 38% 31% 7%	1000
	11th to 20th	Night	13% 12% 39% 29% 7%	1000
	21st to end	Night	13% 9% 43% 31% 4	1100
February	1st to 10th	Night	17% 10% 43% 27% 3	1000
	11th to 20th	Night	14% 15% 40% 29% 3	886
	21st to end	Night	12% 15% 43% 25% 5%	660
March	1st to 10th	Night	13% 16% 41% 26% 5%	643
	11th to 20th	Night	16% 13% 36% 28% 7%	600
	21st to end	Night	20% 14% 40% 21% 4	660
April	1st to 10th	Night	14% 15% 43% 24% 5%	600
	11th to 20th	Night	19% 15% 38% 25% 3	593
	21st to end	Night	18% 10% 40% 25% 7% 1	600
May	1st to 10th	Night	17% 9% 34% 31% 9% 1	600
	11th to 20th	Night	17% 8% 32% 33% 10% 1	591
	21st to end	Night	14% 7% 30% 34% 13% 1	650
June	1st to 10th	Night	7% 4 27% 41% 21% 1	600
	11th to 20th	Night	6% 4 33% 41% 17% 1	600
	21st to end	Night	7% 3 35% 45% 11% 1	600
July	1st to 10th	Night	7% 2 19% 46% 25% 1	585
	11th to 20th	Night	3 1 23% 48% 24% 2	582
	21st to end	Night	5% 1 17% 49% 25% 2	657
August	1st to 10th	Night	5% 2 22% 46% 24% 1	597
	11th to 20th	Night	6% 3 16% 53% 20% 2	594
	21st to end	Night	8% 3 18% 45% 23% 3	660
September	1st to 10th	Night	9% 4 25% 44% 17% 2	600
	11th to 20th	Night	10% 2 28% 40% 18% 2	600
	21st to end	Night	9% 4 31% 38% 18% 1	600
October	1st to 10th	Night	14% 7% 30% 32% 15% 1	693
	11th to 20th	Night	14% 9% 40% 28% 8%	800
	21st to end	Night	16% 13% 31% 32% 8%	880
November	1st to 10th	Night	10% 10% 35% 36% 9% 1	981
	11th to 20th	Night	11% 13% 40% 30% 6%	1050
	21st to end	Night	16% 12% 34% 30% 8%	1050
December	1st to 10th	Night	12% 12% 39% 31% 6%	1050
	11th to 20th	Night	16% 12% 39% 29% 4	1036
	21st to end	Night	17% 13% 35% 30% 4	1100

Page generated at 2025-12-15 00:13:54. Version ac07

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