Cold Spring
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cold Spring clear sky chart from 2005-11-06 to 2026-07-16.

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% 8% 3 8% 5% 4 5% 4 5% 7% 39%	138860
	Night	11% 9% 3 8% 5% 4 5% 4 5% 7% 39%	134102
Transparency	Day	43% 5% 13% 26% 12% 1	142431
	Night	44% 4 13% 25% 13% 2	138599
Seeing	Day	16% 9% 31% 27% 13% 3	18403
	Night	15% 9% 32% 32% 11% 1	28275

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% 4 16% 10% 6% 6% 5% 5% 7% 21%	4153
	11th to 20th	Day	5% 10% 5% 13% 8% 7% 7% 7% 9% 6% 22%	4890
	21st to end	Day	3 10% 7% 12% 6% 5% 6% 4 6% 7% 35%	5812
February	1st to 10th	Day	9% 12% 5% 10% 6% 7% 4 3 5% 6% 33%	1890
	11th to 20th	Day	7% 11% 4 11% 7% 5% 5% 4 7% 6% 34%	1844
	21st to end	Day	8% 12% 4 10% 7% 5% 5% 4 5% 7% 34%	1567
March	1st to 10th	Day	11% 10% 3 7% 4 3 4 3 5% 7% 43%	5046
	11th to 20th	Day	9% 10% 3 8% 4 4 4 4 5% 8% 40%	5090
	21st to end	Day	20% 12% 4 9% 6% 5% 4 3 5% 6% 25%	5583
April	1st to 10th	Day	17% 11% 3 8% 5% 3 3 3 5% 7% 35%	2497
	11th to 20th	Day	17% 13% 5% 7% 5% 4 4 3 4 6% 31%	2594
	21st to end	Day	23% 9% 3 6% 5% 3 4 3 4 6% 32%	2730
May	1st to 10th	Day	11% 5% 2 5% 5% 4 4 3 5% 6% 51%	7792
	11th to 20th	Day	16% 8% 2 6% 3 3 3 3 4 6% 45%	8222
	21st to end	Day	15% 7% 2 6% 4 4 5% 4 6% 8% 39%	9047
June	1st to 10th	Day	11% 6% 2 6% 4 4 5% 3 6% 8% 44%	2978
	11th to 20th	Day	14% 7% 3 8% 5% 4 5% 4 6% 8% 37%	3150
	21st to end	Day	11% 5% 2 6% 5% 4 5% 5% 7% 10% 41%	3150
July	1st to 10th	Day	7% 4 2 5% 4 5% 5% 5% 7% 10% 46%	6950
	11th to 20th	Day	9% 3 1 4 3 3 4 3 5% 8% 55%	6616
	21st to end	Day	8% 4 2 6% 4 4 5% 4 6% 10% 47%	6707
August	1st to 10th	Day	13% 6% 2 6% 4 4 5% 4 5% 8% 44%	4234
	11th to 20th	Day	12% 5% 2 6% 4 4 5% 4 7% 9% 41%	4171
	21st to end	Day	10% 6% 2 6% 4 4 4 4 5% 8% 48%	4562
September	1st to 10th	Day	9% 5% 1 5% 4 3 4 3 6% 9% 49%	2400
	11th to 20th	Day	11% 5% 2 6% 5% 4 5% 4 6% 7% 46%	2295
	21st to end	Day	15% 5% 2 5% 4 3 3 4 5% 7% 47%	2150
October	1st to 10th	Day	16% 7% 2 5% 4 4 4 4 6% 8% 42%	2000
	11th to 20th	Day	15% 11% 2 7% 4 4 4 3 4 7% 40%	2000
	21st to end	Day	18% 10% 3 7% 4 4 3 2 4 7% 37%	2198
November	1st to 10th	Day	14% 11% 3 8% 4 5% 4 4 5% 6% 36%	1672
	11th to 20th	Day	9% 13% 6% 12% 6% 5% 4 3 6% 6% 31%	1680
	21st to end	Day	12% 10% 5% 9% 5% 4 4 4 6% 8% 33%	1680
December	1st to 10th	Day	8% 10% 5% 12% 10% 8% 6% 5% 6% 6% 25%	2690
	11th to 20th	Day	9% 16% 7% 10% 6% 4 4 3 5% 6% 30%	3088
	21st to end	Day	19% 18% 5% 20% 5% 4 3 2 3 4 17%	3732
January	1st to 10th	Night	8% 10% 5% 15% 9% 6% 5% 4 6% 6% 28%	8763
	11th to 20th	Night	5% 12% 4 11% 8% 6% 10% 8% 7% 6% 23%	8082
	21st to end	Night	4 13% 6% 8% 5% 5% 5% 4 6% 7% 36%	8402
February	1st to 10th	Night	7% 12% 4 10% 7% 5% 4 5% 6% 7% 35%	2730
	11th to 20th	Night	6% 8% 5% 8% 5% 4 6% 4 6% 8% 39%	2663
	21st to end	Night	10% 11% 3 8% 5% 5% 4 5% 6% 6% 37%	2248
March	1st to 10th	Night	10% 8% 2 6% 4 3 4 3 6% 7% 47%	5036
	11th to 20th	Night	10% 8% 2 7% 4 4 4 4 8% 9% 40%	5090
	21st to end	Night	22% 12% 4 11% 5% 4 4 3 4 5% 28%	5588
April	1st to 10th	Night	14% 10% 3 6% 5% 4 5% 3 4 7% 39%	2122
	11th to 20th	Night	16% 11% 4 7% 3 4 4 3 5% 6% 37%	1973
	21st to end	Night	19% 10% 3 7% 3 4 4 3 4 6% 37%	1890
May	1st to 10th	Night	10% 6% 2 4 3 3 3 3 5% 7% 55%	5088
	11th to 20th	Night	16% 6% 2 4 3 4 3 3 4 5% 50%	4670
	21st to end	Night	16% 8% 2 6% 4 3 4 3 6% 7% 40%	5139
June	1st to 10th	Night	11% 5% 2 4 4 4 5% 5% 7% 9% 46%	1636
	11th to 20th	Night	10% 5% 2 5% 4 4 5% 4 6% 8% 47%	1470
	21st to end	Night	9% 5% 1 6% 4 3 4 4 6% 8% 51%	1470
July	1st to 10th	Night	9% 3 1 4 3 4 5% 4 7% 8% 51%	3248
	11th to 20th	Night	7% 4 1 4 3 3 3 3 6% 8% 59%	3469
	21st to end	Night	9% 4 2 6% 4 4 5% 4 6% 7% 49%	4161
August	1st to 10th	Night	11% 6% 2 5% 4 3 4 3 5% 7% 49%	2926
	11th to 20th	Night	14% 5% 2 5% 4 4 4 4 6% 7% 48%	2888
	21st to end	Night	10% 5% 2 6% 3 3 4 3 5% 8% 50%	3330
September	1st to 10th	Night	8% 3 2 5% 3 3 4 3 6% 7% 56%	2000
	11th to 20th	Night	10% 5% 2 5% 3 4 4 3 4 8% 53%	2100
	21st to end	Night	12% 5% 2 5% 3 3 3 3 5% 6% 54%	2230
October	1st to 10th	Night	14% 6% 2 5% 3 3 3 4 5% 6% 50%	2400
	11th to 20th	Night	15% 8% 3 5% 4 4 4 3 5% 7% 43%	2400
	21st to end	Night	17% 9% 3 7% 4 4 4 2 4 7% 38%	2640
November	1st to 10th	Night	11% 9% 3 6% 4 4 5% 3 6% 7% 40%	2846
	11th to 20th	Night	12% 11% 5% 10% 5% 4 4 3 4 5% 35%	2940
	21st to end	Night	12% 10% 4 9% 5% 4 4 3 5% 7% 38%	2940
December	1st to 10th	Night	6% 7% 4 12% 9% 7% 6% 4 6% 8% 31%	4720
	11th to 20th	Night	10% 14% 5% 13% 8% 6% 4 4 5% 6% 25%	5339
	21st to end	Night	19% 17% 6% 16% 5% 4 4 3 3 5% 18%	7465

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% 4 11% 13% 9%	4154
	11th to 20th	Day	57% 3 11% 19% 9%	4890
	21st to end	Day	49% 4 14% 23% 11%	5812
February	1st to 10th	Day	52% 3 12% 22% 9% 1	1890
	11th to 20th	Day	49% 5% 13% 25% 7% 1	1853
	21st to end	Day	50% 4 13% 22% 11% 1	1567
March	1st to 10th	Day	41% 4 16% 26% 11% 3	5046
	11th to 20th	Day	42% 4 14% 29% 10% 1	5090
	21st to end	Day	60% 5% 10% 18% 7%	5585
April	1st to 10th	Day	49% 4 11% 22% 13% 1	2497
	11th to 20th	Day	54% 4 10% 18% 12% 1	2594
	21st to end	Day	52% 5% 11% 21% 10% 1	2730
May	1st to 10th	Day	34% 4 12% 29% 20% 1	7830
	11th to 20th	Day	40% 3 8% 26% 17% 6%	8226
	21st to end	Day	43% 5% 10% 31% 10% 1	9061
June	1st to 10th	Day	37% 5% 15% 30% 11% 1	2978
	11th to 20th	Day	44% 6% 14% 21% 13% 1	3150
	21st to end	Day	36% 6% 18% 27% 11% 2	3150
July	1st to 10th	Day	31% 7% 19% 31% 11%	6876
	11th to 20th	Day	26% 5% 17% 37% 14% 1	6536
	21st to end	Day	32% 6% 17% 31% 13% 1	6516
August	1st to 10th	Day	38% 4 13% 30% 12% 2	4220
	11th to 20th	Day	38% 6% 14% 32% 9%	4210
	21st to end	Day	34% 6% 17% 30% 12% 1	4561
September	1st to 10th	Day	31% 5% 15% 37% 12%	2400
	11th to 20th	Day	36% 6% 19% 29% 9% 1	2295
	21st to end	Day	37% 4 11% 34% 12% 1	2150
October	1st to 10th	Day	31% 3 10% 33% 22% 1	3260
	11th to 20th	Day	38% 4 12% 22% 21% 2	3240
	21st to end	Day	46% 3 14% 27% 9%	3525
November	1st to 10th	Day	48% 6% 12% 20% 13% 2	1672
	11th to 20th	Day	54% 4 13% 20% 10% 1	1680
	21st to end	Day	50% 5% 15% 22% 7% 2	1680
December	1st to 10th	Day	58% 6% 14% 16% 4 1	2690
	11th to 20th	Day	57% 3 14% 19% 7%	3085
	21st to end	Day	72% 3 8% 11% 5%	3732
January	1st to 10th	Night	57% 4 13% 17% 9%	8764
	11th to 20th	Night	59% 4 10% 16% 10% 1	8082
	21st to end	Night	47% 4 11% 27% 10%	8402
February	1st to 10th	Night	48% 4 14% 22% 11% 1	2730
	11th to 20th	Night	42% 5% 14% 26% 12% 1	2664
	21st to end	Night	46% 5% 13% 22% 13% 2	2248
March	1st to 10th	Night	35% 4 13% 29% 16% 2	5036
	11th to 20th	Night	38% 4 14% 28% 14%	5090
	21st to end	Night	60% 4 8% 18% 9% 1	5588
April	1st to 10th	Night	46% 5% 10% 26% 13% 1	2122
	11th to 20th	Night	47% 4 8% 23% 15% 2	1973
	21st to end	Night	49% 4 9% 22% 14% 2	1890
May	1st to 10th	Night	29% 5% 11% 35% 19% 2	5115
	11th to 20th	Night	37% 4 7% 19% 24% 9%	4671
	21st to end	Night	43% 5% 10% 29% 13% 1	5149
June	1st to 10th	Night	33% 6% 16% 30% 14% 2	1636
	11th to 20th	Night	33% 5% 17% 26% 15% 3	1470
	21st to end	Night	31% 6% 15% 29% 16% 3	1470
July	1st to 10th	Night	29% 6% 20% 27% 17% 1	3215
	11th to 20th	Night	24% 5% 16% 38% 15% 2	3429
	21st to end	Night	33% 6% 16% 31% 12% 2	4041
August	1st to 10th	Night	35% 4 14% 28% 14% 4	2916
	11th to 20th	Night	36% 5% 14% 33% 12%	2915
	21st to end	Night	32% 6% 18% 30% 12% 2	3330
September	1st to 10th	Night	26% 5% 18% 34% 16% 1	2000
	11th to 20th	Night	31% 4 18% 31% 16%	2100
	21st to end	Night	31% 4 12% 35% 17% 1	2230
October	1st to 10th	Night	23% 3 7% 37% 25% 4	3920
	11th to 20th	Night	34% 3 12% 27% 21% 3	3899
	21st to end	Night	42% 4 14% 27% 12%	4252
November	1st to 10th	Night	42% 4 14% 26% 13% 2	2846
	11th to 20th	Night	51% 4 13% 20% 12% 1	2940
	21st to end	Night	47% 4 17% 23% 7% 2	2940
December	1st to 10th	Night	51% 5% 18% 20% 6%	4720
	11th to 20th	Night	60% 4 11% 19% 6% 1	5341
	21st to end	Night	71% 3 8% 14% 4	7465

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	15% 10% 31% 30% 12% 2	330
	11th to 20th	Day	17% 9% 40% 29% 5%	330
	21st to end	Day	12% 12% 42% 20% 12% 1	363
February	1st to 10th	Day	15% 16% 44% 21% 3 1	330
	11th to 20th	Day	13% 18% 36% 24% 9%	330
	21st to end	Day	16% 12% 42% 26% 3	273
March	1st to 10th	Day	21% 12% 41% 21% 5% 1	330
	11th to 20th	Day	22% 9% 38% 22% 7% 1	330
	21st to end	Day	25% 13% 30% 22% 8% 2	363
April	1st to 10th	Day	26% 14% 31% 23% 5%	517
	11th to 20th	Day	27% 15% 28% 22% 8% 1	632
	21st to end	Day	25% 9% 37% 19% 8% 2	750
May	1st to 10th	Day	21% 10% 33% 23% 10% 2	753
	11th to 20th	Day	20% 10% 29% 26% 12% 3	775
	21st to end	Day	18% 6% 28% 32% 13% 2	844
June	1st to 10th	Day	11% 9% 26% 30% 20% 4	780
	11th to 20th	Day	17% 8% 34% 28% 12% 1	780
	21st to end	Day	14% 7% 33% 27% 15% 4	780
July	1st to 10th	Day	7% 4 22% 33% 25% 9%	771
	11th to 20th	Day	9% 6% 28% 30% 19% 8%	744
	21st to end	Day	7% 4 27% 35% 22% 6%	794
August	1st to 10th	Day	12% 4 23% 32% 25% 5%	726
	11th to 20th	Day	12% 5% 22% 33% 22% 6%	715
	21st to end	Day	10% 6% 24% 34% 22% 5%	742
September	1st to 10th	Day	12% 6% 30% 32% 16% 5%	530
	11th to 20th	Day	10% 4 30% 33% 18% 5%	425
	21st to end	Day	21% 9% 26% 21% 16% 6%	330
October	1st to 10th	Day	16% 12% 32% 24% 12% 5%	330
	11th to 20th	Day	17% 16% 36% 21% 8% 2	330
	21st to end	Day	25% 14% 36% 18% 6% 1	363
November	1st to 10th	Day	22% 14% 31% 25% 7% 2	330
	11th to 20th	Day	18% 18% 40% 20% 4 1	330
	21st to end	Day	19% 16% 36% 24% 5% 1	330
December	1st to 10th	Day	15% 10% 42% 25% 8% 1	330
	11th to 20th	Day	20% 14% 38% 25% 3	330
	21st to end	Day	30% 10% 37% 20% 3 1	363
January	1st to 10th	Night	12% 11% 37% 31% 8% 2	1050
	11th to 20th	Night	16% 11% 38% 28% 7% 1	1050
	21st to end	Night	15% 12% 37% 27% 8%	1155
February	1st to 10th	Night	12% 12% 38% 28% 8% 1	1050
	11th to 20th	Night	11% 12% 42% 28% 7% 1	1029
	21st to end	Night	15% 11% 35% 30% 7% 1	864
March	1st to 10th	Night	15% 11% 36% 29% 8% 1	637
	11th to 20th	Night	17% 11% 41% 25% 5% 1	630
	21st to end	Night	23% 9% 32% 25% 9% 2	693
April	1st to 10th	Night	20% 9% 38% 27% 6%	630
	11th to 20th	Night	22% 13% 30% 27% 8%	623
	21st to end	Night	23% 8% 30% 29% 8% 1	630
May	1st to 10th	Night	18% 8% 33% 28% 11% 1	630
	11th to 20th	Night	17% 7% 31% 33% 10% 1	621
	21st to end	Night	16% 6% 28% 36% 14% 1	683
June	1st to 10th	Night	14% 4 27% 38% 16%	630
	11th to 20th	Night	13% 3 32% 43% 9%	630
	21st to end	Night	11% 5% 28% 40% 16%	630
July	1st to 10th	Night	6% 2 21% 43% 27% 2	615
	11th to 20th	Night	8% 2 24% 47% 16% 2	597
	21st to end	Night	6% 1 22% 47% 21% 2	657
August	1st to 10th	Night	9% 2 19% 47% 21% 2	597
	11th to 20th	Night	13% 2 18% 40% 25% 3	594
	21st to end	Night	8% 4 24% 39% 23% 2	660
September	1st to 10th	Night	10% 4 25% 41% 18% 2	600
	11th to 20th	Night	11% 6% 30% 32% 20% 1	600
	21st to end	Night	13% 8% 31% 32% 14% 2	630
October	1st to 10th	Night	15% 9% 32% 32% 11% 1	800
	11th to 20th	Night	20% 9% 35% 29% 6% 1	800
	21st to end	Night	23% 11% 31% 28% 7%	880
November	1st to 10th	Night	16% 11% 33% 31% 8% 1	1025
	11th to 20th	Night	18% 13% 34% 27% 8% 1	1050
	21st to end	Night	17% 14% 37% 25% 8%	1050
December	1st to 10th	Night	15% 11% 37% 29% 8% 1	1050
	11th to 20th	Night	21% 11% 35% 28% 5% 1	1050
	21st to end	Night	25% 10% 34% 25% 5% 1	1155

Page generated at 2026-07-13 02:14:52. Version ac07

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