Cobblestone Creek Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cobblestone Creek Observatory clear sky chart from 2005-11-06 to 2026-02-16.

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	15% 10% 4 9% 5% 5% 5% 4 5% 7% 32%	131965
	Night	15% 11% 4 9% 5% 4 4 4 5% 6% 33%	128916
Transparency	Day	50% 6% 11% 20% 12% 1	135593
	Night	50% 5% 11% 20% 13% 2	133358
Seeing	Day	19% 10% 26% 23% 15% 7%	17012
	Night	19% 8% 27% 30% 14% 2	26575

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	18% 18% 7% 16% 7% 5% 4 3 4 4 14%	5258
	11th to 20th	Day	13% 18% 6% 14% 8% 7% 6% 3 3 4 18%	5280
	21st to end	Day	20% 14% 7% 13% 7% 7% 6% 4 4 5% 13%	5780
February	1st to 10th	Day	17% 16% 6% 11% 7% 6% 4 2 5% 4 22%	1890
	11th to 20th	Day	15% 12% 7% 14% 6% 5% 4 3 4 6% 22%	1977
	21st to end	Day	17% 13% 4 10% 5% 5% 4 4 5% 6% 27%	1650
March	1st to 10th	Day	18% 13% 7% 14% 6% 4 4 3 4 4 25%	4654
	11th to 20th	Day	12% 10% 4 8% 5% 4 4 3 5% 7% 39%	4980
	21st to end	Day	20% 12% 5% 9% 5% 5% 4 3 5% 5% 27%	5465
April	1st to 10th	Day	16% 13% 3 8% 6% 5% 4 4 5% 7% 30%	2275
	11th to 20th	Day	17% 10% 3 7% 6% 4 4 4 5% 7% 34%	2520
	21st to end	Day	19% 9% 3 7% 4 4 5% 3 5% 7% 34%	2600
May	1st to 10th	Day	22% 10% 3 8% 5% 5% 5% 4 5% 6% 27%	5862
	11th to 20th	Day	19% 9% 3 8% 5% 4 4 3 5% 7% 33%	5861
	21st to end	Day	16% 7% 2 6% 4 5% 5% 5% 6% 8% 35%	6433
June	1st to 10th	Day	13% 6% 2 7% 6% 5% 5% 4 7% 9% 38%	2600
	11th to 20th	Day	11% 7% 3 7% 5% 5% 5% 5% 7% 9% 38%	2747
	21st to end	Day	11% 4 2 6% 5% 5% 5% 5% 7% 11% 39%	2800
July	1st to 10th	Day	8% 6% 3 7% 5% 5% 5% 4 6% 9% 41%	6360
	11th to 20th	Day	9% 6% 3 7% 5% 5% 6% 5% 7% 11% 37%	5997
	21st to end	Day	9% 6% 2 7% 5% 5% 6% 5% 8% 10% 37%	6424
August	1st to 10th	Day	9% 6% 2 7% 5% 5% 5% 5% 7% 9% 40%	4234
	11th to 20th	Day	8% 5% 2 7% 4 5% 6% 5% 9% 10% 40%	4174
	21st to end	Day	7% 5% 2 6% 5% 5% 5% 5% 6% 11% 44%	4583
September	1st to 10th	Day	11% 5% 2 6% 4 4 4 2 5% 7% 49%	2225
	11th to 20th	Day	10% 5% 2 6% 4 5% 5% 4 5% 9% 47%	2200
	21st to end	Day	17% 7% 2 5% 4 4 4 3 4 6% 43%	2200
October	1st to 10th	Day	14% 7% 2 6% 4 4 3 4 5% 7% 44%	2150
	11th to 20th	Day	15% 7% 2 7% 4 4 4 4 5% 7% 41%	2000
	21st to end	Day	20% 10% 3 7% 5% 5% 4 3 5% 7% 31%	2106
November	1st to 10th	Day	12% 8% 3 7% 5% 4 4 3 4 7% 44%	1852
	11th to 20th	Day	17% 13% 4 6% 4 5% 4 3 4 6% 33%	1890
	21st to end	Day	18% 15% 7% 8% 5% 3 3 2 4 6% 27%	1890
December	1st to 10th	Day	18% 14% 6% 14% 6% 4 3 3 4 5% 23%	3020
	11th to 20th	Day	20% 16% 8% 9% 5% 5% 4 3 5% 5% 20%	3463
	21st to end	Day	25% 21% 6% 12% 6% 4 4 3 3 4 12%	4565
January	1st to 10th	Night	15% 18% 7% 16% 6% 6% 5% 3 4 5% 15%	7635
	11th to 20th	Night	10% 19% 8% 16% 7% 7% 6% 3 4 4 16%	7680
	21st to end	Night	19% 15% 5% 9% 6% 5% 4 4 5% 5% 23%	8401
February	1st to 10th	Night	20% 14% 4 10% 6% 5% 4 3 5% 5% 25%	2730
	11th to 20th	Night	17% 13% 5% 10% 6% 5% 5% 4 6% 5% 25%	2416
	21st to end	Night	20% 15% 5% 10% 4 4 4 3 4 4 27%	1980
March	1st to 10th	Night	20% 13% 4 8% 4 3 4 3 4 5% 33%	5198
	11th to 20th	Night	12% 8% 2 6% 4 4 4 3 7% 8% 42%	4980
	21st to end	Night	19% 9% 3 7% 5% 4 4 3 4 5% 37%	5467
April	1st to 10th	Night	17% 10% 3 7% 5% 4 4 3 5% 7% 35%	2140
	11th to 20th	Night	16% 8% 3 7% 5% 5% 4 4 6% 7% 37%	1827
	21st to end	Night	16% 8% 3 7% 4 4 5% 3 6% 7% 37%	1800
May	1st to 10th	Night	22% 10% 3 9% 5% 5% 5% 4 5% 6% 27%	4033
	11th to 20th	Night	16% 8% 3 7% 3 4 4 3 6% 8% 38%	4032
	21st to end	Night	14% 6% 2 6% 5% 5% 5% 4 6% 9% 40%	4421
June	1st to 10th	Night	10% 7% 2 7% 4 4 4 4 5% 8% 45%	1800
	11th to 20th	Night	9% 6% 2 4 4 4 5% 4 7% 10% 44%	1646
	21st to end	Night	9% 4 2 5% 5% 4 5% 5% 7% 10% 45%	1600
July	1st to 10th	Night	9% 5% 2 6% 3 5% 5% 4 7% 9% 45%	3618
	11th to 20th	Night	8% 5% 2 7% 5% 4 6% 5% 7% 9% 42%	3959
	21st to end	Night	8% 6% 2 8% 5% 5% 5% 4 6% 8% 43%	4427
August	1st to 10th	Night	9% 7% 3 7% 5% 4 5% 4 8% 9% 38%	2915
	11th to 20th	Night	7% 8% 3 7% 5% 5% 4 4 6% 7% 43%	2875
	21st to end	Night	4 4 2 6% 5% 5% 5% 5% 8% 8% 49%	3312
September	1st to 10th	Night	11% 5% 2 5% 4 3 4 4 4 6% 52%	2154
	11th to 20th	Night	9% 5% 2 4 3 2 3 3 5% 6% 56%	2200
	21st to end	Night	15% 6% 3 6% 4 4 4 3 5% 6% 45%	2200
October	1st to 10th	Night	10% 5% 1 6% 4 4 4 3 5% 7% 50%	2249
	11th to 20th	Night	16% 7% 2 6% 4 5% 4 4 5% 6% 42%	2400
	21st to end	Night	20% 8% 3 6% 4 4 4 3 5% 7% 37%	2730
November	1st to 10th	Night	13% 7% 3 6% 4 4 4 3 5% 6% 46%	2666
	11th to 20th	Night	16% 13% 3 7% 3 4 4 3 6% 6% 35%	2730
	21st to end	Night	19% 14% 4 7% 5% 4 4 3 5% 6% 27%	2730
December	1st to 10th	Night	16% 12% 5% 11% 6% 5% 5% 4 5% 6% 24%	4380
	11th to 20th	Night	19% 18% 6% 13% 5% 4 3 3 4 5% 21%	4952
	21st to end	Night	25% 21% 6% 10% 4 4 3 3 4 5% 15%	6633

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	74% 4 9% 10% 2	5259
	11th to 20th	Day	72% 3 8% 7% 10%	5280
	21st to end	Day	74% 3 7% 10% 5%	5780
February	1st to 10th	Day	66% 5% 9% 14% 6%	1890
	11th to 20th	Day	65% 4 8% 15% 7% 1	1987
	21st to end	Day	58% 4 13% 15% 7% 2	1650
March	1st to 10th	Day	63% 4 8% 19% 6%	4654
	11th to 20th	Day	46% 4 10% 29% 9% 1	4980
	21st to end	Day	58% 4 11% 19% 8% 1	5465
April	1st to 10th	Day	53% 6% 12% 16% 11% 1	2275
	11th to 20th	Day	49% 6% 12% 19% 13% 2	2520
	21st to end	Day	49% 6% 10% 21% 11% 2	2600
May	1st to 10th	Day	56% 7% 10% 16% 10% 1	5897
	11th to 20th	Day	49% 6% 13% 21% 10% 1	5865
	21st to end	Day	43% 8% 12% 23% 12% 2	6447
June	1st to 10th	Day	42% 7% 10% 24% 15% 1	2600
	11th to 20th	Day	41% 8% 15% 21% 14% 1	2747
	21st to end	Day	37% 10% 14% 21% 15% 3	2800
July	1st to 10th	Day	39% 6% 10% 28% 16% 2	6291
	11th to 20th	Day	38% 7% 14% 23% 16% 1	5925
	21st to end	Day	39% 8% 12% 20% 18% 3	6240
August	1st to 10th	Day	38% 8% 16% 24% 14% 1	4221
	11th to 20th	Day	36% 7% 12% 29% 15% 1	4213
	21st to end	Day	34% 7% 13% 30% 13% 3	4582
September	1st to 10th	Day	35% 6% 11% 24% 20% 4	2225
	11th to 20th	Day	35% 6% 11% 26% 20% 3	2200
	21st to end	Day	43% 5% 10% 20% 21% 1	2200
October	1st to 10th	Day	27% 5% 11% 34% 22% 1	3501
	11th to 20th	Day	36% 4 11% 26% 22% 2	3240
	21st to end	Day	42% 4 10% 24% 19% 1	3382
November	1st to 10th	Day	41% 5% 11% 25% 16% 2	1852
	11th to 20th	Day	53% 4 11% 20% 11% 2	1890
	21st to end	Day	60% 4 10% 17% 8% 1	1890
December	1st to 10th	Day	65% 4 13% 14% 3	3020
	11th to 20th	Day	66% 5% 12% 13% 5%	3460
	21st to end	Day	77% 4 7% 8% 4	4565
January	1st to 10th	Night	72% 4 8% 13% 3	7636
	11th to 20th	Night	73% 3 8% 9% 6% 1	7680
	21st to end	Night	63% 3 12% 14% 7% 1	8401
February	1st to 10th	Night	62% 5% 10% 15% 7% 1	2730
	11th to 20th	Night	59% 5% 10% 15% 9% 1	2417
	21st to end	Night	61% 4 9% 15% 9% 2	1980
March	1st to 10th	Night	53% 4 9% 22% 9% 1	5198
	11th to 20th	Night	38% 5% 13% 31% 11% 1	4980
	21st to end	Night	50% 4 9% 22% 14% 1	5467
April	1st to 10th	Night	48% 5% 13% 18% 14% 2	2140
	11th to 20th	Night	46% 5% 12% 18% 17% 3	1827
	21st to end	Night	46% 6% 12% 20% 15% 2	1800
May	1st to 10th	Night	56% 6% 10% 14% 11% 2	4060
	11th to 20th	Night	44% 7% 11% 23% 15% 1	4033
	21st to end	Night	39% 8% 13% 26% 13% 1	4429
June	1st to 10th	Night	37% 7% 12% 22% 20% 2	1800
	11th to 20th	Night	33% 9% 13% 26% 16% 3	1646
	21st to end	Night	33% 8% 15% 24% 17% 4	1600
July	1st to 10th	Night	34% 6% 12% 26% 18% 4	3580
	11th to 20th	Night	35% 8% 14% 28% 15% 1	3911
	21st to end	Night	37% 7% 13% 20% 20% 3	4297
August	1st to 10th	Night	39% 8% 14% 23% 14% 1	2904
	11th to 20th	Night	38% 6% 10% 27% 18%	2902
	21st to end	Night	30% 7% 14% 29% 17% 2	3312
September	1st to 10th	Night	33% 6% 11% 27% 18% 6%	2154
	11th to 20th	Night	28% 5% 10% 28% 26% 3	2200
	21st to end	Night	39% 6% 9% 20% 23% 2	2200
October	1st to 10th	Night	25% 4 8% 29% 33% 1	3678
	11th to 20th	Night	33% 4 10% 28% 22% 3	3899
	21st to end	Night	36% 3 9% 28% 20% 4	4404
November	1st to 10th	Night	40% 4 12% 23% 18% 2	2666
	11th to 20th	Night	50% 4 9% 22% 13% 2	2730
	21st to end	Night	58% 4 12% 19% 7% 1	2730
December	1st to 10th	Night	61% 4 11% 17% 7% 1	4380
	11th to 20th	Night	66% 4 12% 13% 5%	4954
	21st to end	Night	73% 4 9% 10% 4	6633

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	30% 12% 35% 16% 6% 1	330
	11th to 20th	Day	25% 21% 38% 13% 3	330
	21st to end	Day	28% 17% 31% 19% 5%	363
February	1st to 10th	Day	28% 15% 35% 18% 3 1	330
	11th to 20th	Day	25% 20% 31% 19% 4	315
	21st to end	Day	24% 17% 43% 14% 2	249
March	1st to 10th	Day	23% 17% 35% 19% 6%	370
	11th to 20th	Day	24% 16% 33% 19% 5% 2	500
	21st to end	Day	30% 15% 29% 21% 5%	550
April	1st to 10th	Day	23% 14% 31% 22% 8% 2	500
	11th to 20th	Day	21% 17% 29% 20% 9% 5%	492
	21st to end	Day	23% 13% 29% 25% 8% 3	500
May	1st to 10th	Day	26% 10% 29% 23% 9% 3	503
	11th to 20th	Day	23% 7% 26% 22% 15% 6%	527
	21st to end	Day	13% 8% 25% 23% 20% 11%	573
June	1st to 10th	Day	12% 7% 22% 30% 22% 8%	530
	11th to 20th	Day	14% 7% 23% 28% 22% 6%	677
	21st to end	Day	13% 5% 27% 26% 20% 8%	730
July	1st to 10th	Day	13% 2 17% 27% 24% 17%	721
	11th to 20th	Day	12% 4 19% 24% 26% 16%	566
	21st to end	Day	11% 3 18% 23% 28% 17%	576
August	1st to 10th	Day	10% 2 13% 25% 31% 17%	526
	11th to 20th	Day	12% 2 18% 28% 26% 14%	519
	21st to end	Day	8% 4 15% 25% 31% 17%	583
September	1st to 10th	Day	12% 4 17% 25% 28% 14%	530
	11th to 20th	Day	8% 3 13% 22% 32% 22%	530
	21st to end	Day	20% 8% 18% 25% 18% 11%	530
October	1st to 10th	Day	11% 7% 22% 28% 20% 12%	530
	11th to 20th	Day	15% 11% 35% 22% 14% 4	530
	21st to end	Day	24% 15% 34% 21% 6% 1	489
November	1st to 10th	Day	15% 12% 36% 24% 9% 4	330
	11th to 20th	Day	24% 18% 29% 18% 9% 2	330
	21st to end	Day	28% 13% 39% 17% 2	330
December	1st to 10th	Day	24% 16% 37% 16% 6% 2	330
	11th to 20th	Day	25% 14% 39% 18% 3	330
	21st to end	Day	34% 16% 27% 20% 3	363
January	1st to 10th	Night	24% 13% 36% 23% 4	840
	11th to 20th	Night	29% 14% 34% 18% 4 1	840
	21st to end	Night	24% 13% 35% 24% 3	924
February	1st to 10th	Night	25% 11% 34% 27% 3	840
	11th to 20th	Night	25% 12% 34% 26% 3	804
	21st to end	Night	27% 11% 39% 20% 3	660
March	1st to 10th	Night	24% 10% 33% 26% 7% 1	800
	11th to 20th	Night	20% 13% 34% 26% 5% 1	800
	21st to end	Night	24% 11% 32% 28% 6%	880
April	1st to 10th	Night	22% 11% 34% 27% 5% 1	740
	11th to 20th	Night	20% 10% 35% 25% 9% 1	593
	21st to end	Night	19% 9% 37% 26% 8% 1	600
May	1st to 10th	Night	22% 7% 28% 31% 10% 1	600
	11th to 20th	Night	23% 5% 26% 32% 14% 1	591
	21st to end	Night	11% 4 22% 39% 22% 2	650
June	1st to 10th	Night	10% 4 23% 42% 20% 1	600
	11th to 20th	Night	12% 2 18% 46% 22% 1	600
	21st to end	Night	11% 2 20% 41% 25% 2	600
July	1st to 10th	Night	11% 1 15% 35% 34% 4	585
	11th to 20th	Night	7% 4 14% 41% 30% 4	582
	21st to end	Night	9% 2 14% 39% 34% 2	657
August	1st to 10th	Night	9% 1 11% 44% 32% 4	597
	11th to 20th	Night	10% 2 11% 40% 32% 5%	594
	21st to end	Night	7% 2 13% 38% 36% 5%	660
September	1st to 10th	Night	12% 2 16% 35% 29% 6%	754
	11th to 20th	Night	11% 3 12% 34% 34% 6%	800
	21st to end	Night	17% 6% 18% 32% 24% 3	800
October	1st to 10th	Night	12% 5% 22% 34% 23% 4	800
	11th to 20th	Night	19% 9% 28% 30% 12% 1	800
	21st to end	Night	24% 10% 31% 26% 9%	880
November	1st to 10th	Night	18% 8% 31% 30% 13% 1	820
	11th to 20th	Night	21% 15% 29% 27% 7% 1	840
	21st to end	Night	27% 10% 30% 26% 7% 1	840
December	1st to 10th	Night	26% 11% 34% 24% 5%	840
	11th to 20th	Night	25% 11% 35% 24% 5%	840
	21st to end	Night	31% 12% 30% 23% 3	924

Page generated at 2026-02-13 01:42:12. Version ac07

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