County Road 2C
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the County Road 2C clear sky chart from 2005-11-06 to 2025-05-11.

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	4 4 2 4 3 3 4 3 5% 7% 60%	117677
	Night	5% 5% 2 5% 4 4 4 3 5% 7% 56%	120120
Transparency	Day	23% 5% 10% 25% 26% 11%	117418
	Night	27% 5% 10% 24% 24% 10%	119969
Seeing	Day	7% 7% 25% 31% 22% 7%	16195
	Night	7% 6% 30% 40% 15% 1	26300

By Month

Percentage Cloud Cover SW (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	3 7% 3 7% 4 3 3 3 5% 6% 56%	3638
	11th to 20th	Day	2 5% 2 6% 5% 4 4 4 5% 6% 58%	3640
	21st to end	Day	3 7% 2 5% 3 3 3 2 4 6% 64%	4446
February	1st to 10th	Day	3 8% 2 5% 4 3 3 4 5% 7% 56%	1921
	11th to 20th	Day	2 6% 2 7% 5% 4 3 3 5% 6% 57%	1949
	21st to end	Day	3 6% 2 8% 4 3 4 3 3 5% 60%	1650
March	1st to 10th	Day	2 3 2 4 3 3 4 3 4 6% 66%	4500
	11th to 20th	Day	5% 5% 2 4 3 3 4 3 5% 7% 59%	4699
	21st to end	Day	3 4 2 5% 4 4 4 3 7% 8% 56%	5969
April	1st to 10th	Day	5% 5% 1 4 3 3 4 4 5% 8% 57%	2400
	11th to 20th	Day	8% 5% 2 5% 4 4 4 3 5% 7% 52%	2371
	21st to end	Day	8% 5% 2 5% 4 4 4 4 6% 8% 50%	2405
May	1st to 10th	Day	9% 6% 2 4 3 3 3 3 5% 7% 54%	4250
	11th to 20th	Day	7% 4 1 6% 4 4 5% 4 6% 8% 53%	4098
	21st to end	Day	6% 3 1 4 3 3 3 4 6% 9% 58%	4825
June	1st to 10th	Day	6% 3 1 3 3 3 4 4 7% 12% 56%	2660
	11th to 20th	Day	5% 3 1 4 3 3 4 4 5% 8% 60%	2660
	21st to end	Day	3 3 1 5% 3 4 4 5% 7% 9% 56%	2660
July	1st to 10th	Day	4 3 1 4 4 5% 6% 5% 7% 9% 52%	4430
	11th to 20th	Day	2 2 1 4 3 4 5% 5% 8% 9% 56%	4430
	21st to end	Day	3 2 1 3 3 3 4 4 6% 10% 58%	4802
August	1st to 10th	Day	10% 4 1 3 3 3 4 4 7% 10% 49%	3935
	11th to 20th	Day	4 3 1 3 3 4 5% 4 7% 10% 55%	3726
	21st to end	Day	3 3 1 4 3 3 4 4 7% 10% 57%	4180
September	1st to 10th	Day	4 4 1 4 3 3 4 3 5% 6% 62%	2280
	11th to 20th	Day	6% 3 1 3 2 2 4 3 4 6% 66%	2180
	21st to end	Day	6% 3 1 3 2 3 2 3 3 5% 68%	2090
October	1st to 10th	Day	5% 2 1 2 1 1 1 2 3 4 78%	3418
	11th to 20th	Day	5% 4 2 5% 2 2 2 2 4 6% 66%	3150
	21st to end	Day	4 4 1 3 2 2 2 2 3 4 72%	3191
November	1st to 10th	Day	4 4 1 3 2 2 3 3 5% 6% 66%	1763
	11th to 20th	Day	2 4 2 4 3 2 3 2 3 6% 69%	1800
	21st to end	Day	4 5% 2 3 2 3 3 3 4 6% 66%	1800
December	1st to 10th	Day	2 7% 1 4 2 1 2 3 3 5% 70%	2731
	11th to 20th	Day	2 4 2 4 3 2 3 2 6% 7% 66%	3026
	21st to end	Day	3 6% 2 6% 3 3 4 3 5% 7% 58%	4004
January	1st to 10th	Night	3 7% 3 6% 4 3 4 4 5% 6% 55%	6327
	11th to 20th	Night	1 6% 2 6% 4 3 4 3 5% 7% 59%	6340
	21st to end	Night	3 6% 2 5% 3 3 3 3 4 6% 62%	6562
February	1st to 10th	Night	4 6% 2 5% 4 4 4 3 4 7% 56%	2476
	11th to 20th	Night	3 8% 4 7% 4 4 4 4 5% 8% 49%	2338
	21st to end	Night	4 5% 3 5% 3 2 3 3 4 6% 62%	1980
March	1st to 10th	Night	3 5% 3 6% 3 3 3 3 4 5% 62%	5374
	11th to 20th	Night	7% 7% 2 5% 3 3 3 3 5% 6% 55%	5282
	21st to end	Night	7% 6% 2 6% 4 4 4 3 6% 8% 49%	4984
April	1st to 10th	Night	6% 6% 2 5% 3 5% 4 3 6% 7% 53%	2000
	11th to 20th	Night	9% 5% 2 5% 3 4 5% 4 6% 8% 49%	1977
	21st to end	Night	11% 7% 3 5% 5% 4 4 3 5% 9% 46%	1993
May	1st to 10th	Night	11% 7% 2 6% 4 4 3 3 6% 7% 48%	2940
	11th to 20th	Night	11% 8% 2 6% 3 4 4 4 6% 7% 44%	2810
	21st to end	Night	11% 5% 2 6% 4 4 4 4 7% 8% 45%	2762
June	1st to 10th	Night	4 3 2 4 4 4 6% 4 7% 11% 52%	1520
	11th to 20th	Night	4 4 1 4 4 4 4 4 6% 10% 55%	1520
	21st to end	Night	5% 4 2 6% 5% 4 5% 6% 6% 10% 48%	1520
July	1st to 10th	Night	6% 4 2 6% 4 5% 5% 5% 8% 10% 45%	2540
	11th to 20th	Night	4 3 1 5% 4 5% 6% 5% 7% 12% 49%	2540
	21st to end	Night	5% 4 2 5% 4 4 4 4 6% 8% 53%	2761
August	1st to 10th	Night	12% 6% 3 8% 7% 6% 6% 5% 7% 8% 33%	2985
	11th to 20th	Night	7% 5% 2 7% 5% 5% 6% 4 7% 9% 41%	3113
	21st to end	Night	3 3 1 6% 5% 6% 7% 6% 9% 11% 44%	3487
September	1st to 10th	Night	7% 4 1 4 3 3 4 4 6% 7% 56%	1900
	11th to 20th	Night	6% 3 1 3 2 3 3 3 7% 8% 61%	2000
	21st to end	Night	6% 3 1 3 3 3 3 2 4 6% 66%	2090
October	1st to 10th	Night	5% 3 1 3 2 3 3 3 4 5% 69%	3540
	11th to 20th	Night	6% 3 2 4 2 3 3 3 4 7% 61%	3778
	21st to end	Night	4 4 1 4 2 3 3 3 4 5% 68%	4335
November	1st to 10th	Night	4 4 1 3 2 3 3 3 4 7% 67%	2535
	11th to 20th	Night	2 5% 2 4 2 2 2 2 3 5% 70%	2600
	21st to end	Night	3 5% 2 5% 3 3 3 3 4 6% 63%	2600
December	1st to 10th	Night	1 3 1 4 3 3 3 3 4 6% 71%	4456
	11th to 20th	Night	2 5% 2 4 4 3 3 3 5% 7% 62%	5181
	21st to end	Night	3 5% 2 6% 4 4 4 4 6% 7% 54%	6974

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	28% 4 8% 33% 19% 9%	3639
	11th to 20th	Day	25% 5% 10% 23% 27% 10%	3640
	21st to end	Day	24% 3 9% 25% 29% 10%	4446
February	1st to 10th	Day	28% 4 9% 26% 23% 10%	1921
	11th to 20th	Day	28% 4 8% 26% 25% 8%	1959
	21st to end	Day	28% 3 8% 18% 26% 17%	1650
March	1st to 10th	Day	18% 4 6% 19% 34% 18%	4500
	11th to 20th	Day	25% 3 6% 23% 33% 9%	4699
	21st to end	Day	23% 5% 11% 38% 19% 3	5969
April	1st to 10th	Day	25% 5% 10% 25% 24% 11%	2400
	11th to 20th	Day	30% 5% 11% 25% 20% 11%	2374
	21st to end	Day	30% 5% 12% 24% 23% 6%	2405
May	1st to 10th	Day	29% 5% 11% 24% 18% 13%	4250
	11th to 20th	Day	28% 6% 15% 24% 23% 4	4102
	21st to end	Day	21% 7% 15% 23% 23% 11%	4825
June	1st to 10th	Day	20% 7% 16% 29% 18% 9%	2660
	11th to 20th	Day	21% 6% 11% 21% 24% 17%	2660
	21st to end	Day	21% 7% 11% 23% 25% 14%	2660
July	1st to 10th	Day	25% 7% 10% 17% 30% 12%	4361
	11th to 20th	Day	18% 7% 14% 24% 28% 9%	4355
	21st to end	Day	19% 6% 13% 22% 21% 19%	4651
August	1st to 10th	Day	28% 7% 16% 30% 14% 5%	3920
	11th to 20th	Day	23% 6% 15% 23% 26% 7%	3762
	21st to end	Day	21% 5% 11% 28% 24% 12%	4179
September	1st to 10th	Day	21% 5% 8% 23% 26% 16%	2280
	11th to 20th	Day	20% 4 9% 18% 30% 20%	2180
	21st to end	Day	20% 3 6% 19% 36% 17%	2090
October	1st to 10th	Day	13% 2 5% 16% 37% 26%	3418
	11th to 20th	Day	21% 3 7% 26% 33% 10%	3150
	21st to end	Day	18% 2 5% 23% 37% 15%	3191
November	1st to 10th	Day	18% 3 9% 26% 28% 16%	1763
	11th to 20th	Day	19% 3 6% 28% 33% 12%	1800
	21st to end	Day	21% 3 8% 21% 31% 16%	1800
December	1st to 10th	Day	19% 2 7% 29% 34% 9%	2731
	11th to 20th	Day	18% 2 8% 29% 35% 7%	3024
	21st to end	Day	26% 4 8% 28% 26% 8%	4004
January	1st to 10th	Night	29% 4 8% 34% 19% 6%	6327
	11th to 20th	Night	24% 4 11% 21% 26% 14%	6340
	21st to end	Night	24% 4 8% 25% 27% 11%	6562
February	1st to 10th	Night	29% 5% 9% 24% 23% 9%	2476
	11th to 20th	Night	33% 4 11% 26% 21% 5%	2338
	21st to end	Night	24% 3 7% 22% 30% 15%	1980
March	1st to 10th	Night	23% 3 7% 16% 34% 17%	5374
	11th to 20th	Night	29% 4 11% 16% 26% 14%	5282
	21st to end	Night	31% 6% 13% 31% 17% 3	4984
April	1st to 10th	Night	29% 5% 10% 24% 22% 10%	2000
	11th to 20th	Night	30% 6% 12% 23% 20% 9%	1977
	21st to end	Night	36% 5% 12% 25% 18% 5%	1993
May	1st to 10th	Night	32% 9% 15% 21% 14% 9%	2940
	11th to 20th	Night	36% 7% 17% 23% 12% 5%	2811
	21st to end	Night	34% 9% 14% 22% 16% 5%	2762
June	1st to 10th	Night	23% 10% 23% 24% 14% 6%	1520
	11th to 20th	Night	23% 8% 14% 23% 20% 13%	1520
	21st to end	Night	29% 6% 11% 24% 19% 10%	1520
July	1st to 10th	Night	31% 7% 12% 23% 23% 4	2500
	11th to 20th	Night	27% 6% 17% 22% 24% 4	2492
	21st to end	Night	28% 7% 12% 20% 22% 11%	2674
August	1st to 10th	Night	46% 8% 15% 18% 8% 5%	2977
	11th to 20th	Night	36% 8% 13% 22% 16% 4	3143
	21st to end	Night	29% 8% 15% 26% 17% 6%	3487
September	1st to 10th	Night	26% 6% 11% 21% 24% 13%	1900
	11th to 20th	Night	19% 5% 11% 22% 25% 17%	2000
	21st to end	Night	21% 4 8% 20% 34% 13%	2090
October	1st to 10th	Night	18% 5% 6% 19% 30% 22%	3540
	11th to 20th	Night	22% 4 7% 27% 27% 12%	3778
	21st to end	Night	20% 3 7% 26% 30% 15%	4335
November	1st to 10th	Night	18% 4 10% 25% 27% 16%	2535
	11th to 20th	Night	19% 3 6% 25% 34% 13%	2600
	21st to end	Night	23% 3 8% 22% 29% 15%	2600
December	1st to 10th	Night	17% 3 7% 34% 30% 9%	4456
	11th to 20th	Night	23% 2 6% 29% 34% 7%	5182
	21st to end	Night	27% 5% 9% 24% 26% 8%	6974

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	6% 5% 29% 39% 16% 5%	300
	11th to 20th	Day	11% 8% 28% 36% 17% 1	300
	21st to end	Day	6% 9% 30% 36% 15% 4	330
February	1st to 10th	Day	6% 10% 41% 32% 9% 2	300
	11th to 20th	Day	5% 5% 48% 30% 11% 1	300
	21st to end	Day	4 14% 39% 31% 8% 3	249
March	1st to 10th	Day	4 9% 30% 32% 22% 3	300
	11th to 20th	Day	9% 10% 32% 29% 18% 2	347
	21st to end	Day	12% 15% 35% 26% 11% 1	550
April	1st to 10th	Day	9% 16% 37% 23% 11% 3	500
	11th to 20th	Day	11% 17% 36% 24% 10% 2	492
	21st to end	Day	11% 17% 31% 26% 13% 2	505
May	1st to 10th	Day	13% 13% 28% 28% 15% 3	703
	11th to 20th	Day	13% 7% 27% 28% 21% 4	676
	21st to end	Day	9% 11% 28% 27% 20% 5%	734
June	1st to 10th	Day	6% 5% 20% 31% 27% 11%	680
	11th to 20th	Day	5% 6% 27% 34% 23% 5%	680
	21st to end	Day	5% 5% 22% 35% 26% 7%	680
July	1st to 10th	Day	7% 3 15% 33% 31% 12%	671
	11th to 20th	Day	3 1 13% 32% 39% 12%	668
	21st to end	Day	6% 1 10% 30% 39% 14%	739
August	1st to 10th	Day	7% 1 13% 32% 33% 13%	535
	11th to 20th	Day	5% 1 18% 34% 32% 10%	477
	21st to end	Day	4 1 17% 40% 27% 12%	539
September	1st to 10th	Day	5% 2 17% 35% 29% 13%	490
	11th to 20th	Day	4 2 19% 36% 27% 12%	390
	21st to end	Day	10% 4 19% 24% 27% 15%	300
October	1st to 10th	Day	9% 4 21% 25% 25% 16%	300
	11th to 20th	Day	6% 3 28% 33% 21% 9%	300
	21st to end	Day	10% 9% 28% 24% 21% 8%	330
November	1st to 10th	Day	8% 6% 29% 32% 21% 5%	300
	11th to 20th	Day	4 7% 33% 31% 21% 4	300
	21st to end	Day	9% 8% 24% 36% 19% 4	300
December	1st to 10th	Day	7% 5% 30% 38% 16% 4	300
	11th to 20th	Day	5% 9% 28% 37% 18% 2	300
	21st to end	Day	7% 11% 35% 34% 12% 2	330
January	1st to 10th	Night	6% 6% 32% 40% 14% 2	1000
	11th to 20th	Night	5% 7% 36% 39% 12% 1	1000
	21st to end	Night	3 7% 34% 44% 10% 2	922
February	1st to 10th	Night	7% 6% 39% 40% 7%	800
	11th to 20th	Night	7% 7% 41% 36% 9% 1	784
	21st to end	Night	6% 6% 43% 37% 7%	660
March	1st to 10th	Night	7% 8% 35% 39% 9% 1	800
	11th to 20th	Night	10% 7% 34% 37% 11% 1	790
	21st to end	Night	9% 11% 40% 33% 7%	660
April	1st to 10th	Night	9% 12% 42% 33% 5%	600
	11th to 20th	Night	12% 12% 40% 28% 7%	593
	21st to end	Night	14% 15% 29% 32% 10% 1	600
May	1st to 10th	Night	13% 9% 34% 32% 11%	600
	11th to 20th	Night	13% 7% 29% 34% 15% 1	563
	21st to end	Night	13% 9% 37% 32% 10% 1	617
June	1st to 10th	Night	6% 5% 29% 43% 17% 1	570
	11th to 20th	Night	4 4 37% 42% 12%	570
	21st to end	Night	7% 5% 26% 45% 17% 1	570
July	1st to 10th	Night	7% 3 19% 45% 25% 1	555
	11th to 20th	Night	5% 2 13% 48% 30% 2	552
	21st to end	Night	8% 1 13% 42% 33% 2	624
August	1st to 10th	Night	8% 2 15% 42% 32% 2	567
	11th to 20th	Night	6% 2 18% 52% 21% 1	564
	21st to end	Night	5% 1 14% 50% 28% 2	627
September	1st to 10th	Night	9% 3 18% 47% 22% 1	570
	11th to 20th	Night	6% 3 22% 42% 25% 3	570
	21st to end	Night	7% 3 24% 43% 22% 2	570
October	1st to 10th	Night	11% 6% 27% 38% 16% 2	604
	11th to 20th	Night	5% 6% 27% 38% 20% 3	760
	21st to end	Night	7% 9% 27% 36% 18% 3	963
November	1st to 10th	Night	6% 4 28% 43% 18% 2	975
	11th to 20th	Night	5% 6% 32% 40% 15% 2	1000
	21st to end	Night	7% 7% 29% 39% 16% 3	1000
December	1st to 10th	Night	4 5% 34% 43% 12% 2	1000
	11th to 20th	Night	6% 6% 32% 41% 14% 1	1000
	21st to end	Night	7% 10% 33% 39% 10% 1	1100

Page generated at 2025-05-08 07:34:01. Version ac07

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