City of Rocks National Reserve
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the City of Rocks National Reserve clear sky chart from 2005-11-06 to 2025-10-04.

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	3 6% 2 7% 5% 5% 5% 4 6% 7% 51%	134730
	Night	2 5% 2 7% 5% 5% 5% 4 6% 7% 51%	131998
Transparency	Day	17% 40% 5% 14% 15% 10%	129475
	Night	17% 40% 6% 15% 15% 7%	128253
Seeing	Day	15% 20% 30% 23% 10% 2	15738
	Night	12% 13% 21% 32% 19% 4	25452

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	1 9% 4 14% 10% 9% 7% 4 6% 8% 29%	3639
	11th to 20th	Day	1 7% 5% 13% 6% 6% 5% 5% 6% 7% 39%	3640
	21st to end	Day	2 7% 3 9% 6% 4 5% 4 5% 7% 48%	4441
February	1st to 10th	Day	3 10% 5% 13% 8% 7% 6% 5% 6% 6% 31%	1800
	11th to 20th	Day	3 11% 5% 11% 8% 7% 6% 4 7% 6% 31%	1905
	21st to end	Day	2 9% 4 12% 9% 6% 6% 5% 6% 8% 32%	1650
March	1st to 10th	Day	2 11% 4 11% 7% 6% 6% 4 5% 6% 38%	4601
	11th to 20th	Day	2 8% 4 8% 4 4 5% 5% 6% 7% 47%	5000
	21st to end	Day	3 10% 4 13% 7% 7% 7% 5% 7% 7% 29%	5486
April	1st to 10th	Day	4 11% 4 9% 5% 5% 6% 4 6% 7% 38%	2323
	11th to 20th	Day	5% 9% 4 8% 6% 5% 5% 4 6% 6% 42%	2512
	21st to end	Day	5% 9% 3 9% 6% 5% 6% 4 6% 8% 42%	2600
May	1st to 10th	Day	4 6% 2 6% 4 5% 6% 5% 7% 7% 48%	5880
	11th to 20th	Day	4 5% 2 6% 5% 4 5% 4 5% 7% 51%	5841
	21st to end	Day	3 5% 2 6% 4 4 5% 4 7% 8% 52%	6423
June	1st to 10th	Day	4 5% 1 6% 5% 4 5% 4 7% 8% 50%	2784
	11th to 20th	Day	5% 4 1 5% 3 4 4 4 5% 9% 57%	2800
	21st to end	Day	2 2 1 3 2 3 4 3 5% 6% 69%	2800
July	1st to 10th	Day	1 1 1 3 3 3 3 3 5% 5% 72%	6319
	11th to 20th	Day	1 2 1 4 4 4 4 4 5% 6% 64%	6320
	21st to end	Day	2 3 1 4 3 4 4 4 6% 7% 62%	6493
August	1st to 10th	Day	2 2 1 4 3 3 5% 4 6% 8% 61%	5779
	11th to 20th	Day	1 2 1 3 3 4 5% 3 6% 7% 67%	5798
	21st to end	Day	3 4 2 5% 3 3 4 3 5% 6% 62%	6322
September	1st to 10th	Day	3 2 1 3 3 3 4 3 4 7% 66%	2289
	11th to 20th	Day	3 4 1 5% 4 3 4 4 6% 7% 61%	2200
	21st to end	Day	5% 4 1 4 3 3 4 3 3 5% 66%	2200
October	1st to 10th	Day	3 4 1 4 3 3 4 3 5% 5% 64%	3493
	11th to 20th	Day	3 5% 2 5% 3 3 3 3 5% 6% 63%	3150
	21st to end	Day	2 5% 2 5% 4 4 4 4 6% 9% 57%	3168
November	1st to 10th	Day	5% 11% 3 8% 5% 4 4 4 6% 7% 43%	1764
	11th to 20th	Day	5% 8% 3 8% 6% 5% 5% 5% 7% 8% 40%	1800
	21st to end	Day	3 11% 3 8% 6% 7% 5% 4 5% 7% 41%	1800
December	1st to 10th	Day	2 6% 3 7% 4 4 3 3 4 5% 59%	2663
	11th to 20th	Day	2 9% 4 11% 7% 7% 7% 6% 8% 9% 30%	3043
	21st to end	Day	3 9% 4 12% 7% 8% 7% 5% 7% 7% 31%	4004
January	1st to 10th	Night	2 7% 4 11% 8% 7% 7% 6% 8% 8% 33%	6306
	11th to 20th	Night	2 7% 3 11% 8% 6% 7% 7% 7% 7% 35%	6320
	21st to end	Night	1 6% 4 7% 5% 5% 6% 5% 7% 6% 48%	6530
February	1st to 10th	Night	2 9% 4 12% 7% 7% 7% 6% 7% 7% 32%	2600
	11th to 20th	Night	2 8% 3 10% 7% 6% 5% 4 7% 7% 41%	2381
	21st to end	Night	1 7% 3 10% 6% 6% 6% 5% 7% 9% 40%	1980
March	1st to 10th	Night	2 9% 4 8% 5% 5% 5% 4 7% 8% 43%	5293
	11th to 20th	Night	1 5% 3 7% 5% 5% 5% 4 7% 9% 49%	5000
	21st to end	Night	3 6% 2 7% 5% 5% 7% 6% 8% 10% 42%	5489
April	1st to 10th	Night	3 8% 3 6% 5% 5% 5% 4 7% 7% 46%	2075
	11th to 20th	Night	4 6% 2 6% 4 5% 6% 5% 7% 6% 50%	1836
	21st to end	Night	5% 5% 2 6% 6% 5% 5% 4 6% 8% 50%	1800
May	1st to 10th	Night	2 5% 2 6% 4 4 3 3 6% 7% 57%	4100
	11th to 20th	Night	2 4 2 5% 4 4 5% 4 6% 9% 55%	4074
	21st to end	Night	3 4 2 5% 3 4 4 4 6% 7% 58%	4474
June	1st to 10th	Night	3 4 1 5% 5% 5% 4 5% 7% 9% 53%	1611
	11th to 20th	Night	4 4 2 4 2 4 4 4 4 7% 61%	1600
	21st to end	Night	2 2 1 3 3 3 3 3 5% 7% 68%	1600
July	1st to 10th	Night	1 2 1 3 3 3 3 3 4 4 72%	3640
	11th to 20th	Night	1 2 1 4 3 3 3 3 4 6% 71%	3640
	21st to end	Night	1 2 1 4 4 3 4 4 5% 7% 65%	4372
August	1st to 10th	Night	1 2 2 4 3 4 5% 3 6% 6% 63%	4033
	11th to 20th	Night	1 2 1 5% 4 4 5% 4 4 6% 64%	4051
	21st to end	Night	2 3 1 4 3 4 4 3 5% 5% 66%	4645
September	1st to 10th	Night	2 2 1 3 3 3 3 3 5% 6% 70%	2110
	11th to 20th	Night	4 3 1 3 2 3 3 3 4 5% 68%	2200
	21st to end	Night	5% 2 1 3 2 3 3 3 3 4 71%	2200
October	1st to 10th	Night	3 3 1 3 3 2 2 3 4 5% 70%	3551
	11th to 20th	Night	3 4 1 5% 3 4 5% 4 6% 6% 57%	3778
	21st to end	Night	2 3 2 6% 4 5% 5% 4 6% 9% 55%	4386
November	1st to 10th	Night	6% 7% 2 7% 5% 4 6% 4 6% 7% 45%	2535
	11th to 20th	Night	3 6% 3 7% 6% 5% 6% 6% 6% 7% 45%	2600
	21st to end	Night	2 8% 3 7% 6% 6% 5% 5% 7% 7% 44%	2600
December	1st to 10th	Night	2 5% 2 6% 4 4 4 3 5% 6% 58%	4470
	11th to 20th	Night	3 8% 3 9% 6% 7% 6% 5% 9% 9% 35%	5166
	21st to end	Night	3 8% 3 10% 7% 7% 7% 6% 8% 9% 32%	6952

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	35% 31% 10% 14% 9%	3639
	11th to 20th	Day	30% 29% 9% 22% 8% 2	3640
	21st to end	Day	23% 30% 8% 19% 18% 3	4441
February	1st to 10th	Day	20% 68% 5% 3 3 1	1800
	11th to 20th	Day	17% 64% 6% 8% 3 2	1915
	21st to end	Day	16% 64% 5% 8% 6% 2	1650
March	1st to 10th	Day	30% 32% 5% 16% 12% 6%	4601
	11th to 20th	Day	19% 31% 8% 25% 17%	5000
	21st to end	Day	33% 34% 12% 16% 4	5486
April	1st to 10th	Day	16% 64% 7% 8% 5%	2323
	11th to 20th	Day	13% 64% 5% 10% 7% 1	2515
	21st to end	Day	15% 64% 4 11% 6%	2600
May	1st to 10th	Day	19% 34% 6% 19% 19% 3	5880
	11th to 20th	Day	21% 30% 5% 22% 19% 3	5844
	21st to end	Day	14% 31% 5% 22% 26% 3	6424
June	1st to 10th	Day	6% 63% 5% 13% 11% 2	2784
	11th to 20th	Day	7% 62% 5% 12% 10% 3	2800
	21st to end	Day	7% 61% 3 9% 14% 7%	2800
July	1st to 10th	Day	8% 27% 2 8% 11% 43%	6251
	11th to 20th	Day	13% 27% 3 5% 16% 36%	6245
	21st to end	Day	14% 27% 3 5% 23% 29%	6306
August	1st to 10th	Day	13% 37% 3 9% 19% 18%	4208
	11th to 20th	Day	8% 38% 3 10% 24% 18%	4197
	21st to end	Day	10% 36% 2 11% 20% 22%	4553
September	1st to 10th	Day	9% 57% 4 8% 16% 7%	2289
	11th to 20th	Day	10% 58% 4 12% 13% 4	2200
	21st to end	Day	12% 57% 2 9% 15% 4	2200
October	1st to 10th	Day	9% 37% 3 9% 24% 18%	3493
	11th to 20th	Day	11% 37% 3 14% 27% 8%	3150
	21st to end	Day	13% 38% 5% 24% 14% 6%	3168
November	1st to 10th	Day	15% 58% 6% 11% 9% 1	1764
	11th to 20th	Day	15% 59% 7% 14% 5% 1	1800
	21st to end	Day	20% 59% 6% 8% 5% 2	1800
December	1st to 10th	Day	12% 38% 5% 33% 12%	2663
	11th to 20th	Day	27% 34% 14% 16% 8%	3042
	21st to end	Day	29% 31% 9% 17% 12% 2	4004
January	1st to 10th	Night	31% 34% 7% 17% 10% 1	6306
	11th to 20th	Night	29% 33% 7% 22% 8% 2	6320
	21st to end	Night	21% 32% 9% 18% 18% 3	6530
February	1st to 10th	Night	18% 68% 6% 4 4 1	2600
	11th to 20th	Night	16% 64% 5% 8% 6% 1	2382
	21st to end	Night	13% 65% 4 11% 5% 2	1980
March	1st to 10th	Night	26% 32% 6% 15% 14% 8%	5293
	11th to 20th	Night	18% 32% 8% 21% 20%	5000
	21st to end	Night	21% 33% 14% 20% 12% 1	5489
April	1st to 10th	Night	10% 65% 7% 11% 6% 1	2075
	11th to 20th	Night	9% 65% 5% 11% 8% 1	1836
	21st to end	Night	14% 62% 5% 11% 8%	1800
May	1st to 10th	Night	15% 31% 8% 21% 24% 2	4097
	11th to 20th	Night	17% 30% 5% 21% 23% 4	4075
	21st to end	Night	13% 30% 5% 23% 26% 4	4474
June	1st to 10th	Night	7% 63% 6% 10% 12% 2	1611
	11th to 20th	Night	8% 63% 3 11% 12% 4	1600
	21st to end	Night	6% 60% 3 8% 14% 9%	1600
July	1st to 10th	Night	10% 26% 2 8% 12% 43%	3600
	11th to 20th	Night	11% 26% 1 4 19% 40%	3592
	21st to end	Night	11% 26% 2 6% 25% 29%	4247
August	1st to 10th	Night	12% 37% 2 8% 17% 23%	2928
	11th to 20th	Night	10% 36% 2 10% 25% 16%	2928
	21st to end	Night	8% 36% 2 8% 22% 24%	3342
September	1st to 10th	Night	7% 57% 3 8% 17% 8%	2110
	11th to 20th	Night	8% 57% 3 12% 16% 5%	2200
	21st to end	Night	10% 57% 4 9% 17% 4	2200
October	1st to 10th	Night	7% 36% 2 8% 28% 18%	3551
	11th to 20th	Night	15% 38% 3 16% 21% 7%	3778
	21st to end	Night	14% 38% 5% 23% 15% 4	4386
November	1st to 10th	Night	12% 59% 6% 10% 12% 1	2535
	11th to 20th	Night	12% 60% 6% 14% 8% 1	2600
	21st to end	Night	16% 62% 4 9% 8% 1	2600
December	1st to 10th	Night	12% 39% 5% 29% 15%	4470
	11th to 20th	Night	24% 36% 13% 17% 9%	5166
	21st to end	Night	28% 31% 14% 14% 10% 3	6952

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	27% 25% 24% 16% 8% 1	200
	11th to 20th	Day	16% 27% 25% 21% 10% 3	200
	21st to end	Day	14% 25% 26% 25% 8% 2	315
February	1st to 10th	Day	27% 33% 22% 12% 4 1	300
	11th to 20th	Day	25% 29% 25% 15% 6%	450
	21st to end	Day	18% 29% 30% 18% 5%	414
March	1st to 10th	Day	22% 24% 34% 16% 4	500
	11th to 20th	Day	18% 27% 28% 17% 9% 1	500
	21st to end	Day	23% 32% 28% 13% 3 1	550
April	1st to 10th	Day	23% 25% 27% 16% 7% 1	500
	11th to 20th	Day	23% 27% 30% 14% 6%	492
	21st to end	Day	21% 26% 28% 19% 4 2	500
May	1st to 10th	Day	17% 24% 32% 20% 7% 1	503
	11th to 20th	Day	21% 22% 29% 20% 8% 1	528
	21st to end	Day	16% 17% 29% 23% 12% 3	573
June	1st to 10th	Day	11% 15% 32% 26% 13% 3	530
	11th to 20th	Day	14% 23% 37% 18% 8% 1	530
	21st to end	Day	5% 17% 39% 25% 12% 2	530
July	1st to 10th	Day	5% 13% 38% 31% 11% 2	526
	11th to 20th	Day	4 12% 44% 29% 9% 2	524
	21st to end	Day	4 9% 32% 35% 15% 4	575
August	1st to 10th	Day	8% 14% 32% 29% 14% 3	527
	11th to 20th	Day	4 12% 32% 30% 16% 6%	517
	21st to end	Day	6% 13% 28% 28% 20% 5%	583
September	1st to 10th	Day	6% 10% 28% 32% 16% 8%	530
	11th to 20th	Day	9% 14% 33% 25% 15% 5%	530
	21st to end	Day	10% 14% 28% 26% 16% 5%	530
October	1st to 10th	Day	15% 15% 25% 24% 16% 5%	485
	11th to 20th	Day	14% 18% 21% 22% 21% 4	300
	21st to end	Day	15% 22% 30% 23% 8% 1	330
November	1st to 10th	Day	23% 19% 25% 20% 12% 1	300
	11th to 20th	Day	16% 21% 29% 22% 10% 2	300
	21st to end	Day	20% 20% 19% 27% 11% 2	300
December	1st to 10th	Day	20% 18% 27% 19% 12% 4	300
	11th to 20th	Day	16% 27% 26% 21% 8% 2	246
	21st to end	Day	26% 25% 25% 17% 7% 1	220
January	1st to 10th	Night	18% 15% 20% 28% 17% 3	800
	11th to 20th	Night	16% 15% 22% 28% 16% 4	800
	21st to end	Night	15% 15% 21% 27% 18% 4	880
February	1st to 10th	Night	18% 23% 25% 21% 13% 2	800
	11th to 20th	Night	15% 18% 23% 27% 14% 2	784
	21st to end	Night	13% 18% 26% 27% 14% 2	660
March	1st to 10th	Night	14% 16% 26% 30% 11% 3	800
	11th to 20th	Night	11% 17% 23% 30% 17% 3	800
	21st to end	Night	18% 19% 24% 26% 12% 1	880
April	1st to 10th	Night	17% 16% 22% 30% 13% 2	800
	11th to 20th	Night	11% 20% 29% 27% 11% 2	648
	21st to end	Night	12% 17% 26% 30% 13% 2	600
May	1st to 10th	Night	12% 13% 27% 29% 18% 2	600
	11th to 20th	Night	11% 11% 21% 31% 22% 4	591
	21st to end	Night	13% 10% 18% 29% 26% 4	650
June	1st to 10th	Night	7% 9% 15% 40% 25% 5%	411
	11th to 20th	Night	9% 10% 22% 42% 16% 2	400
	21st to end	Night	5% 4 21% 40% 26% 5%	400
July	1st to 10th	Night	3 1 12% 49% 29% 6%	390
	11th to 20th	Night	3 2 18% 48% 27% 2	388
	21st to end	Night	3 1 14% 43% 34% 4	609
August	1st to 10th	Night	6% 4 16% 45% 27% 3	597
	11th to 20th	Night	4 5% 14% 43% 30% 4	594
	21st to end	Night	6% 5% 17% 41% 28% 3	718
September	1st to 10th	Night	5% 4 15% 38% 30% 9%	800
	11th to 20th	Night	7% 5% 17% 34% 29% 9%	800
	21st to end	Night	8% 7% 16% 32% 26% 11%	800
October	1st to 10th	Night	10% 9% 20% 33% 23% 6%	772
	11th to 20th	Night	10% 12% 16% 30% 27% 5%	760
	21st to end	Night	12% 13% 21% 28% 21% 4	836
November	1st to 10th	Night	16% 14% 18% 29% 20% 4	780
	11th to 20th	Night	14% 15% 25% 30% 15% 2	800
	21st to end	Night	12% 17% 20% 28% 18% 6%	800
December	1st to 10th	Night	15% 15% 22% 29% 17% 1	939
	11th to 20th	Night	18% 15% 23% 29% 13% 3	885
	21st to end	Night	21% 19% 24% 26% 8% 2	880

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