Fort Sumner
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fort Sumner clear sky chart from 2005-11-06 to 2025-07-06.

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 3 1 3 2 3 3 3 5% 7% 65%	123510
	Night	4 3 1 4 3 3 3 3 5% 7% 63%	124197
Transparency	Day	18% 4 8% 20% 28% 22%	123269
	Night	20% 5% 8% 18% 28% 22%	124026
Seeing	Day	6% 6% 23% 33% 25% 8%	16025
	Night	6% 5% 30% 43% 16% 1	26077

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	5% 9% 3 4 3 2 3 2 4 6% 58%	3753
	11th to 20th	Day	2 2 1 3 2 2 3 2 4 6% 74%	4100
	21st to end	Day	3 5% 2 6% 4 3 3 3 5% 7% 59%	4621
February	1st to 10th	Day	3 5% 2 4 4 3 3 3 4 6% 66%	2000
	11th to 20th	Day	5% 5% 2 5% 3 2 3 2 4 6% 62%	1949
	21st to end	Day	2 3 2 3 3 2 3 3 3 6% 69%	1650
March	1st to 10th	Day	3 4 1 4 2 3 3 2 4 5% 69%	4500
	11th to 20th	Day	10% 4 1 3 3 3 3 3 5% 7% 59%	4857
	21st to end	Day	2 4 2 5% 3 4 4 3 6% 8% 61%	5895
April	1st to 10th	Day	3 3 1 3 3 3 3 3 4 7% 69%	2400
	11th to 20th	Day	5% 3 2 4 2 3 2 3 4 6% 68%	2371
	21st to end	Day	3 3 1 2 2 2 2 3 4 6% 72%	2400
May	1st to 10th	Day	5% 2 1 3 3 3 4 4 5% 6% 64%	5440
	11th to 20th	Day	7% 2 1 2 2 3 2 3 4 6% 68%	5811
	21st to end	Day	6% 2 1 2 2 2 3 3 5% 7% 68%	6476
June	1st to 10th	Day	4 2 1 3 2 3 4 4 7% 10% 61%	2800
	11th to 20th	Day	2 2 1 2 2 2 2 3 5% 7% 73%	2800
	21st to end	Day	4 3 1 3 3 3 3 4 6% 9% 60%	2800
July	1st to 10th	Day	7% 4 2 4 4 4 4 4 7% 10% 51%	4501
	11th to 20th	Day	2 2 1 3 2 3 3 3 6% 9% 65%	4305
	21st to end	Day	5% 3 1 3 3 3 4 4 6% 10% 58%	4316
August	1st to 10th	Day	2 2 1 2 2 3 3 4 6% 10% 66%	3784
	11th to 20th	Day	3 2 1 2 2 2 4 3 5% 8% 68%	3726
	21st to end	Day	3 2 1 4 3 4 5% 5% 7% 11% 54%	4180
September	1st to 10th	Day	6% 4 1 5% 4 4 4 3 6% 7% 56%	2280
	11th to 20th	Day	8% 3 2 3 3 3 4 3 5% 6% 59%	2201
	21st to end	Day	6% 3 1 3 2 2 2 3 4 4 70%	2090
October	1st to 10th	Day	5% 2 1 2 1 2 1 2 3 3 78%	3401
	11th to 20th	Day	8% 3 1 3 2 3 3 3 3 5% 66%	3150
	21st to end	Day	3 2 1 1 1 2 2 3 4 81%	3438
November	1st to 10th	Day	5% 3 1 3 2 2 3 2 3 7% 70%	1777
	11th to 20th	Day	2 3 1 3 2 2 3 2 4 6% 72%	1800
	21st to end	Day	7% 5% 1 3 3 2 2 2 4 5% 66%	1800
December	1st to 10th	Day	4 5% 1 4 3 3 3 2 4 6% 64%	2940
	11th to 20th	Day	2 3 1 4 3 3 3 3 4 6% 68%	3194
	21st to end	Day	3 3 1 3 2 2 2 2 3 5% 74%	4004
January	1st to 10th	Night	3 6% 2 5% 3 3 4 3 5% 7% 58%	6253
	11th to 20th	Night	2 3 1 3 2 2 2 3 4 6% 72%	5880
	21st to end	Night	3 4 1 4 3 3 4 3 5% 8% 62%	6353
February	1st to 10th	Night	3 5% 1 4 2 3 3 3 4 7% 65%	2400
	11th to 20th	Night	5% 6% 2 4 3 3 3 3 5% 6% 61%	2338
	21st to end	Night	4 5% 1 4 2 2 2 3 4 6% 66%	1980
March	1st to 10th	Night	3 3 1 3 2 2 3 2 4 5% 71%	5374
	11th to 20th	Night	9% 5% 1 4 3 2 3 2 3 5% 62%	5132
	21st to end	Night	2 3 1 3 3 3 3 3 5% 8% 67%	5059
April	1st to 10th	Night	3 3 1 3 3 2 3 4 5% 6% 67%	2000
	11th to 20th	Night	6% 3 1 4 3 2 2 3 4 7% 66%	1977
	21st to end	Night	4 3 1 2 2 3 3 3 4 6% 69%	2000
May	1st to 10th	Night	8% 2 1 3 3 2 3 3 4 7% 64%	4540
	11th to 20th	Night	7% 2 1 3 3 3 4 3 5% 6% 63%	4102
	21st to end	Night	4 2 1 2 2 2 3 3 4 6% 72%	4416
June	1st to 10th	Night	3 3 2 4 6% 5% 6% 5% 8% 8% 51%	1600
	11th to 20th	Night	2 2 1 2 3 3 3 3 5% 8% 68%	1600
	21st to end	Night	4 3 1 4 4 4 4 5% 7% 10% 55%	1600
July	1st to 10th	Night	4 3 2 6% 4 4 6% 5% 8% 11% 48%	2580
	11th to 20th	Night	4 3 1 5% 4 4 5% 4 9% 10% 50%	2659
	21st to end	Night	6% 4 2 5% 4 3 6% 5% 10% 12% 44%	3245
August	1st to 10th	Night	3 3 2 5% 4 6% 6% 6% 8% 11% 46%	3155
	11th to 20th	Night	3 2 1 3 3 4 5% 4 7% 12% 56%	3113
	21st to end	Night	3 3 1 6% 6% 5% 7% 5% 10% 11% 42%	3487
September	1st to 10th	Night	5% 4 1 5% 4 4 5% 3 6% 8% 53%	1900
	11th to 20th	Night	8% 4 1 4 3 3 3 2 5% 7% 60%	1977
	21st to end	Night	7% 3 1 2 2 2 3 2 4 6% 68%	2090
October	1st to 10th	Night	5% 2 1 2 2 1 2 2 3 4 77%	3558
	11th to 20th	Night	11% 3 1 2 2 2 2 2 3 5% 65%	3778
	21st to end	Night	5% 2 1 3 2 2 2 2 3 5% 74%	4120
November	1st to 10th	Night	5% 2 1 2 2 2 2 2 4 5% 73%	2499
	11th to 20th	Night	2 3 1 2 2 3 2 2 5% 6% 73%	2600
	21st to end	Night	6% 4 1 4 2 2 3 2 4 6% 65%	2600
December	1st to 10th	Night	5% 5% 2 4 3 3 4 3 5% 7% 61%	4250
	11th to 20th	Night	2 3 1 3 2 3 3 3 4 7% 69%	5008
	21st to end	Night	3 3 1 4 3 2 3 2 4 6% 69%	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	27% 3 6% 21% 33% 10%	3754
	11th to 20th	Day	13% 3 7% 21% 35% 21%	4100
	21st to end	Day	25% 5% 7% 18% 28% 18%	4621
February	1st to 10th	Day	21% 3 7% 19% 29% 22%	2000
	11th to 20th	Day	25% 3 5% 20% 28% 19%	1959
	21st to end	Day	17% 3 4 13% 35% 28%	1650
March	1st to 10th	Day	18% 3 4 10% 30% 36%	4500
	11th to 20th	Day	24% 4 6% 15% 26% 26%	4857
	21st to end	Day	20% 4 6% 16% 31% 23%	5895
April	1st to 10th	Day	16% 3 6% 14% 33% 27%	2400
	11th to 20th	Day	18% 4 6% 17% 27% 29%	2374
	21st to end	Day	13% 3 6% 20% 34% 24%	2400
May	1st to 10th	Day	18% 5% 10% 21% 21% 25%	5440
	11th to 20th	Day	17% 4 6% 12% 25% 35%	5815
	21st to end	Day	15% 4 9% 15% 17% 39%	6477
June	1st to 10th	Day	16% 6% 12% 25% 22% 18%	2800
	11th to 20th	Day	12% 4 7% 17% 25% 35%	2800
	21st to end	Day	21% 6% 12% 21% 23% 18%	2800
July	1st to 10th	Day	27% 6% 16% 19% 19% 13%	4432
	11th to 20th	Day	15% 6% 16% 28% 28% 7%	4230
	21st to end	Day	20% 6% 15% 28% 27% 3	4179
August	1st to 10th	Day	13% 6% 14% 31% 23% 13%	3772
	11th to 20th	Day	14% 5% 11% 24% 31% 14%	3762
	21st to end	Day	22% 7% 18% 25% 23% 5%	4179
September	1st to 10th	Day	27% 6% 12% 20% 22% 14%	2280
	11th to 20th	Day	25% 5% 8% 19% 27% 15%	2201
	21st to end	Day	17% 4 6% 19% 33% 20%	2090
October	1st to 10th	Day	13% 2 5% 12% 31% 37%	3401
	11th to 20th	Day	22% 3 7% 16% 26% 26%	3150
	21st to end	Day	10% 2 3 20% 34% 31%	3438
November	1st to 10th	Day	16% 3 6% 18% 34% 23%	1777
	11th to 20th	Day	14% 4 5% 22% 33% 21%	1800
	21st to end	Day	22% 3 5% 18% 29% 24%	1800
December	1st to 10th	Day	21% 4 6% 26% 25% 19%	2940
	11th to 20th	Day	18% 3 5% 21% 36% 17%	3192
	21st to end	Day	15% 2 4 25% 35% 20%	4004
January	1st to 10th	Night	25% 4 6% 22% 35% 9%	6253
	11th to 20th	Night	13% 4 8% 21% 38% 16%	5880
	21st to end	Night	19% 6% 8% 20% 30% 17%	6353
February	1st to 10th	Night	19% 4 7% 18% 28% 25%	2400
	11th to 20th	Night	23% 4 7% 20% 24% 22%	2338
	21st to end	Night	19% 2 5% 13% 31% 30%	1980
March	1st to 10th	Night	15% 3 4 11% 29% 38%	5374
	11th to 20th	Night	25% 4 5% 13% 24% 29%	5132
	21st to end	Night	14% 5% 8% 16% 31% 26%	5059
April	1st to 10th	Night	17% 4 7% 14% 29% 28%	2000
	11th to 20th	Night	19% 4 8% 17% 23% 30%	1977
	21st to end	Night	17% 4 8% 19% 27% 25%	2000
May	1st to 10th	Night	21% 4 11% 17% 16% 32%	4537
	11th to 20th	Night	20% 7% 7% 12% 21% 33%	4103
	21st to end	Night	13% 4 11% 15% 11% 45%	4417
June	1st to 10th	Night	25% 9% 12% 19% 18% 18%	1600
	11th to 20th	Night	14% 4 11% 16% 20% 36%	1600
	21st to end	Night	22% 7% 15% 20% 21% 15%	1600
July	1st to 10th	Night	27% 8% 17% 23% 18% 7%	2540
	11th to 20th	Night	26% 7% 14% 21% 27% 6%	2611
	21st to end	Night	28% 8% 14% 27% 22% 2	3143
August	1st to 10th	Night	27% 8% 13% 23% 17% 12%	3144
	11th to 20th	Night	19% 8% 11% 23% 30% 9%	3143
	21st to end	Night	30% 9% 18% 19% 19% 5%	3487
September	1st to 10th	Night	26% 7% 13% 20% 21% 13%	1900
	11th to 20th	Night	25% 5% 13% 19% 22% 17%	1977
	21st to end	Night	18% 3 8% 20% 30% 21%	2090
October	1st to 10th	Night	14% 3 4 11% 33% 35%	3558
	11th to 20th	Night	22% 3 6% 14% 27% 28%	3778
	21st to end	Night	15% 3 4 17% 36% 26%	4120
November	1st to 10th	Night	16% 2 5% 16% 34% 27%	2499
	11th to 20th	Night	14% 2 5% 21% 36% 22%	2600
	21st to end	Night	22% 2 6% 17% 32% 21%	2600
December	1st to 10th	Night	23% 4 6% 25% 29% 13%	4250
	11th to 20th	Night	16% 3 4 17% 40% 20%	5009
	21st to end	Night	17% 3 6% 20% 37% 17%	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	8% 7% 34% 36% 12% 3	300
	11th to 20th	Day	8% 9% 34% 35% 11% 3	300
	21st to end	Day	5% 7% 29% 41% 15% 3	330
February	1st to 10th	Day	5% 10% 33% 38% 13%	300
	11th to 20th	Day	7% 8% 45% 30% 10% 1	300
	21st to end	Day	6% 11% 43% 34% 6% 1	249
March	1st to 10th	Day	4 11% 40% 30% 14% 1	300
	11th to 20th	Day	12% 13% 31% 30% 9% 3	435
	21st to end	Day	6% 17% 38% 26% 12% 1	550
April	1st to 10th	Day	8% 13% 34% 31% 12% 2	500
	11th to 20th	Day	8% 12% 44% 25% 10% 2	492
	21st to end	Day	6% 9% 41% 30% 12% 1	500
May	1st to 10th	Day	4 8% 36% 35% 15% 3	503
	11th to 20th	Day	8% 9% 24% 33% 23% 3	700
	21st to end	Day	5% 6% 26% 40% 20% 2	789
June	1st to 10th	Day	4 3 17% 41% 28% 7%	730
	11th to 20th	Day	1 2 22% 42% 28% 5%	730
	21st to end	Day	5% 2 13% 39% 35% 6%	730
July	1st to 10th	Day	5% 1 7% 31% 40% 15%	697
	11th to 20th	Day	2 4 27% 45% 22%	595
	21st to end	Day	2 1 4 25% 41% 28%	531
August	1st to 10th	Day	2 1 5% 28% 42% 22%	487
	11th to 20th	Day	4 1 6% 27% 41% 21%	477
	21st to end	Day	4 1 6% 29% 45% 15%	539
September	1st to 10th	Day	6% 1 8% 32% 39% 14%	490
	11th to 20th	Day	6% 1 10% 33% 38% 11%	411
	21st to end	Day	10% 1 12% 30% 38% 9%	300
October	1st to 10th	Day	12% 2 18% 25% 34% 9%	300
	11th to 20th	Day	8% 4 19% 36% 26% 7%	300
	21st to end	Day	9% 5% 20% 32% 27% 7%	330
November	1st to 10th	Day	10% 7% 31% 26% 22% 4	300
	11th to 20th	Day	3 6% 28% 39% 17% 7%	300
	21st to end	Day	12% 11% 29% 29% 17% 3	300
December	1st to 10th	Day	7% 9% 28% 38% 16% 2	300
	11th to 20th	Day	4 7% 31% 42% 15% 1	300
	21st to end	Day	7% 10% 39% 32% 9% 2	330
January	1st to 10th	Night	4 6% 35% 43% 12%	965
	11th to 20th	Night	5% 5% 40% 41% 9% 1	800
	21st to end	Night	5% 5% 35% 46% 8%	880
February	1st to 10th	Night	5% 7% 41% 39% 7%	800
	11th to 20th	Night	8% 8% 40% 39% 5%	784
	21st to end	Night	7% 8% 46% 37% 2	660
March	1st to 10th	Night	7% 7% 38% 43% 5%	800
	11th to 20th	Night	10% 11% 33% 37% 9%	800
	21st to end	Night	5% 9% 45% 36% 6%	696
April	1st to 10th	Night	5% 8% 45% 38% 4	600
	11th to 20th	Night	7% 10% 47% 32% 3	593
	21st to end	Night	4 10% 46% 34% 6%	600
May	1st to 10th	Night	4 6% 41% 43% 6%	600
	11th to 20th	Night	7% 7% 31% 42% 13%	591
	21st to end	Night	5% 5% 34% 48% 8%	650
June	1st to 10th	Night	3 4 29% 51% 13%	600
	11th to 20th	Night	2 3 32% 52% 12%	600
	21st to end	Night	4 3 24% 49% 20%	600
July	1st to 10th	Night	6% 1 11% 44% 36% 2	570
	11th to 20th	Night	3 1 6% 47% 42% 1	552
	21st to end	Night	3 2 6% 43% 44% 2	624
August	1st to 10th	Night	5% 1 8% 38% 46% 2	567
	11th to 20th	Night	5% 1 8% 43% 41% 2	564
	21st to end	Night	5% 1 7% 42% 43% 1	627
September	1st to 10th	Night	6% 1 9% 53% 29% 1	570
	11th to 20th	Night	9% 2 14% 54% 21% 1	570
	21st to end	Night	7% 3 17% 50% 22% 1	570
October	1st to 10th	Night	8% 2 22% 47% 20% 1	609
	11th to 20th	Night	8% 3 26% 46% 17% 1	760
	21st to end	Night	7% 5% 23% 42% 23% 1	836
November	1st to 10th	Night	6% 3 24% 50% 17%	939
	11th to 20th	Night	3 5% 31% 43% 16% 1	1000
	21st to end	Night	8% 4 30% 43% 14% 1	1000
December	1st to 10th	Night	7% 6% 33% 44% 9%	1000
	11th to 20th	Night	5% 6% 35% 46% 9%	1000
	21st to end	Night	8% 8% 39% 38% 8%	1100

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