Roswell
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Roswell clear sky chart from 2005-11-06 to 2024-11-03.

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	5% 3 1 3 3 3 3 3 5% 7% 64%	100707
	Night	5% 3 1 3 3 3 3 3 5% 7% 63%	98477
Transparency	Day	20% 4 7% 18% 27% 24%	100473
	Night	21% 4 7% 17% 28% 24%	98303
Seeing	Day	5% 5% 19% 34% 28% 10%	14971
	Night	6% 3 25% 45% 20% 1	25024

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 8% 2 5% 3 2 4 3 4 5% 60%	2763
	11th to 20th	Day	2 3 1 1 2 1 2 2 4 6% 76%	2860
	21st to end	Day	5% 5% 2 6% 3 3 4 3 5% 7% 57%	3271
February	1st to 10th	Day	3 5% 2 4 3 2 3 3 4 5% 68%	1900
	11th to 20th	Day	5% 5% 2 3 2 2 3 2 5% 6% 64%	1849
	21st to end	Day	2 4 1 4 2 3 3 2 4 5% 70%	1570
March	1st to 10th	Day	4 3 1 3 2 2 3 4 5% 7% 66%	3130
	11th to 20th	Day	13% 4 1 4 3 3 3 3 4 7% 56%	3449
	21st to end	Day	3 5% 1 5% 3 4 4 3 5% 7% 59%	4089
April	1st to 10th	Day	3 3 1 2 2 2 2 3 3 6% 72%	2280
	11th to 20th	Day	4 3 1 3 2 2 2 3 4 5% 69%	2251
	21st to end	Day	3 2 1 3 2 2 2 3 3 5% 74%	2280
May	1st to 10th	Day	4 2 1 2 2 2 2 2 3 5% 76%	3800
	11th to 20th	Day	7% 3 1 3 3 3 3 3 5% 7% 62%	3909
	21st to end	Day	4 2 1 2 2 2 2 3 4 6% 73%	4489
June	1st to 10th	Day	2 2 1 3 3 3 3 4 7% 11% 60%	2615
	11th to 20th	Day	2 2 1 2 3 2 3 4 5% 7% 70%	2660
	21st to end	Day	5% 2 1 3 3 3 3 4 7% 9% 58%	2660
July	1st to 10th	Day	6% 4 2 5% 4 5% 6% 5% 9% 10% 45%	4416
	11th to 20th	Day	3 2 1 3 3 4 4 4 5% 9% 62%	4110
	21st to end	Day	5% 3 2 4 3 3 4 4 7% 11% 55%	4271
August	1st to 10th	Day	2 2 1 2 2 3 3 3 6% 9% 67%	3784
	11th to 20th	Day	4 2 1 3 2 3 3 3 6% 8% 66%	3726
	21st to end	Day	4 3 1 4 3 5% 5% 5% 8% 11% 51%	4180
September	1st to 10th	Day	8% 5% 2 3 3 3 4 3 7% 8% 54%	2280
	11th to 20th	Day	8% 4 1 3 3 4 4 3 5% 6% 58%	2214
	21st to end	Day	7% 3 1 2 2 2 3 2 4 6% 69%	2090
October	1st to 10th	Day	6% 3 1 4 3 3 3 3 4 6% 65%	2034
	11th to 20th	Day	7% 3 1 2 2 2 2 1 3 3 73%	1900
	21st to end	Day	5% 2 2 1 1 2 2 3 4 76%	2090
November	1st to 10th	Day	5% 2 1 2 1 2 2 2 4 5% 74%	1764
	11th to 20th	Day	3 3 1 4 2 2 3 3 3 6% 70%	1710
	21st to end	Day	6% 5% 1 3 3 2 3 2 5% 4 65%	1710
December	1st to 10th	Day	6% 4 2 4 2 2 3 3 4 7% 63%	1710
	11th to 20th	Day	4 2 1 3 3 3 4 3 7% 9% 61%	2099
	21st to end	Day	4 4 1 3 2 2 3 2 3 5% 70%	2794
January	1st to 10th	Night	3 6% 3 4 3 3 3 3 4 6% 62%	4221
	11th to 20th	Night	3 3 1 3 2 2 2 2 5% 6% 71%	4110
	21st to end	Night	5% 4 2 4 3 3 4 4 5% 7% 60%	4392
February	1st to 10th	Night	3 4 1 4 2 2 3 2 5% 7% 66%	2280
	11th to 20th	Night	7% 5% 1 4 2 3 3 2 5% 5% 63%	2218
	21st to end	Night	3 5% 2 2 3 3 5% 3 4 5% 65%	1884
March	1st to 10th	Night	4 5% 2 3 2 2 2 2 3 6% 70%	3734
	11th to 20th	Night	18% 4 1 4 2 2 2 2 4 5% 56%	3526
	21st to end	Night	2 6% 2 3 3 3 3 3 5% 7% 61%	3555
April	1st to 10th	Night	3 3 1 3 3 2 3 2 4 6% 70%	1900
	11th to 20th	Night	6% 2 1 3 2 3 3 2 4 5% 69%	1877
	21st to end	Night	4 3 2 2 2 3 3 4 5% 71%	1900
May	1st to 10th	Night	4 2 2 2 1 2 2 3 5% 77%	3170
	11th to 20th	Night	9% 2 1 3 2 3 3 2 4 6% 64%	2992
	21st to end	Night	3 1 2 1 2 2 2 3 4 79%	3098
June	1st to 10th	Night	3 2 1 3 3 4 5% 4 8% 10% 57%	1558
	11th to 20th	Night	2 2 1 2 2 3 3 3 5% 7% 71%	1520
	21st to end	Night	4 2 1 4 3 4 4 5% 8% 10% 53%	1520
July	1st to 10th	Night	5% 3 2 5% 4 4 5% 5% 8% 11% 48%	2540
	11th to 20th	Night	3 3 2 4 3 4 4 4 8% 9% 56%	2854
	21st to end	Night	6% 4 2 5% 3 3 4 5% 9% 15% 43%	3287
August	1st to 10th	Night	3 2 1 4 4 4 5% 5% 8% 13% 50%	3155
	11th to 20th	Night	3 2 1 3 3 4 4 4 6% 11% 60%	3113
	21st to end	Night	3 4 2 5% 4 6% 5% 5% 9% 13% 43%	3487
September	1st to 10th	Night	8% 4 1 3 4 3 4 4 6% 10% 54%	1900
	11th to 20th	Night	7% 4 1 4 3 3 3 3 5% 7% 60%	1966
	21st to end	Night	7% 3 2 3 2 2 3 2 4 6% 67%	2090
October	1st to 10th	Night	7% 3 1 3 3 2 3 2 4 5% 67%	2141
	11th to 20th	Night	7% 3 1 3 2 2 2 1 2 4 74%	2280
	21st to end	Night	6% 2 1 2 2 2 2 1 3 5% 74%	2508
November	1st to 10th	Night	5% 2 1 2 1 2 2 2 4 6% 72%	2339
	11th to 20th	Night	3 2 1 3 2 2 2 2 4 6% 73%	2470
	21st to end	Night	7% 4 1 4 3 2 3 2 4 5% 65%	2470
December	1st to 10th	Night	7% 4 2 3 2 2 2 2 4 7% 64%	2470
	11th to 20th	Night	4 3 1 4 3 4 4 3 5% 7% 62%	3079
	21st to end	Night	4 4 1 3 2 3 3 3 4 6% 68%	4873

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	26% 4 4 17% 29% 21%	2764
	11th to 20th	Day	12% 2 8% 17% 45% 16%	2860
	21st to end	Day	26% 4 7% 20% 28% 15%	3271
February	1st to 10th	Day	20% 3 6% 18% 26% 27%	1900
	11th to 20th	Day	23% 2 4 17% 29% 24%	1859
	21st to end	Day	18% 3 3 11% 31% 35%	1570
March	1st to 10th	Day	18% 3 3 11% 33% 32%	3130
	11th to 20th	Day	29% 4 4 15% 27% 19%	3449
	21st to end	Day	23% 5% 4 13% 25% 30%	4089
April	1st to 10th	Day	15% 3 4 11% 30% 36%	2280
	11th to 20th	Day	17% 3 5% 13% 24% 38%	2254
	21st to end	Day	14% 3 5% 15% 29% 36%	2280
May	1st to 10th	Day	14% 2 4 13% 17% 50%	3800
	11th to 20th	Day	21% 5% 8% 13% 24% 29%	3913
	21st to end	Day	13% 4 5% 13% 16% 49%	4489
June	1st to 10th	Day	16% 6% 9% 23% 25% 21%	2615
	11th to 20th	Day	13% 4 5% 15% 23% 40%	2660
	21st to end	Day	20% 5% 10% 19% 24% 21%	2660
July	1st to 10th	Day	30% 6% 13% 22% 18% 10%	4347
	11th to 20th	Day	19% 4 11% 27% 30% 10%	4041
	21st to end	Day	23% 5% 11% 27% 30% 4	4136
August	1st to 10th	Day	14% 4 8% 27% 33% 13%	3772
	11th to 20th	Day	16% 4 10% 21% 32% 16%	3762
	21st to end	Day	24% 5% 16% 25% 23% 6%	4179
September	1st to 10th	Day	27% 6% 12% 18% 21% 17%	2280
	11th to 20th	Day	26% 4 8% 20% 28% 13%	2214
	21st to end	Day	18% 3 4 19% 33% 22%	2090
October	1st to 10th	Day	22% 4 6% 19% 24% 26%	2034
	11th to 20th	Day	18% 2 5% 12% 30% 32%	1900
	21st to end	Day	14% 2 3 21% 33% 27%	2090
November	1st to 10th	Day	14% 2 5% 17% 32% 29%	1764
	11th to 20th	Day	18% 3 4 17% 34% 23%	1710
	21st to end	Day	23% 3 5% 14% 31% 25%	1710
December	1st to 10th	Day	23% 3 6% 23% 31% 15%	1710
	11th to 20th	Day	21% 4 8% 21% 28% 18%	2097
	21st to end	Day	19% 2 4 20% 31% 24%	2794
January	1st to 10th	Night	23% 3 4 17% 37% 16%	4221
	11th to 20th	Night	15% 3 8% 16% 40% 18%	4110
	21st to end	Night	23% 5% 6% 22% 30% 14%	4392
February	1st to 10th	Night	18% 3 6% 17% 26% 30%	2280
	11th to 20th	Night	24% 3 4 14% 27% 28%	2218
	21st to end	Night	21% 3 4 8% 26% 37%	1884
March	1st to 10th	Night	18% 3 2 10% 29% 38%	3734
	11th to 20th	Night	32% 4 4 14% 27% 19%	3526
	21st to end	Night	21% 4 4 12% 29% 30%	3555
April	1st to 10th	Night	16% 2 5% 11% 25% 39%	1900
	11th to 20th	Night	19% 3 6% 13% 22% 38%	1877
	21st to end	Night	15% 4 5% 17% 23% 35%	1900
May	1st to 10th	Night	13% 2 4 11% 15% 55%	3170
	11th to 20th	Night	20% 5% 9% 17% 18% 31%	2993
	21st to end	Night	11% 3 5% 12% 12% 57%	3099
June	1st to 10th	Night	20% 7% 11% 20% 21% 22%	1558
	11th to 20th	Night	13% 3 6% 18% 20% 40%	1520
	21st to end	Night	22% 7% 14% 19% 20% 18%	1520
July	1st to 10th	Night	27% 5% 14% 28% 19% 7%	2500
	11th to 20th	Night	22% 4 12% 22% 33% 7%	2801
	21st to end	Night	28% 6% 12% 28% 23% 3	3184
August	1st to 10th	Night	22% 6% 9% 24% 28% 11%	3144
	11th to 20th	Night	18% 5% 9% 22% 34% 13%	3143
	21st to end	Night	29% 6% 15% 22% 20% 7%	3487
September	1st to 10th	Night	25% 7% 12% 19% 20% 16%	1900
	11th to 20th	Night	24% 5% 12% 20% 24% 16%	1966
	21st to end	Night	19% 3 5% 17% 33% 22%	2090
October	1st to 10th	Night	21% 3 7% 16% 27% 26%	2141
	11th to 20th	Night	18% 2 4 10% 32% 33%	2280
	21st to end	Night	16% 3 4 15% 31% 32%	2508
November	1st to 10th	Night	15% 3 4 14% 33% 31%	2339
	11th to 20th	Night	14% 3 4 18% 34% 27%	2470
	21st to end	Night	23% 3 4 15% 32% 24%	2470
December	1st to 10th	Night	22% 2 5% 21% 30% 21%	2470
	11th to 20th	Night	23% 3 5% 20% 33% 16%	3080
	21st to end	Night	19% 2 4 15% 38% 22%	4873

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	7% 6% 22% 43% 21% 2	270
	11th to 20th	Day	10% 4 27% 38% 18% 3	270
	21st to end	Day	4 7% 24% 41% 22% 3	297
February	1st to 10th	Day	7% 8% 27% 36% 20% 2	270
	11th to 20th	Day	9% 8% 30% 37% 14% 2	270
	21st to end	Day	8% 12% 35% 36% 7% 1	225
March	1st to 10th	Day	4 8% 32% 41% 14% 2	270
	11th to 20th	Day	10% 11% 29% 32% 15% 3	432
	21st to end	Day	5% 18% 35% 28% 12% 1	506
April	1st to 10th	Day	7% 10% 34% 35% 13% 2	460
	11th to 20th	Day	6% 14% 36% 32% 10% 2	452
	21st to end	Day	5% 12% 33% 34% 13% 3	460
May	1st to 10th	Day	3 7% 36% 36% 15% 2	463
	11th to 20th	Day	7% 4 22% 37% 23% 6%	567
	21st to end	Day	5% 6% 24% 42% 21% 2	734
June	1st to 10th	Day	3 1 19% 39% 32% 7%	680
	11th to 20th	Day	2 2 19% 41% 30% 7%	680
	21st to end	Day	5% 2 10% 36% 39% 8%	680
July	1st to 10th	Day	5% 1 4 27% 46% 17%	670
	11th to 20th	Day	1 4 25% 41% 28%	484
	21st to end	Day	2 1 2 25% 42% 28%	531
August	1st to 10th	Day	2 1 4 22% 46% 25%	487
	11th to 20th	Day	5% 1 5% 25% 39% 26%	477
	21st to end	Day	5% 1 4 25% 41% 24%	539
September	1st to 10th	Day	7% 8% 28% 39% 18%	490
	11th to 20th	Day	4 2 8% 29% 43% 13%	424
	21st to end	Day	8% 2 9% 24% 38% 18%	300
October	1st to 10th	Day	10% 1 13% 31% 31% 14%	300
	11th to 20th	Day	9% 4 13% 29% 34% 10%	300
	21st to end	Day	10% 4 13% 32% 31% 11%	330
November	1st to 10th	Day	11% 5% 18% 35% 25% 5%	276
	11th to 20th	Day	2 7% 19% 34% 29% 8%	270
	21st to end	Day	9% 8% 25% 36% 19% 4	270
December	1st to 10th	Day	8% 5% 20% 42% 22% 3	270
	11th to 20th	Day	3 9% 23% 43% 21% 2	270
	21st to end	Day	10% 3 23% 50% 14% 1	297
January	1st to 10th	Night	6% 3 25% 52% 14% 1	832
	11th to 20th	Night	7% 4 28% 46% 13% 1	760
	21st to end	Night	5% 5% 31% 46% 13%	836
February	1st to 10th	Night	5% 4 35% 42% 14%	760
	11th to 20th	Night	8% 5% 36% 44% 6%	744
	21st to end	Night	6% 6% 45% 39% 3	628
March	1st to 10th	Night	8% 6% 37% 41% 8%	760
	11th to 20th	Night	10% 8% 32% 40% 10%	760
	21st to end	Night	4 7% 44% 40% 5%	679
April	1st to 10th	Night	4 8% 44% 40% 4	570
	11th to 20th	Night	7% 8% 43% 39% 3	563
	21st to end	Night	4 6% 45% 38% 6%	570
May	1st to 10th	Night	4 4 41% 46% 5%	570
	11th to 20th	Night	8% 3 28% 48% 12%	561
	21st to end	Night	3 3 33% 51% 9%	617
June	1st to 10th	Night	4 1 26% 54% 14%	570
	11th to 20th	Night	3 1 28% 56% 11%	570
	21st to end	Night	4 1 19% 53% 23%	570
July	1st to 10th	Night	5% 9% 49% 34% 3	555
	11th to 20th	Night	2 1 8% 45% 42% 2	552
	21st to end	Night	4 1 7% 35% 49% 3	624
August	1st to 10th	Night	4 1 5% 35% 53% 3	567
	11th to 20th	Night	4 1 6% 33% 54% 2	564
	21st to end	Night	4 6% 35% 51% 3	627
September	1st to 10th	Night	8% 1 6% 45% 38% 1	570
	11th to 20th	Night	7% 1 11% 49% 31% 1	570
	21st to end	Night	7% 2 15% 48% 27% 1	570
October	1st to 10th	Night	8% 2 18% 50% 22%	621
	11th to 20th	Night	9% 3 18% 47% 22% 1	760
	21st to end	Night	7% 3 20% 41% 27% 2	836
November	1st to 10th	Night	5% 3 18% 49% 25%	843
	11th to 20th	Night	3 3 22% 48% 23% 1	950
	21st to end	Night	9% 4 24% 42% 20% 1	950
December	1st to 10th	Night	9% 2 25% 48% 16%	950
	11th to 20th	Night	6% 4 29% 49% 12%	950
	21st to end	Night	6% 5% 29% 48% 11% 1	1045

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