Van Horn
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Van Horn clear sky chart from 2005-11-06 to 2025-01-07.

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 3 1 3 3 3 3 3 5% 7% 66%	108710
	Night	3 3 1 4 3 3 4 3 5% 7% 64%	109026
Transparency	Day	20% 2 6% 18% 28% 27%	108485
	Night	21% 2 6% 16% 28% 27%	108840
Seeing	Day	5% 8% 23% 31% 24% 9%	14675
	Night	5% 5% 22% 43% 24% 2	25006

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 2 1 2 2 2 3 3 4 6% 72%	2912
	11th to 20th	Day	2 1 2 2 2 3 3 4 5% 76%	2889
	21st to end	Day	4 4 1 4 4 3 4 3 5% 7% 60%	3487
February	1st to 10th	Day	3 3 1 4 3 3 4 3 4 7% 66%	1900
	11th to 20th	Day	3 4 1 4 3 3 4 3 5% 6% 63%	1849
	21st to end	Day	3 3 1 3 3 2 3 3 4 5% 71%	1570
March	1st to 10th	Day	2 4 2 4 3 4 4 3 5% 7% 63%	3184
	11th to 20th	Day	6% 4 1 4 3 3 3 3 5% 6% 63%	3490
	21st to end	Day	1 3 2 3 4 4 4 4 5% 7% 65%	4041
April	1st to 10th	Day	2 2 1 3 3 3 3 3 5% 7% 69%	2280
	11th to 20th	Day	2 2 1 3 2 3 3 2 4 6% 71%	2251
	21st to end	Day	2 2 1 2 2 2 2 2 4 6% 75%	2280
May	1st to 10th	Day	1 1 2 2 2 2 2 3 4 81%	3800
	11th to 20th	Day	2 2 1 2 2 2 3 2 4 5% 75%	3765
	21st to end	Day	1 2 1 3 1 2 1 2 3 4 80%	4205
June	1st to 10th	Day	2 2 1 2 2 2 3 3 5% 8% 71%	2470
	11th to 20th	Day	2 2 3 3 3 4 3 5% 7% 66%	2625
	21st to end	Day	4 3 1 3 3 3 4 4 6% 9% 59%	2534
July	1st to 10th	Day	4 3 2 6% 5% 5% 5% 5% 7% 9% 49%	4110
	11th to 20th	Day	2 2 1 3 3 4 5% 4 7% 10% 59%	4048
	21st to end	Day	4 3 1 4 5% 6% 6% 5% 8% 11% 46%	4118
August	1st to 10th	Day	2 2 1 3 3 5% 6% 5% 8% 10% 54%	3784
	11th to 20th	Day	3 2 1 3 4 4 5% 4 7% 10% 55%	3726
	21st to end	Day	3 2 2 5% 4 4 5% 5% 8% 10% 52%	4180
September	1st to 10th	Day	8% 5% 2 6% 4 4 5% 3 6% 7% 51%	2280
	11th to 20th	Day	7% 4 2 5% 4 4 4 4 7% 8% 50%	2223
	21st to end	Day	5% 3 1 4 2 3 3 3 4 7% 64%	2090
October	1st to 10th	Day	2 2 1 2 1 2 2 2 4 4 79%	3392
	11th to 20th	Day	3 2 1 2 2 2 2 2 3 4 78%	3150
	21st to end	Day	1 1 1 1 1 1 2 2 3 3 83%	3438
November	1st to 10th	Day	4 2 1 3 2 2 3 2 3 5% 72%	1959
	11th to 20th	Day	2 2 1 3 3 3 2 3 4 5% 73%	1823
	21st to end	Day	5% 3 1 3 3 3 3 3 5% 7% 64%	1800
December	1st to 10th	Day	5% 6% 3 6% 3 3 3 3 5% 6% 59%	2940
	11th to 20th	Day	1 2 1 4 4 3 4 3 4 6% 68%	3391
	21st to end	Day	2 2 1 2 1 2 2 2 4 6% 75%	4726
January	1st to 10th	Night	3 2 1 4 2 2 3 2 4 6% 70%	4175
	11th to 20th	Night	2 3 1 2 2 2 3 3 4 5% 74%	4074
	21st to end	Night	5% 4 2 5% 4 4 4 3 5% 8% 57%	4180
February	1st to 10th	Night	4 3 1 2 3 2 2 3 5% 8% 66%	2280
	11th to 20th	Night	4 3 1 4 3 4 4 4 5% 6% 61%	2218
	21st to end	Night	4 3 2 3 3 2 4 3 4 6% 67%	1884
March	1st to 10th	Night	3 4 1 4 3 3 4 3 4 6% 64%	3677
	11th to 20th	Night	6% 7% 2 4 4 3 4 3 5% 8% 54%	3490
	21st to end	Night	3 3 1 3 3 4 4 4 5% 7% 64%	3605
April	1st to 10th	Night	3 4 1 4 3 3 3 3 5% 6% 66%	1900
	11th to 20th	Night	3 3 1 3 3 3 3 3 5% 7% 68%	1877
	21st to end	Night	2 2 3 2 3 2 2 5% 4 74%	1900
May	1st to 10th	Night	2 3 1 2 2 1 2 2 3 4 79%	3170
	11th to 20th	Night	3 3 1 3 3 3 3 3 4 5% 68%	3140
	21st to end	Night	2 2 1 3 3 3 3 3 4 6% 73%	3360
June	1st to 10th	Night	3 3 1 3 4 4 5% 4 7% 10% 56%	1710
	11th to 20th	Night	2 3 2 5% 3 4 4 4 6% 8% 59%	1548
	21st to end	Night	3 3 1 4 5% 5% 5% 5% 6% 9% 54%	1637
July	1st to 10th	Night	3 3 2 6% 5% 5% 5% 5% 7% 11% 47%	2860
	11th to 20th	Night	2 2 1 3 3 3 4 4 7% 10% 61%	2916
	21st to end	Night	4 4 2 6% 5% 5% 6% 5% 9% 11% 45%	3445
August	1st to 10th	Night	2 2 1 3 4 4 7% 6% 8% 12% 51%	3155
	11th to 20th	Night	3 3 1 5% 4 5% 6% 5% 7% 11% 51%	3113
	21st to end	Night	4 2 1 5% 4 4 5% 5% 9% 13% 48%	3487
September	1st to 10th	Night	5% 4 2 6% 5% 4 5% 5% 7% 9% 48%	1900
	11th to 20th	Night	5% 3 2 6% 4 5% 4 4 7% 9% 49%	1957
	21st to end	Night	6% 3 1 5% 4 4 4 4 6% 8% 56%	2090
October	1st to 10th	Night	3 1 1 2 2 2 3 3 3 4 76%	3566
	11th to 20th	Night	4 2 1 3 2 3 3 2 5% 5% 70%	3778
	21st to end	Night	2 1 1 2 1 1 2 2 3 4 82%	4120
November	1st to 10th	Night	4 3 1 2 2 2 2 2 4 5% 74%	2340
	11th to 20th	Night	3 3 1 4 2 3 3 3 4 6% 69%	2553
	21st to end	Night	5% 3 1 3 3 3 3 3 5% 5% 66%	2600
December	1st to 10th	Night	5% 4 2 5% 4 5% 4 4 5% 6% 59%	4250
	11th to 20th	Night	1 2 1 3 3 2 3 3 4 7% 70%	4816
	21st to end	Night	2 2 1 2 2 2 2 2 3 4 78%	6255

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	16% 2 2 13% 35% 32%	2913
	11th to 20th	Day	13% 2 3 17% 41% 25%	2889
	21st to end	Day	25% 1 6% 24% 30% 14%	3487
February	1st to 10th	Day	19% 3 4 15% 28% 31%	1900
	11th to 20th	Day	22% 3 4 15% 27% 29%	1859
	21st to end	Day	18% 2 2 10% 33% 36%	1570
March	1st to 10th	Day	23% 2 1 9% 31% 34%	3184
	11th to 20th	Day	24% 1 3 19% 26% 27%	3490
	21st to end	Day	22% 1 2 7% 33% 36%	4041
April	1st to 10th	Day	16% 2 3 11% 29% 39%	2280
	11th to 20th	Day	16% 2 2 11% 28% 42%	2254
	21st to end	Day	14% 2 3 10% 28% 44%	2280
May	1st to 10th	Day	10% 1 2 7% 17% 64%	3800
	11th to 20th	Day	14% 2 4 11% 23% 47%	3768
	21st to end	Day	12% 1 3 9% 16% 59%	4205
June	1st to 10th	Day	13% 3 6% 19% 30% 28%	2470
	11th to 20th	Day	18% 3 3 13% 26% 36%	2625
	21st to end	Day	22% 3 8% 21% 24% 22%	2534
July	1st to 10th	Day	30% 3 12% 26% 20% 8%	4046
	11th to 20th	Day	20% 4 12% 25% 29% 11%	3979
	21st to end	Day	30% 4 11% 29% 21% 5%	3988
August	1st to 10th	Day	24% 4 11% 30% 26% 5%	3772
	11th to 20th	Day	24% 4 10% 29% 28% 6%	3762
	21st to end	Day	27% 4 16% 30% 19% 5%	4179
September	1st to 10th	Day	33% 5% 10% 18% 19% 14%	2280
	11th to 20th	Day	31% 4 10% 18% 24% 13%	2223
	21st to end	Day	22% 4 7% 21% 28% 18%	2090
October	1st to 10th	Day	12% 2 5% 12% 26% 43%	3392
	11th to 20th	Day	14% 1 6% 20% 22% 37%	3150
	21st to end	Day	9% 1 1 13% 43% 33%	3438
November	1st to 10th	Day	17% 2 5% 17% 31% 28%	1959
	11th to 20th	Day	16% 2 5% 21% 30% 25%	1823
	21st to end	Day	22% 2 5% 17% 33% 20%	1800
December	1st to 10th	Day	28% 2 4 19% 32% 16%	2940
	11th to 20th	Day	20% 1 3 18% 37% 20%	3389
	21st to end	Day	13% 1 2 15% 45% 24%	4726
January	1st to 10th	Night	18% 2 2 11% 39% 29%	4175
	11th to 20th	Night	15% 1 4 15% 39% 25%	4074
	21st to end	Night	28% 1 4 22% 30% 14%	4180
February	1st to 10th	Night	19% 2 4 13% 29% 33%	2280
	11th to 20th	Night	24% 3 4 11% 26% 32%	2218
	21st to end	Night	21% 2 3 9% 27% 39%	1884
March	1st to 10th	Night	23% 2 1 10% 27% 38%	3677
	11th to 20th	Night	28% 1 5% 17% 25% 24%	3490
	21st to end	Night	21% 1 2 9% 35% 32%	3605
April	1st to 10th	Night	21% 2 2 9% 30% 37%	1900
	11th to 20th	Night	18% 3 4 12% 24% 39%	1877
	21st to end	Night	14% 2 3 13% 24% 44%	1900
May	1st to 10th	Night	13% 1 1 6% 15% 63%	3170
	11th to 20th	Night	21% 2 5% 12% 18% 43%	3141
	21st to end	Night	16% 1 4 10% 17% 52%	3361
June	1st to 10th	Night	22% 5% 8% 19% 24% 23%	1710
	11th to 20th	Night	23% 4 5% 12% 23% 33%	1548
	21st to end	Night	27% 2 10% 20% 21% 19%	1637
July	1st to 10th	Night	31% 4 16% 28% 16% 6%	2815
	11th to 20th	Night	17% 3 13% 30% 29% 7%	2862
	21st to end	Night	31% 4 11% 29% 21% 3	3336
August	1st to 10th	Night	24% 4 10% 29% 26% 7%	3144
	11th to 20th	Night	27% 4 11% 27% 26% 6%	3143
	21st to end	Night	26% 5% 16% 26% 21% 6%	3487
September	1st to 10th	Night	31% 7% 12% 16% 19% 15%	1900
	11th to 20th	Night	32% 5% 13% 19% 18% 13%	1957
	21st to end	Night	28% 4 8% 18% 23% 19%	2090
October	1st to 10th	Night	15% 2 6% 10% 19% 49%	3566
	11th to 20th	Night	18% 2 8% 16% 17% 40%	3778
	21st to end	Night	10% 1 2 12% 37% 38%	4120
November	1st to 10th	Night	16% 2 4 14% 35% 29%	2340
	11th to 20th	Night	19% 3 4 18% 28% 29%	2553
	21st to end	Night	22% 2 5% 15% 32% 24%	2600
December	1st to 10th	Night	28% 2 4 18% 31% 17%	4250
	11th to 20th	Night	17% 1 2 14% 40% 26%	4817
	21st to end	Night	13% 1 1 13% 43% 29%	6255

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	9% 11% 33% 31% 15% 2	288
	11th to 20th	Day	5% 11% 33% 34% 14% 2	270
	21st to end	Day	4 13% 38% 27% 15% 3	297
February	1st to 10th	Day	6% 10% 33% 32% 18% 1	270
	11th to 20th	Day	11% 13% 37% 26% 11% 1	270
	21st to end	Day	11% 18% 35% 28% 7% 1	225
March	1st to 10th	Day	7% 14% 38% 29% 10% 1	298
	11th to 20th	Day	12% 19% 33% 25% 9% 2	460
	21st to end	Day	8% 24% 38% 24% 6% 1	506
April	1st to 10th	Day	5% 18% 39% 27% 10% 1	460
	11th to 20th	Day	6% 19% 44% 24% 5% 1	452
	21st to end	Day	7% 16% 39% 31% 6% 1	460
May	1st to 10th	Day	2 15% 42% 28% 11% 2	463
	11th to 20th	Day	2 10% 36% 40% 12% 1	488
	21st to end	Day	2 8% 32% 38% 18% 1	567
June	1st to 10th	Day	2 3 18% 44% 30% 4	680
	11th to 20th	Day	3 2 13% 43% 35% 5%	680
	21st to end	Day	3 3 11% 33% 36% 14%	554
July	1st to 10th	Day	3 1 7% 27% 40% 22%	486
	11th to 20th	Day	1 5% 29% 43% 22%	484
	21st to end	Day	2 5% 30% 40% 23%	531
August	1st to 10th	Day	1 1 4 22% 45% 27%	487
	11th to 20th	Day	5% 2 5% 31% 35% 22%	477
	21st to end	Day	3 1 4 27% 41% 24%	539
September	1st to 10th	Day	7% 2 9% 32% 36% 14%	490
	11th to 20th	Day	5% 9% 30% 37% 18%	433
	21st to end	Day	5% 2 9% 25% 39% 20%	300
October	1st to 10th	Day	6% 3 16% 29% 33% 14%	300
	11th to 20th	Day	6% 5% 19% 35% 25% 10%	300
	21st to end	Day	6% 8% 21% 32% 21% 13%	330
November	1st to 10th	Day	7% 9% 22% 32% 24% 5%	300
	11th to 20th	Day	5% 14% 19% 30% 24% 8%	300
	21st to end	Day	11% 13% 27% 30% 15% 4	300
December	1st to 10th	Day	10% 8% 26% 33% 21% 2	300
	11th to 20th	Day	3 11% 31% 37% 15% 3	300
	21st to end	Day	5% 10% 32% 37% 14% 2	330
January	1st to 10th	Night	7% 5% 27% 45% 15% 1	784
	11th to 20th	Night	6% 6% 26% 44% 16% 2	760
	21st to end	Night	6% 7% 27% 45% 14% 1	836
February	1st to 10th	Night	6% 6% 28% 40% 18% 1	760
	11th to 20th	Night	6% 6% 36% 43% 9%	744
	21st to end	Night	6% 7% 43% 39% 6%	628
March	1st to 10th	Night	7% 9% 32% 42% 10%	760
	11th to 20th	Night	6% 10% 31% 39% 13%	760
	21st to end	Night	5% 9% 39% 40% 8% 1	703
April	1st to 10th	Night	4 10% 36% 42% 8% 1	570
	11th to 20th	Night	3 10% 39% 41% 7%	563
	21st to end	Night	2 10% 37% 40% 11%	570
May	1st to 10th	Night	3 7% 34% 46% 8%	570
	11th to 20th	Night	5% 4 28% 49% 14%	561
	21st to end	Night	3 5% 26% 52% 14%	617
June	1st to 10th	Night	4 4 18% 52% 22% 1	570
	11th to 20th	Night	2 1 16% 56% 24%	570
	21st to end	Night	3 2 11% 48% 35% 1	570
July	1st to 10th	Night	5% 1 5% 42% 45% 3	555
	11th to 20th	Night	5% 3 39% 50% 3	552
	21st to end	Night	3 1 4 37% 52% 4	624
August	1st to 10th	Night	3 1 4 27% 60% 5%	567
	11th to 20th	Night	3 1 4 26% 58% 8%	564
	21st to end	Night	6% 1 4 29% 55% 5%	627
September	1st to 10th	Night	6% 1 5% 35% 50% 2	570
	11th to 20th	Night	5% 1 6% 43% 43% 2	570
	21st to end	Night	6% 2 10% 39% 40% 2	570
October	1st to 10th	Night	6% 1 11% 49% 33% 1	617
	11th to 20th	Night	5% 4 15% 45% 28% 2	760
	21st to end	Night	4 4 14% 45% 30% 3	836
November	1st to 10th	Night	5% 3 16% 44% 29% 3	780
	11th to 20th	Night	4 4 21% 45% 24% 1	953
	21st to end	Night	6% 7% 24% 42% 19% 2	1000
December	1st to 10th	Night	7% 5% 24% 46% 18% 1	1000
	11th to 20th	Night	4 6% 29% 47% 15% 1	1000
	21st to end	Night	4 8% 26% 47% 13% 1	965

Page generated at 2025-01-04 02:23:59. Version ac07

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