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 2026-05-02.

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 2 1 3 3 3 3 3 5% 7% 66%	139962
	Night	3 3 1 4 3 3 4 3 5% 7% 64%	139934
Transparency	Day	19% 2 6% 18% 28% 27%	135065
	Night	21% 2 6% 16% 27% 28%	135836
Seeing	Day	5% 8% 22% 31% 24% 9%	16387
	Night	5% 5% 22% 43% 24% 2	26733

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	2 2 1 3 2 3 3 3 5% 6% 69%	5318
	11th to 20th	Day	2 2 1 2 2 2 2 2 3 6% 77%	5395
	21st to end	Day	4 4 1 4 3 4 5% 4 6% 6% 59%	6468
February	1st to 10th	Day	3 3 1 4 3 3 4 3 4 7% 66%	2100
	11th to 20th	Day	3 4 1 4 3 3 4 3 4 6% 64%	2049
	21st to end	Day	3 3 1 3 2 2 3 3 4 5% 72%	1730
March	1st to 10th	Day	1 3 1 4 2 3 3 3 5% 6% 68%	4683
	11th to 20th	Day	4 3 1 3 2 2 3 3 5% 6% 68%	5110
	21st to end	Day	2 3 2 4 3 3 3 3 5% 6% 66%	5921
April	1st to 10th	Day	2 2 1 3 3 3 3 4 5% 6% 67%	2520
	11th to 20th	Day	2 2 1 3 2 3 3 3 4 6% 70%	2491
	21st to end	Day	2 2 1 2 2 2 2 2 4 6% 74%	2520
May	1st to 10th	Day	2 1 2 1 2 2 2 3 4 80%	5453
	11th to 20th	Day	2 1 1 2 2 2 3 2 4 7% 73%	5405
	21st to end	Day	1 2 1 3 2 2 2 3 4 5% 76%	6036
June	1st to 10th	Day	2 2 1 2 2 2 3 3 5% 8% 71%	2600
	11th to 20th	Day	2 2 3 3 3 4 3 5% 7% 66%	2763
	21st to end	Day	4 4 1 4 4 4 4 4 6% 9% 57%	2667
July	1st to 10th	Day	4 3 2 5% 4 5% 5% 5% 6% 8% 53%	5879
	11th to 20th	Day	2 2 1 3 3 3 5% 4 7% 11% 59%	5792
	21st to end	Day	3 3 1 4 4 5% 5% 5% 8% 13% 49%	5922
August	1st to 10th	Day	1 1 1 3 3 4 5% 4 7% 11% 60%	5348
	11th to 20th	Day	2 2 1 4 4 5% 7% 6% 10% 13% 46%	5366
	21st to end	Day	2 2 1 4 4 4 5% 4 7% 10% 57%	5984
September	1st to 10th	Day	8% 5% 2 6% 4 4 5% 3 6% 7% 50%	2400
	11th to 20th	Day	7% 4 2 5% 4 4 4 4 7% 9% 49%	2340
	21st to end	Day	5% 3 1 4 2 3 3 3 5% 7% 63%	2200
October	1st to 10th	Day	2 1 1 2 1 2 2 2 4 4 78%	3499
	11th to 20th	Day	3 2 1 2 2 2 2 2 3 4 78%	3250
	21st to end	Day	1 1 1 1 1 1 2 2 3 4 83%	3548
November	1st to 10th	Day	4 2 1 3 2 2 3 2 3 5% 74%	2059
	11th to 20th	Day	2 2 1 3 3 3 2 3 4 5% 73%	1914
	21st to end	Day	5% 2 1 3 3 3 3 3 5% 7% 65%	1890
December	1st to 10th	Day	5% 6% 3 6% 3 2 3 3 5% 6% 60%	3030
	11th to 20th	Day	1 2 2 4 4 3 4 3 4 6% 68%	3481
	21st to end	Day	2 2 1 2 1 2 2 2 4 6% 75%	4831
January	1st to 10th	Night	2 2 2 5% 3 3 3 3 4 6% 67%	7605
	11th to 20th	Night	2 2 1 2 2 2 2 3 4 4 76%	7562
	21st to end	Night	5% 4 2 4 3 3 4 4 7% 8% 55%	7746
February	1st to 10th	Night	3 3 1 3 3 3 2 3 5% 7% 66%	2520
	11th to 20th	Night	4 3 1 4 3 4 4 4 5% 6% 62%	2458
	21st to end	Night	4 3 2 3 3 2 3 2 4 6% 69%	2076
March	1st to 10th	Night	2 3 1 4 2 2 3 3 5% 6% 69%	5409
	11th to 20th	Night	4 5% 1 3 3 2 3 2 4 7% 66%	5110
	21st to end	Night	2 3 1 3 3 3 3 3 4 6% 68%	5282
April	1st to 10th	Night	3 4 1 4 3 3 2 3 5% 6% 66%	2100
	11th to 20th	Night	2 3 1 3 3 3 3 3 5% 7% 67%	2077
	21st to end	Night	2 2 1 3 2 3 3 2 5% 4 73%	2100
May	1st to 10th	Night	2 3 1 3 2 2 2 2 3 4 76%	4550
	11th to 20th	Night	3 3 1 3 3 3 4 4 6% 8% 63%	4510
	21st to end	Night	2 2 1 3 3 3 3 3 5% 7% 70%	4825
June	1st to 10th	Night	3 3 1 3 4 4 4 4 7% 10% 57%	1800
	11th to 20th	Night	2 2 2 5% 3 4 4 4 6% 8% 60%	1629
	21st to end	Night	4 4 2 5% 5% 5% 5% 5% 6% 8% 51%	1723
July	1st to 10th	Night	4 4 2 6% 5% 4 4 5% 7% 11% 49%	4100
	11th to 20th	Night	2 2 1 3 3 3 5% 5% 8% 12% 57%	4182
	21st to end	Night	3 4 2 6% 5% 5% 6% 5% 9% 12% 42%	4951
August	1st to 10th	Night	2 1 1 2 3 3 5% 5% 7% 12% 59%	4464
	11th to 20th	Night	2 3 2 6% 5% 6% 7% 5% 9% 13% 41%	4483
	21st to end	Night	3 2 1 5% 4 4 5% 5% 9% 12% 50%	4993
September	1st to 10th	Night	5% 4 2 6% 4 4 5% 5% 7% 9% 47%	2000
	11th to 20th	Night	5% 3 2 7% 5% 5% 5% 4 7% 9% 48%	2060
	21st to end	Night	6% 3 1 5% 4 4 4 4 6% 8% 55%	2200
October	1st to 10th	Night	3 1 1 2 2 2 3 3 3 4 75%	3679
	11th to 20th	Night	4 2 1 3 2 3 3 2 5% 6% 70%	3898
	21st to end	Night	2 1 1 2 1 1 2 2 3 4 82%	4252
November	1st to 10th	Night	4 3 1 2 2 2 2 1 4 4 75%	2460
	11th to 20th	Night	3 3 1 4 2 3 3 3 4 5% 70%	2681
	21st to end	Night	5% 3 1 3 3 3 3 3 4 5% 67%	2730
December	1st to 10th	Night	4 3 1 5% 4 5% 4 4 5% 6% 59%	4380
	11th to 20th	Night	1 2 1 3 3 2 3 3 4 7% 71%	4946
	21st to end	Night	2 2 1 2 2 2 2 2 3 4 78%	6393

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	18% 1 4 18% 33% 26%	5321
	11th to 20th	Day	12% 1 2 19% 42% 25%	5395
	21st to end	Day	27% 1 3 19% 29% 21%	6468
February	1st to 10th	Day	20% 2 4 15% 27% 32%	2100
	11th to 20th	Day	21% 3 4 16% 28% 28%	2059
	21st to end	Day	17% 2 2 9% 34% 36%	1730
March	1st to 10th	Day	19% 1 1 7% 25% 47%	4683
	11th to 20th	Day	18% 1 2 13% 26% 39%	5110
	21st to end	Day	21% 1 2 6% 29% 42%	5921
April	1st to 10th	Day	18% 2 3 11% 29% 37%	2520
	11th to 20th	Day	17% 2 2 11% 28% 41%	2494
	21st to end	Day	15% 1 3 10% 28% 43%	2520
May	1st to 10th	Day	11% 1 2 11% 23% 53%	5453
	11th to 20th	Day	14% 1 3 10% 25% 47%	5408
	21st to end	Day	14% 1 4 13% 16% 52%	6037
June	1st to 10th	Day	13% 3 6% 21% 30% 28%	2600
	11th to 20th	Day	18% 3 3 13% 26% 37%	2763
	21st to end	Day	25% 3 8% 21% 23% 21%	2667
July	1st to 10th	Day	29% 3 12% 24% 24% 7%	5816
	11th to 20th	Day	18% 3 14% 33% 23% 8%	5723
	21st to end	Day	27% 3 17% 30% 20% 4	5752
August	1st to 10th	Day	23% 3 11% 30% 27% 6%	3892
	11th to 20th	Day	24% 4 11% 29% 27% 5%	3882
	21st to end	Day	26% 4 16% 30% 19% 5%	4311
September	1st to 10th	Day	34% 5% 10% 19% 19% 14%	2400
	11th to 20th	Day	31% 4 10% 18% 23% 13%	2340
	21st to end	Day	22% 4 7% 21% 28% 18%	2200
October	1st to 10th	Day	12% 2 5% 12% 26% 42%	3499
	11th to 20th	Day	14% 1 6% 20% 22% 36%	3250
	21st to end	Day	9% 1 1 13% 42% 33%	3548
November	1st to 10th	Day	16% 2 4 17% 31% 30%	2059
	11th to 20th	Day	16% 2 5% 21% 31% 25%	1914
	21st to end	Day	22% 2 5% 17% 34% 20%	1890
December	1st to 10th	Day	27% 2 5% 19% 32% 16%	3030
	11th to 20th	Day	20% 1 3 17% 37% 21%	3479
	21st to end	Day	13% 1 2 15% 44% 24%	4831
January	1st to 10th	Night	21% 1 3 18% 33% 24%	7605
	11th to 20th	Night	15% 1 3 15% 35% 31%	7562
	21st to end	Night	29% 2 2 19% 27% 21%	7746
February	1st to 10th	Night	19% 2 3 13% 28% 35%	2520
	11th to 20th	Night	24% 3 4 12% 27% 30%	2458
	21st to end	Night	20% 2 2 9% 28% 39%	2076
March	1st to 10th	Night	18% 1 1 7% 26% 47%	5409
	11th to 20th	Night	20% 1 4 12% 25% 39%	5110
	21st to end	Night	20% 1 2 9% 27% 42%	5282
April	1st to 10th	Night	22% 2 2 10% 29% 35%	2100
	11th to 20th	Night	19% 3 4 12% 24% 38%	2077
	21st to end	Night	15% 2 3 12% 25% 43%	2100
May	1st to 10th	Night	16% 1 1 12% 19% 51%	4547
	11th to 20th	Night	21% 1 4 13% 21% 41%	4511
	21st to end	Night	18% 1 6% 12% 15% 47%	4826
June	1st to 10th	Night	21% 5% 8% 19% 25% 22%	1800
	11th to 20th	Night	22% 3 5% 12% 24% 33%	1629
	21st to end	Night	30% 2 10% 20% 20% 18%	1723
July	1st to 10th	Night	30% 5% 14% 28% 18% 5%	4055
	11th to 20th	Night	19% 3 17% 33% 24% 5%	4128
	21st to end	Night	34% 3 13% 29% 19% 2	4808
August	1st to 10th	Night	23% 4 10% 29% 26% 8%	3244
	11th to 20th	Night	28% 4 11% 26% 25% 6%	3243
	21st to end	Night	26% 5% 16% 26% 22% 6%	3597
September	1st to 10th	Night	32% 6% 12% 17% 19% 14%	2000
	11th to 20th	Night	33% 5% 14% 19% 18% 13%	2060
	21st to end	Night	28% 4 8% 19% 23% 18%	2200
October	1st to 10th	Night	15% 2 6% 10% 19% 49%	3679
	11th to 20th	Night	18% 2 8% 16% 16% 40%	3898
	21st to end	Night	10% 1 2 12% 37% 38%	4252
November	1st to 10th	Night	15% 2 4 14% 34% 32%	2460
	11th to 20th	Night	18% 3 4 17% 29% 28%	2681
	21st to end	Night	21% 2 5% 15% 33% 23%	2730
December	1st to 10th	Night	28% 2 4 18% 31% 17%	4380
	11th to 20th	Night	17% 1 2 14% 39% 27%	4947
	21st to end	Night	13% 1 2 14% 42% 28%	6393

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% 11% 34% 30% 14% 2	330
	11th to 20th	Day	5% 11% 32% 34% 17% 2	330
	21st to end	Day	6% 11% 36% 28% 17% 3	363
February	1st to 10th	Day	6% 9% 31% 30% 20% 4	330
	11th to 20th	Day	10% 15% 35% 27% 11% 2	330
	21st to end	Day	9% 16% 32% 30% 10% 3	273
March	1st to 10th	Day	8% 14% 35% 29% 12% 2	361
	11th to 20th	Day	11% 19% 32% 25% 10% 3	540
	21st to end	Day	7% 21% 36% 25% 9% 3	594
April	1st to 10th	Day	6% 16% 37% 27% 11% 2	540
	11th to 20th	Day	6% 19% 43% 23% 7% 2	532
	21st to end	Day	7% 15% 39% 30% 8% 1	540
May	1st to 10th	Day	2 15% 42% 28% 11% 2	508
	11th to 20th	Day	2 12% 35% 38% 12% 1	528
	21st to end	Day	2 8% 32% 38% 20% 1	613
June	1st to 10th	Day	2 3 18% 44% 30% 4	730
	11th to 20th	Day	3 2 12% 42% 36% 5%	730
	21st to end	Day	4 3 11% 32% 37% 14%	597
July	1st to 10th	Day	4 1 7% 26% 41% 21%	526
	11th to 20th	Day	2 1 4 28% 43% 23%	524
	21st to end	Day	2 1 4 29% 40% 24%	575
August	1st to 10th	Day	1 1 4 21% 45% 29%	527
	11th to 20th	Day	5% 2 4 29% 35% 25%	517
	21st to end	Day	3 1 4 26% 40% 25%	583
September	1st to 10th	Day	8% 2 9% 31% 36% 15%	530
	11th to 20th	Day	5% 9% 31% 37% 18%	470
	21st to end	Day	5% 2 9% 24% 39% 21%	330
October	1st to 10th	Day	5% 2 15% 30% 33% 14%	330
	11th to 20th	Day	6% 5% 18% 35% 27% 9%	330
	21st to end	Day	6% 7% 20% 32% 23% 12%	363
November	1st to 10th	Day	6% 8% 21% 31% 25% 7%	330
	11th to 20th	Day	5% 14% 18% 30% 25% 9%	330
	21st to end	Day	10% 12% 30% 30% 15% 4	330
December	1st to 10th	Day	9% 7% 28% 33% 21% 2	330
	11th to 20th	Day	3 10% 29% 37% 16% 5%	330
	21st to end	Day	5% 9% 31% 34% 15% 5%	363
January	1st to 10th	Night	7% 5% 28% 44% 15% 1	840
	11th to 20th	Night	6% 6% 26% 46% 14% 1	840
	21st to end	Night	6% 7% 27% 45% 13% 1	924
February	1st to 10th	Night	6% 5% 26% 42% 19% 1	840
	11th to 20th	Night	6% 6% 36% 42% 9%	824
	21st to end	Night	5% 7% 41% 40% 6%	692
March	1st to 10th	Night	7% 8% 32% 42% 10%	840
	11th to 20th	Night	6% 11% 31% 39% 13%	840
	21st to end	Night	4 8% 37% 40% 11% 1	777
April	1st to 10th	Night	5% 9% 34% 42% 9% 1	630
	11th to 20th	Night	4 10% 39% 41% 6%	623
	21st to end	Night	3 10% 36% 41% 10%	630
May	1st to 10th	Night	4 7% 34% 46% 8%	603
	11th to 20th	Night	5% 4 29% 48% 13%	591
	21st to end	Night	3 5% 26% 52% 14%	650
June	1st to 10th	Night	3 4 19% 53% 21% 1	600
	11th to 20th	Night	2 1 16% 56% 24%	600
	21st to end	Night	4 2 11% 47% 36% 1	600
July	1st to 10th	Night	5% 1 5% 41% 45% 3	585
	11th to 20th	Night	5% 3 38% 51% 3	582
	21st to end	Night	3 1 4 36% 51% 5%	657
August	1st to 10th	Night	3 1 4 28% 60% 5%	597
	11th to 20th	Night	3 2 4 25% 59% 8%	594
	21st to end	Night	6% 1 4 30% 54% 5%	660
September	1st to 10th	Night	6% 1 5% 36% 50% 2	600
	11th to 20th	Night	6% 1 6% 43% 42% 2	600
	21st to end	Night	7% 2 10% 39% 40% 3	600
October	1st to 10th	Night	5% 1 11% 49% 33% 1	650
	11th to 20th	Night	6% 4 15% 45% 28% 2	800
	21st to end	Night	4 3 14% 45% 31% 3	880
November	1st to 10th	Night	5% 3 16% 44% 30% 3	820
	11th to 20th	Night	4 4 21% 45% 24% 1	1001
	21st to end	Night	6% 7% 25% 42% 19% 2	1050
December	1st to 10th	Night	7% 4 25% 46% 17% 1	1050
	11th to 20th	Night	3 5% 28% 47% 16% 1	1050
	21st to end	Night	4 8% 25% 47% 14% 1	1013

Page generated at 2026-04-29 01:21:41. Version ac07

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