Dixon Lomax Memorial Observing Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Dixon Lomax Memorial Observing Site clear sky chart from 2005-11-06 to 2025-06-10.

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	15% 5% 2 5% 4 4 4 4 6% 7% 43%	119709
	Night	16% 5% 2 5% 4 4 4 3 5% 7% 45%	118531
Transparency	Day	25% 39% 6% 12% 12% 5%	123488
	Night	25% 39% 5% 12% 14% 5%	122889
Seeing	Day	20% 8% 23% 24% 17% 8%	15741
	Night	19% 7% 21% 30% 19% 4	25830

By Month

Percentage Cloud Cover SE (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	16% 4 2 3 3 3 3 2 5% 5% 55%	4056
	11th to 20th	Day	13% 4 2 4 3 3 2 2 3 3 61%	4060
	21st to end	Day	21% 5% 2 6% 4 3 3 3 3 4 46%	4466
February	1st to 10th	Day	17% 6% 2 6% 4 3 4 4 5% 6% 45%	1970
	11th to 20th	Day	22% 6% 2 5% 3 2 3 3 5% 6% 43%	1948
	21st to end	Day	20% 5% 2 6% 4 4 3 2 4 4 45%	1650
March	1st to 10th	Day	23% 6% 2 5% 3 3 4 3 4 5% 41%	4749
	11th to 20th	Day	12% 4 2 4 3 3 4 3 4 6% 56%	4980
	21st to end	Day	20% 4 2 5% 4 4 3 3 4 4 46%	5465
April	1st to 10th	Day	14% 3 2 4 3 4 5% 5% 5% 7% 46%	2200
	11th to 20th	Day	14% 4 2 4 4 4 4 4 5% 7% 47%	2387
	21st to end	Day	13% 4 2 4 4 4 4 3 5% 8% 49%	2600
May	1st to 10th	Day	14% 7% 3 7% 5% 5% 5% 5% 6% 8% 36%	5862
	11th to 20th	Day	20% 6% 3 7% 5% 5% 5% 4 7% 8% 29%	5861
	21st to end	Day	14% 4 2 6% 5% 5% 5% 4 6% 8% 41%	6433
June	1st to 10th	Day	11% 6% 2 6% 6% 6% 6% 5% 8% 10% 34%	2587
	11th to 20th	Day	6% 4 2 6% 5% 6% 7% 5% 9% 12% 39%	2470
	21st to end	Day	8% 4 2 6% 6% 5% 7% 6% 8% 11% 38%	2470
July	1st to 10th	Day	8% 5% 2 7% 6% 6% 7% 5% 8% 12% 34%	4120
	11th to 20th	Day	10% 4 2 6% 6% 6% 7% 6% 8% 10% 35%	4120
	21st to end	Day	11% 7% 3 9% 7% 10% 9% 7% 9% 9% 19%	4466
August	1st to 10th	Day	11% 6% 2 6% 5% 6% 6% 5% 8% 10% 35%	4104
	11th to 20th	Day	9% 5% 2 6% 5% 6% 5% 4 7% 11% 39%	4018
	21st to end	Day	9% 4 2 5% 4 4 5% 4 6% 8% 50%	4098
September	1st to 10th	Day	10% 6% 2 7% 6% 5% 6% 4 7% 8% 39%	2090
	11th to 20th	Day	18% 5% 2 5% 4 5% 4 4 6% 7% 38%	2090
	21st to end	Day	17% 5% 2 4 4 4 5% 3 4 7% 45%	2090
October	1st to 10th	Day	16% 4 1 3 3 3 2 3 4 6% 55%	2090
	11th to 20th	Day	13% 5% 1 4 3 2 2 3 4 5% 58%	1914
	21st to end	Day	15% 4 1 3 2 3 3 2 4 4 59%	2090
November	1st to 10th	Day	16% 4 1 4 2 3 2 3 3 5% 57%	1836
	11th to 20th	Day	15% 5% 1 4 3 3 3 2 5% 6% 54%	1800
	21st to end	Day	16% 4 1 4 3 3 3 3 5% 6% 51%	1800
December	1st to 10th	Day	20% 4 2 4 3 3 3 2 4 4 51%	2930
	11th to 20th	Day	20% 5% 2 5% 4 3 4 4 4 5% 43%	3373
	21st to end	Day	25% 4 1 3 2 2 3 2 4 6% 47%	4466
January	1st to 10th	Night	16% 4 2 4 3 3 3 2 3 5% 56%	5889
	11th to 20th	Night	14% 5% 2 4 3 3 3 2 4 5% 55%	5900
	21st to end	Night	20% 5% 2 4 3 3 3 2 4 5% 49%	6490
February	1st to 10th	Night	16% 5% 1 5% 4 3 4 3 5% 6% 49%	2428
	11th to 20th	Night	23% 6% 1 5% 3 3 3 3 5% 5% 44%	2338
	21st to end	Night	19% 5% 2 5% 4 4 4 4 5% 6% 43%	1980
March	1st to 10th	Night	22% 6% 2 5% 4 3 4 3 5% 6% 41%	5102
	11th to 20th	Night	11% 3 1 3 3 3 3 3 6% 7% 56%	4980
	21st to end	Night	18% 5% 2 5% 4 3 4 3 4 6% 45%	5467
April	1st to 10th	Night	15% 4 2 4 3 3 4 3 5% 7% 50%	2200
	11th to 20th	Night	12% 5% 2 5% 3 3 4 3 4 8% 51%	1978
	21st to end	Night	12% 5% 2 5% 4 3 4 3 5% 7% 51%	1800
May	1st to 10th	Night	14% 7% 2 7% 5% 5% 5% 5% 6% 8% 37%	4033
	11th to 20th	Night	24% 6% 2 5% 4 5% 5% 3 5% 8% 32%	4032
	21st to end	Night	15% 5% 2 5% 4 4 4 4 6% 9% 42%	4421
June	1st to 10th	Night	11% 7% 2 8% 6% 5% 5% 6% 7% 9% 35%	1797
	11th to 20th	Night	8% 5% 2 5% 5% 5% 5% 5% 7% 10% 43%	1710
	21st to end	Night	8% 4 2 6% 5% 4 6% 6% 8% 10% 42%	1710
July	1st to 10th	Night	14% 7% 3 8% 6% 7% 5% 4 7% 10% 28%	2840
	11th to 20th	Night	9% 5% 2 7% 5% 6% 7% 6% 9% 11% 33%	2840
	21st to end	Night	15% 8% 4 10% 7% 5% 7% 5% 8% 10% 23%	3087
August	1st to 10th	Night	13% 7% 2 6% 4 5% 5% 5% 8% 10% 34%	2825
	11th to 20th	Night	17% 7% 3 7% 5% 5% 6% 4 6% 9% 32%	2807
	21st to end	Night	10% 5% 2 6% 4 5% 6% 3 6% 9% 44%	3524
September	1st to 10th	Night	12% 6% 2 7% 5% 5% 5% 4 7% 9% 38%	2090
	11th to 20th	Night	18% 6% 2 7% 4 4 5% 3 7% 7% 37%	2090
	21st to end	Night	16% 5% 2 6% 4 4 4 3 4 6% 45%	2090
October	1st to 10th	Night	15% 4 1 4 4 3 4 3 4 5% 54%	2090
	11th to 20th	Night	14% 4 2 5% 3 3 3 3 4 5% 55%	2265
	21st to end	Night	15% 4 1 4 2 3 3 2 4 4 58%	2508
November	1st to 10th	Night	15% 5% 2 4 3 2 3 3 4 4 56%	2458
	11th to 20th	Night	17% 5% 2 4 3 3 2 2 4 5% 53%	2600
	21st to end	Night	17% 5% 2 4 3 4 4 4 5% 6% 48%	2600
December	1st to 10th	Night	18% 5% 1 4 3 3 3 2 4 4 52%	4250
	11th to 20th	Night	22% 5% 2 5% 3 3 3 3 4 4 46%	4822
	21st to end	Night	24% 5% 2 4 3 3 3 3 4 6% 44%	6490

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	24% 25% 2 14% 27% 8%	4057
	11th to 20th	Day	20% 25% 2 10% 30% 12%	4060
	21st to end	Day	33% 27% 2 11% 16% 10%	4466
February	1st to 10th	Day	16% 61% 3 10% 8% 2	1970
	11th to 20th	Day	19% 60% 3 7% 8% 3	1958
	21st to end	Day	19% 61% 2 5% 9% 4	1650
March	1st to 10th	Day	38% 28% 3 9% 12% 10%	4749
	11th to 20th	Day	20% 28% 3 9% 22% 19%	4980
	21st to end	Day	31% 27% 2 19% 15% 6%	5465
April	1st to 10th	Day	17% 62% 4 7% 9% 2	2200
	11th to 20th	Day	17% 62% 4 8% 7% 3	2387
	21st to end	Day	15% 62% 5% 10% 8% 1	2600
May	1st to 10th	Day	35% 29% 10% 16% 9% 1	5897
	11th to 20th	Day	41% 29% 10% 13% 7%	5865
	21st to end	Day	32% 28% 9% 13% 15% 2	6447
June	1st to 10th	Day	17% 62% 6% 9% 3 1	2587
	11th to 20th	Day	12% 66% 9% 8% 4	2470
	21st to end	Day	14% 65% 8% 8% 4	2470
July	1st to 10th	Day	24% 41% 17% 15% 2	4055
	11th to 20th	Day	26% 39% 19% 15% 1	4051
	21st to end	Day	43% 40% 8% 7% 3	4324
August	1st to 10th	Day	28% 39% 10% 20% 4	4091
	11th to 20th	Day	19% 40% 18% 11% 10% 2	4057
	21st to end	Day	14% 38% 10% 21% 17% 1	4098
September	1st to 10th	Day	16% 60% 6% 8% 9% 1	2090
	11th to 20th	Day	18% 60% 6% 8% 8% 1	2090
	21st to end	Day	17% 59% 6% 8% 8% 1	2090
October	1st to 10th	Day	15% 37% 3 11% 27% 6%	3480
	11th to 20th	Day	10% 36% 2 8% 21% 23%	3154
	21st to end	Day	19% 37% 2 15% 16% 11%	3428
November	1st to 10th	Day	19% 56% 3 8% 11% 4	1836
	11th to 20th	Day	16% 56% 2 9% 13% 4	1800
	21st to end	Day	14% 56% 4 9% 14% 3	1800
December	1st to 10th	Day	23% 35% 2 11% 18% 11%	2930
	11th to 20th	Day	32% 32% 3 9% 15% 9%	3370
	21st to end	Day	31% 25% 4 22% 17% 1	4466
January	1st to 10th	Night	25% 25% 3 12% 26% 10%	5889
	11th to 20th	Night	24% 25% 2 12% 27% 11%	5900
	21st to end	Night	29% 26% 3 11% 22% 9%	6490
February	1st to 10th	Night	14% 62% 3 10% 9% 2	2428
	11th to 20th	Night	21% 60% 2 7% 8% 2	2339
	21st to end	Night	17% 61% 2 7% 9% 4	1980
March	1st to 10th	Night	36% 29% 3 9% 19% 5%	5102
	11th to 20th	Night	18% 28% 3 11% 22% 18%	4980
	21st to end	Night	30% 28% 3 17% 14% 8%	5467
April	1st to 10th	Night	16% 61% 4 7% 9% 3	2200
	11th to 20th	Night	16% 62% 3 10% 6% 3	1978
	21st to end	Night	15% 61% 5% 12% 7% 1	1800
May	1st to 10th	Night	36% 29% 10% 17% 7% 1	4060
	11th to 20th	Night	40% 28% 11% 13% 7%	4033
	21st to end	Night	29% 29% 9% 19% 13% 1	4429
June	1st to 10th	Night	18% 63% 6% 7% 5% 1	1797
	11th to 20th	Night	12% 66% 9% 8% 5%	1710
	21st to end	Night	12% 64% 9% 9% 6%	1710
July	1st to 10th	Night	32% 40% 13% 13% 2	2795
	11th to 20th	Night	25% 41% 19% 14% 1	2786
	21st to end	Night	41% 39% 10% 7% 2 1	2988
August	1st to 10th	Night	28% 39% 15% 15% 2	2814
	11th to 20th	Night	31% 40% 10% 10% 9%	2834
	21st to end	Night	18% 38% 9% 21% 13% 1	3524
September	1st to 10th	Night	17% 60% 6% 8% 9% 1	2090
	11th to 20th	Night	18% 61% 6% 9% 6% 1	2090
	21st to end	Night	19% 59% 5% 9% 6% 1	2090
October	1st to 10th	Night	16% 38% 7% 10% 24% 5%	3480
	11th to 20th	Night	8% 36% 3 11% 23% 20%	3764
	21st to end	Night	19% 36% 1 13% 18% 13%	4120
November	1st to 10th	Night	20% 55% 4 9% 9% 4	2458
	11th to 20th	Night	16% 56% 2 8% 13% 5%	2600
	21st to end	Night	15% 56% 3 11% 13% 3	2600
December	1st to 10th	Night	24% 36% 2 12% 20% 7%	4250
	11th to 20th	Night	31% 32% 4 11% 15% 7%	4824
	21st to end	Night	34% 25% 4 21% 15% 2	6490

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	28% 17% 38% 14% 3 1	300
	11th to 20th	Day	30% 18% 31% 16% 4 1	300
	21st to end	Day	30% 19% 34% 12% 3 1	330
February	1st to 10th	Day	23% 17% 40% 17% 4	300
	11th to 20th	Day	39% 16% 34% 11% 1	300
	21st to end	Day	34% 18% 35% 12% 1	249
March	1st to 10th	Day	28% 14% 30% 21% 7%	413
	11th to 20th	Day	27% 13% 33% 20% 5% 1	500
	21st to end	Day	28% 15% 30% 20% 7% 1	550
April	1st to 10th	Day	25% 12% 27% 25% 9% 2	500
	11th to 20th	Day	17% 14% 34% 22% 12% 2	492
	21st to end	Day	19% 8% 26% 27% 15% 4	500
May	1st to 10th	Day	16% 12% 30% 23% 11% 7%	503
	11th to 20th	Day	22% 6% 20% 24% 19% 9%	527
	21st to end	Day	18% 7% 19% 25% 19% 12%	573
June	1st to 10th	Day	15% 5% 16% 30% 21% 12%	526
	11th to 20th	Day	9% 4 16% 28% 24% 18%	490
	21st to end	Day	12% 3 18% 32% 21% 15%	490
July	1st to 10th	Day	12% 2 10% 26% 28% 22%	485
	11th to 20th	Day	8% 3 9% 27% 28% 25%	484
	21st to end	Day	7% 2 9% 29% 31% 22%	532
August	1st to 10th	Day	17% 5% 13% 20% 25% 21%	486
	11th to 20th	Day	11% 5% 9% 25% 33% 17%	479
	21st to end	Day	16% 3 8% 26% 29% 18%	539
September	1st to 10th	Day	12% 2 13% 28% 31% 14%	490
	11th to 20th	Day	19% 4 12% 23% 31% 11%	490
	21st to end	Day	21% 4 16% 28% 24% 7%	490
October	1st to 10th	Day	20% 4 19% 30% 19% 9%	490
	11th to 20th	Day	16% 6% 24% 32% 18% 3	490
	21st to end	Day	21% 6% 25% 29% 15% 4	539
November	1st to 10th	Day	23% 5% 30% 25% 13% 3	374
	11th to 20th	Day	21% 16% 33% 24% 6%	300
	21st to end	Day	17% 10% 38% 24% 9% 2	300
December	1st to 10th	Day	30% 14% 32% 20% 3 1	300
	11th to 20th	Day	27% 11% 37% 18% 5% 1	300
	21st to end	Day	35% 11% 30% 17% 5% 2	330
January	1st to 10th	Night	24% 12% 33% 25% 6%	800
	11th to 20th	Night	22% 11% 32% 29% 6%	800
	21st to end	Night	22% 11% 36% 27% 4	880
February	1st to 10th	Night	21% 9% 31% 35% 5%	800
	11th to 20th	Night	27% 13% 32% 25% 3	783
	21st to end	Night	22% 12% 35% 28% 3	660
March	1st to 10th	Night	21% 10% 31% 34% 5%	800
	11th to 20th	Night	20% 9% 34% 28% 8% 1	800
	21st to end	Night	21% 11% 28% 30% 9%	880
April	1st to 10th	Night	19% 11% 28% 32% 10% 1	800
	11th to 20th	Night	16% 10% 23% 35% 15% 1	640
	21st to end	Night	16% 5% 20% 37% 20% 2	600
May	1st to 10th	Night	15% 5% 24% 33% 23% 1	600
	11th to 20th	Night	21% 4 17% 32% 21% 5%	591
	21st to end	Night	15% 3 12% 29% 31% 10%	650
June	1st to 10th	Night	14% 3 11% 34% 32% 7%	599
	11th to 20th	Night	10% 2 11% 32% 31% 15%	570
	21st to end	Night	8% 2 9% 33% 39% 9%	570
July	1st to 10th	Night	14% 3 6% 22% 42% 14%	555
	11th to 20th	Night	12% 3 4 22% 43% 16%	552
	21st to end	Night	9% 2 6% 25% 45% 13%	624
August	1st to 10th	Night	17% 1 5% 23% 41% 13%	567
	11th to 20th	Night	17% 3 6% 25% 38% 10%	564
	21st to end	Night	13% 4 4 26% 40% 12%	649
September	1st to 10th	Night	13% 3 9% 28% 38% 9%	760
	11th to 20th	Night	20% 3 12% 24% 35% 7%	760
	21st to end	Night	17% 3 12% 34% 30% 4	760
October	1st to 10th	Night	17% 4 15% 30% 26% 7%	760
	11th to 20th	Night	16% 5% 20% 36% 20% 3	760
	21st to end	Night	17% 6% 19% 37% 18% 3	836
November	1st to 10th	Night	18% 6% 19% 35% 19% 3	780
	11th to 20th	Night	19% 8% 25% 33% 13% 2	800
	21st to end	Night	21% 6% 26% 34% 12% 1	800
December	1st to 10th	Night	26% 8% 26% 32% 8% 1	800
	11th to 20th	Night	22% 7% 28% 33% 9% 1	800
	21st to end	Night	30% 8% 23% 33% 6%	880

Page generated at 2025-06-07 10:28:16. Version ac07

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