Cameron County Dark Skies
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cameron County Dark Skies clear sky chart from 2005-11-06 to 2026-01-02.

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	17% 11% 4 9% 5% 5% 4 4 5% 6% 30%	127387
	Night	17% 12% 5% 10% 5% 4 4 3 5% 6% 29%	123948
Transparency	Day	53% 5% 11% 19% 10% 1	130982
	Night	55% 5% 11% 18% 10% 1	128439
Seeing	Day	27% 16% 26% 17% 10% 4	16105
	Night	25% 15% 24% 24% 11% 1	25612

By Month

Percentage Cloud Cover NE (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	15% 18% 10% 20% 5% 3 3 2 4 3 17%	3605
	11th to 20th	Day	10% 20% 11% 21% 7% 6% 3 3 3 3 13%	3998
	21st to end	Day	19% 16% 9% 12% 6% 4 4 2 4 5% 18%	4466
February	1st to 10th	Day	16% 17% 5% 13% 8% 6% 4 3 4 4 21%	1800
	11th to 20th	Day	15% 15% 8% 13% 6% 4 5% 3 4 5% 23%	1753
	21st to end	Day	20% 15% 3 12% 5% 3 3 3 4 6% 27%	1599
March	1st to 10th	Day	18% 14% 6% 9% 4 3 3 3 4 5% 32%	4927
	11th to 20th	Day	14% 13% 5% 9% 5% 4 3 2 4 6% 35%	4980
	21st to end	Day	16% 12% 4 10% 6% 5% 5% 3 4 5% 31%	5479
April	1st to 10th	Day	18% 15% 3 8% 4 4 4 3 4 6% 29%	2400
	11th to 20th	Day	18% 12% 3 7% 4 3 4 4 5% 6% 32%	2374
	21st to end	Day	21% 9% 2 8% 5% 4 4 4 4 5% 35%	2527
May	1st to 10th	Day	26% 9% 3 8% 5% 5% 5% 4 5% 5% 26%	5888
	11th to 20th	Day	25% 10% 3 8% 5% 5% 4 4 6% 7% 25%	6244
	21st to end	Day	21% 7% 2 6% 5% 5% 5% 5% 6% 8% 31%	6949
June	1st to 10th	Day	16% 7% 3 8% 6% 5% 4 4 6% 7% 34%	2800
	11th to 20th	Day	16% 7% 3 7% 5% 6% 5% 4 6% 8% 32%	2800
	21st to end	Day	14% 6% 2 7% 5% 5% 6% 4 7% 9% 36%	2800
July	1st to 10th	Day	10% 6% 2 8% 5% 5% 6% 4 6% 9% 39%	6360
	11th to 20th	Day	10% 7% 3 9% 6% 6% 7% 5% 7% 9% 32%	6324
	21st to end	Day	12% 6% 3 7% 5% 5% 5% 4 5% 8% 41%	6424
August	1st to 10th	Day	19% 8% 3 7% 4 5% 5% 4 6% 8% 30%	4234
	11th to 20th	Day	15% 7% 3 8% 6% 6% 6% 5% 7% 9% 30%	4174
	21st to end	Day	14% 6% 2 6% 4 5% 6% 4 7% 10% 36%	4322
September	1st to 10th	Day	18% 7% 2 6% 4 5% 4 3 4 7% 40%	2400
	11th to 20th	Day	14% 7% 2 6% 4 4 3 4 5% 7% 44%	2360
	21st to end	Day	25% 7% 2 7% 4 4 4 3 4 7% 32%	2110
October	1st to 10th	Day	17% 8% 3 7% 4 4 4 4 5% 8% 36%	2000
	11th to 20th	Day	19% 10% 3 8% 5% 4 4 4 6% 6% 33%	2000
	21st to end	Day	22% 12% 3 7% 5% 4 4 4 5% 6% 28%	2200
November	1st to 10th	Day	14% 11% 3 7% 4 5% 5% 4 5% 7% 37%	1931
	11th to 20th	Day	17% 16% 5% 10% 5% 4 4 3 5% 5% 25%	1685
	21st to end	Day	20% 19% 5% 8% 6% 4 4 4 4 5% 21%	1680
December	1st to 10th	Day	19% 22% 12% 15% 5% 4 4 2 3 3 12%	2680
	11th to 20th	Day	21% 19% 6% 9% 4 3 4 2 4 5% 22%	3066
	21st to end	Day	24% 19% 6% 12% 5% 3 4 3 4 4 15%	4048
January	1st to 10th	Night	14% 16% 7% 22% 7% 4 4 2 4 4 14%	6364
	11th to 20th	Night	12% 16% 8% 21% 9% 6% 4 3 5% 5% 12%	5883
	21st to end	Night	19% 17% 7% 16% 6% 5% 5% 3 3 3 17%	6490
February	1st to 10th	Night	15% 17% 6% 11% 6% 5% 5% 4 5% 5% 22%	2600
	11th to 20th	Night	16% 12% 6% 13% 7% 5% 6% 4 5% 6% 21%	2533
	21st to end	Night	17% 13% 4 14% 6% 4 4 4 5% 5% 24%	2030
March	1st to 10th	Night	18% 14% 6% 8% 8% 4 4 3 4 4 28%	4908
	11th to 20th	Night	14% 14% 5% 7% 3 3 4 3 4 7% 35%	4979
	21st to end	Night	16% 12% 4 9% 4 4 3 3 4 5% 35%	5452
April	1st to 10th	Night	20% 13% 4 9% 5% 4 4 3 5% 5% 29%	2000
	11th to 20th	Night	18% 11% 3 7% 4 4 4 4 5% 6% 35%	1975
	21st to end	Night	16% 10% 4 7% 3 4 4 4 5% 7% 35%	1890
May	1st to 10th	Night	29% 11% 3 7% 4 4 3 3 4 5% 27%	4053
	11th to 20th	Night	26% 10% 3 6% 4 4 3 4 5% 5% 30%	3632
	21st to end	Night	21% 8% 3 6% 4 4 4 4 6% 7% 31%	3926
June	1st to 10th	Night	14% 7% 2 7% 4 5% 4 4 6% 8% 40%	1600
	11th to 20th	Night	13% 5% 2 7% 5% 4 5% 5% 6% 8% 39%	1600
	21st to end	Night	14% 5% 2 7% 4 4 4 3 7% 8% 41%	1600
July	1st to 10th	Night	12% 7% 3 7% 5% 5% 5% 4 6% 8% 40%	3600
	11th to 20th	Night	11% 8% 3 7% 5% 5% 5% 4 7% 10% 37%	3632
	21st to end	Night	11% 5% 2 5% 4 4 4 3 6% 8% 47%	4428
August	1st to 10th	Night	18% 6% 3 7% 5% 4 4 4 6% 7% 36%	2915
	11th to 20th	Night	17% 6% 2 6% 4 4 5% 3 5% 7% 39%	2875
	21st to end	Night	14% 5% 2 5% 4 3 5% 4 6% 8% 45%	3542
September	1st to 10th	Night	15% 6% 2 6% 5% 3 4 3 4 7% 46%	2000
	11th to 20th	Night	12% 5% 2 6% 3 3 3 4 5% 7% 49%	2035
	21st to end	Night	20% 9% 3 7% 5% 4 4 3 5% 6% 35%	2290
October	1st to 10th	Night	17% 7% 2 5% 4 3 4 3 5% 7% 43%	2400
	11th to 20th	Night	20% 10% 2 5% 4 5% 4 4 5% 6% 35%	2400
	21st to end	Night	22% 12% 2 6% 4 4 4 4 5% 6% 31%	2640
November	1st to 10th	Night	12% 11% 2 6% 4 4 4 4 5% 7% 41%	2585
	11th to 20th	Night	17% 15% 4 9% 5% 4 4 4 6% 6% 27%	2933
	21st to end	Night	18% 17% 5% 9% 5% 4 5% 3 5% 6% 22%	2940
December	1st to 10th	Night	17% 17% 10% 16% 5% 4 5% 3 5% 5% 14%	4720
	11th to 20th	Night	22% 15% 6% 11% 5% 4 4 3 3 4 22%	5348
	21st to end	Night	23% 19% 7% 11% 5% 4 4 3 4 5% 16%	7150

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	72% 4 8% 10% 5% 1	3606
	11th to 20th	Day	78% 3 7% 8% 4	4032
	21st to end	Day	70% 4 8% 13% 5% 1	4466
February	1st to 10th	Day	67% 5% 9% 12% 7%	1800
	11th to 20th	Day	64% 4 8% 16% 7%	1762
	21st to end	Day	62% 3 9% 18% 6% 2	1599
March	1st to 10th	Day	55% 3 12% 19% 9% 1	4930
	11th to 20th	Day	51% 4 17% 18% 8% 3	4980
	21st to end	Day	56% 4 8% 16% 14% 2	5479
April	1st to 10th	Day	56% 4 9% 18% 12% 1	2400
	11th to 20th	Day	52% 5% 11% 17% 13% 2	2374
	21st to end	Day	52% 5% 8% 20% 13% 2	2527
May	1st to 10th	Day	59% 6% 8% 17% 8% 3	5897
	11th to 20th	Day	58% 7% 8% 18% 9% 1	6248
	21st to end	Day	49% 7% 11% 21% 11% 1	6949
June	1st to 10th	Day	47% 8% 11% 19% 13% 1	2800
	11th to 20th	Day	48% 8% 14% 18% 11% 1	2800
	21st to end	Day	42% 8% 14% 23% 12% 1	2800
July	1st to 10th	Day	41% 7% 12% 25% 14% 1	6290
	11th to 20th	Day	45% 8% 13% 21% 12%	6249
	21st to end	Day	40% 6% 10% 27% 17% 1	6240
August	1st to 10th	Day	50% 8% 12% 20% 9%	4221
	11th to 20th	Day	47% 8% 15% 22% 8%	4213
	21st to end	Day	41% 7% 13% 27% 10% 1	4322
September	1st to 10th	Day	45% 4 10% 23% 15% 2	2400
	11th to 20th	Day	39% 6% 12% 25% 18% 1	2360
	21st to end	Day	53% 5% 10% 18% 14%	2110
October	1st to 10th	Day	43% 5% 11% 22% 17% 2	3260
	11th to 20th	Day	45% 4 14% 19% 16% 2	3240
	21st to end	Day	41% 5% 15% 25% 12% 1	3538
November	1st to 10th	Day	47% 5% 12% 20% 13% 3	1931
	11th to 20th	Day	61% 4 10% 17% 6% 2	1685
	21st to end	Day	65% 6% 10% 14% 6% 1	1680
December	1st to 10th	Day	79% 4 7% 9% 2	2680
	11th to 20th	Day	66% 4 11% 13% 6%	3066
	21st to end	Day	73% 4 10% 9% 4 1	4048
January	1st to 10th	Night	74% 4 7% 11% 4	6364
	11th to 20th	Night	74% 4 10% 8% 3 1	5924
	21st to end	Night	73% 3 8% 9% 6% 1	6490
February	1st to 10th	Night	64% 5% 10% 15% 6%	2600
	11th to 20th	Night	64% 5% 10% 14% 7%	2535
	21st to end	Night	61% 4 10% 15% 9% 1	2030
March	1st to 10th	Night	61% 4 12% 16% 7% 1	4918
	11th to 20th	Night	49% 6% 16% 19% 7% 3	4980
	21st to end	Night	52% 4 9% 17% 17% 2	5452
April	1st to 10th	Night	58% 5% 9% 16% 12% 1	2000
	11th to 20th	Night	50% 6% 11% 19% 12% 2	1975
	21st to end	Night	47% 5% 11% 21% 13% 2	1890
May	1st to 10th	Night	60% 5% 8% 15% 9% 3	4060
	11th to 20th	Night	54% 8% 10% 18% 10%	3633
	21st to end	Night	49% 7% 11% 18% 11% 3	3927
June	1st to 10th	Night	41% 8% 12% 23% 15% 1	1600
	11th to 20th	Night	41% 9% 12% 24% 13% 2	1600
	21st to end	Night	39% 7% 13% 26% 14% 1	1600
July	1st to 10th	Night	42% 6% 11% 25% 15% 1	3560
	11th to 20th	Night	41% 8% 15% 23% 12% 1	3584
	21st to end	Night	34% 7% 13% 25% 21% 1	4297
August	1st to 10th	Night	46% 8% 13% 24% 9% 1	2904
	11th to 20th	Night	43% 7% 13% 28% 10%	2902
	21st to end	Night	36% 6% 14% 32% 10% 2	3542
September	1st to 10th	Night	39% 6% 10% 26% 16% 3	2000
	11th to 20th	Night	34% 6% 13% 28% 18% 1	2035
	21st to end	Night	50% 5% 12% 19% 13% 1	2290
October	1st to 10th	Night	42% 5% 11% 22% 19% 1	3920
	11th to 20th	Night	41% 5% 13% 21% 16% 4	3899
	21st to end	Night	40% 4 16% 25% 14% 2	4252
November	1st to 10th	Night	43% 6% 12% 22% 15% 2	2585
	11th to 20th	Night	57% 6% 11% 16% 8% 2	2933
	21st to end	Night	62% 6% 11% 16% 5% 1	2940
December	1st to 10th	Night	72% 6% 9% 9% 3	4720
	11th to 20th	Night	67% 4 10% 15% 4	5348
	21st to end	Night	71% 5% 9% 11% 4	7150

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	35% 27% 26% 6% 5% 1	202
	11th to 20th	Day	41% 26% 25% 6% 1	293
	21st to end	Day	36% 25% 30% 8% 1	330
February	1st to 10th	Day	38% 28% 25% 8% 1	300
	11th to 20th	Day	43% 27% 26% 4	300
	21st to end	Day	43% 21% 26% 9% 1	363
March	1st to 10th	Day	34% 23% 25% 13% 4	500
	11th to 20th	Day	32% 26% 25% 13% 3 1	500
	21st to end	Day	36% 22% 25% 12% 4 1	550
April	1st to 10th	Day	35% 22% 24% 13% 4 1	500
	11th to 20th	Day	33% 22% 23% 12% 7% 3	492
	21st to end	Day	30% 20% 29% 13% 7% 1	500
May	1st to 10th	Day	31% 18% 28% 11% 9% 4	503
	11th to 20th	Day	28% 15% 30% 14% 8% 4	527
	21st to end	Day	21% 13% 30% 17% 12% 6%	573
June	1st to 10th	Day	23% 15% 29% 21% 11% 2	530
	11th to 20th	Day	23% 13% 25% 22% 12% 4	530
	21st to end	Day	19% 13% 30% 24% 11% 3	530
July	1st to 10th	Day	13% 10% 28% 25% 18% 7%	525
	11th to 20th	Day	11% 10% 30% 23% 18% 8%	524
	21st to end	Day	16% 10% 29% 24% 16% 5%	576
August	1st to 10th	Day	13% 9% 24% 28% 18% 9%	526
	11th to 20th	Day	16% 8% 27% 24% 15% 10%	519
	21st to end	Day	16% 8% 28% 23% 15% 9%	583
September	1st to 10th	Day	23% 13% 16% 22% 17% 9%	530
	11th to 20th	Day	14% 5% 22% 25% 22% 12%	530
	21st to end	Day	31% 11% 20% 21% 13% 4	530
October	1st to 10th	Day	21% 13% 22% 22% 17% 5%	530
	11th to 20th	Day	29% 17% 28% 16% 8% 2	530
	21st to end	Day	34% 18% 25% 16% 7% 1	583
November	1st to 10th	Day	26% 20% 24% 16% 13% 1	469
	11th to 20th	Day	38% 23% 22% 12% 5%	225
	21st to end	Day	36% 23% 31% 7% 2	220
December	1st to 10th	Day	42% 26% 21% 8% 2 1	220
	11th to 20th	Day	46% 18% 27% 8% 2	220
	21st to end	Day	40% 19% 30% 7% 3	242
January	1st to 10th	Night	34% 23% 27% 13% 3	805
	11th to 20th	Night	32% 24% 25% 17% 3	800
	21st to end	Night	31% 24% 28% 15% 2	880
February	1st to 10th	Night	33% 20% 28% 17% 2	800
	11th to 20th	Night	34% 25% 28% 11% 1	783
	21st to end	Night	34% 20% 27% 17% 2	660
March	1st to 10th	Night	30% 21% 29% 18% 2	800
	11th to 20th	Night	30% 22% 24% 20% 4 1	800
	21st to end	Night	26% 21% 30% 16% 6%	880
April	1st to 10th	Night	30% 20% 26% 21% 4	800
	11th to 20th	Night	27% 17% 26% 21% 8% 1	791
	21st to end	Night	24% 13% 26% 30% 7%	690
May	1st to 10th	Night	25% 11% 19% 30% 14% 1	600
	11th to 20th	Night	20% 11% 24% 36% 7%	425
	21st to end	Night	16% 8% 21% 31% 23% 1	433
June	1st to 10th	Night	16% 6% 24% 39% 16% 1	400
	11th to 20th	Night	14% 11% 19% 37% 19%	400
	21st to end	Night	14% 5% 25% 37% 19% 1	400
July	1st to 10th	Night	14% 3 21% 37% 23% 3	390
	11th to 20th	Night	9% 3 19% 40% 28% 1	394
	21st to end	Night	12% 4 16% 40% 25% 2	657
August	1st to 10th	Night	10% 3 16% 40% 30% 2	597
	11th to 20th	Night	16% 5% 13% 33% 29% 4	594
	21st to end	Night	14% 4 18% 32% 29% 3	849
September	1st to 10th	Night	18% 8% 18% 29% 24% 3	800
	11th to 20th	Night	15% 5% 18% 27% 31% 5%	800
	21st to end	Night	23% 11% 18% 25% 20% 4	800
October	1st to 10th	Night	21% 9% 21% 26% 21% 3	800
	11th to 20th	Night	27% 13% 24% 25% 10% 1	800
	21st to end	Night	31% 12% 26% 25% 6%	880
November	1st to 10th	Night	22% 14% 25% 29% 10%	820
	11th to 20th	Night	31% 17% 24% 20% 6% 1	840
	21st to end	Night	32% 17% 28% 17% 5% 1	840
December	1st to 10th	Night	33% 25% 24% 14% 4	840
	11th to 20th	Night	31% 23% 25% 18% 4	840
	21st to end	Night	33% 20% 25% 19% 2	924

Page generated at 2025-12-30 01:14:04. Version ac07

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