Red River Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Red River Observatory clear sky chart from 2005-11-06 to 2026-04-17.

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	13% 6% 2 6% 4 4 4 3 5% 7% 47%	131901
	Night	13% 5% 2 5% 3 3 3 3 4 6% 52%	130546
Transparency	Day	36% 5% 10% 24% 20% 6%	135525
	Night	32% 4 9% 22% 23% 10%	134985
Seeing	Day	14% 7% 21% 27% 23% 8%	17094
	Night	14% 6% 24% 34% 19% 2	27048

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	15% 5% 2 6% 4 3 3 2 4 6% 50%	5289
	11th to 20th	Day	8% 5% 2 4 2 2 3 2 4 6% 61%	5310
	21st to end	Day	23% 7% 2 6% 3 3 2 2 4 4 43%	5812
February	1st to 10th	Day	22% 8% 2 7% 4 4 3 2 3 4 42%	1890
	11th to 20th	Day	20% 7% 3 6% 3 4 3 3 4 4 42%	1973
	21st to end	Day	24% 7% 1 5% 2 2 4 1 3 5% 46%	1890
March	1st to 10th	Day	20% 7% 2 5% 3 2 3 3 4 6% 44%	5046
	11th to 20th	Day	12% 5% 2 5% 3 4 3 3 4 5% 53%	5090
	21st to end	Day	16% 7% 3 7% 4 4 4 3 4 6% 42%	5583
April	1st to 10th	Day	15% 7% 2 7% 4 3 3 2 5% 6% 44%	2355
	11th to 20th	Day	17% 6% 2 6% 4 4 3 3 5% 6% 44%	2446
	21st to end	Day	15% 7% 2 6% 4 4 4 4 5% 6% 43%	2400
May	1st to 10th	Day	19% 8% 2 7% 4 5% 4 3 5% 6% 38%	5770
	11th to 20th	Day	15% 7% 3 7% 5% 4 5% 4 5% 7% 40%	5862
	21st to end	Day	15% 7% 3 8% 5% 4 4 4 6% 7% 38%	6434
June	1st to 10th	Day	7% 5% 2 6% 4 5% 5% 5% 6% 10% 44%	2600
	11th to 20th	Day	7% 5% 2 6% 5% 6% 5% 5% 6% 8% 45%	2600
	21st to end	Day	5% 3 2 4 4 4 5% 5% 8% 10% 52%	2600
July	1st to 10th	Day	8% 5% 2 7% 6% 6% 6% 5% 7% 11% 36%	5900
	11th to 20th	Day	4 3 1 4 3 3 4 3 6% 9% 59%	5900
	21st to end	Day	7% 5% 3 7% 4 4 5% 4 6% 9% 44%	6422
August	1st to 10th	Day	3 2 1 3 3 3 4 4 5% 8% 65%	4234
	11th to 20th	Day	5% 4 2 5% 4 4 4 5% 7% 9% 53%	4087
	21st to end	Day	5% 4 2 5% 5% 6% 6% 5% 7% 10% 46%	4312
September	1st to 10th	Day	10% 5% 3 6% 3 4 5% 3 5% 6% 51%	2320
	11th to 20th	Day	10% 5% 2 6% 5% 4 4 4 6% 7% 47%	2200
	21st to end	Day	9% 4 1 4 4 4 4 3 5% 7% 57%	2200
October	1st to 10th	Day	7% 3 1 4 3 3 4 4 5% 6% 60%	2020
	11th to 20th	Day	14% 5% 1 4 3 2 3 2 2 4 61%	2000
	21st to end	Day	17% 5% 2 5% 3 3 4 2 4 4 52%	2200
November	1st to 10th	Day	12% 6% 2 4 3 3 4 3 4 7% 51%	2058
	11th to 20th	Day	12% 4 2 4 3 3 3 2 3 5% 58%	2100
	21st to end	Day	18% 7% 2 4 3 2 2 2 3 5% 51%	1900
December	1st to 10th	Day	19% 4 2 4 3 2 3 3 4 5% 52%	3030
	11th to 20th	Day	21% 8% 2 6% 3 3 3 3 3 6% 42%	3481
	21st to end	Day	21% 9% 3 6% 3 3 3 2 3 5% 43%	4587
January	1st to 10th	Night	14% 6% 2 5% 3 3 3 3 5% 6% 52%	7634
	11th to 20th	Night	9% 4 1 3 2 2 2 2 2 4 70%	7680
	21st to end	Night	25% 7% 2 6% 3 3 3 2 3 4 42%	8402
February	1st to 10th	Night	19% 6% 2 5% 3 3 3 3 3 5% 48%	2730
	11th to 20th	Night	19% 7% 2 5% 3 3 3 3 3 5% 46%	2550
	21st to end	Night	17% 7% 2 4 3 3 2 2 3 4 52%	1914
March	1st to 10th	Night	20% 7% 2 6% 4 3 3 2 4 5% 44%	5029
	11th to 20th	Night	11% 6% 2 5% 3 3 4 3 5% 7% 52%	5090
	21st to end	Night	14% 6% 2 5% 4 3 4 3 5% 6% 48%	5588
April	1st to 10th	Night	12% 5% 2 6% 4 3 4 3 5% 7% 49%	2263
	11th to 20th	Night	13% 6% 2 4 4 4 4 3 5% 7% 49%	2035
	21st to end	Night	12% 5% 2 5% 4 2 3 3 4 7% 52%	2000
May	1st to 10th	Night	18% 6% 3 7% 4 4 4 3 5% 7% 38%	4125
	11th to 20th	Night	13% 6% 2 7% 4 4 4 3 6% 7% 42%	4053
	21st to end	Night	13% 6% 2 5% 3 4 4 4 6% 8% 44%	4443
June	1st to 10th	Night	6% 5% 2 5% 4 4 3 3 6% 10% 54%	1800
	11th to 20th	Night	5% 4 1 4 3 3 3 3 6% 9% 60%	1800
	21st to end	Night	4 2 1 3 3 3 4 3 6% 10% 61%	1800
July	1st to 10th	Night	6% 4 2 6% 5% 5% 5% 5% 8% 12% 43%	4078
	11th to 20th	Night	4 2 1 4 3 2 3 3 5% 11% 63%	4077
	21st to end	Night	5% 4 2 5% 4 4 4 4 6% 9% 53%	4449
August	1st to 10th	Night	2 2 1 2 2 2 2 2 5% 8% 73%	2926
	11th to 20th	Night	4 2 1 3 2 3 3 4 6% 12% 60%	2969
	21st to end	Night	3 3 1 5% 4 4 5% 5% 7% 9% 54%	3586
September	1st to 10th	Night	6% 5% 2 5% 4 3 3 3 5% 7% 56%	2074
	11th to 20th	Night	10% 4 2 4 4 4 4 4 5% 7% 52%	2200
	21st to end	Night	7% 3 1 4 3 3 3 2 5% 6% 63%	2200
October	1st to 10th	Night	7% 3 1 3 3 2 3 2 4 6% 65%	2358
	11th to 20th	Night	11% 4 1 3 3 2 2 2 4 5% 62%	2400
	21st to end	Night	15% 5% 2 4 3 2 2 2 3 4 58%	2640
November	1st to 10th	Night	13% 4 1 4 3 2 3 2 4 5% 58%	2460
	11th to 20th	Night	10% 6% 2 5% 3 3 2 2 4 5% 59%	2520
	21st to end	Night	16% 5% 2 5% 3 3 3 2 3 5% 52%	2714
December	1st to 10th	Night	16% 6% 2 5% 3 3 3 2 4 4 53%	4380
	11th to 20th	Night	17% 8% 3 6% 4 4 3 2 3 3 48%	4946
	21st to end	Night	17% 9% 3 6% 3 2 3 2 3 4 47%	6633

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	38% 2 8% 29% 21% 2	5290
	11th to 20th	Day	26% 2 8% 25% 35% 4	5310
	21st to end	Day	47% 2 4 16% 21% 11%	5812
February	1st to 10th	Day	48% 3 6% 18% 19% 6%	1890
	11th to 20th	Day	46% 3 7% 20% 18% 6%	1982
	21st to end	Day	44% 2 6% 15% 24% 9%	1890
March	1st to 10th	Day	42% 3 6% 14% 21% 14%	5046
	11th to 20th	Day	34% 4 7% 16% 20% 19%	5090
	21st to end	Day	44% 4 9% 23% 17% 3	5585
April	1st to 10th	Day	42% 3 8% 21% 17% 8%	2355
	11th to 20th	Day	41% 4 9% 19% 20% 7%	2446
	21st to end	Day	41% 5% 10% 20% 20% 4	2400
May	1st to 10th	Day	46% 6% 10% 25% 11% 2	5807
	11th to 20th	Day	43% 6% 10% 20% 19% 2	5866
	21st to end	Day	45% 6% 12% 20% 14% 3	6447
June	1st to 10th	Day	34% 8% 13% 28% 15% 2	2600
	11th to 20th	Day	35% 8% 13% 24% 18% 2	2600
	21st to end	Day	25% 8% 14% 32% 19% 2	2600
July	1st to 10th	Day	39% 9% 19% 25% 8%	5836
	11th to 20th	Day	21% 6% 14% 38% 21% 1	5831
	21st to end	Day	34% 7% 13% 32% 12% 1	6240
August	1st to 10th	Day	17% 5% 12% 30% 26% 8%	4220
	11th to 20th	Day	26% 6% 19% 37% 11% 2	4126
	21st to end	Day	31% 9% 15% 30% 14% 2	4311
September	1st to 10th	Day	34% 6% 10% 20% 21% 9%	2320
	11th to 20th	Day	34% 7% 11% 23% 19% 7%	2200
	21st to end	Day	28% 5% 11% 21% 24% 12%	2200
October	1st to 10th	Day	15% 3 7% 12% 31% 32%	3293
	11th to 20th	Day	20% 2 4 18% 34% 22%	3240
	21st to end	Day	29% 3 5% 28% 27% 8%	3538
November	1st to 10th	Day	34% 4 8% 21% 25% 8%	2058
	11th to 20th	Day	31% 3 7% 21% 28% 10%	2100
	21st to end	Day	38% 2 5% 19% 27% 7%	1900
December	1st to 10th	Day	37% 3 7% 29% 21% 4	3030
	11th to 20th	Day	45% 3 4 18% 23% 6%	3479
	21st to end	Day	46% 3 5% 19% 23% 4	4587
January	1st to 10th	Night	34% 3 8% 26% 25% 3	7635
	11th to 20th	Night	22% 2 6% 20% 37% 14%	7680
	21st to end	Night	47% 3 6% 14% 20% 11%	8402
February	1st to 10th	Night	41% 4 7% 20% 21% 9%	2730
	11th to 20th	Night	43% 3 7% 18% 22% 7%	2551
	21st to end	Night	38% 3 7% 16% 24% 13%	1914
March	1st to 10th	Night	45% 3 5% 12% 20% 15%	5029
	11th to 20th	Night	32% 4 7% 18% 17% 22%	5090
	21st to end	Night	38% 4 10% 20% 24% 5%	5588
April	1st to 10th	Night	36% 5% 9% 20% 19% 12%	2263
	11th to 20th	Night	35% 5% 9% 20% 22% 10%	2035
	21st to end	Night	32% 5% 11% 24% 24% 4	2000
May	1st to 10th	Night	44% 7% 11% 22% 12% 4	4152
	11th to 20th	Night	39% 7% 12% 20% 20% 2	4054
	21st to end	Night	37% 7% 15% 20% 13% 8%	4452
June	1st to 10th	Night	26% 6% 13% 28% 22% 4	1800
	11th to 20th	Night	22% 5% 12% 35% 22% 5%	1800
	21st to end	Night	19% 7% 14% 29% 28% 4	1800
July	1st to 10th	Night	31% 8% 20% 28% 12% 1	4035
	11th to 20th	Night	18% 5% 14% 38% 23% 2	4026
	21st to end	Night	26% 7% 16% 32% 16% 3	4320
August	1st to 10th	Night	11% 4 13% 27% 38% 6%	2916
	11th to 20th	Night	18% 5% 17% 37% 19% 4	2996
	21st to end	Night	24% 7% 14% 28% 24% 3	3586
September	1st to 10th	Night	27% 5% 11% 22% 24% 11%	2074
	11th to 20th	Night	31% 6% 10% 24% 20% 9%	2200
	21st to end	Night	23% 4 9% 22% 27% 15%	2200
October	1st to 10th	Night	14% 3 5% 14% 24% 40%	3852
	11th to 20th	Night	18% 2 4 16% 35% 25%	3899
	21st to end	Night	25% 3 5% 24% 28% 15%	4252
November	1st to 10th	Night	30% 4 8% 19% 27% 13%	2460
	11th to 20th	Night	29% 3 7% 19% 27% 13%	2520
	21st to end	Night	37% 2 6% 19% 26% 9%	2714
December	1st to 10th	Night	37% 3 6% 24% 24% 5%	4380
	11th to 20th	Night	44% 2 5% 16% 22% 11%	4947
	21st to end	Night	42% 2 7% 19% 24% 5%	6633

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	24% 10% 35% 26% 5%	330
	11th to 20th	Day	17% 17% 36% 24% 5% 1	330
	21st to end	Day	22% 14% 37% 19% 8%	363
February	1st to 10th	Day	26% 10% 39% 19% 6%	330
	11th to 20th	Day	25% 15% 38% 16% 5%	330
	21st to end	Day	30% 13% 41% 11% 5%	273
March	1st to 10th	Day	23% 13% 35% 22% 6%	330
	11th to 20th	Day	21% 19% 38% 16% 6% 1	330
	21st to end	Day	17% 15% 37% 25% 5%	363
April	1st to 10th	Day	20% 14% 34% 23% 8% 1	375
	11th to 20th	Day	22% 15% 29% 25% 8% 1	516
	21st to end	Day	18% 11% 32% 26% 10% 2	500
May	1st to 10th	Day	15% 10% 30% 34% 11% 1	662
	11th to 20th	Day	15% 8% 25% 31% 17% 3	725
	21st to end	Day	12% 5% 21% 38% 18% 5%	789
June	1st to 10th	Day	8% 3 14% 32% 33% 10%	730
	11th to 20th	Day	7% 3 12% 34% 35% 9%	730
	21st to end	Day	6% 1 11% 28% 38% 15%	730
July	1st to 10th	Day	7% 1 8% 28% 39% 16%	721
	11th to 20th	Day	4 1 6% 30% 40% 19%	718
	21st to end	Day	6% 2 4 27% 41% 20%	794
August	1st to 10th	Day	5% 2 6% 26% 48% 15%	726
	11th to 20th	Day	9% 1 5% 25% 46% 14%	670
	21st to end	Day	9% 1 4 21% 39% 25%	583
September	1st to 10th	Day	10% 1 7% 26% 38% 20%	450
	11th to 20th	Day	5% 1 8% 26% 35% 24%	330
	21st to end	Day	10% 2 13% 30% 24% 20%	330
October	1st to 10th	Day	5% 13% 41% 30% 11%	330
	11th to 20th	Day	12% 6% 26% 30% 18% 8%	330
	21st to end	Day	23% 9% 23% 23% 18% 3	363
November	1st to 10th	Day	15% 9% 29% 26% 17% 3	330
	11th to 20th	Day	15% 7% 30% 34% 12% 2	330
	21st to end	Day	21% 13% 28% 26% 10% 2	330
December	1st to 10th	Day	20% 10% 33% 27% 9% 2	330
	11th to 20th	Day	25% 11% 35% 19% 10% 1	330
	21st to end	Day	23% 14% 36% 21% 5% 1	363
January	1st to 10th	Night	19% 9% 32% 33% 6%	1050
	11th to 20th	Night	19% 10% 37% 26% 7%	1050
	21st to end	Night	21% 8% 35% 31% 5%	1155
February	1st to 10th	Night	23% 9% 34% 29% 5%	1050
	11th to 20th	Night	24% 11% 34% 27% 3	916
	21st to end	Night	22% 12% 36% 27% 3	530
March	1st to 10th	Night	21% 11% 33% 30% 5%	630
	11th to 20th	Night	17% 11% 33% 34% 5%	630
	21st to end	Night	16% 9% 37% 31% 7%	693
April	1st to 10th	Night	14% 10% 37% 31% 7%	630
	11th to 20th	Night	14% 11% 36% 26% 12%	611
	21st to end	Night	13% 7% 37% 31% 11% 1	600
May	1st to 10th	Night	10% 7% 32% 40% 10% 1	600
	11th to 20th	Night	12% 6% 27% 36% 18% 2	591
	21st to end	Night	10% 5% 22% 40% 20% 3	650
June	1st to 10th	Night	6% 3 11% 41% 37% 3	600
	11th to 20th	Night	7% 1 11% 48% 31% 2	600
	21st to end	Night	3 1 9% 37% 44% 7%	600
July	1st to 10th	Night	5% 1 4 35% 49% 5%	585
	11th to 20th	Night	3 5% 35% 49% 7%	582
	21st to end	Night	4 5% 33% 49% 9%	657
August	1st to 10th	Night	3 1 4 35% 52% 5%	597
	11th to 20th	Night	7% 1 5% 32% 50% 6%	594
	21st to end	Night	5% 6% 35% 46% 7%	660
September	1st to 10th	Night	9% 2 7% 32% 46% 6%	600
	11th to 20th	Night	12% 8% 33% 42% 4	600
	21st to end	Night	8% 2 11% 39% 35% 4	600
October	1st to 10th	Night	8% 1 12% 45% 32% 3	758
	11th to 20th	Night	13% 4 20% 43% 19% 2	800
	21st to end	Night	16% 7% 25% 32% 16% 2	880
November	1st to 10th	Night	15% 3 24% 41% 15% 1	820
	11th to 20th	Night	12% 7% 28% 40% 11% 1	840
	21st to end	Night	18% 9% 29% 32% 12%	1034
December	1st to 10th	Night	18% 8% 30% 38% 7%	1050
	11th to 20th	Night	22% 8% 28% 35% 7%	1050
	21st to end	Night	21% 9% 31% 31% 7%	1155

Page generated at 2026-04-14 01:44:28. Version ac07

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