The Cowpasture
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the The Cowpasture clear sky chart from 2005-11-06 to 2026-07-31.

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	12% 6% 2 6% 4 4 5% 4 6% 8% 43%	136581
	Night	13% 6% 2 6% 4 4 4 3 5% 7% 45%	136560
Transparency	Day	39% 4 11% 21% 18% 6%	140218
	Night	38% 4 10% 20% 20% 8%	141003
Seeing	Day	14% 8% 21% 25% 22% 11%	17373
	Night	14% 7% 23% 31% 21% 4	27029

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% 11% 4 9% 3 3 3 2 4 6% 40%	5289
	11th to 20th	Day	11% 4 2 5% 3 3 3 3 5% 7% 54%	5310
	21st to end	Day	23% 10% 3 7% 4 3 3 2 3 4 38%	5865
February	1st to 10th	Day	16% 9% 3 6% 4 3 4 3 5% 6% 41%	2100
	11th to 20th	Day	20% 9% 3 6% 4 3 3 3 4 5% 40%	2048
	21st to end	Day	17% 7% 3 9% 4 4 4 3 5% 5% 40%	1730
March	1st to 10th	Day	19% 8% 3 9% 5% 5% 4 3 5% 6% 32%	4851
	11th to 20th	Day	13% 6% 2 6% 4 4 5% 3 5% 6% 45%	5090
	21st to end	Day	13% 8% 3 9% 5% 5% 4 3 5% 5% 40%	5816
April	1st to 10th	Day	12% 5% 2 7% 4 4 5% 4 6% 7% 43%	2520
	11th to 20th	Day	15% 5% 2 7% 4 3 3 3 5% 6% 45%	2494
	21st to end	Day	10% 4 2 5% 5% 5% 5% 4 6% 8% 45%	2520
May	1st to 10th	Day	18% 7% 3 7% 4 4 5% 3 6% 8% 35%	7021
	11th to 20th	Day	10% 6% 2 7% 5% 5% 5% 4 6% 8% 40%	7031
	21st to end	Day	11% 6% 3 7% 5% 6% 6% 5% 8% 11% 34%	7887
June	1st to 10th	Day	8% 5% 2 6% 6% 6% 6% 5% 7% 10% 38%	2940
	11th to 20th	Day	5% 4 2 7% 6% 5% 6% 6% 7% 9% 41%	2940
	21st to end	Day	6% 4 2 6% 6% 5% 6% 6% 9% 10% 40%	2821
July	1st to 10th	Day	5% 5% 2 7% 7% 7% 7% 6% 8% 11% 34%	6030
	11th to 20th	Day	6% 4 2 6% 5% 6% 6% 6% 8% 12% 39%	6030
	21st to end	Day	10% 6% 2 7% 5% 6% 5% 5% 8% 10% 36%	6384
August	1st to 10th	Day	3 2 1 4 3 3 4 3 6% 8% 64%	3905
	11th to 20th	Day	5% 3 2 6% 4 4 6% 4 7% 10% 48%	3849
	21st to end	Day	9% 5% 2 5% 4 5% 5% 4 6% 9% 46%	4312
September	1st to 10th	Day	9% 4 2 7% 6% 5% 6% 5% 6% 9% 41%	2400
	11th to 20th	Day	12% 6% 2 6% 4 4 4 4 5% 8% 44%	2366
	21st to end	Day	11% 4 2 4 3 3 4 4 5% 7% 54%	2200
October	1st to 10th	Day	7% 3 2 5% 3 4 4 3 5% 6% 59%	2041
	11th to 20th	Day	9% 4 1 6% 3 3 3 2 5% 6% 58%	2000
	21st to end	Day	13% 4 2 4 3 2 3 3 3 5% 57%	2200
November	1st to 10th	Day	10% 5% 1 5% 4 4 3 3 5% 6% 54%	2058
	11th to 20th	Day	11% 6% 3 5% 4 3 4 3 4 6% 54%	1935
	21st to end	Day	16% 6% 2 5% 3 3 4 3 5% 6% 47%	1890
December	1st to 10th	Day	18% 9% 2 5% 3 3 3 3 4 6% 43%	3020
	11th to 20th	Day	15% 9% 4 7% 5% 4 4 2 4 6% 41%	3289
	21st to end	Day	15% 7% 2 5% 3 3 3 2 4 6% 49%	4399
January	1st to 10th	Night	19% 7% 4 6% 3 3 3 3 4 4 43%	7634
	11th to 20th	Night	14% 6% 3 5% 3 2 3 3 4 6% 51%	7680
	21st to end	Night	25% 9% 2 6% 4 3 3 2 3 4 37%	8342
February	1st to 10th	Night	16% 8% 3 5% 4 3 3 3 4 6% 44%	2520
	11th to 20th	Night	20% 8% 2 5% 3 3 3 3 4 4 44%	2458
	21st to end	Night	20% 8% 3 5% 4 3 3 3 4 5% 42%	2076
March	1st to 10th	Night	17% 8% 2 7% 4 4 4 3 5% 6% 39%	5263
	11th to 20th	Night	11% 6% 2 5% 4 4 4 3 5% 7% 49%	5090
	21st to end	Night	16% 7% 2 6% 4 4 4 3 5% 5% 43%	5354
April	1st to 10th	Night	13% 6% 2 5% 3 5% 4 4 6% 7% 46%	2100
	11th to 20th	Night	12% 5% 2 5% 5% 4 3 3 6% 7% 49%	2075
	21st to end	Night	8% 4 2 6% 4 4 4 3 6% 8% 51%	2100
May	1st to 10th	Night	19% 6% 2 6% 4 4 4 3 5% 8% 39%	5832
	11th to 20th	Night	13% 6% 3 7% 4 4 5% 4 6% 8% 38%	5829
	21st to end	Night	12% 6% 3 8% 5% 5% 5% 5% 8% 11% 34%	6229
June	1st to 10th	Night	6% 6% 1 6% 6% 5% 5% 5% 6% 9% 45%	1680
	11th to 20th	Night	4 4 1 4 4 4 4 5% 8% 11% 50%	1680
	21st to end	Night	4 4 2 5% 4 5% 6% 4 8% 11% 47%	1788
July	1st to 10th	Night	5% 4 2 7% 5% 6% 5% 5% 8% 11% 41%	4168
	11th to 20th	Night	6% 3 1 5% 4 5% 5% 5% 10% 16% 39%	4167
	21st to end	Night	7% 6% 2 8% 5% 5% 5% 5% 8% 12% 37%	4687
August	1st to 10th	Night	2 2 1 3 3 4 3 3 6% 9% 64%	3244
	11th to 20th	Night	4 3 2 5% 3 4 6% 5% 9% 12% 48%	3200
	21st to end	Night	6% 5% 2 7% 5% 4 5% 4 6% 8% 48%	3586
September	1st to 10th	Night	9% 4 2 5% 5% 4 4 4 6% 10% 46%	2000
	11th to 20th	Night	9% 4 2 6% 3 4 5% 4 7% 8% 47%	2011
	21st to end	Night	9% 4 1 4 3 3 3 3 5% 7% 56%	2200
October	1st to 10th	Night	6% 3 2 3 2 3 3 3 5% 6% 63%	2353
	11th to 20th	Night	10% 5% 2 4 3 3 3 3 3 5% 58%	2400
	21st to end	Night	14% 5% 1 5% 3 3 2 2 3 5% 57%	2640
November	1st to 10th	Night	12% 5% 1 4 3 3 2 3 3 6% 58%	2460
	11th to 20th	Night	12% 5% 1 4 2 3 3 3 4 6% 56%	2681
	21st to end	Night	13% 6% 2 5% 3 4 4 3 5% 6% 49%	2730
December	1st to 10th	Night	21% 6% 2 5% 4 3 4 3 4 4 45%	4380
	11th to 20th	Night	15% 9% 2 6% 4 4 4 2 4 5% 45%	5120
	21st to end	Night	18% 9% 2 5% 3 3 2 2 4 5% 47%	6803

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	48% 2 6% 22% 19% 3	5290
	11th to 20th	Day	31% 3 6% 24% 30% 6%	5310
	21st to end	Day	53% 2 4 10% 19% 12%	5865
February	1st to 10th	Day	45% 3 7% 18% 18% 9%	2100
	11th to 20th	Day	48% 3 6% 18% 18% 7%	2058
	21st to end	Day	48% 3 6% 13% 20% 10%	1730
March	1st to 10th	Day	53% 4 5% 15% 17% 7%	4851
	11th to 20th	Day	39% 4 6% 16% 19% 16%	5090
	21st to end	Day	47% 3 7% 19% 17% 7%	5818
April	1st to 10th	Day	39% 5% 9% 23% 17% 7%	2520
	11th to 20th	Day	39% 3 8% 19% 24% 6%	2494
	21st to end	Day	36% 4 10% 25% 22% 3	2520
May	1st to 10th	Day	48% 5% 10% 21% 13% 3	7056
	11th to 20th	Day	42% 4 15% 18% 19% 2	7035
	21st to end	Day	43% 6% 18% 21% 12% 1	7901
June	1st to 10th	Day	39% 8% 14% 24% 14% 1	2940
	11th to 20th	Day	37% 7% 17% 23% 14% 3	2940
	21st to end	Day	36% 8% 19% 23% 13% 2	2821
July	1st to 10th	Day	42% 6% 20% 22% 9% 1	5966
	11th to 20th	Day	35% 6% 32% 24% 3 1	5961
	21st to end	Day	43% 6% 18% 29% 4	6204
August	1st to 10th	Day	20% 5% 13% 32% 28% 2	3893
	11th to 20th	Day	30% 6% 20% 29% 14% 2	3885
	21st to end	Day	36% 6% 15% 21% 19% 3	4311
September	1st to 10th	Day	38% 8% 15% 18% 16% 6%	2400
	11th to 20th	Day	39% 6% 9% 20% 20% 7%	2366
	21st to end	Day	29% 4 12% 25% 20% 10%	2200
October	1st to 10th	Day	19% 2 5% 16% 25% 33%	3327
	11th to 20th	Day	17% 2 4 14% 33% 30%	3240
	21st to end	Day	23% 2 3 18% 38% 16%	3538
November	1st to 10th	Day	33% 3 7% 18% 29% 11%	2058
	11th to 20th	Day	33% 3 6% 16% 28% 13%	1935
	21st to end	Day	40% 3 6% 18% 23% 10%	1890
December	1st to 10th	Day	44% 2 7% 18% 24% 5%	3020
	11th to 20th	Day	47% 2 7% 17% 19% 8%	3286
	21st to end	Day	37% 3 5% 24% 28% 2	4399
January	1st to 10th	Night	47% 2 5% 21% 21% 5%	7635
	11th to 20th	Night	37% 2 4 15% 29% 12%	7680
	21st to end	Night	53% 2 3 15% 18% 9%	8342
February	1st to 10th	Night	43% 3 5% 17% 23% 9%	2520
	11th to 20th	Night	44% 3 7% 17% 19% 9%	2459
	21st to end	Night	45% 4 6% 15% 17% 12%	2076
March	1st to 10th	Night	46% 4 6% 14% 20% 10%	5263
	11th to 20th	Night	35% 4 6% 18% 19% 17%	5090
	21st to end	Night	43% 3 10% 18% 19% 7%	5354
April	1st to 10th	Night	36% 5% 11% 19% 19% 10%	2100
	11th to 20th	Night	34% 4 9% 21% 23% 9%	2075
	21st to end	Night	31% 4 10% 25% 24% 5%	2100
May	1st to 10th	Night	45% 4 11% 21% 16% 4	5862
	11th to 20th	Night	44% 4 14% 22% 15% 2	5830
	21st to end	Night	44% 7% 16% 20% 11% 2	6240
June	1st to 10th	Night	33% 8% 16% 24% 17% 2	1680
	11th to 20th	Night	28% 7% 19% 27% 15% 4	1680
	21st to end	Night	30% 6% 22% 24% 15% 3	1788
July	1st to 10th	Night	36% 7% 24% 23% 8% 1	4125
	11th to 20th	Night	32% 9% 33% 22% 3 1	4116
	21st to end	Night	39% 7% 20% 27% 6%	4555
August	1st to 10th	Night	17% 7% 17% 32% 27% 2	3232
	11th to 20th	Night	27% 7% 22% 32% 11% 2	3230
	21st to end	Night	34% 7% 13% 22% 20% 5%	3586
September	1st to 10th	Night	33% 7% 15% 20% 17% 7%	2000
	11th to 20th	Night	33% 6% 14% 16% 21% 9%	2011
	21st to end	Night	28% 4 10% 25% 21% 11%	2200
October	1st to 10th	Night	17% 2 6% 16% 24% 35%	3847
	11th to 20th	Night	20% 3 3 16% 26% 33%	3899
	21st to end	Night	22% 2 5% 14% 36% 21%	4252
November	1st to 10th	Night	31% 2 7% 18% 29% 13%	2460
	11th to 20th	Night	31% 3 7% 17% 27% 15%	2681
	21st to end	Night	36% 3 7% 20% 21% 13%	2730
December	1st to 10th	Night	44% 2 6% 17% 25% 5%	4380
	11th to 20th	Night	45% 2 7% 16% 24% 6%	5122
	21st to end	Night	41% 2 5% 21% 27% 3	6803

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% 18% 38% 16% 3 1	330
	11th to 20th	Day	23% 20% 36% 15% 6%	330
	21st to end	Day	27% 21% 34% 15% 3	363
February	1st to 10th	Day	21% 18% 40% 15% 5% 1	330
	11th to 20th	Day	32% 14% 37% 13% 3	330
	21st to end	Day	24% 23% 38% 12% 3	273
March	1st to 10th	Day	24% 17% 35% 21% 3	330
	11th to 20th	Day	22% 19% 36% 19% 4	330
	21st to end	Day	18% 15% 36% 23% 8%	467
April	1st to 10th	Day	17% 16% 34% 23% 9% 1	540
	11th to 20th	Day	20% 13% 29% 26% 9% 2	532
	21st to end	Day	14% 9% 29% 31% 15% 2	540
May	1st to 10th	Day	15% 11% 28% 30% 13% 3	543
	11th to 20th	Day	13% 6% 24% 31% 19% 8%	567
	21st to end	Day	7% 4 21% 33% 25% 10%	618
June	1st to 10th	Day	10% 4 14% 31% 29% 11%	780
	11th to 20th	Day	8% 4 13% 33% 32% 11%	780
	21st to end	Day	8% 2 11% 28% 32% 20%	780
July	1st to 10th	Day	5% 1 7% 27% 39% 22%	771
	11th to 20th	Day	6% 2 4 20% 40% 28%	768
	21st to end	Day	8% 1 6% 23% 40% 22%	776
August	1st to 10th	Day	6% 1 6% 21% 38% 28%	526
	11th to 20th	Day	6% 1 6% 19% 39% 29%	519
	21st to end	Day	15% 1 7% 18% 34% 25%	583
September	1st to 10th	Day	8% 2 9% 26% 38% 17%	530
	11th to 20th	Day	12% 3 10% 19% 36% 21%	530
	21st to end	Day	11% 3 12% 32% 30% 12%	530
October	1st to 10th	Day	8% 2 23% 38% 20% 9%	371
	11th to 20th	Day	8% 6% 25% 37% 18% 6%	330
	21st to end	Day	20% 8% 23% 26% 17% 5%	363
November	1st to 10th	Day	17% 7% 26% 33% 14% 4	330
	11th to 20th	Day	12% 13% 35% 27% 11% 1	330
	21st to end	Day	17% 14% 38% 18% 10% 3	330
December	1st to 10th	Day	22% 17% 36% 18% 6% 1	330
	11th to 20th	Day	19% 13% 35% 26% 6% 1	330
	21st to end	Day	20% 17% 35% 21% 7% 1	363
January	1st to 10th	Night	22% 11% 33% 28% 4	1050
	11th to 20th	Night	20% 12% 34% 26% 8%	1050
	21st to end	Night	24% 12% 33% 28% 4	1134
February	1st to 10th	Night	20% 12% 34% 30% 4	840
	11th to 20th	Night	24% 13% 31% 27% 4	823
	21st to end	Night	24% 16% 36% 23% 2	692
March	1st to 10th	Night	18% 12% 33% 31% 6%	740
	11th to 20th	Night	16% 9% 37% 30% 7%	630
	21st to end	Night	16% 9% 36% 31% 8%	693
April	1st to 10th	Night	16% 10% 34% 30% 10%	630
	11th to 20th	Night	12% 11% 32% 33% 11% 1	623
	21st to end	Night	9% 7% 34% 36% 14%	630
May	1st to 10th	Night	12% 5% 25% 41% 14% 2	630
	11th to 20th	Night	11% 3 24% 39% 21% 2	621
	21st to end	Night	7% 2 17% 36% 32% 6%	683
June	1st to 10th	Night	9% 1 10% 39% 37% 5%	630
	11th to 20th	Night	6% 1 9% 36% 42% 7%	630
	21st to end	Night	4 1 9% 28% 45% 13%	630
July	1st to 10th	Night	5% 1 6% 27% 50% 11%	615
	11th to 20th	Night	6% 1 4 22% 49% 17%	612
	21st to end	Night	5% 1 5% 26% 50% 14%	687
August	1st to 10th	Night	3 1 3 23% 52% 18%	597
	11th to 20th	Night	7% 4 21% 52% 15%	594
	21st to end	Night	10% 1 6% 24% 45% 14%	660
September	1st to 10th	Night	9% 1 10% 31% 42% 8%	600
	11th to 20th	Night	10% 1 7% 28% 44% 10%	611
	21st to end	Night	11% 2 10% 35% 36% 5%	800
October	1st to 10th	Night	7% 2 15% 38% 32% 6%	800
	11th to 20th	Night	13% 5% 20% 37% 24% 2	800
	21st to end	Night	16% 6% 19% 35% 21% 3	880
November	1st to 10th	Night	14% 6% 18% 39% 20% 2	820
	11th to 20th	Night	13% 7% 28% 36% 14% 1	840
	21st to end	Night	15% 8% 29% 34% 13% 2	840
December	1st to 10th	Night	20% 9% 31% 31% 9%	840
	11th to 20th	Night	20% 9% 30% 33% 9%	919
	21st to end	Night	23% 11% 29% 28% 8%	1155

Page generated at 2026-07-28 02:25:21. Version ac07

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