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 2024-10-20.

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% 5% 4 5% 4 6% 8% 43%	100157
	Night	12% 6% 2 5% 4 4 4 3 5% 7% 46%	98543
Transparency	Day	39% 6% 11% 21% 18% 5%	99969
	Night	37% 5% 11% 20% 20% 7%	98402
Seeing	Day	14% 8% 21% 25% 22% 11%	14995
	Night	14% 7% 23% 31% 22% 4	24691

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% 12% 2 6% 3 2 2 3 5% 7% 42%	2847
	11th to 20th	Day	17% 6% 3 6% 3 3 3 3 4 5% 48%	2850
	21st to end	Day	22% 9% 3 6% 3 3 3 3 3 5% 41%	3162
February	1st to 10th	Day	17% 9% 3 6% 4 3 4 3 5% 6% 40%	1900
	11th to 20th	Day	20% 9% 3 5% 4 3 3 3 4 5% 41%	1848
	21st to end	Day	18% 8% 3 9% 4 4 4 3 4 5% 39%	1570
March	1st to 10th	Day	21% 9% 4 9% 5% 5% 4 3 5% 6% 29%	3302
	11th to 20th	Day	16% 8% 3 7% 5% 5% 5% 4 7% 7% 34%	3480
	21st to end	Day	12% 9% 3 9% 5% 4 4 3 5% 5% 40%	3972
April	1st to 10th	Day	12% 5% 3 6% 4 4 5% 4 6% 7% 44%	2280
	11th to 20th	Day	16% 6% 2 7% 4 3 3 4 6% 6% 42%	2254
	21st to end	Day	9% 4 3 5% 5% 5% 5% 4 6% 8% 47%	2280
May	1st to 10th	Day	10% 5% 2 6% 5% 5% 6% 4 7% 11% 39%	3765
	11th to 20th	Day	12% 6% 2 6% 4 4 4 4 5% 8% 44%	3764
	21st to end	Day	8% 5% 2 6% 5% 5% 6% 5% 7% 11% 41%	4224
June	1st to 10th	Day	8% 5% 2 6% 6% 6% 6% 5% 7% 10% 38%	2660
	11th to 20th	Day	5% 4 2 7% 6% 5% 6% 6% 7% 8% 43%	2660
	21st to end	Day	6% 4 2 6% 6% 5% 6% 6% 9% 9% 40%	2553
July	1st to 10th	Day	6% 6% 2 8% 7% 7% 7% 7% 8% 12% 30%	4120
	11th to 20th	Day	8% 5% 3 7% 6% 7% 7% 7% 9% 11% 31%	4120
	21st to end	Day	13% 8% 3 9% 6% 6% 5% 5% 7% 9% 28%	4354
August	1st to 10th	Day	3 2 1 4 3 3 4 3 6% 7% 64%	3785
	11th to 20th	Day	5% 3 2 6% 4 4 6% 4 7% 10% 48%	3729
	21st to end	Day	9% 5% 2 5% 4 5% 5% 4 6% 9% 46%	4180
September	1st to 10th	Day	9% 4 2 7% 6% 5% 6% 5% 6% 9% 40%	2280
	11th to 20th	Day	12% 6% 2 6% 4 4 4 4 5% 8% 43%	2248
	21st to end	Day	11% 4 2 4 3 3 4 4 5% 7% 54%	2090
October	1st to 10th	Day	7% 3 2 5% 3 3 4 3 5% 6% 59%	1939
	11th to 20th	Day	9% 4 1 6% 3 3 3 2 5% 6% 57%	1890
	21st to end	Day	14% 4 2 4 3 2 3 3 3 5% 56%	1980
November	1st to 10th	Day	10% 5% 1 4 4 3 3 3 5% 6% 55%	1858
	11th to 20th	Day	11% 6% 3 5% 4 3 4 3 4 6% 52%	1751
	21st to end	Day	17% 6% 2 5% 3 3 4 3 5% 5% 47%	1710
December	1st to 10th	Day	17% 8% 2 5% 4 4 4 3 4 7% 42%	1710
	11th to 20th	Day	15% 10% 4 6% 4 4 4 3 4 6% 41%	2035
	21st to end	Day	15% 7% 2 5% 3 3 4 3 6% 7% 44%	3007
January	1st to 10th	Night	18% 9% 2 5% 3 3 4 3 4 5% 45%	4108
	11th to 20th	Night	15% 8% 2 6% 3 3 3 3 4 6% 48%	4120
	21st to end	Night	24% 9% 2 4 3 2 2 2 3 4 43%	4500
February	1st to 10th	Night	17% 8% 4 6% 4 3 3 3 4 6% 42%	2280
	11th to 20th	Night	20% 8% 2 4 3 3 3 3 4 4 46%	2218
	21st to end	Night	21% 8% 3 5% 4 3 3 3 5% 5% 40%	1884
March	1st to 10th	Night	19% 10% 3 7% 5% 4 4 3 5% 6% 35%	3578
	11th to 20th	Night	12% 7% 3 6% 5% 5% 5% 4 6% 8% 40%	3480
	21st to end	Night	16% 8% 2 7% 4 5% 4 4 6% 5% 40%	3658
April	1st to 10th	Night	12% 6% 2 4 3 5% 4 4 6% 8% 47%	1900
	11th to 20th	Night	12% 5% 2 5% 5% 4 3 3 6% 7% 48%	1875
	21st to end	Night	7% 4 2 6% 4 4 4 3 6% 8% 54%	1900
May	1st to 10th	Night	10% 5% 2 5% 4 3 4 3 6% 10% 47%	3130
	11th to 20th	Night	15% 6% 2 6% 3 3 4 4 5% 7% 44%	3129
	21st to end	Night	7% 5% 2 7% 4 5% 5% 5% 7% 10% 43%	3323
June	1st to 10th	Night	6% 6% 1 6% 6% 4 5% 5% 6% 9% 46%	1520
	11th to 20th	Night	4 4 1 4 3 4 4 5% 8% 11% 52%	1520
	21st to end	Night	4 4 2 4 4 5% 6% 4 8% 11% 47%	1618
July	1st to 10th	Night	6% 5% 2 7% 4 6% 4 4 7% 11% 42%	2850
	11th to 20th	Night	7% 4 2 6% 5% 6% 6% 6% 10% 14% 35%	2850
	21st to end	Night	9% 8% 3 9% 5% 4 5% 4 6% 11% 35%	3205
August	1st to 10th	Night	2 2 1 2 3 4 3 3 7% 9% 64%	3144
	11th to 20th	Night	4 3 2 5% 3 4 6% 5% 9% 12% 47%	3100
	21st to end	Night	6% 5% 2 7% 5% 4 5% 4 6% 8% 48%	3476
September	1st to 10th	Night	9% 4 2 5% 5% 4 4 4 6% 10% 47%	1900
	11th to 20th	Night	10% 4 2 6% 3 4 5% 4 7% 8% 47%	1910
	21st to end	Night	9% 4 1 4 3 3 3 3 5% 7% 56%	2090
October	1st to 10th	Night	6% 3 1 3 2 3 3 3 5% 6% 64%	2235
	11th to 20th	Night	11% 5% 2 5% 3 3 3 4 4 5% 57%	2275
	21st to end	Night	14% 5% 2 5% 3 3 3 2 3 5% 57%	2376
November	1st to 10th	Night	12% 5% 1 4 3 3 2 3 3 6% 58%	2220
	11th to 20th	Night	13% 5% 2 4 2 3 4 3 4 6% 55%	2425
	21st to end	Night	13% 6% 2 5% 3 4 4 4 5% 6% 49%	2470
December	1st to 10th	Night	17% 6% 2 5% 4 4 4 3 5% 6% 44%	2470
	11th to 20th	Night	15% 7% 3 6% 4 4 4 3 4 5% 45%	3150
	21st to end	Night	16% 10% 3 6% 3 3 3 3 5% 5% 42%	4656

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	44% 3 4 17% 26% 5%	2848
	11th to 20th	Day	38% 4 8% 22% 22% 6%	2850
	21st to end	Day	48% 2 5% 14% 22% 8%	3162
February	1st to 10th	Day	46% 4 7% 17% 17% 9%	1900
	11th to 20th	Day	46% 3 5% 18% 20% 8%	1858
	21st to end	Day	49% 3 6% 14% 19% 9%	1570
March	1st to 10th	Day	56% 5% 7% 12% 15% 5%	3302
	11th to 20th	Day	46% 6% 8% 20% 15% 5%	3480
	21st to end	Day	46% 4 6% 17% 21% 6%	3972
April	1st to 10th	Day	39% 5% 9% 23% 17% 8%	2280
	11th to 20th	Day	42% 4 8% 18% 23% 6%	2254
	21st to end	Day	34% 5% 9% 26% 23% 3	2280
May	1st to 10th	Day	37% 9% 12% 25% 14% 3	3800
	11th to 20th	Day	38% 6% 12% 21% 21% 1	3768
	21st to end	Day	33% 9% 18% 28% 11% 1	4237
June	1st to 10th	Day	39% 8% 15% 24% 13% 2	2660
	11th to 20th	Day	35% 7% 16% 24% 15% 3	2660
	21st to end	Day	36% 8% 17% 22% 14% 2	2553
July	1st to 10th	Day	44% 8% 21% 20% 6% 1	4056
	11th to 20th	Day	42% 8% 27% 19% 4 1	4051
	21st to end	Day	52% 7% 14% 21% 6% 1	4216
August	1st to 10th	Day	20% 5% 13% 31% 29% 2	3773
	11th to 20th	Day	31% 6% 19% 29% 14% 2	3765
	21st to end	Day	36% 6% 15% 22% 19% 3	4179
September	1st to 10th	Day	39% 8% 14% 17% 16% 6%	2280
	11th to 20th	Day	40% 6% 9% 18% 20% 7%	2248
	21st to end	Day	29% 4 11% 25% 20% 11%	2090
October	1st to 10th	Day	26% 4 8% 21% 25% 16%	1939
	11th to 20th	Day	28% 4 6% 17% 31% 15%	1890
	21st to end	Day	33% 3 4 17% 31% 12%	1980
November	1st to 10th	Day	32% 3 6% 18% 30% 11%	1858
	11th to 20th	Day	35% 3 5% 15% 28% 13%	1751
	21st to end	Day	40% 4 6% 18% 22% 10%	1710
December	1st to 10th	Day	43% 3 10% 18% 17% 9%	1710
	11th to 20th	Day	46% 3 6% 16% 23% 6%	2032
	21st to end	Day	39% 5% 6% 20% 27% 3	3007
January	1st to 10th	Night	43% 3 5% 15% 26% 8%	4108
	11th to 20th	Night	38% 4 6% 20% 20% 11%	4120
	21st to end	Night	47% 3 5% 16% 23% 6%	4500
February	1st to 10th	Night	44% 3 6% 17% 21% 8%	2280
	11th to 20th	Night	42% 4 6% 17% 21% 10%	2219
	21st to end	Night	46% 5% 6% 15% 17% 12%	1884
March	1st to 10th	Night	50% 5% 7% 16% 15% 7%	3578
	11th to 20th	Night	41% 6% 9% 20% 18% 6%	3480
	21st to end	Night	44% 5% 8% 17% 21% 4	3658
April	1st to 10th	Night	35% 5% 11% 19% 19% 10%	1900
	11th to 20th	Night	35% 4 9% 20% 22% 10%	1875
	21st to end	Night	29% 4 9% 26% 26% 6%	1900
May	1st to 10th	Night	33% 7% 11% 27% 19% 4	3160
	11th to 20th	Night	38% 6% 11% 26% 18% 1	3130
	21st to end	Night	33% 9% 15% 26% 14% 3	3331
June	1st to 10th	Night	33% 8% 16% 24% 16% 2	1520
	11th to 20th	Night	25% 7% 19% 29% 17% 4	1520
	21st to end	Night	29% 7% 22% 23% 16% 3	1618
July	1st to 10th	Night	36% 9% 23% 23% 7% 2	2805
	11th to 20th	Night	37% 8% 27% 22% 5% 1	2796
	21st to end	Night	44% 7% 19% 22% 7% 1	3103
August	1st to 10th	Night	16% 7% 17% 32% 27% 2	3132
	11th to 20th	Night	27% 7% 21% 32% 11% 2	3130
	21st to end	Night	34% 7% 13% 22% 20% 5%	3476
September	1st to 10th	Night	32% 8% 15% 21% 18% 7%	1900
	11th to 20th	Night	34% 7% 15% 15% 20% 9%	1910
	21st to end	Night	28% 4 9% 26% 21% 11%	2090
October	1st to 10th	Night	22% 3 9% 22% 26% 18%	2235
	11th to 20th	Night	30% 4 5% 16% 28% 17%	2275
	21st to end	Night	33% 3 6% 16% 26% 16%	2376
November	1st to 10th	Night	30% 2 6% 18% 29% 14%	2220
	11th to 20th	Night	31% 4 7% 16% 27% 15%	2425
	21st to end	Night	37% 4 7% 19% 21% 13%	2470
December	1st to 10th	Night	41% 4 10% 18% 20% 7%	2470
	11th to 20th	Night	43% 3 6% 13% 27% 8%	3152
	21st to end	Night	44% 3 6% 17% 25% 5%	4656

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	23% 19% 39% 15% 3 1	270
	11th to 20th	Day	26% 19% 33% 15% 7%	270
	21st to end	Day	27% 20% 35% 15% 3	297
February	1st to 10th	Day	23% 20% 37% 14% 6% 1	270
	11th to 20th	Day	34% 11% 39% 13% 2	270
	21st to end	Day	25% 24% 39% 12% 1	225
March	1st to 10th	Day	25% 17% 36% 19% 4	270
	11th to 20th	Day	22% 19% 35% 20% 4	270
	21st to end	Day	18% 16% 36% 21% 8%	391
April	1st to 10th	Day	18% 15% 34% 23% 10% 1	460
	11th to 20th	Day	23% 13% 26% 26% 10% 2	452
	21st to end	Day	12% 9% 31% 31% 16% 2	460
May	1st to 10th	Day	12% 10% 28% 32% 14% 3	463
	11th to 20th	Day	13% 4 22% 31% 21% 9%	487
	21st to end	Day	6% 3 22% 32% 26% 12%	530
June	1st to 10th	Day	11% 4 13% 30% 30% 13%	680
	11th to 20th	Day	7% 3 13% 32% 33% 12%	680
	21st to end	Day	9% 2 11% 28% 32% 18%	680
July	1st to 10th	Day	6% 1 7% 28% 37% 21%	671
	11th to 20th	Day	6% 2 5% 20% 40% 28%	668
	21st to end	Day	9% 7% 24% 37% 22%	677
August	1st to 10th	Day	7% 1 6% 21% 36% 29%	486
	11th to 20th	Day	7% 1 7% 20% 40% 26%	479
	21st to end	Day	15% 1 6% 17% 34% 26%	539
September	1st to 10th	Day	9% 1 10% 24% 38% 18%	490
	11th to 20th	Day	13% 3 11% 20% 34% 19%	490
	21st to end	Day	11% 3 11% 31% 31% 13%	490
October	1st to 10th	Day	8% 3 22% 38% 19% 9%	339
	11th to 20th	Day	9% 7% 24% 37% 19% 4	297
	21st to end	Day	22% 9% 24% 26% 15% 4	297
November	1st to 10th	Day	17% 6% 24% 36% 14% 4	270
	11th to 20th	Day	14% 14% 35% 24% 11% 1	270
	21st to end	Day	18% 14% 36% 18% 11% 3	270
December	1st to 10th	Day	23% 15% 34% 20% 7% 1	270
	11th to 20th	Day	21% 14% 34% 24% 6% 1	270
	21st to end	Day	23% 16% 35% 21% 5%	297
January	1st to 10th	Night	23% 12% 32% 28% 5%	950
	11th to 20th	Night	20% 12% 33% 26% 8%	950
	21st to end	Night	23% 12% 34% 28% 4	1026
February	1st to 10th	Night	21% 13% 33% 29% 4	760
	11th to 20th	Night	24% 13% 31% 28% 5%	743
	21st to end	Night	25% 15% 35% 22% 1	628
March	1st to 10th	Night	19% 12% 32% 31% 6%	670
	11th to 20th	Night	16% 9% 37% 30% 7% 1	570
	21st to end	Night	17% 9% 37% 29% 8%	627
April	1st to 10th	Night	14% 9% 36% 29% 11% 1	570
	11th to 20th	Night	13% 11% 31% 31% 11% 1	563
	21st to end	Night	8% 7% 36% 36% 14%	570
May	1st to 10th	Night	10% 6% 26% 41% 15% 2	570
	11th to 20th	Night	11% 2 21% 41% 22% 3	561
	21st to end	Night	6% 2 17% 35% 33% 6%	617
June	1st to 10th	Night	9% 1 10% 38% 37% 5%	570
	11th to 20th	Night	5% 1 8% 34% 44% 7%	570
	21st to end	Night	4 2 9% 29% 44% 12%	570
July	1st to 10th	Night	5% 1 6% 29% 48% 11%	555
	11th to 20th	Night	5% 1 5% 23% 49% 17%	552
	21st to end	Night	5% 1 5% 27% 48% 14%	624
August	1st to 10th	Night	3 1 3 23% 52% 19%	567
	11th to 20th	Night	8% 4 22% 52% 13%	564
	21st to end	Night	10% 1 5% 23% 45% 15%	627
September	1st to 10th	Night	9% 1 9% 29% 44% 8%	570
	11th to 20th	Night	10% 2 8% 29% 42% 9%	580
	21st to end	Night	11% 2 10% 34% 37% 6%	760
October	1st to 10th	Night	7% 1 15% 39% 32% 6%	760
	11th to 20th	Night	13% 5% 21% 36% 23% 2	759
	21st to end	Night	17% 6% 20% 34% 20% 3	792
November	1st to 10th	Night	14% 6% 18% 39% 21% 2	740
	11th to 20th	Night	14% 7% 29% 35% 14% 1	760
	21st to end	Night	15% 8% 28% 34% 14% 2	760
December	1st to 10th	Night	19% 9% 31% 32% 9%	760
	11th to 20th	Night	20% 9% 30% 32% 9%	831
	21st to end	Night	24% 11% 30% 28% 7%	1045

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