Ashland
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ashland clear sky chart from 2005-11-06 to 2025-08-05.

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	7% 9% 3 6% 4 3 3 3 4 6% 52%	129937
	Night	8% 11% 3 7% 4 4 4 3 4 6% 46%	126972
Transparency	Day	32% 6% 10% 22% 19% 10%	129645
	Night	38% 7% 10% 21% 16% 7%	126779
Seeing	Day	16% 16% 28% 25% 12% 3	15863
	Night	15% 9% 19% 32% 21% 3	24902

By Month

Percentage Cloud Cover SW (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	13% 20% 5% 10% 5% 4 5% 4 5% 7% 21%	3639
	11th to 20th	Day	14% 13% 3 6% 4 4 4 2 3 4 42%	3852
	21st to end	Day	10% 10% 3 7% 4 4 4 3 5% 6% 44%	4510
February	1st to 10th	Day	8% 16% 4 9% 5% 6% 6% 4 8% 5% 30%	1800
	11th to 20th	Day	9% 16% 4 8% 5% 4 5% 4 6% 7% 32%	1755
	21st to end	Day	11% 20% 5% 8% 6% 4 3 3 4 7% 30%	1618
March	1st to 10th	Day	10% 19% 6% 10% 6% 5% 4 3 4 5% 29%	4818
	11th to 20th	Day	8% 17% 4 9% 5% 4 4 4 5% 6% 34%	5000
	21st to end	Day	10% 18% 5% 10% 6% 5% 5% 4 6% 6% 26%	5567
April	1st to 10th	Day	12% 19% 5% 10% 5% 5% 4 3 4 6% 28%	2400
	11th to 20th	Day	13% 16% 4 7% 5% 4 3 3 5% 7% 33%	2369
	21st to end	Day	10% 14% 4 7% 5% 4 4 3 6% 8% 36%	2493
May	1st to 10th	Day	8% 10% 3 5% 3 3 2 2 4 6% 54%	5965
	11th to 20th	Day	7% 8% 3 6% 4 4 4 3 5% 6% 51%	6277
	21st to end	Day	6% 6% 2 4 3 3 3 3 5% 8% 59%	6902
June	1st to 10th	Day	11% 9% 2 5% 5% 4 3 3 5% 8% 45%	2800
	11th to 20th	Day	7% 6% 2 5% 4 4 3 3 5% 7% 55%	2800
	21st to end	Day	5% 3 1 3 2 2 3 2 4 5% 69%	2800
July	1st to 10th	Day	1 1 1 1 1 1 2 2 3 3 84%	6319
	11th to 20th	Day	1 1 2 1 2 2 2 3 3 82%	6320
	21st to end	Day	1 1 2 1 1 2 2 3 4 83%	6560
August	1st to 10th	Day	2 2 1 2 2 3 3 3 3 5% 74%	4144
	11th to 20th	Day	1 1 1 2 1 2 2 2 3 5% 79%	4026
	21st to end	Day	2 2 1 3 2 2 2 2 3 4 77%	4194
September	1st to 10th	Day	2 2 1 2 2 1 1 2 4 5% 78%	2280
	11th to 20th	Day	4 4 1 4 3 3 3 4 6% 7% 60%	2280
	21st to end	Day	6% 4 1 4 3 2 3 3 5% 7% 63%	1995
October	1st to 10th	Day	5% 3 1 3 3 2 3 2 3 4 70%	3180
	11th to 20th	Day	6% 6% 2 4 4 4 5% 4 5% 8% 52%	3161
	21st to end	Day	10% 10% 3 8% 5% 4 4 4 5% 7% 40%	3448
November	1st to 10th	Day	14% 12% 3 7% 5% 4 4 4 5% 8% 33%	1803
	11th to 20th	Day	16% 11% 3 8% 5% 5% 6% 5% 8% 8% 26%	1610
	21st to end	Day	11% 14% 3 7% 5% 5% 4 3 5% 7% 36%	1600
December	1st to 10th	Day	6% 7% 2 5% 4 3 5% 4 7% 8% 49%	2620
	11th to 20th	Day	12% 16% 5% 10% 6% 6% 5% 4 6% 7% 22%	3028
	21st to end	Day	15% 17% 5% 11% 6% 6% 6% 5% 6% 7% 16%	4004
January	1st to 10th	Night	13% 20% 6% 11% 5% 5% 5% 4 5% 6% 21%	6306
	11th to 20th	Night	13% 14% 5% 7% 4 3 3 3 4 5% 40%	6102
	21st to end	Night	11% 13% 4 8% 4 4 4 3 4 5% 40%	6468
February	1st to 10th	Night	10% 14% 5% 10% 5% 5% 4 4 6% 6% 31%	2600
	11th to 20th	Night	11% 17% 5% 8% 5% 5% 5% 3 5% 6% 31%	2532
	21st to end	Night	8% 18% 6% 10% 5% 4 5% 4 5% 6% 29%	2011
March	1st to 10th	Night	11% 20% 6% 10% 5% 4 4 3 4 6% 26%	5074
	11th to 20th	Night	7% 15% 4 9% 5% 5% 5% 3 5% 5% 37%	5000
	21st to end	Night	8% 20% 7% 12% 6% 6% 4 3 5% 6% 25%	5407
April	1st to 10th	Night	11% 18% 5% 10% 4 4 4 4 5% 6% 29%	2000
	11th to 20th	Night	11% 16% 4 7% 4 3 4 4 5% 6% 36%	1979
	21st to end	Night	14% 15% 4 6% 3 2 3 3 6% 10% 34%	1904
May	1st to 10th	Night	10% 13% 3 7% 3 2 2 2 3 5% 50%	4008
	11th to 20th	Night	8% 15% 4 6% 3 3 2 2 4 5% 49%	3616
	21st to end	Night	7% 9% 2 4 2 2 3 3 4 5% 59%	3972
June	1st to 10th	Night	11% 9% 2 5% 5% 4 4 3 6% 6% 46%	1600
	11th to 20th	Night	7% 8% 3 6% 4 3 3 3 5% 5% 54%	1600
	21st to end	Night	5% 4 1 3 2 2 2 2 4 5% 70%	1600
July	1st to 10th	Night	1 1 1 2 2 2 3 2 3 3 80%	3640
	11th to 20th	Night	1 2 2 2 1 1 1 2 3 85%	3640
	21st to end	Night	1 2 1 2 2 2 2 1 2 4 82%	4288
August	1st to 10th	Night	2 2 1 2 2 2 2 3 4 5% 77%	2884
	11th to 20th	Night	1 1 2 1 2 2 2 3 4 80%	2812
	21st to end	Night	5% 3 1 3 1 2 2 1 3 4 75%	3484
September	1st to 10th	Night	2 2 1 2 1 1 2 2 3 5% 79%	1900
	11th to 20th	Night	4 4 1 4 3 3 3 3 6% 6% 62%	1900
	21st to end	Night	8% 6% 2 4 2 2 3 2 4 5% 62%	2178
October	1st to 10th	Night	4 4 1 3 2 3 3 2 3 4 70%	3800
	11th to 20th	Night	9% 7% 2 6% 3 3 3 2 4 6% 55%	3777
	21st to end	Night	7% 9% 3 7% 5% 5% 5% 4 7% 7% 41%	4121
November	1st to 10th	Night	15% 14% 3 8% 4 4 5% 4 4 6% 33%	2495
	11th to 20th	Night	16% 12% 2 7% 5% 5% 6% 5% 6% 8% 27%	2786
	21st to end	Night	12% 13% 4 6% 4 4 4 3 5% 7% 38%	2800
December	1st to 10th	Night	8% 9% 2 5% 3 4 3 4 5% 7% 49%	4560
	11th to 20th	Night	9% 15% 5% 11% 6% 7% 7% 5% 6% 7% 21%	5176
	21st to end	Night	14% 16% 5% 10% 5% 6% 5% 4 5% 7% 22%	6952

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	60% 10% 10% 12% 8% 1	3639
	11th to 20th	Day	46% 5% 6% 22% 18% 4	3852
	21st to end	Day	39% 7% 10% 10% 19% 14%	4510
February	1st to 10th	Day	51% 10% 14% 13% 10% 2	1800
	11th to 20th	Day	50% 8% 12% 18% 9% 2	1764
	21st to end	Day	55% 7% 9% 17% 9% 3	1618
March	1st to 10th	Day	55% 7% 7% 21% 8% 1	4818
	11th to 20th	Day	48% 9% 10% 14% 18% 1	5000
	21st to end	Day	54% 9% 13% 17% 6%	5567
April	1st to 10th	Day	55% 8% 13% 14% 8% 2	2400
	11th to 20th	Day	49% 8% 13% 16% 10% 4	2372
	21st to end	Day	43% 8% 14% 22% 12% 1	2493
May	1st to 10th	Day	29% 7% 10% 28% 24% 3	5965
	11th to 20th	Day	31% 6% 12% 24% 23% 3	6280
	21st to end	Day	21% 7% 15% 44% 13%	6904
June	1st to 10th	Day	35% 7% 14% 30% 13% 1	2800
	11th to 20th	Day	25% 8% 11% 34% 19% 3	2800
	21st to end	Day	17% 4 10% 29% 30% 10%	2800
July	1st to 10th	Day	8% 2 4 24% 27% 36%	6251
	11th to 20th	Day	9% 2 3 14% 29% 42%	6245
	21st to end	Day	8% 2 4 33% 34% 20%	6371
August	1st to 10th	Day	14% 3 5% 17% 33% 27%	4129
	11th to 20th	Day	9% 3 6% 31% 35% 15%	4065
	21st to end	Day	13% 3 5% 31% 32% 17%	4193
September	1st to 10th	Day	10% 3 4 21% 33% 29%	2280
	11th to 20th	Day	22% 5% 10% 25% 27% 12%	2280
	21st to end	Day	22% 6% 9% 23% 25% 16%	1995
October	1st to 10th	Day	19% 4 11% 15% 24% 27%	3180
	11th to 20th	Day	28% 6% 17% 30% 15% 4	3161
	21st to end	Day	39% 6% 10% 23% 17% 5%	3448
November	1st to 10th	Day	48% 7% 12% 18% 13% 2	1803
	11th to 20th	Day	52% 10% 13% 12% 10% 4	1610
	21st to end	Day	49% 6% 11% 15% 13% 6%	1600
December	1st to 10th	Day	31% 6% 10% 23% 22% 8%	2620
	11th to 20th	Day	58% 9% 14% 13% 6%	3028
	21st to end	Day	63% 10% 10% 13% 3 1	4004
January	1st to 10th	Night	61% 9% 8% 13% 7% 1	6306
	11th to 20th	Night	47% 5% 7% 19% 16% 5%	6102
	21st to end	Night	48% 6% 6% 9% 16% 16%	6468
February	1st to 10th	Night	51% 7% 13% 16% 11% 2	2600
	11th to 20th	Night	53% 9% 10% 16% 9% 2	2534
	21st to end	Night	51% 11% 13% 14% 9% 2	2011
March	1st to 10th	Night	55% 8% 12% 17% 4 3	5074
	11th to 20th	Night	46% 8% 10% 18% 17% 1	5000
	21st to end	Night	56% 11% 13% 15% 4	5407
April	1st to 10th	Night	52% 9% 16% 16% 6% 1	2000
	11th to 20th	Night	45% 10% 15% 17% 10% 4	1979
	21st to end	Night	44% 10% 17% 21% 7% 1	1904
May	1st to 10th	Night	31% 9% 10% 27% 22% 1	4005
	11th to 20th	Night	34% 8% 12% 32% 11% 3	3616
	21st to end	Night	20% 12% 23% 40% 5%	3972
June	1st to 10th	Night	36% 9% 16% 32% 7%	1600
	11th to 20th	Night	27% 9% 14% 34% 15% 1	1600
	21st to end	Night	17% 4 12% 39% 22% 6%	1600
July	1st to 10th	Night	10% 3 5% 27% 22% 33%	3600
	11th to 20th	Night	8% 2 3 15% 37% 34%	3592
	21st to end	Night	10% 2 5% 36% 33% 14%	4166
August	1st to 10th	Night	11% 3 5% 22% 46% 13%	2875
	11th to 20th	Night	8% 3 8% 40% 29% 11%	2839
	21st to end	Night	16% 3 7% 33% 31% 10%	3484
September	1st to 10th	Night	9% 2 7% 23% 35% 24%	1900
	11th to 20th	Night	20% 4 13% 25% 27% 10%	1900
	21st to end	Night	25% 4 10% 24% 19% 18%	2178
October	1st to 10th	Night	19% 5% 7% 17% 28% 24%	3800
	11th to 20th	Night	31% 5% 11% 35% 12% 6%	3777
	21st to end	Night	38% 7% 12% 19% 16% 7%	4121
November	1st to 10th	Night	50% 7% 11% 14% 13% 5%	2495
	11th to 20th	Night	52% 10% 11% 13% 10% 4	2786
	21st to end	Night	46% 7% 11% 14% 15% 7%	2800
December	1st to 10th	Night	33% 6% 7% 21% 25% 7%	4560
	11th to 20th	Night	59% 9% 11% 13% 7% 1	5176
	21st to end	Night	57% 10% 13% 15% 5% 1	6952

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	32% 20% 29% 15% 4 2	200
	11th to 20th	Day	25% 19% 28% 17% 9% 2	295
	21st to end	Day	22% 19% 24% 23% 12%	440
February	1st to 10th	Day	22% 20% 28% 23% 7% 1	400
	11th to 20th	Day	27% 24% 23% 21% 6%	395
	21st to end	Day	23% 22% 29% 21% 4	399
March	1st to 10th	Day	26% 23% 27% 18% 5%	500
	11th to 20th	Day	24% 20% 25% 20% 10%	500
	21st to end	Day	26% 26% 26% 18% 5%	550
April	1st to 10th	Day	24% 22% 29% 18% 7% 1	500
	11th to 20th	Day	27% 20% 27% 18% 6% 2	492
	21st to end	Day	21% 20% 28% 20% 9% 2	500
May	1st to 10th	Day	18% 23% 28% 21% 8% 2	503
	11th to 20th	Day	25% 19% 24% 19% 10% 3	528
	21st to end	Day	19% 13% 29% 25% 10% 5%	573
June	1st to 10th	Day	14% 18% 30% 21% 13% 5%	530
	11th to 20th	Day	14% 20% 30% 23% 9% 2	530
	21st to end	Day	5% 12% 34% 29% 14% 6%	530
July	1st to 10th	Day	6% 12% 35% 28% 14% 6%	526
	11th to 20th	Day	2 9% 39% 29% 14% 6%	524
	21st to end	Day	1 8% 34% 31% 17% 9%	575
August	1st to 10th	Day	2 10% 33% 31% 16% 8%	504
	11th to 20th	Day	3 13% 25% 33% 18% 8%	477
	21st to end	Day	5% 9% 28% 36% 18% 4	539
September	1st to 10th	Day	3 10% 28% 38% 18% 3	490
	11th to 20th	Day	8% 12% 27% 35% 16% 2	490
	21st to end	Day	9% 11% 30% 32% 16% 1	490
October	1st to 10th	Day	12% 13% 27% 30% 18% 1	490
	11th to 20th	Day	16% 11% 22% 28% 21% 1	490
	21st to end	Day	18% 17% 26% 22% 15% 2	539
November	1st to 10th	Day	19% 16% 22% 30% 12% 1	339
	11th to 20th	Day	20% 14% 23% 30% 10% 2	205
	21st to end	Day	20% 14% 27% 28% 12%	200
December	1st to 10th	Day	22% 11% 33% 23% 10% 4	200
	11th to 20th	Day	29% 15% 25% 23% 8% 2	200
	21st to end	Day	26% 19% 25% 21% 9%	220
January	1st to 10th	Night	22% 15% 29% 24% 9% 2	800
	11th to 20th	Night	18% 15% 25% 28% 13% 2	800
	21st to end	Night	19% 12% 21% 33% 13% 3	880
February	1st to 10th	Night	18% 13% 23% 35% 11% 1	800
	11th to 20th	Night	21% 13% 24% 29% 13% 1	784
	21st to end	Night	17% 14% 25% 33% 10% 1	660
March	1st to 10th	Night	23% 15% 23% 28% 9% 2	800
	11th to 20th	Night	18% 13% 24% 27% 16% 2	800
	21st to end	Night	21% 18% 22% 27% 11% 1	880
April	1st to 10th	Night	19% 14% 24% 30% 13% 1	800
	11th to 20th	Night	19% 12% 23% 27% 16% 2	791
	21st to end	Night	22% 9% 18% 29% 19% 2	704
May	1st to 10th	Night	17% 9% 18% 34% 20% 1	560
	11th to 20th	Night	15% 7% 18% 36% 22% 2	394
	21st to end	Night	19% 7% 17% 31% 24% 2	433
June	1st to 10th	Night	13% 7% 15% 38% 27% 1	400
	11th to 20th	Night	10% 7% 21% 41% 20% 1	400
	21st to end	Night	7% 2 11% 45% 34% 1	400
July	1st to 10th	Night	2 2 12% 41% 43% 1	390
	11th to 20th	Night	4 1 11% 47% 37% 1	388
	21st to end	Night	1 1 6% 36% 50% 5%	577
August	1st to 10th	Night	3 1 6% 36% 47% 7%	579
	11th to 20th	Night	3 1 8% 37% 44% 8%	564
	21st to end	Night	3 3 17% 37% 36% 4	822
September	1st to 10th	Night	3 3 14% 38% 36% 5%	760
	11th to 20th	Night	6% 4 14% 35% 35% 6%	760
	21st to end	Night	12% 4 14% 34% 30% 7%	760
October	1st to 10th	Night	9% 3 17% 39% 28% 3	760
	11th to 20th	Night	13% 5% 15% 37% 25% 5%	760
	21st to end	Night	14% 8% 19% 33% 20% 6%	836
November	1st to 10th	Night	21% 8% 23% 31% 14% 3	780
	11th to 20th	Night	22% 11% 23% 32% 12% 1	800
	21st to end	Night	20% 10% 24% 30% 15% 2	800
December	1st to 10th	Night	18% 13% 22% 33% 13% 2	800
	11th to 20th	Night	22% 16% 24% 26% 11% 2	800
	21st to end	Night	27% 19% 24% 22% 6% 1	880

Page generated at 2025-08-01 22:32:28. Version ac07

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