Achray Campground
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Achray Campground clear sky chart from 2005-11-06 to 2026-10-14.

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	15% 11% 4 9% 5% 5% 5% 4 5% 7% 31%	150656
	Night	15% 12% 4 10% 6% 5% 4 3 5% 6% 29%	141016
Transparency	Day	52% 5% 11% 21% 10% 1	154188
	Night	55% 5% 11% 19% 9% 1	145573
Seeing	Day	24% 16% 31% 19% 8% 2	17111
	Night	23% 13% 30% 25% 9% 1	25900

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	13% 15% 7% 15% 9% 6% 5% 4 5% 5% 17%	4661
	11th to 20th	Day	9% 20% 7% 18% 9% 6% 4 3 4 5% 16%	4650
	21st to end	Day	9% 15% 8% 17% 9% 7% 5% 3 4 4 19%	5618
February	1st to 10th	Day	10% 17% 6% 16% 8% 5% 6% 3 5% 5% 21%	1890
	11th to 20th	Day	11% 17% 6% 12% 7% 6% 5% 4 6% 5% 22%	1843
	21st to end	Day	16% 16% 6% 10% 7% 6% 5% 3 5% 5% 22%	1630
March	1st to 10th	Day	17% 15% 6% 12% 5% 4 3 4 4 5% 24%	4845
	11th to 20th	Day	12% 14% 5% 11% 7% 5% 5% 3 6% 8% 26%	5090
	21st to end	Day	15% 13% 4 10% 5% 4 3 2 4 4 35%	5715
April	1st to 10th	Day	21% 14% 4 8% 6% 4 4 2 4 5% 28%	2520
	11th to 20th	Day	22% 12% 3 8% 5% 4 3 3 4 4 33%	2518
	21st to end	Day	21% 11% 3 8% 5% 4 4 3 4 4 34%	2730
May	1st to 10th	Day	17% 10% 3 8% 6% 5% 5% 4 6% 7% 29%	8136
	11th to 20th	Day	17% 9% 3 7% 5% 4 5% 3 5% 7% 35%	8221
	21st to end	Day	19% 9% 3 8% 4 4 4 3 4 6% 37%	9060
June	1st to 10th	Day	20% 8% 3 7% 5% 5% 5% 4 6% 6% 31%	2940
	11th to 20th	Day	15% 7% 2 6% 5% 5% 5% 4 6% 8% 36%	2968
	21st to end	Day	16% 7% 3 7% 6% 5% 5% 4 6% 8% 33%	3150
July	1st to 10th	Day	14% 5% 2 6% 5% 5% 6% 5% 7% 9% 36%	8519
	11th to 20th	Day	10% 5% 2 5% 4 4 5% 4 7% 9% 46%	8280
	21st to end	Day	11% 5% 2 6% 4 4 5% 4 6% 9% 43%	8993
August	1st to 10th	Day	16% 8% 3 8% 5% 5% 5% 4 6% 7% 33%	6118
	11th to 20th	Day	15% 6% 2 6% 4 5% 5% 4 7% 10% 37%	5951
	21st to end	Day	12% 6% 2 7% 4 5% 6% 5% 8% 11% 34%	6242
September	1st to 10th	Day	15% 7% 2 6% 4 4 5% 4 5% 7% 40%	2520
	11th to 20th	Day	13% 6% 2 7% 3 3 4 3 6% 6% 46%	2520
	21st to end	Day	18% 8% 2 9% 4 5% 4 4 5% 6% 35%	2193
October	1st to 10th	Day	17% 11% 3 7% 4 4 3 4 5% 7% 35%	2100
	11th to 20th	Day	22% 14% 3 9% 5% 4 4 3 4 6% 25%	2030
	21st to end	Day	26% 15% 4 9% 4 4 4 3 4 4 22%	2125
November	1st to 10th	Day	16% 14% 4 9% 4 4 4 3 6% 6% 29%	1726
	11th to 20th	Day	16% 18% 6% 10% 5% 5% 4 3 4 5% 23%	1680
	21st to end	Day	21% 18% 7% 12% 6% 5% 4 3 4 5% 17%	1680
December	1st to 10th	Day	16% 23% 7% 14% 7% 6% 4 3 4 4 12%	2680
	11th to 20th	Day	16% 18% 7% 14% 7% 4 4 2 3 3 21%	3066
	21st to end	Day	19% 20% 6% 16% 6% 4 4 2 3 3 18%	4048
January	1st to 10th	Night	11% 18% 10% 18% 9% 5% 5% 3 4 4 14%	8234
	11th to 20th	Night	10% 16% 7% 18% 8% 6% 6% 4 5% 5% 16%	8235
	21st to end	Night	8% 16% 8% 15% 8% 8% 6% 4 4 5% 18%	8547
February	1st to 10th	Night	10% 15% 6% 12% 8% 6% 6% 4 5% 6% 21%	2730
	11th to 20th	Night	11% 15% 5% 12% 9% 5% 4 3 4 5% 25%	2663
	21st to end	Night	12% 16% 4 12% 8% 6% 4 4 4 6% 23%	2175
March	1st to 10th	Night	16% 16% 5% 10% 5% 4 4 4 4 5% 28%	5213
	11th to 20th	Night	10% 14% 5% 11% 6% 5% 6% 4 6% 8% 26%	5089
	21st to end	Night	15% 12% 5% 10% 6% 4 4 4 5% 6% 29%	5459
April	1st to 10th	Night	19% 13% 3 9% 5% 4 4 3 4 5% 30%	2100
	11th to 20th	Night	20% 12% 3 6% 4 3 3 3 5% 6% 35%	2069
	21st to end	Night	20% 10% 3 8% 5% 4 5% 3 4 5% 32%	1890
May	1st to 10th	Night	19% 9% 3 6% 5% 5% 5% 4 6% 7% 32%	4747
	11th to 20th	Night	15% 8% 2 7% 5% 4 4 3 5% 7% 39%	4639
	21st to end	Night	18% 8% 3 6% 5% 4 4 4 5% 6% 37%	5114
June	1st to 10th	Night	16% 8% 3 8% 5% 4 4 4 5% 7% 35%	1680
	11th to 20th	Night	15% 5% 2 6% 4 5% 3 4 6% 8% 42%	1641
	21st to end	Night	16% 7% 2 6% 5% 4 4 5% 6% 8% 37%	1470
July	1st to 10th	Night	12% 6% 2 7% 5% 5% 5% 4 6% 9% 39%	4429
	11th to 20th	Night	11% 6% 2 6% 3 4 4 4 5% 7% 49%	4680
	21st to end	Night	11% 6% 2 7% 4 4 4 4 6% 7% 45%	5084
August	1st to 10th	Night	13% 5% 2 6% 4 4 5% 4 6% 8% 42%	4015
	11th to 20th	Night	15% 5% 2 6% 3 3 5% 4 6% 8% 43%	4095
	21st to end	Night	13% 6% 3 7% 4 4 4 4 6% 9% 41%	4835
September	1st to 10th	Night	12% 6% 3 6% 4 4 4 3 6% 8% 46%	2100
	11th to 20th	Night	13% 6% 3 5% 3 3 3 3 5% 6% 50%	2100
	21st to end	Night	17% 8% 2 6% 4 4 3 3 4 6% 43%	2423
October	1st to 10th	Night	19% 8% 2 6% 4 3 4 2 5% 5% 42%	2520
	11th to 20th	Night	21% 12% 3 8% 5% 4 4 3 6% 5% 29%	2437
	21st to end	Night	23% 14% 4 8% 4 5% 4 3 5% 5% 25%	2715
November	1st to 10th	Night	17% 12% 5% 8% 6% 4 4 3 5% 5% 31%	2790
	11th to 20th	Night	15% 15% 5% 10% 6% 5% 4 3 5% 5% 25%	2940
	21st to end	Night	21% 17% 5% 13% 6% 4 4 2 4 4 19%	2940
December	1st to 10th	Night	18% 21% 6% 14% 7% 5% 5% 3 4 5% 13%	4720
	11th to 20th	Night	16% 18% 6% 14% 5% 5% 4 3 4 5% 22%	5348
	21st to end	Night	22% 19% 5% 14% 6% 4 3 2 3 4 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	69% 4 10% 11% 5%	4662
	11th to 20th	Day	71% 4 7% 9% 9%	4680
	21st to end	Day	68% 4 6% 13% 8% 1	5618
February	1st to 10th	Day	66% 4 8% 15% 6% 1	1890
	11th to 20th	Day	62% 5% 11% 13% 8% 1	1852
	21st to end	Day	64% 4 7% 14% 9% 1	1630
March	1st to 10th	Day	62% 4 8% 11% 13% 2	4848
	11th to 20th	Day	57% 4 14% 15% 8% 2	5090
	21st to end	Day	54% 3 6% 20% 14% 3	5715
April	1st to 10th	Day	59% 3 7% 19% 10% 3	2520
	11th to 20th	Day	55% 3 6% 21% 13% 2	2518
	21st to end	Day	55% 3 6% 18% 15% 3	2730
May	1st to 10th	Day	51% 5% 9% 21% 9% 4	8147
	11th to 20th	Day	48% 6% 9% 25% 11% 1	8225
	21st to end	Day	49% 4 9% 22% 14% 2	9061
June	1st to 10th	Day	52% 5% 9% 20% 13% 1	2940
	11th to 20th	Day	44% 6% 11% 24% 13% 2	2968
	21st to end	Day	47% 7% 11% 22% 12% 1	3150
July	1st to 10th	Day	42% 7% 14% 25% 11%	8450
	11th to 20th	Day	33% 5% 14% 36% 11% 1	8205
	21st to end	Day	37% 6% 15% 32% 10%	8795
August	1st to 10th	Day	49% 6% 12% 22% 10% 1	6104
	11th to 20th	Day	41% 6% 18% 27% 8%	5990
	21st to end	Day	42% 8% 16% 27% 7% 1	6242
September	1st to 10th	Day	43% 5% 14% 27% 11%	2520
	11th to 20th	Day	38% 5% 12% 31% 13%	2520
	21st to end	Day	49% 6% 12% 22% 12%	2193
October	1st to 10th	Day	51% 5% 10% 27% 7%	3360
	11th to 20th	Day	55% 5% 11% 21% 8%	3270
	21st to end	Day	62% 5% 14% 14% 4 1	3415
November	1st to 10th	Day	54% 5% 13% 21% 6%	1726
	11th to 20th	Day	63% 5% 11% 14% 6% 1	1680
	21st to end	Day	71% 5% 10% 9% 5% 1	1680
December	1st to 10th	Day	77% 4 7% 9% 2	2680
	11th to 20th	Day	70% 3 5% 13% 9%	3066
	21st to end	Day	74% 3 5% 14% 4	4048
January	1st to 10th	Night	74% 4 8% 10% 4	8234
	11th to 20th	Night	70% 5% 9% 10% 7%	8280
	21st to end	Night	68% 4 6% 11% 10%	8547
February	1st to 10th	Night	63% 5% 10% 14% 7% 1	2730
	11th to 20th	Night	61% 3 10% 19% 6%	2665
	21st to end	Night	62% 4 8% 18% 7% 1	2175
March	1st to 10th	Night	59% 5% 9% 14% 10% 4	5223
	11th to 20th	Night	55% 6% 15% 15% 8% 1	5090
	21st to end	Night	54% 4 7% 19% 13% 2	5459
April	1st to 10th	Night	57% 4 7% 18% 12% 2	2100
	11th to 20th	Night	51% 4 7% 24% 13% 2	2069
	21st to end	Night	54% 4 7% 19% 14% 2	1890
May	1st to 10th	Night	48% 6% 9% 24% 10% 3	4753
	11th to 20th	Night	43% 7% 10% 23% 14% 3	4640
	21st to end	Night	46% 5% 10% 24% 12% 1	5115
June	1st to 10th	Night	46% 7% 10% 21% 15% 1	1680
	11th to 20th	Night	39% 6% 11% 27% 16% 2	1641
	21st to end	Night	44% 7% 14% 21% 13% 1	1470
July	1st to 10th	Night	40% 7% 16% 25% 12% 1	4389
	11th to 20th	Night	35% 5% 14% 33% 12%	4632
	21st to end	Night	38% 6% 13% 32% 12%	4967
August	1st to 10th	Night	39% 6% 15% 25% 14% 1	4005
	11th to 20th	Night	37% 7% 19% 30% 7%	4122
	21st to end	Night	40% 6% 15% 29% 8% 1	4835
September	1st to 10th	Night	36% 6% 14% 31% 12%	2100
	11th to 20th	Night	35% 5% 14% 33% 12%	2100
	21st to end	Night	43% 5% 13% 27% 12%	2423
October	1st to 10th	Night	41% 5% 12% 30% 12%	4040
	11th to 20th	Night	50% 5% 14% 20% 10%	3936
	21st to end	Night	54% 5% 18% 16% 7%	4375
November	1st to 10th	Night	55% 4 13% 19% 8%	2790
	11th to 20th	Night	60% 5% 12% 16% 7% 1	2940
	21st to end	Night	68% 5% 11% 13% 3	2940
December	1st to 10th	Night	75% 5% 11% 8% 2	4720
	11th to 20th	Night	66% 4 7% 12% 11%	5348
	21st to end	Night	73% 3 5% 12% 7%	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	20% 22% 37% 17% 5%	220
	11th to 20th	Day	24% 17% 37% 17% 4 1	220
	21st to end	Day	20% 20% 36% 18% 6% 1	333
February	1st to 10th	Day	28% 25% 30% 12% 4 1	330
	11th to 20th	Day	26% 27% 39% 7% 1	330
	21st to end	Day	32% 19% 36% 12% 1	346
March	1st to 10th	Day	29% 21% 34% 13% 2	540
	11th to 20th	Day	29% 19% 32% 17% 3 1	540
	21st to end	Day	31% 22% 28% 15% 4 1	594
April	1st to 10th	Day	31% 20% 30% 14% 4 1	540
	11th to 20th	Day	36% 19% 23% 13% 7% 2	532
	21st to end	Day	30% 17% 31% 14% 6% 1	540
May	1st to 10th	Day	29% 15% 29% 18% 7% 2	543
	11th to 20th	Day	23% 16% 29% 19% 9% 3	567
	21st to end	Day	23% 17% 31% 19% 9% 2	617
June	1st to 10th	Day	24% 11% 35% 21% 8% 1	570
	11th to 20th	Day	19% 15% 30% 24% 10% 2	598
	21st to end	Day	19% 14% 33% 22% 9% 2	780
July	1st to 10th	Day	13% 10% 34% 31% 10% 2	649
	11th to 20th	Day	14% 13% 34% 24% 11% 3	564
	21st to end	Day	13% 9% 35% 28% 11% 4	620
August	1st to 10th	Day	15% 7% 31% 28% 14% 4	566
	11th to 20th	Day	15% 8% 28% 28% 16% 5%	559
	21st to end	Day	14% 13% 32% 22% 13% 5%	627
September	1st to 10th	Day	18% 12% 30% 20% 14% 6%	570
	11th to 20th	Day	15% 10% 24% 22% 20% 9%	570
	21st to end	Day	20% 13% 25% 21% 15% 5%	570
October	1st to 10th	Day	24% 16% 25% 19% 11% 4	570
	11th to 20th	Day	29% 20% 29% 15% 6% 1	542
	21st to end	Day	34% 16% 26% 19% 4	542
November	1st to 10th	Day	29% 20% 32% 13% 5% 1	300
	11th to 20th	Day	30% 18% 36% 10% 6%	220
	21st to end	Day	33% 24% 30% 12% 2	220
December	1st to 10th	Day	31% 17% 37% 11% 5%	220
	11th to 20th	Day	32% 24% 32% 9% 2 1	220
	21st to end	Day	31% 19% 32% 13% 5% 1	242
January	1st to 10th	Night	25% 15% 34% 21% 5%	840
	11th to 20th	Night	25% 18% 28% 22% 6% 1	840
	21st to end	Night	18% 15% 34% 26% 6% 1	924
February	1st to 10th	Night	20% 18% 36% 22% 4	840
	11th to 20th	Night	22% 18% 37% 19% 3	823
	21st to end	Night	22% 20% 32% 24% 2	692
March	1st to 10th	Night	23% 20% 33% 21% 3	840
	11th to 20th	Night	24% 18% 33% 18% 5% 1	840
	21st to end	Night	21% 17% 34% 21% 7%	924
April	1st to 10th	Night	31% 15% 30% 21% 4	840
	11th to 20th	Night	28% 15% 28% 21% 8%	825
	21st to end	Night	27% 11% 28% 23% 10%	630
May	1st to 10th	Night	22% 9% 28% 31% 10%	455
	11th to 20th	Night	23% 9% 32% 27% 8%	414
	21st to end	Night	17% 9% 33% 30% 11%	455
June	1st to 10th	Night	18% 7% 38% 31% 5% 1	420
	11th to 20th	Night	19% 9% 28% 33% 11%	420
	21st to end	Night	19% 8% 29% 32% 11% 1	420
July	1st to 10th	Night	11% 5% 33% 37% 13% 1	410
	11th to 20th	Night	12% 6% 27% 41% 13% 1	408
	21st to end	Night	10% 6% 30% 37% 17%	460
August	1st to 10th	Night	13% 5% 24% 36% 22% 1	572
	11th to 20th	Night	13% 4 21% 39% 20% 2	624
	21st to end	Night	15% 7% 28% 32% 17% 2	827
September	1st to 10th	Night	15% 8% 28% 30% 17% 2	840
	11th to 20th	Night	17% 5% 23% 28% 23% 3	840
	21st to end	Night	20% 8% 23% 28% 19% 2	840
October	1st to 10th	Night	24% 10% 28% 25% 11% 2	840
	11th to 20th	Night	27% 14% 29% 22% 7% 1	813
	21st to end	Night	30% 14% 28% 24% 4	880
November	1st to 10th	Night	26% 16% 27% 24% 6% 1	820
	11th to 20th	Night	25% 16% 33% 16% 9% 1	840
	21st to end	Night	33% 15% 25% 23% 4	840
December	1st to 10th	Night	31% 16% 31% 18% 4	840
	11th to 20th	Night	27% 17% 32% 20% 3 1	840
	21st to end	Night	34% 14% 29% 19% 3 1	924

Page generated at 2026-10-11 05:06:28. Version ac07

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