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 2025-06-10.

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	16% 12% 4 9% 5% 5% 4 3 5% 6% 30%	120272
	Night	15% 13% 5% 10% 6% 5% 4 3 5% 6% 29%	117917
Transparency	Day	54% 5% 10% 20% 10% 1	123847
	Night	56% 5% 11% 18% 9% 1	122503
Seeing	Day	24% 16% 31% 19% 8% 2	15317
	Night	23% 13% 30% 25% 9% 1	24287

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% 16% 10% 6% 4 3 4 4 17%	3597
	11th to 20th	Day	10% 16% 6% 17% 9% 6% 4 3 4 6% 18%	3570
	21st to end	Day	12% 19% 9% 15% 6% 5% 4 3 3 5% 20%	4346
February	1st to 10th	Day	10% 17% 6% 16% 9% 5% 6% 3 5% 5% 20%	1800
	11th to 20th	Day	11% 17% 6% 12% 7% 6% 5% 4 5% 5% 22%	1753
	21st to end	Day	16% 16% 5% 9% 7% 6% 5% 4 5% 5% 22%	1555
March	1st to 10th	Day	18% 15% 6% 12% 5% 4 3 4 4 5% 24%	4740
	11th to 20th	Day	11% 13% 5% 11% 6% 5% 5% 3 6% 8% 26%	4980
	21st to end	Day	15% 13% 4 10% 5% 4 3 2 4 4 35%	5592
April	1st to 10th	Day	21% 13% 4 8% 6% 4 4 2 4 5% 29%	2400
	11th to 20th	Day	22% 11% 3 8% 5% 4 3 3 4 4 34%	2397
	21st to end	Day	21% 10% 3 8% 5% 4 4 3 4 4 33%	2600
May	1st to 10th	Day	20% 10% 3 7% 5% 5% 4 3 5% 6% 32%	6272
	11th to 20th	Day	15% 9% 3 7% 5% 4 4 3 5% 7% 37%	6318
	21st to end	Day	20% 9% 3 8% 4 5% 4 3 4 6% 35%	6949
June	1st to 10th	Day	20% 8% 3 7% 5% 5% 5% 4 6% 6% 30%	2786
	11th to 20th	Day	15% 6% 2 6% 5% 4 6% 4 7% 8% 37%	2685
	21st to end	Day	17% 8% 3 7% 5% 5% 5% 4 6% 8% 32%	2850
July	1st to 10th	Day	14% 7% 3 7% 5% 5% 6% 5% 7% 8% 33%	4568
	11th to 20th	Day	12% 6% 3 6% 6% 5% 5% 5% 7% 8% 38%	4440
	21st to end	Day	11% 5% 2 6% 4 4 5% 4 6% 7% 46%	4814
August	1st to 10th	Day	13% 7% 3 8% 6% 6% 6% 5% 6% 8% 33%	4178
	11th to 20th	Day	17% 6% 2 7% 4 5% 5% 4 6% 8% 35%	4044
	21st to end	Day	10% 5% 2 6% 5% 5% 6% 5% 8% 10% 39%	4286
September	1st to 10th	Day	15% 7% 2 6% 4 4 5% 4 5% 7% 41%	2280
	11th to 20th	Day	14% 7% 2 7% 3 3 4 3 5% 6% 45%	2280
	21st to end	Day	19% 8% 2 9% 4 5% 4 4 5% 6% 34%	1985
October	1st to 10th	Day	17% 11% 3 8% 4 4 4 4 4 6% 34%	1900
	11th to 20th	Day	23% 14% 3 9% 5% 4 4 3 4 6% 25%	1900
	21st to end	Day	27% 15% 4 8% 5% 4 4 3 4 5% 21%	2019
November	1st to 10th	Day	16% 14% 4 8% 4 4 4 3 6% 7% 30%	1642
	11th to 20th	Day	16% 17% 6% 10% 6% 5% 4 3 4 5% 24%	1600
	21st to end	Day	21% 18% 7% 12% 6% 5% 4 3 4 5% 17%	1600
December	1st to 10th	Day	17% 22% 7% 14% 7% 6% 4 3 4 4 12%	2600
	11th to 20th	Day	16% 18% 7% 14% 7% 4 4 2 3 3 21%	2986
	21st to end	Day	19% 20% 6% 16% 6% 4 4 2 3 3 18%	3960
January	1st to 10th	Night	12% 19% 11% 17% 8% 5% 4 2 3 4 15%	6349
	11th to 20th	Night	10% 14% 6% 18% 9% 7% 6% 4 5% 5% 17%	6315
	21st to end	Night	10% 18% 9% 15% 7% 7% 5% 3 4 4 17%	6608
February	1st to 10th	Night	11% 15% 7% 12% 8% 6% 6% 4 5% 6% 21%	2600
	11th to 20th	Night	12% 15% 5% 12% 9% 5% 5% 3 4 5% 25%	2533
	21st to end	Night	13% 16% 4 12% 8% 6% 4 3 4 6% 24%	2075
March	1st to 10th	Night	16% 16% 5% 10% 5% 4 4 4 4 5% 28%	5098
	11th to 20th	Night	10% 14% 5% 11% 6% 5% 6% 4 6% 8% 26%	4979
	21st to end	Night	15% 12% 5% 10% 6% 4 4 4 5% 6% 30%	5340
April	1st to 10th	Night	19% 13% 4 10% 5% 4 4 3 4 5% 30%	2000
	11th to 20th	Night	20% 11% 3 6% 4 4 3 3 5% 5% 36%	1969
	21st to end	Night	21% 11% 3 8% 5% 4 5% 3 4 5% 31%	1800
May	1st to 10th	Night	21% 9% 3 6% 4 5% 4 4 6% 6% 31%	3653
	11th to 20th	Night	14% 8% 2 7% 4 4 4 3 5% 7% 42%	3575
	21st to end	Night	18% 9% 3 7% 5% 4 4 4 6% 6% 35%	3926
June	1st to 10th	Night	16% 9% 3 9% 5% 4 4 5% 6% 7% 35%	1598
	11th to 20th	Night	15% 6% 2 6% 4 5% 3 4 6% 8% 42%	1485
	21st to end	Night	18% 7% 2 6% 5% 4 4 4 6% 8% 37%	1330
July	1st to 10th	Night	11% 7% 2 8% 6% 4 5% 4 5% 7% 40%	2386
	11th to 20th	Night	13% 7% 2 7% 3 4 5% 4 5% 7% 43%	2520
	21st to end	Night	9% 5% 2 5% 4 5% 4 4 6% 8% 47%	2739
August	1st to 10th	Night	12% 5% 2 6% 4 4 5% 4 6% 8% 44%	2749
	11th to 20th	Night	16% 5% 3 6% 4 3 5% 4 5% 7% 43%	2785
	21st to end	Night	13% 5% 2 6% 4 4 4 4 5% 9% 45%	3336
September	1st to 10th	Night	11% 6% 3 5% 4 4 4 3 6% 8% 47%	1900
	11th to 20th	Night	14% 7% 2 5% 3 3 3 3 5% 6% 49%	1900
	21st to end	Night	18% 8% 2 6% 4 4 3 3 4 7% 41%	2192
October	1st to 10th	Night	21% 8% 3 6% 4 3 4 2 5% 5% 40%	2280
	11th to 20th	Night	21% 12% 3 9% 5% 3 4 3 6% 5% 29%	2280
	21st to end	Night	23% 14% 4 8% 4 4 3 3 5% 6% 25%	2579
November	1st to 10th	Night	17% 11% 5% 8% 5% 4 4 4 5% 5% 32%	2654
	11th to 20th	Night	16% 14% 5% 10% 7% 5% 5% 3 5% 5% 25%	2800
	21st to end	Night	21% 17% 5% 12% 6% 4 4 2 4 5% 20%	2800
December	1st to 10th	Night	18% 21% 6% 14% 7% 5% 5% 3 4 5% 12%	4580
	11th to 20th	Night	16% 18% 6% 14% 5% 4 4 2 4 4 22%	5208
	21st to end	Night	22% 19% 5% 14% 6% 4 3 2 3 4 16%	6996

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	71% 4 9% 10% 6%	3598
	11th to 20th	Day	68% 4 9% 10% 8%	3600
	21st to end	Day	68% 4 6% 13% 8% 1	4346
February	1st to 10th	Day	67% 4 9% 14% 6% 1	1800
	11th to 20th	Day	62% 5% 11% 13% 8% 1	1762
	21st to end	Day	63% 4 8% 14% 10% 1	1555
March	1st to 10th	Day	62% 4 8% 11% 13% 2	4743
	11th to 20th	Day	56% 4 15% 15% 9% 2	4980
	21st to end	Day	53% 3 6% 20% 14% 3	5592
April	1st to 10th	Day	58% 3 7% 19% 10% 3	2400
	11th to 20th	Day	54% 3 6% 21% 14% 2	2397
	21st to end	Day	55% 3 6% 17% 15% 3	2600
May	1st to 10th	Day	52% 5% 8% 21% 9% 5%	6283
	11th to 20th	Day	46% 6% 9% 24% 14% 1	6322
	21st to end	Day	51% 5% 9% 20% 12% 2	6949
June	1st to 10th	Day	53% 5% 10% 19% 12% 1	2786
	11th to 20th	Day	43% 6% 11% 24% 14% 2	2685
	21st to end	Day	48% 7% 11% 21% 12% 1	2850
July	1st to 10th	Day	46% 6% 13% 25% 9% 1	4498
	11th to 20th	Day	40% 7% 15% 29% 9% 1	4365
	21st to end	Day	36% 6% 12% 34% 12%	4661
August	1st to 10th	Day	47% 6% 13% 24% 9%	4164
	11th to 20th	Day	44% 6% 16% 26% 8%	4083
	21st to end	Day	37% 7% 13% 32% 10% 1	4286
September	1st to 10th	Day	42% 5% 13% 27% 12%	2280
	11th to 20th	Day	40% 5% 12% 30% 12%	2280
	21st to end	Day	50% 6% 12% 23% 9%	1985
October	1st to 10th	Day	52% 5% 10% 26% 7%	3160
	11th to 20th	Day	55% 5% 11% 22% 7%	3140
	21st to end	Day	62% 6% 14% 14% 4 1	3309
November	1st to 10th	Day	53% 5% 14% 21% 6%	1642
	11th to 20th	Day	63% 5% 11% 14% 7% 1	1600
	21st to end	Day	71% 5% 10% 10% 5% 1	1600
December	1st to 10th	Day	77% 4 8% 9% 2	2600
	11th to 20th	Day	69% 3 5% 13% 9%	2986
	21st to end	Day	74% 3 5% 14% 4	3960
January	1st to 10th	Night	74% 4 8% 10% 4	6349
	11th to 20th	Night	67% 5% 10% 11% 6%	6360
	21st to end	Night	70% 4 6% 9% 10%	6608
February	1st to 10th	Night	64% 5% 10% 14% 7% 1	2600
	11th to 20th	Night	61% 3 10% 19% 6% 1	2535
	21st to end	Night	61% 4 8% 19% 7% 1	2075
March	1st to 10th	Night	59% 5% 9% 14% 10% 4	5108
	11th to 20th	Night	55% 6% 15% 15% 8% 1	4980
	21st to end	Night	54% 4 7% 20% 13% 2	5340
April	1st to 10th	Night	57% 4 7% 18% 12% 2	2000
	11th to 20th	Night	50% 4 7% 24% 14% 2	1969
	21st to end	Night	55% 4 7% 17% 15% 3	1800
May	1st to 10th	Night	50% 6% 9% 21% 10% 4	3659
	11th to 20th	Night	40% 8% 12% 22% 15% 3	3576
	21st to end	Night	49% 6% 11% 20% 12% 2	3927
June	1st to 10th	Night	47% 7% 11% 21% 14% 1	1598
	11th to 20th	Night	39% 6% 11% 27% 16% 2	1485
	21st to end	Night	44% 8% 14% 21% 13% 1	1330
July	1st to 10th	Night	42% 7% 14% 23% 13% 1	2346
	11th to 20th	Night	40% 6% 14% 31% 9% 1	2472
	21st to end	Night	33% 7% 13% 33% 14%	2651
August	1st to 10th	Night	37% 6% 15% 27% 14%	2739
	11th to 20th	Night	39% 7% 18% 28% 8%	2812
	21st to end	Night	35% 6% 16% 30% 11% 2	3336
September	1st to 10th	Night	35% 7% 14% 31% 13%	1900
	11th to 20th	Night	36% 5% 14% 32% 12%	1900
	21st to end	Night	44% 5% 14% 27% 10%	2192
October	1st to 10th	Night	42% 5% 12% 29% 12%	3800
	11th to 20th	Night	50% 5% 15% 20% 10%	3779
	21st to end	Night	55% 5% 18% 15% 7%	4239
November	1st to 10th	Night	54% 5% 14% 20% 8%	2654
	11th to 20th	Night	60% 5% 11% 16% 7% 1	2800
	21st to end	Night	67% 5% 11% 14% 3	2800
December	1st to 10th	Night	75% 5% 11% 7% 2	4580
	11th to 20th	Night	67% 4 7% 12% 11%	5208
	21st to end	Night	73% 3 5% 12% 7%	6996

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% 23% 36% 18% 4	200
	11th to 20th	Day	23% 16% 39% 18% 5% 1	200
	21st to end	Day	21% 20% 35% 17% 6% 1	303
February	1st to 10th	Day	28% 27% 32% 9% 3 1	300
	11th to 20th	Day	26% 28% 39% 6% 1	300
	21st to end	Day	33% 20% 35% 11% 1	319
March	1st to 10th	Day	29% 21% 33% 14% 3	500
	11th to 20th	Day	26% 19% 33% 17% 4 1	500
	21st to end	Day	31% 21% 29% 15% 4 1	550
April	1st to 10th	Day	30% 20% 30% 14% 5% 1	500
	11th to 20th	Day	35% 18% 23% 13% 7% 3	492
	21st to end	Day	30% 17% 31% 14% 6% 2	500
May	1st to 10th	Day	29% 14% 28% 19% 7% 2	503
	11th to 20th	Day	22% 17% 29% 20% 9% 3	527
	21st to end	Day	22% 15% 31% 20% 10% 2	573
June	1st to 10th	Day	24% 12% 35% 21% 7% 1	526
	11th to 20th	Day	18% 13% 31% 25% 11% 2	515
	21st to end	Day	20% 15% 33% 21% 10% 2	680
July	1st to 10th	Day	13% 10% 33% 33% 10% 2	561
	11th to 20th	Day	14% 12% 35% 24% 13% 3	484
	21st to end	Day	14% 8% 35% 29% 11% 4	532
August	1st to 10th	Day	15% 7% 32% 27% 13% 5%	486
	11th to 20th	Day	16% 8% 26% 27% 18% 5%	479
	21st to end	Day	15% 13% 32% 22% 14% 5%	539
September	1st to 10th	Day	16% 12% 30% 21% 14% 6%	490
	11th to 20th	Day	16% 9% 25% 20% 21% 9%	490
	21st to end	Day	20% 14% 25% 21% 14% 5%	490
October	1st to 10th	Day	24% 17% 26% 18% 11% 4	490
	11th to 20th	Day	30% 20% 28% 15% 6% 1	490
	21st to end	Day	34% 17% 26% 18% 4	502
November	1st to 10th	Day	27% 20% 33% 14% 5% 1	276
	11th to 20th	Day	29% 18% 38% 11% 5% 1	200
	21st to end	Day	33% 24% 29% 13% 2 1	200
December	1st to 10th	Day	32% 16% 37% 12% 5%	200
	11th to 20th	Day	32% 24% 31% 10% 3 2	200
	21st to end	Day	30% 19% 33% 14% 5%	220
January	1st to 10th	Night	25% 16% 34% 21% 5%	800
	11th to 20th	Night	25% 17% 29% 22% 6% 1	800
	21st to end	Night	18% 14% 35% 26% 6% 1	880
February	1st to 10th	Night	20% 18% 37% 21% 4	800
	11th to 20th	Night	22% 18% 37% 19% 3	783
	21st to end	Night	22% 20% 31% 23% 2	660
March	1st to 10th	Night	24% 20% 32% 22% 3	800
	11th to 20th	Night	23% 18% 34% 18% 5% 1	800
	21st to end	Night	20% 17% 34% 22% 7%	880
April	1st to 10th	Night	30% 15% 30% 22% 4	800
	11th to 20th	Night	28% 15% 28% 21% 8%	785
	21st to end	Night	29% 11% 27% 23% 11% 1	600
May	1st to 10th	Night	22% 8% 29% 30% 10%	433
	11th to 20th	Night	22% 8% 32% 28% 9%	394
	21st to end	Night	16% 9% 33% 31% 11%	433
June	1st to 10th	Night	18% 8% 39% 31% 4 1	400
	11th to 20th	Night	19% 8% 28% 32% 13% 1	380
	21st to end	Night	20% 8% 29% 31% 11% 1	380
July	1st to 10th	Night	11% 5% 32% 37% 14% 1	370
	11th to 20th	Night	12% 5% 27% 40% 15% 1	368
	21st to end	Night	10% 5% 31% 36% 17%	416
August	1st to 10th	Night	13% 5% 24% 36% 21% 1	517
	11th to 20th	Night	12% 4 21% 39% 21% 3	564
	21st to end	Night	15% 6% 28% 32% 17% 2	748
September	1st to 10th	Night	15% 8% 28% 30% 17% 2	760
	11th to 20th	Night	18% 5% 23% 26% 23% 3	760
	21st to end	Night	22% 8% 23% 28% 18% 2	760
October	1st to 10th	Night	25% 9% 28% 25% 11% 2	760
	11th to 20th	Night	27% 14% 28% 22% 8% 1	760
	21st to end	Night	32% 14% 28% 23% 4	836
November	1st to 10th	Night	26% 16% 27% 24% 7% 1	780
	11th to 20th	Night	25% 17% 34% 16% 9% 1	800
	21st to end	Night	32% 15% 25% 23% 5%	800
December	1st to 10th	Night	32% 16% 31% 17% 4	800
	11th to 20th	Night	27% 17% 32% 20% 3 1	800
	21st to end	Night	34% 14% 29% 20% 3 1	880

Page generated at 2025-06-07 10:28:15. Version ac07

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