Dornoch
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Dornoch clear sky chart from 2005-11-06 to 2025-07-21.

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	17% 13% 5% 10% 5% 4 4 3 5% 6% 29%	120250
	Night	16% 14% 6% 11% 6% 4 4 3 4 5% 26%	118897
Transparency	Day	56% 6% 11% 17% 10% 1	123841
	Night	58% 6% 10% 15% 9% 1	123467
Seeing	Day	22% 14% 29% 22% 10% 3	15995
	Night	23% 11% 29% 27% 10% 1	25143

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	11% 18% 10% 22% 11% 5% 3 2 2 3 12%	3185
	11th to 20th	Day	9% 23% 11% 24% 13% 7% 3 1 2 2 5%	3864
	21st to end	Day	13% 20% 9% 22% 7% 6% 4 3 3 3 8%	4466
February	1st to 10th	Day	14% 21% 7% 21% 9% 6% 3 3 3 4 11%	1800
	11th to 20th	Day	14% 16% 8% 18% 10% 5% 4 3 5% 4 13%	1753
	21st to end	Day	14% 21% 7% 13% 8% 5% 5% 4 5% 4 15%	1597
March	1st to 10th	Day	16% 13% 6% 14% 7% 5% 3 2 4 5% 24%	4832
	11th to 20th	Day	13% 16% 7% 10% 5% 4 5% 4 5% 6% 25%	4980
	21st to end	Day	19% 16% 7% 10% 4 3 4 3 4 5% 25%	5465
April	1st to 10th	Day	19% 17% 5% 9% 4 4 4 4 4 6% 26%	2305
	11th to 20th	Day	19% 13% 3 6% 2 3 3 3 5% 6% 34%	2555
	21st to end	Day	21% 12% 3 7% 4 3 4 3 5% 7% 32%	2600
May	1st to 10th	Day	19% 10% 3 6% 4 4 4 4 5% 7% 36%	5888
	11th to 20th	Day	17% 9% 3 8% 5% 4 4 3 5% 6% 36%	6124
	21st to end	Day	22% 8% 2 6% 3 4 3 3 5% 7% 37%	6949
June	1st to 10th	Day	16% 8% 2 7% 4 4 4 4 5% 7% 38%	2879
	11th to 20th	Day	13% 5% 2 6% 4 4 5% 4 6% 9% 40%	3000
	21st to end	Day	19% 6% 2 6% 5% 4 5% 4 5% 8% 37%	3000
July	1st to 10th	Day	16% 6% 2 6% 5% 6% 5% 4 7% 8% 36%	4910
	11th to 20th	Day	14% 5% 2 5% 5% 5% 5% 4 6% 8% 43%	4702
	21st to end	Day	12% 6% 2 6% 5% 4 4 4 6% 8% 44%	4466
August	1st to 10th	Day	14% 6% 2 7% 5% 5% 5% 4 7% 8% 36%	4104
	11th to 20th	Day	15% 6% 2 7% 5% 5% 5% 3 7% 8% 35%	4044
	21st to end	Day	11% 5% 2 6% 5% 5% 4 5% 6% 9% 43%	4473
September	1st to 10th	Day	15% 7% 3 7% 5% 4 4 4 5% 7% 38%	2271
	11th to 20th	Day	13% 7% 2 6% 4 4 5% 3 5% 7% 44%	2090
	21st to end	Day	19% 8% 3 8% 4 4 6% 4 4 8% 33%	2090
October	1st to 10th	Day	21% 10% 3 6% 4 4 4 3 5% 6% 33%	1916
	11th to 20th	Day	25% 15% 3 8% 5% 4 5% 4 4 6% 21%	1900
	21st to end	Day	28% 18% 4 8% 4 4 4 3 4 5% 18%	2043
November	1st to 10th	Day	17% 21% 4 8% 6% 4 4 2 4 5% 25%	1715
	11th to 20th	Day	17% 20% 5% 11% 5% 4 4 4 5% 6% 18%	1600
	21st to end	Day	19% 28% 8% 9% 5% 4 3 4 5% 4 12%	1600
December	1st to 10th	Day	15% 28% 12% 14% 5% 4 4 2 3 4 8%	2600
	11th to 20th	Day	22% 23% 7% 15% 5% 3 3 2 3 4 12%	2986
	21st to end	Day	25% 22% 7% 14% 6% 4 3 2 3 4 10%	3498
January	1st to 10th	Night	13% 19% 9% 25% 9% 4 3 2 3 3 11%	6766
	11th to 20th	Night	12% 18% 10% 25% 10% 6% 4 2 3 4 7%	6024
	21st to end	Night	13% 18% 11% 19% 7% 6% 5% 3 3 4 11%	6490
February	1st to 10th	Night	13% 20% 7% 17% 11% 6% 4 4 4 4 12%	2600
	11th to 20th	Night	13% 16% 8% 17% 9% 4 4 3 4 5% 17%	2533
	21st to end	Night	15% 16% 6% 13% 7% 5% 5% 3 4 6% 20%	2030
March	1st to 10th	Night	16% 15% 5% 11% 5% 4 4 3 4 6% 27%	5007
	11th to 20th	Night	10% 14% 7% 9% 5% 5% 5% 4 6% 7% 30%	4979
	21st to end	Night	22% 11% 5% 11% 4 4 3 3 3 4 28%	5467
April	1st to 10th	Night	19% 14% 5% 9% 5% 4 3 3 5% 6% 28%	2095
	11th to 20th	Night	19% 12% 3 6% 5% 4 4 3 4 6% 36%	1811
	21st to end	Night	18% 12% 4 8% 5% 4 5% 3 4 5% 32%	1800
May	1st to 10th	Night	18% 8% 3 7% 4 4 3 3 4 7% 37%	4053
	11th to 20th	Night	15% 6% 2 6% 4 4 4 3 4 7% 43%	3769
	21st to end	Night	20% 7% 1 5% 4 3 4 3 5% 6% 41%	3926
June	1st to 10th	Night	15% 7% 3 6% 5% 4 3 4 6% 7% 40%	1516
	11th to 20th	Night	13% 5% 2 5% 5% 4 5% 4 8% 9% 39%	1400
	21st to end	Night	15% 6% 4 5% 5% 4 5% 3 6% 7% 42%	1400
July	1st to 10th	Night	10% 6% 3 6% 4 4 4 3 5% 7% 47%	2280
	11th to 20th	Night	16% 5% 2 4 3 3 3 3 5% 7% 50%	2478
	21st to end	Night	9% 7% 2 5% 5% 4 4 4 6% 7% 48%	3087
August	1st to 10th	Night	14% 6% 3 7% 4 4 4 3 4 6% 45%	2825
	11th to 20th	Night	18% 6% 3 6% 4 3 4 4 5% 8% 40%	2785
	21st to end	Night	15% 5% 2 6% 4 4 3 4 4 6% 47%	3149
September	1st to 10th	Night	12% 6% 2 6% 4 4 4 3 6% 8% 46%	1907
	11th to 20th	Night	14% 5% 2 4 3 3 4 3 5% 7% 49%	2090
	21st to end	Night	17% 7% 3 7% 5% 4 4 4 6% 7% 37%	2090
October	1st to 10th	Night	20% 8% 3 7% 4 4 5% 3 5% 5% 36%	2263
	11th to 20th	Night	24% 13% 3 8% 4 5% 4 3 4 5% 26%	2280
	21st to end	Night	26% 15% 4 7% 6% 4 4 3 5% 6% 21%	2554
November	1st to 10th	Night	18% 18% 3 8% 5% 4 5% 3 4 5% 26%	2581
	11th to 20th	Night	18% 20% 5% 9% 5% 5% 4 4 5% 6% 20%	2800
	21st to end	Night	21% 20% 6% 10% 5% 5% 4 3 4 6% 15%	2800
December	1st to 10th	Night	17% 27% 9% 12% 5% 5% 4 3 4 4 10%	4580
	11th to 20th	Night	14% 27% 9% 16% 5% 4 4 3 3 3 12%	5208
	21st to end	Night	21% 23% 8% 15% 5% 5% 3 3 3 4 10%	7474

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	77% 6% 7% 5% 5% 1	3186
	11th to 20th	Day	89% 4 3 3 2	3898
	21st to end	Day	81% 5% 7% 5% 3	4466
February	1st to 10th	Day	79% 4 7% 8% 2	1800
	11th to 20th	Day	75% 4 8% 9% 4 1	1762
	21st to end	Day	73% 4 8% 10% 4	1597
March	1st to 10th	Day	63% 4 14% 11% 8% 1	4835
	11th to 20th	Day	59% 5% 12% 16% 5% 2	4980
	21st to end	Day	60% 6% 11% 16% 7% 1	5465
April	1st to 10th	Day	60% 5% 9% 17% 9%	2305
	11th to 20th	Day	51% 5% 9% 21% 13% 1	2555
	21st to end	Day	53% 6% 10% 17% 12% 2	2600
May	1st to 10th	Day	47% 7% 12% 19% 11% 5%	5897
	11th to 20th	Day	48% 7% 10% 17% 17% 1	6128
	21st to end	Day	47% 5% 10% 19% 14% 5%	6949
June	1st to 10th	Day	44% 6% 11% 22% 15% 1	2879
	11th to 20th	Day	39% 7% 12% 24% 16% 1	3000
	21st to end	Day	43% 7% 13% 23% 13% 1	3000
July	1st to 10th	Day	44% 7% 13% 19% 16% 2	4836
	11th to 20th	Day	38% 6% 12% 30% 13% 1	4621
	21st to end	Day	38% 6% 11% 24% 18% 2	4324
August	1st to 10th	Day	44% 7% 13% 21% 14% 1	4091
	11th to 20th	Day	46% 8% 14% 23% 10%	4083
	21st to end	Day	37% 7% 14% 30% 11% 1	4473
September	1st to 10th	Day	44% 8% 13% 22% 11% 2	2271
	11th to 20th	Day	39% 6% 15% 27% 13%	2090
	21st to end	Day	48% 7% 13% 23% 8% 1	2090
October	1st to 10th	Day	48% 6% 11% 22% 12% 1	3176
	11th to 20th	Day	52% 7% 12% 19% 10%	3140
	21st to end	Day	62% 4 12% 17% 4	3345
November	1st to 10th	Day	62% 5% 11% 15% 6%	1715
	11th to 20th	Day	66% 7% 11% 10% 6% 1	1600
	21st to end	Day	74% 7% 10% 8% 1	1600
December	1st to 10th	Day	82% 5% 8% 5% 1	2600
	11th to 20th	Day	77% 6% 7% 8% 3	2986
	21st to end	Day	80% 6% 5% 5% 4	3498
January	1st to 10th	Night	78% 6% 6% 6% 4	6766
	11th to 20th	Night	84% 4 6% 4 3	6065
	21st to end	Night	77% 6% 7% 5% 5%	6490
February	1st to 10th	Night	76% 6% 8% 9% 1	2600
	11th to 20th	Night	70% 6% 9% 11% 4	2535
	21st to end	Night	64% 6% 11% 11% 7%	2030
March	1st to 10th	Night	58% 5% 12% 15% 9% 1	5017
	11th to 20th	Night	51% 7% 16% 16% 8% 1	4980
	21st to end	Night	58% 6% 9% 15% 11% 2	5467
April	1st to 10th	Night	58% 5% 9% 16% 11% 1	2095
	11th to 20th	Night	50% 5% 8% 20% 16% 1	1811
	21st to end	Night	54% 6% 8% 15% 15% 2	1800
May	1st to 10th	Night	46% 6% 9% 17% 14% 7%	4060
	11th to 20th	Night	41% 8% 12% 21% 16% 1	3770
	21st to end	Night	43% 6% 10% 24% 15% 2	3927
June	1st to 10th	Night	42% 6% 12% 21% 17% 2	1516
	11th to 20th	Night	38% 8% 13% 24% 16% 1	1400
	21st to end	Night	40% 6% 12% 25% 16% 1	1400
July	1st to 10th	Night	35% 5% 14% 23% 18% 5%	2245
	11th to 20th	Night	34% 5% 11% 34% 15% 1	2436
	21st to end	Night	35% 7% 14% 26% 16% 1	2988
August	1st to 10th	Night	39% 6% 11% 27% 16% 1	2814
	11th to 20th	Night	43% 7% 15% 23% 12% 1	2812
	21st to end	Night	38% 6% 11% 31% 13% 1	3149
September	1st to 10th	Night	36% 8% 13% 29% 13% 2	1907
	11th to 20th	Night	35% 5% 14% 29% 17% 1	2090
	21st to end	Night	46% 7% 13% 23% 10%	2090
October	1st to 10th	Night	41% 7% 9% 25% 17% 1	3783
	11th to 20th	Night	52% 4 13% 18% 13%	3779
	21st to end	Night	54% 7% 15% 19% 5%	4202
November	1st to 10th	Night	59% 6% 12% 17% 5% 1	2581
	11th to 20th	Night	64% 7% 12% 11% 4 1	2800
	21st to end	Night	70% 8% 12% 8% 2	2800
December	1st to 10th	Night	78% 7% 10% 4 1	4580
	11th to 20th	Night	76% 6% 8% 8% 2	5208
	21st to end	Night	80% 5% 6% 7% 2	7474

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	22% 23% 35% 14% 5% 1	207
	11th to 20th	Day	24% 24% 33% 15% 4	300
	21st to end	Day	27% 19% 30% 21% 3	330
February	1st to 10th	Day	30% 27% 29% 10% 4	300
	11th to 20th	Day	27% 23% 36% 11% 1	300
	21st to end	Day	28% 29% 31% 12% 1	249
March	1st to 10th	Day	24% 19% 36% 15% 6%	448
	11th to 20th	Day	25% 17% 34% 18% 5% 1	500
	21st to end	Day	30% 15% 31% 18% 6% 1	550
April	1st to 10th	Day	26% 18% 32% 16% 7% 1	500
	11th to 20th	Day	31% 16% 24% 15% 8% 5%	492
	21st to end	Day	29% 13% 28% 21% 7% 2	500
May	1st to 10th	Day	25% 13% 26% 25% 9% 2	503
	11th to 20th	Day	21% 11% 28% 21% 16% 3	527
	21st to end	Day	22% 10% 26% 24% 15% 4	573
June	1st to 10th	Day	18% 12% 29% 25% 13% 2	609
	11th to 20th	Day	15% 11% 33% 27% 11% 2	730
	21st to end	Day	21% 9% 34% 24% 10% 2	730
July	1st to 10th	Day	12% 8% 29% 28% 19% 3	721
	11th to 20th	Day	15% 9% 30% 28% 13% 6%	653
	21st to end	Day	13% 5% 28% 32% 17% 5%	532
August	1st to 10th	Day	13% 6% 26% 29% 16% 9%	486
	11th to 20th	Day	15% 5% 20% 28% 21% 10%	479
	21st to end	Day	17% 6% 23% 29% 17% 8%	539
September	1st to 10th	Day	16% 11% 26% 24% 15% 8%	490
	11th to 20th	Day	11% 8% 22% 27% 21% 12%	490
	21st to end	Day	20% 11% 26% 24% 15% 5%	490
October	1st to 10th	Day	25% 12% 24% 23% 12% 4	490
	11th to 20th	Day	28% 20% 29% 16% 5% 1	490
	21st to end	Day	40% 13% 28% 15% 4	492
November	1st to 10th	Day	30% 23% 26% 15% 6%	275
	11th to 20th	Day	31% 20% 32% 14% 2 2	200
	21st to end	Day	32% 27% 30% 11% 2	200
December	1st to 10th	Day	29% 27% 29% 14% 2 1	200
	11th to 20th	Day	34% 23% 29% 11% 3 1	200
	21st to end	Day	39% 19% 28% 12% 3	220
January	1st to 10th	Night	23% 18% 33% 21% 5%	1000
	11th to 20th	Night	30% 15% 29% 19% 6% 1	874
	21st to end	Night	21% 13% 33% 27% 6% 1	880
February	1st to 10th	Night	22% 19% 36% 20% 3	800
	11th to 20th	Night	22% 16% 34% 22% 5% 1	783
	21st to end	Night	22% 18% 37% 20% 3	660
March	1st to 10th	Night	20% 16% 36% 21% 6% 1	800
	11th to 20th	Night	20% 16% 37% 22% 5% 1	800
	21st to end	Night	24% 11% 29% 26% 8% 1	880
April	1st to 10th	Night	27% 14% 31% 24% 5%	800
	11th to 20th	Night	24% 13% 28% 24% 10% 1	627
	21st to end	Night	27% 10% 27% 26% 10%	600
May	1st to 10th	Night	20% 6% 28% 33% 12% 1	600
	11th to 20th	Night	19% 7% 26% 37% 11% 1	484
	21st to end	Night	16% 3 28% 39% 15%	433
June	1st to 10th	Night	17% 6% 31% 35% 11% 1	400
	11th to 20th	Night	15% 6% 27% 41% 12%	400
	21st to end	Night	20% 4 23% 37% 15% 1	400
July	1st to 10th	Night	10% 4 17% 50% 18% 1	390
	11th to 20th	Night	13% 4 24% 37% 22% 1	437
	21st to end	Night	13% 3 19% 44% 22% 1	624
August	1st to 10th	Night	14% 2 17% 38% 27% 1	567
	11th to 20th	Night	15% 2 14% 37% 28% 4	564
	21st to end	Night	16% 3 22% 32% 24% 2	639
September	1st to 10th	Night	15% 6% 23% 34% 19% 4	760
	11th to 20th	Night	15% 4 18% 38% 21% 4	760
	21st to end	Night	19% 7% 23% 31% 16% 4	760
October	1st to 10th	Night	23% 7% 28% 28% 13% 1	760
	11th to 20th	Night	31% 11% 25% 24% 7% 1	760
	21st to end	Night	33% 12% 30% 20% 4	836
November	1st to 10th	Night	29% 12% 30% 20% 7% 1	780
	11th to 20th	Night	27% 17% 31% 19% 5% 1	800
	21st to end	Night	29% 15% 32% 20% 3	800
December	1st to 10th	Night	31% 17% 31% 17% 4 1	800
	11th to 20th	Night	24% 20% 38% 15% 4 1	800
	21st to end	Night	33% 14% 32% 18% 3	1085

Page generated at 2025-07-18 01:10:04. Version ac07

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