Tobermory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Tobermory clear sky chart from 2005-11-06 to 2026-08-15.

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	14% 11% 4 9% 5% 5% 4 3 5% 6% 34%	143891
	Night	15% 14% 5% 12% 6% 5% 4 3 4 5% 27%	138112
Transparency	Day	48% 7% 12% 21% 11% 1	147409
	Night	56% 7% 10% 16% 9% 1	142682
Seeing	Day	17% 8% 22% 31% 19% 4	17611
	Night	21% 10% 26% 26% 14% 3	26776

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	14% 21% 10% 18% 10% 6% 3 3 3 3 9%	4134
	11th to 20th	Day	12% 24% 11% 25% 11% 7% 3 2 2 2 3	4679
	21st to end	Day	13% 16% 8% 17% 10% 8% 6% 3 4 4 11%	5640
February	1st to 10th	Day	13% 20% 6% 16% 9% 6% 5% 2 4 5% 15%	1890
	11th to 20th	Day	13% 16% 6% 13% 9% 8% 5% 4 5% 4 18%	1843
	21st to end	Day	14% 15% 6% 12% 6% 6% 5% 4 5% 5% 21%	1704
March	1st to 10th	Day	16% 11% 4 10% 5% 5% 4 4 5% 6% 31%	4827
	11th to 20th	Day	12% 13% 5% 11% 6% 5% 5% 3 6% 7% 27%	5090
	21st to end	Day	17% 11% 4 9% 5% 4 4 3 4 5% 32%	5586
April	1st to 10th	Day	18% 10% 3 8% 4 4 4 4 5% 6% 34%	2448
	11th to 20th	Day	19% 7% 3 6% 5% 4 3 3 4 6% 40%	2702
	21st to end	Day	17% 9% 3 6% 4 4 4 3 6% 7% 37%	2730
May	1st to 10th	Day	13% 6% 3 7% 4 4 4 3 6% 7% 43%	7642
	11th to 20th	Day	12% 8% 3 7% 5% 4 4 4 5% 7% 42%	7923
	21st to end	Day	16% 8% 3 6% 3 4 4 3 5% 6% 44%	9195
June	1st to 10th	Day	12% 6% 2 7% 4 5% 5% 4 6% 7% 41%	3150
	11th to 20th	Day	11% 6% 3 6% 5% 4 4 4 6% 9% 42%	3150
	21st to end	Day	13% 7% 3 6% 5% 4 4 4 6% 8% 40%	3150
July	1st to 10th	Day	11% 7% 3 8% 5% 5% 5% 5% 6% 7% 39%	8879
	11th to 20th	Day	8% 5% 2 5% 3 4 4 3 5% 8% 53%	8706
	21st to end	Day	7% 5% 2 5% 3 4 4 4 5% 8% 52%	8559
August	1st to 10th	Day	10% 5% 2 6% 4 4 5% 4 7% 9% 45%	4364
	11th to 20th	Day	14% 6% 2 6% 3 3 3 4 7% 8% 45%	4226
	21st to end	Day	8% 6% 2 6% 4 5% 5% 4 6% 7% 47%	4675
September	1st to 10th	Day	13% 5% 2 6% 4 5% 4 4 5% 7% 43%	2361
	11th to 20th	Day	11% 5% 2 5% 4 3 4 4 6% 8% 48%	2200
	21st to end	Day	17% 7% 3 8% 4 5% 4 4 5% 7% 38%	2200
October	1st to 10th	Day	17% 9% 3 7% 4 5% 4 3 6% 7% 35%	2046
	11th to 20th	Day	26% 11% 4 8% 5% 4 4 3 5% 6% 25%	2000
	21st to end	Day	25% 15% 4 9% 4 4 4 3 5% 5% 20%	2075
November	1st to 10th	Day	19% 17% 5% 9% 4 5% 4 4 5% 6% 22%	1817
	11th to 20th	Day	18% 20% 5% 11% 6% 5% 4 4 5% 6% 16%	1680
	21st to end	Day	23% 23% 6% 13% 6% 4 4 3 4 4 10%	1680
December	1st to 10th	Day	17% 32% 9% 14% 7% 4 4 2 2 3 7%	2680
	11th to 20th	Day	21% 23% 8% 19% 6% 4 3 2 3 3 7%	2707
	21st to end	Day	27% 24% 7% 17% 5% 7% 3 2 3 3 3	3553
January	1st to 10th	Night	13% 23% 11% 21% 10% 6% 3 2 2 2 7%	8789
	11th to 20th	Night	12% 23% 10% 24% 10% 5% 3 3 2 2 5%	8236
	21st to end	Night	10% 16% 8% 19% 10% 9% 5% 3 4 3 13%	8545
February	1st to 10th	Night	12% 20% 7% 17% 9% 5% 3 3 4 5% 16%	2730
	11th to 20th	Night	13% 17% 6% 14% 8% 6% 5% 4 4 4 19%	2663
	21st to end	Night	15% 15% 6% 11% 6% 6% 4 4 5% 5% 22%	2097
March	1st to 10th	Night	15% 9% 5% 10% 6% 5% 5% 3 5% 5% 33%	5232
	11th to 20th	Night	12% 12% 4 9% 5% 4 5% 5% 6% 8% 32%	5089
	21st to end	Night	19% 11% 5% 10% 6% 4 4 3 4 5% 29%	5588
April	1st to 10th	Night	20% 11% 3 7% 4 4 4 3 6% 6% 32%	2189
	11th to 20th	Night	18% 8% 3 6% 4 4 4 4 6% 7% 37%	1867
	21st to end	Night	19% 9% 3 7% 5% 5% 5% 3 5% 5% 34%	1890
May	1st to 10th	Night	12% 7% 3 9% 5% 5% 5% 4 6% 7% 37%	5257
	11th to 20th	Night	15% 7% 3 6% 5% 4 3 3 4 7% 43%	4921
	21st to end	Night	16% 7% 3 7% 4 4 3 3 5% 7% 41%	4970
June	1st to 10th	Night	12% 8% 3 6% 5% 4 5% 3 5% 8% 41%	1470
	11th to 20th	Night	9% 6% 3 6% 5% 4 5% 5% 6% 8% 43%	1470
	21st to end	Night	11% 7% 2 6% 5% 6% 4 5% 6% 8% 40%	1470
July	1st to 10th	Night	10% 6% 3 8% 5% 4 4 3 5% 9% 44%	4110
	11th to 20th	Night	9% 5% 2 5% 4 4 4 4 6% 8% 49%	4280
	21st to end	Night	9% 6% 2 6% 3 4 4 3 6% 8% 48%	5514
August	1st to 10th	Night	10% 6% 2 7% 4 4 5% 3 6% 7% 46%	3005
	11th to 20th	Night	12% 6% 3 6% 4 5% 6% 3 6% 8% 42%	2911
	21st to end	Night	9% 5% 2 6% 4 5% 5% 3 6% 7% 46%	3223
September	1st to 10th	Night	12% 5% 2 5% 4 4 5% 3 5% 7% 47%	2015
	11th to 20th	Night	12% 5% 2 6% 3 4 4 4 6% 6% 49%	2200
	21st to end	Night	19% 7% 3 6% 5% 4 4 3 5% 6% 39%	2200
October	1st to 10th	Night	20% 8% 2 7% 5% 5% 4 3 5% 6% 35%	2352
	11th to 20th	Night	25% 12% 4 8% 5% 5% 5% 3 4 6% 24%	2400
	21st to end	Night	25% 16% 5% 7% 5% 5% 4 3 5% 6% 20%	2761
November	1st to 10th	Night	21% 17% 3 8% 6% 4 3 3 5% 6% 24%	2699
	11th to 20th	Night	18% 23% 6% 11% 6% 4 5% 3 4 4 16%	2940
	21st to end	Night	24% 25% 6% 10% 6% 4 4 2 4 4 10%	2940
December	1st to 10th	Night	19% 26% 9% 15% 5% 4 4 2 3 3 9%	4720
	11th to 20th	Night	17% 23% 10% 19% 7% 5% 4 2 3 3 7%	5702
	21st to end	Night	24% 24% 9% 16% 7% 6% 3 2 2 2 6%	7667

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	76% 8% 8% 6% 2	4135
	11th to 20th	Day	88% 5% 3 3 1	4710
	21st to end	Day	72% 9% 9% 7% 4	5640
February	1st to 10th	Day	70% 6% 9% 12% 3	1890
	11th to 20th	Day	66% 7% 10% 11% 6%	1852
	21st to end	Day	61% 7% 11% 17% 4	1704
March	1st to 10th	Day	50% 8% 15% 12% 13% 2	4830
	11th to 20th	Day	54% 7% 13% 17% 7% 1	5090
	21st to end	Day	50% 8% 15% 17% 8% 1	5586
April	1st to 10th	Day	50% 6% 13% 20% 11% 1	2448
	11th to 20th	Day	44% 6% 8% 25% 15% 2	2702
	21st to end	Day	45% 7% 13% 21% 12% 3	2730
May	1st to 10th	Day	38% 7% 12% 25% 16% 3	7651
	11th to 20th	Day	40% 8% 10% 23% 18% 1	7927
	21st to end	Day	41% 6% 11% 23% 17% 3	9196
June	1st to 10th	Day	40% 7% 11% 26% 15% 2	3150
	11th to 20th	Day	36% 7% 11% 28% 16% 1	3150
	21st to end	Day	40% 8% 13% 25% 13% 2	3150
July	1st to 10th	Day	40% 8% 15% 23% 12% 1	8806
	11th to 20th	Day	27% 6% 14% 39% 12% 1	8625
	21st to end	Day	29% 7% 13% 31% 19%	8372
August	1st to 10th	Day	33% 8% 15% 29% 14% 1	4351
	11th to 20th	Day	35% 7% 17% 29% 11%	4265
	21st to end	Day	33% 8% 16% 33% 10% 1	4674
September	1st to 10th	Day	38% 8% 14% 27% 11% 1	2361
	11th to 20th	Day	33% 8% 16% 31% 11% 1	2200
	21st to end	Day	46% 7% 14% 24% 9%	2200
October	1st to 10th	Day	38% 6% 12% 27% 17%	3332
	11th to 20th	Day	52% 6% 13% 22% 8%	3240
	21st to end	Day	58% 6% 14% 17% 5%	3325
November	1st to 10th	Day	61% 8% 12% 15% 5%	1817
	11th to 20th	Day	66% 8% 11% 10% 4	1680
	21st to end	Day	77% 7% 9% 6% 2	1680
December	1st to 10th	Day	80% 7% 8% 3 1	2680
	11th to 20th	Day	80% 7% 8% 5%	2707
	21st to end	Day	85% 6% 5% 3 1	3553
January	1st to 10th	Night	79% 8% 6% 5% 2	8789
	11th to 20th	Night	82% 6% 4 5% 2	8280
	21st to end	Night	72% 8% 7% 8% 4 1	8545
February	1st to 10th	Night	69% 6% 9% 12% 3	2730
	11th to 20th	Night	65% 8% 9% 13% 6%	2665
	21st to end	Night	60% 8% 11% 14% 7%	2097
March	1st to 10th	Night	50% 7% 15% 16% 11% 2	5242
	11th to 20th	Night	49% 7% 15% 19% 8% 1	5090
	21st to end	Night	55% 8% 8% 16% 12% 2	5588
April	1st to 10th	Night	51% 5% 10% 21% 11% 2	2189
	11th to 20th	Night	45% 5% 8% 22% 17% 2	1867
	21st to end	Night	51% 6% 9% 17% 15% 3	1890
May	1st to 10th	Night	43% 6% 9% 21% 17% 4	5264
	11th to 20th	Night	41% 6% 8% 23% 20% 1	4922
	21st to end	Night	43% 5% 8% 24% 17% 4	4971
June	1st to 10th	Night	40% 7% 9% 22% 19% 3	1470
	11th to 20th	Night	37% 7% 12% 23% 20% 1	1470
	21st to end	Night	41% 7% 15% 23% 13% 2	1470
July	1st to 10th	Night	36% 7% 13% 24% 16% 3	4075
	11th to 20th	Night	30% 7% 11% 36% 15% 1	4238
	21st to end	Night	33% 7% 11% 29% 19% 1	5387
August	1st to 10th	Night	35% 7% 14% 29% 15% 1	2994
	11th to 20th	Night	39% 8% 16% 23% 13% 1	2938
	21st to end	Night	34% 8% 14% 32% 12% 1	3223
September	1st to 10th	Night	36% 8% 13% 28% 14% 2	2015
	11th to 20th	Night	35% 7% 14% 31% 13%	2200
	21st to end	Night	46% 7% 14% 23% 11%	2200
October	1st to 10th	Night	37% 6% 11% 30% 16%	3846
	11th to 20th	Night	52% 6% 14% 19% 9%	3899
	21st to end	Night	55% 8% 15% 17% 5%	4461
November	1st to 10th	Night	60% 7% 11% 17% 5%	2699
	11th to 20th	Night	68% 8% 11% 8% 4 1	2940
	21st to end	Night	76% 8% 9% 6% 1	2940
December	1st to 10th	Night	77% 9% 9% 4 1	4720
	11th to 20th	Night	79% 8% 8% 4 1	5701
	21st to end	Night	82% 8% 8% 2 1	7667

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% 15% 34% 20% 8%	228
	11th to 20th	Day	20% 14% 37% 20% 9%	330
	21st to end	Day	24% 11% 24% 32% 9% 1	363
February	1st to 10th	Day	18% 14% 35% 24% 7% 1	330
	11th to 20th	Day	19% 12% 36% 28% 5%	330
	21st to end	Day	20% 16% 35% 26% 4	273
March	1st to 10th	Day	17% 14% 30% 29% 9% 1	437
	11th to 20th	Day	17% 16% 26% 30% 10% 1	540
	21st to end	Day	24% 8% 27% 31% 9% 1	594
April	1st to 10th	Day	20% 10% 26% 32% 10% 2	540
	11th to 20th	Day	23% 9% 23% 27% 13% 5%	532
	21st to end	Day	21% 9% 24% 32% 13% 1	540
May	1st to 10th	Day	19% 6% 20% 37% 16% 2	543
	11th to 20th	Day	15% 4 18% 34% 25% 5%	567
	21st to end	Day	15% 3 16% 35% 24% 7%	661
June	1st to 10th	Day	12% 2 17% 39% 25% 4	780
	11th to 20th	Day	13% 3 18% 37% 24% 4	780
	21st to end	Day	15% 3 16% 39% 23% 4	780
July	1st to 10th	Day	9% 1 11% 44% 29% 6%	771
	11th to 20th	Day	11% 2 16% 35% 30% 7%	768
	21st to end	Day	11% 2 14% 37% 30% 5%	699
August	1st to 10th	Day	14% 3 14% 30% 32% 8%	566
	11th to 20th	Day	11% 2 11% 31% 35% 10%	535
	21st to end	Day	12% 4 17% 33% 26% 8%	583
September	1st to 10th	Day	14% 5% 18% 26% 28% 8%	530
	11th to 20th	Day	10% 4 15% 26% 31% 14%	530
	21st to end	Day	18% 8% 17% 26% 24% 7%	530
October	1st to 10th	Day	20% 9% 22% 25% 19% 5%	530
	11th to 20th	Day	25% 13% 25% 28% 8% 1	530
	21st to end	Day	28% 14% 28% 23% 6% 1	458
November	1st to 10th	Day	24% 14% 30% 23% 8% 1	311
	11th to 20th	Day	27% 14% 32% 23% 5%	220
	21st to end	Day	27% 17% 34% 20% 2	220
December	1st to 10th	Day	25% 20% 29% 20% 5%	220
	11th to 20th	Day	31% 21% 28% 16% 3	220
	21st to end	Day	32% 18% 31% 15% 3	242
January	1st to 10th	Night	24% 17% 30% 22% 6% 1	1050
	11th to 20th	Night	24% 17% 29% 23% 6% 1	1050
	21st to end	Night	20% 11% 35% 25% 8% 1	977
February	1st to 10th	Night	19% 13% 37% 24% 6% 1	840
	11th to 20th	Night	19% 12% 33% 26% 9%	823
	21st to end	Night	21% 12% 34% 28% 5%	692
March	1st to 10th	Night	17% 10% 34% 31% 8% 1	840
	11th to 20th	Night	19% 10% 34% 26% 9% 2	840
	21st to end	Night	19% 7% 30% 30% 13% 1	924
April	1st to 10th	Night	23% 10% 30% 29% 8% 1	803
	11th to 20th	Night	22% 9% 22% 30% 13% 4	623
	21st to end	Night	24% 7% 22% 29% 16% 2	630
May	1st to 10th	Night	16% 2 21% 39% 20% 3	630
	11th to 20th	Night	16% 5% 16% 36% 24% 3	516
	21st to end	Night	16% 2 16% 39% 20% 6%	455
June	1st to 10th	Night	15% 5% 17% 38% 22% 3	420
	11th to 20th	Night	12% 3 17% 41% 23% 4	420
	21st to end	Night	12% 3 14% 39% 29% 4	420
July	1st to 10th	Night	7% 3 11% 47% 29% 4	410
	11th to 20th	Night	10% 2 15% 34% 31% 8%	461
	21st to end	Night	9% 3 12% 39% 33% 4	690
August	1st to 10th	Night	10% 3 15% 34% 32% 6%	627
	11th to 20th	Night	12% 2 14% 30% 32% 9%	606
	21st to end	Night	13% 5% 17% 32% 26% 7%	660
September	1st to 10th	Night	13% 4 20% 28% 25% 10%	765
	11th to 20th	Night	14% 5% 17% 26% 27% 11%	800
	21st to end	Night	20% 6% 19% 23% 25% 8%	800
October	1st to 10th	Night	23% 6% 23% 25% 20% 3	800
	11th to 20th	Night	29% 12% 25% 22% 11% 1	800
	21st to end	Night	31% 11% 27% 24% 6% 1	880
November	1st to 10th	Night	26% 16% 26% 22% 9% 1	820
	11th to 20th	Night	27% 18% 31% 16% 8%	840
	21st to end	Night	34% 16% 29% 16% 4 1	840
December	1st to 10th	Night	31% 18% 29% 15% 7%	840
	11th to 20th	Night	27% 19% 35% 14% 4	1029
	21st to end	Night	32% 16% 32% 15% 5%	1155

Page generated at 2026-08-12 03:37:16. Version ac07

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