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 2025-04-11.

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% 4 3 5% 6% 32%	113090
	Night	16% 14% 6% 12% 6% 5% 4 3 4 5% 25%	115245
Transparency	Day	50% 7% 12% 19% 10% 1	116651
	Night	58% 7% 10% 15% 9% 1	119847
Seeing	Day	18% 7% 22% 30% 19% 4	15728
	Night	21% 10% 26% 26% 14% 3	25171

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% 21% 11% 17% 11% 7% 3 3 2 3 9%	3184
	11th to 20th	Day	12% 22% 10% 26% 11% 6% 3 2 2 2 3	3589
	21st to end	Day	16% 19% 9% 17% 7% 7% 5% 3 4 4 9%	4352
February	1st to 10th	Day	13% 20% 6% 16% 9% 6% 5% 2 4 5% 14%	1800
	11th to 20th	Day	12% 16% 6% 13% 8% 8% 5% 4 5% 5% 18%	1753
	21st to end	Day	14% 16% 6% 12% 6% 5% 5% 4 5% 5% 22%	1625
March	1st to 10th	Day	16% 11% 4 9% 5% 5% 4 4 5% 6% 31%	4722
	11th to 20th	Day	11% 13% 5% 11% 6% 6% 5% 3 6% 7% 27%	4980
	21st to end	Day	17% 11% 4 9% 5% 4 4 3 4 5% 32%	5465
April	1st to 10th	Day	18% 10% 3 8% 4 4 4 4 5% 6% 33%	2331
	11th to 20th	Day	18% 7% 3 5% 5% 4 3 3 4 7% 40%	2442
	21st to end	Day	18% 9% 3 6% 4 4 4 3 6% 7% 38%	2470
May	1st to 10th	Day	15% 7% 3 6% 4 4 4 3 5% 6% 43%	4108
	11th to 20th	Day	13% 7% 2 6% 4 4 4 4 6% 7% 43%	4238
	21st to end	Day	14% 6% 2 6% 3 4 4 3 5% 7% 46%	4916
June	1st to 10th	Day	13% 6% 2 7% 4 5% 5% 4 6% 7% 41%	2850
	11th to 20th	Day	10% 6% 2 6% 5% 4 4 4 6% 9% 43%	2850
	21st to end	Day	13% 7% 3 6% 5% 4 4 4 7% 8% 40%	2850
July	1st to 10th	Day	12% 7% 3 7% 5% 5% 5% 5% 6% 7% 39%	4760
	11th to 20th	Day	9% 5% 2 5% 4 4 4 4 6% 8% 52%	4670
	21st to end	Day	9% 5% 2 5% 3 4 4 3 5% 8% 53%	4576
August	1st to 10th	Day	11% 5% 2 5% 4 4 4 4 7% 9% 44%	4104
	11th to 20th	Day	14% 6% 2 6% 3 3 3 4 7% 7% 45%	4044
	21st to end	Day	8% 6% 2 6% 4 5% 5% 4 6% 7% 47%	4532
September	1st to 10th	Day	13% 5% 2 6% 4 5% 4 4 5% 7% 44%	2243
	11th to 20th	Day	12% 5% 2 5% 4 3 4 4 6% 8% 48%	2090
	21st to end	Day	17% 7% 2 7% 4 5% 4 4 5% 7% 38%	2090
October	1st to 10th	Day	18% 9% 3 7% 4 5% 4 3 6% 7% 34%	1944
	11th to 20th	Day	26% 11% 4 9% 5% 4 4 3 5% 6% 24%	1900
	21st to end	Day	26% 15% 4 9% 4 4 5% 3 5% 5% 19%	1971
November	1st to 10th	Day	19% 17% 5% 9% 4 4 4 4 5% 6% 23%	1729
	11th to 20th	Day	18% 20% 5% 11% 5% 5% 4 4 5% 6% 16%	1600
	21st to end	Day	24% 23% 6% 13% 6% 4 4 2 4 4 10%	1600
December	1st to 10th	Day	17% 32% 9% 14% 7% 4 4 2 2 3 7%	2600
	11th to 20th	Day	21% 23% 8% 19% 6% 4 3 2 3 3 7%	2636
	21st to end	Day	27% 24% 7% 17% 4 7% 3 2 3 3 3	3476
January	1st to 10th	Night	13% 23% 11% 21% 11% 6% 3 2 2 2 6%	6780
	11th to 20th	Night	14% 20% 10% 25% 10% 5% 4 3 2 3 6%	6316
	21st to end	Night	12% 18% 9% 18% 8% 8% 4 3 4 3 11%	6606
February	1st to 10th	Night	12% 20% 7% 18% 9% 5% 3 3 4 4 14%	2600
	11th to 20th	Night	13% 17% 7% 14% 8% 5% 4 4 4 4 19%	2533
	21st to end	Night	14% 15% 5% 11% 7% 6% 4 4 6% 5% 23%	2000
March	1st to 10th	Night	15% 10% 5% 10% 6% 5% 5% 3 5% 5% 33%	5117
	11th to 20th	Night	11% 12% 4 9% 5% 4 5% 5% 6% 8% 32%	4979
	21st to end	Night	19% 11% 5% 10% 6% 4 4 3 4 5% 29%	5467
April	1st to 10th	Night	21% 11% 3 6% 4 4 4 3 6% 6% 33%	2085
	11th to 20th	Night	18% 8% 3 6% 4 4 4 4 6% 7% 37%	1693
	21st to end	Night	20% 9% 3 7% 4 5% 5% 3 5% 5% 33%	1710
May	1st to 10th	Night	13% 7% 3 10% 5% 5% 4 4 5% 6% 38%	2833
	11th to 20th	Night	12% 7% 3 6% 5% 5% 4 4 5% 8% 42%	2639
	21st to end	Night	13% 6% 3 8% 5% 4 4 3 5% 7% 43%	2659
June	1st to 10th	Night	12% 8% 3 7% 6% 4 5% 3 5% 8% 39%	1330
	11th to 20th	Night	9% 5% 3 6% 5% 4 5% 5% 7% 8% 44%	1330
	21st to end	Night	11% 8% 2 6% 5% 6% 4 5% 6% 8% 40%	1330
July	1st to 10th	Night	10% 7% 2 7% 4 4 3 3 5% 8% 47%	2210
	11th to 20th	Night	10% 5% 2 5% 4 4 4 3 5% 8% 50%	2296
	21st to end	Night	8% 6% 2 5% 3 4 4 3 5% 8% 51%	2965
August	1st to 10th	Night	10% 6% 2 7% 4 4 5% 3 6% 7% 46%	2825
	11th to 20th	Night	12% 6% 3 6% 4 5% 6% 3 6% 8% 41%	2785
	21st to end	Night	9% 5% 2 6% 4 5% 5% 3 6% 7% 46%	3124
September	1st to 10th	Night	12% 5% 2 5% 4 4 4 3 5% 7% 47%	1914
	11th to 20th	Night	12% 5% 2 6% 3 4 4 4 6% 6% 48%	2090
	21st to end	Night	19% 7% 3 6% 5% 4 4 3 5% 6% 38%	2090
October	1st to 10th	Night	21% 9% 2 8% 5% 5% 4 3 5% 6% 33%	2234
	11th to 20th	Night	25% 12% 4 9% 5% 4 5% 3 4 5% 24%	2280
	21st to end	Night	26% 16% 5% 8% 5% 5% 4 3 5% 6% 18%	2623
November	1st to 10th	Night	21% 17% 3 8% 6% 4 4 3 4 6% 25%	2567
	11th to 20th	Night	18% 23% 6% 11% 6% 4 5% 3 3 4 16%	2800
	21st to end	Night	24% 25% 6% 11% 6% 4 4 3 4 4 10%	2800
December	1st to 10th	Night	20% 26% 9% 15% 6% 5% 4 2 3 3 8%	4580
	11th to 20th	Night	17% 24% 10% 18% 7% 5% 4 2 3 3 7%	5553
	21st to end	Night	24% 24% 9% 16% 7% 6% 3 2 2 2 6%	7502

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% 8% 7% 5% 2 1	3185
	11th to 20th	Day	88% 5% 4 3 1	3620
	21st to end	Day	74% 9% 8% 7% 3	4352
February	1st to 10th	Day	72% 6% 9% 11% 2	1800
	11th to 20th	Day	66% 7% 10% 11% 6%	1762
	21st to end	Day	60% 7% 11% 17% 4	1625
March	1st to 10th	Day	50% 8% 15% 11% 13% 2	4725
	11th to 20th	Day	54% 7% 13% 18% 7% 1	4980
	21st to end	Day	50% 8% 15% 18% 8% 2	5465
April	1st to 10th	Day	50% 6% 12% 20% 11% 1	2331
	11th to 20th	Day	45% 5% 8% 26% 14% 2	2442
	21st to end	Day	45% 6% 13% 20% 13% 3	2470
May	1st to 10th	Day	40% 8% 11% 20% 19% 2	4120
	11th to 20th	Day	38% 8% 13% 25% 14% 1	4242
	21st to end	Day	38% 7% 13% 17% 22% 3	4916
June	1st to 10th	Day	40% 7% 12% 26% 14% 1	2850
	11th to 20th	Day	36% 7% 11% 28% 18% 1	2850
	21st to end	Day	39% 8% 12% 25% 13% 2	2850
July	1st to 10th	Day	41% 7% 15% 22% 13% 1	4686
	11th to 20th	Day	29% 7% 16% 34% 13% 1	4589
	21st to end	Day	28% 7% 11% 29% 23% 1	4431
August	1st to 10th	Day	33% 8% 15% 29% 14% 1	4091
	11th to 20th	Day	36% 7% 17% 28% 11%	4083
	21st to end	Day	33% 8% 15% 33% 10% 1	4531
September	1st to 10th	Day	38% 8% 13% 28% 12% 1	2243
	11th to 20th	Day	34% 8% 16% 31% 11% 1	2090
	21st to end	Day	46% 7% 14% 24% 9%	2090
October	1st to 10th	Day	38% 7% 12% 26% 17%	3230
	11th to 20th	Day	52% 6% 13% 21% 8%	3140
	21st to end	Day	58% 6% 14% 16% 5%	3221
November	1st to 10th	Day	61% 7% 12% 15% 5%	1729
	11th to 20th	Day	67% 8% 10% 10% 4	1600
	21st to end	Day	77% 7% 9% 5% 2	1600
December	1st to 10th	Day	80% 8% 8% 3 1	2600
	11th to 20th	Day	80% 7% 8% 5%	2636
	21st to end	Day	85% 7% 5% 3 1	3476
January	1st to 10th	Night	81% 8% 6% 4 1	6780
	11th to 20th	Night	81% 7% 5% 5% 2	6360
	21st to end	Night	73% 8% 7% 6% 4 1	6606
February	1st to 10th	Night	71% 6% 9% 11% 3	2600
	11th to 20th	Night	65% 7% 8% 13% 6%	2535
	21st to end	Night	60% 8% 11% 14% 7%	2000
March	1st to 10th	Night	50% 7% 15% 16% 11% 3	5127
	11th to 20th	Night	48% 7% 16% 19% 8% 1	4980
	21st to end	Night	55% 8% 8% 16% 12% 2	5467
April	1st to 10th	Night	51% 5% 9% 21% 12% 2	2085
	11th to 20th	Night	45% 5% 8% 23% 17% 2	1693
	21st to end	Night	52% 6% 9% 16% 15% 3	1710
May	1st to 10th	Night	44% 7% 11% 20% 17% 2	2840
	11th to 20th	Night	40% 7% 10% 23% 18% 2	2640
	21st to end	Night	41% 7% 11% 21% 16% 5%	2660
June	1st to 10th	Night	42% 7% 9% 22% 18% 2	1330
	11th to 20th	Night	35% 7% 13% 23% 21% 1	1330
	21st to end	Night	40% 7% 14% 23% 13% 2	1330
July	1st to 10th	Night	35% 6% 13% 24% 16% 5%	2175
	11th to 20th	Night	32% 7% 10% 36% 15% 1	2254
	21st to end	Night	31% 7% 12% 24% 25% 1	2870
August	1st to 10th	Night	35% 7% 14% 29% 14% 1	2814
	11th to 20th	Night	39% 8% 16% 23% 13% 1	2812
	21st to end	Night	34% 8% 13% 31% 12% 1	3124
September	1st to 10th	Night	36% 7% 12% 28% 14% 2	1914
	11th to 20th	Night	35% 8% 14% 30% 12%	2090
	21st to end	Night	46% 7% 14% 23% 10%	2090
October	1st to 10th	Night	38% 6% 11% 29% 16%	3728
	11th to 20th	Night	52% 6% 14% 20% 8%	3779
	21st to end	Night	55% 8% 15% 17% 5%	4323
November	1st to 10th	Night	59% 7% 11% 18% 5%	2567
	11th to 20th	Night	68% 8% 11% 8% 4 1	2800
	21st to end	Night	76% 8% 9% 6% 1	2800
December	1st to 10th	Night	78% 9% 9% 4 1	4580
	11th to 20th	Night	79% 8% 8% 4 1	5552
	21st to end	Night	82% 8% 8% 2 1	7502

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% 13% 35% 22% 8%	207
	11th to 20th	Day	20% 10% 38% 21% 10%	300
	21st to end	Day	26% 10% 23% 31% 9% 1	330
February	1st to 10th	Day	20% 14% 35% 24% 7%	300
	11th to 20th	Day	18% 12% 37% 28% 4	300
	21st to end	Day	20% 15% 36% 25% 4	249
March	1st to 10th	Day	17% 12% 31% 30% 9% 1	402
	11th to 20th	Day	16% 14% 26% 32% 11% 1	500
	21st to end	Day	24% 7% 27% 32% 9% 1	550
April	1st to 10th	Day	20% 8% 26% 33% 10% 2	500
	11th to 20th	Day	23% 8% 25% 27% 12% 6%	452
	21st to end	Day	22% 8% 24% 32% 13% 1	460
May	1st to 10th	Day	21% 3 19% 37% 18% 2	463
	11th to 20th	Day	17% 3 15% 33% 26% 6%	487
	21st to end	Day	13% 2 16% 34% 27% 8%	569
June	1st to 10th	Day	13% 2 18% 38% 26% 4	680
	11th to 20th	Day	13% 3 17% 37% 26% 5%	680
	21st to end	Day	16% 3 16% 37% 25% 4	680
July	1st to 10th	Day	8% 1 11% 44% 30% 6%	671
	11th to 20th	Day	11% 2 15% 34% 30% 7%	668
	21st to end	Day	12% 2 13% 36% 32% 5%	603
August	1st to 10th	Day	14% 3 15% 27% 31% 9%	486
	11th to 20th	Day	11% 2 10% 29% 37% 10%	479
	21st to end	Day	13% 4 17% 33% 26% 8%	539
September	1st to 10th	Day	14% 4 19% 27% 28% 8%	490
	11th to 20th	Day	10% 4 16% 27% 30% 12%	490
	21st to end	Day	18% 8% 18% 26% 24% 7%	490
October	1st to 10th	Day	21% 9% 23% 24% 18% 5%	490
	11th to 20th	Day	25% 13% 24% 28% 8% 1	490
	21st to end	Day	29% 14% 28% 22% 6% 1	420
November	1st to 10th	Day	23% 13% 31% 25% 8% 1	283
	11th to 20th	Day	28% 14% 32% 22% 5%	200
	21st to end	Day	27% 16% 36% 20% 2	200
December	1st to 10th	Day	26% 20% 29% 20% 6% 1	200
	11th to 20th	Day	31% 21% 30% 16% 4	200
	21st to end	Day	32% 17% 33% 15% 3	220
January	1st to 10th	Night	25% 16% 31% 22% 6% 1	1000
	11th to 20th	Night	25% 16% 29% 23% 6% 1	1000
	21st to end	Night	20% 10% 35% 25% 8% 2	931
February	1st to 10th	Night	19% 14% 37% 24% 6% 1	800
	11th to 20th	Night	19% 12% 34% 26% 9%	783
	21st to end	Night	21% 11% 35% 28% 6%	660
March	1st to 10th	Night	17% 10% 34% 30% 8% 1	800
	11th to 20th	Night	18% 10% 34% 27% 10% 2	800
	21st to end	Night	19% 6% 31% 30% 13% 1	880
April	1st to 10th	Night	24% 10% 28% 30% 8% 1	765
	11th to 20th	Night	22% 8% 23% 29% 14% 4	565
	21st to end	Night	25% 6% 23% 29% 15% 2	570
May	1st to 10th	Night	16% 2 21% 38% 20% 3	570
	11th to 20th	Night	16% 4 16% 37% 25% 3	466
	21st to end	Night	15% 2 16% 39% 21% 6%	411
June	1st to 10th	Night	15% 4 17% 38% 22% 3	380
	11th to 20th	Night	11% 3 16% 41% 24% 5%	380
	21st to end	Night	12% 3 14% 38% 29% 4	380
July	1st to 10th	Night	7% 2 12% 45% 29% 5%	370
	11th to 20th	Night	9% 2 15% 34% 31% 8%	415
	21st to end	Night	9% 2 13% 39% 33% 4	624
August	1st to 10th	Night	11% 2 15% 33% 32% 7%	567
	11th to 20th	Night	12% 2 14% 29% 33% 10%	564
	21st to end	Night	13% 4 18% 31% 27% 7%	627
September	1st to 10th	Night	13% 3 20% 29% 25% 10%	727
	11th to 20th	Night	15% 4 18% 26% 26% 10%	760
	21st to end	Night	21% 6% 19% 23% 24% 8%	760
October	1st to 10th	Night	24% 7% 24% 24% 18% 3	760
	11th to 20th	Night	29% 12% 25% 22% 11% 1	760
	21st to end	Night	32% 11% 28% 23% 6% 1	836
November	1st to 10th	Night	27% 14% 26% 22% 9% 1	780
	11th to 20th	Night	28% 18% 31% 16% 8%	800
	21st to end	Night	33% 16% 29% 17% 5% 1	800
December	1st to 10th	Night	33% 18% 29% 14% 7%	800
	11th to 20th	Night	28% 19% 34% 13% 5% 1	980
	21st to end	Night	32% 16% 31% 15% 5%	1100

Page generated at 2025-04-08 09:17:23. Version ac07

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