Embro Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Embro Observatory clear sky chart from 2005-11-06 to 2026-01-17.

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 10% 5% 5% 5% 4 6% 7% 30%	128123
	Night	14% 11% 4 10% 6% 5% 4 4 5% 7% 32%	123525
Transparency	Day	52% 4 11% 20% 11% 1	131718
	Night	51% 4 11% 20% 12% 1	128019
Seeing	Day	19% 10% 28% 24% 13% 5%	16432
	Night	20% 9% 29% 29% 12% 1	25533

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% 16% 8% 21% 8% 5% 4 3 3 4 17%	3887
	11th to 20th	Day	10% 20% 9% 23% 8% 7% 4 3 5% 4 7%	4080
	21st to end	Day	18% 17% 6% 17% 8% 5% 6% 3 4 4 13%	4466
February	1st to 10th	Day	14% 18% 5% 13% 9% 7% 6% 3 4 5% 16%	1800
	11th to 20th	Day	13% 16% 7% 13% 8% 5% 7% 3 4 5% 19%	1753
	21st to end	Day	16% 15% 5% 12% 7% 6% 5% 3 4 5% 22%	1623
March	1st to 10th	Day	17% 12% 6% 14% 7% 4 4 3 4 5% 25%	4841
	11th to 20th	Day	11% 12% 5% 9% 6% 5% 5% 4 5% 8% 30%	4980
	21st to end	Day	17% 12% 6% 11% 5% 5% 4 3 4 5% 28%	5465
April	1st to 10th	Day	16% 13% 4 8% 5% 5% 4 3 5% 7% 28%	2290
	11th to 20th	Day	18% 10% 3 7% 5% 4 4 3 6% 7% 33%	2533
	21st to end	Day	19% 11% 3 8% 5% 4 4 2 5% 6% 33%	2600
May	1st to 10th	Day	19% 9% 4 8% 5% 4 4 3 5% 7% 32%	5888
	11th to 20th	Day	16% 10% 3 8% 4 4 5% 3 6% 8% 32%	5952
	21st to end	Day	17% 8% 2 7% 4 4 5% 4 5% 7% 38%	6949
June	1st to 10th	Day	13% 6% 3 6% 5% 5% 5% 5% 7% 8% 38%	2800
	11th to 20th	Day	10% 6% 2 7% 5% 5% 6% 5% 7% 10% 37%	2942
	21st to end	Day	12% 6% 2 6% 5% 5% 5% 5% 6% 10% 39%	3000
July	1st to 10th	Day	9% 5% 2 7% 4 5% 6% 5% 7% 10% 39%	6819
	11th to 20th	Day	8% 5% 2 6% 5% 5% 5% 5% 7% 10% 41%	6050
	21st to end	Day	8% 5% 2 6% 5% 5% 5% 4 6% 9% 46%	6424
August	1st to 10th	Day	14% 7% 2 6% 4 5% 5% 5% 7% 9% 36%	4234
	11th to 20th	Day	10% 7% 3 7% 6% 5% 6% 5% 7% 10% 35%	4174
	21st to end	Day	8% 6% 3 7% 5% 5% 6% 4 7% 9% 39%	4586
September	1st to 10th	Day	11% 6% 2 7% 5% 5% 5% 4 7% 8% 39%	2371
	11th to 20th	Day	11% 5% 2 6% 4 4 5% 4 6% 8% 45%	2200
	21st to end	Day	15% 7% 3 8% 5% 5% 5% 4 7% 7% 35%	2200
October	1st to 10th	Day	16% 9% 2 8% 5% 4 4 3 6% 7% 37%	2025
	11th to 20th	Day	21% 9% 3 8% 4 4 5% 4 6% 6% 30%	2000
	21st to end	Day	21% 13% 3 9% 6% 4 5% 4 6% 7% 22%	2180
November	1st to 10th	Day	13% 11% 3 9% 6% 5% 4 4 6% 7% 31%	1852
	11th to 20th	Day	14% 15% 4 9% 6% 5% 5% 4 6% 8% 23%	1685
	21st to end	Day	18% 17% 7% 11% 6% 4 5% 4 5% 6% 16%	1680
December	1st to 10th	Day	17% 20% 8% 13% 7% 6% 5% 4 5% 4 11%	2680
	11th to 20th	Day	20% 19% 7% 11% 5% 5% 4 3 4 5% 16%	3066
	21st to end	Day	26% 19% 7% 13% 6% 5% 3 2 4 4 10%	4048
January	1st to 10th	Night	13% 13% 6% 18% 7% 6% 5% 4 5% 6% 16%	6277
	11th to 20th	Night	11% 15% 8% 18% 11% 7% 6% 5% 5% 5% 9%	5938
	21st to end	Night	16% 13% 8% 15% 6% 5% 5% 4 5% 6% 18%	6490
February	1st to 10th	Night	14% 16% 6% 13% 8% 6% 4 4 4 6% 20%	2600
	11th to 20th	Night	14% 13% 6% 11% 7% 6% 5% 3 5% 7% 23%	2533
	21st to end	Night	15% 13% 5% 12% 6% 5% 5% 5% 5% 6% 23%	2005
March	1st to 10th	Night	13% 10% 4 9% 7% 5% 5% 4 6% 7% 32%	4997
	11th to 20th	Night	9% 8% 3 9% 5% 5% 5% 4 7% 9% 35%	4979
	21st to end	Night	17% 10% 4 9% 4 4 4 3 4 4 37%	5467
April	1st to 10th	Night	18% 10% 3 8% 5% 5% 4 3 6% 7% 31%	2109
	11th to 20th	Night	17% 9% 4 8% 5% 4 4 3 5% 7% 35%	1832
	21st to end	Night	14% 9% 3 8% 5% 5% 4 4 7% 8% 34%	1800
May	1st to 10th	Night	19% 8% 3 7% 4 4 4 3 5% 7% 36%	4053
	11th to 20th	Night	13% 10% 4 9% 5% 5% 4 3 5% 6% 36%	3926
	21st to end	Night	17% 6% 2 5% 3 3 3 4 5% 7% 45%	3926
June	1st to 10th	Night	11% 6% 2 5% 5% 4 5% 3 7% 7% 45%	1600
	11th to 20th	Night	9% 5% 2 7% 4 5% 5% 3 7% 10% 43%	1450
	21st to end	Night	9% 5% 2 6% 4 5% 5% 5% 5% 8% 46%	1400
July	1st to 10th	Night	6% 5% 2 5% 4 4 5% 4 7% 10% 49%	3160
	11th to 20th	Night	8% 6% 2 5% 4 4 4 3 6% 8% 49%	3876
	21st to end	Night	7% 6% 2 5% 4 4 4 4 5% 7% 51%	4428
August	1st to 10th	Night	10% 5% 2 7% 3 4 5% 4 6% 7% 46%	2915
	11th to 20th	Night	10% 7% 2 5% 4 4 4 3 6% 8% 46%	2875
	21st to end	Night	7% 5% 2 6% 4 4 5% 4 6% 9% 47%	3277
September	1st to 10th	Night	9% 6% 2 7% 4 4 3 3 6% 6% 48%	2025
	11th to 20th	Night	9% 4 2 5% 3 3 4 4 5% 7% 55%	2200
	21st to end	Night	16% 8% 2 7% 5% 4 4 3 5% 7% 40%	2200
October	1st to 10th	Night	14% 8% 2 6% 4 4 4 4 5% 7% 43%	2375
	11th to 20th	Night	18% 9% 3 7% 6% 4 4 3 5% 6% 35%	2400
	21st to end	Night	20% 9% 3 8% 5% 4 5% 3 6% 6% 30%	2656
November	1st to 10th	Night	14% 9% 3 7% 5% 5% 5% 4 6% 8% 35%	2666
	11th to 20th	Night	15% 13% 3 9% 5% 5% 5% 5% 6% 7% 26%	2932
	21st to end	Night	19% 14% 6% 9% 6% 5% 4 4 5% 7% 21%	2940
December	1st to 10th	Night	12% 17% 7% 15% 8% 7% 6% 4 5% 5% 14%	4720
	11th to 20th	Night	13% 21% 6% 12% 6% 4 4 3 5% 6% 20%	5348
	21st to end	Night	22% 19% 7% 11% 6% 5% 4 3 4 5% 15%	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	72% 3 7% 12% 6%	3888
	11th to 20th	Day	81% 3 7% 6% 3	4114
	21st to end	Day	76% 3 9% 7% 6%	4466
February	1st to 10th	Day	72% 2 8% 14% 4 1	1800
	11th to 20th	Day	68% 3 7% 14% 7%	1762
	21st to end	Day	65% 3 11% 13% 7% 1	1623
March	1st to 10th	Day	62% 2 12% 17% 6% 1	4844
	11th to 20th	Day	53% 3 15% 20% 7% 2	4980
	21st to end	Day	59% 3 9% 19% 10% 1	5465
April	1st to 10th	Day	57% 3 10% 19% 11% 1	2290
	11th to 20th	Day	52% 3 10% 21% 13% 1	2533
	21st to end	Day	53% 2 10% 20% 12% 2	2600
May	1st to 10th	Day	52% 3 9% 20% 10% 5%	5897
	11th to 20th	Day	50% 3 12% 21% 12% 2	5956
	21st to end	Day	46% 3 10% 19% 17% 4	6949
June	1st to 10th	Day	43% 3 12% 26% 14% 2	2800
	11th to 20th	Day	42% 4 12% 24% 16% 2	2942
	21st to end	Day	41% 5% 12% 26% 17%	3000
July	1st to 10th	Day	37% 6% 12% 26% 16% 2	6746
	11th to 20th	Day	35% 6% 13% 30% 15% 1	5977
	21st to end	Day	34% 6% 11% 27% 20% 1	6240
August	1st to 10th	Day	43% 6% 13% 24% 13% 1	4221
	11th to 20th	Day	42% 6% 16% 27% 9% 1	4213
	21st to end	Day	38% 6% 12% 31% 12% 1	4586
September	1st to 10th	Day	41% 4 13% 28% 13% 1	2371
	11th to 20th	Day	37% 3 12% 32% 16%	2200
	21st to end	Day	48% 4 12% 26% 11% 1	2200
October	1st to 10th	Day	39% 5% 14% 24% 18% 1	3298
	11th to 20th	Day	41% 3 13% 23% 19%	3240
	21st to end	Day	50% 5% 15% 22% 7%	3506
November	1st to 10th	Day	53% 4 10% 24% 8% 1	1852
	11th to 20th	Day	57% 4 13% 15% 9% 1	1685
	21st to end	Day	68% 3 11% 14% 4	1680
December	1st to 10th	Day	74% 5% 9% 8% 3	2680
	11th to 20th	Day	71% 3 8% 12% 6%	3066
	21st to end	Day	80% 3 6% 9% 3	4048
January	1st to 10th	Night	66% 5% 10% 14% 5%	6277
	11th to 20th	Night	76% 4 7% 9% 3	5979
	21st to end	Night	68% 3 8% 12% 8% 1	6490
February	1st to 10th	Night	67% 2 8% 16% 6%	2600
	11th to 20th	Night	61% 4 10% 17% 8%	2535
	21st to end	Night	63% 2 10% 18% 7%	2005
March	1st to 10th	Night	51% 3 14% 21% 9% 2	5007
	11th to 20th	Night	45% 4 17% 23% 11% 1	4980
	21st to end	Night	51% 3 8% 21% 16% 2	5467
April	1st to 10th	Night	54% 2 8% 20% 14% 1	2109
	11th to 20th	Night	50% 3 8% 20% 17% 2	1832
	21st to end	Night	48% 2 9% 21% 16% 3	1800
May	1st to 10th	Night	49% 3 11% 16% 13% 8%	4060
	11th to 20th	Night	49% 3 11% 23% 11% 3	3927
	21st to end	Night	40% 2 13% 24% 18% 2	3927
June	1st to 10th	Night	38% 2 12% 28% 17% 3	1600
	11th to 20th	Night	37% 3 14% 27% 17% 2	1450
	21st to end	Night	37% 4 14% 24% 20% 1	1400
July	1st to 10th	Night	30% 5% 14% 28% 19% 4	3125
	11th to 20th	Night	32% 5% 11% 28% 20% 3	3827
	21st to end	Night	32% 6% 11% 25% 23% 4	4297
August	1st to 10th	Night	36% 5% 13% 26% 18% 1	2904
	11th to 20th	Night	36% 5% 16% 29% 13% 1	2902
	21st to end	Night	32% 5% 13% 33% 16% 1	3277
September	1st to 10th	Night	37% 3 12% 30% 16% 2	2025
	11th to 20th	Night	30% 3 12% 35% 20% 1	2200
	21st to end	Night	45% 3 12% 27% 13% 1	2200
October	1st to 10th	Night	32% 4 9% 31% 24% 1	3882
	11th to 20th	Night	44% 3 13% 23% 17% 1	3899
	21st to end	Night	43% 4 13% 26% 13%	4280
November	1st to 10th	Night	46% 4 11% 25% 13% 1	2666
	11th to 20th	Night	55% 3 12% 20% 8% 1	2932
	21st to end	Night	63% 3 15% 13% 5% 1	2940
December	1st to 10th	Night	70% 6% 10% 11% 3	4720
	11th to 20th	Night	65% 3 9% 14% 8% 1	5348
	21st to end	Night	72% 3 9% 10% 5%	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	22% 19% 36% 18% 4 1	270
	11th to 20th	Day	24% 19% 38% 14% 4 1	318
	21st to end	Day	29% 12% 35% 20% 2 1	330
February	1st to 10th	Day	26% 17% 39% 15% 3 1	300
	11th to 20th	Day	27% 19% 39% 11% 3	300
	21st to end	Day	27% 25% 33% 14%	249
March	1st to 10th	Day	24% 14% 36% 19% 6%	457
	11th to 20th	Day	24% 12% 38% 20% 5% 1	500
	21st to end	Day	28% 13% 29% 23% 6% 1	550
April	1st to 10th	Day	22% 17% 31% 23% 5% 2	500
	11th to 20th	Day	28% 13% 27% 17% 11% 4	492
	21st to end	Day	26% 9% 33% 22% 7% 2	500
May	1st to 10th	Day	25% 7% 28% 23% 13% 3	503
	11th to 20th	Day	17% 8% 29% 22% 17% 6%	527
	21st to end	Day	17% 4 26% 30% 16% 7%	573
June	1st to 10th	Day	15% 6% 32% 29% 14% 4	530
	11th to 20th	Day	12% 8% 31% 31% 15% 4	672
	21st to end	Day	14% 7% 30% 32% 13% 4	730
July	1st to 10th	Day	10% 6% 22% 30% 23% 9%	721
	11th to 20th	Day	13% 3 26% 26% 21% 11%	538
	21st to end	Day	10% 2 23% 34% 24% 8%	576
August	1st to 10th	Day	10% 4 19% 30% 24% 14%	526
	11th to 20th	Day	13% 3 18% 29% 20% 16%	519
	21st to end	Day	13% 5% 19% 28% 24% 11%	583
September	1st to 10th	Day	14% 6% 22% 24% 20% 14%	530
	11th to 20th	Day	9% 3 16% 26% 31% 15%	530
	21st to end	Day	19% 8% 23% 27% 14% 9%	530
October	1st to 10th	Day	19% 8% 23% 24% 21% 5%	530
	11th to 20th	Day	21% 13% 32% 23% 9% 2	530
	21st to end	Day	27% 12% 32% 22% 6% 1	563
November	1st to 10th	Day	22% 22% 31% 17% 7% 2	330
	11th to 20th	Day	26% 18% 31% 16% 7% 3	223
	21st to end	Day	26% 17% 39% 15% 3	220
December	1st to 10th	Day	29% 19% 32% 15% 5% 1	220
	11th to 20th	Day	29% 23% 30% 15% 2	220
	21st to end	Day	32% 17% 36% 11% 3	242
January	1st to 10th	Night	23% 16% 36% 19% 4 2	840
	11th to 20th	Night	28% 15% 32% 21% 4	825
	21st to end	Night	20% 12% 35% 27% 7%	880
February	1st to 10th	Night	23% 15% 35% 24% 2	800
	11th to 20th	Night	23% 14% 34% 23% 5%	783
	21st to end	Night	23% 16% 34% 24% 3	660
March	1st to 10th	Night	20% 13% 35% 25% 7%	800
	11th to 20th	Night	19% 14% 38% 22% 6% 1	800
	21st to end	Night	23% 10% 32% 25% 10% 1	880
April	1st to 10th	Night	23% 13% 30% 30% 5%	800
	11th to 20th	Night	22% 10% 31% 26% 9% 1	648
	21st to end	Night	19% 8% 32% 33% 8% 1	600
May	1st to 10th	Night	20% 5% 29% 31% 14% 1	600
	11th to 20th	Night	17% 4 26% 37% 15% 1	550
	21st to end	Night	12% 4 26% 40% 17% 1	433
June	1st to 10th	Night	16% 3 27% 42% 12% 1	400
	11th to 20th	Night	11% 3 30% 44% 13% 1	400
	21st to end	Night	13% 4 24% 44% 16% 1	400
July	1st to 10th	Night	6% 1 21% 47% 22% 3	390
	11th to 20th	Night	9% 1 21% 40% 25% 3	524
	21st to end	Night	11% 1 15% 47% 23% 3	657
August	1st to 10th	Night	10% 1 14% 42% 30% 3	597
	11th to 20th	Night	11% 1 12% 41% 29% 5%	594
	21st to end	Night	9% 2 21% 39% 26% 3	688
September	1st to 10th	Night	13% 3 22% 33% 24% 5%	800
	11th to 20th	Night	11% 3 16% 37% 29% 5%	800
	21st to end	Night	20% 5% 19% 33% 19% 5%	800
October	1st to 10th	Night	18% 5% 23% 31% 20% 2	800
	11th to 20th	Night	23% 9% 30% 27% 10% 1	800
	21st to end	Night	25% 9% 32% 28% 5%	880
November	1st to 10th	Night	20% 12% 26% 31% 10% 1	820
	11th to 20th	Night	22% 14% 33% 22% 8% 1	840
	21st to end	Night	28% 11% 31% 24% 6%	840
December	1st to 10th	Night	28% 15% 32% 20% 5%	840
	11th to 20th	Night	24% 17% 36% 19% 4	840
	21st to end	Night	29% 14% 33% 20% 3	924

Page generated at 2026-01-14 01:14:32. Version ac07

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