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 2024-11-25.

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% 10% 4 9% 5% 5% 5% 4 6% 7% 30%	102120
	Night	14% 11% 4 9% 5% 5% 4 4 5% 7% 32%	97316
Transparency	Day	51% 4 11% 21% 11% 1	105725
	Night	51% 3 11% 22% 12% 1	101801
Seeing	Day	19% 9% 28% 24% 13% 6%	15006
	Night	20% 9% 28% 30% 12% 2	24057

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	15% 18% 9% 12% 6% 5% 4 4 4 4 19%	2652
	11th to 20th	Day	12% 20% 9% 20% 7% 4 4 4 6% 5% 9%	2840
	21st to end	Day	22% 21% 7% 13% 7% 5% 6% 3 4 4 10%	3124
February	1st to 10th	Day	14% 18% 5% 13% 9% 7% 6% 3 4 5% 16%	1710
	11th to 20th	Day	12% 16% 7% 13% 8% 5% 7% 3 4 5% 19%	1663
	21st to end	Day	16% 15% 5% 11% 6% 6% 5% 3 4 6% 22%	1544
March	1st to 10th	Day	19% 15% 5% 10% 5% 5% 4 3 4 5% 25%	3369
	11th to 20th	Day	12% 14% 6% 10% 6% 5% 4 4 5% 7% 28%	3480
	21st to end	Day	16% 11% 4 10% 5% 5% 4 3 5% 5% 31%	3815
April	1st to 10th	Day	16% 14% 4 8% 5% 5% 5% 3 5% 7% 28%	2175
	11th to 20th	Day	18% 10% 3 7% 5% 4 4 3 6% 7% 33%	2405
	21st to end	Day	20% 11% 3 8% 5% 4 4 2 5% 6% 32%	2470
May	1st to 10th	Day	18% 8% 3 7% 5% 4 5% 4 6% 8% 33%	4108
	11th to 20th	Day	15% 9% 3 8% 4 5% 5% 4 7% 9% 30%	4144
	21st to end	Day	12% 6% 2 6% 4 3 5% 4 5% 8% 45%	4837
June	1st to 10th	Day	13% 6% 3 6% 5% 5% 5% 5% 7% 8% 37%	2660
	11th to 20th	Day	10% 6% 2 7% 5% 5% 6% 5% 7% 10% 38%	2795
	21st to end	Day	13% 6% 2 6% 5% 5% 5% 5% 6% 10% 38%	2850
July	1st to 10th	Day	10% 5% 2 7% 5% 5% 6% 5% 7% 10% 38%	4760
	11th to 20th	Day	10% 5% 2 6% 5% 5% 5% 5% 7% 10% 40%	4214
	21st to end	Day	8% 5% 2 7% 5% 5% 5% 5% 7% 9% 40%	4466
August	1st to 10th	Day	15% 7% 2 6% 4 5% 5% 4 7% 9% 35%	4104
	11th to 20th	Day	10% 7% 3 7% 6% 5% 6% 5% 7% 10% 34%	4044
	21st to end	Day	8% 6% 3 7% 5% 5% 6% 4 7% 9% 39%	4446
September	1st to 10th	Day	12% 7% 2 7% 5% 5% 5% 4 7% 8% 39%	2253
	11th to 20th	Day	11% 6% 2 6% 4 4 5% 4 6% 8% 44%	2090
	21st to end	Day	15% 7% 3 8% 4 5% 5% 4 7% 8% 34%	2090
October	1st to 10th	Day	16% 9% 2 8% 5% 4 4 3 6% 6% 35%	1924
	11th to 20th	Day	21% 9% 3 9% 5% 4 4 4 6% 6% 29%	1900
	21st to end	Day	22% 13% 3 9% 6% 4 5% 4 6% 7% 22%	2071
November	1st to 10th	Day	13% 11% 3 9% 6% 5% 4 4 6% 7% 31%	1762
	11th to 20th	Day	15% 15% 4 9% 6% 4 5% 4 7% 9% 23%	1605
	21st to end	Day	19% 17% 7% 11% 6% 4 5% 4 5% 6% 17%	1552
December	1st to 10th	Day	15% 19% 7% 12% 6% 5% 5% 4 5% 5% 16%	1520
	11th to 20th	Day	17% 18% 7% 13% 6% 6% 5% 3 5% 5% 15%	1906
	21st to end	Day	28% 20% 8% 13% 6% 4 3 2 4 4 8%	2772
January	1st to 10th	Night	17% 15% 7% 14% 6% 6% 5% 4 5% 6% 15%	4292
	11th to 20th	Night	14% 16% 8% 15% 8% 8% 6% 5% 5% 5% 11%	4120
	21st to end	Night	21% 15% 9% 14% 6% 5% 4 3 3 4 15%	4532
February	1st to 10th	Night	14% 17% 6% 12% 8% 6% 4 4 4 6% 20%	2470
	11th to 20th	Night	13% 13% 6% 11% 7% 7% 5% 3 5% 7% 23%	2403
	21st to end	Night	16% 13% 4 12% 6% 5% 5% 5% 5% 6% 23%	1908
March	1st to 10th	Night	15% 10% 4 9% 5% 5% 4 3 5% 6% 33%	3469
	11th to 20th	Night	11% 9% 4 9% 5% 5% 4 4 6% 8% 34%	3479
	21st to end	Night	16% 10% 3 8% 4 4 4 3 5% 5% 39%	3817
April	1st to 10th	Night	18% 10% 3 8% 5% 4 4 3 5% 7% 32%	2004
	11th to 20th	Night	17% 8% 4 8% 5% 4 4 3 5% 7% 35%	1739
	21st to end	Night	14% 9% 3 8% 5% 5% 4 4 7% 8% 33%	1710
May	1st to 10th	Night	18% 8% 3 6% 4 4 3 3 5% 8% 39%	2833
	11th to 20th	Night	11% 9% 4 8% 5% 5% 5% 4 6% 8% 36%	2734
	21st to end	Night	10% 5% 2 5% 3 4 3 4 6% 8% 51%	2738
June	1st to 10th	Night	11% 6% 2 5% 5% 4 5% 3 8% 7% 44%	1520
	11th to 20th	Night	9% 5% 2 7% 4 5% 5% 3 8% 10% 42%	1378
	21st to end	Night	10% 5% 2 6% 4 4 4 5% 5% 8% 46%	1330
July	1st to 10th	Night	6% 4 2 5% 4 3 4 3 6% 11% 52%	2210
	11th to 20th	Night	8% 5% 2 5% 3 3 4 3 6% 8% 52%	2711
	21st to end	Night	5% 6% 2 6% 4 5% 5% 4 6% 9% 48%	3087
August	1st to 10th	Night	11% 6% 2 7% 3 4 5% 4 6% 7% 46%	2825
	11th to 20th	Night	10% 7% 2 5% 4 4 4 3 6% 8% 46%	2785
	21st to end	Night	7% 5% 2 6% 5% 4 5% 4 6% 9% 47%	3176
September	1st to 10th	Night	10% 6% 2 7% 5% 4 3 3 5% 6% 48%	1924
	11th to 20th	Night	10% 4 2 5% 3 3 4 4 4 7% 54%	2090
	21st to end	Night	16% 8% 2 7% 5% 4 4 3 5% 7% 40%	2090
October	1st to 10th	Night	15% 8% 3 6% 4 4 4 4 5% 7% 41%	2256
	11th to 20th	Night	18% 9% 3 8% 6% 4 4 3 5% 7% 34%	2280
	21st to end	Night	21% 9% 3 8% 5% 4 5% 3 6% 6% 29%	2523
November	1st to 10th	Night	14% 9% 3 7% 5% 5% 5% 4 6% 7% 35%	2536
	11th to 20th	Night	16% 13% 3 9% 5% 5% 5% 4 6% 7% 26%	2792
	21st to end	Night	19% 14% 6% 9% 6% 5% 4 4 5% 7% 22%	2723
December	1st to 10th	Night	17% 17% 7% 12% 7% 5% 4 4 5% 5% 17%	2660
	11th to 20th	Night	13% 20% 6% 12% 6% 4 4 3 5% 6% 19%	3288
	21st to end	Night	26% 21% 8% 11% 6% 5% 3 3 4 4 11%	4884

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	70% 2 9% 13% 6%	2653
	11th to 20th	Day	78% 2 8% 8% 4	2840
	21st to end	Day	81% 2 6% 7% 3 1	3124
February	1st to 10th	Day	72% 1 8% 13% 4 1	1710
	11th to 20th	Day	68% 3 8% 14% 8%	1672
	21st to end	Day	64% 2 11% 14% 7% 1	1544
March	1st to 10th	Day	63% 2 8% 21% 5% 1	3372
	11th to 20th	Day	57% 2 12% 20% 7% 1	3480
	21st to end	Day	56% 2 9% 19% 12% 2	3815
April	1st to 10th	Day	57% 3 10% 19% 11%	2175
	11th to 20th	Day	52% 2 10% 21% 13% 1	2405
	21st to end	Day	54% 2 10% 20% 12% 2	2470
May	1st to 10th	Day	51% 2 10% 23% 12% 3	4120
	11th to 20th	Day	51% 2 15% 23% 7% 1	4148
	21st to end	Day	39% 2 12% 21% 21% 4	4837
June	1st to 10th	Day	43% 3 12% 26% 14% 2	2660
	11th to 20th	Day	41% 4 12% 24% 17% 2	2795
	21st to end	Day	41% 5% 12% 26% 16%	2850
July	1st to 10th	Day	39% 6% 13% 26% 14% 3	4686
	11th to 20th	Day	36% 5% 13% 33% 13% 1	4141
	21st to end	Day	38% 7% 12% 23% 19% 1	4324
August	1st to 10th	Day	44% 5% 13% 24% 13% 1	4091
	11th to 20th	Day	42% 6% 16% 26% 9% 1	4083
	21st to end	Day	38% 7% 12% 30% 12% 1	4446
September	1st to 10th	Day	42% 3 13% 27% 13% 1	2253
	11th to 20th	Day	38% 3 12% 31% 16%	2090
	21st to end	Day	48% 4 12% 26% 10% 1	2090
October	1st to 10th	Day	40% 5% 14% 23% 18% 1	3197
	11th to 20th	Day	41% 3 13% 23% 19%	3140
	21st to end	Day	51% 5% 16% 22% 7%	3397
November	1st to 10th	Day	52% 4 10% 24% 8% 1	1762
	11th to 20th	Day	57% 4 14% 15% 9% 1	1605
	21st to end	Day	68% 2 11% 14% 4	1552
December	1st to 10th	Day	70% 3 11% 11% 5%	1520
	11th to 20th	Day	73% 2 9% 11% 4	1906
	21st to end	Day	83% 1 7% 8% 1	2772
January	1st to 10th	Night	70% 2 11% 12% 5%	4292
	11th to 20th	Night	76% 2 8% 11% 3	4120
	21st to end	Night	75% 1 7% 12% 3 1	4532
February	1st to 10th	Night	67% 2 8% 17% 6%	2470
	11th to 20th	Night	61% 4 10% 17% 8%	2405
	21st to end	Night	63% 2 9% 18% 7%	1908
March	1st to 10th	Night	54% 1 12% 25% 7% 1	3479
	11th to 20th	Night	47% 4 14% 22% 12% 1	3480
	21st to end	Night	49% 2 8% 25% 15% 2	3817
April	1st to 10th	Night	53% 2 8% 21% 15% 1	2004
	11th to 20th	Night	50% 3 8% 20% 17% 2	1739
	21st to end	Night	49% 2 9% 21% 15% 3	1710
May	1st to 10th	Night	46% 1 11% 21% 16% 4	2840
	11th to 20th	Night	47% 2 13% 26% 9% 2	2735
	21st to end	Night	33% 2 13% 25% 23% 4	2739
June	1st to 10th	Night	38% 2 12% 28% 17% 3	1520
	11th to 20th	Night	37% 2 14% 27% 18% 2	1378
	21st to end	Night	37% 4 14% 25% 20% 1	1330
July	1st to 10th	Night	28% 4 13% 29% 20% 6%	2175
	11th to 20th	Night	30% 4 13% 32% 19% 2	2662
	21st to end	Night	32% 7% 14% 25% 18% 3	2988
August	1st to 10th	Night	37% 5% 12% 27% 18% 1	2814
	11th to 20th	Night	36% 5% 16% 28% 13% 1	2812
	21st to end	Night	32% 5% 13% 32% 17% 1	3176
September	1st to 10th	Night	38% 3 12% 28% 17% 2	1924
	11th to 20th	Night	31% 3 11% 35% 19% 1	2090
	21st to end	Night	45% 3 13% 27% 12%	2090
October	1st to 10th	Night	32% 4 9% 30% 24% 1	3763
	11th to 20th	Night	43% 3 13% 23% 16% 1	3779
	21st to end	Night	43% 4 13% 27% 13%	4147
November	1st to 10th	Night	46% 4 11% 25% 13% 1	2536
	11th to 20th	Night	56% 3 12% 20% 8% 1	2792
	21st to end	Night	63% 3 15% 14% 5% 1	2723
December	1st to 10th	Night	70% 3 9% 14% 4	2660
	11th to 20th	Night	66% 2 12% 15% 4 1	3288
	21st to end	Night	79% 1 10% 8% 2	4884

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	24% 17% 33% 20% 5% 1	220
	11th to 20th	Day	23% 15% 40% 16% 4 1	270
	21st to end	Day	30% 10% 35% 22% 3 1	297
February	1st to 10th	Day	27% 15% 40% 15% 3 1	270
	11th to 20th	Day	26% 18% 40% 12% 3	270
	21st to end	Day	28% 27% 32% 14%	225
March	1st to 10th	Day	25% 13% 36% 20% 6%	419
	11th to 20th	Day	23% 12% 38% 20% 5% 2	460
	21st to end	Day	28% 12% 29% 23% 7% 1	506
April	1st to 10th	Day	20% 16% 32% 24% 6% 2	460
	11th to 20th	Day	30% 12% 27% 17% 11% 4	452
	21st to end	Day	27% 9% 32% 22% 7% 3	460
May	1st to 10th	Day	25% 7% 27% 25% 14% 4	463
	11th to 20th	Day	17% 8% 28% 23% 18% 6%	487
	21st to end	Day	15% 4 25% 32% 17% 8%	529
June	1st to 10th	Day	15% 6% 31% 29% 14% 4	490
	11th to 20th	Day	12% 7% 30% 31% 16% 4	625
	21st to end	Day	15% 6% 30% 31% 13% 4	680
July	1st to 10th	Day	10% 5% 22% 30% 24% 9%	671
	11th to 20th	Day	13% 3 25% 26% 21% 11%	497
	21st to end	Day	10% 2 23% 34% 23% 8%	532
August	1st to 10th	Day	11% 4 20% 28% 23% 14%	486
	11th to 20th	Day	13% 3 17% 29% 20% 16%	479
	21st to end	Day	13% 5% 19% 27% 24% 12%	539
September	1st to 10th	Day	14% 6% 21% 25% 20% 13%	490
	11th to 20th	Day	9% 3 17% 27% 29% 15%	490
	21st to end	Day	19% 8% 24% 27% 13% 9%	490
October	1st to 10th	Day	20% 9% 23% 23% 20% 5%	490
	11th to 20th	Day	22% 13% 30% 23% 9% 2	490
	21st to end	Day	28% 11% 32% 22% 6% 1	520
November	1st to 10th	Day	21% 21% 31% 17% 7% 2	300
	11th to 20th	Day	26% 16% 33% 16% 6% 3	203
	21st to end	Day	27% 15% 39% 16% 3	188
December	1st to 10th	Day	31% 17% 34% 13% 4 1	180
	11th to 20th	Day	29% 20% 31% 18% 2 1	180
	21st to end	Day	32% 17% 37% 12% 3	198
January	1st to 10th	Night	24% 15% 36% 19% 5% 2	760
	11th to 20th	Night	29% 13% 32% 22% 4	760
	21st to end	Night	20% 10% 34% 28% 7%	836
February	1st to 10th	Night	23% 15% 35% 24% 3	760
	11th to 20th	Night	23% 14% 34% 24% 6%	743
	21st to end	Night	24% 15% 34% 24% 3	628
March	1st to 10th	Night	20% 12% 35% 26% 7%	760
	11th to 20th	Night	19% 13% 38% 22% 6% 1	760
	21st to end	Night	22% 10% 32% 26% 10% 1	836
April	1st to 10th	Night	23% 12% 30% 30% 5%	760
	11th to 20th	Night	22% 9% 31% 26% 10% 1	615
	21st to end	Night	20% 7% 31% 34% 8%	570
May	1st to 10th	Night	20% 5% 29% 31% 14% 1	570
	11th to 20th	Night	17% 3 26% 38% 15% 1	522
	21st to end	Night	11% 3 26% 41% 18% 1	411
June	1st to 10th	Night	16% 3 27% 41% 13% 1	380
	11th to 20th	Night	11% 3 29% 44% 13% 1	380
	21st to end	Night	13% 4 23% 44% 15% 1	380
July	1st to 10th	Night	6% 1 21% 47% 22% 3	370
	11th to 20th	Night	9% 1 20% 40% 26% 3	497
	21st to end	Night	10% 1 15% 47% 23% 3	624
August	1st to 10th	Night	10% 1 15% 42% 30% 3	567
	11th to 20th	Night	11% 1 13% 41% 29% 6%	564
	21st to end	Night	10% 1 21% 38% 26% 4	653
September	1st to 10th	Night	13% 3 22% 33% 23% 5%	760
	11th to 20th	Night	12% 3 16% 36% 28% 5%	760
	21st to end	Night	20% 4 20% 33% 18% 5%	760
October	1st to 10th	Night	19% 5% 24% 31% 19% 2	760
	11th to 20th	Night	23% 9% 29% 27% 10% 1	760
	21st to end	Night	26% 9% 31% 28% 6%	836
November	1st to 10th	Night	21% 11% 26% 31% 10% 1	780
	11th to 20th	Night	23% 14% 33% 21% 8% 1	800
	21st to end	Night	28% 10% 31% 25% 7%	779
December	1st to 10th	Night	29% 14% 32% 19% 5%	760
	11th to 20th	Night	24% 16% 35% 19% 5%	760
	21st to end	Night	30% 13% 33% 20% 3	836

Page generated at 2024-11-22 08:02:24. Version ac07

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