Emerald Lane Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Emerald Lane Observatory clear sky chart from 2005-11-06 to 2024-11-10.

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	12% 7% 2 6% 5% 5% 5% 4 6% 8% 41%	101345
	Night	12% 7% 2 6% 4 4 4 4 5% 7% 44%	97754
Transparency	Day	40% 5% 11% 22% 18% 5%	105124
	Night	38% 4 10% 22% 20% 6%	102101
Seeing	Day	15% 10% 22% 24% 19% 10%	14839
	Night	15% 9% 23% 29% 21% 4	24484

By Month

Percentage Cloud Cover SE (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% 12% 3 8% 4 3 4 4 5% 6% 34%	2836
	11th to 20th	Day	18% 9% 5% 8% 4 3 2 3 4 4 41%	2913
	21st to end	Day	21% 12% 4 5% 4 3 3 3 4 6% 38%	3476
February	1st to 10th	Day	17% 11% 3 7% 4 3 4 3 5% 5% 39%	1900
	11th to 20th	Day	19% 9% 4 7% 6% 4 3 3 3 5% 38%	1848
	21st to end	Day	19% 9% 3 7% 5% 3 4 4 4 5% 37%	1570
March	1st to 10th	Day	21% 11% 3 6% 5% 4 4 4 5% 5% 31%	3120
	11th to 20th	Day	13% 8% 2 6% 4 3 4 3 5% 7% 45%	3315
	21st to end	Day	13% 8% 2 6% 6% 6% 5% 4 6% 7% 38%	4051
April	1st to 10th	Day	13% 6% 2 6% 4 3 3 4 5% 7% 45%	2280
	11th to 20th	Day	12% 7% 2 6% 4 4 4 4 4 7% 45%	2254
	21st to end	Day	9% 6% 2 5% 5% 5% 4 4 7% 9% 44%	2280
May	1st to 10th	Day	11% 6% 2 7% 5% 5% 5% 4 6% 9% 41%	4048
	11th to 20th	Day	15% 8% 3 7% 5% 4 4 4 7% 8% 37%	4081
	21st to end	Day	10% 6% 2 7% 5% 4 5% 4 6% 9% 42%	4476
June	1st to 10th	Day	8% 6% 2 8% 5% 6% 7% 5% 6% 10% 36%	2470
	11th to 20th	Day	4 3 2 5% 5% 5% 6% 6% 8% 11% 45%	2470
	21st to end	Day	6% 4 2 7% 6% 5% 6% 5% 7% 11% 41%	2656
July	1st to 10th	Day	6% 6% 2 8% 6% 8% 8% 6% 9% 11% 30%	4381
	11th to 20th	Day	7% 5% 2 7% 7% 7% 8% 6% 9% 13% 29%	4120
	21st to end	Day	13% 9% 4 10% 7% 7% 6% 5% 7% 9% 22%	4418
August	1st to 10th	Day	3 3 1 5% 4 5% 5% 5% 8% 11% 51%	3785
	11th to 20th	Day	5% 4 2 6% 4 6% 6% 5% 8% 11% 43%	3729
	21st to end	Day	7% 4 2 5% 5% 5% 5% 4 6% 7% 51%	4180
September	1st to 10th	Day	10% 5% 2 6% 5% 5% 5% 5% 7% 9% 41%	2250
	11th to 20th	Day	11% 6% 2 7% 5% 4 5% 4 6% 8% 42%	2090
	21st to end	Day	12% 4 2 5% 3 4 4 4 5% 8% 50%	2090
October	1st to 10th	Day	9% 4 2 6% 4 4 3 3 5% 5% 56%	2090
	11th to 20th	Day	9% 4 1 4 4 3 4 2 5% 7% 55%	2071
	21st to end	Day	13% 5% 2 5% 3 3 3 3 4 6% 52%	1937
November	1st to 10th	Day	12% 7% 2 4 3 4 4 3 3 6% 53%	1753
	11th to 20th	Day	11% 7% 2 5% 3 4 4 3 4 6% 51%	1710
	21st to end	Day	14% 8% 2 5% 5% 4 5% 3 5% 6% 44%	1710
December	1st to 10th	Day	19% 8% 3 7% 5% 5% 4 4 6% 4 36%	1710
	11th to 20th	Day	15% 8% 3 7% 4 5% 5% 4 3 5% 40%	2153
	21st to end	Day	14% 10% 4 9% 5% 5% 4 3 6% 7% 33%	3124
January	1st to 10th	Night	17% 10% 3 7% 3 4 4 3 4 4 40%	4109
	11th to 20th	Night	18% 8% 4 6% 4 3 3 3 5% 5% 41%	4042
	21st to end	Night	19% 14% 3 7% 3 3 3 2 4 5% 37%	4180
February	1st to 10th	Night	18% 9% 2 7% 4 3 4 3 5% 5% 40%	2280
	11th to 20th	Night	20% 10% 2 6% 4 3 4 3 4 4 41%	2218
	21st to end	Night	20% 7% 3 7% 5% 4 4 3 4 5% 37%	1884
March	1st to 10th	Night	23% 10% 3 6% 4 4 3 2 4 6% 34%	3733
	11th to 20th	Night	12% 6% 2 5% 4 4 4 4 6% 8% 47%	3644
	21st to end	Night	15% 8% 3 8% 5% 4 4 4 5% 5% 41%	3608
April	1st to 10th	Night	11% 5% 1 5% 5% 4 4 4 6% 7% 46%	1900
	11th to 20th	Night	13% 6% 2 5% 4 4 3 3 6% 7% 48%	1875
	21st to end	Night	11% 6% 1 5% 4 4 4 3 5% 7% 50%	1900
May	1st to 10th	Night	10% 6% 3 7% 5% 5% 4 4 6% 8% 43%	2845
	11th to 20th	Night	12% 8% 4 8% 5% 4 4 3 6% 8% 39%	2812
	21st to end	Night	6% 5% 2 6% 5% 4 6% 5% 7% 10% 44%	3079
June	1st to 10th	Night	5% 5% 2 8% 7% 5% 5% 4 6% 11% 43%	1710
	11th to 20th	Night	3 2 1 4 5% 4 5% 5% 8% 11% 52%	1702
	21st to end	Night	5% 4 2 5% 5% 4 5% 4 8% 11% 48%	1520
July	1st to 10th	Night	7% 6% 3 8% 6% 6% 6% 6% 7% 10% 36%	2578
	11th to 20th	Night	7% 6% 2 6% 4 5% 6% 5% 8% 12% 37%	2840
	21st to end	Night	10% 9% 4 11% 7% 7% 6% 5% 7% 8% 25%	3118
August	1st to 10th	Night	3 2 1 4 3 4 5% 5% 7% 10% 57%	3144
	11th to 20th	Night	5% 4 1 4 4 4 5% 4 7% 10% 52%	3100
	21st to end	Night	5% 3 2 4 3 4 4 3 5% 7% 58%	3476
September	1st to 10th	Night	7% 4 2 5% 5% 5% 4 4 6% 8% 49%	1909
	11th to 20th	Night	9% 7% 3 7% 4 5% 4 4 6% 9% 43%	2090
	21st to end	Night	8% 5% 2 5% 4 4 4 2 5% 7% 54%	2090
October	1st to 10th	Night	10% 4 1 4 3 3 2 2 4 6% 59%	2090
	11th to 20th	Night	12% 5% 2 6% 3 3 3 3 4 5% 54%	2104
	21st to end	Night	14% 6% 2 4 3 2 3 3 4 5% 54%	2660
November	1st to 10th	Night	12% 5% 2 5% 3 4 4 3 4 5% 53%	2530
	11th to 20th	Night	12% 6% 2 5% 4 3 3 3 5% 5% 53%	2470
	21st to end	Night	14% 7% 2 5% 4 4 4 3 4 6% 46%	2470
December	1st to 10th	Night	17% 10% 3 6% 4 4 4 3 5% 7% 38%	2470
	11th to 20th	Night	15% 7% 3 5% 4 3 4 3 4 6% 46%	3042
	21st to end	Night	15% 10% 4 9% 5% 5% 5% 4 6% 6% 31%	4532

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	50% 3 6% 19% 20% 3	2837
	11th to 20th	Day	48% 2 6% 20% 22% 2	2913
	21st to end	Day	49% 3 6% 20% 18% 2	3476
February	1st to 10th	Day	48% 3 7% 20% 20% 3	1900
	11th to 20th	Day	52% 2 5% 19% 17% 5%	1858
	21st to end	Day	50% 3 7% 14% 19% 6%	1570
March	1st to 10th	Day	54% 3 8% 12% 14% 9%	3120
	11th to 20th	Day	40% 3 8% 24% 19% 6%	3315
	21st to end	Day	45% 3 11% 21% 18% 2	4051
April	1st to 10th	Day	38% 3 11% 25% 17% 6%	2280
	11th to 20th	Day	39% 3 7% 21% 23% 6%	2254
	21st to end	Day	36% 4 9% 29% 19% 3	2280
May	1st to 10th	Day	40% 3 14% 26% 15% 2	4086
	11th to 20th	Day	44% 4 13% 27% 12%	4085
	21st to end	Day	39% 4 12% 26% 18% 1	4489
June	1st to 10th	Day	42% 6% 14% 21% 16% 1	2470
	11th to 20th	Day	30% 6% 16% 28% 18% 2	2470
	21st to end	Day	36% 8% 16% 21% 15% 4	2656
July	1st to 10th	Day	41% 10% 20% 22% 6% 1	4313
	11th to 20th	Day	40% 11% 21% 22% 5% 2	4051
	21st to end	Day	57% 7% 13% 17% 6%	4277
August	1st to 10th	Day	24% 6% 14% 37% 18% 1	3773
	11th to 20th	Day	32% 6% 17% 27% 15% 3	3765
	21st to end	Day	31% 6% 13% 21% 24% 4	4179
September	1st to 10th	Day	39% 6% 16% 18% 18% 5%	2250
	11th to 20th	Day	39% 5% 12% 19% 21% 3	2090
	21st to end	Day	33% 4 10% 25% 20% 7%	2090
October	1st to 10th	Day	23% 3 5% 16% 34% 20%	3480
	11th to 20th	Day	21% 2 5% 19% 31% 23%	3427
	21st to end	Day	26% 4 6% 22% 34% 9%	3162
November	1st to 10th	Day	34% 3 7% 20% 27% 8%	1753
	11th to 20th	Day	36% 3 5% 21% 27% 8%	1710
	21st to end	Day	41% 3 5% 20% 24% 6%	1710
December	1st to 10th	Day	51% 3 7% 17% 18% 5%	1710
	11th to 20th	Day	48% 3 5% 21% 19% 4	2150
	21st to end	Day	51% 2 8% 22% 13% 3	3124
January	1st to 10th	Night	48% 2 5% 19% 23% 2	4109
	11th to 20th	Night	46% 3 5% 21% 18% 6%	4042
	21st to end	Night	52% 2 4 19% 19% 3	4180
February	1st to 10th	Night	46% 3 7% 19% 21% 4	2280
	11th to 20th	Night	48% 3 6% 18% 18% 7%	2219
	21st to end	Night	51% 3 5% 16% 18% 7%	1884
March	1st to 10th	Night	53% 2 8% 14% 16% 7%	3733
	11th to 20th	Night	36% 3 9% 21% 21% 9%	3644
	21st to end	Night	47% 2 7% 21% 21% 2	3608
April	1st to 10th	Night	36% 4 11% 24% 21% 5%	1900
	11th to 20th	Night	36% 3 8% 21% 23% 11%	1875
	21st to end	Night	34% 4 10% 28% 20% 4	1900
May	1st to 10th	Night	38% 4 13% 25% 18% 2	2872
	11th to 20th	Night	43% 5% 16% 24% 12% 1	2813
	21st to end	Night	34% 5% 14% 28% 17% 2	3087
June	1st to 10th	Night	37% 6% 14% 23% 18% 3	1710
	11th to 20th	Night	24% 5% 19% 28% 21% 3	1702
	21st to end	Night	28% 6% 18% 26% 18% 4	1520
July	1st to 10th	Night	40% 8% 22% 21% 6% 2	2537
	11th to 20th	Night	34% 10% 23% 24% 7% 2	2786
	21st to end	Night	54% 8% 15% 16% 7%	3018
August	1st to 10th	Night	20% 6% 14% 38% 21% 1	3132
	11th to 20th	Night	25% 7% 21% 29% 16% 2	3130
	21st to end	Night	25% 5% 15% 24% 27% 5%	3476
September	1st to 10th	Night	32% 6% 18% 21% 18% 5%	1909
	11th to 20th	Night	36% 6% 14% 18% 22% 4	2090
	21st to end	Night	30% 4 9% 23% 24% 9%	2090
October	1st to 10th	Night	20% 3 6% 17% 34% 19%	3480
	11th to 20th	Night	21% 2 3 18% 32% 24%	3487
	21st to end	Night	23% 2 4 27% 28% 16%	4372
November	1st to 10th	Night	33% 4 7% 21% 23% 12%	2530
	11th to 20th	Night	34% 2 7% 18% 28% 11%	2470
	21st to end	Night	39% 3 5% 22% 24% 6%	2470
December	1st to 10th	Night	46% 3 8% 20% 19% 3	2470
	11th to 20th	Night	41% 3 6% 20% 26% 5%	3044
	21st to end	Night	52% 3 7% 19% 16% 2	4532

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% 27% 34% 12% 4	270
	11th to 20th	Day	29% 21% 33% 10% 5% 1	270
	21st to end	Day	22% 26% 33% 15% 3	297
February	1st to 10th	Day	25% 24% 31% 17% 3 1	270
	11th to 20th	Day	34% 17% 35% 11% 1 1	270
	21st to end	Day	36% 21% 32% 8% 2	225
March	1st to 10th	Day	25% 21% 31% 17% 3 2	270
	11th to 20th	Day	22% 19% 33% 19% 6% 1	360
	21st to end	Day	23% 18% 35% 18% 7%	506
April	1st to 10th	Day	20% 18% 30% 22% 9% 2	460
	11th to 20th	Day	18% 16% 31% 24% 11% 1	452
	21st to end	Day	15% 14% 30% 29% 10% 2	460
May	1st to 10th	Day	16% 8% 31% 25% 13% 6%	463
	11th to 20th	Day	13% 6% 23% 29% 20% 9%	487
	21st to end	Day	11% 6% 20% 29% 20% 13%	529
June	1st to 10th	Day	13% 3 16% 30% 23% 14%	490
	11th to 20th	Day	4 3 17% 29% 25% 22%	490
	21st to end	Day	8% 3 17% 29% 29% 15%	676
July	1st to 10th	Day	9% 2 9% 28% 33% 20%	639
	11th to 20th	Day	8% 2 6% 25% 29% 30%	484
	21st to end	Day	8% 1 8% 25% 33% 24%	532
August	1st to 10th	Day	8% 1 10% 26% 33% 23%	486
	11th to 20th	Day	9% 1 10% 30% 34% 15%	479
	21st to end	Day	14% 2 9% 20% 33% 22%	539
September	1st to 10th	Day	9% 2 11% 29% 34% 15%	490
	11th to 20th	Day	12% 3 12% 27% 29% 17%	490
	21st to end	Day	15% 4 14% 28% 29% 9%	490
October	1st to 10th	Day	11% 2 21% 31% 26% 8%	490
	11th to 20th	Day	12% 8% 29% 35% 13% 3	471
	21st to end	Day	21% 12% 21% 32% 12% 2	330
November	1st to 10th	Day	19% 12% 26% 27% 12% 2	297
	11th to 20th	Day	13% 17% 39% 24% 6%	270
	21st to end	Day	17% 19% 32% 22% 8% 2	270
December	1st to 10th	Day	29% 18% 27% 20% 6%	270
	11th to 20th	Day	20% 23% 32% 14% 11%	270
	21st to end	Day	21% 20% 41% 13% 5% 1	297
January	1st to 10th	Night	22% 19% 34% 21% 5%	760
	11th to 20th	Night	23% 18% 30% 22% 7%	760
	21st to end	Night	20% 17% 35% 25% 2	836
February	1st to 10th	Night	22% 15% 33% 25% 5%	760
	11th to 20th	Night	27% 14% 31% 24% 3	743
	21st to end	Night	26% 18% 32% 21% 2	628
March	1st to 10th	Night	20% 17% 29% 27% 6%	760
	11th to 20th	Night	19% 13% 37% 23% 8% 1	760
	21st to end	Night	17% 14% 33% 25% 11%	717
April	1st to 10th	Night	15% 12% 35% 26% 12%	570
	11th to 20th	Night	15% 10% 34% 27% 12% 1	563
	21st to end	Night	14% 9% 31% 29% 16% 1	570
May	1st to 10th	Night	11% 6% 30% 31% 21% 3	570
	11th to 20th	Night	12% 4 22% 34% 23% 4	561
	21st to end	Night	6% 2 18% 36% 32% 6%	617
June	1st to 10th	Night	8% 2 15% 35% 35% 6%	570
	11th to 20th	Night	4 2 11% 33% 41% 9%	570
	21st to end	Night	7% 1 11% 31% 42% 8%	570
July	1st to 10th	Night	8% 2 8% 29% 42% 12%	555
	11th to 20th	Night	7% 1 5% 29% 41% 17%	552
	21st to end	Night	8% 2 7% 29% 41% 13%	624
August	1st to 10th	Night	4 1 2 29% 53% 11%	567
	11th to 20th	Night	9% 1 6% 34% 41% 10%	564
	21st to end	Night	10% 2 6% 29% 42% 10%	627
September	1st to 10th	Night	9% 2 10% 30% 41% 8%	579
	11th to 20th	Night	11% 3 14% 28% 37% 7%	760
	21st to end	Night	11% 3 13% 33% 36% 3	760
October	1st to 10th	Night	11% 4 19% 31% 28% 7%	760
	11th to 20th	Night	14% 6% 25% 34% 18% 2	760
	21st to end	Night	17% 7% 22% 32% 21% 2	836
November	1st to 10th	Night	15% 8% 21% 33% 19% 3	779
	11th to 20th	Night	16% 10% 31% 31% 11% 2	760
	21st to end	Night	19% 11% 28% 30% 11% 1	760
December	1st to 10th	Night	23% 15% 26% 29% 7%	760
	11th to 20th	Night	22% 13% 30% 26% 9%	760
	21st to end	Night	23% 15% 30% 26% 6%	836

Page generated at 2024-11-07 05:55:43. Version ac07

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