Leif Everson Observatory (LEO)
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Leif Everson Observatory (LEO) 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	12% 8% 3 7% 5% 5% 5% 4 6% 8% 38%	143997
	Night	13% 10% 4 8% 5% 4 5% 4 5% 7% 36%	138221
Transparency	Day	42% 6% 13% 25% 12% 1	147484
	Night	46% 5% 13% 23% 12% 1	142811
Seeing	Day	15% 9% 28% 29% 15% 4	18473
	Night	18% 9% 28% 29% 14% 2	28272

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	11% 11% 5% 12% 5% 5% 5% 5% 7% 7% 26%	4691
	11th to 20th	Day	11% 13% 4 11% 6% 6% 6% 4 5% 7% 27%	4710
	21st to end	Day	11% 12% 4 9% 4 5% 6% 4 6% 9% 29%	5156
February	1st to 10th	Day	9% 10% 3 9% 6% 6% 6% 4 7% 8% 30%	1790
	11th to 20th	Day	11% 11% 3 8% 4 5% 5% 5% 7% 7% 34%	2048
	21st to end	Day	11% 13% 5% 9% 6% 5% 5% 4 5% 7% 32%	1730
March	1st to 10th	Day	12% 8% 2 5% 4 4 4 3 5% 7% 46%	4580
	11th to 20th	Day	10% 9% 3 8% 5% 5% 5% 4 6% 8% 35%	4759
	21st to end	Day	23% 11% 4 9% 5% 4 3 3 4 5% 30%	6070
April	1st to 10th	Day	14% 11% 3 8% 6% 5% 5% 4 5% 7% 31%	2520
	11th to 20th	Day	18% 8% 3 7% 5% 4 4 4 6% 6% 35%	2510
	21st to end	Day	15% 9% 3 8% 5% 4 4 4 6% 8% 35%	2730
May	1st to 10th	Day	10% 6% 2 6% 5% 4 6% 4 6% 8% 43%	7674
	11th to 20th	Day	11% 8% 3 7% 5% 5% 5% 4 6% 6% 40%	8222
	21st to end	Day	12% 7% 3 7% 4 4 4 3 5% 7% 46%	9047
June	1st to 10th	Day	11% 6% 2 5% 5% 4 5% 5% 7% 8% 44%	2940
	11th to 20th	Day	12% 6% 2 6% 5% 5% 6% 4 6% 9% 39%	2940
	21st to end	Day	10% 6% 1 7% 4 5% 5% 4 6% 8% 43%	2940
July	1st to 10th	Day	10% 6% 2 6% 4 4 5% 4 7% 11% 40%	8280
	11th to 20th	Day	5% 4 1 4 3 4 4 4 7% 10% 54%	8280
	21st to end	Day	7% 5% 2 6% 4 4 5% 4 6% 9% 48%	8990
August	1st to 10th	Day	8% 6% 2 6% 5% 5% 5% 4 7% 9% 44%	4703
	11th to 20th	Day	11% 5% 2 5% 3 3 4 3 5% 7% 52%	4174
	21st to end	Day	11% 5% 2 7% 4 4 5% 4 5% 7% 46%	4312
September	1st to 10th	Day	12% 5% 2 7% 4 5% 5% 4 6% 7% 44%	2400
	11th to 20th	Day	10% 6% 2 5% 4 4 4 4 6% 8% 46%	2253
	21st to end	Day	13% 7% 2 7% 6% 4 5% 4 6% 8% 38%	2200
October	1st to 10th	Day	14% 7% 3 6% 4 4 3 3 6% 7% 42%	2160
	11th to 20th	Day	20% 10% 4 9% 4 4 5% 3 5% 6% 28%	1901
	21st to end	Day	17% 11% 3 8% 5% 5% 5% 5% 5% 7% 29%	1980
November	1st to 10th	Day	15% 10% 4 6% 4 5% 5% 4 5% 7% 35%	1852
	11th to 20th	Day	12% 15% 4 11% 7% 5% 5% 5% 6% 6% 24%	1890
	21st to end	Day	18% 12% 5% 12% 7% 4 4 3 4 6% 24%	1717
December	1st to 10th	Day	11% 15% 6% 12% 8% 6% 6% 4 6% 6% 21%	2690
	11th to 20th	Day	15% 16% 5% 10% 6% 6% 7% 5% 6% 7% 19%	3088
	21st to end	Day	20% 20% 6% 13% 6% 5% 5% 3 3 4 14%	4070
January	1st to 10th	Night	13% 12% 4 9% 6% 5% 5% 4 5% 5% 31%	8232
	11th to 20th	Night	9% 16% 5% 13% 7% 7% 7% 4 5% 5% 21%	8280
	21st to end	Night	8% 11% 4 11% 6% 6% 5% 4 6% 8% 31%	9058
February	1st to 10th	Night	10% 14% 6% 11% 6% 4 5% 4 5% 6% 31%	2829
	11th to 20th	Night	11% 12% 4 10% 5% 4 5% 3 6% 6% 35%	2458
	21st to end	Night	14% 13% 4 8% 5% 3 4 5% 5% 7% 32%	2076
March	1st to 10th	Night	14% 8% 2 6% 4 4 4 3 5% 6% 44%	5493
	11th to 20th	Night	10% 9% 3 6% 5% 5% 5% 4 7% 9% 37%	5420
	21st to end	Night	20% 10% 3 8% 5% 4 5% 3 5% 6% 32%	5130
April	1st to 10th	Night	17% 11% 3 8% 5% 4 4 3 4 7% 33%	2100
	11th to 20th	Night	19% 9% 3 6% 4 4 3 4 4 5% 38%	2059
	21st to end	Night	17% 9% 4 7% 5% 4 4 3 5% 5% 37%	1890
May	1st to 10th	Night	12% 8% 2 7% 4 4 5% 4 5% 8% 42%	5167
	11th to 20th	Night	8% 7% 3 8% 4 5% 5% 4 7% 8% 40%	4670
	21st to end	Night	15% 7% 3 6% 5% 4 4 3 5% 6% 42%	5139
June	1st to 10th	Night	11% 6% 2 5% 4 5% 5% 4 6% 8% 43%	1680
	11th to 20th	Night	13% 7% 2 7% 4 4 5% 4 6% 8% 39%	1680
	21st to end	Night	10% 6% 3 7% 5% 4 5% 3 5% 6% 46%	1680
July	1st to 10th	Night	12% 6% 3 7% 4 4 5% 4 6% 8% 41%	4708
	11th to 20th	Night	6% 3 2 4 3 3 3 4 6% 11% 57%	4707
	21st to end	Night	5% 4 2 6% 5% 4 4 4 6% 8% 51%	5117
August	1st to 10th	Night	10% 6% 2 7% 5% 4 5% 3 5% 8% 46%	2677
	11th to 20th	Night	12% 4 1 5% 3 4 4 3 5% 8% 51%	2960
	21st to end	Night	10% 6% 2 6% 4 4 4 3 5% 7% 48%	3586
September	1st to 10th	Night	9% 5% 2 7% 4 4 4 3 5% 7% 51%	2000
	11th to 20th	Night	10% 6% 3 6% 3 3 5% 3 5% 6% 50%	2126
	21st to end	Night	12% 8% 4 7% 5% 4 5% 3 5% 6% 42%	2200
October	1st to 10th	Night	15% 7% 2 6% 4 4 4 3 5% 6% 44%	2237
	11th to 20th	Night	18% 10% 3 6% 5% 4 4 3 5% 7% 34%	2498
	21st to end	Night	20% 11% 3 6% 5% 4 5% 3 6% 6% 31%	2860
November	1st to 10th	Night	14% 9% 3 8% 5% 4 4 3 5% 6% 38%	2666
	11th to 20th	Night	15% 12% 4 11% 6% 5% 4 3 5% 6% 29%	2730
	21st to end	Night	15% 13% 5% 11% 6% 4 5% 3 5% 6% 26%	2899
December	1st to 10th	Night	15% 12% 5% 9% 6% 5% 5% 5% 6% 7% 27%	4720
	11th to 20th	Night	14% 16% 6% 12% 7% 6% 6% 3 5% 5% 20%	5339
	21st to end	Night	22% 18% 6% 10% 5% 4 5% 4 4 5% 18%	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	53% 6% 17% 18% 6%	4692
	11th to 20th	Day	56% 5% 11% 20% 8% 1	4710
	21st to end	Day	51% 4 13% 18% 13%	5156
February	1st to 10th	Day	48% 6% 16% 23% 6%	1790
	11th to 20th	Day	47% 5% 15% 22% 11% 1	2058
	21st to end	Day	52% 5% 12% 20% 9% 1	1730
March	1st to 10th	Day	37% 5% 17% 20% 18% 4	4580
	11th to 20th	Day	45% 6% 15% 23% 10% 1	4759
	21st to end	Day	57% 4 10% 18% 10%	6072
April	1st to 10th	Day	51% 6% 11% 22% 10% 1	2520
	11th to 20th	Day	47% 5% 11% 23% 12% 2	2510
	21st to end	Day	46% 5% 12% 20% 14% 2	2730
May	1st to 10th	Day	35% 6% 12% 30% 14% 2	7709
	11th to 20th	Day	41% 6% 11% 27% 14% 1	8226
	21st to end	Day	38% 4 9% 25% 19% 4	9061
June	1st to 10th	Day	35% 6% 14% 29% 14% 2	2940
	11th to 20th	Day	39% 6% 13% 25% 15% 1	2940
	21st to end	Day	37% 6% 17% 25% 13% 1	2940
July	1st to 10th	Day	36% 8% 16% 28% 10% 2	8211
	11th to 20th	Day	24% 6% 13% 38% 18% 1	8205
	21st to end	Day	31% 7% 14% 29% 18% 1	8794
August	1st to 10th	Day	34% 7% 16% 29% 13% 1	4688
	11th to 20th	Day	32% 6% 17% 33% 12% 1	4213
	21st to end	Day	35% 8% 16% 26% 14% 1	4311
September	1st to 10th	Day	39% 6% 15% 28% 12% 1	2400
	11th to 20th	Day	36% 6% 18% 30% 10%	2253
	21st to end	Day	42% 6% 15% 28% 10%	2200
October	1st to 10th	Day	27% 4 12% 36% 20% 1	3524
	11th to 20th	Day	50% 6% 10% 23% 11%	3078
	21st to end	Day	47% 5% 16% 25% 7%	3180
November	1st to 10th	Day	48% 5% 13% 21% 12% 1	1852
	11th to 20th	Day	58% 5% 15% 16% 7%	1890
	21st to end	Day	61% 5% 15% 15% 3	1717
December	1st to 10th	Day	62% 7% 15% 14% 3	2690
	11th to 20th	Day	62% 7% 13% 12% 6%	3085
	21st to end	Day	72% 6% 7% 12% 3	4070
January	1st to 10th	Night	52% 5% 12% 25% 5%	8233
	11th to 20th	Night	63% 4 11% 11% 9% 1	8280
	21st to end	Night	50% 5% 13% 21% 11%	9058
February	1st to 10th	Night	53% 4 12% 21% 9% 1	2829
	11th to 20th	Night	49% 3 12% 23% 10% 1	2459
	21st to end	Night	51% 5% 14% 21% 9% 1	2076
March	1st to 10th	Night	40% 4 17% 25% 13% 1	5493
	11th to 20th	Night	42% 5% 18% 21% 12% 2	5420
	21st to end	Night	53% 5% 10% 20% 11% 1	5130
April	1st to 10th	Night	52% 4 8% 20% 14% 1	2100
	11th to 20th	Night	48% 4 8% 22% 15% 3	2059
	21st to end	Night	49% 4 11% 21% 13% 2	1890
May	1st to 10th	Night	40% 5% 12% 26% 15% 2	5194
	11th to 20th	Night	39% 6% 11% 26% 16% 2	4671
	21st to end	Night	42% 4 9% 23% 14% 7%	5149
June	1st to 10th	Night	37% 6% 10% 29% 16% 2	1680
	11th to 20th	Night	41% 6% 11% 24% 17% 2	1680
	21st to end	Night	38% 6% 13% 28% 13% 2	1680
July	1st to 10th	Night	40% 6% 13% 25% 12% 4	4670
	11th to 20th	Night	22% 5% 13% 38% 19% 2	4662
	21st to end	Night	29% 6% 14% 28% 22% 1	5002
August	1st to 10th	Night	37% 6% 13% 28% 16% 1	2668
	11th to 20th	Night	32% 5% 15% 32% 16% 1	2987
	21st to end	Night	36% 6% 13% 25% 19% 2	3586
September	1st to 10th	Night	33% 5% 13% 31% 17% 2	2000
	11th to 20th	Night	34% 4 15% 32% 13% 1	2126
	21st to end	Night	42% 4 14% 26% 13% 1	2200
October	1st to 10th	Night	34% 4 10% 36% 15% 1	3653
	11th to 20th	Night	41% 5% 15% 24% 14% 1	4060
	21st to end	Night	48% 4 13% 23% 12%	4610
November	1st to 10th	Night	46% 4 13% 24% 11% 1	2666
	11th to 20th	Night	55% 5% 13% 19% 7% 1	2730
	21st to end	Night	58% 5% 15% 19% 3 1	2899
December	1st to 10th	Night	53% 8% 19% 17% 3	4720
	11th to 20th	Night	64% 5% 13% 13% 5%	5341
	21st to end	Night	66% 7% 10% 12% 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	16% 10% 36% 30% 7% 1	330
	11th to 20th	Day	20% 14% 37% 21% 7% 1	330
	21st to end	Day	20% 10% 34% 30% 6%	363
February	1st to 10th	Day	15% 16% 40% 22% 6% 1	330
	11th to 20th	Day	15% 21% 36% 23% 5% 1	330
	21st to end	Day	18% 17% 40% 21% 3 1	273
March	1st to 10th	Day	16% 16% 42% 20% 5%	330
	11th to 20th	Day	20% 14% 31% 25% 8% 2	391
	21st to end	Day	25% 11% 30% 26% 7% 1	594
April	1st to 10th	Day	20% 13% 32% 27% 6% 1	540
	11th to 20th	Day	22% 14% 28% 26% 9% 2	532
	21st to end	Day	19% 10% 27% 29% 14% 2	540
May	1st to 10th	Day	17% 7% 35% 28% 10% 3	563
	11th to 20th	Day	16% 6% 33% 30% 12% 3	775
	21st to end	Day	14% 5% 28% 32% 16% 5%	844
June	1st to 10th	Day	11% 4 28% 35% 17% 4	780
	11th to 20th	Day	16% 5% 25% 38% 14% 3	780
	21st to end	Day	13% 3 24% 36% 21% 3	780
July	1st to 10th	Day	8% 3 21% 36% 26% 7%	771
	11th to 20th	Day	7% 4 22% 37% 24% 6%	768
	21st to end	Day	6% 3 22% 37% 26% 7%	849
August	1st to 10th	Day	8% 4 18% 37% 26% 7%	776
	11th to 20th	Day	11% 4 17% 32% 28% 8%	535
	21st to end	Day	13% 6% 17% 28% 27% 8%	583
September	1st to 10th	Day	15% 6% 22% 30% 19% 8%	530
	11th to 20th	Day	9% 5% 19% 32% 26% 9%	530
	21st to end	Day	17% 10% 21% 25% 22% 6%	530
October	1st to 10th	Day	18% 11% 24% 27% 17% 2	490
	11th to 20th	Day	18% 16% 33% 22% 9%	330
	21st to end	Day	23% 11% 32% 24% 9% 1	363
November	1st to 10th	Day	17% 16% 32% 25% 10% 1	330
	11th to 20th	Day	17% 19% 35% 22% 7%	330
	21st to end	Day	24% 15% 35% 22% 5%	330
December	1st to 10th	Day	20% 17% 36% 20% 6% 1	330
	11th to 20th	Day	22% 20% 41% 13% 3 1	330
	21st to end	Day	28% 19% 31% 18% 4 1	363
January	1st to 10th	Night	17% 12% 38% 26% 5%	1050
	11th to 20th	Night	22% 14% 32% 24% 7%	1050
	21st to end	Night	18% 11% 37% 25% 7% 1	1155
February	1st to 10th	Night	16% 15% 35% 26% 6% 1	1050
	11th to 20th	Night	18% 15% 35% 23% 9%	823
	21st to end	Night	20% 14% 35% 27% 4	692
March	1st to 10th	Night	19% 8% 33% 28% 10% 1	840
	11th to 20th	Night	18% 9% 36% 28% 8% 1	840
	21st to end	Night	19% 8% 32% 30% 10% 1	725
April	1st to 10th	Night	22% 7% 33% 31% 5% 1	630
	11th to 20th	Night	24% 8% 26% 27% 12% 2	623
	21st to end	Night	20% 6% 26% 35% 11% 2	630
May	1st to 10th	Night	17% 8% 24% 35% 14% 1	630
	11th to 20th	Night	17% 4 27% 35% 15% 2	621
	21st to end	Night	14% 4 18% 40% 22% 3	683
June	1st to 10th	Night	14% 3 22% 38% 20% 3	630
	11th to 20th	Night	16% 4 20% 34% 23% 3	630
	21st to end	Night	12% 4 15% 41% 25% 2	630
July	1st to 10th	Night	8% 2 14% 40% 31% 5%	615
	11th to 20th	Night	8% 3 15% 36% 34% 5%	612
	21st to end	Night	7% 2 18% 39% 30% 4	690
August	1st to 10th	Night	10% 2 13% 39% 30% 6%	627
	11th to 20th	Night	9% 3 13% 35% 33% 6%	606
	21st to end	Night	10% 4 17% 38% 28% 3	660
September	1st to 10th	Night	10% 4 22% 31% 26% 8%	600
	11th to 20th	Night	12% 4 20% 30% 25% 9%	726
	21st to end	Night	16% 7% 20% 32% 22% 4	800
October	1st to 10th	Night	19% 8% 23% 28% 19% 3	800
	11th to 20th	Night	25% 11% 29% 26% 9% 1	800
	21st to end	Night	26% 10% 27% 27% 8% 1	880
November	1st to 10th	Night	21% 10% 34% 29% 6%	820
	11th to 20th	Night	22% 16% 33% 22% 6% 1	840
	21st to end	Night	21% 16% 32% 24% 7%	1009
December	1st to 10th	Night	23% 15% 33% 22% 6%	1050
	11th to 20th	Night	24% 15% 34% 20% 5% 2	1050
	21st to end	Night	28% 14% 33% 22% 3	1155

Page generated at 2026-08-12 02:37:16. Version ac07

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