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 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	13% 9% 3 8% 5% 5% 5% 4 6% 7% 37%	113388
	Night	14% 10% 4 8% 5% 4 5% 4 5% 7% 35%	115097
Transparency	Day	44% 6% 14% 24% 12% 1	116922
	Night	47% 5% 13% 22% 11% 1	119706
Seeing	Day	16% 9% 29% 28% 14% 4	16483
	Night	18% 9% 28% 29% 13% 2	26531

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	10% 9% 5% 13% 5% 5% 5% 5% 8% 7% 27%	3617
	11th to 20th	Day	13% 12% 4 10% 6% 6% 6% 5% 5% 6% 27%	3620
	21st to end	Day	15% 14% 5% 10% 4 5% 5% 4 5% 8% 25%	3982
February	1st to 10th	Day	10% 10% 3 9% 7% 6% 6% 5% 7% 8% 30%	1705
	11th to 20th	Day	11% 11% 3 8% 5% 5% 5% 5% 7% 7% 33%	1948
	21st to end	Day	11% 12% 5% 9% 6% 5% 5% 4 5% 7% 32%	1650
March	1st to 10th	Day	11% 7% 2 5% 4 4 4 3 5% 7% 46%	4480
	11th to 20th	Day	10% 9% 3 8% 5% 5% 5% 4 6% 8% 35%	4656
	21st to end	Day	23% 10% 4 9% 5% 4 3 3 4 5% 30%	5939
April	1st to 10th	Day	14% 12% 4 8% 6% 5% 5% 4 5% 7% 31%	2400
	11th to 20th	Day	19% 8% 3 6% 5% 4 4 4 6% 6% 36%	2268
	21st to end	Day	16% 8% 2 8% 5% 4 4 4 6% 8% 35%	2470
May	1st to 10th	Day	13% 7% 3 6% 4 5% 5% 4 5% 7% 42%	4113
	11th to 20th	Day	11% 6% 3 7% 5% 4 5% 4 6% 7% 42%	4399
	21st to end	Day	10% 7% 3 8% 5% 5% 5% 4 6% 8% 40%	4824
June	1st to 10th	Day	11% 6% 1 5% 4 4 4 4 7% 8% 45%	2660
	11th to 20th	Day	12% 6% 2 6% 5% 5% 6% 4 6% 9% 40%	2660
	21st to end	Day	10% 6% 1 6% 4 5% 5% 4 6% 8% 43%	2660
July	1st to 10th	Day	13% 6% 2 6% 4 4 5% 4 6% 10% 40%	4440
	11th to 20th	Day	5% 3 1 4 4 4 4 4 7% 10% 54%	4440
	21st to end	Day	6% 5% 2 5% 4 4 4 4 6% 8% 51%	4813
August	1st to 10th	Day	7% 6% 2 6% 5% 4 5% 4 7% 9% 44%	4423
	11th to 20th	Day	11% 5% 2 5% 3 3 3 3 5% 7% 52%	3994
	21st to end	Day	11% 5% 2 7% 4 4 5% 4 5% 7% 46%	4180
September	1st to 10th	Day	12% 6% 2 7% 4 5% 5% 4 6% 7% 44%	2280
	11th to 20th	Day	11% 6% 2 5% 4 4 4 4 6% 8% 46%	2141
	21st to end	Day	13% 6% 2 7% 6% 5% 5% 4 6% 9% 38%	2090
October	1st to 10th	Day	14% 8% 3 6% 4 4 3 3 5% 7% 42%	2052
	11th to 20th	Day	21% 10% 4 9% 4 4 5% 4 5% 6% 28%	1806
	21st to end	Day	18% 12% 3 9% 6% 5% 5% 5% 4 6% 27%	1881
November	1st to 10th	Day	15% 10% 4 6% 4 4 5% 4 5% 7% 36%	1762
	11th to 20th	Day	12% 15% 5% 11% 7% 5% 5% 5% 6% 6% 23%	1800
	21st to end	Day	18% 12% 5% 11% 7% 4 4 3 5% 6% 25%	1635
December	1st to 10th	Day	11% 15% 6% 12% 8% 6% 6% 4 6% 6% 21%	2610
	11th to 20th	Day	15% 17% 5% 10% 6% 6% 7% 5% 6% 7% 18%	3008
	21st to end	Day	20% 20% 6% 13% 6% 5% 5% 3 3 4 14%	3982
January	1st to 10th	Night	10% 12% 5% 11% 7% 5% 5% 4 5% 5% 32%	6348
	11th to 20th	Night	11% 15% 5% 10% 7% 7% 8% 5% 5% 6% 23%	6360
	21st to end	Night	11% 13% 5% 10% 5% 5% 5% 4 5% 8% 30%	6996
February	1st to 10th	Night	10% 14% 5% 11% 6% 4 5% 4 5% 6% 31%	2695
	11th to 20th	Night	10% 12% 4 10% 5% 4 5% 3 6% 6% 34%	2338
	21st to end	Night	15% 12% 4 7% 6% 3 4 5% 5% 7% 32%	1980
March	1st to 10th	Night	14% 8% 2 6% 4 4 4 3 5% 7% 44%	5373
	11th to 20th	Night	9% 9% 3 6% 5% 5% 5% 4 7% 9% 37%	5303
	21st to end	Night	20% 10% 3 8% 5% 4 4 3 5% 6% 32%	5018
April	1st to 10th	Night	17% 11% 3 8% 5% 4 4 3 4 7% 33%	2000
	11th to 20th	Night	18% 9% 3 6% 4 3 3 4 4 5% 39%	1867
	21st to end	Night	18% 9% 3 7% 5% 4 4 3 5% 5% 37%	1710
May	1st to 10th	Night	15% 8% 3 7% 4 5% 4 4 5% 6% 39%	2768
	11th to 20th	Night	11% 7% 3 8% 4 5% 5% 4 6% 7% 40%	2506
	21st to end	Night	17% 7% 3 6% 5% 4 5% 4 6% 7% 38%	2743
June	1st to 10th	Night	12% 6% 2 5% 4 5% 5% 4 6% 7% 43%	1520
	11th to 20th	Night	12% 7% 2 7% 4 4 5% 5% 6% 8% 41%	1520
	21st to end	Night	9% 5% 2 7% 5% 4 6% 4 5% 6% 46%	1520
July	1st to 10th	Night	13% 6% 3 7% 5% 4 4 4 5% 7% 43%	2530
	11th to 20th	Night	5% 3 2 5% 3 4 4 4 5% 9% 56%	2530
	21st to end	Night	7% 5% 3 7% 6% 4 4 3 5% 7% 49%	2750
August	1st to 10th	Night	10% 6% 2 7% 5% 4 5% 3 5% 8% 45%	2517
	11th to 20th	Night	12% 4 1 5% 3 3 4 3 5% 8% 51%	2833
	21st to end	Night	10% 6% 3 7% 4 4 4 3 5% 7% 47%	3476
September	1st to 10th	Night	9% 5% 2 7% 3 4 4 3 5% 7% 51%	1900
	11th to 20th	Night	11% 6% 3 6% 3 3 5% 3 5% 6% 50%	2019
	21st to end	Night	13% 8% 4 6% 5% 4 5% 3 5% 7% 41%	2090
October	1st to 10th	Night	16% 7% 2 6% 4 4 4 3 5% 5% 44%	2125
	11th to 20th	Night	18% 11% 3 7% 5% 4 4 3 5% 7% 34%	2373
	21st to end	Night	21% 11% 3 6% 5% 4 5% 3 6% 6% 29%	2717
November	1st to 10th	Night	14% 10% 3 7% 5% 4 4 3 5% 6% 39%	2536
	11th to 20th	Night	15% 13% 5% 11% 6% 5% 4 3 5% 6% 28%	2600
	21st to end	Night	16% 13% 5% 11% 6% 4 5% 3 5% 6% 26%	2761
December	1st to 10th	Night	15% 11% 5% 9% 6% 5% 5% 5% 7% 7% 27%	4580
	11th to 20th	Night	14% 16% 6% 12% 7% 6% 6% 3 5% 5% 19%	5199
	21st to end	Night	22% 18% 6% 10% 5% 4 5% 4 4 5% 17%	6996

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	52% 7% 16% 18% 7%	3618
	11th to 20th	Day	57% 4 11% 18% 9% 1	3620
	21st to end	Day	57% 4 15% 15% 10%	3982
February	1st to 10th	Day	49% 6% 16% 22% 6%	1705
	11th to 20th	Day	48% 5% 15% 21% 10% 1	1958
	21st to end	Day	52% 5% 13% 21% 9% 2	1650
March	1st to 10th	Day	37% 5% 17% 20% 18% 4	4480
	11th to 20th	Day	44% 6% 15% 23% 10% 1	4656
	21st to end	Day	57% 4 9% 18% 10%	5941
April	1st to 10th	Day	52% 6% 11% 21% 10% 1	2400
	11th to 20th	Day	47% 5% 10% 23% 13% 2	2268
	21st to end	Day	46% 5% 11% 21% 15% 2	2470
May	1st to 10th	Day	40% 6% 11% 28% 14% 1	4151
	11th to 20th	Day	38% 5% 13% 29% 14% 2	4403
	21st to end	Day	41% 5% 12% 22% 16% 4	4837
June	1st to 10th	Day	35% 5% 14% 31% 14% 2	2660
	11th to 20th	Day	39% 6% 13% 25% 16% 2	2660
	21st to end	Day	37% 6% 17% 25% 14% 1	2660
July	1st to 10th	Day	39% 7% 15% 26% 12% 2	4371
	11th to 20th	Day	23% 7% 15% 38% 15% 2	4365
	21st to end	Day	30% 7% 13% 28% 20% 2	4662
August	1st to 10th	Day	34% 7% 16% 30% 13% 1	4408
	11th to 20th	Day	31% 5% 17% 33% 13% 1	4033
	21st to end	Day	36% 8% 16% 25% 14% 1	4179
September	1st to 10th	Day	39% 6% 14% 28% 13% 1	2280
	11th to 20th	Day	35% 6% 19% 31% 9%	2141
	21st to end	Day	42% 5% 16% 27% 10%	2090
October	1st to 10th	Day	26% 4 12% 36% 20% 1	3416
	11th to 20th	Day	50% 6% 10% 23% 11%	2983
	21st to end	Day	48% 5% 16% 24% 7%	3081
November	1st to 10th	Day	48% 5% 13% 22% 12%	1762
	11th to 20th	Day	59% 5% 14% 15% 6%	1800
	21st to end	Day	60% 5% 16% 15% 4	1635
December	1st to 10th	Day	62% 7% 15% 14% 2	2610
	11th to 20th	Day	63% 7% 12% 12% 6%	3005
	21st to end	Day	72% 6% 7% 12% 3	3982
January	1st to 10th	Night	51% 6% 11% 27% 5%	6348
	11th to 20th	Night	61% 4 12% 12% 10% 1	6360
	21st to end	Night	52% 5% 16% 20% 7%	6996
February	1st to 10th	Night	53% 4 12% 21% 9% 1	2695
	11th to 20th	Night	50% 4 12% 23% 10% 2	2339
	21st to end	Night	51% 5% 13% 22% 9% 1	1980
March	1st to 10th	Night	39% 4 17% 25% 13% 1	5373
	11th to 20th	Night	42% 5% 18% 21% 12% 2	5303
	21st to end	Night	53% 5% 10% 20% 11% 1	5018
April	1st to 10th	Night	52% 4 8% 20% 14% 1	2000
	11th to 20th	Night	47% 4 8% 22% 16% 3	1867
	21st to end	Night	49% 4 10% 21% 13% 3	1710
May	1st to 10th	Night	46% 4 12% 22% 15% 2	2795
	11th to 20th	Night	40% 6% 12% 27% 14% 1	2507
	21st to end	Night	44% 5% 12% 19% 12% 8%	2751
June	1st to 10th	Night	37% 6% 10% 29% 16% 2	1520
	11th to 20th	Night	39% 6% 11% 24% 18% 2	1520
	21st to end	Night	37% 5% 14% 28% 13% 3	1520
July	1st to 10th	Night	41% 5% 14% 24% 11% 5%	2490
	11th to 20th	Night	24% 6% 15% 36% 17% 2	2482
	21st to end	Night	34% 6% 11% 22% 24% 2	2662
August	1st to 10th	Night	37% 6% 12% 27% 16% 1	2508
	11th to 20th	Night	31% 5% 15% 32% 16% 1	2860
	21st to end	Night	36% 6% 13% 24% 20% 2	3476
September	1st to 10th	Night	32% 5% 13% 31% 18% 2	1900
	11th to 20th	Night	34% 4 15% 33% 13% 1	2019
	21st to end	Night	43% 4 14% 26% 12% 1	2090
October	1st to 10th	Night	34% 4 9% 36% 15% 1	3541
	11th to 20th	Night	41% 5% 15% 24% 14% 1	3935
	21st to end	Night	49% 4 13% 22% 11%	4467
November	1st to 10th	Night	46% 4 13% 25% 11% 1	2536
	11th to 20th	Night	56% 5% 13% 18% 7% 1	2600
	21st to end	Night	57% 5% 16% 19% 3 1	2761
December	1st to 10th	Night	52% 9% 19% 17% 3	4580
	11th to 20th	Night	65% 5% 12% 12% 5%	5201
	21st to end	Night	66% 7% 10% 12% 5%	6996

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	300
	11th to 20th	Day	22% 14% 35% 21% 7% 1	300
	21st to end	Day	22% 10% 32% 30% 6%	330
February	1st to 10th	Day	16% 16% 41% 20% 6% 1	300
	11th to 20th	Day	15% 22% 37% 20% 5% 1	300
	21st to end	Day	18% 17% 40% 22% 2 1	249
March	1st to 10th	Day	15% 16% 43% 19% 6%	300
	11th to 20th	Day	20% 13% 32% 24% 9% 2	358
	21st to end	Day	25% 11% 30% 26% 8% 1	550
April	1st to 10th	Day	20% 13% 33% 27% 6% 1	500
	11th to 20th	Day	23% 14% 28% 24% 9% 2	452
	21st to end	Day	21% 10% 28% 26% 13% 2	460
May	1st to 10th	Day	19% 8% 37% 25% 10% 3	481
	11th to 20th	Day	17% 5% 32% 31% 11% 3	675
	21st to end	Day	14% 6% 30% 30% 16% 5%	734
June	1st to 10th	Day	12% 5% 31% 33% 16% 3	680
	11th to 20th	Day	16% 4 26% 37% 14% 3	680
	21st to end	Day	14% 3 25% 35% 20% 4	680
July	1st to 10th	Day	8% 3 22% 35% 25% 7%	671
	11th to 20th	Day	7% 4 24% 37% 23% 6%	668
	21st to end	Day	6% 2 23% 36% 26% 7%	739
August	1st to 10th	Day	8% 4 20% 38% 24% 7%	676
	11th to 20th	Day	11% 4 18% 30% 28% 9%	479
	21st to end	Day	14% 6% 18% 27% 27% 8%	539
September	1st to 10th	Day	16% 7% 22% 30% 19% 7%	490
	11th to 20th	Day	10% 5% 21% 34% 24% 7%	490
	21st to end	Day	17% 10% 22% 26% 20% 5%	490
October	1st to 10th	Day	18% 12% 25% 27% 15% 2	452
	11th to 20th	Day	20% 16% 35% 20% 9%	300
	21st to end	Day	25% 12% 35% 21% 5% 1	330
November	1st to 10th	Day	18% 15% 32% 24% 10% 1	300
	11th to 20th	Day	18% 19% 35% 21% 6%	300
	21st to end	Day	24% 14% 35% 21% 5%	300
December	1st to 10th	Day	21% 17% 36% 18% 7% 1	300
	11th to 20th	Day	24% 19% 40% 13% 4 1	300
	21st to end	Day	27% 19% 30% 18% 4 1	330
January	1st to 10th	Night	17% 12% 39% 26% 6% 1	1000
	11th to 20th	Night	23% 14% 32% 24% 7% 1	1000
	21st to end	Night	19% 11% 36% 25% 8% 1	1100
February	1st to 10th	Night	17% 16% 35% 26% 6% 1	1000
	11th to 20th	Night	19% 15% 35% 22% 8% 1	783
	21st to end	Night	20% 13% 36% 27% 4	660
March	1st to 10th	Night	20% 8% 34% 28% 10% 1	800
	11th to 20th	Night	17% 9% 37% 28% 8% 1	800
	21st to end	Night	20% 8% 31% 30% 10% 1	690
April	1st to 10th	Night	23% 7% 32% 32% 6% 1	600
	11th to 20th	Night	24% 8% 27% 27% 12% 2	565
	21st to end	Night	21% 6% 26% 35% 11% 2	570
May	1st to 10th	Night	18% 8% 24% 34% 14% 2	570
	11th to 20th	Night	18% 4 27% 35% 14% 2	561
	21st to end	Night	14% 4 18% 38% 23% 3	617
June	1st to 10th	Night	15% 3 23% 36% 19% 3	570
	11th to 20th	Night	15% 3 21% 34% 24% 3	570
	21st to end	Night	12% 4 16% 40% 26% 2	570
July	1st to 10th	Night	8% 1 15% 41% 31% 5%	555
	11th to 20th	Night	8% 3 17% 36% 33% 5%	552
	21st to end	Night	8% 2 18% 39% 30% 4	624
August	1st to 10th	Night	9% 2 14% 39% 30% 5%	567
	11th to 20th	Night	9% 3 14% 34% 34% 7%	564
	21st to end	Night	11% 4 17% 38% 27% 3	627
September	1st to 10th	Night	10% 4 22% 31% 26% 8%	570
	11th to 20th	Night	13% 4 21% 31% 23% 8%	689
	21st to end	Night	16% 8% 21% 31% 21% 3	760
October	1st to 10th	Night	20% 8% 24% 27% 19% 3	760
	11th to 20th	Night	25% 11% 29% 25% 9% 1	760
	21st to end	Night	27% 11% 28% 27% 7% 1	836
November	1st to 10th	Night	21% 10% 34% 29% 6%	780
	11th to 20th	Night	23% 17% 32% 22% 6% 1	800
	21st to end	Night	21% 16% 31% 24% 7%	961
December	1st to 10th	Night	23% 16% 34% 21% 6%	1000
	11th to 20th	Night	25% 14% 34% 20% 5% 2	1000
	21st to end	Night	28% 14% 33% 23% 3	1100

Page generated at 2025-04-08 08:17:26. Version ac07

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