Lakehenge Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lakehenge Observatory clear sky chart from 2005-11-06 to 2026-05-02.

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	15% 9% 3 8% 5% 4 5% 4 5% 7% 35%	132066
	Night	15% 10% 3 8% 5% 5% 5% 4 5% 7% 34%	130402
Transparency	Day	47% 6% 13% 22% 12% 1	135621
	Night	49% 5% 12% 20% 12% 1	134933
Seeing	Day	19% 12% 29% 24% 12% 4	16295
	Night	20% 10% 29% 28% 12% 1	25692

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	16% 12% 4 10% 6% 5% 5% 4 5% 6% 27%	4661
	11th to 20th	Day	10% 20% 9% 16% 8% 6% 5% 4 5% 4 15%	4745
	21st to end	Day	12% 16% 6% 12% 6% 5% 5% 4 4 6% 23%	5780
February	1st to 10th	Day	12% 16% 4 12% 7% 4 5% 5% 5% 5% 25%	1890
	11th to 20th	Day	14% 11% 5% 12% 7% 6% 5% 4 5% 5% 27%	1843
	21st to end	Day	19% 13% 3 10% 6% 5% 5% 4 4 6% 25%	1659
March	1st to 10th	Day	19% 11% 3 8% 4 4 4 3 4 6% 33%	4894
	11th to 20th	Day	10% 12% 4 9% 6% 5% 6% 4 5% 7% 32%	5090
	21st to end	Day	18% 9% 3 7% 4 4 3 3 4 5% 39%	5679
April	1st to 10th	Day	18% 11% 3 8% 5% 4 5% 4 5% 6% 33%	2520
	11th to 20th	Day	20% 9% 2 7% 5% 4 3 2 4 5% 38%	2494
	21st to end	Day	19% 8% 2 7% 5% 5% 4 4 5% 5% 34%	2699
May	1st to 10th	Day	20% 9% 3 8% 5% 4 4 3 5% 6% 32%	6131
	11th to 20th	Day	15% 9% 3 8% 5% 4 4 3 5% 7% 37%	6318
	21st to end	Day	18% 7% 3 6% 4 4 4 3 6% 8% 37%	6949
June	1st to 10th	Day	16% 7% 2 7% 5% 4 5% 4 6% 8% 36%	2800
	11th to 20th	Day	11% 6% 3 5% 4 4 5% 4 6% 9% 42%	2800
	21st to end	Day	14% 7% 2 5% 4 4 4 4 6% 9% 41%	2800
July	1st to 10th	Day	9% 5% 2 6% 4 5% 4 4 5% 9% 46%	6360
	11th to 20th	Day	9% 4 2 5% 4 4 5% 4 6% 9% 49%	6360
	21st to end	Day	6% 4 2 6% 4 4 5% 5% 7% 9% 48%	6819
August	1st to 10th	Day	16% 7% 2 5% 4 3 4 4 6% 7% 41%	4234
	11th to 20th	Day	12% 5% 3 6% 4 4 5% 4 7% 10% 40%	4174
	21st to end	Day	10% 5% 2 5% 4 4 5% 4 7% 9% 45%	4361
September	1st to 10th	Day	11% 5% 2 6% 4 4 4 4 5% 9% 46%	2400
	11th to 20th	Day	9% 5% 2 5% 3 4 3 3 6% 8% 52%	2400
	21st to end	Day	14% 6% 2 6% 4 4 5% 4 6% 7% 41%	2088
October	1st to 10th	Day	16% 9% 2 7% 4 4 5% 4 5% 6% 38%	2000
	11th to 20th	Day	18% 8% 3 7% 6% 5% 5% 4 6% 6% 34%	2000
	21st to end	Day	23% 10% 3 7% 5% 4 5% 3 5% 7% 27%	2175
November	1st to 10th	Day	14% 9% 3 8% 5% 4 4 3 5% 8% 37%	1789
	11th to 20th	Day	14% 11% 3 7% 6% 5% 4 4 7% 7% 32%	1680
	21st to end	Day	19% 12% 4 9% 6% 4 5% 3 6% 6% 25%	1680
December	1st to 10th	Day	19% 15% 4 10% 6% 5% 5% 4 5% 7% 21%	2680
	11th to 20th	Day	16% 16% 5% 10% 5% 4 4 3 5% 5% 27%	3066
	21st to end	Day	25% 13% 4 10% 5% 4 5% 3 4 5% 22%	4048
January	1st to 10th	Night	14% 13% 5% 12% 6% 6% 5% 4 5% 6% 25%	8234
	11th to 20th	Night	13% 15% 6% 14% 8% 6% 6% 3 5% 6% 18%	8138
	21st to end	Night	13% 13% 5% 10% 7% 6% 5% 4 5% 6% 27%	8401
February	1st to 10th	Night	14% 15% 5% 11% 6% 5% 4 4 5% 6% 27%	2730
	11th to 20th	Night	14% 14% 4 9% 5% 5% 5% 4 6% 6% 28%	2663
	21st to end	Night	15% 11% 3 8% 5% 5% 5% 5% 6% 7% 30%	2145
March	1st to 10th	Night	16% 11% 3 8% 6% 4 5% 4 5% 6% 31%	5160
	11th to 20th	Night	12% 9% 3 8% 4 5% 4 4 6% 8% 37%	5089
	21st to end	Night	20% 8% 3 6% 3 3 3 2 5% 6% 41%	5495
April	1st to 10th	Night	19% 9% 3 7% 4 4 4 4 5% 7% 34%	2100
	11th to 20th	Night	18% 8% 2 7% 5% 4 4 3 5% 5% 39%	2075
	21st to end	Night	18% 7% 3 6% 4 4 6% 4 7% 5% 37%	1937
May	1st to 10th	Night	27% 8% 3 7% 4 4 4 3 5% 5% 29%	3816
	11th to 20th	Night	14% 8% 3 7% 5% 4 5% 3 6% 6% 40%	3575
	21st to end	Night	18% 6% 2 7% 4 4 5% 4 5% 7% 38%	3926
June	1st to 10th	Night	13% 6% 3 6% 5% 5% 5% 5% 6% 7% 38%	1600
	11th to 20th	Night	11% 5% 2 6% 4 5% 4 4 7% 9% 43%	1600
	21st to end	Night	12% 6% 3 7% 6% 5% 4 4 5% 7% 41%	1600
July	1st to 10th	Night	8% 5% 2 6% 5% 4 5% 5% 7% 10% 42%	3600
	11th to 20th	Night	9% 5% 2 6% 4 4 5% 4 5% 8% 49%	3600
	21st to end	Night	8% 5% 2 5% 3 3 4 3 6% 8% 51%	4029
August	1st to 10th	Night	10% 5% 2 6% 4 5% 4 4 6% 8% 48%	2915
	11th to 20th	Night	12% 5% 2 6% 4 4 3 3 5% 8% 48%	2875
	21st to end	Night	9% 5% 1 4 4 4 5% 5% 6% 10% 49%	3502
September	1st to 10th	Night	11% 4 2 6% 5% 3 4 4 6% 8% 47%	2000
	11th to 20th	Night	11% 4 2 4 4 4 4 4 6% 7% 53%	2000
	21st to end	Night	17% 6% 2 6% 4 4 4 3 4 7% 43%	2309
October	1st to 10th	Night	15% 7% 2 6% 5% 5% 3 4 5% 6% 41%	2400
	11th to 20th	Night	19% 7% 3 8% 5% 5% 5% 4 6% 6% 33%	2400
	21st to end	Night	21% 8% 3 7% 5% 4 5% 4 5% 8% 31%	2665
November	1st to 10th	Night	17% 7% 3 6% 4 4 4 3 5% 7% 39%	2725
	11th to 20th	Night	15% 10% 3 6% 5% 6% 5% 4 6% 8% 32%	2940
	21st to end	Night	20% 11% 2 7% 5% 5% 5% 4 7% 7% 26%	2940
December	1st to 10th	Night	18% 15% 3 8% 5% 5% 5% 4 6% 7% 23%	4720
	11th to 20th	Night	18% 15% 4 8% 4 4 4 3 5% 6% 27%	5348
	21st to end	Night	26% 14% 4 10% 5% 4 4 3 5% 5% 19%	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	55% 7% 12% 16% 8% 1	4662
	11th to 20th	Day	72% 5% 9% 8% 6% 1	4775
	21st to end	Day	62% 4 12% 13% 9% 1	5780
February	1st to 10th	Day	59% 5% 12% 17% 5% 1	1890
	11th to 20th	Day	57% 6% 10% 16% 9% 1	1852
	21st to end	Day	58% 6% 9% 17% 8% 1	1659
March	1st to 10th	Day	52% 5% 12% 16% 15% 1	4897
	11th to 20th	Day	48% 7% 19% 15% 10% 2	5090
	21st to end	Day	48% 3 8% 22% 17% 2	5679
April	1st to 10th	Day	52% 5% 9% 19% 12% 2	2520
	11th to 20th	Day	49% 4 8% 22% 15% 1	2494
	21st to end	Day	50% 5% 10% 20% 12% 3	2699
May	1st to 10th	Day	52% 5% 10% 19% 11% 3	6140
	11th to 20th	Day	48% 6% 13% 16% 16% 1	6322
	21st to end	Day	44% 6% 14% 23% 11% 2	6949
June	1st to 10th	Day	44% 7% 12% 22% 14% 1	2800
	11th to 20th	Day	37% 6% 14% 28% 14% 2	2800
	21st to end	Day	40% 6% 14% 24% 15% 1	2800
July	1st to 10th	Day	35% 6% 14% 30% 14% 1	6290
	11th to 20th	Day	31% 7% 14% 32% 15% 1	6285
	21st to end	Day	30% 8% 15% 34% 13%	6623
August	1st to 10th	Day	41% 6% 15% 24% 13% 1	4221
	11th to 20th	Day	37% 7% 16% 30% 10%	4213
	21st to end	Day	34% 7% 13% 36% 10% 1	4361
September	1st to 10th	Day	35% 7% 15% 31% 12% 1	2400
	11th to 20th	Day	30% 5% 15% 33% 16% 1	2400
	21st to end	Day	41% 7% 15% 27% 9%	2088
October	1st to 10th	Day	38% 5% 14% 30% 13% 1	3260
	11th to 20th	Day	39% 5% 18% 24% 13%	3240
	21st to end	Day	48% 6% 15% 21% 10%	3489
November	1st to 10th	Day	46% 5% 15% 22% 11% 1	1789
	11th to 20th	Day	50% 5% 17% 18% 9% 1	1680
	21st to end	Day	58% 6% 13% 17% 7%	1680
December	1st to 10th	Day	62% 6% 17% 11% 4	2680
	11th to 20th	Day	59% 5% 12% 15% 9%	3066
	21st to end	Day	64% 6% 10% 14% 7%	4048
January	1st to 10th	Night	60% 6% 12% 15% 8%	8234
	11th to 20th	Night	66% 6% 12% 9% 7% 1	8183
	21st to end	Night	57% 6% 10% 13% 13% 1	8401
February	1st to 10th	Night	58% 4 13% 18% 6% 1	2730
	11th to 20th	Night	55% 5% 11% 19% 9% 1	2665
	21st to end	Night	52% 4 14% 20% 8% 1	2145
March	1st to 10th	Night	53% 4 9% 17% 12% 4	5170
	11th to 20th	Night	45% 6% 17% 20% 11% 2	5090
	21st to end	Night	45% 4 8% 23% 18% 2	5495
April	1st to 10th	Night	48% 5% 11% 21% 13% 2	2100
	11th to 20th	Night	47% 5% 10% 20% 17% 1	2075
	21st to end	Night	46% 5% 10% 20% 15% 3	1937
May	1st to 10th	Night	57% 4 10% 14% 11% 4	3823
	11th to 20th	Night	43% 6% 15% 21% 14% 2	3576
	21st to end	Night	45% 6% 12% 21% 15% 2	3927
June	1st to 10th	Night	42% 6% 11% 24% 14% 3	1600
	11th to 20th	Night	36% 5% 13% 22% 20% 3	1600
	21st to end	Night	41% 6% 13% 24% 15% 2	1600
July	1st to 10th	Night	36% 6% 16% 21% 20% 1	3560
	11th to 20th	Night	33% 6% 12% 32% 17% 1	3552
	21st to end	Night	30% 6% 13% 32% 17% 1	3910
August	1st to 10th	Night	35% 5% 14% 29% 15% 2	2904
	11th to 20th	Night	36% 5% 16% 29% 12% 2	2902
	21st to end	Night	30% 6% 14% 37% 13% 1	3502
September	1st to 10th	Night	34% 6% 16% 30% 14% 1	2000
	11th to 20th	Night	30% 5% 13% 35% 17% 1	2000
	21st to end	Night	43% 4 11% 27% 14% 1	2309
October	1st to 10th	Night	35% 4 11% 27% 21% 1	3920
	11th to 20th	Night	42% 5% 14% 30% 9%	3899
	21st to end	Night	42% 5% 15% 27% 10% 1	4301
November	1st to 10th	Night	44% 5% 14% 22% 13% 1	2725
	11th to 20th	Night	49% 5% 15% 20% 10% 1	2940
	21st to end	Night	55% 6% 17% 16% 5% 1	2940
December	1st to 10th	Night	59% 6% 13% 17% 4	4720
	11th to 20th	Night	57% 7% 13% 12% 11% 1	5348
	21st to end	Night	66% 5% 11% 11% 7%	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% 17% 37% 16% 7% 1	220
	11th to 20th	Day	23% 22% 32% 18% 4 1	237
	21st to end	Day	22% 23% 32% 18% 4 2	363
February	1st to 10th	Day	25% 24% 31% 15% 5% 1	330
	11th to 20th	Day	23% 21% 40% 14% 3	330
	21st to end	Day	29% 20% 36% 14% 2	375
March	1st to 10th	Day	23% 17% 34% 20% 6% 1	540
	11th to 20th	Day	25% 18% 32% 20% 4 1	540
	21st to end	Day	29% 16% 32% 15% 7% 1	594
April	1st to 10th	Day	25% 18% 33% 17% 6% 1	540
	11th to 20th	Day	27% 15% 29% 17% 8% 3	532
	21st to end	Day	27% 12% 34% 20% 7% 2	540
May	1st to 10th	Day	22% 11% 32% 22% 9% 4	507
	11th to 20th	Day	17% 11% 26% 29% 12% 4	527
	21st to end	Day	14% 7% 30% 29% 16% 4	573
June	1st to 10th	Day	18% 10% 28% 29% 14% 2	530
	11th to 20th	Day	12% 8% 32% 28% 16% 4	530
	21st to end	Day	18% 9% 27% 28% 14% 4	530
July	1st to 10th	Day	8% 6% 23% 33% 24% 6%	525
	11th to 20th	Day	12% 6% 24% 31% 19% 8%	524
	21st to end	Day	9% 5% 29% 37% 15% 6%	576
August	1st to 10th	Day	11% 4 25% 30% 21% 8%	526
	11th to 20th	Day	12% 3 21% 31% 24% 8%	519
	21st to end	Day	11% 7% 25% 31% 18% 8%	583
September	1st to 10th	Day	12% 8% 26% 25% 20% 9%	530
	11th to 20th	Day	9% 6% 21% 25% 24% 16%	530
	21st to end	Day	15% 7% 28% 27% 18% 5%	530
October	1st to 10th	Day	20% 10% 25% 21% 18% 6%	530
	11th to 20th	Day	18% 16% 30% 25% 8% 2	530
	21st to end	Day	27% 14% 28% 24% 7% 1	569
November	1st to 10th	Day	25% 15% 26% 25% 7% 1	363
	11th to 20th	Day	19% 18% 38% 19% 5% 1	220
	21st to end	Day	25% 18% 32% 17% 6%	220
December	1st to 10th	Day	25% 16% 35% 15% 8%	220
	11th to 20th	Day	28% 24% 30% 15% 2	220
	21st to end	Day	33% 18% 32% 13% 3 1	242
January	1st to 10th	Night	25% 16% 35% 19% 6%	840
	11th to 20th	Night	26% 16% 32% 21% 5%	840
	21st to end	Night	21% 14% 33% 26% 6% 1	924
February	1st to 10th	Night	22% 15% 38% 21% 3	840
	11th to 20th	Night	22% 14% 36% 22% 5%	823
	21st to end	Night	23% 16% 35% 22% 4	692
March	1st to 10th	Night	22% 14% 34% 27% 4	840
	11th to 20th	Night	23% 14% 34% 25% 4 1	840
	21st to end	Night	21% 10% 34% 26% 7% 1	924
April	1st to 10th	Night	22% 10% 37% 27% 5%	840
	11th to 20th	Night	20% 12% 33% 25% 9% 1	831
	21st to end	Night	21% 8% 29% 30% 12% 1	677
May	1st to 10th	Night	22% 6% 27% 30% 14% 2	500
	11th to 20th	Night	14% 6% 26% 40% 14%	394
	21st to end	Night	13% 5% 26% 35% 19% 2	433
June	1st to 10th	Night	12% 4 31% 38% 15% 1	400
	11th to 20th	Night	11% 5% 25% 40% 19% 1	400
	21st to end	Night	12% 7% 23% 41% 17% 1	400
July	1st to 10th	Night	6% 4 22% 45% 21% 2	390
	11th to 20th	Night	10% 4 18% 41% 26% 2	388
	21st to end	Night	9% 2 20% 45% 21% 2	479
August	1st to 10th	Night	10% 3 15% 39% 29% 4	597
	11th to 20th	Night	10% 3 15% 37% 30% 5%	594
	21st to end	Night	11% 4 20% 36% 26% 3	822
September	1st to 10th	Night	13% 4 22% 34% 25% 3	800
	11th to 20th	Night	12% 4 16% 31% 30% 7%	800
	21st to end	Night	19% 6% 21% 29% 21% 5%	800
October	1st to 10th	Night	18% 7% 27% 26% 20% 3	800
	11th to 20th	Night	22% 10% 31% 28% 9% 1	800
	21st to end	Night	24% 10% 32% 27% 7%	880
November	1st to 10th	Night	21% 13% 27% 28% 10% 1	820
	11th to 20th	Night	21% 15% 33% 24% 6% 2	840
	21st to end	Night	26% 13% 31% 23% 7%	840
December	1st to 10th	Night	27% 17% 31% 20% 5%	840
	11th to 20th	Night	25% 15% 38% 17% 4	840
	21st to end	Night	31% 13% 33% 19% 4	924

Page generated at 2026-04-29 02:21:41. Version ac07

Copyright © 2026 Attilla Danko.