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 2025-01-07.

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 7% 5% 4 5% 4 5% 7% 36%	105120
	Night	16% 10% 3 7% 5% 4 4 4 5% 7% 35%	103901
Transparency	Day	45% 6% 14% 23% 11% 1	108693
	Night	48% 6% 13% 21% 11% 1	108416
Seeing	Day	19% 12% 29% 24% 12% 4	14623
	Night	20% 10% 29% 28% 12% 1	23990

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% 15% 4 9% 5% 5% 4 3 4 6% 29%	2565
	11th to 20th	Day	12% 18% 8% 13% 7% 6% 5% 5% 5% 5% 16%	2559
	21st to end	Day	19% 20% 6% 10% 5% 5% 4 3 3 4 21%	3124
February	1st to 10th	Day	12% 16% 4 13% 7% 5% 5% 5% 5% 5% 24%	1710
	11th to 20th	Day	13% 11% 5% 12% 6% 5% 5% 4 5% 5% 28%	1663
	21st to end	Day	19% 13% 3 10% 6% 5% 4 4 4 6% 26%	1505
March	1st to 10th	Day	20% 11% 3 8% 5% 4 5% 3 5% 6% 32%	3330
	11th to 20th	Day	9% 14% 4 10% 5% 5% 5% 4 5% 6% 33%	3480
	21st to end	Day	14% 9% 3 6% 4 4 3 3 5% 6% 44%	3878
April	1st to 10th	Day	18% 11% 3 7% 6% 4 5% 4 5% 5% 33%	2280
	11th to 20th	Day	20% 8% 2 7% 5% 4 3 2 4 6% 40%	2254
	21st to end	Day	19% 8% 2 7% 6% 5% 4 4 5% 5% 34%	2441
May	1st to 10th	Day	17% 7% 3 8% 5% 5% 5% 3 5% 7% 35%	4268
	11th to 20th	Day	15% 9% 3 8% 5% 4 4 3 5% 8% 36%	4398
	21st to end	Day	11% 5% 2 5% 5% 5% 4 4 6% 8% 46%	4837
June	1st to 10th	Day	16% 7% 2 7% 5% 4 5% 4 6% 8% 36%	2660
	11th to 20th	Day	11% 6% 3 5% 4 4 5% 4 6% 9% 42%	2660
	21st to end	Day	14% 7% 2 5% 4 4 4 4 6% 9% 41%	2660
July	1st to 10th	Day	9% 5% 2 6% 5% 5% 5% 4 6% 9% 45%	4440
	11th to 20th	Day	10% 4 2 4 3 4 5% 5% 6% 9% 47%	4440
	21st to end	Day	6% 4 2 6% 4 5% 5% 5% 7% 9% 44%	4735
August	1st to 10th	Day	16% 7% 2 6% 4 3 4 4 6% 8% 40%	4104
	11th to 20th	Day	12% 5% 2 6% 4 4 5% 4 7% 10% 40%	4044
	21st to end	Day	11% 5% 2 5% 4 4 5% 4 7% 9% 45%	4227
September	1st to 10th	Day	12% 5% 3 6% 4 4 4 4 5% 9% 45%	2280
	11th to 20th	Day	10% 5% 2 5% 4 4 3 3 6% 8% 51%	2280
	21st to end	Day	14% 5% 2 7% 4 4 5% 4 6% 7% 41%	1984
October	1st to 10th	Day	16% 9% 2 7% 4 4 5% 4 6% 6% 36%	1900
	11th to 20th	Day	18% 8% 3 7% 5% 5% 5% 4 5% 7% 34%	1900
	21st to end	Day	24% 10% 2 7% 5% 4 5% 3 5% 7% 27%	2066
November	1st to 10th	Day	13% 9% 3 8% 5% 5% 4 3 5% 8% 36%	1702
	11th to 20th	Day	14% 11% 3 8% 6% 4 4 4 7% 7% 32%	1600
	21st to end	Day	20% 12% 4 8% 6% 4 5% 3 6% 6% 26%	1600
December	1st to 10th	Day	19% 14% 4 10% 6% 5% 5% 5% 5% 7% 20%	2600
	11th to 20th	Day	16% 16% 5% 10% 5% 4 4 3 5% 5% 28%	2986
	21st to end	Day	25% 13% 4 10% 5% 5% 5% 3 4 5% 22%	3960
January	1st to 10th	Night	18% 15% 4 10% 6% 5% 5% 3 5% 5% 24%	4514
	11th to 20th	Night	15% 12% 5% 11% 9% 7% 7% 4 4 6% 20%	4399
	21st to end	Night	21% 15% 5% 9% 6% 4 5% 3 4 5% 24%	4532
February	1st to 10th	Night	14% 15% 5% 11% 6% 5% 5% 4 5% 6% 25%	2470
	11th to 20th	Night	14% 14% 4 8% 5% 5% 5% 4 6% 6% 29%	2403
	21st to end	Night	16% 10% 3 8% 5% 5% 5% 5% 6% 7% 31%	1947
March	1st to 10th	Night	18% 11% 4 8% 6% 4 5% 4 4 5% 31%	3505
	11th to 20th	Night	16% 12% 3 9% 4 5% 3 3 5% 6% 33%	3479
	21st to end	Night	16% 7% 3 5% 3 3 3 3 4 6% 48%	3754
April	1st to 10th	Night	20% 9% 3 6% 4 4 4 4 5% 7% 35%	1900
	11th to 20th	Night	18% 7% 2 7% 5% 4 4 3 5% 5% 39%	1875
	21st to end	Night	18% 7% 3 6% 4 4 5% 4 7% 5% 36%	1753
May	1st to 10th	Night	21% 9% 3 7% 5% 4 4 4 5% 5% 35%	2657
	11th to 20th	Night	15% 8% 3 7% 5% 5% 5% 3 6% 6% 38%	2495
	21st to end	Night	10% 5% 2 6% 4 4 5% 5% 5% 8% 46%	2738
June	1st to 10th	Night	13% 6% 3 6% 5% 5% 5% 5% 6% 8% 38%	1520
	11th to 20th	Night	10% 5% 3 5% 4 4 4 4 7% 9% 43%	1520
	21st to end	Night	12% 6% 3 7% 6% 4 4 5% 5% 8% 41%	1520
July	1st to 10th	Night	8% 5% 2 6% 5% 4 5% 5% 7% 9% 44%	2520
	11th to 20th	Night	11% 5% 2 5% 4 3 4 3 5% 8% 49%	2520
	21st to end	Night	8% 6% 2 5% 3 3 4 4 6% 8% 50%	2814
August	1st to 10th	Night	10% 5% 2 6% 4 5% 4 4 6% 8% 47%	2825
	11th to 20th	Night	12% 6% 2 6% 4 4 3 3 5% 8% 48%	2785
	21st to end	Night	9% 4 1 4 4 3 5% 4 6% 10% 49%	3395
September	1st to 10th	Night	12% 4 2 6% 5% 3 4 4 6% 8% 46%	1900
	11th to 20th	Night	11% 4 2 4 4 4 4 4 6% 7% 52%	1900
	21st to end	Night	16% 6% 2 6% 4 4 4 3 4 7% 43%	2193
October	1st to 10th	Night	16% 7% 3 7% 5% 5% 4 4 5% 6% 39%	2280
	11th to 20th	Night	19% 7% 3 8% 5% 5% 5% 4 6% 6% 33%	2280
	21st to end	Night	21% 8% 3 7% 5% 4 5% 4 5% 8% 30%	2532
November	1st to 10th	Night	17% 7% 3 6% 4 4 4 3 5% 7% 39%	2592
	11th to 20th	Night	16% 10% 3 6% 5% 5% 4 4 6% 8% 33%	2800
	21st to end	Night	20% 11% 2 7% 5% 5% 5% 4 7% 7% 27%	2800
December	1st to 10th	Night	18% 15% 3 8% 5% 5% 5% 4 6% 7% 23%	4580
	11th to 20th	Night	18% 15% 4 8% 4 4 4 3 5% 6% 27%	5208
	21st to end	Night	26% 14% 4 10% 5% 4 4 3 5% 5% 19%	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	55% 8% 16% 13% 7% 1	2566
	11th to 20th	Day	67% 7% 12% 8% 5%	2559
	21st to end	Day	68% 4 10% 12% 4 1	3124
February	1st to 10th	Day	61% 5% 13% 16% 4 1	1710
	11th to 20th	Day	56% 6% 10% 16% 10% 2	1672
	21st to end	Day	58% 6% 10% 16% 9% 1	1505
March	1st to 10th	Day	52% 6% 12% 20% 9% 1	3333
	11th to 20th	Day	49% 8% 15% 17% 10% 2	3480
	21st to end	Day	41% 4 10% 27% 17% 3	3878
April	1st to 10th	Day	52% 5% 9% 20% 12% 3	2280
	11th to 20th	Day	47% 4 9% 23% 16% 2	2254
	21st to end	Day	51% 5% 9% 19% 13% 3	2441
May	1st to 10th	Day	47% 6% 11% 23% 12% 2	4280
	11th to 20th	Day	47% 6% 16% 20% 10% 1	4402
	21st to end	Day	34% 6% 15% 27% 15% 3	4837
June	1st to 10th	Day	44% 7% 12% 21% 14% 1	2660
	11th to 20th	Day	36% 6% 14% 27% 14% 2	2660
	21st to end	Day	39% 7% 14% 24% 15% 1	2660
July	1st to 10th	Day	34% 6% 13% 31% 15% 1	4370
	11th to 20th	Day	30% 7% 16% 37% 10%	4365
	21st to end	Day	33% 9% 16% 28% 14%	4584
August	1st to 10th	Day	42% 6% 15% 24% 13% 1	4091
	11th to 20th	Day	37% 7% 16% 30% 10%	4083
	21st to end	Day	34% 7% 13% 35% 10% 1	4227
September	1st to 10th	Day	35% 7% 15% 30% 12% 1	2280
	11th to 20th	Day	31% 5% 15% 33% 16% 1	2280
	21st to end	Day	41% 7% 15% 28% 9%	1984
October	1st to 10th	Day	38% 5% 14% 30% 13% 1	3160
	11th to 20th	Day	38% 6% 18% 24% 13%	3140
	21st to end	Day	48% 6% 15% 22% 9%	3380
November	1st to 10th	Day	46% 5% 16% 21% 11% 1	1702
	11th to 20th	Day	50% 5% 16% 18% 10% 1	1600
	21st to end	Day	58% 6% 12% 17% 7%	1600
December	1st to 10th	Day	62% 6% 18% 10% 4	2600
	11th to 20th	Day	59% 5% 12% 15% 8%	2986
	21st to end	Day	64% 6% 10% 14% 7%	3960
January	1st to 10th	Night	61% 7% 14% 13% 5%	4514
	11th to 20th	Night	64% 8% 16% 9% 3 1	4399
	21st to end	Night	64% 7% 10% 13% 5%	4532
February	1st to 10th	Night	60% 5% 13% 17% 4 1	2470
	11th to 20th	Night	54% 6% 11% 20% 9% 1	2405
	21st to end	Night	52% 4 14% 20% 9% 1	1947
March	1st to 10th	Night	54% 5% 9% 22% 10% 1	3515
	11th to 20th	Night	51% 5% 14% 18% 11% 1	3480
	21st to end	Night	38% 4 8% 27% 20% 3	3754
April	1st to 10th	Night	48% 5% 10% 22% 13% 2	1900
	11th to 20th	Night	47% 4 10% 19% 18% 2	1875
	21st to end	Night	46% 6% 11% 19% 16% 3	1753
May	1st to 10th	Night	50% 4 12% 17% 14% 2	2664
	11th to 20th	Night	45% 6% 16% 21% 10% 2	2496
	21st to end	Night	35% 6% 14% 23% 21% 2	2739
June	1st to 10th	Night	42% 6% 12% 24% 14% 3	1520
	11th to 20th	Night	36% 5% 13% 22% 21% 3	1520
	21st to end	Night	41% 6% 13% 23% 15% 2	1520
July	1st to 10th	Night	34% 6% 14% 23% 21% 1	2480
	11th to 20th	Night	33% 5% 13% 33% 15%	2472
	21st to end	Night	31% 7% 16% 32% 13% 1	2724
August	1st to 10th	Night	36% 5% 14% 29% 15% 2	2814
	11th to 20th	Night	36% 5% 17% 29% 12% 2	2812
	21st to end	Night	30% 6% 13% 37% 13% 1	3395
September	1st to 10th	Night	35% 6% 16% 28% 14% 1	1900
	11th to 20th	Night	31% 5% 13% 33% 17% 1	1900
	21st to end	Night	43% 4 12% 27% 13% 1	2193
October	1st to 10th	Night	36% 4 12% 27% 21% 1	3800
	11th to 20th	Night	42% 5% 14% 30% 9%	3779
	21st to end	Night	43% 5% 15% 27% 9% 1	4168
November	1st to 10th	Night	44% 6% 14% 22% 13% 1	2592
	11th to 20th	Night	48% 5% 15% 20% 10% 1	2800
	21st to end	Night	55% 6% 17% 17% 5% 1	2800
December	1st to 10th	Night	59% 6% 14% 17% 4	4580
	11th to 20th	Night	57% 7% 13% 12% 11% 1	5208
	21st to end	Night	66% 5% 11% 11% 7%	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	23% 17% 35% 16% 7% 2	192
	11th to 20th	Day	23% 20% 34% 19% 4 1	193
	21st to end	Day	24% 20% 32% 19% 4 1	297
February	1st to 10th	Day	26% 25% 33% 12% 4	270
	11th to 20th	Day	22% 23% 42% 12% 1	270
	21st to end	Day	31% 19% 36% 13% 2	317
March	1st to 10th	Day	23% 17% 34% 19% 6% 1	460
	11th to 20th	Day	25% 17% 33% 21% 3 1	460
	21st to end	Day	28% 15% 33% 15% 8% 1	506
April	1st to 10th	Day	24% 18% 33% 18% 7% 1	460
	11th to 20th	Day	27% 15% 29% 17% 9% 4	452
	21st to end	Day	27% 12% 35% 19% 6% 2	460
May	1st to 10th	Day	21% 11% 32% 22% 10% 4	463
	11th to 20th	Day	17% 11% 26% 30% 12% 5%	487
	21st to end	Day	12% 6% 31% 30% 16% 4	529
June	1st to 10th	Day	18% 10% 28% 28% 14% 2	490
	11th to 20th	Day	12% 8% 31% 28% 16% 5%	490
	21st to end	Day	18% 9% 27% 27% 14% 5%	490
July	1st to 10th	Day	8% 7% 24% 31% 26% 6%	485
	11th to 20th	Day	13% 6% 25% 30% 19% 8%	484
	21st to end	Day	9% 5% 29% 37% 14% 6%	532
August	1st to 10th	Day	12% 4 27% 29% 20% 8%	486
	11th to 20th	Day	11% 4 23% 32% 23% 8%	479
	21st to end	Day	12% 6% 25% 32% 17% 9%	539
September	1st to 10th	Day	12% 7% 27% 26% 19% 9%	490
	11th to 20th	Day	10% 6% 22% 25% 22% 16%	490
	21st to end	Day	15% 8% 29% 26% 18% 5%	490
October	1st to 10th	Day	21% 11% 27% 20% 16% 6%	490
	11th to 20th	Day	19% 17% 29% 25% 8% 2	490
	21st to end	Day	28% 14% 27% 23% 6% 1	526
November	1st to 10th	Day	25% 15% 26% 25% 8% 1	336
	11th to 20th	Day	19% 18% 39% 20% 5% 2	200
	21st to end	Day	25% 18% 32% 18% 7% 1	200
December	1st to 10th	Day	26% 16% 35% 16% 8%	200
	11th to 20th	Day	30% 24% 29% 14% 3 1	200
	21st to end	Day	33% 18% 32% 13% 4 1	220
January	1st to 10th	Night	26% 15% 34% 19% 6%	785
	11th to 20th	Night	27% 14% 31% 22% 6%	760
	21st to end	Night	22% 12% 32% 27% 6% 1	836
February	1st to 10th	Night	23% 16% 38% 20% 3	760
	11th to 20th	Night	22% 14% 37% 22% 5%	743
	21st to end	Night	23% 15% 36% 21% 4	628
March	1st to 10th	Night	22% 13% 33% 28% 4 1	760
	11th to 20th	Night	23% 13% 34% 24% 4 1	760
	21st to end	Night	20% 10% 34% 27% 8% 1	836
April	1st to 10th	Night	22% 10% 36% 27% 5%	760
	11th to 20th	Night	20% 12% 33% 23% 10% 1	751
	21st to end	Night	21% 8% 30% 29% 12% 1	613
May	1st to 10th	Night	20% 6% 28% 30% 15% 2	472
	11th to 20th	Night	14% 6% 26% 40% 14%	374
	21st to end	Night	11% 5% 27% 36% 19% 2	411
June	1st to 10th	Night	12% 4 32% 36% 15% 1	380
	11th to 20th	Night	10% 5% 25% 40% 19% 1	380
	21st to end	Night	12% 7% 24% 40% 17% 1	380
July	1st to 10th	Night	7% 4 22% 45% 21% 2	370
	11th to 20th	Night	10% 4 18% 42% 24% 2	368
	21st to end	Night	8% 2 20% 46% 21% 2	455
August	1st to 10th	Night	10% 3 16% 39% 28% 4	567
	11th to 20th	Night	9% 3 16% 38% 29% 4	564
	21st to end	Night	11% 3 20% 36% 27% 3	781
September	1st to 10th	Night	13% 4 22% 34% 24% 3	760
	11th to 20th	Night	13% 4 16% 30% 29% 7%	760
	21st to end	Night	18% 6% 22% 28% 21% 5%	760
October	1st to 10th	Night	19% 7% 27% 26% 19% 3	760
	11th to 20th	Night	22% 10% 29% 28% 9% 1	760
	21st to end	Night	25% 11% 31% 26% 7%	836
November	1st to 10th	Night	21% 12% 27% 28% 11% 1	780
	11th to 20th	Night	21% 15% 32% 24% 6% 2	800
	21st to end	Night	26% 13% 31% 23% 7%	800
December	1st to 10th	Night	27% 17% 31% 20% 5%	800
	11th to 20th	Night	26% 15% 37% 18% 4	800
	21st to end	Night	31% 13% 33% 19% 4	880

Page generated at 2025-01-04 03:23:59. Version ac07

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