Lake Sundown
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lake Sundown clear sky chart from 2005-11-06 to 2024-11-28.

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% 4 4 4 6% 7% 40%	101605
	Night	12% 8% 3 8% 4 4 4 3 5% 6% 43%	98035
Transparency	Day	41% 6% 12% 24% 15% 2	105245
	Night	41% 5% 12% 23% 17% 3	102535
Seeing	Day	16% 10% 29% 27% 15% 4	15861
	Night	16% 10% 32% 30% 12% 1	25722

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% 13% 4 14% 6% 5% 5% 4 5% 6% 27%	2527
	11th to 20th	Day	11% 12% 4 11% 7% 7% 8% 3 6% 6% 25%	2822
	21st to end	Day	14% 16% 7% 16% 6% 4 4 3 4 4 21%	3135
February	1st to 10th	Day	13% 12% 4 10% 7% 5% 5% 4 5% 7% 29%	1710
	11th to 20th	Day	12% 10% 3 8% 5% 5% 5% 3 6% 6% 36%	1664
	21st to end	Day	15% 10% 3 7% 6% 4 3 4 4 7% 37%	1560
March	1st to 10th	Day	16% 11% 4 8% 4 3 3 2 3 5% 41%	3397
	11th to 20th	Day	10% 7% 3 7% 5% 4 4 3 5% 7% 46%	3480
	21st to end	Day	21% 14% 4 9% 4 4 4 3 5% 7% 25%	3861
April	1st to 10th	Day	16% 10% 3 7% 4 4 4 4 5% 6% 37%	2280
	11th to 20th	Day	15% 10% 3 8% 4 4 4 4 6% 5% 38%	2254
	21st to end	Day	21% 7% 3 8% 5% 4 4 3 5% 6% 34%	2323
May	1st to 10th	Day	16% 7% 4 8% 5% 4 4 4 6% 8% 35%	4082
	11th to 20th	Day	16% 8% 3 7% 5% 4 4 3 5% 7% 38%	4362
	21st to end	Day	13% 6% 2 5% 5% 4 5% 3 6% 7% 46%	4824
June	1st to 10th	Day	8% 5% 2 6% 4 4 5% 5% 7% 9% 44%	2660
	11th to 20th	Day	8% 4 2 6% 5% 4 5% 5% 7% 8% 45%	2660
	21st to end	Day	9% 5% 2 6% 5% 5% 5% 5% 7% 8% 42%	2660
July	1st to 10th	Day	9% 8% 3 8% 4 6% 6% 4 7% 9% 36%	4440
	11th to 20th	Day	6% 5% 2 5% 4 4 5% 4 7% 9% 50%	4419
	21st to end	Day	5% 4 2 5% 5% 5% 6% 6% 8% 11% 43%	4465
August	1st to 10th	Day	5% 4 2 6% 4 4 6% 4 8% 10% 45%	4104
	11th to 20th	Day	13% 6% 2 6% 4 5% 5% 4 6% 9% 40%	4017
	21st to end	Day	7% 5% 2 5% 4 4 4 4 6% 8% 51%	4180
September	1st to 10th	Day	13% 5% 2 4 3 4 3 3 5% 7% 52%	2280
	11th to 20th	Day	10% 4 2 5% 3 3 5% 4 6% 8% 50%	2278
	21st to end	Day	10% 6% 2 5% 4 4 4 4 4 6% 51%	1981
October	1st to 10th	Day	14% 6% 2 4 5% 3 4 2 5% 6% 49%	1900
	11th to 20th	Day	15% 7% 2 5% 3 3 3 3 4 5% 49%	1900
	21st to end	Day	15% 9% 3 7% 4 4 3 3 5% 6% 42%	2090
November	1st to 10th	Day	11% 8% 2 5% 4 4 4 4 6% 8% 46%	1829
	11th to 20th	Day	13% 10% 3 8% 3 4 4 3 5% 6% 42%	1664
	21st to end	Day	16% 11% 4 7% 3 3 3 2 6% 7% 39%	1576
December	1st to 10th	Day	12% 13% 4 11% 5% 4 3 3 5% 6% 35%	1520
	11th to 20th	Day	12% 11% 3 8% 4 5% 5% 3 5% 9% 35%	1918
	21st to end	Day	20% 15% 8% 13% 5% 4 4 3 4 5% 19%	2783
January	1st to 10th	Night	11% 11% 5% 18% 6% 5% 4 3 4 6% 28%	4428
	11th to 20th	Night	11% 14% 6% 11% 5% 4 6% 4 7% 5% 26%	4143
	21st to end	Night	16% 15% 6% 14% 4 4 4 3 4 5% 24%	4532
February	1st to 10th	Night	13% 12% 4 10% 5% 4 4 4 5% 6% 34%	2470
	11th to 20th	Night	12% 10% 3 8% 5% 4 4 3 4 6% 41%	2403
	21st to end	Night	13% 10% 4 8% 5% 4 4 2 4 4 41%	1894
March	1st to 10th	Night	16% 11% 2 6% 3 3 3 3 3 5% 44%	3484
	11th to 20th	Night	12% 7% 2 6% 3 3 3 2 4 6% 52%	3480
	21st to end	Night	20% 11% 5% 11% 5% 5% 4 3 4 6% 26%	3768
April	1st to 10th	Night	12% 8% 2 6% 5% 3 4 4 5% 6% 44%	1900
	11th to 20th	Night	12% 9% 2 6% 5% 4 5% 3 5% 6% 43%	1875
	21st to end	Night	17% 7% 3 6% 4 4 4 3 5% 5% 42%	1853
May	1st to 10th	Night	17% 8% 3 6% 4 4 5% 3 5% 6% 38%	2823
	11th to 20th	Night	12% 7% 2 6% 5% 4 5% 3 5% 7% 45%	2543
	21st to end	Night	9% 6% 2 6% 4 4 4 5% 5% 8% 49%	2743
June	1st to 10th	Night	7% 5% 2 5% 3 3 5% 4 7% 10% 49%	1520
	11th to 20th	Night	7% 5% 2 4 4 4 5% 3 5% 10% 51%	1520
	21st to end	Night	7% 5% 2 5% 5% 5% 6% 4 6% 8% 49%	1520
July	1st to 10th	Night	11% 6% 2 5% 4 4 4 4 7% 8% 46%	2530
	11th to 20th	Night	3 3 1 4 3 3 4 3 6% 9% 61%	2547
	21st to end	Night	7% 4 2 5% 4 4 4 4 6% 11% 50%	3098
August	1st to 10th	Night	4 3 1 4 3 3 3 4 6% 8% 60%	2836
	11th to 20th	Night	10% 6% 1 4 3 3 4 3 4 7% 55%	2819
	21st to end	Night	5% 3 2 5% 3 3 4 4 6% 9% 56%	3476
September	1st to 10th	Night	10% 4 1 5% 3 2 3 3 5% 7% 56%	1900
	11th to 20th	Night	10% 4 2 5% 4 4 4 3 5% 6% 53%	1900
	21st to end	Night	9% 4 2 4 3 3 4 3 5% 6% 58%	2177
October	1st to 10th	Night	12% 6% 2 5% 3 4 4 3 4 5% 53%	2280
	11th to 20th	Night	13% 6% 2 6% 3 3 3 3 3 6% 53%	2280
	21st to end	Night	16% 7% 2 6% 4 4 3 3 4 6% 45%	2508
November	1st to 10th	Night	10% 6% 2 5% 2 3 3 3 5% 7% 55%	2469
	11th to 20th	Night	12% 8% 2 6% 4 4 3 3 5% 6% 45%	2734
	21st to end	Night	16% 11% 4 6% 4 3 3 3 4 5% 42%	2759
December	1st to 10th	Night	12% 11% 3 9% 5% 4 4 3 4 6% 40%	2660
	11th to 20th	Night	13% 10% 3 9% 5% 3 4 3 4 5% 41%	3279
	21st to end	Night	19% 16% 8% 11% 6% 4 3 3 3 4 23%	4884

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% 14% 15% 8% 1	2528
	11th to 20th	Day	59% 6% 10% 18% 8%	2822
	21st to end	Day	67% 5% 9% 13% 6%	3135
February	1st to 10th	Day	54% 6% 12% 17% 10% 1	1710
	11th to 20th	Day	48% 5% 13% 22% 11% 1	1673
	21st to end	Day	47% 4 12% 23% 11% 2	1560
March	1st to 10th	Day	47% 5% 9% 21% 17% 1	3397
	11th to 20th	Day	37% 6% 14% 23% 19% 1	3480
	21st to end	Day	57% 8% 15% 15% 4 1	3861
April	1st to 10th	Day	47% 5% 11% 26% 10%	2280
	11th to 20th	Day	46% 6% 10% 23% 13% 1	2254
	21st to end	Day	51% 5% 11% 20% 12% 1	2323
May	1st to 10th	Day	46% 8% 12% 19% 14% 1	4120
	11th to 20th	Day	46% 6% 10% 28% 10%	4366
	21st to end	Day	37% 6% 10% 27% 19% 1	4837
June	1st to 10th	Day	33% 8% 17% 27% 13% 2	2660
	11th to 20th	Day	32% 8% 13% 23% 20% 2	2660
	21st to end	Day	36% 8% 15% 24% 14% 2	2660
July	1st to 10th	Day	41% 8% 13% 25% 11% 2	4371
	11th to 20th	Day	28% 7% 15% 31% 18% 2	4344
	21st to end	Day	29% 12% 18% 26% 15% 1	4325
August	1st to 10th	Day	31% 8% 15% 32% 14% 1	4090
	11th to 20th	Day	39% 6% 14% 24% 16% 1	4056
	21st to end	Day	30% 6% 16% 30% 15% 4	4179
September	1st to 10th	Day	32% 5% 11% 26% 22% 4	2280
	11th to 20th	Day	30% 6% 10% 31% 20% 3	2278
	21st to end	Day	34% 6% 10% 29% 20% 2	1981
October	1st to 10th	Day	24% 3 5% 18% 47% 3	3160
	11th to 20th	Day	25% 3 8% 25% 31% 8%	3140
	21st to end	Day	39% 5% 9% 27% 19% 2	3428
November	1st to 10th	Day	34% 5% 15% 23% 19% 3	1829
	11th to 20th	Day	43% 4 10% 24% 17% 2	1664
	21st to end	Day	46% 4 14% 22% 13%	1576
December	1st to 10th	Day	51% 5% 13% 22% 9% 1	1520
	11th to 20th	Day	46% 5% 13% 24% 10% 1	1915
	21st to end	Day	69% 5% 7% 13% 5% 1	2783
January	1st to 10th	Night	58% 5% 9% 18% 9% 1	4428
	11th to 20th	Night	58% 3 12% 14% 11% 1	4143
	21st to end	Night	62% 4 11% 15% 7% 1	4532
February	1st to 10th	Night	51% 4 12% 20% 11% 2	2470
	11th to 20th	Night	44% 5% 11% 25% 13% 2	2404
	21st to end	Night	47% 4 9% 22% 16% 4	1894
March	1st to 10th	Night	44% 4 10% 24% 18% 1	3484
	11th to 20th	Night	34% 5% 10% 30% 16% 5%	3480
	21st to end	Night	59% 7% 17% 13% 5%	3768
April	1st to 10th	Night	39% 6% 12% 26% 15% 3	1900
	11th to 20th	Night	42% 5% 9% 24% 15% 4	1875
	21st to end	Night	44% 5% 13% 22% 15% 2	1853
May	1st to 10th	Night	45% 7% 12% 19% 15% 1	2850
	11th to 20th	Night	38% 8% 14% 25% 14% 1	2544
	21st to end	Night	33% 8% 12% 22% 24% 2	2751
June	1st to 10th	Night	28% 9% 17% 27% 17% 2	1520
	11th to 20th	Night	28% 7% 13% 27% 20% 4	1520
	21st to end	Night	30% 7% 15% 25% 19% 3	1520
July	1st to 10th	Night	34% 7% 13% 29% 13% 4	2490
	11th to 20th	Night	19% 6% 18% 34% 22% 2	2499
	21st to end	Night	27% 9% 20% 24% 19% 2	2999
August	1st to 10th	Night	21% 7% 17% 35% 18% 1	2826
	11th to 20th	Night	30% 5% 14% 31% 19% 1	2846
	21st to end	Night	24% 6% 16% 32% 17% 6%	3476
September	1st to 10th	Night	28% 5% 9% 26% 25% 6%	1900
	11th to 20th	Night	32% 4 10% 29% 20% 4	1900
	21st to end	Night	27% 4 11% 31% 24% 3	2177
October	1st to 10th	Night	23% 4 6% 19% 45% 4	3800
	11th to 20th	Night	26% 3 8% 23% 30% 9%	3779
	21st to end	Night	41% 4 8% 22% 21% 3	4120
November	1st to 10th	Night	29% 4 16% 26% 20% 4	2469
	11th to 20th	Night	39% 5% 11% 27% 16% 2	2734
	21st to end	Night	46% 3 10% 25% 14% 2	2759
December	1st to 10th	Night	46% 5% 12% 25% 11% 1	2660
	11th to 20th	Night	47% 4 11% 27% 11% 1	3281
	21st to end	Night	67% 4 7% 14% 6% 1	4884

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	24% 11% 33% 24% 8%	270
	11th to 20th	Day	24% 17% 40% 18% 1	270
	21st to end	Day	21% 17% 39% 20% 3	297
February	1st to 10th	Day	21% 19% 38% 17% 4	270
	11th to 20th	Day	20% 17% 38% 19% 6%	270
	21st to end	Day	20% 16% 45% 14% 4	225
March	1st to 10th	Day	20% 16% 46% 14% 3	270
	11th to 20th	Day	22% 15% 34% 23% 4	270
	21st to end	Day	38% 13% 32% 13% 3 1	319
April	1st to 10th	Day	23% 15% 36% 20% 5% 1	460
	11th to 20th	Day	21% 16% 33% 21% 8% 1	452
	21st to end	Day	23% 15% 36% 18% 7% 1	503
May	1st to 10th	Day	22% 14% 34% 20% 9% 1	653
	11th to 20th	Day	20% 11% 29% 25% 12% 2	675
	21st to end	Day	15% 8% 30% 28% 15% 4	734
June	1st to 10th	Day	7% 4 25% 34% 23% 7%	680
	11th to 20th	Day	8% 7% 28% 35% 19% 3	680
	21st to end	Day	9% 9% 34% 30% 15% 3	680
July	1st to 10th	Day	7% 4 18% 32% 26% 13%	671
	11th to 20th	Day	8% 2 25% 35% 23% 7%	668
	21st to end	Day	7% 3 21% 37% 27% 5%	739
August	1st to 10th	Day	8% 2 21% 37% 26% 6%	676
	11th to 20th	Day	11% 4 19% 32% 26% 7%	654
	21st to end	Day	10% 2 16% 37% 26% 9%	539
September	1st to 10th	Day	14% 5% 17% 32% 24% 8%	490
	11th to 20th	Day	9% 3 22% 34% 23% 8%	488
	21st to end	Day	12% 10% 28% 25% 20% 5%	300
October	1st to 10th	Day	20% 7% 29% 24% 13% 7%	300
	11th to 20th	Day	17% 19% 36% 20% 7% 1	300
	21st to end	Day	22% 20% 32% 18% 6% 1	330
November	1st to 10th	Day	18% 9% 40% 25% 6% 2	300
	11th to 20th	Day	21% 17% 34% 19% 7% 2	300
	21st to end	Day	23% 16% 36% 20% 4	291
December	1st to 10th	Day	15% 13% 42% 20% 7% 3	270
	11th to 20th	Day	19% 15% 37% 21% 6% 1	270
	21st to end	Day	27% 22% 32% 16% 2	297
January	1st to 10th	Night	16% 14% 42% 20% 8%	950
	11th to 20th	Night	16% 16% 40% 20% 7%	950
	21st to end	Night	18% 14% 39% 25% 4	1045
February	1st to 10th	Night	20% 13% 40% 23% 4	950
	11th to 20th	Night	19% 13% 38% 27% 3	929
	21st to end	Night	20% 15% 39% 22% 3 1	638
March	1st to 10th	Night	18% 13% 40% 22% 7% 1	613
	11th to 20th	Night	20% 12% 33% 28% 7%	570
	21st to end	Night	27% 11% 35% 22% 5%	627
April	1st to 10th	Night	16% 15% 41% 25% 4	570
	11th to 20th	Night	18% 15% 34% 27% 6% 1	563
	21st to end	Night	20% 11% 33% 27% 8% 1	570
May	1st to 10th	Night	17% 8% 36% 32% 7% 1	570
	11th to 20th	Night	17% 8% 32% 29% 13% 1	561
	21st to end	Night	14% 5% 28% 35% 17% 1	617
June	1st to 10th	Night	9% 3 26% 41% 19% 2	570
	11th to 20th	Night	8% 4 26% 43% 18% 1	570
	21st to end	Night	8% 4 31% 41% 15% 1	570
July	1st to 10th	Night	8% 2 14% 40% 33% 3	555
	11th to 20th	Night	4 2 19% 45% 27% 3	552
	21st to end	Night	8% 2 16% 45% 28% 1	624
August	1st to 10th	Night	7% 2 16% 46% 27% 2	567
	11th to 20th	Night	9% 2 14% 43% 28% 4	564
	21st to end	Night	7% 2 14% 44% 30% 3	627
September	1st to 10th	Night	11% 4 19% 37% 27% 2	570
	11th to 20th	Night	12% 2 20% 38% 24% 4	570
	21st to end	Night	11% 6% 26% 35% 20% 2	659
October	1st to 10th	Night	14% 7% 30% 31% 17% 2	760
	11th to 20th	Night	16% 12% 35% 30% 8%	760
	21st to end	Night	18% 12% 35% 27% 8%	836
November	1st to 10th	Night	14% 10% 37% 32% 7%	780
	11th to 20th	Night	17% 15% 40% 22% 5%	934
	21st to end	Night	22% 13% 35% 24% 6%	986
December	1st to 10th	Night	18% 14% 38% 23% 6% 1	950
	11th to 20th	Night	19% 12% 36% 26% 5% 1	950
	21st to end	Night	21% 17% 37% 22% 3	1045

Page generated at 2024-11-24 23:22:17. Version ac07

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