Waldo Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Waldo Lake clear sky chart from 2005-11-06 to 2026-08-30.

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	6% 11% 4 8% 4 4 4 3 4 5% 47%	153316
	Night	6% 12% 5% 10% 5% 5% 4 3 5% 5% 40%	146238
Transparency	Day	37% 6% 9% 19% 18% 10%	148147
	Night	43% 7% 9% 16% 16% 9%	142415
Seeing	Day	19% 19% 27% 21% 11% 2	17037
	Night	16% 15% 21% 30% 17% 1	26000

By Month

Percentage Cloud Cover SW (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	7% 21% 9% 18% 8% 6% 5% 3 4 4 14%	4722
	11th to 20th	Day	7% 11% 4 8% 3 2 2 2 4 5% 51%	4740
	21st to end	Day	8% 15% 4 8% 6% 6% 6% 4 5% 5% 34%	5783
February	1st to 10th	Day	9% 19% 7% 11% 6% 6% 4 5% 5% 6% 22%	1890
	11th to 20th	Day	8% 19% 8% 12% 7% 5% 4 3 5% 5% 24%	1845
	21st to end	Day	7% 23% 9% 13% 6% 4 4 4 5% 5% 22%	1704
March	1st to 10th	Day	6% 16% 8% 14% 6% 4 4 4 5% 7% 27%	4788
	11th to 20th	Day	6% 21% 7% 12% 6% 5% 4 2 3 4 30%	5110
	21st to end	Day	6% 22% 9% 14% 7% 6% 5% 3 5% 6% 17%	5778
April	1st to 10th	Day	9% 23% 8% 11% 6% 5% 4 4 4 4 21%	2520
	11th to 20th	Day	9% 20% 6% 10% 6% 4 4 3 5% 4 30%	2489
	21st to end	Day	6% 20% 5% 8% 5% 4 4 3 5% 7% 32%	2620
May	1st to 10th	Day	7% 11% 5% 6% 4 4 4 3 5% 6% 45%	8021
	11th to 20th	Day	4 10% 5% 10% 5% 4 4 3 4 6% 45%	8160
	21st to end	Day	7% 9% 3 6% 4 4 4 3 6% 8% 45%	8992
June	1st to 10th	Day	13% 12% 3 7% 5% 3 4 3 5% 6% 40%	2940
	11th to 20th	Day	8% 13% 2 7% 4 4 5% 3 5% 6% 44%	2940
	21st to end	Day	6% 5% 2 4 3 3 3 3 5% 6% 61%	2940
July	1st to 10th	Day	1 1 1 2 2 2 2 2 2 3 81%	8219
	11th to 20th	Day	3 2 1 3 2 2 2 2 3 3 77%	8220
	21st to end	Day	2 2 1 2 2 2 2 2 3 3 79%	8892
August	1st to 10th	Day	3 3 1 3 2 2 3 2 5% 6% 70%	5907
	11th to 20th	Day	2 2 1 3 3 3 3 3 4 6% 71%	5926
	21st to end	Day	5% 4 1 4 3 3 3 3 5% 6% 64%	6107
September	1st to 10th	Day	3 3 1 4 2 3 3 2 3 6% 68%	2400
	11th to 20th	Day	7% 7% 2 6% 4 4 3 3 5% 6% 54%	2400
	21st to end	Day	8% 7% 2 5% 3 3 3 3 5% 5% 55%	2120
October	1st to 10th	Day	6% 7% 1 5% 2 3 3 2 4 5% 61%	3280
	11th to 20th	Day	7% 10% 4 7% 5% 6% 5% 4 6% 7% 40%	3261
	21st to end	Day	8% 11% 5% 11% 6% 6% 6% 4 5% 6% 32%	3494
November	1st to 10th	Day	13% 19% 4 9% 6% 5% 4 4 5% 6% 26%	1848
	11th to 20th	Day	10% 20% 5% 10% 5% 6% 5% 3 5% 7% 22%	1680
	21st to end	Day	8% 19% 6% 10% 6% 6% 5% 3 5% 5% 29%	1680
December	1st to 10th	Day	6% 10% 4 8% 5% 5% 5% 4 6% 6% 42%	2700
	11th to 20th	Day	10% 20% 6% 14% 7% 7% 6% 4 6% 6% 16%	3108
	21st to end	Day	8% 19% 8% 15% 8% 8% 7% 4 5% 5% 14%	4092
January	1st to 10th	Night	7% 20% 7% 15% 9% 8% 7% 4 5% 5% 13%	8172
	11th to 20th	Night	5% 12% 5% 10% 4 3 3 3 5% 6% 45%	8220
	21st to end	Night	9% 14% 5% 11% 6% 6% 4 3 4 4 35%	8414
February	1st to 10th	Night	6% 17% 7% 12% 8% 6% 6% 4 6% 5% 23%	2730
	11th to 20th	Night	7% 16% 8% 13% 7% 6% 6% 3 5% 5% 23%	2662
	21st to end	Night	6% 19% 7% 14% 6% 6% 4 4 4 5% 24%	2100
March	1st to 10th	Night	5% 14% 7% 15% 7% 6% 7% 5% 6% 7% 22%	5321
	11th to 20th	Night	4 14% 6% 14% 7% 6% 6% 3 4 4 30%	5110
	21st to end	Night	5% 18% 7% 15% 9% 9% 7% 3 5% 5% 16%	5438
April	1st to 10th	Night	8% 20% 8% 13% 6% 5% 4 3 4 6% 23%	2100
	11th to 20th	Night	7% 17% 8% 12% 6% 5% 5% 3 6% 5% 27%	2079
	21st to end	Night	7% 19% 6% 10% 5% 5% 4 4 6% 6% 28%	1995
May	1st to 10th	Night	8% 9% 7% 8% 3 4 3 3 4 6% 45%	4904
	11th to 20th	Night	4 10% 7% 13% 6% 5% 5% 4 5% 6% 36%	4700
	21st to end	Night	7% 13% 4 7% 4 4 4 3 5% 8% 42%	5181
June	1st to 10th	Night	11% 14% 3 7% 4 4 4 4 4 6% 38%	1680
	11th to 20th	Night	6% 13% 4 6% 4 4 4 4 6% 6% 44%	1680
	21st to end	Night	5% 4 2 5% 3 3 4 3 5% 6% 59%	1680
July	1st to 10th	Night	2 2 1 2 3 2 2 2 3 5% 75%	4740
	11th to 20th	Night	2 3 1 3 2 2 2 2 2 3 78%	4740
	21st to end	Night	2 2 1 2 2 2 2 2 3 4 79%	5169
August	1st to 10th	Night	1 3 2 5% 3 3 3 3 5% 7% 65%	4125
	11th to 20th	Night	3 3 2 5% 3 3 4 3 5% 6% 66%	4142
	21st to end	Night	5% 3 1 5% 4 3 3 3 5% 5% 64%	5076
September	1st to 10th	Night	3 4 2 4 2 2 2 2 5% 5% 70%	2000
	11th to 20th	Night	4 6% 2 7% 4 4 4 4 5% 6% 54%	2000
	21st to end	Night	7% 7% 2 6% 4 4 4 3 5% 5% 54%	2276
October	1st to 10th	Night	4 7% 2 6% 3 3 3 2 3 5% 63%	3920
	11th to 20th	Night	7% 9% 3 7% 5% 4 5% 4 6% 7% 44%	3897
	21st to end	Night	6% 11% 5% 13% 7% 7% 7% 4 4 6% 31%	4315
November	1st to 10th	Night	11% 18% 5% 11% 6% 5% 4 4 5% 6% 25%	2670
	11th to 20th	Night	11% 19% 5% 9% 7% 6% 5% 4 5% 5% 23%	2940
	21st to end	Night	6% 16% 5% 10% 6% 5% 5% 4 5% 6% 31%	2940
December	1st to 10th	Night	6% 9% 3 8% 5% 5% 5% 4 5% 7% 44%	4700
	11th to 20th	Night	8% 21% 7% 14% 7% 7% 5% 4 5% 6% 16%	5316
	21st to end	Night	11% 18% 7% 15% 7% 6% 5% 4 4 4 18%	7106

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	67% 9% 8% 9% 5% 2	4723
	11th to 20th	Day	36% 4 6% 12% 21% 21%	4740
	21st to end	Day	50% 6% 6% 10% 17% 10%	5783
February	1st to 10th	Day	58% 7% 10% 14% 8% 1	1890
	11th to 20th	Day	59% 7% 9% 13% 8% 3	1854
	21st to end	Day	63% 7% 9% 10% 7% 3	1704
March	1st to 10th	Day	51% 8% 9% 19% 11% 2	4788
	11th to 20th	Day	56% 6% 8% 18% 11% 1	5110
	21st to end	Day	61% 12% 12% 10% 4	5778
April	1st to 10th	Day	62% 8% 10% 12% 6% 1	2520
	11th to 20th	Day	54% 8% 11% 15% 10% 3	2492
	21st to end	Day	49% 9% 12% 17% 11% 1	2620
May	1st to 10th	Day	34% 8% 9% 25% 21% 3	8021
	11th to 20th	Day	38% 4 13% 27% 18% 1	8163
	21st to end	Day	32% 8% 18% 30% 10% 2	8994
June	1st to 10th	Day	43% 7% 14% 24% 11% 1	2940
	11th to 20th	Day	36% 7% 13% 25% 16% 3	2940
	21st to end	Day	24% 4 11% 30% 23% 7%	2940
July	1st to 10th	Day	10% 2 5% 21% 33% 30%	8151
	11th to 20th	Day	14% 2 3 10% 25% 46%	8145
	21st to end	Day	12% 3 3 26% 37% 20%	8693
August	1st to 10th	Day	16% 3 6% 20% 34% 22%	4336
	11th to 20th	Day	16% 3 6% 31% 33% 11%	4325
	21st to end	Day	18% 3 7% 28% 26% 19%	4434
September	1st to 10th	Day	18% 3 6% 23% 32% 18%	2400
	11th to 20th	Day	29% 5% 10% 24% 22% 10%	2400
	21st to end	Day	30% 5% 9% 23% 23% 10%	2120
October	1st to 10th	Day	26% 4 8% 17% 32% 13%	3280
	11th to 20th	Day	39% 6% 14% 24% 15% 3	3261
	21st to end	Day	49% 6% 9% 18% 16% 3	3494
November	1st to 10th	Day	57% 7% 10% 13% 11% 2	1848
	11th to 20th	Day	59% 8% 9% 11% 9% 3	1680
	21st to end	Day	55% 6% 8% 12% 14% 5%	1680
December	1st to 10th	Day	39% 6% 8% 16% 19% 11%	2700
	11th to 20th	Day	66% 8% 9% 10% 6% 1	3108
	21st to end	Day	67% 9% 9% 9% 4 1	4092
January	1st to 10th	Night	65% 11% 8% 9% 5% 1	8172
	11th to 20th	Night	37% 5% 5% 14% 18% 21%	8220
	21st to end	Night	52% 5% 5% 7% 15% 16%	8414
February	1st to 10th	Night	56% 10% 10% 12% 10% 2	2730
	11th to 20th	Night	59% 9% 9% 12% 8% 4	2664
	21st to end	Night	59% 8% 8% 12% 11% 2	2100
March	1st to 10th	Night	52% 10% 11% 16% 7% 4	5321
	11th to 20th	Night	54% 7% 9% 18% 12%	5110
	21st to end	Night	62% 13% 9% 13% 3 1	5438
April	1st to 10th	Night	59% 10% 12% 12% 7%	2100
	11th to 20th	Night	55% 9% 10% 14% 9% 2	2079
	21st to end	Night	51% 10% 12% 15% 11% 1	1995
May	1st to 10th	Night	35% 7% 10% 25% 22% 2	4902
	11th to 20th	Night	42% 7% 10% 22% 18% 1	4700
	21st to end	Night	35% 9% 17% 30% 8% 1	5182
June	1st to 10th	Night	44% 8% 11% 25% 11% 1	1680
	11th to 20th	Night	36% 7% 13% 26% 14% 3	1680
	21st to end	Night	25% 6% 11% 30% 21% 7%	1680
July	1st to 10th	Night	13% 2 5% 22% 30% 28%	4700
	11th to 20th	Night	14% 2 3 11% 26% 45%	4692
	21st to end	Night	12% 2 3 26% 38% 18%	5056
August	1st to 10th	Night	17% 3 5% 18% 38% 20%	3019
	11th to 20th	Night	17% 3 7% 29% 33% 10%	3019
	21st to end	Night	18% 4 7% 26% 26% 18%	3682
September	1st to 10th	Night	16% 3 8% 23% 33% 17%	2000
	11th to 20th	Night	28% 6% 9% 20% 25% 11%	2000
	21st to end	Night	30% 5% 10% 20% 21% 13%	2276
October	1st to 10th	Night	26% 4 7% 18% 32% 14%	3920
	11th to 20th	Night	38% 6% 15% 23% 14% 5%	3897
	21st to end	Night	53% 6% 8% 13% 17% 4	4315
November	1st to 10th	Night	56% 8% 11% 11% 11% 3	2670
	11th to 20th	Night	60% 8% 10% 11% 9% 3	2940
	21st to end	Night	51% 7% 9% 11% 14% 7%	2940
December	1st to 10th	Night	37% 6% 7% 14% 24% 11%	4700
	11th to 20th	Night	65% 9% 9% 10% 6% 1	5316
	21st to end	Night	64% 8% 9% 11% 6% 1	7106

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	40% 20% 22% 12% 6%	220
	11th to 20th	Day	30% 15% 23% 19% 7% 6%	220
	21st to end	Day	25% 20% 22% 20% 10% 2	452
February	1st to 10th	Day	26% 23% 27% 14% 10%	430
	11th to 20th	Day	28% 29% 23% 15% 4 1	425
	21st to end	Day	33% 20% 25% 18% 4	432
March	1st to 10th	Day	29% 25% 26% 17% 3	540
	11th to 20th	Day	27% 24% 23% 20% 6%	540
	21st to end	Day	34% 26% 24% 12% 4	594
April	1st to 10th	Day	29% 23% 23% 18% 6% 2	540
	11th to 20th	Day	29% 23% 27% 14% 5% 1	532
	21st to end	Day	23% 24% 29% 16% 7% 1	540
May	1st to 10th	Day	21% 22% 28% 19% 8% 1	543
	11th to 20th	Day	29% 19% 23% 17% 9% 2	568
	21st to end	Day	20% 18% 29% 18% 12% 3	617
June	1st to 10th	Day	18% 21% 27% 20% 11% 4	570
	11th to 20th	Day	18% 23% 27% 24% 7% 2	570
	21st to end	Day	9% 18% 27% 29% 15% 2	570
July	1st to 10th	Day	5% 12% 39% 26% 15% 4	566
	11th to 20th	Day	3 17% 35% 26% 16% 3	564
	21st to end	Day	4 12% 36% 25% 18% 5%	619
August	1st to 10th	Day	3 13% 35% 26% 17% 5%	567
	11th to 20th	Day	5% 12% 28% 30% 18% 8%	557
	21st to end	Day	9% 12% 31% 27% 15% 5%	620
September	1st to 10th	Day	5% 13% 32% 27% 20% 3	530
	11th to 20th	Day	12% 14% 29% 28% 15% 3	530
	21st to end	Day	13% 18% 26% 27% 15% 2	530
October	1st to 10th	Day	18% 17% 27% 21% 15% 2	530
	11th to 20th	Day	22% 15% 23% 21% 18% 1	530
	21st to end	Day	24% 21% 24% 18% 12% 2	543
November	1st to 10th	Day	27% 17% 22% 24% 9% 2	326
	11th to 20th	Day	25% 18% 26% 20% 10% 1	220
	21st to end	Day	23% 18% 22% 25% 10% 2	220
December	1st to 10th	Day	25% 19% 23% 19% 12% 3	220
	11th to 20th	Day	30% 23% 22% 17% 7%	220
	21st to end	Day	33% 22% 19% 16% 9% 1	242
January	1st to 10th	Night	26% 20% 25% 20% 8% 1	840
	11th to 20th	Night	22% 17% 20% 26% 13% 2	840
	21st to end	Night	19% 17% 21% 30% 12% 2	924
February	1st to 10th	Night	18% 19% 27% 27% 8% 1	840
	11th to 20th	Night	18% 21% 26% 26% 8%	824
	21st to end	Night	20% 19% 27% 27% 6%	692
March	1st to 10th	Night	20% 23% 22% 24% 9% 1	840
	11th to 20th	Night	20% 18% 23% 28% 10% 1	840
	21st to end	Night	22% 23% 25% 23% 8%	924
April	1st to 10th	Night	21% 19% 22% 26% 11% 1	840
	11th to 20th	Night	15% 25% 24% 23% 12% 1	831
	21st to end	Night	16% 20% 25% 26% 12% 1	735
May	1st to 10th	Night	17% 14% 20% 31% 16% 1	484
	11th to 20th	Night	17% 14% 20% 29% 20% 1	414
	21st to end	Night	16% 13% 18% 32% 20% 1	455
June	1st to 10th	Night	18% 11% 17% 31% 22% 1	420
	11th to 20th	Night	11% 12% 22% 33% 21% 1	420
	21st to end	Night	10% 5% 18% 42% 25% 1	420
July	1st to 10th	Night	4 5% 14% 46% 29% 2	410
	11th to 20th	Night	2 3 18% 50% 25%	408
	21st to end	Night	1 2 13% 47% 36% 1	464
August	1st to 10th	Night	2 2 11% 38% 43% 4	627
	11th to 20th	Night	4 2 9% 40% 39% 5%	624
	21st to end	Night	4 4 21% 41% 28% 1	900
September	1st to 10th	Night	5% 4 18% 42% 29% 3	800
	11th to 20th	Night	8% 6% 16% 37% 31% 3	800
	21st to end	Night	10% 8% 16% 38% 25% 3	800
October	1st to 10th	Night	12% 9% 24% 32% 20% 3	800
	11th to 20th	Night	15% 12% 16% 34% 21% 1	800
	21st to end	Night	19% 15% 19% 27% 17% 3	880
November	1st to 10th	Night	22% 18% 21% 28% 11% 1	820
	11th to 20th	Night	23% 21% 20% 25% 10%	840
	21st to end	Night	16% 20% 24% 28% 11% 1	840
December	1st to 10th	Night	21% 16% 22% 27% 13% 1	840
	11th to 20th	Night	24% 20% 21% 25% 9% 1	840
	21st to end	Night	26% 24% 24% 20% 6% 1	924

Page generated at 2026-08-27 01:07:12. Version ac07

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