Mew Lake Campground
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mew Lake Campground clear sky chart from 2005-11-06 to 2025-07-21.

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	16% 13% 5% 10% 5% 5% 4 3 5% 6% 29%	121080
	Night	14% 14% 5% 11% 6% 5% 4 3 4 5% 27%	117999
Transparency	Day	56% 5% 9% 19% 9% 1	124675
	Night	58% 5% 10% 17% 9% 1	122566
Seeing	Day	24% 18% 31% 18% 7% 2	15674
	Night	23% 16% 31% 21% 8% 1	24419

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	11% 16% 7% 18% 9% 8% 7% 3 5% 4 13%	3597
	11th to 20th	Day	9% 18% 8% 19% 10% 7% 4 4 4 4 12%	3570
	21st to end	Day	12% 20% 11% 16% 6% 5% 4 3 3 4 17%	4466
February	1st to 10th	Day	10% 18% 8% 15% 10% 6% 4 3 4 4 17%	1800
	11th to 20th	Day	10% 16% 8% 14% 8% 6% 5% 3 5% 5% 21%	1753
	21st to end	Day	14% 18% 5% 13% 8% 5% 5% 4 4 5% 19%	1525
March	1st to 10th	Day	16% 16% 5% 13% 5% 5% 3 3 5% 5% 24%	4838
	11th to 20th	Day	10% 15% 6% 12% 6% 5% 4 4 5% 6% 26%	4980
	21st to end	Day	15% 16% 6% 9% 4 4 3 2 3 4 33%	5505
April	1st to 10th	Day	19% 17% 5% 8% 4 3 4 3 4 6% 27%	2400
	11th to 20th	Day	20% 13% 5% 8% 4 4 3 3 4 4 34%	2435
	21st to end	Day	20% 15% 4 8% 4 3 4 2 3 5% 32%	2600
May	1st to 10th	Day	19% 11% 3 7% 5% 4 4 3 5% 6% 31%	6159
	11th to 20th	Day	15% 11% 3 7% 5% 4 4 3 4 7% 37%	6318
	21st to end	Day	21% 10% 3 7% 4 4 3 3 4 6% 34%	6949
June	1st to 10th	Day	20% 11% 3 7% 5% 4 4 4 6% 7% 29%	2800
	11th to 20th	Day	15% 8% 3 6% 5% 4 5% 5% 5% 8% 37%	2924
	21st to end	Day	19% 8% 2 7% 5% 5% 5% 4 5% 8% 31%	3000
July	1st to 10th	Day	16% 7% 2 7% 6% 6% 5% 5% 7% 8% 32%	4860
	11th to 20th	Day	14% 7% 2 6% 4 5% 5% 5% 6% 7% 38%	4580
	21st to end	Day	11% 7% 3 6% 4 4 4 4 5% 8% 44%	4785
August	1st to 10th	Day	15% 7% 3 8% 5% 6% 6% 4 6% 8% 31%	4104
	11th to 20th	Day	19% 8% 2 7% 5% 5% 5% 5% 7% 6% 33%	4044
	21st to end	Day	11% 6% 2 6% 5% 6% 5% 4 7% 9% 40%	4340
September	1st to 10th	Day	16% 8% 2 5% 4 4 5% 4 6% 7% 38%	2280
	11th to 20th	Day	16% 6% 3 6% 4 4 3 4 5% 6% 43%	2239
	21st to end	Day	20% 10% 3 7% 5% 4 5% 3 4 7% 33%	2009
October	1st to 10th	Day	20% 10% 4 7% 4 4 5% 3 4 6% 32%	1900
	11th to 20th	Day	23% 18% 4 8% 5% 5% 4 2 4 5% 21%	1900
	21st to end	Day	27% 17% 5% 9% 5% 4 3 2 4 4 18%	2064
November	1st to 10th	Day	16% 17% 4 9% 5% 4 4 3 5% 7% 26%	1610
	11th to 20th	Day	16% 19% 6% 14% 5% 5% 4 2 4 5% 20%	1600
	21st to end	Day	19% 22% 9% 13% 5% 5% 4 3 4 3 13%	1600
December	1st to 10th	Day	15% 24% 10% 17% 6% 5% 4 2 4 4 10%	2600
	11th to 20th	Day	14% 24% 8% 14% 7% 4 3 2 3 3 18%	2986
	21st to end	Day	18% 21% 9% 15% 7% 3 3 2 3 4 15%	3960
January	1st to 10th	Night	11% 19% 9% 18% 8% 8% 5% 3 4 3 13%	6349
	11th to 20th	Night	8% 17% 7% 21% 12% 9% 5% 3 4 4 11%	6297
	21st to end	Night	10% 18% 10% 19% 6% 7% 6% 3 4 4 13%	6490
February	1st to 10th	Night	10% 17% 7% 14% 8% 7% 5% 4 5% 6% 17%	2600
	11th to 20th	Night	9% 16% 8% 14% 7% 6% 5% 4 5% 5% 23%	2533
	21st to end	Night	10% 18% 6% 14% 7% 7% 5% 3 5% 5% 20%	2105
March	1st to 10th	Night	14% 15% 5% 12% 6% 5% 4 4 4 5% 26%	4998
	11th to 20th	Night	8% 14% 6% 11% 6% 5% 6% 4 6% 8% 25%	4979
	21st to end	Night	15% 14% 6% 10% 6% 4 4 3 4 5% 29%	5426
April	1st to 10th	Night	19% 16% 5% 8% 4 4 4 2 4 6% 29%	2000
	11th to 20th	Night	17% 12% 5% 7% 4 4 4 3 4 5% 36%	1932
	21st to end	Night	20% 10% 4 9% 5% 4 4 4 4 5% 31%	1800
May	1st to 10th	Night	19% 10% 3 6% 4 4 4 4 6% 7% 32%	3782
	11th to 20th	Night	14% 9% 2 5% 4 4 4 3 5% 8% 42%	3575
	21st to end	Night	18% 10% 2 7% 4 4 4 3 5% 6% 35%	3926
June	1st to 10th	Night	17% 10% 3 6% 5% 4 6% 4 5% 7% 34%	1600
	11th to 20th	Night	15% 6% 2 5% 4 3 5% 3 5% 8% 44%	1470
	21st to end	Night	15% 10% 3 7% 5% 5% 4 4 6% 7% 36%	1400
July	1st to 10th	Night	12% 9% 2 8% 5% 4 4 4 5% 6% 41%	2310
	11th to 20th	Night	16% 8% 3 6% 3 4 4 3 4 6% 44%	2600
	21st to end	Night	11% 7% 2 5% 4 3 4 4 5% 7% 47%	2765
August	1st to 10th	Night	12% 4 2 5% 4 4 4 5% 7% 8% 45%	2825
	11th to 20th	Night	17% 8% 2 6% 4 4 5% 3 4 5% 41%	2785
	21st to end	Night	14% 4 2 5% 4 4 4 3 6% 8% 47%	3283
September	1st to 10th	Night	12% 6% 2 6% 3 4 4 4 5% 7% 46%	1900
	11th to 20th	Night	14% 9% 2 5% 4 3 3 2 5% 7% 47%	1938
	21st to end	Night	18% 8% 3 7% 4 4 3 3 4 7% 39%	2171
October	1st to 10th	Night	19% 11% 3 6% 4 4 4 4 5% 6% 36%	2280
	11th to 20th	Night	22% 15% 3 8% 4 4 4 3 4 5% 26%	2280
	21st to end	Night	24% 17% 5% 9% 5% 4 3 3 4 5% 22%	2532
November	1st to 10th	Night	16% 16% 5% 9% 4 4 4 3 5% 5% 28%	2684
	11th to 20th	Night	15% 17% 5% 10% 6% 5% 4 3 5% 6% 23%	2800
	21st to end	Night	17% 23% 7% 12% 7% 5% 4 3 4 5% 15%	2800
December	1st to 10th	Night	15% 24% 8% 17% 9% 5% 4 3 4 3 9%	4580
	11th to 20th	Night	14% 21% 8% 15% 7% 5% 4 3 3 4 17%	5208
	21st to end	Night	18% 22% 7% 15% 7% 4 4 3 3 4 13%	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	75% 4 7% 9% 6%	3598
	11th to 20th	Day	74% 5% 6% 8% 7% 1	3600
	21st to end	Day	72% 3 5% 10% 8% 2	4466
February	1st to 10th	Day	70% 4 6% 13% 7% 1	1800
	11th to 20th	Day	65% 4 10% 12% 9% 1	1762
	21st to end	Day	67% 4 7% 12% 9% 1	1525
March	1st to 10th	Day	62% 4 10% 8% 14% 2	4841
	11th to 20th	Day	58% 5% 13% 15% 7% 2	4980
	21st to end	Day	56% 4 7% 18% 14% 2	5505
April	1st to 10th	Day	59% 4 8% 17% 9% 2	2400
	11th to 20th	Day	55% 4 7% 21% 12% 1	2435
	21st to end	Day	55% 5% 7% 17% 13% 3	2600
May	1st to 10th	Day	52% 5% 9% 20% 8% 5%	6168
	11th to 20th	Day	48% 5% 8% 23% 15% 1	6322
	21st to end	Day	53% 5% 10% 18% 12% 3	6949
June	1st to 10th	Day	53% 6% 10% 20% 11% 1	2800
	11th to 20th	Day	45% 6% 10% 24% 14% 1	2924
	21st to end	Day	51% 6% 12% 20% 10% 1	3000
July	1st to 10th	Day	46% 7% 14% 24% 9% 1	4787
	11th to 20th	Day	42% 7% 14% 29% 8% 1	4505
	21st to end	Day	37% 6% 11% 31% 14%	4632
August	1st to 10th	Day	48% 7% 13% 24% 7% 1	4091
	11th to 20th	Day	47% 7% 13% 26% 6% 1	4083
	21st to end	Day	39% 7% 12% 32% 11%	4340
September	1st to 10th	Day	44% 6% 12% 25% 12% 1	2280
	11th to 20th	Day	42% 5% 13% 27% 13%	2239
	21st to end	Day	52% 6% 10% 23% 9%	2009
October	1st to 10th	Day	52% 6% 11% 24% 7% 1	3160
	11th to 20th	Day	58% 5% 9% 19% 9% 1	3140
	21st to end	Day	66% 5% 12% 13% 4	3378
November	1st to 10th	Day	59% 5% 13% 18% 5% 1	1610
	11th to 20th	Day	67% 5% 9% 12% 7% 1	1600
	21st to end	Day	76% 5% 8% 7% 4 1	1600
December	1st to 10th	Day	79% 4 7% 7% 3	2600
	11th to 20th	Day	74% 2 5% 11% 8% 1	2986
	21st to end	Day	75% 4 4 11% 6%	3960
January	1st to 10th	Night	76% 4 7% 8% 5%	6349
	11th to 20th	Night	76% 5% 6% 6% 6% 1	6342
	21st to end	Night	74% 4 6% 8% 9% 1	6490
February	1st to 10th	Night	66% 6% 9% 12% 6% 1	2600
	11th to 20th	Night	63% 4 8% 16% 8% 1	2535
	21st to end	Night	64% 4 7% 17% 7% 1	2105
March	1st to 10th	Night	60% 4 8% 12% 11% 4	5008
	11th to 20th	Night	55% 7% 15% 15% 7% 1	4980
	21st to end	Night	57% 4 7% 18% 12% 2	5426
April	1st to 10th	Night	58% 4 7% 18% 12% 1	2000
	11th to 20th	Night	51% 4 6% 23% 14% 1	1932
	21st to end	Night	55% 5% 7% 16% 15% 2	1800
May	1st to 10th	Night	50% 5% 9% 21% 11% 4	3789
	11th to 20th	Night	40% 6% 12% 23% 16% 2	3576
	21st to end	Night	50% 5% 10% 21% 12% 1	3927
June	1st to 10th	Night	49% 5% 11% 21% 13% 1	1600
	11th to 20th	Night	38% 5% 13% 27% 15% 1	1470
	21st to end	Night	47% 6% 14% 21% 11% 1	1400
July	1st to 10th	Night	42% 7% 15% 22% 13% 1	2275
	11th to 20th	Night	41% 6% 13% 31% 9% 1	2552
	21st to end	Night	34% 6% 12% 32% 14% 1	2677
August	1st to 10th	Night	36% 7% 17% 26% 13% 1	2814
	11th to 20th	Night	43% 7% 18% 25% 7%	2812
	21st to end	Night	34% 6% 15% 32% 11% 2	3283
September	1st to 10th	Night	36% 8% 15% 28% 12% 1	1900
	11th to 20th	Night	39% 5% 13% 30% 13%	1938
	21st to end	Night	46% 6% 12% 26% 10%	2171
October	1st to 10th	Night	43% 5% 10% 28% 14%	3800
	11th to 20th	Night	53% 5% 12% 18% 11%	3779
	21st to end	Night	59% 5% 17% 13% 5%	4168
November	1st to 10th	Night	58% 5% 12% 18% 7%	2684
	11th to 20th	Night	62% 5% 12% 13% 6% 1	2800
	21st to end	Night	73% 5% 9% 9% 3	2800
December	1st to 10th	Night	79% 6% 7% 6% 2	4580
	11th to 20th	Night	72% 3 5% 10% 9%	5208
	21st to end	Night	77% 3 4 9% 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	25% 24% 35% 12% 4 1	200
	11th to 20th	Day	31% 18% 35% 13% 3 1	200
	21st to end	Day	25% 22% 34% 13% 5%	330
February	1st to 10th	Day	30% 30% 31% 6% 3	300
	11th to 20th	Day	27% 33% 34% 6%	300
	21st to end	Day	36% 22% 33% 9% 1	289
March	1st to 10th	Day	27% 23% 36% 12% 2	500
	11th to 20th	Day	25% 23% 35% 12% 4 1	500
	21st to end	Day	29% 24% 29% 14% 4	550
April	1st to 10th	Day	27% 24% 33% 12% 4 1	500
	11th to 20th	Day	34% 20% 23% 13% 7% 3	492
	21st to end	Day	30% 19% 32% 12% 6% 1	500
May	1st to 10th	Day	27% 17% 30% 20% 5% 2	503
	11th to 20th	Day	22% 19% 30% 19% 8% 2	527
	21st to end	Day	22% 19% 29% 21% 7% 2	573
June	1st to 10th	Day	25% 14% 35% 19% 5% 1	530
	11th to 20th	Day	18% 14% 36% 21% 9% 2	654
	21st to end	Day	23% 14% 35% 20% 7% 1	730
July	1st to 10th	Day	14% 13% 35% 29% 9% 1	698
	11th to 20th	Day	16% 13% 34% 25% 9% 3	524
	21st to end	Day	13% 13% 33% 28% 10% 3	532
August	1st to 10th	Day	17% 10% 31% 27% 9% 6%	486
	11th to 20th	Day	16% 9% 27% 29% 13% 6%	479
	21st to end	Day	17% 13% 33% 22% 11% 4	539
September	1st to 10th	Day	19% 12% 33% 20% 12% 5%	490
	11th to 20th	Day	19% 9% 25% 22% 16% 9%	490
	21st to end	Day	23% 16% 26% 21% 11% 3	490
October	1st to 10th	Day	26% 19% 26% 16% 11% 2	490
	11th to 20th	Day	30% 22% 30% 12% 4 1	490
	21st to end	Day	38% 18% 27% 14% 2	524
November	1st to 10th	Day	32% 22% 32% 11% 3	244
	11th to 20th	Day	35% 19% 32% 11% 4	200
	21st to end	Day	33% 22% 34% 10% 1 1	200
December	1st to 10th	Day	29% 22% 34% 15% 1	200
	11th to 20th	Day	33% 27% 30% 9% 2 1	200
	21st to end	Day	29% 28% 24% 15% 4	220
January	1st to 10th	Night	25% 22% 37% 13% 3	800
	11th to 20th	Night	26% 21% 32% 18% 4 1	800
	21st to end	Night	18% 19% 34% 21% 6% 1	880
February	1st to 10th	Night	20% 25% 38% 15% 3	800
	11th to 20th	Night	20% 22% 39% 16% 3	783
	21st to end	Night	22% 23% 33% 18% 3	660
March	1st to 10th	Night	22% 25% 32% 19% 3	800
	11th to 20th	Night	22% 19% 38% 16% 4 1	800
	21st to end	Night	20% 21% 33% 20% 6%	880
April	1st to 10th	Night	28% 16% 33% 19% 4	800
	11th to 20th	Night	26% 17% 28% 20% 9% 1	748
	21st to end	Night	26% 13% 29% 22% 11%	600
May	1st to 10th	Night	24% 9% 27% 29% 9% 1	485
	11th to 20th	Night	21% 10% 34% 27% 8%	394
	21st to end	Night	17% 10% 35% 28% 10%	433
June	1st to 10th	Night	20% 14% 31% 29% 7% 1	400
	11th to 20th	Night	18% 8% 31% 33% 10% 1	400
	21st to end	Night	21% 9% 27% 31% 11% 1	400
July	1st to 10th	Night	13% 7% 32% 33% 15% 1	390
	11th to 20th	Night	14% 6% 29% 36% 14% 1	388
	21st to end	Night	12% 6% 34% 35% 13% 1	430
August	1st to 10th	Night	14% 5% 25% 36% 18% 2	567
	11th to 20th	Night	12% 7% 23% 34% 22% 3	564
	21st to end	Night	16% 8% 30% 27% 17% 2	721
September	1st to 10th	Night	14% 9% 31% 28% 16% 2	760
	11th to 20th	Night	20% 7% 25% 25% 18% 4	760
	21st to end	Night	23% 11% 23% 27% 14% 2	760
October	1st to 10th	Night	26% 15% 25% 21% 10% 2	760
	11th to 20th	Night	29% 17% 30% 16% 7% 1	760
	21st to end	Night	33% 18% 30% 16% 4	836
November	1st to 10th	Night	30% 17% 29% 18% 5% 1	780
	11th to 20th	Night	26% 23% 28% 16% 6%	800
	21st to end	Night	32% 20% 27% 17% 3	800
December	1st to 10th	Night	32% 20% 33% 11% 4	800
	11th to 20th	Night	27% 23% 32% 15% 2 1	800
	21st to end	Night	33% 19% 30% 15% 3	880

Page generated at 2025-07-18 01:10:02. Version ac07

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