Glacial Lakes State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Glacial Lakes State Park clear sky chart from 2005-11-06 to 2025-10-04.

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 8% 5% 5% 5% 4 6% 7% 38%	126776
	Night	10% 9% 4 8% 5% 5% 5% 4 6% 7% 37%	122853
Transparency	Day	43% 6% 14% 25% 11% 1	130318
	Night	44% 5% 13% 24% 12% 1	127392
Seeing	Day	15% 10% 31% 28% 14% 3	17353
	Night	14% 9% 33% 33% 10% 1	27157

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	9% 13% 3 12% 13% 9% 9% 5% 6% 6% 16%	3178
	11th to 20th	Day	5% 8% 5% 13% 7% 8% 10% 8% 12% 8% 16%	3561
	21st to end	Day	4 10% 9% 17% 8% 6% 5% 4 5% 6% 26%	4488
February	1st to 10th	Day	8% 13% 5% 10% 6% 6% 7% 4 7% 8% 26%	1800
	11th to 20th	Day	6% 11% 4 9% 8% 8% 6% 5% 8% 6% 29%	1754
	21st to end	Day	8% 13% 4 11% 7% 7% 5% 5% 8% 6% 27%	1555
March	1st to 10th	Day	11% 9% 3 9% 5% 4 4 3 4 6% 42%	4841
	11th to 20th	Day	10% 9% 3 7% 5% 4 5% 4 5% 9% 39%	4980
	21st to end	Day	20% 13% 5% 10% 7% 5% 4 3 5% 7% 21%	5462
April	1st to 10th	Day	17% 10% 3 7% 3 4 4 3 6% 8% 36%	2331
	11th to 20th	Day	18% 12% 3 8% 4 4 4 3 5% 6% 32%	2539
	21st to end	Day	23% 10% 3 6% 4 4 4 3 4 5% 34%	2600
May	1st to 10th	Day	12% 6% 2 5% 3 4 3 3 5% 6% 51%	5862
	11th to 20th	Day	18% 8% 2 5% 4 3 3 3 5% 6% 44%	6312
	21st to end	Day	16% 7% 3 6% 4 4 5% 4 6% 8% 38%	6935
June	1st to 10th	Day	11% 6% 2 6% 4 4 4 4 7% 8% 43%	2961
	11th to 20th	Day	15% 7% 3 6% 5% 5% 4 4 7% 7% 37%	3000
	21st to end	Day	10% 5% 2 5% 4 3 5% 5% 7% 9% 45%	3000
July	1st to 10th	Day	7% 4 1 5% 4 4 5% 5% 8% 11% 46%	6800
	11th to 20th	Day	8% 4 2 4 3 4 4 3 6% 9% 54%	6800
	21st to end	Day	7% 5% 2 5% 4 4 5% 5% 7% 10% 47%	6526
August	1st to 10th	Day	13% 5% 2 5% 4 3 4 4 6% 8% 45%	4234
	11th to 20th	Day	11% 6% 2 6% 4 4 5% 4 6% 10% 41%	4171
	21st to end	Day	9% 5% 2 5% 4 4 5% 4 5% 8% 49%	4650
September	1st to 10th	Day	10% 4 2 5% 3 4 4 3 5% 8% 52%	2400
	11th to 20th	Day	11% 5% 2 5% 4 4 5% 3 7% 7% 47%	2225
	21st to end	Day	14% 5% 2 4 3 3 3 3 5% 8% 50%	2195
October	1st to 10th	Day	15% 8% 2 5% 4 4 2 4 5% 7% 43%	1930
	11th to 20th	Day	15% 12% 2 5% 3 3 4 3 4 6% 42%	1900
	21st to end	Day	16% 11% 3 7% 5% 3 4 3 5% 6% 37%	2027
November	1st to 10th	Day	13% 13% 3 8% 6% 3 3 2 6% 7% 36%	1648
	11th to 20th	Day	11% 12% 5% 14% 8% 5% 5% 4 4 5% 28%	1600
	21st to end	Day	12% 10% 4 11% 7% 5% 5% 4 6% 6% 30%	1600
December	1st to 10th	Day	6% 10% 6% 13% 12% 10% 8% 5% 6% 5% 19%	2610
	11th to 20th	Day	8% 17% 8% 12% 7% 6% 4 4 5% 6% 24%	2803
	21st to end	Day	17% 17% 6% 19% 8% 4 3 2 3 5% 16%	3498
January	1st to 10th	Night	6% 10% 4 14% 12% 8% 8% 5% 7% 7% 19%	6787
	11th to 20th	Night	5% 9% 5% 12% 8% 8% 11% 8% 8% 6% 19%	6403
	21st to end	Night	5% 14% 9% 11% 6% 4 6% 5% 5% 7% 28%	6490
February	1st to 10th	Night	6% 11% 4 10% 7% 6% 6% 4 7% 8% 30%	2600
	11th to 20th	Night	6% 10% 4 8% 6% 6% 7% 5% 7% 7% 36%	2533
	21st to end	Night	11% 9% 4 9% 5% 5% 6% 4 6% 7% 34%	2090
March	1st to 10th	Night	10% 7% 2 5% 4 3 4 4 6% 8% 47%	5016
	11th to 20th	Night	10% 7% 3 6% 4 4 5% 5% 8% 9% 39%	4980
	21st to end	Night	20% 11% 5% 9% 5% 4 4 3 5% 5% 29%	5467
April	1st to 10th	Night	15% 10% 3 6% 3 4 4 3 5% 7% 40%	2068
	11th to 20th	Night	17% 9% 4 7% 4 4 4 3 4 6% 37%	1809
	21st to end	Night	19% 11% 3 6% 3 3 5% 3 4 5% 38%	1800
May	1st to 10th	Night	12% 5% 2 5% 3 2 3 2 4 6% 56%	4053
	11th to 20th	Night	15% 9% 2 6% 3 4 3 3 4 5% 47%	3601
	21st to end	Night	17% 8% 3 7% 4 4 4 3 5% 7% 38%	3942
June	1st to 10th	Night	10% 6% 2 4 4 3 4 4 5% 9% 49%	1434
	11th to 20th	Night	11% 4 2 5% 4 4 5% 3 6% 8% 48%	1400
	21st to end	Night	9% 5% 2 4 4 3 3 3 6% 7% 56%	1400
July	1st to 10th	Night	8% 5% 2 5% 3 4 4 4 7% 9% 48%	3178
	11th to 20th	Night	6% 3 1 4 3 3 4 3 5% 9% 59%	3177
	21st to end	Night	8% 6% 2 6% 4 4 5% 4 6% 9% 47%	4326
August	1st to 10th	Night	10% 6% 2 5% 3 3 4 3 6% 7% 50%	2926
	11th to 20th	Night	12% 5% 2 5% 3 4 3 3 5% 8% 51%	2888
	21st to end	Night	9% 4 2 5% 3 3 3 4 5% 8% 54%	3257
September	1st to 10th	Night	8% 5% 2 4 3 2 3 3 5% 7% 58%	2000
	11th to 20th	Night	10% 5% 2 5% 4 4 4 4 5% 6% 52%	2171
	21st to end	Night	11% 5% 2 5% 3 3 3 3 5% 6% 55%	2200
October	1st to 10th	Night	13% 8% 2 6% 4 3 3 3 4 7% 47%	2301
	11th to 20th	Night	14% 9% 2 6% 4 3 3 4 5% 6% 44%	2280
	21st to end	Night	16% 11% 3 8% 4 3 4 3 5% 6% 38%	2570
November	1st to 10th	Night	11% 9% 3 6% 5% 5% 5% 4 5% 6% 40%	2650
	11th to 20th	Night	11% 12% 5% 11% 5% 4 4 3 4 5% 36%	2800
	21st to end	Night	10% 10% 4 10% 6% 5% 4 3 5% 7% 36%	2800
December	1st to 10th	Night	5% 8% 5% 12% 9% 9% 6% 4 7% 8% 27%	4580
	11th to 20th	Night	10% 12% 5% 14% 8% 7% 5% 4 5% 6% 23%	5396
	21st to end	Night	16% 17% 6% 17% 8% 5% 4 4 4 4 15%	7480

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% 5% 9% 13% 6%	3179
	11th to 20th	Day	57% 6% 11% 21% 5%	3561
	21st to end	Day	58% 6% 13% 15% 8%	4488
February	1st to 10th	Day	55% 6% 11% 20% 8% 1	1800
	11th to 20th	Day	52% 7% 13% 22% 6% 1	1763
	21st to end	Day	55% 6% 13% 19% 8%	1555
March	1st to 10th	Day	44% 4 16% 26% 9% 1	4841
	11th to 20th	Day	43% 5% 13% 29% 9% 1	4980
	21st to end	Day	64% 5% 11% 17% 3	5464
April	1st to 10th	Day	46% 6% 12% 24% 12% 1	2331
	11th to 20th	Day	52% 5% 12% 18% 13% 1	2539
	21st to end	Day	52% 5% 11% 23% 8% 1	2600
May	1st to 10th	Day	34% 6% 12% 29% 19%	5900
	11th to 20th	Day	42% 5% 9% 22% 15% 8%	6316
	21st to end	Day	42% 6% 11% 30% 10% 1	6949
June	1st to 10th	Day	37% 6% 16% 29% 11% 1	2961
	11th to 20th	Day	43% 8% 14% 20% 14% 1	3000
	21st to end	Day	32% 7% 19% 27% 13% 1	3000
July	1st to 10th	Day	30% 8% 21% 30% 11%	6726
	11th to 20th	Day	27% 6% 16% 37% 14% 1	6719
	21st to end	Day	31% 7% 19% 30% 12% 1	6341
August	1st to 10th	Day	35% 5% 14% 32% 12% 2	4220
	11th to 20th	Day	37% 7% 16% 32% 8% 1	4210
	21st to end	Day	32% 7% 17% 31% 12% 1	4649
September	1st to 10th	Day	30% 6% 16% 36% 12% 1	2400
	11th to 20th	Day	34% 6% 19% 30% 10%	2225
	21st to end	Day	33% 6% 13% 33% 14% 2	2195
October	1st to 10th	Day	32% 3 8% 33% 23% 1	3190
	11th to 20th	Day	37% 4 12% 23% 22% 1	3140
	21st to end	Day	47% 4 14% 26% 9%	3320
November	1st to 10th	Day	47% 4 13% 22% 11% 3	1648
	11th to 20th	Day	58% 4 12% 18% 8%	1600
	21st to end	Day	52% 5% 17% 19% 6% 2	1600
December	1st to 10th	Day	62% 7% 16% 12% 4	2610
	11th to 20th	Day	62% 4 14% 15% 5%	2800
	21st to end	Day	72% 4 8% 11% 5%	3498
January	1st to 10th	Night	61% 6% 10% 16% 7%	6787
	11th to 20th	Night	59% 6% 11% 14% 9% 1	6403
	21st to end	Night	53% 6% 15% 20% 6%	6490
February	1st to 10th	Night	50% 6% 13% 19% 11% 1	2600
	11th to 20th	Night	45% 6% 13% 23% 12% 1	2534
	21st to end	Night	47% 6% 13% 20% 12% 2	2090
March	1st to 10th	Night	35% 4 14% 31% 14% 2	5016
	11th to 20th	Night	37% 5% 15% 30% 12%	4980
	21st to end	Night	56% 5% 10% 19% 8% 1	5467
April	1st to 10th	Night	43% 5% 12% 27% 11% 2	2068
	11th to 20th	Night	48% 4 7% 24% 15% 2	1809
	21st to end	Night	48% 4 11% 22% 13% 2	1800
May	1st to 10th	Night	30% 4 11% 32% 20% 3	4080
	11th to 20th	Night	40% 5% 8% 19% 22% 7%	3602
	21st to end	Night	45% 6% 11% 26% 12% 1	3950
June	1st to 10th	Night	32% 5% 15% 30% 15% 2	1434
	11th to 20th	Night	32% 7% 17% 25% 16% 3	1400
	21st to end	Night	28% 4 18% 30% 18% 2	1400
July	1st to 10th	Night	30% 7% 19% 28% 16% 1	3145
	11th to 20th	Night	22% 4 17% 42% 13% 2	3138
	21st to end	Night	33% 6% 17% 31% 11% 1	4201
August	1st to 10th	Night	33% 5% 16% 27% 15% 4	2916
	11th to 20th	Night	32% 5% 17% 33% 12% 1	2915
	21st to end	Night	28% 6% 18% 31% 14% 2	3257
September	1st to 10th	Night	25% 5% 17% 34% 18% 1	2000
	11th to 20th	Night	31% 6% 16% 30% 17%	2171
	21st to end	Night	31% 4 12% 34% 19% 1	2200
October	1st to 10th	Night	24% 3 7% 36% 25% 4	3821
	11th to 20th	Night	33% 4 12% 28% 20% 2	3779
	21st to end	Night	41% 5% 15% 25% 13% 1	4231
November	1st to 10th	Night	42% 5% 14% 24% 12% 2	2650
	11th to 20th	Night	50% 5% 14% 20% 11% 1	2800
	21st to end	Night	47% 6% 17% 21% 8% 1	2800
December	1st to 10th	Night	53% 6% 18% 18% 6%	4580
	11th to 20th	Night	60% 5% 12% 18% 4	5398
	21st to end	Night	71% 5% 9% 12% 3	7480

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	16% 8% 35% 29% 9% 3	300
	11th to 20th	Day	13% 11% 35% 31% 9% 1	300
	21st to end	Day	12% 12% 38% 23% 12% 2	330
February	1st to 10th	Day	14% 15% 39% 29% 3	300
	11th to 20th	Day	12% 14% 39% 27% 8%	300
	21st to end	Day	12% 14% 41% 26% 7%	249
March	1st to 10th	Day	15% 15% 38% 25% 6%	300
	11th to 20th	Day	19% 8% 37% 24% 10% 2	300
	21st to end	Day	24% 12% 27% 24% 9% 3	330
April	1st to 10th	Day	26% 13% 33% 22% 6%	431
	11th to 20th	Day	26% 15% 26% 23% 9% 1	657
	21st to end	Day	25% 11% 33% 20% 11% 1	700
May	1st to 10th	Day	18% 12% 33% 24% 11% 2	703
	11th to 20th	Day	20% 12% 26% 27% 12% 2	725
	21st to end	Day	17% 8% 31% 28% 13% 2	789
June	1st to 10th	Day	11% 9% 25% 33% 20% 3	730
	11th to 20th	Day	15% 9% 36% 27% 11% 2	730
	21st to end	Day	14% 6% 34% 29% 14% 3	730
July	1st to 10th	Day	6% 4 25% 34% 26% 6%	721
	11th to 20th	Day	7% 7% 26% 34% 19% 5%	718
	21st to end	Day	6% 3 26% 36% 23% 6%	794
August	1st to 10th	Day	10% 3 24% 32% 25% 5%	726
	11th to 20th	Day	13% 4 22% 31% 23% 6%	715
	21st to end	Day	10% 6% 26% 32% 21% 5%	791
September	1st to 10th	Day	11% 8% 28% 31% 18% 4	530
	11th to 20th	Day	11% 4 34% 33% 15% 4	355
	21st to end	Day	16% 12% 28% 25% 15% 3	330
October	1st to 10th	Day	17% 12% 28% 27% 12% 4	309
	11th to 20th	Day	16% 17% 38% 20% 7% 2	300
	21st to end	Day	22% 17% 35% 18% 6% 1	330
November	1st to 10th	Day	24% 12% 26% 29% 8% 1	300
	11th to 20th	Day	19% 16% 40% 21% 3	300
	21st to end	Day	19% 19% 34% 24% 4	300
December	1st to 10th	Day	11% 10% 43% 27% 9%	300
	11th to 20th	Day	15% 13% 43% 23% 5%	300
	21st to end	Day	27% 10% 35% 22% 5%	330
January	1st to 10th	Night	11% 9% 40% 30% 9% 2	1000
	11th to 20th	Night	12% 12% 37% 30% 8% 1	1000
	21st to end	Night	14% 11% 38% 30% 7%	1100
February	1st to 10th	Night	11% 10% 38% 32% 8% 1	1000
	11th to 20th	Night	11% 11% 41% 28% 8% 1	979
	21st to end	Night	15% 11% 31% 32% 9% 1	770
March	1st to 10th	Night	15% 11% 35% 31% 7% 1	649
	11th to 20th	Night	17% 10% 38% 29% 5% 1	600
	21st to end	Night	18% 9% 31% 29% 12% 1	660
April	1st to 10th	Night	18% 11% 37% 29% 4	600
	11th to 20th	Night	21% 12% 32% 27% 7% 1	593
	21st to end	Night	22% 10% 31% 28% 8% 1	600
May	1st to 10th	Night	18% 10% 32% 30% 10% 1	600
	11th to 20th	Night	16% 9% 33% 32% 10%	591
	21st to end	Night	15% 9% 27% 39% 10%	650
June	1st to 10th	Night	12% 8% 26% 38% 16% 1	600
	11th to 20th	Night	12% 4 33% 44% 7%	600
	21st to end	Night	10% 4 26% 46% 14% 1	600
July	1st to 10th	Night	5% 3 21% 44% 25% 2	585
	11th to 20th	Night	5% 3 25% 48% 17% 2	582
	21st to end	Night	6% 2 23% 47% 20% 2	657
August	1st to 10th	Night	9% 2 22% 45% 21% 1	597
	11th to 20th	Night	11% 4 22% 38% 23% 3	594
	21st to end	Night	7% 4 26% 39% 22% 1	660
September	1st to 10th	Night	12% 4 26% 40% 16% 2	600
	11th to 20th	Night	12% 5% 29% 37% 16% 1	600
	21st to end	Night	12% 7% 34% 32% 14% 1	600
October	1st to 10th	Night	17% 10% 34% 28% 10%	757
	11th to 20th	Night	18% 11% 32% 30% 8% 1	760
	21st to end	Night	20% 12% 34% 28% 5%	898
November	1st to 10th	Night	16% 11% 32% 33% 9%	975
	11th to 20th	Night	16% 13% 37% 25% 8% 1	1000
	21st to end	Night	15% 13% 38% 27% 7%	1000
December	1st to 10th	Night	12% 11% 38% 31% 8% 1	1000
	11th to 20th	Night	17% 11% 35% 30% 5% 1	1000
	21st to end	Night	23% 10% 35% 25% 6% 1	1100

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