Snow College Planetarium
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Snow College Planetarium clear sky chart from 2005-11-06 to 2026-02-16.

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	3 7% 3 7% 4 4 4 4 5% 7% 51%	139882
	Night	3 8% 3 7% 4 4 4 3 5% 7% 53%	138480
Transparency	Day	33% 7% 8% 18% 21% 12%	134643
	Night	31% 6% 8% 21% 22% 12%	134724
Seeing	Day	9% 14% 30% 29% 14% 4	16382
	Night	8% 7% 28% 34% 19% 3	26871

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	2 14% 7% 14% 6% 4 4 3 4 6% 35%	5318
	11th to 20th	Day	3 11% 5% 10% 4 3 3 3 3 4 50%	5340
	21st to end	Day	3 10% 4 8% 3 3 3 3 5% 6% 51%	5844
February	1st to 10th	Day	6% 13% 5% 12% 6% 4 3 3 5% 6% 37%	1890
	11th to 20th	Day	7% 14% 6% 9% 5% 4 4 3 4 6% 39%	1886
	21st to end	Day	3 15% 4 11% 5% 4 3 3 4 7% 40%	1650
March	1st to 10th	Day	3 16% 6% 11% 5% 4 4 3 4 5% 39%	4885
	11th to 20th	Day	2 10% 7% 10% 7% 5% 5% 4 5% 7% 38%	5000
	21st to end	Day	4 15% 6% 13% 7% 6% 5% 3 5% 5% 30%	5486
April	1st to 10th	Day	5% 12% 3 8% 5% 5% 4 3 5% 6% 42%	2215
	11th to 20th	Day	5% 11% 4 8% 6% 4 5% 3 6% 5% 43%	2478
	21st to end	Day	6% 12% 3 6% 4 4 4 4 5% 7% 44%	2600
May	1st to 10th	Day	6% 12% 3 7% 5% 4 4 4 6% 8% 42%	5880
	11th to 20th	Day	4 6% 3 8% 5% 6% 6% 4 6% 7% 44%	5841
	21st to end	Day	4 5% 2 6% 4 5% 5% 4 6% 8% 52%	6423
June	1st to 10th	Day	3 3 1 4 3 5% 5% 4 7% 7% 59%	2600
	11th to 20th	Day	4 3 1 4 3 2 4 3 5% 7% 63%	2600
	21st to end	Day	2 2 1 3 3 3 4 3 5% 7% 68%	2600
July	1st to 10th	Day	1 2 1 3 3 3 4 3 4 5% 71%	5879
	11th to 20th	Day	1 2 1 4 4 5% 6% 5% 8% 9% 55%	5880
	21st to end	Day	2 2 1 3 3 4 5% 4 6% 9% 61%	6401
August	1st to 10th	Day	1 2 1 3 3 5% 5% 4 7% 8% 60%	5779
	11th to 20th	Day	1 2 1 3 3 4 5% 4 5% 7% 64%	5798
	21st to end	Day	2 3 1 5% 4 5% 6% 4 7% 8% 53%	6344
September	1st to 10th	Day	3 3 1 4 3 4 5% 4 6% 6% 61%	2254
	11th to 20th	Day	3 3 1 5% 3 4 4 4 5% 5% 62%	2200
	21st to end	Day	4 4 2 4 3 3 4 2 4 5% 65%	2200
October	1st to 10th	Day	3 4 1 3 2 3 3 2 4 6% 69%	3435
	11th to 20th	Day	4 8% 2 5% 4 3 4 3 6% 8% 53%	3250
	21st to end	Day	3 7% 2 4 2 2 4 3 4 6% 63%	3548
November	1st to 10th	Day	5% 7% 4 6% 3 3 4 3 5% 6% 54%	1904
	11th to 20th	Day	6% 9% 2 5% 4 4 3 4 6% 6% 51%	1890
	21st to end	Day	5% 9% 5% 7% 3 3 3 3 4 7% 51%	1883
December	1st to 10th	Day	3 8% 2 6% 4 3 2 2 4 8% 59%	2700
	11th to 20th	Day	3 9% 3 9% 4 4 4 3 5% 8% 46%	3392
	21st to end	Day	3 14% 5% 11% 5% 5% 5% 4 6% 8% 34%	4609
January	1st to 10th	Night	3 12% 9% 16% 5% 4 3 3 4 6% 36%	7605
	11th to 20th	Night	4 13% 3 10% 4 3 3 2 3 4 51%	7650
	21st to end	Night	2 10% 4 7% 3 3 3 3 5% 6% 53%	8370
February	1st to 10th	Night	5% 11% 4 9% 6% 4 4 4 5% 6% 42%	2730
	11th to 20th	Night	5% 12% 4 10% 4 4 4 3 4 7% 42%	2508
	21st to end	Night	4 14% 3 10% 5% 4 4 3 5% 6% 43%	1980
March	1st to 10th	Night	3 15% 5% 9% 4 4 3 3 4 7% 44%	4996
	11th to 20th	Night	2 10% 3 9% 6% 6% 5% 4 6% 9% 40%	5000
	21st to end	Night	3 12% 4 8% 5% 4 4 4 5% 7% 44%	5489
April	1st to 10th	Night	5% 10% 4 6% 4 4 4 4 5% 6% 48%	2184
	11th to 20th	Night	6% 9% 3 5% 5% 4 4 4 7% 8% 46%	1868
	21st to end	Night	6% 9% 3 5% 4 4 4 4 6% 8% 46%	1800
May	1st to 10th	Night	6% 10% 3 7% 4 4 4 4 5% 8% 46%	4100
	11th to 20th	Night	2 4 1 6% 4 5% 5% 4 7% 7% 55%	4074
	21st to end	Night	4 4 1 4 3 3 3 3 5% 8% 63%	4474
June	1st to 10th	Night	2 4 1 4 3 4 4 3 6% 8% 62%	1800
	11th to 20th	Night	3 2 1 3 3 3 3 2 5% 6% 68%	1800
	21st to end	Night	2 2 1 3 3 3 4 3 5% 5% 69%	1800
July	1st to 10th	Night	1 2 1 3 3 3 3 3 5% 5% 72%	4100
	11th to 20th	Night	1 2 2 5% 5% 5% 5% 5% 7% 8% 55%	4100
	21st to end	Night	1 2 1 5% 4 4 5% 4 7% 8% 59%	4472
August	1st to 10th	Night	1 2 1 3 3 4 6% 5% 7% 9% 60%	4033
	11th to 20th	Night	1 2 1 4 3 4 4 4 5% 7% 65%	4051
	21st to end	Night	2 3 1 6% 4 4 4 4 5% 7% 60%	4631
September	1st to 10th	Night	2 2 1 2 2 2 4 4 7% 6% 67%	2142
	11th to 20th	Night	2 2 1 3 3 3 3 3 4 6% 69%	2200
	21st to end	Night	5% 3 1 3 2 2 3 2 4 5% 71%	2200
October	1st to 10th	Night	3 3 1 3 2 2 3 3 4 6% 71%	3760
	11th to 20th	Night	4 5% 2 5% 3 3 4 4 5% 6% 58%	3898
	21st to end	Night	3 5% 2 5% 3 2 3 2 5% 7% 63%	4252
November	1st to 10th	Night	4 7% 3 4 4 2 4 3 5% 7% 57%	2611
	11th to 20th	Night	5% 7% 2 5% 4 3 4 4 5% 7% 54%	2730
	21st to end	Night	5% 9% 4 7% 4 3 3 3 5% 6% 51%	2730
December	1st to 10th	Night	4 8% 3 5% 3 2 3 2 5% 6% 60%	4672
	11th to 20th	Night	5% 10% 4 8% 4 3 4 3 5% 6% 49%	5059
	21st to end	Night	4 13% 4 12% 5% 4 4 4 6% 7% 36%	6611

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	48% 6% 14% 19% 10% 3	5321
	11th to 20th	Day	38% 5% 8% 18% 22% 9%	5340
	21st to end	Day	33% 6% 12% 18% 23% 8%	5844
February	1st to 10th	Day	49% 5% 11% 16% 14% 5%	1890
	11th to 20th	Day	47% 4 11% 18% 17% 4	1895
	21st to end	Day	43% 7% 8% 22% 15% 5%	1650
March	1st to 10th	Day	45% 8% 5% 17% 17% 8%	4885
	11th to 20th	Day	44% 12% 10% 20% 12% 2	5000
	21st to end	Day	56% 7% 11% 18% 7% 1	5486
April	1st to 10th	Day	42% 7% 9% 20% 18% 4	2215
	11th to 20th	Day	42% 5% 9% 21% 20% 3	2481
	21st to end	Day	41% 6% 8% 26% 18% 2	2600
May	1st to 10th	Day	37% 10% 10% 20% 20% 4	5880
	11th to 20th	Day	35% 8% 7% 25% 24% 1	5844
	21st to end	Day	27% 10% 7% 24% 29% 2	6424
June	1st to 10th	Day	24% 7% 9% 21% 30% 9%	2600
	11th to 20th	Day	23% 4 7% 12% 30% 24%	2600
	21st to end	Day	18% 6% 6% 10% 26% 34%	2600
July	1st to 10th	Day	17% 6% 4 7% 14% 53%	5816
	11th to 20th	Day	25% 10% 5% 13% 24% 24%	5811
	21st to end	Day	19% 11% 5% 15% 24% 26%	6217
August	1st to 10th	Day	28% 10% 12% 21% 15% 16%	4208
	11th to 20th	Day	24% 8% 10% 14% 23% 21%	4197
	21st to end	Day	23% 9% 7% 12% 29% 21%	4575
September	1st to 10th	Day	25% 7% 9% 12% 25% 21%	2254
	11th to 20th	Day	25% 7% 7% 16% 26% 20%	2200
	21st to end	Day	23% 5% 6% 19% 32% 16%	2200
October	1st to 10th	Day	20% 7% 4 14% 44% 11%	3435
	11th to 20th	Day	31% 8% 3 23% 29% 6%	3250
	21st to end	Day	25% 5% 5% 28% 30% 7%	3548
November	1st to 10th	Day	31% 6% 10% 20% 25% 8%	1904
	11th to 20th	Day	31% 4 11% 25% 23% 5%	1890
	21st to end	Day	35% 5% 11% 22% 19% 9%	1883
December	1st to 10th	Day	28% 5% 10% 29% 22% 6%	2700
	11th to 20th	Day	37% 6% 13% 21% 19% 3	3391
	21st to end	Day	47% 7% 9% 15% 15% 8%	4609
January	1st to 10th	Night	50% 6% 10% 17% 14% 4	7605
	11th to 20th	Night	37% 6% 6% 20% 20% 11%	7650
	21st to end	Night	33% 5% 11% 17% 25% 9%	8370
February	1st to 10th	Night	44% 5% 10% 20% 16% 5%	2730
	11th to 20th	Night	44% 6% 7% 19% 19% 5%	2509
	21st to end	Night	41% 5% 10% 20% 17% 7%	1980
March	1st to 10th	Night	39% 6% 8% 20% 19% 8%	4996
	11th to 20th	Night	39% 12% 10% 23% 14% 2	5000
	21st to end	Night	39% 7% 14% 21% 17% 1	5489
April	1st to 10th	Night	35% 6% 10% 21% 21% 7%	2184
	11th to 20th	Night	35% 6% 10% 23% 22% 4	1868
	21st to end	Night	35% 7% 10% 28% 17% 2	1800
May	1st to 10th	Night	33% 8% 10% 24% 22% 3	4097
	11th to 20th	Night	26% 8% 8% 30% 27% 3	4075
	21st to end	Night	19% 7% 7% 33% 29% 5%	4474
June	1st to 10th	Night	22% 5% 10% 24% 29% 10%	1800
	11th to 20th	Night	19% 3 7% 14% 33% 23%	1800
	21st to end	Night	18% 5% 5% 9% 26% 37%	1800
July	1st to 10th	Night	16% 4 4 6% 15% 55%	4055
	11th to 20th	Night	26% 6% 5% 13% 21% 28%	4046
	21st to end	Night	22% 10% 7% 14% 21% 28%	4344
August	1st to 10th	Night	27% 8% 11% 24% 14% 17%	2928
	11th to 20th	Night	24% 6% 10% 13% 22% 24%	2928
	21st to end	Night	16% 4 9% 14% 32% 24%	3331
September	1st to 10th	Night	18% 6% 10% 15% 25% 26%	2142
	11th to 20th	Night	18% 6% 7% 21% 25% 23%	2200
	21st to end	Night	19% 3 5% 18% 35% 20%	2200
October	1st to 10th	Night	18% 5% 4 17% 38% 19%	3760
	11th to 20th	Night	27% 7% 4 26% 28% 7%	3898
	21st to end	Night	24% 5% 5% 28% 33% 5%	4252
November	1st to 10th	Night	28% 5% 9% 25% 24% 9%	2611
	11th to 20th	Night	30% 5% 9% 27% 24% 5%	2730
	21st to end	Night	35% 4 8% 22% 21% 10%	2730
December	1st to 10th	Night	26% 5% 8% 25% 29% 7%	4672
	11th to 20th	Night	36% 5% 12% 27% 16% 3	5059
	21st to end	Night	44% 7% 11% 19% 12% 7%	6611

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	18% 12% 32% 24% 11% 3	330
	11th to 20th	Day	11% 13% 34% 25% 15% 2	330
	21st to end	Day	8% 9% 44% 23% 14% 2	363
February	1st to 10th	Day	14% 18% 36% 24% 8% 1	330
	11th to 20th	Day	13% 18% 36% 23% 8% 1	401
	21st to end	Day	9% 23% 39% 22% 5% 1	414
March	1st to 10th	Day	16% 23% 29% 22% 9% 2	500
	11th to 20th	Day	12% 19% 34% 24% 10% 2	500
	21st to end	Day	15% 25% 36% 20% 3	550
April	1st to 10th	Day	16% 23% 27% 21% 11% 2	500
	11th to 20th	Day	14% 25% 33% 20% 6% 1	492
	21st to end	Day	16% 23% 28% 21% 10% 2	500
May	1st to 10th	Day	10% 21% 33% 25% 9% 2	503
	11th to 20th	Day	12% 16% 28% 28% 12% 4	528
	21st to end	Day	9% 18% 26% 29% 14% 3	573
June	1st to 10th	Day	4 11% 32% 35% 15% 3	530
	11th to 20th	Day	8% 17% 34% 28% 12% 2	530
	21st to end	Day	4 12% 36% 35% 11% 2	530
July	1st to 10th	Day	4 7% 27% 40% 18% 3	526
	11th to 20th	Day	3 3 28% 42% 20% 5%	524
	21st to end	Day	4 7% 18% 41% 22% 7%	575
August	1st to 10th	Day	4 7% 30% 38% 17% 4	527
	11th to 20th	Day	4 7% 29% 35% 19% 6%	517
	21st to end	Day	6% 6% 29% 35% 18% 6%	583
September	1st to 10th	Day	4 8% 26% 33% 19% 9%	530
	11th to 20th	Day	7% 12% 30% 30% 15% 6%	530
	21st to end	Day	7% 10% 26% 29% 20% 8%	530
October	1st to 10th	Day	8% 14% 23% 30% 17% 7%	430
	11th to 20th	Day	7% 13% 25% 28% 20% 8%	330
	21st to end	Day	10% 13% 28% 32% 15% 2	363
November	1st to 10th	Day	11% 15% 28% 22% 18% 5%	330
	11th to 20th	Day	7% 10% 33% 32% 13% 5%	330
	21st to end	Day	10% 10% 28% 29% 18% 5%	330
December	1st to 10th	Day	12% 10% 32% 30% 12% 4	330
	11th to 20th	Day	13% 12% 30% 31% 13% 2	330
	21st to end	Day	13% 15% 32% 27% 11% 1	363
January	1st to 10th	Night	13% 8% 30% 30% 14% 4	840
	11th to 20th	Night	11% 7% 32% 33% 15% 3	840
	21st to end	Night	9% 9% 34% 32% 13% 3	924
February	1st to 10th	Night	12% 9% 38% 29% 9% 4	840
	11th to 20th	Night	10% 10% 39% 30% 10% 2	804
	21st to end	Night	11% 9% 37% 35% 8%	660
March	1st to 10th	Night	11% 11% 33% 32% 12% 2	800
	11th to 20th	Night	9% 7% 32% 33% 18% 2	800
	21st to end	Night	10% 12% 36% 30% 10% 2	880
April	1st to 10th	Night	12% 12% 34% 30% 12% 1	784
	11th to 20th	Night	10% 11% 36% 32% 10% 1	593
	21st to end	Night	11% 13% 30% 31% 13% 2	600
May	1st to 10th	Night	11% 10% 33% 33% 13% 2	600
	11th to 20th	Night	8% 7% 25% 37% 19% 4	591
	21st to end	Night	8% 10% 23% 35% 21% 3	650
June	1st to 10th	Night	5% 5% 25% 41% 24% 1	600
	11th to 20th	Night	5% 10% 27% 39% 18% 1	600
	21st to end	Night	3 4 25% 42% 24% 3	600
July	1st to 10th	Night	4 2 20% 36% 35% 4	585
	11th to 20th	Night	4 2 14% 41% 35% 4	582
	21st to end	Night	3 2 14% 35% 41% 5%	657
August	1st to 10th	Night	4 3 18% 44% 29% 3	597
	11th to 20th	Night	3 2 17% 44% 29% 4	594
	21st to end	Night	3 4 18% 37% 32% 6%	660
September	1st to 10th	Night	3 2 15% 38% 35% 7%	742
	11th to 20th	Night	2 4 22% 35% 29% 7%	800
	21st to end	Night	6% 4 20% 33% 29% 8%	800
October	1st to 10th	Night	8% 5% 28% 34% 22% 3	800
	11th to 20th	Night	7% 6% 25% 35% 22% 5%	800
	21st to end	Night	8% 6% 29% 32% 20% 5%	880
November	1st to 10th	Night	7% 8% 28% 34% 19% 5%	820
	11th to 20th	Night	9% 6% 35% 30% 17% 4	840
	21st to end	Night	10% 7% 28% 31% 19% 5%	840
December	1st to 10th	Night	12% 7% 32% 33% 13% 3	1025
	11th to 20th	Night	13% 8% 32% 32% 14% 1	919
	21st to end	Night	16% 10% 33% 29% 10% 1	924

Page generated at 2026-02-12 23:42:14. Version ac07

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