Glacier Basin Campground
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Glacier Basin Campground clear sky chart from 2005-11-06 to 2025-04-11.

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 6% 3 7% 5% 5% 5% 4 6% 8% 48%	117491
	Night	2 4 2 5% 4 3 4 4 6% 8% 58%	119667
Transparency	Day	27% 9% 13% 24% 20% 8%	117236
	Night	21% 7% 14% 27% 23% 8%	119512
Seeing	Day	19% 26% 28% 17% 7% 2	16126
	Night	15% 30% 25% 20% 9% 2	26317

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	3 3 11% 5% 4 3 4 7% 7% 54%	3638
	11th to 20th	Day	2 2 7% 6% 8% 5% 6% 8% 9% 47%	3778
	21st to end	Day	4 4 9% 4 3 4 4 5% 7% 57%	4510
February	1st to 10th	Day	1 4 3 8% 5% 5% 5% 4 7% 9% 50%	1800
	11th to 20th	Day	4 2 6% 5% 4 5% 6% 8% 8% 52%	1878
	21st to end	Day	5% 4 9% 5% 5% 4 4 7% 11% 47%	1650
March	1st to 10th	Day	1 6% 4 10% 5% 5% 6% 4 5% 5% 51%	4518
	11th to 20th	Day	1 7% 6% 9% 4 5% 6% 4 6% 10% 43%	5000
	21st to end	Day	1 7% 4 6% 4 4 5% 5% 7% 11% 46%	5766
April	1st to 10th	Day	2 8% 3 6% 5% 5% 4 4 6% 11% 46%	2400
	11th to 20th	Day	4 14% 5% 8% 5% 5% 5% 4 7% 8% 36%	2252
	21st to end	Day	5% 13% 3 8% 5% 5% 6% 4 6% 8% 36%	2280
May	1st to 10th	Day	6% 16% 4 7% 4 6% 6% 5% 6% 8% 32%	4075
	11th to 20th	Day	7% 11% 3 6% 5% 5% 5% 5% 8% 8% 37%	4388
	21st to end	Day	5% 6% 2 5% 4 4 6% 5% 8% 9% 46%	4825
June	1st to 10th	Day	5% 6% 2 5% 6% 5% 6% 5% 7% 9% 45%	2660
	11th to 20th	Day	6% 6% 2 5% 4 3 5% 4 7% 8% 50%	2660
	21st to end	Day	3 5% 2 6% 5% 5% 6% 5% 7% 8% 47%	2660
July	1st to 10th	Day	5% 4 2 6% 5% 5% 6% 5% 7% 7% 47%	4430
	11th to 20th	Day	4 4 2 8% 6% 6% 7% 6% 8% 8% 40%	4430
	21st to end	Day	5% 6% 2 7% 6% 5% 7% 5% 7% 7% 42%	4691
August	1st to 10th	Day	5% 6% 2 9% 7% 6% 7% 6% 8% 9% 34%	4092
	11th to 20th	Day	5% 4 2 7% 5% 5% 6% 6% 8% 9% 44%	3793
	21st to end	Day	6% 4 2 6% 5% 4 5% 4 6% 9% 49%	4180
September	1st to 10th	Day	7% 5% 2 5% 4 4 5% 3 5% 7% 53%	2280
	11th to 20th	Day	7% 4 2 5% 4 4 5% 4 5% 7% 54%	2280
	21st to end	Day	6% 6% 2 4 3 3 3 3 5% 6% 59%	2066
October	1st to 10th	Day	3 4 2 4 2 3 3 2 4 6% 69%	3170
	11th to 20th	Day	2 5% 1 4 4 4 5% 4 7% 9% 54%	3150
	21st to end	Day	3 6% 2 5% 3 3 3 3 4 6% 62%	3348
November	1st to 10th	Day	1 5% 2 4 3 3 4 4 6% 8% 61%	1763
	11th to 20th	Day	1 5% 2 4 3 2 3 3 6% 11% 60%	1800
	21st to end	Day	3 2 7% 5% 4 4 3 6% 8% 57%	1630
December	1st to 10th	Day	2 2 4 2 3 3 3 4 8% 67%	2620
	11th to 20th	Day	1 3 1 4 3 3 4 5% 8% 11% 57%	3026
	21st to end	Day	5% 3 9% 5% 4 4 5% 6% 9% 50%	4004
January	1st to 10th	Night	2 3 9% 6% 4 4 4 5% 8% 55%	6327
	11th to 20th	Night	1 1 6% 6% 4 5% 4 6% 8% 58%	6233
	21st to end	Night	4 3 7% 4 3 3 3 6% 8% 60%	6468
February	1st to 10th	Night	4 3 6% 4 3 4 3 5% 9% 59%	2600
	11th to 20th	Night	4 2 5% 4 3 3 4 7% 10% 57%	2407
	21st to end	Night	5% 3 8% 4 4 3 4 4 8% 57%	1980
March	1st to 10th	Night	5% 4 8% 5% 4 4 3 5% 7% 56%	5341
	11th to 20th	Night	1 6% 4 8% 3 4 4 4 5% 8% 53%	5000
	21st to end	Night	1 6% 3 5% 3 3 4 6% 8% 9% 51%	5196
April	1st to 10th	Night	1 6% 3 5% 4 4 4 3 6% 7% 57%	2000
	11th to 20th	Night	4 8% 3 6% 3 4 4 3 5% 8% 52%	1882
	21st to end	Night	6% 11% 2 4 3 3 3 4 6% 8% 50%	1900
May	1st to 10th	Night	4 10% 2 5% 3 4 4 4 6% 7% 50%	2878
	11th to 20th	Night	6% 11% 2 5% 4 4 4 4 5% 7% 47%	2517
	21st to end	Night	3 4 1 4 4 4 4 3 6% 7% 60%	2762
June	1st to 10th	Night	4 3 1 3 3 3 4 4 6% 10% 58%	1520
	11th to 20th	Night	4 4 1 3 2 3 3 4 6% 7% 62%	1520
	21st to end	Night	3 3 1 3 3 4 4 5% 7% 8% 59%	1520
July	1st to 10th	Night	3 5% 1 4 4 3 5% 3 6% 7% 59%	2540
	11th to 20th	Night	2 2 1 3 4 4 5% 6% 10% 11% 54%	2540
	21st to end	Night	3 4 2 3 4 4 5% 3 6% 7% 59%	2869
August	1st to 10th	Night	4 5% 2 5% 4 5% 5% 5% 9% 10% 47%	2847
	11th to 20th	Night	3 3 1 4 4 5% 5% 5% 6% 10% 54%	3044
	21st to end	Night	2 4 1 4 3 5% 5% 4 7% 10% 55%	3487
September	1st to 10th	Night	5% 5% 1 4 4 4 4 3 5% 7% 59%	1900
	11th to 20th	Night	5% 3 1 4 2 2 4 3 5% 6% 65%	1900
	21st to end	Night	5% 4 1 3 2 3 3 3 5% 6% 64%	2109
October	1st to 10th	Night	2 3 1 2 2 2 2 2 3 6% 74%	3800
	11th to 20th	Night	2 4 1 4 3 3 3 3 5% 8% 63%	3778
	21st to end	Night	2 5% 2 3 2 2 3 2 4 7% 67%	4177
November	1st to 10th	Night	1 4 1 4 2 2 3 3 5% 9% 64%	2535
	11th to 20th	Night	4 2 4 3 2 3 3 6% 9% 62%	2600
	21st to end	Night	1 4 2 6% 3 2 4 3 5% 10% 58%	2765
December	1st to 10th	Night	2 1 3 2 2 2 3 5% 7% 73%	4570
	11th to 20th	Night	2 2 5% 3 3 3 4 6% 10% 62%	5181
	21st to end	Night	5% 3 8% 4 4 5% 5% 7% 11% 48%	6974

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	23% 6% 15% 28% 22% 6%	3639
	11th to 20th	Day	25% 8% 19% 20% 19% 8%	3778
	21st to end	Day	22% 7% 12% 25% 21% 13%	4510
February	1st to 10th	Day	27% 8% 20% 25% 15% 6%	1800
	11th to 20th	Day	22% 8% 16% 31% 18% 5%	1887
	21st to end	Day	25% 9% 15% 24% 21% 6%	1650
March	1st to 10th	Day	27% 8% 10% 24% 23% 8%	4518
	11th to 20th	Day	30% 8% 14% 26% 20% 3	5000
	21st to end	Day	25% 7% 21% 36% 10% 1	5766
April	1st to 10th	Day	28% 9% 13% 26% 18% 6%	2400
	11th to 20th	Day	39% 8% 15% 19% 16% 3	2255
	21st to end	Day	40% 9% 14% 25% 12% 1	2280
May	1st to 10th	Day	40% 10% 14% 20% 15% 2	4075
	11th to 20th	Day	35% 12% 15% 23% 13% 2	4392
	21st to end	Day	25% 10% 14% 25% 23% 4	4825
June	1st to 10th	Day	29% 12% 16% 21% 15% 6%	2660
	11th to 20th	Day	28% 9% 12% 18% 23% 11%	2660
	21st to end	Day	28% 9% 11% 20% 21% 10%	2660
July	1st to 10th	Day	26% 9% 10% 15% 19% 21%	4361
	11th to 20th	Day	30% 11% 11% 19% 18% 11%	4355
	21st to end	Day	30% 11% 11% 17% 15% 17%	4543
August	1st to 10th	Day	36% 13% 14% 16% 13% 7%	4078
	11th to 20th	Day	28% 11% 13% 17% 19% 12%	3830
	21st to end	Day	26% 8% 12% 18% 24% 12%	4179
September	1st to 10th	Day	26% 9% 9% 19% 25% 12%	2280
	11th to 20th	Day	25% 9% 11% 19% 24% 11%	2280
	21st to end	Day	24% 5% 8% 23% 32% 7%	2066
October	1st to 10th	Day	18% 5% 8% 17% 31% 22%	3170
	11th to 20th	Day	22% 6% 11% 35% 21% 4	3150
	21st to end	Day	21% 4 9% 29% 32% 5%	3348
November	1st to 10th	Day	19% 6% 16% 25% 29% 4	1763
	11th to 20th	Day	17% 5% 18% 29% 23% 7%	1800
	21st to end	Day	24% 6% 13% 30% 19% 8%	1630
December	1st to 10th	Day	15% 5% 14% 36% 25% 6%	2620
	11th to 20th	Day	15% 8% 13% 39% 24% 2	3024
	21st to end	Day	24% 8% 12% 26% 23% 7%	4004
January	1st to 10th	Night	24% 6% 14% 29% 20% 7%	6327
	11th to 20th	Night	19% 8% 19% 24% 19% 12%	6233
	21st to end	Night	22% 6% 15% 22% 21% 14%	6468
February	1st to 10th	Night	22% 7% 22% 27% 17% 5%	2600
	11th to 20th	Night	21% 6% 19% 32% 19% 4	2408
	21st to end	Night	24% 5% 15% 26% 22% 8%	1980
March	1st to 10th	Night	25% 6% 10% 22% 26% 11%	5341
	11th to 20th	Night	25% 6% 11% 24% 28% 6%	5000
	21st to end	Night	23% 7% 22% 32% 14% 1	5196
April	1st to 10th	Night	24% 7% 15% 30% 18% 5%	2000
	11th to 20th	Night	29% 6% 16% 28% 17% 4	1882
	21st to end	Night	31% 7% 15% 29% 17% 1	1900
May	1st to 10th	Night	30% 8% 14% 31% 13% 3	2878
	11th to 20th	Night	34% 9% 15% 28% 14%	2518
	21st to end	Night	21% 9% 15% 29% 22% 4	2762
June	1st to 10th	Night	21% 10% 19% 29% 16% 6%	1520
	11th to 20th	Night	20% 6% 13% 21% 25% 15%	1520
	21st to end	Night	18% 8% 13% 23% 26% 12%	1520
July	1st to 10th	Night	22% 7% 9% 19% 21% 22%	2500
	11th to 20th	Night	16% 7% 14% 32% 20% 10%	2492
	21st to end	Night	21% 7% 13% 26% 15% 18%	2779
August	1st to 10th	Night	26% 10% 21% 20% 19% 3	2838
	11th to 20th	Night	22% 7% 22% 19% 20% 9%	3073
	21st to end	Night	20% 8% 15% 21% 29% 7%	3487
September	1st to 10th	Night	24% 6% 10% 20% 27% 13%	1900
	11th to 20th	Night	19% 6% 11% 27% 24% 13%	1900
	21st to end	Night	21% 5% 9% 29% 28% 8%	2109
October	1st to 10th	Night	14% 3 7% 24% 34% 18%	3800
	11th to 20th	Night	20% 4 12% 35% 23% 6%	3778
	21st to end	Night	18% 3 10% 33% 30% 6%	4177
November	1st to 10th	Night	17% 6% 16% 26% 27% 8%	2535
	11th to 20th	Night	17% 6% 16% 31% 24% 7%	2600
	21st to end	Night	21% 5% 13% 31% 22% 7%	2765
December	1st to 10th	Night	11% 4 15% 36% 28% 6%	4570
	11th to 20th	Night	15% 7% 12% 34% 30% 2	5182
	21st to end	Night	25% 8% 13% 23% 26% 5%	6974

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	29% 32% 19% 12% 7%	300
	11th to 20th	Day	27% 43% 18% 10% 2 1	300
	21st to end	Day	19% 46% 22% 11% 2 1	330
February	1st to 10th	Day	41% 38% 16% 3 1 1	300
	11th to 20th	Day	39% 36% 17% 7% 1	300
	21st to end	Day	37% 39% 15% 8%	249
March	1st to 10th	Day	29% 38% 24% 6% 3	305
	11th to 20th	Day	24% 33% 30% 11% 3	500
	21st to end	Day	25% 40% 26% 8% 1	550
April	1st to 10th	Day	26% 38% 27% 7% 2	500
	11th to 20th	Day	29% 35% 25% 8% 2	453
	21st to end	Day	23% 29% 32% 11% 4 1	460
May	1st to 10th	Day	27% 29% 26% 12% 5% 1	567
	11th to 20th	Day	19% 20% 34% 18% 8% 1	675
	21st to end	Day	17% 18% 33% 21% 10% 1	734
June	1st to 10th	Day	9% 19% 32% 23% 14% 4	680
	11th to 20th	Day	12% 25% 33% 20% 8% 2	680
	21st to end	Day	10% 17% 36% 21% 13% 3	680
July	1st to 10th	Day	8% 11% 30% 31% 17% 4	671
	11th to 20th	Day	6% 11% 33% 29% 14% 6%	668
	21st to end	Day	8% 9% 29% 33% 17% 5%	677
August	1st to 10th	Day	12% 17% 33% 27% 10% 1	487
	11th to 20th	Day	11% 16% 33% 27% 10% 3	477
	21st to end	Day	11% 16% 31% 29% 10% 3	539
September	1st to 10th	Day	10% 17% 33% 27% 11% 2	490
	11th to 20th	Day	11% 23% 38% 16% 10% 1	490
	21st to end	Day	13% 23% 27% 22% 11% 4	304
October	1st to 10th	Day	15% 21% 32% 20% 9% 4	300
	11th to 20th	Day	23% 32% 26% 14% 4 1	300
	21st to end	Day	29% 32% 24% 12% 2 1	330
November	1st to 10th	Day	28% 35% 21% 10% 6%	300
	11th to 20th	Day	29% 39% 21% 8% 3 1	300
	21st to end	Day	20% 41% 27% 10% 2	300
December	1st to 10th	Day	26% 38% 23% 9% 2 2	300
	11th to 20th	Day	31% 47% 14% 7% 1	300
	21st to end	Day	29% 43% 18% 8% 2 1	330
January	1st to 10th	Night	21% 40% 20% 13% 5% 1	1000
	11th to 20th	Night	25% 41% 19% 10% 4 1	958
	21st to end	Night	14% 48% 25% 10% 3	880
February	1st to 10th	Night	19% 49% 20% 9% 3	800
	11th to 20th	Night	20% 41% 27% 11% 2	784
	21st to end	Night	25% 42% 21% 10% 2	660
March	1st to 10th	Night	14% 43% 26% 12% 5%	800
	11th to 20th	Night	14% 35% 26% 18% 6%	800
	21st to end	Night	17% 36% 27% 16% 3 1	755
April	1st to 10th	Night	17% 33% 33% 15% 3	600
	11th to 20th	Night	16% 32% 26% 19% 6% 1	565
	21st to end	Night	16% 26% 30% 19% 8% 1	570
May	1st to 10th	Night	14% 21% 33% 22% 9% 1	570
	11th to 20th	Night	15% 12% 31% 29% 12% 1	561
	21st to end	Night	10% 14% 29% 30% 15% 1	617
June	1st to 10th	Night	7% 9% 30% 32% 19% 3	570
	11th to 20th	Night	6% 17% 33% 32% 11% 1	570
	21st to end	Night	6% 10% 25% 35% 21% 3	570
July	1st to 10th	Night	6% 5% 18% 38% 30% 4	555
	11th to 20th	Night	3 4 25% 35% 27% 6%	552
	21st to end	Night	5% 5% 14% 39% 32% 5%	624
August	1st to 10th	Night	7% 4 19% 42% 24% 3	567
	11th to 20th	Night	6% 5% 22% 43% 20% 4	564
	21st to end	Night	4 8% 19% 36% 27% 5%	627
September	1st to 10th	Night	8% 6% 27% 34% 19% 5%	570
	11th to 20th	Night	8% 13% 27% 33% 15% 4	570
	21st to end	Night	10% 14% 28% 30% 14% 4	594
October	1st to 10th	Night	10% 26% 26% 25% 10% 2	760
	11th to 20th	Night	11% 32% 30% 19% 6% 2	760
	21st to end	Night	15% 36% 30% 12% 5% 2	869
November	1st to 10th	Night	14% 42% 26% 13% 4 1	975
	11th to 20th	Night	23% 41% 25% 8% 2 1	1000
	21st to end	Night	16% 40% 29% 12% 2	1000
December	1st to 10th	Night	20% 45% 24% 9% 3	1000
	11th to 20th	Night	23% 43% 21% 10% 2	1000
	21st to end	Night	23% 42% 21% 11% 4	1100

Page generated at 2025-04-08 07:17:28. Version ac07

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