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 2026-08-15.

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% 2 6% 5% 5% 6% 5% 7% 9% 48%	152781
	Night	2 4 2 5% 3 4 4 4 6% 9% 57%	146629
Transparency	Day	26% 8% 13% 24% 20% 9%	147710
	Night	21% 6% 14% 27% 23% 8%	142709
Seeing	Day	21% 27% 28% 16% 7% 2	18087
	Night	16% 30% 25% 19% 9% 1	28046

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	4 3 11% 5% 4 4 4 6% 7% 53%	4720
	11th to 20th	Day	2 2 5% 4 6% 4 5% 8% 8% 56%	4920
	21st to end	Day	3 3 7% 3 3 3 4 6% 8% 59%	5844
February	1st to 10th	Day	1 4 3 8% 5% 5% 4 3 6% 9% 51%	1890
	11th to 20th	Day	4 2 7% 5% 4 5% 6% 8% 8% 52%	1975
	21st to end	Day	4 4 8% 5% 5% 4 4 7% 10% 49%	1730
March	1st to 10th	Day	1 6% 4 10% 5% 5% 6% 4 5% 5% 51%	4618
	11th to 20th	Day	1 7% 6% 9% 4 4 5% 4 6% 10% 44%	5110
	21st to end	Day	1 6% 3 6% 4 4 5% 5% 7% 11% 46%	5893
April	1st to 10th	Day	2 8% 3 6% 4 5% 4 4 6% 11% 47%	2520
	11th to 20th	Day	4 13% 5% 8% 4 5% 5% 4 7% 8% 39%	2491
	21st to end	Day	5% 12% 3 8% 5% 5% 6% 4 6% 8% 36%	2520
May	1st to 10th	Day	6% 15% 4 7% 4 5% 6% 4 6% 7% 36%	7561
	11th to 20th	Day	6% 10% 3 6% 4 5% 5% 5% 8% 8% 41%	8191
	21st to end	Day	5% 6% 2 6% 5% 6% 7% 6% 9% 9% 39%	9026
June	1st to 10th	Day	5% 6% 2 5% 6% 5% 6% 5% 7% 9% 44%	2940
	11th to 20th	Day	6% 5% 2 4 4 3 5% 5% 7% 8% 52%	2940
	21st to end	Day	3 5% 2 6% 4 5% 6% 5% 7% 9% 48%	2940
July	1st to 10th	Day	3 3 1 5% 5% 5% 7% 6% 8% 9% 47%	8249
	11th to 20th	Day	2 3 2 6% 6% 5% 7% 6% 8% 9% 45%	8250
	21st to end	Day	4 5% 2 7% 6% 7% 8% 6% 8% 9% 37%	8748
August	1st to 10th	Day	4 4 2 7% 6% 6% 7% 6% 9% 11% 39%	5909
	11th to 20th	Day	4 3 1 6% 5% 5% 6% 6% 8% 9% 46%	5511
	21st to end	Day	7% 6% 3 9% 6% 6% 6% 5% 6% 8% 39%	5984
September	1st to 10th	Day	6% 5% 2 5% 4 4 5% 4 5% 7% 52%	2400
	11th to 20th	Day	6% 4 2 5% 5% 4 5% 4 5% 7% 53%	2400
	21st to end	Day	7% 6% 2 4 3 3 3 3 5% 6% 59%	2174
October	1st to 10th	Day	3 4 2 4 2 3 3 2 4 6% 68%	3270
	11th to 20th	Day	2 5% 1 4 4 4 5% 4 7% 9% 54%	3250
	21st to end	Day	3 6% 2 5% 3 3 3 3 4 7% 62%	3455
November	1st to 10th	Day	1 4 2 4 3 3 4 3 6% 8% 61%	1853
	11th to 20th	Day	4 2 4 4 2 3 3 6% 11% 60%	1890
	21st to end	Day	3 2 7% 5% 5% 4 3 6% 8% 57%	1711
December	1st to 10th	Day	2 2 4 2 3 3 3 4 8% 67%	2700
	11th to 20th	Day	1 3 1 4 3 3 4 5% 8% 11% 57%	3106
	21st to end	Day	5% 3 8% 5% 4 4 5% 6% 9% 51%	4092
January	1st to 10th	Night	2 2 8% 5% 4 5% 5% 6% 8% 55%	8201
	11th to 20th	Night	1 1 6% 5% 4 5% 4 6% 8% 60%	8115
	21st to end	Night	3 2 6% 4 3 3 3 6% 8% 61%	8370
February	1st to 10th	Night	4 2 6% 4 3 4 3 5% 9% 60%	2730
	11th to 20th	Night	4 2 5% 4 3 3 4 7% 10% 57%	2530
	21st to end	Night	5% 3 7% 4 4 3 3 4 9% 58%	2076
March	1st to 10th	Night	5% 4 8% 5% 4 3 3 5% 7% 56%	5461
	11th to 20th	Night	1 6% 4 8% 3 4 4 4 5% 8% 53%	5110
	21st to end	Night	1 6% 3 5% 3 3 4 6% 8% 9% 52%	5311
April	1st to 10th	Night	1 6% 3 5% 3 4 4 4 6% 7% 57%	2100
	11th to 20th	Night	3 8% 3 6% 3 4 4 3 4 8% 52%	2077
	21st to end	Night	5% 11% 2 4 4 3 3 4 6% 8% 50%	2100
May	1st to 10th	Night	5% 13% 3 5% 3 4 4 4 5% 7% 47%	5355
	11th to 20th	Night	5% 9% 3 6% 4 4 4 3 5% 8% 49%	4701
	21st to end	Night	3 6% 2 5% 4 5% 4 3 6% 8% 54%	5181
June	1st to 10th	Night	4 4 1 4 3 3 4 4 6% 10% 58%	1680
	11th to 20th	Night	3 4 1 3 2 3 3 4 6% 7% 63%	1680
	21st to end	Night	3 3 2 3 3 4 4 5% 7% 8% 59%	1680
July	1st to 10th	Night	2 3 1 3 3 3 5% 4 7% 9% 61%	4740
	11th to 20th	Night	1 3 1 2 3 3 4 5% 8% 10% 61%	4740
	21st to end	Night	2 3 1 4 4 5% 6% 5% 9% 10% 51%	5344
August	1st to 10th	Night	3 4 2 4 4 5% 5% 5% 10% 11% 48%	4123
	11th to 20th	Night	2 2 1 4 3 4 4 4 6% 10% 58%	4425
	21st to end	Night	4 5% 2 5% 4 5% 5% 4 7% 10% 48%	4993
September	1st to 10th	Night	5% 5% 1 4 4 4 4 3 5% 7% 59%	2000
	11th to 20th	Night	5% 4 1 4 2 3 4 3 5% 6% 64%	2000
	21st to end	Night	5% 4 1 3 2 3 3 3 5% 5% 63%	2220
October	1st to 10th	Night	2 3 1 2 2 2 2 2 3 6% 74%	3920
	11th to 20th	Night	2 4 1 5% 3 3 3 3 5% 8% 63%	3898
	21st to end	Night	2 4 2 3 2 2 3 2 4 7% 68%	4311
November	1st to 10th	Night	1 4 1 4 2 2 3 3 5% 9% 65%	2665
	11th to 20th	Night	4 2 4 3 3 3 3 6% 10% 62%	2730
	21st to end	Night	1 4 2 6% 3 3 4 4 5% 10% 58%	2903
December	1st to 10th	Night	2 1 4 2 2 2 3 5% 8% 72%	4710
	11th to 20th	Night	2 2 5% 3 3 3 4 6% 10% 62%	5321
	21st to end	Night	5% 3 8% 4 4 5% 5% 7% 11% 49%	7128

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	24% 5% 13% 30% 24% 5%	4723
	11th to 20th	Day	20% 7% 18% 27% 18% 11%	4920
	21st to end	Day	20% 6% 12% 26% 24% 12%	5844
February	1st to 10th	Day	26% 8% 20% 27% 15% 6%	1890
	11th to 20th	Day	22% 8% 15% 31% 19% 5%	1984
	21st to end	Day	24% 9% 15% 24% 22% 6%	1730
March	1st to 10th	Day	27% 8% 10% 24% 23% 8%	4618
	11th to 20th	Day	29% 8% 14% 26% 20% 4	5110
	21st to end	Day	25% 7% 21% 36% 10% 1	5893
April	1st to 10th	Day	27% 9% 13% 27% 18% 6%	2520
	11th to 20th	Day	37% 8% 14% 19% 18% 4	2494
	21st to end	Day	39% 8% 14% 24% 13% 2	2520
May	1st to 10th	Day	38% 9% 13% 26% 13% 2	7561
	11th to 20th	Day	31% 9% 12% 20% 20% 7%	8195
	21st to end	Day	29% 11% 13% 22% 21% 4	9027
June	1st to 10th	Day	28% 12% 16% 21% 16% 6%	2940
	11th to 20th	Day	26% 8% 11% 17% 24% 13%	2940
	21st to end	Day	27% 9% 11% 20% 22% 11%	2940
July	1st to 10th	Day	22% 7% 9% 15% 23% 24%	8181
	11th to 20th	Day	22% 10% 11% 23% 18% 15%	8175
	21st to end	Day	31% 13% 16% 16% 13% 12%	8553
August	1st to 10th	Day	35% 13% 13% 16% 14% 9%	4338
	11th to 20th	Day	27% 12% 14% 17% 19% 12%	4004
	21st to end	Day	27% 8% 12% 18% 23% 12%	4311
September	1st to 10th	Day	26% 9% 9% 20% 25% 11%	2400
	11th to 20th	Day	25% 9% 11% 19% 24% 11%	2400
	21st to end	Day	24% 5% 8% 23% 32% 7%	2174
October	1st to 10th	Day	18% 5% 8% 17% 31% 21%	3270
	11th to 20th	Day	22% 6% 10% 35% 22% 5%	3250
	21st to end	Day	21% 4 9% 29% 32% 5%	3455
November	1st to 10th	Day	19% 6% 15% 25% 31% 4	1853
	11th to 20th	Day	18% 5% 17% 30% 23% 7%	1890
	21st to end	Day	23% 6% 13% 31% 19% 8%	1711
December	1st to 10th	Day	15% 5% 14% 36% 25% 6%	2700
	11th to 20th	Day	15% 7% 13% 39% 23% 2	3104
	21st to end	Day	24% 8% 12% 26% 24% 7%	4092
January	1st to 10th	Night	22% 5% 12% 33% 21% 7%	8202
	11th to 20th	Night	17% 7% 18% 26% 21% 12%	8115
	21st to end	Night	19% 6% 14% 21% 25% 15%	8370
February	1st to 10th	Night	21% 7% 21% 28% 18% 5%	2730
	11th to 20th	Night	21% 5% 19% 32% 19% 4	2531
	21st to end	Night	23% 5% 15% 25% 24% 8%	2076
March	1st to 10th	Night	25% 6% 10% 22% 26% 10%	5461
	11th to 20th	Night	25% 6% 11% 24% 27% 7%	5110
	21st to end	Night	23% 7% 22% 32% 14% 2	5311
April	1st to 10th	Night	23% 7% 16% 30% 18% 5%	2100
	11th to 20th	Night	29% 6% 15% 27% 19% 4	2077
	21st to end	Night	30% 7% 14% 29% 18% 1	2100
May	1st to 10th	Night	35% 7% 14% 30% 13% 1	5353
	11th to 20th	Night	32% 6% 12% 27% 17% 5%	4702
	21st to end	Night	25% 8% 15% 27% 22% 3	5182
June	1st to 10th	Night	21% 9% 18% 29% 17% 6%	1680
	11th to 20th	Night	19% 6% 13% 22% 25% 16%	1680
	21st to end	Night	19% 8% 12% 23% 26% 14%	1680
July	1st to 10th	Night	17% 6% 6% 17% 32% 21%	4700
	11th to 20th	Night	14% 6% 15% 31% 21% 13%	4692
	21st to end	Night	22% 10% 23% 20% 13% 12%	5227
August	1st to 10th	Night	26% 10% 20% 19% 21% 5%	3018
	11th to 20th	Night	22% 7% 22% 19% 21% 9%	3208
	21st to end	Night	20% 8% 15% 21% 28% 7%	3597
September	1st to 10th	Night	24% 6% 10% 22% 27% 12%	2000
	11th to 20th	Night	19% 6% 11% 27% 24% 12%	2000
	21st to end	Night	21% 5% 9% 29% 28% 8%	2220
October	1st to 10th	Night	14% 3 7% 24% 34% 18%	3920
	11th to 20th	Night	20% 4 12% 34% 24% 6%	3898
	21st to end	Night	18% 3 9% 32% 31% 7%	4311
November	1st to 10th	Night	16% 6% 15% 27% 27% 8%	2665
	11th to 20th	Night	17% 6% 16% 32% 23% 6%	2730
	21st to end	Night	21% 5% 13% 31% 22% 7%	2903
December	1st to 10th	Night	11% 4 15% 35% 28% 6%	4710
	11th to 20th	Night	14% 7% 12% 34% 30% 3	5322
	21st to end	Night	24% 8% 13% 24% 26% 5%	7128

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	33% 31% 18% 11% 6%	330
	11th to 20th	Day	31% 41% 17% 9% 2 1	330
	21st to end	Day	24% 44% 20% 10% 2 1	363
February	1st to 10th	Day	42% 36% 15% 4 1 1	330
	11th to 20th	Day	41% 35% 16% 6% 1	330
	21st to end	Day	40% 38% 14% 8%	273
March	1st to 10th	Day	31% 39% 22% 5% 2	335
	11th to 20th	Day	29% 31% 27% 10% 3	540
	21st to end	Day	26% 41% 24% 7% 1	594
April	1st to 10th	Day	27% 37% 27% 7% 2	540
	11th to 20th	Day	32% 36% 22% 7% 2	532
	21st to end	Day	26% 29% 31% 11% 3 1	540
May	1st to 10th	Day	27% 31% 26% 12% 5%	658
	11th to 20th	Day	21% 23% 32% 16% 7% 1	775
	21st to end	Day	17% 21% 33% 19% 8% 1	844
June	1st to 10th	Day	11% 21% 32% 21% 13% 3	780
	11th to 20th	Day	14% 27% 32% 18% 7% 2	780
	21st to end	Day	12% 19% 36% 19% 11% 3	780
July	1st to 10th	Day	7% 13% 32% 29% 15% 3	771
	11th to 20th	Day	6% 12% 35% 29% 13% 5%	768
	21st to end	Day	9% 12% 29% 31% 15% 4	780
August	1st to 10th	Day	12% 22% 32% 23% 9% 1	567
	11th to 20th	Day	11% 16% 34% 26% 10% 3	534
	21st to end	Day	11% 17% 33% 27% 9% 3	583
September	1st to 10th	Day	10% 18% 34% 26% 10% 2	530
	11th to 20th	Day	12% 25% 37% 16% 9% 1	530
	21st to end	Day	14% 23% 27% 21% 10% 4	334
October	1st to 10th	Day	16% 23% 31% 19% 8% 3	330
	11th to 20th	Day	27% 30% 25% 13% 4 1	330
	21st to end	Day	29% 33% 24% 11% 2 1	363
November	1st to 10th	Day	31% 35% 19% 9% 5%	330
	11th to 20th	Day	30% 38% 20% 8% 2 1	330
	21st to end	Day	22% 40% 26% 10% 2	330
December	1st to 10th	Day	32% 36% 21% 8% 2 2	330
	11th to 20th	Day	35% 45% 13% 7% 1	330
	21st to end	Day	34% 40% 16% 7% 1 1	363
January	1st to 10th	Night	23% 38% 20% 13% 5% 1	1050
	11th to 20th	Night	27% 41% 19% 10% 4 1	1006
	21st to end	Night	17% 48% 23% 9% 3	924
February	1st to 10th	Night	20% 49% 19% 9% 3	840
	11th to 20th	Night	20% 42% 26% 10% 2	824
	21st to end	Night	27% 41% 20% 10% 2	692
March	1st to 10th	Night	15% 43% 25% 11% 5%	840
	11th to 20th	Night	18% 34% 25% 17% 5%	840
	21st to end	Night	18% 37% 26% 15% 3 1	793
April	1st to 10th	Night	17% 33% 33% 15% 3	630
	11th to 20th	Night	18% 33% 26% 17% 5% 1	623
	21st to end	Night	17% 26% 31% 18% 7% 1	630
May	1st to 10th	Night	14% 23% 33% 22% 8% 1	630
	11th to 20th	Night	16% 15% 31% 27% 11% 1	621
	21st to end	Night	10% 15% 31% 28% 14% 1	683
June	1st to 10th	Night	8% 11% 31% 30% 18% 2	630
	11th to 20th	Night	6% 18% 36% 29% 10% 1	630
	21st to end	Night	7% 12% 26% 33% 19% 3	630
July	1st to 10th	Night	6% 6% 21% 37% 27% 3	615
	11th to 20th	Night	3 5% 26% 36% 25% 5%	612
	21st to end	Night	4 5% 17% 40% 29% 5%	690
August	1st to 10th	Night	7% 7% 23% 39% 22% 3	627
	11th to 20th	Night	5% 5% 24% 43% 19% 4	606
	21st to end	Night	5% 8% 20% 36% 26% 5%	660
September	1st to 10th	Night	8% 7% 28% 34% 19% 5%	600
	11th to 20th	Night	8% 14% 28% 31% 14% 4	600
	21st to end	Night	10% 15% 29% 29% 14% 4	625
October	1st to 10th	Night	11% 26% 27% 24% 10% 2	800
	11th to 20th	Night	13% 32% 30% 18% 6% 2	800
	21st to end	Night	16% 36% 30% 12% 5% 2	915
November	1st to 10th	Night	16% 43% 25% 12% 4	1025
	11th to 20th	Night	24% 41% 25% 8% 2 1	1050
	21st to end	Night	17% 40% 28% 12% 2	1050
December	1st to 10th	Night	22% 43% 23% 9% 3	1050
	11th to 20th	Night	26% 41% 20% 10% 2	1050
	21st to end	Night	24% 42% 20% 10% 4	1155

Page generated at 2026-08-12 01:37:19. Version ac07

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