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 2024-10-24.

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% 46%	101298
	Night	2 5% 2 5% 4 4 4 4 6% 8% 56%	97702
Transparency	Day	28% 10% 14% 23% 18% 7%	101043
	Night	23% 8% 16% 27% 20% 7%	97547
Seeing	Day	18% 26% 29% 18% 8% 2	15587
	Night	14% 29% 25% 20% 10% 2	25575

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 10% 5% 5% 4 3 6% 8% 54%	2538
	11th to 20th	Day	3 3 10% 6% 8% 5% 4 7% 9% 45%	2636
	21st to end	Day	6% 5% 9% 4 3 4 3 5% 7% 53%	3146
February	1st to 10th	Day	1 4 4 8% 5% 5% 5% 4 6% 9% 49%	1710
	11th to 20th	Day	4 2 6% 5% 4 4 5% 8% 8% 53%	1781
	21st to end	Day	5% 4 9% 5% 5% 4 4 7% 11% 45%	1570
March	1st to 10th	Day	1 7% 4 11% 5% 5% 6% 5% 6% 6% 47%	3148
	11th to 20th	Day	1 10% 8% 11% 3 4 4 3 6% 9% 42%	3490
	21st to end	Day	1 9% 5% 8% 5% 5% 5% 4 6% 10% 42%	4027
April	1st to 10th	Day	2 9% 3 5% 5% 5% 4 4 6% 11% 46%	2280
	11th to 20th	Day	4 14% 5% 8% 5% 5% 5% 4 7% 8% 36%	2251
	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	5% 6% 2 6% 3 4 4 3 5% 7% 54%	1900
	11th to 20th	Day	2 5% 1 4 3 4 4 3 5% 7% 62%	1900
	21st to end	Day	3 7% 2 6% 3 4 4 3 4 6% 57%	1959
November	1st to 10th	Day	1 4 2 4 3 3 4 4 6% 7% 63%	1673
	11th to 20th	Day	1 5% 2 4 4 2 3 3 5% 11% 60%	1710
	21st to end	Day	4 2 7% 5% 4 4 3 6% 8% 56%	1549
December	1st to 10th	Day	4 4 7% 3 5% 3 4 5% 10% 55%	1520
	11th to 20th	Day	1 4 2 6% 4 4 4 4 9% 11% 51%	1926
	21st to end	Day	5% 3 11% 5% 5% 4 3 5% 8% 49%	2794
January	1st to 10th	Night	2 2 9% 7% 5% 4 4 5% 8% 53%	4417
	11th to 20th	Night	2 1 6% 7% 4 4 4 6% 9% 58%	4365
	21st to end	Night	5% 3 8% 3 3 3 3 5% 9% 57%	4521
February	1st to 10th	Night	4 3 6% 5% 3 4 3 5% 9% 57%	2470
	11th to 20th	Night	4 2 5% 4 3 3 4 6% 9% 58%	2284
	21st to end	Night	5% 3 8% 4 4 3 4 4 8% 56%	1884
March	1st to 10th	Night	5% 4 6% 4 4 4 3 6% 8% 56%	3714
	11th to 20th	Night	1 8% 6% 9% 3 3 3 3 5% 7% 53%	3490
	21st to end	Night	1 6% 3 5% 4 4 4 4 7% 9% 53%	3619
April	1st to 10th	Night	1 6% 3 5% 3 4 4 3 6% 7% 57%	1900
	11th to 20th	Night	4 8% 3 6% 3 4 4 3 5% 8% 52%	1877
	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	4 5% 2 4 3 3 3 3 5% 8% 61%	2280
	11th to 20th	Night	2 3 1 4 3 2 2 3 5% 7% 68%	2280
	21st to end	Night	3 6% 2 5% 3 3 3 3 5% 8% 58%	2443
November	1st to 10th	Night	1 4 1 4 2 2 4 3 5% 9% 65%	2405
	11th to 20th	Night	4 2 4 3 2 3 3 6% 9% 62%	2470
	21st to end	Night	1 5% 2 6% 3 3 4 4 5% 10% 58%	2626
December	1st to 10th	Night	3 1 5% 3 3 3 3 5% 10% 63%	2660
	11th to 20th	Night	1 4 3 6% 4 4 3 4 7% 12% 53%	3271
	21st to end	Night	6% 3 9% 5% 4 4 4 6% 8% 51%	4873

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% 9% 21% 26% 18% 4	2539
	11th to 20th	Day	27% 12% 26% 20% 12% 3	2636
	21st to end	Day	26% 9% 17% 26% 17% 5%	3146
February	1st to 10th	Day	28% 8% 20% 25% 14% 4	1710
	11th to 20th	Day	22% 8% 16% 31% 18% 5%	1790
	21st to end	Day	26% 9% 16% 25% 18% 6%	1570
March	1st to 10th	Day	27% 11% 13% 27% 19% 4	3148
	11th to 20th	Day	33% 11% 17% 27% 11% 2	3490
	21st to end	Day	32% 9% 20% 29% 9% 1	4027
April	1st to 10th	Day	28% 9% 14% 26% 18% 6%	2280
	11th to 20th	Day	39% 8% 15% 19% 16% 3	2254
	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	27% 8% 10% 22% 25% 8%	1900
	11th to 20th	Day	20% 7% 10% 31% 26% 7%	1900
	21st to end	Day	24% 7% 13% 29% 20% 7%	1959
November	1st to 10th	Day	18% 6% 16% 26% 30% 4	1673
	11th to 20th	Day	18% 5% 19% 30% 23% 5%	1710
	21st to end	Day	24% 6% 13% 30% 18% 8%	1549
December	1st to 10th	Day	23% 8% 21% 28% 15% 5%	1520
	11th to 20th	Day	20% 10% 16% 34% 18% 1	1924
	21st to end	Day	28% 10% 13% 23% 21% 6%	2794
January	1st to 10th	Night	25% 8% 19% 29% 17% 3	4417
	11th to 20th	Night	17% 11% 26% 25% 14% 7%	4365
	21st to end	Night	25% 9% 19% 26% 16% 6%	4521
February	1st to 10th	Night	22% 7% 22% 28% 16% 4	2470
	11th to 20th	Night	21% 6% 20% 31% 19% 4	2285
	21st to end	Night	25% 6% 16% 26% 21% 7%	1884
March	1st to 10th	Night	22% 8% 14% 29% 21% 6%	3714
	11th to 20th	Night	28% 7% 15% 31% 16% 3	3490
	21st to end	Night	25% 8% 22% 31% 12% 2	3619
April	1st to 10th	Night	24% 7% 16% 29% 18% 6%	1900
	11th to 20th	Night	29% 6% 16% 28% 16% 4	1877
	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	23% 5% 11% 26% 26% 10%	2280
	11th to 20th	Night	17% 4 15% 30% 25% 10%	2280
	21st to end	Night	25% 5% 14% 27% 23% 6%	2443
November	1st to 10th	Night	16% 6% 17% 27% 26% 8%	2405
	11th to 20th	Night	17% 6% 17% 32% 22% 6%	2470
	21st to end	Night	21% 6% 14% 31% 21% 8%	2626
December	1st to 10th	Night	18% 7% 24% 27% 18% 6%	2660
	11th to 20th	Night	20% 10% 18% 29% 21% 3	3272
	21st to end	Night	26% 10% 15% 23% 21% 5%	4873

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	26% 32% 21% 13% 8%	270
	11th to 20th	Day	27% 41% 18% 11% 3 1	270
	21st to end	Day	15% 47% 23% 12% 2 1	297
February	1st to 10th	Day	35% 41% 18% 3 1 1	270
	11th to 20th	Day	37% 37% 18% 7% 1	270
	21st to end	Day	36% 40% 14% 9%	225
March	1st to 10th	Day	29% 37% 25% 6% 3	275
	11th to 20th	Day	20% 32% 32% 12% 3	460
	21st to end	Day	23% 40% 27% 8% 2	506
April	1st to 10th	Day	25% 37% 28% 8% 2	460
	11th to 20th	Day	29% 35% 25% 8% 2	452
	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	28% 31% 25% 13% 2 1	306
November	1st to 10th	Day	27% 36% 20% 10% 6%	270
	11th to 20th	Day	24% 41% 22% 9% 3 1	270
	21st to end	Day	16% 41% 30% 11% 2	270
December	1st to 10th	Day	25% 40% 23% 10% 2 1	270
	11th to 20th	Day	26% 49% 16% 8% 1	270
	21st to end	Day	26% 44% 19% 9% 2 1	297
January	1st to 10th	Night	19% 40% 21% 13% 5% 1	950
	11th to 20th	Night	24% 42% 19% 11% 4 1	911
	21st to end	Night	13% 49% 24% 10% 3	836
February	1st to 10th	Night	16% 50% 21% 9% 3	760
	11th to 20th	Night	18% 41% 28% 11% 2	744
	21st to end	Night	23% 43% 22% 11% 2	628
March	1st to 10th	Night	13% 43% 25% 12% 6%	760
	11th to 20th	Night	12% 35% 27% 19% 6%	760
	21st to end	Night	16% 37% 27% 16% 3 1	717
April	1st to 10th	Night	16% 32% 34% 15% 3	570
	11th to 20th	Night	16% 32% 26% 19% 6% 1	563
	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	14% 36% 31% 13% 6% 2	835
November	1st to 10th	Night	14% 42% 26% 13% 5% 1	925
	11th to 20th	Night	21% 40% 26% 9% 2 1	950
	21st to end	Night	14% 40% 31% 13% 2	950
December	1st to 10th	Night	19% 45% 23% 9% 3	950
	11th to 20th	Night	21% 44% 22% 11% 3	950
	21st to end	Night	21% 41% 22% 11% 4	1045

Page generated at 2024-10-21 00:19:59. Version ac07

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