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 2024-02-20.

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	4 6% 3 6% 6% 3 5% 5% 6% 8% 47%	78453
	Night	2 4 2 5% 4 3 4 4 5% 9% 57%	80800
Transparency	Day	30% 9% 15% 23% 18% 6%	78160
	Night	23% 8% 17% 27% 20% 6%	80615
Seeing	Day	18% 26% 29% 18% 8% 2	14567
	Night	14% 29% 25% 20% 10% 2	24777

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 9% 6% 3 4 4 5% 8% 54%	2538
	11th to 20th	Day	3 3 8% 8% 6% 5% 5% 7% 9% 45%	2636
	21st to end	Day	5% 6% 8% 5% 3 4 4 5% 7% 53%	3146
February	1st to 10th	Day	1 4 4 7% 6% 4 6% 4 7% 9% 49%	1710
	11th to 20th	Day	4 2 5% 6% 2 5% 6% 7% 9% 54%	1771
	21st to end	Day	4 5% 8% 7% 4 4 5% 7% 12% 44%	1480
March	1st to 10th	Day	1 6% 3 6% 6% 4 6% 5% 6% 8% 48%	1804
	11th to 20th	Day	2 8% 5% 8% 4 3 4 5% 6% 10% 46%	1980
	21st to end	Day	2 10% 5% 7% 5% 3 5% 6% 7% 12% 39%	2290
April	1st to 10th	Day	3 8% 3 4 5% 3 5% 5% 6% 11% 46%	2160
	11th to 20th	Day	5% 12% 6% 7% 5% 4 5% 5% 7% 8% 36%	2131
	21st to end	Day	6% 11% 4 7% 6% 4 6% 6% 5% 9% 35%	2160
May	1st to 10th	Day	8% 13% 4 6% 5% 4 6% 6% 6% 8% 34%	2312
	11th to 20th	Day	11% 13% 3 5% 6% 3 6% 6% 6% 8% 34%	2478
	21st to end	Day	8% 9% 3 6% 6% 4 7% 7% 7% 8% 34%	2724
June	1st to 10th	Day	5% 6% 2 5% 6% 4 6% 6% 6% 10% 45%	2520
	11th to 20th	Day	7% 5% 2 4 5% 2 4 5% 7% 9% 50%	2520
	21st to end	Day	4 4 3 5% 5% 3 6% 6% 6% 9% 47%	2520
July	1st to 10th	Day	7% 4 3 6% 7% 3 7% 6% 7% 8% 41%	2520
	11th to 20th	Day	5% 4 2 6% 6% 3 6% 6% 7% 9% 44%	2520
	21st to end	Day	7% 7% 3 7% 7% 4 7% 7% 8% 8% 35%	2684
August	1st to 10th	Day	9% 7% 3 8% 7% 4 6% 7% 6% 8% 35%	2328
	11th to 20th	Day	8% 5% 2 6% 7% 4 5% 5% 6% 7% 44%	2166
	21st to end	Day	8% 6% 2 6% 7% 4 5% 6% 6% 8% 41%	2376
September	1st to 10th	Day	7% 4 2 5% 5% 3 5% 5% 5% 6% 53%	2160
	11th to 20th	Day	7% 4 2 4 5% 3 5% 5% 5% 7% 53%	2160
	21st to end	Day	7% 6% 2 3 4 2 3 4 5% 6% 59%	1958
October	1st to 10th	Day	5% 6% 2 5% 4 3 5% 5% 5% 8% 52%	1800
	11th to 20th	Day	3 5% 1 3 4 2 4 3 5% 7% 63%	1800
	21st to end	Day	3 7% 2 5% 4 3 5% 4 4 7% 57%	1929
November	1st to 10th	Day	1 4 2 3 4 2 3 4 5% 8% 63%	1673
	11th to 20th	Day	1 4 3 4 4 2 3 4 5% 11% 60%	1710
	21st to end	Day	3 3 6% 6% 3 4 4 5% 9% 56%	1549
December	1st to 10th	Day	3 4 6% 4 3 5% 5% 5% 10% 55%	1520
	11th to 20th	Day	1 4 2 5% 5% 3 4 5% 9% 10% 51%	1926
	21st to end	Day	5% 4 9% 6% 4 5% 4 5% 9% 49%	2794
January	1st to 10th	Night	2 2 7% 8% 3 5% 5% 6% 9% 53%	4417
	11th to 20th	Night	2 1 5% 8% 3 4 5% 5% 9% 58%	4365
	21st to end	Night	5% 3 7% 4 2 4 3 5% 8% 57%	4521
February	1st to 10th	Night	4 3 6% 5% 2 4 4 5% 10% 58%	2470
	11th to 20th	Night	3 3 5% 4 2 4 4 6% 10% 58%	2278
	21st to end	Night	5% 4 7% 5% 3 3 5% 4 8% 55%	1776
March	1st to 10th	Night	4 2 4 4 3 4 4 7% 12% 56%	2153
	11th to 20th	Night	2 5% 3 6% 3 2 4 4 5% 8% 57%	1980
	21st to end	Night	2 6% 3 4 4 2 4 5% 6% 10% 54%	2066
April	1st to 10th	Night	1 6% 3 5% 4 3 4 4 6% 8% 57%	1800
	11th to 20th	Night	4 8% 3 5% 4 3 4 4 4 8% 52%	1777
	21st to end	Night	6% 10% 2 3 4 3 3 5% 6% 9% 50%	1800
May	1st to 10th	Night	7% 9% 2 5% 4 3 5% 5% 6% 8% 46%	1644
	11th to 20th	Night	8% 11% 2 4 5% 3 4 4 4 8% 46%	1417
	21st to end	Night	5% 5% 2 4 5% 3 6% 5% 6% 8% 51%	1552
June	1st to 10th	Night	4 3 1 3 3 2 4 5% 5% 10% 58%	1440
	11th to 20th	Night	4 3 1 3 3 2 3 5% 6% 7% 62%	1440
	21st to end	Night	3 3 2 3 3 2 4 6% 6% 8% 59%	1440
July	1st to 10th	Night	5% 4 2 4 5% 3 6% 5% 7% 9% 51%	1440
	11th to 20th	Night	3 2 2 2 3 2 4 5% 7% 9% 60%	1440
	21st to end	Night	4 4 2 4 6% 4 5% 5% 7% 9% 49%	1631
August	1st to 10th	Night	5% 4 2 3 5% 3 5% 6% 7% 9% 49%	1611
	11th to 20th	Night	5% 3 2 4 4 3 4 5% 6% 8% 57%	1733
	21st to end	Night	3 4 1 4 4 4 5% 4 6% 9% 55%	1980
September	1st to 10th	Night	5% 5% 2 4 4 3 4 3 5% 7% 58%	1800
	11th to 20th	Night	5% 3 1 4 2 2 3 4 5% 6% 64%	1800
	21st to end	Night	5% 4 1 3 3 3 3 4 4 6% 64%	1997
October	1st to 10th	Night	4 5% 2 3 4 2 3 4 5% 9% 59%	2160
	11th to 20th	Night	2 3 1 3 3 2 2 3 4 7% 69%	2160
	21st to end	Night	3 6% 2 5% 4 2 3 4 5% 8% 58%	2407
November	1st to 10th	Night	1 4 1 3 3 1 4 4 5% 9% 66%	2405
	11th to 20th	Night	4 2 4 3 2 3 4 6% 10% 62%	2470
	21st to end	Night	1 4 2 5% 4 2 3 5% 5% 11% 58%	2626
December	1st to 10th	Night	3 1 5% 3 2 4 3 5% 10% 63%	2660
	11th to 20th	Night	1 4 3 5% 4 3 3 4 6% 12% 53%	3271
	21st to end	Night	5% 3 8% 6% 2 5% 4 5% 9% 52%	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	23% 8% 16% 31% 18% 5%	1780
	21st to end	Day	27% 10% 16% 25% 17% 5%	1480
March	1st to 10th	Day	29% 8% 15% 29% 18% 1	1804
	11th to 20th	Day	31% 8% 16% 25% 16% 4	1980
	21st to end	Day	34% 8% 18% 26% 11% 2	2290
April	1st to 10th	Day	29% 9% 14% 26% 16% 6%	2160
	11th to 20th	Day	39% 8% 15% 19% 16% 3	2134
	21st to end	Day	40% 8% 14% 25% 11% 1	2160
May	1st to 10th	Day	43% 9% 14% 20% 12% 2	2312
	11th to 20th	Day	45% 9% 14% 22% 9% 1	2482
	21st to end	Day	39% 13% 13% 18% 13% 3	2724
June	1st to 10th	Day	30% 12% 16% 20% 15% 6%	2520
	11th to 20th	Day	29% 9% 12% 17% 23% 11%	2520
	21st to end	Day	28% 10% 11% 20% 22% 10%	2520
July	1st to 10th	Day	32% 11% 13% 18% 18% 8%	2451
	11th to 20th	Day	29% 11% 13% 20% 16% 10%	2445
	21st to end	Day	38% 13% 16% 17% 11% 5%	2535
August	1st to 10th	Day	38% 14% 14% 16% 13% 6%	2313
	11th to 20th	Day	33% 11% 9% 19% 20% 8%	2166
	21st to end	Day	34% 10% 12% 16% 22% 6%	2376
September	1st to 10th	Day	26% 9% 9% 19% 25% 12%	2160
	11th to 20th	Day	25% 10% 11% 19% 24% 11%	2160
	21st to end	Day	25% 5% 8% 24% 32% 6%	1958
October	1st to 10th	Day	29% 8% 11% 22% 25% 6%	1800
	11th to 20th	Day	20% 7% 9% 30% 26% 8%	1800
	21st to end	Day	24% 7% 13% 29% 20% 8%	1929
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	2279
	21st to end	Night	26% 6% 16% 26% 20% 6%	1776
March	1st to 10th	Night	20% 7% 15% 34% 22% 2	2153
	11th to 20th	Night	23% 7% 16% 30% 19% 6%	1980
	21st to end	Night	26% 7% 19% 31% 14% 3	2066
April	1st to 10th	Night	24% 7% 16% 29% 18% 6%	1800
	11th to 20th	Night	29% 6% 17% 29% 16% 3	1777
	21st to end	Night	31% 7% 15% 29% 18% 1	1800
May	1st to 10th	Night	35% 10% 16% 24% 14% 2	1644
	11th to 20th	Night	37% 7% 18% 27% 11%	1418
	21st to end	Night	28% 9% 15% 26% 18% 4	1552
June	1st to 10th	Night	21% 9% 20% 28% 16% 6%	1440
	11th to 20th	Night	20% 6% 13% 21% 25% 15%	1440
	21st to end	Night	19% 8% 12% 24% 26% 12%	1440
July	1st to 10th	Night	26% 11% 13% 24% 18% 8%	1400
	11th to 20th	Night	17% 8% 16% 29% 18% 12%	1392
	21st to end	Night	28% 10% 18% 26% 12% 6%	1540
August	1st to 10th	Night	26% 11% 20% 22% 15% 5%	1602
	11th to 20th	Night	23% 6% 14% 23% 25% 9%	1733
	21st to end	Night	24% 9% 12% 24% 25% 7%	1980
September	1st to 10th	Night	25% 6% 10% 19% 27% 13%	1800
	11th to 20th	Night	20% 7% 11% 27% 24% 12%	1800
	21st to end	Night	21% 6% 10% 30% 27% 8%	1997
October	1st to 10th	Night	24% 5% 11% 27% 25% 8%	2160
	11th to 20th	Night	16% 4 15% 29% 25% 10%	2160
	21st to end	Night	25% 5% 15% 26% 23% 6%	2407
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	36% 37% 18% 8% 1	267
	21st to end	Day	31% 43% 15% 11% 1	198
March	1st to 10th	Day	30% 37% 26% 5% 2	244
	11th to 20th	Day	21% 34% 31% 11% 3	420
	21st to end	Day	23% 41% 27% 8% 2	462
April	1st to 10th	Day	25% 38% 27% 7% 2	420
	11th to 20th	Day	30% 36% 24% 8% 2	412
	21st to end	Day	23% 30% 30% 11% 4 1	420
May	1st to 10th	Day	24% 29% 27% 13% 6% 1	521
	11th to 20th	Day	21% 20% 33% 17% 8% 1	625
	21st to end	Day	17% 17% 33% 22% 10% 1	679
June	1st to 10th	Day	8% 18% 31% 23% 15% 4	630
	11th to 20th	Day	12% 23% 33% 21% 9% 2	630
	21st to end	Day	9% 14% 38% 22% 14% 3	630
July	1st to 10th	Day	6% 8% 31% 33% 18% 4	621
	11th to 20th	Day	6% 10% 33% 30% 15% 6%	618
	21st to end	Day	8% 7% 29% 33% 18% 5%	626
August	1st to 10th	Day	12% 15% 33% 27% 11% 2	447
	11th to 20th	Day	10% 13% 35% 29% 11% 3	437
	21st to end	Day	11% 15% 31% 30% 11% 3	495
September	1st to 10th	Day	11% 18% 32% 27% 11% 2	450
	11th to 20th	Day	9% 22% 39% 17% 11% 2	450
	21st to end	Day	13% 23% 27% 23% 10% 4	274
October	1st to 10th	Day	15% 20% 30% 22% 9% 4	270
	11th to 20th	Day	24% 32% 25% 13% 4 1	270
	21st to end	Day	28% 30% 26% 13% 2 1	297
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% 27% 11% 2	742
	21st to end	Night	20% 44% 23% 11% 2	592
March	1st to 10th	Night	13% 43% 26% 12% 6%	720
	11th to 20th	Night	12% 36% 27% 18% 6%	720
	21st to end	Night	15% 37% 27% 17% 4 1	680
April	1st to 10th	Night	16% 32% 34% 16% 3	540
	11th to 20th	Night	16% 32% 26% 20% 6% 1	533
	21st to end	Night	16% 25% 30% 19% 8% 1	540
May	1st to 10th	Night	13% 21% 33% 22% 9% 1	540
	11th to 20th	Night	15% 11% 29% 30% 13% 2	531
	21st to end	Night	9% 13% 30% 30% 16% 2	584
June	1st to 10th	Night	7% 9% 29% 33% 20% 3	540
	11th to 20th	Night	6% 15% 33% 33% 11% 1	540
	21st to end	Night	5% 9% 23% 37% 22% 4	540
July	1st to 10th	Night	6% 3 17% 39% 31% 4	525
	11th to 20th	Night	3 4 22% 36% 29% 6%	522
	21st to end	Night	5% 3 14% 40% 33% 6%	591
August	1st to 10th	Night	7% 4 18% 42% 26% 3	537
	11th to 20th	Night	5% 4 20% 45% 22% 4	534
	21st to end	Night	4 7% 18% 36% 29% 6%	594
September	1st to 10th	Night	8% 6% 27% 34% 20% 5%	540
	11th to 20th	Night	7% 12% 26% 34% 16% 4	540
	21st to end	Night	9% 13% 28% 30% 15% 4	562
October	1st to 10th	Night	10% 26% 25% 26% 11% 3	720
	11th to 20th	Night	12% 33% 28% 19% 6% 2	720
	21st to end	Night	14% 35% 31% 13% 6% 2	823
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 2024-02-17 04:28:39. Version ac07

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