Baum Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Baum Lake clear sky chart from 2005-11-06 to 2025-11-18.

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 4 1 4 3 3 3 3 5% 6% 63%	135899
	Night	5% 6% 2 5% 3 3 4 3 5% 6% 58%	131864
Transparency	Day	21% 6% 10% 21% 24% 18%	130784
	Night	25% 8% 11% 23% 21% 13%	127967
Seeing	Day	8% 12% 25% 29% 20% 8%	16317
	Night	7% 5% 19% 41% 25% 2	25469

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	7% 9% 3 9% 5% 6% 6% 4 7% 8% 36%	3639
	11th to 20th	Day	8% 8% 2 6% 4 3 3 2 4 5% 52%	3820
	21st to end	Day	11% 7% 3 6% 5% 4 4 3 4 6% 49%	4510
February	1st to 10th	Day	7% 7% 2 6% 5% 5% 5% 4 7% 8% 46%	1800
	11th to 20th	Day	6% 8% 2 6% 5% 5% 4 4 6% 8% 46%	1811
	21st to end	Day	4 6% 2 6% 5% 6% 6% 5% 6% 6% 47%	1650
March	1st to 10th	Day	6% 9% 3 8% 6% 6% 7% 5% 6% 7% 38%	4684
	11th to 20th	Day	5% 9% 3 5% 4 4 4 4 6% 8% 48%	5000
	21st to end	Day	5% 8% 3 8% 6% 6% 6% 4 7% 9% 38%	5675
April	1st to 10th	Day	5% 8% 3 7% 6% 4 5% 4 6% 8% 44%	2400
	11th to 20th	Day	6% 6% 1 5% 4 4 4 4 7% 7% 52%	2369
	21st to end	Day	5% 5% 2 5% 3 3 3 4 5% 8% 58%	2400
May	1st to 10th	Day	4 4 1 3 3 2 2 3 4 6% 68%	5968
	11th to 20th	Day	3 3 1 3 2 2 3 3 5% 6% 69%	6277
	21st to end	Day	3 2 1 2 2 2 2 2 4 6% 75%	6902
June	1st to 10th	Day	5% 3 1 3 4 4 5% 3 5% 8% 61%	2800
	11th to 20th	Day	2 2 1 2 2 2 2 2 4 5% 75%	2800
	21st to end	Day	2 1 1 1 2 1 2 2 3 4 81%	2800
July	1st to 10th	Day	1 1 1 1 1 1 2 3 89%	6319
	11th to 20th	Day	1 1 1 1 1 1 1 2 3 88%	6320
	21st to end	Day	1 2 1 2 1 2 3 2 4 4 78%	6623
August	1st to 10th	Day	1 1 2 1 1 2 2 4 5% 79%	5777
	11th to 20th	Day	1 1 1 1 1 1 2 3 89%	5623
	21st to end	Day	2 2 2 1 2 2 2 4 4 79%	5984
September	1st to 10th	Day	1 1 1 1 1 2 2 4 4 84%	2400
	11th to 20th	Day	3 1 1 3 2 2 3 3 4 6% 72%	2400
	21st to end	Day	3 2 1 3 2 2 3 2 3 5% 76%	2139
October	1st to 10th	Day	2 2 1 2 2 2 2 2 4 4 77%	3280
	11th to 20th	Day	4 2 1 3 3 3 4 3 5% 7% 65%	3261
	21st to end	Day	5% 4 2 5% 4 3 5% 4 6% 9% 53%	3558
November	1st to 10th	Day	8% 5% 2 5% 4 5% 4 3 5% 8% 51%	1859
	11th to 20th	Day	7% 6% 1 6% 5% 5% 6% 5% 7% 9% 43%	1799
	21st to end	Day	5% 5% 2 5% 5% 4 5% 4 6% 9% 51%	1600
December	1st to 10th	Day	4 5% 1 4 4 4 4 4 6% 7% 55%	2620
	11th to 20th	Day	11% 10% 3 9% 7% 7% 7% 6% 7% 8% 25%	3028
	21st to end	Day	11% 8% 3 9% 7% 7% 6% 5% 8% 8% 29%	4004
January	1st to 10th	Night	5% 9% 4 9% 5% 6% 6% 5% 7% 10% 35%	6306
	11th to 20th	Night	7% 9% 3 5% 3 4 4 3 5% 6% 52%	6144
	21st to end	Night	10% 9% 3 7% 4 4 4 3 4 5% 46%	6468
February	1st to 10th	Night	6% 7% 3 6% 5% 5% 5% 4 6% 8% 46%	2600
	11th to 20th	Night	6% 8% 2 6% 4 5% 5% 4 6% 9% 45%	2474
	21st to end	Night	5% 10% 3 5% 5% 5% 5% 4 6% 8% 45%	1980
March	1st to 10th	Night	7% 12% 4 7% 5% 5% 5% 4 6% 7% 38%	5208
	11th to 20th	Night	5% 9% 3 6% 3 3 4 4 6% 8% 49%	5000
	21st to end	Night	6% 10% 3 7% 5% 4 5% 4 6% 8% 41%	5299
April	1st to 10th	Night	6% 7% 2 5% 5% 5% 5% 3 6% 8% 47%	2000
	11th to 20th	Night	7% 5% 1 4 3 3 4 3 6% 8% 54%	1979
	21st to end	Night	8% 4 2 5% 4 3 3 3 5% 8% 55%	2000
May	1st to 10th	Night	3 5% 2 5% 3 2 2 2 3 5% 68%	4000
	11th to 20th	Night	4 4 1 3 2 3 3 3 3 6% 69%	3616
	21st to end	Night	4 3 1 3 2 1 2 2 3 4 73%	3972
June	1st to 10th	Night	6% 4 1 3 3 4 4 3 5% 8% 59%	1600
	11th to 20th	Night	5% 2 1 2 2 2 2 2 3 6% 73%	1600
	21st to end	Night	2 2 1 2 2 2 3 2 4 5% 77%	1600
July	1st to 10th	Night	1 1 1 1 1 2 3 89%	3640
	11th to 20th	Night	1 1 1 1 1 1 1 1 1 3 87%	3640
	21st to end	Night	1 1 1 2 2 2 2 2 3 5% 80%	4235
August	1st to 10th	Night	2 1 1 2 2 2 2 2 4 6% 77%	4035
	11th to 20th	Night	2 1 1 1 1 1 1 2 3 89%	4231
	21st to end	Night	3 2 1 2 1 2 2 1 3 3 80%	5015
September	1st to 10th	Night	2 1 1 1 1 1 2 1 2 4 84%	2000
	11th to 20th	Night	4 3 1 3 2 1 3 2 4 6% 74%	2000
	21st to end	Night	2 2 1 3 2 3 2 2 4 5% 74%	2255
October	1st to 10th	Night	3 2 1 2 2 2 2 2 2 3 78%	3920
	11th to 20th	Night	4 3 1 3 2 3 3 3 4 6% 69%	3897
	21st to end	Night	5% 3 1 3 2 3 3 3 5% 9% 61%	4253
November	1st to 10th	Night	7% 6% 2 5% 4 5% 5% 5% 6% 8% 47%	2658
	11th to 20th	Night	7% 6% 2 6% 5% 5% 5% 4 7% 9% 43%	2751
	21st to end	Night	5% 6% 2 5% 4 4 4 4 6% 9% 51%	2800
December	1st to 10th	Night	5% 3 1 4 3 4 4 3 5% 7% 61%	4560
	11th to 20th	Night	11% 12% 3 9% 7% 6% 6% 5% 7% 9% 24%	5176
	21st to end	Night	13% 11% 4 10% 5% 5% 5% 4 6% 8% 30%	6952

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	38% 14% 16% 24% 8% 1	3639
	11th to 20th	Day	32% 9% 10% 27% 17% 4	3820
	21st to end	Day	34% 9% 10% 14% 24% 9%	4510
February	1st to 10th	Day	35% 8% 15% 21% 17% 4	1800
	11th to 20th	Day	35% 8% 14% 24% 17% 2	1820
	21st to end	Day	34% 9% 14% 25% 13% 5%	1650
March	1st to 10th	Day	38% 12% 11% 22% 14% 4	4684
	11th to 20th	Day	30% 7% 17% 23% 22% 1	5000
	21st to end	Day	35% 13% 17% 24% 9% 2	5675
April	1st to 10th	Day	37% 8% 15% 22% 15% 3	2400
	11th to 20th	Day	30% 7% 13% 23% 19% 7%	2372
	21st to end	Day	25% 7% 17% 26% 22% 4	2400
May	1st to 10th	Day	17% 4 9% 24% 35% 10%	5968
	11th to 20th	Day	16% 3 11% 24% 29% 17%	6280
	21st to end	Day	13% 3 10% 32% 35% 6%	6904
June	1st to 10th	Day	23% 6% 11% 26% 26% 9%	2800
	11th to 20th	Day	12% 3 8% 23% 35% 18%	2800
	21st to end	Day	9% 2 5% 19% 34% 31%	2800
July	1st to 10th	Day	5% 1 3 12% 24% 56%	6251
	11th to 20th	Day	6% 1 3 8% 20% 63%	6245
	21st to end	Day	10% 2 5% 18% 27% 36%	6431
August	1st to 10th	Day	11% 2 4 10% 25% 48%	4206
	11th to 20th	Day	4 1 2 15% 41% 37%	4070
	21st to end	Day	8% 1 3 21% 37% 30%	4311
September	1st to 10th	Day	6% 2 4 13% 29% 46%	2400
	11th to 20th	Day	15% 3 7% 22% 33% 20%	2400
	21st to end	Day	13% 3 7% 21% 31% 25%	2139
October	1st to 10th	Day	13% 2 6% 18% 25% 36%	3280
	11th to 20th	Day	18% 4 9% 34% 26% 9%	3261
	21st to end	Day	23% 6% 14% 27% 21% 9%	3558
November	1st to 10th	Day	32% 7% 14% 22% 19% 6%	1859
	11th to 20th	Day	34% 8% 17% 22% 15% 3	1799
	21st to end	Day	28% 9% 13% 23% 21% 6%	1600
December	1st to 10th	Day	26% 7% 9% 28% 27% 3	2620
	11th to 20th	Day	49% 13% 14% 17% 7%	3028
	21st to end	Day	42% 14% 17% 21% 6% 1	4004
January	1st to 10th	Night	37% 14% 18% 23% 8% 1	6306
	11th to 20th	Night	28% 13% 9% 26% 20% 4	6144
	21st to end	Night	38% 9% 8% 12% 24% 9%	6468
February	1st to 10th	Night	34% 10% 13% 23% 16% 5%	2600
	11th to 20th	Night	33% 9% 16% 24% 16% 2	2476
	21st to end	Night	34% 9% 18% 22% 14% 4	1980
March	1st to 10th	Night	37% 12% 14% 23% 9% 4	5208
	11th to 20th	Night	27% 10% 17% 27% 18% 1	5000
	21st to end	Night	34% 14% 19% 23% 10% 1	5299
April	1st to 10th	Night	32% 10% 19% 26% 11% 3	2000
	11th to 20th	Night	26% 9% 19% 23% 16% 6%	1979
	21st to end	Night	26% 7% 18% 30% 16% 3	2000
May	1st to 10th	Night	19% 5% 9% 26% 32% 9%	3997
	11th to 20th	Night	18% 4 11% 28% 30% 11%	3616
	21st to end	Night	14% 5% 12% 36% 30% 2	3972
June	1st to 10th	Night	23% 8% 13% 30% 22% 4	1600
	11th to 20th	Night	14% 4 10% 23% 38% 11%	1600
	21st to end	Night	11% 3 6% 19% 34% 26%	1600
July	1st to 10th	Night	4 1 3 15% 26% 52%	3600
	11th to 20th	Night	6% 1 2 7% 24% 60%	3592
	21st to end	Night	10% 2 7% 20% 28% 33%	4115
August	1st to 10th	Night	11% 2 4 13% 26% 45%	2929
	11th to 20th	Night	4 1 2 16% 42% 34%	3056
	21st to end	Night	8% 1 3 22% 41% 24%	3608
September	1st to 10th	Night	7% 3 4 11% 29% 46%	2000
	11th to 20th	Night	13% 4 7% 21% 35% 19%	2000
	21st to end	Night	13% 4 7% 21% 28% 27%	2255
October	1st to 10th	Night	14% 2 6% 14% 32% 32%	3920
	11th to 20th	Night	15% 5% 9% 39% 23% 9%	3897
	21st to end	Night	19% 4 14% 34% 20% 10%	4253
November	1st to 10th	Night	31% 10% 16% 21% 16% 7%	2658
	11th to 20th	Night	33% 10% 16% 22% 16% 3	2751
	21st to end	Night	28% 8% 16% 22% 20% 6%	2800
December	1st to 10th	Night	22% 6% 10% 32% 25% 5%	4560
	11th to 20th	Night	46% 15% 12% 19% 8%	5176
	21st to end	Night	43% 16% 13% 20% 7% 1	6952

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	20% 12% 25% 34% 9% 2	200
	11th to 20th	Day	12% 16% 20% 32% 12% 7%	276
	21st to end	Day	13% 14% 21% 28% 16% 8%	440
February	1st to 10th	Day	13% 17% 20% 31% 17% 2	400
	11th to 20th	Day	12% 21% 26% 27% 13% 1	423
	21st to end	Day	10% 17% 26% 30% 16% 1	414
March	1st to 10th	Day	16% 24% 28% 20% 9% 2	500
	11th to 20th	Day	16% 18% 27% 24% 13% 2	500
	21st to end	Day	13% 23% 29% 23% 11% 2	550
April	1st to 10th	Day	12% 19% 30% 26% 10% 2	500
	11th to 20th	Day	14% 20% 25% 22% 15% 5%	492
	21st to end	Day	7% 16% 28% 25% 19% 5%	500
May	1st to 10th	Day	8% 18% 33% 23% 14% 4	503
	11th to 20th	Day	13% 13% 26% 24% 17% 7%	528
	21st to end	Day	8% 10% 23% 29% 22% 9%	573
June	1st to 10th	Day	4 13% 28% 24% 22% 9%	530
	11th to 20th	Day	5% 13% 30% 27% 18% 6%	530
	21st to end	Day	1 8% 24% 33% 24% 10%	530
July	1st to 10th	Day	2 4 28% 31% 25% 9%	526
	11th to 20th	Day	4 26% 30% 27% 13%	524
	21st to end	Day	1 3 22% 34% 26% 14%	575
August	1st to 10th	Day	1 4 23% 33% 23% 16%	527
	11th to 20th	Day	2 5% 22% 28% 27% 16%	517
	21st to end	Day	2 4 26% 30% 24% 14%	583
September	1st to 10th	Day	1 6% 23% 34% 28% 8%	530
	11th to 20th	Day	6% 7% 22% 32% 25% 9%	530
	21st to end	Day	4 8% 23% 34% 25% 6%	530
October	1st to 10th	Day	5% 11% 23% 27% 24% 10%	530
	11th to 20th	Day	5% 10% 21% 28% 28% 7%	530
	21st to end	Day	8% 11% 22% 28% 22% 9%	583
November	1st to 10th	Day	11% 10% 18% 28% 25% 8%	335
	11th to 20th	Day	11% 7% 19% 35% 21% 7%	288
	21st to end	Day	8% 9% 18% 34% 23% 9%	200
December	1st to 10th	Day	16% 7% 19% 30% 20% 10%	200
	11th to 20th	Day	14% 8% 22% 32% 20% 7%	200
	21st to end	Day	15% 13% 21% 35% 14% 2	220
January	1st to 10th	Night	11% 8% 25% 39% 16% 1	800
	11th to 20th	Night	9% 8% 26% 40% 16% 1	800
	21st to end	Night	12% 5% 24% 40% 18% 1	880
February	1st to 10th	Night	9% 8% 27% 40% 16% 1	800
	11th to 20th	Night	9% 7% 27% 40% 15% 1	784
	21st to end	Night	9% 10% 25% 43% 13%	660
March	1st to 10th	Night	12% 11% 25% 36% 14% 2	800
	11th to 20th	Night	10% 10% 25% 33% 21% 1	800
	21st to end	Night	10% 10% 28% 36% 16%	880
April	1st to 10th	Night	9% 7% 26% 43% 15% 1	800
	11th to 20th	Night	9% 6% 25% 40% 17% 3	791
	21st to end	Night	7% 7% 21% 43% 19% 2	800
May	1st to 10th	Night	5% 5% 29% 40% 20% 1	565
	11th to 20th	Night	9% 4 20% 39% 25% 3	394
	21st to end	Night	9% 3 15% 42% 30% 1	433
June	1st to 10th	Night	6% 2 16% 46% 30% 1	400
	11th to 20th	Night	4 4 20% 46% 24% 2	400
	21st to end	Night	2 1 11% 49% 38% 1	400
July	1st to 10th	Night	1 1 4 51% 42% 2	390
	11th to 20th	Night	1 5% 53% 40% 1	388
	21st to end	Night	1 1 2 41% 53% 3	550
August	1st to 10th	Night	2 1 2 40% 50% 5%	597
	11th to 20th	Night	2 1 6% 42% 45% 5%	669
	21st to end	Night	2 1 6% 45% 42% 4	880
September	1st to 10th	Night	2 1 11% 44% 40% 3	800
	11th to 20th	Night	4 2 11% 36% 41% 6%	800
	21st to end	Night	3 3 11% 44% 34% 6%	800
October	1st to 10th	Night	5% 2 17% 41% 31% 4	800
	11th to 20th	Night	4 3 15% 43% 32% 3	800
	21st to end	Night	8% 4 17% 40% 27% 4	880
November	1st to 10th	Night	8% 7% 18% 39% 25% 3	820
	11th to 20th	Night	9% 6% 24% 43% 16% 3	828
	21st to end	Night	6% 7% 24% 39% 22% 2	800
December	1st to 10th	Night	11% 6% 22% 42% 18% 2	800
	11th to 20th	Night	12% 8% 22% 41% 15% 2	800
	21st to end	Night	14% 9% 29% 38% 10%	880

Page generated at 2025-11-14 21:55:55. Version ac07

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