Mt. Baldy
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mt. Baldy clear sky chart from 2005-11-06 to 2026-01-17.

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	17% 13% 4 10% 6% 6% 5% 4 6% 7% 22%	132035
	Night	14% 15% 5% 11% 6% 5% 5% 4 6% 7% 22%	128465
Transparency	Day	61% 11% 11% 11% 5% 1	131677
	Night	57% 8% 10% 13% 9% 3	128403
Seeing	Day	22% 13% 24% 24% 14% 3	19471
	Night	20% 11% 23% 26% 16% 3	24065

By Month

Percentage Cloud Cover NW (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	9% 15% 3 9% 8% 6% 6% 4 9% 9% 22%	1859
	11th to 20th	Day	8% 16% 4 10% 6% 5% 6% 5% 7% 9% 24%	2431
	21st to end	Day	14% 15% 4 9% 7% 9% 5% 3 4 4 24%	2992
February	1st to 10th	Day	8% 15% 5% 8% 4 3 5% 4 6% 11% 31%	1369
	11th to 20th	Day	11% 23% 5% 11% 7% 6% 5% 5% 5% 5% 18%	1559
	21st to end	Day	8% 13% 6% 11% 6% 6% 6% 4 5% 7% 30%	1425
March	1st to 10th	Day	7% 18% 8% 13% 7% 6% 4 3 5% 5% 24%	4420
	11th to 20th	Day	6% 13% 5% 13% 7% 6% 7% 4 7% 8% 23%	4655
	21st to end	Day	8% 17% 5% 10% 6% 5% 5% 4 6% 7% 26%	5959
April	1st to 10th	Day	8% 15% 6% 10% 7% 7% 5% 4 6% 7% 25%	2445
	11th to 20th	Day	7% 12% 5% 9% 6% 6% 6% 5% 6% 7% 33%	2766
	21st to end	Day	9% 15% 4 8% 6% 6% 6% 5% 7% 7% 26%	2835
May	1st to 10th	Day	15% 17% 5% 11% 7% 6% 6% 4 6% 6% 16%	7164
	11th to 20th	Day	13% 13% 5% 12% 6% 5% 4 4 6% 6% 26%	7213
	21st to end	Day	18% 13% 5% 11% 6% 5% 6% 4 6% 6% 20%	8583
June	1st to 10th	Day	15% 10% 4 9% 6% 5% 7% 5% 8% 8% 23%	3600
	11th to 20th	Day	14% 9% 3 9% 6% 6% 7% 6% 7% 8% 26%	3600
	21st to end	Day	16% 9% 4 9% 6% 5% 6% 6% 8% 9% 22%	3600
July	1st to 10th	Day	23% 10% 4 9% 6% 6% 5% 4 6% 6% 21%	8160
	11th to 20th	Day	23% 13% 4 10% 6% 6% 5% 4 6% 6% 17%	7984
	21st to end	Day	26% 10% 3 7% 5% 4 4 4 6% 7% 24%	7904
August	1st to 10th	Day	28% 10% 4 10% 5% 5% 5% 4 5% 6% 19%	5189
	11th to 20th	Day	29% 10% 3 8% 5% 4 4 3 5% 6% 22%	4560
	21st to end	Day	24% 11% 4 9% 6% 5% 5% 4 6% 7% 20%	5038
September	1st to 10th	Day	29% 11% 4 9% 6% 5% 6% 4 5% 5% 16%	2471
	11th to 20th	Day	31% 13% 4 10% 5% 4 4 3 4 4 18%	2400
	21st to end	Day	23% 13% 5% 8% 5% 5% 4 3 6% 6% 22%	2130
October	1st to 10th	Day	18% 12% 4 9% 7% 7% 7% 5% 7% 6% 20%	3228
	11th to 20th	Day	12% 11% 3 9% 4 4 5% 3 5% 8% 36%	2902
	21st to end	Day	17% 11% 4 7% 5% 5% 5% 4 6% 10% 27%	2753
November	1st to 10th	Day	11% 17% 6% 11% 7% 6% 8% 5% 6% 5% 19%	1441
	11th to 20th	Day	9% 13% 4 10% 7% 6% 7% 8% 10% 9% 17%	1262
	21st to end	Day	10% 18% 6% 12% 9% 6% 6% 6% 6% 9% 13%	1071
December	1st to 10th	Day	17% 15% 6% 13% 6% 6% 6% 4 7% 6% 13%	1464
	11th to 20th	Day	8% 22% 6% 13% 6% 6% 5% 5% 6% 6% 17%	1557
	21st to end	Day	5% 12% 5% 12% 9% 8% 6% 7% 8% 7% 21%	2046
January	1st to 10th	Night	9% 16% 5% 10% 6% 6% 6% 5% 7% 7% 24%	8326
	11th to 20th	Night	10% 18% 5% 12% 6% 5% 4 3 5% 8% 23%	7630
	21st to end	Night	12% 14% 4 8% 6% 6% 6% 4 5% 6% 29%	7986
February	1st to 10th	Night	8% 14% 4 8% 5% 4 5% 5% 7% 8% 31%	3029
	11th to 20th	Night	14% 19% 6% 12% 6% 6% 4 3 5% 6% 19%	2728
	21st to end	Night	8% 13% 4 12% 7% 6% 5% 4 5% 8% 27%	2202
March	1st to 10th	Night	7% 20% 6% 12% 5% 5% 4 3 5% 6% 27%	5434
	11th to 20th	Night	6% 16% 7% 13% 6% 6% 5% 4 6% 8% 23%	5300
	21st to end	Night	7% 18% 5% 11% 6% 5% 5% 5% 7% 7% 27%	4972
April	1st to 10th	Night	10% 18% 6% 10% 7% 5% 5% 4 4 5% 25%	1954
	11th to 20th	Night	9% 13% 3 10% 6% 6% 5% 4 6% 5% 32%	1583
	21st to end	Night	10% 14% 5% 10% 8% 4 5% 3 5% 6% 31%	1565
May	1st to 10th	Night	16% 19% 5% 13% 6% 6% 5% 4 6% 6% 15%	2813
	11th to 20th	Night	18% 19% 5% 11% 6% 5% 5% 3 4 5% 20%	2702
	21st to end	Night	24% 15% 5% 9% 5% 5% 4 3 6% 6% 19%	2300
June	1st to 10th	Night	20% 14% 3 10% 6% 5% 6% 3 6% 7% 20%	800
	11th to 20th	Night	15% 12% 4 10% 7% 5% 5% 4 7% 7% 24%	800
	21st to end	Night	20% 11% 4 11% 7% 6% 7% 2 4 7% 22%	800
July	1st to 10th	Night	31% 12% 4 9% 6% 5% 4 4 6% 5% 14%	1820
	11th to 20th	Night	31% 12% 4 9% 7% 5% 4 3 4 4 17%	2001
	21st to end	Night	30% 11% 3 9% 5% 5% 4 4 4 6% 19%	2962
August	1st to 10th	Night	32% 11% 3 8% 4 4 4 3 4 6% 20%	1970
	11th to 20th	Night	31% 9% 3 8% 4 4 4 4 5% 6% 21%	2498
	21st to end	Night	30% 12% 4 9% 6% 5% 4 3 5% 5% 18%	2871
September	1st to 10th	Night	33% 11% 4 10% 5% 5% 5% 4 5% 4 15%	1927
	11th to 20th	Night	32% 12% 3 9% 5% 4 5% 3 4 4 19%	2000
	21st to end	Night	26% 11% 5% 8% 5% 4 5% 3 5% 5% 22%	2270
October	1st to 10th	Night	21% 13% 4 11% 6% 6% 5% 4 6% 6% 17%	3953
	11th to 20th	Night	14% 11% 3 8% 5% 5% 4 4 6% 7% 32%	4244
	21st to end	Night	17% 15% 4 9% 5% 5% 6% 3 4 8% 23%	5048
November	1st to 10th	Night	13% 17% 5% 11% 6% 7% 5% 4 5% 6% 21%	3077
	11th to 20th	Night	9% 13% 3 9% 6% 7% 8% 8% 8% 10% 21%	3355
	21st to end	Night	10% 18% 5% 12% 7% 6% 6% 7% 7% 8% 15%	3549
December	1st to 10th	Night	15% 18% 5% 12% 6% 7% 6% 5% 7% 6% 12%	5942
	11th to 20th	Night	8% 22% 6% 12% 7% 6% 6% 4 6% 7% 16%	6880
	21st to end	Night	7% 14% 5% 13% 8% 6% 7% 6% 8% 8% 17%	9174

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	50% 7% 11% 13% 13% 5%	1859
	11th to 20th	Day	51% 8% 11% 12% 13% 5%	2446
	21st to end	Day	60% 5% 4 7% 17% 6%	2992
February	1st to 10th	Day	46% 8% 10% 17% 13% 7%	1369
	11th to 20th	Day	64% 8% 7% 11% 7% 2	1566
	21st to end	Day	55% 7% 7% 16% 13% 2	1425
March	1st to 10th	Day	58% 6% 5% 10% 14% 5%	4420
	11th to 20th	Day	55% 11% 7% 11% 14% 2	4655
	21st to end	Day	57% 10% 10% 11% 12% 1	5959
April	1st to 10th	Day	62% 11% 8% 12% 6% 1	2445
	11th to 20th	Day	53% 13% 10% 17% 7%	2766
	21st to end	Day	59% 9% 9% 14% 8% 1	2835
May	1st to 10th	Day	67% 9% 7% 12% 5%	7164
	11th to 20th	Day	59% 14% 7% 17% 3	7216
	21st to end	Day	62% 11% 11% 13% 2	8584
June	1st to 10th	Day	62% 14% 12% 12% 1	3600
	11th to 20th	Day	59% 13% 13% 13% 3	3600
	21st to end	Day	61% 14% 17% 8%	3600
July	1st to 10th	Day	64% 14% 15% 7%	8071
	11th to 20th	Day	69% 13% 15% 3	7885
	21st to end	Day	60% 11% 20% 9%	7682
August	1st to 10th	Day	69% 10% 14% 6% 1	5170
	11th to 20th	Day	63% 11% 14% 11% 1	4603
	21st to end	Day	65% 12% 13% 9% 1	5037
September	1st to 10th	Day	73% 10% 8% 7% 1	2471
	11th to 20th	Day	71% 8% 10% 10% 1	2400
	21st to end	Day	65% 10% 8% 13% 3	2130
October	1st to 10th	Day	59% 11% 13% 15% 3	3228
	11th to 20th	Day	48% 8% 12% 18% 14%	2902
	21st to end	Day	49% 11% 10% 21% 7% 1	2753
November	1st to 10th	Day	58% 8% 10% 13% 9% 3	1441
	11th to 20th	Day	49% 6% 8% 23% 12% 1	1262
	21st to end	Day	59% 4 11% 11% 12% 3	1071
December	1st to 10th	Day	64% 8% 8% 11% 8% 1	1464
	11th to 20th	Day	62% 7% 9% 14% 6% 1	1560
	21st to end	Day	48% 6% 9% 19% 10% 7%	2046
January	1st to 10th	Night	49% 7% 11% 13% 13% 7%	8326
	11th to 20th	Night	56% 6% 10% 10% 14% 3	7678
	21st to end	Night	51% 6% 5% 9% 20% 9%	7986
February	1st to 10th	Night	46% 7% 8% 20% 13% 7%	3029
	11th to 20th	Night	64% 7% 8% 10% 9% 2	2732
	21st to end	Night	55% 9% 7% 13% 12% 2	2202
March	1st to 10th	Night	56% 7% 5% 11% 14% 7%	5434
	11th to 20th	Night	53% 6% 7% 15% 17% 2	5302
	21st to end	Night	54% 10% 8% 13% 14% 1	4972
April	1st to 10th	Night	59% 7% 11% 15% 6%	1954
	11th to 20th	Night	51% 9% 12% 19% 9%	1583
	21st to end	Night	54% 7% 11% 17% 10%	1565
May	1st to 10th	Night	63% 8% 10% 15% 4	2810
	11th to 20th	Night	66% 6% 8% 14% 6%	2703
	21st to end	Night	61% 8% 15% 15% 2	2300
June	1st to 10th	Night	63% 10% 15% 12% 1	800
	11th to 20th	Night	58% 13% 15% 12% 3	800
	21st to end	Night	63% 11% 19% 8%	800
July	1st to 10th	Night	67% 12% 15% 5%	1800
	11th to 20th	Night	70% 8% 18% 4	1977
	21st to end	Night	64% 9% 21% 6%	2879
August	1st to 10th	Night	65% 9% 18% 7%	1964
	11th to 20th	Night	63% 11% 14% 11% 2	2521
	21st to end	Night	69% 8% 12% 9% 2	2871
September	1st to 10th	Night	73% 9% 8% 8% 2	1927
	11th to 20th	Night	70% 9% 10% 10% 2	2000
	21st to end	Night	65% 8% 12% 12% 4	2270
October	1st to 10th	Night	63% 8% 10% 16% 3	3953
	11th to 20th	Night	47% 8% 13% 19% 12%	4244
	21st to end	Night	56% 7% 11% 18% 8% 1	5048
November	1st to 10th	Night	59% 7% 9% 13% 9% 2	3077
	11th to 20th	Night	47% 9% 9% 21% 13% 1	3355
	21st to end	Night	58% 6% 10% 13% 10% 4	3549
December	1st to 10th	Night	65% 8% 9% 11% 7% 1	5942
	11th to 20th	Night	62% 7% 10% 12% 7% 1	6876
	21st to end	Night	51% 6% 10% 18% 10% 5%	9174

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	5% 19% 20% 28% 20% 8%	110
	11th to 20th	Day	15% 17% 26% 26% 10% 7%	303
	21st to end	Day	19% 13% 21% 25% 15% 7%	330
February	1st to 10th	Day	13% 11% 23% 25% 17% 11%	304
	11th to 20th	Day	18% 20% 26% 22% 11% 3	395
	21st to end	Day	16% 16% 30% 21% 10% 7%	331
March	1st to 10th	Day	15% 12% 31% 25% 14% 3	400
	11th to 20th	Day	10% 14% 32% 22% 18% 4	457
	21st to end	Day	12% 15% 27% 27% 17% 3	660
April	1st to 10th	Day	13% 20% 29% 24% 13% 2	616
	11th to 20th	Day	13% 13% 23% 30% 19% 2	690
	21st to end	Day	17% 12% 24% 29% 15% 3	700
May	1st to 10th	Day	20% 20% 25% 23% 11% 1	703
	11th to 20th	Day	18% 15% 25% 25% 14% 3	725
	21st to end	Day	25% 15% 22% 26% 11% 1	882
June	1st to 10th	Day	20% 14% 25% 21% 16% 4	930
	11th to 20th	Day	18% 11% 25% 28% 16% 3	930
	21st to end	Day	18% 11% 24% 26% 17% 4	930
July	1st to 10th	Day	23% 11% 22% 27% 16% 2	916
	11th to 20th	Day	26% 10% 23% 23% 14% 3	912
	21st to end	Day	26% 10% 25% 20% 15% 4	799
August	1st to 10th	Day	31% 9% 23% 22% 13% 3	726
	11th to 20th	Day	29% 14% 24% 19% 12% 2	715
	21st to end	Day	32% 12% 22% 19% 13% 1	803
September	1st to 10th	Day	34% 15% 22% 18% 9% 2	645
	11th to 20th	Day	36% 13% 18% 20% 12% 2	620
	21st to end	Day	29% 13% 18% 21% 15% 4	420
October	1st to 10th	Day	32% 14% 21% 20% 11% 2	420
	11th to 20th	Day	25% 9% 26% 24% 13% 4	420
	21st to end	Day	21% 14% 22% 24% 15% 4	462
November	1st to 10th	Day	19% 12% 24% 21% 15% 8%	425
	11th to 20th	Day	15% 8% 25% 22% 23% 7%	320
	21st to end	Day	14% 20% 15% 27% 15% 8%	131
December	1st to 10th	Day	26% 14% 15% 24% 17% 5%	110
	11th to 20th	Day	14% 15% 32% 26% 9% 5%	110
	21st to end	Day	13% 17% 31% 24% 10% 6%	121
January	1st to 10th	Night	10% 13% 24% 29% 20% 3	1060
	11th to 20th	Night	19% 15% 27% 24% 12% 4	999
	21st to end	Night	20% 11% 27% 24% 14% 4	990
February	1st to 10th	Night	13% 11% 26% 31% 15% 4	900
	11th to 20th	Night	19% 17% 29% 25% 9% 1	884
	21st to end	Night	12% 14% 33% 26% 11% 4	635
March	1st to 10th	Night	13% 14% 29% 27% 15% 2	700
	11th to 20th	Night	10% 11% 24% 33% 17% 5%	700
	21st to end	Night	13% 10% 25% 26% 21% 6%	664
April	1st to 10th	Night	17% 11% 26% 26% 17% 3	600
	11th to 20th	Night	14% 12% 17% 26% 26% 6%	593
	21st to end	Night	14% 9% 24% 33% 18% 2	600
May	1st to 10th	Night	18% 11% 22% 28% 18% 2	441
	11th to 20th	Night	20% 8% 19% 28% 24% 1	394
	21st to end	Night	19% 8% 19% 35% 18% 1	240
June	1st to 10th	Night	24% 13% 14% 30% 19% 1	200
	11th to 20th	Night	20% 5% 21% 32% 22% 1	200
	21st to end	Night	21% 5% 18% 32% 25% 1	200
July	1st to 10th	Night	27% 9% 14% 23% 27%	195
	11th to 20th	Night	34% 7% 11% 20% 25% 2	271
	21st to end	Night	31% 5% 16% 22% 21% 5%	438
August	1st to 10th	Night	34% 8% 15% 23% 18% 2	398
	11th to 20th	Night	36% 9% 19% 20% 14% 1	548
	21st to end	Night	36% 7% 17% 21% 17% 2	660
September	1st to 10th	Night	37% 9% 20% 20% 12% 2	600
	11th to 20th	Night	35% 10% 16% 18% 18% 3	600
	21st to end	Night	32% 8% 15% 22% 18% 4	639
October	1st to 10th	Night	33% 13% 18% 19% 15% 2	730
	11th to 20th	Night	22% 10% 20% 25% 19% 3	910
	21st to end	Night	22% 10% 22% 26% 17% 3	1001
November	1st to 10th	Night	20% 10% 26% 28% 15% 2	930
	11th to 20th	Night	13% 10% 26% 32% 16% 3	950
	21st to end	Night	16% 15% 25% 24% 16% 5%	950
December	1st to 10th	Night	23% 13% 25% 23% 13% 3	1019
	11th to 20th	Night	13% 12% 31% 26% 13% 4	1060
	21st to end	Night	16% 17% 28% 22% 13% 5%	1166

Page generated at 2026-01-13 21:14:27. Version ac07

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