Bass Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bass Lake clear sky chart from 2005-11-06 to 2026-09-29.

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	13% 10% 4 9% 5% 4 4 3 5% 6% 36%	149275
	Night	14% 13% 5% 11% 6% 5% 4 3 4 6% 30%	142457
Transparency	Day	34% 33% 8% 15% 9% 1	152775
	Night	39% 34% 7% 13% 7% 1	147034
Seeing	Day	18% 14% 29% 25% 11% 3	18559
	Night	21% 12% 27% 27% 11% 2	28329

By Month

Percentage Cloud Cover SE (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	13% 25% 13% 26% 5% 3 2 2 2 2 7%	4691
	11th to 20th	Day	10% 17% 10% 24% 14% 11% 4 2 2 2 3	4710
	21st to end	Day	11% 16% 9% 17% 12% 7% 7% 2 2 3 13%	5156
February	1st to 10th	Day	10% 16% 7% 17% 13% 6% 4 3 4 4 16%	1856
	11th to 20th	Day	13% 16% 7% 18% 10% 6% 4 2 4 4 17%	2048
	21st to end	Day	12% 16% 6% 14% 7% 5% 4 3 5% 5% 21%	1730
March	1st to 10th	Day	13% 10% 5% 12% 5% 5% 4 4 5% 5% 33%	4580
	11th to 20th	Day	12% 9% 7% 8% 5% 4 4 3 5% 7% 35%	4855
	21st to end	Day	22% 11% 6% 11% 4 3 3 3 5% 5% 27%	5929
April	1st to 10th	Day	18% 14% 4 6% 4 4 4 4 5% 6% 32%	2520
	11th to 20th	Day	19% 10% 3 6% 5% 4 4 3 5% 6% 35%	2535
	21st to end	Day	16% 9% 2 7% 5% 4 4 4 5% 6% 37%	2730
May	1st to 10th	Day	13% 6% 2 6% 3 3 4 3 6% 8% 46%	7616
	11th to 20th	Day	13% 8% 2 6% 4 4 4 3 5% 7% 43%	7956
	21st to end	Day	13% 6% 2 5% 3 4 3 3 5% 7% 48%	9047
June	1st to 10th	Day	12% 6% 1 5% 4 4 4 3 5% 8% 47%	2940
	11th to 20th	Day	13% 5% 2 5% 4 4 4 4 5% 9% 45%	2940
	21st to end	Day	12% 5% 2 5% 4 4 4 3 6% 9% 46%	2940
July	1st to 10th	Day	13% 6% 2 6% 4 4 4 4 6% 9% 43%	8280
	11th to 20th	Day	7% 4 1 4 3 3 4 3 5% 9% 57%	8280
	21st to end	Day	9% 4 2 5% 4 4 4 4 6% 9% 50%	8990
August	1st to 10th	Day	12% 5% 2 6% 4 4 4 4 6% 9% 44%	6273
	11th to 20th	Day	12% 5% 2 5% 4 4 4 3 5% 7% 50%	5951
	21st to end	Day	11% 6% 2 6% 4 4 4 4 6% 8% 45%	6088
September	1st to 10th	Day	13% 6% 2 6% 4 5% 4 4 5% 7% 45%	2520
	11th to 20th	Day	12% 5% 2 6% 4 3 3 3 6% 7% 48%	2318
	21st to end	Day	14% 7% 2 6% 4 4 4 4 5% 7% 42%	2288
October	1st to 10th	Day	15% 7% 3 7% 4 3 4 3 5% 7% 43%	2200
	11th to 20th	Day	24% 12% 3 8% 5% 5% 4 4 5% 6% 24%	1906
	21st to end	Day	24% 14% 3 8% 4 4 4 3 5% 5% 25%	1980
November	1st to 10th	Day	16% 16% 3 7% 5% 4 4 3 4 6% 32%	1852
	11th to 20th	Day	15% 23% 7% 10% 5% 4 4 3 5% 5% 19%	1890
	21st to end	Day	20% 22% 9% 11% 5% 3 3 2 4 4 16%	1832
December	1st to 10th	Day	12% 28% 18% 14% 5% 4 3 2 2 2 10%	2690
	11th to 20th	Day	14% 25% 12% 15% 10% 3 3 2 4 4 8%	3088
	21st to end	Day	21% 22% 9% 14% 6% 4 3 2 4 3 12%	4070
January	1st to 10th	Night	14% 23% 11% 25% 6% 4 3 2 2 2 9%	8232
	11th to 20th	Night	10% 22% 10% 25% 10% 10% 2 2 2 2 5%	8280
	21st to end	Night	10% 19% 9% 19% 12% 8% 6% 2 2 3 9%	9058
February	1st to 10th	Night	12% 19% 6% 16% 12% 5% 4 3 3 4 17%	2760
	11th to 20th	Night	13% 14% 7% 16% 10% 7% 3 3 4 4 19%	2458
	21st to end	Night	14% 17% 5% 13% 7% 5% 4 2 4 6% 21%	2076
March	1st to 10th	Night	16% 10% 4 11% 4 3 3 3 5% 6% 35%	5493
	11th to 20th	Night	12% 11% 3 8% 5% 4 4 3 5% 8% 37%	5325
	21st to end	Night	18% 12% 4 10% 5% 4 4 3 5% 5% 30%	5274
April	1st to 10th	Night	18% 12% 3 7% 4 4 3 3 6% 6% 33%	2100
	11th to 20th	Night	21% 9% 3 5% 4 4 4 3 6% 5% 35%	2034
	21st to end	Night	17% 10% 3 7% 4 3 4 3 5% 5% 39%	1890
May	1st to 10th	Night	12% 6% 2 7% 4 5% 5% 4 6% 8% 41%	5237
	11th to 20th	Night	11% 6% 2 6% 4 5% 5% 4 6% 8% 44%	4919
	21st to end	Night	17% 6% 2 5% 4 4 4 4 5% 6% 45%	5139
June	1st to 10th	Night	11% 6% 3 5% 4 4 5% 4 7% 8% 43%	1680
	11th to 20th	Night	11% 6% 2 7% 5% 4 4 4 5% 8% 44%	1680
	21st to end	Night	10% 6% 3 5% 4 4 5% 4 6% 9% 44%	1680
July	1st to 10th	Night	13% 7% 2 7% 4 5% 4 4 6% 9% 39%	4708
	11th to 20th	Night	6% 4 1 4 3 3 4 3 6% 8% 57%	4707
	21st to end	Night	8% 6% 2 6% 4 3 4 4 6% 7% 50%	5117
August	1st to 10th	Night	15% 6% 2 6% 5% 3 4 3 6% 7% 43%	3884
	11th to 20th	Night	11% 5% 2 6% 4 4 4 4 6% 8% 48%	4095
	21st to end	Night	11% 5% 2 5% 4 5% 5% 4 6% 8% 45%	5023
September	1st to 10th	Night	11% 5% 2 5% 5% 4 4 3 5% 6% 49%	2100
	11th to 20th	Night	12% 5% 2 4 3 3 3 3 5% 6% 54%	2280
	21st to end	Night	15% 6% 2 5% 4 4 5% 3 5% 7% 43%	2289
October	1st to 10th	Night	17% 7% 2 5% 4 3 4 2 4 7% 46%	2200
	11th to 20th	Night	24% 11% 3 7% 4 4 4 2 4 5% 32%	2491
	21st to end	Night	25% 13% 2 7% 4 4 3 4 4 6% 28%	2860
November	1st to 10th	Night	16% 15% 3 8% 4 4 3 3 4 6% 33%	2666
	11th to 20th	Night	16% 22% 6% 11% 4 4 4 3 4 4 21%	2730
	21st to end	Night	19% 23% 8% 9% 4 4 3 3 4 4 19%	2783
December	1st to 10th	Night	14% 25% 12% 17% 5% 4 4 2 3 3 11%	4720
	11th to 20th	Night	16% 26% 9% 14% 10% 4 3 2 3 3 9%	5339
	21st to end	Night	23% 22% 8% 12% 5% 4 3 3 4 4 13%	7150

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	73% 21% 2 3 1	4692
	11th to 20th	Day	76% 21% 2 2	4710
	21st to end	Day	62% 25% 5% 7% 2	5156
February	1st to 10th	Day	32% 60% 3 4 2	1856
	11th to 20th	Day	29% 59% 4 6% 2	2058
	21st to end	Day	28% 60% 5% 5% 1	1730
March	1st to 10th	Day	36% 31% 12% 13% 7% 1	4580
	11th to 20th	Day	35% 29% 13% 15% 7%	4855
	21st to end	Day	46% 29% 7% 10% 7%	5931
April	1st to 10th	Day	23% 60% 5% 8% 4	2520
	11th to 20th	Day	21% 60% 5% 8% 6% 1	2535
	21st to end	Day	19% 60% 6% 9% 6% 1	2730
May	1st to 10th	Day	28% 24% 8% 24% 13% 3	7651
	11th to 20th	Day	33% 25% 9% 18% 14% 1	7960
	21st to end	Day	29% 23% 6% 19% 19% 3	9061
June	1st to 10th	Day	13% 59% 5% 13% 8% 1	2940
	11th to 20th	Day	20% 60% 5% 9% 5%	2940
	21st to end	Day	16% 59% 7% 12% 6%	2940
July	1st to 10th	Day	34% 21% 12% 21% 11% 1	8211
	11th to 20th	Day	21% 21% 10% 27% 20% 1	8205
	21st to end	Day	26% 21% 13% 24% 16% 1	8794
August	1st to 10th	Day	28% 27% 11% 22% 12%	6258
	11th to 20th	Day	29% 27% 12% 23% 9%	5990
	21st to end	Day	29% 28% 12% 23% 7%	6087
September	1st to 10th	Day	19% 56% 8% 12% 4	2520
	11th to 20th	Day	15% 56% 6% 13% 9% 1	2318
	21st to end	Day	18% 56% 6% 13% 7% 1	2288
October	1st to 10th	Day	15% 36% 5% 29% 13% 2	3590
	11th to 20th	Day	29% 37% 8% 17% 10%	3070
	21st to end	Day	34% 37% 11% 13% 6%	3180
November	1st to 10th	Day	30% 54% 5% 7% 4	1852
	11th to 20th	Day	31% 55% 6% 6% 2	1890
	21st to end	Day	36% 55% 4 3 2	1832
December	1st to 10th	Day	57% 35% 4 3 1	2690
	11th to 20th	Day	59% 32% 6% 2 1	3085
	21st to end	Day	58% 29% 4 8% 2	4070
January	1st to 10th	Night	68% 22% 6% 4 1	8233
	11th to 20th	Night	74% 21% 3 1 1	8280
	21st to end	Night	65% 24% 5% 5% 1	9058
February	1st to 10th	Night	31% 59% 3 4 3	2760
	11th to 20th	Night	26% 59% 4 8% 3	2459
	21st to end	Night	26% 60% 5% 7% 2	2076
March	1st to 10th	Night	38% 30% 11% 15% 5%	5493
	11th to 20th	Night	34% 29% 14% 16% 6% 1	5325
	21st to end	Night	42% 31% 7% 13% 7%	5274
April	1st to 10th	Night	24% 59% 4 8% 5%	2100
	11th to 20th	Night	24% 59% 3 8% 5% 2	2034
	21st to end	Night	20% 59% 4 9% 7% 1	1890
May	1st to 10th	Night	31% 25% 9% 21% 12% 2	5264
	11th to 20th	Night	29% 25% 10% 22% 13% 1	4920
	21st to end	Night	33% 23% 5% 18% 14% 7%	5149
June	1st to 10th	Night	15% 60% 5% 11% 8% 1	1680
	11th to 20th	Night	20% 59% 5% 9% 6% 1	1680
	21st to end	Night	16% 59% 6% 11% 7% 1	1680
July	1st to 10th	Night	37% 21% 11% 17% 10% 4	4670
	11th to 20th	Night	20% 20% 8% 30% 19% 2	4662
	21st to end	Night	27% 22% 11% 21% 18% 1	5002
August	1st to 10th	Night	33% 26% 9% 17% 14%	3875
	11th to 20th	Night	28% 27% 14% 23% 8%	4122
	21st to end	Night	29% 27% 11% 21% 11% 1	5023
September	1st to 10th	Night	17% 56% 5% 14% 7% 1	2100
	11th to 20th	Night	14% 55% 6% 14% 9% 2	2280
	21st to end	Night	19% 56% 5% 11% 8% 1	2289
October	1st to 10th	Night	23% 36% 6% 24% 10% 1	3590
	11th to 20th	Night	27% 37% 6% 20% 10%	4066
	21st to end	Night	30% 36% 8% 18% 8%	4610
November	1st to 10th	Night	29% 54% 4 7% 5%	2666
	11th to 20th	Night	29% 55% 5% 7% 3	2730
	21st to end	Night	34% 54% 5% 4 2 1	2783
December	1st to 10th	Night	52% 36% 6% 4 1	4720
	11th to 20th	Night	60% 32% 4 4 1	5341
	21st to end	Night	56% 28% 7% 6% 3	7150

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	19% 22% 34% 18% 5% 1	330
	11th to 20th	Day	23% 21% 40% 13% 2	330
	21st to end	Day	25% 21% 31% 21% 2	363
February	1st to 10th	Day	20% 31% 29% 14% 5% 2	330
	11th to 20th	Day	21% 29% 33% 16% 1	330
	21st to end	Day	22% 29% 40% 10% 1	273
March	1st to 10th	Day	21% 25% 39% 12% 2	330
	11th to 20th	Day	24% 19% 29% 19% 8% 1	435
	21st to end	Day	28% 18% 30% 18% 6% 1	594
April	1st to 10th	Day	25% 17% 35% 20% 3 1	540
	11th to 20th	Day	27% 20% 28% 16% 8% 1	532
	21st to end	Day	21% 15% 30% 25% 8% 1	540
May	1st to 10th	Day	20% 14% 36% 21% 7% 2	543
	11th to 20th	Day	18% 13% 30% 25% 11% 2	676
	21st to end	Day	15% 9% 31% 29% 13% 3	844
June	1st to 10th	Day	13% 8% 33% 31% 13% 2	780
	11th to 20th	Day	18% 8% 32% 28% 11% 3	780
	21st to end	Day	15% 9% 29% 32% 12% 3	780
July	1st to 10th	Day	7% 6% 26% 37% 18% 5%	771
	11th to 20th	Day	9% 7% 26% 36% 17% 4	768
	21st to end	Day	9% 4 31% 35% 16% 4	849
August	1st to 10th	Day	9% 5% 25% 33% 22% 6%	683
	11th to 20th	Day	14% 4 19% 32% 22% 9%	559
	21st to end	Day	15% 8% 23% 29% 19% 6%	627
September	1st to 10th	Day	16% 8% 23% 30% 16% 6%	570
	11th to 20th	Day	12% 6% 21% 29% 23% 7%	570
	21st to end	Day	14% 11% 23% 27% 18% 7%	562
October	1st to 10th	Day	17% 14% 28% 22% 17% 3	530
	11th to 20th	Day	28% 14% 33% 21% 4	364
	21st to end	Day	32% 16% 32% 16% 4 1	363
November	1st to 10th	Day	25% 21% 29% 18% 6% 1	330
	11th to 20th	Day	25% 27% 31% 13% 4 1	330
	21st to end	Day	29% 22% 34% 13% 1	330
December	1st to 10th	Day	26% 27% 27% 15% 4 1	330
	11th to 20th	Day	29% 27% 30% 10% 4 1	330
	21st to end	Day	32% 26% 28% 10% 3 1	363
January	1st to 10th	Night	24% 19% 33% 19% 5%	1050
	11th to 20th	Night	26% 20% 32% 17% 5%	1050
	21st to end	Night	21% 16% 36% 21% 5%	1155
February	1st to 10th	Night	21% 16% 34% 24% 4 1	959
	11th to 20th	Night	21% 19% 32% 22% 6%	823
	21st to end	Night	23% 17% 35% 22% 3	692
March	1st to 10th	Night	19% 15% 32% 25% 9% 1	840
	11th to 20th	Night	18% 15% 33% 26% 8% 1	840
	21st to end	Night	22% 12% 27% 31% 7% 1	791
April	1st to 10th	Night	23% 14% 30% 26% 6% 1	630
	11th to 20th	Night	26% 12% 26% 26% 9% 1	623
	21st to end	Night	21% 9% 29% 30% 11%	630
May	1st to 10th	Night	17% 6% 32% 34% 11% 1	630
	11th to 20th	Night	17% 6% 25% 34% 17% 1	621
	21st to end	Night	16% 6% 23% 37% 17% 2	683
June	1st to 10th	Night	13% 5% 23% 41% 16% 2	630
	11th to 20th	Night	16% 5% 24% 35% 17% 3	630
	21st to end	Night	13% 4 21% 41% 20% 1	630
July	1st to 10th	Night	11% 1 16% 41% 26% 5%	615
	11th to 20th	Night	9% 2 20% 38% 27% 3	612
	21st to end	Night	8% 4 19% 40% 27% 2	690
August	1st to 10th	Night	11% 3 16% 41% 26% 4	627
	11th to 20th	Night	11% 2 15% 38% 28% 6%	624
	21st to end	Night	12% 5% 18% 39% 24% 2	693
September	1st to 10th	Night	13% 6% 20% 35% 20% 6%	630
	11th to 20th	Night	12% 7% 17% 34% 24% 5%	810
	21st to end	Night	17% 9% 21% 29% 21% 3	833
October	1st to 10th	Night	20% 9% 24% 29% 16% 2	800
	11th to 20th	Night	29% 12% 26% 24% 8% 1	800
	21st to end	Night	30% 14% 27% 22% 6%	880
November	1st to 10th	Night	25% 14% 30% 23% 7% 1	820
	11th to 20th	Night	27% 21% 28% 19% 5%	840
	21st to end	Night	32% 16% 29% 20% 3	893
December	1st to 10th	Night	28% 22% 29% 17% 3	1050
	11th to 20th	Night	30% 20% 30% 16% 3 1	1050
	21st to end	Night	32% 17% 31% 18% 2	1155

Page generated at 2026-09-26 04:18:40. Version ac07

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