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 2025-05-26.

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	14% 11% 5% 9% 5% 4 4 3 5% 6% 34%	113866
	Night	15% 14% 5% 11% 5% 4 4 3 4 5% 29%	115608
Transparency	Day	31% 43% 7% 12% 7% 1	117413
	Night	36% 41% 6% 10% 6% 1	120204
Seeing	Day	18% 14% 29% 25% 11% 3	16596
	Night	21% 12% 27% 27% 12% 2	26575

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	10% 25% 13% 26% 6% 4 2 2 2 3 8%	3617
	11th to 20th	Day	10% 17% 9% 24% 16% 9% 5% 2 2 2 3	3620
	21st to end	Day	14% 19% 10% 18% 8% 4 6% 2 3 3 12%	3982
February	1st to 10th	Day	10% 17% 7% 16% 13% 6% 4 3 4 4 16%	1768
	11th to 20th	Day	13% 16% 7% 18% 10% 6% 4 2 3 4 16%	1948
	21st to end	Day	13% 16% 6% 14% 8% 5% 4 3 5% 6% 21%	1650
March	1st to 10th	Day	12% 10% 5% 12% 5% 5% 4 4 5% 5% 33%	4480
	11th to 20th	Day	12% 9% 7% 8% 5% 4 4 3 5% 7% 35%	4750
	21st to end	Day	22% 11% 6% 11% 4 3 3 3 4 5% 28%	5801
April	1st to 10th	Day	18% 14% 4 6% 4 4 4 4 5% 6% 32%	2400
	11th to 20th	Day	20% 10% 3 5% 5% 4 4 4 5% 6% 36%	2413
	21st to end	Day	16% 9% 2 7% 5% 4 5% 4 5% 6% 36%	2600
May	1st to 10th	Day	14% 7% 2 7% 3 4 4 3 6% 7% 43%	4212
	11th to 20th	Day	12% 7% 2 5% 4 4 4 3 6% 7% 47%	4393
	21st to end	Day	11% 6% 2 5% 4 4 4 4 6% 8% 47%	4895
June	1st to 10th	Day	12% 6% 1 5% 4 4 4 3 6% 7% 48%	2660
	11th to 20th	Day	13% 5% 2 5% 3 4 4 3 5% 9% 47%	2660
	21st to end	Day	12% 5% 2 5% 4 4 4 3 6% 9% 46%	2660
July	1st to 10th	Day	15% 6% 2 6% 4 3 4 4 6% 8% 43%	4440
	11th to 20th	Day	6% 3 1 4 3 3 4 3 5% 8% 59%	4440
	21st to end	Day	8% 4 2 5% 4 4 5% 4 5% 9% 51%	4813
August	1st to 10th	Day	10% 4 2 5% 4 4 5% 5% 7% 9% 44%	4274
	11th to 20th	Day	11% 4 2 5% 3 4 3 3 5% 6% 54%	4044
	21st to end	Day	10% 5% 2 6% 4 4 4 4 5% 8% 48%	4188
September	1st to 10th	Day	13% 5% 2 6% 4 5% 3 4 5% 6% 46%	2280
	11th to 20th	Day	11% 5% 2 6% 4 3 3 3 6% 7% 49%	2098
	21st to end	Day	15% 7% 2 6% 4 4 4 4 5% 7% 41%	2090
October	1st to 10th	Day	16% 7% 3 6% 4 3 4 3 5% 7% 42%	2090
	11th to 20th	Day	25% 13% 3 8% 5% 4 4 4 5% 6% 23%	1812
	21st to end	Day	25% 14% 3 8% 4 4 4 4 5% 5% 24%	1881
November	1st to 10th	Day	17% 16% 3 7% 5% 4 4 3 4 6% 32%	1762
	11th to 20th	Day	15% 24% 7% 10% 5% 4 4 3 5% 5% 18%	1800
	21st to end	Day	20% 22% 9% 11% 5% 3 3 3 4 4 16%	1745
December	1st to 10th	Day	13% 28% 18% 13% 5% 4 3 2 2 2 10%	2610
	11th to 20th	Day	14% 26% 12% 15% 10% 3 3 2 4 4 8%	3008
	21st to end	Day	21% 22% 9% 14% 6% 4 3 2 4 3 12%	3982
January	1st to 10th	Night	11% 23% 12% 26% 6% 4 3 2 2 3 9%	6348
	11th to 20th	Night	12% 21% 10% 24% 10% 11% 3 2 2 2 5%	6360
	21st to end	Night	13% 23% 10% 18% 7% 6% 5% 2 2 3 11%	6996
February	1st to 10th	Night	12% 19% 6% 16% 12% 5% 4 3 3 4 17%	2629
	11th to 20th	Night	13% 14% 7% 17% 10% 8% 3 3 4 4 17%	2338
	21st to end	Night	14% 16% 5% 13% 7% 5% 4 2 4 6% 21%	1980
March	1st to 10th	Night	16% 10% 4 11% 4 3 3 3 4 6% 35%	5373
	11th to 20th	Night	12% 10% 3 8% 5% 4 4 3 5% 8% 38%	5210
	21st to end	Night	18% 12% 4 10% 5% 4 4 3 5% 5% 30%	5159
April	1st to 10th	Night	17% 12% 3 8% 4 4 3 3 6% 6% 33%	2000
	11th to 20th	Night	21% 9% 3 5% 4 4 4 3 6% 6% 35%	1936
	21st to end	Night	17% 10% 3 7% 4 3 4 3 5% 5% 38%	1800
May	1st to 10th	Night	14% 7% 2 8% 5% 5% 5% 4 6% 7% 38%	2903
	11th to 20th	Night	15% 7% 3 6% 5% 5% 5% 4 6% 7% 40%	2724
	21st to end	Night	18% 7% 3 5% 4 3 3 3 5% 6% 42%	2788
June	1st to 10th	Night	12% 6% 2 5% 4 4 5% 4 7% 8% 43%	1520
	11th to 20th	Night	11% 6% 2 6% 5% 4 3 3 5% 8% 46%	1520
	21st to end	Night	9% 6% 3 5% 4 4 5% 4 7% 10% 45%	1520
July	1st to 10th	Night	13% 8% 2 5% 4 5% 5% 5% 5% 8% 41%	2530
	11th to 20th	Night	6% 4 1 5% 4 3 3 3 6% 7% 57%	2530
	21st to end	Night	7% 5% 2 6% 5% 3 4 4 6% 7% 51%	2750
August	1st to 10th	Night	12% 5% 2 6% 4 4 4 4 7% 8% 45%	2657
	11th to 20th	Night	12% 5% 2 5% 3 3 3 3 5% 6% 52%	2785
	21st to end	Night	10% 5% 2 5% 4 5% 4 4 5% 6% 48%	3466
September	1st to 10th	Night	12% 5% 2 5% 4 4 4 3 5% 6% 50%	1900
	11th to 20th	Night	12% 5% 2 4 3 3 3 3 5% 6% 54%	2062
	21st to end	Night	16% 6% 2 5% 4 4 5% 3 5% 7% 42%	2090
October	1st to 10th	Night	17% 7% 2 5% 4 3 4 2 4 7% 45%	2090
	11th to 20th	Night	24% 11% 3 7% 4 4 4 2 4 5% 32%	2366
	21st to end	Night	26% 13% 2 7% 4 4 4 4 4 6% 26%	2717
November	1st to 10th	Night	16% 16% 3 8% 4 4 3 3 4 6% 33%	2536
	11th to 20th	Night	17% 22% 6% 12% 4 4 4 3 4 4 20%	2600
	21st to end	Night	19% 23% 8% 9% 4 4 3 3 4 4 19%	2650
December	1st to 10th	Night	14% 25% 12% 17% 5% 4 4 2 3 3 12%	4580
	11th to 20th	Night	16% 26% 9% 14% 10% 4 3 2 3 4 9%	5199
	21st to end	Night	23% 22% 8% 12% 5% 4 3 3 4 4 13%	6996

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	67% 27% 2 4	3618
	11th to 20th	Day	70% 27% 2 2	3620
	21st to end	Day	56% 32% 5% 6% 1	3982
February	1st to 10th	Day	30% 63% 2 4 1	1768
	11th to 20th	Day	29% 61% 3 5% 2	1958
	21st to end	Day	25% 63% 5% 5% 1	1650
March	1st to 10th	Day	36% 32% 12% 13% 7% 1	4480
	11th to 20th	Day	35% 30% 14% 15% 7%	4750
	21st to end	Day	45% 30% 7% 10% 7%	5803
April	1st to 10th	Day	22% 63% 4 7% 4	2400
	11th to 20th	Day	20% 63% 4 7% 5% 1	2413
	21st to end	Day	18% 63% 5% 8% 6% 1	2600
May	1st to 10th	Day	23% 41% 8% 15% 9% 3	4250
	11th to 20th	Day	21% 43% 8% 16% 10% 2	4397
	21st to end	Day	21% 41% 7% 14% 15% 1	4908
June	1st to 10th	Day	11% 65% 4 12% 7% 1	2660
	11th to 20th	Day	17% 66% 4 8% 5%	2660
	21st to end	Day	14% 65% 6% 9% 6%	2660
July	1st to 10th	Day	32% 36% 9% 14% 8% 1	4371
	11th to 20th	Day	13% 36% 12% 24% 14% 1	4365
	21st to end	Day	20% 37% 11% 17% 15% 1	4662
August	1st to 10th	Day	24% 38% 8% 18% 11%	4259
	11th to 20th	Day	23% 38% 9% 19% 11%	4083
	21st to end	Day	24% 38% 10% 18% 9%	4187
September	1st to 10th	Day	17% 62% 7% 10% 4	2280
	11th to 20th	Day	12% 61% 5% 12% 9% 1	2098
	21st to end	Day	17% 61% 6% 12% 4	2090
October	1st to 10th	Day	14% 37% 5% 28% 13% 2	3480
	11th to 20th	Day	28% 38% 8% 17% 10%	2976
	21st to end	Day	34% 38% 11% 12% 5%	3081
November	1st to 10th	Day	29% 56% 5% 6% 3	1762
	11th to 20th	Day	30% 58% 5% 5% 2	1800
	21st to end	Day	34% 58% 4 3 2	1745
December	1st to 10th	Day	56% 36% 4 4 1	2610
	11th to 20th	Day	58% 33% 6% 2 1	3005
	21st to end	Day	57% 29% 4 8% 2	3982
January	1st to 10th	Night	62% 28% 4 4 1	6348
	11th to 20th	Night	69% 27% 2 1 1	6360
	21st to end	Night	58% 30% 5% 6%	6996
February	1st to 10th	Night	28% 62% 3 4 3	2629
	11th to 20th	Night	26% 62% 4 6% 2	2339
	21st to end	Night	24% 63% 5% 6% 2	1980
March	1st to 10th	Night	37% 31% 11% 15% 5%	5373
	11th to 20th	Night	33% 30% 14% 17% 6%	5210
	21st to end	Night	42% 31% 7% 13% 7%	5159
April	1st to 10th	Night	22% 62% 3 8% 5%	2000
	11th to 20th	Night	22% 62% 3 7% 4 2	1936
	21st to end	Night	19% 62% 4 7% 7% 1	1800
May	1st to 10th	Night	26% 42% 9% 11% 9% 3	2930
	11th to 20th	Night	25% 42% 8% 17% 8% 1	2725
	21st to end	Night	28% 41% 5% 12% 8% 6%	2796
June	1st to 10th	Night	12% 66% 5% 10% 6% 1	1520
	11th to 20th	Night	16% 65% 4 8% 6% 1	1520
	21st to end	Night	13% 65% 6% 9% 6% 1	1520
July	1st to 10th	Night	32% 36% 7% 14% 5% 5%	2490
	11th to 20th	Night	15% 37% 9% 26% 12% 2	2482
	21st to end	Night	21% 37% 10% 11% 19% 1	2662
August	1st to 10th	Night	25% 38% 8% 17% 12%	2648
	11th to 20th	Night	24% 38% 6% 21% 11%	2812
	21st to end	Night	24% 38% 8% 14% 14% 2	3466
September	1st to 10th	Night	14% 62% 4 12% 7% 1	1900
	11th to 20th	Night	12% 61% 5% 13% 8% 2	2062
	21st to end	Night	17% 61% 5% 10% 6%	2090
October	1st to 10th	Night	23% 37% 6% 24% 10% 1	3480
	11th to 20th	Night	26% 38% 7% 20% 10%	3941
	21st to end	Night	30% 37% 9% 18% 7%	4467
November	1st to 10th	Night	28% 57% 4 6% 4	2536
	11th to 20th	Night	29% 58% 4 6% 4	2600
	21st to end	Night	32% 57% 5% 3 2 1	2650
December	1st to 10th	Night	51% 38% 7% 4 1	4580
	11th to 20th	Night	59% 33% 4 4 1	5201
	21st to end	Night	56% 29% 7% 5% 3	6996

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	18% 21% 35% 19% 6% 1	300
	11th to 20th	Day	23% 19% 40% 14% 3	300
	21st to end	Day	25% 20% 29% 23% 3	330
February	1st to 10th	Day	20% 30% 29% 14% 5% 2	300
	11th to 20th	Day	22% 28% 33% 16% 1	300
	21st to end	Day	21% 29% 39% 10% 1	249
March	1st to 10th	Day	19% 26% 39% 13% 3	300
	11th to 20th	Day	22% 19% 30% 21% 8% 1	400
	21st to end	Day	28% 16% 30% 19% 6% 1	550
April	1st to 10th	Day	24% 16% 36% 21% 3 1	500
	11th to 20th	Day	26% 21% 27% 16% 9% 1	492
	21st to end	Day	21% 16% 30% 24% 8% 2	500
May	1st to 10th	Day	21% 14% 36% 21% 7% 2	503
	11th to 20th	Day	18% 11% 30% 27% 12% 2	631
	21st to end	Day	15% 9% 30% 29% 14% 3	760
June	1st to 10th	Day	13% 7% 33% 32% 13% 2	680
	11th to 20th	Day	16% 7% 31% 31% 13% 3	680
	21st to end	Day	15% 8% 28% 33% 12% 4	680
July	1st to 10th	Day	8% 6% 25% 36% 20% 5%	671
	11th to 20th	Day	9% 6% 25% 37% 18% 5%	668
	21st to end	Day	8% 3 27% 38% 17% 5%	739
August	1st to 10th	Day	9% 5% 24% 33% 23% 6%	592
	11th to 20th	Day	13% 4 18% 31% 24% 10%	479
	21st to end	Day	15% 7% 21% 30% 21% 5%	539
September	1st to 10th	Day	16% 8% 22% 31% 18% 6%	490
	11th to 20th	Day	11% 6% 21% 31% 24% 7%	490
	21st to end	Day	16% 12% 23% 26% 17% 6%	490
October	1st to 10th	Day	18% 14% 27% 21% 16% 3	490
	11th to 20th	Day	29% 14% 32% 21% 4	333
	21st to end	Day	35% 16% 31% 14% 3 1	330
November	1st to 10th	Day	25% 21% 29% 18% 7% 1	300
	11th to 20th	Day	23% 28% 32% 13% 4	300
	21st to end	Day	28% 21% 35% 14% 1	300
December	1st to 10th	Day	25% 28% 27% 16% 4	300
	11th to 20th	Day	27% 28% 30% 10% 4 1	300
	21st to end	Day	31% 26% 28% 11% 4 1	330
January	1st to 10th	Night	23% 19% 33% 19% 5% 1	1000
	11th to 20th	Night	26% 19% 32% 17% 5% 1	1000
	21st to end	Night	22% 15% 36% 21% 6%	1100
February	1st to 10th	Night	21% 17% 34% 24% 4 1	914
	11th to 20th	Night	21% 19% 32% 22% 6%	783
	21st to end	Night	22% 17% 35% 22% 3	660
March	1st to 10th	Night	18% 15% 32% 25% 9% 1	800
	11th to 20th	Night	17% 15% 33% 26% 8% 1	800
	21st to end	Night	22% 11% 26% 32% 8% 1	753
April	1st to 10th	Night	22% 14% 31% 27% 6% 1	600
	11th to 20th	Night	25% 12% 26% 27% 9% 1	593
	21st to end	Night	22% 9% 29% 30% 11% 1	600
May	1st to 10th	Night	18% 6% 31% 34% 11% 1	600
	11th to 20th	Night	17% 6% 24% 34% 18% 1	591
	21st to end	Night	16% 5% 21% 37% 18% 3	634
June	1st to 10th	Night	13% 6% 22% 41% 16% 2	570
	11th to 20th	Night	15% 4 24% 35% 19% 3	570
	21st to end	Night	12% 4 20% 41% 21% 2	570
July	1st to 10th	Night	10% 1 16% 41% 27% 5%	555
	11th to 20th	Night	10% 3 20% 35% 28% 4	552
	21st to end	Night	8% 4 18% 39% 28% 3	624
August	1st to 10th	Night	10% 3 16% 41% 27% 4	567
	11th to 20th	Night	11% 2 16% 35% 29% 7%	564
	21st to end	Night	13% 4 17% 40% 23% 3	627
September	1st to 10th	Night	13% 6% 21% 35% 20% 6%	570
	11th to 20th	Night	12% 7% 18% 36% 23% 5%	732
	21st to end	Night	18% 9% 21% 28% 21% 3	760
October	1st to 10th	Night	20% 10% 23% 29% 16% 2	760
	11th to 20th	Night	29% 11% 26% 24% 8% 1	760
	21st to end	Night	31% 14% 28% 21% 6%	836
November	1st to 10th	Night	25% 15% 30% 23% 7% 1	780
	11th to 20th	Night	27% 21% 28% 19% 5%	800
	21st to end	Night	31% 16% 30% 20% 4	850
December	1st to 10th	Night	29% 22% 29% 17% 3	1000
	11th to 20th	Night	29% 20% 30% 17% 4 1	1000
	21st to end	Night	32% 16% 31% 18% 2	1100

Page generated at 2025-05-23 09:20:58. Version ac07

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