Biolab Boat Ramp
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Biolab Boat Ramp clear sky chart from 2005-11-06 to 2026-01-02.

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	7% 5% 2 6% 5% 5% 6% 5% 8% 11% 40%	126888
	Night	8% 6% 2 7% 5% 5% 5% 4 7% 10% 42%	124495
Transparency	Day	21% 41% 13% 14% 8% 2	130557
	Night	23% 40% 12% 14% 8% 3	128895
Seeing	Day	8% 5% 20% 27% 24% 16%	17298
	Night	9% 4 17% 31% 30% 9%	27398

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	7% 5% 2 5% 4 4 4 3 6% 8% 51%	4065
	11th to 20th	Day	18% 10% 4 8% 5% 5% 5% 4 6% 6% 30%	4060
	21st to end	Day	16% 6% 3 6% 4 4 4 3 6% 8% 42%	4466
February	1st to 10th	Day	11% 6% 3 6% 5% 5% 4 5% 6% 8% 43%	1969
	11th to 20th	Day	7% 4 2 6% 5% 5% 4 4 5% 7% 51%	1966
	21st to end	Day	9% 6% 2 4 4 4 5% 3 6% 8% 48%	1815
March	1st to 10th	Day	6% 5% 2 7% 5% 5% 6% 5% 6% 10% 42%	4935
	11th to 20th	Day	4 3 1 4 3 3 3 3 5% 8% 62%	4980
	21st to end	Day	8% 5% 2 6% 4 4 5% 5% 7% 10% 43%	5465
April	1st to 10th	Day	6% 4 2 5% 4 5% 5% 5% 7% 8% 50%	2200
	11th to 20th	Day	8% 4 2 6% 4 5% 6% 5% 7% 9% 44%	2284
	21st to end	Day	5% 3 1 5% 4 4 5% 5% 7% 11% 50%	2400
May	1st to 10th	Day	3 2 1 5% 4 4 6% 5% 8% 12% 50%	5497
	11th to 20th	Day	8% 5% 2 6% 4 5% 5% 5% 7% 9% 44%	5861
	21st to end	Day	4 4 2 6% 5% 5% 6% 5% 8% 11% 44%	6433
June	1st to 10th	Day	11% 7% 3 7% 7% 7% 7% 5% 9% 9% 27%	2600
	11th to 20th	Day	5% 5% 2 8% 6% 7% 8% 7% 10% 12% 30%	2600
	21st to end	Day	7% 7% 3 7% 7% 6% 7% 6% 9% 11% 30%	2600
July	1st to 10th	Day	6% 6% 2 8% 6% 7% 8% 7% 10% 14% 26%	5900
	11th to 20th	Day	4 4 2 6% 5% 6% 7% 6% 10% 14% 37%	5900
	21st to end	Day	4 4 2 5% 5% 5% 7% 6% 9% 15% 38%	6424
August	1st to 10th	Day	5% 5% 3 8% 6% 7% 8% 7% 9% 14% 29%	4234
	11th to 20th	Day	4 4 2 7% 5% 6% 7% 6% 11% 13% 35%	3959
	21st to end	Day	6% 5% 3 8% 6% 6% 7% 6% 10% 15% 28%	4086
September	1st to 10th	Day	7% 6% 3 9% 7% 8% 8% 8% 9% 11% 24%	2200
	11th to 20th	Day	9% 7% 3 8% 7% 7% 7% 6% 9% 12% 26%	2200
	21st to end	Day	10% 6% 3 9% 7% 6% 8% 5% 8% 9% 29%	2200
October	1st to 10th	Day	12% 7% 3 7% 7% 6% 6% 5% 7% 9% 32%	2110
	11th to 20th	Day	6% 5% 2 6% 6% 5% 5% 4 8% 9% 44%	2000
	21st to end	Day	8% 4 2 6% 4 4 5% 4 7% 9% 47%	2200
November	1st to 10th	Day	7% 5% 3 7% 6% 5% 6% 6% 7% 9% 40%	2057
	11th to 20th	Day	9% 6% 2 6% 6% 5% 5% 5% 6% 8% 43%	2100
	21st to end	Day	8% 6% 2 7% 5% 5% 5% 5% 7% 9% 41%	2074
December	1st to 10th	Day	5% 4 2 5% 4 4 4 4 6% 9% 53%	3020
	11th to 20th	Day	9% 7% 3 7% 5% 6% 7% 4 8% 10% 34%	3463
	21st to end	Day	10% 6% 3 8% 6% 6% 5% 5% 6% 8% 36%	4565
January	1st to 10th	Night	8% 6% 2 5% 3 3 4 3 6% 8% 52%	5903
	11th to 20th	Night	16% 10% 4 9% 5% 5% 5% 4 7% 7% 29%	5900
	21st to end	Night	14% 6% 2 6% 4 4 4 4 6% 8% 41%	6490
February	1st to 10th	Night	10% 7% 2 6% 4 4 4 4 6% 7% 44%	2427
	11th to 20th	Night	11% 4 2 6% 5% 4 4 4 6% 7% 49%	2318
	21st to end	Night	7% 3 1 5% 4 4 5% 4 5% 8% 53%	1815
March	1st to 10th	Night	9% 6% 3 7% 4 5% 5% 4 6% 7% 45%	4918
	11th to 20th	Night	5% 3 1 3 3 3 4 3 6% 11% 57%	4980
	21st to end	Night	6% 5% 2 6% 4 5% 5% 4 7% 8% 47%	5467
April	1st to 10th	Night	5% 4 2 5% 3 4 4 4 7% 9% 54%	2200
	11th to 20th	Night	5% 5% 2 6% 4 4 5% 4 6% 8% 50%	2061
	21st to end	Night	6% 4 2 5% 4 4 4 4 6% 8% 54%	2000
May	1st to 10th	Night	4 3 2 5% 4 4 5% 5% 6% 11% 52%	4426
	11th to 20th	Night	7% 6% 2 6% 4 4 5% 4 6% 9% 45%	4032
	21st to end	Night	4 4 2 7% 5% 4 5% 5% 8% 11% 45%	4421
June	1st to 10th	Night	10% 7% 3 8% 6% 5% 6% 6% 8% 10% 32%	1800
	11th to 20th	Night	4 7% 3 7% 7% 8% 6% 6% 10% 12% 31%	1800
	21st to end	Night	7% 5% 3 8% 5% 5% 7% 5% 7% 12% 35%	1800
July	1st to 10th	Night	8% 7% 3 9% 6% 6% 6% 5% 9% 13% 29%	4058
	11th to 20th	Night	3 4 2 6% 5% 5% 6% 5% 8% 15% 40%	4057
	21st to end	Night	3 4 2 6% 5% 5% 6% 5% 8% 13% 41%	4427
August	1st to 10th	Night	4 6% 3 8% 6% 6% 7% 6% 8% 13% 35%	2915
	11th to 20th	Night	3 4 2 7% 5% 6% 7% 5% 9% 12% 39%	3057
	21st to end	Night	7% 6% 2 7% 5% 6% 7% 5% 10% 13% 31%	3806
September	1st to 10th	Night	7% 7% 4 8% 7% 7% 8% 7% 8% 11% 27%	2200
	11th to 20th	Night	8% 8% 4 10% 8% 5% 6% 5% 9% 12% 25%	2200
	21st to end	Night	9% 7% 3 9% 5% 6% 6% 5% 9% 10% 31%	2200
October	1st to 10th	Night	10% 7% 3 9% 6% 4 6% 5% 7% 8% 34%	2289
	11th to 20th	Night	6% 6% 2 6% 5% 5% 5% 4 6% 8% 47%	2400
	21st to end	Night	8% 5% 2 6% 5% 5% 4 4 6% 9% 47%	2640
November	1st to 10th	Night	8% 6% 3 7% 6% 5% 5% 4 7% 8% 42%	2461
	11th to 20th	Night	7% 6% 2 7% 5% 4 5% 4 7% 9% 43%	2520
	21st to end	Night	9% 6% 3 7% 5% 5% 7% 5% 6% 9% 39%	2542
December	1st to 10th	Night	5% 3 2 5% 5% 4 5% 4 6% 9% 52%	4380
	11th to 20th	Night	11% 9% 3 7% 5% 5% 5% 4 6% 8% 38%	4952
	21st to end	Night	10% 8% 3 8% 5% 5% 5% 4 6% 7% 39%	6633

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% 27% 9% 12% 22% 7%	4066
	11th to 20th	Day	46% 28% 4 11% 9% 2	4060
	21st to end	Day	29% 30% 6% 21% 10% 4	4466
February	1st to 10th	Day	14% 63% 6% 7% 8% 2	1969
	11th to 20th	Day	10% 62% 4 11% 11% 3	1976
	21st to end	Day	14% 63% 4 8% 8% 3	1815
March	1st to 10th	Day	30% 31% 11% 11% 15% 2	4935
	11th to 20th	Day	13% 29% 7% 21% 17% 13%	4980
	21st to end	Day	26% 30% 8% 21% 11% 4	5465
April	1st to 10th	Day	11% 63% 6% 11% 7% 2	2200
	11th to 20th	Day	9% 64% 4 8% 10% 4	2284
	21st to end	Day	8% 63% 6% 12% 10% 1	2400
May	1st to 10th	Day	17% 35% 19% 20% 7% 2	5529
	11th to 20th	Day	25% 31% 13% 24% 7%	5865
	21st to end	Day	17% 32% 14% 27% 9%	6447
June	1st to 10th	Day	16% 65% 11% 7% 1	2600
	11th to 20th	Day	16% 67% 9% 8%	2600
	21st to end	Day	12% 66% 14% 7% 2	2600
July	1st to 10th	Day	29% 35% 26% 8% 2	5835
	11th to 20th	Day	20% 35% 34% 10% 1	5831
	21st to end	Day	21% 35% 25% 19% 1	6240
August	1st to 10th	Day	26% 43% 22% 7% 1	4221
	11th to 20th	Day	17% 45% 19% 13% 6%	3998
	21st to end	Day	21% 45% 23% 10% 1	4086
September	1st to 10th	Day	21% 65% 8% 3 3	2200
	11th to 20th	Day	19% 61% 12% 8% 1	2200
	21st to end	Day	17% 60% 10% 8% 4 1	2200
October	1st to 10th	Day	38% 41% 11% 7% 2	3435
	11th to 20th	Day	16% 39% 6% 16% 19% 3	3240
	21st to end	Day	13% 37% 6% 19% 22% 3	3538
November	1st to 10th	Day	17% 56% 8% 9% 8% 2	2057
	11th to 20th	Day	19% 55% 4 11% 7% 4	2100
	21st to end	Day	18% 55% 5% 12% 7% 3	2074
December	1st to 10th	Day	15% 36% 13% 21% 9% 6%	3020
	11th to 20th	Day	28% 35% 9% 11% 14% 4	3460
	21st to end	Day	33% 29% 10% 17% 9% 2	4565
January	1st to 10th	Night	23% 26% 7% 15% 21% 8%	5903
	11th to 20th	Night	44% 28% 8% 11% 7% 1	5900
	21st to end	Night	30% 29% 7% 18% 12% 4	6490
February	1st to 10th	Night	13% 63% 6% 9% 7% 2	2427
	11th to 20th	Night	12% 61% 4 9% 11% 2	2319
	21st to end	Night	11% 63% 6% 9% 8% 3	1815
March	1st to 10th	Night	32% 31% 9% 12% 12% 5%	4918
	11th to 20th	Night	14% 29% 13% 17% 14% 12%	4980
	21st to end	Night	26% 31% 8% 18% 14% 3	5467
April	1st to 10th	Night	11% 63% 7% 11% 5% 3	2200
	11th to 20th	Night	10% 63% 5% 11% 8% 3	2061
	21st to end	Night	9% 63% 6% 13% 8% 2	2000
May	1st to 10th	Night	20% 33% 17% 21% 7% 2	4456
	11th to 20th	Night	25% 30% 17% 22% 6%	4033
	21st to end	Night	19% 32% 16% 26% 8%	4429
June	1st to 10th	Night	17% 64% 12% 6% 1	1800
	11th to 20th	Night	16% 68% 9% 7%	1800
	21st to end	Night	14% 64% 12% 8% 2	1800
July	1st to 10th	Night	33% 35% 22% 10% 1	4015
	11th to 20th	Night	19% 35% 36% 9%	4006
	21st to end	Night	24% 34% 23% 19% 1	4297
August	1st to 10th	Night	26% 41% 25% 6% 1	2904
	11th to 20th	Night	19% 43% 20% 13% 4	3084
	21st to end	Night	22% 44% 25% 8% 1	3806
September	1st to 10th	Night	22% 63% 8% 5% 3	2200
	11th to 20th	Night	19% 61% 11% 8% 1	2200
	21st to end	Night	18% 61% 8% 10% 4 1	2200
October	1st to 10th	Night	42% 40% 8% 7% 2	3744
	11th to 20th	Night	20% 39% 5% 16% 17% 3	3899
	21st to end	Night	17% 38% 6% 16% 21% 3	4252
November	1st to 10th	Night	17% 55% 7% 10% 7% 3	2461
	11th to 20th	Night	18% 56% 5% 8% 9% 3	2520
	21st to end	Night	18% 55% 6% 11% 7% 3	2542
December	1st to 10th	Night	15% 36% 12% 23% 6% 7%	4380
	11th to 20th	Night	27% 35% 10% 12% 10% 6%	4954
	21st to end	Night	33% 30% 10% 17% 7% 3	6633

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	14% 8% 44% 24% 8% 2	303
	11th to 20th	Day	7% 13% 40% 22% 14% 3	300
	21st to end	Day	15% 13% 42% 24% 5%	330
February	1st to 10th	Day	12% 12% 34% 25% 16% 2	300
	11th to 20th	Day	9% 8% 37% 32% 11% 3	318
	21st to end	Day	9% 6% 31% 33% 18% 3	414
March	1st to 10th	Day	3 12% 38% 33% 12% 1	500
	11th to 20th	Day	7% 9% 32% 31% 18% 3	500
	21st to end	Day	7% 7% 30% 34% 19% 3	550
April	1st to 10th	Day	8% 9% 32% 34% 14% 3	500
	11th to 20th	Day	8% 7% 29% 29% 22% 5%	492
	21st to end	Day	5% 4 23% 36% 22% 9%	500
May	1st to 10th	Day	5% 4 21% 36% 25% 9%	503
	11th to 20th	Day	9% 5% 14% 33% 25% 14%	527
	21st to end	Day	7% 3 11% 29% 29% 22%	573
June	1st to 10th	Day	12% 3 10% 25% 29% 19%	530
	11th to 20th	Day	5% 2 8% 22% 32% 31%	530
	21st to end	Day	7% 2 4 16% 35% 35%	530
July	1st to 10th	Day	7% 1 6% 11% 32% 44%	525
	11th to 20th	Day	6% 1 3 13% 35% 43%	524
	21st to end	Day	7% 2 3 17% 32% 40%	576
August	1st to 10th	Day	7% 3 5% 14% 35% 36%	526
	11th to 20th	Day	3 1 4 12% 32% 49%	519
	21st to end	Day	10% 1 6% 19% 32% 32%	583
September	1st to 10th	Day	9% 2 8% 18% 31% 32%	530
	11th to 20th	Day	10% 4 9% 24% 28% 24%	530
	21st to end	Day	11% 2 9% 25% 30% 23%	530
October	1st to 10th	Day	17% 3 17% 35% 20% 8%	530
	11th to 20th	Day	6% 5% 19% 35% 27% 8%	530
	21st to end	Day	6% 5% 22% 38% 23% 6%	583
November	1st to 10th	Day	8% 7% 21% 35% 24% 5%	535
	11th to 20th	Day	11% 6% 23% 35% 21% 3	540
	21st to end	Day	10% 5% 27% 35% 20% 3	514
December	1st to 10th	Day	6% 9% 37% 32% 12% 3	330
	11th to 20th	Day	8% 10% 33% 34% 15% 1	330
	21st to end	Day	8% 6% 33% 34% 16% 3	363
January	1st to 10th	Night	12% 9% 27% 36% 15% 1	805
	11th to 20th	Night	11% 8% 27% 36% 17% 2	800
	21st to end	Night	15% 8% 33% 35% 9%	880
February	1st to 10th	Night	12% 7% 26% 37% 17% 1	800
	11th to 20th	Night	12% 8% 28% 39% 13% 1	783
	21st to end	Night	8% 5% 31% 43% 13%	660
March	1st to 10th	Night	5% 6% 33% 39% 15% 1	800
	11th to 20th	Night	7% 7% 23% 42% 18% 2	800
	21st to end	Night	7% 5% 28% 37% 22% 1	880
April	1st to 10th	Night	6% 5% 28% 42% 18% 2	800
	11th to 20th	Night	7% 5% 25% 37% 24% 2	791
	21st to end	Night	6% 3 20% 44% 25% 3	800
May	1st to 10th	Night	6% 3 15% 47% 27% 2	775
	11th to 20th	Night	8% 3 14% 32% 36% 7%	591
	21st to end	Night	8% 2 6% 27% 46% 12%	650
June	1st to 10th	Night	12% 1 7% 28% 43% 9%	600
	11th to 20th	Night	6% 2 5% 21% 45% 22%	600
	21st to end	Night	7% 2 5% 17% 44% 25%	600
July	1st to 10th	Night	8% 2 3 13% 47% 28%	585
	11th to 20th	Night	6% 2 2 10% 50% 30%	582
	21st to end	Night	5% 1 1 12% 51% 30%	657
August	1st to 10th	Night	5% 3 3 10% 50% 29%	597
	11th to 20th	Night	4 1 3 11% 50% 32%	698
	21st to end	Night	12% 1 4 16% 42% 24%	880
September	1st to 10th	Night	9% 3 6% 15% 45% 23%	800
	11th to 20th	Night	10% 3 6% 21% 45% 16%	800
	21st to end	Night	11% 3 6% 21% 43% 16%	800
October	1st to 10th	Night	12% 3 13% 34% 31% 7%	800
	11th to 20th	Night	8% 4 13% 33% 35% 8%	800
	21st to end	Night	11% 2 17% 34% 31% 5%	880
November	1st to 10th	Night	10% 3 19% 35% 29% 4	820
	11th to 20th	Night	9% 5% 21% 38% 25% 2	840
	21st to end	Night	9% 4 26% 38% 21% 3	840
December	1st to 10th	Night	7% 5% 26% 34% 25% 3	840
	11th to 20th	Night	11% 7% 22% 36% 21% 3	840
	21st to end	Night	11% 5% 25% 36% 21% 2	924

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