Pescadero
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Pescadero clear sky chart from 2005-11-06 to 2026-07-16.

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	8% 8% 2 5% 3 3 4 4 6% 10% 47%	146495
	Night	10% 11% 4 7% 4 3 3 3 5% 7% 43%	143668
Transparency	Day	21% 36% 7% 12% 15% 8%	141419
	Night	27% 36% 5% 10% 13% 8%	139733
Seeing	Day	12% 12% 26% 30% 16% 4	17695
	Night	14% 8% 15% 29% 27% 8%	27042

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	18% 7% 2 5% 3 3 3 3 6% 8% 43%	5183
	11th to 20th	Day	10% 5% 2 6% 3 4 3 3 4 6% 55%	5340
	21st to end	Day	13% 9% 3 8% 4 4 4 3 5% 8% 38%	5843
February	1st to 10th	Day	18% 8% 2 5% 3 3 4 3 5% 6% 43%	1890
	11th to 20th	Day	16% 9% 2 7% 4 4 5% 3 5% 8% 37%	1934
	21st to end	Day	14% 7% 2 6% 4 3 4 4 6% 6% 43%	1730
March	1st to 10th	Day	16% 11% 4 10% 6% 4 5% 5% 6% 6% 29%	5033
	11th to 20th	Day	13% 7% 2 5% 3 4 5% 3 5% 8% 45%	5110
	21st to end	Day	13% 12% 3 8% 5% 5% 5% 4 6% 9% 29%	5651
April	1st to 10th	Day	14% 9% 3 5% 3 3 4 4 6% 7% 42%	2520
	11th to 20th	Day	9% 8% 2 7% 3 4 3 4 6% 8% 45%	2489
	21st to end	Day	9% 8% 2 6% 3 3 3 4 6% 10% 45%	2520
May	1st to 10th	Day	6% 8% 2 5% 3 3 4 4 7% 8% 50%	7283
	11th to 20th	Day	4 4 1 3 2 2 2 3 5% 11% 63%	7611
	21st to end	Day	4 13% 3 6% 4 4 4 4 6% 8% 45%	8992
June	1st to 10th	Day	6% 7% 2 5% 4 4 4 4 7% 11% 47%	2940
	11th to 20th	Day	3 4 1 4 3 3 4 3 7% 10% 56%	2940
	21st to end	Day	3 5% 2 4 3 3 3 4 6% 12% 54%	2940
July	1st to 10th	Day	1 3 1 3 2 2 3 4 7% 11% 62%	6334
	11th to 20th	Day	1 4 2 5% 3 3 3 4 8% 17% 49%	5946
	21st to end	Day	1 19% 3 7% 3 3 4 4 9% 14% 32%	6402
August	1st to 10th	Day	1 6% 2 6% 3 4 5% 5% 10% 16% 41%	5777
	11th to 20th	Day	3 6% 1 4 2 3 3 3 8% 12% 55%	5520
	21st to end	Day	1 4 2 5% 4 4 4 4 7% 13% 53%	5984
September	1st to 10th	Day	3 4 1 3 3 2 3 4 6% 11% 60%	2400
	11th to 20th	Day	5% 8% 2 6% 3 4 4 4 8% 11% 46%	2400
	21st to end	Day	5% 4 1 3 2 2 3 2 5% 9% 64%	2110
October	1st to 10th	Day	3 4 2 3 2 2 2 2 5% 7% 67%	3280
	11th to 20th	Day	5% 7% 2 6% 3 3 3 2 6% 8% 55%	3261
	21st to end	Day	7% 5% 2 4 3 3 3 3 6% 9% 54%	3558
November	1st to 10th	Day	8% 5% 2 5% 3 4 4 4 5% 7% 52%	2059
	11th to 20th	Day	10% 8% 3 6% 4 3 4 4 4 8% 46%	1892
	21st to end	Day	12% 6% 2 4 3 3 3 3 5% 6% 52%	1723
December	1st to 10th	Day	7% 5% 2 4 3 3 4 4 7% 9% 53%	2700
	11th to 20th	Day	22% 9% 3 6% 4 4 3 3 6% 6% 34%	3108
	21st to end	Day	23% 13% 3 7% 4 3 4 3 5% 6% 29%	4092
January	1st to 10th	Night	15% 10% 2 6% 3 3 4 3 5% 7% 41%	7718
	11th to 20th	Night	11% 6% 3 6% 3 3 3 3 5% 7% 51%	7650
	21st to end	Night	14% 12% 4 8% 4 3 3 3 4 7% 37%	8371
February	1st to 10th	Night	17% 9% 2 5% 3 3 3 2 4 6% 45%	2730
	11th to 20th	Night	15% 11% 3 6% 4 4 5% 3 5% 7% 37%	2572
	21st to end	Night	13% 9% 2 6% 4 3 3 3 5% 8% 43%	2076
March	1st to 10th	Night	18% 16% 5% 8% 4 4 3 3 4 5% 31%	5066
	11th to 20th	Night	16% 9% 2 6% 4 3 3 2 4 6% 45%	5110
	21st to end	Night	17% 17% 4 6% 4 3 3 3 4 6% 32%	5566
April	1st to 10th	Night	11% 11% 4 7% 4 4 5% 3 5% 6% 41%	2100
	11th to 20th	Night	12% 10% 3 6% 3 3 3 3 5% 8% 43%	2079
	21st to end	Night	8% 9% 2 4 3 3 4 4 6% 9% 47%	2100
May	1st to 10th	Night	9% 17% 5% 7% 3 2 2 2 3 4 47%	5666
	11th to 20th	Night	3 11% 4 7% 5% 4 4 2 5% 6% 50%	5262
	21st to end	Night	6% 20% 6% 6% 3 2 3 2 3 5% 44%	5181
June	1st to 10th	Night	5% 11% 3 6% 5% 4 4 3 5% 7% 46%	1680
	11th to 20th	Night	2 7% 3 7% 4 3 3 3 5% 9% 54%	1680
	21st to end	Night	3 9% 3 7% 3 3 3 2 4 8% 54%	1680
July	1st to 10th	Night	1 8% 5% 10% 4 3 3 2 5% 8% 52%	3832
	11th to 20th	Night	1 7% 10% 17% 5% 3 4 4 6% 9% 35%	4145
	21st to end	Night	1 35% 8% 7% 4 3 4 3 4 6% 24%	4472
August	1st to 10th	Night	2 13% 5% 14% 6% 4 5% 4 8% 9% 30%	4035
	11th to 20th	Night	1 17% 4 6% 4 3 4 4 7% 7% 45%	4328
	21st to end	Night	1 7% 4 12% 5% 4 3 4 6% 9% 45%	5015
September	1st to 10th	Night	2 6% 3 6% 4 4 3 3 6% 8% 55%	2000
	11th to 20th	Night	5% 9% 2 9% 4 3 4 4 6% 8% 47%	2000
	21st to end	Night	3 5% 3 4 3 3 2 2 5% 9% 61%	2284
October	1st to 10th	Night	3 4 1 4 3 3 3 2 5% 6% 66%	3920
	11th to 20th	Night	5% 15% 3 5% 4 3 3 2 4 6% 51%	3897
	21st to end	Night	7% 6% 2 5% 3 2 4 3 5% 7% 55%	4253
November	1st to 10th	Night	8% 6% 3 5% 3 3 3 3 6% 8% 52%	2460
	11th to 20th	Night	11% 7% 2 5% 4 4 4 3 5% 8% 46%	2725
	21st to end	Night	10% 6% 2 5% 4 3 3 3 5% 5% 54%	2893
December	1st to 10th	Night	8% 5% 2 5% 4 4 3 3 4 6% 56%	4700
	11th to 20th	Night	22% 10% 2 6% 3 4 4 4 7% 8% 29%	5316
	21st to end	Night	25% 12% 3 8% 5% 4 4 3 4 5% 27%	7106

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	30% 22% 14% 18% 12% 3	5184
	11th to 20th	Day	26% 21% 5% 7% 21% 20%	5340
	21st to end	Day	35% 23% 5% 13% 12% 11%	5843
February	1st to 10th	Day	20% 59% 3 8% 6% 4	1890
	11th to 20th	Day	21% 59% 4 6% 8% 2	1943
	21st to end	Day	16% 59% 5% 11% 6% 3	1730
March	1st to 10th	Day	40% 31% 6% 11% 11% 1	5033
	11th to 20th	Day	22% 30% 11% 21% 8% 8%	5110
	21st to end	Day	36% 32% 11% 14% 7% 1	5651
April	1st to 10th	Day	17% 60% 4 11% 7% 1	2520
	11th to 20th	Day	14% 60% 5% 12% 7% 2	2492
	21st to end	Day	15% 60% 6% 10% 8% 1	2520
May	1st to 10th	Day	21% 28% 8% 18% 18% 7%	7283
	11th to 20th	Day	12% 25% 5% 25% 27% 8%	7614
	21st to end	Day	25% 30% 5% 17% 22% 2	8994
June	1st to 10th	Day	11% 59% 4 9% 13% 4	2940
	11th to 20th	Day	9% 59% 4 10% 14% 4	2940
	21st to end	Day	11% 57% 3 5% 13% 11%	2940
July	1st to 10th	Day	11% 26% 9% 5% 16% 32%	6268
	11th to 20th	Day	14% 24% 15% 5% 16% 25%	5877
	21st to end	Day	34% 29% 9% 7% 10% 10%	6217
August	1st to 10th	Day	17% 39% 16% 7% 17% 5%	4206
	11th to 20th	Day	14% 37% 8% 7% 28% 5%	3990
	21st to end	Day	16% 37% 6% 9% 21% 11%	4311
September	1st to 10th	Day	11% 57% 2 7% 14% 10%	2400
	11th to 20th	Day	13% 59% 2 9% 12% 5%	2400
	21st to end	Day	10% 57% 3 11% 14% 6%	2110
October	1st to 10th	Day	9% 35% 3 7% 18% 28%	3280
	11th to 20th	Day	19% 40% 4 11% 20% 7%	3261
	21st to end	Day	17% 36% 5% 17% 16% 9%	3558
November	1st to 10th	Day	9% 54% 4 15% 14% 5%	2059
	11th to 20th	Day	19% 54% 4 12% 8% 2	1892
	21st to end	Day	15% 55% 5% 9% 14% 3	1723
December	1st to 10th	Day	16% 34% 4 18% 22% 6%	2700
	11th to 20th	Day	35% 32% 6% 10% 11% 6%	3108
	21st to end	Day	43% 27% 7% 13% 8% 2	4092
January	1st to 10th	Night	33% 23% 14% 14% 13% 2	7718
	11th to 20th	Night	27% 21% 6% 7% 22% 17%	7650
	21st to end	Night	38% 23% 4 11% 14% 10%	8371
February	1st to 10th	Night	21% 59% 3 6% 6% 5%	2730
	11th to 20th	Night	22% 58% 3 8% 7% 2	2574
	21st to end	Night	16% 59% 4 12% 6% 3	2076
March	1st to 10th	Night	42% 30% 5% 12% 10% 1	5066
	11th to 20th	Night	26% 31% 7% 16% 13% 7%	5110
	21st to end	Night	39% 32% 6% 15% 7% 1	5566
April	1st to 10th	Night	18% 59% 4 9% 9% 1	2100
	11th to 20th	Night	17% 60% 4 10% 7% 3	2079
	21st to end	Night	17% 60% 5% 10% 7% 2	2100
May	1st to 10th	Night	33% 25% 5% 13% 18% 7%	5664
	11th to 20th	Night	18% 30% 6% 13% 21% 11%	5263
	21st to end	Night	33% 26% 5% 11% 23% 2	5182
June	1st to 10th	Night	15% 59% 2 7% 12% 5%	1680
	11th to 20th	Night	14% 58% 3 7% 12% 6%	1680
	21st to end	Night	11% 57% 2 4 12% 14%	1680
July	1st to 10th	Night	24% 25% 6% 5% 8% 32%	3790
	11th to 20th	Night	37% 25% 6% 3 9% 20%	4091
	21st to end	Night	50% 25% 2 3 10% 10%	4345
August	1st to 10th	Night	31% 40% 7% 7% 10% 5%	2929
	11th to 20th	Night	21% 38% 3 4 29% 5%	3127
	21st to end	Night	21% 37% 8% 5% 19% 9%	3608
September	1st to 10th	Night	15% 58% 1 4 12% 10%	2000
	11th to 20th	Night	14% 58% 2 10% 10% 7%	2000
	21st to end	Night	12% 57% 2 9% 11% 10%	2284
October	1st to 10th	Night	9% 35% 2 5% 16% 32%	3920
	11th to 20th	Night	26% 37% 2 11% 13% 11%	3897
	21st to end	Night	17% 37% 6% 13% 15% 13%	4253
November	1st to 10th	Night	10% 54% 3 14% 12% 7%	2460
	11th to 20th	Night	19% 54% 5% 12% 8% 3	2725
	21st to end	Night	17% 55% 3 10% 11% 5%	2893
December	1st to 10th	Night	18% 35% 4 16% 19% 8%	4700
	11th to 20th	Night	36% 33% 5% 9% 12% 6%	5316
	21st to end	Night	45% 28% 7% 11% 7% 2	7106

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	28% 18% 24% 17% 11% 2	383
	11th to 20th	Day	17% 13% 23% 26% 16% 4	430
	21st to end	Day	18% 13% 26% 25% 15% 3	473
February	1st to 10th	Day	22% 17% 23% 23% 11% 5%	430
	11th to 20th	Day	24% 23% 25% 19% 8% 1	472
	21st to end	Day	16% 16% 36% 22% 9% 1	446
March	1st to 10th	Day	25% 17% 30% 21% 6% 1	540
	11th to 20th	Day	23% 13% 26% 23% 12% 3	540
	21st to end	Day	18% 19% 32% 20% 8% 2	594
April	1st to 10th	Day	18% 17% 30% 22% 10% 2	540
	11th to 20th	Day	16% 20% 27% 25% 10% 2	532
	21st to end	Day	13% 19% 31% 23% 10% 4	540
May	1st to 10th	Day	11% 16% 32% 28% 10% 3	543
	11th to 20th	Day	15% 14% 32% 25% 12% 2	568
	21st to end	Day	18% 15% 22% 26% 14% 4	617
June	1st to 10th	Day	9% 10% 32% 34% 13% 3	570
	11th to 20th	Day	4 13% 30% 39% 12% 1	570
	21st to end	Day	4 6% 30% 39% 17% 3	570
July	1st to 10th	Day	5% 5% 25% 43% 19% 4	566
	11th to 20th	Day	4 2 19% 49% 22% 4	545
	21st to end	Day	3 6% 18% 43% 23% 6%	575
August	1st to 10th	Day	6% 4 30% 41% 15% 5%	527
	11th to 20th	Day	5% 3 24% 40% 22% 6%	517
	21st to end	Day	3 3 22% 43% 23% 6%	583
September	1st to 10th	Day	5% 7% 20% 42% 21% 5%	530
	11th to 20th	Day	9% 8% 25% 35% 20% 4	530
	21st to end	Day	7% 8% 19% 37% 24% 5%	530
October	1st to 10th	Day	7% 9% 21% 32% 22% 8%	530
	11th to 20th	Day	10% 7% 20% 30% 25% 8%	530
	21st to end	Day	10% 8% 26% 30% 20% 6%	583
November	1st to 10th	Day	11% 12% 20% 28% 23% 6%	535
	11th to 20th	Day	13% 13% 23% 25% 20% 6%	332
	21st to end	Day	13% 12% 24% 25% 18% 8%	242
December	1st to 10th	Day	13% 14% 20% 22% 26% 5%	220
	11th to 20th	Day	18% 16% 20% 18% 19% 8%	220
	21st to end	Day	24% 22% 25% 15% 11% 3	242
January	1st to 10th	Night	23% 9% 14% 28% 23% 4	840
	11th to 20th	Night	17% 7% 13% 31% 25% 7%	840
	21st to end	Night	19% 8% 12% 31% 25% 5%	924
February	1st to 10th	Night	22% 10% 14% 28% 22% 6%	840
	11th to 20th	Night	21% 13% 14% 29% 19% 4	824
	21st to end	Night	17% 12% 20% 32% 16% 3	692
March	1st to 10th	Night	23% 12% 17% 27% 19% 3	840
	11th to 20th	Night	20% 8% 15% 30% 23% 4	840
	21st to end	Night	22% 9% 22% 27% 17% 3	924
April	1st to 10th	Night	16% 11% 21% 29% 20% 3	840
	11th to 20th	Night	16% 14% 19% 25% 19% 5%	831
	21st to end	Night	13% 12% 25% 23% 19% 8%	840
May	1st to 10th	Night	11% 10% 21% 29% 23% 6%	754
	11th to 20th	Night	14% 7% 20% 28% 25% 7%	614
	21st to end	Night	18% 11% 17% 25% 24% 5%	455
June	1st to 10th	Night	10% 6% 23% 29% 26% 6%	420
	11th to 20th	Night	7% 6% 20% 35% 28% 4	420
	21st to end	Night	6% 3 13% 34% 36% 8%	420
July	1st to 10th	Night	6% 4 15% 30% 36% 10%	455
	11th to 20th	Night	7% 3 6% 29% 39% 18%	597
	21st to end	Night	7% 4 7% 28% 40% 14%	657
August	1st to 10th	Night	14% 2 9% 29% 34% 12%	597
	11th to 20th	Night	6% 2 11% 30% 41% 9%	714
	21st to end	Night	6% 2 9% 28% 43% 13%	880
September	1st to 10th	Night	5% 3 10% 31% 38% 13%	800
	11th to 20th	Night	10% 5% 11% 32% 34% 9%	800
	21st to end	Night	5% 5% 11% 28% 37% 14%	800
October	1st to 10th	Night	9% 4 12% 30% 34% 11%	800
	11th to 20th	Night	10% 7% 10% 26% 36% 11%	800
	21st to end	Night	11% 6% 11% 27% 31% 14%	880
November	1st to 10th	Night	10% 7% 15% 25% 33% 10%	820
	11th to 20th	Night	15% 5% 15% 30% 30% 6%	840
	21st to end	Night	11% 7% 15% 36% 24% 7%	840
December	1st to 10th	Night	16% 6% 17% 29% 25% 7%	840
	11th to 20th	Night	24% 8% 13% 29% 22% 4	840
	21st to end	Night	23% 15% 18% 25% 16% 3	924

Page generated at 2026-07-13 00:14:52. Version ac07

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