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 2024-02-20.

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	10% 7% 2 5% 4 3 4 5% 6% 9% 45%	78544
	Night	11% 9% 3 6% 5% 3 4 4 5% 8% 43%	80674
Transparency	Day	22% 37% 5% 12% 14% 10%	78267
	Night	25% 37% 5% 11% 12% 10%	80473
Seeing	Day	12% 12% 26% 30% 16% 4	14464
	Night	14% 7% 15% 29% 28% 8%	23955

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	19% 8% 3 5% 4 2 3 4 5% 6% 40%	2777
	11th to 20th	Day	18% 10% 3 8% 6% 4 5% 4 5% 6% 32%	2860
	21st to end	Day	21% 11% 4 7% 5% 3 5% 4 5% 7% 29%	3146
February	1st to 10th	Day	18% 7% 3 4 4 3 4 4 5% 6% 43%	1710
	11th to 20th	Day	15% 8% 2 5% 4 3 5% 4 5% 8% 40%	1736
	21st to end	Day	15% 7% 2 6% 4 2 5% 4 5% 6% 44%	1480
March	1st to 10th	Day	19% 8% 3 5% 4 3 5% 6% 6% 8% 34%	1965
	11th to 20th	Day	17% 8% 4 6% 5% 3 6% 5% 6% 7% 33%	1980
	21st to end	Day	13% 7% 3 5% 5% 4 5% 4 5% 9% 41%	2196
April	1st to 10th	Day	15% 8% 4 5% 4 2 4 5% 6% 7% 41%	2160
	11th to 20th	Day	10% 7% 3 6% 3 3 3 4 5% 8% 47%	2129
	21st to end	Day	9% 7% 2 5% 4 2 3 5% 6% 10% 47%	2160
May	1st to 10th	Day	8% 7% 2 4 4 2 4 4 7% 9% 47%	2230
	11th to 20th	Day	10% 7% 3 4 4 3 5% 5% 6% 9% 44%	2304
	21st to end	Day	11% 13% 3 5% 5% 3 3 5% 5% 8% 39%	2723
June	1st to 10th	Day	7% 7% 3 4 5% 3 4 5% 7% 10% 46%	2520
	11th to 20th	Day	3 4 1 4 3 2 4 4 8% 10% 57%	2520
	21st to end	Day	3 5% 2 4 4 2 3 4 6% 12% 54%	2520
July	1st to 10th	Day	3 5% 2 4 4 3 4 6% 9% 12% 49%	2476
	11th to 20th	Day	3 6% 2 4 4 2 4 5% 10% 15% 45%	2340
	21st to end	Day	1 3 2 4 3 3 4 5% 10% 16% 50%	2546
August	1st to 10th	Day	3 7% 3 6% 4 3 4 8% 10% 13% 38%	2328
	11th to 20th	Day	1 3 1 3 4 3 4 5% 6% 14% 54%	2190
	21st to end	Day	1 5% 2 5% 4 3 4 6% 8% 13% 49%	2376
September	1st to 10th	Day	3 3 1 3 3 2 3 4 6% 12% 60%	2160
	11th to 20th	Day	5% 6% 2 5% 4 3 5% 4 7% 11% 47%	2160
	21st to end	Day	4 4 1 3 2 2 3 3 5% 8% 66%	1900
October	1st to 10th	Day	6% 3 2 3 3 2 2 3 5% 8% 63%	1800
	11th to 20th	Day	8% 4 2 3 3 2 3 3 6% 7% 58%	1800
	21st to end	Day	8% 5% 2 5% 4 3 3 4 5% 8% 55%	1980
November	1st to 10th	Day	9% 5% 2 5% 4 3 4 5% 5% 7% 50%	1859
	11th to 20th	Day	9% 6% 3 5% 5% 2 4 5% 4 7% 48%	1712
	21st to end	Day	11% 6% 2 4 3 2 3 4 5% 6% 52%	1559
December	1st to 10th	Day	12% 7% 3 5% 4 3 4 5% 6% 8% 42%	1520
	11th to 20th	Day	27% 9% 3 5% 5% 3 4 3 6% 6% 30%	1928
	21st to end	Day	18% 11% 4 6% 5% 2 4 4 5% 8% 34%	2794
January	1st to 10th	Night	15% 11% 3 5% 4 2 4 4 4 6% 41%	4159
	11th to 20th	Night	20% 9% 3 7% 6% 3 5% 5% 5% 7% 30%	4110
	21st to end	Night	22% 14% 4 7% 5% 3 4 4 4 6% 28%	4521
February	1st to 10th	Night	17% 8% 3 4 4 2 4 3 4 6% 45%	2470
	11th to 20th	Night	13% 9% 4 6% 4 3 5% 5% 5% 8% 39%	2315
	21st to end	Night	14% 9% 3 5% 4 2 3 3 5% 8% 44%	1776
March	1st to 10th	Night	18% 11% 4 6% 6% 2 3 4 4 6% 35%	1993
	11th to 20th	Night	17% 9% 3 5% 5% 3 4 4 4 8% 39%	1980
	21st to end	Night	15% 10% 3 4 5% 2 4 3 4 6% 43%	2160
April	1st to 10th	Night	12% 11% 4 5% 4 3 5% 4 5% 7% 41%	1800
	11th to 20th	Night	12% 9% 4 5% 4 2 3 3 4 8% 45%	1779
	21st to end	Night	8% 7% 2 4 4 2 4 5% 6% 9% 49%	1800
May	1st to 10th	Night	6% 10% 4 5% 4 2 4 4 5% 7% 49%	1727
	11th to 20th	Night	8% 11% 4 6% 6% 3 5% 3 5% 8% 42%	1588
	21st to end	Night	9% 14% 4 5% 6% 3 5% 5% 5% 7% 38%	1552
June	1st to 10th	Night	6% 10% 3 5% 5% 3 5% 4 6% 7% 46%	1440
	11th to 20th	Night	2 5% 3 5% 5% 3 3 5% 5% 10% 54%	1440
	21st to end	Night	3 9% 2 6% 4 2 4 2 5% 8% 55%	1440
July	1st to 10th	Night	2 8% 3 6% 5% 3 5% 4 7% 10% 48%	1480
	11th to 20th	Night	2 7% 3 5% 7% 3 5% 7% 9% 11% 41%	1620
	21st to end	Night	1 6% 5% 9% 8% 4 7% 7% 7% 10% 37%	1773
August	1st to 10th	Night	3 12% 5% 9% 8% 3 5% 6% 7% 11% 31%	1611
	11th to 20th	Night	1 6% 2 6% 7% 3 6% 6% 8% 11% 44%	1710
	21st to end	Night	2 7% 4 8% 7% 4 4 4 6% 11% 43%	1980
September	1st to 10th	Night	2 4 3 5% 5% 2 4 4 7% 8% 56%	1800
	11th to 20th	Night	4 7% 2 7% 6% 2 4 4 6% 9% 49%	1800
	21st to end	Night	3 5% 2 3 3 2 2 3 5% 10% 63%	2054
October	1st to 10th	Night	5% 6% 2 4 4 2 3 3 4 7% 61%	2160
	11th to 20th	Night	8% 5% 2 4 4 2 4 3 5% 7% 55%	2160
	21st to end	Night	7% 6% 2 4 4 2 3 4 5% 7% 56%	2376
November	1st to 10th	Night	9% 6% 3 5% 3 2 3 4 6% 8% 51%	2220
	11th to 20th	Night	10% 6% 2 4 5% 3 5% 4 5% 8% 48%	2465
	21st to end	Night	9% 5% 2 4 4 2 3 4 5% 6% 55%	2617
December	1st to 10th	Night	14% 7% 2 5% 5% 3 3 4 4 6% 45%	2660
	11th to 20th	Night	28% 10% 3 5% 4 2 4 4 5% 6% 29%	3276
	21st to end	Night	18% 11% 3 6% 6% 3 5% 4 5% 6% 32%	4862

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	33% 26% 10% 22% 7% 2	2777
	11th to 20th	Day	42% 25% 7% 11% 9% 6%	2860
	21st to end	Day	47% 24% 6% 11% 8% 4	3146
February	1st to 10th	Day	25% 34% 4 14% 14% 8%	1710
	11th to 20th	Day	28% 37% 6% 13% 13% 4	1745
	21st to end	Day	28% 37% 4 14% 12% 5%	1480
March	1st to 10th	Day	29% 37% 6% 16% 9% 3	1965
	11th to 20th	Day	33% 37% 7% 12% 9% 1	1980
	21st to end	Day	28% 38% 7% 15% 10% 3	2196
April	1st to 10th	Day	26% 38% 9% 11% 13% 3	2160
	11th to 20th	Day	24% 37% 8% 14% 12% 4	2132
	21st to end	Day	19% 37% 7% 19% 14% 3	2160
May	1st to 10th	Day	18% 38% 5% 15% 20% 5%	2230
	11th to 20th	Day	15% 41% 4 18% 17% 6%	2307
	21st to end	Day	22% 40% 8% 14% 14% 2	2724
June	1st to 10th	Day	21% 40% 7% 14% 14% 3	2520
	11th to 20th	Day	13% 38% 5% 13% 22% 9%	2520
	21st to end	Day	10% 43% 1 8% 21% 17%	2520
July	1st to 10th	Day	8% 45% 1 4 15% 27%	2409
	11th to 20th	Day	13% 43% 1 4 15% 24%	2271
	21st to end	Day	9% 43% 1 4 20% 23%	2405
August	1st to 10th	Day	14% 45% 1 4 18% 18%	2312
	11th to 20th	Day	10% 39% 1 7% 21% 23%	2190
	21st to end	Day	11% 43% 1 5% 20% 20%	2376
September	1st to 10th	Day	9% 37% 1 5% 17% 31%	2160
	11th to 20th	Day	15% 41% 2 13% 17% 11%	2160
	21st to end	Day	8% 37% 2 14% 23% 16%	1900
October	1st to 10th	Day	17% 35% 5% 13% 19% 11%	1800
	11th to 20th	Day	16% 37% 4 13% 17% 13%	1800
	21st to end	Day	18% 37% 4 15% 14% 12%	1980
November	1st to 10th	Day	25% 42% 6% 11% 11% 5%	1859
	11th to 20th	Day	22% 40% 5% 13% 14% 6%	1712
	21st to end	Day	18% 39% 6% 10% 16% 10%	1559
December	1st to 10th	Day	21% 39% 5% 13% 15% 6%	1520
	11th to 20th	Day	42% 32% 6% 10% 8% 3	1928
	21st to end	Day	42% 26% 9% 14% 7% 2	2794
January	1st to 10th	Night	32% 26% 13% 19% 7% 2	4159
	11th to 20th	Night	42% 25% 11% 9% 7% 6%	4110
	21st to end	Night	48% 25% 5% 8% 8% 5%	4521
February	1st to 10th	Night	25% 35% 5% 12% 13% 10%	2470
	11th to 20th	Night	28% 37% 5% 11% 14% 5%	2317
	21st to end	Night	26% 37% 7% 16% 10% 3	1776
March	1st to 10th	Night	31% 38% 7% 12% 9% 4	1993
	11th to 20th	Night	31% 38% 4 13% 10% 3	1980
	21st to end	Night	29% 38% 8% 12% 10% 4	2160
April	1st to 10th	Night	26% 39% 9% 13% 10% 3	1800
	11th to 20th	Night	25% 38% 6% 14% 13% 5%	1779
	21st to end	Night	17% 38% 5% 19% 15% 6%	1800
May	1st to 10th	Night	17% 38% 4 13% 18% 9%	1727
	11th to 20th	Night	19% 41% 3 12% 19% 6%	1589
	21st to end	Night	22% 41% 5% 14% 16% 2	1552
June	1st to 10th	Night	21% 42% 6% 12% 16% 3	1440
	11th to 20th	Night	14% 39% 3 10% 21% 14%	1440
	21st to end	Night	14% 43% 6% 19% 17%	1440
July	1st to 10th	Night	7% 47% 1 3 12% 29%	1438
	11th to 20th	Night	15% 45% 1 4 10% 25%	1566
	21st to end	Night	18% 48% 1 3 11% 19%	1674
August	1st to 10th	Night	19% 47% 1 4 11% 18%	1602
	11th to 20th	Night	14% 42% 1 6% 15% 21%	1710
	21st to end	Night	13% 44% 1 4 15% 23%	1980
September	1st to 10th	Night	11% 40% 5% 12% 32%	1800
	11th to 20th	Night	18% 42% 1 10% 16% 12%	1800
	21st to end	Night	10% 38% 1 12% 21% 19%	2054
October	1st to 10th	Night	17% 38% 4 11% 14% 14%	2160
	11th to 20th	Night	16% 38% 3 13% 14% 16%	2160
	21st to end	Night	18% 39% 2 12% 17% 13%	2376
November	1st to 10th	Night	22% 42% 6% 11% 10% 8%	2220
	11th to 20th	Night	19% 41% 5% 14% 14% 7%	2465
	21st to end	Night	17% 39% 5% 12% 14% 13%	2617
December	1st to 10th	Night	22% 40% 3 12% 14% 9%	2660
	11th to 20th	Night	41% 34% 5% 9% 9% 2	3276
	21st to end	Night	44% 27% 10% 10% 6% 2	4862

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	30% 18% 23% 17% 11% 2	327
	11th to 20th	Day	20% 15% 24% 26% 12% 2	370
	21st to end	Day	19% 13% 26% 25% 15% 2	407
February	1st to 10th	Day	22% 17% 24% 22% 11% 5%	370
	11th to 20th	Day	23% 22% 26% 20% 9% 1	400
	21st to end	Day	18% 17% 36% 18% 9% 1	346
March	1st to 10th	Day	26% 16% 29% 22% 6% 1	420
	11th to 20th	Day	26% 14% 28% 20% 10% 3	420
	21st to end	Day	17% 20% 34% 20% 8% 1	462
April	1st to 10th	Day	19% 19% 32% 20% 8% 1	420
	11th to 20th	Day	17% 21% 30% 22% 8% 2	412
	21st to end	Day	10% 20% 32% 23% 10% 4	420
May	1st to 10th	Day	11% 15% 32% 29% 10% 3	423
	11th to 20th	Day	17% 15% 33% 22% 11% 2	448
	21st to end	Day	20% 16% 22% 25% 14% 4	485
June	1st to 10th	Day	10% 11% 31% 32% 12% 3	450
	11th to 20th	Day	4 13% 30% 39% 12% 1	450
	21st to end	Day	4 5% 32% 39% 18% 2	450
July	1st to 10th	Day	6% 4 26% 45% 18% 2	446
	11th to 20th	Day	4 1 20% 49% 22% 4	444
	21st to end	Day	3 2 18% 47% 24% 7%	487
August	1st to 10th	Day	6% 3 31% 42% 14% 4	447
	11th to 20th	Day	4 1 22% 42% 24% 7%	437
	21st to end	Day	4 2 22% 44% 23% 5%	495
September	1st to 10th	Day	5% 5% 20% 43% 21% 5%	450
	11th to 20th	Day	6% 8% 26% 36% 20% 4	450
	21st to end	Day	6% 8% 20% 36% 25% 5%	450
October	1st to 10th	Day	7% 10% 22% 33% 21% 8%	450
	11th to 20th	Day	10% 6% 20% 32% 24% 8%	450
	21st to end	Day	11% 8% 26% 28% 20% 7%	495
November	1st to 10th	Day	12% 13% 20% 27% 23% 5%	455
	11th to 20th	Day	11% 11% 22% 25% 24% 7%	272
	21st to end	Day	11% 13% 26% 25% 18% 8%	198
December	1st to 10th	Day	16% 16% 22% 20% 23% 4	180
	11th to 20th	Day	18% 18% 21% 19% 17% 6%	180
	21st to end	Day	23% 20% 27% 15% 13% 4	198
January	1st to 10th	Night	23% 8% 13% 27% 23% 5%	760
	11th to 20th	Night	18% 8% 14% 30% 24% 7%	760
	21st to end	Night	21% 9% 11% 29% 25% 5%	836
February	1st to 10th	Night	21% 10% 14% 27% 22% 6%	760
	11th to 20th	Night	19% 13% 13% 29% 21% 5%	742
	21st to end	Night	18% 13% 20% 28% 17% 4	592
March	1st to 10th	Night	23% 11% 17% 26% 20% 3	720
	11th to 20th	Night	20% 7% 15% 30% 23% 5%	720
	21st to end	Night	21% 9% 23% 26% 17% 3	792
April	1st to 10th	Night	17% 11% 21% 29% 19% 3	720
	11th to 20th	Night	16% 15% 20% 24% 19% 6%	711
	21st to end	Night	11% 13% 26% 22% 20% 9%	720
May	1st to 10th	Night	11% 9% 21% 28% 23% 6%	647
	11th to 20th	Night	14% 7% 20% 29% 24% 7%	526
	21st to end	Night	19% 10% 16% 26% 23% 6%	389
June	1st to 10th	Night	10% 6% 23% 29% 26% 6%	360
	11th to 20th	Night	6% 7% 18% 36% 28% 5%	360
	21st to end	Night	7% 1 13% 35% 37% 7%	360
July	1st to 10th	Night	7% 3 14% 31% 36% 10%	388
	11th to 20th	Night	7% 1 6% 30% 38% 19%	522
	21st to end	Night	6% 2 5% 30% 42% 15%	591
August	1st to 10th	Night	15% 2 9% 28% 35% 11%	537
	11th to 20th	Night	6% 1 11% 30% 43% 10%	642
	21st to end	Night	6% 2 8% 27% 44% 13%	792
September	1st to 10th	Night	4 2 10% 31% 39% 14%	720
	11th to 20th	Night	8% 3 11% 33% 36% 8%	720
	21st to end	Night	5% 4 11% 28% 38% 14%	720
October	1st to 10th	Night	8% 4 13% 30% 33% 11%	720
	11th to 20th	Night	10% 6% 8% 27% 38% 11%	720
	21st to end	Night	11% 5% 11% 27% 31% 15%	792
November	1st to 10th	Night	10% 7% 15% 26% 33% 10%	740
	11th to 20th	Night	13% 5% 14% 30% 32% 7%	760
	21st to end	Night	10% 8% 15% 36% 24% 7%	760
December	1st to 10th	Night	18% 7% 19% 27% 24% 6%	760
	11th to 20th	Night	24% 8% 14% 28% 21% 4	760
	21st to end	Night	21% 16% 17% 26% 17% 3	836

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