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 2025-03-12.

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% 7% 2 5% 3 3 4 4 6% 9% 48%	112803
	Night	10% 10% 3 7% 4 3 4 3 5% 7% 45%	115026
Transparency	Day	19% 44% 5% 10% 13% 9%	112565
	Night	23% 43% 5% 9% 12% 9%	114853
Seeing	Day	12% 12% 26% 30% 16% 4	15870
	Night	14% 7% 15% 29% 28% 8%	25349

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	15% 6% 2 4 3 3 3 3 6% 8% 47%	3989
	11th to 20th	Day	13% 7% 3 7% 3 4 3 2 4 5% 50%	4100
	21st to end	Day	16% 10% 3 8% 4 4 4 3 4 6% 38%	4510
February	1st to 10th	Day	19% 8% 3 5% 3 3 4 3 5% 5% 43%	1800
	11th to 20th	Day	15% 8% 2 6% 4 4 5% 3 5% 8% 38%	1840
	21st to end	Day	14% 7% 2 6% 4 3 4 4 6% 6% 44%	1650
March	1st to 10th	Day	17% 12% 4 10% 5% 4 5% 4 5% 6% 27%	3536
	11th to 20th	Day	11% 6% 2 4 3 3 4 3 6% 8% 49%	3503
	21st to end	Day	14% 12% 4 8% 5% 5% 5% 4 6% 8% 29%	3855
April	1st to 10th	Day	14% 9% 3 6% 3 3 4 4 6% 7% 41%	2280
	11th to 20th	Day	10% 8% 2 6% 3 4 3 4 5% 8% 47%	2249
	21st to end	Day	8% 8% 2 6% 3 3 3 4 6% 10% 46%	2280
May	1st to 10th	Day	7% 5% 1 3 2 2 3 2 5% 7% 62%	3922
	11th to 20th	Day	6% 4 2 3 2 3 3 3 6% 12% 55%	4087
	21st to end	Day	6% 13% 2 5% 3 3 4 4 5% 7% 47%	4813
June	1st to 10th	Day	7% 8% 2 5% 4 4 4 5% 6% 10% 46%	2660
	11th to 20th	Day	3 4 1 4 3 3 4 3 7% 10% 57%	2660
	21st to end	Day	3 5% 2 4 3 3 3 4 6% 12% 54%	2660
July	1st to 10th	Day	2 3 1 3 2 2 2 4 6% 8% 69%	4337
	11th to 20th	Day	1 4 2 4 3 3 4 4 8% 15% 51%	4110
	21st to end	Day	1 11% 2 6% 3 3 4 5% 9% 14% 42%	4455
August	1st to 10th	Day	2 4 2 6% 3 5% 7% 6% 12% 18% 34%	4091
	11th to 20th	Day	1 5% 1 4 3 3 3 4 7% 12% 57%	3828
	21st to end	Day	1 5% 2 6% 4 4 4 4 7% 11% 52%	4180
September	1st to 10th	Day	3 4 1 3 2 2 3 3 6% 11% 61%	2280
	11th to 20th	Day	5% 7% 2 6% 3 4 4 4 8% 11% 46%	2280
	21st to end	Day	4 4 1 3 2 2 3 2 5% 8% 65%	2005
October	1st to 10th	Day	3 3 1 3 2 2 2 2 5% 7% 67%	3180
	11th to 20th	Day	5% 7% 2 6% 3 3 3 2 6% 8% 54%	3161
	21st to end	Day	7% 5% 2 5% 3 3 3 3 6% 8% 55%	3448
November	1st to 10th	Day	8% 5% 2 5% 3 4 4 4 5% 8% 51%	1959
	11th to 20th	Day	9% 7% 3 6% 4 3 4 4 4 8% 48%	1802
	21st to end	Day	12% 6% 2 5% 3 3 4 3 5% 6% 51%	1641
December	1st to 10th	Day	7% 5% 2 4 3 3 4 4 7% 9% 52%	2620
	11th to 20th	Day	22% 9% 3 6% 4 4 3 3 6% 6% 34%	3028
	21st to end	Day	22% 13% 3 7% 4 3 4 3 5% 6% 29%	4004
January	1st to 10th	Night	11% 9% 2 5% 3 3 4 4 5% 8% 45%	5955
	11th to 20th	Night	14% 7% 4 7% 4 4 4 3 4 5% 45%	5880
	21st to end	Night	16% 13% 4 7% 4 3 3 2 4 5% 38%	6468
February	1st to 10th	Night	18% 9% 2 5% 3 3 3 2 4 5% 45%	2600
	11th to 20th	Night	14% 10% 3 6% 4 4 5% 3 5% 7% 38%	2447
	21st to end	Night	13% 9% 2 6% 4 3 3 3 4 8% 44%	1980
March	1st to 10th	Night	17% 16% 5% 8% 5% 4 3 3 4 5% 30%	3555
	11th to 20th	Night	13% 7% 2 7% 5% 3 3 2 4 6% 48%	3505
	21st to end	Night	17% 18% 4 7% 5% 4 3 3 4 5% 30%	3798
April	1st to 10th	Night	11% 11% 3 6% 4 4 5% 3 5% 6% 41%	1900
	11th to 20th	Night	12% 9% 3 6% 3 3 3 3 5% 8% 44%	1879
	21st to end	Night	8% 9% 2 4 3 3 4 4 7% 9% 48%	1900
May	1st to 10th	Night	6% 12% 3 5% 2 2 3 2 3 5% 58%	3037
	11th to 20th	Night	4 9% 4 7% 7% 5% 5% 3 6% 8% 43%	2814
	21st to end	Night	5% 12% 6% 6% 4 3 3 2 3 4 52%	2762
June	1st to 10th	Night	6% 11% 2 6% 5% 4 5% 3 6% 7% 46%	1520
	11th to 20th	Night	2 6% 3 6% 4 3 4 4 6% 10% 54%	1520
	21st to end	Night	2 9% 3 7% 4 3 3 2 5% 8% 55%	1520
July	1st to 10th	Night	1 5% 2 7% 3 3 3 2 5% 8% 63%	2622
	11th to 20th	Night	1 6% 8% 10% 5% 3 4 5% 7% 10% 42%	2860
	21st to end	Night	1 23% 6% 9% 5% 4 5% 4 5% 8% 30%	3109
August	1st to 10th	Night	2 8% 5% 17% 7% 5% 6% 5% 11% 11% 22%	2848
	11th to 20th	Night	1 11% 3 6% 4 3 5% 4 6% 8% 49%	3004
	21st to end	Night	2 9% 3 9% 4 4 3 3 7% 10% 46%	3498
September	1st to 10th	Night	2 5% 3 6% 4 4 3 3 7% 8% 56%	1900
	11th to 20th	Night	5% 8% 2 9% 4 3 3 4 6% 9% 48%	1900
	21st to end	Night	2 5% 2 4 3 3 2 2 5% 9% 62%	2169
October	1st to 10th	Night	3 4 1 4 3 2 3 2 5% 6% 66%	3800
	11th to 20th	Night	5% 15% 3 5% 4 3 3 2 4 6% 50%	3777
	21st to end	Night	7% 6% 2 5% 3 2 4 3 5% 7% 56%	4121
November	1st to 10th	Night	9% 6% 3 5% 3 3 3 3 6% 8% 52%	2340
	11th to 20th	Night	9% 7% 2 5% 4 4 4 3 5% 8% 48%	2595
	21st to end	Night	10% 6% 2 5% 4 3 3 3 5% 6% 53%	2755
December	1st to 10th	Night	8% 5% 2 5% 4 4 4 3 4 6% 55%	4560
	11th to 20th	Night	23% 10% 2 6% 3 4 4 4 7% 8% 29%	5176
	21st to end	Night	25% 12% 3 8% 5% 4 4 3 4 5% 27%	6952

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	24% 27% 15% 18% 12% 4	3989
	11th to 20th	Day	31% 27% 6% 8% 15% 12%	4100
	21st to end	Day	35% 29% 4 10% 9% 13%	4510
February	1st to 10th	Day	20% 62% 3 7% 5% 3	1800
	11th to 20th	Day	18% 61% 4 6% 8% 3	1849
	21st to end	Day	15% 62% 3 11% 6% 3	1650
March	1st to 10th	Day	39% 41% 5% 6% 7% 1	3536
	11th to 20th	Day	13% 40% 7% 20% 10% 10%	3503
	21st to end	Day	33% 43% 8% 11% 4	3855
April	1st to 10th	Day	15% 65% 4 9% 6% 1	2280
	11th to 20th	Day	11% 65% 4 12% 7% 1	2252
	21st to end	Day	12% 66% 5% 8% 8% 1	2280
May	1st to 10th	Day	11% 40% 7% 19% 16% 7%	3922
	11th to 20th	Day	11% 42% 1 15% 24% 7%	4090
	21st to end	Day	17% 45% 2 15% 20% 2	4814
June	1st to 10th	Day	11% 64% 2 8% 11% 4	2660
	11th to 20th	Day	8% 65% 2 10% 12% 3	2660
	21st to end	Day	9% 63% 2 4 12% 10%	2660
July	1st to 10th	Day	8% 35% 1 2 12% 41%	4270
	11th to 20th	Day	12% 35% 9% 4 11% 29%	4041
	21st to end	Day	22% 35% 9% 5% 14% 15%	4315
August	1st to 10th	Day	17% 39% 16% 6% 16% 5%	4076
	11th to 20th	Day	14% 38% 8% 7% 28% 5%	3866
	21st to end	Day	16% 38% 6% 9% 20% 11%	4179
September	1st to 10th	Day	9% 60% 1 6% 14% 10%	2280
	11th to 20th	Day	12% 61% 2 8% 12% 5%	2280
	21st to end	Day	9% 60% 2 10% 14% 5%	2005
October	1st to 10th	Day	8% 36% 2 6% 18% 29%	3180
	11th to 20th	Day	19% 41% 4 10% 19% 7%	3161
	21st to end	Day	16% 37% 5% 17% 16% 9%	3448
November	1st to 10th	Day	8% 56% 3 15% 13% 5%	1959
	11th to 20th	Day	17% 57% 4 12% 8% 2	1802
	21st to end	Day	16% 58% 4 7% 13% 2	1641
December	1st to 10th	Day	16% 36% 4 16% 22% 5%	2620
	11th to 20th	Day	35% 33% 6% 10% 11% 5%	3028
	21st to end	Day	43% 28% 7% 13% 8% 2	4004
January	1st to 10th	Night	25% 29% 15% 15% 12% 3	5955
	11th to 20th	Night	33% 27% 8% 8% 16% 8%	5880
	21st to end	Night	36% 29% 3 7% 12% 12%	6468
February	1st to 10th	Night	21% 61% 3 6% 6% 4	2600
	11th to 20th	Night	19% 61% 3 8% 7% 2	2449
	21st to end	Night	14% 61% 3 12% 6% 3	1980
March	1st to 10th	Night	39% 41% 5% 7% 7% 1	3555
	11th to 20th	Night	17% 42% 4 13% 16% 9%	3505
	21st to end	Night	37% 42% 4 12% 4 1	3798
April	1st to 10th	Night	15% 65% 3 8% 7% 2	1900
	11th to 20th	Night	13% 65% 3 10% 6% 2	1879
	21st to end	Night	14% 66% 4 8% 7% 2	1900
May	1st to 10th	Night	16% 43% 4 15% 12% 10%	3037
	11th to 20th	Night	13% 53% 1 8% 13% 11%	2815
	21st to end	Night	18% 44% 2 14% 19% 4	2762
June	1st to 10th	Night	13% 65% 1 6% 10% 5%	1520
	11th to 20th	Night	11% 64% 2 7% 11% 4	1520
	21st to end	Night	9% 63% 1 3 10% 13%	1520
July	1st to 10th	Night	11% 36% 1 3 6% 42%	2580
	11th to 20th	Night	24% 35% 4 4 5% 27%	2806
	21st to end	Night	35% 34% 2 3 11% 15%	3011
August	1st to 10th	Night	31% 41% 7% 7% 9% 5%	2839
	11th to 20th	Night	20% 39% 3 4 29% 5%	3031
	21st to end	Night	21% 37% 8% 5% 19% 9%	3498
September	1st to 10th	Night	13% 61% 1 3 12% 10%	1900
	11th to 20th	Night	11% 60% 2 10% 10% 7%	1900
	21st to end	Night	10% 60% 2 8% 11% 9%	2169
October	1st to 10th	Night	9% 36% 2 4 16% 33%	3800
	11th to 20th	Night	26% 38% 2 9% 13% 11%	3777
	21st to end	Night	16% 38% 6% 13% 14% 13%	4121
November	1st to 10th	Night	10% 55% 3 14% 12% 7%	2340
	11th to 20th	Night	16% 56% 5% 12% 8% 3	2595
	21st to end	Night	17% 57% 3 8% 10% 5%	2755
December	1st to 10th	Night	18% 36% 4 15% 20% 7%	4560
	11th to 20th	Night	36% 34% 5% 8% 12% 5%	5176
	21st to end	Night	44% 28% 7% 11% 7% 2	6952

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	355
	11th to 20th	Day	19% 15% 24% 27% 13% 3	400
	21st to end	Day	18% 13% 26% 25% 15% 3	440
February	1st to 10th	Day	24% 17% 23% 22% 10% 5%	400
	11th to 20th	Day	22% 23% 26% 20% 8% 1	438
	21st to end	Day	17% 15% 36% 21% 9% 1	414
March	1st to 10th	Day	26% 17% 29% 20% 6% 1	500
	11th to 20th	Day	25% 14% 27% 21% 11% 2	465
	21st to end	Day	19% 20% 33% 19% 8% 1	506
April	1st to 10th	Day	19% 18% 32% 20% 9% 2	460
	11th to 20th	Day	17% 21% 28% 23% 9% 2	452
	21st to end	Day	11% 20% 33% 22% 10% 4	460
May	1st to 10th	Day	12% 15% 33% 28% 9% 3	463
	11th to 20th	Day	15% 14% 32% 25% 13% 2	488
	21st to end	Day	19% 15% 22% 26% 13% 4	529
June	1st to 10th	Day	10% 10% 33% 32% 12% 3	490
	11th to 20th	Day	4 13% 32% 38% 12% 2	490
	21st to end	Day	3 4 31% 41% 18% 2	490
July	1st to 10th	Day	5% 3 24% 45% 19% 3	486
	11th to 20th	Day	4 1 20% 50% 22% 4	484
	21st to end	Day	3 4 18% 46% 24% 7%	531
August	1st to 10th	Day	6% 3 30% 43% 15% 4	487
	11th to 20th	Day	4 2 25% 40% 22% 6%	477
	21st to end	Day	4 3 22% 42% 23% 6%	539
September	1st to 10th	Day	4 6% 20% 43% 21% 5%	490
	11th to 20th	Day	7% 9% 26% 36% 19% 4	490
	21st to end	Day	6% 8% 19% 37% 25% 5%	490
October	1st to 10th	Day	6% 9% 21% 33% 22% 8%	490
	11th to 20th	Day	10% 7% 20% 31% 24% 8%	490
	21st to end	Day	10% 8% 26% 30% 20% 6%	539
November	1st to 10th	Day	11% 13% 21% 27% 23% 5%	495
	11th to 20th	Day	12% 13% 21% 25% 22% 7%	302
	21st to end	Day	14% 12% 25% 25% 16% 7%	220
December	1st to 10th	Day	14% 15% 21% 22% 25% 5%	200
	11th to 20th	Day	18% 18% 21% 19% 18% 6%	200
	21st to end	Day	23% 21% 27% 14% 12% 3	220
January	1st to 10th	Night	22% 8% 14% 28% 24% 5%	800
	11th to 20th	Night	17% 8% 14% 31% 24% 7%	800
	21st to end	Night	20% 8% 12% 30% 25% 5%	880
February	1st to 10th	Night	23% 10% 14% 27% 21% 6%	800
	11th to 20th	Night	20% 12% 13% 30% 20% 5%	784
	21st to end	Night	17% 12% 19% 31% 17% 3	660
March	1st to 10th	Night	23% 11% 17% 26% 19% 3	800
	11th to 20th	Night	20% 8% 15% 30% 23% 4	766
	21st to end	Night	22% 9% 22% 27% 17% 3	836
April	1st to 10th	Night	17% 11% 21% 28% 19% 3	760
	11th to 20th	Night	16% 14% 19% 25% 20% 6%	751
	21st to end	Night	12% 13% 26% 22% 19% 8%	760
May	1st to 10th	Night	11% 9% 22% 29% 23% 6%	682
	11th to 20th	Night	14% 6% 19% 28% 26% 6%	555
	21st to end	Night	18% 9% 17% 25% 24% 6%	411
June	1st to 10th	Night	10% 6% 23% 30% 25% 6%	380
	11th to 20th	Night	6% 7% 20% 36% 28% 4	380
	21st to end	Night	6% 2 13% 35% 37% 7%	380
July	1st to 10th	Night	6% 2 14% 30% 37% 10%	411
	11th to 20th	Night	7% 2 6% 30% 38% 18%	552
	21st to end	Night	6% 3 6% 29% 41% 15%	624
August	1st to 10th	Night	14% 2 9% 30% 35% 11%	567
	11th to 20th	Night	6% 1 12% 30% 42% 10%	678
	21st to end	Night	6% 2 8% 27% 44% 13%	836
September	1st to 10th	Night	4 3 10% 31% 39% 14%	760
	11th to 20th	Night	9% 4 11% 32% 36% 9%	760
	21st to end	Night	5% 4 10% 28% 38% 14%	760
October	1st to 10th	Night	8% 4 12% 30% 34% 12%	760
	11th to 20th	Night	10% 7% 9% 27% 36% 11%	760
	21st to end	Night	11% 5% 12% 27% 31% 14%	836
November	1st to 10th	Night	10% 7% 15% 25% 33% 9%	780
	11th to 20th	Night	13% 5% 15% 31% 30% 6%	800
	21st to end	Night	12% 7% 15% 36% 23% 7%	800
December	1st to 10th	Night	17% 7% 18% 28% 24% 7%	800
	11th to 20th	Night	24% 8% 13% 29% 21% 4	800
	21st to end	Night	22% 16% 18% 26% 16% 3	880

Page generated at 2025-03-09 05:08:46. Version ac07

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