Redwood Mountain View
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Redwood Mountain View clear sky chart from 2005-11-06 to 2024-01-13.

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% 1 3 3 2 3 3 4 5% 63%	74798
	Night	8% 4 1 3 3 2 3 3 4 5% 64%	74949
Transparency	Day	23% 3 9% 19% 26% 18%	74509
	Night	23% 4 10% 21% 26% 16%	74761
Seeing	Day	10% 10% 31% 34% 13% 2	14132
	Night	9% 2 17% 39% 29% 4	23805

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	16% 7% 2 3 4 2 4 3 6% 8% 46%	1519
	11th to 20th	Day	11% 5% 1 4 5% 2 3 5% 5% 7% 53%	1542
	21st to end	Day	14% 10% 2 4 5% 3 4 3 4 6% 43%	1782
February	1st to 10th	Day	14% 9% 2 3 3 2 4 3 5% 6% 51%	1768
	11th to 20th	Day	11% 13% 3 5% 3 2 3 3 4 5% 48%	1750
	21st to end	Day	17% 12% 3 5% 4 3 3 2 3 6% 41%	1480
March	1st to 10th	Day	16% 13% 2 5% 5% 3 4 3 4 6% 39%	1800
	11th to 20th	Day	12% 11% 2 5% 5% 3 3 4 5% 7% 42%	1890
	21st to end	Day	14% 13% 2 5% 3 3 4 3 4 6% 43%	2358
April	1st to 10th	Day	11% 8% 3 4 4 3 3 3 4 7% 49%	2160
	11th to 20th	Day	13% 8% 2 4 4 2 4 3 4 5% 50%	2129
	21st to end	Day	10% 7% 1 4 4 3 3 4 5% 7% 54%	2160
May	1st to 10th	Day	9% 6% 2 3 3 2 3 2 4 6% 61%	2242
	11th to 20th	Day	7% 4 1 3 3 2 3 4 4 7% 63%	2301
	21st to end	Day	9% 4 1 3 3 2 3 4 5% 6% 60%	2653
June	1st to 10th	Day	4 3 1 3 3 2 3 4 4 7% 66%	2520
	11th to 20th	Day	2 1 1 1 1 1 2 1 3 4 83%	2520
	21st to end	Day	1 1 1 2 1 1 2 2 2 3 84%	2520
July	1st to 10th	Day	1 1 1 2 2 1 2 2 2 4 83%	2520
	11th to 20th	Day	2 1 1 1 2 2 3 3 3 4 79%	2520
	21st to end	Day	2 1 1 2 2 2 3 3 3 5% 75%	2631
August	1st to 10th	Day	1 2 1 2 2 1 2 2 3 2 83%	2154
	11th to 20th	Day	1 1 1 2 1 2 2 2 4 83%	2122
	21st to end	Day	2 1 1 2 1 1 2 3 4 84%	2376
September	1st to 10th	Day	2 1 2 1 1 1 2 3 3 84%	2160
	11th to 20th	Day	2 1 1 1 2 1 2 2 2 4 82%	2082
	21st to end	Day	3 2 1 1 2 2 2 2 3 4 79%	1980
October	1st to 10th	Day	6% 4 1 2 3 2 3 3 4 4 69%	1929
	11th to 20th	Day	4 2 1 2 3 3 3 3 3 4 72%	1800
	21st to end	Day	5% 2 1 3 3 1 2 3 3 4 71%	1937
November	1st to 10th	Day	7% 8% 2 4 4 2 3 3 4 6% 58%	1674
	11th to 20th	Day	8% 3 2 2 2 2 3 3 4 6% 64%	1710
	21st to end	Day	8% 6% 2 4 3 2 4 3 5% 6% 57%	1710
December	1st to 10th	Day	12% 4 2 3 4 2 3 4 5% 7% 54%	1677
	11th to 20th	Day	18% 9% 3 7% 5% 3 4 4 4 6% 38%	1928
	21st to end	Day	12% 10% 2 6% 5% 3 4 5% 5% 8% 39%	2794
January	1st to 10th	Night	16% 6% 2 3 3 2 3 3 5% 6% 50%	2646
	11th to 20th	Night	10% 5% 1 4 4 2 4 4 5% 7% 55%	2470
	21st to end	Night	14% 7% 2 3 3 2 3 3 4 7% 51%	2574
February	1st to 10th	Night	13% 6% 2 3 3 2 4 2 4 6% 53%	2189
	11th to 20th	Night	11% 7% 2 3 3 2 4 3 4 6% 55%	2098
	21st to end	Night	14% 9% 3 4 3 2 4 3 4 5% 49%	1776
March	1st to 10th	Night	14% 9% 2 4 4 3 4 5% 5% 5% 44%	2160
	11th to 20th	Night	12% 7% 2 4 4 2 3 4 6% 8% 48%	2066
	21st to end	Night	13% 8% 1 3 3 2 3 4 4 7% 51%	1998
April	1st to 10th	Night	10% 5% 2 3 3 2 4 3 4 6% 58%	1800
	11th to 20th	Night	9% 4 1 3 4 2 4 4 4 5% 60%	1779
	21st to end	Night	7% 4 1 2 3 2 3 3 4 7% 64%	1800
May	1st to 10th	Night	7% 3 1 3 3 1 4 3 4 8% 64%	1715
	11th to 20th	Night	6% 3 1 3 2 1 2 2 3 5% 72%	1594
	21st to end	Night	6% 2 1 3 3 2 2 3 4 4 70%	1618
June	1st to 10th	Night	5% 3 1 2 2 1 2 2 2 7% 72%	1440
	11th to 20th	Night	1 1 1 2 2 1 2 2 2 5% 83%	1440
	21st to end	Night	1 1 1 1 1 1 1 2 3 2 87%	1440
July	1st to 10th	Night	2 1 1 1 2 2 2 3 87%	1440
	11th to 20th	Night	2 1 1 1 2 1 2 3 3 4 80%	1440
	21st to end	Night	2 1 1 3 2 1 3 3 4 5% 76%	1683
August	1st to 10th	Night	2 1 1 1 2 1 1 1 2 3 84%	1783
	11th to 20th	Night	1 1 1 1 1 2 3 3 87%	1780
	21st to end	Night	1 1 1 2 1 1 2 2 3 86%	1980
September	1st to 10th	Night	1 1 1 1 1 1 2 1 3 88%	1800
	11th to 20th	Night	1 1 1 1 1 2 1 2 3 3 84%	1876
	21st to end	Night	2 1 1 2 2 1 2 2 3 4 81%	1980
October	1st to 10th	Night	4 2 1 2 2 2 3 2 3 4 74%	2027
	11th to 20th	Night	3 2 1 2 3 2 3 3 4 4 73%	2160
	21st to end	Night	5% 2 1 2 1 1 2 2 3 4 77%	2416
November	1st to 10th	Night	8% 5% 1 2 3 1 3 3 4 5% 64%	2405
	11th to 20th	Night	7% 3 2 3 3 1 2 4 5% 8% 63%	2470
	21st to end	Night	8% 6% 2 3 4 1 3 4 4 6% 58%	2470
December	1st to 10th	Night	12% 5% 2 4 4 2 4 3 4 7% 54%	2498
	11th to 20th	Night	20% 7% 3 4 4 3 4 4 5% 6% 40%	3276
	21st to end	Night	11% 7% 3 5% 5% 3 5% 5% 6% 8% 41%	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	37% 7% 13% 22% 18% 4	1519
	11th to 20th	Day	30% 6% 15% 21% 17% 12%	1542
	21st to end	Day	42% 5% 10% 17% 19% 6%	1782
February	1st to 10th	Day	34% 3 11% 24% 18% 9%	1768
	11th to 20th	Day	37% 6% 9% 19% 21% 8%	1760
	21st to end	Day	46% 5% 9% 25% 15% 1	1480
March	1st to 10th	Day	44% 4 12% 17% 20% 3	1800
	11th to 20th	Day	39% 5% 14% 21% 17% 4	1890
	21st to end	Day	40% 6% 16% 23% 13% 3	2358
April	1st to 10th	Day	34% 3 15% 26% 18% 3	2160
	11th to 20th	Day	34% 3 14% 23% 22% 4	2132
	21st to end	Day	28% 4 13% 33% 19% 2	2160
May	1st to 10th	Day	22% 4 12% 29% 30% 4	2242
	11th to 20th	Day	20% 3 12% 31% 27% 6%	2304
	21st to end	Day	22% 5% 12% 34% 24% 4	2653
June	1st to 10th	Day	17% 4 12% 21% 35% 11%	2520
	11th to 20th	Day	8% 2 7% 18% 41% 24%	2520
	21st to end	Day	8% 1 4 11% 40% 36%	2520
July	1st to 10th	Day	7% 2 3 10% 28% 49%	2451
	11th to 20th	Day	10% 2 5% 10% 31% 41%	2445
	21st to end	Day	11% 2 8% 15% 28% 37%	2485
August	1st to 10th	Day	10% 1 5% 7% 34% 43%	2139
	11th to 20th	Day	7% 1 4 12% 37% 38%	2122
	21st to end	Day	6% 1 4 9% 39% 41%	2376
September	1st to 10th	Day	7% 1 5% 9% 36% 42%	2160
	11th to 20th	Day	9% 1 5% 20% 38% 26%	2082
	21st to end	Day	11% 2 5% 18% 39% 26%	1980
October	1st to 10th	Day	18% 4 6% 18% 28% 26%	1929
	11th to 20th	Day	16% 3 5% 22% 30% 25%	1800
	21st to end	Day	17% 2 7% 21% 31% 22%	1937
November	1st to 10th	Day	27% 4 9% 19% 26% 15%	1674
	11th to 20th	Day	21% 4 11% 24% 28% 12%	1710
	21st to end	Day	28% 4 9% 16% 26% 16%	1710
December	1st to 10th	Day	29% 6% 12% 19% 22% 12%	1677
	11th to 20th	Day	48% 6% 11% 14% 13% 8%	1928
	21st to end	Day	41% 6% 17% 22% 10% 4	2794
January	1st to 10th	Night	34% 7% 14% 23% 19% 3	2646
	11th to 20th	Night	28% 5% 15% 24% 18% 10%	2470
	21st to end	Night	33% 5% 12% 21% 22% 7%	2574
February	1st to 10th	Night	34% 3 9% 26% 20% 8%	2189
	11th to 20th	Night	29% 6% 9% 24% 24% 7%	2099
	21st to end	Night	37% 4 13% 26% 16% 3	1776
March	1st to 10th	Night	37% 6% 13% 21% 19% 4	2160
	11th to 20th	Night	32% 5% 15% 23% 20% 5%	2066
	21st to end	Night	33% 6% 17% 28% 13% 3	1998
April	1st to 10th	Night	28% 4 15% 29% 18% 7%	1800
	11th to 20th	Night	25% 5% 14% 27% 22% 7%	1779
	21st to end	Night	20% 5% 15% 36% 23% 2	1800
May	1st to 10th	Night	19% 4 12% 28% 31% 6%	1715
	11th to 20th	Night	18% 3 8% 29% 36% 6%	1595
	21st to end	Night	17% 4 12% 30% 31% 6%	1618
June	1st to 10th	Night	15% 3 10% 23% 38% 10%	1440
	11th to 20th	Night	7% 3 6% 21% 37% 26%	1440
	21st to end	Night	6% 1 4 12% 40% 37%	1440
July	1st to 10th	Night	6% 1 3 9% 31% 51%	1400
	11th to 20th	Night	9% 3 6% 10% 29% 43%	1392
	21st to end	Night	11% 3 6% 11% 31% 38%	1590
August	1st to 10th	Night	8% 1 2 13% 31% 44%	1774
	11th to 20th	Night	5% 1 3 12% 38% 41%	1780
	21st to end	Night	7% 1 2 9% 41% 39%	1980
September	1st to 10th	Night	5% 1 3 10% 31% 50%	1800
	11th to 20th	Night	7% 2 4 17% 42% 28%	1876
	21st to end	Night	8% 2 5% 19% 40% 26%	1980
October	1st to 10th	Night	14% 3 7% 19% 31% 26%	2027
	11th to 20th	Night	14% 3 7% 19% 32% 24%	2160
	21st to end	Night	13% 2 6% 25% 32% 23%	2416
November	1st to 10th	Night	22% 4 11% 21% 26% 17%	2405
	11th to 20th	Night	20% 3 11% 23% 28% 15%	2470
	21st to end	Night	27% 4 10% 17% 29% 12%	2470
December	1st to 10th	Night	30% 5% 13% 20% 20% 12%	2498
	11th to 20th	Night	42% 7% 12% 17% 15% 7%	3276
	21st to end	Night	38% 6% 20% 22% 10% 5%	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	28% 7% 34% 21% 8% 2	180
	11th to 20th	Day	17% 12% 29% 27% 13% 3	250
	21st to end	Day	20% 7% 33% 27% 11% 2	374
February	1st to 10th	Day	19% 8% 34% 25% 11% 3	406
	11th to 20th	Day	18% 13% 37% 23% 8% 1	415
	21st to end	Day	20% 16% 35% 24% 4	346
March	1st to 10th	Day	24% 13% 36% 20% 6% 1	420
	11th to 20th	Day	19% 17% 32% 22% 9% 1	420
	21st to end	Day	22% 20% 31% 23% 4	462
April	1st to 10th	Day	16% 17% 32% 26% 9%	420
	11th to 20th	Day	21% 18% 31% 25% 5%	412
	21st to end	Day	11% 16% 33% 26% 12% 2	420
May	1st to 10th	Day	12% 18% 36% 23% 10% 1	423
	11th to 20th	Day	12% 12% 34% 28% 13% 2	448
	21st to end	Day	13% 12% 29% 31% 13% 2	485
June	1st to 10th	Day	5% 13% 28% 35% 16% 3	450
	11th to 20th	Day	4 12% 28% 41% 13% 3	450
	21st to end	Day	2 9% 31% 38% 18% 3	450
July	1st to 10th	Day	1 2 28% 48% 17% 4	446
	11th to 20th	Day	2 1 16% 54% 20% 7%	444
	21st to end	Day	2 1 21% 52% 18% 6%	487
August	1st to 10th	Day	2 5% 34% 42% 12% 5%	447
	11th to 20th	Day	2 4 25% 48% 14% 7%	437
	21st to end	Day	2 2 28% 49% 15% 5%	495
September	1st to 10th	Day	2 3 31% 46% 15% 3	450
	11th to 20th	Day	3 8% 34% 41% 12% 1	450
	21st to end	Day	4 11% 28% 42% 14% 1	450
October	1st to 10th	Day	5% 13% 32% 36% 14%	450
	11th to 20th	Day	5% 10% 31% 40% 14% 1	450
	21st to end	Day	5% 10% 31% 38% 16% 1	452
November	1st to 10th	Day	10% 10% 30% 30% 19% 1	270
	11th to 20th	Day	7% 7% 32% 35% 16% 3	270
	21st to end	Day	11% 10% 28% 33% 16% 2	270
December	1st to 10th	Day	16% 8% 33% 31% 12% 1	255
	11th to 20th	Day	14% 11% 33% 26% 16% 1	180
	21st to end	Day	22% 10% 32% 23% 11% 2	198
January	1st to 10th	Night	19% 3 21% 32% 19% 6%	760
	11th to 20th	Night	12% 5% 23% 37% 20% 3	732
	21st to end	Night	19% 2 24% 35% 17% 3	792
February	1st to 10th	Night	17% 2 21% 39% 18% 3	720
	11th to 20th	Night	14% 4 25% 34% 20% 4	704
	21st to end	Night	20% 5% 21% 39% 14% 2	592
March	1st to 10th	Night	16% 5% 21% 40% 15% 2	720
	11th to 20th	Night	14% 5% 20% 34% 23% 4	720
	21st to end	Night	17% 4 22% 38% 19% 1	792
April	1st to 10th	Night	13% 2 21% 44% 19% 1	720
	11th to 20th	Night	10% 4 22% 40% 22% 1	711
	21st to end	Night	7% 4 20% 41% 26% 3	720
May	1st to 10th	Night	6% 3 21% 42% 25% 2	635
	11th to 20th	Night	7% 2 17% 43% 29% 2	531
	21st to end	Night	6% 4 19% 38% 30% 3	456
June	1st to 10th	Night	5% 2 13% 41% 34% 5%	360
	11th to 20th	Night	1 1 12% 48% 34% 4	360
	21st to end	Night	1 12% 40% 43% 4	360
July	1st to 10th	Night	1 5% 36% 55% 3	350
	11th to 20th	Night	1 3 36% 54% 6%	348
	21st to end	Night	2 5% 32% 53% 9%	501
August	1st to 10th	Night	2 8% 39% 46% 5%	709
	11th to 20th	Night	1 5% 35% 53% 5%	712
	21st to end	Night	2 5% 34% 54% 6%	792
September	1st to 10th	Night	1 1 7% 36% 49% 6%	720
	11th to 20th	Night	1 1 11% 47% 35% 6%	720
	21st to end	Night	2 1 13% 42% 39% 5%	720
October	1st to 10th	Night	3 1 14% 48% 27% 6%	720
	11th to 20th	Night	4 1 17% 41% 33% 4	720
	21st to end	Night	5% 2 18% 34% 33% 8%	792
November	1st to 10th	Night	9% 3 14% 40% 28% 7%	740
	11th to 20th	Night	8% 2 17% 43% 26% 4	760
	21st to end	Night	10% 2 21% 41% 22% 4	760
December	1st to 10th	Night	13% 4 23% 39% 18% 4	760
	11th to 20th	Night	19% 3 24% 35% 17% 3	760
	21st to end	Night	16% 5% 26% 36% 13% 4	836

Page generated at 2024-01-10 07:16:13. Version ac07

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