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 2024-11-11.

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	6% 5% 1 3 2 3 3 2 4 5% 66%	104959
	Night	8% 5% 1 3 2 2 3 2 4 5% 65%	102906
Transparency	Day	21% 4 9% 18% 26% 23%	104707
	Night	22% 4 10% 20% 25% 20%	102749
Seeing	Day	10% 10% 31% 34% 12% 2	15306
	Night	9% 3 18% 39% 28% 4	24865

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	10% 10% 3 6% 3 4 4 2 5% 7% 45%	2539
	11th to 20th	Day	12% 7% 2 8% 5% 5% 6% 4 6% 7% 38%	2682
	21st to end	Day	15% 9% 2 6% 4 4 5% 4 6% 8% 36%	3146
February	1st to 10th	Day	15% 10% 2 3 3 3 3 3 5% 5% 49%	1866
	11th to 20th	Day	11% 14% 2 5% 3 3 3 3 4 6% 47%	1850
	21st to end	Day	16% 13% 3 6% 4 3 3 2 3 6% 41%	1570
March	1st to 10th	Day	13% 17% 3 6% 5% 4 4 3 4 7% 34%	3138
	11th to 20th	Day	7% 9% 1 4 3 4 3 3 4 6% 54%	3335
	21st to end	Day	14% 17% 3 6% 4 4 4 3 4 5% 35%	4134
April	1st to 10th	Day	11% 9% 2 5% 4 4 3 2 5% 7% 50%	2280
	11th to 20th	Day	12% 9% 2 4 4 3 4 2 5% 5% 50%	2249
	21st to end	Day	9% 7% 1 4 3 3 3 3 5% 6% 54%	2280
May	1st to 10th	Day	6% 5% 1 3 2 2 2 2 3 5% 68%	3947
	11th to 20th	Day	4 2 2 2 2 2 3 4 6% 73%	4071
	21st to end	Day	5% 2 1 2 2 2 2 2 3 4 75%	4691
June	1st to 10th	Day	4 3 1 3 3 2 3 3 5% 7% 66%	2660
	11th to 20th	Day	2 1 1 1 1 1 2 1 3 4 83%	2660
	21st to end	Day	1 1 1 2 1 2 2 2 2 3 85%	2660
July	1st to 10th	Day	1 1 1 1 1 1 1 1 2 90%	4420
	11th to 20th	Day	2 1 1 2 2 2 2 2 3 4 80%	4420
	21st to end	Day	1 1 2 1 1 1 2 2 3 85%	4592
August	1st to 10th	Day	1 2 1 2 1 1 1 1 2 2 85%	3788
	11th to 20th	Day	1 1 1 1 1 1 1 2 90%	3724
	21st to end	Day	1 1 1 1 1 1 1 2 3 88%	4180
September	1st to 10th	Day	1 1 2 1 2 1 1 3 4 84%	2280
	11th to 20th	Day	2 1 1 2 2 2 2 1 2 4 81%	2197
	21st to end	Day	2 2 1 2 1 2 2 1 3 3 81%	2090
October	1st to 10th	Day	4 3 1 2 2 2 3 2 3 4 74%	3400
	11th to 20th	Day	3 2 1 3 2 3 2 2 2 3 77%	3161
	21st to end	Day	5% 4 1 4 3 3 3 3 4 6% 63%	3366
November	1st to 10th	Day	6% 8% 2 4 3 2 3 2 5% 6% 58%	1764
	11th to 20th	Day	8% 4 1 2 3 2 2 3 5% 6% 64%	1710
	21st to end	Day	8% 6% 2 4 3 3 4 3 5% 6% 57%	1710
December	1st to 10th	Day	12% 5% 2 3 3 3 3 3 5% 7% 54%	1677
	11th to 20th	Day	18% 10% 2 7% 4 4 4 3 4 6% 37%	1928
	21st to end	Day	11% 10% 3 7% 4 4 4 4 5% 8% 39%	2794
January	1st to 10th	Night	13% 8% 2 5% 2 3 4 2 4 5% 50%	4406
	11th to 20th	Night	14% 10% 3 6% 4 4 4 3 5% 7% 40%	4265
	21st to end	Night	15% 9% 3 5% 4 4 5% 3 6% 8% 37%	4521
February	1st to 10th	Night	14% 9% 2 4 3 4 3 2 5% 5% 50%	2311
	11th to 20th	Night	12% 8% 2 4 2 3 3 3 4 6% 54%	2218
	21st to end	Night	14% 9% 3 4 3 3 3 2 5% 5% 49%	1884
March	1st to 10th	Night	15% 11% 2 5% 3 4 4 5% 6% 7% 39%	3736
	11th to 20th	Night	7% 6% 2 3 3 4 3 3 5% 7% 57%	3628
	21st to end	Night	18% 9% 2 5% 4 3 4 3 5% 6% 41%	3519
April	1st to 10th	Night	10% 6% 1 4 3 4 3 3 4 6% 57%	1900
	11th to 20th	Night	9% 5% 1 4 4 3 4 3 4 5% 59%	1879
	21st to end	Night	7% 5% 1 2 3 2 3 3 4 6% 63%	1900
May	1st to 10th	Night	7% 3 1 2 2 2 2 2 3 5% 72%	3025
	11th to 20th	Night	3 2 1 2 1 1 2 2 3 5% 78%	2834
	21st to end	Night	3 2 1 2 2 1 1 1 2 3 81%	2870
June	1st to 10th	Night	5% 3 1 3 2 1 2 2 3 7% 72%	1520
	11th to 20th	Night	1 1 1 2 1 2 2 1 2 4 83%	1520
	21st to end	Night	1 1 1 1 1 1 1 2 3 2 87%	1520
July	1st to 10th	Night	1 1 1 1 1 1 2 92%	2540
	11th to 20th	Night	2 1 1 2 2 2 2 2 2 4 81%	2540
	21st to end	Night	1 1 2 1 1 1 1 2 3 85%	2949
August	1st to 10th	Night	1 1 1 2 1 1 2 1 3 4 83%	3159
	11th to 20th	Night	1 1 1 1 1 1 1 2 92%	3126
	21st to end	Night	2 1 1 1 1 1 1 1 2 89%	3498
September	1st to 10th	Night	1 1 1 1 1 1 1 1 3 89%	1900
	11th to 20th	Night	1 2 1 2 1 2 2 2 3 3 83%	1981
	21st to end	Night	2 1 1 2 1 2 2 2 3 3 82%	2090
October	1st to 10th	Night	2 2 1 1 1 2 2 1 2 3 83%	3576
	11th to 20th	Night	2 2 1 2 2 2 3 2 3 3 79%	3777
	21st to end	Night	4 2 1 3 1 1 2 2 3 5% 76%	4197
November	1st to 10th	Night	7% 5% 1 2 3 2 3 3 4 5% 65%	2535
	11th to 20th	Night	7% 3 1 3 2 2 2 3 5% 8% 63%	2476
	21st to end	Night	8% 6% 2 4 4 2 3 3 4 7% 58%	2470
December	1st to 10th	Night	12% 5% 2 4 3 3 4 2 4 7% 54%	2498
	11th to 20th	Night	20% 7% 2 5% 3 4 4 3 6% 6% 40%	3276
	21st to end	Night	11% 7% 3 6% 4 5% 5% 4 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	36% 8% 21% 21% 11% 2	2539
	11th to 20th	Day	39% 12% 17% 15% 10% 7%	2682
	21st to end	Day	42% 9% 14% 20% 12% 3	3146
February	1st to 10th	Day	36% 3 12% 23% 18% 8%	1866
	11th to 20th	Day	37% 6% 9% 20% 20% 8%	1860
	21st to end	Day	45% 5% 9% 25% 15% 1	1570
March	1st to 10th	Day	44% 6% 14% 18% 16% 2	3138
	11th to 20th	Day	25% 6% 16% 32% 14% 6%	3335
	21st to end	Day	43% 6% 18% 19% 12% 2	4134
April	1st to 10th	Day	34% 3 15% 27% 19% 3	2280
	11th to 20th	Day	33% 3 14% 23% 21% 4	2252
	21st to end	Day	28% 4 12% 33% 20% 2	2280
May	1st to 10th	Day	16% 3 10% 31% 31% 9%	3947
	11th to 20th	Day	13% 3 8% 29% 40% 7%	4074
	21st to end	Day	13% 3 9% 31% 39% 6%	4691
June	1st to 10th	Day	16% 4 12% 21% 36% 11%	2660
	11th to 20th	Day	7% 2 7% 19% 42% 23%	2660
	21st to end	Day	8% 1 3 11% 39% 38%	2660
July	1st to 10th	Day	4 1 2 6% 16% 72%	4351
	11th to 20th	Day	9% 2 3 6% 21% 58%	4345
	21st to end	Day	6% 1 4 14% 26% 49%	4447
August	1st to 10th	Day	9% 1 3 7% 38% 43%	3774
	11th to 20th	Day	4 1 2 7% 30% 56%	3760
	21st to end	Day	5% 1 2 10% 35% 47%	4179
September	1st to 10th	Day	7% 1 5% 8% 36% 43%	2280
	11th to 20th	Day	10% 1 5% 20% 39% 25%	2197
	21st to end	Day	10% 2 5% 17% 38% 28%	2090
October	1st to 10th	Day	14% 3 3 10% 25% 44%	3400
	11th to 20th	Day	15% 2 3 24% 35% 21%	3161
	21st to end	Day	23% 2 4 17% 35% 19%	3366
November	1st to 10th	Day	26% 4 9% 21% 26% 15%	1764
	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% 11% 17% 24% 12% 2	4406
	11th to 20th	Night	40% 8% 19% 16% 10% 6%	4265
	21st to end	Night	40% 9% 12% 21% 13% 4	4521
February	1st to 10th	Night	36% 3 9% 25% 19% 7%	2311
	11th to 20th	Night	30% 6% 10% 24% 23% 7%	2219
	21st to end	Night	36% 4 14% 26% 16% 3	1884
March	1st to 10th	Night	39% 6% 14% 21% 17% 2	3736
	11th to 20th	Night	23% 6% 17% 32% 15% 7%	3628
	21st to end	Night	40% 7% 19% 22% 11% 2	3519
April	1st to 10th	Night	28% 4 15% 29% 18% 6%	1900
	11th to 20th	Night	25% 6% 14% 29% 21% 6%	1879
	21st to end	Night	20% 5% 15% 36% 23% 1	1900
May	1st to 10th	Night	16% 2 9% 31% 34% 8%	3025
	11th to 20th	Night	11% 2 7% 29% 42% 8%	2835
	21st to end	Night	10% 2 8% 27% 47% 6%	2870
June	1st to 10th	Night	14% 3 11% 23% 38% 10%	1520
	11th to 20th	Night	7% 2 6% 22% 38% 26%	1520
	21st to end	Night	6% 1 4 11% 40% 39%	1520
July	1st to 10th	Night	3 1 1 5% 17% 72%	2500
	11th to 20th	Night	9% 2 4 6% 21% 58%	2492
	21st to end	Night	6% 2 3 14% 24% 51%	2857
August	1st to 10th	Night	9% 1 1 12% 34% 42%	3150
	11th to 20th	Night	3 1 2 7% 24% 63%	3156
	21st to end	Night	6% 1 2 7% 35% 50%	3498
September	1st to 10th	Night	5% 1 3 9% 32% 50%	1900
	11th to 20th	Night	8% 2 4 17% 42% 27%	1981
	21st to end	Night	8% 2 5% 18% 40% 28%	2090
October	1st to 10th	Night	9% 2 4 11% 26% 49%	3576
	11th to 20th	Night	11% 2 4 21% 43% 19%	3777
	21st to end	Night	13% 1 3 21% 38% 23%	4197
November	1st to 10th	Night	21% 3 11% 22% 26% 16%	2535
	11th to 20th	Night	20% 3 11% 23% 28% 15%	2476
	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	270
	21st to end	Day	19% 9% 32% 27% 11% 2	407
February	1st to 10th	Day	20% 10% 34% 24% 10% 3	444
	11th to 20th	Day	18% 13% 36% 24% 7% 1	455
	21st to end	Day	19% 16% 37% 23% 4	382
March	1st to 10th	Day	24% 14% 37% 20% 6% 1	460
	11th to 20th	Day	17% 18% 33% 22% 9% 1	460
	21st to end	Day	21% 21% 32% 22% 4	506
April	1st to 10th	Day	15% 18% 32% 26% 9%	460
	11th to 20th	Day	19% 18% 30% 27% 6%	452
	21st to end	Day	10% 16% 33% 27% 12% 2	460
May	1st to 10th	Day	12% 18% 37% 22% 9% 2	463
	11th to 20th	Day	11% 11% 34% 29% 14% 2	488
	21st to end	Day	12% 11% 30% 32% 13% 2	529
June	1st to 10th	Day	5% 12% 28% 38% 16% 3	490
	11th to 20th	Day	4 12% 30% 39% 12% 3	490
	21st to end	Day	1 8% 32% 39% 17% 4	490
July	1st to 10th	Day	1 2 29% 47% 16% 5%	486
	11th to 20th	Day	2 1 17% 54% 19% 7%	484
	21st to end	Day	2 2 21% 51% 17% 7%	531
August	1st to 10th	Day	2 5% 33% 42% 12% 6%	487
	11th to 20th	Day	2 6% 26% 45% 14% 7%	477
	21st to end	Day	2 2 27% 48% 15% 6%	539
September	1st to 10th	Day	2 3 32% 45% 15% 3	490
	11th to 20th	Day	4 9% 33% 40% 13% 1	490
	21st to end	Day	4 11% 29% 42% 13% 1	490
October	1st to 10th	Day	5% 12% 31% 37% 14%	490
	11th to 20th	Day	5% 10% 32% 39% 13% 1	490
	21st to end	Day	6% 9% 32% 37% 15% 1	493
November	1st to 10th	Day	9% 10% 32% 31% 17% 1	300
	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% 24% 37% 20% 3	760
	21st to end	Night	18% 3 25% 35% 17% 3	836
February	1st to 10th	Night	18% 3 21% 37% 17% 3	760
	11th to 20th	Night	14% 4 26% 34% 19% 4	744
	21st to end	Night	19% 5% 23% 38% 13% 2	628
March	1st to 10th	Night	17% 5% 22% 39% 15% 2	760
	11th to 20th	Night	13% 5% 22% 33% 22% 4	760
	21st to end	Night	17% 5% 23% 36% 18% 1	836
April	1st to 10th	Night	12% 3 22% 43% 19% 1	760
	11th to 20th	Night	10% 4 23% 40% 22% 1	751
	21st to end	Night	7% 4 20% 41% 25% 3	760
May	1st to 10th	Night	6% 3 21% 42% 24% 2	670
	11th to 20th	Night	7% 2 16% 44% 29% 2	561
	21st to end	Night	6% 3 19% 40% 29% 3	481
June	1st to 10th	Night	5% 2 13% 43% 33% 4	380
	11th to 20th	Night	1 1 15% 46% 33% 4	380
	21st to end	Night	1 13% 41% 41% 4	380
July	1st to 10th	Night	1 1 5% 38% 52% 3	370
	11th to 20th	Night	1 3 37% 53% 6%	368
	21st to end	Night	2 1 6% 33% 51% 8%	529
August	1st to 10th	Night	2 9% 40% 45% 4	749
	11th to 20th	Night	1 7% 36% 51% 5%	752
	21st to end	Night	2 6% 35% 52% 6%	836
September	1st to 10th	Night	1 1 8% 37% 47% 6%	760
	11th to 20th	Night	1 1 12% 46% 34% 6%	760
	21st to end	Night	2 1 14% 42% 37% 4	760
October	1st to 10th	Night	3 1 15% 49% 25% 5%	760
	11th to 20th	Night	4 1 19% 41% 32% 4	760
	21st to end	Night	5% 2 20% 33% 32% 8%	836
November	1st to 10th	Night	9% 3 16% 39% 27% 7%	780
	11th to 20th	Night	8% 2 17% 43% 25% 4	762
	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 2024-11-08 03:44:50. Version ac07

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