Clear Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Clear Lake clear sky chart from 2005-11-06 to 2024-02-10.

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% 4 2 4 3 2 3 3 4 6% 60%	78417
	Night	10% 5% 2 4 4 2 4 4 4 6% 56%	80574
Transparency	Day	27% 4 8% 19% 24% 18%	78135
	Night	30% 5% 9% 18% 21% 17%	80378
Seeing	Day	10% 10% 21% 29% 22% 8%	14240
	Night	11% 7% 16% 30% 30% 8%	23609

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	13% 8% 3 5% 7% 4 5% 5% 5% 7% 39%	2649
	11th to 20th	Day	22% 9% 4 7% 5% 3 4 3 5% 6% 32%	2860
	21st to end	Day	22% 8% 4 7% 5% 2 4 4 5% 7% 32%	3146
February	1st to 10th	Day	14% 8% 3 4 4 3 4 5% 5% 6% 44%	1702
	11th to 20th	Day	11% 7% 2 5% 5% 3 4 4 6% 8% 46%	1597
	21st to end	Day	16% 6% 2 4 4 2 4 3 5% 8% 45%	1480
March	1st to 10th	Day	15% 10% 4 8% 4 3 5% 5% 5% 6% 35%	1963
	11th to 20th	Day	13% 9% 3 6% 5% 3 5% 4 5% 8% 37%	1980
	21st to end	Day	13% 6% 2 6% 5% 2 5% 5% 5% 7% 44%	2188
April	1st to 10th	Day	11% 8% 3 5% 6% 3 5% 4 5% 9% 42%	2160
	11th to 20th	Day	7% 5% 2 4 4 3 4 4 5% 7% 55%	2129
	21st to end	Day	4 3 2 4 4 2 3 4 5% 8% 60%	2160
May	1st to 10th	Day	4 4 1 3 3 2 3 4 5% 8% 63%	2322
	11th to 20th	Day	5% 3 1 3 3 2 3 4 6% 8% 62%	2370
	21st to end	Day	5% 2 1 3 3 2 4 4 5% 8% 63%	2723
June	1st to 10th	Day	4 4 2 3 3 2 3 3 5% 8% 63%	2520
	11th to 20th	Day	1 1 1 2 2 1 2 3 4 6% 78%	2520
	21st to end	Day	2 1 1 1 2 1 2 2 2 3 84%	2520
July	1st to 10th	Day	1 1 1 1 1 1 2 2 4 86%	2520
	11th to 20th	Day	1 1 1 1 2 2 3 4 85%	2391
	21st to end	Day	1 1 1 2 1 1 2 2 4 87%	2546
August	1st to 10th	Day	1 1 1 2 1 2 2 3 4 83%	2328
	11th to 20th	Day	1 1 1 1 1 1 1 2 4 87%	2249
	21st to end	Day	1 1 1 1 1 1 2 4 89%	2376
September	1st to 10th	Day	1 1 1 2 2 2 4 86%	2160
	11th to 20th	Day	2 1 1 2 2 1 2 3 3 7% 75%	2152
	21st to end	Day	2 1 1 2 2 1 2 3 3 6% 78%	1896
October	1st to 10th	Day	5% 3 2 2 2 2 2 3 3 5% 73%	1800
	11th to 20th	Day	6% 3 1 3 3 1 3 3 4 6% 68%	1800
	21st to end	Day	9% 3 1 3 3 2 3 3 4 6% 63%	1980
November	1st to 10th	Day	9% 3 2 5% 3 2 4 5% 5% 7% 55%	1817
	11th to 20th	Day	9% 6% 2 6% 4 3 4 4 5% 7% 51%	1651
	21st to end	Day	9% 6% 2 4 4 2 4 4 5% 7% 52%	1520
December	1st to 10th	Day	13% 8% 3 5% 4 3 4 4 3 6% 47%	1520
	11th to 20th	Day	27% 12% 4 7% 4 2 3 3 4 4 31%	1928
	21st to end	Day	22% 7% 2 6% 5% 2 4 5% 6% 8% 33%	2794
January	1st to 10th	Night	13% 9% 3 5% 5% 3 4 5% 5% 8% 39%	4283
	11th to 20th	Night	19% 10% 3 8% 6% 4 5% 5% 4 5% 31%	4110
	21st to end	Night	23% 9% 3 7% 5% 3 5% 5% 4 7% 31%	4521
February	1st to 10th	Night	13% 6% 2 5% 4 3 4 4 5% 6% 49%	2462
	11th to 20th	Night	10% 6% 3 5% 5% 3 5% 4 7% 7% 46%	2249
	21st to end	Night	11% 6% 2 4 4 2 5% 4 5% 7% 50%	1776
March	1st to 10th	Night	14% 8% 3 7% 5% 3 5% 5% 5% 6% 39%	1994
	11th to 20th	Night	12% 8% 3 6% 5% 3 4 4 6% 9% 42%	1980
	21st to end	Night	11% 7% 3 5% 4 2 4 4 4 5% 50%	2166
April	1st to 10th	Night	8% 6% 3 5% 6% 3 4 4 4 9% 49%	1800
	11th to 20th	Night	7% 4 1 4 4 2 4 3 5% 9% 56%	1779
	21st to end	Night	4 2 1 2 3 2 4 4 5% 9% 64%	1800
May	1st to 10th	Night	3 4 1 3 3 3 3 4 3 5% 67%	1634
	11th to 20th	Night	2 2 1 2 4 2 4 4 5% 8% 66%	1523
	21st to end	Night	3 2 1 3 2 1 3 5% 5% 7% 68%	1552
June	1st to 10th	Night	5% 3 1 2 3 2 3 4 5% 8% 64%	1440
	11th to 20th	Night	1 1 1 1 1 2 3 3 4 82%	1440
	21st to end	Night	1 2 1 2 2 1 2 3 2 3 81%	1440
July	1st to 10th	Night	1 1 1 1 1 2 2 4 88%	1440
	11th to 20th	Night	1 1 1 1 2 1 2 4 86%	1565
	21st to end	Night	1 1 1 1 1 2 3 4 87%	1773
August	1st to 10th	Night	1 1 2 1 2 2 2 3 85%	1611
	11th to 20th	Night	1 1 1 2 2 3 4 85%	1651
	21st to end	Night	1 2 1 2 2 2 3 86%	1980
September	1st to 10th	Night	1 1 1 1 2 2 5% 87%	1800
	11th to 20th	Night	2 2 1 2 2 1 2 3 4 5% 75%	1804
	21st to end	Night	1 1 1 1 2 1 2 2 4 7% 78%	2062
October	1st to 10th	Night	4 2 1 2 3 2 2 2 3 5% 73%	2160
	11th to 20th	Night	4 2 1 3 3 2 3 3 5% 6% 68%	2160
	21st to end	Night	8% 3 1 3 3 2 3 4 4 7% 63%	2376
November	1st to 10th	Night	7% 5% 2 5% 4 3 5% 4 5% 8% 52%	2258
	11th to 20th	Night	9% 4 2 4 4 3 4 5% 7% 8% 50%	2527
	21st to end	Night	7% 5% 3 4 5% 3 4 3 4 7% 55%	2660
December	1st to 10th	Night	16% 7% 3 5% 5% 2 3 4 4 7% 45%	2660
	11th to 20th	Night	27% 9% 3 5% 4 3 4 4 4 6% 32%	3276
	21st to end	Night	20% 10% 3 6% 5% 3 5% 5% 5% 6% 34%	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	47% 6% 10% 24% 9% 4	2649
	11th to 20th	Day	55% 5% 9% 13% 10% 9%	2860
	21st to end	Day	53% 4 8% 16% 13% 5%	3146
February	1st to 10th	Day	42% 5% 7% 17% 19% 9%	1702
	11th to 20th	Day	37% 5% 8% 20% 21% 8%	1606
	21st to end	Day	39% 6% 9% 22% 16% 7%	1480
March	1st to 10th	Day	49% 7% 10% 15% 14% 5%	1963
	11th to 20th	Day	46% 6% 8% 19% 15% 6%	1980
	21st to end	Day	42% 7% 12% 18% 17% 4	2188
April	1st to 10th	Day	42% 5% 11% 21% 15% 5%	2160
	11th to 20th	Day	31% 5% 13% 23% 22% 7%	2132
	21st to end	Day	23% 7% 14% 29% 21% 7%	2160
May	1st to 10th	Day	21% 6% 10% 29% 26% 8%	2322
	11th to 20th	Day	21% 5% 9% 30% 27% 8%	2373
	21st to end	Day	21% 6% 13% 36% 19% 4	2724
June	1st to 10th	Day	21% 5% 12% 29% 26% 8%	2520
	11th to 20th	Day	9% 3 10% 23% 35% 19%	2520
	21st to end	Day	8% 2 4 16% 38% 32%	2520
July	1st to 10th	Day	6% 2 3 12% 31% 45%	2451
	11th to 20th	Day	6% 3 5% 11% 32% 44%	2319
	21st to end	Day	6% 2 2 10% 27% 53%	2405
August	1st to 10th	Day	8% 3 4 18% 33% 35%	2312
	11th to 20th	Day	5% 2 2 13% 38% 39%	2249
	21st to end	Day	5% 2 3 14% 37% 39%	2376
September	1st to 10th	Day	5% 2 3 10% 31% 49%	2160
	11th to 20th	Day	12% 4 5% 25% 37% 17%	2152
	21st to end	Day	10% 4 5% 21% 33% 27%	1896
October	1st to 10th	Day	18% 3 5% 17% 31% 25%	1800
	11th to 20th	Day	20% 4 8% 18% 24% 26%	1800
	21st to end	Day	24% 4 7% 18% 27% 20%	1980
November	1st to 10th	Day	29% 7% 7% 26% 19% 13%	1817
	11th to 20th	Day	34% 5% 11% 21% 19% 9%	1651
	21st to end	Day	32% 6% 10% 18% 19% 15%	1520
December	1st to 10th	Day	40% 5% 7% 16% 20% 12%	1520
	11th to 20th	Day	59% 4 5% 12% 16% 5%	1928
	21st to end	Day	50% 5% 10% 18% 12% 4	2794
January	1st to 10th	Night	43% 5% 18% 19% 10% 4	4283
	11th to 20th	Night	56% 5% 9% 11% 11% 8%	4110
	21st to end	Night	54% 7% 7% 12% 13% 6%	4521
February	1st to 10th	Night	38% 6% 7% 18% 20% 12%	2462
	11th to 20th	Night	36% 6% 8% 20% 22% 8%	2251
	21st to end	Night	33% 6% 13% 23% 21% 5%	1776
March	1st to 10th	Night	46% 9% 10% 14% 17% 4	1994
	11th to 20th	Night	41% 6% 8% 20% 17% 8%	1980
	21st to end	Night	38% 6% 13% 21% 17% 5%	2166
April	1st to 10th	Night	36% 7% 14% 21% 17% 6%	1800
	11th to 20th	Night	27% 7% 13% 24% 20% 9%	1779
	21st to end	Night	21% 6% 12% 31% 25% 6%	1800
May	1st to 10th	Night	21% 5% 5% 26% 32% 10%	1634
	11th to 20th	Night	18% 5% 9% 28% 30% 10%	1523
	21st to end	Night	15% 6% 17% 33% 24% 5%	1552
June	1st to 10th	Night	20% 5% 10% 24% 31% 9%	1440
	11th to 20th	Night	9% 3 9% 22% 35% 22%	1440
	21st to end	Night	10% 3 3 13% 34% 37%	1440
July	1st to 10th	Night	5% 2 2 10% 31% 50%	1400
	11th to 20th	Night	5% 1 4 11% 26% 52%	1515
	21st to end	Night	5% 1 2 9% 22% 61%	1674
August	1st to 10th	Night	8% 2 2 12% 32% 44%	1602
	11th to 20th	Night	6% 2 3 10% 31% 48%	1651
	21st to end	Night	6% 2 3 12% 33% 44%	1980
September	1st to 10th	Night	4 1 3 11% 29% 53%	1800
	11th to 20th	Night	12% 3 5% 17% 37% 25%	1804
	21st to end	Night	8% 4 5% 22% 27% 33%	2062
October	1st to 10th	Night	17% 3 6% 18% 28% 28%	2160
	11th to 20th	Night	18% 6% 6% 18% 24% 28%	2160
	21st to end	Night	23% 5% 6% 19% 22% 25%	2376
November	1st to 10th	Night	30% 7% 10% 21% 18% 14%	2258
	11th to 20th	Night	31% 6% 14% 20% 20% 10%	2527
	21st to end	Night	32% 4 8% 18% 23% 15%	2660
December	1st to 10th	Night	40% 6% 7% 14% 20% 12%	2660
	11th to 20th	Night	55% 4 6% 14% 16% 5%	3276
	21st to end	Night	52% 5% 11% 17% 12% 4	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	33% 13% 23% 16% 13% 2	251
	11th to 20th	Day	24% 14% 21% 24% 14% 3	370
	21st to end	Day	15% 15% 22% 27% 16% 5%	407
February	1st to 10th	Day	21% 13% 23% 23% 18% 3	368
	11th to 20th	Day	20% 19% 24% 21% 15% 1	345
	21st to end	Day	19% 14% 25% 26% 14% 2	346
March	1st to 10th	Day	23% 18% 27% 21% 9% 2	420
	11th to 20th	Day	24% 13% 26% 22% 13% 3	420
	21st to end	Day	17% 16% 34% 23% 9% 2	462
April	1st to 10th	Day	17% 17% 27% 22% 13% 4	420
	11th to 20th	Day	16% 21% 25% 21% 14% 3	412
	21st to end	Day	7% 17% 32% 23% 17% 5%	420
May	1st to 10th	Day	9% 17% 27% 25% 17% 4	423
	11th to 20th	Day	9% 14% 30% 23% 16% 7%	448
	21st to end	Day	7% 12% 21% 30% 24% 7%	485
June	1st to 10th	Day	6% 14% 22% 32% 18% 8%	450
	11th to 20th	Day	5% 10% 29% 31% 21% 4	450
	21st to end	Day	1 5% 23% 34% 28% 9%	450
July	1st to 10th	Day	2 2 17% 41% 31% 7%	446
	11th to 20th	Day	1 1 15% 38% 32% 13%	444
	21st to end	Day	1 8% 42% 31% 17%	487
August	1st to 10th	Day	2 1 16% 36% 32% 12%	447
	11th to 20th	Day	2 1 16% 35% 31% 14%	437
	21st to end	Day	1 3 13% 34% 36% 14%	495
September	1st to 10th	Day	3 14% 37% 38% 8%	450
	11th to 20th	Day	4 5% 18% 34% 30% 9%	450
	21st to end	Day	3 8% 20% 34% 26% 9%	450
October	1st to 10th	Day	6% 8% 23% 27% 25% 11%	450
	11th to 20th	Day	6% 9% 16% 26% 29% 13%	450
	21st to end	Day	11% 9% 17% 29% 25% 8%	495
November	1st to 10th	Day	12% 10% 20% 21% 28% 9%	413
	11th to 20th	Day	10% 7% 16% 26% 24% 16%	241
	21st to end	Day	13% 9% 22% 27% 19% 10%	180
December	1st to 10th	Day	22% 11% 19% 22% 16% 11%	180
	11th to 20th	Day	27% 14% 17% 20% 12% 11%	180
	21st to end	Day	20% 13% 21% 27% 15% 4	198
January	1st to 10th	Night	21% 8% 15% 29% 22% 5%	760
	11th to 20th	Night	21% 9% 16% 32% 18% 5%	760
	21st to end	Night	18% 7% 17% 31% 21% 5%	836
February	1st to 10th	Night	18% 8% 16% 32% 22% 3	758
	11th to 20th	Night	15% 10% 19% 29% 22% 5%	704
	21st to end	Night	17% 12% 21% 30% 18% 2	592
March	1st to 10th	Night	20% 11% 17% 29% 19% 4	720
	11th to 20th	Night	18% 9% 17% 30% 22% 3	720
	21st to end	Night	16% 13% 25% 28% 16% 3	792
April	1st to 10th	Night	12% 12% 26% 27% 19% 4	720
	11th to 20th	Night	10% 13% 22% 30% 19% 6%	711
	21st to end	Night	7% 12% 25% 27% 23% 6%	720
May	1st to 10th	Night	6% 8% 24% 29% 26% 6%	554
	11th to 20th	Night	5% 4 21% 32% 32% 6%	461
	21st to end	Night	4 8% 20% 30% 33% 5%	389
June	1st to 10th	Night	5% 9% 19% 33% 31% 4	360
	11th to 20th	Night	3 5% 21% 34% 36% 1	360
	21st to end	Night	2 3 9% 41% 40% 5%	360
July	1st to 10th	Night	1 1 13% 33% 47% 5%	350
	11th to 20th	Night	1 7% 26% 52% 14%	471
	21st to end	Night	1 5% 24% 52% 18%	591
August	1st to 10th	Night	1 1 6% 28% 46% 18%	537
	11th to 20th	Night	8% 31% 45% 16%	583
	21st to end	Night	1 1 6% 27% 53% 12%	792
September	1st to 10th	Night	1 2 7% 29% 49% 11%	720
	11th to 20th	Night	3 3 10% 33% 37% 14%	720
	21st to end	Night	2 5% 14% 28% 36% 15%	720
October	1st to 10th	Night	6% 4 16% 29% 34% 12%	720
	11th to 20th	Night	6% 5% 12% 26% 42% 9%	720
	21st to end	Night	9% 5% 12% 29% 31% 14%	792
November	1st to 10th	Night	11% 9% 13% 26% 32% 9%	740
	11th to 20th	Night	12% 6% 14% 33% 29% 6%	760
	21st to end	Night	9% 10% 17% 33% 24% 8%	760
December	1st to 10th	Night	21% 8% 14% 29% 21% 8%	760
	11th to 20th	Night	24% 10% 13% 28% 21% 5%	760
	21st to end	Night	22% 8% 19% 31% 17% 2	836

Page generated at 2024-02-07 03:11:59. Version ac07

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