Lake San Antonio
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lake San Antonio clear sky chart from 2005-11-06 to 2024-04-10.

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	4 3 2 4 4 2 4 4 5% 6% 63%	83394
	Night	5% 4 2 4 4 3 4 4 4 6% 61%	85485
Transparency	Day	22% 5% 8% 19% 26% 22%	83115
	Night	23% 5% 9% 19% 24% 19%	85287
Seeing	Day	5% 6% 17% 29% 27% 15%	14711
	Night	6% 2 10% 37% 37% 7%	24358

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	5% 4 2 6% 7% 4 6% 6% 6% 7% 47%	2708
	11th to 20th	Day	7% 7% 4 7% 7% 3 7% 5% 6% 7% 41%	2860
	21st to end	Day	11% 8% 3 6% 6% 3 6% 6% 7% 8% 35%	3146
February	1st to 10th	Day	9% 5% 2 5% 4 3 4 4 6% 7% 50%	1737
	11th to 20th	Day	7% 4 3 5% 6% 3 4 5% 6% 7% 50%	1850
	21st to end	Day	8% 5% 2 6% 4 3 5% 5% 5% 8% 48%	1570
March	1st to 10th	Day	6% 5% 3 7% 7% 5% 7% 7% 7% 9% 37%	3278
	11th to 20th	Day	4 3 2 3 4 3 4 4 5% 7% 60%	3490
	21st to end	Day	6% 5% 3 6% 7% 4 6% 7% 7% 7% 42%	3969
April	1st to 10th	Day	6% 4 2 4 3 3 4 4 5% 9% 54%	2270
	11th to 20th	Day	4 4 2 4 4 2 4 5% 6% 6% 60%	2129
	21st to end	Day	4 2 1 4 3 2 3 4 4 7% 67%	2160
May	1st to 10th	Day	2 2 2 3 3 2 3 3 4 6% 70%	2160
	11th to 20th	Day	2 1 1 2 2 2 4 3 4 7% 73%	2244
	21st to end	Day	2 3 1 2 3 2 3 3 3 6% 72%	2723
June	1st to 10th	Day	2 2 1 2 2 2 3 3 4 8% 73%	2520
	11th to 20th	Day	1 1 1 1 1 2 1 2 4 85%	2520
	21st to end	Day	1 1 1 1 1 2 3 4 85%	2520
July	1st to 10th	Day	1 1 1 1 1 2 3 5% 86%	2520
	11th to 20th	Day	1 1 1 1 1 1 2 2 3 5% 82%	2352
	21st to end	Day	1 1 1 2 2 1 2 3 4 6% 77%	2546
August	1st to 10th	Day	2 1 2 2 1 2 2 3 5% 80%	2267
	11th to 20th	Day	1 1 1 1 1 2 2 3 4 85%	2122
	21st to end	Day	1 1 1 1 2 1 2 2 3 4 82%	2376
September	1st to 10th	Day	1 1 1 1 1 2 2 2 5% 84%	2160
	11th to 20th	Day	1 1 1 2 2 1 2 2 3 4 80%	2160
	21st to end	Day	1 1 2 2 1 3 3 4 5% 78%	1963
October	1st to 10th	Day	2 2 1 2 2 2 3 4 4 7% 71%	1800
	11th to 20th	Day	2 2 1 2 3 2 4 3 4 6% 70%	1800
	21st to end	Day	2 3 1 3 3 2 3 3 5% 7% 67%	1980
November	1st to 10th	Day	3 4 2 4 4 3 4 4 5% 7% 61%	1798
	11th to 20th	Day	3 4 2 5% 4 2 5% 5% 6% 6% 59%	1710
	21st to end	Day	4 4 2 5% 4 3 4 4 5% 6% 59%	1710
December	1st to 10th	Day	7% 6% 3 5% 5% 3 4 5% 5% 9% 48%	1554
	11th to 20th	Day	14% 8% 4 7% 7% 3 5% 4 5% 8% 33%	1928
	21st to end	Day	12% 8% 3 9% 6% 4 5% 5% 6% 8% 34%	2794
January	1st to 10th	Night	7% 5% 2 8% 7% 4 5% 4 5% 6% 47%	4237
	11th to 20th	Night	7% 8% 3 8% 6% 4 5% 5% 6% 8% 41%	4110
	21st to end	Night	12% 8% 3 6% 6% 4 5% 5% 5% 6% 40%	4521
February	1st to 10th	Night	8% 5% 2 5% 5% 3 4 4 5% 7% 53%	2441
	11th to 20th	Night	6% 4 2 4 4 3 4 4 5% 7% 58%	2218
	21st to end	Night	7% 4 3 4 4 3 3 4 5% 7% 57%	1884
March	1st to 10th	Night	6% 7% 4 6% 7% 5% 7% 7% 7% 8% 37%	3594
	11th to 20th	Night	3 3 1 4 4 2 4 4 6% 6% 62%	3490
	21st to end	Night	6% 5% 3 5% 6% 4 5% 5% 5% 8% 47%	3683
April	1st to 10th	Night	5% 3 1 4 4 3 3 5% 5% 7% 60%	1900
	11th to 20th	Night	4 3 1 3 3 2 3 3 4 6% 69%	1779
	21st to end	Night	2 2 1 2 3 2 4 3 3 8% 70%	1800
May	1st to 10th	Night	2 2 1 2 3 2 2 4 4 8% 71%	1800
	11th to 20th	Night	2 1 1 2 2 1 3 3 3 6% 76%	1640
	21st to end	Night	2 2 1 2 3 1 3 2 4 7% 74%	1552
June	1st to 10th	Night	2 1 1 2 2 1 3 3 4 6% 76%	1440
	11th to 20th	Night	1 1 1 1 1 2 3 5% 84%	1440
	21st to end	Night	1 1 1 1 1 4 90%	1440
July	1st to 10th	Night	1 1 2 1 3 4 87%	1440
	11th to 20th	Night	1 1 1 1 2 3 2 3 85%	1603
	21st to end	Night	1 1 1 2 2 1 3 3 4 6% 77%	1773
August	1st to 10th	Night	1 1 2 1 3 3 2 4 83%	1671
	11th to 20th	Night	2 1 1 2 2 3 4 84%	1780
	21st to end	Night	1 1 1 1 1 2 2 2 5% 85%	1980
September	1st to 10th	Night	1 1 1 1 1 2 2 2 4 86%	1800
	11th to 20th	Night	1 1 1 2 2 1 2 3 3 4 81%	1800
	21st to end	Night	1 1 1 2 1 1 2 2 3 4 84%	1992
October	1st to 10th	Night	2 3 1 2 2 2 2 3 5% 6% 73%	2160
	11th to 20th	Night	3 2 2 3 2 2 3 4 4 5% 71%	2160
	21st to end	Night	2 3 1 2 3 2 3 4 4 5% 72%	2376
November	1st to 10th	Night	3 3 1 3 3 2 4 3 4 7% 67%	2281
	11th to 20th	Night	3 3 2 3 4 2 4 4 5% 6% 63%	2470
	21st to end	Night	4 3 2 3 4 3 4 5% 6% 7% 59%	2470
December	1st to 10th	Night	7% 5% 2 5% 4 3 5% 5% 5% 7% 52%	2622
	11th to 20th	Night	12% 9% 3 7% 7% 4 5% 5% 6% 6% 35%	3276
	21st to end	Night	10% 8% 4 9% 7% 4 6% 5% 6% 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	29% 10% 14% 29% 15% 4	2708
	11th to 20th	Day	39% 7% 12% 18% 15% 9%	2860
	21st to end	Day	42% 9% 11% 17% 15% 7%	3146
February	1st to 10th	Day	33% 5% 7% 19% 21% 15%	1737
	11th to 20th	Day	32% 5% 9% 20% 23% 11%	1860
	21st to end	Day	33% 6% 10% 21% 24% 7%	1570
March	1st to 10th	Day	35% 11% 15% 18% 17% 4	3278
	11th to 20th	Day	23% 6% 11% 31% 17% 12%	3490
	21st to end	Day	34% 11% 13% 24% 14% 4	3969
April	1st to 10th	Day	28% 5% 12% 23% 23% 9%	2270
	11th to 20th	Day	24% 5% 9% 26% 27% 9%	2132
	21st to end	Day	19% 5% 10% 27% 31% 9%	2160
May	1st to 10th	Day	17% 4 9% 22% 35% 13%	2160
	11th to 20th	Day	13% 4 7% 27% 35% 14%	2247
	21st to end	Day	15% 4 8% 31% 33% 9%	2724
June	1st to 10th	Day	12% 4 10% 21% 33% 20%	2520
	11th to 20th	Day	7% 2 5% 14% 40% 32%	2520
	21st to end	Day	6% 2 3 10% 33% 46%	2520
July	1st to 10th	Day	5% 1 2 7% 28% 57%	2451
	11th to 20th	Day	8% 2 4 9% 29% 48%	2282
	21st to end	Day	10% 2 4 11% 27% 46%	2405
August	1st to 10th	Day	10% 2 2 10% 27% 50%	2251
	11th to 20th	Day	7% 1 2 9% 33% 48%	2122
	21st to end	Day	9% 1 2 9% 36% 44%	2376
September	1st to 10th	Day	6% 1 4 8% 28% 53%	2160
	11th to 20th	Day	10% 2 3 17% 39% 30%	2160
	21st to end	Day	10% 2 3 17% 39% 29%	1963
October	1st to 10th	Day	14% 4 5% 20% 23% 34%	1800
	11th to 20th	Day	17% 2 6% 18% 28% 28%	1800
	21st to end	Day	17% 3 6% 18% 28% 28%	1980
November	1st to 10th	Day	22% 3 8% 18% 31% 17%	1798
	11th to 20th	Day	24% 5% 9% 21% 26% 16%	1710
	21st to end	Day	26% 5% 6% 18% 26% 18%	1710
December	1st to 10th	Day	32% 6% 9% 18% 21% 14%	1554
	11th to 20th	Day	50% 5% 8% 17% 14% 7%	1928
	21st to end	Day	42% 9% 12% 20% 13% 4	2794
January	1st to 10th	Night	30% 9% 14% 27% 18% 3	4237
	11th to 20th	Night	38% 8% 12% 21% 11% 9%	4110
	21st to end	Night	40% 8% 12% 16% 17% 7%	4521
February	1st to 10th	Night	32% 4 8% 19% 24% 13%	2441
	11th to 20th	Night	26% 5% 8% 23% 28% 10%	2219
	21st to end	Night	28% 6% 10% 25% 24% 8%	1884
March	1st to 10th	Night	39% 9% 12% 20% 16% 4	3594
	11th to 20th	Night	20% 6% 12% 28% 22% 11%	3490
	21st to end	Night	31% 9% 16% 24% 17% 4	3683
April	1st to 10th	Night	23% 4 15% 27% 20% 11%	1900
	11th to 20th	Night	19% 3 11% 30% 27% 10%	1779
	21st to end	Night	16% 5% 9% 31% 32% 8%	1800
May	1st to 10th	Night	13% 4 11% 24% 32% 16%	1800
	11th to 20th	Night	12% 2 8% 28% 38% 12%	1642
	21st to end	Night	13% 4 11% 30% 31% 12%	1552
June	1st to 10th	Night	12% 3 13% 21% 30% 21%	1440
	11th to 20th	Night	7% 2 5% 17% 38% 32%	1440
	21st to end	Night	3 1 2 12% 34% 47%	1440
July	1st to 10th	Night	4 1 3 8% 29% 55%	1400
	11th to 20th	Night	7% 1 3 10% 29% 50%	1550
	21st to end	Night	10% 2 3 12% 31% 43%	1674
August	1st to 10th	Night	8% 2 2 10% 30% 49%	1662
	11th to 20th	Night	6% 2 2 8% 31% 51%	1780
	21st to end	Night	7% 1 2 9% 34% 47%	1980
September	1st to 10th	Night	6% 2 3 7% 27% 55%	1800
	11th to 20th	Night	9% 2 3 17% 33% 37%	1800
	21st to end	Night	8% 2 4 16% 40% 31%	1992
October	1st to 10th	Night	13% 3 6% 21% 24% 32%	2160
	11th to 20th	Night	15% 3 8% 18% 30% 27%	2160
	21st to end	Night	15% 3 5% 18% 31% 28%	2376
November	1st to 10th	Night	18% 4 8% 20% 30% 20%	2281
	11th to 20th	Night	21% 5% 10% 19% 27% 18%	2470
	21st to end	Night	24% 4 11% 17% 27% 17%	2470
December	1st to 10th	Night	30% 6% 9% 17% 24% 15%	2622
	11th to 20th	Night	48% 6% 9% 14% 16% 7%	3276
	21st to end	Night	42% 9% 13% 18% 13% 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	15% 10% 23% 25% 21% 7%	284
	11th to 20th	Day	8% 8% 20% 27% 26% 10%	370
	21st to end	Day	12% 6% 20% 26% 25% 11%	407
February	1st to 10th	Day	11% 12% 19% 23% 21% 13%	383
	11th to 20th	Day	11% 10% 22% 27% 24% 7%	455
	21st to end	Day	10% 10% 21% 34% 21% 4	382
March	1st to 10th	Day	10% 14% 22% 33% 20% 2	460
	11th to 20th	Day	11% 10% 22% 30% 21% 7%	460
	21st to end	Day	10% 11% 26% 33% 14% 7%	506
April	1st to 10th	Day	10% 9% 25% 29% 18% 10%	457
	11th to 20th	Day	7% 12% 27% 29% 17% 8%	412
	21st to end	Day	4 9% 28% 30% 17% 12%	420
May	1st to 10th	Day	4 7% 26% 33% 19% 11%	423
	11th to 20th	Day	3 7% 21% 35% 20% 13%	448
	21st to end	Day	3 9% 19% 31% 21% 16%	485
June	1st to 10th	Day	2 6% 16% 30% 27% 19%	450
	11th to 20th	Day	1 3 20% 34% 25% 16%	450
	21st to end	Day	1 14% 32% 30% 22%	450
July	1st to 10th	Day	9% 35% 32% 24%	446
	11th to 20th	Day	2 3 32% 33% 30%	444
	21st to end	Day	1 8% 31% 36% 25%	487
August	1st to 10th	Day	2 10% 30% 36% 22%	447
	11th to 20th	Day	1 7% 27% 37% 28%	437
	21st to end	Day	1 6% 25% 38% 29%	495
September	1st to 10th	Day	1 2 10% 26% 32% 29%	450
	11th to 20th	Day	2 1 14% 27% 36% 20%	450
	21st to end	Day	3 10% 30% 39% 18%	450
October	1st to 10th	Day	2 3 17% 30% 32% 14%	450
	11th to 20th	Day	3 5% 17% 26% 34% 15%	450
	21st to end	Day	4 3 17% 27% 33% 17%	495
November	1st to 10th	Day	5% 6% 14% 27% 32% 16%	394
	11th to 20th	Day	5% 2 17% 27% 37% 11%	270
	21st to end	Day	6% 3 14% 31% 32% 13%	270
December	1st to 10th	Day	11% 7% 17% 27% 28% 10%	196
	11th to 20th	Day	11% 8% 17% 23% 27% 14%	180
	21st to end	Day	14% 8% 26% 24% 21% 8%	198
January	1st to 10th	Night	11% 3 14% 42% 26% 4	760
	11th to 20th	Night	9% 1 10% 45% 31% 4	760
	21st to end	Night	12% 1 11% 45% 27% 3	836
February	1st to 10th	Night	11% 4 12% 39% 29% 5%	760
	11th to 20th	Night	9% 3 14% 43% 28% 4	744
	21st to end	Night	9% 4 14% 50% 21% 3	628
March	1st to 10th	Night	10% 4 15% 45% 23% 3	760
	11th to 20th	Night	7% 2 16% 41% 30% 5%	760
	21st to end	Night	8% 3 19% 40% 27% 3	836
April	1st to 10th	Night	6% 4 18% 41% 27% 3	760
	11th to 20th	Night	5% 6% 21% 36% 28% 5%	711
	21st to end	Night	3 4 23% 34% 29% 7%	720
May	1st to 10th	Night	3 3 17% 38% 32% 7%	720
	11th to 20th	Night	2 2 15% 35% 40% 5%	578
	21st to end	Night	3 3 15% 40% 33% 7%	389
June	1st to 10th	Night	3 3 9% 42% 39% 4	360
	11th to 20th	Night	1 1 11% 37% 43% 6%	360
	21st to end	Night	6% 37% 51% 7%	360
July	1st to 10th	Night	2 29% 59% 9%	350
	11th to 20th	Night	1 1 14% 61% 24%	506
	21st to end	Night	2 1 16% 59% 23%	591
August	1st to 10th	Night	1 2 27% 56% 14%	597
	11th to 20th	Night	1 2 25% 59% 14%	712
	21st to end	Night	1 1 21% 61% 15%	792
September	1st to 10th	Night	1 3 27% 56% 12%	720
	11th to 20th	Night	2 4 36% 46% 12%	720
	21st to end	Night	2 1 6% 31% 51% 10%	720
October	1st to 10th	Night	3 1 8% 40% 39% 9%	720
	11th to 20th	Night	4 3 8% 35% 42% 8%	720
	21st to end	Night	3 1 9% 35% 42% 10%	792
November	1st to 10th	Night	5% 1 9% 39% 40% 6%	740
	11th to 20th	Night	6% 1 9% 43% 37% 5%	760
	21st to end	Night	5% 3 9% 43% 35% 5%	760
December	1st to 10th	Night	11% 3 11% 42% 29% 4	760
	11th to 20th	Night	12% 1 10% 45% 28% 4	760
	21st to end	Night	11% 3 13% 46% 24% 2	836

Page generated at 2024-04-07 06:28:11. Version ac07

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