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 2024-11-05.

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	3 3 1 4 3 3 3 3 4 6% 67%	104832
	Night	4 4 1 4 3 3 3 3 4 6% 65%	102989
Transparency	Day	19% 4 7% 18% 26% 27%	104590
	Night	21% 4 8% 19% 25% 23%	102822
Seeing	Day	5% 5% 17% 29% 27% 16%	15547
	Night	5% 2 10% 37% 38% 7%	25057

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 7% 6% 6% 5% 4 7% 7% 47%	2708
	11th to 20th	Day	7% 7% 3 7% 6% 5% 6% 4 6% 7% 41%	2860
	21st to end	Day	11% 8% 3 7% 5% 5% 6% 5% 7% 8% 35%	3146
February	1st to 10th	Day	9% 6% 2 6% 4 4 3 4 6% 7% 50%	1737
	11th to 20th	Day	7% 5% 2 6% 5% 4 4 4 6% 7% 50%	1850
	21st to end	Day	8% 6% 2 7% 4 4 5% 4 5% 8% 48%	1570
March	1st to 10th	Day	6% 5% 3 8% 6% 7% 7% 5% 8% 9% 37%	3278
	11th to 20th	Day	4 3 2 4 4 4 4 3 5% 7% 59%	3490
	21st to end	Day	6% 5% 2 7% 6% 6% 7% 5% 7% 7% 42%	3969
April	1st to 10th	Day	6% 5% 2 5% 3 4 4 4 6% 8% 54%	2280
	11th to 20th	Day	4 5% 2 5% 4 3 4 4 6% 6% 59%	2249
	21st to end	Day	4 3 1 4 3 3 3 3 4 7% 66%	2280
May	1st to 10th	Day	2 2 1 3 2 2 2 2 3 4 78%	3800
	11th to 20th	Day	1 1 1 3 2 2 3 2 3 5% 76%	3988
	21st to end	Day	1 2 1 2 2 1 2 2 3 5% 81%	4813
June	1st to 10th	Day	2 2 1 2 2 2 3 2 5% 8% 73%	2660
	11th to 20th	Day	1 1 2 1 1 1 2 4 85%	2660
	21st to end	Day	1 1 1 1 2 1 3 4 85%	2660
July	1st to 10th	Day	1 1 1 1 1 2 4 89%	4420
	11th to 20th	Day	1 1 1 2 1 2 2 2 3 4 81%	4122
	21st to end	Day	1 2 1 1 2 2 3 4 83%	4455
August	1st to 10th	Day	1 1 1 2 1 1 2 2 3 5% 81%	3978
	11th to 20th	Day	1 1 1 1 1 1 2 3 90%	3724
	21st to end	Day	1 1 1 1 2 1 3 4 86%	4180
September	1st to 10th	Day	1 1 1 1 2 1 3 5% 84%	2280
	11th to 20th	Day	1 2 1 2 2 2 2 2 3 5% 79%	2280
	21st to end	Day	1 2 2 2 2 2 4 5% 78%	2071
October	1st to 10th	Day	1 1 1 1 2 2 3 4 5% 7% 73%	3180
	11th to 20th	Day	1 2 1 3 3 2 3 2 4 5% 74%	3161
	21st to end	Day	2 3 1 4 3 4 4 3 6% 7% 64%	3448
November	1st to 10th	Day	3 4 1 4 4 4 4 3 5% 7% 62%	1839
	11th to 20th	Day	3 5% 2 5% 4 4 4 4 6% 6% 58%	1710
	21st to end	Day	4 4 2 5% 4 4 3 4 5% 6% 59%	1710
December	1st to 10th	Day	6% 7% 2 6% 4 4 4 4 5% 9% 48%	1554
	11th to 20th	Day	14% 9% 4 9% 6% 4 5% 3 5% 8% 33%	1928
	21st to end	Day	12% 9% 3 10% 5% 5% 5% 4 6% 8% 34%	2794
January	1st to 10th	Night	7% 6% 2 9% 6% 5% 5% 3 5% 6% 47%	4237
	11th to 20th	Night	7% 8% 3 9% 5% 5% 5% 4 6% 7% 41%	4110
	21st to end	Night	12% 8% 3 7% 5% 5% 5% 4 5% 6% 40%	4521
February	1st to 10th	Night	8% 5% 2 5% 4 3 4 3 5% 6% 53%	2441
	11th to 20th	Night	5% 5% 2 5% 3 3 4 3 5% 8% 57%	2218
	21st to end	Night	7% 4 2 5% 4 4 3 3 5% 7% 57%	1884
March	1st to 10th	Night	6% 7% 4 8% 6% 6% 7% 5% 7% 8% 37%	3594
	11th to 20th	Night	3 3 1 4 3 3 4 4 6% 6% 62%	3490
	21st to end	Night	6% 6% 2 6% 5% 5% 5% 4 6% 8% 47%	3683
April	1st to 10th	Night	5% 3 1 4 4 3 3 4 6% 7% 60%	1900
	11th to 20th	Night	4 4 1 3 2 2 3 3 4 6% 68%	1879
	21st to end	Night	2 2 1 3 3 3 3 2 3 8% 70%	1900
May	1st to 10th	Night	1 1 1 2 2 1 2 2 3 6% 80%	3180
	11th to 20th	Night	1 2 1 4 3 3 3 2 3 5% 73%	2908
	21st to end	Night	1 1 1 1 1 2 1 3 4 83%	2762
June	1st to 10th	Night	2 1 1 2 1 2 3 3 4 6% 76%	1520
	11th to 20th	Night	1 1 1 1 1 2 3 5% 85%	1520
	21st to end	Night	1 1 1 1 1 1 4 90%	1520
July	1st to 10th	Night	1 1 1 2 3 92%	2540
	11th to 20th	Night	1 1 1 2 2 2 2 4 86%	2843
	21st to end	Night	1 1 1 1 1 1 2 2 3 5% 83%	3109
August	1st to 10th	Night	1 1 1 1 2 2 3 4 84%	2964
	11th to 20th	Night	1 1 1 1 1 2 2 90%	3126
	21st to end	Night	1 1 1 1 1 1 2 3 88%	3498
September	1st to 10th	Night	1 1 1 1 1 1 1 2 4 86%	1900
	11th to 20th	Night	1 1 1 2 2 2 2 2 3 4 80%	1900
	21st to end	Night	1 1 1 2 1 1 2 1 3 4 83%	2104
October	1st to 10th	Night	1 2 1 1 1 2 3 3 5% 6% 75%	3800
	11th to 20th	Night	1 3 1 3 1 2 3 3 4 4 75%	3777
	21st to end	Night	1 2 1 4 2 2 2 3 4 6% 72%	4121
November	1st to 10th	Night	3 3 1 4 2 3 3 3 5% 7% 67%	2340
	11th to 20th	Night	3 4 1 4 3 3 3 3 5% 6% 63%	2470
	21st to end	Night	4 3 2 4 4 4 4 4 6% 7% 59%	2470
December	1st to 10th	Night	7% 6% 2 6% 3 4 5% 4 5% 7% 52%	2622
	11th to 20th	Night	12% 10% 3 9% 6% 5% 5% 4 7% 6% 34%	3276
	21st to end	Night	10% 9% 4 10% 6% 6% 5% 4 6% 6% 33%	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% 24% 22% 9%	2280
	11th to 20th	Day	24% 6% 9% 26% 26% 9%	2252
	21st to end	Day	18% 5% 10% 27% 30% 9%	2280
May	1st to 10th	Day	13% 3 6% 23% 35% 20%	3800
	11th to 20th	Day	12% 3 6% 29% 35% 16%	3991
	21st to end	Day	9% 3 6% 30% 42% 11%	4814
June	1st to 10th	Day	12% 3 10% 22% 33% 19%	2660
	11th to 20th	Day	7% 2 5% 14% 41% 32%	2660
	21st to end	Day	6% 2 3 10% 32% 48%	2660
July	1st to 10th	Day	4 1 1 4 16% 74%	4351
	11th to 20th	Day	9% 2 2 5% 19% 63%	4052
	21st to end	Day	8% 1 2 8% 28% 53%	4315
August	1st to 10th	Day	9% 1 1 13% 31% 45%	3963
	11th to 20th	Day	5% 1 1 5% 31% 57%	3760
	21st to end	Day	7% 1 1 9% 30% 51%	4179
September	1st to 10th	Day	6% 1 3 8% 29% 53%	2280
	11th to 20th	Day	10% 2 3 17% 39% 29%	2280
	21st to end	Day	10% 2 3 17% 38% 30%	2071
October	1st to 10th	Day	12% 4 3 12% 24% 46%	3180
	11th to 20th	Day	16% 1 6% 19% 37% 22%	3161
	21st to end	Day	20% 2 3 15% 34% 25%	3448
November	1st to 10th	Day	22% 3 8% 19% 30% 17%	1839
	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	20% 3 11% 31% 26% 9%	1879
	21st to end	Night	16% 5% 9% 31% 31% 9%	1900
May	1st to 10th	Night	8% 3 8% 28% 32% 21%	3180
	11th to 20th	Night	17% 2 7% 30% 25% 18%	2910
	21st to end	Night	8% 3 8% 37% 34% 11%	2762
June	1st to 10th	Night	12% 3 12% 22% 31% 20%	1520
	11th to 20th	Night	7% 2 4 17% 39% 31%	1520
	21st to end	Night	4 1 2 12% 33% 48%	1520
July	1st to 10th	Night	3 2 5% 16% 74%	2500
	11th to 20th	Night	7% 1 1 6% 18% 67%	2790
	21st to end	Night	7% 1 2 9% 32% 50%	3011
August	1st to 10th	Night	7% 1 1 11% 34% 45%	2955
	11th to 20th	Night	4 1 1 4 26% 63%	3156
	21st to end	Night	6% 1 2 9% 34% 49%	3498
September	1st to 10th	Night	5% 2 3 7% 28% 55%	1900
	11th to 20th	Night	10% 2 3 16% 34% 35%	1900
	21st to end	Night	8% 2 4 15% 40% 32%	2104
October	1st to 10th	Night	11% 4 4 13% 30% 39%	3800
	11th to 20th	Night	15% 2 5% 22% 36% 21%	3777
	21st to end	Night	16% 2 3 20% 39% 20%	4121
November	1st to 10th	Night	17% 4 8% 21% 30% 19%	2340
	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% 8% 25% 28% 18% 11%	460
	11th to 20th	Day	8% 11% 26% 29% 18% 8%	452
	21st to end	Day	3 8% 28% 31% 18% 12%	460
May	1st to 10th	Day	4 7% 26% 34% 19% 10%	463
	11th to 20th	Day	3 7% 20% 35% 21% 15%	488
	21st to end	Day	3 9% 19% 31% 22% 17%	529
June	1st to 10th	Day	2 6% 15% 32% 26% 19%	490
	11th to 20th	Day	1 3 22% 33% 26% 16%	490
	21st to end	Day	1 13% 33% 29% 23%	490
July	1st to 10th	Day	8% 35% 32% 25%	486
	11th to 20th	Day	2 4 31% 32% 31%	484
	21st to end	Day	1 8% 30% 35% 26%	531
August	1st to 10th	Day	2 10% 29% 35% 23%	487
	11th to 20th	Day	1 7% 28% 37% 26%	477
	21st to end	Day	1 1 6% 26% 37% 29%	539
September	1st to 10th	Day	1 1 10% 27% 33% 28%	490
	11th to 20th	Day	2 2 16% 27% 35% 19%	490
	21st to end	Day	3 10% 29% 39% 19%	490
October	1st to 10th	Day	2 3 16% 30% 33% 16%	490
	11th to 20th	Day	3 5% 17% 26% 33% 17%	490
	21st to end	Day	4 4 17% 26% 33% 17%	539
November	1st to 10th	Day	5% 7% 15% 26% 32% 16%	411
	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% 42% 27% 3	760
	11th to 20th	Night	6% 5% 20% 35% 29% 5%	751
	21st to end	Night	3 3 23% 35% 29% 7%	760
May	1st to 10th	Night	3 3 17% 40% 31% 7%	760
	11th to 20th	Night	2 2 14% 35% 41% 5%	610
	21st to end	Night	2 3 14% 40% 34% 7%	411
June	1st to 10th	Night	3 3 9% 42% 39% 4	380
	11th to 20th	Night	1 1 12% 38% 42% 6%	380
	21st to end	Night	6% 36% 51% 7%	380
July	1st to 10th	Night	2 28% 60% 9%	370
	11th to 20th	Night	1 1 15% 61% 23%	536
	21st to end	Night	1 17% 59% 22%	624
August	1st to 10th	Night	1 2 26% 56% 14%	631
	11th to 20th	Night	1 2 27% 57% 13%	752
	21st to end	Night	1 2 22% 60% 14%	836
September	1st to 10th	Night	1 3 28% 56% 12%	760
	11th to 20th	Night	2 5% 37% 44% 12%	760
	21st to end	Night	2 1 5% 31% 50% 10%	760
October	1st to 10th	Night	3 1 7% 40% 40% 9%	760
	11th to 20th	Night	4 3 8% 35% 42% 8%	760
	21st to end	Night	3 1 9% 36% 42% 9%	836
November	1st to 10th	Night	5% 1 9% 40% 39% 6%	760
	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 2024-11-02 23:11:25. Version ac07

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