Tularcitos Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Tularcitos Observatory clear sky chart from 2005-11-06 to 2025-04-11.

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	4 4 2 4 3 3 3 3 4 6% 63%	117406
	Night	5% 6% 2 5% 4 4 4 3 5% 7% 55%	119788
Transparency	Day	21% 4 8% 17% 24% 26%	117166
	Night	24% 5% 10% 16% 21% 25%	119618
Seeing	Day	9% 10% 25% 32% 19% 5%	16030
	Night	9% 5% 14% 31% 32% 9%	25595

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	8% 7% 3 6% 4 3 4 3 4 8% 51%	3961
	11th to 20th	Day	6% 5% 3 7% 4 4 4 3 4 5% 56%	4100
	21st to end	Day	9% 8% 3 7% 5% 5% 4 4 5% 7% 42%	4510
February	1st to 10th	Day	11% 9% 2 6% 5% 5% 5% 3 4 6% 44%	1800
	11th to 20th	Day	9% 8% 3 7% 5% 4 5% 4 5% 7% 44%	1905
	21st to end	Day	11% 10% 3 5% 6% 4 4 3 7% 4 44%	1650
March	1st to 10th	Day	9% 9% 3 9% 7% 6% 7% 6% 7% 7% 31%	4821
	11th to 20th	Day	7% 7% 2 7% 5% 5% 5% 3 5% 7% 48%	5000
	21st to end	Day	7% 8% 3 8% 5% 6% 6% 4 6% 9% 38%	5611
April	1st to 10th	Day	9% 8% 3 6% 4 4 4 4 5% 8% 45%	2400
	11th to 20th	Day	7% 7% 2 4 5% 4 4 4 6% 7% 51%	2251
	21st to end	Day	6% 5% 1 4 4 3 3 3 5% 8% 57%	2280
May	1st to 10th	Day	3 4 2 3 2 2 2 2 4 5% 70%	3800
	11th to 20th	Day	2 2 1 2 1 2 2 2 3 6% 77%	4081
	21st to end	Day	3 3 1 3 2 2 3 3 4 6% 69%	4813
June	1st to 10th	Day	2 3 1 4 3 3 3 3 5% 8% 64%	2660
	11th to 20th	Day	1 2 1 2 2 1 1 2 3 5% 79%	2660
	21st to end	Day	1 1 1 2 1 1 2 1 3 4 84%	2660
July	1st to 10th	Day	1 1 1 2 2 91%	4368
	11th to 20th	Day	1 1 1 1 1 2 1 4 4 83%	4110
	21st to end	Day	1 1 1 1 2 3 4 86%	4455
August	1st to 10th	Day	1 1 1 1 1 2 2 5% 6% 78%	4091
	11th to 20th	Day	1 1 1 1 1 2 4 89%	3729
	21st to end	Day	1 1 1 2 2 3 5% 84%	4180
September	1st to 10th	Day	1 1 1 1 1 2 1 2 3 87%	2280
	11th to 20th	Day	1 3 1 3 2 2 3 2 4 8% 72%	2280
	21st to end	Day	2 2 1 2 2 2 2 2 3 5% 78%	2037
October	1st to 10th	Day	1 2 1 2 2 2 3 2 4 5% 75%	3180
	11th to 20th	Day	2 2 1 3 3 3 3 3 4 5% 73%	3161
	21st to end	Day	3 2 1 4 3 3 5% 4 6% 7% 63%	3448
November	1st to 10th	Day	7% 5% 2 4 4 3 4 3 4 8% 57%	1932
	11th to 20th	Day	6% 4 2 5% 4 4 4 4 6% 7% 54%	1800
	21st to end	Day	9% 6% 2 5% 4 4 4 3 5% 6% 53%	1740
December	1st to 10th	Day	4 5% 2 5% 4 4 4 4 5% 8% 53%	2620
	11th to 20th	Day	9% 9% 4 8% 5% 4 5% 4 6% 7% 38%	3028
	21st to end	Day	12% 10% 3 9% 6% 5% 5% 5% 6% 7% 32%	4004
January	1st to 10th	Night	6% 10% 3 6% 4 3 4 3 5% 8% 47%	5982
	11th to 20th	Night	7% 7% 2 7% 4 4 4 4 5% 6% 51%	5880
	21st to end	Night	9% 9% 3 7% 5% 5% 5% 3 5% 7% 43%	6468
February	1st to 10th	Night	10% 8% 3 7% 5% 4 4 4 5% 7% 45%	2600
	11th to 20th	Night	9% 8% 2 7% 5% 4 5% 4 6% 8% 42%	2380
	21st to end	Night	9% 9% 3 7% 5% 4 4 4 5% 7% 44%	1980
March	1st to 10th	Night	10% 16% 4 9% 6% 5% 5% 4 5% 6% 31%	5069
	11th to 20th	Night	6% 9% 2 8% 5% 5% 5% 4 5% 6% 46%	5000
	21st to end	Night	9% 12% 4 9% 5% 4 5% 4 6% 7% 34%	5363
April	1st to 10th	Night	7% 8% 2 6% 5% 5% 5% 4 7% 7% 44%	2000
	11th to 20th	Night	6% 7% 3 5% 4 4 5% 3 5% 6% 52%	1883
	21st to end	Night	4 5% 2 5% 4 3 4 5% 7% 10% 52%	1900
May	1st to 10th	Night	1 5% 2 5% 4 3 4 3 5% 8% 60%	3180
	11th to 20th	Night	2 3 1 2 3 2 3 3 5% 10% 66%	2812
	21st to end	Night	1 3 1 3 2 3 3 4 7% 8% 64%	2762
June	1st to 10th	Night	2 3 1 4 3 3 4 4 5% 8% 62%	1520
	11th to 20th	Night	2 4 2 2 3 2 5% 7% 73%	1520
	21st to end	Night	1 1 2 1 2 2 2 3 6% 80%	1520
July	1st to 10th	Night	1 1 1 3 5% 87%	2589
	11th to 20th	Night	1 1 1 1 2 2 6% 7% 79%	2860
	21st to end	Night	1 1 2 4 3 6% 7% 75%	3109
August	1st to 10th	Night	1 1 1 2 2 2 2 3 5% 7% 75%	2848
	11th to 20th	Night	1 1 1 1 2 2 3 4 85%	3121
	21st to end	Night	1 1 2 1 1 2 3 4 6% 79%	3498
September	1st to 10th	Night	1 2 2 2 2 1 2 5% 82%	1900
	11th to 20th	Night	2 3 1 3 2 2 2 3 5% 6% 72%	1900
	21st to end	Night	2 1 1 3 1 2 2 2 3 6% 77%	2138
October	1st to 10th	Night	2 2 1 2 2 2 3 2 4 5% 75%	3800
	11th to 20th	Night	2 3 1 3 3 3 4 2 5% 6% 68%	3777
	21st to end	Night	3 4 2 6% 3 3 4 3 4 7% 63%	4121
November	1st to 10th	Night	6% 5% 2 4 3 3 3 4 5% 7% 57%	2365
	11th to 20th	Night	6% 6% 2 5% 4 4 4 3 6% 8% 53%	2600
	21st to end	Night	7% 5% 2 4 4 4 4 4 5% 6% 54%	2655
December	1st to 10th	Night	5% 4 2 5% 4 4 4 4 6% 6% 57%	4560
	11th to 20th	Night	9% 10% 4 8% 6% 5% 5% 5% 8% 8% 32%	5176
	21st to end	Night	9% 11% 4 11% 7% 8% 7% 5% 7% 7% 26%	6952

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	30% 6% 15% 25% 17% 8%	3961
	11th to 20th	Day	30% 6% 8% 13% 19% 24%	4100
	21st to end	Day	37% 6% 7% 13% 20% 17%	4510
February	1st to 10th	Day	39% 4 8% 14% 21% 13%	1800
	11th to 20th	Day	36% 7% 9% 19% 20% 9%	1915
	21st to end	Day	40% 6% 8% 20% 19% 8%	1650
March	1st to 10th	Day	41% 9% 12% 13% 19% 5%	4821
	11th to 20th	Day	33% 5% 10% 29% 14% 9%	5000
	21st to end	Day	34% 9% 14% 28% 13% 2	5611
April	1st to 10th	Day	35% 4 13% 24% 19% 6%	2400
	11th to 20th	Day	26% 7% 14% 25% 21% 7%	2254
	21st to end	Day	21% 6% 13% 29% 23% 7%	2280
May	1st to 10th	Day	15% 4 9% 24% 31% 17%	3800
	11th to 20th	Day	9% 3 11% 25% 35% 17%	4084
	21st to end	Day	11% 5% 14% 24% 35% 11%	4814
June	1st to 10th	Day	14% 6% 13% 23% 29% 15%	2660
	11th to 20th	Day	7% 3 9% 18% 34% 30%	2660
	21st to end	Day	7% 2 5% 11% 29% 47%	2660
July	1st to 10th	Day	2 1 3 7% 14% 74%	4300
	11th to 20th	Day	6% 2 4 6% 16% 66%	4041
	21st to end	Day	3 1 3 9% 24% 60%	4315
August	1st to 10th	Day	7% 2 3 11% 27% 50%	4076
	11th to 20th	Day	3 1 2 6% 30% 58%	3765
	21st to end	Day	5% 1 3 10% 29% 52%	4179
September	1st to 10th	Day	5% 2 5% 7% 28% 54%	2280
	11th to 20th	Day	8% 3 6% 20% 35% 27%	2280
	21st to end	Day	10% 2 4 19% 39% 26%	2037
October	1st to 10th	Day	12% 2 5% 10% 25% 46%	3180
	11th to 20th	Day	12% 3 6% 23% 34% 22%	3161
	21st to end	Day	19% 2 6% 21% 31% 21%	3448
November	1st to 10th	Day	26% 3 10% 20% 24% 17%	1932
	11th to 20th	Day	25% 5% 12% 20% 25% 14%	1800
	21st to end	Day	31% 3 8% 16% 27% 15%	1740
December	1st to 10th	Day	28% 4 7% 15% 30% 16%	2620
	11th to 20th	Day	44% 4 10% 15% 18% 9%	3028
	21st to end	Day	45% 7% 13% 20% 10% 5%	4004
January	1st to 10th	Night	28% 7% 14% 24% 21% 7%	5982
	11th to 20th	Night	30% 6% 9% 12% 19% 24%	5880
	21st to end	Night	35% 6% 8% 11% 18% 22%	6468
February	1st to 10th	Night	36% 5% 10% 14% 20% 15%	2600
	11th to 20th	Night	33% 6% 12% 18% 22% 8%	2381
	21st to end	Night	35% 5% 11% 22% 18% 8%	1980
March	1st to 10th	Night	46% 9% 10% 11% 17% 7%	5069
	11th to 20th	Night	33% 5% 12% 22% 19% 9%	5000
	21st to end	Night	36% 10% 15% 21% 15% 3	5363
April	1st to 10th	Night	31% 6% 15% 22% 18% 8%	2000
	11th to 20th	Night	27% 5% 14% 23% 21% 9%	1883
	21st to end	Night	19% 7% 15% 25% 24% 9%	1900
May	1st to 10th	Night	11% 8% 15% 20% 27% 20%	3180
	11th to 20th	Night	12% 3 16% 19% 25% 25%	2813
	21st to end	Night	10% 6% 17% 20% 30% 17%	2762
June	1st to 10th	Night	13% 6% 15% 23% 24% 20%	1520
	11th to 20th	Night	8% 5% 10% 15% 27% 35%	1520
	21st to end	Night	3 1 9% 11% 24% 51%	1520
July	1st to 10th	Night	1 1 4 8% 13% 72%	2548
	11th to 20th	Night	4 2 4 7% 16% 67%	2806
	21st to end	Night	4 2 4 9% 20% 60%	3011
August	1st to 10th	Night	7% 2 5% 10% 17% 60%	2839
	11th to 20th	Night	3 1 3 6% 18% 68%	3151
	21st to end	Night	6% 1 5% 10% 26% 51%	3498
September	1st to 10th	Night	4 2 6% 8% 22% 57%	1900
	11th to 20th	Night	9% 2 7% 18% 29% 35%	1900
	21st to end	Night	9% 3 6% 14% 36% 32%	2138
October	1st to 10th	Night	10% 3 5% 10% 20% 52%	3800
	11th to 20th	Night	14% 3 4 21% 35% 23%	3777
	21st to end	Night	18% 4 5% 18% 27% 28%	4121
November	1st to 10th	Night	21% 4 10% 19% 25% 20%	2365
	11th to 20th	Night	25% 6% 12% 18% 24% 15%	2600
	21st to end	Night	27% 6% 10% 16% 25% 17%	2655
December	1st to 10th	Night	26% 4 7% 15% 29% 20%	4560
	11th to 20th	Night	45% 4 10% 13% 17% 10%	5176
	21st to end	Night	49% 7% 12% 19% 10% 5%	6952

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	26% 16% 24% 20% 12% 1	340
	11th to 20th	Day	12% 15% 26% 29% 16% 3	400
	21st to end	Day	16% 13% 25% 28% 17% 3	440
February	1st to 10th	Day	20% 20% 23% 17% 17% 5%	400
	11th to 20th	Day	22% 14% 28% 24% 11% 1	472
	21st to end	Day	16% 14% 32% 26% 12%	414
March	1st to 10th	Day	23% 16% 29% 23% 8% 1	500
	11th to 20th	Day	21% 16% 27% 22% 11% 2	500
	21st to end	Day	19% 18% 33% 21% 7% 1	550
April	1st to 10th	Day	16% 15% 32% 23% 13% 2	500
	11th to 20th	Day	14% 17% 31% 27% 10% 2	453
	21st to end	Day	9% 15% 32% 27% 11% 5%	460
May	1st to 10th	Day	10% 11% 33% 30% 12% 3	463
	11th to 20th	Day	8% 13% 31% 28% 15% 5%	488
	21st to end	Day	9% 11% 30% 29% 16% 6%	529
June	1st to 10th	Day	4 7% 32% 32% 17% 7%	490
	11th to 20th	Day	3 8% 29% 38% 18% 5%	490
	21st to end	Day	1 4 24% 40% 24% 6%	490
July	1st to 10th	Day	1 21% 47% 23% 8%	486
	11th to 20th	Day	1 1 14% 47% 27% 11%	484
	21st to end	Day	1 15% 47% 25% 12%	531
August	1st to 10th	Day	1 2 23% 45% 20% 8%	487
	11th to 20th	Day	1 23% 42% 24% 10%	477
	21st to end	Day	2 17% 47% 25% 9%	539
September	1st to 10th	Day	1 4 17% 43% 28% 7%	490
	11th to 20th	Day	3 7% 28% 35% 21% 6%	490
	21st to end	Day	4 6% 18% 38% 28% 6%	490
October	1st to 10th	Day	3 6% 23% 36% 26% 5%	490
	11th to 20th	Day	4 8% 21% 30% 29% 8%	490
	21st to end	Day	7% 7% 24% 32% 24% 7%	539
November	1st to 10th	Day	9% 10% 20% 28% 28% 5%	468
	11th to 20th	Day	8% 10% 22% 30% 23% 7%	300
	21st to end	Day	12% 10% 22% 31% 20% 4	270
December	1st to 10th	Day	11% 16% 22% 32% 14% 6%	200
	11th to 20th	Day	15% 15% 21% 25% 19% 6%	200
	21st to end	Day	18% 19% 24% 22% 13% 4	220
January	1st to 10th	Night	15% 7% 18% 32% 21% 8%	800
	11th to 20th	Night	12% 7% 15% 33% 26% 7%	800
	21st to end	Night	16% 6% 15% 35% 23% 5%	880
February	1st to 10th	Night	18% 8% 17% 29% 23% 6%	800
	11th to 20th	Night	16% 9% 15% 32% 22% 5%	784
	21st to end	Night	16% 7% 20% 36% 19% 3	660
March	1st to 10th	Night	19% 10% 19% 30% 19% 4	800
	11th to 20th	Night	14% 9% 20% 31% 22% 6%	800
	21st to end	Night	13% 10% 21% 31% 21% 4	880
April	1st to 10th	Night	12% 8% 21% 33% 24% 3	800
	11th to 20th	Night	11% 11% 20% 28% 24% 6%	753
	21st to end	Night	6% 9% 24% 29% 23% 9%	760
May	1st to 10th	Night	4 8% 20% 35% 26% 7%	760
	11th to 20th	Night	6% 4 18% 32% 31% 9%	553
	21st to end	Night	6% 5% 18% 30% 33% 8%	411
June	1st to 10th	Night	3 6% 18% 34% 31% 9%	380
	11th to 20th	Night	2 3 15% 36% 37% 7%	380
	21st to end	Night	2 8% 34% 46% 10%	380
July	1st to 10th	Night	6% 27% 52% 14%	392
	11th to 20th	Night	1 2 18% 55% 23%	552
	21st to end	Night	1 18% 56% 24%	624
August	1st to 10th	Night	1 1 6% 26% 52% 15%	567
	11th to 20th	Night	1 1 4 34% 47% 14%	747
	21st to end	Night	1 4 22% 55% 17%	836
September	1st to 10th	Night	1 1 5% 29% 50% 14%	760
	11th to 20th	Night	3 2 9% 34% 42% 10%	760
	21st to end	Night	3 2 8% 24% 48% 15%	760
October	1st to 10th	Night	5% 3 9% 34% 39% 11%	760
	11th to 20th	Night	5% 4 10% 31% 36% 15%	760
	21st to end	Night	5% 4 8% 34% 33% 16%	836
November	1st to 10th	Night	9% 5% 13% 32% 30% 11%	780
	11th to 20th	Night	11% 5% 15% 32% 31% 8%	800
	21st to end	Night	10% 4 17% 37% 24% 8%	800
December	1st to 10th	Night	12% 7% 16% 33% 25% 7%	800
	11th to 20th	Night	20% 6% 16% 32% 22% 5%	800
	21st to end	Night	19% 12% 18% 28% 18% 5%	880

Page generated at 2025-04-08 06:17:27. Version ac07

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