San Jacinto Battleground State Historic Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the San Jacinto Battleground State Historic Site clear sky chart from 2005-11-06 to 2025-12-18.

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	13% 6% 2 6% 5% 5% 5% 4 6% 8% 40%	126925
	Night	15% 7% 2 5% 4 3 4 3 5% 7% 45%	124335
Transparency	Day	38% 9% 13% 19% 15% 7%	130560
	Night	37% 7% 13% 19% 16% 8%	128750
Seeing	Day	12% 6% 19% 27% 24% 12%	16286
	Night	15% 5% 19% 32% 25% 3	26140

By Month

Percentage Cloud Cover SE (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	22% 11% 3 6% 4 3 3 2 3 4 39%	4077
	11th to 20th	Day	16% 6% 2 5% 4 3 3 2 3 6% 50%	4080
	21st to end	Day	29% 8% 2 6% 4 3 3 3 4 6% 32%	4488
February	1st to 10th	Day	22% 9% 3 7% 4 4 4 4 4 6% 34%	1870
	11th to 20th	Day	23% 9% 3 6% 4 3 4 3 4 6% 36%	2000
	21st to end	Day	21% 8% 2 7% 3 4 4 3 4 5% 38%	1815
March	1st to 10th	Day	18% 8% 3 7% 4 4 4 4 5% 7% 36%	4936
	11th to 20th	Day	14% 5% 2 7% 4 5% 4 3 4 5% 45%	4980
	21st to end	Day	20% 7% 2 7% 5% 4 4 3 5% 6% 39%	5462
April	1st to 10th	Day	16% 7% 3 8% 5% 4 5% 4 6% 5% 38%	2200
	11th to 20th	Day	16% 7% 2 7% 5% 4 4 3 5% 6% 39%	2349
	21st to end	Day	11% 7% 2 7% 5% 4 5% 5% 6% 7% 42%	2400
May	1st to 10th	Day	18% 8% 3 8% 6% 5% 5% 5% 6% 7% 28%	5405
	11th to 20th	Day	11% 6% 3 7% 5% 4 4 4 5% 8% 45%	5856
	21st to end	Day	9% 6% 2 6% 5% 5% 6% 5% 7% 11% 36%	6434
June	1st to 10th	Day	6% 5% 2 7% 5% 4 6% 5% 9% 10% 42%	2600
	11th to 20th	Day	5% 4 2 6% 6% 6% 7% 6% 9% 10% 39%	2600
	21st to end	Day	6% 6% 3 7% 7% 8% 9% 6% 8% 10% 31%	2600
July	1st to 10th	Day	7% 5% 2 7% 6% 7% 7% 7% 9% 14% 29%	5900
	11th to 20th	Day	6% 6% 3 9% 7% 7% 7% 5% 9% 12% 30%	5900
	21st to end	Day	10% 7% 3 7% 5% 6% 5% 5% 7% 10% 35%	6422
August	1st to 10th	Day	2 2 1 3 4 4 5% 5% 8% 11% 56%	4234
	11th to 20th	Day	3 2 1 5% 4 5% 6% 5% 9% 14% 48%	3951
	21st to end	Day	8% 4 2 6% 6% 7% 7% 6% 9% 9% 36%	4297
September	1st to 10th	Day	7% 6% 2 7% 5% 6% 7% 6% 8% 10% 36%	2200
	11th to 20th	Day	14% 6% 2 7% 5% 5% 5% 4 7% 7% 37%	2200
	21st to end	Day	10% 5% 2 6% 4 4 4 4 6% 8% 49%	2200
October	1st to 10th	Day	7% 4 2 4 3 3 4 4 6% 8% 56%	2057
	11th to 20th	Day	10% 4 2 5% 4 4 3 3 5% 6% 54%	2000
	21st to end	Day	12% 5% 2 5% 3 3 4 3 3 6% 54%	2200
November	1st to 10th	Day	10% 5% 2 5% 5% 6% 4 3 6% 6% 48%	2058
	11th to 20th	Day	11% 5% 2 7% 4 5% 4 4 6% 5% 47%	2100
	21st to end	Day	16% 7% 2 7% 4 4 4 3 5% 6% 42%	2082
December	1st to 10th	Day	24% 9% 2 6% 4 3 3 2 5% 7% 35%	3030
	11th to 20th	Day	13% 7% 2 7% 5% 4 4 4 5% 6% 43%	3454
	21st to end	Day	16% 6% 2 5% 4 4 4 3 5% 6% 46%	4488
January	1st to 10th	Night	20% 7% 2 6% 3 3 4 3 4 6% 42%	5888
	11th to 20th	Night	17% 8% 2 5% 3 3 3 2 4 5% 48%	5900
	21st to end	Night	30% 9% 2 6% 3 3 3 2 4 6% 32%	6490
February	1st to 10th	Night	21% 9% 3 6% 4 3 4 3 4 6% 38%	2546
	11th to 20th	Night	22% 10% 3 5% 3 2 3 2 4 5% 41%	2284
	21st to end	Night	23% 8% 2 6% 4 3 2 3 4 5% 39%	1815
March	1st to 10th	Night	24% 10% 3 6% 3 3 3 3 4 5% 36%	4919
	11th to 20th	Night	19% 8% 3 6% 4 3 3 2 4 5% 43%	4980
	21st to end	Night	18% 9% 2 6% 4 4 3 3 4 5% 41%	5467
April	1st to 10th	Night	17% 6% 2 7% 5% 4 4 4 6% 6% 39%	2200
	11th to 20th	Night	19% 6% 2 4 4 3 3 3 6% 6% 45%	1997
	21st to end	Night	14% 7% 2 6% 4 4 4 4 6% 7% 43%	2000
May	1st to 10th	Night	26% 9% 2 6% 5% 4 4 3 5% 7% 27%	4490
	11th to 20th	Night	16% 7% 2 6% 4 4 4 4 5% 7% 41%	4053
	21st to end	Night	16% 8% 3 6% 5% 5% 5% 5% 8% 11% 30%	4443
June	1st to 10th	Night	5% 3 1 4 3 3 4 3 6% 12% 56%	1800
	11th to 20th	Night	6% 3 1 3 3 3 3 4 7% 12% 54%	1800
	21st to end	Night	6% 5% 2 5% 6% 4 5% 5% 9% 11% 44%	1800
July	1st to 10th	Night	5% 5% 3 5% 4 4 5% 4 8% 14% 43%	4078
	11th to 20th	Night	3 3 2 6% 5% 5% 6% 5% 6% 11% 49%	4077
	21st to end	Night	7% 5% 2 7% 4 5% 5% 4 6% 9% 45%	4449
August	1st to 10th	Night	1 1 1 2 2 2 3 3 5% 10% 69%	2926
	11th to 20th	Night	2 2 1 3 2 3 3 4 7% 14% 60%	3100
	21st to end	Night	5% 3 1 4 4 5% 5% 5% 9% 12% 47%	3586
September	1st to 10th	Night	6% 5% 3 5% 5% 4 4 5% 7% 11% 46%	2195
	11th to 20th	Night	11% 6% 2 6% 3 4 4 3 5% 9% 46%	2200
	21st to end	Night	9% 4 2 5% 3 3 3 4 6% 7% 54%	2200
October	1st to 10th	Night	5% 3 2 4 4 3 3 3 5% 6% 61%	2320
	11th to 20th	Night	9% 3 1 3 3 3 3 3 5% 7% 61%	2400
	21st to end	Night	11% 5% 2 4 3 3 3 3 3 5% 60%	2640
November	1st to 10th	Night	11% 5% 1 4 3 4 3 3 5% 6% 55%	2460
	11th to 20th	Night	11% 5% 2 5% 3 4 3 3 5% 6% 54%	2520
	21st to end	Night	16% 6% 2 6% 4 3 4 3 4 5% 46%	2534
December	1st to 10th	Night	22% 10% 4 7% 5% 3 3 2 4 6% 34%	4380
	11th to 20th	Night	15% 9% 3 7% 4 4 4 3 4 5% 43%	4908
	21st to end	Night	16% 7% 2 6% 3 4 3 3 3 6% 47%	6490

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	50% 4 4 18% 17% 7%	4078
	11th to 20th	Day	37% 4 5% 20% 22% 12%	4080
	21st to end	Day	53% 3 3 13% 15% 12%	4488
February	1st to 10th	Day	50% 6% 6% 13% 15% 11%	1870
	11th to 20th	Day	51% 6% 6% 13% 16% 8%	2010
	21st to end	Day	48% 6% 8% 14% 14% 10%	1815
March	1st to 10th	Day	45% 8% 9% 14% 13% 11%	4936
	11th to 20th	Day	38% 7% 7% 11% 20% 16%	4980
	21st to end	Day	44% 7% 8% 18% 19% 4	5464
April	1st to 10th	Day	45% 8% 8% 16% 14% 9%	2200
	11th to 20th	Day	44% 7% 9% 15% 16% 9%	2349
	21st to end	Day	37% 8% 11% 18% 19% 6%	2400
May	1st to 10th	Day	49% 10% 11% 17% 10% 3	5440
	11th to 20th	Day	36% 8% 12% 21% 20% 2	5860
	21st to end	Day	36% 11% 16% 27% 9% 1	6447
June	1st to 10th	Day	32% 12% 17% 24% 15% 1	2600
	11th to 20th	Day	33% 11% 16% 25% 13% 2	2600
	21st to end	Day	40% 14% 18% 20% 7%	2600
July	1st to 10th	Day	37% 13% 29% 18% 2	5836
	11th to 20th	Day	40% 13% 26% 17% 3	5831
	21st to end	Day	41% 11% 19% 24% 6%	6240
August	1st to 10th	Day	18% 10% 17% 39% 16%	4220
	11th to 20th	Day	22% 12% 33% 29% 4 1	3989
	21st to end	Day	37% 15% 16% 18% 13% 1	4296
September	1st to 10th	Day	38% 14% 15% 16% 13% 4	2200
	11th to 20th	Day	41% 11% 12% 18% 15% 3	2200
	21st to end	Day	32% 8% 14% 19% 16% 11%	2200
October	1st to 10th	Day	19% 5% 7% 15% 16% 38%	3343
	11th to 20th	Day	21% 5% 7% 18% 37% 14%	3240
	21st to end	Day	25% 6% 6% 17% 34% 13%	3538
November	1st to 10th	Day	34% 7% 10% 19% 21% 9%	2058
	11th to 20th	Day	36% 7% 10% 14% 20% 13%	2100
	21st to end	Day	41% 6% 9% 15% 18% 10%	2082
December	1st to 10th	Day	49% 5% 7% 15% 20% 4	3030
	11th to 20th	Day	39% 7% 10% 15% 20% 9%	3452
	21st to end	Day	38% 6% 6% 16% 22% 11%	4488
January	1st to 10th	Night	42% 6% 7% 20% 18% 8%	5888
	11th to 20th	Night	39% 4 5% 17% 24% 11%	5900
	21st to end	Night	53% 4 4 13% 15% 10%	6490
February	1st to 10th	Night	47% 4 8% 11% 16% 13%	2546
	11th to 20th	Night	46% 5% 7% 13% 18% 11%	2284
	21st to end	Night	48% 5% 6% 14% 16% 11%	1815
March	1st to 10th	Night	49% 6% 7% 13% 15% 10%	4919
	11th to 20th	Night	43% 6% 7% 13% 16% 15%	4980
	21st to end	Night	44% 6% 8% 15% 19% 8%	5467
April	1st to 10th	Night	44% 7% 10% 16% 14% 9%	2200
	11th to 20th	Night	40% 5% 10% 17% 15% 13%	1997
	21st to end	Night	38% 8% 10% 21% 17% 6%	2000
May	1st to 10th	Night	53% 8% 11% 16% 9% 3	4520
	11th to 20th	Night	39% 8% 12% 21% 16% 3	4054
	21st to end	Night	42% 13% 18% 21% 6% 1	4452
June	1st to 10th	Night	21% 8% 23% 31% 17%	1800
	11th to 20th	Night	22% 7% 20% 31% 17% 3	1800
	21st to end	Night	30% 11% 23% 26% 10%	1800
July	1st to 10th	Night	30% 9% 36% 23% 2	4035
	11th to 20th	Night	28% 10% 31% 27% 4	4026
	21st to end	Night	34% 11% 21% 29% 5%	4320
August	1st to 10th	Night	10% 7% 20% 48% 14%	2916
	11th to 20th	Night	14% 9% 37% 35% 4	3128
	21st to end	Night	28% 15% 21% 26% 9% 1	3586
September	1st to 10th	Night	31% 11% 23% 19% 13% 4	2195
	11th to 20th	Night	35% 9% 16% 20% 16% 4	2200
	21st to end	Night	29% 8% 14% 22% 18% 10%	2200
October	1st to 10th	Night	17% 5% 9% 18% 17% 35%	3788
	11th to 20th	Night	15% 5% 6% 23% 33% 18%	3899
	21st to end	Night	20% 4 7% 15% 38% 16%	4252
November	1st to 10th	Night	30% 6% 11% 21% 21% 10%	2460
	11th to 20th	Night	32% 4 10% 20% 21% 13%	2520
	21st to end	Night	40% 5% 8% 20% 18% 9%	2534
December	1st to 10th	Night	52% 4 7% 15% 16% 6%	4380
	11th to 20th	Night	42% 6% 9% 11% 19% 13%	4909
	21st to end	Night	39% 6% 7% 13% 27% 8%	6490

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	25% 10% 35% 22% 8% 1	300
	11th to 20th	Day	21% 14% 30% 27% 7% 2	300
	21st to end	Day	20% 15% 31% 25% 9%	330
February	1st to 10th	Day	21% 14% 34% 25% 7%	300
	11th to 20th	Day	27% 17% 28% 21% 6% 1	300
	21st to end	Day	22% 16% 39% 19% 4	249
March	1st to 10th	Day	27% 15% 30% 23% 5%	300
	11th to 20th	Day	15% 17% 44% 17% 4 2	300
	21st to end	Day	18% 17% 32% 23% 9% 1	330
April	1st to 10th	Day	19% 16% 32% 24% 8% 1	300
	11th to 20th	Day	20% 13% 29% 24% 12% 1	467
	21st to end	Day	16% 7% 31% 29% 16% 1	500
May	1st to 10th	Day	14% 10% 30% 30% 16% 1	503
	11th to 20th	Day	11% 5% 29% 32% 20% 3	719
	21st to end	Day	10% 4 25% 37% 20% 3	789
June	1st to 10th	Day	7% 2 12% 35% 32% 12%	730
	11th to 20th	Day	7% 3 11% 37% 30% 13%	730
	21st to end	Day	7% 2 9% 29% 33% 19%	730
July	1st to 10th	Day	7% 2 7% 24% 37% 22%	721
	11th to 20th	Day	5% 1 4 22% 40% 27%	718
	21st to end	Day	6% 2 5% 23% 40% 25%	794
August	1st to 10th	Day	2 1 3 21% 43% 30%	726
	11th to 20th	Day	3 1 2 15% 44% 36%	585
	21st to end	Day	10% 2 5% 16% 36% 31%	581
September	1st to 10th	Day	7% 3 8% 23% 33% 25%	330
	11th to 20th	Day	10% 2 7% 23% 35% 23%	330
	21st to end	Day	9% 1 6% 29% 35% 18%	330
October	1st to 10th	Day	6% 1 8% 37% 35% 12%	330
	11th to 20th	Day	8% 4 14% 37% 27% 10%	330
	21st to end	Day	16% 7% 23% 29% 19% 6%	363
November	1st to 10th	Day	13% 6% 20% 31% 23% 6%	330
	11th to 20th	Day	14% 6% 21% 39% 17% 3	330
	21st to end	Day	14% 17% 30% 23% 14% 2	330
December	1st to 10th	Day	22% 7% 30% 24% 13% 5%	330
	11th to 20th	Day	15% 12% 31% 29% 12% 2	321
	21st to end	Day	19% 9% 35% 25% 10% 2	330
January	1st to 10th	Night	22% 8% 29% 31% 9%	1000
	11th to 20th	Night	22% 9% 27% 34% 8% 1	1000
	21st to end	Night	22% 8% 27% 35% 7%	1100
February	1st to 10th	Night	25% 8% 29% 32% 5%	946
	11th to 20th	Night	26% 10% 29% 29% 7%	730
	21st to end	Night	25% 10% 32% 27% 5%	495
March	1st to 10th	Night	24% 7% 30% 32% 7%	600
	11th to 20th	Night	19% 10% 28% 35% 9% 1	600
	21st to end	Night	17% 7% 29% 36% 11% 1	660
April	1st to 10th	Night	18% 8% 31% 37% 7%	600
	11th to 20th	Night	21% 9% 24% 35% 11%	593
	21st to end	Night	16% 7% 24% 39% 14% 1	600
May	1st to 10th	Night	16% 8% 24% 42% 10%	600
	11th to 20th	Night	12% 4 22% 41% 19% 2	591
	21st to end	Night	7% 4 19% 39% 28% 2	650
June	1st to 10th	Night	5% 1 6% 43% 40% 4	600
	11th to 20th	Night	6% 1 7% 40% 42% 4	600
	21st to end	Night	6% 1 9% 24% 52% 8%	600
July	1st to 10th	Night	5% 2 3 26% 53% 11%	585
	11th to 20th	Night	4 1 2 21% 60% 12%	582
	21st to end	Night	4 1 3 22% 60% 10%	657
August	1st to 10th	Night	2 1 2 15% 68% 12%	597
	11th to 20th	Night	4 1 2 15% 67% 11%	594
	21st to end	Night	5% 2 3 20% 56% 15%	660
September	1st to 10th	Night	7% 2 7% 22% 52% 11%	600
	11th to 20th	Night	13% 1 4 23% 51% 9%	600
	21st to end	Night	10% 1 7% 29% 46% 7%	600
October	1st to 10th	Night	5% 1 9% 36% 42% 7%	720
	11th to 20th	Night	9% 2 16% 40% 30% 3	800
	21st to end	Night	12% 6% 19% 36% 24% 3	880
November	1st to 10th	Night	12% 3 16% 40% 26% 3	820
	11th to 20th	Night	12% 6% 20% 41% 20% 1	840
	21st to end	Night	17% 6% 27% 33% 15% 1	854
December	1st to 10th	Night	21% 7% 25% 31% 15% 1	1050
	11th to 20th	Night	21% 8% 24% 35% 11%	1036
	21st to end	Night	20% 8% 29% 34% 9%	1100

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