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 2024-01-13.

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	12% 5% 3 5% 6% 4 5% 5% 6% 8% 40%	74968
	Night	13% 5% 2 4 4 3 4 4 5% 8% 47%	74797
Transparency	Day	39% 9% 12% 18% 15% 6%	74693
	Night	35% 7% 14% 20% 16% 8%	74592
Seeing	Day	12% 5% 17% 27% 25% 13%	13700
	Night	14% 5% 19% 33% 26% 4	23667

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	19% 6% 2 5% 6% 2 4 4 5% 4 42%	1707
	11th to 20th	Day	19% 7% 3 5% 4 2 3 3 4 6% 45%	1643
	21st to end	Day	19% 7% 3 6% 5% 3 4 4 4 6% 41%	1782
February	1st to 10th	Day	23% 8% 3 6% 5% 2 5% 3 5% 6% 34%	1683
	11th to 20th	Day	24% 8% 3 5% 4 3 4 4 4 6% 36%	1795
	21st to end	Day	22% 8% 2 5% 4 3 4 4 4 5% 38%	1628
March	1st to 10th	Day	22% 8% 3 6% 5% 2 5% 4 4 6% 35%	1980
	11th to 20th	Day	18% 7% 4 6% 5% 3 4 5% 4 6% 40%	1980
	21st to end	Day	16% 6% 3 5% 5% 3 4 4 5% 7% 43%	2178
April	1st to 10th	Day	17% 6% 3 7% 6% 3 5% 5% 6% 5% 38%	1980
	11th to 20th	Day	18% 7% 3 6% 5% 3 4 4 4 7% 39%	2111
	21st to end	Day	10% 6% 3 5% 6% 3 4 5% 6% 7% 44%	2160
May	1st to 10th	Day	11% 6% 3 7% 6% 4 6% 5% 6% 7% 40%	2160
	11th to 20th	Day	9% 5% 3 7% 6% 3 5% 6% 5% 9% 42%	2296
	21st to end	Day	8% 6% 3 6% 7% 5% 7% 7% 8% 12% 31%	2531
June	1st to 10th	Day	6% 4 2 6% 6% 3 7% 6% 8% 10% 42%	2340
	11th to 20th	Day	5% 3 2 5% 7% 4 7% 8% 9% 10% 39%	2340
	21st to end	Day	7% 5% 4 6% 8% 5% 10% 7% 8% 10% 29%	2340
July	1st to 10th	Day	10% 5% 3 5% 6% 5% 7% 9% 9% 13% 30%	2340
	11th to 20th	Day	5% 4 2 7% 6% 4 7% 8% 10% 12% 34%	2340
	21st to end	Day	5% 4 3 5% 7% 5% 8% 7% 9% 12% 35%	2546
August	1st to 10th	Day	3 3 2 4 6% 5% 6% 8% 10% 13% 41%	2328
	11th to 20th	Day	4 3 2 6% 7% 4 8% 7% 9% 12% 37%	2185
	21st to end	Day	9% 4 3 6% 6% 4 7% 7% 9% 10% 34%	2375
September	1st to 10th	Day	7% 5% 2 5% 7% 5% 7% 8% 9% 10% 35%	1980
	11th to 20th	Day	15% 6% 3 6% 6% 4 5% 6% 7% 7% 34%	1980
	21st to end	Day	10% 5% 2 5% 4 3 4 4 6% 8% 48%	1980
October	1st to 10th	Day	8% 4 2 4 4 2 4 4 6% 8% 54%	1852
	11th to 20th	Day	11% 4 2 5% 5% 3 4 4 5% 7% 51%	1800
	21st to end	Day	13% 5% 2 4 3 2 3 4 3 6% 54%	1980
November	1st to 10th	Day	10% 4 3 4 5% 4 5% 4 5% 7% 48%	1858
	11th to 20th	Day	11% 5% 3 6% 5% 3 5% 4 6% 5% 47%	1900
	21st to end	Day	17% 6% 3 6% 5% 4 4 4 5% 6% 41%	1884
December	1st to 10th	Day	16% 8% 3 5% 5% 3 4 4 5% 7% 40%	1710
	11th to 20th	Day	14% 6% 3 6% 6% 3 5% 5% 5% 6% 41%	2161
	21st to end	Day	17% 6% 2 4 4 3 4 4 5% 6% 44%	3135
January	1st to 10th	Night	19% 7% 2 5% 4 2 3 4 4 6% 44%	2458
	11th to 20th	Night	20% 6% 3 4 3 2 3 3 4 4 48%	2379
	21st to end	Night	19% 6% 3 6% 4 3 3 4 5% 5% 43%	2574
February	1st to 10th	Night	21% 8% 3 6% 5% 2 3 3 4 6% 39%	2291
	11th to 20th	Night	22% 9% 3 4 4 2 3 2 4 6% 42%	2049
	21st to end	Night	25% 7% 2 5% 5% 2 3 3 4 5% 38%	1628
March	1st to 10th	Night	21% 7% 3 5% 3 3 3 4 5% 7% 40%	1980
	11th to 20th	Night	16% 8% 3 5% 4 3 4 4 5% 6% 41%	1980
	21st to end	Night	15% 6% 3 5% 4 3 3 3 4 6% 48%	2178
April	1st to 10th	Night	15% 6% 3 6% 5% 3 4 5% 6% 7% 39%	1980
	11th to 20th	Night	19% 6% 3 4 4 2 3 4 5% 6% 44%	1795
	21st to end	Night	14% 7% 2 5% 5% 2 5% 4 6% 7% 44%	1800
May	1st to 10th	Night	12% 6% 2 5% 5% 3 4 5% 6% 8% 42%	1800
	11th to 20th	Night	10% 5% 2 5% 5% 3 4 6% 6% 7% 47%	1593
	21st to end	Night	7% 4 2 4 5% 3 6% 5% 7% 11% 45%	1745
June	1st to 10th	Night	5% 3 1 3 3 2 4 4 6% 11% 56%	1620
	11th to 20th	Night	6% 3 2 3 3 2 4 5% 7% 12% 54%	1620
	21st to end	Night	6% 4 2 5% 6% 3 6% 5% 9% 12% 43%	1620
July	1st to 10th	Night	6% 4 3 5% 5% 3 6% 6% 7% 12% 44%	1620
	11th to 20th	Night	3 3 1 3 4 3 5% 4 6% 12% 56%	1620
	21st to end	Night	3 2 2 4 4 2 5% 6% 7% 11% 52%	1772
August	1st to 10th	Night	2 1 1 2 3 2 3 3 6% 12% 65%	1611
	11th to 20th	Night	4 2 1 3 3 3 4 5% 7% 14% 53%	1715
	21st to end	Night	6% 3 2 4 5% 4 5% 5% 8% 12% 45%	1980
September	1st to 10th	Night	5% 4 3 5% 5% 3 5% 5% 7% 11% 48%	1975
	11th to 20th	Night	12% 6% 3 5% 4 3 4 5% 5% 9% 45%	1980
	21st to end	Night	9% 4 2 3 4 3 3 4 6% 7% 53%	1980
October	1st to 10th	Night	5% 3 2 4 4 2 3 4 5% 7% 60%	2088
	11th to 20th	Night	10% 3 1 3 3 2 3 3 5% 7% 58%	2160
	21st to end	Night	11% 4 2 3 3 2 3 3 4 4 59%	2376
November	1st to 10th	Night	10% 5% 1 3 4 3 3 3 5% 7% 55%	2220
	11th to 20th	Night	12% 4 2 4 4 3 4 4 5% 6% 51%	2280
	21st to end	Night	16% 6% 3 5% 5% 2 4 4 4 5% 46%	2292
December	1st to 10th	Night	18% 7% 3 5% 5% 3 4 4 4 6% 42%	2470
	11th to 20th	Night	16% 8% 3 5% 5% 3 4 4 4 6% 42%	3036
	21st to end	Night	16% 7% 2 5% 5% 3 4 4 4 6% 44%	4532

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	44% 4 7% 15% 21% 9%	1708
	11th to 20th	Day	43% 4 5% 17% 20% 12%	1643
	21st to end	Day	45% 4 6% 15% 17% 12%	1782
February	1st to 10th	Day	51% 5% 6% 13% 15% 10%	1683
	11th to 20th	Day	51% 6% 6% 13% 17% 8%	1805
	21st to end	Day	49% 6% 8% 13% 14% 10%	1628
March	1st to 10th	Day	49% 7% 9% 13% 16% 6%	1980
	11th to 20th	Day	45% 6% 9% 13% 18% 8%	1980
	21st to end	Day	40% 7% 10% 15% 22% 6%	2178
April	1st to 10th	Day	45% 7% 9% 17% 14% 8%	1980
	11th to 20th	Day	45% 6% 9% 15% 16% 9%	2111
	21st to end	Day	37% 7% 11% 18% 20% 6%	2160
May	1st to 10th	Day	40% 9% 11% 16% 17% 7%	2160
	11th to 20th	Day	37% 9% 11% 23% 16% 3	2300
	21st to end	Day	41% 11% 15% 21% 11% 1	2531
June	1st to 10th	Day	33% 11% 16% 24% 15% 1	2340
	11th to 20th	Day	32% 11% 17% 26% 12% 2	2340
	21st to end	Day	43% 14% 17% 19% 7%	2340
July	1st to 10th	Day	38% 15% 22% 21% 5%	2276
	11th to 20th	Day	34% 15% 24% 21% 6%	2271
	21st to end	Day	34% 15% 23% 24% 4 1	2405
August	1st to 10th	Day	27% 14% 23% 27% 9%	2314
	11th to 20th	Day	34% 16% 21% 24% 6% 1	2185
	21st to end	Day	38% 16% 19% 19% 7% 2	2375
September	1st to 10th	Day	36% 15% 16% 17% 12% 4	1980
	11th to 20th	Day	44% 12% 12% 15% 14% 3	1980
	21st to end	Day	33% 8% 15% 19% 16% 9%	1980
October	1st to 10th	Day	26% 7% 11% 25% 18% 13%	1852
	11th to 20th	Day	32% 7% 8% 20% 20% 14%	1800
	21st to end	Day	32% 5% 6% 16% 24% 17%	1980
November	1st to 10th	Day	34% 7% 11% 19% 20% 9%	1858
	11th to 20th	Day	37% 6% 10% 14% 20% 12%	1900
	21st to end	Day	43% 6% 8% 15% 18% 11%	1884
December	1st to 10th	Day	43% 6% 10% 18% 16% 7%	1710
	11th to 20th	Day	42% 7% 9% 13% 20% 9%	2159
	21st to end	Day	40% 6% 7% 15% 20% 11%	3135
January	1st to 10th	Night	42% 4 7% 15% 21% 11%	2458
	11th to 20th	Night	41% 4 7% 16% 20% 12%	2379
	21st to end	Night	44% 4 6% 15% 18% 13%	2574
February	1st to 10th	Night	47% 4 9% 11% 16% 12%	2291
	11th to 20th	Night	46% 5% 8% 13% 18% 12%	2049
	21st to end	Night	49% 5% 6% 14% 15% 12%	1628
March	1st to 10th	Night	43% 6% 10% 16% 16% 9%	1980
	11th to 20th	Night	43% 6% 12% 12% 18% 8%	1980
	21st to end	Night	37% 5% 12% 17% 20% 9%	2178
April	1st to 10th	Night	43% 7% 11% 17% 14% 9%	1980
	11th to 20th	Night	41% 6% 10% 16% 14% 13%	1795
	21st to end	Night	39% 8% 8% 21% 17% 7%	1800
May	1st to 10th	Night	38% 8% 13% 18% 15% 8%	1800
	11th to 20th	Night	34% 7% 12% 24% 19% 4	1594
	21st to end	Night	30% 11% 20% 27% 11% 1	1746
June	1st to 10th	Night	21% 8% 23% 30% 17%	1620
	11th to 20th	Night	22% 7% 19% 32% 17% 2	1620
	21st to end	Night	31% 11% 21% 26% 10%	1620
July	1st to 10th	Night	32% 11% 26% 26% 5%	1575
	11th to 20th	Night	21% 12% 30% 30% 7%	1566
	21st to end	Night	22% 12% 29% 31% 4	1673
August	1st to 10th	Night	12% 9% 31% 38% 9%	1601
	11th to 20th	Night	20% 12% 30% 31% 6% 1	1715
	21st to end	Night	30% 12% 24% 26% 7% 2	1980
September	1st to 10th	Night	29% 11% 25% 20% 13% 3	1975
	11th to 20th	Night	36% 9% 16% 19% 15% 4	1980
	21st to end	Night	29% 8% 14% 22% 19% 8%	1980
October	1st to 10th	Night	23% 6% 13% 27% 19% 12%	2088
	11th to 20th	Night	25% 7% 10% 24% 22% 13%	2160
	21st to end	Night	28% 4 8% 16% 24% 20%	2376
November	1st to 10th	Night	29% 6% 11% 22% 21% 10%	2220
	11th to 20th	Night	34% 5% 11% 20% 20% 11%	2280
	21st to end	Night	41% 5% 8% 19% 18% 9%	2292
December	1st to 10th	Night	43% 5% 10% 19% 14% 9%	2470
	11th to 20th	Night	43% 5% 8% 11% 18% 14%	3037
	21st to end	Night	41% 6% 7% 13% 25% 7%	4532

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	24% 8% 35% 24% 9% 1	270
	11th to 20th	Day	20% 13% 28% 30% 8% 2	248
	21st to end	Day	17% 14% 32% 28% 9%	264
February	1st to 10th	Day	24% 10% 34% 24% 7%	240
	11th to 20th	Day	27% 15% 28% 22% 7% 1	240
	21st to end	Day	22% 15% 41% 19% 2 1	198
March	1st to 10th	Day	29% 11% 31% 23% 6%	240
	11th to 20th	Day	17% 14% 42% 20% 5% 3	240
	21st to end	Day	18% 16% 30% 25% 10% 1	264
April	1st to 10th	Day	18% 13% 34% 25% 10%	240
	11th to 20th	Day	23% 12% 26% 24% 14% 2	389
	21st to end	Day	15% 7% 30% 30% 17% 1	420
May	1st to 10th	Day	12% 9% 28% 32% 18% 1	423
	11th to 20th	Day	11% 3 27% 34% 22% 3	619
	21st to end	Day	9% 3 21% 39% 23% 4	679
June	1st to 10th	Day	7% 2 10% 34% 33% 14%	630
	11th to 20th	Day	7% 1 10% 37% 31% 14%	630
	21st to end	Day	8% 2 9% 27% 33% 20%	630
July	1st to 10th	Day	7% 2 6% 24% 38% 23%	621
	11th to 20th	Day	5% 3 20% 41% 30%	618
	21st to end	Day	4 1 4 22% 42% 28%	684
August	1st to 10th	Day	3 3 20% 43% 31%	626
	11th to 20th	Day	4 1 2 13% 42% 38%	499
	21st to end	Day	10% 1 4 15% 34% 36%	494
September	1st to 10th	Day	7% 1 4 21% 37% 30%	270
	11th to 20th	Day	11% 1 7% 20% 37% 23%	270
	21st to end	Day	11% 1 5% 27% 36% 20%	270
October	1st to 10th	Day	7% 1 7% 34% 38% 13%	270
	11th to 20th	Day	9% 5% 13% 34% 27% 12%	270
	21st to end	Day	19% 7% 22% 27% 20% 5%	297
November	1st to 10th	Day	13% 4 18% 34% 25% 6%	270
	11th to 20th	Day	16% 5% 20% 39% 16% 4	270
	21st to end	Day	15% 16% 30% 23% 14% 2	270
December	1st to 10th	Day	18% 7% 28% 26% 15% 6%	270
	11th to 20th	Day	16% 12% 31% 30% 10% 1	270
	21st to end	Day	20% 9% 34% 26% 10% 2	297
January	1st to 10th	Night	22% 8% 29% 32% 9%	950
	11th to 20th	Night	22% 8% 26% 36% 9% 1	915
	21st to end	Night	21% 8% 28% 35% 8%	990
February	1st to 10th	Night	25% 7% 30% 33% 6%	851
	11th to 20th	Night	25% 9% 28% 30% 7%	655
	21st to end	Night	27% 9% 32% 27% 5%	444
March	1st to 10th	Night	23% 6% 31% 32% 8%	540
	11th to 20th	Night	19% 8% 26% 36% 10% 1	540
	21st to end	Night	17% 6% 28% 37% 11% 1	594
April	1st to 10th	Night	16% 7% 32% 38% 8%	540
	11th to 20th	Night	21% 8% 24% 35% 12%	533
	21st to end	Night	16% 6% 25% 38% 14% 1	540
May	1st to 10th	Night	14% 6% 24% 44% 10%	540
	11th to 20th	Night	11% 3 21% 43% 20% 2	531
	21st to end	Night	6% 3 17% 41% 30% 3	584
June	1st to 10th	Night	5% 1 5% 44% 41% 4	540
	11th to 20th	Night	6% 1 6% 40% 43% 4	540
	21st to end	Night	7% 1 9% 24% 51% 8%	540
July	1st to 10th	Night	5% 2 3 26% 53% 11%	525
	11th to 20th	Night	4 1 1 20% 60% 14%	522
	21st to end	Night	4 3 21% 62% 10%	591
August	1st to 10th	Night	2 1 2 16% 68% 12%	537
	11th to 20th	Night	5% 1 2 14% 67% 12%	534
	21st to end	Night	6% 1 3 19% 56% 15%	594
September	1st to 10th	Night	6% 1 5% 20% 55% 12%	540
	11th to 20th	Night	14% 1 4 22% 51% 8%	540
	21st to end	Night	11% 1 6% 27% 47% 8%	540
October	1st to 10th	Night	6% 1 9% 34% 42% 7%	648
	11th to 20th	Night	10% 2 16% 38% 31% 3	720
	21st to end	Night	13% 5% 19% 36% 24% 3	792
November	1st to 10th	Night	12% 2 16% 41% 27% 3	740
	11th to 20th	Night	13% 6% 20% 41% 20% 1	760
	21st to end	Night	18% 5% 27% 33% 16% 1	772
December	1st to 10th	Night	19% 7% 25% 32% 17% 1	950
	11th to 20th	Night	22% 8% 25% 35% 11%	950
	21st to end	Night	20% 8% 30% 33% 9%	1045

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