Cedar Hill Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cedar Hill Park clear sky chart from 2005-11-06 to 2025-03-27.

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% 8% 3 6% 4 4 4 4 5% 7% 43%	109000
	Night	14% 8% 3 7% 4 4 4 3 5% 6% 43%	110523
Transparency	Day	39% 5% 11% 25% 18% 3	112633
	Night	40% 5% 10% 24% 18% 3	115031
Seeing	Day	17% 12% 27% 25% 15% 4	16038
	Night	17% 11% 29% 28% 13% 1	26035

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	12% 12% 6% 13% 6% 4 3 3 5% 5% 30%	3617
	11th to 20th	Day	9% 10% 4 7% 4 5% 4 3 5% 7% 43%	3988
	21st to end	Day	17% 13% 4 7% 4 3 3 2 5% 5% 36%	4488
February	1st to 10th	Day	16% 12% 4 8% 4 4 4 3 5% 6% 34%	1800
	11th to 20th	Day	15% 9% 3 8% 6% 4 4 3 4 6% 37%	1923
	21st to end	Day	14% 10% 2 6% 4 4 4 4 5% 7% 40%	1650
March	1st to 10th	Day	18% 12% 3 6% 3 2 3 3 4 4 42%	3305
	11th to 20th	Day	13% 7% 2 5% 3 3 4 3 4 6% 50%	3590
	21st to end	Day	15% 8% 3 7% 5% 4 5% 4 5% 7% 36%	4067
April	1st to 10th	Day	11% 6% 2 7% 5% 4 4 4 6% 8% 43%	2280
	11th to 20th	Day	16% 9% 3 5% 4 4 4 4 5% 6% 41%	2254
	21st to end	Day	19% 7% 2 7% 5% 5% 4 3 5% 7% 37%	2280
May	1st to 10th	Day	14% 8% 3 7% 5% 5% 6% 5% 7% 9% 32%	3817
	11th to 20th	Day	18% 8% 2 6% 4 4 4 3 5% 7% 38%	4358
	21st to end	Day	10% 6% 2 7% 5% 5% 5% 4 6% 7% 44%	4824
June	1st to 10th	Day	8% 6% 2 5% 4 5% 5% 4 6% 8% 46%	2660
	11th to 20th	Day	8% 4 2 5% 4 4 5% 4 7% 10% 50%	2660
	21st to end	Day	4 4 2 6% 5% 5% 6% 4 8% 9% 48%	2660
July	1st to 10th	Day	13% 5% 2 6% 5% 5% 4 4 6% 10% 41%	4440
	11th to 20th	Day	4 4 2 4 4 4 5% 4 7% 12% 49%	4440
	21st to end	Day	6% 6% 3 7% 5% 5% 6% 5% 7% 11% 39%	4509
August	1st to 10th	Day	5% 4 2 5% 4 4 5% 5% 7% 9% 51%	4086
	11th to 20th	Day	12% 5% 2 5% 5% 5% 4 4 6% 8% 44%	3729
	21st to end	Day	7% 4 2 5% 3 4 4 3 6% 9% 52%	4180
September	1st to 10th	Day	13% 5% 2 4 4 3 4 3 6% 7% 49%	2280
	11th to 20th	Day	11% 5% 2 6% 4 4 4 3 5% 8% 49%	2265
	21st to end	Day	8% 4 2 5% 5% 3 4 3 5% 8% 52%	2071
October	1st to 10th	Day	9% 4 2 6% 4 3 3 3 4 7% 56%	1900
	11th to 20th	Day	14% 6% 2 4 4 3 2 2 4 6% 53%	1900
	21st to end	Day	18% 8% 2 4 4 3 3 3 4 6% 47%	2090
November	1st to 10th	Day	12% 5% 2 5% 4 3 3 3 4 6% 54%	1764
	11th to 20th	Day	13% 7% 3 5% 4 4 2 3 5% 7% 47%	1800
	21st to end	Day	16% 11% 3 5% 3 3 3 3 4 5% 43%	1725
December	1st to 10th	Day	9% 10% 2 6% 4 3 3 3 4 6% 49%	2610
	11th to 20th	Day	12% 10% 5% 7% 5% 4 3 3 4 6% 39%	3008
	21st to end	Day	22% 17% 6% 9% 5% 4 4 3 4 4 24%	3982
January	1st to 10th	Night	16% 11% 7% 12% 5% 4 3 2 4 4 32%	6348
	11th to 20th	Night	11% 10% 4 13% 5% 6% 5% 3 3 4 36%	5976
	21st to end	Night	18% 12% 4 8% 4 4 3 2 3 4 37%	6490
February	1st to 10th	Night	17% 12% 4 8% 5% 3 4 3 5% 5% 34%	2600
	11th to 20th	Night	16% 9% 4 8% 4 4 4 2 4 5% 41%	2362
	21st to end	Night	15% 9% 3 8% 4 4 3 3 4 5% 42%	1980
March	1st to 10th	Night	21% 11% 2 5% 3 3 3 2 3 4 42%	3797
	11th to 20th	Night	13% 7% 2 5% 3 3 3 3 4 6% 51%	3590
	21st to end	Night	17% 10% 3 8% 6% 5% 4 4 5% 6% 33%	3702
April	1st to 10th	Night	11% 6% 2 6% 4 4 4 3 5% 7% 47%	1900
	11th to 20th	Night	14% 8% 3 5% 4 4 3 3 5% 7% 44%	1875
	21st to end	Night	20% 7% 2 6% 3 4 3 3 4 7% 41%	1900
May	1st to 10th	Night	18% 7% 3 5% 4 3 4 3 5% 8% 39%	3076
	11th to 20th	Night	15% 7% 3 4 4 3 4 3 4 8% 44%	2542
	21st to end	Night	10% 7% 2 6% 5% 5% 5% 4 6% 9% 41%	2743
June	1st to 10th	Night	8% 4 2 5% 4 4 4 4 7% 9% 48%	1520
	11th to 20th	Night	5% 4 2 4 3 4 4 3 6% 10% 55%	1520
	21st to end	Night	4 4 2 3 4 5% 4 4 7% 9% 55%	1520
July	1st to 10th	Night	12% 4 2 5% 4 4 3 4 6% 10% 46%	2530
	11th to 20th	Night	5% 4 2 5% 3 4 4 3 6% 8% 57%	2530
	21st to end	Night	6% 5% 3 7% 5% 5% 5% 4 8% 9% 43%	3050
August	1st to 10th	Night	5% 3 1 4 3 4 3 3 6% 9% 59%	2851
	11th to 20th	Night	10% 5% 2 6% 5% 4 4 3 6% 8% 47%	3100
	21st to end	Night	5% 3 1 5% 3 4 4 4 5% 10% 57%	3476
September	1st to 10th	Night	11% 6% 2 5% 3 3 3 2 6% 6% 53%	1900
	11th to 20th	Night	9% 5% 1 5% 4 3 4 4 5% 7% 53%	1900
	21st to end	Night	10% 5% 1 4 3 4 5% 3 5% 6% 54%	2101
October	1st to 10th	Night	8% 4 1 5% 3 3 3 2 5% 7% 60%	2280
	11th to 20th	Night	14% 5% 2 5% 3 2 3 2 5% 6% 54%	2280
	21st to end	Night	18% 8% 2 4 2 2 3 3 3 6% 48%	2508
November	1st to 10th	Night	11% 6% 2 4 3 3 2 3 4 6% 56%	2531
	11th to 20th	Night	15% 6% 3 5% 4 3 3 3 4 6% 49%	2600
	21st to end	Night	17% 10% 3 5% 3 3 3 2 5% 5% 44%	2670
December	1st to 10th	Night	12% 10% 2 6% 4 3 3 3 4 5% 47%	4580
	11th to 20th	Night	15% 9% 4 7% 4 4 3 3 4 6% 41%	5199
	21st to end	Night	23% 17% 4 8% 5% 4 4 3 4 5% 23%	6996

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	54% 4 11% 19% 10% 2	3618
	11th to 20th	Day	42% 3 8% 23% 19% 4	3988
	21st to end	Day	51% 2 9% 16% 16% 6%	4488
February	1st to 10th	Day	50% 5% 10% 22% 11% 1	1800
	11th to 20th	Day	49% 5% 9% 19% 15% 4	1933
	21st to end	Day	43% 4 10% 23% 15% 4	1650
March	1st to 10th	Day	47% 4 6% 20% 17% 7%	3305
	11th to 20th	Day	36% 4 10% 26% 17% 6%	3590
	21st to end	Day	45% 7% 16% 22% 10% 1	4067
April	1st to 10th	Day	38% 5% 12% 25% 19% 1	2280
	11th to 20th	Day	42% 5% 10% 23% 16% 4	2254
	21st to end	Day	47% 6% 10% 23% 14% 1	2280
May	1st to 10th	Day	44% 9% 13% 22% 11% 1	3852
	11th to 20th	Day	44% 6% 10% 26% 13% 1	4362
	21st to end	Day	38% 8% 9% 21% 22% 1	4837
June	1st to 10th	Day	34% 8% 11% 27% 18% 2	2660
	11th to 20th	Day	29% 7% 11% 27% 22% 3	2660
	21st to end	Day	28% 9% 16% 26% 16% 5%	2660
July	1st to 10th	Day	39% 6% 11% 29% 12% 2	4371
	11th to 20th	Day	27% 6% 15% 33% 17% 2	4365
	21st to end	Day	39% 6% 16% 27% 11% 1	4367
August	1st to 10th	Day	27% 6% 15% 34% 17%	4072
	11th to 20th	Day	39% 5% 12% 24% 18% 2	3765
	21st to end	Day	29% 5% 14% 35% 14% 3	4179
September	1st to 10th	Day	34% 5% 11% 25% 20% 5%	2280
	11th to 20th	Day	34% 5% 9% 26% 24% 2	2265
	21st to end	Day	30% 7% 8% 28% 25% 3	2071
October	1st to 10th	Day	18% 3 6% 20% 45% 9%	3160
	11th to 20th	Day	23% 3 6% 21% 37% 10%	3140
	21st to end	Day	32% 3 7% 28% 27% 3	3428
November	1st to 10th	Day	33% 3 12% 25% 21% 6%	1764
	11th to 20th	Day	38% 4 8% 23% 22% 5%	1800
	21st to end	Day	44% 4 9% 27% 16%	1725
December	1st to 10th	Day	37% 3 10% 33% 16% 1	2610
	11th to 20th	Day	46% 3 11% 22% 16% 1	3005
	21st to end	Day	64% 4 11% 13% 7% 1	3982
January	1st to 10th	Night	57% 3 9% 21% 9% 1	6348
	11th to 20th	Night	52% 4 6% 23% 13% 2	5976
	21st to end	Night	52% 3 8% 19% 16% 2	6490
February	1st to 10th	Night	52% 5% 10% 20% 13% 1	2600
	11th to 20th	Night	47% 4 9% 21% 17% 3	2363
	21st to end	Night	46% 3 9% 22% 15% 4	1980
March	1st to 10th	Night	47% 4 7% 23% 16% 3	3797
	11th to 20th	Night	36% 4 11% 24% 20% 5%	3590
	21st to end	Night	50% 7% 10% 25% 8%	3702
April	1st to 10th	Night	36% 4 11% 27% 18% 3	1900
	11th to 20th	Night	40% 4 9% 25% 18% 4	1875
	21st to end	Night	45% 4 9% 24% 16% 2	1900
May	1st to 10th	Night	43% 8% 14% 20% 13% 2	3106
	11th to 20th	Night	39% 7% 13% 26% 14% 1	2543
	21st to end	Night	37% 9% 12% 23% 17% 2	2751
June	1st to 10th	Night	32% 6% 14% 26% 18% 4	1520
	11th to 20th	Night	23% 9% 11% 28% 25% 4	1520
	21st to end	Night	23% 7% 15% 28% 19% 7%	1520
July	1st to 10th	Night	35% 5% 13% 28% 15% 4	2490
	11th to 20th	Night	25% 5% 11% 37% 20% 3	2482
	21st to end	Night	36% 5% 19% 25% 14% 2	2953
August	1st to 10th	Night	22% 6% 17% 33% 20% 1	2841
	11th to 20th	Night	36% 5% 14% 25% 18% 3	3130
	21st to end	Night	24% 5% 15% 36% 18% 3	3476
September	1st to 10th	Night	32% 6% 8% 26% 22% 6%	1900
	11th to 20th	Night	31% 6% 10% 25% 26% 3	1900
	21st to end	Night	30% 7% 9% 24% 27% 4	2101
October	1st to 10th	Night	15% 3 6% 16% 50% 10%	3800
	11th to 20th	Night	22% 3 7% 21% 36% 11%	3779
	21st to end	Night	31% 3 8% 26% 27% 5%	4120
November	1st to 10th	Night	31% 4 12% 25% 23% 6%	2531
	11th to 20th	Night	37% 4 7% 23% 24% 5%	2600
	21st to end	Night	42% 4 9% 25% 19% 2	2670
December	1st to 10th	Night	40% 3 9% 32% 15% 1	4580
	11th to 20th	Night	45% 3 12% 22% 18% 1	5201
	21st to end	Night	63% 5% 12% 13% 6% 1	6996

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	27% 21% 34% 15% 3 1	300
	11th to 20th	Day	28% 25% 34% 12%	300
	21st to end	Day	18% 29% 38% 12% 2	330
February	1st to 10th	Day	26% 24% 36% 12% 2	300
	11th to 20th	Day	30% 29% 24% 13% 3 1	300
	21st to end	Day	29% 23% 36% 12% 1	249
March	1st to 10th	Day	23% 24% 40% 11% 2	300
	11th to 20th	Day	34% 18% 32% 12% 3 1	300
	21st to end	Day	30% 19% 35% 12% 4	425
April	1st to 10th	Day	20% 19% 36% 19% 6%	460
	11th to 20th	Day	25% 19% 30% 19% 7%	452
	21st to end	Day	24% 15% 36% 18% 6% 1	460
May	1st to 10th	Day	22% 15% 33% 22% 8%	463
	11th to 20th	Day	20% 12% 29% 24% 12% 3	647
	21st to end	Day	12% 8% 34% 26% 14% 6%	734
June	1st to 10th	Day	10% 7% 24% 30% 23% 6%	680
	11th to 20th	Day	9% 3 25% 40% 17% 6%	680
	21st to end	Day	5% 8% 29% 35% 17% 6%	680
July	1st to 10th	Day	12% 3 16% 29% 28% 11%	671
	11th to 20th	Day	5% 4 21% 40% 24% 7%	668
	21st to end	Day	9% 4 18% 33% 29% 7%	739
August	1st to 10th	Day	8% 3 17% 38% 27% 8%	671
	11th to 20th	Day	13% 4 19% 30% 26% 8%	479
	21st to end	Day	11% 1 15% 30% 32% 11%	539
September	1st to 10th	Day	13% 4 17% 29% 30% 7%	490
	11th to 20th	Day	10% 2 15% 32% 27% 12%	490
	21st to end	Day	12% 8% 23% 30% 19% 8%	471
October	1st to 10th	Day	11% 10% 26% 35% 14% 4	300
	11th to 20th	Day	17% 16% 33% 24% 9% 1	300
	21st to end	Day	29% 19% 28% 19% 4	330
November	1st to 10th	Day	17% 12% 41% 18% 9% 3	300
	11th to 20th	Day	21% 20% 32% 17% 8% 2	300
	21st to end	Day	28% 17% 31% 17% 6% 1	300
December	1st to 10th	Day	19% 21% 35% 16% 7% 2	300
	11th to 20th	Day	24% 19% 34% 17% 5%	300
	21st to end	Day	28% 23% 34% 12% 3	330
January	1st to 10th	Night	20% 21% 33% 22% 4	1000
	11th to 20th	Night	22% 23% 34% 18% 3	1000
	21st to end	Night	19% 20% 38% 21% 2	1100
February	1st to 10th	Night	24% 19% 33% 22% 2	1000
	11th to 20th	Night	24% 20% 37% 18% 2	807
	21st to end	Night	23% 19% 37% 19% 2	660
March	1st to 10th	Night	25% 17% 34% 22% 3	770
	11th to 20th	Night	24% 13% 35% 23% 5%	600
	21st to end	Night	26% 13% 33% 23% 4	647
April	1st to 10th	Night	17% 16% 36% 25% 5%	570
	11th to 20th	Night	19% 13% 33% 26% 8% 1	563
	21st to end	Night	24% 10% 36% 22% 7%	570
May	1st to 10th	Night	17% 10% 32% 31% 9% 1	570
	11th to 20th	Night	19% 7% 26% 32% 16% 1	561
	21st to end	Night	11% 6% 25% 36% 19% 3	617
June	1st to 10th	Night	10% 4 20% 38% 26% 1	570
	11th to 20th	Night	6% 2 24% 45% 21% 1	570
	21st to end	Night	5% 3 24% 44% 23% 2	570
July	1st to 10th	Night	10% 1 12% 37% 33% 6%	555
	11th to 20th	Night	5% 2 14% 43% 32% 3	552
	21st to end	Night	8% 1 17% 39% 32% 4	624
August	1st to 10th	Night	8% 1 14% 39% 36% 2	567
	11th to 20th	Night	8% 2 13% 40% 33% 4	564
	21st to end	Night	7% 1 14% 34% 39% 4	627
September	1st to 10th	Night	13% 2 16% 35% 30% 5%	570
	11th to 20th	Night	11% 3 13% 35% 32% 6%	570
	21st to end	Night	11% 6% 23% 30% 26% 4	755
October	1st to 10th	Night	8% 5% 28% 32% 23% 5%	760
	11th to 20th	Night	17% 12% 30% 27% 14% 1	760
	21st to end	Night	24% 13% 31% 26% 6%	836
November	1st to 10th	Night	14% 10% 37% 29% 10%	780
	11th to 20th	Night	19% 16% 31% 26% 7%	800
	21st to end	Night	23% 15% 32% 23% 6%	870
December	1st to 10th	Night	24% 13% 33% 25% 5% 1	1000
	11th to 20th	Night	24% 14% 31% 27% 4	1000
	21st to end	Night	25% 18% 33% 21% 3	1100

Page generated at 2025-03-24 08:04:32. Version ac07

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