Petit Jean State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Petit Jean State Park clear sky chart from 2005-11-06 to 2026-06-16.

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% 4 4 4 4 5% 7% 45%	136469
	Night	13% 6% 2 5% 4 4 3 3 5% 6% 49%	135705
Transparency	Day	37% 5% 10% 23% 19% 5%	140075
	Night	34% 5% 10% 23% 21% 7%	140178
Seeing	Day	15% 6% 19% 26% 24% 10%	17524
	Night	15% 5% 20% 37% 21% 2	27353

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	17% 7% 2 7% 4 3 3 3 4 5% 46%	5289
	11th to 20th	Day	9% 7% 2 6% 3 3 4 3 3 4 56%	5310
	21st to end	Day	19% 7% 2 5% 2 2 3 2 4 5% 48%	5812
February	1st to 10th	Day	21% 9% 2 5% 3 3 3 2 4 5% 43%	1890
	11th to 20th	Day	18% 8% 3 6% 4 3 3 3 4 5% 44%	1943
	21st to end	Day	20% 10% 2 5% 3 4 3 3 5% 5% 41%	1820
March	1st to 10th	Day	19% 9% 3 7% 4 3 3 3 4 5% 39%	5046
	11th to 20th	Day	11% 5% 2 5% 4 3 4 3 4 6% 53%	5090
	21st to end	Day	14% 8% 3 6% 4 4 4 3 5% 6% 44%	5583
April	1st to 10th	Day	15% 6% 2 6% 5% 4 5% 3 4 6% 43%	2492
	11th to 20th	Day	16% 7% 2 6% 4 3 5% 2 5% 6% 44%	2494
	21st to end	Day	16% 6% 3 7% 6% 4 4 4 5% 6% 38%	2520
May	1st to 10th	Day	16% 8% 3 7% 4 4 4 3 5% 6% 38%	7116
	11th to 20th	Day	12% 6% 3 8% 5% 5% 5% 4 6% 8% 38%	7627
	21st to end	Day	18% 9% 3 8% 6% 5% 6% 4 6% 7% 28%	8392
June	1st to 10th	Day	8% 6% 3 6% 5% 5% 6% 5% 6% 9% 41%	2730
	11th to 20th	Day	5% 5% 2 6% 6% 6% 6% 4 9% 9% 42%	2666
	21st to end	Day	4 3 1 5% 5% 4 5% 4 7% 10% 51%	2600
July	1st to 10th	Day	8% 4 2 6% 5% 5% 7% 5% 8% 13% 36%	5900
	11th to 20th	Day	4 4 2 4 4 4 5% 4 7% 10% 53%	5900
	21st to end	Day	7% 6% 2 6% 5% 5% 5% 5% 7% 11% 40%	6422
August	1st to 10th	Day	4 3 1 4 3 4 4 4 5% 9% 61%	4234
	11th to 20th	Day	10% 5% 2 7% 4 4 4 4 7% 11% 42%	3928
	21st to end	Day	5% 3 2 5% 4 4 5% 5% 7% 8% 52%	4312
September	1st to 10th	Day	11% 6% 2 5% 4 4 4 4 6% 7% 47%	2400
	11th to 20th	Day	13% 5% 2 5% 4 4 3 4 5% 9% 45%	2360
	21st to end	Day	10% 5% 2 6% 3 4 4 3 4 6% 53%	2105
October	1st to 10th	Day	7% 4 2 4 3 3 4 3 5% 6% 59%	2000
	11th to 20th	Day	14% 4 1 4 2 3 3 2 4 5% 58%	2000
	21st to end	Day	18% 6% 2 4 3 3 3 3 4 5% 50%	2200
November	1st to 10th	Day	12% 6% 2 4 3 3 3 2 4 6% 55%	2058
	11th to 20th	Day	12% 6% 1 4 3 3 3 3 4 6% 55%	2079
	21st to end	Day	18% 7% 2 4 4 3 3 2 5% 5% 47%	1786
December	1st to 10th	Day	17% 6% 2 6% 3 3 2 3 4 5% 49%	2690
	11th to 20th	Day	17% 8% 3 7% 4 4 3 3 4 4 44%	3088
	21st to end	Day	20% 9% 3 7% 4 3 3 3 4 5% 39%	4587
January	1st to 10th	Night	16% 6% 2 5% 3 3 3 3 5% 7% 46%	7634
	11th to 20th	Night	9% 4 2 4 3 2 2 2 3 5% 65%	7680
	21st to end	Night	22% 8% 2 5% 3 3 3 2 3 4 44%	8402
February	1st to 10th	Night	19% 7% 2 6% 3 4 3 3 5% 5% 42%	2730
	11th to 20th	Night	18% 8% 2 6% 3 3 3 2 4 6% 45%	2563
	21st to end	Night	18% 6% 2 5% 4 2 2 3 4 5% 49%	2003
March	1st to 10th	Night	19% 7% 3 6% 3 3 3 3 4 4 43%	5029
	11th to 20th	Night	11% 5% 2 6% 4 3 3 3 5% 7% 51%	5090
	21st to end	Night	13% 6% 2 6% 4 4 4 3 5% 8% 45%	5588
April	1st to 10th	Night	14% 5% 2 5% 4 3 3 2 5% 7% 50%	2126
	11th to 20th	Night	11% 6% 2 5% 4 4 3 3 5% 6% 49%	2075
	21st to end	Night	16% 7% 2 5% 4 3 4 2 6% 7% 45%	2100
May	1st to 10th	Night	16% 7% 3 7% 4 4 5% 4 6% 7% 37%	5724
	11th to 20th	Night	14% 8% 3 7% 4 4 4 4 6% 7% 38%	5265
	21st to end	Night	21% 9% 3 8% 5% 4 4 3 5% 6% 32%	5793
June	1st to 10th	Night	6% 4 2 5% 4 4 4 3 7% 11% 50%	1874
	11th to 20th	Night	5% 4 1 4 3 4 3 3 6% 10% 56%	1753
	21st to end	Night	3 3 1 3 3 3 3 4 6% 9% 62%	1800
July	1st to 10th	Night	6% 5% 2 7% 5% 5% 6% 5% 7% 10% 42%	4078
	11th to 20th	Night	4 3 1 3 3 3 4 3 6% 10% 58%	4077
	21st to end	Night	5% 5% 2 6% 4 5% 5% 5% 7% 10% 48%	4449
August	1st to 10th	Night	2 2 1 3 3 3 3 3 5% 8% 66%	2926
	11th to 20th	Night	4 4 1 5% 3 5% 4 3 5% 9% 56%	3110
	21st to end	Night	4 2 2 4 4 4 4 4 6% 8% 57%	3586
September	1st to 10th	Night	7% 4 2 5% 4 3 3 4 5% 7% 56%	2000
	11th to 20th	Night	10% 6% 2 5% 4 3 4 3 5% 7% 51%	2035
	21st to end	Night	9% 4 1 4 2 3 4 3 5% 6% 60%	2275
October	1st to 10th	Night	8% 4 1 3 3 2 4 3 5% 7% 61%	2400
	11th to 20th	Night	11% 4 2 4 3 3 3 2 4 4 62%	2400
	21st to end	Night	18% 5% 2 5% 2 3 3 2 2 4 54%	2640
November	1st to 10th	Night	11% 5% 2 4 3 2 3 3 4 6% 57%	2460
	11th to 20th	Night	12% 4 2 4 2 2 3 2 4 7% 57%	2536
	21st to end	Night	16% 6% 2 4 4 4 2 3 3 5% 52%	2830
December	1st to 10th	Night	15% 6% 2 5% 3 4 3 3 4 4 51%	4720
	11th to 20th	Night	20% 6% 2 6% 4 3 3 2 3 4 47%	5321
	21st to end	Night	19% 8% 2 6% 4 4 3 2 4 5% 41%	6633

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	43% 2 9% 27% 17% 2	5290
	11th to 20th	Day	33% 2 7% 21% 30% 6%	5310
	21st to end	Day	40% 3 5% 20% 25% 8%	5812
February	1st to 10th	Day	45% 4 9% 22% 16% 4	1890
	11th to 20th	Day	43% 4 9% 21% 18% 5%	1952
	21st to end	Day	47% 3 7% 15% 19% 9%	1820
March	1st to 10th	Day	47% 5% 5% 16% 14% 13%	5046
	11th to 20th	Day	32% 4 8% 19% 25% 13%	5090
	21st to end	Day	41% 5% 9% 26% 18% 1	5585
April	1st to 10th	Day	41% 5% 9% 20% 21% 4	2492
	11th to 20th	Day	41% 5% 9% 20% 18% 7%	2494
	21st to end	Day	45% 6% 10% 20% 17% 2	2520
May	1st to 10th	Day	46% 6% 8% 20% 19% 2	7151
	11th to 20th	Day	42% 8% 11% 22% 15% 2	7631
	21st to end	Day	52% 8% 12% 14% 13% 1	8405
June	1st to 10th	Day	37% 9% 14% 24% 15% 2	2730
	11th to 20th	Day	34% 7% 15% 24% 18% 2	2666
	21st to end	Day	27% 7% 14% 29% 20% 4	2600
July	1st to 10th	Day	35% 8% 17% 28% 10% 1	5836
	11th to 20th	Day	24% 7% 15% 36% 16% 2	5831
	21st to end	Day	35% 8% 15% 29% 12%	6240
August	1st to 10th	Day	21% 6% 16% 31% 21% 6%	4220
	11th to 20th	Day	36% 7% 15% 30% 12% 1	3965
	21st to end	Day	27% 7% 13% 32% 18% 3	4311
September	1st to 10th	Day	34% 6% 12% 21% 18% 8%	2400
	11th to 20th	Day	36% 6% 12% 21% 21% 5%	2360
	21st to end	Day	33% 4 8% 20% 28% 7%	2105
October	1st to 10th	Day	16% 3 6% 13% 40% 22%	3260
	11th to 20th	Day	19% 3 4 20% 38% 17%	3240
	21st to end	Day	31% 4 6% 30% 24% 6%	3538
November	1st to 10th	Day	31% 4 7% 26% 24% 8%	2058
	11th to 20th	Day	30% 4 8% 24% 26% 9%	2079
	21st to end	Day	41% 3 8% 20% 24% 5%	1786
December	1st to 10th	Day	40% 3 7% 28% 19% 3	2690
	11th to 20th	Day	44% 4 6% 21% 21% 3	3085
	21st to end	Day	47% 5% 7% 24% 13% 4	4587
January	1st to 10th	Night	38% 3 10% 29% 18% 2	7635
	11th to 20th	Night	24% 3 7% 20% 37% 9%	7680
	21st to end	Night	45% 3 7% 15% 23% 7%	8402
February	1st to 10th	Night	44% 4 8% 22% 17% 5%	2730
	11th to 20th	Night	42% 4 7% 22% 20% 5%	2564
	21st to end	Night	39% 3 7% 18% 23% 10%	2003
March	1st to 10th	Night	42% 5% 8% 14% 18% 13%	5029
	11th to 20th	Night	33% 4 6% 24% 19% 14%	5090
	21st to end	Night	38% 5% 10% 26% 20% 3	5588
April	1st to 10th	Night	35% 4 10% 23% 20% 8%	2126
	11th to 20th	Night	34% 6% 8% 24% 20% 9%	2075
	21st to end	Night	39% 4 11% 24% 20% 3	2100
May	1st to 10th	Night	44% 6% 13% 19% 14% 3	5754
	11th to 20th	Night	43% 7% 12% 20% 14% 3	5266
	21st to end	Night	52% 7% 13% 16% 10% 3	5805
June	1st to 10th	Night	25% 9% 13% 30% 20% 2	1874
	11th to 20th	Night	23% 6% 13% 32% 24% 2	1753
	21st to end	Night	19% 7% 13% 31% 24% 7%	1800
July	1st to 10th	Night	35% 7% 17% 26% 14% 1	4035
	11th to 20th	Night	20% 7% 15% 38% 18% 2	4026
	21st to end	Night	30% 8% 16% 28% 17% 1	4320
August	1st to 10th	Night	16% 4 16% 35% 24% 5%	2916
	11th to 20th	Night	25% 6% 18% 34% 15% 2	3138
	21st to end	Night	23% 6% 12% 31% 26% 3	3586
September	1st to 10th	Night	27% 6% 10% 26% 22% 9%	2000
	11th to 20th	Night	32% 6% 10% 22% 24% 6%	2035
	21st to end	Night	26% 4 10% 22% 30% 8%	2275
October	1st to 10th	Night	15% 3 8% 14% 31% 29%	3920
	11th to 20th	Night	17% 2 5% 15% 39% 22%	3899
	21st to end	Night	29% 4 4 22% 29% 11%	4252
November	1st to 10th	Night	29% 4 8% 23% 25% 10%	2460
	11th to 20th	Night	29% 3 7% 26% 25% 10%	2536
	21st to end	Night	36% 4 8% 22% 26% 5%	2830
December	1st to 10th	Night	37% 4 8% 31% 18% 3	4720
	11th to 20th	Night	43% 3 5% 22% 21% 7%	5323
	21st to end	Night	45% 4 10% 25% 14% 3	6633

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% 7% 28% 26% 10% 2	330
	11th to 20th	Day	22% 12% 36% 25% 4 1	330
	21st to end	Day	20% 14% 33% 24% 8% 1	363
February	1st to 10th	Day	28% 9% 31% 20% 11% 2	330
	11th to 20th	Day	27% 10% 37% 21% 5%	330
	21st to end	Day	30% 9% 34% 21% 5% 1	273
March	1st to 10th	Day	24% 12% 29% 26% 8% 1	330
	11th to 20th	Day	22% 16% 33% 23% 6%	330
	21st to end	Day	21% 11% 40% 20% 7% 1	363
April	1st to 10th	Day	21% 11% 30% 26% 10% 2	512
	11th to 20th	Day	20% 12% 29% 28% 10% 1	532
	21st to end	Day	19% 8% 29% 30% 12% 2	540
May	1st to 10th	Day	17% 8% 27% 32% 14% 2	574
	11th to 20th	Day	16% 5% 21% 30% 23% 5%	775
	21st to end	Day	11% 5% 18% 32% 25% 8%	844
June	1st to 10th	Day	10% 4 13% 26% 33% 14%	780
	11th to 20th	Day	6% 3 13% 29% 33% 16%	756
	21st to end	Day	4 2 12% 32% 32% 17%	730
July	1st to 10th	Day	7% 2 7% 26% 36% 22%	721
	11th to 20th	Day	5% 1 6% 27% 37% 24%	718
	21st to end	Day	8% 2 6% 22% 39% 25%	794
August	1st to 10th	Day	7% 2 5% 27% 44% 15%	726
	11th to 20th	Day	13% 3 6% 19% 41% 19%	574
	21st to end	Day	12% 1 4 15% 39% 29%	583
September	1st to 10th	Day	10% 3 5% 22% 41% 19%	530
	11th to 20th	Day	11% 2 6% 20% 40% 22%	490
	21st to end	Day	14% 3 11% 29% 26% 17%	330
October	1st to 10th	Day	7% 2 17% 31% 28% 15%	330
	11th to 20th	Day	12% 5% 25% 30% 23% 5%	330
	21st to end	Day	24% 10% 25% 25% 12% 4	363
November	1st to 10th	Day	17% 6% 27% 26% 18% 6%	330
	11th to 20th	Day	14% 5% 32% 32% 16% 2	330
	21st to end	Day	21% 14% 24% 23% 17% 2	330
December	1st to 10th	Day	20% 10% 32% 24% 12% 3	330
	11th to 20th	Day	24% 9% 29% 24% 12% 1	330
	21st to end	Day	21% 12% 30% 28% 7% 1	363
January	1st to 10th	Night	23% 8% 26% 37% 5%	1050
	11th to 20th	Night	19% 9% 33% 34% 5%	1050
	21st to end	Night	21% 5% 34% 35% 4	1155
February	1st to 10th	Night	24% 8% 29% 35% 5%	1050
	11th to 20th	Night	21% 9% 34% 34% 2	929
	21st to end	Night	21% 9% 36% 33% 1	619
March	1st to 10th	Night	22% 7% 28% 39% 4	630
	11th to 20th	Night	19% 8% 29% 39% 6%	630
	21st to end	Night	17% 7% 31% 37% 8%	693
April	1st to 10th	Night	17% 6% 33% 36% 8%	630
	11th to 20th	Night	13% 9% 31% 37% 10%	623
	21st to end	Night	18% 6% 29% 34% 12%	630
May	1st to 10th	Night	15% 5% 19% 47% 14% 1	630
	11th to 20th	Night	16% 4 19% 37% 24% 1	621
	21st to end	Night	12% 3 14% 42% 24% 5%	683
June	1st to 10th	Night	6% 2 8% 40% 39% 4	630
	11th to 20th	Night	7% 1 8% 39% 43% 3	615
	21st to end	Night	3 1 6% 34% 52% 5%	600
July	1st to 10th	Night	5% 2 5% 31% 48% 9%	585
	11th to 20th	Night	4 1 3 29% 51% 10%	582
	21st to end	Night	3 2 3 30% 52% 10%	657
August	1st to 10th	Night	5% 2 3 34% 51% 5%	597
	11th to 20th	Night	8% 1 4 35% 44% 8%	594
	21st to end	Night	7% 1 6% 29% 50% 7%	660
September	1st to 10th	Night	9% 2 4 33% 48% 5%	600
	11th to 20th	Night	11% 3 5% 31% 44% 5%	600
	21st to end	Night	12% 1 9% 34% 39% 4	675
October	1st to 10th	Night	9% 2 8% 39% 39% 3	800
	11th to 20th	Night	13% 3 19% 44% 21% 1	800
	21st to end	Night	20% 5% 20% 36% 17% 1	880
November	1st to 10th	Night	13% 4 20% 44% 17% 2	820
	11th to 20th	Night	15% 7% 22% 43% 13%	840
	21st to end	Night	17% 9% 23% 37% 14%	940
December	1st to 10th	Night	20% 6% 28% 39% 7%	1050
	11th to 20th	Night	23% 7% 22% 41% 7%	1050
	21st to end	Night	21% 10% 26% 36% 7%	1155

Page generated at 2026-06-13 01:31:40. Version ac07

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