Zion Camp
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Zion Camp clear sky chart from 2005-11-06 to 2026-07-31.

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	16% 10% 4 9% 5% 5% 5% 4 5% 7% 32%	138791
	Night	16% 12% 4 10% 6% 5% 4 3 5% 6% 29%	134219
Transparency	Day	52% 5% 12% 21% 10% 1	142297
	Night	56% 4 11% 19% 9% 1	138802
Seeing	Day	24% 15% 29% 20% 9% 3	16552
	Night	23% 12% 27% 27% 10% 1	25638

By Month

Percentage Cloud Cover NE (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	13% 16% 6% 16% 8% 5% 4 3 4 5% 20%	4661
	11th to 20th	Day	11% 20% 7% 16% 9% 6% 4 3 4 5% 17%	4650
	21st to end	Day	9% 15% 7% 16% 9% 7% 5% 3 4 5% 20%	5480
February	1st to 10th	Day	12% 15% 5% 15% 8% 5% 5% 4 5% 4 23%	1890
	11th to 20th	Day	12% 16% 5% 12% 7% 4 5% 4 6% 6% 25%	1843
	21st to end	Day	17% 15% 4 10% 7% 5% 4 3 5% 5% 24%	1681
March	1st to 10th	Day	19% 13% 5% 12% 5% 4 4 3 4 6% 25%	4710
	11th to 20th	Day	13% 13% 5% 10% 6% 5% 4 4 6% 6% 28%	5090
	21st to end	Day	17% 11% 3 8% 5% 4 3 3 4 4 38%	5809
April	1st to 10th	Day	22% 13% 3 6% 5% 4 3 3 5% 5% 31%	2520
	11th to 20th	Day	22% 10% 3 7% 5% 3 3 3 4 4 34%	2494
	21st to end	Day	22% 10% 3 8% 5% 4 3 3 4 5% 33%	2697
May	1st to 10th	Day	19% 9% 3 7% 5% 5% 5% 4 6% 7% 29%	8237
	11th to 20th	Day	16% 7% 3 7% 5% 4 5% 4 6% 8% 34%	8221
	21st to end	Day	19% 8% 3 7% 4 4 4 3 5% 6% 36%	9060
June	1st to 10th	Day	19% 9% 3 8% 5% 5% 5% 4 6% 6% 31%	2940
	11th to 20th	Day	15% 7% 2 6% 4 5% 5% 5% 6% 8% 38%	2940
	21st to end	Day	16% 7% 2 7% 5% 6% 6% 5% 6% 8% 33%	2940
July	1st to 10th	Day	14% 6% 2 7% 5% 5% 6% 4 7% 9% 35%	6500
	11th to 20th	Day	10% 6% 2 6% 4 5% 5% 4 6% 8% 44%	6500
	21st to end	Day	9% 5% 2 6% 4 4 4 3 6% 10% 47%	7066
August	1st to 10th	Day	13% 7% 3 8% 5% 5% 5% 4 7% 7% 35%	4406
	11th to 20th	Day	17% 7% 3 6% 4 4 5% 4 5% 8% 37%	4174
	21st to end	Day	10% 5% 2 7% 4 5% 5% 5% 8% 11% 39%	4349
September	1st to 10th	Day	14% 6% 2 6% 5% 4 5% 3 6% 8% 42%	2400
	11th to 20th	Day	13% 5% 2 6% 5% 4 5% 4 5% 6% 45%	2400
	21st to end	Day	18% 7% 2 7% 4 5% 4 4 6% 7% 36%	2111
October	1st to 10th	Day	20% 8% 3 7% 5% 5% 4 3 4 7% 34%	2000
	11th to 20th	Day	22% 11% 3 9% 5% 4 4 3 5% 6% 28%	2000
	21st to end	Day	25% 11% 4 9% 5% 4 5% 3 5% 5% 25%	2080
November	1st to 10th	Day	16% 12% 3 8% 5% 4 4 3 5% 6% 33%	1788
	11th to 20th	Day	17% 14% 4 9% 6% 6% 5% 4 5% 6% 24%	1680
	21st to end	Day	23% 16% 6% 10% 7% 6% 4 3 5% 4 16%	1680
December	1st to 10th	Day	19% 22% 6% 12% 6% 6% 5% 3 4 4 13%	2680
	11th to 20th	Day	16% 17% 6% 14% 6% 5% 4 3 3 5% 22%	3066
	21st to end	Day	21% 19% 5% 14% 5% 5% 4 2 3 4 19%	4048
January	1st to 10th	Night	12% 18% 9% 18% 7% 5% 4 3 4 4 17%	8234
	11th to 20th	Night	12% 16% 6% 16% 8% 6% 6% 3 5% 5% 17%	8235
	21st to end	Night	9% 17% 7% 13% 8% 7% 5% 4 4 5% 21%	8699
February	1st to 10th	Night	11% 15% 5% 14% 8% 6% 5% 4 4 5% 22%	2730
	11th to 20th	Night	12% 16% 6% 12% 6% 5% 4 3 4 5% 26%	2663
	21st to end	Night	13% 15% 5% 11% 7% 5% 4 3 4 6% 26%	2124
March	1st to 10th	Night	19% 15% 5% 9% 5% 5% 4 2 4 4 29%	5348
	11th to 20th	Night	13% 13% 4 9% 5% 5% 6% 5% 7% 8% 26%	5089
	21st to end	Night	17% 11% 4 10% 5% 4 4 3 5% 6% 31%	5365
April	1st to 10th	Night	20% 12% 4 8% 5% 5% 3 3 5% 5% 30%	2100
	11th to 20th	Night	20% 10% 4 7% 5% 3 4 3 5% 5% 34%	2075
	21st to end	Night	20% 9% 4 8% 4 5% 4 3 5% 5% 33%	1939
May	1st to 10th	Night	20% 10% 3 8% 5% 5% 5% 4 6% 7% 27%	4660
	11th to 20th	Night	15% 7% 3 8% 5% 4 5% 3 5% 7% 38%	4639
	21st to end	Night	19% 7% 3 7% 5% 5% 4 4 6% 7% 34%	5114
June	1st to 10th	Night	16% 8% 3 7% 5% 4 5% 4 6% 7% 36%	1680
	11th to 20th	Night	14% 6% 2 6% 5% 4 4 3 5% 7% 44%	1680
	21st to end	Night	17% 6% 2 7% 6% 4 4 3 6% 8% 36%	1680
July	1st to 10th	Night	14% 6% 3 7% 5% 5% 5% 5% 6% 8% 35%	3680
	11th to 20th	Night	12% 6% 2 6% 4 4 5% 4 5% 8% 44%	3680
	21st to end	Night	8% 5% 2 6% 4 4 5% 4 6% 8% 47%	4006
August	1st to 10th	Night	11% 6% 2 7% 5% 6% 5% 4 7% 8% 40%	2740
	11th to 20th	Night	16% 6% 3 6% 4 4 5% 4 5% 7% 41%	2875
	21st to end	Night	14% 5% 2 6% 5% 4 5% 4 6% 8% 41%	3515
September	1st to 10th	Night	10% 6% 3 7% 5% 4 5% 3 5% 7% 46%	2000
	11th to 20th	Night	15% 5% 2 6% 3 3 3 3 5% 7% 49%	2000
	21st to end	Night	17% 7% 2 7% 4 4 4 2 5% 6% 42%	2285
October	1st to 10th	Night	19% 7% 2 6% 4 4 4 3 5% 5% 41%	2400
	11th to 20th	Night	21% 11% 2 7% 6% 5% 5% 4 4 5% 30%	2400
	21st to end	Night	22% 13% 3 8% 4 5% 5% 3 4 6% 27%	2760
November	1st to 10th	Night	19% 12% 4 7% 4 4 4 4 6% 6% 31%	2726
	11th to 20th	Night	18% 13% 4 9% 5% 6% 5% 3 4 6% 27%	2940
	21st to end	Night	21% 17% 5% 11% 6% 5% 4 3 5% 5% 20%	2940
December	1st to 10th	Night	19% 19% 6% 13% 6% 5% 4 4 5% 5% 14%	4720
	11th to 20th	Night	20% 15% 5% 12% 6% 4 4 2 4 5% 23%	5348
	21st to end	Night	25% 18% 4 12% 5% 4 3 2 4 4 19%	7150

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	68% 3 10% 14% 5%	4662
	11th to 20th	Day	71% 3 7% 10% 9%	4680
	21st to end	Day	67% 3 8% 13% 8% 1	5480
February	1st to 10th	Day	63% 4 9% 17% 6% 1	1890
	11th to 20th	Day	60% 4 12% 15% 9% 1	1852
	21st to end	Day	62% 3 10% 14% 10% 1	1681
March	1st to 10th	Day	61% 3 8% 13% 12% 2	4713
	11th to 20th	Day	56% 3 15% 15% 9% 2	5090
	21st to end	Day	51% 2 7% 21% 16% 2	5809
April	1st to 10th	Day	55% 3 7% 19% 13% 3	2520
	11th to 20th	Day	54% 3 6% 20% 15% 2	2494
	21st to end	Day	55% 2 7% 18% 15% 3	2697
May	1st to 10th	Day	51% 5% 9% 22% 10% 3	8249
	11th to 20th	Day	47% 5% 13% 24% 10% 1	8225
	21st to end	Day	50% 4 11% 21% 13% 1	9061
June	1st to 10th	Day	53% 4 9% 20% 13% 1	2940
	11th to 20th	Day	43% 5% 12% 24% 13% 2	2940
	21st to end	Day	47% 6% 14% 21% 11% 1	2940
July	1st to 10th	Day	44% 6% 15% 26% 9%	6430
	11th to 20th	Day	36% 6% 15% 33% 11%	6425
	21st to end	Day	33% 5% 17% 35% 9%	6868
August	1st to 10th	Day	46% 6% 15% 24% 8%	4392
	11th to 20th	Day	44% 6% 16% 26% 7% 1	4213
	21st to end	Day	37% 6% 16% 28% 11% 1	4349
September	1st to 10th	Day	40% 6% 15% 29% 11%	2400
	11th to 20th	Day	38% 5% 12% 33% 12% 1	2400
	21st to end	Day	46% 6% 14% 24% 10%	2111
October	1st to 10th	Day	50% 5% 10% 27% 7%	3260
	11th to 20th	Day	52% 6% 13% 23% 6% 1	3240
	21st to end	Day	54% 5% 19% 17% 5% 1	3344
November	1st to 10th	Day	53% 4 15% 22% 7%	1788
	11th to 20th	Day	62% 5% 12% 14% 7% 1	1680
	21st to end	Day	71% 5% 10% 8% 5%	1680
December	1st to 10th	Day	76% 5% 8% 9% 2	2680
	11th to 20th	Day	67% 3 7% 15% 8%	3066
	21st to end	Day	70% 4 8% 15% 4	4048
January	1st to 10th	Night	72% 3 10% 11% 4	8234
	11th to 20th	Night	70% 3 10% 11% 5%	8280
	21st to end	Night	66% 3 7% 11% 11%	8699
February	1st to 10th	Night	63% 4 9% 17% 7% 1	2730
	11th to 20th	Night	62% 3 9% 20% 6%	2665
	21st to end	Night	60% 3 9% 18% 9% 1	2124
March	1st to 10th	Night	61% 3 9% 14% 10% 3	5358
	11th to 20th	Night	54% 6% 16% 15% 8% 2	5090
	21st to end	Night	54% 4 8% 19% 12% 3	5365
April	1st to 10th	Night	56% 4 8% 18% 12% 2	2100
	11th to 20th	Night	51% 4 7% 22% 14% 2	2075
	21st to end	Night	54% 3 6% 18% 17% 2	1939
May	1st to 10th	Night	54% 5% 8% 21% 9% 3	4666
	11th to 20th	Night	45% 6% 12% 22% 13% 2	4640
	21st to end	Night	49% 5% 11% 21% 14% 1	5115
June	1st to 10th	Night	46% 5% 12% 25% 10% 1	1680
	11th to 20th	Night	40% 5% 12% 27% 15% 2	1680
	21st to end	Night	46% 6% 13% 22% 13% 1	1680
July	1st to 10th	Night	45% 7% 16% 22% 10% 1	3640
	11th to 20th	Night	38% 6% 13% 31% 11%	3632
	21st to end	Night	34% 6% 12% 37% 12%	3889
August	1st to 10th	Night	40% 7% 14% 26% 13%	2730
	11th to 20th	Night	41% 6% 16% 28% 9%	2902
	21st to end	Night	40% 6% 15% 26% 11% 2	3515
September	1st to 10th	Night	38% 6% 11% 31% 14%	2000
	11th to 20th	Night	35% 5% 15% 35% 10% 1	2000
	21st to end	Night	44% 4 13% 27% 11%	2285
October	1st to 10th	Night	40% 5% 13% 29% 12%	3920
	11th to 20th	Night	49% 5% 14% 23% 8% 1	3899
	21st to end	Night	52% 5% 18% 17% 8%	4446
November	1st to 10th	Night	54% 5% 14% 19% 8%	2726
	11th to 20th	Night	59% 5% 12% 16% 8% 1	2940
	21st to end	Night	67% 5% 12% 14% 3	2940
December	1st to 10th	Night	73% 5% 10% 10% 2	4720
	11th to 20th	Night	66% 3 7% 14% 10%	5348
	21st to end	Night	70% 3 6% 12% 9%	7150

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	22% 18% 35% 21% 4	220
	11th to 20th	Day	30% 20% 31% 15% 3 1	220
	21st to end	Day	19% 19% 35% 21% 6%	308
February	1st to 10th	Day	28% 21% 33% 13% 5%	330
	11th to 20th	Day	27% 26% 36% 10% 1	330
	21st to end	Day	31% 18% 35% 15% 1	397
March	1st to 10th	Day	26% 21% 34% 15% 4	540
	11th to 20th	Day	29% 20% 30% 17% 4	540
	21st to end	Day	29% 21% 30% 15% 5% 1	594
April	1st to 10th	Day	35% 21% 24% 14% 6% 1	540
	11th to 20th	Day	37% 18% 20% 13% 8% 3	532
	21st to end	Day	29% 21% 28% 15% 6% 1	540
May	1st to 10th	Day	26% 17% 28% 20% 7% 2	543
	11th to 20th	Day	20% 17% 33% 18% 8% 3	567
	21st to end	Day	24% 15% 29% 21% 8% 2	617
June	1st to 10th	Day	26% 12% 29% 22% 9% 1	570
	11th to 20th	Day	19% 15% 29% 23% 12% 3	570
	21st to end	Day	20% 14% 30% 21% 12% 2	570
July	1st to 10th	Day	12% 10% 28% 35% 13% 3	565
	11th to 20th	Day	13% 11% 35% 25% 13% 3	564
	21st to end	Day	13% 8% 32% 29% 13% 4	616
August	1st to 10th	Day	14% 7% 25% 31% 18% 5%	526
	11th to 20th	Day	16% 6% 24% 30% 16% 8%	519
	21st to end	Day	14% 11% 27% 27% 15% 6%	583
September	1st to 10th	Day	18% 8% 30% 22% 14% 7%	530
	11th to 20th	Day	15% 9% 20% 23% 21% 13%	530
	21st to end	Day	20% 12% 28% 21% 13% 6%	530
October	1st to 10th	Day	24% 15% 22% 21% 15% 3	530
	11th to 20th	Day	29% 18% 30% 15% 7% 1	530
	21st to end	Day	31% 17% 25% 21% 5% 1	517
November	1st to 10th	Day	30% 15% 33% 15% 7% 1	362
	11th to 20th	Day	24% 21% 35% 11% 7% 1	220
	21st to end	Day	36% 20% 30% 10% 3 1	220
December	1st to 10th	Day	29% 16% 39% 14% 2	220
	11th to 20th	Day	30% 23% 33% 10% 4	220
	21st to end	Day	33% 17% 32% 14% 4 1	242
January	1st to 10th	Night	30% 14% 31% 21% 4	840
	11th to 20th	Night	31% 15% 25% 22% 7% 1	840
	21st to end	Night	18% 14% 34% 26% 7%	924
February	1st to 10th	Night	19% 18% 35% 25% 4 1	840
	11th to 20th	Night	22% 17% 36% 21% 3 1	823
	21st to end	Night	23% 18% 30% 26% 4	692
March	1st to 10th	Night	25% 16% 31% 23% 5%	840
	11th to 20th	Night	24% 17% 33% 20% 5%	840
	21st to end	Night	24% 16% 30% 22% 8%	924
April	1st to 10th	Night	28% 13% 30% 22% 6%	840
	11th to 20th	Night	25% 16% 29% 21% 8%	831
	21st to end	Night	26% 14% 28% 24% 7% 1	679
May	1st to 10th	Night	22% 9% 28% 30% 10% 1	420
	11th to 20th	Night	23% 10% 26% 33% 8%	414
	21st to end	Night	16% 7% 36% 31% 10%	455
June	1st to 10th	Night	18% 10% 26% 37% 8%	420
	11th to 20th	Night	18% 8% 25% 36% 12%	420
	21st to end	Night	20% 6% 21% 41% 11%	420
July	1st to 10th	Night	11% 4 25% 45% 15%	410
	11th to 20th	Night	14% 6% 22% 39% 19%	408
	21st to end	Night	12% 4 21% 46% 16% 1	458
August	1st to 10th	Night	12% 3 19% 40% 25% 1	487
	11th to 20th	Night	14% 4 16% 37% 26% 4	594
	21st to end	Night	15% 6% 24% 34% 19% 2	835
September	1st to 10th	Night	15% 7% 24% 34% 19% 2	800
	11th to 20th	Night	17% 6% 18% 33% 22% 4	800
	21st to end	Night	20% 9% 22% 29% 19% 2	800
October	1st to 10th	Night	22% 10% 25% 26% 15% 1	800
	11th to 20th	Night	28% 11% 29% 22% 9% 1	800
	21st to end	Night	30% 13% 26% 25% 6% 1	880
November	1st to 10th	Night	26% 15% 26% 26% 7% 1	820
	11th to 20th	Night	28% 14% 30% 19% 9%	840
	21st to end	Night	33% 15% 24% 21% 6%	840
December	1st to 10th	Night	31% 16% 30% 18% 5%	840
	11th to 20th	Night	29% 18% 27% 21% 5% 1	840
	21st to end	Night	35% 14% 27% 20% 4	924

Page generated at 2026-07-28 03:25:20. Version ac07

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