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 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	16% 11% 4 9% 5% 5% 4 4 5% 6% 31%	109113
	Night	16% 12% 4 10% 6% 5% 4 3 5% 6% 29%	110215
Transparency	Day	52% 4 12% 21% 9% 1	112665
	Night	56% 4 11% 19% 9% 1	114827
Seeing	Day	23% 15% 29% 20% 9% 3	14787
	Night	24% 12% 27% 26% 10% 1	24086

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% 17% 9% 5% 4 3 3 4 20%	3597
	11th to 20th	Day	12% 16% 6% 15% 9% 6% 5% 3 4 5% 19%	3570
	21st to end	Day	11% 18% 7% 15% 7% 5% 4 2 4 5% 21%	4234
February	1st to 10th	Day	12% 16% 6% 15% 8% 5% 4 4 5% 4 22%	1800
	11th to 20th	Day	12% 16% 5% 11% 7% 4 5% 3 5% 6% 25%	1753
	21st to end	Day	17% 15% 4 10% 6% 5% 4 3 5% 5% 25%	1603
March	1st to 10th	Day	20% 14% 5% 10% 5% 4 4 3 3 5% 27%	3308
	11th to 20th	Day	11% 16% 6% 11% 6% 5% 4 4 5% 5% 27%	3590
	21st to end	Day	13% 8% 3 7% 5% 4 3 3 5% 5% 44%	4030
April	1st to 10th	Day	22% 13% 3 6% 5% 4 3 3 5% 6% 30%	2280
	11th to 20th	Day	22% 9% 3 7% 5% 3 3 3 5% 4 35%	2254
	21st to end	Day	23% 10% 3 7% 5% 4 3 3 5% 5% 33%	2439
May	1st to 10th	Day	19% 9% 3 8% 5% 4 5% 4 5% 7% 32%	4426
	11th to 20th	Day	17% 8% 3 7% 5% 4 5% 4 5% 8% 35%	4398
	21st to end	Day	16% 7% 2 7% 5% 5% 4 4 5% 7% 37%	4837
June	1st to 10th	Day	19% 9% 3 8% 5% 5% 5% 4 6% 6% 30%	2660
	11th to 20th	Day	15% 6% 2 6% 4 4 5% 5% 6% 8% 39%	2660
	21st to end	Day	17% 7% 2 7% 5% 6% 5% 5% 6% 7% 33%	2660
July	1st to 10th	Day	12% 7% 3 7% 5% 5% 6% 4 7% 9% 35%	4440
	11th to 20th	Day	12% 6% 2 6% 4 5% 5% 5% 6% 9% 40%	4440
	21st to end	Day	10% 6% 2 6% 4 4 4 3 6% 8% 47%	4814
August	1st to 10th	Day	13% 7% 3 8% 5% 5% 5% 4 7% 8% 34%	4271
	11th to 20th	Day	17% 7% 3 6% 4 4 5% 4 5% 8% 37%	4044
	21st to end	Day	10% 5% 2 7% 5% 5% 5% 5% 8% 11% 39%	4216
September	1st to 10th	Day	14% 6% 2 6% 5% 4 5% 3 6% 8% 42%	2280
	11th to 20th	Day	14% 6% 2 6% 5% 4 5% 4 6% 6% 44%	2280
	21st to end	Day	18% 7% 2 7% 4 5% 4 4 6% 7% 36%	2006
October	1st to 10th	Day	20% 8% 3 7% 5% 5% 5% 4 4 6% 33%	1900
	11th to 20th	Day	23% 11% 4 9% 5% 4 4 3 5% 6% 27%	1900
	21st to end	Day	25% 11% 3 8% 5% 4 5% 3 5% 5% 25%	1976
November	1st to 10th	Day	16% 12% 3 8% 5% 4 4 4 5% 6% 34%	1701
	11th to 20th	Day	18% 14% 4 9% 6% 6% 5% 4 4 6% 25%	1600
	21st to end	Day	23% 16% 6% 9% 7% 6% 5% 3 5% 4 16%	1600
December	1st to 10th	Day	19% 22% 6% 12% 6% 6% 5% 3 4 4 13%	2600
	11th to 20th	Day	16% 17% 6% 13% 6% 5% 4 3 3 5% 22%	2986
	21st to end	Day	22% 19% 5% 14% 5% 5% 4 2 3 4 19%	3960
January	1st to 10th	Night	13% 19% 9% 18% 6% 5% 4 3 3 4 17%	6349
	11th to 20th	Night	11% 14% 6% 15% 9% 6% 6% 4 5% 5% 19%	6315
	21st to end	Night	11% 19% 7% 13% 7% 6% 4 3 4 4 20%	6720
February	1st to 10th	Night	12% 15% 5% 14% 8% 6% 5% 4 4 5% 22%	2600
	11th to 20th	Night	12% 16% 6% 11% 6% 5% 4 3 4 5% 26%	2533
	21st to end	Night	14% 14% 5% 11% 7% 5% 4 3 4 6% 27%	2026
March	1st to 10th	Night	20% 13% 5% 7% 5% 5% 4 2 4 4 31%	3750
	11th to 20th	Night	16% 17% 5% 10% 5% 5% 5% 4 5% 6% 24%	3589
	21st to end	Night	13% 9% 3 9% 5% 5% 4 3 5% 7% 37%	3741
April	1st to 10th	Night	20% 12% 4 8% 5% 4 4 3 4 5% 30%	1900
	11th to 20th	Night	20% 9% 3 7% 5% 3 4 3 5% 6% 35%	1875
	21st to end	Night	21% 10% 4 9% 4 4 4 3 5% 5% 32%	1755
May	1st to 10th	Night	21% 10% 3 8% 4 4 4 3 5% 6% 31%	2514
	11th to 20th	Night	18% 7% 3 8% 5% 5% 4 4 6% 7% 33%	2495
	21st to end	Night	13% 7% 3 7% 5% 5% 5% 4 5% 7% 39%	2738
June	1st to 10th	Night	16% 8% 3 8% 5% 4 5% 4 6% 7% 35%	1520
	11th to 20th	Night	13% 6% 2 6% 5% 4 4 4 5% 7% 44%	1520
	21st to end	Night	18% 7% 2 7% 6% 4 4 3 5% 7% 36%	1520
July	1st to 10th	Night	12% 7% 3 8% 6% 6% 6% 5% 6% 7% 35%	2520
	11th to 20th	Night	14% 6% 3 6% 4 5% 5% 5% 5% 7% 40%	2520
	21st to end	Night	9% 6% 2 6% 4 4 5% 4 6% 9% 45%	2739
August	1st to 10th	Night	11% 6% 2 7% 5% 6% 5% 4 7% 8% 40%	2655
	11th to 20th	Night	16% 6% 3 6% 4 4 5% 4 5% 7% 41%	2785
	21st to end	Night	13% 5% 2 6% 5% 4 5% 4 6% 8% 42%	3407
September	1st to 10th	Night	11% 6% 3 6% 5% 4 5% 3 5% 6% 46%	1900
	11th to 20th	Night	15% 5% 2 6% 3 3 3 3 5% 7% 48%	1900
	21st to end	Night	18% 7% 2 7% 4 3 3 2 5% 6% 42%	2170
October	1st to 10th	Night	20% 7% 2 6% 4 4 4 3 5% 5% 40%	2280
	11th to 20th	Night	21% 11% 2 7% 6% 5% 4 4 4 5% 30%	2280
	21st to end	Night	23% 13% 3 8% 4 5% 5% 4 4 6% 26%	2622
November	1st to 10th	Night	19% 11% 4 7% 4 4 4 4 5% 6% 31%	2593
	11th to 20th	Night	18% 12% 4 9% 5% 6% 5% 3 4 6% 27%	2800
	21st to end	Night	21% 16% 5% 11% 6% 5% 4 3 5% 5% 20%	2800
December	1st to 10th	Night	19% 20% 6% 13% 6% 5% 4 3 5% 5% 14%	4580
	11th to 20th	Night	21% 15% 5% 11% 6% 4 4 2 3 5% 23%	5208
	21st to end	Night	25% 18% 4 12% 5% 4 3 2 4 4 19%	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	71% 2 9% 11% 6%	3598
	11th to 20th	Day	68% 4 9% 11% 7%	3600
	21st to end	Day	67% 3 9% 13% 7% 1	4234
February	1st to 10th	Day	64% 4 9% 17% 6% 1	1800
	11th to 20th	Day	60% 4 12% 14% 9% 1	1762
	21st to end	Day	61% 3 10% 14% 10% 1	1603
March	1st to 10th	Day	62% 2 9% 16% 10% 1	3311
	11th to 20th	Day	60% 3 12% 15% 9% 2	3590
	21st to end	Day	42% 3 9% 26% 17% 3	4030
April	1st to 10th	Day	55% 3 7% 19% 12% 3	2280
	11th to 20th	Day	53% 3 7% 21% 15% 2	2254
	21st to end	Day	55% 2 7% 17% 14% 3	2439
May	1st to 10th	Day	51% 5% 10% 22% 11% 2	4440
	11th to 20th	Day	47% 4 14% 24% 11% 1	4402
	21st to end	Day	46% 4 12% 19% 16% 2	4837
June	1st to 10th	Day	54% 4 10% 20% 12% 1	2660
	11th to 20th	Day	43% 5% 12% 24% 14% 2	2660
	21st to end	Day	48% 6% 14% 20% 11% 1	2660
July	1st to 10th	Day	43% 5% 15% 26% 10% 1	4370
	11th to 20th	Day	39% 6% 17% 29% 9%	4365
	21st to end	Day	35% 5% 15% 34% 10%	4661
August	1st to 10th	Day	47% 6% 15% 24% 8%	4257
	11th to 20th	Day	45% 6% 16% 26% 7% 1	4083
	21st to end	Day	37% 6% 16% 28% 12% 1	4216
September	1st to 10th	Day	40% 6% 14% 29% 11%	2280
	11th to 20th	Day	39% 5% 12% 31% 11% 1	2280
	21st to end	Day	46% 6% 14% 24% 9%	2006
October	1st to 10th	Day	51% 5% 10% 27% 6%	3160
	11th to 20th	Day	52% 6% 13% 23% 6%	3140
	21st to end	Day	53% 5% 19% 17% 5%	3240
November	1st to 10th	Day	52% 4 15% 22% 6%	1701
	11th to 20th	Day	61% 5% 13% 14% 7% 1	1600
	21st to end	Day	71% 5% 10% 9% 5%	1600
December	1st to 10th	Day	76% 5% 8% 9% 2	2600
	11th to 20th	Day	67% 3 7% 15% 8%	2986
	21st to end	Day	70% 4 8% 15% 4	3960
January	1st to 10th	Night	73% 2 10% 11% 3	6349
	11th to 20th	Night	67% 3 12% 13% 5%	6360
	21st to end	Night	68% 3 8% 10% 11%	6720
February	1st to 10th	Night	64% 4 9% 16% 7% 1	2600
	11th to 20th	Night	62% 3 9% 19% 7%	2535
	21st to end	Night	59% 3 9% 18% 9% 1	2026
March	1st to 10th	Night	58% 3 11% 18% 9% 2	3760
	11th to 20th	Night	61% 3 13% 15% 7% 1	3590
	21st to end	Night	47% 4 8% 21% 16% 4	3741
April	1st to 10th	Night	55% 4 9% 18% 12% 2	1900
	11th to 20th	Night	50% 4 7% 22% 14% 2	1875
	21st to end	Night	55% 3 6% 17% 16% 2	1755
May	1st to 10th	Night	53% 4 10% 20% 10% 3	2520
	11th to 20th	Night	49% 5% 11% 22% 11% 2	2496
	21st to end	Night	46% 4 11% 21% 16% 2	2739
June	1st to 10th	Night	47% 5% 13% 25% 8% 1	1520
	11th to 20th	Night	40% 5% 12% 26% 15% 2	1520
	21st to end	Night	47% 6% 13% 21% 13% 1	1520
July	1st to 10th	Night	45% 7% 15% 19% 13% 1	2480
	11th to 20th	Night	43% 6% 12% 30% 9%	2472
	21st to end	Night	36% 6% 13% 32% 13%	2651
August	1st to 10th	Night	41% 8% 13% 26% 13%	2645
	11th to 20th	Night	42% 6% 16% 27% 8%	2812
	21st to end	Night	40% 6% 15% 26% 12% 2	3407
September	1st to 10th	Night	39% 6% 10% 30% 14%	1900
	11th to 20th	Night	36% 5% 15% 34% 10% 1	1900
	21st to end	Night	44% 4 14% 28% 10%	2170
October	1st to 10th	Night	41% 5% 13% 29% 12%	3800
	11th to 20th	Night	50% 5% 14% 23% 8%	3779
	21st to end	Night	53% 5% 18% 16% 7%	4308
November	1st to 10th	Night	53% 5% 14% 19% 8%	2593
	11th to 20th	Night	59% 5% 12% 16% 8% 1	2800
	21st to end	Night	66% 5% 12% 14% 3	2800
December	1st to 10th	Night	73% 5% 10% 10% 2	4580
	11th to 20th	Night	66% 3 7% 14% 10%	5208
	21st to end	Night	70% 3 6% 12% 9%	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	23% 19% 35% 20% 4 1	200
	11th to 20th	Day	29% 19% 32% 17% 4 1	200
	21st to end	Day	20% 20% 35% 20% 6%	280
February	1st to 10th	Day	30% 22% 32% 12% 4	300
	11th to 20th	Day	29% 26% 36% 9% 1	300
	21st to end	Day	31% 19% 34% 15% 1	367
March	1st to 10th	Day	27% 20% 33% 16% 4	500
	11th to 20th	Day	25% 21% 31% 18% 4	500
	21st to end	Day	28% 20% 30% 16% 5% 1	530
April	1st to 10th	Day	33% 19% 25% 15% 7% 1	460
	11th to 20th	Day	37% 17% 21% 15% 8% 3	452
	21st to end	Day	29% 22% 26% 15% 6% 1	460
May	1st to 10th	Day	28% 14% 27% 22% 7% 3	463
	11th to 20th	Day	20% 17% 31% 19% 9% 4	487
	21st to end	Day	22% 15% 30% 23% 8% 2	529
June	1st to 10th	Day	25% 12% 30% 23% 9% 1	490
	11th to 20th	Day	18% 14% 28% 24% 13% 3	490
	21st to end	Day	21% 13% 30% 21% 13% 2	490
July	1st to 10th	Day	12% 9% 26% 37% 13% 3	485
	11th to 20th	Day	12% 9% 35% 26% 14% 4	484
	21st to end	Day	13% 8% 31% 31% 14% 4	532
August	1st to 10th	Day	15% 8% 26% 29% 17% 5%	486
	11th to 20th	Day	16% 6% 24% 29% 16% 9%	479
	21st to end	Day	15% 11% 26% 27% 15% 6%	539
September	1st to 10th	Day	18% 8% 31% 23% 13% 7%	490
	11th to 20th	Day	16% 9% 21% 21% 20% 12%	490
	21st to end	Day	20% 12% 27% 22% 13% 7%	490
October	1st to 10th	Day	25% 15% 22% 20% 14% 3	490
	11th to 20th	Day	30% 19% 28% 15% 8% 1	490
	21st to end	Day	31% 17% 25% 21% 5% 1	479
November	1st to 10th	Day	29% 14% 33% 16% 7% 1	335
	11th to 20th	Day	25% 23% 34% 12% 7% 1	200
	21st to end	Day	35% 20% 30% 11% 4 2	200
December	1st to 10th	Day	31% 14% 39% 14% 2 1	200
	11th to 20th	Day	30% 25% 32% 10% 4 1	200
	21st to end	Day	34% 15% 31% 15% 4 1	220
January	1st to 10th	Night	30% 14% 32% 19% 4	800
	11th to 20th	Night	30% 14% 26% 23% 7% 1	800
	21st to end	Night	19% 14% 34% 26% 7%	880
February	1st to 10th	Night	20% 18% 35% 23% 4 1	800
	11th to 20th	Night	23% 17% 36% 21% 3 1	783
	21st to end	Night	23% 18% 29% 26% 4	660
March	1st to 10th	Night	25% 16% 31% 23% 5%	800
	11th to 20th	Night	24% 17% 33% 21% 5% 1	800
	21st to end	Night	23% 16% 31% 22% 9%	863
April	1st to 10th	Night	28% 13% 30% 23% 6%	760
	11th to 20th	Night	25% 16% 29% 21% 8%	751
	21st to end	Night	26% 14% 28% 24% 8% 1	615
May	1st to 10th	Night	22% 8% 28% 31% 9% 1	380
	11th to 20th	Night	24% 8% 26% 33% 8%	374
	21st to end	Night	16% 5% 37% 31% 10%	411
June	1st to 10th	Night	19% 10% 26% 37% 8% 1	380
	11th to 20th	Night	17% 7% 25% 37% 13% 1	380
	21st to end	Night	21% 7% 21% 40% 12% 1	380
July	1st to 10th	Night	11% 4 26% 43% 16%	370
	11th to 20th	Night	14% 6% 21% 39% 20%	368
	21st to end	Night	11% 4 21% 47% 17% 1	416
August	1st to 10th	Night	12% 4 20% 39% 24% 1	462
	11th to 20th	Night	14% 4 15% 37% 26% 4	564
	21st to end	Night	15% 6% 24% 34% 19% 2	793
September	1st to 10th	Night	15% 7% 24% 33% 19% 2	760
	11th to 20th	Night	18% 6% 18% 32% 22% 4	760
	21st to end	Night	21% 9% 22% 28% 18% 2	760
October	1st to 10th	Night	23% 11% 25% 25% 15% 1	760
	11th to 20th	Night	28% 11% 28% 22% 10% 1	760
	21st to end	Night	31% 13% 26% 24% 6% 1	836
November	1st to 10th	Night	25% 15% 26% 26% 7% 1	780
	11th to 20th	Night	28% 14% 30% 19% 9% 1	800
	21st to end	Night	34% 15% 23% 21% 7%	800
December	1st to 10th	Night	32% 16% 29% 18% 5%	800
	11th to 20th	Night	29% 17% 27% 22% 5% 1	800
	21st to end	Night	35% 14% 26% 20% 5%	880

Page generated at 2025-03-24 09:04:33. Version ac07

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