Pompeys Pillar National Monument
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Pompeys Pillar National Monument clear sky chart from 2005-11-06 to 2026-02-01.

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	8% 7% 2 6% 4 4 4 4 6% 8% 48%	137531
	Night	8% 8% 3 7% 5% 4 4 4 6% 7% 44%	131933
Transparency	Day	34% 6% 12% 26% 18% 5%	132271
	Night	38% 6% 13% 24% 15% 4	128198
Seeing	Day	12% 8% 26% 31% 19% 5%	17615
	Night	12% 6% 28% 39% 14% 1	27321

By Month

Percentage Cloud Cover SW (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	8% 13% 4 11% 6% 6% 6% 4 5% 6% 31%	3718
	11th to 20th	Day	5% 12% 4 11% 6% 6% 6% 4 7% 7% 33%	3720
	21st to end	Day	2 6% 4 8% 4 4 4 3 5% 6% 53%	4497
February	1st to 10th	Day	10% 12% 5% 10% 7% 6% 5% 4 6% 7% 29%	1800
	11th to 20th	Day	7% 12% 3 11% 6% 6% 5% 4 5% 7% 33%	1755
	21st to end	Day	5% 10% 3 10% 5% 4 5% 5% 7% 8% 38%	1544
March	1st to 10th	Day	4 8% 4 9% 6% 4 4 3 6% 8% 44%	4744
	11th to 20th	Day	6% 9% 3 8% 5% 5% 5% 5% 7% 8% 39%	5000
	21st to end	Day	13% 15% 4 9% 4 4 4 4 6% 8% 28%	5587
April	1st to 10th	Day	11% 10% 3 6% 5% 4 4 4 7% 9% 37%	2400
	11th to 20th	Day	11% 11% 4 7% 5% 5% 5% 4 6% 8% 34%	2393
	21st to end	Day	15% 10% 3 7% 5% 4 4 4 5% 7% 37%	2600
May	1st to 10th	Day	17% 7% 2 5% 3 4 5% 4 5% 6% 42%	6248
	11th to 20th	Day	12% 5% 2 5% 5% 5% 6% 5% 8% 10% 37%	6298
	21st to end	Day	11% 4 2 5% 4 4 5% 4 6% 8% 47%	6925
June	1st to 10th	Day	9% 5% 2 6% 4 4 5% 4 6% 9% 45%	2800
	11th to 20th	Day	8% 5% 2 6% 5% 5% 6% 4 7% 8% 44%	2908
	21st to end	Day	4 3 1 3 3 4 4 4 8% 8% 58%	3000
July	1st to 10th	Day	4 3 1 4 3 4 5% 4 7% 9% 57%	6674
	11th to 20th	Day	5% 2 1 2 2 2 3 3 5% 8% 67%	6340
	21st to end	Day	5% 3 1 4 3 3 4 4 6% 9% 57%	6903
August	1st to 10th	Day	3 2 1 3 3 3 4 4 8% 10% 58%	5855
	11th to 20th	Day	4 2 1 3 2 3 3 4 6% 8% 64%	5798
	21st to end	Day	8% 5% 2 5% 3 3 3 3 4 6% 58%	6207
September	1st to 10th	Day	7% 3 2 3 3 3 3 3 5% 8% 62%	2400
	11th to 20th	Day	9% 5% 2 5% 3 3 3 3 6% 7% 53%	2390
	21st to end	Day	12% 4 1 3 2 3 3 2 4 7% 59%	2110
October	1st to 10th	Day	7% 4 1 4 3 3 3 2 3 6% 63%	3270
	11th to 20th	Day	10% 7% 2 5% 3 2 3 3 4 4 57%	3250
	21st to end	Day	7% 6% 2 5% 3 4 4 4 7% 10% 48%	3431
November	1st to 10th	Day	10% 11% 3 5% 4 4 3 3 5% 7% 43%	1708
	11th to 20th	Day	8% 9% 3 8% 5% 5% 4 5% 6% 6% 40%	1680
	21st to end	Day	6% 9% 3 9% 5% 5% 6% 3 6% 7% 41%	1680
December	1st to 10th	Day	4 8% 3 7% 4 4 5% 4 6% 7% 47%	2700
	11th to 20th	Day	6% 8% 3 8% 7% 6% 5% 4 6% 8% 39%	3106
	21st to end	Day	6% 13% 4 8% 5% 4 4 3 5% 6% 41%	4092
January	1st to 10th	Night	7% 15% 5% 10% 5% 4 5% 4 5% 6% 36%	6467
	11th to 20th	Night	6% 14% 5% 13% 6% 5% 4 3 4 6% 35%	6480
	21st to end	Night	3 8% 4 7% 5% 5% 5% 4 6% 7% 46%	6755
February	1st to 10th	Night	9% 14% 6% 11% 6% 5% 6% 4 5% 6% 28%	2600
	11th to 20th	Night	7% 14% 6% 9% 6% 5% 5% 4 5% 7% 31%	2532
	21st to end	Night	6% 13% 4 11% 5% 4 5% 4 5% 6% 36%	2085
March	1st to 10th	Night	5% 10% 4 8% 5% 4 5% 4 6% 7% 42%	5137
	11th to 20th	Night	8% 9% 3 6% 4 4 5% 4 6% 9% 43%	5000
	21st to end	Night	13% 14% 5% 10% 6% 5% 5% 4 5% 7% 25%	5382
April	1st to 10th	Night	12% 11% 3 7% 5% 5% 4 4 6% 7% 37%	2000
	11th to 20th	Night	12% 10% 5% 8% 6% 5% 5% 4 7% 7% 31%	1952
	21st to end	Night	15% 10% 3 8% 6% 4 4 4 5% 6% 35%	1800
May	1st to 10th	Night	14% 8% 2 6% 4 4 4 4 5% 7% 41%	3732
	11th to 20th	Night	15% 8% 2 7% 5% 5% 5% 5% 6% 8% 35%	3617
	21st to end	Night	9% 4 2 5% 5% 5% 5% 4 6% 9% 48%	3972
June	1st to 10th	Night	10% 5% 2 7% 6% 5% 7% 5% 7% 9% 39%	1600
	11th to 20th	Night	9% 5% 2 6% 5% 5% 5% 5% 6% 10% 42%	1485
	21st to end	Night	7% 4 1 5% 3 5% 4 3 6% 9% 54%	1400
July	1st to 10th	Night	3 3 2 4 4 5% 5% 5% 8% 10% 52%	3272
	11th to 20th	Night	6% 3 2 5% 4 5% 5% 4 5% 7% 54%	3640
	21st to end	Night	5% 3 2 5% 4 5% 5% 5% 8% 10% 47%	3970
August	1st to 10th	Night	3 3 1 6% 5% 5% 6% 5% 7% 10% 49%	3941
	11th to 20th	Night	4 3 1 4 4 4 5% 5% 8% 10% 53%	4051
	21st to end	Night	8% 5% 2 5% 3 3 3 3 5% 7% 55%	4768
September	1st to 10th	Night	6% 4 2 5% 3 3 4 3 6% 6% 59%	2000
	11th to 20th	Night	11% 4 1 5% 4 4 4 3 6% 8% 49%	2006
	21st to end	Night	11% 4 2 4 3 3 3 2 4 7% 56%	2290
October	1st to 10th	Night	9% 4 2 4 2 3 3 3 5% 7% 59%	3920
	11th to 20th	Night	11% 7% 2 5% 3 3 3 2 4 5% 55%	3898
	21st to end	Night	9% 6% 2 6% 4 3 3 3 5% 7% 51%	4335
November	1st to 10th	Night	10% 9% 3 7% 4 4 3 4 5% 8% 43%	2807
	11th to 20th	Night	7% 10% 4 8% 5% 5% 4 4 5% 7% 42%	2940
	21st to end	Night	5% 11% 3 7% 5% 4 4 4 6% 8% 43%	2940
December	1st to 10th	Night	5% 11% 3 8% 5% 4 4 4 5% 6% 43%	4710
	11th to 20th	Night	5% 11% 4 9% 6% 4 5% 4 5% 6% 42%	5321
	21st to end	Night	5% 10% 3 8% 4 4 4 4 5% 8% 45%	7128

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	52% 6% 10% 26% 6%	3719
	11th to 20th	Day	48% 7% 14% 17% 13% 1	3720
	21st to end	Day	31% 5% 16% 31% 16% 1	4497
February	1st to 10th	Day	53% 5% 14% 18% 10%	1800
	11th to 20th	Day	50% 6% 11% 22% 8% 2	1764
	21st to end	Day	42% 6% 15% 23% 12% 2	1544
March	1st to 10th	Day	36% 5% 10% 27% 19% 3	4744
	11th to 20th	Day	41% 6% 13% 30% 9% 1	5000
	21st to end	Day	52% 8% 13% 23% 4	5587
April	1st to 10th	Day	43% 6% 14% 24% 12% 2	2400
	11th to 20th	Day	47% 6% 13% 23% 10% 1	2396
	21st to end	Day	47% 6% 11% 22% 13% 1	2600
May	1st to 10th	Day	41% 6% 11% 25% 15% 2	6248
	11th to 20th	Day	37% 10% 15% 27% 10% 1	6302
	21st to end	Day	33% 7% 13% 32% 15% 1	6926
June	1st to 10th	Day	34% 8% 17% 27% 13% 2	2800
	11th to 20th	Day	36% 7% 16% 23% 14% 4	2908
	21st to end	Day	21% 7% 14% 29% 22% 8%	3000
July	1st to 10th	Day	22% 6% 10% 30% 22% 10%	6603
	11th to 20th	Day	16% 3 7% 26% 35% 13%	6265
	21st to end	Day	22% 5% 11% 22% 25% 14%	6705
August	1st to 10th	Day	23% 5% 11% 24% 23% 14%	4257
	11th to 20th	Day	21% 5% 9% 28% 29% 7%	4197
	21st to end	Day	21% 4 8% 28% 30% 10%	4474
September	1st to 10th	Day	22% 4 8% 25% 28% 13%	2400
	11th to 20th	Day	29% 5% 11% 26% 22% 7%	2390
	21st to end	Day	26% 4 9% 28% 26% 6%	2110
October	1st to 10th	Day	26% 4 7% 22% 30% 11%	3270
	11th to 20th	Day	32% 3 9% 29% 24% 3	3250
	21st to end	Day	32% 5% 12% 30% 19% 3	3431
November	1st to 10th	Day	40% 5% 11% 27% 14% 4	1708
	11th to 20th	Day	42% 6% 14% 23% 12% 3	1680
	21st to end	Day	42% 5% 13% 24% 13% 2	1680
December	1st to 10th	Day	35% 5% 19% 25% 14% 2	2700
	11th to 20th	Day	42% 6% 22% 23% 7% 1	3104
	21st to end	Day	44% 5% 9% 26% 13% 4	4092
January	1st to 10th	Night	49% 5% 15% 24% 6%	6467
	11th to 20th	Night	52% 4 13% 18% 12% 2	6480
	21st to end	Night	35% 8% 14% 30% 11% 3	6755
February	1st to 10th	Night	56% 6% 11% 17% 9% 1	2600
	11th to 20th	Night	52% 6% 13% 20% 9% 1	2533
	21st to end	Night	47% 6% 14% 20% 11% 2	2085
March	1st to 10th	Night	38% 5% 11% 29% 16% 1	5137
	11th to 20th	Night	37% 7% 18% 27% 12% 1	5000
	21st to end	Night	56% 9% 14% 15% 5%	5382
April	1st to 10th	Night	47% 6% 14% 20% 11% 2	2000
	11th to 20th	Night	49% 7% 12% 23% 8%	1952
	21st to end	Night	48% 7% 11% 21% 12% 1	1800
May	1st to 10th	Night	41% 6% 12% 23% 16% 2	3730
	11th to 20th	Night	44% 8% 13% 24% 9% 2	3618
	21st to end	Night	32% 8% 15% 32% 13% 1	3972
June	1st to 10th	Night	39% 8% 16% 24% 10% 2	1600
	11th to 20th	Night	37% 9% 17% 21% 13% 4	1485
	21st to end	Night	27% 6% 14% 25% 22% 6%	1400
July	1st to 10th	Night	23% 7% 14% 30% 18% 8%	3235
	11th to 20th	Night	28% 6% 7% 19% 28% 11%	3592
	21st to end	Night	27% 8% 13% 21% 23% 9%	3856
August	1st to 10th	Night	28% 6% 13% 23% 17% 12%	2863
	11th to 20th	Night	26% 6% 12% 30% 21% 5%	2928
	21st to end	Night	24% 5% 9% 23% 30% 9%	3432
September	1st to 10th	Night	24% 5% 9% 21% 26% 14%	2000
	11th to 20th	Night	31% 6% 10% 25% 22% 6%	2006
	21st to end	Night	30% 3 9% 26% 25% 7%	2290
October	1st to 10th	Night	26% 5% 7% 24% 25% 12%	3920
	11th to 20th	Night	33% 3 9% 25% 27% 3	3898
	21st to end	Night	33% 4 13% 29% 15% 7%	4335
November	1st to 10th	Night	40% 6% 12% 25% 14% 4	2807
	11th to 20th	Night	41% 5% 14% 26% 13% 2	2940
	21st to end	Night	38% 5% 16% 27% 12% 3	2940
December	1st to 10th	Night	40% 6% 17% 25% 11% 1	4710
	11th to 20th	Night	43% 6% 15% 27% 9% 1	5322
	21st to end	Night	38% 4 12% 29% 15% 3	7128

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	8% 10% 34% 31% 14% 3	330
	11th to 20th	Day	15% 13% 29% 28% 14% 2	330
	21st to end	Day	7% 9% 46% 29% 7% 2	363
February	1st to 10th	Day	17% 14% 36% 27% 5% 1	300
	11th to 20th	Day	12% 13% 31% 34% 8% 2	300
	21st to end	Day	12% 14% 34% 30% 9% 2	249
March	1st to 10th	Day	9% 13% 33% 30% 13% 2	401
	11th to 20th	Day	14% 11% 27% 30% 15% 3	500
	21st to end	Day	20% 12% 25% 29% 12% 2	550
April	1st to 10th	Day	17% 11% 31% 28% 11% 1	500
	11th to 20th	Day	17% 12% 36% 26% 8% 1	492
	21st to end	Day	19% 10% 25% 26% 16% 4	500
May	1st to 10th	Day	16% 8% 20% 28% 22% 6%	663
	11th to 20th	Day	18% 6% 22% 28% 19% 6%	725
	21st to end	Day	17% 5% 21% 28% 19% 10%	789
June	1st to 10th	Day	9% 6% 24% 30% 24% 8%	730
	11th to 20th	Day	12% 10% 26% 33% 16% 3	730
	21st to end	Day	6% 5% 23% 36% 25% 5%	730
July	1st to 10th	Day	4 4 19% 35% 31% 6%	721
	11th to 20th	Day	5% 6% 21% 39% 26% 4	718
	21st to end	Day	5% 3 20% 38% 28% 7%	794
August	1st to 10th	Day	6% 3 23% 37% 25% 6%	564
	11th to 20th	Day	9% 2 16% 35% 30% 8%	517
	21st to end	Day	4 4 20% 34% 26% 11%	583
September	1st to 10th	Day	7% 5% 20% 35% 24% 8%	530
	11th to 20th	Day	11% 5% 20% 29% 26% 9%	530
	21st to end	Day	13% 6% 19% 27% 27% 8%	440
October	1st to 10th	Day	16% 4 18% 29% 25% 7%	330
	11th to 20th	Day	16% 8% 25% 26% 18% 7%	330
	21st to end	Day	13% 11% 32% 27% 13% 4	363
November	1st to 10th	Day	17% 9% 26% 32% 13% 2	330
	11th to 20th	Day	12% 11% 33% 29% 15% 1	330
	21st to end	Day	11% 10% 32% 36% 12%	330
December	1st to 10th	Day	11% 12% 42% 25% 8% 1	330
	11th to 20th	Day	15% 11% 32% 31% 10% 1	330
	21st to end	Day	11% 9% 34% 34% 10% 1	363
January	1st to 10th	Night	13% 8% 34% 35% 10% 1	1050
	11th to 20th	Night	14% 11% 34% 30% 10%	1050
	21st to end	Night	13% 9% 39% 31% 8% 1	990
February	1st to 10th	Night	16% 10% 34% 31% 9% 1	800
	11th to 20th	Night	14% 7% 33% 37% 9%	784
	21st to end	Night	12% 8% 31% 36% 12% 2	660
March	1st to 10th	Night	11% 6% 34% 36% 12% 1	800
	11th to 20th	Night	12% 4 30% 41% 12% 1	800
	21st to end	Night	18% 8% 24% 36% 14% 1	837
April	1st to 10th	Night	18% 7% 27% 38% 10%	600
	11th to 20th	Night	15% 9% 29% 37% 9%	593
	21st to end	Night	20% 6% 23% 39% 13% 1	600
May	1st to 10th	Night	16% 6% 19% 38% 20% 1	600
	11th to 20th	Night	17% 5% 18% 37% 22% 1	591
	21st to end	Night	18% 4 19% 39% 19%	650
June	1st to 10th	Night	10% 6% 24% 39% 20% 2	600
	11th to 20th	Night	12% 6% 29% 40% 13%	485
	21st to end	Night	9% 2 20% 48% 21% 1	400
July	1st to 10th	Night	5% 2 16% 50% 26%	428
	11th to 20th	Night	5% 5% 26% 48% 15%	582
	21st to end	Night	4 3 22% 54% 18%	657
August	1st to 10th	Night	6% 3 20% 51% 20% 1	597
	11th to 20th	Night	5% 2 18% 54% 20% 1	594
	21st to end	Night	8% 4 20% 48% 19% 1	660
September	1st to 10th	Night	8% 3 22% 46% 21% 1	600
	11th to 20th	Night	13% 3 16% 47% 20% 2	606
	21st to end	Night	13% 4 20% 37% 24% 1	800
October	1st to 10th	Night	17% 5% 18% 38% 21% 2	800
	11th to 20th	Night	16% 6% 24% 36% 18% 1	800
	21st to end	Night	12% 7% 29% 37% 13% 1	927
November	1st to 10th	Night	15% 9% 27% 40% 9% 1	1025
	11th to 20th	Night	13% 9% 34% 34% 9%	1050
	21st to end	Night	10% 7% 35% 39% 8%	1050
December	1st to 10th	Night	11% 9% 36% 34% 9%	1050
	11th to 20th	Night	12% 8% 35% 36% 8% 1	1050
	21st to end	Night	14% 8% 32% 37% 9%	1155

Page generated at 2026-01-28 23:21:42. Version ac07

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