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 2024-07-02.

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	9% 7% 2 6% 4 4 5% 4 6% 8% 45%	90176
	Night	8% 9% 3 7% 5% 4 5% 4 6% 8% 42%	89174
Transparency	Day	36% 6% 13% 25% 15% 4	89876
	Night	40% 6% 14% 24% 13% 3	88996
Seeing	Day	12% 8% 26% 31% 19% 5%	15466
	Night	13% 6% 28% 39% 14% 1	25117

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	5% 11% 4 11% 6% 6% 7% 5% 5% 6% 35%	2538
	11th to 20th	Day	6% 9% 3 8% 6% 7% 7% 6% 8% 7% 32%	2540
	21st to end	Day	3 7% 3 7% 4 4 5% 4 6% 8% 51%	3064
February	1st to 10th	Day	9% 12% 5% 9% 7% 6% 5% 4 6% 7% 30%	1710
	11th to 20th	Day	7% 12% 3 11% 5% 6% 5% 4 5% 7% 32%	1665
	21st to end	Day	5% 10% 3 10% 6% 4 5% 5% 7% 8% 37%	1469
March	1st to 10th	Day	5% 7% 3 7% 6% 5% 4 4 7% 9% 44%	3304
	11th to 20th	Day	6% 8% 3 8% 4 5% 4 4 6% 7% 46%	3490
	21st to end	Day	14% 16% 4 10% 5% 5% 4 4 5% 7% 26%	3900
April	1st to 10th	Day	12% 10% 3 6% 5% 4 4 5% 7% 9% 36%	2280
	11th to 20th	Day	11% 11% 4 7% 5% 5% 5% 4 6% 8% 33%	2272
	21st to end	Day	15% 9% 3 7% 5% 4 4 4 5% 7% 37%	2470
May	1st to 10th	Day	19% 9% 3 7% 4 5% 5% 4 6% 6% 33%	4366
	11th to 20th	Day	9% 5% 2 6% 5% 5% 6% 5% 8% 10% 40%	4388
	21st to end	Day	15% 5% 2 5% 5% 4 5% 5% 7% 9% 39%	4825
June	1st to 10th	Day	10% 5% 2 6% 4 5% 5% 4 7% 10% 44%	2660
	11th to 20th	Day	8% 5% 2 6% 6% 5% 6% 4 7% 8% 44%	2762
	21st to end	Day	4 3 1 3 3 4 4 4 8% 8% 58%	2850
July	1st to 10th	Day	4 3 1 3 3 4 4 3 7% 9% 58%	2678
	11th to 20th	Day	2 2 1 4 3 3 4 3 5% 10% 62%	2520
	21st to end	Day	3 2 1 4 3 3 4 3 6% 8% 64%	2742
August	1st to 10th	Day	5% 3 1 3 3 3 4 3 6% 8% 59%	2362
	11th to 20th	Day	6% 3 1 4 2 3 3 3 6% 7% 61%	2299
	21st to end	Day	5% 3 1 3 3 3 4 3 6% 9% 60%	2469
September	1st to 10th	Day	8% 4 2 3 3 3 3 3 5% 8% 60%	2160
	11th to 20th	Day	9% 5% 2 5% 3 3 3 3 5% 7% 56%	2152
	21st to end	Day	13% 5% 1 4 2 2 3 2 4 7% 57%	1900
October	1st to 10th	Day	13% 8% 2 6% 5% 4 3 3 4 7% 45%	1800
	11th to 20th	Day	13% 8% 3 6% 4 3 4 4 5% 5% 45%	1800
	21st to end	Day	10% 8% 3 6% 4 3 4 4 6% 8% 45%	1919
November	1st to 10th	Day	11% 11% 3 5% 4 4 3 3 5% 7% 44%	1542
	11th to 20th	Day	8% 10% 3 8% 5% 5% 4 5% 6% 7% 40%	1520
	21st to end	Day	7% 9% 3 8% 5% 5% 5% 3 6% 7% 42%	1520
December	1st to 10th	Day	6% 11% 3 10% 5% 5% 6% 3 7% 6% 38%	1520
	11th to 20th	Day	6% 8% 3 8% 6% 6% 4 4 6% 9% 40%	1926
	21st to end	Day	6% 10% 3 7% 5% 4 4 3 5% 6% 46%	2794
January	1st to 10th	Night	5% 10% 4 9% 6% 5% 5% 4 5% 7% 40%	4417
	11th to 20th	Night	6% 13% 5% 12% 7% 5% 4 3 5% 7% 33%	4430
	21st to end	Night	5% 8% 3 8% 5% 6% 5% 5% 8% 9% 39%	4620
February	1st to 10th	Night	9% 14% 5% 11% 6% 5% 6% 4 5% 6% 28%	2470
	11th to 20th	Night	7% 14% 5% 9% 6% 5% 5% 4 5% 7% 31%	2402
	21st to end	Night	6% 13% 4 11% 5% 4 6% 4 5% 6% 34%	1984
March	1st to 10th	Night	5% 10% 5% 9% 6% 4 5% 5% 6% 7% 38%	3562
	11th to 20th	Night	6% 7% 2 5% 4 5% 5% 4 6% 9% 48%	3490
	21st to end	Night	14% 15% 5% 11% 6% 5% 5% 4 5% 7% 22%	3749
April	1st to 10th	Night	13% 11% 3 7% 5% 5% 4 4 6% 7% 36%	1900
	11th to 20th	Night	12% 11% 5% 8% 6% 5% 5% 4 7% 7% 31%	1854
	21st to end	Night	15% 10% 3 7% 6% 4 4 4 5% 6% 35%	1710
May	1st to 10th	Night	18% 11% 3 6% 5% 4 4 4 6% 8% 33%	2604
	11th to 20th	Night	9% 7% 2 7% 5% 5% 6% 5% 7% 8% 39%	2517
	21st to end	Night	12% 5% 2 6% 6% 5% 6% 4 6% 9% 38%	2762
June	1st to 10th	Night	10% 5% 2 6% 6% 4 7% 4 7% 9% 39%	1520
	11th to 20th	Night	10% 5% 2 6% 5% 5% 4 5% 6% 10% 42%	1411
	21st to end	Night	7% 4 1 5% 4 5% 4 3 6% 8% 54%	1330
July	1st to 10th	Night	5% 3 2 3 3 5% 4 4 7% 11% 54%	1306
	11th to 20th	Night	4 3 2 4 4 5% 5% 4 6% 8% 56%	1440
	21st to end	Night	3 3 2 4 3 4 5% 4 7% 9% 55%	1576
August	1st to 10th	Night	4 4 1 5% 4 5% 4 5% 6% 9% 54%	1575
	11th to 20th	Night	5% 4 1 4 3 3 4 3 6% 7% 58%	1602
	21st to end	Night	7% 4 2 6% 4 4 4 4 5% 8% 51%	1885
September	1st to 10th	Night	6% 5% 2 5% 3 3 4 3 5% 6% 58%	1800
	11th to 20th	Night	11% 4 1 4 4 4 4 3 6% 8% 52%	1804
	21st to end	Night	12% 5% 2 4 3 3 3 3 4 7% 54%	2060
October	1st to 10th	Night	14% 7% 3 6% 3 4 4 4 6% 7% 43%	2160
	11th to 20th	Night	12% 7% 2 5% 4 3 4 3 4 6% 50%	2160
	21st to end	Night	10% 6% 2 6% 5% 3 4 3 7% 8% 44%	2417
November	1st to 10th	Night	11% 9% 3 7% 5% 4 3 4 5% 8% 42%	2533
	11th to 20th	Night	7% 10% 4 8% 5% 4 4 4 5% 7% 42%	2660
	21st to end	Night	6% 11% 3 6% 5% 4 4 4 6% 7% 45%	2660
December	1st to 10th	Night	6% 12% 3 11% 7% 5% 4 4 5% 7% 36%	2660
	11th to 20th	Night	5% 8% 4 8% 5% 4 5% 4 5% 7% 46%	3271
	21st to end	Night	6% 9% 3 7% 4 4 4 3 5% 8% 49%	4873

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	47% 8% 10% 30% 5%	2539
	11th to 20th	Day	46% 9% 14% 20% 10% 1	2540
	21st to end	Day	31% 7% 21% 27% 13% 1	3064
February	1st to 10th	Day	52% 5% 14% 18% 9%	1710
	11th to 20th	Day	50% 6% 12% 22% 8% 2	1674
	21st to end	Day	44% 6% 15% 22% 12% 2	1469
March	1st to 10th	Day	35% 5% 13% 28% 18% 1	3304
	11th to 20th	Day	36% 7% 16% 31% 10% 1	3490
	21st to end	Day	55% 9% 13% 18% 5%	3900
April	1st to 10th	Day	43% 6% 14% 23% 11% 2	2280
	11th to 20th	Day	48% 6% 14% 22% 10% 1	2275
	21st to end	Day	47% 6% 11% 22% 13% 1	2470
May	1st to 10th	Day	49% 7% 12% 23% 9% 2	4366
	11th to 20th	Day	34% 10% 13% 29% 12% 2	4392
	21st to end	Day	39% 8% 14% 30% 9% 1	4825
June	1st to 10th	Day	35% 8% 18% 25% 12% 2	2660
	11th to 20th	Day	36% 7% 16% 23% 15% 4	2762
	21st to end	Day	21% 7% 14% 28% 22% 8%	2850
July	1st to 10th	Day	21% 5% 11% 31% 24% 7%	2606
	11th to 20th	Day	18% 4 8% 24% 30% 15%	2445
	21st to end	Day	17% 4 9% 22% 32% 17%	2590
August	1st to 10th	Day	22% 4 9% 25% 27% 12%	2346
	11th to 20th	Day	22% 4 8% 26% 30% 10%	2299
	21st to end	Day	21% 4 9% 24% 29% 13%	2469
September	1st to 10th	Day	23% 4 8% 23% 28% 14%	2160
	11th to 20th	Day	28% 5% 10% 26% 23% 7%	2152
	21st to end	Day	28% 4 10% 29% 24% 6%	1900
October	1st to 10th	Day	40% 6% 10% 24% 15% 5%	1800
	11th to 20th	Day	40% 5% 12% 27% 12% 5%	1800
	21st to end	Day	38% 6% 14% 26% 15% 2	1919
November	1st to 10th	Day	40% 5% 11% 26% 14% 4	1542
	11th to 20th	Day	42% 7% 15% 22% 12% 3	1520
	21st to end	Day	41% 5% 13% 24% 15% 2	1520
December	1st to 10th	Day	45% 6% 13% 24% 10% 2	1520
	11th to 20th	Day	39% 7% 23% 24% 6% 1	1924
	21st to end	Day	37% 6% 11% 27% 14% 5%	2794
January	1st to 10th	Night	43% 6% 17% 26% 8% 1	4417
	11th to 20th	Night	52% 4 13% 18% 11% 1	4430
	21st to end	Night	38% 10% 17% 25% 9% 1	4620
February	1st to 10th	Night	56% 6% 12% 17% 9%	2470
	11th to 20th	Night	52% 6% 13% 20% 8% 1	2403
	21st to end	Night	49% 6% 13% 20% 10% 2	1984
March	1st to 10th	Night	41% 6% 13% 24% 16%	3562
	11th to 20th	Night	31% 8% 23% 27% 10% 1	3490
	21st to end	Night	59% 10% 13% 14% 4	3749
April	1st to 10th	Night	47% 6% 15% 19% 11% 2	1900
	11th to 20th	Night	49% 7% 13% 23% 8%	1854
	21st to end	Night	48% 7% 11% 22% 12% 1	1710
May	1st to 10th	Night	48% 7% 10% 21% 12% 2	2604
	11th to 20th	Night	38% 9% 12% 29% 10% 3	2518
	21st to end	Night	39% 10% 16% 27% 8%	2762
June	1st to 10th	Night	39% 9% 17% 24% 9% 2	1520
	11th to 20th	Night	37% 9% 16% 21% 13% 4	1411
	21st to end	Night	27% 6% 14% 25% 22% 6%	1330
July	1st to 10th	Night	22% 6% 13% 35% 20% 5%	1269
	11th to 20th	Night	24% 7% 9% 20% 25% 14%	1392
	21st to end	Night	22% 5% 9% 20% 32% 12%	1488
August	1st to 10th	Night	26% 5% 14% 24% 23% 8%	1567
	11th to 20th	Night	24% 5% 10% 24% 29% 9%	1602
	21st to end	Night	31% 5% 9% 19% 25% 11%	1885
September	1st to 10th	Night	26% 5% 9% 20% 25% 15%	1800
	11th to 20th	Night	30% 6% 10% 24% 24% 6%	1804
	21st to end	Night	32% 3 9% 27% 23% 6%	2060
October	1st to 10th	Night	40% 7% 11% 20% 18% 4	2160
	11th to 20th	Night	36% 4 11% 27% 17% 4	2160
	21st to end	Night	36% 6% 16% 24% 14% 4	2417
November	1st to 10th	Night	41% 6% 12% 23% 14% 4	2533
	11th to 20th	Night	42% 5% 13% 26% 13% 2	2660
	21st to end	Night	37% 5% 15% 27% 13% 3	2660
December	1st to 10th	Night	47% 6% 13% 22% 11% 2	2660
	11th to 20th	Night	38% 6% 17% 30% 8%	3272
	21st to end	Night	34% 5% 14% 28% 16% 4	4873

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% 9% 34% 31% 14% 3	270
	11th to 20th	Day	15% 9% 27% 30% 17% 2	270
	21st to end	Day	9% 8% 43% 30% 8% 2	297
February	1st to 10th	Day	16% 14% 37% 27% 5% 1	270
	11th to 20th	Day	13% 14% 33% 33% 6% 2	270
	21st to end	Day	12% 12% 33% 31% 10% 2	225
March	1st to 10th	Day	9% 13% 33% 31% 13% 1	366
	11th to 20th	Day	14% 10% 26% 30% 16% 3	460
	21st to end	Day	19% 11% 25% 30% 13% 2	506
April	1st to 10th	Day	17% 12% 33% 27% 10% 1	460
	11th to 20th	Day	17% 13% 36% 25% 7% 1	452
	21st to end	Day	19% 9% 25% 26% 16% 5%	460
May	1st to 10th	Day	16% 8% 20% 28% 21% 6%	615
	11th to 20th	Day	18% 6% 22% 27% 20% 7%	675
	21st to end	Day	18% 6% 21% 27% 19% 10%	734
June	1st to 10th	Day	9% 5% 24% 31% 24% 7%	680
	11th to 20th	Day	13% 10% 26% 32% 16% 3	680
	21st to end	Day	6% 5% 23% 36% 25% 5%	680
July	1st to 10th	Day	5% 4 20% 33% 33% 6%	627
	11th to 20th	Day	4 6% 22% 40% 24% 3	618
	21st to end	Day	4 2 20% 39% 27% 7%	684
August	1st to 10th	Day	7% 3 22% 38% 24% 6%	481
	11th to 20th	Day	10% 2 17% 33% 29% 8%	437
	21st to end	Day	5% 4 19% 34% 27% 12%	495
September	1st to 10th	Day	8% 5% 22% 36% 22% 6%	450
	11th to 20th	Day	10% 5% 19% 29% 27% 10%	450
	21st to end	Day	16% 6% 19% 28% 25% 6%	370
October	1st to 10th	Day	17% 4 20% 27% 25% 6%	270
	11th to 20th	Day	16% 7% 26% 27% 16% 7%	270
	21st to end	Day	15% 13% 32% 24% 13% 3	297
November	1st to 10th	Day	20% 8% 26% 32% 11% 3	270
	11th to 20th	Day	11% 11% 36% 28% 14% 1	270
	21st to end	Day	12% 11% 34% 33% 10%	270
December	1st to 10th	Day	10% 13% 40% 28% 8% 1	270
	11th to 20th	Day	14% 11% 31% 33% 10%	270
	21st to end	Day	11% 9% 34% 34% 11% 1	297
January	1st to 10th	Night	13% 7% 34% 34% 11% 1	950
	11th to 20th	Night	14% 10% 33% 31% 11%	950
	21st to end	Night	13% 8% 39% 31% 8% 1	896
February	1st to 10th	Night	16% 9% 34% 31% 10% 1	760
	11th to 20th	Night	14% 8% 34% 36% 8%	744
	21st to end	Night	12% 8% 29% 36% 12% 2	628
March	1st to 10th	Night	11% 6% 35% 36% 11% 1	760
	11th to 20th	Night	11% 4 30% 41% 13% 1	760
	21st to end	Night	17% 7% 23% 37% 14% 1	795
April	1st to 10th	Night	18% 7% 27% 38% 10%	570
	11th to 20th	Night	15% 9% 29% 37% 10%	563
	21st to end	Night	20% 6% 22% 39% 13% 1	570
May	1st to 10th	Night	17% 6% 19% 39% 18% 1	570
	11th to 20th	Night	16% 4 18% 38% 23% 1	561
	21st to end	Night	19% 4 20% 38% 19%	617
June	1st to 10th	Night	11% 5% 25% 37% 20% 2	570
	11th to 20th	Night	12% 6% 30% 39% 13%	461
	21st to end	Night	8% 2 21% 46% 22% 1	380
July	1st to 10th	Night	5% 3 17% 48% 27% 1	387
	11th to 20th	Night	5% 5% 27% 48% 16%	522
	21st to end	Night	4 3 22% 53% 18%	591
August	1st to 10th	Night	6% 3 19% 52% 20% 1	537
	11th to 20th	Night	6% 2 18% 52% 21% 1	534
	21st to end	Night	9% 3 19% 48% 20% 1	594
September	1st to 10th	Night	9% 3 23% 45% 20% 1	540
	11th to 20th	Night	13% 2 16% 46% 21% 2	544
	21st to end	Night	14% 4 21% 37% 23% 1	720
October	1st to 10th	Night	18% 5% 18% 38% 20% 2	720
	11th to 20th	Night	16% 5% 24% 35% 19% 1	720
	21st to end	Night	12% 7% 29% 37% 14% 1	833
November	1st to 10th	Night	15% 8% 27% 39% 10% 1	925
	11th to 20th	Night	13% 10% 33% 35% 9%	950
	21st to end	Night	10% 7% 36% 38% 8%	950
December	1st to 10th	Night	11% 9% 36% 34% 9%	950
	11th to 20th	Night	11% 7% 35% 37% 8% 1	950
	21st to end	Night	15% 8% 31% 35% 10%	1045

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