Dell City
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Dell City clear sky chart from 2005-11-06 to 2024-01-14.

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	3 2 1 3 3 2 4 4 5% 8% 64%	74753
	Night	4 3 1 3 3 2 4 4 5% 7% 64%	74992
Transparency	Day	18% 5% 9% 18% 26% 24%	74487
	Night	19% 5% 8% 17% 27% 25%	74780
Seeing	Day	4 7% 17% 32% 27% 13%	13506
	Night	5% 4 21% 45% 24% 2	23827

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	4 4 2 3 3 3 4 4 4 7% 63%	1708
	11th to 20th	Day	3 3 1 3 2 2 3 3 4 7% 70%	1647
	21st to end	Day	5% 3 2 4 4 2 3 3 4 6% 65%	1857
February	1st to 10th	Day	3 2 1 2 2 2 4 3 4 8% 69%	1800
	11th to 20th	Day	4 4 1 3 4 3 3 3 4 7% 63%	1749
	21st to end	Day	4 2 1 2 3 1 2 3 4 6% 71%	1480
March	1st to 10th	Day	4 3 2 3 4 2 4 4 6% 8% 60%	1854
	11th to 20th	Day	4 3 2 4 3 2 3 3 4 6% 65%	1980
	21st to end	Day	2 2 1 3 3 2 3 3 5% 6% 71%	2285
April	1st to 10th	Day	1 2 1 2 3 2 3 4 4 8% 71%	2160
	11th to 20th	Day	2 2 1 2 2 1 2 3 3 5% 78%	2131
	21st to end	Day	2 1 1 1 2 1 3 3 3 5% 79%	2160
May	1st to 10th	Day	2 2 1 1 2 2 3 3 3 5% 76%	2160
	11th to 20th	Day	2 2 1 2 3 2 3 3 5% 7% 70%	2125
	21st to end	Day	2 1 1 2 2 2 3 4 5% 77%	2404
June	1st to 10th	Day	2 1 1 2 2 2 3 4 5% 7% 71%	2450
	11th to 20th	Day	1 1 1 2 3 2 2 3 4 7% 74%	2520
	21st to end	Day	3 2 1 2 3 2 5% 7% 7% 9% 60%	2445
July	1st to 10th	Day	3 3 2 4 5% 3 6% 7% 8% 11% 49%	2340
	11th to 20th	Day	3 3 1 3 5% 3 6% 6% 8% 11% 51%	2340
	21st to end	Day	4 2 1 3 5% 4 6% 7% 9% 13% 45%	2429
August	1st to 10th	Day	3 2 1 3 4 3 5% 6% 9% 12% 54%	2149
	11th to 20th	Day	4 3 2 5% 5% 4 7% 7% 9% 12% 43%	2123
	21st to end	Day	4 3 2 5% 5% 3 6% 6% 8% 11% 48%	2376
September	1st to 10th	Day	7% 3 2 3 4 3 4 4 5% 8% 56%	2160
	11th to 20th	Day	7% 4 1 4 4 2 4 5% 6% 8% 55%	2129
	21st to end	Day	4 2 1 2 3 2 3 3 4 7% 68%	1980
October	1st to 10th	Day	4 2 1 3 4 2 2 4 5% 8% 66%	1877
	11th to 20th	Day	5% 3 1 3 4 2 3 3 3 4 71%	1800
	21st to end	Day	1 2 1 2 2 1 3 3 3 5% 77%	1980
November	1st to 10th	Day	3 3 1 3 3 2 2 2 4 6% 71%	1859
	11th to 20th	Day	1 2 1 2 2 2 3 4 4 6% 73%	1729
	21st to end	Day	5% 3 1 3 3 2 4 5% 5% 6% 64%	1710
December	1st to 10th	Day	5% 4 1 3 3 2 4 4 5% 7% 61%	1710
	11th to 20th	Day	2 4 2 4 5% 3 4 4 5% 9% 58%	2157
	21st to end	Day	4 2 1 2 4 2 3 3 5% 8% 65%	2990
January	1st to 10th	Night	5% 4 1 3 3 2 3 4 5% 6% 65%	2457
	11th to 20th	Night	5% 4 1 2 3 2 3 4 4 6% 67%	2385
	21st to end	Night	5% 3 1 3 4 2 3 3 4 5% 66%	2495
February	1st to 10th	Night	3 3 1 2 3 1 3 4 5% 7% 68%	2160
	11th to 20th	Night	4 2 2 4 3 2 4 4 5% 6% 64%	2098
	21st to end	Night	4 3 1 3 3 2 2 3 5% 7% 68%	1776
March	1st to 10th	Night	5% 3 1 3 4 2 3 3 4 7% 64%	2102
	11th to 20th	Night	5% 3 2 2 3 2 3 4 4 7% 64%	1980
	21st to end	Night	2 2 1 2 2 1 3 4 5% 7% 72%	2070
April	1st to 10th	Night	3 2 1 3 3 1 3 4 5% 6% 69%	1800
	11th to 20th	Night	4 2 1 2 2 2 2 4 4 6% 71%	1777
	21st to end	Night	2 1 1 2 2 1 3 3 3 5% 76%	1800
May	1st to 10th	Night	3 2 1 2 3 1 3 4 4 5% 73%	1800
	11th to 20th	Night	2 2 1 2 3 1 4 3 5% 7% 69%	1770
	21st to end	Night	2 1 1 2 3 2 3 3 5% 6% 71%	1863
June	1st to 10th	Night	2 2 1 3 4 2 5% 5% 7% 11% 59%	1504
	11th to 20th	Night	2 2 1 2 3 2 4 4 6% 6% 68%	1440
	21st to end	Night	2 2 1 4 4 2 5% 5% 8% 9% 56%	1506
July	1st to 10th	Night	1 1 2 4 5% 4 6% 6% 8% 11% 51%	1620
	11th to 20th	Night	2 3 1 3 5% 3 5% 6% 8% 12% 52%	1620
	21st to end	Night	3 2 2 5% 5% 4 6% 6% 8% 11% 49%	1885
August	1st to 10th	Night	4 3 2 3 5% 4 7% 8% 9% 12% 45%	1790
	11th to 20th	Night	2 3 2 4 6% 4 6% 5% 9% 13% 47%	1778
	21st to end	Night	3 3 2 4 5% 3 6% 6% 7% 12% 47%	1980
September	1st to 10th	Night	5% 3 2 4 3 3 6% 6% 7% 8% 53%	1800
	11th to 20th	Night	5% 4 2 5% 4 3 4 4 7% 9% 52%	1830
	21st to end	Night	4 2 2 4 3 3 3 5% 6% 7% 61%	1980
October	1st to 10th	Night	4 3 2 2 4 2 4 4 5% 7% 63%	2078
	11th to 20th	Night	5% 3 1 3 3 2 3 3 3 5% 70%	2160
	21st to end	Night	4 2 1 3 2 2 2 3 3 4 75%	2376
November	1st to 10th	Night	3 2 1 2 2 1 2 2 3 6% 75%	2220
	11th to 20th	Night	2 1 1 3 3 1 3 3 4 6% 72%	2429
	21st to end	Night	6% 3 1 2 3 2 3 3 5% 6% 67%	2470
December	1st to 10th	Night	6% 3 1 3 3 2 3 4 5% 6% 64%	2470
	11th to 20th	Night	3 3 1 4 4 2 4 3 4 8% 62%	3036
	21st to end	Night	3 3 1 3 3 2 3 3 4 6% 69%	4687

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	21% 3 6% 22% 33% 15%	1709
	11th to 20th	Day	16% 3 6% 19% 36% 20%	1647
	21st to end	Day	22% 4 6% 14% 34% 21%	1857
February	1st to 10th	Day	15% 4 7% 17% 28% 29%	1800
	11th to 20th	Day	22% 4 7% 16% 27% 24%	1759
	21st to end	Day	16% 3 3 13% 30% 36%	1480
March	1st to 10th	Day	21% 3 7% 15% 29% 25%	1854
	11th to 20th	Day	21% 3 5% 13% 26% 32%	1980
	21st to end	Day	15% 3 6% 13% 30% 33%	2285
April	1st to 10th	Day	12% 3 5% 12% 32% 36%	2160
	11th to 20th	Day	12% 2 4 12% 26% 43%	2134
	21st to end	Day	10% 3 4 13% 29% 42%	2160
May	1st to 10th	Day	11% 4 4 9% 25% 46%	2160
	11th to 20th	Day	14% 5% 7% 15% 25% 34%	2128
	21st to end	Day	10% 3 6% 17% 22% 41%	2404
June	1st to 10th	Day	12% 4 9% 19% 26% 29%	2450
	11th to 20th	Day	11% 3 6% 13% 25% 43%	2520
	21st to end	Day	17% 7% 11% 19% 21% 25%	2445
July	1st to 10th	Day	25% 10% 16% 21% 18% 10%	2276
	11th to 20th	Day	22% 9% 15% 22% 22% 10%	2271
	21st to end	Day	24% 11% 19% 29% 14% 3	2294
August	1st to 10th	Day	19% 10% 16% 29% 21% 5%	2136
	11th to 20th	Day	28% 9% 18% 24% 15% 5%	2123
	21st to end	Day	27% 10% 14% 25% 17% 7%	2376
September	1st to 10th	Day	26% 6% 13% 18% 21% 16%	2160
	11th to 20th	Day	26% 6% 11% 18% 26% 13%	2129
	21st to end	Day	17% 5% 8% 19% 34% 18%	1980
October	1st to 10th	Day	18% 5% 10% 16% 28% 23%	1877
	11th to 20th	Day	18% 5% 6% 12% 28% 32%	1800
	21st to end	Day	12% 3 5% 16% 35% 30%	1980
November	1st to 10th	Day	16% 3 6% 19% 30% 26%	1859
	11th to 20th	Day	13% 3 8% 21% 30% 24%	1729
	21st to end	Day	20% 3 7% 19% 31% 19%	1710
December	1st to 10th	Day	21% 4 9% 25% 29% 12%	1710
	11th to 20th	Day	23% 4 9% 22% 29% 13%	2155
	21st to end	Day	16% 4 7% 19% 34% 20%	2990
January	1st to 10th	Night	21% 4 5% 19% 34% 17%	2457
	11th to 20th	Night	18% 4 6% 15% 35% 21%	2385
	21st to end	Night	21% 3 6% 15% 33% 22%	2495
February	1st to 10th	Night	16% 3 8% 16% 26% 32%	2160
	11th to 20th	Night	20% 4 7% 13% 27% 29%	2098
	21st to end	Night	17% 3 6% 10% 25% 39%	1776
March	1st to 10th	Night	21% 3 5% 14% 25% 31%	2102
	11th to 20th	Night	20% 4 6% 13% 25% 31%	1980
	21st to end	Night	13% 3 6% 14% 29% 35%	2070
April	1st to 10th	Night	16% 3 4 10% 31% 36%	1800
	11th to 20th	Night	14% 4 7% 12% 23% 40%	1777
	21st to end	Night	11% 3 5% 13% 27% 41%	1800
May	1st to 10th	Night	15% 4 5% 10% 21% 47%	1800
	11th to 20th	Night	16% 4 9% 14% 24% 32%	1771
	21st to end	Night	13% 6% 7% 14% 22% 39%	1864
June	1st to 10th	Night	19% 6% 9% 17% 20% 28%	1504
	11th to 20th	Night	14% 4 8% 12% 19% 42%	1440
	21st to end	Night	22% 8% 13% 17% 18% 22%	1506
July	1st to 10th	Night	23% 9% 17% 23% 20% 8%	1575
	11th to 20th	Night	20% 11% 15% 20% 23% 11%	1566
	21st to end	Night	25% 9% 18% 24% 19% 5%	1780
August	1st to 10th	Night	25% 11% 16% 23% 19% 6%	1779
	11th to 20th	Night	26% 9% 18% 27% 16% 5%	1778
	21st to end	Night	27% 9% 15% 21% 19% 8%	1980
September	1st to 10th	Night	25% 10% 12% 18% 18% 17%	1800
	11th to 20th	Night	27% 7% 12% 20% 17% 17%	1830
	21st to end	Night	21% 5% 9% 17% 29% 19%	1980
October	1st to 10th	Night	21% 6% 9% 15% 23% 26%	2078
	11th to 20th	Night	19% 3 5% 14% 25% 34%	2160
	21st to end	Night	15% 2 4 14% 30% 34%	2376
November	1st to 10th	Night	14% 2 5% 17% 33% 30%	2220
	11th to 20th	Night	14% 3 6% 18% 33% 26%	2429
	21st to end	Night	20% 4 5% 17% 30% 23%	2470
December	1st to 10th	Night	20% 4 7% 23% 28% 17%	2470
	11th to 20th	Night	21% 4 6% 21% 31% 15%	3037
	21st to end	Night	16% 3 5% 17% 39% 19%	4687

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	9% 8% 21% 42% 19%	270
	11th to 20th	Day	5% 6% 21% 43% 22% 2	249
	21st to end	Day	4 9% 23% 43% 17% 5%	264
February	1st to 10th	Day	6% 4 22% 40% 24% 5%	240
	11th to 20th	Day	10% 9% 30% 35% 17% 1	240
	21st to end	Day	8% 13% 28% 38% 10% 3	198
March	1st to 10th	Day	7% 13% 24% 41% 13% 1	294
	11th to 20th	Day	9% 14% 28% 30% 15% 5%	420
	21st to end	Day	6% 20% 31% 29% 11% 2	462
April	1st to 10th	Day	4 13% 33% 32% 16% 2	420
	11th to 20th	Day	5% 19% 32% 32% 9% 3	412
	21st to end	Day	4 15% 38% 27% 14% 2	420
May	1st to 10th	Day	2 11% 35% 31% 17% 3	423
	11th to 20th	Day	2 9% 25% 37% 20% 7%	448
	21st to end	Day	2 6% 25% 41% 22% 3	552
June	1st to 10th	Day	2 3 12% 39% 36% 8%	630
	11th to 20th	Day	1 1 13% 38% 37% 9%	630
	21st to end	Day	3 1 9% 34% 38% 16%	555
July	1st to 10th	Day	2 7% 24% 34% 33%	446
	11th to 20th	Day	4 1 3 20% 34% 38%	444
	21st to end	Day	2 1 3 21% 37% 37%	487
August	1st to 10th	Day	2 2 15% 41% 40%	447
	11th to 20th	Day	4 3 5% 22% 38% 29%	437
	21st to end	Day	5% 1 5% 20% 36% 32%	495
September	1st to 10th	Day	7% 1 4 26% 38% 24%	450
	11th to 20th	Day	5% 1 6% 24% 42% 22%	419
	21st to end	Day	6% 1 5% 25% 37% 27%	270
October	1st to 10th	Day	7% 3 8% 31% 34% 17%	270
	11th to 20th	Day	6% 4 10% 29% 39% 11%	270
	21st to end	Day	4 7% 16% 31% 25% 17%	297
November	1st to 10th	Day	6% 9% 13% 36% 29% 9%	270
	11th to 20th	Day	2 7% 11% 34% 38% 9%	270
	21st to end	Day	9% 11% 20% 34% 20% 6%	270
December	1st to 10th	Day	9% 6% 14% 36% 31% 4	270
	11th to 20th	Day	4 9% 17% 49% 21% 1	270
	21st to end	Day	8% 9% 20% 43% 17% 2	297
January	1st to 10th	Night	7% 4 24% 49% 15% 1	760
	11th to 20th	Night	6% 4 26% 48% 15% 2	734
	21st to end	Night	6% 7% 26% 46% 14% 1	792
February	1st to 10th	Night	5% 5% 26% 48% 16%	720
	11th to 20th	Night	5% 6% 35% 45% 9% 1	704
	21st to end	Night	5% 7% 41% 41% 5%	592
March	1st to 10th	Night	7% 8% 32% 45% 8%	720
	11th to 20th	Night	7% 8% 26% 45% 13% 1	720
	21st to end	Night	4 6% 39% 43% 8%	684
April	1st to 10th	Night	3 7% 38% 44% 8%	540
	11th to 20th	Night	4 8% 39% 41% 8%	533
	21st to end	Night	2 9% 37% 43% 9%	540
May	1st to 10th	Night	4 5% 36% 48% 7%	540
	11th to 20th	Night	3 6% 23% 53% 16%	531
	21st to end	Night	2 2 25% 56% 15%	584
June	1st to 10th	Night	3 3 15% 56% 24%	540
	11th to 20th	Night	2 1 14% 59% 24%	540
	21st to end	Night	3 1 9% 51% 34% 1	540
July	1st to 10th	Night	1 1 4 40% 50% 4	525
	11th to 20th	Night	2 1 3 34% 57% 3	522
	21st to end	Night	2 1 2 31% 58% 6%	591
August	1st to 10th	Night	5% 1 3 20% 65% 6%	537
	11th to 20th	Night	2 1 3 25% 61% 7%	534
	21st to end	Night	4 1 2 30% 58% 5%	594
September	1st to 10th	Night	7% 1 4 37% 47% 4	540
	11th to 20th	Night	6% 1 4 42% 44% 2	540
	21st to end	Night	6% 1 9% 46% 37% 2	540
October	1st to 10th	Night	5% 2 12% 51% 28% 1	638
	11th to 20th	Night	6% 2 17% 48% 26% 1	720
	21st to end	Night	4 4 15% 45% 28% 4	792
November	1st to 10th	Night	5% 2 17% 46% 28% 2	740
	11th to 20th	Night	2 4 18% 50% 25% 2	909
	21st to end	Night	6% 5% 25% 41% 21% 2	950
December	1st to 10th	Night	7% 4 21% 49% 18%	950
	11th to 20th	Night	5% 5% 26% 50% 13%	950
	21st to end	Night	6% 6% 25% 50% 13%	941

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