Cox Field
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cox Field clear sky chart from 2005-11-06 to 2026-08-15.

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	12% 6% 2 7% 5% 5% 5% 4 6% 8% 40%	143378
	Night	12% 6% 2 6% 4 4 4 4 6% 8% 43%	138519
Transparency	Day	39% 7% 12% 19% 17% 6%	147176
	Night	37% 6% 11% 19% 19% 7%	142792
Seeing	Day	16% 10% 24% 24% 18% 8%	17236
	Night	15% 9% 23% 29% 20% 4	27205

By Month

Percentage Cloud Cover SE (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	16% 9% 3 7% 4 3 3 3 4 5% 45%	5258
	11th to 20th	Day	10% 7% 3 4 2 2 2 3 4 6% 57%	5280
	21st to end	Day	21% 10% 3 8% 3 3 3 2 4 6% 36%	6156
February	1st to 10th	Day	14% 8% 3 7% 4 4 4 3 6% 6% 40%	2100
	11th to 20th	Day	20% 8% 2 5% 3 3 3 3 4 5% 42%	2048
	21st to end	Day	16% 8% 3 7% 4 4 4 3 4 7% 40%	1730
March	1st to 10th	Day	20% 9% 3 8% 4 3 4 3 5% 6% 36%	4715
	11th to 20th	Day	9% 5% 2 5% 4 4 4 4 6% 7% 51%	5090
	21st to end	Day	15% 7% 2 7% 4 4 3 3 5% 6% 44%	5586
April	1st to 10th	Day	11% 6% 2 6% 5% 4 5% 4 6% 6% 47%	2368
	11th to 20th	Day	10% 6% 2 5% 4 3 4 4 5% 7% 50%	2494
	21st to end	Day	8% 5% 2 6% 6% 4 4 3 6% 6% 51%	2656
May	1st to 10th	Day	13% 7% 3 8% 5% 5% 5% 4 6% 8% 37%	7616
	11th to 20th	Day	14% 6% 2 7% 5% 5% 5% 5% 7% 9% 35%	7626
	21st to end	Day	12% 7% 3 8% 5% 6% 5% 5% 6% 8% 34%	8391
June	1st to 10th	Day	9% 6% 3 9% 6% 7% 6% 6% 7% 9% 32%	2730
	11th to 20th	Day	6% 4 2 6% 5% 6% 7% 5% 8% 11% 39%	2730
	21st to end	Day	5% 5% 2 7% 7% 7% 8% 5% 8% 10% 35%	2730
July	1st to 10th	Day	7% 4 2 8% 6% 6% 8% 6% 10% 13% 30%	7680
	11th to 20th	Day	5% 5% 2 7% 6% 6% 7% 6% 9% 12% 33%	7680
	21st to end	Day	6% 6% 3 8% 7% 7% 8% 7% 10% 12% 25%	8340
August	1st to 10th	Day	8% 6% 2 7% 5% 6% 7% 6% 9% 12% 33%	4338
	11th to 20th	Day	6% 4 2 5% 4 5% 5% 4 7% 9% 48%	3897
	21st to end	Day	8% 4 2 5% 4 5% 6% 5% 7% 9% 46%	4312
September	1st to 10th	Day	11% 6% 2 6% 6% 6% 6% 5% 7% 7% 37%	2205
	11th to 20th	Day	13% 6% 3 5% 4 5% 5% 5% 6% 8% 40%	2200
	21st to end	Day	13% 5% 3 6% 4 4 5% 4 4 7% 46%	2200
October	1st to 10th	Day	12% 5% 2 5% 3 3 4 3 4 6% 53%	2200
	11th to 20th	Day	11% 4 1 4 2 3 3 3 5% 7% 58%	2111
	21st to end	Day	12% 5% 2 5% 3 4 3 3 4 5% 55%	2200
November	1st to 10th	Day	11% 7% 2 4 4 3 4 3 4 5% 53%	1883
	11th to 20th	Day	13% 4 2 3 3 3 3 3 4 7% 55%	1890
	21st to end	Day	12% 6% 2 5% 4 4 4 4 5% 8% 47%	1890
December	1st to 10th	Day	16% 7% 2 6% 3 3 3 3 4 5% 47%	3020
	11th to 20th	Day	15% 8% 2 6% 4 4 4 3 4 5% 45%	3463
	21st to end	Day	19% 8% 2 6% 3 3 3 3 5% 6% 42%	4565
January	1st to 10th	Night	13% 8% 3 6% 4 4 4 3 5% 6% 45%	7635
	11th to 20th	Night	13% 7% 3 6% 3 3 3 3 4 6% 49%	7680
	21st to end	Night	19% 11% 2 7% 3 3 4 3 4 4 39%	8007
February	1st to 10th	Night	13% 7% 2 7% 5% 4 2 3 5% 6% 45%	2520
	11th to 20th	Night	20% 7% 3 5% 4 3 3 3 4 5% 42%	2458
	21st to end	Night	15% 7% 2 5% 5% 4 4 3 5% 6% 43%	2076
March	1st to 10th	Night	19% 9% 3 7% 4 4 4 3 5% 6% 36%	5357
	11th to 20th	Night	10% 5% 2 5% 3 4 4 3 5% 7% 51%	5090
	21st to end	Night	14% 6% 2 6% 4 4 4 3 5% 6% 47%	5588
April	1st to 10th	Night	11% 5% 2 5% 5% 4 5% 4 6% 6% 47%	2268
	11th to 20th	Night	11% 5% 2 5% 3 4 3 3 5% 8% 52%	2075
	21st to end	Night	7% 5% 2 5% 4 4 4 4 6% 6% 53%	1964
May	1st to 10th	Night	13% 6% 2 6% 4 4 5% 4 7% 11% 38%	5237
	11th to 20th	Night	13% 6% 2 6% 4 5% 5% 4 6% 10% 39%	5234
	21st to end	Night	11% 7% 3 7% 5% 5% 4 4 7% 10% 36%	5761
June	1st to 10th	Night	6% 6% 3 7% 5% 6% 6% 6% 8% 11% 37%	1890
	11th to 20th	Night	5% 5% 1 6% 4 4 5% 5% 8% 12% 45%	1890
	21st to end	Night	5% 5% 2 7% 5% 6% 5% 5% 9% 12% 40%	1890
July	1st to 10th	Night	7% 5% 2 8% 6% 6% 6% 6% 8% 13% 32%	5278
	11th to 20th	Night	6% 5% 3 8% 6% 6% 6% 6% 10% 13% 33%	5277
	21st to end	Night	6% 6% 2 8% 6% 6% 8% 6% 10% 13% 29%	5736
August	1st to 10th	Night	7% 4 2 8% 6% 6% 8% 6% 8% 12% 32%	3027
	11th to 20th	Night	6% 4 2 6% 4 4 5% 3 7% 11% 47%	3240
	21st to end	Night	6% 5% 2 5% 4 4 4 4 6% 8% 52%	3586
September	1st to 10th	Night	8% 5% 2 6% 5% 6% 5% 5% 7% 10% 41%	2173
	11th to 20th	Night	12% 6% 2 7% 4 4 5% 3 6% 7% 45%	2200
	21st to end	Night	10% 5% 2 6% 5% 4 4 4 6% 8% 46%	2200
October	1st to 10th	Night	9% 5% 2 5% 3 3 3 3 5% 7% 55%	2200
	11th to 20th	Night	10% 4 2 4 2 3 3 3 4 5% 60%	2286
	21st to end	Night	11% 5% 2 4 4 3 3 3 4 5% 58%	2640
November	1st to 10th	Night	11% 6% 2 4 3 3 3 3 5% 4 56%	2631
	11th to 20th	Night	13% 5% 2 5% 3 4 3 3 3 5% 55%	2730
	21st to end	Night	12% 6% 2 5% 4 3 4 3 5% 6% 49%	2730
December	1st to 10th	Night	14% 7% 2 5% 3 3 3 2 4 6% 51%	4380
	11th to 20th	Night	15% 5% 2 6% 3 3 3 3 5% 7% 48%	4952
	21st to end	Night	18% 8% 3 6% 4 4 4 3 4 5% 41%	6633

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	41% 5% 6% 21% 22% 6%	5259
	11th to 20th	Day	30% 3 4 19% 30% 14%	5280
	21st to end	Day	51% 2 5% 13% 20% 8%	6156
February	1st to 10th	Day	43% 4 7% 17% 22% 6%	2100
	11th to 20th	Day	45% 4 5% 18% 22% 6%	2058
	21st to end	Day	45% 5% 7% 15% 20% 9%	1730
March	1st to 10th	Day	48% 5% 8% 12% 21% 6%	4715
	11th to 20th	Day	32% 5% 7% 15% 22% 20%	5090
	21st to end	Day	41% 4 7% 20% 19% 9%	5586
April	1st to 10th	Day	37% 5% 9% 21% 20% 8%	2368
	11th to 20th	Day	32% 5% 7% 20% 25% 10%	2494
	21st to end	Day	32% 6% 10% 22% 26% 4	2656
May	1st to 10th	Day	44% 7% 11% 19% 17% 2	7651
	11th to 20th	Day	43% 8% 17% 20% 11% 2	7630
	21st to end	Day	45% 10% 12% 17% 15% 1	8405
June	1st to 10th	Day	44% 10% 14% 18% 12% 2	2730
	11th to 20th	Day	34% 9% 19% 22% 14% 1	2730
	21st to end	Day	38% 12% 16% 20% 11% 3	2730
July	1st to 10th	Day	39% 13% 25% 19% 3	7615
	11th to 20th	Day	38% 16% 28% 15% 3	7611
	21st to end	Day	43% 14% 20% 17% 5%	8156
August	1st to 10th	Day	39% 10% 16% 28% 7%	4325
	11th to 20th	Day	31% 9% 14% 31% 14% 1	3933
	21st to end	Day	31% 10% 16% 24% 16% 3	4311
September	1st to 10th	Day	42% 9% 14% 16% 15% 4	2205
	11th to 20th	Day	39% 8% 11% 20% 19% 3	2200
	21st to end	Day	38% 5% 10% 21% 20% 6%	2200
October	1st to 10th	Day	27% 4 7% 14% 33% 15%	3590
	11th to 20th	Day	17% 3 4 17% 29% 30%	3416
	21st to end	Day	24% 3 5% 17% 38% 13%	3538
November	1st to 10th	Day	35% 4 6% 15% 27% 13%	1883
	11th to 20th	Day	30% 4 8% 19% 27% 13%	1890
	21st to end	Day	36% 5% 8% 17% 25% 8%	1890
December	1st to 10th	Day	40% 3 6% 18% 25% 8%	3020
	11th to 20th	Day	41% 3 9% 17% 22% 8%	3460
	21st to end	Day	42% 5% 7% 22% 22% 3	4565
January	1st to 10th	Night	39% 4 7% 22% 22% 6%	7636
	11th to 20th	Night	37% 4 5% 17% 27% 10%	7680
	21st to end	Night	48% 3 4 14% 24% 7%	8007
February	1st to 10th	Night	41% 3 6% 19% 21% 10%	2520
	11th to 20th	Night	45% 4 5% 17% 21% 9%	2459
	21st to end	Night	42% 4 8% 16% 18% 12%	2076
March	1st to 10th	Night	47% 5% 8% 15% 15% 10%	5357
	11th to 20th	Night	32% 5% 8% 13% 23% 19%	5090
	21st to end	Night	38% 5% 6% 20% 21% 11%	5588
April	1st to 10th	Night	36% 5% 9% 20% 19% 10%	2268
	11th to 20th	Night	31% 5% 5% 23% 25% 11%	2075
	21st to end	Night	30% 6% 11% 23% 24% 6%	1964
May	1st to 10th	Night	38% 8% 17% 18% 16% 3	5264
	11th to 20th	Night	40% 8% 15% 24% 12% 1	5235
	21st to end	Night	42% 8% 16% 18% 14% 2	5771
June	1st to 10th	Night	36% 12% 17% 19% 15% 1	1890
	11th to 20th	Night	29% 9% 21% 27% 11% 2	1890
	21st to end	Night	32% 10% 21% 21% 13% 3	1890
July	1st to 10th	Night	39% 13% 27% 17% 4 1	5235
	11th to 20th	Night	38% 15% 29% 14% 3 1	5226
	21st to end	Night	42% 13% 24% 15% 5% 1	5606
August	1st to 10th	Night	39% 11% 17% 26% 6%	3016
	11th to 20th	Night	29% 9% 17% 30% 14% 1	3270
	21st to end	Night	29% 7% 15% 27% 19% 2	3586
September	1st to 10th	Night	35% 10% 17% 18% 16% 4	2173
	11th to 20th	Night	38% 8% 10% 23% 17% 4	2200
	21st to end	Night	35% 8% 11% 18% 20% 8%	2200
October	1st to 10th	Night	28% 5% 9% 14% 27% 16%	3590
	11th to 20th	Night	17% 2 4 15% 30% 32%	3720
	21st to end	Night	21% 3 4 21% 33% 18%	4252
November	1st to 10th	Night	32% 4 8% 16% 27% 13%	2631
	11th to 20th	Night	32% 3 5% 17% 27% 15%	2730
	21st to end	Night	36% 4 7% 17% 26% 9%	2730
December	1st to 10th	Night	36% 3 6% 19% 27% 9%	4380
	11th to 20th	Night	36% 4 11% 17% 24% 7%	4954
	21st to end	Night	44% 4 6% 23% 20% 2	6633

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	29% 19% 40% 11% 1	330
	11th to 20th	Day	25% 24% 33% 11% 5% 2	330
	21st to end	Day	25% 29% 33% 10% 3 1	363
February	1st to 10th	Day	22% 24% 38% 14% 2	330
	11th to 20th	Day	35% 21% 33% 10% 2	330
	21st to end	Day	32% 20% 34% 12% 3	273
March	1st to 10th	Day	23% 19% 33% 20% 5% 1	387
	11th to 20th	Day	22% 19% 32% 19% 7% 1	540
	21st to end	Day	20% 20% 30% 23% 6% 1	594
April	1st to 10th	Day	19% 17% 32% 21% 9% 1	540
	11th to 20th	Day	14% 16% 30% 26% 12% 3	532
	21st to end	Day	13% 13% 32% 25% 14% 4	540
May	1st to 10th	Day	14% 13% 30% 27% 12% 4	543
	11th to 20th	Day	12% 8% 24% 32% 17% 8%	567
	21st to end	Day	16% 7% 19% 30% 19% 9%	617
June	1st to 10th	Day	12% 3 21% 28% 26% 10%	570
	11th to 20th	Day	7% 4 18% 31% 26% 15%	570
	21st to end	Day	8% 3 16% 29% 28% 17%	570
July	1st to 10th	Day	8% 1 11% 25% 30% 24%	565
	11th to 20th	Day	7% 3 6% 25% 37% 22%	564
	21st to end	Day	8% 2 10% 27% 34% 20%	620
August	1st to 10th	Day	12% 2 11% 28% 26% 21%	566
	11th to 20th	Day	8% 1 9% 27% 35% 19%	535
	21st to end	Day	14% 3 11% 31% 27% 15%	583
September	1st to 10th	Day	11% 3 13% 31% 28% 14%	530
	11th to 20th	Day	15% 3 12% 30% 29% 10%	530
	21st to end	Day	13% 3 19% 30% 27% 9%	530
October	1st to 10th	Day	15% 5% 27% 29% 18% 7%	530
	11th to 20th	Day	13% 8% 23% 30% 20% 5%	530
	21st to end	Day	17% 10% 25% 27% 17% 4	583
November	1st to 10th	Day	21% 11% 27% 24% 13% 2	361
	11th to 20th	Day	16% 16% 39% 23% 6% 1	330
	21st to end	Day	15% 18% 39% 21% 6% 1	330
December	1st to 10th	Day	27% 20% 32% 17% 4	330
	11th to 20th	Day	26% 17% 35% 16% 7%	330
	21st to end	Day	28% 14% 37% 17% 3 1	363
January	1st to 10th	Night	23% 20% 30% 22% 5%	840
	11th to 20th	Night	23% 17% 28% 25% 6%	840
	21st to end	Night	22% 18% 34% 22% 3	924
February	1st to 10th	Night	18% 15% 32% 28% 6%	840
	11th to 20th	Night	24% 17% 32% 24% 3	823
	21st to end	Night	20% 20% 34% 23% 3	692
March	1st to 10th	Night	18% 15% 32% 29% 6%	840
	11th to 20th	Night	17% 16% 33% 25% 9%	840
	21st to end	Night	17% 14% 30% 29% 9%	924
April	1st to 10th	Night	14% 15% 30% 29% 12%	798
	11th to 20th	Night	15% 13% 28% 28% 15% 1	623
	21st to end	Night	10% 8% 25% 38% 17% 1	630
May	1st to 10th	Night	11% 7% 27% 32% 21% 2	630
	11th to 20th	Night	12% 5% 22% 36% 22% 4	621
	21st to end	Night	13% 2 14% 35% 30% 6%	683
June	1st to 10th	Night	7% 2 14% 38% 34% 5%	630
	11th to 20th	Night	6% 2 13% 32% 35% 12%	630
	21st to end	Night	6% 1 10% 33% 39% 10%	630
July	1st to 10th	Night	8% 1 7% 25% 46% 13%	615
	11th to 20th	Night	8% 1 5% 22% 47% 17%	612
	21st to end	Night	7% 1 9% 27% 45% 13%	690
August	1st to 10th	Night	8% 1 8% 28% 43% 12%	627
	11th to 20th	Night	10% 1 7% 29% 43% 11%	606
	21st to end	Night	13% 3 11% 26% 34% 14%	660
September	1st to 10th	Night	9% 2 10% 27% 38% 12%	773
	11th to 20th	Night	13% 3 12% 29% 38% 5%	800
	21st to end	Night	13% 3 14% 35% 32% 4	800
October	1st to 10th	Night	12% 4 22% 33% 23% 6%	800
	11th to 20th	Night	14% 7% 21% 33% 23% 3	800
	21st to end	Night	14% 8% 22% 33% 19% 3	880
November	1st to 10th	Night	16% 7% 22% 35% 18% 2	820
	11th to 20th	Night	16% 11% 29% 29% 14% 1	840
	21st to end	Night	16% 13% 28% 30% 12% 1	840
December	1st to 10th	Night	20% 14% 30% 26% 9% 1	840
	11th to 20th	Night	21% 12% 30% 27% 8% 1	840
	21st to end	Night	24% 15% 27% 27% 7%	924

Page generated at 2026-08-12 03:37:15. Version ac07

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