Fox Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fox Observatory clear sky chart from 2005-11-06 to 2024-03-18.

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% 6% 3 7% 8% 5% 7% 7% 7% 9% 32%	79057
	Night	8% 5% 2 5% 6% 4 5% 6% 7% 10% 42%	80715
Transparency	Day	45% 8% 15% 18% 11% 3	78780
	Night	36% 8% 19% 22% 12% 3	80511
Seeing	Day	8% 3 15% 27% 25% 21%	15064
	Night	8% 3 13% 32% 32% 13%	25265

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	10% 7% 4 6% 5% 3 5% 6% 6% 8% 39%	2836
	11th to 20th	Day	16% 6% 3 8% 7% 4 6% 7% 7% 9% 27%	2840
	21st to end	Day	7% 6% 4 8% 7% 4 6% 6% 6% 7% 38%	3170
February	1st to 10th	Day	10% 7% 2 5% 7% 3 5% 5% 6% 8% 40%	1900
	11th to 20th	Day	8% 4 1 4 4 3 5% 4 6% 10% 50%	1958
	21st to end	Day	7% 4 2 5% 5% 4 6% 6% 6% 9% 46%	1727
March	1st to 10th	Day	5% 4 2 5% 6% 4 6% 6% 7% 9% 45%	2090
	11th to 20th	Day	7% 4 2 5% 5% 3 6% 7% 7% 8% 46%	2058
	21st to end	Day	6% 5% 2 5% 6% 4 6% 6% 5% 10% 46%	2178
April	1st to 10th	Day	5% 3 2 5% 6% 4 6% 6% 7% 12% 44%	1980
	11th to 20th	Day	8% 4 3 7% 7% 5% 6% 7% 8% 10% 38%	2038
	21st to end	Day	7% 4 2 5% 6% 4 7% 6% 7% 10% 42%	2160
May	1st to 10th	Day	4 3 1 4 5% 4 7% 6% 7% 10% 47%	2160
	11th to 20th	Day	10% 7% 4 7% 7% 5% 8% 7% 8% 9% 28%	2149
	21st to end	Day	11% 7% 3 8% 9% 5% 7% 7% 7% 8% 27%	2531
June	1st to 10th	Day	16% 9% 4 10% 10% 6% 8% 7% 7% 8% 16%	2340
	11th to 20th	Day	8% 7% 5% 10% 10% 5% 9% 8% 8% 10% 19%	2340
	21st to end	Day	9% 7% 4 8% 10% 6% 9% 10% 8% 9% 20%	2340
July	1st to 10th	Day	9% 7% 4 9% 9% 6% 9% 8% 10% 10% 20%	2340
	11th to 20th	Day	9% 7% 3 7% 10% 5% 9% 8% 9% 11% 21%	2340
	21st to end	Day	7% 7% 3 8% 9% 5% 9% 8% 9% 12% 22%	2547
August	1st to 10th	Day	10% 6% 3 8% 9% 6% 9% 9% 9% 13% 20%	2288
	11th to 20th	Day	6% 5% 3 7% 9% 5% 9% 9% 10% 13% 23%	2126
	21st to end	Day	9% 7% 4 9% 10% 6% 9% 9% 9% 12% 18%	2210
September	1st to 10th	Day	9% 6% 4 10% 10% 7% 9% 10% 7% 10% 19%	1980
	11th to 20th	Day	10% 7% 3 9% 10% 5% 9% 7% 8% 10% 21%	1980
	21st to end	Day	13% 9% 5% 10% 9% 5% 8% 8% 7% 7% 19%	1980
October	1st to 10th	Day	9% 8% 3 8% 9% 6% 8% 9% 8% 10% 23%	1895
	11th to 20th	Day	10% 5% 4 7% 8% 5% 9% 8% 8% 8% 28%	1800
	21st to end	Day	14% 6% 2 7% 7% 4 5% 6% 5% 9% 35%	1980
November	1st to 10th	Day	8% 5% 2 6% 7% 4 6% 6% 7% 10% 40%	1857
	11th to 20th	Day	11% 5% 3 7% 9% 5% 5% 7% 6% 9% 33%	1900
	21st to end	Day	8% 5% 3 5% 6% 4 7% 7% 7% 8% 40%	1900
December	1st to 10th	Day	8% 5% 3 6% 6% 4 7% 5% 7% 8% 42%	1862
	11th to 20th	Day	10% 5% 2 5% 6% 4 5% 5% 6% 8% 43%	2153
	21st to end	Day	13% 5% 2 6% 7% 4 7% 7% 8% 10% 31%	3124
January	1st to 10th	Night	8% 6% 3 6% 6% 4 5% 6% 6% 10% 39%	4109
	11th to 20th	Night	17% 8% 4 7% 7% 4 5% 5% 6% 8% 28%	4120
	21st to end	Night	8% 6% 3 7% 7% 4 6% 6% 6% 7% 40%	4468
February	1st to 10th	Night	8% 5% 2 5% 5% 3 4 5% 6% 9% 47%	2280
	11th to 20th	Night	7% 3 1 3 4 3 4 6% 5% 7% 57%	2107
	21st to end	Night	5% 2 2 3 4 3 4 5% 5% 8% 59%	1727
March	1st to 10th	Night	4 3 1 4 4 2 4 5% 7% 8% 58%	2090
	11th to 20th	Night	6% 3 1 4 4 3 4 5% 6% 9% 55%	2068
	21st to end	Night	5% 4 2 3 4 2 4 4 7% 9% 56%	2178
April	1st to 10th	Night	4 2 1 3 3 2 4 5% 6% 11% 59%	1980
	11th to 20th	Night	7% 3 2 4 4 3 5% 6% 7% 10% 51%	1870
	21st to end	Night	7% 4 2 4 4 3 5% 5% 6% 10% 52%	1800
May	1st to 10th	Night	4 2 1 4 4 2 4 5% 6% 11% 59%	1800
	11th to 20th	Night	8% 4 2 5% 6% 3 6% 7% 7% 11% 41%	1757
	21st to end	Night	9% 5% 3 5% 5% 4 5% 6% 8% 12% 38%	1744
June	1st to 10th	Night	12% 7% 4 7% 8% 5% 8% 8% 7% 10% 25%	1620
	11th to 20th	Night	6% 6% 3 5% 7% 4 6% 7% 9% 14% 34%	1620
	21st to end	Night	6% 5% 2 6% 7% 4 7% 7% 10% 14% 32%	1620
July	1st to 10th	Night	5% 5% 3 6% 8% 5% 6% 7% 8% 12% 36%	1620
	11th to 20th	Night	5% 5% 2 6% 6% 3 7% 7% 8% 12% 38%	1620
	21st to end	Night	3 4 2 6% 6% 3 6% 7% 10% 14% 40%	1771
August	1st to 10th	Night	6% 4 2 5% 6% 3 6% 6% 8% 15% 38%	1629
	11th to 20th	Night	4 4 2 5% 5% 5% 7% 8% 9% 13% 37%	1774
	21st to end	Night	8% 6% 3 7% 7% 3 7% 7% 9% 12% 32%	2139
September	1st to 10th	Night	6% 4 3 6% 7% 6% 7% 9% 10% 12% 30%	1980
	11th to 20th	Night	8% 6% 3 8% 7% 5% 6% 6% 8% 12% 31%	1980
	21st to end	Night	10% 6% 3 7% 8% 6% 8% 8% 8% 11% 25%	1980
October	1st to 10th	Night	9% 5% 3 6% 8% 5% 6% 7% 9% 11% 31%	2061
	11th to 20th	Night	8% 5% 2 6% 5% 3 6% 6% 7% 11% 41%	2160
	21st to end	Night	11% 6% 2 5% 5% 3 5% 5% 6% 9% 43%	2376
November	1st to 10th	Night	9% 4 2 4 5% 3 4 5% 5% 8% 50%	2221
	11th to 20th	Night	8% 5% 3 5% 7% 4 6% 5% 6% 8% 41%	2280
	21st to end	Night	7% 5% 2 5% 6% 3 5% 5% 6% 9% 46%	2280
December	1st to 10th	Night	7% 4 2 4 5% 3 5% 5% 6% 9% 50%	2312
	11th to 20th	Night	12% 5% 2 5% 4 2 4 3 5% 9% 48%	3042
	21st to end	Night	10% 7% 3 7% 7% 4 6% 6% 7% 9% 35%	4532

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% 10% 24% 16% 5%	2837
	11th to 20th	Day	53% 6% 14% 15% 9% 3	2840
	21st to end	Day	44% 5% 9% 21% 16% 6%	3170
February	1st to 10th	Day	40% 5% 10% 24% 16% 5%	1900
	11th to 20th	Day	29% 5% 9% 28% 22% 7%	1968
	21st to end	Day	33% 6% 10% 19% 24% 9%	1727
March	1st to 10th	Day	32% 6% 12% 25% 20% 5%	2090
	11th to 20th	Day	33% 5% 11% 28% 18% 5%	2058
	21st to end	Day	34% 5% 10% 24% 20% 7%	2178
April	1st to 10th	Day	31% 6% 17% 28% 16% 3	1980
	11th to 20th	Day	40% 6% 16% 21% 15% 2	2038
	21st to end	Day	36% 6% 10% 24% 20% 4	2160
May	1st to 10th	Day	29% 6% 14% 25% 18% 8%	2160
	11th to 20th	Day	49% 8% 14% 22% 7%	2153
	21st to end	Day	52% 8% 13% 15% 11% 1	2531
June	1st to 10th	Day	64% 9% 15% 10% 3	2340
	11th to 20th	Day	56% 13% 18% 11% 1	2340
	21st to end	Day	54% 13% 23% 9% 1	2340
July	1st to 10th	Day	52% 13% 26% 8%	2275
	11th to 20th	Day	52% 11% 26% 11%	2271
	21st to end	Day	49% 13% 28% 10%	2405
August	1st to 10th	Day	50% 12% 25% 12% 1	2275
	11th to 20th	Day	46% 13% 29% 11%	2126
	21st to end	Day	54% 15% 22% 8% 1	2210
September	1st to 10th	Day	55% 14% 18% 12% 1	1980
	11th to 20th	Day	54% 12% 22% 10% 3	1980
	21st to end	Day	61% 10% 14% 10% 4 1	1980
October	1st to 10th	Day	51% 10% 16% 16% 7% 1	1895
	11th to 20th	Day	49% 8% 12% 17% 12% 2	1800
	21st to end	Day	45% 6% 9% 18% 17% 5%	1980
November	1st to 10th	Day	38% 5% 12% 20% 18% 7%	1857
	11th to 20th	Day	47% 6% 10% 18% 14% 5%	1900
	21st to end	Day	40% 6% 11% 19% 21% 3	1900
December	1st to 10th	Day	38% 6% 12% 24% 18% 2	1862
	11th to 20th	Day	39% 5% 9% 20% 19% 7%	2150
	21st to end	Day	46% 6% 13% 19% 14% 2	3124
January	1st to 10th	Night	40% 5% 14% 23% 15% 3	4109
	11th to 20th	Night	54% 5% 13% 16% 9% 2	4120
	21st to end	Night	41% 6% 10% 22% 15% 6%	4468
February	1st to 10th	Night	32% 5% 13% 29% 17% 4	2280
	11th to 20th	Night	25% 6% 11% 28% 23% 7%	2108
	21st to end	Night	23% 6% 11% 26% 27% 7%	1727
March	1st to 10th	Night	22% 5% 14% 30% 22% 7%	2090
	11th to 20th	Night	25% 5% 17% 30% 18% 4	2068
	21st to end	Night	25% 5% 13% 30% 22% 5%	2178
April	1st to 10th	Night	20% 5% 19% 36% 17% 3	1980
	11th to 20th	Night	27% 7% 19% 25% 19% 3	1870
	21st to end	Night	27% 6% 15% 29% 19% 4	1800
May	1st to 10th	Night	20% 6% 16% 35% 18% 5%	1800
	11th to 20th	Night	36% 8% 19% 25% 11%	1758
	21st to end	Night	37% 8% 21% 24% 11%	1745
June	1st to 10th	Night	51% 11% 22% 14% 2	1620
	11th to 20th	Night	38% 13% 29% 17% 3	1620
	21st to end	Night	38% 15% 35% 11% 1	1620
July	1st to 10th	Night	39% 15% 33% 12% 1	1575
	11th to 20th	Night	36% 12% 37% 15% 1	1566
	21st to end	Night	32% 14% 38% 14% 2	1672
August	1st to 10th	Night	33% 13% 35% 17% 2	1618
	11th to 20th	Night	32% 18% 35% 15%	1774
	21st to end	Night	41% 15% 32% 11% 2	2139
September	1st to 10th	Night	40% 17% 28% 14% 1	1980
	11th to 20th	Night	44% 15% 27% 13% 2	1980
	21st to end	Night	50% 14% 18% 13% 6%	1980
October	1st to 10th	Night	43% 10% 19% 20% 7% 1	2061
	11th to 20th	Night	37% 7% 20% 22% 13% 1	2160
	21st to end	Night	38% 6% 12% 23% 15% 6%	2376
November	1st to 10th	Night	32% 5% 14% 23% 19% 7%	2221
	11th to 20th	Night	40% 5% 12% 24% 14% 5%	2280
	21st to end	Night	34% 6% 14% 23% 19% 4	2280
December	1st to 10th	Night	31% 6% 14% 29% 17% 3	2312
	11th to 20th	Night	34% 5% 9% 24% 19% 9%	3044
	21st to end	Night	43% 8% 15% 18% 14% 2	4532

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	11% 8% 32% 36% 12% 2	270
	11th to 20th	Day	12% 7% 33% 31% 13% 3	270
	21st to end	Day	11% 6% 46% 27% 8% 1	297
February	1st to 10th	Day	10% 7% 28% 39% 13% 3	270
	11th to 20th	Day	8% 3 26% 38% 19% 6%	381
	21st to end	Day	5% 5% 22% 37% 27% 3	382
March	1st to 10th	Day	4 7% 30% 35% 21% 3	460
	11th to 20th	Day	7% 5% 26% 37% 22% 3	449
	21st to end	Day	5% 3 26% 37% 24% 6%	462
April	1st to 10th	Day	4 5% 29% 31% 24% 7%	420
	11th to 20th	Day	9% 4 25% 32% 21% 8%	412
	21st to end	Day	7% 3 21% 33% 26% 9%	420
May	1st to 10th	Day	4 1 17% 33% 29% 15%	423
	11th to 20th	Day	9% 2 16% 30% 28% 15%	447
	21st to end	Day	12% 4 6% 26% 27% 24%	485
June	1st to 10th	Day	16% 3 8% 22% 29% 22%	450
	11th to 20th	Day	8% 3 3 19% 30% 37%	450
	21st to end	Day	6% 1 1 17% 24% 51%	450
July	1st to 10th	Day	5% 2 1 11% 29% 52%	445
	11th to 20th	Day	7% 2 13% 31% 47%	444
	21st to end	Day	5% 3 2 15% 28% 48%	488
August	1st to 10th	Day	8% 2 1 13% 29% 47%	446
	11th to 20th	Day	7% 3 2 14% 28% 46%	439
	21st to end	Day	9% 2 2 21% 29% 35%	495
September	1st to 10th	Day	9% 3 2 13% 29% 44%	450
	11th to 20th	Day	6% 2 3 14% 28% 46%	450
	21st to end	Day	13% 3 4 19% 28% 33%	450
October	1st to 10th	Day	11% 2 8% 35% 31% 13%	450
	11th to 20th	Day	11% 15% 30% 29% 15%	450
	21st to end	Day	11% 3 15% 34% 28% 10%	495
November	1st to 10th	Day	9% 4 20% 34% 24% 8%	455
	11th to 20th	Day	12% 3 22% 31% 25% 8%	460
	21st to end	Day	6% 2 23% 35% 29% 5%	460
December	1st to 10th	Day	11% 3 18% 38% 25% 5%	422
	11th to 20th	Day	9% 5% 24% 37% 19% 6%	270
	21st to end	Day	11% 6% 27% 35% 15% 6%	297
January	1st to 10th	Night	9% 5% 19% 41% 24% 2	760
	11th to 20th	Night	10% 5% 24% 41% 19% 1	760
	21st to end	Night	8% 5% 28% 43% 15% 1	836
February	1st to 10th	Night	10% 5% 22% 42% 19% 2	760
	11th to 20th	Night	7% 4 24% 43% 22% 1	743
	21st to end	Night	7% 3 20% 48% 21% 1	628
March	1st to 10th	Night	5% 3 27% 44% 19% 1	760
	11th to 20th	Night	7% 3 19% 47% 22% 1	752
	21st to end	Night	7% 4 22% 44% 23% 2	792
April	1st to 10th	Night	4 2 17% 50% 25% 2	720
	11th to 20th	Night	7% 3 20% 46% 23% 2	711
	21st to end	Night	8% 2 17% 46% 25% 3	720
May	1st to 10th	Night	4 2 14% 44% 33% 3	720
	11th to 20th	Night	9% 2 10% 42% 33% 4	696
	21st to end	Night	8% 2 4 30% 44% 11%	584
June	1st to 10th	Night	12% 2 3 21% 46% 16%	540
	11th to 20th	Night	6% 2 2 12% 47% 31%	540
	21st to end	Night	5% 2 1 9% 44% 39%	540
July	1st to 10th	Night	5% 1 1 8% 40% 45%	525
	11th to 20th	Night	5% 2 8% 44% 41%	522
	21st to end	Night	2 1 6% 45% 46%	591
August	1st to 10th	Night	7% 2 7% 46% 38%	555
	11th to 20th	Night	4 2 2 10% 43% 39%	710
	21st to end	Night	9% 2 2 17% 40% 29%	792
September	1st to 10th	Night	6% 2 3 12% 41% 36%	720
	11th to 20th	Night	9% 3 2 14% 43% 30%	720
	21st to end	Night	12% 2 3 18% 41% 24%	720
October	1st to 10th	Night	10% 2 7% 35% 37% 11%	720
	11th to 20th	Night	11% 2 6% 32% 40% 10%	720
	21st to end	Night	14% 2 12% 34% 31% 8%	792
November	1st to 10th	Night	10% 3 18% 35% 30% 4	740
	11th to 20th	Night	9% 2 17% 37% 30% 5%	760
	21st to end	Night	8% 3 16% 43% 27% 3	760
December	1st to 10th	Night	7% 2 14% 40% 33% 4	760
	11th to 20th	Night	10% 4 17% 38% 28% 3	760
	21st to end	Night	8% 2 20% 39% 28% 3	836

Page generated at 2024-03-15 14:01:44. Version ac07

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