Foxmead Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Foxmead Observatory clear sky chart from 2005-11-06 to 2026-01-17.

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	15% 11% 4 9% 5% 5% 4 3 5% 6% 32%	128521
	Night	14% 13% 5% 10% 6% 5% 4 3 5% 6% 29%	123157
Transparency	Day	51% 5% 12% 20% 10% 1	132106
	Night	55% 5% 12% 18% 10% 1	127661
Seeing	Day	24% 17% 30% 18% 8% 3	16348
	Night	23% 15% 29% 23% 9% 1	25230

By Month

Percentage Cloud Cover NE (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	13% 15% 8% 14% 6% 5% 4 3 4 4 25%	3677
	11th to 20th	Day	9% 17% 9% 19% 9% 8% 6% 4 3 4 12%	3864
	21st to end	Day	12% 19% 9% 16% 7% 6% 5% 4 5% 5% 14%	4466
February	1st to 10th	Day	12% 19% 6% 15% 10% 5% 5% 3 3 4 18%	1800
	11th to 20th	Day	11% 17% 7% 13% 7% 5% 4 4 5% 4 23%	1753
	21st to end	Day	16% 18% 6% 10% 8% 6% 5% 4 4 5% 20%	1516
March	1st to 10th	Day	18% 12% 5% 11% 6% 4 3 3 4 5% 29%	4932
	11th to 20th	Day	11% 15% 5% 10% 6% 5% 6% 4 5% 7% 26%	4980
	21st to end	Day	18% 16% 5% 9% 4 3 3 2 4 5% 32%	5465
April	1st to 10th	Day	18% 15% 4 8% 5% 4 4 3 4 5% 30%	2365
	11th to 20th	Day	20% 12% 3 6% 4 4 4 2 4 4 36%	2482
	21st to end	Day	20% 12% 3 6% 4 3 3 3 4 6% 35%	2600
May	1st to 10th	Day	17% 10% 3 7% 4 4 4 4 5% 6% 36%	5931
	11th to 20th	Day	14% 10% 3 6% 5% 4 4 3 5% 7% 38%	6318
	21st to end	Day	21% 9% 2 6% 4 4 4 3 5% 7% 35%	6949
June	1st to 10th	Day	19% 7% 2 6% 5% 4 4 4 5% 8% 37%	2800
	11th to 20th	Day	13% 6% 2 6% 4 5% 5% 4 7% 9% 39%	2963
	21st to end	Day	17% 6% 2 6% 5% 4 4 4 5% 8% 38%	3000
July	1st to 10th	Day	13% 6% 2 7% 5% 5% 5% 4 6% 9% 39%	6819
	11th to 20th	Day	11% 5% 2 5% 4 4 4 3 5% 7% 49%	6408
	21st to end	Day	8% 5% 2 6% 3 5% 5% 4 6% 8% 49%	6592
August	1st to 10th	Day	13% 7% 2 7% 5% 4 5% 4 6% 9% 39%	4234
	11th to 20th	Day	14% 8% 3 6% 4 4 5% 4 7% 10% 36%	4174
	21st to end	Day	9% 5% 2 7% 4 4 4 4 7% 9% 44%	4525
September	1st to 10th	Day	14% 6% 3 8% 4 4 5% 3 5% 7% 41%	2400
	11th to 20th	Day	13% 6% 2 6% 4 3 4 4 5% 9% 45%	2281
	21st to end	Day	16% 8% 3 7% 5% 5% 5% 4 5% 6% 36%	2160
October	1st to 10th	Day	18% 8% 3 7% 6% 4 4 4 6% 7% 34%	2000
	11th to 20th	Day	22% 11% 3 8% 6% 5% 5% 5% 5% 5% 25%	2000
	21st to end	Day	25% 14% 4 9% 5% 5% 4 3 5% 5% 20%	2200
November	1st to 10th	Day	18% 16% 4 8% 6% 4 4 3 4 7% 25%	1713
	11th to 20th	Day	16% 16% 4 11% 7% 4 6% 6% 5% 6% 20%	1680
	21st to end	Day	17% 23% 5% 10% 7% 6% 4 4 5% 4 14%	1680
December	1st to 10th	Day	14% 26% 7% 12% 7% 5% 4 4 4 5% 10%	2680
	11th to 20th	Day	15% 21% 8% 15% 5% 5% 4 3 4 5% 16%	3066
	21st to end	Day	21% 18% 6% 15% 6% 5% 4 3 3 3 15%	4048
January	1st to 10th	Night	12% 20% 9% 17% 7% 5% 4 3 4 4 15%	6489
	11th to 20th	Night	10% 15% 8% 18% 8% 7% 6% 4 5% 6% 13%	6148
	21st to end	Night	12% 17% 7% 14% 6% 6% 5% 3 5% 5% 19%	6490
February	1st to 10th	Night	11% 19% 5% 16% 10% 5% 5% 4 5% 4 17%	2600
	11th to 20th	Night	12% 16% 7% 13% 6% 5% 5% 3 4 5% 23%	2533
	21st to end	Night	15% 15% 4 11% 7% 5% 5% 3 5% 6% 23%	2110
March	1st to 10th	Night	15% 11% 5% 11% 5% 5% 5% 4 4 6% 29%	4908
	11th to 20th	Night	9% 13% 6% 9% 6% 5% 6% 4 6% 7% 30%	4979
	21st to end	Night	18% 12% 6% 9% 5% 4 4 3 5% 5% 29%	5467
April	1st to 10th	Night	20% 12% 4 10% 5% 4 4 3 4 5% 29%	2035
	11th to 20th	Night	19% 11% 3 6% 4 4 4 4 5% 5% 35%	1885
	21st to end	Night	17% 11% 3 9% 5% 5% 4 3 5% 6% 32%	1800
May	1st to 10th	Night	17% 9% 3 7% 5% 4 4 3 5% 8% 35%	4007
	11th to 20th	Night	12% 7% 2 7% 5% 4 4 3 5% 8% 42%	3575
	21st to end	Night	19% 8% 2 6% 4 4 3 3 5% 7% 39%	3926
June	1st to 10th	Night	15% 7% 3 6% 5% 4 4 5% 5% 9% 37%	1600
	11th to 20th	Night	11% 7% 2 6% 5% 3 4 5% 7% 10% 41%	1430
	21st to end	Night	14% 7% 3 7% 5% 5% 5% 3 7% 8% 37%	1400
July	1st to 10th	Night	11% 6% 3 7% 4 5% 4 4 6% 8% 42%	3160
	11th to 20th	Night	12% 6% 2 5% 4 4 4 3 5% 7% 49%	3550
	21st to end	Night	9% 6% 3 5% 4 4 4 4 5% 8% 49%	4243
August	1st to 10th	Night	9% 7% 3 6% 4 4 5% 3 6% 8% 46%	2915
	11th to 20th	Night	14% 7% 3 6% 4 4 4 3 5% 6% 45%	2875
	21st to end	Night	13% 6% 2 5% 4 4 4 3 5% 7% 45%	3340
September	1st to 10th	Night	10% 5% 2 6% 4 4 5% 5% 5% 8% 45%	2000
	11th to 20th	Night	11% 6% 2 5% 4 4 5% 3 5% 6% 49%	2115
	21st to end	Night	16% 7% 3 7% 4 4 4 3 5% 6% 41%	2240
October	1st to 10th	Night	16% 8% 3 7% 5% 5% 5% 3 6% 6% 37%	2400
	11th to 20th	Night	21% 12% 4 9% 4 4 5% 3 5% 6% 27%	2400
	21st to end	Night	22% 12% 4 10% 5% 5% 4 3 5% 5% 24%	2640
November	1st to 10th	Night	18% 14% 3 9% 6% 5% 5% 3 4 6% 29%	2799
	11th to 20th	Night	15% 17% 6% 10% 6% 5% 4 4 5% 6% 22%	2940
	21st to end	Night	20% 19% 6% 12% 6% 5% 5% 4 5% 5% 15%	2940
December	1st to 10th	Night	14% 24% 8% 14% 7% 5% 5% 3 5% 5% 11%	4720
	11th to 20th	Night	14% 18% 8% 19% 8% 6% 4 3 4 4 11%	5348
	21st to end	Night	20% 21% 7% 15% 6% 4 3 3 4 3 13%	7150

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	63% 5% 11% 12% 9%	3678
	11th to 20th	Day	75% 4 9% 7% 4	3897
	21st to end	Day	71% 5% 10% 8% 6%	4466
February	1st to 10th	Day	72% 3 7% 13% 3 1	1800
	11th to 20th	Day	64% 5% 9% 14% 7% 1	1762
	21st to end	Day	68% 3 8% 14% 6%	1516
March	1st to 10th	Day	59% 3 14% 11% 13%	4935
	11th to 20th	Day	57% 4 13% 17% 7% 2	4980
	21st to end	Day	55% 5% 8% 19% 12% 1	5465
April	1st to 10th	Day	58% 4 8% 19% 10% 1	2365
	11th to 20th	Day	53% 3 8% 23% 13%	2482
	21st to end	Day	52% 4 10% 19% 12% 3	2600
May	1st to 10th	Day	49% 5% 11% 19% 11% 5%	5940
	11th to 20th	Day	45% 6% 11% 18% 18% 1	6322
	21st to end	Day	49% 4 11% 20% 13% 3	6949
June	1st to 10th	Day	46% 5% 11% 24% 14%	2800
	11th to 20th	Day	39% 7% 13% 26% 15% 1	2963
	21st to end	Day	45% 4 14% 24% 12% 1	3000
July	1st to 10th	Day	40% 7% 15% 25% 12% 1	6746
	11th to 20th	Day	34% 6% 13% 33% 14% 1	6331
	21st to end	Day	31% 6% 14% 33% 15%	6404
August	1st to 10th	Day	41% 6% 15% 25% 11% 1	4221
	11th to 20th	Day	41% 7% 18% 25% 9%	4213
	21st to end	Day	34% 7% 14% 34% 10% 1	4525
September	1st to 10th	Day	43% 5% 12% 29% 10% 1	2400
	11th to 20th	Day	37% 5% 14% 31% 13%	2281
	21st to end	Day	48% 5% 12% 25% 9%	2160
October	1st to 10th	Day	43% 6% 13% 27% 10% 1	3260
	11th to 20th	Day	50% 5% 14% 21% 10%	3240
	21st to end	Day	58% 7% 13% 17% 5%	3538
November	1st to 10th	Day	60% 4 12% 18% 6%	1713
	11th to 20th	Day	63% 7% 12% 13% 5% 1	1680
	21st to end	Day	73% 6% 9% 10% 2	1680
December	1st to 10th	Day	74% 6% 11% 7% 2	2680
	11th to 20th	Day	70% 6% 9% 11% 4	3066
	21st to end	Day	74% 5% 7% 8% 6%	4048
January	1st to 10th	Night	72% 4 7% 11% 5%	6489
	11th to 20th	Night	70% 6% 11% 8% 5%	6190
	21st to end	Night	66% 4 11% 10% 8% 1	6490
February	1st to 10th	Night	70% 5% 8% 13% 3 1	2600
	11th to 20th	Night	64% 4 10% 15% 6%	2535
	21st to end	Night	63% 4 10% 16% 6%	2110
March	1st to 10th	Night	55% 4 12% 15% 12% 3	4918
	11th to 20th	Night	53% 4 18% 16% 8% 1	4980
	21st to end	Night	55% 6% 8% 17% 12% 2	5467
April	1st to 10th	Night	58% 5% 8% 18% 10% 1	2035
	11th to 20th	Night	51% 3 7% 22% 15% 2	1885
	21st to end	Night	53% 4 9% 16% 16% 1	1800
May	1st to 10th	Night	48% 4 12% 16% 16% 4	4014
	11th to 20th	Night	41% 5% 12% 23% 18% 2	3576
	21st to end	Night	45% 4 12% 24% 13% 1	3927
June	1st to 10th	Night	44% 4 11% 23% 16% 2	1600
	11th to 20th	Night	37% 5% 13% 26% 19% 1	1430
	21st to end	Night	44% 5% 14% 23% 13% 1	1400
July	1st to 10th	Night	38% 7% 14% 25% 14% 2	3125
	11th to 20th	Night	35% 5% 13% 30% 17% 1	3504
	21st to end	Night	33% 6% 10% 34% 16% 1	4117
August	1st to 10th	Night	36% 5% 16% 27% 16% 1	2904
	11th to 20th	Night	39% 6% 18% 24% 14% 1	2902
	21st to end	Night	36% 6% 13% 33% 11% 1	3340
September	1st to 10th	Night	36% 6% 16% 28% 12% 1	2000
	11th to 20th	Night	36% 4 15% 29% 16% 1	2115
	21st to end	Night	45% 4 13% 26% 11%	2240
October	1st to 10th	Night	37% 6% 13% 25% 18% 1	3920
	11th to 20th	Night	49% 5% 15% 21% 10%	3899
	21st to end	Night	51% 7% 15% 21% 6%	4252
November	1st to 10th	Night	57% 4 13% 18% 8%	2799
	11th to 20th	Night	62% 7% 12% 13% 5% 1	2940
	21st to end	Night	70% 7% 11% 10% 2	2940
December	1st to 10th	Night	74% 7% 11% 6% 2	4720
	11th to 20th	Night	75% 6% 10% 7% 2	5348
	21st to end	Night	76% 4 7% 8% 5%	7150

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	22% 28% 35% 10% 5%	220
	11th to 20th	Day	24% 29% 32% 12% 3 1	266
	21st to end	Day	28% 22% 33% 15% 2	330
February	1st to 10th	Day	32% 29% 28% 7% 3	300
	11th to 20th	Day	32% 28% 32% 6% 1	300
	21st to end	Day	38% 26% 32% 4	250
March	1st to 10th	Day	28% 20% 37% 11% 3	500
	11th to 20th	Day	26% 24% 32% 14% 3	500
	21st to end	Day	34% 20% 28% 13% 5%	550
April	1st to 10th	Day	32% 20% 32% 11% 5% 1	500
	11th to 20th	Day	37% 18% 22% 14% 6% 3	492
	21st to end	Day	31% 19% 32% 10% 6% 2	500
May	1st to 10th	Day	27% 15% 34% 15% 7% 2	503
	11th to 20th	Day	20% 15% 32% 19% 11% 3	527
	21st to end	Day	20% 16% 30% 20% 10% 3	573
June	1st to 10th	Day	22% 16% 31% 23% 6% 1	530
	11th to 20th	Day	16% 15% 32% 25% 10% 2	693
	21st to end	Day	22% 11% 36% 21% 7% 2	730
July	1st to 10th	Day	12% 10% 33% 28% 13% 3	721
	11th to 20th	Day	16% 11% 27% 29% 10% 6%	544
	21st to end	Day	11% 9% 37% 27% 11% 5%	576
August	1st to 10th	Day	14% 7% 29% 27% 14% 8%	526
	11th to 20th	Day	17% 7% 23% 31% 14% 8%	519
	21st to end	Day	13% 13% 29% 26% 12% 6%	583
September	1st to 10th	Day	18% 11% 27% 25% 13% 7%	530
	11th to 20th	Day	11% 9% 27% 23% 19% 11%	530
	21st to end	Day	21% 13% 27% 25% 11% 3	530
October	1st to 10th	Day	23% 15% 27% 18% 14% 3	530
	11th to 20th	Day	27% 21% 31% 14% 6% 1	530
	21st to end	Day	33% 19% 31% 13% 3	583
November	1st to 10th	Day	34% 20% 28% 15% 3	260
	11th to 20th	Day	32% 20% 33% 11% 3	220
	21st to end	Day	32% 22% 35% 10% 1	220
December	1st to 10th	Day	32% 25% 27% 12% 4	220
	11th to 20th	Day	35% 25% 29% 9% 2	220
	21st to end	Day	34% 30% 26% 9% 1	242
January	1st to 10th	Night	29% 22% 29% 16% 3	840
	11th to 20th	Night	31% 19% 29% 17% 4	825
	21st to end	Night	23% 16% 32% 22% 6% 1	880
February	1st to 10th	Night	23% 25% 31% 18% 2	800
	11th to 20th	Night	23% 22% 32% 18% 4	783
	21st to end	Night	27% 23% 27% 19% 4	660
March	1st to 10th	Night	25% 20% 33% 19% 3	800
	11th to 20th	Night	24% 20% 34% 17% 4 1	800
	21st to end	Night	25% 17% 29% 22% 7%	880
April	1st to 10th	Night	30% 17% 32% 18% 4	800
	11th to 20th	Night	26% 16% 29% 20% 8% 1	701
	21st to end	Night	23% 16% 30% 22% 9%	600
May	1st to 10th	Night	21% 8% 27% 31% 12% 1	580
	11th to 20th	Night	18% 11% 34% 28% 9% 1	394
	21st to end	Night	14% 8% 31% 33% 13%	433
June	1st to 10th	Night	16% 10% 33% 32% 9% 1	400
	11th to 20th	Night	14% 9% 28% 37% 12%	400
	21st to end	Night	17% 6% 28% 35% 13% 1	400
July	1st to 10th	Night	8% 5% 22% 47% 16% 1	390
	11th to 20th	Night	13% 7% 25% 36% 19% 1	388
	21st to end	Night	11% 5% 26% 38% 20% 1	576
August	1st to 10th	Night	11% 6% 22% 34% 25% 2	597
	11th to 20th	Night	10% 5% 21% 36% 25% 3	594
	21st to end	Night	16% 8% 24% 30% 21% 2	725
September	1st to 10th	Night	14% 6% 29% 30% 18% 3	800
	11th to 20th	Night	15% 6% 23% 31% 20% 5%	800
	21st to end	Night	20% 9% 23% 30% 16% 3	800
October	1st to 10th	Night	22% 12% 29% 22% 14% 1	800
	11th to 20th	Night	29% 17% 26% 19% 8% 1	800
	21st to end	Night	29% 19% 30% 19% 3	880
November	1st to 10th	Night	30% 15% 29% 19% 6% 1	820
	11th to 20th	Night	27% 22% 28% 17% 6%	840
	21st to end	Night	34% 18% 29% 16% 2	840
December	1st to 10th	Night	31% 24% 29% 11% 4	840
	11th to 20th	Night	28% 23% 35% 11% 2 1	840
	21st to end	Night	35% 19% 30% 14% 2	924

Page generated at 2026-01-14 01:14:31. Version ac07

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