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 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	16% 10% 4 7% 6% 3 5% 5% 5% 7% 32%	75193
	Night	16% 12% 5% 8% 7% 3 5% 4 5% 6% 29%	74544
Transparency	Day	53% 5% 11% 20% 10% 1	74900
	Night	56% 5% 11% 18% 9% 1	74373
Seeing	Day	23% 16% 31% 19% 8% 3	13744
	Night	24% 15% 29% 23% 9% 1	22717

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	15% 16% 7% 12% 10% 5% 5% 4 4 4 18%	1517
	11th to 20th	Day	16% 18% 8% 11% 8% 3 5% 3 4 4 19%	1558
	21st to end	Day	13% 16% 8% 12% 9% 5% 4 5% 5% 5% 18%	1782
February	1st to 10th	Day	13% 18% 7% 14% 11% 5% 5% 5% 3 4 16%	1620
	11th to 20th	Day	12% 15% 7% 12% 7% 4 4 4 5% 5% 25%	1573
	21st to end	Day	17% 16% 7% 8% 8% 4 6% 5% 4 5% 21%	1358
March	1st to 10th	Day	14% 13% 3 9% 8% 5% 4 4 4 5% 31%	1977
	11th to 20th	Day	12% 13% 6% 8% 7% 4 5% 4 3 6% 31%	1980
	21st to end	Day	18% 12% 4 6% 5% 3 4 3 4 6% 36%	2178
April	1st to 10th	Day	19% 13% 5% 7% 6% 3 4 4 4 5% 30%	2128
	11th to 20th	Day	20% 11% 3 5% 5% 3 5% 3 4 5% 37%	2230
	21st to end	Day	21% 11% 3 5% 4 3 3 3 4 7% 35%	2340
May	1st to 10th	Day	19% 9% 3 5% 5% 3 5% 5% 5% 6% 35%	2355
	11th to 20th	Day	15% 8% 3 4 5% 3 5% 4 5% 6% 42%	2478
	21st to end	Day	12% 6% 3 5% 5% 3 4 5% 6% 7% 42%	2725
June	1st to 10th	Day	19% 6% 2 5% 5% 3 4 5% 6% 8% 38%	2520
	11th to 20th	Day	13% 6% 2 5% 5% 3 5% 5% 6% 9% 41%	2666
	21st to end	Day	16% 6% 2 5% 6% 4 4 5% 5% 9% 39%	2700
July	1st to 10th	Day	10% 4 2 5% 4 3 5% 5% 6% 9% 46%	2700
	11th to 20th	Day	13% 6% 2 6% 6% 2 5% 6% 5% 7% 42%	2540
	21st to end	Day	10% 5% 3 6% 6% 4 6% 5% 7% 9% 39%	2617
August	1st to 10th	Day	12% 5% 2 5% 5% 4 5% 5% 6% 9% 43%	2327
	11th to 20th	Day	11% 6% 3 5% 5% 3 5% 5% 7% 10% 41%	2303
	21st to end	Day	11% 6% 3 7% 6% 3 5% 6% 6% 9% 38%	2498
September	1st to 10th	Day	15% 6% 3 6% 6% 3 5% 4 5% 7% 40%	2160
	11th to 20th	Day	14% 6% 2 6% 5% 3 4 5% 5% 9% 42%	2053
	21st to end	Day	16% 7% 3 6% 6% 4 6% 5% 5% 6% 36%	1944
October	1st to 10th	Day	19% 8% 3 7% 7% 3 4 5% 6% 7% 32%	1800
	11th to 20th	Day	24% 10% 4 8% 7% 4 5% 6% 5% 5% 23%	1800
	21st to end	Day	27% 14% 5% 8% 6% 3 4 4 5% 5% 19%	1980
November	1st to 10th	Day	18% 14% 5% 7% 8% 3 4 4 4 7% 25%	1548
	11th to 20th	Day	17% 15% 5% 9% 8% 3 6% 8% 5% 6% 19%	1520
	21st to end	Day	19% 20% 5% 9% 8% 5% 6% 5% 5% 4 15%	1520
December	1st to 10th	Day	16% 22% 9% 11% 8% 4 4 4 4 5% 12%	1520
	11th to 20th	Day	18% 17% 6% 10% 7% 4 5% 4 5% 5% 19%	1906
	21st to end	Day	24% 19% 7% 12% 7% 4 4 4 3 4 12%	2772
January	1st to 10th	Night	16% 19% 8% 12% 10% 3 5% 4 4 5% 14%	2649
	11th to 20th	Night	18% 17% 7% 11% 8% 3 5% 5% 4 5% 17%	2470
	21st to end	Night	12% 16% 6% 11% 9% 5% 5% 5% 6% 5% 20%	2574
February	1st to 10th	Night	12% 18% 6% 14% 11% 4 5% 5% 5% 4 15%	2340
	11th to 20th	Night	13% 15% 8% 11% 7% 4 5% 5% 4 5% 24%	2273
	21st to end	Night	16% 15% 5% 10% 8% 3 5% 4 4 6% 24%	1894
March	1st to 10th	Night	14% 11% 5% 9% 7% 3 5% 4 4 6% 33%	1970
	11th to 20th	Night	14% 12% 6% 7% 6% 3 5% 3 5% 4 34%	1979
	21st to end	Night	15% 11% 4 8% 6% 3 4 4 5% 5% 35%	2178
April	1st to 10th	Night	21% 11% 5% 8% 6% 2 4 4 4 5% 29%	1832
	11th to 20th	Night	19% 9% 4 5% 5% 3 3 5% 4 5% 37%	1695
	21st to end	Night	17% 10% 4 8% 6% 3 4 4 5% 6% 33%	1620
May	1st to 10th	Night	17% 7% 2 5% 6% 3 4 5% 5% 8% 38%	1602
	11th to 20th	Night	14% 8% 3 5% 4 3 5% 3 5% 7% 43%	1415
	21st to end	Night	11% 4 2 5% 5% 3 4 4 6% 8% 48%	1550
June	1st to 10th	Night	15% 6% 3 6% 5% 3 5% 6% 5% 9% 37%	1440
	11th to 20th	Night	11% 6% 2 4 5% 2 5% 5% 7% 10% 43%	1288
	21st to end	Night	13% 7% 3 6% 6% 4 4 5% 6% 8% 38%	1260
July	1st to 10th	Night	8% 4 2 5% 4 3 4 5% 5% 7% 54%	1260
	11th to 20th	Night	10% 6% 2 4 5% 4 4 4 6% 8% 46%	1416
	21st to end	Night	10% 5% 2 5% 5% 3 4 6% 5% 7% 47%	1698
August	1st to 10th	Night	8% 5% 3 4 5% 2 5% 4 6% 8% 49%	1611
	11th to 20th	Night	7% 6% 2 5% 6% 4 4 5% 6% 7% 47%	1598
	21st to end	Night	13% 6% 3 6% 6% 3 5% 5% 4 7% 41%	1840
September	1st to 10th	Night	11% 5% 2 6% 5% 3 5% 6% 5% 8% 44%	1800
	11th to 20th	Night	12% 6% 2 5% 5% 3 5% 4 5% 7% 46%	1903
	21st to end	Night	16% 7% 3 6% 5% 3 4 3 5% 7% 41%	2016
October	1st to 10th	Night	18% 8% 3 7% 6% 3 5% 5% 6% 6% 33%	2160
	11th to 20th	Night	23% 11% 4 8% 5% 3 5% 5% 4 5% 25%	2160
	21st to end	Night	24% 12% 4 9% 6% 4 4 5% 5% 5% 22%	2376
November	1st to 10th	Night	19% 12% 4 7% 6% 3 4 4 4 6% 30%	2525
	11th to 20th	Night	17% 15% 6% 8% 7% 4 4 5% 5% 6% 22%	2660
	21st to end	Night	20% 17% 6% 9% 7% 3 5% 5% 5% 6% 16%	2660
December	1st to 10th	Night	18% 21% 9% 11% 7% 4 5% 5% 4 5% 12%	2660
	11th to 20th	Night	16% 18% 8% 13% 8% 3 5% 4 5% 5% 16%	3288
	21st to end	Night	24% 21% 7% 13% 7% 3 4 4 3 3 9%	4884

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	70% 4 10% 11% 4	1518
	11th to 20th	Day	71% 3 8% 9% 8% 1	1558
	21st to end	Day	68% 4 7% 10% 10% 1	1782
February	1st to 10th	Day	74% 3 7% 12% 3 1	1620
	11th to 20th	Day	63% 5% 9% 15% 8% 2	1582
	21st to end	Day	68% 3 8% 14% 6%	1358
March	1st to 10th	Day	57% 4 14% 15% 9% 1	1980
	11th to 20th	Day	56% 4 9% 18% 11% 2	1980
	21st to end	Day	52% 4 9% 18% 16% 3	2178
April	1st to 10th	Day	58% 4 9% 18% 10% 1	2128
	11th to 20th	Day	52% 4 8% 23% 13% 1	2230
	21st to end	Day	52% 4 9% 19% 12% 3	2340
May	1st to 10th	Day	49% 5% 8% 22% 13% 2	2355
	11th to 20th	Day	44% 5% 9% 26% 15% 1	2482
	21st to end	Day	41% 6% 14% 23% 14% 2	2725
June	1st to 10th	Day	45% 5% 12% 25% 14%	2520
	11th to 20th	Day	39% 6% 12% 25% 16% 1	2666
	21st to end	Day	44% 4 14% 24% 12% 1	2700
July	1st to 10th	Day	35% 6% 14% 27% 17% 1	2626
	11th to 20th	Day	40% 6% 14% 30% 10% 1	2463
	21st to end	Day	43% 6% 12% 27% 12% 1	2471
August	1st to 10th	Day	38% 6% 16% 25% 13% 1	2314
	11th to 20th	Day	39% 6% 17% 27% 11%	2303
	21st to end	Day	42% 6% 15% 26% 11% 1	2498
September	1st to 10th	Day	44% 5% 11% 29% 10% 1	2160
	11th to 20th	Day	40% 5% 14% 30% 11%	2053
	21st to end	Day	48% 5% 13% 26% 7%	1944
October	1st to 10th	Day	52% 5% 11% 20% 10% 1	1800
	11th to 20th	Day	63% 4 13% 14% 6% 1	1800
	21st to end	Day	68% 4 10% 11% 6%	1980
November	1st to 10th	Day	61% 4 12% 17% 6%	1548
	11th to 20th	Day	64% 7% 12% 12% 5%	1520
	21st to end	Day	72% 5% 10% 11% 2	1520
December	1st to 10th	Day	75% 5% 8% 9% 3	1520
	11th to 20th	Day	68% 7% 9% 11% 6%	1906
	21st to end	Day	79% 3 8% 8% 2	2772
January	1st to 10th	Night	74% 4 8% 10% 4	2649
	11th to 20th	Night	70% 5% 8% 9% 6% 1	2470
	21st to end	Night	66% 6% 8% 12% 8% 1	2574
February	1st to 10th	Night	73% 5% 7% 12% 3 1	2340
	11th to 20th	Night	63% 4 10% 16% 6%	2275
	21st to end	Night	64% 4 10% 16% 6%	1894
March	1st to 10th	Night	53% 5% 14% 16% 11% 1	1980
	11th to 20th	Night	54% 3 10% 20% 12% 2	1980
	21st to end	Night	51% 4 9% 20% 15% 2	2178
April	1st to 10th	Night	57% 5% 8% 18% 11% 1	1832
	11th to 20th	Night	50% 3 7% 22% 16% 2	1695
	21st to end	Night	53% 4 9% 16% 16% 1	1620
May	1st to 10th	Night	45% 4 11% 19% 18% 3	1602
	11th to 20th	Night	42% 4 9% 24% 19% 2	1416
	21st to end	Night	35% 4 15% 26% 16% 3	1551
June	1st to 10th	Night	44% 4 11% 23% 16% 1	1440
	11th to 20th	Night	36% 5% 13% 25% 20% 1	1288
	21st to end	Night	44% 5% 14% 23% 13% 1	1260
July	1st to 10th	Night	29% 4 14% 28% 22% 3	1225
	11th to 20th	Night	36% 4 14% 31% 14% 1	1370
	21st to end	Night	36% 5% 12% 30% 16% 1	1604
August	1st to 10th	Night	33% 5% 18% 29% 14% 1	1600
	11th to 20th	Night	35% 5% 17% 25% 17% 1	1598
	21st to end	Night	41% 5% 14% 27% 12% 1	1840
September	1st to 10th	Night	37% 6% 16% 27% 13% 2	1800
	11th to 20th	Night	38% 4 15% 28% 14%	1903
	21st to end	Night	45% 4 14% 28% 9%	2016
October	1st to 10th	Night	51% 5% 12% 19% 12% 1	2160
	11th to 20th	Night	60% 5% 11% 19% 5%	2160
	21st to end	Night	63% 6% 9% 14% 8%	2376
November	1st to 10th	Night	56% 4 13% 19% 8%	2525
	11th to 20th	Night	62% 7% 12% 13% 6% 1	2660
	21st to end	Night	69% 7% 12% 10% 3	2660
December	1st to 10th	Night	75% 5% 10% 8% 3	2660
	11th to 20th	Night	71% 5% 12% 10% 3	3288
	21st to end	Night	81% 3 7% 7% 2	4884

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	21% 28% 33% 11% 7% 1	180
	11th to 20th	Day	24% 28% 32% 11% 3 1	208
	21st to end	Day	30% 21% 33% 14% 2	264
February	1st to 10th	Day	32% 30% 29% 6% 3	240
	11th to 20th	Day	31% 26% 36% 6% 1	240
	21st to end	Day	40% 27% 30% 4	198
March	1st to 10th	Day	27% 20% 38% 12% 3	420
	11th to 20th	Day	24% 25% 33% 15% 4	420
	21st to end	Day	33% 19% 29% 13% 5%	462
April	1st to 10th	Day	30% 20% 32% 12% 5% 1	420
	11th to 20th	Day	35% 18% 22% 15% 7% 3	412
	21st to end	Day	30% 19% 32% 11% 6% 2	420
May	1st to 10th	Day	29% 13% 32% 16% 7% 3	423
	11th to 20th	Day	21% 15% 32% 19% 10% 3	447
	21st to end	Day	18% 15% 31% 21% 11% 3	485
June	1st to 10th	Day	22% 14% 32% 24% 7% 1	450
	11th to 20th	Day	18% 13% 30% 26% 11% 2	596
	21st to end	Day	19% 11% 37% 23% 8% 2	630
July	1st to 10th	Day	12% 9% 33% 28% 14% 4	621
	11th to 20th	Day	17% 10% 27% 29% 11% 6%	462
	21st to end	Day	12% 8% 36% 29% 10% 5%	488
August	1st to 10th	Day	16% 7% 29% 26% 14% 9%	446
	11th to 20th	Day	15% 6% 24% 31% 14% 10%	439
	21st to end	Day	13% 14% 29% 25% 12% 6%	495
September	1st to 10th	Day	17% 10% 29% 26% 13% 6%	450
	11th to 20th	Day	13% 11% 30% 22% 17% 8%	450
	21st to end	Day	20% 13% 27% 25% 10% 4	450
October	1st to 10th	Day	24% 16% 26% 17% 12% 4	450
	11th to 20th	Day	29% 21% 30% 14% 5%	450
	21st to end	Day	35% 20% 29% 13% 4	495
November	1st to 10th	Day	30% 21% 28% 17% 3	215
	11th to 20th	Day	33% 19% 34% 11% 3 1	180
	21st to end	Day	31% 21% 38% 8% 2	180
December	1st to 10th	Day	31% 27% 29% 9% 4	180
	11th to 20th	Day	33% 27% 27% 10% 2 1	180
	21st to end	Day	34% 31% 27% 8% 1	198
January	1st to 10th	Night	29% 23% 27% 17% 4 1	760
	11th to 20th	Night	32% 18% 29% 16% 4	735
	21st to end	Night	23% 15% 32% 23% 6% 1	792
February	1st to 10th	Night	24% 25% 31% 17% 2	720
	11th to 20th	Night	23% 22% 32% 19% 5%	703
	21st to end	Night	28% 23% 27% 18% 4	592
March	1st to 10th	Night	25% 20% 32% 20% 3	720
	11th to 20th	Night	25% 20% 33% 17% 4 1	720
	21st to end	Night	24% 16% 30% 23% 7%	792
April	1st to 10th	Night	30% 16% 31% 19% 4	720
	11th to 20th	Night	26% 15% 29% 21% 9% 1	631
	21st to end	Night	23% 15% 30% 23% 9%	540
May	1st to 10th	Night	22% 7% 27% 30% 12% 2	522
	11th to 20th	Night	18% 11% 32% 29% 9% 1	354
	21st to end	Night	11% 8% 33% 33% 14%	389
June	1st to 10th	Night	16% 9% 33% 32% 9% 1	360
	11th to 20th	Night	14% 8% 28% 37% 13%	360
	21st to end	Night	17% 5% 28% 36% 14% 1	360
July	1st to 10th	Night	9% 5% 22% 47% 17% 1	350
	11th to 20th	Night	13% 7% 25% 35% 19% 1	348
	21st to end	Night	11% 5% 27% 37% 19% 1	518
August	1st to 10th	Night	12% 5% 23% 33% 25% 2	537
	11th to 20th	Night	8% 6% 21% 36% 25% 3	534
	21st to end	Night	16% 7% 25% 29% 21% 2	652
September	1st to 10th	Night	14% 6% 29% 30% 19% 3	720
	11th to 20th	Night	16% 7% 25% 31% 17% 4	720
	21st to end	Night	20% 9% 23% 29% 16% 3	720
October	1st to 10th	Night	24% 12% 28% 22% 13% 1	720
	11th to 20th	Night	30% 17% 27% 18% 8% 1	720
	21st to end	Night	31% 19% 29% 18% 3	792
November	1st to 10th	Night	30% 14% 29% 19% 7% 1	740
	11th to 20th	Night	28% 21% 28% 17% 6%	760
	21st to end	Night	33% 18% 29% 17% 3	760
December	1st to 10th	Night	34% 23% 28% 11% 4 1	760
	11th to 20th	Night	28% 21% 36% 11% 3 1	760
	21st to end	Night	35% 19% 30% 15% 2	836

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