Buckingham
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Buckingham clear sky chart from 2005-11-06 to 2025-09-04.

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% 7% 2 6% 4 4 4 4 5% 7% 40%	126224
	Night	16% 7% 2 6% 4 4 4 3 5% 6% 43%	122487
Transparency	Day	41% 6% 11% 22% 17% 3	129739
	Night	41% 5% 11% 23% 17% 3	127059
Seeing	Day	23% 15% 29% 21% 10% 3	16040
	Night	20% 13% 31% 26% 9% 1	25244

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% 6% 2 6% 3 3 4 3 4 5% 50%	3597
	11th to 20th	Day	13% 8% 4 10% 5% 4 4 3 5% 5% 40%	3616
	21st to end	Day	18% 8% 3 7% 4 3 3 3 3 5% 41%	4466
February	1st to 10th	Day	17% 8% 2 7% 5% 4 5% 4 5% 6% 38%	1800
	11th to 20th	Day	17% 9% 3 8% 5% 4 3 3 5% 6% 39%	1908
	21st to end	Day	19% 9% 3 7% 3 3 4 3 5% 5% 39%	1650
March	1st to 10th	Day	21% 6% 2 5% 4 4 3 2 4 5% 44%	4476
	11th to 20th	Day	12% 6% 2 6% 4 5% 4 3 5% 7% 44%	4951
	21st to end	Day	18% 6% 2 6% 3 4 4 3 5% 6% 43%	5822
April	1st to 10th	Day	17% 8% 3 6% 4 5% 4 3 5% 6% 39%	2400
	11th to 20th	Day	16% 7% 2 6% 5% 4 4 3 6% 7% 40%	2374
	21st to end	Day	15% 5% 3 7% 5% 5% 4 3 6% 7% 40%	2400
May	1st to 10th	Day	26% 7% 2 5% 4 5% 4 4 6% 8% 29%	5853
	11th to 20th	Day	24% 9% 3 6% 4 4 4 3 5% 6% 33%	6318
	21st to end	Day	20% 7% 2 5% 4 5% 4 4 6% 8% 35%	6949
June	1st to 10th	Day	13% 6% 2 6% 5% 5% 5% 5% 7% 8% 38%	2800
	11th to 20th	Day	14% 6% 2 7% 5% 5% 6% 4 7% 8% 37%	2800
	21st to end	Day	11% 5% 2 6% 4 5% 5% 5% 6% 9% 41%	2800
July	1st to 10th	Day	9% 6% 2 8% 5% 5% 6% 4 7% 10% 38%	6360
	11th to 20th	Day	11% 8% 3 8% 5% 6% 6% 5% 8% 10% 32%	6360
	21st to end	Day	11% 7% 3 6% 5% 5% 5% 4 6% 9% 40%	6883
August	1st to 10th	Day	20% 5% 2 6% 5% 5% 5% 4 6% 7% 34%	4234
	11th to 20th	Day	12% 6% 2 6% 4 4 5% 4 6% 9% 42%	3850
	21st to end	Day	11% 5% 2 5% 3 3 4 3 5% 8% 49%	4312
September	1st to 10th	Day	14% 6% 2 6% 4 4 3 4 6% 8% 44%	2316
	11th to 20th	Day	12% 5% 2 4 3 3 3 4 5% 8% 50%	2242
	21st to end	Day	19% 7% 2 6% 5% 4 4 3 4 5% 39%	2090
October	1st to 10th	Day	18% 6% 2 5% 3 3 4 4 4 7% 43%	1914
	11th to 20th	Day	14% 6% 2 5% 3 4 4 2 5% 6% 48%	1900
	21st to end	Day	19% 7% 2 5% 3 3 4 3 5% 6% 45%	2005
November	1st to 10th	Day	13% 6% 2 5% 3 4 2 3 3 6% 53%	1761
	11th to 20th	Day	16% 5% 1 5% 3 3 4 4 5% 5% 48%	1800
	21st to end	Day	15% 6% 2 5% 3 3 3 4 5% 8% 45%	1671
December	1st to 10th	Day	14% 8% 2 5% 4 4 3 4 5% 7% 43%	2600
	11th to 20th	Day	22% 9% 2 4 3 3 3 2 4 6% 43%	2986
	21st to end	Day	17% 5% 3 6% 5% 5% 5% 4 5% 7% 38%	3960
January	1st to 10th	Night	12% 6% 2 6% 3 4 4 3 4 6% 50%	6349
	11th to 20th	Night	14% 8% 2 5% 4 4 3 3 4 5% 48%	6251
	21st to end	Night	18% 9% 2 5% 4 3 4 3 4 5% 43%	6490
February	1st to 10th	Night	17% 9% 3 5% 4 4 4 3 4 6% 41%	2600
	11th to 20th	Night	18% 8% 2 6% 4 4 3 3 4 5% 41%	2378
	21st to end	Night	17% 8% 3 6% 3 3 4 3 4 6% 42%	1980
March	1st to 10th	Night	19% 8% 2 5% 3 3 3 2 4 5% 44%	5364
	11th to 20th	Night	12% 8% 3 6% 4 3 3 3 4 5% 50%	4991
	21st to end	Night	16% 8% 2 7% 4 4 4 3 5% 5% 43%	5110
April	1st to 10th	Night	18% 6% 3 6% 5% 4 4 4 5% 6% 39%	2000
	11th to 20th	Night	16% 6% 3 7% 4 4 4 4 5% 6% 40%	1975
	21st to end	Night	18% 6% 2 5% 3 4 3 3 5% 8% 44%	2000
May	1st to 10th	Night	23% 9% 3 6% 4 4 4 4 6% 8% 29%	4129
	11th to 20th	Night	23% 9% 3 7% 4 4 3 3 4 6% 33%	3575
	21st to end	Night	21% 6% 2 6% 4 5% 3 3 6% 8% 37%	3926
June	1st to 10th	Night	16% 6% 2 5% 4 5% 4 4 6% 6% 42%	1600
	11th to 20th	Night	12% 7% 2 6% 5% 5% 5% 4 6% 9% 40%	1600
	21st to end	Night	11% 4 2 6% 5% 4 5% 5% 6% 10% 43%	1600
July	1st to 10th	Night	9% 6% 2 8% 5% 6% 5% 5% 7% 9% 37%	3600
	11th to 20th	Night	14% 8% 3 9% 5% 5% 5% 4 7% 9% 31%	3600
	21st to end	Night	12% 6% 2 6% 4 5% 5% 4 6% 8% 43%	3965
August	1st to 10th	Night	22% 6% 2 6% 5% 3 4 4 6% 8% 33%	2915
	11th to 20th	Night	12% 8% 3 7% 4 5% 4 4 6% 7% 40%	3166
	21st to end	Night	11% 5% 2 5% 4 3 4 4 6% 8% 50%	3586
September	1st to 10th	Night	15% 6% 2 5% 5% 3 4 4 4 6% 46%	1931
	11th to 20th	Night	12% 6% 2 5% 4 3 3 2 4 7% 53%	1938
	21st to end	Night	18% 7% 2 5% 4 4 4 4 4 6% 41%	2090
October	1st to 10th	Night	18% 7% 2 5% 4 4 4 3 4 5% 44%	2262
	11th to 20th	Night	15% 5% 2 4 3 3 3 2 5% 6% 51%	2280
	21st to end	Night	18% 7% 3 5% 3 3 3 3 4 6% 46%	2590
November	1st to 10th	Night	11% 6% 2 5% 3 3 3 3 4 6% 54%	2537
	11th to 20th	Night	17% 7% 2 4 3 3 3 3 4 5% 48%	2600
	21st to end	Night	13% 6% 2 5% 4 4 4 3 6% 7% 44%	2725
December	1st to 10th	Night	13% 8% 3 6% 4 4 3 3 5% 6% 47%	4580
	11th to 20th	Night	23% 7% 2 5% 3 3 3 3 4 6% 41%	5208
	21st to end	Night	20% 8% 3 6% 4 3 4 3 4 5% 41%	6996

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	35% 4 9% 28% 21% 3	3598
	11th to 20th	Day	45% 4 9% 21% 15% 5%	3646
	21st to end	Day	46% 5% 11% 21% 15% 1	4466
February	1st to 10th	Day	45% 5% 14% 23% 11% 2	1800
	11th to 20th	Day	47% 4 9% 22% 16% 3	1917
	21st to end	Day	47% 5% 10% 22% 12% 3	1650
March	1st to 10th	Day	42% 4 9% 23% 15% 7%	4479
	11th to 20th	Day	38% 5% 12% 27% 13% 5%	4951
	21st to end	Day	42% 4 10% 15% 23% 5%	5822
April	1st to 10th	Day	45% 6% 10% 20% 15% 5%	2400
	11th to 20th	Day	42% 5% 12% 21% 17% 4	2374
	21st to end	Day	41% 5% 11% 21% 18% 4	2400
May	1st to 10th	Day	52% 7% 13% 17% 10% 1	5864
	11th to 20th	Day	51% 6% 9% 21% 12% 1	6322
	21st to end	Day	44% 7% 11% 22% 14% 1	6949
June	1st to 10th	Day	41% 9% 12% 22% 15% 1	2800
	11th to 20th	Day	42% 8% 13% 23% 11% 2	2800
	21st to end	Day	37% 8% 14% 24% 16% 1	2800
July	1st to 10th	Day	39% 10% 13% 20% 16% 2	6290
	11th to 20th	Day	43% 10% 17% 19% 10% 1	6285
	21st to end	Day	39% 7% 10% 20% 22% 1	6685
August	1st to 10th	Day	47% 8% 11% 23% 11%	4221
	11th to 20th	Day	37% 8% 12% 28% 14% 1	3886
	21st to end	Day	33% 7% 9% 27% 22% 2	4312
September	1st to 10th	Day	39% 6% 11% 20% 21% 3	2316
	11th to 20th	Day	32% 5% 10% 24% 24% 4	2242
	21st to end	Day	47% 5% 8% 17% 20% 2	2090
October	1st to 10th	Day	37% 5% 9% 17% 27% 5%	3174
	11th to 20th	Day	25% 5% 11% 25% 28% 6%	3140
	21st to end	Day	26% 3 13% 24% 29% 5%	3282
November	1st to 10th	Day	35% 3 13% 25% 21% 4	1761
	11th to 20th	Day	37% 5% 11% 24% 21% 3	1800
	21st to end	Day	38% 5% 14% 30% 12% 3	1671
December	1st to 10th	Day	40% 4 16% 26% 12% 2	2600
	11th to 20th	Day	45% 4 11% 28% 11% 2	2986
	21st to end	Day	43% 6% 11% 22% 16% 2	3960
January	1st to 10th	Night	36% 4 9% 26% 21% 5%	6349
	11th to 20th	Night	39% 3 13% 23% 15% 7%	6296
	21st to end	Night	44% 3 9% 22% 18% 3	6490
February	1st to 10th	Night	45% 5% 13% 25% 11% 2	2600
	11th to 20th	Night	45% 3 9% 20% 18% 4	2380
	21st to end	Night	43% 4 8% 23% 18% 4	1980
March	1st to 10th	Night	42% 4 8% 24% 12% 9%	5374
	11th to 20th	Night	36% 5% 15% 25% 15% 5%	4992
	21st to end	Night	43% 5% 7% 16% 24% 5%	5110
April	1st to 10th	Night	45% 5% 10% 19% 16% 4	2000
	11th to 20th	Night	43% 6% 9% 19% 20% 3	1975
	21st to end	Night	39% 5% 9% 22% 20% 5%	2000
May	1st to 10th	Night	52% 8% 11% 17% 10% 2	4135
	11th to 20th	Night	52% 7% 11% 16% 13% 2	3576
	21st to end	Night	45% 7% 13% 21% 13% 2	3927
June	1st to 10th	Night	41% 7% 11% 21% 20% 2	1600
	11th to 20th	Night	41% 7% 13% 25% 13% 1	1600
	21st to end	Night	36% 9% 14% 26% 14% 2	1600
July	1st to 10th	Night	41% 11% 15% 18% 15% 2	3560
	11th to 20th	Night	46% 9% 15% 18% 10% 1	3552
	21st to end	Night	35% 8% 13% 22% 20% 1	3848
August	1st to 10th	Night	47% 8% 18% 16% 10% 1	2904
	11th to 20th	Night	41% 7% 12% 25% 14% 1	3196
	21st to end	Night	32% 6% 10% 29% 21% 2	3586
September	1st to 10th	Night	39% 6% 11% 20% 21% 2	1931
	11th to 20th	Night	33% 5% 10% 22% 27% 4	1938
	21st to end	Night	43% 5% 8% 21% 21% 2	2090
October	1st to 10th	Night	40% 6% 10% 21% 21% 2	3782
	11th to 20th	Night	25% 4 9% 29% 29% 5%	3779
	21st to end	Night	28% 4 11% 31% 23% 3	4263
November	1st to 10th	Night	32% 4 13% 24% 22% 5%	2537
	11th to 20th	Night	40% 4 9% 23% 20% 5%	2600
	21st to end	Night	39% 4 13% 27% 16% 2	2725
December	1st to 10th	Night	39% 4 12% 30% 13% 2	4580
	11th to 20th	Night	45% 4 10% 24% 13% 3	5208
	21st to end	Night	46% 4 10% 21% 17% 3	6996

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	34% 23% 29% 12% 3 1	200
	11th to 20th	Day	40% 20% 32% 8% 1	210
	21st to end	Day	29% 26% 29% 13% 3	330
February	1st to 10th	Day	30% 26% 33% 8% 2	300
	11th to 20th	Day	34% 23% 32% 9% 2	456
	21st to end	Day	31% 23% 31% 11% 3	414
March	1st to 10th	Day	31% 19% 32% 14% 3	500
	11th to 20th	Day	29% 22% 31% 14% 3 1	500
	21st to end	Day	28% 25% 29% 12% 5% 1	550
April	1st to 10th	Day	33% 21% 27% 13% 5% 1	500
	11th to 20th	Day	27% 24% 30% 12% 6% 2	492
	21st to end	Day	24% 21% 33% 17% 4 1	500
May	1st to 10th	Day	32% 16% 29% 15% 5% 2	503
	11th to 20th	Day	25% 13% 35% 18% 7% 2	527
	21st to end	Day	20% 9% 28% 26% 14% 3	573
June	1st to 10th	Day	18% 12% 31% 24% 13% 2	530
	11th to 20th	Day	19% 13% 29% 25% 11% 3	530
	21st to end	Day	16% 12% 30% 28% 11% 2	530
July	1st to 10th	Day	12% 7% 24% 31% 19% 7%	525
	11th to 20th	Day	9% 5% 26% 32% 23% 4	524
	21st to end	Day	13% 8% 30% 33% 13% 3	576
August	1st to 10th	Day	12% 5% 29% 32% 16% 6%	526
	11th to 20th	Day	14% 5% 23% 33% 19% 6%	519
	21st to end	Day	13% 8% 28% 28% 16% 7%	583
September	1st to 10th	Day	17% 10% 25% 25% 17% 7%	502
	11th to 20th	Day	15% 6% 26% 29% 14% 10%	490
	21st to end	Day	26% 12% 24% 23% 10% 5%	490
October	1st to 10th	Day	25% 8% 27% 22% 11% 7%	490
	11th to 20th	Day	17% 17% 30% 23% 10% 2	490
	21st to end	Day	23% 15% 33% 16% 12% 2	494
November	1st to 10th	Day	20% 12% 33% 22% 10% 3	395
	11th to 20th	Day	24% 17% 34% 20% 4 1	400
	21st to end	Day	27% 18% 35% 14% 4	271
December	1st to 10th	Day	33% 23% 29% 10% 6%	200
	11th to 20th	Day	37% 23% 25% 12% 4	200
	21st to end	Day	30% 18% 30% 16% 6%	220
January	1st to 10th	Night	22% 22% 34% 19% 3	800
	11th to 20th	Night	26% 17% 34% 20% 3	800
	21st to end	Night	21% 19% 38% 21% 1	880
February	1st to 10th	Night	22% 17% 36% 23% 2	800
	11th to 20th	Night	29% 21% 34% 15% 1	783
	21st to end	Night	26% 19% 37% 17% 2	660
March	1st to 10th	Night	25% 21% 31% 20% 3	800
	11th to 20th	Night	24% 20% 34% 18% 4	800
	21st to end	Night	22% 16% 39% 18% 5%	880
April	1st to 10th	Night	24% 19% 38% 16% 4	800
	11th to 20th	Night	20% 17% 37% 20% 6%	791
	21st to end	Night	22% 13% 35% 25% 5%	800
May	1st to 10th	Night	24% 14% 32% 24% 6%	636
	11th to 20th	Night	21% 11% 36% 26% 6%	394
	21st to end	Night	17% 8% 25% 36% 12% 1	433
June	1st to 10th	Night	17% 7% 30% 34% 12%	400
	11th to 20th	Night	13% 6% 28% 41% 13%	400
	21st to end	Night	11% 6% 25% 47% 12% 1	400
July	1st to 10th	Night	12% 3 24% 43% 17% 2	390
	11th to 20th	Night	9% 4 24% 41% 21% 2	388
	21st to end	Night	9% 3 27% 42% 18% 1	452
August	1st to 10th	Night	14% 2 18% 42% 23% 2	597
	11th to 20th	Night	13% 4 20% 36% 25% 2	771
	21st to end	Night	15% 4 20% 37% 23% 2	880
September	1st to 10th	Night	17% 4 24% 34% 18% 3	773
	11th to 20th	Night	14% 5% 22% 34% 21% 4	760
	21st to end	Night	22% 6% 23% 30% 18% 1	760
October	1st to 10th	Night	22% 8% 25% 24% 17% 4	760
	11th to 20th	Night	17% 10% 28% 31% 13%	760
	21st to end	Night	21% 13% 32% 25% 8% 1	836
November	1st to 10th	Night	15% 11% 35% 27% 11% 1	780
	11th to 20th	Night	23% 15% 29% 26% 7%	800
	21st to end	Night	17% 18% 34% 25% 6% 1	800
December	1st to 10th	Night	27% 16% 32% 19% 5% 1	800
	11th to 20th	Night	23% 15% 35% 22% 5%	800
	21st to end	Night	24% 16% 32% 26% 3	880

Page generated at 2025-09-01 01:51:06. Version ac07

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