Sleaford Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sleaford Observatory clear sky chart from 2005-11-06 to 2024-03-28.

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	10% 8% 4 7% 7% 4 5% 5% 6% 8% 35%	78001
	Night	8% 9% 4 8% 7% 4 6% 5% 6% 8% 35%	81941
Transparency	Day	46% 7% 15% 22% 8% 1	77704
	Night	46% 7% 15% 22% 9% 1	81819
Seeing	Day	13% 7% 27% 31% 17% 5%	14893
	Night	12% 6% 30% 35% 15% 2	24464

By Month

Percentage Cloud Cover NW (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	6% 16% 7% 13% 10% 5% 5% 6% 5% 6% 20%	2128
	11th to 20th	Day	4 8% 5% 10% 12% 9% 11% 8% 8% 6% 19%	2199
	21st to end	Day	6% 11% 5% 10% 8% 5% 6% 5% 6% 7% 30%	2679
February	1st to 10th	Day	7% 10% 5% 10% 10% 5% 8% 9% 7% 7% 21%	1567
	11th to 20th	Day	7% 11% 5% 10% 9% 4 7% 6% 7% 8% 26%	1665
	21st to end	Day	4 9% 7% 11% 13% 6% 6% 8% 7% 8% 22%	1465
March	1st to 10th	Day	9% 11% 6% 12% 10% 5% 8% 5% 5% 6% 22%	1900
	11th to 20th	Day	7% 11% 6% 9% 8% 3 5% 6% 6% 7% 31%	2035
	21st to end	Day	10% 10% 4 9% 7% 4 5% 6% 7% 9% 30%	2391
April	1st to 10th	Day	7% 9% 5% 8% 6% 4 5% 7% 7% 8% 35%	2160
	11th to 20th	Day	14% 10% 4 7% 6% 3 5% 5% 6% 8% 30%	2201
	21st to end	Day	13% 9% 4 8% 7% 3 5% 5% 6% 7% 34%	2520
May	1st to 10th	Day	12% 7% 2 6% 5% 4 5% 5% 7% 8% 38%	2520
	11th to 20th	Day	8% 5% 3 6% 7% 4 6% 6% 6% 8% 42%	2478
	21st to end	Day	18% 7% 2 5% 5% 3 5% 5% 6% 9% 34%	2945
June	1st to 10th	Day	14% 7% 3 6% 7% 3 6% 6% 7% 9% 33%	2880
	11th to 20th	Day	22% 8% 3 6% 6% 4 5% 6% 6% 8% 26%	2880
	21st to end	Day	11% 5% 3 5% 6% 4 6% 6% 8% 9% 36%	2880
July	1st to 10th	Day	8% 4 2 4 5% 4 5% 6% 7% 10% 44%	2861
	11th to 20th	Day	11% 4 2 4 5% 4 6% 5% 6% 9% 44%	2700
	21st to end	Day	7% 4 2 4 4 3 5% 5% 7% 8% 51%	2840
August	1st to 10th	Day	9% 5% 2 5% 5% 3 5% 6% 8% 10% 43%	2507
	11th to 20th	Day	10% 6% 2 5% 5% 3 4 5% 6% 10% 44%	2469
	21st to end	Day	13% 6% 2 4 4 3 3 5% 5% 7% 48%	2494
September	1st to 10th	Day	10% 5% 2 5% 5% 4 5% 5% 6% 8% 46%	2160
	11th to 20th	Day	12% 8% 3 6% 6% 2 4 5% 5% 7% 42%	2160
	21st to end	Day	10% 5% 2 4 5% 3 4 5% 6% 8% 49%	1923
October	1st to 10th	Day	14% 10% 3 5% 4 3 3 4 5% 8% 41%	1800
	11th to 20th	Day	11% 9% 3 8% 6% 4 4 5% 5% 7% 39%	1743
	21st to end	Day	10% 11% 5% 9% 8% 4 5% 5% 6% 7% 30%	1760
November	1st to 10th	Day	17% 14% 5% 9% 6% 4 4 4 5% 7% 26%	1488
	11th to 20th	Day	7% 16% 6% 11% 12% 5% 5% 4 5% 5% 24%	1520
	21st to end	Day	8% 11% 8% 13% 7% 5% 6% 5% 5% 6% 25%	1333
December	1st to 10th	Day	5% 11% 6% 10% 11% 7% 7% 7% 6% 8% 21%	1221
	11th to 20th	Day	8% 12% 7% 11% 8% 5% 8% 5% 5% 6% 25%	1439
	21st to end	Day	4 7% 5% 8% 7% 4 5% 5% 7% 6% 42%	2090
January	1st to 10th	Night	4 13% 6% 13% 10% 6% 6% 6% 7% 7% 21%	4813
	11th to 20th	Night	4 7% 4 13% 14% 8% 9% 6% 8% 8% 18%	4699
	21st to end	Night	6% 11% 5% 9% 9% 5% 7% 6% 6% 8% 29%	4983
February	1st to 10th	Night	7% 10% 5% 11% 8% 6% 7% 6% 6% 9% 25%	2628
	11th to 20th	Night	4 10% 6% 9% 7% 3 7% 5% 7% 7% 34%	2402
	21st to end	Night	4 7% 4 9% 8% 5% 6% 7% 8% 10% 31%	1989
March	1st to 10th	Night	8% 10% 4 9% 8% 5% 6% 5% 6% 8% 29%	2280
	11th to 20th	Night	6% 10% 4 7% 7% 4 6% 6% 7% 8% 35%	2142
	21st to end	Night	9% 10% 4 8% 7% 4 4 6% 6% 7% 34%	2119
April	1st to 10th	Night	6% 8% 4 8% 6% 3 4 5% 7% 8% 43%	1800
	11th to 20th	Night	10% 12% 4 6% 7% 4 6% 5% 5% 7% 33%	1708
	21st to end	Night	14% 9% 3 7% 6% 3 5% 5% 5% 9% 33%	1440
May	1st to 10th	Night	11% 6% 3 6% 6% 3 4 5% 7% 8% 41%	1440
	11th to 20th	Night	10% 5% 3 5% 5% 3 5% 5% 6% 8% 45%	1418
	21st to end	Night	16% 6% 2 5% 5% 3 6% 5% 5% 7% 40%	1326
June	1st to 10th	Night	11% 5% 3 6% 5% 3 4 5% 8% 10% 41%	1080
	11th to 20th	Night	17% 8% 2 6% 6% 4 6% 5% 5% 7% 32%	1080
	21st to end	Night	9% 5% 2 4 6% 3 5% 5% 9% 9% 44%	1080
July	1st to 10th	Night	5% 3 2 4 4 4 6% 5% 8% 11% 49%	1096
	11th to 20th	Night	9% 4 2 4 4 3 4 4 6% 9% 50%	1260
	21st to end	Night	4 2 1 3 4 3 4 3 6% 10% 61%	1477
August	1st to 10th	Night	6% 2 1 3 3 3 4 5% 6% 9% 56%	1432
	11th to 20th	Night	7% 3 2 3 4 3 5% 5% 7% 10% 52%	1431
	21st to end	Night	10% 5% 2 5% 4 2 4 4 6% 7% 52%	1862
September	1st to 10th	Night	10% 5% 2 4 4 3 5% 5% 7% 7% 48%	1800
	11th to 20th	Night	12% 5% 2 5% 5% 3 4 5% 6% 8% 46%	1800
	21st to end	Night	9% 6% 2 4 3 3 4 4 6% 8% 51%	2034
October	1st to 10th	Night	14% 9% 3 5% 5% 3 5% 5% 5% 7% 40%	2160
	11th to 20th	Night	8% 7% 4 6% 6% 3 4 4 5% 8% 45%	2198
	21st to end	Night	10% 11% 4 9% 8% 4 5% 5% 6% 6% 33%	2596
November	1st to 10th	Night	15% 14% 5% 8% 6% 4 5% 5% 5% 7% 27%	2590
	11th to 20th	Night	7% 12% 6% 11% 10% 4 6% 5% 6% 6% 27%	2660
	21st to end	Night	7% 11% 6% 12% 8% 4 5% 5% 6% 8% 29%	2845
December	1st to 10th	Night	6% 9% 6% 10% 10% 6% 6% 6% 6% 8% 26%	2954
	11th to 20th	Night	7% 14% 6% 12% 9% 5% 7% 6% 6% 7% 21%	3753
	21st to end	Night	3 7% 3 7% 7% 4 5% 5% 6% 6% 49%	5566

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	64% 6% 11% 11% 7%	2128
	11th to 20th	Day	60% 6% 14% 15% 5%	2220
	21st to end	Day	51% 8% 14% 20% 7%	2679
February	1st to 10th	Day	59% 8% 12% 14% 7%	1567
	11th to 20th	Day	54% 6% 14% 17% 9% 1	1674
	21st to end	Day	56% 6% 10% 19% 8%	1465
March	1st to 10th	Day	63% 6% 9% 16% 5%	1900
	11th to 20th	Day	52% 6% 13% 20% 9%	2036
	21st to end	Day	50% 8% 15% 18% 8%	2391
April	1st to 10th	Day	43% 8% 15% 22% 12% 1	2160
	11th to 20th	Day	51% 6% 14% 18% 9% 1	2201
	21st to end	Day	48% 7% 14% 22% 8% 1	2520
May	1st to 10th	Day	43% 6% 13% 27% 11% 1	2520
	11th to 20th	Day	39% 6% 14% 26% 12% 2	2482
	21st to end	Day	46% 6% 14% 21% 11% 1	2945
June	1st to 10th	Day	45% 6% 15% 22% 10% 1	2880
	11th to 20th	Day	54% 8% 12% 18% 7% 1	2880
	21st to end	Day	40% 10% 18% 24% 7%	2880
July	1st to 10th	Day	33% 9% 21% 30% 7%	2783
	11th to 20th	Day	36% 9% 20% 26% 8%	2619
	21st to end	Day	30% 10% 20% 32% 8%	2682
August	1st to 10th	Day	34% 10% 21% 26% 9%	2491
	11th to 20th	Day	35% 7% 24% 27% 6%	2469
	21st to end	Day	35% 6% 15% 35% 8%	2494
September	1st to 10th	Day	35% 7% 17% 27% 11% 2	2160
	11th to 20th	Day	41% 7% 16% 27% 9% 1	2160
	21st to end	Day	33% 6% 16% 31% 12% 1	1923
October	1st to 10th	Day	42% 6% 19% 24% 8%	1800
	11th to 20th	Day	44% 7% 13% 27% 9% 1	1743
	21st to end	Day	52% 7% 16% 21% 5%	1760
November	1st to 10th	Day	60% 6% 12% 15% 7%	1488
	11th to 20th	Day	63% 6% 14% 13% 5%	1520
	21st to end	Day	60% 5% 15% 15% 5%	1333
December	1st to 10th	Day	59% 6% 14% 13% 7% 1	1221
	11th to 20th	Day	58% 8% 18% 9% 6%	1440
	21st to end	Day	41% 7% 12% 19% 17% 5%	2090
January	1st to 10th	Night	59% 7% 14% 16% 4	4813
	11th to 20th	Night	61% 6% 13% 15% 4	4740
	21st to end	Night	52% 8% 14% 19% 6%	4983
February	1st to 10th	Night	56% 6% 12% 18% 8% 1	2628
	11th to 20th	Night	47% 7% 13% 21% 12%	2403
	21st to end	Night	44% 7% 15% 24% 10%	1989
March	1st to 10th	Night	51% 6% 15% 20% 8%	2280
	11th to 20th	Night	44% 8% 16% 21% 10% 1	2142
	21st to end	Night	47% 6% 15% 19% 11% 1	2119
April	1st to 10th	Night	39% 5% 15% 24% 14% 2	1800
	11th to 20th	Night	50% 5% 11% 19% 12% 2	1708
	21st to end	Night	47% 7% 13% 20% 12% 1	1440
May	1st to 10th	Night	38% 6% 11% 28% 15% 2	1440
	11th to 20th	Night	37% 6% 12% 24% 18% 2	1418
	21st to end	Night	43% 5% 14% 22% 15% 1	1326
June	1st to 10th	Night	35% 7% 15% 29% 12% 2	1080
	11th to 20th	Night	49% 9% 13% 18% 11% 1	1080
	21st to end	Night	34% 10% 20% 26% 10%	1080
July	1st to 10th	Night	26% 10% 21% 34% 8%	1066
	11th to 20th	Night	31% 7% 21% 33% 8%	1218
	21st to end	Night	21% 7% 23% 38% 10% 1	1395
August	1st to 10th	Night	24% 7% 25% 32% 11% 1	1424
	11th to 20th	Night	27% 8% 19% 35% 11% 1	1431
	21st to end	Night	31% 6% 14% 36% 13%	1862
September	1st to 10th	Night	33% 8% 14% 27% 14% 4	1800
	11th to 20th	Night	35% 7% 16% 30% 11% 1	1800
	21st to end	Night	30% 6% 14% 32% 16% 2	2034
October	1st to 10th	Night	43% 7% 14% 27% 9%	2160
	11th to 20th	Night	38% 6% 15% 28% 12% 1	2198
	21st to end	Night	50% 6% 13% 22% 8% 1	2596
November	1st to 10th	Night	58% 6% 12% 16% 7% 1	2590
	11th to 20th	Night	58% 7% 16% 15% 4	2660
	21st to end	Night	53% 8% 16% 18% 5%	2845
December	1st to 10th	Night	56% 6% 14% 18% 6% 1	2954
	11th to 20th	Night	61% 7% 14% 13% 5%	3751
	21st to end	Night	36% 6% 11% 26% 17% 5%	5566

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	12% 8% 31% 28% 14% 6%	180
	11th to 20th	Day	13% 6% 29% 32% 18% 2	180
	21st to end	Day	13% 7% 28% 33% 17% 2	267
February	1st to 10th	Day	10% 9% 34% 33% 12% 3	270
	11th to 20th	Day	10% 6% 29% 35% 15% 5%	270
	21st to end	Day	6% 4 27% 41% 19% 2	225
March	1st to 10th	Day	14% 7% 27% 36% 12% 4	270
	11th to 20th	Day	12% 9% 33% 28% 15% 3	406
	21st to end	Day	14% 5% 27% 34% 16% 3	491
April	1st to 10th	Day	8% 9% 33% 30% 14% 5%	420
	11th to 20th	Day	18% 10% 29% 27% 13% 3	424
	21st to end	Day	15% 9% 31% 29% 14% 2	600
May	1st to 10th	Day	11% 8% 24% 33% 19% 5%	603
	11th to 20th	Day	12% 7% 25% 32% 18% 6%	625
	21st to end	Day	17% 9% 21% 28% 19% 6%	679
June	1st to 10th	Day	14% 9% 28% 31% 14% 5%	630
	11th to 20th	Day	24% 9% 25% 25% 13% 4	630
	21st to end	Day	12% 6% 23% 28% 23% 7%	630
July	1st to 10th	Day	9% 5% 24% 36% 20% 6%	621
	11th to 20th	Day	10% 6% 26% 30% 21% 6%	618
	21st to end	Day	7% 5% 25% 32% 21% 10%	684
August	1st to 10th	Day	8% 7% 22% 31% 23% 9%	626
	11th to 20th	Day	9% 6% 20% 35% 23% 8%	607
	21st to end	Day	14% 6% 24% 33% 19% 4	495
September	1st to 10th	Day	15% 10% 28% 30% 15% 2	450
	11th to 20th	Day	16% 10% 25% 35% 12% 2	450
	21st to end	Day	14% 8% 28% 31% 17% 2	298
October	1st to 10th	Day	15% 5% 29% 23% 23% 5%	270
	11th to 20th	Day	13% 10% 31% 29% 15% 2	270
	21st to end	Day	11% 9% 40% 24% 13% 3	297
November	1st to 10th	Day	20% 9% 26% 32% 9% 4	270
	11th to 20th	Day	14% 8% 39% 30% 7% 2	270
	21st to end	Day	10% 9% 34% 33% 10% 4	270
December	1st to 10th	Day	6% 8% 25% 39% 16% 5%	219
	11th to 20th	Day	13% 7% 37% 34% 8% 1	180
	21st to end	Day	12% 4 30% 30% 17% 7%	198
January	1st to 10th	Night	11% 7% 35% 32% 13% 2	950
	11th to 20th	Night	12% 7% 38% 32% 10% 2	950
	21st to end	Night	11% 7% 38% 33% 10% 1	1045
February	1st to 10th	Night	12% 6% 30% 35% 16% 2	918
	11th to 20th	Night	8% 7% 31% 37% 14% 3	744
	21st to end	Night	6% 4 26% 35% 25% 4	628
March	1st to 10th	Night	11% 6% 31% 37% 13% 2	760
	11th to 20th	Night	10% 8% 33% 35% 14% 1	760
	21st to end	Night	14% 6% 27% 38% 12% 3	684
April	1st to 10th	Night	8% 7% 30% 38% 15% 2	540
	11th to 20th	Night	16% 7% 30% 34% 12% 1	533
	21st to end	Night	18% 8% 28% 34% 11% 1	540
May	1st to 10th	Night	12% 6% 28% 36% 17% 1	540
	11th to 20th	Night	12% 7% 29% 34% 16% 1	531
	21st to end	Night	16% 7% 24% 33% 16% 4	466
June	1st to 10th	Night	11% 6% 27% 37% 17% 2	360
	11th to 20th	Night	20% 7% 24% 28% 18% 2	360
	21st to end	Night	11% 5% 20% 42% 19% 2	360
July	1st to 10th	Night	7% 3 23% 39% 25% 2	350
	11th to 20th	Night	12% 5% 21% 40% 20% 2	348
	21st to end	Night	4 4 21% 45% 23% 4	492
August	1st to 10th	Night	7% 2 23% 38% 27% 3	537
	11th to 20th	Night	8% 4 16% 43% 26% 3	534
	21st to end	Night	12% 4 24% 37% 20% 1	594
September	1st to 10th	Night	12% 3 27% 38% 18% 2	540
	11th to 20th	Night	14% 4 24% 40% 17% 1	540
	21st to end	Night	11% 7% 31% 38% 12% 2	622
October	1st to 10th	Night	20% 5% 24% 36% 13% 2	720
	11th to 20th	Night	11% 6% 33% 35% 14% 2	758
	21st to end	Night	16% 8% 31% 33% 11% 1	990
November	1st to 10th	Night	21% 7% 31% 31% 10% 1	925
	11th to 20th	Night	13% 8% 34% 32% 11% 2	950
	21st to end	Night	11% 9% 38% 32% 8% 1	950
December	1st to 10th	Night	10% 5% 32% 34% 16% 3	950
	11th to 20th	Night	12% 9% 33% 33% 11% 1	950
	21st to end	Night	10% 5% 29% 36% 16% 4	1045

Page generated at 2024-03-24 21:37:01. Version ac07

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