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 2024-11-04.

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	9% 8% 3 8% 5% 5% 5% 4 6% 8% 37%	105511
	Night	7% 9% 3 9% 6% 5% 5% 4 6% 8% 37%	102054
Transparency	Day	44% 6% 16% 25% 8% 1	105256
	Night	44% 6% 15% 24% 9% 1	101956
Seeing	Day	13% 8% 27% 31% 17% 5%	15855
	Night	12% 6% 30% 35% 15% 2	25124

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% 17% 6% 16% 8% 6% 5% 5% 6% 5% 20%	2128
	11th to 20th	Day	4 8% 5% 11% 10% 12% 10% 6% 8% 6% 19%	2199
	21st to end	Day	6% 11% 5% 11% 7% 6% 6% 4 6% 8% 30%	2679
February	1st to 10th	Day	7% 11% 5% 12% 9% 7% 9% 8% 7% 7% 20%	1567
	11th to 20th	Day	7% 12% 5% 12% 8% 6% 7% 5% 7% 7% 26%	1665
	21st to end	Day	4 11% 6% 12% 11% 8% 5% 7% 7% 8% 22%	1465
March	1st to 10th	Day	7% 12% 6% 13% 8% 8% 8% 4 5% 6% 24%	3130
	11th to 20th	Day	6% 11% 5% 13% 8% 5% 4 4 6% 8% 32%	3409
	21st to end	Day	7% 8% 3 8% 5% 6% 6% 5% 7% 9% 36%	4059
April	1st to 10th	Day	6% 10% 3 8% 6% 5% 5% 5% 7% 8% 36%	2280
	11th to 20th	Day	13% 11% 4 8% 6% 4 5% 4 6% 8% 30%	2326
	21st to end	Day	13% 10% 3 8% 6% 4 4 4 6% 7% 34%	2660
May	1st to 10th	Day	16% 12% 3 7% 4 4 4 3 5% 6% 35%	4430
	11th to 20th	Day	9% 7% 3 8% 6% 6% 6% 4 7% 8% 36%	4388
	21st to end	Day	13% 10% 3 8% 5% 5% 5% 4 6% 8% 33%	5221
June	1st to 10th	Day	14% 8% 2 7% 6% 5% 5% 5% 7% 8% 33%	3040
	11th to 20th	Day	21% 8% 3 7% 5% 5% 5% 5% 6% 8% 26%	3040
	21st to end	Day	12% 5% 3 6% 5% 5% 5% 6% 8% 9% 36%	3040
July	1st to 10th	Day	7% 4 2 5% 4 5% 5% 5% 8% 9% 46%	5013
	11th to 20th	Day	8% 4 2 4 4 4 5% 4 8% 10% 48%	4740
	21st to end	Day	5% 3 1 4 4 4 5% 4 7% 9% 54%	4965
August	1st to 10th	Day	10% 6% 2 6% 4 4 4 5% 6% 8% 44%	4412
	11th to 20th	Day	7% 6% 2 6% 4 4 4 4 6% 10% 47%	4321
	21st to end	Day	12% 5% 2 4 3 3 4 3 5% 7% 52%	4376
September	1st to 10th	Day	9% 5% 2 6% 4 5% 4 4 6% 8% 47%	2280
	11th to 20th	Day	13% 9% 3 7% 5% 4 3 4 5% 7% 41%	2280
	21st to end	Day	10% 5% 2 5% 4 4 4 4 6% 8% 49%	2029
October	1st to 10th	Day	9% 8% 3 6% 4 3 4 4 6% 9% 45%	3170
	11th to 20th	Day	7% 6% 2 7% 5% 5% 5% 6% 8% 13% 37%	3039
	21st to end	Day	7% 9% 4 9% 6% 6% 6% 5% 6% 7% 35%	3045
November	1st to 10th	Day	16% 15% 5% 10% 5% 4 4 3 6% 6% 26%	1512
	11th to 20th	Day	7% 17% 6% 13% 10% 7% 4 4 5% 5% 24%	1520
	21st to end	Day	8% 13% 7% 14% 7% 6% 6% 4 5% 6% 25%	1333
December	1st to 10th	Day	5% 13% 5% 11% 11% 7% 7% 5% 7% 8% 21%	1221
	11th to 20th	Day	8% 13% 7% 12% 6% 7% 7% 4 6% 5% 25%	1439
	21st to end	Day	4 8% 4 10% 6% 5% 5% 4 8% 6% 41%	2090
January	1st to 10th	Night	4 13% 6% 16% 8% 7% 6% 5% 7% 7% 21%	4813
	11th to 20th	Night	4 8% 4 15% 12% 10% 8% 5% 8% 8% 18%	4699
	21st to end	Night	5% 12% 4 11% 7% 7% 6% 4 6% 7% 29%	4983
February	1st to 10th	Night	7% 11% 4 13% 7% 7% 7% 5% 6% 9% 25%	2628
	11th to 20th	Night	4 10% 5% 10% 7% 5% 7% 4 7% 7% 34%	2402
	21st to end	Night	4 9% 3 9% 7% 6% 7% 6% 8% 10% 31%	1989
March	1st to 10th	Night	6% 12% 4 12% 7% 7% 7% 5% 8% 8% 24%	3734
	11th to 20th	Night	6% 10% 3 9% 6% 5% 5% 5% 8% 9% 34%	3566
	21st to end	Night	7% 8% 3 8% 6% 5% 4 5% 7% 8% 38%	3585
April	1st to 10th	Night	5% 9% 3 8% 5% 4 4 4 7% 8% 43%	1900
	11th to 20th	Night	10% 13% 3 7% 6% 6% 6% 3 6% 7% 33%	1803
	21st to end	Night	13% 9% 3 8% 5% 5% 5% 4 5% 9% 34%	1520
May	1st to 10th	Night	17% 10% 3 7% 5% 4 4 4 5% 6% 34%	2540
	11th to 20th	Night	11% 8% 2 7% 5% 5% 5% 5% 6% 8% 38%	2518
	21st to end	Night	14% 8% 2 8% 5% 5% 5% 4 5% 8% 35%	2340
June	1st to 10th	Night	10% 6% 3 7% 4 3 4 4 8% 10% 41%	1140
	11th to 20th	Night	17% 9% 2 7% 5% 6% 5% 4 6% 7% 33%	1140
	21st to end	Night	9% 5% 1 5% 5% 5% 4 4 9% 8% 45%	1140
July	1st to 10th	Night	7% 4 2 4 3 5% 5% 4 9% 13% 44%	1930
	11th to 20th	Night	6% 4 2 4 3 4 4 4 5% 9% 56%	2220
	21st to end	Night	3 2 1 3 3 3 4 3 6% 9% 63%	2593
August	1st to 10th	Night	7% 3 2 6% 3 4 4 4 6% 8% 54%	2528
	11th to 20th	Night	5% 4 2 4 4 5% 5% 5% 7% 11% 48%	2517
	21st to end	Night	8% 5% 2 5% 3 3 4 3 6% 7% 54%	3291
September	1st to 10th	Night	10% 5% 2 5% 3 4 4 4 7% 7% 50%	1900
	11th to 20th	Night	11% 5% 2 7% 4 4 4 4 6% 8% 45%	1900
	21st to end	Night	8% 6% 2 4 3 4 4 3 5% 8% 51%	2148
October	1st to 10th	Night	10% 8% 2 5% 4 4 4 3 5% 7% 49%	3800
	11th to 20th	Night	6% 6% 2 7% 5% 4 5% 4 6% 8% 48%	3857
	21st to end	Night	8% 8% 3 7% 5% 5% 5% 4 6% 7% 41%	4513
November	1st to 10th	Night	15% 15% 5% 10% 5% 5% 4 4 5% 7% 27%	2639
	11th to 20th	Night	7% 13% 5% 13% 8% 6% 5% 4 6% 6% 26%	2660
	21st to end	Night	7% 12% 5% 13% 7% 5% 4 4 6% 8% 29%	2845
December	1st to 10th	Night	6% 11% 6% 12% 8% 8% 6% 5% 6% 7% 26%	2954
	11th to 20th	Night	7% 14% 6% 14% 7% 6% 7% 5% 7% 7% 21%	3753
	21st to end	Night	3 7% 2 8% 6% 5% 5% 4 6% 6% 48%	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	61% 6% 13% 12% 8%	3130
	11th to 20th	Day	50% 9% 18% 18% 6%	3410
	21st to end	Day	42% 7% 13% 22% 16%	4059
April	1st to 10th	Day	42% 8% 16% 22% 11% 1	2280
	11th to 20th	Day	52% 6% 14% 18% 9% 1	2326
	21st to end	Day	47% 7% 14% 23% 8% 1	2660
May	1st to 10th	Day	49% 5% 14% 23% 9% 1	4430
	11th to 20th	Day	42% 8% 13% 25% 11% 1	4392
	21st to end	Day	45% 7% 16% 23% 8% 1	5221
June	1st to 10th	Day	45% 6% 15% 22% 11% 1	3040
	11th to 20th	Day	54% 8% 12% 19% 7% 1	3040
	21st to end	Day	41% 10% 18% 24% 7%	3040
July	1st to 10th	Day	32% 6% 27% 29% 6%	4935
	11th to 20th	Day	31% 6% 16% 40% 8%	4659
	21st to end	Day	26% 5% 18% 40% 11%	4808
August	1st to 10th	Day	37% 6% 20% 30% 8%	4396
	11th to 20th	Day	33% 4 20% 37% 6%	4363
	21st to end	Day	33% 4 21% 35% 7%	4375
September	1st to 10th	Day	34% 7% 17% 28% 12% 2	2280
	11th to 20th	Day	43% 6% 16% 26% 8% 1	2280
	21st to end	Day	33% 6% 16% 32% 13% 2	2029
October	1st to 10th	Day	37% 4 24% 27% 9%	3170
	11th to 20th	Day	38% 4 19% 31% 8% 1	3039
	21st to end	Day	47% 4 19% 26% 4	3045
November	1st to 10th	Day	59% 6% 12% 16% 7%	1512
	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	54% 7% 16% 18% 5%	3734
	11th to 20th	Night	43% 8% 20% 19% 9%	3566
	21st to end	Night	41% 5% 13% 23% 18%	3585
April	1st to 10th	Night	38% 5% 16% 25% 14% 2	1900
	11th to 20th	Night	50% 5% 11% 20% 12% 2	1803
	21st to end	Night	46% 6% 14% 20% 12% 1	1520
May	1st to 10th	Night	49% 7% 11% 23% 9% 1	2540
	11th to 20th	Night	41% 8% 12% 21% 17% 1	2518
	21st to end	Night	45% 7% 13% 26% 8% 1	2340
June	1st to 10th	Night	35% 7% 15% 29% 12% 2	1140
	11th to 20th	Night	48% 9% 13% 19% 11% 1	1140
	21st to end	Night	34% 9% 20% 26% 11%	1140
July	1st to 10th	Night	29% 7% 27% 31% 6%	1900
	11th to 20th	Night	26% 4 14% 47% 8%	2178
	21st to end	Night	18% 4 19% 45% 11% 2	2511
August	1st to 10th	Night	29% 4 23% 31% 12% 1	2520
	11th to 20th	Night	29% 5% 20% 35% 10%	2541
	21st to end	Night	29% 4 18% 36% 13%	3291
September	1st to 10th	Night	31% 8% 14% 28% 14% 4	1900
	11th to 20th	Night	37% 7% 15% 29% 11% 1	1900
	21st to end	Night	30% 6% 13% 32% 17% 2	2148
October	1st to 10th	Night	36% 4 17% 35% 8%	3800
	11th to 20th	Night	35% 3 14% 34% 13% 1	3857
	21st to end	Night	42% 4 18% 30% 6%	4513
November	1st to 10th	Night	58% 6% 12% 16% 7% 1	2639
	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	506
April	1st to 10th	Day	8% 9% 33% 29% 15% 6%	460
	11th to 20th	Day	18% 12% 29% 27% 12% 3	465
	21st to end	Day	14% 8% 30% 30% 15% 3	650
May	1st to 10th	Day	13% 9% 24% 32% 18% 5%	653
	11th to 20th	Day	11% 7% 25% 32% 19% 6%	675
	21st to end	Day	16% 9% 21% 28% 19% 6%	734
June	1st to 10th	Day	15% 9% 28% 30% 14% 4	680
	11th to 20th	Day	24% 10% 26% 25% 13% 4	680
	21st to end	Day	14% 6% 24% 27% 23% 6%	680
July	1st to 10th	Day	9% 5% 22% 35% 22% 7%	671
	11th to 20th	Day	10% 6% 25% 29% 22% 8%	668
	21st to end	Day	7% 6% 24% 32% 22% 9%	739
August	1st to 10th	Day	9% 7% 23% 31% 22% 9%	676
	11th to 20th	Day	9% 5% 20% 35% 23% 8%	656
	21st to end	Day	13% 6% 26% 32% 18% 5%	539
September	1st to 10th	Day	14% 10% 27% 29% 17% 3	490
	11th to 20th	Day	18% 9% 26% 35% 11% 2	490
	21st to end	Day	15% 8% 29% 30% 16% 2	329
October	1st to 10th	Day	15% 5% 31% 23% 22% 4	300
	11th to 20th	Day	12% 10% 33% 28% 16% 2	300
	21st to end	Day	11% 9% 42% 23% 12% 3	330
November	1st to 10th	Day	20% 9% 27% 32% 9% 4	279
	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% 26% 38% 12% 3	696
April	1st to 10th	Night	8% 7% 31% 37% 15% 2	570
	11th to 20th	Night	16% 7% 31% 34% 12% 1	563
	21st to end	Night	17% 8% 28% 35% 11% 1	570
May	1st to 10th	Night	13% 6% 29% 34% 17% 1	570
	11th to 20th	Night	12% 7% 29% 35% 16% 1	561
	21st to end	Night	15% 8% 24% 34% 16% 3	492
June	1st to 10th	Night	12% 7% 27% 37% 16% 2	380
	11th to 20th	Night	20% 7% 25% 28% 18% 2	380
	21st to end	Night	11% 6% 20% 43% 19% 2	380
July	1st to 10th	Night	8% 3 22% 39% 26% 3	370
	11th to 20th	Night	11% 5% 21% 40% 21% 2	368
	21st to end	Night	4 4 21% 44% 23% 4	520
August	1st to 10th	Night	7% 2 23% 38% 28% 3	567
	11th to 20th	Night	8% 4 16% 43% 26% 3	564
	21st to end	Night	12% 4 26% 37% 20% 1	627
September	1st to 10th	Night	11% 3 27% 39% 18% 2	570
	11th to 20th	Night	15% 4 24% 39% 17% 1	570
	21st to end	Night	11% 7% 32% 37% 12% 2	657
October	1st to 10th	Night	19% 5% 26% 36% 13% 2	760
	11th to 20th	Night	10% 6% 34% 34% 14% 2	801
	21st to end	Night	16% 8% 32% 33% 11% 1	1045
November	1st to 10th	Night	21% 6% 31% 31% 10% 1	943
	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 2024-11-01 20:47:31. Version ac07

Copyright © 2024 Attilla Danko.