Canton de Shefford
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Canton de Shefford clear sky chart from 2005-11-06 to 2026-06-16.

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	19% 12% 4 9% 5% 5% 4 4 5% 6% 27%	137695
	Night	18% 14% 5% 10% 6% 4 4 3 4 5% 26%	134351
Transparency	Day	56% 7% 11% 18% 8% 1	141152
	Night	59% 6% 10% 16% 8% 1	138983
Seeing	Day	27% 17% 28% 18% 7% 2	16629
	Night	27% 14% 27% 23% 9% 1	25577

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% 22% 8% 18% 6% 6% 3 2 3 4 13%	4661
	11th to 20th	Day	10% 18% 10% 23% 9% 6% 6% 3 4 3 10%	4650
	21st to end	Day	10% 16% 7% 13% 10% 10% 5% 4 4 5% 15%	5124
February	1st to 10th	Day	15% 18% 6% 13% 8% 6% 4 3 4 4 19%	1790
	11th to 20th	Day	14% 19% 7% 13% 7% 4 5% 4 4 5% 18%	2011
	21st to end	Day	15% 18% 6% 10% 7% 6% 3 4 4 6% 21%	1730
March	1st to 10th	Day	19% 16% 7% 13% 6% 5% 5% 3 3 4 19%	4576
	11th to 20th	Day	14% 18% 4 9% 5% 4 4 3 5% 5% 28%	4761
	21st to end	Day	20% 15% 6% 10% 5% 4 3 3 4 4 27%	6102
April	1st to 10th	Day	23% 16% 5% 7% 5% 4 4 3 4 5% 25%	2520
	11th to 20th	Day	21% 13% 4 7% 4 4 4 2 4 4 33%	2504
	21st to end	Day	24% 11% 3 7% 5% 5% 3 4 4 6% 29%	2730
May	1st to 10th	Day	27% 12% 3 9% 5% 4 4 4 5% 6% 21%	7894
	11th to 20th	Day	20% 8% 3 8% 5% 6% 5% 4 6% 8% 27%	8221
	21st to end	Day	22% 9% 3 7% 4 5% 4 4 5% 6% 31%	9060
June	1st to 10th	Day	25% 8% 2 6% 5% 4 4 4 6% 7% 29%	2940
	11th to 20th	Day	18% 6% 2 6% 5% 5% 4 4 7% 7% 35%	2870
	21st to end	Day	24% 8% 3 7% 4 5% 5% 4 5% 6% 29%	2800
July	1st to 10th	Day	16% 7% 3 7% 5% 6% 6% 5% 7% 9% 28%	6360
	11th to 20th	Day	14% 6% 2 7% 5% 5% 5% 5% 7% 8% 36%	6360
	21st to end	Day	14% 7% 2 5% 4 4 4 4 6% 10% 41%	6926
August	1st to 10th	Day	18% 7% 3 7% 5% 6% 5% 4 7% 9% 29%	4563
	11th to 20th	Day	18% 6% 2 7% 5% 5% 5% 4 7% 8% 33%	4133
	21st to end	Day	19% 7% 3 5% 4 4 4 3 6% 8% 38%	4312
September	1st to 10th	Day	16% 6% 2 6% 4 4 5% 3 6% 7% 42%	2400
	11th to 20th	Day	17% 5% 2 5% 3 4 4 3 5% 7% 45%	2270
	21st to end	Day	19% 7% 2 6% 4 3 4 4 6% 7% 38%	2200
October	1st to 10th	Day	25% 8% 2 5% 4 4 4 4 6% 7% 31%	2133
	11th to 20th	Day	23% 9% 4 7% 6% 4 4 4 4 7% 28%	1910
	21st to end	Day	27% 16% 3 8% 3 4 4 2 3 5% 24%	1980
November	1st to 10th	Day	21% 15% 3 6% 5% 4 5% 3 4 4 29%	1851
	11th to 20th	Day	18% 19% 5% 9% 5% 5% 3 3 4 5% 24%	1879
	21st to end	Day	22% 20% 6% 10% 4 4 4 3 5% 4 18%	1680
December	1st to 10th	Day	18% 25% 7% 15% 6% 4 3 2 3 4 12%	2680
	11th to 20th	Day	20% 18% 7% 13% 5% 4 4 2 4 4 19%	3066
	21st to end	Day	20% 19% 5% 13% 5% 4 5% 3 4 5% 18%	4048
January	1st to 10th	Night	14% 23% 9% 15% 6% 5% 3 2 3 4 16%	8234
	11th to 20th	Night	12% 21% 9% 20% 8% 6% 4 3 3 3 11%	8235
	21st to end	Night	10% 16% 6% 15% 11% 6% 4 4 4 4 19%	9057
February	1st to 10th	Night	14% 19% 5% 14% 7% 5% 4 3 4 5% 19%	2829
	11th to 20th	Night	14% 17% 6% 14% 7% 5% 4 3 4 4 21%	2493
	21st to end	Night	14% 19% 5% 10% 6% 5% 4 3 4 4 26%	2076
March	1st to 10th	Night	20% 15% 5% 9% 5% 5% 3 2 4 4 27%	5484
	11th to 20th	Night	16% 17% 5% 9% 6% 4 4 3 5% 6% 25%	5412
	21st to end	Night	16% 19% 6% 11% 5% 4 3 3 4 4 26%	5072
April	1st to 10th	Night	24% 13% 4 9% 3 4 5% 3 4 5% 26%	2100
	11th to 20th	Night	25% 11% 3 7% 5% 4 3 3 3 6% 31%	2065
	21st to end	Night	22% 10% 3 7% 3 4 4 3 4 6% 33%	1890
May	1st to 10th	Night	25% 11% 3 9% 4 4 4 3 5% 7% 23%	5047
	11th to 20th	Night	23% 7% 3 9% 5% 4 5% 4 6% 6% 28%	4639
	21st to end	Night	20% 10% 3 7% 5% 4 4 3 5% 7% 33%	5114
June	1st to 10th	Night	25% 8% 3 5% 4 4 4 4 5% 8% 30%	1680
	11th to 20th	Night	20% 6% 3 6% 5% 3 5% 3 6% 8% 36%	1640
	21st to end	Night	20% 8% 3 6% 5% 5% 6% 4 6% 7% 32%	1600
July	1st to 10th	Night	16% 8% 3 8% 6% 5% 5% 4 7% 8% 30%	3600
	11th to 20th	Night	19% 7% 2 5% 4 4 4 4 5% 7% 38%	3600
	21st to end	Night	13% 7% 2 7% 5% 4 5% 5% 7% 7% 38%	3926
August	1st to 10th	Night	23% 8% 3 6% 4 4 3 3 5% 7% 33%	2586
	11th to 20th	Night	16% 8% 2 8% 6% 5% 5% 4 6% 6% 34%	2880
	21st to end	Night	18% 7% 2 5% 4 4 4 3 5% 6% 41%	3586
September	1st to 10th	Night	17% 6% 3 5% 5% 3 4 3 5% 6% 43%	2000
	11th to 20th	Night	15% 5% 2 5% 4 3 4 3 5% 6% 47%	2130
	21st to end	Night	21% 5% 2 5% 5% 4 3 3 4 7% 41%	2200
October	1st to 10th	Night	20% 8% 3 7% 5% 3 4 3 5% 6% 36%	2265
	11th to 20th	Night	22% 10% 4 8% 5% 4 4 3 5% 5% 31%	2490
	21st to end	Night	27% 12% 3 8% 5% 4 4 3 5% 5% 26%	2860
November	1st to 10th	Night	22% 14% 3 7% 4 5% 5% 3 4 5% 28%	2667
	11th to 20th	Night	21% 16% 4 8% 4 4 3 3 4 5% 26%	2736
	21st to end	Night	22% 18% 5% 10% 5% 3 3 3 4 5% 22%	2940
December	1st to 10th	Night	17% 28% 9% 13% 5% 4 3 2 3 3 11%	4720
	11th to 20th	Night	22% 20% 5% 14% 6% 4 4 2 2 2 19%	5348
	21st to end	Night	21% 19% 5% 10% 5% 4 4 2 3 6% 21%	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	75% 5% 8% 10% 2	4662
	11th to 20th	Day	77% 7% 5% 8% 3	4680
	21st to end	Day	70% 8% 6% 9% 7%	5124
February	1st to 10th	Day	70% 5% 7% 13% 5% 1	1790
	11th to 20th	Day	69% 6% 8% 11% 5% 1	2020
	21st to end	Day	66% 6% 8% 13% 6% 1	1730
March	1st to 10th	Day	68% 5% 7% 10% 8% 2	4579
	11th to 20th	Day	57% 6% 13% 12% 10% 1	4761
	21st to end	Day	61% 5% 6% 13% 13% 1	6102
April	1st to 10th	Day	62% 5% 7% 16% 8% 1	2520
	11th to 20th	Day	55% 6% 6% 19% 12% 1	2504
	21st to end	Day	57% 5% 9% 18% 10% 2	2730
May	1st to 10th	Day	61% 7% 8% 17% 7% 1	7906
	11th to 20th	Day	52% 8% 15% 17% 7% 1	8225
	21st to end	Day	51% 7% 11% 22% 9%	9061
June	1st to 10th	Day	53% 7% 11% 20% 9% 1	2940
	11th to 20th	Day	45% 6% 13% 23% 11% 2	2870
	21st to end	Day	55% 7% 10% 19% 9% 1	2800
July	1st to 10th	Day	49% 8% 14% 22% 6%	6290
	11th to 20th	Day	42% 8% 14% 29% 7%	6285
	21st to end	Day	39% 7% 14% 33% 6%	6728
August	1st to 10th	Day	50% 8% 15% 20% 6%	4549
	11th to 20th	Day	47% 8% 18% 21% 6%	4172
	21st to end	Day	44% 7% 16% 20% 13% 1	4312
September	1st to 10th	Day	41% 6% 13% 29% 10% 1	2400
	11th to 20th	Day	39% 5% 11% 31% 13%	2270
	21st to end	Day	44% 6% 13% 25% 11% 1	2200
October	1st to 10th	Day	45% 7% 14% 27% 7%	3471
	11th to 20th	Day	52% 5% 14% 24% 5%	3087
	21st to end	Day	53% 5% 16% 19% 7% 1	3180
November	1st to 10th	Day	58% 7% 10% 18% 7%	1851
	11th to 20th	Day	64% 7% 8% 13% 7% 1	1879
	21st to end	Day	70% 6% 11% 10% 3	1680
December	1st to 10th	Day	77% 5% 8% 8% 2	2680
	11th to 20th	Day	69% 5% 6% 15% 5%	3066
	21st to end	Day	69% 5% 6% 11% 8%	4048
January	1st to 10th	Night	73% 5% 8% 10% 3	8234
	11th to 20th	Night	78% 6% 6% 7% 3	8280
	21st to end	Night	68% 5% 7% 10% 9%	9057
February	1st to 10th	Night	68% 5% 7% 14% 6%	2829
	11th to 20th	Night	66% 6% 8% 14% 6%	2495
	21st to end	Night	62% 5% 8% 14% 10% 1	2076
March	1st to 10th	Night	61% 5% 7% 14% 10% 3	5494
	11th to 20th	Night	59% 6% 12% 13% 9% 1	5413
	21st to end	Night	61% 6% 5% 17% 9% 1	5072
April	1st to 10th	Night	60% 4 7% 16% 11% 1	2100
	11th to 20th	Night	56% 5% 7% 19% 12% 1	2065
	21st to end	Night	52% 5% 9% 18% 13% 2	1890
May	1st to 10th	Night	59% 6% 11% 15% 7% 1	5053
	11th to 20th	Night	53% 8% 11% 21% 7% 1	4640
	21st to end	Night	51% 5% 10% 20% 14% 1	5115
June	1st to 10th	Night	51% 6% 10% 22% 10% 1	1680
	11th to 20th	Night	46% 7% 12% 21% 12% 3	1640
	21st to end	Night	50% 7% 12% 20% 10% 1	1600
July	1st to 10th	Night	48% 8% 16% 19% 8%	3560
	11th to 20th	Night	43% 7% 14% 27% 8%	3552
	21st to end	Night	41% 8% 16% 26% 9%	3809
August	1st to 10th	Night	50% 7% 13% 24% 6%	2576
	11th to 20th	Night	48% 7% 17% 20% 7%	2907
	21st to end	Night	43% 6% 13% 24% 14% 1	3586
September	1st to 10th	Night	41% 6% 12% 27% 13% 1	2000
	11th to 20th	Night	37% 5% 14% 29% 13%	2130
	21st to end	Night	43% 6% 11% 25% 14% 1	2200
October	1st to 10th	Night	50% 6% 10% 23% 10%	3707
	11th to 20th	Night	50% 5% 10% 26% 8%	4052
	21st to end	Night	53% 5% 12% 18% 10% 1	4610
November	1st to 10th	Night	58% 6% 10% 18% 7% 1	2667
	11th to 20th	Night	60% 6% 9% 14% 9% 2	2736
	21st to end	Night	66% 6% 10% 14% 4	2940
December	1st to 10th	Night	79% 5% 7% 7% 2	4720
	11th to 20th	Night	73% 5% 4 11% 7%	5348
	21st to end	Night	67% 5% 7% 12% 9%	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	31% 20% 30% 14% 5%	220
	11th to 20th	Day	28% 28% 31% 10% 2	220
	21st to end	Day	27% 21% 33% 14% 4	242
February	1st to 10th	Day	29% 32% 27% 8% 3	278
	11th to 20th	Day	31% 23% 33% 11% 2	499
	21st to end	Day	28% 23% 32% 15% 1	446
March	1st to 10th	Day	31% 21% 30% 14% 3	540
	11th to 20th	Day	31% 22% 31% 12% 3 1	540
	21st to end	Day	33% 24% 25% 12% 6% 1	594
April	1st to 10th	Day	37% 17% 27% 14% 5% 1	540
	11th to 20th	Day	36% 19% 24% 14% 5% 2	532
	21st to end	Day	33% 17% 30% 12% 6% 1	540
May	1st to 10th	Day	36% 17% 25% 16% 5% 2	543
	11th to 20th	Day	25% 16% 29% 21% 7% 2	567
	21st to end	Day	22% 20% 32% 19% 5% 1	617
June	1st to 10th	Day	28% 14% 30% 20% 7% 1	570
	11th to 20th	Day	23% 13% 33% 20% 10% 1	550
	21st to end	Day	27% 13% 32% 19% 6% 2	530
July	1st to 10th	Day	17% 11% 33% 26% 12% 2	525
	11th to 20th	Day	17% 11% 35% 27% 7% 3	524
	21st to end	Day	20% 12% 31% 28% 8% 2	576
August	1st to 10th	Day	18% 10% 29% 28% 13% 2	526
	11th to 20th	Day	19% 9% 26% 26% 16% 3	519
	21st to end	Day	22% 12% 25% 24% 12% 5%	583
September	1st to 10th	Day	17% 14% 29% 23% 12% 5%	530
	11th to 20th	Day	18% 9% 23% 23% 19% 8%	530
	21st to end	Day	18% 14% 26% 25% 12% 4	530
October	1st to 10th	Day	24% 15% 25% 21% 12% 3	530
	11th to 20th	Day	29% 18% 24% 19% 9% 1	480
	21st to end	Day	39% 16% 23% 17% 4	462
November	1st to 10th	Day	35% 19% 26% 15% 4	425
	11th to 20th	Day	29% 23% 25% 15% 6% 1	419
	21st to end	Day	38% 22% 29% 9% 2	220
December	1st to 10th	Day	34% 21% 27% 13% 5% 1	220
	11th to 20th	Day	33% 29% 27% 9% 2	220
	21st to end	Day	37% 18% 27% 14% 3 1	242
January	1st to 10th	Night	31% 18% 31% 16% 3	840
	11th to 20th	Night	28% 21% 31% 15% 5%	840
	21st to end	Night	22% 17% 33% 21% 6%	924
February	1st to 10th	Night	26% 17% 34% 19% 4	840
	11th to 20th	Night	24% 21% 33% 18% 3	823
	21st to end	Night	26% 17% 34% 22% 2	692
March	1st to 10th	Night	29% 18% 28% 20% 4	840
	11th to 20th	Night	29% 18% 26% 21% 5%	840
	21st to end	Night	28% 17% 27% 20% 7% 1	924
April	1st to 10th	Night	32% 16% 27% 20% 5%	840
	11th to 20th	Night	31% 15% 27% 20% 7%	821
	21st to end	Night	29% 17% 27% 20% 8%	630
May	1st to 10th	Night	29% 12% 29% 22% 7% 1	560
	11th to 20th	Night	25% 10% 32% 25% 8% 1	414
	21st to end	Night	22% 8% 33% 29% 7%	455
June	1st to 10th	Night	28% 10% 24% 29% 9%	420
	11th to 20th	Night	20% 8% 25% 34% 12%	410
	21st to end	Night	21% 9% 26% 33% 12% 1	400
July	1st to 10th	Night	15% 6% 29% 36% 13% 1	390
	11th to 20th	Night	15% 5% 24% 39% 17% 1	388
	21st to end	Night	15% 6% 25% 40% 13%	438
August	1st to 10th	Night	20% 4 19% 36% 20% 1	398
	11th to 20th	Night	16% 8% 19% 33% 22% 2	586
	21st to end	Night	19% 7% 22% 32% 18% 1	880
September	1st to 10th	Night	19% 8% 24% 32% 15% 1	800
	11th to 20th	Night	18% 7% 20% 29% 24% 2	800
	21st to end	Night	23% 8% 27% 25% 16% 2	800
October	1st to 10th	Night	25% 11% 26% 25% 13% 1	800
	11th to 20th	Night	29% 13% 24% 24% 9% 2	800
	21st to end	Night	34% 13% 27% 20% 5%	880
November	1st to 10th	Night	32% 16% 27% 19% 6% 1	820
	11th to 20th	Night	28% 19% 25% 17% 9% 1	840
	21st to end	Night	33% 19% 26% 16% 5% 1	840
December	1st to 10th	Night	35% 19% 27% 15% 4	840
	11th to 20th	Night	32% 20% 28% 15% 5% 1	840
	21st to end	Night	35% 19% 26% 16% 4	924

Page generated at 2026-06-13 02:31:39. Version ac07

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