Shediac River Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Shediac River Observatory clear sky chart from 2005-11-06 to 2026-05-17.

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	17% 11% 3 8% 5% 4 4 4 5% 6% 32%	132104
	Night	18% 12% 4 8% 5% 4 4 3 5% 6% 33%	130861
Transparency	Day	51% 5% 12% 21% 10% 1	135647
	Night	52% 4 11% 20% 10% 1	135405
Seeing	Day	22% 16% 31% 23% 7% 1	18824
	Night	24% 15% 32% 23% 6%	26478

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	14% 20% 5% 12% 6% 4 4 3 4 4 25%	4093
	11th to 20th	Day	15% 17% 7% 13% 5% 4 4 3 3 5% 26%	4392
	21st to end	Day	8% 10% 5% 9% 7% 4 4 3 5% 6% 40%	5781
February	1st to 10th	Day	15% 13% 5% 10% 5% 5% 4 3 5% 5% 31%	1890
	11th to 20th	Day	16% 13% 4 11% 5% 4 5% 4 3 5% 29%	1843
	21st to end	Day	11% 14% 4 8% 5% 4 3 4 5% 7% 34%	1563
March	1st to 10th	Day	19% 14% 6% 13% 5% 4 4 3 4 5% 24%	4995
	11th to 20th	Day	16% 15% 4 10% 5% 4 5% 4 6% 7% 25%	5090
	21st to end	Day	24% 16% 5% 8% 5% 3 4 3 5% 5% 22%	5587
April	1st to 10th	Day	22% 12% 4 8% 6% 5% 4 3 4 5% 27%	2494
	11th to 20th	Day	20% 12% 3 7% 5% 5% 4 4 4 6% 30%	2644
	21st to end	Day	23% 11% 3 8% 4 4 4 3 4 7% 29%	2730
May	1st to 10th	Day	25% 16% 3 8% 5% 4 4 3 4 5% 24%	6200
	11th to 20th	Day	21% 11% 3 7% 4 4 4 3 4 6% 33%	6402
	21st to end	Day	18% 12% 3 7% 5% 4 4 4 6% 7% 29%	6948
June	1st to 10th	Day	25% 9% 3 6% 5% 4 5% 3 5% 6% 28%	2960
	11th to 20th	Day	20% 6% 2 7% 5% 5% 5% 4 6% 7% 32%	3000
	21st to end	Day	25% 10% 3 7% 5% 4 4 3 5% 6% 29%	3000
July	1st to 10th	Day	15% 8% 3 8% 5% 6% 6% 5% 7% 9% 26%	6820
	11th to 20th	Day	13% 6% 2 7% 5% 4 5% 4 6% 8% 41%	6712
	21st to end	Day	11% 7% 3 6% 5% 5% 5% 4 7% 8% 38%	6795
August	1st to 10th	Day	17% 9% 3 7% 5% 5% 5% 4 6% 7% 32%	4235
	11th to 20th	Day	13% 6% 3 6% 4 6% 6% 4 7% 9% 37%	4175
	21st to end	Day	14% 4 2 5% 4 4 5% 4 6% 8% 45%	4576
September	1st to 10th	Day	15% 5% 2 6% 4 5% 4 3 6% 7% 44%	2400
	11th to 20th	Day	17% 6% 3 7% 4 4 3 3 5% 5% 43%	2291
	21st to end	Day	17% 7% 2 6% 4 4 4 3 4 6% 44%	2157
October	1st to 10th	Day	17% 8% 2 6% 3 3 4 4 5% 7% 42%	2000
	11th to 20th	Day	19% 9% 3 7% 4 4 5% 4 4 6% 36%	2000
	21st to end	Day	21% 9% 2 7% 5% 5% 5% 4 4 6% 32%	2165
November	1st to 10th	Day	19% 11% 3 8% 5% 5% 4 3 3 5% 32%	1655
	11th to 20th	Day	20% 14% 3 6% 4 5% 4 4 4 6% 31%	1680
	21st to end	Day	18% 15% 3 8% 5% 4 4 4 5% 6% 29%	1680
December	1st to 10th	Day	17% 12% 4 7% 4 4 3 3 5% 6% 33%	2690
	11th to 20th	Day	17% 15% 5% 7% 5% 3 3 2 3 4 35%	2908
	21st to end	Day	16% 11% 5% 13% 6% 4 4 3 4 4 30%	3553
January	1st to 10th	Night	15% 16% 5% 10% 5% 4 3 3 4 5% 31%	8831
	11th to 20th	Night	16% 16% 6% 11% 5% 4 4 3 4 4 26%	8509
	21st to end	Night	8% 12% 4 8% 6% 4 4 3 5% 6% 40%	8400
February	1st to 10th	Night	15% 15% 4 9% 5% 5% 5% 4 5% 6% 29%	2730
	11th to 20th	Night	16% 14% 4 10% 5% 5% 5% 3 6% 5% 28%	2663
	21st to end	Night	13% 14% 4 8% 6% 4 4 3 5% 5% 34%	2239
March	1st to 10th	Night	25% 15% 3 10% 5% 4 4 3 3 4 24%	5053
	11th to 20th	Night	20% 15% 3 9% 5% 4 5% 4 4 6% 25%	5089
	21st to end	Night	27% 13% 4 8% 4 4 4 3 4 3 26%	5587
April	1st to 10th	Night	23% 13% 3 9% 5% 4 4 3 5% 4 27%	2126
	11th to 20th	Night	23% 11% 2 7% 5% 4 3 3 4 6% 31%	1922
	21st to end	Night	21% 12% 3 9% 4 4 4 2 3 6% 31%	1890
May	1st to 10th	Night	27% 14% 3 7% 5% 4 4 4 5% 6% 23%	3966
	11th to 20th	Night	22% 9% 2 6% 4 4 3 3 5% 6% 35%	3645
	21st to end	Night	18% 10% 2 6% 4 5% 5% 4 5% 7% 34%	3948
June	1st to 10th	Night	25% 8% 2 6% 4 5% 4 4 5% 7% 30%	1456
	11th to 20th	Night	20% 7% 4 5% 5% 5% 5% 3 5% 8% 34%	1400
	21st to end	Night	24% 9% 4 8% 5% 4 4 4 5% 5% 28%	1400
July	1st to 10th	Night	15% 8% 3 9% 6% 5% 6% 5% 7% 8% 28%	3160
	11th to 20th	Night	9% 8% 3 9% 5% 6% 5% 4 6% 8% 37%	3206
	21st to end	Night	12% 7% 2 7% 4 5% 5% 4 7% 8% 38%	4071
August	1st to 10th	Night	16% 8% 3 9% 6% 5% 6% 3 7% 7% 30%	2915
	11th to 20th	Night	11% 6% 3 8% 6% 6% 6% 5% 6% 8% 37%	2872
	21st to end	Night	13% 5% 2 5% 4 4 4 4 5% 7% 48%	3321
September	1st to 10th	Night	16% 6% 2 5% 4 3 4 3 5% 7% 45%	2000
	11th to 20th	Night	15% 7% 2 5% 3 3 4 3 4 6% 47%	2105
	21st to end	Night	16% 5% 2 6% 4 3 4 3 6% 5% 45%	2242
October	1st to 10th	Night	18% 6% 3 7% 4 4 4 3 4 6% 41%	2400
	11th to 20th	Night	18% 9% 3 6% 4 3 4 3 5% 6% 39%	2400
	21st to end	Night	22% 9% 3 7% 4 4 4 3 5% 5% 34%	2672
November	1st to 10th	Night	20% 10% 2 7% 4 5% 4 3 5% 5% 35%	2860
	11th to 20th	Night	20% 12% 4 7% 5% 4 4 3 5% 6% 31%	2940
	21st to end	Night	23% 11% 3 7% 5% 4 3 3 4 6% 31%	2940
December	1st to 10th	Night	15% 9% 3 7% 5% 4 4 4 5% 6% 38%	4720
	11th to 20th	Night	17% 15% 4 7% 3 3 3 3 4 4 37%	5516
	21st to end	Night	20% 14% 5% 11% 4 4 4 3 4 5% 28%	7667

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% 3 10% 13% 9%	4094
	11th to 20th	Day	61% 5% 10% 12% 11% 1	4419
	21st to end	Day	45% 4 9% 21% 19% 2	5781
February	1st to 10th	Day	56% 4 11% 16% 11% 2	1890
	11th to 20th	Day	56% 6% 8% 18% 10% 1	1851
	21st to end	Day	49% 4 11% 21% 13% 2	1563
March	1st to 10th	Day	63% 4 8% 14% 10% 2	4999
	11th to 20th	Day	57% 6% 14% 16% 5% 2	5090
	21st to end	Day	63% 4 5% 18% 9% 1	5587
April	1st to 10th	Day	60% 4 7% 15% 11% 3	2494
	11th to 20th	Day	53% 7% 8% 20% 11% 1	2644
	21st to end	Day	54% 5% 9% 16% 12% 3	2730
May	1st to 10th	Day	62% 5% 8% 16% 9% 1	6211
	11th to 20th	Day	53% 5% 12% 24% 6%	6406
	21st to end	Day	51% 8% 11% 19% 10%	6948
June	1st to 10th	Day	56% 5% 11% 19% 8%	2960
	11th to 20th	Day	49% 7% 11% 22% 10% 1	3000
	21st to end	Day	56% 5% 11% 17% 9% 1	3000
July	1st to 10th	Day	52% 6% 16% 19% 7% 1	6745
	11th to 20th	Day	40% 6% 15% 29% 9% 1	6631
	21st to end	Day	41% 7% 17% 28% 6%	6600
August	1st to 10th	Day	51% 7% 11% 25% 7%	4222
	11th to 20th	Day	42% 7% 14% 26% 11%	4214
	21st to end	Day	36% 6% 15% 26% 17% 1	4576
September	1st to 10th	Day	38% 6% 15% 28% 13%	2400
	11th to 20th	Day	43% 4 12% 26% 13% 1	2291
	21st to end	Day	42% 5% 10% 27% 16% 1	2157
October	1st to 10th	Day	43% 7% 12% 29% 9%	3260
	11th to 20th	Day	45% 5% 10% 31% 9% 1	3240
	21st to end	Day	42% 5% 16% 20% 17%	3479
November	1st to 10th	Day	54% 5% 10% 22% 8% 1	1655
	11th to 20th	Day	56% 4 13% 16% 10% 1	1680
	21st to end	Day	56% 6% 14% 17% 7%	1680
December	1st to 10th	Day	52% 5% 13% 23% 7%	2690
	11th to 20th	Day	55% 4 11% 18% 11% 2	2907
	21st to end	Day	59% 3 12% 18% 8% 1	3553
January	1st to 10th	Night	57% 3 11% 23% 6%	8831
	11th to 20th	Night	61% 5% 9% 16% 8%	8557
	21st to end	Night	45% 3 10% 22% 17% 3	8400
February	1st to 10th	Night	56% 4 10% 17% 12% 2	2730
	11th to 20th	Night	57% 4 9% 18% 11% 1	2666
	21st to end	Night	51% 4 8% 21% 13% 3	2239
March	1st to 10th	Night	65% 3 5% 11% 13% 2	5062
	11th to 20th	Night	61% 5% 11% 14% 8% 1	5090
	21st to end	Night	64% 3 4 16% 12% 2	5587
April	1st to 10th	Night	60% 4 8% 14% 11% 3	2126
	11th to 20th	Night	54% 4 9% 21% 11% 1	1922
	21st to end	Night	56% 3 10% 15% 14% 2	1890
May	1st to 10th	Night	62% 4 9% 14% 10% 1	3972
	11th to 20th	Night	50% 5% 13% 22% 8% 1	3646
	21st to end	Night	48% 7% 18% 19% 8%	3949
June	1st to 10th	Night	53% 6% 13% 19% 9%	1456
	11th to 20th	Night	49% 6% 11% 23% 10% 1	1400
	21st to end	Night	58% 6% 11% 15% 9% 1	1400
July	1st to 10th	Night	52% 6% 13% 21% 9%	3125
	11th to 20th	Night	45% 6% 16% 25% 8%	3164
	21st to end	Night	41% 8% 17% 24% 10%	3952
August	1st to 10th	Night	53% 8% 12% 21% 6%	2903
	11th to 20th	Night	42% 7% 18% 23% 10%	2899
	21st to end	Night	35% 5% 17% 28% 15% 1	3320
September	1st to 10th	Night	39% 5% 11% 30% 14%	2000
	11th to 20th	Night	38% 6% 13% 29% 13% 1	2105
	21st to end	Night	41% 5% 12% 27% 14% 1	2242
October	1st to 10th	Night	49% 4 11% 27% 9%	3920
	11th to 20th	Night	37% 5% 12% 33% 12%	3899
	21st to end	Night	44% 4 14% 23% 14%	4308
November	1st to 10th	Night	52% 5% 13% 20% 10% 1	2860
	11th to 20th	Night	55% 4 13% 18% 9% 1	2940
	21st to end	Night	55% 5% 13% 19% 7%	2940
December	1st to 10th	Night	46% 4 15% 25% 10%	4720
	11th to 20th	Night	52% 3 11% 21% 11% 2	5518
	21st to end	Night	60% 3 11% 16% 9% 1	7667

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	29% 24% 30% 15% 1	220
	11th to 20th	Day	28% 22% 31% 15% 4	294
	21st to end	Day	15% 20% 37% 23% 4	473
February	1st to 10th	Day	21% 20% 34% 19% 5% 1	430
	11th to 20th	Day	24% 24% 33% 15% 4	426
	21st to end	Day	17% 24% 35% 19% 5%	359
March	1st to 10th	Day	24% 23% 36% 15% 2 1	540
	11th to 20th	Day	21% 25% 32% 18% 4	540
	21st to end	Day	29% 21% 30% 15% 3 2	594
April	1st to 10th	Day	28% 25% 32% 12% 3	540
	11th to 20th	Day	26% 20% 33% 16% 5%	532
	21st to end	Day	26% 18% 29% 20% 6% 1	540
May	1st to 10th	Day	30% 17% 29% 19% 5%	623
	11th to 20th	Day	25% 13% 30% 23% 8% 1	754
	21st to end	Day	23% 16% 32% 24% 6%	790
June	1st to 10th	Day	29% 13% 28% 23% 6%	730
	11th to 20th	Day	20% 12% 31% 28% 7% 1	730
	21st to end	Day	26% 10% 29% 26% 8% 1	730
July	1st to 10th	Day	19% 9% 33% 29% 9% 1	720
	11th to 20th	Day	15% 7% 30% 36% 11% 1	718
	21st to end	Day	17% 5% 31% 36% 11% 1	738
August	1st to 10th	Day	14% 8% 27% 38% 11% 2	526
	11th to 20th	Day	16% 8% 25% 32% 16% 3	519
	21st to end	Day	15% 11% 27% 32% 12% 2	583
September	1st to 10th	Day	12% 9% 37% 31% 10% 2	530
	11th to 20th	Day	20% 15% 24% 28% 12% 1	530
	21st to end	Day	18% 14% 33% 24% 9% 2	505
October	1st to 10th	Day	18% 14% 29% 24% 13% 1	420
	11th to 20th	Day	21% 20% 28% 20% 9% 1	420
	21st to end	Day	24% 21% 31% 17% 6% 1	462
November	1st to 10th	Day	26% 22% 29% 17% 5% 1	425
	11th to 20th	Day	30% 21% 31% 13% 4 1	430
	21st to end	Day	28% 23% 33% 13% 3 1	430
December	1st to 10th	Day	28% 19% 35% 15% 3	430
	11th to 20th	Day	28% 32% 26% 11% 1	351
	21st to end	Day	20% 29% 35% 14% 2	242
January	1st to 10th	Night	25% 19% 34% 17% 4	950
	11th to 20th	Night	24% 20% 31% 20% 5%	931
	21st to end	Night	17% 21% 36% 20% 6%	924
February	1st to 10th	Night	25% 16% 37% 18% 4 1	840
	11th to 20th	Night	25% 21% 34% 17% 3 1	823
	21st to end	Night	22% 16% 35% 24% 4 1	692
March	1st to 10th	Night	25% 18% 36% 20% 2	840
	11th to 20th	Night	24% 18% 30% 22% 5% 1	840
	21st to end	Night	27% 15% 34% 19% 5% 1	924
April	1st to 10th	Night	29% 18% 29% 21% 3	656
	11th to 20th	Night	29% 13% 32% 21% 5%	624
	21st to end	Night	27% 15% 30% 20% 8%	630
May	1st to 10th	Night	31% 12% 27% 22% 7% 1	630
	11th to 20th	Night	28% 9% 30% 24% 9%	611
	21st to end	Night	19% 10% 40% 26% 4	649
June	1st to 10th	Night	28% 7% 27% 32% 7%	456
	11th to 20th	Night	20% 9% 34% 31% 7% 1	400
	21st to end	Night	26% 8% 30% 29% 8% 1	400
July	1st to 10th	Night	18% 5% 38% 28% 11%	390
	11th to 20th	Night	15% 8% 31% 34% 11%	408
	21st to end	Night	16% 6% 31% 37% 9%	656
August	1st to 10th	Night	16% 3 31% 38% 11% 1	598
	11th to 20th	Night	17% 7% 27% 34% 15% 1	592
	21st to end	Night	16% 6% 30% 36% 12% 1	660
September	1st to 10th	Night	18% 7% 36% 31% 8%	600
	11th to 20th	Night	17% 11% 26% 35% 10% 1	705
	21st to end	Night	18% 11% 34% 28% 9%	800
October	1st to 10th	Night	22% 10% 32% 26% 10%	800
	11th to 20th	Night	22% 15% 35% 21% 7% 1	800
	21st to end	Night	27% 21% 29% 19% 4	880
November	1st to 10th	Night	27% 19% 32% 17% 5%	924
	11th to 20th	Night	27% 20% 30% 17% 5% 1	950
	21st to end	Night	30% 20% 31% 16% 3	950
December	1st to 10th	Night	29% 17% 34% 17% 3	950
	11th to 20th	Night	28% 23% 34% 12% 3	950
	21st to end	Night	29% 22% 27% 19% 2 1	1045

Page generated at 2026-05-14 02:58:53. Version ac07

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