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 2024-01-22.

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% 9% 4 6% 6% 3 4 4 5% 6% 33%	74806
	Night	19% 10% 4 7% 5% 3 4 4 5% 6% 33%	75122
Transparency	Day	52% 6% 11% 20% 10% 1	74502
	Night	53% 5% 12% 20% 10% 1	74961
Seeing	Day	22% 16% 31% 23% 7% 1	15671
	Night	24% 15% 32% 23% 6%	23410

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	18% 16% 5% 9% 6% 2 3 4 4 5% 29%	1327
	11th to 20th	Day	18% 15% 5% 9% 7% 2 4 4 4 5% 26%	1424
	21st to end	Day	12% 10% 5% 7% 6% 4 3 5% 5% 5% 39%	1792
February	1st to 10th	Day	17% 10% 5% 8% 6% 4 4 4 5% 5% 33%	1620
	11th to 20th	Day	18% 12% 5% 9% 6% 3 5% 5% 3 5% 28%	1573
	21st to end	Day	11% 12% 6% 8% 5% 3 4 4 5% 7% 34%	1336
March	1st to 10th	Day	17% 15% 6% 8% 6% 3 4 4 4 5% 27%	1958
	11th to 20th	Day	14% 11% 5% 11% 7% 3 4 4 4 6% 30%	1980
	21st to end	Day	19% 15% 6% 7% 6% 2 3 3 4 5% 30%	2178
April	1st to 10th	Day	22% 12% 4 7% 6% 4 4 4 4 5% 26%	2137
	11th to 20th	Day	20% 11% 3 6% 5% 3 4 5% 4 7% 32%	2262
	21st to end	Day	24% 11% 4 6% 5% 3 4 4 4 7% 27%	2340
May	1st to 10th	Day	26% 10% 3 7% 6% 3 4 5% 3 5% 28%	2408
	11th to 20th	Day	23% 9% 3 5% 5% 2 4 4 4 6% 35%	2478
	21st to end	Day	20% 9% 3 6% 5% 3 4 5% 5% 7% 34%	2724
June	1st to 10th	Day	27% 9% 3 5% 6% 3 4 4 5% 6% 27%	2664
	11th to 20th	Day	21% 6% 2 6% 5% 4 5% 5% 5% 7% 32%	2700
	21st to end	Day	25% 9% 3 6% 6% 3 5% 4 4 6% 30%	2700
July	1st to 10th	Day	18% 6% 3 5% 5% 4 5% 5% 6% 9% 35%	2700
	11th to 20th	Day	13% 6% 3 5% 6% 4 6% 6% 6% 9% 34%	2662
	21st to end	Day	17% 7% 4 6% 7% 4 6% 5% 6% 9% 29%	2694
August	1st to 10th	Day	17% 7% 3 4 5% 4 6% 5% 6% 8% 36%	2327
	11th to 20th	Day	16% 6% 3 6% 6% 4 6% 6% 7% 9% 32%	2304
	21st to end	Day	15% 5% 2 5% 6% 3 4 5% 5% 7% 43%	2520
September	1st to 10th	Day	16% 5% 2 4 5% 3 5% 4 6% 7% 43%	2160
	11th to 20th	Day	18% 6% 3 6% 5% 2 4 4 5% 5% 41%	2063
	21st to end	Day	18% 7% 2 5% 4 3 4 4 4 5% 45%	1942
October	1st to 10th	Day	18% 7% 3 5% 4 2 4 5% 4 7% 41%	1800
	11th to 20th	Day	20% 9% 3 6% 5% 3 4 5% 4 6% 36%	1800
	21st to end	Day	22% 8% 3 6% 6% 4 5% 4 4 6% 32%	1949
November	1st to 10th	Day	20% 9% 4 8% 5% 4 4 5% 4 5% 33%	1495
	11th to 20th	Day	19% 13% 3 6% 5% 4 5% 5% 4 6% 32%	1520
	21st to end	Day	17% 14% 4 6% 6% 3 4 5% 4 6% 30%	1520
December	1st to 10th	Day	24% 13% 4 6% 5% 3 3 3 4 5% 30%	1520
	11th to 20th	Day	18% 18% 5% 7% 6% 3 4 3 4 4 28%	1798
	21st to end	Day	19% 11% 6% 11% 7% 3 3 3 3 5% 28%	2431
January	1st to 10th	Night	18% 13% 5% 8% 6% 4 4 4 4 5% 29%	2838
	11th to 20th	Night	17% 12% 5% 8% 7% 3 4 4 5% 5% 30%	2747
	21st to end	Night	13% 12% 4 7% 6% 2 4 4 4 7% 36%	2598
February	1st to 10th	Night	16% 12% 4 7% 6% 4 5% 5% 5% 6% 31%	2340
	11th to 20th	Night	17% 13% 4 8% 7% 3 6% 4 5% 5% 27%	2273
	21st to end	Night	14% 12% 5% 7% 7% 4 4 4 5% 6% 33%	1916
March	1st to 10th	Night	17% 16% 4 8% 6% 3 4 3 4 5% 29%	1989
	11th to 20th	Night	17% 11% 4 8% 6% 3 5% 6% 4 5% 31%	1979
	21st to end	Night	19% 14% 5% 7% 5% 3 5% 3 3 4 32%	2178
April	1st to 10th	Night	25% 11% 3 7% 6% 3 5% 4 5% 4 26%	1823
	11th to 20th	Night	23% 11% 2 6% 6% 3 3 4 4 6% 32%	1645
	21st to end	Night	22% 11% 4 7% 5% 3 5% 3 4 5% 31%	1620
May	1st to 10th	Night	25% 11% 3 6% 5% 3 4 4 6% 5% 30%	1550
	11th to 20th	Night	23% 9% 3 6% 5% 2 3 4 5% 6% 34%	1416
	21st to end	Night	16% 8% 3 5% 5% 4 6% 5% 5% 7% 35%	1550
June	1st to 10th	Night	25% 7% 3 6% 4 3 5% 5% 5% 7% 29%	1311
	11th to 20th	Night	22% 7% 4 5% 5% 4 4 3 4 8% 34%	1260
	21st to end	Night	24% 8% 4 7% 5% 3 5% 5% 5% 5% 30%	1260
July	1st to 10th	Night	17% 7% 3 5% 5% 2 5% 6% 6% 8% 35%	1260
	11th to 20th	Night	13% 7% 3 7% 5% 4 6% 6% 6% 9% 35%	1278
	21st to end	Night	16% 8% 3 7% 6% 5% 6% 5% 6% 7% 32%	1621
August	1st to 10th	Night	14% 6% 3 6% 5% 4 6% 4 6% 7% 38%	1612
	11th to 20th	Night	16% 7% 4 7% 6% 4 5% 5% 5% 7% 35%	1596
	21st to end	Night	14% 5% 3 6% 5% 3 4 5% 5% 8% 42%	1835
September	1st to 10th	Night	17% 5% 2 4 6% 2 4 4 5% 7% 44%	1800
	11th to 20th	Night	17% 7% 3 5% 4 3 3 4 4 6% 46%	1894
	21st to end	Night	16% 5% 3 5% 4 3 4 4 5% 5% 46%	2017
October	1st to 10th	Night	19% 6% 2 6% 5% 3 4 4 4 6% 41%	2160
	11th to 20th	Night	18% 8% 3 6% 5% 2 3 4 5% 6% 39%	2160
	21st to end	Night	24% 8% 3 6% 6% 3 4 4 4 5% 33%	2404
November	1st to 10th	Night	21% 9% 2 6% 4 3 5% 5% 5% 5% 35%	2580
	11th to 20th	Night	19% 10% 4 7% 6% 3 4 3 5% 6% 32%	2660
	21st to end	Night	22% 11% 4 6% 5% 3 4 4 4 6% 32%	2660
December	1st to 10th	Night	24% 11% 3 6% 5% 3 4 5% 4 5% 29%	2660
	11th to 20th	Night	21% 18% 5% 7% 4 3 3 4 3 4 28%	3396
	21st to end	Night	23% 14% 5% 8% 4 2 3 3 3 5% 28%	5236

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	59% 5% 11% 14% 10% 1	1328
	11th to 20th	Day	62% 5% 8% 14% 10% 1	1424
	21st to end	Day	47% 6% 11% 18% 18% 1	1792
February	1st to 10th	Day	54% 4 11% 17% 11% 2	1620
	11th to 20th	Day	58% 7% 8% 17% 9% 1	1581
	21st to end	Day	49% 4 11% 21% 13% 2	1336
March	1st to 10th	Day	59% 5% 8% 19% 9% 1	1962
	11th to 20th	Day	56% 4 9% 19% 9% 3	1980
	21st to end	Day	57% 4 7% 18% 10% 3	2178
April	1st to 10th	Day	60% 5% 7% 15% 11% 3	2137
	11th to 20th	Day	51% 7% 9% 20% 12% 2	2262
	21st to end	Day	56% 5% 10% 15% 11% 3	2340
May	1st to 10th	Day	58% 6% 7% 16% 11% 1	2408
	11th to 20th	Day	52% 4 8% 24% 12% 1	2482
	21st to end	Day	50% 6% 12% 23% 9% 1	2724
June	1st to 10th	Day	57% 5% 11% 19% 8%	2664
	11th to 20th	Day	51% 7% 11% 22% 9% 1	2700
	21st to end	Day	56% 5% 11% 17% 9% 1	2700
July	1st to 10th	Day	44% 7% 17% 22% 9% 1	2625
	11th to 20th	Day	43% 8% 17% 23% 9% 1	2581
	21st to end	Day	50% 8% 13% 21% 8%	2543
August	1st to 10th	Day	45% 7% 13% 27% 8%	2314
	11th to 20th	Day	46% 8% 16% 24% 6%	2304
	21st to end	Day	40% 6% 15% 27% 12%	2520
September	1st to 10th	Day	39% 6% 16% 26% 13%	2160
	11th to 20th	Day	45% 4 11% 25% 14% 1	2063
	21st to end	Day	42% 5% 10% 26% 16% 1	1942
October	1st to 10th	Day	43% 6% 11% 28% 11% 1	1800
	11th to 20th	Day	50% 5% 12% 24% 8% 1	1800
	21st to end	Day	54% 5% 12% 17% 11% 1	1949
November	1st to 10th	Day	54% 5% 11% 21% 9% 1	1495
	11th to 20th	Day	54% 5% 14% 16% 11% 1	1520
	21st to end	Day	55% 6% 15% 18% 7%	1520
December	1st to 10th	Day	59% 6% 14% 15% 6%	1520
	11th to 20th	Day	62% 4 10% 16% 8% 1	1797
	21st to end	Day	61% 3 14% 14% 6% 1	2431
January	1st to 10th	Night	58% 4 11% 18% 8% 1	2838
	11th to 20th	Night	56% 6% 11% 17% 9% 1	2747
	21st to end	Night	49% 4 11% 23% 12% 2	2598
February	1st to 10th	Night	54% 4 11% 17% 12% 2	2340
	11th to 20th	Night	58% 4 9% 16% 11% 1	2276
	21st to end	Night	52% 4 9% 19% 13% 2	1916
March	1st to 10th	Night	58% 4 7% 18% 10% 2	1998
	11th to 20th	Night	55% 4 8% 19% 12% 2	1980
	21st to end	Night	57% 4 7% 18% 12% 3	2178
April	1st to 10th	Night	60% 4 8% 13% 10% 3	1823
	11th to 20th	Night	53% 4 9% 21% 12% 1	1645
	21st to end	Night	57% 3 10% 15% 14% 1	1620
May	1st to 10th	Night	56% 5% 9% 18% 12% 2	1550
	11th to 20th	Night	51% 4 10% 22% 11% 1	1417
	21st to end	Night	47% 8% 14% 20% 10% 1	1551
June	1st to 10th	Night	54% 6% 13% 18% 9%	1311
	11th to 20th	Night	50% 6% 10% 23% 10% 1	1260
	21st to end	Night	56% 6% 11% 16% 9% 1	1260
July	1st to 10th	Night	44% 7% 17% 25% 8%	1225
	11th to 20th	Night	45% 7% 16% 22% 10%	1236
	21st to end	Night	50% 8% 15% 19% 8%	1532
August	1st to 10th	Night	44% 7% 15% 25% 8%	1600
	11th to 20th	Night	48% 6% 18% 22% 6%	1596
	21st to end	Night	39% 6% 17% 28% 10%	1835
September	1st to 10th	Night	40% 5% 12% 30% 13%	1800
	11th to 20th	Night	40% 5% 13% 27% 13% 1	1894
	21st to end	Night	41% 5% 12% 27% 14% 1	2017
October	1st to 10th	Night	45% 5% 11% 27% 12%	2160
	11th to 20th	Night	45% 5% 14% 28% 7%	2160
	21st to end	Night	55% 5% 10% 20% 9% 1	2404
November	1st to 10th	Night	52% 5% 13% 19% 10% 1	2580
	11th to 20th	Night	54% 4 14% 18% 10% 1	2660
	21st to end	Night	54% 6% 14% 18% 7%	2660
December	1st to 10th	Night	58% 4 16% 16% 7%	2660
	11th to 20th	Night	61% 3 9% 18% 7%	3398
	21st to end	Night	61% 3 13% 15% 6% 1	5236

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	28% 23% 32% 16% 1	180
	11th to 20th	Day	26% 25% 31% 15% 2	246
	21st to end	Day	16% 18% 38% 24% 4	378
February	1st to 10th	Day	24% 19% 35% 19% 3	340
	11th to 20th	Day	24% 24% 34% 14% 3 1	336
	21st to end	Day	16% 23% 37% 19% 5%	282
March	1st to 10th	Day	24% 22% 36% 15% 2 1	420
	11th to 20th	Day	19% 24% 34% 19% 4	420
	21st to end	Day	27% 19% 31% 17% 4 2	462
April	1st to 10th	Day	27% 23% 33% 13% 3	420
	11th to 20th	Day	25% 18% 33% 18% 5%	412
	21st to end	Day	27% 17% 29% 21% 5% 1	420
May	1st to 10th	Day	29% 16% 28% 21% 5%	491
	11th to 20th	Day	25% 14% 28% 24% 9% 1	624
	21st to end	Day	23% 16% 31% 24% 6%	680
June	1st to 10th	Day	31% 11% 29% 22% 7%	630
	11th to 20th	Day	23% 12% 29% 28% 7% 1	630
	21st to end	Day	26% 7% 28% 29% 9% 1	630
July	1st to 10th	Day	19% 8% 32% 30% 10% 1	620
	11th to 20th	Day	15% 6% 29% 37% 12% 1	618
	21st to end	Day	18% 4 29% 37% 12% 1	634
August	1st to 10th	Day	15% 7% 26% 40% 11% 1	446
	11th to 20th	Day	18% 8% 25% 32% 15% 2	439
	21st to end	Day	16% 11% 25% 34% 13% 2	495
September	1st to 10th	Day	12% 8% 36% 31% 10% 2	450
	11th to 20th	Day	22% 16% 24% 26% 10% 1	450
	21st to end	Day	19% 15% 32% 23% 9% 3	430
October	1st to 10th	Day	19% 15% 28% 22% 15% 1	360
	11th to 20th	Day	20% 19% 30% 20% 9% 1	360
	21st to end	Day	25% 20% 30% 19% 5% 1	396
November	1st to 10th	Day	24% 21% 29% 19% 6% 1	365
	11th to 20th	Day	27% 21% 33% 14% 4 1	370
	21st to end	Day	28% 24% 32% 14% 3	370
December	1st to 10th	Day	29% 18% 33% 15% 4	370
	11th to 20th	Day	29% 33% 26% 11% 1	299
	21st to end	Day	22% 30% 34% 13% 1	198
January	1st to 10th	Night	24% 20% 34% 17% 4	850
	11th to 20th	Night	23% 21% 32% 19% 5%	835
	21st to end	Night	17% 19% 36% 21% 6%	800
February	1st to 10th	Night	25% 16% 38% 18% 3	720
	11th to 20th	Night	26% 20% 34% 16% 2 1	703
	21st to end	Night	22% 16% 34% 23% 4 1	592
March	1st to 10th	Night	24% 16% 38% 21% 2	720
	11th to 20th	Night	23% 17% 30% 22% 6% 1	720
	21st to end	Night	26% 14% 33% 21% 5% 1	792
April	1st to 10th	Night	30% 17% 29% 21% 4	563
	11th to 20th	Night	28% 13% 32% 22% 6%	534
	21st to end	Night	27% 15% 30% 19% 8%	540
May	1st to 10th	Night	30% 11% 27% 24% 7% 1	540
	11th to 20th	Night	28% 9% 30% 25% 8%	532
	21st to end	Night	20% 10% 39% 27% 4	583
June	1st to 10th	Night	28% 6% 27% 32% 7%	411
	11th to 20th	Night	21% 8% 30% 33% 7% 1	360
	21st to end	Night	25% 7% 30% 30% 8% 1	360
July	1st to 10th	Night	19% 4 39% 27% 11%	350
	11th to 20th	Night	15% 8% 30% 35% 12% 1	366
	21st to end	Night	17% 5% 29% 39% 9% 1	590
August	1st to 10th	Night	16% 3 30% 38% 11% 1	538
	11th to 20th	Night	18% 6% 27% 34% 14% 1	532
	21st to end	Night	15% 5% 29% 37% 12% 1	594
September	1st to 10th	Night	19% 7% 36% 30% 9%	540
	11th to 20th	Night	19% 11% 27% 33% 9% 1	634
	21st to end	Night	18% 12% 33% 28% 9%	720
October	1st to 10th	Night	22% 9% 32% 26% 10%	720
	11th to 20th	Night	21% 14% 36% 22% 8%	720
	21st to end	Night	28% 21% 29% 19% 3	792
November	1st to 10th	Night	26% 19% 31% 19% 5%	824
	11th to 20th	Night	24% 21% 31% 17% 6% 1	850
	21st to end	Night	28% 22% 30% 17% 3	850
December	1st to 10th	Night	31% 16% 33% 16% 3	850
	11th to 20th	Night	29% 22% 34% 13% 3	850
	21st to end	Night	29% 21% 27% 19% 2 1	935

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