Acadia University
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Acadia University clear sky chart from 2005-11-06 to 2025-08-05.

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% 12% 4 10% 6% 5% 4 3 5% 6% 28%	127009
	Night	17% 13% 5% 11% 6% 5% 4 3 5% 6% 26%	121141
Transparency	Day	55% 7% 11% 17% 9% 1	130587
	Night	57% 7% 11% 17% 8% 1	125650
Seeing	Day	26% 18% 30% 19% 7% 1	18368
	Night	27% 16% 29% 22% 6%	25599

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% 23% 7% 18% 8% 5% 3 2 3 3 14%	3580
	11th to 20th	Day	12% 19% 10% 22% 7% 5% 5% 3 3 4 11%	3749
	21st to end	Day	12% 13% 7% 13% 9% 9% 5% 3 4 5% 20%	4466
February	1st to 10th	Day	17% 15% 6% 13% 9% 7% 4 3 5% 4 16%	1800
	11th to 20th	Day	16% 15% 5% 14% 10% 6% 4 4 4 4 18%	1753
	21st to end	Day	11% 13% 7% 10% 8% 6% 4 2 4 7% 28%	1501
March	1st to 10th	Day	20% 17% 4 14% 6% 7% 3 2 2 4 19%	4930
	11th to 20th	Day	12% 16% 5% 10% 6% 5% 4 3 5% 6% 27%	4980
	21st to end	Day	20% 19% 6% 11% 5% 5% 4 3 3 4 20%	5466
April	1st to 10th	Day	21% 15% 4 9% 5% 4 3 3 5% 5% 25%	2375
	11th to 20th	Day	18% 14% 3 6% 4 4 4 3 5% 8% 32%	2475
	21st to end	Day	21% 11% 3 8% 4 4 4 3 5% 7% 29%	2600
May	1st to 10th	Day	27% 15% 3 7% 5% 4 5% 4 5% 6% 20%	5996
	11th to 20th	Day	19% 12% 3 9% 5% 4 4 3 5% 6% 30%	6318
	21st to end	Day	16% 12% 3 8% 5% 4 4 3 6% 8% 31%	6948
June	1st to 10th	Day	24% 9% 3 7% 6% 4 5% 4 5% 7% 26%	2800
	11th to 20th	Day	20% 9% 3 6% 5% 5% 4 3 6% 7% 33%	3000
	21st to end	Day	23% 10% 4 7% 5% 4 4 4 5% 6% 27%	3000
July	1st to 10th	Day	19% 9% 3 7% 5% 4 5% 4 6% 8% 28%	6820
	11th to 20th	Day	14% 8% 3 7% 5% 4 5% 4 6% 8% 37%	6388
	21st to end	Day	11% 7% 3 7% 5% 5% 5% 4 7% 9% 37%	6682
August	1st to 10th	Day	19% 10% 3 9% 5% 5% 5% 4 5% 6% 29%	4157
	11th to 20th	Day	13% 7% 3 8% 5% 5% 5% 4 6% 7% 36%	4045
	21st to end	Day	12% 6% 2 5% 4 4 4 4 6% 8% 46%	4382
September	1st to 10th	Day	16% 7% 2 5% 4 4 3 3 5% 7% 43%	2280
	11th to 20th	Day	17% 7% 2 6% 4 3 3 3 4 6% 45%	2185
	21st to end	Day	17% 6% 3 6% 4 3 4 3 5% 7% 42%	2043
October	1st to 10th	Day	17% 7% 3 6% 4 4 4 4 5% 8% 38%	1900
	11th to 20th	Day	18% 10% 3 7% 4 4 4 4 6% 7% 33%	1900
	21st to end	Day	18% 14% 4 8% 5% 4 4 3 5% 5% 30%	2090
November	1st to 10th	Day	20% 14% 3 9% 5% 5% 4 2 4 6% 28%	1612
	11th to 20th	Day	18% 19% 6% 9% 6% 5% 4 3 4 5% 22%	1600
	21st to end	Day	18% 18% 5% 10% 7% 6% 5% 3 4 5% 19%	1600
December	1st to 10th	Day	17% 16% 9% 19% 5% 5% 4 3 4 4 13%	2610
	11th to 20th	Day	21% 16% 6% 15% 8% 5% 3 2 3 4 17%	2996
	21st to end	Day	18% 15% 9% 15% 7% 4 4 2 4 4 17%	3982
January	1st to 10th	Night	13% 19% 8% 20% 7% 5% 4 2 3 4 14%	6349
	11th to 20th	Night	13% 18% 8% 21% 7% 5% 5% 3 3 3 13%	6135
	21st to end	Night	12% 12% 5% 17% 13% 8% 5% 4 5% 6% 16%	6490
February	1st to 10th	Night	17% 15% 5% 14% 10% 6% 5% 4 5% 4 16%	2600
	11th to 20th	Night	16% 14% 6% 12% 10% 7% 5% 3 5% 5% 18%	2533
	21st to end	Night	12% 16% 5% 11% 6% 5% 5% 3 5% 5% 27%	2124
March	1st to 10th	Night	20% 15% 5% 14% 10% 5% 4 3 3 4 19%	4910
	11th to 20th	Night	16% 17% 6% 8% 5% 4 4 4 5% 6% 27%	4979
	21st to end	Night	24% 15% 6% 10% 5% 4 3 2 3 4 24%	5466
April	1st to 10th	Night	21% 15% 5% 6% 6% 5% 4 3 4 4 27%	2024
	11th to 20th	Night	21% 12% 4 7% 3 4 4 2 4 6% 32%	1872
	21st to end	Night	21% 13% 3 7% 4 5% 4 3 4 5% 30%	1800
May	1st to 10th	Night	25% 15% 3 8% 5% 5% 4 3 4 5% 22%	3949
	11th to 20th	Night	21% 12% 3 7% 4 4 4 4 5% 7% 30%	3596
	21st to end	Night	15% 13% 3 8% 4 4 4 3 5% 7% 32%	3948
June	1st to 10th	Night	24% 9% 2 7% 5% 4 4 4 6% 9% 28%	1600
	11th to 20th	Night	19% 8% 3 7% 4 5% 4 3 5% 7% 36%	1414
	21st to end	Night	22% 9% 4 7% 5% 5% 4 3 6% 7% 28%	1400
July	1st to 10th	Night	17% 10% 4 10% 5% 5% 5% 4 6% 8% 27%	3160
	11th to 20th	Night	14% 7% 2 5% 4 4 5% 4 7% 9% 38%	3528
	21st to end	Night	13% 6% 2 6% 4 4 5% 4 7% 9% 41%	4178
August	1st to 10th	Night	19% 9% 2 7% 4 4 4 4 6% 7% 33%	2862
	11th to 20th	Night	12% 7% 3 8% 6% 5% 4 4 7% 8% 37%	2782
	21st to end	Night	14% 5% 2 5% 3 3 4 3 5% 7% 49%	3273
September	1st to 10th	Night	12% 6% 3 6% 4 4 4 4 5% 8% 44%	1900
	11th to 20th	Night	16% 7% 3 6% 3 3 3 3 6% 7% 44%	1992
	21st to end	Night	17% 7% 3 6% 4 3 5% 4 5% 7% 38%	2136
October	1st to 10th	Night	17% 7% 2 5% 3 4 4 3 6% 7% 40%	2280
	11th to 20th	Night	18% 8% 3 7% 4 4 5% 3 5% 8% 36%	2280
	21st to end	Night	23% 11% 3 7% 4 4 4 3 4 6% 31%	2508
November	1st to 10th	Night	19% 13% 3 8% 5% 5% 4 3 5% 5% 31%	2684
	11th to 20th	Night	18% 18% 4 11% 7% 5% 4 3 5% 5% 21%	2800
	21st to end	Night	21% 17% 5% 10% 6% 4 4 3 4 5% 22%	2800
December	1st to 10th	Night	14% 15% 8% 19% 6% 5% 4 4 4 5% 16%	4580
	11th to 20th	Night	16% 18% 6% 14% 6% 5% 4 3 3 4 22%	5213
	21st to end	Night	21% 15% 6% 13% 7% 3 3 2 3 4 22%	6996

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	74% 5% 13% 6% 2	3581
	11th to 20th	Day	75% 6% 7% 9% 2	3779
	21st to end	Day	62% 8% 9% 9% 10% 2	4466
February	1st to 10th	Day	70% 5% 9% 9% 6% 1	1800
	11th to 20th	Day	68% 6% 9% 12% 4	1761
	21st to end	Day	56% 5% 11% 17% 9% 1	1501
March	1st to 10th	Day	68% 5% 7% 12% 7% 1	4934
	11th to 20th	Day	55% 7% 14% 17% 6% 1	4980
	21st to end	Day	68% 4 5% 13% 8% 1	5466
April	1st to 10th	Day	61% 5% 8% 12% 12% 3	2375
	11th to 20th	Day	52% 4 9% 21% 12% 1	2475
	21st to end	Day	55% 4 10% 18% 11% 2	2600
May	1st to 10th	Day	63% 7% 8% 14% 7% 1	6007
	11th to 20th	Day	52% 9% 11% 21% 6% 1	6322
	21st to end	Day	49% 8% 14% 18% 11%	6948
June	1st to 10th	Day	57% 6% 11% 18% 7% 1	2800
	11th to 20th	Day	48% 7% 13% 20% 10% 1	3000
	21st to end	Day	56% 7% 11% 16% 10% 1	3000
July	1st to 10th	Day	50% 7% 15% 17% 10% 1	6745
	11th to 20th	Day	43% 9% 15% 23% 9%	6311
	21st to end	Day	42% 9% 16% 24% 9%	6491
August	1st to 10th	Day	54% 7% 11% 19% 9%	4144
	11th to 20th	Day	45% 8% 14% 22% 11%	4084
	21st to end	Day	34% 8% 15% 25% 17% 1	4382
September	1st to 10th	Day	41% 5% 13% 25% 14% 2	2280
	11th to 20th	Day	42% 4 12% 24% 16% 1	2185
	21st to end	Day	42% 5% 10% 28% 15% 1	2043
October	1st to 10th	Day	43% 10% 13% 23% 11%	3160
	11th to 20th	Day	42% 7% 11% 26% 14%	3140
	21st to end	Day	46% 5% 14% 22% 13%	3428
November	1st to 10th	Day	59% 6% 9% 17% 8% 1	1612
	11th to 20th	Day	63% 6% 12% 13% 5% 1	1600
	21st to end	Day	67% 7% 11% 11% 4	1600
December	1st to 10th	Day	71% 8% 8% 11% 2	2610
	11th to 20th	Day	71% 6% 6% 12% 5% 1	2995
	21st to end	Day	70% 6% 11% 9% 4	3982
January	1st to 10th	Night	70% 7% 11% 11% 2	6349
	11th to 20th	Night	74% 6% 8% 8% 3	6180
	21st to end	Night	64% 8% 11% 11% 5%	6490
February	1st to 10th	Night	71% 6% 8% 9% 6% 1	2600
	11th to 20th	Night	66% 6% 10% 12% 5% 1	2536
	21st to end	Night	58% 5% 10% 18% 8% 1	2124
March	1st to 10th	Night	70% 4 5% 11% 9% 1	4919
	11th to 20th	Night	57% 6% 13% 17% 7% 1	4980
	21st to end	Night	65% 4 7% 15% 8% 1	5466
April	1st to 10th	Night	60% 5% 8% 13% 11% 3	2024
	11th to 20th	Night	54% 5% 6% 20% 13% 1	1872
	21st to end	Night	56% 5% 10% 15% 12% 2	1800
May	1st to 10th	Night	64% 6% 10% 12% 7% 1	3955
	11th to 20th	Night	53% 8% 9% 22% 7% 2	3597
	21st to end	Night	51% 9% 14% 20% 6% 1	3949
June	1st to 10th	Night	53% 9% 11% 21% 7% 1	1600
	11th to 20th	Night	48% 6% 12% 22% 11% 1	1414
	21st to end	Night	54% 10% 11% 15% 8% 2	1400
July	1st to 10th	Night	54% 8% 14% 16% 8%	3125
	11th to 20th	Night	40% 10% 18% 21% 11% 1	3482
	21st to end	Night	38% 9% 17% 24% 12%	4055
August	1st to 10th	Night	50% 8% 14% 22% 6%	2850
	11th to 20th	Night	43% 10% 16% 23% 8%	2809
	21st to end	Night	33% 7% 17% 26% 16% 1	3272
September	1st to 10th	Night	38% 8% 11% 28% 14% 1	1900
	11th to 20th	Night	40% 5% 12% 29% 14% 1	1992
	21st to end	Night	44% 7% 10% 25% 13% 1	2136
October	1st to 10th	Night	47% 6% 12% 23% 11%	3800
	11th to 20th	Night	38% 7% 13% 25% 16%	3779
	21st to end	Night	44% 5% 12% 23% 15%	4120
November	1st to 10th	Night	54% 6% 12% 19% 9% 1	2684
	11th to 20th	Night	63% 7% 10% 14% 6%	2800
	21st to end	Night	64% 7% 13% 13% 4	2800
December	1st to 10th	Night	66% 8% 11% 13% 2	4580
	11th to 20th	Night	65% 6% 8% 15% 5%	5215
	21st to end	Night	66% 5% 10% 14% 5%	6996

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	30% 26% 30% 12% 2	364
	11th to 20th	Day	31% 24% 29% 12% 4	400
	21st to end	Day	21% 28% 35% 14% 2	440
February	1st to 10th	Day	31% 23% 32% 11% 4 1	400
	11th to 20th	Day	32% 30% 24% 13% 1	396
	21st to end	Day	24% 20% 37% 16% 3	337
March	1st to 10th	Day	29% 24% 32% 11% 3	500
	11th to 20th	Day	24% 25% 35% 12% 4	500
	21st to end	Day	31% 27% 26% 11% 4	550
April	1st to 10th	Day	39% 24% 26% 10% 2	500
	11th to 20th	Day	26% 26% 31% 13% 3 1	492
	21st to end	Day	27% 21% 30% 14% 8%	500
May	1st to 10th	Day	32% 19% 29% 14% 4 1	548
	11th to 20th	Day	24% 18% 26% 23% 7% 1	724
	21st to end	Day	26% 15% 33% 19% 6% 1	790
June	1st to 10th	Day	30% 13% 27% 22% 8% 1	730
	11th to 20th	Day	24% 13% 31% 24% 7% 1	730
	21st to end	Day	29% 12% 27% 23% 8% 2	730
July	1st to 10th	Day	21% 7% 34% 27% 9% 1	720
	11th to 20th	Day	18% 8% 31% 28% 13% 2	718
	21st to end	Day	22% 7% 32% 28% 11% 1	690
August	1st to 10th	Day	14% 8% 33% 33% 10% 2	502
	11th to 20th	Day	20% 9% 29% 25% 12% 4	479
	21st to end	Day	15% 13% 29% 23% 16% 4	539
September	1st to 10th	Day	19% 10% 34% 25% 10% 1	490
	11th to 20th	Day	22% 14% 26% 25% 10% 3	490
	21st to end	Day	20% 15% 31% 22% 11% 2	465
October	1st to 10th	Day	22% 13% 30% 22% 9% 3	390
	11th to 20th	Day	25% 18% 28% 19% 8% 2	390
	21st to end	Day	26% 22% 29% 18% 4 1	429
November	1st to 10th	Day	30% 19% 30% 16% 4 1	395
	11th to 20th	Day	39% 20% 24% 12% 6% 1	400
	21st to end	Day	33% 22% 30% 12% 2 1	400
December	1st to 10th	Day	35% 22% 29% 12% 2 1	400
	11th to 20th	Day	39% 24% 26% 9% 2	400
	21st to end	Day	32% 25% 29% 11% 3 1	440
January	1st to 10th	Night	30% 24% 30% 14% 2	900
	11th to 20th	Night	30% 22% 29% 16% 3	862
	21st to end	Night	26% 24% 31% 14% 3	880
February	1st to 10th	Night	31% 23% 30% 14% 2	800
	11th to 20th	Night	32% 25% 28% 13% 2	783
	21st to end	Night	24% 22% 32% 18% 4	660
March	1st to 10th	Night	29% 20% 32% 17% 3	800
	11th to 20th	Night	24% 19% 31% 21% 5%	800
	21st to end	Night	29% 19% 31% 16% 6%	880
April	1st to 10th	Night	33% 19% 29% 16% 3	624
	11th to 20th	Night	28% 18% 33% 16% 5%	594
	21st to end	Night	29% 17% 30% 18% 6% 1	600
May	1st to 10th	Night	32% 13% 29% 21% 6%	600
	11th to 20th	Night	27% 11% 28% 26% 7%	592
	21st to end	Night	22% 10% 37% 26% 5%	649
June	1st to 10th	Night	28% 11% 29% 27% 6%	600
	11th to 20th	Night	22% 9% 28% 34% 7%	414
	21st to end	Night	24% 8% 27% 31% 9% 1	400
July	1st to 10th	Night	19% 6% 29% 37% 9%	390
	11th to 20th	Night	15% 6% 29% 36% 13%	544
	21st to end	Night	18% 5% 26% 40% 9%	656
August	1st to 10th	Night	16% 5% 26% 40% 12% 1	581
	11th to 20th	Night	17% 6% 27% 33% 15% 1	562
	21st to end	Night	17% 7% 24% 34% 18% 1	627
September	1st to 10th	Night	14% 9% 30% 34% 12% 1	570
	11th to 20th	Night	19% 10% 26% 32% 12% 1	662
	21st to end	Night	22% 11% 30% 25% 10% 2	760
October	1st to 10th	Night	23% 11% 31% 24% 10% 1	760
	11th to 20th	Night	23% 16% 33% 20% 8% 1	760
	21st to end	Night	32% 19% 25% 19% 5%	836
November	1st to 10th	Night	28% 20% 27% 19% 5%	863
	11th to 20th	Night	32% 21% 26% 17% 4	900
	21st to end	Night	35% 19% 27% 17% 2	900
December	1st to 10th	Night	33% 21% 28% 15% 3	900
	11th to 20th	Night	34% 25% 27% 11% 2	900
	21st to end	Night	32% 22% 27% 16% 3 1	990

Page generated at 2025-08-02 02:32:22. Version ac07

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