Charlottetown
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Charlottetown clear sky chart from 2005-11-06 to 2025-09-04.

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	16% 11% 4 9% 5% 5% 4 4 5% 7% 29%	127487
	Night	17% 12% 4 9% 5% 5% 5% 4 5% 6% 28%	121396
Transparency	Day	35% 38% 8% 13% 5%	131015
	Night	37% 38% 7% 12% 5%	125959
Seeing	Day	23% 14% 31% 22% 8% 1	18712
	Night	25% 13% 30% 24% 7% 1	25697

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	13% 21% 8% 19% 8% 6% 4 3 4 4 12%	3616
	11th to 20th	Day	12% 15% 9% 13% 6% 5% 4 3 5% 6% 21%	3591
	21st to end	Day	9% 9% 4 12% 5% 6% 5% 4 6% 8% 32%	4355
February	1st to 10th	Day	16% 14% 4 10% 6% 5% 5% 4 4 5% 28%	1800
	11th to 20th	Day	16% 14% 3 10% 6% 5% 5% 4 5% 4 26%	1753
	21st to end	Day	10% 13% 4 9% 6% 7% 5% 4 5% 8% 29%	1532
March	1st to 10th	Day	18% 14% 5% 11% 6% 5% 4 3 4 5% 25%	4768
	11th to 20th	Day	12% 14% 6% 12% 7% 5% 5% 4 6% 6% 23%	4980
	21st to end	Day	22% 17% 5% 13% 7% 5% 3 3 4 4 17%	5552
April	1st to 10th	Day	19% 12% 5% 9% 5% 4 4 3 5% 6% 29%	2400
	11th to 20th	Day	19% 12% 3 6% 4 4 4 3 5% 8% 32%	2427
	21st to end	Day	20% 13% 4 7% 4 4 4 4 5% 6% 30%	2600
May	1st to 10th	Day	24% 15% 4 6% 4 4 3 3 4 6% 27%	6250
	11th to 20th	Day	18% 11% 3 7% 5% 4 4 3 4 6% 33%	6318
	21st to end	Day	17% 11% 3 8% 5% 4 5% 4 5% 7% 32%	6948
June	1st to 10th	Day	23% 11% 3 8% 5% 4 5% 4 5% 7% 26%	2800
	11th to 20th	Day	19% 8% 3 6% 5% 5% 4 4 5% 6% 35%	2985
	21st to end	Day	23% 10% 3 7% 5% 4 4 3 5% 7% 30%	3000
July	1st to 10th	Day	16% 9% 3 8% 5% 5% 5% 5% 7% 8% 28%	6787
	11th to 20th	Day	14% 6% 3 7% 4 4 4 4 6% 7% 41%	6360
	21st to end	Day	11% 7% 3 7% 5% 4 5% 4 7% 9% 37%	6927
August	1st to 10th	Day	15% 10% 3 9% 5% 5% 5% 4 6% 8% 31%	4303
	11th to 20th	Day	13% 6% 3 6% 4 4 6% 4 7% 8% 38%	4175
	21st to end	Day	11% 6% 2 6% 4 5% 4 4 7% 9% 43%	4459
September	1st to 10th	Day	16% 7% 2 6% 4 4 4 4 6% 9% 39%	2316
	11th to 20th	Day	17% 9% 3 8% 3 4 5% 3 4 6% 38%	2266
	21st to end	Day	16% 9% 3 7% 5% 4 4 3 5% 7% 37%	1992
October	1st to 10th	Day	18% 8% 3 8% 5% 5% 5% 3 6% 7% 33%	1900
	11th to 20th	Day	19% 9% 4 9% 6% 5% 6% 4 6% 7% 25%	1900
	21st to end	Day	18% 13% 4 10% 5% 5% 5% 4 6% 7% 24%	2028
November	1st to 10th	Day	18% 16% 4 9% 5% 6% 4 4 5% 5% 24%	1611
	11th to 20th	Day	20% 18% 5% 8% 6% 5% 4 3 5% 7% 19%	1600
	21st to end	Day	18% 15% 6% 11% 7% 6% 5% 3 7% 6% 18%	1600
December	1st to 10th	Day	16% 14% 6% 14% 7% 6% 5% 3 5% 6% 18%	2610
	11th to 20th	Day	21% 15% 5% 12% 6% 5% 4 3 3 5% 22%	2996
	21st to end	Day	17% 13% 7% 17% 7% 5% 5% 4 4 4 16%	3982
January	1st to 10th	Night	13% 18% 6% 12% 6% 6% 6% 4 5% 6% 18%	6349
	11th to 20th	Night	14% 16% 8% 13% 6% 5% 4 4 4 5% 22%	6314
	21st to end	Night	10% 10% 5% 13% 6% 6% 6% 3 6% 6% 29%	6605
February	1st to 10th	Night	17% 15% 3 10% 6% 4 4 4 5% 5% 29%	2600
	11th to 20th	Night	16% 15% 4 11% 6% 5% 5% 4 5% 5% 24%	2533
	21st to end	Night	12% 14% 4 9% 6% 5% 5% 4 5% 6% 31%	2097
March	1st to 10th	Night	21% 14% 5% 10% 5% 4 4 3 4 5% 24%	5058
	11th to 20th	Night	16% 16% 7% 10% 6% 4 4 3 4 5% 24%	4979
	21st to end	Night	24% 15% 5% 9% 5% 5% 5% 4 4 4 21%	5379
April	1st to 10th	Night	21% 12% 4 9% 5% 5% 5% 3 5% 6% 26%	2000
	11th to 20th	Night	22% 12% 3 6% 5% 5% 4 2 5% 5% 32%	1920
	21st to end	Night	22% 13% 5% 7% 5% 4 2 2 5% 5% 29%	1800
May	1st to 10th	Night	26% 15% 4 8% 5% 4 4 3 4 5% 22%	3704
	11th to 20th	Night	17% 10% 3 7% 5% 5% 5% 4 5% 7% 33%	3596
	21st to end	Night	16% 11% 3 7% 5% 5% 5% 4 5% 8% 33%	3948
June	1st to 10th	Night	26% 10% 3 7% 5% 5% 4 3 5% 6% 28%	1600
	11th to 20th	Night	18% 8% 3 5% 4 5% 4 4 5% 7% 39%	1429
	21st to end	Night	22% 11% 3 8% 4 4 5% 4 6% 5% 27%	1400
July	1st to 10th	Night	13% 9% 4 8% 7% 6% 7% 5% 7% 8% 26%	3160
	11th to 20th	Night	10% 7% 3 7% 5% 5% 5% 4 7% 9% 38%	3590
	21st to end	Night	14% 8% 3 7% 4 4 5% 3 6% 8% 38%	3948
August	1st to 10th	Night	16% 9% 3 8% 5% 4 6% 4 6% 8% 30%	2845
	11th to 20th	Night	10% 7% 3 7% 5% 5% 5% 4 6% 8% 40%	2872
	21st to end	Night	12% 7% 2 5% 5% 4 4 4 5% 7% 44%	3438
September	1st to 10th	Night	13% 7% 3 7% 5% 4 4 3 4 7% 43%	1931
	11th to 20th	Night	17% 6% 2 6% 4 4 4 3 5% 6% 42%	1910
	21st to end	Night	16% 7% 2 7% 4 4 3 4 5% 7% 41%	2187
October	1st to 10th	Night	18% 8% 3 7% 5% 4 4 3 5% 7% 37%	2280
	11th to 20th	Night	18% 8% 4 8% 5% 5% 5% 3 6% 7% 33%	2280
	21st to end	Night	23% 11% 3 8% 5% 4 4 3 5% 6% 27%	2570
November	1st to 10th	Night	19% 14% 4 8% 6% 5% 5% 3 4 5% 27%	2685
	11th to 20th	Night	21% 14% 3 9% 5% 5% 4 4 5% 7% 22%	2800
	21st to end	Night	25% 15% 4 8% 5% 4 4 4 4 6% 19%	2800
December	1st to 10th	Night	15% 13% 4 11% 7% 5% 5% 4 5% 7% 24%	4580
	11th to 20th	Night	22% 14% 4 10% 6% 5% 4 3 4 5% 23%	5213
	21st to end	Night	22% 14% 5% 15% 5% 4 4 4 4 5% 18%	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	60% 27% 7% 3 2	3617
	11th to 20th	Day	47% 29% 10% 8% 5%	3620
	21st to end	Day	36% 30% 7% 16% 9% 2	4355
February	1st to 10th	Day	23% 62% 3 7% 5% 1	1800
	11th to 20th	Day	22% 62% 3 8% 4	1761
	21st to end	Day	19% 62% 4 8% 7% 1	1532
March	1st to 10th	Day	45% 29% 5% 13% 8% 1	4772
	11th to 20th	Day	45% 30% 12% 9% 3	4980
	21st to end	Day	54% 28% 5% 9% 3 1	5552
April	1st to 10th	Day	24% 62% 3 5% 5% 2	2400
	11th to 20th	Day	21% 63% 4 8% 4	2427
	21st to end	Day	22% 63% 5% 5% 5% 1	2600
May	1st to 10th	Day	44% 30% 9% 11% 5%	6262
	11th to 20th	Day	39% 30% 11% 17% 3	6322
	21st to end	Day	37% 31% 8% 18% 6%	6948
June	1st to 10th	Day	20% 63% 4 10% 3	2800
	11th to 20th	Day	18% 62% 6% 10% 3	2985
	21st to end	Day	21% 60% 4 8% 6%	3000
July	1st to 10th	Day	42% 25% 13% 13% 6%	6712
	11th to 20th	Day	32% 26% 12% 25% 5%	6284
	21st to end	Day	31% 26% 16% 22% 5%	6730
August	1st to 10th	Day	36% 37% 8% 15% 3	4289
	11th to 20th	Day	28% 37% 9% 18% 9% 1	4214
	21st to end	Day	25% 36% 8% 21% 10%	4459
September	1st to 10th	Day	15% 60% 7% 12% 5%	2316
	11th to 20th	Day	22% 60% 5% 9% 4	2266
	21st to end	Day	17% 60% 4 13% 6%	1992
October	1st to 10th	Day	35% 36% 6% 18% 4	3160
	11th to 20th	Day	32% 37% 5% 21% 5%	3140
	21st to end	Day	31% 37% 12% 14% 5%	3322
November	1st to 10th	Day	29% 57% 5% 7% 2	1611
	11th to 20th	Day	33% 58% 4 4 1	1600
	21st to end	Day	31% 58% 6% 3 2	1600
December	1st to 10th	Day	44% 36% 3 16% 1	2610
	11th to 20th	Day	46% 31% 7% 8% 7%	2995
	21st to end	Day	53% 27% 7% 10% 2	3982
January	1st to 10th	Night	51% 29% 9% 9% 2	6349
	11th to 20th	Night	49% 28% 8% 10% 4	6360
	21st to end	Night	42% 30% 5% 12% 11% 1	6605
February	1st to 10th	Night	24% 61% 3 5% 6% 1	2600
	11th to 20th	Night	24% 61% 3 7% 4	2536
	21st to end	Night	20% 61% 3 8% 6% 2	2097
March	1st to 10th	Night	47% 28% 4 10% 10% 2	5067
	11th to 20th	Night	47% 29% 9% 8% 6% 1	4980
	21st to end	Night	53% 28% 4 10% 6%	5379
April	1st to 10th	Night	23% 61% 4 6% 4 1	2000
	11th to 20th	Night	23% 63% 3 8% 3 1	1920
	21st to end	Night	24% 62% 3 6% 4 1	1800
May	1st to 10th	Night	50% 30% 5% 8% 7%	3709
	11th to 20th	Night	37% 32% 10% 16% 5%	3597
	21st to end	Night	36% 31% 14% 16% 3	3949
June	1st to 10th	Night	19% 62% 5% 10% 4	1600
	11th to 20th	Night	16% 62% 5% 11% 5%	1429
	21st to end	Night	22% 61% 4 8% 5% 1	1400
July	1st to 10th	Night	45% 26% 10% 13% 5% 1	3125
	11th to 20th	Night	32% 26% 14% 21% 6%	3543
	21st to end	Night	33% 26% 15% 20% 6%	3831
August	1st to 10th	Night	36% 38% 10% 13% 3	2834
	11th to 20th	Night	26% 39% 12% 15% 7% 1	2899
	21st to end	Night	25% 36% 11% 20% 8%	3437
September	1st to 10th	Night	15% 59% 5% 15% 5%	1931
	11th to 20th	Night	19% 61% 5% 12% 4	1910
	21st to end	Night	16% 61% 5% 14% 4	2187
October	1st to 10th	Night	34% 36% 9% 17% 4	3800
	11th to 20th	Night	25% 37% 6% 24% 8%	3779
	21st to end	Night	32% 36% 10% 15% 7%	4230
November	1st to 10th	Night	27% 57% 7% 6% 3	2685
	11th to 20th	Night	29% 58% 6% 5% 2	2800
	21st to end	Night	31% 58% 6% 4 2	2800
December	1st to 10th	Night	38% 36% 6% 18% 3	4580
	11th to 20th	Night	45% 31% 6% 13% 5% 1	5215
	21st to end	Night	51% 27% 9% 10% 3	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	27% 20% 37% 13% 3	400
	11th to 20th	Day	27% 20% 29% 17% 6% 1	400
	21st to end	Day	17% 15% 41% 23% 4	440
February	1st to 10th	Day	26% 22% 31% 16% 5% 1	400
	11th to 20th	Day	26% 22% 33% 15% 4	396
	21st to end	Day	20% 18% 31% 24% 6% 2	331
March	1st to 10th	Day	22% 19% 33% 22% 4	463
	11th to 20th	Day	17% 21% 32% 22% 5% 1	500
	21st to end	Day	28% 18% 32% 15% 7% 1	550
April	1st to 10th	Day	28% 21% 36% 11% 4	500
	11th to 20th	Day	25% 20% 33% 14% 7% 1	492
	21st to end	Day	25% 16% 28% 21% 8% 1	500
May	1st to 10th	Day	32% 16% 27% 17% 6% 2	660
	11th to 20th	Day	23% 13% 29% 23% 11% 2	724
	21st to end	Day	23% 13% 36% 21% 7% 1	790
June	1st to 10th	Day	30% 10% 29% 22% 9% 1	730
	11th to 20th	Day	21% 10% 34% 25% 9% 1	730
	21st to end	Day	28% 7% 30% 25% 9% 2	730
July	1st to 10th	Day	20% 4 33% 30% 11% 2	720
	11th to 20th	Day	17% 4 33% 29% 15% 1	718
	21st to end	Day	20% 4 31% 31% 12% 2	795
August	1st to 10th	Day	14% 3 29% 35% 15% 4	568
	11th to 20th	Day	18% 6% 27% 28% 17% 5%	519
	21st to end	Day	16% 8% 28% 30% 14% 4	583
September	1st to 10th	Day	16% 7% 35% 27% 12% 2	502
	11th to 20th	Day	22% 12% 29% 22% 12% 2	490
	21st to end	Day	19% 14% 29% 22% 13% 3	437
October	1st to 10th	Day	20% 14% 27% 21% 14% 4	390
	11th to 20th	Day	21% 19% 30% 19% 9% 3	390
	21st to end	Day	24% 22% 31% 17% 6% 1	429
November	1st to 10th	Day	25% 23% 30% 16% 5% 2	395
	11th to 20th	Day	30% 25% 26% 14% 4 1	400
	21st to end	Day	31% 23% 28% 16% 2 1	400
December	1st to 10th	Day	30% 18% 31% 17% 3 1	400
	11th to 20th	Day	31% 25% 31% 12% 2	400
	21st to end	Day	24% 22% 34% 17% 2 1	440
January	1st to 10th	Night	26% 20% 32% 18% 4	900
	11th to 20th	Night	26% 17% 31% 20% 6%	900
	21st to end	Night	21% 18% 34% 21% 5% 1	905
February	1st to 10th	Night	27% 17% 31% 21% 4	800
	11th to 20th	Night	26% 18% 34% 18% 4	783
	21st to end	Night	20% 15% 31% 25% 8% 1	660
March	1st to 10th	Night	24% 15% 37% 21% 3	800
	11th to 20th	Night	22% 15% 29% 26% 7%	800
	21st to end	Night	28% 14% 28% 20% 8% 1	844
April	1st to 10th	Night	28% 16% 29% 22% 5%	600
	11th to 20th	Night	28% 11% 33% 19% 8%	594
	21st to end	Night	29% 11% 31% 22% 6% 1	600
May	1st to 10th	Night	32% 9% 28% 22% 8% 1	600
	11th to 20th	Night	23% 8% 29% 30% 8% 1	592
	21st to end	Night	22% 12% 34% 28% 5%	649
June	1st to 10th	Night	29% 10% 27% 28% 6% 1	600
	11th to 20th	Night	20% 7% 33% 33% 7% 1	429
	21st to end	Night	27% 5% 30% 31% 6% 1	400
July	1st to 10th	Night	18% 5% 30% 33% 13% 1	390
	11th to 20th	Night	16% 5% 31% 38% 9%	566
	21st to end	Night	19% 5% 29% 35% 12%	656
August	1st to 10th	Night	17% 4 25% 41% 12% 2	598
	11th to 20th	Night	17% 4 25% 36% 17% 1	592
	21st to end	Night	14% 7% 25% 37% 16% 1	660
September	1st to 10th	Night	16% 7% 32% 34% 11% 1	580
	11th to 20th	Night	20% 8% 22% 37% 11% 1	580
	21st to end	Night	21% 9% 33% 27% 9% 1	760
October	1st to 10th	Night	24% 9% 26% 29% 12% 1	760
	11th to 20th	Night	23% 13% 31% 24% 9% 1	760
	21st to end	Night	30% 18% 29% 20% 3	869
November	1st to 10th	Night	28% 17% 32% 19% 4 1	880
	11th to 20th	Night	29% 20% 28% 18% 4 1	900
	21st to end	Night	35% 18% 27% 17% 3	900
December	1st to 10th	Night	30% 18% 31% 15% 6%	900
	11th to 20th	Night	28% 24% 31% 14% 3	900
	21st to end	Night	30% 18% 29% 17% 4 1	990

Page generated at 2025-09-01 02:51:01. Version ac07

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