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 2024-11-04.

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	17% 11% 4 9% 5% 5% 4 4 5% 7% 29%	102299
	Night	18% 12% 4 9% 5% 5% 5% 4 5% 6% 28%	96817
Transparency	Day	30% 47% 7% 11% 5%	105845
	Night	31% 47% 7% 10% 4	101364
Seeing	Day	23% 14% 31% 22% 8% 2	17525
	Night	25% 13% 30% 24% 7% 1	24591

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% 14% 6% 21% 9% 6% 4 3 4 4 15%	2526
	11th to 20th	Day	12% 12% 5% 11% 7% 6% 5% 4 5% 6% 27%	2530
	21st to end	Day	12% 9% 5% 14% 6% 5% 4 4 6% 7% 28%	3039
February	1st to 10th	Day	17% 14% 4 10% 6% 5% 4 4 4 5% 27%	1710
	11th to 20th	Day	17% 14% 3 10% 6% 5% 5% 4 5% 5% 26%	1663
	21st to end	Day	10% 13% 4 9% 6% 7% 5% 4 5% 8% 29%	1457
March	1st to 10th	Day	20% 14% 4 8% 4 5% 3 3 4 6% 29%	3324
	11th to 20th	Day	10% 18% 7% 13% 8% 5% 4 4 4 5% 21%	3480
	21st to end	Day	22% 18% 5% 11% 6% 4 3 3 4 4 20%	3874
April	1st to 10th	Day	18% 13% 5% 9% 5% 4 4 3 5% 6% 29%	2280
	11th to 20th	Day	19% 12% 3 6% 4 4 4 3 5% 8% 33%	2304
	21st to end	Day	20% 13% 3 7% 4 4 4 4 5% 6% 30%	2470
May	1st to 10th	Day	23% 17% 3 6% 4 4 3 3 4 6% 27%	4358
	11th to 20th	Day	15% 9% 3 7% 5% 5% 5% 4 5% 6% 36%	4398
	21st to end	Day	16% 10% 3 8% 5% 5% 5% 4 6% 7% 30%	4836
June	1st to 10th	Day	24% 11% 3 8% 5% 4 5% 3 5% 7% 25%	2660
	11th to 20th	Day	20% 8% 3 6% 5% 5% 4 3 5% 6% 35%	2836
	21st to end	Day	23% 10% 3 7% 5% 4 4 3 5% 7% 29%	2850
July	1st to 10th	Day	17% 8% 3 7% 5% 5% 4 5% 7% 7% 32%	4741
	11th to 20th	Day	15% 7% 3 7% 5% 5% 5% 4 7% 8% 35%	4440
	21st to end	Day	11% 8% 3 7% 5% 4 5% 4 7% 10% 35%	4815
August	1st to 10th	Day	16% 10% 3 9% 5% 5% 5% 4 6% 8% 29%	4171
	11th to 20th	Day	14% 6% 3 7% 5% 4 6% 4 7% 8% 37%	4045
	21st to end	Day	11% 6% 2 6% 4 5% 4 4 6% 9% 43%	4322
September	1st to 10th	Day	16% 7% 2 6% 4 4 4 4 5% 9% 40%	2280
	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%	1555
	11th to 20th	Day	19% 18% 5% 8% 6% 5% 4 3 5% 8% 20%	1520
	21st to end	Day	17% 13% 6% 11% 7% 6% 5% 3 7% 7% 18%	1520
December	1st to 10th	Day	21% 18% 6% 9% 6% 5% 4 3 6% 7% 14%	1520
	11th to 20th	Day	21% 18% 6% 12% 7% 6% 5% 3 4 5% 13%	1906
	21st to end	Day	20% 14% 6% 14% 7% 5% 4 3 4 5% 18%	2783
January	1st to 10th	Night	12% 13% 5% 12% 7% 7% 6% 4 6% 7% 21%	4429
	11th to 20th	Night	16% 13% 5% 10% 5% 5% 4 4 5% 6% 27%	4440
	21st to end	Night	13% 12% 5% 14% 6% 6% 7% 3 5% 6% 23%	4619
February	1st to 10th	Night	17% 15% 3 9% 5% 4 4 4 5% 5% 29%	2470
	11th to 20th	Night	16% 15% 4 11% 6% 5% 5% 4 5% 5% 23%	2403
	21st to end	Night	12% 14% 4 9% 6% 5% 5% 4 5% 6% 31%	1996
March	1st to 10th	Night	20% 12% 4 10% 5% 5% 3 3 5% 5% 26%	3516
	11th to 20th	Night	18% 20% 7% 11% 7% 5% 3 3 3 5% 19%	3479
	21st to end	Night	24% 15% 5% 9% 5% 5% 5% 4 4 3 22%	3757
April	1st to 10th	Night	21% 12% 4 9% 5% 5% 5% 3 5% 6% 26%	1900
	11th to 20th	Night	21% 12% 3 6% 5% 5% 4 2 4 5% 33%	1823
	21st to end	Night	22% 13% 5% 7% 5% 4 2 2 5% 5% 30%	1710
May	1st to 10th	Night	25% 15% 4 8% 4 4 5% 4 5% 5% 22%	2588
	11th to 20th	Night	15% 9% 3 6% 5% 5% 4 3 6% 8% 38%	2506
	21st to end	Night	16% 9% 3 8% 6% 5% 6% 4 6% 8% 28%	2749
June	1st to 10th	Night	26% 10% 3 7% 5% 5% 4 3 5% 6% 26%	1520
	11th to 20th	Night	18% 8% 3 5% 4 4 4 3 5% 7% 39%	1358
	21st to end	Night	22% 11% 3 8% 4 4 5% 4 6% 5% 27%	1330
July	1st to 10th	Night	13% 10% 4 8% 7% 5% 7% 4 7% 8% 28%	2210
	11th to 20th	Night	13% 7% 3 7% 5% 5% 5% 5% 8% 8% 33%	2514
	21st to end	Night	12% 7% 3 6% 4 4 4 4 6% 8% 43%	2750
August	1st to 10th	Night	17% 9% 3 8% 6% 5% 6% 4 6% 8% 28%	2757
	11th to 20th	Night	10% 7% 3 7% 5% 5% 5% 4 6% 8% 39%	2782
	21st to end	Night	12% 7% 2 5% 5% 4 4 4 5% 7% 44%	3333
September	1st to 10th	Night	13% 7% 3 7% 5% 4 4 3 4 7% 43%	1900
	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% 13% 4 8% 5% 5% 5% 3 4 5% 28%	2594
	11th to 20th	Night	20% 13% 3 9% 5% 5% 4 4 5% 7% 23%	2660
	21st to end	Night	24% 14% 4 9% 5% 5% 5% 4 4 6% 20%	2660
December	1st to 10th	Night	23% 17% 5% 10% 6% 4 5% 4 5% 7% 16%	2660
	11th to 20th	Night	25% 17% 6% 10% 6% 4 3 2 3 5% 18%	3293
	21st to end	Night	25% 15% 5% 13% 5% 4 3 3 4 5% 19%	4884

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	48% 39% 8% 2 3	2527
	11th to 20th	Day	33% 40% 9% 10% 8%	2530
	21st to end	Day	34% 43% 8% 8% 6% 1	3039
February	1st to 10th	Day	21% 65% 3 7% 3 1	1710
	11th to 20th	Day	21% 65% 3 7% 4	1671
	21st to end	Day	17% 65% 4 7% 7% 1	1457
March	1st to 10th	Day	34% 40% 6% 15% 4	3328
	11th to 20th	Day	43% 42% 6% 6% 3	3480
	21st to end	Day	45% 40% 6% 6% 2 1	3874
April	1st to 10th	Day	22% 65% 4 5% 4 2	2280
	11th to 20th	Day	19% 66% 4 8% 4	2304
	21st to end	Day	20% 66% 4 4 5% 1	2470
May	1st to 10th	Day	35% 43% 10% 9% 3	4373
	11th to 20th	Day	28% 43% 9% 16% 4	4402
	21st to end	Day	32% 44% 8% 11% 5%	4836
June	1st to 10th	Day	20% 66% 3 8% 3	2660
	11th to 20th	Day	17% 65% 5% 9% 3	2836
	21st to end	Day	19% 64% 4 7% 6%	2850
July	1st to 10th	Day	34% 36% 11% 10% 8%	4666
	11th to 20th	Day	32% 37% 10% 18% 4	4364
	21st to end	Day	27% 37% 14% 18% 5%	4662
August	1st to 10th	Day	37% 38% 8% 15% 2	4157
	11th to 20th	Day	28% 38% 8% 17% 8% 1	4084
	21st to end	Day	25% 37% 8% 20% 10%	4322
September	1st to 10th	Day	15% 61% 7% 12% 5%	2280
	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	28% 59% 4 7% 2	1555
	11th to 20th	Day	30% 61% 4 4 1	1520
	21st to end	Day	28% 61% 7% 3 2	1520
December	1st to 10th	Day	29% 61% 3 5% 1	1520
	11th to 20th	Day	41% 48% 4 5% 2	1905
	21st to end	Day	45% 39% 9% 4 3	2783
January	1st to 10th	Night	37% 42% 11% 8% 2	4429
	11th to 20th	Night	35% 40% 8% 11% 6%	4440
	21st to end	Night	41% 43% 6% 7% 3	4619
February	1st to 10th	Night	22% 64% 3 4 5% 1	2470
	11th to 20th	Night	22% 64% 3 7% 4	2406
	21st to end	Night	18% 64% 3 7% 6% 2	1996
March	1st to 10th	Night	35% 40% 5% 12% 6% 2	3525
	11th to 20th	Night	47% 41% 4 4 3	3480
	21st to end	Night	45% 40% 4 7% 3	3757
April	1st to 10th	Night	21% 64% 4 6% 4 1	1900
	11th to 20th	Night	20% 66% 3 7% 3 1	1823
	21st to end	Night	22% 65% 3 5% 5% 1	1710
May	1st to 10th	Night	42% 42% 6% 7% 3	2593
	11th to 20th	Night	24% 44% 12% 15% 5%	2507
	21st to end	Night	33% 44% 13% 7% 3	2750
June	1st to 10th	Night	19% 66% 5% 8% 3	1520
	11th to 20th	Night	15% 65% 5% 11% 4	1358
	21st to end	Night	20% 64% 4 8% 4	1330
July	1st to 10th	Night	38% 36% 9% 11% 4 2	2175
	11th to 20th	Night	31% 37% 14% 14% 3	2467
	21st to end	Night	23% 37% 15% 16% 8%	2663
August	1st to 10th	Night	37% 39% 10% 12% 2	2746
	11th to 20th	Night	25% 40% 12% 15% 7% 1	2809
	21st to end	Night	25% 37% 11% 20% 8%	3332
September	1st to 10th	Night	15% 60% 5% 14% 5%	1900
	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	25% 59% 7% 6% 3	2594
	11th to 20th	Night	26% 61% 6% 5% 2	2660
	21st to end	Night	28% 61% 6% 3 2	2660
December	1st to 10th	Night	29% 61% 3 5% 1	2660
	11th to 20th	Night	36% 48% 5% 7% 3	3295
	21st to end	Night	44% 38% 8% 7% 2 1	4884

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	25% 21% 37% 14% 3	370
	11th to 20th	Day	27% 21% 30% 15% 6% 1	370
	21st to end	Day	18% 16% 38% 24% 4	407
February	1st to 10th	Day	27% 21% 29% 16% 5% 1	370
	11th to 20th	Day	25% 23% 33% 16% 4	366
	21st to end	Day	20% 19% 31% 24% 5% 2	307
March	1st to 10th	Day	22% 18% 32% 22% 4	427
	11th to 20th	Day	18% 22% 31% 22% 6% 2	460
	21st to end	Day	28% 19% 31% 14% 7% 1	506
April	1st to 10th	Day	27% 20% 36% 12% 4	460
	11th to 20th	Day	24% 21% 33% 14% 7% 1	452
	21st to end	Day	24% 17% 28% 22% 9% 1	460
May	1st to 10th	Day	32% 16% 28% 17% 6% 2	612
	11th to 20th	Day	21% 13% 29% 24% 12% 2	674
	21st to end	Day	23% 13% 36% 21% 7% 1	735
June	1st to 10th	Day	31% 10% 30% 20% 9% 1	680
	11th to 20th	Day	22% 10% 33% 25% 9% 1	680
	21st to end	Day	28% 6% 30% 25% 9% 2	680
July	1st to 10th	Day	19% 4 34% 29% 11% 2	670
	11th to 20th	Day	18% 4 33% 28% 15% 1	668
	21st to end	Day	21% 4 30% 32% 11% 2	740
August	1st to 10th	Day	15% 3 29% 35% 14% 3	526
	11th to 20th	Day	19% 6% 27% 27% 16% 4	479
	21st to end	Day	16% 9% 27% 31% 14% 4	539
September	1st to 10th	Day	17% 7% 36% 27% 11% 2	490
	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% 29% 16% 5% 2	374
	11th to 20th	Day	26% 26% 28% 15% 5% 1	370
	21st to end	Day	28% 24% 28% 16% 2 1	370
December	1st to 10th	Day	32% 18% 31% 16% 3 1	370
	11th to 20th	Day	31% 26% 31% 12% 1	370
	21st to end	Day	25% 23% 34% 15% 1 1	407
January	1st to 10th	Night	26% 19% 32% 19% 3	850
	11th to 20th	Night	26% 18% 32% 20% 4	850
	21st to end	Night	22% 17% 33% 22% 6% 1	859
February	1st to 10th	Night	27% 17% 30% 21% 4	760
	11th to 20th	Night	26% 18% 35% 18% 4	743
	21st to end	Night	20% 16% 31% 25% 8% 1	628
March	1st to 10th	Night	23% 15% 37% 21% 3	760
	11th to 20th	Night	22% 15% 29% 26% 8%	760
	21st to end	Night	28% 15% 28% 21% 8% 1	802
April	1st to 10th	Night	28% 15% 30% 23% 5%	570
	11th to 20th	Night	27% 11% 33% 20% 8%	564
	21st to end	Night	28% 11% 32% 21% 6% 1	570
May	1st to 10th	Night	31% 9% 28% 22% 9% 1	570
	11th to 20th	Night	23% 8% 28% 31% 9% 1	562
	21st to end	Night	21% 12% 35% 27% 4	616
June	1st to 10th	Night	30% 10% 27% 27% 6% 1	570
	11th to 20th	Night	20% 6% 33% 33% 8% 1	408
	21st to end	Night	26% 5% 30% 32% 6% 1	380
July	1st to 10th	Night	18% 5% 31% 34% 12% 1	370
	11th to 20th	Night	17% 5% 31% 37% 10%	537
	21st to end	Night	19% 5% 28% 36% 11%	623
August	1st to 10th	Night	17% 4 26% 41% 12% 1	568
	11th to 20th	Night	17% 4 26% 36% 16% 1	562
	21st to end	Night	14% 7% 24% 37% 17% 1	627
September	1st to 10th	Night	16% 7% 32% 34% 10% 1	570
	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	27% 16% 32% 20% 4 1	848
	11th to 20th	Night	27% 20% 29% 19% 4 2	850
	21st to end	Night	33% 19% 27% 18% 3	850
December	1st to 10th	Night	31% 19% 30% 15% 5%	850
	11th to 20th	Night	28% 24% 31% 14% 3	850
	21st to end	Night	31% 19% 29% 16% 4 1	935

Page generated at 2024-11-01 23:47:40. Version ac07

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