Port Perry
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Port Perry clear sky chart from 2005-11-06 to 2024-11-25.

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	15% 10% 3 8% 5% 5% 5% 4 5% 7% 33%	101664
	Night	15% 10% 4 8% 5% 5% 4 4 5% 6% 34%	97819
Transparency	Day	47% 8% 14% 20% 10% 1	105265
	Night	47% 8% 13% 20% 11% 1	102306
Seeing	Day	20% 15% 30% 21% 10% 4	14478
	Night	19% 12% 31% 27% 10% 1	23839

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	16% 16% 5% 8% 5% 5% 4 3 4 6% 28%	2517
	11th to 20th	Day	10% 18% 8% 15% 8% 6% 5% 3 4 4 18%	2677
	21st to end	Day	20% 20% 6% 12% 6% 4 4 3 4 4 17%	3124
February	1st to 10th	Day	14% 17% 5% 12% 8% 6% 5% 4 4 4 21%	1710
	11th to 20th	Day	12% 15% 7% 14% 7% 4 4 3 5% 5% 25%	1663
	21st to end	Day	16% 15% 5% 11% 6% 6% 5% 3 3 4 26%	1452
March	1st to 10th	Day	17% 13% 5% 9% 5% 4 4 3 4 5% 31%	3432
	11th to 20th	Day	11% 16% 5% 10% 5% 5% 6% 4 5% 5% 29%	3480
	21st to end	Day	16% 9% 3 8% 5% 5% 4 4 4 5% 37%	3815
April	1st to 10th	Day	19% 13% 3 8% 5% 4 4 4 5% 6% 29%	2268
	11th to 20th	Day	20% 11% 3 7% 4 3 4 4 4 6% 35%	2301
	21st to end	Day	21% 9% 3 8% 5% 3 4 3 4 6% 34%	2470
May	1st to 10th	Day	18% 9% 2 8% 4 5% 5% 4 6% 7% 33%	4163
	11th to 20th	Day	16% 9% 3 8% 5% 5% 4 4 6% 8% 32%	4398
	21st to end	Day	13% 6% 2 6% 4 4 4 4 5% 7% 45%	4837
June	1st to 10th	Day	15% 8% 3 7% 4 5% 5% 5% 6% 7% 35%	2660
	11th to 20th	Day	13% 6% 3 6% 5% 5% 5% 4 7% 8% 39%	2660
	21st to end	Day	15% 6% 2 6% 5% 5% 5% 4 7% 9% 36%	2660
July	1st to 10th	Day	11% 5% 2 6% 5% 5% 5% 5% 7% 11% 38%	4440
	11th to 20th	Day	11% 5% 2 6% 5% 5% 5% 4 7% 10% 41%	4440
	21st to end	Day	7% 5% 2 6% 6% 5% 6% 6% 7% 8% 42%	4603
August	1st to 10th	Day	15% 8% 3 7% 4 4 5% 4 6% 7% 37%	4104
	11th to 20th	Day	12% 7% 3 7% 5% 4 5% 4 7% 10% 36%	4044
	21st to end	Day	9% 6% 2 6% 5% 4 5% 4 6% 9% 43%	4322
September	1st to 10th	Day	13% 6% 2 7% 5% 4 5% 3 6% 8% 41%	2280
	11th to 20th	Day	11% 6% 2 5% 4 4 5% 4 5% 7% 45%	2205
	21st to end	Day	14% 7% 2 8% 4 4 6% 4 5% 6% 39%	2028
October	1st to 10th	Day	19% 8% 3 7% 5% 4 4 4 5% 6% 35%	1900
	11th to 20th	Day	20% 10% 3 9% 6% 4 5% 3 5% 6% 30%	1900
	21st to end	Day	23% 13% 4 8% 5% 3 5% 3 5% 6% 23%	2090
November	1st to 10th	Day	15% 11% 3 8% 6% 4 5% 4 5% 6% 32%	1671
	11th to 20th	Day	14% 15% 4 10% 5% 5% 5% 5% 6% 7% 25%	1600
	21st to end	Day	17% 17% 5% 10% 7% 4 4 4 4 6% 22%	1552
December	1st to 10th	Day	16% 16% 6% 12% 6% 6% 6% 5% 5% 6% 15%	1520
	11th to 20th	Day	17% 15% 5% 9% 5% 4 5% 3 6% 7% 23%	1906
	21st to end	Day	25% 18% 5% 11% 6% 4 5% 3 4 4 14%	2772
January	1st to 10th	Night	16% 15% 5% 11% 7% 6% 4 3 4 6% 22%	4429
	11th to 20th	Night	13% 14% 6% 14% 9% 6% 5% 4 5% 5% 19%	4280
	21st to end	Night	19% 13% 5% 10% 6% 5% 5% 4 5% 5% 22%	4532
February	1st to 10th	Night	12% 16% 5% 10% 7% 7% 5% 4 5% 5% 23%	2470
	11th to 20th	Night	14% 13% 6% 11% 7% 4 4 3 5% 5% 28%	2403
	21st to end	Night	12% 13% 4 11% 6% 5% 5% 4 6% 6% 28%	1998
March	1st to 10th	Night	16% 11% 4 8% 6% 5% 4 4 4 5% 33%	3408
	11th to 20th	Night	13% 11% 4 9% 6% 5% 5% 4 5% 6% 33%	3479
	21st to end	Night	15% 8% 3 6% 4 4 5% 4 5% 7% 39%	3817
April	1st to 10th	Night	18% 12% 3 7% 5% 4 4 4 5% 7% 31%	1910
	11th to 20th	Night	16% 8% 3 7% 5% 4 4 4 5% 6% 37%	1844
	21st to end	Night	16% 11% 3 7% 4 5% 4 4 5% 7% 34%	1710
May	1st to 10th	Night	17% 8% 3 6% 4 4 5% 3 5% 6% 38%	2776
	11th to 20th	Night	14% 9% 3 6% 5% 4 4 5% 5% 8% 37%	2495
	21st to end	Night	10% 5% 2 5% 4 3 4 3 6% 8% 49%	2738
June	1st to 10th	Night	12% 7% 2 6% 5% 5% 5% 4 6% 8% 39%	1520
	11th to 20th	Night	9% 6% 2 7% 5% 5% 4 5% 7% 8% 43%	1520
	21st to end	Night	11% 7% 3 6% 4 5% 4 4 5% 8% 42%	1520
July	1st to 10th	Night	6% 5% 3 5% 5% 4 5% 4 7% 8% 49%	2520
	11th to 20th	Night	11% 5% 2 5% 4 3 3 4 6% 8% 49%	2520
	21st to end	Night	8% 5% 2 5% 3 4 4 4 6% 8% 52%	2946
August	1st to 10th	Night	9% 5% 2 6% 4 4 4 4 6% 7% 48%	2825
	11th to 20th	Night	11% 5% 2 6% 3 3 3 3 5% 7% 49%	2785
	21st to end	Night	9% 6% 2 7% 4 4 4 3 5% 7% 48%	3302
September	1st to 10th	Night	9% 6% 2 7% 4 4 4 4 6% 7% 47%	1900
	11th to 20th	Night	11% 4 2 5% 4 4 3 3 4 8% 53%	1971
	21st to end	Night	16% 7% 3 7% 4 4 3 3 5% 6% 42%	2152
October	1st to 10th	Night	15% 7% 2 7% 5% 4 4 3 5% 7% 40%	2280
	11th to 20th	Night	19% 9% 3 7% 6% 5% 5% 3 6% 6% 32%	2280
	21st to end	Night	20% 10% 4 8% 5% 4 5% 3 5% 7% 29%	2508
November	1st to 10th	Night	18% 8% 2 8% 5% 4 4 4 6% 6% 34%	2626
	11th to 20th	Night	17% 11% 4 9% 6% 6% 5% 4 6% 8% 27%	2800
	21st to end	Night	19% 13% 3 9% 5% 6% 5% 5% 5% 6% 23%	2723
December	1st to 10th	Night	17% 16% 5% 10% 6% 5% 4 4 6% 6% 20%	2660
	11th to 20th	Night	15% 18% 5% 11% 6% 6% 5% 4 6% 5% 20%	3288
	21st to end	Night	26% 17% 5% 12% 5% 5% 5% 3 4 4 14%	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	55% 11% 15% 12% 7% 1	2518
	11th to 20th	Day	67% 8% 10% 9% 5%	2677
	21st to end	Day	69% 8% 10% 9% 4 1	3124
February	1st to 10th	Day	64% 7% 9% 14% 5% 1	1710
	11th to 20th	Day	60% 6% 10% 15% 7% 1	1672
	21st to end	Day	60% 6% 10% 16% 7% 1	1452
March	1st to 10th	Day	52% 8% 14% 16% 10%	3435
	11th to 20th	Day	51% 9% 14% 16% 8% 1	3480
	21st to end	Day	43% 9% 11% 20% 15% 2	3815
April	1st to 10th	Day	54% 6% 11% 17% 10% 1	2268
	11th to 20th	Day	49% 6% 10% 20% 14% 1	2301
	21st to end	Day	50% 7% 10% 17% 13% 2	2470
May	1st to 10th	Day	47% 10% 12% 18% 12% 2	4175
	11th to 20th	Day	46% 10% 15% 19% 10% 1	4402
	21st to end	Day	35% 9% 15% 23% 15% 3	4837
June	1st to 10th	Day	45% 8% 14% 20% 13% 1	2660
	11th to 20th	Day	40% 8% 14% 23% 15% 1	2660
	21st to end	Day	42% 9% 15% 22% 12% 1	2660
July	1st to 10th	Day	38% 7% 16% 23% 14% 1	4370
	11th to 20th	Day	36% 7% 16% 32% 9% 1	4365
	21st to end	Day	36% 10% 14% 25% 15%	4456
August	1st to 10th	Day	44% 7% 15% 20% 12% 1	4091
	11th to 20th	Day	41% 7% 17% 26% 9%	4083
	21st to end	Day	36% 7% 14% 32% 10% 1	4322
September	1st to 10th	Day	41% 7% 14% 27% 10% 1	2280
	11th to 20th	Day	35% 8% 15% 28% 14%	2205
	21st to end	Day	43% 10% 13% 24% 9%	2028
October	1st to 10th	Day	40% 7% 15% 26% 12% 1	3160
	11th to 20th	Day	43% 6% 16% 21% 13%	3140
	21st to end	Day	53% 7% 15% 19% 6%	3428
November	1st to 10th	Day	50% 8% 15% 18% 8% 1	1671
	11th to 20th	Day	55% 10% 12% 14% 8% 1	1600
	21st to end	Day	62% 8% 13% 14% 3	1552
December	1st to 10th	Day	64% 11% 14% 9% 2	1520
	11th to 20th	Day	59% 10% 13% 12% 6%	1906
	21st to end	Day	71% 10% 8% 9% 2	2772
January	1st to 10th	Night	60% 10% 15% 11% 4	4429
	11th to 20th	Night	63% 10% 13% 11% 3 1	4280
	21st to end	Night	61% 9% 13% 11% 5% 1	4532
February	1st to 10th	Night	61% 8% 10% 15% 5% 1	2470
	11th to 20th	Night	56% 7% 12% 17% 8%	2405
	21st to end	Night	54% 6% 13% 18% 7% 1	1998
March	1st to 10th	Night	51% 7% 12% 21% 8% 1	3418
	11th to 20th	Night	46% 9% 16% 19% 8% 2	3480
	21st to end	Night	38% 9% 12% 24% 15% 2	3817
April	1st to 10th	Night	51% 6% 11% 18% 13% 1	1910
	11th to 20th	Night	46% 8% 10% 19% 16% 2	1844
	21st to end	Night	47% 7% 13% 15% 16% 2	1710
May	1st to 10th	Night	43% 9% 13% 17% 16% 3	2783
	11th to 20th	Night	41% 10% 15% 21% 10% 2	2496
	21st to end	Night	29% 10% 14% 24% 20% 2	2739
June	1st to 10th	Night	40% 8% 13% 22% 15% 2	1520
	11th to 20th	Night	36% 7% 13% 22% 20% 2	1520
	21st to end	Night	39% 8% 14% 23% 15% 1	1520
July	1st to 10th	Night	31% 6% 16% 25% 20% 2	2480
	11th to 20th	Night	32% 6% 14% 32% 15% 1	2472
	21st to end	Night	29% 7% 15% 31% 16% 1	2852
August	1st to 10th	Night	34% 5% 15% 28% 16% 2	2814
	11th to 20th	Night	34% 5% 19% 29% 12% 1	2812
	21st to end	Night	33% 7% 13% 32% 13% 1	3302
September	1st to 10th	Night	35% 7% 16% 27% 14% 1	1900
	11th to 20th	Night	31% 6% 13% 31% 18% 1	1971
	21st to end	Night	41% 7% 13% 27% 11%	2152
October	1st to 10th	Night	33% 6% 11% 27% 22% 1	3800
	11th to 20th	Night	42% 7% 16% 25% 10%	3779
	21st to end	Night	43% 7% 16% 26% 8%	4120
November	1st to 10th	Night	47% 8% 13% 21% 11% 1	2626
	11th to 20th	Night	54% 8% 14% 15% 8% 2	2800
	21st to end	Night	58% 11% 15% 11% 4	2723
December	1st to 10th	Night	62% 9% 14% 12% 3	2660
	11th to 20th	Night	62% 9% 12% 13% 4	3288
	21st to end	Night	70% 10% 10% 8% 3	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	22% 24% 30% 18% 5% 1	180
	11th to 20th	Day	21% 29% 32% 13% 4 1	224
	21st to end	Day	25% 23% 35% 14% 2	297
February	1st to 10th	Day	26% 29% 29% 13% 3	270
	11th to 20th	Day	24% 29% 38% 8% 1	270
	21st to end	Day	33% 26% 32% 8%	263
March	1st to 10th	Day	21% 22% 38% 16% 3	460
	11th to 20th	Day	24% 24% 32% 17% 2 1	460
	21st to end	Day	30% 18% 31% 15% 5% 1	506
April	1st to 10th	Day	25% 19% 36% 14% 5% 1	460
	11th to 20th	Day	28% 21% 26% 15% 8% 3	452
	21st to end	Day	24% 18% 34% 15% 7% 1	460
May	1st to 10th	Day	22% 14% 30% 23% 8% 4	463
	11th to 20th	Day	19% 13% 30% 25% 10% 3	487
	21st to end	Day	15% 11% 28% 28% 13% 5%	529
June	1st to 10th	Day	18% 12% 33% 26% 9% 2	490
	11th to 20th	Day	15% 11% 28% 29% 13% 3	490
	21st to end	Day	19% 10% 31% 27% 10% 3	490
July	1st to 10th	Day	10% 7% 29% 32% 18% 5%	485
	11th to 20th	Day	14% 8% 26% 27% 18% 7%	484
	21st to end	Day	9% 5% 33% 33% 13% 6%	532
August	1st to 10th	Day	14% 6% 27% 30% 15% 8%	486
	11th to 20th	Day	11% 7% 24% 28% 22% 8%	479
	21st to end	Day	14% 9% 25% 27% 17% 8%	539
September	1st to 10th	Day	14% 8% 28% 25% 16% 8%	490
	11th to 20th	Day	10% 6% 27% 23% 19% 15%	490
	21st to end	Day	15% 13% 28% 25% 13% 6%	490
October	1st to 10th	Day	21% 11% 31% 18% 15% 3	490
	11th to 20th	Day	20% 20% 34% 18% 6% 2	490
	21st to end	Day	28% 20% 28% 20% 4	539
November	1st to 10th	Day	23% 21% 30% 19% 7%	287
	11th to 20th	Day	24% 19% 41% 12% 4 1	200
	21st to end	Day	26% 26% 36% 10% 3	188
December	1st to 10th	Day	25% 22% 32% 17% 4 1	180
	11th to 20th	Day	26% 27% 29% 15% 2 1	180
	21st to end	Day	30% 24% 32% 13% 1	198
January	1st to 10th	Night	21% 20% 36% 17% 5%	760
	11th to 20th	Night	26% 17% 33% 21% 4 1	760
	21st to end	Night	19% 14% 36% 25% 6%	836
February	1st to 10th	Night	20% 18% 41% 20% 2	760
	11th to 20th	Night	22% 16% 40% 18% 4	743
	21st to end	Night	19% 18% 39% 20% 4	628
March	1st to 10th	Night	20% 17% 37% 23% 3	760
	11th to 20th	Night	20% 21% 33% 21% 4 1	760
	21st to end	Night	19% 13% 35% 25% 7%	836
April	1st to 10th	Night	22% 17% 35% 23% 3	760
	11th to 20th	Night	19% 14% 36% 21% 9% 1	720
	21st to end	Night	21% 11% 33% 26% 9%	570
May	1st to 10th	Night	20% 7% 28% 32% 12% 2	539
	11th to 20th	Night	16% 6% 32% 33% 11%	374
	21st to end	Night	10% 7% 26% 40% 17% 1	411
June	1st to 10th	Night	12% 7% 33% 35% 13%	380
	11th to 20th	Night	10% 9% 26% 40% 14% 1	380
	21st to end	Night	13% 5% 29% 41% 13%	380
July	1st to 10th	Night	5% 4 27% 43% 19% 1	370
	11th to 20th	Night	10% 5% 25% 38% 23% 1	368
	21st to end	Night	9% 2 24% 43% 20% 2	535
August	1st to 10th	Night	10% 4 17% 41% 26% 2	567
	11th to 20th	Night	8% 2 19% 39% 28% 4	564
	21st to end	Night	11% 4 24% 37% 22% 2	727
September	1st to 10th	Night	12% 5% 26% 34% 18% 4	760
	11th to 20th	Night	11% 5% 22% 32% 23% 7%	760
	21st to end	Night	18% 8% 21% 32% 17% 4	760
October	1st to 10th	Night	18% 7% 30% 28% 16% 2	760
	11th to 20th	Night	22% 15% 28% 25% 8% 1	760
	21st to end	Night	26% 13% 33% 24% 4	836
November	1st to 10th	Night	24% 14% 29% 25% 8% 1	780
	11th to 20th	Night	21% 17% 34% 21% 6% 1	800
	21st to end	Night	26% 16% 31% 22% 5%	779
December	1st to 10th	Night	27% 18% 34% 18% 3	760
	11th to 20th	Night	21% 17% 38% 20% 3 1	760
	21st to end	Night	30% 15% 35% 18% 2	836

Page generated at 2024-11-22 08:02:23. Version ac07

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