Peterborough
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Peterborough clear sky chart from 2005-11-06 to 2024-03-28.

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% 10% 4 7% 6% 3 5% 5% 5% 7% 33%	78681
	Night	16% 10% 4 7% 6% 3 5% 5% 5% 7% 33%	81304
Transparency	Day	50% 7% 12% 19% 11% 1	78390
	Night	51% 7% 12% 19% 10% 1	81129
Seeing	Day	21% 16% 31% 19% 9% 4	13561
	Night	20% 15% 31% 24% 10% 1	23029

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% 17% 6% 8% 6% 2 3 4 4 5% 29%	2517
	11th to 20th	Day	12% 16% 7% 14% 10% 4 6% 4 4 4 20%	2591
	21st to end	Day	20% 20% 6% 11% 7% 3 4 4 3 4 19%	3124
February	1st to 10th	Day	14% 16% 6% 12% 7% 3 6% 5% 5% 5% 23%	1710
	11th to 20th	Day	12% 14% 6% 11% 8% 5% 5% 3 4 5% 27%	1663
	21st to end	Day	17% 13% 5% 8% 8% 4 5% 4 5% 3 26%	1475
March	1st to 10th	Day	15% 12% 4 8% 6% 4 5% 5% 4 7% 30%	2049
	11th to 20th	Day	14% 12% 5% 7% 6% 4 5% 4 5% 5% 32%	2090
	21st to end	Day	19% 10% 3 5% 5% 3 4 5% 4 6% 36%	2269
April	1st to 10th	Day	20% 11% 4 6% 6% 3 4 4 5% 6% 31%	2160
	11th to 20th	Day	20% 9% 2 5% 4 3 4 4 4 5% 39%	2147
	21st to end	Day	20% 10% 3 6% 5% 4 4 5% 4 5% 34%	2340
May	1st to 10th	Day	18% 8% 4 6% 6% 3 4 4 5% 7% 34%	2412
	11th to 20th	Day	15% 8% 3 6% 4 3 4 5% 5% 7% 40%	2478
	21st to end	Day	13% 6% 2 5% 5% 3 4 6% 5% 8% 41%	2725
June	1st to 10th	Day	17% 6% 3 6% 5% 3 5% 6% 7% 8% 35%	2520
	11th to 20th	Day	14% 6% 2 5% 5% 4 5% 5% 6% 10% 40%	2520
	21st to end	Day	15% 7% 3 6% 5% 3 5% 5% 6% 9% 38%	2520
July	1st to 10th	Day	9% 4 2 5% 5% 4 5% 5% 7% 9% 44%	2520
	11th to 20th	Day	12% 5% 2 5% 5% 4 6% 6% 6% 10% 38%	2520
	21st to end	Day	10% 5% 3 6% 7% 4 7% 6% 6% 9% 38%	2682
August	1st to 10th	Day	11% 6% 2 5% 5% 3 6% 7% 6% 8% 40%	2327
	11th to 20th	Day	10% 6% 2 6% 6% 4 5% 6% 7% 8% 39%	2303
	21st to end	Day	12% 6% 2 6% 5% 3 5% 5% 7% 10% 38%	2440
September	1st to 10th	Day	13% 5% 2 6% 6% 4 4 5% 5% 8% 41%	2160
	11th to 20th	Day	12% 5% 2 5% 4 2 5% 5% 5% 8% 46%	2129
	21st to end	Day	14% 6% 3 7% 6% 4 4 5% 5% 6% 41%	1898
October	1st to 10th	Day	18% 10% 4 7% 5% 3 5% 4 5% 6% 33%	1800
	11th to 20th	Day	22% 9% 3 8% 6% 4 4 5% 6% 6% 27%	1800
	21st to end	Day	25% 11% 5% 7% 6% 3 3 4 5% 6% 24%	1978
November	1st to 10th	Day	15% 11% 3 6% 5% 3 4 5% 5% 7% 35%	1576
	11th to 20th	Day	16% 12% 4 7% 7% 4 4 5% 6% 8% 28%	1520
	21st to end	Day	21% 13% 4 8% 7% 4 4 5% 5% 6% 23%	1520
December	1st to 10th	Day	16% 16% 7% 10% 7% 5% 5% 5% 5% 4 20%	1520
	11th to 20th	Day	19% 14% 6% 7% 6% 3 4 4 4 5% 27%	1906
	21st to end	Day	27% 16% 6% 9% 6% 3 3 3 3 5% 17%	2772
January	1st to 10th	Night	18% 15% 6% 9% 7% 4 5% 4 5% 6% 20%	4429
	11th to 20th	Night	13% 12% 8% 13% 10% 4 5% 4 5% 5% 22%	4367
	21st to end	Night	19% 14% 7% 10% 7% 3 4 4 5% 6% 23%	4532
February	1st to 10th	Night	12% 15% 5% 9% 9% 4 6% 5% 5% 6% 24%	2470
	11th to 20th	Night	13% 12% 5% 9% 8% 3 6% 5% 6% 5% 29%	2403
	21st to end	Night	15% 11% 3 9% 7% 3 5% 5% 6% 7% 29%	1977
March	1st to 10th	Night	15% 9% 5% 8% 6% 3 4 4 5% 6% 34%	2113
	11th to 20th	Night	16% 11% 5% 7% 5% 3 5% 4 4 4 35%	2089
	21st to end	Night	16% 7% 3 6% 7% 3 4 5% 5% 6% 40%	2241
April	1st to 10th	Night	18% 9% 4 6% 5% 3 4 5% 5% 7% 33%	1800
	11th to 20th	Night	17% 8% 3 5% 5% 3 5% 5% 5% 7% 38%	1775
	21st to end	Night	16% 9% 3 5% 5% 4 6% 5% 6% 7% 34%	1620
May	1st to 10th	Night	17% 5% 2 6% 6% 4 5% 6% 5% 7% 37%	1548
	11th to 20th	Night	12% 6% 2 4 5% 4 5% 5% 6% 6% 45%	1415
	21st to end	Night	10% 5% 2 4 4 4 4 3 6% 7% 51%	1550
June	1st to 10th	Night	13% 6% 3 5% 6% 3 5% 5% 6% 9% 39%	1440
	11th to 20th	Night	10% 5% 2 5% 6% 3 5% 6% 6% 8% 45%	1440
	21st to end	Night	11% 6% 3 7% 6% 3 5% 5% 6% 7% 41%	1440
July	1st to 10th	Night	6% 4 2 6% 4 4 4 6% 6% 7% 52%	1440
	11th to 20th	Night	9% 6% 2 4 4 3 5% 5% 6% 8% 48%	1440
	21st to end	Night	9% 4 2 4 5% 3 5% 5% 7% 9% 48%	1632
August	1st to 10th	Night	9% 5% 2 5% 5% 3 4 5% 5% 9% 48%	1611
	11th to 20th	Night	8% 5% 2 5% 5% 3 4 4 6% 9% 47%	1598
	21st to end	Night	8% 5% 3 5% 6% 3 5% 5% 6% 8% 46%	1898
September	1st to 10th	Night	10% 6% 2 6% 5% 3 4 5% 6% 8% 44%	1800
	11th to 20th	Night	12% 4 2 4 4 2 4 4 7% 8% 52%	1826
	21st to end	Night	16% 6% 3 5% 5% 3 3 5% 4 6% 45%	2061
October	1st to 10th	Night	16% 7% 4 6% 6% 3 5% 5% 4 6% 37%	2160
	11th to 20th	Night	21% 8% 3 6% 6% 4 5% 4 4 7% 31%	2160
	21st to end	Night	21% 10% 4 7% 6% 3 5% 4 5% 6% 27%	2376
November	1st to 10th	Night	18% 9% 3 5% 5% 3 5% 4 5% 7% 37%	2501
	11th to 20th	Night	17% 10% 4 7% 6% 4 5% 5% 6% 7% 29%	2660
	21st to end	Night	20% 10% 4 8% 7% 5% 6% 5% 6% 7% 24%	2660
December	1st to 10th	Night	20% 13% 6% 9% 6% 4 5% 5% 5% 6% 21%	2660
	11th to 20th	Night	16% 17% 5% 10% 6% 3 4 5% 5% 6% 23%	3288
	21st to end	Night	28% 16% 5% 11% 6% 3 4 4 4 5% 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	57% 7% 14% 13% 8% 1	2518
	11th to 20th	Day	68% 6% 9% 10% 7%	2591
	21st to end	Day	70% 4 9% 10% 6% 1	3124
February	1st to 10th	Day	63% 5% 11% 15% 5% 1	1710
	11th to 20th	Day	60% 5% 9% 14% 11% 1	1672
	21st to end	Day	61% 5% 9% 15% 9% 1	1475
March	1st to 10th	Day	55% 6% 15% 14% 10% 1	2052
	11th to 20th	Day	53% 5% 10% 17% 11% 2	2090
	21st to end	Day	50% 5% 8% 18% 16% 3	2269
April	1st to 10th	Day	54% 5% 10% 18% 11% 2	2160
	11th to 20th	Day	47% 5% 10% 22% 16% 1	2147
	21st to end	Day	52% 5% 9% 18% 13% 3	2340
May	1st to 10th	Day	49% 6% 7% 20% 14% 3	2412
	11th to 20th	Day	43% 6% 10% 24% 16% 1	2482
	21st to end	Day	40% 8% 14% 22% 13% 2	2725
June	1st to 10th	Day	44% 8% 12% 20% 15% 1	2520
	11th to 20th	Day	40% 7% 13% 25% 14% 1	2520
	21st to end	Day	43% 8% 13% 22% 13% 1	2520
July	1st to 10th	Day	34% 8% 13% 26% 17% 1	2450
	11th to 20th	Day	38% 9% 16% 27% 10% 1	2445
	21st to end	Day	41% 9% 13% 25% 11% 1	2532
August	1st to 10th	Day	39% 9% 15% 24% 11% 1	2314
	11th to 20th	Day	38% 10% 15% 25% 12% 1	2303
	21st to end	Day	39% 8% 14% 26% 12% 1	2440
September	1st to 10th	Day	40% 8% 13% 28% 11% 1	2160
	11th to 20th	Day	34% 8% 14% 29% 14% 1	2129
	21st to end	Day	43% 8% 14% 26% 9%	1898
October	1st to 10th	Day	51% 6% 12% 19% 11% 1	1800
	11th to 20th	Day	55% 8% 13% 18% 6% 1	1800
	21st to end	Day	60% 7% 11% 14% 7%	1978
November	1st to 10th	Day	47% 8% 15% 20% 9% 1	1576
	11th to 20th	Day	53% 8% 15% 14% 9% 1	1520
	21st to end	Day	60% 9% 12% 14% 5%	1520
December	1st to 10th	Day	66% 8% 10% 11% 5%	1520
	11th to 20th	Day	60% 8% 11% 12% 9%	1906
	21st to end	Day	70% 6% 9% 11% 4	2772
January	1st to 10th	Night	62% 9% 11% 12% 5%	4429
	11th to 20th	Night	63% 8% 11% 12% 4 1	4367
	21st to end	Night	63% 7% 11% 13% 6% 1	4532
February	1st to 10th	Night	60% 7% 10% 17% 6% 1	2470
	11th to 20th	Night	55% 6% 11% 18% 9%	2405
	21st to end	Night	53% 7% 12% 19% 8% 1	1977
March	1st to 10th	Night	50% 6% 12% 19% 11% 2	2123
	11th to 20th	Night	51% 6% 10% 20% 12% 2	2090
	21st to end	Night	45% 6% 8% 21% 16% 3	2241
April	1st to 10th	Night	51% 5% 9% 20% 13% 2	1800
	11th to 20th	Night	45% 6% 10% 20% 17% 2	1775
	21st to end	Night	47% 8% 11% 16% 15% 2	1620
May	1st to 10th	Night	45% 7% 11% 19% 15% 3	1548
	11th to 20th	Night	38% 6% 10% 25% 17% 4	1416
	21st to end	Night	33% 7% 14% 25% 18% 4	1551
June	1st to 10th	Night	40% 8% 13% 22% 15% 2	1440
	11th to 20th	Night	35% 7% 12% 22% 20% 2	1440
	21st to end	Night	41% 8% 13% 22% 15% 2	1440
July	1st to 10th	Night	29% 9% 12% 27% 21% 2	1400
	11th to 20th	Night	33% 8% 12% 30% 16% 1	1392
	21st to end	Night	31% 7% 15% 32% 13% 1	1541
August	1st to 10th	Night	33% 8% 17% 27% 14% 1	1600
	11th to 20th	Night	32% 8% 17% 28% 13% 1	1598
	21st to end	Night	35% 10% 11% 29% 14% 1	1898
September	1st to 10th	Night	36% 9% 15% 26% 14% 1	1800
	11th to 20th	Night	30% 6% 15% 32% 16% 1	1826
	21st to end	Night	40% 7% 11% 29% 12% 1	2061
October	1st to 10th	Night	46% 8% 12% 19% 14% 1	2160
	11th to 20th	Night	52% 7% 13% 20% 7%	2160
	21st to end	Night	56% 8% 11% 14% 11% 1	2376
November	1st to 10th	Night	47% 6% 14% 21% 12% 1	2501
	11th to 20th	Night	52% 7% 14% 16% 9% 2	2660
	21st to end	Night	57% 9% 16% 14% 5%	2660
December	1st to 10th	Night	62% 9% 11% 13% 5%	2660
	11th to 20th	Night	61% 6% 12% 14% 6%	3288
	21st to end	Night	72% 7% 8% 9% 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% 34% 13% 5% 1	180
	11th to 20th	Day	23% 26% 33% 14% 3 1	202
	21st to end	Day	26% 24% 32% 14% 4	297
February	1st to 10th	Day	29% 26% 32% 10% 3	270
	11th to 20th	Day	24% 28% 38% 9% 1	270
	21st to end	Day	35% 23% 32% 9%	287
March	1st to 10th	Day	22% 22% 37% 15% 3	460
	11th to 20th	Day	27% 22% 31% 17% 3 1	460
	21st to end	Day	34% 14% 32% 13% 6% 1	490
April	1st to 10th	Day	28% 21% 31% 12% 6% 1	420
	11th to 20th	Day	30% 20% 23% 14% 8% 5%	412
	21st to end	Day	29% 19% 33% 12% 7% 1	420
May	1st to 10th	Day	26% 14% 30% 18% 6% 5%	423
	11th to 20th	Day	20% 13% 36% 17% 10% 3	447
	21st to end	Day	16% 13% 31% 22% 12% 5%	485
June	1st to 10th	Day	16% 12% 40% 22% 9% 1	450
	11th to 20th	Day	17% 12% 31% 23% 14% 4	450
	21st to end	Day	21% 9% 31% 25% 10% 4	450
July	1st to 10th	Day	9% 9% 31% 33% 14% 5%	445
	11th to 20th	Day	16% 10% 27% 25% 15% 8%	444
	21st to end	Day	10% 9% 33% 33% 11% 4	488
August	1st to 10th	Day	10% 7% 29% 30% 16% 8%	446
	11th to 20th	Day	12% 8% 25% 29% 18% 8%	439
	21st to end	Day	13% 9% 30% 27% 14% 7%	495
September	1st to 10th	Day	13% 12% 29% 23% 15% 8%	450
	11th to 20th	Day	12% 9% 29% 21% 18% 10%	450
	21st to end	Day	15% 16% 28% 25% 11% 7%	450
October	1st to 10th	Day	23% 15% 28% 16% 12% 6%	450
	11th to 20th	Day	23% 23% 32% 16% 4 2	450
	21st to end	Day	30% 22% 28% 16% 5%	493
November	1st to 10th	Day	26% 17% 30% 19% 8%	270
	11th to 20th	Day	24% 26% 34% 12% 3 1	180
	21st to end	Day	27% 19% 38% 13% 2	180
December	1st to 10th	Day	26% 27% 32% 13% 3	180
	11th to 20th	Day	26% 30% 27% 13% 3 1	180
	21st to end	Day	35% 20% 35% 9% 1	198
January	1st to 10th	Night	26% 24% 29% 16% 6%	760
	11th to 20th	Night	27% 18% 30% 19% 6%	760
	21st to end	Night	22% 16% 33% 22% 6% 1	836
February	1st to 10th	Night	21% 21% 38% 17% 2	760
	11th to 20th	Night	20% 22% 37% 18% 3	743
	21st to end	Night	22% 23% 33% 18% 3	628
March	1st to 10th	Night	21% 19% 36% 20% 4	760
	11th to 20th	Night	22% 20% 35% 18% 4 1	760
	21st to end	Night	22% 15% 34% 21% 8%	821
April	1st to 10th	Night	23% 18% 33% 20% 5%	720
	11th to 20th	Night	22% 15% 31% 21% 9% 1	711
	21st to end	Night	21% 12% 30% 27% 9% 1	540
May	1st to 10th	Night	21% 8% 29% 28% 12% 2	468
	11th to 20th	Night	16% 7% 35% 32% 10%	354
	21st to end	Night	12% 8% 31% 34% 14% 1	389
June	1st to 10th	Night	16% 7% 35% 29% 13% 1	360
	11th to 20th	Night	11% 9% 30% 36% 13% 1	360
	21st to end	Night	13% 6% 29% 37% 15%	360
July	1st to 10th	Night	7% 5% 28% 42% 18%	350
	11th to 20th	Night	9% 4 32% 32% 22% 1	348
	21st to end	Night	10% 2 33% 39% 16% 1	452
August	1st to 10th	Night	12% 4 23% 34% 26% 2	537
	11th to 20th	Night	10% 5% 20% 36% 26% 3	534
	21st to end	Night	12% 5% 29% 32% 21% 2	710
September	1st to 10th	Night	12% 8% 28% 30% 19% 3	720
	11th to 20th	Night	13% 5% 26% 30% 22% 5%	720
	21st to end	Night	18% 9% 23% 28% 18% 4	720
October	1st to 10th	Night	19% 11% 29% 23% 15% 2	720
	11th to 20th	Night	25% 16% 30% 20% 9% 1	720
	21st to end	Night	28% 17% 29% 22% 4	792
November	1st to 10th	Night	23% 16% 28% 24% 8% 1	740
	11th to 20th	Night	22% 20% 32% 19% 6% 1	760
	21st to end	Night	25% 19% 30% 20% 5%	760
December	1st to 10th	Night	28% 23% 31% 15% 4	760
	11th to 20th	Night	23% 22% 33% 17% 4 1	760
	21st to end	Night	31% 20% 31% 15% 3	836

Page generated at 2024-03-24 23:37:00. Version ac07

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