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 2024-11-04.

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	15% 10% 3 8% 5% 5% 4 4 5% 7% 34%	101513
	Night	15% 10% 4 8% 5% 4 4 4 5% 6% 34%	97491
Transparency	Day	47% 7% 12% 21% 11% 1	105099
	Night	48% 7% 12% 21% 11% 1	101993
Seeing	Day	21% 16% 31% 19% 9% 4	14441
	Night	20% 15% 31% 24% 10% 1	23707

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% 18% 6% 9% 5% 3 3 3 4 4 29%	2517
	11th to 20th	Day	11% 16% 7% 15% 9% 6% 5% 3 4 4 20%	2591
	21st to end	Day	20% 21% 5% 11% 6% 4 4 3 3 4 19%	3124
February	1st to 10th	Day	13% 17% 6% 13% 6% 5% 5% 3 5% 5% 23%	1710
	11th to 20th	Day	12% 15% 6% 13% 7% 6% 4 3 4 5% 27%	1663
	21st to end	Day	17% 14% 5% 10% 7% 6% 4 3 5% 3 26%	1475
March	1st to 10th	Day	18% 14% 4 7% 4 5% 3 3 4 6% 30%	3371
	11th to 20th	Day	11% 15% 5% 9% 6% 5% 5% 4 5% 6% 29%	3480
	21st to end	Day	15% 9% 2 6% 4 3 4 4 4 6% 44%	3842
April	1st to 10th	Day	20% 12% 4 7% 5% 4 4 3 5% 6% 31%	2280
	11th to 20th	Day	21% 10% 2 6% 4 4 3 3 4 5% 38%	2268
	21st to end	Day	20% 10% 3 7% 5% 4 4 3 4 5% 34%	2470
May	1st to 10th	Day	19% 8% 2 7% 5% 5% 4 4 5% 7% 34%	4236
	11th to 20th	Day	16% 11% 3 8% 5% 4 5% 4 6% 8% 32%	4398
	21st to end	Day	13% 7% 2 6% 4 4 4 4 5% 8% 43%	4837
June	1st to 10th	Day	17% 7% 3 7% 5% 5% 5% 4 7% 8% 33%	2660
	11th to 20th	Day	13% 6% 2 7% 4 5% 5% 4 6% 10% 39%	2660
	21st to end	Day	16% 8% 3 6% 4 4 4 4 6% 8% 37%	2660
July	1st to 10th	Day	10% 5% 2 7% 5% 5% 5% 5% 8% 10% 38%	4440
	11th to 20th	Day	11% 5% 2 5% 4 5% 4 5% 6% 10% 43%	4440
	21st to end	Day	7% 5% 2 7% 5% 5% 5% 5% 6% 10% 43%	4699
August	1st to 10th	Day	16% 9% 3 7% 4 4 5% 4 5% 7% 38%	4104
	11th to 20th	Day	13% 7% 3 7% 4 5% 4 4 7% 9% 37%	4044
	21st to end	Day	9% 6% 2 7% 4 5% 5% 4 7% 10% 41%	4286
September	1st to 10th	Day	13% 6% 2 7% 5% 5% 5% 4 5% 8% 41%	2280
	11th to 20th	Day	11% 5% 2 5% 3 3 5% 4 6% 8% 47%	2247
	21st to end	Day	15% 7% 3 8% 5% 4 4 3 5% 6% 40%	2003
October	1st to 10th	Day	17% 10% 3 7% 4 4 5% 3 6% 7% 34%	1900
	11th to 20th	Day	21% 9% 3 9% 5% 5% 4 4 5% 6% 28%	1900
	21st to end	Day	24% 12% 4 8% 5% 5% 3 4 6% 6% 24%	2087
November	1st to 10th	Day	14% 11% 3 7% 4 4 5% 4 5% 7% 35%	1603
	11th to 20th	Day	16% 13% 3 8% 6% 5% 4 4 6% 7% 28%	1520
	21st to end	Day	21% 13% 4 9% 6% 4 4 4 5% 6% 23%	1520
December	1st to 10th	Day	16% 17% 7% 11% 6% 6% 5% 4 5% 5% 19%	1520
	11th to 20th	Day	19% 16% 5% 8% 5% 4 4 3 4 5% 27%	1906
	21st to end	Day	27% 17% 5% 10% 5% 4 3 3 4 5% 17%	2772
January	1st to 10th	Night	18% 16% 6% 10% 6% 5% 5% 3 5% 6% 20%	4429
	11th to 20th	Night	13% 13% 7% 14% 8% 5% 5% 3 5% 5% 21%	4367
	21st to end	Night	18% 14% 7% 11% 6% 4 4 3 5% 6% 23%	4532
February	1st to 10th	Night	12% 16% 4 10% 8% 6% 5% 4 4 6% 24%	2470
	11th to 20th	Night	13% 13% 5% 10% 7% 5% 5% 4 6% 5% 28%	2403
	21st to end	Night	15% 12% 3 9% 6% 5% 5% 4 6% 7% 29%	1977
March	1st to 10th	Night	17% 10% 4 9% 5% 4 4 3 5% 6% 32%	3452
	11th to 20th	Night	14% 13% 5% 9% 5% 5% 5% 4 4 5% 31%	3479
	21st to end	Night	16% 8% 2 6% 5% 3 4 3 5% 6% 43%	3789
April	1st to 10th	Night	18% 10% 4 6% 4 4 4 4 5% 6% 32%	1900
	11th to 20th	Night	18% 9% 2 6% 4 4 4 3 5% 7% 38%	1875
	21st to end	Night	17% 9% 3 6% 4 5% 5% 4 6% 6% 34%	1710
May	1st to 10th	Night	18% 8% 3 7% 4 4 5% 3 5% 6% 37%	2705
	11th to 20th	Night	15% 8% 2 7% 4 5% 5% 4 6% 6% 37%	2495
	21st to end	Night	10% 6% 2 6% 4 4 4 3 5% 8% 48%	2738
June	1st to 10th	Night	13% 7% 2 6% 6% 4 5% 4 6% 9% 38%	1520
	11th to 20th	Night	10% 6% 2 5% 5% 4 5% 5% 7% 8% 44%	1520
	21st to end	Night	12% 6% 4 9% 5% 5% 4 4 6% 7% 39%	1520
July	1st to 10th	Night	7% 5% 2 7% 4 5% 5% 5% 7% 8% 45%	2520
	11th to 20th	Night	11% 6% 2 5% 3 4 4 3 5% 8% 49%	2520
	21st to end	Night	9% 5% 2 4 4 3 4 4 6% 9% 51%	2850
August	1st to 10th	Night	10% 5% 2 6% 4 4 4 4 5% 8% 48%	2825
	11th to 20th	Night	13% 6% 2 5% 4 3 3 3 5% 8% 48%	2785
	21st to end	Night	8% 5% 2 6% 4 3 4 4 6% 8% 48%	3338
September	1st to 10th	Night	10% 6% 2 6% 4 4 5% 4 6% 8% 45%	1900
	11th to 20th	Night	11% 4 1 4 3 3 4 4 7% 7% 53%	1928
	21st to end	Night	16% 7% 2 6% 4 4 3 4 5% 6% 44%	2176
October	1st to 10th	Night	16% 7% 4 7% 5% 4 4 4 4 6% 39%	2280
	11th to 20th	Night	20% 9% 3 7% 6% 5% 4 3 5% 7% 32%	2280
	21st to end	Night	21% 11% 4 8% 5% 5% 5% 3 5% 6% 28%	2509
November	1st to 10th	Night	18% 10% 3 6% 5% 4 4 3 5% 7% 37%	2547
	11th to 20th	Night	17% 11% 3 8% 5% 5% 5% 4 6% 7% 29%	2660
	21st to end	Night	20% 10% 3 8% 6% 6% 6% 4 6% 7% 24%	2660
December	1st to 10th	Night	20% 15% 5% 10% 5% 5% 5% 4 5% 6% 21%	2660
	11th to 20th	Night	16% 18% 4 11% 5% 4 4 4 5% 6% 23%	3288
	21st to end	Night	27% 17% 5% 12% 5% 4 4 3 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	54% 6% 13% 16% 10% 1	3374
	11th to 20th	Day	53% 6% 14% 16% 9% 1	3480
	21st to end	Day	41% 6% 9% 23% 19% 2	3842
April	1st to 10th	Day	54% 5% 10% 19% 11% 2	2280
	11th to 20th	Day	48% 5% 9% 21% 16% 1	2268
	21st to end	Day	52% 5% 9% 18% 13% 3	2470
May	1st to 10th	Day	48% 7% 10% 22% 12% 2	4248
	11th to 20th	Day	47% 9% 12% 19% 11% 1	4402
	21st to end	Day	37% 8% 13% 23% 15% 3	4837
June	1st to 10th	Day	46% 8% 12% 20% 14% 1	2660
	11th to 20th	Day	40% 7% 13% 25% 14% 1	2660
	21st to end	Day	43% 8% 13% 22% 13% 1	2660
July	1st to 10th	Day	38% 8% 15% 24% 14% 1	4370
	11th to 20th	Day	33% 8% 16% 33% 9%	4365
	21st to end	Day	35% 9% 14% 29% 14%	4549
August	1st to 10th	Day	44% 7% 13% 22% 12% 1	4091
	11th to 20th	Day	40% 8% 14% 28% 9%	4083
	21st to end	Day	36% 7% 13% 33% 10% 1	4286
September	1st to 10th	Day	39% 8% 13% 28% 11% 1	2280
	11th to 20th	Day	33% 8% 14% 31% 14% 1	2247
	21st to end	Day	44% 7% 14% 25% 10%	2003
October	1st to 10th	Day	40% 7% 13% 28% 12% 1	3160
	11th to 20th	Day	44% 7% 16% 22% 12% 1	3140
	21st to end	Day	50% 7% 15% 19% 8%	3413
November	1st to 10th	Day	47% 8% 15% 21% 9% 1	1603
	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	52% 6% 10% 21% 10% 1	3462
	11th to 20th	Night	51% 8% 15% 16% 9% 1	3480
	21st to end	Night	39% 6% 11% 23% 19% 2	3789
April	1st to 10th	Night	51% 5% 9% 20% 13% 2	1900
	11th to 20th	Night	46% 6% 10% 19% 17% 2	1875
	21st to end	Night	47% 8% 11% 16% 16% 2	1710
May	1st to 10th	Night	46% 7% 13% 16% 16% 2	2712
	11th to 20th	Night	44% 9% 12% 22% 10% 2	2496
	21st to end	Night	34% 7% 12% 25% 19% 2	2739
June	1st to 10th	Night	41% 8% 12% 22% 15% 2	1520
	11th to 20th	Night	35% 8% 13% 22% 20% 2	1520
	21st to end	Night	42% 8% 12% 21% 15% 2	1520
July	1st to 10th	Night	34% 8% 15% 25% 18% 1	2480
	11th to 20th	Night	33% 6% 12% 34% 14%	2472
	21st to end	Night	29% 7% 16% 34% 13% 1	2759
August	1st to 10th	Night	35% 6% 13% 27% 17% 1	2814
	11th to 20th	Night	35% 6% 18% 28% 11% 1	2812
	21st to end	Night	31% 8% 12% 34% 13% 1	3338
September	1st to 10th	Night	35% 9% 14% 27% 14% 1	1900
	11th to 20th	Night	29% 6% 14% 32% 17% 1	1928
	21st to end	Night	41% 7% 11% 28% 12% 1	2176
October	1st to 10th	Night	34% 6% 11% 28% 21% 1	3800
	11th to 20th	Night	42% 7% 16% 27% 9%	3779
	21st to end	Night	45% 8% 14% 25% 8%	4133
November	1st to 10th	Night	47% 6% 13% 21% 11% 1	2547
	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	33% 14% 33% 13% 6% 1	506
April	1st to 10th	Day	29% 21% 31% 12% 5% 1	460
	11th to 20th	Day	32% 21% 23% 13% 7% 4	452
	21st to end	Day	29% 19% 32% 12% 7% 1	460
May	1st to 10th	Day	25% 14% 31% 19% 6% 5%	463
	11th to 20th	Day	19% 13% 34% 20% 11% 3	487
	21st to end	Day	16% 14% 32% 22% 12% 5%	529
June	1st to 10th	Day	17% 13% 37% 22% 9% 1	490
	11th to 20th	Day	16% 12% 32% 23% 13% 3	490
	21st to end	Day	23% 11% 30% 23% 10% 4	490
July	1st to 10th	Day	9% 8% 31% 33% 13% 5%	485
	11th to 20th	Day	16% 10% 28% 24% 14% 8%	484
	21st to end	Day	10% 9% 32% 33% 12% 4	532
August	1st to 10th	Day	12% 8% 28% 28% 16% 7%	486
	11th to 20th	Day	13% 9% 25% 28% 18% 8%	479
	21st to end	Day	12% 9% 31% 26% 15% 6%	539
September	1st to 10th	Day	14% 11% 29% 23% 15% 8%	490
	11th to 20th	Day	11% 9% 26% 21% 20% 13%	490
	21st to end	Day	16% 16% 26% 25% 10% 6%	490
October	1st to 10th	Day	22% 16% 28% 16% 12% 6%	490
	11th to 20th	Day	22% 23% 32% 16% 6% 2	490
	21st to end	Day	29% 22% 28% 16% 5%	536
November	1st to 10th	Day	26% 17% 30% 19% 8%	279
	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	21% 15% 34% 21% 8%	836
April	1st to 10th	Night	24% 18% 33% 21% 5%	760
	11th to 20th	Night	23% 16% 31% 21% 8% 1	751
	21st to end	Night	22% 12% 31% 26% 9% 1	570
May	1st to 10th	Night	20% 8% 30% 28% 12% 2	494
	11th to 20th	Night	16% 8% 33% 33% 10%	374
	21st to end	Night	12% 8% 31% 34% 13% 1	411
June	1st to 10th	Night	16% 7% 34% 29% 13% 1	380
	11th to 20th	Night	10% 9% 30% 37% 13% 1	380
	21st to end	Night	13% 7% 30% 36% 14%	380
July	1st to 10th	Night	6% 5% 29% 42% 17%	370
	11th to 20th	Night	10% 4 31% 33% 21% 1	368
	21st to end	Night	10% 2 31% 39% 17% 1	478
August	1st to 10th	Night	11% 4 23% 34% 26% 2	567
	11th to 20th	Night	11% 5% 20% 35% 25% 3	564
	21st to end	Night	11% 5% 29% 32% 21% 2	750
September	1st to 10th	Night	12% 8% 28% 30% 19% 3	760
	11th to 20th	Night	12% 5% 25% 29% 24% 5%	760
	21st to end	Night	19% 9% 22% 28% 17% 3	760
October	1st to 10th	Night	19% 11% 30% 23% 15% 2	760
	11th to 20th	Night	24% 16% 29% 21% 9% 1	760
	21st to end	Night	27% 17% 30% 21% 5%	836
November	1st to 10th	Night	23% 16% 28% 24% 8% 1	755
	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 2024-11-01 22:47:39. Version ac07

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