Plymouth
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Plymouth clear sky chart from 2005-11-06 to 2024-11-10.

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% 8% 2 7% 5% 5% 5% 4 6% 7% 34%	101397
	Night	17% 8% 3 7% 5% 4 4 4 6% 7% 35%	97749
Transparency	Day	46% 6% 12% 22% 13% 2	104909
	Night	46% 6% 12% 22% 12% 1	102313
Seeing	Day	25% 17% 27% 19% 9% 3	14886
	Night	23% 15% 24% 28% 10% 1	23763

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% 8% 3 7% 5% 5% 5% 5% 6% 7% 35%	2517
	11th to 20th	Day	15% 10% 5% 10% 7% 7% 6% 4 6% 6% 26%	2520
	21st to end	Day	16% 11% 3 10% 6% 5% 4 4 6% 6% 28%	2772
February	1st to 10th	Day	14% 11% 3 8% 7% 5% 4 4 5% 7% 31%	1681
	11th to 20th	Day	11% 10% 3 10% 6% 5% 5% 5% 6% 6% 33%	1848
	21st to end	Day	16% 10% 4 8% 5% 5% 5% 4 5% 6% 32%	1570
March	1st to 10th	Day	20% 15% 3 9% 5% 5% 4 2 5% 5% 27%	3116
	11th to 20th	Day	14% 9% 3 9% 6% 5% 5% 5% 6% 7% 30%	3307
	21st to end	Day	19% 10% 3 8% 5% 5% 4 3 4 7% 32%	4070
April	1st to 10th	Day	19% 10% 3 7% 5% 4 4 3 4 7% 32%	2280
	11th to 20th	Day	17% 6% 2 5% 5% 5% 5% 4 6% 8% 36%	2277
	21st to end	Day	22% 8% 3 7% 4 5% 5% 4 5% 6% 31%	2470
May	1st to 10th	Day	24% 11% 4 8% 5% 5% 4 3 5% 6% 26%	4106
	11th to 20th	Day	19% 8% 3 8% 6% 5% 5% 4 6% 7% 30%	4317
	21st to end	Day	14% 5% 2 6% 4 5% 5% 5% 7% 9% 38%	4837
June	1st to 10th	Day	19% 7% 2 7% 5% 6% 5% 5% 7% 8% 28%	2660
	11th to 20th	Day	16% 6% 2 6% 5% 5% 5% 4 7% 8% 36%	2660
	21st to end	Day	19% 7% 3 6% 6% 6% 6% 4 6% 7% 30%	2660
July	1st to 10th	Day	13% 6% 2 6% 4 5% 6% 6% 7% 10% 35%	4440
	11th to 20th	Day	11% 5% 2 6% 5% 6% 6% 5% 8% 11% 36%	4440
	21st to end	Day	19% 6% 2 6% 4 5% 5% 4 6% 6% 37%	4814
August	1st to 10th	Day	14% 6% 2 6% 6% 6% 6% 5% 8% 8% 34%	4272
	11th to 20th	Day	18% 7% 2 6% 5% 5% 6% 5% 7% 9% 30%	4019
	21st to end	Day	10% 4 2 5% 4 4 6% 5% 7% 10% 43%	4180
September	1st to 10th	Day	12% 4 2 5% 4 4 5% 4 6% 8% 46%	2280
	11th to 20th	Day	14% 4 1 5% 3 4 4 4 4 5% 52%	2109
	21st to end	Day	16% 5% 2 5% 4 4 4 4 6% 7% 43%	2090
October	1st to 10th	Day	22% 7% 2 7% 4 5% 5% 3 5% 6% 34%	2090
	11th to 20th	Day	16% 7% 2 6% 5% 5% 5% 3 5% 7% 39%	1809
	21st to end	Day	25% 8% 2 6% 4 5% 4 3 5% 5% 32%	1881
November	1st to 10th	Day	14% 6% 2 7% 5% 5% 5% 3 5% 8% 41%	1752
	11th to 20th	Day	19% 6% 2 5% 5% 5% 5% 4 6% 7% 37%	1710
	21st to end	Day	21% 8% 1 5% 4 5% 4 3 6% 7% 35%	1645
December	1st to 10th	Day	20% 10% 2 9% 5% 5% 5% 4 7% 7% 26%	1520
	11th to 20th	Day	22% 9% 2 6% 3 4 4 3 5% 6% 36%	1906
	21st to end	Day	24% 11% 3 5% 5% 5% 5% 3 5% 6% 27%	2772
January	1st to 10th	Night	16% 9% 2 6% 4 5% 4 4 6% 7% 36%	4429
	11th to 20th	Night	13% 10% 3 11% 8% 6% 6% 5% 7% 7% 26%	4440
	21st to end	Night	17% 12% 4 10% 5% 5% 4 3 6% 6% 27%	4884
February	1st to 10th	Night	14% 9% 3 7% 6% 5% 5% 4 6% 7% 32%	2495
	11th to 20th	Night	11% 8% 3 8% 5% 5% 5% 5% 7% 9% 34%	2218
	21st to end	Night	13% 9% 3 6% 5% 5% 5% 4 6% 9% 35%	1884
March	1st to 10th	Night	24% 12% 2 5% 5% 4 4 3 5% 6% 29%	3724
	11th to 20th	Night	13% 10% 4 9% 6% 6% 6% 4 5% 6% 31%	3651
	21st to end	Night	21% 11% 3 6% 4 4 4 3 5% 7% 32%	3544
April	1st to 10th	Night	19% 9% 2 6% 5% 4 4 3 5% 5% 36%	1900
	11th to 20th	Night	20% 8% 2 6% 4 5% 4 3 6% 6% 36%	1851
	21st to end	Night	21% 8% 3 5% 4 4 4 3 5% 7% 36%	1710
May	1st to 10th	Night	28% 10% 3 7% 5% 4 4 4 5% 6% 24%	2834
	11th to 20th	Night	19% 11% 3 8% 6% 5% 6% 5% 6% 6% 27%	2605
	21st to end	Night	16% 5% 2 5% 5% 4 4 4 6% 8% 41%	2738
June	1st to 10th	Night	20% 7% 3 6% 4 4 4 4 6% 8% 33%	1520
	11th to 20th	Night	19% 6% 2 6% 5% 4 5% 4 5% 7% 38%	1520
	21st to end	Night	18% 7% 2 7% 5% 4 4 5% 6% 7% 36%	1520
July	1st to 10th	Night	12% 5% 2 6% 4 4 6% 6% 7% 10% 38%	2520
	11th to 20th	Night	15% 5% 2 5% 4 4 4 4 6% 8% 43%	2520
	21st to end	Night	18% 6% 2 5% 4 4 4 4 6% 8% 40%	2739
August	1st to 10th	Night	21% 7% 3 7% 4 4 4 4 5% 6% 35%	2625
	11th to 20th	Night	17% 8% 2 6% 4 4 4 4 6% 8% 37%	2804
	21st to end	Night	10% 4 1 5% 4 5% 4 4 7% 10% 46%	3476
September	1st to 10th	Night	12% 5% 2 4 4 3 3 3 6% 7% 50%	1900
	11th to 20th	Night	14% 5% 1 5% 3 3 4 3 4 7% 50%	2071
	21st to end	Night	16% 6% 2 5% 4 4 4 4 6% 7% 43%	2090
October	1st to 10th	Night	21% 7% 2 6% 4 4 4 4 5% 6% 37%	2090
	11th to 20th	Night	16% 7% 2 6% 5% 4 4 5% 6% 6% 38%	2366
	21st to end	Night	24% 7% 2 6% 5% 4 4 4 5% 7% 33%	2717
November	1st to 10th	Night	14% 6% 2 6% 5% 4 4 5% 6% 7% 41%	2531
	11th to 20th	Night	17% 7% 2 6% 5% 4 4 3 5% 8% 38%	2470
	21st to end	Night	16% 7% 2 6% 5% 5% 4 4 7% 7% 37%	2531
December	1st to 10th	Night	20% 10% 3 8% 7% 5% 4 4 6% 7% 28%	2660
	11th to 20th	Night	20% 9% 3 5% 4 4 4 4 7% 7% 33%	3288
	21st to end	Night	23% 13% 4 8% 4 4 5% 4 5% 5% 27%	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	45% 6% 10% 29% 10% 1	2518
	11th to 20th	Day	52% 10% 10% 20% 6% 2	2520
	21st to end	Day	53% 7% 10% 20% 9% 1	2772
February	1st to 10th	Day	51% 5% 12% 20% 10% 2	1681
	11th to 20th	Day	48% 6% 10% 20% 13% 3	1857
	21st to end	Day	51% 5% 11% 18% 12% 2	1570
March	1st to 10th	Day	59% 5% 10% 13% 11% 2	3119
	11th to 20th	Day	49% 7% 11% 15% 14% 4	3307
	21st to end	Day	51% 4 6% 15% 19% 4	4070
April	1st to 10th	Day	50% 5% 8% 20% 13% 4	2280
	11th to 20th	Day	44% 6% 11% 21% 16% 2	2277
	21st to end	Day	53% 5% 8% 18% 14% 3	2470
May	1st to 10th	Day	59% 6% 9% 18% 7% 1	4120
	11th to 20th	Day	51% 7% 15% 16% 9% 1	4321
	21st to end	Day	38% 9% 14% 25% 14% 1	4837
June	1st to 10th	Day	49% 7% 12% 21% 10%	2660
	11th to 20th	Day	44% 7% 11% 21% 15% 2	2660
	21st to end	Day	50% 8% 11% 18% 11% 1	2660
July	1st to 10th	Day	41% 6% 14% 24% 14% 1	4370
	11th to 20th	Day	40% 7% 16% 27% 10%	4365
	21st to end	Day	45% 5% 12% 22% 14% 1	4661
August	1st to 10th	Day	45% 7% 15% 22% 10%	4258
	11th to 20th	Day	47% 8% 15% 24% 7%	4058
	21st to end	Day	33% 6% 16% 27% 17% 1	4180
September	1st to 10th	Day	34% 7% 12% 31% 15% 1	2280
	11th to 20th	Day	34% 5% 9% 30% 20% 2	2109
	21st to end	Day	38% 6% 12% 26% 17% 2	2090
October	1st to 10th	Day	46% 6% 9% 23% 15% 1	3480
	11th to 20th	Day	41% 4 13% 25% 15% 2	2973
	21st to end	Day	39% 4 10% 28% 16% 3	3081
November	1st to 10th	Day	41% 5% 14% 24% 15% 1	1752
	11th to 20th	Day	44% 6% 11% 19% 17% 2	1710
	21st to end	Day	47% 5% 18% 19% 9% 1	1645
December	1st to 10th	Day	54% 7% 13% 16% 9% 1	1520
	11th to 20th	Day	49% 6% 9% 19% 17% 1	1906
	21st to end	Day	58% 5% 9% 18% 10%	2772
January	1st to 10th	Night	44% 6% 15% 24% 10% 2	4429
	11th to 20th	Night	50% 10% 12% 16% 10% 2	4440
	21st to end	Night	56% 6% 11% 18% 9% 1	4884
February	1st to 10th	Night	49% 5% 12% 20% 12% 2	2495
	11th to 20th	Night	44% 6% 10% 24% 15% 2	2220
	21st to end	Night	46% 5% 12% 22% 12% 4	1884
March	1st to 10th	Night	55% 5% 10% 18% 11% 2	3734
	11th to 20th	Night	52% 5% 10% 17% 14% 2	3652
	21st to end	Night	52% 4 6% 14% 18% 5%	3544
April	1st to 10th	Night	50% 4 9% 20% 15% 2	1900
	11th to 20th	Night	48% 4 8% 23% 16% 1	1851
	21st to end	Night	47% 4 12% 19% 16% 3	1710
May	1st to 10th	Night	60% 5% 9% 17% 8% 1	2840
	11th to 20th	Night	55% 7% 12% 16% 8% 2	2606
	21st to end	Night	40% 6% 18% 21% 13% 2	2739
June	1st to 10th	Night	48% 6% 13% 21% 11%	1520
	11th to 20th	Night	45% 5% 15% 20% 13% 2	1520
	21st to end	Night	45% 7% 15% 21% 10% 1	1520
July	1st to 10th	Night	39% 8% 17% 22% 14%	2480
	11th to 20th	Night	40% 5% 16% 26% 14%	2472
	21st to end	Night	41% 6% 12% 28% 12% 1	2651
August	1st to 10th	Night	50% 6% 12% 22% 9%	2615
	11th to 20th	Night	45% 7% 18% 20% 10%	2831
	21st to end	Night	31% 7% 19% 29% 15%	3476
September	1st to 10th	Night	33% 5% 15% 30% 17%	1900
	11th to 20th	Night	34% 5% 10% 30% 19% 2	2071
	21st to end	Night	39% 5% 11% 28% 15% 1	2090
October	1st to 10th	Night	44% 6% 14% 24% 11% 1	3480
	11th to 20th	Night	37% 4 12% 25% 19% 2	3928
	21st to end	Night	40% 4 11% 30% 13% 2	4467
November	1st to 10th	Night	40% 6% 12% 25% 15% 2	2531
	11th to 20th	Night	43% 5% 11% 24% 15% 2	2470
	21st to end	Night	44% 6% 17% 23% 9% 1	2531
December	1st to 10th	Night	54% 7% 10% 21% 8%	2660
	11th to 20th	Night	48% 6% 12% 17% 15% 1	3288
	21st to end	Night	57% 6% 9% 21% 7% 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	29% 20% 32% 16% 3 1	180
	11th to 20th	Day	32% 26% 29% 10% 2 2	180
	21st to end	Day	21% 27% 29% 17% 6%	198
February	1st to 10th	Day	30% 26% 29% 13% 3	291
	11th to 20th	Day	27% 29% 29% 12% 3	456
	21st to end	Day	32% 24% 24% 17% 3	382
March	1st to 10th	Day	30% 20% 29% 16% 4	460
	11th to 20th	Day	33% 23% 26% 13% 4 1	460
	21st to end	Day	32% 21% 24% 15% 6% 2	506
April	1st to 10th	Day	33% 20% 25% 13% 6% 2	460
	11th to 20th	Day	30% 26% 22% 15% 6% 2	452
	21st to end	Day	30% 21% 29% 11% 5% 3	460
May	1st to 10th	Day	31% 22% 26% 13% 5% 3	463
	11th to 20th	Day	22% 18% 33% 17% 7% 2	487
	21st to end	Day	22% 14% 30% 22% 9% 2	529
June	1st to 10th	Day	21% 13% 36% 18% 11% 1	490
	11th to 20th	Day	19% 15% 31% 21% 11% 3	490
	21st to end	Day	22% 15% 30% 19% 12% 2	490
July	1st to 10th	Day	19% 11% 30% 24% 13% 4	485
	11th to 20th	Day	15% 8% 32% 30% 12% 2	484
	21st to end	Day	16% 11% 34% 26% 10% 3	532
August	1st to 10th	Day	13% 13% 28% 27% 16% 3	486
	11th to 20th	Day	19% 11% 27% 23% 14% 6%	479
	21st to end	Day	14% 12% 28% 25% 16% 6%	539
September	1st to 10th	Day	16% 12% 27% 22% 16% 7%	490
	11th to 20th	Day	18% 11% 25% 21% 16% 10%	490
	21st to end	Day	16% 17% 25% 25% 11% 7%	490
October	1st to 10th	Day	29% 13% 19% 21% 13% 5%	490
	11th to 20th	Day	25% 17% 22% 22% 11% 2	433
	21st to end	Day	37% 15% 21% 20% 7%	429
November	1st to 10th	Day	24% 17% 24% 22% 11% 1	392
	11th to 20th	Day	32% 16% 24% 20% 7% 1	370
	21st to end	Day	33% 19% 26% 15% 7%	305
December	1st to 10th	Day	27% 25% 26% 17% 5%	180
	11th to 20th	Day	36% 21% 29% 12% 2	180
	21st to end	Day	32% 19% 27% 17% 4 1	198
January	1st to 10th	Night	22% 21% 28% 26% 3	760
	11th to 20th	Night	27% 19% 24% 27% 3	760
	21st to end	Night	19% 24% 29% 23% 4	836
February	1st to 10th	Night	22% 21% 32% 23% 2	760
	11th to 20th	Night	22% 24% 31% 20% 3	743
	21st to end	Night	23% 21% 27% 26% 4	628
March	1st to 10th	Night	28% 16% 29% 24% 3	760
	11th to 20th	Night	24% 21% 24% 23% 6%	760
	21st to end	Night	27% 18% 24% 23% 7% 1	836
April	1st to 10th	Night	27% 17% 28% 24% 4	760
	11th to 20th	Night	25% 18% 25% 25% 6%	727
	21st to end	Night	27% 17% 27% 23% 6%	570
May	1st to 10th	Night	28% 12% 24% 26% 8% 1	570
	11th to 20th	Night	21% 13% 24% 32% 10%	445
	21st to end	Night	20% 8% 21% 37% 13% 1	411
June	1st to 10th	Night	22% 9% 22% 35% 12% 1	380
	11th to 20th	Night	21% 9% 24% 31% 15% 1	380
	21st to end	Night	21% 5% 23% 37% 13% 1	380
July	1st to 10th	Night	15% 6% 19% 42% 17% 1	370
	11th to 20th	Night	15% 3 20% 38% 21% 2	368
	21st to end	Night	17% 3 19% 41% 19% 1	416
August	1st to 10th	Night	17% 3 17% 43% 20% 1	445
	11th to 20th	Night	17% 7% 26% 29% 19% 2	571
	21st to end	Night	16% 6% 17% 33% 24% 3	836
September	1st to 10th	Night	14% 8% 22% 34% 21% 2	760
	11th to 20th	Night	16% 10% 18% 30% 21% 5%	760
	21st to end	Night	19% 9% 20% 32% 17% 2	760
October	1st to 10th	Night	24% 12% 18% 29% 16% 2	760
	11th to 20th	Night	22% 16% 22% 26% 13% 1	760
	21st to end	Night	29% 16% 21% 26% 8%	836
November	1st to 10th	Night	20% 15% 24% 31% 9% 1	779
	11th to 20th	Night	24% 18% 24% 25% 8% 1	760
	21st to end	Night	24% 19% 23% 28% 6% 1	760
December	1st to 10th	Night	27% 20% 27% 21% 5%	760
	11th to 20th	Night	28% 20% 26% 22% 4 1	760
	21st to end	Night	29% 22% 23% 23% 3	836

Page generated at 2024-11-07 06:55:47. Version ac07

Copyright © 2024 Attilla Danko.