Gloucester
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Gloucester clear sky chart from 2005-11-06 to 2024-11-08.

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% 7% 2 6% 4 4 4 4 5% 7% 40%	101231
	Night	18% 8% 3 6% 4 4 4 3 5% 6% 38%	97874
Transparency	Day	42% 5% 12% 23% 15% 2	104783
	Night	45% 5% 12% 21% 15% 2	102411
Seeing	Day	19% 4 19% 33% 21% 5%	15094
	Night	20% 7% 27% 30% 15% 2	23933

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% 7% 3 6% 3 3 3 3 4 6% 45%	2517
	11th to 20th	Day	18% 8% 3 7% 3 3 3 3 5% 6% 41%	2520
	21st to end	Day	21% 11% 3 8% 4 4 4 3 4 6% 33%	2772
February	1st to 10th	Day	20% 8% 3 5% 4 4 5% 4 6% 6% 34%	1764
	11th to 20th	Day	14% 8% 2 6% 4 4 4 4 6% 8% 39%	1848
	21st to end	Day	16% 10% 2 6% 5% 4 4 4 6% 6% 36%	1570
March	1st to 10th	Day	25% 12% 3 7% 4 4 3 3 4 6% 30%	3116
	11th to 20th	Day	14% 7% 2 6% 4 4 4 4 5% 7% 42%	3380
	21st to end	Day	25% 8% 2 5% 4 4 4 4 4 5% 36%	3960
April	1st to 10th	Day	19% 8% 2 6% 4 4 4 4 5% 5% 39%	2280
	11th to 20th	Day	16% 8% 2 4 5% 4 4 4 5% 7% 41%	2302
	21st to end	Day	19% 6% 2 6% 4 4 4 4 5% 7% 39%	2470
May	1st to 10th	Day	21% 11% 4 7% 4 4 4 4 5% 7% 29%	4106
	11th to 20th	Day	21% 8% 3 9% 5% 4 3 3 4 6% 34%	4081
	21st to end	Day	15% 6% 2 5% 4 4 3 3 5% 8% 45%	4836
June	1st to 10th	Day	18% 7% 2 5% 4 5% 4 4 6% 8% 36%	2660
	11th to 20th	Day	15% 6% 2 5% 4 4 4 4 6% 8% 41%	2660
	21st to end	Day	16% 5% 2 6% 5% 5% 5% 4 6% 8% 38%	2660
July	1st to 10th	Day	10% 7% 3 7% 5% 5% 5% 4 7% 10% 38%	4440
	11th to 20th	Day	8% 6% 2 6% 4 5% 6% 4 7% 10% 42%	4440
	21st to end	Day	16% 6% 3 6% 4 4 4 4 6% 8% 40%	4797
August	1st to 10th	Day	14% 6% 3 6% 4 4 6% 5% 7% 8% 38%	4105
	11th to 20th	Day	13% 8% 3 7% 4 4 4 4 5% 7% 41%	4045
	21st to end	Day	7% 3 1 4 3 4 5% 5% 6% 9% 51%	4219
September	1st to 10th	Day	12% 6% 2 5% 4 3 3 4 5% 7% 50%	2248
	11th to 20th	Day	14% 7% 2 3 3 3 3 2 5% 5% 54%	2090
	21st to end	Day	16% 6% 2 5% 4 3 4 3 5% 7% 45%	2090
October	1st to 10th	Day	21% 5% 2 5% 3 3 3 3 5% 5% 43%	2090
	11th to 20th	Day	14% 6% 2 4 4 3 5% 3 5% 8% 46%	1861
	21st to end	Day	21% 6% 2 6% 3 3 3 4 5% 5% 42%	1881
November	1st to 10th	Day	17% 7% 2 5% 3 4 3 3 4 6% 47%	1734
	11th to 20th	Day	18% 8% 2 5% 3 3 4 3 4 7% 44%	1710
	21st to end	Day	18% 8% 2 4 3 4 3 4 4 7% 42%	1710
December	1st to 10th	Day	19% 9% 3 6% 4 4 3 3 4 6% 39%	1591
	11th to 20th	Day	22% 8% 2 6% 3 3 4 3 5% 5% 40%	1906
	21st to end	Day	22% 10% 3 7% 4 4 4 3 4 6% 32%	2772
January	1st to 10th	Night	19% 7% 2 5% 3 3 3 3 4 7% 45%	4429
	11th to 20th	Night	16% 9% 3 8% 5% 4 4 3 4 5% 38%	4440
	21st to end	Night	22% 13% 4 7% 4 4 4 3 5% 6% 28%	4884
February	1st to 10th	Night	17% 10% 3 7% 5% 4 4 4 6% 7% 35%	2410
	11th to 20th	Night	16% 10% 3 6% 4 3 4 4 6% 6% 38%	2218
	21st to end	Night	18% 9% 3 5% 4 4 3 3 5% 5% 42%	1884
March	1st to 10th	Night	31% 10% 2 5% 3 3 2 3 4 5% 32%	3724
	11th to 20th	Night	12% 10% 3 7% 6% 5% 5% 4 5% 6% 38%	3578
	21st to end	Night	26% 8% 2 7% 4 4 4 4 5% 4 33%	3669
April	1st to 10th	Night	19% 9% 3 7% 5% 4 4 4 5% 5% 36%	1900
	11th to 20th	Night	19% 8% 2 5% 5% 4 3 3 4 5% 40%	1826
	21st to end	Night	19% 7% 2 8% 5% 5% 5% 3 5% 5% 37%	1710
May	1st to 10th	Night	22% 11% 3 9% 5% 4 4 3 5% 7% 27%	2834
	11th to 20th	Night	22% 10% 3 7% 5% 4 6% 4 6% 7% 26%	2813
	21st to end	Night	16% 7% 3 7% 4 4 4 3 6% 7% 39%	2753
June	1st to 10th	Night	19% 8% 2 7% 4 4 5% 3 5% 6% 37%	1520
	11th to 20th	Night	17% 9% 2 6% 4 4 4 4 5% 9% 37%	1520
	21st to end	Night	17% 7% 2 6% 5% 4 4 3 8% 8% 37%	1520
July	1st to 10th	Night	10% 6% 3 7% 5% 5% 6% 4 8% 9% 37%	2520
	11th to 20th	Night	9% 6% 2 8% 5% 6% 6% 5% 7% 9% 38%	2520
	21st to end	Night	16% 9% 4 8% 4 4 5% 3 6% 7% 35%	2739
August	1st to 10th	Night	17% 7% 3 8% 5% 5% 6% 4 6% 8% 31%	2811
	11th to 20th	Night	10% 9% 3 8% 5% 5% 6% 5% 7% 8% 34%	2782
	21st to end	Night	9% 5% 2 5% 4 4 4 3 6% 8% 51%	3434
September	1st to 10th	Night	12% 6% 3 5% 4 4 4 3 5% 7% 48%	1931
	11th to 20th	Night	14% 5% 2 5% 3 3 3 2 4 5% 54%	2090
	21st to end	Night	16% 5% 2 5% 4 4 4 4 5% 7% 44%	2090
October	1st to 10th	Night	20% 5% 2 7% 4 4 3 3 5% 6% 41%	2090
	11th to 20th	Night	15% 7% 2 5% 3 4 4 3 5% 7% 46%	2313
	21st to end	Night	22% 8% 2 5% 4 3 3 3 5% 6% 40%	2717
November	1st to 10th	Night	15% 5% 2 6% 4 4 4 3 5% 6% 46%	2505
	11th to 20th	Night	17% 7% 2 5% 3 3 3 3 4 6% 45%	2470
	21st to end	Night	16% 7% 2 5% 4 4 3 4 5% 7% 42%	2470
December	1st to 10th	Night	21% 9% 3 6% 5% 4 4 4 4 5% 36%	2588
	11th to 20th	Night	19% 8% 2 5% 3 3 4 4 6% 7% 39%	3288
	21st to end	Night	21% 11% 3 6% 4 3 3 3 5% 6% 35%	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	41% 4 12% 32% 10% 1	2518
	11th to 20th	Day	44% 6% 12% 26% 12% 1	2520
	21st to end	Day	53% 6% 12% 21% 7% 1	2772
February	1st to 10th	Day	49% 6% 13% 18% 12% 2	1764
	11th to 20th	Day	43% 6% 14% 22% 13% 2	1857
	21st to end	Day	46% 6% 13% 19% 13% 3	1570
March	1st to 10th	Day	56% 5% 10% 15% 12% 2	3119
	11th to 20th	Day	38% 7% 16% 23% 14% 3	3380
	21st to end	Day	51% 4 7% 16% 15% 7%	3960
April	1st to 10th	Day	45% 5% 9% 20% 18% 4	2280
	11th to 20th	Day	42% 6% 11% 24% 15% 3	2302
	21st to end	Day	43% 6% 10% 22% 17% 3	2470
May	1st to 10th	Day	53% 8% 11% 17% 10% 1	4120
	11th to 20th	Day	52% 6% 13% 17% 10% 2	4085
	21st to end	Day	36% 7% 13% 25% 19% 1	4836
June	1st to 10th	Day	45% 7% 13% 22% 12% 1	2660
	11th to 20th	Day	40% 6% 14% 21% 17% 2	2660
	21st to end	Day	42% 7% 15% 22% 13% 1	2660
July	1st to 10th	Day	42% 6% 14% 21% 16% 1	4370
	11th to 20th	Day	38% 5% 17% 25% 14% 1	4365
	21st to end	Day	42% 6% 14% 23% 13% 2	4644
August	1st to 10th	Day	42% 7% 18% 25% 8%	4092
	11th to 20th	Day	42% 5% 13% 28% 11%	4084
	21st to end	Day	29% 5% 13% 33% 19% 1	4219
September	1st to 10th	Day	34% 6% 12% 27% 21% 1	2248
	11th to 20th	Day	34% 4 10% 27% 23% 3	2090
	21st to end	Day	40% 4 10% 23% 21% 2	2090
October	1st to 10th	Day	41% 3 9% 26% 19% 2	3480
	11th to 20th	Day	31% 3 7% 31% 24% 4	3064
	21st to end	Day	32% 3 11% 31% 20% 2	3081
November	1st to 10th	Day	39% 4 14% 25% 16% 2	1734
	11th to 20th	Day	41% 4 10% 23% 20% 2	1710
	21st to end	Day	42% 6% 16% 22% 13% 1	1710
December	1st to 10th	Day	48% 5% 15% 15% 16% 1	1591
	11th to 20th	Day	47% 6% 13% 16% 15% 4	1906
	21st to end	Day	53% 5% 11% 20% 10% 1	2772
January	1st to 10th	Night	41% 5% 14% 27% 11% 2	4429
	11th to 20th	Night	48% 5% 12% 21% 12% 2	4440
	21st to end	Night	59% 5% 10% 16% 10% 1	4884
February	1st to 10th	Night	48% 7% 14% 18% 11% 2	2410
	11th to 20th	Night	47% 5% 11% 20% 15% 3	2220
	21st to end	Night	45% 3 11% 24% 13% 4	1884
March	1st to 10th	Night	56% 4 9% 17% 11% 3	3734
	11th to 20th	Night	45% 7% 12% 17% 17% 2	3579
	21st to end	Night	54% 4 6% 14% 15% 7%	3669
April	1st to 10th	Night	48% 5% 10% 16% 17% 3	1900
	11th to 20th	Night	46% 4 9% 20% 18% 3	1826
	21st to end	Night	48% 6% 9% 17% 17% 3	1710
May	1st to 10th	Night	56% 7% 12% 16% 8% 2	2840
	11th to 20th	Night	55% 8% 14% 12% 8% 2	2814
	21st to end	Night	43% 7% 14% 19% 16% 1	2754
June	1st to 10th	Night	48% 7% 11% 21% 13%	1520
	11th to 20th	Night	44% 7% 13% 20% 15% 1	1520
	21st to end	Night	42% 10% 12% 22% 13% 2	1520
July	1st to 10th	Night	42% 6% 13% 21% 17%	2480
	11th to 20th	Night	41% 5% 16% 23% 14% 1	2472
	21st to end	Night	49% 5% 11% 20% 14% 1	2651
August	1st to 10th	Night	51% 5% 13% 20% 9% 1	2800
	11th to 20th	Night	45% 7% 14% 24% 10%	2809
	21st to end	Night	31% 4 14% 27% 23% 1	3434
September	1st to 10th	Night	35% 6% 13% 25% 20% 1	1931
	11th to 20th	Night	33% 5% 10% 25% 25% 2	2090
	21st to end	Night	38% 6% 9% 25% 20% 2	2090
October	1st to 10th	Night	43% 3 12% 26% 14% 2	3480
	11th to 20th	Night	29% 3 11% 27% 28% 3	3849
	21st to end	Night	34% 3 11% 30% 19% 2	4467
November	1st to 10th	Night	39% 6% 12% 24% 17% 3	2505
	11th to 20th	Night	41% 4 12% 22% 18% 3	2470
	21st to end	Night	42% 5% 15% 24% 12% 2	2470
December	1st to 10th	Night	49% 6% 13% 20% 11% 1	2588
	11th to 20th	Night	45% 6% 16% 16% 17% 1	3288
	21st to end	Night	50% 6% 11% 24% 10%	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% 7% 31% 29% 7% 1	180
	11th to 20th	Day	19% 12% 32% 29% 8% 1	180
	21st to end	Day	21% 5% 34% 28% 11% 2	198
February	1st to 10th	Day	25% 10% 33% 27% 5%	386
	11th to 20th	Day	20% 8% 43% 24% 5%	456
	21st to end	Day	19% 9% 29% 35% 8% 1	382
March	1st to 10th	Day	20% 8% 29% 33% 10%	460
	11th to 20th	Day	16% 9% 31% 36% 7%	460
	21st to end	Day	24% 6% 27% 30% 9% 3	506
April	1st to 10th	Day	23% 7% 26% 29% 12% 2	460
	11th to 20th	Day	20% 4 19% 43% 12% 1	452
	21st to end	Day	22% 3 17% 41% 15% 2	460
May	1st to 10th	Day	25% 3 19% 36% 14% 3	463
	11th to 20th	Day	17% 2 16% 40% 20% 5%	487
	21st to end	Day	17% 2 10% 36% 29% 6%	529
June	1st to 10th	Day	18% 3 7% 40% 27% 6%	490
	11th to 20th	Day	15% 3 9% 39% 28% 6%	490
	21st to end	Day	15% 2 9% 40% 28% 6%	490
July	1st to 10th	Day	15% 2 5% 32% 37% 9%	485
	11th to 20th	Day	11% 2 7% 32% 39% 10%	484
	21st to end	Day	12% 1 5% 36% 42% 4	532
August	1st to 10th	Day	11% 2 7% 31% 42% 7%	486
	11th to 20th	Day	13% 2 6% 35% 32% 13%	479
	21st to end	Day	12% 1 7% 32% 37% 10%	539
September	1st to 10th	Day	17% 1 11% 30% 28% 12%	490
	11th to 20th	Day	19% 2 12% 28% 27% 12%	490
	21st to end	Day	20% 1 13% 36% 23% 7%	490
October	1st to 10th	Day	24% 1 17% 27% 24% 7%	490
	11th to 20th	Day	14% 4 26% 28% 24% 4	416
	21st to end	Day	25% 4 24% 32% 13% 1	429
November	1st to 10th	Day	15% 6% 24% 36% 17% 3	386
	11th to 20th	Day	23% 9% 28% 29% 11%	370
	21st to end	Day	23% 7% 30% 26% 12% 2	370
December	1st to 10th	Day	21% 7% 38% 26% 8%	251
	11th to 20th	Day	21% 6% 38% 29% 6%	180
	21st to end	Day	24% 8% 31% 28% 8% 1	198
January	1st to 10th	Night	22% 12% 41% 21% 4	760
	11th to 20th	Night	26% 13% 36% 21% 4	760
	21st to end	Night	19% 13% 40% 24% 5%	836
February	1st to 10th	Night	22% 12% 37% 26% 3	760
	11th to 20th	Night	21% 12% 44% 20% 4	743
	21st to end	Night	22% 10% 37% 23% 7%	628
March	1st to 10th	Night	23% 9% 37% 25% 6%	760
	11th to 20th	Night	21% 7% 36% 27% 8% 1	760
	21st to end	Night	23% 8% 32% 26% 10% 1	836
April	1st to 10th	Night	24% 5% 29% 33% 10%	760
	11th to 20th	Night	20% 3 28% 36% 12%	702
	21st to end	Night	22% 3 25% 35% 15% 1	570
May	1st to 10th	Night	24% 3 19% 38% 13% 2	570
	11th to 20th	Night	23% 1 18% 38% 17% 2	562
	21st to end	Night	21% 3 10% 42% 22% 2	426
June	1st to 10th	Night	22% 2 13% 38% 22% 4	380
	11th to 20th	Night	18% 3 11% 41% 25% 2	380
	21st to end	Night	20% 1 10% 43% 24% 2	380
July	1st to 10th	Night	15% 2 6% 40% 33% 4	370
	11th to 20th	Night	13% 2 6% 39% 36% 4	368
	21st to end	Night	15% 2 7% 38% 35% 2	416
August	1st to 10th	Night	10% 3 8% 40% 36% 3	554
	11th to 20th	Night	12% 1 9% 41% 31% 5%	562
	21st to end	Night	14% 1 12% 29% 37% 7%	807
September	1st to 10th	Night	14% 1 14% 37% 30% 5%	760
	11th to 20th	Night	16% 3 15% 31% 26% 9%	760
	21st to end	Night	19% 2 15% 33% 25% 6%	760
October	1st to 10th	Night	23% 4 19% 29% 20% 5%	760
	11th to 20th	Night	17% 5% 28% 32% 16% 2	760
	21st to end	Night	24% 6% 31% 29% 9% 1	836
November	1st to 10th	Night	18% 5% 30% 34% 13% 2	771
	11th to 20th	Night	20% 11% 34% 25% 8% 1	760
	21st to end	Night	19% 14% 34% 26% 7% 1	760
December	1st to 10th	Night	24% 11% 38% 22% 5%	760
	11th to 20th	Night	23% 13% 38% 22% 4	760
	21st to end	Night	24% 13% 37% 22% 3	836

Page generated at 2024-11-05 08:15:49. Version ac07

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