Roxbury Airport
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Roxbury Airport clear sky chart from 2005-11-06 to 2024-12-02.

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	18% 7% 2 6% 4 4 4 4 5% 7% 38%	101521
	Night	18% 8% 2 6% 4 4 4 3 5% 6% 40%	98128
Transparency	Day	43% 6% 12% 22% 15% 2	105067
	Night	43% 6% 12% 23% 15% 2	102671
Seeing	Day	24% 17% 30% 19% 8% 2	15061
	Night	22% 15% 31% 24% 7% 1	24140

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	15% 8% 3 6% 3 5% 4 3 4 5% 46%	2517
	11th to 20th	Day	17% 9% 4 7% 4 5% 5% 4 5% 5% 35%	2520
	21st to end	Day	22% 12% 4 8% 4 3 4 3 4 4 31%	2877
February	1st to 10th	Day	18% 8% 2 7% 4 5% 5% 4 6% 6% 36%	1748
	11th to 20th	Day	15% 7% 2 6% 4 5% 3 4 5% 7% 41%	1848
	21st to end	Day	20% 10% 2 7% 4 3 5% 3 4 6% 36%	1570
March	1st to 10th	Day	27% 11% 2 6% 4 3 3 2 3 5% 33%	3116
	11th to 20th	Day	12% 4 2 6% 5% 5% 6% 5% 7% 7% 42%	3271
	21st to end	Day	21% 7% 2 6% 4 4 4 3 5% 6% 38%	4166
April	1st to 10th	Day	19% 8% 3 6% 5% 4 4 4 5% 6% 37%	2280
	11th to 20th	Day	19% 6% 2 5% 4 4 4 3 5% 7% 40%	2254
	21st to end	Day	21% 6% 2 6% 4 4 4 3 5% 5% 40%	2365
May	1st to 10th	Day	28% 8% 3 6% 3 4 3 3 6% 7% 30%	4106
	11th to 20th	Day	22% 7% 2 6% 5% 5% 3 4 5% 6% 33%	4324
	21st to end	Day	16% 5% 1 5% 3 4 4 4 6% 8% 45%	4837
June	1st to 10th	Day	18% 6% 2 4 5% 5% 5% 4 7% 8% 35%	2660
	11th to 20th	Day	17% 7% 2 6% 5% 4 4 5% 7% 8% 36%	2660
	21st to end	Day	13% 6% 2 7% 5% 5% 5% 4 7% 9% 37%	2660
July	1st to 10th	Day	12% 7% 2 7% 6% 5% 6% 4 7% 9% 35%	4440
	11th to 20th	Day	13% 6% 2 6% 4 5% 5% 5% 7% 9% 39%	4440
	21st to end	Day	17% 8% 3 7% 5% 5% 5% 4 7% 7% 32%	4814
August	1st to 10th	Day	21% 7% 3 7% 5% 4 5% 4 7% 8% 31%	4280
	11th to 20th	Day	13% 6% 3 6% 5% 4 4 4 6% 9% 40%	3730
	21st to end	Day	10% 5% 2 6% 4 4 5% 4 6% 9% 45%	4180
September	1st to 10th	Day	14% 6% 3 6% 4 5% 4 4 5% 6% 43%	2280
	11th to 20th	Day	13% 6% 2 5% 3 3 4 3 5% 7% 50%	2166
	21st to end	Day	19% 6% 2 6% 4 4 4 4 5% 6% 41%	2090
October	1st to 10th	Day	22% 7% 2 5% 4 3 3 4 5% 5% 40%	2033
	11th to 20th	Day	14% 6% 2 6% 4 3 4 4 5% 6% 47%	1900
	21st to end	Day	22% 6% 2 4 5% 4 4 4 5% 5% 40%	1882
November	1st to 10th	Day	14% 6% 2 5% 4 3 2 3 4 7% 49%	1761
	11th to 20th	Day	18% 6% 2 4 3 4 3 3 5% 6% 46%	1800
	21st to end	Day	18% 7% 2 6% 4 3 3 3 6% 6% 42%	1740
December	1st to 10th	Day	20% 8% 2 6% 5% 4 3 3 5% 6% 37%	1528
	11th to 20th	Day	23% 6% 2 4 2 3 3 3 5% 6% 42%	1906
	21st to end	Day	19% 11% 3 7% 5% 5% 4 3 5% 6% 32%	2772
January	1st to 10th	Night	17% 7% 2 5% 4 3 3 3 5% 6% 45%	4429
	11th to 20th	Night	17% 8% 3 7% 4 4 4 3 5% 5% 41%	4440
	21st to end	Night	24% 13% 3 6% 3 3 3 3 4 5% 32%	4774
February	1st to 10th	Night	16% 9% 3 6% 4 4 4 3 4 5% 40%	2431
	11th to 20th	Night	15% 8% 4 6% 4 4 3 4 5% 6% 41%	2218
	21st to end	Night	20% 8% 2 6% 4 4 3 3 4 5% 41%	1884
March	1st to 10th	Night	25% 12% 2 6% 3 3 3 3 4 5% 34%	3724
	11th to 20th	Night	11% 7% 2 7% 5% 5% 4 4 5% 6% 44%	3683
	21st to end	Night	21% 8% 3 6% 3 3 3 3 4 5% 41%	3466
April	1st to 10th	Night	19% 8% 3 5% 4 4 5% 4 5% 7% 36%	1900
	11th to 20th	Night	20% 6% 2 5% 5% 4 4 4 5% 6% 39%	1875
	21st to end	Night	20% 7% 3 6% 5% 3 3 2 5% 5% 42%	1814
May	1st to 10th	Night	25% 10% 3 7% 5% 4 3 3 5% 7% 28%	2834
	11th to 20th	Night	22% 9% 3 8% 5% 4 4 3 5% 6% 32%	2597
	21st to end	Night	17% 7% 2 5% 3 3 4 3 6% 6% 43%	2738
June	1st to 10th	Night	18% 6% 2 5% 5% 4 4 4 4 7% 40%	1520
	11th to 20th	Night	17% 6% 2 5% 4 3 4 4 5% 10% 40%	1520
	21st to end	Night	15% 6% 2 5% 3 5% 4 4 5% 10% 42%	1520
July	1st to 10th	Night	14% 5% 2 6% 4 4 6% 4 8% 8% 39%	2520
	11th to 20th	Night	17% 7% 2 6% 5% 4 4 4 6% 9% 37%	2520
	21st to end	Night	19% 8% 2 6% 5% 4 5% 4 6% 6% 35%	2739
August	1st to 10th	Night	24% 8% 2 7% 5% 4 4 4 6% 6% 31%	2614
	11th to 20th	Night	16% 6% 2 6% 5% 4 4 3 5% 7% 41%	3097
	21st to end	Night	12% 5% 1 4 3 3 3 3 5% 8% 53%	3476
September	1st to 10th	Night	16% 7% 2 5% 4 4 3 3 4 6% 46%	1900
	11th to 20th	Night	14% 5% 2 4 3 3 3 3 4 6% 54%	2014
	21st to end	Night	18% 7% 2 4 3 3 5% 3 5% 4 44%	2090
October	1st to 10th	Night	20% 7% 3 6% 4 3 3 3 5% 6% 42%	2143
	11th to 20th	Night	15% 5% 2 5% 4 4 3 3 4 6% 48%	2280
	21st to end	Night	22% 6% 2 4 4 3 3 3 5% 6% 41%	2714
November	1st to 10th	Night	13% 6% 2 6% 4 3 4 3 5% 6% 49%	2537
	11th to 20th	Night	18% 7% 2 4 4 3 4 2 4 5% 46%	2600
	21st to end	Night	15% 7% 2 5% 4 4 4 3 4 6% 45%	2659
December	1st to 10th	Night	21% 7% 2 6% 4 3 4 3 5% 6% 39%	2686
	11th to 20th	Night	20% 8% 2 5% 3 4 4 4 5% 6% 39%	3288
	21st to end	Night	23% 11% 3 6% 4 3 3 3 5% 5% 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	39% 6% 11% 33% 10% 2	2518
	11th to 20th	Day	50% 6% 10% 23% 9% 1	2520
	21st to end	Day	55% 5% 8% 20% 10% 2	2877
February	1st to 10th	Day	47% 6% 13% 20% 13% 1	1748
	11th to 20th	Day	42% 5% 11% 23% 16% 3	1857
	21st to end	Day	49% 4 11% 21% 13% 3	1570
March	1st to 10th	Day	54% 4 11% 18% 11% 2	3119
	11th to 20th	Day	34% 8% 16% 30% 11% 1	3271
	21st to end	Day	46% 4 7% 17% 20% 6%	4166
April	1st to 10th	Day	47% 6% 10% 20% 14% 3	2280
	11th to 20th	Day	43% 6% 11% 21% 16% 3	2254
	21st to end	Day	44% 6% 10% 21% 15% 4	2365
May	1st to 10th	Day	53% 7% 13% 14% 12% 1	4120
	11th to 20th	Day	50% 9% 12% 19% 9% 1	4328
	21st to end	Day	35% 8% 12% 26% 17% 2	4837
June	1st to 10th	Day	44% 7% 14% 22% 12% 1	2660
	11th to 20th	Day	43% 8% 14% 23% 11% 1	2660
	21st to end	Day	41% 8% 15% 22% 13% 1	2660
July	1st to 10th	Day	44% 8% 11% 20% 16% 1	4370
	11th to 20th	Day	40% 7% 16% 23% 13% 1	4365
	21st to end	Day	49% 7% 12% 16% 14% 1	4661
August	1st to 10th	Day	50% 7% 14% 21% 8%	4266
	11th to 20th	Day	39% 7% 15% 29% 10% 1	3766
	21st to end	Day	35% 6% 12% 30% 15% 1	4180
September	1st to 10th	Day	40% 8% 10% 22% 19% 1	2280
	11th to 20th	Day	34% 6% 10% 24% 24% 2	2166
	21st to end	Day	43% 6% 10% 20% 17% 3	2090
October	1st to 10th	Day	39% 5% 9% 18% 25% 4	3384
	11th to 20th	Day	29% 4 9% 25% 29% 4	3140
	21st to end	Day	32% 4 15% 24% 22% 3	3082
November	1st to 10th	Day	36% 4 13% 26% 19% 2	1761
	11th to 20th	Day	38% 4 12% 23% 20% 4	1800
	21st to end	Day	41% 4 14% 27% 11% 2	1740
December	1st to 10th	Day	48% 5% 14% 18% 14% 1	1528
	11th to 20th	Day	42% 5% 15% 20% 15% 2	1906
	21st to end	Day	53% 6% 10% 22% 9% 1	2772
January	1st to 10th	Night	40% 4 12% 30% 11% 3	4429
	11th to 20th	Night	44% 5% 13% 24% 11% 3	4440
	21st to end	Night	55% 4 9% 20% 11% 2	4774
February	1st to 10th	Night	46% 5% 13% 23% 12% 2	2431
	11th to 20th	Night	44% 5% 10% 20% 17% 4	2220
	21st to end	Night	45% 4 9% 23% 14% 4	1884
March	1st to 10th	Night	52% 5% 10% 19% 11% 2	3734
	11th to 20th	Night	37% 7% 15% 24% 15% 2	3684
	21st to end	Night	45% 4 7% 14% 24% 5%	3466
April	1st to 10th	Night	45% 7% 11% 21% 14% 3	1900
	11th to 20th	Night	44% 6% 11% 19% 19% 1	1875
	21st to end	Night	44% 6% 9% 22% 15% 4	1814
May	1st to 10th	Night	55% 7% 12% 15% 9% 1	2840
	11th to 20th	Night	52% 10% 12% 16% 10% 1	2598
	21st to end	Night	40% 7% 15% 24% 13% 2	2739
June	1st to 10th	Night	45% 6% 9% 22% 16% 1	1520
	11th to 20th	Night	39% 9% 15% 25% 11% 1	1520
	21st to end	Night	37% 9% 14% 25% 14% 1	1520
July	1st to 10th	Night	41% 9% 16% 18% 15% 1	2480
	11th to 20th	Night	43% 8% 15% 22% 12%	2472
	21st to end	Night	48% 7% 13% 15% 16% 2	2651
August	1st to 10th	Night	53% 8% 13% 17% 8% 1	2604
	11th to 20th	Night	43% 7% 14% 29% 8% 1	3127
	21st to end	Night	30% 7% 13% 35% 16% 1	3476
September	1st to 10th	Night	40% 6% 9% 25% 18% 1	1900
	11th to 20th	Night	32% 6% 11% 24% 25% 2	2014
	21st to end	Night	41% 6% 9% 21% 20% 2	2090
October	1st to 10th	Night	39% 5% 12% 22% 20% 2	3572
	11th to 20th	Night	27% 4 9% 27% 28% 4	3779
	21st to end	Night	34% 4 14% 29% 18% 2	4464
November	1st to 10th	Night	36% 5% 12% 22% 21% 4	2537
	11th to 20th	Night	41% 4 10% 23% 19% 4	2600
	21st to end	Night	40% 5% 14% 29% 12% 1	2659
December	1st to 10th	Night	45% 6% 12% 23% 13% 1	2686
	11th to 20th	Night	44% 6% 14% 19% 15% 2	3288
	21st to end	Night	51% 5% 12% 21% 11%	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	34% 22% 28% 14% 2	180
	11th to 20th	Day	32% 32% 25% 11% 1	180
	21st to end	Day	25% 30% 31% 9% 5%	229
February	1st to 10th	Day	34% 28% 27% 10% 1	308
	11th to 20th	Day	30% 27% 32% 10% 1	456
	21st to end	Day	33% 24% 30% 10% 3	382
March	1st to 10th	Day	30% 20% 34% 13% 3	460
	11th to 20th	Day	29% 27% 30% 11% 2 1	460
	21st to end	Day	32% 23% 31% 10% 3 2	506
April	1st to 10th	Day	32% 26% 24% 10% 7% 1	460
	11th to 20th	Day	31% 21% 29% 13% 5% 1	452
	21st to end	Day	30% 20% 32% 13% 5% 1	460
May	1st to 10th	Day	34% 20% 28% 11% 6% 1	463
	11th to 20th	Day	24% 18% 35% 17% 5% 1	487
	21st to end	Day	21% 11% 32% 24% 10% 2	529
June	1st to 10th	Day	22% 12% 32% 23% 10% 2	490
	11th to 20th	Day	18% 14% 34% 21% 11% 1	490
	21st to end	Day	17% 13% 32% 26% 11% 1	490
July	1st to 10th	Day	16% 7% 33% 27% 14% 3	485
	11th to 20th	Day	12% 9% 33% 29% 15% 2	484
	21st to end	Day	12% 12% 36% 28% 12% 1	532
August	1st to 10th	Day	15% 9% 28% 32% 11% 5%	486
	11th to 20th	Day	15% 8% 28% 31% 13% 5%	479
	21st to end	Day	11% 11% 31% 25% 15% 6%	539
September	1st to 10th	Day	19% 12% 26% 21% 15% 6%	490
	11th to 20th	Day	15% 11% 28% 26% 11% 9%	490
	21st to end	Day	22% 14% 30% 20% 9% 4	490
October	1st to 10th	Day	30% 10% 28% 15% 13% 4	490
	11th to 20th	Day	16% 23% 30% 22% 8% 2	490
	21st to end	Day	29% 14% 29% 18% 7% 1	429
November	1st to 10th	Day	22% 17% 28% 24% 8% 2	395
	11th to 20th	Day	29% 22% 28% 17% 4 1	400
	21st to end	Day	27% 22% 29% 17% 5%	340
December	1st to 10th	Day	30% 21% 32% 13% 4	182
	11th to 20th	Day	39% 23% 25% 11% 1	180
	21st to end	Day	28% 27% 26% 14% 4 2	198
January	1st to 10th	Night	25% 19% 38% 16% 3	760
	11th to 20th	Night	27% 21% 31% 19% 2	760
	21st to end	Night	23% 23% 35% 17% 3	836
February	1st to 10th	Night	25% 20% 35% 18% 2	760
	11th to 20th	Night	26% 23% 37% 13% 1	743
	21st to end	Night	29% 21% 30% 17% 3	628
March	1st to 10th	Night	26% 20% 34% 17% 3	760
	11th to 20th	Night	23% 25% 33% 16% 2 1	760
	21st to end	Night	25% 22% 33% 16% 4	836
April	1st to 10th	Night	26% 21% 32% 18% 2	760
	11th to 20th	Night	23% 21% 33% 19% 3	751
	21st to end	Night	24% 21% 34% 17% 4 1	674
May	1st to 10th	Night	28% 15% 32% 20% 5%	570
	11th to 20th	Night	22% 18% 34% 23% 3	437
	21st to end	Night	20% 9% 29% 33% 8% 1	411
June	1st to 10th	Night	21% 8% 32% 29% 10% 1	380
	11th to 20th	Night	17% 8% 30% 33% 11%	380
	21st to end	Night	17% 5% 27% 41% 10%	380
July	1st to 10th	Night	15% 5% 23% 38% 20%	370
	11th to 20th	Night	13% 5% 25% 41% 14% 2	368
	21st to end	Night	14% 4 27% 39% 15%	416
August	1st to 10th	Night	12% 4 28% 40% 15% 1	434
	11th to 20th	Night	16% 7% 22% 36% 19% 2	750
	21st to end	Night	16% 6% 21% 37% 18% 2	836
September	1st to 10th	Night	17% 6% 30% 32% 12% 2	760
	11th to 20th	Night	16% 8% 24% 31% 18% 3	760
	21st to end	Night	23% 8% 26% 26% 15% 2	760
October	1st to 10th	Night	23% 11% 27% 25% 12% 1	760
	11th to 20th	Night	18% 15% 32% 26% 9% 1	760
	21st to end	Night	27% 13% 32% 20% 7%	836
November	1st to 10th	Night	18% 15% 33% 25% 8% 1	780
	11th to 20th	Night	23% 18% 33% 19% 7% 1	800
	21st to end	Night	24% 18% 30% 22% 5% 1	800
December	1st to 10th	Night	28% 17% 31% 19% 4 1	768
	11th to 20th	Night	25% 22% 29% 21% 3	760
	21st to end	Night	29% 18% 34% 17% 2	836

Page generated at 2024-11-29 10:43:09. Version ac07

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