New England Sci-Tech Astronomy
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the New England Sci-Tech Astronomy clear sky chart from 2005-11-06 to 2024-11-25.

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% 38%	101396
	Night	18% 8% 3 6% 4 4 4 3 5% 6% 39%	98091
Transparency	Day	44% 5% 11% 23% 16% 2	104947
	Night	44% 5% 11% 22% 16% 2	102629
Seeing	Day	24% 14% 33% 20% 8% 2	15118
	Night	22% 12% 33% 25% 7% 1	24026

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% 2 7% 4 3 4 3 4 5% 45%	2517
	11th to 20th	Day	16% 7% 3 7% 3 4 4 4 5% 5% 41%	2520
	21st to end	Day	21% 11% 3 5% 4 4 4 3 6% 5% 34%	2772
February	1st to 10th	Day	20% 7% 3 6% 5% 5% 5% 3 6% 5% 36%	1775
	11th to 20th	Day	12% 9% 2 6% 6% 4 5% 4 4 7% 40%	1848
	21st to end	Day	19% 10% 2 6% 5% 5% 4 3 5% 5% 37%	1570
March	1st to 10th	Day	24% 15% 3 6% 4 4 3 3 4 5% 30%	3116
	11th to 20th	Day	13% 6% 2 6% 4 5% 5% 4 6% 8% 41%	3338
	21st to end	Day	22% 10% 3 6% 4 4 4 4 6% 6% 33%	4028
April	1st to 10th	Day	19% 8% 3 7% 5% 4 4 3 4 6% 37%	2280
	11th to 20th	Day	19% 7% 2 5% 5% 4 5% 3 6% 7% 38%	2265
	21st to end	Day	20% 6% 3 7% 5% 4 4 3 5% 6% 36%	2470
May	1st to 10th	Day	24% 11% 3 7% 5% 4 4 3 5% 7% 27%	4106
	11th to 20th	Day	23% 8% 3 7% 4 4 4 3 5% 7% 32%	4140
	21st to end	Day	15% 5% 2 5% 4 4 4 4 5% 9% 44%	4837
June	1st to 10th	Day	19% 6% 2 6% 5% 4 4 4 6% 9% 35%	2660
	11th to 20th	Day	16% 6% 2 6% 4 5% 5% 4 7% 7% 37%	2660
	21st to end	Day	16% 6% 2 7% 4 5% 5% 4 6% 8% 35%	2660
July	1st to 10th	Day	14% 6% 2 7% 6% 5% 5% 5% 6% 9% 35%	4440
	11th to 20th	Day	11% 6% 2 7% 4 5% 5% 4 6% 9% 40%	4440
	21st to end	Day	17% 7% 3 7% 5% 4 5% 4 5% 7% 36%	4814
August	1st to 10th	Day	15% 5% 3 7% 5% 6% 5% 5% 6% 9% 33%	4146
	11th to 20th	Day	13% 8% 3 7% 4 5% 5% 4 5% 7% 38%	3987
	21st to end	Day	8% 4 2 6% 4 5% 5% 4 7% 9% 47%	4180
September	1st to 10th	Day	14% 6% 1 5% 4 4 4 4 5% 7% 46%	2275
	11th to 20th	Day	15% 6% 2 4 3 3 3 3 4 6% 51%	2090
	21st to end	Day	18% 6% 2 6% 4 3 4 3 5% 6% 44%	2090
October	1st to 10th	Day	24% 5% 2 5% 3 3 4 3 4 6% 41%	2090
	11th to 20th	Day	15% 6% 2 5% 4 3 3 3 4 7% 47%	1858
	21st to end	Day	20% 7% 2 5% 3 4 4 3 5% 6% 41%	1881
November	1st to 10th	Day	16% 6% 2 5% 3 4 3 2 4 4 50%	1761
	11th to 20th	Day	18% 7% 2 4 3 3 3 3 5% 4 48%	1800
	21st to end	Day	18% 7% 2 5% 4 3 5% 3 5% 6% 43%	1746
December	1st to 10th	Day	18% 8% 3 6% 5% 4 4 4 4 5% 40%	1558
	11th to 20th	Day	22% 7% 2 4 3 4 3 3 4 5% 44%	1906
	21st to end	Day	22% 11% 3 6% 4 4 4 3 5% 5% 34%	2772
January	1st to 10th	Night	17% 8% 2 5% 3 3 3 3 3 5% 47%	4429
	11th to 20th	Night	15% 10% 3 9% 4 4 4 3 4 6% 39%	4440
	21st to end	Night	21% 14% 3 7% 5% 4 4 2 4 4 30%	4884
February	1st to 10th	Night	16% 10% 2 7% 4 4 3 4 5% 6% 38%	2398
	11th to 20th	Night	15% 9% 3 6% 5% 4 4 4 4 7% 39%	2218
	21st to end	Night	19% 9% 2 6% 4 3 3 3 4 6% 41%	1884
March	1st to 10th	Night	28% 11% 2 5% 3 4 3 3 4 5% 32%	3724
	11th to 20th	Night	11% 9% 3 7% 5% 5% 4 4 5% 6% 40%	3620
	21st to end	Night	24% 9% 2 5% 4 4 4 4 5% 5% 34%	3600
April	1st to 10th	Night	18% 8% 3 7% 5% 4 4 3 5% 5% 37%	1900
	11th to 20th	Night	19% 8% 2 6% 4 5% 3 3 4 6% 40%	1862
	21st to end	Night	21% 8% 3 5% 5% 3 4 3 4 5% 40%	1710
May	1st to 10th	Night	24% 10% 4 8% 4 3 4 4 5% 7% 27%	2834
	11th to 20th	Night	22% 8% 3 7% 5% 5% 5% 4 6% 8% 26%	2781
	21st to end	Night	16% 6% 3 6% 4 4 3 3 6% 8% 41%	2738
June	1st to 10th	Night	16% 8% 3 7% 5% 4 5% 3 5% 7% 37%	1520
	11th to 20th	Night	18% 6% 2 6% 5% 4 4 3 6% 8% 36%	1520
	21st to end	Night	15% 6% 2 6% 4 5% 4 4 6% 10% 40%	1520
July	1st to 10th	Night	12% 6% 2 7% 5% 4 6% 5% 8% 9% 35%	2520
	11th to 20th	Night	12% 7% 3 8% 5% 4 4 4 7% 9% 39%	2520
	21st to end	Night	15% 8% 4 7% 5% 4 4 4 5% 7% 36%	2739
August	1st to 10th	Night	19% 7% 3 8% 5% 4 5% 5% 6% 7% 32%	2752
	11th to 20th	Night	10% 7% 3 7% 6% 6% 6% 4 6% 8% 37%	2836
	21st to end	Night	9% 4 1 4 4 3 4 3 5% 8% 56%	3476
September	1st to 10th	Night	14% 5% 2 6% 4 3 4 3 6% 6% 47%	1905
	11th to 20th	Night	14% 5% 2 4 3 3 3 3 4 6% 52%	2090
	21st to end	Night	18% 6% 2 6% 4 3 4 4 5% 5% 43%	2090
October	1st to 10th	Night	20% 6% 2 6% 4 3 3 3 4 5% 42%	2090
	11th to 20th	Night	15% 5% 2 6% 3 4 4 3 5% 5% 48%	2317
	21st to end	Night	21% 8% 2 6% 3 4 3 3 5% 7% 39%	2717
November	1st to 10th	Night	14% 5% 2 5% 3 4 4 3 5% 5% 49%	2537
	11th to 20th	Night	18% 7% 2 5% 3 3 4 3 4 5% 47%	2600
	21st to end	Night	17% 6% 2 5% 4 3 4 4 4 6% 44%	2529
December	1st to 10th	Night	19% 8% 3 6% 5% 4 3 3 5% 6% 38%	2619
	11th to 20th	Night	20% 7% 2 5% 4 3 4 3 5% 5% 42%	3288
	21st to end	Night	20% 10% 4 6% 4 4 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% 3 7% 33% 13% 2	2518
	11th to 20th	Day	46% 5% 9% 26% 13% 2	2520
	21st to end	Day	52% 5% 9% 23% 11% 2	2772
February	1st to 10th	Day	48% 3 12% 20% 14% 3	1775
	11th to 20th	Day	44% 5% 11% 22% 16% 3	1857
	21st to end	Day	49% 3 9% 20% 15% 3	1570
March	1st to 10th	Day	58% 3 9% 16% 11% 3	3119
	11th to 20th	Day	38% 7% 14% 25% 14% 3	3338
	21st to end	Day	51% 5% 5% 16% 16% 7%	4028
April	1st to 10th	Day	49% 4 8% 19% 17% 4	2280
	11th to 20th	Day	44% 5% 10% 21% 17% 3	2265
	21st to end	Day	48% 4 8% 18% 17% 4	2470
May	1st to 10th	Day	56% 6% 11% 15% 10% 1	4120
	11th to 20th	Day	52% 5% 14% 16% 10% 2	4144
	21st to end	Day	37% 5% 10% 25% 20% 2	4837
June	1st to 10th	Day	46% 6% 12% 25% 11% 1	2660
	11th to 20th	Day	44% 5% 12% 20% 17% 2	2660
	21st to end	Day	46% 6% 12% 21% 15% 1	2660
July	1st to 10th	Day	45% 6% 10% 22% 15% 2	4370
	11th to 20th	Day	40% 5% 15% 25% 13% 2	4365
	21st to end	Day	48% 5% 11% 20% 14% 2	4661
August	1st to 10th	Day	47% 7% 15% 22% 9% 1	4132
	11th to 20th	Day	44% 6% 12% 27% 10% 1	4026
	21st to end	Day	33% 5% 11% 30% 19% 1	4180
September	1st to 10th	Day	38% 5% 10% 25% 21% 2	2275
	11th to 20th	Day	35% 3 7% 28% 23% 3	2090
	21st to end	Day	42% 3 8% 22% 22% 2	2090
October	1st to 10th	Day	41% 4 8% 23% 20% 3	3480
	11th to 20th	Day	32% 3 7% 27% 27% 4	3061
	21st to end	Day	33% 3 11% 30% 20% 3	3081
November	1st to 10th	Day	39% 3 11% 26% 18% 2	1761
	11th to 20th	Day	40% 3 8% 23% 24% 3	1800
	21st to end	Day	42% 4 13% 25% 13% 2	1746
December	1st to 10th	Day	47% 4 14% 16% 18% 1	1558
	11th to 20th	Day	44% 2 13% 18% 17% 5%	1906
	21st to end	Day	52% 5% 11% 20% 11% 1	2772
January	1st to 10th	Night	40% 4 11% 29% 13% 3	4429
	11th to 20th	Night	47% 4 10% 23% 13% 3	4440
	21st to end	Night	57% 4 8% 17% 11% 2	4884
February	1st to 10th	Night	46% 4 12% 21% 14% 2	2398
	11th to 20th	Night	45% 4 9% 21% 17% 4	2220
	21st to end	Night	46% 3 7% 24% 16% 5%	1884
March	1st to 10th	Night	55% 4 7% 20% 12% 3	3734
	11th to 20th	Night	42% 7% 13% 19% 17% 3	3621
	21st to end	Night	53% 4 5% 13% 18% 7%	3600
April	1st to 10th	Night	48% 4 9% 19% 17% 3	1900
	11th to 20th	Night	47% 4 8% 21% 18% 3	1862
	21st to end	Night	47% 3 10% 19% 17% 4	1710
May	1st to 10th	Night	55% 7% 11% 17% 8% 2	2840
	11th to 20th	Night	55% 7% 14% 14% 9% 2	2782
	21st to end	Night	40% 7% 14% 22% 15% 1	2739
June	1st to 10th	Night	47% 6% 12% 23% 12% 1	1520
	11th to 20th	Night	45% 5% 13% 22% 15% 1	1520
	21st to end	Night	40% 7% 13% 24% 14% 1	1520
July	1st to 10th	Night	42% 6% 14% 21% 15% 1	2480
	11th to 20th	Night	41% 6% 15% 24% 14% 1	2472
	21st to end	Night	47% 6% 11% 20% 15% 1	2651
August	1st to 10th	Night	50% 6% 14% 19% 10% 1	2742
	11th to 20th	Night	44% 7% 14% 25% 10%	2863
	21st to end	Night	27% 5% 15% 29% 23% 1	3476
September	1st to 10th	Night	38% 4 11% 25% 20% 2	1905
	11th to 20th	Night	34% 4 9% 24% 27% 2	2090
	21st to end	Night	42% 4 8% 23% 21% 2	2090
October	1st to 10th	Night	40% 4 14% 23% 16% 2	3480
	11th to 20th	Night	27% 3 9% 27% 30% 3	3853
	21st to end	Night	35% 2 11% 31% 19% 2	4467
November	1st to 10th	Night	38% 4 11% 23% 21% 4	2537
	11th to 20th	Night	41% 4 9% 22% 21% 4	2600
	21st to end	Night	41% 3 13% 26% 14% 2	2529
December	1st to 10th	Night	47% 4 12% 22% 14% 1	2619
	11th to 20th	Night	44% 4 14% 18% 19% 2	3288
	21st to end	Night	50% 4 8% 26% 11% 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	27% 21% 31% 15% 6%	180
	11th to 20th	Day	32% 17% 36% 11% 4	180
	21st to end	Day	26% 20% 37% 12% 5%	198
February	1st to 10th	Day	31% 14% 34% 18% 3	373
	11th to 20th	Day	26% 20% 39% 13% 2	456
	21st to end	Day	31% 14% 33% 17% 5% 1	382
March	1st to 10th	Day	30% 15% 33% 18% 3	460
	11th to 20th	Day	29% 19% 32% 14% 4 1	460
	21st to end	Day	31% 17% 34% 8% 8% 2	506
April	1st to 10th	Day	33% 20% 25% 16% 5% 1	460
	11th to 20th	Day	30% 21% 31% 12% 5% 1	452
	21st to end	Day	28% 18% 33% 16% 3 2	460
May	1st to 10th	Day	35% 19% 28% 14% 4 1	463
	11th to 20th	Day	27% 15% 38% 14% 6% 1	487
	21st to end	Day	20% 11% 38% 21% 7% 2	529
June	1st to 10th	Day	23% 10% 39% 18% 8% 2	490
	11th to 20th	Day	17% 13% 39% 23% 6% 1	490
	21st to end	Day	18% 12% 38% 21% 9% 2	490
July	1st to 10th	Day	20% 8% 32% 27% 12% 2	485
	11th to 20th	Day	16% 6% 33% 30% 12% 3	484
	21st to end	Day	15% 7% 38% 31% 8% 1	532
August	1st to 10th	Day	12% 9% 32% 33% 12% 2	486
	11th to 20th	Day	16% 7% 33% 29% 13% 3	479
	21st to end	Day	14% 8% 32% 27% 14% 5%	539
September	1st to 10th	Day	20% 10% 30% 22% 16% 3	490
	11th to 20th	Day	21% 9% 27% 21% 12% 10%	490
	21st to end	Day	24% 10% 31% 21% 9% 5%	490
October	1st to 10th	Day	28% 11% 25% 21% 10% 4	490
	11th to 20th	Day	21% 15% 31% 20% 11% 2	435
	21st to end	Day	27% 13% 33% 19% 8% 1	429
November	1st to 10th	Day	24% 13% 35% 18% 9% 2	395
	11th to 20th	Day	30% 16% 32% 18% 4 1	400
	21st to end	Day	29% 18% 28% 18% 7% 1	382
December	1st to 10th	Day	25% 21% 33% 17% 3	218
	11th to 20th	Day	34% 19% 34% 11% 2	180
	21st to end	Day	28% 18% 34% 14% 4 2	198
January	1st to 10th	Night	23% 16% 39% 19% 3	760
	11th to 20th	Night	29% 16% 35% 18% 3	760
	21st to end	Night	22% 17% 35% 22% 4	836
February	1st to 10th	Night	24% 15% 37% 22% 2	760
	11th to 20th	Night	23% 17% 41% 18% 2	743
	21st to end	Night	26% 16% 33% 21% 3	628
March	1st to 10th	Night	27% 15% 34% 20% 4	760
	11th to 20th	Night	23% 17% 38% 18% 4	760
	21st to end	Night	26% 15% 35% 19% 5%	836
April	1st to 10th	Night	26% 18% 31% 22% 4	760
	11th to 20th	Night	25% 17% 33% 20% 5%	738
	21st to end	Night	24% 16% 35% 21% 3	570
May	1st to 10th	Night	29% 13% 32% 21% 5%	570
	11th to 20th	Night	22% 14% 37% 22% 4	543
	21st to end	Night	21% 7% 35% 31% 5% 1	411
June	1st to 10th	Night	22% 5% 33% 31% 8% 1	380
	11th to 20th	Night	18% 7% 36% 32% 6% 1	380
	21st to end	Night	17% 5% 36% 35% 7%	380
July	1st to 10th	Night	14% 4 32% 38% 11%	370
	11th to 20th	Night	14% 3 32% 39% 13%	368
	21st to end	Night	14% 4 30% 42% 9% 1	416
August	1st to 10th	Night	13% 4 34% 40% 9% 1	520
	11th to 20th	Night	12% 6% 29% 41% 11% 1	590
	21st to end	Night	16% 3 23% 40% 15% 2	836
September	1st to 10th	Night	18% 5% 31% 33% 13% 1	760
	11th to 20th	Night	19% 5% 26% 27% 20% 2	760
	21st to end	Night	21% 7% 26% 31% 12% 2	760
October	1st to 10th	Night	24% 9% 27% 27% 12% 2	760
	11th to 20th	Night	20% 10% 31% 25% 12% 1	760
	21st to end	Night	28% 11% 32% 23% 7%	836
November	1st to 10th	Night	18% 13% 32% 27% 8% 1	780
	11th to 20th	Night	24% 16% 33% 20% 7%	800
	21st to end	Night	23% 18% 31% 21% 5% 1	779
December	1st to 10th	Night	27% 15% 33% 21% 4	760
	11th to 20th	Night	25% 17% 30% 24% 4	760
	21st to end	Night	27% 14% 34% 23% 3	836

Page generated at 2024-11-22 08:02:22. Version ac07

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