Nashua
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Nashua clear sky chart from 2005-11-06 to 2025-07-06.

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% 3 6% 4 4 4 4 5% 7% 38%	119558
	Night	18% 8% 3 6% 4 4 4 3 5% 6% 39%	119249
Transparency	Day	28% 40% 7% 13% 10% 2	123123
	Night	28% 39% 7% 13% 10% 2	123845
Seeing	Day	25% 15% 31% 19% 8% 2	15811
	Night	23% 13% 31% 25% 7% 1	24725

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	13% 6% 3 9% 5% 5% 5% 4 5% 5% 38%	3597
	11th to 20th	Day	14% 8% 3 6% 4 4 4 4 4 6% 45%	3570
	21st to end	Day	16% 9% 2 5% 4 4 4 3 4 5% 44%	3960
February	1st to 10th	Day	18% 8% 3 5% 5% 5% 4 5% 7% 5% 36%	1840
	11th to 20th	Day	13% 8% 3 7% 4 4 5% 3 6% 7% 39%	1948
	21st to end	Day	17% 10% 3 7% 4 5% 4 4 4 5% 37%	1650
March	1st to 10th	Day	21% 10% 3 7% 4 4 4 3 4 4 35%	4476
	11th to 20th	Day	17% 8% 2 6% 4 4 4 4 5% 6% 39%	4750
	21st to end	Day	25% 9% 2 6% 4 4 4 3 5% 7% 32%	5800
April	1st to 10th	Day	19% 10% 3 6% 5% 5% 3 3 4 6% 37%	2400
	11th to 20th	Day	18% 6% 3 5% 4 5% 5% 5% 5% 7% 39%	2389
	21st to end	Day	21% 7% 3 7% 4 4 4 3 4 6% 36%	2600
May	1st to 10th	Day	31% 10% 3 6% 4 4 4 3 5% 6% 24%	5886
	11th to 20th	Day	20% 7% 3 8% 5% 5% 5% 3 5% 7% 31%	6036
	21st to end	Day	19% 6% 2 6% 4 4 4 4 6% 8% 35%	6949
June	1st to 10th	Day	19% 6% 2 6% 6% 4 6% 4 6% 8% 34%	2800
	11th to 20th	Day	16% 6% 2 6% 5% 4 5% 4 6% 8% 38%	2800
	21st to end	Day	18% 7% 2 7% 5% 4 4 4 6% 8% 36%	2800
July	1st to 10th	Day	13% 6% 2 7% 5% 5% 5% 5% 7% 9% 37%	4510
	11th to 20th	Day	10% 6% 2 6% 4 5% 6% 4 7% 10% 40%	4440
	21st to end	Day	16% 8% 3 7% 5% 4 4 4 6% 7% 36%	4814
August	1st to 10th	Day	14% 7% 2 7% 5% 5% 6% 4 7% 8% 34%	4183
	11th to 20th	Day	15% 7% 3 7% 4 5% 6% 4 6% 8% 36%	3991
	21st to end	Day	8% 4 2 6% 5% 5% 5% 5% 7% 10% 43%	4180
September	1st to 10th	Day	13% 5% 2 5% 4 4 4 4 6% 6% 47%	2280
	11th to 20th	Day	15% 6% 2 5% 3 3 3 2 4 6% 51%	2095
	21st to end	Day	17% 5% 2 6% 4 3 4 3 4 7% 44%	2090
October	1st to 10th	Day	22% 7% 2 6% 4 4 4 3 5% 5% 39%	2090
	11th to 20th	Day	15% 5% 2 5% 4 4 4 3 5% 7% 46%	1844
	21st to end	Day	22% 7% 2 5% 4 4 3 3 5% 5% 40%	1881
November	1st to 10th	Day	15% 6% 2 4 4 4 3 2 4 6% 49%	1761
	11th to 20th	Day	18% 6% 2 4 3 3 4 3 4 5% 48%	1800
	21st to end	Day	20% 6% 3 5% 4 4 3 3 4 6% 43%	1800
December	1st to 10th	Day	15% 8% 2 6% 4 3 4 3 5% 6% 43%	2602
	11th to 20th	Day	20% 7% 2 4 3 3 3 3 4 5% 46%	2986
	21st to end	Day	20% 10% 3 6% 4 4 4 3 4 5% 37%	3960
January	1st to 10th	Night	14% 7% 2 6% 4 4 4 3 4 6% 46%	6349
	11th to 20th	Night	13% 8% 3 9% 6% 5% 4 3 5% 6% 39%	6315
	21st to end	Night	15% 10% 3 7% 4 5% 4 3 5% 5% 38%	6996
February	1st to 10th	Night	16% 10% 2 6% 4 4 4 4 6% 6% 38%	2557
	11th to 20th	Night	14% 9% 2 6% 4 5% 4 4 6% 6% 39%	2338
	21st to end	Night	17% 8% 2 6% 5% 4 4 3 5% 6% 41%	1980
March	1st to 10th	Night	24% 8% 2 5% 4 3 3 3 5% 6% 37%	5364
	11th to 20th	Night	16% 10% 3 7% 5% 4 5% 4 5% 6% 37%	5209
	21st to end	Night	26% 9% 3 5% 3 4 4 3 6% 6% 32%	5128
April	1st to 10th	Night	20% 8% 3 6% 5% 5% 4 4 5% 6% 35%	2000
	11th to 20th	Night	21% 7% 2 5% 5% 3 4 3 5% 6% 39%	1960
	21st to end	Night	20% 8% 2 5% 5% 3 3 3 4 6% 40%	1800
May	1st to 10th	Night	34% 10% 3 5% 4 3 3 3 4 7% 24%	4054
	11th to 20th	Night	17% 8% 3 7% 6% 5% 6% 5% 6% 8% 29%	3899
	21st to end	Night	21% 8% 3 7% 5% 4 4 4 5% 6% 34%	3926
June	1st to 10th	Night	18% 9% 2 7% 5% 5% 5% 3 4 6% 38%	1600
	11th to 20th	Night	19% 6% 2 5% 4 4 4 4 6% 6% 38%	1600
	21st to end	Night	17% 7% 3 5% 3 5% 4 5% 6% 8% 39%	1600
July	1st to 10th	Night	11% 5% 3 8% 5% 6% 6% 5% 6% 9% 37%	2560
	11th to 20th	Night	12% 7% 3 7% 5% 4 5% 4 6% 8% 40%	2520
	21st to end	Night	15% 8% 2 6% 4 4 6% 4 5% 6% 39%	2739
August	1st to 10th	Night	20% 6% 3 7% 5% 5% 5% 4 5% 7% 34%	2714
	11th to 20th	Night	12% 8% 3 7% 5% 4 6% 5% 6% 8% 36%	2832
	21st to end	Night	9% 4 1 4 3 3 4 4 5% 8% 54%	3476
September	1st to 10th	Night	13% 6% 1 5% 4 3 3 3 5% 6% 50%	1900
	11th to 20th	Night	14% 5% 2 4 3 3 3 3 4 6% 53%	2085
	21st to end	Night	16% 6% 2 6% 3 3 3 3 5% 7% 45%	2090
October	1st to 10th	Night	21% 6% 2 6% 4 3 4 3 5% 5% 42%	2090
	11th to 20th	Night	16% 4 2 5% 4 3 4 4 5% 7% 46%	2335
	21st to end	Night	23% 6% 2 6% 4 3 3 3 5% 6% 40%	2717
November	1st to 10th	Night	16% 5% 2 4 4 4 4 3 5% 5% 48%	2537
	11th to 20th	Night	18% 6% 2 5% 4 4 3 3 4 5% 47%	2600
	21st to end	Night	16% 7% 2 6% 3 4 4 3 5% 6% 43%	2600
December	1st to 10th	Night	18% 9% 2 6% 4 4 4 3 5% 5% 39%	4575
	11th to 20th	Night	23% 7% 2 5% 4 3 3 3 4 5% 41%	5208
	21st to end	Night	18% 10% 3 7% 5% 4 4 2 4 5% 38%	6996

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	34% 28% 5% 20% 12% 1	3598
	11th to 20th	Day	28% 27% 7% 19% 16% 3	3600
	21st to end	Day	33% 30% 4 15% 15% 3	3960
February	1st to 10th	Day	17% 62% 6% 9% 5% 1	1840
	11th to 20th	Day	19% 61% 3 7% 9% 2	1957
	21st to end	Day	16% 62% 4 9% 7% 1	1650
March	1st to 10th	Day	41% 29% 5% 8% 8% 9%	4479
	11th to 20th	Day	33% 30% 9% 18% 9% 1	4750
	21st to end	Day	41% 29% 3 11% 11% 5%	5800
April	1st to 10th	Day	22% 62% 2 7% 6% 2	2400
	11th to 20th	Day	17% 63% 3 8% 8% 2	2389
	21st to end	Day	20% 61% 2 8% 8% 1	2600
May	1st to 10th	Day	47% 30% 10% 8% 5%	5897
	11th to 20th	Day	41% 29% 12% 12% 5% 1	6040
	21st to end	Day	36% 31% 8% 14% 10% 1	6949
June	1st to 10th	Day	17% 62% 4 9% 7%	2800
	11th to 20th	Day	16% 62% 4 10% 7% 1	2800
	21st to end	Day	17% 61% 4 10% 7% 1	2800
July	1st to 10th	Day	28% 37% 8% 14% 12% 1	4440
	11th to 20th	Day	24% 39% 10% 18% 8% 1	4365
	21st to end	Day	34% 36% 8% 12% 10% 1	4661
August	1st to 10th	Day	30% 39% 10% 15% 5%	4169
	11th to 20th	Day	29% 39% 10% 17% 5%	4030
	21st to end	Day	20% 39% 8% 21% 11% 1	4180
September	1st to 10th	Day	14% 60% 6% 12% 8% 1	2280
	11th to 20th	Day	17% 59% 3 9% 10% 1	2095
	21st to end	Day	17% 59% 4 11% 8% 1	2090
October	1st to 10th	Day	28% 38% 5% 14% 13% 2	3480
	11th to 20th	Day	18% 37% 4 18% 20% 2	3034
	21st to end	Day	19% 37% 4 24% 15% 2	3081
November	1st to 10th	Day	18% 56% 6% 11% 7% 1	1761
	11th to 20th	Day	16% 56% 4 8% 14% 2	1800
	21st to end	Day	17% 57% 6% 11% 8% 1	1800
December	1st to 10th	Day	25% 36% 10% 23% 6%	2602
	11th to 20th	Day	29% 32% 8% 12% 15% 5%	2986
	21st to end	Day	38% 26% 5% 15% 12% 5%	3960
January	1st to 10th	Night	28% 27% 8% 24% 10% 2	6349
	11th to 20th	Night	33% 28% 8% 16% 11% 3	6360
	21st to end	Night	38% 28% 6% 11% 12% 4	6996
February	1st to 10th	Night	18% 62% 5% 8% 6% 2	2557
	11th to 20th	Night	17% 61% 4 7% 9% 2	2340
	21st to end	Night	17% 62% 3 9% 7% 3	1980
March	1st to 10th	Night	37% 30% 6% 9% 11% 6%	5374
	11th to 20th	Night	35% 30% 11% 13% 9% 2	5210
	21st to end	Night	40% 30% 2 8% 15% 5%	5128
April	1st to 10th	Night	22% 61% 3 6% 6% 2	2000
	11th to 20th	Night	19% 62% 4 7% 8% 1	1960
	21st to end	Night	18% 62% 3 7% 8% 1	1800
May	1st to 10th	Night	48% 30% 9% 8% 5%	4060
	11th to 20th	Night	39% 31% 13% 11% 6%	3900
	21st to end	Night	40% 31% 10% 12% 7% 1	3927
June	1st to 10th	Night	17% 62% 3 11% 8%	1600
	11th to 20th	Night	15% 63% 5% 10% 6% 1	1600
	21st to end	Night	16% 61% 4 12% 7% 1	1600
July	1st to 10th	Night	27% 38% 8% 16% 10%	2520
	11th to 20th	Night	27% 39% 9% 14% 11%	2472
	21st to end	Night	32% 37% 7% 12% 12% 1	2651
August	1st to 10th	Night	36% 39% 7% 11% 7% 1	2704
	11th to 20th	Night	29% 41% 10% 15% 6%	2859
	21st to end	Night	14% 39% 11% 20% 16%	3476
September	1st to 10th	Night	14% 60% 5% 13% 8% 1	1900
	11th to 20th	Night	15% 60% 3 10% 11% 1	2085
	21st to end	Night	18% 59% 3 12% 7%	2090
October	1st to 10th	Night	25% 38% 11% 16% 10% 1	3480
	11th to 20th	Night	13% 37% 7% 17% 23% 3	3884
	21st to end	Night	20% 37% 6% 25% 11% 1	4467
November	1st to 10th	Night	18% 56% 4 12% 9% 2	2537
	11th to 20th	Night	16% 56% 3 9% 13% 2	2600
	21st to end	Night	17% 56% 6% 12% 8% 1	2600
December	1st to 10th	Night	30% 37% 7% 19% 7%	4575
	11th to 20th	Night	34% 32% 7% 9% 17% 1	5208
	21st to end	Night	37% 27% 5% 17% 12% 3	6996

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	33% 21% 29% 15% 3	200
	11th to 20th	Day	35% 20% 31% 12% 3 1	200
	21st to end	Day	30% 22% 34% 10% 4	220
February	1st to 10th	Day	34% 21% 31% 12% 2	380
	11th to 20th	Day	33% 27% 27% 11% 2	496
	21st to end	Day	28% 21% 35% 13% 3	414
March	1st to 10th	Day	34% 18% 33% 12% 2	500
	11th to 20th	Day	32% 23% 29% 11% 3 1	500
	21st to end	Day	33% 22% 28% 10% 5% 2	550
April	1st to 10th	Day	34% 20% 27% 12% 6% 1	500
	11th to 20th	Day	33% 22% 28% 12% 5% 1	492
	21st to end	Day	29% 16% 34% 15% 5% 2	500
May	1st to 10th	Day	36% 18% 27% 13% 5% 1	503
	11th to 20th	Day	24% 15% 37% 18% 5% 1	527
	21st to end	Day	20% 14% 34% 25% 6% 1	573
June	1st to 10th	Day	20% 12% 38% 18% 9% 2	530
	11th to 20th	Day	19% 15% 33% 23% 8% 2	530
	21st to end	Day	20% 15% 34% 20% 9% 2	530
July	1st to 10th	Day	17% 8% 31% 29% 11% 4	505
	11th to 20th	Day	15% 7% 32% 30% 13% 3	484
	21st to end	Day	14% 10% 34% 30% 11% 2	532
August	1st to 10th	Day	13% 9% 31% 30% 15% 2	486
	11th to 20th	Day	18% 9% 27% 28% 14% 5%	479
	21st to end	Day	14% 8% 31% 29% 13% 5%	539
September	1st to 10th	Day	18% 12% 27% 22% 16% 6%	490
	11th to 20th	Day	21% 10% 25% 21% 13% 10%	490
	21st to end	Day	21% 11% 31% 20% 11% 6%	490
October	1st to 10th	Day	29% 11% 24% 21% 11% 4	490
	11th to 20th	Day	23% 14% 29% 21% 11% 2	435
	21st to end	Day	31% 13% 29% 20% 7% 1	429
November	1st to 10th	Day	21% 17% 31% 20% 10% 2	395
	11th to 20th	Day	31% 18% 27% 19% 5% 1	400
	21st to end	Day	32% 18% 28% 17% 5% 1	400
December	1st to 10th	Day	23% 26% 29% 17% 5%	202
	11th to 20th	Day	36% 21% 31% 11% 2	200
	21st to end	Day	28% 20% 29% 17% 5% 2	220
January	1st to 10th	Night	22% 22% 35% 18% 3	800
	11th to 20th	Night	27% 18% 32% 20% 3	800
	21st to end	Night	24% 18% 34% 21% 3	880
February	1st to 10th	Night	25% 17% 33% 23% 2	800
	11th to 20th	Night	25% 20% 36% 17% 2	783
	21st to end	Night	26% 18% 33% 21% 3	660
March	1st to 10th	Night	27% 18% 33% 20% 2	800
	11th to 20th	Night	24% 20% 34% 17% 5%	800
	21st to end	Night	28% 19% 30% 19% 4	880
April	1st to 10th	Night	27% 16% 33% 20% 4	800
	11th to 20th	Night	26% 19% 31% 18% 6%	776
	21st to end	Night	25% 16% 35% 22% 3 1	600
May	1st to 10th	Night	28% 14% 31% 22% 5%	600
	11th to 20th	Night	23% 14% 33% 24% 6%	536
	21st to end	Night	20% 7% 34% 32% 7%	433
June	1st to 10th	Night	20% 9% 32% 31% 8% 1	400
	11th to 20th	Night	21% 8% 30% 32% 8% 1	400
	21st to end	Night	18% 6% 32% 35% 9%	400
July	1st to 10th	Night	16% 5% 28% 40% 10% 1	380
	11th to 20th	Night	14% 2 24% 45% 13% 1	368
	21st to end	Night	15% 3 27% 42% 12%	416
August	1st to 10th	Night	13% 4 27% 41% 14% 1	495
	11th to 20th	Night	15% 4 29% 36% 14% 2	586
	21st to end	Night	15% 4 23% 38% 17% 2	836
September	1st to 10th	Night	16% 6% 30% 33% 14% 1	760
	11th to 20th	Night	16% 7% 27% 28% 19% 3	760
	21st to end	Night	17% 9% 28% 29% 14% 2	760
October	1st to 10th	Night	26% 9% 24% 26% 13% 2	760
	11th to 20th	Night	20% 10% 31% 25% 12% 1	760
	21st to end	Night	27% 13% 30% 24% 5%	836
November	1st to 10th	Night	21% 13% 32% 26% 8% 1	780
	11th to 20th	Night	23% 16% 31% 23% 6% 1	800
	21st to end	Night	25% 17% 32% 21% 6%	800
December	1st to 10th	Night	26% 15% 35% 20% 4	800
	11th to 20th	Night	26% 17% 30% 24% 3	800
	21st to end	Night	26% 16% 33% 22% 3	880

Page generated at 2025-07-03 01:30:11. Version ac07

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