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 2024-03-18.

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% 3 5% 5% 3 4 4 5% 7% 40%	78517
	Night	18% 7% 3 5% 5% 3 4 4 5% 6% 41%	81268
Transparency	Day	45% 4 11% 23% 15% 3	78222
	Night	45% 4 11% 23% 15% 2	81097
Seeing	Day	25% 15% 31% 19% 8% 2	14091
	Night	23% 13% 31% 25% 7% 1	23154

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 5% 4 3 5% 4 4 6% 44%	2517
	11th to 20th	Day	17% 7% 3 6% 5% 3 4 5% 4 5% 40%	2520
	21st to end	Day	20% 11% 3 5% 5% 3 4 3 5% 5% 35%	2772
February	1st to 10th	Day	19% 7% 3 4 5% 3 4 5% 7% 6% 36%	1748
	11th to 20th	Day	13% 8% 3 6% 5% 3 5% 5% 6% 7% 40%	1848
	21st to end	Day	18% 10% 4 6% 5% 3 4 4 4 5% 37%	1570
March	1st to 10th	Day	17% 8% 3 6% 4 3 5% 4 5% 7% 37%	1897
	11th to 20th	Day	17% 6% 3 6% 5% 3 4 4 5% 6% 40%	1964
	21st to end	Day	19% 7% 3 6% 5% 2 4 3 4 6% 40%	2304
April	1st to 10th	Day	18% 8% 4 5% 6% 3 4 3 5% 6% 38%	2160
	11th to 20th	Day	17% 5% 3 5% 4 3 5% 5% 5% 7% 39%	2147
	21st to end	Day	22% 7% 3 6% 5% 3 4 4 4 7% 34%	2340
May	1st to 10th	Day	24% 8% 3 6% 5% 3 4 4 5% 6% 33%	2340
	11th to 20th	Day	18% 6% 3 6% 5% 3 4 4 4 7% 40%	2364
	21st to end	Day	15% 5% 2 5% 5% 3 5% 4 5% 8% 43%	2725
June	1st to 10th	Day	20% 5% 2 6% 6% 4 5% 6% 6% 8% 34%	2520
	11th to 20th	Day	17% 5% 2 5% 6% 3 5% 5% 6% 8% 38%	2520
	21st to end	Day	18% 6% 3 6% 6% 3 5% 5% 5% 8% 35%	2520
July	1st to 10th	Day	15% 5% 2 5% 5% 3 5% 5% 6% 8% 41%	2520
	11th to 20th	Day	12% 6% 2 5% 6% 4 5% 6% 6% 9% 40%	2520
	21st to end	Day	12% 5% 2 5% 6% 3 6% 6% 7% 9% 40%	2744
August	1st to 10th	Day	10% 6% 2 6% 5% 4 6% 7% 6% 8% 39%	2377
	11th to 20th	Day	13% 5% 2 5% 5% 4 7% 5% 6% 9% 38%	2278
	21st to end	Day	13% 4 1 4 5% 4 4 5% 7% 9% 44%	2376
September	1st to 10th	Day	14% 5% 3 4 4 3 4 5% 5% 7% 46%	2160
	11th to 20th	Day	15% 6% 2 4 3 3 3 3 4 6% 51%	1985
	21st to end	Day	17% 5% 2 5% 4 3 4 4 4 7% 46%	1980
October	1st to 10th	Day	23% 7% 2 5% 4 3 4 3 5% 5% 39%	1980
	11th to 20th	Day	15% 5% 2 4 5% 3 4 5% 5% 7% 46%	1748
	21st to end	Day	23% 7% 2 5% 5% 3 3 4 5% 5% 38%	1782
November	1st to 10th	Day	16% 6% 3 4 5% 3 3 3 4 6% 49%	1671
	11th to 20th	Day	20% 6% 2 4 3 2 3 4 4 5% 47%	1710
	21st to end	Day	20% 6% 3 4 4 2 4 4 4 6% 43%	1710
December	1st to 10th	Day	18% 8% 3 6% 5% 3 5% 4 6% 6% 37%	1522
	11th to 20th	Day	22% 8% 2 4 4 2 3 3 4 5% 44%	1906
	21st to end	Day	23% 10% 3 6% 5% 3 4 4 4 6% 32%	2772
January	1st to 10th	Night	18% 8% 2 4 4 2 3 4 4 6% 46%	4429
	11th to 20th	Night	15% 7% 3 8% 7% 4 4 4 4 6% 39%	4440
	21st to end	Night	22% 13% 4 7% 5% 3 4 4 4 5% 31%	4884
February	1st to 10th	Night	16% 9% 3 5% 5% 3 4 5% 6% 6% 39%	2431
	11th to 20th	Night	14% 9% 3 5% 5% 3 5% 5% 6% 6% 40%	2218
	21st to end	Night	18% 7% 3 5% 5% 3 4 4 5% 6% 41%	1884
March	1st to 10th	Night	17% 8% 3 6% 4 3 4 4 5% 6% 40%	2270
	11th to 20th	Night	16% 7% 3 7% 5% 3 6% 6% 5% 5% 39%	2161
	21st to end	Night	18% 9% 3 4 4 3 4 4 4 6% 41%	2048
April	1st to 10th	Night	19% 7% 3 6% 5% 3 4 4 5% 7% 37%	1800
	11th to 20th	Night	21% 6% 3 4 5% 2 4 4 5% 6% 40%	1762
	21st to end	Night	21% 7% 3 5% 6% 3 3 4 5% 6% 39%	1620
May	1st to 10th	Night	23% 7% 3 5% 6% 3 5% 4 5% 8% 32%	1620
	11th to 20th	Night	19% 6% 2 5% 5% 3 6% 5% 5% 6% 38%	1543
	21st to end	Night	17% 7% 2 6% 5% 3 4 5% 5% 6% 40%	1550
June	1st to 10th	Night	18% 8% 2 6% 5% 3 5% 4 5% 6% 38%	1440
	11th to 20th	Night	20% 5% 3 4 5% 3 4 5% 6% 6% 38%	1440
	21st to end	Night	16% 5% 3 4 3 3 5% 6% 6% 8% 40%	1440
July	1st to 10th	Night	15% 5% 3 6% 5% 3 5% 5% 4 8% 41%	1440
	11th to 20th	Night	13% 5% 2 6% 5% 3 5% 6% 6% 9% 40%	1440
	21st to end	Night	12% 5% 2 5% 4 3 6% 5% 5% 7% 46%	1574
August	1st to 10th	Night	10% 5% 2 6% 5% 3 4 5% 6% 8% 46%	1542
	11th to 20th	Night	12% 7% 3 6% 6% 3 7% 7% 6% 8% 36%	1618
	21st to end	Night	15% 4 1 4 4 3 4 4 5% 8% 48%	1980
September	1st to 10th	Night	14% 5% 2 4 4 3 3 3 5% 7% 50%	1800
	11th to 20th	Night	14% 5% 2 4 3 2 3 4 4 6% 53%	1975
	21st to end	Night	16% 5% 2 5% 4 3 3 3 5% 7% 47%	1980
October	1st to 10th	Night	22% 6% 2 5% 4 2 4 3 4 5% 42%	1980
	11th to 20th	Night	17% 5% 2 4 5% 2 4 5% 6% 7% 44%	2211
	21st to end	Night	23% 6% 2 5% 5% 2 4 4 4 6% 38%	2574
November	1st to 10th	Night	16% 5% 2 4 4 3 4 4 5% 6% 47%	2407
	11th to 20th	Night	18% 5% 2 5% 4 3 3 3 4 5% 46%	2470
	21st to end	Night	16% 7% 3 5% 4 3 5% 4 4 7% 44%	2470
December	1st to 10th	Night	20% 9% 3 6% 5% 3 5% 4 5% 6% 37%	2655
	11th to 20th	Night	20% 6% 2 4 4 3 4 4 5% 6% 41%	3288
	21st to end	Night	21% 10% 3 6% 6% 3 4 3 4 5% 34%	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	43% 3 8% 34% 11% 1	2518
	11th to 20th	Day	46% 4 10% 26% 12% 2	2520
	21st to end	Day	52% 5% 9% 23% 9% 2	2772
February	1st to 10th	Day	48% 3 13% 22% 12% 3	1748
	11th to 20th	Day	44% 5% 11% 21% 15% 4	1857
	21st to end	Day	50% 4 9% 20% 14% 3	1570
March	1st to 10th	Day	48% 3 11% 20% 13% 4	1900
	11th to 20th	Day	45% 4 10% 20% 16% 4	1964
	21st to end	Day	48% 4 6% 18% 17% 7%	2304
April	1st to 10th	Day	48% 4 8% 19% 18% 4	2160
	11th to 20th	Day	45% 4 9% 21% 18% 3	2147
	21st to end	Day	52% 3 7% 18% 17% 4	2340
May	1st to 10th	Day	52% 4 7% 21% 14% 2	2340
	11th to 20th	Day	44% 5% 9% 21% 19% 3	2368
	21st to end	Day	40% 5% 14% 24% 14% 3	2725
June	1st to 10th	Day	49% 5% 12% 22% 11% 1	2520
	11th to 20th	Day	44% 5% 11% 20% 17% 3	2520
	21st to end	Day	47% 6% 11% 23% 12% 1	2520
July	1st to 10th	Day	41% 5% 12% 23% 17% 2	2450
	11th to 20th	Day	40% 6% 13% 27% 13% 1	2445
	21st to end	Day	39% 6% 14% 24% 14% 3	2591
August	1st to 10th	Day	41% 6% 14% 24% 13% 1	2363
	11th to 20th	Day	42% 5% 13% 25% 13% 2	2278
	21st to end	Day	35% 5% 13% 26% 19% 3	2376
September	1st to 10th	Day	37% 5% 12% 24% 20% 2	2160
	11th to 20th	Day	37% 3 7% 27% 24% 2	1985
	21st to end	Day	39% 4 8% 24% 22% 2	1980
October	1st to 10th	Day	48% 3 8% 22% 14% 4	1980
	11th to 20th	Day	38% 4 12% 31% 14% 2	1748
	21st to end	Day	49% 4 10% 20% 14% 3	1782
November	1st to 10th	Day	39% 3 12% 26% 17% 2	1671
	11th to 20th	Day	42% 3 8% 24% 20% 3	1710
	21st to end	Day	43% 3 15% 23% 14% 2	1710
December	1st to 10th	Day	47% 4 14% 18% 15% 1	1522
	11th to 20th	Day	45% 3 11% 20% 17% 5%	1906
	21st to end	Day	55% 3 11% 20% 11% 1	2772
January	1st to 10th	Night	41% 3 12% 29% 11% 3	4429
	11th to 20th	Night	47% 4 11% 23% 12% 3	4440
	21st to end	Night	58% 3 9% 17% 11% 2	4884
February	1st to 10th	Night	45% 5% 12% 20% 14% 3	2431
	11th to 20th	Night	44% 4 10% 22% 17% 3	2220
	21st to end	Night	44% 4 9% 25% 15% 4	1884
March	1st to 10th	Night	46% 4 8% 23% 15% 4	2280
	11th to 20th	Night	48% 5% 10% 17% 17% 4	2162
	21st to end	Night	45% 3 8% 18% 20% 5%	2048
April	1st to 10th	Night	47% 4 10% 19% 18% 3	1800
	11th to 20th	Night	46% 3 9% 22% 18% 2	1762
	21st to end	Night	47% 4 11% 19% 15% 4	1620
May	1st to 10th	Night	53% 4 8% 19% 13% 3	1620
	11th to 20th	Night	45% 6% 11% 18% 15% 3	1544
	21st to end	Night	45% 6% 13% 22% 12% 2	1551
June	1st to 10th	Night	49% 4 10% 24% 12% 1	1440
	11th to 20th	Night	45% 6% 12% 20% 15% 2	1440
	21st to end	Night	41% 8% 14% 22% 14% 1	1440
July	1st to 10th	Night	41% 8% 12% 24% 15% 1	1400
	11th to 20th	Night	40% 7% 15% 28% 11%	1392
	21st to end	Night	35% 7% 13% 30% 12% 2	1486
August	1st to 10th	Night	36% 7% 14% 26% 16% 1	1532
	11th to 20th	Night	43% 7% 15% 22% 12% 1	1618
	21st to end	Night	35% 5% 10% 28% 20% 1	1980
September	1st to 10th	Night	35% 5% 12% 27% 20% 1	1800
	11th to 20th	Night	33% 4 10% 25% 26% 2	1975
	21st to end	Night	37% 5% 8% 28% 20% 2	1980
October	1st to 10th	Night	46% 4 11% 23% 13% 3	1980
	11th to 20th	Night	38% 5% 13% 29% 14% 1	2211
	21st to end	Night	48% 4 11% 22% 13% 1	2574
November	1st to 10th	Night	39% 4 10% 24% 19% 3	2407
	11th to 20th	Night	42% 3 10% 23% 20% 3	2470
	21st to end	Night	42% 3 13% 26% 15% 2	2470
December	1st to 10th	Night	48% 4 11% 23% 13% 1	2655
	11th to 20th	Night	44% 5% 13% 18% 19% 2	3288
	21st to end	Night	53% 3 8% 25% 10% 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	30% 20% 30% 17% 3	180
	11th to 20th	Day	36% 19% 31% 11% 3 1	180
	21st to end	Day	29% 21% 35% 12% 4	198
February	1st to 10th	Day	33% 21% 32% 13% 2	348
	11th to 20th	Day	31% 27% 28% 12% 2	456
	21st to end	Day	29% 20% 34% 13% 4	382
March	1st to 10th	Day	33% 17% 35% 13% 3	460
	11th to 20th	Day	31% 23% 30% 12% 3 1	449
	21st to end	Day	31% 20% 30% 11% 5% 2	462
April	1st to 10th	Day	31% 21% 27% 13% 6% 1	420
	11th to 20th	Day	29% 22% 30% 12% 6% 1	412
	21st to end	Day	31% 15% 33% 15% 5% 2	420
May	1st to 10th	Day	35% 18% 27% 13% 4 2	423
	11th to 20th	Day	24% 15% 39% 17% 4 1	447
	21st to end	Day	20% 14% 34% 25% 7% 1	485
June	1st to 10th	Day	21% 13% 37% 17% 10% 2	450
	11th to 20th	Day	18% 16% 33% 24% 7% 2	450
	21st to end	Day	20% 13% 35% 21% 10% 2	450
July	1st to 10th	Day	18% 7% 28% 30% 12% 4	445
	11th to 20th	Day	16% 6% 32% 30% 14% 3	444
	21st to end	Day	13% 8% 35% 31% 11% 2	488
August	1st to 10th	Day	13% 9% 30% 30% 15% 3	446
	11th to 20th	Day	17% 8% 27% 29% 14% 5%	439
	21st to end	Day	15% 8% 31% 29% 13% 4	495
September	1st to 10th	Day	19% 11% 25% 22% 17% 6%	450
	11th to 20th	Day	22% 11% 26% 20% 12% 8%	450
	21st to end	Day	21% 11% 32% 20% 11% 6%	450
October	1st to 10th	Day	30% 11% 24% 21% 10% 4	450
	11th to 20th	Day	22% 14% 30% 21% 10% 2	401
	21st to end	Day	32% 12% 28% 19% 8% 1	396
November	1st to 10th	Day	21% 16% 30% 21% 10% 2	365
	11th to 20th	Day	31% 18% 26% 19% 5% 1	370
	21st to end	Day	30% 17% 29% 17% 5% 1	370
December	1st to 10th	Day	23% 26% 29% 18% 4	182
	11th to 20th	Day	36% 19% 32% 12% 2	180
	21st to end	Day	29% 22% 27% 17% 4 2	198
January	1st to 10th	Night	22% 21% 35% 18% 3	760
	11th to 20th	Night	28% 19% 32% 19% 3	760
	21st to end	Night	24% 19% 33% 21% 3	836
February	1st to 10th	Night	25% 17% 34% 23% 2	760
	11th to 20th	Night	23% 20% 37% 18% 2	743
	21st to end	Night	27% 17% 32% 21% 3	628
March	1st to 10th	Night	27% 17% 33% 21% 2	760
	11th to 20th	Night	24% 19% 36% 17% 5%	752
	21st to end	Night	27% 19% 30% 20% 5%	792
April	1st to 10th	Night	25% 17% 33% 21% 4	720
	11th to 20th	Night	25% 19% 31% 18% 7%	698
	21st to end	Night	25% 15% 34% 22% 3 1	540
May	1st to 10th	Night	27% 14% 31% 23% 5%	540
	11th to 20th	Night	24% 15% 32% 23% 6%	482
	21st to end	Night	20% 7% 34% 32% 7%	389
June	1st to 10th	Night	21% 9% 31% 30% 9% 1	360
	11th to 20th	Night	22% 9% 28% 33% 8% 1	360
	21st to end	Night	18% 5% 32% 37% 8%	360
July	1st to 10th	Night	17% 5% 27% 40% 11% 1	350
	11th to 20th	Night	15% 2 23% 46% 13% 1	348
	21st to end	Night	14% 3 27% 42% 13% 1	394
August	1st to 10th	Night	11% 3 29% 41% 14% 1	468
	11th to 20th	Night	15% 4 28% 36% 14% 2	554
	21st to end	Night	16% 4 23% 38% 17% 3	792
September	1st to 10th	Night	16% 5% 30% 33% 14% 1	720
	11th to 20th	Night	17% 8% 28% 27% 18% 3	720
	21st to end	Night	17% 9% 29% 28% 15% 2	720
October	1st to 10th	Night	27% 9% 24% 26% 12% 2	720
	11th to 20th	Night	20% 10% 31% 26% 12% 1	720
	21st to end	Night	28% 12% 31% 24% 5% 1	792
November	1st to 10th	Night	21% 12% 31% 27% 8% 1	740
	11th to 20th	Night	24% 16% 30% 23% 6% 1	760
	21st to end	Night	24% 17% 32% 21% 6%	760
December	1st to 10th	Night	26% 16% 35% 20% 4	760
	11th to 20th	Night	26% 17% 30% 24% 3	760
	21st to end	Night	27% 16% 34% 21% 3	836

Page generated at 2024-03-15 14:01:43. Version ac07

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