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 2024-11-03.

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%	101241
	Night	18% 8% 2 6% 4 4 4 3 5% 6% 39%	97768
Transparency	Day	25% 48% 6% 12% 8% 1	100999
	Night	25% 49% 6% 11% 8% 1	97630
Seeing	Day	24% 15% 31% 19% 8% 2	14991
	Night	22% 13% 31% 25% 7% 1	23872

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% 7% 2 6% 3 4 4 3 5% 6% 43%	2517
	11th to 20th	Day	17% 7% 3 7% 4 4 4 4 5% 5% 40%	2520
	21st to end	Day	20% 11% 3 6% 4 4 4 3 5% 5% 35%	2772
February	1st to 10th	Day	19% 8% 3 5% 5% 5% 3 5% 7% 5% 36%	1748
	11th to 20th	Day	13% 8% 2 7% 4 4 5% 3 6% 7% 40%	1848
	21st to end	Day	18% 11% 3 6% 5% 5% 4 3 4 5% 37%	1570
March	1st to 10th	Day	24% 13% 3 7% 4 4 4 3 4 4 30%	3116
	11th to 20th	Day	14% 7% 2 6% 4 4 4 4 6% 6% 41%	3320
	21st to end	Day	22% 9% 2 7% 4 4 4 3 5% 7% 34%	4052
April	1st to 10th	Day	18% 9% 3 6% 5% 5% 3 3 4 6% 37%	2280
	11th to 20th	Day	18% 6% 3 5% 4 5% 5% 5% 4 7% 39%	2268
	21st to end	Day	21% 7% 3 7% 4 4 4 3 4 6% 35%	2470
May	1st to 10th	Day	23% 11% 3 7% 5% 4 4 3 5% 7% 27%	4106
	11th to 20th	Day	22% 7% 3 7% 5% 4 4 3 4 7% 32%	4200
	21st to end	Day	15% 5% 2 5% 4 4 4 4 6% 9% 44%	4837
June	1st to 10th	Day	19% 6% 2 6% 5% 4 6% 5% 6% 7% 34%	2660
	11th to 20th	Day	16% 6% 2 6% 5% 4 5% 4 6% 8% 38%	2660
	21st to end	Day	18% 7% 2 7% 5% 4 4 4 6% 8% 35%	2660
July	1st to 10th	Day	13% 6% 2 7% 5% 5% 5% 5% 7% 9% 37%	4440
	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%	1689
	11th to 20th	Day	19% 7% 2 5% 3 3 3 3 4 5% 47%	1710
	21st to end	Day	20% 6% 3 5% 4 4 3 3 4 6% 43%	1710
December	1st to 10th	Day	18% 9% 3 6% 4 4 5% 3 6% 6% 37%	1522
	11th to 20th	Day	22% 8% 2 4 3 3 2 3 4 5% 43%	1906
	21st to end	Day	23% 10% 3 7% 4 4 4 3 5% 6% 32%	2772
January	1st to 10th	Night	17% 8% 2 4 3 3 4 3 4 5% 46%	4429
	11th to 20th	Night	14% 8% 3 9% 5% 5% 4 3 5% 6% 39%	4440
	21st to end	Night	22% 13% 4 8% 4 4 4 3 4 4 31%	4884
February	1st to 10th	Night	16% 9% 2 6% 4 4 4 4 6% 6% 38%	2431
	11th to 20th	Night	14% 10% 2 6% 4 5% 4 4 6% 6% 40%	2218
	21st to end	Night	18% 8% 2 5% 4 3 4 3 5% 6% 41%	1884
March	1st to 10th	Night	28% 10% 2 5% 3 3 3 3 5% 5% 33%	3724
	11th to 20th	Night	12% 9% 3 7% 6% 5% 5% 4 5% 6% 38%	3639
	21st to end	Night	25% 8% 3 4 3 4 4 4 6% 6% 33%	3576
April	1st to 10th	Night	19% 8% 3 6% 5% 5% 3 4 5% 6% 36%	1900
	11th to 20th	Night	21% 7% 2 5% 4 3 4 3 5% 6% 40%	1861
	21st to end	Night	21% 7% 2 5% 5% 3 3 3 4 6% 39%	1710
May	1st to 10th	Night	25% 11% 3 7% 5% 4 4 3 5% 7% 26%	2834
	11th to 20th	Night	20% 8% 3 7% 6% 5% 6% 5% 6% 7% 28%	2721
	21st to end	Night	16% 6% 2 6% 4 4 3 4 6% 7% 42%	2738
June	1st to 10th	Night	17% 9% 2 7% 5% 5% 5% 3 5% 6% 38%	1520
	11th to 20th	Night	19% 6% 2 5% 4 4 4 4 6% 6% 39%	1520
	21st to end	Night	17% 6% 3 5% 3 5% 4 5% 6% 8% 38%	1520
July	1st to 10th	Night	11% 5% 3 8% 5% 6% 6% 5% 6% 9% 37%	2520
	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% 6% 2 4 4 3 4 3 5% 5% 47%	2434
	11th to 20th	Night	18% 6% 2 5% 4 4 3 3 4 5% 46%	2470
	21st to end	Night	16% 7% 2 6% 3 4 4 3 5% 6% 43%	2470
December	1st to 10th	Night	20% 9% 3 6% 4 4 4 3 5% 6% 37%	2655
	11th to 20th	Night	20% 7% 2 5% 4 4 4 3 6% 6% 41%	3288
	21st to end	Night	21% 10% 3 7% 5% 4 4 2 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	27% 37% 5% 24% 6% 1	2518
	11th to 20th	Day	29% 37% 5% 19% 8% 1	2520
	21st to end	Day	38% 41% 4 12% 4 1	2772
February	1st to 10th	Day	16% 65% 5% 8% 4 1	1748
	11th to 20th	Day	17% 64% 3 7% 8% 1	1857
	21st to end	Day	15% 65% 4 8% 6% 1	1570
March	1st to 10th	Day	41% 40% 4 6% 7% 1	3119
	11th to 20th	Day	24% 42% 9% 13% 11% 2	3320
	21st to end	Day	33% 41% 2 9% 9% 5%	4052
April	1st to 10th	Day	20% 65% 2 6% 5% 2	2280
	11th to 20th	Day	15% 66% 3 8% 7% 1	2268
	21st to end	Day	19% 65% 2 6% 7% 1	2470
May	1st to 10th	Day	37% 41% 8% 9% 5%	4120
	11th to 20th	Day	35% 40% 12% 10% 3	4204
	21st to end	Day	22% 42% 7% 15% 14% 1	4837
June	1st to 10th	Day	15% 65% 4 9% 6%	2660
	11th to 20th	Day	14% 65% 4 9% 7% 1	2660
	21st to end	Day	16% 65% 3 9% 7%	2660
July	1st to 10th	Day	28% 38% 8% 14% 12% 1	4370
	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	20% 60% 2 9% 6% 3	2090
	11th to 20th	Day	14% 59% 5% 12% 8% 1	1844
	21st to end	Day	21% 59% 3 10% 6% 1	1881
November	1st to 10th	Day	18% 58% 6% 10% 7% 1	1689
	11th to 20th	Day	17% 59% 4 8% 11% 1	1710
	21st to end	Day	15% 59% 6% 10% 8% 1	1710
December	1st to 10th	Day	19% 60% 6% 6% 8%	1522
	11th to 20th	Day	25% 48% 5% 9% 9% 4	1906
	21st to end	Day	36% 37% 6% 13% 7% 1	2772
January	1st to 10th	Night	25% 36% 9% 20% 7% 3	4429
	11th to 20th	Night	28% 38% 7% 16% 10% 2	4440
	21st to end	Night	42% 39% 6% 9% 4 1	4884
February	1st to 10th	Night	16% 65% 5% 7% 5% 2	2431
	11th to 20th	Night	16% 63% 3 7% 8% 2	2220
	21st to end	Night	15% 65% 3 8% 6% 3	1884
March	1st to 10th	Night	37% 41% 5% 9% 6% 2	3734
	11th to 20th	Night	27% 42% 7% 11% 11% 2	3640
	21st to end	Night	33% 41% 2 7% 11% 5%	3576
April	1st to 10th	Night	20% 65% 3 5% 6% 1	1900
	11th to 20th	Night	16% 65% 4 6% 7% 1	1861
	21st to end	Night	17% 65% 3 7% 7% 1	1710
May	1st to 10th	Night	38% 41% 7% 10% 3	2840
	11th to 20th	Night	37% 40% 12% 7% 3	2722
	21st to end	Night	25% 42% 10% 12% 9% 1	2739
June	1st to 10th	Night	15% 65% 3 10% 8%	1520
	11th to 20th	Night	14% 66% 5% 9% 6% 1	1520
	21st to end	Night	14% 64% 4 11% 6% 1	1520
July	1st to 10th	Night	27% 39% 8% 16% 10%	2480
	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	18% 60% 5% 11% 4 2	2090
	11th to 20th	Night	12% 60% 6% 13% 9% 1	2335
	21st to end	Night	21% 59% 4 10% 5% 1	2717
November	1st to 10th	Night	18% 58% 4 11% 8% 1	2434
	11th to 20th	Night	16% 59% 3 9% 11% 2	2470
	21st to end	Night	15% 59% 6% 12% 7% 1	2470
December	1st to 10th	Night	21% 60% 5% 8% 6%	2655
	11th to 20th	Night	23% 50% 5% 9% 12% 1	3288
	21st to end	Night	36% 37% 4 16% 7%	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	32% 23% 30% 11% 3 1	460
	21st to end	Day	32% 21% 29% 10% 5% 2	506
April	1st to 10th	Day	32% 20% 28% 13% 6% 1	460
	11th to 20th	Day	30% 22% 29% 12% 5% 1	452
	21st to end	Day	29% 15% 34% 15% 5% 2	460
May	1st to 10th	Day	34% 18% 28% 13% 5% 2	463
	11th to 20th	Day	24% 14% 37% 18% 5% 1	487
	21st to end	Day	19% 14% 34% 25% 6% 1	529
June	1st to 10th	Day	20% 13% 38% 18% 10% 2	490
	11th to 20th	Day	17% 16% 33% 25% 8% 2	490
	21st to end	Day	20% 15% 34% 19% 9% 2	490
July	1st to 10th	Day	18% 8% 30% 29% 12% 4	485
	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% 29% 21% 10% 2	371
	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	23% 19% 36% 16% 5%	760
	21st to end	Night	28% 19% 30% 19% 4	836
April	1st to 10th	Night	26% 16% 34% 21% 4	760
	11th to 20th	Night	26% 19% 31% 18% 6%	737
	21st to end	Night	25% 15% 35% 22% 3 1	570
May	1st to 10th	Night	26% 14% 31% 22% 5%	570
	11th to 20th	Night	23% 14% 32% 24% 6%	509
	21st to end	Night	20% 7% 34% 32% 7%	411
June	1st to 10th	Night	21% 9% 31% 30% 8% 1	380
	11th to 20th	Night	22% 8% 29% 32% 8% 1	380
	21st to end	Night	18% 6% 32% 36% 8%	380
July	1st to 10th	Night	16% 5% 28% 40% 10% 1	370
	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% 31% 24% 5%	836
November	1st to 10th	Night	21% 13% 31% 26% 8% 1	749
	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 2024-10-31 03:39:23. Version ac07

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