Northampton
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Northampton clear sky chart from 2005-11-06 to 2025-09-04.

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 6% 4 4 4 4 6% 7% 38%	125949
	Night	18% 8% 3 6% 4 4 4 3 5% 6% 40%	122765
Transparency	Day	44% 7% 12% 21% 14% 2	129456
	Night	43% 6% 13% 21% 14% 2	127345
Seeing	Day	22% 17% 30% 20% 9% 3	16003
	Night	21% 13% 31% 27% 7% 1	24941

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	12% 6% 4 10% 5% 5% 5% 4 6% 6% 38%	3597
	11th to 20th	Day	13% 9% 4 8% 4 4 4 4 5% 5% 40%	3570
	21st to end	Day	16% 9% 3 7% 4 4 4 3 5% 6% 40%	3978
February	1st to 10th	Day	16% 7% 3 6% 5% 6% 5% 5% 6% 7% 34%	1856
	11th to 20th	Day	13% 8% 3 8% 5% 4 5% 3 6% 7% 38%	1948
	21st to end	Day	19% 8% 3 7% 4 5% 4 4 4 6% 36%	1650
March	1st to 10th	Day	21% 10% 4 7% 4 3 3 3 4 5% 35%	4476
	11th to 20th	Day	15% 7% 3 6% 5% 4 5% 4 6% 7% 39%	4646
	21st to end	Day	24% 8% 2 6% 4 3 3 3 5% 5% 36%	5970
April	1st to 10th	Day	19% 8% 3 7% 4 4 4 3 5% 7% 37%	2400
	11th to 20th	Day	17% 7% 2 6% 4 4 5% 4 6% 7% 39%	2374
	21st to end	Day	19% 7% 3 6% 5% 4 5% 3 5% 6% 38%	2543
May	1st to 10th	Day	31% 8% 3 6% 4 4 4 4 6% 6% 24%	5886
	11th to 20th	Day	20% 8% 3 8% 5% 4 4 3 5% 7% 33%	6180
	21st to end	Day	18% 7% 2 6% 5% 4 5% 4 7% 8% 33%	6949
June	1st to 10th	Day	16% 6% 2 6% 5% 4 5% 4 7% 9% 35%	2800
	11th to 20th	Day	17% 6% 2 5% 5% 4 5% 4 6% 10% 36%	2800
	21st to end	Day	15% 7% 2 7% 5% 4 5% 5% 6% 8% 36%	2800
July	1st to 10th	Day	13% 6% 2 7% 5% 5% 5% 5% 7% 9% 35%	6360
	11th to 20th	Day	10% 6% 2 7% 5% 5% 6% 5% 8% 11% 36%	6360
	21st to end	Day	15% 6% 2 6% 4 4 4 4 5% 7% 43%	6926
August	1st to 10th	Day	16% 6% 3 7% 5% 6% 5% 4 6% 9% 33%	4415
	11th to 20th	Day	13% 5% 2 6% 5% 5% 5% 4 6% 8% 40%	3950
	21st to end	Day	9% 4 2 5% 4 5% 6% 5% 7% 10% 43%	4312
September	1st to 10th	Day	13% 5% 2 6% 5% 4 5% 4 5% 6% 45%	2316
	11th to 20th	Day	15% 6% 2 5% 4 3 3 2 4 7% 50%	2142
	21st to end	Day	18% 5% 2 5% 4 5% 4 4 5% 7% 41%	2090
October	1st to 10th	Day	22% 6% 2 6% 3 4 4 3 5% 5% 39%	2066
	11th to 20th	Day	14% 6% 2 4 4 4 5% 3 5% 8% 45%	1858
	21st to end	Day	21% 7% 3 6% 4 4 4 3 5% 6% 38%	1881
November	1st to 10th	Day	12% 7% 2 6% 3 4 3 3 4 6% 49%	1761
	11th to 20th	Day	18% 6% 2 4 3 3 3 4 5% 7% 45%	1800
	21st to end	Day	19% 6% 2 6% 5% 4 4 3 5% 6% 41%	1743
December	1st to 10th	Day	17% 8% 2 5% 4 4 5% 4 5% 6% 40%	2600
	11th to 20th	Day	21% 7% 2 5% 3 3 3 3 4 6% 43%	2986
	21st to end	Day	19% 11% 3 6% 4 3 4 3 3 6% 38%	3960
January	1st to 10th	Night	14% 7% 3 7% 4 4 4 4 5% 6% 42%	6349
	11th to 20th	Night	12% 8% 4 10% 5% 4 4 4 5% 6% 37%	6315
	21st to end	Night	15% 10% 2 6% 4 4 5% 4 5% 6% 38%	6974
February	1st to 10th	Night	15% 10% 3 5% 4 4 5% 4 5% 5% 38%	2542
	11th to 20th	Night	13% 7% 3 8% 4 6% 4 4 5% 6% 39%	2338
	21st to end	Night	17% 8% 3 7% 5% 4 4 4 5% 6% 38%	1980
March	1st to 10th	Night	22% 7% 3 5% 4 4 4 3 5% 6% 37%	5364
	11th to 20th	Night	16% 9% 2 6% 4 4 5% 4 5% 7% 39%	5297
	21st to end	Night	23% 9% 2 6% 3 3 4 3 6% 5% 36%	4962
April	1st to 10th	Night	19% 8% 2 7% 5% 5% 5% 3 5% 6% 36%	2000
	11th to 20th	Night	20% 7% 2 5% 4 5% 5% 3 4 6% 38%	1975
	21st to end	Night	22% 7% 2 6% 3 3 3 2 5% 6% 40%	1855
May	1st to 10th	Night	33% 8% 3 6% 3 3 3 3 5% 6% 26%	4054
	11th to 20th	Night	19% 9% 4 8% 5% 6% 5% 4 5% 6% 29%	3741
	21st to end	Night	22% 7% 4 7% 4 4 3 3 6% 7% 33%	3926
June	1st to 10th	Night	17% 7% 3 6% 5% 5% 3 3 4 7% 40%	1600
	11th to 20th	Night	18% 6% 2 6% 4 5% 4 4 6% 7% 39%	1600
	21st to end	Night	15% 6% 2 6% 3 4 4 4 5% 9% 42%	1600
July	1st to 10th	Night	13% 6% 2 6% 4 4 5% 4 7% 9% 40%	3600
	11th to 20th	Night	13% 7% 2 8% 5% 5% 5% 5% 7% 9% 37%	3600
	21st to end	Night	11% 6% 3 6% 3 4 4 3 5% 7% 49%	3926
August	1st to 10th	Night	22% 6% 2 7% 5% 5% 5% 4 5% 6% 34%	2703
	11th to 20th	Night	14% 7% 3 6% 5% 5% 5% 4 6% 7% 39%	3093
	21st to end	Night	10% 4 2 4 3 3 4 4 5% 8% 54%	3586
September	1st to 10th	Night	14% 5% 2 5% 4 4 4 3 5% 6% 47%	1931
	11th to 20th	Night	13% 6% 3 4 3 3 3 3 4 7% 52%	2038
	21st to end	Night	17% 7% 1 6% 4 4 4 3 4 6% 44%	2090
October	1st to 10th	Night	21% 6% 2 6% 3 4 3 3 4 7% 41%	2112
	11th to 20th	Night	16% 6% 2 6% 3 3 4 4 6% 6% 47%	2321
	21st to end	Night	23% 7% 2 5% 5% 4 3 3 5% 5% 39%	2717
November	1st to 10th	Night	14% 6% 2 5% 3 4 3 3 5% 6% 49%	2537
	11th to 20th	Night	20% 5% 2 5% 3 4 3 3 4 5% 46%	2600
	21st to end	Night	16% 8% 2 5% 5% 3 4 3 5% 6% 44%	2655
December	1st to 10th	Night	19% 8% 2 6% 4 4 4 3 5% 6% 40%	4580
	11th to 20th	Night	25% 8% 2 5% 3 2 3 3 5% 5% 40%	5208
	21st to end	Night	20% 11% 3 6% 4 3 3 3 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	43% 6% 10% 28% 12% 1	3598
	11th to 20th	Day	43% 7% 11% 19% 15% 4	3600
	21st to end	Day	45% 6% 10% 21% 17% 1	3978
February	1st to 10th	Day	47% 8% 13% 19% 12% 1	1856
	11th to 20th	Day	46% 6% 10% 22% 13% 3	1957
	21st to end	Day	48% 6% 11% 20% 14% 2	1650
March	1st to 10th	Day	50% 5% 12% 15% 11% 8%	4479
	11th to 20th	Day	41% 9% 17% 23% 9% 2	4646
	21st to end	Day	49% 4 6% 17% 19% 6%	5970
April	1st to 10th	Day	47% 6% 9% 21% 13% 3	2400
	11th to 20th	Day	42% 8% 11% 19% 17% 2	2374
	21st to end	Day	45% 7% 9% 19% 16% 3	2543
May	1st to 10th	Day	59% 8% 11% 13% 9% 1	5897
	11th to 20th	Day	51% 6% 13% 18% 11% 1	6184
	21st to end	Day	45% 7% 13% 22% 12% 1	6949
June	1st to 10th	Day	43% 9% 14% 21% 12% 1	2800
	11th to 20th	Day	42% 8% 15% 20% 13% 1	2800
	21st to end	Day	43% 9% 14% 20% 14% 1	2800
July	1st to 10th	Day	45% 7% 13% 20% 15% 1	6290
	11th to 20th	Day	41% 7% 17% 24% 11% 1	6285
	21st to end	Day	40% 5% 12% 26% 16% 1	6728
August	1st to 10th	Day	47% 7% 16% 20% 9% 1	4401
	11th to 20th	Day	41% 7% 14% 28% 9% 1	3989
	21st to end	Day	34% 8% 14% 28% 15% 1	4312
September	1st to 10th	Day	37% 8% 12% 25% 16% 1	2316
	11th to 20th	Day	35% 6% 9% 25% 22% 2	2142
	21st to end	Day	40% 7% 12% 22% 17% 3	2090
October	1st to 10th	Day	41% 5% 8% 22% 21% 3	3430
	11th to 20th	Day	32% 5% 8% 28% 25% 2	3061
	21st to end	Day	35% 5% 13% 28% 16% 4	3081
November	1st to 10th	Day	37% 7% 14% 25% 15% 2	1761
	11th to 20th	Day	38% 7% 12% 21% 20% 3	1800
	21st to end	Day	44% 5% 14% 24% 10% 2	1743
December	1st to 10th	Day	44% 6% 15% 26% 8% 1	2600
	11th to 20th	Day	43% 4 15% 19% 17% 2	2986
	21st to end	Day	48% 5% 9% 18% 14% 4	3960
January	1st to 10th	Night	42% 5% 11% 27% 14% 2	6349
	11th to 20th	Night	45% 6% 14% 18% 13% 4	6360
	21st to end	Night	46% 6% 11% 16% 17% 4	6974
February	1st to 10th	Night	45% 7% 14% 22% 11% 2	2542
	11th to 20th	Night	44% 7% 12% 20% 14% 3	2340
	21st to end	Night	45% 8% 10% 22% 11% 4	1980
March	1st to 10th	Night	47% 6% 13% 15% 15% 4	5374
	11th to 20th	Night	42% 7% 19% 19% 10% 2	5298
	21st to end	Night	48% 5% 6% 14% 22% 4	4962
April	1st to 10th	Night	48% 6% 11% 19% 14% 2	2000
	11th to 20th	Night	47% 6% 10% 18% 18% 1	1975
	21st to end	Night	44% 7% 9% 20% 15% 5%	1855
May	1st to 10th	Night	58% 7% 14% 11% 9% 1	4060
	11th to 20th	Night	53% 9% 11% 16% 10% 2	3742
	21st to end	Night	50% 7% 14% 18% 10% 1	3927
June	1st to 10th	Night	44% 7% 12% 24% 13% 1	1600
	11th to 20th	Night	42% 9% 15% 23% 11% 1	1600
	21st to end	Night	38% 10% 15% 23% 14% 1	1600
July	1st to 10th	Night	40% 7% 16% 21% 16% 1	3560
	11th to 20th	Night	43% 6% 17% 21% 12% 1	3552
	21st to end	Night	36% 5% 13% 29% 16% 1	3809
August	1st to 10th	Night	50% 9% 11% 20% 9% 1	2693
	11th to 20th	Night	43% 7% 15% 25% 10%	3120
	21st to end	Night	29% 6% 14% 34% 16% 1	3586
September	1st to 10th	Night	37% 7% 11% 26% 18% 1	1931
	11th to 20th	Night	34% 5% 11% 24% 24% 2	2038
	21st to end	Night	41% 6% 9% 23% 18% 3	2090
October	1st to 10th	Night	39% 5% 14% 23% 17% 2	3528
	11th to 20th	Night	28% 4 11% 28% 28% 1	3857
	21st to end	Night	35% 4 13% 32% 15% 1	4467
November	1st to 10th	Night	36% 7% 12% 23% 19% 3	2537
	11th to 20th	Night	41% 6% 12% 20% 18% 3	2600
	21st to end	Night	40% 6% 16% 26% 11% 1	2655
December	1st to 10th	Night	45% 5% 12% 28% 10%	4580
	11th to 20th	Night	46% 5% 15% 15% 16% 2	5208
	21st to end	Night	48% 5% 10% 20% 12% 5%	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	25% 29% 27% 17% 4	200
	11th to 20th	Day	27% 29% 31% 10% 4	200
	21st to end	Day	21% 27% 35% 13% 4	223
February	1st to 10th	Day	29% 29% 32% 9% 1	356
	11th to 20th	Day	30% 25% 32% 12% 1	496
	21st to end	Day	28% 20% 33% 16% 2	414
March	1st to 10th	Day	27% 24% 34% 13% 3	500
	11th to 20th	Day	29% 23% 31% 12% 4	500
	21st to end	Day	29% 25% 30% 9% 5% 2	550
April	1st to 10th	Day	31% 22% 28% 11% 6% 1	500
	11th to 20th	Day	31% 22% 28% 13% 5% 1	492
	21st to end	Day	28% 21% 29% 15% 5% 1	500
May	1st to 10th	Day	33% 20% 26% 13% 7% 1	503
	11th to 20th	Day	21% 18% 37% 17% 6% 1	527
	21st to end	Day	20% 13% 31% 23% 11% 2	573
June	1st to 10th	Day	17% 15% 32% 23% 9% 3	530
	11th to 20th	Day	19% 15% 32% 23% 9% 2	530
	21st to end	Day	15% 15% 35% 21% 10% 3	530
July	1st to 10th	Day	15% 8% 33% 27% 14% 2	525
	11th to 20th	Day	12% 7% 31% 31% 16% 3	524
	21st to end	Day	14% 8% 34% 26% 15% 2	576
August	1st to 10th	Day	10% 9% 26% 33% 17% 5%	526
	11th to 20th	Day	14% 8% 30% 25% 17% 6%	519
	21st to end	Day	11% 11% 29% 28% 15% 6%	583
September	1st to 10th	Day	19% 8% 24% 26% 15% 8%	502
	11th to 20th	Day	17% 11% 24% 22% 16% 11%	490
	21st to end	Day	20% 11% 29% 23% 11% 6%	490
October	1st to 10th	Day	26% 12% 22% 21% 13% 5%	490
	11th to 20th	Day	17% 18% 27% 25% 10% 3	467
	21st to end	Day	28% 14% 26% 23% 8% 1	429
November	1st to 10th	Day	21% 15% 29% 24% 9% 2	395
	11th to 20th	Day	27% 20% 30% 18% 5% 1	400
	21st to end	Day	28% 18% 29% 19% 5% 1	343
December	1st to 10th	Day	23% 25% 32% 15% 6%	200
	11th to 20th	Day	35% 21% 32% 10% 3	200
	21st to end	Day	23% 24% 32% 17% 3 1	220
January	1st to 10th	Night	21% 17% 38% 21% 3	800
	11th to 20th	Night	25% 18% 33% 23% 3	800
	21st to end	Night	18% 17% 40% 23% 3	880
February	1st to 10th	Night	22% 18% 37% 22% 1	800
	11th to 20th	Night	21% 22% 40% 15% 1	783
	21st to end	Night	24% 20% 33% 20% 3	660
March	1st to 10th	Night	23% 19% 37% 19% 2	800
	11th to 20th	Night	22% 22% 33% 20% 3	800
	21st to end	Night	23% 18% 35% 19% 5%	880
April	1st to 10th	Night	24% 19% 34% 20% 4	800
	11th to 20th	Night	24% 18% 32% 20% 5%	791
	21st to end	Night	24% 19% 31% 22% 3	655
May	1st to 10th	Night	28% 15% 32% 22% 4	600
	11th to 20th	Night	19% 14% 38% 23% 6%	469
	21st to end	Night	19% 9% 28% 35% 8%	433
June	1st to 10th	Night	19% 7% 31% 35% 9%	400
	11th to 20th	Night	18% 8% 31% 34% 9%	400
	21st to end	Night	17% 5% 29% 38% 11% 1	400
July	1st to 10th	Night	14% 3 26% 42% 15% 1	390
	11th to 20th	Night	15% 4 24% 41% 16% 1	388
	21st to end	Night	10% 4 26% 46% 14%	438
August	1st to 10th	Night	13% 3 25% 45% 14% 1	463
	11th to 20th	Night	13% 5% 23% 39% 18% 2	722
	21st to end	Night	15% 6% 21% 39% 18% 1	880
September	1st to 10th	Night	17% 5% 26% 35% 15% 2	773
	11th to 20th	Night	15% 7% 24% 31% 21% 3	760
	21st to end	Night	18% 8% 25% 33% 14% 2	760
October	1st to 10th	Night	25% 8% 24% 29% 13% 2	760
	11th to 20th	Night	18% 11% 32% 30% 9%	760
	21st to end	Night	26% 12% 31% 25% 6%	836
November	1st to 10th	Night	17% 14% 32% 28% 8% 1	780
	11th to 20th	Night	22% 15% 33% 23% 7% 1	800
	21st to end	Night	21% 16% 30% 27% 5% 1	800
December	1st to 10th	Night	24% 15% 37% 19% 5%	800
	11th to 20th	Night	26% 16% 31% 24% 3	800
	21st to end	Night	25% 16% 36% 21% 2	880

Page generated at 2025-09-01 01:51:03. Version ac07

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