New Haven
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the New Haven clear sky chart from 2005-11-06 to 2025-10-04.

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	14% 9% 3 8% 5% 5% 5% 4 6% 7% 34%	125829
	Night	14% 10% 4 8% 5% 4 4 4 5% 6% 35%	123624
Transparency	Day	46% 7% 13% 20% 12% 1	129401
	Night	48% 6% 12% 21% 12% 1	128122
Seeing	Day	16% 8% 27% 27% 16% 6%	16540
	Night	18% 8% 29% 31% 13% 2	26062

By Month

Percentage Cloud Cover SE (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% 15% 6% 14% 5% 4 4 3 4 5% 28%	3617
	11th to 20th	Day	14% 17% 5% 17% 8% 8% 5% 4 4 5% 14%	3677
	21st to end	Day	22% 17% 6% 10% 6% 4 5% 3 4 4 18%	4466
February	1st to 10th	Day	15% 15% 5% 12% 8% 6% 5% 4 4 5% 22%	1800
	11th to 20th	Day	14% 15% 5% 11% 8% 5% 5% 3 4 6% 25%	1852
	21st to end	Day	14% 16% 5% 12% 7% 4 4 3 4 5% 26%	1650
March	1st to 10th	Day	15% 13% 6% 10% 5% 4 4 3 4 5% 31%	4654
	11th to 20th	Day	12% 12% 4 8% 5% 5% 5% 4 5% 7% 34%	4980
	21st to end	Day	20% 14% 4 8% 5% 4 4 3 5% 5% 29%	5465
April	1st to 10th	Day	15% 13% 4 9% 6% 4 4 3 5% 6% 32%	2286
	11th to 20th	Day	17% 9% 3 8% 5% 5% 4 4 5% 7% 34%	2567
	21st to end	Day	17% 9% 3 8% 5% 5% 4 3 4 7% 35%	2600
May	1st to 10th	Day	19% 9% 3 8% 4 4 4 4 5% 7% 34%	5862
	11th to 20th	Day	17% 8% 3 7% 5% 4 5% 4 5% 7% 35%	5861
	21st to end	Day	14% 7% 3 7% 5% 4 4 4 5% 7% 40%	6473
June	1st to 10th	Day	9% 5% 3 7% 5% 5% 5% 4 7% 9% 41%	2942
	11th to 20th	Day	10% 5% 3 7% 5% 5% 5% 4 8% 9% 41%	3000
	21st to end	Day	9% 6% 2 6% 5% 6% 5% 5% 7% 9% 40%	2983
July	1st to 10th	Day	9% 5% 2 7% 5% 5% 6% 5% 7% 10% 38%	6360
	11th to 20th	Day	6% 5% 2 6% 5% 5% 5% 5% 6% 10% 45%	6360
	21st to end	Day	7% 5% 2 6% 5% 5% 5% 5% 8% 10% 43%	6430
August	1st to 10th	Day	11% 5% 2 6% 4 5% 5% 5% 7% 9% 41%	4234
	11th to 20th	Day	9% 5% 2 7% 5% 5% 6% 5% 8% 10% 38%	4174
	21st to end	Day	9% 5% 2 7% 5% 5% 6% 5% 7% 9% 39%	4675
September	1st to 10th	Day	9% 6% 2 6% 5% 5% 5% 4 6% 10% 42%	2259
	11th to 20th	Day	9% 4 2 6% 3 5% 5% 4 6% 9% 48%	2200
	21st to end	Day	14% 7% 3 7% 4 4 5% 5% 6% 8% 36%	2200
October	1st to 10th	Day	12% 7% 3 7% 4 5% 5% 3 6% 7% 43%	2042
	11th to 20th	Day	17% 9% 3 7% 5% 5% 4 4 4 7% 34%	1900
	21st to end	Day	18% 11% 4 8% 4 3 5% 3 4 7% 30%	1967
November	1st to 10th	Day	12% 9% 3 8% 4 6% 5% 4 6% 7% 37%	1762
	11th to 20th	Day	15% 11% 4 7% 6% 4 5% 4 6% 6% 33%	1800
	21st to end	Day	18% 12% 5% 10% 6% 4 4 3 6% 6% 26%	1601
December	1st to 10th	Day	14% 14% 6% 12% 5% 4 4 3 6% 7% 24%	2600
	11th to 20th	Day	20% 19% 4 9% 4 4 4 3 6% 5% 21%	2842
	21st to end	Day	26% 19% 7% 10% 4 4 4 2 3 5% 14%	3688
January	1st to 10th	Night	13% 14% 5% 12% 5% 4 4 3 5% 5% 29%	6348
	11th to 20th	Night	12% 16% 6% 15% 8% 5% 5% 4 5% 5% 19%	6296
	21st to end	Night	18% 17% 8% 9% 5% 4 5% 3 4 4 23%	6490
February	1st to 10th	Night	14% 16% 5% 13% 6% 5% 5% 4 5% 5% 22%	2600
	11th to 20th	Night	14% 14% 5% 9% 7% 4 5% 5% 5% 5% 28%	2431
	21st to end	Night	18% 12% 4 9% 5% 5% 5% 3 6% 5% 29%	1980
March	1st to 10th	Night	16% 13% 4 8% 5% 4 3 3 5% 6% 34%	5198
	11th to 20th	Night	9% 8% 3 8% 5% 5% 5% 4 6% 8% 40%	4980
	21st to end	Night	16% 10% 3 7% 5% 4 4 3 4 5% 38%	5467
April	1st to 10th	Night	18% 10% 3 6% 5% 4 4 4 5% 6% 35%	2130
	11th to 20th	Night	18% 8% 3 6% 4 5% 4 4 5% 7% 37%	1780
	21st to end	Night	15% 8% 3 5% 5% 4 4 4 6% 8% 38%	1800
May	1st to 10th	Night	20% 8% 3 7% 5% 4 4 3 5% 6% 34%	4033
	11th to 20th	Night	16% 8% 3 8% 5% 4 4 4 4 7% 39%	4032
	21st to end	Night	14% 5% 2 6% 4 4 4 3 5% 7% 44%	4376
June	1st to 10th	Night	10% 5% 2 6% 4 3 4 4 6% 8% 47%	1453
	11th to 20th	Night	10% 6% 2 6% 3 4 5% 5% 6% 8% 45%	1400
	21st to end	Night	8% 5% 2 6% 5% 4 3 4 5% 8% 50%	1411
July	1st to 10th	Night	8% 4 2 6% 4 4 5% 4 7% 11% 47%	3618
	11th to 20th	Night	9% 4 2 5% 4 4 5% 4 6% 10% 48%	3617
	21st to end	Night	7% 5% 2 5% 4 5% 4 4 7% 9% 49%	4417
August	1st to 10th	Night	11% 5% 2 6% 4 4 4 3 5% 8% 47%	2915
	11th to 20th	Night	9% 6% 2 6% 4 4 5% 4 5% 8% 46%	2875
	21st to end	Night	8% 5% 2 6% 5% 4 5% 4 5% 7% 49%	3223
September	1st to 10th	Night	9% 6% 3 6% 5% 4 4 3 5% 8% 48%	2118
	11th to 20th	Night	9% 5% 2 4 3 3 3 3 5% 8% 55%	2200
	21st to end	Night	15% 7% 2 6% 4 5% 3 4 5% 7% 43%	2200
October	1st to 10th	Night	13% 6% 3 7% 3 3 4 3 5% 6% 47%	2205
	11th to 20th	Night	19% 8% 3 8% 4 5% 4 3 5% 6% 36%	2280
	21st to end	Night	20% 9% 3 6% 4 5% 5% 4 5% 7% 32%	2627
November	1st to 10th	Night	13% 8% 2 7% 4 4 4 3 6% 7% 42%	2536
	11th to 20th	Night	15% 11% 3 8% 5% 5% 4 4 6% 7% 31%	2600
	21st to end	Night	19% 14% 4 8% 5% 3 4 3 5% 6% 28%	2795
December	1st to 10th	Night	14% 13% 5% 12% 6% 5% 5% 4 6% 7% 24%	4580
	11th to 20th	Night	15% 19% 6% 10% 6% 5% 4 3 4 6% 22%	5341
	21st to end	Night	26% 19% 6% 10% 5% 4 4 3 4 4 17%	7272

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	59% 6% 12% 14% 7% 2	3618
	11th to 20th	Day	72% 6% 9% 6% 6% 1	3677
	21st to end	Day	68% 5% 12% 8% 6%	4466
February	1st to 10th	Day	64% 6% 9% 14% 6%	1800
	11th to 20th	Day	60% 4 11% 16% 7% 1	1861
	21st to end	Day	59% 6% 11% 16% 6% 1	1650
March	1st to 10th	Day	54% 5% 15% 17% 8% 2	4654
	11th to 20th	Day	48% 5% 15% 21% 8% 1	4980
	21st to end	Day	56% 5% 13% 15% 10% 1	5465
April	1st to 10th	Day	51% 6% 12% 19% 11% 1	2286
	11th to 20th	Day	48% 5% 11% 20% 14% 2	2567
	21st to end	Day	48% 6% 13% 19% 13% 2	2600
May	1st to 10th	Day	47% 6% 12% 19% 12% 4	5897
	11th to 20th	Day	45% 8% 13% 20% 12% 1	5865
	21st to end	Day	41% 6% 11% 19% 18% 5%	6488
June	1st to 10th	Day	38% 8% 12% 26% 14% 2	2942
	11th to 20th	Day	37% 7% 14% 23% 15% 3	3000
	21st to end	Day	37% 9% 14% 23% 16% 2	2983
July	1st to 10th	Day	37% 7% 13% 25% 16% 2	6291
	11th to 20th	Day	31% 7% 15% 29% 16% 1	6285
	21st to end	Day	32% 9% 16% 22% 21% 1	6246
August	1st to 10th	Day	36% 9% 15% 24% 16% 1	4221
	11th to 20th	Day	36% 9% 13% 31% 10% 1	4213
	21st to end	Day	38% 7% 14% 27% 13% 1	4674
September	1st to 10th	Day	37% 8% 14% 25% 14% 2	2259
	11th to 20th	Day	31% 8% 13% 33% 15% 1	2200
	21st to end	Day	43% 8% 13% 24% 12% 1	2200
October	1st to 10th	Day	31% 6% 12% 33% 17% 1	3367
	11th to 20th	Day	41% 5% 12% 25% 17%	3140
	21st to end	Day	45% 6% 14% 22% 12% 1	3217
November	1st to 10th	Day	43% 8% 13% 24% 11% 1	1762
	11th to 20th	Day	51% 7% 13% 18% 10% 1	1800
	21st to end	Day	58% 7% 12% 17% 6% 1	1601
December	1st to 10th	Day	59% 6% 17% 14% 4	2600
	11th to 20th	Day	64% 5% 12% 12% 7%	2838
	21st to end	Day	73% 5% 8% 8% 6%	3688
January	1st to 10th	Night	56% 5% 11% 20% 7% 2	6348
	11th to 20th	Night	66% 7% 11% 10% 5%	6296
	21st to end	Night	65% 4 10% 14% 7%	6490
February	1st to 10th	Night	62% 6% 10% 14% 7% 1	2600
	11th to 20th	Night	57% 6% 11% 17% 8% 1	2433
	21st to end	Night	55% 5% 12% 18% 8% 1	1980
March	1st to 10th	Night	51% 4 14% 20% 10% 1	5198
	11th to 20th	Night	41% 6% 16% 24% 14% 1	4980
	21st to end	Night	48% 4 11% 20% 15% 1	5467
April	1st to 10th	Night	49% 5% 11% 20% 12% 2	2130
	11th to 20th	Night	45% 6% 12% 18% 17% 2	1780
	21st to end	Night	43% 7% 11% 20% 16% 4	1800
May	1st to 10th	Night	51% 5% 10% 16% 13% 5%	4060
	11th to 20th	Night	44% 6% 12% 23% 12% 2	4033
	21st to end	Night	38% 7% 11% 23% 16% 5%	4383
June	1st to 10th	Night	35% 6% 11% 27% 19% 2	1453
	11th to 20th	Night	35% 7% 14% 24% 18% 2	1400
	21st to end	Night	33% 6% 12% 26% 22% 1	1411
July	1st to 10th	Night	30% 6% 14% 28% 16% 5%	3580
	11th to 20th	Night	31% 7% 14% 31% 17% 1	3572
	21st to end	Night	31% 7% 14% 22% 24% 2	4288
August	1st to 10th	Night	35% 6% 14% 26% 17% 1	2904
	11th to 20th	Night	34% 7% 13% 32% 12% 2	2902
	21st to end	Night	34% 7% 12% 32% 15% 1	3223
September	1st to 10th	Night	34% 7% 13% 29% 15% 2	2118
	11th to 20th	Night	27% 7% 14% 31% 20% 1	2200
	21st to end	Night	40% 7% 11% 28% 12% 1	2200
October	1st to 10th	Night	26% 4 10% 32% 26% 1	3660
	11th to 20th	Night	43% 5% 11% 23% 17% 1	3779
	21st to end	Night	41% 5% 14% 25% 13% 1	4327
November	1st to 10th	Night	41% 6% 12% 26% 14% 1	2536
	11th to 20th	Night	50% 6% 13% 19% 10% 1	2600
	21st to end	Night	56% 6% 14% 17% 6%	2795
December	1st to 10th	Night	59% 7% 17% 13% 3	4580
	11th to 20th	Night	63% 5% 12% 12% 7% 1	5344
	21st to end	Night	71% 5% 10% 8% 5%	7272

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	21% 14% 38% 19% 6% 1	300
	11th to 20th	Day	20% 14% 45% 17% 4 1	300
	21st to end	Day	29% 8% 36% 21% 5% 1	330
February	1st to 10th	Day	21% 17% 38% 21% 3 1	300
	11th to 20th	Day	20% 16% 38% 24% 2	300
	21st to end	Day	18% 20% 43% 16% 3	249
March	1st to 10th	Day	19% 16% 39% 22% 4 1	370
	11th to 20th	Day	18% 14% 33% 27% 7% 1	500
	21st to end	Day	25% 12% 30% 26% 6% 1	550
April	1st to 10th	Day	16% 12% 38% 25% 8% 1	500
	11th to 20th	Day	24% 11% 29% 21% 11% 4	492
	21st to end	Day	22% 10% 27% 28% 10% 2	500
May	1st to 10th	Day	22% 8% 28% 28% 12% 3	503
	11th to 20th	Day	18% 6% 25% 28% 17% 6%	527
	21st to end	Day	15% 4 21% 30% 22% 9%	573
June	1st to 10th	Day	10% 5% 26% 37% 16% 5%	672
	11th to 20th	Day	10% 4 26% 34% 21% 4	730
	21st to end	Day	11% 5% 24% 35% 20% 5%	730
July	1st to 10th	Day	8% 3 17% 32% 26% 13%	721
	11th to 20th	Day	9% 3 22% 35% 22% 8%	718
	21st to end	Day	7% 4 16% 36% 27% 10%	582
August	1st to 10th	Day	9% 2 15% 32% 29% 14%	526
	11th to 20th	Day	11% 3 13% 35% 27% 11%	519
	21st to end	Day	12% 3 17% 31% 24% 13%	583
September	1st to 10th	Day	10% 3 24% 22% 27% 13%	530
	11th to 20th	Day	8% 3 15% 22% 34% 18%	530
	21st to end	Day	16% 7% 22% 24% 20% 10%	530
October	1st to 10th	Day	14% 7% 27% 23% 20% 10%	502
	11th to 20th	Day	21% 13% 30% 25% 9% 3	490
	21st to end	Day	23% 13% 33% 22% 8% 1	416
November	1st to 10th	Day	17% 13% 33% 25% 11% 1	300
	11th to 20th	Day	21% 19% 32% 20% 7% 1	300
	21st to end	Day	25% 15% 35% 21% 5%	200
December	1st to 10th	Day	21% 16% 38% 17% 9% 1	200
	11th to 20th	Day	29% 14% 39% 16% 4 1	200
	21st to end	Day	26% 14% 37% 18% 4	267
January	1st to 10th	Night	23% 11% 38% 22% 6% 1	1000
	11th to 20th	Night	25% 11% 34% 25% 4 1	975
	21st to end	Night	20% 9% 36% 29% 6%	880
February	1st to 10th	Night	20% 9% 41% 26% 4	800
	11th to 20th	Night	21% 11% 35% 29% 5%	783
	21st to end	Night	23% 10% 39% 24% 3	660
March	1st to 10th	Night	20% 9% 36% 29% 6%	800
	11th to 20th	Night	16% 11% 39% 26% 7% 1	800
	21st to end	Night	23% 8% 31% 29% 9% 1	880
April	1st to 10th	Night	21% 10% 33% 30% 5%	730
	11th to 20th	Night	21% 9% 32% 27% 10% 2	593
	21st to end	Night	19% 5% 33% 34% 9%	600
May	1st to 10th	Night	18% 4 29% 36% 12% 1	600
	11th to 20th	Night	19% 4 27% 32% 18% 1	591
	21st to end	Night	11% 3 21% 39% 23% 3	630
June	1st to 10th	Night	12% 3 25% 43% 18%	400
	11th to 20th	Night	11% 3 23% 46% 17% 1	400
	21st to end	Night	10% 2 19% 44% 24%	411
July	1st to 10th	Night	8% 2 14% 41% 30% 5%	585
	11th to 20th	Night	9% 3 16% 40% 28% 4	582
	21st to end	Night	6% 2 16% 45% 28% 3	657
August	1st to 10th	Night	9% 2 13% 37% 36% 3	597
	11th to 20th	Night	6% 2 16% 38% 33% 5%	594
	21st to end	Night	9% 2 16% 38% 32% 3	660
September	1st to 10th	Night	11% 4 18% 34% 27% 6%	745
	11th to 20th	Night	10% 3 15% 33% 34% 6%	800
	21st to end	Night	17% 5% 18% 34% 20% 6%	800
October	1st to 10th	Night	15% 6% 26% 32% 19% 3	773
	11th to 20th	Night	22% 11% 27% 29% 9% 2	760
	21st to end	Night	25% 10% 32% 28% 6%	836
November	1st to 10th	Night	17% 10% 31% 28% 14% 1	780
	11th to 20th	Night	20% 14% 35% 23% 7% 1	800
	21st to end	Night	27% 12% 35% 22% 5%	800
December	1st to 10th	Night	25% 11% 36% 21% 6% 1	800
	11th to 20th	Night	23% 12% 38% 24% 4	860
	21st to end	Night	29% 10% 33% 24% 3	1100

Page generated at 2025-10-01 01:39:03. Version ac07

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