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 2026-08-15.

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% 2 5% 4 4 4 4 5% 7% 41%	143622
	Night	18% 8% 2 6% 4 4 4 3 5% 6% 42%	138278
Transparency	Day	42% 5% 12% 22% 16% 3	147153
	Night	43% 4 11% 22% 16% 3	142836
Seeing	Day	21% 17% 31% 21% 8% 2	17303
	Night	21% 13% 32% 25% 8% 1	26279

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% 7% 2 6% 4 5% 4 4 5% 5% 44%	4661
	11th to 20th	Day	16% 8% 3 6% 3 3 4 4 4 5% 45%	4650
	21st to end	Day	16% 7% 2 6% 4 4 4 4 5% 6% 43%	5304
February	1st to 10th	Day	16% 7% 2 6% 5% 5% 5% 3 5% 6% 39%	1964
	11th to 20th	Day	16% 7% 2 5% 4 4 4 4 6% 7% 42%	2048
	21st to end	Day	20% 8% 3 5% 4 3 3 3 5% 6% 38%	1730
March	1st to 10th	Day	23% 8% 2 5% 3 3 3 3 4 5% 41%	4576
	11th to 20th	Day	15% 8% 2 5% 4 3 4 4 6% 7% 43%	4769
	21st to end	Day	20% 7% 2 6% 4 4 4 4 5% 6% 38%	6102
April	1st to 10th	Day	20% 8% 2 5% 4 4 4 3 5% 7% 39%	2520
	11th to 20th	Day	19% 6% 2 5% 3 4 4 3 3 7% 42%	2494
	21st to end	Day	20% 5% 2 5% 4 3 4 3 5% 6% 41%	2629
May	1st to 10th	Day	27% 8% 2 5% 3 3 3 3 5% 7% 33%	7639
	11th to 20th	Day	21% 7% 2 6% 4 4 4 3 5% 7% 38%	7972
	21st to end	Day	23% 6% 3 6% 4 4 4 4 6% 8% 32%	9060
June	1st to 10th	Day	18% 5% 2 5% 4 4 5% 5% 6% 8% 38%	2940
	11th to 20th	Day	16% 6% 2 5% 4 4 4 4 6% 10% 38%	2940
	21st to end	Day	13% 6% 2 5% 4 4 5% 4 6% 9% 40%	2940
July	1st to 10th	Day	16% 6% 2 6% 4 4 4 4 6% 10% 37%	8280
	11th to 20th	Day	12% 5% 2 6% 4 4 5% 4 7% 10% 42%	8280
	21st to end	Day	15% 6% 2 6% 4 4 4 4 5% 7% 42%	8993
August	1st to 10th	Day	19% 6% 2 6% 5% 5% 5% 4 6% 8% 34%	4517
	11th to 20th	Day	12% 6% 2 6% 4 3 4 4 6% 9% 43%	3903
	21st to end	Day	8% 5% 2 6% 5% 4 4 4 6% 10% 47%	4312
September	1st to 10th	Day	14% 5% 2 5% 5% 4 4 4 5% 6% 46%	2400
	11th to 20th	Day	12% 5% 2 4 3 4 4 3 5% 6% 52%	2262
	21st to end	Day	20% 6% 2 5% 5% 4 4 3 4 7% 40%	2200
October	1st to 10th	Day	20% 7% 2 5% 4 3 3 3 4 6% 43%	2169
	11th to 20th	Day	15% 4 1 5% 4 3 4 4 5% 7% 48%	1989
	21st to end	Day	19% 6% 1 4 4 4 4 4 5% 7% 42%	1980
November	1st to 10th	Day	13% 6% 2 6% 4 4 3 3 4 6% 49%	1851
	11th to 20th	Day	18% 6% 2 4 2 3 3 2 5% 7% 48%	1890
	21st to end	Day	18% 6% 2 5% 3 3 4 3 5% 6% 44%	1864
December	1st to 10th	Day	16% 6% 2 5% 4 4 3 4 4 7% 45%	2680
	11th to 20th	Day	22% 7% 2 4 3 2 3 2 4 6% 47%	3066
	21st to end	Day	20% 9% 3 6% 4 3 3 3 4 6% 40%	4048
January	1st to 10th	Night	15% 7% 2 5% 3 4 3 3 4 6% 47%	8234
	11th to 20th	Night	16% 9% 3 7% 4 3 3 3 4 5% 44%	8235
	21st to end	Night	16% 8% 2 6% 4 4 4 3 4 5% 42%	8860
February	1st to 10th	Night	16% 9% 3 6% 4 3 4 4 5% 5% 41%	2654
	11th to 20th	Night	18% 8% 3 5% 4 3 3 3 4 7% 41%	2458
	21st to end	Night	19% 8% 3 6% 4 4 4 3 3 6% 40%	2076
March	1st to 10th	Night	21% 10% 2 5% 3 3 3 3 4 5% 41%	5484
	11th to 20th	Night	17% 10% 3 5% 4 4 4 3 4 6% 42%	5406
	21st to end	Night	21% 9% 3 6% 4 3 4 3 5% 5% 38%	5072
April	1st to 10th	Night	20% 6% 2 6% 4 4 4 4 5% 6% 37%	2100
	11th to 20th	Night	21% 6% 2 5% 4 4 3 3 5% 6% 41%	2075
	21st to end	Night	20% 7% 2 6% 4 3 4 3 4 5% 43%	1990
May	1st to 10th	Night	26% 10% 3 6% 4 3 4 3 5% 6% 31%	5259
	11th to 20th	Night	21% 9% 3 6% 4 4 4 3 5% 8% 34%	4942
	21st to end	Night	24% 9% 3 6% 5% 4 4 3 4 5% 32%	5114
June	1st to 10th	Night	18% 6% 2 6% 5% 4 4 4 5% 6% 41%	1680
	11th to 20th	Night	17% 7% 2 6% 4 3 4 4 5% 9% 39%	1680
	21st to end	Night	14% 6% 2 6% 4 5% 4 3 5% 8% 42%	1680
July	1st to 10th	Night	18% 8% 2 7% 4 4 4 4 6% 8% 35%	4680
	11th to 20th	Night	17% 8% 2 6% 4 4 4 4 6% 8% 37%	4680
	21st to end	Night	16% 6% 2 6% 4 4 4 4 6% 7% 41%	5084
August	1st to 10th	Night	23% 6% 2 7% 4 5% 5% 5% 6% 7% 30%	2818
	11th to 20th	Night	14% 6% 3 7% 4 4 6% 4 5% 7% 40%	3230
	21st to end	Night	10% 4 1 4 3 3 4 3 5% 8% 55%	3586
September	1st to 10th	Night	15% 5% 3 5% 4 4 4 3 4 8% 44%	2000
	11th to 20th	Night	14% 5% 2 4 3 3 4 3 4 6% 53%	2136
	21st to end	Night	19% 7% 3 5% 4 4 4 3 4 5% 43%	2200
October	1st to 10th	Night	19% 6% 3 6% 4 3 4 2 4 6% 43%	2229
	11th to 20th	Night	16% 5% 2 6% 3 3 3 2 4 6% 49%	2410
	21st to end	Night	22% 7% 2 5% 3 3 4 3 5% 5% 42%	2860
November	1st to 10th	Night	12% 6% 2 5% 3 3 4 4 5% 6% 50%	2667
	11th to 20th	Night	18% 6% 2 4 3 3 3 3 4 6% 48%	2730
	21st to end	Night	16% 5% 1 5% 4 4 4 3 4 7% 47%	2751
December	1st to 10th	Night	17% 6% 2 5% 3 3 4 3 4 4 49%	4720
	11th to 20th	Night	26% 7% 2 4 3 3 4 2 4 4 43%	5348
	21st to end	Night	20% 9% 3 6% 3 3 3 3 3 5% 42%	7150

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	41% 5% 10% 26% 16% 3	4662
	11th to 20th	Day	42% 3 10% 21% 15% 8%	4680
	21st to end	Day	41% 5% 10% 25% 17% 1	5304
February	1st to 10th	Day	45% 5% 13% 20% 15% 2	1964
	11th to 20th	Day	41% 5% 11% 23% 16% 3	2057
	21st to end	Day	46% 5% 11% 20% 15% 3	1730
March	1st to 10th	Day	46% 4 11% 16% 13% 10%	4579
	11th to 20th	Day	40% 5% 16% 26% 12% 2	4769
	21st to end	Day	47% 4 9% 15% 19% 6%	6102
April	1st to 10th	Day	45% 5% 10% 19% 16% 4	2520
	11th to 20th	Day	43% 5% 12% 20% 18% 3	2494
	21st to end	Day	44% 5% 9% 21% 16% 4	2629
May	1st to 10th	Day	52% 6% 14% 16% 12% 1	7651
	11th to 20th	Day	45% 6% 13% 22% 13% 1	7976
	21st to end	Day	49% 6% 12% 20% 12% 1	9061
June	1st to 10th	Day	42% 8% 13% 23% 14% 1	2940
	11th to 20th	Day	40% 8% 15% 22% 13% 2	2940
	21st to end	Day	39% 9% 14% 22% 14% 1	2940
July	1st to 10th	Day	45% 8% 13% 20% 14% 1	8210
	11th to 20th	Day	37% 5% 17% 28% 13% 1	8205
	21st to end	Day	41% 5% 11% 23% 19% 1	8795
August	1st to 10th	Day	47% 7% 15% 21% 9% 1	4503
	11th to 20th	Day	37% 6% 14% 31% 11% 1	3939
	21st to end	Day	34% 7% 13% 27% 17% 2	4312
September	1st to 10th	Day	37% 7% 12% 23% 19% 2	2400
	11th to 20th	Day	32% 6% 12% 24% 25% 2	2262
	21st to end	Day	44% 6% 9% 19% 19% 3	2200
October	1st to 10th	Day	36% 5% 10% 20% 24% 6%	3533
	11th to 20th	Day	28% 3 10% 24% 31% 4	3217
	21st to end	Day	31% 5% 13% 25% 23% 3	3180
November	1st to 10th	Day	38% 4 14% 21% 22% 2	1851
	11th to 20th	Day	37% 4 12% 22% 22% 3	1890
	21st to end	Day	41% 5% 13% 27% 12% 3	1864
December	1st to 10th	Day	40% 4 15% 27% 13% 1	2680
	11th to 20th	Day	41% 3 15% 19% 19% 3	3066
	21st to end	Day	48% 4 8% 20% 16% 5%	4048
January	1st to 10th	Night	40% 4 11% 25% 18% 3	8234
	11th to 20th	Night	43% 4 11% 20% 16% 6%	8280
	21st to end	Night	45% 4 8% 20% 19% 4	8860
February	1st to 10th	Night	44% 6% 11% 24% 13% 2	2654
	11th to 20th	Night	44% 5% 9% 21% 17% 4	2460
	21st to end	Night	47% 3 9% 22% 14% 4	2076
March	1st to 10th	Night	47% 4 11% 18% 14% 7%	5494
	11th to 20th	Night	44% 5% 15% 21% 11% 4	5407
	21st to end	Night	49% 3 6% 12% 24% 5%	5072
April	1st to 10th	Night	47% 5% 10% 19% 15% 4	2100
	11th to 20th	Night	44% 5% 11% 19% 20% 1	2075
	21st to end	Night	45% 4 9% 21% 16% 4	1990
May	1st to 10th	Night	54% 5% 13% 14% 12% 1	5265
	11th to 20th	Night	49% 6% 13% 19% 10% 3	4943
	21st to end	Night	54% 5% 12% 20% 9% 1	5115
June	1st to 10th	Night	44% 6% 9% 21% 18% 2	1680
	11th to 20th	Night	41% 7% 14% 25% 12% 1	1680
	21st to end	Night	40% 7% 13% 25% 14% 1	1680
July	1st to 10th	Night	48% 7% 14% 19% 12% 1	4640
	11th to 20th	Night	44% 4 15% 24% 12% 1	4632
	21st to end	Night	41% 5% 14% 24% 16% 1	4967
August	1st to 10th	Night	53% 7% 13% 16% 10% 1	2808
	11th to 20th	Night	43% 6% 14% 28% 9% 1	3260
	21st to end	Night	28% 5% 15% 32% 19% 1	3586
September	1st to 10th	Night	39% 6% 10% 26% 18% 2	2000
	11th to 20th	Night	33% 5% 10% 24% 26% 2	2136
	21st to end	Night	44% 5% 8% 20% 20% 2	2200
October	1st to 10th	Night	38% 4 12% 24% 19% 3	3645
	11th to 20th	Night	26% 4 9% 27% 30% 4	3921
	21st to end	Night	32% 4 13% 27% 21% 2	4610
November	1st to 10th	Night	36% 5% 12% 23% 20% 4	2667
	11th to 20th	Night	40% 3 9% 23% 20% 4	2730
	21st to end	Night	39% 4 12% 29% 13% 2	2751
December	1st to 10th	Night	40% 4 12% 29% 14% 1	4720
	11th to 20th	Night	47% 3 12% 17% 18% 2	5348
	21st to end	Night	46% 3 10% 19% 17% 4	7150

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	27% 25% 28% 17% 2	220
	11th to 20th	Day	27% 32% 28% 12%	220
	21st to end	Day	25% 29% 31% 10% 4 1	275
February	1st to 10th	Day	25% 26% 34% 14% 1	404
	11th to 20th	Day	24% 29% 34% 12% 1	536
	21st to end	Day	27% 26% 31% 13% 3	446
March	1st to 10th	Day	24% 24% 35% 15% 2	540
	11th to 20th	Day	23% 26% 33% 14% 3 1	540
	21st to end	Day	28% 24% 34% 10% 3 1	594
April	1st to 10th	Day	29% 24% 31% 11% 5% 1	540
	11th to 20th	Day	27% 21% 31% 16% 5% 1	532
	21st to end	Day	26% 18% 35% 16% 4 1	540
May	1st to 10th	Day	29% 21% 31% 13% 5% 1	543
	11th to 20th	Day	21% 17% 36% 21% 5% 1	567
	21st to end	Day	22% 12% 30% 24% 10% 2	617
June	1st to 10th	Day	17% 12% 34% 25% 11% 2	570
	11th to 20th	Day	19% 13% 33% 25% 8% 1	570
	21st to end	Day	16% 10% 33% 27% 12% 2	570
July	1st to 10th	Day	17% 7% 28% 31% 15% 2	565
	11th to 20th	Day	13% 8% 29% 33% 14% 4	564
	21st to end	Day	15% 8% 34% 33% 9% 2	620
August	1st to 10th	Day	13% 8% 29% 33% 13% 5%	566
	11th to 20th	Day	13% 5% 30% 31% 17% 4	535
	21st to end	Day	10% 10% 32% 27% 14% 6%	583
September	1st to 10th	Day	18% 8% 29% 24% 16% 4	530
	11th to 20th	Day	14% 6% 32% 27% 14% 7%	530
	21st to end	Day	22% 10% 33% 22% 10% 2	530
October	1st to 10th	Day	25% 11% 25% 22% 12% 4	530
	11th to 20th	Day	17% 20% 28% 25% 8% 2	523
	21st to end	Day	25% 16% 32% 17% 8% 2	462
November	1st to 10th	Day	17% 19% 29% 23% 10% 2	425
	11th to 20th	Day	24% 25% 28% 19% 4	430
	21st to end	Day	24% 22% 28% 19% 6%	404
December	1st to 10th	Day	24% 20% 36% 15% 5%	220
	11th to 20th	Day	30% 26% 30% 12% 1	220
	21st to end	Day	29% 19% 33% 14% 5%	242
January	1st to 10th	Night	21% 21% 36% 18% 3	840
	11th to 20th	Night	28% 20% 31% 19% 2	840
	21st to end	Night	21% 21% 36% 19% 2	924
February	1st to 10th	Night	22% 20% 34% 22% 2	840
	11th to 20th	Night	23% 21% 38% 16% 2	823
	21st to end	Night	26% 19% 36% 16% 3	692
March	1st to 10th	Night	24% 18% 35% 20% 3	840
	11th to 20th	Night	23% 15% 37% 21% 4 1	840
	21st to end	Night	23% 20% 36% 18% 3	924
April	1st to 10th	Night	25% 17% 35% 19% 4	840
	11th to 20th	Night	23% 14% 37% 22% 4	831
	21st to end	Night	22% 15% 37% 21% 5%	730
May	1st to 10th	Night	26% 12% 34% 21% 7%	630
	11th to 20th	Night	23% 11% 37% 23% 6%	524
	21st to end	Night	22% 5% 25% 37% 9%	455
June	1st to 10th	Night	21% 5% 29% 34% 10%	420
	11th to 20th	Night	20% 6% 29% 34% 11%	420
	21st to end	Night	16% 5% 27% 41% 10% 1	420
July	1st to 10th	Night	15% 5% 24% 40% 15% 1	410
	11th to 20th	Night	15% 2 22% 44% 16% 1	408
	21st to end	Night	16% 3 23% 43% 13% 1	460
August	1st to 10th	Night	14% 3 27% 40% 16% 1	505
	11th to 20th	Night	15% 3 21% 42% 17% 2	799
	21st to end	Night	14% 4 25% 36% 18% 3	880
September	1st to 10th	Night	17% 4 29% 33% 15% 3	800
	11th to 20th	Night	17% 5% 25% 32% 19% 3	800
	21st to end	Night	22% 6% 26% 30% 15% 1	800
October	1st to 10th	Night	22% 10% 26% 26% 14% 3	800
	11th to 20th	Night	20% 13% 30% 27% 9% 1	800
	21st to end	Night	26% 12% 34% 21% 8%	880
November	1st to 10th	Night	16% 14% 33% 25% 11% 1	820
	11th to 20th	Night	22% 18% 34% 20% 5% 1	840
	21st to end	Night	22% 17% 31% 24% 5% 1	840
December	1st to 10th	Night	26% 17% 32% 20% 5% 1	840
	11th to 20th	Night	27% 19% 31% 21% 3	840
	21st to end	Night	27% 18% 36% 18% 2	924

Page generated at 2026-08-12 03:37:15. Version ac07

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