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 2025-04-11.

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 5% 4 4 4 4 5% 7% 41%	113150
	Night	18% 7% 2 6% 4 3 4 3 4 6% 42%	115117
Transparency	Day	42% 6% 12% 22% 16% 3	116727
	Night	43% 5% 11% 22% 16% 3	119704
Seeing	Day	21% 16% 31% 22% 8% 2	15509
	Night	21% 13% 32% 25% 8% 1	24697

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	14% 6% 2 5% 4 5% 4 4 5% 5% 46%	3597
	11th to 20th	Day	15% 8% 3 6% 4 4 4 4 5% 5% 43%	3570
	21st to end	Day	18% 7% 3 8% 5% 4 4 3 4 5% 40%	4098
February	1st to 10th	Day	17% 7% 3 6% 5% 5% 5% 4 5% 6% 38%	1870
	11th to 20th	Day	16% 7% 2 5% 4 4 4 4 6% 7% 42%	1948
	21st to end	Day	21% 8% 3 5% 4 4 3 3 6% 6% 38%	1650
March	1st to 10th	Day	23% 8% 2 5% 3 3 3 3 4 5% 41%	4476
	11th to 20th	Day	15% 8% 2 5% 4 3 4 4 6% 7% 43%	4666
	21st to end	Day	20% 8% 2 6% 4 4 4 4 5% 6% 38%	5970
April	1st to 10th	Day	20% 8% 2 5% 4 4 4 3 5% 7% 38%	2400
	11th to 20th	Day	20% 6% 2 6% 4 4 4 3 3 7% 42%	2254
	21st to end	Day	21% 5% 2 5% 4 3 5% 3 5% 5% 40%	2379
May	1st to 10th	Day	28% 9% 2 5% 3 3 3 3 5% 7% 31%	4106
	11th to 20th	Day	24% 7% 2 6% 4 4 4 3 5% 7% 33%	4260
	21st to end	Day	16% 5% 2 4 3 3 4 3 6% 8% 46%	4837
June	1st to 10th	Day	18% 5% 2 5% 4 4 5% 5% 6% 8% 37%	2660
	11th to 20th	Day	16% 6% 2 5% 5% 4 4 4 6% 10% 38%	2660
	21st to end	Day	13% 7% 2 5% 5% 5% 5% 4 6% 8% 40%	2660
July	1st to 10th	Day	14% 6% 2 7% 5% 5% 5% 4 7% 9% 36%	4440
	11th to 20th	Day	15% 5% 2 6% 4 4 5% 4 7% 9% 40%	4440
	21st to end	Day	17% 8% 3 7% 5% 4 5% 4 6% 7% 34%	4814
August	1st to 10th	Day	20% 6% 2 7% 5% 5% 5% 4 6% 8% 33%	4247
	11th to 20th	Day	12% 6% 2 6% 4 3 4 3 6% 9% 44%	3735
	21st to end	Day	8% 5% 2 6% 5% 4 4 4 6% 10% 46%	4180
September	1st to 10th	Day	13% 5% 2 5% 5% 4 4 4 5% 6% 46%	2280
	11th to 20th	Day	13% 5% 2 4 3 4 4 3 5% 6% 52%	2149
	21st to end	Day	20% 6% 2 5% 5% 4 4 3 4 6% 41%	2090
October	1st to 10th	Day	21% 7% 2 5% 4 3 3 3 4 6% 41%	2061
	11th to 20th	Day	15% 4 1 5% 4 3 3 4 5% 7% 48%	1890
	21st to end	Day	20% 6% 1 4 4 4 4 4 5% 7% 41%	1881
November	1st to 10th	Day	13% 7% 2 5% 4 4 2 3 4 6% 50%	1761
	11th to 20th	Day	19% 6% 2 4 2 3 3 2 5% 7% 48%	1800
	21st to end	Day	17% 6% 2 5% 4 3 4 3 6% 6% 44%	1775
December	1st to 10th	Day	16% 6% 2 5% 4 4 3 4 4 7% 46%	2600
	11th to 20th	Day	22% 7% 2 4 3 2 3 2 4 6% 46%	2986
	21st to end	Day	20% 9% 3 6% 4 3 3 3 4 6% 40%	3960
January	1st to 10th	Night	14% 6% 2 5% 3 4 3 4 5% 6% 49%	6349
	11th to 20th	Night	15% 8% 3 7% 4 3 3 3 4 5% 46%	6315
	21st to end	Night	18% 9% 3 6% 4 4 4 4 4 5% 39%	6841
February	1st to 10th	Night	17% 9% 3 6% 4 3 3 3 4 5% 41%	2528
	11th to 20th	Night	18% 8% 3 5% 4 3 3 3 4 7% 42%	2338
	21st to end	Night	20% 8% 3 6% 4 3 4 3 3 6% 41%	1980
March	1st to 10th	Night	21% 10% 2 5% 3 3 3 3 4 5% 41%	5364
	11th to 20th	Night	17% 10% 3 5% 4 4 3 3 4 6% 42%	5289
	21st to end	Night	21% 9% 3 6% 4 3 3 3 5% 5% 39%	4962
April	1st to 10th	Night	20% 7% 2 6% 4 5% 4 4 6% 6% 37%	2000
	11th to 20th	Night	21% 6% 2 6% 4 3 3 3 5% 6% 42%	1882
	21st to end	Night	20% 7% 2 7% 5% 3 4 3 4 5% 42%	1800
May	1st to 10th	Night	25% 11% 3 7% 5% 3 4 3 5% 6% 29%	2834
	11th to 20th	Night	23% 8% 3 7% 4 4 4 4 4 6% 31%	2660
	21st to end	Night	19% 8% 2 4 3 4 4 3 4 6% 42%	2738
June	1st to 10th	Night	19% 6% 2 6% 5% 4 4 4 5% 6% 39%	1520
	11th to 20th	Night	17% 7% 2 5% 4 3 4 4 5% 9% 40%	1520
	21st to end	Night	14% 6% 2 6% 4 5% 4 3 5% 9% 42%	1520
July	1st to 10th	Night	14% 8% 2 7% 5% 4 5% 4 7% 8% 35%	2520
	11th to 20th	Night	18% 7% 2 5% 4 5% 5% 4 7% 9% 35%	2520
	21st to end	Night	21% 8% 2 6% 5% 4 4 4 7% 7% 33%	2739
August	1st to 10th	Night	24% 6% 2 7% 5% 5% 5% 5% 6% 7% 29%	2650
	11th to 20th	Night	15% 6% 3 7% 4 4 6% 4 5% 7% 40%	3089
	21st to end	Night	10% 4 1 4 3 3 4 3 5% 8% 55%	3476
September	1st to 10th	Night	15% 5% 3 5% 4 4 4 3 4 7% 44%	1900
	11th to 20th	Night	15% 5% 2 4 3 3 3 3 4 6% 53%	2029
	21st to end	Night	18% 7% 3 5% 4 4 4 3 4 5% 43%	2090
October	1st to 10th	Night	20% 7% 2 6% 4 4 4 2 4 6% 41%	2117
	11th to 20th	Night	15% 5% 2 6% 3 3 3 2 5% 6% 50%	2289
	21st to end	Night	22% 7% 2 5% 3 3 4 3 5% 5% 42%	2717
November	1st to 10th	Night	12% 6% 2 5% 4 3 4 3 5% 6% 50%	2537
	11th to 20th	Night	19% 7% 2 4 3 3 3 3 4 6% 48%	2600
	21st to end	Night	16% 5% 1 5% 4 4 4 3 5% 7% 46%	2620
December	1st to 10th	Night	18% 6% 2 5% 3 3 4 3 4 4 49%	4580
	11th to 20th	Night	26% 6% 2 4 3 3 4 2 3 4 42%	5208
	21st to end	Night	20% 10% 3 6% 3 3 3 3 3 5% 42%	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	38% 5% 8% 28% 18% 3	3598
	11th to 20th	Day	41% 4 11% 22% 15% 7%	3600
	21st to end	Day	46% 6% 9% 22% 15% 2	4098
February	1st to 10th	Day	45% 6% 13% 20% 14% 2	1870
	11th to 20th	Day	41% 5% 11% 23% 16% 3	1957
	21st to end	Day	46% 6% 11% 19% 15% 3	1650
March	1st to 10th	Day	46% 4 12% 16% 13% 10%	4479
	11th to 20th	Day	40% 5% 16% 26% 12% 2	4666
	21st to end	Day	47% 4 8% 15% 20% 6%	5970
April	1st to 10th	Day	45% 6% 10% 19% 16% 4	2400
	11th to 20th	Day	43% 5% 11% 20% 18% 3	2254
	21st to end	Day	44% 6% 10% 21% 16% 4	2379
May	1st to 10th	Day	52% 7% 15% 14% 11% 2	4120
	11th to 20th	Day	48% 8% 14% 19% 9% 2	4264
	21st to end	Day	35% 7% 13% 25% 18% 2	4837
June	1st to 10th	Day	43% 8% 13% 23% 12% 1	2660
	11th to 20th	Day	40% 8% 15% 23% 13% 1	2660
	21st to end	Day	39% 9% 14% 23% 14% 1	2660
July	1st to 10th	Day	44% 9% 11% 20% 16% 1	4370
	11th to 20th	Day	40% 6% 17% 22% 14% 1	4365
	21st to end	Day	48% 6% 13% 17% 15% 2	4661
August	1st to 10th	Day	48% 8% 15% 21% 8%	4233
	11th to 20th	Day	37% 6% 14% 31% 11% 1	3771
	21st to end	Day	34% 7% 13% 27% 17% 2	4180
September	1st to 10th	Day	37% 8% 12% 22% 19% 2	2280
	11th to 20th	Day	33% 6% 11% 23% 24% 2	2149
	21st to end	Day	44% 6% 8% 20% 19% 3	2090
October	1st to 10th	Day	36% 5% 10% 20% 23% 6%	3425
	11th to 20th	Day	27% 4 10% 24% 32% 4	3118
	21st to end	Day	31% 5% 14% 25% 23% 3	3081
November	1st to 10th	Day	38% 4 14% 21% 21% 2	1761
	11th to 20th	Day	37% 4 12% 22% 22% 4	1800
	21st to end	Day	40% 5% 13% 27% 12% 3	1775
December	1st to 10th	Day	40% 4 15% 27% 13% 1	2600
	11th to 20th	Day	41% 3 15% 19% 19% 3	2986
	21st to end	Day	48% 4 8% 20% 16% 5%	3960
January	1st to 10th	Night	37% 4 9% 27% 20% 3	6349
	11th to 20th	Night	41% 4 13% 21% 16% 6%	6360
	21st to end	Night	48% 4 9% 19% 16% 4	6841
February	1st to 10th	Night	45% 5% 12% 24% 12% 2	2528
	11th to 20th	Night	43% 5% 10% 20% 18% 4	2340
	21st to end	Night	47% 3 9% 22% 15% 4	1980
March	1st to 10th	Night	47% 4 11% 18% 14% 7%	5374
	11th to 20th	Night	44% 5% 15% 21% 11% 4	5290
	21st to end	Night	49% 3 6% 12% 24% 5%	4962
April	1st to 10th	Night	47% 5% 10% 19% 16% 3	2000
	11th to 20th	Night	44% 5% 11% 19% 20% 1	1882
	21st to end	Night	46% 4 9% 22% 15% 4	1800
May	1st to 10th	Night	56% 7% 12% 14% 10% 1	2840
	11th to 20th	Night	53% 9% 13% 14% 9% 2	2661
	21st to end	Night	42% 5% 15% 24% 13% 1	2739
June	1st to 10th	Night	45% 6% 10% 20% 17% 2	1520
	11th to 20th	Night	40% 7% 14% 27% 12% 1	1520
	21st to end	Night	40% 8% 13% 25% 14%	1520
July	1st to 10th	Night	46% 9% 13% 18% 12% 1	2480
	11th to 20th	Night	45% 6% 17% 23% 9% 1	2472
	21st to end	Night	49% 6% 14% 15% 15% 2	2651
August	1st to 10th	Night	54% 7% 14% 15% 9% 1	2640
	11th to 20th	Night	43% 6% 14% 28% 8% 1	3119
	21st to end	Night	28% 5% 15% 33% 18% 1	3476
September	1st to 10th	Night	39% 6% 10% 25% 18% 2	1900
	11th to 20th	Night	33% 5% 10% 24% 25% 3	2029
	21st to end	Night	44% 5% 8% 20% 20% 3	2090
October	1st to 10th	Night	39% 4 12% 23% 19% 2	3533
	11th to 20th	Night	25% 4 9% 27% 31% 4	3800
	21st to end	Night	32% 4 13% 27% 21% 2	4467
November	1st to 10th	Night	36% 4 12% 22% 21% 4	2537
	11th to 20th	Night	40% 3 10% 23% 20% 4	2600
	21st to end	Night	39% 5% 12% 29% 13% 2	2620
December	1st to 10th	Night	41% 4 11% 29% 14% 1	4580
	11th to 20th	Night	48% 3 12% 17% 18% 2	5208
	21st to end	Night	46% 3 10% 19% 17% 4	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	28% 26% 27% 19% 2	200
	11th to 20th	Day	24% 33% 29% 14% 1 1	200
	21st to end	Day	23% 28% 32% 11% 4 2	250
February	1st to 10th	Day	26% 26% 33% 14% 1	370
	11th to 20th	Day	25% 29% 33% 12% 1	496
	21st to end	Day	26% 25% 32% 14% 4	414
March	1st to 10th	Day	23% 25% 34% 15% 2	500
	11th to 20th	Day	21% 27% 34% 14% 3 1	500
	21st to end	Day	26% 24% 35% 10% 4 1	550
April	1st to 10th	Day	27% 25% 30% 12% 5% 1	500
	11th to 20th	Day	27% 20% 31% 17% 5% 1	452
	21st to end	Day	25% 18% 34% 17% 4 2	460
May	1st to 10th	Day	27% 21% 30% 16% 6% 1	463
	11th to 20th	Day	21% 15% 36% 22% 5% 1	487
	21st to end	Day	19% 10% 30% 27% 12% 2	529
June	1st to 10th	Day	17% 12% 32% 26% 12% 2	490
	11th to 20th	Day	17% 11% 34% 27% 10% 1	490
	21st to end	Day	16% 10% 33% 27% 12% 2	490
July	1st to 10th	Day	16% 5% 28% 31% 17% 3	485
	11th to 20th	Day	13% 6% 28% 34% 15% 4	484
	21st to end	Day	15% 7% 32% 33% 9% 2	532
August	1st to 10th	Day	14% 7% 28% 33% 14% 5%	486
	11th to 20th	Day	13% 6% 29% 30% 18% 5%	479
	21st to end	Day	11% 9% 30% 29% 14% 6%	539
September	1st to 10th	Day	17% 9% 28% 25% 17% 4	490
	11th to 20th	Day	15% 6% 32% 26% 14% 8%	490
	21st to end	Day	22% 11% 32% 22% 10% 3	490
October	1st to 10th	Day	27% 11% 24% 22% 12% 4	490
	11th to 20th	Day	16% 18% 29% 27% 9% 2	484
	21st to end	Day	25% 16% 32% 18% 8% 2	429
November	1st to 10th	Day	16% 18% 30% 23% 10% 3	395
	11th to 20th	Day	24% 24% 28% 20% 5%	400
	21st to end	Day	21% 22% 29% 20% 7%	375
December	1st to 10th	Day	22% 21% 36% 16% 6%	200
	11th to 20th	Day	29% 27% 31% 13% 2	200
	21st to end	Day	25% 20% 35% 15% 5%	220
January	1st to 10th	Night	21% 22% 36% 18% 3	800
	11th to 20th	Night	27% 19% 32% 20% 3	800
	21st to end	Night	20% 21% 37% 19% 3	880
February	1st to 10th	Night	22% 20% 34% 22% 2	800
	11th to 20th	Night	23% 21% 38% 16% 2	783
	21st to end	Night	25% 19% 36% 17% 3	660
March	1st to 10th	Night	24% 18% 36% 19% 3	800
	11th to 20th	Night	23% 15% 38% 21% 4 1	800
	21st to end	Night	23% 20% 36% 18% 3	880
April	1st to 10th	Night	24% 18% 35% 20% 3	800
	11th to 20th	Night	22% 14% 36% 23% 4	754
	21st to end	Night	22% 14% 37% 21% 6%	660
May	1st to 10th	Night	25% 12% 33% 22% 7%	570
	11th to 20th	Night	23% 11% 38% 22% 6%	474
	21st to end	Night	20% 5% 23% 40% 10%	411
June	1st to 10th	Night	22% 5% 29% 33% 10% 1	380
	11th to 20th	Night	19% 4 29% 35% 12%	380
	21st to end	Night	16% 6% 26% 41% 10% 1	380
July	1st to 10th	Night	14% 5% 24% 41% 16% 1	370
	11th to 20th	Night	14% 2 20% 45% 17% 1	368
	21st to end	Night	16% 3 25% 42% 13% 1	416
August	1st to 10th	Night	12% 3 28% 40% 15% 1	457
	11th to 20th	Night	15% 3 20% 42% 17% 2	742
	21st to end	Night	14% 4 24% 37% 19% 3	836
September	1st to 10th	Night	17% 4 28% 33% 15% 3	760
	11th to 20th	Night	17% 5% 25% 31% 19% 3	760
	21st to end	Night	22% 6% 27% 29% 16% 1	760
October	1st to 10th	Night	23% 10% 26% 26% 13% 3	760
	11th to 20th	Night	19% 13% 31% 28% 9% 1	760
	21st to end	Night	26% 11% 34% 21% 8%	836
November	1st to 10th	Night	15% 14% 33% 25% 11% 1	780
	11th to 20th	Night	23% 17% 34% 20% 6% 1	800
	21st to end	Night	22% 17% 32% 24% 5% 1	800
December	1st to 10th	Night	26% 16% 32% 20% 5% 1	800
	11th to 20th	Night	26% 19% 31% 20% 3	800
	21st to end	Night	26% 17% 36% 18% 2	880

Page generated at 2025-04-08 09:17:29. Version ac07

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