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 2024-01-12.

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% 4 7% 6% 3 5% 5% 6% 8% 34%	74636
	Night	15% 9% 4 7% 6% 3 4 5% 5% 7% 35%	75049
Transparency	Day	47% 7% 13% 20% 11% 1	74347
	Night	48% 7% 12% 20% 11% 1	74859
Seeing	Day	16% 8% 27% 27% 16% 6%	14145
	Night	18% 7% 29% 31% 13% 2	23857

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	17% 12% 6% 11% 7% 4 4 4 5% 5% 24%	1517
	11th to 20th	Day	15% 16% 7% 11% 7% 5% 5% 5% 5% 5% 18%	1466
	21st to end	Day	16% 17% 7% 8% 10% 3 6% 5% 4 4 19%	1782
February	1st to 10th	Day	16% 14% 6% 11% 9% 4 6% 4 4 5% 21%	1620
	11th to 20th	Day	14% 12% 6% 10% 9% 3 6% 4 4 6% 25%	1662
	21st to end	Day	15% 15% 6% 10% 8% 3 4 5% 4 5% 27%	1480
March	1st to 10th	Day	15% 12% 5% 9% 7% 4 5% 4 4 7% 28%	1862
	11th to 20th	Day	14% 12% 4 7% 7% 3 4 4 5% 7% 33%	1980
	21st to end	Day	20% 12% 4 8% 6% 4 5% 4 4 5% 28%	2178
April	1st to 10th	Day	15% 11% 5% 8% 7% 3 4 4 5% 6% 32%	2056
	11th to 20th	Day	17% 9% 3 7% 6% 3 5% 5% 5% 7% 34%	2307
	21st to end	Day	19% 8% 3 7% 6% 3 4 4 5% 7% 34%	2340
May	1st to 10th	Day	17% 7% 3 7% 7% 3 5% 5% 5% 7% 33%	2340
	11th to 20th	Day	17% 8% 3 6% 5% 3 5% 5% 5% 7% 36%	2301
	21st to end	Day	11% 5% 3 7% 5% 3 5% 5% 5% 9% 41%	2544
June	1st to 10th	Day	10% 5% 4 6% 5% 3 5% 5% 7% 9% 41%	2647
	11th to 20th	Day	10% 4 3 5% 6% 3 5% 4 7% 9% 42%	2700
	21st to end	Day	9% 5% 3 5% 5% 4 6% 6% 6% 10% 40%	2685
July	1st to 10th	Day	8% 4 2 6% 5% 3 5% 5% 6% 9% 47%	2520
	11th to 20th	Day	8% 4 3 5% 5% 3 5% 6% 7% 10% 45%	2520
	21st to end	Day	7% 5% 3 5% 5% 3 6% 7% 8% 10% 41%	2553
August	1st to 10th	Day	8% 5% 2 6% 6% 3 5% 8% 8% 10% 40%	2327
	11th to 20th	Day	9% 4 2 6% 6% 4 6% 6% 8% 10% 40%	2303
	21st to end	Day	11% 6% 3 6% 5% 3 5% 4 6% 8% 43%	2574
September	1st to 10th	Day	11% 6% 3 5% 6% 4 5% 6% 6% 9% 40%	2034
	11th to 20th	Day	9% 4 2 5% 4 4 5% 6% 6% 9% 46%	1980
	21st to end	Day	14% 6% 3 6% 5% 3 6% 6% 6% 8% 37%	1980
October	1st to 10th	Day	12% 7% 3 6% 6% 3 5% 4 6% 7% 42%	1904
	11th to 20th	Day	18% 9% 4 6% 6% 4 5% 5% 4 7% 33%	1800
	21st to end	Day	19% 11% 4 8% 5% 3 5% 5% 4 6% 30%	1864
November	1st to 10th	Day	12% 8% 3 7% 5% 4 5% 5% 6% 7% 37%	1672
	11th to 20th	Day	15% 10% 4 6% 7% 3 5% 5% 6% 6% 34%	1710
	21st to end	Day	19% 11% 5% 8% 6% 3 4 4 6% 6% 28%	1521
December	1st to 10th	Day	15% 12% 7% 11% 8% 4 5% 4 5% 6% 22%	1520
	11th to 20th	Day	17% 15% 5% 8% 5% 3 5% 5% 7% 6% 25%	1814
	21st to end	Day	26% 18% 8% 9% 6% 3 4 4 4 6% 12%	2573
January	1st to 10th	Night	18% 11% 5% 9% 8% 4 5% 5% 5% 6% 25%	2648
	11th to 20th	Night	19% 16% 5% 10% 7% 3 5% 5% 4 5% 22%	2513
	21st to end	Night	13% 15% 8% 10% 8% 4 4 5% 5% 6% 24%	2574
February	1st to 10th	Night	16% 15% 6% 11% 7% 3 5% 4 5% 5% 22%	2340
	11th to 20th	Night	14% 13% 6% 8% 7% 4 5% 6% 5% 5% 27%	2182
	21st to end	Night	19% 12% 5% 8% 6% 4 5% 4 5% 5% 29%	1776
March	1st to 10th	Night	15% 10% 4 7% 7% 3 4 5% 5% 6% 32%	2097
	11th to 20th	Night	14% 8% 3 5% 5% 3 5% 5% 6% 7% 38%	1980
	21st to end	Night	21% 8% 4 6% 5% 3 4 5% 5% 6% 33%	2178
April	1st to 10th	Night	18% 8% 3 5% 5% 3 4 5% 5% 7% 36%	1918
	11th to 20th	Night	18% 8% 3 5% 5% 3 4 4 5% 7% 38%	1600
	21st to end	Night	16% 8% 3 5% 5% 2 4 5% 6% 7% 38%	1620
May	1st to 10th	Night	15% 7% 4 7% 7% 3 4 5% 5% 8% 34%	1620
	11th to 20th	Night	17% 6% 3 6% 4 3 4 4 5% 7% 41%	1592
	21st to end	Night	9% 4 3 5% 5% 3 5% 5% 6% 9% 47%	1726
June	1st to 10th	Night	10% 5% 2 6% 5% 2 4 5% 5% 8% 47%	1309
	11th to 20th	Night	10% 6% 2 5% 4 3 5% 7% 5% 8% 47%	1260
	21st to end	Night	8% 5% 3 5% 5% 3 3 5% 5% 8% 50%	1269
July	1st to 10th	Night	8% 4 2 4 5% 2 5% 4 6% 8% 53%	1440
	11th to 20th	Night	8% 4 2 4 4 1 5% 4 6% 10% 52%	1440
	21st to end	Night	6% 4 2 4 4 3 5% 6% 8% 10% 49%	1761
August	1st to 10th	Night	8% 3 2 5% 5% 3 5% 4 6% 9% 50%	1611
	11th to 20th	Night	6% 4 2 5% 5% 3 6% 6% 6% 8% 49%	1598
	21st to end	Night	8% 5% 2 5% 5% 3 4 5% 5% 6% 53%	1782
September	1st to 10th	Night	9% 6% 3 5% 5% 4 4 4 6% 8% 46%	1905
	11th to 20th	Night	10% 5% 2 4 4 2 4 4 5% 7% 52%	1980
	21st to end	Night	14% 6% 2 5% 5% 3 4 5% 6% 7% 44%	1980
October	1st to 10th	Night	14% 6% 3 6% 4 3 4 3 5% 6% 45%	2056
	11th to 20th	Night	19% 8% 3 7% 5% 3 4 5% 5% 6% 35%	2160
	21st to end	Night	22% 9% 3 5% 5% 4 5% 5% 5% 7% 31%	2488
November	1st to 10th	Night	14% 7% 3 6% 5% 3 4 4 5% 7% 43%	2406
	11th to 20th	Night	15% 9% 3 7% 6% 4 5% 5% 6% 7% 32%	2470
	21st to end	Night	19% 13% 4 7% 6% 2 4 4 5% 6% 29%	2655
December	1st to 10th	Night	19% 13% 5% 9% 7% 3 5% 5% 5% 6% 23%	2660
	11th to 20th	Night	14% 13% 5% 9% 7% 4 5% 4 5% 7% 26%	3379
	21st to end	Night	28% 19% 6% 9% 6% 3 4 3 3 4 14%	5076

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	61% 6% 13% 13% 6% 1	1518
	11th to 20th	Day	66% 8% 12% 9% 5%	1466
	21st to end	Day	68% 5% 9% 11% 6% 1	1782
February	1st to 10th	Day	66% 6% 9% 13% 6%	1620
	11th to 20th	Day	60% 4 12% 16% 7% 2	1671
	21st to end	Day	60% 6% 10% 16% 7% 2	1480
March	1st to 10th	Day	56% 6% 13% 17% 8% 1	1862
	11th to 20th	Day	50% 7% 11% 18% 12% 2	1980
	21st to end	Day	57% 7% 9% 18% 7% 1	2178
April	1st to 10th	Day	51% 6% 12% 19% 11% 1	2056
	11th to 20th	Day	49% 5% 11% 18% 14% 2	2307
	21st to end	Day	49% 6% 13% 17% 12% 2	2340
May	1st to 10th	Day	47% 8% 11% 21% 11% 2	2340
	11th to 20th	Day	46% 7% 11% 19% 14% 2	2305
	21st to end	Day	39% 8% 14% 22% 16% 2	2544
June	1st to 10th	Day	38% 8% 13% 27% 13% 2	2647
	11th to 20th	Day	37% 7% 14% 23% 15% 3	2700
	21st to end	Day	37% 9% 14% 24% 16% 2	2685
July	1st to 10th	Day	33% 8% 11% 27% 19% 3	2451
	11th to 20th	Day	32% 8% 15% 27% 16% 2	2445
	21st to end	Day	33% 10% 16% 21% 17% 2	2411
August	1st to 10th	Day	33% 11% 16% 26% 13% 1	2314
	11th to 20th	Day	36% 9% 15% 26% 12% 2	2303
	21st to end	Day	38% 7% 13% 25% 16% 1	2574
September	1st to 10th	Day	39% 9% 15% 22% 13% 2	2034
	11th to 20th	Day	33% 9% 13% 32% 14%	1980
	21st to end	Day	41% 9% 13% 24% 12% 1	1980
October	1st to 10th	Day	40% 7% 12% 26% 13% 2	1904
	11th to 20th	Day	51% 6% 14% 19% 10% 1	1800
	21st to end	Day	54% 7% 13% 17% 8%	1864
November	1st to 10th	Day	43% 8% 13% 23% 11% 1	1672
	11th to 20th	Day	50% 7% 13% 18% 10% 1	1710
	21st to end	Day	56% 7% 13% 17% 6% 1	1521
December	1st to 10th	Day	62% 8% 11% 15% 4	1520
	11th to 20th	Day	58% 8% 14% 15% 6%	1810
	21st to end	Day	74% 6% 10% 7% 3	2573
January	1st to 10th	Night	60% 6% 10% 17% 7% 1	2648
	11th to 20th	Night	65% 6% 12% 12% 5%	2513
	21st to end	Night	61% 6% 11% 16% 5%	2574
February	1st to 10th	Night	64% 6% 9% 13% 7% 1	2340
	11th to 20th	Night	58% 6% 11% 16% 9% 1	2184
	21st to end	Night	56% 5% 12% 18% 8% 1	1776
March	1st to 10th	Night	52% 6% 11% 21% 10% 1	2097
	11th to 20th	Night	44% 7% 11% 22% 14% 2	1980
	21st to end	Night	53% 5% 9% 22% 11% 1	2178
April	1st to 10th	Night	47% 6% 12% 21% 14% 2	1918
	11th to 20th	Night	45% 5% 11% 18% 18% 2	1600
	21st to end	Night	43% 7% 11% 20% 15% 4	1620
May	1st to 10th	Night	47% 7% 11% 20% 12% 3	1620
	11th to 20th	Night	42% 6% 11% 18% 19% 3	1593
	21st to end	Night	33% 8% 13% 24% 18% 3	1727
June	1st to 10th	Night	35% 6% 11% 28% 17% 3	1309
	11th to 20th	Night	34% 8% 14% 24% 18% 2	1260
	21st to end	Night	33% 7% 11% 27% 21% 1	1269
July	1st to 10th	Night	28% 7% 12% 28% 22% 4	1400
	11th to 20th	Night	28% 7% 14% 33% 16% 2	1392
	21st to end	Night	26% 10% 18% 23% 19% 3	1663
August	1st to 10th	Night	29% 7% 16% 31% 14% 2	1600
	11th to 20th	Night	31% 9% 14% 31% 13% 3	1598
	21st to end	Night	31% 7% 13% 29% 19% 1	1782
September	1st to 10th	Night	36% 7% 14% 27% 14% 2	1905
	11th to 20th	Night	30% 7% 14% 30% 19% 1	1980
	21st to end	Night	38% 8% 12% 30% 12% 1	1980
October	1st to 10th	Night	39% 6% 11% 24% 18% 1	2056
	11th to 20th	Night	48% 7% 13% 19% 12% 1	2160
	21st to end	Night	52% 7% 11% 20% 9% 1	2488
November	1st to 10th	Night	41% 6% 12% 26% 14% 1	2406
	11th to 20th	Night	50% 6% 14% 20% 9% 1	2470
	21st to end	Night	55% 6% 14% 18% 6%	2655
December	1st to 10th	Night	61% 9% 12% 14% 5%	2660
	11th to 20th	Night	56% 7% 14% 14% 8%	3382
	21st to end	Night	74% 6% 10% 7% 3	5076

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	22% 14% 37% 19% 7% 1	270
	11th to 20th	Day	21% 10% 45% 18% 5% 1	243
	21st to end	Day	28% 6% 38% 21% 5% 1	264
February	1st to 10th	Day	23% 15% 40% 20% 2	240
	11th to 20th	Day	21% 15% 40% 21% 3	240
	21st to end	Day	19% 19% 43% 16% 3	198
March	1st to 10th	Day	20% 16% 38% 22% 4 1	302
	11th to 20th	Day	18% 13% 33% 27% 7% 2	420
	21st to end	Day	26% 10% 28% 27% 7% 1	462
April	1st to 10th	Day	14% 11% 38% 26% 10% 1	420
	11th to 20th	Day	25% 10% 27% 21% 12% 5%	412
	21st to end	Day	24% 7% 28% 27% 11% 2	420
May	1st to 10th	Day	22% 6% 28% 28% 12% 3	423
	11th to 20th	Day	19% 5% 24% 29% 17% 6%	447
	21st to end	Day	15% 3 18% 30% 24% 9%	485
June	1st to 10th	Day	11% 3 25% 38% 17% 5%	577
	11th to 20th	Day	11% 4 25% 34% 22% 4	630
	21st to end	Day	11% 5% 23% 35% 21% 5%	630
July	1st to 10th	Day	8% 3 15% 33% 27% 14%	621
	11th to 20th	Day	10% 3 20% 35% 23% 8%	618
	21st to end	Day	7% 4 17% 35% 27% 11%	494
August	1st to 10th	Day	8% 2 14% 32% 28% 16%	446
	11th to 20th	Day	11% 3 12% 34% 27% 13%	439
	21st to end	Day	13% 4 17% 29% 24% 13%	495
September	1st to 10th	Day	12% 2 23% 24% 28% 12%	450
	11th to 20th	Day	9% 3 18% 23% 30% 17%	450
	21st to end	Day	15% 8% 23% 24% 21% 10%	450
October	1st to 10th	Day	14% 7% 28% 22% 18% 10%	450
	11th to 20th	Day	22% 13% 30% 24% 8% 2	450
	21st to end	Day	25% 13% 33% 23% 6% 1	379
November	1st to 10th	Day	16% 13% 33% 26% 12% 1	270
	11th to 20th	Day	19% 20% 31% 21% 8% 1	270
	21st to end	Day	26% 14% 34% 21% 4	180
December	1st to 10th	Day	21% 16% 39% 14% 8% 1	180
	11th to 20th	Day	26% 14% 41% 16% 4 1	180
	21st to end	Day	25% 14% 38% 20% 5%	240
January	1st to 10th	Night	23% 10% 37% 22% 6% 1	950
	11th to 20th	Night	26% 11% 33% 25% 4 1	884
	21st to end	Night	20% 7% 36% 30% 7%	792
February	1st to 10th	Night	22% 8% 41% 26% 3	720
	11th to 20th	Night	21% 10% 35% 29% 5%	703
	21st to end	Night	25% 10% 39% 23% 3	592
March	1st to 10th	Night	20% 8% 36% 29% 6%	720
	11th to 20th	Night	17% 9% 38% 27% 7% 1	720
	21st to end	Night	24% 7% 30% 29% 10% 1	792
April	1st to 10th	Night	20% 9% 33% 32% 5%	658
	11th to 20th	Night	21% 8% 31% 28% 11% 2	533
	21st to end	Night	19% 5% 31% 34% 10%	540
May	1st to 10th	Night	18% 4 29% 37% 12% 1	540
	11th to 20th	Night	19% 4 26% 33% 18% 1	531
	21st to end	Night	10% 2 20% 40% 25% 3	566
June	1st to 10th	Night	11% 3 24% 43% 18%	360
	11th to 20th	Night	10% 3 23% 46% 18% 1	360
	21st to end	Night	11% 2 18% 45% 24% 1	369
July	1st to 10th	Night	8% 2 13% 40% 31% 6%	525
	11th to 20th	Night	9% 2 16% 40% 28% 4	522
	21st to end	Night	6% 2 17% 45% 28% 3	591
August	1st to 10th	Night	9% 1 13% 38% 35% 3	537
	11th to 20th	Night	6% 1 16% 38% 34% 5%	534
	21st to end	Night	9% 2 16% 38% 32% 4	594
September	1st to 10th	Night	11% 4 18% 35% 27% 6%	670
	11th to 20th	Night	11% 3 17% 35% 30% 5%	720
	21st to end	Night	16% 5% 19% 33% 21% 6%	720
October	1st to 10th	Night	16% 6% 25% 31% 19% 3	720
	11th to 20th	Night	22% 11% 27% 29% 9% 2	720
	21st to end	Night	26% 10% 32% 28% 5%	792
November	1st to 10th	Night	16% 9% 31% 28% 14% 1	740
	11th to 20th	Night	20% 13% 36% 23% 8% 1	760
	21st to end	Night	26% 12% 34% 22% 6%	760
December	1st to 10th	Night	26% 11% 36% 21% 6% 1	760
	11th to 20th	Night	22% 11% 38% 24% 4	817
	21st to end	Night	29% 11% 33% 24% 3	1045

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