Old Lyme
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Old Lyme clear sky chart from 2005-11-06 to 2024-04-03.

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% 6% 2 5% 4 3 4 4 5% 7% 41%	78703
	Night	19% 7% 3 5% 5% 3 4 4 5% 6% 41%	81412
Transparency	Day	41% 6% 12% 23% 15% 2	78408
	Night	44% 5% 12% 22% 15% 2	81241
Seeing	Day	20% 13% 31% 24% 10% 2	14239
	Night	21% 12% 30% 26% 10% 1	23399

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	17% 6% 2 4 5% 2 4 4 4 5% 45%	2517
	11th to 20th	Day	18% 8% 2 5% 5% 3 5% 5% 5% 5% 39%	2520
	21st to end	Day	23% 12% 3 5% 5% 2 3 3 4 5% 35%	2804
February	1st to 10th	Day	18% 7% 2 5% 5% 3 6% 4 5% 6% 38%	1817
	11th to 20th	Day	15% 7% 2 5% 5% 3 4 5% 6% 6% 43%	1848
	21st to end	Day	21% 8% 4 4 5% 2 4 4 5% 6% 36%	1570
March	1st to 10th	Day	19% 6% 2 5% 4 3 3 3 4 7% 44%	1897
	11th to 20th	Day	15% 6% 3 4 5% 3 5% 5% 5% 8% 40%	1958
	21st to end	Day	20% 8% 3 6% 4 3 3 4 4 5% 39%	2488
April	1st to 10th	Day	19% 6% 3 4 4 2 5% 4 5% 6% 40%	2184
	11th to 20th	Day	19% 7% 2 4 4 2 4 4 4 7% 43%	2134
	21st to end	Day	22% 5% 2 5% 5% 3 4 4 6% 7% 39%	2283
May	1st to 10th	Day	25% 7% 3 5% 4 3 4 4 4 6% 35%	2340
	11th to 20th	Day	20% 6% 2 4 4 3 4 4 5% 8% 40%	2354
	21st to end	Day	16% 6% 3 4 4 2 4 3 6% 8% 43%	2725
June	1st to 10th	Day	19% 5% 2 4 5% 4 5% 5% 7% 9% 35%	2520
	11th to 20th	Day	18% 6% 2 5% 4 3 5% 5% 5% 9% 38%	2520
	21st to end	Day	13% 6% 3 5% 5% 3 5% 4 6% 9% 40%	2520
July	1st to 10th	Day	14% 5% 2 5% 4 3 5% 5% 6% 9% 41%	2520
	11th to 20th	Day	14% 5% 3 4 4 3 5% 5% 6% 9% 42%	2520
	21st to end	Day	14% 5% 3 6% 5% 3 5% 6% 6% 9% 39%	2744
August	1st to 10th	Day	12% 5% 2 5% 5% 3 6% 6% 7% 9% 40%	2377
	11th to 20th	Day	14% 5% 2 5% 5% 3 4 4 6% 9% 42%	2173
	21st to end	Day	12% 6% 3 6% 5% 3 4 5% 7% 9% 42%	2376
September	1st to 10th	Day	15% 5% 3 5% 5% 3 4 4 5% 7% 44%	2160
	11th to 20th	Day	14% 5% 2 4 3 2 3 4 5% 7% 52%	2012
	21st to end	Day	20% 5% 2 5% 4 2 4 4 4 7% 43%	1980
October	1st to 10th	Day	23% 7% 2 4 3 3 3 4 4 6% 41%	1980
	11th to 20th	Day	15% 5% 2 5% 4 3 3 4 5% 8% 47%	1771
	21st to end	Day	19% 6% 2 5% 5% 2 4 5% 4 7% 41%	1782
November	1st to 10th	Day	15% 6% 2 5% 4 3 4 3 4 6% 48%	1671
	11th to 20th	Day	18% 6% 2 3 4 3 3 3 5% 7% 47%	1710
	21st to end	Day	17% 6% 3 4 5% 3 3 4 4 6% 45%	1710
December	1st to 10th	Day	20% 6% 2 6% 4 3 5% 5% 5% 6% 38%	1540
	11th to 20th	Day	23% 6% 2 4 3 2 2 3 4 5% 46%	1906
	21st to end	Day	20% 10% 3 6% 5% 3 4 3 4 6% 36%	2772
January	1st to 10th	Night	17% 6% 2 4 4 2 3 3 4 7% 47%	4429
	11th to 20th	Night	18% 9% 3 6% 4 2 3 4 3 4 43%	4440
	21st to end	Night	24% 10% 3 6% 5% 3 4 4 3 5% 33%	4848
February	1st to 10th	Night	17% 8% 3 5% 5% 2 3 4 4 5% 41%	2361
	11th to 20th	Night	18% 8% 3 4 4 3 4 4 4 6% 42%	2218
	21st to end	Night	21% 7% 2 5% 4 3 3 4 5% 5% 40%	1884
March	1st to 10th	Night	19% 6% 2 4 4 3 3 4 5% 6% 43%	2270
	11th to 20th	Night	16% 7% 3 5% 6% 4 4 5% 6% 7% 40%	2220
	21st to end	Night	20% 7% 3 5% 5% 2 4 4 4 5% 42%	2107
April	1st to 10th	Night	21% 7% 3 5% 5% 3 4 4 4 7% 38%	1821
	11th to 20th	Night	20% 5% 3 4 5% 3 3 4 5% 6% 42%	1775
	21st to end	Night	23% 6% 2 5% 4 3 3 3 4 5% 41%	1675
May	1st to 10th	Night	23% 8% 3 5% 5% 4 5% 4 4 7% 33%	1620
	11th to 20th	Night	20% 7% 3 6% 3 3 3 4 5% 8% 36%	1553
	21st to end	Night	19% 6% 3 5% 5% 3 4 4 5% 7% 39%	1550
June	1st to 10th	Night	19% 7% 2 5% 5% 3 4 4 5% 6% 38%	1440
	11th to 20th	Night	20% 5% 3 5% 5% 3 4 4 6% 8% 38%	1440
	21st to end	Night	16% 6% 2 4 4 3 4 5% 5% 10% 40%	1440
July	1st to 10th	Night	14% 5% 3 5% 6% 3 5% 5% 6% 7% 38%	1440
	11th to 20th	Night	15% 7% 2 4 5% 2 5% 6% 7% 10% 38%	1440
	21st to end	Night	13% 6% 3 6% 5% 3 5% 5% 7% 8% 39%	1574
August	1st to 10th	Night	10% 5% 2 7% 5% 3 5% 6% 8% 9% 40%	1542
	11th to 20th	Night	12% 6% 2 6% 7% 4 6% 6% 6% 8% 37%	1724
	21st to end	Night	14% 5% 3 4 5% 3 4 4 6% 8% 45%	1980
September	1st to 10th	Night	15% 7% 3 5% 5% 3 5% 6% 5% 6% 41%	1800
	11th to 20th	Night	15% 5% 2 5% 3 2 3 3 3 6% 53%	1948
	21st to end	Night	19% 7% 3 5% 5% 3 5% 4 4 5% 41%	1980
October	1st to 10th	Night	21% 7% 2 5% 5% 2 3 3 4 5% 42%	1980
	11th to 20th	Night	16% 6% 2 5% 5% 2 3 3 5% 6% 47%	2184
	21st to end	Night	22% 6% 2 5% 4 3 3 4 4 5% 40%	2574
November	1st to 10th	Night	14% 6% 2 5% 4 2 4 4 4 6% 48%	2407
	11th to 20th	Night	19% 6% 2 4 4 2 3 4 4 6% 46%	2470
	21st to end	Night	16% 5% 2 5% 5% 3 3 4 4 7% 48%	2470
December	1st to 10th	Night	22% 7% 3 4 4 3 4 4 4 6% 40%	2636
	11th to 20th	Night	21% 6% 2 3 4 3 4 4 5% 6% 42%	3288
	21st to end	Night	22% 11% 3 5% 4 2 3 3 4 5% 38%	4884

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	40% 4 10% 30% 14% 2	2518
	11th to 20th	Day	45% 7% 11% 24% 11% 1	2520
	21st to end	Day	52% 4 9% 23% 11% 2	2804
February	1st to 10th	Day	46% 4 15% 21% 13% 1	1817
	11th to 20th	Day	40% 5% 11% 26% 16% 3	1857
	21st to end	Day	46% 5% 12% 19% 14% 4	1570
March	1st to 10th	Day	41% 4 13% 23% 15% 4	1900
	11th to 20th	Day	39% 6% 12% 26% 15% 2	1958
	21st to end	Day	46% 5% 8% 18% 17% 5%	2488
April	1st to 10th	Day	42% 5% 12% 20% 17% 4	2184
	11th to 20th	Day	41% 5% 10% 22% 20% 3	2134
	21st to end	Day	43% 6% 10% 21% 16% 4	2283
May	1st to 10th	Day	48% 6% 9% 21% 13% 2	2340
	11th to 20th	Day	42% 5% 11% 21% 18% 3	2358
	21st to end	Day	39% 7% 16% 22% 14% 2	2725
June	1st to 10th	Day	42% 8% 13% 25% 12% 1	2520
	11th to 20th	Day	40% 7% 14% 25% 13% 1	2520
	21st to end	Day	37% 8% 14% 27% 13% 1	2520
July	1st to 10th	Day	36% 7% 16% 23% 16% 2	2450
	11th to 20th	Day	36% 7% 15% 29% 12% 2	2445
	21st to end	Day	36% 8% 15% 22% 17% 3	2591
August	1st to 10th	Day	35% 8% 16% 26% 14%	2363
	11th to 20th	Day	37% 7% 15% 26% 14% 1	2173
	21st to end	Day	35% 8% 12% 23% 19% 2	2376
September	1st to 10th	Day	38% 7% 13% 22% 18% 2	2160
	11th to 20th	Day	31% 6% 12% 24% 25% 3	2012
	21st to end	Day	42% 5% 9% 21% 21% 2	1980
October	1st to 10th	Day	43% 5% 10% 22% 17% 3	1980
	11th to 20th	Day	36% 4 13% 29% 17% 1	1771
	21st to end	Day	42% 6% 11% 22% 16% 3	1782
November	1st to 10th	Day	38% 5% 14% 20% 20% 3	1671
	11th to 20th	Day	38% 4 13% 22% 20% 3	1710
	21st to end	Day	40% 4 14% 26% 13% 3	1710
December	1st to 10th	Day	47% 4 14% 18% 15% 1	1540
	11th to 20th	Day	43% 3 15% 18% 19% 2	1906
	21st to end	Day	51% 5% 11% 23% 10%	2772
January	1st to 10th	Night	39% 3 12% 31% 12% 4	4429
	11th to 20th	Night	45% 4 12% 24% 13% 3	4440
	21st to end	Night	55% 4 9% 19% 11% 2	4848
February	1st to 10th	Night	46% 4 14% 22% 12% 2	2361
	11th to 20th	Night	44% 4 10% 21% 17% 4	2220
	21st to end	Night	46% 4 9% 23% 15% 4	1884
March	1st to 10th	Night	42% 4 12% 22% 16% 3	2280
	11th to 20th	Night	43% 5% 11% 21% 15% 4	2221
	21st to end	Night	44% 5% 8% 17% 20% 6%	2107
April	1st to 10th	Night	46% 5% 9% 21% 15% 4	1821
	11th to 20th	Night	43% 4 10% 21% 20% 2	1775
	21st to end	Night	47% 4 9% 20% 14% 5%	1675
May	1st to 10th	Night	52% 5% 10% 17% 14% 2	1620
	11th to 20th	Night	48% 5% 10% 19% 14% 4	1554
	21st to end	Night	46% 8% 16% 18% 11% 1	1551
June	1st to 10th	Night	46% 6% 11% 19% 16% 2	1440
	11th to 20th	Night	42% 6% 14% 25% 11% 1	1440
	21st to end	Night	39% 8% 14% 25% 14% 1	1440
July	1st to 10th	Night	44% 7% 13% 20% 14% 2	1400
	11th to 20th	Night	37% 8% 16% 28% 9% 1	1392
	21st to end	Night	39% 8% 15% 23% 13% 2	1486
August	1st to 10th	Night	35% 8% 17% 24% 14% 2	1532
	11th to 20th	Night	40% 9% 15% 25% 11% 1	1724
	21st to end	Night	36% 6% 14% 24% 19% 2	1980
September	1st to 10th	Night	43% 6% 11% 23% 16% 2	1800
	11th to 20th	Night	34% 4 11% 23% 25% 3	1948
	21st to end	Night	45% 6% 8% 18% 20% 3	1980
October	1st to 10th	Night	46% 5% 9% 21% 14% 3	1980
	11th to 20th	Night	39% 4 13% 28% 15% 1	2184
	21st to end	Night	46% 5% 13% 20% 15% 2	2574
November	1st to 10th	Night	39% 5% 12% 22% 19% 4	2407
	11th to 20th	Night	42% 3 10% 24% 18% 3	2470
	21st to end	Night	39% 4 13% 29% 13% 2	2470
December	1st to 10th	Night	47% 4 14% 20% 14% 1	2636
	11th to 20th	Night	44% 5% 14% 19% 17% 2	3288
	21st to end	Night	50% 5% 11% 22% 12% 1	4884

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% 24% 33% 15% 6%	180
	11th to 20th	Day	20% 34% 29% 13% 2 1	180
	21st to end	Day	22% 21% 38% 14% 5%	207
February	1st to 10th	Day	25% 15% 41% 17% 3	377
	11th to 20th	Day	22% 23% 40% 13% 1	456
	21st to end	Day	27% 20% 32% 15% 5%	382
March	1st to 10th	Day	22% 21% 36% 17% 3	460
	11th to 20th	Day	20% 20% 40% 16% 3 1	460
	21st to end	Day	25% 19% 35% 16% 4 1	506
April	1st to 10th	Day	24% 19% 33% 16% 6% 1	428
	11th to 20th	Day	23% 16% 34% 20% 7%	412
	21st to end	Day	28% 11% 36% 18% 5% 2	420
May	1st to 10th	Day	30% 13% 34% 16% 6% 1	423
	11th to 20th	Day	20% 11% 39% 22% 8% 1	447
	21st to end	Day	21% 7% 23% 30% 16% 2	485
June	1st to 10th	Day	19% 7% 28% 28% 16% 2	450
	11th to 20th	Day	17% 9% 31% 30% 11% 2	450
	21st to end	Day	14% 6% 31% 33% 13% 3	450
July	1st to 10th	Day	16% 4 24% 33% 19% 3	445
	11th to 20th	Day	11% 5% 21% 39% 17% 6%	444
	21st to end	Day	12% 5% 32% 36% 12% 2	488
August	1st to 10th	Day	12% 5% 23% 39% 16% 5%	446
	11th to 20th	Day	16% 4 23% 34% 18% 5%	439
	21st to end	Day	11% 5% 28% 33% 17% 6%	495
September	1st to 10th	Day	19% 6% 25% 27% 17% 5%	450
	11th to 20th	Day	13% 6% 32% 28% 12% 8%	450
	21st to end	Day	21% 8% 34% 24% 12% 2	450
October	1st to 10th	Day	26% 10% 24% 23% 14% 3	450
	11th to 20th	Day	17% 14% 29% 27% 11% 2	430
	21st to end	Day	24% 14% 34% 19% 7% 1	396
November	1st to 10th	Day	16% 11% 35% 25% 10% 3	365
	11th to 20th	Day	22% 21% 32% 18% 6%	370
	21st to end	Day	19% 21% 29% 24% 7%	370
December	1st to 10th	Day	21% 23% 34% 16% 6% 1	200
	11th to 20th	Day	27% 24% 32% 13% 3	180
	21st to end	Day	24% 20% 34% 14% 6% 2	198
January	1st to 10th	Night	19% 22% 37% 18% 3	760
	11th to 20th	Night	28% 20% 32% 18% 2	760
	21st to end	Night	20% 22% 35% 19% 3	836
February	1st to 10th	Night	21% 17% 38% 21% 2	760
	11th to 20th	Night	23% 20% 40% 15% 2	743
	21st to end	Night	25% 20% 33% 18% 4	628
March	1st to 10th	Night	23% 15% 37% 22% 4	760
	11th to 20th	Night	21% 14% 39% 21% 5% 1	760
	21st to end	Night	22% 15% 37% 19% 6%	836
April	1st to 10th	Night	24% 13% 32% 26% 5%	729
	11th to 20th	Night	22% 10% 34% 28% 7%	711
	21st to end	Night	26% 8% 34% 24% 7% 1	595
May	1st to 10th	Night	27% 7% 29% 25% 11% 1	540
	11th to 20th	Night	23% 9% 36% 25% 8%	492
	21st to end	Night	22% 3 21% 36% 17% 2	389
June	1st to 10th	Night	24% 4 21% 33% 17% 1	360
	11th to 20th	Night	21% 3 20% 40% 15% 1	360
	21st to end	Night	17% 3 22% 40% 18% 1	360
July	1st to 10th	Night	17% 3 17% 41% 21% 2	350
	11th to 20th	Night	14% 4 16% 43% 21% 3	348
	21st to end	Night	16% 2 22% 42% 16% 1	394
August	1st to 10th	Night	9% 2 21% 46% 20% 1	468
	11th to 20th	Night	12% 3 17% 39% 24% 3	660
	21st to end	Night	14% 5% 17% 37% 22% 6%	792
September	1st to 10th	Night	17% 3 24% 35% 18% 4	720
	11th to 20th	Night	16% 5% 25% 29% 19% 6%	720
	21st to end	Night	20% 8% 25% 28% 17% 2	720
October	1st to 10th	Night	24% 9% 28% 23% 13% 4	720
	11th to 20th	Night	19% 12% 31% 26% 11% 1	720
	21st to end	Night	24% 14% 36% 18% 8% 1	792
November	1st to 10th	Night	16% 13% 33% 23% 12% 2	740
	11th to 20th	Night	22% 18% 33% 20% 6% 1	760
	21st to end	Night	19% 20% 33% 21% 6% 1	760
December	1st to 10th	Night	26% 18% 30% 21% 5% 1	760
	11th to 20th	Night	24% 21% 32% 20% 4	760
	21st to end	Night	25% 17% 37% 18% 3	836

Page generated at 2024-03-31 06:08:52. Version ac07

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