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 2024-11-06.

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 6% 4 4 4 3 5% 7% 39%	101199
	Night	19% 8% 2 6% 4 4 4 3 5% 6% 40%	97863
Transparency	Day	41% 6% 13% 23% 15% 2	104749
	Night	44% 5% 12% 22% 15% 2	102402
Seeing	Day	20% 12% 31% 24% 10% 2	15089
	Night	21% 12% 30% 26% 10% 1	24081

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% 7% 2 5% 4 3 4 3 4 5% 45%	2517
	11th to 20th	Day	17% 9% 2 6% 4 5% 5% 3 5% 5% 39%	2520
	21st to end	Day	23% 13% 3 6% 4 3 3 3 4 5% 35%	2804
February	1st to 10th	Day	18% 8% 2 6% 4 4 5% 4 5% 6% 38%	1817
	11th to 20th	Day	15% 7% 2 6% 4 4 4 4 6% 6% 42%	1848
	21st to end	Day	21% 9% 3 5% 4 3 4 3 5% 6% 36%	1570
March	1st to 10th	Day	28% 9% 2 6% 3 2 3 2 3 5% 36%	3116
	11th to 20th	Day	11% 6% 2 5% 4 5% 5% 4 6% 8% 45%	3270
	21st to end	Day	21% 7% 3 6% 4 4 4 4 5% 7% 36%	4133
April	1st to 10th	Day	19% 7% 3 5% 4 3 5% 3 5% 6% 39%	2280
	11th to 20th	Day	20% 7% 2 5% 3 4 4 3 5% 7% 41%	2254
	21st to end	Day	21% 6% 2 5% 4 4 4 3 6% 7% 39%	2410
May	1st to 10th	Day	28% 10% 3 5% 4 3 3 3 4 7% 30%	4106
	11th to 20th	Day	23% 8% 3 7% 4 4 4 3 4 7% 33%	4190
	21st to end	Day	16% 5% 2 5% 3 3 4 3 5% 8% 45%	4837
June	1st to 10th	Day	18% 6% 2 5% 5% 5% 5% 4 7% 8% 36%	2660
	11th to 20th	Day	17% 7% 2 5% 4 4 5% 4 5% 9% 39%	2660
	21st to end	Day	14% 7% 3 6% 4 5% 4 4 7% 9% 39%	2660
July	1st to 10th	Day	16% 7% 2 7% 5% 5% 5% 4 6% 8% 36%	4440
	11th to 20th	Day	16% 5% 2 5% 4 4 4 4 7% 9% 39%	4440
	21st to end	Day	20% 8% 3 7% 4 4 5% 4 6% 8% 32%	4814
August	1st to 10th	Day	20% 7% 2 7% 4 5% 5% 4 6% 8% 32%	4183
	11th to 20th	Day	13% 5% 2 6% 4 4 4 4 6% 9% 42%	3803
	21st to end	Day	7% 5% 2 6% 5% 5% 6% 5% 8% 9% 43%	4180
September	1st to 10th	Day	15% 5% 2 6% 4 4 4 3 5% 6% 45%	2280
	11th to 20th	Day	13% 5% 2 5% 3 3 3 3 5% 7% 52%	2123
	21st to end	Day	20% 6% 2 6% 4 4 3 4 4 6% 40%	2090
October	1st to 10th	Day	22% 7% 2 5% 3 4 3 3 4 6% 41%	2090
	11th to 20th	Day	14% 5% 2 5% 3 3 3 3 5% 7% 49%	1868
	21st to end	Day	18% 6% 2 6% 4 3 4 3 4 7% 42%	1881
November	1st to 10th	Day	14% 6% 2 6% 4 3 4 2 4 5% 48%	1717
	11th to 20th	Day	18% 7% 2 3 3 3 3 3 5% 6% 47%	1710
	21st to end	Day	17% 7% 2 5% 4 4 3 3 4 6% 45%	1710
December	1st to 10th	Day	20% 7% 2 6% 3 4 4 4 5% 6% 38%	1540
	11th to 20th	Day	23% 6% 2 4 3 3 2 2 4 5% 46%	1906
	21st to end	Day	20% 11% 3 7% 5% 4 3 3 4 5% 36%	2772
January	1st to 10th	Night	17% 7% 2 5% 3 3 3 3 4 7% 47%	4429
	11th to 20th	Night	18% 9% 3 7% 3 3 3 3 4 4 43%	4440
	21st to end	Night	24% 11% 3 7% 4 4 3 3 4 5% 32%	4848
February	1st to 10th	Night	17% 9% 3 6% 4 3 3 3 4 5% 41%	2361
	11th to 20th	Night	17% 9% 2 5% 4 4 3 3 4 6% 42%	2218
	21st to end	Night	21% 8% 2 5% 4 3 4 4 5% 5% 40%	1884
March	1st to 10th	Night	27% 11% 2 5% 3 3 3 2 4 5% 35%	3724
	11th to 20th	Night	11% 7% 2 7% 5% 5% 5% 4 6% 6% 44%	3688
	21st to end	Night	23% 8% 2 5% 3 3 4 4 4 5% 38%	3483
April	1st to 10th	Night	21% 7% 2 6% 4 4 4 3 5% 7% 37%	1900
	11th to 20th	Night	20% 6% 2 6% 4 4 4 3 5% 6% 41%	1875
	21st to end	Night	23% 6% 2 6% 4 3 4 2 4 5% 41%	1768
May	1st to 10th	Night	25% 11% 4 7% 4 4 4 3 4 6% 28%	2834
	11th to 20th	Night	24% 9% 3 7% 4 4 5% 3 5% 7% 27%	2731
	21st to end	Night	19% 7% 2 5% 4 3 4 3 6% 7% 41%	2738
June	1st to 10th	Night	18% 8% 2 6% 5% 4 4 4 5% 6% 39%	1520
	11th to 20th	Night	19% 6% 2 5% 4 3 4 4 6% 9% 38%	1520
	21st to end	Night	16% 6% 2 5% 3 4 5% 5% 5% 10% 39%	1520
July	1st to 10th	Night	18% 8% 3 7% 6% 5% 4 4 6% 7% 32%	2520
	11th to 20th	Night	19% 7% 2 4 4 3 4 4 6% 10% 35%	2520
	21st to end	Night	21% 9% 3 6% 4 4 5% 3 6% 6% 33%	2739
August	1st to 10th	Night	24% 8% 3 8% 4 4 4 4 6% 8% 27%	2714
	11th to 20th	Night	12% 7% 2 7% 5% 5% 6% 4 6% 7% 39%	3021
	21st to end	Night	9% 4 2 4 3 3 4 3 5% 8% 55%	3476
September	1st to 10th	Night	15% 7% 2 5% 4 4 5% 4 5% 6% 42%	1900
	11th to 20th	Night	15% 5% 2 5% 3 3 3 2 4 6% 53%	2057
	21st to end	Night	19% 7% 3 6% 4 4 4 4 4 5% 39%	2090
October	1st to 10th	Night	20% 7% 2 6% 4 3 3 3 5% 5% 42%	2090
	11th to 20th	Night	15% 6% 2 5% 4 2 3 3 5% 6% 49%	2307
	21st to end	Night	21% 6% 2 6% 3 3 3 3 5% 6% 42%	2717
November	1st to 10th	Night	14% 6% 2 5% 4 3 4 3 4 6% 48%	2483
	11th to 20th	Night	19% 7% 2 5% 3 3 3 3 4 5% 46%	2470
	21st to end	Night	16% 5% 2 5% 4 4 3 3 4 7% 47%	2470
December	1st to 10th	Night	22% 7% 3 5% 4 4 4 3 4 6% 40%	2636
	11th to 20th	Night	21% 7% 2 4 4 4 4 3 5% 5% 42%	3288
	21st to end	Night	22% 11% 3 6% 3 3 3 3 4 5% 37%	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	49% 6% 11% 20% 13% 2	3119
	11th to 20th	Day	30% 8% 13% 33% 14% 2	3270
	21st to end	Day	46% 4 7% 18% 18% 5%	4133
April	1st to 10th	Day	43% 6% 11% 20% 16% 3	2280
	11th to 20th	Day	42% 5% 10% 21% 19% 2	2254
	21st to end	Day	43% 6% 10% 22% 16% 4	2410
May	1st to 10th	Day	54% 5% 15% 15% 10% 1	4120
	11th to 20th	Day	49% 5% 17% 17% 10% 2	4194
	21st to end	Day	36% 7% 12% 26% 18% 2	4837
June	1st to 10th	Day	42% 8% 12% 25% 12% 1	2660
	11th to 20th	Day	39% 7% 15% 25% 13% 1	2660
	21st to end	Day	37% 8% 14% 26% 14% 1	2660
July	1st to 10th	Day	45% 8% 11% 20% 15% 1	4370
	11th to 20th	Day	40% 6% 17% 23% 13% 1	4365
	21st to end	Day	48% 6% 13% 18% 14% 2	4661
August	1st to 10th	Day	47% 6% 17% 22% 8%	4169
	11th to 20th	Day	37% 5% 15% 31% 10% 1	3841
	21st to end	Day	30% 6% 16% 29% 17% 1	4180
September	1st to 10th	Day	37% 7% 12% 22% 20% 2	2280
	11th to 20th	Day	31% 6% 11% 24% 25% 3	2123
	21st to end	Day	45% 5% 9% 20% 20% 2	2090
October	1st to 10th	Day	35% 4 11% 21% 23% 5%	3480
	11th to 20th	Day	27% 3 9% 24% 32% 3	3071
	21st to end	Day	32% 4 14% 27% 20% 3	3081
November	1st to 10th	Day	38% 5% 15% 20% 21% 3	1717
	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	53% 3 10% 20% 12% 2	3734
	11th to 20th	Night	38% 6% 14% 24% 15% 3	3689
	21st to end	Night	48% 4 7% 13% 23% 6%	3483
April	1st to 10th	Night	45% 5% 10% 21% 15% 4	1900
	11th to 20th	Night	44% 4 9% 21% 19% 2	1875
	21st to end	Night	46% 4 9% 21% 15% 5%	1768
May	1st to 10th	Night	58% 5% 12% 15% 9% 1	2840
	11th to 20th	Night	56% 7% 13% 14% 8% 2	2732
	21st to end	Night	42% 7% 15% 22% 12% 1	2739
June	1st to 10th	Night	45% 6% 11% 19% 16% 2	1520
	11th to 20th	Night	40% 6% 15% 26% 12% 1	1520
	21st to end	Night	40% 7% 14% 24% 13% 1	1520
July	1st to 10th	Night	51% 6% 12% 18% 12% 1	2480
	11th to 20th	Night	42% 7% 17% 24% 9% 1	2472
	21st to end	Night	49% 5% 14% 14% 16% 1	2651
August	1st to 10th	Night	53% 7% 14% 17% 8% 1	2704
	11th to 20th	Night	41% 7% 16% 28% 8%	3049
	21st to end	Night	27% 5% 17% 31% 19% 1	3476
September	1st to 10th	Night	41% 6% 10% 24% 18% 2	1900
	11th to 20th	Night	33% 4 11% 24% 24% 2	2057
	21st to end	Night	46% 6% 8% 18% 19% 3	2090
October	1st to 10th	Night	40% 5% 11% 24% 18% 3	3480
	11th to 20th	Night	26% 3 10% 25% 32% 4	3843
	21st to end	Night	33% 4 13% 26% 22% 2	4467
November	1st to 10th	Night	38% 5% 12% 22% 19% 4	2483
	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% 35% 16% 6% 1	460
	11th to 20th	Day	24% 16% 35% 18% 7%	452
	21st to end	Day	27% 11% 35% 19% 5% 2	460
May	1st to 10th	Day	30% 12% 35% 17% 6% 1	463
	11th to 20th	Day	20% 10% 38% 23% 8% 1	487
	21st to end	Day	21% 8% 24% 30% 16% 2	529
June	1st to 10th	Day	18% 7% 29% 28% 16% 2	490
	11th to 20th	Day	16% 8% 31% 31% 13% 2	490
	21st to end	Day	14% 6% 31% 34% 13% 3	490
July	1st to 10th	Day	16% 4 23% 34% 19% 4	485
	11th to 20th	Day	11% 5% 21% 40% 17% 6%	484
	21st to end	Day	14% 5% 31% 35% 13% 2	532
August	1st to 10th	Day	13% 5% 22% 39% 16% 5%	486
	11th to 20th	Day	16% 4 23% 34% 18% 6%	479
	21st to end	Day	10% 5% 27% 33% 19% 6%	539
September	1st to 10th	Day	19% 6% 25% 28% 17% 5%	490
	11th to 20th	Day	13% 6% 30% 27% 16% 9%	490
	21st to end	Day	22% 7% 32% 24% 11% 2	490
October	1st to 10th	Day	25% 9% 23% 24% 15% 3	490
	11th to 20th	Day	16% 14% 30% 27% 11% 2	467
	21st to end	Day	22% 14% 33% 21% 8% 2	429
November	1st to 10th	Day	16% 11% 35% 25% 10% 3	381
	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	23% 15% 37% 19% 6%	836
April	1st to 10th	Night	24% 13% 32% 26% 5%	760
	11th to 20th	Night	22% 11% 34% 27% 7%	751
	21st to end	Night	25% 8% 35% 25% 7% 1	628
May	1st to 10th	Night	26% 8% 29% 26% 11% 1	570
	11th to 20th	Night	23% 9% 35% 25% 8%	519
	21st to end	Night	21% 3 21% 36% 17% 1	411
June	1st to 10th	Night	23% 5% 21% 33% 17% 1	380
	11th to 20th	Night	20% 3 19% 41% 16% 1	380
	21st to end	Night	17% 3 24% 38% 17% 1	380
July	1st to 10th	Night	18% 3 16% 40% 22% 2	370
	11th to 20th	Night	13% 5% 15% 43% 21% 3	368
	21st to end	Night	17% 2 22% 41% 17% 1	416
August	1st to 10th	Night	11% 2 20% 46% 19% 2	495
	11th to 20th	Night	13% 3 17% 39% 24% 4	698
	21st to end	Night	13% 4 17% 37% 23% 6%	836
September	1st to 10th	Night	16% 3 24% 35% 19% 3	760
	11th to 20th	Night	16% 5% 24% 29% 21% 6%	760
	21st to end	Night	20% 7% 26% 28% 17% 2	760
October	1st to 10th	Night	23% 9% 28% 23% 14% 4	760
	11th to 20th	Night	18% 12% 31% 27% 11% 1	760
	21st to end	Night	23% 13% 35% 19% 9% 1	836
November	1st to 10th	Night	16% 13% 34% 23% 12% 2	764
	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 2024-11-03 13:19:05. Version ac07

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