Yarmouth
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Yarmouth clear sky chart from 2005-11-06 to 2024-01-16.

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	22% 10% 4 8% 6% 3 4 4 4 6% 29%	74828
	Night	22% 13% 5% 9% 6% 3 4 4 4 5% 25%	74946
Transparency	Day	37% 38% 8% 11% 6% 1	74534
	Night	41% 37% 7% 10% 5%	74775
Seeing	Day	30% 18% 29% 16% 5% 1	15483
	Night	30% 16% 27% 20% 6% 1	23512

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	21% 21% 7% 14% 9% 4 3 3 2 5% 12%	1384
	11th to 20th	Day	25% 16% 9% 12% 11% 4 3 3 3 4 12%	1610
	21st to end	Day	17% 12% 7% 19% 12% 3 4 4 3 4 13%	1782
February	1st to 10th	Day	22% 15% 8% 15% 8% 3 5% 4 4 4 12%	1620
	11th to 20th	Day	19% 15% 7% 14% 11% 4 3 4 4 4 15%	1573
	21st to end	Day	12% 14% 8% 12% 10% 3 4 5% 5% 5% 22%	1454
March	1st to 10th	Day	18% 12% 6% 12% 9% 3 3 3 3 5% 26%	1922
	11th to 20th	Day	18% 12% 5% 9% 6% 3 4 2 4 6% 30%	1980
	21st to end	Day	20% 10% 5% 7% 6% 3 4 3 5% 7% 33%	2178
April	1st to 10th	Day	25% 11% 3 5% 5% 3 4 3 4 5% 32%	2057
	11th to 20th	Day	22% 7% 3 4 4 3 4 4 4 7% 39%	2302
	21st to end	Day	24% 9% 3 5% 4 2 4 4 5% 7% 35%	2340
May	1st to 10th	Day	26% 9% 3 6% 5% 3 4 3 4 5% 31%	2340
	11th to 20th	Day	22% 7% 2 4 4 3 3 3 5% 7% 38%	2355
	21st to end	Day	24% 9% 3 4 5% 2 4 4 5% 8% 32%	2724
June	1st to 10th	Day	27% 8% 2 4 5% 2 5% 3 4 7% 32%	2590
	11th to 20th	Day	23% 7% 3 5% 5% 3 4 5% 4 6% 35%	2700
	21st to end	Day	26% 10% 3 6% 5% 3 4 4 4 7% 29%	2700
July	1st to 10th	Day	23% 9% 3 6% 4 3 4 5% 5% 8% 31%	2700
	11th to 20th	Day	23% 9% 3 6% 6% 3 6% 5% 6% 7% 25%	2512
	21st to end	Day	23% 9% 3 6% 5% 3 5% 4 7% 8% 26%	2548
August	1st to 10th	Day	20% 8% 3 5% 5% 3 5% 5% 5% 8% 34%	2327
	11th to 20th	Day	22% 9% 3 5% 5% 3 5% 5% 6% 6% 30%	2304
	21st to end	Day	18% 7% 2 4 4 3 4 4 4 8% 41%	2549
September	1st to 10th	Day	16% 6% 2 5% 4 3 3 3 5% 8% 44%	2130
	11th to 20th	Day	17% 7% 2 5% 4 3 4 4 3 5% 45%	1980
	21st to end	Day	19% 7% 3 6% 5% 2 3 3 4 5% 43%	1980
October	1st to 10th	Day	19% 8% 3 5% 5% 2 4 4 4 7% 39%	1829
	11th to 20th	Day	20% 8% 2 5% 6% 2 4 5% 6% 6% 35%	1800
	21st to end	Day	22% 10% 4 7% 6% 3 4 4 4 6% 30%	1934
November	1st to 10th	Day	23% 10% 4 7% 5% 3 4 4 4 5% 32%	1663
	11th to 20th	Day	22% 15% 5% 9% 6% 3 3 3 4 6% 23%	1520
	21st to end	Day	21% 17% 8% 10% 6% 3 4 3 4 5% 18%	1520
December	1st to 10th	Day	26% 19% 7% 12% 5% 3 3 3 3 4 15%	1520
	11th to 20th	Day	27% 15% 8% 12% 8% 4 3 4 3 4 11%	1906
	21st to end	Day	25% 15% 9% 14% 5% 3 3 3 3 4 17%	2495
January	1st to 10th	Night	21% 22% 8% 15% 8% 2 3 3 3 4 11%	2777
	11th to 20th	Night	22% 16% 8% 15% 10% 3 4 3 4 4 10%	2468
	21st to end	Night	16% 16% 10% 20% 10% 3 3 3 3 4 11%	2574
February	1st to 10th	Night	22% 16% 9% 17% 9% 3 4 3 3 3 12%	2340
	11th to 20th	Night	20% 16% 8% 15% 11% 3 4 3 3 4 13%	2273
	21st to end	Night	14% 13% 7% 13% 10% 4 4 4 5% 5% 19%	1798
March	1st to 10th	Night	18% 12% 6% 11% 8% 4 4 5% 3 5% 24%	2025
	11th to 20th	Night	21% 10% 6% 11% 6% 3 4 4 4 5% 26%	1979
	21st to end	Night	19% 11% 4 9% 5% 3 3 3 5% 5% 33%	2178
April	1st to 10th	Night	24% 12% 4 7% 5% 3 3 4 5% 6% 28%	1901
	11th to 20th	Night	23% 9% 3 5% 4 3 4 4 4 7% 33%	1605
	21st to end	Night	25% 9% 2 6% 5% 3 4 4 4 6% 31%	1620
May	1st to 10th	Night	23% 10% 3 6% 5% 2 3 4 4 7% 30%	1620
	11th to 20th	Night	26% 9% 2 6% 5% 3 3 4 5% 5% 31%	1536
	21st to end	Night	23% 12% 5% 5% 5% 3 3 4 3 6% 30%	1550
June	1st to 10th	Night	29% 9% 3 6% 4 3 5% 5% 6% 5% 26%	1383
	11th to 20th	Night	21% 9% 3 7% 6% 3 4 3 5% 7% 31%	1260
	21st to end	Night	28% 13% 3 4 5% 2 4 3 5% 7% 27%	1260
July	1st to 10th	Night	24% 13% 2 6% 5% 3 6% 4 6% 5% 26%	1260
	11th to 20th	Night	26% 13% 4 6% 6% 3 4 5% 4 6% 22%	1421
	21st to end	Night	25% 12% 4 7% 7% 3 5% 4 5% 4 25%	1770
August	1st to 10th	Night	20% 10% 4 7% 4 3 3 4 6% 8% 32%	1612
	11th to 20th	Night	25% 14% 4 5% 4 2 4 3 5% 6% 27%	1596
	21st to end	Night	18% 9% 3 4 5% 2 4 3 5% 7% 39%	1805
September	1st to 10th	Night	19% 7% 2 4 4 3 4 4 5% 7% 41%	1826
	11th to 20th	Night	21% 7% 3 4 3 2 3 4 4 6% 43%	1980
	21st to end	Night	22% 7% 2 5% 4 2 4 3 4 7% 40%	1980
October	1st to 10th	Night	22% 7% 2 5% 4 2 3 4 4 7% 39%	2130
	11th to 20th	Night	19% 9% 3 5% 6% 3 4 4 5% 7% 37%	2160
	21st to end	Night	27% 11% 3 6% 4 3 3 4 4 6% 30%	2420
November	1st to 10th	Night	20% 11% 4 7% 6% 3 4 5% 4 6% 31%	2412
	11th to 20th	Night	21% 16% 6% 9% 5% 3 4 4 4 6% 21%	2660
	21st to end	Night	20% 19% 7% 8% 5% 3 5% 4 4 5% 21%	2660
December	1st to 10th	Night	28% 17% 9% 10% 6% 3 4 4 4 4 12%	2660
	11th to 20th	Night	26% 15% 8% 13% 7% 3 4 3 3 4 15%	3293
	21st to end	Night	25% 15% 6% 13% 6% 3 3 3 3 5% 18%	5154

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	47% 42% 6% 5% 2	1385
	11th to 20th	Day	49% 42% 6% 4	1610
	21st to end	Day	48% 40% 6% 6%	1782
February	1st to 10th	Day	51% 37% 6% 4 2	1620
	11th to 20th	Day	49% 38% 7% 6% 1	1581
	21st to end	Day	45% 38% 7% 7% 3	1454
March	1st to 10th	Day	42% 37% 7% 10% 3 1	1926
	11th to 20th	Day	34% 37% 8% 13% 6% 1	1980
	21st to end	Day	34% 37% 8% 14% 6% 1	2178
April	1st to 10th	Day	35% 36% 7% 11% 10% 1	2057
	11th to 20th	Day	32% 36% 6% 15% 10% 1	2302
	21st to end	Day	32% 37% 8% 13% 9% 1	2340
May	1st to 10th	Day	38% 37% 6% 11% 7% 1	2340
	11th to 20th	Day	31% 37% 8% 13% 11% 1	2359
	21st to end	Day	32% 39% 9% 11% 9%	2724
June	1st to 10th	Day	37% 37% 7% 14% 4 1	2590
	11th to 20th	Day	35% 38% 6% 12% 7% 1	2700
	21st to end	Day	41% 39% 9% 9% 3 1	2700
July	1st to 10th	Day	34% 40% 11% 9% 5%	2625
	11th to 20th	Day	36% 40% 8% 11% 4 1	2432
	21st to end	Day	33% 40% 9% 13% 5%	2406
August	1st to 10th	Day	34% 38% 9% 12% 7%	2314
	11th to 20th	Day	35% 38% 8% 11% 7%	2304
	21st to end	Day	30% 38% 8% 15% 9% 1	2549
September	1st to 10th	Day	27% 38% 8% 13% 14% 1	2130
	11th to 20th	Day	28% 36% 7% 16% 11% 1	1980
	21st to end	Day	32% 36% 4 14% 12% 2	1980
October	1st to 10th	Day	29% 37% 9% 17% 8%	1829
	11th to 20th	Day	32% 39% 9% 15% 5%	1800
	21st to end	Day	36% 38% 7% 11% 7% 1	1934
November	1st to 10th	Day	34% 41% 7% 12% 6%	1663
	11th to 20th	Day	37% 42% 8% 9% 4	1520
	21st to end	Day	43% 42% 8% 7% 1	1520
December	1st to 10th	Day	46% 40% 6% 7% 1	1520
	11th to 20th	Day	54% 35% 5% 5% 1	1905
	21st to end	Day	52% 30% 13% 4 1	2495
January	1st to 10th	Night	50% 40% 5% 4 1	2777
	11th to 20th	Night	48% 42% 5% 4 1	2468
	21st to end	Night	51% 38% 5% 5% 1	2574
February	1st to 10th	Night	52% 36% 6% 5% 1	2340
	11th to 20th	Night	51% 38% 5% 5% 2	2276
	21st to end	Night	42% 39% 8% 9% 2	1798
March	1st to 10th	Night	42% 38% 7% 8% 5% 1	2034
	11th to 20th	Night	39% 38% 9% 8% 5% 1	1980
	21st to end	Night	33% 37% 6% 16% 7% 1	2178
April	1st to 10th	Night	38% 37% 7% 11% 6% 1	1901
	11th to 20th	Night	34% 36% 7% 14% 9% 1	1605
	21st to end	Night	35% 37% 7% 13% 8%	1620
May	1st to 10th	Night	38% 36% 7% 12% 7%	1620
	11th to 20th	Night	35% 38% 5% 13% 8% 1	1537
	21st to end	Night	36% 37% 7% 12% 6% 1	1551
June	1st to 10th	Night	40% 38% 6% 13% 2 1	1383
	11th to 20th	Night	39% 36% 8% 10% 7% 1	1260
	21st to end	Night	44% 37% 7% 8% 4	1260
July	1st to 10th	Night	39% 39% 9% 8% 4	1225
	11th to 20th	Night	41% 39% 7% 9% 3 1	1378
	21st to end	Night	38% 39% 7% 11% 5% 1	1672
August	1st to 10th	Night	36% 37% 6% 16% 4	1600
	11th to 20th	Night	40% 35% 5% 11% 7%	1596
	21st to end	Night	33% 37% 8% 15% 8%	1805
September	1st to 10th	Night	29% 37% 6% 16% 10% 1	1826
	11th to 20th	Night	28% 36% 5% 18% 12% 1	1980
	21st to end	Night	32% 36% 5% 13% 13% 1	1980
October	1st to 10th	Night	29% 37% 8% 15% 10% 1	2130
	11th to 20th	Night	31% 38% 8% 16% 6%	2160
	21st to end	Night	38% 38% 6% 10% 7% 1	2420
November	1st to 10th	Night	32% 42% 8% 13% 6%	2412
	11th to 20th	Night	37% 42% 8% 9% 4	2660
	21st to end	Night	40% 42% 8% 8% 2	2660
December	1st to 10th	Night	48% 40% 7% 5% 1	2660
	11th to 20th	Night	51% 34% 5% 8% 2	3295
	21st to end	Night	52% 28% 10% 9% 1	5154

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	40% 25% 28% 5% 2	180
	11th to 20th	Day	39% 24% 27% 8% 2	300
	21st to end	Day	24% 31% 31% 12% 2	374
February	1st to 10th	Day	36% 22% 31% 9% 1	340
	11th to 20th	Day	37% 33% 20% 8% 2	336
	21st to end	Day	31% 27% 30% 11% 1	335
March	1st to 10th	Day	31% 25% 33% 9% 2	420
	11th to 20th	Day	36% 24% 26% 10% 4 1	420
	21st to end	Day	30% 24% 28% 12% 5% 1	462
April	1st to 10th	Day	40% 24% 23% 10% 3	420
	11th to 20th	Day	32% 24% 32% 9% 3	412
	21st to end	Day	33% 20% 28% 13% 5% 1	420
May	1st to 10th	Day	31% 24% 29% 12% 3	423
	11th to 20th	Day	28% 22% 28% 18% 5%	501
	21st to end	Day	32% 14% 29% 18% 7% 1	680
June	1st to 10th	Day	33% 13% 28% 19% 7%	630
	11th to 20th	Day	25% 13% 32% 23% 6% 1	630
	21st to end	Day	34% 12% 30% 19% 5% 1	630
July	1st to 10th	Day	28% 8% 31% 22% 10% 1	620
	11th to 20th	Day	26% 7% 34% 25% 7% 1	521
	21st to end	Day	24% 10% 37% 21% 7%	488
August	1st to 10th	Day	20% 10% 36% 26% 8% 1	446
	11th to 20th	Day	26% 11% 31% 21% 8% 2	439
	21st to end	Day	23% 9% 32% 22% 11% 3	495
September	1st to 10th	Day	20% 12% 36% 22% 9% 2	450
	11th to 20th	Day	24% 15% 29% 21% 7% 4	450
	21st to end	Day	21% 15% 35% 19% 6% 4	450
October	1st to 10th	Day	26% 14% 28% 21% 9% 3	374
	11th to 20th	Day	25% 19% 29% 18% 7% 3	360
	21st to end	Day	30% 21% 27% 16% 5% 1	396
November	1st to 10th	Day	29% 19% 30% 14% 7% 1	365
	11th to 20th	Day	39% 19% 25% 13% 3 1	370
	21st to end	Day	34% 25% 28% 9% 3 1	370
December	1st to 10th	Day	35% 26% 25% 11% 3	370
	11th to 20th	Day	42% 29% 19% 8% 1	370
	21st to end	Day	44% 28% 17% 8% 2 1	236
January	1st to 10th	Night	35% 24% 26% 12% 2	821
	11th to 20th	Night	36% 20% 27% 14% 3	744
	21st to end	Night	28% 25% 29% 15% 2	792
February	1st to 10th	Night	36% 22% 29% 12% 1	720
	11th to 20th	Night	34% 28% 22% 12% 2 1	703
	21st to end	Night	24% 24% 32% 15% 4	592
March	1st to 10th	Night	28% 23% 32% 15% 2	720
	11th to 20th	Night	28% 21% 27% 18% 6%	720
	21st to end	Night	26% 21% 29% 18% 6% 1	792
April	1st to 10th	Night	35% 19% 27% 15% 3	641
	11th to 20th	Night	28% 17% 33% 19% 3	534
	21st to end	Night	31% 14% 27% 20% 8%	540
May	1st to 10th	Night	29% 12% 31% 22% 5% 1	540
	11th to 20th	Night	30% 11% 31% 23% 5%	532
	21st to end	Night	28% 10% 29% 27% 5% 1	583
June	1st to 10th	Night	33% 7% 29% 23% 8%	483
	11th to 20th	Night	23% 7% 29% 32% 7% 1	360
	21st to end	Night	32% 4 25% 28% 11%	360
July	1st to 10th	Night	27% 6% 25% 30% 11%	350
	11th to 20th	Night	26% 7% 25% 28% 13% 1	415
	21st to end	Night	26% 7% 27% 31% 10%	590
August	1st to 10th	Night	25% 6% 24% 31% 12% 1	538
	11th to 20th	Night	30% 8% 23% 28% 12% 1	532
	21st to end	Night	23% 6% 23% 31% 15% 1	594
September	1st to 10th	Night	22% 7% 26% 31% 13% 1	566
	11th to 20th	Night	24% 10% 25% 23% 16% 3	720
	21st to end	Night	26% 10% 26% 23% 14% 2	720
October	1st to 10th	Night	26% 10% 26% 25% 12% 1	720
	11th to 20th	Night	24% 17% 27% 21% 9% 2	720
	21st to end	Night	34% 18% 23% 20% 5%	792
November	1st to 10th	Night	28% 14% 29% 21% 7% 1	743
	11th to 20th	Night	32% 21% 24% 18% 5%	850
	21st to end	Night	33% 23% 24% 14% 5%	850
December	1st to 10th	Night	36% 22% 26% 14% 2	850
	11th to 20th	Night	38% 25% 25% 10% 2	850
	21st to end	Night	37% 23% 21% 16% 3	935

Page generated at 2024-01-13 10:37:55. Version ac07

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