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 2026-04-02.

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% 12% 4 10% 5% 4 4 3 4 5% 26%	131484
	Night	22% 14% 5% 12% 5% 4 3 3 4 5% 23%	130373
Transparency	Day	58% 6% 10% 17% 9% 1	135047
	Night	62% 6% 9% 15% 8% 1	134897
Seeing	Day	31% 19% 29% 16% 5% 1	18460
	Night	30% 17% 26% 20% 6% 1	26463

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	19% 20% 10% 24% 7% 3 2 2 3 4 8%	4264
	11th to 20th	Day	21% 17% 11% 21% 7% 4 3 2 3 3 8%	5082
	21st to end	Day	17% 15% 7% 26% 11% 4 2 2 2 2 10%	5781
February	1st to 10th	Day	20% 18% 6% 17% 7% 4 4 3 4 4 12%	1890
	11th to 20th	Day	17% 16% 5% 19% 7% 4 3 3 4 4 17%	1843
	21st to end	Day	13% 15% 7% 14% 8% 4 4 4 5% 5% 23%	1700
March	1st to 10th	Day	26% 13% 4 12% 8% 3 3 3 4 5% 20%	4904
	11th to 20th	Day	19% 14% 4 8% 5% 4 4 3 5% 6% 29%	5090
	21st to end	Day	29% 11% 5% 9% 4 4 4 2 4 5% 22%	5587
April	1st to 10th	Day	25% 12% 3 6% 4 4 3 2 4 5% 32%	2298
	11th to 20th	Day	21% 8% 3 5% 4 3 3 3 4 6% 39%	2562
	21st to end	Day	22% 9% 2 5% 3 3 4 3 5% 7% 37%	2600
May	1st to 10th	Day	28% 15% 4 8% 4 3 3 2 4 6% 22%	5886
	11th to 20th	Day	22% 11% 3 8% 4 4 4 3 5% 6% 31%	6013
	21st to end	Day	21% 12% 4 9% 5% 4 3 3 4 6% 29%	6948
June	1st to 10th	Day	26% 9% 1 5% 5% 3 4 3 4 7% 33%	2878
	11th to 20th	Day	22% 8% 3 6% 5% 3 4 3 5% 6% 37%	3000
	21st to end	Day	27% 10% 3 7% 4 4 3 3 4 6% 29%	3000
July	1st to 10th	Day	32% 14% 3 6% 3 3 3 3 4 6% 23%	6820
	11th to 20th	Day	27% 14% 3 7% 5% 5% 5% 3 4 6% 22%	6324
	21st to end	Day	16% 11% 3 7% 4 4 4 3 5% 8% 35%	6425
August	1st to 10th	Day	31% 11% 3 6% 4 4 4 3 4 5% 25%	4235
	11th to 20th	Day	18% 9% 3 8% 4 5% 6% 3 5% 6% 32%	4175
	21st to end	Day	12% 6% 2 5% 4 4 5% 2 5% 7% 47%	4620
September	1st to 10th	Day	16% 7% 2 6% 4 4 3 3 5% 7% 42%	2366
	11th to 20th	Day	17% 6% 2 6% 3 4 4 3 3 5% 47%	2200
	21st to end	Day	17% 7% 3 7% 4 3 4 3 4 6% 43%	2200
October	1st to 10th	Day	17% 8% 3 6% 4 4 4 3 5% 7% 40%	2031
	11th to 20th	Day	19% 9% 2 6% 5% 4 5% 4 6% 6% 34%	2000
	21st to end	Day	20% 11% 4 8% 5% 4 4 3 5% 6% 31%	2148
November	1st to 10th	Day	22% 11% 3 8% 4 4 4 3 4 6% 31%	1841
	11th to 20th	Day	22% 18% 5% 10% 5% 4 3 2 4 6% 22%	1680
	21st to end	Day	21% 18% 7% 12% 6% 4 3 3 4 5% 17%	1680
December	1st to 10th	Day	24% 18% 10% 16% 5% 4 3 2 3 4 11%	2690
	11th to 20th	Day	26% 14% 5% 15% 6% 5% 3 3 4 4 14%	3076
	21st to end	Day	22% 17% 6% 18% 4 3 3 2 3 3 19%	3647
January	1st to 10th	Night	16% 22% 9% 28% 6% 3 2 2 2 2 8%	8633
	11th to 20th	Night	23% 18% 10% 19% 7% 3 3 2 3 3 10%	7785
	21st to end	Night	15% 15% 8% 26% 10% 4 3 2 3 4 11%	8400
February	1st to 10th	Night	21% 18% 8% 19% 7% 3 3 2 3 3 12%	2730
	11th to 20th	Night	18% 16% 7% 17% 9% 4 3 2 4 4 16%	2663
	21st to end	Night	15% 14% 6% 13% 8% 5% 3 3 6% 5% 21%	2102
March	1st to 10th	Night	26% 13% 5% 13% 9% 4 3 3 3 4 19%	5156
	11th to 20th	Night	18% 14% 5% 9% 4 4 5% 3 5% 6% 26%	5089
	21st to end	Night	31% 12% 4 8% 3 3 3 2 4 4 26%	5587
April	1st to 10th	Night	25% 13% 4 7% 4 4 3 3 4 6% 29%	2123
	11th to 20th	Night	23% 10% 3 5% 3 4 4 4 5% 7% 32%	1785
	21st to end	Night	23% 10% 2 7% 4 4 4 4 4 6% 32%	1800
May	1st to 10th	Night	31% 13% 4 6% 3 3 3 2 4 6% 25%	4054
	11th to 20th	Night	25% 12% 3 7% 4 4 3 2 4 5% 31%	3885
	21st to end	Night	20% 17% 3 7% 4 3 3 2 4 6% 31%	3948
June	1st to 10th	Night	28% 10% 2 7% 4 4 5% 3 6% 6% 27%	1536
	11th to 20th	Night	20% 10% 2 8% 5% 3 4 3 5% 7% 33%	1400
	21st to end	Night	27% 14% 3 4 5% 3 4 3 5% 7% 26%	1400
July	1st to 10th	Night	32% 15% 4 7% 3 3 4 3 5% 6% 19%	3160
	11th to 20th	Night	31% 17% 3 6% 4 3 3 2 3 4 22%	3576
	21st to end	Night	18% 12% 4 8% 5% 4 4 3 5% 6% 33%	4428
August	1st to 10th	Night	30% 13% 3 7% 3 3 2 3 4 6% 26%	2915
	11th to 20th	Night	22% 13% 4 7% 4 4 3 3 6% 5% 29%	2872
	21st to end	Night	13% 11% 2 6% 4 3 3 3 5% 6% 45%	3276
September	1st to 10th	Night	19% 8% 2 5% 4 4 3 3 6% 6% 40%	2030
	11th to 20th	Night	20% 7% 2 5% 2 3 3 3 4 6% 44%	2200
	21st to end	Night	21% 7% 2 6% 4 4 4 3 4 7% 39%	2200
October	1st to 10th	Night	20% 7% 2 5% 3 3 3 3 5% 7% 41%	2368
	11th to 20th	Night	18% 10% 3 6% 5% 4 4 3 5% 7% 38%	2400
	21st to end	Night	26% 11% 3 6% 4 3 3 3 4 6% 31%	2690
November	1st to 10th	Night	20% 11% 3 8% 5% 4 4 3 4 6% 32%	2674
	11th to 20th	Night	20% 19% 5% 10% 5% 4 4 3 4 6% 20%	2940
	21st to end	Night	21% 20% 6% 9% 5% 4 4 3 4 5% 20%	2940
December	1st to 10th	Night	19% 19% 8% 17% 6% 6% 5% 3 4 3 11%	4720
	11th to 20th	Night	22% 14% 6% 16% 5% 5% 4 3 4 5% 16%	5353
	21st to end	Night	23% 16% 6% 16% 5% 3 3 2 3 4 21%	7555

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	81% 6% 8% 5% 1	4265
	11th to 20th	Day	82% 6% 5% 5% 2	5115
	21st to end	Day	80% 6% 6% 5% 4	5781
February	1st to 10th	Day	74% 6% 9% 7% 4	1890
	11th to 20th	Day	72% 4 8% 12% 3	1851
	21st to end	Day	61% 7% 10% 14% 7% 1	1700
March	1st to 10th	Day	70% 4 9% 11% 5% 1	4908
	11th to 20th	Day	56% 6% 13% 18% 7%	5090
	21st to end	Day	67% 3 6% 14% 9% 1	5587
April	1st to 10th	Day	58% 3 10% 16% 13% 1	2298
	11th to 20th	Day	48% 5% 10% 23% 13% 2	2562
	21st to end	Day	48% 4 10% 21% 15% 2	2600
May	1st to 10th	Day	65% 5% 8% 17% 5% 1	5897
	11th to 20th	Day	54% 7% 11% 19% 8% 2	6017
	21st to end	Day	56% 6% 10% 14% 12% 1	6948
June	1st to 10th	Day	52% 6% 9% 23% 10% 1	2878
	11th to 20th	Day	47% 6% 11% 20% 14% 2	3000
	21st to end	Day	55% 7% 11% 18% 9% 1	3000
July	1st to 10th	Day	58% 6% 11% 15% 10% 1	6745
	11th to 20th	Day	56% 6% 9% 20% 9%	6244
	21st to end	Day	43% 7% 14% 23% 12% 1	6242
August	1st to 10th	Day	58% 5% 10% 17% 9%	4222
	11th to 20th	Day	47% 8% 15% 23% 7%	4214
	21st to end	Day	34% 6% 12% 27% 20% 1	4620
September	1st to 10th	Day	40% 5% 11% 23% 19% 1	2366
	11th to 20th	Day	41% 4 11% 25% 18% 2	2200
	21st to end	Day	43% 6% 8% 22% 19% 3	2200
October	1st to 10th	Day	43% 7% 11% 28% 11% 1	3304
	11th to 20th	Day	43% 5% 10% 25% 17%	3240
	21st to end	Day	45% 4 11% 25% 11% 3	3450
November	1st to 10th	Day	54% 6% 12% 19% 8% 1	1841
	11th to 20th	Day	64% 6% 10% 13% 6% 1	1680
	21st to end	Day	69% 6% 11% 12% 2	1680
December	1st to 10th	Day	73% 7% 9% 10% 1	2690
	11th to 20th	Day	71% 6% 10% 9% 3	3075
	21st to end	Day	66% 8% 12% 9% 5%	3647
January	1st to 10th	Night	84% 5% 6% 5% 1	8633
	11th to 20th	Night	78% 6% 5% 9% 2	7827
	21st to end	Night	78% 6% 6% 7% 3	8400
February	1st to 10th	Night	76% 5% 8% 7% 4	2730
	11th to 20th	Night	70% 5% 7% 13% 4	2666
	21st to end	Night	60% 8% 10% 15% 6%	2102
March	1st to 10th	Night	70% 4 8% 9% 8% 1	5165
	11th to 20th	Night	58% 7% 14% 14% 6%	5090
	21st to end	Night	62% 3 7% 16% 10% 1	5587
April	1st to 10th	Night	57% 4 9% 15% 12% 2	2123
	11th to 20th	Night	51% 5% 9% 22% 11% 1	1785
	21st to end	Night	52% 6% 9% 18% 13% 1	1800
May	1st to 10th	Night	62% 4 11% 15% 8%	4060
	11th to 20th	Night	55% 6% 9% 18% 9% 2	3886
	21st to end	Night	55% 6% 10% 20% 8% 1	3949
June	1st to 10th	Night	56% 6% 9% 22% 7% 1	1536
	11th to 20th	Night	51% 5% 12% 19% 12% 1	1400
	21st to end	Night	58% 5% 11% 15% 10% 1	1400
July	1st to 10th	Night	66% 6% 8% 13% 8%	3125
	11th to 20th	Night	63% 6% 9% 11% 9% 1	3533
	21st to end	Night	50% 7% 10% 20% 11% 2	4297
August	1st to 10th	Night	60% 5% 9% 19% 7%	2903
	11th to 20th	Night	55% 7% 13% 20% 6%	2899
	21st to end	Night	39% 5% 11% 27% 17% 1	3275
September	1st to 10th	Night	42% 6% 9% 26% 16% 2	2030
	11th to 20th	Night	42% 5% 8% 27% 17% 1	2200
	21st to end	Night	47% 5% 8% 21% 18% 1	2200
October	1st to 10th	Night	44% 6% 13% 22% 14% 1	3875
	11th to 20th	Night	38% 5% 12% 25% 19% 1	3899
	21st to end	Night	46% 5% 10% 26% 13% 1	4338
November	1st to 10th	Night	51% 7% 12% 19% 10%	2674
	11th to 20th	Night	62% 7% 11% 14% 6%	2940
	21st to end	Night	64% 7% 13% 12% 4	2940
December	1st to 10th	Night	71% 7% 10% 11% 1	4720
	11th to 20th	Night	67% 7% 11% 12% 3	5355
	21st to end	Night	66% 6% 10% 12% 7% 1	7555

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% 26% 28% 5% 1	220
	11th to 20th	Day	41% 23% 25% 8% 2	369
	21st to end	Day	28% 30% 30% 11% 1	473
February	1st to 10th	Day	35% 23% 30% 10% 2	430
	11th to 20th	Day	35% 33% 21% 8% 2	426
	21st to end	Day	32% 27% 29% 11% 1	431
March	1st to 10th	Day	33% 24% 32% 9% 2	540
	11th to 20th	Day	38% 22% 26% 9% 3 1	540
	21st to end	Day	36% 23% 26% 10% 4 1	594
April	1st to 10th	Day	41% 24% 23% 9% 2	504
	11th to 20th	Day	33% 26% 30% 9% 3	492
	21st to end	Day	31% 23% 29% 12% 5% 1	500
May	1st to 10th	Day	32% 24% 30% 11% 3	503
	11th to 20th	Day	27% 22% 27% 18% 5% 1	588
	21st to end	Day	31% 15% 30% 17% 6% 1	790
June	1st to 10th	Day	32% 15% 28% 18% 7%	730
	11th to 20th	Day	25% 13% 32% 23% 6% 1	730
	21st to end	Day	35% 13% 28% 18% 5% 1	730
July	1st to 10th	Day	29% 8% 32% 21% 9% 1	720
	11th to 20th	Day	29% 8% 32% 23% 8% 1	609
	21st to end	Day	23% 11% 40% 20% 7%	576
August	1st to 10th	Day	21% 9% 36% 25% 8% 1	526
	11th to 20th	Day	25% 12% 30% 23% 8% 3	519
	21st to end	Day	22% 11% 32% 21% 10% 3	583
September	1st to 10th	Day	21% 13% 35% 21% 8% 2	530
	11th to 20th	Day	23% 14% 29% 22% 8% 4	530
	21st to end	Day	19% 16% 34% 21% 6% 3	530
October	1st to 10th	Day	24% 14% 28% 22% 9% 3	436
	11th to 20th	Day	27% 18% 28% 17% 6% 2	420
	21st to end	Day	29% 22% 27% 16% 5% 1	462
November	1st to 10th	Day	32% 20% 28% 14% 6% 1	425
	11th to 20th	Day	42% 19% 23% 12% 3	430
	21st to end	Day	35% 26% 27% 9% 3 1	430
December	1st to 10th	Day	37% 25% 25% 11% 2	430
	11th to 20th	Day	42% 27% 20% 8% 2	430
	21st to end	Day	43% 27% 18% 8% 2 1	284
January	1st to 10th	Night	36% 24% 26% 12% 2	914
	11th to 20th	Night	37% 20% 26% 14% 3	840
	21st to end	Night	29% 27% 28% 14% 2	924
February	1st to 10th	Night	36% 21% 28% 14% 2	840
	11th to 20th	Night	33% 28% 24% 12% 2 1	823
	21st to end	Night	25% 24% 32% 15% 4	692
March	1st to 10th	Night	30% 23% 31% 14% 2	840
	11th to 20th	Night	28% 21% 26% 18% 6%	840
	21st to end	Night	28% 21% 29% 16% 5% 1	924
April	1st to 10th	Night	37% 19% 27% 15% 3	716
	11th to 20th	Night	28% 17% 33% 19% 3	594
	21st to end	Night	30% 14% 28% 21% 7%	600
May	1st to 10th	Night	30% 13% 31% 21% 4 1	600
	11th to 20th	Night	30% 11% 30% 23% 6%	592
	21st to end	Night	28% 10% 30% 27% 5% 1	649
June	1st to 10th	Night	32% 7% 28% 23% 9%	536
	11th to 20th	Night	23% 7% 29% 34% 6% 1	400
	21st to end	Night	32% 5% 24% 30% 10%	400
July	1st to 10th	Night	29% 6% 25% 29% 10%	390
	11th to 20th	Night	28% 6% 25% 28% 13% 1	463
	21st to end	Night	25% 8% 27% 31% 9%	656
August	1st to 10th	Night	26% 6% 23% 32% 12% 1	598
	11th to 20th	Night	29% 8% 22% 28% 13% 1	592
	21st to end	Night	22% 6% 24% 31% 15% 1	660
September	1st to 10th	Night	22% 8% 24% 32% 13% 1	630
	11th to 20th	Night	23% 9% 23% 25% 17% 3	800
	21st to end	Night	25% 10% 26% 25% 13% 2	800
October	1st to 10th	Night	25% 10% 25% 26% 13% 1	800
	11th to 20th	Night	25% 18% 26% 22% 9% 1	800
	21st to end	Night	32% 18% 23% 21% 6%	880
November	1st to 10th	Night	29% 14% 30% 20% 7% 1	825
	11th to 20th	Night	32% 22% 24% 17% 5%	950
	21st to end	Night	34% 23% 23% 14% 5%	950
December	1st to 10th	Night	35% 22% 26% 15% 2	950
	11th to 20th	Night	38% 25% 24% 10% 2	950
	21st to end	Night	36% 22% 23% 16% 3	1045

Page generated at 2026-03-30 03:18:40. Version ac07

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