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 2024-12-09.

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% 11% 4 9% 5% 4 4 3 4 6% 28%	101870
	Night	23% 14% 5% 10% 5% 4 3 3 4 5% 25%	97930
Transparency	Day	55% 6% 11% 18% 10% 1	105444
	Night	59% 6% 10% 16% 8% 1	102445
Seeing	Day	30% 18% 29% 16% 5% 1	16747
	Night	30% 16% 26% 20% 6% 1	24656

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	22% 17% 7% 17% 6% 4 3 3 4 5% 11%	2300
	11th to 20th	Day	20% 15% 8% 18% 7% 4 3 2 4 4 13%	2745
	21st to end	Day	22% 15% 7% 17% 6% 3 3 2 3 3 17%	3124
February	1st to 10th	Day	22% 18% 6% 16% 7% 5% 4 3 4 4 12%	1710
	11th to 20th	Day	18% 18% 5% 18% 7% 4 3 3 4 4 16%	1663
	21st to end	Day	13% 15% 7% 13% 8% 4 4 4 5% 5% 22%	1542
March	1st to 10th	Day	28% 14% 4 10% 6% 3 2 2 4 5% 23%	3339
	11th to 20th	Day	19% 15% 4 8% 5% 4 4 3 5% 7% 26%	3480
	21st to end	Day	31% 10% 5% 10% 4 3 3 2 4 5% 23%	3816
April	1st to 10th	Day	24% 12% 3 6% 4 4 4 2 4 5% 33%	2172
	11th to 20th	Day	21% 8% 3 4 4 3 3 3 4 6% 40%	2432
	21st to end	Day	22% 9% 2 5% 3 3 4 3 5% 7% 36%	2470
May	1st to 10th	Day	23% 10% 4 7% 5% 4 4 3 5% 8% 28%	4106
	11th to 20th	Day	21% 8% 3 7% 4 4 4 3 5% 7% 33%	4191
	21st to end	Day	20% 11% 4 9% 5% 3 3 3 4 6% 31%	4836
June	1st to 10th	Day	26% 9% 1 5% 5% 3 4 3 4 7% 33%	2734
	11th to 20th	Day	22% 8% 3 6% 5% 3 4 3 5% 6% 36%	2850
	21st to end	Day	27% 11% 3 7% 4 4 3 3 4 6% 28%	2850
July	1st to 10th	Day	30% 13% 3 6% 4 3 3 3 4 6% 26%	4760
	11th to 20th	Day	30% 12% 3 7% 4 5% 5% 3 5% 6% 21%	4418
	21st to end	Day	20% 9% 3 7% 4 4 4 3 5% 8% 32%	4467
August	1st to 10th	Day	32% 12% 3 6% 4 4 4 3 4 5% 24%	4105
	11th to 20th	Day	18% 9% 3 8% 4 5% 5% 4 5% 6% 32%	4045
	21st to end	Day	12% 6% 2 5% 4 4 5% 3 5% 7% 47%	4479
September	1st to 10th	Day	16% 7% 2 6% 4 4 3 3 5% 8% 43%	2248
	11th to 20th	Day	17% 6% 2 6% 3 4 4 3 3 5% 45%	2090
	21st to end	Day	18% 8% 3 7% 4 3 4 3 4 6% 42%	2090
October	1st to 10th	Day	18% 8% 3 6% 4 4 4 3 5% 7% 38%	1930
	11th to 20th	Day	19% 8% 2 6% 5% 3 5% 3 6% 6% 36%	1900
	21st to end	Day	20% 11% 4 8% 5% 4 4 3 5% 6% 31%	2041
November	1st to 10th	Day	22% 11% 3 8% 4 4 4 3 4 5% 32%	1752
	11th to 20th	Day	22% 16% 5% 10% 5% 4 3 3 4 6% 23%	1600
	21st to end	Day	21% 18% 8% 11% 5% 4 3 3 5% 5% 17%	1600
December	1st to 10th	Day	25% 21% 6% 13% 4 4 3 2 3 4 14%	1584
	11th to 20th	Day	27% 17% 6% 14% 6% 4 3 3 4 4 11%	1906
	21st to end	Day	25% 16% 8% 15% 5% 3 3 2 3 4 16%	2495
January	1st to 10th	Night	17% 20% 8% 23% 6% 4 3 2 3 3 12%	4648
	11th to 20th	Night	19% 18% 8% 18% 8% 4 4 2 4 3 12%	4211
	21st to end	Night	20% 17% 8% 19% 6% 3 3 2 3 4 14%	4532
February	1st to 10th	Night	22% 19% 8% 18% 7% 3 3 2 3 3 13%	2470
	11th to 20th	Night	19% 17% 7% 17% 9% 4 3 2 4 4 14%	2403
	21st to end	Night	15% 14% 6% 14% 8% 5% 3 4 6% 5% 20%	1908
March	1st to 10th	Night	26% 13% 4 10% 8% 4 3 3 2 4 23%	3501
	11th to 20th	Night	17% 16% 5% 10% 4 4 5% 3 5% 6% 25%	3479
	21st to end	Night	34% 11% 5% 9% 3 3 2 1 3 3 26%	3816
April	1st to 10th	Night	23% 13% 4 7% 4 4 3 3 5% 6% 29%	2006
	11th to 20th	Night	23% 10% 3 5% 3 4 4 4 5% 7% 33%	1695
	21st to end	Night	24% 9% 2 7% 4 4 4 4 4 6% 32%	1710
May	1st to 10th	Night	23% 13% 4 6% 4 3 3 3 5% 7% 30%	2834
	11th to 20th	Night	24% 10% 3 8% 5% 5% 4 3 5% 5% 29%	2704
	21st to end	Night	20% 15% 4 7% 4 3 3 3 4 6% 32%	2749
June	1st to 10th	Night	28% 10% 2 7% 4 4 5% 3 5% 5% 26%	1459
	11th to 20th	Night	20% 10% 2 8% 6% 3 3 3 5% 7% 32%	1330
	21st to end	Night	28% 14% 3 5% 5% 3 4 2 5% 7% 25%	1330
July	1st to 10th	Night	33% 14% 2 6% 4 3 4 3 5% 5% 21%	2210
	11th to 20th	Night	34% 14% 2 6% 4 3 3 3 4 5% 22%	2505
	21st to end	Night	20% 11% 3 8% 6% 4 4 3 6% 7% 29%	3087
August	1st to 10th	Night	31% 13% 3 7% 3 3 2 2 4 6% 25%	2825
	11th to 20th	Night	22% 14% 4 7% 4 4 3 3 6% 5% 29%	2782
	21st to end	Night	13% 11% 2 6% 4 3 3 3 5% 6% 45%	3175
September	1st to 10th	Night	18% 7% 2 5% 4 4 3 3 5% 6% 41%	1928
	11th to 20th	Night	20% 7% 2 5% 2 3 3 3 4 6% 43%	2090
	21st to end	Night	22% 7% 2 5% 4 4 4 3 4 7% 39%	2090
October	1st to 10th	Night	21% 8% 2 6% 3 3 3 3 5% 7% 39%	2249
	11th to 20th	Night	18% 9% 3 6% 5% 4 4 3 5% 7% 38%	2280
	21st to end	Night	26% 11% 3 6% 4 3 3 3 4 6% 31%	2555
November	1st to 10th	Night	19% 12% 3 8% 5% 4 4 3 4 6% 32%	2543
	11th to 20th	Night	20% 18% 5% 10% 5% 4 4 3 4 6% 21%	2800
	21st to end	Night	21% 20% 6% 9% 4 4 4 3 4 5% 20%	2800
December	1st to 10th	Night	26% 20% 7% 12% 5% 4 4 3 4 4 12%	2779
	11th to 20th	Night	26% 17% 7% 14% 5% 4 3 2 3 5% 14%	3293
	21st to end	Night	24% 16% 6% 14% 5% 4 3 2 3 4 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	72% 8% 11% 7% 2	2301
	11th to 20th	Day	74% 7% 8% 8% 3	2745
	21st to end	Day	71% 7% 9% 8% 5%	3124
February	1st to 10th	Day	75% 6% 9% 6% 4	1710
	11th to 20th	Day	73% 4 8% 11% 3	1671
	21st to end	Day	61% 7% 11% 14% 6% 1	1542
March	1st to 10th	Day	66% 3 10% 14% 6% 1	3343
	11th to 20th	Day	58% 6% 12% 16% 7% 1	3480
	21st to end	Day	67% 3 7% 14% 9% 1	3816
April	1st to 10th	Day	58% 3 10% 16% 13% 1	2172
	11th to 20th	Day	47% 5% 10% 23% 13% 1	2432
	21st to end	Day	49% 4 10% 20% 15% 2	2470
May	1st to 10th	Day	55% 6% 11% 21% 6% 1	4120
	11th to 20th	Day	50% 7% 14% 20% 8% 1	4195
	21st to end	Day	52% 7% 12% 14% 14% 1	4836
June	1st to 10th	Day	52% 6% 9% 23% 10% 1	2734
	11th to 20th	Day	48% 6% 11% 20% 13% 2	2850
	21st to end	Day	55% 7% 11% 17% 8% 1	2850
July	1st to 10th	Day	55% 6% 10% 17% 11% 1	4685
	11th to 20th	Day	57% 6% 10% 17% 9% 1	4338
	21st to end	Day	47% 7% 13% 22% 11% 1	4325
August	1st to 10th	Day	60% 5% 10% 17% 8%	4092
	11th to 20th	Day	47% 8% 15% 23% 7%	4084
	21st to end	Day	33% 6% 13% 27% 20% 1	4479
September	1st to 10th	Day	40% 6% 11% 23% 20% 1	2248
	11th to 20th	Day	41% 4 11% 25% 17% 2	2090
	21st to end	Day	43% 6% 8% 23% 18% 2	2090
October	1st to 10th	Day	44% 7% 11% 27% 10% 1	3203
	11th to 20th	Day	42% 5% 10% 25% 18%	3140
	21st to end	Day	45% 4 11% 25% 12% 3	3343
November	1st to 10th	Day	54% 6% 12% 19% 8% 1	1752
	11th to 20th	Day	63% 6% 10% 14% 6% 1	1600
	21st to end	Day	69% 6% 11% 12% 2	1600
December	1st to 10th	Day	73% 6% 8% 10% 2	1584
	11th to 20th	Day	74% 8% 7% 8% 3	1905
	21st to end	Day	69% 8% 15% 6% 2	2495
January	1st to 10th	Night	77% 6% 8% 8% 1	4648
	11th to 20th	Night	76% 6% 6% 9% 3	4211
	21st to end	Night	74% 6% 8% 9% 4	4532
February	1st to 10th	Night	76% 5% 8% 7% 4	2470
	11th to 20th	Night	72% 6% 7% 11% 4	2406
	21st to end	Night	60% 9% 11% 14% 6% 1	1908
March	1st to 10th	Night	67% 4 8% 10% 9% 1	3510
	11th to 20th	Night	59% 7% 14% 12% 8%	3480
	21st to end	Night	65% 3 7% 15% 9% 1	3816
April	1st to 10th	Night	57% 4 9% 16% 12% 2	2006
	11th to 20th	Night	51% 5% 9% 22% 11% 1	1695
	21st to end	Night	52% 6% 10% 18% 13% 1	1710
May	1st to 10th	Night	54% 6% 15% 18% 7%	2840
	11th to 20th	Night	55% 8% 12% 18% 7% 1	2705
	21st to end	Night	54% 7% 12% 22% 5% 1	2750
June	1st to 10th	Night	57% 6% 9% 21% 6% 1	1459
	11th to 20th	Night	51% 5% 12% 19% 11% 1	1330
	21st to end	Night	59% 5% 11% 14% 9% 1	1330
July	1st to 10th	Night	63% 6% 8% 12% 10%	2175
	11th to 20th	Night	64% 6% 8% 12% 9% 1	2462
	21st to end	Night	52% 8% 11% 17% 11% 1	2989
August	1st to 10th	Night	61% 5% 9% 18% 6%	2813
	11th to 20th	Night	55% 7% 13% 19% 5%	2809
	21st to end	Night	39% 5% 11% 26% 17% 1	3174
September	1st to 10th	Night	41% 6% 9% 26% 16% 2	1928
	11th to 20th	Night	42% 5% 8% 27% 16% 1	2090
	21st to end	Night	47% 5% 8% 21% 18% 2	2090
October	1st to 10th	Night	46% 6% 13% 22% 13% 1	3756
	11th to 20th	Night	37% 5% 13% 25% 20% 1	3779
	21st to end	Night	46% 5% 10% 26% 13% 1	4203
November	1st to 10th	Night	51% 7% 13% 20% 9%	2543
	11th to 20th	Night	62% 7% 11% 14% 6%	2800
	21st to end	Night	64% 7% 13% 12% 3	2800
December	1st to 10th	Night	72% 7% 10% 9% 2	2779
	11th to 20th	Night	73% 6% 7% 11% 3	3295
	21st to end	Night	67% 7% 12% 12% 2	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	40% 24% 26% 8% 2	314
	21st to end	Day	26% 29% 31% 12% 2	407
February	1st to 10th	Day	35% 23% 30% 10% 2	370
	11th to 20th	Day	36% 34% 20% 8% 2	366
	21st to end	Day	32% 26% 29% 12% 1	369
March	1st to 10th	Day	33% 23% 32% 10% 2	460
	11th to 20th	Day	37% 23% 26% 10% 4 1	460
	21st to end	Day	33% 24% 26% 11% 4 1	506
April	1st to 10th	Day	39% 25% 24% 10% 3	460
	11th to 20th	Day	31% 25% 32% 9% 3	452
	21st to end	Day	30% 23% 28% 13% 5% 1	460
May	1st to 10th	Day	30% 24% 31% 12% 3	463
	11th to 20th	Day	26% 21% 28% 19% 5%	545
	21st to end	Day	30% 15% 30% 18% 6% 1	735
June	1st to 10th	Day	32% 14% 28% 18% 7%	680
	11th to 20th	Day	24% 13% 33% 24% 6% 1	680
	21st to end	Day	35% 13% 28% 18% 5% 1	680
July	1st to 10th	Day	29% 7% 31% 21% 9% 1	670
	11th to 20th	Day	28% 7% 33% 24% 7% 1	565
	21st to end	Day	23% 11% 38% 20% 7%	532
August	1st to 10th	Day	23% 9% 35% 24% 8% 1	486
	11th to 20th	Day	25% 11% 31% 22% 9% 2	479
	21st to end	Day	22% 10% 32% 22% 10% 4	539
September	1st to 10th	Day	20% 13% 36% 21% 9% 2	490
	11th to 20th	Day	24% 14% 28% 22% 8% 4	490
	21st to end	Day	20% 16% 34% 21% 6% 3	490
October	1st to 10th	Day	24% 14% 28% 21% 9% 3	405
	11th to 20th	Day	26% 18% 28% 18% 7% 3	390
	21st to end	Day	29% 22% 27% 17% 5% 1	429
November	1st to 10th	Day	29% 21% 29% 14% 6% 1	395
	11th to 20th	Day	41% 19% 24% 13% 3 1	400
	21st to end	Day	34% 27% 27% 9% 3 1	400
December	1st to 10th	Day	34% 26% 25% 11% 3	394
	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	37% 20% 26% 14% 3	760
	21st to end	Night	28% 26% 29% 15% 2	836
February	1st to 10th	Night	36% 21% 28% 13% 1	760
	11th to 20th	Night	34% 28% 23% 12% 2 1	743
	21st to end	Night	25% 24% 31% 15% 4	628
March	1st to 10th	Night	29% 23% 31% 15% 2	760
	11th to 20th	Night	28% 21% 27% 18% 6%	760
	21st to end	Night	27% 22% 28% 17% 5% 1	836
April	1st to 10th	Night	35% 19% 28% 16% 3	676
	11th to 20th	Night	28% 17% 34% 18% 3	564
	21st to end	Night	30% 14% 28% 20% 7%	570
May	1st to 10th	Night	29% 13% 32% 22% 4 1	570
	11th to 20th	Night	29% 10% 30% 23% 6%	562
	21st to end	Night	27% 10% 30% 27% 5% 1	616
June	1st to 10th	Night	32% 7% 29% 22% 9%	509
	11th to 20th	Night	22% 8% 29% 34% 7% 1	380
	21st to end	Night	33% 4 24% 29% 10%	380
July	1st to 10th	Night	29% 6% 25% 29% 11%	370
	11th to 20th	Night	28% 6% 25% 28% 13% 1	439
	21st to end	Night	25% 7% 27% 31% 9%	623
August	1st to 10th	Night	27% 6% 23% 31% 12% 1	568
	11th to 20th	Night	29% 7% 22% 28% 12% 1	562
	21st to end	Night	23% 6% 24% 31% 16% 1	627
September	1st to 10th	Night	22% 8% 25% 31% 13% 1	598
	11th to 20th	Night	24% 9% 24% 24% 17% 3	760
	21st to end	Night	26% 10% 26% 24% 13% 2	760
October	1st to 10th	Night	26% 10% 25% 26% 13% 1	760
	11th to 20th	Night	24% 17% 27% 21% 9% 1	760
	21st to end	Night	33% 17% 23% 21% 5%	836
November	1st to 10th	Night	27% 14% 31% 20% 7% 1	784
	11th to 20th	Night	32% 22% 24% 17% 5%	900
	21st to end	Night	34% 23% 24% 14% 5%	900
December	1st to 10th	Night	35% 22% 26% 15% 2	893
	11th to 20th	Night	38% 25% 25% 10% 2	850
	21st to end	Night	37% 23% 21% 16% 3	935

Page generated at 2024-12-06 04:54:48. Version ac07

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