Tangier Island Public Beach
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Tangier Island Public Beach clear sky chart from 2005-11-06 to 2025-09-04.

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	12% 6% 2 6% 4 4 4 4 6% 8% 44%	125825
	Night	14% 6% 2 6% 4 4 4 4 5% 7% 44%	122885
Transparency	Day	36% 7% 13% 23% 17% 4	129414
	Night	38% 5% 11% 23% 18% 4	127365
Seeing	Day	15% 7% 22% 30% 21% 6%	16267
	Night	16% 8% 26% 31% 16% 2	25744

By Month

Percentage Cloud Cover SE (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	14% 4 1 4 3 3 4 3 4 6% 56%	3704
	11th to 20th	Day	11% 7% 2 6% 4 3 4 3 4 5% 51%	4060
	21st to end	Day	11% 8% 3 8% 5% 4 4 4 4 6% 43%	4466
February	1st to 10th	Day	13% 8% 2 5% 5% 4 5% 4 7% 7% 40%	1800
	11th to 20th	Day	20% 7% 2 5% 3 3 3 3 4 5% 45%	1899
	21st to end	Day	15% 9% 2 6% 5% 4 5% 4 6% 5% 40%	1650
March	1st to 10th	Day	17% 6% 2 6% 5% 4 4 4 5% 8% 40%	4709
	11th to 20th	Day	10% 7% 2 4 3 3 3 3 5% 6% 53%	4980
	21st to end	Day	14% 7% 2 5% 3 4 4 3 6% 6% 45%	5648
April	1st to 10th	Day	11% 7% 2 6% 3 3 4 3 5% 7% 48%	2400
	11th to 20th	Day	9% 6% 2 5% 4 5% 4 3 5% 8% 50%	2374
	21st to end	Day	13% 6% 2 5% 4 4 5% 3 5% 8% 46%	2400
May	1st to 10th	Day	14% 7% 2 7% 4 5% 5% 4 7% 9% 36%	5441
	11th to 20th	Day	17% 7% 3 6% 5% 4 5% 4 6% 9% 34%	6198
	21st to end	Day	13% 5% 2 6% 4 4 4 4 6% 10% 43%	6934
June	1st to 10th	Day	10% 4 2 5% 3 4 5% 4 7% 10% 45%	2800
	11th to 20th	Day	10% 4 1 4 4 3 4 5% 8% 10% 46%	2800
	21st to end	Day	7% 3 2 5% 5% 5% 5% 4 7% 10% 48%	2800
July	1st to 10th	Day	7% 4 1 5% 5% 5% 5% 4 8% 12% 45%	6360
	11th to 20th	Day	11% 6% 3 6% 5% 5% 6% 5% 8% 12% 33%	6183
	21st to end	Day	7% 4 2 6% 5% 5% 6% 5% 8% 11% 42%	6424
August	1st to 10th	Day	14% 8% 2 6% 4 5% 5% 5% 8% 11% 33%	4217
	11th to 20th	Day	10% 6% 2 7% 5% 5% 6% 4 7% 8% 41%	3850
	21st to end	Day	9% 4 1 4 3 3 4 4 6% 10% 52%	4312
September	1st to 10th	Day	13% 4 2 6% 4 3 4 3 6% 9% 46%	2316
	11th to 20th	Day	11% 7% 3 6% 4 4 5% 3 5% 7% 46%	2280
	21st to end	Day	18% 8% 2 7% 4 3 3 3 4 7% 39%	2037
October	1st to 10th	Day	14% 6% 2 7% 3 3 3 3 5% 7% 47%	1900
	11th to 20th	Day	15% 5% 2 5% 3 3 3 3 5% 5% 52%	1900
	21st to end	Day	12% 5% 2 6% 3 4 3 3 5% 6% 51%	2090
November	1st to 10th	Day	14% 5% 2 4 3 4 4 3 5% 6% 50%	1828
	11th to 20th	Day	14% 6% 2 5% 3 3 4 4 5% 6% 48%	1800
	21st to end	Day	15% 4 2 4 4 3 4 3 5% 6% 50%	1715
December	1st to 10th	Day	11% 5% 2 5% 3 3 3 3 4 6% 55%	2600
	11th to 20th	Day	18% 8% 2 6% 3 3 2 2 4 5% 46%	2990
	21st to end	Day	11% 6% 2 5% 4 3 4 3 5% 8% 48%	3960
January	1st to 10th	Night	12% 6% 2 5% 4 3 4 3 4 6% 51%	6239
	11th to 20th	Night	12% 6% 2 6% 3 3 3 2 4 4 54%	5900
	21st to end	Night	14% 7% 3 6% 3 3 3 3 4 5% 48%	6490
February	1st to 10th	Night	16% 8% 2 5% 4 3 4 3 5% 7% 43%	2600
	11th to 20th	Night	20% 7% 2 5% 3 3 4 3 5% 5% 42%	2385
	21st to end	Night	17% 8% 2 4 4 2 3 3 5% 6% 46%	1980
March	1st to 10th	Night	17% 6% 2 6% 3 3 3 3 5% 5% 45%	5126
	11th to 20th	Night	13% 6% 3 5% 3 4 3 3 5% 6% 49%	4980
	21st to end	Night	14% 7% 3 6% 4 4 3 3 4 6% 46%	5269
April	1st to 10th	Night	14% 8% 2 5% 5% 5% 3 5% 6% 8% 40%	2000
	11th to 20th	Night	12% 6% 2 5% 4 3 4 3 6% 7% 48%	1975
	21st to end	Night	14% 7% 2 6% 4 4 4 2 5% 8% 45%	2000
May	1st to 10th	Night	15% 7% 3 7% 5% 5% 5% 4 7% 8% 33%	4490
	11th to 20th	Night	22% 8% 3 7% 4 4 4 3 6% 7% 32%	3685
	21st to end	Night	15% 7% 2 7% 4 4 5% 4 6% 9% 37%	3920
June	1st to 10th	Night	11% 6% 3 5% 4 5% 6% 4 6% 9% 40%	1600
	11th to 20th	Night	10% 5% 1 5% 6% 6% 6% 4 7% 10% 40%	1600
	21st to end	Night	8% 5% 1 5% 6% 5% 5% 4 8% 10% 44%	1600
July	1st to 10th	Night	9% 5% 2 7% 5% 5% 6% 5% 8% 11% 37%	3598
	11th to 20th	Night	10% 6% 2 7% 5% 5% 6% 5% 8% 13% 33%	3770
	21st to end	Night	10% 6% 2 8% 6% 5% 6% 5% 7% 9% 38%	4427
August	1st to 10th	Night	16% 8% 3 8% 5% 5% 4 5% 7% 9% 30%	2915
	11th to 20th	Night	10% 6% 2 6% 5% 5% 5% 4 7% 9% 40%	3182
	21st to end	Night	10% 5% 2 6% 3 3 4 3 5% 9% 50%	3586
September	1st to 10th	Night	12% 5% 2 6% 3 4 4 4 5% 7% 48%	1931
	11th to 20th	Night	11% 5% 2 7% 4 4 4 4 6% 7% 46%	1900
	21st to end	Night	20% 7% 2 6% 4 4 5% 4 5% 6% 36%	2138
October	1st to 10th	Night	15% 6% 2 6% 4 4 4 4 5% 7% 44%	2280
	11th to 20th	Night	16% 5% 2 5% 3 4 3 2 5% 5% 50%	2280
	21st to end	Night	15% 5% 2 5% 3 2 3 3 5% 7% 50%	2508
November	1st to 10th	Night	14% 6% 2 5% 4 3 4 3 4 6% 47%	2470
	11th to 20th	Night	16% 7% 2 5% 4 4 4 3 5% 5% 46%	2600
	21st to end	Night	12% 6% 2 5% 4 3 4 3 5% 7% 50%	2680
December	1st to 10th	Night	10% 5% 2 5% 4 3 4 3 5% 5% 54%	4580
	11th to 20th	Night	18% 7% 2 6% 5% 4 4 3 5% 6% 39%	5205
	21st to end	Night	11% 7% 3 7% 4 3 3 4 5% 7% 46%	6996

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	31% 3 8% 25% 23% 9%	3705
	11th to 20th	Day	37% 3 6% 22% 25% 7%	4060
	21st to end	Day	42% 4 9% 28% 14% 2	4466
February	1st to 10th	Day	42% 5% 12% 26% 13% 3	1800
	11th to 20th	Day	41% 4 9% 22% 19% 4	1908
	21st to end	Day	44% 6% 12% 18% 16% 5%	1650
March	1st to 10th	Day	42% 5% 9% 18% 19% 7%	4709
	11th to 20th	Day	31% 5% 10% 22% 24% 8%	4980
	21st to end	Day	40% 6% 11% 18% 19% 6%	5648
April	1st to 10th	Day	35% 5% 13% 21% 20% 6%	2400
	11th to 20th	Day	34% 6% 12% 23% 20% 5%	2374
	21st to end	Day	37% 6% 11% 24% 17% 5%	2400
May	1st to 10th	Day	44% 9% 16% 20% 10% 1	5473
	11th to 20th	Day	44% 10% 14% 22% 8% 1	6202
	21st to end	Day	35% 9% 14% 25% 14% 2	6949
June	1st to 10th	Day	33% 9% 16% 27% 13% 2	2800
	11th to 20th	Day	31% 11% 16% 26% 14% 2	2800
	21st to end	Day	31% 9% 16% 25% 17% 2	2800
July	1st to 10th	Day	31% 10% 22% 21% 13% 2	6290
	11th to 20th	Day	43% 12% 24% 17% 4 1	6108
	21st to end	Day	34% 9% 17% 21% 19% 1	6240
August	1st to 10th	Day	43% 9% 17% 24% 6%	4204
	11th to 20th	Day	40% 8% 13% 26% 13% 1	3886
	21st to end	Day	27% 7% 15% 30% 19% 2	4312
September	1st to 10th	Day	36% 9% 16% 19% 17% 4	2316
	11th to 20th	Day	38% 6% 11% 25% 19% 2	2280
	21st to end	Day	46% 5% 9% 21% 15% 3	2037
October	1st to 10th	Day	32% 4 10% 25% 25% 4	3160
	11th to 20th	Day	25% 4 7% 21% 35% 8%	3140
	21st to end	Day	23% 4 8% 29% 26% 10%	3428
November	1st to 10th	Day	35% 4 10% 26% 19% 4	1828
	11th to 20th	Day	37% 5% 11% 19% 22% 6%	1800
	21st to end	Day	35% 3 11% 26% 21% 3	1715
December	1st to 10th	Day	32% 4 10% 30% 20% 4	2600
	11th to 20th	Day	42% 4 13% 20% 16% 5%	2986
	21st to end	Day	34% 5% 14% 30% 16% 1	3960
January	1st to 10th	Night	36% 2 8% 21% 26% 7%	6239
	11th to 20th	Night	35% 3 6% 24% 26% 6%	5900
	21st to end	Night	39% 3 8% 29% 18% 3	6490
February	1st to 10th	Night	42% 4 11% 24% 16% 2	2600
	11th to 20th	Night	44% 3 8% 21% 18% 5%	2387
	21st to end	Night	40% 4 9% 21% 19% 6%	1980
March	1st to 10th	Night	41% 3 8% 21% 19% 8%	5126
	11th to 20th	Night	37% 4 8% 21% 22% 8%	4980
	21st to end	Night	40% 4 7% 24% 18% 7%	5269
April	1st to 10th	Night	42% 6% 10% 17% 21% 4	2000
	11th to 20th	Night	34% 5% 11% 22% 22% 5%	1975
	21st to end	Night	38% 6% 12% 22% 18% 4	2000
May	1st to 10th	Night	47% 8% 15% 20% 9% 1	4520
	11th to 20th	Night	50% 7% 12% 22% 9% 1	3686
	21st to end	Night	42% 7% 14% 23% 13%	3927
June	1st to 10th	Night	39% 8% 14% 22% 16% 1	1600
	11th to 20th	Night	37% 10% 14% 23% 14% 1	1600
	21st to end	Night	35% 9% 14% 25% 15% 3	1600
July	1st to 10th	Night	39% 10% 17% 20% 13% 1	3560
	11th to 20th	Night	41% 11% 25% 18% 4	3725
	21st to end	Night	41% 9% 13% 23% 15%	4297
August	1st to 10th	Night	49% 9% 16% 21% 6%	2904
	11th to 20th	Night	39% 8% 16% 25% 12%	3212
	21st to end	Night	32% 7% 10% 26% 24% 1	3586
September	1st to 10th	Night	36% 8% 15% 21% 16% 4	1931
	11th to 20th	Night	37% 7% 9% 25% 20% 2	1900
	21st to end	Night	47% 7% 11% 16% 17% 2	2138
October	1st to 10th	Night	38% 5% 10% 22% 22% 4	3800
	11th to 20th	Night	27% 3 7% 22% 31% 9%	3779
	21st to end	Night	22% 3 7% 33% 25% 11%	4120
November	1st to 10th	Night	37% 5% 12% 24% 19% 4	2470
	11th to 20th	Night	40% 4 10% 21% 18% 8%	2600
	21st to end	Night	34% 4 9% 27% 22% 4	2680
December	1st to 10th	Night	32% 4 9% 27% 24% 4	4580
	11th to 20th	Night	47% 4 13% 19% 13% 5%	5208
	21st to end	Night	36% 5% 14% 29% 15% 1	6996

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	16% 18% 36% 26% 5%	222
	11th to 20th	Day	16% 18% 41% 22% 3	300
	21st to end	Day	15% 11% 33% 36% 5%	330
February	1st to 10th	Day	17% 13% 33% 30% 7%	300
	11th to 20th	Day	26% 13% 38% 21% 3	447
	21st to end	Day	20% 10% 39% 25% 6%	414
March	1st to 10th	Day	17% 11% 34% 31% 7% 1	500
	11th to 20th	Day	16% 13% 35% 27% 8% 1	500
	21st to end	Day	15% 10% 34% 34% 6% 1	550
April	1st to 10th	Day	14% 12% 35% 29% 9% 1	500
	11th to 20th	Day	11% 8% 27% 40% 12% 3	492
	21st to end	Day	14% 7% 28% 34% 15% 1	500
May	1st to 10th	Day	16% 7% 28% 32% 16% 2	503
	11th to 20th	Day	19% 3 24% 32% 19% 3	527
	21st to end	Day	19% 3 17% 31% 24% 7%	573
June	1st to 10th	Day	12% 3 12% 37% 29% 6%	530
	11th to 20th	Day	10% 3 15% 33% 29% 10%	530
	21st to end	Day	10% 2 12% 35% 32% 10%	530
July	1st to 10th	Day	10% 2 8% 29% 38% 13%	525
	11th to 20th	Day	6% 1 5% 27% 47% 13%	524
	21st to end	Day	9% 1 9% 34% 35% 12%	576
August	1st to 10th	Day	12% 3 10% 30% 35% 9%	526
	11th to 20th	Day	14% 1 9% 27% 39% 11%	519
	21st to end	Day	10% 2 9% 32% 34% 14%	583
September	1st to 10th	Day	15% 2 11% 28% 31% 13%	502
	11th to 20th	Day	12% 4 14% 29% 30% 10%	490
	21st to end	Day	25% 6% 19% 26% 21% 4	490
October	1st to 10th	Day	19% 3 18% 26% 24% 10%	490
	11th to 20th	Day	16% 7% 24% 28% 23% 3	490
	21st to end	Day	12% 10% 27% 29% 16% 6%	539
November	1st to 10th	Day	17% 7% 24% 29% 18% 5%	430
	11th to 20th	Day	16% 15% 28% 31% 11% 1	400
	21st to end	Day	16% 14% 24% 30% 14% 1	315
December	1st to 10th	Day	21% 9% 33% 26% 11% 1	200
	11th to 20th	Day	22% 9% 32% 31% 8%	200
	21st to end	Day	18% 11% 27% 29% 14%	220
January	1st to 10th	Night	18% 16% 37% 24% 5%	800
	11th to 20th	Night	19% 13% 35% 27% 7%	800
	21st to end	Night	19% 13% 36% 29% 3	880
February	1st to 10th	Night	20% 10% 38% 29% 4	800
	11th to 20th	Night	23% 15% 39% 20% 3	783
	21st to end	Night	20% 13% 34% 29% 4	660
March	1st to 10th	Night	18% 12% 35% 29% 7%	800
	11th to 20th	Night	20% 11% 34% 28% 6% 2	800
	21st to end	Night	19% 8% 37% 30% 6%	880
April	1st to 10th	Night	17% 11% 37% 28% 7%	800
	11th to 20th	Night	14% 8% 32% 35% 10% 1	791
	21st to end	Night	17% 6% 28% 38% 10% 2	800
May	1st to 10th	Night	17% 7% 27% 37% 10% 1	800
	11th to 20th	Night	17% 6% 21% 40% 14% 1	452
	21st to end	Night	15% 3 15% 33% 29% 4	433
June	1st to 10th	Night	14% 2 14% 40% 27% 3	400
	11th to 20th	Night	10% 2 17% 41% 28% 4	400
	21st to end	Night	7% 2 15% 43% 29% 5%	400
July	1st to 10th	Night	11% 2 11% 38% 34% 4	390
	11th to 20th	Night	8% 8% 36% 40% 8%	457
	21st to end	Night	8% 1 11% 42% 33% 5%	657
August	1st to 10th	Night	11% 2 10% 39% 33% 5%	597
	11th to 20th	Night	13% 2 11% 34% 36% 4	775
	21st to end	Night	11% 2 12% 31% 35% 8%	880
September	1st to 10th	Night	15% 2 10% 34% 32% 8%	773
	11th to 20th	Night	13% 2 15% 30% 33% 7%	760
	21st to end	Night	21% 6% 16% 32% 23% 2	760
October	1st to 10th	Night	17% 5% 19% 28% 24% 6%	760
	11th to 20th	Night	17% 9% 24% 30% 18% 2	760
	21st to end	Night	17% 11% 23% 28% 17% 3	836
November	1st to 10th	Night	17% 8% 24% 30% 18% 3	780
	11th to 20th	Night	19% 11% 28% 29% 12% 1	800
	21st to end	Night	14% 14% 29% 30% 12% 2	800
December	1st to 10th	Night	18% 12% 35% 24% 10% 2	800
	11th to 20th	Night	18% 10% 38% 27% 8%	800
	21st to end	Night	18% 9% 33% 32% 8%	880

Page generated at 2025-09-01 01:51:04. Version ac07

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