Woodbridge
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Woodbridge clear sky chart from 2005-11-06 to 2024-02-25.

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	15% 9% 4 8% 6% 4 5% 5% 6% 7% 31%	78577
	Night	15% 9% 4 7% 6% 4 5% 5% 5% 7% 33%	80689
Transparency	Day	49% 8% 14% 18% 10% 1	78293
	Night	49% 8% 13% 19% 10% 1	80508
Seeing	Day	18% 13% 30% 24% 11% 4	13617
	Night	19% 10% 31% 28% 11% 1	23013

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% 12% 5% 9% 7% 4 5% 4 5% 6% 26%	2517
	11th to 20th	Day	11% 17% 7% 14% 11% 4 5% 4 4 5% 18%	2772
	21st to end	Day	21% 19% 7% 9% 7% 3 5% 4 4 5% 16%	3124
February	1st to 10th	Day	15% 15% 5% 11% 8% 4 5% 5% 5% 5% 21%	1710
	11th to 20th	Day	12% 13% 7% 10% 8% 4 5% 4 5% 6% 25%	1663
	21st to end	Day	17% 15% 5% 9% 6% 3 5% 5% 4 6% 25%	1418
March	1st to 10th	Day	14% 10% 5% 9% 7% 4 5% 5% 5% 7% 30%	1977
	11th to 20th	Day	13% 11% 5% 8% 7% 4 5% 5% 5% 4 32%	1980
	21st to end	Day	18% 9% 4 8% 7% 3 4 4 5% 5% 32%	2178
April	1st to 10th	Day	16% 11% 4 8% 7% 3 5% 4 5% 7% 29%	2119
	11th to 20th	Day	19% 8% 4 6% 5% 3 4 5% 5% 6% 36%	2210
	21st to end	Day	20% 7% 3 6% 7% 3 5% 4 5% 6% 33%	2340
May	1st to 10th	Day	16% 8% 3 7% 7% 3 5% 4 6% 8% 33%	2340
	11th to 20th	Day	15% 8% 2 6% 5% 3 5% 5% 5% 7% 40%	2454
	21st to end	Day	11% 5% 3 6% 5% 4 5% 5% 6% 8% 43%	2725
June	1st to 10th	Day	13% 7% 2 6% 6% 3 5% 6% 6% 8% 38%	2520
	11th to 20th	Day	12% 5% 2 5% 5% 3 5% 5% 6% 11% 39%	2520
	21st to end	Day	13% 5% 2 5% 6% 4 5% 6% 6% 10% 39%	2673
July	1st to 10th	Day	7% 4 2 5% 5% 4 6% 6% 7% 9% 43%	2561
	11th to 20th	Day	10% 5% 2 6% 5% 3 6% 6% 8% 9% 39%	2520
	21st to end	Day	9% 5% 3 7% 6% 4 6% 7% 8% 10% 34%	2564
August	1st to 10th	Day	8% 5% 2 6% 6% 4 6% 6% 8% 11% 38%	2327
	11th to 20th	Day	8% 6% 3 7% 6% 4 6% 6% 7% 10% 38%	2303
	21st to end	Day	11% 5% 3 6% 6% 3 6% 6% 7% 10% 38%	2484
September	1st to 10th	Day	13% 6% 2 6% 6% 4 5% 5% 6% 8% 40%	2160
	11th to 20th	Day	11% 5% 2 6% 5% 4 4 4 5% 9% 44%	2046
	21st to end	Day	13% 6% 3 6% 7% 5% 6% 5% 6% 9% 35%	1949
October	1st to 10th	Day	19% 9% 3 6% 5% 3 4 6% 5% 6% 34%	1800
	11th to 20th	Day	20% 8% 4 8% 7% 4 6% 4 6% 7% 28%	1800
	21st to end	Day	24% 11% 4 7% 7% 4 5% 5% 5% 6% 22%	1980
November	1st to 10th	Day	13% 9% 4 8% 6% 3 5% 5% 6% 8% 32%	1605
	11th to 20th	Day	15% 11% 4 9% 7% 3 6% 6% 6% 8% 25%	1520
	21st to end	Day	18% 14% 5% 8% 7% 4 6% 5% 5% 7% 21%	1520
December	1st to 10th	Day	16% 15% 7% 11% 8% 5% 6% 5% 5% 6% 16%	1520
	11th to 20th	Day	19% 13% 4 10% 7% 4 5% 5% 6% 6% 22%	1906
	21st to end	Day	29% 17% 6% 11% 7% 3 4 4 4 4 12%	2772
January	1st to 10th	Night	18% 14% 6% 9% 7% 4 5% 4 4 6% 22%	4429
	11th to 20th	Night	15% 13% 6% 10% 11% 6% 5% 6% 5% 6% 17%	4184
	21st to end	Night	21% 12% 6% 9% 9% 4 6% 5% 5% 5% 19%	4532
February	1st to 10th	Night	13% 15% 5% 9% 8% 4 6% 5% 5% 6% 25%	2470
	11th to 20th	Night	13% 13% 6% 8% 8% 4 6% 5% 5% 5% 27%	2403
	21st to end	Night	13% 12% 4 9% 8% 3 5% 5% 5% 6% 30%	1928
March	1st to 10th	Night	13% 7% 5% 7% 8% 5% 4 5% 5% 5% 35%	1970
	11th to 20th	Night	15% 12% 4 6% 7% 3 5% 3 4 7% 35%	1979
	21st to end	Night	16% 9% 4 6% 5% 3 5% 4 4 6% 39%	2178
April	1st to 10th	Night	18% 9% 4 7% 6% 3 5% 5% 5% 6% 32%	1840
	11th to 20th	Night	15% 8% 3 6% 6% 3 5% 5% 5% 6% 39%	1715
	21st to end	Night	16% 8% 4 5% 5% 3 5% 5% 6% 8% 35%	1620
May	1st to 10th	Night	16% 6% 2 5% 5% 3 6% 5% 5% 7% 39%	1620
	11th to 20th	Night	14% 5% 3 5% 4 2 4 5% 6% 7% 46%	1438
	21st to end	Night	10% 4 2 3 4 3 4 4 6% 7% 52%	1550
June	1st to 10th	Night	12% 5% 3 5% 6% 4 5% 4 6% 8% 43%	1440
	11th to 20th	Night	9% 6% 3 5% 5% 4 5% 6% 5% 10% 44%	1440
	21st to end	Night	10% 5% 2 5% 5% 4 5% 4 6% 7% 47%	1273
July	1st to 10th	Night	6% 4 2 4 4 2 4 4 4 9% 58%	1386
	11th to 20th	Night	9% 5% 2 4 4 2 5% 6% 6% 8% 50%	1440
	21st to end	Night	7% 3 2 6% 5% 2 6% 4 6% 9% 51%	1751
August	1st to 10th	Night	6% 5% 2 5% 5% 3 5% 4 6% 8% 50%	1611
	11th to 20th	Night	6% 5% 1 5% 5% 2 4 4 6% 10% 52%	1598
	21st to end	Night	10% 4 2 5% 4 4 5% 4 5% 7% 48%	1854
September	1st to 10th	Night	9% 5% 2 5% 6% 3 4 6% 7% 6% 47%	1800
	11th to 20th	Night	11% 4 2 3 4 2 3 5% 5% 8% 52%	1912
	21st to end	Night	14% 6% 3 6% 5% 3 4 4 6% 7% 42%	2011
October	1st to 10th	Night	16% 7% 3 6% 5% 3 5% 5% 5% 6% 38%	2160
	11th to 20th	Night	18% 8% 2 7% 7% 3 4 5% 5% 6% 34%	2160
	21st to end	Night	20% 10% 4 7% 5% 4 4 6% 5% 7% 27%	2376
November	1st to 10th	Night	17% 8% 3 6% 6% 3 5% 4 6% 6% 38%	2469
	11th to 20th	Night	16% 10% 3 7% 7% 4 6% 5% 5% 7% 30%	2660
	21st to end	Night	19% 11% 4 8% 7% 4 5% 5% 5% 7% 26%	2660
December	1st to 10th	Night	20% 14% 5% 8% 6% 3 5% 5% 6% 6% 22%	2660
	11th to 20th	Night	16% 16% 5% 10% 7% 4 5% 5% 5% 6% 21%	3288
	21st to end	Night	29% 15% 5% 9% 7% 4 5% 4 4 5% 13%	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	56% 9% 17% 10% 7%	2518
	11th to 20th	Day	69% 6% 12% 10% 3	2772
	21st to end	Day	70% 7% 10% 8% 4 1	3124
February	1st to 10th	Day	62% 8% 11% 14% 3 1	1710
	11th to 20th	Day	58% 8% 13% 14% 7% 1	1672
	21st to end	Day	59% 7% 11% 14% 7% 1	1418
March	1st to 10th	Day	53% 7% 14% 16% 9% 1	1980
	11th to 20th	Day	53% 7% 10% 17% 11% 2	1980
	21st to end	Day	53% 5% 10% 17% 12% 2	2178
April	1st to 10th	Day	54% 6% 11% 17% 10% 1	2119
	11th to 20th	Day	47% 6% 11% 20% 14% 1	2210
	21st to end	Day	51% 7% 11% 18% 11% 2	2340
May	1st to 10th	Day	47% 6% 12% 19% 14% 1	2340
	11th to 20th	Day	42% 8% 13% 23% 13% 2	2458
	21st to end	Day	37% 8% 16% 23% 14% 2	2725
June	1st to 10th	Day	41% 8% 13% 21% 15% 1	2520
	11th to 20th	Day	38% 8% 14% 24% 15% 1	2520
	21st to end	Day	38% 9% 15% 24% 14% 1	2673
July	1st to 10th	Day	33% 8% 15% 24% 17% 3	2491
	11th to 20th	Day	36% 9% 15% 27% 11% 1	2445
	21st to end	Day	39% 10% 16% 20% 13% 1	2421
August	1st to 10th	Day	36% 11% 18% 22% 12% 1	2314
	11th to 20th	Day	36% 10% 19% 24% 11%	2303
	21st to end	Day	38% 9% 15% 26% 11% 1	2484
September	1st to 10th	Day	39% 9% 15% 25% 10% 1	2160
	11th to 20th	Day	35% 7% 16% 28% 13%	2046
	21st to end	Day	43% 9% 14% 25% 8%	1949
October	1st to 10th	Day	47% 9% 14% 18% 11% 1	1800
	11th to 20th	Day	54% 7% 14% 18% 6% 1	1800
	21st to end	Day	60% 8% 12% 14% 5%	1980
November	1st to 10th	Day	47% 8% 17% 20% 8% 1	1605
	11th to 20th	Day	53% 10% 14% 14% 8%	1520
	21st to end	Day	59% 10% 16% 14% 3	1520
December	1st to 10th	Day	66% 9% 12% 11% 3	1520
	11th to 20th	Day	60% 11% 14% 11% 4	1906
	21st to end	Day	73% 9% 9% 8% 1	2772
January	1st to 10th	Night	60% 10% 13% 13% 4	4429
	11th to 20th	Night	63% 12% 13% 9% 3 1	4184
	21st to end	Night	64% 9% 13% 10% 4 1	4532
February	1st to 10th	Night	57% 7% 11% 19% 5% 1	2470
	11th to 20th	Night	56% 8% 13% 16% 8%	2405
	21st to end	Night	53% 7% 14% 17% 8% 1	1928
March	1st to 10th	Night	48% 8% 14% 19% 10% 1	1980
	11th to 20th	Night	50% 6% 11% 19% 12% 2	1980
	21st to end	Night	46% 6% 8% 22% 15% 3	2178
April	1st to 10th	Night	51% 6% 12% 18% 13% 1	1840
	11th to 20th	Night	46% 6% 11% 21% 15% 2	1715
	21st to end	Night	45% 8% 12% 17% 15% 2	1620
May	1st to 10th	Night	43% 6% 11% 21% 17% 2	1620
	11th to 20th	Night	37% 6% 11% 25% 17% 4	1439
	21st to end	Night	31% 6% 16% 24% 18% 4	1551
June	1st to 10th	Night	37% 7% 13% 24% 18% 2	1440
	11th to 20th	Night	35% 7% 12% 23% 22% 2	1440
	21st to end	Night	35% 7% 13% 26% 17% 1	1273
July	1st to 10th	Night	25% 7% 12% 26% 26% 4	1346
	11th to 20th	Night	30% 6% 14% 29% 18% 2	1392
	21st to end	Night	30% 7% 15% 29% 16% 3	1654
August	1st to 10th	Night	31% 8% 17% 28% 14% 2	1600
	11th to 20th	Night	27% 8% 16% 33% 14% 2	1598
	21st to end	Night	33% 8% 13% 28% 16% 1	1854
September	1st to 10th	Night	33% 9% 16% 26% 14% 1	1800
	11th to 20th	Night	29% 7% 13% 34% 17% 1	1912
	21st to end	Night	40% 7% 13% 27% 11%	2011
October	1st to 10th	Night	44% 7% 13% 21% 14% 1	2160
	11th to 20th	Night	49% 8% 14% 22% 7%	2160
	21st to end	Night	54% 8% 12% 16% 9% 1	2376
November	1st to 10th	Night	45% 6% 15% 22% 11% 1	2469
	11th to 20th	Night	50% 9% 14% 17% 8% 1	2660
	21st to end	Night	55% 8% 19% 14% 3	2660
December	1st to 10th	Night	60% 9% 14% 14% 4	2660
	11th to 20th	Night	60% 8% 15% 13% 3	3288
	21st to end	Night	71% 9% 10% 7% 2	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	23% 17% 32% 22% 6% 1	180
	11th to 20th	Day	23% 25% 32% 13% 6% 1	250
	21st to end	Day	25% 20% 32% 20% 4	297
February	1st to 10th	Day	25% 22% 39% 11% 3	270
	11th to 20th	Day	22% 22% 41% 11% 3	270
	21st to end	Day	30% 25% 33% 11%	220
March	1st to 10th	Day	21% 17% 35% 20% 6%	420
	11th to 20th	Day	22% 16% 39% 17% 5% 1	420
	21st to end	Day	26% 17% 31% 19% 6% 1	462
April	1st to 10th	Day	20% 20% 34% 19% 7%	420
	11th to 20th	Day	25% 19% 28% 17% 8% 3	412
	21st to end	Day	23% 12% 36% 19% 7% 2	420
May	1st to 10th	Day	22% 12% 31% 21% 9% 5%	423
	11th to 20th	Day	17% 11% 30% 25% 12% 5%	447
	21st to end	Day	16% 7% 27% 29% 16% 6%	485
June	1st to 10th	Day	13% 11% 30% 33% 11% 2	450
	11th to 20th	Day	15% 9% 26% 31% 17% 2	450
	21st to end	Day	16% 7% 30% 33% 11% 4	603
July	1st to 10th	Day	8% 5% 26% 34% 21% 7%	486
	11th to 20th	Day	13% 5% 22% 33% 18% 9%	444
	21st to end	Day	8% 4 27% 39% 15% 7%	488
August	1st to 10th	Day	11% 6% 22% 29% 23% 10%	446
	11th to 20th	Day	9% 4 24% 30% 21% 12%	439
	21st to end	Day	10% 8% 26% 27% 20% 9%	495
September	1st to 10th	Day	13% 7% 25% 28% 16% 10%	450
	11th to 20th	Day	10% 6% 24% 26% 21% 13%	450
	21st to end	Day	13% 10% 30% 23% 16% 7%	450
October	1st to 10th	Day	20% 13% 26% 21% 14% 5%	450
	11th to 20th	Day	19% 18% 36% 18% 8% 2	450
	21st to end	Day	30% 14% 29% 21% 5%	495
November	1st to 10th	Day	19% 23% 26% 22% 9% 1	257
	11th to 20th	Day	21% 24% 31% 19% 3 2	180
	21st to end	Day	24% 15% 42% 17% 2	180
December	1st to 10th	Day	26% 19% 36% 15% 4	180
	11th to 20th	Day	24% 24% 32% 16% 4	180
	21st to end	Day	26% 20% 40% 12% 2	198
January	1st to 10th	Night	23% 16% 37% 20% 4	760
	11th to 20th	Night	26% 17% 31% 24% 3	760
	21st to end	Night	19% 10% 40% 23% 7%	836
February	1st to 10th	Night	21% 16% 40% 21% 3	760
	11th to 20th	Night	22% 15% 38% 22% 3	743
	21st to end	Night	20% 16% 39% 22% 3	611
March	1st to 10th	Night	18% 15% 39% 23% 5%	720
	11th to 20th	Night	20% 16% 35% 22% 6%	720
	21st to end	Night	20% 10% 34% 27% 8%	792
April	1st to 10th	Night	23% 10% 37% 26% 4	720
	11th to 20th	Night	16% 13% 38% 23% 9% 1	651
	21st to end	Night	19% 9% 32% 30% 9%	540
May	1st to 10th	Night	17% 6% 30% 31% 14% 2	540
	11th to 20th	Night	17% 4 32% 36% 11% 1	377
	21st to end	Night	10% 4 29% 36% 21% 1	389
June	1st to 10th	Night	14% 4 29% 37% 16% 1	360
	11th to 20th	Night	10% 6% 29% 39% 15% 1	360
	21st to end	Night	11% 6% 22% 45% 16%	360
July	1st to 10th	Night	6% 4 22% 45% 23% 1	350
	11th to 20th	Night	11% 3 25% 41% 20% 2	348
	21st to end	Night	8% 3 21% 44% 23% 2	571
August	1st to 10th	Night	9% 1 17% 43% 29% 2	537
	11th to 20th	Night	7% 2 16% 45% 27% 3	534
	21st to end	Night	11% 3 24% 35% 25% 3	666
September	1st to 10th	Night	11% 6% 24% 33% 21% 4	720
	11th to 20th	Night	12% 5% 21% 32% 26% 5%	720
	21st to end	Night	16% 6% 22% 31% 20% 4	720
October	1st to 10th	Night	19% 6% 28% 27% 18% 2	720
	11th to 20th	Night	20% 11% 32% 27% 9% 1	720
	21st to end	Night	26% 11% 32% 26% 4	792
November	1st to 10th	Night	21% 10% 30% 28% 10% 1	740
	11th to 20th	Night	20% 14% 35% 23% 7% 2	760
	21st to end	Night	25% 12% 33% 24% 5%	760
December	1st to 10th	Night	28% 13% 37% 17% 4	760
	11th to 20th	Night	23% 15% 40% 19% 3	760
	21st to end	Night	31% 14% 33% 20% 2	836

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