Vaughan
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Vaughan clear sky chart from 2005-11-06 to 2024-02-05.

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 7% 6% 3 5% 5% 6% 7% 32%	78354
	Night	16% 9% 4 7% 6% 3 5% 5% 5% 7% 33%	80471
Transparency	Day	50% 7% 12% 20% 11% 1	78069
	Night	50% 6% 12% 20% 11% 1	80290
Seeing	Day	18% 12% 30% 24% 11% 4	13523
	Night	19% 9% 31% 28% 11% 1	22920

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% 11% 5% 9% 7% 3 5% 4 4 7% 28%	2517
	11th to 20th	Day	11% 17% 7% 14% 10% 5% 6% 4 4 4 18%	2751
	21st to end	Day	21% 19% 7% 9% 7% 3 4 4 4 5% 17%	3124
February	1st to 10th	Day	15% 17% 4 11% 7% 5% 6% 5% 4 5% 21%	1656
	11th to 20th	Day	13% 14% 6% 11% 7% 3 4 5% 5% 6% 25%	1573
	21st to end	Day	18% 14% 6% 9% 7% 3 5% 4 4 4 26%	1381
March	1st to 10th	Day	14% 10% 5% 8% 8% 3 5% 5% 5% 6% 30%	1977
	11th to 20th	Day	14% 11% 5% 8% 7% 4 5% 6% 5% 5% 32%	1980
	21st to end	Day	18% 10% 4 7% 7% 3 4 4 5% 5% 32%	2178
April	1st to 10th	Day	17% 11% 5% 8% 6% 3 4 5% 5% 7% 29%	2124
	11th to 20th	Day	20% 8% 3 7% 4 3 4 4 6% 5% 36%	2206
	21st to end	Day	21% 8% 3 6% 6% 4 4 4 5% 6% 33%	2340
May	1st to 10th	Day	17% 8% 4 7% 6% 3 4 5% 5% 7% 34%	2340
	11th to 20th	Day	15% 7% 4 5% 5% 4 4 5% 5% 7% 40%	2461
	21st to end	Day	12% 5% 2 6% 5% 3 5% 5% 5% 8% 44%	2725
June	1st to 10th	Day	14% 6% 2 6% 6% 4 5% 5% 6% 8% 38%	2520
	11th to 20th	Day	13% 5% 2 6% 5% 2 4 6% 7% 11% 39%	2520
	21st to end	Day	14% 5% 2 5% 6% 4 6% 5% 6% 9% 40%	2656
July	1st to 10th	Day	9% 4 2 5% 6% 3 6% 6% 6% 9% 45%	2543
	11th to 20th	Day	11% 5% 2 5% 6% 4 6% 5% 7% 9% 40%	2520
	21st to end	Day	9% 5% 3 7% 6% 4 7% 6% 7% 10% 34%	2575
August	1st to 10th	Day	9% 5% 2 5% 7% 3 6% 6% 8% 10% 39%	2327
	11th to 20th	Day	9% 6% 2 6% 6% 3 5% 6% 7% 9% 39%	2303
	21st to end	Day	11% 6% 2 6% 6% 3 5% 6% 6% 10% 39%	2481
September	1st to 10th	Day	14% 5% 3 5% 5% 3 5% 5% 6% 8% 41%	2160
	11th to 20th	Day	12% 5% 2 6% 5% 3 5% 4 6% 8% 44%	2052
	21st to end	Day	13% 5% 4 6% 7% 3 6% 5% 6% 9% 36%	1944
October	1st to 10th	Day	19% 8% 4 6% 5% 3 4 5% 5% 8% 34%	1800
	11th to 20th	Day	21% 8% 4 6% 7% 4 5% 5% 6% 6% 29%	1800
	21st to end	Day	24% 12% 4 7% 6% 4 5% 5% 5% 5% 22%	1980
November	1st to 10th	Day	14% 9% 4 8% 6% 3 5% 5% 6% 7% 33%	1602
	11th to 20th	Day	15% 11% 4 10% 7% 3 7% 7% 5% 7% 25%	1520
	21st to end	Day	18% 13% 6% 8% 6% 4 5% 6% 6% 6% 22%	1520
December	1st to 10th	Day	17% 15% 6% 11% 7% 4 6% 5% 6% 5% 17%	1520
	11th to 20th	Day	19% 12% 5% 9% 7% 4 5% 5% 6% 6% 22%	1906
	21st to end	Day	28% 16% 7% 11% 7% 3 4 4 4 4 13%	2772
January	1st to 10th	Night	18% 14% 6% 9% 7% 4 5% 5% 4 6% 22%	4429
	11th to 20th	Night	15% 12% 6% 10% 11% 6% 6% 5% 5% 6% 18%	4207
	21st to end	Night	21% 13% 5% 9% 9% 4 5% 5% 5% 5% 19%	4532
February	1st to 10th	Night	14% 14% 6% 9% 8% 4 6% 5% 4 6% 24%	2399
	11th to 20th	Night	15% 13% 5% 9% 8% 4 5% 5% 5% 5% 27%	2273
	21st to end	Night	14% 12% 5% 9% 7% 3 5% 5% 6% 6% 29%	1871
March	1st to 10th	Night	12% 8% 5% 8% 7% 4 5% 5% 5% 5% 35%	1970
	11th to 20th	Night	16% 11% 4 8% 5% 4 4 4 4 6% 35%	1979
	21st to end	Night	16% 9% 3 6% 5% 3 4 4 4 6% 39%	2178
April	1st to 10th	Night	18% 9% 3 7% 5% 3 4 5% 6% 7% 32%	1836
	11th to 20th	Night	15% 8% 3 6% 5% 3 5% 4 5% 6% 38%	1719
	21st to end	Night	17% 8% 4 5% 5% 3 4 5% 5% 7% 36%	1620
May	1st to 10th	Night	17% 6% 2 5% 5% 3 5% 6% 5% 7% 39%	1620
	11th to 20th	Night	14% 5% 3 5% 4 3 4 4 5% 8% 46%	1429
	21st to end	Night	10% 4 2 4 4 3 4 5% 5% 7% 52%	1550
June	1st to 10th	Night	12% 5% 3 5% 6% 3 5% 4 5% 9% 42%	1440
	11th to 20th	Night	9% 6% 2 5% 5% 3 5% 5% 6% 10% 43%	1440
	21st to end	Night	11% 5% 3 4 5% 4 5% 4 6% 8% 46%	1288
July	1st to 10th	Night	6% 3 2 4 4 2 4 4 6% 8% 57%	1404
	11th to 20th	Night	9% 4 1 4 4 3 5% 5% 6% 8% 50%	1440
	21st to end	Night	7% 4 2 5% 4 3 5% 5% 6% 8% 51%	1741
August	1st to 10th	Night	7% 4 2 5% 6% 4 5% 4 6% 8% 50%	1611
	11th to 20th	Night	7% 4 2 4 4 3 4 5% 6% 9% 52%	1598
	21st to end	Night	10% 5% 2 4 4 4 4 5% 6% 6% 49%	1856
September	1st to 10th	Night	9% 5% 2 5% 6% 3 4 5% 6% 8% 47%	1800
	11th to 20th	Night	11% 4 2 4 4 2 4 4 6% 7% 53%	1905
	21st to end	Night	15% 6% 3 6% 5% 2 4 4 5% 7% 44%	2016
October	1st to 10th	Night	16% 7% 3 6% 5% 3 5% 5% 5% 6% 38%	2160
	11th to 20th	Night	19% 7% 3 6% 6% 3 5% 5% 5% 7% 33%	2160
	21st to end	Night	21% 9% 5% 6% 6% 3 4 5% 6% 7% 28%	2376
November	1st to 10th	Night	17% 8% 3 6% 5% 3 5% 5% 6% 6% 38%	2472
	11th to 20th	Night	17% 9% 4 7% 6% 4 5% 6% 5% 7% 30%	2660
	21st to end	Night	20% 11% 5% 7% 6% 4 5% 5% 5% 7% 27%	2660
December	1st to 10th	Night	20% 13% 5% 9% 6% 4 4 5% 6% 6% 22%	2660
	11th to 20th	Night	15% 16% 5% 9% 7% 4 5% 5% 5% 6% 22%	3288
	21st to end	Night	30% 14% 5% 8% 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	55% 7% 17% 12% 7% 1	2518
	11th to 20th	Day	68% 6% 10% 11% 4	2751
	21st to end	Day	69% 6% 10% 9% 5% 1	3124
February	1st to 10th	Day	64% 6% 10% 16% 4 1	1656
	11th to 20th	Day	59% 4 12% 15% 8% 2	1582
	21st to end	Day	60% 7% 9% 16% 7% 1	1381
March	1st to 10th	Day	53% 7% 13% 17% 10% 1	1980
	11th to 20th	Day	54% 6% 9% 18% 12% 2	1980
	21st to end	Day	53% 5% 9% 17% 13% 2	2178
April	1st to 10th	Day	55% 4 11% 18% 11% 1	2124
	11th to 20th	Day	49% 5% 10% 21% 15% 1	2206
	21st to end	Day	52% 5% 11% 18% 12% 3	2340
May	1st to 10th	Day	49% 5% 11% 20% 14% 1	2340
	11th to 20th	Day	43% 6% 11% 24% 14% 1	2465
	21st to end	Day	38% 6% 15% 24% 14% 2	2725
June	1st to 10th	Day	43% 7% 12% 22% 15% 1	2520
	11th to 20th	Day	38% 8% 12% 25% 16% 2	2520
	21st to end	Day	39% 7% 14% 24% 15% 1	2656
July	1st to 10th	Day	34% 8% 12% 25% 19% 3	2473
	11th to 20th	Day	37% 8% 13% 28% 12% 1	2445
	21st to end	Day	41% 9% 14% 21% 13% 1	2431
August	1st to 10th	Day	37% 9% 16% 23% 14% 2	2314
	11th to 20th	Day	36% 8% 17% 26% 12% 1	2303
	21st to end	Day	38% 8% 13% 27% 12% 1	2481
September	1st to 10th	Day	39% 7% 14% 27% 11% 1	2160
	11th to 20th	Day	36% 6% 14% 29% 15% 1	2052
	21st to end	Day	44% 7% 13% 26% 9%	1944
October	1st to 10th	Day	48% 6% 14% 19% 12% 1	1800
	11th to 20th	Day	54% 7% 12% 20% 7% 1	1800
	21st to end	Day	61% 6% 12% 15% 6% 1	1980
November	1st to 10th	Day	48% 8% 13% 21% 9% 1	1602
	11th to 20th	Day	55% 8% 14% 14% 8% 1	1520
	21st to end	Day	59% 7% 15% 15% 3	1520
December	1st to 10th	Day	65% 7% 13% 11% 4	1520
	11th to 20th	Day	60% 8% 16% 11% 6%	1906
	21st to end	Day	74% 6% 8% 10% 3	2772
January	1st to 10th	Night	59% 9% 12% 14% 5% 1	4429
	11th to 20th	Night	63% 9% 12% 12% 4 1	4207
	21st to end	Night	64% 8% 12% 11% 5% 1	4532
February	1st to 10th	Night	60% 5% 10% 18% 6% 1	2399
	11th to 20th	Night	58% 6% 10% 16% 9% 1	2275
	21st to end	Night	54% 5% 14% 19% 8% 1	1871
March	1st to 10th	Night	50% 6% 13% 20% 10% 2	1980
	11th to 20th	Night	53% 3 9% 20% 12% 2	1980
	21st to end	Night	47% 5% 9% 21% 16% 3	2178
April	1st to 10th	Night	51% 5% 10% 18% 15% 1	1836
	11th to 20th	Night	48% 4 9% 21% 15% 2	1719
	21st to end	Night	46% 6% 11% 19% 15% 3	1620
May	1st to 10th	Night	43% 6% 9% 21% 17% 3	1620
	11th to 20th	Night	38% 5% 10% 25% 18% 4	1430
	21st to end	Night	30% 6% 16% 25% 18% 5%	1551
June	1st to 10th	Night	38% 6% 11% 25% 18% 2	1440
	11th to 20th	Night	37% 5% 12% 23% 22% 2	1440
	21st to end	Night	36% 6% 13% 27% 18% 1	1288
July	1st to 10th	Night	26% 5% 11% 27% 26% 4	1364
	11th to 20th	Night	30% 6% 12% 31% 18% 2	1392
	21st to end	Night	30% 6% 15% 30% 16% 3	1644
August	1st to 10th	Night	32% 7% 17% 29% 14% 2	1600
	11th to 20th	Night	27% 7% 15% 34% 14% 2	1598
	21st to end	Night	33% 6% 14% 29% 16% 1	1856
September	1st to 10th	Night	34% 7% 16% 28% 14% 1	1800
	11th to 20th	Night	31% 5% 10% 36% 18% 1	1905
	21st to end	Night	40% 6% 12% 29% 12% 1	2016
October	1st to 10th	Night	44% 7% 11% 21% 15% 1	2160
	11th to 20th	Night	50% 6% 12% 24% 8%	2160
	21st to end	Night	55% 6% 11% 16% 11% 1	2376
November	1st to 10th	Night	45% 5% 12% 24% 12% 1	2472
	11th to 20th	Night	51% 7% 14% 18% 10% 1	2660
	21st to end	Night	56% 7% 17% 16% 4	2660
December	1st to 10th	Night	60% 7% 11% 15% 6%	2660
	11th to 20th	Night	61% 6% 14% 14% 4	3288
	21st to end	Night	71% 7% 11% 8% 3	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% 16% 31% 23% 6% 1	180
	11th to 20th	Day	24% 22% 34% 15% 5% 1	247
	21st to end	Day	25% 18% 35% 18% 4	297
February	1st to 10th	Day	27% 23% 36% 11% 3	252
	11th to 20th	Day	25% 23% 40% 10% 2	240
	21st to end	Day	32% 27% 29% 12%	211
March	1st to 10th	Day	20% 17% 37% 20% 6%	420
	11th to 20th	Day	21% 15% 39% 19% 5% 1	420
	21st to end	Day	27% 16% 30% 20% 6% 1	462
April	1st to 10th	Day	19% 20% 35% 19% 7%	420
	11th to 20th	Day	26% 17% 27% 17% 8% 3	412
	21st to end	Day	24% 14% 33% 19% 8% 2	420
May	1st to 10th	Day	24% 9% 31% 21% 9% 6%	423
	11th to 20th	Day	17% 10% 30% 27% 11% 5%	447
	21st to end	Day	15% 8% 26% 29% 15% 6%	485
June	1st to 10th	Day	14% 10% 32% 31% 11% 2	450
	11th to 20th	Day	15% 11% 25% 31% 16% 3	450
	21st to end	Day	15% 8% 28% 34% 11% 4	586
July	1st to 10th	Day	10% 4 24% 34% 22% 6%	468
	11th to 20th	Day	13% 5% 23% 31% 19% 9%	444
	21st to end	Day	9% 3 27% 37% 16% 7%	488
August	1st to 10th	Day	11% 5% 21% 30% 21% 11%	446
	11th to 20th	Day	10% 3 23% 30% 23% 10%	439
	21st to end	Day	11% 8% 24% 29% 19% 10%	495
September	1st to 10th	Day	12% 7% 27% 26% 17% 11%	450
	11th to 20th	Day	10% 6% 24% 26% 20% 14%	450
	21st to end	Day	13% 11% 29% 25% 16% 7%	450
October	1st to 10th	Day	22% 11% 26% 22% 13% 6%	450
	11th to 20th	Day	21% 15% 36% 19% 7% 2	450
	21st to end	Day	31% 13% 29% 22% 4	495
November	1st to 10th	Day	18% 21% 28% 22% 9% 1	258
	11th to 20th	Day	23% 21% 32% 18% 4 2	180
	21st to end	Day	24% 14% 41% 18% 2	180
December	1st to 10th	Day	26% 16% 37% 16% 5%	180
	11th to 20th	Day	24% 26% 26% 19% 4	180
	21st to end	Day	28% 18% 40% 14% 1	198
January	1st to 10th	Night	24% 14% 37% 21% 5%	760
	11th to 20th	Night	26% 15% 31% 24% 4	760
	21st to end	Night	20% 9% 39% 25% 7%	836
February	1st to 10th	Night	20% 15% 41% 21% 3	739
	11th to 20th	Night	22% 14% 37% 23% 4	703
	21st to end	Night	20% 15% 40% 21% 4	592
March	1st to 10th	Night	19% 14% 38% 24% 5%	720
	11th to 20th	Night	21% 16% 36% 20% 6% 1	720
	21st to end	Night	21% 10% 34% 27% 8%	792
April	1st to 10th	Night	24% 13% 35% 25% 4	720
	11th to 20th	Night	17% 12% 36% 24% 9% 1	655
	21st to end	Night	20% 9% 32% 29% 9%	540
May	1st to 10th	Night	18% 5% 30% 32% 14% 2	540
	11th to 20th	Night	15% 4 35% 34% 12% 1	368
	21st to end	Night	11% 5% 28% 37% 20% 1	389
June	1st to 10th	Night	14% 3 31% 37% 14% 1	360
	11th to 20th	Night	11% 7% 30% 37% 14% 1	360
	21st to end	Night	11% 6% 23% 44% 15% 1	360
July	1st to 10th	Night	7% 3 23% 45% 21% 1	350
	11th to 20th	Night	11% 2 25% 40% 20% 2	348
	21st to end	Night	6% 3 21% 48% 20% 2	561
August	1st to 10th	Night	10% 1 17% 42% 28% 2	537
	11th to 20th	Night	7% 2 17% 44% 28% 3	534
	21st to end	Night	11% 4 22% 35% 24% 3	668
September	1st to 10th	Night	12% 5% 25% 34% 20% 5%	720
	11th to 20th	Night	14% 3 21% 33% 24% 5%	720
	21st to end	Night	17% 6% 23% 31% 20% 4	720
October	1st to 10th	Night	18% 7% 28% 28% 17% 2	720
	11th to 20th	Night	21% 9% 32% 28% 9% 1	720
	21st to end	Night	26% 10% 32% 28% 5%	792
November	1st to 10th	Night	21% 10% 29% 29% 10% 1	740
	11th to 20th	Night	21% 13% 35% 23% 7% 1	760
	21st to end	Night	25% 11% 33% 26% 5%	760
December	1st to 10th	Night	28% 12% 37% 18% 4	760
	11th to 20th	Night	23% 14% 39% 21% 4	760
	21st to end	Night	31% 11% 35% 20% 2	836

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