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 2025-02-25.

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% 10% 3 8% 5% 5% 5% 4 6% 7% 32%	108996
	Night	15% 10% 4 8% 5% 5% 5% 4 6% 7% 33%	109630
Transparency	Day	48% 7% 13% 20% 11% 1	112634
	Night	47% 7% 13% 21% 12% 1	114155
Seeing	Day	18% 12% 30% 24% 11% 4	14869
	Night	19% 9% 31% 29% 11% 1	24260

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	13% 10% 4 13% 6% 5% 6% 4 6% 7% 26%	3597
	11th to 20th	Day	10% 17% 6% 18% 9% 8% 5% 4 4 4 16%	3909
	21st to end	Day	16% 16% 6% 13% 7% 5% 6% 4 5% 5% 18%	4466
February	1st to 10th	Day	15% 17% 4 12% 6% 6% 6% 4 5% 5% 21%	1800
	11th to 20th	Day	12% 15% 6% 12% 7% 4 5% 3 4 6% 24%	1753
	21st to end	Day	17% 16% 4 10% 6% 4 6% 4 4 5% 25%	1501
March	1st to 10th	Day	19% 12% 4 8% 6% 4 4 3 4 5% 31%	3432
	11th to 20th	Day	11% 14% 4 10% 6% 6% 5% 5% 5% 6% 29%	3480
	21st to end	Day	16% 10% 3 7% 5% 4 4 4 5% 6% 36%	3815
April	1st to 10th	Day	17% 13% 4 8% 5% 4 4 4 5% 7% 29%	2242
	11th to 20th	Day	20% 9% 3 7% 4 4 5% 3 6% 5% 36%	2331
	21st to end	Day	20% 9% 2 7% 5% 5% 4 3 5% 6% 33%	2470
May	1st to 10th	Day	18% 8% 3 8% 4 4 5% 4 6% 8% 33%	4108
	11th to 20th	Day	16% 9% 3 9% 5% 5% 4 4 5% 8% 31%	4381
	21st to end	Day	12% 5% 2 5% 4 4 4 3 5% 8% 46%	4837
June	1st to 10th	Day	14% 7% 2 7% 5% 5% 5% 4 7% 8% 36%	2660
	11th to 20th	Day	13% 5% 2 7% 4 3 5% 5% 7% 11% 38%	2660
	21st to end	Day	14% 5% 2 6% 5% 5% 5% 4 7% 8% 39%	2804
July	1st to 10th	Day	10% 5% 2 6% 5% 5% 6% 5% 7% 11% 39%	4477
	11th to 20th	Day	10% 5% 1 5% 4 5% 6% 4 7% 10% 44%	4440
	21st to end	Day	7% 5% 2 7% 5% 6% 6% 5% 7% 9% 40%	4508
August	1st to 10th	Day	16% 7% 2 6% 5% 4 5% 4 6% 8% 37%	4104
	11th to 20th	Day	10% 7% 3 8% 5% 5% 6% 5% 7% 9% 35%	4044
	21st to end	Day	9% 5% 2 6% 5% 5% 5% 4 7% 10% 42%	4355
September	1st to 10th	Day	13% 6% 2 6% 4 4 5% 4 6% 8% 42%	2280
	11th to 20th	Day	11% 5% 2 6% 4 4 5% 3 6% 8% 45%	2166
	21st to end	Day	14% 6% 3 7% 6% 4 6% 4 6% 9% 36%	2052
October	1st to 10th	Day	18% 8% 3 6% 4 4 4 4 5% 8% 35%	1900
	11th to 20th	Day	20% 8% 3 7% 6% 5% 5% 4 6% 6% 30%	1900
	21st to end	Day	23% 12% 3 8% 5% 6% 5% 4 5% 6% 22%	2090
November	1st to 10th	Day	14% 10% 3 9% 6% 4 5% 4 6% 6% 33%	1688
	11th to 20th	Day	15% 12% 3 11% 6% 5% 7% 5% 6% 7% 25%	1600
	21st to end	Day	18% 14% 5% 10% 6% 5% 5% 4 7% 6% 21%	1600
December	1st to 10th	Day	18% 17% 5% 11% 6% 6% 6% 4 6% 5% 16%	2600
	11th to 20th	Day	20% 16% 5% 10% 6% 5% 4 3 5% 5% 21%	2986
	21st to end	Day	26% 16% 7% 13% 5% 4 4 3 4 4 14%	3960
January	1st to 10th	Night	14% 11% 5% 11% 6% 6% 5% 5% 6% 7% 24%	6349
	11th to 20th	Night	13% 13% 6% 14% 10% 7% 6% 4 6% 6% 16%	5974
	21st to end	Night	16% 13% 5% 11% 7% 5% 5% 4 6% 6% 22%	6490
February	1st to 10th	Night	13% 15% 5% 10% 7% 4 5% 4 5% 6% 25%	2600
	11th to 20th	Night	14% 14% 4 10% 7% 5% 5% 4 6% 5% 26%	2533
	21st to end	Night	14% 12% 4 10% 6% 4 5% 4 6% 6% 28%	2043
March	1st to 10th	Night	17% 10% 3 9% 5% 5% 5% 4 5% 5% 32%	3408
	11th to 20th	Night	13% 10% 3 8% 4 5% 5% 4 5% 7% 36%	3479
	21st to end	Night	17% 7% 3 5% 4 3 4 3 5% 6% 44%	3817
April	1st to 10th	Night	18% 11% 2 8% 5% 4 5% 4 6% 6% 32%	1937
	11th to 20th	Night	16% 8% 3 7% 4 5% 4 3 5% 7% 38%	1815
	21st to end	Night	17% 8% 3 6% 4 4 5% 4 6% 8% 36%	1710
May	1st to 10th	Night	18% 7% 2 6% 4 4 4 4 5% 6% 40%	2833
	11th to 20th	Night	14% 9% 3 6% 4 4 4 4 5% 8% 37%	2509
	21st to end	Night	10% 4 2 5% 4 4 4 3 5% 8% 51%	2738
June	1st to 10th	Night	13% 5% 3 6% 5% 5% 4 4 6% 8% 42%	1520
	11th to 20th	Night	9% 6% 2 6% 4 4 4 5% 7% 10% 42%	1520
	21st to end	Night	11% 6% 2 5% 4 5% 4 4 6% 7% 45%	1359
July	1st to 10th	Night	6% 5% 2 5% 4 4 4 4 7% 9% 51%	2458
	11th to 20th	Night	11% 4 1 4 3 3 4 3 6% 9% 51%	2520
	21st to end	Night	7% 4 2 5% 4 4 4 4 6% 8% 51%	3043
August	1st to 10th	Night	9% 5% 2 7% 4 5% 4 3 6% 8% 47%	2825
	11th to 20th	Night	11% 4 2 6% 3 4 4 4 5% 8% 50%	2785
	21st to end	Night	10% 6% 2 5% 4 4 4 4 7% 7% 47%	3268
September	1st to 10th	Night	9% 5% 2 6% 4 4 5% 4 6% 8% 48%	1900
	11th to 20th	Night	10% 4 2 4 3 3 4 3 6% 7% 54%	2011
	21st to end	Night	15% 6% 3 7% 4 3 4 3 5% 6% 42%	2128
October	1st to 10th	Night	16% 7% 3 7% 4 4 4 4 5% 6% 39%	2280
	11th to 20th	Night	18% 8% 3 7% 5% 5% 5% 4 6% 6% 35%	2280
	21st to end	Night	20% 9% 4 7% 5% 4 5% 4 6% 7% 30%	2508
November	1st to 10th	Night	16% 9% 3 6% 5% 4 4 3 6% 6% 37%	2606
	11th to 20th	Night	17% 11% 3 8% 6% 5% 5% 4 6% 7% 30%	2800
	21st to end	Night	20% 11% 4 8% 5% 5% 5% 4 5% 7% 26%	2800
December	1st to 10th	Night	17% 14% 5% 11% 6% 6% 5% 4 6% 6% 18%	4580
	11th to 20th	Night	16% 17% 5% 10% 6% 5% 5% 4 5% 5% 22%	5208
	21st to end	Night	25% 14% 6% 12% 5% 5% 4 3 4 5% 16%	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	54% 8% 14% 14% 9%	3598
	11th to 20th	Day	69% 6% 10% 11% 4	3943
	21st to end	Day	65% 6% 11% 9% 7% 1	4466
February	1st to 10th	Day	62% 6% 10% 17% 4 1	1800
	11th to 20th	Day	59% 5% 12% 15% 7% 1	1762
	21st to end	Day	59% 7% 10% 16% 7% 1	1501
March	1st to 10th	Day	54% 7% 13% 17% 9% 1	3435
	11th to 20th	Day	52% 6% 13% 18% 9% 2	3480
	21st to end	Day	47% 5% 12% 19% 14% 2	3815
April	1st to 10th	Day	54% 5% 11% 18% 11% 1	2242
	11th to 20th	Day	49% 5% 11% 20% 15% 1	2331
	21st to end	Day	52% 5% 11% 18% 12% 3	2470
May	1st to 10th	Day	47% 7% 12% 19% 14% 2	4120
	11th to 20th	Day	48% 9% 13% 20% 9% 1	4385
	21st to end	Day	35% 7% 13% 24% 17% 3	4837
June	1st to 10th	Day	44% 7% 11% 22% 15% 1	2660
	11th to 20th	Day	37% 8% 13% 25% 16% 1	2660
	21st to end	Day	40% 7% 13% 24% 15% 1	2804
July	1st to 10th	Day	35% 7% 15% 25% 15% 2	4407
	11th to 20th	Day	32% 7% 14% 35% 12% 1	4365
	21st to end	Day	37% 10% 14% 21% 18% 1	4364
August	1st to 10th	Day	43% 8% 14% 21% 14% 1	4091
	11th to 20th	Day	40% 8% 16% 25% 10% 1	4083
	21st to end	Day	35% 8% 13% 33% 11% 1	4355
September	1st to 10th	Day	39% 7% 14% 28% 11% 1	2280
	11th to 20th	Day	35% 6% 14% 30% 15% 1	2166
	21st to end	Day	44% 7% 13% 26% 9%	2052
October	1st to 10th	Day	36% 7% 16% 27% 13% 1	3160
	11th to 20th	Day	39% 6% 15% 26% 14%	3140
	21st to end	Day	53% 7% 14% 20% 6%	3428
November	1st to 10th	Day	48% 8% 13% 21% 9% 1	1688
	11th to 20th	Day	55% 8% 14% 15% 9% 1	1600
	21st to end	Day	60% 7% 15% 15% 3	1600
December	1st to 10th	Day	66% 7% 14% 9% 4	2600
	11th to 20th	Day	62% 8% 13% 9% 8%	2986
	21st to end	Day	72% 6% 6% 9% 6%	3960
January	1st to 10th	Night	54% 9% 12% 19% 6% 1	6349
	11th to 20th	Night	63% 9% 11% 13% 4	6015
	21st to end	Night	59% 7% 12% 11% 10% 1	6490
February	1st to 10th	Night	58% 5% 11% 19% 6% 1	2600
	11th to 20th	Night	57% 6% 11% 17% 9% 1	2535
	21st to end	Night	53% 5% 14% 19% 8%	2043
March	1st to 10th	Night	52% 6% 12% 22% 8% 1	3418
	11th to 20th	Night	45% 6% 15% 20% 12% 2	3480
	21st to end	Night	40% 5% 11% 22% 20% 2	3817
April	1st to 10th	Night	51% 5% 10% 18% 14% 1	1937
	11th to 20th	Night	48% 5% 9% 21% 15% 2	1815
	21st to end	Night	46% 6% 11% 19% 16% 2	1710
May	1st to 10th	Night	44% 6% 13% 18% 16% 4	2840
	11th to 20th	Night	44% 8% 16% 19% 11% 2	2510
	21st to end	Night	29% 7% 14% 25% 22% 3	2739
June	1st to 10th	Night	39% 6% 10% 25% 18% 2	1520
	11th to 20th	Night	36% 5% 13% 23% 22% 2	1520
	21st to end	Night	36% 6% 13% 26% 18% 1	1359
July	1st to 10th	Night	29% 5% 15% 26% 22% 3	2418
	11th to 20th	Night	30% 6% 13% 34% 16% 1	2472
	21st to end	Night	29% 9% 14% 30% 16% 2	2946
August	1st to 10th	Night	35% 6% 13% 29% 15% 2	2814
	11th to 20th	Night	32% 6% 15% 33% 12% 1	2812
	21st to end	Night	33% 7% 14% 31% 14% 1	3268
September	1st to 10th	Night	33% 7% 15% 29% 15% 1	1900
	11th to 20th	Night	30% 5% 10% 36% 19% 1	2011
	21st to end	Night	42% 6% 12% 28% 12% 1	2128
October	1st to 10th	Night	33% 6% 10% 27% 24% 1	3800
	11th to 20th	Night	42% 6% 13% 27% 12%	3779
	21st to end	Night	39% 7% 16% 26% 11% 1	4120
November	1st to 10th	Night	46% 5% 12% 24% 12% 1	2606
	11th to 20th	Night	51% 7% 14% 18% 10% 1	2800
	21st to end	Night	56% 7% 17% 16% 4	2800
December	1st to 10th	Night	62% 8% 12% 14% 4	4580
	11th to 20th	Night	61% 7% 11% 13% 8%	5208
	21st to end	Night	68% 7% 11% 9% 5%	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	21% 18% 33% 23% 5% 1	200
	11th to 20th	Day	23% 23% 33% 16% 5% 1	275
	21st to end	Day	24% 19% 36% 18% 3	330
February	1st to 10th	Day	26% 23% 36% 12% 3	300
	11th to 20th	Day	23% 25% 39% 11% 2	300
	21st to end	Day	31% 25% 30% 14% 1	251
March	1st to 10th	Day	21% 16% 37% 20% 6%	460
	11th to 20th	Day	20% 17% 39% 19% 5% 1	460
	21st to end	Day	26% 17% 30% 20% 6% 1	506
April	1st to 10th	Day	20% 20% 35% 18% 6%	460
	11th to 20th	Day	28% 17% 27% 17% 8% 3	452
	21st to end	Day	24% 15% 33% 18% 8% 2	460
May	1st to 10th	Day	23% 9% 31% 21% 10% 5%	463
	11th to 20th	Day	16% 10% 29% 28% 12% 5%	487
	21st to end	Day	15% 9% 27% 29% 15% 6%	529
June	1st to 10th	Day	14% 12% 31% 30% 11% 2	490
	11th to 20th	Day	14% 10% 26% 32% 15% 3	490
	21st to end	Day	16% 8% 29% 32% 11% 3	634
July	1st to 10th	Day	10% 5% 24% 34% 21% 6%	509
	11th to 20th	Day	13% 5% 23% 31% 19% 8%	484
	21st to end	Day	9% 3 26% 36% 18% 8%	532
August	1st to 10th	Day	13% 5% 22% 29% 20% 10%	486
	11th to 20th	Day	10% 4 25% 28% 23% 11%	479
	21st to end	Day	11% 8% 23% 30% 19% 10%	539
September	1st to 10th	Day	12% 8% 27% 26% 17% 11%	490
	11th to 20th	Day	10% 6% 22% 24% 23% 16%	490
	21st to end	Day	14% 10% 29% 24% 17% 6%	490
October	1st to 10th	Day	20% 10% 28% 22% 13% 6%	490
	11th to 20th	Day	20% 14% 36% 20% 8% 2	490
	21st to end	Day	30% 13% 29% 23% 5%	539
November	1st to 10th	Day	18% 21% 29% 22% 9% 1	284
	11th to 20th	Day	24% 22% 33% 17% 5% 2	200
	21st to end	Day	24% 15% 43% 18% 2	200
December	1st to 10th	Day	27% 16% 36% 16% 5%	200
	11th to 20th	Day	27% 25% 26% 18% 5%	200
	21st to end	Day	29% 16% 39% 14% 2 1	220
January	1st to 10th	Night	23% 14% 38% 21% 5%	800
	11th to 20th	Night	25% 15% 32% 24% 4 1	800
	21st to end	Night	20% 10% 40% 24% 6%	880
February	1st to 10th	Night	20% 16% 40% 22% 3	800
	11th to 20th	Night	21% 15% 37% 24% 3	783
	21st to end	Night	19% 16% 39% 22% 4	647
March	1st to 10th	Night	19% 14% 37% 25% 4	760
	11th to 20th	Night	21% 17% 36% 20% 6% 1	760
	21st to end	Night	21% 11% 34% 26% 8%	836
April	1st to 10th	Night	24% 13% 35% 24% 4	760
	11th to 20th	Night	18% 12% 37% 23% 8% 1	691
	21st to end	Night	20% 9% 32% 29% 9%	570
May	1st to 10th	Night	18% 5% 30% 32% 13% 2	570
	11th to 20th	Night	15% 4 34% 34% 13% 1	388
	21st to end	Night	11% 4 28% 37% 18%	411
June	1st to 10th	Night	15% 3 30% 37% 14% 1	380
	11th to 20th	Night	11% 7% 29% 38% 15% 1	380
	21st to end	Night	11% 6% 24% 43% 15% 1	380
July	1st to 10th	Night	7% 3 24% 44% 21% 1	370
	11th to 20th	Night	11% 2 24% 40% 21% 2	368
	21st to end	Night	6% 3 20% 48% 21% 2	593
August	1st to 10th	Night	11% 1 16% 43% 27% 2	567
	11th to 20th	Night	7% 2 17% 43% 28% 2	564
	21st to end	Night	11% 4 22% 36% 25% 3	706
September	1st to 10th	Night	11% 5% 25% 34% 20% 5%	760
	11th to 20th	Night	13% 3 20% 33% 27% 5%	760
	21st to end	Night	17% 6% 23% 31% 20% 4	760
October	1st to 10th	Night	18% 7% 28% 28% 17% 2	760
	11th to 20th	Night	21% 9% 31% 29% 9% 1	760
	21st to end	Night	24% 9% 32% 29% 5%	836
November	1st to 10th	Night	21% 11% 29% 29% 9% 1	780
	11th to 20th	Night	21% 13% 34% 24% 7% 1	800
	21st to end	Night	25% 11% 34% 25% 5%	800
December	1st to 10th	Night	27% 12% 37% 19% 5%	800
	11th to 20th	Night	23% 14% 39% 21% 3	800
	21st to end	Night	30% 11% 35% 21% 2	880

Page generated at 2025-02-22 06:51:36. Version ac07

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