Victoria
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Victoria 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	13% 8% 3 7% 5% 4 4 4 5% 7% 40%	130307
	Night	16% 9% 3 7% 5% 4 4 4 5% 6% 36%	127126
Transparency	Day	44% 8% 18% 21% 8% 1	130015
	Night	49% 8% 16% 19% 8% 1	126995
Seeing	Day	15% 6% 15% 27% 26% 10%	16472
	Night	20% 7% 18% 27% 22% 6%	24595

By Month

Percentage Cloud Cover NW (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	27% 13% 4 11% 6% 6% 5% 4 5% 5% 14%	3179
	11th to 20th	Day	14% 12% 4 9% 6% 5% 5% 4 6% 8% 28%	3183
	21st to end	Day	21% 14% 5% 11% 6% 6% 4 3 4 5% 21%	4167
February	1st to 10th	Day	23% 15% 4 9% 6% 6% 4 4 7% 6% 17%	1800
	11th to 20th	Day	21% 12% 5% 9% 5% 5% 4 4 4 6% 24%	1755
	21st to end	Day	18% 13% 4 9% 7% 7% 6% 4 6% 6% 20%	1496
March	1st to 10th	Day	13% 13% 4 10% 7% 7% 6% 5% 7% 8% 20%	4731
	11th to 20th	Day	14% 12% 4 9% 5% 4 5% 4 5% 7% 31%	5000
	21st to end	Day	17% 12% 4 10% 6% 6% 6% 5% 6% 7% 21%	5589
April	1st to 10th	Day	17% 11% 3 8% 6% 5% 6% 5% 7% 8% 25%	2400
	11th to 20th	Day	15% 9% 3 7% 5% 5% 6% 5% 6% 8% 33%	2473
	21st to end	Day	14% 9% 3 6% 5% 4 5% 4 6% 8% 35%	2620
May	1st to 10th	Day	11% 5% 2 6% 4 5% 4 3 4 7% 47%	6320
	11th to 20th	Day	9% 6% 2 6% 4 4 5% 5% 7% 9% 43%	6277
	21st to end	Day	13% 8% 2 6% 4 4 5% 4 6% 8% 39%	6963
June	1st to 10th	Day	13% 6% 2 6% 5% 5% 4 4 6% 7% 41%	3000
	11th to 20th	Day	9% 7% 2 7% 6% 5% 5% 4 5% 8% 42%	3000
	21st to end	Day	8% 6% 2 5% 4 4 5% 5% 7% 7% 47%	3000
July	1st to 10th	Day	5% 2 1 3 2 2 3 2 4 5% 72%	6780
	11th to 20th	Day	3 2 1 2 2 2 2 2 3 4 77%	6780
	21st to end	Day	6% 2 1 2 2 2 3 2 4 6% 72%	6930
August	1st to 10th	Day	3 2 1 2 2 2 2 2 4 6% 74%	4419
	11th to 20th	Day	8% 6% 3 7% 4 5% 4 4 5% 7% 48%	4156
	21st to end	Day	10% 5% 3 6% 4 3 4 3 5% 6% 51%	4555
September	1st to 10th	Day	7% 5% 2 5% 3 4 3 3 5% 8% 55%	2317
	11th to 20th	Day	11% 7% 2 7% 4 4 5% 3 5% 6% 45%	2256
	21st to end	Day	15% 8% 2 6% 4 4 4 3 5% 8% 41%	2013
October	1st to 10th	Day	15% 6% 2 6% 5% 5% 6% 5% 7% 8% 33%	3180
	11th to 20th	Day	24% 11% 3 9% 4 4 4 3 5% 6% 26%	3161
	21st to end	Day	16% 10% 3 10% 6% 5% 5% 5% 6% 8% 27%	3243
November	1st to 10th	Day	26% 11% 4 11% 6% 5% 4 4 6% 6% 17%	1568
	11th to 20th	Day	23% 12% 4 9% 6% 6% 5% 3 4 6% 23%	1600
	21st to end	Day	24% 12% 5% 10% 7% 5% 5% 3 4 6% 19%	1600
December	1st to 10th	Day	15% 15% 5% 11% 6% 5% 5% 3 5% 6% 23%	2620
	11th to 20th	Day	28% 13% 4 9% 6% 5% 6% 4 5% 6% 14%	2678
	21st to end	Day	23% 18% 5% 12% 6% 5% 4 4 5% 5% 12%	3498
January	1st to 10th	Night	26% 15% 5% 11% 6% 6% 5% 4 5% 5% 13%	6766
	11th to 20th	Night	16% 10% 3 7% 3 4 4 3 5% 7% 37%	6712
	21st to end	Night	21% 12% 4 9% 5% 4 4 3 5% 5% 27%	6793
February	1st to 10th	Night	22% 13% 4 9% 6% 5% 5% 4 4 6% 23%	2600
	11th to 20th	Night	19% 12% 3 9% 5% 5% 5% 3 5% 6% 30%	2532
	21st to end	Night	22% 13% 3 9% 5% 5% 4 4 5% 6% 24%	2133
March	1st to 10th	Night	12% 9% 3 9% 7% 7% 7% 6% 8% 8% 25%	5161
	11th to 20th	Night	12% 10% 3 7% 5% 5% 5% 5% 6% 8% 33%	4999
	21st to end	Night	21% 13% 5% 11% 6% 5% 5% 4 6% 5% 20%	5385
April	1st to 10th	Night	18% 10% 4 8% 5% 5% 5% 4 6% 8% 28%	2000
	11th to 20th	Night	13% 9% 3 7% 6% 4 5% 4 6% 8% 36%	1875
	21st to end	Night	16% 8% 3 8% 5% 4 5% 4 5% 8% 34%	1780
May	1st to 10th	Night	12% 7% 2 6% 3 3 3 2 4 5% 53%	3640
	11th to 20th	Night	9% 6% 3 6% 5% 4 4 4 6% 8% 46%	3616
	21st to end	Night	11% 7% 3 7% 6% 6% 6% 5% 7% 8% 35%	3908
June	1st to 10th	Night	13% 6% 3 6% 6% 4 4 4 6% 5% 41%	1400
	11th to 20th	Night	11% 5% 3 6% 4 4 4 4 8% 9% 42%	1400
	21st to end	Night	8% 5% 2 4 4 3 4 4 7% 9% 51%	1400
July	1st to 10th	Night	6% 2 1 3 2 2 2 1 3 5% 73%	3180
	11th to 20th	Night	2 1 1 2 2 1 2 1 3 4 81%	3180
	21st to end	Night	6% 2 1 3 2 2 2 2 4 6% 72%	3912
August	1st to 10th	Night	3 2 1 2 2 2 2 2 3 6% 76%	2732
	11th to 20th	Night	9% 4 2 6% 3 4 3 4 5% 7% 53%	2902
	21st to end	Night	10% 3 1 4 3 3 4 3 5% 9% 54%	3344
September	1st to 10th	Night	6% 2 1 4 3 2 3 3 5% 7% 64%	1930
	11th to 20th	Night	13% 6% 3 5% 4 4 3 3 4 6% 49%	1920
	21st to end	Night	13% 7% 3 6% 4 3 5% 3 5% 7% 45%	2166
October	1st to 10th	Night	13% 5% 2 6% 4 4 4 4 5% 7% 45%	3800
	11th to 20th	Night	22% 7% 4 8% 4 4 4 4 5% 7% 32%	3777
	21st to end	Night	21% 8% 3 8% 5% 5% 4 4 6% 7% 31%	4313
November	1st to 10th	Night	26% 10% 4 8% 5% 5% 6% 4 5% 5% 22%	2730
	11th to 20th	Night	23% 11% 3 8% 5% 5% 5% 4 5% 6% 25%	2800
	21st to end	Night	21% 14% 4 10% 6% 5% 5% 4 6% 5% 22%	2800
December	1st to 10th	Night	17% 10% 4 9% 6% 6% 6% 4 6% 8% 26%	4560
	11th to 20th	Night	27% 16% 5% 11% 6% 5% 5% 4 5% 5% 12%	5522
	21st to end	Night	23% 14% 5% 10% 6% 5% 6% 3 5% 5% 18%	7458

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	70% 10% 7% 10% 3	3179
	11th to 20th	Day	54% 10% 17% 14% 4	3204
	21st to end	Day	65% 8% 13% 12% 3	4167
February	1st to 10th	Day	66% 9% 11% 10% 3 1	1800
	11th to 20th	Day	61% 10% 10% 13% 5%	1764
	21st to end	Day	62% 8% 12% 12% 5% 1	1496
March	1st to 10th	Day	56% 9% 13% 16% 5%	4731
	11th to 20th	Day	51% 7% 15% 22% 4 1	5000
	21st to end	Day	61% 10% 14% 12% 2	5589
April	1st to 10th	Day	53% 10% 19% 15% 3	2400
	11th to 20th	Day	46% 9% 14% 21% 8% 1	2473
	21st to end	Day	46% 10% 16% 21% 7% 1	2620
May	1st to 10th	Day	38% 6% 17% 27% 11% 1	6320
	11th to 20th	Day	36% 10% 24% 25% 5%	6280
	21st to end	Day	42% 9% 25% 19% 3 1	6964
June	1st to 10th	Day	42% 8% 22% 19% 7% 1	3000
	11th to 20th	Day	41% 8% 22% 23% 5%	3000
	21st to end	Day	35% 8% 24% 23% 9% 1	3000
July	1st to 10th	Day	18% 5% 22% 26% 21% 9%	6706
	11th to 20th	Day	13% 4 20% 34% 27% 2	6699
	21st to end	Day	16% 4 31% 34% 12% 2	6735
August	1st to 10th	Day	15% 5% 19% 44% 16% 2	4402
	11th to 20th	Day	35% 9% 25% 22% 8% 1	4195
	21st to end	Day	35% 6% 19% 29% 10% 1	4554
September	1st to 10th	Day	30% 8% 22% 25% 13% 3	2317
	11th to 20th	Day	41% 10% 16% 20% 13% 1	2256
	21st to end	Day	44% 9% 16% 22% 9%	2013
October	1st to 10th	Day	48% 8% 18% 22% 4	3180
	11th to 20th	Day	60% 7% 13% 16% 5%	3161
	21st to end	Day	56% 9% 15% 13% 7%	3243
November	1st to 10th	Day	66% 9% 12% 10% 3 1	1568
	11th to 20th	Day	63% 7% 12% 13% 4 1	1600
	21st to end	Day	66% 9% 9% 12% 5%	1600
December	1st to 10th	Day	64% 7% 11% 15% 3	2620
	11th to 20th	Day	72% 9% 10% 7% 2	2681
	21st to end	Day	71% 9% 10% 8% 2	3498
January	1st to 10th	Night	73% 8% 9% 8% 2	6766
	11th to 20th	Night	48% 8% 19% 20% 4	6753
	21st to end	Night	60% 8% 13% 14% 5%	6793
February	1st to 10th	Night	63% 8% 13% 10% 6% 1	2600
	11th to 20th	Night	57% 8% 13% 15% 6% 1	2534
	21st to end	Night	61% 7% 12% 13% 6% 1	2133
March	1st to 10th	Night	52% 10% 15% 16% 7%	5161
	11th to 20th	Night	46% 8% 15% 26% 4 1	5000
	21st to end	Night	64% 9% 12% 13% 1	5385
April	1st to 10th	Night	54% 9% 16% 17% 4	2000
	11th to 20th	Night	46% 9% 14% 21% 8% 2	1875
	21st to end	Night	50% 8% 15% 18% 8%	1780
May	1st to 10th	Night	36% 5% 13% 31% 14% 1	3637
	11th to 20th	Night	35% 9% 25% 24% 7%	3616
	21st to end	Night	44% 11% 20% 21% 4	3908
June	1st to 10th	Night	44% 6% 17% 24% 7% 2	1400
	11th to 20th	Night	37% 10% 22% 26% 5%	1400
	21st to end	Night	32% 8% 25% 23% 10% 3	1400
July	1st to 10th	Night	17% 5% 18% 33% 16% 10%	3145
	11th to 20th	Night	11% 3 18% 34% 31% 3	3138
	21st to end	Night	17% 3 23% 37% 18% 2	3802
August	1st to 10th	Night	13% 4 16% 37% 26% 3	2724
	11th to 20th	Night	31% 8% 25% 22% 9% 3	2929
	21st to end	Night	29% 8% 16% 34% 12% 1	3344
September	1st to 10th	Night	22% 7% 20% 31% 17% 5%	1930
	11th to 20th	Night	37% 8% 14% 21% 16% 4	1920
	21st to end	Night	41% 7% 15% 24% 12% 1	2166
October	1st to 10th	Night	41% 6% 20% 25% 8%	3800
	11th to 20th	Night	53% 5% 16% 21% 5%	3777
	21st to end	Night	53% 7% 15% 17% 9%	4313
November	1st to 10th	Night	63% 8% 12% 13% 3 1	2730
	11th to 20th	Night	60% 6% 14% 12% 5% 2	2800
	21st to end	Night	64% 9% 12% 10% 5% 1	2800
December	1st to 10th	Night	57% 8% 14% 17% 4	4560
	11th to 20th	Night	73% 8% 10% 6% 2	5518
	21st to end	Night	65% 9% 12% 10% 2	7458

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	27% 12% 31% 18% 12% 1	200
	11th to 20th	Day	24% 13% 25% 22% 15% 2	200
	21st to end	Day	28% 9% 24% 23% 15% 1	292
February	1st to 10th	Day	27% 9% 25% 25% 13% 2	400
	11th to 20th	Day	25% 9% 21% 29% 14% 2	395
	21st to end	Day	20% 16% 20% 25% 15% 4	338
March	1st to 10th	Day	20% 7% 20% 30% 19% 4	500
	11th to 20th	Day	23% 8% 19% 25% 18% 7%	500
	21st to end	Day	22% 9% 18% 29% 19% 4	550
April	1st to 10th	Day	15% 10% 21% 28% 20% 6%	500
	11th to 20th	Day	16% 5% 18% 32% 19% 9%	492
	21st to end	Day	17% 6% 19% 26% 24% 9%	500
May	1st to 10th	Day	11% 6% 13% 27% 36% 8%	503
	11th to 20th	Day	13% 5% 12% 24% 33% 13%	528
	21st to end	Day	12% 4 12% 32% 27% 12%	594
June	1st to 10th	Day	13% 4 14% 32% 29% 8%	730
	11th to 20th	Day	9% 7% 18% 36% 24% 6%	730
	21st to end	Day	8% 2 13% 30% 33% 14%	730
July	1st to 10th	Day	7% 2 9% 30% 35% 16%	721
	11th to 20th	Day	4 1 10% 30% 39% 15%	718
	21st to end	Day	3 2 7% 24% 39% 24%	605
August	1st to 10th	Day	5% 2 6% 23% 35% 29%	527
	11th to 20th	Day	4 2 6% 21% 44% 23%	517
	21st to end	Day	8% 2 9% 26% 39% 16%	583
September	1st to 10th	Day	10% 1 7% 28% 39% 15%	503
	11th to 20th	Day	12% 2 11% 26% 32% 16%	490
	21st to end	Day	15% 5% 12% 27% 31% 10%	490
October	1st to 10th	Day	19% 5% 15% 25% 25% 12%	490
	11th to 20th	Day	25% 6% 14% 25% 21% 9%	490
	21st to end	Day	22% 12% 22% 28% 12% 5%	436
November	1st to 10th	Day	28% 6% 24% 29% 14% 1	200
	11th to 20th	Day	25% 11% 20% 22% 18% 6%	200
	21st to end	Day	26% 12% 25% 20% 12% 6%	200
December	1st to 10th	Day	28% 9% 24% 18% 19% 3	200
	11th to 20th	Day	33% 18% 19% 21% 11%	200
	21st to end	Day	35% 15% 24% 20% 7%	220
January	1st to 10th	Night	30% 10% 26% 21% 11% 2	900
	11th to 20th	Night	28% 9% 18% 25% 19% 1	893
	21st to end	Night	27% 8% 18% 25% 19% 4	880
February	1st to 10th	Night	28% 10% 21% 26% 13% 3	800
	11th to 20th	Night	25% 8% 21% 27% 17% 2	784
	21st to end	Night	25% 12% 23% 22% 13% 5%	660
March	1st to 10th	Night	21% 9% 20% 27% 19% 5%	800
	11th to 20th	Night	22% 9% 22% 24% 18% 5%	800
	21st to end	Night	23% 10% 18% 27% 18% 4	880
April	1st to 10th	Night	20% 8% 20% 27% 21% 4	800
	11th to 20th	Night	17% 5% 24% 29% 20% 5%	687
	21st to end	Night	19% 5% 22% 33% 16% 5%	580
May	1st to 10th	Night	11% 4 21% 33% 26% 6%	400
	11th to 20th	Night	11% 4 18% 28% 32% 8%	394
	21st to end	Night	11% 4 18% 31% 29% 6%	433
June	1st to 10th	Night	15% 5% 20% 28% 31% 3	400
	11th to 20th	Night	13% 3 22% 37% 21% 4	400
	21st to end	Night	11% 4 16% 32% 28% 10%	400
July	1st to 10th	Night	9% 2 14% 32% 37% 7%	390
	11th to 20th	Night	6% 1 14% 37% 36% 6%	388
	21st to end	Night	4 3 10% 34% 39% 10%	438
August	1st to 10th	Night	5% 2 8% 29% 41% 15%	469
	11th to 20th	Night	5% 2 6% 23% 48% 16%	594
	21st to end	Night	9% 2 11% 29% 40% 9%	720
September	1st to 10th	Night	8% 2 8% 33% 35% 15%	772
	11th to 20th	Night	13% 3 10% 25% 31% 18%	760
	21st to end	Night	15% 4 14% 28% 31% 9%	760
October	1st to 10th	Night	18% 3 13% 25% 28% 13%	760
	11th to 20th	Night	23% 4 14% 26% 24% 9%	760
	21st to end	Night	25% 6% 20% 26% 19% 5%	836
November	1st to 10th	Night	29% 7% 21% 25% 16% 2	780
	11th to 20th	Night	28% 10% 22% 22% 15% 3	800
	21st to end	Night	27% 9% 22% 23% 14% 5%	800
December	1st to 10th	Night	25% 9% 18% 27% 19% 3	800
	11th to 20th	Night	30% 11% 26% 22% 10% 1	887
	21st to end	Night	31% 12% 28% 20% 8% 1	990

Page generated at 2025-08-31 22:51:08. Version ac07

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