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 2024-11-28.

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% 5% 5% 5% 4 6% 8% 40%	101212
	Night	14% 6% 2 5% 4 3 4 3 5% 7% 46%	98418
Transparency	Day	39% 7% 11% 21% 15% 7%	104994
	Night	36% 6% 13% 21% 16% 9%	102763
Seeing	Day	13% 6% 21% 29% 22% 9%	14751
	Night	15% 5% 21% 34% 22% 2	24672

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	19% 10% 3 6% 4 4 3 3 4 5% 40%	2847
	11th to 20th	Day	17% 6% 2 4 3 2 3 2 4 6% 52%	2850
	21st to end	Day	23% 7% 3 5% 4 4 4 3 6% 6% 36%	3272
February	1st to 10th	Day	22% 9% 3 6% 3 3 3 4 4 4 39%	1900
	11th to 20th	Day	19% 9% 2 7% 4 3 4 3 5% 5% 40%	1849
	21st to end	Day	19% 8% 2 6% 4 3 3 3 5% 6% 42%	1641
March	1st to 10th	Day	17% 8% 3 8% 5% 5% 5% 4 7% 8% 31%	3436
	11th to 20th	Day	22% 9% 4 9% 6% 5% 5% 4 5% 5% 28%	3480
	21st to end	Day	13% 5% 3 6% 5% 4 4 3 6% 8% 44%	3814
April	1st to 10th	Day	14% 8% 2 6% 5% 4 5% 4 6% 6% 40%	2090
	11th to 20th	Day	17% 7% 3 6% 5% 4 4 3 5% 7% 38%	2080
	21st to end	Day	13% 8% 2 7% 5% 4 4 5% 5% 6% 41%	2280
May	1st to 10th	Day	19% 7% 2 8% 5% 4 4 4 6% 7% 33%	4077
	11th to 20th	Day	14% 6% 3 7% 5% 4 4 4 6% 6% 41%	4082
	21st to end	Day	7% 5% 2 6% 5% 5% 5% 5% 8% 11% 41%	4477
June	1st to 10th	Day	5% 4 2 5% 5% 5% 6% 5% 9% 10% 43%	2470
	11th to 20th	Day	5% 4 2 6% 5% 5% 6% 5% 9% 11% 42%	2470
	21st to end	Day	7% 6% 3 8% 7% 7% 7% 5% 9% 10% 32%	2470
July	1st to 10th	Day	8% 5% 2 6% 5% 6% 6% 5% 7% 10% 39%	4120
	11th to 20th	Day	6% 7% 3 8% 8% 7% 8% 5% 9% 11% 28%	4120
	21st to end	Day	12% 7% 3 7% 6% 5% 6% 5% 7% 10% 31%	4465
August	1st to 10th	Day	1 1 1 3 3 3 4 4 6% 10% 63%	4104
	11th to 20th	Day	2 3 2 4 4 5% 6% 6% 9% 13% 47%	3863
	21st to end	Day	6% 5% 2 7% 6% 7% 7% 5% 8% 11% 37%	3828
September	1st to 10th	Day	8% 6% 2 10% 6% 7% 7% 5% 7% 10% 32%	2090
	11th to 20th	Day	10% 7% 3 8% 6% 6% 6% 5% 6% 7% 36%	2090
	21st to end	Day	8% 5% 1 5% 5% 5% 6% 5% 7% 9% 44%	2090
October	1st to 10th	Day	6% 4 2 6% 4 5% 5% 5% 6% 7% 52%	2090
	11th to 20th	Day	11% 6% 2 4 3 4 4 3 5% 6% 50%	1900
	21st to end	Day	10% 4 2 4 4 4 5% 3 4 7% 52%	2090
November	1st to 10th	Day	12% 6% 2 6% 5% 5% 5% 4 6% 7% 42%	1958
	11th to 20th	Day	14% 6% 2 6% 4 4 3 4 4 6% 47%	2000
	21st to end	Day	16% 7% 2 7% 6% 4 4 3 5% 5% 41%	1813
December	1st to 10th	Day	21% 7% 2 5% 4 3 4 3 5% 5% 40%	1710
	11th to 20th	Day	17% 8% 3 6% 5% 4 4 4 5% 6% 39%	2161
	21st to end	Day	16% 7% 3 7% 4 4 3 2 4 7% 45%	3135
January	1st to 10th	Night	22% 10% 2 5% 3 2 3 2 4 5% 41%	4108
	11th to 20th	Night	15% 6% 2 4 3 2 2 2 3 7% 54%	4120
	21st to end	Night	26% 6% 2 6% 4 3 3 3 5% 7% 36%	4423
February	1st to 10th	Night	20% 8% 3 7% 4 4 3 3 4 5% 39%	2280
	11th to 20th	Night	21% 6% 2 5% 3 3 3 3 4 6% 44%	2218
	21st to end	Night	22% 9% 3 5% 3 4 3 3 4 5% 40%	1811
March	1st to 10th	Night	25% 10% 2 5% 3 4 4 4 5% 6% 31%	3419
	11th to 20th	Night	27% 8% 3 7% 5% 4 4 3 4 6% 27%	3480
	21st to end	Night	16% 7% 2 5% 3 3 3 3 4 6% 49%	3817
April	1st to 10th	Night	17% 8% 2 5% 4 4 5% 4 6% 7% 38%	2090
	11th to 20th	Night	20% 6% 2 5% 4 4 3 3 5% 7% 40%	2048
	21st to end	Night	18% 8% 3 6% 4 4 3 4 6% 6% 39%	1900
May	1st to 10th	Night	29% 8% 3 5% 4 3 3 3 5% 6% 30%	2823
	11th to 20th	Night	16% 7% 2 5% 3 4 4 4 5% 7% 42%	2823
	21st to end	Night	14% 6% 2 6% 5% 4 4 4 7% 10% 37%	3090
June	1st to 10th	Night	6% 3 2 3 3 3 4 4 6% 11% 55%	1710
	11th to 20th	Night	5% 4 2 4 4 4 5% 4 7% 9% 53%	1710
	21st to end	Night	7% 5% 2 6% 4 4 6% 5% 8% 10% 44%	1710
July	1st to 10th	Night	6% 3 1 4 4 3 5% 4 6% 9% 54%	2850
	11th to 20th	Night	4 5% 2 7% 5% 5% 6% 5% 8% 10% 43%	2850
	21st to end	Night	8% 5% 3 6% 4 5% 5% 5% 7% 11% 41%	3098
August	1st to 10th	Night	1 1 2 1 2 3 2 4 7% 77%	2836
	11th to 20th	Night	2 2 1 3 2 3 4 4 7% 12% 61%	2958
	21st to end	Night	4 2 1 3 4 4 4 3 8% 12% 55%	3824
September	1st to 10th	Night	6% 4 2 6% 5% 4 5% 4 7% 10% 47%	2090
	11th to 20th	Night	8% 5% 2 6% 4 4 4 4 6% 8% 49%	2090
	21st to end	Night	7% 3 2 4 3 3 4 4 5% 9% 55%	2090
October	1st to 10th	Night	4 4 1 4 3 3 4 3 5% 7% 61%	2090
	11th to 20th	Night	9% 6% 1 4 3 2 2 2 4 5% 60%	2259
	21st to end	Night	10% 4 1 3 3 2 3 3 4 4 63%	2508
November	1st to 10th	Night	10% 5% 2 5% 4 4 4 3 5% 6% 53%	2340
	11th to 20th	Night	14% 6% 2 5% 3 3 4 3 4 5% 51%	2400
	21st to end	Night	15% 6% 2 6% 4 4 5% 4 5% 6% 44%	2517
December	1st to 10th	Night	20% 6% 2 5% 4 3 4 3 4 6% 44%	2470
	11th to 20th	Night	18% 7% 3 7% 5% 4 4 4 5% 6% 39%	3036
	21st to end	Night	15% 7% 3 7% 4 4 4 2 5% 6% 44%	4532

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	48% 4 5% 13% 18% 12%	2848
	11th to 20th	Day	34% 4 6% 23% 19% 13%	2850
	21st to end	Day	47% 3 5% 14% 23% 7%	3272
February	1st to 10th	Day	48% 4 6% 11% 18% 13%	1900
	11th to 20th	Day	47% 4 8% 15% 15% 12%	1859
	21st to end	Day	44% 6% 9% 15% 15% 11%	1641
March	1st to 10th	Day	49% 7% 10% 17% 12% 5%	3436
	11th to 20th	Day	58% 6% 7% 9% 13% 7%	3480
	21st to end	Day	37% 6% 10% 19% 18% 10%	3814
April	1st to 10th	Day	43% 7% 9% 15% 16% 10%	2090
	11th to 20th	Day	46% 6% 8% 15% 14% 11%	2080
	21st to end	Day	42% 7% 8% 19% 16% 9%	2280
May	1st to 10th	Day	49% 8% 12% 18% 10% 4	4115
	11th to 20th	Day	41% 8% 9% 18% 18% 6%	4086
	21st to end	Day	33% 8% 13% 36% 9% 1	4489
June	1st to 10th	Day	31% 9% 16% 26% 17% 1	2470
	11th to 20th	Day	34% 8% 13% 26% 16% 4	2470
	21st to end	Day	43% 10% 13% 24% 9% 1	2470
July	1st to 10th	Day	36% 10% 21% 28% 5%	4056
	11th to 20th	Day	45% 11% 17% 20% 8%	4051
	21st to end	Day	43% 11% 19% 24% 3	4325
August	1st to 10th	Day	17% 7% 13% 49% 15%	4090
	11th to 20th	Day	25% 11% 26% 31% 6% 1	3902
	21st to end	Day	37% 11% 16% 23% 11% 1	3827
September	1st to 10th	Day	44% 11% 12% 15% 14% 4	2090
	11th to 20th	Day	44% 8% 12% 19% 14% 3	2090
	21st to end	Day	34% 8% 13% 17% 17% 11%	2090
October	1st to 10th	Day	22% 4 8% 13% 19% 36%	3480
	11th to 20th	Day	26% 4 8% 19% 24% 18%	3140
	21st to end	Day	29% 4 8% 18% 27% 13%	3428
November	1st to 10th	Day	40% 6% 10% 15% 20% 9%	1958
	11th to 20th	Day	39% 5% 9% 16% 18% 14%	2000
	21st to end	Day	45% 5% 8% 15% 15% 12%	1813
December	1st to 10th	Day	47% 4 7% 17% 18% 7%	1710
	11th to 20th	Day	46% 6% 6% 10% 20% 12%	2159
	21st to end	Day	41% 4 6% 18% 19% 13%	3135
January	1st to 10th	Night	45% 3 8% 11% 15% 17%	4108
	11th to 20th	Night	32% 3 6% 18% 25% 15%	4120
	21st to end	Night	48% 4 6% 12% 21% 10%	4423
February	1st to 10th	Night	47% 4 9% 10% 16% 15%	2280
	11th to 20th	Night	43% 5% 7% 16% 16% 13%	2218
	21st to end	Night	47% 4 7% 15% 16% 11%	1811
March	1st to 10th	Night	52% 6% 10% 14% 12% 5%	3419
	11th to 20th	Night	58% 6% 8% 12% 9% 6%	3480
	21st to end	Night	37% 4 12% 15% 21% 11%	3817
April	1st to 10th	Night	43% 6% 12% 16% 13% 9%	2090
	11th to 20th	Night	44% 5% 10% 14% 13% 14%	2048
	21st to end	Night	44% 6% 10% 17% 14% 8%	1900
May	1st to 10th	Night	54% 6% 10% 15% 9% 5%	2850
	11th to 20th	Night	40% 7% 12% 20% 16% 6%	2824
	21st to end	Night	39% 9% 15% 28% 7%	3099
June	1st to 10th	Night	23% 7% 20% 32% 17% 1	1710
	11th to 20th	Night	26% 8% 12% 34% 18% 3	1710
	21st to end	Night	33% 9% 20% 28% 9% 1	1710
July	1st to 10th	Night	27% 8% 27% 35% 3	2805
	11th to 20th	Night	34% 9% 24% 24% 8%	2796
	21st to end	Night	36% 11% 25% 24% 3	2999
August	1st to 10th	Night	9% 4 18% 56% 13%	2826
	11th to 20th	Night	17% 7% 39% 33% 4	2985
	21st to end	Night	21% 12% 26% 31% 9% 1	3824
September	1st to 10th	Night	32% 10% 22% 20% 13% 4	2090
	11th to 20th	Night	33% 8% 17% 24% 14% 3	2090
	21st to end	Night	27% 8% 15% 25% 17% 9%	2090
October	1st to 10th	Night	16% 4 9% 17% 19% 35%	3480
	11th to 20th	Night	19% 3 10% 21% 30% 17%	3745
	21st to end	Night	20% 4 6% 26% 30% 14%	4120
November	1st to 10th	Night	32% 6% 12% 19% 21% 10%	2340
	11th to 20th	Night	36% 5% 11% 16% 18% 14%	2400
	21st to end	Night	40% 5% 8% 18% 17% 11%	2517
December	1st to 10th	Night	43% 4 9% 20% 16% 9%	2470
	11th to 20th	Night	46% 5% 7% 12% 16% 15%	3037
	21st to end	Night	42% 5% 7% 15% 22% 10%	4532

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% 8% 35% 24% 9% 1	270
	11th to 20th	Day	27% 11% 30% 23% 7% 1	270
	21st to end	Day	21% 12% 34% 21% 11%	297
February	1st to 10th	Day	27% 16% 27% 20% 10% 1	270
	11th to 20th	Day	25% 18% 29% 21% 6%	270
	21st to end	Day	23% 14% 43% 16% 4	225
March	1st to 10th	Day	21% 15% 37% 22% 6%	270
	11th to 20th	Day	20% 15% 41% 18% 5%	270
	21st to end	Day	15% 16% 40% 21% 7%	297
April	1st to 10th	Day	16% 17% 38% 22% 6%	270
	11th to 20th	Day	18% 15% 36% 22% 7% 1	278
	21st to end	Day	17% 10% 36% 27% 10%	460
May	1st to 10th	Day	14% 10% 44% 24% 8%	648
	11th to 20th	Day	13% 6% 33% 33% 12% 2	675
	21st to end	Day	9% 5% 33% 34% 17% 2	734
June	1st to 10th	Day	6% 2 17% 36% 30% 8%	680
	11th to 20th	Day	7% 2 17% 42% 26% 7%	680
	21st to end	Day	8% 3 13% 35% 29% 12%	680
July	1st to 10th	Day	9% 2 8% 36% 30% 15%	671
	11th to 20th	Day	5% 2 5% 34% 38% 17%	668
	21st to end	Day	6% 2 5% 36% 34% 17%	739
August	1st to 10th	Day	3 1 3 33% 37% 22%	676
	11th to 20th	Day	3 1 4 34% 37% 21%	565
	21st to end	Day	9% 2 4 20% 30% 35%	330
September	1st to 10th	Day	9% 2 8% 22% 39% 20%	300
	11th to 20th	Day	9% 2 5% 25% 38% 21%	300
	21st to end	Day	9% 1 6% 33% 37% 14%	300
October	1st to 10th	Day	6% 2 13% 30% 39% 10%	300
	11th to 20th	Day	11% 3 13% 37% 24% 11%	300
	21st to end	Day	14% 7% 26% 28% 19% 6%	330
November	1st to 10th	Day	15% 5% 22% 32% 22% 4	300
	11th to 20th	Day	21% 4 20% 32% 18% 5%	300
	21st to end	Day	22% 12% 30% 20% 12% 4	291
December	1st to 10th	Day	22% 8% 27% 26% 11% 6%	270
	11th to 20th	Day	25% 12% 30% 24% 8% 1	270
	21st to end	Day	23% 9% 34% 21% 10% 2	297
January	1st to 10th	Night	23% 9% 29% 30% 10% 1	950
	11th to 20th	Night	23% 7% 27% 34% 9%	950
	21st to end	Night	23% 7% 30% 34% 6%	975
February	1st to 10th	Night	24% 11% 28% 30% 6%	760
	11th to 20th	Night	23% 10% 28% 33% 6%	744
	21st to end	Night	27% 9% 35% 25% 4	555
March	1st to 10th	Night	24% 8% 29% 32% 6%	570
	11th to 20th	Night	23% 8% 30% 34% 5%	570
	21st to end	Night	18% 7% 35% 32% 7%	627
April	1st to 10th	Night	20% 7% 36% 31% 6%	570
	11th to 20th	Night	23% 9% 28% 32% 8%	563
	21st to end	Night	22% 7% 35% 28% 8%	570
May	1st to 10th	Night	17% 5% 37% 33% 7%	570
	11th to 20th	Night	13% 4 28% 40% 14% 1	561
	21st to end	Night	11% 3 25% 43% 18%	617
June	1st to 10th	Night	7% 1 11% 47% 33% 1	570
	11th to 20th	Night	6% 1 13% 53% 26% 1	570
	21st to end	Night	8% 1 11% 38% 36% 6%	570
July	1st to 10th	Night	6% 1 5% 39% 43% 6%	555
	11th to 20th	Night	3 1 3 34% 51% 7%	552
	21st to end	Night	3 1 5% 35% 49% 6%	624
August	1st to 10th	Night	1 3 34% 55% 7%	567
	11th to 20th	Night	4 1 2 33% 55% 5%	564
	21st to end	Night	5% 1 3 26% 53% 12%	627
September	1st to 10th	Night	8% 1 3 27% 52% 9%	570
	11th to 20th	Night	11% 2 3 30% 47% 8%	570
	21st to end	Night	8% 7% 30% 50% 5%	570
October	1st to 10th	Night	6% 2 7% 36% 45% 4	570
	11th to 20th	Night	10% 3 17% 44% 24% 2	739
	21st to end	Night	10% 5% 22% 40% 22% 2	836
November	1st to 10th	Night	11% 5% 18% 41% 23% 2	780
	11th to 20th	Night	19% 5% 22% 35% 19% 1	800
	21st to end	Night	18% 7% 26% 32% 16% 1	941
December	1st to 10th	Night	22% 8% 23% 32% 15% 2	950
	11th to 20th	Night	23% 9% 27% 31% 10% 1	950
	21st to end	Night	20% 8% 29% 32% 10%	1045

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