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 2024-01-14.

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% 3 5% 5% 3 5% 5% 6% 8% 41%	74899
	Night	13% 5% 2 4 4 3 4 4 5% 8% 47%	74885
Transparency	Day	40% 7% 11% 19% 15% 7%	74624
	Night	36% 6% 13% 20% 16% 9%	74680
Seeing	Day	13% 6% 21% 30% 22% 9%	13565
	Night	15% 5% 21% 34% 22% 2	23609

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	20% 5% 3 4 5% 2 5% 4 4 5% 43%	1707
	11th to 20th	Day	22% 5% 3 5% 4 3 3 3 4 5% 43%	1647
	21st to end	Day	17% 8% 3 5% 5% 3 4 3 4 5% 44%	1863
February	1st to 10th	Day	22% 8% 3 5% 4 2 4 4 4 5% 39%	1800
	11th to 20th	Day	19% 9% 2 6% 4 2 4 4 5% 5% 39%	1749
	21st to end	Day	20% 7% 3 5% 4 2 3 4 5% 6% 41%	1547
March	1st to 10th	Day	20% 7% 3 7% 5% 3 4 3 6% 7% 35%	1980
	11th to 20th	Day	18% 6% 4 7% 6% 3 4 5% 4 5% 39%	1980
	21st to end	Day	14% 6% 3 5% 5% 3 4 4 6% 8% 43%	2178
April	1st to 10th	Day	14% 7% 3 5% 6% 3 4 5% 6% 6% 40%	1980
	11th to 20th	Day	18% 7% 3 5% 5% 3 5% 4 5% 7% 39%	1969
	21st to end	Day	13% 7% 3 6% 5% 3 4 6% 5% 6% 42%	2160
May	1st to 10th	Day	12% 6% 3 6% 6% 3 5% 4 6% 8% 41%	2335
	11th to 20th	Day	11% 5% 3 5% 5% 3 6% 6% 6% 8% 40%	2302
	21st to end	Day	8% 6% 3 6% 6% 4 6% 6% 8% 12% 34%	2531
June	1st to 10th	Day	5% 4 2 4 6% 3 6% 7% 8% 11% 43%	2340
	11th to 20th	Day	5% 4 3 5% 6% 4 6% 6% 8% 11% 43%	2340
	21st to end	Day	7% 5% 3 7% 7% 5% 8% 7% 8% 10% 31%	2340
July	1st to 10th	Day	11% 6% 3 6% 6% 4 6% 6% 8% 10% 33%	2340
	11th to 20th	Day	4 4 3 5% 8% 4 7% 7% 8% 11% 40%	2340
	21st to end	Day	5% 3 2 5% 6% 4 7% 7% 8% 12% 42%	2546
August	1st to 10th	Day	2 2 2 4 5% 3 7% 6% 7% 11% 50%	2328
	11th to 20th	Day	4 4 2 4 5% 4 7% 8% 8% 12% 42%	2207
	21st to end	Day	8% 5% 3 6% 7% 5% 8% 7% 8% 11% 35%	2178
September	1st to 10th	Day	8% 5% 3 8% 8% 5% 7% 6% 7% 10% 33%	1980
	11th to 20th	Day	10% 6% 3 7% 8% 4 6% 6% 6% 7% 35%	1980
	21st to end	Day	9% 5% 2 5% 6% 4 6% 6% 7% 9% 43%	1980
October	1st to 10th	Day	6% 3 2 5% 5% 4 5% 5% 6% 7% 51%	1980
	11th to 20th	Day	12% 6% 3 4 4 3 4 4 5% 6% 49%	1800
	21st to end	Day	11% 4 2 4 5% 3 5% 4 4 7% 52%	1980
November	1st to 10th	Day	12% 6% 2 5% 6% 4 5% 5% 5% 8% 42%	1858
	11th to 20th	Day	14% 6% 3 5% 5% 3 4 5% 4 6% 46%	1900
	21st to end	Day	17% 7% 2 6% 6% 3 4 4 5% 5% 39%	1748
December	1st to 10th	Day	22% 6% 3 5% 4 2 4 3 5% 5% 40%	1710
	11th to 20th	Day	17% 8% 3 5% 6% 3 4 4 4 6% 39%	2161
	21st to end	Day	16% 6% 3 6% 4 3 3 3 4 7% 45%	3135
January	1st to 10th	Night	20% 6% 2 4 4 2 3 3 5% 5% 46%	2458
	11th to 20th	Night	19% 6% 3 4 4 2 3 3 3 6% 48%	2392
	21st to end	Night	20% 5% 3 5% 4 3 3 3 4 5% 44%	2507
February	1st to 10th	Night	20% 8% 3 6% 5% 2 4 4 4 6% 39%	2160
	11th to 20th	Night	22% 6% 2 4 4 2 3 4 4 6% 44%	2098
	21st to end	Night	23% 8% 3 5% 3 3 4 3 4 5% 40%	1707
March	1st to 10th	Night	19% 7% 3 4 4 3 3 4 4 7% 40%	1980
	11th to 20th	Night	18% 8% 4 5% 5% 3 4 4 5% 7% 38%	1980
	21st to end	Night	16% 7% 2 4 3 2 3 4 4 7% 48%	2178
April	1st to 10th	Night	16% 7% 2 5% 4 3 5% 5% 6% 8% 38%	1980
	11th to 20th	Night	19% 6% 3 4 4 3 4 4 4 8% 42%	1939
	21st to end	Night	18% 7% 3 5% 4 3 4 4 5% 7% 40%	1800
May	1st to 10th	Night	14% 7% 3 5% 6% 4 4 5% 6% 7% 41%	1620
	11th to 20th	Night	11% 5% 1 4 4 3 5% 5% 6% 9% 45%	1593
	21st to end	Night	9% 5% 2 4 6% 3 5% 6% 8% 11% 40%	1745
June	1st to 10th	Night	6% 3 2 3 4 2 4 4 6% 11% 56%	1620
	11th to 20th	Night	5% 3 2 3 4 3 5% 5% 7% 10% 52%	1620
	21st to end	Night	7% 4 2 5% 5% 4 6% 7% 8% 10% 42%	1620
July	1st to 10th	Night	7% 4 2 5% 5% 2 5% 6% 7% 11% 44%	1620
	11th to 20th	Night	3 2 2 3 3 2 4 6% 7% 11% 56%	1620
	21st to end	Night	2 1 1 3 3 3 4 5% 6% 13% 56%	1772
August	1st to 10th	Night	1 1 2 2 2 4 4 5% 10% 68%	1611
	11th to 20th	Night	3 3 1 4 3 2 4 5% 7% 11% 56%	1690
	21st to end	Night	5% 3 1 3 5% 4 4 4 8% 12% 50%	2174
September	1st to 10th	Night	6% 4 2 4 6% 3 4 6% 7% 10% 48%	1980
	11th to 20th	Night	9% 5% 2 5% 5% 3 4 5% 6% 9% 48%	1980
	21st to end	Night	8% 3 2 4 4 3 4 5% 5% 9% 54%	1980
October	1st to 10th	Night	5% 4 2 4 3 2 4 4 5% 7% 60%	1980
	11th to 20th	Night	9% 6% 2 4 3 2 3 3 4 5% 59%	2140
	21st to end	Night	11% 4 1 2 3 2 3 3 3 5% 63%	2376
November	1st to 10th	Night	9% 4 2 4 4 3 3 4 5% 6% 55%	2220
	11th to 20th	Night	15% 6% 2 4 4 2 4 4 4 5% 50%	2280
	21st to end	Night	16% 6% 2 5% 5% 3 4 5% 5% 6% 43%	2427
December	1st to 10th	Night	20% 6% 2 4 4 2 4 3 4 6% 44%	2470
	11th to 20th	Night	18% 7% 3 6% 5% 3 4 5% 5% 6% 39%	3036
	21st to end	Night	15% 7% 3 6% 5% 3 4 3 4 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	45% 4 6% 14% 19% 12%	1708
	11th to 20th	Day	44% 4 6% 13% 17% 15%	1647
	21st to end	Day	43% 4 6% 15% 20% 13%	1863
February	1st to 10th	Day	49% 4 6% 11% 18% 13%	1800
	11th to 20th	Day	47% 4 8% 15% 15% 11%	1759
	21st to end	Day	44% 6% 9% 15% 16% 11%	1547
March	1st to 10th	Day	48% 6% 9% 14% 15% 7%	1980
	11th to 20th	Day	48% 5% 7% 12% 16% 12%	1980
	21st to end	Day	39% 6% 10% 17% 17% 11%	2178
April	1st to 10th	Day	43% 6% 9% 15% 17% 8%	1980
	11th to 20th	Day	46% 6% 7% 15% 15% 11%	1969
	21st to end	Day	41% 7% 7% 18% 17% 9%	2160
May	1st to 10th	Day	41% 7% 10% 21% 14% 8%	2335
	11th to 20th	Day	39% 8% 10% 20% 18% 4	2306
	21st to end	Day	41% 9% 13% 21% 14% 2	2531
June	1st to 10th	Day	31% 9% 16% 26% 17% 1	2340
	11th to 20th	Day	34% 8% 13% 27% 15% 4	2340
	21st to end	Day	44% 10% 13% 23% 9% 1	2340
July	1st to 10th	Day	41% 11% 15% 24% 8%	2276
	11th to 20th	Day	34% 11% 18% 24% 13%	2271
	21st to end	Day	28% 12% 22% 31% 6% 1	2405
August	1st to 10th	Day	26% 10% 18% 35% 11%	2314
	11th to 20th	Day	32% 12% 18% 29% 9% 1	2207
	21st to end	Day	41% 11% 17% 21% 8% 2	2178
September	1st to 10th	Day	44% 11% 12% 15% 14% 4	1980
	11th to 20th	Day	45% 8% 12% 18% 13% 3	1980
	21st to end	Day	36% 8% 13% 17% 17% 9%	1980
October	1st to 10th	Day	31% 6% 12% 22% 21% 10%	1980
	11th to 20th	Day	35% 5% 10% 17% 18% 15%	1800
	21st to end	Day	32% 5% 8% 15% 22% 18%	1980
November	1st to 10th	Day	40% 6% 11% 15% 19% 9%	1858
	11th to 20th	Day	40% 5% 9% 17% 17% 13%	1900
	21st to end	Day	47% 5% 8% 15% 15% 11%	1748
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	41% 3 8% 13% 20% 14%	2458
	11th to 20th	Night	40% 3 6% 17% 17% 15%	2392
	21st to end	Night	43% 3 6% 15% 18% 15%	2507
February	1st to 10th	Night	48% 4 9% 10% 16% 14%	2160
	11th to 20th	Night	43% 5% 7% 16% 16% 13%	2098
	21st to end	Night	48% 4 7% 15% 15% 11%	1707
March	1st to 10th	Night	44% 6% 11% 16% 15% 9%	1980
	11th to 20th	Night	46% 6% 9% 13% 14% 11%	1980
	21st to end	Night	39% 4 13% 15% 18% 12%	2178
April	1st to 10th	Night	43% 6% 12% 17% 14% 8%	1980
	11th to 20th	Night	43% 4 10% 15% 13% 14%	1939
	21st to end	Night	44% 6% 10% 17% 15% 9%	1800
May	1st to 10th	Night	42% 6% 12% 17% 13% 9%	1620
	11th to 20th	Night	35% 7% 13% 24% 18% 3	1594
	21st to end	Night	36% 10% 17% 25% 12% 1	1746
June	1st to 10th	Night	23% 7% 19% 32% 17% 1	1620
	11th to 20th	Night	26% 8% 12% 34% 17% 3	1620
	21st to end	Night	34% 10% 20% 26% 9% 1	1620
July	1st to 10th	Night	33% 10% 22% 29% 6%	1575
	11th to 20th	Night	20% 10% 28% 32% 10%	1566
	21st to end	Night	18% 9% 32% 34% 6% 1	1673
August	1st to 10th	Night	12% 6% 29% 44% 8%	1601
	11th to 20th	Night	22% 8% 31% 33% 6%	1690
	21st to end	Night	25% 11% 25% 29% 8% 2	2174
September	1st to 10th	Night	30% 10% 23% 21% 13% 4	1980
	11th to 20th	Night	34% 8% 18% 24% 13% 3	1980
	21st to end	Night	27% 8% 15% 25% 18% 7%	1980
October	1st to 10th	Night	23% 6% 12% 27% 20% 11%	1980
	11th to 20th	Night	29% 4 11% 22% 20% 14%	2140
	21st to end	Night	26% 5% 7% 18% 24% 20%	2376
November	1st to 10th	Night	31% 6% 12% 20% 22% 10%	2220
	11th to 20th	Night	37% 5% 12% 16% 18% 13%	2280
	21st to end	Night	41% 5% 9% 18% 17% 10%	2427
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	28% 10% 29% 24% 7% 1	249
	21st to end	Day	20% 12% 37% 21% 10%	264
February	1st to 10th	Day	29% 13% 28% 20% 10% 1	240
	11th to 20th	Day	25% 17% 29% 22% 7%	240
	21st to end	Day	24% 13% 42% 16% 5%	198
March	1st to 10th	Day	22% 14% 37% 22% 5%	240
	11th to 20th	Day	20% 14% 40% 20% 5%	240
	21st to end	Day	15% 15% 40% 21% 8%	264
April	1st to 10th	Day	17% 14% 40% 22% 7%	240
	11th to 20th	Day	20% 16% 32% 23% 7% 2	247
	21st to end	Day	17% 9% 35% 28% 11%	420
May	1st to 10th	Day	12% 9% 44% 25% 9%	598
	11th to 20th	Day	13% 5% 33% 33% 13% 2	625
	21st to end	Day	9% 5% 31% 34% 18% 3	679
June	1st to 10th	Day	7% 1 15% 37% 32% 9%	630
	11th to 20th	Day	7% 2 17% 41% 27% 7%	630
	21st to end	Day	9% 3 12% 35% 29% 12%	630
July	1st to 10th	Day	9% 2 8% 36% 30% 15%	621
	11th to 20th	Day	4 1 4 35% 38% 18%	618
	21st to end	Day	4 1 5% 36% 36% 18%	684
August	1st to 10th	Day	3 1 4 34% 37% 21%	626
	11th to 20th	Day	3 1 4 34% 37% 21%	521
	21st to end	Day	9% 2 4 20% 29% 35%	297
September	1st to 10th	Day	9% 1 4 23% 41% 22%	270
	11th to 20th	Day	9% 2 4 23% 40% 22%	270
	21st to end	Day	10% 1 6% 32% 37% 14%	270
October	1st to 10th	Day	6% 2 13% 29% 39% 11%	270
	11th to 20th	Day	12% 3 13% 37% 24% 11%	270
	21st to end	Day	15% 7% 26% 27% 20% 5%	297
November	1st to 10th	Day	15% 5% 19% 32% 24% 5%	270
	11th to 20th	Day	22% 4 20% 31% 19% 4	270
	21st to end	Day	23% 13% 30% 20% 11% 3	270
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%	920
	21st to end	Night	23% 7% 30% 34% 6%	923
February	1st to 10th	Night	25% 11% 28% 30% 6%	720
	11th to 20th	Night	23% 10% 27% 33% 6%	704
	21st to end	Night	28% 9% 35% 24% 4	523
March	1st to 10th	Night	24% 8% 28% 33% 7%	540
	11th to 20th	Night	22% 8% 30% 34% 6%	540
	21st to end	Night	18% 7% 34% 33% 7%	594
April	1st to 10th	Night	20% 6% 36% 32% 6%	540
	11th to 20th	Night	23% 8% 28% 32% 9%	533
	21st to end	Night	22% 7% 34% 29% 8%	540
May	1st to 10th	Night	15% 5% 37% 35% 7%	540
	11th to 20th	Night	13% 3 27% 40% 15% 1	531
	21st to end	Night	10% 3 23% 45% 18% 1	584
June	1st to 10th	Night	6% 1 10% 48% 34% 1	540
	11th to 20th	Night	5% 1 13% 53% 26% 1	540
	21st to end	Night	8% 1 10% 38% 37% 6%	540
July	1st to 10th	Night	7% 1 5% 38% 43% 6%	525
	11th to 20th	Night	3 1 3 33% 52% 7%	522
	21st to end	Night	2 1 4 36% 50% 6%	591
August	1st to 10th	Night	1 3 34% 54% 7%	537
	11th to 20th	Night	4 1 2 32% 54% 6%	534
	21st to end	Night	6% 1 4 26% 52% 13%	594
September	1st to 10th	Night	7% 1 2 27% 54% 9%	540
	11th to 20th	Night	11% 1 2 29% 47% 8%	540
	21st to end	Night	8% 7% 30% 50% 5%	540
October	1st to 10th	Night	6% 3 7% 35% 45% 4	540
	11th to 20th	Night	11% 3 16% 43% 24% 2	700
	21st to end	Night	10% 5% 21% 40% 21% 1	792
November	1st to 10th	Night	10% 4 17% 42% 24% 2	740
	11th to 20th	Night	19% 5% 22% 35% 19% 1	760
	21st to end	Night	18% 7% 26% 32% 16% 1	907
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

Page generated at 2024-01-11 12:32:00. Version ac07

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