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 2024-03-28.

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	15% 8% 3 6% 6% 3 5% 5% 5% 7% 36%	78374
	Night	18% 9% 4 7% 6% 3 5% 5% 5% 6% 33%	81570
Transparency	Day	48% 9% 16% 19% 7% 1	78085
	Night	52% 8% 14% 17% 7% 1	81439
Seeing	Day	15% 5% 15% 27% 27% 11%	14481
	Night	20% 6% 18% 26% 23% 6%	22926

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% 11% 5% 9% 9% 4 5% 6% 5% 5% 14%	2219
	11th to 20th	Day	21% 14% 5% 8% 7% 4 5% 5% 5% 5% 22%	2209
	21st to end	Day	27% 17% 7% 11% 8% 5% 5% 4 4 4 9%	2901
February	1st to 10th	Day	25% 13% 4 7% 7% 4 5% 5% 7% 6% 17%	1710
	11th to 20th	Day	22% 12% 5% 8% 6% 4 4 5% 4 7% 24%	1665
	21st to end	Day	17% 12% 5% 8% 8% 5% 7% 5% 6% 6% 21%	1423
March	1st to 10th	Day	14% 11% 5% 8% 8% 5% 6% 6% 7% 8% 23%	1988
	11th to 20th	Day	20% 11% 5% 8% 5% 3 5% 5% 6% 6% 27%	2090
	21st to end	Day	18% 12% 4 8% 7% 4 6% 6% 6% 7% 22%	2295
April	1st to 10th	Day	17% 9% 4 7% 6% 3 7% 6% 7% 9% 26%	2160
	11th to 20th	Day	16% 8% 3 7% 6% 4 6% 6% 6% 7% 30%	2222
	21st to end	Day	15% 8% 3 6% 5% 3 5% 6% 6% 9% 33%	2358
May	1st to 10th	Day	11% 5% 3 7% 5% 4 6% 5% 5% 9% 40%	2520
	11th to 20th	Day	12% 6% 3 5% 6% 3 5% 6% 7% 8% 39%	2477
	21st to end	Day	14% 7% 3 6% 5% 3 5% 4 5% 7% 40%	2741
June	1st to 10th	Day	14% 6% 3 5% 7% 4 5% 4 6% 7% 40%	2700
	11th to 20th	Day	10% 6% 3 6% 6% 3 6% 5% 5% 9% 42%	2700
	21st to end	Day	8% 5% 2 4 4 3 4 6% 7% 8% 49%	2700
July	1st to 10th	Day	7% 4 2 3 3 2 5% 3 4 6% 60%	2700
	11th to 20th	Day	6% 2 1 4 4 2 4 4 5% 7% 62%	2700
	21st to end	Day	4 2 1 2 2 1 2 2 3 6% 75%	2769
August	1st to 10th	Day	6% 4 1 3 4 2 2 2 4 7% 66%	2441
	11th to 20th	Day	5% 3 1 3 3 2 4 3 5% 7% 62%	2298
	21st to end	Day	7% 4 2 4 4 2 4 4 5% 8% 56%	2520
September	1st to 10th	Day	7% 5% 2 4 4 3 3 4 4 8% 55%	2160
	11th to 20th	Day	11% 6% 3 6% 5% 4 4 4 5% 6% 45%	2138
	21st to end	Day	15% 7% 2 5% 5% 3 4 4 5% 8% 42%	1908
October	1st to 10th	Day	17% 7% 2 5% 6% 3 5% 6% 6% 6% 38%	1800
	11th to 20th	Day	20% 11% 4 7% 7% 4 5% 5% 5% 7% 26%	1800
	21st to end	Day	21% 9% 4 9% 5% 3 5% 5% 5% 8% 26%	1868
November	1st to 10th	Day	26% 11% 4 10% 7% 4 3 5% 5% 6% 18%	1488
	11th to 20th	Day	24% 10% 5% 8% 6% 5% 5% 4 4 6% 23%	1520
	21st to end	Day	25% 10% 6% 9% 8% 3 6% 4 4 6% 19%	1520
December	1st to 10th	Day	22% 13% 6% 7% 7% 3 5% 5% 4 5% 25%	1520
	11th to 20th	Day	25% 14% 5% 9% 8% 4 6% 7% 6% 4 13%	1704
	21st to end	Day	22% 17% 5% 11% 8% 4 5% 5% 5% 6% 12%	2442
January	1st to 10th	Night	23% 13% 5% 10% 9% 5% 6% 5% 5% 5% 14%	4726
	11th to 20th	Night	23% 12% 5% 8% 5% 3 4 4 4 6% 26%	4686
	21st to end	Night	27% 15% 6% 10% 7% 4 5% 4 4 4 14%	4755
February	1st to 10th	Night	24% 12% 4 7% 7% 3 5% 5% 5% 6% 22%	2470
	11th to 20th	Night	18% 11% 3 8% 6% 3 6% 4 5% 6% 29%	2402
	21st to end	Night	22% 12% 3 8% 6% 4 5% 4 5% 6% 25%	2030
March	1st to 10th	Night	17% 9% 3 7% 7% 4 6% 6% 7% 7% 27%	2190
	11th to 20th	Night	18% 10% 4 7% 6% 4 5% 6% 6% 8% 26%	2089
	21st to end	Night	20% 11% 5% 9% 7% 3 4 5% 6% 6% 24%	2215
April	1st to 10th	Night	19% 9% 4 6% 6% 3 5% 6% 5% 7% 29%	1800
	11th to 20th	Night	15% 8% 3 6% 6% 3 5% 6% 6% 8% 34%	1687
	21st to end	Night	17% 8% 4 8% 6% 3 5% 5% 5% 8% 34%	1602
May	1st to 10th	Night	10% 6% 3 5% 5% 4 4 5% 5% 7% 46%	1440
	11th to 20th	Night	10% 5% 3 6% 6% 4 5% 6% 6% 8% 41%	1416
	21st to end	Night	12% 6% 3 6% 5% 3 6% 4 6% 9% 41%	1530
June	1st to 10th	Night	14% 5% 4 5% 7% 3 4 5% 6% 6% 40%	1260
	11th to 20th	Night	12% 5% 3 5% 5% 3 4 5% 8% 10% 41%	1260
	21st to end	Night	7% 4 2 3 4 2 3 5% 7% 9% 52%	1260
July	1st to 10th	Night	8% 3 2 3 4 2 4 3 4 7% 61%	1260
	11th to 20th	Night	6% 2 2 4 3 2 3 3 4 5% 66%	1260
	21st to end	Night	3 2 1 2 1 1 2 2 4 5% 76%	1547
August	1st to 10th	Night	4 3 1 3 3 2 3 3 4 6% 68%	1495
	11th to 20th	Night	3 2 1 2 3 2 2 4 4 7% 70%	1602
	21st to end	Night	7% 3 1 4 3 2 3 4 5% 10% 57%	1836
September	1st to 10th	Night	7% 2 1 3 3 2 3 3 5% 7% 63%	1800
	11th to 20th	Night	13% 6% 3 4 4 3 3 5% 4 6% 50%	1818
	21st to end	Night	13% 6% 3 5% 5% 2 5% 4 4 7% 45%	2052
October	1st to 10th	Night	14% 7% 3 6% 5% 3 5% 5% 4 6% 44%	2160
	11th to 20th	Night	20% 7% 3 7% 4 3 3 5% 6% 6% 34%	2160
	21st to end	Night	23% 8% 2 6% 5% 3 4 4 5% 6% 34%	2482
November	1st to 10th	Night	25% 10% 4 7% 6% 4 6% 5% 5% 5% 23%	2590
	11th to 20th	Night	24% 10% 4 7% 6% 4 5% 5% 5% 7% 26%	2660
	21st to end	Night	21% 12% 5% 8% 7% 3 6% 5% 5% 5% 23%	2660
December	1st to 10th	Night	22% 11% 4 7% 6% 3 6% 4 5% 6% 25%	2660
	11th to 20th	Night	24% 14% 5% 10% 8% 4 6% 5% 5% 6% 14%	3496
	21st to end	Night	23% 15% 5% 8% 7% 4 5% 4 5% 5% 19%	5214

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	69% 11% 8% 9% 3	2219
	11th to 20th	Day	62% 10% 13% 9% 5%	2230
	21st to end	Day	76% 10% 8% 5% 1	2901
February	1st to 10th	Day	66% 10% 11% 9% 4 1	1710
	11th to 20th	Day	61% 10% 11% 13% 5%	1674
	21st to end	Day	61% 8% 12% 12% 6% 1	1423
March	1st to 10th	Day	55% 10% 15% 15% 4 1	1988
	11th to 20th	Day	56% 8% 14% 17% 4 1	2090
	21st to end	Day	60% 9% 15% 14% 2	2295
April	1st to 10th	Day	53% 10% 19% 15% 3	2160
	11th to 20th	Day	50% 9% 14% 19% 7% 1	2222
	21st to end	Day	47% 10% 15% 19% 7% 1	2358
May	1st to 10th	Day	42% 9% 20% 20% 7% 1	2520
	11th to 20th	Day	42% 9% 21% 21% 6%	2480
	21st to end	Day	44% 10% 21% 21% 5%	2742
June	1st to 10th	Day	44% 8% 22% 18% 7% 1	2700
	11th to 20th	Day	41% 8% 23% 22% 5%	2700
	21st to end	Day	34% 8% 24% 23% 9% 1	2700
July	1st to 10th	Day	27% 8% 19% 30% 13% 3	2626
	11th to 20th	Day	24% 7% 21% 33% 14% 1	2619
	21st to end	Day	13% 5% 21% 42% 15% 3	2615
August	1st to 10th	Day	21% 7% 23% 33% 13% 2	2424
	11th to 20th	Day	22% 9% 21% 33% 13% 2	2298
	21st to end	Day	27% 7% 23% 34% 8% 1	2520
September	1st to 10th	Day	30% 8% 21% 25% 13% 3	2160
	11th to 20th	Day	41% 10% 14% 21% 13% 1	2138
	21st to end	Day	43% 9% 16% 22% 9%	1908
October	1st to 10th	Day	47% 8% 17% 21% 7%	1800
	11th to 20th	Day	59% 8% 15% 14% 3	1800
	21st to end	Day	56% 9% 13% 13% 7%	1868
November	1st to 10th	Day	65% 9% 12% 10% 3 1	1488
	11th to 20th	Day	64% 7% 12% 13% 4 1	1520
	21st to end	Day	66% 9% 8% 12% 5%	1520
December	1st to 10th	Day	63% 8% 11% 13% 5%	1520
	11th to 20th	Day	72% 11% 8% 6% 2 1	1707
	21st to end	Day	70% 11% 10% 6% 3	2442
January	1st to 10th	Night	70% 9% 10% 7% 3	4726
	11th to 20th	Night	60% 7% 15% 15% 3 1	4727
	21st to end	Night	73% 10% 8% 8% 2	4755
February	1st to 10th	Night	64% 8% 13% 10% 4 1	2470
	11th to 20th	Night	57% 8% 13% 15% 6% 1	2404
	21st to end	Night	60% 7% 12% 13% 6% 1	2030
March	1st to 10th	Night	55% 9% 13% 16% 5%	2190
	11th to 20th	Night	54% 8% 13% 18% 4 2	2090
	21st to end	Night	61% 10% 13% 15% 2	2215
April	1st to 10th	Night	54% 9% 16% 16% 5%	1800
	11th to 20th	Night	49% 9% 13% 20% 7% 1	1687
	21st to end	Night	51% 8% 14% 18% 9%	1602
May	1st to 10th	Night	38% 8% 20% 22% 11% 1	1440
	11th to 20th	Night	40% 10% 19% 22% 8% 1	1416
	21st to end	Night	43% 9% 21% 21% 6%	1530
June	1st to 10th	Night	45% 7% 16% 24% 6% 2	1260
	11th to 20th	Night	38% 10% 23% 24% 4	1260
	21st to end	Night	30% 8% 25% 24% 10% 3	1260
July	1st to 10th	Night	25% 10% 18% 28% 16% 4	1225
	11th to 20th	Night	24% 5% 20% 30% 19% 2	1218
	21st to end	Night	11% 5% 17% 38% 24% 5%	1461
August	1st to 10th	Night	20% 8% 19% 31% 19% 4	1487
	11th to 20th	Night	15% 8% 22% 32% 17% 6%	1602
	21st to end	Night	24% 9% 20% 34% 13% 1	1836
September	1st to 10th	Night	22% 7% 20% 30% 16% 4	1800
	11th to 20th	Night	37% 7% 14% 21% 17% 4	1818
	21st to end	Night	41% 7% 15% 24% 12% 1	2052
October	1st to 10th	Night	45% 6% 15% 22% 12%	2160
	11th to 20th	Night	50% 7% 17% 19% 7%	2160
	21st to end	Night	52% 7% 13% 19% 9%	2482
November	1st to 10th	Night	62% 8% 12% 13% 4 1	2590
	11th to 20th	Night	60% 6% 14% 12% 5% 2	2660
	21st to end	Night	63% 8% 12% 10% 6% 1	2660
December	1st to 10th	Night	61% 7% 13% 13% 5%	2660
	11th to 20th	Night	71% 10% 11% 5% 3	3492
	21st to end	Night	66% 10% 11% 9% 3	5214

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	25% 12% 31% 19% 13% 1	180
	11th to 20th	Day	26% 13% 22% 22% 14% 2	180
	21st to end	Day	30% 8% 24% 23% 13% 1	266
February	1st to 10th	Day	28% 7% 24% 26% 14% 2	370
	11th to 20th	Day	24% 9% 21% 28% 15% 2	365
	21st to end	Day	19% 15% 21% 26% 16% 4	313
March	1st to 10th	Day	20% 7% 21% 29% 19% 4	460
	11th to 20th	Day	22% 7% 18% 25% 20% 8%	460
	21st to end	Day	21% 8% 17% 30% 20% 4	491
April	1st to 10th	Day	16% 10% 20% 27% 20% 7%	420
	11th to 20th	Day	19% 4 16% 30% 20% 11%	412
	21st to end	Day	17% 5% 19% 26% 24% 9%	420
May	1st to 10th	Day	11% 5% 12% 29% 36% 8%	423
	11th to 20th	Day	13% 3 10% 24% 34% 15%	448
	21st to end	Day	12% 3 10% 34% 28% 13%	503
June	1st to 10th	Day	14% 3 14% 32% 28% 9%	630
	11th to 20th	Day	9% 6% 16% 37% 26% 6%	630
	21st to end	Day	7% 2 11% 31% 35% 15%	630
July	1st to 10th	Day	7% 2 7% 28% 38% 18%	621
	11th to 20th	Day	5% 1 10% 29% 40% 16%	618
	21st to end	Day	2 1 6% 23% 41% 27%	515
August	1st to 10th	Day	5% 2 5% 21% 35% 32%	447
	11th to 20th	Day	3 1 4 19% 47% 25%	437
	21st to end	Day	7% 2 8% 26% 40% 17%	495
September	1st to 10th	Day	11% 1 8% 29% 39% 13%	450
	11th to 20th	Day	12% 2 10% 26% 34% 17%	450
	21st to end	Day	15% 4 11% 28% 32% 11%	450
October	1st to 10th	Day	19% 3 14% 25% 26% 13%	450
	11th to 20th	Day	23% 5% 14% 26% 22% 10%	450
	21st to end	Day	22% 11% 22% 28% 12% 6%	399
November	1st to 10th	Day	28% 4 25% 28% 13% 1	180
	11th to 20th	Day	25% 9% 20% 22% 18% 6%	180
	21st to end	Day	27% 11% 25% 19% 12% 6%	180
December	1st to 10th	Day	28% 9% 24% 18% 17% 3	180
	11th to 20th	Day	31% 16% 21% 22% 11%	180
	21st to end	Day	32% 14% 24% 22% 8%	198
January	1st to 10th	Night	30% 10% 26% 20% 12% 2	850
	11th to 20th	Night	29% 9% 18% 23% 19% 1	844
	21st to end	Night	28% 8% 18% 24% 19% 3	836
February	1st to 10th	Night	28% 9% 21% 26% 14% 3	760
	11th to 20th	Night	24% 8% 22% 27% 17% 2	744
	21st to end	Night	25% 12% 23% 21% 14% 5%	628
March	1st to 10th	Night	22% 10% 19% 26% 18% 5%	760
	11th to 20th	Night	21% 9% 22% 24% 19% 5%	760
	21st to end	Night	22% 10% 19% 27% 18% 4	820
April	1st to 10th	Night	21% 8% 20% 26% 21% 5%	720
	11th to 20th	Night	18% 5% 24% 28% 20% 6%	619
	21st to end	Night	20% 5% 21% 34% 16% 4	522
May	1st to 10th	Night	10% 4 21% 33% 27% 6%	360
	11th to 20th	Night	11% 3 15% 29% 34% 8%	354
	21st to end	Night	12% 3 17% 31% 31% 6%	389
June	1st to 10th	Night	15% 4 20% 28% 30% 3	360
	11th to 20th	Night	13% 2 21% 37% 22% 4	360
	21st to end	Night	10% 3 16% 32% 29% 10%	360
July	1st to 10th	Night	9% 1 11% 32% 39% 7%	350
	11th to 20th	Night	7% 1 11% 38% 37% 7%	348
	21st to end	Night	4 1 8% 34% 42% 11%	394
August	1st to 10th	Night	5% 2 7% 27% 42% 17%	421
	11th to 20th	Night	4 1 5% 22% 50% 18%	534
	21st to end	Night	8% 2 11% 30% 40% 9%	648
September	1st to 10th	Night	8% 2 8% 33% 35% 14%	720
	11th to 20th	Night	13% 2 9% 25% 32% 19%	720
	21st to end	Night	15% 3 13% 28% 31% 10%	720
October	1st to 10th	Night	18% 3 13% 25% 28% 13%	720
	11th to 20th	Night	23% 4 14% 26% 24% 9%	720
	21st to end	Night	25% 6% 20% 26% 19% 5%	792
November	1st to 10th	Night	28% 7% 22% 26% 16% 2	740
	11th to 20th	Night	27% 10% 23% 22% 15% 3	760
	21st to end	Night	26% 9% 22% 23% 14% 6%	760
December	1st to 10th	Night	26% 9% 18% 27% 18% 2	760
	11th to 20th	Night	29% 10% 27% 22% 10% 1	838
	21st to end	Night	31% 11% 28% 20% 8% 1	935

Page generated at 2024-03-24 20:36:59. Version ac07

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