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 2024-11-04.

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	14% 8% 3 7% 5% 4 4 4 5% 7% 40%	105515
	Night	17% 9% 3 8% 5% 4 4 3 5% 6% 36%	102089
Transparency	Day	44% 8% 17% 21% 9% 1	105265
	Night	49% 8% 15% 19% 8% 1	101985
Seeing	Day	15% 5% 15% 27% 27% 11%	15404
	Night	20% 6% 18% 26% 22% 6%	23577

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	26% 12% 4 11% 7% 5% 5% 4 5% 5% 14%	2219
	11th to 20th	Day	20% 15% 5% 9% 6% 5% 4 4 5% 5% 22%	2209
	21st to end	Day	27% 18% 6% 13% 7% 6% 4 3 4 4 9%	2901
February	1st to 10th	Day	24% 15% 4 9% 5% 6% 4 4 7% 6% 17%	1710
	11th to 20th	Day	22% 12% 5% 9% 5% 5% 4 4 4 6% 24%	1665
	21st to end	Day	17% 13% 4 9% 7% 7% 6% 4 6% 6% 21%	1423
March	1st to 10th	Day	10% 12% 4 10% 7% 7% 6% 6% 8% 9% 20%	3286
	11th to 20th	Day	13% 10% 4 8% 4 4 4 4 6% 7% 38%	3490
	21st to end	Day	16% 12% 4 9% 6% 5% 5% 4 6% 7% 25%	3902
April	1st to 10th	Day	17% 11% 3 8% 6% 5% 6% 5% 7% 8% 25%	2280
	11th to 20th	Day	15% 9% 3 7% 5% 5% 5% 5% 6% 7% 31%	2348
	21st to end	Day	15% 9% 3 7% 5% 4 5% 5% 6% 8% 33%	2489
May	1st to 10th	Day	13% 6% 2 5% 4 5% 4 3 4 7% 46%	4420
	11th to 20th	Day	7% 5% 2 4 4 4 5% 5% 7% 11% 48%	4377
	21st to end	Day	17% 10% 3 7% 4 4 4 3 6% 7% 35%	4859
June	1st to 10th	Day	14% 7% 2 6% 5% 5% 5% 4 6% 7% 39%	2850
	11th to 20th	Day	9% 7% 2 7% 6% 4 5% 4 5% 8% 43%	2850
	21st to end	Day	8% 5% 2 5% 4 4 5% 5% 7% 7% 48%	2850
July	1st to 10th	Day	4 3 1 3 2 2 2 2 3 4 74%	4740
	11th to 20th	Day	3 2 1 3 2 2 2 2 3 5% 75%	4740
	21st to end	Day	9% 2 1 2 2 2 2 2 3 6% 68%	4832
August	1st to 10th	Day	3 2 1 2 2 2 2 2 4 6% 75%	4283
	11th to 20th	Day	8% 6% 3 7% 4 4 4 4 5% 7% 48%	4026
	21st to end	Day	10% 5% 3 6% 4 3 4 3 4 6% 51%	4415
September	1st to 10th	Day	7% 5% 2 5% 3 4 3 3 5% 8% 55%	2280
	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 5% 6% 18%	1512
	11th to 20th	Day	23% 12% 4 8% 5% 5% 5% 3 4 6% 23%	1520
	21st to end	Day	25% 12% 5% 9% 7% 4 5% 3 4 6% 19%	1520
December	1st to 10th	Day	21% 15% 4 8% 6% 4 5% 3 4 5% 25%	1520
	11th to 20th	Day	24% 15% 5% 10% 7% 6% 7% 5% 6% 4 13%	1704
	21st to end	Day	22% 18% 5% 12% 7% 5% 4 4 5% 5% 12%	2442
January	1st to 10th	Night	23% 13% 5% 11% 7% 7% 6% 4 5% 5% 14%	4726
	11th to 20th	Night	23% 13% 4 9% 4 4 4 3 4 6% 26%	4686
	21st to end	Night	27% 15% 6% 11% 6% 5% 4 3 4 4 13%	4755
February	1st to 10th	Night	23% 12% 3 9% 6% 5% 5% 4 4 6% 22%	2470
	11th to 20th	Night	18% 12% 3 9% 5% 5% 5% 3 5% 6% 29%	2402
	21st to end	Night	22% 13% 3 9% 5% 5% 4 4 5% 6% 25%	2030
March	1st to 10th	Night	12% 10% 3 10% 7% 7% 7% 5% 8% 8% 23%	3586
	11th to 20th	Night	12% 8% 2 6% 4 4 4 5% 7% 8% 40%	3489
	21st to end	Night	18% 12% 5% 11% 6% 5% 5% 4 5% 5% 24%	3750
April	1st to 10th	Night	18% 10% 4 7% 5% 5% 5% 4 5% 8% 28%	1900
	11th to 20th	Night	14% 9% 3 7% 6% 4 5% 4 6% 8% 35%	1781
	21st to end	Night	17% 9% 3 9% 5% 4 5% 4 5% 7% 33%	1691
May	1st to 10th	Night	12% 7% 2 5% 3 3 3 3 4 6% 51%	2540
	11th to 20th	Night	6% 4 2 5% 4 4 4 4 5% 8% 54%	2516
	21st to end	Night	13% 8% 3 8% 5% 5% 5% 4 6% 8% 35%	2712
June	1st to 10th	Night	14% 6% 4 6% 6% 4 5% 4 6% 5% 39%	1330
	11th to 20th	Night	11% 6% 3 5% 4 4 4 4 8% 9% 41%	1330
	21st to end	Night	8% 4 2 4 4 3 4 4 7% 9% 51%	1330
July	1st to 10th	Night	5% 2 1 3 3 2 3 2 3 5% 73%	2220
	11th to 20th	Night	3 2 1 2 2 2 2 1 3 4 78%	2220
	21st to end	Night	8% 3 1 3 2 2 2 2 4 6% 68%	2719
August	1st to 10th	Night	2 2 1 2 2 2 2 2 3 6% 76%	2648
	11th to 20th	Night	9% 4 2 6% 3 4 3 4 5% 7% 53%	2812
	21st to end	Night	11% 3 1 5% 3 4 4 3 5% 9% 53%	3242
September	1st to 10th	Night	7% 2 1 4 3 2 3 3 5% 7% 63%	1900
	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	25% 11% 4 8% 5% 5% 6% 4 5% 5% 23%	2638
	11th to 20th	Night	24% 11% 3 8% 5% 5% 4 4 5% 6% 25%	2660
	21st to end	Night	21% 14% 4 9% 6% 5% 5% 4 6% 5% 22%	2660
December	1st to 10th	Night	21% 12% 4 8% 5% 5% 5% 4 5% 6% 25%	2660
	11th to 20th	Night	23% 15% 5% 11% 6% 6% 5% 4 6% 6% 14%	3496
	21st to end	Night	23% 15% 5% 10% 6% 5% 5% 3 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	51% 12% 14% 17% 6%	3286
	11th to 20th	Day	44% 8% 17% 26% 4 1	3490
	21st to end	Day	55% 11% 16% 14% 3	3902
April	1st to 10th	Day	53% 11% 18% 15% 3	2280
	11th to 20th	Day	48% 9% 14% 19% 8% 2	2348
	21st to end	Day	47% 10% 15% 20% 7% 1	2489
May	1st to 10th	Day	38% 7% 17% 26% 11% 1	4420
	11th to 20th	Day	27% 11% 27% 27% 7%	4380
	21st to end	Day	48% 10% 22% 17% 3	4860
June	1st to 10th	Day	44% 8% 22% 18% 7% 1	2850
	11th to 20th	Day	40% 8% 23% 23% 5%	2850
	21st to end	Day	34% 8% 24% 23% 9% 1	2850
July	1st to 10th	Day	17% 5% 11% 30% 25% 12%	4666
	11th to 20th	Day	14% 4 14% 36% 29% 2	4659
	21st to end	Day	20% 5% 26% 31% 16% 3	4679
August	1st to 10th	Day	14% 5% 18% 44% 17% 2	4266
	11th to 20th	Day	35% 9% 25% 22% 7% 1	4065
	21st to end	Day	36% 6% 20% 29% 9%	4414
September	1st to 10th	Day	30% 8% 21% 25% 14% 3	2280
	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	65% 9% 12% 10% 3 1	1512
	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	54% 11% 14% 16% 6%	3586
	11th to 20th	Night	39% 9% 19% 29% 3 1	3490
	21st to end	Night	61% 11% 13% 14% 2	3750
April	1st to 10th	Night	53% 10% 16% 16% 5%	1900
	11th to 20th	Night	48% 9% 13% 20% 8% 2	1781
	21st to end	Night	52% 8% 13% 18% 9%	1691
May	1st to 10th	Night	35% 6% 15% 30% 12% 1	2540
	11th to 20th	Night	27% 9% 27% 28% 9%	2516
	21st to end	Night	46% 12% 20% 18% 5%	2712
June	1st to 10th	Night	45% 7% 16% 24% 6% 2	1330
	11th to 20th	Night	38% 10% 22% 25% 5%	1330
	21st to end	Night	32% 8% 25% 23% 10% 3	1330
July	1st to 10th	Night	16% 6% 10% 32% 21% 15%	2185
	11th to 20th	Night	14% 3 12% 33% 35% 2	2178
	21st to end	Night	21% 4 15% 34% 23% 3	2633
August	1st to 10th	Night	13% 4 15% 37% 27% 3	2640
	11th to 20th	Night	31% 8% 26% 22% 9% 3	2839
	21st to end	Night	29% 9% 16% 34% 12% 1	3242
September	1st to 10th	Night	22% 7% 20% 30% 17% 5%	1900
	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	2638
	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% 9% 17% 30% 20% 4	506
April	1st to 10th	Day	15% 10% 21% 28% 20% 6%	460
	11th to 20th	Day	18% 5% 16% 31% 19% 10%	452
	21st to end	Day	18% 6% 19% 26% 22% 8%	460
May	1st to 10th	Day	11% 5% 12% 28% 36% 8%	463
	11th to 20th	Day	12% 4 11% 25% 35% 14%	488
	21st to end	Day	13% 3 11% 33% 27% 13%	549
June	1st to 10th	Day	14% 3 15% 31% 29% 8%	680
	11th to 20th	Day	9% 6% 17% 37% 25% 6%	680
	21st to end	Day	7% 2 13% 30% 34% 14%	680
July	1st to 10th	Day	7% 2 8% 29% 37% 17%	671
	11th to 20th	Day	4 1 9% 29% 40% 16%	668
	21st to end	Day	3 3 7% 23% 39% 25%	560
August	1st to 10th	Day	4 2 6% 23% 34% 31%	487
	11th to 20th	Day	3 1 5% 20% 46% 25%	477
	21st to end	Day	9% 2 9% 26% 39% 16%	539
September	1st to 10th	Day	10% 1 8% 28% 39% 15%	490
	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	27% 5% 26% 27% 13% 1	186
	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% 28% 18% 4	836
April	1st to 10th	Night	20% 8% 20% 27% 21% 5%	760
	11th to 20th	Night	17% 4 24% 29% 20% 6%	653
	21st to end	Night	19% 5% 22% 33% 16% 4	551
May	1st to 10th	Night	10% 4 20% 33% 27% 6%	380
	11th to 20th	Night	10% 3 17% 28% 33% 8%	374
	21st to end	Night	12% 4 18% 30% 30% 6%	411
June	1st to 10th	Night	15% 5% 21% 27% 30% 3	380
	11th to 20th	Night	13% 3 22% 37% 21% 4	380
	21st to end	Night	10% 4 16% 32% 28% 10%	380
July	1st to 10th	Night	9% 1 13% 32% 38% 7%	370
	11th to 20th	Night	7% 1 12% 38% 37% 7%	368
	21st to end	Night	4 2 9% 33% 40% 11%	416
August	1st to 10th	Night	4 2 7% 28% 42% 16%	445
	11th to 20th	Night	4 1 5% 23% 49% 17%	564
	21st to end	Night	9% 2 11% 30% 39% 9%	684
September	1st to 10th	Night	8% 2 8% 32% 35% 15%	760
	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	28% 7% 22% 26% 16% 2	754
	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 2024-11-01 19:47:38. Version ac07

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