Victor Mine
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Victor Mine clear sky chart from 2005-11-06 to 2025-12-18.

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% 11% 4 10% 6% 6% 6% 4 6% 7% 27%	128004
	Night	11% 13% 5% 12% 7% 6% 6% 5% 6% 6% 23%	123274
Transparency	Day	55% 6% 12% 20% 7% 1	131352
	Night	58% 6% 11% 18% 7%	128013
Seeing	Day	19% 9% 28% 26% 13% 4	17018
	Night	19% 8% 30% 30% 12% 2	26105

By Month

Percentage Cloud Cover NE (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	6% 19% 7% 16% 8% 8% 8% 5% 10% 5% 8%	3158
	11th to 20th	Day	4 12% 7% 20% 14% 11% 8% 7% 8% 4 4	3133
	21st to end	Day	8% 13% 6% 16% 7% 7% 8% 8% 9% 7% 12%	3844
February	1st to 10th	Day	6% 12% 6% 10% 7% 7% 8% 7% 11% 8% 16%	1600
	11th to 20th	Day	5% 12% 4 12% 7% 7% 8% 7% 11% 8% 17%	1699
	21st to end	Day	4 9% 4 11% 7% 7% 10% 9% 9% 8% 22%	1585
March	1st to 10th	Day	3 8% 6% 17% 10% 8% 8% 5% 7% 6% 21%	4478
	11th to 20th	Day	8% 12% 5% 16% 10% 8% 7% 5% 5% 6% 18%	4906
	21st to end	Day	7% 11% 6% 14% 7% 10% 10% 5% 7% 6% 18%	5616
April	1st to 10th	Day	12% 14% 4 10% 6% 7% 7% 4 5% 5% 27%	2478
	11th to 20th	Day	14% 12% 5% 10% 5% 5% 5% 3 4 5% 30%	2572
	21st to end	Day	13% 12% 4 10% 5% 4 4 3 5% 6% 34%	2600
May	1st to 10th	Day	10% 12% 4 9% 5% 4 4 3 4 5% 38%	6524
	11th to 20th	Day	20% 15% 4 8% 4 4 4 3 4 5% 29%	6776
	21st to end	Day	18% 10% 3 6% 4 3 3 3 5% 7% 40%	7451
June	1st to 10th	Day	19% 9% 3 8% 5% 4 4 3 5% 6% 33%	3000
	11th to 20th	Day	17% 7% 3 7% 4 5% 5% 3 6% 8% 36%	3000
	21st to end	Day	17% 8% 2 7% 5% 5% 4 4 5% 8% 36%	3000
July	1st to 10th	Day	11% 7% 2 6% 5% 5% 4 4 6% 9% 41%	6819
	11th to 20th	Day	19% 7% 2 7% 5% 5% 5% 5% 7% 8% 31%	6820
	21st to end	Day	13% 6% 2 7% 5% 5% 6% 4 7% 9% 35%	7428
August	1st to 10th	Day	21% 6% 2 6% 4 4 5% 4 6% 8% 32%	4602
	11th to 20th	Day	13% 6% 2 6% 4 4 4 4 5% 8% 43%	4301
	21st to end	Day	15% 7% 3 7% 5% 4 4 3 5% 7% 38%	4675
September	1st to 10th	Day	20% 11% 4 8% 6% 4 5% 3 6% 8% 26%	2505
	11th to 20th	Day	25% 11% 4 8% 5% 5% 4 3 4 6% 27%	2200
	21st to end	Day	24% 13% 4 6% 4 4 4 3 5% 6% 28%	2200
October	1st to 10th	Day	23% 17% 4 7% 5% 5% 5% 4 5% 5% 20%	2080
	11th to 20th	Day	21% 23% 4 9% 5% 5% 4 3 4 5% 17%	1826
	21st to end	Day	19% 22% 6% 11% 6% 5% 3 3 4 4 16%	1980
November	1st to 10th	Day	20% 20% 6% 12% 7% 5% 5% 3 5% 3 14%	1656
	11th to 20th	Day	20% 23% 9% 12% 6% 5% 3 3 3 5% 12%	1526
	21st to end	Day	17% 22% 7% 14% 8% 7% 4 3 3 4 10%	1470
December	1st to 10th	Day	8% 14% 7% 20% 10% 7% 7% 4 5% 5% 12%	2350
	11th to 20th	Day	8% 14% 7% 13% 6% 11% 8% 6% 7% 5% 14%	2670
	21st to end	Day	12% 20% 6% 15% 8% 6% 6% 5% 4 5% 14%	3476
January	1st to 10th	Night	6% 18% 8% 20% 8% 8% 7% 4 7% 5% 8%	6808
	11th to 20th	Night	5% 15% 8% 18% 11% 12% 9% 6% 7% 4 5%	6772
	21st to end	Night	6% 15% 6% 12% 7% 7% 8% 8% 9% 6% 16%	7120
February	1st to 10th	Night	5% 10% 4 12% 9% 8% 10% 8% 10% 9% 15%	2800
	11th to 20th	Night	6% 12% 5% 12% 9% 7% 9% 7% 9% 7% 16%	2587
	21st to end	Night	3 10% 4 12% 6% 6% 9% 8% 8% 8% 25%	2042
March	1st to 10th	Night	6% 9% 5% 12% 9% 7% 7% 5% 7% 8% 24%	5362
	11th to 20th	Night	8% 12% 6% 15% 9% 10% 5% 4 5% 6% 20%	5038
	21st to end	Night	7% 12% 5% 13% 7% 8% 8% 4 5% 6% 25%	5358
April	1st to 10th	Night	11% 12% 4 10% 7% 7% 6% 4 5% 6% 29%	1921
	11th to 20th	Night	14% 11% 4 10% 6% 5% 4 4 5% 6% 31%	1777
	21st to end	Night	12% 10% 4 9% 6% 5% 5% 3 5% 5% 36%	1800
May	1st to 10th	Night	10% 8% 4 11% 4 3 4 3 5% 5% 41%	3430
	11th to 20th	Night	20% 13% 3 8% 4 3 4 4 5% 6% 28%	3139
	21st to end	Night	19% 9% 2 6% 3 4 3 3 4 6% 39%	3447
June	1st to 10th	Night	19% 8% 2 5% 4 5% 5% 4 5% 6% 36%	1400
	11th to 20th	Night	16% 8% 2 7% 5% 5% 4 4 5% 7% 38%	1400
	21st to end	Night	16% 7% 2 6% 4 4 5% 4 6% 7% 41%	1400
July	1st to 10th	Night	12% 6% 2 7% 4 4 6% 4 7% 8% 38%	3160
	11th to 20th	Night	14% 8% 2 7% 4 5% 5% 4 6% 7% 38%	3160
	21st to end	Night	12% 5% 2 6% 4 5% 4 5% 6% 8% 45%	3446
August	1st to 10th	Night	19% 6% 2 6% 4 4 4 4 6% 9% 37%	2554
	11th to 20th	Night	10% 6% 3 6% 4 3 4 3 6% 9% 47%	2751
	21st to end	Night	11% 6% 2 6% 3 3 4 3 5% 10% 46%	3223
September	1st to 10th	Night	18% 10% 2 7% 4 5% 4 4 6% 7% 33%	1873
	11th to 20th	Night	20% 10% 3 9% 5% 5% 5% 4 5% 6% 28%	2200
	21st to end	Night	20% 11% 4 8% 5% 5% 4 3 4 6% 31%	2200
October	1st to 10th	Night	21% 14% 3 8% 4 5% 4 3 4 6% 28%	2320
	11th to 20th	Night	21% 18% 5% 10% 5% 5% 4 3 5% 7% 19%	2570
	21st to end	Night	17% 21% 6% 10% 5% 5% 5% 3 5% 6% 18%	2860
November	1st to 10th	Night	18% 22% 6% 12% 6% 4 4 3 4 5% 15%	2860
	11th to 20th	Night	18% 22% 7% 12% 6% 5% 4 3 4 5% 13%	3092
	21st to end	Night	15% 23% 9% 16% 7% 6% 4 3 4 4 11%	3150
December	1st to 10th	Night	7% 18% 7% 18% 9% 6% 7% 5% 6% 6% 10%	5060
	11th to 20th	Night	8% 16% 6% 14% 10% 8% 7% 6% 6% 4 14%	5692
	21st to end	Night	14% 16% 6% 12% 8% 7% 6% 4 7% 6% 14%	7502

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	71% 4 10% 10% 4 1	3159
	11th to 20th	Day	79% 3 8% 8% 2	3160
	21st to end	Day	66% 4 7% 18% 5%	3844
February	1st to 10th	Day	58% 5% 10% 19% 9%	1600
	11th to 20th	Day	57% 6% 10% 20% 6%	1708
	21st to end	Day	52% 5% 12% 21% 9%	1585
March	1st to 10th	Day	59% 5% 8% 14% 11% 3	4480
	11th to 20th	Day	64% 5% 9% 12% 10%	4906
	21st to end	Day	63% 5% 8% 16% 8%	5616
April	1st to 10th	Day	58% 5% 9% 15% 12% 1	2478
	11th to 20th	Day	55% 5% 8% 21% 10% 1	2572
	21st to end	Day	51% 5% 8% 22% 12% 2	2600
May	1st to 10th	Day	46% 7% 8% 23% 15% 1	6533
	11th to 20th	Day	57% 6% 9% 16% 12%	6780
	21st to end	Day	44% 5% 9% 23% 16% 3	7451
June	1st to 10th	Day	51% 5% 11% 21% 11% 1	3000
	11th to 20th	Day	45% 6% 11% 26% 12%	3000
	21st to end	Day	45% 8% 14% 24% 9% 1	3000
July	1st to 10th	Day	40% 7% 18% 31% 5%	6746
	11th to 20th	Day	49% 8% 18% 22% 4	6739
	21st to end	Day	43% 8% 21% 25% 3	7216
August	1st to 10th	Day	48% 7% 18% 24% 3	4586
	11th to 20th	Day	38% 6% 16% 36% 4	4343
	21st to end	Day	45% 6% 14% 23% 11%	4674
September	1st to 10th	Day	56% 9% 16% 16% 4	2505
	11th to 20th	Day	60% 5% 14% 20% 2	2200
	21st to end	Day	57% 6% 11% 19% 7%	2200
October	1st to 10th	Day	64% 6% 14% 13% 3	3392
	11th to 20th	Day	60% 6% 17% 15% 2	2951
	21st to end	Day	68% 5% 9% 16% 2	3180
November	1st to 10th	Day	73% 5% 10% 9% 2	1656
	11th to 20th	Day	77% 4 8% 10% 2	1526
	21st to end	Day	78% 4 7% 8% 3	1470
December	1st to 10th	Day	70% 8% 7% 13% 3	2350
	11th to 20th	Day	66% 5% 9% 16% 4	2670
	21st to end	Day	72% 4 6% 14% 5%	3476
January	1st to 10th	Night	75% 4 8% 7% 4 1	6808
	11th to 20th	Night	77% 5% 9% 7% 2	6820
	21st to end	Night	62% 5% 9% 17% 8%	7120
February	1st to 10th	Night	58% 6% 11% 18% 7%	2800
	11th to 20th	Night	59% 6% 11% 18% 7%	2589
	21st to end	Night	50% 7% 12% 21% 10%	2042
March	1st to 10th	Night	54% 4 9% 17% 15% 1	5373
	11th to 20th	Night	62% 6% 8% 14% 10% 1	5039
	21st to end	Night	58% 5% 7% 20% 10% 1	5358
April	1st to 10th	Night	55% 5% 8% 17% 13% 2	1921
	11th to 20th	Night	52% 5% 8% 21% 12% 1	1777
	21st to end	Night	50% 5% 6% 23% 15% 2	1800
May	1st to 10th	Night	44% 5% 8% 25% 17% 1	3437
	11th to 20th	Night	55% 6% 11% 17% 11%	3140
	21st to end	Night	45% 6% 8% 19% 19% 3	3448
June	1st to 10th	Night	47% 7% 10% 24% 12%	1400
	11th to 20th	Night	45% 7% 12% 21% 15%	1400
	21st to end	Night	41% 7% 14% 26% 11% 1	1400
July	1st to 10th	Night	41% 8% 17% 31% 4	3125
	11th to 20th	Night	43% 7% 16% 27% 6%	3118
	21st to end	Night	36% 7% 27% 27% 3	3344
August	1st to 10th	Night	43% 9% 16% 27% 4	2546
	11th to 20th	Night	34% 6% 22% 34% 4	2775
	21st to end	Night	35% 6% 14% 36% 9%	3223
September	1st to 10th	Night	48% 9% 17% 22% 5%	1873
	11th to 20th	Night	55% 8% 16% 18% 3	2200
	21st to end	Night	54% 6% 15% 18% 7%	2200
October	1st to 10th	Night	57% 5% 13% 21% 5%	3788
	11th to 20th	Night	57% 7% 16% 19% 2	4184
	21st to end	Night	66% 6% 10% 16% 2	4610
November	1st to 10th	Night	72% 6% 9% 9% 3	2860
	11th to 20th	Night	73% 6% 10% 10% 1	3092
	21st to end	Night	77% 4 8% 10% 2	3150
December	1st to 10th	Night	71% 5% 9% 13% 1	5060
	11th to 20th	Night	69% 4 9% 13% 5%	5691
	21st to end	Night	69% 4 8% 14% 6%	7502

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	12% 12% 32% 26% 16% 3	200
	11th to 20th	Day	11% 10% 27% 33% 14% 6%	200
	21st to end	Day	13% 4 25% 35% 17% 6%	300
February	1st to 10th	Day	8% 9% 32% 33% 15% 3	300
	11th to 20th	Day	10% 7% 36% 28% 14% 6%	300
	21st to end	Day	10% 11% 40% 26% 11% 2	249
March	1st to 10th	Day	11% 12% 29% 27% 16% 6%	300
	11th to 20th	Day	11% 12% 30% 30% 14% 4	465
	21st to end	Day	10% 9% 31% 33% 14% 3	550
April	1st to 10th	Day	14% 7% 29% 31% 16% 4	500
	11th to 20th	Day	21% 11% 26% 25% 11% 6%	492
	21st to end	Day	15% 8% 28% 29% 15% 5%	500
May	1st to 10th	Day	18% 11% 30% 23% 14% 3	660
	11th to 20th	Day	21% 14% 28% 25% 10% 2	725
	21st to end	Day	23% 9% 27% 28% 11% 3	789
June	1st to 10th	Day	20% 9% 31% 25% 12% 3	730
	11th to 20th	Day	20% 8% 27% 27% 14% 4	730
	21st to end	Day	19% 7% 30% 24% 16% 4	730
July	1st to 10th	Day	17% 8% 27% 28% 16% 5%	721
	11th to 20th	Day	19% 7% 25% 31% 15% 2	718
	21st to end	Day	19% 7% 23% 28% 17% 7%	794
August	1st to 10th	Day	23% 6% 22% 27% 17% 5%	726
	11th to 20th	Day	19% 8% 21% 25% 18% 9%	598
	21st to end	Day	24% 6% 24% 25% 15% 6%	583
September	1st to 10th	Day	22% 9% 29% 28% 8% 3	530
	11th to 20th	Day	25% 10% 25% 24% 13% 3	530
	21st to end	Day	28% 9% 27% 19% 12% 5%	530
October	1st to 10th	Day	28% 12% 29% 21% 8% 2	530
	11th to 20th	Day	32% 13% 26% 17% 10% 3	356
	21st to end	Day	23% 10% 31% 23% 10% 3	363
November	1st to 10th	Day	27% 12% 30% 23% 8% 1	225
	11th to 20th	Day	29% 10% 27% 24% 6% 4	220
	21st to end	Day	25% 12% 35% 15% 9% 3	220
December	1st to 10th	Day	15% 7% 33% 31% 9% 4	220
	11th to 20th	Day	15% 8% 33% 31% 9% 4	214
	21st to end	Day	16% 7% 33% 26% 15% 3	220
January	1st to 10th	Night	16% 9% 31% 33% 9% 1	1000
	11th to 20th	Night	16% 10% 26% 34% 12% 2	1000
	21st to end	Night	12% 8% 26% 32% 17% 4	1100
February	1st to 10th	Night	8% 7% 30% 37% 17% 1	1000
	11th to 20th	Night	11% 6% 31% 34% 15% 3	837
	21st to end	Night	8% 7% 27% 37% 18% 4	660
March	1st to 10th	Night	14% 7% 30% 34% 14% 2	800
	11th to 20th	Night	11% 9% 36% 33% 11% 2	800
	21st to end	Night	14% 9% 31% 32% 13% 2	835
April	1st to 10th	Night	16% 7% 33% 31% 12% 1	600
	11th to 20th	Night	17% 7% 30% 33% 12% 2	593
	21st to end	Night	17% 7% 30% 32% 14% 1	600
May	1st to 10th	Night	21% 9% 28% 30% 11% 1	485
	11th to 20th	Night	20% 10% 35% 26% 9%	394
	21st to end	Night	22% 10% 32% 29% 7%	433
June	1st to 10th	Night	22% 8% 32% 26% 12%	400
	11th to 20th	Night	19% 6% 32% 33% 9% 1	400
	21st to end	Night	18% 7% 30% 35% 10%	400
July	1st to 10th	Night	18% 8% 27% 34% 12% 1	390
	11th to 20th	Night	12% 4 33% 38% 13%	388
	21st to end	Night	17% 4 28% 34% 16% 1	438
August	1st to 10th	Night	18% 4 17% 43% 16% 1	567
	11th to 20th	Night	18% 6% 23% 35% 17% 1	594
	21st to end	Night	20% 6% 24% 32% 17% 2	660
September	1st to 10th	Night	20% 6% 30% 33% 10%	603
	11th to 20th	Night	26% 7% 28% 30% 10%	800
	21st to end	Night	25% 9% 27% 29% 9% 2	800
October	1st to 10th	Night	28% 10% 33% 23% 7% 1	800
	11th to 20th	Night	31% 8% 28% 21% 11% 1	800
	21st to end	Night	25% 9% 30% 24% 11% 2	880
November	1st to 10th	Night	29% 9% 29% 22% 9% 1	820
	11th to 20th	Night	28% 11% 29% 23% 8% 1	992
	21st to end	Night	26% 13% 31% 21% 8% 1	1050
December	1st to 10th	Night	16% 11% 35% 26% 10% 2	1050
	11th to 20th	Night	16% 9% 31% 28% 15% 2	1036
	21st to end	Night	20% 7% 32% 24% 12% 4	1100

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