Virden
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Virden clear sky chart from 2005-11-06 to 2026-06-16.

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	10% 8% 3 9% 6% 5% 5% 4 6% 8% 36%	141852
	Night	8% 9% 3 10% 6% 5% 5% 4 6% 8% 35%	139055
Transparency	Day	46% 4 15% 25% 9% 1	141569
	Night	47% 4 14% 24% 10% 1	138923
Seeing	Day	14% 9% 29% 29% 15% 3	18458
	Night	14% 7% 30% 35% 12% 1	28454

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	4 13% 6% 17% 9% 7% 6% 5% 7% 8% 19%	4139
	11th to 20th	Day	3 8% 4 15% 11% 9% 11% 9% 7% 7% 16%	4716
	21st to end	Day	6% 10% 5% 11% 5% 7% 5% 4 7% 8% 31%	5188
February	1st to 10th	Day	9% 15% 4 14% 8% 7% 5% 4 7% 6% 22%	1680
	11th to 20th	Day	6% 12% 4 11% 7% 7% 7% 4 7% 7% 26%	1873
	21st to end	Day	5% 12% 4 12% 7% 7% 6% 8% 6% 7% 25%	1730
March	1st to 10th	Day	7% 13% 6% 13% 8% 6% 5% 4 7% 8% 23%	4600
	11th to 20th	Day	9% 13% 6% 14% 9% 6% 5% 4 5% 6% 24%	4880
	21st to end	Day	10% 13% 5% 14% 7% 6% 6% 4 6% 7% 23%	5883
April	1st to 10th	Day	8% 11% 3 8% 6% 4 4 4 6% 8% 38%	2520
	11th to 20th	Day	13% 13% 4 9% 5% 5% 5% 3 5% 8% 29%	2664
	21st to end	Day	12% 9% 3 8% 6% 5% 4 4 5% 8% 35%	2730
May	1st to 10th	Day	12% 6% 2 5% 5% 4 4 4 6% 7% 44%	8070
	11th to 20th	Day	21% 9% 3 7% 4 4 5% 3 5% 7% 32%	8425
	21st to end	Day	12% 6% 2 6% 4 3 4 3 5% 8% 48%	9683
June	1st to 10th	Day	13% 6% 2 6% 5% 5% 5% 4 7% 9% 39%	3150
	11th to 20th	Day	15% 6% 3 7% 5% 5% 5% 5% 7% 8% 33%	3076
	21st to end	Day	12% 5% 2 6% 5% 5% 6% 4 7% 9% 39%	3000
July	1st to 10th	Day	7% 4 2 6% 5% 5% 6% 5% 8% 10% 43%	6800
	11th to 20th	Day	9% 5% 2 6% 4 4 5% 4 7% 9% 46%	6672
	21st to end	Day	7% 4 1 5% 4 4 5% 4 7% 11% 48%	6898
August	1st to 10th	Day	9% 5% 2 6% 4 4 4 4 6% 9% 45%	4552
	11th to 20th	Day	9% 5% 2 5% 3 4 4 4 6% 10% 48%	4292
	21st to end	Day	10% 5% 2 5% 4 4 4 4 6% 8% 49%	4619
September	1st to 10th	Day	10% 4 2 6% 4 4 4 4 5% 7% 51%	2400
	11th to 20th	Day	15% 6% 2 6% 5% 4 4 3 5% 7% 43%	2246
	21st to end	Day	13% 6% 1 6% 4 4 3 3 5% 6% 49%	2200
October	1st to 10th	Day	10% 7% 3 7% 4 4 4 3 4 7% 46%	3503
	11th to 20th	Day	8% 6% 2 6% 4 4 4 4 6% 9% 47%	2922
	21st to end	Day	9% 10% 5% 9% 5% 4 4 3 4 7% 39%	3190
November	1st to 10th	Day	16% 12% 4 10% 6% 4 5% 3 4 6% 29%	1853
	11th to 20th	Day	9% 15% 5% 12% 7% 4 4 4 5% 5% 28%	1584
	21st to end	Day	8% 14% 6% 11% 7% 6% 5% 4 5% 6% 27%	1470
December	1st to 10th	Day	6% 13% 6% 19% 9% 10% 7% 4 4 5% 17%	2360
	11th to 20th	Day	9% 12% 6% 13% 10% 8% 6% 4 5% 8% 19%	2709
	21st to end	Day	5% 10% 3 13% 9% 7% 6% 4 5% 6% 33%	3575
January	1st to 10th	Night	5% 11% 6% 17% 10% 7% 6% 4 6% 7% 21%	8781
	11th to 20th	Night	5% 9% 4 13% 8% 7% 10% 7% 9% 8% 19%	8212
	21st to end	Night	5% 10% 4 14% 7% 6% 7% 5% 7% 9% 27%	9026
February	1st to 10th	Night	8% 13% 6% 12% 5% 6% 5% 5% 7% 8% 25%	2940
	11th to 20th	Night	5% 10% 3 9% 7% 6% 6% 5% 6% 7% 35%	2652
	21st to end	Night	6% 10% 4 10% 7% 5% 5% 5% 6% 8% 34%	2076
March	1st to 10th	Night	7% 11% 4 12% 6% 6% 6% 5% 8% 9% 26%	5494
	11th to 20th	Night	8% 11% 4 10% 6% 5% 4 4 6% 7% 34%	5307
	21st to end	Night	9% 13% 5% 13% 7% 5% 4 4 6% 7% 27%	5302
April	1st to 10th	Night	5% 9% 3 7% 5% 5% 5% 5% 7% 8% 42%	2100
	11th to 20th	Night	13% 12% 4 9% 5% 5% 3 4 6% 7% 33%	1906
	21st to end	Night	15% 8% 2 6% 4 4 6% 5% 6% 6% 38%	1890
May	1st to 10th	Night	10% 6% 2 6% 4 5% 5% 4 5% 6% 47%	4862
	11th to 20th	Night	16% 7% 2 6% 5% 4 5% 5% 6% 9% 34%	4468
	21st to end	Night	12% 7% 3 6% 4 4 3 3 5% 6% 48%	4523
June	1st to 10th	Night	13% 5% 2 5% 4 4 4 4 7% 8% 43%	1470
	11th to 20th	Night	13% 6% 2 7% 4 4 5% 4 6% 10% 41%	1435
	21st to end	Night	12% 4 2 5% 4 4 4 5% 7% 11% 42%	1400
July	1st to 10th	Night	5% 4 2 5% 3 4 5% 4 8% 10% 50%	3180
	11th to 20th	Night	9% 5% 2 5% 3 3 4 4 5% 8% 52%	3305
	21st to end	Night	6% 4 1 5% 4 3 4 4 7% 9% 53%	3968
August	1st to 10th	Night	6% 4 1 5% 3 4 4 4 6% 9% 54%	2608
	11th to 20th	Night	5% 4 2 6% 5% 4 4 4 7% 9% 51%	2767
	21st to end	Night	8% 4 2 5% 3 4 4 4 5% 9% 52%	3288
September	1st to 10th	Night	9% 5% 1 4 3 4 4 4 6% 7% 55%	2000
	11th to 20th	Night	12% 6% 2 5% 3 3 4 4 6% 8% 46%	2153
	21st to end	Night	12% 7% 2 5% 4 4 3 3 6% 7% 46%	2200
October	1st to 10th	Night	11% 7% 2 5% 4 3 3 3 5% 7% 50%	3642
	11th to 20th	Night	9% 6% 2 6% 5% 5% 5% 4 6% 8% 44%	4227
	21st to end	Night	8% 8% 3 8% 5% 4 5% 3 6% 7% 44%	4610
November	1st to 10th	Night	13% 11% 3 9% 5% 5% 4 4 6% 7% 32%	2665
	11th to 20th	Night	9% 13% 4 11% 7% 6% 5% 4 5% 6% 31%	3035
	21st to end	Night	8% 12% 4 9% 7% 5% 5% 4 7% 7% 32%	3150
December	1st to 10th	Night	7% 12% 4 14% 10% 8% 7% 6% 6% 7% 19%	5050
	11th to 20th	Night	9% 14% 5% 12% 8% 6% 7% 5% 5% 7% 22%	5718
	21st to end	Night	5% 8% 4 14% 8% 7% 7% 5% 6% 7% 29%	7645

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	63% 4 10% 16% 7%	4139
	11th to 20th	Day	64% 4 10% 16% 7%	4740
	21st to end	Day	50% 3 16% 25% 7%	5188
February	1st to 10th	Day	60% 4 11% 17% 7% 1	1680
	11th to 20th	Day	55% 5% 11% 20% 9%	1882
	21st to end	Day	55% 6% 13% 18% 7%	1730
March	1st to 10th	Day	58% 5% 16% 16% 6%	4600
	11th to 20th	Day	61% 5% 12% 17% 6%	4882
	21st to end	Day	60% 4 11% 18% 7%	5883
April	1st to 10th	Day	44% 4 16% 24% 11% 1	2520
	11th to 20th	Day	53% 4 12% 19% 10% 1	2664
	21st to end	Day	47% 5% 15% 24% 9% 1	2730
May	1st to 10th	Day	39% 3 12% 31% 14% 1	8070
	11th to 20th	Day	52% 4 10% 21% 11% 2	8429
	21st to end	Day	36% 4 9% 26% 24% 2	9683
June	1st to 10th	Day	41% 5% 18% 24% 10% 2	3150
	11th to 20th	Day	46% 6% 16% 22% 9% 1	3076
	21st to end	Day	41% 6% 19% 27% 7% 1	3000
July	1st to 10th	Day	35% 4 27% 29% 5%	6726
	11th to 20th	Day	35% 3 19% 36% 6%	6591
	21st to end	Day	30% 3 25% 33% 8% 1	6705
August	1st to 10th	Day	35% 3 18% 33% 11%	4536
	11th to 20th	Day	31% 4 23% 35% 8%	4334
	21st to end	Day	34% 3 19% 36% 9%	4618
September	1st to 10th	Day	33% 4 16% 34% 13% 1	2400
	11th to 20th	Day	42% 4 18% 26% 10% 1	2246
	21st to end	Day	37% 3 13% 33% 14%	2200
October	1st to 10th	Day	40% 2 14% 35% 9%	3503
	11th to 20th	Day	35% 3 16% 36% 10%	2922
	21st to end	Day	46% 3 11% 31% 9%	3190
November	1st to 10th	Day	57% 4 13% 19% 7% 1	1853
	11th to 20th	Day	57% 3 16% 15% 7% 1	1584
	21st to end	Day	57% 5% 15% 18% 5%	1470
December	1st to 10th	Day	70% 4 12% 11% 3	2360
	11th to 20th	Day	63% 4 14% 15% 3	2710
	21st to end	Day	53% 4 9% 23% 11% 1	3575
January	1st to 10th	Night	63% 4 9% 18% 6%	8782
	11th to 20th	Night	58% 4 12% 18% 7%	8250
	21st to end	Night	54% 4 15% 20% 7%	9026
February	1st to 10th	Night	56% 4 13% 17% 10% 1	2940
	11th to 20th	Night	47% 4 13% 23% 12%	2653
	21st to end	Night	48% 4 14% 23% 11%	2076
March	1st to 10th	Night	51% 5% 18% 20% 5%	5494
	11th to 20th	Night	48% 4 15% 23% 9%	5307
	21st to end	Night	56% 4 11% 24% 6%	5302
April	1st to 10th	Night	38% 5% 13% 27% 16% 2	2100
	11th to 20th	Night	51% 3 10% 23% 12% 1	1906
	21st to end	Night	45% 4 14% 23% 12% 2	1890
May	1st to 10th	Night	37% 3 10% 31% 18% 1	4862
	11th to 20th	Night	46% 4 12% 27% 9% 2	4468
	21st to end	Night	38% 3 9% 26% 23% 2	4526
June	1st to 10th	Night	37% 5% 16% 25% 14% 3	1470
	11th to 20th	Night	39% 6% 17% 22% 13% 1	1435
	21st to end	Night	34% 8% 19% 31% 7% 1	1400
July	1st to 10th	Night	29% 6% 28% 30% 7% 1	3145
	11th to 20th	Night	32% 3 18% 40% 6% 1	3263
	21st to end	Night	29% 3 24% 30% 13% 1	3856
August	1st to 10th	Night	28% 4 20% 34% 14% 1	2600
	11th to 20th	Night	29% 4 21% 37% 8% 1	2791
	21st to end	Night	30% 3 19% 36% 11% 1	3288
September	1st to 10th	Night	27% 5% 14% 35% 17% 2	2000
	11th to 20th	Night	36% 5% 18% 28% 13% 1	2153
	21st to end	Night	38% 4 12% 32% 12% 2	2200
October	1st to 10th	Night	36% 3 13% 32% 14% 3	3642
	11th to 20th	Night	38% 3 11% 35% 12% 1	4227
	21st to end	Night	40% 3 14% 33% 10%	4610
November	1st to 10th	Night	50% 5% 14% 21% 8% 2	2665
	11th to 20th	Night	54% 6% 15% 18% 6% 1	3035
	21st to end	Night	51% 6% 17% 20% 6%	3150
December	1st to 10th	Night	64% 4 15% 12% 4	5050
	11th to 20th	Night	62% 3 14% 16% 4	5716
	21st to end	Night	54% 4 10% 20% 11% 1	7645

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	11% 8% 31% 32% 14% 4	330
	11th to 20th	Day	9% 11% 34% 35% 9% 2	330
	21st to end	Day	16% 9% 30% 32% 12% 2	363
February	1st to 10th	Day	14% 12% 35% 30% 8% 1	330
	11th to 20th	Day	12% 6% 31% 31% 15% 5%	330
	21st to end	Day	6% 9% 30% 37% 16% 2	273
March	1st to 10th	Day	13% 9% 36% 26% 13% 3	330
	11th to 20th	Day	12% 10% 33% 28% 15% 2	330
	21st to end	Day	19% 11% 30% 26% 12% 2	493
April	1st to 10th	Day	14% 12% 36% 30% 7% 2	540
	11th to 20th	Day	20% 13% 29% 26% 11%	702
	21st to end	Day	16% 11% 31% 27% 14% 1	750
May	1st to 10th	Day	15% 12% 27% 30% 13% 3	753
	11th to 20th	Day	20% 10% 29% 24% 15% 3	775
	21st to end	Day	19% 8% 24% 29% 15% 4	844
June	1st to 10th	Day	14% 11% 29% 27% 15% 4	780
	11th to 20th	Day	17% 9% 33% 27% 11% 3	756
	21st to end	Day	13% 9% 25% 31% 18% 4	730
July	1st to 10th	Day	8% 6% 22% 36% 20% 8%	721
	11th to 20th	Day	11% 7% 29% 28% 18% 6%	718
	21st to end	Day	7% 6% 23% 36% 21% 7%	794
August	1st to 10th	Day	12% 6% 24% 32% 20% 6%	726
	11th to 20th	Day	12% 4 24% 27% 26% 6%	715
	21st to end	Day	12% 6% 25% 34% 19% 4	773
September	1st to 10th	Day	11% 9% 35% 25% 15% 5%	530
	11th to 20th	Day	18% 11% 25% 32% 11% 2	376
	21st to end	Day	18% 10% 30% 25% 15% 2	330
October	1st to 10th	Day	22% 9% 24% 26% 15% 4	330
	11th to 20th	Day	18% 12% 32% 26% 8% 3	330
	21st to end	Day	19% 9% 39% 24% 7% 2	363
November	1st to 10th	Day	23% 12% 27% 26% 12% 1	330
	11th to 20th	Day	18% 12% 36% 25% 9% 1	330
	21st to end	Day	14% 13% 34% 30% 7% 2	330
December	1st to 10th	Day	12% 9% 36% 28% 12% 2	330
	11th to 20th	Day	18% 9% 38% 27% 7% 1	330
	21st to end	Day	13% 6% 31% 31% 15% 3	363
January	1st to 10th	Night	13% 8% 31% 36% 10% 1	1050
	11th to 20th	Night	15% 10% 32% 33% 9% 1	1050
	21st to end	Night	11% 10% 36% 32% 10% 1	1155
February	1st to 10th	Night	13% 10% 32% 31% 13% 2	1050
	11th to 20th	Night	10% 6% 29% 40% 12% 3	951
	21st to end	Night	11% 5% 29% 37% 16% 2	692
March	1st to 10th	Night	16% 8% 29% 31% 13% 3	840
	11th to 20th	Night	10% 6% 35% 36% 11% 2	730
	21st to end	Night	17% 4 29% 36% 12% 2	693
April	1st to 10th	Night	9% 7% 35% 37% 12%	630
	11th to 20th	Night	18% 8% 32% 32% 9% 1	623
	21st to end	Night	18% 8% 29% 33% 12%	630
May	1st to 10th	Night	13% 7% 30% 37% 12%	630
	11th to 20th	Night	16% 6% 30% 34% 12%	621
	21st to end	Night	21% 5% 25% 36% 13%	683
June	1st to 10th	Night	17% 5% 33% 31% 14%	630
	11th to 20th	Night	16% 6% 33% 33% 12%	615
	21st to end	Night	14% 3 28% 37% 16% 1	600
July	1st to 10th	Night	8% 3 23% 42% 23% 2	585
	11th to 20th	Night	8% 5% 26% 43% 16% 2	582
	21st to end	Night	6% 2 22% 49% 18% 3	657
August	1st to 10th	Night	7% 3 22% 46% 20% 1	597
	11th to 20th	Night	8% 4 20% 42% 24% 3	594
	21st to end	Night	12% 4 25% 42% 16% 2	660
September	1st to 10th	Night	10% 4 27% 36% 20% 3	600
	11th to 20th	Night	15% 7% 31% 35% 12% 1	600
	21st to end	Night	15% 9% 29% 35% 12% 1	600
October	1st to 10th	Night	18% 8% 31% 31% 12% 1	626
	11th to 20th	Night	18% 10% 26% 34% 11% 1	1000
	21st to end	Night	15% 10% 34% 31% 8% 1	1100
November	1st to 10th	Night	18% 11% 32% 30% 9% 1	1025
	11th to 20th	Night	15% 9% 36% 29% 9% 2	1050
	21st to end	Night	14% 12% 33% 32% 8% 1	1050
December	1st to 10th	Night	11% 8% 34% 32% 13% 3	1050
	11th to 20th	Night	18% 10% 31% 32% 9% 1	1050
	21st to end	Night	14% 6% 31% 34% 12% 3	1155

Page generated at 2026-06-13 01:31:38. Version ac07

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