Dominion City
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Dominion City clear sky chart from 2005-11-06 to 2025-08-05.

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	11% 9% 3 8% 6% 5% 5% 4 6% 8% 35%	129916
	Night	9% 10% 4 10% 6% 5% 5% 4 6% 7% 34%	126921
Transparency	Day	28% 41% 11% 15% 6%	129616
	Night	30% 40% 9% 14% 6%	126802
Seeing	Day	14% 10% 31% 29% 14% 4	17283
	Night	14% 7% 33% 33% 12% 1	27175

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	5% 13% 7% 14% 8% 6% 6% 7% 8% 9% 17%	3179
	11th to 20th	Day	4 8% 4 15% 10% 9% 10% 10% 8% 8% 12%	3232
	21st to end	Day	6% 15% 7% 16% 9% 6% 7% 4 5% 8% 16%	4004
February	1st to 10th	Day	8% 13% 5% 10% 9% 7% 8% 6% 7% 5% 21%	1742
	11th to 20th	Day	6% 10% 3 11% 9% 8% 7% 6% 8% 8% 24%	1754
	21st to end	Day	6% 10% 3 13% 9% 8% 8% 6% 6% 7% 24%	1576
March	1st to 10th	Day	9% 10% 3 8% 10% 5% 5% 4 6% 9% 29%	4623
	11th to 20th	Day	9% 10% 4 14% 9% 7% 6% 5% 6% 9% 21%	4978
	21st to end	Day	10% 14% 7% 12% 6% 5% 5% 4 5% 6% 26%	5464
April	1st to 10th	Day	9% 13% 4 8% 5% 4 5% 4 6% 8% 34%	2420
	11th to 20th	Day	13% 11% 3 8% 6% 4 5% 4 5% 7% 32%	2572
	21st to end	Day	20% 8% 3 8% 5% 4 4 4 5% 7% 33%	2600
May	1st to 10th	Day	13% 7% 3 6% 4 4 4 3 5% 7% 45%	6031
	11th to 20th	Day	17% 8% 2 7% 5% 5% 5% 4 5% 8% 34%	6548
	21st to end	Day	14% 8% 2 6% 4 4 4 3 5% 6% 45%	7428
June	1st to 10th	Day	12% 7% 3 7% 5% 4 5% 4 7% 9% 38%	3000
	11th to 20th	Day	15% 6% 2 5% 4 5% 5% 4 7% 8% 39%	3000
	21st to end	Day	12% 6% 2 6% 5% 5% 6% 5% 7% 9% 37%	3000
July	1st to 10th	Day	8% 4 2 5% 4 5% 5% 5% 8% 10% 46%	6800
	11th to 20th	Day	10% 5% 2 6% 4 4 5% 4 6% 8% 46%	6800
	21st to end	Day	8% 4 2 6% 4 5% 5% 4 7% 9% 46%	7229
August	1st to 10th	Day	8% 5% 2 5% 5% 4 5% 4 6% 8% 47%	4270
	11th to 20th	Day	11% 5% 2 6% 4 4 4 3 6% 9% 46%	4041
	21st to end	Day	11% 5% 2 5% 4 4 4 3 5% 8% 50%	4532
September	1st to 10th	Day	11% 6% 1 5% 3 3 4 4 6% 8% 49%	2344
	11th to 20th	Day	13% 6% 2 5% 5% 5% 5% 4 6% 8% 42%	2090
	21st to end	Day	15% 6% 2 5% 4 4 4 3 6% 7% 43%	2090
October	1st to 10th	Day	11% 6% 2 6% 5% 4 4 4 4 6% 49%	3226
	11th to 20th	Day	12% 8% 3 7% 4 4 4 3 5% 8% 41%	3095
	21st to end	Day	14% 9% 3 8% 5% 5% 5% 4 5% 7% 35%	3091
November	1st to 10th	Day	14% 15% 4 8% 5% 5% 4 3 4 6% 30%	1615
	11th to 20th	Day	11% 16% 5% 14% 6% 4 4 3 6% 6% 25%	1600
	21st to end	Day	13% 14% 5% 11% 9% 5% 5% 4 5% 6% 23%	1515
December	1st to 10th	Day	9% 15% 6% 14% 9% 10% 7% 4 5% 6% 15%	2290
	11th to 20th	Day	10% 14% 5% 13% 6% 6% 6% 4 7% 8% 21%	2639
	21st to end	Day	9% 14% 6% 21% 8% 7% 7% 4 5% 5% 15%	3498
January	1st to 10th	Night	4 12% 7% 16% 8% 9% 7% 6% 7% 8% 17%	6787
	11th to 20th	Night	4 13% 6% 13% 9% 9% 10% 7% 7% 6% 16%	6685
	21st to end	Night	7% 17% 8% 15% 6% 5% 5% 5% 6% 6% 20%	6974
February	1st to 10th	Night	8% 12% 5% 11% 7% 7% 7% 5% 6% 7% 25%	2657
	11th to 20th	Night	7% 10% 3 9% 7% 7% 6% 6% 8% 8% 30%	2533
	21st to end	Night	7% 10% 4 15% 7% 6% 5% 4 5% 6% 31%	2070
March	1st to 10th	Night	8% 9% 4 9% 7% 5% 5% 4 6% 8% 34%	5244
	11th to 20th	Night	8% 10% 4 9% 6% 5% 5% 5% 6% 7% 34%	4980
	21st to end	Night	10% 14% 5% 13% 6% 5% 4 3 4 5% 31%	5467
April	1st to 10th	Night	10% 8% 2 6% 4 6% 6% 4 7% 7% 40%	1976
	11th to 20th	Night	14% 10% 4 8% 5% 5% 4 4 4 5% 35%	1779
	21st to end	Night	15% 9% 2 8% 4 5% 5% 4 5% 6% 37%	1800
May	1st to 10th	Night	13% 8% 2 6% 4 4 4 3 6% 7% 44%	3947
	11th to 20th	Night	14% 9% 3 7% 5% 4 5% 4 6% 9% 36%	3364
	21st to end	Night	14% 6% 2 4 3 3 4 3 5% 6% 49%	3470
June	1st to 10th	Night	11% 5% 2 5% 4 4 5% 4 7% 7% 45%	1400
	11th to 20th	Night	11% 7% 2 6% 4 5% 4 4 5% 9% 44%	1400
	21st to end	Night	10% 5% 2 5% 6% 5% 4 5% 6% 9% 44%	1400
July	1st to 10th	Night	7% 4 2 4 4 4 5% 4 7% 10% 51%	3180
	11th to 20th	Night	6% 3 1 5% 3 4 4 4 7% 8% 55%	3180
	21st to end	Night	6% 3 2 6% 4 4 5% 4 8% 10% 48%	3634
August	1st to 10th	Night	4 4 1 6% 5% 5% 5% 4 7% 8% 51%	2758
	11th to 20th	Night	11% 4 1 4 4 4 4 4 6% 9% 48%	2798
	21st to end	Night	10% 4 2 6% 4 4 4 3 5% 7% 50%	3135
September	1st to 10th	Night	9% 5% 3 4 3 3 3 4 5% 8% 55%	1833
	11th to 20th	Night	10% 5% 3 5% 3 4 4 4 5% 9% 49%	2090
	21st to end	Night	15% 6% 2 5% 5% 3 4 3 5% 7% 45%	2090
October	1st to 10th	Night	13% 6% 2 6% 4 4 4 3 4 7% 48%	3702
	11th to 20th	Night	11% 9% 3 6% 4 4 4 3 5% 7% 45%	3810
	21st to end	Night	10% 10% 3 8% 5% 4 4 3 5% 7% 40%	4467
November	1st to 10th	Night	13% 13% 4 9% 6% 4 4 4 5% 6% 31%	2683
	11th to 20th	Night	12% 15% 5% 12% 6% 5% 4 4 4 5% 27%	2800
	21st to end	Night	11% 14% 5% 12% 8% 6% 4 3 4 6% 27%	2880
December	1st to 10th	Night	7% 15% 6% 17% 13% 8% 6% 4 5% 5% 15%	4900
	11th to 20th	Night	8% 15% 5% 15% 8% 6% 5% 3 7% 5% 22%	5568
	21st to end	Night	9% 14% 5% 17% 10% 7% 6% 4 5% 5% 18%	7480

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	44% 29% 8% 14% 5%	3179
	11th to 20th	Day	47% 31% 6% 11% 5%	3253
	21st to end	Day	46% 33% 9% 10% 2	4004
February	1st to 10th	Day	26% 63% 5% 4 2	1742
	11th to 20th	Day	21% 62% 6% 9% 2	1763
	21st to end	Day	21% 64% 6% 6% 4	1576
March	1st to 10th	Day	30% 34% 15% 12% 8%	4623
	11th to 20th	Day	40% 35% 12% 10% 3	4980
	21st to end	Day	41% 31% 8% 16% 4	5464
April	1st to 10th	Day	19% 64% 5% 9% 4	2420
	11th to 20th	Day	19% 63% 5% 8% 4 1	2572
	21st to end	Day	17% 62% 6% 10% 3 1	2600
May	1st to 10th	Day	23% 31% 11% 19% 14% 1	6031
	11th to 20th	Day	34% 32% 8% 16% 10%	6552
	21st to end	Day	25% 31% 6% 19% 16% 3	7428
June	1st to 10th	Day	14% 63% 8% 11% 4	3000
	11th to 20th	Day	17% 64% 6% 9% 4	3000
	21st to end	Day	17% 64% 8% 9% 3	3000
July	1st to 10th	Day	24% 31% 22% 20% 3	6726
	11th to 20th	Day	26% 29% 18% 24% 3	6719
	21st to end	Day	24% 30% 19% 21% 5%	7025
August	1st to 10th	Day	20% 40% 13% 20% 8%	4254
	11th to 20th	Day	23% 40% 12% 23% 2	4080
	21st to end	Day	21% 39% 18% 19% 3	4531
September	1st to 10th	Day	12% 61% 8% 15% 4	2344
	11th to 20th	Day	16% 62% 9% 11% 2 1	2090
	21st to end	Day	18% 61% 7% 11% 3	2090
October	1st to 10th	Day	21% 37% 9% 21% 11%	3226
	11th to 20th	Day	21% 38% 7% 21% 12%	3095
	21st to end	Day	30% 38% 8% 18% 6%	3091
November	1st to 10th	Day	27% 56% 7% 8% 1	1615
	11th to 20th	Day	25% 58% 8% 7% 2	1600
	21st to end	Day	29% 59% 4 6% 2	1515
December	1st to 10th	Day	48% 38% 7% 5% 2	2290
	11th to 20th	Day	37% 34% 11% 11% 7%	2640
	21st to end	Day	51% 30% 5% 11% 3	3498
January	1st to 10th	Night	46% 31% 8% 10% 5%	6787
	11th to 20th	Night	47% 31% 6% 13% 4	6726
	21st to end	Night	46% 32% 10% 10% 2	6974
February	1st to 10th	Night	24% 62% 6% 5% 3	2657
	11th to 20th	Night	17% 62% 7% 11% 3	2534
	21st to end	Night	20% 62% 4 9% 4	2070
March	1st to 10th	Night	29% 34% 15% 12% 7% 3	5244
	11th to 20th	Night	31% 34% 12% 15% 8%	4980
	21st to end	Night	40% 31% 6% 16% 7%	5467
April	1st to 10th	Night	16% 62% 5% 9% 6% 1	1976
	11th to 20th	Night	17% 63% 3 9% 6% 1	1779
	21st to end	Night	18% 63% 4 10% 4 2	1800
May	1st to 10th	Night	25% 33% 8% 19% 15%	3947
	11th to 20th	Night	32% 32% 7% 15% 12% 1	3364
	21st to end	Night	23% 30% 7% 17% 19% 4	3470
June	1st to 10th	Night	11% 64% 7% 12% 6%	1400
	11th to 20th	Night	15% 63% 5% 10% 6%	1400
	21st to end	Night	15% 62% 7% 13% 3	1400
July	1st to 10th	Night	22% 32% 21% 20% 5% 1	3145
	11th to 20th	Night	20% 28% 16% 31% 5%	3138
	21st to end	Night	22% 30% 22% 22% 3	3533
August	1st to 10th	Night	18% 39% 11% 22% 9% 1	2750
	11th to 20th	Night	21% 41% 15% 18% 4	2825
	21st to end	Night	24% 39% 13% 20% 4	3135
September	1st to 10th	Night	12% 61% 7% 15% 5% 1	1833
	11th to 20th	Night	14% 62% 9% 10% 3	2090
	21st to end	Night	17% 61% 6% 10% 6% 1	2090
October	1st to 10th	Night	22% 37% 6% 24% 10% 1	3702
	11th to 20th	Night	22% 38% 7% 23% 11%	3810
	21st to end	Night	27% 38% 8% 21% 6%	4467
November	1st to 10th	Night	26% 57% 7% 8% 2	2683
	11th to 20th	Night	25% 58% 7% 7% 3	2800
	21st to end	Night	28% 58% 5% 6% 3	2880
December	1st to 10th	Night	50% 38% 5% 5% 1	4900
	11th to 20th	Night	39% 35% 9% 10% 8%	5566
	21st to end	Night	47% 30% 7% 12% 3	7480

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	10% 8% 34% 32% 14% 2	300
	11th to 20th	Day	11% 10% 30% 37% 11% 1	300
	21st to end	Day	11% 11% 35% 30% 11% 2	330
February	1st to 10th	Day	13% 13% 33% 35% 5% 1	300
	11th to 20th	Day	9% 13% 36% 30% 11% 2	300
	21st to end	Day	8% 8% 45% 29% 10% 1	249
March	1st to 10th	Day	13% 8% 34% 32% 11% 2	300
	11th to 20th	Day	13% 12% 33% 28% 13% 2	300
	21st to end	Day	14% 13% 29% 30% 12% 2	330
April	1st to 10th	Day	12% 16% 31% 29% 9% 3	520
	11th to 20th	Day	19% 14% 33% 23% 10% 1	690
	21st to end	Day	22% 11% 30% 25% 11% 2	700
May	1st to 10th	Day	15% 13% 31% 28% 10% 2	703
	11th to 20th	Day	19% 10% 31% 25% 12% 3	725
	21st to end	Day	17% 10% 24% 30% 16% 4	789
June	1st to 10th	Day	13% 11% 28% 27% 16% 5%	730
	11th to 20th	Day	15% 11% 32% 28% 12% 2	730
	21st to end	Day	12% 8% 30% 29% 15% 5%	730
July	1st to 10th	Day	8% 4 29% 29% 20% 9%	721
	11th to 20th	Day	11% 7% 29% 28% 19% 6%	718
	21st to end	Day	6% 5% 26% 35% 21% 8%	794
August	1st to 10th	Day	6% 5% 25% 33% 24% 7%	697
	11th to 20th	Day	10% 5% 22% 34% 19% 9%	665
	21st to end	Day	12% 8% 27% 29% 19% 5%	748
September	1st to 10th	Day	10% 7% 34% 31% 15% 3	554
	11th to 20th	Day	14% 11% 35% 25% 11% 3	300
	21st to end	Day	19% 9% 36% 24% 10% 1	300
October	1st to 10th	Day	19% 14% 29% 26% 10% 3	300
	11th to 20th	Day	13% 13% 39% 25% 10%	300
	21st to end	Day	24% 12% 35% 22% 7% 1	330
November	1st to 10th	Day	24% 10% 29% 28% 9% 1	300
	11th to 20th	Day	18% 12% 37% 24% 9% 1	300
	21st to end	Day	19% 11% 39% 25% 5%	300
December	1st to 10th	Day	15% 9% 34% 31% 11% 1	300
	11th to 20th	Day	16% 12% 36% 31% 6%	300
	21st to end	Day	14% 9% 34% 26% 12% 4	330
January	1st to 10th	Night	9% 8% 37% 30% 14% 2	1000
	11th to 20th	Night	14% 8% 34% 35% 9%	1000
	21st to end	Night	13% 8% 38% 31% 9% 1	1100
February	1st to 10th	Night	13% 7% 32% 35% 13% 1	1000
	11th to 20th	Night	11% 6% 33% 35% 13% 2	979
	21st to end	Night	10% 7% 37% 32% 12% 1	750
March	1st to 10th	Night	15% 7% 34% 30% 12% 2	748
	11th to 20th	Night	11% 7% 41% 30% 10% 1	600
	21st to end	Night	18% 8% 28% 30% 13% 3	660
April	1st to 10th	Night	14% 9% 32% 35% 10% 1	600
	11th to 20th	Night	17% 9% 32% 31% 10%	593
	21st to end	Night	18% 6% 28% 35% 12%	600
May	1st to 10th	Night	15% 9% 34% 33% 10%	600
	11th to 20th	Night	15% 12% 31% 30% 12% 1	591
	21st to end	Night	17% 6% 33% 32% 12% 1	650
June	1st to 10th	Night	14% 5% 30% 37% 14% 1	600
	11th to 20th	Night	13% 5% 34% 35% 13% 1	600
	21st to end	Night	11% 5% 27% 39% 18% 1	600
July	1st to 10th	Night	7% 3 24% 43% 22% 1	585
	11th to 20th	Night	7% 4 26% 44% 19% 1	582
	21st to end	Night	6% 3 24% 44% 21% 2	657
August	1st to 10th	Night	7% 3 25% 44% 20% 1	579
	11th to 20th	Night	11% 3 23% 38% 22% 3	564
	21st to end	Night	11% 6% 26% 37% 20%	627
September	1st to 10th	Night	10% 3 33% 35% 16% 2	570
	11th to 20th	Night	15% 4 31% 38% 12% 1	570
	21st to end	Night	18% 6% 32% 34% 10% 1	570
October	1st to 10th	Night	22% 8% 33% 29% 8%	701
	11th to 20th	Night	21% 8% 35% 26% 9%	779
	21st to end	Night	18% 10% 35% 30% 8% 1	1045
November	1st to 10th	Night	20% 8% 37% 27% 8%	975
	11th to 20th	Night	18% 9% 34% 28% 8% 2	1000
	21st to end	Night	17% 10% 42% 25% 6% 1	1000
December	1st to 10th	Night	13% 9% 33% 32% 12% 1	1000
	11th to 20th	Night	16% 8% 37% 31% 6% 1	1000
	21st to end	Night	19% 8% 33% 29% 10% 1	1100

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