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 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	11% 9% 3 8% 6% 5% 5% 4 6% 8% 36%	105513
	Night	10% 10% 4 9% 6% 5% 5% 4 6% 7% 35%	102090
Transparency	Day	24% 49% 10% 14% 4	105258
	Night	25% 49% 8% 13% 5%	101992
Seeing	Day	14% 10% 31% 29% 14% 4	16217
	Night	14% 7% 33% 33% 12% 1	26119

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	6% 15% 6% 12% 9% 6% 5% 6% 7% 5% 22%	2219
	11th to 20th	Day	4 8% 5% 18% 12% 11% 12% 7% 5% 6% 11%	2244
	21st to end	Day	8% 17% 7% 16% 7% 6% 6% 5% 5% 6% 16%	2794
February	1st to 10th	Day	8% 14% 6% 10% 8% 7% 8% 6% 7% 5% 21%	1654
	11th to 20th	Day	6% 11% 3 11% 9% 8% 7% 6% 7% 8% 24%	1664
	21st to end	Day	7% 10% 3 14% 9% 8% 8% 5% 6% 7% 24%	1499
March	1st to 10th	Day	13% 11% 3 9% 13% 6% 5% 4 6% 7% 23%	3214
	11th to 20th	Day	8% 10% 5% 14% 10% 6% 6% 5% 6% 8% 22%	3478
	21st to end	Day	10% 14% 6% 12% 5% 4 4 3 5% 7% 29%	3814
April	1st to 10th	Day	9% 13% 4 8% 5% 4 5% 4 6% 8% 34%	2299
	11th to 20th	Day	14% 11% 3 8% 6% 4 5% 5% 5% 7% 32%	2442
	21st to end	Day	18% 9% 3 9% 5% 4 4 4 5% 7% 33%	2470
May	1st to 10th	Day	19% 9% 3 7% 4 4 4 4 5% 7% 33%	4209
	11th to 20th	Day	18% 7% 2 7% 5% 5% 5% 4 6% 7% 34%	4563
	21st to end	Day	19% 10% 3 7% 5% 5% 4 4 5% 7% 33%	5173
June	1st to 10th	Day	12% 7% 3 7% 5% 4 5% 4 7% 9% 37%	2850
	11th to 20th	Day	15% 6% 2 5% 4 5% 5% 4 7% 8% 38%	2850
	21st to end	Day	12% 6% 2 6% 5% 5% 6% 5% 7% 9% 37%	2850
July	1st to 10th	Day	8% 3 1 4 4 5% 5% 5% 8% 11% 45%	4750
	11th to 20th	Day	8% 4 1 4 4 4 4 4 6% 9% 51%	4750
	21st to end	Day	6% 3 2 5% 3 4 4 4 6% 9% 52%	5035
August	1st to 10th	Day	9% 5% 2 5% 5% 4 5% 4 6% 8% 47%	4213
	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	15% 15% 4 8% 5% 5% 4 3 4 6% 30%	1559
	11th to 20th	Day	9% 16% 5% 14% 6% 4 4 3 6% 6% 25%	1520
	21st to end	Day	13% 14% 6% 10% 9% 5% 5% 4 5% 6% 24%	1440
December	1st to 10th	Day	8% 15% 5% 14% 8% 8% 7% 5% 4 7% 19%	1330
	11th to 20th	Day	10% 15% 6% 15% 6% 7% 7% 5% 7% 7% 17%	1679
	21st to end	Day	10% 14% 5% 14% 8% 8% 8% 4 6% 6% 17%	2442
January	1st to 10th	Night	5% 13% 7% 13% 7% 9% 7% 6% 7% 7% 20%	4737
	11th to 20th	Night	5% 13% 6% 15% 11% 10% 10% 5% 5% 5% 15%	4663
	21st to end	Night	8% 17% 7% 15% 7% 5% 6% 5% 6% 5% 19%	4873
February	1st to 10th	Night	8% 12% 5% 11% 7% 6% 7% 5% 6% 7% 25%	2525
	11th to 20th	Night	7% 10% 3 9% 7% 7% 5% 5% 8% 8% 30%	2403
	21st to end	Night	7% 10% 4 14% 7% 6% 5% 4 5% 6% 31%	1970
March	1st to 10th	Night	11% 10% 3 9% 8% 5% 5% 4 5% 7% 32%	3646
	11th to 20th	Night	6% 9% 4 10% 7% 5% 5% 4 6% 8% 36%	3480
	21st to end	Night	10% 13% 5% 13% 6% 4 4 3 4 6% 31%	3817
April	1st to 10th	Night	9% 7% 2 6% 5% 6% 6% 4 7% 7% 41%	1877
	11th to 20th	Night	14% 10% 4 8% 5% 5% 4 4 4 6% 36%	1689
	21st to end	Night	15% 9% 3 8% 4 4 4 4 6% 6% 37%	1710
May	1st to 10th	Night	18% 9% 3 7% 5% 4 4 3 6% 7% 34%	2759
	11th to 20th	Night	14% 9% 3 7% 4 4 5% 3 5% 7% 40%	2339
	21st to end	Night	19% 7% 2 4 3 3 3 3 5% 6% 43%	2414
June	1st to 10th	Night	11% 5% 2 5% 4 4 5% 4 7% 7% 45%	1330
	11th to 20th	Night	12% 7% 2 5% 4 5% 4 3 5% 9% 44%	1330
	21st to end	Night	10% 5% 2 5% 6% 5% 4 5% 6% 9% 45%	1330
July	1st to 10th	Night	8% 3 2 3 3 3 4 4 7% 11% 53%	2220
	11th to 20th	Night	5% 2 1 4 3 4 3 4 6% 8% 59%	2220
	21st to end	Night	6% 3 2 5% 4 3 5% 5% 7% 10% 50%	2526
August	1st to 10th	Night	4 4 2 6% 5% 5% 5% 4 6% 8% 51%	2726
	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 10% 6% 5% 4 4 5% 6% 30%	2592
	11th to 20th	Night	11% 15% 5% 12% 6% 5% 4 4 4 5% 27%	2660
	21st to end	Night	11% 14% 4 11% 8% 6% 4 3 4 6% 28%	2736
December	1st to 10th	Night	7% 15% 5% 13% 9% 7% 5% 5% 6% 6% 22%	2850
	11th to 20th	Night	10% 15% 6% 15% 8% 6% 5% 3 5% 5% 22%	3518
	21st to end	Night	11% 14% 4 12% 9% 7% 5% 4 6% 6% 21%	5225

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	38% 39% 9% 11% 3	2219
	11th to 20th	Day	45% 41% 7% 6% 1	2265
	21st to end	Day	39% 44% 5% 9% 2	2794
February	1st to 10th	Day	23% 66% 6% 4 2	1654
	11th to 20th	Day	20% 65% 6% 7% 2	1673
	21st to end	Day	18% 66% 5% 6% 4	1499
March	1st to 10th	Day	29% 46% 12% 12% 2	3214
	11th to 20th	Day	34% 47% 9% 8% 2	3480
	21st to end	Day	32% 42% 7% 14% 5%	3814
April	1st to 10th	Day	17% 67% 5% 8% 3	2299
	11th to 20th	Day	17% 66% 5% 7% 4 1	2442
	21st to end	Day	15% 65% 6% 9% 3 1	2470
May	1st to 10th	Day	28% 43% 9% 14% 5% 1	4209
	11th to 20th	Day	29% 44% 8% 11% 7%	4567
	21st to end	Day	31% 43% 8% 14% 4	5173
June	1st to 10th	Day	12% 66% 8% 10% 4	2850
	11th to 20th	Day	16% 67% 5% 8% 4	2850
	21st to end	Day	15% 66% 7% 9% 2	2850
July	1st to 10th	Day	20% 42% 20% 16% 3	4676
	11th to 20th	Day	16% 39% 18% 23% 4	4669
	21st to end	Day	16% 39% 17% 24% 4	4876
August	1st to 10th	Day	20% 41% 13% 20% 7%	4197
	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	26% 58% 6% 8% 2	1559
	11th to 20th	Day	23% 61% 8% 6% 2	1520
	21st to end	Day	27% 61% 4 6% 2	1440
December	1st to 10th	Day	26% 62% 6% 5% 2	1330
	11th to 20th	Day	29% 52% 9% 7% 3	1680
	21st to end	Day	37% 42% 6% 11% 4	2442
January	1st to 10th	Night	37% 43% 8% 9% 3	4737
	11th to 20th	Night	45% 41% 5% 7% 2	4704
	21st to end	Night	40% 43% 8% 8% 1	4873
February	1st to 10th	Night	22% 65% 6% 5% 2	2525
	11th to 20th	Night	16% 66% 7% 9% 2	2404
	21st to end	Night	18% 65% 4 8% 4	1970
March	1st to 10th	Night	25% 46% 11% 13% 5%	3646
	11th to 20th	Night	21% 47% 13% 13% 5%	3480
	21st to end	Night	34% 42% 6% 13% 5% 1	3817
April	1st to 10th	Night	14% 65% 5% 8% 6%	1877
	11th to 20th	Night	16% 66% 3 8% 6% 1	1689
	21st to end	Night	16% 66% 3 10% 4 2	1710
May	1st to 10th	Night	28% 45% 8% 14% 5%	2759
	11th to 20th	Night	26% 43% 7% 15% 7% 2	2339
	21st to end	Night	25% 41% 8% 19% 7%	2414
June	1st to 10th	Night	11% 67% 6% 11% 5%	1330
	11th to 20th	Night	15% 66% 4 9% 6%	1330
	21st to end	Night	14% 65% 7% 12% 2	1330
July	1st to 10th	Night	16% 42% 20% 18% 3	2185
	11th to 20th	Night	13% 38% 14% 30% 5%	2178
	21st to end	Night	18% 38% 19% 21% 4	2446
August	1st to 10th	Night	19% 39% 11% 21% 9% 1	2718
	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	25% 59% 7% 7% 1	2592
	11th to 20th	Night	22% 61% 6% 6% 3	2660
	21st to end	Night	25% 61% 5% 6% 3	2736
December	1st to 10th	Night	25% 61% 5% 7% 2	2850
	11th to 20th	Night	28% 51% 8% 9% 3	3516
	21st to end	Night	33% 41% 9% 12% 5%	5225

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% 7% 34% 32% 13% 3	270
	11th to 20th	Day	11% 10% 29% 37% 11% 1	270
	21st to end	Day	12% 9% 33% 32% 11% 2	297
February	1st to 10th	Day	13% 11% 34% 36% 5% 1	270
	11th to 20th	Day	10% 14% 37% 26% 12% 1	270
	21st to end	Day	8% 8% 44% 29% 10% 1	225
March	1st to 10th	Day	13% 8% 34% 32% 10% 2	270
	11th to 20th	Day	12% 12% 32% 28% 13% 2	270
	21st to end	Day	13% 13% 28% 31% 12% 2	297
April	1st to 10th	Day	13% 15% 31% 29% 10% 3	479
	11th to 20th	Day	19% 13% 33% 23% 11% 1	640
	21st to end	Day	20% 11% 32% 24% 11% 2	650
May	1st to 10th	Day	16% 13% 30% 28% 10% 2	653
	11th to 20th	Day	19% 10% 30% 26% 13% 3	675
	21st to end	Day	18% 10% 25% 30% 15% 2	734
June	1st to 10th	Day	13% 11% 28% 27% 16% 6%	680
	11th to 20th	Day	16% 12% 32% 27% 11% 3	680
	21st to end	Day	12% 8% 28% 31% 16% 6%	680
July	1st to 10th	Day	8% 4 29% 28% 21% 10%	671
	11th to 20th	Day	10% 7% 28% 29% 20% 6%	668
	21st to end	Day	6% 5% 26% 34% 21% 9%	739
August	1st to 10th	Day	6% 5% 25% 33% 23% 7%	676
	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% 9% 29% 29% 8% 1	279
	11th to 20th	Day	15% 13% 38% 24% 10%	270
	21st to end	Day	20% 11% 41% 24% 4	270
December	1st to 10th	Day	14% 9% 34% 31% 11% 1	270
	11th to 20th	Day	16% 12% 36% 30% 6%	270
	21st to end	Day	13% 9% 35% 27% 12% 3	297
January	1st to 10th	Night	9% 8% 36% 31% 14% 1	950
	11th to 20th	Night	14% 7% 35% 35% 9%	950
	21st to end	Night	13% 7% 38% 32% 9% 1	1045
February	1st to 10th	Night	13% 7% 31% 35% 13% 1	950
	11th to 20th	Night	11% 6% 33% 35% 13% 2	929
	21st to end	Night	10% 6% 37% 33% 13% 1	714
March	1st to 10th	Night	15% 6% 32% 31% 13% 2	711
	11th to 20th	Night	10% 7% 41% 30% 11% 1	570
	21st to end	Night	18% 8% 28% 30% 13% 3	627
April	1st to 10th	Night	13% 9% 32% 35% 10% 1	570
	11th to 20th	Night	17% 9% 32% 31% 11%	563
	21st to end	Night	18% 6% 28% 36% 12%	570
May	1st to 10th	Night	15% 9% 33% 32% 10%	570
	11th to 20th	Night	14% 12% 30% 31% 12% 1	561
	21st to end	Night	18% 6% 34% 31% 11% 1	617
June	1st to 10th	Night	14% 5% 29% 37% 14% 1	570
	11th to 20th	Night	13% 5% 34% 34% 14% 1	570
	21st to end	Night	11% 4 26% 39% 19% 1	570
July	1st to 10th	Night	7% 3 24% 43% 22% 1	555
	11th to 20th	Night	7% 4 26% 43% 20% 1	552
	21st to end	Night	6% 3 23% 43% 21% 3	624
August	1st to 10th	Night	8% 3 25% 44% 20% 1	567
	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%	943
	11th to 20th	Night	17% 9% 35% 29% 8% 1	950
	21st to end	Night	17% 10% 42% 24% 6% 1	950
December	1st to 10th	Night	13% 8% 33% 33% 12% 1	950
	11th to 20th	Night	17% 8% 36% 32% 6% 1	950
	21st to end	Night	19% 8% 33% 29% 10% 1	1045

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