Dorion
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Dorion clear sky chart from 2005-11-06 to 2026-07-01.

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	12% 9% 3 8% 5% 5% 5% 4 6% 7% 35%	137854
	Night	12% 11% 4 9% 6% 5% 5% 4 6% 7% 32%	134822
Transparency	Day	46% 7% 14% 22% 11% 1	141258
	Night	50% 7% 13% 21% 9% 1	139504
Seeing	Day	19% 16% 35% 20% 7% 2	18131
	Night	19% 11% 31% 28% 10% 1	27768

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	7% 11% 5% 12% 6% 6% 6% 5% 6% 9% 27%	4691
	11th to 20th	Day	6% 12% 6% 14% 7% 6% 7% 7% 10% 8% 19%	4679
	21st to end	Day	7% 11% 8% 11% 6% 7% 7% 6% 7% 9% 23%	5156
February	1st to 10th	Day	7% 12% 4 10% 6% 5% 7% 5% 5% 7% 32%	1730
	11th to 20th	Day	7% 12% 5% 9% 7% 6% 5% 5% 5% 6% 34%	1885
	21st to end	Day	6% 13% 5% 10% 7% 7% 5% 4 6% 7% 31%	1730
March	1st to 10th	Day	10% 11% 4 9% 6% 5% 4 4 5% 6% 35%	4578
	11th to 20th	Day	8% 11% 5% 12% 6% 6% 6% 5% 6% 6% 31%	4792
	21st to end	Day	17% 14% 4 9% 6% 4 4 3 4 5% 31%	6101
April	1st to 10th	Day	13% 13% 5% 8% 6% 4 4 3 5% 7% 32%	2520
	11th to 20th	Day	17% 11% 4 9% 6% 5% 4 3 6% 7% 30%	2530
	21st to end	Day	17% 12% 3 7% 5% 4 5% 4 5% 5% 33%	2787
May	1st to 10th	Day	12% 10% 3 7% 5% 4 4 3 5% 7% 40%	8241
	11th to 20th	Day	17% 8% 3 6% 4 4 4 3 5% 7% 39%	8222
	21st to end	Day	10% 6% 2 6% 4 4 5% 4 6% 8% 47%	9061
June	1st to 10th	Day	17% 7% 2 6% 5% 4 5% 4 6% 8% 37%	3139
	11th to 20th	Day	13% 7% 2 7% 5% 5% 6% 4 6% 9% 37%	3150
	21st to end	Day	17% 6% 2 6% 5% 5% 5% 4 6% 8% 36%	3150
July	1st to 10th	Day	12% 4 2 5% 4 4 5% 4 7% 9% 44%	6373
	11th to 20th	Day	10% 6% 2 6% 4 5% 5% 4 7% 9% 41%	6360
	21st to end	Day	10% 5% 2 6% 5% 5% 5% 5% 8% 10% 40%	6926
August	1st to 10th	Day	10% 5% 3 8% 6% 6% 6% 5% 8% 9% 34%	4563
	11th to 20th	Day	12% 4 1 4 4 4 4 4 7% 8% 47%	4440
	21st to end	Day	11% 6% 3 7% 4 5% 5% 5% 6% 9% 40%	4326
September	1st to 10th	Day	13% 6% 2 7% 4 5% 5% 4 6% 7% 40%	2400
	11th to 20th	Day	16% 7% 3 7% 4 4 4 3 6% 9% 36%	2323
	21st to end	Day	17% 8% 3 8% 5% 4 4 4 5% 8% 34%	2200
October	1st to 10th	Day	18% 11% 3 7% 5% 4 4 3 5% 6% 33%	2040
	11th to 20th	Day	17% 12% 4 9% 6% 5% 5% 4 6% 7% 23%	1900
	21st to end	Day	20% 13% 4 9% 6% 6% 5% 4 4 5% 25%	1980
November	1st to 10th	Day	14% 11% 4 10% 8% 6% 5% 5% 6% 7% 25%	1842
	11th to 20th	Day	17% 16% 5% 11% 5% 5% 5% 3 5% 5% 23%	1680
	21st to end	Day	15% 12% 5% 12% 7% 6% 6% 4 6% 6% 20%	1563
December	1st to 10th	Day	12% 12% 5% 13% 8% 6% 6% 4 6% 6% 24%	2350
	11th to 20th	Day	8% 14% 6% 11% 7% 6% 5% 4 6% 6% 27%	2691
	21st to end	Day	17% 20% 5% 10% 6% 4 3 3 4 6% 21%	3755
January	1st to 10th	Night	7% 13% 5% 11% 6% 6% 6% 5% 6% 7% 29%	8233
	11th to 20th	Night	5% 13% 5% 15% 9% 7% 6% 6% 8% 7% 18%	8236
	21st to end	Night	5% 9% 6% 13% 7% 7% 7% 6% 9% 8% 24%	9058
February	1st to 10th	Night	8% 10% 5% 10% 6% 5% 7% 6% 7% 7% 31%	2887
	11th to 20th	Night	9% 10% 3 8% 6% 7% 7% 5% 7% 8% 30%	2621
	21st to end	Night	8% 13% 5% 11% 7% 7% 6% 4 5% 7% 29%	2076
March	1st to 10th	Night	11% 9% 3 9% 5% 5% 6% 4 7% 7% 35%	5482
	11th to 20th	Night	9% 14% 4 10% 6% 6% 5% 4 5% 7% 28%	5429
	21st to end	Night	15% 14% 4 9% 5% 6% 4 3 5% 5% 30%	5072
April	1st to 10th	Night	14% 12% 3 8% 6% 6% 5% 4 6% 7% 31%	2100
	11th to 20th	Night	17% 11% 3 8% 5% 4 4 4 6% 7% 33%	2039
	21st to end	Night	16% 11% 3 7% 6% 4 3 3 5% 7% 35%	1831
May	1st to 10th	Night	13% 7% 2 5% 3 4 4 4 5% 7% 45%	4688
	11th to 20th	Night	18% 8% 3 6% 4 4 4 3 4 5% 40%	4670
	21st to end	Night	14% 5% 2 5% 4 4 4 3 5% 5% 48%	5148
June	1st to 10th	Night	15% 9% 2 7% 5% 5% 4 4 5% 8% 36%	1479
	11th to 20th	Night	13% 8% 3 7% 5% 4 5% 3 6% 7% 39%	1470
	21st to end	Night	16% 6% 2 5% 5% 4 6% 3 7% 9% 37%	1470
July	1st to 10th	Night	7% 5% 2 8% 5% 5% 5% 4 6% 9% 45%	3588
	11th to 20th	Night	11% 5% 2 7% 4 4 4 4 5% 8% 45%	3620
	21st to end	Night	11% 5% 2 6% 4 4 5% 4 7% 10% 41%	3948
August	1st to 10th	Night	12% 6% 2 5% 5% 4 5% 4 6% 10% 42%	2597
	11th to 20th	Night	12% 4 2 4 4 4 4 4 6% 9% 48%	2616
	21st to end	Night	14% 6% 3 6% 4 4 4 3 5% 6% 46%	3570
September	1st to 10th	Night	14% 5% 2 6% 3 4 5% 4 6% 6% 46%	2000
	11th to 20th	Night	14% 7% 2 5% 4 4 4 4 6% 8% 41%	2056
	21st to end	Night	17% 7% 3 7% 4 4 3 3 6% 7% 39%	2200
October	1st to 10th	Night	18% 7% 3 7% 4 4 5% 4 5% 6% 36%	2356
	11th to 20th	Night	16% 11% 3 8% 4 5% 4 3 6% 7% 32%	2500
	21st to end	Night	19% 12% 3 9% 5% 5% 5% 4 5% 6% 27%	2860
November	1st to 10th	Night	14% 12% 3 9% 6% 5% 5% 4 6% 6% 29%	2671
	11th to 20th	Night	17% 13% 5% 11% 6% 5% 5% 4 5% 5% 23%	2940
	21st to end	Night	15% 14% 5% 12% 7% 5% 5% 5% 5% 6% 23%	3054
December	1st to 10th	Night	10% 17% 5% 12% 7% 5% 6% 4 6% 7% 21%	5060
	11th to 20th	Night	9% 13% 5% 13% 6% 5% 4 4 5% 7% 29%	5736
	21st to end	Night	19% 20% 5% 10% 6% 4 4 3 4 5% 20%	7461

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	52% 8% 14% 17% 8% 1	4692
	11th to 20th	Day	57% 6% 11% 20% 6%	4710
	21st to end	Day	56% 6% 12% 15% 10%	5156
February	1st to 10th	Day	47% 7% 13% 20% 11% 1	1730
	11th to 20th	Day	48% 6% 14% 21% 10% 1	1894
	21st to end	Day	52% 5% 12% 17% 14% 1	1730
March	1st to 10th	Day	49% 5% 12% 17% 15% 2	4580
	11th to 20th	Day	52% 6% 11% 18% 12% 1	4792
	21st to end	Day	54% 5% 8% 15% 15% 2	6101
April	1st to 10th	Day	51% 6% 10% 20% 11% 2	2520
	11th to 20th	Day	52% 6% 13% 20% 7% 1	2530
	21st to end	Day	51% 6% 10% 18% 14% 2	2787
May	1st to 10th	Day	42% 6% 11% 24% 16% 1	8250
	11th to 20th	Day	43% 6% 10% 21% 18% 2	8226
	21st to end	Day	33% 7% 13% 24% 19% 3	9061
June	1st to 10th	Day	45% 8% 14% 19% 14% 1	3139
	11th to 20th	Day	41% 8% 14% 25% 11% 1	3150
	21st to end	Day	45% 7% 15% 24% 9% 1	3150
July	1st to 10th	Day	33% 9% 18% 30% 9%	6305
	11th to 20th	Day	35% 8% 19% 31% 6%	6285
	21st to end	Day	36% 8% 18% 29% 8%	6728
August	1st to 10th	Day	40% 10% 17% 26% 7% 1	4548
	11th to 20th	Day	33% 8% 19% 29% 11%	4482
	21st to end	Day	39% 8% 14% 28% 10%	4325
September	1st to 10th	Day	41% 8% 16% 25% 10%	2400
	11th to 20th	Day	44% 9% 21% 22% 4	2323
	21st to end	Day	47% 8% 18% 19% 7% 1	2200
October	1st to 10th	Day	43% 6% 17% 20% 13% 1	3326
	11th to 20th	Day	52% 6% 14% 24% 3	3077
	21st to end	Day	56% 7% 16% 18% 3	3180
November	1st to 10th	Day	57% 8% 14% 16% 5% 1	1842
	11th to 20th	Day	64% 6% 13% 13% 4	1680
	21st to end	Day	63% 9% 13% 9% 5%	1563
December	1st to 10th	Day	59% 9% 16% 11% 4	2350
	11th to 20th	Day	55% 6% 13% 14% 11%	2691
	21st to end	Day	64% 6% 8% 17% 5%	3755
January	1st to 10th	Night	54% 7% 12% 16% 8% 2	8233
	11th to 20th	Night	62% 5% 9% 17% 6%	8280
	21st to end	Night	54% 7% 12% 19% 8%	9058
February	1st to 10th	Night	49% 8% 12% 19% 11% 1	2887
	11th to 20th	Night	50% 6% 13% 20% 10%	2622
	21st to end	Night	53% 6% 11% 20% 9% 1	2076
March	1st to 10th	Night	46% 5% 11% 15% 17% 5%	5493
	11th to 20th	Night	53% 7% 13% 18% 8% 1	5430
	21st to end	Night	56% 5% 8% 18% 11% 1	5072
April	1st to 10th	Night	52% 5% 9% 22% 12%	2100
	11th to 20th	Night	49% 6% 11% 21% 12% 2	2039
	21st to end	Night	47% 5% 11% 22% 13% 3	1831
May	1st to 10th	Night	37% 6% 12% 29% 13% 3	4695
	11th to 20th	Night	46% 5% 11% 23% 13% 3	4671
	21st to end	Night	38% 5% 10% 29% 17% 1	5149
June	1st to 10th	Night	45% 7% 11% 20% 14% 2	1479
	11th to 20th	Night	42% 7% 11% 24% 14% 1	1470
	21st to end	Night	43% 11% 14% 22% 9% 1	1470
July	1st to 10th	Night	36% 8% 16% 28% 12%	3548
	11th to 20th	Night	34% 9% 21% 29% 6% 1	3572
	21st to end	Night	37% 8% 15% 30% 10%	3832
August	1st to 10th	Night	38% 8% 17% 30% 7% 1	2588
	11th to 20th	Night	32% 7% 20% 32% 8%	2640
	21st to end	Night	41% 7% 16% 26% 11%	3570
September	1st to 10th	Night	38% 8% 16% 27% 12%	2000
	11th to 20th	Night	40% 10% 20% 26% 4	2056
	21st to end	Night	47% 7% 16% 25% 6%	2200
October	1st to 10th	Night	37% 6% 17% 26% 15%	3850
	11th to 20th	Night	47% 7% 13% 24% 8%	4062
	21st to end	Night	57% 8% 15% 15% 5%	4610
November	1st to 10th	Night	55% 8% 14% 18% 5% 1	2671
	11th to 20th	Night	62% 6% 14% 13% 4	2940
	21st to end	Night	62% 8% 14% 11% 5%	3054
December	1st to 10th	Night	60% 7% 17% 12% 3	5060
	11th to 20th	Night	55% 6% 12% 19% 8%	5735
	21st to end	Night	67% 7% 8% 15% 4	7461

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	17% 13% 43% 21% 6%	330
	11th to 20th	Day	15% 15% 40% 23% 7% 1	330
	21st to end	Day	16% 13% 45% 18% 6% 2	363
February	1st to 10th	Day	17% 19% 44% 15% 5% 1	330
	11th to 20th	Day	13% 21% 43% 20% 3	330
	21st to end	Day	18% 29% 36% 14% 3	273
March	1st to 10th	Day	16% 22% 39% 18% 3 1	330
	11th to 20th	Day	16% 30% 36% 11% 5% 1	334
	21st to end	Day	21% 16% 37% 19% 5% 2	594
April	1st to 10th	Day	22% 21% 31% 21% 6%	540
	11th to 20th	Day	26% 20% 26% 17% 9% 2	532
	21st to end	Day	25% 19% 27% 18% 7% 3	597
May	1st to 10th	Day	20% 20% 34% 18% 6% 2	753
	11th to 20th	Day	21% 18% 36% 17% 6% 2	775
	21st to end	Day	20% 17% 34% 21% 6% 2	844
June	1st to 10th	Day	19% 14% 41% 19% 6% 2	780
	11th to 20th	Day	18% 17% 39% 17% 6% 2	780
	21st to end	Day	20% 15% 33% 23% 7% 1	780
July	1st to 10th	Day	10% 12% 38% 26% 10% 3	722
	11th to 20th	Day	12% 13% 39% 24% 10% 3	718
	21st to end	Day	10% 11% 36% 25% 12% 5%	794
August	1st to 10th	Day	13% 13% 37% 26% 10% 2	726
	11th to 20th	Day	16% 9% 32% 28% 11% 4	685
	21st to end	Day	17% 14% 33% 22% 11% 2	583
September	1st to 10th	Day	16% 12% 30% 26% 12% 3	530
	11th to 20th	Day	20% 12% 32% 23% 12% 2	530
	21st to end	Day	22% 13% 32% 20% 12% 2	530
October	1st to 10th	Day	29% 18% 28% 17% 6% 1	370
	11th to 20th	Day	23% 21% 34% 19% 3	330
	21st to end	Day	31% 22% 33% 11% 4	363
November	1st to 10th	Day	24% 22% 33% 16% 5%	330
	11th to 20th	Day	32% 22% 30% 10% 5%	330
	21st to end	Day	27% 19% 34% 15% 5%	268
December	1st to 10th	Day	22% 15% 33% 20% 7% 3	220
	11th to 20th	Day	24% 20% 33% 19% 5% 1	220
	21st to end	Day	27% 16% 30% 21% 5% 1	287
January	1st to 10th	Night	17% 12% 39% 26% 6%	1050
	11th to 20th	Night	16% 13% 36% 26% 8% 1	1050
	21st to end	Night	16% 8% 40% 26% 8% 1	1155
February	1st to 10th	Night	15% 12% 36% 28% 8% 1	1050
	11th to 20th	Night	15% 12% 37% 26% 8% 1	987
	21st to end	Night	14% 12% 38% 27% 7% 1	692
March	1st to 10th	Night	14% 13% 37% 27% 8% 1	840
	11th to 20th	Night	19% 16% 32% 27% 6% 1	793
	21st to end	Night	17% 11% 32% 27% 11% 2	693
April	1st to 10th	Night	19% 14% 28% 31% 7% 1	630
	11th to 20th	Night	22% 11% 27% 29% 11% 1	623
	21st to end	Night	22% 6% 28% 31% 12% 1	630
May	1st to 10th	Night	20% 10% 27% 32% 11% 1	630
	11th to 20th	Night	18% 10% 29% 33% 9% 1	621
	21st to end	Night	21% 9% 23% 34% 12% 1	683
June	1st to 10th	Night	17% 7% 32% 33% 11%	429
	11th to 20th	Night	16% 8% 28% 40% 8%	420
	21st to end	Night	20% 5% 30% 35% 10%	420
July	1st to 10th	Night	12% 4 31% 39% 14% 1	566
	11th to 20th	Night	11% 4 30% 41% 13% 1	582
	21st to end	Night	9% 4 26% 41% 19% 1	657
August	1st to 10th	Night	12% 5% 28% 39% 16% 1	597
	11th to 20th	Night	14% 6% 22% 33% 22% 3	594
	21st to end	Night	17% 7% 28% 29% 17% 2	660
September	1st to 10th	Night	17% 6% 24% 34% 18% 2	600
	11th to 20th	Night	17% 9% 29% 30% 13% 1	656
	21st to end	Night	22% 9% 27% 29% 12% 1	800
October	1st to 10th	Night	23% 13% 31% 23% 10% 1	800
	11th to 20th	Night	22% 14% 31% 23% 9% 1	800
	21st to end	Night	27% 10% 32% 23% 7% 1	880
November	1st to 10th	Night	22% 14% 33% 24% 6% 1	825
	11th to 20th	Night	26% 16% 30% 20% 7% 1	1050
	21st to end	Night	24% 17% 32% 21% 6%	1050
December	1st to 10th	Night	18% 16% 34% 25% 7% 1	1050
	11th to 20th	Night	21% 13% 30% 27% 8% 1	1050
	21st to end	Night	24% 13% 30% 26% 6% 1	1155

Page generated at 2026-06-28 02:10:47. Version ac07

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