Davin Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Davin Observatory 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	9% 8% 3 9% 6% 5% 5% 4 6% 8% 37%	131356
	Night	7% 9% 4 9% 6% 6% 6% 4 6% 7% 35%	128431
Transparency	Day	44% 6% 15% 25% 10% 1	131072
	Night	46% 6% 15% 23% 10% 1	128295
Seeing	Day	12% 9% 31% 30% 14% 3	17638
	Night	12% 8% 33% 33% 12% 1	27127

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% 16% 6% 16% 8% 9% 9% 5% 6% 7% 14%	3291
	11th to 20th	Day	3 8% 3 12% 11% 9% 8% 8% 11% 11% 15%	3616
	21st to end	Day	4 12% 6% 15% 8% 6% 5% 3 5% 7% 28%	4004
February	1st to 10th	Day	7% 14% 5% 12% 8% 8% 7% 6% 8% 6% 18%	1624
	11th to 20th	Day	6% 12% 5% 12% 6% 7% 8% 6% 7% 7% 24%	1755
	21st to end	Day	5% 10% 5% 13% 10% 6% 7% 6% 9% 9% 21%	1639
March	1st to 10th	Day	6% 11% 4 16% 7% 5% 7% 4 5% 7% 26%	4500
	11th to 20th	Day	6% 12% 6% 15% 7% 6% 5% 4 6% 7% 27%	4694
	21st to end	Day	8% 12% 6% 13% 6% 5% 5% 4 6% 7% 28%	5957
April	1st to 10th	Day	6% 8% 3 7% 6% 6% 6% 5% 7% 8% 37%	2400
	11th to 20th	Day	13% 14% 4 11% 5% 5% 5% 3 5% 7% 27%	2422
	21st to end	Day	13% 10% 3 8% 6% 5% 4 4 6% 7% 36%	2730
May	1st to 10th	Day	14% 9% 2 5% 3 3 4 4 6% 8% 41%	6340
	11th to 20th	Day	16% 8% 3 6% 5% 5% 5% 4 7% 9% 31%	6298
	21st to end	Day	12% 6% 2 6% 4 4 4 4 6% 7% 45%	7192
June	1st to 10th	Day	14% 7% 2 6% 5% 4 5% 5% 7% 8% 37%	3039
	11th to 20th	Day	18% 8% 3 8% 5% 5% 5% 5% 6% 8% 31%	3200
	21st to end	Day	11% 5% 1 5% 5% 5% 5% 5% 8% 8% 41%	3200
July	1st to 10th	Day	5% 5% 1 6% 4 4 5% 5% 8% 10% 46%	7115
	11th to 20th	Day	8% 5% 2 6% 4 4 5% 5% 7% 10% 43%	6433
	21st to end	Day	6% 4 1 5% 4 4 4 4 6% 8% 55%	6898
August	1st to 10th	Day	9% 5% 2 6% 5% 4 5% 4 6% 7% 46%	4552
	11th to 20th	Day	6% 4 2 5% 4 5% 5% 4 7% 10% 48%	4483
	21st to end	Day	9% 4 2 6% 4 3 4 4 5% 7% 53%	4394
September	1st to 10th	Day	11% 4 2 5% 5% 4 4 3 4 8% 49%	2400
	11th to 20th	Day	13% 8% 3 7% 4 4 3 4 6% 8% 42%	2365
	21st to end	Day	12% 7% 2 4 3 3 4 4 4 8% 49%	2200
October	1st to 10th	Day	9% 8% 3 7% 5% 4 5% 4 6% 8% 42%	3273
	11th to 20th	Day	7% 7% 2 5% 3 3 4 4 7% 10% 47%	3069
	21st to end	Day	6% 10% 4 10% 5% 4 5% 4 6% 8% 38%	3190
November	1st to 10th	Day	11% 14% 5% 10% 6% 5% 4 4 5% 6% 29%	1758
	11th to 20th	Day	7% 13% 4 14% 8% 6% 5% 5% 5% 6% 26%	1677
	21st to end	Day	8% 14% 5% 12% 6% 7% 6% 5% 5% 5% 27%	1470
December	1st to 10th	Day	5% 11% 4 14% 11% 9% 7% 5% 5% 7% 21%	2360
	11th to 20th	Day	7% 18% 6% 15% 7% 8% 6% 4 6% 6% 18%	2688
	21st to end	Day	4 9% 4 12% 9% 5% 5% 6% 6% 6% 35%	3130
January	1st to 10th	Night	3 12% 5% 14% 9% 9% 8% 5% 7% 8% 20%	6641
	11th to 20th	Night	4 8% 4 11% 10% 10% 10% 7% 10% 7% 18%	6302
	21st to end	Night	4 10% 5% 13% 9% 6% 6% 4 6% 7% 28%	6974
February	1st to 10th	Night	8% 12% 4 10% 8% 8% 7% 6% 8% 8% 21%	2795
	11th to 20th	Night	4 11% 4 11% 8% 6% 8% 5% 8% 7% 29%	2532
	21st to end	Night	4 7% 4 11% 9% 7% 6% 5% 7% 9% 31%	1990
March	1st to 10th	Night	4 10% 5% 14% 6% 5% 6% 5% 8% 9% 28%	5374
	11th to 20th	Night	6% 10% 4 10% 8% 7% 6% 6% 7% 8% 29%	5291
	21st to end	Night	7% 12% 5% 14% 8% 6% 5% 4 5% 6% 26%	4995
April	1st to 10th	Night	7% 7% 3 6% 5% 5% 5% 4 7% 8% 43%	2000
	11th to 20th	Night	13% 12% 3 8% 5% 4 5% 3 6% 8% 33%	1928
	21st to end	Night	13% 7% 2 7% 5% 6% 5% 6% 6% 6% 36%	1668
May	1st to 10th	Night	12% 8% 2 7% 4 4 4 3 5% 7% 45%	3640
	11th to 20th	Night	19% 7% 3 6% 4 4 5% 4 6% 7% 35%	3618
	21st to end	Night	13% 6% 2 5% 3 4 3 3 5% 6% 48%	3705
June	1st to 10th	Night	12% 5% 2 4 3 4 5% 4 8% 9% 44%	1357
	11th to 20th	Night	15% 7% 3 6% 4 5% 5% 4 6% 8% 38%	1200
	21st to end	Night	11% 6% 2 4 4 3 4 4 8% 9% 46%	1200
July	1st to 10th	Night	7% 4 1 5% 4 4 5% 4 7% 11% 47%	2827
	11th to 20th	Night	10% 5% 2 5% 4 4 4 3 6% 8% 49%	3540
	21st to end	Night	5% 3 1 4 3 3 3 3 5% 8% 62%	3968
August	1st to 10th	Night	6% 4 2 5% 4 3 3 4 6% 7% 56%	2608
	11th to 20th	Night	5% 3 2 4 3 4 5% 4 7% 10% 53%	2576
	21st to end	Night	6% 4 2 5% 3 3 4 4 5% 8% 54%	3511
September	1st to 10th	Night	8% 4 2 5% 3 4 4 4 5% 7% 53%	2000
	11th to 20th	Night	10% 6% 3 6% 3 4 5% 4 6% 7% 46%	2035
	21st to end	Night	11% 6% 2 5% 4 4 4 3 5% 6% 51%	2200
October	1st to 10th	Night	9% 8% 2 6% 4 3 4 3 5% 7% 48%	3915
	11th to 20th	Night	5% 7% 2 6% 4 4 5% 4 7% 10% 47%	4047
	21st to end	Night	7% 8% 3 9% 5% 4 4 3 6% 7% 43%	4610
November	1st to 10th	Night	14% 13% 5% 10% 5% 5% 4 4 4 6% 31%	2755
	11th to 20th	Night	7% 13% 5% 12% 8% 5% 5% 4 5% 6% 28%	2940
	21st to end	Night	8% 12% 4 13% 7% 6% 5% 4 6% 8% 28%	3150
December	1st to 10th	Night	6% 14% 6% 15% 9% 9% 7% 4 6% 6% 17%	5050
	11th to 20th	Night	7% 13% 6% 13% 9% 7% 7% 6% 6% 6% 20%	5674
	21st to end	Night	3 7% 3 12% 9% 7% 6% 4 7% 6% 36%	7815

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	68% 4 10% 12% 5%	3291
	11th to 20th	Day	55% 5% 14% 14% 11%	3640
	21st to end	Day	56% 4 17% 19% 4	4004
February	1st to 10th	Day	61% 6% 11% 14% 7% 1	1624
	11th to 20th	Day	56% 6% 9% 15% 13% 1	1764
	21st to end	Day	56% 7% 13% 15% 9%	1639
March	1st to 10th	Day	57% 4 15% 18% 7%	4500
	11th to 20th	Day	55% 7% 15% 17% 5%	4695
	21st to end	Day	54% 6% 12% 17% 10% 2	5957
April	1st to 10th	Day	41% 7% 17% 24% 10% 1	2400
	11th to 20th	Day	56% 6% 11% 18% 7% 2	2422
	21st to end	Day	47% 6% 16% 24% 7% 1	2730
May	1st to 10th	Day	40% 5% 13% 26% 16% 1	6340
	11th to 20th	Day	46% 7% 12% 24% 10%	6302
	21st to end	Day	35% 7% 11% 27% 19% 1	7192
June	1st to 10th	Day	42% 7% 15% 26% 9% 1	3039
	11th to 20th	Day	50% 7% 13% 20% 10% 1	3200
	21st to end	Day	37% 9% 17% 28% 9%	3200
July	1st to 10th	Day	30% 8% 24% 28% 9%	7038
	11th to 20th	Day	35% 7% 16% 34% 8%	6355
	21st to end	Day	27% 6% 18% 34% 13% 2	6705
August	1st to 10th	Day	34% 7% 17% 25% 16% 1	4536
	11th to 20th	Day	29% 7% 19% 38% 7%	4525
	21st to end	Day	31% 5% 15% 38% 10% 1	4393
September	1st to 10th	Day	35% 5% 13% 32% 14% 2	2400
	11th to 20th	Day	41% 6% 14% 27% 11% 2	2365
	21st to end	Day	34% 4 14% 32% 14% 2	2200
October	1st to 10th	Day	40% 5% 16% 29% 10% 1	3273
	11th to 20th	Day	32% 4 16% 36% 11% 1	3069
	21st to end	Day	45% 4 16% 28% 7%	3190
November	1st to 10th	Day	56% 5% 15% 17% 7% 1	1758
	11th to 20th	Day	57% 6% 14% 17% 7% 1	1677
	21st to end	Day	58% 7% 13% 16% 5%	1470
December	1st to 10th	Day	61% 6% 16% 12% 4	2360
	11th to 20th	Day	65% 5% 17% 10% 2	2689
	21st to end	Day	47% 4 9% 23% 12% 6%	3130
January	1st to 10th	Night	59% 6% 12% 17% 6%	6641
	11th to 20th	Night	58% 6% 13% 14% 8%	6340
	21st to end	Night	53% 6% 19% 17% 4	6974
February	1st to 10th	Night	56% 6% 11% 18% 8% 1	2795
	11th to 20th	Night	51% 5% 12% 19% 12% 1	2533
	21st to end	Night	47% 6% 14% 23% 10%	1990
March	1st to 10th	Night	49% 6% 21% 18% 6%	5374
	11th to 20th	Night	50% 7% 17% 20% 6%	5291
	21st to end	Night	57% 5% 9% 19% 9% 1	4995
April	1st to 10th	Night	36% 6% 14% 25% 19% 1	2000
	11th to 20th	Night	50% 5% 10% 23% 11% 2	1928
	21st to end	Night	45% 7% 11% 24% 12% 1	1668
May	1st to 10th	Night	38% 5% 11% 26% 18% 2	3640
	11th to 20th	Night	46% 7% 15% 19% 11% 2	3618
	21st to end	Night	34% 7% 11% 27% 20% 1	3705
June	1st to 10th	Night	34% 7% 14% 30% 12% 2	1357
	11th to 20th	Night	42% 6% 17% 22% 12% 1	1200
	21st to end	Night	33% 8% 19% 30% 10% 1	1200
July	1st to 10th	Night	29% 8% 25% 31% 6%	2795
	11th to 20th	Night	33% 6% 14% 35% 11% 1	3495
	21st to end	Night	21% 5% 20% 34% 15% 4	3856
August	1st to 10th	Night	26% 6% 20% 32% 16% 1	2600
	11th to 20th	Night	25% 5% 19% 39% 11% 1	2600
	21st to end	Night	28% 5% 16% 36% 13% 1	3511
September	1st to 10th	Night	30% 6% 10% 31% 21% 2	2000
	11th to 20th	Night	37% 7% 14% 27% 15% 1	2035
	21st to end	Night	34% 5% 12% 32% 16% 2	2200
October	1st to 10th	Night	36% 4 15% 33% 9% 3	3915
	11th to 20th	Night	33% 4 14% 36% 12% 1	4047
	21st to end	Night	40% 4 12% 32% 11% 1	4610
November	1st to 10th	Night	55% 4 12% 19% 8% 2	2755
	11th to 20th	Night	56% 6% 16% 16% 6% 1	2940
	21st to end	Night	54% 6% 16% 19% 5%	3150
December	1st to 10th	Night	66% 7% 12% 11% 3	5050
	11th to 20th	Night	62% 5% 16% 12% 4	5672
	21st to end	Night	46% 4 10% 21% 14% 5%	7815

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% 10% 37% 27% 13% 3	240
	11th to 20th	Day	7% 11% 39% 33% 10%	300
	21st to end	Day	13% 8% 38% 29% 10% 2	330
February	1st to 10th	Day	15% 10% 38% 26% 9% 1	300
	11th to 20th	Day	12% 6% 35% 30% 13% 4	300
	21st to end	Day	8% 7% 37% 33% 14% 2	249
March	1st to 10th	Day	13% 8% 39% 27% 10% 3	300
	11th to 20th	Day	9% 13% 35% 29% 9% 4	364
	21st to end	Day	13% 10% 34% 28% 13% 2	550
April	1st to 10th	Day	8% 14% 38% 31% 7% 1	500
	11th to 20th	Day	19% 14% 32% 27% 8% 1	540
	21st to end	Day	14% 10% 32% 28% 15% 1	700
May	1st to 10th	Day	12% 9% 30% 30% 16% 3	703
	11th to 20th	Day	15% 8% 29% 27% 16% 6%	725
	21st to end	Day	16% 7% 25% 28% 18% 6%	789
June	1st to 10th	Day	15% 13% 28% 24% 16% 5%	730
	11th to 20th	Day	17% 11% 32% 26% 11% 3	730
	21st to end	Day	14% 7% 28% 29% 19% 4	730
July	1st to 10th	Day	7% 5% 25% 36% 21% 6%	721
	11th to 20th	Day	8% 7% 29% 30% 19% 7%	718
	21st to end	Day	7% 6% 26% 32% 21% 8%	794
August	1st to 10th	Day	10% 5% 22% 37% 20% 6%	726
	11th to 20th	Day	9% 4 24% 36% 21% 5%	715
	21st to end	Day	10% 6% 24% 36% 20% 4	615
September	1st to 10th	Day	13% 10% 29% 29% 14% 5%	530
	11th to 20th	Day	18% 11% 25% 29% 15% 2	495
	21st to end	Day	14% 9% 30% 35% 11% 2	330
October	1st to 10th	Day	18% 11% 28% 28% 14% 2	330
	11th to 20th	Day	15% 11% 36% 26% 9% 3	330
	21st to end	Day	14% 13% 36% 29% 7% 1	363
November	1st to 10th	Day	18% 8% 36% 26% 10% 1	330
	11th to 20th	Day	15% 11% 42% 26% 6%	330
	21st to end	Day	11% 12% 35% 33% 9%	330
December	1st to 10th	Day	10% 10% 42% 26% 9% 2	330
	11th to 20th	Day	12% 11% 46% 25% 5% 1	321
	21st to end	Day	13% 5% 35% 32% 13% 2	250
January	1st to 10th	Night	8% 9% 40% 31% 11% 1	1000
	11th to 20th	Night	14% 12% 35% 31% 8% 1	1000
	21st to end	Night	11% 12% 39% 29% 8%	1100
February	1st to 10th	Night	14% 9% 34% 30% 12% 1	995
	11th to 20th	Night	9% 8% 37% 34% 11% 2	784
	21st to end	Night	7% 6% 30% 36% 17% 4	660
March	1st to 10th	Night	11% 8% 36% 33% 10% 2	800
	11th to 20th	Night	11% 8% 36% 31% 14% 1	800
	21st to end	Night	14% 6% 31% 34% 13% 2	671
April	1st to 10th	Night	9% 10% 33% 36% 11% 1	600
	11th to 20th	Night	18% 10% 33% 31% 7% 1	593
	21st to end	Night	17% 8% 33% 33% 8% 1	600
May	1st to 10th	Night	14% 6% 31% 35% 15% 1	600
	11th to 20th	Night	15% 7% 31% 32% 13% 2	591
	21st to end	Night	18% 7% 25% 33% 15% 2	650
June	1st to 10th	Night	15% 6% 29% 36% 13% 1	557
	11th to 20th	Night	18% 6% 28% 35% 13% 1	400
	21st to end	Night	13% 7% 25% 39% 16% 1	400
July	1st to 10th	Night	8% 4 25% 39% 22% 2	390
	11th to 20th	Night	9% 4 28% 42% 17%	537
	21st to end	Night	5% 5% 26% 40% 21% 2	657
August	1st to 10th	Night	6% 4 27% 42% 19% 3	597
	11th to 20th	Night	8% 3 24% 41% 22% 2	594
	21st to end	Night	10% 4 25% 42% 18% 1	660
September	1st to 10th	Night	11% 6% 26% 38% 18% 2	600
	11th to 20th	Night	14% 5% 29% 37% 15% 1	600
	21st to end	Night	12% 7% 32% 38% 10% 1	600
October	1st to 10th	Night	15% 7% 27% 36% 14% 1	795
	11th to 20th	Night	13% 8% 30% 36% 11% 1	885
	21st to end	Night	15% 11% 34% 32% 7% 1	1100
November	1st to 10th	Night	20% 9% 35% 29% 6%	1025
	11th to 20th	Night	14% 11% 38% 27% 8% 2	1050
	21st to end	Night	12% 11% 41% 29% 7% 1	1050
December	1st to 10th	Night	12% 7% 40% 29% 9% 2	1050
	11th to 20th	Night	11% 11% 39% 31% 7% 1	1036
	21st to end	Night	11% 7% 36% 32% 12% 2	1100

Page generated at 2025-12-15 00:13:50. Version ac07

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