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 2024-01-13.

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% 4 7% 7% 4 5% 5% 6% 8% 36%	74792
	Night	8% 8% 4 8% 7% 4 5% 6% 6% 8% 36%	74936
Transparency	Day	45% 6% 15% 23% 9% 1	74484
	Night	45% 6% 14% 23% 11% 1	74762
Seeing	Day	13% 9% 31% 30% 15% 4	14914
	Night	12% 8% 33% 34% 12% 1	24560

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	7% 13% 4 13% 9% 5% 7% 6% 7% 8% 21%	1373
	11th to 20th	Day	5% 11% 7% 13% 11% 5% 6% 5% 7% 9% 20%	1456
	21st to end	Day	5% 14% 8% 13% 11% 5% 9% 5% 6% 7% 17%	1584
February	1st to 10th	Day	7% 12% 5% 12% 9% 6% 7% 8% 7% 7% 19%	1461
	11th to 20th	Day	7% 12% 6% 11% 8% 5% 10% 7% 6% 7% 21%	1575
	21st to end	Day	6% 9% 6% 11% 12% 4 8% 6% 9% 9% 21%	1470
March	1st to 10th	Day	10% 13% 5% 12% 12% 4 8% 5% 6% 6% 19%	1800
	11th to 20th	Day	6% 12% 6% 8% 7% 4 5% 4 7% 9% 31%	1856
	21st to end	Day	8% 11% 6% 9% 8% 4 6% 5% 6% 8% 28%	2364
April	1st to 10th	Day	7% 7% 4 7% 7% 3 6% 7% 7% 7% 37%	2160
	11th to 20th	Day	14% 14% 4 9% 6% 4 5% 4 5% 7% 27%	2176
	21st to end	Day	13% 9% 3 7% 7% 4 5% 4 5% 7% 36%	2456
May	1st to 10th	Day	10% 8% 3 6% 5% 3 6% 5% 6% 9% 39%	2520
	11th to 20th	Day	9% 7% 3 6% 6% 4 5% 5% 6% 9% 40%	2478
	21st to end	Day	19% 6% 3 7% 6% 4 5% 5% 7% 8% 31%	2822
June	1st to 10th	Day	14% 6% 3 5% 5% 3 5% 5% 7% 8% 37%	2735
	11th to 20th	Day	19% 7% 3 7% 6% 3 5% 5% 6% 9% 31%	2880
	21st to end	Day	11% 4 2 5% 6% 4 6% 7% 8% 8% 40%	2880
July	1st to 10th	Day	7% 5% 2 5% 4 2 5% 4 6% 9% 50%	2839
	11th to 20th	Day	8% 4 2 5% 5% 3 5% 5% 6% 9% 48%	2561
	21st to end	Day	6% 4 1 4 4 3 5% 5% 7% 7% 54%	2742
August	1st to 10th	Day	8% 4 2 5% 5% 3 4 5% 6% 9% 49%	2507
	11th to 20th	Day	9% 4 2 4 5% 3 5% 5% 6% 9% 48%	2477
	21st to end	Day	10% 4 2 4 4 3 3 4 5% 7% 51%	2429
September	1st to 10th	Day	12% 5% 2 5% 6% 2 4 4 4 8% 48%	2160
	11th to 20th	Day	13% 7% 3 6% 4 2 4 4 5% 8% 44%	2129
	21st to end	Day	13% 7% 2 4 4 3 4 4 4 8% 47%	1980
October	1st to 10th	Day	14% 11% 4 7% 5% 3 3 4 5% 7% 37%	1803
	11th to 20th	Day	10% 9% 4 7% 6% 3 4 4 6% 7% 41%	1706
	21st to end	Day	10% 12% 7% 11% 6% 3 4 4 4 7% 32%	1782
November	1st to 10th	Day	13% 14% 6% 9% 7% 4 5% 4 5% 6% 28%	1588
	11th to 20th	Day	7% 11% 5% 12% 10% 6% 6% 5% 5% 7% 26%	1518
	21st to end	Day	9% 14% 5% 10% 7% 4 6% 6% 4 5% 28%	1330
December	1st to 10th	Day	8% 11% 5% 12% 12% 6% 7% 7% 5% 7% 20%	1330
	11th to 20th	Day	7% 15% 7% 15% 10% 5% 7% 5% 6% 5% 18%	1679
	21st to end	Day	5% 8% 4 6% 7% 4 5% 6% 5% 7% 44%	2186
January	1st to 10th	Night	4 10% 6% 10% 9% 4 7% 7% 10% 8% 26%	2784
	11th to 20th	Night	7% 11% 6% 12% 8% 5% 6% 6% 6% 8% 24%	2561
	21st to end	Night	5% 13% 6% 12% 10% 5% 8% 7% 8% 8% 17%	2772
February	1st to 10th	Night	7% 10% 5% 9% 9% 5% 8% 8% 9% 8% 22%	2516
	11th to 20th	Night	4 11% 5% 10% 9% 5% 8% 7% 7% 7% 27%	2272
	21st to end	Night	5% 6% 5% 11% 10% 5% 7% 6% 7% 9% 30%	1785
March	1st to 10th	Night	7% 10% 6% 11% 10% 3 6% 5% 5% 8% 29%	2160
	11th to 20th	Night	6% 10% 4 8% 8% 4 6% 6% 6% 8% 34%	2102
	21st to end	Night	9% 9% 5% 8% 8% 5% 6% 7% 6% 8% 30%	1991
April	1st to 10th	Night	7% 6% 4 5% 5% 4 5% 6% 7% 8% 43%	1800
	11th to 20th	Night	14% 11% 3 7% 6% 3 5% 4 6% 7% 33%	1734
	21st to end	Night	14% 7% 3 6% 5% 4 5% 7% 6% 7% 35%	1502
May	1st to 10th	Night	10% 8% 3 6% 6% 3 5% 5% 6% 8% 41%	1440
	11th to 20th	Night	11% 5% 3 5% 5% 2 5% 6% 6% 8% 45%	1418
	21st to end	Night	15% 6% 3 5% 5% 3 5% 5% 7% 8% 38%	1453
June	1st to 10th	Night	12% 5% 2 4 4 2 4 6% 7% 9% 44%	1222
	11th to 20th	Night	15% 6% 3 5% 4 3 5% 6% 6% 8% 38%	1080
	21st to end	Night	10% 6% 2 4 5% 2 4 5% 8% 9% 45%	1080
July	1st to 10th	Night	6% 3 1 3 5% 2 5% 6% 5% 9% 56%	1117
	11th to 20th	Night	6% 3 2 2 4 4 4 4 5% 9% 57%	1396
	21st to end	Night	4 2 2 3 3 2 4 5% 5% 8% 62%	1576
August	1st to 10th	Night	5% 3 1 3 5% 3 4 4 7% 7% 58%	1432
	11th to 20th	Night	6% 4 2 3 4 3 5% 4 6% 10% 54%	1424
	21st to end	Night	8% 4 2 4 3 2 2 3 5% 7% 58%	1924
September	1st to 10th	Night	9% 5% 2 4 4 3 5% 5% 5% 7% 51%	1800
	11th to 20th	Night	10% 6% 2 4 4 3 4 5% 5% 7% 49%	1831
	21st to end	Night	12% 5% 3 4 4 3 4 5% 6% 6% 48%	1980
October	1st to 10th	Night	12% 10% 3 6% 5% 3 3 4 5% 8% 41%	2155
	11th to 20th	Night	8% 9% 3 6% 4 3 4 4 6% 7% 46%	2236
	21st to end	Night	10% 11% 5% 10% 7% 4 5% 4 6% 7% 33%	2574
November	1st to 10th	Night	15% 12% 6% 8% 7% 4 4 5% 4 6% 30%	2485
	11th to 20th	Night	7% 11% 6% 10% 10% 4 6% 6% 5% 6% 28%	2660
	21st to end	Night	8% 10% 5% 11% 8% 4 4 5% 5% 9% 30%	2850
December	1st to 10th	Night	6% 11% 6% 11% 11% 6% 7% 6% 6% 7% 24%	2850
	11th to 20th	Night	7% 11% 6% 14% 10% 5% 5% 7% 6% 7% 22%	3518
	21st to end	Night	4 7% 4 8% 7% 3 5% 6% 7% 7% 43%	5456

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	60% 5% 11% 17% 7%	1373
	11th to 20th	Day	59% 6% 16% 14% 5% 1	1456
	21st to end	Day	66% 4 11% 13% 6%	1584
February	1st to 10th	Day	61% 7% 12% 15% 6%	1461
	11th to 20th	Day	60% 7% 9% 14% 10% 1	1584
	21st to end	Day	57% 7% 12% 15% 9%	1470
March	1st to 10th	Day	64% 6% 11% 15% 4	1800
	11th to 20th	Day	48% 6% 17% 20% 8%	1857
	21st to end	Day	52% 8% 16% 19% 5%	2364
April	1st to 10th	Day	43% 7% 16% 24% 10% 1	2160
	11th to 20th	Day	56% 6% 11% 17% 7% 2	2176
	21st to end	Day	47% 6% 16% 23% 7% 1	2456
May	1st to 10th	Day	41% 6% 13% 27% 12% 1	2520
	11th to 20th	Day	41% 6% 12% 28% 13%	2482
	21st to end	Day	50% 7% 13% 20% 10% 1	2822
June	1st to 10th	Day	43% 7% 16% 25% 8% 1	2735
	11th to 20th	Day	50% 8% 13% 19% 10%	2880
	21st to end	Day	37% 10% 17% 27% 9% 1	2880
July	1st to 10th	Day	28% 8% 21% 32% 10%	2762
	11th to 20th	Day	32% 8% 18% 27% 14% 1	2483
	21st to end	Day	27% 7% 16% 36% 13% 1	2590
August	1st to 10th	Day	31% 8% 21% 28% 11% 1	2491
	11th to 20th	Day	31% 7% 20% 32% 9% 1	2477
	21st to end	Day	32% 6% 12% 34% 15% 1	2429
September	1st to 10th	Day	35% 5% 14% 30% 14% 1	2160
	11th to 20th	Day	40% 5% 13% 29% 12% 2	2129
	21st to end	Day	36% 4 14% 32% 12% 2	1980
October	1st to 10th	Day	46% 6% 15% 24% 8% 1	1803
	11th to 20th	Day	43% 5% 11% 30% 10% 1	1706
	21st to end	Day	53% 5% 17% 19% 5%	1782
November	1st to 10th	Day	57% 6% 14% 16% 7% 1	1588
	11th to 20th	Day	57% 6% 14% 17% 7% 1	1518
	21st to end	Day	58% 7% 14% 16% 5%	1330
December	1st to 10th	Day	62% 6% 11% 13% 6% 1	1330
	11th to 20th	Day	65% 6% 15% 10% 3	1680
	21st to end	Day	38% 4 13% 25% 12% 8%	2186
January	1st to 10th	Night	51% 6% 15% 20% 7% 1	2784
	11th to 20th	Night	57% 6% 14% 16% 6% 1	2561
	21st to end	Night	61% 6% 11% 13% 8%	2772
February	1st to 10th	Night	54% 6% 12% 19% 8% 1	2516
	11th to 20th	Night	54% 5% 13% 17% 10% 1	2273
	21st to end	Night	48% 6% 12% 22% 11%	1785
March	1st to 10th	Night	54% 5% 14% 19% 7%	2160
	11th to 20th	Night	48% 6% 13% 26% 7% 1	2102
	21st to end	Night	50% 7% 15% 17% 10%	1991
April	1st to 10th	Night	36% 5% 14% 25% 19% 1	1800
	11th to 20th	Night	50% 5% 10% 21% 11% 2	1734
	21st to end	Night	46% 7% 11% 24% 11% 1	1502
May	1st to 10th	Night	40% 6% 13% 23% 17% 1	1440
	11th to 20th	Night	36% 7% 13% 26% 17% 1	1418
	21st to end	Night	42% 7% 15% 20% 13% 2	1453
June	1st to 10th	Night	34% 8% 15% 30% 12% 2	1222
	11th to 20th	Night	42% 6% 18% 20% 13% 1	1080
	21st to end	Night	33% 8% 20% 29% 10% 1	1080
July	1st to 10th	Night	24% 7% 22% 33% 13% 1	1085
	11th to 20th	Night	25% 7% 17% 34% 15% 2	1351
	21st to end	Night	18% 7% 18% 37% 17% 3	1488
August	1st to 10th	Night	24% 8% 19% 35% 14% 1	1424
	11th to 20th	Night	25% 6% 19% 35% 13% 1	1424
	21st to end	Night	26% 4 13% 36% 19% 2	1924
September	1st to 10th	Night	32% 7% 10% 28% 21% 2	1800
	11th to 20th	Night	35% 7% 14% 28% 16% 1	1831
	21st to end	Night	36% 5% 13% 30% 15% 1	1980
October	1st to 10th	Night	42% 5% 17% 25% 10% 1	2155
	11th to 20th	Night	38% 5% 15% 29% 12% 1	2236
	21st to end	Night	51% 5% 13% 24% 8% 1	2574
November	1st to 10th	Night	56% 4 12% 17% 8% 2	2485
	11th to 20th	Night	56% 6% 16% 15% 6% 1	2660
	21st to end	Night	52% 6% 17% 19% 5%	2850
December	1st to 10th	Night	58% 5% 14% 17% 6% 1	2850
	11th to 20th	Night	61% 7% 12% 15% 6% 1	3516
	21st to end	Night	38% 4 12% 22% 16% 7%	5456

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	13% 9% 37% 26% 13% 3	216
	11th to 20th	Day	8% 10% 34% 35% 12%	246
	21st to end	Day	15% 8% 38% 30% 9% 1	264
February	1st to 10th	Day	15% 9% 39% 27% 9% 2	240
	11th to 20th	Day	14% 6% 35% 32% 11% 1	240
	21st to end	Day	8% 6% 36% 33% 15% 3	198
March	1st to 10th	Day	15% 5% 39% 30% 9% 3	240
	11th to 20th	Day	8% 12% 35% 29% 9% 5%	297
	21st to end	Day	14% 10% 34% 27% 14% 2	462
April	1st to 10th	Day	9% 15% 40% 30% 6% 1	420
	11th to 20th	Day	20% 12% 29% 28% 9% 1	454
	21st to end	Day	13% 10% 32% 29% 15% 1	600
May	1st to 10th	Day	10% 9% 31% 30% 17% 3	603
	11th to 20th	Day	14% 8% 28% 27% 17% 7%	625
	21st to end	Day	17% 8% 24% 27% 18% 6%	679
June	1st to 10th	Day	14% 11% 28% 25% 17% 5%	630
	11th to 20th	Day	18% 10% 32% 25% 12% 3	630
	21st to end	Day	13% 7% 26% 30% 20% 4	630
July	1st to 10th	Day	7% 5% 25% 36% 21% 5%	621
	11th to 20th	Day	7% 8% 31% 30% 19% 5%	618
	21st to end	Day	7% 6% 27% 32% 19% 9%	684
August	1st to 10th	Day	9% 5% 22% 38% 20% 6%	626
	11th to 20th	Day	9% 5% 23% 37% 21% 6%	615
	21st to end	Day	11% 6% 23% 36% 20% 5%	525
September	1st to 10th	Day	14% 11% 31% 29% 12% 4	450
	11th to 20th	Day	18% 10% 26% 29% 16% 2	419
	21st to end	Day	16% 8% 30% 34% 10% 2	270
October	1st to 10th	Day	20% 9% 27% 27% 16% 2	270
	11th to 20th	Day	13% 12% 34% 28% 10% 4	270
	21st to end	Day	15% 13% 36% 28% 6% 2	297
November	1st to 10th	Day	21% 7% 34% 25% 11% 1	270
	11th to 20th	Day	13% 10% 43% 27% 6%	270
	21st to end	Day	12% 12% 35% 31% 9%	270
December	1st to 10th	Day	10% 9% 39% 29% 11% 2	270
	11th to 20th	Day	12% 10% 48% 23% 6% 1	270
	21st to end	Day	14% 5% 37% 30% 12% 2	225
January	1st to 10th	Night	8% 9% 40% 31% 11% 1	950
	11th to 20th	Night	14% 12% 32% 32% 8% 1	915
	21st to end	Night	12% 12% 37% 29% 9% 1	990
February	1st to 10th	Night	13% 8% 34% 30% 13% 2	896
	11th to 20th	Night	10% 9% 37% 33% 11% 2	704
	21st to end	Night	7% 5% 28% 37% 18% 4	592
March	1st to 10th	Night	11% 8% 36% 33% 10% 2	720
	11th to 20th	Night	11% 7% 35% 32% 14% 1	720
	21st to end	Night	14% 6% 31% 34% 14% 2	605
April	1st to 10th	Night	9% 10% 33% 36% 11% 1	540
	11th to 20th	Night	19% 10% 32% 32% 8% 1	533
	21st to end	Night	18% 8% 32% 33% 8% 1	540
May	1st to 10th	Night	14% 5% 30% 35% 15% 1	540
	11th to 20th	Night	14% 6% 31% 34% 14% 2	531
	21st to end	Night	19% 7% 24% 32% 16% 2	584
June	1st to 10th	Night	15% 5% 28% 36% 14% 2	502
	11th to 20th	Night	19% 6% 27% 34% 14% 1	360
	21st to end	Night	13% 7% 23% 39% 17% 1	360
July	1st to 10th	Night	8% 3 27% 41% 20% 1	350
	11th to 20th	Night	8% 4 29% 42% 16%	481
	21st to end	Night	5% 6% 27% 40% 21% 2	591
August	1st to 10th	Night	6% 3 27% 41% 20% 3	537
	11th to 20th	Night	8% 3 22% 42% 23% 2	534
	21st to end	Night	11% 4 25% 41% 19% 1	594
September	1st to 10th	Night	12% 6% 26% 36% 17% 2	540
	11th to 20th	Night	14% 4 29% 37% 15% 1	540
	21st to end	Night	13% 7% 32% 37% 11% 1	540
October	1st to 10th	Night	16% 7% 27% 34% 15% 1	715
	11th to 20th	Night	12% 8% 29% 37% 12% 1	796
	21st to end	Night	16% 11% 33% 32% 8% 1	990
November	1st to 10th	Night	20% 9% 34% 29% 7% 1	925
	11th to 20th	Night	14% 11% 37% 27% 9% 2	950
	21st to end	Night	13% 11% 41% 28% 6% 1	950
December	1st to 10th	Night	12% 7% 39% 29% 10% 3	950
	11th to 20th	Night	11% 10% 39% 31% 8% 1	950
	21st to end	Night	11% 7% 36% 31% 12% 2	1045

Page generated at 2024-01-10 09:16:13. Version ac07

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