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 2024-11-11.

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 8% 6% 5% 5% 4 6% 8% 38%	105756
	Night	7% 8% 3 9% 6% 5% 5% 4 6% 8% 38%	102009
Transparency	Day	43% 6% 15% 26% 9% 1	105514
	Night	43% 6% 15% 25% 10% 1	101897
Seeing	Day	12% 9% 31% 30% 15% 4	16135
	Night	12% 8% 33% 34% 12% 1	25596

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% 15% 5% 15% 7% 8% 8% 5% 7% 6% 17%	2289
	11th to 20th	Day	4 9% 4 13% 11% 10% 10% 8% 9% 8% 14%	2516
	21st to end	Day	5% 12% 6% 13% 8% 7% 6% 4 5% 7% 28%	2794
February	1st to 10th	Day	7% 14% 5% 13% 9% 8% 7% 6% 7% 6% 19%	1542
	11th to 20th	Day	7% 12% 5% 12% 6% 7% 9% 6% 7% 7% 23%	1665
	21st to end	Day	5% 10% 5% 13% 11% 6% 6% 6% 9% 9% 21%	1559
March	1st to 10th	Day	8% 13% 5% 13% 8% 6% 9% 4 5% 6% 24%	3130
	11th to 20th	Day	5% 11% 6% 13% 7% 5% 4 3 6% 8% 33%	3282
	21st to end	Day	6% 11% 6% 13% 6% 5% 5% 4 6% 7% 31%	4153
April	1st to 10th	Day	6% 8% 3 7% 6% 6% 6% 5% 7% 8% 37%	2280
	11th to 20th	Day	13% 15% 4 11% 5% 5% 5% 3 5% 7% 27%	2299
	21st to end	Day	12% 10% 3 8% 6% 5% 4 4 5% 7% 36%	2593
May	1st to 10th	Day	17% 11% 3 6% 4 3 4 3 6% 8% 35%	4430
	11th to 20th	Day	11% 7% 3 7% 6% 5% 6% 5% 7% 9% 35%	4388
	21st to end	Day	14% 6% 2 8% 5% 5% 6% 5% 8% 8% 34%	5007
June	1st to 10th	Day	14% 7% 2 6% 5% 5% 5% 5% 7% 8% 37%	2887
	11th to 20th	Day	18% 8% 3 8% 5% 5% 5% 5% 6% 8% 31%	3040
	21st to end	Day	11% 5% 2 5% 5% 5% 5% 5% 8% 8% 41%	3040
July	1st to 10th	Day	5% 5% 2 6% 5% 4 6% 5% 8% 10% 45%	4977
	11th to 20th	Day	6% 3 2 5% 4 4 4 4 6% 11% 52%	4497
	21st to end	Day	4 3 1 4 3 3 5% 4 6% 8% 59%	4802
August	1st to 10th	Day	9% 5% 2 6% 5% 4 5% 4 6% 8% 47%	4412
	11th to 20th	Day	6% 4 2 5% 4 5% 5% 4 7% 10% 48%	4343
	21st to end	Day	9% 4 2 6% 4 3 4 4 5% 7% 52%	4260
September	1st to 10th	Day	12% 5% 2 5% 5% 3 4 3 5% 8% 49%	2280
	11th to 20th	Day	12% 7% 3 6% 4 4 3 3 5% 8% 43%	2247
	21st to end	Day	12% 7% 2 4 3 3 4 4 4 8% 48%	2090
October	1st to 10th	Day	9% 8% 3 7% 5% 4 5% 4 6% 8% 42%	3173
	11th to 20th	Day	7% 7% 2 5% 3 3 4 4 7% 10% 48%	2974
	21st to end	Day	7% 10% 4 10% 5% 4 5% 4 6% 8% 38%	3091
November	1st to 10th	Day	12% 15% 5% 9% 7% 5% 4 4 6% 6% 28%	1673
	11th to 20th	Day	7% 12% 4 14% 8% 7% 5% 5% 6% 6% 26%	1518
	21st to end	Day	9% 15% 5% 11% 6% 6% 5% 5% 4 5% 28%	1330
December	1st to 10th	Day	8% 13% 5% 13% 11% 7% 6% 5% 5% 7% 19%	1330
	11th to 20th	Day	7% 17% 6% 17% 8% 7% 6% 4 6% 5% 18%	1679
	21st to end	Day	5% 8% 3 7% 6% 5% 5% 5% 5% 7% 44%	2186
January	1st to 10th	Night	4 14% 6% 13% 8% 6% 6% 5% 7% 7% 25%	4652
	11th to 20th	Night	4 8% 4 13% 11% 12% 10% 6% 7% 6% 19%	4392
	21st to end	Night	6% 12% 5% 10% 7% 7% 6% 5% 7% 7% 29%	4873
February	1st to 10th	Night	8% 12% 4 10% 8% 7% 7% 6% 8% 8% 22%	2656
	11th to 20th	Night	4 12% 4 11% 8% 6% 8% 5% 8% 6% 28%	2402
	21st to end	Night	4 8% 4 11% 10% 7% 6% 5% 6% 9% 30%	1894
March	1st to 10th	Night	5% 11% 6% 13% 8% 5% 6% 4 6% 8% 29%	3734
	11th to 20th	Night	5% 10% 4 8% 6% 6% 6% 6% 6% 9% 35%	3690
	21st to end	Night	6% 9% 5% 13% 8% 6% 4 5% 5% 7% 32%	3488
April	1st to 10th	Night	7% 8% 2 6% 5% 5% 5% 4 7% 9% 43%	1900
	11th to 20th	Night	13% 12% 3 9% 4 4 5% 3 6% 8% 33%	1831
	21st to end	Night	13% 7% 2 7% 5% 6% 5% 6% 6% 7% 36%	1585
May	1st to 10th	Night	16% 11% 3 9% 5% 4 4 3 5% 6% 35%	2540
	11th to 20th	Night	13% 6% 2 6% 5% 3 5% 5% 6% 8% 42%	2518
	21st to end	Night	13% 6% 2 6% 5% 5% 4 4 6% 8% 42%	2579
June	1st to 10th	Night	12% 5% 2 4 3 4 4 4 8% 9% 44%	1289
	11th to 20th	Night	15% 7% 3 5% 4 5% 5% 4 6% 8% 38%	1140
	21st to end	Night	10% 6% 2 4 4 3 4 4 8% 9% 46%	1140
July	1st to 10th	Night	7% 3 1 4 3 3 4 4 7% 13% 49%	1979
	11th to 20th	Night	5% 3 1 4 4 4 4 3 5% 8% 57%	2468
	21st to end	Night	3 2 1 3 3 3 3 3 5% 8% 66%	2762
August	1st to 10th	Night	6% 4 2 5% 4 3 3 4 6% 7% 57%	2528
	11th to 20th	Night	5% 3 2 4 3 4 5% 4 7% 10% 53%	2496
	21st to end	Night	7% 4 2 5% 3 3 4 4 6% 9% 53%	3404
September	1st to 10th	Night	9% 4 2 5% 3 4 5% 4 5% 7% 52%	1900
	11th to 20th	Night	10% 6% 2 5% 3 4 5% 4 6% 7% 48%	1933
	21st to end	Night	11% 6% 2 5% 4 4 4 4 5% 6% 49%	2090
October	1st to 10th	Night	10% 8% 2 6% 4 3 4 3 5% 7% 48%	3795
	11th to 20th	Night	5% 7% 2 6% 4 4 5% 4 7% 10% 47%	3923
	21st to end	Night	7% 8% 3 9% 5% 4 4 3 6% 7% 43%	4467
November	1st to 10th	Night	14% 13% 5% 10% 5% 5% 3 4 4 6% 30%	2620
	11th to 20th	Night	7% 13% 5% 12% 9% 5% 5% 4 5% 6% 28%	2667
	21st to end	Night	8% 12% 4 13% 6% 5% 4 4 6% 8% 30%	2850
December	1st to 10th	Night	6% 12% 5% 12% 10% 7% 6% 5% 6% 7% 24%	2850
	11th to 20th	Night	7% 12% 6% 15% 9% 6% 6% 5% 6% 7% 22%	3518
	21st to end	Night	4 7% 3 9% 6% 4 5% 4 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	65% 5% 13% 12% 4	2289
	11th to 20th	Day	62% 6% 15% 13% 4	2540
	21st to end	Day	56% 4 11% 23% 6%	2794
February	1st to 10th	Day	61% 6% 11% 15% 6%	1542
	11th to 20th	Day	57% 7% 10% 14% 12% 1	1674
	21st to end	Day	56% 7% 13% 14% 9%	1559
March	1st to 10th	Day	59% 4 13% 19% 4	3130
	11th to 20th	Day	48% 8% 19% 19% 5%	3283
	21st to end	Day	50% 7% 14% 17% 11% 2	4153
April	1st to 10th	Day	41% 7% 17% 24% 10% 1	2280
	11th to 20th	Day	56% 6% 11% 18% 7% 2	2299
	21st to end	Day	47% 6% 16% 23% 7% 1	2593
May	1st to 10th	Day	47% 6% 14% 24% 8%	4430
	11th to 20th	Day	41% 9% 11% 24% 14%	4392
	21st to end	Day	42% 9% 13% 28% 8%	5007
June	1st to 10th	Day	43% 7% 16% 25% 9% 1	2887
	11th to 20th	Day	49% 8% 13% 20% 10% 1	3040
	21st to end	Day	37% 10% 17% 27% 9%	3040
July	1st to 10th	Day	30% 9% 24% 29% 6%	4900
	11th to 20th	Day	26% 6% 15% 40% 12%	4419
	21st to end	Day	23% 5% 15% 39% 15% 2	4651
August	1st to 10th	Day	34% 7% 17% 25% 16% 1	4396
	11th to 20th	Day	29% 7% 18% 39% 7% 1	4385
	21st to end	Day	31% 5% 15% 38% 10% 1	4259
September	1st to 10th	Day	34% 5% 14% 30% 15% 2	2280
	11th to 20th	Day	40% 5% 14% 28% 11% 2	2247
	21st to end	Day	36% 4 14% 32% 13% 2	2090
October	1st to 10th	Day	40% 5% 16% 29% 10% 1	3173
	11th to 20th	Day	31% 4 16% 37% 11% 1	2974
	21st to end	Day	45% 4 16% 28% 7%	3091
November	1st to 10th	Day	57% 5% 14% 16% 7% 1	1673
	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	54% 6% 15% 18% 6%	4652
	11th to 20th	Night	62% 7% 13% 14% 4	4430
	21st to end	Night	51% 7% 16% 22% 5%	4873
February	1st to 10th	Night	55% 6% 12% 19% 8% 1	2656
	11th to 20th	Night	53% 5% 12% 18% 11% 1	2403
	21st to end	Night	48% 6% 13% 22% 10%	1894
March	1st to 10th	Night	52% 5% 17% 19% 6%	3734
	11th to 20th	Night	43% 8% 21% 22% 6%	3690
	21st to end	Night	51% 6% 12% 19% 12% 1	3488
April	1st to 10th	Night	36% 6% 14% 25% 18% 1	1900
	11th to 20th	Night	50% 5% 10% 22% 11% 2	1831
	21st to end	Night	44% 7% 11% 25% 11% 1	1585
May	1st to 10th	Night	49% 6% 11% 21% 12% 1	2540
	11th to 20th	Night	38% 7% 13% 22% 16% 3	2518
	21st to end	Night	37% 9% 14% 30% 10% 1	2579
June	1st to 10th	Night	34% 7% 14% 30% 12% 2	1289
	11th to 20th	Night	42% 6% 18% 21% 13% 1	1140
	21st to end	Night	33% 8% 19% 30% 10% 1	1140
July	1st to 10th	Night	25% 9% 30% 28% 7%	1947
	11th to 20th	Night	25% 6% 13% 39% 16% 1	2423
	21st to end	Night	17% 5% 17% 37% 17% 6%	2674
August	1st to 10th	Night	26% 6% 19% 32% 16% 1	2520
	11th to 20th	Night	25% 5% 19% 39% 11% 1	2520
	21st to end	Night	28% 5% 16% 37% 13% 1	3404
September	1st to 10th	Night	31% 6% 10% 29% 22% 2	1900
	11th to 20th	Night	35% 7% 14% 28% 15% 1	1933
	21st to end	Night	35% 5% 13% 30% 15% 2	2090
October	1st to 10th	Night	37% 4 15% 33% 9% 3	3795
	11th to 20th	Night	32% 4 14% 37% 12% 1	3923
	21st to end	Night	40% 4 12% 32% 11%	4467
November	1st to 10th	Night	56% 4 13% 18% 7% 2	2620
	11th to 20th	Night	56% 6% 16% 15% 6% 1	2667
	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% 11% 37% 33% 11%	270
	21st to end	Day	14% 7% 35% 31% 11% 2	297
February	1st to 10th	Day	16% 9% 39% 27% 9% 1	270
	11th to 20th	Day	13% 7% 36% 30% 12% 3	270
	21st to end	Day	8% 6% 36% 34% 14% 2	225
March	1st to 10th	Day	14% 8% 38% 27% 10% 3	270
	11th to 20th	Day	9% 15% 34% 28% 10% 5%	331
	21st to end	Day	13% 10% 35% 26% 14% 2	506
April	1st to 10th	Day	8% 15% 40% 29% 7% 1	460
	11th to 20th	Day	19% 13% 30% 28% 9% 1	497
	21st to end	Day	13% 10% 32% 29% 15% 1	650
May	1st to 10th	Day	12% 9% 31% 29% 16% 3	653
	11th to 20th	Day	14% 8% 28% 28% 16% 6%	675
	21st to end	Day	16% 8% 26% 27% 17% 6%	734
June	1st to 10th	Day	14% 13% 28% 24% 17% 4	680
	11th to 20th	Day	18% 11% 31% 25% 11% 3	680
	21st to end	Day	14% 7% 26% 29% 20% 4	680
July	1st to 10th	Day	7% 5% 24% 36% 22% 6%	671
	11th to 20th	Day	7% 7% 29% 30% 19% 7%	668
	21st to end	Day	6% 6% 27% 32% 20% 9%	739
August	1st to 10th	Day	9% 5% 23% 37% 20% 6%	676
	11th to 20th	Day	9% 4 23% 37% 21% 6%	665
	21st to end	Day	10% 6% 25% 36% 19% 5%	570
September	1st to 10th	Day	13% 10% 30% 30% 13% 4	490
	11th to 20th	Day	18% 11% 26% 29% 15% 2	457
	21st to end	Day	15% 9% 31% 33% 10% 2	300
October	1st to 10th	Day	19% 10% 28% 26% 15% 2	300
	11th to 20th	Day	12% 12% 35% 28% 10% 4	300
	21st to end	Day	14% 13% 36% 29% 7% 2	330
November	1st to 10th	Day	19% 8% 35% 26% 11% 1	300
	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% 30% 11% 1	950
	11th to 20th	Night	14% 12% 34% 32% 8% 1	950
	21st to end	Night	12% 12% 37% 30% 9%	1045
February	1st to 10th	Night	13% 8% 34% 31% 12% 1	946
	11th to 20th	Night	9% 9% 37% 33% 11% 1	744
	21st to end	Night	7% 5% 29% 36% 18% 4	628
March	1st to 10th	Night	12% 8% 35% 33% 10% 2	760
	11th to 20th	Night	11% 8% 36% 31% 14% 1	760
	21st to end	Night	13% 5% 31% 34% 14% 2	638
April	1st to 10th	Night	9% 11% 33% 34% 11% 1	570
	11th to 20th	Night	18% 10% 33% 31% 7% 1	563
	21st to end	Night	18% 8% 34% 33% 8% 1	570
May	1st to 10th	Night	14% 5% 31% 34% 15% 1	570
	11th to 20th	Night	14% 6% 31% 34% 14% 2	561
	21st to end	Night	18% 7% 25% 33% 15% 2	617
June	1st to 10th	Night	15% 6% 29% 36% 13% 2	529
	11th to 20th	Night	18% 6% 28% 34% 13% 1	380
	21st to end	Night	13% 7% 24% 38% 17% 1	380
July	1st to 10th	Night	8% 3 26% 40% 22% 2	370
	11th to 20th	Night	8% 4 29% 42% 17%	509
	21st to end	Night	5% 6% 27% 40% 21% 2	624
August	1st to 10th	Night	6% 4 28% 41% 19% 3	567
	11th to 20th	Night	8% 3 23% 42% 23% 2	564
	21st to end	Night	11% 4 26% 41% 18% 1	627
September	1st to 10th	Night	11% 6% 26% 38% 17% 2	570
	11th to 20th	Night	14% 4 29% 37% 15% 1	570
	21st to end	Night	12% 7% 32% 37% 11% 1	570
October	1st to 10th	Night	16% 7% 27% 35% 15% 1	755
	11th to 20th	Night	12% 8% 30% 37% 12% 1	841
	21st to end	Night	15% 10% 34% 32% 8% 1	1045
November	1st to 10th	Night	20% 8% 34% 30% 7% 1	975
	11th to 20th	Night	14% 11% 37% 27% 9% 2	953
	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 2024-11-08 05:44:47. Version ac07

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