D'Auria Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the D'Auria Observatory clear sky chart from 2005-11-06 to 2026-09-29.

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	5% 5% 2 7% 6% 6% 7% 6% 8% 11% 36%	147735
	Night	5% 5% 2 6% 5% 5% 5% 5% 7% 10% 44%	143657
Transparency	Day	36% 10% 20% 22% 10% 2	151414
	Night	32% 10% 21% 23% 12% 3	148050
Seeing	Day	7% 3 17% 30% 25% 19%	18640
	Night	7% 2 14% 32% 32% 13%	28734

By Month

Percentage Cloud Cover SE (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	5% 4 2 5% 4 4 4 4 7% 11% 52%	5258
	11th to 20th	Day	12% 7% 3 9% 6% 6% 6% 5% 8% 9% 29%	5280
	21st to end	Day	8% 7% 3 8% 6% 6% 5% 4 6% 8% 40%	6020
February	1st to 10th	Day	7% 6% 2 6% 5% 6% 6% 4 6% 10% 42%	2100
	11th to 20th	Day	6% 3 2 6% 3 4 4 5% 8% 10% 49%	2167
	21st to end	Day	5% 5% 2 5% 5% 4 6% 4 8% 10% 48%	1903
March	1st to 10th	Day	3 3 2 6% 5% 6% 7% 6% 9% 9% 45%	5045
	11th to 20th	Day	4 2 1 4 3 4 4 4 6% 9% 58%	5090
	21st to end	Day	6% 4 2 7% 5% 5% 5% 5% 7% 10% 44%	5586
April	1st to 10th	Day	4 3 1 6% 5% 5% 5% 6% 8% 11% 45%	2310
	11th to 20th	Day	4 4 2 7% 5% 6% 6% 5% 9% 11% 42%	2354
	21st to end	Day	5% 3 2 6% 6% 5% 6% 5% 6% 10% 46%	2520
May	1st to 10th	Day	3 3 1 4 3 4 5% 4 7% 12% 54%	7021
	11th to 20th	Day	5% 4 2 6% 5% 6% 6% 5% 8% 10% 43%	7086
	21st to end	Day	4 4 2 7% 6% 7% 8% 7% 10% 12% 32%	8391
June	1st to 10th	Day	13% 9% 4 11% 9% 9% 8% 6% 7% 7% 16%	2730
	11th to 20th	Day	7% 7% 4 10% 10% 10% 9% 6% 8% 10% 18%	2730
	21st to end	Day	6% 7% 3 11% 11% 9% 9% 8% 9% 9% 18%	2730
July	1st to 10th	Day	4 6% 2 9% 7% 7% 8% 7% 9% 14% 27%	7680
	11th to 20th	Day	4 4 2 9% 7% 8% 8% 7% 9% 13% 29%	7680
	21st to end	Day	2 3 1 6% 6% 7% 8% 7% 10% 15% 34%	8340
August	1st to 10th	Day	3 4 3 10% 9% 9% 9% 8% 10% 13% 24%	5902
	11th to 20th	Day	3 4 2 7% 6% 6% 7% 6% 10% 12% 37%	5420
	21st to end	Day	3 3 2 7% 7% 9% 10% 8% 11% 16% 25%	5566
September	1st to 10th	Day	6% 6% 3 12% 9% 9% 8% 8% 11% 12% 17%	2310
	11th to 20th	Day	8% 8% 4 12% 9% 8% 8% 7% 9% 9% 18%	2310
	21st to end	Day	10% 10% 4 11% 7% 7% 7% 7% 8% 9% 21%	2288
October	1st to 10th	Day	7% 7% 4 11% 7% 7% 7% 6% 9% 12% 21%	2125
	11th to 20th	Day	9% 5% 3 9% 7% 7% 7% 7% 8% 10% 27%	2000
	21st to end	Day	10% 7% 3 7% 7% 6% 6% 5% 7% 10% 34%	2200
November	1st to 10th	Day	6% 6% 2 7% 6% 7% 7% 6% 7% 9% 38%	2057
	11th to 20th	Day	7% 6% 3 8% 7% 6% 6% 5% 8% 7% 36%	2100
	21st to end	Day	7% 5% 2 7% 6% 5% 5% 5% 7% 9% 42%	2100
December	1st to 10th	Day	5% 4 1 4 4 4 5% 3 6% 9% 55%	3308
	11th to 20th	Day	8% 5% 2 7% 5% 6% 6% 5% 8% 11% 38%	3463
	21st to end	Day	10% 6% 2 9% 7% 7% 7% 5% 8% 9% 30%	4565
January	1st to 10th	Night	4 4 2 5% 4 4 5% 4 7% 9% 51%	7635
	11th to 20th	Night	12% 8% 3 8% 5% 5% 5% 5% 7% 8% 33%	7680
	21st to end	Night	9% 7% 3 8% 5% 4 5% 4 5% 7% 43%	8143
February	1st to 10th	Night	6% 6% 2 5% 4 4 4 4 6% 9% 50%	2520
	11th to 20th	Night	5% 3 1 5% 4 3 4 4 6% 7% 57%	2335
	21st to end	Night	4 3 1 4 4 3 4 3 6% 10% 59%	1903
March	1st to 10th	Night	3 3 2 6% 4 5% 5% 4 6% 9% 52%	5028
	11th to 20th	Night	4 3 1 3 3 3 4 3 5% 8% 63%	5090
	21st to end	Night	5% 3 2 5% 4 5% 5% 4 6% 8% 53%	5588
April	1st to 10th	Night	3 3 1 4 3 3 4 4 7% 9% 59%	2310
	11th to 20th	Night	4 3 1 5% 3 4 4 4 5% 10% 55%	2212
	21st to end	Night	5% 4 2 5% 3 4 5% 4 6% 10% 52%	2100
May	1st to 10th	Night	3 2 1 3 3 3 4 4 6% 10% 62%	5833
	11th to 20th	Night	5% 4 2 6% 4 4 5% 4 7% 9% 50%	5814
	21st to end	Night	3 3 1 4 4 4 5% 6% 9% 14% 45%	5761
June	1st to 10th	Night	11% 9% 3 9% 6% 6% 6% 6% 8% 10% 26%	1890
	11th to 20th	Night	6% 6% 2 6% 6% 6% 8% 7% 9% 14% 32%	1890
	21st to end	Night	4 4 2 6% 6% 6% 8% 7% 10% 14% 33%	1890
July	1st to 10th	Night	3 4 2 7% 5% 5% 6% 5% 10% 15% 37%	5278
	11th to 20th	Night	3 4 2 6% 5% 5% 5% 6% 10% 14% 40%	5277
	21st to end	Night	1 3 1 4 3 5% 5% 5% 9% 15% 48%	5736
August	1st to 10th	Night	2 3 2 7% 6% 7% 8% 7% 10% 15% 33%	4200
	11th to 20th	Night	2 3 2 5% 4 4 6% 5% 8% 12% 49%	4604
	21st to end	Night	3 3 2 6% 5% 7% 8% 7% 12% 16% 31%	5559
September	1st to 10th	Night	5% 4 2 7% 6% 7% 7% 7% 9% 14% 33%	2310
	11th to 20th	Night	6% 7% 3 8% 8% 7% 7% 6% 9% 11% 28%	2310
	21st to end	Night	7% 7% 3 9% 7% 6% 7% 6% 9% 11% 28%	2289
October	1st to 10th	Night	7% 5% 3 10% 7% 7% 7% 6% 9% 11% 29%	2273
	11th to 20th	Night	8% 6% 3 7% 5% 5% 6% 5% 8% 11% 36%	2400
	21st to end	Night	9% 6% 3 8% 5% 5% 5% 4 6% 8% 42%	2640
November	1st to 10th	Night	7% 4 2 7% 5% 5% 5% 5% 7% 8% 45%	2461
	11th to 20th	Night	7% 8% 2 6% 5% 5% 5% 6% 6% 9% 40%	2520
	21st to end	Night	6% 4 2 5% 5% 5% 5% 4 6% 8% 49%	2520
December	1st to 10th	Night	4 4 2 5% 3 3 3 4 6% 9% 57%	4073
	11th to 20th	Night	10% 7% 3 7% 5% 4 4 4 6% 8% 44%	4952
	21st to end	Night	9% 8% 3 9% 6% 6% 6% 5% 7% 8% 32%	6633

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	25% 6% 9% 35% 17% 7%	5259
	11th to 20th	Day	46% 9% 15% 20% 7% 3	5280
	21st to end	Day	40% 6% 9% 26% 16% 4	6020
February	1st to 10th	Day	33% 6% 10% 25% 20% 5%	2100
	11th to 20th	Day	26% 6% 11% 28% 24% 5%	2177
	21st to end	Day	28% 6% 11% 23% 24% 8%	1903
March	1st to 10th	Day	27% 9% 14% 24% 23% 3	5045
	11th to 20th	Day	19% 7% 14% 30% 17% 13%	5090
	21st to end	Day	30% 7% 11% 28% 20% 5%	5586
April	1st to 10th	Day	27% 8% 14% 32% 16% 3	2310
	11th to 20th	Day	28% 10% 15% 23% 19% 6%	2354
	21st to end	Day	29% 7% 13% 26% 21% 4	2520
May	1st to 10th	Day	19% 7% 15% 39% 18% 2	7053
	11th to 20th	Day	29% 8% 19% 34% 9%	7090
	21st to end	Day	33% 13% 22% 26% 5%	8405
June	1st to 10th	Day	61% 10% 16% 10% 3	2730
	11th to 20th	Day	55% 12% 19% 13% 2	2730
	21st to end	Day	52% 15% 23% 10% 1	2730
July	1st to 10th	Day	38% 15% 35% 12%	7615
	11th to 20th	Day	38% 12% 34% 15%	7611
	21st to end	Day	29% 14% 33% 22% 1	8156
August	1st to 10th	Day	42% 16% 28% 12% 1	5889
	11th to 20th	Day	31% 13% 26% 23% 7%	5456
	21st to end	Day	37% 17% 39% 7%	5566
September	1st to 10th	Day	52% 16% 21% 10%	2310
	11th to 20th	Day	55% 15% 19% 9% 2	2310
	21st to end	Day	55% 14% 14% 12% 6%	2288
October	1st to 10th	Day	47% 11% 21% 16% 5% 1	3463
	11th to 20th	Day	48% 13% 15% 14% 9% 1	3240
	21st to end	Day	38% 7% 12% 26% 15% 3	3538
November	1st to 10th	Day	37% 8% 14% 17% 19% 6%	2057
	11th to 20th	Day	42% 7% 9% 18% 19% 5%	2100
	21st to end	Day	37% 8% 12% 18% 22% 4	2100
December	1st to 10th	Day	25% 6% 11% 31% 23% 4	3308
	11th to 20th	Day	35% 7% 15% 21% 18% 4	3460
	21st to end	Day	46% 8% 15% 15% 15% 2	4565
January	1st to 10th	Night	26% 7% 12% 31% 19% 5%	7636
	11th to 20th	Night	46% 9% 17% 18% 8% 3	7680
	21st to end	Night	38% 6% 10% 29% 14% 3	8143
February	1st to 10th	Night	30% 5% 13% 25% 21% 5%	2520
	11th to 20th	Night	23% 6% 12% 26% 24% 8%	2336
	21st to end	Night	22% 5% 13% 23% 29% 9%	1903
March	1st to 10th	Night	26% 8% 12% 25% 24% 6%	5028
	11th to 20th	Night	18% 6% 17% 29% 19% 11%	5090
	21st to end	Night	26% 7% 13% 27% 22% 5%	5588
April	1st to 10th	Night	20% 6% 16% 36% 17% 3	2310
	11th to 20th	Night	23% 8% 17% 25% 22% 5%	2212
	21st to end	Night	25% 7% 15% 28% 22% 3	2100
May	1st to 10th	Night	16% 7% 19% 43% 14% 1	5863
	11th to 20th	Night	27% 9% 19% 32% 12% 1	5815
	21st to end	Night	23% 11% 32% 26% 7%	5771
June	1st to 10th	Night	49% 12% 22% 15% 3	1890
	11th to 20th	Night	38% 14% 26% 19% 2	1890
	21st to end	Night	36% 16% 36% 12%	1890
July	1st to 10th	Night	31% 15% 42% 12%	5235
	11th to 20th	Night	30% 13% 42% 15%	5226
	21st to end	Night	23% 13% 38% 24% 2	5606
August	1st to 10th	Night	37% 16% 34% 12% 1	4189
	11th to 20th	Night	25% 13% 32% 26% 5%	4634
	21st to end	Night	33% 19% 40% 7%	5559
September	1st to 10th	Night	37% 19% 30% 13% 1	2310
	11th to 20th	Night	45% 17% 26% 11% 1	2310
	21st to end	Night	45% 15% 21% 14% 5%	2289
October	1st to 10th	Night	45% 13% 19% 18% 4 1	3715
	11th to 20th	Night	47% 10% 19% 13% 10% 1	3899
	21st to end	Night	38% 7% 12% 26% 15% 3	4252
November	1st to 10th	Night	33% 7% 13% 22% 19% 5%	2461
	11th to 20th	Night	39% 6% 11% 24% 16% 4	2520
	21st to end	Night	31% 7% 14% 22% 21% 5%	2520
December	1st to 10th	Night	24% 7% 13% 35% 17% 4	4073
	11th to 20th	Night	37% 6% 13% 22% 17% 5%	4954
	21st to end	Night	46% 9% 14% 16% 14% 2	6633

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	8% 7% 32% 38% 14% 2	330
	11th to 20th	Day	12% 11% 37% 30% 8% 2	330
	21st to end	Day	10% 9% 42% 30% 8%	363
February	1st to 10th	Day	4 8% 35% 37% 15% 1	330
	11th to 20th	Day	6% 4 25% 41% 21% 3	450
	21st to end	Day	4 4 26% 38% 26% 2	446
March	1st to 10th	Day	4 6% 31% 39% 18% 2	540
	11th to 20th	Day	7% 5% 32% 32% 21% 3	540
	21st to end	Day	4 4 29% 36% 22% 5%	594
April	1st to 10th	Day	4 5% 30% 37% 18% 6%	540
	11th to 20th	Day	3 4 30% 36% 18% 9%	532
	21st to end	Day	4 3 25% 36% 23% 10%	540
May	1st to 10th	Day	2 2 18% 36% 27% 14%	543
	11th to 20th	Day	8% 3 21% 31% 23% 14%	567
	21st to end	Day	7% 3 9% 30% 28% 23%	617
June	1st to 10th	Day	14% 2 11% 26% 26% 20%	570
	11th to 20th	Day	7% 2 6% 26% 28% 32%	570
	21st to end	Day	4 1 3 19% 29% 43%	570
July	1st to 10th	Day	5% 2 16% 29% 47%	565
	11th to 20th	Day	5% 1 4 18% 35% 37%	564
	21st to end	Day	5% 3 18% 30% 44%	620
August	1st to 10th	Day	5% 1 5% 17% 30% 42%	566
	11th to 20th	Day	5% 1 2 18% 29% 45%	559
	21st to end	Day	6% 1 6% 22% 29% 36%	627
September	1st to 10th	Day	6% 2 4 17% 29% 42%	570
	11th to 20th	Day	7% 2 6% 16% 30% 38%	570
	21st to end	Day	9% 2 6% 23% 28% 32%	562
October	1st to 10th	Day	8% 2 12% 35% 31% 12%	530
	11th to 20th	Day	9% 2 15% 32% 29% 13%	530
	21st to end	Day	8% 3 17% 37% 27% 8%	583
November	1st to 10th	Day	6% 4 22% 36% 25% 7%	535
	11th to 20th	Day	10% 3 21% 37% 23% 5%	540
	21st to end	Day	7% 3 22% 37% 26% 5%	540
December	1st to 10th	Day	9% 4 20% 38% 26% 3	514
	11th to 20th	Day	8% 5% 24% 41% 18% 4	330
	21st to end	Day	9% 5% 28% 36% 17% 6%	363
January	1st to 10th	Night	6% 4 19% 43% 25% 3	840
	11th to 20th	Night	10% 4 25% 41% 19% 1	840
	21st to end	Night	7% 6% 28% 43% 15% 1	924
February	1st to 10th	Night	8% 5% 21% 42% 22% 1	840
	11th to 20th	Night	5% 3 24% 44% 22% 1	823
	21st to end	Night	5% 2 20% 47% 25% 1	692
March	1st to 10th	Night	5% 3 24% 45% 21% 2	840
	11th to 20th	Night	5% 2 22% 45% 23% 2	840
	21st to end	Night	5% 3 23% 44% 23% 1	924
April	1st to 10th	Night	4 3 20% 47% 24% 2	840
	11th to 20th	Night	5% 2 21% 45% 25% 1	831
	21st to end	Night	5% 3 17% 46% 28% 2	840
May	1st to 10th	Night	3 14% 44% 35% 3	840
	11th to 20th	Night	8% 2 15% 39% 33% 3	826
	21st to end	Night	6% 2 6% 24% 49% 13%	683
June	1st to 10th	Night	13% 1 5% 23% 42% 15%	630
	11th to 20th	Night	8% 2 3 12% 45% 31%	630
	21st to end	Night	3 1 3 10% 43% 40%	630
July	1st to 10th	Night	5% 1 2 6% 45% 41%	615
	11th to 20th	Night	3 1 2 11% 43% 41%	612
	21st to end	Night	3 1 2 8% 40% 46%	690
August	1st to 10th	Night	6% 1 3 8% 47% 36%	653
	11th to 20th	Night	2 1 2 12% 46% 37%	830
	21st to end	Night	7% 1 5% 15% 40% 31%	924
September	1st to 10th	Night	6% 5% 11% 40% 37%	840
	11th to 20th	Night	8% 2 5% 13% 40% 32%	840
	21st to end	Night	9% 2 6% 18% 40% 24%	833
October	1st to 10th	Night	9% 2 8% 33% 38% 10%	800
	11th to 20th	Night	10% 2 9% 29% 40% 10%	800
	21st to end	Night	13% 2 15% 35% 28% 6%	880
November	1st to 10th	Night	9% 2 20% 37% 30% 3	820
	11th to 20th	Night	9% 4 16% 34% 33% 4	840
	21st to end	Night	8% 2 16% 44% 28% 3	840
December	1st to 10th	Night	6% 2 16% 40% 33% 3	840
	11th to 20th	Night	9% 4 17% 40% 28% 3	840
	21st to end	Night	7% 4 19% 38% 29% 4	924

Page generated at 2026-09-26 04:18:37. Version ac07

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