Albert L. Ruppel Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Albert L. Ruppel Observatory clear sky chart from 2005-11-06 to 2024-04-03.

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	13% 7% 3 6% 5% 3 5% 4 5% 7% 42%	78915
	Night	14% 8% 3 6% 5% 3 4 4 4 6% 43%	81263
Transparency	Day	41% 5% 12% 24% 16% 2	78625
	Night	42% 5% 10% 24% 16% 3	81074
Seeing	Day	17% 12% 28% 25% 14% 4	14709
	Night	17% 11% 30% 28% 12% 1	24733

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	9% 12% 7% 9% 7% 3 4 5% 6% 7% 30%	2527
	11th to 20th	Day	13% 9% 4 7% 6% 4 5% 4 5% 6% 36%	2758
	21st to end	Day	21% 16% 6% 6% 4 2 3 3 3 4 30%	3135
February	1st to 10th	Day	15% 10% 5% 8% 5% 2 5% 4 6% 6% 34%	1710
	11th to 20th	Day	15% 8% 3 6% 5% 4 4 5% 5% 6% 38%	1820
	21st to end	Day	15% 10% 3 7% 5% 3 4 3 4 7% 39%	1570
March	1st to 10th	Day	15% 9% 4 6% 5% 3 4 4 4 6% 41%	1938
	11th to 20th	Day	18% 10% 4 5% 6% 3 4 4 5% 6% 36%	2090
	21st to end	Day	19% 11% 4 7% 6% 3 5% 5% 5% 5% 30%	2411
April	1st to 10th	Day	11% 6% 2 6% 6% 3 6% 4 6% 7% 43%	2184
	11th to 20th	Day	17% 8% 2 6% 5% 3 4 4 5% 6% 40%	2134
	21st to end	Day	18% 6% 3 7% 6% 3 5% 4 5% 6% 37%	2160
May	1st to 10th	Day	17% 6% 3 6% 5% 4 4 5% 6% 8% 37%	2196
	11th to 20th	Day	17% 6% 2 5% 4 3 4 5% 6% 7% 40%	2460
	21st to end	Day	11% 5% 3 6% 6% 4 6% 5% 7% 9% 37%	2725
June	1st to 10th	Day	8% 4 2 5% 5% 4 5% 6% 6% 8% 47%	2520
	11th to 20th	Day	7% 3 2 4 4 3 5% 5% 6% 10% 49%	2520
	21st to end	Day	5% 3 2 4 5% 3 6% 5% 8% 12% 47%	2520
July	1st to 10th	Day	10% 3 2 4 5% 4 5% 6% 7% 11% 43%	2520
	11th to 20th	Day	4 3 2 4 4 3 5% 5% 7% 10% 52%	2520
	21st to end	Day	8% 4 2 5% 5% 3 5% 6% 6% 9% 46%	2593
August	1st to 10th	Day	7% 4 2 5% 5% 5% 5% 6% 8% 10% 43%	2328
	11th to 20th	Day	9% 4 2 6% 5% 4 6% 7% 7% 10% 41%	2125
	21st to end	Day	9% 5% 2 4 4 3 4 5% 6% 8% 52%	2376
September	1st to 10th	Day	14% 4 2 5% 4 3 3 4 5% 9% 49%	2160
	11th to 20th	Day	10% 4 2 5% 4 2 4 4 5% 9% 50%	2143
	21st to end	Day	7% 5% 2 4 4 2 5% 3 5% 8% 55%	1963
October	1st to 10th	Day	10% 5% 2 4 5% 3 4 3 5% 7% 53%	1800
	11th to 20th	Day	14% 6% 2 5% 4 2 3 3 4 6% 51%	1800
	21st to end	Day	18% 8% 2 4 4 3 3 3 4 5% 46%	1974
November	1st to 10th	Day	11% 4 2 4 4 2 4 3 4 6% 55%	1672
	11th to 20th	Day	14% 7% 3 5% 4 3 3 3 5% 6% 47%	1710
	21st to end	Day	16% 9% 3 6% 4 3 5% 4 3 5% 42%	1632
December	1st to 10th	Day	13% 11% 4 6% 4 2 5% 4 4 7% 40%	1520
	11th to 20th	Day	13% 11% 4 6% 5% 3 4 5% 5% 5% 39%	1918
	21st to end	Day	19% 14% 5% 7% 6% 3 4 4 5% 5% 27%	2783
January	1st to 10th	Night	15% 9% 6% 9% 6% 3 4 4 4 5% 35%	4428
	11th to 20th	Night	13% 10% 4 10% 7% 5% 7% 4 4 4 31%	4211
	21st to end	Night	23% 16% 5% 7% 5% 2 3 3 3 5% 28%	4532
February	1st to 10th	Night	16% 11% 4 7% 6% 3 4 4 5% 5% 35%	2470
	11th to 20th	Night	15% 7% 4 7% 6% 3 4 3 4 5% 42%	2244
	21st to end	Night	16% 9% 3 8% 6% 2 4 3 4 5% 40%	1884
March	1st to 10th	Night	16% 11% 3 5% 5% 2 3 3 4 5% 43%	2256
	11th to 20th	Night	19% 8% 3 7% 4 3 4 4 5% 6% 39%	2090
	21st to end	Night	20% 10% 3 7% 5% 3 5% 4 5% 6% 31%	2185
April	1st to 10th	Night	12% 5% 3 6% 5% 2 4 5% 4 7% 47%	1820
	11th to 20th	Night	13% 7% 3 5% 6% 3 4 3 5% 7% 44%	1775
	21st to end	Night	19% 7% 3 6% 4 2 3 3 4 7% 41%	1800
May	1st to 10th	Night	16% 7% 2 4 4 2 5% 4 5% 7% 44%	1762
	11th to 20th	Night	16% 7% 2 5% 3 3 3 4 3 8% 44%	1432
	21st to end	Night	9% 6% 3 6% 5% 3 5% 5% 7% 9% 42%	1551
June	1st to 10th	Night	8% 4 2 5% 4 3 4 5% 6% 10% 48%	1440
	11th to 20th	Night	6% 3 2 4 3 3 5% 4 5% 8% 56%	1440
	21st to end	Night	4 3 1 3 4 3 4 6% 6% 9% 55%	1440
July	1st to 10th	Night	9% 4 2 3 4 3 5% 5% 5% 10% 49%	1440
	11th to 20th	Night	5% 3 2 4 4 3 3 5% 6% 9% 55%	1440
	21st to end	Night	6% 4 2 5% 6% 3 5% 5% 6% 9% 50%	1721
August	1st to 10th	Night	7% 3 1 5% 4 3 5% 4 7% 8% 52%	1611
	11th to 20th	Night	6% 4 2 5% 5% 3 5% 5% 6% 8% 50%	1775
	21st to end	Night	5% 3 2 5% 4 3 4 5% 4 9% 56%	1980
September	1st to 10th	Night	13% 5% 2 4 4 2 5% 4 5% 6% 52%	1800
	11th to 20th	Night	8% 4 2 5% 4 3 4 5% 5% 7% 52%	1800
	21st to end	Night	8% 4 2 4 4 3 4 4 4 7% 56%	1991
October	1st to 10th	Night	9% 4 2 4 4 2 3 4 4 6% 58%	2160
	11th to 20th	Night	14% 5% 2 4 3 3 3 4 4 6% 52%	2160
	21st to end	Night	18% 8% 2 4 3 2 4 3 3 5% 47%	2380
November	1st to 10th	Night	11% 5% 2 3 4 2 3 3 4 6% 57%	2406
	11th to 20th	Night	14% 5% 3 5% 4 2 4 3 4 6% 49%	2470
	21st to end	Night	19% 7% 3 4 3 2 2 3 5% 6% 44%	2546
December	1st to 10th	Night	16% 11% 3 5% 6% 3 4 4 5% 6% 37%	2660
	11th to 20th	Night	16% 9% 4 6% 5% 3 4 3 4 5% 41%	3279
	21st to end	Night	17% 18% 5% 9% 7% 3 4 4 4 5% 23%	4884

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	50% 7% 12% 22% 9% 1	2528
	11th to 20th	Day	47% 5% 12% 22% 13%	2758
	21st to end	Day	58% 4 9% 16% 12% 1	3135
February	1st to 10th	Day	51% 4 11% 23% 10% 1	1710
	11th to 20th	Day	47% 5% 10% 20% 15% 3	1830
	21st to end	Day	46% 4 9% 23% 14% 4	1570
March	1st to 10th	Day	45% 4 10% 22% 17% 3	1938
	11th to 20th	Day	50% 4 11% 19% 14% 2	2090
	21st to end	Day	56% 5% 12% 18% 9% 1	2411
April	1st to 10th	Day	40% 5% 11% 26% 17% 1	2184
	11th to 20th	Day	45% 4 10% 23% 14% 3	2134
	21st to end	Day	47% 5% 11% 23% 13% 1	2160
May	1st to 10th	Day	46% 7% 13% 23% 10% 1	2196
	11th to 20th	Day	41% 6% 13% 24% 14% 1	2464
	21st to end	Day	41% 7% 15% 21% 13% 2	2725
June	1st to 10th	Day	34% 6% 14% 27% 17% 2	2520
	11th to 20th	Day	29% 6% 13% 26% 23% 3	2520
	21st to end	Day	28% 7% 19% 25% 16% 5%	2520
July	1st to 10th	Day	33% 7% 17% 27% 13% 4	2451
	11th to 20th	Day	26% 7% 16% 28% 20% 4	2445
	21st to end	Day	34% 7% 12% 30% 15% 2	2449
August	1st to 10th	Day	34% 8% 14% 28% 16%	2314
	11th to 20th	Day	36% 8% 14% 27% 14% 1	2125
	21st to end	Day	30% 6% 14% 24% 20% 5%	2376
September	1st to 10th	Day	35% 4 10% 29% 18% 5%	2160
	11th to 20th	Day	32% 4 10% 27% 25% 3	2143
	21st to end	Day	28% 5% 8% 30% 25% 3	1963
October	1st to 10th	Day	31% 5% 9% 26% 25% 4	1800
	11th to 20th	Day	36% 3 9% 26% 21% 5%	1800
	21st to end	Day	41% 4 9% 26% 17% 4	1974
November	1st to 10th	Day	32% 4 13% 26% 20% 6%	1672
	11th to 20th	Day	38% 3 10% 25% 21% 5%	1710
	21st to end	Day	45% 4 8% 27% 15%	1632
December	1st to 10th	Day	45% 5% 11% 26% 12% 1	1520
	11th to 20th	Day	47% 4 11% 23% 14% 2	1915
	21st to end	Day	59% 4 11% 15% 9% 1	2783
January	1st to 10th	Night	52% 4 10% 24% 10% 1	4428
	11th to 20th	Night	57% 5% 8% 20% 9% 1	4211
	21st to end	Night	60% 4 8% 20% 7% 1	4532
February	1st to 10th	Night	52% 4 10% 20% 13% 1	2470
	11th to 20th	Night	45% 4 9% 21% 18% 2	2245
	21st to end	Night	48% 3 11% 20% 14% 4	1884
March	1st to 10th	Night	46% 4 8% 23% 16% 3	2256
	11th to 20th	Night	48% 4 9% 22% 14% 3	2090
	21st to end	Night	54% 5% 12% 20% 9% 1	2185
April	1st to 10th	Night	37% 5% 10% 26% 18% 3	1820
	11th to 20th	Night	40% 4 11% 24% 17% 4	1775
	21st to end	Night	44% 4 8% 26% 17% 2	1800
May	1st to 10th	Night	40% 6% 13% 24% 16% 2	1762
	11th to 20th	Night	40% 6% 12% 25% 15% 2	1433
	21st to end	Night	37% 8% 15% 21% 16% 3	1552
June	1st to 10th	Night	30% 5% 16% 28% 17% 3	1440
	11th to 20th	Night	26% 5% 11% 28% 25% 4	1440
	21st to end	Night	24% 7% 15% 29% 19% 6%	1440
July	1st to 10th	Night	31% 6% 16% 28% 15% 5%	1400
	11th to 20th	Night	25% 5% 15% 30% 21% 4	1392
	21st to end	Night	28% 7% 13% 31% 19% 2	1625
August	1st to 10th	Night	27% 8% 14% 34% 15% 2	1601
	11th to 20th	Night	30% 6% 12% 28% 21% 2	1775
	21st to end	Night	25% 7% 14% 26% 23% 5%	1980
September	1st to 10th	Night	34% 4 9% 25% 22% 6%	1800
	11th to 20th	Night	30% 6% 8% 26% 25% 4	1800
	21st to end	Night	28% 6% 8% 25% 28% 4	1991
October	1st to 10th	Night	28% 4 10% 26% 27% 5%	2160
	11th to 20th	Night	34% 3 7% 28% 21% 7%	2160
	21st to end	Night	41% 3 9% 22% 22% 4	2380
November	1st to 10th	Night	30% 4 12% 26% 23% 6%	2406
	11th to 20th	Night	37% 3 8% 25% 23% 4	2470
	21st to end	Night	42% 3 11% 25% 17% 2	2546
December	1st to 10th	Night	48% 4 9% 24% 12% 1	2660
	11th to 20th	Night	46% 3 10% 24% 16% 1	3281
	21st to end	Night	62% 6% 9% 14% 7% 1	4884

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	22% 22% 37% 15% 4	270
	11th to 20th	Day	32% 20% 35% 12%	270
	21st to end	Day	23% 24% 36% 15% 2	297
February	1st to 10th	Day	24% 23% 38% 12% 3	270
	11th to 20th	Day	26% 28% 30% 13% 3	270
	21st to end	Day	31% 23% 36% 9% 1	225
March	1st to 10th	Day	20% 23% 46% 9% 1	270
	11th to 20th	Day	31% 21% 33% 11% 3 1	270
	21st to end	Day	33% 19% 31% 13% 4	409
April	1st to 10th	Day	20% 18% 38% 17% 7% 1	428
	11th to 20th	Day	25% 16% 31% 19% 8%	412
	21st to end	Day	26% 14% 38% 16% 6%	420
May	1st to 10th	Day	22% 16% 33% 21% 7% 2	423
	11th to 20th	Day	18% 14% 31% 24% 11% 2	606
	21st to end	Day	13% 8% 33% 28% 13% 6%	679
June	1st to 10th	Day	11% 5% 23% 34% 21% 6%	630
	11th to 20th	Day	9% 4 23% 40% 19% 5%	630
	21st to end	Day	5% 7% 31% 34% 17% 5%	630
July	1st to 10th	Day	11% 3 14% 30% 29% 13%	621
	11th to 20th	Day	6% 4 22% 37% 25% 6%	618
	21st to end	Day	9% 3 20% 33% 30% 5%	684
August	1st to 10th	Day	9% 3 16% 38% 26% 8%	626
	11th to 20th	Day	13% 5% 15% 33% 25% 9%	439
	21st to end	Day	10% 3 15% 31% 29% 11%	495
September	1st to 10th	Day	14% 4 17% 30% 26% 8%	450
	11th to 20th	Day	10% 2 16% 32% 26% 14%	450
	21st to end	Day	10% 8% 21% 32% 21% 7%	433
October	1st to 10th	Day	11% 12% 28% 35% 11% 3	270
	11th to 20th	Day	22% 20% 31% 21% 6%	270
	21st to end	Day	34% 16% 29% 16% 5%	297
November	1st to 10th	Day	15% 10% 39% 22% 10% 4	270
	11th to 20th	Day	21% 19% 31% 20% 7% 2	270
	21st to end	Day	27% 16% 31% 19% 6% 1	270
December	1st to 10th	Day	17% 25% 36% 14% 6% 3	270
	11th to 20th	Day	21% 22% 33% 20% 3	270
	21st to end	Day	27% 23% 37% 10% 2	297
January	1st to 10th	Night	20% 17% 38% 20% 4	950
	11th to 20th	Night	23% 21% 33% 18% 4	950
	21st to end	Night	19% 19% 39% 21% 2	1045
February	1st to 10th	Night	23% 17% 37% 21% 2	950
	11th to 20th	Night	22% 18% 38% 20% 2	769
	21st to end	Night	24% 18% 37% 18% 2	628
March	1st to 10th	Night	23% 16% 38% 19% 4	736
	11th to 20th	Night	24% 12% 38% 21% 5%	570
	21st to end	Night	27% 14% 33% 21% 4	627
April	1st to 10th	Night	16% 16% 37% 24% 6%	546
	11th to 20th	Night	18% 13% 35% 25% 8%	533
	21st to end	Night	22% 11% 37% 23% 6%	540
May	1st to 10th	Night	18% 6% 36% 31% 9% 1	540
	11th to 20th	Night	19% 5% 30% 31% 14% 2	531
	21st to end	Night	11% 5% 25% 36% 20% 2	584
June	1st to 10th	Night	9% 3 20% 41% 26% 1	540
	11th to 20th	Night	7% 2 23% 46% 20% 1	540
	21st to end	Night	5% 3 25% 45% 19% 2	540
July	1st to 10th	Night	10% 2 11% 39% 32% 6%	525
	11th to 20th	Night	6% 2 16% 43% 30% 3	522
	21st to end	Night	7% 2 16% 42% 31% 3	591
August	1st to 10th	Night	7% 2 13% 41% 34% 3	537
	11th to 20th	Night	7% 2 13% 42% 32% 4	534
	21st to end	Night	6% 1 15% 39% 35% 3	594
September	1st to 10th	Night	14% 3 13% 37% 28% 6%	540
	11th to 20th	Night	10% 3 16% 32% 33% 6%	540
	21st to end	Night	9% 7% 24% 31% 24% 4	718
October	1st to 10th	Night	10% 6% 29% 31% 21% 4	720
	11th to 20th	Night	17% 13% 32% 28% 10% 1	720
	21st to end	Night	25% 11% 35% 23% 6%	792
November	1st to 10th	Night	13% 10% 39% 26% 11% 1	740
	11th to 20th	Night	18% 16% 34% 26% 6%	760
	21st to end	Night	23% 14% 34% 23% 6% 1	836
December	1st to 10th	Night	23% 14% 36% 23% 4 1	950
	11th to 20th	Night	24% 13% 31% 27% 5%	950
	21st to end	Night	27% 17% 34% 20% 3	1045

Page generated at 2024-03-31 05:08:49. Version ac07

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