AASO/Ridgemont Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the AASO/Ridgemont 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	14% 7% 3 5% 5% 3 4 5% 5% 7% 42%	78923
	Night	15% 6% 3 5% 4 3 4 4 5% 7% 45%	81247
Transparency	Day	40% 6% 11% 23% 16% 3	78630
	Night	39% 6% 10% 23% 18% 4	81061
Seeing	Day	15% 7% 21% 26% 20% 11%	14545
	Night	16% 6% 25% 32% 18% 2	24526

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	15% 10% 3 8% 5% 3 4 4 5% 5% 38%	2527
	11th to 20th	Day	19% 8% 3 5% 5% 3 5% 3 4 5% 41%	2635
	21st to end	Day	25% 11% 3 6% 5% 3 3 3 4 5% 31%	3135
February	1st to 10th	Day	18% 10% 4 5% 5% 3 3 4 6% 6% 37%	1881
	11th to 20th	Day	18% 9% 3 6% 4 4 4 3 4 6% 39%	1848
	21st to end	Day	19% 9% 4 7% 6% 3 3 4 4 6% 36%	1570
March	1st to 10th	Day	17% 9% 2 4 4 3 4 4 4 6% 41%	1900
	11th to 20th	Day	20% 8% 3 6% 6% 2 4 3 4 6% 37%	1984
	21st to end	Day	19% 9% 3 6% 5% 3 5% 4 5% 6% 34%	2504
April	1st to 10th	Day	12% 6% 3 6% 4 3 4 4 5% 8% 46%	2184
	11th to 20th	Day	15% 8% 3 6% 6% 2 3 5% 4 7% 41%	2134
	21st to end	Day	18% 6% 3 6% 4 3 4 5% 5% 7% 39%	2160
May	1st to 10th	Day	16% 7% 2 5% 5% 3 5% 5% 5% 8% 38%	2276
	11th to 20th	Day	16% 5% 3 6% 6% 3 5% 4 5% 7% 40%	2301
	21st to end	Day	9% 6% 3 6% 7% 4 6% 6% 7% 9% 38%	2641
June	1st to 10th	Day	9% 4 2 5% 5% 3 6% 6% 8% 9% 46%	2520
	11th to 20th	Day	5% 3 2 5% 5% 3 6% 6% 7% 9% 50%	2520
	21st to end	Day	6% 4 3 4 5% 3 6% 7% 6% 11% 46%	2520
July	1st to 10th	Day	8% 4 2 6% 7% 4 6% 6% 7% 10% 39%	2520
	11th to 20th	Day	6% 3 2 5% 5% 3 5% 6% 7% 10% 47%	2520
	21st to end	Day	6% 4 2 5% 6% 4 5% 7% 8% 11% 43%	2679
August	1st to 10th	Day	8% 5% 2 4 5% 4 5% 5% 7% 10% 45%	2148
	11th to 20th	Day	10% 5% 2 5% 5% 3 5% 5% 6% 10% 43%	2125
	21st to end	Day	7% 4 2 5% 5% 4 5% 5% 7% 10% 46%	2376
September	1st to 10th	Day	12% 5% 2 4 5% 3 4 5% 6% 7% 48%	2160
	11th to 20th	Day	11% 5% 2 5% 4 4 4 5% 5% 6% 50%	2051
	21st to end	Day	12% 4 2 4 4 2 4 4 4 7% 53%	1980
October	1st to 10th	Day	9% 4 1 4 5% 2 3 4 4 6% 58%	1954
	11th to 20th	Day	15% 5% 2 4 5% 3 3 3 3 5% 52%	1800
	21st to end	Day	21% 6% 2 4 3 2 3 4 4 5% 47%	1890
November	1st to 10th	Day	11% 5% 2 4 3 3 4 4 4 6% 54%	1672
	11th to 20th	Day	16% 6% 3 5% 4 2 3 3 4 6% 49%	1710
	21st to end	Day	19% 7% 3 5% 4 2 3 4 4 6% 43%	1710
December	1st to 10th	Day	18% 9% 2 6% 4 3 3 5% 5% 5% 40%	1687
	11th to 20th	Day	16% 8% 3 6% 5% 4 5% 5% 5% 6% 37%	1918
	21st to end	Day	21% 12% 4 6% 6% 3 4 4 3 5% 32%	2783
January	1st to 10th	Night	19% 8% 2 4 3 3 4 5% 5% 6% 40%	4428
	11th to 20th	Night	16% 9% 4 6% 5% 3 5% 4 4 6% 38%	4330
	21st to end	Night	26% 10% 4 4 4 2 3 4 5% 6% 33%	4532
February	1st to 10th	Night	22% 9% 4 7% 5% 3 4 4 4 5% 35%	2297
	11th to 20th	Night	18% 7% 3 7% 5% 2 4 4 4 6% 41%	2218
	21st to end	Night	18% 9% 3 6% 6% 3 4 5% 4 4 38%	1884
March	1st to 10th	Night	18% 7% 3 4 4 3 4 4 4 5% 42%	2280
	11th to 20th	Night	18% 9% 4 5% 4 2 4 4 4 6% 41%	2213
	21st to end	Night	18% 8% 4 6% 5% 3 4 4 5% 6% 36%	2092
April	1st to 10th	Night	13% 4 2 4 4 2 5% 4 6% 7% 49%	1820
	11th to 20th	Night	15% 5% 2 5% 4 2 4 4 4 7% 47%	1775
	21st to end	Night	17% 6% 3 4 4 3 3 4 6% 7% 42%	1800
May	1st to 10th	Night	16% 6% 3 4 4 2 4 5% 4 8% 43%	1683
	11th to 20th	Night	15% 5% 2 6% 6% 3 4 5% 4 8% 42%	1592
	21st to end	Night	6% 4 2 5% 5% 4 5% 7% 7% 11% 44%	1630
June	1st to 10th	Night	10% 4 3 4 5% 3 5% 6% 6% 9% 48%	1440
	11th to 20th	Night	4 2 1 5% 4 3 4 5% 8% 9% 55%	1440
	21st to end	Night	4 1 2 3 4 3 4 5% 9% 14% 51%	1440
July	1st to 10th	Night	7% 3 2 4 5% 3 5% 7% 6% 9% 48%	1440
	11th to 20th	Night	7% 3 2 4 4 2 4 5% 4 11% 53%	1440
	21st to end	Night	6% 3 2 4 4 2 4 5% 7% 10% 52%	1634
August	1st to 10th	Night	6% 4 1 4 5% 2 5% 6% 6% 8% 53%	1790
	11th to 20th	Night	7% 4 1 4 5% 2 4 5% 6% 9% 53%	1776
	21st to end	Night	7% 4 2 3 4 3 4 5% 7% 8% 52%	1980
September	1st to 10th	Night	9% 5% 2 5% 4 2 3 3 4 6% 56%	1800
	11th to 20th	Night	8% 5% 2 5% 4 2 4 3 5% 7% 54%	1890
	21st to end	Night	10% 4 2 3 4 2 4 3 4 7% 57%	1980
October	1st to 10th	Night	8% 4 2 4 4 2 4 2 4 7% 60%	2002
	11th to 20th	Night	15% 4 2 4 4 3 3 3 4 4 54%	2160
	21st to end	Night	19% 6% 2 5% 4 2 4 3 4 5% 46%	2463
November	1st to 10th	Night	12% 5% 2 4 3 2 3 3 4 6% 57%	2406
	11th to 20th	Night	14% 5% 2 4 3 3 3 3 4 6% 51%	2470
	21st to end	Night	17% 6% 2 5% 4 2 3 3 4 5% 49%	2470
December	1st to 10th	Night	19% 8% 3 5% 5% 2 4 4 5% 6% 39%	2489
	11th to 20th	Night	18% 8% 3 4 5% 2 4 4 4 5% 44%	3279
	21st to end	Night	19% 11% 4 7% 6% 4 5% 4 4 5% 32%	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	47% 5% 8% 27% 11% 2	2528
	11th to 20th	Day	46% 5% 9% 24% 15% 2	2635
	21st to end	Day	56% 4 9% 19% 10% 2	3135
February	1st to 10th	Day	48% 4 9% 24% 13% 2	1881
	11th to 20th	Day	48% 4 10% 21% 13% 5%	1858
	21st to end	Day	50% 4 9% 18% 13% 6%	1570
March	1st to 10th	Day	46% 4 8% 22% 16% 4	1900
	11th to 20th	Day	50% 5% 10% 20% 12% 3	1984
	21st to end	Day	49% 6% 12% 20% 12% 1	2504
April	1st to 10th	Day	37% 6% 11% 26% 18% 2	2184
	11th to 20th	Day	43% 5% 9% 22% 18% 3	2134
	21st to end	Day	44% 6% 10% 25% 14% 2	2160
May	1st to 10th	Day	43% 8% 12% 24% 11% 1	2276
	11th to 20th	Day	43% 8% 12% 20% 15% 1	2305
	21st to end	Day	39% 10% 16% 21% 11% 2	2641
June	1st to 10th	Day	32% 9% 14% 23% 21% 2	2520
	11th to 20th	Day	27% 8% 14% 27% 21% 3	2520
	21st to end	Day	30% 10% 15% 23% 16% 5%	2520
July	1st to 10th	Day	36% 9% 16% 22% 13% 5%	2451
	11th to 20th	Day	30% 8% 16% 25% 16% 4	2445
	21st to end	Day	32% 9% 16% 28% 13% 2	2530
August	1st to 10th	Day	33% 8% 17% 27% 14% 1	2136
	11th to 20th	Day	35% 9% 14% 25% 15% 1	2125
	21st to end	Day	30% 7% 16% 25% 16% 5%	2376
September	1st to 10th	Day	35% 7% 10% 25% 19% 3	2160
	11th to 20th	Day	34% 6% 9% 24% 24% 3	2051
	21st to end	Day	32% 5% 8% 25% 25% 6%	1980
October	1st to 10th	Day	29% 5% 11% 25% 26% 6%	1954
	11th to 20th	Day	36% 3 7% 24% 22% 8%	1800
	21st to end	Day	41% 4 7% 24% 19% 4	1890
November	1st to 10th	Day	32% 5% 9% 25% 24% 6%	1672
	11th to 20th	Day	38% 4 7% 22% 23% 5%	1710
	21st to end	Day	44% 3 7% 25% 17% 4	1710
December	1st to 10th	Day	46% 4 11% 24% 14% 2	1687
	11th to 20th	Day	46% 6% 9% 24% 13% 2	1915
	21st to end	Day	54% 6% 12% 17% 11% 1	2783
January	1st to 10th	Night	44% 5% 9% 29% 12% 1	4428
	11th to 20th	Night	46% 6% 9% 23% 13% 2	4330
	21st to end	Night	51% 5% 9% 22% 11% 1	4532
February	1st to 10th	Night	53% 4 8% 20% 14% 1	2297
	11th to 20th	Night	46% 4 7% 22% 17% 3	2219
	21st to end	Night	49% 5% 9% 16% 17% 4	1884
March	1st to 10th	Night	45% 5% 8% 16% 20% 7%	2280
	11th to 20th	Night	46% 5% 11% 20% 14% 4	2213
	21st to end	Night	49% 7% 10% 22% 11% 2	2092
April	1st to 10th	Night	34% 5% 11% 26% 20% 4	1820
	11th to 20th	Night	37% 5% 10% 22% 21% 6%	1775
	21st to end	Night	41% 6% 10% 23% 18% 2	1800
May	1st to 10th	Night	39% 7% 11% 23% 18% 2	1683
	11th to 20th	Night	40% 6% 13% 23% 15% 2	1593
	21st to end	Night	31% 10% 15% 25% 16% 3	1631
June	1st to 10th	Night	32% 8% 13% 22% 23% 2	1440
	11th to 20th	Night	23% 8% 16% 27% 21% 5%	1440
	21st to end	Night	21% 10% 18% 26% 18% 7%	1440
July	1st to 10th	Night	30% 10% 15% 24% 17% 4	1400
	11th to 20th	Night	26% 7% 18% 25% 17% 6%	1392
	21st to end	Night	26% 8% 15% 33% 17% 1	1543
August	1st to 10th	Night	26% 9% 17% 28% 18% 1	1778
	11th to 20th	Night	26% 8% 16% 26% 20% 3	1776
	21st to end	Night	28% 8% 15% 25% 19% 5%	1980
September	1st to 10th	Night	30% 6% 9% 30% 20% 5%	1800
	11th to 20th	Night	29% 6% 8% 27% 24% 5%	1890
	21st to end	Night	28% 4 10% 26% 24% 7%	1980
October	1st to 10th	Night	27% 5% 8% 23% 30% 7%	2002
	11th to 20th	Night	34% 4 7% 22% 26% 8%	2160
	21st to end	Night	41% 4 6% 22% 20% 6%	2463
November	1st to 10th	Night	30% 3 8% 26% 26% 6%	2406
	11th to 20th	Night	35% 3 7% 24% 23% 9%	2470
	21st to end	Night	39% 4 7% 24% 23% 3	2470
December	1st to 10th	Night	47% 5% 10% 22% 14% 2	2489
	11th to 20th	Night	43% 5% 9% 22% 19% 2	3281
	21st to end	Night	52% 7% 9% 17% 11% 3	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	25% 13% 34% 22% 6% 1	270
	11th to 20th	Day	26% 16% 35% 19% 4	270
	21st to end	Day	19% 15% 40% 21% 5%	297
February	1st to 10th	Day	26% 13% 36% 19% 4 2	270
	11th to 20th	Day	27% 17% 38% 16% 3 1	270
	21st to end	Day	29% 13% 35% 17% 5%	225
March	1st to 10th	Day	20% 12% 42% 19% 6% 1	270
	11th to 20th	Day	22% 17% 35% 21% 4 1	270
	21st to end	Day	24% 15% 32% 21% 7% 1	502
April	1st to 10th	Day	15% 12% 34% 27% 11% 1	428
	11th to 20th	Day	18% 13% 26% 27% 13% 2	412
	21st to end	Day	20% 10% 29% 28% 10% 4	420
May	1st to 10th	Day	17% 14% 26% 29% 12% 4	423
	11th to 20th	Day	19% 6% 20% 27% 19% 8%	447
	21st to end	Day	11% 2 21% 29% 23% 14%	595
June	1st to 10th	Day	10% 4 15% 26% 27% 18%	630
	11th to 20th	Day	6% 1 15% 34% 30% 14%	630
	21st to end	Day	7% 1 16% 34% 27% 15%	630
July	1st to 10th	Day	9% 1 10% 25% 28% 26%	621
	11th to 20th	Day	6% 2 11% 26% 37% 18%	618
	21st to end	Day	6% 1 10% 29% 34% 20%	679
August	1st to 10th	Day	10% 1 8% 27% 32% 21%	446
	11th to 20th	Day	13% 1 10% 25% 32% 18%	439
	21st to end	Day	11% 1 5% 22% 37% 24%	495
September	1st to 10th	Day	9% 3 9% 24% 36% 20%	450
	11th to 20th	Day	10% 1 8% 24% 34% 23%	450
	21st to end	Day	14% 5% 16% 26% 26% 14%	450
October	1st to 10th	Day	11% 2 17% 34% 28% 8%	424
	11th to 20th	Day	14% 9% 31% 28% 13% 5%	270
	21st to end	Day	25% 13% 25% 22% 12% 3	297
November	1st to 10th	Day	14% 6% 29% 30% 15% 6%	270
	11th to 20th	Day	12% 14% 29% 29% 14% 2	270
	21st to end	Day	20% 14% 26% 28% 11% 2	270
December	1st to 10th	Day	17% 14% 33% 22% 11% 3	270
	11th to 20th	Day	24% 13% 27% 24% 12%	270
	21st to end	Day	27% 16% 33% 21% 3	297
January	1st to 10th	Night	23% 11% 32% 28% 6%	950
	11th to 20th	Night	25% 11% 37% 22% 5%	950
	21st to end	Night	21% 8% 39% 29% 2	1045
February	1st to 10th	Night	25% 9% 35% 27% 3	777
	11th to 20th	Night	21% 12% 40% 25% 2	743
	21st to end	Night	22% 14% 37% 24% 2	628
March	1st to 10th	Night	22% 12% 30% 31% 6%	760
	11th to 20th	Night	21% 9% 35% 28% 7%	693
	21st to end	Night	20% 11% 29% 32% 8%	627
April	1st to 10th	Night	14% 8% 35% 35% 8% 1	546
	11th to 20th	Night	16% 10% 27% 33% 13% 1	533
	21st to end	Night	18% 5% 33% 31% 12% 1	540
May	1st to 10th	Night	17% 6% 26% 35% 14% 2	540
	11th to 20th	Night	16% 3 19% 38% 22% 2	531
	21st to end	Night	7% 3 15% 40% 30% 5%	584
June	1st to 10th	Night	11% 3 13% 38% 31% 4	540
	11th to 20th	Night	5% 11% 45% 37% 2	540
	21st to end	Night	4 1 12% 45% 33% 5%	540
July	1st to 10th	Night	7% 2 7% 29% 45% 11%	525
	11th to 20th	Night	7% 2 9% 28% 45% 9%	522
	21st to end	Night	6% 1 10% 32% 42% 8%	591
August	1st to 10th	Night	6% 1 7% 33% 45% 7%	537
	11th to 20th	Night	9% 1 7% 38% 40% 6%	534
	21st to end	Night	8% 1 6% 28% 48% 9%	594
September	1st to 10th	Night	11% 1 9% 31% 42% 6%	540
	11th to 20th	Night	9% 1 10% 32% 41% 8%	630
	21st to end	Night	11% 2 16% 35% 31% 5%	720
October	1st to 10th	Night	9% 3 18% 36% 29% 5%	720
	11th to 20th	Night	17% 4 25% 34% 17% 2	720
	21st to end	Night	22% 8% 25% 32% 12% 1	792
November	1st to 10th	Night	13% 6% 26% 37% 16% 1	740
	11th to 20th	Night	15% 7% 34% 31% 12%	760
	21st to end	Night	19% 9% 29% 30% 12% 1	760
December	1st to 10th	Night	23% 9% 28% 31% 8% 1	779
	11th to 20th	Night	23% 6% 30% 33% 7%	950
	21st to end	Night	27% 9% 31% 28% 4	1045

Page generated at 2024-03-31 05:08:55. Version ac07

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