River Ridge Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the River Ridge Observatory clear sky chart from 2005-11-06 to 2024-04-25.

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% 6% 2 5% 5% 3 4 5% 5% 7% 45%	83422
	Night	13% 5% 2 4 4 2 4 4 5% 7% 50%	85712
Transparency	Day	38% 6% 10% 22% 19% 5%	83145
	Night	35% 5% 10% 23% 22% 6%	85509
Seeing	Day	14% 10% 22% 26% 20% 6%	14540
	Night	14% 8% 26% 32% 18% 2	24517

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	17% 8% 3 6% 4 2 3 3 3 4 45%	2847
	11th to 20th	Day	12% 9% 3 5% 5% 3 3 4 3 5% 50%	2850
	21st to end	Day	25% 7% 2 4 4 1 3 2 3 3 47%	3135
February	1st to 10th	Day	21% 7% 3 5% 4 2 3 4 5% 4 43%	1710
	11th to 20th	Day	17% 7% 3 5% 5% 3 4 3 5% 5% 43%	1779
	21st to end	Day	21% 8% 3 5% 5% 3 3 4 4 5% 37%	1627
March	1st to 10th	Day	19% 9% 3 6% 5% 3 3 3 4 4 40%	3436
	11th to 20th	Day	13% 6% 3 5% 4 3 4 4 4 6% 46%	3480
	21st to end	Day	16% 8% 3 6% 5% 3 4 3 4 5% 43%	3814
April	1st to 10th	Day	13% 5% 3 4 5% 3 4 5% 5% 7% 46%	2271
	11th to 20th	Day	15% 6% 2 6% 5% 3 4 4 4 6% 46%	2254
	21st to end	Day	15% 5% 3 5% 6% 3 4 5% 5% 6% 42%	2209
May	1st to 10th	Day	15% 6% 3 6% 5% 2 5% 4 5% 8% 41%	2160
	11th to 20th	Day	12% 5% 2 4 6% 3 6% 5% 7% 8% 43%	2288
	21st to end	Day	9% 5% 3 6% 6% 4 7% 7% 7% 9% 37%	2531
June	1st to 10th	Day	8% 5% 3 5% 6% 3 5% 7% 6% 9% 43%	2452
	11th to 20th	Day	4 3 2 5% 5% 4 6% 6% 8% 10% 46%	2517
	21st to end	Day	4 3 2 4 6% 3 6% 6% 7% 9% 50%	2340
July	1st to 10th	Day	6% 4 3 6% 7% 5% 7% 7% 8% 11% 35%	2340
	11th to 20th	Day	5% 3 2 5% 6% 4 7% 6% 8% 9% 45%	2340
	21st to end	Day	7% 4 2 5% 6% 4 6% 6% 8% 10% 41%	2546
August	1st to 10th	Day	7% 4 2 6% 6% 4 6% 7% 8% 11% 39%	2328
	11th to 20th	Day	11% 5% 1 5% 6% 3 4 6% 7% 10% 42%	2148
	21st to end	Day	7% 5% 2 4 6% 4 5% 6% 6% 9% 45%	2376
September	1st to 10th	Day	12% 5% 2 5% 5% 2 5% 5% 5% 7% 47%	2160
	11th to 20th	Day	14% 5% 2 4 4 3 4 6% 5% 7% 48%	2158
	21st to end	Day	10% 4 2 4 3 3 5% 5% 4 6% 54%	1877
October	1st to 10th	Day	7% 4 2 5% 4 2 4 5% 5% 6% 57%	1800
	11th to 20th	Day	14% 5% 2 4 4 2 3 3 4 5% 56%	1800
	21st to end	Day	18% 4 2 4 3 2 3 3 4 5% 52%	1980
November	1st to 10th	Day	12% 5% 2 3 3 2 3 3 4 6% 57%	1858
	11th to 20th	Day	10% 6% 2 4 3 3 2 3 5% 7% 56%	1844
	21st to end	Day	17% 7% 2 4 5% 2 4 3 3 6% 46%	1654
December	1st to 10th	Day	18% 6% 3 4 4 2 3 3 4 6% 47%	1520
	11th to 20th	Day	13% 8% 3 6% 5% 3 5% 4 4 4 44%	1918
	21st to end	Day	12% 7% 3 7% 6% 4 5% 5% 5% 6% 39%	3075
January	1st to 10th	Night	15% 7% 3 6% 5% 3 3 4 4 5% 46%	4108
	11th to 20th	Night	16% 6% 2 4 3 2 3 3 4 4 53%	4120
	21st to end	Night	24% 6% 2 3 2 2 3 2 3 4 48%	4532
February	1st to 10th	Night	19% 7% 3 6% 4 2 3 3 4 6% 43%	2470
	11th to 20th	Night	17% 7% 3 5% 4 2 4 2 4 6% 46%	2286
	21st to end	Night	18% 7% 2 4 3 2 4 4 4 5% 47%	1841
March	1st to 10th	Night	20% 7% 3 5% 4 2 4 4 5% 5% 41%	3419
	11th to 20th	Night	15% 6% 3 5% 4 2 3 3 4 5% 51%	3480
	21st to end	Night	12% 5% 3 6% 5% 3 4 4 5% 8% 44%	3817
April	1st to 10th	Night	12% 5% 2 4 4 3 3 4 4 7% 51%	1907
	11th to 20th	Night	12% 4 2 4 4 3 3 4 5% 7% 51%	1875
	21st to end	Night	13% 5% 2 6% 5% 2 4 4 4 6% 49%	1850
May	1st to 10th	Night	13% 4 2 4 4 2 4 3 5% 9% 49%	1800
	11th to 20th	Night	12% 6% 3 4 4 2 4 4 6% 8% 46%	1603
	21st to end	Night	8% 5% 3 5% 6% 3 5% 4 7% 10% 45%	1745
June	1st to 10th	Night	4 4 2 4 4 3 4 4 6% 10% 55%	1499
	11th to 20th	Night	3 3 2 3 4 3 4 4 5% 9% 60%	1440
	21st to end	Night	3 3 1 3 3 2 3 5% 5% 9% 61%	1609
July	1st to 10th	Night	3 4 2 4 5% 3 5% 6% 7% 12% 48%	1620
	11th to 20th	Night	4 2 1 4 4 3 5% 5% 7% 12% 53%	1620
	21st to end	Night	3 2 1 4 4 3 5% 6% 7% 12% 53%	1772
August	1st to 10th	Night	5% 3 2 5% 5% 4 4 5% 7% 11% 50%	1611
	11th to 20th	Night	6% 4 2 4 3 3 5% 5% 6% 10% 52%	1751
	21st to end	Night	5% 3 1 4 5% 3 5% 6% 6% 10% 51%	1980
September	1st to 10th	Night	7% 4 2 4 3 3 4 4 5% 6% 58%	1800
	11th to 20th	Night	10% 4 2 4 4 2 4 5% 5% 7% 53%	1800
	21st to end	Night	8% 4 1 3 3 3 2 4 6% 7% 60%	2062
October	1st to 10th	Night	8% 3 1 4 4 2 3 4 4 7% 61%	2160
	11th to 20th	Night	10% 4 2 3 4 2 3 3 3 5% 60%	2160
	21st to end	Night	17% 4 1 4 4 3 3 2 2 4 55%	2376
November	1st to 10th	Night	11% 3 2 4 3 2 3 2 5% 5% 59%	2220
	11th to 20th	Night	11% 4 2 3 4 2 4 3 4 7% 57%	2331
	21st to end	Night	14% 5% 3 4 4 2 4 4 4 6% 51%	2522
December	1st to 10th	Night	17% 5% 2 5% 5% 3 3 4 5% 5% 46%	2660
	11th to 20th	Night	15% 5% 3 5% 4 3 4 4 3 4 49%	3279
	21st to end	Night	14% 7% 3 5% 5% 3 4 4 4 6% 45%	4587

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	44% 3 5% 25% 20% 4	2848
	11th to 20th	Day	40% 3 10% 22% 22% 3	2850
	21st to end	Day	45% 3 6% 17% 23% 7%	3135
February	1st to 10th	Day	45% 4 9% 21% 16% 4	1710
	11th to 20th	Day	45% 4 6% 20% 19% 5%	1788
	21st to end	Day	50% 4 7% 15% 16% 8%	1627
March	1st to 10th	Day	49% 4 7% 13% 18% 10%	3436
	11th to 20th	Day	40% 4 9% 23% 19% 4	3480
	21st to end	Day	45% 4 8% 21% 20% 1	3814
April	1st to 10th	Day	37% 6% 9% 22% 21% 5%	2271
	11th to 20th	Day	41% 5% 9% 22% 17% 7%	2254
	21st to end	Day	42% 6% 9% 20% 20% 2	2209
May	1st to 10th	Day	43% 6% 11% 18% 19% 3	2160
	11th to 20th	Day	38% 8% 13% 24% 16% 2	2292
	21st to end	Day	40% 9% 13% 24% 13% 1	2531
June	1st to 10th	Day	35% 8% 14% 24% 16% 2	2452
	11th to 20th	Day	29% 9% 14% 28% 18% 2	2517
	21st to end	Day	29% 8% 10% 27% 21% 4	2340
July	1st to 10th	Day	35% 13% 15% 23% 13% 1	2276
	11th to 20th	Day	33% 9% 12% 27% 17% 3	2271
	21st to end	Day	33% 10% 16% 28% 12% 1	2405
August	1st to 10th	Day	34% 10% 16% 29% 11% 1	2314
	11th to 20th	Day	36% 9% 12% 23% 17% 2	2148
	21st to end	Day	33% 9% 13% 25% 14% 5%	2376
September	1st to 10th	Day	36% 8% 10% 21% 19% 7%	2160
	11th to 20th	Day	36% 6% 11% 17% 24% 5%	2158
	21st to end	Day	31% 5% 7% 21% 26% 8%	1877
October	1st to 10th	Day	27% 6% 9% 23% 27% 8%	1800
	11th to 20th	Day	32% 3 5% 20% 29% 10%	1800
	21st to end	Day	35% 4 5% 23% 23% 9%	1980
November	1st to 10th	Day	30% 4 8% 27% 23% 8%	1858
	11th to 20th	Day	29% 4 9% 21% 28% 9%	1844
	21st to end	Day	43% 3 6% 18% 24% 6%	1654
December	1st to 10th	Day	42% 3 8% 24% 18% 6%	1520
	11th to 20th	Day	44% 3 6% 20% 22% 5%	1915
	21st to end	Day	44% 5% 9% 18% 18% 6%	3075
January	1st to 10th	Night	42% 3 5% 19% 28% 3	4108
	11th to 20th	Night	36% 4 10% 21% 25% 5%	4120
	21st to end	Night	42% 3 9% 18% 23% 4	4532
February	1st to 10th	Night	45% 3 8% 20% 19% 6%	2470
	11th to 20th	Night	43% 3 6% 21% 21% 6%	2287
	21st to end	Night	41% 3 8% 17% 21% 9%	1841
March	1st to 10th	Night	43% 6% 8% 13% 18% 11%	3419
	11th to 20th	Night	37% 4 8% 26% 19% 6%	3480
	21st to end	Night	39% 5% 8% 25% 21% 2	3817
April	1st to 10th	Night	33% 4 11% 22% 20% 10%	1907
	11th to 20th	Night	32% 5% 8% 23% 22% 9%	1875
	21st to end	Night	36% 4 10% 24% 22% 3	1850
May	1st to 10th	Night	35% 6% 11% 23% 19% 6%	1800
	11th to 20th	Night	36% 5% 13% 26% 17% 2	1604
	21st to end	Night	34% 8% 16% 26% 16% 1	1746
June	1st to 10th	Night	24% 7% 14% 31% 21% 2	1499
	11th to 20th	Night	22% 5% 12% 32% 26% 3	1440
	21st to end	Night	20% 7% 13% 29% 24% 7%	1609
July	1st to 10th	Night	26% 10% 20% 27% 17% 2	1575
	11th to 20th	Night	22% 9% 18% 28% 18% 5%	1566
	21st to end	Night	22% 10% 15% 34% 18% 1	1673
August	1st to 10th	Night	25% 8% 20% 33% 14% 1	1601
	11th to 20th	Night	27% 7% 15% 29% 20% 2	1751
	21st to end	Night	27% 8% 17% 27% 18% 4	1980
September	1st to 10th	Night	27% 7% 11% 26% 22% 8%	1800
	11th to 20th	Night	30% 7% 9% 22% 26% 7%	1800
	21st to end	Night	24% 5% 10% 22% 30% 9%	2062
October	1st to 10th	Night	25% 4 11% 24% 24% 11%	2160
	11th to 20th	Night	28% 3 7% 17% 33% 11%	2160
	21st to end	Night	36% 3 6% 19% 26% 10%	2376
November	1st to 10th	Night	29% 3 7% 24% 26% 11%	2220
	11th to 20th	Night	29% 4 5% 24% 28% 10%	2331
	21st to end	Night	36% 4 7% 20% 28% 6%	2522
December	1st to 10th	Night	40% 3 9% 20% 21% 7%	2660
	11th to 20th	Night	40% 3 5% 21% 25% 6%	3281
	21st to end	Night	41% 5% 8% 23% 20% 4	4587

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	27% 15% 33% 19% 5% 1	270
	11th to 20th	Day	26% 21% 36% 16% 2	270
	21st to end	Day	19% 26% 33% 16% 6%	297
February	1st to 10th	Day	27% 19% 33% 17% 4	270
	11th to 20th	Day	27% 26% 29% 14% 4	270
	21st to end	Day	34% 25% 30% 9% 2	225
March	1st to 10th	Day	23% 22% 31% 19% 6%	270
	11th to 20th	Day	26% 26% 34% 14% 1	270
	21st to end	Day	26% 22% 35% 13% 4	297
April	1st to 10th	Day	19% 18% 34% 20% 7% 1	451
	11th to 20th	Day	21% 20% 30% 21% 7%	452
	21st to end	Day	20% 14% 34% 22% 10% 1	437
May	1st to 10th	Day	17% 14% 29% 29% 10% 1	423
	11th to 20th	Day	14% 7% 26% 31% 19% 3	611
	21st to end	Day	8% 6% 24% 34% 22% 6%	679
June	1st to 10th	Day	10% 4 18% 30% 29% 9%	630
	11th to 20th	Day	5% 2 17% 38% 31% 7%	630
	21st to end	Day	4 3 18% 38% 27% 10%	630
July	1st to 10th	Day	5% 3 11% 33% 36% 13%	621
	11th to 20th	Day	4 2 12% 32% 33% 17%	618
	21st to end	Day	6% 2 8% 32% 35% 17%	684
August	1st to 10th	Day	7% 1 11% 34% 37% 10%	626
	11th to 20th	Day	14% 2 7% 30% 35% 11%	462
	21st to end	Day	11% 2 5% 24% 40% 18%	495
September	1st to 10th	Day	11% 2 8% 26% 39% 14%	450
	11th to 20th	Day	10% 1 13% 25% 38% 13%	448
	21st to end	Day	12% 5% 17% 36% 21% 8%	270
October	1st to 10th	Day	8% 4 27% 34% 22% 5%	270
	11th to 20th	Day	14% 12% 33% 26% 12% 2	270
	21st to end	Day	27% 14% 29% 20% 9% 1	297
November	1st to 10th	Day	16% 12% 32% 23% 16% 2	270
	11th to 20th	Day	11% 18% 35% 27% 8% 1	270
	21st to end	Day	24% 18% 26% 23% 9% 1	270
December	1st to 10th	Day	22% 20% 31% 17% 9% 1	270
	11th to 20th	Day	25% 17% 31% 19% 8%	270
	21st to end	Day	19% 23% 37% 17% 4	297
January	1st to 10th	Night	21% 13% 34% 28% 5%	950
	11th to 20th	Night	20% 15% 35% 25% 4	950
	21st to end	Night	20% 12% 38% 26% 4	1045
February	1st to 10th	Night	22% 14% 34% 26% 4	950
	11th to 20th	Night	21% 13% 41% 24% 1	811
	21st to end	Night	23% 16% 38% 20% 2	585
March	1st to 10th	Night	19% 10% 36% 31% 4	570
	11th to 20th	Night	20% 13% 34% 28% 5%	570
	21st to end	Night	15% 12% 38% 28% 7%	627
April	1st to 10th	Night	16% 12% 36% 30% 6%	570
	11th to 20th	Night	15% 11% 38% 27% 9% 1	563
	21st to end	Night	13% 10% 38% 29% 9%	555
May	1st to 10th	Night	15% 5% 27% 43% 9%	540
	11th to 20th	Night	15% 6% 27% 31% 18% 2	531
	21st to end	Night	9% 3 20% 39% 25% 4	584
June	1st to 10th	Night	5% 1 14% 38% 37% 5%	540
	11th to 20th	Night	3 1 10% 48% 35% 3	540
	21st to end	Night	4 1 11% 40% 38% 6%	540
July	1st to 10th	Night	3 1 7% 40% 42% 6%	525
	11th to 20th	Night	4 1 9% 34% 46% 7%	522
	21st to end	Night	4 8% 36% 43% 9%	591
August	1st to 10th	Night	4 1 5% 39% 44% 6%	537
	11th to 20th	Night	8% 1 8% 36% 40% 7%	534
	21st to end	Night	6% 1 8% 31% 48% 6%	594
September	1st to 10th	Night	8% 1 7% 37% 42% 4	540
	11th to 20th	Night	11% 1 10% 34% 39% 3	540
	21st to end	Night	9% 2 15% 33% 37% 4	624
October	1st to 10th	Night	10% 3 18% 35% 32% 3	720
	11th to 20th	Night	12% 6% 28% 37% 17% 1	720
	21st to end	Night	18% 8% 27% 31% 14% 1	792
November	1st to 10th	Night	12% 6% 26% 41% 15% 1	740
	11th to 20th	Night	13% 11% 30% 36% 11%	760
	21st to end	Night	15% 13% 30% 30% 11%	812
December	1st to 10th	Night	21% 9% 34% 31% 6%	950
	11th to 20th	Night	23% 11% 27% 33% 6%	950
	21st to end	Night	20% 15% 31% 29% 4	1045

Page generated at 2024-04-22 08:25:42. Version ac07

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