River Moss Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the River Moss Observatory clear sky chart from 2005-11-06 to 2024-02-15.

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 4 5% 5% 7% 42%	78387
	Night	14% 8% 3 6% 5% 3 4 4 5% 7% 42%	80740
Transparency	Day	41% 6% 12% 24% 15% 2	78096
	Night	42% 5% 10% 24% 16% 3	80552
Seeing	Day	14% 7% 23% 28% 21% 7%	14571
	Night	16% 7% 27% 33% 15% 2	24587

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% 6% 9% 7% 4 4 5% 6% 7% 30%	2527
	11th to 20th	Day	13% 8% 3 6% 6% 7% 6% 5% 5% 7% 33%	2733
	21st to end	Day	21% 16% 6% 7% 6% 2 4 3 3 5% 28%	3135
February	1st to 10th	Day	15% 10% 5% 8% 5% 3 5% 5% 4 7% 34%	1710
	11th to 20th	Day	15% 8% 4 6% 7% 3 5% 5% 6% 7% 36%	1754
	21st to end	Day	16% 11% 4 6% 5% 4 4 3 4 6% 37%	1480
March	1st to 10th	Day	15% 8% 3 7% 5% 3 4 4 4 5% 41%	1835
	11th to 20th	Day	19% 9% 3 6% 5% 3 4 5% 5% 5% 34%	1980
	21st to end	Day	20% 9% 4 8% 6% 3 5% 5% 5% 6% 29%	2286
April	1st to 10th	Day	12% 5% 3 6% 7% 3 4 6% 5% 8% 43%	2160
	11th to 20th	Day	17% 6% 3 7% 5% 3 4 4 4 5% 41%	2134
	21st to end	Day	17% 7% 3 7% 6% 3 4 5% 5% 6% 38%	2160
May	1st to 10th	Day	16% 6% 3 6% 6% 3 5% 5% 6% 8% 37%	2204
	11th to 20th	Day	16% 5% 2 5% 5% 3 5% 4 6% 8% 41%	2468
	21st to end	Day	10% 5% 3 6% 5% 4 7% 6% 7% 9% 38%	2725
June	1st to 10th	Day	7% 6% 1 5% 5% 3 5% 5% 6% 9% 48%	2520
	11th to 20th	Day	7% 4 2 4 4 3 6% 5% 6% 9% 50%	2520
	21st to end	Day	5% 3 2 4 5% 3 6% 7% 8% 12% 46%	2520
July	1st to 10th	Day	9% 4 2 4 4 3 6% 6% 7% 10% 44%	2520
	11th to 20th	Day	5% 3 1 4 5% 3 5% 5% 7% 9% 53%	2520
	21st to end	Day	8% 4 2 5% 5% 3 4 6% 5% 10% 48%	2605
August	1st to 10th	Day	7% 4 2 5% 6% 4 5% 6% 7% 10% 43%	2328
	11th to 20th	Day	8% 5% 2 6% 6% 4 6% 5% 6% 9% 42%	2130
	21st to end	Day	8% 4 2 4 4 3 5% 5% 6% 8% 51%	2376
September	1st to 10th	Day	13% 4 2 4 4 3 3 3 5% 8% 50%	2160
	11th to 20th	Day	9% 5% 2 3 4 3 4 5% 6% 8% 51%	2143
	21st to end	Day	6% 5% 2 5% 4 3 4 4 5% 7% 55%	1962
October	1st to 10th	Day	10% 4 3 5% 4 3 2 4 4 7% 54%	1800
	11th to 20th	Day	16% 6% 2 4 3 2 3 3 4 6% 51%	1800
	21st to end	Day	18% 7% 3 4 4 2 3 3 3 6% 46%	1968
November	1st to 10th	Day	11% 4 2 4 4 3 3 3 4 6% 55%	1672
	11th to 20th	Day	15% 7% 3 4 4 3 2 5% 5% 6% 47%	1710
	21st to end	Day	16% 9% 4 6% 5% 2 4 4 4 6% 41%	1621
December	1st to 10th	Day	13% 11% 3 6% 4 3 4 3 4 7% 40%	1520
	11th to 20th	Day	14% 9% 4 5% 6% 3 4 5% 4 7% 40%	1918
	21st to end	Day	21% 13% 4 8% 7% 4 4 4 5% 6% 25%	2783
January	1st to 10th	Night	14% 11% 6% 8% 5% 3 4 4 4 5% 35%	4428
	11th to 20th	Night	13% 12% 5% 9% 6% 4 7% 5% 4 5% 31%	4234
	21st to end	Night	24% 15% 4 7% 5% 2 3 4 4 7% 25%	4532
February	1st to 10th	Night	15% 11% 6% 7% 6% 3 4 4 4 5% 35%	2470
	11th to 20th	Night	16% 8% 4 7% 5% 2 4 4 4 6% 41%	2185
	21st to end	Night	16% 9% 4 7% 6% 2 4 3 4 5% 40%	1776
March	1st to 10th	Night	16% 10% 4 5% 4 3 4 3 4 5% 42%	2142
	11th to 20th	Night	19% 7% 3 6% 5% 3 4 4 5% 6% 37%	1980
	21st to end	Night	19% 11% 4 6% 6% 3 5% 4 5% 7% 32%	2070
April	1st to 10th	Night	11% 6% 3 6% 5% 2 4 4 4 7% 47%	1800
	11th to 20th	Night	13% 6% 3 5% 6% 3 3 4 6% 8% 44%	1775
	21st to end	Night	18% 6% 4 6% 5% 2 3 4 5% 6% 41%	1800
May	1st to 10th	Night	15% 6% 2 4 4 3 4 5% 6% 8% 44%	1755
	11th to 20th	Night	15% 7% 2 5% 4 2 4 4 5% 7% 44%	1424
	21st to end	Night	9% 5% 3 6% 5% 3 5% 6% 7% 9% 43%	1551
June	1st to 10th	Night	7% 4 2 4 5% 3 3 6% 7% 7% 51%	1440
	11th to 20th	Night	6% 3 2 4 4 2 4 5% 5% 10% 54%	1440
	21st to end	Night	4 3 1 4 5% 3 5% 5% 6% 11% 53%	1440
July	1st to 10th	Night	9% 4 2 4 4 3 4 6% 6% 10% 49%	1440
	11th to 20th	Night	4 3 2 4 5% 2 5% 4 6% 11% 56%	1440
	21st to end	Night	7% 4 2 6% 5% 2 5% 6% 5% 9% 50%	1709
August	1st to 10th	Night	7% 3 2 4 4 2 5% 5% 7% 8% 52%	1611
	11th to 20th	Night	7% 4 3 5% 4 2 5% 5% 6% 7% 51%	1768
	21st to end	Night	5% 4 2 3 4 3 5% 4 6% 8% 57%	1980
September	1st to 10th	Night	11% 5% 2 5% 5% 2 3 4 5% 7% 52%	1800
	11th to 20th	Night	8% 4 2 5% 5% 2 5% 4 6% 7% 52%	1800
	21st to end	Night	8% 4 1 4 5% 2 4 4 6% 7% 56%	1990
October	1st to 10th	Night	9% 4 2 4 4 2 4 4 3 6% 58%	2160
	11th to 20th	Night	14% 5% 2 4 3 2 2 4 5% 6% 52%	2160
	21st to end	Night	19% 6% 2 4 4 2 4 3 4 5% 46%	2386
November	1st to 10th	Night	10% 5% 2 3 5% 2 4 3 4 6% 56%	2406
	11th to 20th	Night	14% 6% 2 5% 4 2 4 4 4 7% 49%	2470
	21st to end	Night	18% 8% 3 5% 3 2 3 4 4 5% 45%	2555
December	1st to 10th	Night	15% 10% 4 6% 6% 3 4 4 5% 7% 36%	2660
	11th to 20th	Night	16% 8% 4 6% 4 3 4 3 4 6% 41%	3279
	21st to end	Night	20% 18% 5% 8% 7% 3 4 4 4 4 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	51% 6% 11% 23% 8% 1	2528
	11th to 20th	Day	48% 7% 14% 19% 12%	2733
	21st to end	Day	59% 4 11% 15% 10% 1	3135
February	1st to 10th	Day	51% 5% 11% 21% 11% 1	1710
	11th to 20th	Day	47% 4 13% 21% 13% 2	1764
	21st to end	Day	50% 3 9% 23% 12% 3	1480
March	1st to 10th	Day	46% 4 9% 24% 14% 2	1835
	11th to 20th	Day	51% 5% 11% 18% 13% 2	1980
	21st to end	Day	56% 5% 12% 17% 9% 1	2286
April	1st to 10th	Day	40% 5% 12% 26% 17% 1	2160
	11th to 20th	Day	45% 4 10% 24% 14% 3	2134
	21st to end	Day	46% 6% 11% 24% 13% 1	2160
May	1st to 10th	Day	45% 7% 14% 23% 10% 1	2204
	11th to 20th	Day	41% 7% 12% 24% 15% 1	2472
	21st to end	Day	40% 10% 14% 21% 13% 2	2725
June	1st to 10th	Day	32% 7% 14% 28% 17% 2	2520
	11th to 20th	Day	30% 7% 13% 25% 23% 3	2520
	21st to end	Day	28% 9% 18% 25% 16% 5%	2520
July	1st to 10th	Day	33% 7% 15% 28% 13% 4	2451
	11th to 20th	Day	25% 7% 16% 28% 20% 3	2445
	21st to end	Day	32% 7% 14% 30% 16% 2	2460
August	1st to 10th	Day	34% 9% 14% 27% 15% 1	2314
	11th to 20th	Day	36% 8% 14% 27% 14% 1	2130
	21st to end	Day	29% 6% 15% 24% 20% 6%	2376
September	1st to 10th	Day	33% 4 11% 27% 19% 5%	2160
	11th to 20th	Day	31% 4 9% 28% 25% 3	2143
	21st to end	Day	29% 5% 9% 28% 25% 3	1962
October	1st to 10th	Day	31% 4 9% 26% 25% 4	1800
	11th to 20th	Day	36% 3 9% 25% 23% 5%	1800
	21st to end	Day	42% 3 9% 26% 16% 4	1968
November	1st to 10th	Day	31% 4 12% 27% 21% 5%	1672
	11th to 20th	Day	37% 4 9% 26% 20% 4	1710
	21st to end	Day	47% 4 10% 26% 14%	1621
December	1st to 10th	Day	46% 4 12% 26% 12%	1520
	11th to 20th	Day	45% 4 12% 25% 12% 2	1915
	21st to end	Day	60% 6% 11% 14% 9% 1	2783
January	1st to 10th	Night	51% 5% 10% 24% 9% 1	4428
	11th to 20th	Night	57% 5% 8% 20% 9% 1	4234
	21st to end	Night	61% 4 8% 19% 7% 1	4532
February	1st to 10th	Night	52% 4 9% 21% 12% 1	2470
	11th to 20th	Night	46% 4 10% 22% 17% 2	2186
	21st to end	Night	48% 4 11% 22% 12% 3	1776
March	1st to 10th	Night	46% 3 9% 23% 16% 3	2142
	11th to 20th	Night	49% 5% 9% 22% 13% 3	1980
	21st to end	Night	54% 5% 12% 20% 9% 1	2070
April	1st to 10th	Night	38% 4 10% 26% 18% 3	1800
	11th to 20th	Night	39% 4 10% 24% 18% 4	1775
	21st to end	Night	44% 5% 8% 24% 17% 2	1800
May	1st to 10th	Night	39% 7% 14% 23% 16% 1	1755
	11th to 20th	Night	40% 6% 12% 25% 15% 2	1425
	21st to end	Night	36% 8% 15% 20% 16% 4	1552
June	1st to 10th	Night	29% 7% 15% 27% 19% 3	1440
	11th to 20th	Night	25% 7% 12% 27% 25% 4	1440
	21st to end	Night	25% 6% 16% 27% 19% 7%	1440
July	1st to 10th	Night	30% 7% 14% 30% 15% 4	1400
	11th to 20th	Night	23% 5% 15% 31% 21% 4	1392
	21st to end	Night	29% 7% 12% 31% 19% 2	1614
August	1st to 10th	Night	26% 9% 14% 33% 16% 2	1601
	11th to 20th	Night	30% 7% 12% 29% 21% 2	1768
	21st to end	Night	24% 6% 16% 25% 24% 5%	1980
September	1st to 10th	Night	33% 5% 9% 25% 22% 7%	1800
	11th to 20th	Night	31% 5% 8% 26% 25% 5%	1800
	21st to end	Night	28% 5% 10% 25% 28% 4	1990
October	1st to 10th	Night	28% 6% 10% 24% 27% 5%	2160
	11th to 20th	Night	32% 4 7% 28% 21% 6%	2160
	21st to end	Night	40% 4 8% 22% 21% 4	2386
November	1st to 10th	Night	31% 4 11% 26% 22% 6%	2406
	11th to 20th	Night	36% 3 8% 27% 21% 4	2470
	21st to end	Night	42% 4 11% 24% 17% 1	2555
December	1st to 10th	Night	49% 4 10% 24% 11% 1	2660
	11th to 20th	Night	45% 3 10% 25% 15% 1	3281
	21st to end	Night	65% 5% 8% 13% 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	19% 13% 35% 21% 10% 1	270
	11th to 20th	Day	26% 13% 34% 21% 5%	270
	21st to end	Day	17% 14% 39% 23% 5% 1	297
February	1st to 10th	Day	22% 11% 39% 24% 3	270
	11th to 20th	Day	23% 10% 36% 21% 9% 1	252
	21st to end	Day	27% 9% 36% 24% 4	198
March	1st to 10th	Day	18% 9% 48% 21% 4	240
	11th to 20th	Day	28% 12% 31% 21% 8% 1	240
	21st to end	Day	30% 10% 32% 21% 6% 1	372
April	1st to 10th	Day	15% 10% 36% 25% 13% 1	420
	11th to 20th	Day	21% 10% 28% 25% 15%	412
	21st to end	Day	21% 10% 32% 27% 9% 1	420
May	1st to 10th	Day	17% 10% 26% 32% 11% 3	423
	11th to 20th	Day	18% 7% 23% 31% 17% 5%	614
	21st to end	Day	12% 5% 23% 33% 17% 9%	679
June	1st to 10th	Day	9% 5% 15% 29% 30% 12%	630
	11th to 20th	Day	8% 2 18% 32% 31% 9%	630
	21st to end	Day	4 4 22% 34% 28% 8%	630
July	1st to 10th	Day	10% 2 8% 25% 36% 19%	621
	11th to 20th	Day	6% 2 12% 36% 32% 12%	618
	21st to end	Day	9% 2 11% 30% 37% 11%	684
August	1st to 10th	Day	8% 2 9% 35% 33% 13%	626
	11th to 20th	Day	12% 1 10% 24% 38% 14%	444
	21st to end	Day	8% 2 8% 27% 37% 17%	495
September	1st to 10th	Day	13% 2 12% 29% 29% 15%	450
	11th to 20th	Day	9% 2 11% 26% 34% 18%	450
	21st to end	Day	8% 5% 19% 28% 28% 13%	432
October	1st to 10th	Day	11% 6% 22% 33% 21% 6%	270
	11th to 20th	Day	14% 13% 33% 26% 11% 3	270
	21st to end	Day	28% 12% 26% 24% 9%	297
November	1st to 10th	Day	13% 6% 30% 28% 18% 5%	270
	11th to 20th	Day	16% 16% 31% 20% 14% 3	270
	21st to end	Day	22% 9% 29% 28% 11% 1	270
December	1st to 10th	Day	13% 10% 40% 25% 8% 4	270
	11th to 20th	Day	19% 11% 33% 28% 9% 1	270
	21st to end	Day	24% 15% 37% 17% 5% 1	297
January	1st to 10th	Night	18% 12% 37% 27% 6%	950
	11th to 20th	Night	22% 13% 35% 25% 4	950
	21st to end	Night	20% 11% 37% 30% 2	1045
February	1st to 10th	Night	22% 10% 36% 29% 3	950
	11th to 20th	Night	20% 12% 38% 27% 3	754
	21st to end	Night	21% 12% 39% 25% 2	592
March	1st to 10th	Night	21% 10% 38% 27% 5%	702
	11th to 20th	Night	23% 9% 30% 30% 7%	540
	21st to end	Night	25% 9% 31% 29% 5%	594
April	1st to 10th	Night	15% 12% 36% 30% 7%	540
	11th to 20th	Night	16% 9% 32% 34% 10%	533
	21st to end	Night	22% 5% 35% 31% 6%	540
May	1st to 10th	Night	17% 4 30% 40% 10%	540
	11th to 20th	Night	19% 2 24% 36% 18% 1	531
	21st to end	Night	11% 3 20% 41% 22% 3	584
June	1st to 10th	Night	9% 2 16% 41% 31% 1	540
	11th to 20th	Night	8% 1 15% 49% 25% 1	540
	21st to end	Night	5% 1 19% 49% 24% 2	540
July	1st to 10th	Night	10% 2 6% 36% 38% 8%	525
	11th to 20th	Night	5% 1 10% 43% 37% 4	522
	21st to end	Night	6% 2 9% 42% 39% 3	591
August	1st to 10th	Night	8% 2 6% 40% 41% 3	537
	11th to 20th	Night	8% 2 7% 40% 37% 5%	534
	21st to end	Night	7% 8% 38% 41% 5%	594
September	1st to 10th	Night	13% 1 11% 37% 32% 6%	540
	11th to 20th	Night	9% 2 12% 34% 38% 6%	540
	21st to end	Night	10% 4 19% 36% 27% 5%	717
October	1st to 10th	Night	11% 3 23% 33% 26% 4	720
	11th to 20th	Night	17% 7% 29% 34% 12% 1	720
	21st to end	Night	23% 8% 30% 32% 6% 1	792
November	1st to 10th	Night	13% 6% 32% 36% 12% 1	740
	11th to 20th	Night	16% 11% 33% 32% 8%	760
	21st to end	Night	22% 9% 31% 31% 7%	845
December	1st to 10th	Night	20% 9% 35% 30% 5% 1	950
	11th to 20th	Night	24% 7% 28% 35% 6%	950
	21st to end	Night	27% 10% 33% 27% 3	1045

Page generated at 2024-02-12 05:35:35. Version ac07

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