Ridgeway
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ridgeway clear sky chart from 2005-11-06 to 2024-04-10.

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	15% 5% 2 5% 5% 3 5% 5% 5% 8% 43%	83590
	Night	15% 5% 2 4 4 3 4 4 5% 7% 45%	85201
Transparency	Day	26% 34% 8% 15% 13% 3	83312
	Night	26% 34% 7% 15% 14% 4	84998
Seeing	Day	18% 10% 24% 25% 17% 7%	14529
	Night	17% 7% 25% 31% 18% 2	24726

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	18% 5% 2 3 3 2 3 4 4 6% 51%	2836
	11th to 20th	Day	15% 6% 2 5% 3 2 4 3 3 6% 50%	2840
	21st to end	Day	23% 8% 3 5% 5% 2 3 3 3 4 42%	3124
February	1st to 10th	Day	13% 6% 2 6% 5% 3 4 5% 4 7% 44%	1710
	11th to 20th	Day	19% 6% 2 4 4 2 4 5% 5% 7% 43%	1707
	21st to end	Day	20% 6% 3 5% 5% 3 4 3 5% 6% 40%	1665
March	1st to 10th	Day	24% 6% 3 4 4 2 3 4 5% 7% 38%	3435
	11th to 20th	Day	11% 4 2 4 3 2 3 5% 4 7% 54%	3480
	21st to end	Day	20% 7% 2 5% 4 2 4 4 5% 6% 42%	3815
April	1st to 10th	Day	10% 4 2 4 5% 2 3 4 7% 7% 51%	2151
	11th to 20th	Day	13% 5% 2 5% 5% 2 4 3 6% 8% 48%	2134
	21st to end	Day	15% 5% 3 5% 5% 3 5% 4 4 7% 43%	2245
May	1st to 10th	Day	13% 5% 2 5% 6% 3 6% 6% 7% 8% 39%	2340
	11th to 20th	Day	15% 5% 3 6% 6% 4 6% 4 6% 9% 35%	2301
	21st to end	Day	13% 5% 2 6% 6% 3 5% 6% 7% 9% 38%	2531
June	1st to 10th	Day	10% 4 1 4 6% 3 6% 5% 7% 10% 42%	2340
	11th to 20th	Day	9% 4 3 5% 5% 3 6% 6% 7% 10% 41%	2340
	21st to end	Day	9% 4 2 6% 5% 4 7% 6% 7% 10% 40%	2340
July	1st to 10th	Day	11% 5% 2 6% 6% 4 6% 6% 7% 10% 37%	2340
	11th to 20th	Day	6% 4 3 6% 6% 4 7% 7% 9% 13% 36%	2340
	21st to end	Day	9% 4 3 6% 7% 4 7% 6% 7% 10% 35%	2547
August	1st to 10th	Day	11% 5% 2 6% 7% 4 6% 7% 7% 11% 34%	2327
	11th to 20th	Day	11% 5% 3 6% 7% 4 8% 7% 8% 10% 32%	2303
	21st to end	Day	11% 5% 2 5% 5% 4 6% 7% 7% 10% 38%	2377
September	1st to 10th	Day	13% 4 2 4 4 3 4 4 6% 7% 48%	2134
	11th to 20th	Day	15% 4 2 5% 4 3 5% 5% 6% 8% 42%	1980
	21st to end	Day	23% 6% 3 5% 4 2 4 4 5% 6% 38%	1980
October	1st to 10th	Day	16% 5% 2 4 4 2 4 4 4 5% 52%	1806
	11th to 20th	Day	15% 3 2 4 4 2 3 3 5% 6% 52%	1800
	21st to end	Day	15% 5% 2 5% 3 2 2 4 3 6% 55%	1980
November	1st to 10th	Day	15% 5% 2 3 4 2 3 3 3 6% 55%	1857
	11th to 20th	Day	14% 4 2 5% 3 2 3 4 4 6% 53%	1788
	21st to end	Day	14% 4 1 4 4 3 4 4 5% 7% 50%	1710
December	1st to 10th	Day	18% 7% 2 5% 4 3 5% 5% 5% 7% 39%	1710
	11th to 20th	Day	16% 4 1 3 3 2 3 4 4 6% 55%	2153
	21st to end	Day	20% 5% 2 4 4 2 4 5% 6% 7% 40%	3124
January	1st to 10th	Night	15% 6% 2 4 4 3 4 4 4 5% 49%	4109
	11th to 20th	Night	15% 7% 3 5% 4 2 3 4 5% 5% 47%	4120
	21st to end	Night	24% 6% 2 4 4 2 4 3 4 5% 43%	4532
February	1st to 10th	Night	17% 6% 2 4 5% 3 4 5% 5% 5% 44%	2470
	11th to 20th	Night	20% 6% 2 4 4 2 3 4 5% 5% 45%	2356
	21st to end	Night	16% 7% 2 6% 4 2 4 5% 5% 7% 42%	1788
March	1st to 10th	Night	22% 7% 3 6% 4 3 4 4 5% 6% 36%	3418
	11th to 20th	Night	12% 5% 2 4 4 2 4 4 4 6% 54%	3480
	21st to end	Night	18% 5% 2 4 4 2 3 4 4 6% 47%	3817
April	1st to 10th	Night	14% 6% 3 4 5% 3 4 4 5% 6% 46%	2018
	11th to 20th	Night	13% 5% 2 4 4 3 3 4 4 8% 49%	1775
	21st to end	Night	16% 4 2 4 4 3 4 4 6% 7% 46%	1729
May	1st to 10th	Night	10% 5% 2 6% 5% 4 4 5% 5% 7% 46%	1620
	11th to 20th	Night	15% 7% 3 5% 6% 3 5% 4 7% 6% 38%	1592
	21st to end	Night	14% 6% 3 5% 5% 2 4 4 6% 10% 40%	1744
June	1st to 10th	Night	10% 4 2 4 4 4 5% 5% 8% 12% 41%	1620
	11th to 20th	Night	10% 5% 2 5% 4 3 5% 4 8% 11% 44%	1620
	21st to end	Night	8% 4 1 4 5% 3 5% 6% 7% 12% 42%	1620
July	1st to 10th	Night	7% 5% 2 6% 6% 4 6% 6% 8% 11% 39%	1620
	11th to 20th	Night	5% 3 3 4 6% 4 7% 8% 8% 11% 41%	1620
	21st to end	Night	8% 4 2 5% 5% 4 6% 8% 9% 12% 38%	1771
August	1st to 10th	Night	12% 6% 3 5% 6% 5% 5% 6% 7% 11% 34%	1611
	11th to 20th	Night	11% 7% 2 6% 7% 3 5% 6% 9% 10% 36%	1598
	21st to end	Night	9% 5% 2 5% 6% 4 6% 6% 7% 11% 38%	1959
September	1st to 10th	Night	12% 5% 2 4 5% 2 4 5% 7% 8% 44%	1822
	11th to 20th	Night	14% 6% 3 5% 5% 3 4 5% 5% 7% 42%	1980
	21st to end	Night	22% 7% 3 5% 4 3 4 4 5% 4 39%	1980
October	1st to 10th	Night	16% 6% 2 4 4 3 4 4 4 6% 48%	2152
	11th to 20th	Night	14% 4 2 4 4 3 3 3 4 5% 53%	2160
	21st to end	Night	14% 4 2 3 4 2 4 3 4 5% 55%	2376
November	1st to 10th	Night	15% 5% 2 4 3 2 3 3 3 6% 54%	2221
	11th to 20th	Night	13% 4 2 4 4 2 3 4 5% 6% 53%	2389
	21st to end	Night	15% 3 2 4 4 2 3 4 5% 6% 51%	2470
December	1st to 10th	Night	19% 6% 2 5% 5% 2 4 4 5% 6% 42%	2470
	11th to 20th	Night	16% 6% 2 5% 4 3 3 4 4 5% 48%	3042
	21st to end	Night	21% 5% 2 4 4 3 4 5% 6% 7% 39%	4532

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	24% 26% 6% 25% 15% 4	2837
	11th to 20th	Day	27% 25% 5% 15% 22% 4	2840
	21st to end	Day	40% 23% 4 15% 16% 2	3124
February	1st to 10th	Day	26% 34% 7% 16% 15% 3	1710
	11th to 20th	Day	26% 35% 6% 16% 13% 4	1716
	21st to end	Day	30% 34% 10% 11% 11% 4	1665
March	1st to 10th	Day	37% 24% 6% 16% 10% 6%	3435
	11th to 20th	Day	22% 24% 7% 19% 18% 10%	3480
	21st to end	Day	36% 23% 7% 17% 14% 2	3815
April	1st to 10th	Day	18% 35% 9% 16% 16% 7%	2151
	11th to 20th	Day	22% 36% 8% 14% 15% 6%	2134
	21st to end	Day	28% 37% 7% 14% 11% 3	2245
May	1st to 10th	Day	27% 38% 11% 11% 10% 2	2340
	11th to 20th	Day	31% 40% 9% 12% 6% 2	2305
	21st to end	Day	27% 39% 10% 16% 7%	2531
June	1st to 10th	Day	23% 39% 11% 17% 8% 1	2340
	11th to 20th	Day	25% 39% 11% 14% 9% 2	2340
	21st to end	Day	22% 40% 10% 16% 10% 1	2340
July	1st to 10th	Day	26% 41% 10% 12% 9% 3	2275
	11th to 20th	Day	24% 42% 13% 11% 8% 1	2271
	21st to end	Day	25% 42% 14% 14% 5%	2405
August	1st to 10th	Day	25% 39% 12% 16% 6%	2314
	11th to 20th	Day	29% 40% 10% 14% 7%	2303
	21st to end	Day	28% 39% 11% 13% 6% 2	2377
September	1st to 10th	Day	22% 38% 8% 15% 14% 3	2134
	11th to 20th	Day	25% 37% 8% 16% 12% 2	1980
	21st to end	Day	28% 37% 6% 11% 15% 3	1980
October	1st to 10th	Day	21% 37% 6% 16% 17% 3	1806
	11th to 20th	Day	23% 37% 5% 17% 13% 5%	1800
	21st to end	Day	22% 37% 4 16% 16% 4	1980
November	1st to 10th	Day	16% 40% 6% 14% 19% 5%	1857
	11th to 20th	Day	20% 39% 6% 15% 14% 5%	1788
	21st to end	Day	22% 39% 5% 15% 16% 4	1710
December	1st to 10th	Day	25% 41% 6% 13% 13% 2	1710
	11th to 20th	Day	21% 32% 6% 16% 19% 6%	2150
	21st to end	Day	28% 27% 10% 20% 13% 1	3124
January	1st to 10th	Night	26% 27% 7% 19% 19% 2	4109
	11th to 20th	Night	28% 27% 7% 13% 22% 4	4120
	21st to end	Night	38% 23% 6% 17% 12% 5%	4532
February	1st to 10th	Night	26% 34% 6% 16% 15% 3	2470
	11th to 20th	Night	26% 35% 5% 14% 14% 5%	2358
	21st to end	Night	29% 34% 8% 13% 13% 3	1788
March	1st to 10th	Night	41% 25% 7% 12% 13% 3	3418
	11th to 20th	Night	22% 25% 6% 14% 20% 13%	3480
	21st to end	Night	31% 22% 6% 21% 15% 4	3817
April	1st to 10th	Night	25% 35% 8% 12% 16% 5%	2018
	11th to 20th	Night	21% 35% 7% 14% 16% 7%	1775
	21st to end	Night	25% 37% 7% 16% 12% 3	1729
May	1st to 10th	Night	25% 38% 9% 16% 11% 1	1620
	11th to 20th	Night	31% 39% 8% 13% 8% 2	1593
	21st to end	Night	25% 40% 10% 17% 7% 1	1745
June	1st to 10th	Night	22% 39% 11% 16% 11%	1620
	11th to 20th	Night	25% 40% 11% 13% 10% 1	1620
	21st to end	Night	20% 41% 10% 15% 10% 3	1620
July	1st to 10th	Night	24% 42% 11% 12% 8% 3	1575
	11th to 20th	Night	23% 43% 13% 10% 9% 3	1566
	21st to end	Night	23% 43% 15% 15% 5%	1672
August	1st to 10th	Night	27% 41% 10% 13% 8% 1	1600
	11th to 20th	Night	27% 38% 11% 14% 8% 2	1598
	21st to end	Night	27% 41% 11% 14% 5% 2	1959
September	1st to 10th	Night	23% 39% 8% 15% 11% 5%	1822
	11th to 20th	Night	27% 38% 7% 13% 14% 1	1980
	21st to end	Night	29% 38% 5% 11% 14% 3	1980
October	1st to 10th	Night	24% 37% 5% 15% 17% 2	2152
	11th to 20th	Night	24% 37% 6% 17% 13% 3	2160
	21st to end	Night	22% 37% 5% 15% 17% 5%	2376
November	1st to 10th	Night	17% 41% 6% 12% 19% 6%	2221
	11th to 20th	Night	21% 40% 6% 14% 14% 5%	2389
	21st to end	Night	22% 40% 4 15% 15% 5%	2470
December	1st to 10th	Night	24% 41% 6% 13% 15% 2	2470
	11th to 20th	Night	27% 33% 5% 13% 15% 6%	3044
	21st to end	Night	28% 28% 9% 18% 15% 2	4532

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	24% 23% 34% 14% 4 1	270
	11th to 20th	Day	27% 19% 37% 14% 3	270
	21st to end	Day	26% 19% 37% 15% 2	297
February	1st to 10th	Day	18% 21% 40% 16% 5%	270
	11th to 20th	Day	32% 24% 33% 9% 2	270
	21st to end	Day	27% 20% 33% 18% 3	320
March	1st to 10th	Day	22% 15% 35% 21% 7% 1	460
	11th to 20th	Day	22% 17% 35% 20% 5% 1	460
	21st to end	Day	23% 15% 35% 21% 6%	506
April	1st to 10th	Day	20% 15% 34% 22% 7% 1	457
	11th to 20th	Day	18% 16% 26% 23% 13% 4	412
	21st to end	Day	20% 13% 31% 23% 11% 3	420
May	1st to 10th	Day	19% 14% 32% 23% 8% 4	423
	11th to 20th	Day	17% 5% 25% 25% 19% 9%	447
	21st to end	Day	17% 4 17% 28% 24% 11%	485
June	1st to 10th	Day	12% 5% 21% 31% 21% 10%	450
	11th to 20th	Day	11% 4 19% 28% 22% 14%	450
	21st to end	Day	11% 5% 16% 34% 26% 8%	450
July	1st to 10th	Day	13% 1 12% 27% 35% 13%	445
	11th to 20th	Day	6% 2 12% 29% 35% 16%	444
	21st to end	Day	8% 2 12% 33% 27% 17%	488
August	1st to 10th	Day	13% 3 16% 25% 26% 16%	446
	11th to 20th	Day	10% 3 10% 30% 29% 18%	439
	21st to end	Day	11% 3 11% 29% 27% 19%	495
September	1st to 10th	Day	16% 2 15% 20% 26% 20%	450
	11th to 20th	Day	15% 2 12% 28% 27% 15%	450
	21st to end	Day	28% 6% 18% 25% 19% 4	450
October	1st to 10th	Day	20% 6% 18% 29% 21% 7%	450
	11th to 20th	Day	14% 7% 25% 27% 22% 4	450
	21st to end	Day	17% 9% 26% 33% 12% 3	495
November	1st to 10th	Day	20% 8% 25% 26% 16% 3	455
	11th to 20th	Day	17% 16% 29% 25% 12% 1	348
	21st to end	Day	14% 18% 30% 25% 12% 1	270
December	1st to 10th	Day	23% 14% 40% 17% 5% 1	270
	11th to 20th	Day	19% 14% 37% 23% 6% 1	270
	21st to end	Day	28% 12% 32% 17% 9% 1	297
January	1st to 10th	Night	19% 13% 36% 27% 5% 1	760
	11th to 20th	Night	19% 12% 36% 29% 4	760
	21st to end	Night	21% 10% 39% 28% 2	836
February	1st to 10th	Night	20% 13% 34% 30% 3	760
	11th to 20th	Night	24% 14% 39% 21% 2	743
	21st to end	Night	19% 13% 39% 25% 3	628
March	1st to 10th	Night	18% 14% 34% 29% 5%	760
	11th to 20th	Night	20% 13% 35% 25% 7% 1	760
	21st to end	Night	20% 10% 38% 27% 5%	836
April	1st to 10th	Night	18% 15% 34% 26% 7%	760
	11th to 20th	Night	16% 11% 33% 27% 12% 1	711
	21st to end	Night	18% 6% 33% 33% 10%	649
May	1st to 10th	Night	13% 8% 32% 34% 13% 1	540
	11th to 20th	Night	17% 4 25% 33% 21% 1	531
	21st to end	Night	17% 2 10% 34% 33% 4	584
June	1st to 10th	Night	11% 3 14% 40% 30% 3	540
	11th to 20th	Night	12% 2 14% 31% 37% 4	540
	21st to end	Night	9% 3 14% 37% 34% 3	540
July	1st to 10th	Night	10% 2 8% 32% 42% 6%	525
	11th to 20th	Night	4 2 8% 32% 48% 7%	522
	21st to end	Night	8% 1 10% 39% 37% 5%	591
August	1st to 10th	Night	15% 2 7% 34% 36% 6%	537
	11th to 20th	Night	12% 2 8% 31% 43% 4	534
	21st to end	Night	12% 2 9% 31% 38% 8%	771
September	1st to 10th	Night	14% 2 8% 30% 38% 8%	720
	11th to 20th	Night	15% 3 11% 31% 35% 5%	720
	21st to end	Night	24% 3 16% 32% 23% 2	720
October	1st to 10th	Night	18% 5% 19% 27% 26% 5%	720
	11th to 20th	Night	16% 6% 26% 33% 17% 2	720
	21st to end	Night	16% 7% 26% 35% 15% 1	792
November	1st to 10th	Night	17% 7% 24% 35% 15% 2	740
	11th to 20th	Night	15% 9% 30% 34% 11%	760
	21st to end	Night	17% 6% 32% 33% 11% 1	760
December	1st to 10th	Night	21% 10% 32% 30% 7%	760
	11th to 20th	Night	18% 8% 33% 35% 6%	760
	21st to end	Night	25% 11% 27% 31% 6%	836

Page generated at 2024-04-07 09:28:15. Version ac07

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