Raven Run Nature Conservancy
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Raven Run Nature Conservancy clear sky chart from 2005-11-06 to 2024-01-12.

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% 8% 3 6% 5% 3 5% 5% 5% 7% 38%	75042
	Night	15% 7% 3 6% 5% 3 4 4 5% 7% 40%	74661
Transparency	Day	44% 7% 11% 21% 14% 2	74765
	Night	43% 7% 11% 21% 15% 3	74457
Seeing	Day	18% 9% 23% 24% 17% 9%	13783
	Night	18% 8% 24% 30% 18% 2	23726

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	19% 10% 5% 8% 6% 2 4 4 4 6% 31%	1706
	11th to 20th	Day	21% 12% 6% 10% 7% 3 4 4 4 6% 25%	1635
	21st to end	Day	17% 11% 6% 7% 5% 4 5% 4 4 5% 32%	1782
February	1st to 10th	Day	20% 11% 6% 9% 6% 2 4 4 4 5% 28%	1750
	11th to 20th	Day	20% 10% 4 7% 6% 3 4 4 5% 5% 31%	1748
	21st to end	Day	21% 12% 4 6% 6% 3 4 5% 5% 5% 30%	1480
March	1st to 10th	Day	19% 10% 2 6% 4 3 5% 4 4 6% 37%	1821
	11th to 20th	Day	21% 10% 3 6% 6% 3 5% 5% 5% 6% 32%	1980
	21st to end	Day	20% 9% 4 6% 6% 3 5% 4 5% 6% 32%	2178
April	1st to 10th	Day	13% 7% 4 6% 6% 3 4 4 5% 7% 41%	2101
	11th to 20th	Day	16% 8% 3 5% 5% 3 4 4 5% 6% 41%	2163
	21st to end	Day	16% 7% 3 6% 6% 4 5% 4 6% 7% 36%	2340
May	1st to 10th	Day	18% 6% 3 6% 6% 3 5% 5% 5% 7% 36%	2340
	11th to 20th	Day	17% 7% 3 7% 5% 3 5% 4 5% 6% 37%	2301
	21st to end	Day	8% 6% 2 6% 7% 4 6% 6% 7% 10% 38%	2531
June	1st to 10th	Day	11% 4 3 5% 7% 4 5% 5% 6% 7% 42%	2340
	11th to 20th	Day	7% 5% 2 4 6% 4 6% 6% 7% 8% 43%	2340
	21st to end	Day	9% 5% 2 5% 5% 3 6% 6% 7% 10% 41%	2457
July	1st to 10th	Day	12% 6% 3 6% 6% 4 5% 6% 7% 9% 37%	2399
	11th to 20th	Day	10% 5% 2 6% 5% 4 6% 7% 7% 10% 38%	2340
	21st to end	Day	12% 5% 2 5% 6% 4 6% 6% 6% 9% 38%	2547
August	1st to 10th	Day	11% 5% 2 5% 6% 4 5% 5% 7% 9% 42%	2327
	11th to 20th	Day	10% 6% 2 7% 6% 5% 6% 6% 7% 11% 35%	2285
	21st to end	Day	9% 5% 2 5% 5% 4 6% 6% 7% 10% 42%	2376
September	1st to 10th	Day	14% 6% 2 4 5% 4 5% 6% 6% 8% 40%	2034
	11th to 20th	Day	11% 5% 2 5% 4 3 4 5% 6% 9% 46%	1980
	21st to end	Day	14% 6% 2 5% 4 3 3 3 4 6% 49%	1980
October	1st to 10th	Day	11% 4 2 5% 5% 3 4 3 5% 7% 53%	1980
	11th to 20th	Day	14% 6% 2 6% 4 2 4 4 4 6% 49%	1841
	21st to end	Day	19% 8% 2 5% 4 2 4 4 4 6% 43%	1881
November	1st to 10th	Day	12% 5% 3 4 4 2 4 3 4 6% 54%	1672
	11th to 20th	Day	16% 9% 3 5% 4 3 3 4 4 6% 44%	1710
	21st to end	Day	17% 9% 4 6% 5% 2 3 4 4 6% 40%	1710
December	1st to 10th	Day	21% 13% 5% 6% 4 3 5% 4 4 5% 31%	1710
	11th to 20th	Day	15% 13% 4 7% 6% 3 4 4 4 5% 33%	2153
	21st to end	Day	19% 16% 4 7% 7% 4 5% 5% 5% 6% 22%	3124
January	1st to 10th	Night	17% 11% 5% 9% 7% 3 5% 4 4 5% 30%	2459
	11th to 20th	Night	22% 11% 6% 8% 7% 3 4 4 4 4 26%	2365
	21st to end	Night	17% 10% 5% 7% 6% 3 4 4 4 5% 34%	2574
February	1st to 10th	Night	22% 10% 5% 9% 5% 2 4 3 4 6% 28%	2205
	11th to 20th	Night	21% 10% 3 8% 5% 3 3 4 4 7% 32%	2098
	21st to end	Night	24% 11% 4 8% 6% 3 5% 3 5% 5% 29%	1776
March	1st to 10th	Night	17% 10% 4 5% 6% 2 4 4 4 5% 40%	2138
	11th to 20th	Night	19% 8% 3 6% 5% 3 4 4 5% 5% 37%	1980
	21st to end	Night	16% 10% 4 6% 6% 4 4 4 5% 6% 35%	2178
April	1st to 10th	Night	11% 6% 3 5% 5% 3 5% 6% 6% 7% 44%	1872
	11th to 20th	Night	14% 7% 3 6% 5% 3 4 3 5% 6% 43%	1745
	21st to end	Night	17% 6% 2 5% 6% 3 5% 5% 5% 7% 39%	1620
May	1st to 10th	Night	15% 8% 3 7% 6% 3 5% 6% 5% 7% 35%	1620
	11th to 20th	Night	16% 5% 2 6% 6% 3 5% 6% 6% 8% 36%	1592
	21st to end	Night	6% 5% 2 5% 7% 4 6% 6% 8% 11% 40%	1744
June	1st to 10th	Night	8% 5% 2 4 4 2 4 5% 7% 11% 46%	1620
	11th to 20th	Night	5% 4 3 5% 4 3 5% 6% 8% 11% 47%	1620
	21st to end	Night	7% 3 2 4 5% 4 6% 5% 8% 13% 43%	1485
July	1st to 10th	Night	8% 5% 3 6% 6% 4 4 6% 5% 9% 43%	1548
	11th to 20th	Night	6% 3 2 5% 4 3 6% 6% 7% 10% 49%	1620
	21st to end	Night	9% 4 2 5% 4 4 6% 6% 6% 10% 44%	1771
August	1st to 10th	Night	8% 4 2 5% 5% 3 4 4 6% 9% 49%	1611
	11th to 20th	Night	6% 5% 2 5% 5% 5% 5% 5% 7% 8% 46%	1611
	21st to end	Night	7% 4 2 5% 5% 3 4 4 6% 10% 51%	1980
September	1st to 10th	Night	12% 4 2 4 5% 3 4 6% 5% 7% 48%	1908
	11th to 20th	Night	11% 4 2 5% 4 3 3 5% 5% 8% 50%	1980
	21st to end	Night	10% 5% 2 5% 5% 2 4 4 4 6% 52%	1980
October	1st to 10th	Night	11% 4 1 4 3 2 4 4 4 8% 55%	1980
	11th to 20th	Night	15% 6% 2 4 5% 3 3 4 4 8% 47%	2118
	21st to end	Night	18% 8% 2 4 5% 2 4 4 4 6% 44%	2473
November	1st to 10th	Night	12% 6% 3 5% 4 2 3 3 4 6% 52%	2406
	11th to 20th	Night	16% 7% 4 5% 3 3 4 3 4 7% 45%	2470
	21st to end	Night	17% 8% 4 5% 5% 3 3 4 4 7% 41%	2470
December	1st to 10th	Night	22% 11% 4 6% 4 3 4 5% 4 6% 33%	2470
	11th to 20th	Night	18% 10% 4 7% 5% 3 4 3 4 5% 36%	3042
	21st to end	Night	18% 14% 4 8% 8% 5% 6% 5% 5% 6% 21%	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	55% 6% 9% 19% 11% 1	1707
	11th to 20th	Day	61% 5% 9% 16% 8% 1	1635
	21st to end	Day	54% 4 10% 22% 8% 2	1782
February	1st to 10th	Day	58% 5% 8% 19% 8% 2	1750
	11th to 20th	Day	55% 5% 8% 19% 10% 2	1758
	21st to end	Day	55% 6% 8% 18% 10% 3	1480
March	1st to 10th	Day	49% 4 10% 21% 14% 2	1821
	11th to 20th	Day	52% 6% 11% 18% 12% 2	1980
	21st to end	Day	52% 6% 11% 21% 9% 1	2178
April	1st to 10th	Day	43% 6% 11% 24% 13% 3	2101
	11th to 20th	Day	44% 5% 10% 21% 16% 4	2163
	21st to end	Day	46% 7% 10% 23% 11% 2	2340
May	1st to 10th	Day	47% 7% 12% 24% 9% 1	2340
	11th to 20th	Day	48% 7% 12% 20% 12% 1	2305
	21st to end	Day	39% 10% 16% 22% 12% 1	2531
June	1st to 10th	Day	40% 8% 10% 26% 15% 1	2340
	11th to 20th	Day	34% 11% 14% 22% 17% 2	2340
	21st to end	Day	35% 10% 15% 19% 16% 4	2457
July	1st to 10th	Day	41% 10% 14% 18% 14% 2	2334
	11th to 20th	Day	38% 12% 14% 20% 13% 3	2271
	21st to end	Day	39% 9% 14% 24% 11% 3	2405
August	1st to 10th	Day	36% 10% 15% 25% 13% 1	2314
	11th to 20th	Day	41% 9% 14% 22% 13% 1	2285
	21st to end	Day	35% 9% 14% 23% 15% 4	2376
September	1st to 10th	Day	40% 8% 14% 17% 16% 5%	2034
	11th to 20th	Day	34% 7% 13% 22% 21% 3	1980
	21st to end	Day	36% 5% 8% 25% 22% 3	1980
October	1st to 10th	Day	32% 6% 9% 23% 26% 3	1980
	11th to 20th	Day	37% 5% 9% 23% 22% 4	1841
	21st to end	Day	43% 5% 9% 25% 16% 3	1881
November	1st to 10th	Day	33% 4 8% 27% 23% 4	1672
	11th to 20th	Day	43% 3 8% 23% 19% 4	1710
	21st to end	Day	46% 5% 9% 21% 18% 2	1710
December	1st to 10th	Day	57% 5% 9% 19% 9% 1	1710
	11th to 20th	Day	52% 6% 9% 17% 14% 1	2150
	21st to end	Day	59% 8% 10% 17% 5% 1	3124
January	1st to 10th	Night	56% 5% 8% 17% 12% 2	2459
	11th to 20th	Night	61% 5% 8% 15% 9% 1	2365
	21st to end	Night	52% 5% 10% 22% 10% 2	2574
February	1st to 10th	Night	57% 5% 11% 18% 8% 1	2205
	11th to 20th	Night	54% 5% 8% 20% 12% 2	2099
	21st to end	Night	59% 5% 10% 13% 11% 3	1776
March	1st to 10th	Night	48% 4 7% 20% 19% 3	2138
	11th to 20th	Night	49% 6% 10% 21% 12% 2	1980
	21st to end	Night	49% 6% 11% 21% 10% 2	2178
April	1st to 10th	Night	37% 8% 12% 23% 19% 2	1872
	11th to 20th	Night	42% 6% 8% 20% 18% 7%	1745
	21st to end	Night	44% 7% 12% 21% 14% 2	1620
May	1st to 10th	Night	47% 9% 9% 22% 10% 3	1620
	11th to 20th	Night	44% 9% 12% 20% 13% 2	1593
	21st to end	Night	34% 11% 15% 22% 14% 2	1745
June	1st to 10th	Night	29% 8% 17% 26% 16% 4	1620
	11th to 20th	Night	27% 11% 17% 23% 19% 3	1620
	21st to end	Night	31% 10% 17% 22% 14% 6%	1485
July	1st to 10th	Night	36% 11% 13% 21% 16% 3	1503
	11th to 20th	Night	28% 11% 16% 23% 18% 4	1566
	21st to end	Night	32% 10% 14% 27% 15% 2	1672
August	1st to 10th	Night	30% 10% 16% 25% 17% 2	1600
	11th to 20th	Night	33% 9% 16% 25% 15% 2	1611
	21st to end	Night	28% 8% 16% 25% 20% 4	1980
September	1st to 10th	Night	33% 10% 12% 21% 18% 6%	1908
	11th to 20th	Night	31% 6% 13% 24% 23% 3	1980
	21st to end	Night	33% 7% 7% 24% 26% 4	1980
October	1st to 10th	Night	29% 6% 11% 24% 24% 5%	1980
	11th to 20th	Night	37% 5% 9% 23% 22% 4	2118
	21st to end	Night	42% 5% 7% 22% 20% 4	2473
November	1st to 10th	Night	34% 4 8% 25% 23% 5%	2406
	11th to 20th	Night	41% 4 8% 19% 22% 6%	2470
	21st to end	Night	45% 4 8% 24% 16% 2	2470
December	1st to 10th	Night	53% 5% 10% 19% 12% 1	2470
	11th to 20th	Night	50% 5% 9% 21% 13% 2	3044
	21st to end	Night	61% 8% 10% 14% 7%	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	26% 17% 34% 16% 7% 1	270
	11th to 20th	Day	28% 19% 33% 16% 5%	245
	21st to end	Day	21% 24% 36% 17% 3	264
February	1st to 10th	Day	29% 18% 38% 11% 5%	240
	11th to 20th	Day	36% 18% 33% 11% 3	240
	21st to end	Day	35% 17% 34% 12% 3	198
March	1st to 10th	Day	26% 19% 39% 13% 3	261
	11th to 20th	Day	23% 16% 35% 19% 6% 1	420
	21st to end	Day	28% 13% 29% 21% 8% 1	462
April	1st to 10th	Day	16% 16% 29% 25% 11% 3	420
	11th to 20th	Day	21% 14% 25% 23% 12% 4	412
	21st to end	Day	21% 13% 28% 24% 10% 4	420
May	1st to 10th	Day	21% 11% 29% 21% 14% 4	423
	11th to 20th	Day	16% 9% 23% 28% 17% 8%	447
	21st to end	Day	14% 4 20% 26% 21% 16%	485
June	1st to 10th	Day	14% 3 18% 25% 27% 13%	450
	11th to 20th	Day	9% 4 20% 28% 25% 13%	450
	21st to end	Day	8% 4 21% 31% 21% 13%	567
July	1st to 10th	Day	13% 3 14% 24% 20% 27%	504
	11th to 20th	Day	10% 2 17% 23% 29% 19%	444
	21st to end	Day	12% 2 12% 27% 29% 17%	488
August	1st to 10th	Day	13% 3 13% 25% 27% 19%	446
	11th to 20th	Day	13% 3 13% 29% 28% 14%	439
	21st to end	Day	11% 2 11% 27% 29% 20%	495
September	1st to 10th	Day	14% 2 13% 25% 27% 19%	450
	11th to 20th	Day	13% 2 10% 23% 33% 19%	450
	21st to end	Day	17% 8% 15% 24% 25% 11%	450
October	1st to 10th	Day	12% 6% 17% 30% 25% 10%	450
	11th to 20th	Day	14% 11% 27% 30% 13% 4	450
	21st to end	Day	21% 11% 30% 26% 12% 1	396
November	1st to 10th	Day	17% 8% 30% 27% 14% 4	270
	11th to 20th	Day	24% 16% 25% 27% 7% 1	270
	21st to end	Day	24% 13% 30% 25% 7% 1	270
December	1st to 10th	Day	26% 19% 27% 23% 5% 1	270
	11th to 20th	Day	21% 14% 37% 19% 9%	270
	21st to end	Day	28% 18% 33% 17% 4	297
January	1st to 10th	Night	23% 15% 33% 23% 5%	760
	11th to 20th	Night	29% 16% 30% 22% 4	728
	21st to end	Night	23% 14% 35% 25% 2	792
February	1st to 10th	Night	28% 12% 33% 25% 3	720
	11th to 20th	Night	29% 13% 36% 20% 1	703
	21st to end	Night	28% 15% 36% 19% 2	592
March	1st to 10th	Night	21% 16% 31% 27% 5%	720
	11th to 20th	Night	24% 11% 34% 24% 8%	720
	21st to end	Night	20% 12% 30% 29% 9%	792
April	1st to 10th	Night	16% 11% 32% 33% 8%	612
	11th to 20th	Night	17% 8% 30% 30% 14% 1	533
	21st to end	Night	18% 6% 34% 31% 10% 1	540
May	1st to 10th	Night	19% 6% 29% 29% 15% 2	540
	11th to 20th	Night	17% 5% 20% 36% 20% 2	531
	21st to end	Night	8% 3 14% 37% 32% 6%	584
June	1st to 10th	Night	8% 1 17% 44% 26% 4	540
	11th to 20th	Night	7% 2 14% 40% 32% 5%	540
	21st to end	Night	7% 3 15% 39% 31% 4	540
July	1st to 10th	Night	8% 2 12% 33% 36% 10%	525
	11th to 20th	Night	6% 2 9% 35% 43% 5%	522
	21st to end	Night	11% 3 7% 34% 39% 6%	591
August	1st to 10th	Night	9% 2 7% 33% 43% 5%	537
	11th to 20th	Night	8% 3 11% 34% 38% 6%	534
	21st to end	Night	7% 1 9% 32% 43% 8%	594
September	1st to 10th	Night	13% 1 9% 32% 38% 7%	648
	11th to 20th	Night	11% 2 13% 28% 40% 6%	720
	21st to end	Night	12% 3 18% 34% 30% 3	720
October	1st to 10th	Night	12% 4 16% 34% 29% 4	720
	11th to 20th	Night	17% 6% 25% 33% 17% 2	720
	21st to end	Night	21% 8% 27% 30% 13% 2	792
November	1st to 10th	Night	15% 8% 23% 34% 18% 2	740
	11th to 20th	Night	19% 11% 31% 30% 9% 1	760
	21st to end	Night	20% 11% 25% 32% 10% 1	760
December	1st to 10th	Night	26% 10% 29% 28% 6%	760
	11th to 20th	Night	24% 10% 32% 28% 6% 1	760
	21st to end	Night	25% 15% 28% 28% 4	836

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