Raven Rock State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Raven Rock State Park clear sky chart from 2005-11-06 to 2024-01-17.

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% 5% 2 5% 5% 3 5% 5% 6% 8% 43%	74732
	Night	13% 6% 2 5% 5% 3 4 5% 5% 7% 45%	75077
Transparency	Day	38% 8% 12% 20% 18% 4	74454
	Night	38% 7% 11% 19% 19% 5%	74874
Seeing	Day	16% 11% 24% 25% 18% 7%	14294
	Night	16% 8% 26% 31% 17% 2	24588

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% 6% 3 5% 5% 3 4 4 3 4 46%	1706
	11th to 20th	Day	18% 6% 3 5% 4 2 4 4 4 5% 45%	1674
	21st to end	Day	17% 6% 2 4 3 3 3 4 4 5% 49%	1782
February	1st to 10th	Day	16% 6% 2 5% 5% 3 4 4 4 7% 44%	1620
	11th to 20th	Day	21% 5% 2 4 3 2 4 3 4 5% 47%	1587
	21st to end	Day	19% 7% 3 6% 6% 2 3 3 4 5% 42%	1625
March	1st to 10th	Day	15% 5% 2 3 3 2 4 4 4 5% 52%	1980
	11th to 20th	Day	15% 6% 3 6% 5% 3 4 5% 5% 8% 41%	1980
	21st to end	Day	16% 6% 3 6% 4 3 4 5% 6% 7% 40%	2178
April	1st to 10th	Day	11% 3 2 3 4 2 4 4 5% 8% 53%	2086
	11th to 20th	Day	10% 5% 3 5% 4 3 4 4 5% 8% 49%	2134
	21st to end	Day	13% 5% 2 5% 4 3 4 4 5% 7% 47%	2160
May	1st to 10th	Day	10% 5% 3 5% 5% 4 5% 5% 6% 9% 43%	2304
	11th to 20th	Day	13% 6% 3 6% 6% 4 5% 5% 5% 7% 39%	2301
	21st to end	Day	11% 6% 2 6% 6% 4 6% 6% 6% 9% 39%	2531
June	1st to 10th	Day	10% 6% 2 5% 6% 4 6% 7% 7% 10% 37%	2340
	11th to 20th	Day	8% 4 3 5% 6% 4 5% 6% 7% 10% 42%	2340
	21st to end	Day	8% 4 2 6% 6% 5% 6% 7% 9% 11% 37%	2340
July	1st to 10th	Day	8% 5% 2 6% 8% 4 7% 7% 9% 12% 31%	2340
	11th to 20th	Day	7% 5% 3 7% 7% 4 6% 7% 9% 12% 33%	2340
	21st to end	Day	6% 4 3 8% 7% 4 6% 8% 7% 11% 36%	2547
August	1st to 10th	Day	10% 6% 2 7% 6% 5% 6% 8% 8% 10% 32%	2327
	11th to 20th	Day	11% 6% 3 7% 7% 4 7% 8% 8% 9% 30%	2227
	21st to end	Day	11% 6% 3 6% 7% 4 6% 6% 7% 10% 36%	2376
September	1st to 10th	Day	8% 4 2 5% 5% 4 6% 6% 7% 9% 45%	2160
	11th to 20th	Day	13% 6% 4 6% 6% 3 4 5% 6% 6% 43%	2030
	21st to end	Day	19% 6% 2 5% 5% 3 5% 5% 5% 6% 39%	1944
October	1st to 10th	Day	16% 6% 3 4 3 2 3 3 4 7% 49%	1800
	11th to 20th	Day	12% 4 2 3 4 2 3 4 4 6% 56%	1800
	21st to end	Day	11% 5% 2 4 4 2 3 3 3 6% 56%	1980
November	1st to 10th	Day	14% 6% 2 4 3 2 2 3 4 5% 56%	1857
	11th to 20th	Day	14% 5% 2 4 3 2 3 3 4 7% 53%	1900
	21st to end	Day	14% 5% 3 4 4 2 3 4 5% 6% 51%	1673
December	1st to 10th	Day	18% 7% 2 5% 4 2 4 4 5% 8% 41%	1520
	11th to 20th	Day	16% 4 2 4 3 2 2 3 4 4 56%	2119
	21st to end	Day	16% 6% 2 5% 6% 2 4 4 5% 7% 43%	3124
January	1st to 10th	Night	17% 6% 2 4 5% 3 3 3 4 5% 47%	2459
	11th to 20th	Night	15% 7% 3 5% 6% 2 5% 4 5% 5% 44%	2430
	21st to end	Night	17% 6% 2 4 4 2 4 3 4 5% 49%	2574
February	1st to 10th	Night	17% 5% 3 5% 5% 3 3 3 5% 6% 45%	2340
	11th to 20th	Night	20% 7% 3 4 4 2 4 4 5% 6% 42%	2256
	21st to end	Night	16% 6% 2 4 3 3 4 4 4 6% 47%	1628
March	1st to 10th	Night	14% 4 2 5% 4 3 3 4 5% 5% 52%	1980
	11th to 20th	Night	16% 6% 2 5% 6% 3 5% 5% 5% 6% 40%	1980
	21st to end	Night	15% 5% 3 5% 5% 3 4 5% 5% 6% 45%	2178
April	1st to 10th	Night	14% 6% 2 4 4 2 3 3 4 8% 49%	1872
	11th to 20th	Night	13% 5% 2 4 5% 3 4 5% 4 7% 50%	1775
	21st to end	Night	10% 4 3 4 5% 3 6% 5% 6% 8% 48%	1800
May	1st to 10th	Night	9% 5% 2 5% 5% 3 5% 5% 6% 7% 46%	1670
	11th to 20th	Night	12% 6% 3 6% 5% 4 5% 5% 5% 9% 40%	1592
	21st to end	Night	10% 5% 2 6% 5% 3 6% 6% 6% 10% 41%	1744
June	1st to 10th	Night	10% 5% 3 6% 6% 3 6% 6% 7% 11% 39%	1620
	11th to 20th	Night	10% 5% 3 5% 5% 4 5% 7% 8% 9% 40%	1620
	21st to end	Night	7% 6% 3 5% 6% 3 6% 6% 9% 12% 37%	1620
July	1st to 10th	Night	6% 6% 3 7% 7% 4 6% 9% 7% 10% 34%	1620
	11th to 20th	Night	6% 5% 2 6% 7% 4 7% 8% 9% 13% 33%	1620
	21st to end	Night	6% 5% 3 7% 7% 4 6% 6% 8% 13% 35%	1771
August	1st to 10th	Night	9% 5% 3 7% 8% 4 5% 7% 7% 11% 34%	1611
	11th to 20th	Night	10% 6% 3 6% 7% 5% 7% 7% 8% 9% 32%	1654
	21st to end	Night	10% 5% 2 6% 7% 4 5% 6% 8% 11% 36%	1980
September	1st to 10th	Night	10% 5% 2 7% 5% 3 4 5% 6% 8% 45%	1800
	11th to 20th	Night	12% 6% 3 6% 5% 3 4 4 7% 8% 43%	1926
	21st to end	Night	18% 7% 3 6% 5% 3 5% 4 5% 6% 38%	2016
October	1st to 10th	Night	14% 5% 2 5% 4 3 3 4 4 6% 50%	2160
	11th to 20th	Night	13% 5% 2 4 4 2 3 4 4 6% 53%	2160
	21st to end	Night	12% 5% 2 4 3 2 2 3 4 7% 55%	2376
November	1st to 10th	Night	14% 6% 2 4 3 1 4 3 4 5% 53%	2221
	11th to 20th	Night	13% 5% 3 4 4 2 4 3 5% 6% 50%	2280
	21st to end	Night	14% 4 2 4 4 3 4 3 6% 6% 51%	2491
December	1st to 10th	Night	17% 7% 4 5% 4 2 4 5% 5% 5% 42%	2660
	11th to 20th	Night	17% 6% 2 5% 3 2 3 4 4 4 48%	3061
	21st to end	Night	17% 6% 2 4 4 2 4 3 4 6% 47%	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	42% 5% 7% 20% 20% 6%	1707
	11th to 20th	Day	42% 5% 7% 19% 22% 5%	1674
	21st to end	Day	38% 4 6% 20% 25% 7%	1782
February	1st to 10th	Day	41% 5% 10% 20% 18% 6%	1620
	11th to 20th	Day	42% 4 6% 19% 23% 6%	1596
	21st to end	Day	45% 4 8% 17% 19% 6%	1625
March	1st to 10th	Day	35% 5% 9% 21% 23% 7%	1980
	11th to 20th	Day	40% 7% 10% 20% 17% 7%	1980
	21st to end	Day	43% 7% 11% 17% 19% 4	2178
April	1st to 10th	Day	29% 5% 11% 22% 25% 8%	2086
	11th to 20th	Day	33% 6% 11% 22% 19% 9%	2134
	21st to end	Day	35% 7% 12% 21% 19% 5%	2160
May	1st to 10th	Day	36% 9% 15% 20% 18% 3	2304
	11th to 20th	Day	43% 8% 13% 21% 14% 1	2305
	21st to end	Day	38% 9% 16% 22% 14% 1	2531
June	1st to 10th	Day	38% 9% 16% 20% 15% 1	2340
	11th to 20th	Day	35% 10% 17% 22% 14% 2	2340
	21st to end	Day	36% 12% 16% 20% 14% 2	2340
July	1st to 10th	Day	39% 12% 17% 20% 10% 3	2275
	11th to 20th	Day	39% 13% 21% 18% 7% 2	2271
	21st to end	Day	36% 14% 19% 20% 10% 1	2405
August	1st to 10th	Day	42% 14% 17% 18% 9% 1	2314
	11th to 20th	Day	45% 13% 15% 18% 8% 1	2227
	21st to end	Day	41% 10% 16% 20% 9% 3	2376
September	1st to 10th	Day	33% 11% 15% 19% 17% 5%	2160
	11th to 20th	Day	40% 7% 10% 17% 21% 4	2030
	21st to end	Day	45% 7% 9% 18% 15% 4	1944
October	1st to 10th	Day	37% 5% 10% 21% 23% 4	1800
	11th to 20th	Day	30% 4 9% 26% 23% 7%	1800
	21st to end	Day	31% 4 6% 22% 25% 10%	1980
November	1st to 10th	Day	32% 4 8% 20% 27% 9%	1857
	11th to 20th	Day	32% 4 9% 20% 28% 8%	1900
	21st to end	Day	34% 5% 7% 23% 24% 8%	1673
December	1st to 10th	Day	43% 5% 12% 18% 18% 4	1520
	11th to 20th	Day	33% 3 7% 23% 25% 9%	2116
	21st to end	Day	41% 5% 9% 21% 22% 2	3124
January	1st to 10th	Night	39% 4 9% 18% 24% 6%	2459
	11th to 20th	Night	42% 6% 9% 17% 21% 6%	2430
	21st to end	Night	38% 3 6% 21% 25% 7%	2574
February	1st to 10th	Night	41% 4 9% 20% 20% 6%	2340
	11th to 20th	Night	43% 5% 8% 16% 21% 7%	2258
	21st to end	Night	38% 5% 8% 19% 21% 8%	1628
March	1st to 10th	Night	35% 5% 8% 19% 24% 9%	1980
	11th to 20th	Night	43% 6% 9% 16% 19% 6%	1980
	21st to end	Night	39% 7% 11% 19% 19% 5%	2178
April	1st to 10th	Night	35% 5% 9% 18% 25% 8%	1872
	11th to 20th	Night	34% 6% 10% 21% 21% 8%	1775
	21st to end	Night	33% 7% 13% 24% 18% 5%	1800
May	1st to 10th	Night	34% 8% 15% 20% 19% 4	1670
	11th to 20th	Night	40% 9% 13% 20% 16% 1	1593
	21st to end	Night	36% 11% 15% 23% 14% 1	1745
June	1st to 10th	Night	37% 11% 16% 21% 13% 2	1620
	11th to 20th	Night	37% 11% 18% 18% 15% 1	1620
	21st to end	Night	36% 12% 17% 19% 12% 3	1620
July	1st to 10th	Night	39% 15% 17% 17% 10% 2	1575
	11th to 20th	Night	36% 14% 21% 19% 8% 2	1566
	21st to end	Night	37% 13% 20% 19% 11%	1672
August	1st to 10th	Night	41% 12% 19% 21% 6% 1	1600
	11th to 20th	Night	42% 13% 19% 17% 8% 1	1654
	21st to end	Night	38% 13% 19% 19% 9% 2	1980
September	1st to 10th	Night	35% 10% 13% 20% 16% 6%	1800
	11th to 20th	Night	38% 8% 13% 18% 19% 3	1926
	21st to end	Night	47% 6% 11% 15% 17% 4	2016
October	1st to 10th	Night	35% 5% 9% 21% 24% 5%	2160
	11th to 20th	Night	33% 5% 10% 20% 24% 8%	2160
	21st to end	Night	30% 4 9% 21% 26% 11%	2376
November	1st to 10th	Night	34% 4 8% 17% 27% 11%	2221
	11th to 20th	Night	36% 4 8% 16% 24% 12%	2280
	21st to end	Night	34% 5% 7% 22% 25% 8%	2491
December	1st to 10th	Night	43% 6% 9% 19% 18% 5%	2660
	11th to 20th	Night	39% 4 8% 18% 22% 9%	3063
	21st to end	Night	39% 4 7% 23% 24% 3	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	23% 25% 34% 15% 3	270
	11th to 20th	Day	24% 24% 34% 16% 3	258
	21st to end	Day	19% 27% 37% 14% 3	264
February	1st to 10th	Day	21% 22% 35% 18% 4	240
	11th to 20th	Day	35% 21% 33% 10% 2	254
	21st to end	Day	23% 22% 30% 20% 4	346
March	1st to 10th	Day	18% 21% 32% 23% 6%	420
	11th to 20th	Day	21% 22% 34% 16% 5% 1	420
	21st to end	Day	21% 19% 36% 18% 6% 1	462
April	1st to 10th	Day	20% 18% 32% 20% 10% 1	420
	11th to 20th	Day	13% 20% 29% 22% 13% 4	412
	21st to end	Day	16% 14% 29% 24% 15% 2	420
May	1st to 10th	Day	15% 17% 29% 25% 10% 4	423
	11th to 20th	Day	16% 6% 23% 29% 21% 6%	447
	21st to end	Day	19% 5% 16% 26% 24% 10%	485
June	1st to 10th	Day	13% 3 22% 34% 19% 8%	450
	11th to 20th	Day	11% 4 20% 29% 26% 11%	450
	21st to end	Day	8% 4 16% 34% 30% 8%	450
July	1st to 10th	Day	10% 2 9% 31% 33% 16%	445
	11th to 20th	Day	7% 2 10% 26% 40% 15%	444
	21st to end	Day	7% 2 13% 33% 32% 13%	488
August	1st to 10th	Day	12% 4 16% 27% 27% 14%	446
	11th to 20th	Day	12% 2 12% 25% 29% 19%	439
	21st to end	Day	14% 2 12% 25% 28% 19%	495
September	1st to 10th	Day	11% 2 15% 27% 26% 19%	450
	11th to 20th	Day	16% 3 14% 31% 24% 13%	450
	21st to end	Day	21% 6% 21% 28% 20% 5%	450
October	1st to 10th	Day	19% 7% 20% 26% 20% 8%	450
	11th to 20th	Day	12% 9% 26% 28% 20% 5%	450
	21st to end	Day	12% 12% 26% 28% 18% 4	495
November	1st to 10th	Day	18% 9% 26% 27% 14% 4	455
	11th to 20th	Day	16% 15% 32% 25% 11% 2	460
	21st to end	Day	13% 18% 31% 22% 13% 2	255
December	1st to 10th	Day	21% 15% 40% 17% 7%	180
	11th to 20th	Day	22% 16% 33% 20% 9% 1	254
	21st to end	Day	22% 19% 30% 19% 9% 2	297
January	1st to 10th	Night	20% 14% 35% 26% 5% 1	760
	11th to 20th	Night	19% 14% 33% 29% 6%	748
	21st to end	Night	20% 12% 37% 27% 4	792
February	1st to 10th	Night	20% 11% 36% 28% 4	720
	11th to 20th	Night	24% 16% 39% 20% 1	703
	21st to end	Night	18% 16% 36% 25% 4	592
March	1st to 10th	Night	17% 14% 36% 29% 5%	720
	11th to 20th	Night	21% 12% 35% 23% 8% 1	720
	21st to end	Night	18% 13% 38% 25% 6%	792
April	1st to 10th	Night	18% 15% 34% 25% 7%	720
	11th to 20th	Night	14% 13% 32% 28% 11% 1	711
	21st to end	Night	13% 7% 36% 36% 8%	720
May	1st to 10th	Night	11% 9% 34% 38% 8%	590
	11th to 20th	Night	17% 5% 26% 37% 14% 1	531
	21st to end	Night	13% 3 15% 42% 27% 2	584
June	1st to 10th	Night	11% 3 17% 45% 21% 2	540
	11th to 20th	Night	11% 3 17% 36% 27% 6%	540
	21st to end	Night	9% 2 17% 41% 30% 2	540
July	1st to 10th	Night	8% 1 12% 37% 37% 5%	525
	11th to 20th	Night	8% 2 9% 36% 39% 5%	522
	21st to end	Night	8% 1 16% 41% 31% 3	591
August	1st to 10th	Night	11% 2 9% 37% 37% 3	537
	11th to 20th	Night	12% 3 13% 33% 34% 6%	590
	21st to end	Night	12% 2 13% 30% 38% 6%	792
September	1st to 10th	Night	13% 1 10% 33% 37% 6%	720
	11th to 20th	Night	15% 3 14% 31% 33% 4	720
	21st to end	Night	23% 5% 16% 32% 23% 2	720
October	1st to 10th	Night	16% 4 18% 30% 28% 4	720
	11th to 20th	Night	16% 8% 25% 28% 21% 2	720
	21st to end	Night	15% 8% 27% 29% 20% 1	792
November	1st to 10th	Night	17% 7% 25% 32% 16% 2	740
	11th to 20th	Night	15% 11% 28% 32% 13% 1	760
	21st to end	Night	14% 9% 30% 31% 15% 1	760
December	1st to 10th	Night	20% 10% 29% 33% 6%	760
	11th to 20th	Night	19% 10% 29% 32% 9%	760
	21st to end	Night	21% 12% 26% 32% 8%	836

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