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 2026-05-02.

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	12% 6% 2 6% 4 4 5% 4 6% 8% 42%	131499
	Night	13% 6% 2 6% 4 4 4 3 5% 7% 44%	131001
Transparency	Day	38% 7% 12% 20% 18% 6%	135104
	Night	38% 6% 11% 19% 20% 7%	135466
Seeing	Day	16% 11% 25% 25% 17% 6%	17393
	Night	16% 8% 26% 32% 16% 2	27717

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	14% 5% 2 5% 3 3 3 2 3 5% 54%	5258
	11th to 20th	Day	13% 6% 2 4 3 2 3 2 3 3 60%	5280
	21st to end	Day	17% 8% 3 6% 4 4 4 3 4 5% 42%	5780
February	1st to 10th	Day	15% 6% 2 6% 3 3 3 4 5% 7% 45%	1890
	11th to 20th	Day	21% 6% 2 6% 3 3 3 2 4 5% 45%	1860
	21st to end	Day	19% 7% 2 7% 5% 3 3 3 4 5% 42%	1900
March	1st to 10th	Day	20% 7% 2 6% 4 4 4 3 5% 6% 40%	5045
	11th to 20th	Day	10% 5% 2 5% 4 3 4 3 4 6% 53%	5090
	21st to end	Day	14% 5% 2 6% 3 4 3 4 5% 5% 48%	5586
April	1st to 10th	Day	10% 4 2 4 3 4 4 3 6% 8% 52%	2434
	11th to 20th	Day	10% 5% 2 5% 4 4 4 4 6% 7% 50%	2494
	21st to end	Day	12% 5% 2 6% 4 4 4 3 5% 7% 47%	2520
May	1st to 10th	Day	8% 7% 3 8% 5% 6% 6% 5% 7% 10% 35%	5797
	11th to 20th	Day	18% 7% 3 7% 5% 5% 6% 5% 7% 8% 29%	5861
	21st to end	Day	12% 5% 2 6% 5% 5% 5% 4 6% 9% 42%	6433
June	1st to 10th	Day	9% 6% 2 6% 6% 5% 6% 6% 7% 10% 37%	2600
	11th to 20th	Day	8% 5% 2 6% 6% 5% 5% 5% 7% 10% 42%	2600
	21st to end	Day	7% 4 2 6% 5% 6% 6% 5% 9% 11% 38%	2600
July	1st to 10th	Day	9% 6% 3 7% 7% 6% 7% 5% 9% 11% 30%	5900
	11th to 20th	Day	7% 6% 3 9% 7% 7% 7% 7% 9% 13% 26%	5900
	21st to end	Day	8% 6% 3 8% 6% 6% 6% 5% 8% 12% 32%	6424
August	1st to 10th	Day	21% 9% 3 8% 6% 6% 6% 5% 7% 9% 22%	4234
	11th to 20th	Day	10% 6% 3 8% 6% 6% 6% 6% 8% 10% 33%	4024
	21st to end	Day	6% 4 2 5% 4 5% 5% 4 7% 10% 48%	4312
September	1st to 10th	Day	8% 4 2 6% 4 5% 5% 5% 6% 9% 46%	2400
	11th to 20th	Day	13% 6% 3 7% 4 4 4 3 6% 6% 42%	2255
	21st to end	Day	19% 6% 2 6% 4 4 5% 4 5% 6% 38%	2160
October	1st to 10th	Day	15% 6% 3 5% 3 3 3 2 4 6% 49%	2000
	11th to 20th	Day	12% 4 2 4 3 3 3 3 5% 5% 58%	2000
	21st to end	Day	11% 5% 2 5% 3 3 3 2 3 6% 57%	2200
November	1st to 10th	Day	13% 6% 2 4 3 3 2 2 5% 5% 55%	2057
	11th to 20th	Day	13% 5% 2 4 3 2 3 3 4 7% 54%	2100
	21st to end	Day	13% 5% 3 5% 4 3 3 4 5% 6% 51%	1847
December	1st to 10th	Day	12% 6% 2 6% 4 3 3 3 4 6% 51%	2680
	11th to 20th	Day	16% 6% 2 6% 4 4 3 3 5% 5% 46%	3413
	21st to end	Day	16% 6% 2 6% 4 3 3 3 5% 6% 45%	4565
January	1st to 10th	Night	10% 6% 2 5% 3 3 3 3 4 5% 55%	7635
	11th to 20th	Night	13% 6% 2 5% 3 3 3 2 4 4 56%	7680
	21st to end	Night	17% 8% 3 6% 3 3 4 3 4 5% 44%	8401
February	1st to 10th	Night	17% 5% 3 5% 4 3 4 2 5% 6% 46%	2730
	11th to 20th	Night	19% 7% 3 5% 4 3 4 3 5% 6% 41%	2643
	21st to end	Night	15% 7% 2 4 3 4 4 3 5% 6% 48%	1903
March	1st to 10th	Night	19% 8% 3 7% 4 4 3 3 4 5% 42%	5028
	11th to 20th	Night	12% 5% 2 5% 3 3 3 3 4 7% 54%	5090
	21st to end	Night	13% 4 2 5% 4 4 4 4 4 5% 50%	5588
April	1st to 10th	Night	13% 6% 2 5% 4 3 3 3 4 8% 48%	2184
	11th to 20th	Night	11% 5% 1 5% 4 4 4 4 5% 7% 51%	2075
	21st to end	Night	10% 4 2 5% 4 5% 5% 4 6% 8% 47%	2100
May	1st to 10th	Night	11% 8% 3 8% 5% 5% 4 4 6% 9% 38%	4163
	11th to 20th	Night	16% 9% 3 7% 5% 5% 4 4 6% 8% 34%	4032
	21st to end	Night	14% 5% 2 6% 4 4 4 4 6% 9% 42%	4421
June	1st to 10th	Night	10% 5% 3 7% 5% 4 5% 5% 8% 10% 38%	1800
	11th to 20th	Night	9% 6% 3 6% 5% 4 5% 6% 7% 9% 40%	1800
	21st to end	Night	7% 6% 2 6% 5% 5% 5% 5% 9% 11% 38%	1800
July	1st to 10th	Night	12% 8% 3 8% 5% 6% 6% 5% 8% 11% 28%	4058
	11th to 20th	Night	12% 7% 3 9% 6% 6% 7% 6% 9% 12% 23%	4057
	21st to end	Night	12% 8% 3 9% 6% 6% 6% 4 7% 11% 28%	4427
August	1st to 10th	Night	23% 7% 3 9% 6% 5% 5% 5% 6% 8% 23%	2915
	11th to 20th	Night	9% 6% 2 7% 6% 6% 6% 5% 8% 10% 34%	2990
	21st to end	Night	6% 4 1 6% 4 5% 4 4 8% 11% 47%	3586
September	1st to 10th	Night	10% 5% 2 7% 4 4 4 4 6% 8% 45%	2000
	11th to 20th	Night	12% 6% 2 7% 5% 4 4 3 7% 8% 41%	2140
	21st to end	Night	19% 7% 3 7% 4 4 5% 3 5% 6% 38%	2240
October	1st to 10th	Night	13% 6% 2 6% 4 3 3 3 4 6% 50%	2400
	11th to 20th	Night	13% 5% 2 5% 3 3 3 3 4 6% 54%	2400
	21st to end	Night	12% 5% 2 5% 3 3 2 3 4 6% 55%	2640
November	1st to 10th	Night	14% 6% 2 5% 3 2 3 3 4 6% 53%	2461
	11th to 20th	Night	12% 6% 3 5% 3 3 4 3 5% 6% 51%	2520
	21st to end	Night	13% 4 2 5% 3 4 4 3 6% 6% 51%	2755
December	1st to 10th	Night	13% 6% 3 5% 3 3 4 3 4 5% 52%	4720
	11th to 20th	Night	16% 8% 3 8% 4 4 4 3 4 4 41%	4986
	21st to end	Night	15% 6% 2 6% 4 3 4 3 4 6% 49%	6633

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	35% 3 9% 20% 27% 6%	5259
	11th to 20th	Day	30% 3 3 14% 36% 13%	5280
	21st to end	Day	44% 3 4 18% 20% 9%	5780
February	1st to 10th	Day	39% 5% 10% 20% 19% 6%	1890
	11th to 20th	Day	43% 4 6% 18% 22% 6%	1869
	21st to end	Day	45% 4 7% 17% 21% 6%	1900
March	1st to 10th	Day	44% 5% 7% 16% 18% 11%	5045
	11th to 20th	Day	31% 5% 8% 15% 26% 15%	5090
	21st to end	Day	38% 4 9% 21% 21% 7%	5586
April	1st to 10th	Day	29% 5% 12% 23% 24% 8%	2434
	11th to 20th	Day	31% 5% 11% 24% 20% 8%	2494
	21st to end	Day	35% 7% 13% 22% 19% 4	2520
May	1st to 10th	Day	40% 9% 18% 21% 11% 1	5831
	11th to 20th	Day	49% 8% 13% 20% 10%	5865
	21st to end	Day	35% 8% 14% 21% 19% 3	6447
June	1st to 10th	Day	37% 10% 16% 21% 15% 1	2600
	11th to 20th	Day	35% 10% 17% 22% 15% 2	2600
	21st to end	Day	35% 12% 16% 21% 15% 2	2600
July	1st to 10th	Day	42% 10% 18% 20% 8% 1	5835
	11th to 20th	Day	44% 13% 29% 11% 3 1	5831
	21st to end	Day	41% 10% 18% 21% 10%	6240
August	1st to 10th	Day	56% 9% 17% 12% 5%	4221
	11th to 20th	Day	42% 10% 17% 21% 8% 1	4063
	21st to end	Day	30% 8% 14% 31% 16% 2	4312
September	1st to 10th	Day	33% 10% 15% 20% 18% 5%	2400
	11th to 20th	Day	41% 7% 11% 17% 20% 4	2255
	21st to end	Day	46% 7% 10% 19% 14% 4	2160
October	1st to 10th	Day	33% 5% 8% 21% 25% 8%	3260
	11th to 20th	Day	19% 3 6% 20% 26% 26%	3240
	21st to end	Day	25% 4 6% 24% 24% 18%	3538
November	1st to 10th	Day	32% 4 8% 21% 28% 8%	2057
	11th to 20th	Day	32% 4 9% 21% 27% 7%	2100
	21st to end	Day	33% 5% 7% 23% 24% 7%	1847
December	1st to 10th	Day	35% 4 8% 19% 25% 9%	2680
	11th to 20th	Day	40% 4 11% 17% 21% 6%	3410
	21st to end	Day	39% 4 11% 24% 20% 2	4565
January	1st to 10th	Night	32% 3 10% 21% 28% 6%	7636
	11th to 20th	Night	33% 3 5% 14% 34% 11%	7680
	21st to end	Night	43% 3 4 17% 23% 9%	8401
February	1st to 10th	Night	40% 4 9% 21% 21% 6%	2730
	11th to 20th	Night	44% 4 8% 16% 21% 7%	2645
	21st to end	Night	37% 5% 8% 19% 23% 8%	1903
March	1st to 10th	Night	44% 5% 7% 12% 23% 9%	5028
	11th to 20th	Night	32% 5% 7% 14% 26% 18%	5090
	21st to end	Night	36% 5% 9% 22% 22% 7%	5588
April	1st to 10th	Night	35% 5% 10% 19% 22% 8%	2184
	11th to 20th	Night	32% 6% 10% 22% 22% 8%	2075
	21st to end	Night	33% 7% 12% 25% 18% 4	2100
May	1st to 10th	Night	41% 9% 18% 18% 13% 2	4191
	11th to 20th	Night	46% 8% 14% 17% 13% 1	4033
	21st to end	Night	37% 8% 13% 23% 17% 2	4429
June	1st to 10th	Night	38% 11% 16% 20% 14% 2	1800
	11th to 20th	Night	37% 11% 17% 19% 15% 1	1800
	21st to end	Night	35% 12% 18% 20% 12% 3	1800
July	1st to 10th	Night	46% 11% 19% 16% 7% 1	4015
	11th to 20th	Night	49% 15% 22% 11% 3 1	4006
	21st to end	Night	48% 9% 17% 18% 9%	4297
August	1st to 10th	Night	57% 8% 16% 14% 4 1	2904
	11th to 20th	Night	41% 11% 21% 21% 6% 1	3017
	21st to end	Night	29% 9% 13% 28% 19% 2	3586
September	1st to 10th	Night	35% 9% 13% 21% 16% 5%	2000
	11th to 20th	Night	39% 8% 13% 19% 18% 3	2140
	21st to end	Night	47% 6% 12% 16% 15% 4	2240
October	1st to 10th	Night	37% 5% 7% 21% 24% 6%	3920
	11th to 20th	Night	24% 3 6% 16% 27% 23%	3899
	21st to end	Night	25% 3 8% 24% 24% 17%	4252
November	1st to 10th	Night	33% 4 8% 18% 27% 10%	2461
	11th to 20th	Night	35% 4 7% 17% 26% 11%	2520
	21st to end	Night	33% 5% 7% 22% 25% 8%	2755
December	1st to 10th	Night	35% 4 6% 19% 27% 9%	4720
	11th to 20th	Night	47% 4 8% 16% 16% 8%	4988
	21st to end	Night	38% 4 11% 23% 22% 2	6633

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	22% 25% 35% 15% 3	330
	11th to 20th	Day	23% 25% 35% 14% 3	330
	21st to end	Day	20% 25% 39% 13% 3	363
February	1st to 10th	Day	21% 18% 40% 17% 4 1	330
	11th to 20th	Day	35% 22% 32% 11% 1	347
	21st to end	Day	24% 20% 31% 21% 4	446
March	1st to 10th	Day	19% 20% 31% 24% 6%	540
	11th to 20th	Day	20% 23% 33% 18% 6% 1	540
	21st to end	Day	19% 19% 37% 19% 6% 1	594
April	1st to 10th	Day	19% 18% 33% 20% 10% 1	540
	11th to 20th	Day	12% 18% 31% 24% 12% 3	532
	21st to end	Day	14% 13% 28% 27% 17% 2	540
May	1st to 10th	Day	14% 16% 30% 26% 10% 4	507
	11th to 20th	Day	17% 7% 24% 29% 18% 5%	527
	21st to end	Day	18% 7% 19% 26% 21% 9%	573
June	1st to 10th	Day	12% 4 24% 34% 18% 8%	530
	11th to 20th	Day	10% 3 18% 32% 26% 10%	530
	21st to end	Day	7% 3 14% 34% 32% 10%	530
July	1st to 10th	Day	10% 2 9% 30% 34% 15%	525
	11th to 20th	Day	7% 2 9% 26% 40% 16%	524
	21st to end	Day	7% 2 13% 32% 31% 15%	576
August	1st to 10th	Day	16% 4 16% 27% 25% 13%	526
	11th to 20th	Day	13% 3 12% 26% 29% 18%	519
	21st to end	Day	13% 2 13% 27% 28% 18%	583
September	1st to 10th	Day	10% 2 16% 29% 25% 17%	530
	11th to 20th	Day	16% 3 16% 29% 23% 12%	530
	21st to end	Day	22% 6% 21% 27% 20% 5%	530
October	1st to 10th	Day	17% 8% 19% 28% 21% 8%	530
	11th to 20th	Day	13% 9% 27% 27% 20% 4	530
	21st to end	Day	13% 12% 26% 26% 19% 4	583
November	1st to 10th	Day	17% 10% 27% 30% 13% 3	535
	11th to 20th	Day	15% 15% 33% 25% 11% 1	540
	21st to end	Day	13% 19% 30% 24% 11% 2	309
December	1st to 10th	Day	20% 15% 41% 17% 7%	220
	11th to 20th	Day	21% 14% 34% 21% 9% 1	311
	21st to end	Day	20% 18% 33% 19% 7% 2	363
January	1st to 10th	Night	19% 14% 36% 26% 5% 1	840
	11th to 20th	Night	18% 16% 33% 28% 5%	840
	21st to end	Night	21% 12% 37% 27% 3	924
February	1st to 10th	Night	20% 11% 38% 29% 3	840
	11th to 20th	Night	23% 17% 39% 21% 1	823
	21st to end	Night	18% 16% 37% 25% 4	692
March	1st to 10th	Night	17% 14% 34% 30% 5%	840
	11th to 20th	Night	20% 12% 35% 25% 7% 1	840
	21st to end	Night	17% 13% 41% 24% 5%	924
April	1st to 10th	Night	17% 15% 34% 26% 7%	840
	11th to 20th	Night	13% 13% 34% 29% 10% 1	831
	21st to end	Night	13% 7% 35% 37% 9%	840
May	1st to 10th	Night	12% 9% 34% 37% 8%	660
	11th to 20th	Night	17% 7% 26% 37% 13% 1	591
	21st to end	Night	13% 3 17% 40% 25% 2	650
June	1st to 10th	Night	12% 3 17% 45% 21% 2	600
	11th to 20th	Night	10% 3 17% 38% 26% 5%	600
	21st to end	Night	8% 2 17% 40% 32% 2	600
July	1st to 10th	Night	9% 1 12% 37% 37% 4	585
	11th to 20th	Night	8% 2 9% 35% 40% 5%	582
	21st to end	Night	8% 2 15% 40% 31% 4	657
August	1st to 10th	Night	13% 3 8% 37% 35% 3	597
	11th to 20th	Night	11% 3 12% 33% 34% 6%	657
	21st to end	Night	11% 2 12% 32% 37% 5%	880
September	1st to 10th	Night	13% 1 12% 34% 34% 5%	800
	11th to 20th	Night	15% 3 15% 31% 32% 4	800
	21st to end	Night	23% 5% 16% 33% 22% 1	800
October	1st to 10th	Night	15% 4 18% 31% 27% 4	800
	11th to 20th	Night	16% 8% 25% 30% 20% 2	800
	21st to end	Night	15% 8% 26% 29% 21% 1	880
November	1st to 10th	Night	16% 7% 26% 34% 15% 2	820
	11th to 20th	Night	15% 11% 28% 33% 12%	840
	21st to end	Night	13% 10% 31% 32% 14% 1	840
December	1st to 10th	Night	21% 10% 29% 33% 6%	840
	11th to 20th	Night	19% 10% 29% 32% 9%	840
	21st to end	Night	20% 12% 27% 33% 8%	924

Page generated at 2026-04-29 02:21:43. Version ac07

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