Pennyrile Forest Observing Field
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Pennyrile Forest Observing Field clear sky chart from 2005-11-06 to 2025-06-10.

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	13% 8% 3 7% 4 4 4 4 5% 7% 41%	119210
	Night	15% 8% 3 6% 4 4 4 3 5% 6% 43%	119109
Transparency	Day	41% 5% 10% 24% 17% 3	122898
	Night	41% 4 9% 23% 19% 4	123561
Seeing	Day	17% 12% 26% 24% 15% 6%	16136
	Night	18% 11% 26% 28% 16% 2	25989

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	15% 11% 7% 9% 5% 4 4 3 5% 5% 31%	3617
	11th to 20th	Day	14% 8% 3 9% 5% 3 5% 3 4 6% 40%	3620
	21st to end	Day	20% 9% 5% 6% 4 4 4 3 4 5% 37%	4661
February	1st to 10th	Day	18% 13% 4 6% 4 3 2 4 5% 6% 37%	2000
	11th to 20th	Day	20% 10% 4 7% 4 4 3 3 4 5% 36%	1948
	21st to end	Day	17% 10% 3 7% 5% 4 5% 3 4 6% 36%	1650
March	1st to 10th	Day	16% 13% 4 7% 4 3 3 3 4 4 38%	4480
	11th to 20th	Day	13% 9% 3 6% 3 3 3 2 4 5% 49%	4648
	21st to end	Day	12% 8% 3 8% 4 4 4 3 6% 6% 41%	5965
April	1st to 10th	Day	15% 6% 2 6% 5% 4 4 3 5% 7% 44%	2400
	11th to 20th	Day	16% 7% 3 7% 5% 4 4 3 5% 6% 40%	2374
	21st to end	Day	17% 7% 2 6% 4 4 5% 3 5% 8% 40%	2405
May	1st to 10th	Day	19% 9% 3 9% 6% 5% 6% 4 6% 8% 26%	5862
	11th to 20th	Day	17% 8% 3 8% 5% 5% 5% 4 6% 8% 32%	5861
	21st to end	Day	15% 6% 3 7% 5% 5% 4 4 6% 7% 38%	6472
June	1st to 10th	Day	11% 5% 2 5% 4 4 5% 4 6% 9% 46%	2787
	11th to 20th	Day	5% 4 2 5% 5% 5% 5% 5% 7% 9% 48%	2660
	21st to end	Day	6% 4 2 6% 5% 5% 6% 5% 7% 11% 44%	2660
July	1st to 10th	Day	10% 5% 2 7% 5% 6% 6% 5% 7% 10% 38%	4440
	11th to 20th	Day	7% 4 2 4 3 4 5% 5% 7% 11% 46%	4440
	21st to end	Day	12% 10% 4 9% 7% 6% 5% 5% 7% 8% 28%	4642
August	1st to 10th	Day	5% 3 2 5% 4 4 4 4 6% 9% 55%	3831
	11th to 20th	Day	9% 5% 2 6% 4 5% 6% 4 7% 10% 41%	3729
	21st to end	Day	5% 4 2 5% 4 4 3 4 5% 9% 57%	4180
September	1st to 10th	Day	11% 5% 2 5% 5% 4 6% 4 5% 8% 45%	2280
	11th to 20th	Day	11% 5% 2 6% 5% 5% 4 4 5% 7% 46%	2114
	21st to end	Day	12% 5% 2 5% 4 3 3 3 5% 6% 49%	2090
October	1st to 10th	Day	10% 5% 2 5% 2 3 3 2 4 8% 57%	2090
	11th to 20th	Day	12% 5% 2 6% 4 3 4 3 4 6% 52%	1957
	21st to end	Day	20% 7% 2 5% 3 2 3 3 4 5% 47%	1932
November	1st to 10th	Day	11% 5% 2 6% 3 3 4 2 4 6% 54%	1762
	11th to 20th	Day	16% 7% 2 4 4 3 4 2 5% 6% 47%	1800
	21st to end	Day	17% 9% 3 6% 3 3 4 3 4 5% 43%	1800
December	1st to 10th	Day	16% 10% 2 6% 3 3 4 3 4 5% 44%	2930
	11th to 20th	Day	17% 12% 4 8% 4 4 4 3 5% 5% 34%	3141
	21st to end	Day	20% 14% 4 8% 5% 4 4 3 4 6% 26%	3982
January	1st to 10th	Night	17% 13% 4 9% 3 3 4 3 5% 5% 34%	6348
	11th to 20th	Night	16% 11% 4 8% 4 4 4 2 3 4 38%	6360
	21st to end	Night	21% 10% 4 6% 3 3 3 2 4 5% 39%	6290
February	1st to 10th	Night	23% 10% 4 8% 4 4 3 3 4 4 33%	2400
	11th to 20th	Night	21% 8% 4 8% 5% 4 3 2 4 5% 36%	2338
	21st to end	Night	21% 9% 3 7% 4 4 3 3 5% 4 36%	1980
March	1st to 10th	Night	18% 12% 4 7% 3 4 3 3 4 5% 36%	5373
	11th to 20th	Night	12% 7% 2 5% 4 3 3 3 5% 6% 49%	5310
	21st to end	Night	14% 8% 3 7% 5% 4 4 3 5% 7% 40%	4993
April	1st to 10th	Night	14% 5% 2 5% 3 4 4 4 6% 6% 47%	2000
	11th to 20th	Night	15% 6% 2 5% 3 4 4 3 5% 7% 46%	1975
	21st to end	Night	15% 7% 3 5% 5% 4 4 4 6% 8% 39%	1994
May	1st to 10th	Night	19% 10% 3 6% 4 4 4 4 7% 8% 31%	4033
	11th to 20th	Night	15% 9% 3 8% 5% 5% 5% 4 6% 8% 32%	4032
	21st to end	Night	14% 7% 2 6% 5% 5% 5% 4 6% 7% 39%	4378
June	1st to 10th	Night	13% 5% 2 5% 4 4 4 4 5% 8% 46%	1597
	11th to 20th	Night	5% 3 1 4 4 4 4 5% 7% 9% 55%	1520
	21st to end	Night	2 3 1 5% 4 4 4 5% 8% 13% 50%	1520
July	1st to 10th	Night	6% 5% 2 6% 4 4 5% 5% 6% 9% 46%	2530
	11th to 20th	Night	6% 4 2 5% 3 3 4 3 6% 9% 55%	2530
	21st to end	Night	9% 8% 3 10% 6% 6% 6% 5% 8% 8% 31%	2903
August	1st to 10th	Night	5% 3 1 4 3 4 4 3 6% 8% 60%	3080
	11th to 20th	Night	5% 4 1 6% 4 4 5% 4 7% 9% 52%	3100
	21st to end	Night	5% 3 1 4 3 3 4 4 5% 8% 61%	3476
September	1st to 10th	Night	10% 5% 2 5% 4 3 4 3 4 6% 54%	1900
	11th to 20th	Night	9% 5% 3 5% 4 3 4 4 5% 7% 51%	2047
	21st to end	Night	11% 6% 2 4 3 4 3 3 4 7% 53%	2090
October	1st to 10th	Night	8% 5% 1 5% 2 3 4 2 3 6% 61%	2090
	11th to 20th	Night	15% 5% 2 5% 3 3 3 3 4 5% 54%	2218
	21st to end	Night	18% 7% 2 4 3 3 3 3 4 6% 47%	2665
November	1st to 10th	Night	13% 6% 2 5% 4 3 2 3 4 7% 52%	2536
	11th to 20th	Night	14% 6% 2 5% 4 3 3 3 5% 6% 49%	2600
	21st to end	Night	17% 8% 2 5% 4 3 3 3 4 6% 46%	2600
December	1st to 10th	Night	18% 9% 3 7% 3 3 3 3 4 4 43%	4250
	11th to 20th	Night	20% 9% 2 6% 4 3 3 3 5% 6% 40%	5057
	21st to end	Night	22% 13% 5% 9% 5% 4 4 3 4 5% 27%	6996

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	54% 5% 10% 21% 10% 2	3618
	11th to 20th	Day	46% 4 5% 25% 18% 2	3620
	21st to end	Day	49% 4 8% 18% 16% 5%	4661
February	1st to 10th	Day	49% 4 10% 23% 13% 2	2000
	11th to 20th	Day	51% 4 7% 20% 13% 4	1958
	21st to end	Day	49% 4 8% 17% 16% 5%	1650
March	1st to 10th	Day	51% 3 4 19% 18% 6%	4480
	11th to 20th	Day	39% 4 7% 26% 21% 4	4648
	21st to end	Day	43% 4 10% 27% 16% 1	5967
April	1st to 10th	Day	40% 6% 11% 22% 19% 2	2400
	11th to 20th	Day	44% 5% 8% 22% 17% 4	2374
	21st to end	Day	42% 5% 10% 27% 13% 2	2405
May	1st to 10th	Day	54% 7% 12% 17% 9% 1	5897
	11th to 20th	Day	49% 6% 13% 21% 10%	5865
	21st to end	Day	43% 7% 10% 20% 17% 3	6486
June	1st to 10th	Day	34% 7% 13% 24% 19% 3	2787
	11th to 20th	Day	29% 9% 14% 26% 19% 3	2660
	21st to end	Day	31% 9% 15% 23% 17% 5%	2660
July	1st to 10th	Day	40% 6% 14% 27% 11% 2	4371
	11th to 20th	Day	32% 5% 13% 37% 11% 2	4365
	21st to end	Day	53% 6% 13% 20% 8% 1	4495
August	1st to 10th	Day	26% 5% 14% 33% 22% 1	3818
	11th to 20th	Day	38% 5% 12% 25% 18% 1	3765
	21st to end	Day	26% 5% 10% 36% 20% 3	4179
September	1st to 10th	Day	36% 8% 10% 23% 19% 4	2280
	11th to 20th	Day	36% 6% 11% 22% 22% 3	2114
	21st to end	Day	35% 5% 9% 24% 22% 6%	2090
October	1st to 10th	Day	18% 3 6% 19% 47% 8%	3480
	11th to 20th	Day	23% 3 7% 27% 30% 10%	3236
	21st to end	Day	30% 3 5% 27% 28% 6%	3157
November	1st to 10th	Day	33% 4 10% 23% 25% 5%	1762
	11th to 20th	Day	38% 4 8% 24% 21% 6%	1800
	21st to end	Day	45% 4 6% 26% 16% 4	1800
December	1st to 10th	Day	43% 3 7% 28% 18% 1	2930
	11th to 20th	Day	52% 4 8% 20% 13% 3	3138
	21st to end	Day	58% 5% 11% 18% 7%	3982
January	1st to 10th	Night	52% 3 9% 23% 11% 1	6348
	11th to 20th	Night	50% 4 5% 21% 17% 3	6360
	21st to end	Night	48% 3 7% 22% 16% 4	6290
February	1st to 10th	Night	55% 4 9% 18% 12% 1	2400
	11th to 20th	Night	51% 4 6% 21% 15% 3	2339
	21st to end	Night	51% 4 8% 18% 16% 4	1980
March	1st to 10th	Night	51% 3 5% 16% 20% 6%	5373
	11th to 20th	Night	37% 4 8% 22% 20% 10%	5310
	21st to end	Night	44% 4 10% 25% 15% 2	4993
April	1st to 10th	Night	36% 5% 11% 25% 19% 3	2000
	11th to 20th	Night	38% 5% 9% 21% 21% 6%	1975
	21st to end	Night	41% 6% 10% 24% 17% 2	1994
May	1st to 10th	Night	49% 6% 12% 22% 10% 1	4060
	11th to 20th	Night	49% 7% 14% 19% 10% 1	4033
	21st to end	Night	43% 7% 13% 22% 15% 1	4386
June	1st to 10th	Night	36% 4 12% 24% 20% 3	1597
	11th to 20th	Night	23% 7% 16% 26% 25% 4	1520
	21st to end	Night	23% 9% 17% 27% 19% 6%	1520
July	1st to 10th	Night	33% 6% 13% 30% 15% 3	2490
	11th to 20th	Night	26% 5% 13% 37% 16% 3	2482
	21st to end	Night	49% 7% 14% 21% 9% 1	2810
August	1st to 10th	Night	23% 5% 12% 38% 21% 1	3069
	11th to 20th	Night	28% 5% 16% 29% 19% 1	3130
	21st to end	Night	22% 5% 9% 37% 24% 3	3476
September	1st to 10th	Night	31% 6% 9% 26% 23% 5%	1900
	11th to 20th	Night	33% 5% 8% 26% 24% 4	2047
	21st to end	Night	31% 5% 9% 23% 25% 7%	2090
October	1st to 10th	Night	18% 3 5% 15% 48% 11%	3480
	11th to 20th	Night	21% 2 5% 22% 39% 10%	3678
	21st to end	Night	29% 2 7% 23% 28% 11%	4390
November	1st to 10th	Night	34% 3 7% 24% 25% 6%	2536
	11th to 20th	Night	35% 4 6% 24% 22% 9%	2600
	21st to end	Night	41% 4 8% 25% 20% 4	2600
December	1st to 10th	Night	46% 3 8% 24% 19% 1	4250
	11th to 20th	Night	46% 3 9% 23% 18% 2	5059
	21st to end	Night	59% 5% 8% 18% 8% 2	6996

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	29% 25% 30% 14% 3	300
	11th to 20th	Day	28% 28% 35% 8% 2	300
	21st to end	Day	24% 28% 38% 9% 1	330
February	1st to 10th	Day	29% 27% 32% 9% 2 1	300
	11th to 20th	Day	34% 29% 30% 6% 1	300
	21st to end	Day	33% 22% 34% 10% 1	249
March	1st to 10th	Day	28% 24% 33% 11% 3	300
	11th to 20th	Day	28% 27% 31% 11% 3	350
	21st to end	Day	27% 21% 34% 13% 5%	550
April	1st to 10th	Day	23% 20% 29% 21% 5% 1	500
	11th to 20th	Day	24% 19% 28% 21% 7% 1	492
	21st to end	Day	21% 18% 30% 21% 8% 2	500
May	1st to 10th	Day	21% 19% 29% 21% 7% 3	503
	11th to 20th	Day	19% 10% 26% 29% 11% 4	527
	21st to end	Day	12% 8% 28% 27% 15% 10%	586
June	1st to 10th	Day	12% 6% 23% 28% 21% 10%	726
	11th to 20th	Day	5% 4 23% 36% 22% 9%	680
	21st to end	Day	6% 4 26% 34% 20% 10%	680
July	1st to 10th	Day	11% 3 16% 28% 25% 17%	671
	11th to 20th	Day	9% 4 18% 31% 28% 11%	668
	21st to end	Day	9% 3 17% 32% 26% 13%	643
August	1st to 10th	Day	12% 2 13% 33% 26% 14%	486
	11th to 20th	Day	14% 3 16% 35% 26% 7%	479
	21st to end	Day	10% 2 13% 28% 31% 17%	539
September	1st to 10th	Day	10% 3 18% 29% 28% 12%	490
	11th to 20th	Day	10% 3 14% 28% 32% 12%	490
	21st to end	Day	19% 8% 20% 26% 20% 8%	490
October	1st to 10th	Day	9% 6% 26% 32% 21% 6%	490
	11th to 20th	Day	14% 14% 34% 22% 12% 4	357
	21st to end	Day	26% 17% 29% 20% 6% 1	330
November	1st to 10th	Day	16% 16% 36% 19% 11% 1	300
	11th to 20th	Day	18% 22% 34% 22% 4 1	300
	21st to end	Day	26% 14% 33% 19% 7% 1	300
December	1st to 10th	Day	24% 23% 31% 16% 6%	300
	11th to 20th	Day	27% 17% 34% 17% 4	300
	21st to end	Day	27% 25% 34% 12% 2	330
January	1st to 10th	Night	26% 19% 30% 21% 4	1000
	11th to 20th	Night	28% 18% 33% 18% 3	1000
	21st to end	Night	23% 19% 36% 20% 2	1013
February	1st to 10th	Night	27% 17% 33% 20% 2	800
	11th to 20th	Night	28% 20% 32% 18% 2	783
	21st to end	Night	27% 19% 35% 18% 1	660
March	1st to 10th	Night	23% 18% 31% 24% 5%	800
	11th to 20th	Night	22% 17% 34% 22% 5%	800
	21st to end	Night	22% 14% 29% 28% 6%	678
April	1st to 10th	Night	18% 13% 35% 25% 8% 1	600
	11th to 20th	Night	19% 14% 30% 26% 11%	593
	21st to end	Night	18% 12% 32% 28% 10% 1	600
May	1st to 10th	Night	21% 9% 30% 25% 13% 2	600
	11th to 20th	Night	14% 7% 23% 35% 20% 2	591
	21st to end	Night	10% 4 23% 33% 27% 4	650
June	1st to 10th	Night	14% 3 17% 34% 28% 3	599
	11th to 20th	Night	5% 2 15% 44% 30% 3	570
	21st to end	Night	3 2 19% 39% 33% 4	570
July	1st to 10th	Night	8% 1 11% 33% 38% 10%	555
	11th to 20th	Night	9% 2 12% 28% 42% 7%	552
	21st to end	Night	8% 3 13% 35% 32% 9%	624
August	1st to 10th	Night	8% 1 9% 34% 40% 7%	567
	11th to 20th	Night	8% 2 11% 41% 34% 5%	564
	21st to end	Night	8% 2 7% 33% 41% 8%	627
September	1st to 10th	Night	12% 2 13% 33% 34% 5%	570
	11th to 20th	Night	11% 2 12% 30% 38% 6%	717
	21st to end	Night	13% 5% 22% 30% 26% 5%	760
October	1st to 10th	Night	11% 6% 19% 33% 27% 5%	760
	11th to 20th	Night	17% 8% 26% 31% 16% 2	760
	21st to end	Night	20% 11% 29% 26% 12% 1	836
November	1st to 10th	Night	14% 11% 29% 31% 13% 1	780
	11th to 20th	Night	16% 13% 33% 28% 9% 1	800
	21st to end	Night	23% 14% 27% 26% 10% 1	800
December	1st to 10th	Night	26% 12% 33% 25% 5%	800
	11th to 20th	Night	25% 13% 31% 25% 6%	910
	21st to end	Night	29% 15% 30% 23% 3	1100

Page generated at 2025-06-07 09:28:18. Version ac07

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