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 2026-10-14.

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% 7% 3 7% 4 4 4 4 6% 8% 41%	148765
	Night	14% 8% 3 6% 4 4 4 3 5% 7% 43%	143145
Transparency	Day	41% 4 11% 24% 16% 3	152409
	Night	41% 4 10% 24% 18% 3	147576
Seeing	Day	17% 12% 26% 24% 15% 6%	18048
	Night	18% 10% 26% 28% 16% 2	27725

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% 11% 7% 9% 5% 4 4 3 5% 5% 33%	4691
	11th to 20th	Day	12% 8% 3 8% 5% 3 4 2 4 6% 46%	4710
	21st to end	Day	19% 10% 4 7% 4 4 4 3 4 5% 36%	6037
February	1st to 10th	Day	17% 12% 4 6% 4 3 2 4 5% 6% 37%	2100
	11th to 20th	Day	20% 10% 4 7% 4 4 3 3 4 5% 36%	2048
	21st to end	Day	17% 10% 3 7% 5% 4 5% 3 4 6% 35%	1730
March	1st to 10th	Day	16% 13% 4 7% 4 3 3 3 4 4 37%	4580
	11th to 20th	Day	13% 9% 3 6% 3 3 3 2 4 5% 49%	4751
	21st to end	Day	12% 8% 3 8% 4 4 4 3 6% 6% 42%	6097
April	1st to 10th	Day	15% 6% 2 6% 5% 4 4 3 5% 7% 44%	2520
	11th to 20th	Day	16% 7% 3 7% 5% 4 4 3 5% 6% 40%	2494
	21st to end	Day	16% 7% 2 6% 4 4 5% 3 6% 8% 40%	2525
May	1st to 10th	Day	17% 8% 3 8% 5% 5% 5% 4 6% 8% 31%	7616
	11th to 20th	Day	15% 7% 3 7% 5% 5% 4 4 6% 8% 37%	7626
	21st to end	Day	18% 9% 3 8% 5% 5% 5% 4 6% 6% 31%	8444
June	1st to 10th	Day	11% 5% 2 5% 4 4 5% 4 6% 9% 46%	2940
	11th to 20th	Day	6% 5% 2 5% 5% 5% 5% 5% 7% 9% 46%	2940
	21st to end	Day	6% 4 2 6% 5% 5% 5% 4 7% 11% 45%	2940
July	1st to 10th	Day	9% 6% 3 7% 5% 5% 6% 5% 7% 10% 37%	8280
	11th to 20th	Day	6% 5% 2 6% 5% 6% 7% 6% 9% 13% 35%	8280
	21st to end	Day	8% 6% 3 7% 5% 5% 6% 5% 8% 12% 35%	8680
August	1st to 10th	Day	7% 4 2 6% 4 4 4 4 7% 9% 49%	5621
	11th to 20th	Day	7% 5% 2 6% 4 5% 5% 4 7% 10% 46%	5486
	21st to end	Day	4 3 1 4 3 3 3 3 5% 9% 62%	6080
September	1st to 10th	Day	10% 5% 2 5% 5% 4 6% 4 5% 8% 46%	2520
	11th to 20th	Day	10% 4 1 6% 4 4 4 4 5% 7% 48%	2336
	21st to end	Day	12% 5% 2 6% 5% 3 4 3 5% 6% 49%	2310
October	1st to 10th	Day	11% 4 2 5% 2 3 3 2 4 8% 57%	2310
	11th to 20th	Day	11% 5% 2 6% 4 3 4 3 4 6% 54%	2093
	21st to end	Day	20% 7% 2 5% 3 2 3 3 4 5% 47%	2033
November	1st to 10th	Day	11% 6% 3 6% 3 3 4 2 4 6% 53%	1852
	11th to 20th	Day	16% 7% 2 4 4 3 4 3 5% 6% 47%	1890
	21st to end	Day	17% 9% 3 6% 3 3 4 3 4 5% 42%	1890
December	1st to 10th	Day	16% 10% 2 6% 3 3 4 3 4 5% 44%	3020
	11th to 20th	Day	17% 12% 4 8% 4 4 4 3 5% 5% 35%	3225
	21st to end	Day	20% 14% 4 8% 5% 5% 4 3 4 6% 26%	4070
January	1st to 10th	Night	17% 12% 3 8% 3 3 4 3 5% 5% 38%	8232
	11th to 20th	Night	14% 10% 4 9% 4 4 4 2 3 4 41%	8280
	21st to end	Night	19% 10% 5% 8% 4 4 3 2 4 5% 37%	8133
February	1st to 10th	Night	22% 10% 4 8% 4 4 3 3 4 4 32%	2520
	11th to 20th	Night	21% 8% 3 8% 4 4 3 2 4 5% 37%	2458
	21st to end	Night	21% 8% 3 7% 4 4 3 3 5% 4 37%	2076
March	1st to 10th	Night	18% 12% 4 7% 3 4 4 3 4 5% 36%	5493
	11th to 20th	Night	12% 7% 2 5% 4 3 4 3 5% 6% 49%	5427
	21st to end	Night	14% 8% 3 7% 5% 4 4 3 5% 7% 40%	5104
April	1st to 10th	Night	13% 5% 2 5% 3 4 4 4 6% 7% 47%	2100
	11th to 20th	Night	14% 6% 2 5% 4 4 4 4 5% 7% 45%	2075
	21st to end	Night	15% 7% 3 5% 5% 4 4 3 6% 8% 40%	2094
May	1st to 10th	Night	17% 9% 3 6% 5% 4 4 4 6% 8% 34%	5237
	11th to 20th	Night	13% 8% 3 8% 5% 5% 5% 4 6% 8% 37%	5234
	21st to end	Night	17% 9% 3 8% 6% 5% 5% 4 6% 7% 32%	5705
June	1st to 10th	Night	12% 5% 2 5% 4 4 4 4 6% 9% 46%	1680
	11th to 20th	Night	6% 4 2 5% 4 4 4 5% 6% 9% 53%	1680
	21st to end	Night	3 3 1 5% 4 4 5% 5% 8% 13% 50%	1680
July	1st to 10th	Night	6% 5% 2 7% 4 4 5% 5% 6% 9% 45%	4708
	11th to 20th	Night	6% 5% 2 6% 4 5% 5% 5% 8% 12% 43%	4707
	21st to end	Night	6% 6% 3 7% 5% 5% 6% 5% 8% 12% 37%	5400
August	1st to 10th	Night	6% 5% 2 5% 4 4 4 3 6% 8% 54%	4510
	11th to 20th	Night	4 3 1 4 4 4 4 3 6% 9% 58%	4560
	21st to end	Night	4 3 1 4 3 3 3 3 5% 8% 63%	5046
September	1st to 10th	Night	9% 4 2 4 4 3 4 3 4 6% 55%	2100
	11th to 20th	Night	9% 4 3 5% 4 3 4 3 5% 7% 53%	2263
	21st to end	Night	11% 6% 2 4 3 3 3 3 4 7% 52%	2310
October	1st to 10th	Night	8% 5% 2 5% 3 3 4 3 3 6% 61%	2310
	11th to 20th	Night	15% 5% 2 4 3 2 3 2 3 5% 56%	2369
	21st to end	Night	18% 8% 2 4 3 3 3 3 4 6% 46%	2805
November	1st to 10th	Night	12% 6% 2 5% 3 3 2 3 4 6% 52%	2666
	11th to 20th	Night	13% 6% 2 5% 4 3 3 3 5% 6% 50%	2730
	21st to end	Night	18% 8% 2 5% 4 3 3 3 4 6% 45%	2730
December	1st to 10th	Night	18% 9% 3 7% 3 3 3 3 4 4 42%	4380
	11th to 20th	Night	20% 9% 2 6% 4 4 3 3 5% 6% 40%	5193
	21st to end	Night	23% 12% 5% 9% 5% 4 4 3 4 5% 27%	7150

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	53% 4 11% 22% 8% 1	4692
	11th to 20th	Day	41% 3 4 29% 21% 2	4710
	21st to end	Day	51% 3 8% 19% 14% 5%	6037
February	1st to 10th	Day	49% 4 10% 23% 13% 2	2100
	11th to 20th	Day	51% 4 8% 21% 13% 4	2058
	21st to end	Day	50% 4 8% 18% 15% 5%	1730
March	1st to 10th	Day	51% 3 4 18% 18% 6%	4580
	11th to 20th	Day	39% 4 7% 26% 20% 4	4751
	21st to end	Day	42% 4 10% 27% 16% 1	6099
April	1st to 10th	Day	39% 5% 11% 23% 19% 2	2520
	11th to 20th	Day	44% 5% 9% 22% 17% 4	2494
	21st to end	Day	41% 5% 10% 28% 13% 2	2525
May	1st to 10th	Day	49% 6% 12% 22% 10% 1	7651
	11th to 20th	Day	46% 5% 13% 21% 14% 1	7630
	21st to end	Day	53% 6% 10% 17% 13% 2	8458
June	1st to 10th	Day	35% 7% 13% 24% 19% 3	2940
	11th to 20th	Day	31% 8% 13% 27% 18% 3	2940
	21st to end	Day	31% 8% 15% 25% 16% 4	2940
July	1st to 10th	Day	42% 4 13% 28% 11% 1	8211
	11th to 20th	Day	40% 5% 19% 29% 7% 1	8205
	21st to end	Day	41% 4 23% 24% 7% 1	8489
August	1st to 10th	Day	32% 4 13% 29% 21% 1	5608
	11th to 20th	Day	34% 4 16% 28% 17% 1	5522
	21st to end	Day	21% 4 10% 40% 23% 2	6079
September	1st to 10th	Day	35% 7% 9% 24% 20% 4	2520
	11th to 20th	Day	35% 6% 10% 24% 23% 2	2336
	21st to end	Day	36% 5% 8% 22% 22% 6%	2310
October	1st to 10th	Day	19% 2 5% 19% 46% 8%	3700
	11th to 20th	Day	23% 3 7% 27% 31% 10%	3372
	21st to end	Day	30% 3 5% 27% 28% 6%	3258
November	1st to 10th	Day	34% 3 9% 24% 25% 5%	1852
	11th to 20th	Day	38% 4 8% 24% 21% 5%	1890
	21st to end	Day	45% 3 6% 26% 16% 4	1890
December	1st to 10th	Day	44% 3 7% 28% 17% 1	3020
	11th to 20th	Day	52% 4 9% 20% 13% 2	3222
	21st to end	Day	58% 5% 11% 18% 7%	4070
January	1st to 10th	Night	50% 2 12% 25% 10% 1	8233
	11th to 20th	Night	47% 3 4 22% 20% 3	8280
	21st to end	Night	52% 2 8% 20% 15% 3	8133
February	1st to 10th	Night	55% 4 9% 18% 12% 1	2520
	11th to 20th	Night	51% 3 6% 22% 14% 3	2459
	21st to end	Night	51% 4 8% 18% 16% 3	2076
March	1st to 10th	Night	51% 3 5% 15% 19% 5%	5493
	11th to 20th	Night	37% 4 8% 22% 19% 10%	5427
	21st to end	Night	44% 4 10% 25% 14% 2	5104
April	1st to 10th	Night	36% 5% 12% 25% 19% 3	2100
	11th to 20th	Night	38% 5% 11% 20% 21% 6%	2075
	21st to end	Night	41% 6% 10% 24% 18% 2	2094
May	1st to 10th	Night	48% 5% 12% 24% 10% 1	5264
	11th to 20th	Night	45% 6% 14% 20% 14% 1	5235
	21st to end	Night	51% 6% 13% 19% 11% 1	5715
June	1st to 10th	Night	36% 4 12% 25% 20% 4	1680
	11th to 20th	Night	26% 7% 15% 25% 24% 3	1680
	21st to end	Night	24% 8% 16% 28% 18% 5%	1680
July	1st to 10th	Night	35% 6% 14% 27% 16% 2	4670
	11th to 20th	Night	34% 7% 22% 26% 9% 1	4662
	21st to end	Night	39% 4 22% 26% 8%	5278
August	1st to 10th	Night	29% 4 13% 33% 21% 1	4499
	11th to 20th	Night	24% 4 19% 36% 17% 1	4590
	21st to end	Night	21% 3 8% 40% 25% 2	5046
September	1st to 10th	Night	30% 6% 9% 27% 23% 5%	2100
	11th to 20th	Night	31% 4 9% 27% 24% 4	2263
	21st to end	Night	33% 5% 9% 22% 25% 7%	2310
October	1st to 10th	Night	19% 2 5% 16% 46% 12%	3700
	11th to 20th	Night	21% 2 5% 22% 39% 11%	3829
	21st to end	Night	30% 2 7% 23% 28% 10%	4530
November	1st to 10th	Night	34% 3 7% 25% 25% 6%	2666
	11th to 20th	Night	35% 4 6% 25% 21% 9%	2730
	21st to end	Night	42% 4 8% 25% 19% 4	2730
December	1st to 10th	Night	46% 3 8% 24% 18% 1	4380
	11th to 20th	Night	46% 3 9% 23% 18% 2	5195
	21st to end	Night	59% 5% 8% 18% 8% 2	7150

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	28% 25% 29% 14% 3	330
	11th to 20th	Day	28% 29% 35% 7% 2	330
	21st to end	Day	26% 28% 37% 9% 1	363
February	1st to 10th	Day	28% 27% 33% 9% 3 1	330
	11th to 20th	Day	34% 30% 29% 6% 1	330
	21st to end	Day	34% 23% 33% 10% 1	273
March	1st to 10th	Day	29% 24% 34% 10% 3	330
	11th to 20th	Day	28% 27% 33% 10% 2	383
	21st to end	Day	26% 21% 36% 13% 4	594
April	1st to 10th	Day	23% 20% 30% 21% 5% 1	540
	11th to 20th	Day	24% 19% 29% 20% 6% 1	532
	21st to end	Day	20% 18% 31% 21% 8% 2	540
May	1st to 10th	Day	21% 19% 30% 20% 6% 3	543
	11th to 20th	Day	19% 11% 28% 28% 11% 4	567
	21st to end	Day	14% 8% 27% 27% 14% 9%	631
June	1st to 10th	Day	12% 6% 25% 28% 21% 9%	780
	11th to 20th	Day	7% 4 24% 35% 21% 8%	780
	21st to end	Day	7% 4 24% 34% 21% 10%	780
July	1st to 10th	Day	12% 3 15% 27% 26% 17%	771
	11th to 20th	Day	9% 3 17% 33% 28% 11%	768
	21st to end	Day	9% 3 18% 32% 26% 13%	743
August	1st to 10th	Day	12% 2 13% 34% 26% 12%	566
	11th to 20th	Day	12% 2 16% 36% 26% 7%	559
	21st to end	Day	9% 2 14% 29% 31% 15%	627
September	1st to 10th	Day	9% 3 19% 31% 27% 11%	570
	11th to 20th	Day	9% 3 14% 28% 34% 11%	570
	21st to end	Day	18% 8% 22% 27% 19% 7%	570
October	1st to 10th	Day	10% 6% 27% 33% 20% 5%	570
	11th to 20th	Day	14% 12% 33% 25% 12% 3	402
	21st to end	Day	28% 18% 29% 19% 6% 1	363
November	1st to 10th	Day	18% 16% 36% 19% 10% 1	330
	11th to 20th	Day	17% 22% 35% 22% 4 1	330
	21st to end	Day	27% 13% 34% 18% 7% 1	330
December	1st to 10th	Day	25% 24% 31% 15% 5%	330
	11th to 20th	Day	26% 18% 35% 16% 3	330
	21st to end	Day	28% 26% 34% 11% 1	363
January	1st to 10th	Night	26% 18% 30% 21% 3	1050
	11th to 20th	Night	27% 19% 33% 17% 3	1050
	21st to end	Night	23% 19% 36% 20% 2	1063
February	1st to 10th	Night	26% 17% 34% 20% 2	840
	11th to 20th	Night	28% 20% 33% 18% 2	823
	21st to end	Night	27% 18% 35% 19% 1	692
March	1st to 10th	Night	23% 18% 31% 23% 5%	840
	11th to 20th	Night	23% 17% 34% 22% 5%	840
	21st to end	Night	22% 15% 30% 27% 6%	712
April	1st to 10th	Night	17% 13% 36% 26% 8% 1	630
	11th to 20th	Night	19% 14% 31% 25% 11%	623
	21st to end	Night	18% 12% 32% 27% 10% 1	630
May	1st to 10th	Night	21% 9% 30% 25% 13% 2	630
	11th to 20th	Night	14% 8% 23% 35% 19% 2	621
	21st to end	Night	11% 4 22% 33% 26% 4	683
June	1st to 10th	Night	13% 3 18% 35% 28% 3	630
	11th to 20th	Night	7% 2 16% 42% 29% 3	630
	21st to end	Night	4 2 19% 38% 34% 4	630
July	1st to 10th	Night	8% 1 10% 33% 39% 9%	615
	11th to 20th	Night	8% 2 11% 29% 42% 7%	612
	21st to end	Night	8% 2 13% 35% 33% 9%	690
August	1st to 10th	Night	8% 1 10% 34% 40% 7%	627
	11th to 20th	Night	8% 2 11% 41% 34% 5%	624
	21st to end	Night	8% 2 8% 35% 40% 8%	693
September	1st to 10th	Night	12% 2 13% 33% 35% 5%	630
	11th to 20th	Night	11% 2 12% 31% 38% 6%	793
	21st to end	Night	13% 5% 21% 31% 25% 5%	840
October	1st to 10th	Night	11% 5% 19% 35% 26% 5%	840
	11th to 20th	Night	17% 8% 26% 32% 16% 2	813
	21st to end	Night	22% 10% 30% 26% 12% 1	880
November	1st to 10th	Night	14% 11% 30% 31% 13% 1	820
	11th to 20th	Night	16% 13% 34% 28% 9%	840
	21st to end	Night	24% 14% 27% 26% 9% 1	840
December	1st to 10th	Night	26% 12% 32% 25% 5%	840
	11th to 20th	Night	25% 13% 32% 24% 6%	956
	21st to end	Night	30% 15% 30% 22% 3	1155

Page generated at 2026-10-11 04:06:27. Version ac07

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