Pickersville Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Pickersville Observatory clear sky chart from 2005-11-06 to 2026-09-29.

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%	148130
	Night	13% 6% 2 6% 4 4 4 4 5% 7% 43%	143278
Transparency	Day	38% 7% 12% 20% 17% 5%	151733
	Night	38% 7% 11% 19% 19% 6%	147747
Seeing	Day	15% 8% 23% 25% 20% 9%	18011
	Night	15% 7% 25% 34% 18% 2	28287

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	13% 5% 2 6% 3 3 3 2 3 5% 55%	5258
	11th to 20th	Day	13% 5% 1 5% 3 2 2 2 3 4 59%	5280
	21st to end	Day	16% 8% 3 8% 4 4 4 4 4 5% 41%	5780
February	1st to 10th	Day	15% 6% 2 6% 3 4 4 3 5% 8% 43%	1890
	11th to 20th	Day	21% 6% 2 5% 3 3 3 2 4 5% 44%	1890
	21st to end	Day	19% 7% 3 5% 4 4 4 3 4 6% 42%	1877
March	1st to 10th	Day	19% 7% 2 6% 4 4 4 4 5% 6% 39%	5045
	11th to 20th	Day	10% 5% 2 6% 4 3 4 3 5% 6% 53%	5090
	21st to end	Day	13% 6% 2 6% 4 4 4 3 5% 6% 49%	5586
April	1st to 10th	Day	10% 4 1 4 4 4 3 3 6% 7% 54%	2452
	11th to 20th	Day	10% 4 2 5% 3 3 4 4 6% 7% 51%	2494
	21st to end	Day	11% 5% 2 5% 4 4 4 3 6% 7% 50%	2520
May	1st to 10th	Day	11% 6% 3 8% 5% 5% 5% 4 6% 9% 38%	7376
	11th to 20th	Day	13% 6% 2 6% 4 4 5% 4 6% 8% 42%	7626
	21st to end	Day	11% 6% 3 8% 5% 5% 5% 5% 7% 9% 36%	8391
June	1st to 10th	Day	9% 6% 2 7% 5% 6% 5% 5% 7% 9% 38%	2730
	11th to 20th	Day	8% 5% 2 5% 5% 5% 6% 5% 7% 11% 42%	2730
	21st to end	Day	7% 5% 2 6% 5% 5% 6% 6% 8% 11% 40%	2730
July	1st to 10th	Day	7% 5% 2 6% 5% 6% 7% 5% 10% 13% 35%	7680
	11th to 20th	Day	8% 6% 3 8% 5% 6% 7% 6% 9% 12% 29%	7680
	21st to end	Day	11% 6% 3 8% 6% 6% 6% 5% 8% 11% 31%	8340
August	1st to 10th	Day	16% 9% 3 10% 6% 6% 6% 5% 8% 11% 18%	6014
	11th to 20th	Day	7% 5% 3 7% 5% 5% 5% 5% 8% 13% 37%	5676
	21st to end	Day	9% 5% 2 6% 4 4 5% 4 7% 10% 44%	6080
September	1st to 10th	Day	8% 5% 2 6% 5% 4 5% 5% 6% 9% 44%	2520
	11th to 20th	Day	13% 6% 2 7% 4 5% 4 3 6% 7% 42%	2405
	21st to end	Day	18% 7% 3 6% 5% 5% 4 4 6% 7% 37%	2228
October	1st to 10th	Day	14% 6% 3 5% 3 3 4 3 5% 6% 47%	2000
	11th to 20th	Day	11% 5% 2 5% 3 3 2 2 4 5% 57%	2000
	21st to end	Day	12% 5% 2 5% 4 3 3 2 4 5% 57%	2200
November	1st to 10th	Day	13% 6% 2 5% 3 3 3 3 4 6% 53%	2057
	11th to 20th	Day	14% 5% 2 5% 3 3 3 4 4 6% 52%	2100
	21st to end	Day	14% 5% 1 4 3 3 4 3 5% 7% 50%	1833
December	1st to 10th	Day	12% 5% 2 5% 4 4 4 3 5% 5% 51%	2680
	11th to 20th	Day	16% 6% 2 7% 3 3 4 3 5% 6% 46%	3327
	21st to end	Day	16% 6% 2 6% 4 3 4 3 5% 6% 45%	4565
January	1st to 10th	Night	10% 6% 2 5% 3 3 3 3 5% 6% 55%	7635
	11th to 20th	Night	12% 6% 2 5% 3 3 3 3 4 4 55%	7680
	21st to end	Night	17% 8% 3 6% 4 4 3 3 4 5% 43%	8401
February	1st to 10th	Night	17% 6% 2 5% 3 4 4 3 4 7% 45%	2730
	11th to 20th	Night	19% 6% 2 6% 4 3 4 3 4 6% 42%	2614
	21st to end	Night	16% 7% 2 5% 3 4 4 3 5% 6% 47%	1924
March	1st to 10th	Night	18% 8% 3 7% 4 4 3 3 4 5% 41%	5028
	11th to 20th	Night	12% 5% 2 4 3 4 3 3 5% 7% 52%	5090
	21st to end	Night	13% 5% 2 5% 4 4 4 3 5% 5% 50%	5588
April	1st to 10th	Night	12% 5% 2 6% 3 3 4 3 5% 7% 49%	2168
	11th to 20th	Night	10% 4 2 6% 4 5% 4 3 5% 6% 52%	2075
	21st to end	Night	11% 3 2 5% 4 4 5% 4 6% 7% 49%	2100
May	1st to 10th	Night	11% 8% 3 8% 5% 5% 5% 4 6% 9% 37%	5520
	11th to 20th	Night	13% 6% 3 6% 4 4 4 3 5% 8% 43%	5234
	21st to end	Night	15% 7% 3 7% 5% 5% 5% 4 6% 9% 34%	5761
June	1st to 10th	Night	10% 5% 3 6% 6% 5% 5% 5% 7% 12% 38%	1890
	11th to 20th	Night	10% 5% 2 6% 6% 4 5% 5% 6% 9% 40%	1890
	21st to end	Night	7% 4 2 6% 6% 6% 6% 5% 9% 11% 39%	1890
July	1st to 10th	Night	9% 6% 3 8% 6% 5% 6% 5% 9% 11% 32%	5278
	11th to 20th	Night	12% 8% 3 8% 6% 6% 6% 5% 8% 13% 26%	5277
	21st to end	Night	13% 8% 4 9% 6% 6% 6% 5% 8% 10% 27%	5736
August	1st to 10th	Night	16% 8% 4 9% 6% 5% 6% 4 7% 11% 25%	4135
	11th to 20th	Night	6% 6% 3 8% 6% 6% 7% 5% 9% 13% 33%	4321
	21st to end	Night	8% 6% 2 7% 4 4 5% 5% 7% 10% 41%	5045
September	1st to 10th	Night	10% 4 2 6% 4 5% 4 3 6% 8% 48%	2100
	11th to 20th	Night	12% 6% 3 7% 5% 5% 5% 4 6% 7% 41%	2210
	21st to end	Night	19% 7% 3 7% 5% 5% 4 3 3 6% 38%	2347
October	1st to 10th	Night	14% 6% 2 5% 4 3 4 2 4 7% 49%	2400
	11th to 20th	Night	14% 4 2 5% 3 2 3 3 4 4 55%	2400
	21st to end	Night	12% 5% 2 5% 4 3 3 2 4 6% 56%	2640
November	1st to 10th	Night	13% 6% 2 5% 3 3 3 3 3 5% 54%	2461
	11th to 20th	Night	13% 6% 2 5% 3 3 3 3 4 7% 50%	2520
	21st to end	Night	13% 4 2 5% 3 3 3 3 5% 7% 52%	2773
December	1st to 10th	Night	13% 6% 2 5% 3 3 3 3 4 5% 53%	4720
	11th to 20th	Night	15% 7% 3 7% 5% 4 4 3 4 5% 41%	5064
	21st to end	Night	13% 6% 2 6% 4 3 4 3 5% 6% 48%	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	34% 3 8% 22% 26% 7%	5259
	11th to 20th	Day	31% 2 4 14% 35% 14%	5280
	21st to end	Day	46% 3 5% 16% 19% 10%	5780
February	1st to 10th	Day	40% 4 11% 19% 19% 6%	1890
	11th to 20th	Day	43% 4 6% 18% 23% 6%	1899
	21st to end	Day	44% 4 8% 17% 20% 6%	1877
March	1st to 10th	Day	45% 4 7% 15% 19% 9%	5045
	11th to 20th	Day	31% 5% 8% 15% 26% 14%	5090
	21st to end	Day	37% 4 9% 22% 21% 7%	5586
April	1st to 10th	Day	29% 5% 11% 24% 24% 7%	2452
	11th to 20th	Day	30% 6% 11% 24% 21% 7%	2494
	21st to end	Day	33% 5% 14% 23% 20% 4	2520
May	1st to 10th	Day	42% 8% 15% 23% 10% 2	7408
	11th to 20th	Day	39% 7% 12% 24% 16% 2	7630
	21st to end	Day	42% 9% 13% 18% 15% 3	8405
June	1st to 10th	Day	40% 10% 13% 20% 16% 2	2730
	11th to 20th	Day	34% 10% 17% 23% 14% 2	2730
	21st to end	Day	33% 12% 17% 23% 12% 2	2730
July	1st to 10th	Day	35% 12% 19% 25% 7% 1	7615
	11th to 20th	Day	43% 15% 23% 13% 6% 1	7611
	21st to end	Day	43% 11% 16% 17% 11%	8156
August	1st to 10th	Day	57% 12% 18% 9% 4	6001
	11th to 20th	Day	35% 10% 21% 26% 7%	5715
	21st to end	Day	35% 7% 15% 30% 12% 1	6080
September	1st to 10th	Day	34% 10% 14% 20% 18% 4	2520
	11th to 20th	Day	40% 7% 12% 17% 20% 3	2405
	21st to end	Day	46% 6% 10% 19% 15% 4	2228
October	1st to 10th	Day	34% 5% 9% 21% 25% 6%	3260
	11th to 20th	Day	21% 3 6% 20% 25% 26%	3240
	21st to end	Day	25% 3 5% 23% 26% 17%	3538
November	1st to 10th	Day	33% 4 8% 19% 27% 8%	2057
	11th to 20th	Day	34% 4 8% 21% 25% 8%	2100
	21st to end	Day	34% 4 7% 23% 24% 7%	1833
December	1st to 10th	Day	35% 5% 8% 18% 24% 10%	2680
	11th to 20th	Day	40% 4 11% 18% 21% 6%	3324
	21st to end	Day	40% 4 10% 23% 21% 2	4565
January	1st to 10th	Night	31% 4 10% 21% 29% 6%	7636
	11th to 20th	Night	33% 4 5% 13% 33% 11%	7680
	21st to end	Night	44% 3 5% 16% 23% 9%	8401
February	1st to 10th	Night	40% 4 9% 20% 21% 7%	2730
	11th to 20th	Night	44% 5% 9% 15% 20% 7%	2616
	21st to end	Night	39% 5% 8% 17% 23% 8%	1924
March	1st to 10th	Night	46% 5% 6% 12% 23% 8%	5028
	11th to 20th	Night	32% 5% 8% 12% 26% 17%	5090
	21st to end	Night	36% 5% 9% 23% 21% 6%	5588
April	1st to 10th	Night	35% 4 12% 18% 21% 8%	2168
	11th to 20th	Night	33% 5% 10% 23% 21% 8%	2075
	21st to end	Night	31% 8% 13% 25% 19% 4	2100
May	1st to 10th	Night	42% 8% 17% 20% 11% 2	5550
	11th to 20th	Night	39% 7% 14% 23% 17% 1	5235
	21st to end	Night	44% 9% 13% 20% 13% 1	5771
June	1st to 10th	Night	37% 10% 18% 21% 12% 2	1890
	11th to 20th	Night	38% 10% 18% 21% 12% 1	1890
	21st to end	Night	35% 12% 18% 23% 10% 2	1890
July	1st to 10th	Night	42% 11% 19% 22% 6% 1	5235
	11th to 20th	Night	46% 15% 21% 11% 6% 1	5226
	21st to end	Night	49% 10% 16% 15% 9% 1	5606
August	1st to 10th	Night	52% 12% 21% 12% 3	4124
	11th to 20th	Night	37% 13% 23% 21% 5%	4348
	21st to end	Night	36% 9% 14% 27% 13% 1	5045
September	1st to 10th	Night	34% 10% 14% 22% 16% 5%	2100
	11th to 20th	Night	40% 8% 13% 18% 18% 3	2210
	21st to end	Night	48% 7% 11% 17% 14% 3	2347
October	1st to 10th	Night	37% 5% 7% 21% 23% 6%	3920
	11th to 20th	Night	22% 3 6% 17% 26% 26%	3899
	21st to end	Night	25% 4 7% 25% 23% 17%	4252
November	1st to 10th	Night	34% 4 7% 18% 27% 10%	2461
	11th to 20th	Night	34% 4 9% 16% 26% 11%	2520
	21st to end	Night	33% 4 8% 22% 26% 8%	2773
December	1st to 10th	Night	33% 4 7% 16% 30% 10%	4720
	11th to 20th	Night	45% 5% 9% 16% 17% 8%	5066
	21st to end	Night	37% 5% 10% 24% 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	16% 18% 42% 19% 5%	330
	11th to 20th	Day	18% 23% 32% 19% 6%	330
	21st to end	Day	17% 19% 39% 19% 6%	363
February	1st to 10th	Day	19% 13% 40% 21% 6% 1	330
	11th to 20th	Day	33% 12% 37% 16% 1	377
	21st to end	Day	23% 15% 33% 21% 8% 1	446
March	1st to 10th	Day	17% 16% 31% 26% 9% 1	540
	11th to 20th	Day	16% 14% 38% 24% 6% 1	540
	21st to end	Day	15% 14% 35% 27% 8% 1	594
April	1st to 10th	Day	15% 15% 30% 25% 12% 2	540
	11th to 20th	Day	11% 10% 31% 26% 17% 5%	532
	21st to end	Day	15% 8% 25% 25% 22% 4	540
May	1st to 10th	Day	11% 10% 37% 23% 14% 5%	543
	11th to 20th	Day	15% 4 20% 27% 26% 8%	567
	21st to end	Day	16% 5% 17% 25% 23% 14%	617
June	1st to 10th	Day	12% 3 16% 34% 23% 12%	570
	11th to 20th	Day	10% 2 15% 28% 30% 15%	570
	21st to end	Day	6% 3 12% 27% 35% 16%	570
July	1st to 10th	Day	10% 3 7% 23% 35% 23%	565
	11th to 20th	Day	9% 2 7% 22% 37% 23%	564
	21st to end	Day	8% 2 10% 26% 37% 17%	620
August	1st to 10th	Day	15% 3 12% 24% 29% 17%	566
	11th to 20th	Day	12% 2 9% 22% 32% 23%	559
	21st to end	Day	12% 2 10% 25% 27% 23%	627
September	1st to 10th	Day	9% 2 14% 26% 27% 22%	570
	11th to 20th	Day	16% 4 11% 24% 30% 15%	570
	21st to end	Day	22% 3 18% 28% 21% 7%	562
October	1st to 10th	Day	15% 7% 18% 24% 25% 11%	530
	11th to 20th	Day	13% 6% 25% 28% 22% 6%	530
	21st to end	Day	13% 8% 22% 29% 21% 6%	583
November	1st to 10th	Day	17% 7% 23% 33% 15% 5%	535
	11th to 20th	Day	15% 10% 32% 31% 11% 2	540
	21st to end	Day	12% 11% 32% 26% 17% 2	322
December	1st to 10th	Day	19% 11% 38% 22% 10%	220
	11th to 20th	Day	18% 8% 39% 21% 12% 2	286
	21st to end	Day	21% 14% 34% 21% 8% 2	363
January	1st to 10th	Night	18% 12% 37% 27% 6% 1	840
	11th to 20th	Night	17% 12% 35% 30% 7%	840
	21st to end	Night	19% 9% 39% 30% 4	924
February	1st to 10th	Night	20% 9% 36% 31% 4	840
	11th to 20th	Night	23% 12% 40% 24% 1	823
	21st to end	Night	17% 13% 38% 27% 5%	692
March	1st to 10th	Night	17% 11% 33% 32% 6%	840
	11th to 20th	Night	17% 10% 39% 27% 7%	840
	21st to end	Night	15% 10% 39% 30% 6%	924
April	1st to 10th	Night	15% 12% 35% 32% 7%	840
	11th to 20th	Night	12% 9% 35% 34% 10% 1	831
	21st to end	Night	13% 7% 28% 42% 10% 1	840
May	1st to 10th	Night	9% 8% 33% 38% 12%	734
	11th to 20th	Night	15% 5% 22% 41% 17%	621
	21st to end	Night	13% 2 13% 40% 29% 1	683
June	1st to 10th	Night	10% 2 17% 44% 24% 2	630
	11th to 20th	Night	11% 3 14% 39% 28% 5%	630
	21st to end	Night	7% 2 12% 42% 35% 2	630
July	1st to 10th	Night	8% 2 9% 34% 42% 5%	615
	11th to 20th	Night	8% 2 6% 35% 43% 6%	612
	21st to end	Night	9% 3 10% 37% 37% 4	690
August	1st to 10th	Night	14% 3 9% 35% 37% 4	627
	11th to 20th	Night	11% 2 9% 32% 40% 6%	720
	21st to end	Night	12% 2 9% 35% 37% 6%	924
September	1st to 10th	Night	11% 2 12% 32% 38% 5%	840
	11th to 20th	Night	14% 4 12% 32% 34% 4	840
	21st to end	Night	22% 4 16% 33% 23% 2	833
October	1st to 10th	Night	17% 4 17% 32% 27% 4	800
	11th to 20th	Night	15% 4 25% 33% 21% 2	800
	21st to end	Night	14% 5% 24% 34% 21% 2	880
November	1st to 10th	Night	15% 6% 24% 37% 16% 3	820
	11th to 20th	Night	14% 11% 28% 35% 13% 1	840
	21st to end	Night	14% 6% 29% 35% 15% 1	840
December	1st to 10th	Night	19% 10% 28% 36% 6%	840
	11th to 20th	Night	19% 7% 29% 36% 9%	840
	21st to end	Night	18% 9% 29% 35% 8%	924

Page generated at 2026-09-26 04:18:38. Version ac07

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