Weeksville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Weeksville 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%	131383
	Night	13% 6% 2 6% 4 4 4 4 5% 7% 43%	131119
Transparency	Day	25% 38% 9% 14% 11% 3	134976
	Night	26% 37% 8% 14% 12% 4	135596
Seeing	Day	15% 10% 26% 27% 17% 5%	17292
	Night	16% 9% 27% 31% 15% 2	27008

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	11% 4 2 5% 3 3 4 2 4 6% 57%	5038
	11th to 20th	Day	14% 5% 2 5% 3 3 3 2 3 5% 55%	5280
	21st to end	Day	12% 10% 3 7% 5% 4 4 3 5% 5% 41%	5780
February	1st to 10th	Day	14% 7% 2 6% 4 4 4 4 6% 7% 42%	1890
	11th to 20th	Day	19% 7% 3 5% 4 4 3 3 4 5% 43%	2047
	21st to end	Day	16% 7% 2 6% 4 4 5% 3 5% 7% 41%	1730
March	1st to 10th	Day	18% 8% 3 6% 4 4 4 3 4 6% 40%	4854
	11th to 20th	Day	10% 5% 3 6% 3 4 3 3 4 6% 54%	5090
	21st to end	Day	12% 5% 2 5% 4 3 4 3 5% 6% 50%	5772
April	1st to 10th	Day	11% 5% 2 5% 4 3 4 3 5% 8% 52%	2520
	11th to 20th	Day	8% 6% 1 5% 4 4 4 4 6% 7% 51%	2494
	21st to end	Day	10% 5% 2 5% 5% 4 5% 4 6% 7% 48%	2520
May	1st to 10th	Day	10% 6% 2 8% 5% 6% 6% 4 7% 9% 37%	5417
	11th to 20th	Day	16% 7% 3 7% 5% 5% 5% 4 6% 9% 32%	5884
	21st to end	Day	12% 6% 3 6% 4 5% 5% 4 7% 9% 41%	6934
June	1st to 10th	Day	10% 5% 2 5% 5% 5% 5% 5% 8% 11% 40%	2800
	11th to 20th	Day	9% 6% 1 5% 4 4 6% 5% 9% 10% 41%	2800
	21st to end	Day	6% 4 2 6% 6% 4 6% 6% 8% 12% 40%	2800
July	1st to 10th	Day	9% 4 2 6% 5% 6% 7% 6% 10% 13% 33%	6360
	11th to 20th	Day	9% 5% 3 8% 6% 6% 6% 5% 9% 12% 31%	5948
	21st to end	Day	10% 5% 2 7% 5% 5% 6% 5% 9% 12% 33%	6424
August	1st to 10th	Day	18% 9% 3 9% 6% 6% 6% 4 7% 10% 23%	4138
	11th to 20th	Day	9% 6% 2 7% 5% 5% 6% 5% 7% 10% 38%	3850
	21st to end	Day	8% 4 2 6% 5% 6% 5% 5% 7% 11% 41%	4312
September	1st to 10th	Day	11% 6% 2 7% 5% 5% 5% 4 7% 8% 40%	2400
	11th to 20th	Day	14% 6% 3 7% 4 4 5% 3 6% 9% 38%	2400
	21st to end	Day	18% 8% 3 8% 4 4 4 4 6% 8% 34%	2153
October	1st to 10th	Day	14% 7% 2 5% 4 5% 4 3 4 7% 46%	2000
	11th to 20th	Day	12% 6% 2 6% 4 4 3 3 5% 5% 50%	2000
	21st to end	Day	11% 5% 2 6% 4 3 4 3 4 5% 52%	2200
November	1st to 10th	Day	15% 6% 2 5% 3 4 4 4 5% 6% 47%	1970
	11th to 20th	Day	14% 6% 2 4 3 3 3 3 5% 6% 50%	1890
	21st to end	Day	13% 5% 2 4 3 3 4 3 5% 7% 49%	1890
December	1st to 10th	Day	12% 5% 2 5% 4 3 3 3 5% 5% 53%	2680
	11th to 20th	Day	13% 7% 3 7% 4 4 4 3 4 6% 45%	3070
	21st to end	Day	13% 5% 2 5% 4 3 4 3 5% 8% 49%	4048
January	1st to 10th	Night	11% 5% 2 5% 3 3 4 3 4 7% 51%	7840
	11th to 20th	Night	10% 5% 2 6% 4 3 3 3 4 5% 54%	7680
	21st to end	Night	15% 8% 3 7% 4 4 4 3 4 6% 42%	8401
February	1st to 10th	Night	18% 7% 2 5% 3 3 4 4 6% 7% 42%	2729
	11th to 20th	Night	19% 8% 3 5% 4 4 4 3 5% 6% 40%	2458
	21st to end	Night	15% 8% 2 5% 4 4 3 3 4 6% 45%	2076
March	1st to 10th	Night	18% 8% 2 7% 4 4 4 3 5% 5% 41%	5216
	11th to 20th	Night	13% 6% 2 5% 4 4 5% 3 4 5% 49%	5090
	21st to end	Night	14% 6% 3 5% 4 4 4 3 4 5% 49%	5401
April	1st to 10th	Night	12% 5% 2 6% 4 4 4 4 5% 7% 46%	2100
	11th to 20th	Night	9% 7% 2 6% 4 4 4 4 5% 7% 49%	2075
	21st to end	Night	11% 6% 2 5% 4 3 3 4 5% 7% 48%	2100
May	1st to 10th	Night	10% 6% 3 8% 6% 6% 6% 5% 7% 10% 34%	4501
	11th to 20th	Night	18% 8% 3 7% 5% 5% 5% 4 6% 8% 31%	4047
	21st to end	Night	13% 7% 3 7% 5% 5% 4 4 6% 9% 38%	3920
June	1st to 10th	Night	11% 6% 2 6% 5% 4 5% 5% 7% 9% 41%	1600
	11th to 20th	Night	9% 5% 3 6% 4 6% 5% 5% 8% 11% 38%	1600
	21st to end	Night	8% 4 2 6% 5% 4 5% 5% 8% 10% 43%	1600
July	1st to 10th	Night	7% 4 2 6% 4 5% 6% 6% 9% 15% 35%	3598
	11th to 20th	Night	9% 5% 2 8% 6% 6% 7% 6% 9% 13% 29%	4003
	21st to end	Night	12% 6% 3 8% 5% 5% 6% 5% 7% 10% 35%	4427
August	1st to 10th	Night	16% 8% 3 8% 5% 5% 6% 5% 6% 9% 29%	2977
	11th to 20th	Night	10% 6% 3 8% 5% 6% 6% 5% 6% 9% 37%	3197
	21st to end	Night	9% 5% 2 7% 5% 4 5% 4 7% 10% 43%	3586
September	1st to 10th	Night	11% 5% 3 6% 5% 5% 4 4 6% 7% 42%	2000
	11th to 20th	Night	15% 8% 2 6% 5% 4 4 4 4 8% 39%	2000
	21st to end	Night	17% 8% 3 7% 5% 5% 5% 3 5% 8% 34%	2240
October	1st to 10th	Night	13% 5% 2 6% 5% 4 4 3 5% 6% 47%	2400
	11th to 20th	Night	14% 5% 2 5% 3 3 3 3 4 6% 51%	2400
	21st to end	Night	12% 5% 1 5% 3 3 3 3 5% 7% 53%	2640
November	1st to 10th	Night	14% 6% 1 5% 4 3 4 3 5% 6% 48%	2545
	11th to 20th	Night	15% 7% 2 5% 4 4 4 3 5% 6% 46%	2730
	21st to end	Night	11% 5% 2 5% 4 3 3 3 5% 7% 50%	2730
December	1st to 10th	Night	10% 5% 2 5% 3 4 4 4 5% 5% 52%	4717
	11th to 20th	Night	16% 6% 2 7% 5% 4 5% 4 5% 6% 39%	5345
	21st to end	Night	11% 5% 2 5% 3 3 4 3 5% 8% 50%	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	24% 21% 10% 20% 16% 9%	5039
	11th to 20th	Day	26% 20% 3 11% 32% 7%	5280
	21st to end	Day	38% 23% 4 16% 13% 5%	5780
February	1st to 10th	Day	18% 58% 6% 9% 6% 2	1890
	11th to 20th	Day	21% 58% 5% 6% 7% 2	2056
	21st to end	Day	19% 58% 4 9% 8% 2	1730
March	1st to 10th	Day	37% 29% 5% 11% 10% 7%	4854
	11th to 20th	Day	22% 29% 4 13% 22% 11%	5090
	21st to end	Day	24% 29% 10% 18% 15% 5%	5772
April	1st to 10th	Day	14% 59% 7% 10% 9% 1	2520
	11th to 20th	Day	13% 60% 5% 14% 6% 2	2494
	21st to end	Day	14% 59% 7% 12% 7% 1	2520
May	1st to 10th	Day	32% 33% 14% 14% 6% 1	5449
	11th to 20th	Day	37% 31% 13% 14% 6%	5888
	21st to end	Day	28% 31% 10% 21% 9%	6949
June	1st to 10th	Day	15% 64% 6% 9% 6% 1	2800
	11th to 20th	Day	10% 64% 9% 10% 6%	2800
	21st to end	Day	12% 62% 9% 13% 5%	2800
July	1st to 10th	Day	30% 32% 18% 15% 4	6290
	11th to 20th	Day	34% 33% 23% 9% 1	5877
	21st to end	Day	32% 30% 11% 19% 6%	6240
August	1st to 10th	Day	42% 38% 12% 7% 2	4125
	11th to 20th	Day	22% 40% 13% 17% 8%	3886
	21st to end	Day	20% 38% 11% 21% 9% 1	4312
September	1st to 10th	Day	18% 60% 8% 9% 5% 1	2400
	11th to 20th	Day	19% 58% 5% 9% 6% 2	2400
	21st to end	Day	23% 58% 6% 9% 3	2153
October	1st to 10th	Day	19% 38% 6% 18% 18% 2	3260
	11th to 20th	Day	14% 36% 3 14% 22% 12%	3240
	21st to end	Day	10% 35% 5% 22% 23% 6%	3538
November	1st to 10th	Day	19% 54% 5% 11% 9% 2	1970
	11th to 20th	Day	17% 54% 3 11% 11% 3	1890
	21st to end	Day	15% 55% 5% 13% 11% 2	1890
December	1st to 10th	Day	22% 35% 5% 19% 16% 3	2680
	11th to 20th	Day	31% 31% 8% 14% 11% 5%	3066
	21st to end	Day	25% 27% 9% 23% 14%	4048
January	1st to 10th	Night	28% 21% 9% 16% 19% 7%	7841
	11th to 20th	Night	25% 21% 4 14% 28% 9%	7680
	21st to end	Night	36% 23% 5% 15% 15% 6%	8401
February	1st to 10th	Night	16% 59% 6% 11% 7% 2	2729
	11th to 20th	Night	22% 58% 4 8% 7% 1	2460
	21st to end	Night	18% 59% 2 10% 7% 3	2076
March	1st to 10th	Night	37% 30% 6% 11% 10% 6%	5216
	11th to 20th	Night	25% 29% 6% 9% 19% 12%	5090
	21st to end	Night	28% 29% 7% 19% 12% 5%	5401
April	1st to 10th	Night	16% 61% 6% 8% 8% 1	2100
	11th to 20th	Night	15% 60% 5% 13% 6% 1	2075
	21st to end	Night	15% 59% 5% 13% 7% 1	2100
May	1st to 10th	Night	33% 34% 14% 14% 4 1	4531
	11th to 20th	Night	39% 30% 9% 16% 5%	4048
	21st to end	Night	34% 31% 9% 16% 9% 1	3927
June	1st to 10th	Night	16% 63% 6% 8% 6% 1	1600
	11th to 20th	Night	12% 64% 7% 11% 5%	1600
	21st to end	Night	11% 62% 7% 15% 6%	1600
July	1st to 10th	Night	26% 31% 22% 16% 4	3560
	11th to 20th	Night	36% 33% 20% 10% 1	3954
	21st to end	Night	35% 29% 11% 15% 10%	4297
August	1st to 10th	Night	38% 39% 12% 10% 1	2966
	11th to 20th	Night	27% 39% 11% 15% 8%	3227
	21st to end	Night	21% 37% 11% 20% 11% 1	3586
September	1st to 10th	Night	18% 59% 10% 8% 5% 1	2000
	11th to 20th	Night	21% 58% 4 8% 6% 2	2000
	21st to end	Night	24% 58% 8% 8% 3	2240
October	1st to 10th	Night	25% 36% 5% 16% 17% 1	3920
	11th to 20th	Night	13% 36% 4 12% 22% 14%	3899
	21st to end	Night	9% 35% 5% 22% 19% 10%	4252
November	1st to 10th	Night	21% 53% 3 11% 10% 2	2545
	11th to 20th	Night	20% 54% 3 7% 10% 5%	2730
	21st to end	Night	15% 54% 5% 14% 11% 2	2730
December	1st to 10th	Night	21% 35% 4 14% 19% 7%	4717
	11th to 20th	Night	33% 31% 9% 10% 11% 5%	5348
	21st to end	Night	24% 27% 13% 22% 13% 1	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	17% 21% 41% 18% 3	289
	11th to 20th	Day	18% 22% 35% 21% 3	330
	21st to end	Day	20% 19% 40% 18% 3 1	363
February	1st to 10th	Day	18% 18% 39% 19% 5%	330
	11th to 20th	Day	29% 19% 35% 16% 2	535
	21st to end	Day	20% 17% 33% 24% 4 1	446
March	1st to 10th	Day	16% 19% 34% 23% 7%	540
	11th to 20th	Day	21% 16% 36% 20% 6% 1	540
	21st to end	Day	15% 16% 39% 22% 7% 1	594
April	1st to 10th	Day	14% 17% 34% 24% 8% 2	540
	11th to 20th	Day	11% 15% 34% 26% 10% 4	532
	21st to end	Day	13% 12% 31% 28% 14% 3	540
May	1st to 10th	Day	14% 13% 32% 28% 11% 3	507
	11th to 20th	Day	16% 8% 27% 32% 14% 3	527
	21st to end	Day	14% 6% 24% 30% 19% 8%	573
June	1st to 10th	Day	12% 3 24% 32% 24% 5%	530
	11th to 20th	Day	9% 4 18% 33% 25% 10%	530
	21st to end	Day	6% 3 17% 33% 31% 9%	530
July	1st to 10th	Day	9% 2 14% 34% 30% 12%	525
	11th to 20th	Day	8% 2 10% 32% 37% 12%	524
	21st to end	Day	9% 4 14% 33% 31% 9%	576
August	1st to 10th	Day	16% 4 15% 30% 26% 8%	526
	11th to 20th	Day	12% 2 11% 30% 30% 15%	519
	21st to end	Day	11% 3 15% 32% 28% 11%	583
September	1st to 10th	Day	14% 3 18% 28% 24% 13%	530
	11th to 20th	Day	17% 4 20% 28% 23% 8%	530
	21st to end	Day	21% 7% 20% 25% 21% 7%	530
October	1st to 10th	Day	17% 8% 20% 25% 22% 8%	530
	11th to 20th	Day	15% 9% 28% 26% 18% 4	530
	21st to end	Day	12% 11% 27% 26% 19% 5%	583
November	1st to 10th	Day	17% 10% 27% 30% 12% 4	488
	11th to 20th	Day	16% 15% 31% 27% 11% 1	430
	21st to end	Day	13% 15% 30% 24% 15% 2	430
December	1st to 10th	Day	18% 15% 43% 17% 6% 1	220
	11th to 20th	Day	16% 17% 34% 22% 10%	220
	21st to end	Day	19% 13% 34% 21% 12% 1	242
January	1st to 10th	Night	17% 21% 34% 23% 5%	840
	11th to 20th	Night	18% 16% 34% 26% 6%	840
	21st to end	Night	18% 16% 39% 24% 3	924
February	1st to 10th	Night	22% 13% 34% 28% 3	840
	11th to 20th	Night	24% 17% 39% 19% 2	823
	21st to end	Night	18% 16% 37% 24% 5%	692
March	1st to 10th	Night	17% 14% 38% 25% 6%	840
	11th to 20th	Night	18% 14% 39% 22% 6%	840
	21st to end	Night	16% 13% 37% 28% 5%	924
April	1st to 10th	Night	15% 14% 38% 27% 5%	840
	11th to 20th	Night	12% 11% 37% 30% 8% 1	831
	21st to end	Night	14% 7% 36% 35% 7% 1	840
May	1st to 10th	Night	14% 10% 35% 32% 9%	805
	11th to 20th	Night	17% 7% 25% 38% 12%	606
	21st to end	Night	12% 3 17% 41% 24% 3	433
June	1st to 10th	Night	12% 3 20% 43% 20% 2	400
	11th to 20th	Night	10% 3 17% 44% 24% 3	400
	21st to end	Night	7% 2 15% 49% 26% 1	400
July	1st to 10th	Night	8% 2 12% 43% 33% 3	390
	11th to 20th	Night	8% 2 8% 41% 34% 7%	556
	21st to end	Night	9% 2 13% 42% 28% 5%	657
August	1st to 10th	Night	14% 3 12% 37% 31% 4	633
	11th to 20th	Night	10% 1 13% 37% 33% 5%	790
	21st to end	Night	13% 2 12% 31% 35% 6%	880
September	1st to 10th	Night	12% 2 15% 32% 30% 9%	800
	11th to 20th	Night	18% 4 14% 34% 26% 4	800
	21st to end	Night	20% 5% 17% 32% 24% 3	800
October	1st to 10th	Night	14% 5% 20% 30% 25% 6%	800
	11th to 20th	Night	18% 8% 24% 29% 19% 2	800
	21st to end	Night	14% 9% 26% 29% 19% 4	880
November	1st to 10th	Night	17% 7% 25% 33% 13% 4	820
	11th to 20th	Night	19% 11% 28% 30% 11% 1	840
	21st to end	Night	13% 13% 31% 28% 15% 1	840
December	1st to 10th	Night	19% 13% 32% 27% 8%	840
	11th to 20th	Night	17% 11% 35% 29% 9%	840
	21st to end	Night	16% 11% 35% 30% 8%	924

Page generated at 2026-04-29 02:21:44. Version ac07

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