Clearfield
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Clearfield clear sky chart from 2005-11-06 to 2025-11-18.

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	16% 10% 4 9% 5% 5% 5% 4 5% 7% 30%	126938
	Night	16% 10% 4 10% 5% 4 4 4 5% 6% 31%	123416
Transparency	Day	52% 7% 11% 19% 10% 1	130533
	Night	52% 7% 11% 19% 10% 1	127890
Seeing	Day	24% 17% 27% 18% 10% 4	16056
	Night	23% 16% 26% 24% 10% 1	25523

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% 18% 8% 23% 5% 3 4 3 3 4 16%	3663
	11th to 20th	Day	10% 18% 10% 22% 8% 8% 4 3 3 3 12%	4060
	21st to end	Day	19% 16% 8% 11% 7% 4 4 3 4 5% 19%	4466
February	1st to 10th	Day	16% 16% 6% 11% 8% 5% 5% 4 5% 4 21%	1800
	11th to 20th	Day	15% 13% 5% 13% 7% 5% 6% 4 6% 7% 20%	1753
	21st to end	Day	18% 15% 3 11% 5% 4 4 4 4 6% 25%	1612
March	1st to 10th	Day	16% 12% 5% 9% 5% 4 3 3 5% 6% 32%	4935
	11th to 20th	Day	12% 10% 5% 10% 5% 4 4 4 5% 7% 33%	4980
	21st to end	Day	14% 9% 3 8% 6% 6% 6% 4 5% 6% 33%	5465
April	1st to 10th	Day	17% 13% 3 8% 6% 4 5% 4 5% 6% 29%	2390
	11th to 20th	Day	15% 12% 3 8% 5% 5% 4 4 4 6% 34%	2374
	21st to end	Day	19% 10% 3 7% 6% 4 3 3 5% 6% 33%	2527
May	1st to 10th	Day	23% 9% 3 8% 5% 5% 5% 4 5% 6% 26%	5862
	11th to 20th	Day	23% 10% 3 8% 5% 4 4 4 6% 8% 26%	6152
	21st to end	Day	19% 7% 2 6% 5% 5% 6% 4 6% 8% 32%	6934
June	1st to 10th	Day	14% 8% 2 7% 5% 6% 6% 4 5% 8% 35%	2800
	11th to 20th	Day	15% 7% 3 8% 6% 5% 4 4 6% 9% 34%	2800
	21st to end	Day	14% 6% 2 7% 4 6% 5% 4 6% 9% 37%	2800
July	1st to 10th	Day	8% 6% 2 8% 5% 5% 6% 4 6% 8% 40%	6360
	11th to 20th	Day	10% 6% 3 8% 7% 7% 6% 5% 7% 10% 32%	6206
	21st to end	Day	12% 6% 3 7% 5% 5% 4 4 6% 7% 42%	6424
August	1st to 10th	Day	18% 9% 3 8% 5% 5% 5% 4 6% 8% 29%	4234
	11th to 20th	Day	12% 6% 3 8% 5% 6% 6% 5% 7% 8% 33%	4174
	21st to end	Day	13% 6% 2 6% 4 5% 6% 5% 7% 10% 38%	4322
September	1st to 10th	Day	16% 7% 3 6% 4 4 4 2 5% 6% 43%	2400
	11th to 20th	Day	13% 6% 1 6% 4 3 4 4 5% 8% 44%	2342
	21st to end	Day	21% 9% 3 8% 5% 4 5% 3 5% 6% 33%	2120
October	1st to 10th	Day	14% 9% 3 9% 3 4 5% 4 5% 7% 38%	2000
	11th to 20th	Day	18% 11% 3 7% 5% 4 4 3 6% 6% 33%	2000
	21st to end	Day	19% 11% 3 6% 5% 4 4 4 5% 7% 32%	2200
November	1st to 10th	Day	12% 8% 3 8% 6% 4 4 4 6% 6% 40%	1967
	11th to 20th	Day	15% 17% 5% 8% 5% 4 4 3 5% 5% 28%	1666
	21st to end	Day	18% 17% 5% 9% 5% 5% 6% 4 4 6% 23%	1600
December	1st to 10th	Day	16% 18% 9% 19% 6% 4 4 3 4 3 15%	2600
	11th to 20th	Day	23% 17% 7% 9% 4 3 3 3 3 5% 22%	2990
	21st to end	Day	22% 21% 6% 11% 5% 4 4 3 4 5% 15%	3960
January	1st to 10th	Night	13% 14% 7% 25% 7% 4 4 3 4 4 15%	6280
	11th to 20th	Night	11% 14% 7% 20% 9% 7% 5% 4 5% 5% 13%	5900
	21st to end	Night	18% 13% 6% 13% 7% 6% 5% 3 4 4 19%	6490
February	1st to 10th	Night	16% 13% 5% 10% 7% 5% 5% 5% 4 5% 25%	2600
	11th to 20th	Night	15% 12% 5% 10% 7% 6% 5% 4 5% 6% 25%	2533
	21st to end	Night	17% 11% 4 11% 6% 5% 4 3 5% 6% 27%	2014
March	1st to 10th	Night	18% 11% 6% 9% 6% 4 3 3 4 5% 31%	4918
	11th to 20th	Night	12% 9% 6% 8% 4 4 4 4 5% 6% 39%	4980
	21st to end	Night	15% 11% 4 8% 4 4 4 3 4 6% 37%	5467
April	1st to 10th	Night	17% 13% 4 9% 5% 3 4 3 5% 7% 30%	2010
	11th to 20th	Night	16% 10% 3 7% 4 4 5% 3 6% 5% 37%	1975
	21st to end	Night	16% 9% 3 7% 6% 4 4 4 6% 7% 35%	1890
May	1st to 10th	Night	27% 9% 3 8% 5% 4 4 3 5% 6% 27%	4033
	11th to 20th	Night	22% 11% 3 6% 4 4 3 3 5% 6% 32%	3724
	21st to end	Night	20% 8% 3 7% 4 4 4 4 5% 8% 34%	3920
June	1st to 10th	Night	11% 7% 3 6% 5% 5% 5% 4 6% 7% 42%	1600
	11th to 20th	Night	12% 6% 2 7% 6% 4 5% 4 7% 9% 39%	1600
	21st to end	Night	12% 7% 2 5% 4 4 4 4 6% 9% 43%	1600
July	1st to 10th	Night	11% 6% 3 7% 5% 4 4 4 6% 9% 40%	3598
	11th to 20th	Night	10% 5% 3 7% 6% 5% 7% 5% 7% 10% 36%	3733
	21st to end	Night	10% 6% 2 5% 5% 5% 5% 3 5% 8% 45%	4427
August	1st to 10th	Night	18% 6% 2 6% 5% 5% 4 3 5% 7% 37%	2915
	11th to 20th	Night	15% 7% 2 7% 5% 4 5% 4 6% 7% 41%	2875
	21st to end	Night	12% 6% 2 6% 4 4 5% 4 6% 7% 45%	3541
September	1st to 10th	Night	15% 5% 2 6% 4 3 4 3 4 6% 47%	2000
	11th to 20th	Night	10% 5% 2 6% 4 4 3 3 5% 7% 51%	2055
	21st to end	Night	19% 7% 3 7% 4 4 4 4 5% 6% 37%	2280
October	1st to 10th	Night	15% 6% 2 6% 4 3 4 3 5% 7% 44%	2400
	11th to 20th	Night	17% 8% 3 7% 4 4 4 3 5% 7% 39%	2400
	21st to end	Night	20% 9% 3 7% 4 4 4 4 5% 6% 35%	2640
November	1st to 10th	Night	12% 9% 3 6% 4 4 4 3 6% 6% 44%	2550
	11th to 20th	Night	16% 13% 4 9% 6% 5% 4 3 6% 7% 29%	2887
	21st to end	Night	16% 14% 5% 8% 6% 4 4 4 5% 7% 27%	2800
December	1st to 10th	Night	16% 13% 8% 17% 5% 5% 4 4 5% 5% 18%	4580
	11th to 20th	Night	22% 13% 6% 11% 5% 4 4 3 4 5% 23%	5205
	21st to end	Night	19% 17% 6% 12% 6% 5% 4 3 5% 6% 17%	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	73% 5% 8% 9% 5% 1	3664
	11th to 20th	Day	79% 4 6% 7% 3	4060
	21st to end	Day	69% 4 9% 12% 5%	4466
February	1st to 10th	Day	66% 6% 11% 12% 6%	1800
	11th to 20th	Day	63% 7% 10% 14% 6%	1762
	21st to end	Day	60% 5% 11% 16% 6% 1	1612
March	1st to 10th	Day	53% 6% 12% 20% 8% 1	4935
	11th to 20th	Day	50% 7% 15% 19% 7% 2	4980
	21st to end	Day	50% 7% 9% 18% 13% 2	5465
April	1st to 10th	Day	54% 7% 10% 16% 10% 2	2390
	11th to 20th	Day	50% 7% 11% 17% 13% 2	2374
	21st to end	Day	52% 6% 9% 20% 12% 1	2527
May	1st to 10th	Day	56% 7% 10% 15% 8% 2	5897
	11th to 20th	Day	55% 9% 9% 19% 8% 1	6156
	21st to end	Day	46% 9% 13% 21% 10% 1	6949
June	1st to 10th	Day	46% 8% 12% 21% 12% 1	2800
	11th to 20th	Day	47% 8% 14% 18% 12% 1	2800
	21st to end	Day	42% 8% 15% 24% 12%	2800
July	1st to 10th	Day	41% 7% 12% 27% 13% 1	6290
	11th to 20th	Day	45% 8% 15% 22% 11%	6131
	21st to end	Day	40% 6% 10% 26% 18%	6240
August	1st to 10th	Day	51% 8% 14% 19% 8%	4221
	11th to 20th	Day	45% 8% 12% 26% 9%	4213
	21st to end	Day	39% 8% 13% 28% 11% 1	4322
September	1st to 10th	Day	43% 5% 9% 24% 16% 3	2400
	11th to 20th	Day	37% 6% 12% 25% 18% 1	2342
	21st to end	Day	52% 7% 10% 17% 13% 1	2120
October	1st to 10th	Day	41% 6% 10% 24% 17% 3	3260
	11th to 20th	Day	44% 6% 10% 22% 15% 3	3240
	21st to end	Day	37% 5% 13% 28% 15% 1	3538
November	1st to 10th	Day	43% 7% 13% 20% 15% 3	1967
	11th to 20th	Day	57% 5% 12% 15% 8% 2	1666
	21st to end	Day	61% 7% 11% 15% 6%	1600
December	1st to 10th	Day	74% 6% 8% 9% 3	2600
	11th to 20th	Day	67% 4 10% 16% 4	2986
	21st to end	Day	73% 5% 9% 9% 4	3960
January	1st to 10th	Night	71% 7% 7% 10% 4	6280
	11th to 20th	Night	71% 8% 10% 8% 4 1	5900
	21st to end	Night	67% 6% 9% 11% 6% 1	6490
February	1st to 10th	Night	61% 7% 10% 16% 6%	2600
	11th to 20th	Night	60% 6% 11% 16% 7%	2535
	21st to end	Night	58% 6% 10% 15% 10% 1	2014
March	1st to 10th	Night	55% 6% 11% 18% 8% 2	4918
	11th to 20th	Night	43% 9% 17% 21% 7% 3	4980
	21st to end	Night	47% 6% 9% 19% 17% 1	5467
April	1st to 10th	Night	54% 7% 10% 16% 12% 1	2010
	11th to 20th	Night	46% 8% 11% 20% 13% 2	1975
	21st to end	Night	47% 7% 10% 22% 12% 2	1890
May	1st to 10th	Night	58% 7% 9% 14% 9% 3	4060
	11th to 20th	Night	51% 9% 11% 20% 10% 1	3725
	21st to end	Night	46% 10% 11% 19% 12% 3	3927
June	1st to 10th	Night	39% 8% 13% 25% 14% 1	1600
	11th to 20th	Night	39% 10% 12% 24% 12% 2	1600
	21st to end	Night	37% 9% 14% 25% 14% 1	1600
July	1st to 10th	Night	41% 6% 12% 24% 14% 1	3560
	11th to 20th	Night	41% 9% 17% 21% 11% 1	3688
	21st to end	Night	36% 7% 11% 24% 21% 1	4297
August	1st to 10th	Night	46% 8% 13% 23% 9% 1	2904
	11th to 20th	Night	42% 7% 11% 28% 11% 1	2902
	21st to end	Night	37% 7% 12% 32% 10% 2	3541
September	1st to 10th	Night	38% 7% 10% 25% 17% 3	2000
	11th to 20th	Night	33% 6% 13% 28% 18% 1	2055
	21st to end	Night	47% 7% 12% 19% 15% 1	2280
October	1st to 10th	Night	38% 7% 10% 24% 20% 1	3920
	11th to 20th	Night	37% 6% 11% 23% 18% 5%	3899
	21st to end	Night	37% 5% 13% 25% 17% 2	4252
November	1st to 10th	Night	40% 7% 14% 21% 17% 3	2550
	11th to 20th	Night	53% 8% 10% 17% 9% 3	2887
	21st to end	Night	56% 7% 12% 18% 6% 1	2800
December	1st to 10th	Night	66% 9% 11% 12% 2	4580
	11th to 20th	Night	65% 5% 11% 15% 4	5208
	21st to end	Night	68% 7% 8% 12% 5%	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	33% 30% 25% 8% 3	215
	11th to 20th	Day	35% 30% 29% 4 1 1	300
	21st to end	Day	29% 32% 28% 8% 2	330
February	1st to 10th	Day	31% 31% 29% 7% 2	300
	11th to 20th	Day	40% 27% 27% 6%	300
	21st to end	Day	37% 24% 29% 9% 1	359
March	1st to 10th	Day	31% 25% 29% 13% 3	500
	11th to 20th	Day	31% 24% 27% 13% 4 1	500
	21st to end	Day	31% 25% 28% 11% 4 1	550
April	1st to 10th	Day	32% 23% 26% 15% 4 1	500
	11th to 20th	Day	25% 26% 26% 14% 7% 3	492
	21st to end	Day	29% 20% 31% 14% 5% 1	500
May	1st to 10th	Day	30% 17% 29% 15% 7% 2	503
	11th to 20th	Day	27% 16% 31% 14% 8% 4	527
	21st to end	Day	19% 14% 27% 21% 14% 5%	573
June	1st to 10th	Day	20% 14% 28% 24% 12% 3	530
	11th to 20th	Day	19% 16% 26% 22% 13% 4	530
	21st to end	Day	15% 14% 31% 28% 10% 3	530
July	1st to 10th	Day	10% 9% 26% 28% 16% 10%	525
	11th to 20th	Day	9% 8% 30% 29% 16% 8%	524
	21st to end	Day	13% 6% 30% 30% 15% 6%	576
August	1st to 10th	Day	13% 8% 25% 27% 20% 7%	526
	11th to 20th	Day	13% 8% 25% 29% 16% 10%	519
	21st to end	Day	14% 8% 27% 27% 15% 10%	583
September	1st to 10th	Day	19% 9% 21% 25% 16% 9%	530
	11th to 20th	Day	12% 6% 21% 28% 23% 10%	530
	21st to end	Day	27% 13% 24% 19% 13% 4	530
October	1st to 10th	Day	20% 13% 22% 21% 18% 5%	530
	11th to 20th	Day	26% 18% 29% 17% 8% 2	530
	21st to end	Day	28% 20% 28% 17% 7% 1	583
November	1st to 10th	Day	20% 21% 29% 18% 11% 1	487
	11th to 20th	Day	34% 24% 27% 11% 4	224
	21st to end	Day	30% 26% 33% 10% 2	200
December	1st to 10th	Day	33% 30% 27% 7% 3 1	200
	11th to 20th	Day	38% 21% 28% 12% 1	200
	21st to end	Day	35% 23% 28% 10% 3	220
January	1st to 10th	Night	29% 27% 31% 11% 3	800
	11th to 20th	Night	29% 25% 29% 15% 3	800
	21st to end	Night	26% 27% 30% 15% 2	880
February	1st to 10th	Night	31% 20% 29% 18% 2	800
	11th to 20th	Night	31% 28% 30% 10% 1	783
	21st to end	Night	30% 24% 29% 15% 2	660
March	1st to 10th	Night	26% 22% 31% 19% 3	800
	11th to 20th	Night	29% 22% 25% 19% 5% 1	800
	21st to end	Night	24% 21% 35% 16% 5% 1	880
April	1st to 10th	Night	26% 21% 31% 18% 4	800
	11th to 20th	Night	24% 19% 29% 19% 8% 1	791
	21st to end	Night	21% 15% 30% 28% 7%	690
May	1st to 10th	Night	24% 12% 25% 30% 9% 1	600
	11th to 20th	Night	19% 9% 31% 31% 10%	465
	21st to end	Night	12% 9% 27% 32% 20% 1	433
June	1st to 10th	Night	13% 8% 28% 37% 16%	400
	11th to 20th	Night	15% 7% 26% 38% 14% 1	400
	21st to end	Night	12% 6% 30% 37% 15% 1	400
July	1st to 10th	Night	12% 5% 19% 41% 20% 3	390
	11th to 20th	Night	9% 4 21% 39% 26% 2	446
	21st to end	Night	12% 4 20% 39% 24% 1	657
August	1st to 10th	Night	11% 3 19% 40% 26% 2	597
	11th to 20th	Night	14% 7% 12% 38% 26% 4	594
	21st to end	Night	14% 4 19% 34% 25% 4	848
September	1st to 10th	Night	18% 6% 19% 32% 22% 3	800
	11th to 20th	Night	13% 5% 16% 32% 30% 4	800
	21st to end	Night	21% 10% 21% 27% 17% 3	800
October	1st to 10th	Night	18% 11% 22% 27% 19% 3	800
	11th to 20th	Night	23% 16% 29% 24% 9% 1	800
	21st to end	Night	26% 15% 28% 26% 5%	880
November	1st to 10th	Night	19% 14% 29% 27% 10% 1	820
	11th to 20th	Night	28% 18% 27% 20% 5% 1	829
	21st to end	Night	27% 20% 31% 18% 5%	800
December	1st to 10th	Night	31% 25% 27% 13% 4	800
	11th to 20th	Night	29% 24% 27% 17% 3	800
	21st to end	Night	29% 23% 28% 18% 2	880

Page generated at 2025-11-15 00:56:00. Version ac07

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