Altoona
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Altoona clear sky chart from 2005-11-06 to 2025-08-05.

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	14% 8% 3 9% 6% 5% 5% 4 6% 7% 32%	125745
	Night	14% 8% 3 8% 5% 5% 5% 4 6% 7% 34%	122304
Transparency	Day	48% 8% 12% 20% 11% 1	129340
	Night	47% 8% 13% 20% 11% 2	126778
Seeing	Day	24% 17% 27% 19% 10% 3	15706
	Night	21% 15% 26% 27% 10% 1	25208

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% 11% 6% 17% 6% 6% 5% 4 5% 5% 23%	3717
	11th to 20th	Day	10% 16% 7% 17% 9% 7% 6% 3 4 4 15%	4060
	21st to end	Day	15% 13% 9% 12% 7% 5% 4 3 4 5% 22%	4466
February	1st to 10th	Day	13% 15% 5% 11% 7% 6% 5% 4 5% 6% 24%	1800
	11th to 20th	Day	13% 10% 4 13% 7% 5% 6% 4 7% 7% 25%	1753
	21st to end	Day	15% 11% 5% 11% 6% 5% 4 4 5% 6% 27%	1630
March	1st to 10th	Day	16% 9% 4 8% 6% 5% 5% 4 5% 6% 33%	4935
	11th to 20th	Day	11% 8% 3 10% 6% 5% 5% 4 6% 7% 34%	4980
	21st to end	Day	13% 8% 3 8% 6% 6% 5% 4 5% 6% 37%	5465
April	1st to 10th	Day	14% 12% 4 9% 5% 5% 5% 3 6% 7% 30%	2387
	11th to 20th	Day	14% 10% 3 8% 6% 4 5% 4 6% 6% 35%	2374
	21st to end	Day	18% 9% 3 8% 5% 4 4 4 5% 6% 34%	2507
May	1st to 10th	Day	22% 8% 3 7% 5% 5% 6% 5% 6% 6% 27%	5862
	11th to 20th	Day	23% 7% 3 7% 4 5% 4 4 6% 8% 29%	6102
	21st to end	Day	16% 6% 3 6% 5% 5% 6% 5% 7% 9% 31%	6934
June	1st to 10th	Day	13% 7% 2 6% 5% 5% 6% 5% 7% 8% 35%	2800
	11th to 20th	Day	13% 7% 3 7% 6% 5% 6% 5% 7% 9% 33%	2800
	21st to end	Day	11% 5% 2 7% 6% 6% 4 5% 6% 10% 38%	2800
July	1st to 10th	Day	6% 5% 2 7% 6% 6% 7% 5% 7% 9% 40%	6360
	11th to 20th	Day	7% 6% 2 8% 6% 7% 7% 6% 9% 10% 33%	6134
	21st to end	Day	9% 6% 3 8% 5% 5% 5% 4 6% 8% 41%	6424
August	1st to 10th	Day	17% 6% 2 6% 5% 5% 6% 5% 7% 9% 31%	4156
	11th to 20th	Day	10% 6% 2 8% 5% 7% 7% 6% 7% 8% 35%	4044
	21st to end	Day	12% 6% 2 6% 4 5% 5% 4 7% 9% 41%	4180
September	1st to 10th	Day	16% 6% 2 5% 4 5% 5% 3 4 6% 43%	2280
	11th to 20th	Day	14% 6% 2 5% 3 4 4 3 6% 7% 45%	2225
	21st to end	Day	20% 8% 2 6% 4 4 5% 5% 6% 7% 33%	2013
October	1st to 10th	Day	15% 8% 2 7% 5% 5% 4 4 6% 6% 37%	1900
	11th to 20th	Day	16% 8% 3 7% 4 4 5% 4 6% 7% 36%	1900
	21st to end	Day	16% 9% 3 7% 4 4 4 4 5% 7% 36%	2090
November	1st to 10th	Day	10% 6% 3 7% 4 5% 5% 4 6% 6% 43%	1887
	11th to 20th	Day	14% 8% 3 7% 7% 5% 5% 4 6% 7% 33%	1630
	21st to end	Day	14% 12% 5% 9% 6% 6% 6% 4 5% 6% 28%	1600
December	1st to 10th	Day	14% 10% 5% 13% 6% 5% 5% 5% 6% 7% 25%	2600
	11th to 20th	Day	20% 15% 4 8% 5% 4 4 3 5% 5% 27%	2990
	21st to end	Day	18% 15% 6% 12% 7% 6% 6% 3 5% 5% 16%	3960
January	1st to 10th	Night	10% 9% 4 18% 7% 6% 7% 4 6% 7% 20%	6211
	11th to 20th	Night	10% 11% 6% 14% 8% 6% 6% 4 6% 7% 22%	5900
	21st to end	Night	16% 10% 5% 10% 8% 5% 5% 4 6% 6% 25%	6490
February	1st to 10th	Night	14% 10% 4 9% 6% 5% 5% 4 6% 8% 29%	2600
	11th to 20th	Night	13% 11% 2 10% 7% 5% 6% 5% 6% 7% 28%	2533
	21st to end	Night	14% 12% 3 10% 6% 6% 5% 5% 5% 5% 28%	1996
March	1st to 10th	Night	16% 10% 4 8% 6% 5% 4 4 6% 5% 32%	4918
	11th to 20th	Night	10% 6% 5% 7% 4 4 4 4 5% 7% 44%	4980
	21st to end	Night	10% 9% 3 8% 5% 5% 5% 3 6% 8% 39%	5467
April	1st to 10th	Night	15% 11% 3 9% 6% 5% 4 3 5% 6% 32%	2011
	11th to 20th	Night	14% 7% 3 6% 5% 5% 5% 4 6% 8% 38%	1975
	21st to end	Night	17% 6% 2 7% 5% 5% 4 3 5% 8% 38%	1910
May	1st to 10th	Night	25% 9% 3 7% 5% 4 5% 4 6% 7% 27%	4033
	11th to 20th	Night	27% 7% 2 5% 4 4 3 3 6% 7% 33%	3787
	21st to end	Night	19% 7% 2 8% 4 5% 4 4 6% 9% 33%	3920
June	1st to 10th	Night	11% 6% 2 5% 6% 4 5% 3 6% 8% 44%	1600
	11th to 20th	Night	11% 5% 2 6% 4 5% 5% 5% 6% 9% 41%	1600
	21st to end	Night	9% 5% 1 6% 3 4 6% 4 7% 10% 45%	1600
July	1st to 10th	Night	6% 5% 2 7% 5% 5% 6% 5% 7% 9% 42%	3598
	11th to 20th	Night	6% 5% 3 7% 6% 6% 7% 5% 8% 10% 37%	3818
	21st to end	Night	7% 6% 2 7% 5% 5% 5% 4 7% 8% 45%	4427
August	1st to 10th	Night	16% 6% 2 5% 4 4 5% 4 7% 9% 37%	2861
	11th to 20th	Night	11% 6% 2 6% 5% 4 5% 4 7% 8% 43%	2785
	21st to end	Night	14% 4 2 5% 4 3 4 4 6% 7% 48%	3444
September	1st to 10th	Night	15% 6% 2 5% 4 4 5% 4 4 5% 46%	1900
	11th to 20th	Night	11% 5% 1 4 3 3 4 3 5% 9% 51%	1951
	21st to end	Night	20% 6% 2 6% 4 4 4 3 5% 7% 41%	2166
October	1st to 10th	Night	15% 7% 2 6% 4 4 4 4 4 7% 44%	2280
	11th to 20th	Night	16% 6% 2 6% 4 4 5% 3 5% 6% 42%	2280
	21st to end	Night	18% 9% 2 5% 4 4 4 3 5% 7% 39%	2508
November	1st to 10th	Night	9% 6% 3 7% 5% 4 4 3 5% 6% 47%	2409
	11th to 20th	Night	14% 8% 4 7% 5% 5% 6% 4 6% 7% 34%	2765
	21st to end	Night	14% 10% 4 8% 5% 5% 5% 4 6% 8% 32%	2800
December	1st to 10th	Night	12% 7% 4 12% 6% 6% 6% 4 6% 8% 29%	4580
	11th to 20th	Night	17% 10% 4 10% 5% 6% 5% 4 5% 6% 26%	5205
	21st to end	Night	17% 14% 6% 11% 8% 6% 5% 4 5% 6% 20%	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	61% 9% 10% 14% 5% 1	3718
	11th to 20th	Day	70% 7% 7% 8% 6% 2	4060
	21st to end	Day	63% 5% 11% 13% 7%	4466
February	1st to 10th	Day	60% 5% 14% 14% 6% 1	1800
	11th to 20th	Day	56% 7% 13% 17% 7%	1762
	21st to end	Day	56% 5% 14% 16% 7% 3	1630
March	1st to 10th	Day	49% 7% 11% 21% 8% 3	4935
	11th to 20th	Day	46% 6% 15% 23% 8% 2	4980
	21st to end	Day	46% 7% 11% 20% 13% 2	5465
April	1st to 10th	Day	53% 7% 11% 16% 11% 2	2387
	11th to 20th	Day	48% 7% 10% 18% 15% 2	2374
	21st to end	Day	49% 6% 10% 21% 13% 2	2507
May	1st to 10th	Day	55% 8% 10% 16% 10% 2	5897
	11th to 20th	Day	52% 7% 10% 20% 9% 1	6106
	21st to end	Day	45% 10% 13% 20% 11% 1	6949
June	1st to 10th	Day	44% 8% 12% 22% 13% 1	2800
	11th to 20th	Day	44% 9% 14% 18% 13% 1	2800
	21st to end	Day	39% 9% 14% 25% 13% 1	2800
July	1st to 10th	Day	39% 9% 12% 26% 13% 2	6290
	11th to 20th	Day	41% 12% 15% 21% 11%	6059
	21st to end	Day	39% 7% 9% 25% 19% 1	6240
August	1st to 10th	Day	47% 10% 15% 20% 9%	4143
	11th to 20th	Day	43% 9% 11% 26% 10% 1	4083
	21st to end	Day	37% 7% 13% 27% 13% 2	4180
September	1st to 10th	Day	41% 7% 10% 21% 16% 4	2280
	11th to 20th	Day	36% 5% 12% 27% 18% 2	2225
	21st to end	Day	48% 6% 13% 18% 14% 1	2013
October	1st to 10th	Day	38% 6% 9% 26% 18% 3	3160
	11th to 20th	Day	40% 7% 10% 23% 14% 5%	3140
	21st to end	Day	31% 5% 14% 29% 19% 1	3428
November	1st to 10th	Day	39% 6% 16% 19% 16% 4	1887
	11th to 20th	Day	50% 6% 14% 18% 10% 2	1630
	21st to end	Day	55% 7% 13% 19% 7%	1600
December	1st to 10th	Day	57% 9% 15% 15% 4 1	2600
	11th to 20th	Day	59% 5% 12% 20% 4	2986
	21st to end	Day	67% 7% 11% 9% 5%	3960
January	1st to 10th	Night	61% 8% 12% 13% 6%	6211
	11th to 20th	Night	58% 9% 13% 13% 5% 2	5900
	21st to end	Night	57% 8% 12% 16% 6% 1	6490
February	1st to 10th	Night	53% 6% 14% 19% 7%	2600
	11th to 20th	Night	54% 7% 12% 18% 9%	2535
	21st to end	Night	54% 8% 11% 17% 10% 2	1996
March	1st to 10th	Night	50% 7% 13% 20% 9% 1	4918
	11th to 20th	Night	38% 6% 18% 26% 8% 4	4980
	21st to end	Night	43% 7% 13% 18% 17% 2	5467
April	1st to 10th	Night	53% 6% 11% 16% 13% 1	2011
	11th to 20th	Night	43% 7% 13% 21% 15% 2	1975
	21st to end	Night	43% 6% 11% 25% 13% 3	1910
May	1st to 10th	Night	56% 7% 9% 14% 9% 3	4060
	11th to 20th	Night	50% 7% 12% 22% 8% 1	3788
	21st to end	Night	46% 8% 14% 20% 10% 3	3927
June	1st to 10th	Night	38% 8% 12% 26% 15% 2	1600
	11th to 20th	Night	38% 10% 15% 23% 13% 2	1600
	21st to end	Night	32% 10% 17% 25% 15% 1	1600
July	1st to 10th	Night	37% 10% 13% 24% 13% 2	3560
	11th to 20th	Night	40% 11% 17% 19% 12% 1	3773
	21st to end	Night	35% 9% 12% 23% 22% 1	4297
August	1st to 10th	Night	42% 10% 16% 22% 9% 1	2850
	11th to 20th	Night	38% 8% 13% 28% 12% 1	2812
	21st to end	Night	35% 7% 13% 31% 12% 2	3444
September	1st to 10th	Night	39% 6% 10% 22% 18% 3	1900
	11th to 20th	Night	31% 6% 13% 29% 20% 1	1951
	21st to end	Night	43% 6% 12% 22% 16% 1	2166
October	1st to 10th	Night	35% 5% 11% 26% 21% 1	3800
	11th to 20th	Night	32% 7% 11% 25% 19% 6%	3779
	21st to end	Night	31% 5% 13% 27% 21% 2	4120
November	1st to 10th	Night	37% 6% 14% 22% 18% 3	2409
	11th to 20th	Night	47% 7% 12% 21% 11% 3	2765
	21st to end	Night	50% 6% 15% 20% 8% 1	2800
December	1st to 10th	Night	52% 9% 19% 16% 3	4580
	11th to 20th	Night	57% 7% 14% 17% 4	5208
	21st to end	Night	64% 7% 11% 12% 6%	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	34% 29% 25% 9% 2	227
	11th to 20th	Day	39% 25% 29% 6% 1	300
	21st to end	Day	27% 30% 33% 7% 2	330
February	1st to 10th	Day	34% 30% 26% 9% 1	300
	11th to 20th	Day	44% 25% 27% 3	300
	21st to end	Day	36% 25% 29% 10% 1	370
March	1st to 10th	Day	32% 21% 27% 16% 3	500
	11th to 20th	Day	32% 23% 27% 13% 4 1	500
	21st to end	Day	30% 25% 27% 13% 4 1	550
April	1st to 10th	Day	32% 24% 26% 13% 4 1	500
	11th to 20th	Day	27% 20% 26% 17% 7% 3	492
	21st to end	Day	30% 21% 28% 14% 6% 1	500
May	1st to 10th	Day	30% 19% 26% 15% 7% 2	503
	11th to 20th	Day	26% 18% 28% 15% 9% 3	527
	21st to end	Day	21% 14% 26% 21% 12% 5%	573
June	1st to 10th	Day	19% 18% 28% 21% 12% 2	530
	11th to 20th	Day	20% 13% 28% 25% 12% 3	530
	21st to end	Day	14% 13% 31% 27% 14% 2	530
July	1st to 10th	Day	10% 8% 29% 28% 17% 7%	525
	11th to 20th	Day	7% 10% 30% 30% 16% 7%	524
	21st to end	Day	11% 10% 30% 29% 16% 5%	576
August	1st to 10th	Day	13% 8% 26% 28% 18% 8%	502
	11th to 20th	Day	14% 8% 26% 25% 18% 9%	479
	21st to end	Day	14% 8% 24% 27% 15% 11%	539
September	1st to 10th	Day	20% 8% 20% 26% 17% 9%	490
	11th to 20th	Day	16% 5% 22% 29% 20% 8%	490
	21st to end	Day	29% 14% 22% 18% 12% 5%	490
October	1st to 10th	Day	21% 13% 21% 25% 16% 4	490
	11th to 20th	Day	25% 18% 26% 22% 9% 2	490
	21st to end	Day	21% 21% 30% 20% 7% 1	539
November	1st to 10th	Day	21% 17% 29% 20% 12% 2	460
	11th to 20th	Day	28% 23% 30% 15% 3	230
	21st to end	Day	31% 24% 33% 10% 3	200
December	1st to 10th	Day	32% 33% 22% 10% 3 1	200
	11th to 20th	Day	36% 21% 30% 12% 1	200
	21st to end	Day	31% 23% 27% 16% 3	220
January	1st to 10th	Night	25% 25% 34% 15% 2	800
	11th to 20th	Night	29% 20% 31% 17% 2	800
	21st to end	Night	22% 25% 33% 18% 2	880
February	1st to 10th	Night	28% 19% 31% 20% 2	800
	11th to 20th	Night	28% 25% 32% 14% 1	783
	21st to end	Night	26% 20% 33% 19% 2	660
March	1st to 10th	Night	25% 20% 31% 21% 3	800
	11th to 20th	Night	28% 21% 27% 20% 5% 1	800
	21st to end	Night	22% 21% 33% 19% 5%	880
April	1st to 10th	Night	26% 23% 29% 19% 4	800
	11th to 20th	Night	21% 18% 27% 27% 7% 1	791
	21st to end	Night	22% 14% 26% 32% 6%	710
May	1st to 10th	Night	24% 12% 24% 31% 10% 1	600
	11th to 20th	Night	21% 9% 26% 34% 10%	489
	21st to end	Night	13% 10% 23% 35% 17% 2	433
June	1st to 10th	Night	12% 7% 26% 39% 16% 1	400
	11th to 20th	Night	14% 7% 25% 38% 17% 1	400
	21st to end	Night	10% 5% 27% 40% 18%	400
July	1st to 10th	Night	9% 4 18% 45% 21% 2	390
	11th to 20th	Night	7% 4 18% 41% 29% 2	479
	21st to end	Night	8% 4 21% 42% 24% 1	657
August	1st to 10th	Night	9% 3 17% 42% 28% 1	579
	11th to 20th	Night	11% 5% 16% 38% 26% 3	564
	21st to end	Night	14% 3 18% 37% 25% 3	817
September	1st to 10th	Night	17% 4 18% 35% 23% 3	760
	11th to 20th	Night	12% 6% 17% 32% 29% 4	760
	21st to end	Night	23% 7% 21% 28% 18% 3	760
October	1st to 10th	Night	18% 9% 23% 30% 18% 2	760
	11th to 20th	Night	20% 13% 29% 27% 10% 1	760
	21st to end	Night	24% 15% 26% 27% 8%	836
November	1st to 10th	Night	14% 13% 32% 31% 10% 1	780
	11th to 20th	Night	25% 18% 27% 24% 6% 1	800
	21st to end	Night	24% 20% 28% 23% 5% 1	800
December	1st to 10th	Night	27% 19% 31% 18% 4	800
	11th to 20th	Night	26% 20% 31% 22% 2	800
	21st to end	Night	23% 22% 29% 25% 1	880

Page generated at 2025-08-02 01:32:29. Version ac07

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