Chambersburg
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Chambersburg clear sky chart from 2005-11-06 to 2024-10-25.

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 7% 5% 5% 5% 4 6% 7% 38%	101169
	Night	14% 8% 3 7% 5% 4 4 4 5% 7% 39%	97561
Transparency	Day	43% 8% 13% 22% 13% 2	100970
	Night	42% 7% 12% 23% 13% 2	97430
Seeing	Day	20% 14% 26% 22% 13% 4	14832
	Night	18% 12% 27% 30% 12% 1	24304

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	16% 9% 4 9% 6% 5% 3 4 5% 5% 35%	2558
	11th to 20th	Day	13% 14% 5% 12% 7% 5% 4 3 5% 5% 27%	2840
	21st to end	Day	17% 14% 4 9% 6% 4 4 3 4 6% 29%	3124
February	1st to 10th	Day	15% 11% 3 8% 6% 5% 4 4 5% 7% 33%	1710
	11th to 20th	Day	14% 10% 3 8% 6% 5% 4 3 6% 7% 35%	1671
	21st to end	Day	18% 11% 3 8% 4 4 3 3 5% 5% 34%	1570
March	1st to 10th	Day	21% 9% 2 7% 5% 5% 5% 4 5% 6% 32%	3405
	11th to 20th	Day	11% 7% 3 7% 5% 5% 4 4 6% 7% 42%	3480
	21st to end	Day	18% 10% 3 6% 4 3 4 3 5% 6% 39%	3846
April	1st to 10th	Day	15% 10% 2 6% 6% 4 5% 4 6% 6% 35%	2280
	11th to 20th	Day	13% 7% 3 8% 4 5% 4 3 5% 6% 42%	2254
	21st to end	Day	18% 7% 2 7% 4 4 4 4 6% 6% 38%	2307
May	1st to 10th	Day	26% 7% 2 6% 4 4 4 4 5% 7% 29%	4082
	11th to 20th	Day	22% 8% 3 6% 5% 5% 4 4 6% 7% 29%	4297
	21st to end	Day	11% 5% 2 5% 4 5% 5% 4 7% 8% 42%	4823
June	1st to 10th	Day	12% 6% 2 5% 5% 5% 5% 4 7% 10% 39%	2660
	11th to 20th	Day	12% 6% 2 6% 5% 6% 5% 4 7% 9% 38%	2660
	21st to end	Day	10% 5% 1 6% 4 5% 4 4 7% 10% 43%	2660
July	1st to 10th	Day	6% 4 2 6% 5% 6% 7% 5% 7% 11% 41%	4440
	11th to 20th	Day	7% 6% 2 6% 5% 5% 5% 5% 8% 10% 41%	4328
	21st to end	Day	11% 8% 3 7% 5% 5% 5% 4 6% 8% 38%	4466
August	1st to 10th	Day	14% 7% 3 7% 5% 5% 5% 4 7% 9% 33%	4104
	11th to 20th	Day	11% 6% 2 6% 5% 5% 6% 4 7% 9% 40%	3953
	21st to end	Day	11% 6% 2 5% 4 4 4 4 6% 8% 46%	4180
September	1st to 10th	Day	15% 5% 2 6% 4 4 4 4 5% 6% 45%	2280
	11th to 20th	Day	11% 5% 2 5% 3 4 4 4 6% 8% 48%	2280
	21st to end	Day	19% 8% 2 6% 4 4 4 3 5% 7% 38%	1983
October	1st to 10th	Day	15% 6% 2 6% 4 4 4 4 4 7% 44%	1900
	11th to 20th	Day	15% 5% 3 6% 4 4 4 4 5% 7% 44%	1900
	21st to end	Day	15% 7% 2 5% 4 3 4 4 5% 6% 44%	2027
November	1st to 10th	Day	11% 7% 3 5% 4 3 4 3 4 8% 47%	1759
	11th to 20th	Day	14% 8% 3 5% 4 4 4 4 5% 6% 43%	1620
	21st to end	Day	15% 8% 3 6% 5% 4 5% 4 4 7% 39%	1520
December	1st to 10th	Day	18% 10% 3 7% 5% 5% 4 5% 7% 8% 29%	1520
	11th to 20th	Day	16% 12% 3 6% 5% 4 4 4 6% 6% 34%	1910
	21st to end	Day	19% 12% 4 8% 5% 5% 5% 5% 6% 7% 26%	2772
January	1st to 10th	Night	12% 10% 4 11% 6% 5% 5% 4 5% 6% 33%	4384
	11th to 20th	Night	15% 10% 5% 9% 6% 4 4 3 4 6% 34%	4120
	21st to end	Night	20% 11% 3 10% 6% 4 4 3 4 5% 30%	4532
February	1st to 10th	Night	15% 9% 3 7% 5% 4 5% 3 6% 6% 36%	2470
	11th to 20th	Night	16% 10% 3 7% 5% 5% 4 4 6% 6% 35%	2394
	21st to end	Night	17% 10% 3 8% 4 4 4 3 5% 7% 34%	1884
March	1st to 10th	Night	21% 9% 3 6% 5% 4 3 3 5% 6% 37%	3433
	11th to 20th	Night	12% 8% 3 7% 4 4 4 3 5% 6% 44%	3480
	21st to end	Night	13% 8% 3 6% 4 4 4 3 5% 5% 45%	3786
April	1st to 10th	Night	16% 10% 3 8% 5% 4 5% 4 6% 6% 34%	1900
	11th to 20th	Night	13% 7% 2 6% 5% 4 4 3 6% 9% 41%	1875
	21st to end	Night	17% 5% 2 5% 5% 4 5% 4 6% 6% 41%	1889
May	1st to 10th	Night	26% 8% 3 7% 4 4 4 3 5% 7% 30%	2813
	11th to 20th	Night	22% 8% 4 7% 5% 4 5% 3 5% 7% 31%	2595
	21st to end	Night	11% 6% 2 6% 4 5% 5% 5% 7% 10% 39%	2732
June	1st to 10th	Night	11% 6% 2 5% 4 4 4 4 6% 7% 46%	1520
	11th to 20th	Night	11% 5% 2 7% 4 5% 5% 5% 5% 9% 40%	1520
	21st to end	Night	9% 5% 2 6% 4 4 5% 3 7% 9% 45%	1520
July	1st to 10th	Night	7% 5% 2 5% 5% 5% 6% 5% 6% 11% 42%	2520
	11th to 20th	Night	6% 6% 2 7% 5% 5% 6% 5% 8% 11% 40%	2614
	21st to end	Night	11% 8% 2 7% 5% 5% 4 4 6% 8% 39%	3087
August	1st to 10th	Night	14% 8% 3 7% 5% 4 5% 5% 7% 9% 34%	2825
	11th to 20th	Night	11% 7% 2 6% 4 5% 4 4 6% 7% 42%	2844
	21st to end	Night	11% 5% 2 6% 4 5% 4 4 5% 9% 46%	3476
September	1st to 10th	Night	13% 5% 2 5% 4 4 4 3 5% 7% 47%	1900
	11th to 20th	Night	9% 6% 2 5% 4 3 3 3 4 7% 53%	1900
	21st to end	Night	17% 7% 3 5% 4 4 5% 4 5% 6% 40%	2193
October	1st to 10th	Night	16% 6% 3 6% 4 4 4 3 5% 6% 44%	2280
	11th to 20th	Night	13% 5% 2 5% 4 5% 4 3 5% 6% 47%	2280
	21st to end	Night	15% 6% 2 5% 4 4 4 3 6% 6% 44%	2435
November	1st to 10th	Night	9% 7% 2 7% 3 4 4 3 4 6% 51%	2316
	11th to 20th	Night	14% 8% 3 6% 4 4 4 3 6% 6% 43%	2555
	21st to end	Night	14% 7% 3 6% 6% 4 5% 4 5% 8% 39%	2660
December	1st to 10th	Night	16% 10% 3 8% 5% 4 5% 4 6% 6% 34%	2660
	11th to 20th	Night	17% 9% 3 7% 5% 5% 4 4 5% 6% 35%	3285
	21st to end	Night	16% 10% 3 8% 6% 6% 6% 5% 6% 7% 27%	4884

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	47% 6% 13% 23% 8% 3	2559
	11th to 20th	Day	53% 9% 12% 14% 11% 2	2840
	21st to end	Day	54% 7% 9% 21% 6% 1	3124
February	1st to 10th	Day	50% 6% 12% 21% 10% 1	1710
	11th to 20th	Day	48% 7% 11% 22% 11% 2	1680
	21st to end	Day	51% 5% 12% 19% 10% 3	1570
March	1st to 10th	Day	48% 8% 11% 21% 11% 1	3405
	11th to 20th	Day	36% 7% 14% 26% 14% 3	3480
	21st to end	Day	45% 6% 11% 20% 15% 2	3846
April	1st to 10th	Day	46% 7% 13% 17% 15% 3	2280
	11th to 20th	Day	41% 8% 10% 22% 16% 3	2254
	21st to end	Day	45% 8% 9% 21% 15% 3	2307
May	1st to 10th	Day	52% 9% 9% 19% 10% 1	4120
	11th to 20th	Day	52% 9% 13% 17% 7% 2	4301
	21st to end	Day	34% 10% 15% 23% 16% 2	4837
June	1st to 10th	Day	38% 8% 15% 23% 15% 1	2660
	11th to 20th	Day	39% 10% 15% 20% 13% 1	2660
	21st to end	Day	34% 8% 15% 28% 13% 1	2660
July	1st to 10th	Day	36% 9% 16% 25% 12% 3	4370
	11th to 20th	Day	35% 8% 19% 25% 13% 1	4253
	21st to end	Day	43% 7% 10% 21% 17% 1	4324
August	1st to 10th	Day	45% 8% 15% 23% 7%	4091
	11th to 20th	Day	38% 7% 13% 29% 13% 1	3992
	21st to end	Day	35% 6% 13% 27% 17% 2	4180
September	1st to 10th	Day	39% 7% 11% 20% 20% 3	2280
	11th to 20th	Day	33% 8% 11% 25% 20% 3	2280
	21st to end	Day	46% 5% 11% 17% 19% 2	1983
October	1st to 10th	Day	40% 6% 12% 22% 17% 2	1900
	11th to 20th	Day	38% 6% 13% 24% 17% 1	1900
	21st to end	Day	39% 6% 11% 24% 18% 2	2027
November	1st to 10th	Day	35% 5% 14% 23% 19% 4	1759
	11th to 20th	Day	41% 6% 12% 21% 17% 3	1620
	21st to end	Day	44% 6% 12% 27% 10% 1	1520
December	1st to 10th	Day	50% 8% 13% 20% 8% 1	1520
	11th to 20th	Day	48% 6% 13% 26% 6% 1	1906
	21st to end	Day	51% 11% 15% 16% 8%	2772
January	1st to 10th	Night	45% 8% 12% 22% 10% 2	4384
	11th to 20th	Night	47% 7% 14% 21% 9% 2	4120
	21st to end	Night	53% 6% 10% 22% 7% 1	4532
February	1st to 10th	Night	47% 6% 13% 22% 11% 1	2470
	11th to 20th	Night	47% 7% 10% 18% 16% 2	2396
	21st to end	Night	48% 6% 12% 18% 12% 4	1884
March	1st to 10th	Night	47% 6% 10% 26% 10% 1	3433
	11th to 20th	Night	36% 8% 11% 31% 12% 2	3480
	21st to end	Night	39% 6% 9% 22% 20% 4	3786
April	1st to 10th	Night	48% 7% 10% 17% 15% 3	1900
	11th to 20th	Night	39% 7% 11% 22% 17% 5%	1875
	21st to end	Night	39% 8% 12% 22% 15% 4	1889
May	1st to 10th	Night	54% 7% 8% 17% 12% 3	2840
	11th to 20th	Night	52% 10% 12% 16% 9% 1	2596
	21st to end	Night	35% 12% 16% 26% 9% 2	2739
June	1st to 10th	Night	34% 9% 11% 27% 16% 3	1520
	11th to 20th	Night	38% 9% 13% 25% 13% 2	1520
	21st to end	Night	34% 9% 15% 25% 16% 2	1520
July	1st to 10th	Night	36% 8% 19% 18% 14% 5%	2480
	11th to 20th	Night	35% 9% 17% 23% 15% 2	2566
	21st to end	Night	40% 8% 14% 18% 18% 1	2988
August	1st to 10th	Night	45% 8% 17% 21% 8%	2814
	11th to 20th	Night	37% 9% 12% 27% 15% 1	2871
	21st to end	Night	34% 7% 14% 28% 15% 2	3476
September	1st to 10th	Night	36% 8% 12% 21% 19% 4	1900
	11th to 20th	Night	31% 5% 11% 28% 22% 3	1900
	21st to end	Night	43% 7% 12% 20% 17% 2	2193
October	1st to 10th	Night	40% 7% 12% 23% 16% 2	2280
	11th to 20th	Night	37% 6% 9% 27% 17% 3	2280
	21st to end	Night	39% 5% 9% 26% 19% 2	2435
November	1st to 10th	Night	34% 6% 10% 27% 19% 4	2316
	11th to 20th	Night	41% 5% 10% 24% 17% 4	2555
	21st to end	Night	41% 6% 13% 24% 14% 2	2660
December	1st to 10th	Night	48% 7% 13% 21% 10% 1	2660
	11th to 20th	Night	46% 6% 13% 21% 12% 2	3288
	21st to end	Night	49% 11% 15% 18% 7%	4884

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	31% 24% 27% 13% 4 2	193
	11th to 20th	Day	36% 22% 30% 10% 2	270
	21st to end	Day	26% 29% 28% 14% 3	297
February	1st to 10th	Day	30% 25% 31% 11% 3	270
	11th to 20th	Day	38% 26% 31% 4 1	278
	21st to end	Day	32% 20% 30% 17% 1	382
March	1st to 10th	Day	28% 21% 27% 20% 3	460
	11th to 20th	Day	28% 24% 29% 14% 5% 1	460
	21st to end	Day	29% 21% 28% 16% 4 2	506
April	1st to 10th	Day	26% 21% 28% 18% 5% 2	460
	11th to 20th	Day	20% 20% 29% 16% 11% 4	452
	21st to end	Day	27% 17% 31% 16% 7% 2	460
May	1st to 10th	Day	28% 18% 26% 16% 8% 3	463
	11th to 20th	Day	24% 15% 25% 22% 10% 3	487
	21st to end	Day	17% 11% 23% 26% 16% 7%	529
June	1st to 10th	Day	16% 12% 27% 22% 18% 5%	490
	11th to 20th	Day	14% 10% 29% 27% 16% 4	490
	21st to end	Day	10% 10% 31% 26% 18% 4	490
July	1st to 10th	Day	9% 5% 22% 31% 23% 10%	485
	11th to 20th	Day	6% 3 26% 31% 25% 9%	484
	21st to end	Day	14% 5% 22% 30% 23% 6%	532
August	1st to 10th	Day	10% 4 21% 31% 25% 9%	486
	11th to 20th	Day	11% 5% 20% 32% 22% 10%	479
	21st to end	Day	12% 5% 20% 30% 22% 12%	539
September	1st to 10th	Day	18% 7% 19% 24% 21% 10%	490
	11th to 20th	Day	12% 6% 19% 31% 22% 11%	490
	21st to end	Day	27% 11% 23% 22% 14% 5%	490
October	1st to 10th	Day	20% 9% 23% 24% 18% 5%	490
	11th to 20th	Day	18% 17% 25% 25% 12% 3	490
	21st to end	Day	18% 16% 32% 24% 9% 2	514
November	1st to 10th	Day	16% 14% 29% 25% 13% 2	408
	11th to 20th	Day	25% 19% 27% 20% 8% 1	280
	21st to end	Day	22% 25% 29% 19% 5%	180
December	1st to 10th	Day	29% 24% 30% 12% 4 1	180
	11th to 20th	Day	28% 21% 32% 14% 6%	180
	21st to end	Day	27% 19% 31% 20% 4	198
January	1st to 10th	Night	18% 22% 36% 20% 4	760
	11th to 20th	Night	22% 18% 32% 25% 3	760
	21st to end	Night	19% 20% 36% 23% 2	836
February	1st to 10th	Night	20% 20% 30% 28% 2	760
	11th to 20th	Night	23% 25% 33% 18% 1	743
	21st to end	Night	23% 22% 34% 19% 3	628
March	1st to 10th	Night	22% 18% 35% 21% 4	760
	11th to 20th	Night	26% 18% 28% 22% 6%	760
	21st to end	Night	21% 17% 35% 21% 5% 1	836
April	1st to 10th	Night	21% 20% 31% 23% 5%	760
	11th to 20th	Night	16% 15% 30% 30% 8%	751
	21st to end	Night	20% 14% 30% 27% 9%	749
May	1st to 10th	Night	22% 10% 25% 28% 15% 1	570
	11th to 20th	Night	19% 7% 27% 37% 10%	435
	21st to end	Night	14% 4 22% 36% 21% 2	411
June	1st to 10th	Night	13% 3 24% 37% 22% 1	380
	11th to 20th	Night	13% 5% 22% 41% 19%	380
	21st to end	Night	11% 3 21% 46% 20%	380
July	1st to 10th	Night	11% 2 19% 37% 28% 3	370
	11th to 20th	Night	8% 1 15% 43% 31% 2	423
	21st to end	Night	9% 2 15% 42% 28% 3	624
August	1st to 10th	Night	11% 2 11% 44% 29% 3	567
	11th to 20th	Night	11% 4 12% 40% 30% 4	597
	21st to end	Night	12% 3 15% 39% 28% 4	836
September	1st to 10th	Night	16% 3 18% 34% 26% 3	760
	11th to 20th	Night	12% 4 16% 35% 28% 5%	760
	21st to end	Night	21% 5% 21% 28% 21% 3	760
October	1st to 10th	Night	21% 6% 21% 28% 21% 3	760
	11th to 20th	Night	17% 11% 25% 34% 11% 1	760
	21st to end	Night	19% 10% 30% 29% 11%	812
November	1st to 10th	Night	13% 11% 29% 35% 11% 1	740
	11th to 20th	Night	18% 20% 25% 28% 7% 1	760
	21st to end	Night	18% 19% 29% 29% 6% 1	760
December	1st to 10th	Night	23% 16% 32% 22% 6%	760
	11th to 20th	Night	21% 15% 32% 28% 3	760
	21st to end	Night	19% 16% 33% 29% 3	836

Page generated at 2024-10-22 20:21:01. Version ac07

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