Harrisburg
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Harrisburg clear sky chart from 2005-11-06 to 2026-05-17.

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% 7% 3 7% 5% 4 5% 4 6% 7% 42%	131747
	Night	13% 7% 3 7% 4 4 4 3 5% 6% 43%	131305
Transparency	Day	40% 5% 11% 25% 17% 3	135349
	Night	40% 4 10% 24% 18% 3	135780
Seeing	Day	16% 13% 25% 24% 16% 6%	17512
	Night	17% 11% 27% 29% 15% 2	27394

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% 10% 5% 11% 5% 5% 5% 3 4 5% 34%	4691
	11th to 20th	Day	11% 7% 3 6% 4 4 5% 3 4 7% 45%	4807
	21st to end	Day	17% 11% 4 9% 4 4 3 3 5% 5% 34%	5812
February	1st to 10th	Day	14% 12% 4 8% 4 4 4 3 4 6% 37%	2058
	11th to 20th	Day	16% 10% 3 9% 5% 4 3 4 4 5% 37%	2048
	21st to end	Day	13% 11% 3 9% 4 4 5% 4 5% 6% 36%	1730
March	1st to 10th	Day	17% 11% 3 6% 4 3 3 3 4 4 42%	4580
	11th to 20th	Day	11% 8% 2 5% 4 3 3 3 5% 7% 50%	4820
	21st to end	Day	11% 8% 3 7% 5% 5% 5% 4 5% 7% 40%	6099
April	1st to 10th	Day	11% 6% 2 6% 5% 4 4 4 6% 9% 43%	2520
	11th to 20th	Day	13% 8% 3 7% 4 4 5% 3 5% 7% 41%	2494
	21st to end	Day	16% 7% 2 6% 4 4 4 4 5% 7% 40%	2520
May	1st to 10th	Day	17% 8% 3 8% 6% 6% 6% 5% 7% 9% 27%	5915
	11th to 20th	Day	15% 7% 2 7% 5% 5% 5% 4 6% 8% 35%	5939
	21st to end	Day	12% 7% 2 7% 5% 5% 5% 5% 6% 7% 39%	6798
June	1st to 10th	Day	9% 5% 2 5% 5% 5% 4 5% 6% 9% 45%	2800
	11th to 20th	Day	7% 4 2 5% 4 5% 5% 5% 7% 10% 48%	2800
	21st to end	Day	6% 4 2 5% 6% 5% 5% 5% 7% 10% 46%	2800
July	1st to 10th	Day	10% 4 2 5% 4 4 5% 4 6% 10% 45%	6360
	11th to 20th	Day	6% 4 2 6% 4 5% 6% 5% 7% 11% 43%	6360
	21st to end	Day	6% 6% 2 7% 6% 6% 6% 6% 8% 11% 36%	6884
August	1st to 10th	Day	7% 4 2 4 3 3 4 4 6% 10% 54%	3920
	11th to 20th	Day	8% 5% 2 6% 5% 5% 6% 5% 7% 9% 43%	3849
	21st to end	Day	6% 3 1 4 4 3 4 4 6% 8% 56%	4312
September	1st to 10th	Day	10% 5% 2 7% 4 4 4 4 6% 7% 47%	2400
	11th to 20th	Day	8% 5% 2 5% 4 4 5% 3 5% 7% 51%	2275
	21st to end	Day	11% 5% 2 5% 3 3 3 3 5% 7% 52%	2200
October	1st to 10th	Day	9% 3 2 5% 3 4 3 2 5% 6% 58%	2170
	11th to 20th	Day	11% 5% 2 5% 4 3 3 3 4 7% 53%	2000
	21st to end	Day	18% 7% 2 4 4 3 3 2 4 5% 46%	2075
November	1st to 10th	Day	8% 6% 3 6% 3 3 5% 4 5% 6% 52%	1852
	11th to 20th	Day	13% 8% 2 5% 5% 4 4 3 5% 5% 47%	1890
	21st to end	Day	18% 11% 3 6% 4 3 2 2 5% 6% 42%	1890
December	1st to 10th	Day	11% 9% 2 6% 4 3 3 3 4 5% 49%	2921
	11th to 20th	Day	12% 9% 5% 10% 5% 5% 4 3 5% 6% 36%	3088
	21st to end	Day	23% 15% 4 8% 5% 4 4 3 4 5% 25%	4070
January	1st to 10th	Night	15% 11% 4 9% 4 4 4 3 4 6% 37%	8232
	11th to 20th	Night	12% 9% 4 9% 4 4 5% 2 4 5% 42%	8180
	21st to end	Night	17% 10% 4 8% 4 4 3 3 4 5% 38%	8402
February	1st to 10th	Night	18% 12% 5% 8% 5% 3 4 3 4 5% 33%	2559
	11th to 20th	Night	16% 8% 3 7% 5% 4 3 3 5% 6% 39%	2458
	21st to end	Night	16% 10% 4 7% 4 4 3 4 5% 4 39%	2076
March	1st to 10th	Night	19% 10% 3 6% 5% 4 4 3 5% 5% 37%	5493
	11th to 20th	Night	12% 6% 2 6% 3 3 4 3 5% 6% 48%	5401
	21st to end	Night	14% 7% 3 8% 5% 5% 5% 4 6% 6% 37%	5072
April	1st to 10th	Night	12% 6% 2 6% 4 4 4 3 4 7% 47%	2100
	11th to 20th	Night	15% 5% 2 5% 4 4 5% 5% 5% 6% 45%	2075
	21st to end	Night	17% 7% 3 6% 5% 4 4 4 6% 6% 38%	2100
May	1st to 10th	Night	17% 8% 3 8% 5% 4 5% 4 5% 9% 32%	4199
	11th to 20th	Night	13% 6% 3 8% 5% 5% 5% 4 6% 7% 37%	4086
	21st to end	Night	13% 6% 2 7% 5% 4 5% 4 6% 8% 40%	4056
June	1st to 10th	Night	10% 5% 1 7% 4 4 4 4 6% 10% 46%	1600
	11th to 20th	Night	5% 4 1 5% 4 4 4 4 6% 9% 54%	1600
	21st to end	Night	3 3 1 4 3 4 5% 5% 8% 11% 52%	1600
July	1st to 10th	Night	10% 4 2 5% 4 4 4 4 6% 7% 50%	3618
	11th to 20th	Night	6% 4 1 6% 4 4 6% 4 6% 9% 51%	3617
	21st to end	Night	6% 5% 2 6% 5% 5% 5% 4 8% 12% 42%	3983
August	1st to 10th	Night	6% 4 2 4 3 3 4 3 5% 9% 57%	3227
	11th to 20th	Night	8% 4 1 5% 4 4 4 4 6% 8% 52%	3200
	21st to end	Night	4 4 1 4 4 3 4 3 6% 8% 60%	3586
September	1st to 10th	Night	10% 5% 2 5% 4 3 4 2 4 6% 54%	2000
	11th to 20th	Night	7% 5% 2 6% 3 3 4 3 5% 7% 54%	2105
	21st to end	Night	12% 5% 2 4 4 4 4 3 5% 6% 53%	2200
October	1st to 10th	Night	7% 4 1 5% 4 3 4 2 4 5% 60%	2225
	11th to 20th	Night	14% 4 2 4 3 3 3 2 4 6% 56%	2400
	21st to end	Night	19% 7% 2 5% 3 2 3 2 4 5% 46%	2763
November	1st to 10th	Night	11% 5% 2 4 3 3 4 3 4 6% 55%	2666
	11th to 20th	Night	12% 6% 2 6% 4 3 3 3 4 7% 50%	2730
	21st to end	Night	18% 7% 3 5% 4 3 3 3 4 5% 45%	2730
December	1st to 10th	Night	16% 10% 3 8% 3 3 3 2 4 4 44%	4477
	11th to 20th	Night	14% 9% 3 6% 4 4 4 3 5% 5% 43%	5339
	21st to end	Night	23% 13% 4 8% 5% 5% 4 3 4 4 27%	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	53% 4 12% 24% 7% 1	4692
	11th to 20th	Day	40% 4 8% 29% 18% 2	4807
	21st to end	Day	53% 2 11% 18% 11% 6%	5812
February	1st to 10th	Day	49% 4 12% 23% 11% 2	2058
	11th to 20th	Day	50% 4 9% 20% 14% 3	2058
	21st to end	Day	49% 5% 9% 20% 13% 4	1730
March	1st to 10th	Day	47% 3 4 21% 21% 4	4580
	11th to 20th	Day	36% 4 9% 27% 20% 4	4820
	21st to end	Day	43% 4 12% 27% 14% 1	6101
April	1st to 10th	Day	38% 5% 13% 26% 17% 1	2520
	11th to 20th	Day	43% 5% 11% 23% 15% 3	2494
	21st to end	Day	43% 4 10% 28% 12% 2	2520
May	1st to 10th	Day	52% 7% 10% 20% 10% 1	5952
	11th to 20th	Day	46% 7% 11% 24% 12% 1	5943
	21st to end	Day	42% 7% 9% 21% 19% 3	6812
June	1st to 10th	Day	35% 6% 13% 26% 18% 2	2800
	11th to 20th	Day	30% 8% 12% 27% 22% 3	2800
	21st to end	Day	32% 7% 15% 24% 17% 5%	2800
July	1st to 10th	Day	34% 7% 10% 28% 19% 2	6291
	11th to 20th	Day	32% 9% 16% 29% 12% 1	6285
	21st to end	Day	39% 9% 18% 25% 9% 1	6688
August	1st to 10th	Day	26% 6% 14% 34% 19% 1	3907
	11th to 20th	Day	36% 6% 14% 26% 18% 1	3885
	21st to end	Day	25% 5% 12% 35% 19% 3	4311
September	1st to 10th	Day	36% 5% 9% 27% 19% 5%	2400
	11th to 20th	Day	32% 6% 9% 26% 26% 2	2275
	21st to end	Day	32% 5% 7% 26% 27% 4	2200
October	1st to 10th	Day	18% 2 5% 24% 44% 7%	3534
	11th to 20th	Day	23% 3 9% 23% 35% 8%	3240
	21st to end	Day	32% 3 5% 26% 29% 5%	3326
November	1st to 10th	Day	33% 6% 9% 29% 18% 6%	1852
	11th to 20th	Day	39% 4 8% 24% 20% 5%	1890
	21st to end	Day	46% 3 8% 25% 16% 2	1890
December	1st to 10th	Day	39% 3 12% 30% 16% 1	2921
	11th to 20th	Day	48% 4 10% 24% 12% 2	3085
	21st to end	Day	62% 4 12% 14% 7%	4070
January	1st to 10th	Night	50% 3 13% 26% 8%	8233
	11th to 20th	Night	46% 3 6% 24% 19% 3	8180
	21st to end	Night	50% 3 9% 20% 16% 1	8402
February	1st to 10th	Night	55% 4 9% 21% 11% 1	2559
	11th to 20th	Night	47% 4 8% 24% 15% 2	2459
	21st to end	Night	48% 4 9% 21% 15% 4	2076
March	1st to 10th	Night	50% 3 7% 18% 19% 3	5493
	11th to 20th	Night	37% 4 10% 22% 20% 7%	5401
	21st to end	Night	47% 5% 11% 24% 12% 1	5072
April	1st to 10th	Night	37% 4 11% 27% 16% 3	2100
	11th to 20th	Night	39% 5% 10% 23% 19% 5%	2075
	21st to end	Night	45% 5% 9% 23% 15% 2	2100
May	1st to 10th	Night	49% 6% 14% 22% 9% 1	4226
	11th to 20th	Night	45% 7% 12% 22% 13% 1	4087
	21st to end	Night	41% 6% 12% 25% 13% 3	4064
June	1st to 10th	Night	32% 6% 14% 24% 21% 3	1600
	11th to 20th	Night	26% 6% 13% 25% 25% 5%	1600
	21st to end	Night	23% 7% 17% 27% 19% 7%	1600
July	1st to 10th	Night	33% 6% 10% 26% 22% 3	3580
	11th to 20th	Night	30% 8% 18% 30% 12% 2	3572
	21st to end	Night	33% 7% 22% 27% 11% 1	3868
August	1st to 10th	Night	23% 6% 18% 34% 19% 1	3216
	11th to 20th	Night	29% 6% 14% 29% 20% 2	3230
	21st to end	Night	22% 5% 12% 36% 22% 3	3586
September	1st to 10th	Night	33% 5% 7% 28% 21% 7%	2000
	11th to 20th	Night	30% 4 8% 30% 24% 4	2105
	21st to end	Night	33% 4 9% 23% 26% 6%	2200
October	1st to 10th	Night	18% 2 5% 16% 49% 10%	3641
	11th to 20th	Night	21% 2 6% 23% 41% 7%	3899
	21st to end	Night	32% 3 5% 24% 25% 10%	4462
November	1st to 10th	Night	31% 4 9% 26% 24% 5%	2666
	11th to 20th	Night	36% 3 7% 25% 22% 6%	2730
	21st to end	Night	43% 3 8% 25% 19% 2	2730
December	1st to 10th	Night	45% 3 9% 26% 17% 1	4477
	11th to 20th	Night	44% 3 12% 22% 18% 1	5341
	21st to end	Night	61% 4 9% 17% 7% 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	23% 22% 32% 18% 4	330
	11th to 20th	Day	25% 27% 32% 13% 2	330
	21st to end	Day	22% 25% 39% 12% 2	363
February	1st to 10th	Day	22% 23% 38% 14% 2	330
	11th to 20th	Day	26% 31% 32% 10% 1	330
	21st to end	Day	29% 24% 30% 14% 2	273
March	1st to 10th	Day	23% 27% 34% 11% 4 1	330
	11th to 20th	Day	25% 25% 36% 10% 2	334
	21st to end	Day	24% 23% 32% 16% 5% 1	594
April	1st to 10th	Day	17% 22% 31% 24% 5%	540
	11th to 20th	Day	21% 23% 24% 23% 9%	532
	21st to end	Day	20% 18% 33% 19% 8% 2	540
May	1st to 10th	Day	20% 17% 30% 23% 7% 2	543
	11th to 20th	Day	19% 10% 30% 25% 12% 4	551
	21st to end	Day	12% 9% 28% 28% 16% 6%	730
June	1st to 10th	Day	12% 5% 22% 26% 25% 9%	730
	11th to 20th	Day	7% 5% 21% 37% 23% 8%	730
	21st to end	Day	8% 5% 27% 33% 20% 8%	730
July	1st to 10th	Day	11% 3 15% 27% 25% 19%	721
	11th to 20th	Day	6% 4 15% 35% 28% 11%	718
	21st to end	Day	8% 3 15% 31% 32% 11%	794
August	1st to 10th	Day	9% 3 13% 33% 27% 15%	541
	11th to 20th	Day	13% 2 16% 29% 29% 11%	519
	21st to end	Day	8% 3 14% 26% 33% 15%	583
September	1st to 10th	Day	10% 3 15% 29% 33% 10%	530
	11th to 20th	Day	9% 3 11% 29% 33% 15%	530
	21st to end	Day	16% 7% 22% 24% 23% 9%	530
October	1st to 10th	Day	10% 5% 23% 33% 21% 8%	500
	11th to 20th	Day	15% 14% 33% 23% 11% 4	330
	21st to end	Day	26% 15% 31% 22% 5%	363
November	1st to 10th	Day	12% 17% 34% 25% 11% 2	330
	11th to 20th	Day	18% 20% 31% 23% 8%	330
	21st to end	Day	29% 18% 25% 19% 7% 1	330
December	1st to 10th	Day	19% 24% 34% 15% 6% 2	330
	11th to 20th	Day	21% 20% 37% 18% 5%	330
	21st to end	Day	28% 23% 34% 14% 2	363
January	1st to 10th	Night	22% 18% 32% 24% 3	1050
	11th to 20th	Night	23% 21% 35% 18% 3	1050
	21st to end	Night	20% 17% 40% 21% 2	1155
February	1st to 10th	Night	24% 16% 36% 22% 2	879
	11th to 20th	Night	24% 19% 35% 21% 1	823
	21st to end	Night	25% 17% 37% 20% 1	692
March	1st to 10th	Night	22% 17% 34% 24% 3	840
	11th to 20th	Night	22% 14% 37% 21% 6%	777
	21st to end	Night	23% 15% 31% 25% 6% 1	693
April	1st to 10th	Night	16% 15% 36% 28% 6%	630
	11th to 20th	Night	17% 15% 29% 27% 11% 1	623
	21st to end	Night	19% 11% 31% 29% 9% 1	630
May	1st to 10th	Night	17% 9% 29% 34% 10% 1	630
	11th to 20th	Night	16% 6% 26% 33% 17% 2	609
	21st to end	Night	9% 4 23% 40% 21% 4	650
June	1st to 10th	Night	12% 3 20% 38% 27% 2	600
	11th to 20th	Night	6% 2 17% 45% 28% 2	600
	21st to end	Night	5% 3 19% 42% 29% 3	600
July	1st to 10th	Night	9% 2 10% 33% 38% 9%	585
	11th to 20th	Night	6% 2 11% 38% 37% 6%	582
	21st to end	Night	7% 2 13% 36% 37% 6%	657
August	1st to 10th	Night	8% 2 10% 38% 36% 7%	597
	11th to 20th	Night	9% 1 12% 35% 39% 4	594
	21st to end	Night	7% 2 10% 36% 39% 7%	660
September	1st to 10th	Night	11% 2 14% 32% 36% 5%	600
	11th to 20th	Night	9% 3 13% 32% 38% 6%	705
	21st to end	Night	13% 6% 20% 31% 24% 6%	800
October	1st to 10th	Night	9% 6% 19% 35% 26% 5%	800
	11th to 20th	Night	16% 9% 29% 28% 17% 2	800
	21st to end	Night	22% 11% 32% 25% 9% 1	880
November	1st to 10th	Night	14% 10% 32% 32% 11% 1	820
	11th to 20th	Night	14% 13% 32% 30% 10% 1	840
	21st to end	Night	22% 13% 30% 26% 9%	840
December	1st to 10th	Night	23% 12% 33% 27% 5%	898
	11th to 20th	Night	22% 13% 33% 26% 5%	1050
	21st to end	Night	25% 17% 35% 19% 3	1155

Page generated at 2026-05-14 00:58:56. Version ac07

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