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 2025-01-22.

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 6% 4 4 4 4 5% 7% 42%	104933
	Night	14% 7% 3 6% 4 4 4 3 5% 6% 44%	104495
Transparency	Day	39% 5% 10% 25% 17% 3	108578
	Night	40% 4 10% 24% 18% 3	108991
Seeing	Day	16% 12% 25% 25% 16% 6%	15743
	Night	17% 10% 27% 29% 15% 2	25649

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% 12% 5% 10% 5% 4 4 3 5% 5% 34%	2607
	11th to 20th	Day	17% 8% 3 7% 5% 5% 6% 4 4 6% 36%	2653
	21st to end	Day	23% 16% 4 9% 4 3 3 3 4 4 27%	3144
February	1st to 10th	Day	15% 12% 4 7% 4 4 4 4 4 6% 37%	1862
	11th to 20th	Day	15% 10% 3 8% 5% 4 4 4 5% 5% 37%	1848
	21st to end	Day	14% 11% 3 8% 4 4 5% 4 5% 6% 35%	1570
March	1st to 10th	Day	21% 13% 3 7% 4 4 3 3 4 4 35%	3120
	11th to 20th	Day	14% 7% 2 5% 4 2 3 3 4 6% 50%	3300
	21st to end	Day	12% 8% 3 7% 5% 5% 5% 4 5% 7% 39%	4165
April	1st to 10th	Day	11% 6% 2 6% 5% 4 4 4 5% 9% 44%	2280
	11th to 20th	Day	13% 8% 3 7% 4 4 5% 3 5% 7% 41%	2254
	21st to end	Day	17% 8% 3 6% 4 4 4 4 5% 7% 40%	2280
May	1st to 10th	Day	14% 7% 3 8% 6% 6% 6% 5% 7% 9% 30%	4035
	11th to 20th	Day	17% 7% 2 6% 4 4 4 3 6% 8% 37%	4081
	21st to end	Day	9% 6% 2 7% 5% 5% 5% 5% 7% 7% 41%	4729
June	1st to 10th	Day	9% 5% 3 5% 5% 5% 4 5% 6% 9% 45%	2660
	11th to 20th	Day	6% 3 2 5% 4 5% 5% 5% 6% 10% 49%	2660
	21st to end	Day	6% 4 2 5% 5% 5% 5% 4 8% 10% 46%	2660
July	1st to 10th	Day	12% 5% 2 5% 4 4 5% 5% 7% 10% 41%	4440
	11th to 20th	Day	5% 4 2 5% 4 5% 6% 4 6% 10% 50%	4440
	21st to end	Day	8% 7% 3 9% 6% 7% 7% 6% 8% 8% 32%	4787
August	1st to 10th	Day	7% 4 2 3 4 3 4 4 6% 10% 54%	3799
	11th to 20th	Day	9% 5% 2 6% 5% 5% 6% 5% 6% 9% 42%	3729
	21st to end	Day	6% 3 1 4 3 3 4 4 6% 8% 56%	4180
September	1st to 10th	Day	10% 5% 2 7% 4 4 4 4 5% 7% 47%	2280
	11th to 20th	Day	9% 5% 2 5% 4 4 5% 4 5% 7% 50%	2161
	21st to end	Day	11% 5% 2 5% 3 3 3 3 5% 7% 52%	2090
October	1st to 10th	Day	9% 4 2 5% 3 4 3 2 5% 6% 58%	2062
	11th to 20th	Day	12% 5% 2 5% 4 3 4 3 4 7% 52%	1900
	21st to end	Day	17% 7% 2 4 4 3 4 2 4 6% 46%	1971
November	1st to 10th	Day	8% 5% 3 5% 3 3 5% 4 5% 6% 52%	1762
	11th to 20th	Day	13% 8% 2 6% 5% 4 4 3 5% 5% 47%	1800
	21st to end	Day	17% 10% 2 6% 4 3 2 2 5% 6% 42%	1800
December	1st to 10th	Day	11% 9% 2 6% 4 3 3 3 4 5% 49%	2834
	11th to 20th	Day	12% 9% 5% 10% 5% 5% 4 3 5% 6% 35%	3008
	21st to end	Day	23% 15% 4 8% 5% 4 4 3 4 4 25%	3982
January	1st to 10th	Night	17% 10% 4 8% 4 4 4 3 4 7% 35%	4568
	11th to 20th	Night	14% 11% 5% 9% 5% 5% 6% 3 4 5% 32%	4534
	21st to end	Night	24% 14% 6% 8% 4 3 3 3 3 5% 28%	4546
February	1st to 10th	Night	19% 12% 5% 8% 5% 3 4 2 4 4 33%	2316
	11th to 20th	Night	15% 8% 3 7% 5% 4 3 4 5% 6% 40%	2218
	21st to end	Night	16% 11% 4 7% 5% 4 3 4 5% 4 37%	1884
March	1st to 10th	Night	22% 9% 2 5% 4 3 4 3 4 5% 37%	3733
	11th to 20th	Night	13% 6% 2 6% 3 3 3 3 4 7% 49%	3686
	21st to end	Night	15% 8% 3 7% 5% 5% 4 3 5% 6% 38%	3466
April	1st to 10th	Night	11% 6% 2 6% 5% 4 4 3 4 7% 47%	1900
	11th to 20th	Night	16% 5% 2 5% 4 4 4 4 5% 6% 45%	1875
	21st to end	Night	17% 7% 3 6% 5% 3 3 4 6% 7% 38%	1900
May	1st to 10th	Night	15% 7% 3 7% 5% 3 5% 3 5% 8% 38%	2859
	11th to 20th	Night	15% 7% 2 6% 4 5% 4 3 5% 6% 43%	2812
	21st to end	Night	8% 5% 2 7% 5% 5% 5% 4 6% 9% 44%	2818
June	1st to 10th	Night	10% 5% 1 6% 4 4 4 4 6% 10% 47%	1520
	11th to 20th	Night	5% 3 1 5% 4 4 4 4 6% 9% 55%	1520
	21st to end	Night	3 4 1 4 3 4 5% 5% 8% 11% 52%	1520
July	1st to 10th	Night	11% 4 2 5% 4 5% 4 4 6% 8% 49%	2530
	11th to 20th	Night	6% 3 1 5% 3 3 4 3 6% 8% 58%	2530
	21st to end	Night	8% 7% 2 8% 6% 6% 6% 5% 8% 9% 36%	2772
August	1st to 10th	Night	6% 3 2 4 3 3 4 3 5% 9% 58%	3128
	11th to 20th	Night	8% 4 1 5% 4 4 4 4 6% 8% 52%	3100
	21st to end	Night	4 4 1 4 4 3 4 3 6% 8% 60%	3476
September	1st to 10th	Night	11% 5% 2 5% 4 3 4 2 4 6% 54%	1900
	11th to 20th	Night	7% 5% 2 6% 4 3 4 4 5% 7% 53%	2000
	21st to end	Night	11% 5% 2 4 4 4 4 3 5% 6% 53%	2090
October	1st to 10th	Night	8% 4 1 5% 4 3 4 2 5% 5% 60%	2114
	11th to 20th	Night	14% 4 2 4 3 3 3 2 4 6% 55%	2280
	21st to end	Night	18% 7% 2 5% 3 2 3 2 5% 5% 47%	2625
November	1st to 10th	Night	11% 5% 2 4 3 3 4 3 4 6% 56%	2536
	11th to 20th	Night	13% 5% 2 6% 5% 3 3 3 4 7% 50%	2600
	21st to end	Night	17% 7% 3 5% 4 3 3 3 4 5% 46%	2600
December	1st to 10th	Night	16% 10% 3 8% 3 3 3 2 4 4 44%	4344
	11th to 20th	Night	15% 9% 3 6% 4 4 4 3 5% 5% 43%	5199
	21st to end	Night	23% 13% 4 8% 5% 5% 4 3 4 4 27%	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	52% 4 9% 25% 9% 1	2608
	11th to 20th	Day	50% 4 9% 24% 13% 1	2653
	21st to end	Day	62% 3 7% 19% 8% 1	3144
February	1st to 10th	Day	49% 4 11% 23% 11% 2	1862
	11th to 20th	Day	48% 4 9% 20% 14% 3	1858
	21st to end	Day	50% 5% 10% 18% 13% 5%	1570
March	1st to 10th	Day	54% 4 4 19% 14% 5%	3120
	11th to 20th	Day	37% 4 10% 28% 16% 5%	3300
	21st to end	Day	44% 5% 13% 23% 14% 1	4165
April	1st to 10th	Day	38% 4 12% 27% 17% 2	2280
	11th to 20th	Day	43% 5% 10% 23% 16% 3	2254
	21st to end	Day	44% 4 10% 27% 12% 2	2280
May	1st to 10th	Day	47% 8% 12% 23% 9% 1	4073
	11th to 20th	Day	45% 7% 10% 26% 12% 1	4085
	21st to end	Day	39% 8% 10% 19% 23% 2	4742
June	1st to 10th	Day	35% 6% 13% 26% 18% 2	2660
	11th to 20th	Day	28% 8% 12% 27% 22% 3	2660
	21st to end	Day	31% 7% 15% 24% 17% 5%	2660
July	1st to 10th	Day	37% 7% 12% 26% 16% 3	4371
	11th to 20th	Day	28% 7% 13% 34% 17% 2	4365
	21st to end	Day	45% 9% 14% 22% 9% 1	4636
August	1st to 10th	Day	26% 6% 15% 34% 19% 1	3786
	11th to 20th	Day	36% 6% 13% 26% 18% 1	3765
	21st to end	Day	25% 5% 12% 35% 19% 3	4179
September	1st to 10th	Day	36% 5% 9% 27% 18% 5%	2280
	11th to 20th	Day	33% 6% 8% 26% 25% 2	2161
	21st to end	Day	31% 5% 8% 27% 26% 4	2090
October	1st to 10th	Day	18% 2 5% 23% 44% 7%	3426
	11th to 20th	Day	23% 3 8% 23% 35% 8%	3140
	21st to end	Day	32% 3 5% 27% 29% 5%	3222
November	1st to 10th	Day	32% 6% 9% 28% 19% 6%	1762
	11th to 20th	Day	39% 4 7% 24% 20% 6%	1800
	21st to end	Day	45% 3 8% 25% 16% 2	1800
December	1st to 10th	Day	38% 3 12% 30% 16% 1	2834
	11th to 20th	Day	49% 4 9% 24% 12% 2	3005
	21st to end	Day	63% 4 12% 14% 7%	3982
January	1st to 10th	Night	50% 4 9% 26% 10% 1	4568
	11th to 20th	Night	54% 4 7% 22% 11% 2	4534
	21st to end	Night	60% 3 8% 18% 9% 1	4546
February	1st to 10th	Night	56% 3 8% 20% 12% 1	2316
	11th to 20th	Night	45% 4 8% 24% 16% 3	2219
	21st to end	Night	50% 4 9% 19% 14% 4	1884
March	1st to 10th	Night	50% 4 7% 18% 18% 3	3733
	11th to 20th	Night	36% 5% 13% 22% 18% 7%	3686
	21st to end	Night	46% 5% 11% 26% 11% 1	3466
April	1st to 10th	Night	38% 4 10% 27% 17% 4	1900
	11th to 20th	Night	39% 5% 9% 23% 20% 5%	1875
	21st to end	Night	45% 5% 10% 23% 15% 3	1900
May	1st to 10th	Night	44% 6% 15% 25% 8% 1	2886
	11th to 20th	Night	42% 6% 12% 25% 14% 1	2813
	21st to end	Night	36% 7% 13% 26% 16% 2	2826
June	1st to 10th	Night	32% 6% 14% 24% 22% 3	1520
	11th to 20th	Night	24% 6% 13% 26% 25% 5%	1520
	21st to end	Night	23% 7% 17% 27% 19% 7%	1520
July	1st to 10th	Night	34% 5% 11% 28% 18% 4	2490
	11th to 20th	Night	24% 5% 13% 37% 17% 4	2482
	21st to end	Night	41% 7% 17% 23% 11% 1	2684
August	1st to 10th	Night	22% 6% 18% 34% 19% 1	3117
	11th to 20th	Night	30% 6% 14% 28% 20% 2	3130
	21st to end	Night	22% 5% 12% 37% 21% 3	3476
September	1st to 10th	Night	33% 4 7% 28% 21% 7%	1900
	11th to 20th	Night	31% 5% 7% 30% 23% 5%	2000
	21st to end	Night	32% 4 9% 24% 25% 6%	2090
October	1st to 10th	Night	18% 2 5% 16% 49% 10%	3530
	11th to 20th	Night	22% 2 5% 23% 41% 7%	3779
	21st to end	Night	32% 3 6% 24% 25% 10%	4324
November	1st to 10th	Night	31% 4 10% 25% 25% 6%	2536
	11th to 20th	Night	36% 3 7% 24% 23% 7%	2600
	21st to end	Night	42% 3 8% 25% 20% 2	2600
December	1st to 10th	Night	45% 3 9% 26% 17% 1	4344
	11th to 20th	Night	44% 3 12% 22% 18% 1	5201
	21st to end	Night	62% 4 9% 17% 7% 2	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	24% 22% 32% 19% 3	300
	11th to 20th	Day	26% 26% 32% 13% 2	300
	21st to end	Day	24% 26% 35% 13% 2	300
February	1st to 10th	Day	24% 25% 36% 13% 2	270
	11th to 20th	Day	27% 32% 30% 10% 1	270
	21st to end	Day	31% 25% 28% 13% 3	225
March	1st to 10th	Day	23% 27% 36% 10% 4	270
	11th to 20th	Day	26% 26% 34% 11% 3	274
	21st to end	Day	26% 23% 30% 16% 5% 1	506
April	1st to 10th	Day	16% 24% 30% 24% 5%	460
	11th to 20th	Day	22% 21% 24% 23% 9%	452
	21st to end	Day	21% 19% 33% 17% 8% 2	460
May	1st to 10th	Day	20% 17% 30% 23% 8% 2	463
	11th to 20th	Day	20% 9% 29% 24% 13% 5%	487
	21st to end	Day	11% 8% 28% 28% 17% 7%	678
June	1st to 10th	Day	12% 5% 22% 26% 26% 9%	680
	11th to 20th	Day	7% 5% 21% 37% 22% 8%	680
	21st to end	Day	8% 5% 29% 33% 19% 7%	680
July	1st to 10th	Day	12% 3 15% 27% 24% 20%	671
	11th to 20th	Day	6% 4 16% 35% 28% 11%	668
	21st to end	Day	8% 3 16% 32% 30% 10%	739
August	1st to 10th	Day	9% 3 13% 33% 27% 15%	500
	11th to 20th	Day	14% 2 18% 29% 28% 9%	479
	21st to end	Day	9% 3 14% 26% 33% 16%	539
September	1st to 10th	Day	10% 3 15% 29% 32% 10%	490
	11th to 20th	Day	9% 4 11% 30% 32% 14%	490
	21st to end	Day	16% 8% 22% 24% 22% 9%	490
October	1st to 10th	Day	10% 5% 24% 33% 19% 8%	462
	11th to 20th	Day	16% 15% 34% 22% 9% 4	300
	21st to end	Day	25% 16% 30% 23% 5%	330
November	1st to 10th	Day	11% 17% 34% 25% 12% 2	300
	11th to 20th	Day	17% 22% 30% 23% 7%	300
	21st to end	Day	29% 18% 25% 20% 7% 1	300
December	1st to 10th	Day	20% 24% 32% 15% 7% 2	300
	11th to 20th	Day	23% 19% 35% 18% 5%	300
	21st to end	Day	28% 24% 33% 13% 2	330
January	1st to 10th	Night	22% 19% 33% 23% 3	1000
	11th to 20th	Night	24% 21% 35% 17% 3	1000
	21st to end	Night	21% 17% 39% 21% 2	1051
February	1st to 10th	Night	25% 17% 35% 21% 2	796
	11th to 20th	Night	22% 19% 36% 21% 2	743
	21st to end	Night	26% 17% 37% 19% 1	628
March	1st to 10th	Night	22% 16% 35% 24% 3	760
	11th to 20th	Night	22% 13% 37% 21% 6%	703
	21st to end	Night	24% 14% 30% 25% 6% 1	627
April	1st to 10th	Night	15% 15% 36% 28% 6%	570
	11th to 20th	Night	18% 14% 28% 26% 12% 1	563
	21st to end	Night	20% 12% 31% 28% 8% 1	570
May	1st to 10th	Night	17% 9% 29% 33% 11% 1	570
	11th to 20th	Night	16% 6% 25% 33% 18% 2	561
	21st to end	Night	9% 4 22% 40% 22% 4	617
June	1st to 10th	Night	11% 2 20% 37% 27% 2	570
	11th to 20th	Night	6% 2 18% 45% 28% 2	570
	21st to end	Night	4 3 20% 43% 27% 2	570
July	1st to 10th	Night	9% 2 10% 34% 37% 8%	555
	11th to 20th	Night	6% 2 11% 38% 36% 6%	552
	21st to end	Night	7% 2 14% 37% 35% 5%	624
August	1st to 10th	Night	8% 1 10% 38% 36% 6%	567
	11th to 20th	Night	9% 1 13% 36% 36% 4	564
	21st to end	Night	7% 2 9% 36% 40% 7%	627
September	1st to 10th	Night	11% 2 14% 31% 37% 5%	570
	11th to 20th	Night	9% 3 13% 31% 37% 6%	670
	21st to end	Night	13% 6% 21% 31% 24% 6%	760
October	1st to 10th	Night	9% 6% 20% 35% 25% 5%	760
	11th to 20th	Night	16% 9% 30% 27% 15% 2	760
	21st to end	Night	22% 11% 32% 25% 9% 1	836
November	1st to 10th	Night	14% 10% 31% 32% 12% 1	780
	11th to 20th	Night	15% 13% 32% 30% 10% 1	800
	21st to end	Night	22% 13% 30% 26% 9% 1	800
December	1st to 10th	Night	23% 13% 33% 27% 5%	855
	11th to 20th	Night	22% 13% 32% 27% 6% 1	1000
	21st to end	Night	25% 18% 35% 19% 3	1100

Page generated at 2025-01-19 02:06:44. Version ac07

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