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 2025-09-04.

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	15% 7% 2 6% 4 4 5% 4 6% 8% 38%	126238
	Night	16% 7% 2 6% 4 4 4 4 5% 7% 39%	122478
Transparency	Day	42% 6% 12% 22% 15% 2	129830
	Night	42% 6% 12% 22% 16% 3	126954
Seeing	Day	22% 15% 28% 21% 11% 3	15931
	Night	20% 13% 28% 27% 11% 1	25289

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	12% 7% 2 11% 6% 5% 4 4 5% 5% 40%	3597
	11th to 20th	Day	12% 10% 3 9% 7% 6% 5% 4 5% 7% 32%	3946
	21st to end	Day	16% 9% 3 8% 5% 5% 5% 3 5% 6% 34%	4466
February	1st to 10th	Day	14% 10% 3 7% 4 5% 6% 4 5% 7% 34%	1800
	11th to 20th	Day	15% 8% 3 7% 5% 4 4 4 5% 7% 38%	1800
	21st to end	Day	19% 9% 3 7% 5% 4 5% 4 4 5% 36%	1650
March	1st to 10th	Day	20% 5% 2 5% 4 5% 5% 3 5% 6% 41%	4755
	11th to 20th	Day	11% 7% 3 7% 5% 4 5% 4 5% 8% 42%	4980
	21st to end	Day	16% 7% 2 5% 4 4 5% 4 5% 6% 41%	5602
April	1st to 10th	Day	16% 7% 3 7% 4 5% 6% 4 5% 7% 36%	2400
	11th to 20th	Day	15% 7% 2 7% 4 4 4 4 5% 7% 41%	2374
	21st to end	Day	17% 6% 2 6% 4 4 5% 4 6% 7% 40%	2400
May	1st to 10th	Day	25% 7% 2 6% 4 4 5% 4 6% 8% 31%	5856
	11th to 20th	Day	23% 8% 3 6% 5% 4 4 4 6% 8% 30%	6318
	21st to end	Day	18% 6% 2 6% 4 4 5% 4 7% 9% 35%	6934
June	1st to 10th	Day	12% 6% 2 6% 4 5% 5% 5% 6% 9% 40%	2800
	11th to 20th	Day	14% 6% 2 6% 5% 5% 5% 4 7% 9% 39%	2800
	21st to end	Day	10% 5% 2 5% 5% 4 5% 5% 7% 11% 43%	2800
July	1st to 10th	Day	6% 5% 2 7% 6% 6% 6% 5% 7% 10% 41%	6360
	11th to 20th	Day	8% 6% 3 8% 5% 6% 6% 5% 8% 12% 32%	6360
	21st to end	Day	10% 7% 2 7% 5% 5% 5% 4 6% 10% 41%	6497
August	1st to 10th	Day	18% 5% 2 7% 5% 5% 6% 4 7% 9% 33%	4234
	11th to 20th	Day	14% 5% 2 6% 4 4 5% 5% 7% 7% 40%	4018
	21st to end	Day	13% 5% 2 5% 3 3 4 3 5% 9% 49%	4312
September	1st to 10th	Day	15% 6% 2 5% 4 4 3 3 4 7% 47%	2316
	11th to 20th	Day	13% 5% 1 4 3 4 4 4 6% 8% 49%	2280
	21st to end	Day	21% 8% 2 6% 4 4 4 3 5% 7% 37%	2008
October	1st to 10th	Day	17% 5% 2 5% 4 4 4 4 6% 6% 43%	1900
	11th to 20th	Day	16% 6% 2 6% 4 3 3 4 5% 7% 44%	1900
	21st to end	Day	15% 7% 2 5% 4 4 4 3 6% 7% 43%	2090
November	1st to 10th	Day	12% 7% 2 4 3 2 3 3 6% 8% 50%	1790
	11th to 20th	Day	17% 5% 2 4 4 5% 4 4 6% 6% 43%	1745
	21st to end	Day	17% 6% 2 5% 5% 5% 5% 4 5% 6% 41%	1600
December	1st to 10th	Day	14% 7% 3 7% 4 4 4 4 6% 8% 38%	2600
	11th to 20th	Day	21% 8% 2 6% 3 4 4 4 6% 7% 35%	2990
	21st to end	Day	18% 8% 3 9% 5% 5% 6% 5% 6% 7% 28%	3960
January	1st to 10th	Night	12% 8% 3 9% 4 5% 5% 4 5% 8% 38%	6349
	11th to 20th	Night	13% 7% 2 7% 4 5% 4 5% 6% 8% 38%	6010
	21st to end	Night	17% 7% 2 6% 4 4 4 4 5% 7% 38%	6490
February	1st to 10th	Night	16% 8% 3 6% 5% 4 5% 4 6% 7% 37%	2600
	11th to 20th	Night	17% 8% 3 6% 4 4 4 4 6% 7% 38%	2484
	21st to end	Night	17% 8% 3 8% 4 5% 4 4 5% 6% 38%	1980
March	1st to 10th	Night	18% 8% 2 6% 4 3 4 3 4 6% 42%	5083
	11th to 20th	Night	10% 7% 2 5% 4 4 4 3 5% 6% 49%	4980
	21st to end	Night	14% 7% 2 6% 4 4 4 4 5% 6% 43%	5330
April	1st to 10th	Night	18% 9% 3 7% 6% 4 4 3 6% 6% 35%	2000
	11th to 20th	Night	14% 6% 3 6% 4 4 4 4 6% 8% 40%	1975
	21st to end	Night	18% 5% 2 5% 4 3 4 4 5% 7% 43%	2000
May	1st to 10th	Night	27% 8% 2 7% 5% 4 4 4 5% 7% 27%	4068
	11th to 20th	Night	25% 8% 3 6% 4 4 4 3 5% 9% 31%	3575
	21st to end	Night	19% 7% 3 7% 4 4 4 3 5% 8% 37%	3920
June	1st to 10th	Night	13% 5% 2 6% 5% 4 4 4 6% 8% 45%	1600
	11th to 20th	Night	12% 5% 2 6% 4 5% 4 5% 6% 10% 39%	1600
	21st to end	Night	9% 5% 2 5% 4 5% 5% 6% 7% 10% 42%	1600
July	1st to 10th	Night	8% 6% 3 7% 5% 5% 6% 5% 6% 10% 40%	3598
	11th to 20th	Night	11% 6% 3 9% 6% 6% 6% 5% 7% 9% 32%	3597
	21st to end	Night	11% 5% 2 6% 5% 5% 5% 4 6% 8% 42%	4336
August	1st to 10th	Night	19% 5% 3 6% 4 4 6% 4 6% 8% 35%	2915
	11th to 20th	Night	13% 7% 2 7% 4 4 5% 4 6% 7% 39%	2997
	21st to end	Night	14% 5% 2 5% 4 4 5% 4 6% 8% 44%	3586
September	1st to 10th	Night	14% 6% 2 6% 3 4 3 3 5% 6% 47%	1931
	11th to 20th	Night	11% 5% 2 5% 3 3 4 3 4 7% 52%	1900
	21st to end	Night	21% 5% 2 6% 4 3 5% 3 5% 6% 40%	2167
October	1st to 10th	Night	20% 6% 2 5% 3 4 4 3 4 5% 45%	2280
	11th to 20th	Night	16% 6% 1 5% 4 3 4 3 4 6% 48%	2280
	21st to end	Night	17% 6% 2 4 3 4 4 4 5% 7% 44%	2508
November	1st to 10th	Night	10% 5% 2 5% 4 4 3 3 6% 6% 52%	2507
	11th to 20th	Night	15% 7% 2 6% 4 4 4 3 6% 6% 44%	2651
	21st to end	Night	15% 6% 2 6% 4 5% 5% 3 5% 7% 42%	2800
December	1st to 10th	Night	13% 7% 3 7% 4 4 5% 4 5% 7% 40%	4580
	11th to 20th	Night	22% 7% 2 4 4 4 5% 3 5% 7% 37%	5205
	21st to end	Night	18% 9% 3 8% 5% 5% 5% 4 6% 7% 30%	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	46% 4 11% 23% 15% 2	3598
	11th to 20th	Day	51% 4 12% 15% 14% 4	3946
	21st to end	Day	50% 5% 11% 20% 13% 1	4466
February	1st to 10th	Day	48% 6% 13% 21% 10% 2	1800
	11th to 20th	Day	47% 5% 10% 24% 12% 2	1809
	21st to end	Day	50% 4 10% 21% 10% 4	1650
March	1st to 10th	Day	43% 4 10% 23% 14% 6%	4755
	11th to 20th	Day	39% 5% 14% 26% 11% 5%	4980
	21st to end	Day	43% 5% 10% 19% 19% 4	5602
April	1st to 10th	Day	46% 6% 12% 18% 15% 4	2400
	11th to 20th	Day	42% 5% 12% 21% 16% 4	2374
	21st to end	Day	42% 5% 11% 22% 16% 4	2400
May	1st to 10th	Day	50% 7% 11% 18% 11% 2	5890
	11th to 20th	Day	51% 7% 10% 20% 11% 1	6322
	21st to end	Day	42% 7% 12% 22% 15% 2	6949
June	1st to 10th	Day	40% 8% 12% 22% 17% 2	2800
	11th to 20th	Day	41% 9% 13% 23% 13% 2	2800
	21st to end	Day	35% 8% 14% 26% 16% 1	2800
July	1st to 10th	Day	37% 10% 12% 23% 16% 2	6290
	11th to 20th	Day	41% 10% 15% 23% 11% 1	6285
	21st to end	Day	40% 6% 10% 20% 23% 1	6311
August	1st to 10th	Day	46% 9% 13% 23% 10%	4221
	11th to 20th	Day	39% 7% 11% 27% 14% 1	4057
	21st to end	Day	33% 5% 11% 30% 19% 2	4312
September	1st to 10th	Day	38% 6% 12% 20% 20% 4	2316
	11th to 20th	Day	32% 6% 12% 25% 22% 4	2280
	21st to end	Day	47% 5% 9% 16% 20% 2	2008
October	1st to 10th	Day	37% 6% 9% 22% 22% 4	3160
	11th to 20th	Day	28% 4 14% 28% 22% 3	3140
	21st to end	Day	27% 5% 12% 30% 25% 2	3428
November	1st to 10th	Day	33% 4 15% 24% 20% 4	1790
	11th to 20th	Day	41% 5% 12% 22% 17% 3	1745
	21st to end	Day	43% 6% 12% 28% 10% 2	1600
December	1st to 10th	Day	45% 5% 15% 24% 9% 2	2600
	11th to 20th	Day	48% 5% 15% 24% 7% 1	2986
	21st to end	Day	51% 6% 16% 16% 9% 1	3960
January	1st to 10th	Night	43% 5% 12% 22% 15% 2	6349
	11th to 20th	Night	42% 6% 14% 20% 14% 5%	6010
	21st to end	Night	45% 6% 11% 21% 15% 2	6490
February	1st to 10th	Night	46% 6% 13% 24% 9% 1	2600
	11th to 20th	Night	46% 5% 10% 20% 17% 2	2486
	21st to end	Night	47% 5% 9% 20% 15% 3	1980
March	1st to 10th	Night	45% 5% 9% 23% 12% 7%	5083
	11th to 20th	Night	35% 5% 15% 28% 12% 5%	4980
	21st to end	Night	42% 4 9% 18% 24% 3	5330
April	1st to 10th	Night	49% 4 10% 18% 15% 3	2000
	11th to 20th	Night	40% 6% 11% 21% 18% 3	1975
	21st to end	Night	40% 6% 10% 23% 18% 5%	2000
May	1st to 10th	Night	56% 6% 8% 16% 11% 3	4095
	11th to 20th	Night	50% 8% 11% 19% 11% 1	3576
	21st to end	Night	46% 7% 10% 21% 13% 3	3927
June	1st to 10th	Night	38% 7% 11% 23% 19% 2	1600
	11th to 20th	Night	39% 9% 13% 20% 18% 2	1600
	21st to end	Night	34% 9% 13% 26% 17% 2	1600
July	1st to 10th	Night	39% 9% 14% 19% 16% 4	3560
	11th to 20th	Night	45% 9% 14% 19% 12% 1	3552
	21st to end	Night	38% 6% 12% 21% 22% 1	4208
August	1st to 10th	Night	46% 7% 14% 22% 10% 1	2904
	11th to 20th	Night	42% 7% 10% 24% 17% 1	3024
	21st to end	Night	36% 7% 10% 29% 17% 2	3586
September	1st to 10th	Night	37% 6% 12% 21% 21% 4	1931
	11th to 20th	Night	32% 6% 9% 27% 23% 3	1900
	21st to end	Night	45% 5% 10% 18% 20% 2	2167
October	1st to 10th	Night	41% 5% 10% 21% 21% 2	3800
	11th to 20th	Night	29% 5% 10% 27% 25% 4	3779
	21st to end	Night	27% 4 11% 32% 23% 2	4120
November	1st to 10th	Night	32% 6% 11% 25% 21% 4	2507
	11th to 20th	Night	41% 5% 9% 24% 17% 4	2651
	21st to end	Night	41% 6% 12% 26% 14% 1	2800
December	1st to 10th	Night	43% 5% 14% 27% 10%	4580
	11th to 20th	Night	47% 4 14% 22% 11% 2	5208
	21st to end	Night	51% 6% 12% 18% 12%	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	35% 25% 27% 12% 1 1	200
	11th to 20th	Day	40% 21% 28% 11% 1	276
	21st to end	Day	28% 25% 35% 9% 3 1	330
February	1st to 10th	Day	29% 27% 30% 11% 2	300
	11th to 20th	Day	38% 26% 29% 6% 1	347
	21st to end	Day	34% 21% 27% 15% 2	414
March	1st to 10th	Day	31% 18% 30% 16% 3	500
	11th to 20th	Day	28% 26% 28% 13% 3 1	500
	21st to end	Day	27% 25% 31% 12% 3 1	550
April	1st to 10th	Day	29% 24% 27% 13% 5% 1	500
	11th to 20th	Day	25% 24% 25% 16% 7% 3	492
	21st to end	Day	26% 18% 33% 16% 7% 2	500
May	1st to 10th	Day	28% 19% 30% 15% 7% 2	503
	11th to 20th	Day	25% 16% 29% 19% 9% 2	527
	21st to end	Day	23% 10% 26% 22% 14% 5%	573
June	1st to 10th	Day	18% 12% 30% 22% 14% 4	530
	11th to 20th	Day	19% 9% 29% 25% 15% 2	530
	21st to end	Day	13% 9% 32% 26% 15% 4	530
July	1st to 10th	Day	11% 5% 24% 30% 23% 7%	525
	11th to 20th	Day	6% 6% 26% 31% 23% 7%	524
	21st to end	Day	13% 6% 27% 32% 18% 4	576
August	1st to 10th	Day	13% 5% 22% 31% 22% 7%	526
	11th to 20th	Day	16% 5% 23% 31% 19% 7%	519
	21st to end	Day	14% 6% 23% 31% 15% 11%	583
September	1st to 10th	Day	17% 8% 24% 23% 18% 10%	502
	11th to 20th	Day	14% 5% 25% 26% 21% 9%	490
	21st to end	Day	29% 10% 23% 21% 12% 4	490
October	1st to 10th	Day	24% 6% 23% 24% 17% 5%	490
	11th to 20th	Day	21% 16% 26% 23% 11% 2	490
	21st to end	Day	19% 16% 34% 19% 10% 1	539
November	1st to 10th	Day	19% 16% 29% 22% 12% 2	410
	11th to 20th	Day	23% 19% 32% 18% 7%	345
	21st to end	Day	27% 26% 29% 15% 4	200
December	1st to 10th	Day	33% 21% 31% 13% 3 2	200
	11th to 20th	Day	32% 22% 30% 14% 4	200
	21st to end	Day	30% 19% 29% 18% 5%	220
January	1st to 10th	Night	23% 22% 34% 18% 3	800
	11th to 20th	Night	26% 17% 31% 23% 3	800
	21st to end	Night	20% 22% 34% 23% 1	880
February	1st to 10th	Night	24% 18% 30% 26% 1	800
	11th to 20th	Night	28% 22% 32% 17% 1	783
	21st to end	Night	26% 21% 33% 17% 3	660
March	1st to 10th	Night	23% 19% 34% 21% 3	800
	11th to 20th	Night	25% 20% 31% 19% 5%	800
	21st to end	Night	23% 18% 35% 19% 5%	880
April	1st to 10th	Night	25% 20% 31% 19% 4	800
	11th to 20th	Night	19% 17% 34% 22% 7%	791
	21st to end	Night	23% 14% 30% 26% 6%	800
May	1st to 10th	Night	24% 11% 28% 28% 10%	622
	11th to 20th	Night	23% 8% 30% 28% 10%	394
	21st to end	Night	15% 8% 25% 35% 17%	433
June	1st to 10th	Night	14% 5% 27% 33% 21%	400
	11th to 20th	Night	14% 6% 29% 36% 15%	400
	21st to end	Night	12% 2 30% 41% 16%	400
July	1st to 10th	Night	14% 2 22% 38% 21% 2	390
	11th to 20th	Night	8% 2 18% 44% 26% 2	388
	21st to end	Night	12% 3 20% 39% 25% 2	618
August	1st to 10th	Night	14% 1 15% 41% 27% 1	597
	11th to 20th	Night	15% 5% 14% 36% 28% 3	664
	21st to end	Night	14% 4 18% 34% 28% 3	880
September	1st to 10th	Night	17% 4 22% 34% 21% 2	773
	11th to 20th	Night	13% 5% 20% 33% 26% 3	760
	21st to end	Night	23% 8% 19% 28% 19% 2	760
October	1st to 10th	Night	23% 6% 23% 26% 18% 3	760
	11th to 20th	Night	20% 12% 28% 28% 11% 1	760
	21st to end	Night	21% 14% 27% 28% 10%	836
November	1st to 10th	Night	14% 12% 33% 29% 10% 1	780
	11th to 20th	Night	19% 21% 28% 24% 7% 1	800
	21st to end	Night	21% 18% 31% 23% 6%	800
December	1st to 10th	Night	25% 18% 33% 19% 5%	800
	11th to 20th	Night	22% 16% 34% 24% 4	800
	21st to end	Night	22% 17% 31% 27% 2	880

Page generated at 2025-09-01 01:51:03. Version ac07

Copyright © 2025 Attilla Danko.