Susquehanna University
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Susquehanna University clear sky chart from 2005-11-06 to 2025-11-03.

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% 8% 3 7% 5% 5% 5% 4 6% 7% 35%	126973
	Night	16% 8% 3 7% 5% 4 4 4 5% 7% 37%	123071
Transparency	Day	45% 7% 12% 22% 13% 2	130564
	Night	45% 6% 12% 21% 14% 2	127566
Seeing	Day	22% 16% 27% 20% 11% 3	16117
	Night	19% 13% 29% 27% 10% 1	25442

By Month

Percentage Cloud Cover NE (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% 11% 3 10% 5% 4 5% 4 5% 5% 36%	3597
	11th to 20th	Day	12% 13% 6% 15% 6% 6% 5% 4 4 6% 23%	3860
	21st to end	Day	16% 13% 4 10% 4 4 4 3 4 6% 31%	4466
February	1st to 10th	Day	16% 11% 4 9% 6% 5% 5% 4 5% 6% 28%	1800
	11th to 20th	Day	14% 11% 4 10% 5% 5% 4 4 5% 6% 32%	1791
	21st to end	Day	18% 10% 3 9% 6% 4 4 4 5% 4 32%	1650
March	1st to 10th	Day	21% 7% 3 8% 5% 4 4 3 4 4 38%	4742
	11th to 20th	Day	12% 9% 3 8% 5% 4 4 3 5% 7% 39%	4980
	21st to end	Day	14% 9% 3 7% 4 4 5% 3 5% 6% 40%	5619
April	1st to 10th	Day	17% 10% 3 8% 5% 5% 4 4 5% 6% 34%	2400
	11th to 20th	Day	16% 9% 3 6% 5% 4 4 4 5% 5% 38%	2374
	21st to end	Day	17% 6% 2 6% 4 5% 4 4 6% 7% 38%	2400
May	1st to 10th	Day	25% 7% 3 7% 4 4 5% 4 5% 7% 29%	5974
	11th to 20th	Day	23% 8% 3 7% 5% 5% 5% 4 5% 7% 28%	6318
	21st to end	Day	19% 6% 3 6% 4 5% 6% 4 7% 9% 34%	6949
June	1st to 10th	Day	13% 6% 3 7% 6% 5% 5% 5% 6% 8% 38%	2800
	11th to 20th	Day	14% 6% 2 7% 5% 5% 6% 4 6% 8% 38%	2800
	21st to end	Day	11% 5% 2 6% 4 5% 5% 5% 7% 10% 41%	2800
July	1st to 10th	Day	6% 5% 3 8% 6% 6% 6% 5% 7% 10% 39%	6360
	11th to 20th	Day	7% 6% 3 9% 6% 6% 7% 5% 9% 11% 31%	6360
	21st to end	Day	10% 7% 3 7% 5% 5% 5% 4 6% 9% 38%	6570
August	1st to 10th	Day	19% 7% 3 7% 5% 5% 5% 5% 6% 8% 32%	4234
	11th to 20th	Day	14% 6% 3 6% 4 5% 6% 5% 7% 9% 35%	4042
	21st to end	Day	13% 6% 2 5% 4 4 5% 3 5% 10% 43%	4312
September	1st to 10th	Day	15% 6% 2 5% 4 4 4 4 5% 6% 46%	2400
	11th to 20th	Day	13% 5% 2 4 4 4 4 3 5% 7% 50%	2400
	21st to end	Day	21% 9% 2 6% 4 4 3 3 4 6% 37%	2113
October	1st to 10th	Day	18% 7% 2 5% 4 4 4 3 5% 7% 42%	2000
	11th to 20th	Day	17% 7% 2 6% 4 4 6% 4 5% 7% 39%	2000
	21st to end	Day	18% 7% 2 6% 5% 5% 4 4 5% 6% 37%	2200
November	1st to 10th	Day	13% 7% 2 6% 4 4 4 3 5% 6% 47%	1792
	11th to 20th	Day	18% 7% 2 6% 4 5% 4 4 6% 6% 38%	1724
	21st to end	Day	17% 8% 2 7% 5% 5% 5% 5% 6% 6% 36%	1600
December	1st to 10th	Day	15% 10% 5% 9% 6% 5% 4 3 5% 7% 30%	2600
	11th to 20th	Day	22% 12% 2 7% 4 3 4 3 5% 6% 31%	2986
	21st to end	Day	19% 11% 3 9% 6% 6% 5% 4 6% 6% 24%	3960
January	1st to 10th	Night	13% 11% 4 10% 6% 5% 4 3 4 6% 34%	6349
	11th to 20th	Night	12% 9% 5% 10% 6% 5% 5% 4 6% 7% 32%	6023
	21st to end	Night	17% 9% 3 9% 5% 5% 5% 4 6% 5% 33%	6490
February	1st to 10th	Night	16% 11% 3 7% 6% 4 4 4 6% 6% 33%	2600
	11th to 20th	Night	16% 9% 3 8% 6% 5% 4 4 5% 7% 32%	2494
	21st to end	Night	17% 9% 3 8% 6% 4 5% 3 5% 5% 34%	1980
March	1st to 10th	Night	18% 11% 3 8% 4 3 3 3 4 5% 38%	5093
	11th to 20th	Night	11% 10% 3 6% 4 3 4 3 5% 6% 46%	4979
	21st to end	Night	14% 8% 3 7% 5% 4 4 3 4 5% 40%	5312
April	1st to 10th	Night	18% 11% 3 8% 5% 4 4 4 5% 7% 32%	2000
	11th to 20th	Night	15% 7% 2 8% 5% 4 4 4 5% 8% 38%	1975
	21st to end	Night	18% 6% 2 6% 4 3 4 4 5% 7% 42%	2000
May	1st to 10th	Night	28% 8% 3 6% 4 4 4 3 5% 7% 28%	3993
	11th to 20th	Night	22% 9% 3 7% 4 4 4 4 6% 7% 31%	3575
	21st to end	Night	20% 7% 3 6% 4 4 4 3 5% 7% 37%	3926
June	1st to 10th	Night	14% 6% 3 6% 4 4 4 4 6% 8% 43%	1600
	11th to 20th	Night	13% 6% 1 6% 6% 4 4 4 6% 9% 41%	1600
	21st to end	Night	10% 5% 2 5% 4 4 5% 5% 7% 10% 41%	1600
July	1st to 10th	Night	9% 6% 3 7% 5% 5% 6% 4 7% 10% 39%	3600
	11th to 20th	Night	10% 7% 3 8% 5% 6% 7% 5% 8% 10% 32%	3600
	21st to end	Night	11% 6% 2 6% 5% 5% 4 4 5% 8% 44%	4278
August	1st to 10th	Night	19% 7% 2 7% 4 5% 4 4 6% 8% 34%	2915
	11th to 20th	Night	13% 8% 3 7% 4 4 4 3 5% 8% 40%	2973
	21st to end	Night	13% 5% 2 5% 4 3 4 4 7% 8% 44%	3586
September	1st to 10th	Night	14% 5% 2 6% 5% 3 3 3 5% 7% 46%	2000
	11th to 20th	Night	11% 5% 2 5% 3 4 3 4 4 8% 52%	2000
	21st to end	Night	20% 6% 3 6% 3 4 4 3 5% 6% 40%	2283
October	1st to 10th	Night	18% 7% 2 5% 4 4 3 3 5% 7% 43%	2400
	11th to 20th	Night	16% 7% 2 5% 4 3 4 3 4 7% 45%	2400
	21st to end	Night	19% 6% 2 6% 4 4 4 3 5% 7% 41%	2640
November	1st to 10th	Night	10% 8% 2 5% 4 3 4 3 4 6% 50%	2549
	11th to 20th	Night	17% 10% 2 6% 4 3 4 3 5% 6% 39%	2674
	21st to end	Night	16% 9% 3 6% 6% 4 3 3 5% 7% 37%	2800
December	1st to 10th	Night	12% 10% 3 8% 5% 5% 5% 4 6% 7% 35%	4580
	11th to 20th	Night	22% 10% 2 6% 4 4 4 3 5% 6% 33%	5208
	21st to end	Night	19% 12% 4 9% 5% 4 5% 4 5% 6% 26%	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	48% 5% 12% 21% 12% 1	3598
	11th to 20th	Day	60% 5% 10% 13% 10% 3	3894
	21st to end	Day	54% 5% 11% 19% 11%	4466
February	1st to 10th	Day	54% 6% 12% 18% 9% 1	1800
	11th to 20th	Day	52% 6% 9% 22% 8% 1	1800
	21st to end	Day	53% 5% 11% 19% 9% 2	1650
March	1st to 10th	Day	48% 6% 10% 22% 9% 5%	4745
	11th to 20th	Day	42% 6% 15% 24% 9% 4	4980
	21st to end	Day	46% 5% 11% 17% 18% 4	5619
April	1st to 10th	Day	50% 7% 10% 18% 12% 4	2400
	11th to 20th	Day	45% 6% 11% 20% 14% 3	2374
	21st to end	Day	43% 7% 10% 22% 14% 4	2400
May	1st to 10th	Day	54% 7% 12% 16% 10% 2	5983
	11th to 20th	Day	53% 8% 10% 18% 9% 1	6322
	21st to end	Day	45% 7% 13% 22% 12% 2	6949
June	1st to 10th	Day	43% 8% 12% 22% 14% 2	2800
	11th to 20th	Day	43% 8% 14% 21% 13% 2	2800
	21st to end	Day	36% 8% 15% 26% 14% 1	2800
July	1st to 10th	Day	40% 9% 12% 25% 13% 1	6290
	11th to 20th	Day	42% 9% 16% 23% 10% 1	6285
	21st to end	Day	41% 7% 11% 20% 20% 1	6382
August	1st to 10th	Day	48% 8% 15% 19% 10%	4221
	11th to 20th	Day	42% 8% 13% 27% 10% 1	4081
	21st to end	Day	36% 5% 13% 31% 13% 2	4312
September	1st to 10th	Day	39% 7% 11% 22% 18% 3	2400
	11th to 20th	Day	34% 6% 11% 26% 21% 3	2400
	21st to end	Day	48% 6% 10% 17% 17% 2	2113
October	1st to 10th	Day	40% 5% 9% 24% 18% 4	3260
	11th to 20th	Day	35% 6% 10% 27% 20% 2	3240
	21st to end	Day	30% 4 15% 30% 19% 1	3538
November	1st to 10th	Day	38% 5% 14% 24% 17% 3	1792
	11th to 20th	Day	45% 7% 11% 22% 12% 2	1724
	21st to end	Day	47% 6% 12% 26% 8% 1	1600
December	1st to 10th	Day	53% 6% 13% 21% 6% 2	2600
	11th to 20th	Day	52% 5% 16% 22% 5%	2986
	21st to end	Day	58% 6% 16% 12% 7% 1	3960
January	1st to 10th	Night	49% 6% 12% 19% 12% 2	6349
	11th to 20th	Night	50% 7% 14% 15% 10% 4	6064
	21st to end	Night	50% 5% 11% 17% 14% 2	6490
February	1st to 10th	Night	50% 7% 13% 22% 7% 1	2600
	11th to 20th	Night	51% 6% 11% 20% 11% 1	2496
	21st to end	Night	50% 6% 10% 19% 13% 2	1980
March	1st to 10th	Night	48% 5% 11% 20% 11% 5%	5103
	11th to 20th	Night	38% 6% 15% 27% 9% 5%	4980
	21st to end	Night	46% 5% 8% 17% 21% 4	5312
April	1st to 10th	Night	51% 6% 9% 18% 13% 2	2000
	11th to 20th	Night	44% 6% 11% 20% 16% 2	1975
	21st to end	Night	40% 7% 12% 23% 15% 3	2000
May	1st to 10th	Night	56% 6% 10% 17% 9% 3	4000
	11th to 20th	Night	50% 10% 13% 14% 12% 1	3576
	21st to end	Night	46% 7% 12% 20% 13% 3	3927
June	1st to 10th	Night	39% 8% 11% 23% 18% 1	1600
	11th to 20th	Night	39% 9% 14% 21% 15% 2	1600
	21st to end	Night	35% 9% 14% 26% 15% 1	1600
July	1st to 10th	Night	40% 8% 14% 21% 14% 3	3560
	11th to 20th	Night	44% 8% 14% 22% 11% 1	3552
	21st to end	Night	36% 7% 12% 21% 22% 1	4151
August	1st to 10th	Night	46% 8% 15% 20% 10% 1	2904
	11th to 20th	Night	41% 7% 13% 24% 16%	3000
	21st to end	Night	34% 7% 11% 32% 14% 1	3586
September	1st to 10th	Night	38% 6% 11% 24% 18% 3	2000
	11th to 20th	Night	31% 6% 11% 29% 21% 3	2000
	21st to end	Night	44% 5% 10% 21% 19% 1	2283
October	1st to 10th	Night	42% 5% 11% 21% 21% 1	3920
	11th to 20th	Night	31% 5% 10% 29% 23% 2	3899
	21st to end	Night	31% 5% 14% 28% 20% 2	4252
November	1st to 10th	Night	35% 5% 13% 25% 19% 3	2549
	11th to 20th	Night	45% 5% 10% 23% 14% 3	2674
	21st to end	Night	45% 6% 15% 23% 9% 2	2800
December	1st to 10th	Night	46% 6% 15% 26% 6%	4580
	11th to 20th	Night	52% 5% 15% 19% 9% 1	5208
	21st to end	Night	56% 7% 12% 16% 9%	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% 26% 25% 13% 2 1	200
	11th to 20th	Day	35% 24% 30% 10% 1	263
	21st to end	Day	25% 34% 28% 10% 4	330
February	1st to 10th	Day	30% 29% 29% 10% 1	300
	11th to 20th	Day	33% 26% 35% 4 1	338
	21st to end	Day	32% 22% 29% 15% 2	414
March	1st to 10th	Day	31% 21% 28% 16% 3	500
	11th to 20th	Day	28% 25% 28% 15% 4 1	500
	21st to end	Day	28% 25% 27% 14% 4 2	550
April	1st to 10th	Day	28% 24% 29% 14% 5% 1	500
	11th to 20th	Day	26% 27% 23% 15% 6% 3	492
	21st to end	Day	25% 19% 33% 14% 7% 2	500
May	1st to 10th	Day	28% 21% 27% 13% 8% 2	503
	11th to 20th	Day	23% 19% 28% 19% 9% 2	527
	21st to end	Day	21% 11% 27% 20% 17% 4	573
June	1st to 10th	Day	17% 13% 30% 25% 12% 3	530
	11th to 20th	Day	17% 14% 28% 25% 14% 2	530
	21st to end	Day	14% 12% 32% 27% 12% 3	530
July	1st to 10th	Day	11% 6% 26% 32% 19% 6%	525
	11th to 20th	Day	7% 7% 28% 33% 21% 5%	524
	21st to end	Day	12% 9% 28% 30% 17% 4	576
August	1st to 10th	Day	14% 8% 22% 28% 21% 7%	526
	11th to 20th	Day	13% 7% 24% 30% 19% 7%	519
	21st to end	Day	13% 8% 24% 29% 15% 11%	583
September	1st to 10th	Day	17% 10% 20% 25% 18% 10%	530
	11th to 20th	Day	14% 6% 22% 26% 22% 9%	530
	21st to end	Day	27% 13% 22% 20% 13% 4	530
October	1st to 10th	Day	22% 10% 24% 23% 16% 6%	530
	11th to 20th	Day	21% 16% 30% 21% 10% 2	530
	21st to end	Day	21% 17% 33% 19% 9% 1	583
November	1st to 10th	Day	20% 16% 29% 23% 11% 2	407
	11th to 20th	Day	26% 19% 27% 19% 8%	324
	21st to end	Day	25% 26% 34% 13% 4 1	200
December	1st to 10th	Day	29% 28% 30% 9% 4 1	200
	11th to 20th	Day	35% 22% 30% 11% 4	200
	21st to end	Day	25% 26% 27% 18% 4	220
January	1st to 10th	Night	21% 21% 39% 17% 3	800
	11th to 20th	Night	24% 20% 33% 20% 3	800
	21st to end	Night	18% 21% 38% 21% 2	880
February	1st to 10th	Night	24% 17% 34% 24% 1	800
	11th to 20th	Night	25% 22% 36% 16% 1	783
	21st to end	Night	25% 20% 35% 17% 2	660
March	1st to 10th	Night	23% 21% 32% 21% 3	800
	11th to 20th	Night	26% 18% 31% 20% 4	800
	21st to end	Night	23% 18% 35% 19% 5%	880
April	1st to 10th	Night	24% 20% 32% 20% 4	800
	11th to 20th	Night	21% 16% 33% 23% 7%	791
	21st to end	Night	20% 16% 30% 28% 6%	800
May	1st to 10th	Night	24% 11% 30% 24% 10%	579
	11th to 20th	Night	17% 9% 33% 32% 9%	394
	21st to end	Night	17% 8% 24% 36% 15%	433
June	1st to 10th	Night	15% 6% 25% 37% 18%	400
	11th to 20th	Night	15% 6% 25% 42% 12%	400
	21st to end	Night	12% 3 26% 46% 13% 1	400
July	1st to 10th	Night	14% 2 23% 38% 21% 2	390
	11th to 20th	Night	9% 3 18% 46% 23% 1	388
	21st to end	Night	10% 4 21% 41% 23% 1	585
August	1st to 10th	Night	13% 2 15% 42% 26% 2	597
	11th to 20th	Night	12% 4 15% 38% 28% 3	653
	21st to end	Night	11% 5% 19% 35% 28% 2	880
September	1st to 10th	Night	15% 5% 23% 36% 20% 2	800
	11th to 20th	Night	12% 5% 20% 33% 26% 4	800
	21st to end	Night	21% 7% 21% 32% 17% 2	800
October	1st to 10th	Night	21% 8% 23% 26% 20% 2	800
	11th to 20th	Night	18% 11% 29% 32% 10% 1	800
	21st to end	Night	23% 12% 29% 29% 7%	880
November	1st to 10th	Night	14% 14% 31% 31% 10% 1	789
	11th to 20th	Night	21% 18% 30% 23% 7% 1	800
	21st to end	Night	20% 18% 33% 24% 5%	800
December	1st to 10th	Night	26% 17% 33% 20% 5%	800
	11th to 20th	Night	23% 17% 34% 24% 3	800
	21st to end	Night	23% 16% 34% 24% 3	880

Page generated at 2025-10-31 02:02:41. Version ac07

Copyright © 2025 Attilla Danko.