HighBridge Hills Northern Lights Educational Center
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the HighBridge Hills Northern Lights Educational Center clear sky chart from 2005-11-06 to 2025-12-18.

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	13% 11% 4 9% 5% 5% 4 4 5% 6% 34%	127618
	Night	12% 12% 5% 10% 6% 5% 5% 4 5% 6% 32%	123689
Transparency	Day	49% 5% 13% 22% 10% 1	131069
	Night	52% 6% 12% 20% 9% 1	128324
Seeing	Day	21% 18% 34% 19% 7% 2	17623
	Night	20% 15% 33% 24% 8% 1	27540

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	6% 13% 8% 21% 11% 9% 6% 3 3 4 17%	3617
	11th to 20th	Day	6% 15% 7% 15% 8% 12% 9% 8% 6% 3 10%	3589
	21st to end	Day	8% 17% 8% 16% 6% 5% 6% 3 5% 5% 21%	4056
February	1st to 10th	Day	7% 14% 6% 13% 6% 6% 7% 4 4 5% 27%	1800
	11th to 20th	Day	7% 13% 5% 13% 8% 6% 6% 5% 4 5% 27%	1754
	21st to end	Day	11% 15% 8% 11% 7% 5% 5% 3 5% 6% 25%	1640
March	1st to 10th	Day	12% 10% 3 9% 4 4 4 4 5% 7% 37%	4478
	11th to 20th	Day	9% 14% 4 12% 6% 4 4 4 6% 7% 30%	4968
	21st to end	Day	20% 14% 5% 11% 4 3 4 3 4 5% 28%	5781
April	1st to 10th	Day	16% 18% 5% 9% 5% 4 4 3 4 6% 28%	2400
	11th to 20th	Day	20% 15% 5% 7% 4 3 4 3 4 5% 30%	2374
	21st to end	Day	20% 12% 4 8% 5% 4 3 4 4 5% 32%	2580
May	1st to 10th	Day	15% 8% 2 5% 3 4 3 2 4 4 49%	6348
	11th to 20th	Day	15% 9% 2 6% 5% 5% 4 3 5% 6% 39%	6319
	21st to end	Day	15% 9% 3 8% 5% 4 4 3 5% 6% 38%	6949
June	1st to 10th	Day	13% 7% 2 6% 5% 5% 4 4 6% 8% 40%	2800
	11th to 20th	Day	14% 8% 3 7% 5% 5% 5% 4 6% 7% 36%	2800
	21st to end	Day	15% 7% 2 6% 6% 4 5% 5% 6% 8% 37%	2800
July	1st to 10th	Day	9% 6% 2 6% 4 4 4 4 6% 9% 47%	6359
	11th to 20th	Day	13% 4 2 5% 4 3 4 3 6% 9% 48%	6360
	21st to end	Day	10% 5% 2 5% 4 4 4 4 6% 8% 49%	6926
August	1st to 10th	Day	14% 7% 3 7% 5% 5% 5% 4 6% 7% 37%	4563
	11th to 20th	Day	15% 5% 2 5% 3 3 3 3 5% 7% 49%	4176
	21st to end	Day	14% 6% 2 6% 4 4 4 4 6% 9% 41%	4322
September	1st to 10th	Day	15% 6% 2 6% 4 4 5% 4 5% 9% 40%	2400
	11th to 20th	Day	14% 6% 2 6% 4 4 5% 5% 6% 8% 40%	2399
	21st to end	Day	20% 9% 2 6% 4 3 3 3 5% 6% 39%	2133
October	1st to 10th	Day	18% 11% 3 5% 3 4 4 3 5% 6% 37%	2000
	11th to 20th	Day	18% 17% 4 8% 5% 4 4 3 4 6% 27%	2000
	21st to end	Day	20% 16% 4 7% 5% 5% 5% 3 4 5% 27%	2013
November	1st to 10th	Day	12% 18% 5% 9% 5% 4 4 3 5% 6% 30%	1822
	11th to 20th	Day	13% 18% 9% 12% 7% 5% 4 3 4 5% 21%	1680
	21st to end	Day	13% 15% 7% 16% 7% 5% 4 3 4 5% 20%	1680
December	1st to 10th	Day	8% 16% 10% 28% 10% 5% 4 2 3 3 11%	2690
	11th to 20th	Day	9% 16% 7% 13% 12% 6% 5% 4 5% 5% 19%	3060
	21st to end	Day	16% 16% 7% 17% 7% 6% 5% 4 4 4 15%	3982
January	1st to 10th	Night	7% 13% 6% 21% 9% 7% 6% 3 4 3 21%	6348
	11th to 20th	Night	6% 14% 8% 14% 10% 9% 9% 8% 5% 4 13%	6316
	21st to end	Night	7% 19% 8% 13% 7% 6% 5% 4 5% 5% 22%	6907
February	1st to 10th	Night	7% 15% 6% 12% 7% 7% 6% 5% 4 5% 25%	2600
	11th to 20th	Night	7% 10% 5% 11% 9% 8% 8% 5% 5% 6% 26%	2533
	21st to end	Night	12% 16% 5% 10% 6% 5% 4 4 5% 7% 27%	1990
March	1st to 10th	Night	10% 8% 3 8% 4 4 5% 4 6% 7% 42%	5362
	11th to 20th	Night	12% 12% 5% 14% 6% 5% 4 4 5% 6% 27%	5035
	21st to end	Night	20% 16% 5% 10% 5% 4 4 3 3 4 27%	5149
April	1st to 10th	Night	19% 14% 4 9% 5% 4 4 2 4 6% 28%	2000
	11th to 20th	Night	21% 12% 4 6% 4 3 4 3 5% 6% 33%	1975
	21st to end	Night	19% 13% 3 6% 4 3 4 3 5% 5% 34%	1815
May	1st to 10th	Night	14% 7% 3 6% 3 3 3 3 4 6% 47%	3613
	11th to 20th	Night	13% 7% 3 5% 5% 4 4 3 5% 5% 46%	3596
	21st to end	Night	12% 8% 3 8% 4 4 5% 5% 6% 7% 39%	3949
June	1st to 10th	Night	13% 6% 3 6% 4 4 4 4 6% 8% 42%	1600
	11th to 20th	Night	13% 6% 3 6% 5% 5% 5% 5% 7% 8% 38%	1600
	21st to end	Night	13% 6% 2 8% 4 5% 4 4 7% 7% 41%	1600
July	1st to 10th	Night	9% 6% 2 5% 3 5% 4 4 6% 8% 48%	3620
	11th to 20th	Night	12% 5% 2 4 3 3 3 3 5% 7% 53%	3620
	21st to end	Night	10% 7% 2 5% 3 4 4 4 5% 8% 48%	3948
August	1st to 10th	Night	14% 6% 2 6% 4 3 4 3 5% 9% 44%	2597
	11th to 20th	Night	14% 5% 2 4 3 3 4 3 5% 7% 51%	2880
	21st to end	Night	17% 6% 2 5% 2 3 4 3 5% 7% 45%	3576
September	1st to 10th	Night	12% 5% 2 5% 4 3 4 4 5% 7% 49%	2000
	11th to 20th	Night	10% 6% 2 5% 4 4 5% 5% 6% 8% 47%	2000
	21st to end	Night	18% 8% 2 7% 4 4 4 3 5% 7% 41%	2245
October	1st to 10th	Night	17% 8% 2 6% 4 3 3 3 4 7% 42%	2400
	11th to 20th	Night	18% 13% 4 7% 4 4 4 3 4 6% 32%	2400
	21st to end	Night	20% 15% 3 7% 5% 5% 4 3 5% 5% 27%	2825
November	1st to 10th	Night	14% 15% 4 9% 6% 4 4 4 4 6% 30%	2692
	11th to 20th	Night	11% 17% 7% 13% 6% 5% 4 3 5% 5% 26%	2940
	21st to end	Night	13% 15% 6% 14% 8% 5% 4 4 4 6% 22%	2940
December	1st to 10th	Night	9% 16% 6% 23% 8% 6% 5% 3 4 4 15%	4720
	11th to 20th	Night	9% 16% 7% 16% 7% 6% 7% 3 5% 5% 19%	5302
	21st to end	Night	18% 17% 6% 13% 6% 5% 4 3 4 5% 18%	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	72% 4 6% 12% 5%	3618
	11th to 20th	Day	72% 6% 7% 10% 5%	3620
	21st to end	Day	65% 5% 9% 16% 5%	4056
February	1st to 10th	Day	58% 6% 11% 15% 10%	1800
	11th to 20th	Day	58% 8% 9% 19% 7%	1763
	21st to end	Day	59% 8% 9% 15% 9% 1	1640
March	1st to 10th	Day	46% 6% 15% 20% 11% 2	4480
	11th to 20th	Day	51% 5% 15% 17% 11% 1	4968
	21st to end	Day	59% 5% 9% 15% 11%	5781
April	1st to 10th	Day	58% 6% 10% 16% 10% 1	2400
	11th to 20th	Day	57% 4 10% 19% 8% 1	2374
	21st to end	Day	54% 6% 10% 19% 10% 1	2580
May	1st to 10th	Day	39% 5% 11% 26% 18% 1	6357
	11th to 20th	Day	44% 7% 12% 22% 10% 4	6323
	21st to end	Day	46% 6% 9% 22% 17% 1	6949
June	1st to 10th	Day	39% 8% 15% 26% 12% 1	2800
	11th to 20th	Day	45% 8% 14% 20% 13% 1	2800
	21st to end	Day	42% 9% 15% 24% 8% 1	2800
July	1st to 10th	Day	35% 4 19% 32% 9% 1	6291
	11th to 20th	Day	33% 5% 19% 31% 11% 1	6285
	21st to end	Day	33% 3 16% 31% 15%	6728
August	1st to 10th	Day	45% 5% 16% 23% 10% 1	4548
	11th to 20th	Day	36% 4 19% 31% 10%	4215
	21st to end	Day	41% 5% 18% 26% 10% 1	4321
September	1st to 10th	Day	40% 7% 16% 27% 10%	2400
	11th to 20th	Day	40% 9% 19% 25% 7%	2399
	21st to end	Day	45% 8% 13% 25% 10%	2133
October	1st to 10th	Day	37% 4 15% 29% 14% 1	3260
	11th to 20th	Day	54% 3 9% 22% 11% 1	3240
	21st to end	Day	53% 4 16% 21% 6%	3225
November	1st to 10th	Day	56% 6% 11% 18% 8% 1	1822
	11th to 20th	Day	67% 4 9% 14% 5%	1680
	21st to end	Day	66% 6% 12% 11% 3	1680
December	1st to 10th	Day	80% 4 6% 8% 2	2690
	11th to 20th	Day	67% 6% 10% 10% 7%	3061
	21st to end	Day	73% 4 7% 13% 3	3982
January	1st to 10th	Night	68% 6% 9% 13% 5%	6348
	11th to 20th	Night	70% 8% 10% 8% 3	6360
	21st to end	Night	64% 5% 10% 15% 5%	6907
February	1st to 10th	Night	59% 7% 9% 17% 8% 1	2600
	11th to 20th	Night	55% 8% 12% 17% 7% 1	2534
	21st to end	Night	56% 6% 12% 18% 6% 1	1990
March	1st to 10th	Night	40% 6% 16% 20% 16% 2	5373
	11th to 20th	Night	56% 5% 13% 19% 6%	5036
	21st to end	Night	62% 4 8% 14% 12% 1	5149
April	1st to 10th	Night	57% 6% 7% 17% 12% 1	2000
	11th to 20th	Night	52% 6% 10% 20% 10% 2	1975
	21st to end	Night	50% 6% 9% 22% 12% 1	1815
May	1st to 10th	Night	39% 6% 14% 25% 14% 2	3620
	11th to 20th	Night	39% 6% 12% 23% 14% 6%	3597
	21st to end	Night	41% 8% 13% 23% 14% 1	3950
June	1st to 10th	Night	38% 8% 16% 26% 11% 2	1600
	11th to 20th	Night	41% 9% 12% 20% 16% 2	1600
	21st to end	Night	40% 8% 14% 24% 13% 1	1600
July	1st to 10th	Night	34% 5% 20% 30% 9% 2	3580
	11th to 20th	Night	31% 5% 19% 33% 11% 1	3572
	21st to end	Night	36% 4 14% 27% 18% 1	3832
August	1st to 10th	Night	39% 4 15% 27% 13% 2	2588
	11th to 20th	Night	34% 5% 17% 32% 11% 1	2907
	21st to end	Night	39% 6% 17% 26% 11% 1	3576
September	1st to 10th	Night	33% 7% 15% 31% 13% 1	2000
	11th to 20th	Night	34% 8% 18% 33% 8%	2000
	21st to end	Night	44% 5% 16% 26% 9%	2245
October	1st to 10th	Night	32% 4 9% 33% 20% 2	3920
	11th to 20th	Night	48% 4 11% 23% 14%	3899
	21st to end	Night	56% 4 11% 21% 7%	4563
November	1st to 10th	Night	54% 6% 13% 19% 8%	2692
	11th to 20th	Night	61% 6% 12% 14% 6% 1	2940
	21st to end	Night	63% 6% 14% 12% 4 1	2940
December	1st to 10th	Night	73% 6% 9% 10% 2	4720
	11th to 20th	Night	68% 6% 9% 13% 4	5300
	21st to end	Night	70% 4 7% 13% 6%	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	17% 24% 36% 17% 5% 1	300
	11th to 20th	Day	23% 21% 32% 22% 2	300
	21st to end	Day	20% 17% 43% 18% 2	330
February	1st to 10th	Day	19% 27% 41% 10% 3	300
	11th to 20th	Day	16% 34% 33% 10% 5%	300
	21st to end	Day	25% 27% 41% 7%	249
March	1st to 10th	Day	21% 22% 39% 15% 3	300
	11th to 20th	Day	24% 21% 38% 12% 5%	300
	21st to end	Day	26% 20% 34% 13% 5% 2	466
April	1st to 10th	Day	28% 20% 34% 13% 4	500
	11th to 20th	Day	30% 20% 28% 16% 5%	492
	21st to end	Day	28% 20% 28% 16% 7% 1	595
May	1st to 10th	Day	24% 20% 31% 18% 5% 1	703
	11th to 20th	Day	22% 18% 33% 20% 5% 2	725
	21st to end	Day	21% 18% 33% 20% 7% 2	789
June	1st to 10th	Day	18% 20% 33% 20% 8% 1	730
	11th to 20th	Day	20% 16% 38% 19% 5% 2	730
	21st to end	Day	18% 16% 36% 19% 9% 2	730
July	1st to 10th	Day	10% 9% 36% 26% 14% 4	721
	11th to 20th	Day	13% 12% 34% 26% 11% 3	718
	21st to end	Day	10% 9% 39% 24% 12% 4	794
August	1st to 10th	Day	14% 12% 32% 27% 13% 2	726
	11th to 20th	Day	18% 7% 31% 28% 13% 3	715
	21st to end	Day	20% 10% 30% 24% 14% 2	593
September	1st to 10th	Day	19% 15% 29% 24% 11% 3	530
	11th to 20th	Day	15% 13% 34% 27% 8% 2	530
	21st to end	Day	24% 14% 28% 21% 11% 1	463
October	1st to 10th	Day	24% 20% 29% 19% 7% 1	330
	11th to 20th	Day	29% 28% 31% 8% 3	330
	21st to end	Day	30% 23% 35% 10% 1 1	363
November	1st to 10th	Day	24% 25% 38% 9% 3	330
	11th to 20th	Day	27% 28% 35% 7% 3	330
	21st to end	Day	29% 21% 37% 12% 2	330
December	1st to 10th	Day	18% 20% 45% 13% 4	330
	11th to 20th	Day	23% 25% 37% 13% 1	321
	21st to end	Day	26% 24% 36% 11% 2 1	330
January	1st to 10th	Night	15% 21% 40% 19% 5%	1000
	11th to 20th	Night	19% 17% 42% 16% 5%	1000
	21st to end	Night	18% 18% 40% 20% 3	1100
February	1st to 10th	Night	17% 21% 37% 20% 5% 1	1000
	11th to 20th	Night	14% 23% 37% 18% 7% 1	979
	21st to end	Night	20% 19% 36% 21% 4	670
March	1st to 10th	Night	17% 18% 37% 23% 5% 1	800
	11th to 20th	Night	20% 21% 32% 19% 7% 1	630
	21st to end	Night	22% 15% 29% 23% 9% 2	660
April	1st to 10th	Night	27% 16% 30% 23% 4 1	600
	11th to 20th	Night	29% 11% 28% 24% 8%	593
	21st to end	Night	28% 10% 27% 27% 8% 1	600
May	1st to 10th	Night	22% 13% 33% 26% 6% 1	600
	11th to 20th	Night	19% 10% 33% 28% 7% 2	591
	21st to end	Night	17% 9% 33% 31% 9% 1	650
June	1st to 10th	Night	17% 8% 32% 34% 10% 1	600
	11th to 20th	Night	16% 8% 32% 35% 9%	600
	21st to end	Night	17% 7% 31% 31% 13% 1	600
July	1st to 10th	Night	8% 6% 26% 39% 19% 1	585
	11th to 20th	Night	12% 6% 33% 32% 16% 1	582
	21st to end	Night	12% 4 29% 37% 16% 2	657
August	1st to 10th	Night	12% 6% 24% 40% 17% 1	597
	11th to 20th	Night	16% 5% 23% 35% 18% 3	594
	21st to end	Night	15% 8% 28% 30% 18% 2	660
September	1st to 10th	Night	14% 7% 30% 31% 16% 2	600
	11th to 20th	Night	14% 9% 32% 31% 13% 1	600
	21st to end	Night	21% 13% 29% 26% 10% 1	780
October	1st to 10th	Night	24% 13% 29% 24% 10% 1	800
	11th to 20th	Night	28% 18% 31% 16% 6%	800
	21st to end	Night	29% 13% 32% 21% 5%	880
November	1st to 10th	Night	25% 15% 36% 20% 5%	846
	11th to 20th	Night	22% 22% 34% 16% 5%	1050
	21st to end	Night	23% 23% 34% 18% 3	1050
December	1st to 10th	Night	20% 20% 37% 19% 4 1	1050
	11th to 20th	Night	21% 21% 33% 19% 4 1	1036
	21st to end	Night	28% 19% 34% 15% 4	1100

Page generated at 2025-12-15 00:13:53. Version ac07

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