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 2024-01-13.

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	14% 10% 4 8% 6% 3 5% 5% 5% 7% 32%	74758
	Night	14% 11% 5% 8% 7% 4 5% 5% 5% 6% 32%	75001
Transparency	Day	51% 7% 13% 20% 9% 1	74464
	Night	52% 7% 12% 19% 8% 1	74829
Seeing	Day	20% 18% 34% 19% 7% 2	14902
	Night	20% 15% 33% 24% 8% 1	24930

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	9% 12% 7% 13% 10% 5% 7% 5% 4 6% 21%	1517
	11th to 20th	Day	12% 17% 8% 14% 10% 4 6% 8% 4 5% 13%	1456
	21st to end	Day	10% 14% 7% 15% 10% 4 7% 5% 6% 7% 15%	1616
February	1st to 10th	Day	7% 14% 6% 11% 8% 4 8% 6% 5% 5% 27%	1620
	11th to 20th	Day	8% 14% 5% 11% 9% 5% 5% 7% 4 5% 28%	1574
	21st to end	Day	12% 13% 8% 10% 10% 4 5% 3 4 6% 24%	1471
March	1st to 10th	Day	12% 12% 4 9% 7% 3 6% 5% 5% 6% 31%	1798
	11th to 20th	Day	13% 12% 6% 9% 6% 3 3 4 4 7% 34%	1968
	21st to end	Day	15% 13% 5% 9% 6% 3 4 4 6% 7% 27%	2300
April	1st to 10th	Day	15% 16% 6% 8% 6% 3 4 4 4 6% 28%	2160
	11th to 20th	Day	21% 14% 5% 6% 4 3 4 4 4 5% 30%	2134
	21st to end	Day	20% 12% 4 6% 6% 3 3 5% 4 5% 32%	2321
May	1st to 10th	Day	18% 10% 4 6% 5% 4 5% 4 5% 6% 34%	2520
	11th to 20th	Day	17% 10% 3 6% 5% 3 5% 5% 5% 6% 35%	2479
	21st to end	Day	14% 6% 2 6% 6% 4 6% 5% 6% 8% 36%	2725
June	1st to 10th	Day	13% 6% 2 5% 5% 4 5% 5% 6% 8% 40%	2520
	11th to 20th	Day	13% 7% 3 6% 5% 3 6% 5% 6% 8% 38%	2520
	21st to end	Day	14% 6% 2 5% 7% 3 5% 6% 6% 8% 38%	2520
July	1st to 10th	Day	7% 4 2 4 5% 3 5% 5% 7% 10% 48%	2520
	11th to 20th	Day	12% 4 2 5% 5% 3 5% 6% 6% 9% 44%	2520
	21st to end	Day	9% 4 2 4 5% 3 5% 5% 7% 9% 46%	2743
August	1st to 10th	Day	11% 6% 3 6% 5% 3 6% 6% 6% 8% 40%	2507
	11th to 20th	Day	13% 7% 3 5% 5% 3 4 4 4 7% 45%	2306
	21st to end	Day	13% 6% 2 5% 5% 3 4 4 4 8% 47%	2386
September	1st to 10th	Day	15% 6% 3 5% 5% 3 5% 5% 5% 9% 40%	2160
	11th to 20th	Day	15% 6% 2 5% 5% 3 5% 6% 6% 8% 40%	2160
	21st to end	Day	22% 9% 2 5% 5% 3 3 3 5% 6% 36%	1921
October	1st to 10th	Day	19% 11% 3 5% 4 3 5% 4 5% 6% 35%	1800
	11th to 20th	Day	20% 17% 4 7% 6% 3 5% 3 4 6% 26%	1800
	21st to end	Day	21% 16% 5% 6% 6% 3 5% 4 3 5% 26%	1813
November	1st to 10th	Day	12% 17% 5% 7% 5% 3 5% 4 5% 6% 31%	1646
	11th to 20th	Day	13% 18% 10% 12% 8% 4 5% 3 4 5% 19%	1520
	21st to end	Day	13% 14% 7% 14% 8% 4 5% 4 4 5% 22%	1520
December	1st to 10th	Day	10% 16% 10% 16% 10% 5% 5% 4 3 5% 16%	1520
	11th to 20th	Day	10% 15% 9% 11% 13% 5% 6% 5% 4 5% 17%	1914
	21st to end	Day	18% 16% 8% 17% 8% 4 4 5% 3 3 12%	2783
January	1st to 10th	Night	9% 12% 7% 12% 10% 6% 7% 6% 6% 5% 22%	2648
	11th to 20th	Night	12% 14% 8% 12% 9% 5% 6% 7% 4 6% 17%	2561
	21st to end	Night	11% 16% 8% 13% 8% 5% 7% 5% 5% 5% 17%	2739
February	1st to 10th	Night	6% 14% 8% 12% 9% 5% 6% 6% 4 5% 25%	2340
	11th to 20th	Night	8% 10% 5% 8% 9% 6% 8% 6% 6% 6% 27%	2273
	21st to end	Night	13% 15% 5% 9% 8% 4 5% 4 5% 6% 27%	1785
March	1st to 10th	Night	12% 11% 4 9% 7% 3 4 4 6% 6% 34%	2149
	11th to 20th	Night	12% 12% 4 7% 5% 3 4 4 5% 6% 38%	2007
	21st to end	Night	16% 11% 5% 8% 6% 3 5% 4 3 5% 34%	2055
April	1st to 10th	Night	19% 13% 5% 8% 6% 4 4 4 4 7% 27%	1800
	11th to 20th	Night	21% 11% 5% 5% 4 3 4 4 5% 6% 32%	1775
	21st to end	Night	19% 12% 4 6% 5% 3 4 4 5% 5% 33%	1635
May	1st to 10th	Night	18% 9% 4 7% 6% 3 6% 5% 5% 7% 31%	1440
	11th to 20th	Night	15% 8% 3 5% 6% 3 5% 5% 5% 6% 39%	1416
	21st to end	Night	14% 7% 2 6% 6% 3 4 6% 6% 8% 39%	1551
June	1st to 10th	Night	13% 5% 3 4 5% 3 5% 5% 6% 9% 43%	1440
	11th to 20th	Night	12% 5% 2 6% 6% 3 5% 6% 7% 8% 40%	1440
	21st to end	Night	13% 5% 2 7% 4 3 4 5% 6% 7% 42%	1440
July	1st to 10th	Night	6% 4 1 5% 4 2 5% 6% 6% 9% 52%	1440
	11th to 20th	Night	10% 4 2 5% 5% 3 5% 4 6% 9% 48%	1440
	21st to end	Night	8% 4 2 4 3 2 5% 5% 6% 8% 52%	1575
August	1st to 10th	Night	10% 4 2 5% 5% 2 5% 4 5% 9% 50%	1432
	11th to 20th	Night	13% 6% 2 4 3 2 3 5% 5% 6% 50%	1592
	21st to end	Night	14% 5% 2 4 3 2 4 4 5% 8% 49%	1970
September	1st to 10th	Night	11% 5% 2 5% 4 3 3 5% 5% 7% 50%	1800
	11th to 20th	Night	11% 5% 2 4 5% 3 5% 5% 6% 8% 48%	1800
	21st to end	Night	20% 7% 2 6% 5% 3 4 4 5% 8% 37%	2020
October	1st to 10th	Night	19% 8% 2 5% 4 2 4 4 4 7% 40%	2160
	11th to 20th	Night	19% 13% 5% 6% 5% 3 4 4 4 6% 31%	2160
	21st to end	Night	20% 14% 3 7% 6% 3 4 5% 5% 5% 27%	2542
November	1st to 10th	Night	14% 14% 5% 8% 7% 3 4 5% 4 6% 30%	2429
	11th to 20th	Night	12% 15% 8% 12% 8% 4 4 4 5% 5% 24%	2660
	21st to end	Night	13% 13% 6% 12% 8% 4 5% 5% 4 6% 23%	2660
December	1st to 10th	Night	10% 16% 8% 14% 9% 4 6% 4 4 6% 20%	2660
	11th to 20th	Night	11% 14% 7% 12% 10% 5% 5% 5% 5% 6% 20%	3283
	21st to end	Night	22% 19% 6% 12% 7% 3 4 4 3 4 17%	4884

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	64% 7% 10% 15% 5%	1518
	11th to 20th	Day	71% 8% 8% 8% 4	1456
	21st to end	Day	67% 5% 12% 9% 6%	1616
February	1st to 10th	Day	58% 6% 12% 16% 8%	1620
	11th to 20th	Day	57% 8% 9% 19% 7%	1583
	21st to end	Day	61% 7% 8% 14% 9% 1	1471
March	1st to 10th	Day	54% 6% 17% 14% 9% 1	1800
	11th to 20th	Day	52% 5% 14% 19% 10% 1	1968
	21st to end	Day	56% 6% 12% 18% 7% 1	2300
April	1st to 10th	Day	58% 6% 10% 16% 10% 1	2160
	11th to 20th	Day	58% 4 10% 19% 9% 2	2134
	21st to end	Day	54% 7% 10% 19% 10% 1	2321
May	1st to 10th	Day	50% 8% 12% 21% 8% 1	2520
	11th to 20th	Day	48% 7% 12% 22% 9% 1	2483
	21st to end	Day	44% 8% 12% 22% 13% 1	2725
June	1st to 10th	Day	38% 8% 16% 25% 12% 1	2520
	11th to 20th	Day	42% 9% 14% 20% 14% 1	2520
	21st to end	Day	41% 10% 16% 24% 8% 1	2520
July	1st to 10th	Day	28% 9% 18% 29% 15% 1	2451
	11th to 20th	Day	33% 11% 14% 26% 14% 2	2445
	21st to end	Day	32% 8% 18% 26% 15% 1	2591
August	1st to 10th	Day	40% 8% 16% 26% 8% 2	2492
	11th to 20th	Day	39% 7% 18% 25% 11%	2306
	21st to end	Day	37% 7% 15% 26% 14% 1	2386
September	1st to 10th	Day	40% 7% 16% 27% 10%	2160
	11th to 20th	Day	41% 10% 18% 24% 7%	2160
	21st to end	Day	48% 8% 13% 23% 7%	1921
October	1st to 10th	Day	48% 8% 13% 24% 7% 1	1800
	11th to 20th	Day	61% 5% 12% 16% 7%	1800
	21st to end	Day	60% 7% 11% 16% 6%	1813
November	1st to 10th	Day	55% 6% 12% 19% 7% 1	1646
	11th to 20th	Day	70% 5% 10% 11% 5%	1520
	21st to end	Day	64% 7% 13% 12% 3 1	1520
December	1st to 10th	Day	71% 6% 10% 11% 2	1520
	11th to 20th	Day	68% 9% 11% 9% 3	1915
	21st to end	Day	77% 6% 6% 10% 1	2783
January	1st to 10th	Night	63% 8% 12% 14% 4	2648
	11th to 20th	Night	67% 8% 13% 10% 2	2561
	21st to end	Night	68% 6% 8% 12% 4	2739
February	1st to 10th	Night	59% 7% 9% 17% 7% 1	2340
	11th to 20th	Night	55% 8% 12% 17% 8% 1	2274
	21st to end	Night	58% 6% 11% 17% 7% 1	1785
March	1st to 10th	Night	49% 7% 13% 19% 11% 1	2160
	11th to 20th	Night	47% 7% 13% 23% 10% 1	2008
	21st to end	Night	52% 6% 11% 18% 11% 1	2055
April	1st to 10th	Night	58% 6% 8% 16% 12% 1	1800
	11th to 20th	Night	53% 6% 10% 19% 10% 2	1775
	21st to end	Night	51% 6% 9% 20% 12% 1	1635
May	1st to 10th	Night	52% 8% 13% 17% 9% 1	1440
	11th to 20th	Night	46% 6% 11% 23% 12% 2	1417
	21st to end	Night	42% 9% 13% 22% 12% 2	1552
June	1st to 10th	Night	37% 8% 17% 26% 11% 2	1440
	11th to 20th	Night	39% 10% 12% 20% 17% 2	1440
	21st to end	Night	38% 9% 14% 25% 13% 1	1440
July	1st to 10th	Night	27% 9% 15% 32% 16% 1	1400
	11th to 20th	Night	30% 11% 16% 25% 16% 2	1392
	21st to end	Night	28% 9% 15% 29% 17% 2	1487
August	1st to 10th	Night	31% 7% 16% 32% 11% 3	1423
	11th to 20th	Night	34% 8% 15% 26% 15% 2	1592
	21st to end	Night	35% 8% 14% 26% 15% 2	1970
September	1st to 10th	Night	33% 7% 15% 31% 14% 1	1800
	11th to 20th	Night	34% 8% 17% 33% 8%	1800
	21st to end	Night	47% 6% 16% 24% 7%	2020
October	1st to 10th	Night	44% 7% 12% 26% 10% 1	2160
	11th to 20th	Night	53% 7% 14% 18% 7% 1	2160
	21st to end	Night	58% 8% 12% 16% 6%	2542
November	1st to 10th	Night	54% 6% 13% 19% 8%	2429
	11th to 20th	Night	63% 7% 12% 12% 7%	2660
	21st to end	Night	61% 7% 15% 12% 4 1	2660
December	1st to 10th	Night	66% 8% 11% 12% 2	2660
	11th to 20th	Night	64% 9% 12% 13% 2	3281
	21st to end	Night	73% 5% 8% 11% 3	4884

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	19% 23% 37% 16% 5% 1	270
	11th to 20th	Day	26% 20% 30% 22% 2	246
	21st to end	Day	21% 16% 43% 19% 2	264
February	1st to 10th	Day	18% 26% 45% 9% 1	240
	11th to 20th	Day	17% 35% 34% 8% 6%	240
	21st to end	Day	26% 26% 41% 7% 1	198
March	1st to 10th	Day	16% 23% 39% 18% 3	240
	11th to 20th	Day	24% 22% 35% 14% 5%	240
	21st to end	Day	25% 21% 32% 14% 5% 3	386
April	1st to 10th	Day	25% 20% 35% 14% 5%	420
	11th to 20th	Day	29% 18% 29% 18% 6%	412
	21st to end	Day	28% 19% 28% 18% 7% 1	505
May	1st to 10th	Day	25% 20% 32% 18% 4 1	603
	11th to 20th	Day	23% 17% 32% 20% 5% 3	625
	21st to end	Day	21% 16% 33% 20% 7% 2	679
June	1st to 10th	Day	16% 19% 34% 21% 9% 2	630
	11th to 20th	Day	18% 16% 39% 20% 6% 2	630
	21st to end	Day	16% 16% 35% 21% 10% 2	630
July	1st to 10th	Day	9% 10% 37% 27% 13% 5%	621
	11th to 20th	Day	13% 12% 35% 27% 10% 3	618
	21st to end	Day	10% 10% 39% 23% 13% 5%	684
August	1st to 10th	Day	13% 12% 33% 28% 12% 2	626
	11th to 20th	Day	18% 8% 30% 28% 13% 3	615
	21st to end	Day	19% 11% 30% 24% 14% 2	505
September	1st to 10th	Day	18% 15% 28% 26% 11% 2	450
	11th to 20th	Day	16% 15% 32% 27% 7% 2	450
	21st to end	Day	29% 15% 29% 17% 10% 1	391
October	1st to 10th	Day	24% 19% 27% 21% 8%	270
	11th to 20th	Day	29% 29% 31% 8% 3	270
	21st to end	Day	31% 25% 33% 9% 1	297
November	1st to 10th	Day	20% 26% 40% 11% 3	270
	11th to 20th	Day	26% 28% 36% 7% 3	270
	21st to end	Day	27% 23% 36% 11% 2	270
December	1st to 10th	Day	19% 21% 43% 13% 4	270
	11th to 20th	Day	26% 24% 34% 15% 1	270
	21st to end	Day	27% 25% 36% 9% 2	297
January	1st to 10th	Night	15% 21% 39% 19% 5%	950
	11th to 20th	Night	19% 18% 41% 16% 5%	915
	21st to end	Night	19% 18% 40% 19% 3	990
February	1st to 10th	Night	16% 22% 37% 20% 4 1	900
	11th to 20th	Night	15% 22% 37% 17% 8% 1	879
	21st to end	Night	20% 19% 35% 22% 4	601
March	1st to 10th	Night	18% 18% 35% 24% 5% 1	720
	11th to 20th	Night	20% 20% 32% 19% 7% 1	568
	21st to end	Night	21% 15% 28% 23% 10% 2	594
April	1st to 10th	Night	25% 16% 31% 22% 5% 1	540
	11th to 20th	Night	29% 11% 28% 25% 8%	533
	21st to end	Night	28% 9% 26% 27% 9% 1	540
May	1st to 10th	Night	22% 13% 33% 25% 5% 1	540
	11th to 20th	Night	20% 10% 31% 28% 8% 2	531
	21st to end	Night	17% 10% 32% 30% 10% 1	584
June	1st to 10th	Night	16% 8% 31% 35% 10% 1	540
	11th to 20th	Night	15% 8% 33% 35% 10%	540
	21st to end	Night	16% 7% 31% 31% 14% 1	540
July	1st to 10th	Night	8% 6% 27% 39% 19% 1	525
	11th to 20th	Night	11% 7% 35% 30% 16% 1	522
	21st to end	Night	11% 5% 29% 38% 16% 2	591
August	1st to 10th	Night	11% 6% 24% 41% 18% 1	537
	11th to 20th	Night	16% 5% 23% 34% 19% 3	534
	21st to end	Night	15% 8% 28% 29% 18% 2	594
September	1st to 10th	Night	13% 8% 30% 31% 17% 2	540
	11th to 20th	Night	14% 9% 32% 31% 13% 1	540
	21st to end	Night	22% 14% 30% 24% 9% 1	702
October	1st to 10th	Night	25% 13% 28% 23% 10% 1	720
	11th to 20th	Night	29% 18% 30% 16% 6%	720
	21st to end	Night	29% 12% 31% 22% 5%	792
November	1st to 10th	Night	23% 15% 35% 21% 5% 1	763
	11th to 20th	Night	22% 22% 35% 16% 5%	950
	21st to end	Night	22% 23% 34% 17% 3	950
December	1st to 10th	Night	20% 20% 37% 19% 4 1	950
	11th to 20th	Night	20% 22% 33% 20% 5% 1	950
	21st to end	Night	29% 19% 34% 14% 3	1045

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