Northwood Ridge Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Northwood Ridge Observatory clear sky chart from 2005-11-06 to 2026-08-15.

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	17% 7% 2 6% 4 4 4 4 5% 7% 38%	143498
	Night	17% 8% 2 6% 4 4 4 3 5% 7% 39%	138404
Transparency	Day	44% 6% 11% 22% 15% 2	147020
	Night	43% 6% 11% 22% 15% 2	142971
Seeing	Day	25% 18% 32% 17% 7% 2	17218
	Night	22% 16% 32% 23% 7% 1	26014

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	11% 6% 3 8% 5% 6% 6% 5% 6% 7% 36%	4661
	11th to 20th	Day	15% 10% 3 7% 3 3 4 3 5% 6% 42%	4650
	21st to end	Day	12% 8% 2 5% 4 3 4 4 4 7% 46%	5124
February	1st to 10th	Day	16% 8% 2 6% 6% 5% 6% 3 5% 7% 36%	1898
	11th to 20th	Day	12% 7% 2 8% 4 4 5% 4 5% 8% 40%	2048
	21st to end	Day	15% 11% 3 7% 4 5% 4 3 5% 7% 36%	1730
March	1st to 10th	Day	21% 11% 3 7% 5% 4 5% 4 4 5% 32%	4576
	11th to 20th	Day	17% 10% 3 6% 4 4 4 4 6% 6% 37%	4892
	21st to end	Day	26% 9% 2 5% 3 3 4 3 5% 8% 31%	5885
April	1st to 10th	Day	20% 10% 2 7% 4 4 4 3 4 5% 37%	2520
	11th to 20th	Day	17% 7% 2 6% 5% 4 5% 5% 5% 7% 36%	2534
	21st to end	Day	20% 8% 3 7% 4 4 4 3 5% 6% 35%	2730
May	1st to 10th	Day	28% 10% 2 6% 4 4 5% 4 5% 6% 26%	7639
	11th to 20th	Day	19% 7% 3 8% 5% 5% 4 4 5% 7% 33%	7859
	21st to end	Day	21% 7% 2 7% 5% 5% 5% 4 6% 8% 32%	9060
June	1st to 10th	Day	19% 7% 3 7% 5% 4 4 4 6% 8% 32%	2940
	11th to 20th	Day	17% 6% 3 6% 4 5% 5% 5% 6% 8% 37%	2940
	21st to end	Day	19% 8% 3 7% 5% 4 5% 4 6% 7% 33%	2940
July	1st to 10th	Day	16% 6% 2 6% 4 5% 5% 5% 6% 10% 34%	8280
	11th to 20th	Day	9% 5% 2 6% 4 5% 5% 4 6% 10% 44%	8280
	21st to end	Day	16% 6% 2 6% 3 4 4 4 5% 8% 42%	8993
August	1st to 10th	Day	15% 6% 3 8% 5% 5% 5% 4 6% 8% 35%	4449
	11th to 20th	Day	17% 8% 3 6% 4 5% 5% 5% 6% 8% 34%	4227
	21st to end	Day	9% 5% 1 5% 4 5% 5% 5% 7% 9% 45%	4319
September	1st to 10th	Day	13% 4 2 5% 4 5% 5% 4 7% 7% 46%	2394
	11th to 20th	Day	14% 5% 2 5% 3 3 3 3 4 5% 53%	2200
	21st to end	Day	16% 7% 3 5% 3 4 3 3 4 7% 45%	2200
October	1st to 10th	Day	22% 6% 2 5% 4 3 3 3 5% 5% 40%	2200
	11th to 20th	Day	16% 6% 2 7% 3 3 4 4 5% 7% 44%	1930
	21st to end	Day	22% 7% 2 5% 3 3 4 3 5% 6% 40%	1980
November	1st to 10th	Day	15% 6% 2 5% 4 4 3 3 4 6% 47%	1851
	11th to 20th	Day	17% 5% 2 4 3 3 3 4 5% 6% 48%	1890
	21st to end	Day	20% 7% 2 5% 4 3 4 3 5% 6% 41%	1885
December	1st to 10th	Day	15% 8% 2 6% 4 4 3 4 6% 7% 40%	2680
	11th to 20th	Day	19% 6% 2 5% 4 4 4 3 5% 4 44%	3066
	21st to end	Day	21% 9% 2 7% 4 3 4 4 5% 5% 37%	4048
January	1st to 10th	Night	13% 8% 2 6% 4 4 5% 3 6% 6% 43%	8234
	11th to 20th	Night	14% 10% 3 9% 5% 4 4 3 6% 6% 35%	8235
	21st to end	Night	13% 8% 3 6% 4 5% 5% 4 5% 6% 42%	9057
February	1st to 10th	Night	14% 9% 3 7% 4 5% 4 4 6% 7% 38%	2715
	11th to 20th	Night	13% 8% 2 6% 5% 5% 5% 5% 6% 6% 40%	2458
	21st to end	Night	15% 9% 3 5% 4 5% 5% 3 6% 6% 40%	2076
March	1st to 10th	Night	22% 10% 2 5% 4 4 5% 3 5% 6% 35%	5484
	11th to 20th	Night	16% 10% 3 7% 4 4 5% 4 6% 6% 36%	5286
	21st to end	Night	26% 8% 2 5% 3 3 4 3 6% 7% 32%	5273
April	1st to 10th	Night	19% 9% 3 7% 4 3 4 3 5% 5% 37%	2100
	11th to 20th	Night	20% 9% 2 7% 4 3 4 3 4 6% 39%	2034
	21st to end	Night	20% 8% 3 6% 5% 4 3 3 5% 4 40%	1890
May	1st to 10th	Night	30% 10% 3 6% 4 3 3 3 5% 7% 26%	5259
	11th to 20th	Night	14% 8% 3 8% 5% 6% 6% 4 6% 8% 31%	5057
	21st to end	Night	21% 7% 3 7% 5% 5% 4 4 5% 7% 32%	5114
June	1st to 10th	Night	17% 9% 3 7% 5% 4 4 4 5% 7% 37%	1680
	11th to 20th	Night	19% 6% 3 5% 4 4 4 5% 6% 8% 36%	1680
	21st to end	Night	18% 7% 1 6% 5% 4 4 3 6% 8% 36%	1680
July	1st to 10th	Night	14% 6% 2 7% 5% 4 5% 4 6% 10% 37%	4680
	11th to 20th	Night	10% 7% 3 6% 4 4 5% 4 6% 8% 44%	4680
	21st to end	Night	14% 5% 2 5% 3 3 4 3 5% 7% 50%	5084
August	1st to 10th	Night	20% 7% 2 6% 5% 5% 5% 4 4 6% 36%	2887
	11th to 20th	Night	14% 9% 3 7% 5% 4 5% 4 6% 7% 36%	2909
	21st to end	Night	9% 3 2 4 3 4 4 3 6% 9% 52%	3576
September	1st to 10th	Night	12% 6% 2 5% 3 4 3 3 4 7% 51%	2005
	11th to 20th	Night	13% 5% 1 5% 3 3 4 3 4 7% 52%	2200
	21st to end	Night	16% 6% 2 5% 3 4 3 3 4 6% 48%	2200
October	1st to 10th	Night	20% 6% 3 6% 3 3 5% 3 5% 6% 41%	2200
	11th to 20th	Night	15% 6% 2 6% 4 3 4 3 6% 7% 44%	2466
	21st to end	Night	21% 7% 3 6% 4 4 4 4 5% 6% 37%	2860
November	1st to 10th	Night	15% 7% 2 6% 3 4 4 3 4 6% 46%	2667
	11th to 20th	Night	16% 6% 3 4 4 4 3 3 5% 6% 46%	2730
	21st to end	Night	16% 7% 2 6% 4 4 5% 3 5% 7% 42%	2730
December	1st to 10th	Night	14% 11% 3 7% 4 4 4 4 5% 6% 39%	4720
	11th to 20th	Night	23% 7% 2 5% 4 3 4 3 4 5% 40%	5348
	21st to end	Night	19% 10% 3 7% 4 4 4 3 4 5% 37%	7150

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	44% 6% 11% 24% 14% 1	4662
	11th to 20th	Day	42% 5% 11% 22% 17% 3	4680
	21st to end	Day	38% 5% 8% 26% 19% 3	5124
February	1st to 10th	Day	46% 6% 12% 22% 12% 2	1898
	11th to 20th	Day	41% 6% 14% 20% 15% 4	2057
	21st to end	Day	48% 4 9% 21% 14% 2	1730
March	1st to 10th	Day	53% 5% 8% 14% 11% 9%	4579
	11th to 20th	Day	44% 8% 14% 21% 11% 3	4892
	21st to end	Day	51% 4 6% 17% 17% 5%	5885
April	1st to 10th	Day	50% 4 8% 18% 17% 4	2520
	11th to 20th	Day	45% 7% 11% 19% 16% 3	2534
	21st to end	Day	49% 6% 8% 16% 18% 3	2730
May	1st to 10th	Day	57% 7% 10% 15% 10% 1	7651
	11th to 20th	Day	48% 7% 14% 18% 10% 2	7863
	21st to end	Day	49% 7% 11% 21% 12% 1	9061
June	1st to 10th	Day	48% 7% 11% 21% 12% 1	2940
	11th to 20th	Day	43% 8% 12% 19% 16% 3	2940
	21st to end	Day	49% 7% 11% 19% 12% 1	2940
July	1st to 10th	Day	45% 7% 13% 23% 12%	8210
	11th to 20th	Day	33% 7% 14% 28% 16% 1	8205
	21st to end	Day	40% 6% 10% 27% 16% 1	8795
August	1st to 10th	Day	45% 8% 14% 23% 10%	4435
	11th to 20th	Day	45% 7% 14% 24% 9% 1	4266
	21st to end	Day	32% 8% 13% 28% 18% 2	4319
September	1st to 10th	Day	35% 6% 13% 25% 19% 2	2394
	11th to 20th	Day	33% 5% 8% 28% 24% 3	2200
	21st to end	Day	40% 5% 9% 24% 20% 2	2200
October	1st to 10th	Day	43% 6% 8% 22% 19% 2	3590
	11th to 20th	Day	33% 4 10% 29% 19% 4	3120
	21st to end	Day	35% 5% 7% 31% 19% 3	3180
November	1st to 10th	Day	38% 5% 14% 24% 17% 2	1851
	11th to 20th	Day	37% 5% 11% 21% 22% 3	1890
	21st to end	Day	44% 5% 15% 22% 13% 1	1885
December	1st to 10th	Day	41% 5% 14% 29% 9% 1	2680
	11th to 20th	Day	42% 5% 12% 17% 19% 5%	3066
	21st to end	Day	49% 5% 8% 19% 14% 5%	4048
January	1st to 10th	Night	40% 5% 13% 28% 13% 2	8234
	11th to 20th	Night	48% 5% 11% 19% 13% 4	8280
	21st to end	Night	42% 4 8% 21% 20% 5%	9057
February	1st to 10th	Night	44% 7% 12% 20% 14% 2	2715
	11th to 20th	Night	42% 6% 12% 22% 15% 3	2460
	21st to end	Night	43% 6% 11% 23% 14% 4	2076
March	1st to 10th	Night	50% 6% 8% 16% 15% 6%	5494
	11th to 20th	Night	46% 7% 15% 17% 13% 2	5287
	21st to end	Night	50% 4 6% 14% 22% 5%	5273
April	1st to 10th	Night	47% 6% 11% 17% 17% 3	2100
	11th to 20th	Night	46% 5% 8% 21% 18% 2	2034
	21st to end	Night	46% 5% 9% 19% 18% 3	1890
May	1st to 10th	Night	57% 6% 12% 13% 11% 1	5265
	11th to 20th	Night	48% 9% 13% 20% 9% 1	5058
	21st to end	Night	50% 6% 13% 21% 9% 1	5115
June	1st to 10th	Night	47% 6% 11% 23% 12% 1	1680
	11th to 20th	Night	44% 9% 13% 19% 13% 2	1680
	21st to end	Night	45% 8% 14% 21% 11% 1	1680
July	1st to 10th	Night	42% 8% 15% 23% 12%	4640
	11th to 20th	Night	36% 7% 13% 26% 18%	4632
	21st to end	Night	34% 5% 12% 32% 15% 1	4967
August	1st to 10th	Night	49% 7% 12% 20% 10% 1	2877
	11th to 20th	Night	45% 9% 14% 21% 11% 1	2936
	21st to end	Night	27% 8% 15% 29% 20% 1	3576
September	1st to 10th	Night	34% 6% 13% 27% 20% 1	2005
	11th to 20th	Night	32% 5% 10% 27% 23% 2	2200
	21st to end	Night	38% 5% 11% 27% 18% 2	2200
October	1st to 10th	Night	41% 7% 13% 23% 14% 2	3590
	11th to 20th	Night	30% 5% 11% 27% 24% 4	4015
	21st to end	Night	37% 4 10% 31% 16% 2	4610
November	1st to 10th	Night	39% 5% 9% 25% 18% 2	2667
	11th to 20th	Night	40% 4 10% 23% 20% 3	2730
	21st to end	Night	42% 5% 15% 25% 13% 1	2730
December	1st to 10th	Night	45% 5% 10% 29% 10% 1	4720
	11th to 20th	Night	46% 5% 12% 15% 21% 2	5348
	21st to end	Night	49% 5% 8% 21% 15% 3	7150

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	30% 27% 25% 15% 2	220
	11th to 20th	Day	35% 19% 36% 9% 1 1	220
	21st to end	Day	26% 31% 28% 12% 3	242
February	1st to 10th	Day	32% 24% 32% 12% 1	396
	11th to 20th	Day	32% 25% 30% 11% 1	536
	21st to end	Day	30% 23% 32% 14% 1	446
March	1st to 10th	Day	33% 21% 33% 11% 2	540
	11th to 20th	Day	32% 28% 27% 9% 3 1	540
	21st to end	Day	33% 24% 28% 9% 4 1	594
April	1st to 10th	Day	37% 21% 27% 9% 4 1	540
	11th to 20th	Day	32% 27% 25% 11% 4 1	532
	21st to end	Day	27% 20% 33% 13% 5% 1	540
May	1st to 10th	Day	36% 20% 30% 11% 3 1	543
	11th to 20th	Day	23% 20% 37% 14% 4 2	567
	21st to end	Day	23% 15% 36% 19% 6% 1	617
June	1st to 10th	Day	20% 13% 40% 17% 9% 1	570
	11th to 20th	Day	20% 18% 35% 20% 6% 2	570
	21st to end	Day	21% 17% 34% 20% 6% 2	570
July	1st to 10th	Day	18% 10% 36% 24% 10% 2	565
	11th to 20th	Day	15% 11% 34% 27% 11% 2	564
	21st to end	Day	14% 11% 35% 30% 9% 2	620
August	1st to 10th	Day	13% 10% 32% 31% 12% 2	566
	11th to 20th	Day	16% 10% 34% 24% 12% 5%	535
	21st to end	Day	13% 11% 33% 27% 12% 4	583
September	1st to 10th	Day	18% 10% 29% 23% 14% 6%	530
	11th to 20th	Day	17% 13% 27% 19% 14% 8%	530
	21st to end	Day	18% 13% 33% 21% 10% 5%	530
October	1st to 10th	Day	27% 14% 24% 22% 9% 4	530
	11th to 20th	Day	25% 15% 31% 19% 8% 2	458
	21st to end	Day	31% 16% 29% 18% 5%	462
November	1st to 10th	Day	24% 21% 30% 18% 6% 1	425
	11th to 20th	Day	31% 19% 28% 17% 4 1	430
	21st to end	Day	32% 22% 29% 13% 4 1	425
December	1st to 10th	Day	27% 24% 30% 14% 4	220
	11th to 20th	Day	36% 22% 30% 9% 3	220
	21st to end	Day	32% 21% 31% 12% 4	242
January	1st to 10th	Night	22% 25% 33% 18% 1	840
	11th to 20th	Night	29% 19% 33% 16% 2	840
	21st to end	Night	21% 23% 37% 15% 4	924
February	1st to 10th	Night	22% 20% 38% 18% 2	840
	11th to 20th	Night	23% 22% 37% 16% 2	823
	21st to end	Night	24% 20% 34% 19% 3	692
March	1st to 10th	Night	27% 20% 35% 15% 2	840
	11th to 20th	Night	27% 20% 31% 18% 4	840
	21st to end	Night	27% 20% 31% 18% 3	924
April	1st to 10th	Night	29% 19% 31% 18% 3	840
	11th to 20th	Night	26% 19% 33% 17% 5%	790
	21st to end	Night	24% 17% 33% 22% 3	630
May	1st to 10th	Night	26% 13% 35% 21% 6%	630
	11th to 20th	Night	22% 15% 35% 24% 4 1	561
	21st to end	Night	22% 10% 30% 31% 6%	455
June	1st to 10th	Night	19% 10% 31% 31% 9%	420
	11th to 20th	Night	20% 10% 28% 33% 8%	420
	21st to end	Night	18% 9% 31% 36% 6%	420
July	1st to 10th	Night	16% 6% 27% 42% 9%	410
	11th to 20th	Night	13% 5% 25% 40% 16% 1	408
	21st to end	Night	14% 3 29% 43% 10% 1	460
August	1st to 10th	Night	16% 4 23% 43% 14% 1	548
	11th to 20th	Night	15% 8% 30% 32% 14% 1	605
	21st to end	Night	14% 7% 27% 35% 16% 2	870
September	1st to 10th	Night	16% 6% 33% 30% 16% 1	800
	11th to 20th	Night	15% 8% 26% 31% 17% 3	800
	21st to end	Night	17% 9% 31% 28% 14% 2	800
October	1st to 10th	Night	23% 13% 24% 27% 12% 1	800
	11th to 20th	Night	19% 15% 32% 23% 12% 1	800
	21st to end	Night	26% 16% 30% 22% 5%	880
November	1st to 10th	Night	21% 15% 33% 23% 6% 1	820
	11th to 20th	Night	23% 19% 31% 20% 5% 1	840
	21st to end	Night	24% 21% 31% 20% 4	840
December	1st to 10th	Night	24% 19% 35% 18% 4	840
	11th to 20th	Night	27% 21% 30% 19% 2	840
	21st to end	Night	26% 20% 32% 20% 2	924

Page generated at 2026-08-12 03:37:19. Version ac07

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