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 2025-04-11.

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%	113109
	Night	17% 8% 2 6% 4 4 4 3 5% 6% 39%	115161
Transparency	Day	44% 6% 11% 21% 15% 3	116677
	Night	43% 6% 11% 22% 15% 2	119757
Seeing	Day	25% 18% 31% 18% 7% 2	15435
	Night	22% 16% 31% 24% 7% 1	24452

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% 6% 3 7% 5% 5% 6% 4 6% 7% 37%	3597
	11th to 20th	Day	14% 8% 3 6% 4 3 4 3 5% 6% 44%	3570
	21st to end	Day	14% 8% 2 6% 5% 3 4 3 4 6% 44%	3960
February	1st to 10th	Day	17% 8% 2 6% 6% 5% 5% 3 5% 7% 36%	1807
	11th to 20th	Day	13% 7% 2 8% 4 4 5% 4 5% 8% 40%	1948
	21st to end	Day	16% 11% 3 7% 4 5% 4 3 5% 7% 36%	1650
March	1st to 10th	Day	21% 11% 3 7% 5% 4 5% 4 4 5% 32%	4476
	11th to 20th	Day	17% 10% 3 6% 4 4 4 4 6% 6% 37%	4786
	21st to end	Day	26% 9% 2 5% 3 3 4 3 5% 7% 31%	5758
April	1st to 10th	Day	20% 10% 2 7% 5% 4 4 3 4 6% 37%	2400
	11th to 20th	Day	17% 8% 2 6% 5% 4 5% 5% 5% 7% 37%	2290
	21st to end	Day	21% 8% 3 8% 4 4 4 3 5% 6% 34%	2470
May	1st to 10th	Day	23% 12% 3 8% 5% 5% 5% 3 5% 6% 26%	4106
	11th to 20th	Day	21% 8% 3 8% 5% 5% 4 3 5% 7% 32%	4203
	21st to end	Day	15% 5% 2 5% 4 4 4 4 6% 9% 41%	4837
June	1st to 10th	Day	20% 7% 3 7% 5% 4 4 4 6% 8% 32%	2660
	11th to 20th	Day	17% 6% 3 6% 4 5% 5% 5% 6% 8% 37%	2660
	21st to end	Day	20% 8% 3 7% 5% 4 5% 4 6% 7% 32%	2660
July	1st to 10th	Day	14% 6% 2 7% 5% 5% 5% 5% 7% 10% 34%	4440
	11th to 20th	Day	12% 6% 2 6% 5% 5% 5% 5% 7% 10% 38%	4440
	21st to end	Day	18% 7% 3 7% 4 5% 4 4 5% 7% 35%	4814
August	1st to 10th	Day	15% 6% 3 8% 5% 5% 5% 4 6% 8% 34%	4183
	11th to 20th	Day	18% 8% 3 6% 4 5% 5% 5% 6% 8% 33%	4045
	21st to end	Day	9% 5% 1 5% 4 5% 5% 5% 7% 9% 44%	4187
September	1st to 10th	Day	13% 4 2 5% 4 5% 5% 4 6% 6% 46%	2275
	11th to 20th	Day	15% 5% 2 5% 3 3 3 3 4 5% 53%	2090
	21st to end	Day	15% 7% 3 5% 4 4 3 3 4 7% 45%	2090
October	1st to 10th	Day	23% 7% 2 6% 4 3 4 4 6% 5% 38%	2090
	11th to 20th	Day	15% 6% 2 7% 3 4 4 4 5% 7% 44%	1834
	21st to end	Day	23% 7% 2 5% 4 3 4 3 5% 6% 39%	1881
November	1st to 10th	Day	15% 6% 2 5% 4 4 3 3 4 6% 48%	1761
	11th to 20th	Day	18% 5% 2 4 3 3 3 3 5% 5% 48%	1800
	21st to end	Day	20% 7% 3 5% 4 3 4 3 5% 6% 41%	1795
December	1st to 10th	Day	15% 8% 2 6% 4 4 3 4 6% 7% 40%	2600
	11th to 20th	Day	19% 6% 2 5% 4 4 4 3 5% 4 44%	2986
	21st to end	Day	21% 9% 2 7% 3 3 4 4 5% 5% 37%	3960
January	1st to 10th	Night	13% 7% 2 6% 4 4 5% 4 6% 6% 43%	6349
	11th to 20th	Night	12% 9% 3 9% 5% 4 5% 3 6% 6% 37%	6315
	21st to end	Night	15% 9% 3 7% 4 5% 5% 3 5% 6% 39%	6996
February	1st to 10th	Night	15% 9% 3 7% 4 5% 4 4 6% 6% 37%	2586
	11th to 20th	Night	13% 9% 2 6% 5% 5% 5% 4 5% 6% 40%	2338
	21st to end	Night	15% 9% 3 5% 4 5% 5% 3 6% 7% 40%	1980
March	1st to 10th	Night	22% 10% 2 5% 4 4 5% 3 5% 6% 34%	5364
	11th to 20th	Night	15% 10% 3 7% 4 4 5% 4 6% 6% 36%	5172
	21st to end	Night	26% 8% 2 5% 3 3 4 3 6% 7% 32%	5158
April	1st to 10th	Night	19% 9% 3 7% 4 4 4 4 5% 5% 36%	2000
	11th to 20th	Night	19% 9% 2 6% 4 3 4 3 4 6% 39%	1845
	21st to end	Night	21% 7% 3 5% 5% 4 3 3 5% 5% 39%	1710
May	1st to 10th	Night	25% 12% 3 7% 5% 4 4 4 5% 7% 25%	2834
	11th to 20th	Night	17% 9% 3 8% 6% 7% 6% 5% 6% 7% 26%	2719
	21st to end	Night	16% 7% 2 6% 4 4 4 4 5% 7% 40%	2738
June	1st to 10th	Night	18% 9% 2 7% 5% 4 4 4 5% 7% 35%	1520
	11th to 20th	Night	20% 6% 2 5% 4 4 4 5% 6% 8% 36%	1520
	21st to end	Night	18% 7% 1 6% 5% 4 4 3 6% 9% 35%	1520
July	1st to 10th	Night	12% 5% 2 7% 6% 5% 6% 5% 8% 9% 35%	2520
	11th to 20th	Night	12% 7% 3 7% 4 4 5% 4 6% 8% 41%	2520
	21st to end	Night	15% 7% 2 6% 4 4 4 4 5% 7% 41%	2739
August	1st to 10th	Night	21% 7% 2 7% 5% 5% 5% 4 4 6% 35%	2715
	11th to 20th	Night	14% 10% 3 7% 5% 4 5% 4 6% 7% 35%	2782
	21st to end	Night	9% 3 2 4 3 4 4 3 6% 9% 52%	3466
September	1st to 10th	Night	12% 6% 2 5% 3 4 3 3 4 7% 50%	1905
	11th to 20th	Night	14% 5% 1 5% 3 3 4 2 4 7% 51%	2090
	21st to end	Night	15% 6% 2 4 3 4 3 3 4 6% 48%	2090
October	1st to 10th	Night	21% 6% 3 6% 4 3 5% 3 5% 6% 39%	2090
	11th to 20th	Night	15% 6% 2 6% 4 3 4 4 6% 7% 43%	2342
	21st to end	Night	22% 7% 3 6% 4 4 4 3 5% 6% 38%	2717
November	1st to 10th	Night	15% 7% 2 6% 3 4 4 3 4 6% 46%	2537
	11th to 20th	Night	17% 7% 3 4 4 3 3 3 4 6% 46%	2600
	21st to end	Night	16% 8% 2 6% 4 4 4 3 5% 6% 43%	2600
December	1st to 10th	Night	15% 11% 3 6% 4 4 4 4 5% 6% 39%	4580
	11th to 20th	Night	23% 7% 2 5% 4 3 4 3 4 5% 40%	5208
	21st to end	Night	19% 10% 3 7% 4 4 4 3 4 5% 38%	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	43% 6% 10% 26% 15% 1	3598
	11th to 20th	Day	39% 6% 13% 23% 16% 3	3600
	21st to end	Day	41% 6% 7% 23% 19% 4	3960
February	1st to 10th	Day	47% 6% 12% 21% 11% 2	1807
	11th to 20th	Day	42% 6% 14% 19% 15% 4	1957
	21st to end	Day	49% 4 9% 21% 14% 3	1650
March	1st to 10th	Day	54% 4 8% 13% 11% 10%	4479
	11th to 20th	Day	44% 8% 14% 21% 11% 3	4786
	21st to end	Day	51% 4 6% 17% 16% 5%	5758
April	1st to 10th	Day	50% 4 8% 18% 17% 4	2400
	11th to 20th	Day	44% 8% 11% 19% 16% 3	2290
	21st to end	Day	50% 6% 9% 15% 17% 3	2470
May	1st to 10th	Day	57% 9% 9% 15% 9% 1	4120
	11th to 20th	Day	50% 8% 15% 15% 10% 2	4207
	21st to end	Day	37% 8% 14% 22% 17% 2	4837
June	1st to 10th	Day	49% 8% 11% 20% 11% 1	2660
	11th to 20th	Day	43% 8% 11% 19% 15% 3	2660
	21st to end	Day	50% 7% 11% 18% 12% 1	2660
July	1st to 10th	Day	43% 8% 12% 23% 14% 1	4370
	11th to 20th	Day	39% 8% 15% 24% 13% 1	4365
	21st to end	Day	46% 7% 11% 21% 14% 1	4661
August	1st to 10th	Day	46% 8% 14% 23% 10%	4169
	11th to 20th	Day	46% 7% 14% 23% 9% 1	4084
	21st to end	Day	33% 8% 13% 28% 17% 1	4187
September	1st to 10th	Day	35% 7% 13% 24% 19% 2	2275
	11th to 20th	Day	34% 5% 8% 28% 23% 3	2090
	21st to end	Day	40% 5% 9% 24% 20% 2	2090
October	1st to 10th	Day	44% 6% 8% 22% 18% 2	3480
	11th to 20th	Day	33% 4 10% 29% 20% 5%	3024
	21st to end	Day	35% 5% 7% 31% 19% 3	3081
November	1st to 10th	Day	38% 5% 14% 25% 17% 2	1761
	11th to 20th	Day	37% 5% 11% 21% 23% 3	1800
	21st to end	Day	44% 5% 16% 21% 13% 1	1795
December	1st to 10th	Day	41% 6% 14% 29% 9% 1	2600
	11th to 20th	Day	42% 5% 12% 17% 19% 5%	2986
	21st to end	Day	49% 5% 8% 19% 14% 6%	3960
January	1st to 10th	Night	38% 5% 12% 30% 12% 2	6349
	11th to 20th	Night	46% 6% 12% 21% 12% 3	6360
	21st to end	Night	45% 5% 9% 18% 18% 5%	6996
February	1st to 10th	Night	45% 7% 12% 19% 14% 2	2586
	11th to 20th	Night	43% 6% 11% 21% 15% 3	2340
	21st to end	Night	43% 6% 11% 22% 14% 4	1980
March	1st to 10th	Night	50% 6% 8% 15% 15% 7%	5374
	11th to 20th	Night	46% 7% 15% 17% 12% 2	5173
	21st to end	Night	49% 4 6% 14% 22% 5%	5158
April	1st to 10th	Night	47% 6% 11% 17% 16% 3	2000
	11th to 20th	Night	45% 5% 8% 22% 18% 2	1845
	21st to end	Night	47% 5% 9% 19% 17% 3	1710
May	1st to 10th	Night	58% 7% 11% 15% 8% 2	2840
	11th to 20th	Night	53% 10% 14% 14% 8% 2	2720
	21st to end	Night	41% 8% 17% 20% 12% 2	2739
June	1st to 10th	Night	48% 7% 12% 21% 11% 1	1520
	11th to 20th	Night	44% 8% 13% 19% 13% 2	1520
	21st to end	Night	45% 8% 14% 20% 12% 1	1520
July	1st to 10th	Night	41% 9% 15% 22% 12% 1	2480
	11th to 20th	Night	39% 8% 13% 25% 15%	2472
	21st to end	Night	42% 6% 11% 26% 14% 1	2651
August	1st to 10th	Night	50% 8% 11% 20% 10% 1	2705
	11th to 20th	Night	45% 9% 14% 20% 11%	2809
	21st to end	Night	28% 8% 15% 29% 20% 1	3466
September	1st to 10th	Night	34% 6% 13% 26% 20% 1	1905
	11th to 20th	Night	33% 5% 10% 27% 22% 2	2090
	21st to end	Night	37% 5% 11% 27% 18% 2	2090
October	1st to 10th	Night	42% 7% 14% 22% 13% 2	3480
	11th to 20th	Night	30% 5% 11% 27% 24% 4	3891
	21st to end	Night	37% 4 10% 31% 17% 2	4467
November	1st to 10th	Night	39% 6% 10% 25% 18% 2	2537
	11th to 20th	Night	40% 4 10% 23% 20% 3	2600
	21st to end	Night	42% 4 15% 25% 13% 1	2600
December	1st to 10th	Night	45% 5% 10% 29% 10% 1	4580
	11th to 20th	Night	46% 5% 12% 15% 21% 1	5208
	21st to end	Night	49% 5% 8% 21% 15% 3	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	32% 27% 24% 16% 2	200
	11th to 20th	Day	34% 18% 37% 10% 1 2	200
	21st to end	Day	23% 31% 30% 13% 4	220
February	1st to 10th	Day	33% 25% 29% 12% 1	365
	11th to 20th	Day	34% 26% 28% 10% 1	496
	21st to end	Day	30% 22% 31% 14% 1	414
March	1st to 10th	Day	32% 21% 33% 11% 2	500
	11th to 20th	Day	31% 28% 28% 9% 4 1	500
	21st to end	Day	32% 23% 29% 9% 5% 1	550
April	1st to 10th	Day	37% 21% 26% 10% 5% 1	500
	11th to 20th	Day	30% 27% 25% 12% 5% 1	452
	21st to end	Day	28% 20% 33% 13% 4 2	460
May	1st to 10th	Day	33% 20% 31% 11% 4 1	463
	11th to 20th	Day	22% 19% 38% 15% 5% 1	487
	21st to end	Day	21% 15% 36% 21% 6% 1	529
June	1st to 10th	Day	21% 14% 40% 16% 9% 1	490
	11th to 20th	Day	18% 17% 36% 22% 6% 2	490
	21st to end	Day	21% 18% 33% 19% 7% 3	490
July	1st to 10th	Day	18% 9% 35% 25% 11% 2	485
	11th to 20th	Day	15% 9% 35% 28% 10% 2	484
	21st to end	Day	13% 10% 36% 30% 8% 2	532
August	1st to 10th	Day	14% 10% 32% 30% 12% 2	486
	11th to 20th	Day	17% 9% 34% 23% 12% 5%	479
	21st to end	Day	13% 11% 32% 27% 12% 4	539
September	1st to 10th	Day	18% 11% 28% 23% 14% 7%	490
	11th to 20th	Day	19% 14% 27% 18% 14% 9%	490
	21st to end	Day	18% 13% 33% 21% 10% 5%	490
October	1st to 10th	Day	28% 14% 24% 21% 9% 4	490
	11th to 20th	Day	24% 15% 31% 19% 8% 3	425
	21st to end	Day	32% 15% 29% 19% 5%	429
November	1st to 10th	Day	22% 20% 31% 19% 7% 1	395
	11th to 20th	Day	33% 17% 28% 18% 4 1	400
	21st to end	Day	30% 22% 29% 13% 5% 1	395
December	1st to 10th	Day	26% 26% 30% 15% 4 1	200
	11th to 20th	Day	36% 22% 31% 10% 3	200
	21st to end	Day	30% 22% 31% 13% 5%	220
January	1st to 10th	Night	22% 25% 34% 18% 2	800
	11th to 20th	Night	28% 19% 34% 16% 3	800
	21st to end	Night	20% 23% 38% 16% 4	880
February	1st to 10th	Night	23% 20% 37% 18% 2	800
	11th to 20th	Night	24% 22% 36% 15% 2	783
	21st to end	Night	24% 21% 33% 19% 3	660
March	1st to 10th	Night	28% 20% 35% 16% 2	800
	11th to 20th	Night	26% 20% 31% 18% 4	800
	21st to end	Night	27% 20% 31% 18% 4	880
April	1st to 10th	Night	29% 19% 31% 18% 3	800
	11th to 20th	Night	25% 19% 33% 18% 5%	717
	21st to end	Night	25% 18% 33% 21% 3	570
May	1st to 10th	Night	24% 13% 35% 21% 6%	570
	11th to 20th	Night	23% 14% 34% 24% 4 1	507
	21st to end	Night	22% 10% 28% 33% 7%	411
June	1st to 10th	Night	19% 11% 32% 31% 7% 1	380
	11th to 20th	Night	21% 9% 28% 33% 8% 1	380
	21st to end	Night	18% 9% 30% 36% 6%	380
July	1st to 10th	Night	16% 5% 25% 43% 10% 1	370
	11th to 20th	Night	14% 5% 23% 41% 17% 1	368
	21st to end	Night	14% 3 29% 43% 10% 1	416
August	1st to 10th	Night	16% 5% 24% 42% 12% 1	496
	11th to 20th	Night	16% 8% 30% 31% 14% 1	562
	21st to end	Night	15% 6% 26% 35% 17% 2	826
September	1st to 10th	Night	16% 6% 33% 29% 16% 1	760
	11th to 20th	Night	16% 8% 26% 30% 17% 3	760
	21st to end	Night	17% 9% 31% 28% 13% 2	760
October	1st to 10th	Night	23% 13% 24% 27% 12% 1	760
	11th to 20th	Night	18% 15% 32% 23% 12% 1	760
	21st to end	Night	27% 17% 29% 22% 6%	836
November	1st to 10th	Night	20% 14% 33% 24% 7% 1	780
	11th to 20th	Night	24% 19% 31% 20% 5% 1	800
	21st to end	Night	24% 21% 30% 20% 4	800
December	1st to 10th	Night	24% 19% 35% 18% 4	800
	11th to 20th	Night	27% 21% 30% 19% 2	800
	21st to end	Night	25% 20% 33% 20% 2	880

Page generated at 2025-04-08 09:17:25. Version ac07

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