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 2024-10-24.

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	18% 8% 2 6% 4 4 4 4 5% 7% 37%	101172
	Night	17% 8% 2 6% 4 4 4 3 5% 6% 38%	97610
Transparency	Day	45% 7% 12% 21% 14% 2	100930
	Night	45% 6% 12% 21% 14% 2	97472
Seeing	Day	24% 17% 32% 18% 7% 2	14930
	Night	22% 15% 31% 24% 7% 1	23774

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	14% 8% 3 6% 4 4 4 3 4 7% 44%	2517
	11th to 20th	Day	17% 8% 3 8% 4 4 4 4 5% 6% 39%	2520
	21st to end	Day	18% 11% 3 7% 5% 3 5% 4 4 6% 34%	2772
February	1st to 10th	Day	18% 8% 2 5% 6% 5% 6% 3 5% 7% 36%	1715
	11th to 20th	Day	13% 8% 2 8% 4 4 5% 4 5% 7% 41%	1848
	21st to end	Day	16% 11% 3 7% 4 5% 4 3 5% 6% 36%	1570
March	1st to 10th	Day	23% 14% 3 7% 5% 4 4 3 3 4 29%	3116
	11th to 20th	Day	15% 8% 2 6% 4 4 5% 5% 6% 7% 38%	3342
	21st to end	Day	22% 9% 3 6% 4 3 4 3 6% 7% 33%	4024
April	1st to 10th	Day	19% 10% 2 7% 5% 4 4 3 4 6% 37%	2280
	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% 8% 2 5% 4 3 4 3 5% 5% 38%	1809
November	1st to 10th	Day	15% 6% 2 5% 4 4 3 3 4 6% 48%	1671
	11th to 20th	Day	19% 6% 2 4 3 3 3 4 5% 5% 46%	1710
	21st to end	Day	19% 7% 2 5% 4 3 4 3 5% 6% 41%	1706
December	1st to 10th	Day	20% 8% 2 7% 5% 4 4 4 5% 6% 35%	1520
	11th to 20th	Day	22% 6% 2 5% 4 4 4 3 4 4 42%	1906
	21st to end	Day	24% 10% 2 6% 4 3 3 4 5% 5% 32%	2772
January	1st to 10th	Night	17% 8% 2 5% 3 4 4 3 5% 6% 44%	4429
	11th to 20th	Night	14% 7% 2 8% 5% 4 5% 3 6% 7% 38%	4440
	21st to end	Night	21% 11% 3 7% 4 5% 5% 3 4 5% 32%	4884
February	1st to 10th	Night	15% 9% 3 7% 4 5% 4 4 6% 7% 36%	2458
	11th to 20th	Night	13% 9% 2 6% 5% 5% 5% 4 6% 5% 40%	2218
	21st to end	Night	15% 9% 3 4 4 4 5% 3 6% 7% 40%	1884
March	1st to 10th	Night	25% 12% 2 5% 4 3 4 3 4 5% 32%	3724
	11th to 20th	Night	13% 8% 3 7% 5% 5% 6% 4 6% 6% 37%	3616
	21st to end	Night	24% 8% 3 5% 3 4 4 4 6% 8% 32%	3606
April	1st to 10th	Night	19% 9% 3 7% 4 3 4 3 5% 5% 37%	1900
	11th to 20th	Night	19% 9% 2 6% 4 3 4 3 4 6% 40%	1838
	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 3 4 3 5% 6% 37%	2614
November	1st to 10th	Night	15% 7% 2 6% 4 4 4 3 4 6% 45%	2407
	11th to 20th	Night	17% 7% 3 5% 4 4 3 3 4 6% 45%	2470
	21st to end	Night	16% 8% 2 6% 4 4 4 3 5% 6% 43%	2470
December	1st to 10th	Night	19% 10% 3 6% 4 3 4 4 5% 5% 38%	2660
	11th to 20th	Night	20% 8% 2 5% 4 3 4 4 5% 6% 40%	3288
	21st to end	Night	22% 10% 3 7% 4 4 4 3 4 5% 34%	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	40% 5% 11% 31% 11% 1	2518
	11th to 20th	Day	45% 6% 13% 24% 10% 2	2520
	21st to end	Day	50% 7% 9% 23% 10% 1	2772
February	1st to 10th	Day	47% 6% 13% 22% 10% 2	1715
	11th to 20th	Day	42% 6% 14% 19% 15% 4	1857
	21st to end	Day	49% 4 9% 20% 14% 3	1570
March	1st to 10th	Day	59% 5% 9% 13% 11% 3	3119
	11th to 20th	Day	40% 9% 14% 19% 13% 4	3342
	21st to end	Day	49% 4 7% 17% 18% 5%	4024
April	1st to 10th	Day	50% 4 8% 18% 17% 4	2280
	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	46% 6% 9% 21% 16% 3	2090
	11th to 20th	Day	39% 6% 11% 29% 12% 2	1834
	21st to end	Day	47% 6% 9% 22% 13% 3	1809
November	1st to 10th	Day	38% 5% 14% 25% 17% 2	1671
	11th to 20th	Day	39% 5% 11% 22% 20% 3	1710
	21st to end	Day	43% 5% 16% 20% 13% 1	1706
December	1st to 10th	Day	48% 6% 15% 17% 13% 1	1520
	11th to 20th	Day	45% 6% 11% 18% 16% 4	1906
	21st to end	Day	53% 6% 11% 19% 10% 1	2772
January	1st to 10th	Night	40% 5% 14% 27% 11% 3	4429
	11th to 20th	Night	44% 7% 12% 22% 11% 3	4440
	21st to end	Night	54% 6% 10% 18% 10% 2	4884
February	1st to 10th	Night	45% 7% 13% 19% 13% 2	2458
	11th to 20th	Night	43% 6% 11% 21% 15% 3	2220
	21st to end	Night	43% 6% 11% 23% 13% 5%	1884
March	1st to 10th	Night	53% 6% 9% 18% 11% 3	3734
	11th to 20th	Night	44% 9% 12% 18% 15% 2	3617
	21st to end	Night	49% 5% 7% 15% 19% 6%	3606
April	1st to 10th	Night	46% 6% 11% 17% 17% 3	1900
	11th to 20th	Night	45% 5% 8% 22% 18% 2	1838
	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	46% 6% 11% 22% 13% 3	2090
	11th to 20th	Night	38% 7% 12% 27% 14% 1	2342
	21st to end	Night	48% 5% 12% 22% 12% 1	2614
November	1st to 10th	Night	40% 6% 9% 24% 18% 2	2407
	11th to 20th	Night	41% 4 11% 23% 18% 3	2470
	21st to end	Night	42% 5% 14% 25% 13% 1	2470
December	1st to 10th	Night	48% 5% 12% 22% 12% 1	2660
	11th to 20th	Night	44% 6% 14% 17% 18% 1	3288
	21st to end	Night	52% 5% 9% 23% 11% 1	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	31% 25% 24% 18% 2	180
	11th to 20th	Day	34% 17% 37% 9% 1 2	180
	21st to end	Day	22% 30% 30% 14% 4	198
February	1st to 10th	Day	32% 24% 30% 13% 1	333
	11th to 20th	Day	32% 26% 29% 11% 2	456
	21st to end	Day	31% 21% 31% 15% 2	382
March	1st to 10th	Day	30% 20% 35% 12% 2	460
	11th to 20th	Day	30% 29% 27% 9% 3 1	460
	21st to end	Day	31% 23% 29% 10% 5% 2	506
April	1st to 10th	Day	35% 21% 28% 10% 5% 1	460
	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% 14% 29% 20% 5%	405
November	1st to 10th	Day	21% 20% 30% 21% 7% 1	365
	11th to 20th	Day	33% 17% 27% 19% 4 1	370
	21st to end	Day	29% 20% 31% 14% 5% 1	366
December	1st to 10th	Day	26% 26% 28% 15% 4 1	180
	11th to 20th	Day	35% 21% 32% 9% 3	180
	21st to end	Day	31% 23% 30% 12% 4 1	198
January	1st to 10th	Night	21% 24% 34% 19% 2	760
	11th to 20th	Night	29% 19% 34% 16% 2	760
	21st to end	Night	21% 22% 37% 16% 4	836
February	1st to 10th	Night	22% 20% 38% 18% 2	760
	11th to 20th	Night	22% 23% 37% 16% 2	743
	21st to end	Night	25% 20% 33% 19% 3	628
March	1st to 10th	Night	27% 20% 35% 17% 2	760
	11th to 20th	Night	25% 21% 32% 17% 4	760
	21st to end	Night	26% 20% 31% 19% 4	836
April	1st to 10th	Night	28% 18% 32% 19% 3	760
	11th to 20th	Night	25% 19% 33% 18% 5%	714
	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% 16% 29% 22% 5%	805
November	1st to 10th	Night	21% 14% 32% 24% 7% 1	740
	11th to 20th	Night	24% 19% 30% 20% 6% 1	760
	21st to end	Night	23% 21% 30% 21% 4	760
December	1st to 10th	Night	25% 19% 35% 17% 4	760
	11th to 20th	Night	26% 21% 31% 19% 2	760
	21st to end	Night	26% 21% 33% 19% 2	836

Page generated at 2024-10-21 02:20:05. Version ac07

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