Wright's Mill Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Wright's Mill Observatory clear sky chart from 2005-11-06 to 2024-10-25.

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% 39%	101193
	Night	18% 8% 2 6% 4 4 4 3 5% 6% 41%	97596
Transparency	Day	43% 7% 12% 22% 14% 2	100948
	Night	43% 6% 11% 23% 15% 2	97461
Seeing	Day	22% 17% 31% 20% 8% 2	14962
	Night	21% 15% 31% 24% 8% 1	24044

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	16% 7% 2 6% 4 3 4 3 4 5% 46%	2517
	11th to 20th	Day	17% 10% 3 7% 5% 5% 4 4 4 5% 35%	2520
	21st to end	Day	23% 11% 4 7% 4 3 3 3 4 6% 31%	2946
February	1st to 10th	Day	17% 9% 2 6% 4 5% 5% 3 5% 6% 38%	1731
	11th to 20th	Day	15% 8% 2 6% 5% 4 4 3 5% 6% 43%	1848
	21st to end	Day	20% 9% 3 5% 5% 3 4 4 4 5% 38%	1570
March	1st to 10th	Day	27% 9% 2 5% 4 3 3 3 4 5% 35%	3116
	11th to 20th	Day	10% 5% 2 6% 5% 5% 5% 5% 7% 7% 43%	3288
	21st to end	Day	21% 8% 2 6% 3 3 3 3 4 6% 42%	4161
April	1st to 10th	Day	19% 10% 3 6% 4 3 4 3 5% 7% 38%	2280
	11th to 20th	Day	19% 6% 2 6% 4 3 4 4 5% 7% 41%	2254
	21st to end	Day	19% 6% 2 6% 4 4 4 4 6% 6% 40%	2330
May	1st to 10th	Day	28% 9% 2 5% 3 3 4 3 5% 8% 30%	4106
	11th to 20th	Day	23% 9% 3 7% 4 4 4 4 4 7% 30%	4352
	21st to end	Day	15% 5% 1 5% 4 3 4 4 6% 8% 44%	4837
June	1st to 10th	Day	18% 6% 2 5% 4 5% 4 4 7% 8% 37%	2660
	11th to 20th	Day	16% 6% 2 6% 4 5% 5% 5% 6% 8% 37%	2660
	21st to end	Day	13% 6% 3 6% 5% 5% 5% 4 6% 8% 39%	2660
July	1st to 10th	Day	10% 7% 2 8% 6% 5% 6% 5% 8% 9% 34%	4440
	11th to 20th	Day	12% 7% 2 6% 5% 4 5% 5% 7% 10% 37%	4440
	21st to end	Day	15% 8% 3 8% 5% 6% 5% 4 7% 7% 32%	4814
August	1st to 10th	Day	21% 7% 2 7% 4 5% 5% 5% 6% 7% 31%	4216
	11th to 20th	Day	13% 7% 2 6% 4 4 4 4 6% 8% 40%	3730
	21st to end	Day	10% 6% 2 6% 4 4 4 3 6% 10% 45%	4180
September	1st to 10th	Day	14% 5% 2 6% 5% 5% 5% 3 6% 6% 44%	2280
	11th to 20th	Day	13% 5% 2 4 3 3 4 4 5% 7% 49%	2184
	21st to end	Day	17% 6% 2 7% 4 4 4 3 4 6% 40%	2090
October	1st to 10th	Day	22% 7% 2 5% 4 4 3 2 4 6% 42%	2005
	11th to 20th	Day	15% 5% 1 5% 4 4 3 4 4 7% 48%	1900
	21st to end	Day	22% 5% 2 5% 4 4 4 3 5% 6% 41%	1858
November	1st to 10th	Day	15% 6% 2 5% 4 2 2 3 4 6% 51%	1671
	11th to 20th	Day	20% 6% 2 4 2 3 4 3 5% 6% 46%	1710
	21st to end	Day	16% 6% 2 5% 3 4 4 4 5% 7% 44%	1641
December	1st to 10th	Day	19% 7% 2 6% 6% 5% 4 3 5% 6% 36%	1520
	11th to 20th	Day	23% 6% 2 5% 3 3 2 2 5% 5% 44%	1906
	21st to end	Day	19% 9% 3 8% 5% 5% 5% 3 5% 6% 32%	2772
January	1st to 10th	Night	17% 7% 2 5% 4 3 3 3 5% 6% 46%	4429
	11th to 20th	Night	16% 9% 2 7% 4 3 4 3 5% 5% 41%	4440
	21st to end	Night	24% 12% 2 6% 4 3 3 3 4 5% 34%	4692
February	1st to 10th	Night	17% 9% 3 5% 4 3 4 2 4 6% 42%	2447
	11th to 20th	Night	17% 8% 3 6% 5% 3 4 3 5% 5% 42%	2218
	21st to end	Night	18% 8% 3 6% 4 4 4 3 4 5% 42%	1884
March	1st to 10th	Night	25% 10% 3 5% 3 3 4 3 4 5% 36%	3724
	11th to 20th	Night	12% 6% 2 6% 5% 4 4 4 5% 6% 46%	3653
	21st to end	Night	19% 9% 3 6% 3 3 3 3 4 5% 42%	3471
April	1st to 10th	Night	19% 8% 3 6% 4 4 4 4 5% 7% 37%	1900
	11th to 20th	Night	20% 7% 2 6% 3 4 3 2 5% 7% 40%	1875
	21st to end	Night	20% 7% 3 7% 3 3 3 2 5% 5% 42%	1848
May	1st to 10th	Night	26% 9% 3 7% 4 4 4 3 5% 7% 29%	2834
	11th to 20th	Night	22% 10% 3 7% 5% 3 4 3 5% 6% 32%	2569
	21st to end	Night	18% 6% 2 5% 3 3 3 3 5% 7% 43%	2738
June	1st to 10th	Night	18% 6% 1 5% 4 4 3 3 5% 8% 42%	1520
	11th to 20th	Night	14% 8% 1 5% 4 5% 4 4 6% 8% 41%	1520
	21st to end	Night	12% 6% 2 4 4 4 4 4 7% 9% 43%	1520
July	1st to 10th	Night	11% 6% 2 7% 6% 6% 6% 5% 7% 9% 36%	2520
	11th to 20th	Night	14% 7% 2 6% 4 5% 5% 3 7% 9% 38%	2520
	21st to end	Night	19% 8% 3 6% 4 4 4 3 6% 8% 36%	2739
August	1st to 10th	Night	23% 7% 2 7% 5% 5% 5% 4 5% 7% 31%	2677
	11th to 20th	Night	15% 7% 3 7% 5% 4 4 3 6% 7% 39%	3097
	21st to end	Night	11% 5% 2 4 3 3 4 4 5% 8% 52%	3476
September	1st to 10th	Night	15% 5% 2 6% 5% 4 4 3 5% 6% 46%	1900
	11th to 20th	Night	14% 6% 2 3 3 3 3 3 4 7% 52%	1995
	21st to end	Night	18% 7% 2 6% 3 3 4 2 4 6% 44%	2090
October	1st to 10th	Night	19% 8% 3 6% 4 3 3 2 3 6% 43%	2171
	11th to 20th	Night	15% 5% 2 5% 3 3 3 3 5% 6% 49%	2280
	21st to end	Night	23% 6% 2 6% 3 3 3 3 4 5% 42%	2604
November	1st to 10th	Night	13% 6% 2 5% 4 3 3 3 5% 6% 49%	2407
	11th to 20th	Night	19% 7% 2 4 3 2 3 2 5% 5% 47%	2470
	21st to end	Night	15% 6% 2 4 4 3 4 4 5% 7% 46%	2536
December	1st to 10th	Night	20% 8% 2 5% 4 4 4 3 4 6% 39%	2660
	11th to 20th	Night	20% 7% 2 5% 4 4 5% 4 5% 6% 40%	3288
	21st to end	Night	21% 9% 2 6% 4 4 4 3 5% 5% 37%	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	39% 6% 8% 33% 11% 3	2518
	11th to 20th	Day	48% 7% 11% 23% 10% 1	2520
	21st to end	Day	54% 6% 7% 20% 11% 2	2946
February	1st to 10th	Day	46% 5% 12% 22% 13% 2	1731
	11th to 20th	Day	42% 4 10% 23% 18% 3	1857
	21st to end	Day	48% 5% 10% 22% 14% 3	1570
March	1st to 10th	Day	50% 5% 12% 19% 11% 2	3119
	11th to 20th	Day	33% 7% 17% 29% 13% 2	3288
	21st to end	Day	45% 3 7% 16% 22% 6%	4161
April	1st to 10th	Day	46% 5% 9% 21% 15% 4	2280
	11th to 20th	Day	43% 6% 11% 19% 19% 3	2254
	21st to end	Day	43% 6% 10% 21% 16% 3	2330
May	1st to 10th	Day	52% 7% 13% 15% 12% 1	4120
	11th to 20th	Day	50% 9% 12% 18% 9% 1	4356
	21st to end	Day	35% 9% 12% 25% 17% 2	4837
June	1st to 10th	Day	42% 9% 13% 21% 14% 1	2660
	11th to 20th	Day	43% 7% 14% 23% 11% 2	2660
	21st to end	Day	41% 9% 13% 22% 14% 1	2660
July	1st to 10th	Day	42% 10% 11% 20% 15% 1	4370
	11th to 20th	Day	39% 8% 17% 22% 12% 2	4365
	21st to end	Day	47% 9% 12% 17% 14% 1	4661
August	1st to 10th	Day	49% 8% 13% 21% 8%	4202
	11th to 20th	Day	38% 7% 16% 29% 10% 1	3766
	21st to end	Day	33% 7% 13% 28% 18% 1	4180
September	1st to 10th	Day	40% 7% 10% 23% 18% 2	2280
	11th to 20th	Day	34% 5% 11% 23% 26% 1	2184
	21st to end	Day	45% 5% 9% 21% 17% 3	2090
October	1st to 10th	Day	44% 5% 9% 22% 17% 3	2005
	11th to 20th	Day	35% 5% 13% 26% 19% 2	1900
	21st to end	Day	44% 5% 10% 21% 17% 3	1858
November	1st to 10th	Day	36% 4 12% 25% 20% 3	1671
	11th to 20th	Day	40% 4 10% 23% 20% 4	1710
	21st to end	Day	40% 4 13% 28% 13% 2	1641
December	1st to 10th	Day	47% 6% 13% 18% 14% 1	1520
	11th to 20th	Day	43% 4 14% 21% 15% 3	1906
	21st to end	Day	51% 7% 11% 21% 9% 1	2772
January	1st to 10th	Night	39% 5% 11% 30% 12% 4	4429
	11th to 20th	Night	43% 6% 12% 24% 12% 3	4440
	21st to end	Night	53% 5% 9% 21% 12% 2	4692
February	1st to 10th	Night	45% 5% 12% 24% 13% 2	2447
	11th to 20th	Night	44% 5% 10% 19% 18% 5%	2220
	21st to end	Night	45% 4 8% 23% 16% 4	1884
March	1st to 10th	Night	51% 4 10% 20% 12% 2	3734
	11th to 20th	Night	35% 7% 15% 25% 16% 3	3654
	21st to end	Night	45% 5% 7% 14% 24% 6%	3471
April	1st to 10th	Night	46% 5% 11% 20% 15% 3	1900
	11th to 20th	Night	45% 5% 10% 19% 20% 1	1875
	21st to end	Night	44% 6% 9% 20% 17% 4	1848
May	1st to 10th	Night	55% 7% 10% 17% 9% 1	2840
	11th to 20th	Night	52% 8% 13% 15% 10% 1	2570
	21st to end	Night	39% 7% 13% 25% 13% 3	2739
June	1st to 10th	Night	41% 8% 9% 22% 18% 2	1520
	11th to 20th	Night	39% 8% 17% 25% 11% 1	1520
	21st to end	Night	35% 10% 14% 27% 14% 1	1520
July	1st to 10th	Night	42% 8% 15% 18% 15% 2	2480
	11th to 20th	Night	41% 8% 15% 24% 11% 1	2472
	21st to end	Night	46% 6% 14% 15% 17% 2	2651
August	1st to 10th	Night	51% 9% 14% 16% 9% 1	2667
	11th to 20th	Night	43% 7% 13% 28% 9% 1	3127
	21st to end	Night	29% 7% 13% 33% 17% 1	3476
September	1st to 10th	Night	39% 6% 9% 26% 19% 1	1900
	11th to 20th	Night	33% 5% 10% 25% 25% 3	1995
	21st to end	Night	41% 7% 7% 22% 21% 2	2090
October	1st to 10th	Night	45% 5% 11% 22% 14% 3	2171
	11th to 20th	Night	36% 5% 12% 28% 17% 2	2280
	21st to end	Night	43% 5% 11% 22% 16% 2	2604
November	1st to 10th	Night	36% 5% 12% 22% 21% 4	2407
	11th to 20th	Night	40% 3 9% 24% 19% 4	2470
	21st to end	Night	37% 4 13% 31% 13% 2	2536
December	1st to 10th	Night	46% 4 11% 22% 15% 1	2660
	11th to 20th	Night	43% 4 13% 20% 17% 3	3288
	21st to end	Night	47% 6% 12% 23% 12% 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	27% 29% 29% 12% 2 1	180
	11th to 20th	Day	29% 28% 31% 11% 1	180
	21st to end	Day	20% 30% 34% 12% 4	249
February	1st to 10th	Day	31% 29% 30% 9% 1	291
	11th to 20th	Day	26% 29% 35% 10% 1	456
	21st to end	Day	31% 23% 31% 12% 3	382
March	1st to 10th	Day	27% 23% 34% 14% 3	460
	11th to 20th	Day	23% 30% 31% 13% 2 1	460
	21st to end	Day	30% 24% 31% 11% 3 1	506
April	1st to 10th	Day	30% 26% 25% 13% 5% 1	460
	11th to 20th	Day	25% 26% 28% 12% 8% 1	452
	21st to end	Day	28% 18% 34% 14% 4 1	460
May	1st to 10th	Day	32% 20% 28% 13% 5% 2	463
	11th to 20th	Day	22% 16% 37% 20% 5% 1	487
	21st to end	Day	18% 13% 29% 27% 10% 3	529
June	1st to 10th	Day	20% 12% 33% 24% 10% 2	490
	11th to 20th	Day	16% 15% 33% 26% 9% 1	490
	21st to end	Day	15% 14% 30% 27% 13% 2	490
July	1st to 10th	Day	15% 7% 31% 28% 15% 4	485
	11th to 20th	Day	12% 6% 31% 32% 17% 2	484
	21st to end	Day	13% 10% 32% 32% 12% 1	532
August	1st to 10th	Day	16% 9% 26% 30% 14% 5%	486
	11th to 20th	Day	15% 5% 28% 31% 15% 5%	479
	21st to end	Day	12% 10% 28% 28% 15% 7%	539
September	1st to 10th	Day	18% 12% 27% 23% 16% 4	490
	11th to 20th	Day	14% 9% 30% 25% 12% 10%	490
	21st to end	Day	22% 12% 32% 20% 11% 4	490
October	1st to 10th	Day	27% 13% 24% 20% 12% 4	490
	11th to 20th	Day	18% 18% 34% 20% 9% 2	490
	21st to end	Day	27% 16% 29% 19% 8% 1	428
November	1st to 10th	Day	15% 19% 31% 23% 8% 3	365
	11th to 20th	Day	26% 21% 32% 16% 5%	370
	21st to end	Day	21% 23% 31% 20% 5% 1	301
December	1st to 10th	Day	24% 26% 32% 13% 5%	180
	11th to 20th	Day	33% 27% 29% 9% 3	180
	21st to end	Day	27% 22% 33% 14% 4	198
January	1st to 10th	Night	21% 21% 37% 18% 3	760
	11th to 20th	Night	24% 22% 32% 19% 3	760
	21st to end	Night	20% 23% 37% 18% 3	836
February	1st to 10th	Night	23% 20% 37% 19% 2	760
	11th to 20th	Night	24% 25% 35% 14% 1	743
	21st to end	Night	27% 21% 33% 16% 3	628
March	1st to 10th	Night	24% 22% 34% 18% 3	760
	11th to 20th	Night	21% 22% 36% 17% 3	760
	21st to end	Night	23% 22% 34% 16% 4	836
April	1st to 10th	Night	23% 21% 35% 17% 4	760
	11th to 20th	Night	23% 18% 35% 20% 4	751
	21st to end	Night	25% 17% 34% 20% 5%	708
May	1st to 10th	Night	26% 16% 32% 20% 6%	570
	11th to 20th	Night	24% 15% 32% 25% 5%	422
	21st to end	Night	19% 10% 24% 37% 9% 1	411
June	1st to 10th	Night	18% 8% 30% 33% 10% 1	380
	11th to 20th	Night	14% 6% 29% 38% 12%	380
	21st to end	Night	13% 3 30% 42% 11% 1	380
July	1st to 10th	Night	14% 7% 22% 38% 19% 1	370
	11th to 20th	Night	12% 4 24% 41% 17% 1	368
	21st to end	Night	13% 5% 24% 42% 16% 1	416
August	1st to 10th	Night	14% 4 24% 40% 17% 1	471
	11th to 20th	Night	14% 7% 21% 36% 22% 1	750
	21st to end	Night	16% 6% 21% 35% 19% 3	836
September	1st to 10th	Night	18% 6% 28% 32% 14% 2	760
	11th to 20th	Night	16% 6% 25% 31% 18% 4	760
	21st to end	Night	21% 6% 27% 31% 14% 1	760
October	1st to 10th	Night	22% 12% 28% 24% 12% 2	760
	11th to 20th	Night	19% 13% 32% 25% 11%	760
	21st to end	Night	26% 15% 31% 20% 7%	812
November	1st to 10th	Night	15% 14% 36% 24% 10% 1	740
	11th to 20th	Night	24% 16% 33% 20% 6% 1	760
	21st to end	Night	20% 19% 32% 23% 6% 1	760
December	1st to 10th	Night	26% 19% 33% 17% 5% 1	760
	11th to 20th	Night	23% 20% 33% 21% 3	760
	21st to end	Night	25% 20% 35% 17% 3	836

Page generated at 2024-10-22 20:21:01. Version ac07

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