Nealey's Corner
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Nealey's Corner clear sky chart from 2005-11-06 to 2025-12-03.

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% 9% 3 7% 4 4 4 4 5% 7% 36%	126371
	Night	18% 9% 3 7% 4 4 4 4 5% 7% 36%	124357
Transparency	Day	48% 4 11% 22% 13% 2	129879
	Night	47% 4 11% 23% 13% 2	128937
Seeing	Day	27% 16% 31% 18% 7% 2	17099
	Night	24% 14% 31% 24% 6%	25451

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% 9% 3 10% 6% 4 5% 3 5% 5% 36%	3597
	11th to 20th	Day	14% 8% 2 8% 5% 4 3 3 4 6% 42%	3570
	21st to end	Day	12% 10% 4 8% 4 4 4 3 4 5% 42%	4002
February	1st to 10th	Day	16% 11% 3 7% 5% 4 4 3 5% 6% 36%	1800
	11th to 20th	Day	14% 10% 2 7% 6% 5% 5% 4 5% 4 37%	1866
	21st to end	Day	13% 10% 2 10% 7% 5% 4 4 5% 4 36%	1650
March	1st to 10th	Day	23% 13% 3 9% 5% 4 4 3 3 4 29%	4494
	11th to 20th	Day	17% 13% 4 8% 4 4 4 3 4 6% 33%	4980
	21st to end	Day	28% 8% 3 7% 4 4 3 3 6% 6% 29%	5466
April	1st to 10th	Day	22% 12% 3 7% 5% 3 3 3 4 5% 32%	2390
	11th to 20th	Day	19% 9% 2 6% 4 4 4 3 5% 7% 37%	2542
	21st to end	Day	23% 9% 3 6% 5% 3 3 3 4 6% 35%	2600
May	1st to 10th	Day	29% 10% 3 8% 5% 4 4 3 5% 5% 25%	5886
	11th to 20th	Day	20% 9% 3 8% 5% 5% 4 3 5% 6% 31%	5861
	21st to end	Day	19% 8% 3 6% 5% 5% 5% 4 6% 7% 32%	7123
June	1st to 10th	Day	23% 7% 3 7% 4 4 5% 4 6% 7% 30%	3000
	11th to 20th	Day	18% 7% 2 6% 4 5% 5% 4 5% 7% 36%	3000
	21st to end	Day	23% 8% 3 6% 5% 4 4 4 5% 8% 30%	3000
July	1st to 10th	Day	14% 7% 2 7% 5% 5% 6% 5% 8% 10% 30%	6511
	11th to 20th	Day	12% 7% 3 7% 5% 5% 5% 4 7% 9% 37%	6360
	21st to end	Day	14% 6% 2 6% 4 4 4 4 6% 9% 41%	6847
August	1st to 10th	Day	17% 7% 3 8% 5% 5% 5% 4 6% 8% 35%	4235
	11th to 20th	Day	16% 9% 3 7% 5% 5% 4 4 5% 7% 35%	4175
	21st to end	Day	11% 6% 2 5% 3 4 5% 4 7% 8% 44%	4645
September	1st to 10th	Day	11% 5% 2 4 4 3 4 3 6% 8% 49%	2309
	11th to 20th	Day	13% 4 2 5% 4 4 4 3 4 5% 53%	2200
	21st to end	Day	16% 6% 3 6% 3 3 4 4 4 8% 44%	2200
October	1st to 10th	Day	17% 7% 2 6% 5% 4 5% 3 4 7% 41%	2150
	11th to 20th	Day	19% 6% 2 5% 4 4 5% 2 4 7% 41%	1974
	21st to end	Day	22% 9% 2 6% 4 4 4 3 5% 6% 35%	1980
November	1st to 10th	Day	17% 6% 2 6% 4 4 4 4 6% 6% 39%	1851
	11th to 20th	Day	19% 7% 2 5% 4 4 4 4 4 6% 42%	1862
	21st to end	Day	21% 9% 2 5% 4 3 4 4 3 5% 41%	1680
December	1st to 10th	Day	16% 12% 2 5% 3 3 4 2 5% 7% 41%	2405
	11th to 20th	Day	19% 9% 2 6% 3 3 3 2 4 5% 44%	2618
	21st to end	Day	21% 12% 3 6% 4 3 4 3 4 5% 35%	3542
January	1st to 10th	Night	12% 10% 4 9% 5% 4 4 3 5% 6% 38%	6349
	11th to 20th	Night	14% 10% 4 8% 5% 5% 4 4 5% 6% 33%	6315
	21st to end	Night	12% 11% 3 8% 5% 4 5% 4 5% 6% 38%	6952
February	1st to 10th	Night	15% 10% 4 8% 4 5% 5% 4 5% 6% 33%	2600
	11th to 20th	Night	13% 9% 3 9% 6% 5% 4 4 5% 5% 38%	2415
	21st to end	Night	14% 12% 3 7% 6% 4 4 4 4 6% 37%	1980
March	1st to 10th	Night	27% 11% 3 7% 4 4 3 3 4 5% 29%	5346
	11th to 20th	Night	17% 10% 3 7% 4 5% 5% 4 6% 7% 31%	4979
	21st to end	Night	25% 10% 2 6% 4 4 4 3 7% 6% 28%	5466
April	1st to 10th	Night	23% 11% 3 6% 4 3 4 3 5% 5% 33%	2009
	11th to 20th	Night	20% 7% 2 7% 5% 4 4 4 6% 7% 34%	1807
	21st to end	Night	26% 8% 3 5% 4 4 3 4 5% 5% 34%	1800
May	1st to 10th	Night	28% 10% 3 7% 4 4 3 4 5% 6% 26%	4054
	11th to 20th	Night	21% 8% 3 7% 6% 4 5% 4 6% 7% 30%	4033
	21st to end	Night	15% 8% 3 8% 5% 5% 4 4 5% 8% 35%	3790
June	1st to 10th	Night	21% 9% 3 7% 4 4 5% 4 5% 7% 31%	1400
	11th to 20th	Night	17% 7% 2 6% 4 4 4 4 6% 8% 39%	1400
	21st to end	Night	24% 9% 3 6% 4 5% 3 4 7% 7% 30%	1400
July	1st to 10th	Night	11% 7% 3 8% 6% 6% 6% 6% 7% 9% 33%	3438
	11th to 20th	Night	14% 8% 3 8% 5% 5% 5% 3 6% 7% 35%	3600
	21st to end	Night	10% 6% 2 5% 4 5% 5% 4 7% 9% 44%	3957
August	1st to 10th	Night	18% 8% 3 7% 5% 5% 5% 4 6% 7% 31%	2915
	11th to 20th	Night	15% 9% 3 7% 6% 4 6% 5% 6% 8% 32%	2872
	21st to end	Night	10% 6% 3 6% 4 4 5% 3 6% 7% 45%	3249
September	1st to 10th	Night	13% 5% 1 4 3 3 4 4 5% 7% 49%	2090
	11th to 20th	Night	15% 5% 2 4 2 3 3 3 4 6% 53%	2200
	21st to end	Night	16% 6% 2 6% 3 3 4 4 5% 6% 45%	2200
October	1st to 10th	Night	18% 5% 2 6% 4 4 4 3 4 6% 43%	2250
	11th to 20th	Night	18% 6% 2 5% 4 4 4 3 4 7% 43%	2424
	21st to end	Night	23% 9% 2 6% 4 4 4 3 4 6% 36%	2860
November	1st to 10th	Night	18% 7% 2 5% 4 4 3 3 4 6% 42%	2667
	11th to 20th	Night	17% 6% 2 6% 4 4 4 3 5% 7% 40%	2756
	21st to end	Night	18% 9% 3 5% 4 4 4 3 6% 6% 39%	2940
December	1st to 10th	Night	16% 10% 2 6% 4 4 5% 4 6% 7% 36%	4825
	11th to 20th	Night	23% 8% 2 5% 3 3 3 3 4 5% 42%	5591
	21st to end	Night	21% 11% 3 6% 4 3 4 3 4 6% 36%	7428

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	51% 3 10% 25% 10% 1	3598
	11th to 20th	Day	44% 4 10% 29% 11% 2	3600
	21st to end	Day	46% 2 10% 17% 18% 7%	4002
February	1st to 10th	Day	50% 3 11% 19% 15% 3	1800
	11th to 20th	Day	49% 4 10% 21% 14% 2	1874
	21st to end	Day	51% 3 10% 20% 11% 5%	1650
March	1st to 10th	Day	60% 2 6% 10% 15% 6%	4497
	11th to 20th	Day	54% 2 13% 18% 11% 2	4980
	21st to end	Day	56% 3 4 18% 16% 3	5466
April	1st to 10th	Day	55% 3 7% 16% 15% 4	2390
	11th to 20th	Day	48% 4 8% 23% 15% 2	2542
	21st to end	Day	52% 2 7% 19% 15% 4	2600
May	1st to 10th	Day	62% 3 10% 16% 8% 1	5897
	11th to 20th	Day	54% 4 12% 20% 8% 3	5865
	21st to end	Day	50% 4 12% 19% 13% 2	7123
June	1st to 10th	Day	53% 3 11% 21% 11% 1	3000
	11th to 20th	Day	47% 5% 11% 21% 15% 2	3000
	21st to end	Day	52% 5% 11% 21% 10% 2	3000
July	1st to 10th	Day	47% 6% 15% 23% 9%	6441
	11th to 20th	Day	42% 6% 13% 23% 14% 1	6285
	21st to end	Day	40% 4 13% 27% 14% 1	6650
August	1st to 10th	Day	48% 5% 14% 27% 7%	4222
	11th to 20th	Day	48% 5% 16% 23% 8%	4214
	21st to end	Day	35% 5% 12% 27% 18% 1	4645
September	1st to 10th	Day	33% 4 14% 29% 19% 1	2309
	11th to 20th	Day	34% 4 9% 29% 22% 2	2200
	21st to end	Day	40% 3 10% 28% 18% 1	2200
October	1st to 10th	Day	52% 4 8% 22% 13% 1	3501
	11th to 20th	Day	36% 2 10% 32% 19% 1	3190
	21st to end	Day	37% 3 14% 25% 19% 2	3180
November	1st to 10th	Day	44% 3 13% 22% 15% 2	1851
	11th to 20th	Day	44% 3 9% 23% 17% 3	1862
	21st to end	Day	47% 3 15% 24% 10% 1	1680
December	1st to 10th	Day	45% 3 16% 22% 14% 1	2405
	11th to 20th	Day	45% 3 12% 16% 17% 7%	2618
	21st to end	Day	52% 3 10% 20% 12% 3	3542
January	1st to 10th	Night	48% 3 12% 26% 10% 1	6349
	11th to 20th	Night	52% 4 12% 21% 9% 2	6360
	21st to end	Night	47% 3 7% 22% 16% 5%	6952
February	1st to 10th	Night	52% 3 11% 19% 13% 2	2600
	11th to 20th	Night	49% 3 10% 20% 16% 3	2418
	21st to end	Night	49% 4 8% 21% 15% 4	1980
March	1st to 10th	Night	58% 3 6% 13% 14% 6%	5356
	11th to 20th	Night	53% 3 17% 18% 8% 1	4980
	21st to end	Night	55% 2 5% 18% 17% 2	5466
April	1st to 10th	Night	54% 2 7% 17% 17% 3	2009
	11th to 20th	Night	49% 3 9% 23% 15% 2	1807
	21st to end	Night	52% 3 10% 18% 14% 3	1800
May	1st to 10th	Night	60% 3 13% 16% 8% 1	4060
	11th to 20th	Night	54% 4 12% 21% 8% 1	4034
	21st to end	Night	48% 4 15% 23% 11%	3791
June	1st to 10th	Night	53% 4 11% 23% 9% 1	1400
	11th to 20th	Night	44% 4 15% 23% 12% 2	1400
	21st to end	Night	53% 4 12% 20% 9% 2	1400
July	1st to 10th	Night	45% 6% 15% 24% 9%	3398
	11th to 20th	Night	47% 5% 13% 25% 10%	3552
	21st to end	Night	35% 6% 17% 31% 10% 1	3840
August	1st to 10th	Night	52% 6% 13% 22% 7%	2903
	11th to 20th	Night	47% 5% 16% 21% 10%	2899
	21st to end	Night	37% 6% 13% 26% 17% 1	3249
September	1st to 10th	Night	34% 4 13% 33% 16% 1	2090
	11th to 20th	Night	33% 4 11% 31% 20% 2	2200
	21st to end	Night	39% 5% 9% 30% 16% 1	2200
October	1st to 10th	Night	43% 5% 13% 25% 14% 1	3679
	11th to 20th	Night	34% 3 10% 33% 20% 1	3947
	21st to end	Night	40% 3 11% 29% 15% 2	4610
November	1st to 10th	Night	44% 3 11% 25% 15% 1	2667
	11th to 20th	Night	44% 4 9% 24% 17% 2	2756
	21st to end	Night	45% 4 14% 20% 14% 2	2940
December	1st to 10th	Night	46% 4 10% 28% 12%	4825
	11th to 20th	Night	46% 3 10% 21% 18% 2	5592
	21st to end	Night	51% 3 10% 19% 16% 1	7428

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	35% 14% 33% 16% 3	200
	11th to 20th	Day	36% 19% 29% 13% 2 2	200
	21st to end	Day	29% 21% 32% 15% 3	236
February	1st to 10th	Day	30% 21% 29% 16% 4	400
	11th to 20th	Day	31% 25% 32% 10% 2	453
	21st to end	Day	28% 22% 33% 14% 3	414
March	1st to 10th	Day	34% 20% 30% 13% 2	500
	11th to 20th	Day	29% 23% 32% 13% 3 1	500
	21st to end	Day	35% 20% 27% 11% 4 2	550
April	1st to 10th	Day	41% 18% 27% 9% 4 1	500
	11th to 20th	Day	35% 24% 27% 9% 5% 1	492
	21st to end	Day	33% 20% 30% 12% 4 1	500
May	1st to 10th	Day	36% 17% 30% 14% 3 1	503
	11th to 20th	Day	26% 18% 33% 17% 5% 1	527
	21st to end	Day	26% 16% 34% 18% 5%	653
June	1st to 10th	Day	27% 12% 32% 19% 8% 1	730
	11th to 20th	Day	24% 14% 29% 22% 10% 1	730
	21st to end	Day	27% 12% 30% 23% 7% 1	730
July	1st to 10th	Day	21% 12% 37% 21% 9% 1	598
	11th to 20th	Day	19% 10% 39% 21% 10% 1	524
	21st to end	Day	15% 11% 38% 25% 9% 2	576
August	1st to 10th	Day	15% 10% 37% 28% 9% 2	526
	11th to 20th	Day	18% 11% 31% 24% 13% 3	519
	21st to end	Day	19% 12% 32% 25% 10% 2	583
September	1st to 10th	Day	14% 12% 35% 25% 11% 3	530
	11th to 20th	Day	21% 11% 28% 19% 13% 8%	530
	21st to end	Day	18% 15% 33% 19% 11% 5%	530
October	1st to 10th	Day	21% 14% 28% 21% 11% 4	502
	11th to 20th	Day	28% 13% 31% 17% 8% 3	420
	21st to end	Day	33% 14% 31% 17% 5% 1	462
November	1st to 10th	Day	29% 16% 28% 20% 6% 2	425
	11th to 20th	Day	29% 18% 32% 14% 6% 1	430
	21st to end	Day	33% 17% 26% 19% 4	430
December	1st to 10th	Day	30% 18% 32% 15% 4	276
	11th to 20th	Day	36% 28% 25% 9% 3 1	200
	21st to end	Day	38% 18% 24% 15% 4	220
January	1st to 10th	Night	26% 19% 33% 19% 3	800
	11th to 20th	Night	28% 19% 31% 18% 4 1	800
	21st to end	Night	21% 20% 35% 20% 3 1	880
February	1st to 10th	Night	25% 19% 33% 20% 3	800
	11th to 20th	Night	25% 21% 36% 15% 3	783
	21st to end	Night	26% 18% 35% 19% 3	660
March	1st to 10th	Night	29% 16% 35% 18% 1	800
	11th to 20th	Night	25% 19% 32% 19% 5%	800
	21st to end	Night	28% 18% 28% 21% 5%	880
April	1st to 10th	Night	33% 17% 31% 17% 3	800
	11th to 20th	Night	25% 18% 33% 19% 5%	623
	21st to end	Night	32% 13% 31% 19% 5%	600
May	1st to 10th	Night	28% 12% 32% 24% 5%	600
	11th to 20th	Night	26% 11% 36% 21% 5%	592
	21st to end	Night	21% 10% 33% 29% 6%	460
June	1st to 10th	Night	24% 9% 32% 30% 6%	400
	11th to 20th	Night	21% 8% 32% 30% 10%	400
	21st to end	Night	28% 4 32% 31% 6%	400
July	1st to 10th	Night	18% 3 36% 36% 7%	390
	11th to 20th	Night	15% 3 30% 40% 12% 1	388
	21st to end	Night	19% 3 30% 37% 11% 1	444
August	1st to 10th	Night	16% 4 33% 36% 11%	598
	11th to 20th	Night	16% 5% 29% 36% 13% 1	592
	21st to end	Night	17% 7% 27% 36% 11% 1	673
September	1st to 10th	Night	16% 6% 33% 32% 13% 1	800
	11th to 20th	Night	19% 8% 27% 29% 15% 3	800
	21st to end	Night	19% 8% 32% 28% 12% 2	800
October	1st to 10th	Night	22% 9% 27% 28% 13%	800
	11th to 20th	Night	22% 14% 28% 27% 9% 1	800
	21st to end	Night	29% 15% 31% 20% 5%	880
November	1st to 10th	Night	27% 15% 28% 23% 6% 1	820
	11th to 20th	Night	26% 15% 31% 21% 7% 1	854
	21st to end	Night	28% 18% 30% 18% 4 1	950
December	1st to 10th	Night	28% 16% 31% 19% 5%	911
	11th to 20th	Night	28% 22% 30% 17% 4	900
	21st to end	Night	30% 20% 29% 17% 3	973

Page generated at 2025-11-30 01:00:53. Version ac07

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