Raleigh
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Raleigh clear sky chart from 2005-11-06 to 2024-12-06.

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	13% 6% 2 6% 4 4 4 4 6% 8% 42%	100892
	Night	14% 6% 2 6% 4 4 4 4 5% 7% 44%	98784
Transparency	Day	38% 7% 12% 20% 18% 5%	104540
	Night	38% 6% 10% 20% 19% 6%	103276
Seeing	Day	16% 9% 24% 26% 18% 7%	15446
	Night	15% 7% 26% 33% 17% 2	25800

By Month

Percentage Cloud Cover SE (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	18% 6% 2 4 3 3 3 2 3 5% 52%	2836
	11th to 20th	Day	14% 6% 3 5% 3 2 3 3 4 5% 52%	2840
	21st to end	Day	18% 9% 3 6% 3 3 3 3 4 5% 42%	3124
February	1st to 10th	Day	15% 5% 2 5% 4 5% 4 4 6% 6% 45%	1710
	11th to 20th	Day	21% 7% 2 4 3 3 3 3 4 5% 46%	1690
	21st to end	Day	19% 7% 3 5% 4 3 4 3 5% 5% 42%	1696
March	1st to 10th	Day	23% 7% 2 6% 3 4 4 4 5% 6% 36%	3435
	11th to 20th	Day	10% 5% 2 5% 3 3 3 3 5% 6% 55%	3480
	21st to end	Day	19% 7% 2 5% 4 3 4 3 4 6% 43%	3815
April	1st to 10th	Day	10% 4 2 4 3 3 3 4 5% 8% 54%	2219
	11th to 20th	Day	11% 4 2 5% 4 5% 4 4 5% 7% 48%	2254
	21st to end	Day	14% 5% 2 6% 4 4 3 4 6% 7% 45%	2280
May	1st to 10th	Day	10% 6% 3 8% 6% 6% 6% 5% 8% 9% 34%	4007
	11th to 20th	Day	16% 7% 3 7% 5% 5% 4 4 6% 8% 34%	4081
	21st to end	Day	7% 4 2 5% 4 5% 5% 4 7% 9% 49%	4476
June	1st to 10th	Day	9% 6% 2 6% 5% 5% 6% 5% 7% 10% 39%	2470
	11th to 20th	Day	9% 5% 2 5% 4 5% 7% 5% 7% 10% 42%	2470
	21st to end	Day	8% 5% 2 7% 6% 6% 6% 5% 8% 11% 38%	2470
July	1st to 10th	Day	6% 5% 2 7% 6% 7% 6% 5% 9% 11% 34%	4120
	11th to 20th	Day	10% 8% 2 8% 6% 6% 6% 6% 9% 11% 29%	4120
	21st to end	Day	10% 8% 3 8% 7% 6% 7% 6% 8% 10% 28%	4466
August	1st to 10th	Day	19% 8% 4 9% 5% 5% 6% 5% 8% 9% 22%	4104
	11th to 20th	Day	9% 5% 3 8% 6% 6% 6% 5% 8% 10% 35%	3889
	21st to end	Day	6% 5% 2 6% 4 4 4 4 6% 10% 50%	4180
September	1st to 10th	Day	9% 4 2 5% 5% 4 5% 5% 7% 8% 46%	2280
	11th to 20th	Day	15% 6% 2 6% 4 5% 4 3 5% 8% 41%	2174
	21st to end	Day	20% 6% 3 7% 4 3 4 4 5% 8% 37%	2037
October	1st to 10th	Day	14% 7% 2 6% 3 3 3 3 4 6% 49%	1900
	11th to 20th	Day	12% 4 2 4 3 3 3 3 4 6% 58%	1900
	21st to end	Day	11% 4 2 5% 3 4 3 2 4 5% 57%	2090
November	1st to 10th	Day	13% 5% 2 5% 3 4 3 3 4 5% 54%	1957
	11th to 20th	Day	14% 6% 2 4 3 3 3 3 5% 7% 52%	2000
	21st to end	Day	13% 5% 2 6% 3 3 4 3 5% 6% 52%	1657
December	1st to 10th	Day	17% 7% 2 6% 3 4 4 4 4 6% 43%	1560
	11th to 20th	Day	15% 4 2 4 3 2 2 2 4 5% 56%	1981
	21st to end	Day	16% 6% 3 6% 4 4 4 3 5% 6% 43%	3124
January	1st to 10th	Night	15% 7% 2 5% 3 4 3 3 5% 6% 47%	4109
	11th to 20th	Night	14% 8% 3 6% 4 3 3 3 5% 5% 46%	4120
	21st to end	Night	18% 7% 2 6% 3 4 3 3 4 5% 44%	4532
February	1st to 10th	Night	17% 6% 2 5% 4 4 3 4 5% 6% 44%	2470
	11th to 20th	Night	20% 6% 2 6% 3 3 4 3 4 5% 43%	2375
	21st to end	Night	16% 6% 1 5% 3 3 4 3 6% 6% 45%	1755
March	1st to 10th	Night	24% 9% 3 8% 4 4 4 3 4 4 34%	3418
	11th to 20th	Night	13% 6% 2 5% 4 3 4 3 4 6% 51%	3480
	21st to end	Night	17% 5% 2 4 4 3 3 3 4 5% 50%	3817
April	1st to 10th	Night	14% 4 2 5% 4 3 3 3 5% 7% 49%	1959
	11th to 20th	Night	13% 5% 2 5% 4 4 3 4 5% 6% 49%	1875
	21st to end	Night	11% 3 2 6% 5% 4 4 4 5% 7% 49%	1900
May	1st to 10th	Night	11% 9% 3 8% 5% 4 4 4 5% 8% 40%	2915
	11th to 20th	Night	19% 9% 3 8% 4 4 3 4 4 7% 36%	2812
	21st to end	Night	8% 4 2 5% 4 4 4 5% 7% 10% 47%	3079
June	1st to 10th	Night	10% 5% 3 6% 5% 5% 5% 6% 7% 9% 39%	1710
	11th to 20th	Night	10% 6% 2 6% 4 4 5% 4 8% 8% 41%	1710
	21st to end	Night	7% 6% 3 8% 4 5% 4 5% 10% 11% 38%	1710
July	1st to 10th	Night	7% 6% 2 8% 6% 5% 6% 5% 9% 11% 35%	2840
	11th to 20th	Night	14% 7% 2 7% 5% 5% 6% 5% 8% 11% 32%	2840
	21st to end	Night	15% 10% 3 10% 6% 5% 5% 4 6% 8% 28%	3087
August	1st to 10th	Night	22% 8% 3 7% 5% 5% 6% 5% 7% 9% 23%	2825
	11th to 20th	Night	8% 6% 2 7% 6% 6% 6% 5% 7% 12% 34%	2907
	21st to end	Night	6% 4 2 6% 4 4 4 4 7% 10% 48%	3476
September	1st to 10th	Night	11% 5% 2 6% 4 4 4 4 6% 8% 46%	1900
	11th to 20th	Night	13% 6% 2 7% 4 4 4 4 5% 7% 44%	2002
	21st to end	Night	19% 7% 3 7% 5% 4 4 3 5% 6% 37%	2142
October	1st to 10th	Night	13% 6% 2 6% 4 3 3 3 4 6% 49%	2280
	11th to 20th	Night	12% 5% 2 5% 3 3 3 3 3 6% 54%	2280
	21st to end	Night	11% 4 2 5% 3 3 3 3 5% 5% 56%	2508
November	1st to 10th	Night	13% 6% 2 5% 3 3 3 4 5% 5% 53%	2341
	11th to 20th	Night	13% 5% 2 6% 3 3 4 4 4 5% 50%	2400
	21st to end	Night	12% 5% 2 4 3 4 3 3 5% 6% 52%	2734
December	1st to 10th	Night	17% 7% 2 6% 5% 4 4 3 5% 4 42%	2737
	11th to 20th	Night	17% 6% 2 5% 3 3 3 3 4 5% 48%	3207
	21st to end	Night	16% 6% 2 6% 3 3 3 3 4 7% 47%	4532

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	37% 3 5% 25% 23% 6%	2837
	11th to 20th	Day	36% 4 5% 18% 32% 6%	2840
	21st to end	Day	45% 5% 7% 16% 20% 7%	3124
February	1st to 10th	Day	39% 5% 11% 21% 20% 5%	1710
	11th to 20th	Day	41% 4 7% 18% 23% 7%	1699
	21st to end	Day	44% 5% 10% 15% 20% 6%	1696
March	1st to 10th	Day	48% 5% 8% 18% 13% 8%	3435
	11th to 20th	Day	30% 6% 8% 18% 25% 13%	3480
	21st to end	Day	44% 4 7% 21% 20% 3	3815
April	1st to 10th	Day	29% 6% 10% 23% 24% 8%	2219
	11th to 20th	Day	34% 6% 10% 22% 21% 7%	2254
	21st to end	Day	37% 7% 12% 22% 18% 5%	2280
May	1st to 10th	Day	42% 11% 16% 18% 12% 2	4044
	11th to 20th	Day	46% 8% 11% 22% 12% 1	4085
	21st to end	Day	29% 8% 16% 23% 19% 4	4489
June	1st to 10th	Day	37% 10% 15% 21% 15% 1	2470
	11th to 20th	Day	33% 11% 16% 23% 15% 2	2470
	21st to end	Day	37% 11% 15% 21% 15% 1	2470
July	1st to 10th	Day	39% 11% 18% 18% 12% 3	4055
	11th to 20th	Day	44% 11% 23% 16% 5% 1	4051
	21st to end	Day	48% 11% 15% 15% 10%	4324
August	1st to 10th	Day	56% 8% 18% 13% 5%	4091
	11th to 20th	Day	40% 10% 18% 23% 8% 1	3928
	21st to end	Day	30% 7% 14% 31% 16% 2	4180
September	1st to 10th	Day	33% 10% 14% 18% 20% 5%	2280
	11th to 20th	Day	40% 7% 10% 18% 20% 3	2174
	21st to end	Day	45% 6% 10% 19% 15% 4	2037
October	1st to 10th	Day	32% 5% 10% 21% 24% 8%	3160
	11th to 20th	Day	20% 3 5% 20% 27% 25%	3140
	21st to end	Day	24% 4 6% 25% 25% 16%	3428
November	1st to 10th	Day	34% 4 8% 22% 26% 7%	1957
	11th to 20th	Day	34% 4 8% 21% 26% 7%	2000
	21st to end	Day	34% 4 8% 23% 25% 6%	1657
December	1st to 10th	Day	42% 4 11% 21% 18% 4	1560
	11th to 20th	Day	32% 2 8% 25% 24% 9%	1977
	21st to end	Day	41% 5% 10% 21% 21% 2	3124
January	1st to 10th	Night	37% 4 7% 21% 26% 5%	4109
	11th to 20th	Night	40% 4 7% 17% 25% 6%	4120
	21st to end	Night	42% 5% 5% 19% 23% 7%	4532
February	1st to 10th	Night	40% 5% 8% 20% 21% 6%	2470
	11th to 20th	Night	44% 4 8% 15% 21% 8%	2377
	21st to end	Night	38% 5% 9% 19% 22% 8%	1755
March	1st to 10th	Night	55% 4 7% 13% 15% 6%	3418
	11th to 20th	Night	34% 5% 7% 14% 23% 17%	3480
	21st to end	Night	37% 5% 7% 23% 22% 6%	3817
April	1st to 10th	Night	35% 6% 9% 16% 25% 9%	1959
	11th to 20th	Night	34% 5% 10% 21% 21% 8%	1875
	21st to end	Night	34% 7% 11% 25% 18% 4	1900
May	1st to 10th	Night	41% 9% 15% 20% 13% 2	2944
	11th to 20th	Night	47% 8% 9% 19% 16% 1	2813
	21st to end	Night	29% 9% 17% 24% 19% 2	3087
June	1st to 10th	Night	38% 11% 14% 20% 15% 1	1710
	11th to 20th	Night	37% 9% 16% 19% 16% 2	1710
	21st to end	Night	35% 12% 17% 20% 13% 3	1710
July	1st to 10th	Night	39% 13% 20% 16% 11% 1	2795
	11th to 20th	Night	44% 12% 22% 16% 5% 1	2786
	21st to end	Night	53% 9% 12% 16% 10%	2988
August	1st to 10th	Night	54% 10% 17% 15% 4 1	2814
	11th to 20th	Night	40% 10% 20% 23% 6% 1	2934
	21st to end	Night	30% 7% 12% 29% 20% 2	3476
September	1st to 10th	Night	35% 9% 13% 21% 17% 5%	1900
	11th to 20th	Night	40% 6% 12% 18% 21% 3	2002
	21st to end	Night	48% 6% 11% 15% 16% 4	2142
October	1st to 10th	Night	38% 4 8% 20% 24% 6%	3800
	11th to 20th	Night	24% 3 6% 18% 27% 22%	3779
	21st to end	Night	22% 3 7% 27% 24% 16%	4120
November	1st to 10th	Night	34% 4 9% 18% 27% 8%	2341
	11th to 20th	Night	36% 5% 8% 16% 26% 11%	2400
	21st to end	Night	33% 4 7% 22% 26% 7%	2734
December	1st to 10th	Night	44% 5% 8% 19% 19% 5%	2737
	11th to 20th	Night	38% 4 7% 20% 22% 8%	3210
	21st to end	Night	39% 4 7% 25% 23% 3	4532

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	20% 20% 38% 17% 4	270
	11th to 20th	Day	23% 24% 32% 15% 6%	270
	21st to end	Day	19% 21% 40% 17% 3	297
February	1st to 10th	Day	18% 17% 39% 21% 5%	270
	11th to 20th	Day	35% 13% 37% 12% 2	297
	21st to end	Day	24% 18% 33% 21% 3	382
March	1st to 10th	Day	21% 15% 33% 23% 7%	460
	11th to 20th	Day	20% 18% 38% 17% 6% 1	460
	21st to end	Day	21% 15% 36% 21% 7% 1	506
April	1st to 10th	Day	17% 18% 33% 22% 9% 1	460
	11th to 20th	Day	13% 17% 27% 24% 15% 3	452
	21st to end	Day	18% 13% 25% 25% 17% 2	460
May	1st to 10th	Day	14% 16% 30% 23% 12% 5%	463
	11th to 20th	Day	16% 6% 21% 32% 19% 6%	487
	21st to end	Day	17% 6% 18% 27% 21% 11%	529
June	1st to 10th	Day	12% 5% 20% 32% 23% 8%	490
	11th to 20th	Day	10% 3 22% 26% 27% 13%	490
	21st to end	Day	9% 4 16% 31% 30% 10%	490
July	1st to 10th	Day	8% 3 9% 29% 35% 17%	485
	11th to 20th	Day	7% 2 8% 27% 38% 18%	484
	21st to end	Day	9% 2 13% 32% 33% 12%	532
August	1st to 10th	Day	14% 2 13% 30% 27% 12%	486
	11th to 20th	Day	10% 4 14% 27% 29% 18%	479
	21st to end	Day	11% 3 9% 30% 26% 22%	539
September	1st to 10th	Day	10% 2 17% 25% 29% 16%	490
	11th to 20th	Day	16% 3 12% 28% 28% 12%	490
	21st to end	Day	23% 6% 18% 29% 18% 6%	490
October	1st to 10th	Day	16% 6% 22% 22% 24% 10%	490
	11th to 20th	Day	11% 8% 23% 32% 20% 5%	490
	21st to end	Day	13% 9% 24% 31% 18% 6%	539
November	1st to 10th	Day	17% 9% 26% 29% 15% 4	495
	11th to 20th	Day	16% 11% 31% 30% 10% 2	500
	21st to end	Day	15% 16% 27% 25% 15% 3	235
December	1st to 10th	Day	19% 15% 37% 21% 6% 1	190
	11th to 20th	Day	18% 12% 36% 22% 10%	202
	21st to end	Day	24% 12% 33% 21% 9% 1	297
January	1st to 10th	Night	20% 13% 36% 26% 5% 1	760
	11th to 20th	Night	18% 12% 35% 28% 6%	760
	21st to end	Night	19% 9% 39% 28% 4	836
February	1st to 10th	Night	19% 8% 41% 28% 3	760
	11th to 20th	Night	23% 15% 40% 21% 1	743
	21st to end	Night	19% 14% 37% 27% 4	628
March	1st to 10th	Night	16% 14% 34% 32% 5%	760
	11th to 20th	Night	20% 11% 36% 25% 8% 1	760
	21st to end	Night	18% 11% 39% 28% 4	836
April	1st to 10th	Night	16% 16% 34% 28% 7%	760
	11th to 20th	Night	15% 11% 32% 29% 12%	751
	21st to end	Night	13% 6% 37% 35% 9%	760
May	1st to 10th	Night	11% 11% 33% 37% 9%	635
	11th to 20th	Night	18% 4 23% 37% 17% 1	561
	21st to end	Night	11% 2 14% 42% 28% 2	617
June	1st to 10th	Night	11% 4 18% 44% 23% 1	570
	11th to 20th	Night	12% 3 16% 38% 26% 4	570
	21st to end	Night	7% 3 15% 41% 31% 2	570
July	1st to 10th	Night	9% 2 10% 38% 39% 3	555
	11th to 20th	Night	9% 2 8% 39% 37% 5%	552
	21st to end	Night	7% 1 14% 39% 35% 3	624
August	1st to 10th	Night	13% 2 8% 41% 32% 4	567
	11th to 20th	Night	12% 3 11% 36% 34% 5%	634
	21st to end	Night	11% 2 11% 31% 40% 6%	836
September	1st to 10th	Night	13% 1 11% 32% 37% 6%	760
	11th to 20th	Night	15% 3 13% 33% 33% 3	760
	21st to end	Night	23% 4 16% 32% 23% 2	760
October	1st to 10th	Night	16% 4 17% 32% 26% 5%	760
	11th to 20th	Night	14% 8% 26% 30% 21% 2	760
	21st to end	Night	13% 6% 26% 32% 20% 2	836
November	1st to 10th	Night	16% 6% 26% 35% 15% 3	780
	11th to 20th	Night	15% 9% 29% 34% 12%	800
	21st to end	Night	14% 9% 31% 32% 14% 1	800
December	1st to 10th	Night	19% 10% 32% 32% 6%	783
	11th to 20th	Night	20% 7% 32% 35% 8%	760
	21st to end	Night	20% 11% 29% 31% 9%	836

Page generated at 2024-12-03 06:45:13. Version ac07

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