Slidell
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Slidell clear sky chart from 2005-11-06 to 2026-07-31.

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	11% 5% 2 6% 4 5% 5% 4 7% 9% 41%	137637
	Night	12% 6% 2 6% 4 4 4 4 6% 8% 45%	135351
Transparency	Day	36% 6% 15% 20% 16% 6%	141364
	Night	36% 5% 14% 19% 17% 8%	139702
Seeing	Day	11% 4 13% 26% 30% 16%	16838
	Night	12% 4 16% 30% 29% 10%	26210

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	17% 5% 3 5% 4 4 4 4 6% 6% 42%	5856
	11th to 20th	Day	12% 5% 3 5% 3 4 4 3 4 6% 51%	5880
	21st to end	Day	21% 7% 3 6% 4 4 4 4 5% 5% 37%	6436
February	1st to 10th	Day	16% 8% 2 7% 5% 4 4 3 5% 6% 41%	2100
	11th to 20th	Day	15% 8% 3 5% 4 3 4 3 6% 7% 43%	2048
	21st to end	Day	15% 8% 4 7% 5% 4 4 3 6% 6% 39%	1730
March	1st to 10th	Day	18% 8% 3 7% 4 4 4 3 5% 7% 37%	4707
	11th to 20th	Day	12% 5% 2 6% 4 4 5% 3 6% 7% 47%	5090
	21st to end	Day	13% 6% 3 7% 5% 4 5% 5% 5% 6% 43%	5926
April	1st to 10th	Day	11% 6% 2 6% 6% 5% 5% 5% 8% 9% 39%	2520
	11th to 20th	Day	13% 6% 2 6% 4 4 4 4 6% 8% 43%	2494
	21st to end	Day	8% 4 2 5% 4 4 5% 5% 6% 9% 48%	2520
May	1st to 10th	Day	19% 7% 2 6% 4 4 5% 4 7% 9% 34%	7021
	11th to 20th	Day	8% 4 2 5% 4 5% 5% 4 7% 10% 46%	7031
	21st to end	Day	8% 5% 2 6% 5% 5% 6% 5% 9% 13% 35%	7736
June	1st to 10th	Day	9% 6% 2 6% 5% 6% 7% 6% 8% 12% 33%	2639
	11th to 20th	Day	4 5% 1 6% 7% 5% 7% 6% 9% 13% 35%	2673
	21st to end	Day	5% 6% 2 7% 6% 7% 7% 7% 11% 12% 29%	2730
July	1st to 10th	Day	5% 5% 2 6% 5% 7% 8% 6% 9% 13% 33%	6030
	11th to 20th	Day	5% 4 2 7% 5% 6% 6% 7% 10% 14% 34%	5663
	21st to end	Day	6% 5% 2 7% 6% 7% 6% 6% 10% 14% 30%	6042
August	1st to 10th	Day	3 3 1 5% 3 4 6% 5% 9% 12% 49%	3905
	11th to 20th	Day	6% 3 2 6% 5% 6% 6% 5% 9% 13% 39%	3849
	21st to end	Day	8% 5% 2 9% 7% 7% 6% 6% 7% 9% 33%	4312
September	1st to 10th	Day	9% 6% 2 7% 5% 5% 7% 5% 8% 10% 35%	2400
	11th to 20th	Day	9% 6% 2 6% 4 5% 5% 4 7% 11% 40%	2311
	21st to end	Day	8% 4 2 5% 4 5% 4 5% 6% 8% 48%	2200
October	1st to 10th	Day	6% 4 1 5% 3 4 4 4 6% 7% 56%	2170
	11th to 20th	Day	5% 3 2 4 3 3 4 4 5% 8% 60%	2000
	21st to end	Day	9% 4 1 4 3 3 4 2 4 7% 59%	2200
November	1st to 10th	Day	9% 4 2 4 3 4 4 4 5% 6% 57%	2058
	11th to 20th	Day	10% 4 1 4 4 3 3 3 4 6% 56%	1952
	21st to end	Day	11% 5% 2 6% 4 4 5% 3 6% 7% 46%	1890
December	1st to 10th	Day	18% 7% 2 6% 4 4 4 3 5% 5% 42%	3020
	11th to 20th	Day	10% 6% 2 6% 4 4 4 4 6% 7% 48%	3463
	21st to end	Day	17% 8% 2 6% 4 3 3 3 4 6% 43%	5035
January	1st to 10th	Night	17% 6% 2 5% 4 3 4 3 5% 7% 44%	7037
	11th to 20th	Night	17% 6% 2 5% 3 3 3 3 4 7% 47%	7080
	21st to end	Night	21% 8% 3 6% 4 4 4 3 4 6% 37%	7745
February	1st to 10th	Night	16% 7% 2 7% 4 3 4 3 4 6% 44%	2520
	11th to 20th	Night	18% 8% 2 6% 4 3 3 4 5% 6% 41%	2458
	21st to end	Night	18% 8% 3 5% 3 4 4 3 5% 7% 40%	2076
March	1st to 10th	Night	20% 8% 3 7% 3 3 4 3 5% 6% 37%	5407
	11th to 20th	Night	13% 6% 2 5% 3 4 4 4 4 6% 49%	5090
	21st to end	Night	15% 5% 2 4 3 4 4 4 5% 6% 47%	5242
April	1st to 10th	Night	13% 7% 2 6% 4 4 4 4 5% 5% 45%	2100
	11th to 20th	Night	12% 5% 2 6% 5% 4 5% 4 6% 6% 46%	2075
	21st to end	Night	7% 4 1 5% 3 4 3 4 7% 8% 54%	2100
May	1st to 10th	Night	19% 7% 3 7% 4 4 4 3 5% 8% 37%	5832
	11th to 20th	Night	12% 5% 2 5% 4 3 4 4 6% 9% 45%	5829
	21st to end	Night	8% 5% 2 6% 5% 5% 6% 5% 8% 13% 38%	6415
June	1st to 10th	Night	8% 5% 2 6% 4 5% 5% 5% 8% 10% 43%	1960
	11th to 20th	Night	4 5% 2 5% 5% 4 6% 6% 9% 12% 44%	1912
	21st to end	Night	6% 4 3 6% 5% 5% 5% 5% 9% 10% 42%	1890
July	1st to 10th	Night	3 4 2 6% 5% 6% 6% 6% 9% 14% 40%	4168
	11th to 20th	Night	3 3 2 5% 5% 5% 6% 5% 8% 13% 47%	4499
	21st to end	Night	3 4 2 7% 6% 6% 6% 6% 10% 14% 37%	5029
August	1st to 10th	Night	1 3 1 3 3 4 4 5% 7% 12% 57%	3244
	11th to 20th	Night	3 3 1 4 4 4 6% 5% 9% 15% 46%	3200
	21st to end	Night	5% 4 2 7% 6% 5% 6% 5% 8% 10% 41%	3586
September	1st to 10th	Night	8% 5% 2 6% 5% 5% 6% 5% 8% 11% 40%	2000
	11th to 20th	Night	9% 5% 2 6% 4 5% 4 4 6% 11% 44%	2066
	21st to end	Night	8% 5% 2 5% 4 4 4 4 5% 8% 52%	2200
October	1st to 10th	Night	7% 5% 2 5% 3 3 3 3 5% 7% 58%	2225
	11th to 20th	Night	5% 4 1 4 3 3 3 3 4 7% 63%	2400
	21st to end	Night	10% 4 2 4 4 3 3 3 5% 6% 56%	2640
November	1st to 10th	Night	9% 5% 2 5% 3 3 3 2 4 5% 57%	2460
	11th to 20th	Night	11% 5% 2 3 3 3 4 3 4 6% 56%	2663
	21st to end	Night	10% 5% 2 5% 4 4 4 3 5% 6% 50%	2730
December	1st to 10th	Night	14% 6% 3 7% 5% 4 4 3 4 6% 43%	4380
	11th to 20th	Night	12% 6% 2 5% 5% 4 3 4 5% 6% 50%	4952
	21st to end	Night	18% 9% 3 6% 4 3 3 3 4 4 43%	6141

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	41% 5% 9% 18% 22% 6%	5857
	11th to 20th	Day	36% 2 5% 19% 28% 11%	5880
	21st to end	Day	48% 4 6% 14% 16% 11%	6436
February	1st to 10th	Day	44% 4 8% 15% 20% 10%	2100
	11th to 20th	Day	41% 4 8% 19% 19% 9%	2058
	21st to end	Day	46% 4 8% 16% 19% 7%	1730
March	1st to 10th	Day	47% 3 8% 19% 13% 9%	4707
	11th to 20th	Day	36% 4 10% 17% 21% 14%	5090
	21st to end	Day	41% 3 13% 19% 18% 7%	5928
April	1st to 10th	Day	36% 5% 14% 20% 17% 9%	2520
	11th to 20th	Day	38% 4 10% 21% 20% 8%	2494
	21st to end	Day	29% 4 14% 27% 20% 6%	2520
May	1st to 10th	Day	45% 4 16% 21% 11% 3	7056
	11th to 20th	Day	31% 6% 19% 25% 18% 1	7035
	21st to end	Day	34% 9% 22% 25% 9% 1	7749
June	1st to 10th	Day	36% 6% 18% 27% 11% 1	2639
	11th to 20th	Day	33% 9% 21% 25% 11% 1	2673
	21st to end	Day	38% 9% 23% 20% 9%	2730
July	1st to 10th	Day	34% 12% 32% 19% 3	5966
	11th to 20th	Day	33% 13% 42% 11% 1	5597
	21st to end	Day	37% 12% 24% 24% 2	5872
August	1st to 10th	Day	20% 8% 19% 32% 21%	3893
	11th to 20th	Day	28% 10% 26% 28% 6% 1	3885
	21st to end	Day	42% 10% 16% 18% 12% 1	4311
September	1st to 10th	Day	37% 8% 21% 18% 12% 4	2400
	11th to 20th	Day	32% 8% 18% 21% 15% 5%	2311
	21st to end	Day	29% 6% 14% 25% 17% 9%	2200
October	1st to 10th	Day	25% 3 9% 16% 22% 26%	3534
	11th to 20th	Day	14% 2 5% 26% 26% 27%	3240
	21st to end	Day	19% 3 5% 14% 40% 18%	3538
November	1st to 10th	Day	26% 4 10% 23% 26% 11%	2058
	11th to 20th	Day	30% 4 7% 20% 29% 11%	1952
	21st to end	Day	36% 4 9% 21% 19% 11%	1890
December	1st to 10th	Day	44% 4 9% 15% 24% 5%	3020
	11th to 20th	Day	35% 5% 10% 19% 22% 10%	3460
	21st to end	Day	45% 3 7% 17% 23% 5%	5035
January	1st to 10th	Night	40% 4 10% 17% 21% 8%	7038
	11th to 20th	Night	39% 2 5% 17% 26% 11%	7080
	21st to end	Night	49% 3 7% 13% 19% 9%	7745
February	1st to 10th	Night	43% 2 7% 17% 21% 9%	2520
	11th to 20th	Night	44% 4 7% 16% 19% 11%	2459
	21st to end	Night	43% 4 9% 17% 15% 11%	2076
March	1st to 10th	Night	47% 3 10% 14% 18% 9%	5407
	11th to 20th	Night	36% 3 10% 16% 21% 15%	5090
	21st to end	Night	38% 3 11% 22% 19% 8%	5242
April	1st to 10th	Night	39% 4 13% 17% 16% 11%	2100
	11th to 20th	Night	38% 3 8% 25% 17% 9%	2075
	21st to end	Night	26% 4 13% 25% 24% 7%	2100
May	1st to 10th	Night	47% 3 12% 21% 13% 3	5862
	11th to 20th	Night	35% 6% 17% 25% 16% 2	5830
	21st to end	Night	35% 8% 22% 26% 8% 1	6427
June	1st to 10th	Night	34% 7% 20% 27% 13%	1960
	11th to 20th	Night	30% 8% 22% 29% 10% 1	1912
	21st to end	Night	33% 9% 26% 23% 9%	1890
July	1st to 10th	Night	30% 12% 35% 19% 3	4125
	11th to 20th	Night	27% 13% 48% 11% 1	4445
	21st to end	Night	33% 16% 23% 26% 2	4885
August	1st to 10th	Night	18% 8% 24% 29% 20% 1	3232
	11th to 20th	Night	23% 11% 32% 30% 4	3230
	21st to end	Night	37% 11% 20% 20% 10% 3	3586
September	1st to 10th	Night	37% 7% 20% 18% 13% 4	2000
	11th to 20th	Night	35% 7% 17% 19% 15% 7%	2066
	21st to end	Night	29% 5% 12% 28% 16% 10%	2200
October	1st to 10th	Night	29% 3 8% 14% 22% 23%	3641
	11th to 20th	Night	16% 2 5% 22% 29% 26%	3899
	21st to end	Night	19% 2 6% 11% 41% 21%	4252
November	1st to 10th	Night	30% 3 7% 21% 26% 13%	2460
	11th to 20th	Night	29% 3 7% 19% 27% 14%	2663
	21st to end	Night	35% 4 8% 21% 22% 11%	2730
December	1st to 10th	Night	43% 3 7% 17% 23% 8%	4380
	11th to 20th	Night	35% 4 10% 20% 19% 11%	4954
	21st to end	Night	47% 3 6% 16% 22% 7%	6141

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	18% 8% 27% 36% 11%	330
	11th to 20th	Day	15% 9% 28% 35% 12% 1	330
	21st to end	Day	20% 9% 32% 33% 6%	363
February	1st to 10th	Day	22% 7% 25% 35% 10% 1	330
	11th to 20th	Day	19% 8% 28% 34% 9% 1	330
	21st to end	Day	14% 10% 37% 34% 6%	273
March	1st to 10th	Day	15% 5% 32% 38% 11%	330
	11th to 20th	Day	16% 11% 27% 32% 12% 2	330
	21st to end	Day	11% 7% 30% 31% 20% 1	512
April	1st to 10th	Day	14% 7% 26% 38% 14% 1	540
	11th to 20th	Day	12% 8% 23% 37% 17% 2	532
	21st to end	Day	8% 5% 18% 39% 25% 5%	540
May	1st to 10th	Day	14% 3 16% 37% 25% 4	543
	11th to 20th	Day	10% 3 12% 33% 33% 10%	567
	21st to end	Day	5% 2 6% 32% 40% 13%	617
June	1st to 10th	Day	10% 2 3 25% 41% 19%	570
	11th to 20th	Day	8% 3 5% 20% 42% 23%	598
	21st to end	Day	7% 3 3 17% 41% 29%	780
July	1st to 10th	Day	7% 3 2 12% 41% 34%	771
	11th to 20th	Day	7% 2 3 7% 38% 44%	612
	21st to end	Day	8% 1 3 9% 42% 37%	616
August	1st to 10th	Day	5% 1 3 10% 38% 44%	526
	11th to 20th	Day	7% 2 6% 38% 46%	519
	21st to end	Day	10% 1 5% 13% 38% 33%	583
September	1st to 10th	Day	10% 2 2 17% 40% 29%	530
	11th to 20th	Day	10% 2 6% 18% 41% 22%	530
	21st to end	Day	8% 2 7% 22% 43% 19%	530
October	1st to 10th	Day	9% 2 6% 34% 41% 8%	500
	11th to 20th	Day	5% 10% 36% 40% 10%	330
	21st to end	Day	12% 7% 12% 30% 33% 6%	363
November	1st to 10th	Day	11% 2 12% 32% 36% 6%	330
	11th to 20th	Day	15% 4 18% 31% 29% 4	330
	21st to end	Day	13% 5% 23% 39% 17% 4	330
December	1st to 10th	Day	19% 5% 23% 35% 16% 3	330
	11th to 20th	Day	18% 3 25% 37% 16% 1	330
	21st to end	Day	23% 5% 25% 28% 17% 2	363
January	1st to 10th	Night	17% 7% 29% 36% 10% 1	840
	11th to 20th	Night	18% 5% 26% 39% 11% 1	840
	21st to end	Night	21% 6% 29% 34% 9%	924
February	1st to 10th	Night	18% 5% 27% 39% 11%	840
	11th to 20th	Night	20% 8% 27% 32% 13% 1	823
	21st to end	Night	19% 5% 29% 38% 8%	692
March	1st to 10th	Night	16% 5% 29% 37% 13%	806
	11th to 20th	Night	14% 4 24% 35% 21% 1	630
	21st to end	Night	13% 5% 21% 38% 21% 1	693
April	1st to 10th	Night	15% 7% 22% 37% 19% 1	630
	11th to 20th	Night	12% 5% 26% 32% 23% 2	623
	21st to end	Night	8% 4 16% 42% 29% 2	630
May	1st to 10th	Night	11% 2 14% 41% 29% 3	630
	11th to 20th	Night	7% 4 9% 40% 35% 6%	621
	21st to end	Night	6% 2 5% 29% 46% 12%	683
June	1st to 10th	Night	9% 2 5% 27% 45% 12%	630
	11th to 20th	Night	4 2 3 19% 56% 16%	630
	21st to end	Night	7% 2 4 15% 48% 24%	630
July	1st to 10th	Night	6% 2 2 9% 51% 30%	615
	11th to 20th	Night	3 1 1 5% 46% 43%	612
	21st to end	Night	5% 1 2 10% 49% 33%	687
August	1st to 10th	Night	2 1 1 8% 49% 39%	597
	11th to 20th	Night	6% 2 8% 44% 40%	594
	21st to end	Night	9% 2 3 13% 41% 32%	660
September	1st to 10th	Night	9% 1 4 15% 44% 27%	600
	11th to 20th	Night	10% 3 5% 20% 47% 14%	666
	21st to end	Night	9% 2 5% 28% 44% 12%	800
October	1st to 10th	Night	8% 3 7% 34% 39% 10%	800
	11th to 20th	Night	7% 4 14% 32% 37% 7%	800
	21st to end	Night	10% 4 16% 33% 32% 4	880
November	1st to 10th	Night	11% 3 12% 39% 29% 5%	820
	11th to 20th	Night	12% 4 20% 38% 22% 4	840
	21st to end	Night	11% 4 25% 37% 21% 2	840
December	1st to 10th	Night	16% 7% 22% 33% 19% 3	840
	11th to 20th	Night	18% 5% 21% 38% 16% 2	840
	21st to end	Night	21% 7% 22% 35% 13% 2	924

Page generated at 2026-07-28 02:25:22. Version ac07

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