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 2025-03-27.

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% 6% 2 6% 5% 5% 5% 4 7% 9% 41%	109639
	Night	12% 6% 2 6% 4 4 4 4 6% 8% 45%	109675
Transparency	Day	36% 5% 14% 20% 17% 7%	113402
	Night	36% 5% 13% 20% 19% 8%	114051
Seeing	Day	12% 4 14% 26% 29% 16%	14994
	Night	12% 4 16% 30% 29% 10%	24566

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	16% 4 3 5% 4 4 4 4 5% 6% 44%	4516
	11th to 20th	Day	14% 6% 3 5% 3 4 3 3 4 5% 49%	4520
	21st to end	Day	22% 7% 3 6% 4 4 4 4 5% 6% 36%	4972
February	1st to 10th	Day	16% 9% 3 7% 5% 4 4 3 5% 6% 39%	2000
	11th to 20th	Day	15% 8% 2 5% 3 3 4 3 5% 7% 44%	1948
	21st to end	Day	16% 8% 4 7% 5% 4 4 3 6% 6% 38%	1650
March	1st to 10th	Day	22% 9% 4 7% 4 4 4 3 5% 7% 30%	3306
	11th to 20th	Day	13% 7% 3 7% 4 5% 5% 4 7% 8% 37%	3590
	21st to end	Day	11% 5% 3 6% 5% 5% 5% 6% 5% 7% 43%	4120
April	1st to 10th	Day	10% 6% 2 6% 6% 5% 5% 5% 7% 9% 41%	2280
	11th to 20th	Day	14% 7% 2 6% 4 4 4 4 7% 8% 40%	2254
	21st to end	Day	9% 4 2 5% 4 4 5% 5% 6% 8% 49%	2280
May	1st to 10th	Day	9% 6% 2 7% 4 5% 6% 5% 8% 10% 39%	3765
	11th to 20th	Day	13% 6% 2 6% 4 4 4 4 6% 8% 43%	3764
	21st to end	Day	5% 3 2 5% 4 5% 5% 4 8% 12% 47%	4129
June	1st to 10th	Day	9% 6% 2 6% 5% 6% 7% 6% 8% 12% 33%	2388
	11th to 20th	Day	4 5% 1 6% 7% 5% 8% 6% 9% 13% 36%	2418
	21st to end	Day	6% 7% 2 8% 7% 7% 7% 7% 10% 12% 28%	2470
July	1st to 10th	Day	7% 7% 3 8% 6% 7% 8% 7% 10% 12% 26%	4120
	11th to 20th	Day	6% 4 2 7% 6% 7% 7% 7% 11% 14% 29%	3873
	21st to end	Day	7% 6% 3 8% 7% 7% 7% 6% 11% 14% 24%	4118
August	1st to 10th	Day	3 3 1 5% 3 4 6% 5% 9% 12% 50%	3785
	11th to 20th	Day	6% 3 2 6% 5% 6% 6% 5% 9% 12% 39%	3729
	21st to end	Day	8% 5% 2 9% 7% 7% 6% 6% 8% 9% 33%	4180
September	1st to 10th	Day	10% 7% 2 7% 5% 5% 7% 6% 8% 10% 34%	2280
	11th to 20th	Day	9% 7% 2 6% 4 6% 6% 4 7% 10% 39%	2196
	21st to end	Day	8% 4 2 5% 4 5% 4 5% 7% 8% 48%	2090
October	1st to 10th	Day	6% 3 1 5% 3 4 4 4 5% 7% 57%	2062
	11th to 20th	Day	5% 3 2 5% 3 3 4 4 5% 9% 58%	1900
	21st to end	Day	10% 4 1 4 3 3 4 3 4 7% 58%	2090
November	1st to 10th	Day	9% 4 2 4 3 4 4 4 5% 6% 56%	1958
	11th to 20th	Day	11% 5% 2 4 4 3 3 3 4 6% 56%	1859
	21st to end	Day	12% 5% 2 5% 4 4 5% 3 6% 7% 47%	1800
December	1st to 10th	Day	17% 7% 2 6% 4 4 4 3 6% 5% 42%	2930
	11th to 20th	Day	10% 6% 2 6% 4 4 4 4 6% 7% 48%	3373
	21st to end	Day	18% 7% 2 6% 4 3 3 3 4 6% 43%	4926
January	1st to 10th	Night	16% 6% 2 5% 4 3 3 3 4 6% 47%	5429
	11th to 20th	Night	19% 6% 2 5% 3 3 3 2 4 6% 47%	5440
	21st to end	Night	21% 8% 2 5% 3 3 4 3 5% 7% 38%	5984
February	1st to 10th	Night	17% 7% 2 7% 4 4 4 3 4 6% 42%	2400
	11th to 20th	Night	19% 8% 2 6% 3 3 3 4 5% 6% 41%	2338
	21st to end	Night	18% 8% 3 5% 3 4 4 3 5% 7% 39%	1980
March	1st to 10th	Night	23% 10% 4 7% 4 3 4 3 5% 6% 31%	3795
	11th to 20th	Night	14% 7% 3 7% 4 5% 5% 5% 5% 8% 39%	3590
	21st to end	Night	14% 5% 2 5% 3 5% 4 4 6% 6% 46%	3646
April	1st to 10th	Night	13% 7% 2 6% 4 4 4 4 6% 5% 46%	1900
	11th to 20th	Night	13% 5% 2 6% 5% 4 5% 4 6% 6% 44%	1875
	21st to end	Night	7% 4 1 5% 3 4 3 4 7% 8% 56%	1900
May	1st to 10th	Night	12% 6% 2 6% 4 4 4 3 5% 9% 44%	3130
	11th to 20th	Night	14% 6% 2 6% 4 4 5% 4 6% 7% 43%	3129
	21st to end	Night	6% 4 2 5% 4 4 5% 4 8% 13% 47%	3426
June	1st to 10th	Night	8% 5% 2 5% 5% 5% 5% 5% 8% 10% 44%	1773
	11th to 20th	Night	3 5% 2 5% 5% 3 6% 6% 9% 12% 45%	1730
	21st to end	Night	6% 5% 3 6% 5% 5% 5% 5% 9% 10% 41%	1710
July	1st to 10th	Night	4 4 2 6% 5% 6% 6% 6% 8% 14% 38%	2850
	11th to 20th	Night	3 3 1 5% 5% 5% 6% 5% 8% 14% 46%	3084
	21st to end	Night	4 4 2 7% 6% 6% 6% 6% 10% 16% 31%	3435
August	1st to 10th	Night	1 3 1 3 3 4 4 5% 7% 12% 57%	3144
	11th to 20th	Night	3 3 1 4 4 4 6% 5% 9% 15% 46%	3100
	21st to end	Night	5% 5% 2 7% 6% 6% 6% 5% 8% 10% 41%	3476
September	1st to 10th	Night	9% 5% 2 6% 5% 5% 6% 5% 7% 11% 39%	1900
	11th to 20th	Night	9% 5% 2 7% 4 5% 5% 4 6% 11% 43%	1962
	21st to end	Night	8% 5% 2 4 4 4 4 4 5% 8% 52%	2090
October	1st to 10th	Night	6% 5% 2 5% 3 3 3 3 5% 7% 59%	2114
	11th to 20th	Night	5% 4 1 4 3 3 3 3 5% 7% 62%	2280
	21st to end	Night	10% 4 2 4 4 3 3 3 4 5% 57%	2508
November	1st to 10th	Night	10% 5% 2 5% 3 3 3 2 4 6% 56%	2340
	11th to 20th	Night	11% 5% 2 3 3 3 4 3 4 6% 55%	2536
	21st to end	Night	10% 6% 2 6% 4 4 4 4 5% 5% 50%	2600
December	1st to 10th	Night	13% 6% 3 7% 5% 4 4 3 4 6% 44%	4250
	11th to 20th	Night	12% 6% 2 5% 5% 4 3 4 5% 6% 50%	4822
	21st to end	Night	18% 9% 3 6% 4 3 3 3 4 4 43%	6009

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% 3 6% 19% 24% 8%	4517
	11th to 20th	Day	39% 2 5% 16% 29% 9%	4520
	21st to end	Day	49% 4 7% 15% 16% 10%	4972
February	1st to 10th	Day	46% 4 8% 15% 18% 10%	2000
	11th to 20th	Day	41% 4 8% 18% 19% 9%	1958
	21st to end	Day	47% 4 8% 16% 19% 7%	1650
March	1st to 10th	Day	54% 3 9% 19% 12% 4	3306
	11th to 20th	Day	43% 4 11% 20% 17% 5%	3590
	21st to end	Day	38% 3 14% 16% 20% 8%	4120
April	1st to 10th	Day	35% 5% 14% 20% 17% 9%	2280
	11th to 20th	Day	40% 3 10% 21% 19% 7%	2254
	21st to end	Day	29% 4 11% 27% 23% 6%	2280
May	1st to 10th	Day	37% 3 18% 26% 12% 4	3800
	11th to 20th	Day	37% 4 14% 21% 22% 2	3768
	21st to end	Day	27% 4 19% 37% 11% 1	4141
June	1st to 10th	Day	37% 5% 19% 27% 11% 1	2388
	11th to 20th	Day	32% 9% 20% 27% 12% 1	2418
	21st to end	Day	40% 9% 22% 19% 10%	2470
July	1st to 10th	Day	42% 12% 28% 16% 2	4056
	11th to 20th	Day	34% 14% 39% 11% 1 1	3807
	21st to end	Day	43% 13% 24% 17% 3	3987
August	1st to 10th	Day	19% 8% 19% 32% 22%	3773
	11th to 20th	Day	28% 10% 25% 29% 7% 1	3765
	21st to end	Day	43% 10% 16% 18% 13% 1	4179
September	1st to 10th	Day	38% 8% 21% 17% 12% 4	2280
	11th to 20th	Day	34% 9% 18% 20% 15% 6%	2196
	21st to end	Day	29% 6% 14% 25% 17% 9%	2090
October	1st to 10th	Day	25% 3 8% 16% 22% 26%	3426
	11th to 20th	Day	14% 2 5% 26% 26% 27%	3140
	21st to end	Day	19% 3 5% 13% 40% 18%	3428
November	1st to 10th	Day	27% 4 10% 23% 27% 10%	1958
	11th to 20th	Day	31% 4 6% 19% 28% 12%	1859
	21st to end	Day	36% 4 8% 21% 20% 11%	1800
December	1st to 10th	Day	43% 4 9% 15% 24% 5%	2930
	11th to 20th	Day	35% 5% 10% 19% 22% 9%	3370
	21st to end	Day	45% 2 7% 18% 24% 5%	4926
January	1st to 10th	Night	40% 2 6% 18% 24% 9%	5429
	11th to 20th	Night	42% 2 4 16% 29% 7%	5440
	21st to end	Night	47% 3 7% 14% 19% 10%	5984
February	1st to 10th	Night	45% 2 7% 17% 20% 9%	2400
	11th to 20th	Night	44% 4 6% 16% 19% 11%	2339
	21st to end	Night	44% 3 9% 17% 14% 11%	1980
March	1st to 10th	Night	53% 3 10% 15% 13% 6%	3795
	11th to 20th	Night	42% 3 12% 18% 17% 7%	3590
	21st to end	Night	38% 2 10% 22% 19% 8%	3646
April	1st to 10th	Night	38% 4 13% 18% 17% 11%	1900
	11th to 20th	Night	40% 3 8% 23% 16% 9%	1875
	21st to end	Night	26% 4 11% 26% 26% 7%	1900
May	1st to 10th	Night	38% 2 14% 25% 17% 4	3160
	11th to 20th	Night	40% 5% 12% 22% 19% 1	3130
	21st to end	Night	28% 4 20% 33% 13% 2	3435
June	1st to 10th	Night	33% 6% 21% 28% 12%	1773
	11th to 20th	Night	29% 8% 21% 30% 11% 1	1730
	21st to end	Night	34% 9% 26% 22% 10%	1710
July	1st to 10th	Night	32% 12% 36% 17% 2	2805
	11th to 20th	Night	25% 14% 48% 11% 2	3027
	21st to end	Night	36% 18% 25% 18% 2	3325
August	1st to 10th	Night	18% 8% 24% 29% 21% 1	3132
	11th to 20th	Night	23% 11% 31% 30% 5%	3130
	21st to end	Night	37% 11% 20% 20% 10% 3	3476
September	1st to 10th	Night	38% 7% 20% 17% 12% 4	1900
	11th to 20th	Night	36% 7% 18% 18% 14% 8%	1962
	21st to end	Night	29% 5% 12% 27% 16% 10%	2090
October	1st to 10th	Night	29% 3 8% 14% 22% 24%	3530
	11th to 20th	Night	16% 3 5% 22% 29% 25%	3779
	21st to end	Night	19% 2 6% 10% 41% 22%	4120
November	1st to 10th	Night	31% 3 7% 21% 25% 13%	2340
	11th to 20th	Night	31% 3 7% 18% 27% 15%	2536
	21st to end	Night	36% 4 6% 21% 22% 11%	2600
December	1st to 10th	Night	42% 3 8% 17% 23% 8%	4250
	11th to 20th	Night	35% 4 11% 21% 19% 11%	4824
	21st to end	Night	47% 3 6% 16% 22% 6%	6009

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	19% 9% 27% 36% 9%	300
	11th to 20th	Day	17% 9% 27% 35% 11% 1	300
	21st to end	Day	20% 9% 33% 32% 6%	330
February	1st to 10th	Day	24% 7% 25% 33% 9% 1	300
	11th to 20th	Day	21% 8% 27% 33% 9% 1	300
	21st to end	Day	14% 10% 36% 35% 6%	249
March	1st to 10th	Day	15% 4 34% 39% 8%	300
	11th to 20th	Day	18% 11% 27% 31% 12% 1	300
	21st to end	Day	11% 8% 31% 32% 17% 1	452
April	1st to 10th	Day	13% 7% 26% 39% 14% 1	460
	11th to 20th	Day	13% 10% 25% 36% 15% 2	452
	21st to end	Day	9% 5% 18% 37% 25% 5%	460
May	1st to 10th	Day	10% 3 16% 38% 27% 5%	463
	11th to 20th	Day	12% 3 10% 31% 34% 10%	487
	21st to end	Day	4 2 5% 32% 41% 15%	529
June	1st to 10th	Day	11% 2 3 23% 39% 21%	490
	11th to 20th	Day	8% 2 4 20% 44% 22%	515
	21st to end	Day	8% 3 4 18% 39% 28%	680
July	1st to 10th	Day	8% 3 2 12% 41% 33%	671
	11th to 20th	Day	8% 2 2 7% 38% 44%	528
	21st to end	Day	8% 1 3 8% 41% 38%	532
August	1st to 10th	Day	5% 1 3 11% 37% 43%	486
	11th to 20th	Day	7% 2 7% 39% 45%	479
	21st to end	Day	11% 1 5% 13% 38% 33%	539
September	1st to 10th	Day	11% 2 2 16% 39% 31%	490
	11th to 20th	Day	11% 3 7% 19% 40% 21%	490
	21st to end	Day	8% 2 7% 22% 43% 18%	490
October	1st to 10th	Day	7% 2 7% 35% 42% 8%	462
	11th to 20th	Day	5% 10% 36% 39% 9%	300
	21st to end	Day	12% 6% 13% 28% 34% 7%	330
November	1st to 10th	Day	12% 2 12% 33% 35% 6%	300
	11th to 20th	Day	16% 5% 19% 31% 26% 3	300
	21st to end	Day	14% 5% 21% 40% 17% 4	300
December	1st to 10th	Day	18% 5% 23% 35% 17% 3	300
	11th to 20th	Day	19% 3 26% 37% 15% 1	300
	21st to end	Day	24% 6% 25% 29% 15% 2	330
January	1st to 10th	Night	18% 8% 29% 35% 9% 1	800
	11th to 20th	Night	18% 5% 26% 39% 12% 1	800
	21st to end	Night	21% 5% 29% 35% 9%	880
February	1st to 10th	Night	19% 5% 27% 38% 11% 1	800
	11th to 20th	Night	20% 8% 27% 31% 12% 1	783
	21st to end	Night	20% 5% 29% 38% 8%	660
March	1st to 10th	Night	15% 5% 29% 37% 13%	768
	11th to 20th	Night	14% 4 24% 35% 21% 1	600
	21st to end	Night	13% 6% 21% 38% 20% 2	647
April	1st to 10th	Night	15% 6% 22% 36% 19% 1	570
	11th to 20th	Night	13% 5% 26% 31% 23% 2	563
	21st to end	Night	8% 4 16% 41% 29% 2	570
May	1st to 10th	Night	9% 2 14% 41% 31% 3	570
	11th to 20th	Night	6% 4 9% 38% 35% 7%	561
	21st to end	Night	6% 2 5% 29% 46% 12%	617
June	1st to 10th	Night	9% 1 5% 25% 46% 14%	570
	11th to 20th	Night	4 2 3 19% 56% 16%	570
	21st to end	Night	8% 2 4 16% 46% 24%	570
July	1st to 10th	Night	7% 2 2 8% 50% 31%	555
	11th to 20th	Night	3 1 1 5% 47% 43%	552
	21st to end	Night	5% 1 2 10% 48% 34%	624
August	1st to 10th	Night	2 1 1 8% 49% 38%	567
	11th to 20th	Night	7% 2 8% 44% 40%	564
	21st to end	Night	9% 2 3 14% 40% 32%	627
September	1st to 10th	Night	9% 1 4 12% 44% 29%	570
	11th to 20th	Night	10% 4 6% 21% 45% 14%	632
	21st to end	Night	10% 1 5% 28% 44% 12%	760
October	1st to 10th	Night	8% 2 7% 34% 40% 10%	760
	11th to 20th	Night	7% 4 14% 31% 37% 8%	760
	21st to end	Night	11% 4 16% 32% 33% 4	836
November	1st to 10th	Night	12% 3 13% 39% 29% 5%	780
	11th to 20th	Night	13% 4 21% 38% 21% 3	800
	21st to end	Night	11% 4 25% 37% 21% 3	800
December	1st to 10th	Night	16% 7% 21% 34% 20% 3	800
	11th to 20th	Night	18% 5% 21% 38% 16% 2	800
	21st to end	Night	22% 7% 23% 35% 13% 1	880

Page generated at 2025-03-24 08:04:27. Version ac07

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