Lorraine
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lorraine clear sky chart from 2005-11-06 to 2026-03-18.

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	16% 10% 3 8% 5% 5% 5% 4 5% 7% 32%	131256
	Night	17% 11% 4 9% 5% 4 4 3 5% 6% 31%	130268
Transparency	Day	51% 4 12% 21% 10% 1	134701
	Night	54% 4 11% 20% 11% 1	134910
Seeing	Day	21% 10% 28% 25% 12% 4	16172
	Night	22% 8% 28% 31% 10% 1	25276

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% 16% 6% 13% 5% 4 4 3 4 5% 25%	4661
	11th to 20th	Day	11% 16% 6% 13% 7% 4 4 3 4 6% 24%	4650
	21st to end	Day	9% 13% 5% 11% 9% 7% 6% 4 5% 5% 25%	5124
February	1st to 10th	Day	13% 15% 4 10% 6% 4 5% 4 4 6% 28%	1843
	11th to 20th	Day	13% 12% 5% 10% 6% 5% 5% 4 5% 6% 28%	1947
	21st to end	Day	17% 16% 5% 9% 4 4 4 3 5% 5% 27%	1730
March	1st to 10th	Day	19% 13% 4 11% 6% 6% 4 3 5% 5% 26%	4576
	11th to 20th	Day	11% 13% 4 9% 5% 5% 5% 3 5% 7% 32%	4770
	21st to end	Day	19% 9% 4 9% 5% 4 4 3 4 5% 34%	5965
April	1st to 10th	Day	21% 11% 3 7% 6% 4 4 3 4 5% 32%	2400
	11th to 20th	Day	20% 9% 3 7% 6% 4 4 3 3 5% 37%	2374
	21st to end	Day	21% 10% 4 7% 5% 3 4 4 4 5% 33%	2561
May	1st to 10th	Day	25% 10% 4 9% 5% 4 5% 4 5% 6% 23%	6290
	11th to 20th	Day	20% 8% 3 8% 5% 5% 5% 3 5% 7% 30%	6318
	21st to end	Day	21% 9% 2 6% 5% 4 5% 4 6% 7% 31%	6949
June	1st to 10th	Day	20% 8% 3 7% 5% 5% 5% 4 5% 7% 31%	2800
	11th to 20th	Day	14% 6% 3 7% 5% 4 5% 5% 6% 8% 37%	2800
	21st to end	Day	19% 7% 3 8% 6% 5% 5% 4 6% 7% 30%	2800
July	1st to 10th	Day	13% 6% 2 8% 6% 6% 6% 5% 6% 8% 33%	6360
	11th to 20th	Day	11% 6% 2 6% 5% 5% 5% 5% 7% 9% 41%	6360
	21st to end	Day	10% 6% 2 5% 4 4 4 4 6% 9% 47%	6926
August	1st to 10th	Day	13% 6% 2 8% 5% 5% 7% 5% 7% 9% 34%	4563
	11th to 20th	Day	13% 6% 3 8% 5% 5% 4 3 6% 8% 39%	4142
	21st to end	Day	15% 5% 2 6% 5% 4 4 4 6% 8% 40%	4312
September	1st to 10th	Day	11% 5% 2 6% 4 5% 5% 4 6% 9% 43%	2400
	11th to 20th	Day	13% 5% 2 5% 3 4 4 3 5% 6% 51%	2319
	21st to end	Day	16% 6% 3 6% 5% 4 4 3 5% 7% 42%	2200
October	1st to 10th	Day	19% 6% 2 7% 4 4 4 3 5% 7% 38%	2060
	11th to 20th	Day	18% 7% 3 8% 7% 5% 5% 4 6% 7% 31%	1956
	21st to end	Day	23% 9% 3 7% 4 4 3 3 5% 6% 31%	1980
November	1st to 10th	Day	16% 11% 3 8% 4 5% 4 4 5% 8% 33%	1851
	11th to 20th	Day	17% 12% 3 7% 4 5% 5% 3 5% 7% 31%	1795
	21st to end	Day	22% 12% 3 8% 5% 5% 5% 4 5% 6% 25%	1680
December	1st to 10th	Day	20% 18% 6% 13% 5% 4 4 3 4 4 19%	2680
	11th to 20th	Day	18% 14% 4 9% 5% 4 4 4 5% 4 28%	3066
	21st to end	Day	23% 14% 3 10% 5% 4 5% 4 4 5% 24%	4048
January	1st to 10th	Night	13% 16% 7% 16% 6% 5% 4 3 4 4 23%	8234
	11th to 20th	Night	11% 16% 7% 16% 8% 6% 5% 3 5% 5% 19%	8235
	21st to end	Night	10% 13% 5% 13% 8% 6% 5% 3 5% 6% 27%	9057
February	1st to 10th	Night	13% 14% 5% 12% 6% 5% 5% 3 5% 6% 25%	2774
	11th to 20th	Night	14% 12% 4 10% 6% 5% 5% 4 5% 5% 31%	2559
	21st to end	Night	15% 14% 4 9% 5% 4 5% 3 5% 5% 31%	2076
March	1st to 10th	Night	21% 14% 3 8% 5% 4 4 3 4 5% 30%	5484
	11th to 20th	Night	14% 14% 4 8% 4 4 5% 3 6% 7% 30%	5341
	21st to end	Night	15% 11% 4 9% 5% 5% 5% 3 5% 5% 33%	4967
April	1st to 10th	Night	23% 11% 2 7% 4 4 4 4 4 6% 32%	2000
	11th to 20th	Night	21% 9% 3 7% 6% 4 4 3 4 5% 35%	1975
	21st to end	Night	21% 9% 3 6% 4 3 4 3 5% 5% 36%	1838
May	1st to 10th	Night	25% 10% 3 9% 5% 4 4 3 5% 6% 25%	3694
	11th to 20th	Night	22% 8% 3 8% 4 4 4 3 5% 7% 31%	3575
	21st to end	Night	19% 9% 3 8% 5% 5% 4 4 5% 7% 31%	3926
June	1st to 10th	Night	19% 8% 4 7% 4 4 5% 3 7% 7% 32%	1600
	11th to 20th	Night	16% 7% 3 7% 4 4 4 4 6% 7% 39%	1600
	21st to end	Night	18% 7% 3 7% 4 4 6% 3 6% 7% 35%	1600
July	1st to 10th	Night	14% 6% 2 7% 5% 6% 6% 5% 7% 10% 34%	3600
	11th to 20th	Night	14% 6% 2 6% 4 4 5% 4 6% 8% 42%	3600
	21st to end	Night	10% 5% 2 6% 5% 4 4 4 7% 8% 45%	3926
August	1st to 10th	Night	14% 7% 3 7% 5% 4 5% 3 5% 7% 39%	2586
	11th to 20th	Night	14% 7% 3 7% 5% 4 4 3 5% 7% 40%	2870
	21st to end	Night	16% 5% 2 8% 5% 5% 4 4 5% 7% 39%	3586
September	1st to 10th	Night	11% 5% 2 7% 5% 4 4 4 6% 7% 46%	2000
	11th to 20th	Night	13% 5% 3 5% 3 3 3 3 4 7% 51%	2080
	21st to end	Night	16% 5% 2 7% 4 4 4 4 4 7% 44%	2200
October	1st to 10th	Night	18% 6% 2 7% 4 4 4 3 4 6% 41%	2337
	11th to 20th	Night	19% 8% 3 7% 4 4 4 3 5% 6% 37%	2443
	21st to end	Night	21% 9% 3 8% 4 4 4 3 5% 6% 32%	2860
November	1st to 10th	Night	19% 9% 3 7% 5% 4 5% 4 5% 6% 33%	2667
	11th to 20th	Night	19% 10% 3 8% 4 4 4 4 5% 6% 33%	2820
	21st to end	Night	21% 13% 3 9% 6% 4 4 3 5% 5% 28%	2940
December	1st to 10th	Night	17% 16% 5% 11% 6% 6% 5% 4 4 5% 20%	4720
	11th to 20th	Night	23% 13% 4 9% 4 4 4 3 5% 5% 26%	5348
	21st to end	Night	25% 15% 4 9% 4 3 3 3 5% 5% 24%	7150

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	63% 3 11% 18% 4	4662
	11th to 20th	Day	63% 3 9% 15% 9% 1	4680
	21st to end	Day	60% 4 11% 13% 11% 1	5124
February	1st to 10th	Day	57% 3 10% 21% 7% 2	1843
	11th to 20th	Day	57% 4 11% 17% 10% 1	1956
	21st to end	Day	60% 2 9% 16% 11% 2	1730
March	1st to 10th	Day	62% 3 8% 14% 11% 4	4579
	11th to 20th	Day	51% 5% 17% 13% 11% 2	4770
	21st to end	Day	53% 3 7% 16% 18% 2	5965
April	1st to 10th	Day	55% 4 7% 19% 13% 2	2400
	11th to 20th	Day	50% 3 7% 23% 15% 2	2374
	21st to end	Day	54% 4 8% 18% 13% 3	2561
May	1st to 10th	Day	61% 3 7% 20% 7% 1	6301
	11th to 20th	Day	53% 4 14% 19% 8% 2	6322
	21st to end	Day	51% 5% 11% 20% 12% 1	6949
June	1st to 10th	Day	52% 4 10% 19% 13% 2	2800
	11th to 20th	Day	43% 5% 11% 24% 14% 3	2800
	21st to end	Day	51% 4 13% 20% 10% 1	2800
July	1st to 10th	Day	46% 6% 14% 26% 8%	6290
	11th to 20th	Day	38% 6% 15% 30% 11%	6285
	21st to end	Day	34% 5% 15% 37% 9%	6728
August	1st to 10th	Day	45% 6% 18% 23% 9%	4549
	11th to 20th	Day	43% 5% 18% 27% 7%	4184
	21st to end	Day	41% 5% 16% 22% 15% 1	4312
September	1st to 10th	Day	36% 6% 14% 31% 12% 1	2400
	11th to 20th	Day	34% 4 13% 33% 15% 1	2319
	21st to end	Day	42% 4 14% 26% 13% 1	2200
October	1st to 10th	Day	45% 4 13% 27% 10%	3359
	11th to 20th	Day	44% 5% 17% 27% 7%	3159
	21st to end	Day	43% 4 20% 23% 9% 1	3180
November	1st to 10th	Day	49% 5% 13% 23% 9% 1	1851
	11th to 20th	Day	52% 5% 11% 20% 11% 1	1795
	21st to end	Day	59% 5% 14% 15% 6% 1	1680
December	1st to 10th	Day	69% 3 9% 15% 3	2680
	11th to 20th	Day	59% 4 10% 18% 10%	3066
	21st to end	Day	63% 4 11% 14% 7%	4048
January	1st to 10th	Night	66% 3 11% 14% 6% 1	8234
	11th to 20th	Night	67% 4 9% 14% 6%	8280
	21st to end	Night	59% 4 10% 14% 14% 1	9057
February	1st to 10th	Night	60% 4 9% 17% 9% 1	2774
	11th to 20th	Night	54% 3 10% 22% 10% 1	2561
	21st to end	Night	55% 3 9% 18% 13% 1	2076
March	1st to 10th	Night	58% 2 8% 15% 12% 4	5494
	11th to 20th	Night	53% 4 13% 15% 13% 2	5342
	21st to end	Night	54% 3 7% 21% 13% 2	4967
April	1st to 10th	Night	53% 4 7% 19% 15% 2	2000
	11th to 20th	Night	52% 4 6% 21% 15% 2	1975
	21st to end	Night	50% 4 8% 20% 14% 4	1838
May	1st to 10th	Night	61% 3 9% 18% 7% 2	3700
	11th to 20th	Night	53% 4 11% 20% 10% 2	3576
	21st to end	Night	54% 4 10% 17% 14% 1	3927
June	1st to 10th	Night	50% 5% 9% 21% 14% 1	1600
	11th to 20th	Night	43% 5% 12% 23% 15% 3	1600
	21st to end	Night	48% 6% 11% 20% 15% 1	1600
July	1st to 10th	Night	44% 6% 18% 22% 10%	3560
	11th to 20th	Night	40% 4 17% 29% 10%	3552
	21st to end	Night	36% 5% 16% 29% 13%	3809
August	1st to 10th	Night	45% 5% 13% 27% 10%	2576
	11th to 20th	Night	43% 5% 18% 25% 8%	2894
	21st to end	Night	44% 6% 13% 22% 13% 1	3586
September	1st to 10th	Night	36% 5% 14% 28% 16% 1	2000
	11th to 20th	Night	34% 4 14% 34% 13% 1	2080
	21st to end	Night	41% 5% 10% 28% 16%	2200
October	1st to 10th	Night	43% 5% 14% 26% 11% 1	3818
	11th to 20th	Night	43% 4 12% 31% 10%	3979
	21st to end	Night	46% 4 17% 20% 12% 1	4610
November	1st to 10th	Night	52% 4 11% 24% 8% 1	2667
	11th to 20th	Night	52% 5% 12% 20% 10% 1	2820
	21st to end	Night	59% 4 11% 18% 8%	2940
December	1st to 10th	Night	66% 5% 11% 14% 4	4720
	11th to 20th	Night	61% 4 8% 16% 11%	5348
	21st to end	Night	63% 3 8% 15% 11%	7150

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	24% 10% 30% 27% 8%	220
	11th to 20th	Day	25% 16% 32% 20% 4 2	220
	21st to end	Day	20% 16% 30% 26% 7% 2	242
February	1st to 10th	Day	27% 16% 36% 18% 4	305
	11th to 20th	Day	20% 15% 37% 24% 4	434
	21st to end	Day	26% 13% 34% 24% 3	446
March	1st to 10th	Day	25% 14% 32% 21% 7%	540
	11th to 20th	Day	23% 14% 35% 22% 5% 1	528
	21st to end	Day	27% 12% 32% 19% 8% 2	550
April	1st to 10th	Day	28% 15% 26% 20% 8% 2	500
	11th to 20th	Day	30% 15% 23% 21% 10% 2	492
	21st to end	Day	27% 13% 31% 19% 7% 3	500
May	1st to 10th	Day	24% 11% 31% 24% 9% 2	503
	11th to 20th	Day	20% 6% 31% 26% 13% 4	527
	21st to end	Day	20% 10% 31% 25% 12% 3	573
June	1st to 10th	Day	23% 9% 27% 27% 11% 2	530
	11th to 20th	Day	15% 12% 26% 30% 15% 3	530
	21st to end	Day	22% 7% 28% 26% 14% 3	530
July	1st to 10th	Day	14% 6% 26% 32% 18% 5%	525
	11th to 20th	Day	14% 5% 27% 32% 18% 4	524
	21st to end	Day	12% 6% 24% 36% 17% 5%	576
August	1st to 10th	Day	13% 5% 22% 32% 22% 6%	526
	11th to 20th	Day	12% 4 19% 32% 21% 11%	519
	21st to end	Day	15% 7% 25% 24% 21% 8%	583
September	1st to 10th	Day	13% 5% 26% 27% 19% 9%	530
	11th to 20th	Day	13% 6% 20% 27% 21% 13%	530
	21st to end	Day	19% 8% 26% 24% 17% 7%	530
October	1st to 10th	Day	20% 9% 27% 23% 15% 5%	530
	11th to 20th	Day	20% 11% 32% 24% 11% 3	505
	21st to end	Day	31% 11% 25% 24% 9%	462
November	1st to 10th	Day	28% 15% 24% 22% 10% 1	425
	11th to 20th	Day	26% 12% 33% 20% 8% 1	335
	21st to end	Day	33% 14% 26% 19% 7% 1	220
December	1st to 10th	Day	27% 12% 25% 25% 9% 2	220
	11th to 20th	Day	25% 13% 39% 19% 4 1	220
	21st to end	Day	29% 16% 29% 18% 7% 1	242
January	1st to 10th	Night	24% 11% 32% 27% 5%	840
	11th to 20th	Night	24% 12% 31% 26% 7%	840
	21st to end	Night	18% 9% 35% 30% 8% 1	924
February	1st to 10th	Night	21% 8% 36% 29% 6% 1	840
	11th to 20th	Night	21% 11% 37% 27% 5%	823
	21st to end	Night	23% 9% 32% 32% 4	692
March	1st to 10th	Night	25% 11% 32% 28% 5%	840
	11th to 20th	Night	26% 10% 30% 26% 7%	829
	21st to end	Night	22% 9% 31% 31% 7%	880
April	1st to 10th	Night	27% 10% 28% 29% 6%	800
	11th to 20th	Night	26% 9% 30% 28% 6% 1	791
	21st to end	Night	28% 8% 31% 26% 7%	638
May	1st to 10th	Night	26% 6% 31% 29% 7% 2	448
	11th to 20th	Night	24% 3 28% 35% 9% 1	394
	21st to end	Night	19% 5% 36% 31% 8%	433
June	1st to 10th	Night	26% 4 24% 36% 11%	400
	11th to 20th	Night	19% 5% 28% 36% 13% 1	400
	21st to end	Night	21% 5% 24% 35% 15% 1	400
July	1st to 10th	Night	11% 4 27% 42% 16% 1	390
	11th to 20th	Night	13% 3 20% 46% 17%	388
	21st to end	Night	12% 3 19% 47% 18% 1	438
August	1st to 10th	Night	14% 5% 13% 44% 24% 1	398
	11th to 20th	Night	14% 2 18% 37% 25% 3	586
	21st to end	Night	16% 3 22% 37% 21% 2	880
September	1st to 10th	Night	14% 4 23% 42% 18% 1	800
	11th to 20th	Night	15% 5% 16% 38% 24% 3	800
	21st to end	Night	18% 4 26% 33% 17% 2	800
October	1st to 10th	Night	20% 6% 25% 34% 14% 1	800
	11th to 20th	Night	23% 7% 29% 31% 11% 1	800
	21st to end	Night	26% 8% 31% 29% 7%	880
November	1st to 10th	Night	24% 11% 29% 28% 9%	820
	11th to 20th	Night	24% 9% 31% 25% 10% 1	840
	21st to end	Night	28% 13% 29% 23% 8%	840
December	1st to 10th	Night	29% 10% 30% 25% 7%	840
	11th to 20th	Night	27% 12% 32% 23% 5% 1	840
	21st to end	Night	34% 10% 28% 21% 6%	924

Page generated at 2026-03-15 02:23:57. Version ac07

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