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 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	16% 9% 3 8% 5% 5% 5% 4 6% 7% 33%	101817
	Night	17% 10% 4 8% 5% 4 4 3 5% 6% 33%	97920
Transparency	Day	49% 4 13% 22% 10% 1	105280
	Night	52% 4 12% 21% 10% 1	102546
Seeing	Day	21% 10% 28% 25% 12% 4	14634
	Night	22% 7% 28% 31% 10% 1	23630

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	16% 14% 5% 13% 6% 5% 5% 3 4 4 24%	2517
	11th to 20th	Day	14% 12% 6% 10% 6% 4 3 4 5% 7% 28%	2520
	21st to end	Day	13% 16% 5% 10% 6% 6% 5% 4 5% 6% 24%	2772
February	1st to 10th	Day	14% 16% 4 10% 6% 4 5% 4 4 6% 28%	1667
	11th to 20th	Day	13% 12% 4 10% 6% 5% 6% 5% 5% 6% 28%	1757
	21st to end	Day	17% 16% 5% 9% 4 4 4 3 5% 5% 28%	1570
March	1st to 10th	Day	20% 12% 4 10% 6% 5% 4 3 5% 5% 26%	3116
	11th to 20th	Day	13% 17% 5% 10% 6% 4 5% 3 4 5% 28%	3283
	21st to end	Day	15% 8% 3 8% 5% 5% 4 3 5% 5% 39%	4161
April	1st to 10th	Day	21% 11% 3 7% 5% 4 4 3 4 5% 32%	2280
	11th to 20th	Day	21% 8% 2 6% 6% 4 4 3 4 5% 36%	2254
	21st to end	Day	21% 10% 4 7% 5% 3 4 4 4 5% 33%	2433
May	1st to 10th	Day	19% 8% 4 8% 6% 4 5% 4 6% 7% 30%	4384
	11th to 20th	Day	17% 8% 3 8% 5% 5% 5% 3 6% 8% 31%	4398
	21st to end	Day	15% 7% 2 6% 5% 4 5% 4 7% 9% 36%	4837
June	1st to 10th	Day	20% 9% 3 7% 5% 5% 4 4 5% 8% 30%	2660
	11th to 20th	Day	14% 6% 3 7% 5% 4 5% 5% 6% 8% 37%	2660
	21st to end	Day	19% 7% 3 8% 6% 5% 5% 4 7% 7% 29%	2660
July	1st to 10th	Day	11% 6% 2 7% 6% 6% 6% 5% 7% 9% 36%	4440
	11th to 20th	Day	13% 6% 2 6% 5% 5% 5% 5% 7% 9% 37%	4440
	21st to end	Day	11% 6% 2 5% 4 4 4 5% 7% 8% 45%	4814
August	1st to 10th	Day	14% 6% 2 8% 5% 5% 7% 4 7% 9% 33%	4423
	11th to 20th	Day	14% 6% 3 8% 5% 4 4 3 6% 8% 38%	4013
	21st to end	Day	15% 5% 2 6% 5% 4 4 4 6% 8% 40%	4180
September	1st to 10th	Day	11% 5% 2 6% 5% 5% 5% 4 6% 9% 41%	2280
	11th to 20th	Day	13% 5% 2 5% 3 4 4 3 5% 6% 49%	2203
	21st to end	Day	16% 6% 3 6% 5% 4 4 3 5% 7% 41%	2090
October	1st to 10th	Day	20% 6% 2 7% 4 4 5% 3 6% 7% 36%	1957
	11th to 20th	Day	19% 7% 3 8% 7% 5% 5% 4 6% 7% 30%	1858
	21st to end	Day	23% 9% 3 7% 4 4 3 3 5% 6% 31%	1881
November	1st to 10th	Day	16% 10% 3 7% 4 5% 4 4 5% 8% 35%	1761
	11th to 20th	Day	17% 11% 4 7% 4 5% 5% 3 5% 7% 32%	1710
	21st to end	Day	22% 11% 3 7% 5% 5% 5% 4 6% 6% 26%	1600
December	1st to 10th	Day	23% 14% 5% 11% 5% 4 4 3 4 4 21%	1560
	11th to 20th	Day	22% 14% 4 8% 5% 3 4 3 5% 4 28%	1906
	21st to end	Day	27% 17% 3 10% 4 4 3 3 4 4 21%	2772
January	1st to 10th	Night	16% 15% 6% 11% 6% 5% 5% 3 4 5% 24%	4429
	11th to 20th	Night	11% 14% 5% 11% 7% 6% 6% 4 6% 6% 25%	4440
	21st to end	Night	15% 17% 5% 11% 6% 4 4 3 5% 5% 25%	4884
February	1st to 10th	Night	14% 15% 5% 12% 6% 5% 5% 3 5% 6% 24%	2510
	11th to 20th	Night	14% 11% 4 10% 6% 5% 5% 4 5% 6% 31%	2309
	21st to end	Night	15% 14% 4 9% 5% 4 4 3 5% 5% 31%	1884
March	1st to 10th	Night	20% 12% 3 7% 5% 4 4 3 4 5% 33%	3724
	11th to 20th	Night	17% 18% 5% 9% 4 4 4 2 5% 4 28%	3673
	21st to end	Night	12% 10% 4 9% 5% 5% 4 3 5% 5% 39%	3471
April	1st to 10th	Night	23% 11% 2 7% 4 4 4 4 4 6% 31%	1900
	11th to 20th	Night	22% 9% 3 6% 5% 4 4 3 4 5% 35%	1875
	21st to end	Night	21% 9% 3 6% 4 3 4 3 5% 5% 36%	1746
May	1st to 10th	Night	21% 9% 3 8% 5% 4 5% 3 5% 7% 31%	2586
	11th to 20th	Night	21% 8% 3 7% 4 3 4 4 5% 6% 35%	2495
	21st to end	Night	15% 8% 2 8% 5% 4 4 4 5% 8% 36%	2738
June	1st to 10th	Night	20% 8% 3 7% 4 4 5% 3 7% 8% 32%	1520
	11th to 20th	Night	16% 7% 3 6% 4 3 4 4 6% 7% 39%	1520
	21st to end	Night	19% 7% 3 7% 4 4 5% 4 6% 7% 34%	1520
July	1st to 10th	Night	14% 6% 3 8% 5% 5% 5% 4 7% 8% 34%	2520
	11th to 20th	Night	14% 6% 2 6% 4 4 4 4 6% 8% 42%	2520
	21st to end	Night	11% 6% 2 6% 5% 4 4 4 6% 8% 44%	2739
August	1st to 10th	Night	15% 8% 3 7% 5% 4 5% 3 5% 7% 38%	2506
	11th to 20th	Night	15% 7% 3 7% 5% 4 4 4 5% 7% 39%	2780
	21st to end	Night	17% 5% 2 8% 5% 5% 4 4 5% 7% 39%	3476
September	1st to 10th	Night	11% 5% 2 7% 5% 4 4 4 6% 7% 45%	1900
	11th to 20th	Night	14% 5% 3 6% 3 3 3 3 4 7% 50%	1976
	21st to end	Night	16% 5% 2 7% 4 4 4 4 4 7% 44%	2090
October	1st to 10th	Night	18% 6% 2 7% 4 4 4 3 4 6% 40%	2220
	11th to 20th	Night	19% 8% 3 7% 4 4 4 3 4 6% 37%	2321
	21st to end	Night	21% 9% 3 8% 4 4 4 3 5% 6% 32%	2717
November	1st to 10th	Night	19% 9% 3 7% 5% 4 5% 4 5% 7% 33%	2537
	11th to 20th	Night	19% 10% 3 8% 4 4 4 4 5% 5% 34%	2685
	21st to end	Night	22% 13% 3 9% 6% 3 4 3 5% 5% 28%	2800
December	1st to 10th	Night	21% 15% 5% 10% 5% 5% 5% 4 4 6% 22%	2737
	11th to 20th	Night	23% 14% 5% 9% 4 4 3 3 4 5% 27%	3288
	21st to end	Night	28% 16% 5% 10% 4 3 3 2 4 4 22%	4884

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	64% 3 13% 14% 5% 1	2518
	11th to 20th	Day	57% 3 14% 19% 7%	2520
	21st to end	Day	60% 4 15% 14% 6% 1	2772
February	1st to 10th	Day	58% 3 10% 20% 7% 2	1667
	11th to 20th	Day	57% 4 12% 16% 10% 1	1766
	21st to end	Day	59% 2 10% 16% 10% 2	1570
March	1st to 10th	Day	61% 3 9% 18% 8% 1	3119
	11th to 20th	Day	58% 4 11% 13% 12% 3	3283
	21st to end	Day	46% 4 8% 20% 19% 2	4161
April	1st to 10th	Day	55% 4 7% 19% 12% 2	2280
	11th to 20th	Day	50% 4 7% 23% 15% 2	2254
	21st to end	Day	55% 3 8% 18% 13% 4	2433
May	1st to 10th	Day	53% 3 9% 24% 10% 1	4398
	11th to 20th	Day	51% 4 16% 19% 8% 2	4402
	21st to end	Day	44% 4 12% 24% 15% 2	4837
June	1st to 10th	Day	52% 5% 10% 20% 12% 2	2660
	11th to 20th	Day	43% 5% 11% 24% 13% 3	2660
	21st to end	Day	52% 5% 13% 20% 10% 1	2660
July	1st to 10th	Day	43% 6% 14% 27% 10% 1	4370
	11th to 20th	Day	40% 6% 17% 30% 8%	4365
	21st to end	Day	36% 5% 15% 34% 10%	4661
August	1st to 10th	Day	46% 6% 18% 22% 9%	4409
	11th to 20th	Day	43% 5% 18% 27% 6%	4055
	21st to end	Day	41% 5% 16% 22% 15% 1	4180
September	1st to 10th	Day	37% 6% 14% 30% 13% 1	2280
	11th to 20th	Day	34% 4 13% 33% 14% 1	2203
	21st to end	Day	42% 4 14% 27% 12% 1	2090
October	1st to 10th	Day	46% 4 14% 27% 10%	3256
	11th to 20th	Day	44% 5% 18% 27% 7%	3061
	21st to end	Day	43% 4 20% 23% 9% 1	3081
November	1st to 10th	Day	48% 5% 14% 23% 9% 1	1761
	11th to 20th	Day	52% 5% 11% 20% 12% 1	1710
	21st to end	Day	59% 5% 14% 16% 6% 1	1600
December	1st to 10th	Day	68% 3 11% 14% 5%	1560
	11th to 20th	Day	59% 4 11% 19% 7%	1906
	21st to end	Day	69% 3 12% 11% 6%	2772
January	1st to 10th	Night	63% 3 16% 14% 5%	4429
	11th to 20th	Night	59% 4 13% 18% 5% 1	4440
	21st to end	Night	62% 5% 14% 12% 7% 1	4884
February	1st to 10th	Night	61% 4 9% 17% 8% 1	2510
	11th to 20th	Night	54% 4 10% 22% 10% 1	2311
	21st to end	Night	55% 4 9% 17% 13% 2	1884
March	1st to 10th	Night	55% 2 10% 19% 10% 3	3734
	11th to 20th	Night	60% 3 9% 14% 13% 2	3674
	21st to end	Night	49% 3 7% 22% 16% 3	3471
April	1st to 10th	Night	53% 4 7% 19% 15% 2	1900
	11th to 20th	Night	51% 4 6% 22% 15% 2	1875
	21st to end	Night	50% 4 8% 20% 14% 4	1746
May	1st to 10th	Night	54% 2 11% 21% 9% 3	2592
	11th to 20th	Night	50% 4 12% 20% 12% 2	2496
	21st to end	Night	47% 3 10% 20% 18% 1	2739
June	1st to 10th	Night	50% 5% 10% 22% 13% 1	1520
	11th to 20th	Night	43% 5% 12% 23% 15% 3	1520
	21st to end	Night	49% 6% 11% 19% 14% 1	1520
July	1st to 10th	Night	45% 6% 15% 21% 13% 1	2480
	11th to 20th	Night	39% 5% 20% 28% 8%	2472
	21st to end	Night	37% 6% 18% 25% 13%	2651
August	1st to 10th	Night	46% 5% 12% 26% 10%	2496
	11th to 20th	Night	44% 5% 18% 25% 7%	2804
	21st to end	Night	44% 6% 13% 22% 14% 1	3476
September	1st to 10th	Night	37% 5% 14% 27% 16% 1	1900
	11th to 20th	Night	35% 4 14% 34% 13% 1	1976
	21st to end	Night	41% 5% 11% 29% 15%	2090
October	1st to 10th	Night	44% 5% 14% 26% 11% 1	3701
	11th to 20th	Night	43% 4 12% 31% 9%	3857
	21st to end	Night	46% 4 17% 19% 12% 2	4467
November	1st to 10th	Night	51% 4 11% 23% 9% 1	2537
	11th to 20th	Night	51% 5% 12% 20% 11% 1	2685
	21st to end	Night	59% 4 11% 19% 8%	2800
December	1st to 10th	Night	64% 4 11% 16% 4	2737
	11th to 20th	Night	61% 3 8% 19% 7% 1	3288
	21st to end	Night	67% 3 9% 15% 5%	4884

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	23% 10% 28% 30% 8%	180
	11th to 20th	Day	26% 12% 33% 23% 4 2	180
	21st to end	Day	21% 12% 31% 27% 7% 2	198
February	1st to 10th	Day	30% 16% 35% 14% 4	249
	11th to 20th	Day	21% 13% 38% 23% 4	364
	21st to end	Day	28% 12% 32% 24% 4	382
March	1st to 10th	Day	25% 12% 31% 24% 8%	460
	11th to 20th	Day	22% 13% 35% 24% 5% 1	460
	21st to end	Day	27% 11% 32% 19% 9% 2	506
April	1st to 10th	Day	28% 13% 26% 21% 8% 3	460
	11th to 20th	Day	30% 14% 23% 21% 9% 2	452
	21st to end	Day	27% 13% 30% 19% 8% 3	460
May	1st to 10th	Day	22% 10% 32% 25% 9% 2	463
	11th to 20th	Day	20% 6% 31% 26% 13% 3	487
	21st to end	Day	17% 11% 32% 25% 12% 3	529
June	1st to 10th	Day	24% 9% 26% 26% 12% 3	490
	11th to 20th	Day	15% 11% 24% 31% 15% 3	490
	21st to end	Day	23% 7% 26% 26% 14% 4	490
July	1st to 10th	Day	13% 5% 24% 33% 19% 5%	485
	11th to 20th	Day	15% 5% 26% 32% 18% 4	484
	21st to end	Day	12% 6% 22% 37% 17% 5%	532
August	1st to 10th	Day	15% 5% 22% 31% 21% 6%	486
	11th to 20th	Day	12% 4 20% 31% 21% 12%	479
	21st to end	Day	15% 6% 24% 25% 21% 8%	539
September	1st to 10th	Day	14% 5% 27% 28% 18% 9%	490
	11th to 20th	Day	14% 7% 21% 25% 20% 13%	490
	21st to end	Day	19% 8% 26% 24% 17% 7%	490
October	1st to 10th	Day	21% 9% 27% 22% 15% 5%	490
	11th to 20th	Day	21% 11% 31% 23% 11% 3	467
	21st to end	Day	32% 11% 25% 24% 8%	429
November	1st to 10th	Day	27% 13% 25% 23% 11% 1	395
	11th to 20th	Day	25% 13% 35% 19% 7% 1	310
	21st to end	Day	32% 13% 27% 20% 8% 1	200
December	1st to 10th	Day	28% 11% 25% 26% 8% 3	190
	11th to 20th	Day	26% 12% 37% 19% 4 1	180
	21st to end	Day	32% 16% 28% 16% 8% 1	198
January	1st to 10th	Night	25% 11% 30% 28% 6%	760
	11th to 20th	Night	25% 10% 32% 27% 7%	760
	21st to end	Night	18% 8% 35% 30% 8% 1	836
February	1st to 10th	Night	22% 8% 36% 29% 5% 1	760
	11th to 20th	Night	21% 11% 36% 27% 5%	743
	21st to end	Night	24% 8% 32% 32% 4	628
March	1st to 10th	Night	25% 9% 31% 31% 5%	760
	11th to 20th	Night	26% 10% 30% 26% 8%	760
	21st to end	Night	22% 9% 31% 31% 7%	836
April	1st to 10th	Night	26% 10% 28% 30% 6%	760
	11th to 20th	Night	26% 9% 30% 28% 6% 1	751
	21st to end	Night	27% 8% 30% 26% 8%	606
May	1st to 10th	Night	25% 5% 32% 29% 8% 2	426
	11th to 20th	Night	24% 3 28% 35% 9% 1	374
	21st to end	Night	18% 5% 37% 31% 8%	411
June	1st to 10th	Night	26% 4 23% 36% 12%	380
	11th to 20th	Night	19% 4 28% 35% 13% 1	380
	21st to end	Night	21% 4 24% 35% 15% 1	380
July	1st to 10th	Night	11% 4 27% 43% 15% 1	370
	11th to 20th	Night	13% 3 21% 46% 18%	368
	21st to end	Night	12% 3 18% 46% 19% 1	416
August	1st to 10th	Night	15% 4 12% 44% 23% 1	378
	11th to 20th	Night	15% 2 19% 37% 24% 3	556
	21st to end	Night	15% 2 22% 37% 21% 2	836
September	1st to 10th	Night	14% 3 23% 42% 18% 1	760
	11th to 20th	Night	16% 5% 17% 37% 23% 3	760
	21st to end	Night	18% 4 26% 32% 18% 2	760
October	1st to 10th	Night	21% 6% 26% 34% 13% 1	760
	11th to 20th	Night	23% 6% 28% 30% 12% 1	760
	21st to end	Night	26% 8% 30% 28% 7%	836
November	1st to 10th	Night	23% 11% 28% 28% 9%	780
	11th to 20th	Night	24% 9% 32% 26% 10% 1	800
	21st to end	Night	29% 12% 28% 23% 8%	800
December	1st to 10th	Night	29% 9% 29% 25% 7%	783
	11th to 20th	Night	27% 11% 31% 24% 6% 1	760
	21st to end	Night	34% 10% 29% 20% 6%	836

Page generated at 2024-12-03 06:45:08. Version ac07

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