Rue Lambert
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Rue Lambert clear sky chart from 2005-11-06 to 2025-01-22.

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	17% 13% 4 10% 5% 5% 4 4 5% 6% 27%	105211
	Night	17% 14% 5% 11% 6% 5% 4 3 4 5% 26%	104175
Transparency	Day	56% 7% 11% 18% 8% 1	108684
	Night	58% 7% 10% 16% 8% 1	108778
Seeing	Day	26% 17% 29% 18% 8% 2	14850
	Night	24% 15% 28% 24% 8% 1	23860

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	15% 20% 8% 18% 9% 5% 3 3 3 3 13%	2597
	11th to 20th	Day	11% 15% 8% 21% 13% 5% 4 3 4 4 13%	2600
	21st to end	Day	11% 20% 8% 15% 6% 9% 5% 3 3 4 15%	2780
February	1st to 10th	Day	13% 20% 6% 15% 8% 6% 5% 3 4 3 17%	1600
	11th to 20th	Day	12% 19% 8% 15% 8% 5% 5% 3 5% 4 16%	1834
	21st to end	Day	13% 18% 6% 13% 7% 6% 4 4 4 5% 20%	1570
March	1st to 10th	Day	21% 15% 5% 11% 6% 5% 4 3 4 4 21%	3116
	11th to 20th	Day	12% 22% 7% 13% 6% 4 4 3 4 4 22%	3254
	21st to end	Day	16% 14% 5% 12% 5% 4 2 2 3 4 32%	4152
April	1st to 10th	Day	20% 18% 4 10% 5% 4 3 2 3 5% 25%	2280
	11th to 20th	Day	19% 14% 4 8% 4 4 4 3 4 4 33%	2278
	21st to end	Day	23% 13% 4 8% 4 4 4 3 5% 5% 27%	2470
May	1st to 10th	Day	24% 11% 3 7% 5% 4 4 4 6% 7% 26%	4199
	11th to 20th	Day	18% 8% 3 8% 6% 6% 5% 5% 6% 7% 27%	4398
	21st to end	Day	14% 8% 3 7% 5% 6% 5% 4 7% 8% 32%	4837
June	1st to 10th	Day	25% 9% 3 7% 4 4 5% 4 6% 6% 27%	2660
	11th to 20th	Day	17% 8% 3 7% 5% 4 5% 4 6% 9% 34%	2660
	21st to end	Day	24% 9% 3 8% 5% 4 5% 4 6% 6% 28%	2660
July	1st to 10th	Day	14% 7% 3 7% 5% 5% 6% 5% 7% 9% 31%	4440
	11th to 20th	Day	14% 7% 3 7% 5% 5% 5% 5% 8% 8% 32%	4440
	21st to end	Day	15% 8% 2 5% 4 5% 5% 4 6% 7% 38%	4814
August	1st to 10th	Day	18% 9% 3 8% 5% 5% 6% 4 7% 8% 27%	4405
	11th to 20th	Day	18% 7% 3 7% 5% 5% 5% 4 7% 9% 29%	4025
	21st to end	Day	18% 7% 2 6% 4 4 4 4 6% 8% 36%	4180
September	1st to 10th	Day	15% 8% 2 6% 4 4 5% 4 5% 7% 40%	2280
	11th to 20th	Day	18% 7% 3 5% 4 3 3 3 5% 7% 43%	2142
	21st to end	Day	19% 8% 3 6% 4 4 3 4 5% 9% 35%	2090
October	1st to 10th	Day	23% 11% 3 7% 4 5% 5% 3 6% 6% 28%	2047
	11th to 20th	Day	20% 13% 3 9% 5% 4 5% 3 5% 6% 28%	1800
	21st to end	Day	25% 19% 4 8% 4 4 3 2 3 4 24%	1881
November	1st to 10th	Day	18% 17% 4 7% 4 5% 4 3 4 5% 28%	1761
	11th to 20th	Day	16% 20% 7% 11% 5% 3 4 4 3 5% 23%	1800
	21st to end	Day	18% 20% 7% 12% 5% 4 3 4 5% 5% 17%	1615
December	1st to 10th	Day	14% 24% 8% 19% 9% 4 3 2 3 3 10%	2600
	11th to 20th	Day	17% 19% 7% 15% 4 4 4 3 4 4 19%	2986
	21st to end	Day	18% 18% 6% 14% 6% 4 5% 3 4 4 18%	3960
January	1st to 10th	Night	13% 20% 7% 18% 8% 6% 4 3 4 4 13%	4569
	11th to 20th	Night	10% 17% 7% 19% 12% 6% 5% 3 4 3 14%	4580
	21st to end	Night	12% 20% 8% 15% 7% 6% 4 3 3 4 18%	4899
February	1st to 10th	Night	13% 17% 7% 16% 8% 6% 5% 3 4 4 18%	2576
	11th to 20th	Night	11% 15% 6% 17% 8% 6% 5% 3 5% 4 20%	2231
	21st to end	Night	13% 17% 6% 12% 7% 6% 4 4 4 4 25%	1884
March	1st to 10th	Night	20% 14% 5% 9% 5% 4 5% 3 4 5% 27%	3724
	11th to 20th	Night	14% 19% 6% 13% 6% 5% 4 2 3 4 24%	3704
	21st to end	Night	14% 17% 6% 12% 7% 4 3 2 3 3 29%	3479
April	1st to 10th	Night	22% 13% 4 8% 5% 4 4 3 4 5% 27%	1900
	11th to 20th	Night	20% 12% 4 7% 4 5% 4 3 4 6% 31%	1851
	21st to end	Night	22% 10% 3 8% 5% 4 3 3 5% 5% 31%	1710
May	1st to 10th	Night	22% 12% 3 8% 5% 4 5% 4 5% 6% 26%	2770
	11th to 20th	Night	20% 8% 3 8% 5% 5% 5% 4 5% 6% 32%	2495
	21st to end	Night	16% 7% 2 7% 5% 4 5% 4 6% 8% 37%	2738
June	1st to 10th	Night	26% 8% 2 7% 3 3 4 4 6% 7% 30%	1520
	11th to 20th	Night	18% 6% 2 6% 3 4 5% 4 7% 8% 36%	1520
	21st to end	Night	19% 10% 3 6% 5% 5% 5% 4 7% 7% 30%	1520
July	1st to 10th	Night	13% 9% 3 8% 6% 6% 5% 4 6% 8% 32%	2520
	11th to 20th	Night	15% 9% 2 7% 4 4 5% 4 6% 8% 36%	2520
	21st to end	Night	15% 7% 3 7% 5% 4 4 4 6% 6% 38%	2739
August	1st to 10th	Night	22% 9% 3 6% 5% 3 4 4 5% 7% 32%	2506
	11th to 20th	Night	14% 8% 3 8% 6% 4 6% 4 7% 8% 32%	2787
	21st to end	Night	16% 7% 2 6% 4 4 5% 4 5% 7% 40%	3476
September	1st to 10th	Night	16% 7% 2 7% 5% 4 4 3 5% 7% 41%	1900
	11th to 20th	Night	16% 6% 2 5% 3 3 4 3 5% 7% 46%	2038
	21st to end	Night	19% 7% 2 5% 4 4 4 3 5% 7% 41%	2090
October	1st to 10th	Night	20% 9% 3 7% 4 5% 4 4 6% 5% 34%	2128
	11th to 20th	Night	21% 12% 4 8% 6% 5% 4 3 4 5% 29%	2380
	21st to end	Night	24% 14% 4 8% 4 4 4 3 4 5% 26%	2717
November	1st to 10th	Night	18% 14% 5% 8% 5% 5% 5% 4 4 6% 26%	2537
	11th to 20th	Night	17% 14% 6% 11% 6% 5% 3 3 4 5% 27%	2600
	21st to end	Night	17% 18% 7% 13% 6% 4 3 2 4 4 22%	2783
December	1st to 10th	Night	15% 23% 10% 21% 7% 4 3 2 3 3 9%	4580
	11th to 20th	Night	19% 19% 6% 17% 7% 4 3 2 3 3 16%	5208
	21st to end	Night	18% 18% 5% 13% 6% 5% 5% 3 3 5% 20%	6996

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	77% 4 9% 8% 1	2598
	11th to 20th	Day	74% 6% 7% 9% 3	2600
	21st to end	Day	73% 5% 9% 10% 4 1	2780
February	1st to 10th	Day	73% 5% 5% 12% 5% 1	1600
	11th to 20th	Day	72% 5% 9% 9% 5% 1	1843
	21st to end	Day	65% 5% 9% 12% 6% 2	1570
March	1st to 10th	Day	64% 8% 8% 11% 8% 1	3119
	11th to 20th	Day	66% 4 9% 10% 9% 2	3254
	21st to end	Day	57% 3 7% 16% 15% 2	4152
April	1st to 10th	Day	63% 3 8% 15% 9% 1	2280
	11th to 20th	Day	55% 4 8% 19% 13% 1	2278
	21st to end	Day	58% 5% 9% 16% 9% 2	2470
May	1st to 10th	Day	56% 7% 11% 18% 8% 1	4213
	11th to 20th	Day	51% 10% 15% 16% 7% 1	4402
	21st to end	Day	45% 9% 12% 23% 11% 1	4837
June	1st to 10th	Day	54% 7% 12% 18% 9% 1	2660
	11th to 20th	Day	46% 7% 11% 23% 12% 1	2660
	21st to end	Day	55% 8% 11% 18% 8%	2660
July	1st to 10th	Day	44% 9% 15% 24% 9%	4370
	11th to 20th	Day	44% 10% 14% 28% 4	4365
	21st to end	Day	43% 8% 12% 30% 7%	4661
August	1st to 10th	Day	51% 9% 15% 19% 6%	4391
	11th to 20th	Day	48% 9% 18% 19% 5%	4064
	21st to end	Day	44% 7% 15% 19% 12% 2	4180
September	1st to 10th	Day	42% 7% 13% 27% 10% 1	2280
	11th to 20th	Day	41% 6% 12% 29% 13%	2142
	21st to end	Day	45% 8% 13% 24% 10% 1	2090
October	1st to 10th	Day	47% 7% 14% 24% 7%	3398
	11th to 20th	Day	51% 5% 14% 23% 6%	2964
	21st to end	Day	53% 4 14% 21% 8% 1	3081
November	1st to 10th	Day	58% 7% 10% 18% 7%	1761
	11th to 20th	Day	64% 5% 9% 12% 8% 1	1800
	21st to end	Day	68% 6% 13% 11% 2	1615
December	1st to 10th	Day	80% 4 8% 6% 2	2600
	11th to 20th	Day	67% 4 9% 15% 5%	2986
	21st to end	Day	69% 5% 7% 10% 9%	3960
January	1st to 10th	Night	73% 8% 10% 7% 2	4569
	11th to 20th	Night	74% 6% 9% 9% 2	4580
	21st to end	Night	70% 6% 9% 9% 5% 1	4899
February	1st to 10th	Night	69% 5% 8% 11% 5%	2576
	11th to 20th	Night	67% 6% 8% 13% 6%	2233
	21st to end	Night	63% 4 9% 14% 10% 1	1884
March	1st to 10th	Night	58% 8% 10% 15% 7% 3	3734
	11th to 20th	Night	64% 6% 8% 12% 10% 1	3705
	21st to end	Night	61% 5% 5% 16% 11% 1	3479
April	1st to 10th	Night	59% 5% 9% 15% 11% 1	1900
	11th to 20th	Night	53% 6% 8% 19% 13% 1	1851
	21st to end	Night	55% 6% 8% 17% 12% 2	1710
May	1st to 10th	Night	56% 8% 10% 17% 8% 1	2776
	11th to 20th	Night	51% 10% 13% 17% 9% 1	2496
	21st to end	Night	44% 9% 12% 19% 16% 1	2739
June	1st to 10th	Night	51% 6% 11% 22% 8% 1	1520
	11th to 20th	Night	44% 8% 12% 23% 11% 3	1520
	21st to end	Night	51% 8% 13% 19% 9% 1	1520
July	1st to 10th	Night	47% 9% 13% 20% 10%	2480
	11th to 20th	Night	42% 10% 14% 28% 6%	2472
	21st to end	Night	44% 9% 14% 24% 9%	2651
August	1st to 10th	Night	50% 7% 15% 22% 5%	2496
	11th to 20th	Night	45% 11% 18% 19% 7%	2814
	21st to end	Night	42% 8% 13% 23% 13% 1	3476
September	1st to 10th	Night	41% 9% 13% 25% 12%	1900
	11th to 20th	Night	37% 7% 16% 28% 12% 1	2038
	21st to end	Night	43% 7% 12% 25% 12% 1	2090
October	1st to 10th	Night	50% 7% 11% 23% 8%	3544
	11th to 20th	Night	49% 7% 12% 23% 9%	3955
	21st to end	Night	51% 6% 14% 19% 9% 1	4467
November	1st to 10th	Night	58% 6% 12% 17% 7% 1	2537
	11th to 20th	Night	59% 6% 10% 15% 9% 2	2600
	21st to end	Night	66% 7% 10% 13% 4	2783
December	1st to 10th	Night	81% 6% 6% 6% 2	4580
	11th to 20th	Night	73% 4 6% 10% 7%	5208
	21st to end	Night	69% 4 7% 13% 7%	6996

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	27% 24% 30% 17% 3	200
	11th to 20th	Day	25% 28% 32% 11% 4 1	200
	21st to end	Day	24% 22% 33% 14% 7% 1	200
February	1st to 10th	Day	38% 28% 23% 10% 2	218
	11th to 20th	Day	29% 27% 31% 10% 2	442
	21st to end	Day	30% 23% 30% 16% 2	382
March	1st to 10th	Day	32% 19% 30% 16% 3	460
	11th to 20th	Day	30% 25% 28% 13% 4 1	460
	21st to end	Day	31% 25% 23% 14% 7% 1	506
April	1st to 10th	Day	36% 17% 27% 15% 5% 1	460
	11th to 20th	Day	36% 18% 25% 13% 5% 2	452
	21st to end	Day	34% 18% 30% 12% 6% 2	460
May	1st to 10th	Day	32% 17% 25% 17% 6% 2	463
	11th to 20th	Day	23% 17% 30% 20% 7% 2	487
	21st to end	Day	21% 19% 32% 21% 5% 1	529
June	1st to 10th	Day	29% 15% 31% 18% 6% 1	490
	11th to 20th	Day	21% 15% 31% 22% 10% 1	490
	21st to end	Day	27% 14% 34% 17% 7% 2	490
July	1st to 10th	Day	18% 11% 34% 24% 11% 2	485
	11th to 20th	Day	15% 12% 38% 25% 7% 3	484
	21st to end	Day	18% 10% 35% 26% 9% 1	532
August	1st to 10th	Day	17% 12% 28% 28% 13% 2	486
	11th to 20th	Day	18% 9% 28% 28% 14% 3	479
	21st to end	Day	19% 14% 25% 24% 11% 6%	539
September	1st to 10th	Day	19% 12% 29% 22% 13% 5%	490
	11th to 20th	Day	18% 11% 22% 22% 20% 7%	490
	21st to end	Day	19% 14% 26% 22% 14% 4	490
October	1st to 10th	Day	26% 15% 26% 18% 12% 4	490
	11th to 20th	Day	29% 19% 23% 17% 10% 1	437
	21st to end	Day	36% 20% 22% 17% 5%	429
November	1st to 10th	Day	32% 20% 27% 16% 4 1	395
	11th to 20th	Day	28% 24% 28% 13% 6% 2	400
	21st to end	Day	33% 21% 32% 13% 2	215
December	1st to 10th	Day	31% 23% 26% 16% 4 2	200
	11th to 20th	Day	33% 25% 30% 11% 1 1	200
	21st to end	Day	35% 22% 27% 13% 3 1	220
January	1st to 10th	Night	27% 22% 31% 18% 3	800
	11th to 20th	Night	25% 22% 32% 17% 5%	800
	21st to end	Night	20% 20% 33% 22% 5% 1	841
February	1st to 10th	Night	23% 21% 33% 20% 4	760
	11th to 20th	Night	20% 23% 35% 18% 3	743
	21st to end	Night	26% 17% 32% 22% 2	628
March	1st to 10th	Night	29% 18% 28% 22% 3	760
	11th to 20th	Night	29% 17% 28% 20% 6%	760
	21st to end	Night	27% 18% 26% 20% 7% 1	836
April	1st to 10th	Night	30% 16% 29% 20% 5%	760
	11th to 20th	Night	28% 17% 27% 21% 7%	727
	21st to end	Night	30% 15% 28% 20% 7%	570
May	1st to 10th	Night	26% 10% 31% 25% 7% 1	532
	11th to 20th	Night	22% 11% 30% 28% 9% 1	374
	21st to end	Night	20% 11% 30% 30% 8%	411
June	1st to 10th	Night	28% 7% 27% 27% 10%	380
	11th to 20th	Night	20% 7% 27% 32% 13%	380
	21st to end	Night	19% 9% 27% 34% 11% 1	380
July	1st to 10th	Night	14% 7% 29% 36% 14%	370
	11th to 20th	Night	13% 4 26% 39% 17% 1	368
	21st to end	Night	14% 5% 26% 41% 15%	416
August	1st to 10th	Night	20% 6% 16% 39% 19%	378
	11th to 20th	Night	15% 6% 23% 36% 19% 1	554
	21st to end	Night	16% 7% 24% 33% 19% 2	836
September	1st to 10th	Night	17% 8% 25% 34% 14% 1	760
	11th to 20th	Night	18% 8% 20% 31% 22% 2	760
	21st to end	Night	21% 9% 28% 25% 16% 1	760
October	1st to 10th	Night	26% 12% 23% 25% 13% 1	760
	11th to 20th	Night	27% 15% 26% 22% 9% 1	760
	21st to end	Night	30% 17% 28% 22% 3	836
November	1st to 10th	Night	28% 17% 29% 20% 5% 1	780
	11th to 20th	Night	26% 19% 29% 16% 9% 1	800
	21st to end	Night	28% 24% 26% 16% 5% 1	800
December	1st to 10th	Night	31% 24% 26% 16% 4	800
	11th to 20th	Night	30% 20% 29% 17% 4	800
	21st to end	Night	32% 22% 25% 18% 3	880

Page generated at 2025-01-19 03:06:47. Version ac07

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