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 2024-01-22.

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	19% 12% 5% 8% 6% 3 4 4 5% 6% 27%	74852
	Night	18% 12% 5% 9% 7% 4 5% 4 4 5% 27%	75083
Transparency	Day	57% 6% 11% 17% 8% 1	74557
	Night	58% 6% 10% 17% 8% 1	74912
Seeing	Day	26% 17% 28% 18% 8% 2	13584
	Night	25% 15% 28% 24% 8% 1	22616

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	17% 20% 9% 14% 9% 4 5% 4 3 3 12%	1517
	11th to 20th	Day	17% 15% 7% 14% 12% 4 4 4 4 4 15%	1520
	21st to end	Day	9% 17% 6% 11% 10% 4 7% 6% 4 5% 20%	1592
February	1st to 10th	Day	13% 20% 7% 14% 9% 5% 7% 4 4 3 16%	1516
	11th to 20th	Day	13% 17% 9% 15% 8% 4 5% 4 4 4 17%	1735
	21st to end	Day	14% 17% 7% 13% 8% 4 5% 4 4 5% 19%	1480
March	1st to 10th	Day	15% 15% 6% 11% 8% 4 4 4 3 4 24%	1797
	11th to 20th	Day	16% 16% 6% 8% 7% 3 4 4 4 5% 27%	1852
	21st to end	Day	18% 15% 6% 9% 7% 3 3 2 3 4 29%	2362
April	1st to 10th	Day	21% 16% 6% 9% 6% 3 4 3 4 4 24%	2160
	11th to 20th	Day	19% 13% 4 7% 5% 3 4 3 4 4 33%	2156
	21st to end	Day	23% 13% 4 7% 5% 3 4 4 5% 5% 26%	2340
May	1st to 10th	Day	22% 10% 4 7% 5% 2 3 4 5% 7% 31%	2391
	11th to 20th	Day	19% 8% 3 5% 6% 4 5% 5% 5% 7% 32%	2478
	21st to end	Day	19% 7% 3 6% 6% 4 5% 5% 6% 7% 31%	2725
June	1st to 10th	Day	27% 8% 3 6% 4 3 4 5% 6% 6% 27%	2520
	11th to 20th	Day	18% 7% 3 7% 5% 3 4 5% 5% 9% 34%	2520
	21st to end	Day	24% 7% 3 7% 6% 3 5% 5% 6% 6% 28%	2520
July	1st to 10th	Day	17% 7% 2 6% 5% 3 5% 6% 6% 8% 35%	2520
	11th to 20th	Day	15% 6% 3 7% 6% 4 5% 6% 8% 9% 32%	2520
	21st to end	Day	18% 9% 2 5% 5% 4 6% 6% 6% 9% 31%	2744
August	1st to 10th	Day	17% 7% 3 7% 6% 4 5% 6% 6% 8% 31%	2501
	11th to 20th	Day	15% 7% 3 6% 5% 3 5% 6% 7% 9% 33%	2298
	21st to end	Day	17% 7% 3 6% 5% 4 4 5% 6% 9% 35%	2376
September	1st to 10th	Day	16% 8% 2 6% 5% 3 5% 6% 5% 7% 38%	2160
	11th to 20th	Day	19% 7% 3 4 4 2 3 3 5% 7% 43%	2030
	21st to end	Day	19% 8% 3 5% 5% 3 3 5% 5% 9% 35%	1980
October	1st to 10th	Day	24% 10% 3 6% 5% 4 5% 4 6% 6% 27%	1940
	11th to 20th	Day	20% 12% 4 7% 7% 3 5% 4 5% 6% 27%	1706
	21st to end	Day	27% 19% 4 7% 5% 3 3 3 3 4 23%	1782
November	1st to 10th	Day	19% 16% 4 6% 5% 4 4 4 4 5% 28%	1671
	11th to 20th	Day	17% 17% 8% 10% 7% 3 3 5% 3 5% 22%	1710
	21st to end	Day	18% 19% 6% 10% 7% 4 3 4 5% 6% 17%	1535
December	1st to 10th	Day	20% 22% 9% 12% 7% 3 3 3 3 4 14%	1520
	11th to 20th	Day	19% 18% 8% 11% 6% 3 4 3 4 4 19%	1906
	21st to end	Day	23% 17% 6% 14% 7% 3 3 4 4 3 15%	2772
January	1st to 10th	Night	16% 19% 8% 13% 9% 5% 6% 4 5% 4 12%	2649
	11th to 20th	Night	15% 17% 8% 14% 10% 5% 5% 4 3 3 17%	2660
	21st to end	Night	10% 14% 7% 13% 10% 5% 6% 6% 4 5% 20%	2798
February	1st to 10th	Night	13% 16% 8% 15% 9% 4 6% 4 4 4 17%	2440
	11th to 20th	Night	12% 13% 8% 14% 10% 5% 5% 4 5% 4 20%	2110
	21st to end	Night	13% 16% 7% 11% 7% 4 5% 4 3 4 25%	1776
March	1st to 10th	Night	15% 15% 7% 10% 7% 4 5% 4 4 5% 25%	2150
	11th to 20th	Night	17% 14% 5% 8% 7% 3 6% 3 3 4 28%	2106
	21st to end	Night	18% 14% 5% 8% 6% 3 4 4 3 3 31%	1993
April	1st to 10th	Night	22% 12% 6% 8% 6% 3 4 3 4 4 27%	1800
	11th to 20th	Night	20% 11% 4 7% 4 3 5% 3 4 6% 33%	1753
	21st to end	Night	22% 10% 3 7% 6% 3 4 4 5% 6% 30%	1620
May	1st to 10th	Night	20% 10% 4 7% 6% 3 5% 5% 4 6% 30%	1584
	11th to 20th	Night	18% 8% 3 8% 6% 4 4 4 4 6% 36%	1415
	21st to end	Night	17% 7% 3 6% 6% 3 6% 4 5% 8% 35%	1550
June	1st to 10th	Night	26% 7% 2 7% 4 3 4 5% 5% 8% 30%	1440
	11th to 20th	Night	19% 6% 3 5% 4 4 5% 5% 7% 9% 36%	1440
	21st to end	Night	18% 8% 3 5% 5% 4 5% 6% 7% 8% 31%	1440
July	1st to 10th	Night	14% 7% 3 6% 6% 3 4 6% 7% 8% 36%	1440
	11th to 20th	Night	11% 6% 1 6% 6% 3 6% 7% 7% 9% 38%	1440
	21st to end	Night	14% 5% 3 5% 6% 4 4 5% 7% 7% 39%	1574
August	1st to 10th	Night	15% 6% 2 4 5% 2 5% 6% 7% 11% 37%	1432
	11th to 20th	Night	14% 6% 3 6% 7% 3 5% 5% 6% 9% 37%	1587
	21st to end	Night	14% 7% 2 6% 4 4 5% 5% 5% 8% 39%	1980
September	1st to 10th	Night	16% 7% 2 6% 6% 3 5% 4 5% 7% 40%	1800
	11th to 20th	Night	17% 6% 2 4 4 3 4 4 5% 7% 45%	1930
	21st to end	Night	20% 6% 2 4 4 3 4 3 5% 7% 41%	1980
October	1st to 10th	Night	21% 9% 3 5% 5% 4 4 5% 5% 5% 34%	2016
	11th to 20th	Night	21% 11% 4 7% 7% 4 4 5% 4 6% 28%	2254
	21st to end	Night	25% 14% 4 7% 5% 4 4 4 4 5% 25%	2574
November	1st to 10th	Night	19% 13% 5% 7% 6% 4 5% 5% 4 6% 27%	2407
	11th to 20th	Night	18% 13% 6% 10% 7% 3 4 4 4 5% 27%	2470
	21st to end	Night	18% 16% 7% 11% 8% 3 4 3 3 4 23%	2643
December	1st to 10th	Night	20% 23% 8% 11% 7% 3 5% 4 3 3 13%	2660
	11th to 20th	Night	19% 19% 7% 15% 8% 4 4 3 4 3 15%	3288
	21st to end	Night	23% 17% 6% 12% 7% 4 4 4 3 4 17%	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	78% 3 8% 9% 2	1518
	11th to 20th	Day	73% 5% 8% 9% 5%	1520
	21st to end	Day	66% 5% 10% 13% 6% 1	1592
February	1st to 10th	Day	75% 5% 5% 11% 4 1	1516
	11th to 20th	Day	71% 5% 9% 9% 5% 1	1744
	21st to end	Day	66% 5% 9% 12% 7% 2	1480
March	1st to 10th	Day	65% 4 9% 14% 6% 2	1800
	11th to 20th	Day	60% 5% 11% 13% 10% 1	1852
	21st to end	Day	61% 3 7% 18% 9% 2	2362
April	1st to 10th	Day	63% 4 9% 15% 8% 1	2160
	11th to 20th	Day	54% 4 8% 20% 13% 1	2156
	21st to end	Day	59% 5% 9% 16% 9% 2	2340
May	1st to 10th	Day	54% 5% 8% 20% 13% 1	2391
	11th to 20th	Day	50% 6% 10% 19% 12% 2	2482
	21st to end	Day	50% 8% 13% 17% 11% 1	2725
June	1st to 10th	Day	54% 7% 12% 17% 8% 1	2520
	11th to 20th	Day	46% 7% 11% 23% 12% 1	2520
	21st to end	Day	54% 8% 11% 18% 8%	2520
July	1st to 10th	Day	44% 9% 13% 24% 10%	2450
	11th to 20th	Day	45% 9% 13% 26% 6%	2445
	21st to end	Day	49% 8% 14% 22% 6% 1	2591
August	1st to 10th	Day	49% 9% 16% 22% 5%	2487
	11th to 20th	Day	46% 9% 16% 20% 10%	2298
	21st to end	Day	45% 7% 14% 23% 11%	2376
September	1st to 10th	Day	43% 8% 13% 25% 10% 1	2160
	11th to 20th	Day	42% 6% 11% 28% 13%	2030
	21st to end	Day	45% 8% 13% 24% 10% 1	1980
October	1st to 10th	Day	57% 6% 12% 17% 8%	1940
	11th to 20th	Day	57% 6% 14% 17% 6%	1706
	21st to end	Day	67% 4 8% 13% 6% 1	1782
November	1st to 10th	Day	58% 6% 11% 17% 7%	1671
	11th to 20th	Day	65% 5% 9% 11% 7% 1	1710
	21st to end	Day	67% 6% 13% 11% 2	1535
December	1st to 10th	Day	76% 4 9% 8% 3	1520
	11th to 20th	Day	69% 4 9% 14% 5%	1906
	21st to end	Day	74% 6% 8% 9% 4	2772
January	1st to 10th	Night	74% 6% 8% 8% 3	2649
	11th to 20th	Night	73% 5% 7% 10% 4	2660
	21st to end	Night	65% 6% 9% 12% 7% 1	2798
February	1st to 10th	Night	71% 5% 8% 11% 5%	2440
	11th to 20th	Night	67% 6% 8% 13% 6%	2112
	21st to end	Night	63% 4 9% 13% 10% 1	1776
March	1st to 10th	Night	63% 5% 9% 16% 7% 1	2160
	11th to 20th	Night	59% 6% 9% 14% 10% 2	2107
	21st to end	Night	58% 4 7% 18% 10% 3	1993
April	1st to 10th	Night	60% 4 9% 15% 11% 1	1800
	11th to 20th	Night	53% 5% 8% 20% 13% 1	1753
	21st to end	Night	55% 5% 8% 17% 12% 2	1620
May	1st to 10th	Night	54% 5% 6% 18% 14% 2	1584
	11th to 20th	Night	50% 6% 10% 17% 15% 2	1416
	21st to end	Night	48% 8% 11% 20% 12% 1	1551
June	1st to 10th	Night	51% 6% 11% 23% 8% 1	1440
	11th to 20th	Night	44% 8% 12% 23% 11% 3	1440
	21st to end	Night	49% 9% 14% 20% 8%	1440
July	1st to 10th	Night	42% 10% 13% 22% 13% 1	1400
	11th to 20th	Night	38% 10% 15% 29% 8%	1392
	21st to end	Night	42% 9% 16% 25% 8%	1486
August	1st to 10th	Night	38% 9% 21% 25% 7%	1422
	11th to 20th	Night	42% 9% 17% 22% 10%	1587
	21st to end	Night	41% 8% 16% 24% 11%	1980
September	1st to 10th	Night	41% 9% 13% 25% 12% 1	1800
	11th to 20th	Night	37% 8% 15% 28% 11% 1	1930
	21st to end	Night	42% 7% 12% 25% 11% 1	1980
October	1st to 10th	Night	50% 7% 10% 21% 11%	2016
	11th to 20th	Night	56% 8% 11% 20% 6%	2254
	21st to end	Night	60% 7% 11% 14% 8% 1	2574
November	1st to 10th	Night	57% 6% 12% 17% 7% 1	2407
	11th to 20th	Night	59% 6% 11% 14% 8% 2	2470
	21st to end	Night	65% 7% 10% 14% 4	2643
December	1st to 10th	Night	76% 5% 8% 8% 2	2660
	11th to 20th	Night	75% 5% 6% 9% 5%	3288
	21st to end	Night	73% 5% 7% 13% 2	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	27% 21% 30% 19% 3	180
	11th to 20th	Day	26% 29% 29% 12% 4 1	180
	21st to end	Day	25% 22% 33% 13% 7% 1	178
February	1st to 10th	Day	40% 28% 22% 9% 1	194
	11th to 20th	Day	30% 27% 30% 10% 2	403
	21st to end	Day	29% 23% 29% 16% 2	346
March	1st to 10th	Day	31% 20% 30% 15% 4	420
	11th to 20th	Day	29% 25% 27% 13% 5% 1	420
	21st to end	Day	32% 22% 23% 15% 7% 1	462
April	1st to 10th	Day	36% 17% 28% 14% 5% 1	420
	11th to 20th	Day	36% 17% 25% 14% 6% 3	412
	21st to end	Day	33% 18% 30% 12% 5% 2	420
May	1st to 10th	Day	33% 17% 26% 17% 6% 2	423
	11th to 20th	Day	24% 18% 31% 19% 6% 2	447
	21st to end	Day	21% 18% 33% 21% 6% 1	485
June	1st to 10th	Day	31% 15% 31% 17% 5% 1	450
	11th to 20th	Day	22% 15% 29% 23% 10% 1	450
	21st to end	Day	24% 14% 34% 18% 8% 2	450
July	1st to 10th	Day	19% 10% 33% 25% 11% 2	445
	11th to 20th	Day	16% 11% 38% 25% 8% 3	444
	21st to end	Day	19% 10% 35% 25% 10% 1	488
August	1st to 10th	Day	17% 12% 28% 28% 14% 2	446
	11th to 20th	Day	18% 8% 28% 28% 15% 3	439
	21st to end	Day	19% 14% 25% 23% 12% 6%	495
September	1st to 10th	Day	19% 12% 28% 22% 13% 6%	450
	11th to 20th	Day	20% 12% 23% 20% 17% 7%	450
	21st to end	Day	18% 14% 26% 23% 14% 4	450
October	1st to 10th	Day	27% 15% 24% 17% 13% 4	450
	11th to 20th	Day	30% 18% 24% 17% 11% 1	403
	21st to end	Day	38% 18% 21% 17% 5%	396
November	1st to 10th	Day	31% 19% 28% 17% 4 1	365
	11th to 20th	Day	28% 24% 28% 12% 6% 2	370
	21st to end	Day	32% 19% 33% 14% 2	195
December	1st to 10th	Day	32% 23% 24% 16% 4 2	180
	11th to 20th	Day	32% 26% 28% 12% 1 1	180
	21st to end	Day	36% 23% 25% 13% 3	198
January	1st to 10th	Night	28% 21% 30% 18% 3	760
	11th to 20th	Night	25% 22% 32% 17% 4	760
	21st to end	Night	20% 19% 33% 22% 5% 1	800
February	1st to 10th	Night	23% 21% 33% 19% 3	720
	11th to 20th	Night	20% 23% 35% 18% 3	703
	21st to end	Night	27% 17% 32% 22% 2	592
March	1st to 10th	Night	28% 18% 28% 22% 3	720
	11th to 20th	Night	29% 17% 28% 20% 6%	720
	21st to end	Night	27% 18% 26% 21% 8% 1	792
April	1st to 10th	Night	31% 16% 28% 20% 5%	720
	11th to 20th	Night	27% 17% 27% 21% 8%	689
	21st to end	Night	30% 15% 28% 20% 7%	540
May	1st to 10th	Night	26% 11% 31% 25% 8% 1	504
	11th to 20th	Night	22% 11% 30% 28% 8% 1	354
	21st to end	Night	20% 12% 29% 30% 8% 1	389
June	1st to 10th	Night	28% 7% 29% 27% 9%	360
	11th to 20th	Night	20% 7% 28% 33% 13%	360
	21st to end	Night	17% 9% 27% 36% 11% 1	360
July	1st to 10th	Night	14% 6% 30% 35% 15%	350
	11th to 20th	Night	11% 3 27% 39% 18% 1	348
	21st to end	Night	13% 5% 26% 40% 15%	394
August	1st to 10th	Night	18% 5% 16% 41% 20%	358
	11th to 20th	Night	15% 6% 22% 36% 19% 2	523
	21st to end	Night	16% 6% 24% 33% 19% 2	792
September	1st to 10th	Night	17% 8% 24% 35% 14% 1	720
	11th to 20th	Night	19% 9% 21% 31% 19% 2	720
	21st to end	Night	22% 9% 28% 24% 16% 1	720
October	1st to 10th	Night	26% 12% 23% 25% 12% 1	720
	11th to 20th	Night	28% 15% 26% 21% 9% 1	720
	21st to end	Night	30% 17% 28% 22% 3	792
November	1st to 10th	Night	28% 16% 30% 20% 5% 1	740
	11th to 20th	Night	26% 19% 29% 16% 9% 1	760
	21st to end	Night	28% 23% 26% 16% 5% 1	760
December	1st to 10th	Night	31% 24% 25% 16% 4	760
	11th to 20th	Night	29% 20% 29% 18% 4	760
	21st to end	Night	33% 22% 25% 17% 3	836

Page generated at 2024-01-19 09:28:30. Version ac07

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