Lombard
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lombard clear sky chart from 2005-11-06 to 2024-01-13.

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	14% 9% 4 7% 6% 3 5% 5% 5% 7% 36%	74807
	Night	15% 9% 4 6% 5% 3 4 4 5% 6% 39%	74957
Transparency	Day	46% 7% 13% 20% 12% 2	74508
	Night	45% 7% 12% 21% 13% 2	74777
Seeing	Day	18% 15% 31% 23% 10% 3	14632
	Night	18% 12% 31% 27% 11% 1	24611

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	15% 12% 5% 8% 7% 3 5% 4 4 6% 31%	1517
	11th to 20th	Day	14% 16% 7% 11% 7% 2 4 5% 4 5% 24%	1456
	21st to end	Day	15% 17% 7% 11% 6% 3 4 4 4 7% 22%	1624
February	1st to 10th	Day	16% 14% 6% 9% 7% 4 5% 4 4 6% 25%	1662
	11th to 20th	Day	15% 11% 5% 7% 7% 3 5% 4 5% 5% 33%	1748
	21st to end	Day	16% 14% 5% 9% 6% 3 4 4 4 7% 30%	1480
March	1st to 10th	Day	17% 13% 5% 8% 6% 3 4 4 4 6% 29%	1800
	11th to 20th	Day	13% 9% 4 7% 6% 3 5% 4 5% 7% 35%	1852
	21st to end	Day	20% 12% 4 8% 7% 3 5% 5% 4 6% 25%	2376
April	1st to 10th	Day	17% 11% 5% 7% 6% 4 5% 4 5% 7% 31%	2160
	11th to 20th	Day	17% 9% 3 6% 5% 4 5% 5% 5% 7% 34%	2134
	21st to end	Day	21% 8% 3 6% 6% 3 5% 4 5% 6% 32%	2262
May	1st to 10th	Day	18% 8% 4 6% 6% 3 5% 5% 6% 8% 30%	2340
	11th to 20th	Day	19% 8% 4 7% 5% 3 5% 5% 5% 7% 34%	2413
	21st to end	Day	13% 6% 3 6% 6% 3 6% 5% 6% 8% 36%	2725
June	1st to 10th	Day	9% 6% 3 5% 5% 4 4 5% 6% 8% 45%	2520
	11th to 20th	Day	10% 6% 3 5% 6% 3 4 4 7% 7% 45%	2520
	21st to end	Day	12% 5% 3 7% 5% 3 6% 6% 7% 9% 37%	2520
July	1st to 10th	Day	8% 5% 2 5% 6% 4 5% 5% 7% 10% 46%	2520
	11th to 20th	Day	10% 5% 2 5% 5% 3 5% 6% 7% 8% 44%	2520
	21st to end	Day	7% 4 2 5% 6% 4 7% 6% 7% 9% 42%	2743
August	1st to 10th	Day	8% 4 2 7% 6% 4 6% 6% 6% 9% 42%	2453
	11th to 20th	Day	9% 5% 2 6% 5% 4 6% 6% 6% 10% 41%	2142
	21st to end	Day	9% 3 2 4 5% 3 5% 6% 8% 10% 46%	2376
September	1st to 10th	Day	13% 5% 2 5% 5% 4 4 5% 5% 7% 45%	2160
	11th to 20th	Day	12% 5% 2 4 4 2 4 4 5% 7% 51%	2043
	21st to end	Day	10% 6% 3 5% 5% 3 5% 5% 6% 7% 43%	1980
October	1st to 10th	Day	13% 7% 3 6% 5% 3 4 4 4 6% 45%	1940
	11th to 20th	Day	20% 8% 3 7% 6% 4 4 4 4 7% 35%	1783
	21st to end	Day	21% 9% 3 6% 6% 2 4 4 4 6% 35%	1782
November	1st to 10th	Day	13% 7% 5% 5% 4 2 4 4 5% 6% 45%	1672
	11th to 20th	Day	16% 10% 5% 7% 6% 3 4 4 4 7% 34%	1710
	21st to end	Day	19% 10% 4 8% 6% 3 4 3 4 5% 36%	1653
December	1st to 10th	Day	16% 12% 5% 8% 7% 3 5% 3 5% 5% 31%	1520
	11th to 20th	Day	13% 13% 6% 10% 7% 3 5% 4 5% 6% 29%	1918
	21st to end	Day	22% 22% 8% 11% 7% 3 4 3 3 3 15%	2783
January	1st to 10th	Night	15% 12% 6% 8% 7% 3 4 4 4 4 34%	2648
	11th to 20th	Night	17% 15% 6% 9% 5% 2 4 3 4 5% 29%	2561
	21st to end	Night	15% 13% 8% 9% 7% 4 4 4 4 6% 26%	2730
February	1st to 10th	Night	16% 14% 5% 8% 7% 3 5% 3 4 6% 30%	2296
	11th to 20th	Night	15% 10% 5% 7% 6% 3 4 4 5% 5% 36%	2098
	21st to end	Night	19% 11% 3 7% 5% 2 4 4 4 5% 36%	1776
March	1st to 10th	Night	16% 11% 4 9% 6% 3 5% 3 4 4 34%	2160
	11th to 20th	Night	14% 7% 4 5% 5% 3 5% 5% 5% 6% 43%	2124
	21st to end	Night	21% 10% 4 6% 6% 3 4 4 5% 7% 31%	1980
April	1st to 10th	Night	16% 7% 4 5% 6% 2 4 5% 5% 6% 38%	1800
	11th to 20th	Night	19% 8% 4 6% 5% 3 4 4 6% 6% 37%	1775
	21st to end	Night	18% 8% 3 6% 5% 3 4 5% 6% 6% 36%	1697
May	1st to 10th	Night	15% 7% 3 5% 6% 4 5% 5% 6% 7% 35%	1620
	11th to 20th	Night	17% 6% 2 4 4 3 4 5% 6% 8% 40%	1479
	21st to end	Night	12% 6% 3 5% 5% 3 4 5% 6% 8% 42%	1551
June	1st to 10th	Night	10% 4 3 5% 5% 3 5% 5% 6% 6% 49%	1440
	11th to 20th	Night	9% 6% 2 5% 4 3 5% 5% 6% 9% 47%	1440
	21st to end	Night	11% 5% 3 4 5% 4 6% 5% 8% 9% 42%	1440
July	1st to 10th	Night	7% 3 2 4 5% 3 5% 5% 7% 10% 50%	1440
	11th to 20th	Night	8% 3 1 5% 4 2 4 5% 7% 9% 52%	1440
	21st to end	Night	5% 3 2 4 4 3 5% 5% 7% 10% 51%	1575
August	1st to 10th	Night	5% 4 1 5% 5% 3 5% 6% 7% 8% 50%	1483
	11th to 20th	Night	7% 3 2 4 4 3 4 5% 6% 9% 53%	1754
	21st to end	Night	8% 4 1 4 4 3 4 4 5% 8% 55%	1980
September	1st to 10th	Night	10% 6% 3 5% 4 3 4 3 4 7% 52%	1800
	11th to 20th	Night	10% 4 2 4 4 3 3 4 4 8% 55%	1898
	21st to end	Night	11% 6% 2 6% 5% 3 3 4 5% 8% 47%	1980
October	1st to 10th	Night	12% 5% 3 5% 5% 2 4 4 4 6% 49%	2019
	11th to 20th	Night	18% 7% 2 6% 4 2 4 3 3 6% 44%	2175
	21st to end	Night	21% 9% 3 6% 4 2 4 4 4 6% 36%	2574
November	1st to 10th	Night	12% 8% 2 6% 4 2 4 4 4 7% 48%	2406
	11th to 20th	Night	14% 10% 3 7% 6% 3 4 3 5% 6% 37%	2470
	21st to end	Night	17% 9% 4 6% 5% 4 4 4 4 6% 37%	2525
December	1st to 10th	Night	17% 11% 4 8% 6% 3 4 4 5% 6% 32%	2660
	11th to 20th	Night	16% 13% 6% 8% 5% 3 4 4 4 5% 32%	3279
	21st to end	Night	24% 18% 6% 8% 6% 3 5% 4 5% 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	56% 5% 13% 16% 10%	1518
	11th to 20th	Day	62% 6% 14% 12% 5% 1	1456
	21st to end	Day	63% 6% 9% 13% 8%	1624
February	1st to 10th	Day	61% 6% 12% 12% 8% 1	1662
	11th to 20th	Day	54% 5% 10% 20% 9% 2	1758
	21st to end	Day	55% 7% 11% 17% 8% 2	1480
March	1st to 10th	Day	56% 7% 10% 19% 7% 1	1800
	11th to 20th	Day	48% 6% 12% 21% 10% 2	1852
	21st to end	Day	60% 7% 12% 15% 5% 1	2376
April	1st to 10th	Day	53% 7% 11% 18% 11%	2160
	11th to 20th	Day	48% 8% 10% 19% 11% 4	2134
	21st to end	Day	50% 8% 13% 16% 11% 2	2262
May	1st to 10th	Day	50% 9% 13% 21% 7%	2340
	11th to 20th	Day	49% 7% 12% 20% 11% 1	2417
	21st to end	Day	44% 9% 12% 18% 15% 2	2725
June	1st to 10th	Day	35% 9% 13% 24% 17% 2	2520
	11th to 20th	Day	37% 8% 11% 22% 19% 3	2520
	21st to end	Day	40% 11% 14% 20% 13% 2	2520
July	1st to 10th	Day	32% 9% 16% 25% 14% 3	2451
	11th to 20th	Day	34% 8% 17% 23% 16% 2	2445
	21st to end	Day	34% 10% 17% 23% 13% 3	2591
August	1st to 10th	Day	36% 9% 17% 26% 11% 2	2438
	11th to 20th	Day	36% 9% 16% 24% 14% 1	2142
	21st to end	Day	30% 9% 15% 25% 18% 4	2376
September	1st to 10th	Day	36% 8% 13% 22% 16% 4	2160
	11th to 20th	Day	32% 7% 12% 28% 19% 3	2043
	21st to end	Day	38% 7% 11% 24% 19% 1	1980
October	1st to 10th	Day	39% 7% 12% 24% 16% 2	1940
	11th to 20th	Day	50% 5% 12% 20% 13% 1	1783
	21st to end	Day	50% 6% 11% 22% 9% 2	1782
November	1st to 10th	Day	39% 6% 14% 23% 16% 2	1672
	11th to 20th	Day	51% 6% 12% 21% 10% 1	1710
	21st to end	Day	52% 5% 11% 23% 9%	1653
December	1st to 10th	Day	55% 7% 12% 18% 8% 1	1520
	11th to 20th	Day	55% 6% 13% 18% 7% 1	1915
	21st to end	Day	76% 5% 7% 8% 3	2783
January	1st to 10th	Night	53% 6% 11% 19% 11% 1	2648
	11th to 20th	Night	58% 7% 13% 14% 8%	2561
	21st to end	Night	59% 5% 11% 15% 9% 1	2730
February	1st to 10th	Night	57% 5% 11% 16% 9% 1	2296
	11th to 20th	Night	50% 5% 12% 20% 12% 1	2099
	21st to end	Night	52% 5% 11% 18% 11% 3	1776
March	1st to 10th	Night	53% 6% 11% 20% 9% 1	2160
	11th to 20th	Night	41% 7% 13% 21% 16% 3	2124
	21st to end	Night	54% 6% 12% 17% 9% 1	1980
April	1st to 10th	Night	44% 7% 13% 22% 12% 2	1800
	11th to 20th	Night	46% 7% 8% 20% 15% 4	1775
	21st to end	Night	46% 8% 11% 21% 12% 2	1697
May	1st to 10th	Night	46% 7% 12% 23% 11%	1620
	11th to 20th	Night	42% 7% 13% 23% 14% 1	1480
	21st to end	Night	39% 8% 14% 19% 17% 2	1552
June	1st to 10th	Night	32% 8% 13% 24% 20% 4	1440
	11th to 20th	Night	33% 8% 12% 23% 22% 2	1440
	21st to end	Night	37% 10% 14% 21% 16% 2	1440
July	1st to 10th	Night	28% 9% 16% 27% 15% 5%	1400
	11th to 20th	Night	27% 8% 15% 27% 20% 4	1392
	21st to end	Night	25% 8% 18% 25% 19% 5%	1487
August	1st to 10th	Night	27% 9% 18% 29% 15% 2	1474
	11th to 20th	Night	26% 8% 18% 27% 19% 2	1754
	21st to end	Night	27% 7% 13% 28% 19% 5%	1980
September	1st to 10th	Night	32% 6% 14% 23% 22% 3	1800
	11th to 20th	Night	29% 6% 9% 30% 25% 2	1898
	21st to end	Night	35% 7% 11% 29% 15% 2	1980
October	1st to 10th	Night	35% 7% 10% 26% 20% 2	2019
	11th to 20th	Night	41% 5% 10% 23% 19% 2	2175
	21st to end	Night	49% 5% 11% 23% 12% 1	2574
November	1st to 10th	Night	37% 6% 9% 26% 18% 3	2406
	11th to 20th	Night	47% 6% 12% 22% 12% 2	2470
	21st to end	Night	49% 5% 12% 22% 11%	2525
December	1st to 10th	Night	52% 7% 12% 20% 9% 1	2660
	11th to 20th	Night	53% 7% 12% 17% 10% 1	3281
	21st to end	Night	69% 7% 9% 11% 4	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% 20% 38% 16% 3	270
	11th to 20th	Day	26% 22% 35% 15% 2	246
	21st to end	Day	24% 22% 36% 14% 4	264
February	1st to 10th	Day	28% 22% 38% 11% 2	240
	11th to 20th	Day	28% 25% 30% 15% 1	240
	21st to end	Day	28% 26% 35% 9% 1 1	198
March	1st to 10th	Day	23% 31% 34% 11% 1	240
	11th to 20th	Day	29% 21% 34% 13% 3	266
	21st to end	Day	29% 19% 28% 17% 5% 1	462
April	1st to 10th	Day	25% 18% 32% 19% 5%	420
	11th to 20th	Day	25% 22% 24% 19% 8% 2	412
	21st to end	Day	24% 20% 31% 17% 7% 1	420
May	1st to 10th	Day	23% 17% 31% 19% 7% 2	423
	11th to 20th	Day	21% 14% 35% 20% 7% 2	559
	21st to end	Day	16% 13% 33% 22% 12% 4	679
June	1st to 10th	Day	9% 11% 36% 29% 12% 4	630
	11th to 20th	Day	13% 10% 34% 29% 11% 3	630
	21st to end	Day	13% 13% 35% 26% 9% 4	630
July	1st to 10th	Day	8% 7% 28% 28% 19% 11%	621
	11th to 20th	Day	12% 8% 30% 29% 15% 6%	618
	21st to end	Day	7% 7% 35% 32% 13% 5%	684
August	1st to 10th	Day	7% 4 28% 34% 18% 9%	572
	11th to 20th	Day	9% 6% 20% 34% 22% 9%	439
	21st to end	Day	7% 6% 25% 34% 21% 7%	495
September	1st to 10th	Day	16% 7% 26% 30% 17% 4	450
	11th to 20th	Day	11% 6% 24% 30% 23% 7%	450
	21st to end	Day	13% 16% 24% 25% 16% 5%	450
October	1st to 10th	Day	16% 14% 30% 24% 13% 3	410
	11th to 20th	Day	26% 27% 30% 13% 4	270
	21st to end	Day	35% 18% 33% 11% 3	297
November	1st to 10th	Day	19% 19% 34% 19% 6% 2	270
	11th to 20th	Day	27% 23% 30% 15% 5%	270
	21st to end	Day	26% 20% 36% 17% 2	270
December	1st to 10th	Day	20% 27% 36% 13% 4	270
	11th to 20th	Day	23% 23% 38% 13% 4	270
	21st to end	Day	27% 27% 34% 10% 2	297
January	1st to 10th	Night	20% 17% 39% 20% 4	950
	11th to 20th	Night	24% 18% 34% 19% 4 1	915
	21st to end	Night	21% 16% 36% 25% 3	990
February	1st to 10th	Night	24% 15% 36% 20% 4	856
	11th to 20th	Night	21% 17% 35% 24% 3	703
	21st to end	Night	24% 17% 36% 19% 3	592
March	1st to 10th	Night	22% 16% 34% 22% 6%	720
	11th to 20th	Night	17% 13% 39% 24% 7%	710
	21st to end	Night	24% 12% 32% 24% 7% 1	594
April	1st to 10th	Night	20% 15% 35% 24% 6% 1	540
	11th to 20th	Night	22% 15% 29% 25% 8%	533
	21st to end	Night	21% 13% 34% 24% 8%	540
May	1st to 10th	Night	19% 10% 35% 28% 7% 1	540
	11th to 20th	Night	19% 8% 28% 32% 13% 1	531
	21st to end	Night	14% 5% 29% 32% 20%	584
June	1st to 10th	Night	11% 4 28% 40% 16%	540
	11th to 20th	Night	11% 6% 31% 39% 13% 1	540
	21st to end	Night	11% 6% 29% 36% 17% 1	540
July	1st to 10th	Night	8% 2 18% 44% 25% 3	525
	11th to 20th	Night	8% 4 26% 37% 23% 2	522
	21st to end	Night	6% 2 25% 45% 21% 2	591
August	1st to 10th	Night	5% 3 17% 45% 25% 4	537
	11th to 20th	Night	6% 4 18% 39% 30% 4	534
	21st to end	Night	9% 3 20% 38% 29% 2	594
September	1st to 10th	Night	12% 5% 23% 33% 24% 3	540
	11th to 20th	Night	10% 5% 23% 32% 26% 4	638
	21st to end	Night	13% 9% 25% 30% 21% 3	720
October	1st to 10th	Night	14% 8% 27% 33% 17% 2	720
	11th to 20th	Night	21% 16% 31% 24% 8%	720
	21st to end	Night	26% 15% 30% 22% 7%	792
November	1st to 10th	Night	16% 15% 39% 21% 9% 1	740
	11th to 20th	Night	21% 18% 33% 23% 5% 1	760
	21st to end	Night	22% 14% 38% 20% 6%	815
December	1st to 10th	Night	24% 16% 37% 20% 4	950
	11th to 20th	Night	23% 14% 37% 22% 4	950
	21st to end	Night	31% 16% 34% 18% 2	1045

Page generated at 2024-01-10 09:16:08. Version ac07

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