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 2024-11-11.

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	13% 9% 3 8% 5% 4 4 4 6% 7% 37%	101373
	Night	14% 10% 4 7% 4 4 4 3 5% 6% 38%	97877
Transparency	Day	44% 7% 12% 21% 14% 2	104941
	Night	44% 7% 11% 22% 14% 2	102450
Seeing	Day	18% 15% 31% 23% 10% 3	15830
	Night	18% 12% 31% 27% 11% 1	25669

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% 13% 8% 10% 6% 5% 5% 2 4 5% 28%	2527
	11th to 20th	Day	14% 14% 7% 15% 5% 4 4 8% 6% 4 19%	2530
	21st to end	Day	19% 25% 6% 10% 5% 3 3 2 4 6% 18%	2851
February	1st to 10th	Day	15% 15% 5% 9% 7% 5% 5% 4 4 6% 27%	1754
	11th to 20th	Day	14% 11% 5% 8% 6% 4 4 3 5% 5% 34%	1848
	21st to end	Day	15% 14% 5% 10% 5% 4 3 3 5% 7% 30%	1570
March	1st to 10th	Day	16% 15% 4 7% 4 4 4 3 4 6% 34%	3120
	11th to 20th	Day	10% 7% 4 8% 5% 5% 5% 4 6% 8% 39%	3268
	21st to end	Day	19% 13% 6% 13% 7% 4 5% 4 5% 5% 20%	4165
April	1st to 10th	Day	17% 14% 3 8% 5% 5% 3 4 5% 6% 31%	2280
	11th to 20th	Day	16% 10% 3 7% 5% 5% 5% 4 5% 6% 35%	2254
	21st to end	Day	20% 9% 3 7% 4 5% 5% 3 5% 6% 33%	2388
May	1st to 10th	Day	18% 7% 2 6% 5% 4 5% 4 6% 8% 34%	4082
	11th to 20th	Day	16% 6% 2 6% 4 4 4 4 5% 6% 42%	4291
	21st to end	Day	11% 6% 2 6% 4 4 5% 4 6% 10% 42%	4824
June	1st to 10th	Day	10% 6% 2 6% 4 5% 4 4 6% 8% 45%	2660
	11th to 20th	Day	10% 6% 3 6% 5% 4 4 4 7% 7% 45%	2660
	21st to end	Day	11% 6% 2 8% 4 5% 6% 5% 7% 8% 37%	2660
July	1st to 10th	Day	11% 8% 3 7% 5% 5% 6% 5% 7% 9% 33%	4440
	11th to 20th	Day	7% 5% 2 5% 4 4 5% 4 7% 9% 48%	4440
	21st to end	Day	8% 6% 2 7% 6% 5% 6% 4 7% 8% 40%	4813
August	1st to 10th	Day	10% 6% 2 7% 4 5% 5% 4 6% 8% 43%	4327
	11th to 20th	Day	10% 5% 2 6% 4 5% 6% 4 7% 9% 42%	3759
	21st to end	Day	8% 4 2 7% 4 4 4 4 6% 9% 47%	4180
September	1st to 10th	Day	13% 5% 2 6% 4 4 4 4 5% 7% 47%	2280
	11th to 20th	Day	11% 5% 2 4 3 3 4 3 5% 7% 51%	2156
	21st to end	Day	11% 7% 3 5% 5% 4 6% 4 6% 7% 43%	2090
October	1st to 10th	Day	12% 7% 2 7% 4 4 3 3 5% 6% 46%	2047
	11th to 20th	Day	19% 9% 3 7% 5% 4 4 3 4 7% 36%	1882
	21st to end	Day	20% 9% 3 7% 4 3 4 4 5% 6% 35%	1881
November	1st to 10th	Day	13% 9% 4 6% 4 3 3 3 5% 6% 45%	1762
	11th to 20th	Day	16% 12% 4 8% 5% 4 5% 3 5% 6% 33%	1710
	21st to end	Day	19% 10% 3 9% 5% 4 4 2 4 5% 36%	1653
December	1st to 10th	Day	16% 13% 4 10% 6% 4 4 3 5% 5% 31%	1520
	11th to 20th	Day	13% 14% 5% 11% 6% 4 4 4 5% 6% 29%	1918
	21st to end	Day	21% 23% 8% 13% 5% 4 4 2 3 3 15%	2783
January	1st to 10th	Night	15% 15% 8% 10% 5% 4 3 3 4 4 29%	4428
	11th to 20th	Night	16% 18% 7% 13% 5% 3 4 5% 6% 4 19%	4440
	21st to end	Night	22% 18% 8% 9% 5% 4 3 3 3 4 22%	4814
February	1st to 10th	Night	15% 14% 4 8% 6% 5% 4 2 4 6% 31%	2424
	11th to 20th	Night	14% 11% 4 8% 5% 4 4 3 5% 5% 37%	2218
	21st to end	Night	18% 12% 3 8% 4 4 3 4 4 5% 36%	1884
March	1st to 10th	Night	18% 11% 3 7% 4 3 3 3 4 5% 39%	3733
	11th to 20th	Night	10% 7% 2 6% 5% 4 4 3 5% 6% 48%	3722
	21st to end	Night	21% 11% 5% 9% 6% 4 4 3 5% 6% 27%	3466
April	1st to 10th	Night	16% 8% 3 6% 5% 3 5% 4 5% 6% 38%	1900
	11th to 20th	Night	19% 8% 3 6% 4 4 4 3 6% 6% 38%	1875
	21st to end	Night	18% 8% 3 6% 5% 4 4 4 6% 6% 37%	1791
May	1st to 10th	Night	16% 8% 3 6% 6% 5% 4 4 5% 7% 36%	2813
	11th to 20th	Night	15% 6% 2 5% 3 5% 5% 5% 7% 8% 39%	2608
	21st to end	Night	12% 7% 2 6% 4 4 4 3 5% 7% 44%	2743
June	1st to 10th	Night	10% 5% 2 6% 4 4 5% 4 6% 7% 48%	1520
	11th to 20th	Night	8% 6% 2 5% 4 4 5% 4 6% 9% 46%	1520
	21st to end	Night	10% 7% 2 5% 4 6% 4 4 8% 9% 41%	1520
July	1st to 10th	Night	12% 5% 2 8% 5% 4 5% 4 6% 8% 39%	2530
	11th to 20th	Night	6% 4 2 6% 4 4 4 3 6% 8% 54%	2530
	21st to end	Night	5% 5% 2 5% 4 6% 6% 5% 7% 8% 46%	2750
August	1st to 10th	Night	6% 5% 2 7% 4 5% 6% 4 6% 8% 47%	2607
	11th to 20th	Night	8% 5% 2 5% 4 4 4 4 6% 8% 51%	3065
	21st to end	Night	8% 4 1 5% 4 4 4 3 6% 8% 52%	3476
September	1st to 10th	Night	10% 6% 2 5% 4 4 4 2 4 7% 53%	1900
	11th to 20th	Night	9% 4 2 4 3 4 3 3 4 8% 55%	2004
	21st to end	Night	11% 6% 2 7% 4 4 4 4 5% 7% 46%	2090
October	1st to 10th	Night	12% 5% 3 6% 4 3 3 3 4 6% 51%	2132
	11th to 20th	Night	17% 7% 2 7% 3 4 3 3 4 6% 45%	2296
	21st to end	Night	20% 10% 3 7% 4 3 4 3 5% 6% 37%	2717
November	1st to 10th	Night	13% 8% 2 6% 4 3 3 3 3 6% 47%	2536
	11th to 20th	Night	14% 11% 3 8% 4 4 4 3 6% 6% 37%	2477
	21st to end	Night	17% 10% 3 7% 5% 4 4 3 5% 5% 37%	2525
December	1st to 10th	Night	17% 12% 4 9% 5% 4 4 3 5% 6% 32%	2660
	11th to 20th	Night	15% 14% 5% 10% 4 4 4 3 4 5% 32%	3279
	21st to end	Night	24% 19% 6% 10% 5% 4 4 3 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	59% 6% 13% 16% 6%	2528
	11th to 20th	Day	63% 6% 11% 12% 8%	2530
	21st to end	Day	68% 7% 8% 12% 5%	2851
February	1st to 10th	Day	58% 6% 12% 13% 9% 2	1754
	11th to 20th	Day	52% 5% 10% 22% 10% 2	1858
	21st to end	Day	53% 8% 12% 18% 7% 2	1570
March	1st to 10th	Day	50% 8% 10% 20% 11% 2	3120
	11th to 20th	Day	40% 8% 13% 28% 10% 1	3268
	21st to end	Day	63% 11% 13% 10% 3	4165
April	1st to 10th	Day	53% 7% 10% 19% 11%	2280
	11th to 20th	Day	47% 8% 10% 20% 11% 4	2254
	21st to end	Day	49% 8% 13% 16% 12% 2	2388
May	1st to 10th	Day	43% 11% 12% 23% 11% 1	4120
	11th to 20th	Day	40% 8% 12% 26% 14%	4295
	21st to end	Day	35% 9% 14% 19% 19% 4	4837
June	1st to 10th	Day	35% 9% 13% 24% 18% 2	2660
	11th to 20th	Day	36% 8% 11% 23% 20% 3	2660
	21st to end	Day	40% 10% 14% 21% 13% 2	2660
July	1st to 10th	Day	45% 8% 14% 20% 11% 2	4371
	11th to 20th	Day	30% 7% 18% 28% 17% 1	4365
	21st to end	Day	38% 8% 17% 15% 19% 3	4662
August	1st to 10th	Day	36% 8% 16% 26% 13% 1	4312
	11th to 20th	Day	35% 8% 12% 29% 16% 1	3796
	21st to end	Day	32% 7% 13% 26% 20% 2	4179
September	1st to 10th	Day	35% 8% 13% 23% 18% 4	2280
	11th to 20th	Day	30% 7% 11% 28% 21% 3	2156
	21st to end	Day	38% 7% 10% 24% 19% 1	2090
October	1st to 10th	Day	26% 4 8% 31% 29% 2	3398
	11th to 20th	Day	34% 4 12% 26% 23% 1	3110
	21st to end	Day	44% 4 9% 26% 14% 3	3081
November	1st to 10th	Day	40% 6% 14% 23% 15% 2	1762
	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	58% 7% 10% 16% 8% 1	4428
	11th to 20th	Night	65% 6% 11% 12% 6%	4440
	21st to end	Night	66% 5% 10% 13% 6%	4814
February	1st to 10th	Night	55% 5% 12% 16% 11% 2	2424
	11th to 20th	Night	48% 5% 11% 21% 13% 1	2219
	21st to end	Night	51% 5% 11% 19% 11% 3	1884
March	1st to 10th	Night	47% 6% 12% 22% 10% 3	3733
	11th to 20th	Night	36% 7% 11% 26% 18% 2	3722
	21st to end	Night	57% 9% 11% 16% 6% 1	3466
April	1st to 10th	Night	44% 7% 13% 22% 12% 2	1900
	11th to 20th	Night	45% 7% 9% 19% 16% 4	1875
	21st to end	Night	45% 8% 11% 21% 13% 2	1791
May	1st to 10th	Night	45% 8% 13% 20% 12% 2	2840
	11th to 20th	Night	37% 10% 16% 25% 10% 1	2609
	21st to end	Night	36% 9% 12% 17% 20% 6%	2751
June	1st to 10th	Night	32% 8% 13% 24% 19% 3	1520
	11th to 20th	Night	32% 8% 12% 24% 22% 2	1520
	21st to end	Night	38% 10% 14% 20% 17% 2	1520
July	1st to 10th	Night	42% 7% 15% 20% 11% 5%	2490
	11th to 20th	Night	26% 7% 14% 30% 20% 2	2482
	21st to end	Night	32% 8% 17% 17% 22% 4	2662
August	1st to 10th	Night	32% 8% 15% 27% 17% 1	2598
	11th to 20th	Night	30% 7% 14% 28% 20% 1	3094
	21st to end	Night	29% 6% 13% 32% 17% 4	3476
September	1st to 10th	Night	31% 6% 13% 24% 23% 3	1900
	11th to 20th	Night	28% 6% 9% 29% 27% 2	2004
	21st to end	Night	36% 7% 11% 28% 15% 2	2090
October	1st to 10th	Night	22% 4 7% 37% 27% 2	3561
	11th to 20th	Night	36% 3 8% 24% 27% 2	3807
	21st to end	Night	40% 4 9% 25% 18% 3	4467
November	1st to 10th	Night	38% 6% 9% 26% 18% 3	2536
	11th to 20th	Night	47% 6% 12% 22% 12% 2	2477
	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% 23% 35% 14% 2	270
	21st to end	Day	26% 21% 34% 14% 4	297
February	1st to 10th	Day	26% 21% 39% 12% 2	270
	11th to 20th	Day	28% 23% 32% 16% 1	270
	21st to end	Day	26% 26% 36% 9% 2	225
March	1st to 10th	Day	22% 32% 35% 10% 1	270
	11th to 20th	Day	28% 22% 35% 12% 3	298
	21st to end	Day	29% 20% 29% 16% 4 1	506
April	1st to 10th	Day	26% 20% 31% 18% 5%	460
	11th to 20th	Day	24% 24% 24% 19% 8% 2	452
	21st to end	Day	24% 20% 32% 17% 7% 1	460
May	1st to 10th	Day	23% 17% 33% 18% 7% 2	463
	11th to 20th	Day	20% 15% 35% 21% 8% 2	606
	21st to end	Day	15% 14% 33% 22% 12% 4	734
June	1st to 10th	Day	11% 12% 35% 28% 11% 3	680
	11th to 20th	Day	13% 9% 36% 29% 11% 3	680
	21st to end	Day	13% 13% 36% 25% 9% 4	680
July	1st to 10th	Day	8% 7% 29% 28% 18% 10%	671
	11th to 20th	Day	12% 8% 31% 28% 15% 6%	668
	21st to end	Day	7% 7% 34% 32% 13% 5%	739
August	1st to 10th	Day	8% 5% 29% 33% 18% 8%	619
	11th to 20th	Day	10% 7% 22% 33% 20% 8%	479
	21st to end	Day	7% 5% 24% 35% 22% 7%	539
September	1st to 10th	Day	15% 8% 26% 31% 17% 4	490
	11th to 20th	Day	10% 5% 23% 31% 23% 7%	490
	21st to end	Day	15% 16% 25% 25% 15% 5%	490
October	1st to 10th	Day	15% 14% 30% 24% 14% 3	447
	11th to 20th	Day	24% 26% 29% 16% 5%	300
	21st to end	Day	33% 19% 33% 12% 3	330
November	1st to 10th	Day	21% 19% 34% 20% 5% 2	300
	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% 19% 34% 19% 4 1	950
	21st to end	Night	21% 15% 36% 24% 3	1045
February	1st to 10th	Night	23% 15% 36% 22% 4	904
	11th to 20th	Night	20% 17% 36% 24% 3	743
	21st to end	Night	23% 18% 37% 19% 3	628
March	1st to 10th	Night	22% 17% 34% 21% 6%	760
	11th to 20th	Night	17% 14% 39% 23% 6%	749
	21st to end	Night	25% 13% 32% 23% 7%	627
April	1st to 10th	Night	20% 16% 35% 23% 6% 1	570
	11th to 20th	Night	22% 16% 30% 24% 7%	563
	21st to end	Night	21% 14% 34% 24% 8%	570
May	1st to 10th	Night	19% 11% 34% 28% 7% 1	570
	11th to 20th	Night	18% 8% 29% 32% 12% 1	561
	21st to end	Night	14% 6% 29% 32% 19%	617
June	1st to 10th	Night	11% 5% 29% 39% 16%	570
	11th to 20th	Night	10% 6% 32% 39% 13% 1	570
	21st to end	Night	12% 7% 30% 35% 16% 1	570
July	1st to 10th	Night	8% 3 18% 43% 24% 3	555
	11th to 20th	Night	8% 4 25% 37% 24% 2	552
	21st to end	Night	5% 2 24% 46% 22% 2	624
August	1st to 10th	Night	5% 3 18% 44% 26% 3	567
	11th to 20th	Night	6% 3 19% 39% 29% 4	564
	21st to end	Night	8% 3 19% 39% 29% 2	627
September	1st to 10th	Night	12% 5% 22% 33% 25% 3	570
	11th to 20th	Night	10% 4 22% 33% 27% 4	674
	21st to end	Night	13% 9% 26% 30% 20% 3	760
October	1st to 10th	Night	13% 7% 27% 34% 17% 2	760
	11th to 20th	Night	21% 15% 30% 25% 9%	760
	21st to end	Night	25% 15% 30% 21% 8%	836
November	1st to 10th	Night	17% 15% 38% 21% 9% 1	780
	11th to 20th	Night	21% 18% 33% 23% 5% 1	763
	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 2024-11-08 05:44:45. Version ac07

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