Levis
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Levis clear sky chart from 2005-11-06 to 2026-03-18.

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% 10% 3 8% 5% 5% 5% 4 6% 7% 31%	130630
	Night	18% 12% 4 9% 5% 5% 5% 4 5% 6% 28%	130887
Transparency	Day	52% 7% 14% 18% 8% 1	134085
	Night	56% 6% 12% 17% 8% 1	135520
Seeing	Day	23% 15% 30% 21% 9% 2	16880
	Night	24% 12% 30% 27% 8%	25543

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% 17% 6% 12% 5% 4 3 3 4 5% 27%	4661
	11th to 20th	Day	11% 17% 8% 15% 7% 6% 5% 3 4 4 21%	4650
	21st to end	Day	6% 12% 5% 10% 6% 5% 5% 4 7% 8% 32%	5124
February	1st to 10th	Day	10% 14% 5% 12% 7% 5% 5% 4 6% 5% 27%	1683
	11th to 20th	Day	13% 15% 5% 10% 5% 5% 5% 3 5% 5% 28%	2034
	21st to end	Day	12% 14% 4 10% 7% 5% 5% 4 5% 6% 29%	1730
March	1st to 10th	Day	20% 14% 5% 10% 6% 5% 4 3 4 4 26%	4576
	11th to 20th	Day	14% 14% 4 8% 5% 5% 4 4 6% 6% 30%	4821
	21st to end	Day	17% 14% 3 8% 4 4 4 3 4 5% 34%	5804
April	1st to 10th	Day	21% 12% 3 8% 5% 5% 4 4 4 5% 29%	2400
	11th to 20th	Day	20% 8% 2 7% 5% 4 4 3 5% 6% 37%	2471
	21st to end	Day	23% 9% 2 8% 4 4 4 4 4 6% 31%	2600
May	1st to 10th	Day	26% 9% 3 7% 4 4 4 3 5% 6% 29%	6017
	11th to 20th	Day	21% 7% 3 7% 5% 5% 5% 4 6% 8% 30%	6318
	21st to end	Day	19% 8% 3 8% 5% 5% 6% 5% 6% 7% 29%	7013
June	1st to 10th	Day	19% 7% 2 8% 5% 6% 6% 5% 8% 9% 27%	3000
	11th to 20th	Day	18% 7% 3 6% 4 5% 5% 5% 6% 8% 35%	3000
	21st to end	Day	22% 8% 3 8% 6% 5% 5% 4 6% 7% 27%	3000
July	1st to 10th	Day	16% 7% 3 8% 5% 5% 6% 4 7% 9% 28%	6419
	11th to 20th	Day	15% 6% 3 7% 4 5% 6% 4 7% 9% 34%	6360
	21st to end	Day	11% 5% 2 6% 4 4 5% 4 7% 9% 42%	6926
August	1st to 10th	Day	15% 5% 2 7% 4 6% 6% 6% 7% 10% 32%	4536
	11th to 20th	Day	19% 7% 3 8% 5% 5% 5% 4 6% 9% 30%	4175
	21st to end	Day	20% 6% 2 6% 4 4 4 4 5% 7% 38%	4477
September	1st to 10th	Day	15% 7% 3 7% 4 3 4 5% 6% 9% 38%	2400
	11th to 20th	Day	16% 6% 2 4 3 3 3 3 5% 7% 47%	2220
	21st to end	Day	19% 6% 2 7% 4 4 4 3 5% 8% 38%	2200
October	1st to 10th	Day	19% 7% 2 7% 5% 5% 4 4 5% 7% 34%	2200
	11th to 20th	Day	22% 7% 3 10% 5% 5% 5% 4 6% 7% 25%	1830
	21st to end	Day	25% 12% 3 8% 5% 4 4 4 4 6% 24%	1980
November	1st to 10th	Day	19% 12% 3 9% 5% 5% 5% 3 4 6% 30%	1851
	11th to 20th	Day	21% 14% 4 9% 5% 5% 4 3 5% 4 26%	1890
	21st to end	Day	22% 16% 5% 10% 5% 4 4 3 4 5% 22%	1521
December	1st to 10th	Day	18% 16% 4 10% 6% 6% 5% 4 5% 6% 21%	2350
	11th to 20th	Day	20% 13% 5% 10% 6% 5% 4 4 4 4 26%	2688
	21st to end	Day	21% 15% 4 10% 5% 4 4 4 5% 5% 24%	3705
January	1st to 10th	Night	15% 18% 6% 13% 6% 5% 5% 3 4 4 22%	8234
	11th to 20th	Night	12% 22% 7% 16% 7% 5% 4 3 4 4 16%	8235
	21st to end	Night	6% 12% 6% 13% 7% 6% 6% 4 7% 8% 25%	9057
February	1st to 10th	Night	11% 14% 5% 13% 7% 5% 5% 4 4 6% 28%	2936
	11th to 20th	Night	13% 16% 6% 11% 6% 5% 4 4 5% 6% 26%	2468
	21st to end	Night	14% 14% 4 10% 5% 4 4 3 5% 5% 30%	2076
March	1st to 10th	Night	23% 14% 4 9% 5% 4 5% 3 4 5% 25%	5484
	11th to 20th	Night	15% 14% 4 9% 6% 6% 5% 4 5% 7% 24%	5292
	21st to end	Night	19% 16% 4 9% 5% 3 4 3 3 4 30%	5111
April	1st to 10th	Night	21% 14% 3 7% 4 4 4 4 5% 5% 28%	2000
	11th to 20th	Night	20% 9% 2 7% 5% 4 4 4 5% 6% 33%	1877
	21st to end	Night	24% 10% 3 8% 4 2 3 3 5% 5% 34%	1800
May	1st to 10th	Night	24% 8% 3 7% 5% 4 5% 4 5% 6% 28%	3966
	11th to 20th	Night	26% 8% 3 7% 5% 4 4 3 5% 6% 29%	3575
	21st to end	Night	20% 7% 3 7% 4 5% 4 4 6% 8% 34%	3850
June	1st to 10th	Night	22% 7% 2 7% 5% 5% 5% 3 7% 7% 28%	1400
	11th to 20th	Night	19% 7% 2 7% 6% 5% 4 4 6% 6% 35%	1400
	21st to end	Night	22% 9% 3 8% 5% 4 5% 3 5% 7% 30%	1400
July	1st to 10th	Night	16% 7% 3 7% 6% 5% 6% 5% 7% 9% 31%	3525
	11th to 20th	Night	21% 6% 2 6% 5% 4 5% 3 5% 7% 35%	3600
	21st to end	Night	12% 5% 3 7% 5% 5% 5% 4 6% 7% 41%	3926
August	1st to 10th	Night	18% 7% 3 8% 4 5% 5% 4 5% 8% 34%	2586
	11th to 20th	Night	18% 8% 3 8% 5% 5% 6% 5% 6% 7% 30%	2867
	21st to end	Night	20% 7% 3 7% 4 5% 4 4 5% 6% 34%	3417
September	1st to 10th	Night	17% 6% 2 7% 5% 4 4 3 5% 7% 40%	2000
	11th to 20th	Night	16% 6% 2 6% 3 4 4 3 5% 6% 45%	2180
	21st to end	Night	18% 7% 3 6% 4 4 3 3 4 7% 40%	2200
October	1st to 10th	Night	18% 7% 3 6% 4 4 5% 4 6% 7% 36%	2200
	11th to 20th	Night	23% 9% 3 7% 5% 5% 5% 4 5% 4 31%	2567
	21st to end	Night	24% 10% 3 8% 3 4 5% 3 5% 6% 28%	2860
November	1st to 10th	Night	20% 11% 4 7% 6% 5% 3 4 4 6% 30%	2667
	11th to 20th	Night	19% 11% 3 10% 4 4 4 3 5% 5% 30%	2730
	21st to end	Night	22% 16% 5% 9% 6% 5% 5% 3 4 5% 22%	3096
December	1st to 10th	Night	17% 15% 7% 11% 8% 6% 6% 4 5% 5% 17%	5060
	11th to 20th	Night	22% 13% 5% 11% 6% 4 4 4 5% 5% 22%	5741
	21st to end	Night	21% 18% 5% 9% 5% 4 4 4 4 5% 23%	7504

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	60% 5% 9% 17% 8%	4662
	11th to 20th	Day	66% 8% 7% 14% 5% 1	4680
	21st to end	Day	48% 7% 12% 20% 13%	5124
February	1st to 10th	Day	58% 6% 10% 16% 8% 2	1683
	11th to 20th	Day	59% 6% 11% 15% 8% 1	2043
	21st to end	Day	56% 5% 11% 19% 7% 2	1730
March	1st to 10th	Day	59% 7% 9% 11% 10% 3	4579
	11th to 20th	Day	52% 8% 16% 15% 8% 1	4821
	21st to end	Day	53% 5% 8% 18% 14% 2	5804
April	1st to 10th	Day	56% 5% 11% 15% 10% 3	2400
	11th to 20th	Day	48% 6% 10% 22% 11% 2	2471
	21st to end	Day	54% 7% 10% 16% 11% 2	2600
May	1st to 10th	Day	55% 6% 12% 16% 11% 1	6028
	11th to 20th	Day	49% 10% 17% 15% 6% 2	6322
	21st to end	Day	51% 10% 12% 16% 9% 3	7013
June	1st to 10th	Day	50% 11% 13% 18% 7% 1	3000
	11th to 20th	Day	45% 9% 15% 19% 11% 1	3000
	21st to end	Day	56% 8% 12% 16% 9%	3000
July	1st to 10th	Day	50% 8% 15% 21% 6%	6349
	11th to 20th	Day	44% 8% 19% 25% 4	6285
	21st to end	Day	36% 7% 19% 30% 8%	6728
August	1st to 10th	Day	45% 10% 21% 19% 5%	4522
	11th to 20th	Day	49% 10% 20% 17% 5%	4214
	21st to end	Day	46% 7% 16% 19% 11% 1	4477
September	1st to 10th	Day	40% 9% 17% 23% 10%	2400
	11th to 20th	Day	36% 6% 18% 29% 10%	2220
	21st to end	Day	44% 8% 15% 25% 9%	2200
October	1st to 10th	Day	51% 7% 13% 24% 5%	3590
	11th to 20th	Day	52% 7% 19% 21% 2	2955
	21st to end	Day	53% 7% 17% 17% 6%	3180
November	1st to 10th	Day	56% 7% 13% 18% 6%	1851
	11th to 20th	Day	62% 5% 10% 16% 6%	1890
	21st to end	Day	66% 6% 11% 12% 5%	1521
December	1st to 10th	Day	63% 6% 12% 12% 7%	2350
	11th to 20th	Day	60% 6% 10% 14% 10%	2688
	21st to end	Day	62% 7% 10% 12% 8% 1	3705
January	1st to 10th	Night	66% 5% 9% 13% 6%	8234
	11th to 20th	Night	72% 6% 8% 12% 3	8280
	21st to end	Night	55% 6% 11% 16% 11%	9057
February	1st to 10th	Night	58% 5% 10% 17% 8% 1	2936
	11th to 20th	Night	60% 7% 10% 14% 8% 1	2470
	21st to end	Night	56% 6% 9% 17% 11% 1	2076
March	1st to 10th	Night	62% 5% 9% 12% 11% 1	5494
	11th to 20th	Night	59% 8% 13% 13% 7% 1	5293
	21st to end	Night	58% 5% 6% 19% 10% 2	5111
April	1st to 10th	Night	57% 5% 10% 15% 12% 2	2000
	11th to 20th	Night	51% 6% 10% 19% 11% 2	1877
	21st to end	Night	53% 6% 8% 17% 14% 2	1800
May	1st to 10th	Night	55% 7% 11% 15% 11% 1	3972
	11th to 20th	Night	52% 8% 13% 18% 9% 1	3576
	21st to end	Night	47% 7% 13% 16% 14% 2	3851
June	1st to 10th	Night	51% 8% 14% 17% 9% 1	1400
	11th to 20th	Night	46% 9% 11% 19% 12% 3	1400
	21st to end	Night	54% 8% 11% 17% 10%	1400
July	1st to 10th	Night	48% 7% 21% 20% 5%	3485
	11th to 20th	Night	47% 7% 19% 22% 4	3552
	21st to end	Night	42% 8% 17% 26% 7%	3809
August	1st to 10th	Night	48% 8% 16% 22% 6%	2576
	11th to 20th	Night	51% 10% 17% 17% 5% 1	2894
	21st to end	Night	49% 7% 14% 20% 11%	3417
September	1st to 10th	Night	43% 7% 14% 23% 11% 1	2000
	11th to 20th	Night	39% 8% 17% 28% 8% 1	2180
	21st to end	Night	44% 7% 13% 24% 13%	2200
October	1st to 10th	Night	48% 6% 13% 26% 7%	3590
	11th to 20th	Night	52% 6% 15% 23% 3	4181
	21st to end	Night	51% 6% 18% 16% 9%	4610
November	1st to 10th	Night	55% 7% 13% 18% 6% 1	2667
	11th to 20th	Night	55% 8% 13% 15% 8%	2730
	21st to end	Night	65% 7% 11% 12% 5% 1	3096
December	1st to 10th	Night	68% 7% 11% 11% 3	5060
	11th to 20th	Night	64% 6% 8% 17% 5%	5742
	21st to end	Night	63% 5% 9% 16% 6% 1	7504

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% 18% 33% 16% 4 1	220
	11th to 20th	Day	27% 25% 30% 12% 6%	220
	21st to end	Day	17% 22% 36% 21% 4	242
February	1st to 10th	Day	23% 23% 35% 15% 4	223
	11th to 20th	Day	23% 19% 38% 18% 2	530
	21st to end	Day	21% 22% 33% 19% 5%	446
March	1st to 10th	Day	24% 20% 33% 19% 4 1	540
	11th to 20th	Day	25% 18% 34% 16% 5% 2	528
	21st to end	Day	25% 19% 26% 19% 9% 1	550
April	1st to 10th	Day	29% 17% 29% 19% 7%	500
	11th to 20th	Day	28% 15% 28% 20% 7% 1	492
	21st to end	Day	30% 17% 29% 17% 6% 1	500
May	1st to 10th	Day	27% 14% 35% 18% 4 1	503
	11th to 20th	Day	21% 13% 31% 24% 9% 2	527
	21st to end	Day	22% 21% 31% 18% 8% 1	598
June	1st to 10th	Day	21% 14% 29% 26% 8%	730
	11th to 20th	Day	22% 11% 28% 27% 12% 1	730
	21st to end	Day	26% 11% 27% 24% 10% 1	730
July	1st to 10th	Day	17% 14% 30% 26% 12% 1	558
	11th to 20th	Day	16% 10% 35% 26% 11% 2	524
	21st to end	Day	16% 11% 34% 26% 13% 1	576
August	1st to 10th	Day	17% 9% 28% 28% 14% 4	526
	11th to 20th	Day	18% 5% 27% 28% 18% 4	519
	21st to end	Day	21% 11% 25% 22% 15% 6%	583
September	1st to 10th	Day	18% 11% 28% 25% 13% 3	530
	11th to 20th	Day	17% 12% 25% 26% 15% 5%	530
	21st to end	Day	19% 15% 26% 23% 12% 6%	530
October	1st to 10th	Day	22% 13% 29% 22% 11% 3	530
	11th to 20th	Day	26% 16% 28% 19% 9% 2	436
	21st to end	Day	35% 15% 28% 16% 5% 1	462
November	1st to 10th	Day	31% 16% 27% 20% 5%	425
	11th to 20th	Day	28% 20% 30% 16% 7% 1	430
	21st to end	Day	33% 20% 29% 16% 2	230
December	1st to 10th	Day	28% 15% 31% 20% 5% 2	220
	11th to 20th	Day	32% 20% 25% 17% 5% 1	220
	21st to end	Day	30% 20% 32% 13% 4 1	242
January	1st to 10th	Night	24% 17% 34% 21% 3	840
	11th to 20th	Night	24% 17% 33% 21% 5%	840
	21st to end	Night	16% 14% 37% 27% 6%	924
February	1st to 10th	Night	19% 13% 35% 26% 7%	840
	11th to 20th	Night	22% 17% 39% 18% 4	823
	21st to end	Night	23% 14% 32% 27% 4	692
March	1st to 10th	Night	23% 13% 36% 23% 4	840
	11th to 20th	Night	26% 15% 31% 21% 6% 1	829
	21st to end	Night	25% 11% 31% 26% 6% 1	880
April	1st to 10th	Night	28% 15% 28% 24% 5%	800
	11th to 20th	Night	26% 10% 34% 25% 5%	693
	21st to end	Night	30% 12% 30% 22% 6%	600
May	1st to 10th	Night	25% 10% 32% 27% 5%	564
	11th to 20th	Night	27% 8% 27% 31% 6%	394
	21st to end	Night	27% 6% 30% 30% 7%	433
June	1st to 10th	Night	26% 8% 28% 34% 5% 1	400
	11th to 20th	Night	19% 7% 28% 36% 12%	400
	21st to end	Night	22% 8% 26% 35% 9%	400
July	1st to 10th	Night	16% 6% 30% 38% 9% 1	390
	11th to 20th	Night	18% 3 25% 41% 13% 1	388
	21st to end	Night	13% 5% 22% 48% 11%	438
August	1st to 10th	Night	18% 3 18% 45% 17%	398
	11th to 20th	Night	16% 6% 24% 38% 15% 1	587
	21st to end	Night	18% 6% 26% 33% 16% 2	776
September	1st to 10th	Night	20% 6% 26% 33% 14% 1	800
	11th to 20th	Night	20% 6% 24% 32% 17% 2	800
	21st to end	Night	21% 8% 27% 28% 15% 1	800
October	1st to 10th	Night	21% 9% 29% 32% 9% 1	800
	11th to 20th	Night	27% 12% 27% 25% 9% 1	800
	21st to end	Night	29% 12% 31% 23% 5%	880
November	1st to 10th	Night	28% 15% 26% 24% 7%	820
	11th to 20th	Night	25% 15% 27% 24% 8% 1	840
	21st to end	Night	30% 16% 30% 18% 6%	928
December	1st to 10th	Night	30% 14% 29% 21% 6%	950
	11th to 20th	Night	25% 19% 29% 20% 5% 1	950
	21st to end	Night	31% 17% 30% 17% 4	1006

Page generated at 2026-03-15 02:23:50. Version ac07

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