Lozano Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lozano Observatory clear sky chart from 2005-11-06 to 2025-12-18.

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	14% 6% 2 5% 4 4 4 3 5% 7% 45%	127140
	Night	16% 6% 2 5% 3 3 3 3 5% 7% 48%	124199
Transparency	Day	36% 6% 10% 20% 18% 10%	130932
	Night	35% 5% 10% 19% 18% 12%	128470
Seeing	Day	15% 8% 22% 30% 21% 4	16219
	Night	17% 7% 24% 35% 16% 1	26179

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	19% 8% 2 4 2 3 3 2 4 5% 49%	4077
	11th to 20th	Day	17% 6% 2 4 2 2 2 3 4 5% 53%	4080
	21st to end	Day	28% 6% 2 4 2 2 2 2 4 6% 41%	4925
February	1st to 10th	Day	20% 8% 2 6% 3 2 2 3 4 5% 45%	2000
	11th to 20th	Day	20% 7% 2 6% 3 3 3 3 4 5% 43%	1949
	21st to end	Day	20% 7% 2 4 3 2 3 2 4 6% 47%	1650
March	1st to 10th	Day	15% 6% 2 5% 3 3 3 2 4 5% 52%	4848
	11th to 20th	Day	16% 7% 2 5% 4 3 3 2 3 5% 50%	4980
	21st to end	Day	21% 8% 2 4 3 3 3 2 4 6% 45%	5462
April	1st to 10th	Day	15% 7% 3 6% 5% 5% 4 3 4 5% 44%	2200
	11th to 20th	Day	21% 6% 2 5% 3 4 4 4 4 5% 42%	2188
	21st to end	Day	17% 8% 3 6% 5% 4 4 3 4 5% 42%	2518
May	1st to 10th	Day	23% 7% 3 6% 4 4 4 3 5% 6% 33%	5862
	11th to 20th	Day	11% 5% 2 6% 4 4 4 3 5% 8% 47%	5862
	21st to end	Day	13% 7% 3 7% 5% 5% 5% 4 7% 9% 36%	6434
June	1st to 10th	Day	6% 4 2 5% 5% 5% 5% 5% 7% 9% 46%	2600
	11th to 20th	Day	8% 6% 2 6% 5% 4 5% 5% 6% 10% 43%	2600
	21st to end	Day	8% 7% 2 6% 6% 6% 6% 5% 7% 9% 37%	2600
July	1st to 10th	Day	13% 7% 3 7% 6% 5% 5% 4 6% 8% 36%	5900
	11th to 20th	Day	7% 5% 2 6% 5% 6% 6% 5% 7% 11% 40%	5900
	21st to end	Day	8% 5% 2 7% 5% 6% 5% 5% 7% 10% 40%	6422
August	1st to 10th	Day	2 2 1 3 3 3 4 3 6% 9% 67%	4115
	11th to 20th	Day	4 2 1 4 3 3 4 4 9% 11% 54%	3846
	21st to end	Day	5% 4 1 6% 5% 6% 5% 5% 7% 11% 46%	4150
September	1st to 10th	Day	10% 6% 2 8% 5% 6% 6% 4 6% 7% 41%	2200
	11th to 20th	Day	11% 5% 2 6% 5% 5% 5% 5% 8% 7% 41%	2200
	21st to end	Day	9% 5% 2 5% 4 4 5% 4 5% 8% 50%	2200
October	1st to 10th	Day	7% 4 2 4 4 3 5% 4 5% 7% 56%	2200
	11th to 20th	Day	12% 5% 2 5% 4 4 4 3 4 6% 52%	2094
	21st to end	Day	11% 5% 2 4 3 3 4 2 4 5% 57%	2200
November	1st to 10th	Day	15% 8% 2 7% 4 3 3 2 4 6% 45%	2058
	11th to 20th	Day	13% 6% 2 5% 4 4 3 3 4 6% 50%	1958
	21st to end	Day	19% 8% 2 5% 4 4 4 3 3 4 44%	1890
December	1st to 10th	Day	29% 9% 3 5% 3 3 3 2 4 5% 36%	3030
	11th to 20th	Day	20% 7% 2 5% 4 3 3 3 4 5% 43%	3454
	21st to end	Day	15% 6% 2 4 2 2 3 2 3 4 57%	4488
January	1st to 10th	Night	21% 6% 1 3 2 2 2 2 4 5% 50%	5888
	11th to 20th	Night	13% 4 1 2 2 2 3 2 4 5% 62%	5900
	21st to end	Night	32% 5% 2 4 2 2 3 2 4 5% 40%	6096
February	1st to 10th	Night	20% 6% 2 4 3 3 3 2 4 5% 48%	2400
	11th to 20th	Night	21% 7% 1 4 3 3 3 2 3 5% 48%	2338
	21st to end	Night	22% 6% 2 4 4 2 3 2 5% 5% 45%	1980
March	1st to 10th	Night	19% 7% 1 5% 4 3 3 3 4 6% 45%	5008
	11th to 20th	Night	17% 7% 2 5% 3 3 3 2 4 5% 49%	4980
	21st to end	Night	24% 7% 2 4 3 2 3 2 4 5% 42%	5467
April	1st to 10th	Night	15% 7% 1 5% 4 3 3 3 5% 7% 45%	2200
	11th to 20th	Night	21% 6% 2 5% 3 3 3 3 4 5% 45%	2155
	21st to end	Night	21% 7% 2 6% 4 3 3 3 4 5% 44%	1880
May	1st to 10th	Night	27% 8% 2 5% 4 4 3 3 5% 5% 34%	4053
	11th to 20th	Night	12% 4 2 5% 3 4 4 3 6% 8% 48%	4053
	21st to end	Night	15% 7% 2 7% 4 4 5% 3 7% 9% 36%	4443
June	1st to 10th	Night	6% 4 2 4 3 2 4 4 5% 9% 56%	1800
	11th to 20th	Night	6% 4 1 4 3 3 4 4 6% 9% 55%	1800
	21st to end	Night	8% 6% 2 5% 4 4 4 5% 6% 9% 49%	1800
July	1st to 10th	Night	11% 7% 2 7% 5% 4 4 4 6% 9% 40%	4078
	11th to 20th	Night	6% 4 1 5% 4 5% 5% 5% 7% 11% 46%	4077
	21st to end	Night	10% 6% 2 6% 4 4 5% 4 7% 8% 44%	4449
August	1st to 10th	Night	1 1 2 2 2 3 3 4 8% 72%	3039
	11th to 20th	Night	3 2 1 4 3 3 4 4 7% 13% 56%	3213
	21st to end	Night	5% 4 1 4 4 4 4 4 6% 10% 54%	3752
September	1st to 10th	Night	10% 5% 2 6% 5% 4 5% 4 5% 8% 47%	2200
	11th to 20th	Night	10% 6% 3 5% 5% 4 4 4 6% 8% 45%	2200
	21st to end	Night	9% 4 2 6% 3 4 4 3 6% 8% 51%	2200
October	1st to 10th	Night	7% 4 1 4 3 3 4 3 5% 7% 59%	2200
	11th to 20th	Night	13% 5% 2 4 3 3 3 2 5% 5% 56%	2285
	21st to end	Night	15% 4 1 4 2 2 2 2 3 4 61%	2640
November	1st to 10th	Night	14% 6% 2 5% 3 2 2 2 4 5% 54%	2460
	11th to 20th	Night	13% 5% 2 5% 2 3 4 3 4 6% 55%	2657
	21st to end	Night	19% 6% 2 5% 2 3 3 2 4 5% 47%	2730
December	1st to 10th	Night	28% 8% 3 6% 3 3 3 2 3 5% 36%	4380
	11th to 20th	Night	23% 7% 2 5% 3 2 3 2 3 4 46%	4908
	21st to end	Night	19% 6% 1 4 2 2 2 2 3 4 55%	6490

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	39% 3 5% 18% 23% 12%	4078
	11th to 20th	Day	35% 2 4 17% 22% 20%	4080
	21st to end	Day	46% 3 4 11% 24% 13%	4925
February	1st to 10th	Day	44% 3 5% 13% 20% 16%	2000
	11th to 20th	Day	43% 4 6% 17% 19% 12%	1959
	21st to end	Day	39% 4 7% 16% 18% 15%	1650
March	1st to 10th	Day	35% 3 6% 18% 16% 22%	4848
	11th to 20th	Day	38% 4 4 8% 16% 29%	4980
	21st to end	Day	41% 4 7% 19% 19% 10%	5464
April	1st to 10th	Day	42% 5% 8% 15% 17% 13%	2200
	11th to 20th	Day	44% 4 6% 16% 17% 13%	2188
	21st to end	Day	43% 6% 6% 18% 17% 10%	2518
May	1st to 10th	Day	48% 7% 9% 18% 14% 4	5900
	11th to 20th	Day	34% 6% 12% 20% 20% 8%	5866
	21st to end	Day	39% 9% 10% 28% 14% 1	6447
June	1st to 10th	Day	30% 9% 14% 27% 18% 3	2600
	11th to 20th	Day	34% 6% 11% 26% 18% 4	2600
	21st to end	Day	40% 8% 14% 24% 12% 3	2600
July	1st to 10th	Day	44% 7% 15% 28% 5% 1	5836
	11th to 20th	Day	35% 8% 18% 27% 11% 1	5831
	21st to end	Day	35% 9% 16% 24% 14% 2	6240
August	1st to 10th	Day	15% 4 11% 45% 24% 1	4101
	11th to 20th	Day	20% 8% 24% 35% 11% 2	3882
	21st to end	Day	29% 9% 18% 23% 18% 2	4149
September	1st to 10th	Day	40% 7% 11% 17% 17% 8%	2200
	11th to 20th	Day	38% 8% 12% 20% 17% 5%	2200
	21st to end	Day	32% 6% 11% 21% 18% 13%	2200
October	1st to 10th	Day	18% 4 7% 11% 25% 35%	3590
	11th to 20th	Day	26% 4 8% 19% 23% 21%	3386
	21st to end	Day	26% 5% 6% 17% 29% 16%	3538
November	1st to 10th	Day	41% 3 8% 17% 18% 13%	2058
	11th to 20th	Day	36% 3 8% 16% 20% 16%	1958
	21st to end	Day	44% 4 5% 15% 19% 12%	1890
December	1st to 10th	Day	53% 3 5% 16% 14% 10%	3030
	11th to 20th	Day	41% 6% 8% 13% 19% 13%	3452
	21st to end	Day	32% 3 4 17% 27% 16%	4488
January	1st to 10th	Night	36% 3 5% 18% 21% 15%	5888
	11th to 20th	Night	27% 2 4 19% 27% 21%	5900
	21st to end	Night	49% 2 4 10% 20% 15%	6096
February	1st to 10th	Night	39% 4 7% 13% 19% 19%	2400
	11th to 20th	Night	41% 3 6% 17% 18% 16%	2338
	21st to end	Night	41% 4 6% 16% 17% 16%	1980
March	1st to 10th	Night	40% 4 6% 17% 16% 17%	5008
	11th to 20th	Night	37% 5% 7% 11% 14% 26%	4980
	21st to end	Night	43% 4 8% 18% 16% 10%	5467
April	1st to 10th	Night	37% 5% 10% 18% 15% 15%	2200
	11th to 20th	Night	41% 4 9% 14% 16% 16%	2155
	21st to end	Night	43% 6% 9% 18% 15% 10%	1880
May	1st to 10th	Night	50% 6% 8% 16% 14% 6%	4080
	11th to 20th	Night	32% 6% 11% 21% 20% 9%	4054
	21st to end	Night	41% 8% 13% 27% 10% 1	4452
June	1st to 10th	Night	24% 7% 16% 31% 20% 2	1800
	11th to 20th	Night	24% 6% 14% 29% 21% 5%	1800
	21st to end	Night	30% 7% 19% 28% 14% 2	1800
July	1st to 10th	Night	39% 9% 22% 25% 4 1	4035
	11th to 20th	Night	29% 10% 22% 28% 10% 1	4026
	21st to end	Night	34% 9% 19% 23% 12% 2	4320
August	1st to 10th	Night	11% 5% 16% 47% 20%	3029
	11th to 20th	Night	19% 8% 31% 33% 7% 1	3243
	21st to end	Night	25% 10% 23% 25% 15% 2	3752
September	1st to 10th	Night	33% 8% 16% 20% 15% 7%	2200
	11th to 20th	Night	34% 8% 16% 23% 14% 5%	2200
	21st to end	Night	30% 6% 15% 21% 16% 12%	2200
October	1st to 10th	Night	16% 4 7% 16% 20% 36%	3590
	11th to 20th	Night	21% 3 9% 17% 29% 20%	3719
	21st to end	Night	25% 4 7% 18% 30% 16%	4252
November	1st to 10th	Night	35% 3 8% 18% 21% 15%	2460
	11th to 20th	Night	31% 5% 9% 18% 21% 17%	2657
	21st to end	Night	40% 4 7% 17% 19% 14%	2730
December	1st to 10th	Night	53% 3 5% 14% 13% 11%	4380
	11th to 20th	Night	42% 4 6% 10% 20% 17%	4909
	21st to end	Night	34% 3 4 13% 27% 18%	6490

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	25% 14% 37% 18% 4 1	300
	11th to 20th	Day	26% 15% 29% 24% 4 1	300
	21st to end	Day	23% 15% 34% 20% 7%	330
February	1st to 10th	Day	33% 14% 26% 20% 7%	300
	11th to 20th	Day	29% 18% 32% 16% 4 1	300
	21st to end	Day	27% 16% 40% 14% 2	249
March	1st to 10th	Day	21% 19% 41% 17% 2	300
	11th to 20th	Day	17% 18% 45% 17% 4	300
	21st to end	Day	23% 16% 38% 18% 5%	330
April	1st to 10th	Day	22% 18% 37% 22% 2	300
	11th to 20th	Day	19% 20% 36% 21% 5%	306
	21st to end	Day	20% 11% 41% 24% 4	618
May	1st to 10th	Day	21% 12% 35% 25% 6%	703
	11th to 20th	Day	15% 12% 29% 31% 10% 1	725
	21st to end	Day	16% 6% 30% 35% 12% 1	789
June	1st to 10th	Day	7% 3 18% 44% 24% 3	730
	11th to 20th	Day	10% 1 17% 48% 23% 2	730
	21st to end	Day	11% 2 13% 37% 30% 8%	730
July	1st to 10th	Day	11% 2 10% 34% 35% 8%	721
	11th to 20th	Day	7% 1 7% 33% 46% 6%	718
	21st to end	Day	6% 1 6% 34% 44% 9%	794
August	1st to 10th	Day	3 6% 30% 47% 13%	659
	11th to 20th	Day	6% 1 5% 38% 40% 11%	517
	21st to end	Day	6% 2 6% 27% 44% 16%	486
September	1st to 10th	Day	14% 7% 26% 42% 11%	330
	11th to 20th	Day	5% 2 4 32% 45% 11%	330
	21st to end	Day	10% 1 11% 27% 40% 12%	330
October	1st to 10th	Day	6% 2 15% 38% 33% 7%	330
	11th to 20th	Day	10% 4 21% 39% 22% 4	330
	21st to end	Day	17% 12% 23% 28% 16% 4	363
November	1st to 10th	Day	20% 8% 25% 28% 15% 4	330
	11th to 20th	Day	18% 11% 24% 31% 15% 2	330
	21st to end	Day	26% 15% 32% 17% 8% 2	330
December	1st to 10th	Day	23% 10% 35% 22% 7% 2	330
	11th to 20th	Day	24% 16% 27% 22% 8% 2	321
	21st to end	Day	21% 10% 38% 23% 7% 1	330
January	1st to 10th	Night	22% 8% 26% 34% 10%	1000
	11th to 20th	Night	22% 10% 30% 30% 8%	1000
	21st to end	Night	25% 9% 27% 33% 6%	927
February	1st to 10th	Night	26% 11% 28% 29% 6%	800
	11th to 20th	Night	28% 12% 29% 26% 5%	784
	21st to end	Night	26% 14% 33% 25% 2	660
March	1st to 10th	Night	25% 11% 33% 28% 3	641
	11th to 20th	Night	22% 12% 33% 28% 5%	600
	21st to end	Night	21% 10% 40% 25% 3	660
April	1st to 10th	Night	17% 11% 41% 27% 3	600
	11th to 20th	Night	23% 11% 35% 28% 3	593
	21st to end	Night	22% 9% 37% 25% 6% 1	600
May	1st to 10th	Night	20% 8% 41% 27% 4	600
	11th to 20th	Night	17% 7% 35% 34% 8%	591
	21st to end	Night	16% 9% 32% 33% 10%	650
June	1st to 10th	Night	8% 2 26% 43% 20% 1	600
	11th to 20th	Night	8% 1 31% 48% 11% 1	600
	21st to end	Night	10% 2 20% 40% 26% 3	600
July	1st to 10th	Night	11% 2 15% 41% 28% 3	585
	11th to 20th	Night	4 2 11% 49% 32% 2	582
	21st to end	Night	7% 1 10% 49% 31% 2	657
August	1st to 10th	Night	2 1 9% 50% 35% 4	597
	11th to 20th	Night	5% 1 8% 51% 32% 3	594
	21st to end	Night	6% 2 5% 40% 42% 5%	660
September	1st to 10th	Night	11% 1 8% 42% 35% 4	600
	11th to 20th	Night	10% 2 9% 40% 37% 3	600
	21st to end	Night	10% 1 13% 37% 36% 3	600
October	1st to 10th	Night	7% 2 13% 47% 29% 4	600
	11th to 20th	Night	14% 4 18% 42% 20% 2	685
	21st to end	Night	16% 8% 21% 34% 18% 2	880
November	1st to 10th	Night	16% 6% 20% 35% 22% 1	820
	11th to 20th	Night	15% 6% 21% 40% 16% 2	977
	21st to end	Night	23% 9% 23% 32% 13% 1	1050
December	1st to 10th	Night	23% 7% 24% 34% 11% 1	1050
	11th to 20th	Night	26% 8% 24% 31% 11%	1036
	21st to end	Night	22% 8% 25% 35% 9%	1100

Page generated at 2025-12-15 00:13:56. Version ac07

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