Lander
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lander 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	4 4 2 4 4 2 4 5% 6% 9% 57%	74707
	Night	4 5% 2 4 3 2 3 4 5% 9% 59%	75048
Transparency	Day	23% 6% 14% 28% 21% 8%	74420
	Night	24% 5% 14% 29% 21% 8%	74857
Seeing	Day	7% 9% 30% 33% 17% 4	14531
	Night	6% 6% 28% 41% 16% 3	24764

By Month

Percentage Cloud Cover SW (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	3 2 5% 4 2 4 5% 6% 12% 56%	1518
	11th to 20th	Day	1 4 2 4 5% 3 4 4 6% 10% 57%	1591
	21st to end	Day	1 4 3 6% 5% 3 3 5% 6% 10% 55%	1782
February	1st to 10th	Day	4 2 6% 5% 3 5% 4 8% 10% 52%	1620
	11th to 20th	Day	1 4 3 6% 5% 2 3 5% 6% 10% 55%	1575
	21st to end	Day	3 3 5% 4 3 4 6% 5% 10% 56%	1394
March	1st to 10th	Day	1 4 1 5% 4 3 3 4 6% 9% 59%	1970
	11th to 20th	Day	3 6% 2 4 3 2 3 3 4 11% 57%	1980
	21st to end	Day	5% 6% 2 5% 4 3 4 5% 7% 10% 48%	2178
April	1st to 10th	Day	4 8% 2 5% 3 2 4 4 5% 10% 53%	2150
	11th to 20th	Day	4 9% 4 6% 5% 2 4 4 7% 9% 46%	2131
	21st to end	Day	9% 9% 3 4 5% 3 5% 5% 6% 10% 43%	2326
May	1st to 10th	Day	10% 7% 1 4 4 3 5% 6% 6% 10% 44%	2340
	11th to 20th	Day	11% 7% 2 4 3 2 4 5% 6% 10% 45%	2470
	21st to end	Day	9% 5% 2 3 4 3 5% 6% 8% 10% 43%	2724
June	1st to 10th	Day	4 3 1 3 4 3 4 4 8% 12% 54%	2520
	11th to 20th	Day	4 3 1 3 3 2 4 5% 6% 9% 61%	2520
	21st to end	Day	2 2 1 2 2 3 4 5% 6% 8% 66%	2520
July	1st to 10th	Day	3 3 1 2 3 3 5% 5% 7% 8% 61%	2520
	11th to 20th	Day	1 2 1 3 3 2 5% 5% 6% 9% 63%	2520
	21st to end	Day	3 2 1 3 4 2 4 5% 6% 9% 61%	2573
August	1st to 10th	Day	4 2 1 2 4 2 5% 6% 7% 9% 59%	2328
	11th to 20th	Day	3 2 1 3 3 2 4 5% 6% 9% 62%	2299
	21st to end	Day	2 2 1 2 3 2 3 4 6% 8% 67%	2448
September	1st to 10th	Day	4 2 2 3 3 3 3 4 4 7% 65%	2160
	11th to 20th	Day	5% 3 1 2 3 2 3 3 4 6% 68%	2096
	21st to end	Day	6% 2 1 3 3 2 4 4 4 5% 67%	1933
October	1st to 10th	Day	10% 7% 2 4 3 2 4 4 3 7% 55%	1800
	11th to 20th	Day	6% 4 1 2 2 2 3 4 5% 7% 65%	1800
	21st to end	Day	3 5% 2 3 4 2 3 5% 6% 6% 61%	1980
November	1st to 10th	Day	1 4 2 3 2 2 3 5% 6% 9% 64%	1661
	11th to 20th	Day	1 3 2 4 4 2 4 3 6% 9% 63%	1520
	21st to end	Day	1 5% 3 5% 3 2 3 5% 6% 8% 60%	1520
December	1st to 10th	Day	1 3 2 6% 4 2 3 5% 5% 10% 58%	1520
	11th to 20th	Day	1 4 2 3 3 2 3 4 6% 11% 61%	1926
	21st to end	Day	2 5% 2 5% 3 2 3 4 6% 10% 58%	2794
January	1st to 10th	Night	3 2 4 4 3 4 5% 7% 10% 58%	2647
	11th to 20th	Night	1 4 3 5% 4 2 3 4 5% 11% 58%	2427
	21st to end	Night	1 6% 3 5% 4 2 5% 4 6% 9% 55%	2574
February	1st to 10th	Night	1 5% 3 5% 6% 2 5% 5% 5% 9% 54%	2340
	11th to 20th	Night	1 5% 2 5% 5% 2 4 4 6% 10% 56%	2272
	21st to end	Night	1 5% 3 6% 5% 4 4 5% 5% 6% 57%	1862
March	1st to 10th	Night	2 4 2 4 5% 3 4 5% 6% 10% 56%	1987
	11th to 20th	Night	3 6% 2 5% 5% 2 3 4 5% 9% 56%	1980
	21st to end	Night	5% 7% 3 4 4 2 4 5% 6% 10% 50%	2178
April	1st to 10th	Night	5% 7% 2 3 3 2 3 4 5% 9% 56%	1810
	11th to 20th	Night	7% 8% 3 5% 5% 3 3 5% 6% 8% 47%	1777
	21st to end	Night	9% 8% 3 4 4 3 4 4 5% 7% 50%	1632
May	1st to 10th	Night	13% 6% 2 4 2 3 4 4 5% 7% 52%	1620
	11th to 20th	Night	13% 6% 2 4 4 3 3 5% 7% 9% 45%	1422
	21st to end	Night	11% 5% 1 4 4 3 4 5% 7% 10% 46%	1552
June	1st to 10th	Night	5% 3 2 3 3 2 3 3 5% 10% 60%	1440
	11th to 20th	Night	7% 3 1 3 3 2 3 4 5% 7% 62%	1440
	21st to end	Night	3 3 1 2 2 2 3 4 5% 6% 69%	1440
July	1st to 10th	Night	3 1 1 3 3 1 3 4 5% 8% 68%	1440
	11th to 20th	Night	2 1 1 1 1 2 2 3 5% 7% 76%	1440
	21st to end	Night	3 2 1 2 1 3 4 5% 8% 70%	1743
August	1st to 10th	Night	2 1 1 2 3 2 3 5% 6% 10% 65%	1611
	11th to 20th	Night	3 2 1 2 2 1 3 3 4 8% 71%	1602
	21st to end	Night	3 2 1 2 3 2 3 3 5% 8% 69%	1908
September	1st to 10th	Night	5% 3 1 2 2 2 3 3 4 6% 69%	1800
	11th to 20th	Night	5% 3 1 2 2 2 4 4 5% 7% 66%	1862
	21st to end	Night	7% 4 1 2 2 1 2 2 3 7% 69%	2026
October	1st to 10th	Night	9% 8% 2 4 4 3 3 4 3 5% 56%	2160
	11th to 20th	Night	6% 5% 1 3 3 2 3 4 4 6% 63%	2160
	21st to end	Night	3 6% 2 5% 3 2 3 3 4 6% 60%	2376
November	1st to 10th	Night	1 3 1 4 3 2 4 5% 6% 10% 61%	2396
	11th to 20th	Night	2 5% 2 3 4 2 3 4 6% 9% 59%	2660
	21st to end	Night	2 6% 3 4 4 2 3 4 6% 10% 57%	2660
December	1st to 10th	Night	1 4 2 5% 5% 2 3 5% 6% 10% 58%	2660
	11th to 20th	Night	1 4 2 3 3 2 4 4 7% 12% 57%	3271
	21st to end	Night	1 6% 3 4 3 2 3 5% 6% 10% 56%	4873

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	22% 5% 23% 32% 15% 3	1519
	11th to 20th	Day	25% 4 19% 30% 20% 3	1591
	21st to end	Day	26% 5% 20% 32% 15% 3	1782
February	1st to 10th	Day	27% 5% 18% 33% 13% 3	1620
	11th to 20th	Day	25% 5% 19% 31% 15% 5%	1584
	21st to end	Day	24% 5% 19% 28% 20% 5%	1394
March	1st to 10th	Day	23% 5% 17% 35% 17% 3	1970
	11th to 20th	Day	24% 3 19% 34% 19% 2	1980
	21st to end	Day	30% 7% 17% 33% 12% 1	2178
April	1st to 10th	Day	27% 6% 20% 30% 13% 4	2150
	11th to 20th	Day	33% 7% 16% 26% 17% 1	2134
	21st to end	Day	37% 6% 12% 30% 14% 1	2326
May	1st to 10th	Day	34% 7% 15% 28% 14% 2	2340
	11th to 20th	Day	33% 8% 15% 29% 13% 3	2474
	21st to end	Day	30% 8% 19% 28% 13% 1	2724
June	1st to 10th	Day	22% 7% 20% 25% 21% 6%	2520
	11th to 20th	Day	19% 6% 13% 21% 25% 15%	2520
	21st to end	Day	15% 6% 7% 26% 31% 15%	2520
July	1st to 10th	Day	18% 8% 8% 24% 26% 16%	2451
	11th to 20th	Day	16% 5% 7% 21% 27% 24%	2445
	21st to end	Day	19% 6% 7% 21% 26% 22%	2430
August	1st to 10th	Day	19% 7% 9% 24% 24% 17%	2313
	11th to 20th	Day	18% 5% 7% 26% 28% 17%	2299
	21st to end	Day	15% 4 8% 21% 34% 18%	2448
September	1st to 10th	Day	20% 5% 7% 18% 32% 19%	2160
	11th to 20th	Day	18% 4 7% 28% 27% 16%	2096
	21st to end	Day	20% 4 5% 28% 34% 7%	1933
October	1st to 10th	Day	31% 5% 10% 28% 21% 5%	1800
	11th to 20th	Day	20% 5% 13% 35% 22% 6%	1800
	21st to end	Day	24% 3 16% 29% 22% 4	1980
November	1st to 10th	Day	18% 7% 16% 31% 22% 7%	1661
	11th to 20th	Day	20% 4 19% 30% 22% 5%	1520
	21st to end	Day	23% 5% 16% 30% 21% 5%	1520
December	1st to 10th	Day	24% 5% 20% 30% 16% 5%	1520
	11th to 20th	Day	19% 6% 23% 35% 17% 1	1924
	21st to end	Day	23% 5% 11% 32% 22% 6%	2794
January	1st to 10th	Night	22% 4 22% 33% 16% 2	2647
	11th to 20th	Night	23% 4 20% 31% 18% 3	2427
	21st to end	Night	28% 4 15% 33% 15% 4	2574
February	1st to 10th	Night	29% 5% 15% 33% 15% 3	2340
	11th to 20th	Night	26% 4 16% 30% 19% 4	2273
	21st to end	Night	28% 3 15% 26% 23% 5%	1862
March	1st to 10th	Night	25% 5% 15% 35% 19% 2	1987
	11th to 20th	Night	27% 4 16% 32% 19% 2	1980
	21st to end	Night	30% 5% 18% 31% 12% 2	2178
April	1st to 10th	Night	26% 6% 18% 26% 18% 6%	1810
	11th to 20th	Night	35% 4 17% 25% 17% 2	1777
	21st to end	Night	35% 4 12% 31% 18% 1	1632
May	1st to 10th	Night	33% 5% 14% 29% 15% 4	1620
	11th to 20th	Night	35% 6% 14% 30% 12% 3	1423
	21st to end	Night	32% 7% 18% 27% 15% 2	1552
June	1st to 10th	Night	22% 6% 22% 26% 20% 5%	1440
	11th to 20th	Night	22% 3 11% 22% 23% 18%	1440
	21st to end	Night	15% 6% 8% 19% 32% 20%	1440
July	1st to 10th	Night	14% 4 13% 26% 25% 18%	1400
	11th to 20th	Night	11% 3 6% 20% 33% 27%	1392
	21st to end	Night	13% 4 8% 22% 30% 24%	1646
August	1st to 10th	Night	15% 5% 10% 30% 23% 18%	1602
	11th to 20th	Night	14% 4 8% 24% 32% 18%	1602
	21st to end	Night	16% 4 7% 21% 33% 19%	1908
September	1st to 10th	Night	18% 4 8% 18% 29% 23%	1800
	11th to 20th	Night	18% 6% 9% 24% 29% 16%	1862
	21st to end	Night	18% 4 7% 26% 35% 9%	2026
October	1st to 10th	Night	32% 4 10% 25% 21% 8%	2160
	11th to 20th	Night	24% 3 11% 31% 23% 8%	2160
	21st to end	Night	27% 5% 12% 29% 22% 6%	2376
November	1st to 10th	Night	20% 7% 16% 29% 22% 6%	2396
	11th to 20th	Night	22% 4 16% 32% 21% 4	2660
	21st to end	Night	24% 4 15% 30% 21% 5%	2660
December	1st to 10th	Night	24% 5% 18% 31% 18% 4	2660
	11th to 20th	Night	21% 6% 21% 35% 16% 2	3272
	21st to end	Night	26% 5% 10% 32% 21% 6%	4873

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	3 5% 34% 39% 15% 4	270
	11th to 20th	Day	4 5% 32% 39% 19% 1	246
	21st to end	Day	4 6% 36% 38% 15% 2	264
February	1st to 10th	Day	2 13% 55% 25% 4 1	240
	11th to 20th	Day	2 10% 47% 32% 10%	240
	21st to end	Day	4 12% 44% 30% 10% 1	198
March	1st to 10th	Day	4 18% 43% 26% 8% 1	410
	11th to 20th	Day	9% 17% 40% 25% 8% 2	420
	21st to end	Day	13% 16% 32% 26% 10% 2	462
April	1st to 10th	Day	12% 20% 30% 26% 10% 2	420
	11th to 20th	Day	11% 27% 31% 21% 8% 1	412
	21st to end	Day	17% 16% 29% 24% 12% 1	420
May	1st to 10th	Day	16% 13% 33% 24% 11% 2	423
	11th to 20th	Day	19% 8% 18% 31% 18% 6%	617
	21st to end	Day	13% 9% 22% 29% 21% 6%	679
June	1st to 10th	Day	4 9% 26% 33% 22% 6%	630
	11th to 20th	Day	7% 11% 27% 35% 17% 2	630
	21st to end	Day	3 6% 25% 38% 23% 4	630
July	1st to 10th	Day	4 4 18% 38% 28% 6%	621
	11th to 20th	Day	1 5% 27% 38% 26% 3	618
	21st to end	Day	3 2 27% 40% 21% 7%	515
August	1st to 10th	Day	4 4 26% 39% 23% 4	447
	11th to 20th	Day	3 4 25% 38% 23% 8%	437
	21st to end	Day	2 7% 27% 34% 23% 7%	495
September	1st to 10th	Day	4 6% 29% 36% 18% 8%	450
	11th to 20th	Day	6% 9% 28% 28% 22% 7%	450
	21st to end	Day	9% 7% 26% 33% 19% 7%	403
October	1st to 10th	Day	11% 5% 24% 30% 21% 9%	270
	11th to 20th	Day	7% 13% 24% 31% 17% 8%	270
	21st to end	Day	7% 7% 35% 36% 14% 1	297
November	1st to 10th	Day	7% 8% 38% 31% 10% 6%	270
	11th to 20th	Day	6% 7% 36% 33% 15% 3	270
	21st to end	Day	4 6% 29% 44% 15% 2	270
December	1st to 10th	Day	3 5% 33% 41% 15% 3	270
	11th to 20th	Day	7% 5% 39% 38% 10% 1	270
	21st to end	Day	8% 9% 35% 31% 12% 5%	297
January	1st to 10th	Night	2 8% 30% 41% 16% 2	950
	11th to 20th	Night	2 10% 30% 41% 14% 3	789
	21st to end	Night	4 6% 30% 46% 10% 3	792
February	1st to 10th	Night	4 6% 41% 40% 8% 1	720
	11th to 20th	Night	3 8% 36% 38% 12% 2	704
	21st to end	Night	4 9% 39% 36% 10% 1	592
March	1st to 10th	Night	4 7% 37% 40% 10% 2	720
	11th to 20th	Night	6% 7% 32% 40% 13% 2	720
	21st to end	Night	9% 9% 30% 40% 11% 1	792
April	1st to 10th	Night	10% 9% 34% 36% 9% 1	550
	11th to 20th	Night	10% 9% 35% 35% 11%	533
	21st to end	Night	13% 8% 28% 36% 13% 2	540
May	1st to 10th	Night	17% 6% 23% 35% 17% 3	540
	11th to 20th	Night	17% 3 17% 38% 21% 3	531
	21st to end	Night	14% 5% 18% 38% 22% 3	584
June	1st to 10th	Night	5% 5% 23% 38% 23% 5%	540
	11th to 20th	Night	8% 5% 31% 42% 14% 1	540
	21st to end	Night	4 2 19% 45% 27% 2	540
July	1st to 10th	Night	3 1 16% 43% 33% 4	525
	11th to 20th	Night	2 2 20% 51% 24% 2	522
	21st to end	Night	4 2 10% 48% 33% 3	591
August	1st to 10th	Night	2 2 13% 49% 32% 3	537
	11th to 20th	Night	3 1 15% 48% 30% 3	534
	21st to end	Night	3 2 17% 44% 28% 5%	594
September	1st to 10th	Night	7% 3 20% 43% 21% 6%	540
	11th to 20th	Night	6% 2 21% 44% 21% 5%	602
	21st to end	Night	9% 3 21% 38% 20% 8%	720
October	1st to 10th	Night	12% 4 24% 37% 18% 5%	720
	11th to 20th	Night	8% 4 25% 41% 18% 4	720
	21st to end	Night	7% 4 29% 43% 12% 5%	792
November	1st to 10th	Night	4 6% 35% 40% 11% 3	845
	11th to 20th	Night	4 11% 31% 41% 10% 3	950
	21st to end	Night	4 8% 28% 44% 14% 2	950
December	1st to 10th	Night	3 7% 33% 44% 12% 1	950
	11th to 20th	Night	4 5% 34% 45% 11% 1	950
	21st to end	Night	5% 9% 33% 40% 12% 2	1045

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