Vista Trail
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Vista Trail clear sky chart from 2005-11-06 to 2026-02-16.

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	8% 4 2 4 3 3 3 3 5% 10% 55%	139762
	Night	11% 5% 2 5% 3 3 4 3 5% 7% 52%	138561
Transparency	Day	26% 4 10% 21% 24% 14%	134638
	Night	32% 4 9% 18% 22% 15%	134677
Seeing	Day	11% 10% 23% 29% 21% 5%	17000
	Night	13% 7% 16% 31% 28% 6%	26354

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	18% 7% 2 5% 4 3 4 3 5% 6% 41%	5173
	11th to 20th	Day	14% 5% 2 5% 3 3 3 3 5% 6% 51%	5340
	21st to end	Day	16% 7% 2 7% 4 4 5% 3 5% 7% 40%	5843
February	1st to 10th	Day	20% 5% 2 6% 4 3 4 3 3 5% 44%	1890
	11th to 20th	Day	15% 8% 2 6% 3 4 4 5% 5% 8% 40%	1810
	21st to end	Day	16% 6% 2 4 4 3 4 3 5% 7% 46%	1675
March	1st to 10th	Day	17% 11% 3 6% 3 4 4 3 4 7% 37%	4952
	11th to 20th	Day	16% 5% 2 4 3 3 4 3 5% 8% 47%	5000
	21st to end	Day	20% 8% 2 5% 4 4 4 4 7% 9% 34%	5486
April	1st to 10th	Day	13% 7% 2 6% 4 3 3 4 6% 8% 43%	2387
	11th to 20th	Day	8% 5% 2 5% 4 4 4 3 6% 8% 50%	2369
	21st to end	Day	7% 3 1 4 3 3 4 3 6% 10% 56%	2400
May	1st to 10th	Day	4 2 1 2 2 2 2 2 4 6% 74%	5877
	11th to 20th	Day	3 2 1 3 2 2 2 3 5% 11% 67%	5840
	21st to end	Day	2 2 1 2 1 1 2 2 3 6% 78%	6902
June	1st to 10th	Day	6% 5% 2 3 3 3 4 3 7% 11% 54%	2800
	11th to 20th	Day	1 3 1 2 2 2 3 3 5% 10% 69%	2800
	21st to end	Day	2 2 1 3 3 2 2 3 4 9% 70%	2800
July	1st to 10th	Day	1 2 1 2 2 2 2 2 5% 11% 71%	6232
	11th to 20th	Day	3 1 3 3 3 3 3 8% 19% 54%	5880
	21st to end	Day	3 1 3 2 3 3 3 7% 13% 61%	6402
August	1st to 10th	Day	1 2 1 3 2 3 4 3 5% 12% 65%	5777
	11th to 20th	Day	1 1 1 2 2 1 2 2 7% 12% 68%	5694
	21st to end	Day	1 3 1 4 3 3 4 3 7% 18% 54%	5984
September	1st to 10th	Day	1 2 1 3 2 2 3 3 5% 10% 67%	2400
	11th to 20th	Day	4 4 1 4 2 3 3 2 5% 10% 59%	2350
	21st to end	Day	4 3 1 3 2 2 2 2 4 10% 67%	2130
October	1st to 10th	Day	4 3 1 3 2 2 2 2 4 7% 70%	3280
	11th to 20th	Day	10% 3 1 3 2 2 3 4 5% 9% 58%	3261
	21st to end	Day	8% 5% 2 3 3 3 4 3 5% 9% 54%	3558
November	1st to 10th	Day	10% 4 2 5% 4 4 4 3 6% 9% 50%	2059
	11th to 20th	Day	14% 7% 2 6% 3 4 4 3 5% 6% 45%	1831
	21st to end	Day	12% 5% 1 3 4 4 3 3 5% 8% 51%	1680
December	1st to 10th	Day	10% 4 1 4 3 3 4 4 7% 9% 49%	2700
	11th to 20th	Day	29% 9% 2 7% 3 4 4 4 6% 7% 26%	3108
	21st to end	Day	28% 8% 3 6% 4 3 4 4 4 7% 29%	4092
January	1st to 10th	Night	20% 7% 2 4 3 4 4 3 5% 7% 40%	7740
	11th to 20th	Night	12% 5% 2 5% 3 4 3 2 4 6% 54%	7650
	21st to end	Night	17% 7% 3 7% 4 4 4 3 5% 7% 40%	8371
February	1st to 10th	Night	19% 6% 2 5% 3 3 3 3 4 6% 47%	2730
	11th to 20th	Night	15% 8% 3 6% 4 4 4 3 5% 6% 42%	2587
	21st to end	Night	15% 6% 2 4 3 3 3 3 4 6% 52%	1953
March	1st to 10th	Night	16% 12% 3 6% 4 4 4 3 5% 6% 36%	4942
	11th to 20th	Night	19% 5% 1 5% 3 3 3 3 4 5% 50%	5000
	21st to end	Night	18% 10% 2 6% 3 3 4 3 4 8% 39%	5489
April	1st to 10th	Night	12% 6% 2 6% 4 3 3 3 4 6% 50%	2012
	11th to 20th	Night	8% 6% 2 6% 4 3 3 3 4 6% 54%	1979
	21st to end	Night	7% 4 2 4 3 3 3 3 5% 6% 61%	1999
May	1st to 10th	Night	4 3 1 3 2 2 2 2 3 6% 72%	4100
	11th to 20th	Night	3 3 2 6% 4 4 3 3 4 6% 63%	4055
	21st to end	Night	2 2 1 3 2 1 1 1 3 5% 79%	3972
June	1st to 10th	Night	5% 6% 2 4 3 4 4 4 5% 9% 55%	1600
	11th to 20th	Night	2 3 1 3 3 2 4 3 4 6% 71%	1600
	21st to end	Night	3 3 2 3 3 3 2 2 4 6% 71%	1600
July	1st to 10th	Night	1 3 2 4 2 3 4 4 4 6% 68%	3726
	11th to 20th	Night	1 6% 4 9% 4 6% 5% 3 5% 7% 50%	4100
	21st to end	Night	1 6% 3 7% 4 3 3 3 6% 9% 55%	4472
August	1st to 10th	Night	1 2 1 4 2 4 6% 3 6% 8% 62%	4035
	11th to 20th	Night	1 1 5% 2 3 4 3 5% 9% 67%	4144
	21st to end	Night	2 2 1 5% 3 5% 7% 4 5% 9% 56%	5015
September	1st to 10th	Night	1 2 1 4 2 4 3 3 6% 8% 67%	2000
	11th to 20th	Night	5% 4 2 4 3 3 3 3 5% 8% 61%	2045
	21st to end	Night	4 4 1 4 3 3 2 2 4 6% 67%	2270
October	1st to 10th	Night	3 3 1 4 2 2 2 2 4 4 71%	3920
	11th to 20th	Night	6% 6% 2 4 2 3 3 3 4 6% 60%	3897
	21st to end	Night	10% 4 2 3 2 3 3 3 5% 7% 59%	4253
November	1st to 10th	Night	11% 5% 1 5% 3 4 4 3 6% 8% 51%	2460
	11th to 20th	Night	15% 6% 2 4 3 3 4 4 6% 7% 46%	2783
	21st to end	Night	12% 4 2 5% 3 2 3 4 5% 7% 53%	2940
December	1st to 10th	Night	12% 4 2 5% 3 3 3 3 6% 7% 51%	4700
	11th to 20th	Night	30% 7% 1 5% 4 4 4 3 7% 7% 29%	5316
	21st to end	Night	36% 7% 2 5% 3 3 3 2 3 5% 31%	7106

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	41% 7% 14% 21% 11% 6%	5174
	11th to 20th	Day	33% 4 7% 13% 22% 22%	5340
	21st to end	Day	42% 5% 8% 17% 13% 15%	5843
February	1st to 10th	Day	42% 5% 8% 19% 18% 9%	1890
	11th to 20th	Day	41% 6% 10% 20% 18% 5%	1819
	21st to end	Day	37% 6% 9% 27% 15% 7%	1675
March	1st to 10th	Day	45% 6% 8% 19% 19% 2	4952
	11th to 20th	Day	35% 6% 17% 23% 11% 8%	5000
	21st to end	Day	44% 9% 15% 21% 10% 1	5486
April	1st to 10th	Day	39% 5% 13% 24% 15% 4	2387
	11th to 20th	Day	31% 6% 15% 23% 18% 6%	2372
	21st to end	Day	23% 6% 16% 30% 22% 4	2400
May	1st to 10th	Day	13% 3 10% 26% 30% 18%	5877
	11th to 20th	Day	13% 3 11% 35% 29% 9%	5843
	21st to end	Day	10% 4 9% 35% 39% 4	6904
June	1st to 10th	Day	23% 5% 12% 29% 25% 5%	2800
	11th to 20th	Day	14% 4 9% 21% 36% 16%	2800
	21st to end	Day	14% 3 7% 19% 34% 23%	2800
July	1st to 10th	Day	9% 1 5% 11% 34% 39%	6165
	11th to 20th	Day	12% 2 8% 12% 32% 33%	5811
	21st to end	Day	13% 4 10% 16% 32% 25%	6217
August	1st to 10th	Day	17% 2 8% 13% 34% 26%	4206
	11th to 20th	Day	12% 1 5% 18% 37% 26%	4117
	21st to end	Day	18% 2 8% 20% 38% 14%	4311
September	1st to 10th	Day	15% 3 6% 18% 29% 29%	2400
	11th to 20th	Day	23% 3 9% 27% 29% 9%	2350
	21st to end	Day	17% 2 8% 25% 30% 18%	2130
October	1st to 10th	Day	16% 2 6% 14% 26% 37%	3280
	11th to 20th	Day	23% 4 10% 24% 26% 13%	3261
	21st to end	Day	27% 4 11% 26% 22% 10%	3558
November	1st to 10th	Day	31% 5% 10% 28% 18% 7%	2059
	11th to 20th	Day	39% 4 12% 23% 15% 7%	1831
	21st to end	Day	32% 5% 12% 19% 20% 11%	1680
December	1st to 10th	Day	29% 5% 9% 25% 24% 8%	2700
	11th to 20th	Day	57% 4 9% 16% 11% 3	3108
	21st to end	Day	55% 5% 10% 20% 8% 2	4092
January	1st to 10th	Night	43% 6% 17% 19% 11% 4	7740
	11th to 20th	Night	33% 4 6% 15% 22% 20%	7650
	21st to end	Night	43% 4 8% 13% 17% 14%	8371
February	1st to 10th	Night	39% 4 9% 19% 17% 11%	2730
	11th to 20th	Night	41% 5% 9% 20% 18% 6%	2589
	21st to end	Night	32% 5% 13% 25% 18% 6%	1953
March	1st to 10th	Night	45% 7% 9% 18% 17% 3	4942
	11th to 20th	Night	37% 4 10% 22% 18% 8%	5000
	21st to end	Night	43% 8% 14% 23% 11% 2	5489
April	1st to 10th	Night	35% 5% 13% 23% 18% 5%	2012
	11th to 20th	Night	32% 5% 12% 23% 20% 8%	1979
	21st to end	Night	23% 4 10% 32% 24% 6%	1999
May	1st to 10th	Night	17% 2 6% 21% 32% 22%	4097
	11th to 20th	Night	19% 6% 8% 25% 28% 13%	4056
	21st to end	Night	11% 3 8% 29% 43% 6%	3972
June	1st to 10th	Night	26% 5% 10% 20% 32% 8%	1600
	11th to 20th	Night	15% 4 6% 20% 35% 20%	1600
	21st to end	Night	16% 3 6% 14% 30% 31%	1600
July	1st to 10th	Night	13% 2 9% 7% 26% 43%	3685
	11th to 20th	Night	26% 2 11% 9% 15% 37%	4046
	21st to end	Night	24% 4 7% 9% 25% 31%	4345
August	1st to 10th	Night	21% 3 12% 11% 25% 28%	2929
	11th to 20th	Night	14% 2 5% 11% 36% 33%	2995
	21st to end	Night	17% 3 10% 12% 37% 21%	3608
September	1st to 10th	Night	15% 3 5% 14% 30% 33%	2000
	11th to 20th	Night	23% 4 8% 21% 31% 13%	2045
	21st to end	Night	20% 3 5% 19% 28% 24%	2270
October	1st to 10th	Night	18% 3 5% 10% 22% 42%	3920
	11th to 20th	Night	25% 5% 7% 19% 26% 19%	3897
	21st to end	Night	26% 3 6% 22% 28% 15%	4253
November	1st to 10th	Night	33% 4 11% 24% 20% 8%	2460
	11th to 20th	Night	36% 5% 13% 23% 16% 7%	2783
	21st to end	Night	32% 3 10% 22% 21% 12%	2940
December	1st to 10th	Night	31% 4 7% 26% 21% 10%	4700
	11th to 20th	Night	53% 4 9% 16% 13% 4	5316
	21st to end	Night	57% 5% 9% 17% 10% 2	7106

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	30% 11% 26% 16% 14% 3	373
	11th to 20th	Day	21% 10% 21% 25% 18% 5%	430
	21st to end	Day	18% 10% 23% 27% 17% 4	473
February	1st to 10th	Day	21% 12% 20% 23% 20% 4	430
	11th to 20th	Day	23% 17% 23% 22% 13% 1	416
	21st to end	Day	18% 13% 25% 27% 13% 3	414
March	1st to 10th	Day	23% 19% 24% 25% 8% 2	500
	11th to 20th	Day	23% 12% 26% 24% 12% 3	500
	21st to end	Day	18% 16% 33% 22% 8% 2	550
April	1st to 10th	Day	18% 17% 26% 25% 11% 3	500
	11th to 20th	Day	11% 20% 29% 24% 12% 3	492
	21st to end	Day	8% 17% 34% 23% 15% 4	500
May	1st to 10th	Day	8% 17% 33% 27% 15% 2	503
	11th to 20th	Day	12% 11% 30% 24% 19% 4	528
	21st to end	Day	6% 13% 28% 27% 20% 6%	573
June	1st to 10th	Day	6% 13% 30% 28% 19% 4	530
	11th to 20th	Day	5% 12% 29% 35% 17% 2	530
	21st to end	Day	2 5% 24% 38% 26% 6%	530
July	1st to 10th	Day	3 6% 19% 39% 28% 5%	526
	11th to 20th	Day	1 2 20% 42% 30% 5%	524
	21st to end	Day	2 2 15% 42% 32% 8%	575
August	1st to 10th	Day	2 4 22% 40% 26% 6%	527
	11th to 20th	Day	3 3 18% 40% 29% 7%	517
	21st to end	Day	2 4 16% 38% 32% 8%	583
September	1st to 10th	Day	3 4 18% 38% 29% 8%	530
	11th to 20th	Day	5% 8% 20% 37% 21% 9%	530
	21st to end	Day	4 8% 20% 30% 30% 8%	530
October	1st to 10th	Day	7% 7% 23% 26% 26% 12%	530
	11th to 20th	Day	12% 8% 16% 24% 30% 10%	530
	21st to end	Day	13% 7% 19% 26% 27% 7%	583
November	1st to 10th	Day	11% 9% 20% 27% 27% 7%	535
	11th to 20th	Day	17% 11% 14% 25% 23% 10%	306
	21st to end	Day	12% 9% 20% 24% 24% 11%	220
December	1st to 10th	Day	18% 7% 19% 26% 21% 9%	220
	11th to 20th	Day	25% 12% 18% 20% 16% 9%	220
	21st to end	Day	28% 12% 17% 23% 16% 4	242
January	1st to 10th	Night	23% 9% 14% 30% 20% 6%	840
	11th to 20th	Night	20% 6% 14% 32% 24% 4	840
	21st to end	Night	18% 6% 14% 32% 26% 3	924
February	1st to 10th	Night	20% 8% 15% 30% 23% 3	840
	11th to 20th	Night	20% 10% 19% 29% 18% 4	804
	21st to end	Night	16% 12% 19% 34% 15% 3	660
March	1st to 10th	Night	24% 12% 18% 24% 20% 3	800
	11th to 20th	Night	20% 8% 19% 31% 19% 3	800
	21st to end	Night	19% 9% 25% 29% 15% 3	880
April	1st to 10th	Night	14% 11% 25% 28% 18% 4	800
	11th to 20th	Night	10% 13% 24% 29% 19% 5%	791
	21st to end	Night	8% 13% 27% 25% 22% 5%	799
May	1st to 10th	Night	7% 8% 25% 29% 25% 5%	600
	11th to 20th	Night	6% 5% 23% 32% 30% 4	586
	21st to end	Night	7% 10% 22% 33% 22% 5%	433
June	1st to 10th	Night	7% 7% 25% 35% 25% 2	400
	11th to 20th	Night	3 9% 25% 41% 21% 2	400
	21st to end	Night	4 2 16% 42% 34% 3	400
July	1st to 10th	Night	3 2 16% 36% 37% 6%	423
	11th to 20th	Night	2 1 8% 33% 46% 10%	582
	21st to end	Night	4 8% 32% 46% 10%	657
August	1st to 10th	Night	4 1 13% 34% 39% 9%	597
	11th to 20th	Night	2 1 11% 37% 41% 9%	634
	21st to end	Night	3 1 9% 31% 47% 9%	880
September	1st to 10th	Night	2 2 10% 31% 46% 10%	800
	11th to 20th	Night	6% 4 13% 33% 34% 10%	800
	21st to end	Night	5% 4 13% 30% 37% 11%	800
October	1st to 10th	Night	7% 4 13% 30% 36% 9%	800
	11th to 20th	Night	9% 4 13% 27% 38% 9%	800
	21st to end	Night	13% 4 12% 28% 33% 11%	880
November	1st to 10th	Night	12% 7% 14% 25% 34% 8%	820
	11th to 20th	Night	18% 5% 11% 33% 27% 6%	840
	21st to end	Night	14% 5% 14% 34% 27% 5%	840
December	1st to 10th	Night	22% 5% 12% 31% 24% 6%	840
	11th to 20th	Night	26% 8% 13% 28% 21% 4	840
	21st to end	Night	27% 9% 17% 28% 16% 2	924

Page generated at 2026-02-12 22:42:13. Version ac07

Copyright © 2026 Attilla Danko.