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 2024-12-02.

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	9% 5% 2 4 3 3 3 3 5% 9% 55%	105297
	Night	11% 5% 2 5% 3 3 3 3 5% 6% 53%	103071
Transparency	Day	27% 4 10% 21% 23% 15%	105059
	Night	31% 4 9% 18% 21% 16%	102899
Seeing	Day	11% 10% 23% 30% 22% 6%	15490
	Night	12% 7% 16% 31% 29% 6%	24753

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	17% 9% 2 7% 5% 3 4 3 5% 5% 41%	2767
	11th to 20th	Day	25% 9% 4 8% 4 4 3 3 4 5% 30%	2860
	21st to end	Day	23% 9% 3 7% 4 4 4 3 4 6% 31%	3146
February	1st to 10th	Day	19% 5% 2 6% 4 3 4 4 4 6% 44%	1710
	11th to 20th	Day	14% 7% 2 6% 3 4 4 4 5% 8% 41%	1673
	21st to end	Day	16% 6% 3 4 4 3 4 3 5% 7% 46%	1594
March	1st to 10th	Day	22% 14% 4 7% 4 4 3 3 4 5% 32%	3442
	11th to 20th	Day	12% 4 2 4 3 3 3 3 5% 8% 54%	3490
	21st to end	Day	22% 6% 2 5% 3 4 4 5% 6% 7% 35%	3825
April	1st to 10th	Day	13% 7% 2 6% 4 3 3 4 6% 8% 42%	2267
	11th to 20th	Day	8% 5% 2 5% 4 4 4 3 6% 9% 50%	2249
	21st to end	Day	7% 3 1 3 3 3 3 3 6% 10% 56%	2280
May	1st to 10th	Day	5% 3 1 2 2 2 2 2 4 7% 69%	4107
	11th to 20th	Day	4 2 1 3 2 2 3 3 6% 13% 61%	4070
	21st to end	Day	3 3 1 3 1 2 3 2 4 6% 73%	4813
June	1st to 10th	Day	6% 5% 2 3 3 2 4 3 7% 10% 55%	2660
	11th to 20th	Day	2 3 1 2 2 2 3 3 5% 10% 68%	2660
	21st to end	Day	2 2 1 3 3 2 2 3 4 9% 70%	2660
July	1st to 10th	Day	1 1 1 2 1 2 2 2 5% 8% 75%	4359
	11th to 20th	Day	1 2 1 3 2 2 3 3 7% 12% 65%	4110
	21st to end	Day	1 2 1 3 2 2 2 3 6% 12% 67%	4455
August	1st to 10th	Day	1 2 1 4 3 4 5% 4 7% 15% 55%	4091
	11th to 20th	Day	1 2 1 2 2 1 2 2 5% 9% 72%	3950
	21st to end	Day	1 4 1 3 3 3 3 2 6% 16% 57%	4180
September	1st to 10th	Day	1 2 1 3 2 2 3 2 5% 10% 69%	2280
	11th to 20th	Day	4 4 1 4 3 3 3 2 6% 11% 58%	2233
	21st to end	Day	4 2 1 3 2 2 2 2 4 10% 68%	2024
October	1st to 10th	Day	4 3 1 3 2 2 2 2 4 7% 70%	3180
	11th to 20th	Day	10% 3 1 3 2 2 3 4 5% 9% 58%	3161
	21st to end	Day	8% 5% 2 3 3 3 4 3 5% 10% 54%	3448
November	1st to 10th	Day	10% 4 2 5% 4 4 4 3 6% 8% 51%	1959
	11th to 20th	Day	13% 7% 2 6% 3 4 4 3 5% 6% 47%	1744
	21st to end	Day	13% 5% 1 3 4 4 3 4 5% 8% 51%	1600
December	1st to 10th	Day	18% 7% 2 4 4 4 3 4 5% 7% 42%	1528
	11th to 20th	Day	33% 10% 2 7% 3 3 3 3 4 5% 28%	1928
	21st to end	Day	25% 7% 2 6% 4 3 3 3 4 7% 35%	2794
January	1st to 10th	Night	18% 8% 2 6% 3 4 4 3 6% 7% 39%	4181
	11th to 20th	Night	23% 9% 3 8% 5% 5% 4 3 4 5% 30%	4110
	21st to end	Night	25% 9% 4 7% 4 4 3 3 4 6% 30%	4521
February	1st to 10th	Night	18% 6% 2 5% 3 3 3 3 4 6% 47%	2470
	11th to 20th	Night	15% 8% 3 5% 4 3 4 3 5% 7% 42%	2393
	21st to end	Night	15% 6% 2 4 3 3 3 3 4 6% 52%	1859
March	1st to 10th	Night	20% 14% 3 7% 4 4 4 3 5% 5% 33%	3432
	11th to 20th	Night	14% 5% 1 5% 2 3 3 2 4 5% 57%	3490
	21st to end	Night	17% 10% 2 7% 4 4 4 3 4 7% 38%	3828
April	1st to 10th	Night	12% 6% 2 6% 4 2 3 3 5% 6% 50%	1912
	11th to 20th	Night	9% 6% 2 5% 4 3 3 3 4 7% 54%	1879
	21st to end	Night	7% 4 1 4 3 3 3 3 5% 6% 61%	1899
May	1st to 10th	Night	4 3 2 4 3 2 2 2 3 5% 71%	2860
	11th to 20th	Night	2 3 2 8% 5% 4 4 3 5% 6% 59%	2815
	21st to end	Night	3 3 1 3 2 1 2 2 3 5% 76%	2762
June	1st to 10th	Night	5% 6% 2 4 3 4 3 4 5% 9% 56%	1520
	11th to 20th	Night	2 3 1 3 3 2 4 3 4 6% 70%	1520
	21st to end	Night	3 3 2 3 3 3 2 2 4 6% 71%	1520
July	1st to 10th	Night	1 2 1 3 2 2 2 3 3 6% 75%	2598
	11th to 20th	Night	1 2 1 5% 4 3 4 2 5% 8% 64%	2860
	21st to end	Night	1 2 1 4 3 3 4 4 7% 11% 59%	3109
August	1st to 10th	Night	2 3 2 5% 3 6% 8% 4 7% 9% 50%	2848
	11th to 20th	Night	2 1 3 2 2 3 2 4 7% 73%	2876
	21st to end	Night	3 3 1 4 3 4 5% 4 4 8% 62%	3498
September	1st to 10th	Night	1 1 1 4 2 4 3 3 6% 8% 68%	1900
	11th to 20th	Night	5% 4 2 4 3 3 3 3 5% 8% 60%	1943
	21st to end	Night	4 3 1 4 3 3 2 2 4 6% 68%	2156
October	1st to 10th	Night	3 4 1 4 2 2 2 2 4 5% 71%	3800
	11th to 20th	Night	6% 6% 2 4 2 3 3 3 4 6% 60%	3777
	21st to end	Night	9% 4 2 3 2 3 3 3 5% 7% 59%	4121
November	1st to 10th	Night	11% 5% 1 5% 3 4 4 3 6% 8% 51%	2340
	11th to 20th	Night	14% 6% 2 4 3 3 4 4 6% 7% 47%	2650
	21st to end	Night	13% 5% 2 5% 3 2 3 4 5% 6% 53%	2800
December	1st to 10th	Night	21% 7% 2 5% 3 3 3 3 5% 6% 43%	2686
	11th to 20th	Night	33% 7% 1 4 3 3 3 3 5% 6% 32%	3276
	21st to end	Night	25% 8% 2 6% 4 4 4 3 4 6% 35%	4862

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	43% 6% 14% 26% 7% 3	2767
	11th to 20th	Day	56% 5% 10% 13% 9% 7%	2860
	21st to end	Day	53% 5% 10% 17% 10% 5%	3146
February	1st to 10th	Day	42% 5% 8% 19% 18% 8%	1710
	11th to 20th	Day	40% 6% 10% 21% 19% 5%	1682
	21st to end	Day	37% 6% 9% 28% 14% 6%	1594
March	1st to 10th	Day	53% 7% 9% 15% 14% 2	3442
	11th to 20th	Day	30% 5% 14% 26% 14% 11%	3490
	21st to end	Day	43% 9% 15% 20% 11% 2	3825
April	1st to 10th	Day	39% 6% 14% 23% 15% 4	2267
	11th to 20th	Day	31% 6% 15% 24% 18% 5%	2252
	21st to end	Day	22% 6% 16% 30% 22% 4	2280
May	1st to 10th	Day	16% 4 13% 30% 22% 15%	4107
	11th to 20th	Day	16% 3 11% 31% 27% 12%	4073
	21st to end	Day	14% 5% 11% 36% 30% 3	4814
June	1st to 10th	Day	24% 5% 12% 29% 25% 5%	2660
	11th to 20th	Day	14% 4 10% 21% 36% 14%	2660
	21st to end	Day	15% 3 7% 19% 33% 24%	2660
July	1st to 10th	Day	10% 1 4 10% 24% 50%	4291
	11th to 20th	Day	13% 2 6% 13% 22% 44%	4041
	21st to end	Day	13% 2 5% 14% 32% 33%	4315
August	1st to 10th	Day	17% 2 8% 13% 33% 27%	4076
	11th to 20th	Day	12% 1 5% 18% 37% 26%	3989
	21st to end	Day	18% 2 8% 20% 39% 14%	4179
September	1st to 10th	Day	14% 2 6% 18% 30% 30%	2280
	11th to 20th	Day	24% 3 9% 27% 28% 9%	2233
	21st to end	Day	16% 3 8% 25% 30% 18%	2024
October	1st to 10th	Day	15% 2 6% 14% 26% 38%	3180
	11th to 20th	Day	23% 4 10% 23% 26% 14%	3161
	21st to end	Day	27% 4 11% 26% 22% 10%	3448
November	1st to 10th	Day	31% 5% 10% 28% 18% 8%	1959
	11th to 20th	Day	37% 5% 12% 23% 15% 7%	1744
	21st to end	Day	33% 5% 12% 19% 19% 12%	1600
December	1st to 10th	Day	41% 6% 10% 16% 18% 9%	1528
	11th to 20th	Day	60% 3 7% 14% 12% 4	1928
	21st to end	Day	49% 5% 12% 21% 10% 3	2794
January	1st to 10th	Night	42% 7% 18% 21% 8% 3	4181
	11th to 20th	Night	55% 7% 10% 12% 9% 7%	4110
	21st to end	Night	54% 5% 11% 12% 12% 6%	4521
February	1st to 10th	Night	39% 4 9% 20% 17% 10%	2470
	11th to 20th	Night	40% 6% 9% 20% 19% 6%	2395
	21st to end	Night	33% 5% 13% 26% 19% 5%	1859
March	1st to 10th	Night	51% 9% 10% 15% 13% 2	3432
	11th to 20th	Night	31% 3 10% 24% 22% 11%	3490
	21st to end	Night	43% 8% 15% 22% 10% 3	3828
April	1st to 10th	Night	35% 5% 14% 23% 18% 5%	1912
	11th to 20th	Night	31% 6% 12% 25% 20% 7%	1879
	21st to end	Night	23% 5% 10% 31% 24% 6%	1899
May	1st to 10th	Night	19% 2 7% 27% 30% 16%	2860
	11th to 20th	Night	20% 8% 10% 19% 25% 18%	2816
	21st to end	Night	15% 4 9% 36% 32% 5%	2762
June	1st to 10th	Night	26% 5% 10% 19% 32% 8%	1520
	11th to 20th	Night	16% 4 6% 21% 35% 18%	1520
	21st to end	Night	17% 3 5% 13% 29% 32%	1520
July	1st to 10th	Night	11% 1 5% 6% 21% 56%	2557
	11th to 20th	Night	17% 2 7% 11% 18% 45%	2806
	21st to end	Night	19% 2 6% 9% 22% 41%	3011
August	1st to 10th	Night	22% 3 13% 11% 24% 28%	2839
	11th to 20th	Night	14% 2 5% 10% 36% 33%	2903
	21st to end	Night	17% 3 10% 12% 37% 21%	3498
September	1st to 10th	Night	15% 3 4 13% 31% 34%	1900
	11th to 20th	Night	24% 4 7% 20% 31% 13%	1943
	21st to end	Night	19% 3 5% 20% 29% 24%	2156
October	1st to 10th	Night	18% 2 5% 10% 22% 43%	3800
	11th to 20th	Night	25% 5% 7% 18% 26% 19%	3777
	21st to end	Night	26% 3 6% 22% 28% 16%	4121
November	1st to 10th	Night	32% 4 11% 25% 19% 9%	2340
	11th to 20th	Night	35% 5% 13% 23% 17% 7%	2650
	21st to end	Night	33% 3 10% 21% 21% 12%	2800
December	1st to 10th	Night	42% 4 7% 19% 17% 9%	2686
	11th to 20th	Night	55% 4 9% 15% 13% 4	3276
	21st to end	Night	50% 7% 12% 18% 11% 2	4862

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% 12% 25% 15% 15% 4	317
	11th to 20th	Day	25% 11% 20% 24% 16% 5%	370
	21st to end	Day	19% 12% 20% 28% 16% 4	407
February	1st to 10th	Day	19% 13% 19% 24% 21% 4	370
	11th to 20th	Day	20% 17% 24% 24% 14% 2	369
	21st to end	Day	18% 14% 25% 27% 13% 3	382
March	1st to 10th	Day	23% 18% 24% 25% 8% 2	460
	11th to 20th	Day	21% 12% 26% 24% 13% 3	460
	21st to end	Day	17% 16% 34% 23% 8% 2	506
April	1st to 10th	Day	18% 16% 26% 25% 12% 3	460
	11th to 20th	Day	12% 19% 28% 25% 12% 3	452
	21st to end	Day	8% 18% 34% 22% 15% 4	460
May	1st to 10th	Day	8% 16% 33% 27% 14% 2	463
	11th to 20th	Day	10% 11% 30% 24% 20% 4	488
	21st to end	Day	7% 13% 26% 27% 21% 6%	529
June	1st to 10th	Day	6% 14% 28% 27% 20% 4	490
	11th to 20th	Day	4 12% 28% 36% 17% 2	490
	21st to end	Day	2 5% 24% 38% 26% 6%	490
July	1st to 10th	Day	4 5% 17% 41% 29% 4	486
	11th to 20th	Day	1 2 21% 41% 31% 5%	484
	21st to end	Day	2 2 14% 42% 33% 8%	531
August	1st to 10th	Day	2 4 21% 42% 26% 6%	487
	11th to 20th	Day	4 3 18% 39% 30% 7%	477
	21st to end	Day	3 4 16% 37% 33% 8%	539
September	1st to 10th	Day	2 3 18% 39% 30% 8%	490
	11th to 20th	Day	5% 8% 19% 37% 22% 9%	490
	21st to end	Day	3 9% 19% 31% 31% 8%	490
October	1st to 10th	Day	6% 6% 24% 26% 27% 12%	490
	11th to 20th	Day	11% 7% 16% 25% 31% 10%	490
	21st to end	Day	13% 7% 19% 26% 27% 8%	539
November	1st to 10th	Day	11% 9% 20% 27% 27% 6%	495
	11th to 20th	Day	15% 10% 13% 27% 24% 11%	279
	21st to end	Day	14% 10% 19% 24% 23% 12%	200
December	1st to 10th	Day	22% 8% 18% 25% 16% 10%	182
	11th to 20th	Day	24% 12% 19% 21% 14% 9%	180
	21st to end	Day	22% 12% 18% 25% 18% 5%	198
January	1st to 10th	Night	21% 9% 13% 29% 22% 6%	760
	11th to 20th	Night	21% 7% 14% 31% 22% 5%	760
	21st to end	Night	19% 7% 13% 30% 27% 4	836
February	1st to 10th	Night	19% 9% 15% 30% 24% 4	760
	11th to 20th	Night	18% 10% 18% 29% 20% 5%	744
	21st to end	Night	17% 12% 19% 32% 16% 4	628
March	1st to 10th	Night	24% 12% 18% 23% 20% 3	760
	11th to 20th	Night	19% 8% 19% 31% 19% 4	760
	21st to end	Night	18% 9% 25% 29% 15% 3	836
April	1st to 10th	Night	14% 11% 25% 28% 18% 4	760
	11th to 20th	Night	10% 13% 24% 29% 19% 5%	751
	21st to end	Night	8% 13% 28% 24% 22% 5%	759
May	1st to 10th	Night	7% 8% 26% 29% 25% 5%	570
	11th to 20th	Night	6% 4 21% 32% 31% 5%	556
	21st to end	Night	8% 10% 21% 33% 23% 5%	411
June	1st to 10th	Night	7% 7% 25% 35% 24% 2	380
	11th to 20th	Night	3 8% 22% 42% 22% 2	380
	21st to end	Night	3 2 16% 43% 34% 2	380
July	1st to 10th	Night	3 2 16% 36% 37% 6%	401
	11th to 20th	Night	2 1 9% 34% 45% 10%	552
	21st to end	Night	4 7% 32% 46% 10%	624
August	1st to 10th	Night	4 1 12% 35% 39% 9%	567
	11th to 20th	Night	2 1 10% 37% 42% 9%	602
	21st to end	Night	3 1 8% 31% 47% 9%	836
September	1st to 10th	Night	1 2 9% 31% 47% 10%	760
	11th to 20th	Night	6% 4 13% 34% 33% 10%	760
	21st to end	Night	4 4 13% 29% 38% 12%	760
October	1st to 10th	Night	7% 4 14% 30% 36% 9%	760
	11th to 20th	Night	9% 3 13% 26% 39% 9%	760
	21st to end	Night	13% 4 12% 27% 33% 12%	836
November	1st to 10th	Night	12% 7% 14% 26% 33% 9%	780
	11th to 20th	Night	17% 5% 11% 34% 28% 6%	800
	21st to end	Night	15% 6% 14% 32% 27% 6%	800
December	1st to 10th	Night	24% 6% 12% 29% 24% 6%	768
	11th to 20th	Night	26% 9% 13% 29% 20% 4	760
	21st to end	Night	23% 10% 17% 30% 18% 3	836

Page generated at 2024-11-29 07:43:10. Version ac07

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