Vista Hill
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Vista Hill clear sky chart from 2005-11-06 to 2024-01-12.

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	6% 4 2 4 4 2 4 4 5% 8% 57%	74678
	Night	6% 5% 2 5% 4 3 4 4 5% 8% 53%	75057
Transparency	Day	25% 4 11% 20% 24% 16%	74399
	Night	29% 5% 11% 20% 21% 15%	74858
Seeing	Day	8% 12% 26% 31% 18% 5%	14307
	Night	9% 6% 17% 31% 30% 7%	23761

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	15% 8% 3 6% 6% 3 5% 5% 7% 7% 36%	1641
	11th to 20th	Day	9% 5% 2 6% 6% 3 5% 4 5% 8% 48%	1633
	21st to end	Day	12% 7% 4 5% 5% 3 5% 5% 5% 8% 41%	1782
February	1st to 10th	Day	10% 7% 3 5% 5% 3 4 5% 6% 7% 45%	1620
	11th to 20th	Day	10% 7% 4 6% 5% 3 4 4 5% 7% 44%	1660
	21st to end	Day	10% 7% 3 7% 6% 2 3 5% 4 7% 46%	1480
March	1st to 10th	Day	11% 7% 4 7% 5% 3 6% 6% 6% 9% 34%	1948
	11th to 20th	Day	10% 6% 4 8% 7% 4 5% 5% 7% 9% 35%	1980
	21st to end	Day	9% 5% 4 7% 6% 3 4 5% 5% 7% 44%	2204
April	1st to 10th	Day	10% 7% 3 6% 5% 3 4 4 6% 8% 44%	2160
	11th to 20th	Day	8% 5% 2 4 5% 2 3 4 6% 7% 54%	2129
	21st to end	Day	5% 4 2 4 4 2 4 4 5% 9% 57%	2160
May	1st to 10th	Day	3 3 2 4 3 2 3 5% 5% 8% 60%	2218
	11th to 20th	Day	4 4 2 4 3 2 3 4 5% 9% 60%	2330
	21st to end	Day	4 5% 2 3 4 3 4 4 6% 9% 55%	2723
June	1st to 10th	Day	4 4 2 3 3 2 4 4 5% 8% 61%	2520
	11th to 20th	Day	2 1 1 2 1 1 2 3 5% 8% 74%	2520
	21st to end	Day	2 2 1 2 2 2 2 2 3 6% 76%	2520
July	1st to 10th	Day	1 1 1 2 2 1 3 3 3 8% 76%	2509
	11th to 20th	Day	1 2 1 2 2 2 2 3 4 8% 72%	2340
	21st to end	Day	1 1 2 2 1 2 3 4 7% 78%	2546
August	1st to 10th	Day	2 2 1 2 3 2 3 3 4 8% 70%	2328
	11th to 20th	Day	1 1 1 1 1 2 4 4 7% 77%	2181
	21st to end	Day	1 1 1 2 2 2 3 5% 9% 73%	2376
September	1st to 10th	Day	1 2 1 2 2 1 3 3 3 6% 79%	2160
	11th to 20th	Day	2 3 1 3 4 2 3 4 5% 9% 64%	2160
	21st to end	Day	2 2 1 2 2 1 2 2 4 6% 75%	1908
October	1st to 10th	Day	4 2 1 4 3 2 3 3 4 6% 67%	1800
	11th to 20th	Day	4 3 2 3 3 2 3 4 5% 9% 62%	1800
	21st to end	Day	4 4 2 3 4 3 3 4 5% 7% 60%	1980
November	1st to 10th	Day	6% 4 3 4 5% 3 5% 4 6% 8% 52%	1839
	11th to 20th	Day	7% 5% 3 5% 6% 3 4 5% 5% 6% 50%	1710
	21st to end	Day	8% 5% 3 5% 5% 3 4 4 5% 7% 53%	1571
December	1st to 10th	Day	7% 5% 4 7% 7% 3 6% 6% 6% 7% 42%	1520
	11th to 20th	Day	14% 9% 4 9% 7% 4 6% 5% 6% 6% 30%	1928
	21st to end	Day	10% 9% 5% 8% 7% 3 5% 6% 5% 7% 34%	2794
January	1st to 10th	Night	12% 7% 3 6% 6% 3 5% 5% 7% 8% 37%	2521
	11th to 20th	Night	9% 7% 3 6% 6% 3 6% 5% 5% 7% 43%	2366
	21st to end	Night	11% 7% 3 6% 6% 3 5% 5% 4 7% 43%	2574
February	1st to 10th	Night	9% 7% 4 5% 5% 4 4 4 4 6% 48%	2340
	11th to 20th	Night	9% 6% 3 6% 5% 3 5% 5% 5% 9% 43%	2186
	21st to end	Night	8% 7% 3 5% 5% 3 4 4 6% 7% 47%	1776
March	1st to 10th	Night	11% 7% 3 8% 6% 4 4 5% 6% 7% 39%	2008
	11th to 20th	Night	10% 8% 4 6% 6% 3 4 5% 6% 8% 41%	1980
	21st to end	Night	9% 7% 3 6% 5% 3 5% 5% 4 6% 49%	2150
April	1st to 10th	Night	8% 6% 3 6% 6% 3 5% 5% 6% 8% 45%	1800
	11th to 20th	Night	6% 6% 2 5% 4 3 4 4 4 9% 52%	1779
	21st to end	Night	4 3 1 3 3 2 4 5% 5% 10% 59%	1800
May	1st to 10th	Night	2 5% 2 4 4 3 3 5% 7% 9% 56%	1739
	11th to 20th	Night	2 3 2 4 4 2 5% 5% 7% 10% 55%	1560
	21st to end	Night	3 3 1 3 4 3 6% 7% 8% 11% 52%	1552
June	1st to 10th	Night	3 4 1 4 4 2 4 3 6% 10% 59%	1440
	11th to 20th	Night	1 1 1 2 3 1 2 3 5% 9% 73%	1440
	21st to end	Night	1 3 1 3 3 1 3 3 4 7% 74%	1440
July	1st to 10th	Night	2 1 1 2 2 3 2 4 9% 74%	1446
	11th to 20th	Night	1 1 1 2 2 1 3 3 6% 9% 71%	1620
	21st to end	Night	1 1 2 3 2 4 6% 7% 11% 62%	1773
August	1st to 10th	Night	1 3 1 3 4 3 3 4 7% 12% 57%	1611
	11th to 20th	Night	1 1 2 2 1 3 4 7% 10% 68%	1718
	21st to end	Night	2 1 2 2 2 3 3 7% 10% 68%	1980
September	1st to 10th	Night	1 1 2 2 1 3 4 5% 9% 73%	1800
	11th to 20th	Night	3 3 1 3 3 2 4 5% 5% 8% 62%	1800
	21st to end	Night	2 2 1 2 2 1 2 3 4 7% 74%	2048
October	1st to 10th	Night	4 3 1 3 3 2 4 3 5% 7% 66%	2160
	11th to 20th	Night	4 3 2 4 5% 2 4 4 5% 6% 61%	2160
	21st to end	Night	4 3 2 4 4 2 3 4 5% 8% 62%	2376
November	1st to 10th	Night	5% 4 2 4 4 2 4 5% 6% 8% 55%	2239
	11th to 20th	Night	7% 6% 2 5% 4 3 4 4 6% 8% 51%	2470
	21st to end	Night	6% 5% 2 4 4 3 4 5% 4 7% 56%	2607
December	1st to 10th	Night	9% 6% 3 7% 6% 3 5% 4 5% 7% 47%	2660
	11th to 20th	Night	15% 9% 4 8% 7% 4 5% 5% 5% 7% 30%	3276
	21st to end	Night	11% 8% 3 7% 7% 4 6% 6% 6% 7% 34%	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	45% 7% 13% 20% 10% 5%	1641
	11th to 20th	Day	34% 7% 12% 16% 17% 14%	1633
	21st to end	Day	40% 7% 9% 13% 22% 8%	1782
February	1st to 10th	Day	38% 4 9% 20% 18% 11%	1620
	11th to 20th	Day	38% 5% 10% 18% 22% 7%	1669
	21st to end	Day	39% 6% 8% 22% 19% 7%	1480
March	1st to 10th	Day	44% 6% 11% 20% 15% 4	1948
	11th to 20th	Day	44% 7% 11% 18% 17% 4	1980
	21st to end	Day	39% 7% 13% 20% 18% 3	2204
April	1st to 10th	Day	38% 5% 14% 19% 19% 5%	2160
	11th to 20th	Day	30% 5% 16% 23% 21% 5%	2132
	21st to end	Day	24% 5% 15% 28% 23% 5%	2160
May	1st to 10th	Day	22% 6% 12% 25% 29% 6%	2218
	11th to 20th	Day	20% 4 16% 26% 26% 8%	2333
	21st to end	Day	24% 6% 20% 24% 21% 4	2724
June	1st to 10th	Day	21% 6% 15% 25% 24% 9%	2520
	11th to 20th	Day	10% 4 12% 25% 33% 17%	2520
	21st to end	Day	11% 2 7% 18% 32% 30%	2520
July	1st to 10th	Day	8% 2 6% 18% 26% 40%	2440
	11th to 20th	Day	10% 2 8% 17% 25% 37%	2271
	21st to end	Day	7% 2 5% 16% 32% 38%	2405
August	1st to 10th	Day	14% 2 8% 19% 31% 27%	2312
	11th to 20th	Day	8% 2 6% 20% 33% 32%	2181
	21st to end	Day	9% 1 7% 21% 33% 28%	2376
September	1st to 10th	Day	9% 2 5% 13% 30% 41%	2160
	11th to 20th	Day	17% 3 10% 25% 28% 18%	2160
	21st to end	Day	12% 2 8% 22% 34% 22%	1908
October	1st to 10th	Day	19% 3 9% 18% 29% 24%	1800
	11th to 20th	Day	20% 5% 10% 20% 22% 23%	1800
	21st to end	Day	23% 4 9% 20% 23% 20%	1980
November	1st to 10th	Day	30% 6% 9% 22% 21% 12%	1839
	11th to 20th	Day	32% 6% 11% 21% 22% 8%	1710
	21st to end	Day	31% 4 10% 16% 30% 9%	1571
December	1st to 10th	Day	37% 7% 11% 18% 16% 10%	1520
	11th to 20th	Day	54% 6% 10% 13% 13% 5%	1928
	21st to end	Day	48% 6% 13% 19% 11% 3	2794
January	1st to 10th	Night	42% 7% 13% 21% 12% 5%	2521
	11th to 20th	Night	38% 6% 13% 14% 15% 13%	2366
	21st to end	Night	41% 6% 10% 12% 18% 12%	2574
February	1st to 10th	Night	37% 4 8% 19% 19% 12%	2340
	11th to 20th	Night	36% 5% 10% 19% 23% 7%	2188
	21st to end	Night	35% 5% 12% 28% 16% 5%	1776
March	1st to 10th	Night	44% 6% 14% 17% 15% 5%	2008
	11th to 20th	Night	40% 6% 9% 20% 19% 6%	1980
	21st to end	Night	36% 6% 15% 20% 17% 6%	2150
April	1st to 10th	Night	36% 6% 17% 21% 16% 5%	1800
	11th to 20th	Night	30% 6% 13% 24% 19% 8%	1779
	21st to end	Night	20% 6% 15% 31% 21% 7%	1800
May	1st to 10th	Night	23% 5% 13% 23% 24% 11%	1739
	11th to 20th	Night	21% 6% 17% 24% 24% 8%	1561
	21st to end	Night	23% 8% 21% 23% 21% 4	1552
June	1st to 10th	Night	19% 7% 13% 26% 26% 9%	1440
	11th to 20th	Night	10% 4 11% 23% 31% 21%	1440
	21st to end	Night	13% 1 6% 19% 31% 30%	1440
July	1st to 10th	Night	8% 1 5% 18% 31% 37%	1406
	11th to 20th	Night	10% 2 9% 19% 24% 36%	1566
	21st to end	Night	12% 2 7% 21% 28% 30%	1674
August	1st to 10th	Night	18% 3 9% 21% 26% 24%	1602
	11th to 20th	Night	11% 2 6% 20% 30% 31%	1718
	21st to end	Night	11% 2 8% 21% 29% 29%	1980
September	1st to 10th	Night	9% 3 7% 15% 24% 42%	1800
	11th to 20th	Night	18% 4 8% 25% 28% 18%	1800
	21st to end	Night	12% 3 8% 21% 30% 26%	2048
October	1st to 10th	Night	18% 4 9% 19% 25% 26%	2160
	11th to 20th	Night	23% 4 8% 20% 21% 24%	2160
	21st to end	Night	22% 4 9% 20% 25% 21%	2376
November	1st to 10th	Night	26% 5% 12% 24% 19% 14%	2239
	11th to 20th	Night	30% 6% 11% 24% 21% 9%	2470
	21st to end	Night	27% 4 11% 21% 24% 13%	2607
December	1st to 10th	Night	37% 7% 9% 18% 17% 12%	2660
	11th to 20th	Night	53% 5% 10% 14% 15% 4	3276
	21st to end	Night	48% 7% 15% 16% 11% 4	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	24% 18% 23% 21% 12% 2	302
	11th to 20th	Day	16% 15% 24% 30% 12% 3	345
	21st to end	Day	13% 13% 28% 26% 17% 3	374
February	1st to 10th	Day	17% 17% 23% 24% 14% 5%	340
	11th to 20th	Day	17% 22% 27% 24% 10% 1	373
	21st to end	Day	14% 20% 30% 25% 10% 1	346
March	1st to 10th	Day	18% 21% 31% 23% 7% 1	420
	11th to 20th	Day	18% 20% 29% 19% 12% 4	420
	21st to end	Day	14% 21% 34% 23% 7% 1	462
April	1st to 10th	Day	15% 19% 34% 21% 10% 2	420
	11th to 20th	Day	13% 20% 32% 23% 8% 3	412
	21st to end	Day	7% 22% 29% 26% 10% 5%	420
May	1st to 10th	Day	7% 15% 35% 28% 13% 2	423
	11th to 20th	Day	10% 15% 37% 24% 11% 2	448
	21st to end	Day	7% 14% 33% 28% 13% 4	485
June	1st to 10th	Day	6% 12% 32% 30% 16% 4	450
	11th to 20th	Day	2 12% 31% 37% 15% 3	450
	21st to end	Day	1 4 31% 38% 22% 4	450
July	1st to 10th	Day	2 4 22% 47% 22% 3	446
	11th to 20th	Day	1 1 18% 47% 29% 5%	444
	21st to end	Day	1 18% 46% 26% 8%	487
August	1st to 10th	Day	3 2 27% 43% 19% 6%	447
	11th to 20th	Day	1 1 23% 40% 27% 8%	437
	21st to end	Day	1 1 21% 43% 26% 7%	495
September	1st to 10th	Day	2 5% 17% 42% 27% 7%	450
	11th to 20th	Day	3 8% 26% 37% 20% 6%	450
	21st to end	Day	3 10% 21% 34% 27% 6%	450
October	1st to 10th	Day	2 10% 24% 34% 21% 8%	450
	11th to 20th	Day	6% 9% 21% 29% 26% 9%	450
	21st to end	Day	7% 9% 25% 30% 22% 7%	495
November	1st to 10th	Day	9% 12% 22% 26% 23% 7%	435
	11th to 20th	Day	5% 10% 20% 30% 26% 10%	270
	21st to end	Day	7% 9% 26% 29% 25% 4	203
December	1st to 10th	Day	8% 19% 21% 23% 24% 6%	180
	11th to 20th	Day	14% 17% 24% 21% 18% 7%	180
	21st to end	Day	19% 20% 25% 20% 14% 3	198
January	1st to 10th	Night	19% 8% 16% 29% 22% 6%	760
	11th to 20th	Night	15% 8% 15% 31% 23% 8%	728
	21st to end	Night	18% 6% 15% 32% 24% 5%	792
February	1st to 10th	Night	14% 9% 17% 32% 23% 5%	720
	11th to 20th	Night	13% 11% 19% 31% 21% 5%	704
	21st to end	Night	15% 11% 23% 30% 18% 3	592
March	1st to 10th	Night	18% 10% 21% 28% 21% 3	720
	11th to 20th	Night	16% 10% 17% 30% 22% 5%	720
	21st to end	Night	13% 10% 25% 32% 17% 2	792
April	1st to 10th	Night	13% 9% 26% 30% 19% 3	720
	11th to 20th	Night	11% 14% 22% 29% 19% 5%	711
	21st to end	Night	6% 9% 29% 26% 22% 7%	720
May	1st to 10th	Night	6% 7% 25% 32% 24% 5%	659
	11th to 20th	Night	5% 5% 23% 32% 29% 6%	498
	21st to end	Night	5% 10% 23% 32% 26% 4	389
June	1st to 10th	Night	5% 4 24% 34% 28% 4	360
	11th to 20th	Night	1 4 18% 44% 31% 1	360
	21st to end	Night	2 3 13% 39% 38% 6%	360
July	1st to 10th	Night	1 2 12% 35% 46% 4	356
	11th to 20th	Night	1 5% 34% 46% 13%	522
	21st to end	Night	1 7% 30% 51% 11%	591
August	1st to 10th	Night	4 2 11% 32% 42% 9%	537
	11th to 20th	Night	1 1 11% 34% 45% 8%	650
	21st to end	Night	2 1 10% 32% 46% 10%	792
September	1st to 10th	Night	2 2 9% 33% 43% 11%	720
	11th to 20th	Night	4 3 13% 36% 37% 8%	720
	21st to end	Night	2 4 13% 28% 41% 12%	720
October	1st to 10th	Night	5% 3 14% 32% 36% 10%	720
	11th to 20th	Night	6% 4 12% 28% 40% 9%	720
	21st to end	Night	6% 6% 11% 31% 32% 14%	792
November	1st to 10th	Night	7% 5% 17% 27% 34% 9%	740
	11th to 20th	Night	9% 4 14% 33% 32% 7%	760
	21st to end	Night	10% 5% 15% 38% 26% 7%	760
December	1st to 10th	Night	13% 8% 19% 31% 24% 6%	760
	11th to 20th	Night	18% 9% 18% 30% 21% 4	760
	21st to end	Night	17% 14% 20% 29% 18% 3	836

Page generated at 2024-01-09 13:24:21. Version ac07

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