Bella Vista
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bella Vista 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	12% 7% 2 6% 4 4 4 3 5% 7% 46%	130624
	Night	11% 7% 2 5% 3 3 3 3 5% 6% 50%	130493
Transparency	Day	24% 37% 7% 17% 12% 3	134236
	Night	23% 36% 6% 17% 14% 3	134958
Seeing	Day	17% 12% 29% 25% 14% 3	17164
	Night	16% 11% 31% 28% 12% 1	27128

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	13% 10% 4 5% 4 3 3 3 4 5% 45%	5289
	11th to 20th	Day	6% 8% 3 7% 4 3 3 2 4 5% 54%	5310
	21st to end	Day	17% 10% 3 5% 3 2 2 2 4 4 48%	5812
February	1st to 10th	Day	16% 11% 3 7% 5% 4 3 2 4 5% 40%	1890
	11th to 20th	Day	16% 10% 3 6% 4 3 3 2 4 5% 43%	1802
	21st to end	Day	16% 8% 3 6% 3 4 4 3 5% 5% 42%	1791
March	1st to 10th	Day	13% 8% 2 5% 3 4 4 3 4 5% 48%	4936
	11th to 20th	Day	9% 6% 2 4 4 3 4 4 4 6% 54%	4980
	21st to end	Day	14% 9% 3 8% 5% 5% 4 4 5% 8% 36%	5462
April	1st to 10th	Day	15% 7% 2 6% 4 4 3 3 5% 8% 43%	2310
	11th to 20th	Day	17% 8% 2 6% 4 4 4 3 5% 6% 41%	2374
	21st to end	Day	20% 9% 3 7% 5% 4 3 3 4 5% 37%	2415
May	1st to 10th	Day	19% 9% 3 7% 4 4 4 4 5% 6% 35%	5862
	11th to 20th	Day	12% 7% 3 7% 5% 5% 5% 4 6% 6% 40%	5862
	21st to end	Day	19% 7% 3 6% 4 4 4 3 5% 7% 36%	6434
June	1st to 10th	Day	9% 5% 2 6% 4 5% 4 5% 7% 10% 45%	2600
	11th to 20th	Day	8% 5% 2 5% 5% 5% 5% 4 6% 9% 46%	2600
	21st to end	Day	4 3 2 3 4 4 5% 4 7% 9% 54%	2600
July	1st to 10th	Day	8% 4 2 5% 5% 5% 6% 5% 8% 11% 41%	5900
	11th to 20th	Day	6% 5% 2 6% 4 4 5% 4 7% 10% 47%	5900
	21st to end	Day	5% 3 1 5% 3 4 5% 5% 8% 11% 49%	6422
August	1st to 10th	Day	5% 3 1 5% 3 4 4 4 5% 8% 57%	4234
	11th to 20th	Day	8% 4 2 6% 4 5% 5% 4 7% 9% 46%	4138
	21st to end	Day	5% 4 2 5% 4 4 5% 4 5% 8% 55%	4312
September	1st to 10th	Day	11% 5% 2 5% 3 3 4 3 4 6% 53%	2400
	11th to 20th	Day	11% 6% 2 6% 4 5% 4 3 6% 9% 45%	2230
	21st to end	Day	7% 5% 2 5% 4 4 4 4 5% 7% 53%	2173
October	1st to 10th	Day	9% 4 2 4 4 4 3 3 5% 7% 56%	2000
	11th to 20th	Day	13% 5% 2 4 2 3 3 2 3 6% 58%	2000
	21st to end	Day	19% 6% 2 5% 3 2 2 2 3 5% 50%	2200
November	1st to 10th	Day	11% 6% 2 3 3 3 3 2 4 6% 57%	2058
	11th to 20th	Day	13% 8% 2 5% 3 3 3 3 4 5% 51%	2030
	21st to end	Day	17% 9% 2 5% 2 2 3 3 3 6% 48%	1764
December	1st to 10th	Day	12% 10% 2 5% 3 2 3 2 3 4 52%	2690
	11th to 20th	Day	12% 10% 3 6% 3 4 3 2 3 4 50%	3257
	21st to end	Day	19% 17% 5% 6% 4 4 3 2 4 5% 31%	4587
January	1st to 10th	Night	13% 9% 3 8% 5% 3 3 3 4 5% 43%	7634
	11th to 20th	Night	7% 6% 2 7% 4 3 4 3 4 5% 56%	7680
	21st to end	Night	17% 9% 4 6% 3 4 3 2 4 5% 43%	8402
February	1st to 10th	Night	15% 10% 3 6% 4 3 4 3 5% 6% 42%	2730
	11th to 20th	Night	15% 9% 4 7% 3 4 3 2 3 5% 45%	2599
	21st to end	Night	15% 9% 2 6% 4 4 4 3 4 4 46%	1852
March	1st to 10th	Night	14% 10% 3 6% 4 3 3 3 4 4 46%	4919
	11th to 20th	Night	9% 8% 2 5% 3 3 3 3 5% 6% 53%	4980
	21st to end	Night	12% 7% 2 6% 4 4 4 3 5% 8% 43%	5467
April	1st to 10th	Night	14% 7% 1 5% 3 3 3 3 5% 5% 50%	2090
	11th to 20th	Night	13% 6% 2 6% 3 3 4 3 5% 7% 48%	1975
	21st to end	Night	18% 6% 3 6% 3 3 4 3 4 6% 44%	1980
May	1st to 10th	Night	15% 8% 3 6% 4 3 3 3 3 6% 45%	4053
	11th to 20th	Night	12% 7% 2 6% 5% 4 4 4 6% 8% 44%	4053
	21st to end	Night	17% 9% 2 5% 3 4 4 3 5% 7% 41%	4443
June	1st to 10th	Night	7% 4 2 4 4 3 3 3 6% 8% 54%	1800
	11th to 20th	Night	5% 4 1 4 3 4 4 4 6% 11% 55%	1800
	21st to end	Night	2 3 1 4 3 3 4 4 6% 7% 63%	1800
July	1st to 10th	Night	7% 4 2 5% 3 4 5% 4 7% 10% 49%	4078
	11th to 20th	Night	4 3 1 4 3 3 4 4 6% 8% 61%	4077
	21st to end	Night	4 2 1 4 3 3 4 3 6% 10% 58%	4449
August	1st to 10th	Night	3 2 1 3 3 4 4 4 7% 10% 60%	2926
	11th to 20th	Night	7% 4 2 5% 4 4 4 4 6% 8% 52%	2919
	21st to end	Night	3 3 1 3 2 3 3 4 5% 8% 63%	3586
September	1st to 10th	Night	9% 4 2 4 3 3 4 2 5% 7% 57%	2000
	11th to 20th	Night	9% 5% 2 6% 4 3 4 3 5% 8% 52%	2165
	21st to end	Night	8% 4 2 5% 3 4 3 3 5% 7% 56%	2205
October	1st to 10th	Night	6% 3 1 4 3 3 3 2 5% 8% 62%	2400
	11th to 20th	Night	13% 5% 2 4 2 3 4 3 4 5% 57%	2400
	21st to end	Night	17% 7% 2 5% 3 2 3 2 3 4 51%	2640
November	1st to 10th	Night	12% 5% 1 4 3 3 3 2 3 5% 60%	2460
	11th to 20th	Night	10% 7% 2 4 2 3 3 3 4 5% 56%	2587
	21st to end	Night	15% 8% 2 5% 2 3 3 3 4 5% 51%	2849
December	1st to 10th	Night	11% 9% 3 5% 3 2 2 2 4 6% 52%	4720
	11th to 20th	Night	18% 8% 3 5% 3 3 3 2 3 4 49%	5142
	21st to end	Night	18% 15% 6% 7% 4 3 3 2 3 4 34%	6633

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	37% 20% 5% 21% 14% 2	5290
	11th to 20th	Day	27% 20% 6% 24% 18% 5%	5310
	21st to end	Day	32% 22% 5% 17% 18% 6%	5812
February	1st to 10th	Day	19% 59% 4 11% 6% 2	1890
	11th to 20th	Day	19% 59% 5% 9% 7% 1	1811
	21st to end	Day	16% 62% 2 7% 9% 4	1791
March	1st to 10th	Day	27% 30% 4 15% 10% 14%	4936
	11th to 20th	Day	18% 29% 7% 14% 21% 11%	4980
	21st to end	Day	32% 31% 7% 23% 7%	5464
April	1st to 10th	Day	17% 61% 5% 9% 6% 1	2310
	11th to 20th	Day	18% 63% 4 8% 7%	2374
	21st to end	Day	19% 62% 4 9% 6% 1	2415
May	1st to 10th	Day	35% 31% 6% 15% 12% 1	5900
	11th to 20th	Day	30% 32% 8% 17% 12% 2	5866
	21st to end	Day	37% 30% 7% 12% 14% 1	6447
June	1st to 10th	Day	13% 63% 7% 9% 7% 1	2600
	11th to 20th	Day	15% 63% 6% 10% 6% 1	2600
	21st to end	Day	10% 62% 7% 14% 7%	2600
July	1st to 10th	Day	25% 29% 13% 20% 11% 2	5836
	11th to 20th	Day	25% 28% 11% 25% 10%	5831
	21st to end	Day	18% 28% 17% 28% 9%	6240
August	1st to 10th	Day	14% 37% 10% 20% 16% 3	4220
	11th to 20th	Day	22% 39% 12% 18% 8%	4177
	21st to end	Day	18% 38% 8% 29% 7%	4311
September	1st to 10th	Day	11% 57% 7% 14% 8% 3	2400
	11th to 20th	Day	16% 58% 6% 12% 7%	2230
	21st to end	Day	16% 58% 5% 12% 9%	2173
October	1st to 10th	Day	8% 36% 3 7% 30% 15%	3260
	11th to 20th	Day	8% 35% 2 12% 29% 12%	3240
	21st to end	Day	16% 35% 5% 21% 19% 3	3538
November	1st to 10th	Day	16% 53% 3 12% 12% 3	2058
	11th to 20th	Day	16% 54% 4 11% 10% 5%	2030
	21st to end	Day	20% 54% 3 13% 10% 1	1764
December	1st to 10th	Day	24% 34% 4 22% 16%	2690
	11th to 20th	Day	26% 30% 2 22% 18% 2	3255
	21st to end	Day	49% 26% 3 14% 7% 1	4587
January	1st to 10th	Night	38% 21% 7% 21% 11% 2	7635
	11th to 20th	Night	25% 21% 6% 15% 28% 4	7680
	21st to end	Night	38% 22% 7% 12% 19% 3	8402
February	1st to 10th	Night	17% 59% 4 12% 6% 2	2730
	11th to 20th	Night	19% 59% 3 10% 7% 1	2600
	21st to end	Night	15% 61% 3 7% 11% 3	1852
March	1st to 10th	Night	33% 29% 4 12% 15% 7%	4919
	11th to 20th	Night	19% 30% 4 19% 18% 10%	4980
	21st to end	Night	26% 31% 9% 22% 11% 1	5467
April	1st to 10th	Night	15% 62% 5% 10% 8% 1	2090
	11th to 20th	Night	14% 63% 4 11% 6% 1	1975
	21st to end	Night	17% 62% 5% 9% 7% 1	1980
May	1st to 10th	Night	30% 31% 8% 19% 9% 2	4080
	11th to 20th	Night	28% 31% 10% 18% 9% 3	4054
	21st to end	Night	32% 32% 8% 16% 10% 2	4452
June	1st to 10th	Night	11% 63% 5% 11% 8% 2	1800
	11th to 20th	Night	9% 63% 7% 12% 8% 1	1800
	21st to end	Night	8% 61% 8% 14% 9%	1800
July	1st to 10th	Night	24% 29% 14% 20% 10% 3	4035
	11th to 20th	Night	16% 28% 11% 33% 12%	4026
	21st to end	Night	14% 27% 16% 30% 13%	4320
August	1st to 10th	Night	10% 38% 10% 23% 18% 1	2916
	11th to 20th	Night	20% 38% 13% 19% 9% 1	2946
	21st to end	Night	12% 37% 8% 30% 12% 1	3586
September	1st to 10th	Night	10% 58% 6% 14% 9% 3	2000
	11th to 20th	Night	12% 58% 6% 14% 9% 2	2165
	21st to end	Night	15% 57% 6% 10% 10% 1	2205
October	1st to 10th	Night	6% 36% 3 7% 30% 19%	3920
	11th to 20th	Night	10% 35% 3 12% 24% 17%	3899
	21st to end	Night	18% 36% 4 22% 17% 4	4252
November	1st to 10th	Night	16% 53% 3 10% 14% 4	2460
	11th to 20th	Night	13% 54% 3 12% 12% 6%	2587
	21st to end	Night	19% 54% 3 11% 12% 1	2849
December	1st to 10th	Night	23% 34% 4 27% 11% 1	4720
	11th to 20th	Night	27% 31% 3 17% 19% 4	5143
	21st to end	Night	46% 26% 5% 14% 7% 2	6633

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% 19% 41% 12% 3	330
	11th to 20th	Day	24% 24% 40% 10% 1	330
	21st to end	Day	21% 27% 38% 10% 4	363
February	1st to 10th	Day	29% 24% 35% 11% 1	330
	11th to 20th	Day	33% 26% 30% 10% 1	315
	21st to end	Day	32% 25% 33% 9% 1	249
March	1st to 10th	Day	27% 25% 32% 14% 2	300
	11th to 20th	Day	31% 23% 35% 11%	300
	21st to end	Day	31% 26% 34% 6% 2	330
April	1st to 10th	Day	26% 26% 31% 13% 4	410
	11th to 20th	Day	27% 21% 34% 15% 4	492
	21st to end	Day	26% 19% 33% 17% 4	515
May	1st to 10th	Day	20% 17% 39% 19% 5%	703
	11th to 20th	Day	17% 14% 34% 24% 9% 2	725
	21st to end	Day	15% 12% 35% 23% 12% 3	789
June	1st to 10th	Day	8% 6% 25% 36% 20% 4	730
	11th to 20th	Day	9% 4 25% 39% 20% 3	730
	21st to end	Day	4 4 33% 36% 20% 3	730
July	1st to 10th	Day	10% 4 18% 32% 29% 7%	721
	11th to 20th	Day	6% 3 19% 39% 27% 6%	718
	21st to end	Day	7% 2 14% 37% 30% 9%	794
August	1st to 10th	Day	9% 2 20% 41% 24% 4	726
	11th to 20th	Day	10% 3 16% 36% 31% 5%	695
	21st to end	Day	9% 1 16% 36% 30% 9%	583
September	1st to 10th	Day	10% 3 16% 38% 27% 6%	530
	11th to 20th	Day	9% 2 23% 43% 17% 6%	360
	21st to end	Day	9% 10% 30% 30% 17% 4	330
October	1st to 10th	Day	8% 10% 35% 30% 14% 3	330
	11th to 20th	Day	16% 14% 40% 22% 8% 1	330
	21st to end	Day	29% 17% 35% 15% 4 1	363
November	1st to 10th	Day	17% 18% 40% 19% 5% 1	330
	11th to 20th	Day	22% 18% 35% 19% 5% 2	330
	21st to end	Day	30% 16% 34% 15% 4	330
December	1st to 10th	Day	23% 24% 35% 12% 5% 1	330
	11th to 20th	Day	24% 23% 36% 13% 3	330
	21st to end	Day	29% 23% 37% 10% 2	363
January	1st to 10th	Night	20% 20% 34% 22% 4	1050
	11th to 20th	Night	19% 22% 39% 17% 4	1050
	21st to end	Night	19% 21% 37% 21% 3	1155
February	1st to 10th	Night	22% 17% 40% 18% 3	1050
	11th to 20th	Night	23% 20% 38% 17% 2	1005
	21st to end	Night	24% 19% 34% 21% 2	532
March	1st to 10th	Night	21% 15% 39% 22% 3	600
	11th to 20th	Night	24% 16% 34% 23% 3	600
	21st to end	Night	22% 17% 39% 17% 5%	660
April	1st to 10th	Night	18% 17% 38% 23% 3	600
	11th to 20th	Night	17% 17% 36% 24% 7%	593
	21st to end	Night	22% 12% 40% 18% 8%	600
May	1st to 10th	Night	16% 7% 40% 30% 7%	600
	11th to 20th	Night	16% 6% 33% 30% 13% 1	591
	21st to end	Night	14% 8% 32% 29% 17% 1	650
June	1st to 10th	Night	9% 5% 18% 40% 28%	600
	11th to 20th	Night	6% 3 27% 42% 21% 1	600
	21st to end	Night	3 1 26% 47% 21% 2	600
July	1st to 10th	Night	7% 1 14% 40% 35% 4	585
	11th to 20th	Night	5% 1 13% 43% 32% 5%	582
	21st to end	Night	5% 2 12% 45% 32% 6%	657
August	1st to 10th	Night	5% 2 15% 43% 33% 2	597
	11th to 20th	Night	8% 2 14% 43% 29% 4	594
	21st to end	Night	4 2 17% 38% 35% 5%	660
September	1st to 10th	Night	10% 2 17% 41% 29% 2	600
	11th to 20th	Night	12% 1 16% 41% 26% 4	600
	21st to end	Night	10% 4 25% 35% 23% 3	605
October	1st to 10th	Night	7% 4 29% 35% 22% 4	800
	11th to 20th	Night	15% 8% 37% 30% 10%	800
	21st to end	Night	22% 11% 34% 25% 8% 1	880
November	1st to 10th	Night	15% 11% 40% 24% 9% 1	820
	11th to 20th	Night	17% 14% 37% 26% 7%	907
	21st to end	Night	21% 15% 35% 21% 8%	1050
December	1st to 10th	Night	20% 14% 39% 23% 4	1050
	11th to 20th	Night	24% 15% 34% 24% 3	1050
	21st to end	Night	22% 20% 36% 19% 3	1155

Page generated at 2026-02-13 00:42:16. Version ac07

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