Visalia
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Visalia clear sky chart from 2005-11-06 to 2025-05-11.

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	5% 3 1 3 3 2 3 2 4 5% 68%	117730
	Night	7% 3 1 4 3 3 3 2 4 5% 65%	120109
Transparency	Day	19% 4 9% 18% 25% 24%	117480
	Night	21% 5% 10% 20% 24% 20%	119949
Seeing	Day	6% 3 12% 28% 34% 18%	15970
	Night	7% 2 11% 38% 36% 6%	25658

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	7% 11% 3 7% 6% 5% 4 4 5% 7% 41%	3639
	11th to 20th	Day	6% 6% 2 6% 5% 5% 4 3 4 5% 54%	3944
	21st to end	Day	12% 8% 2 6% 4 4 5% 3 5% 7% 44%	4510
February	1st to 10th	Day	12% 7% 2 5% 4 3 3 3 5% 6% 50%	1954
	11th to 20th	Day	11% 5% 2 4 4 3 4 3 5% 8% 52%	1950
	21st to end	Day	12% 7% 2 5% 5% 3 5% 3 5% 6% 48%	1650
March	1st to 10th	Day	13% 6% 2 6% 4 4 5% 4 6% 8% 42%	4518
	11th to 20th	Day	10% 4 2 5% 3 3 4 3 5% 7% 54%	4858
	21st to end	Day	11% 4 2 5% 4 4 4 4 5% 7% 51%	5897
April	1st to 10th	Day	8% 4 1 3 3 3 3 3 5% 7% 62%	2400
	11th to 20th	Day	7% 4 1 4 4 2 3 3 5% 6% 62%	2369
	21st to end	Day	5% 2 1 3 2 2 2 3 5% 6% 69%	2400
May	1st to 10th	Day	3 1 2 1 1 2 1 2 3 82%	4011
	11th to 20th	Day	1 1 2 1 1 2 2 3 4 82%	4073
	21st to end	Day	2 1 1 1 1 2 1 2 3 84%	4709
June	1st to 10th	Day	2 1 1 2 2 2 2 2 4 7% 75%	2660
	11th to 20th	Day	1 1 1 1 1 1 2 2 90%	2660
	21st to end	Day	1 1 1 1 1 1 1 2 2 88%	2660
July	1st to 10th	Day	1 1 1 1 1 1 1 2 93%	4420
	11th to 20th	Day	1 1 1 1 1 2 2 3 3 85%	4420
	21st to end	Day	1 1 1 1 1 1 1 2 3 88%	4520
August	1st to 10th	Day	2 1 1 1 1 1 2 2 3 87%	3797
	11th to 20th	Day	1 1 1 1 2 93%	3724
	21st to end	Day	1 1 1 1 1 1 2 92%	4180
September	1st to 10th	Day	1 1 1 1 1 1 1 2 89%	2280
	11th to 20th	Day	1 1 1 1 1 1 2 3 87%	2210
	21st to end	Day	1 1 2 1 1 2 2 3 4 84%	2090
October	1st to 10th	Day	2 1 1 1 1 2 3 3 5% 80%	3367
	11th to 20th	Day	1 2 1 2 2 2 3 2 3 4 78%	3161
	21st to end	Day	2 2 1 3 2 2 3 3 4 6% 71%	3419
November	1st to 10th	Day	6% 3 1 3 3 2 3 3 4 7% 64%	1764
	11th to 20th	Day	8% 5% 2 5% 3 3 3 2 5% 6% 59%	1800
	21st to end	Day	8% 6% 2 4 4 3 4 3 6% 5% 54%	1800
December	1st to 10th	Day	6% 6% 2 7% 5% 6% 6% 5% 5% 6% 46%	2884
	11th to 20th	Day	13% 7% 3 9% 6% 4 4 4 7% 8% 36%	3028
	21st to end	Day	15% 13% 4 9% 5% 4 5% 5% 5% 6% 28%	4004
January	1st to 10th	Night	11% 7% 3 6% 4 4 4 3 5% 7% 47%	6306
	11th to 20th	Night	8% 5% 2 5% 3 3 3 2 4 6% 58%	6012
	21st to end	Night	14% 6% 2 5% 3 3 4 3 5% 6% 48%	6468
February	1st to 10th	Night	14% 5% 2 4 3 3 3 3 4 6% 53%	2443
	11th to 20th	Night	11% 4 1 4 3 2 2 3 4 6% 58%	2338
	21st to end	Night	13% 4 1 4 3 4 3 3 4 6% 56%	1980
March	1st to 10th	Night	12% 5% 2 6% 3 3 4 4 6% 8% 47%	5376
	11th to 20th	Night	9% 4 2 5% 3 4 4 3 5% 7% 55%	5139
	21st to end	Night	14% 5% 2 6% 4 3 4 3 4 5% 50%	5077
April	1st to 10th	Night	8% 4 1 3 3 3 3 3 4 6% 63%	2000
	11th to 20th	Night	6% 3 1 4 3 2 3 3 5% 6% 65%	1979
	21st to end	Night	5% 3 1 3 2 2 3 3 4 6% 70%	2000
May	1st to 10th	Night	5% 2 1 2 1 1 1 1 2 4 79%	3184
	11th to 20th	Night	2 1 1 1 1 2 2 3 4 82%	2838
	21st to end	Night	2 1 1 1 1 1 1 2 1 3 86%	2865
June	1st to 10th	Night	3 2 1 2 2 2 2 3 6% 77%	1520
	11th to 20th	Night	1 1 1 1 1 2 2 3 88%	1520
	21st to end	Night	1 1 1 1 2 3 90%	1520
July	1st to 10th	Night	1 1 1 1 2 2 93%	2540
	11th to 20th	Night	1 1 1 2 1 1 2 1 2 3 86%	2540
	21st to end	Night	1 1 2 1 1 1 1 2 3 87%	3036
August	1st to 10th	Night	1 1 2 1 1 1 1 3 4 85%	3152
	11th to 20th	Night	1 1 1 1 2 93%	3126
	21st to end	Night	1 1 1 1 1 1 2 91%	3498
September	1st to 10th	Night	1 1 1 1 1 1 1 2 3 89%	1900
	11th to 20th	Night	1 1 1 2 1 2 1 3 3 85%	1968
	21st to end	Night	1 1 1 1 1 1 1 3 5% 84%	2090
October	1st to 10th	Night	2 1 1 1 1 1 1 2 5% 84%	3609
	11th to 20th	Night	1 1 1 1 1 1 2 2 3 4 81%	3777
	21st to end	Night	3 2 1 2 1 2 2 1 2 4 80%	4146
November	1st to 10th	Night	5% 3 1 3 3 3 2 3 3 6% 68%	2535
	11th to 20th	Night	5% 3 1 3 3 2 3 2 4 7% 66%	2600
	21st to end	Night	8% 5% 2 4 4 3 3 3 6% 6% 57%	2600
December	1st to 10th	Night	6% 3 1 5% 4 5% 5% 5% 6% 6% 54%	4299
	11th to 20th	Night	13% 5% 2 6% 5% 5% 5% 4 6% 9% 40%	5176
	21st to end	Night	11% 8% 3 8% 5% 6% 6% 4 7% 8% 32%	6952

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	38% 11% 20% 16% 14% 1	3639
	11th to 20th	Day	30% 9% 11% 15% 21% 14%	3944
	21st to end	Day	36% 8% 13% 16% 24% 4	4510
February	1st to 10th	Day	34% 5% 14% 26% 16% 5%	1954
	11th to 20th	Day	31% 7% 13% 25% 18% 6%	1960
	21st to end	Day	36% 8% 11% 27% 15% 3	1650
March	1st to 10th	Day	37% 8% 13% 20% 20% 3	4518
	11th to 20th	Day	29% 7% 14% 33% 12% 4	4858
	21st to end	Day	31% 7% 14% 30% 15% 3	5897
April	1st to 10th	Day	25% 4 11% 31% 22% 7%	2400
	11th to 20th	Day	23% 5% 12% 27% 24% 9%	2372
	21st to end	Day	18% 6% 11% 31% 28% 7%	2400
May	1st to 10th	Day	11% 3 9% 24% 37% 17%	4011
	11th to 20th	Day	9% 3 5% 26% 42% 15%	4076
	21st to end	Day	8% 3 5% 28% 42% 14%	4709
June	1st to 10th	Day	12% 3 9% 21% 34% 22%	2660
	11th to 20th	Day	4 2 5% 13% 39% 37%	2660
	21st to end	Day	5% 2 2 9% 28% 54%	2660
July	1st to 10th	Day	3 1 1 3 14% 77%	4351
	11th to 20th	Day	6% 2 3 5% 18% 66%	4345
	21st to end	Day	5% 1 2 9% 30% 53%	4377
August	1st to 10th	Day	6% 1 2 5% 32% 53%	3783
	11th to 20th	Day	3 2 5% 25% 64%	3760
	21st to end	Day	3 1 2 8% 31% 55%	4179
September	1st to 10th	Day	6% 1 4 7% 29% 54%	2280
	11th to 20th	Day	6% 2 3 17% 42% 30%	2210
	21st to end	Day	7% 2 4 16% 42% 30%	2090
October	1st to 10th	Day	9% 2 4 13% 24% 48%	3367
	11th to 20th	Day	12% 3 5% 24% 35% 20%	3161
	21st to end	Day	16% 3 6% 18% 36% 21%	3419
November	1st to 10th	Day	20% 6% 10% 24% 28% 12%	1764
	11th to 20th	Day	25% 4 17% 23% 25% 6%	1800
	21st to end	Day	30% 6% 8% 23% 23% 10%	1800
December	1st to 10th	Day	30% 9% 15% 23% 18% 5%	2884
	11th to 20th	Day	42% 9% 12% 20% 14% 3	3028
	21st to end	Day	52% 9% 15% 17% 6% 1	4004
January	1st to 10th	Night	34% 9% 19% 24% 13% 1	6306
	11th to 20th	Night	28% 7% 15% 14% 28% 9%	6012
	21st to end	Night	36% 7% 11% 20% 23% 4	6468
February	1st to 10th	Night	34% 5% 9% 28% 18% 6%	2443
	11th to 20th	Night	28% 4 13% 28% 20% 7%	2339
	21st to end	Night	32% 5% 12% 30% 17% 4	1980
March	1st to 10th	Night	34% 8% 12% 24% 19% 3	5376
	11th to 20th	Night	28% 7% 17% 33% 12% 4	5139
	21st to end	Night	36% 6% 16% 24% 16% 2	5077
April	1st to 10th	Night	24% 5% 11% 31% 21% 8%	2000
	11th to 20th	Night	20% 6% 10% 29% 26% 9%	1979
	21st to end	Night	17% 4 10% 31% 33% 5%	2000
May	1st to 10th	Night	12% 3 5% 28% 37% 15%	3184
	11th to 20th	Night	9% 2 4 24% 42% 19%	2839
	21st to end	Night	8% 3 5% 24% 43% 18%	2865
June	1st to 10th	Night	11% 3 8% 21% 34% 23%	1520
	11th to 20th	Night	4 3 5% 13% 35% 40%	1520
	21st to end	Night	3 1 3 6% 30% 57%	1520
July	1st to 10th	Night	2 1 2 3 13% 80%	2500
	11th to 20th	Night	7% 1 3 6% 14% 70%	2492
	21st to end	Night	6% 1 2 7% 26% 57%	2941
August	1st to 10th	Night	7% 1 2 6% 29% 55%	3143
	11th to 20th	Night	2 2 5% 23% 67%	3156
	21st to end	Night	4 1 1 7% 27% 60%	3498
September	1st to 10th	Night	5% 1 2 8% 28% 57%	1900
	11th to 20th	Night	8% 1 4 14% 41% 32%	1968
	21st to end	Night	7% 1 2 16% 39% 34%	2090
October	1st to 10th	Night	8% 2 2 11% 27% 50%	3609
	11th to 20th	Night	9% 2 4 21% 42% 21%	3777
	21st to end	Night	12% 2 5% 21% 39% 22%	4146
November	1st to 10th	Night	18% 5% 10% 24% 28% 14%	2535
	11th to 20th	Night	19% 4 15% 24% 28% 9%	2600
	21st to end	Night	27% 4 11% 21% 28% 8%	2600
December	1st to 10th	Night	24% 7% 17% 27% 18% 7%	4299
	11th to 20th	Night	37% 9% 16% 19% 16% 2	5176
	21st to end	Night	44% 10% 18% 21% 6% 1	6952

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	20% 7% 10% 33% 23% 9%	200
	11th to 20th	Day	12% 4 10% 35% 24% 16%	335
	21st to end	Day	15% 3 11% 28% 30% 13%	440
February	1st to 10th	Day	14% 4 12% 31% 25% 15%	477
	11th to 20th	Day	13% 4 17% 34% 24% 9%	495
	21st to end	Day	10% 5% 18% 33% 27% 7%	414
March	1st to 10th	Day	13% 6% 17% 33% 23% 8%	500
	11th to 20th	Day	10% 5% 19% 32% 24% 9%	500
	21st to end	Day	12% 6% 23% 31% 21% 7%	550
April	1st to 10th	Day	10% 5% 19% 28% 25% 13%	500
	11th to 20th	Day	7% 7% 22% 30% 28% 7%	492
	21st to end	Day	3 6% 20% 30% 25% 16%	500
May	1st to 10th	Day	3 6% 22% 30% 27% 11%	503
	11th to 20th	Day	2 2 19% 34% 26% 16%	489
	21st to end	Day	4 4 17% 22% 37% 16%	529
June	1st to 10th	Day	1 3 12% 28% 33% 22%	490
	11th to 20th	Day	2 2 14% 24% 42% 17%	490
	21st to end	Day	1 1 7% 30% 40% 22%	490
July	1st to 10th	Day	1 3 22% 49% 24%	486
	11th to 20th	Day	1 2 16% 45% 36%	484
	21st to end	Day	2 2 16% 50% 31%	531
August	1st to 10th	Day	2 7% 24% 45% 21%	487
	11th to 20th	Day	1 4 22% 46% 26%	477
	21st to end	Day	1 1 3 23% 45% 27%	539
September	1st to 10th	Day	1 1 5% 26% 43% 24%	490
	11th to 20th	Day	1 2 11% 29% 43% 15%	490
	21st to end	Day	1 2 11% 24% 39% 23%	490
October	1st to 10th	Day	2 2 11% 30% 32% 23%	490
	11th to 20th	Day	3 3 10% 26% 38% 20%	490
	21st to end	Day	1 4 10% 27% 35% 23%	522
November	1st to 10th	Day	5% 2 9% 28% 36% 20%	300
	11th to 20th	Day	7% 4 7% 31% 33% 19%	300
	21st to end	Day	11% 3 11% 28% 31% 16%	300
December	1st to 10th	Day	12% 3 12% 31% 28% 14%	280
	11th to 20th	Day	11% 5% 10% 32% 21% 22%	200
	21st to end	Day	21% 5% 10% 29% 26% 8%	220
January	1st to 10th	Night	18% 2 9% 35% 27% 9%	800
	11th to 20th	Night	9% 2 9% 42% 32% 7%	800
	21st to end	Night	15% 3 9% 37% 31% 5%	880
February	1st to 10th	Night	15% 2 10% 37% 28% 8%	800
	11th to 20th	Night	13% 3 13% 38% 27% 7%	784
	21st to end	Night	13% 3 12% 44% 25% 3	660
March	1st to 10th	Night	11% 4 13% 45% 25% 3	800
	11th to 20th	Night	11% 4 12% 40% 28% 5%	800
	21st to end	Night	13% 3 17% 39% 25% 3	880
April	1st to 10th	Night	9% 4 22% 37% 27% 2	800
	11th to 20th	Night	6% 5% 20% 39% 28% 2	791
	21st to end	Night	6% 6% 20% 36% 28% 5%	800
May	1st to 10th	Night	5% 4 21% 41% 27% 2	743
	11th to 20th	Night	5% 3 20% 40% 31% 1	563
	21st to end	Night	3 5% 25% 37% 28% 1	476
June	1st to 10th	Night	3 3 21% 46% 24% 2	380
	11th to 20th	Night	1 3 17% 48% 29% 2	380
	21st to end	Night	1 16% 49% 32% 2	380
July	1st to 10th	Night	6% 49% 43% 2	370
	11th to 20th	Night	1 5% 40% 53% 2	368
	21st to end	Night	1 1 3 28% 58% 10%	577
August	1st to 10th	Night	3 5% 36% 50% 5%	742
	11th to 20th	Night	4 34% 55% 7%	752
	21st to end	Night	1 3 26% 62% 9%	836
September	1st to 10th	Night	1 1 4 27% 59% 8%	760
	11th to 20th	Night	1 1 9% 37% 45% 7%	760
	21st to end	Night	1 1 7% 33% 47% 10%	760
October	1st to 10th	Night	4 1 8% 39% 40% 8%	760
	11th to 20th	Night	3 2 8% 34% 43% 10%	760
	21st to end	Night	4 1 7% 33% 40% 14%	836
November	1st to 10th	Night	6% 2 8% 31% 41% 12%	780
	11th to 20th	Night	6% 1 7% 41% 37% 9%	800
	21st to end	Night	10% 2 9% 38% 34% 8%	800
December	1st to 10th	Night	12% 1 8% 41% 32% 6%	800
	11th to 20th	Night	15% 2 8% 41% 29% 6%	800
	21st to end	Night	14% 3 10% 42% 27% 3	880

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