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 2024-11-01.

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 2 2 3 2 4 5% 70%	100925
	Night	7% 3 1 3 2 2 3 2 4 5% 66%	98242
Transparency	Day	18% 4 8% 18% 25% 26%	100675
	Night	21% 5% 9% 19% 23% 22%	98082
Seeing	Day	6% 3 12% 27% 34% 18%	15335
	Night	7% 2 11% 37% 36% 6%	24897

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	10% 14% 4 8% 6% 5% 4 4 5% 6% 33%	2539
	11th to 20th	Day	9% 8% 3 9% 7% 6% 5% 4 6% 7% 36%	2746
	21st to end	Day	16% 10% 3 7% 5% 5% 5% 4 6% 7% 33%	3146
February	1st to 10th	Day	11% 7% 2 4 4 4 3 3 5% 5% 51%	1856
	11th to 20th	Day	10% 5% 2 4 4 3 3 3 5% 7% 53%	1850
	21st to end	Day	13% 7% 2 5% 5% 3 4 3 5% 6% 47%	1570
March	1st to 10th	Day	10% 6% 2 7% 5% 4 5% 4 7% 8% 42%	3138
	11th to 20th	Day	5% 4 1 3 2 2 3 3 5% 7% 63%	3387
	21st to end	Day	12% 5% 2 6% 4 4 5% 4 6% 6% 46%	4119
April	1st to 10th	Day	8% 4 1 3 3 3 3 3 5% 6% 61%	2280
	11th to 20th	Day	7% 4 1 4 4 2 2 3 5% 6% 62%	2249
	21st to end	Day	5% 2 1 3 2 2 2 3 5% 6% 69%	2280
May	1st to 10th	Day	3 1 1 1 1 2 1 2 3 82%	3888
	11th to 20th	Day	1 1 2 1 1 2 2 3 4 82%	4071
	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	3 2 1 2 2 2 3 2 3 5% 75%	2015
	11th to 20th	Day	2 2 2 2 2 3 2 4 4 77%	1900
	21st to end	Day	3 2 1 3 2 2 3 2 3 5% 75%	2073
November	1st to 10th	Day	6% 3 1 3 3 3 3 3 4 7% 64%	1674
	11th to 20th	Day	8% 5% 2 5% 3 3 3 2 5% 5% 59%	1710
	21st to end	Day	8% 5% 1 4 4 3 4 3 6% 6% 56%	1710
December	1st to 10th	Day	10% 7% 2 6% 4 4 5% 4 5% 6% 48%	1672
	11th to 20th	Day	16% 7% 3 9% 5% 4 5% 3 5% 7% 35%	1928
	21st to end	Day	14% 12% 4 9% 5% 5% 5% 5% 5% 6% 30%	2794
January	1st to 10th	Night	15% 9% 3 7% 4 3 4 3 4 6% 42%	4406
	11th to 20th	Night	12% 8% 3 8% 4 5% 4 3 5% 8% 41%	4203
	21st to end	Night	18% 7% 3 6% 4 4 4 3 6% 7% 38%	4521
February	1st to 10th	Night	14% 5% 2 4 3 3 3 3 4 6% 54%	2321
	11th to 20th	Night	10% 4 1 4 2 2 3 3 4 7% 59%	2218
	21st to end	Night	13% 5% 2 4 3 4 4 3 4 6% 54%	1884
March	1st to 10th	Night	12% 5% 2 5% 3 4 4 4 7% 8% 47%	3736
	11th to 20th	Night	6% 3 1 4 2 4 4 3 4 7% 63%	3590
	21st to end	Night	16% 5% 2 6% 4 3 4 3 5% 5% 46%	3533
April	1st to 10th	Night	8% 4 1 4 3 3 3 3 4 6% 63%	1900
	11th to 20th	Night	6% 2 1 3 3 2 3 3 5% 6% 66%	1879
	21st to end	Night	5% 2 1 2 2 2 3 3 4 6% 70%	1900
May	1st to 10th	Night	5% 2 1 2 1 1 1 1 2 4 80%	3087
	11th to 20th	Night	2 1 1 1 1 2 2 3 4 82%	2834
	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	3 2 1 2 2 2 2 2 3 6% 75%	2161
	11th to 20th	Night	2 2 1 2 2 1 2 2 4 5% 76%	2280
	21st to end	Night	4 1 1 1 1 2 2 1 3 3 81%	2522
November	1st to 10th	Night	5% 3 1 3 3 3 3 3 3 6% 68%	2411
	11th to 20th	Night	6% 3 1 3 3 2 3 2 4 7% 66%	2470
	21st to end	Night	8% 4 2 4 3 3 3 3 5% 6% 58%	2470
December	1st to 10th	Night	10% 5% 2 6% 4 3 3 3 4 6% 54%	2503
	11th to 20th	Night	17% 6% 3 6% 4 4 4 4 6% 7% 39%	3276
	21st to end	Night	12% 7% 3 8% 5% 5% 6% 4 6% 7% 37%	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	46% 12% 17% 17% 7% 1	2539
	11th to 20th	Day	42% 14% 16% 15% 9% 4	2746
	21st to end	Day	46% 10% 16% 17% 10% 2	3146
February	1st to 10th	Day	33% 5% 14% 25% 17% 5%	1856
	11th to 20th	Day	31% 7% 12% 25% 19% 6%	1860
	21st to end	Day	37% 8% 11% 26% 16% 2	1570
March	1st to 10th	Day	38% 9% 14% 21% 16% 2	3138
	11th to 20th	Day	21% 8% 13% 35% 17% 6%	3387
	21st to end	Day	35% 8% 15% 25% 15% 3	4119
April	1st to 10th	Day	25% 4 11% 30% 21% 7%	2280
	11th to 20th	Day	23% 5% 12% 27% 23% 9%	2252
	21st to end	Day	17% 6% 11% 31% 29% 7%	2280
May	1st to 10th	Day	11% 3 9% 24% 37% 17%	3888
	11th to 20th	Day	9% 3 5% 26% 42% 15%	4074
	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	14% 3 6% 20% 27% 30%	2015
	11th to 20th	Day	12% 4 5% 23% 30% 25%	1900
	21st to end	Day	14% 3 8% 20% 32% 23%	2073
November	1st to 10th	Day	20% 7% 10% 23% 28% 12%	1674
	11th to 20th	Day	25% 5% 17% 22% 26% 6%	1710
	21st to end	Day	28% 7% 8% 24% 23% 10%	1710
December	1st to 10th	Day	33% 7% 15% 19% 18% 8%	1672
	11th to 20th	Day	47% 8% 12% 16% 13% 4	1928
	21st to end	Day	49% 10% 14% 17% 8% 2	2794
January	1st to 10th	Night	42% 9% 16% 23% 9% 1	4406
	11th to 20th	Night	39% 10% 21% 15% 9% 5%	4203
	21st to end	Night	43% 8% 14% 20% 11% 3	4521
February	1st to 10th	Night	34% 4 10% 27% 18% 6%	2321
	11th to 20th	Night	27% 4 12% 28% 22% 7%	2219
	21st to end	Night	33% 5% 12% 29% 17% 3	1884
March	1st to 10th	Night	32% 10% 13% 26% 17% 3	3736
	11th to 20th	Night	21% 6% 15% 35% 16% 6%	3590
	21st to end	Night	40% 7% 13% 24% 14% 3	3533
April	1st to 10th	Night	24% 5% 11% 30% 21% 9%	1900
	11th to 20th	Night	20% 6% 10% 29% 26% 9%	1879
	21st to end	Night	17% 4 10% 30% 34% 5%	1900
May	1st to 10th	Night	12% 3 5% 28% 37% 16%	3087
	11th to 20th	Night	9% 2 4 24% 42% 19%	2835
	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	13% 3 4 17% 30% 32%	2161
	11th to 20th	Night	12% 3 6% 21% 32% 26%	2280
	21st to end	Night	12% 2 5% 25% 34% 23%	2522
November	1st to 10th	Night	19% 6% 10% 23% 28% 14%	2411
	11th to 20th	Night	19% 4 15% 24% 28% 10%	2470
	21st to end	Night	26% 4 11% 21% 29% 9%	2470
December	1st to 10th	Night	31% 6% 13% 21% 18% 11%	2503
	11th to 20th	Night	42% 8% 13% 19% 15% 4	3276
	21st to end	Night	41% 10% 17% 21% 9% 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	22% 7% 10% 31% 24% 7%	180
	11th to 20th	Day	13% 4 10% 33% 23% 16%	308
	21st to end	Day	15% 3 11% 28% 30% 12%	407
February	1st to 10th	Day	14% 3 11% 30% 25% 16%	439
	11th to 20th	Day	13% 4 17% 34% 23% 10%	455
	21st to end	Day	11% 5% 19% 34% 25% 6%	382
March	1st to 10th	Day	13% 6% 17% 33% 24% 7%	460
	11th to 20th	Day	9% 5% 19% 32% 25% 9%	460
	21st to end	Day	12% 6% 24% 32% 20% 6%	506
April	1st to 10th	Day	11% 5% 19% 27% 26% 12%	460
	11th to 20th	Day	7% 8% 23% 29% 28% 7%	452
	21st to end	Day	3 6% 21% 31% 24% 15%	460
May	1st to 10th	Day	3 6% 24% 30% 27% 11%	463
	11th to 20th	Day	2 2 19% 34% 26% 16%	488
	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	6% 2 9% 28% 36% 19%	270
	11th to 20th	Day	7% 3 5% 30% 34% 21%	270
	21st to end	Day	9% 2 12% 27% 33% 17%	270
December	1st to 10th	Day	12% 3 12% 35% 27% 10%	252
	11th to 20th	Day	11% 5% 9% 33% 21% 21%	180
	21st to end	Day	22% 5% 10% 29% 25% 9%	198
January	1st to 10th	Night	19% 2 9% 34% 28% 9%	760
	11th to 20th	Night	9% 2 9% 40% 32% 7%	760
	21st to end	Night	16% 2 9% 36% 31% 6%	836
February	1st to 10th	Night	15% 2 11% 36% 28% 8%	760
	11th to 20th	Night	12% 2 13% 38% 28% 7%	744
	21st to end	Night	14% 3 12% 44% 24% 3	628
March	1st to 10th	Night	11% 4 13% 44% 25% 3	760
	11th to 20th	Night	10% 4 12% 39% 30% 6%	760
	21st to end	Night	13% 3 17% 39% 25% 3	836
April	1st to 10th	Night	9% 3 22% 36% 27% 2	760
	11th to 20th	Night	6% 5% 20% 38% 28% 3	751
	21st to end	Night	6% 6% 20% 36% 28% 5%	760
May	1st to 10th	Night	5% 4 21% 41% 27% 2	706
	11th to 20th	Night	5% 3 20% 40% 31% 1	561
	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% 41% 14%	836
November	1st to 10th	Night	6% 2 7% 31% 41% 12%	742
	11th to 20th	Night	6% 1 6% 40% 38% 9%	760
	21st to end	Night	10% 2 8% 38% 35% 8%	760
December	1st to 10th	Night	12% 1 9% 42% 31% 6%	760
	11th to 20th	Night	15% 1 8% 42% 29% 5%	760
	21st to end	Night	14% 3 10% 42% 27% 4	836

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