Velveeta Valley Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Velveeta Valley Observatory clear sky chart from 2005-11-06 to 2026-01-02.

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	13% 8% 3 7% 5% 4 4 4 5% 7% 38%	127495
	Night	14% 9% 4 8% 4 4 4 3 5% 6% 39%	124126
Transparency	Day	43% 6% 12% 24% 13% 1	130989
	Night	44% 5% 11% 22% 14% 2	128706
Seeing	Day	17% 11% 29% 25% 14% 5%	17422
	Night	17% 9% 31% 30% 11% 1	27330

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	9% 11% 8% 16% 7% 5% 5% 4 5% 5% 26%	3625
	11th to 20th	Day	9% 11% 6% 12% 4 4 4 6% 7% 6% 30%	3620
	21st to end	Day	12% 15% 8% 9% 4 3 3 2 4 6% 32%	4235
February	1st to 10th	Day	12% 14% 6% 9% 6% 4 6% 4 5% 7% 29%	1800
	11th to 20th	Day	13% 10% 4 9% 6% 4 4 3 4 7% 36%	1898
	21st to end	Day	13% 14% 4 10% 5% 4 4 3 5% 5% 33%	1650
March	1st to 10th	Day	16% 8% 3 6% 4 3 3 3 4 6% 44%	4480
	11th to 20th	Day	11% 6% 3 7% 4 4 4 3 6% 8% 43%	4810
	21st to end	Day	21% 11% 4 10% 6% 5% 4 4 5% 5% 25%	5909
April	1st to 10th	Day	18% 11% 3 8% 5% 4 4 3 4 6% 31%	2400
	11th to 20th	Day	17% 9% 3 8% 5% 5% 5% 3 5% 6% 34%	2374
	21st to end	Day	19% 10% 3 7% 5% 5% 4 3 5% 6% 34%	2450
May	1st to 10th	Day	16% 8% 3 7% 4 4 5% 4 5% 7% 37%	5992
	11th to 20th	Day	15% 5% 2 6% 4 5% 5% 4 5% 7% 42%	6319
	21st to end	Day	14% 6% 2 6% 4 5% 5% 4 7% 9% 38%	6935
June	1st to 10th	Day	11% 4 2 6% 5% 5% 5% 4 7% 7% 43%	2800
	11th to 20th	Day	11% 5% 2 5% 4 5% 5% 4 5% 10% 45%	2800
	21st to end	Day	11% 7% 3 7% 4 4 5% 5% 7% 9% 39%	2800
July	1st to 10th	Day	10% 6% 2 7% 5% 5% 5% 5% 6% 9% 38%	6360
	11th to 20th	Day	9% 5% 2 6% 4 4 5% 4 6% 9% 46%	6360
	21st to end	Day	11% 6% 2 7% 5% 5% 5% 4 6% 10% 39%	6924
August	1st to 10th	Day	10% 4 2 6% 5% 4 6% 5% 7% 10% 42%	4448
	11th to 20th	Day	12% 5% 2 5% 3 3 4 4 6% 8% 47%	3895
	21st to end	Day	9% 5% 2 5% 4 4 4 3 6% 8% 48%	4312
September	1st to 10th	Day	13% 5% 2 5% 5% 4 5% 3 5% 7% 47%	2400
	11th to 20th	Day	12% 4 2 3 3 3 4 3 6% 8% 53%	2330
	21st to end	Day	11% 6% 2 7% 4 4 4 3 5% 7% 46%	2200
October	1st to 10th	Day	13% 6% 2 6% 4 3 3 3 4 6% 50%	2050
	11th to 20th	Day	19% 8% 2 6% 5% 4 4 3 5% 6% 37%	2000
	21st to end	Day	19% 10% 3 6% 4 4 3 3 4 6% 40%	2025
November	1st to 10th	Day	12% 9% 4 6% 4 3 4 3 5% 6% 44%	1852
	11th to 20th	Day	14% 12% 4 7% 5% 4 5% 3 6% 6% 33%	1890
	21st to end	Day	16% 15% 3 9% 3 3 3 3 4 6% 35%	1704
December	1st to 10th	Day	8% 9% 4 9% 5% 3 4 3 4 7% 42%	2690
	11th to 20th	Day	14% 14% 5% 12% 5% 5% 5% 4 5% 6% 24%	3088
	21st to end	Day	21% 22% 8% 12% 5% 4 4 3 4 4 12%	4070
January	1st to 10th	Night	10% 13% 7% 14% 6% 4 4 3 4 4 33%	6363
	11th to 20th	Night	11% 14% 6% 14% 6% 5% 5% 5% 7% 5% 23%	6360
	21st to end	Night	14% 14% 6% 10% 5% 4 4 3 4 5% 31%	6741
February	1st to 10th	Night	13% 13% 6% 9% 6% 5% 4 3 4 4 34%	2600
	11th to 20th	Night	13% 10% 4 7% 5% 5% 4 3 5% 6% 39%	2387
	21st to end	Night	18% 11% 4 6% 4 3 4 3 4 6% 37%	1980
March	1st to 10th	Night	17% 8% 3 6% 4 3 4 3 4 4 43%	5373
	11th to 20th	Night	9% 7% 2 6% 4 4 4 3 4 8% 49%	5192
	21st to end	Night	22% 12% 5% 9% 5% 4 4 3 4 5% 28%	5018
April	1st to 10th	Night	17% 10% 3 5% 4 4 4 3 4 6% 39%	2000
	11th to 20th	Night	18% 9% 2 8% 4 3 3 3 4 6% 39%	1975
	21st to end	Night	17% 9% 2 7% 4 4 5% 4 5% 8% 36%	1950
May	1st to 10th	Night	18% 7% 3 7% 4 4 4 4 5% 6% 38%	3906
	11th to 20th	Night	12% 5% 2 6% 4 4 5% 4 6% 8% 45%	3596
	21st to end	Night	14% 7% 2 6% 4 4 4 4 5% 8% 40%	3942
June	1st to 10th	Night	8% 5% 2 4 5% 4 5% 5% 7% 8% 48%	1600
	11th to 20th	Night	11% 5% 2 6% 4 4 4 4 6% 10% 45%	1600
	21st to end	Night	9% 7% 2 6% 4 5% 5% 4 6% 7% 45%	1600
July	1st to 10th	Night	13% 6% 2 7% 5% 4 5% 4 5% 9% 42%	3618
	11th to 20th	Night	8% 4 2 5% 3 4 4 3 5% 8% 54%	3617
	21st to end	Night	10% 5% 2 6% 4 4 4 4 5% 8% 46%	3947
August	1st to 10th	Night	7% 3 2 6% 4 4 4 4 5% 8% 53%	2695
	11th to 20th	Night	10% 5% 2 5% 4 3 4 4 5% 7% 51%	3152
	21st to end	Night	10% 4 2 5% 4 4 4 3 5% 8% 51%	3586
September	1st to 10th	Night	9% 5% 2 5% 3 4 3 3 5% 6% 56%	2000
	11th to 20th	Night	10% 4 2 4 3 4 4 3 4 7% 53%	2049
	21st to end	Night	11% 5% 2 5% 4 4 4 3 5% 6% 50%	2200
October	1st to 10th	Night	11% 6% 2 6% 4 3 4 3 5% 5% 52%	2345
	11th to 20th	Night	18% 7% 2 5% 4 4 3 3 4 6% 45%	2400
	21st to end	Night	19% 9% 2 7% 4 4 4 3 5% 6% 38%	2815
November	1st to 10th	Night	12% 8% 2 6% 3 3 3 3 4 5% 49%	2666
	11th to 20th	Night	15% 11% 4 7% 4 3 4 3 5% 6% 37%	2730
	21st to end	Night	18% 10% 4 8% 5% 4 3 3 4 6% 36%	2914
December	1st to 10th	Night	9% 9% 3 8% 5% 5% 5% 4 5% 7% 41%	4720
	11th to 20th	Night	16% 16% 4 9% 5% 4 4 3 4 5% 29%	5339
	21st to end	Night	22% 18% 6% 11% 5% 4 4 3 4 4 18%	7150

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	60% 5% 11% 17% 7%	3626
	11th to 20th	Day	50% 6% 13% 10% 18% 3	3620
	21st to end	Day	54% 4 14% 18% 10%	4235
February	1st to 10th	Day	56% 5% 12% 16% 10% 1	1800
	11th to 20th	Day	49% 5% 11% 24% 9% 2	1908
	21st to end	Day	53% 6% 10% 20% 10% 2	1650
March	1st to 10th	Day	42% 4 12% 27% 11% 4	4480
	11th to 20th	Day	38% 5% 13% 31% 12% 1	4810
	21st to end	Day	60% 7% 10% 14% 7% 1	5911
April	1st to 10th	Day	53% 6% 10% 21% 9%	2400
	11th to 20th	Day	50% 6% 10% 21% 11% 2	2374
	21st to end	Day	50% 6% 12% 18% 12% 2	2450
May	1st to 10th	Day	44% 7% 10% 21% 17% 1	6027
	11th to 20th	Day	40% 7% 10% 26% 16%	6323
	21st to end	Day	39% 8% 12% 25% 12% 3	6949
June	1st to 10th	Day	37% 8% 13% 25% 16% 1	2800
	11th to 20th	Day	35% 7% 13% 25% 19% 2	2800
	21st to end	Day	39% 7% 15% 23% 13% 2	2800
July	1st to 10th	Day	40% 7% 14% 26% 11% 1	6291
	11th to 20th	Day	34% 7% 14% 29% 15% 1	6285
	21st to end	Day	39% 8% 16% 20% 15% 2	6728
August	1st to 10th	Day	35% 8% 16% 27% 13% 1	4433
	11th to 20th	Day	32% 7% 14% 33% 14% 1	3931
	21st to end	Day	33% 6% 13% 30% 16% 1	4311
September	1st to 10th	Day	35% 6% 11% 27% 19% 2	2400
	11th to 20th	Day	29% 7% 11% 32% 19% 2	2330
	21st to end	Day	37% 5% 10% 27% 19% 1	2200
October	1st to 10th	Day	24% 4 7% 37% 28% 1	3336
	11th to 20th	Day	34% 4 10% 27% 24% 2	3240
	21st to end	Day	43% 4 8% 29% 14% 3	3250
November	1st to 10th	Day	40% 5% 14% 26% 14% 2	1852
	11th to 20th	Day	52% 5% 12% 20% 10% 1	1890
	21st to end	Day	52% 5% 13% 22% 8%	1704
December	1st to 10th	Day	42% 5% 19% 26% 7% 1	2690
	11th to 20th	Day	60% 4 12% 16% 6% 1	3085
	21st to end	Day	75% 5% 7% 8% 5%	4070
January	1st to 10th	Night	55% 5% 10% 19% 10% 1	6363
	11th to 20th	Night	61% 5% 9% 10% 15% 1	6360
	21st to end	Night	57% 4 12% 17% 10% 1	6741
February	1st to 10th	Night	54% 4 10% 19% 12% 1	2600
	11th to 20th	Night	48% 4 11% 22% 14% 1	2388
	21st to end	Night	49% 4 13% 19% 11% 3	1980
March	1st to 10th	Night	45% 4 12% 22% 11% 6%	5373
	11th to 20th	Night	34% 5% 11% 34% 13% 3	5192
	21st to end	Night	59% 4 10% 16% 9% 1	5018
April	1st to 10th	Night	46% 6% 11% 22% 13% 2	2000
	11th to 20th	Night	46% 4 8% 21% 17% 4	1975
	21st to end	Night	45% 7% 13% 23% 11% 2	1950
May	1st to 10th	Night	44% 7% 12% 17% 18% 2	3933
	11th to 20th	Night	35% 8% 15% 23% 16% 3	3597
	21st to end	Night	38% 9% 12% 23% 15% 3	3950
June	1st to 10th	Night	31% 7% 15% 27% 19% 2	1600
	11th to 20th	Night	34% 7% 10% 24% 23% 2	1600
	21st to end	Night	37% 7% 14% 22% 18% 3	1600
July	1st to 10th	Night	39% 7% 14% 23% 14% 2	3580
	11th to 20th	Night	28% 7% 14% 30% 20% 1	3572
	21st to end	Night	33% 8% 15% 23% 17% 3	3832
August	1st to 10th	Night	28% 6% 15% 31% 18% 2	2686
	11th to 20th	Night	30% 7% 15% 30% 17% 1	3182
	21st to end	Night	30% 6% 13% 31% 17% 3	3586
September	1st to 10th	Night	30% 6% 11% 28% 23% 3	2000
	11th to 20th	Night	30% 6% 10% 32% 19% 3	2049
	21st to end	Night	34% 6% 10% 29% 20% 2	2200
October	1st to 10th	Night	24% 4 6% 35% 29% 1	3839
	11th to 20th	Night	34% 5% 8% 25% 26% 3	3899
	21st to end	Night	42% 4 9% 25% 16% 3	4540
November	1st to 10th	Night	38% 5% 10% 27% 18% 3	2666
	11th to 20th	Night	47% 5% 12% 22% 12% 1	2730
	21st to end	Night	50% 4 12% 22% 10% 1	2914
December	1st to 10th	Night	43% 5% 14% 27% 10% 1	4720
	11th to 20th	Night	57% 5% 12% 17% 9% 1	5341
	21st to end	Night	70% 5% 8% 11% 5%	7150

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	17% 14% 31% 30% 7% 1	303
	11th to 20th	Day	17% 17% 41% 20% 4 1	300
	21st to end	Day	23% 11% 41% 20% 4 1	330
February	1st to 10th	Day	18% 20% 39% 18% 6%	300
	11th to 20th	Day	20% 21% 34% 21% 4	300
	21st to end	Day	24% 18% 43% 11% 4	249
March	1st to 10th	Day	20% 19% 42% 15% 3	300
	11th to 20th	Day	23% 20% 35% 15% 6% 1	300
	21st to end	Day	28% 15% 32% 18% 6% 1	518
April	1st to 10th	Day	26% 15% 32% 22% 5%	500
	11th to 20th	Day	21% 22% 26% 19% 9% 2	492
	21st to end	Day	23% 14% 30% 23% 8% 2	500
May	1st to 10th	Day	20% 13% 32% 25% 8% 3	555
	11th to 20th	Day	22% 11% 28% 24% 12% 3	725
	21st to end	Day	17% 10% 28% 23% 15% 6%	789
June	1st to 10th	Day	10% 8% 30% 29% 18% 5%	730
	11th to 20th	Day	12% 6% 33% 30% 15% 5%	730
	21st to end	Day	14% 7% 28% 31% 15% 4	730
July	1st to 10th	Day	9% 3 17% 33% 26% 13%	721
	11th to 20th	Day	10% 5% 25% 30% 21% 9%	718
	21st to end	Day	8% 3 23% 36% 22% 7%	794
August	1st to 10th	Day	6% 3 21% 33% 25% 10%	726
	11th to 20th	Day	13% 6% 17% 26% 23% 15%	553
	21st to end	Day	10% 4 19% 31% 27% 9%	583
September	1st to 10th	Day	15% 6% 22% 27% 21% 8%	530
	11th to 20th	Day	10% 4 18% 30% 27% 11%	530
	21st to end	Day	14% 11% 25% 25% 18% 8%	530
October	1st to 10th	Day	15% 9% 28% 27% 18% 3	380
	11th to 20th	Day	22% 20% 32% 17% 9%	330
	21st to end	Day	26% 15% 30% 21% 7%	363
November	1st to 10th	Day	17% 19% 34% 19% 8% 2	330
	11th to 20th	Day	22% 17% 36% 17% 6% 1	330
	21st to end	Day	27% 13% 37% 19% 4	330
December	1st to 10th	Day	17% 15% 44% 17% 5% 2	330
	11th to 20th	Day	18% 14% 40% 20% 7% 1	330
	21st to end	Day	27% 16% 37% 17% 2	363
January	1st to 10th	Night	18% 14% 37% 25% 5% 1	1006
	11th to 20th	Night	18% 14% 39% 24% 5% 1	1000
	21st to end	Night	20% 11% 37% 26% 5%	1100
February	1st to 10th	Night	20% 13% 38% 24% 5%	1000
	11th to 20th	Night	18% 14% 39% 25% 5%	832
	21st to end	Night	23% 13% 38% 21% 3	660
March	1st to 10th	Night	22% 11% 37% 24% 6%	800
	11th to 20th	Night	16% 13% 35% 28% 7%	695
	21st to end	Night	25% 10% 34% 24% 6% 1	660
April	1st to 10th	Night	21% 13% 38% 24% 4	600
	11th to 20th	Night	21% 14% 29% 28% 7%	593
	21st to end	Night	21% 9% 32% 29% 9% 1	600
May	1st to 10th	Night	18% 9% 34% 31% 9% 1	600
	11th to 20th	Night	19% 6% 32% 32% 11%	591
	21st to end	Night	14% 5% 31% 34% 14% 1	650
June	1st to 10th	Night	10% 5% 26% 43% 16% 1	600
	11th to 20th	Night	12% 4 29% 42% 13%	600
	21st to end	Night	9% 5% 29% 40% 17% 1	600
July	1st to 10th	Night	8% 3 14% 42% 30% 3	585
	11th to 20th	Night	9% 2 21% 42% 24% 3	582
	21st to end	Night	9% 3 16% 45% 26% 1	657
August	1st to 10th	Night	5% 2 15% 46% 29% 3	597
	11th to 20th	Night	9% 2 14% 38% 31% 6%	594
	21st to end	Night	10% 2 16% 42% 27% 3	660
September	1st to 10th	Night	10% 4 22% 36% 25% 5%	600
	11th to 20th	Night	10% 3 22% 36% 26% 4	649
	21st to end	Night	12% 9% 25% 32% 21% 2	800
October	1st to 10th	Night	14% 7% 29% 33% 17% 1	800
	11th to 20th	Night	20% 12% 31% 28% 10%	800
	21st to end	Night	22% 11% 33% 25% 8%	880
November	1st to 10th	Night	15% 10% 41% 23% 9% 1	820
	11th to 20th	Night	19% 14% 37% 24% 6%	840
	21st to end	Night	22% 13% 34% 24% 6%	1024
December	1st to 10th	Night	21% 12% 39% 22% 6%	1050
	11th to 20th	Night	22% 12% 35% 25% 5% 1	1050
	21st to end	Night	28% 13% 35% 22% 3	1155

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