Fremont
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fremont clear sky chart from 2005-11-06 to 2026-10-29.

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	17% 8% 3 8% 5% 5% 5% 4 6% 7% 32%	149908
	Night	18% 9% 3 8% 5% 4 4 4 5% 7% 33%	142146
Transparency	Day	35% 33% 8% 14% 8% 1	153400
	Night	35% 33% 8% 14% 9% 1	146743
Seeing	Day	27% 17% 27% 18% 8% 3	17389
	Night	25% 16% 26% 24% 9% 1	26500

By Month

Percentage Cloud Cover NE (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	12% 13% 7% 19% 8% 5% 4 3 5% 5% 19%	4661
	11th to 20th	Day	14% 12% 6% 15% 6% 5% 4 3 5% 6% 22%	4650
	21st to end	Day	15% 11% 4 8% 6% 5% 5% 4 5% 7% 31%	5642
February	1st to 10th	Day	15% 12% 3 10% 7% 5% 5% 4 6% 6% 26%	1890
	11th to 20th	Day	14% 12% 5% 10% 6% 5% 5% 3 5% 7% 29%	1969
	21st to end	Day	18% 12% 3 10% 6% 4 4 3 4 6% 30%	1730
March	1st to 10th	Day	21% 11% 4 8% 6% 4 3 3 4 4 32%	4576
	11th to 20th	Day	14% 10% 4 8% 5% 4 4 4 4 6% 36%	5034
	21st to end	Day	19% 10% 3 7% 5% 4 5% 4 6% 6% 33%	5956
April	1st to 10th	Day	20% 12% 3 9% 5% 4 3 3 4 6% 32%	2520
	11th to 20th	Day	17% 9% 3 7% 5% 5% 5% 3 4 7% 35%	2494
	21st to end	Day	18% 9% 4 7% 6% 4 4 3 5% 7% 34%	2520
May	1st to 10th	Day	28% 7% 2 6% 4 4 4 3 5% 7% 28%	7929
	11th to 20th	Day	19% 8% 3 7% 5% 5% 5% 4 5% 7% 32%	8221
	21st to end	Day	23% 6% 2 6% 4 5% 6% 5% 7% 8% 27%	9060
June	1st to 10th	Day	16% 6% 2 7% 6% 5% 5% 5% 6% 8% 34%	2940
	11th to 20th	Day	18% 7% 2 7% 5% 6% 5% 4 6% 9% 31%	2940
	21st to end	Day	16% 7% 2 7% 5% 4 4 4 7% 9% 34%	2940
July	1st to 10th	Day	13% 6% 2 7% 5% 5% 6% 5% 7% 9% 35%	8280
	11th to 20th	Day	11% 5% 2 7% 5% 5% 6% 5% 8% 11% 37%	8280
	21st to end	Day	17% 5% 2 6% 4 4 4 4 6% 9% 39%	8993
August	1st to 10th	Day	20% 7% 3 8% 5% 5% 6% 4 7% 8% 26%	6139
	11th to 20th	Day	15% 5% 2 6% 4 5% 5% 5% 7% 9% 37%	5579
	21st to end	Day	17% 5% 2 5% 4 4 5% 4 7% 10% 36%	6080
September	1st to 10th	Day	17% 6% 2 6% 5% 4 4 3 5% 8% 40%	2520
	11th to 20th	Day	14% 5% 2 5% 4 4 4 4 5% 7% 45%	2479
	21st to end	Day	20% 7% 2 6% 4 5% 5% 4 6% 7% 34%	2310
October	1st to 10th	Day	18% 7% 2 7% 4 4 5% 3 5% 7% 38%	2105
	11th to 20th	Day	17% 9% 2 6% 4 5% 5% 3 6% 8% 36%	2100
	21st to end	Day	21% 10% 3 7% 5% 4 4 3 5% 7% 32%	2152
November	1st to 10th	Day	13% 8% 2 7% 5% 4 4 4 5% 6% 42%	1851
	11th to 20th	Day	16% 12% 2 8% 5% 5% 4 3 5% 5% 35%	1890
	21st to end	Day	19% 11% 4 8% 5% 5% 6% 3 5% 6% 28%	1684
December	1st to 10th	Day	18% 12% 7% 13% 5% 5% 5% 4 4 5% 21%	2680
	11th to 20th	Day	22% 12% 5% 7% 5% 3 3 3 4 5% 30%	3066
	21st to end	Day	19% 13% 6% 10% 5% 5% 4 3 5% 5% 25%	4048
January	1st to 10th	Night	14% 12% 5% 17% 6% 5% 4 4 5% 6% 22%	8234
	11th to 20th	Night	12% 12% 5% 17% 7% 6% 5% 4 5% 6% 21%	8235
	21st to end	Night	13% 9% 3 8% 8% 6% 6% 4 6% 7% 29%	8523
February	1st to 10th	Night	15% 11% 4 8% 6% 5% 5% 4 6% 7% 30%	2730
	11th to 20th	Night	14% 10% 4 11% 5% 5% 5% 5% 7% 8% 27%	2535
	21st to end	Night	17% 11% 3 9% 5% 5% 4 4 6% 7% 29%	2076
March	1st to 10th	Night	20% 10% 3 7% 5% 4 4 4 5% 6% 33%	5484
	11th to 20th	Night	14% 10% 4 8% 5% 4 4 3 5% 7% 36%	5141
	21st to end	Night	17% 11% 3 8% 4 5% 4 3 5% 6% 33%	5218
April	1st to 10th	Night	20% 11% 3 7% 6% 5% 4 4 5% 6% 30%	2100
	11th to 20th	Night	19% 10% 3 7% 4 4 4 3 4 7% 35%	2075
	21st to end	Night	20% 8% 3 7% 4 3 4 3 5% 6% 38%	2100
May	1st to 10th	Night	29% 7% 2 6% 3 4 4 3 5% 6% 29%	5009
	11th to 20th	Night	20% 8% 3 6% 4 4 4 4 6% 7% 34%	4639
	21st to end	Night	24% 8% 3 7% 5% 4 4 3 5% 6% 31%	5114
June	1st to 10th	Night	17% 6% 2 6% 4 5% 4 3 6% 7% 41%	1680
	11th to 20th	Night	17% 6% 2 6% 4 3 3 3 6% 8% 42%	1680
	21st to end	Night	13% 5% 2 4 4 4 5% 5% 7% 9% 44%	1680
July	1st to 10th	Night	15% 6% 2 6% 5% 4 5% 4 6% 9% 38%	4680
	11th to 20th	Night	14% 7% 3 7% 5% 4 5% 4 7% 9% 37%	4680
	21st to end	Night	15% 5% 2 5% 3 4 4 4 6% 8% 43%	5084
August	1st to 10th	Night	21% 7% 2 8% 5% 5% 5% 4 6% 7% 30%	3993
	11th to 20th	Night	17% 6% 2 6% 4 4 5% 4 5% 8% 39%	4419
	21st to end	Night	14% 5% 2 6% 4 4 4 3 6% 8% 44%	5045
September	1st to 10th	Night	17% 6% 2 5% 3 4 3 4 5% 7% 44%	2100
	11th to 20th	Night	14% 6% 2 4 3 3 4 3 4 6% 51%	2140
	21st to end	Night	19% 6% 2 7% 4 3 4 3 5% 7% 39%	2310
October	1st to 10th	Night	20% 6% 2 5% 3 4 4 4 5% 6% 41%	2509
	11th to 20th	Night	20% 8% 2 4 4 3 4 3 5% 6% 41%	2520
	21st to end	Night	21% 9% 3 5% 4 4 5% 3 5% 7% 34%	2864
November	1st to 10th	Night	15% 7% 3 6% 4 4 3 4 5% 7% 43%	2667
	11th to 20th	Night	19% 9% 2 6% 4 4 3 4 6% 6% 35%	2730
	21st to end	Night	16% 10% 3 7% 5% 5% 5% 4 6% 8% 32%	2934
December	1st to 10th	Night	17% 12% 4 10% 4 4 4 4 6% 7% 26%	4720
	11th to 20th	Night	26% 10% 3 7% 4 4 4 3 4 4 32%	5348
	21st to end	Night	22% 14% 5% 8% 5% 4 3 3 5% 6% 25%	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	53% 22% 9% 10% 4 1	4662
	11th to 20th	Day	52% 21% 6% 10% 9% 1	4680
	21st to end	Day	42% 23% 7% 17% 12%	5642
February	1st to 10th	Day	23% 60% 4 8% 4	1890
	11th to 20th	Day	24% 58% 3 8% 6% 1	1978
	21st to end	Day	21% 60% 5% 10% 4	1730
March	1st to 10th	Day	43% 28% 7% 10% 9% 4	4579
	11th to 20th	Day	31% 32% 13% 17% 4 3	5034
	21st to end	Day	37% 30% 7% 7% 16% 4	5956
April	1st to 10th	Day	26% 59% 3 7% 4 1	2520
	11th to 20th	Day	20% 60% 6% 8% 7%	2494
	21st to end	Day	22% 59% 4 9% 6% 1	2520
May	1st to 10th	Day	46% 23% 9% 12% 9%	7941
	11th to 20th	Day	41% 25% 9% 17% 8%	8225
	21st to end	Day	43% 25% 11% 13% 8%	9061
June	1st to 10th	Day	18% 60% 5% 9% 7%	2940
	11th to 20th	Day	19% 60% 6% 9% 6%	2940
	21st to end	Day	20% 58% 4 11% 6%	2940
July	1st to 10th	Day	38% 22% 12% 17% 11%	8210
	11th to 20th	Day	35% 20% 12% 25% 8%	8205
	21st to end	Day	36% 19% 9% 22% 14%	8795
August	1st to 10th	Day	44% 28% 10% 10% 7% 1	6125
	11th to 20th	Day	32% 26% 15% 23% 3	5617
	21st to end	Day	32% 26% 10% 25% 7%	6080
September	1st to 10th	Day	18% 56% 6% 13% 8%	2520
	11th to 20th	Day	17% 55% 4 11% 11% 1	2479
	21st to end	Day	23% 55% 6% 9% 7% 1	2310
October	1st to 10th	Day	30% 34% 3 15% 16% 2	3365
	11th to 20th	Day	26% 34% 5% 17% 12% 7%	3340
	21st to end	Day	18% 35% 13% 21% 11% 3	3403
November	1st to 10th	Day	23% 54% 6% 11% 6%	1851
	11th to 20th	Day	21% 54% 5% 11% 8% 1	1890
	21st to end	Day	25% 55% 8% 8% 3 1	1684
December	1st to 10th	Day	45% 35% 6% 11% 3	2680
	11th to 20th	Day	43% 30% 6% 12% 8%	3066
	21st to end	Day	46% 27% 5% 11% 10% 1	4048
January	1st to 10th	Night	52% 21% 8% 10% 7% 1	8234
	11th to 20th	Night	52% 22% 8% 8% 8% 2	8280
	21st to end	Night	44% 23% 6% 13% 13% 1	8523
February	1st to 10th	Night	20% 60% 6% 9% 4 1	2730
	11th to 20th	Night	24% 58% 4 9% 5%	2537
	21st to end	Night	20% 59% 5% 9% 5% 1	2076
March	1st to 10th	Night	39% 29% 9% 10% 12% 1	5494
	11th to 20th	Night	32% 31% 16% 13% 5% 3	5142
	21st to end	Night	39% 30% 4 12% 14% 1	5218
April	1st to 10th	Night	25% 59% 3 8% 5%	2100
	11th to 20th	Night	20% 59% 5% 8% 8%	2075
	21st to end	Night	21% 59% 4 8% 7% 1	2100
May	1st to 10th	Night	44% 23% 12% 12% 8% 1	5015
	11th to 20th	Night	40% 25% 12% 16% 7%	4640
	21st to end	Night	45% 25% 8% 15% 7%	5115
June	1st to 10th	Night	17% 59% 4 12% 8%	1680
	11th to 20th	Night	18% 59% 7% 10% 6%	1680
	21st to end	Night	17% 58% 7% 10% 7% 1	1680
July	1st to 10th	Night	38% 21% 14% 15% 12% 1	4640
	11th to 20th	Night	38% 20% 10% 21% 10% 1	4632
	21st to end	Night	33% 19% 9% 25% 13%	4967
August	1st to 10th	Night	44% 28% 8% 13% 6% 1	3983
	11th to 20th	Night	33% 26% 13% 24% 4	4447
	21st to end	Night	29% 26% 9% 26% 8% 1	5045
September	1st to 10th	Night	17% 55% 6% 13% 7% 1	2100
	11th to 20th	Night	16% 55% 5% 11% 12% 1	2140
	21st to end	Night	24% 54% 4 10% 7% 1	2310
October	1st to 10th	Night	31% 35% 5% 17% 12% 1	4029
	11th to 20th	Night	22% 34% 7% 15% 15% 6%	4019
	21st to end	Night	21% 34% 12% 21% 11% 1	4563
November	1st to 10th	Night	21% 55% 6% 10% 7%	2667
	11th to 20th	Night	21% 55% 5% 10% 8% 1	2730
	21st to end	Night	23% 55% 8% 10% 3	2934
December	1st to 10th	Night	39% 35% 7% 17% 2	4720
	11th to 20th	Night	41% 31% 8% 11% 9%	5348
	21st to end	Night	46% 27% 6% 8% 11% 2	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	36% 25% 26% 12% 1	220
	11th to 20th	Day	45% 25% 20% 8% 2	220
	21st to end	Day	34% 28% 27% 8% 3	338
February	1st to 10th	Day	34% 31% 29% 5% 1	330
	11th to 20th	Day	39% 26% 27% 7% 1	457
	21st to end	Day	35% 25% 29% 11% 1	446
March	1st to 10th	Day	34% 21% 28% 16% 2	540
	11th to 20th	Day	34% 25% 26% 11% 3 1	540
	21st to end	Day	33% 28% 25% 8% 5% 1	594
April	1st to 10th	Day	37% 23% 24% 12% 4	540
	11th to 20th	Day	34% 22% 25% 11% 6% 3	532
	21st to end	Day	32% 20% 32% 9% 5% 2	540
May	1st to 10th	Day	37% 19% 27% 10% 6% 2	543
	11th to 20th	Day	22% 21% 31% 17% 6% 3	567
	21st to end	Day	24% 12% 29% 21% 10% 3	617
June	1st to 10th	Day	21% 15% 31% 21% 9% 3	570
	11th to 20th	Day	23% 16% 24% 24% 11% 2	570
	21st to end	Day	20% 14% 33% 22% 9% 2	570
July	1st to 10th	Day	14% 10% 28% 29% 16% 3	565
	11th to 20th	Day	13% 7% 31% 31% 15% 3	564
	21st to end	Day	18% 9% 34% 25% 10% 3	620
August	1st to 10th	Day	17% 10% 26% 24% 17% 6%	566
	11th to 20th	Day	17% 9% 26% 27% 15% 6%	559
	21st to end	Day	17% 11% 28% 24% 13% 7%	627
September	1st to 10th	Day	23% 11% 25% 20% 15% 6%	570
	11th to 20th	Day	15% 10% 26% 24% 15% 11%	570
	21st to end	Day	26% 9% 28% 21% 12% 4	570
October	1st to 10th	Day	27% 12% 23% 19% 14% 4	570
	11th to 20th	Day	26% 19% 25% 21% 8% 1	570
	21st to end	Day	31% 16% 26% 19% 8% 1	543
November	1st to 10th	Day	27% 20% 22% 20% 9% 2	425
	11th to 20th	Day	28% 26% 25% 16% 5% 1	430
	21st to end	Day	36% 23% 29% 11% 2	224
December	1st to 10th	Day	34% 25% 25% 12% 4	220
	11th to 20th	Day	40% 23% 27% 8% 2	220
	21st to end	Day	33% 26% 27% 12% 2	242
January	1st to 10th	Night	27% 26% 30% 14% 2	840
	11th to 20th	Night	30% 21% 28% 19% 2	840
	21st to end	Night	22% 25% 35% 15% 3	924
February	1st to 10th	Night	28% 21% 34% 15% 1	840
	11th to 20th	Night	29% 26% 31% 13% 1	823
	21st to end	Night	32% 22% 30% 14% 2	692
March	1st to 10th	Night	29% 22% 31% 15% 3	840
	11th to 20th	Night	28% 25% 26% 18% 3	840
	21st to end	Night	26% 23% 32% 15% 4	924
April	1st to 10th	Night	30% 20% 30% 16% 3	840
	11th to 20th	Night	26% 19% 30% 19% 6%	831
	21st to end	Night	26% 19% 28% 21% 6%	840
May	1st to 10th	Night	32% 14% 25% 24% 6% 1	548
	11th to 20th	Night	21% 11% 30% 29% 8%	414
	21st to end	Night	21% 8% 24% 33% 13% 1	455
June	1st to 10th	Night	18% 7% 26% 33% 15%	420
	11th to 20th	Night	21% 8% 22% 34% 15%	420
	21st to end	Night	15% 4 25% 43% 13%	420
July	1st to 10th	Night	16% 5% 17% 42% 18% 1	410
	11th to 20th	Night	15% 4 21% 40% 18% 1	408
	21st to end	Night	16% 4 19% 42% 18% 1	460
August	1st to 10th	Night	16% 2 20% 37% 23% 2	563
	11th to 20th	Night	17% 5% 16% 40% 19% 4	767
	21st to end	Night	18% 5% 19% 34% 23% 1	924
September	1st to 10th	Night	20% 5% 25% 29% 19% 2	840
	11th to 20th	Night	16% 7% 20% 31% 21% 5%	840
	21st to end	Night	23% 8% 22% 30% 14% 2	840
October	1st to 10th	Night	25% 11% 23% 23% 18% 1	840
	11th to 20th	Night	25% 13% 26% 28% 7%	840
	21st to end	Night	26% 17% 28% 22% 6%	913
November	1st to 10th	Night	21% 19% 27% 25% 8% 1	820
	11th to 20th	Night	29% 20% 23% 21% 6% 1	840
	21st to end	Night	24% 20% 28% 21% 5% 1	840
December	1st to 10th	Night	30% 23% 26% 17% 4	840
	11th to 20th	Night	32% 21% 27% 18% 3	840
	21st to end	Night	31% 23% 27% 17% 2	924

Page generated at 2026-10-26 04:37:49. Version ac07

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