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 2026-03-03.

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	6% 5% 2 5% 3 3 3 3 4 6% 60%	139754
	Night	8% 8% 3 6% 3 3 3 3 4 6% 51%	138919
Transparency	Day	23% 5% 9% 19% 25% 19%	134686
	Night	30% 7% 10% 17% 21% 15%	134974
Seeing	Day	8% 9% 22% 32% 22% 7%	17069
	Night	10% 4 12% 35% 31% 7%	26528

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	15% 7% 2 5% 3 3 4 3 6% 8% 43%	5022
	11th to 20th	Day	8% 5% 2 5% 3 3 3 3 4 6% 58%	5340
	21st to end	Day	13% 8% 3 7% 4 4 4 3 5% 8% 40%	5843
February	1st to 10th	Day	14% 8% 3 5% 4 3 3 3 5% 6% 46%	1890
	11th to 20th	Day	14% 9% 3 6% 4 4 3 4 5% 7% 41%	1954
	21st to end	Day	11% 7% 3 7% 4 3 4 4 6% 7% 44%	1730
March	1st to 10th	Day	11% 10% 4 9% 6% 6% 6% 4 6% 6% 32%	4875
	11th to 20th	Day	11% 5% 2 6% 4 4 4 4 6% 7% 47%	5000
	21st to end	Day	9% 8% 3 8% 5% 6% 6% 5% 7% 8% 35%	5588
April	1st to 10th	Day	12% 8% 2 6% 4 4 3 4 5% 7% 45%	2400
	11th to 20th	Day	9% 6% 2 5% 3 3 3 3 5% 6% 55%	2369
	21st to end	Day	6% 6% 2 4 3 3 4 3 5% 8% 56%	2400
May	1st to 10th	Day	5% 4 1 2 2 2 2 2 3 5% 74%	5567
	11th to 20th	Day	3 4 1 3 2 2 2 2 3 5% 75%	6001
	21st to end	Day	2 7% 2 3 2 2 2 2 3 5% 70%	6902
June	1st to 10th	Day	5% 6% 1 4 2 3 3 3 4 6% 62%	2800
	11th to 20th	Day	2 2 1 2 2 2 2 2 4 6% 75%	2800
	21st to end	Day	3 4 1 3 2 2 2 2 3 4 77%	2800
July	1st to 10th	Day	1 2 1 2 1 1 2 1 2 3 83%	6319
	11th to 20th	Day	1 2 1 3 2 3 2 2 3 4 77%	5931
	21st to end	Day	1 7% 2 4 2 2 2 2 3 5% 71%	6402
August	1st to 10th	Day	1 3 1 4 2 2 3 2 3 5% 73%	5777
	11th to 20th	Day	2 3 1 3 2 2 2 2 2 4 77%	5490
	21st to end	Day	3 2 4 3 3 3 2 3 5% 72%	5984
September	1st to 10th	Day	1 3 2 3 2 2 2 2 3 5% 76%	2400
	11th to 20th	Day	3 6% 2 5% 3 3 3 3 4 6% 64%	2400
	21st to end	Day	3 3 1 3 1 2 2 2 3 6% 74%	2127
October	1st to 10th	Day	2 2 1 3 2 2 3 2 5% 6% 72%	3280
	11th to 20th	Day	4 5% 2 3 2 3 3 3 3 6% 66%	3261
	21st to end	Day	4 4 2 4 3 4 4 3 6% 8% 59%	3558
November	1st to 10th	Day	6% 5% 1 4 4 3 4 3 5% 8% 55%	2011
	11th to 20th	Day	8% 8% 3 6% 4 4 3 3 6% 7% 48%	1890
	21st to end	Day	11% 5% 2 4 3 2 3 3 5% 7% 53%	1743
December	1st to 10th	Day	6% 4 2 5% 3 3 3 3 6% 9% 55%	2700
	11th to 20th	Day	18% 9% 3 7% 4 4 5% 4 7% 7% 31%	3108
	21st to end	Day	19% 12% 4 8% 5% 4 5% 4 5% 7% 29%	4092
January	1st to 10th	Night	13% 8% 3 6% 3 4 4 3 6% 9% 42%	7871
	11th to 20th	Night	9% 5% 2 6% 3 4 4 3 4 6% 52%	7650
	21st to end	Night	12% 10% 4 8% 4 4 4 3 4 7% 39%	8371
February	1st to 10th	Night	14% 9% 2 5% 3 4 3 3 4 5% 47%	2730
	11th to 20th	Night	12% 9% 3 6% 4 4 4 4 5% 7% 40%	2552
	21st to end	Night	11% 7% 2 6% 4 4 4 3 5% 7% 48%	2076
March	1st to 10th	Night	16% 14% 3 8% 5% 5% 4 3 4 5% 32%	5060
	11th to 20th	Night	15% 9% 4 7% 3 3 3 2 3 6% 45%	5000
	21st to end	Night	15% 13% 3 7% 4 4 5% 3 5% 7% 34%	5386
April	1st to 10th	Night	11% 9% 2 5% 4 3 3 3 6% 9% 44%	2000
	11th to 20th	Night	9% 8% 2 5% 3 3 3 4 5% 7% 51%	1979
	21st to end	Night	6% 6% 1 4 4 4 4 4 4 8% 56%	2000
May	1st to 10th	Night	6% 7% 1 3 2 2 2 2 3 5% 66%	4422
	11th to 20th	Night	3 8% 2 5% 3 4 3 3 4 5% 59%	3900
	21st to end	Night	3 11% 2 6% 3 2 2 2 3 4 62%	3972
June	1st to 10th	Night	6% 7% 2 5% 3 2 2 4 4 7% 59%	1600
	11th to 20th	Night	1 3 1 3 2 2 2 3 5% 6% 71%	1600
	21st to end	Night	2 6% 2 3 2 2 1 2 3 4 72%	1600
July	1st to 10th	Night	3 2 3 2 3 2 1 3 4 77%	3640
	11th to 20th	Night	1 5% 5% 6% 3 3 3 2 3 5% 64%	4043
	21st to end	Night	1 22% 4 7% 4 3 3 2 3 6% 45%	4472
August	1st to 10th	Night	2 6% 3 9% 4 3 3 3 4 5% 58%	4035
	11th to 20th	Night	1 9% 2 5% 3 3 3 2 3 5% 64%	4372
	21st to end	Night	2 7% 3 9% 3 3 3 3 3 5% 59%	5015
September	1st to 10th	Night	2 6% 2 5% 2 2 3 2 3 5% 67%	2000
	11th to 20th	Night	5% 9% 3 6% 3 2 3 2 5% 5% 57%	2000
	21st to end	Night	3 5% 2 4 2 2 3 2 3 5% 70%	2269
October	1st to 10th	Night	3 3 1 3 2 2 2 2 4 6% 72%	3920
	11th to 20th	Night	4 11% 4 6% 3 2 3 2 3 4 57%	3897
	21st to end	Night	6% 6% 2 6% 3 3 3 3 5% 6% 59%	4253
November	1st to 10th	Night	8% 6% 2 5% 3 3 4 3 5% 7% 54%	2507
	11th to 20th	Night	10% 8% 2 5% 3 3 4 3 5% 8% 48%	2730
	21st to end	Night	9% 5% 2 5% 3 4 3 3 5% 7% 54%	2875
December	1st to 10th	Night	7% 4 2 4 3 4 4 3 5% 7% 58%	4700
	11th to 20th	Night	20% 9% 3 7% 4 4 5% 4 8% 9% 28%	5316
	21st to end	Night	19% 10% 3 8% 5% 5% 5% 4 6% 6% 28%	7106

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	36% 9% 17% 21% 14% 4	5023
	11th to 20th	Day	28% 5% 6% 14% 26% 21%	5340
	21st to end	Day	40% 6% 8% 16% 18% 13%	5843
February	1st to 10th	Day	39% 5% 9% 19% 19% 10%	1890
	11th to 20th	Day	41% 7% 10% 17% 19% 6%	1963
	21st to end	Day	38% 6% 10% 23% 16% 6%	1730
March	1st to 10th	Day	46% 10% 8% 15% 18% 2	4875
	11th to 20th	Day	32% 7% 15% 27% 11% 7%	5000
	21st to end	Day	38% 13% 16% 21% 11% 1	5588
April	1st to 10th	Day	37% 6% 14% 21% 19% 4	2400
	11th to 20th	Day	29% 6% 14% 24% 21% 6%	2372
	21st to end	Day	24% 6% 13% 28% 24% 4	2400
May	1st to 10th	Day	15% 3 8% 29% 30% 15%	5567
	11th to 20th	Day	12% 2 9% 31% 36% 9%	6004
	21st to end	Day	14% 5% 8% 31% 38% 4	6904
June	1st to 10th	Day	21% 6% 11% 25% 28% 9%	2800
	11th to 20th	Day	10% 4 9% 21% 38% 18%	2800
	21st to end	Day	12% 2 5% 12% 33% 36%	2800
July	1st to 10th	Day	6% 2 4 9% 21% 59%	6251
	11th to 20th	Day	9% 3 6% 6% 17% 60%	5860
	21st to end	Day	14% 3 5% 17% 29% 32%	6217
August	1st to 10th	Day	13% 4 7% 9% 31% 36%	4206
	11th to 20th	Day	7% 3 4 10% 47% 29%	3972
	21st to end	Day	12% 4 6% 11% 34% 33%	4311
September	1st to 10th	Day	12% 2 5% 11% 30% 41%	2400
	11th to 20th	Day	19% 4 8% 21% 31% 17%	2400
	21st to end	Day	12% 3 7% 21% 34% 23%	2127
October	1st to 10th	Day	13% 3 6% 13% 27% 38%	3280
	11th to 20th	Day	18% 5% 7% 23% 28% 18%	3261
	21st to end	Day	20% 6% 9% 21% 30% 14%	3558
November	1st to 10th	Day	27% 5% 12% 22% 24% 11%	2011
	11th to 20th	Day	33% 7% 10% 21% 22% 6%	1890
	21st to end	Day	29% 5% 10% 19% 28% 8%	1743
December	1st to 10th	Day	25% 5% 8% 26% 30% 6%	2700
	11th to 20th	Day	47% 8% 10% 16% 13% 5%	3108
	21st to end	Day	52% 9% 11% 16% 10% 2	4092
January	1st to 10th	Night	37% 10% 17% 19% 14% 3	7871
	11th to 20th	Night	31% 7% 8% 12% 27% 16%	7650
	21st to end	Night	43% 7% 7% 14% 18% 12%	8371
February	1st to 10th	Night	39% 5% 9% 18% 19% 12%	2730
	11th to 20th	Night	40% 6% 11% 17% 19% 6%	2554
	21st to end	Night	35% 6% 12% 27% 17% 4	2076
March	1st to 10th	Night	48% 11% 9% 18% 12% 2	5060
	11th to 20th	Night	37% 7% 13% 21% 14% 8%	5000
	21st to end	Night	44% 12% 14% 17% 10% 2	5386
April	1st to 10th	Night	33% 7% 17% 22% 17% 4	2000
	11th to 20th	Night	31% 5% 13% 25% 18% 8%	1979
	21st to end	Night	24% 6% 13% 29% 23% 5%	2000
May	1st to 10th	Night	17% 6% 9% 28% 29% 12%	4419
	11th to 20th	Night	18% 5% 14% 23% 27% 13%	3901
	21st to end	Night	19% 6% 12% 25% 36% 3	3972
June	1st to 10th	Night	21% 6% 11% 23% 29% 10%	1600
	11th to 20th	Night	11% 4 9% 18% 35% 23%	1600
	21st to end	Night	12% 3 5% 13% 32% 36%	1600
July	1st to 10th	Night	7% 3 4 10% 19% 57%	3600
	11th to 20th	Night	16% 5% 6% 6% 18% 49%	3991
	21st to end	Night	31% 8% 6% 12% 19% 24%	4345
August	1st to 10th	Night	18% 11% 6% 11% 26% 28%	2929
	11th to 20th	Night	12% 5% 7% 9% 42% 26%	3159
	21st to end	Night	19% 5% 6% 10% 31% 28%	3608
September	1st to 10th	Night	16% 4 5% 10% 24% 42%	2000
	11th to 20th	Night	23% 5% 7% 19% 27% 18%	2000
	21st to end	Night	15% 3 7% 19% 31% 25%	2269
October	1st to 10th	Night	14% 3 6% 12% 25% 40%	3920
	11th to 20th	Night	28% 4 7% 20% 21% 20%	3897
	21st to end	Night	24% 4 8% 20% 25% 18%	4253
November	1st to 10th	Night	28% 7% 11% 23% 19% 13%	2507
	11th to 20th	Night	33% 6% 11% 22% 20% 8%	2730
	21st to end	Night	29% 6% 10% 22% 22% 12%	2875
December	1st to 10th	Night	25% 5% 8% 25% 25% 11%	4700
	11th to 20th	Night	49% 7% 9% 15% 15% 4	5316
	21st to end	Night	52% 10% 14% 13% 8% 3	7106

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	24% 11% 21% 25% 17% 2	325
	11th to 20th	Day	14% 6% 20% 32% 22% 6%	430
	21st to end	Day	13% 6% 22% 31% 22% 5%	473
February	1st to 10th	Day	17% 9% 24% 26% 18% 6%	430
	11th to 20th	Day	17% 14% 26% 27% 13% 2	483
	21st to end	Day	11% 12% 28% 32% 16% 1	446
March	1st to 10th	Day	17% 14% 29% 27% 11% 2	509
	11th to 20th	Day	18% 13% 23% 27% 14% 4	500
	21st to end	Day	14% 16% 30% 25% 11% 3	550
April	1st to 10th	Day	13% 12% 30% 26% 15% 4	500
	11th to 20th	Day	12% 16% 29% 26% 12% 5%	492
	21st to end	Day	5% 16% 27% 30% 16% 6%	500
May	1st to 10th	Day	6% 12% 30% 33% 14% 5%	503
	11th to 20th	Day	9% 11% 29% 28% 17% 7%	528
	21st to end	Day	6% 11% 25% 32% 17% 9%	573
June	1st to 10th	Day	4 9% 25% 32% 22% 7%	530
	11th to 20th	Day	1 9% 27% 37% 20% 5%	530
	21st to end	Day	2 6% 21% 36% 26% 9%	530
July	1st to 10th	Day	2 3 17% 42% 27% 9%	526
	11th to 20th	Day	1 1 14% 40% 33% 11%	524
	21st to end	Day	1 3 15% 39% 30% 11%	575
August	1st to 10th	Day	3 4 20% 38% 24% 11%	527
	11th to 20th	Day	2 3 20% 37% 28% 10%	517
	21st to end	Day	1 4 15% 36% 32% 12%	583
September	1st to 10th	Day	3 4 16% 35% 32% 10%	530
	11th to 20th	Day	4 9% 20% 34% 24% 10%	530
	21st to end	Day	3 7% 20% 32% 29% 9%	530
October	1st to 10th	Day	4 7% 21% 33% 23% 12%	530
	11th to 20th	Day	6% 8% 16% 30% 28% 12%	530
	21st to end	Day	5% 7% 25% 30% 25% 8%	583
November	1st to 10th	Day	8% 7% 22% 27% 28% 10%	487
	11th to 20th	Day	8% 8% 17% 30% 27% 10%	330
	21st to end	Day	11% 3 19% 31% 28% 7%	253
December	1st to 10th	Day	10% 7% 16% 29% 25% 13%	220
	11th to 20th	Day	12% 10% 15% 25% 29% 9%	220
	21st to end	Day	23% 10% 20% 28% 17% 3	242
January	1st to 10th	Night	18% 5% 14% 35% 22% 6%	840
	11th to 20th	Night	13% 5% 12% 38% 26% 6%	840
	21st to end	Night	18% 3 13% 38% 23% 5%	924
February	1st to 10th	Night	17% 5% 13% 39% 22% 4	840
	11th to 20th	Night	15% 5% 19% 36% 20% 5%	824
	21st to end	Night	12% 6% 17% 44% 17% 3	692
March	1st to 10th	Night	17% 8% 17% 34% 21% 3	808
	11th to 20th	Night	17% 6% 15% 33% 24% 4	800
	21st to end	Night	16% 5% 19% 38% 20% 3	880
April	1st to 10th	Night	12% 6% 18% 39% 23% 3	800
	11th to 20th	Night	12% 7% 18% 36% 22% 5%	791
	21st to end	Night	7% 4 19% 37% 26% 7%	800
May	1st to 10th	Night	7% 4 17% 40% 28% 5%	740
	11th to 20th	Night	10% 3 9% 35% 35% 8%	522
	21st to end	Night	7% 5% 12% 38% 33% 6%	433
June	1st to 10th	Night	7% 4 8% 39% 38% 4	400
	11th to 20th	Night	2 2 9% 41% 44% 3	400
	21st to end	Night	2 4 7% 36% 46% 6%	400
July	1st to 10th	Night	2 3 4 29% 57% 6%	390
	11th to 20th	Night	3 1 2 22% 56% 15%	553
	21st to end	Night	3 5% 4 18% 54% 15%	657
August	1st to 10th	Night	6% 4 5% 24% 48% 13%	597
	11th to 20th	Night	3 2 8% 32% 46% 9%	733
	21st to end	Night	4 2 6% 30% 45% 13%	880
September	1st to 10th	Night	5% 2 7% 30% 43% 12%	800
	11th to 20th	Night	7% 4 11% 29% 40% 9%	800
	21st to end	Night	4 2 9% 30% 43% 12%	800
October	1st to 10th	Night	6% 2 9% 37% 35% 10%	800
	11th to 20th	Night	7% 4 10% 31% 38% 10%	800
	21st to end	Night	6% 4 9% 36% 31% 13%	880
November	1st to 10th	Night	8% 4 11% 32% 35% 9%	820
	11th to 20th	Night	13% 3 11% 35% 30% 8%	840
	21st to end	Night	11% 2 13% 40% 28% 6%	840
December	1st to 10th	Night	13% 4 11% 40% 26% 6%	840
	11th to 20th	Night	20% 4 13% 37% 20% 5%	840
	21st to end	Night	19% 7% 20% 35% 17% 2	924

Page generated at 2026-02-27 22:40:19. Version ac07

Copyright © 2026 Attilla Danko.