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 2024-01-15.

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	7% 5% 2 4 3 2 3 4 4 6% 58%	74715
	Night	9% 7% 3 4 4 2 4 4 4 7% 52%	75078
Transparency	Day	26% 5% 10% 19% 24% 17%	74434
	Night	30% 5% 10% 18% 21% 16%	74881
Seeing	Day	8% 8% 22% 32% 22% 8%	14274
	Night	10% 4 12% 34% 32% 8%	23726

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	18% 7% 2 5% 5% 3 4 5% 5% 8% 37%	1614
	11th to 20th	Day	11% 6% 2 5% 4 2 4 5% 4 7% 49%	1657
	21st to end	Day	14% 7% 3 6% 5% 2 4 5% 5% 8% 42%	1782
February	1st to 10th	Day	15% 7% 3 5% 4 2 4 3 5% 6% 47%	1620
	11th to 20th	Day	13% 7% 3 5% 5% 2 3 5% 5% 7% 45%	1668
	21st to end	Day	13% 6% 3 6% 4 2 3 4 5% 7% 45%	1480
March	1st to 10th	Day	14% 8% 4 7% 4 3 5% 5% 5% 8% 36%	1930
	11th to 20th	Day	15% 7% 2 6% 6% 4 5% 5% 5% 7% 37%	1980
	21st to end	Day	11% 6% 3 6% 5% 3 6% 5% 5% 7% 44%	2216
April	1st to 10th	Day	12% 8% 3 5% 4 3 4 5% 5% 7% 44%	2160
	11th to 20th	Day	10% 6% 2 5% 3 2 3 3 4 6% 56%	2129
	21st to end	Day	6% 5% 2 4 3 2 4 4 5% 8% 57%	2160
May	1st to 10th	Day	5% 5% 2 4 4 2 3 4 4 7% 61%	2209
	11th to 20th	Day	6% 5% 2 4 3 2 3 3 4 7% 63%	2357
	21st to end	Day	5% 7% 3 3 3 2 3 3 4 6% 59%	2723
June	1st to 10th	Day	5% 6% 2 4 2 2 3 3 4 7% 61%	2520
	11th to 20th	Day	2 2 1 2 2 1 2 3 4 6% 75%	2520
	21st to end	Day	3 4 1 3 2 1 2 3 3 4 76%	2520
July	1st to 10th	Day	1 5% 1 2 2 1 1 2 3 5% 76%	2520
	11th to 20th	Day	1 3 2 3 3 2 2 3 3 5% 73%	2365
	21st to end	Day	1 2 1 2 3 1 2 3 4 5% 75%	2546
August	1st to 10th	Day	2 5% 1 3 3 2 3 3 2 5% 70%	2328
	11th to 20th	Day	1 2 1 2 2 2 2 3 3 5% 76%	2173
	21st to end	Day	4 1 3 2 2 2 3 3 5% 75%	2376
September	1st to 10th	Day	2 3 2 2 2 1 2 2 2 5% 78%	2160
	11th to 20th	Day	3 5% 2 4 4 2 3 3 4 6% 65%	2160
	21st to end	Day	3 2 1 2 2 2 2 2 3 6% 75%	1916
October	1st to 10th	Day	4 2 1 3 3 2 3 3 4 6% 69%	1800
	11th to 20th	Day	5% 4 2 3 3 2 3 4 4 7% 65%	1800
	21st to end	Day	6% 5% 2 3 3 2 4 3 4 7% 61%	1980
November	1st to 10th	Day	7% 5% 2 4 5% 2 4 4 4 9% 54%	1817
	11th to 20th	Day	8% 7% 3 5% 5% 3 3 4 6% 7% 51%	1710
	21st to end	Day	11% 5% 2 4 3 2 3 4 5% 7% 53%	1577
December	1st to 10th	Day	10% 6% 3 6% 5% 3 3 4 6% 6% 46%	1520
	11th to 20th	Day	20% 11% 4 7% 5% 3 4 5% 6% 5% 32%	1928
	21st to end	Day	16% 11% 3 6% 5% 3 4 5% 5% 8% 34%	2794
January	1st to 10th	Night	16% 8% 3 5% 4 3 4 5% 7% 8% 38%	2548
	11th to 20th	Night	12% 6% 3 5% 6% 3 4 4 5% 7% 45%	2397
	21st to end	Night	15% 7% 3 5% 4 3 4 5% 5% 7% 43%	2574
February	1st to 10th	Night	13% 8% 2 4 3 3 4 4 4 6% 49%	2340
	11th to 20th	Night	11% 8% 4 5% 4 3 4 5% 5% 8% 44%	2179
	21st to end	Night	12% 7% 3 4 4 3 3 4 4 7% 49%	1776
March	1st to 10th	Night	16% 9% 3 6% 5% 3 4 5% 5% 6% 39%	2026
	11th to 20th	Night	15% 9% 3 6% 5% 2 4 3 4 9% 41%	1980
	21st to end	Night	13% 7% 2 5% 5% 2 5% 4 5% 5% 47%	2139
April	1st to 10th	Night	11% 9% 3 4 4 3 4 4 6% 9% 44%	1800
	11th to 20th	Night	10% 7% 3 4 3 2 3 4 4 7% 52%	1779
	21st to end	Night	6% 5% 1 4 4 3 4 4 4 8% 58%	1800
May	1st to 10th	Night	6% 7% 2 4 5% 2 3 4 5% 7% 55%	1746
	11th to 20th	Night	6% 9% 3 4 4 3 4 4 5% 7% 51%	1532
	21st to end	Night	6% 10% 2 5% 4 2 2 3 4 7% 54%	1552
June	1st to 10th	Night	7% 6% 3 3 3 1 2 4 4 7% 60%	1440
	11th to 20th	Night	1 3 1 3 3 2 2 3 5% 6% 70%	1440
	21st to end	Night	2 7% 2 3 3 2 2 2 3 4 71%	1440
July	1st to 10th	Night	1 7% 2 3 3 2 3 2 4 5% 69%	1440
	11th to 20th	Night	2 4 2 3 4 2 3 3 4 6% 68%	1591
	21st to end	Night	1 7% 3 4 4 2 4 4 5% 9% 58%	1773
August	1st to 10th	Night	3 9% 4 5% 4 3 3 3 4 6% 56%	1611
	11th to 20th	Night	1 6% 2 3 4 2 3 3 5% 8% 64%	1727
	21st to end	Night	1 7% 3 5% 4 2 3 3 4 6% 63%	1980
September	1st to 10th	Night	2 5% 2 4 3 2 3 3 3 5% 69%	1800
	11th to 20th	Night	5% 8% 2 5% 4 2 3 2 5% 5% 60%	1800
	21st to end	Night	3 4 2 3 3 1 2 3 3 6% 71%	2041
October	1st to 10th	Night	5% 5% 2 3 3 2 3 3 4 6% 66%	2160
	11th to 20th	Night	6% 5% 2 5% 5% 2 3 3 3 5% 60%	2160
	21st to end	Night	6% 5% 2 5% 4 2 3 3 4 6% 61%	2376
November	1st to 10th	Night	9% 5% 2 5% 4 2 4 3 5% 8% 53%	2262
	11th to 20th	Night	9% 7% 2 4 4 2 3 5% 5% 8% 50%	2470
	21st to end	Night	9% 4 2 4 4 3 3 4 5% 7% 56%	2601
December	1st to 10th	Night	13% 7% 3 5% 4 3 4 4 5% 6% 48%	2660
	11th to 20th	Night	23% 11% 3 6% 4 2 4 3 5% 7% 32%	3276
	21st to end	Night	15% 9% 3 6% 6% 4 6% 5% 6% 7% 33%	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	43% 9% 12% 21% 10% 5%	1614
	11th to 20th	Day	35% 7% 12% 16% 18% 12%	1657
	21st to end	Day	41% 7% 10% 12% 22% 7%	1782
February	1st to 10th	Day	38% 4 9% 20% 20% 9%	1620
	11th to 20th	Day	38% 6% 9% 18% 22% 7%	1677
	21st to end	Day	38% 6% 9% 23% 18% 6%	1480
March	1st to 10th	Day	45% 6% 11% 19% 15% 4	1930
	11th to 20th	Day	44% 6% 11% 18% 17% 4	1980
	21st to end	Day	38% 7% 15% 19% 17% 4	2216
April	1st to 10th	Day	39% 6% 14% 19% 18% 4	2160
	11th to 20th	Day	29% 6% 14% 24% 22% 6%	2132
	21st to end	Day	24% 5% 13% 28% 25% 5%	2160
May	1st to 10th	Day	23% 5% 10% 27% 29% 7%	2209
	11th to 20th	Day	22% 3 10% 28% 28% 8%	2360
	21st to end	Day	25% 6% 12% 29% 24% 4	2724
June	1st to 10th	Day	22% 6% 11% 24% 26% 10%	2520
	11th to 20th	Day	10% 4 9% 21% 37% 18%	2520
	21st to end	Day	13% 2 5% 13% 33% 35%	2520
July	1st to 10th	Day	10% 2 5% 11% 24% 48%	2451
	11th to 20th	Day	12% 3 7% 12% 21% 45%	2294
	21st to end	Day	9% 2 5% 10% 30% 44%	2405
August	1st to 10th	Day	16% 2 7% 12% 29% 34%	2312
	11th to 20th	Day	10% 3 5% 13% 34% 36%	2173
	21st to end	Day	12% 2 6% 14% 31% 35%	2376
September	1st to 10th	Day	11% 2 4 10% 30% 43%	2160
	11th to 20th	Day	18% 4 8% 20% 32% 19%	2160
	21st to end	Day	12% 3 8% 21% 34% 23%	1916
October	1st to 10th	Day	17% 4 9% 17% 28% 25%	1800
	11th to 20th	Day	19% 5% 10% 18% 23% 23%	1800
	21st to end	Day	23% 5% 9% 19% 24% 20%	1980
November	1st to 10th	Day	29% 5% 11% 21% 22% 12%	1817
	11th to 20th	Day	32% 7% 10% 21% 23% 7%	1710
	21st to end	Day	29% 5% 10% 18% 29% 9%	1577
December	1st to 10th	Day	37% 6% 12% 18% 17% 10%	1520
	11th to 20th	Day	52% 6% 10% 14% 13% 5%	1928
	21st to end	Day	46% 9% 12% 18% 12% 3	2794
January	1st to 10th	Night	42% 7% 13% 21% 12% 5%	2548
	11th to 20th	Night	38% 7% 13% 15% 14% 13%	2397
	21st to end	Night	40% 7% 11% 11% 19% 11%	2574
February	1st to 10th	Night	37% 4 9% 19% 20% 11%	2340
	11th to 20th	Night	37% 5% 10% 18% 22% 8%	2181
	21st to end	Night	36% 6% 11% 27% 17% 4	1776
March	1st to 10th	Night	44% 6% 14% 16% 15% 4	2026
	11th to 20th	Night	42% 5% 9% 21% 18% 6%	1980
	21st to end	Night	37% 8% 14% 19% 17% 5%	2139
April	1st to 10th	Night	35% 6% 18% 20% 17% 5%	1800
	11th to 20th	Night	31% 5% 13% 24% 19% 8%	1779
	21st to end	Night	23% 6% 13% 29% 24% 6%	1800
May	1st to 10th	Night	25% 5% 10% 23% 25% 11%	1746
	11th to 20th	Night	25% 6% 13% 22% 27% 8%	1533
	21st to end	Night	27% 6% 13% 25% 25% 4	1552
June	1st to 10th	Night	23% 5% 11% 22% 28% 10%	1440
	11th to 20th	Night	12% 4 10% 17% 34% 24%	1440
	21st to end	Night	13% 3 6% 13% 31% 34%	1440
July	1st to 10th	Night	12% 2 5% 11% 23% 48%	1400
	11th to 20th	Night	13% 2 9% 11% 19% 46%	1539
	21st to end	Night	17% 2 8% 11% 23% 39%	1674
August	1st to 10th	Night	24% 3 5% 12% 22% 34%	1602
	11th to 20th	Night	13% 3 7% 10% 28% 38%	1727
	21st to end	Night	17% 2 5% 13% 27% 35%	1980
September	1st to 10th	Night	14% 3 4 10% 23% 45%	1800
	11th to 20th	Night	21% 4 8% 19% 28% 20%	1800
	21st to end	Night	14% 3 7% 19% 31% 25%	2041
October	1st to 10th	Night	18% 4 10% 18% 24% 25%	2160
	11th to 20th	Night	24% 4 9% 18% 22% 23%	2160
	21st to end	Night	23% 4 8% 19% 25% 21%	2376
November	1st to 10th	Night	29% 6% 11% 23% 17% 14%	2262
	11th to 20th	Night	31% 7% 11% 22% 21% 9%	2470
	21st to end	Night	29% 5% 10% 21% 23% 12%	2601
December	1st to 10th	Night	36% 7% 11% 17% 16% 13%	2660
	11th to 20th	Night	52% 5% 11% 13% 15% 3	3276
	21st to end	Night	47% 11% 14% 14% 11% 4	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	25% 9% 20% 26% 17% 3	275
	11th to 20th	Day	17% 6% 20% 31% 20% 5%	353
	21st to end	Day	13% 6% 22% 31% 22% 6%	374
February	1st to 10th	Day	16% 9% 24% 25% 20% 7%	340
	11th to 20th	Day	16% 14% 25% 28% 15% 2	377
	21st to end	Day	12% 11% 28% 29% 17% 1	346
March	1st to 10th	Day	17% 11% 30% 28% 12% 2	420
	11th to 20th	Day	19% 12% 24% 27% 14% 5%	420
	21st to end	Day	13% 16% 31% 26% 12% 2	462
April	1st to 10th	Day	14% 12% 31% 25% 15% 3	420
	11th to 20th	Day	13% 16% 30% 25% 11% 4	412
	21st to end	Day	5% 16% 28% 31% 15% 5%	420
May	1st to 10th	Day	6% 12% 30% 34% 13% 5%	423
	11th to 20th	Day	10% 11% 30% 28% 15% 6%	448
	21st to end	Day	7% 11% 25% 32% 16% 9%	485
June	1st to 10th	Day	5% 10% 26% 30% 22% 8%	450
	11th to 20th	Day	1 8% 26% 39% 19% 6%	450
	21st to end	Day	2 5% 21% 37% 26% 9%	450
July	1st to 10th	Day	3 3 15% 43% 27% 8%	446
	11th to 20th	Day	1 1 14% 40% 33% 12%	444
	21st to end	Day	1 1 14% 39% 33% 12%	487
August	1st to 10th	Day	3 4 18% 39% 25% 11%	447
	11th to 20th	Day	1 2 17% 39% 29% 11%	437
	21st to end	Day	1 3 15% 36% 34% 11%	495
September	1st to 10th	Day	2 3 14% 35% 35% 11%	450
	11th to 20th	Day	4 7% 19% 36% 25% 10%	450
	21st to end	Day	3 7% 19% 32% 30% 9%	450
October	1st to 10th	Day	4 7% 21% 34% 22% 11%	450
	11th to 20th	Day	6% 8% 16% 30% 29% 12%	450
	21st to end	Day	5% 6% 24% 30% 26% 9%	495
November	1st to 10th	Day	8% 7% 21% 28% 29% 8%	413
	11th to 20th	Day	5% 6% 14% 31% 32% 12%	270
	21st to end	Day	10% 3 18% 32% 30% 7%	207
December	1st to 10th	Day	12% 8% 16% 28% 22% 13%	180
	11th to 20th	Day	12% 9% 18% 26% 27% 9%	180
	21st to end	Day	20% 8% 20% 29% 19% 4	198
January	1st to 10th	Night	18% 5% 14% 34% 23% 7%	760
	11th to 20th	Night	14% 5% 12% 37% 25% 7%	738
	21st to end	Night	19% 3 14% 36% 24% 6%	792
February	1st to 10th	Night	16% 4 13% 38% 25% 5%	720
	11th to 20th	Night	13% 3 18% 37% 23% 5%	704
	21st to end	Night	14% 6% 16% 42% 19% 3	592
March	1st to 10th	Night	17% 7% 16% 34% 22% 3	720
	11th to 20th	Night	16% 6% 14% 34% 25% 5%	720
	21st to end	Night	15% 5% 19% 38% 20% 3	792
April	1st to 10th	Night	13% 6% 16% 40% 23% 3	720
	11th to 20th	Night	12% 7% 18% 37% 21% 5%	711
	21st to end	Night	7% 4 19% 37% 26% 7%	720
May	1st to 10th	Night	7% 3 17% 39% 28% 6%	666
	11th to 20th	Night	11% 2 9% 35% 35% 8%	470
	21st to end	Night	7% 4 13% 37% 33% 6%	389
June	1st to 10th	Night	7% 4 9% 39% 38% 4	360
	11th to 20th	Night	3 2 9% 40% 44% 3	360
	21st to end	Night	3 4 7% 36% 46% 6%	360
July	1st to 10th	Night	2 3 3 27% 58% 7%	350
	11th to 20th	Night	3 1 2 21% 57% 15%	495
	21st to end	Night	3 3 4 18% 56% 16%	591
August	1st to 10th	Night	7% 4 4 24% 48% 13%	537
	11th to 20th	Night	3 2 7% 31% 48% 9%	659
	21st to end	Night	4 2 6% 29% 46% 14%	792
September	1st to 10th	Night	4 1 7% 30% 45% 13%	720
	11th to 20th	Night	6% 3 10% 29% 42% 10%	720
	21st to end	Night	3 2 9% 28% 44% 13%	720
October	1st to 10th	Night	6% 2 9% 37% 35% 11%	720
	11th to 20th	Night	7% 3 10% 30% 40% 10%	720
	21st to end	Night	6% 4 9% 35% 31% 15%	792
November	1st to 10th	Night	8% 4 11% 33% 34% 9%	740
	11th to 20th	Night	12% 2 10% 35% 32% 8%	760
	21st to end	Night	11% 2 13% 40% 28% 7%	760
December	1st to 10th	Night	15% 5% 11% 38% 25% 6%	760
	11th to 20th	Night	20% 4 14% 37% 19% 6%	760
	21st to end	Night	18% 7% 20% 35% 18% 3	836

Page generated at 2024-01-12 04:31:49. Version ac07

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