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 2024-12-02.

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	7% 6% 2 5% 3 3 3 3 4 6% 60%	105277
	Night	9% 8% 3 6% 3 3 3 3 4 6% 52%	103125
Transparency	Day	24% 5% 9% 18% 24% 20%	105035
	Night	30% 6% 10% 16% 20% 17%	102957
Seeing	Day	8% 8% 22% 32% 22% 8%	15497
	Night	10% 4 12% 34% 32% 7%	24862

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	17% 9% 2 5% 3 4 4 4 5% 7% 39%	2699
	11th to 20th	Day	16% 9% 4 9% 5% 5% 5% 4 5% 6% 33%	2860
	21st to end	Day	20% 11% 3 8% 4 4 4 3 5% 8% 28%	3146
February	1st to 10th	Day	15% 8% 3 5% 4 3 3 3 5% 6% 46%	1710
	11th to 20th	Day	13% 8% 3 6% 4 3 3 4 5% 7% 43%	1763
	21st to end	Day	12% 7% 3 7% 4 3 4 3 6% 6% 46%	1570
March	1st to 10th	Day	12% 11% 4 10% 6% 6% 6% 4 5% 7% 27%	3370
	11th to 20th	Day	10% 5% 2 5% 4 4 3 3 5% 7% 53%	3490
	21st to end	Day	11% 9% 3 9% 5% 6% 6% 5% 7% 7% 33%	3901
April	1st to 10th	Day	12% 8% 2 5% 4 4 3 4 5% 7% 45%	2280
	11th to 20th	Day	10% 6% 2 5% 3 3 3 3 5% 6% 55%	2249
	21st to end	Day	6% 6% 1 4 3 3 4 3 5% 8% 57%	2280
May	1st to 10th	Day	6% 3 1 3 2 2 2 2 3 5% 71%	3888
	11th to 20th	Day	3 4 1 3 2 2 2 2 3 4 75%	4179
	21st to end	Day	3 8% 2 3 2 2 2 2 3 4 68%	4813
June	1st to 10th	Day	5% 6% 1 4 2 3 3 3 4 7% 61%	2660
	11th to 20th	Day	2 2 1 2 2 2 2 2 4 5% 75%	2660
	21st to end	Day	3 4 1 3 2 2 2 2 3 4 76%	2660
July	1st to 10th	Day	1 3 1 2 1 1 1 1 2 3 84%	4420
	11th to 20th	Day	1 3 1 3 2 3 2 2 3 5% 75%	4148
	21st to end	Day	1 4 1 3 2 2 1 2 3 5% 77%	4455
August	1st to 10th	Day	2 4 1 4 3 3 4 3 4 6% 67%	4091
	11th to 20th	Day	2 1 3 2 2 2 2 3 5% 79%	3811
	21st to end	Day	1 4 2 4 2 2 3 2 3 5% 73%	4180
September	1st to 10th	Day	1 3 1 3 2 2 2 2 3 5% 78%	2280
	11th to 20th	Day	3 5% 2 4 3 3 3 3 4 6% 64%	2280
	21st to end	Day	3 2 1 3 1 2 2 2 3 6% 75%	2021
October	1st to 10th	Day	2 2 1 3 2 2 3 2 5% 6% 72%	3180
	11th to 20th	Day	4 5% 2 3 2 3 3 3 3 6% 66%	3161
	21st to end	Day	4 4 1 4 3 4 4 3 6% 8% 59%	3448
November	1st to 10th	Day	6% 5% 1 4 4 3 4 3 5% 8% 55%	1914
	11th to 20th	Day	7% 8% 3 6% 4 4 3 3 6% 7% 50%	1800
	21st to end	Day	11% 6% 2 5% 3 3 3 3 5% 7% 52%	1660
December	1st to 10th	Day	10% 7% 3 7% 5% 4 3 3 6% 6% 46%	1528
	11th to 20th	Day	20% 11% 4 7% 4 3 4 4 5% 5% 32%	1928
	21st to end	Day	15% 11% 3 7% 5% 4 4 4 5% 8% 34%	2794
January	1st to 10th	Night	14% 8% 3 5% 3 4 4 4 6% 7% 42%	4248
	11th to 20th	Night	17% 9% 3 9% 5% 5% 5% 4 5% 6% 32%	4110
	21st to end	Night	21% 13% 4 7% 4 4 4 3 4 6% 30%	4521
February	1st to 10th	Night	14% 9% 2 5% 3 4 3 3 4 5% 48%	2470
	11th to 20th	Night	11% 9% 3 6% 4 4 4 4 5% 8% 42%	2304
	21st to end	Night	11% 7% 2 5% 4 4 4 3 4 7% 49%	1884
March	1st to 10th	Night	15% 14% 4 8% 5% 5% 5% 4 4 5% 31%	3500
	11th to 20th	Night	12% 8% 4 7% 3 3 3 2 3 6% 50%	3490
	21st to end	Night	15% 14% 3 8% 4 4 5% 4 5% 6% 32%	3751
April	1st to 10th	Night	11% 10% 2 5% 4 3 3 4 6% 8% 44%	1900
	11th to 20th	Night	9% 7% 2 5% 3 3 3 4 5% 7% 51%	1879
	21st to end	Night	6% 5% 1 4 4 4 4 3 4 8% 57%	1900
May	1st to 10th	Night	6% 9% 2 3 3 2 3 2 4 6% 61%	3084
	11th to 20th	Night	3 7% 2 5% 3 3 3 3 4 5% 60%	2716
	21st to end	Night	3 10% 2 5% 3 3 2 2 3 5% 62%	2762
June	1st to 10th	Night	6% 7% 2 4 3 2 2 4 4 7% 59%	1520
	11th to 20th	Night	1 4 1 3 2 2 2 3 5% 6% 70%	1520
	21st to end	Night	2 6% 2 3 3 2 1 2 3 4 72%	1520
July	1st to 10th	Night	1 4 1 2 2 2 1 1 3 4 79%	2540
	11th to 20th	Night	1 6% 4 5% 3 3 2 2 3 6% 66%	2817
	21st to end	Night	1 13% 3 6% 5% 3 3 2 4 7% 53%	3109
August	1st to 10th	Night	3 6% 3 10% 5% 4 3 3 5% 6% 51%	2848
	11th to 20th	Night	6% 1 4 3 3 4 2 3 5% 68%	3034
	21st to end	Night	2 9% 3 7% 3 3 2 2 3 5% 62%	3498
September	1st to 10th	Night	2 5% 2 4 2 2 3 2 3 5% 68%	1900
	11th to 20th	Night	5% 8% 2 6% 3 2 3 2 5% 5% 58%	1900
	21st to end	Night	2 4 2 4 2 1 3 2 3 5% 71%	2155
October	1st to 10th	Night	3 3 1 3 2 2 2 2 4 6% 73%	3800
	11th to 20th	Night	4 11% 4 6% 4 2 3 2 3 4 57%	3777
	21st to end	Night	6% 5% 2 6% 3 3 3 3 5% 7% 59%	4121
November	1st to 10th	Night	9% 6% 2 5% 3 3 4 3 5% 7% 54%	2385
	11th to 20th	Night	9% 7% 2 5% 3 3 4 3 5% 8% 50%	2600
	21st to end	Night	10% 5% 1 5% 3 4 3 3 5% 7% 54%	2738
December	1st to 10th	Night	12% 7% 3 6% 3 4 4 3 5% 6% 48%	2686
	11th to 20th	Night	23% 11% 3 6% 4 3 4 3 5% 6% 32%	3276
	21st to end	Night	15% 9% 3 7% 5% 5% 6% 4 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	42% 9% 13% 26% 8% 3	2699
	11th to 20th	Day	50% 8% 11% 14% 10% 7%	2860
	21st to end	Day	52% 8% 10% 13% 13% 4	3146
February	1st to 10th	Day	39% 5% 9% 20% 19% 9%	1710
	11th to 20th	Day	39% 6% 10% 18% 21% 7%	1772
	21st to end	Day	37% 6% 10% 24% 17% 6%	1570
March	1st to 10th	Day	51% 11% 10% 13% 13% 3	3370
	11th to 20th	Day	29% 6% 13% 26% 15% 11%	3490
	21st to end	Day	41% 13% 16% 18% 10% 2	3901
April	1st to 10th	Day	38% 6% 14% 20% 18% 4	2280
	11th to 20th	Day	29% 6% 14% 24% 21% 5%	2252
	21st to end	Day	24% 6% 14% 28% 25% 4	2280
May	1st to 10th	Day	17% 4 9% 31% 25% 14%	3888
	11th to 20th	Day	12% 2 9% 24% 40% 13%	4182
	21st to end	Day	16% 6% 11% 30% 33% 4	4814
June	1st to 10th	Day	22% 6% 11% 24% 27% 10%	2660
	11th to 20th	Day	10% 4 9% 22% 38% 18%	2660
	21st to end	Day	12% 2 5% 12% 32% 37%	2660
July	1st to 10th	Day	6% 2 3 6% 14% 69%	4351
	11th to 20th	Day	10% 3 6% 8% 14% 59%	4077
	21st to end	Day	9% 3 4 7% 32% 45%	4315
August	1st to 10th	Day	13% 4 7% 9% 30% 37%	4076
	11th to 20th	Day	7% 3 4 10% 47% 29%	3849
	21st to end	Day	12% 4 6% 11% 34% 34%	4179
September	1st to 10th	Day	11% 2 5% 10% 30% 43%	2280
	11th to 20th	Day	19% 4 8% 20% 31% 18%	2280
	21st to end	Day	11% 3 7% 20% 35% 24%	2021
October	1st to 10th	Day	13% 3 6% 12% 28% 39%	3180
	11th to 20th	Day	18% 5% 7% 23% 27% 18%	3161
	21st to end	Day	20% 6% 9% 21% 30% 15%	3448
November	1st to 10th	Day	28% 5% 11% 22% 23% 11%	1914
	11th to 20th	Day	32% 7% 10% 22% 23% 7%	1800
	21st to end	Day	30% 5% 10% 18% 29% 8%	1660
December	1st to 10th	Day	37% 6% 12% 18% 17% 10%	1528
	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	39% 10% 18% 21% 9% 3	4248
	11th to 20th	Night	51% 9% 13% 10% 9% 7%	4110
	21st to end	Night	55% 7% 9% 12% 12% 6%	4521
February	1st to 10th	Night	38% 5% 9% 19% 19% 11%	2470
	11th to 20th	Night	38% 6% 11% 17% 21% 7%	2306
	21st to end	Night	34% 6% 11% 28% 17% 4	1884
March	1st to 10th	Night	49% 11% 12% 12% 13% 3	3500
	11th to 20th	Night	31% 7% 12% 22% 17% 11%	3490
	21st to end	Night	45% 13% 14% 16% 10% 3	3751
April	1st to 10th	Night	34% 6% 18% 20% 17% 5%	1900
	11th to 20th	Night	31% 5% 13% 25% 18% 7%	1879
	21st to end	Night	23% 6% 13% 29% 24% 6%	1900
May	1st to 10th	Night	20% 7% 12% 24% 25% 13%	3084
	11th to 20th	Night	14% 4 15% 17% 31% 19%	2717
	21st to end	Night	17% 5% 15% 27% 33% 4	2762
June	1st to 10th	Night	22% 6% 11% 22% 29% 10%	1520
	11th to 20th	Night	12% 4 10% 18% 34% 23%	1520
	21st to end	Night	13% 2 6% 13% 31% 36%	1520
July	1st to 10th	Night	7% 1 3 6% 14% 68%	2500
	11th to 20th	Night	17% 2 7% 8% 14% 53%	2765
	21st to end	Night	21% 7% 7% 10% 21% 35%	3011
August	1st to 10th	Night	19% 11% 6% 10% 25% 28%	2839
	11th to 20th	Night	11% 4 7% 8% 43% 26%	3062
	21st to end	Night	19% 5% 6% 10% 31% 28%	3498
September	1st to 10th	Night	14% 3 4 9% 24% 44%	1900
	11th to 20th	Night	22% 5% 8% 19% 28% 19%	1900
	21st to end	Night	14% 3 7% 19% 31% 26%	2155
October	1st to 10th	Night	13% 3 6% 11% 25% 42%	3800
	11th to 20th	Night	28% 4 7% 19% 21% 20%	3777
	21st to end	Night	23% 4 8% 21% 25% 19%	4121
November	1st to 10th	Night	28% 6% 10% 23% 19% 13%	2385
	11th to 20th	Night	31% 6% 11% 22% 21% 8%	2600
	21st to end	Night	30% 5% 10% 20% 22% 12%	2738
December	1st to 10th	Night	36% 7% 11% 17% 16% 12%	2686
	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	16% 6% 20% 33% 20% 5%	370
	21st to end	Day	14% 6% 22% 30% 22% 6%	407
February	1st to 10th	Day	16% 10% 24% 25% 19% 6%	370
	11th to 20th	Day	16% 14% 26% 28% 15% 2	412
	21st to end	Day	12% 12% 28% 30% 17% 2	382
March	1st to 10th	Day	17% 12% 29% 28% 12% 2	460
	11th to 20th	Day	17% 13% 23% 27% 15% 5%	460
	21st to end	Day	13% 16% 31% 26% 11% 2	506
April	1st to 10th	Day	13% 12% 30% 26% 14% 4	460
	11th to 20th	Day	13% 15% 28% 26% 12% 5%	452
	21st to end	Day	5% 16% 27% 30% 16% 5%	460
May	1st to 10th	Day	6% 12% 30% 34% 14% 5%	463
	11th to 20th	Day	9% 10% 28% 28% 17% 7%	488
	21st to end	Day	6% 11% 24% 31% 18% 9%	529
June	1st to 10th	Day	4 9% 26% 31% 21% 8%	490
	11th to 20th	Day	1 8% 27% 38% 19% 6%	490
	21st to end	Day	2 4 22% 37% 26% 9%	490
July	1st to 10th	Day	3 3 15% 42% 28% 9%	486
	11th to 20th	Day	1 1 15% 40% 32% 12%	484
	21st to end	Day	1 2 15% 39% 32% 11%	531
August	1st to 10th	Day	3 4 18% 39% 25% 11%	487
	11th to 20th	Day	1 3 20% 38% 28% 10%	477
	21st to end	Day	1 4 15% 36% 32% 12%	539
September	1st to 10th	Day	2 3 16% 34% 34% 11%	490
	11th to 20th	Day	4 8% 20% 35% 24% 9%	490
	21st to end	Day	3 7% 18% 32% 31% 9%	490
October	1st to 10th	Day	3 7% 20% 34% 24% 12%	490
	11th to 20th	Day	6% 8% 16% 30% 28% 12%	490
	21st to end	Day	5% 7% 24% 31% 25% 8%	539
November	1st to 10th	Day	7% 7% 22% 27% 27% 9%	450
	11th to 20th	Day	6% 8% 16% 31% 29% 11%	300
	21st to end	Day	13% 3 20% 30% 28% 6%	230
December	1st to 10th	Day	12% 8% 15% 28% 23% 14%	182
	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% 26% 7%	760
	21st to end	Night	19% 3 13% 36% 23% 5%	836
February	1st to 10th	Night	16% 5% 13% 37% 24% 5%	760
	11th to 20th	Night	13% 4 19% 36% 22% 5%	744
	21st to end	Night	13% 6% 16% 43% 19% 3	628
March	1st to 10th	Night	16% 8% 16% 34% 22% 3	760
	11th to 20th	Night	16% 6% 15% 34% 25% 4	760
	21st to end	Night	16% 6% 19% 38% 19% 3	836
April	1st to 10th	Night	13% 6% 16% 39% 23% 3	760
	11th to 20th	Night	12% 7% 17% 36% 22% 6%	751
	21st to end	Night	7% 4 19% 38% 26% 6%	760
May	1st to 10th	Night	7% 3 17% 40% 28% 5%	703
	11th to 20th	Night	10% 3 9% 34% 36% 8%	496
	21st to end	Night	7% 4 12% 37% 33% 6%	411
June	1st to 10th	Night	7% 4 8% 39% 37% 4	380
	11th to 20th	Night	2 2 9% 41% 44% 3	380
	21st to end	Night	2 3 7% 36% 46% 6%	380
July	1st to 10th	Night	2 3 4 27% 58% 6%	370
	11th to 20th	Night	3 1 2 22% 57% 15%	524
	21st to end	Night	3 4 4 19% 55% 15%	624
August	1st to 10th	Night	7% 4 4 24% 49% 13%	567
	11th to 20th	Night	3 2 8% 32% 46% 9%	696
	21st to end	Night	4 2 6% 29% 45% 13%	836
September	1st to 10th	Night	4 2 7% 30% 45% 12%	760
	11th to 20th	Night	7% 3 10% 30% 41% 9%	760
	21st to end	Night	3 2 9% 29% 44% 13%	760
October	1st to 10th	Night	5% 2 9% 37% 36% 11%	760
	11th to 20th	Night	7% 4 10% 30% 39% 10%	760
	21st to end	Night	6% 4 9% 37% 31% 14%	836
November	1st to 10th	Night	8% 4 12% 33% 34% 9%	780
	11th to 20th	Night	12% 3 11% 35% 31% 8%	800
	21st to end	Night	12% 2 13% 40% 27% 6%	800
December	1st to 10th	Night	15% 5% 11% 38% 26% 6%	768
	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 2024-11-29 07:43:07. Version ac07

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