Merced
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Merced clear sky chart from 2005-11-06 to 2024-11-01.

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	5% 3 1 3 2 2 3 2 4 5% 68%	101075
	Night	8% 4 1 4 3 3 3 2 4 5% 65%	98098
Transparency	Day	20% 4 7% 18% 23% 28%	100828
	Night	22% 4 8% 19% 22% 23%	97934
Seeing	Day	6% 4 16% 29% 31% 14%	15301
	Night	8% 3 17% 42% 27% 4	24718

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	13% 10% 4 11% 6% 6% 5% 3 5% 6% 31%	2539
	11th to 20th	Day	14% 9% 4 10% 7% 5% 5% 3 5% 6% 32%	2831
	21st to end	Day	17% 10% 4 8% 6% 5% 4 3 5% 7% 29%	3146
February	1st to 10th	Day	14% 7% 2 5% 4 3 4 4 5% 7% 46%	1728
	11th to 20th	Day	11% 5% 2 5% 4 3 3 3 5% 8% 51%	1850
	21st to end	Day	13% 6% 1 5% 5% 4 3 3 4 6% 50%	1570
March	1st to 10th	Day	10% 7% 3 7% 5% 5% 6% 4 8% 9% 36%	3186
	11th to 20th	Day	9% 4 1 3 3 2 3 3 4 7% 61%	3490
	21st to end	Day	11% 6% 2 5% 4 4 5% 4 6% 8% 44%	4023
April	1st to 10th	Day	10% 5% 2 4 3 3 3 3 5% 5% 58%	2280
	11th to 20th	Day	6% 4 1 4 3 3 3 3 4 7% 63%	2249
	21st to end	Day	5% 3 1 4 2 3 2 2 3 6% 69%	2280
May	1st to 10th	Day	3 2 1 3 2 1 2 1 3 5% 78%	3800
	11th to 20th	Day	1 1 1 1 1 1 2 2 2 4 84%	4234
	21st to end	Day	2 1 1 1 1 2 2 2 4 83%	4813
June	1st to 10th	Day	2 3 1 2 2 2 2 2 4 6% 76%	2660
	11th to 20th	Day	1 1 1 1 1 1 2 3 87%	2660
	21st to end	Day	2 1 1 2 1 1 2 1 2 2 87%	2660
July	1st to 10th	Day	1 1 1 1 94%	4420
	11th to 20th	Day	1 1 2 1 1 2 2 3 4 84%	4389
	21st to end	Day	1 1 1 1 1 1 1 2 3 89%	4455
August	1st to 10th	Day	1 1 1 1 1 1 1 3 3 85%	4007
	11th to 20th	Day	1 1 1 2 2 92%	3724
	21st to end	Day	1 1 1 1 1 1 1 2 2 91%	4180
September	1st to 10th	Day	1 1 1 1 1 1 1 2 2 90%	2280
	11th to 20th	Day	1 1 1 1 1 2 2 2 3 84%	2272
	21st to end	Day	2 1 2 1 1 1 1 2 4 85%	2090
October	1st to 10th	Day	2 2 1 2 2 1 2 2 3 5% 78%	1900
	11th to 20th	Day	3 1 1 3 2 2 2 2 4 5% 75%	1900
	21st to end	Day	4 2 1 3 2 3 3 3 4 6% 69%	2090
November	1st to 10th	Day	4 4 1 4 4 4 4 3 4 7% 59%	1713
	11th to 20th	Day	7% 7% 1 4 4 3 4 2 4 7% 58%	1710
	21st to end	Day	9% 6% 2 5% 4 3 4 3 5% 7% 52%	1704
December	1st to 10th	Day	13% 7% 3 7% 4 4 3 3 4 8% 44%	1520
	11th to 20th	Day	20% 10% 3 10% 5% 5% 4 3 4 6% 31%	1928
	21st to end	Day	13% 8% 4 9% 7% 5% 5% 5% 7% 9% 28%	2794
January	1st to 10th	Night	14% 7% 3 8% 4 4 4 3 5% 6% 42%	4406
	11th to 20th	Night	17% 8% 3 8% 5% 4 4 4 6% 7% 34%	4136
	21st to end	Night	19% 7% 2 8% 5% 5% 4 3 5% 7% 35%	4521
February	1st to 10th	Night	13% 5% 2 5% 4 2 3 3 5% 6% 52%	2451
	11th to 20th	Night	12% 5% 1 4 3 3 3 3 4 7% 56%	2218
	21st to end	Night	14% 6% 1 3 3 3 4 3 4 5% 54%	1884
March	1st to 10th	Night	14% 6% 2 6% 4 4 5% 4 6% 7% 42%	3684
	11th to 20th	Night	9% 4 1 4 3 3 3 2 4 5% 62%	3490
	21st to end	Night	16% 6% 2 5% 3 3 4 3 5% 7% 48%	3628
April	1st to 10th	Night	10% 4 1 3 2 3 3 4 6% 6% 58%	1900
	11th to 20th	Night	6% 3 1 3 2 3 4 3 4 6% 64%	1879
	21st to end	Night	4 2 3 2 2 3 3 4 7% 70%	1900
May	1st to 10th	Night	2 2 1 2 1 2 1 2 3 4 80%	3180
	11th to 20th	Night	2 1 1 1 1 1 1 3 4 84%	2655
	21st to end	Night	2 1 1 1 1 2 1 2 3 84%	2762
June	1st to 10th	Night	2 2 1 2 2 2 2 2 3 6% 76%	1520
	11th to 20th	Night	1 1 1 1 1 1 2 3 88%	1520
	21st to end	Night	1 1 1 1 1 2 1 2 2 89%	1520
July	1st to 10th	Night	1 1 1 1 1 95%	2540
	11th to 20th	Night	2 2 2 2 1 1 1 2 3 84%	2567
	21st to end	Night	1 1 1 1 1 2 1 2 3 87%	3109
August	1st to 10th	Night	1 1 2 1 1 2 1 3 3 84%	2933
	11th to 20th	Night	1 1 1 2 1 2 2 90%	3126
	21st to end	Night	2 1 1 1 1 1 1 1 2 91%	3498
September	1st to 10th	Night	1 1 1 1 1 1 1 2 91%	1900
	11th to 20th	Night	2 1 1 2 1 1 1 1 2 3 85%	1906
	21st to end	Night	2 1 1 1 1 2 2 1 2 4 84%	2090
October	1st to 10th	Night	3 2 1 2 2 2 2 2 3 4 78%	2276
	11th to 20th	Night	2 2 1 2 2 2 2 2 4 4 77%	2280
	21st to end	Night	5% 1 1 2 1 2 1 2 3 5% 77%	2508
November	1st to 10th	Night	7% 4 2 3 2 3 3 2 4 6% 65%	2369
	11th to 20th	Night	6% 4 1 4 3 3 2 3 5% 7% 62%	2470
	21st to end	Night	8% 4 2 4 3 3 3 3 5% 6% 59%	2474
December	1st to 10th	Night	13% 5% 3 5% 3 3 3 3 4 7% 51%	2660
	11th to 20th	Night	16% 7% 2 7% 5% 5% 4 4 6% 9% 35%	3276
	21st to end	Night	15% 7% 3 9% 6% 5% 5% 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	50% 9% 16% 19% 5% 1	2539
	11th to 20th	Day	52% 8% 11% 16% 10% 3	2831
	21st to end	Day	51% 9% 11% 19% 8% 1	3146
February	1st to 10th	Day	36% 5% 12% 25% 15% 6%	1728
	11th to 20th	Day	33% 5% 12% 25% 20% 6%	1860
	21st to end	Day	35% 5% 11% 26% 20% 2	1570
March	1st to 10th	Day	39% 11% 16% 19% 14% 2	3186
	11th to 20th	Day	24% 5% 12% 31% 17% 11%	3490
	21st to end	Day	34% 7% 15% 25% 16% 3	4023
April	1st to 10th	Day	27% 5% 12% 28% 19% 9%	2280
	11th to 20th	Day	23% 4 11% 28% 25% 9%	2252
	21st to end	Day	19% 3 9% 31% 31% 7%	2280
May	1st to 10th	Day	13% 2 6% 27% 33% 19%	3800
	11th to 20th	Day	8% 2 4 25% 43% 18%	4237
	21st to end	Day	8% 2 6% 28% 38% 18%	4814
June	1st to 10th	Day	12% 3 8% 24% 30% 23%	2660
	11th to 20th	Day	5% 1 4 18% 36% 35%	2660
	21st to end	Day	7% 1 2 9% 29% 53%	2660
July	1st to 10th	Day	2 1 1 3 12% 81%	4351
	11th to 20th	Day	7% 2 2 5% 13% 71%	4314
	21st to end	Day	5% 2 1 4 24% 64%	4315
August	1st to 10th	Day	7% 1 1 5% 23% 62%	3992
	11th to 20th	Day	3 1 1 4 25% 66%	3760
	21st to end	Day	5% 1 2 5% 30% 56%	4179
September	1st to 10th	Day	5% 1 2 6% 25% 60%	2280
	11th to 20th	Day	8% 2 3 19% 40% 29%	2272
	21st to end	Day	7% 2 2 17% 39% 33%	2090
October	1st to 10th	Day	13% 2 5% 19% 28% 34%	1900
	11th to 20th	Day	13% 3 5% 24% 30% 25%	1900
	21st to end	Day	17% 3 7% 22% 32% 20%	2090
November	1st to 10th	Day	24% 5% 10% 26% 27% 9%	1713
	11th to 20th	Day	29% 4 14% 26% 24% 4	1710
	21st to end	Day	32% 4 12% 25% 22% 7%	1704
December	1st to 10th	Day	38% 6% 13% 18% 18% 6%	1520
	11th to 20th	Day	55% 5% 10% 16% 11% 3	1928
	21st to end	Day	46% 12% 16% 17% 8% 2	2794
January	1st to 10th	Night	38% 11% 16% 23% 9% 1	4406
	11th to 20th	Night	46% 9% 13% 17% 9% 7%	4136
	21st to end	Night	46% 7% 12% 19% 12% 3	4521
February	1st to 10th	Night	33% 4 12% 25% 20% 7%	2451
	11th to 20th	Night	29% 3 10% 26% 26% 6%	2219
	21st to end	Night	32% 5% 9% 29% 20% 5%	1884
March	1st to 10th	Night	38% 10% 13% 19% 17% 4	3684
	11th to 20th	Night	26% 5% 11% 27% 23% 9%	3490
	21st to end	Night	34% 8% 14% 27% 13% 4	3628
April	1st to 10th	Night	25% 4 15% 27% 21% 8%	1900
	11th to 20th	Night	19% 4 13% 29% 25% 9%	1879
	21st to end	Night	16% 5% 12% 29% 30% 8%	1900
May	1st to 10th	Night	9% 4 9% 27% 34% 17%	3180
	11th to 20th	Night	7% 2 4 24% 43% 20%	2655
	21st to end	Night	8% 2 6% 29% 44% 11%	2762
June	1st to 10th	Night	12% 3 9% 22% 33% 20%	1520
	11th to 20th	Night	5% 2 5% 17% 37% 35%	1520
	21st to end	Night	6% 1 2 8% 28% 56%	1520
July	1st to 10th	Night	2 1 1 3 13% 81%	2500
	11th to 20th	Night	9% 1 1 3 14% 71%	2519
	21st to end	Night	7% 1 1 4 23% 64%	3011
August	1st to 10th	Night	7% 1 1 6% 20% 65%	2924
	11th to 20th	Night	4 1 1 5% 21% 68%	3156
	21st to end	Night	6% 1 7% 27% 59%	3498
September	1st to 10th	Night	5% 1 2 6% 25% 61%	1900
	11th to 20th	Night	8% 1 2 18% 40% 31%	1906
	21st to end	Night	8% 2 2 15% 38% 36%	2090
October	1st to 10th	Night	13% 2 5% 18% 24% 38%	2276
	11th to 20th	Night	11% 3 7% 20% 28% 32%	2280
	21st to end	Night	12% 2 6% 21% 34% 26%	2508
November	1st to 10th	Night	22% 3 8% 25% 26% 16%	2369
	11th to 20th	Night	22% 4 11% 27% 29% 8%	2470
	21st to end	Night	26% 4 10% 24% 29% 8%	2474
December	1st to 10th	Night	34% 5% 12% 22% 18% 10%	2660
	11th to 20th	Night	44% 8% 13% 17% 15% 3	3276
	21st to end	Night	44% 10% 15% 20% 8% 3	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	26% 7% 17% 24% 18% 7%	180
	11th to 20th	Day	15% 5% 16% 25% 25% 14%	354
	21st to end	Day	14% 4 18% 21% 27% 16%	407
February	1st to 10th	Day	16% 7% 18% 20% 22% 18%	379
	11th to 20th	Day	11% 8% 22% 26% 22% 11%	455
	21st to end	Day	12% 7% 22% 29% 24% 7%	382
March	1st to 10th	Day	13% 8% 22% 29% 20% 8%	460
	11th to 20th	Day	15% 7% 18% 29% 19% 13%	460
	21st to end	Day	14% 9% 21% 29% 20% 7%	506
April	1st to 10th	Day	12% 8% 24% 28% 17% 11%	460
	11th to 20th	Day	9% 9% 24% 31% 18% 11%	452
	21st to end	Day	4 7% 23% 33% 19% 13%	460
May	1st to 10th	Day	3 7% 27% 34% 21% 8%	463
	11th to 20th	Day	4 6% 19% 34% 27% 10%	488
	21st to end	Day	4 6% 16% 30% 30% 14%	529
June	1st to 10th	Day	2 4 19% 32% 31% 12%	490
	11th to 20th	Day	1 3 19% 36% 32% 8%	490
	21st to end	Day	1 1 12% 35% 37% 13%	490
July	1st to 10th	Day	7% 33% 47% 13%	486
	11th to 20th	Day	3 29% 51% 17%	484
	21st to end	Day	1 3 33% 46% 17%	531
August	1st to 10th	Day	3 1 9% 38% 38% 11%	487
	11th to 20th	Day	10% 36% 38% 15%	477
	21st to end	Day	1 1 8% 29% 46% 15%	539
September	1st to 10th	Day	1 1 9% 30% 44% 15%	490
	11th to 20th	Day	2 2 17% 31% 32% 16%	490
	21st to end	Day	1 2 11% 31% 36% 20%	490
October	1st to 10th	Day	2 2 19% 22% 31% 23%	490
	11th to 20th	Day	3 5% 13% 24% 33% 21%	490
	21st to end	Day	4 4 15% 23% 35% 19%	539
November	1st to 10th	Day	6% 4 14% 23% 28% 25%	309
	11th to 20th	Day	3 6% 12% 24% 36% 19%	270
	21st to end	Day	9% 1 12% 30% 33% 15%	266
December	1st to 10th	Day	16% 2 19% 27% 19% 16%	180
	11th to 20th	Day	9% 7% 20% 24% 23% 17%	180
	21st to end	Day	18% 6% 15% 25% 26% 10%	198
January	1st to 10th	Night	18% 3 14% 34% 25% 6%	760
	11th to 20th	Night	13% 3 11% 37% 30% 6%	760
	21st to end	Night	17% 3 12% 36% 29% 4	836
February	1st to 10th	Night	15% 4 14% 36% 26% 6%	760
	11th to 20th	Night	12% 4 18% 33% 29% 5%	744
	21st to end	Night	15% 4 19% 42% 18% 3	628
March	1st to 10th	Night	14% 5% 18% 39% 23% 2	760
	11th to 20th	Night	12% 7% 19% 34% 25% 4	760
	21st to end	Night	14% 4 23% 37% 21% 1	836
April	1st to 10th	Night	10% 4 27% 37% 22% 1	760
	11th to 20th	Night	6% 5% 29% 37% 19% 3	751
	21st to end	Night	4 4 28% 41% 21% 2	760
May	1st to 10th	Night	2 4 29% 44% 19% 2	760
	11th to 20th	Night	5% 2 29% 47% 17%	461
	21st to end	Night	3 3 29% 47% 18%	411
June	1st to 10th	Night	3 4 30% 49% 12% 1	380
	11th to 20th	Night	1 2 29% 53% 15%	380
	21st to end	Night	1 1 23% 56% 18%	380
July	1st to 10th	Night	17% 65% 18%	370
	11th to 20th	Night	1 11% 67% 21%	382
	21st to end	Night	1 10% 52% 34% 2	624
August	1st to 10th	Night	2 13% 55% 27% 2	613
	11th to 20th	Night	16% 54% 27% 2	752
	21st to end	Night	2 1 8% 53% 35% 2	836
September	1st to 10th	Night	1 11% 52% 34% 2	760
	11th to 20th	Night	2 1 18% 46% 31% 3	760
	21st to end	Night	2 1 15% 41% 37% 4	760
October	1st to 10th	Night	4 2 15% 39% 35% 6%	760
	11th to 20th	Night	2 3 15% 39% 36% 6%	760
	21st to end	Night	5% 2 10% 37% 33% 12%	836
November	1st to 10th	Night	8% 1 14% 34% 35% 8%	742
	11th to 20th	Night	8% 1 10% 43% 32% 6%	760
	21st to end	Night	9% 2 12% 37% 35% 6%	760
December	1st to 10th	Night	14% 3 12% 41% 26% 5%	760
	11th to 20th	Night	16% 2 13% 38% 27% 3	760
	21st to end	Night	18% 4 14% 40% 21% 3	836

Page generated at 2024-10-29 08:20:49. Version ac07

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