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 2025-05-11.

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% 3 1 4 3 3 3 2 4 5% 67%	117753
	Night	7% 4 1 4 3 3 3 2 4 5% 63%	120075
Transparency	Day	21% 4 7% 18% 24% 26%	117506
	Night	23% 4 8% 20% 23% 21%	119911
Seeing	Day	6% 4 16% 29% 30% 14%	15924
	Night	8% 3 17% 42% 27% 4	25482

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	11% 7% 3 9% 6% 5% 5% 4 5% 8% 36%	3639
	11th to 20th	Day	10% 6% 3 8% 5% 4 4 2 4 4 50%	4071
	21st to end	Day	13% 8% 3 7% 6% 4 4 3 5% 7% 40%	4510
February	1st to 10th	Day	14% 7% 2 5% 4 3 4 4 5% 7% 46%	1819
	11th to 20th	Day	11% 5% 2 5% 4 3 3 3 6% 8% 50%	1950
	21st to end	Day	13% 6% 1 5% 5% 4 3 3 4 6% 50%	1650
March	1st to 10th	Day	12% 6% 2 6% 4 5% 5% 4 8% 9% 39%	4579
	11th to 20th	Day	12% 4 2 4 3 3 4 3 4 8% 52%	5000
	21st to end	Day	10% 5% 2 5% 4 4 5% 4 6% 9% 48%	5762
April	1st to 10th	Day	10% 4 2 4 3 3 3 3 5% 5% 58%	2400
	11th to 20th	Day	6% 4 1 4 3 3 3 3 4 7% 63%	2369
	21st to end	Day	5% 3 1 4 2 3 2 2 3 6% 68%	2400
May	1st to 10th	Day	3 2 1 3 2 1 2 1 3 4 78%	3920
	11th to 20th	Day	1 1 1 1 1 1 2 2 2 4 84%	4236
	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	1 2 1 2 1 1 1 2 3 5% 81%	3180
	11th to 20th	Day	2 1 1 3 2 2 2 2 3 4 79%	3161
	21st to end	Day	4 2 1 3 2 3 3 3 4 6% 68%	3448
November	1st to 10th	Day	4 4 1 4 3 4 4 3 4 7% 60%	1804
	11th to 20th	Day	7% 6% 1 4 4 3 4 3 4 7% 57%	1800
	21st to end	Day	10% 6% 2 5% 4 3 4 3 5% 7% 51%	1793
December	1st to 10th	Day	8% 4 2 6% 5% 5% 5% 4 6% 9% 45%	2620
	11th to 20th	Day	16% 9% 3 9% 6% 6% 5% 4 6% 7% 29%	3028
	21st to end	Day	15% 8% 4 10% 7% 6% 6% 5% 7% 9% 24%	4004
January	1st to 10th	Night	11% 5% 3 7% 4 5% 4 3 5% 7% 46%	6306
	11th to 20th	Night	12% 5% 2 6% 4 3 3 3 4 6% 52%	5906
	21st to end	Night	14% 6% 2 7% 4 4 3 3 4 6% 48%	6468
February	1st to 10th	Night	14% 6% 2 5% 4 3 3 3 5% 6% 51%	2580
	11th to 20th	Night	12% 5% 1 4 3 3 3 3 4 7% 55%	2338
	21st to end	Night	13% 6% 2 3 3 3 4 3 4 5% 54%	1980
March	1st to 10th	Night	13% 6% 2 7% 4 4 5% 4 5% 7% 42%	5298
	11th to 20th	Night	10% 6% 2 6% 4 4 4 3 4 5% 53%	5000
	21st to end	Night	14% 5% 2 5% 3 3 4 3 5% 7% 50%	5211
April	1st to 10th	Night	10% 4 1 3 2 3 3 4 6% 6% 59%	2000
	11th to 20th	Night	6% 3 1 3 2 3 4 3 4 6% 64%	1979
	21st to end	Night	4 3 3 2 2 3 3 4 6% 69%	2000
May	1st to 10th	Night	2 2 1 2 1 2 1 2 3 4 80%	3280
	11th to 20th	Night	2 1 1 1 1 1 1 3 4 84%	2659
	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	2 1 1 1 1 2 1 3 3 83%	3796
	11th to 20th	Night	1 1 1 2 1 2 2 2 3 4 81%	3777
	21st to end	Night	4 2 1 3 2 2 2 2 3 5% 74%	4121
November	1st to 10th	Night	7% 4 2 2 2 3 3 2 4 6% 65%	2492
	11th to 20th	Night	6% 3 1 4 3 3 2 3 5% 7% 62%	2600
	21st to end	Night	9% 4 2 4 3 4 3 3 5% 6% 58%	2605
December	1st to 10th	Night	8% 3 2 4 3 4 5% 3 6% 9% 53%	4560
	11th to 20th	Night	14% 8% 2 8% 5% 5% 4 4 7% 11% 32%	5176
	21st to end	Night	15% 8% 3 9% 7% 6% 6% 5% 6% 7% 28%	6952

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% 8% 19% 19% 9% 2	3639
	11th to 20th	Day	38% 6% 8% 15% 24% 10%	4071
	21st to end	Day	42% 7% 8% 16% 23% 4	4510
February	1st to 10th	Day	37% 5% 12% 24% 15% 7%	1819
	11th to 20th	Day	33% 5% 12% 25% 19% 5%	1960
	21st to end	Day	36% 5% 11% 26% 20% 3	1650
March	1st to 10th	Day	38% 8% 12% 20% 19% 1	4579
	11th to 20th	Day	31% 4 14% 30% 14% 8%	5000
	21st to end	Day	31% 6% 14% 31% 15% 2	5762
April	1st to 10th	Day	27% 4 12% 28% 20% 9%	2400
	11th to 20th	Day	23% 4 11% 28% 25% 10%	2372
	21st to end	Day	19% 3 9% 31% 30% 7%	2400
May	1st to 10th	Day	13% 2 6% 27% 33% 19%	3920
	11th to 20th	Day	8% 2 4 25% 43% 18%	4239
	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	10% 1 3 12% 24% 50%	3180
	11th to 20th	Day	11% 2 4 24% 38% 22%	3161
	21st to end	Day	18% 2 5% 20% 41% 15%	3448
November	1st to 10th	Day	23% 5% 10% 26% 27% 9%	1804
	11th to 20th	Day	29% 4 14% 27% 23% 4	1800
	21st to end	Day	32% 4 11% 25% 21% 6%	1793
December	1st to 10th	Day	34% 5% 12% 28% 17% 4	2620
	11th to 20th	Day	53% 5% 10% 18% 12% 2	3028
	21st to end	Day	52% 10% 16% 14% 6% 1	4004
January	1st to 10th	Night	34% 9% 18% 26% 12% 2	6306
	11th to 20th	Night	33% 7% 9% 17% 28% 7%	5906
	21st to end	Night	37% 6% 8% 18% 25% 6%	6468
February	1st to 10th	Night	34% 4 11% 24% 20% 7%	2580
	11th to 20th	Night	30% 3 10% 26% 25% 6%	2339
	21st to end	Night	32% 4 9% 30% 20% 6%	1980
March	1st to 10th	Night	39% 8% 10% 20% 20% 3	5298
	11th to 20th	Night	35% 4 11% 27% 17% 6%	5000
	21st to end	Night	33% 6% 15% 29% 14% 3	5211
April	1st to 10th	Night	24% 4 15% 27% 21% 8%	2000
	11th to 20th	Night	20% 4 13% 29% 25% 10%	1979
	21st to end	Night	17% 5% 12% 29% 30% 8%	2000
May	1st to 10th	Night	9% 3 9% 28% 34% 17%	3280
	11th to 20th	Night	7% 2 4 24% 43% 20%	2659
	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	8% 2 3 11% 19% 57%	3796
	11th to 20th	Night	10% 2 4 24% 34% 26%	3777
	21st to end	Night	15% 1 4 18% 39% 23%	4121
November	1st to 10th	Night	21% 3 8% 26% 26% 16%	2492
	11th to 20th	Night	22% 4 11% 28% 28% 8%	2600
	21st to end	Night	27% 4 10% 24% 28% 8%	2605
December	1st to 10th	Night	29% 5% 10% 26% 23% 6%	4560
	11th to 20th	Night	45% 6% 14% 19% 15% 2	5176
	21st to end	Night	49% 8% 15% 19% 6% 2	6952

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% 7% 17% 28% 18% 7%	200
	11th to 20th	Day	14% 5% 16% 26% 26% 14%	384
	21st to end	Day	13% 4 17% 22% 27% 17%	440
February	1st to 10th	Day	16% 7% 20% 20% 21% 17%	410
	11th to 20th	Day	12% 8% 22% 27% 21% 11%	495
	21st to end	Day	12% 6% 22% 29% 25% 7%	414
March	1st to 10th	Day	13% 8% 21% 30% 21% 7%	500
	11th to 20th	Day	15% 7% 18% 30% 18% 12%	500
	21st to end	Day	13% 9% 20% 29% 20% 9%	550
April	1st to 10th	Day	11% 8% 24% 29% 17% 11%	500
	11th to 20th	Day	8% 8% 24% 31% 18% 11%	492
	21st to end	Day	4 7% 23% 33% 20% 14%	500
May	1st to 10th	Day	3 7% 26% 35% 20% 9%	503
	11th to 20th	Day	4 6% 19% 34% 27% 10%	489
	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% 22% 35% 19%	539
November	1st to 10th	Day	6% 4 14% 24% 27% 26%	340
	11th to 20th	Day	3 6% 15% 24% 35% 17%	300
	21st to end	Day	11% 1 14% 29% 31% 14%	295
December	1st to 10th	Day	15% 3 18% 28% 19% 19%	200
	11th to 20th	Day	10% 8% 19% 24% 25% 16%	200
	21st to end	Day	17% 6% 16% 26% 25% 9%	220
January	1st to 10th	Night	17% 3 15% 34% 25% 6%	800
	11th to 20th	Night	12% 2 12% 39% 30% 6%	800
	21st to end	Night	16% 3 12% 35% 30% 4	880
February	1st to 10th	Night	15% 5% 15% 36% 24% 5%	800
	11th to 20th	Night	12% 4 18% 33% 27% 5%	784
	21st to end	Night	14% 4 18% 42% 19% 3	660
March	1st to 10th	Night	14% 4 18% 40% 22% 2	800
	11th to 20th	Night	12% 7% 19% 34% 24% 4	800
	21st to end	Night	14% 5% 23% 37% 20% 1	880
April	1st to 10th	Night	10% 4 27% 37% 22% 1	800
	11th to 20th	Night	6% 5% 29% 38% 19% 3	791
	21st to end	Night	4 4 27% 41% 21% 2	800
May	1st to 10th	Night	2 3 29% 45% 19% 2	800
	11th to 20th	Night	5% 2 29% 47% 17%	463
	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	4 2 11% 37% 33% 12%	836
November	1st to 10th	Night	7% 2 14% 34% 35% 8%	780
	11th to 20th	Night	8% 1 11% 43% 31% 6%	800
	21st to end	Night	9% 2 13% 37% 34% 5%	800
December	1st to 10th	Night	13% 2 11% 41% 26% 6%	800
	11th to 20th	Night	16% 3 13% 37% 27% 3	800
	21st to end	Night	18% 4 15% 40% 20% 3	880

Page generated at 2025-05-08 06:33:59. Version ac07

Copyright © 2025 Attilla Danko.