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 2026-09-14.

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 2 2 4 5% 70%	157159
	Night	7% 3 1 4 3 3 3 2 4 5% 65%	151460
Transparency	Day	19% 3 6% 18% 27% 27%	152155
	Night	22% 4 7% 19% 25% 23%	147446
Seeing	Day	6% 4 15% 30% 30% 14%	17746
	Night	8% 3 17% 43% 26% 3	27134

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	12% 7% 3 9% 6% 5% 4 3 6% 8% 36%	4722
	11th to 20th	Day	7% 5% 2 7% 4 4 4 3 6% 6% 51%	5297
	21st to end	Day	11% 8% 3 8% 6% 5% 4 3 6% 7% 39%	5843
February	1st to 10th	Day	13% 7% 2 5% 4 3 4 4 5% 7% 46%	1910
	11th to 20th	Day	11% 5% 2 5% 4 4 3 3 6% 8% 48%	2050
	21st to end	Day	12% 6% 1 5% 5% 4 4 3 5% 6% 49%	1730
March	1st to 10th	Day	11% 6% 2 6% 4 5% 5% 4 7% 9% 40%	4680
	11th to 20th	Day	11% 4 2 4 3 3 4 3 4 8% 53%	5110
	21st to end	Day	10% 5% 2 5% 4 4 5% 4 6% 9% 48%	5889
April	1st to 10th	Day	9% 4 2 4 3 3 3 3 5% 5% 58%	2520
	11th to 20th	Day	6% 4 1 4 3 3 3 3 4 7% 62%	2489
	21st to end	Day	5% 3 1 4 2 3 2 2 3 7% 68%	2520
May	1st to 10th	Day	3 3 1 3 2 2 2 1 3 5% 77%	7058
	11th to 20th	Day	1 1 1 1 1 1 1 2 4 86%	7889
	21st to end	Day	1 1 1 2 1 1 1 2 2 3 84%	8992
June	1st to 10th	Day	2 2 1 2 2 2 2 2 4 6% 77%	2940
	11th to 20th	Day	1 1 1 1 1 1 2 3 88%	2940
	21st to end	Day	1 1 1 1 1 2 1 2 2 88%	2940
July	1st to 10th	Day	1 1 1 1 1 94%	8219
	11th to 20th	Day	1 1 2 1 1 2 1 2 3 84%	8163
	21st to end	Day	1 1 1 2 3 90%	8304
August	1st to 10th	Day	1 1 1 1 1 1 1 2 2 91%	7388
	11th to 20th	Day	1 1 1 1 1 2 3 89%	7001
	21st to end	Day	2 1 1 2 1 1 2 2 3 5% 81%	7750
September	1st to 10th	Day	1 1 1 1 1 1 1 2 2 89%	2520
	11th to 20th	Day	2 1 1 1 1 2 2 2 3 84%	2428
	21st to end	Day	2 1 2 1 1 1 1 2 4 84%	2200
October	1st to 10th	Day	1 2 1 2 1 1 1 2 3 5% 81%	3280
	11th to 20th	Day	2 1 1 3 2 2 2 2 3 4 79%	3261
	21st to end	Day	3 2 1 3 2 3 3 3 4 6% 68%	3558
November	1st to 10th	Day	4 4 1 4 3 4 4 3 4 7% 61%	1896
	11th to 20th	Day	9% 7% 1 4 4 3 4 3 4 7% 54%	1890
	21st to end	Day	9% 6% 3 5% 4 3 4 3 5% 7% 49%	1882
December	1st to 10th	Day	7% 4 3 7% 5% 5% 5% 4 6% 9% 44%	2700
	11th to 20th	Day	15% 9% 3 10% 6% 6% 5% 4 6% 8% 29%	3108
	21st to end	Day	15% 9% 4 10% 7% 6% 6% 5% 7% 9% 24%	4092
January	1st to 10th	Night	14% 6% 3 7% 4 4 4 3 5% 7% 43%	8172
	11th to 20th	Night	9% 4 2 5% 3 5% 4 4 6% 8% 50%	7676
	21st to end	Night	12% 7% 2 8% 4 4 4 3 4 6% 45%	8371
February	1st to 10th	Night	14% 6% 2 5% 3 3 3 3 5% 6% 51%	2709
	11th to 20th	Night	13% 5% 2 4 3 3 3 3 4 7% 53%	2458
	21st to end	Night	13% 5% 2 4 4 3 4 3 4 5% 54%	2076
March	1st to 10th	Night	13% 6% 2 7% 4 4 5% 4 5% 7% 43%	5417
	11th to 20th	Night	10% 6% 2 6% 4 4 4 3 4 5% 54%	5110
	21st to end	Night	14% 5% 2 5% 3 3 4 3 5% 7% 50%	5326
April	1st to 10th	Night	10% 4 1 3 2 3 3 4 6% 6% 59%	2100
	11th to 20th	Night	6% 3 1 3 2 3 4 3 5% 6% 64%	2079
	21st to end	Night	4 3 1 3 3 2 3 3 4 6% 68%	2100
May	1st to 10th	Night	3 2 1 2 2 2 2 2 3 5% 77%	5919
	11th to 20th	Night	1 1 1 1 1 1 2 3 3 85%	4963
	21st to end	Night	1 1 1 1 1 2 1 2 4 85%	5181
June	1st to 10th	Night	2 2 2 1 2 2 2 3 6% 77%	1680
	11th to 20th	Night	1 1 1 1 1 2 3 89%	1680
	21st to end	Night	1 1 1 1 1 1 1 2 2 89%	1680
July	1st to 10th	Night	1 1 1 96%	4740
	11th to 20th	Night	2 2 1 2 1 1 1 1 2 3 83%	4795
	21st to end	Night	1 1 1 2 1 2 3 90%	5806
August	1st to 10th	Night	1 1 1 1 1 1 2 2 90%	5427
	11th to 20th	Night	1 1 1 2 1 3 4 86%	5886
	21st to end	Night	2 1 1 1 1 2 2 3 4 81%	6499
September	1st to 10th	Night	1 1 1 1 1 1 1 3 90%	2100
	11th to 20th	Night	2 2 1 2 1 1 1 1 2 3 85%	2037
	21st to end	Night	2 1 1 2 1 2 2 2 2 4 83%	2200
October	1st to 10th	Night	2 1 1 1 1 2 1 3 3 83%	3916
	11th to 20th	Night	2 2 1 2 1 1 2 2 3 4 81%	3897
	21st to end	Night	4 2 1 3 2 2 2 2 3 5% 74%	4253
November	1st to 10th	Night	7% 4 2 3 2 3 3 2 4 6% 66%	2620
	11th to 20th	Night	7% 4 1 5% 3 3 2 3 5% 7% 60%	2730
	21st to end	Night	9% 5% 2 4 3 4 3 3 5% 6% 57%	2735
December	1st to 10th	Night	7% 4 2 5% 3 4 5% 3 6% 9% 52%	4700
	11th to 20th	Night	13% 8% 2 8% 5% 5% 4 4 7% 11% 32%	5316
	21st to end	Night	15% 8% 3 9% 7% 6% 6% 5% 6% 7% 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	44% 7% 18% 21% 9% 2	4723
	11th to 20th	Day	32% 6% 6% 17% 28% 11%	5297
	21st to end	Day	42% 7% 7% 20% 21% 3	5843
February	1st to 10th	Day	37% 5% 12% 24% 16% 7%	1910
	11th to 20th	Day	34% 4 12% 25% 19% 5%	2060
	21st to end	Day	36% 5% 12% 26% 19% 2	1730
March	1st to 10th	Day	37% 8% 12% 21% 20% 2	4680
	11th to 20th	Day	30% 4 13% 30% 14% 8%	5110
	21st to end	Day	31% 6% 14% 31% 15% 2	5889
April	1st to 10th	Day	26% 4 12% 27% 21% 9%	2520
	11th to 20th	Day	23% 4 11% 27% 25% 9%	2492
	21st to end	Day	20% 3 9% 31% 29% 7%	2520
May	1st to 10th	Day	14% 2 7% 25% 37% 16%	7058
	11th to 20th	Day	6% 1 3 23% 45% 21%	7892
	21st to end	Day	8% 2 5% 20% 48% 18%	8994
June	1st to 10th	Day	11% 2 8% 24% 31% 23%	2940
	11th to 20th	Day	5% 1 4 16% 35% 39%	2940
	21st to end	Day	7% 1 1 9% 29% 53%	2940
July	1st to 10th	Day	2 1 1 4 17% 75%	8151
	11th to 20th	Day	8% 1 1 5% 11% 73%	8088
	21st to end	Day	3 1 1 8% 30% 57%	8119
August	1st to 10th	Day	5% 1 1 4 25% 64%	5850
	11th to 20th	Day	5% 1 2 15% 31% 47%	5517
	21st to end	Day	9% 1 2 9% 37% 42%	6077
September	1st to 10th	Day	5% 1 2 9% 27% 56%	2520
	11th to 20th	Day	8% 2 2 19% 40% 29%	2428
	21st to end	Day	8% 1 3 17% 38% 32%	2200
October	1st to 10th	Day	10% 1 3 12% 25% 48%	3280
	11th to 20th	Day	12% 2 3 24% 37% 21%	3261
	21st to end	Day	18% 2 5% 20% 41% 14%	3558
November	1st to 10th	Day	23% 5% 11% 27% 27% 8%	1896
	11th to 20th	Day	32% 3 14% 26% 22% 4	1890
	21st to end	Day	34% 4 11% 24% 21% 6%	1882
December	1st to 10th	Day	35% 5% 12% 28% 17% 4	2700
	11th to 20th	Day	53% 5% 10% 18% 12% 2	3108
	21st to end	Day	53% 10% 16% 14% 6% 1	4092
January	1st to 10th	Night	39% 8% 17% 24% 11% 1	8172
	11th to 20th	Night	30% 7% 7% 18% 29% 8%	7676
	21st to end	Night	40% 5% 8% 21% 22% 4	8371
February	1st to 10th	Night	34% 4 11% 24% 20% 7%	2709
	11th to 20th	Night	32% 3 10% 26% 24% 6%	2459
	21st to end	Night	32% 5% 9% 29% 19% 5%	2076
March	1st to 10th	Night	39% 8% 10% 20% 20% 4	5417
	11th to 20th	Night	34% 4 11% 27% 18% 7%	5110
	21st to end	Night	33% 6% 14% 29% 15% 3	5326
April	1st to 10th	Night	24% 4 14% 27% 22% 8%	2100
	11th to 20th	Night	20% 4 13% 29% 25% 9%	2079
	21st to end	Night	18% 4 11% 29% 30% 7%	2100
May	1st to 10th	Night	12% 2 9% 26% 35% 15%	5917
	11th to 20th	Night	7% 1 2 22% 45% 22%	4963
	21st to end	Night	7% 1 5% 22% 51% 13%	5182
June	1st to 10th	Night	12% 3 9% 22% 34% 21%	1680
	11th to 20th	Night	4 1 4 16% 36% 39%	1680
	21st to end	Night	5% 1 1 8% 28% 56%	1680
July	1st to 10th	Night	2 2 18% 77%	4700
	11th to 20th	Night	10% 1 1 3 12% 73%	4747
	21st to end	Night	5% 1 1 7% 30% 57%	5679
August	1st to 10th	Night	6% 1 1 4 21% 67%	4285
	11th to 20th	Night	6% 1 2 16% 26% 48%	4636
	21st to end	Night	10% 1 1 12% 31% 46%	5092
September	1st to 10th	Night	5% 1 2 8% 26% 57%	2100
	11th to 20th	Night	8% 1 2 18% 40% 31%	2037
	21st to end	Night	8% 2 3 16% 37% 35%	2200
October	1st to 10th	Night	8% 2 3 12% 19% 56%	3916
	11th to 20th	Night	10% 2 4 24% 34% 25%	3897
	21st to end	Night	15% 1 4 19% 39% 22%	4253
November	1st to 10th	Night	21% 3 8% 27% 26% 15%	2620
	11th to 20th	Night	24% 4 10% 27% 27% 7%	2730
	21st to end	Night	28% 4 9% 24% 27% 7%	2735
December	1st to 10th	Night	30% 5% 10% 26% 22% 6%	4700
	11th to 20th	Night	45% 6% 14% 18% 14% 2	5316
	21st to end	Night	50% 8% 15% 19% 6% 2	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	23% 9% 18% 25% 17% 8%	220
	11th to 20th	Day	13% 5% 15% 24% 28% 16%	413
	21st to end	Day	13% 4 16% 23% 27% 17%	473
February	1st to 10th	Day	16% 6% 19% 20% 22% 17%	441
	11th to 20th	Day	13% 9% 22% 27% 19% 10%	535
	21st to end	Day	11% 6% 21% 30% 25% 6%	446
March	1st to 10th	Day	12% 8% 22% 31% 21% 7%	540
	11th to 20th	Day	14% 7% 17% 29% 20% 13%	540
	21st to end	Day	13% 9% 19% 30% 21% 9%	594
April	1st to 10th	Day	11% 8% 23% 28% 19% 12%	540
	11th to 20th	Day	8% 8% 24% 30% 19% 11%	532
	21st to end	Day	5% 6% 23% 33% 20% 13%	540
May	1st to 10th	Day	3 6% 26% 34% 22% 8%	543
	11th to 20th	Day	3 7% 20% 34% 26% 10%	568
	21st to end	Day	4 6% 16% 32% 30% 13%	617
June	1st to 10th	Day	2 3 17% 34% 31% 12%	570
	11th to 20th	Day	1 3 18% 38% 31% 8%	570
	21st to end	Day	1 2 14% 33% 36% 13%	570
July	1st to 10th	Day	8% 34% 45% 12%	566
	11th to 20th	Day	1 3 30% 50% 16%	564
	21st to end	Day	1 3 35% 45% 16%	619
August	1st to 10th	Day	2 1 8% 36% 39% 14%	567
	11th to 20th	Day	9% 35% 40% 15%	557
	21st to end	Day	1 8% 31% 45% 14%	627
September	1st to 10th	Day	1 1 10% 32% 42% 14%	570
	11th to 20th	Day	2 2 16% 30% 33% 16%	543
	21st to end	Day	1 2 12% 32% 35% 18%	530
October	1st to 10th	Day	2 2 18% 23% 31% 24%	530
	11th to 20th	Day	4 5% 14% 24% 32% 22%	530
	21st to end	Day	4 4 15% 22% 35% 20%	583
November	1st to 10th	Day	6% 4 13% 23% 26% 28%	372
	11th to 20th	Day	7% 6% 15% 24% 32% 16%	330
	21st to end	Day	11% 1 14% 28% 31% 15%	324
December	1st to 10th	Day	13% 2 16% 29% 20% 19%	220
	11th to 20th	Day	9% 7% 17% 25% 24% 18%	220
	21st to end	Day	18% 6% 17% 26% 25% 8%	242
January	1st to 10th	Night	18% 4 15% 34% 24% 5%	840
	11th to 20th	Night	11% 2 11% 37% 32% 6%	840
	21st to end	Night	16% 2 12% 36% 30% 4	924
February	1st to 10th	Night	15% 4 14% 37% 24% 5%	840
	11th to 20th	Night	13% 5% 18% 33% 27% 4	824
	21st to end	Night	13% 4 18% 44% 18% 2	692
March	1st to 10th	Night	14% 4 18% 40% 22% 2	840
	11th to 20th	Night	11% 6% 19% 35% 25% 4	840
	21st to end	Night	13% 4 22% 38% 21% 1	924
April	1st to 10th	Night	10% 4 26% 38% 22% 1	840
	11th to 20th	Night	6% 5% 29% 38% 19% 3	831
	21st to end	Night	5% 4 27% 41% 21% 2	840
May	1st to 10th	Night	2 3 28% 45% 19% 2	840
	11th to 20th	Night	4 3 29% 48% 16%	510
	21st to end	Night	3 3 28% 49% 17%	455
June	1st to 10th	Night	3 4 29% 51% 12% 1	420
	11th to 20th	Night	1 2 30% 53% 15%	420
	21st to end	Night	1 1 23% 57% 18%	420
July	1st to 10th	Night	18% 65% 16%	410
	11th to 20th	Night	1 11% 68% 19%	424
	21st to end	Night	1 11% 55% 31% 2	690
August	1st to 10th	Night	1 13% 55% 29% 2	678
	11th to 20th	Night	16% 55% 26% 1	832
	21st to end	Night	2 1 9% 54% 33% 1	924
September	1st to 10th	Night	13% 52% 33% 2	840
	11th to 20th	Night	3 1 18% 46% 30% 3	812
	21st to end	Night	2 1 15% 42% 36% 4	800
October	1st to 10th	Night	4 2 16% 40% 34% 5%	800
	11th to 20th	Night	3 3 15% 38% 35% 6%	800
	21st to end	Night	4 2 11% 37% 33% 12%	880
November	1st to 10th	Night	7% 2 14% 34% 35% 8%	820
	11th to 20th	Night	9% 2 11% 43% 30% 6%	840
	21st to end	Night	9% 2 13% 36% 34% 6%	840
December	1st to 10th	Night	13% 2 11% 41% 27% 6%	840
	11th to 20th	Night	16% 3 13% 37% 27% 4	840
	21st to end	Night	18% 4 15% 40% 20% 3	924

Page generated at 2026-09-11 01:11:53. Version ac07

Copyright © 2026 Attilla Danko.