Mendota Wildlife Area
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mendota Wildlife Area clear sky chart from 2005-11-06 to 2026-07-16.

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	4 3 1 3 2 2 3 2 4 5% 71%	146279
	Night	5% 3 1 4 3 3 3 2 4 5% 67%	143914
Transparency	Day	17% 4 8% 18% 28% 26%	141297
	Night	19% 5% 9% 19% 25% 22%	139877
Seeing	Day	5% 4 15% 27% 31% 17%	17575
	Night	6% 3 18% 40% 29% 4	27045

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	9% 7% 3 8% 6% 6% 6% 4 6% 8% 37%	4722
	11th to 20th	Day	5% 4 3 7% 5% 5% 5% 4 5% 7% 50%	5339
	21st to end	Day	8% 7% 4 8% 6% 5% 5% 4 5% 8% 39%	5843
February	1st to 10th	Day	12% 5% 2 5% 4 4 5% 4 6% 7% 47%	1948
	11th to 20th	Day	9% 5% 1 5% 4 3 3 4 5% 8% 52%	2050
	21st to end	Day	10% 5% 2 6% 4 4 4 3 5% 7% 52%	1730
March	1st to 10th	Day	9% 4 2 6% 4 5% 5% 5% 7% 10% 43%	4655
	11th to 20th	Day	8% 4 2 5% 3 3 4 3 5% 7% 57%	5110
	21st to end	Day	8% 4 2 5% 3 4 4 4 6% 10% 51%	5911
April	1st to 10th	Day	6% 4 2 4 3 3 2 3 4 8% 61%	2520
	11th to 20th	Day	5% 3 1 3 3 3 3 3 5% 6% 65%	2489
	21st to end	Day	4 3 1 3 3 2 2 2 4 6% 70%	2520
May	1st to 10th	Day	2 2 1 2 1 1 1 2 2 4 81%	7058
	11th to 20th	Day	1 1 1 1 1 1 1 2 4 88%	7717
	21st to end	Day	1 1 1 1 1 1 1 2 4 86%	8992
June	1st to 10th	Day	1 1 1 2 2 2 2 2 3 6% 78%	2940
	11th to 20th	Day	1 1 1 1 1 1 2 3 90%	2940
	21st to end	Day	1 1 2 1 1 1 1 1 2 89%	2940
July	1st to 10th	Day	1 1 1 95%	6459
	11th to 20th	Day	1 1 1 1 1 1 1 1 2 2 89%	6305
	21st to end	Day	1 1 1 1 1 2 3 88%	6402
August	1st to 10th	Day	1 1 1 1 1 1 2 2 90%	5573
	11th to 20th	Day	1 1 2 95%	5364
	21st to end	Day	1 1 1 1 1 1 2 3 89%	5984
September	1st to 10th	Day	1 1 1 1 1 1 1 1 2 91%	2400
	11th to 20th	Day	2 1 1 1 1 2 1 2 3 86%	2380
	21st to end	Day	1 2 1 1 1 1 2 2 3 3 83%	2200
October	1st to 10th	Day	1 1 1 2 1 1 2 2 3 5% 82%	3317
	11th to 20th	Day	2 2 1 2 1 2 2 2 3 4 79%	3261
	21st to end	Day	3 3 1 4 2 3 3 2 5% 7% 69%	3558
November	1st to 10th	Day	5% 3 2 4 3 3 4 3 5% 8% 62%	1899
	11th to 20th	Day	8% 5% 1 5% 4 3 4 4 6% 6% 54%	1890
	21st to end	Day	6% 7% 2 6% 4 4 3 3 6% 7% 51%	1890
December	1st to 10th	Day	5% 5% 3 8% 5% 6% 6% 4 7% 8% 43%	2773
	11th to 20th	Day	12% 8% 3 10% 7% 6% 5% 5% 6% 8% 31%	3108
	21st to end	Day	13% 9% 3 8% 6% 5% 6% 4 6% 8% 31%	4092
January	1st to 10th	Night	11% 7% 3 7% 5% 4 4 3 5% 7% 44%	8158
	11th to 20th	Night	6% 4 2 5% 4 3 5% 4 5% 7% 55%	7650
	21st to end	Night	10% 6% 3 7% 5% 5% 5% 3 5% 6% 45%	8371
February	1st to 10th	Night	11% 5% 2 4 3 4 4 3 5% 6% 54%	2670
	11th to 20th	Night	9% 3 2 4 3 4 4 3 5% 8% 55%	2458
	21st to end	Night	8% 5% 1 4 3 3 4 3 5% 6% 58%	2076
March	1st to 10th	Night	8% 5% 2 6% 4 5% 5% 5% 6% 8% 47%	5455
	11th to 20th	Night	8% 4 2 5% 4 4 4 3 4 5% 56%	5110
	21st to end	Night	11% 5% 2 5% 3 3 3 3 5% 7% 53%	5304
April	1st to 10th	Night	6% 4 1 3 2 3 3 3 5% 7% 62%	2100
	11th to 20th	Night	4 3 1 3 3 3 3 3 5% 6% 68%	2079
	21st to end	Night	4 2 1 2 2 2 2 3 3 6% 73%	2100
May	1st to 10th	Night	2 2 1 2 1 2 1 2 3 4 81%	5919
	11th to 20th	Night	1 1 1 1 1 1 1 2 3 88%	5144
	21st to end	Night	1 1 1 1 1 1 1 2 2 88%	5181
June	1st to 10th	Night	2 1 1 2 2 1 2 2 3 4 80%	1680
	11th to 20th	Night	1 1 1 1 2 3 90%	1680
	21st to end	Night	1 1 1 1 2 92%	1680
July	1st to 10th	Night	1 1 95%	3720
	11th to 20th	Night	1 1 1 1 1 1 1 1 2 90%	3765
	21st to end	Night	1 1 1 1 1 2 3 89%	4472
August	1st to 10th	Night	1 1 1 1 1 1 1 2 2 90%	4249
	11th to 20th	Night	1 1 1 1 1 1 1 94%	4506
	21st to end	Night	1 1 1 1 1 1 1 2 2 89%	5015
September	1st to 10th	Night	1 1 1 1 1 1 1 1 2 91%	2000
	11th to 20th	Night	2 1 1 2 1 1 1 1 1 2 86%	2020
	21st to end	Night	1 1 1 1 1 1 1 2 4 87%	2200
October	1st to 10th	Night	1 1 1 1 1 1 1 2 4 85%	3878
	11th to 20th	Night	2 1 2 1 1 2 2 3 4 82%	3897
	21st to end	Night	3 2 1 3 1 2 2 2 3 5% 76%	4253
November	1st to 10th	Night	5% 3 1 3 2 3 3 2 4 6% 69%	2618
	11th to 20th	Night	6% 3 1 4 3 3 3 3 4 6% 63%	2730
	21st to end	Night	7% 5% 2 3 4 3 3 3 5% 7% 58%	2730
December	1st to 10th	Night	5% 5% 2 5% 4 4 5% 4 5% 7% 54%	4624
	11th to 20th	Night	10% 6% 3 7% 6% 6% 5% 5% 7% 10% 35%	5316
	21st to end	Night	11% 7% 3 9% 7% 6% 6% 5% 7% 7% 32%	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	36% 10% 20% 22% 11% 1	4723
	11th to 20th	Day	29% 7% 9% 15% 27% 13%	5339
	21st to end	Day	39% 8% 9% 17% 23% 4	5843
February	1st to 10th	Day	32% 7% 11% 25% 18% 7%	1948
	11th to 20th	Day	28% 6% 13% 26% 21% 5%	2060
	21st to end	Day	30% 8% 13% 25% 20% 4	1730
March	1st to 10th	Day	29% 10% 17% 20% 22% 2	4655
	11th to 20th	Day	26% 5% 14% 31% 16% 8%	5110
	21st to end	Day	25% 9% 15% 33% 15% 3	5911
April	1st to 10th	Day	22% 5% 13% 28% 24% 8%	2520
	11th to 20th	Day	19% 4 13% 27% 28% 9%	2492
	21st to end	Day	16% 4 11% 31% 31% 7%	2520
May	1st to 10th	Day	10% 2 8% 22% 40% 18%	7058
	11th to 20th	Day	5% 1 3 21% 48% 21%	7720
	21st to end	Day	7% 1 4 20% 50% 18%	8994
June	1st to 10th	Day	9% 3 8% 21% 34% 24%	2940
	11th to 20th	Day	3 1 4 13% 38% 40%	2940
	21st to end	Day	6% 1 2 7% 27% 56%	2940
July	1st to 10th	Day	2 1 4 15% 78%	6391
	11th to 20th	Day	6% 1 1 4 15% 74%	6230
	21st to end	Day	4 1 1 11% 36% 46%	6217
August	1st to 10th	Day	7% 1 2 6% 31% 54%	4057
	11th to 20th	Day	3 1 1 5% 28% 63%	3880
	21st to end	Day	4 1 2 7% 29% 56%	4311
September	1st to 10th	Day	4 1 2 9% 29% 55%	2400
	11th to 20th	Day	6% 2 3 19% 42% 28%	2380
	21st to end	Day	8% 2 4 17% 39% 31%	2200
October	1st to 10th	Day	7% 2 4 13% 26% 47%	3317
	11th to 20th	Day	11% 2 5% 24% 36% 22%	3261
	21st to end	Day	16% 3 5% 20% 39% 17%	3558
November	1st to 10th	Day	20% 5% 11% 26% 28% 9%	1899
	11th to 20th	Day	25% 8% 14% 26% 23% 3	1890
	21st to end	Day	29% 5% 11% 24% 23% 7%	1890
December	1st to 10th	Day	32% 7% 10% 28% 18% 5%	2773
	11th to 20th	Day	46% 8% 13% 19% 12% 2	3108
	21st to end	Day	42% 12% 20% 18% 8% 1	4092
January	1st to 10th	Night	33% 9% 19% 26% 12% 1	8158
	11th to 20th	Night	25% 6% 10% 19% 30% 10%	7650
	21st to end	Night	37% 7% 10% 20% 20% 6%	8371
February	1st to 10th	Night	30% 5% 9% 25% 22% 8%	2670
	11th to 20th	Night	25% 6% 11% 26% 25% 6%	2459
	21st to end	Night	25% 6% 12% 29% 21% 7%	2076
March	1st to 10th	Night	29% 9% 15% 20% 23% 3	5455
	11th to 20th	Night	27% 6% 13% 28% 18% 8%	5110
	21st to end	Night	28% 7% 17% 28% 16% 4	5304
April	1st to 10th	Night	21% 5% 14% 29% 22% 9%	2100
	11th to 20th	Night	17% 4 12% 30% 27% 10%	2079
	21st to end	Night	14% 4 10% 31% 33% 9%	2100
May	1st to 10th	Night	9% 3 8% 27% 35% 18%	5917
	11th to 20th	Night	5% 1 3 19% 46% 27%	5145
	21st to end	Night	5% 2 4 21% 52% 17%	5182
June	1st to 10th	Night	11% 2 8% 20% 34% 26%	1680
	11th to 20th	Night	3 2 4 14% 35% 42%	1680
	21st to end	Night	3 1 1 7% 27% 60%	1680
July	1st to 10th	Night	2 1 2 14% 81%	3680
	11th to 20th	Night	5% 1 1 3 12% 78%	3717
	21st to end	Night	4 1 1 10% 32% 52%	4345
August	1st to 10th	Night	6% 1 1 6% 23% 63%	3083
	11th to 20th	Night	3 1 2 4 20% 70%	3256
	21st to end	Night	5% 1 1 7% 25% 61%	3608
September	1st to 10th	Night	5% 1 2 7% 25% 60%	2000
	11th to 20th	Night	8% 2 2 15% 39% 34%	2020
	21st to end	Night	6% 1 3 15% 38% 37%	2200
October	1st to 10th	Night	7% 2 4 12% 21% 55%	3878
	11th to 20th	Night	8% 3 4 25% 37% 24%	3897
	21st to end	Night	12% 2 4 19% 42% 21%	4253
November	1st to 10th	Night	16% 4 9% 27% 29% 14%	2618
	11th to 20th	Night	20% 5% 13% 25% 29% 7%	2730
	21st to end	Night	25% 5% 10% 24% 28% 9%	2730
December	1st to 10th	Night	26% 6% 10% 27% 24% 6%	4624
	11th to 20th	Night	40% 9% 18% 17% 15% 2	5316
	21st to end	Night	45% 10% 17% 19% 8% 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	18% 10% 18% 29% 17% 8%	220
	11th to 20th	Day	7% 4 17% 28% 28% 14%	429
	21st to end	Day	11% 4 17% 25% 28% 16%	473
February	1st to 10th	Day	13% 7% 20% 22% 21% 17%	460
	11th to 20th	Day	10% 10% 20% 31% 16% 13%	535
	21st to end	Day	7% 10% 22% 30% 25% 7%	446
March	1st to 10th	Day	10% 7% 21% 33% 23% 6%	540
	11th to 20th	Day	9% 8% 21% 28% 24% 10%	540
	21st to end	Day	10% 10% 21% 30% 19% 8%	594
April	1st to 10th	Day	7% 7% 25% 26% 22% 12%	540
	11th to 20th	Day	5% 8% 25% 31% 19% 12%	532
	21st to end	Day	4 7% 24% 30% 21% 15%	540
May	1st to 10th	Day	3 6% 23% 33% 25% 11%	543
	11th to 20th	Day	2 6% 19% 33% 28% 13%	568
	21st to end	Day	3 6% 16% 29% 29% 18%	617
June	1st to 10th	Day	1 4 14% 32% 33% 16%	570
	11th to 20th	Day	1 2 18% 31% 36% 12%	570
	21st to end	Day	1 13% 26% 40% 20%	570
July	1st to 10th	Day	1 1 6% 26% 44% 23%	566
	11th to 20th	Day	1 2 17% 46% 34%	545
	21st to end	Day	1 2 18% 49% 30%	575
August	1st to 10th	Day	3 1 6% 24% 43% 23%	527
	11th to 20th	Day	1 7% 26% 41% 25%	517
	21st to end	Day	1 4 24% 43% 27%	583
September	1st to 10th	Day	1 1 6% 27% 46% 20%	530
	11th to 20th	Day	2 2 10% 36% 34% 16%	530
	21st to end	Day	2 2 12% 27% 39% 19%	530
October	1st to 10th	Day	1 3 17% 28% 32% 20%	530
	11th to 20th	Day	2 5% 14% 25% 32% 22%	530
	21st to end	Day	3 4 13% 26% 33% 22%	583
November	1st to 10th	Day	6% 2 15% 22% 30% 26%	375
	11th to 20th	Day	7% 5% 16% 26% 28% 18%	330
	21st to end	Day	9% 2 14% 30% 31% 14%	330
December	1st to 10th	Day	11% 3 18% 25% 28% 15%	245
	11th to 20th	Day	8% 7% 15% 30% 24% 16%	220
	21st to end	Day	15% 9% 21% 26% 24% 6%	242
January	1st to 10th	Night	15% 5% 15% 34% 25% 5%	840
	11th to 20th	Night	9% 2 12% 38% 34% 5%	840
	21st to end	Night	12% 2 13% 36% 32% 4	924
February	1st to 10th	Night	12% 4 14% 35% 29% 6%	840
	11th to 20th	Night	10% 6% 19% 33% 29% 4	824
	21st to end	Night	10% 5% 16% 44% 22% 2	692
March	1st to 10th	Night	9% 5% 20% 41% 22% 3	840
	11th to 20th	Night	8% 6% 20% 35% 27% 4	840
	21st to end	Night	8% 5% 25% 39% 20% 2	924
April	1st to 10th	Night	6% 5% 29% 37% 21% 2	840
	11th to 20th	Night	4 7% 29% 36% 21% 3	831
	21st to end	Night	4 6% 29% 38% 20% 3	840
May	1st to 10th	Night	2 4 30% 41% 20% 3	840
	11th to 20th	Night	2 4 32% 46% 16%	575
	21st to end	Night	3 5% 29% 47% 15%	455
June	1st to 10th	Night	2 4 32% 47% 13%	420
	11th to 20th	Night	4 29% 50% 17%	420
	21st to end	Night	1 1 23% 55% 19% 1	420
July	1st to 10th	Night	20% 54% 26%	410
	11th to 20th	Night	2 10% 60% 29%	431
	21st to end	Night	1 11% 46% 40% 2	657
August	1st to 10th	Night	2 15% 49% 31% 3	686
	11th to 20th	Night	1 14% 48% 35% 2	792
	21st to end	Night	1 10% 43% 44% 2	880
September	1st to 10th	Night	1 1 10% 46% 39% 4	800
	11th to 20th	Night	2 1 17% 45% 31% 5%	800
	21st to end	Night	1 1 14% 38% 40% 6%	800
October	1st to 10th	Night	3 3 15% 39% 34% 6%	800
	11th to 20th	Night	4 2 14% 34% 38% 8%	800
	21st to end	Night	4 3 11% 32% 37% 14%	880
November	1st to 10th	Night	4 3 13% 32% 37% 10%	820
	11th to 20th	Night	6% 2 12% 40% 33% 7%	840
	21st to end	Night	8% 2 13% 37% 33% 6%	840
December	1st to 10th	Night	11% 3 13% 36% 31% 6%	840
	11th to 20th	Night	12% 3 13% 39% 27% 5%	840
	21st to end	Night	13% 7% 15% 41% 21% 3	924

Page generated at 2026-07-13 00:14:51. Version ac07

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