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 2025-03-12.

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 4 3 2 3 2 4 5% 69%	112712
	Night	5% 3 1 4 3 3 3 2 4 5% 66%	115125
Transparency	Day	17% 5% 8% 17% 26% 27%	112465
	Night	19% 5% 9% 19% 24% 23%	114962
Seeing	Day	5% 4 15% 27% 31% 17%	15747
	Night	6% 3 18% 40% 29% 4	25356

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	7% 7% 3 8% 6% 5% 6% 4 6% 8% 38%	3639
	11th to 20th	Day	6% 5% 3 8% 5% 5% 4 3 4 5% 50%	4099
	21st to end	Day	10% 7% 4 7% 5% 5% 5% 4 5% 8% 40%	4510
February	1st to 10th	Day	12% 5% 2 5% 4 4 4 4 5% 7% 48%	1855
	11th to 20th	Day	9% 5% 1 5% 4 3 3 4 5% 8% 53%	1950
	21st to end	Day	10% 5% 2 6% 4 4 4 3 4 6% 52%	1650
March	1st to 10th	Day	8% 5% 3 7% 5% 5% 5% 4 7% 10% 40%	3262
	11th to 20th	Day	6% 3 1 4 3 2 3 2 4 7% 64%	3503
	21st to end	Day	9% 5% 2 5% 4 4 4 4 6% 8% 48%	4031
April	1st to 10th	Day	7% 5% 2 4 3 3 2 2 4 7% 61%	2280
	11th to 20th	Day	5% 3 1 3 3 2 3 3 5% 6% 65%	2249
	21st to end	Day	4 2 1 3 3 2 2 2 4 5% 72%	2280
May	1st to 10th	Day	3 2 1 2 1 1 2 2 2 4 80%	3800
	11th to 20th	Day	1 1 1 1 1 2 1 2 4 85%	4139
	21st to end	Day	2 1 1 1 1 1 1 2 4 85%	4813
June	1st to 10th	Day	2 2 1 2 2 2 2 2 3 6% 77%	2660
	11th to 20th	Day	1 1 1 1 1 1 2 3 90%	2660
	21st to end	Day	1 1 2 1 1 1 1 1 2 88%	2660
July	1st to 10th	Day	1 1 1 2 94%	4420
	11th to 20th	Day	1 1 1 2 1 1 1 2 2 3 85%	4360
	21st to end	Day	1 1 1 1 1 1 2 3 89%	4455
August	1st to 10th	Day	2 1 1 1 1 1 1 2 3 86%	3947
	11th to 20th	Day	1 1 1 1 2 93%	3724
	21st to end	Day	1 1 1 1 1 1 1 1 2 92%	4180
September	1st to 10th	Day	1 1 1 1 1 1 1 1 2 91%	2280
	11th to 20th	Day	1 1 1 1 1 2 1 2 3 86%	2261
	21st to end	Day	1 1 1 1 1 1 2 2 3 3 84%	2090
October	1st to 10th	Day	1 1 1 2 1 1 2 2 3 5% 82%	3216
	11th to 20th	Day	2 2 1 2 1 2 3 2 3 3 80%	3161
	21st to end	Day	3 3 1 4 2 3 2 2 5% 7% 69%	3448
November	1st to 10th	Day	5% 3 2 4 3 3 4 3 5% 7% 61%	1807
	11th to 20th	Day	6% 5% 1 4 4 3 4 4 6% 6% 57%	1800
	21st to end	Day	6% 6% 2 6% 3 4 3 3 6% 8% 53%	1800
December	1st to 10th	Day	5% 5% 3 8% 5% 6% 6% 4 7% 8% 44%	2691
	11th to 20th	Day	12% 8% 3 9% 7% 6% 5% 5% 5% 8% 31%	3028
	21st to end	Day	12% 9% 3 8% 6% 5% 6% 4 6% 8% 32%	4004
January	1st to 10th	Night	9% 6% 3 6% 5% 4 4 3 5% 8% 47%	6292
	11th to 20th	Night	8% 5% 2 6% 4 4 4 3 4 5% 55%	5880
	21st to end	Night	12% 6% 2 6% 4 4 4 3 5% 6% 47%	6468
February	1st to 10th	Night	11% 5% 2 3 3 4 3 3 5% 6% 54%	2543
	11th to 20th	Night	8% 3 1 4 3 4 4 3 5% 8% 57%	2338
	21st to end	Night	9% 5% 1 4 3 3 4 2 5% 6% 59%	1980
March	1st to 10th	Night	8% 5% 2 6% 5% 5% 5% 5% 6% 8% 46%	3828
	11th to 20th	Night	6% 4 1 4 3 3 3 3 4 5% 63%	3505
	21st to end	Night	12% 5% 2 5% 4 4 3 3 5% 6% 50%	3620
April	1st to 10th	Night	6% 5% 1 3 2 3 3 3 5% 7% 62%	1900
	11th to 20th	Night	4 2 1 2 3 3 3 2 5% 5% 70%	1879
	21st to end	Night	3 2 2 2 2 2 3 3 7% 75%	1900
May	1st to 10th	Night	1 1 1 1 1 1 1 2 4 85%	3180
	11th to 20th	Night	1 1 1 1 1 1 1 2 4 86%	2753
	21st to end	Night	2 1 1 1 1 1 1 1 1 2 88%	2762
June	1st to 10th	Night	2 2 1 2 2 2 2 2 3 3 79%	1520
	11th to 20th	Night	1 1 1 1 2 3 89%	1520
	21st to end	Night	1 1 1 1 1 2 92%	1520
July	1st to 10th	Night	1 1 1 1 1 2 94%	2540
	11th to 20th	Night	2 1 1 1 1 1 2 1 1 3 86%	2597
	21st to end	Night	1 1 1 2 1 1 2 3 87%	3109
August	1st to 10th	Night	1 1 1 1 1 1 1 3 3 86%	2997
	11th to 20th	Night	1 1 1 1 1 2 1 92%	3126
	21st to end	Night	1 1 1 1 1 1 1 1 2 91%	3498
September	1st to 10th	Night	1 1 1 1 1 1 1 1 2 91%	1900
	11th to 20th	Night	2 1 1 2 1 1 1 1 2 2 87%	1919
	21st to end	Night	1 1 1 1 1 1 1 2 3 87%	2090
October	1st to 10th	Night	1 1 1 1 1 1 1 2 4 85%	3759
	11th to 20th	Night	1 1 2 1 2 2 2 3 4 82%	3777
	21st to end	Night	3 2 1 3 1 2 2 2 3 5% 76%	4121
November	1st to 10th	Night	5% 3 1 3 2 3 3 2 4 5% 68%	2490
	11th to 20th	Night	5% 3 1 4 3 3 3 3 4 6% 66%	2600
	21st to end	Night	7% 4 2 3 4 3 3 3 5% 8% 59%	2600
December	1st to 10th	Night	6% 4 2 4 4 4 5% 4 5% 7% 55%	4486
	11th to 20th	Night	10% 6% 3 6% 6% 5% 5% 5% 7% 10% 36%	5176
	21st to end	Night	11% 7% 3 9% 7% 6% 6% 4 7% 7% 32%	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	34% 11% 22% 20% 11% 2	3639
	11th to 20th	Day	33% 8% 9% 15% 24% 11%	4099
	21st to end	Day	38% 9% 10% 13% 25% 5%	4510
February	1st to 10th	Day	31% 7% 11% 26% 18% 7%	1855
	11th to 20th	Day	28% 7% 13% 26% 21% 5%	1960
	21st to end	Day	30% 8% 12% 24% 21% 4	1650
March	1st to 10th	Day	29% 13% 20% 19% 16% 2	3262
	11th to 20th	Day	21% 5% 14% 31% 19% 11%	3503
	21st to end	Day	28% 10% 17% 25% 16% 4	4031
April	1st to 10th	Day	23% 5% 13% 27% 23% 9%	2280
	11th to 20th	Day	20% 4 13% 28% 27% 9%	2252
	21st to end	Day	15% 4 11% 31% 32% 8%	2280
May	1st to 10th	Day	10% 3 7% 23% 37% 21%	3800
	11th to 20th	Day	7% 2 4 20% 45% 22%	4142
	21st to end	Day	7% 2 5% 25% 40% 21%	4814
June	1st to 10th	Day	10% 4 9% 21% 33% 23%	2660
	11th to 20th	Day	4 1 4 14% 39% 37%	2660
	21st to end	Day	6% 1 2 7% 27% 56%	2660
July	1st to 10th	Day	2 1 1 4 12% 81%	4351
	11th to 20th	Day	7% 2 2 5% 16% 68%	4285
	21st to end	Day	4 2 1 5% 28% 59%	4315
August	1st to 10th	Day	7% 1 2 6% 31% 54%	3932
	11th to 20th	Day	3 1 1 5% 27% 64%	3760
	21st to end	Day	4 1 2 7% 29% 57%	4179
September	1st to 10th	Day	4 1 2 7% 28% 57%	2280
	11th to 20th	Day	6% 2 3 18% 42% 29%	2261
	21st to end	Day	7% 2 3 17% 39% 31%	2090
October	1st to 10th	Day	7% 2 4 12% 25% 48%	3216
	11th to 20th	Day	10% 2 5% 24% 36% 23%	3161
	21st to end	Day	16% 3 5% 20% 39% 17%	3448
November	1st to 10th	Day	21% 5% 11% 26% 28% 10%	1807
	11th to 20th	Day	22% 8% 14% 27% 25% 4	1800
	21st to end	Day	27% 5% 12% 25% 24% 8%	1800
December	1st to 10th	Day	32% 7% 10% 28% 18% 5%	2691
	11th to 20th	Day	46% 8% 13% 19% 12% 2	3028
	21st to end	Day	41% 12% 20% 18% 8% 1	4004
January	1st to 10th	Night	29% 10% 19% 27% 13% 2	6292
	11th to 20th	Night	29% 8% 11% 17% 27% 9%	5880
	21st to end	Night	35% 8% 10% 17% 23% 7%	6468
February	1st to 10th	Night	30% 5% 10% 24% 22% 8%	2543
	11th to 20th	Night	24% 6% 12% 27% 26% 7%	2339
	21st to end	Night	25% 6% 12% 29% 22% 7%	1980
March	1st to 10th	Night	28% 11% 18% 20% 19% 4	3828
	11th to 20th	Night	21% 6% 13% 28% 23% 10%	3505
	21st to end	Night	29% 9% 17% 26% 14% 5%	3620
April	1st to 10th	Night	22% 5% 14% 29% 21% 9%	1900
	11th to 20th	Night	16% 4 12% 31% 28% 10%	1879
	21st to end	Night	12% 4 10% 31% 34% 9%	1900
May	1st to 10th	Night	6% 3 7% 28% 33% 23%	3180
	11th to 20th	Night	6% 2 4 20% 45% 25%	2754
	21st to end	Night	7% 2 4 25% 45% 18%	2762
June	1st to 10th	Night	11% 2 8% 20% 33% 25%	1520
	11th to 20th	Night	4 2 4 15% 36% 39%	1520
	21st to end	Night	3 1 1 7% 27% 60%	1520
July	1st to 10th	Night	2 1 1 2 12% 82%	2500
	11th to 20th	Night	6% 2 2 4 13% 74%	2549
	21st to end	Night	4 2 2 5% 23% 64%	3011
August	1st to 10th	Night	6% 1 1 6% 23% 62%	2988
	11th to 20th	Night	3 1 2 4 19% 71%	3156
	21st to end	Night	5% 1 1 7% 25% 62%	3498
September	1st to 10th	Night	5% 1 2 6% 24% 63%	1900
	11th to 20th	Night	7% 2 2 15% 39% 35%	1919
	21st to end	Night	6% 1 3 14% 39% 37%	2090
October	1st to 10th	Night	8% 2 4 11% 21% 56%	3759
	11th to 20th	Night	8% 3 4 25% 36% 24%	3777
	21st to end	Night	12% 2 4 19% 42% 22%	4121
November	1st to 10th	Night	17% 5% 9% 26% 29% 15%	2490
	11th to 20th	Night	18% 5% 13% 26% 30% 7%	2600
	21st to end	Night	24% 5% 10% 23% 29% 9%	2600
December	1st to 10th	Night	25% 6% 10% 28% 25% 7%	4486
	11th to 20th	Night	39% 9% 18% 17% 15% 2	5176
	21st to end	Night	44% 10% 17% 19% 8% 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	19% 9% 17% 32% 17% 7%	200
	11th to 20th	Day	8% 5% 19% 30% 26% 13%	399
	21st to end	Day	11% 4 18% 23% 28% 16%	440
February	1st to 10th	Day	13% 7% 20% 22% 20% 18%	427
	11th to 20th	Day	9% 9% 20% 32% 17% 13%	495
	21st to end	Day	7% 10% 22% 29% 25% 7%	414
March	1st to 10th	Day	11% 8% 20% 32% 23% 6%	500
	11th to 20th	Day	9% 8% 21% 29% 23% 10%	465
	21st to end	Day	11% 11% 23% 29% 18% 8%	506
April	1st to 10th	Day	8% 8% 26% 25% 20% 12%	460
	11th to 20th	Day	6% 8% 25% 31% 18% 11%	452
	21st to end	Day	3 7% 25% 30% 20% 15%	460
May	1st to 10th	Day	3 7% 22% 34% 25% 9%	463
	11th to 20th	Day	2 5% 18% 32% 30% 13%	488
	21st to end	Day	4 6% 16% 26% 31% 18%	529
June	1st to 10th	Day	1 4 14% 31% 32% 17%	490
	11th to 20th	Day	1 2 18% 29% 37% 13%	490
	21st to end	Day	1 10% 28% 40% 21%	490
July	1st to 10th	Day	1 6% 24% 45% 24%	486
	11th to 20th	Day	1 1 17% 46% 36%	484
	21st to end	Day	1 2 19% 49% 29%	531
August	1st to 10th	Day	3 1 5% 24% 44% 23%	487
	11th to 20th	Day	1 7% 25% 42% 24%	477
	21st to end	Day	1 4 23% 43% 29%	539
September	1st to 10th	Day	1 1 5% 26% 47% 21%	490
	11th to 20th	Day	2 2 11% 36% 34% 15%	490
	21st to end	Day	1 2 12% 25% 40% 20%	490
October	1st to 10th	Day	1 3 17% 27% 31% 20%	490
	11th to 20th	Day	2 5% 13% 26% 32% 22%	490
	21st to end	Day	3 4 13% 24% 34% 22%	539
November	1st to 10th	Day	6% 2 15% 23% 31% 24%	343
	11th to 20th	Day	3 4 16% 26% 30% 20%	300
	21st to end	Day	9% 1 15% 29% 32% 13%	300
December	1st to 10th	Day	11% 3 19% 25% 27% 15%	223
	11th to 20th	Day	9% 8% 15% 30% 24% 15%	200
	21st to end	Day	14% 9% 22% 25% 24% 6%	220
January	1st to 10th	Night	15% 5% 15% 34% 26% 5%	800
	11th to 20th	Night	9% 2 13% 39% 31% 5%	800
	21st to end	Night	13% 2 14% 36% 32% 4	880
February	1st to 10th	Night	12% 4 15% 36% 28% 6%	800
	11th to 20th	Night	9% 5% 18% 33% 30% 4	784
	21st to end	Night	10% 6% 17% 43% 22% 3	660
March	1st to 10th	Night	10% 5% 20% 40% 23% 3	800
	11th to 20th	Night	8% 6% 20% 34% 28% 4	766
	21st to end	Night	8% 6% 26% 38% 20% 2	836
April	1st to 10th	Night	6% 6% 29% 36% 21% 2	760
	11th to 20th	Night	4 8% 29% 35% 21% 3	751
	21st to end	Night	3 5% 30% 38% 20% 4	760
May	1st to 10th	Night	2 4 31% 40% 20% 3	760
	11th to 20th	Night	2 4 31% 47% 17%	520
	21st to end	Night	3 6% 29% 46% 16%	411
June	1st to 10th	Night	3 4 33% 46% 14% 1	380
	11th to 20th	Night	4 26% 52% 18% 1	380
	21st to end	Night	1 1 22% 55% 20% 1	380
July	1st to 10th	Night	18% 53% 28%	370
	11th to 20th	Night	2 10% 58% 30% 1	399
	21st to end	Night	1 10% 44% 42% 3	624
August	1st to 10th	Night	2 15% 49% 31% 3	651
	11th to 20th	Night	1 13% 48% 36% 2	752
	21st to end	Night	1 10% 42% 45% 3	836
September	1st to 10th	Night	1 1 9% 46% 40% 4	760
	11th to 20th	Night	1 1 17% 44% 31% 5%	760
	21st to end	Night	1 1 14% 37% 41% 6%	760
October	1st to 10th	Night	3 3 15% 39% 34% 6%	760
	11th to 20th	Night	3 2 14% 34% 39% 8%	760
	21st to end	Night	3 3 11% 33% 36% 14%	836
November	1st to 10th	Night	4 3 13% 32% 38% 10%	780
	11th to 20th	Night	5% 2 12% 40% 34% 7%	800
	21st to end	Night	8% 2 13% 38% 33% 6%	800
December	1st to 10th	Night	11% 3 13% 36% 31% 6%	800
	11th to 20th	Night	12% 4 14% 39% 27% 5%	800
	21st to end	Night	13% 6% 16% 41% 21% 3	880

Page generated at 2025-03-09 05:08:44. Version ac07

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