Mountain Meadows Observatory
Clear Sky Chart
History

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

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	13% 8% 3 7% 5% 5% 5% 4 6% 7% 38%	101077
	Night	13% 8% 3 7% 5% 5% 5% 4 6% 7% 39%	97928
Transparency	Day	41% 8% 12% 22% 14% 3	104726
	Night	39% 8% 14% 22% 14% 2	102418
Seeing	Day	21% 15% 26% 22% 13% 5%	14924
	Night	18% 13% 25% 30% 13% 1	24621

By Month

Percentage Cloud Cover SE (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	14% 9% 4 8% 5% 5% 5% 3 4 6% 36%	2836
	11th to 20th	Day	11% 13% 5% 12% 8% 5% 4 3 4 4 31%	2840
	21st to end	Day	15% 11% 3 9% 5% 5% 5% 4 5% 5% 34%	3124
February	1st to 10th	Day	12% 11% 4 7% 6% 5% 5% 4 5% 5% 35%	1710
	11th to 20th	Day	15% 9% 4 8% 6% 4 4 3 6% 6% 35%	1663
	21st to end	Day	15% 10% 3 7% 5% 3 4 4 6% 6% 38%	1609
March	1st to 10th	Day	17% 11% 3 8% 5% 4 4 3 4 7% 34%	3435
	11th to 20th	Day	11% 7% 2 6% 4 4 4 3 5% 6% 48%	3480
	21st to end	Day	18% 10% 3 7% 6% 4 4 4 4 5% 36%	3815
April	1st to 10th	Day	11% 10% 4 8% 6% 5% 4 4 5% 7% 37%	2230
	11th to 20th	Day	14% 7% 3 7% 4 3 4 4 5% 6% 43%	2254
	21st to end	Day	18% 9% 2 7% 5% 4 4 3 5% 6% 37%	2371
May	1st to 10th	Day	20% 8% 3 8% 6% 5% 5% 4 6% 7% 28%	4082
	11th to 20th	Day	21% 9% 3 7% 4 4 5% 3 6% 8% 30%	4081
	21st to end	Day	10% 5% 2 7% 5% 7% 6% 5% 7% 10% 37%	4747
June	1st to 10th	Day	13% 6% 3 5% 4 5% 6% 5% 6% 9% 39%	2660
	11th to 20th	Day	11% 6% 2 6% 6% 5% 6% 5% 8% 11% 36%	2660
	21st to end	Day	10% 4 2 6% 6% 6% 5% 5% 7% 9% 40%	2660
July	1st to 10th	Day	6% 5% 2 6% 6% 6% 5% 5% 8% 9% 42%	4287
	11th to 20th	Day	8% 5% 2 7% 5% 5% 6% 6% 7% 10% 38%	4120
	21st to end	Day	11% 8% 3 9% 6% 6% 5% 4 6% 8% 33%	4466
August	1st to 10th	Day	13% 6% 2 8% 6% 7% 7% 5% 7% 9% 31%	4104
	11th to 20th	Day	8% 5% 2 7% 6% 6% 6% 5% 7% 8% 38%	4026
	21st to end	Day	7% 5% 2 6% 5% 5% 5% 4 6% 9% 46%	4180
September	1st to 10th	Day	13% 6% 2 7% 3 5% 5% 4 5% 5% 44%	2280
	11th to 20th	Day	13% 6% 2 5% 4 4 5% 3 6% 8% 43%	2172
	21st to end	Day	20% 8% 3 5% 5% 4 4 4 5% 5% 36%	2043
October	1st to 10th	Day	17% 6% 2 5% 4 4 4 3 5% 7% 44%	1900
	11th to 20th	Day	16% 8% 2 6% 4 4 4 3 4 5% 44%	1900
	21st to end	Day	14% 6% 2 6% 4 3 4 4 5% 5% 46%	2090
November	1st to 10th	Day	10% 6% 2 6% 5% 3 4 3 5% 6% 51%	1908
	11th to 20th	Day	13% 7% 4 6% 5% 4 4 4 6% 7% 41%	1618
	21st to end	Day	15% 9% 1 5% 4 4 4 3 5% 7% 42%	1520
December	1st to 10th	Day	15% 12% 3 8% 6% 5% 4 3 6% 6% 32%	1520
	11th to 20th	Day	15% 9% 3 7% 5% 4 4 4 5% 6% 39%	1910
	21st to end	Day	16% 8% 3 8% 5% 5% 5% 5% 7% 8% 30%	2776
January	1st to 10th	Night	10% 11% 3 10% 6% 6% 5% 4 6% 6% 33%	4109
	11th to 20th	Night	13% 10% 3 10% 4 4 4 3 4 5% 39%	4120
	21st to end	Night	17% 11% 4 7% 5% 4 5% 4 4 5% 34%	4532
February	1st to 10th	Night	11% 8% 4 8% 6% 5% 5% 4 6% 6% 37%	2470
	11th to 20th	Night	15% 10% 3 8% 5% 5% 5% 4 5% 6% 34%	2403
	21st to end	Night	15% 10% 3 8% 6% 5% 4 4 5% 6% 34%	1840
March	1st to 10th	Night	18% 10% 3 8% 5% 5% 4 4 5% 6% 34%	3418
	11th to 20th	Night	9% 8% 3 8% 5% 5% 5% 3 5% 6% 44%	3480
	21st to end	Night	13% 7% 3 8% 4 4 3 3 4 5% 45%	3817
April	1st to 10th	Night	12% 9% 3 8% 6% 6% 4 4 5% 6% 37%	1948
	11th to 20th	Night	12% 7% 3 6% 5% 5% 4 4 5% 8% 41%	1875
	21st to end	Night	16% 6% 2 5% 5% 4 4 3 6% 8% 41%	1824
May	1st to 10th	Night	21% 8% 3 8% 5% 4 4 4 6% 7% 29%	2813
	11th to 20th	Night	22% 9% 3 7% 4 4 5% 4 4 5% 33%	2812
	21st to end	Night	10% 5% 2 6% 4 6% 5% 4 7% 9% 42%	2806
June	1st to 10th	Night	10% 5% 2 6% 4 5% 5% 3 7% 8% 46%	1520
	11th to 20th	Night	10% 6% 3 6% 4 5% 5% 5% 7% 9% 41%	1520
	21st to end	Night	9% 5% 1 6% 5% 4 6% 4 8% 9% 43%	1520
July	1st to 10th	Night	7% 4 2 6% 5% 5% 6% 5% 8% 10% 42%	2668
	11th to 20th	Night	6% 6% 2 8% 5% 6% 6% 5% 6% 10% 40%	2840
	21st to end	Night	8% 7% 3 7% 6% 5% 6% 5% 7% 9% 36%	3087
August	1st to 10th	Night	12% 5% 2 7% 5% 5% 6% 5% 8% 8% 36%	2825
	11th to 20th	Night	9% 7% 3 7% 4 6% 5% 5% 7% 9% 40%	2785
	21st to end	Night	7% 6% 3 7% 3 4 5% 3 6% 9% 48%	3460
September	1st to 10th	Night	13% 6% 2 5% 4 3 4 3 6% 7% 46%	1900
	11th to 20th	Night	12% 5% 2 5% 4 4 4 3 6% 7% 49%	2004
	21st to end	Night	20% 6% 3 5% 4 5% 4 4 4 5% 41%	2137
October	1st to 10th	Night	18% 5% 2 5% 3 4 4 2 5% 6% 45%	2280
	11th to 20th	Night	13% 6% 2 5% 3 4 4 3 5% 6% 48%	2280
	21st to end	Night	14% 6% 3 6% 4 3 4 3 4 6% 47%	2508
November	1st to 10th	Night	9% 8% 3 7% 4 4 4 3 5% 6% 49%	2292
	11th to 20th	Night	12% 7% 3 6% 5% 4 4 4 5% 7% 43%	2555
	21st to end	Night	12% 7% 3 6% 5% 5% 5% 4 5% 7% 41%	2660
December	1st to 10th	Night	14% 10% 4 9% 5% 4 4 4 5% 7% 33%	2660
	11th to 20th	Night	14% 8% 3 7% 6% 5% 5% 4 5% 7% 38%	3285
	21st to end	Night	15% 8% 3 7% 6% 6% 5% 5% 7% 8% 30%	4875

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	46% 6% 9% 23% 13% 2	2837
	11th to 20th	Day	52% 6% 11% 16% 13% 3	2840
	21st to end	Day	48% 8% 11% 18% 14% 2	3124
February	1st to 10th	Day	47% 7% 12% 20% 12% 2	1710
	11th to 20th	Day	47% 5% 12% 19% 14% 2	1672
	21st to end	Day	45% 7% 13% 18% 14% 4	1609
March	1st to 10th	Day	46% 7% 13% 21% 11% 2	3435
	11th to 20th	Day	33% 7% 10% 28% 21% 2	3480
	21st to end	Day	46% 8% 12% 19% 13% 2	3815
April	1st to 10th	Day	43% 7% 12% 18% 15% 5%	2230
	11th to 20th	Day	39% 6% 10% 20% 19% 5%	2254
	21st to end	Day	46% 7% 10% 21% 13% 3	2371
May	1st to 10th	Day	51% 10% 10% 19% 9% 1	4120
	11th to 20th	Day	48% 10% 12% 21% 8% 1	4085
	21st to end	Day	35% 13% 16% 20% 14% 2	4761
June	1st to 10th	Day	38% 11% 14% 22% 15% 1	2660
	11th to 20th	Day	40% 11% 15% 21% 12% 2	2660
	21st to end	Day	37% 9% 15% 24% 13% 2	2660
July	1st to 10th	Day	36% 9% 17% 24% 9% 4	4221
	11th to 20th	Day	38% 8% 15% 30% 9% 1	4051
	21st to end	Day	47% 7% 9% 22% 13% 1	4324
August	1st to 10th	Day	47% 8% 15% 22% 7%	4091
	11th to 20th	Day	40% 8% 11% 28% 13%	4065
	21st to end	Day	34% 7% 15% 27% 15% 1	4180
September	1st to 10th	Day	40% 7% 13% 17% 20% 4	2280
	11th to 20th	Day	38% 6% 9% 25% 18% 3	2172
	21st to end	Day	47% 7% 10% 19% 16% 2	2043
October	1st to 10th	Day	31% 4 9% 24% 26% 6%	3160
	11th to 20th	Day	32% 4 8% 26% 17% 12%	3140
	21st to end	Day	27% 4 9% 29% 24% 7%	3428
November	1st to 10th	Day	33% 5% 11% 25% 21% 5%	1908
	11th to 20th	Day	39% 6% 11% 18% 21% 4	1618
	21st to end	Day	40% 6% 13% 23% 17% 2	1520
December	1st to 10th	Day	50% 7% 11% 20% 11% 1	1520
	11th to 20th	Day	41% 8% 13% 25% 10% 3	1906
	21st to end	Day	44% 11% 16% 18% 9% 1	2776
January	1st to 10th	Night	40% 12% 15% 18% 14% 2	4109
	11th to 20th	Night	42% 8% 12% 22% 13% 4	4120
	21st to end	Night	47% 7% 12% 22% 11% 1	4532
February	1st to 10th	Night	44% 7% 13% 22% 12% 1	2470
	11th to 20th	Night	48% 6% 12% 18% 13% 3	2405
	21st to end	Night	47% 7% 12% 18% 11% 4	1840
March	1st to 10th	Night	46% 8% 12% 22% 9% 2	3418
	11th to 20th	Night	31% 11% 15% 26% 16% 1	3480
	21st to end	Night	37% 8% 11% 24% 18% 3	3817
April	1st to 10th	Night	44% 8% 12% 18% 16% 3	1948
	11th to 20th	Night	38% 9% 12% 22% 15% 5%	1875
	21st to end	Night	41% 7% 11% 25% 13% 3	1824
May	1st to 10th	Night	49% 12% 11% 17% 9% 2	2840
	11th to 20th	Night	48% 11% 12% 21% 8% 1	2813
	21st to end	Night	32% 14% 19% 24% 8% 3	2813
June	1st to 10th	Night	34% 10% 13% 28% 15% 1	1520
	11th to 20th	Night	36% 11% 16% 24% 12% 1	1520
	21st to end	Night	33% 10% 17% 22% 16% 2	1520
July	1st to 10th	Night	34% 9% 23% 18% 12% 3	2624
	11th to 20th	Night	39% 8% 17% 26% 9% 1	2786
	21st to end	Night	40% 9% 16% 23% 12%	2988
August	1st to 10th	Night	42% 9% 18% 24% 7%	2814
	11th to 20th	Night	38% 7% 16% 24% 14%	2812
	21st to end	Night	33% 7% 16% 31% 12% 1	3460
September	1st to 10th	Night	36% 8% 15% 19% 18% 4	1900
	11th to 20th	Night	33% 7% 12% 29% 18% 2	2004
	21st to end	Night	43% 7% 11% 22% 16% 1	2137
October	1st to 10th	Night	37% 3 11% 26% 21% 2	3800
	11th to 20th	Night	29% 4 11% 22% 24% 9%	3779
	21st to end	Night	25% 5% 12% 29% 24% 6%	4120
November	1st to 10th	Night	35% 6% 13% 21% 20% 5%	2292
	11th to 20th	Night	38% 6% 11% 23% 18% 4	2555
	21st to end	Night	41% 7% 13% 20% 17% 3	2660
December	1st to 10th	Night	48% 8% 11% 21% 10% 2	2660
	11th to 20th	Night	42% 7% 12% 22% 16% 1	3288
	21st to end	Night	43% 12% 19% 16% 10% 1	4875

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	29% 30% 24% 13% 3 1	270
	11th to 20th	Day	33% 22% 29% 13% 3	270
	21st to end	Day	29% 28% 31% 10% 2	297
February	1st to 10th	Day	30% 30% 26% 13% 1	270
	11th to 20th	Day	43% 24% 27% 6%	270
	21st to end	Day	36% 23% 24% 16% 1	336
March	1st to 10th	Day	29% 22% 25% 20% 4	460
	11th to 20th	Day	28% 27% 23% 16% 5% 1	460
	21st to end	Day	29% 22% 29% 15% 5% 1	506
April	1st to 10th	Day	25% 25% 26% 18% 6% 1	460
	11th to 20th	Day	22% 19% 28% 18% 10% 3	452
	21st to end	Day	27% 18% 28% 16% 9% 2	460
May	1st to 10th	Day	24% 20% 25% 16% 10% 4	463
	11th to 20th	Day	24% 14% 28% 20% 11% 3	487
	21st to end	Day	17% 9% 27% 23% 17% 7%	529
June	1st to 10th	Day	15% 12% 27% 26% 14% 6%	490
	11th to 20th	Day	14% 9% 29% 23% 17% 7%	490
	21st to end	Day	9% 12% 31% 27% 16% 5%	490
July	1st to 10th	Day	11% 6% 23% 28% 24% 9%	485
	11th to 20th	Day	7% 4 24% 31% 25% 10%	484
	21st to end	Day	14% 6% 21% 29% 22% 8%	532
August	1st to 10th	Day	12% 6% 23% 26% 24% 9%	486
	11th to 20th	Day	11% 6% 24% 23% 25% 11%	479
	21st to end	Day	10% 6% 21% 31% 20% 13%	539
September	1st to 10th	Day	15% 9% 21% 23% 22% 11%	490
	11th to 20th	Day	13% 5% 20% 27% 24% 10%	490
	21st to end	Day	28% 10% 22% 22% 14% 4	490
October	1st to 10th	Day	19% 8% 24% 27% 17% 4	490
	11th to 20th	Day	22% 17% 21% 26% 11% 3	490
	21st to end	Day	19% 17% 29% 23% 9% 3	539
November	1st to 10th	Day	17% 14% 28% 27% 12% 3	476
	11th to 20th	Day	24% 17% 28% 22% 9% 1	254
	21st to end	Day	29% 14% 34% 18% 4 1	180
December	1st to 10th	Day	26% 22% 32% 14% 4 2	180
	11th to 20th	Day	26% 19% 31% 17% 7%	180
	21st to end	Day	23% 23% 27% 22% 6%	200
January	1st to 10th	Night	21% 22% 33% 21% 3	760
	11th to 20th	Night	24% 19% 28% 26% 3	760
	21st to end	Night	19% 22% 35% 22% 2	836
February	1st to 10th	Night	18% 22% 28% 29% 2	760
	11th to 20th	Night	28% 25% 29% 17% 1	743
	21st to end	Night	26% 18% 35% 19% 2	628
March	1st to 10th	Night	22% 18% 32% 25% 3	760
	11th to 20th	Night	24% 22% 26% 22% 5% 1	760
	21st to end	Night	22% 19% 31% 21% 6% 1	836
April	1st to 10th	Night	20% 22% 29% 23% 5%	760
	11th to 20th	Night	18% 18% 28% 28% 9%	751
	21st to end	Night	22% 13% 27% 31% 7%	684
May	1st to 10th	Night	20% 9% 27% 30% 13% 1	570
	11th to 20th	Night	17% 8% 27% 34% 13% 1	561
	21st to end	Night	13% 3 23% 38% 20% 2	460
June	1st to 10th	Night	12% 4 24% 38% 21% 2	380
	11th to 20th	Night	13% 4 19% 44% 18% 2	380
	21st to end	Night	8% 3 21% 49% 19%	380
July	1st to 10th	Night	11% 2 15% 38% 29% 5%	449
	11th to 20th	Night	8% 1 10% 41% 35% 4	552
	21st to end	Night	8% 2 16% 40% 30% 4	624
August	1st to 10th	Night	8% 3 11% 43% 32% 2	567
	11th to 20th	Night	11% 2 12% 41% 30% 4	564
	21st to end	Night	12% 2 15% 38% 29% 4	820
September	1st to 10th	Night	16% 3 17% 33% 27% 5%	760
	11th to 20th	Night	13% 3 16% 33% 31% 4	760
	21st to end	Night	22% 5% 22% 30% 20% 1	760
October	1st to 10th	Night	19% 8% 19% 30% 21% 3	760
	11th to 20th	Night	16% 14% 24% 31% 13% 1	760
	21st to end	Night	18% 13% 26% 31% 11% 1	836
November	1st to 10th	Night	13% 12% 26% 36% 12% 1	764
	11th to 20th	Night	19% 17% 25% 29% 9% 1	760
	21st to end	Night	18% 18% 26% 29% 8%	760
December	1st to 10th	Night	23% 18% 30% 23% 6%	760
	11th to 20th	Night	18% 15% 33% 30% 4	760
	21st to end	Night	19% 17% 28% 35% 2	836

Page generated at 2024-11-03 13:19:01. Version ac07

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