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 2024-01-16.

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	14% 7% 3 6% 6% 3 5% 5% 6% 7% 38%	74632
	Night	13% 7% 3 6% 5% 3 5% 5% 6% 7% 40%	75157
Transparency	Day	43% 8% 12% 20% 14% 2	74352
	Night	40% 8% 14% 22% 14% 2	74956
Seeing	Day	21% 15% 25% 22% 13% 5%	13782
	Night	18% 13% 25% 30% 13% 1	23598

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	12% 9% 4 8% 7% 5% 6% 5% 4 6% 36%	1706
	11th to 20th	Day	15% 8% 4 9% 6% 4 5% 5% 4 5% 34%	1665
	21st to end	Day	15% 9% 4 7% 5% 3 5% 5% 5% 5% 37%	1782
February	1st to 10th	Day	13% 11% 4 7% 7% 3 5% 5% 5% 5% 34%	1620
	11th to 20th	Day	16% 8% 4 8% 6% 3 5% 3 6% 6% 34%	1573
	21st to end	Day	15% 9% 3 7% 6% 2 4 5% 6% 5% 38%	1517
March	1st to 10th	Day	13% 8% 3 5% 5% 3 4 4 4 7% 44%	1980
	11th to 20th	Day	16% 8% 4 6% 5% 3 5% 4 4 6% 38%	1980
	21st to end	Day	18% 9% 4 6% 6% 3 5% 5% 5% 5% 33%	2178
April	1st to 10th	Day	11% 9% 5% 7% 6% 3 4 5% 5% 8% 38%	2112
	11th to 20th	Day	14% 6% 3 6% 4 2 5% 4 5% 6% 43%	2134
	21st to end	Day	18% 8% 3 6% 6% 3 4 4 5% 6% 36%	2246
May	1st to 10th	Day	18% 6% 3 6% 6% 3 4 6% 6% 7% 34%	2340
	11th to 20th	Day	20% 7% 3 6% 6% 3 5% 5% 5% 7% 33%	2301
	21st to end	Day	13% 5% 3 6% 6% 4 6% 5% 5% 9% 38%	2677
June	1st to 10th	Day	13% 5% 3 5% 5% 3 6% 6% 6% 9% 40%	2520
	11th to 20th	Day	12% 6% 2 5% 7% 4 6% 6% 7% 10% 35%	2520
	21st to end	Day	10% 4 3 6% 6% 5% 5% 6% 7% 8% 40%	2520
July	1st to 10th	Day	10% 7% 2 6% 7% 4 6% 6% 7% 8% 37%	2437
	11th to 20th	Day	7% 5% 3 6% 7% 4 7% 7% 7% 10% 38%	2340
	21st to end	Day	12% 6% 3 6% 7% 4 6% 7% 7% 9% 34%	2547
August	1st to 10th	Day	10% 5% 3 7% 7% 5% 8% 7% 7% 9% 32%	2327
	11th to 20th	Day	12% 6% 3 7% 7% 4 6% 7% 6% 9% 34%	2299
	21st to end	Day	12% 5% 3 5% 6% 3 6% 6% 7% 9% 38%	2376
September	1st to 10th	Day	14% 6% 2 6% 4 3 6% 6% 5% 6% 42%	2160
	11th to 20th	Day	12% 5% 2 4 5% 3 5% 5% 6% 8% 43%	2058
	21st to end	Day	19% 7% 3 4 5% 4 4 5% 5% 5% 38%	1936
October	1st to 10th	Day	18% 6% 2 5% 4 3 4 4 5% 7% 42%	1800
	11th to 20th	Day	16% 8% 2 6% 5% 3 4 4 4 6% 43%	1800
	21st to end	Day	15% 6% 2 5% 6% 2 4 5% 5% 6% 44%	1980
November	1st to 10th	Day	10% 5% 2 6% 5% 2 4 4 5% 6% 51%	1857
	11th to 20th	Day	13% 6% 4 5% 5% 3 4 6% 6% 6% 41%	1618
	21st to end	Day	15% 7% 3 4 5% 3 5% 4 5% 7% 42%	1520
December	1st to 10th	Day	15% 11% 3 7% 7% 4 4 4 6% 6% 32%	1520
	11th to 20th	Day	15% 9% 4 6% 6% 3 4 5% 4 6% 39%	1910
	21st to end	Day	16% 8% 3 6% 6% 4 6% 6% 7% 8% 30%	2776
January	1st to 10th	Night	12% 9% 3 7% 6% 4 5% 5% 5% 6% 38%	2459
	11th to 20th	Night	15% 9% 4 7% 5% 3 5% 5% 5% 7% 34%	2406
	21st to end	Night	13% 9% 4 6% 6% 3 5% 6% 5% 5% 37%	2574
February	1st to 10th	Night	12% 8% 4 7% 7% 4 6% 5% 6% 6% 36%	2340
	11th to 20th	Night	15% 9% 4 7% 6% 4 5% 5% 5% 7% 33%	2273
	21st to end	Night	16% 9% 4 7% 7% 4 5% 5% 5% 6% 34%	1734
March	1st to 10th	Night	11% 7% 2 6% 5% 3 5% 5% 5% 7% 44%	1980
	11th to 20th	Night	16% 7% 3 6% 6% 3 5% 4 5% 6% 39%	1980
	21st to end	Night	15% 8% 3 7% 6% 4 4 5% 5% 6% 37%	2178
April	1st to 10th	Night	12% 8% 3 8% 6% 5% 5% 5% 5% 6% 37%	1846
	11th to 20th	Night	12% 7% 3 5% 6% 4 4 5% 5% 8% 41%	1775
	21st to end	Night	17% 6% 3 5% 5% 3 5% 4 5% 8% 40%	1728
May	1st to 10th	Night	17% 6% 3 6% 6% 3 4 4 7% 7% 38%	1620
	11th to 20th	Night	16% 7% 4 6% 5% 3 6% 5% 5% 6% 37%	1592
	21st to end	Night	12% 5% 2 5% 4 4 5% 4 6% 9% 42%	1596
June	1st to 10th	Night	10% 5% 2 5% 4 3 5% 5% 6% 8% 46%	1440
	11th to 20th	Night	11% 5% 3 6% 4 3 5% 6% 6% 8% 41%	1440
	21st to end	Night	9% 4 2 5% 5% 3 6% 6% 8% 9% 43%	1440
July	1st to 10th	Night	11% 5% 2 5% 6% 3 6% 5% 6% 9% 42%	1518
	11th to 20th	Night	7% 4 2 4 5% 3 5% 6% 6% 10% 48%	1620
	21st to end	Night	7% 4 2 4 5% 3 6% 7% 8% 12% 41%	1771
August	1st to 10th	Night	6% 5% 2 5% 6% 4 6% 6% 8% 8% 43%	1611
	11th to 20th	Night	11% 5% 2 5% 5% 4 6% 4 6% 10% 42%	1598
	21st to end	Night	9% 6% 2 6% 5% 3 5% 5% 7% 10% 42%	1964
September	1st to 10th	Night	14% 5% 2 4 5% 2 3 4 6% 8% 46%	1800
	11th to 20th	Night	11% 5% 2 5% 4 3 4 4 5% 7% 50%	1898
	21st to end	Night	19% 5% 3 5% 5% 3 5% 4 4 6% 42%	2024
October	1st to 10th	Night	18% 5% 2 4 4 3 5% 3 5% 6% 45%	2160
	11th to 20th	Night	14% 6% 2 4 4 3 4 4 5% 6% 47%	2160
	21st to end	Night	15% 6% 3 5% 5% 3 4 4 4 6% 45%	2376
November	1st to 10th	Night	9% 7% 3 6% 5% 3 4 4 4 6% 49%	2221
	11th to 20th	Night	12% 6% 3 6% 5% 3 4 5% 5% 7% 43%	2555
	21st to end	Night	13% 6% 3 5% 6% 4 5% 4 5% 7% 42%	2660
December	1st to 10th	Night	14% 10% 4 8% 6% 3 4 5% 5% 7% 33%	2660
	11th to 20th	Night	14% 7% 3 6% 6% 4 5% 5% 5% 7% 38%	3285
	21st to end	Night	15% 8% 4 6% 7% 4 6% 6% 7% 8% 31%	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	48% 6% 9% 20% 15% 3	1707
	11th to 20th	Day	49% 6% 12% 18% 13% 1	1665
	21st to end	Day	47% 6% 13% 17% 15% 3	1782
February	1st to 10th	Day	49% 7% 12% 19% 11% 2	1620
	11th to 20th	Day	48% 5% 12% 19% 13% 2	1582
	21st to end	Day	45% 7% 13% 18% 14% 4	1517
March	1st to 10th	Day	40% 4 11% 24% 18% 2	1980
	11th to 20th	Day	46% 7% 9% 18% 16% 4	1980
	21st to end	Day	49% 7% 11% 17% 12% 3	2178
April	1st to 10th	Day	43% 7% 12% 18% 16% 5%	2112
	11th to 20th	Day	39% 6% 10% 20% 19% 5%	2134
	21st to end	Day	46% 7% 10% 20% 13% 3	2246
May	1st to 10th	Day	46% 9% 13% 18% 12% 2	2340
	11th to 20th	Day	48% 8% 13% 19% 10% 2	2305
	21st to end	Day	43% 9% 14% 22% 10% 1	2677
June	1st to 10th	Day	38% 10% 14% 22% 15% 1	2520
	11th to 20th	Day	41% 11% 15% 19% 12% 2	2520
	21st to end	Day	38% 9% 15% 24% 13% 2	2520
July	1st to 10th	Day	41% 11% 12% 20% 13% 3	2371
	11th to 20th	Day	38% 10% 15% 23% 12% 2	2271
	21st to end	Day	42% 10% 13% 19% 15% 1	2405
August	1st to 10th	Day	45% 12% 13% 20% 10%	2314
	11th to 20th	Day	43% 10% 14% 20% 12% 1	2299
	21st to end	Day	40% 10% 16% 21% 12% 2	2376
September	1st to 10th	Day	41% 8% 14% 17% 18% 3	2160
	11th to 20th	Day	38% 6% 10% 25% 18% 3	2058
	21st to end	Day	46% 7% 10% 20% 16% 2	1936
October	1st to 10th	Day	40% 7% 11% 23% 15% 4	1800
	11th to 20th	Day	41% 6% 10% 22% 19% 2	1800
	21st to end	Day	38% 7% 9% 24% 18% 4	1980
November	1st to 10th	Day	33% 5% 11% 24% 21% 5%	1857
	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	43% 7% 13% 18% 16% 3	2459
	11th to 20th	Night	47% 8% 12% 19% 12% 2	2406
	21st to end	Night	45% 7% 12% 21% 14% 2	2574
February	1st to 10th	Night	45% 6% 14% 21% 12% 1	2340
	11th to 20th	Night	49% 6% 12% 18% 13% 3	2275
	21st to end	Night	48% 7% 12% 18% 11% 4	1734
March	1st to 10th	Night	37% 6% 12% 26% 15% 3	1980
	11th to 20th	Night	43% 8% 13% 21% 14% 2	1980
	21st to end	Night	45% 6% 12% 19% 14% 4	2178
April	1st to 10th	Night	44% 8% 12% 19% 15% 3	1846
	11th to 20th	Night	37% 8% 12% 22% 16% 5%	1775
	21st to end	Night	41% 7% 11% 25% 12% 3	1728
May	1st to 10th	Night	42% 9% 14% 20% 12% 3	1620
	11th to 20th	Night	45% 9% 13% 18% 13% 1	1593
	21st to end	Night	37% 11% 18% 23% 10% 1	1597
June	1st to 10th	Night	34% 10% 13% 28% 15% 1	1440
	11th to 20th	Night	36% 11% 16% 23% 13% 1	1440
	21st to end	Night	32% 11% 17% 22% 16% 2	1440
July	1st to 10th	Night	37% 11% 18% 19% 12% 3	1474
	11th to 20th	Night	29% 11% 18% 27% 13% 2	1566
	21st to end	Night	30% 11% 21% 24% 14%	1672
August	1st to 10th	Night	35% 11% 18% 23% 12% 1	1600
	11th to 20th	Night	36% 10% 19% 23% 12% 1	1598
	21st to end	Night	35% 11% 15% 26% 11% 2	1964
September	1st to 10th	Night	36% 9% 15% 20% 17% 4	1800
	11th to 20th	Night	32% 7% 12% 29% 19% 2	1898
	21st to end	Night	42% 7% 11% 22% 17% 1	2024
October	1st to 10th	Night	40% 5% 13% 24% 16% 2	2160
	11th to 20th	Night	35% 6% 12% 26% 19% 2	2160
	21st to end	Night	38% 7% 10% 22% 20% 2	2376
November	1st to 10th	Night	36% 6% 12% 21% 20% 5%	2221
	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	31% 23% 29% 13% 3	255
	21st to end	Day	30% 30% 28% 9% 3	264
February	1st to 10th	Day	33% 32% 25% 9% 1	240
	11th to 20th	Day	42% 25% 29% 5%	240
	21st to end	Day	36% 22% 25% 16% 1	303
March	1st to 10th	Day	29% 24% 24% 20% 4	420
	11th to 20th	Day	27% 26% 24% 16% 6% 1	420
	21st to end	Day	28% 22% 29% 15% 6% 1	462
April	1st to 10th	Day	25% 24% 25% 19% 6% 1	420
	11th to 20th	Day	22% 18% 26% 19% 10% 3	412
	21st to end	Day	28% 18% 28% 15% 9% 2	420
May	1st to 10th	Day	24% 20% 26% 16% 10% 4	423
	11th to 20th	Day	23% 14% 29% 20% 11% 3	447
	21st to end	Day	18% 9% 26% 23% 17% 7%	485
June	1st to 10th	Day	15% 11% 27% 26% 14% 6%	450
	11th to 20th	Day	16% 10% 28% 22% 17% 7%	450
	21st to end	Day	9% 12% 29% 29% 16% 4	450
July	1st to 10th	Day	11% 5% 20% 28% 24% 10%	445
	11th to 20th	Day	7% 4 21% 31% 27% 11%	444
	21st to end	Day	14% 6% 21% 28% 23% 8%	488
August	1st to 10th	Day	12% 6% 21% 26% 25% 10%	446
	11th to 20th	Day	12% 4 23% 23% 26% 12%	439
	21st to end	Day	11% 6% 21% 29% 20% 14%	495
September	1st to 10th	Day	16% 8% 20% 23% 23% 11%	450
	11th to 20th	Day	13% 5% 19% 27% 25% 10%	450
	21st to end	Day	25% 9% 23% 24% 15% 4	450
October	1st to 10th	Day	19% 8% 22% 27% 18% 5%	450
	11th to 20th	Day	21% 17% 22% 26% 11% 2	450
	21st to end	Day	20% 18% 28% 23% 9% 2	495
November	1st to 10th	Day	17% 15% 26% 27% 12% 3	455
	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% 18% 28% 27% 3	741
	21st to end	Night	19% 22% 35% 22% 2	792
February	1st to 10th	Night	19% 23% 29% 27% 2	720
	11th to 20th	Night	27% 26% 29% 18% 1	703
	21st to end	Night	26% 18% 35% 19% 2	592
March	1st to 10th	Night	21% 19% 33% 24% 2	720
	11th to 20th	Night	24% 22% 26% 22% 5% 1	720
	21st to end	Night	22% 19% 31% 21% 6% 1	792
April	1st to 10th	Night	20% 22% 28% 24% 5%	720
	11th to 20th	Night	17% 17% 27% 28% 10%	711
	21st to end	Night	22% 13% 27% 31% 7%	648
May	1st to 10th	Night	20% 9% 27% 29% 13% 1	540
	11th to 20th	Night	17% 7% 27% 35% 13% 1	531
	21st to end	Night	13% 3 22% 39% 20% 3	436
June	1st to 10th	Night	12% 4 22% 39% 22% 1	360
	11th to 20th	Night	13% 4 19% 43% 19% 2	360
	21st to end	Night	8% 3 20% 50% 19%	360
July	1st to 10th	Night	12% 2 13% 38% 30% 5%	424
	11th to 20th	Night	8% 1 10% 41% 36% 5%	522
	21st to end	Night	7% 2 16% 39% 31% 4	591
August	1st to 10th	Night	8% 3 12% 43% 32% 2	537
	11th to 20th	Night	11% 2 10% 41% 31% 4	534
	21st to end	Night	12% 2 15% 38% 29% 4	776
September	1st to 10th	Night	16% 2 16% 32% 28% 5%	720
	11th to 20th	Night	12% 3 16% 33% 32% 4	720
	21st to end	Night	20% 5% 23% 31% 21% 1	720
October	1st to 10th	Night	20% 8% 19% 29% 21% 3	720
	11th to 20th	Night	16% 14% 24% 31% 13% 1	720
	21st to end	Night	19% 13% 25% 31% 11% 1	792
November	1st to 10th	Night	14% 12% 26% 36% 12% 1	740
	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 2024-01-13 01:38:10. Version ac07

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