Mookie Mountain Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mookie Mountain Observatory clear sky chart from 2005-11-06 to 2024-01-14.

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	11% 7% 3 6% 6% 4 6% 6% 6% 8% 37%	74881
	Night	11% 7% 3 6% 5% 3 5% 5% 6% 8% 41%	74888
Transparency	Day	44% 5% 11% 19% 16% 4	74604
	Night	41% 5% 12% 21% 17% 4	74684
Seeing	Day	17% 11% 21% 21% 18% 12%	13732
	Night	16% 10% 20% 28% 21% 4	23835

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	13% 9% 4 8% 5% 4 4 4 5% 6% 39%	1706
	11th to 20th	Day	14% 11% 4 9% 5% 3 4 4 5% 5% 35%	1647
	21st to end	Day	11% 10% 5% 6% 5% 3 5% 4 5% 5% 42%	1814
February	1st to 10th	Day	15% 10% 5% 7% 6% 3 5% 4 5% 6% 35%	1800
	11th to 20th	Day	16% 9% 5% 7% 5% 3 5% 4 5% 6% 34%	1748
	21st to end	Day	17% 9% 4 7% 6% 4 4 3 4 5% 36%	1480
March	1st to 10th	Day	12% 8% 4 4 5% 3 5% 5% 5% 9% 40%	1849
	11th to 20th	Day	15% 10% 3 6% 5% 4 6% 5% 5% 6% 36%	1980
	21st to end	Day	12% 10% 4 6% 6% 3 4 5% 5% 7% 37%	2178
April	1st to 10th	Day	9% 7% 2 6% 6% 4 5% 6% 6% 7% 43%	2040
	11th to 20th	Day	12% 7% 3 6% 6% 3 4 5% 5% 6% 43%	2134
	21st to end	Day	10% 6% 2 6% 5% 4 6% 5% 6% 7% 43%	2326
May	1st to 10th	Day	10% 6% 3 6% 6% 4 5% 5% 6% 8% 41%	2340
	11th to 20th	Day	12% 7% 4 7% 8% 3 6% 6% 6% 7% 34%	2301
	21st to end	Day	8% 6% 3 6% 7% 4 6% 7% 7% 10% 36%	2531
June	1st to 10th	Day	8% 7% 2 8% 7% 4 7% 8% 7% 9% 32%	2340
	11th to 20th	Day	5% 5% 3 6% 7% 5% 7% 8% 8% 10% 37%	2340
	21st to end	Day	7% 5% 3 6% 7% 5% 8% 7% 8% 10% 34%	2340
July	1st to 10th	Day	8% 6% 4 9% 9% 5% 8% 9% 8% 10% 26%	2340
	11th to 20th	Day	9% 5% 3 7% 8% 6% 9% 9% 9% 9% 25%	2340
	21st to end	Day	7% 6% 4 7% 9% 7% 8% 9% 9% 9% 25%	2547
August	1st to 10th	Day	8% 5% 3 7% 8% 6% 8% 8% 9% 12% 26%	2327
	11th to 20th	Day	10% 7% 3 8% 7% 5% 7% 7% 8% 10% 29%	2205
	21st to end	Day	13% 7% 3 8% 8% 5% 8% 7% 7% 8% 28%	2376
September	1st to 10th	Day	10% 6% 3 7% 8% 4 6% 6% 6% 8% 36%	1994
	11th to 20th	Day	13% 6% 3 7% 6% 4 5% 6% 6% 9% 35%	1980
	21st to end	Day	12% 5% 2 5% 6% 4 5% 6% 5% 7% 43%	1980
October	1st to 10th	Day	10% 4 2 5% 5% 4 4 5% 4 5% 52%	1980
	11th to 20th	Day	11% 6% 2 4 4 2 4 5% 5% 6% 52%	1865
	21st to end	Day	11% 7% 2 4 4 2 4 3 5% 5% 53%	1974
November	1st to 10th	Day	10% 5% 2 4 3 3 4 3 4 6% 56%	1672
	11th to 20th	Day	10% 6% 2 5% 4 3 4 5% 5% 7% 49%	1710
	21st to end	Day	12% 8% 4 5% 5% 3 4 5% 4 7% 44%	1710
December	1st to 10th	Day	16% 10% 4 8% 6% 3 5% 5% 4 6% 34%	1710
	11th to 20th	Day	12% 10% 4 7% 5% 3 5% 5% 5% 6% 38%	2153
	21st to end	Day	14% 11% 6% 6% 5% 3 4 5% 6% 8% 31%	3124
January	1st to 10th	Night	14% 8% 4 8% 6% 4 5% 4 4 5% 37%	2459
	11th to 20th	Night	13% 11% 4 8% 5% 3 5% 6% 5% 6% 33%	2386
	21st to end	Night	12% 10% 4 8% 6% 3 5% 5% 4 4 41%	2538
February	1st to 10th	Night	13% 10% 4 6% 5% 3 5% 4 5% 7% 39%	2160
	11th to 20th	Night	17% 10% 5% 8% 5% 2 4 4 4 5% 36%	2098
	21st to end	Night	17% 10% 4 7% 6% 3 5% 5% 4 6% 33%	1776
March	1st to 10th	Night	12% 8% 4 5% 5% 3 4 4 4 6% 44%	2111
	11th to 20th	Night	14% 8% 3 6% 6% 3 5% 4 6% 7% 38%	1980
	21st to end	Night	11% 10% 4 6% 6% 3 5% 4 5% 6% 40%	2178
April	1st to 10th	Night	10% 5% 2 4 4 3 5% 5% 5% 8% 48%	1934
	11th to 20th	Night	10% 6% 2 6% 5% 3 4 3 4 7% 49%	1775
	21st to end	Night	9% 6% 2 4 6% 3 4 4 5% 8% 48%	1633
May	1st to 10th	Night	9% 5% 2 5% 5% 3 4 6% 6% 9% 45%	1620
	11th to 20th	Night	10% 5% 3 6% 6% 4 6% 6% 6% 10% 40%	1592
	21st to end	Night	6% 5% 2 6% 4 4 5% 7% 8% 12% 41%	1744
June	1st to 10th	Night	6% 5% 2 5% 8% 4 6% 7% 8% 12% 37%	1620
	11th to 20th	Night	3 2 2 4 5% 4 6% 6% 9% 13% 45%	1620
	21st to end	Night	4 5% 2 4 5% 4 6% 6% 8% 10% 45%	1620
July	1st to 10th	Night	8% 5% 3 6% 7% 5% 6% 6% 9% 11% 34%	1620
	11th to 20th	Night	6% 5% 3 5% 5% 4 6% 6% 8% 13% 39%	1620
	21st to end	Night	5% 5% 2 5% 6% 4 7% 7% 10% 13% 35%	1771
August	1st to 10th	Night	7% 5% 3 5% 6% 5% 6% 7% 8% 11% 38%	1611
	11th to 20th	Night	7% 5% 2 5% 6% 6% 6% 5% 7% 10% 40%	1692
	21st to end	Night	9% 7% 3 6% 6% 3 5% 8% 6% 10% 36%	1980
September	1st to 10th	Night	8% 6% 3 5% 6% 4 6% 5% 6% 9% 40%	1948
	11th to 20th	Night	10% 6% 3 6% 6% 3 6% 5% 7% 8% 41%	1980
	21st to end	Night	7% 6% 2 5% 4 3 5% 5% 6% 8% 49%	1980
October	1st to 10th	Night	10% 5% 2 3 3 2 4 4 5% 6% 57%	1980
	11th to 20th	Night	11% 5% 2 4 5% 3 4 4 5% 6% 50%	2093
	21st to end	Night	10% 6% 2 5% 5% 3 3 4 4 5% 53%	2379
November	1st to 10th	Night	11% 6% 2 4 4 2 4 3 4 6% 53%	2406
	11th to 20th	Night	11% 7% 3 4 5% 3 4 3 4 6% 50%	2470
	21st to end	Night	12% 8% 2 5% 6% 3 4 5% 6% 6% 42%	2470
December	1st to 10th	Night	16% 9% 4 7% 6% 4 5% 5% 6% 7% 33%	2470
	11th to 20th	Night	13% 12% 5% 7% 4 3 3 4 4 6% 41%	3042
	21st to end	Night	14% 11% 4 7% 6% 4 5% 5% 6% 8% 29%	4532

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% 4 7% 20% 19% 4	1707
	11th to 20th	Day	50% 3 7% 17% 19% 4	1647
	21st to end	Day	44% 3 7% 22% 19% 5%	1814
February	1st to 10th	Day	51% 3 6% 19% 17% 3	1800
	11th to 20th	Day	51% 4 6% 18% 17% 4	1758
	21st to end	Day	52% 2 7% 13% 20% 6%	1480
March	1st to 10th	Day	42% 4 9% 15% 22% 8%	1849
	11th to 20th	Day	48% 5% 11% 15% 16% 4	1980
	21st to end	Day	47% 5% 10% 23% 14% 2	2178
April	1st to 10th	Day	40% 5% 10% 23% 18% 4	2040
	11th to 20th	Day	42% 3 8% 19% 24% 4	2134
	21st to end	Day	40% 4 11% 28% 15% 2	2326
May	1st to 10th	Day	41% 4 13% 23% 15% 3	2340
	11th to 20th	Day	47% 6% 13% 20% 12% 1	2305
	21st to end	Day	42% 7% 14% 22% 14% 1	2531
June	1st to 10th	Day	45% 8% 16% 21% 8% 1	2340
	11th to 20th	Day	39% 8% 18% 22% 11% 1	2340
	21st to end	Day	41% 8% 17% 20% 12% 2	2340
July	1st to 10th	Day	48% 9% 17% 17% 7% 1	2275
	11th to 20th	Day	47% 10% 18% 13% 9% 2	2271
	21st to end	Day	48% 10% 17% 17% 7%	2405
August	1st to 10th	Day	46% 10% 18% 20% 5% 1	2314
	11th to 20th	Day	47% 9% 15% 17% 10% 1	2205
	21st to end	Day	51% 8% 13% 16% 9% 3	2376
September	1st to 10th	Day	44% 6% 13% 18% 15% 4	1994
	11th to 20th	Day	44% 6% 12% 19% 17% 1	1980
	21st to end	Day	39% 5% 11% 17% 22% 6%	1980
October	1st to 10th	Day	34% 5% 8% 19% 28% 6%	1980
	11th to 20th	Day	34% 4 9% 23% 22% 9%	1865
	21st to end	Day	35% 2 5% 22% 26% 9%	1974
November	1st to 10th	Day	31% 3 8% 15% 33% 10%	1672
	11th to 20th	Day	35% 4 6% 20% 26% 9%	1710
	21st to end	Day	41% 3 7% 18% 25% 5%	1710
December	1st to 10th	Day	52% 4 6% 18% 17% 4	1710
	11th to 20th	Day	47% 3 7% 14% 23% 5%	2150
	21st to end	Day	51% 3 7% 21% 16% 3	3124
January	1st to 10th	Night	50% 3 7% 17% 19% 4	2459
	11th to 20th	Night	50% 5% 9% 15% 16% 4	2386
	21st to end	Night	47% 3 5% 20% 21% 3	2538
February	1st to 10th	Night	46% 3 9% 19% 20% 4	2160
	11th to 20th	Night	52% 4 5% 17% 17% 4	2099
	21st to end	Night	52% 5% 7% 16% 16% 5%	1776
March	1st to 10th	Night	43% 4 8% 17% 20% 8%	2111
	11th to 20th	Night	45% 5% 11% 19% 17% 4	1980
	21st to end	Night	46% 3 11% 24% 15% 2	2178
April	1st to 10th	Night	35% 4 12% 22% 23% 4	1934
	11th to 20th	Night	36% 3 9% 23% 21% 7%	1775
	21st to end	Night	36% 4 12% 29% 17% 2	1633
May	1st to 10th	Night	35% 6% 17% 23% 17% 2	1620
	11th to 20th	Night	40% 7% 17% 24% 11% 1	1593
	21st to end	Night	33% 9% 17% 28% 10% 2	1745
June	1st to 10th	Night	37% 10% 19% 23% 9% 1	1620
	11th to 20th	Night	27% 9% 26% 27% 10% 1	1620
	21st to end	Night	31% 9% 22% 22% 14% 3	1620
July	1st to 10th	Night	40% 9% 20% 20% 10% 1	1575
	11th to 20th	Night	33% 11% 26% 18% 8% 4	1566
	21st to end	Night	36% 11% 22% 21% 8% 1	1672
August	1st to 10th	Night	36% 11% 21% 25% 7%	1600
	11th to 20th	Night	39% 8% 20% 19% 14% 1	1692
	21st to end	Night	41% 8% 19% 22% 9% 2	1980
September	1st to 10th	Night	39% 7% 16% 19% 14% 4	1948
	11th to 20th	Night	39% 8% 13% 21% 19%	1980
	21st to end	Night	33% 5% 12% 23% 21% 6%	1980
October	1st to 10th	Night	29% 4 11% 21% 28% 6%	1980
	11th to 20th	Night	35% 3 9% 23% 22% 8%	2093
	21st to end	Night	34% 3 4 23% 27% 9%	2379
November	1st to 10th	Night	33% 3 7% 22% 25% 9%	2406
	11th to 20th	Night	38% 2 5% 21% 24% 10%	2470
	21st to end	Night	41% 4 7% 22% 21% 5%	2470
December	1st to 10th	Night	51% 4 8% 17% 15% 4	2470
	11th to 20th	Night	46% 4 7% 14% 26% 4	3044
	21st to end	Night	53% 3 7% 20% 15% 2	4532

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	27% 25% 34% 11% 4	270
	11th to 20th	Day	28% 23% 28% 15% 6%	249
	21st to end	Day	22% 32% 27% 13% 5% 1	264
February	1st to 10th	Day	28% 23% 32% 15% 3	240
	11th to 20th	Day	38% 26% 29% 6% 2	240
	21st to end	Day	36% 27% 28% 8% 2	198
March	1st to 10th	Day	26% 18% 32% 17% 7% 1	289
	11th to 20th	Day	27% 19% 25% 20% 9% 1	420
	21st to end	Day	24% 22% 26% 19% 8% 1	462
April	1st to 10th	Day	22% 16% 25% 22% 12% 2	420
	11th to 20th	Day	17% 18% 27% 21% 15% 2	412
	21st to end	Day	20% 13% 24% 23% 14% 5%	420
May	1st to 10th	Day	15% 16% 28% 21% 13% 7%	423
	11th to 20th	Day	15% 7% 22% 26% 18% 12%	447
	21st to end	Day	12% 5% 19% 27% 21% 16%	485
June	1st to 10th	Day	10% 3 19% 28% 24% 16%	450
	11th to 20th	Day	9% 3 16% 24% 26% 22%	450
	21st to end	Day	11% 4 19% 26% 21% 18%	450
July	1st to 10th	Day	12% 3 9% 23% 26% 27%	445
	11th to 20th	Day	9% 2 9% 25% 28% 27%	444
	21st to end	Day	9% 4 7% 22% 28% 31%	488
August	1st to 10th	Day	15% 4 12% 21% 22% 27%	446
	11th to 20th	Day	14% 3 10% 20% 28% 26%	439
	21st to end	Day	16% 3 10% 17% 28% 26%	495
September	1st to 10th	Day	10% 2 13% 22% 32% 22%	450
	11th to 20th	Day	14% 5% 13% 19% 30% 19%	450
	21st to end	Day	14% 5% 13% 27% 30% 12%	450
October	1st to 10th	Day	15% 6% 18% 27% 24% 10%	450
	11th to 20th	Day	15% 12% 23% 24% 19% 7%	450
	21st to end	Day	17% 13% 21% 27% 19% 4	489
November	1st to 10th	Day	18% 13% 29% 23% 12% 5%	270
	11th to 20th	Day	20% 17% 33% 20% 9% 1	270
	21st to end	Day	16% 18% 37% 19% 8% 2	270
December	1st to 10th	Day	28% 24% 23% 20% 4 1	270
	11th to 20th	Day	26% 16% 29% 19% 9% 1	270
	21st to end	Day	27% 23% 28% 14% 7% 1	297
January	1st to 10th	Night	24% 18% 31% 22% 6%	760
	11th to 20th	Night	24% 17% 29% 24% 7%	735
	21st to end	Night	19% 19% 32% 27% 2	792
February	1st to 10th	Night	23% 15% 28% 28% 6%	720
	11th to 20th	Night	27% 19% 30% 21% 2	703
	21st to end	Night	26% 22% 30% 20% 3	592
March	1st to 10th	Night	20% 16% 33% 26% 5%	720
	11th to 20th	Night	20% 17% 27% 26% 8% 2	720
	21st to end	Night	20% 12% 29% 29% 9%	792
April	1st to 10th	Night	16% 14% 28% 32% 10% 1	674
	11th to 20th	Night	15% 13% 25% 31% 15% 1	533
	21st to end	Night	12% 9% 24% 36% 19% 1	540
May	1st to 10th	Night	12% 8% 25% 34% 20% 2	540
	11th to 20th	Night	12% 6% 20% 33% 24% 6%	531
	21st to end	Night	10% 2 12% 33% 35% 9%	584
June	1st to 10th	Night	9% 2 10% 35% 38% 5%	540
	11th to 20th	Night	4 3 11% 31% 37% 14%	540
	21st to end	Night	6% 1 9% 31% 44% 10%	540
July	1st to 10th	Night	10% 1 4 25% 48% 12%	525
	11th to 20th	Night	9% 2 6% 19% 48% 16%	522
	21st to end	Night	6% 2 5% 22% 50% 15%	591
August	1st to 10th	Night	9% 2 5% 24% 45% 16%	537
	11th to 20th	Night	9% 2 6% 25% 49% 9%	534
	21st to end	Night	13% 2 6% 23% 45% 11%	594
September	1st to 10th	Night	11% 3 8% 26% 43% 10%	688
	11th to 20th	Night	13% 2 12% 28% 40% 5%	720
	21st to end	Night	10% 3 12% 36% 34% 4	720
October	1st to 10th	Night	12% 6% 19% 29% 28% 7%	720
	11th to 20th	Night	14% 7% 22% 32% 22% 2	720
	21st to end	Night	15% 10% 19% 35% 19% 2	792
November	1st to 10th	Night	15% 8% 19% 35% 19% 4	740
	11th to 20th	Night	16% 13% 24% 32% 13% 2	760
	21st to end	Night	18% 15% 22% 30% 15% 1	760
December	1st to 10th	Night	24% 16% 23% 28% 9% 1	760
	11th to 20th	Night	21% 14% 26% 29% 9% 1	760
	21st to end	Night	25% 15% 25% 29% 6%	836

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