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 2026-01-17.

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% 8% 3 8% 5% 5% 5% 4 6% 8% 37%	127167
	Night	11% 8% 3 7% 5% 4 5% 4 6% 8% 40%	124551
Transparency	Day	42% 6% 11% 20% 16% 4	130930
	Night	41% 6% 11% 20% 17% 5%	128856
Seeing	Day	18% 12% 21% 21% 17% 11%	16408
	Night	16% 10% 20% 29% 21% 4	26474

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% 10% 5% 7% 4 4 3 3 5% 5% 41%	4146
	11th to 20th	Day	10% 9% 7% 10% 3 3 3 2 4 4 46%	4114
	21st to end	Day	14% 16% 5% 7% 4 4 3 3 4 5% 36%	4554
February	1st to 10th	Day	14% 11% 4 8% 5% 4 5% 4 5% 5% 36%	2000
	11th to 20th	Day	17% 11% 4 8% 4 4 4 3 5% 6% 34%	1948
	21st to end	Day	16% 9% 4 8% 4 6% 3 3 4 5% 37%	1650
March	1st to 10th	Day	15% 10% 4 8% 5% 4 5% 4 5% 6% 35%	4613
	11th to 20th	Day	9% 8% 3 6% 4 4 3 3 4 6% 50%	4980
	21st to end	Day	13% 9% 3 7% 4 4 4 3 4 6% 42%	5465
April	1st to 10th	Day	10% 7% 2 7% 5% 5% 5% 5% 6% 7% 42%	2268
	11th to 20th	Day	11% 8% 3 7% 5% 3 4 4 5% 6% 44%	2374
	21st to end	Day	10% 7% 2 7% 4 5% 5% 4 6% 7% 42%	2585
May	1st to 10th	Day	13% 9% 3 7% 6% 5% 6% 5% 7% 9% 30%	5862
	11th to 20th	Day	13% 9% 4 10% 7% 6% 7% 5% 7% 7% 25%	5861
	21st to end	Day	11% 7% 3 8% 5% 5% 6% 4 7% 8% 36%	6433
June	1st to 10th	Day	8% 7% 2 9% 6% 6% 7% 6% 7% 9% 33%	2600
	11th to 20th	Day	5% 5% 2 7% 5% 7% 6% 7% 9% 10% 36%	2600
	21st to end	Day	7% 5% 3 6% 6% 7% 7% 5% 9% 10% 35%	2600
July	1st to 10th	Day	5% 5% 2 8% 6% 6% 7% 6% 9% 11% 35%	5900
	11th to 20th	Day	7% 5% 2 8% 7% 7% 8% 7% 10% 11% 29%	5900
	21st to end	Day	9% 9% 4 10% 8% 8% 8% 7% 8% 9% 21%	6424
August	1st to 10th	Day	6% 5% 2 8% 6% 6% 7% 5% 8% 12% 34%	4234
	11th to 20th	Day	7% 6% 2 8% 5% 5% 6% 5% 8% 11% 38%	3986
	21st to end	Day	7% 5% 2 7% 5% 6% 6% 4 6% 7% 43%	4312
September	1st to 10th	Day	9% 6% 2 8% 7% 5% 6% 5% 7% 8% 36%	2215
	11th to 20th	Day	13% 6% 2 8% 5% 5% 5% 5% 6% 9% 36%	2200
	21st to end	Day	12% 5% 2 6% 5% 5% 5% 5% 5% 8% 41%	2200
October	1st to 10th	Day	9% 4 2 6% 5% 5% 4 4 5% 5% 52%	2200
	11th to 20th	Day	10% 6% 2 5% 3 3 4 4 5% 6% 54%	2071
	21st to end	Day	11% 7% 2 5% 3 3 4 3 5% 5% 53%	2192
November	1st to 10th	Day	10% 6% 2 6% 3 4 4 2 5% 6% 54%	1852
	11th to 20th	Day	10% 7% 2 5% 4 4 4 4 5% 7% 49%	1890
	21st to end	Day	12% 8% 4 5% 4 4 4 4 4 7% 44%	1890
December	1st to 10th	Day	14% 9% 3 6% 4 3 4 3 3 5% 45%	3020
	11th to 20th	Day	14% 11% 5% 8% 5% 5% 5% 4 4 5% 34%	3463
	21st to end	Day	12% 10% 5% 7% 4 4 4 4 6% 8% 36%	4565
January	1st to 10th	Night	12% 9% 3 9% 5% 5% 5% 3 4 6% 39%	6019
	11th to 20th	Night	11% 10% 3 9% 5% 4 3 3 4 5% 42%	5979
	21st to end	Night	11% 13% 3 8% 4 4 4 3 4 5% 40%	6398
February	1st to 10th	Night	12% 11% 3 7% 4 4 4 3 5% 7% 39%	2400
	11th to 20th	Night	17% 11% 4 9% 5% 3 4 3 4 5% 35%	2338
	21st to end	Night	16% 10% 3 7% 5% 4 5% 4 5% 6% 36%	1980
March	1st to 10th	Night	16% 13% 4 8% 5% 4 4 3 5% 6% 33%	5240
	11th to 20th	Night	10% 7% 2 4 3 3 4 4 6% 8% 50%	4980
	21st to end	Night	11% 9% 3 7% 5% 5% 5% 3 5% 6% 42%	5467
April	1st to 10th	Night	10% 6% 2 5% 4 4 5% 4 6% 9% 46%	2148
	11th to 20th	Night	10% 7% 2 6% 5% 3 4 3 4 7% 49%	1975
	21st to end	Night	9% 7% 2 5% 5% 4 4 3 5% 8% 47%	1813
May	1st to 10th	Night	10% 8% 3 8% 6% 6% 5% 5% 7% 10% 33%	4033
	11th to 20th	Night	13% 11% 4 9% 6% 6% 6% 4 5% 8% 26%	4032
	21st to end	Night	11% 8% 3 7% 4 4 5% 5% 7% 10% 36%	4421
June	1st to 10th	Night	6% 5% 2 7% 7% 5% 6% 5% 8% 12% 36%	1800
	11th to 20th	Night	4 3 2 5% 5% 5% 6% 5% 9% 14% 44%	1800
	21st to end	Night	4 5% 2 5% 5% 6% 5% 5% 9% 10% 45%	1800
July	1st to 10th	Night	8% 6% 2 8% 5% 5% 5% 5% 8% 11% 37%	4058
	11th to 20th	Night	7% 6% 3 7% 5% 6% 5% 4 8% 11% 38%	4057
	21st to end	Night	10% 7% 3 8% 6% 6% 7% 5% 8% 11% 28%	4427
August	1st to 10th	Night	6% 5% 3 7% 5% 6% 5% 5% 7% 12% 40%	2915
	11th to 20th	Night	10% 7% 2 5% 4 5% 5% 3 6% 8% 44%	3058
	21st to end	Night	6% 6% 2 5% 4 4 5% 5% 6% 10% 48%	3586
September	1st to 10th	Night	7% 7% 3 7% 5% 6% 6% 4 6% 8% 39%	2165
	11th to 20th	Night	10% 6% 3 7% 5% 5% 5% 4 7% 8% 41%	2200
	21st to end	Night	9% 6% 2 6% 4 4 5% 4 6% 8% 46%	2200
October	1st to 10th	Night	10% 5% 2 4 3 3 4 3 5% 6% 55%	2200
	11th to 20th	Night	10% 5% 2 5% 4 4 4 3 4 6% 54%	2327
	21st to end	Night	10% 7% 2 5% 4 3 3 4 4 4 54%	2644
November	1st to 10th	Night	11% 7% 2 5% 3 3 3 3 5% 6% 51%	2666
	11th to 20th	Night	11% 8% 3 5% 5% 3 3 3 4 6% 50%	2730
	21st to end	Night	12% 9% 2 6% 5% 4 3 4 6% 6% 43%	2730
December	1st to 10th	Night	14% 9% 3 7% 4 4 4 3 5% 6% 42%	4380
	11th to 20th	Night	17% 12% 5% 7% 4 4 4 3 4 5% 35%	4952
	21st to end	Night	12% 11% 5% 8% 5% 5% 4 3 5% 7% 35%	6633

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	45% 4 4 19% 26% 2	4147
	11th to 20th	Day	43% 2 5% 15% 31% 5%	4114
	21st to end	Day	50% 3 5% 17% 19% 6%	4554
February	1st to 10th	Day	49% 4 6% 19% 18% 3	2000
	11th to 20th	Day	51% 4 6% 17% 18% 5%	1958
	21st to end	Day	50% 2 6% 14% 22% 6%	1650
March	1st to 10th	Day	48% 4 6% 14% 19% 8%	4613
	11th to 20th	Day	35% 4 7% 16% 23% 15%	4980
	21st to end	Day	44% 3 7% 27% 16% 3	5465
April	1st to 10th	Day	40% 5% 10% 23% 18% 4	2268
	11th to 20th	Day	40% 3 8% 20% 24% 5%	2374
	21st to end	Day	40% 4 11% 28% 14% 3	2585
May	1st to 10th	Day	49% 5% 15% 19% 10% 1	5897
	11th to 20th	Day	56% 7% 12% 18% 7%	5865
	21st to end	Day	45% 5% 12% 22% 14% 1	6447
June	1st to 10th	Day	44% 8% 17% 22% 8% 1	2600
	11th to 20th	Day	38% 9% 18% 22% 12% 1	2600
	21st to end	Day	40% 9% 18% 20% 12% 2	2600
July	1st to 10th	Day	38% 12% 20% 23% 8% 1	5835
	11th to 20th	Day	42% 12% 26% 15% 4 1	5831
	21st to end	Day	54% 11% 17% 14% 4	6240
August	1st to 10th	Day	39% 9% 17% 27% 7%	4221
	11th to 20th	Day	35% 9% 20% 21% 13% 1	4025
	21st to end	Day	37% 8% 11% 28% 15% 1	4311
September	1st to 10th	Day	43% 7% 13% 18% 17% 4	2215
	11th to 20th	Day	43% 7% 13% 20% 17% 1	2200
	21st to end	Day	40% 6% 12% 16% 20% 6%	2200
October	1st to 10th	Day	27% 5% 7% 17% 33% 12%	3590
	11th to 20th	Day	21% 3 6% 21% 28% 21%	3350
	21st to end	Day	28% 4 5% 26% 26% 12%	3518
November	1st to 10th	Day	32% 3 8% 16% 31% 9%	1852
	11th to 20th	Day	34% 4 6% 21% 26% 8%	1890
	21st to end	Day	41% 3 7% 20% 24% 5%	1890
December	1st to 10th	Day	43% 4 5% 18% 26% 5%	3020
	11th to 20th	Day	52% 4 7% 16% 18% 4	3460
	21st to end	Day	46% 3 9% 26% 14% 2	4565
January	1st to 10th	Night	44% 5% 6% 18% 24% 3	6019
	11th to 20th	Night	44% 4 5% 16% 22% 9%	5979
	21st to end	Night	46% 4 5% 17% 22% 6%	6398
February	1st to 10th	Night	46% 3 8% 19% 20% 4	2400
	11th to 20th	Night	53% 4 5% 17% 17% 5%	2339
	21st to end	Night	49% 4 7% 17% 18% 5%	1980
March	1st to 10th	Night	52% 3 7% 15% 20% 4	5240
	11th to 20th	Night	33% 3 8% 19% 23% 14%	4980
	21st to end	Night	45% 3 8% 25% 16% 4	5467
April	1st to 10th	Night	36% 4 12% 22% 22% 4	2148
	11th to 20th	Night	36% 3 9% 24% 21% 6%	1975
	21st to end	Night	36% 4 13% 29% 16% 2	1813
May	1st to 10th	Night	45% 7% 19% 21% 9% 1	4060
	11th to 20th	Night	55% 6% 15% 17% 7%	4033
	21st to end	Night	42% 7% 15% 24% 11% 1	4429
June	1st to 10th	Night	38% 10% 19% 23% 10% 1	1800
	11th to 20th	Night	28% 9% 25% 27% 10% 1	1800
	21st to end	Night	31% 9% 22% 21% 14% 3	1800
July	1st to 10th	Night	38% 11% 21% 23% 6%	4015
	11th to 20th	Night	38% 12% 27% 18% 4 1	4006
	21st to end	Night	48% 11% 20% 16% 4	4297
August	1st to 10th	Night	34% 10% 22% 28% 6%	2904
	11th to 20th	Night	36% 8% 21% 23% 12% 1	3085
	21st to end	Night	30% 8% 17% 29% 15% 1	3586
September	1st to 10th	Night	39% 8% 16% 18% 15% 4	2165
	11th to 20th	Night	39% 8% 14% 21% 17%	2200
	21st to end	Night	35% 6% 13% 21% 20% 5%	2200
October	1st to 10th	Night	26% 6% 9% 19% 30% 10%	3590
	11th to 20th	Night	21% 3 6% 20% 33% 16%	3787
	21st to end	Night	25% 4 4 28% 27% 12%	4268
November	1st to 10th	Night	35% 4 8% 22% 24% 8%	2666
	11th to 20th	Night	37% 3 5% 21% 25% 9%	2730
	21st to end	Night	41% 4 7% 22% 21% 5%	2730
December	1st to 10th	Night	43% 5% 6% 17% 24% 5%	4380
	11th to 20th	Night	51% 5% 7% 14% 20% 3	4954
	21st to end	Night	49% 3 9% 23% 15% 1	6633

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% 25% 32% 11% 4	330
	11th to 20th	Day	30% 25% 26% 14% 5%	318
	21st to end	Day	23% 31% 27% 14% 5% 1	330
February	1st to 10th	Day	24% 21% 36% 15% 3	300
	11th to 20th	Day	39% 26% 25% 8% 2	300
	21st to end	Day	34% 26% 27% 10% 4	249
March	1st to 10th	Day	30% 18% 28% 16% 7% 1	355
	11th to 20th	Day	26% 19% 26% 20% 8% 1	500
	21st to end	Day	25% 22% 27% 19% 7% 1	550
April	1st to 10th	Day	23% 19% 25% 20% 10% 2	500
	11th to 20th	Day	18% 18% 28% 20% 14% 2	492
	21st to end	Day	19% 14% 25% 25% 12% 5%	500
May	1st to 10th	Day	16% 17% 28% 21% 12% 6%	503
	11th to 20th	Day	16% 10% 24% 24% 16% 10%	527
	21st to end	Day	13% 7% 22% 27% 19% 14%	573
June	1st to 10th	Day	10% 5% 21% 28% 23% 14%	530
	11th to 20th	Day	8% 4 18% 25% 26% 19%	530
	21st to end	Day	10% 4 18% 25% 23% 20%	530
July	1st to 10th	Day	10% 3 10% 24% 26% 26%	525
	11th to 20th	Day	9% 2 8% 24% 30% 27%	524
	21st to end	Day	9% 5% 7% 24% 28% 28%	576
August	1st to 10th	Day	14% 4 13% 22% 21% 25%	526
	11th to 20th	Day	12% 4 12% 21% 28% 24%	519
	21st to end	Day	13% 4 10% 17% 29% 27%	583
September	1st to 10th	Day	9% 2 14% 25% 31% 19%	530
	11th to 20th	Day	14% 5% 13% 20% 29% 19%	530
	21st to end	Day	15% 5% 15% 25% 29% 11%	530
October	1st to 10th	Day	13% 6% 18% 28% 25% 9%	530
	11th to 20th	Day	14% 12% 23% 24% 21% 6%	530
	21st to end	Day	17% 13% 21% 26% 19% 4	575
November	1st to 10th	Day	17% 13% 31% 22% 12% 4	330
	11th to 20th	Day	20% 17% 32% 19% 11% 1	330
	21st to end	Day	19% 19% 35% 18% 7% 2	330
December	1st to 10th	Day	28% 26% 22% 20% 3 1	330
	11th to 20th	Day	27% 16% 28% 18% 9% 1	330
	21st to end	Day	26% 21% 28% 15% 9% 1	363
January	1st to 10th	Night	24% 18% 30% 23% 5%	840
	11th to 20th	Night	23% 18% 29% 24% 6%	825
	21st to end	Night	19% 20% 31% 28% 2	880
February	1st to 10th	Night	22% 16% 27% 29% 6%	800
	11th to 20th	Night	28% 19% 29% 22% 2	783
	21st to end	Night	23% 22% 31% 21% 3	660
March	1st to 10th	Night	21% 16% 32% 26% 5%	800
	11th to 20th	Night	20% 17% 27% 27% 8% 1	800
	21st to end	Night	20% 13% 29% 29% 9%	880
April	1st to 10th	Night	17% 15% 28% 30% 9% 1	748
	11th to 20th	Night	14% 13% 26% 32% 13% 1	593
	21st to end	Night	12% 9% 25% 36% 18% 1	600
May	1st to 10th	Night	12% 8% 25% 35% 19% 2	600
	11th to 20th	Night	14% 6% 20% 32% 23% 5%	591
	21st to end	Night	11% 3 13% 33% 32% 8%	650
June	1st to 10th	Night	8% 3 12% 36% 36% 5%	600
	11th to 20th	Night	4 3 11% 32% 38% 12%	600
	21st to end	Night	6% 2 8% 29% 46% 10%	600
July	1st to 10th	Night	10% 2 5% 24% 48% 11%	585
	11th to 20th	Night	9% 3 6% 18% 48% 17%	582
	21st to end	Night	7% 3 5% 22% 49% 14%	657
August	1st to 10th	Night	10% 2 5% 25% 44% 14%	597
	11th to 20th	Night	9% 3 7% 25% 48% 8%	594
	21st to end	Night	12% 2 6% 25% 44% 11%	660
September	1st to 10th	Night	10% 3 9% 28% 41% 9%	765
	11th to 20th	Night	13% 2 12% 29% 40% 5%	800
	21st to end	Night	12% 4 12% 36% 33% 4	800
October	1st to 10th	Night	12% 6% 18% 30% 28% 6%	800
	11th to 20th	Night	13% 7% 21% 33% 23% 2	800
	21st to end	Night	15% 10% 19% 35% 19% 2	880
November	1st to 10th	Night	15% 8% 20% 35% 18% 3	820
	11th to 20th	Night	17% 12% 24% 33% 13% 2	840
	21st to end	Night	19% 16% 22% 28% 14% 1	840
December	1st to 10th	Night	24% 16% 24% 27% 8% 1	840
	11th to 20th	Night	22% 14% 25% 30% 8% 1	840
	21st to end	Night	24% 15% 24% 29% 7%	924

Page generated at 2026-01-14 01:14:25. Version ac07

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