Mantrap Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mantrap Lake clear sky chart from 2005-11-06 to 2026-02-01.

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	12% 9% 4 8% 5% 5% 5% 4 6% 7% 35%	127903
	Night	10% 10% 4 10% 6% 5% 5% 4 6% 7% 34%	124352
Transparency	Day	46% 6% 13% 24% 10% 1	131422
	Night	48% 6% 12% 22% 11% 1	128927
Seeing	Day	16% 11% 33% 25% 12% 3	17793
	Night	15% 10% 33% 30% 10% 1	27821

By Month

Percentage Cloud Cover NE (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	5% 13% 5% 14% 10% 8% 6% 3 6% 7% 24%	3248
	11th to 20th	Day	6% 10% 5% 14% 9% 9% 9% 8% 11% 6% 14%	3246
	21st to end	Day	4 12% 9% 18% 9% 7% 5% 4 5% 6% 21%	4538
February	1st to 10th	Day	9% 13% 5% 11% 8% 6% 6% 5% 5% 6% 26%	1800
	11th to 20th	Day	7% 11% 4 8% 7% 6% 7% 5% 7% 8% 30%	1754
	21st to end	Day	8% 11% 4 10% 7% 6% 5% 4 6% 8% 29%	1496
March	1st to 10th	Day	10% 9% 3 8% 4 4 5% 3 6% 9% 39%	4849
	11th to 20th	Day	9% 9% 4 10% 6% 4 5% 4 7% 9% 33%	4980
	21st to end	Day	19% 13% 4 9% 5% 4 4 3 4 5% 30%	5464
April	1st to 10th	Day	15% 12% 4 9% 5% 5% 4 4 5% 5% 32%	2370
	11th to 20th	Day	16% 13% 4 9% 6% 4 4 4 5% 6% 30%	2532
	21st to end	Day	22% 10% 3 7% 5% 4 5% 3 5% 5% 32%	2600
May	1st to 10th	Day	14% 7% 2 5% 4 4 4 3 4 6% 47%	6111
	11th to 20th	Day	15% 10% 3 6% 4 4 4 4 5% 6% 39%	6319
	21st to end	Day	15% 7% 3 7% 5% 4 5% 4 5% 7% 40%	7033
June	1st to 10th	Day	12% 6% 3 6% 5% 4 5% 5% 7% 9% 39%	3000
	11th to 20th	Day	15% 7% 3 6% 5% 5% 5% 4 7% 7% 37%	3000
	21st to end	Day	12% 6% 2 7% 5% 5% 6% 4 8% 9% 38%	3000
July	1st to 10th	Day	6% 4 2 6% 5% 5% 6% 5% 8% 10% 42%	6799
	11th to 20th	Day	12% 6% 2 5% 3 4 4 4 7% 9% 44%	6800
	21st to end	Day	8% 6% 3 6% 5% 5% 5% 4 7% 10% 42%	6954
August	1st to 10th	Day	10% 4 2 6% 4 5% 5% 5% 7% 8% 44%	4234
	11th to 20th	Day	13% 6% 2 6% 5% 5% 5% 4 6% 9% 40%	4171
	21st to end	Day	14% 6% 3 6% 4 4 4 4 6% 6% 44%	4646
September	1st to 10th	Day	12% 5% 2 6% 4 5% 4 3 6% 9% 45%	2400
	11th to 20th	Day	13% 6% 2 7% 4 6% 4 4 6% 7% 42%	2277
	21st to end	Day	15% 9% 3 5% 4 3 4 3 5% 6% 43%	2165
October	1st to 10th	Day	17% 11% 3 5% 4 4 3 4 5% 6% 40%	2000
	11th to 20th	Day	17% 13% 4 7% 4 5% 3 3 4 5% 35%	2000
	21st to end	Day	18% 14% 5% 9% 4 4 4 3 4 6% 29%	2125
November	1st to 10th	Day	12% 15% 5% 10% 6% 4 4 3 5% 5% 31%	1648
	11th to 20th	Day	11% 16% 6% 14% 5% 5% 3 4 4 5% 27%	1680
	21st to end	Day	11% 12% 6% 11% 7% 6% 5% 3 6% 6% 25%	1680
December	1st to 10th	Day	10% 13% 6% 12% 13% 10% 5% 3 6% 6% 16%	2690
	11th to 20th	Day	7% 16% 8% 13% 5% 5% 5% 4 6% 5% 27%	2719
	21st to end	Day	15% 17% 6% 17% 10% 5% 4 3 3 4 16%	3575
January	1st to 10th	Night	4 9% 5% 16% 11% 8% 6% 5% 6% 6% 23%	6937
	11th to 20th	Night	5% 11% 6% 11% 8% 8% 9% 9% 11% 6% 16%	6874
	21st to end	Night	5% 13% 10% 16% 7% 6% 6% 4 5% 8% 20%	6680
February	1st to 10th	Night	7% 11% 5% 9% 6% 6% 6% 5% 7% 8% 30%	2601
	11th to 20th	Night	5% 11% 3 9% 6% 5% 7% 6% 7% 8% 34%	2533
	21st to end	Night	8% 11% 4 11% 7% 6% 6% 4 6% 7% 30%	2145
March	1st to 10th	Night	8% 8% 3 8% 5% 4 4 3 5% 8% 43%	4989
	11th to 20th	Night	9% 10% 3 13% 8% 6% 6% 3 5% 5% 32%	4979
	21st to end	Night	17% 14% 5% 11% 5% 3 3 3 4 5% 29%	5467
April	1st to 10th	Night	14% 11% 3 6% 5% 4 4 4 5% 6% 38%	2030
	11th to 20th	Night	16% 11% 4 8% 5% 4 3 3 4 5% 37%	1813
	21st to end	Night	19% 9% 3 7% 4 4 4 4 5% 6% 35%	1800
May	1st to 10th	Night	13% 9% 2 5% 4 4 3 3 4 5% 49%	3847
	11th to 20th	Night	14% 10% 2 5% 4 4 4 3 4 6% 44%	3596
	21st to end	Night	14% 9% 2 7% 4 4 4 3 5% 6% 40%	3861
June	1st to 10th	Night	12% 5% 2 5% 3 5% 4 5% 7% 9% 45%	1400
	11th to 20th	Night	11% 6% 2 6% 4 4 5% 5% 6% 7% 45%	1400
	21st to end	Night	9% 5% 2 5% 4 4 5% 3 6% 10% 48%	1400
July	1st to 10th	Night	8% 4 2 5% 3 4 5% 5% 8% 10% 47%	3180
	11th to 20th	Night	6% 4 2 4 3 3 4 4 6% 8% 57%	3180
	21st to end	Night	8% 5% 2 6% 4 4 5% 4 6% 9% 46%	3901
August	1st to 10th	Night	8% 5% 2 4 4 4 3 3 6% 8% 52%	2926
	11th to 20th	Night	13% 5% 2 4 3 4 4 3 6% 9% 47%	2888
	21st to end	Night	12% 7% 2 6% 4 3 4 3 5% 8% 47%	3261
September	1st to 10th	Night	10% 4 2 6% 4 3 4 3 6% 6% 51%	2000
	11th to 20th	Night	9% 7% 2 6% 4 4 3 3 5% 7% 49%	2120
	21st to end	Night	13% 7% 2 5% 3 3 3 2 4 7% 50%	2215
October	1st to 10th	Night	14% 8% 2 6% 4 4 4 3 5% 7% 42%	2400
	11th to 20th	Night	16% 10% 3 7% 5% 4 4 4 5% 6% 38%	2400
	21st to end	Night	17% 13% 4 9% 5% 3 4 3 4 6% 31%	2713
November	1st to 10th	Night	11% 13% 5% 9% 6% 4 4 3 5% 7% 32%	2869
	11th to 20th	Night	12% 14% 6% 12% 5% 4 4 3 5% 6% 27%	2940
	21st to end	Night	11% 10% 4 12% 8% 5% 5% 4 5% 7% 29%	2940
December	1st to 10th	Night	6% 10% 6% 15% 13% 10% 7% 5% 6% 6% 17%	4720
	11th to 20th	Night	9% 14% 6% 17% 8% 6% 5% 4 6% 5% 21%	5702
	21st to end	Night	16% 18% 7% 16% 8% 5% 4 3 4 5% 15%	7645

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	58% 5% 8% 18% 10% 1	3249
	11th to 20th	Day	63% 4 6% 21% 5%	3274
	21st to end	Day	63% 4 9% 16% 8%	4538
February	1st to 10th	Day	57% 5% 9% 18% 11%	1800
	11th to 20th	Day	50% 6% 12% 20% 10% 2	1763
	21st to end	Day	51% 7% 13% 17% 11%	1496
March	1st to 10th	Day	41% 5% 15% 24% 11% 3	4851
	11th to 20th	Day	46% 5% 14% 26% 9%	4980
	21st to end	Day	57% 4 10% 21% 7% 1	5464
April	1st to 10th	Day	53% 4 9% 19% 12% 2	2370
	11th to 20th	Day	54% 6% 12% 18% 10% 1	2532
	21st to end	Day	53% 5% 11% 20% 10% 1	2600
May	1st to 10th	Day	37% 5% 14% 27% 17% 1	6122
	11th to 20th	Day	44% 6% 12% 20% 14% 4	6323
	21st to end	Day	41% 7% 9% 29% 12% 1	7033
June	1st to 10th	Day	38% 8% 18% 26% 10%	3000
	11th to 20th	Day	44% 7% 14% 23% 11% 1	3000
	21st to end	Day	40% 8% 16% 27% 9%	3000
July	1st to 10th	Day	33% 8% 22% 29% 8%	6726
	11th to 20th	Day	34% 7% 18% 32% 9% 1	6719
	21st to end	Day	36% 7% 19% 29% 9% 1	6754
August	1st to 10th	Day	35% 7% 16% 28% 13% 1	4220
	11th to 20th	Day	40% 7% 16% 29% 8%	4210
	21st to end	Day	39% 6% 18% 28% 9% 1	4645
September	1st to 10th	Day	36% 5% 15% 34% 10%	2400
	11th to 20th	Day	41% 5% 20% 25% 8%	2277
	21st to end	Day	42% 5% 13% 31% 8% 1	2165
October	1st to 10th	Day	34% 4 14% 32% 15% 1	3260
	11th to 20th	Day	46% 5% 8% 22% 18% 1	3240
	21st to end	Day	54% 4 12% 24% 6%	3418
November	1st to 10th	Day	55% 6% 11% 18% 10% 1	1648
	11th to 20th	Day	60% 5% 12% 16% 7% 1	1680
	21st to end	Day	57% 7% 15% 13% 7% 1	1680
December	1st to 10th	Day	68% 5% 11% 13% 3 1	2690
	11th to 20th	Day	58% 3 9% 19% 10%	2720
	21st to end	Day	73% 4 6% 13% 5%	3575
January	1st to 10th	Night	60% 6% 8% 16% 11%	6937
	11th to 20th	Night	59% 7% 9% 15% 10% 1	6921
	21st to end	Night	61% 5% 11% 18% 5%	6680
February	1st to 10th	Night	48% 6% 12% 22% 10% 1	2601
	11th to 20th	Night	45% 7% 10% 22% 14% 1	2534
	21st to end	Night	52% 6% 10% 20% 11% 1	2145
March	1st to 10th	Night	39% 5% 17% 22% 14% 2	5000
	11th to 20th	Night	53% 6% 9% 19% 13%	4980
	21st to end	Night	59% 4 9% 18% 9% 1	5467
April	1st to 10th	Night	47% 5% 11% 22% 15% 1	2030
	11th to 20th	Night	49% 5% 9% 21% 15% 1	1813
	21st to end	Night	49% 6% 12% 21% 13% 1	1800
May	1st to 10th	Night	37% 6% 13% 26% 17% 1	3856
	11th to 20th	Night	41% 5% 10% 22% 18% 3	3597
	21st to end	Night	42% 6% 10% 27% 13% 2	3862
June	1st to 10th	Night	33% 8% 20% 29% 8% 2	1400
	11th to 20th	Night	36% 7% 16% 25% 14% 2	1400
	21st to end	Night	32% 6% 19% 30% 11% 2	1400
July	1st to 10th	Night	30% 9% 22% 29% 10%	3145
	11th to 20th	Night	24% 6% 21% 37% 11% 1	3138
	21st to end	Night	33% 7% 19% 29% 12% 1	3787
August	1st to 10th	Night	30% 5% 18% 30% 16% 1	2916
	11th to 20th	Night	33% 6% 17% 34% 9% 1	2915
	21st to end	Night	35% 6% 18% 29% 11% 1	3261
September	1st to 10th	Night	31% 6% 16% 35% 11% 1	2000
	11th to 20th	Night	34% 6% 18% 31% 10%	2120
	21st to end	Night	35% 5% 12% 35% 13%	2215
October	1st to 10th	Night	30% 4 9% 36% 17% 4	3920
	11th to 20th	Night	42% 5% 10% 26% 16% 1	3899
	21st to end	Night	50% 4 13% 23% 9%	4374
November	1st to 10th	Night	51% 5% 10% 23% 9% 2	2869
	11th to 20th	Night	57% 5% 13% 16% 8% 1	2940
	21st to end	Night	54% 7% 15% 19% 5% 1	2940
December	1st to 10th	Night	65% 7% 12% 12% 3	4720
	11th to 20th	Night	63% 5% 9% 15% 8% 1	5700
	21st to end	Night	72% 4 7% 11% 5%	7645

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	13% 15% 36% 26% 8% 2	330
	11th to 20th	Day	15% 11% 38% 29% 7%	330
	21st to end	Day	12% 14% 38% 23% 10% 2	363
February	1st to 10th	Day	16% 16% 43% 19% 5% 1	300
	11th to 20th	Day	15% 18% 39% 18% 9% 2	300
	21st to end	Day	12% 15% 45% 22% 5% 1	249
March	1st to 10th	Day	16% 15% 43% 21% 5% 1	300
	11th to 20th	Day	17% 12% 37% 21% 10% 2	300
	21st to end	Day	21% 13% 36% 19% 9% 2	330
April	1st to 10th	Day	22% 16% 32% 23% 7%	470
	11th to 20th	Day	23% 16% 31% 20% 8% 1	650
	21st to end	Day	25% 11% 30% 20% 12% 1	700
May	1st to 10th	Day	20% 13% 32% 22% 10% 2	703
	11th to 20th	Day	20% 11% 31% 26% 10% 2	725
	21st to end	Day	18% 9% 29% 30% 13% 2	789
June	1st to 10th	Day	12% 10% 32% 29% 15% 3	730
	11th to 20th	Day	16% 12% 38% 25% 7% 2	730
	21st to end	Day	14% 9% 33% 26% 13% 5%	730
July	1st to 10th	Day	8% 7% 27% 27% 24% 7%	721
	11th to 20th	Day	11% 8% 28% 26% 21% 5%	718
	21st to end	Day	6% 6% 30% 30% 21% 7%	794
August	1st to 10th	Day	11% 6% 25% 33% 21% 5%	726
	11th to 20th	Day	15% 7% 23% 30% 18% 8%	715
	21st to end	Day	13% 9% 25% 31% 19% 4	787
September	1st to 10th	Day	11% 6% 33% 30% 17% 3	530
	11th to 20th	Day	15% 8% 28% 33% 13% 2	407
	21st to end	Day	17% 13% 33% 21% 12% 3	330
October	1st to 10th	Day	18% 8% 38% 23% 10% 3	330
	11th to 20th	Day	21% 17% 36% 22% 5%	330
	21st to end	Day	26% 17% 35% 15% 7% 1	363
November	1st to 10th	Day	19% 14% 37% 20% 8% 1	330
	11th to 20th	Day	18% 20% 40% 18% 3 1	330
	21st to end	Day	19% 19% 36% 21% 5%	330
December	1st to 10th	Day	15% 14% 42% 23% 6% 1	330
	11th to 20th	Day	18% 17% 38% 23% 5%	330
	21st to end	Day	20% 15% 37% 21% 5% 2	363
January	1st to 10th	Night	11% 13% 35% 29% 9% 2	1050
	11th to 20th	Night	14% 10% 40% 28% 7% 1	1050
	21st to end	Night	14% 13% 39% 26% 7% 1	1155
February	1st to 10th	Night	13% 13% 36% 29% 8% 1	1001
	11th to 20th	Night	10% 15% 42% 24% 8% 2	979
	21st to end	Night	13% 13% 36% 28% 8% 2	825
March	1st to 10th	Night	14% 12% 36% 27% 10% 1	644
	11th to 20th	Night	15% 11% 41% 27% 6% 1	600
	21st to end	Night	22% 9% 30% 25% 12% 2	660
April	1st to 10th	Night	18% 11% 35% 29% 7% 1	600
	11th to 20th	Night	21% 10% 34% 26% 8% 1	593
	21st to end	Night	22% 9% 30% 30% 9%	600
May	1st to 10th	Night	19% 8% 31% 32% 10% 1	600
	11th to 20th	Night	19% 8% 32% 30% 10% 1	591
	21st to end	Night	16% 7% 28% 36% 12%	650
June	1st to 10th	Night	15% 6% 31% 33% 15% 1	600
	11th to 20th	Night	12% 6% 31% 42% 8%	600
	21st to end	Night	11% 6% 27% 39% 16% 1	600
July	1st to 10th	Night	7% 3 22% 44% 23% 2	585
	11th to 20th	Night	7% 3 28% 42% 18% 1	582
	21st to end	Night	5% 2 28% 42% 20% 2	657
August	1st to 10th	Night	7% 2 22% 45% 22% 1	597
	11th to 20th	Night	14% 5% 18% 38% 23% 3	594
	21st to end	Night	11% 5% 26% 36% 20% 2	660
September	1st to 10th	Night	12% 5% 28% 37% 17% 2	600
	11th to 20th	Night	10% 7% 33% 35% 14% 1	600
	21st to end	Night	15% 7% 34% 29% 12% 2	615
October	1st to 10th	Night	18% 11% 33% 27% 10% 1	800
	11th to 20th	Night	20% 12% 35% 26% 7%	800
	21st to end	Night	24% 13% 33% 25% 5%	953
November	1st to 10th	Night	18% 11% 35% 28% 9%	1025
	11th to 20th	Night	18% 15% 34% 25% 7% 1	1050
	21st to end	Night	16% 15% 40% 22% 6%	1050
December	1st to 10th	Night	13% 14% 38% 27% 8% 1	1050
	11th to 20th	Night	19% 14% 36% 24% 5% 1	1050
	21st to end	Night	23% 11% 35% 23% 6% 1	1155

Page generated at 2026-01-29 00:21:47. Version ac07

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