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 2024-11-28.

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%	101937
	Night	11% 10% 4 9% 6% 5% 5% 4 5% 7% 35%	97720
Transparency	Day	46% 6% 13% 25% 9% 1	105473
	Night	47% 6% 12% 23% 10% 1	102276
Seeing	Day	16% 11% 32% 25% 12% 3	16197
	Night	15% 10% 33% 30% 11% 1	26123

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	6% 16% 6% 15% 8% 6% 6% 3 7% 7% 20%	2218
	11th to 20th	Day	5% 10% 4 14% 11% 11% 11% 6% 7% 5% 15%	2229
	21st to end	Day	6% 13% 10% 20% 8% 6% 5% 4 5% 6% 18%	3100
February	1st to 10th	Day	9% 12% 5% 11% 8% 6% 5% 5% 5% 7% 26%	1710
	11th to 20th	Day	7% 12% 4 9% 7% 6% 6% 5% 6% 8% 29%	1664
	21st to end	Day	8% 12% 4 10% 7% 6% 5% 4 6% 8% 29%	1423
March	1st to 10th	Day	11% 11% 4 10% 5% 5% 5% 3 5% 6% 35%	3375
	11th to 20th	Day	9% 9% 5% 11% 6% 4 4 3 6% 8% 34%	3480
	21st to end	Day	19% 13% 4 11% 6% 4 4 4 4 6% 27%	3814
April	1st to 10th	Day	15% 11% 4 9% 5% 5% 4 4 5% 5% 32%	2251
	11th to 20th	Day	17% 13% 4 9% 6% 4 4 4 4 6% 30%	2404
	21st to end	Day	22% 10% 3 7% 5% 4 4 3 5% 5% 32%	2470
May	1st to 10th	Day	18% 8% 2 6% 5% 4 5% 4 5% 7% 34%	4261
	11th to 20th	Day	15% 7% 2 6% 5% 5% 5% 4 6% 7% 38%	4399
	21st to end	Day	18% 7% 2 7% 4 4 5% 4 5% 7% 36%	4895
June	1st to 10th	Day	12% 6% 2 6% 5% 4 5% 4 7% 9% 40%	2850
	11th to 20th	Day	15% 7% 3 6% 5% 5% 5% 3 7% 7% 38%	2850
	21st to end	Day	12% 6% 2 7% 5% 5% 5% 4 8% 9% 38%	2850
July	1st to 10th	Day	7% 5% 3 7% 5% 6% 6% 5% 8% 10% 39%	4750
	11th to 20th	Day	7% 4 1 5% 3 4 5% 4 7% 10% 49%	4750
	21st to end	Day	6% 4 2 6% 5% 5% 5% 5% 7% 10% 45%	4831
August	1st to 10th	Day	10% 4 2 6% 4 5% 6% 5% 7% 8% 44%	4104
	11th to 20th	Day	12% 6% 2 6% 5% 5% 5% 4 6% 9% 39%	4041
	21st to end	Day	15% 7% 3 6% 4 4 4 3 6% 6% 44%	4504
September	1st to 10th	Day	12% 5% 2 5% 4 4 4 3 6% 9% 46%	2280
	11th to 20th	Day	13% 6% 2 7% 4 6% 4 4 6% 6% 43%	2163
	21st to end	Day	15% 9% 3 5% 4 3 4 3 5% 6% 42%	2057
October	1st to 10th	Day	17% 11% 3 5% 4 4 3 3 5% 5% 38%	1900
	11th to 20th	Day	17% 13% 4 7% 4 4 3 3 4 5% 36%	1900
	21st to end	Day	18% 13% 5% 9% 4 4 4 3 4 6% 29%	2019
November	1st to 10th	Day	12% 15% 5% 10% 6% 4 4 3 5% 5% 31%	1568
	11th to 20th	Day	12% 17% 6% 15% 6% 5% 3 4 4 5% 25%	1600
	21st to end	Day	11% 12% 7% 9% 7% 7% 5% 3 7% 6% 25%	1576
December	1st to 10th	Day	9% 15% 5% 14% 8% 6% 4 4 7% 6% 22%	1520
	11th to 20th	Day	8% 16% 6% 13% 7% 7% 6% 4 5% 4 23%	1689
	21st to end	Day	19% 15% 6% 13% 8% 4 4 3 4 4 20%	2442
January	1st to 10th	Night	6% 11% 5% 14% 10% 7% 6% 5% 7% 7% 22%	4737
	11th to 20th	Night	6% 10% 6% 13% 10% 9% 10% 6% 7% 6% 16%	4736
	21st to end	Night	7% 15% 10% 16% 7% 5% 5% 4 5% 6% 19%	4565
February	1st to 10th	Night	6% 10% 5% 9% 6% 6% 6% 5% 7% 9% 31%	2470
	11th to 20th	Night	5% 12% 3 9% 6% 5% 7% 6% 7% 7% 33%	2403
	21st to end	Night	9% 11% 3 11% 7% 6% 6% 4 6% 7% 30%	2041
March	1st to 10th	Night	8% 10% 3 9% 5% 4 5% 3 5% 8% 41%	3461
	11th to 20th	Night	9% 10% 3 13% 8% 6% 6% 3 4 5% 34%	3479
	21st to end	Night	17% 16% 6% 12% 5% 3 3 3 3 4 28%	3817
April	1st to 10th	Night	14% 11% 3 6% 5% 4 4 4 5% 6% 37%	1929
	11th to 20th	Night	16% 11% 4 8% 5% 4 3 3 4 5% 37%	1721
	21st to end	Night	18% 9% 3 7% 4 3 4 4 6% 6% 35%	1710
May	1st to 10th	Night	16% 10% 3 6% 4 4 4 3 4 6% 39%	2687
	11th to 20th	Night	15% 7% 2 5% 4 4 4 3 5% 7% 43%	2506
	21st to end	Night	17% 10% 2 7% 4 4 4 3 4 7% 38%	2688
June	1st to 10th	Night	11% 5% 2 5% 3 5% 4 5% 7% 9% 45%	1330
	11th to 20th	Night	10% 6% 2 6% 4 4 5% 5% 6% 7% 46%	1330
	21st to end	Night	9% 5% 1 5% 5% 4 5% 4 5% 10% 48%	1330
July	1st to 10th	Night	9% 4 1 5% 4 4 6% 5% 8% 10% 44%	2220
	11th to 20th	Night	4 3 1 4 3 3 4 3 5% 8% 64%	2220
	21st to end	Night	5% 3 2 4 4 3 4 5% 7% 10% 53%	2714
August	1st to 10th	Night	8% 5% 2 4 4 4 4 3 6% 8% 53%	2836
	11th to 20th	Night	13% 5% 2 4 3 4 4 3 6% 9% 47%	2798
	21st to end	Night	12% 7% 2 6% 4 3 4 3 5% 8% 47%	3161
September	1st to 10th	Night	10% 4 2 6% 4 3 4 4 6% 7% 51%	1900
	11th to 20th	Night	9% 6% 2 6% 4 4 3 3 5% 7% 50%	2014
	21st to end	Night	14% 7% 2 5% 3 3 3 2 4 7% 49%	2104
October	1st to 10th	Night	14% 8% 2 6% 4 4 5% 3 5% 6% 41%	2280
	11th to 20th	Night	15% 10% 3 7% 5% 4 4 4 5% 6% 38%	2280
	21st to end	Night	17% 12% 4 9% 5% 3 5% 3 4 6% 31%	2577
November	1st to 10th	Night	11% 13% 5% 9% 5% 4 4 3 5% 7% 32%	2729
	11th to 20th	Night	12% 14% 6% 13% 6% 4 4 4 5% 6% 26%	2800
	21st to end	Night	11% 10% 4 11% 7% 5% 5% 5% 5% 7% 30%	2759
December	1st to 10th	Night	8% 14% 6% 12% 8% 7% 6% 5% 7% 7% 21%	2660
	11th to 20th	Night	10% 14% 6% 15% 7% 6% 5% 5% 5% 5% 22%	3503
	21st to end	Night	19% 16% 7% 11% 7% 5% 4 3 5% 6% 19%	5225

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	60% 6% 10% 19% 5%	2219
	11th to 20th	Day	66% 5% 8% 17% 4	2229
	21st to end	Day	67% 5% 8% 14% 7%	3100
February	1st to 10th	Day	56% 5% 9% 19% 11%	1710
	11th to 20th	Day	51% 6% 12% 19% 10% 2	1673
	21st to end	Day	52% 7% 12% 17% 12%	1423
March	1st to 10th	Day	49% 5% 10% 26% 9%	3377
	11th to 20th	Day	47% 6% 12% 27% 8%	3480
	21st to end	Day	59% 5% 10% 22% 4	3814
April	1st to 10th	Day	53% 5% 10% 19% 12% 2	2251
	11th to 20th	Day	54% 6% 11% 18% 10% 1	2404
	21st to end	Day	54% 5% 12% 20% 10% 1	2470
May	1st to 10th	Day	45% 7% 14% 23% 10% 1	4272
	11th to 20th	Day	42% 7% 14% 26% 10% 2	4403
	21st to end	Day	45% 7% 11% 28% 7% 1	4895
June	1st to 10th	Day	38% 8% 18% 26% 10%	2850
	11th to 20th	Day	44% 7% 13% 24% 12% 1	2850
	21st to end	Day	40% 8% 16% 27% 9%	2850
July	1st to 10th	Day	37% 9% 18% 26% 10% 1	4676
	11th to 20th	Day	27% 8% 19% 35% 11% 1	4669
	21st to end	Day	32% 8% 18% 32% 9% 1	4677
August	1st to 10th	Day	34% 7% 16% 29% 13% 1	4090
	11th to 20th	Day	40% 7% 16% 29% 8%	4080
	21st to end	Day	39% 6% 17% 28% 9% 1	4503
September	1st to 10th	Day	36% 5% 15% 34% 10%	2280
	11th to 20th	Day	41% 5% 19% 26% 8%	2163
	21st to end	Day	43% 5% 13% 30% 8% 1	2057
October	1st to 10th	Day	35% 4 14% 32% 15% 1	3160
	11th to 20th	Day	45% 5% 9% 22% 18% 1	3140
	21st to end	Day	54% 4 12% 24% 6%	3312
November	1st to 10th	Day	54% 6% 11% 18% 10% 1	1568
	11th to 20th	Day	62% 5% 11% 15% 7% 1	1600
	21st to end	Day	56% 7% 16% 13% 7% 1	1576
December	1st to 10th	Day	61% 5% 12% 16% 5%	1520
	11th to 20th	Day	62% 5% 11% 18% 4	1690
	21st to end	Day	68% 4 6% 16% 6%	2442
January	1st to 10th	Night	58% 6% 9% 20% 5%	4737
	11th to 20th	Night	64% 7% 10% 13% 5% 1	4736
	21st to end	Night	65% 5% 8% 17% 5%	4565
February	1st to 10th	Night	47% 6% 13% 24% 10% 1	2470
	11th to 20th	Night	46% 8% 11% 22% 12% 1	2404
	21st to end	Night	52% 6% 10% 20% 11% 1	2041
March	1st to 10th	Night	41% 6% 15% 23% 13% 2	3472
	11th to 20th	Night	50% 7% 9% 22% 11% 1	3480
	21st to end	Night	61% 5% 9% 17% 8% 1	3817
April	1st to 10th	Night	47% 5% 11% 22% 15% 1	1929
	11th to 20th	Night	49% 5% 9% 21% 15% 2	1721
	21st to end	Night	48% 6% 12% 21% 12% 1	1710
May	1st to 10th	Night	44% 8% 12% 25% 11% 1	2696
	11th to 20th	Night	40% 6% 11% 25% 15% 3	2507
	21st to end	Night	45% 7% 11% 25% 10% 1	2689
June	1st to 10th	Night	33% 8% 21% 29% 8% 1	1330
	11th to 20th	Night	36% 7% 16% 25% 15% 2	1330
	21st to end	Night	32% 6% 19% 31% 10% 2	1330
July	1st to 10th	Night	32% 10% 21% 24% 12%	2185
	11th to 20th	Night	19% 5% 17% 43% 15% 1	2178
	21st to end	Night	25% 8% 19% 34% 13% 1	2628
August	1st to 10th	Night	29% 6% 18% 31% 15% 2	2826
	11th to 20th	Night	33% 7% 17% 34% 9% 1	2825
	21st to end	Night	35% 6% 18% 29% 11% 1	3161
September	1st to 10th	Night	31% 7% 15% 35% 11% 1	1900
	11th to 20th	Night	33% 6% 18% 31% 10%	2014
	21st to end	Night	36% 5% 12% 34% 12%	2104
October	1st to 10th	Night	31% 4 8% 36% 17% 4	3800
	11th to 20th	Night	42% 5% 10% 26% 16% 1	3779
	21st to end	Night	50% 4 12% 23% 10%	4238
November	1st to 10th	Night	51% 5% 10% 23% 9% 1	2729
	11th to 20th	Night	59% 5% 13% 15% 8% 1	2800
	21st to end	Night	53% 7% 15% 19% 6% 1	2759
December	1st to 10th	Night	59% 7% 13% 15% 5%	2660
	11th to 20th	Night	61% 6% 11% 15% 6% 1	3501
	21st to end	Night	67% 5% 9% 13% 7%	5225

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	14% 13% 33% 28% 9% 2	270
	11th to 20th	Day	14% 10% 37% 31% 7%	270
	21st to end	Day	12% 11% 36% 26% 11% 3	297
February	1st to 10th	Day	16% 15% 44% 20% 5% 1	270
	11th to 20th	Day	16% 17% 39% 17% 9% 1	270
	21st to end	Day	14% 13% 43% 23% 6% 1	225
March	1st to 10th	Day	16% 14% 42% 22% 4 1	270
	11th to 20th	Day	17% 11% 38% 21% 11% 2	270
	21st to end	Day	22% 11% 35% 21% 10% 2	297
April	1st to 10th	Day	22% 16% 33% 22% 7%	431
	11th to 20th	Day	24% 15% 30% 21% 9% 1	602
	21st to end	Day	25% 10% 30% 20% 13% 1	650
May	1st to 10th	Day	21% 14% 32% 22% 10% 1	653
	11th to 20th	Day	19% 11% 31% 26% 11% 3	675
	21st to end	Day	18% 9% 29% 29% 12% 2	734
June	1st to 10th	Day	12% 10% 31% 29% 14% 4	680
	11th to 20th	Day	16% 12% 37% 26% 7% 2	680
	21st to end	Day	13% 8% 33% 26% 13% 6%	680
July	1st to 10th	Day	8% 7% 26% 27% 25% 7%	671
	11th to 20th	Day	10% 8% 27% 27% 22% 6%	668
	21st to end	Day	6% 5% 30% 30% 22% 7%	739
August	1st to 10th	Day	11% 5% 25% 33% 22% 5%	676
	11th to 20th	Day	15% 6% 23% 31% 18% 8%	665
	21st to end	Day	14% 8% 25% 30% 18% 4	733
September	1st to 10th	Day	11% 6% 34% 30% 17% 2	490
	11th to 20th	Day	14% 8% 29% 32% 14% 2	373
	21st to end	Day	19% 14% 34% 21% 12% 1	300
October	1st to 10th	Day	20% 8% 36% 22% 11% 3	300
	11th to 20th	Day	19% 14% 38% 23% 5%	300
	21st to end	Day	25% 17% 35% 15% 7% 1	330
November	1st to 10th	Day	20% 12% 37% 21% 9% 1	300
	11th to 20th	Day	20% 19% 39% 19% 3	300
	21st to end	Day	20% 19% 37% 21% 4	291
December	1st to 10th	Day	14% 14% 42% 23% 6% 1	270
	11th to 20th	Day	15% 15% 41% 24% 5%	270
	21st to end	Day	21% 15% 35% 23% 4 2	297
January	1st to 10th	Night	12% 12% 35% 29% 10% 2	950
	11th to 20th	Night	15% 9% 39% 29% 7% 1	950
	21st to end	Night	15% 12% 38% 26% 7% 1	1045
February	1st to 10th	Night	12% 13% 35% 30% 9% 1	950
	11th to 20th	Night	11% 14% 41% 24% 8% 2	929
	21st to end	Night	13% 12% 36% 28% 8% 2	785
March	1st to 10th	Night	15% 12% 36% 26% 11% 1	612
	11th to 20th	Night	15% 10% 41% 27% 6% 1	570
	21st to end	Night	22% 9% 29% 25% 13% 2	627
April	1st to 10th	Night	18% 10% 36% 29% 6% 1	570
	11th to 20th	Night	22% 9% 33% 26% 9% 1	563
	21st to end	Night	21% 9% 30% 30% 10%	570
May	1st to 10th	Night	19% 8% 32% 31% 9% 1	570
	11th to 20th	Night	19% 7% 32% 30% 11% 1	561
	21st to end	Night	16% 7% 29% 35% 13%	617
June	1st to 10th	Night	15% 6% 31% 32% 15% 1	570
	11th to 20th	Night	12% 6% 31% 42% 9%	570
	21st to end	Night	11% 6% 26% 40% 16% 1	570
July	1st to 10th	Night	7% 2 22% 44% 23% 2	555
	11th to 20th	Night	7% 3 28% 42% 19% 1	552
	21st to end	Night	5% 2 28% 41% 21% 2	624
August	1st to 10th	Night	6% 2 23% 46% 22% 1	567
	11th to 20th	Night	14% 5% 18% 38% 23% 2	564
	21st to end	Night	12% 5% 27% 35% 20% 2	627
September	1st to 10th	Night	11% 5% 29% 37% 16% 2	570
	11th to 20th	Night	9% 7% 33% 34% 15% 1	570
	21st to end	Night	15% 8% 35% 29% 12% 2	584
October	1st to 10th	Night	19% 10% 32% 28% 9% 1	760
	11th to 20th	Night	19% 11% 36% 26% 7%	760
	21st to end	Night	24% 12% 34% 25% 5%	905
November	1st to 10th	Night	18% 10% 34% 28% 9%	975
	11th to 20th	Night	18% 15% 34% 25% 7% 1	1000
	21st to end	Night	17% 15% 39% 23% 6%	986
December	1st to 10th	Night	13% 14% 36% 28% 9% 1	950
	11th to 20th	Night	19% 12% 37% 25% 6% 1	950
	21st to end	Night	25% 10% 35% 23% 6% 1	1045

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