Lost Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lost Lake clear sky chart from 2005-11-06 to 2025-07-06.

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	10% 15% 5% 10% 4 4 3 3 4 5% 36%	124180
	Night	11% 16% 6% 12% 5% 4 3 3 4 5% 32%	123410
Transparency	Day	49% 7% 9% 17% 13% 6%	123924
	Night	52% 8% 9% 15% 12% 5%	123253
Seeing	Day	22% 21% 31% 18% 6% 1	15367
	Night	22% 18% 23% 24% 11% 2	24370

By Month

Percentage Cloud Cover SW (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	18% 31% 9% 13% 5% 3 3 2 3 6% 8%	3639
	11th to 20th	Day	14% 15% 5% 11% 6% 4 3 2 4 4 31%	3640
	21st to end	Day	15% 18% 6% 10% 4 3 3 2 3 5% 31%	4257
February	1st to 10th	Day	15% 21% 9% 16% 6% 3 3 3 5% 4 16%	1800
	11th to 20th	Day	11% 24% 8% 16% 6% 4 4 3 3 4 17%	1755
	21st to end	Day	11% 28% 8% 14% 5% 4 3 2 3 4 18%	1607
March	1st to 10th	Day	7% 17% 8% 15% 6% 5% 6% 4 5% 6% 20%	4606
	11th to 20th	Day	8% 26% 9% 15% 5% 3 2 2 2 3 26%	5000
	21st to end	Day	9% 26% 9% 17% 6% 6% 5% 3 4 3 11%	5695
April	1st to 10th	Day	14% 27% 8% 13% 5% 4 3 3 4 4 16%	2400
	11th to 20th	Day	14% 23% 6% 12% 5% 4 3 2 3 4 24%	2369
	21st to end	Day	13% 23% 6% 11% 4 4 4 3 4 5% 23%	2543
May	1st to 10th	Day	10% 16% 4 9% 4 3 3 2 3 4 41%	6320
	11th to 20th	Day	9% 18% 9% 11% 5% 4 3 3 4 4 30%	6277
	21st to end	Day	11% 15% 5% 10% 5% 4 4 3 5% 7% 31%	6902
June	1st to 10th	Day	19% 13% 4 7% 4 4 4 3 4 5% 33%	2800
	11th to 20th	Day	15% 14% 5% 10% 5% 4 5% 4 5% 6% 28%	2800
	21st to end	Day	9% 7% 2 6% 4 3 4 3 5% 7% 50%	2800
July	1st to 10th	Day	2 3 1 2 2 2 2 2 4 5% 73%	4491
	11th to 20th	Day	4 3 1 2 2 2 2 2 3 4 77%	4420
	21st to end	Day	3 3 2 3 2 1 2 2 4 5% 73%	4790
August	1st to 10th	Day	2 3 2 5% 4 3 3 2 3 5% 68%	4228
	11th to 20th	Day	3 3 1 6% 4 4 5% 4 5% 7% 59%	4026
	21st to end	Day	7% 6% 2 6% 4 3 4 3 5% 6% 55%	4242
September	1st to 10th	Day	5% 4 2 5% 3 2 3 3 5% 6% 62%	2280
	11th to 20th	Day	10% 7% 3 7% 4 4 5% 4 5% 6% 46%	2280
	21st to end	Day	11% 9% 3 7% 4 3 4 3 4 5% 47%	2019
October	1st to 10th	Day	10% 9% 3 6% 4 3 3 3 4 5% 50%	3180
	11th to 20th	Day	10% 12% 6% 10% 5% 5% 4 3 4 7% 32%	3161
	21st to end	Day	13% 16% 10% 15% 5% 5% 4 3 5% 5% 21%	3295
November	1st to 10th	Day	18% 22% 7% 13% 5% 4 4 2 5% 5% 17%	1706
	11th to 20th	Day	17% 24% 6% 14% 4 4 5% 3 4 5% 15%	1600
	21st to end	Day	15% 20% 6% 12% 5% 4 4 3 4 5% 23%	1600
December	1st to 10th	Day	10% 15% 5% 10% 4 4 3 3 5% 7% 35%	2620
	11th to 20th	Day	16% 23% 8% 15% 7% 4 3 3 5% 5% 9%	3028
	21st to end	Day	13% 26% 9% 15% 6% 5% 4 3 3 3 13%	4004
January	1st to 10th	Night	18% 27% 8% 13% 5% 4 4 3 4 5% 10%	6306
	11th to 20th	Night	14% 18% 5% 11% 5% 3 3 2 4 5% 30%	6320
	21st to end	Night	14% 15% 5% 12% 4 3 3 2 3 4 32%	6707
February	1st to 10th	Night	13% 20% 8% 16% 6% 4 4 3 4 4 18%	2600
	11th to 20th	Night	12% 22% 8% 15% 5% 3 3 2 4 3 22%	2532
	21st to end	Night	12% 25% 9% 13% 6% 4 3 2 4 5% 18%	2022
March	1st to 10th	Night	6% 15% 7% 18% 7% 5% 6% 4 5% 6% 20%	5274
	11th to 20th	Night	8% 19% 8% 17% 6% 4 3 2 2 3 28%	5000
	21st to end	Night	9% 26% 9% 18% 6% 5% 4 3 5% 5% 12%	5280
April	1st to 10th	Night	12% 26% 9% 12% 6% 4 3 3 3 4 18%	2000
	11th to 20th	Night	12% 19% 6% 11% 5% 4 4 3 4 5% 27%	1979
	21st to end	Night	13% 22% 4 11% 5% 4 4 2 5% 6% 24%	1851
May	1st to 10th	Night	13% 19% 5% 8% 4 2 2 2 3 5% 38%	3640
	11th to 20th	Night	7% 22% 8% 13% 6% 3 3 2 3 3 30%	3616
	21st to end	Night	11% 19% 4 9% 4 3 4 4 6% 7% 29%	3972
June	1st to 10th	Night	20% 13% 3 8% 4 3 4 3 5% 4 34%	1600
	11th to 20th	Night	12% 15% 5% 10% 4 5% 4 3 4 6% 33%	1600
	21st to end	Night	8% 6% 3 7% 6% 4 4 3 4 7% 50%	1600
July	1st to 10th	Night	3 3 1 3 2 1 2 2 3 4 76%	2580
	11th to 20th	Night	2 2 1 3 3 1 2 2 3 3 75%	2540
	21st to end	Night	2 3 2 3 2 1 2 2 3 4 76%	2761
August	1st to 10th	Night	3 3 1 4 3 2 2 2 4 6% 69%	2704
	11th to 20th	Night	3 3 3 10% 5% 4 3 3 4 6% 56%	2812
	21st to end	Night	5% 7% 3 8% 3 2 3 3 3 4 58%	3434
September	1st to 10th	Night	5% 4 2 6% 3 3 3 3 5% 7% 61%	1900
	11th to 20th	Night	8% 9% 4 9% 4 3 3 3 4 5% 47%	1900
	21st to end	Night	11% 8% 3 9% 3 3 4 3 4 7% 46%	2157
October	1st to 10th	Night	10% 9% 3 6% 3 2 3 3 4 6% 51%	3800
	11th to 20th	Night	10% 11% 6% 10% 4 4 4 4 6% 7% 34%	3777
	21st to end	Night	13% 15% 9% 16% 5% 4 3 3 4 4 24%	4268
November	1st to 10th	Night	19% 19% 6% 13% 6% 4 3 3 3 5% 19%	2590
	11th to 20th	Night	18% 19% 7% 15% 5% 4 4 3 4 4 18%	2800
	21st to end	Night	12% 18% 6% 14% 5% 4 4 3 5% 4 25%	2800
December	1st to 10th	Night	9% 13% 4 13% 5% 3 3 3 4 7% 36%	4560
	11th to 20th	Night	17% 23% 7% 16% 6% 5% 4 3 4 5% 12%	5176
	21st to end	Night	18% 22% 7% 16% 5% 4 4 2 3 4 13%	6952

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	80% 5% 7% 7% 2	3639
	11th to 20th	Day	54% 8% 6% 15% 14% 2	3640
	21st to end	Day	58% 5% 5% 11% 15% 6%	4257
February	1st to 10th	Day	71% 7% 9% 9% 3	1800
	11th to 20th	Day	71% 6% 7% 10% 5% 1	1764
	21st to end	Day	70% 6% 8% 7% 8% 1	1607
March	1st to 10th	Day	61% 7% 12% 12% 7% 2	4606
	11th to 20th	Day	63% 8% 4 20% 5%	5000
	21st to end	Day	73% 10% 8% 6% 3	5695
April	1st to 10th	Day	73% 5% 9% 11% 2	2400
	11th to 20th	Day	65% 4 9% 12% 8% 2	2372
	21st to end	Day	63% 7% 9% 13% 6% 1	2543
May	1st to 10th	Day	46% 4 9% 25% 14% 1	6320
	11th to 20th	Day	49% 13% 14% 17% 7%	6280
	21st to end	Day	49% 10% 18% 19% 3 1	6904
June	1st to 10th	Day	53% 6% 12% 19% 9% 1	2800
	11th to 20th	Day	54% 8% 13% 15% 8% 1	2800
	21st to end	Day	32% 7% 15% 28% 14% 4	2800
July	1st to 10th	Day	14% 4 8% 15% 26% 33%	4422
	11th to 20th	Day	13% 3 5% 13% 26% 41%	4345
	21st to end	Day	12% 6% 8% 22% 37% 15%	4639
August	1st to 10th	Day	20% 4 7% 20% 30% 19%	4212
	11th to 20th	Day	20% 9% 12% 37% 16% 5%	4065
	21st to end	Day	28% 7% 10% 24% 26% 6%	4241
September	1st to 10th	Day	23% 4 10% 27% 24% 12%	2280
	11th to 20th	Day	37% 7% 11% 20% 18% 7%	2280
	21st to end	Day	40% 6% 10% 23% 15% 6%	2019
October	1st to 10th	Day	35% 7% 5% 23% 25% 5%	3180
	11th to 20th	Day	49% 9% 11% 18% 12% 1	3161
	21st to end	Day	56% 14% 5% 16% 8%	3295
November	1st to 10th	Day	71% 5% 8% 12% 4	1706
	11th to 20th	Day	70% 8% 8% 10% 4 1	1600
	21st to end	Day	64% 6% 7% 11% 10% 1	1600
December	1st to 10th	Day	48% 7% 7% 15% 20% 4	2620
	11th to 20th	Day	74% 10% 8% 7% 2	3028
	21st to end	Day	71% 11% 7% 9% 2	4004
January	1st to 10th	Night	76% 7% 7% 7% 3	6306
	11th to 20th	Night	54% 9% 6% 15% 13% 2	6320
	21st to end	Night	57% 5% 5% 10% 16% 7%	6707
February	1st to 10th	Night	71% 7% 8% 10% 5%	2600
	11th to 20th	Night	67% 5% 8% 11% 6% 1	2534
	21st to end	Night	69% 5% 7% 11% 7% 1	2022
March	1st to 10th	Night	59% 9% 12% 13% 4 3	5274
	11th to 20th	Night	56% 11% 9% 18% 7% 1	5000
	21st to end	Night	70% 11% 9% 8% 1	5280
April	1st to 10th	Night	69% 8% 9% 10% 4	2000
	11th to 20th	Night	60% 5% 12% 12% 8% 3	1979
	21st to end	Night	62% 6% 10% 13% 8% 1	1851
May	1st to 10th	Night	49% 5% 7% 22% 17%	3637
	11th to 20th	Night	52% 13% 12% 18% 5% 1	3616
	21st to end	Night	49% 11% 18% 16% 4 1	3972
June	1st to 10th	Night	54% 5% 12% 21% 7% 1	1600
	11th to 20th	Night	52% 7% 14% 19% 8% 1	1600
	21st to end	Night	33% 7% 14% 26% 16% 4	1600
July	1st to 10th	Night	14% 4 7% 15% 29% 31%	2540
	11th to 20th	Night	14% 3 6% 14% 24% 38%	2492
	21st to end	Night	11% 6% 9% 18% 38% 19%	2674
August	1st to 10th	Night	18% 4 8% 20% 28% 23%	2696
	11th to 20th	Night	17% 17% 13% 29% 18% 5%	2839
	21st to end	Night	25% 10% 10% 24% 22% 10%	3434
September	1st to 10th	Night	22% 5% 13% 24% 23% 13%	1900
	11th to 20th	Night	39% 6% 9% 19% 15% 11%	1900
	21st to end	Night	39% 5% 12% 20% 16% 8%	2157
October	1st to 10th	Night	33% 6% 7% 22% 29% 3	3800
	11th to 20th	Night	44% 9% 13% 19% 13% 2	3777
	21st to end	Night	56% 13% 5% 14% 10% 1	4268
November	1st to 10th	Night	70% 4 7% 13% 6% 1	2590
	11th to 20th	Night	68% 8% 7% 9% 7%	2800
	21st to end	Night	62% 6% 7% 13% 11% 1	2800
December	1st to 10th	Night	44% 11% 7% 16% 19% 4	4560
	11th to 20th	Night	73% 10% 7% 7% 3	5176
	21st to end	Night	70% 13% 8% 7% 2	6952

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	37% 30% 19% 10% 4	200
	11th to 20th	Day	32% 23% 30% 10% 5% 1	200
	21st to end	Day	31% 23% 24% 17% 4	330
February	1st to 10th	Day	31% 31% 25% 11% 3	400
	11th to 20th	Day	32% 32% 25% 10% 1 1	395
	21st to end	Day	35% 26% 26% 11% 2	393
March	1st to 10th	Day	28% 30% 29% 8% 4	500
	11th to 20th	Day	31% 25% 26% 12% 5% 1	500
	21st to end	Day	37% 27% 23% 11% 2	550
April	1st to 10th	Day	34% 25% 24% 12% 5%	500
	11th to 20th	Day	29% 30% 26% 11% 2 2	492
	21st to end	Day	28% 24% 32% 13% 2 1	500
May	1st to 10th	Day	27% 20% 32% 15% 6% 1	503
	11th to 20th	Day	28% 20% 27% 18% 6% 2	528
	21st to end	Day	24% 16% 32% 21% 6% 2	573
June	1st to 10th	Day	21% 20% 31% 19% 7% 2	530
	11th to 20th	Day	25% 26% 32% 12% 5% 1	530
	21st to end	Day	11% 17% 38% 24% 9% 1	530
July	1st to 10th	Day	7% 15% 45% 27% 5% 1	507
	11th to 20th	Day	6% 16% 43% 25% 8% 2	484
	21st to end	Day	5% 12% 41% 26% 13% 4	531
August	1st to 10th	Day	3 12% 42% 27% 11% 5%	487
	11th to 20th	Day	4 13% 36% 32% 11% 4	477
	21st to end	Day	9% 19% 37% 24% 9% 3	539
September	1st to 10th	Day	7% 17% 37% 27% 10% 2	490
	11th to 20th	Day	16% 17% 35% 25% 7% 1	490
	21st to end	Day	17% 18% 33% 23% 8% 1	490
October	1st to 10th	Day	21% 17% 31% 23% 8% 1	490
	11th to 20th	Day	24% 21% 26% 20% 8% 2	490
	21st to end	Day	32% 22% 25% 13% 6% 2	448
November	1st to 10th	Day	32% 22% 24% 18% 4	270
	11th to 20th	Day	32% 27% 23% 13% 4 2	200
	21st to end	Day	25% 24% 31% 17% 4	200
December	1st to 10th	Day	30% 18% 26% 20% 5% 2	200
	11th to 20th	Day	34% 29% 28% 9% 2	200
	21st to end	Day	38% 27% 18% 14% 3 1	220
January	1st to 10th	Night	32% 25% 21% 15% 6%	800
	11th to 20th	Night	28% 21% 23% 21% 7% 1	800
	21st to end	Night	25% 19% 25% 23% 7% 1	880
February	1st to 10th	Night	25% 22% 25% 21% 7% 1	800
	11th to 20th	Night	28% 25% 19% 21% 6%	784
	21st to end	Night	29% 24% 22% 20% 4	660
March	1st to 10th	Night	23% 25% 22% 22% 9% 1	800
	11th to 20th	Night	23% 23% 24% 22% 8% 1	800
	21st to end	Night	29% 24% 22% 16% 8% 1	880
April	1st to 10th	Night	28% 19% 24% 19% 8% 1	800
	11th to 20th	Night	26% 21% 24% 18% 9% 3	791
	21st to end	Night	25% 18% 25% 21% 10% 1	651
May	1st to 10th	Night	25% 14% 22% 24% 14% 2	400
	11th to 20th	Night	20% 13% 21% 29% 15% 2	394
	21st to end	Night	18% 15% 22% 28% 15% 2	433
June	1st to 10th	Night	27% 13% 20% 24% 14% 2	400
	11th to 20th	Night	19% 19% 29% 23% 10%	400
	21st to end	Night	12% 11% 27% 33% 17% 1	400
July	1st to 10th	Night	8% 7% 31% 35% 19%	380
	11th to 20th	Night	4 8% 37% 34% 15% 2	368
	21st to end	Night	3 7% 27% 43% 18% 2	416
August	1st to 10th	Night	4 8% 24% 38% 21% 4	475
	11th to 20th	Night	5% 6% 20% 34% 26% 9%	564
	21st to end	Night	7% 10% 30% 31% 19% 4	798
September	1st to 10th	Night	8% 8% 24% 36% 21% 3	760
	11th to 20th	Night	12% 12% 21% 29% 22% 4	760
	21st to end	Night	15% 9% 24% 29% 19% 3	760
October	1st to 10th	Night	18% 13% 23% 29% 15% 4	760
	11th to 20th	Night	19% 15% 18% 27% 17% 3	760
	21st to end	Night	25% 21% 19% 20% 10% 3	836
November	1st to 10th	Night	30% 21% 19% 23% 7% 1	780
	11th to 20th	Night	30% 24% 23% 18% 5% 1	800
	21st to end	Night	20% 25% 24% 23% 7% 1	800
December	1st to 10th	Night	23% 21% 26% 21% 8% 1	800
	11th to 20th	Night	31% 22% 24% 19% 4	800
	21st to end	Night	34% 26% 22% 14% 3 1	880

Page generated at 2025-07-02 22:30:17. Version ac07

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