Silent Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Silent Lake clear sky chart from 2005-11-06 to 2024-12-24.

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	16% 11% 4 8% 5% 4 4 4 5% 6% 32%	101959
	Night	16% 12% 4 9% 5% 4 4 3 5% 6% 31%	98161
Transparency	Day	52% 4 10% 22% 11% 1	105530
	Night	53% 4 11% 21% 11% 1	102678
Seeing	Day	25% 14% 31% 19% 8% 3	14508
	Night	23% 12% 30% 24% 10% 1	23823

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	15% 21% 6% 16% 5% 3 3 2 3 4 22%	2517
	11th to 20th	Day	12% 17% 9% 19% 8% 6% 4 3 3 4 14%	2524
	21st to end	Day	19% 21% 8% 14% 5% 4 3 3 3 3 18%	3124
February	1st to 10th	Day	12% 16% 7% 17% 7% 4 4 4 4 4 20%	1710
	11th to 20th	Day	12% 16% 6% 13% 7% 4 4 3 3 5% 27%	1663
	21st to end	Day	16% 17% 5% 10% 7% 4 4 3 4 5% 23%	1479
March	1st to 10th	Day	18% 16% 5% 8% 5% 4 4 3 4 6% 27%	3337
	11th to 20th	Day	11% 19% 5% 11% 6% 4 3 4 5% 6% 26%	3480
	21st to end	Day	13% 11% 3 7% 4 4 3 3 4 5% 43%	3868
April	1st to 10th	Day	20% 14% 4 7% 5% 4 5% 3 4 5% 29%	2280
	11th to 20th	Day	23% 11% 3 6% 5% 3 4 3 4 4 36%	2269
	21st to end	Day	22% 11% 3 8% 4 4 4 3 4 5% 32%	2470
May	1st to 10th	Day	21% 8% 3 7% 4 5% 5% 3 5% 7% 34%	4295
	11th to 20th	Day	17% 9% 3 7% 5% 4 4 3 6% 8% 32%	4398
	21st to end	Day	16% 6% 2 6% 4 4 4 4 5% 7% 41%	4837
June	1st to 10th	Day	21% 9% 3 7% 6% 4 4 4 5% 7% 30%	2660
	11th to 20th	Day	16% 6% 2 7% 5% 6% 5% 4 6% 7% 36%	2660
	21st to end	Day	18% 8% 2 5% 5% 5% 4 4 5% 8% 34%	2660
July	1st to 10th	Day	13% 6% 3 7% 5% 5% 5% 5% 7% 10% 35%	4440
	11th to 20th	Day	12% 6% 2 6% 4 4 6% 4 6% 8% 42%	4440
	21st to end	Day	9% 6% 2 6% 5% 5% 5% 4 7% 9% 43%	4784
August	1st to 10th	Day	16% 8% 3 8% 5% 5% 6% 4 6% 7% 33%	4104
	11th to 20th	Day	16% 7% 3 7% 5% 5% 5% 5% 7% 8% 33%	4044
	21st to end	Day	11% 6% 2 6% 4 5% 5% 5% 7% 9% 40%	4285
September	1st to 10th	Day	15% 7% 2 6% 5% 4 4 4 6% 7% 40%	2280
	11th to 20th	Day	13% 6% 2 6% 5% 4 4 3 5% 7% 45%	2266
	21st to end	Day	18% 7% 2 7% 5% 4 5% 4 5% 7% 35%	1990
October	1st to 10th	Day	21% 9% 3 8% 4 4 4 3 5% 6% 33%	1900
	11th to 20th	Day	24% 12% 3 9% 4 5% 4 3 4 5% 26%	1900
	21st to end	Day	27% 12% 4 9% 5% 4 4 3 4 5% 23%	2057
November	1st to 10th	Day	17% 13% 4 8% 5% 5% 4 4 5% 5% 32%	1656
	11th to 20th	Day	17% 15% 5% 8% 6% 5% 5% 4 6% 5% 25%	1600
	21st to end	Day	20% 20% 7% 11% 6% 3 5% 3 4 5% 16%	1600
December	1st to 10th	Day	18% 24% 7% 13% 6% 4 3 4 3 5% 14%	1600
	11th to 20th	Day	17% 19% 6% 12% 5% 4 3 2 4 4 23%	1986
	21st to end	Day	24% 22% 7% 12% 4 3 3 2 3 4 17%	2796
January	1st to 10th	Night	17% 19% 9% 13% 5% 5% 4 3 4 5% 16%	4429
	11th to 20th	Night	12% 14% 6% 18% 11% 7% 5% 3 4 4 15%	4434
	21st to end	Night	18% 15% 7% 14% 6% 6% 4 3 4 4 17%	4532
February	1st to 10th	Night	12% 16% 6% 11% 9% 5% 5% 4 6% 6% 20%	2470
	11th to 20th	Night	12% 14% 6% 12% 6% 5% 5% 3 4 5% 28%	2403
	21st to end	Night	14% 15% 4 9% 7% 4 4 4 5% 6% 26%	1975
March	1st to 10th	Night	17% 14% 4 11% 5% 4 4 3 4 5% 29%	3500
	11th to 20th	Night	13% 17% 7% 9% 5% 5% 4 4 5% 6% 26%	3479
	21st to end	Night	15% 7% 3 8% 6% 4 4 4 5% 7% 37%	3763
April	1st to 10th	Night	20% 13% 4 8% 5% 4 4 3 4 5% 31%	1900
	11th to 20th	Night	18% 9% 3 7% 5% 3 4 3 5% 5% 37%	1875
	21st to end	Night	19% 10% 3 7% 5% 4 5% 3 6% 5% 32%	1710
May	1st to 10th	Night	21% 8% 2 6% 3 4 4 4 5% 6% 36%	2643
	11th to 20th	Night	17% 8% 2 7% 4 5% 5% 4 5% 7% 36%	2495
	21st to end	Night	12% 7% 2 6% 5% 4 4 4 4 7% 45%	2738
June	1st to 10th	Night	16% 8% 2 7% 5% 5% 4 3 6% 7% 36%	1520
	11th to 20th	Night	12% 5% 3 5% 5% 5% 5% 3 6% 7% 44%	1520
	21st to end	Night	16% 8% 2 8% 4 5% 3 4 5% 6% 39%	1520
July	1st to 10th	Night	9% 6% 2 8% 6% 6% 5% 4 6% 8% 41%	2520
	11th to 20th	Night	15% 7% 2 5% 4 4 4 3 5% 7% 46%	2520
	21st to end	Night	10% 6% 2 5% 4 3 5% 4 6% 8% 48%	2765
August	1st to 10th	Night	12% 5% 2 5% 4 4 4 4 6% 7% 46%	2825
	11th to 20th	Night	15% 7% 2 6% 4 4 4 3 5% 6% 43%	2785
	21st to end	Night	12% 5% 2 5% 4 3 4 3 6% 8% 47%	3338
September	1st to 10th	Night	11% 5% 2 6% 4 3 4 3 6% 8% 46%	1900
	11th to 20th	Night	12% 5% 1 5% 3 3 4 4 5% 7% 49%	1911
	21st to end	Night	20% 6% 3 5% 3 4 5% 3 5% 5% 41%	2189
October	1st to 10th	Night	18% 7% 3 7% 4 5% 4 3 5% 6% 38%	2280
	11th to 20th	Night	21% 11% 3 8% 5% 5% 4 4 5% 5% 29%	2280
	21st to end	Night	21% 14% 3 8% 5% 5% 5% 4 5% 5% 25%	2539
November	1st to 10th	Night	18% 10% 3 8% 5% 5% 3 3 6% 6% 33%	2642
	11th to 20th	Night	17% 15% 4 8% 5% 4 4 4 5% 7% 28%	2800
	21st to end	Night	20% 16% 5% 10% 6% 5% 5% 4 4 5% 21%	2800
December	1st to 10th	Night	19% 21% 6% 11% 6% 5% 4 3 5% 5% 15%	2800
	11th to 20th	Night	16% 21% 6% 11% 5% 4 3 2 4 5% 22%	3428
	21st to end	Night	26% 21% 7% 12% 4 3 4 3 3 4 13%	4933

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	68% 2 10% 11% 7% 1	2518
	11th to 20th	Day	76% 3 6% 8% 6% 1	2524
	21st to end	Day	73% 2 6% 11% 6% 1	3124
February	1st to 10th	Day	68% 3 8% 15% 5% 1	1710
	11th to 20th	Day	62% 3 9% 14% 11% 2	1672
	21st to end	Day	63% 3 8% 14% 11% 1	1479
March	1st to 10th	Day	59% 3 12% 13% 11% 1	3340
	11th to 20th	Day	59% 3 11% 16% 9% 2	3480
	21st to end	Day	45% 3 7% 24% 17% 4	3868
April	1st to 10th	Day	57% 4 6% 19% 12% 3	2280
	11th to 20th	Day	53% 3 7% 22% 14% 1	2269
	21st to end	Day	55% 3 7% 20% 13% 3	2470
May	1st to 10th	Day	51% 4 7% 26% 11% 2	4307
	11th to 20th	Day	51% 4 10% 24% 10% 1	4402
	21st to end	Day	43% 4 13% 22% 16% 3	4837
June	1st to 10th	Day	53% 4 10% 20% 12% 1	2660
	11th to 20th	Day	45% 4 11% 25% 13% 2	2660
	21st to end	Day	47% 5% 12% 22% 12% 1	2660
July	1st to 10th	Day	43% 5% 14% 25% 12% 1	4370
	11th to 20th	Day	38% 5% 14% 32% 10%	4365
	21st to end	Day	37% 6% 11% 34% 13%	4631
August	1st to 10th	Day	49% 4 13% 23% 11% 1	4091
	11th to 20th	Day	47% 5% 13% 27% 8%	4083
	21st to end	Day	39% 5% 11% 34% 10% 1	4285
September	1st to 10th	Day	42% 4 11% 30% 12% 1	2280
	11th to 20th	Day	39% 3 12% 30% 15% 1	2266
	21st to end	Day	48% 4 13% 24% 12%	1990
October	1st to 10th	Day	46% 4 10% 28% 10% 1	3160
	11th to 20th	Day	52% 4 11% 21% 12% 1	3140
	21st to end	Day	60% 4 11% 19% 6%	3371
November	1st to 10th	Day	53% 4 14% 21% 7% 1	1656
	11th to 20th	Day	59% 4 11% 15% 10% 1	1600
	21st to end	Day	71% 4 9% 10% 6% 1	1600
December	1st to 10th	Day	74% 3 8% 10% 5%	1600
	11th to 20th	Day	66% 4 9% 12% 9% 1	1986
	21st to end	Day	74% 2 5% 14% 5%	2796
January	1st to 10th	Night	71% 2 9% 13% 5%	4429
	11th to 20th	Night	73% 3 8% 10% 5% 1	4434
	21st to end	Night	71% 3 8% 11% 7% 1	4532
February	1st to 10th	Night	63% 3 9% 17% 7% 1	2470
	11th to 20th	Night	59% 2 9% 19% 10%	2405
	21st to end	Night	58% 2 10% 20% 10% 1	1975
March	1st to 10th	Night	58% 3 8% 19% 11% 1	3510
	11th to 20th	Night	58% 3 12% 18% 7% 1	3480
	21st to end	Night	45% 6% 7% 23% 17% 2	3763
April	1st to 10th	Night	55% 3 6% 21% 12% 2	1900
	11th to 20th	Night	49% 3 8% 23% 15% 2	1875
	21st to end	Night	52% 3 9% 18% 16% 2	1710
May	1st to 10th	Night	49% 3 10% 22% 14% 2	2650
	11th to 20th	Night	48% 4 12% 24% 11% 2	2496
	21st to end	Night	40% 4 11% 25% 18% 2	2739
June	1st to 10th	Night	46% 4 12% 23% 14% 1	1520
	11th to 20th	Night	38% 5% 12% 27% 17% 1	1520
	21st to end	Night	45% 4 13% 24% 12% 1	1520
July	1st to 10th	Night	39% 5% 14% 25% 16% 1	2480
	11th to 20th	Night	38% 4 11% 33% 14%	2472
	21st to end	Night	34% 6% 14% 31% 15%	2677
August	1st to 10th	Night	35% 5% 14% 27% 16% 2	2814
	11th to 20th	Night	41% 5% 18% 26% 11% 1	2812
	21st to end	Night	35% 4 13% 34% 12% 2	3338
September	1st to 10th	Night	35% 5% 17% 28% 14% 1	1900
	11th to 20th	Night	34% 4 15% 34% 13% 1	1911
	21st to end	Night	45% 4 11% 29% 12%	2189
October	1st to 10th	Night	39% 4 10% 29% 19%	3800
	11th to 20th	Night	48% 4 13% 25% 10%	3779
	21st to end	Night	52% 5% 15% 21% 7%	4175
November	1st to 10th	Night	51% 4 12% 23% 9% 1	2642
	11th to 20th	Night	56% 4 11% 19% 8% 1	2800
	21st to end	Night	64% 4 11% 15% 5%	2800
December	1st to 10th	Night	71% 3 9% 13% 4	2800
	11th to 20th	Night	66% 3 9% 14% 8%	3428
	21st to end	Night	77% 2 6% 11% 4	4933

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	23% 20% 36% 16% 4 1	180
	11th to 20th	Day	28% 17% 34% 18% 3 1	182
	21st to end	Day	29% 17% 34% 15% 4	297
February	1st to 10th	Day	29% 21% 38% 10% 2	270
	11th to 20th	Day	31% 26% 37% 6% 1	270
	21st to end	Day	36% 20% 34% 10% 1	291
March	1st to 10th	Day	25% 18% 37% 15% 3 1	460
	11th to 20th	Day	28% 17% 33% 15% 5% 1	460
	21st to end	Day	32% 18% 29% 14% 6% 1	506
April	1st to 10th	Day	29% 17% 34% 13% 7%	460
	11th to 20th	Day	36% 19% 23% 10% 9% 2	452
	21st to end	Day	31% 18% 30% 14% 5% 2	460
May	1st to 10th	Day	29% 13% 30% 19% 6% 4	463
	11th to 20th	Day	21% 14% 34% 21% 7% 2	487
	21st to end	Day	20% 16% 32% 19% 10% 3	529
June	1st to 10th	Day	26% 10% 32% 24% 7% 1	490
	11th to 20th	Day	18% 13% 34% 23% 9% 3	490
	21st to end	Day	23% 12% 33% 19% 10% 2	490
July	1st to 10th	Day	15% 8% 32% 27% 14% 4	485
	11th to 20th	Day	17% 10% 31% 25% 13% 5%	484
	21st to end	Day	15% 9% 33% 28% 12% 3	532
August	1st to 10th	Day	17% 6% 31% 29% 13% 5%	486
	11th to 20th	Day	16% 5% 25% 33% 15% 6%	479
	21st to end	Day	17% 9% 30% 24% 14% 6%	539
September	1st to 10th	Day	16% 9% 33% 21% 14% 6%	490
	11th to 20th	Day	15% 8% 24% 21% 19% 12%	490
	21st to end	Day	20% 12% 27% 23% 12% 5%	490
October	1st to 10th	Day	26% 15% 27% 17% 13% 2	490
	11th to 20th	Day	31% 17% 30% 15% 6% 1	490
	21st to end	Day	36% 16% 29% 15% 4	522
November	1st to 10th	Day	30% 13% 33% 17% 6% 1	290
	11th to 20th	Day	33% 18% 33% 12% 4 2	200
	21st to end	Day	30% 21% 37% 9% 3 1	200
December	1st to 10th	Day	32% 19% 31% 16% 2 1	200
	11th to 20th	Day	38% 21% 28% 11% 2 1	200
	21st to end	Day	34% 20% 29% 11% 4 1	204
January	1st to 10th	Night	29% 18% 32% 16% 4 1	760
	11th to 20th	Night	29% 15% 32% 19% 5%	760
	21st to end	Night	21% 14% 34% 23% 7% 1	836
February	1st to 10th	Night	23% 20% 33% 21% 2	760
	11th to 20th	Night	21% 18% 39% 17% 4	743
	21st to end	Night	25% 19% 33% 18% 4	628
March	1st to 10th	Night	25% 18% 35% 18% 4	760
	11th to 20th	Night	24% 16% 34% 19% 5% 1	760
	21st to end	Night	22% 13% 34% 22% 8% 1	836
April	1st to 10th	Night	27% 13% 31% 23% 5%	760
	11th to 20th	Night	26% 17% 29% 19% 8% 1	751
	21st to end	Night	24% 10% 31% 24% 11%	570
May	1st to 10th	Night	26% 7% 26% 26% 13% 2	458
	11th to 20th	Night	17% 10% 33% 32% 9%	374
	21st to end	Night	14% 7% 35% 31% 12% 1	411
June	1st to 10th	Night	18% 7% 32% 33% 8% 1	380
	11th to 20th	Night	15% 9% 28% 36% 12% 1	380
	21st to end	Night	19% 7% 26% 35% 12%	380
July	1st to 10th	Night	7% 6% 32% 38% 15% 1	370
	11th to 20th	Night	13% 5% 27% 35% 18% 1	368
	21st to end	Night	10% 4 30% 38% 16% 1	430
August	1st to 10th	Night	14% 2 22% 35% 25% 2	567
	11th to 20th	Night	12% 4 20% 36% 24% 3	564
	21st to end	Night	13% 5% 29% 31% 20% 2	750
September	1st to 10th	Night	15% 6% 30% 29% 17% 3	760
	11th to 20th	Night	14% 5% 25% 28% 23% 5%	760
	21st to end	Night	23% 9% 21% 28% 16% 4	760
October	1st to 10th	Night	22% 10% 28% 23% 15% 2	760
	11th to 20th	Night	29% 12% 29% 21% 8% 1	760
	21st to end	Night	30% 14% 30% 20% 5%	836
November	1st to 10th	Night	24% 15% 29% 24% 8% 1	780
	11th to 20th	Night	27% 15% 32% 17% 8% 1	800
	21st to end	Night	31% 16% 28% 20% 5% 1	800
December	1st to 10th	Night	33% 16% 31% 16% 4	800
	11th to 20th	Night	27% 19% 34% 17% 3 1	800
	21st to end	Night	34% 13% 33% 16% 3	851

Page generated at 2024-12-21 04:13:46. Version ac07

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