Sharbot Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sharbot Lake clear sky chart from 2005-11-06 to 2025-02-25.

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% 5% 4 4 5% 7% 32%	108794
	Night	17% 11% 4 9% 5% 5% 4 3 5% 6% 31%	109872
Transparency	Day	50% 6% 11% 21% 10% 1	112346
	Night	52% 6% 11% 20% 10% 1	114484
Seeing	Day	23% 17% 31% 18% 8% 3	14748
	Night	22% 14% 31% 23% 9% 1	24078

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	12% 15% 6% 11% 7% 6% 5% 3 5% 5% 25%	3597
	11th to 20th	Day	11% 19% 8% 13% 6% 5% 5% 4 3 4 21%	3570
	21st to end	Day	14% 17% 7% 16% 6% 5% 4 3 4 4 20%	4305
February	1st to 10th	Day	15% 16% 4 12% 7% 6% 4 5% 5% 6% 22%	1800
	11th to 20th	Day	12% 15% 5% 11% 7% 5% 4 4 4 4 28%	1753
	21st to end	Day	19% 14% 4 10% 6% 7% 4 4 5% 4 23%	1583
March	1st to 10th	Day	20% 14% 5% 9% 6% 4 4 3 3 5% 28%	3207
	11th to 20th	Day	11% 16% 5% 9% 6% 5% 5% 3 4 6% 31%	3480
	21st to end	Day	13% 10% 3 7% 4 4 3 3 5% 6% 43%	3964
April	1st to 10th	Day	20% 12% 3 8% 5% 4 4 3 4 6% 32%	2280
	11th to 20th	Day	22% 9% 3 6% 4 4 4 3 4 5% 37%	2254
	21st to end	Day	22% 11% 3 8% 5% 4 4 3 4 5% 32%	2398
May	1st to 10th	Day	20% 8% 3 8% 5% 4 5% 4 5% 6% 33%	4416
	11th to 20th	Day	17% 8% 3 8% 6% 4 4 3 5% 7% 33%	4398
	21st to end	Day	13% 7% 2 6% 4 5% 5% 4 5% 8% 41%	4837
June	1st to 10th	Day	20% 8% 3 7% 5% 5% 5% 4 6% 7% 29%	2660
	11th to 20th	Day	15% 6% 2 6% 5% 4 5% 5% 6% 9% 37%	2660
	21st to end	Day	17% 8% 3 8% 5% 5% 5% 4 6% 7% 32%	2660
July	1st to 10th	Day	11% 7% 2 7% 6% 6% 5% 5% 7% 9% 36%	4440
	11th to 20th	Day	13% 5% 2 5% 4 5% 5% 5% 7% 9% 40%	4440
	21st to end	Day	10% 6% 2 7% 4 5% 5% 5% 7% 9% 40%	4814
August	1st to 10th	Day	17% 8% 3 8% 5% 5% 4 4 5% 7% 36%	4211
	11th to 20th	Day	17% 6% 3 6% 4 5% 5% 4 7% 8% 35%	4044
	21st to end	Day	14% 5% 2 6% 4 5% 4 5% 6% 9% 39%	4180
September	1st to 10th	Day	13% 7% 2 6% 4 4 4 4 5% 8% 42%	2280
	11th to 20th	Day	12% 5% 2 5% 3 4 4 3 5% 7% 48%	2280
	21st to end	Day	18% 6% 2 7% 5% 4 4 3 5% 8% 39%	2007
October	1st to 10th	Day	21% 8% 2 8% 4 3 4 3 4 7% 36%	1900
	11th to 20th	Day	21% 10% 3 7% 5% 5% 5% 3 5% 6% 29%	1900
	21st to end	Day	26% 10% 4 8% 5% 5% 4 4 4 6% 25%	1990
November	1st to 10th	Day	15% 10% 4 8% 5% 5% 5% 4 6% 5% 35%	1740
	11th to 20th	Day	17% 15% 4 8% 5% 6% 5% 3 5% 6% 29%	1600
	21st to end	Day	21% 16% 5% 9% 6% 4 5% 4 4 6% 21%	1600
December	1st to 10th	Day	22% 17% 5% 11% 6% 5% 4 3 5% 5% 17%	2600
	11th to 20th	Day	17% 20% 6% 10% 6% 4 4 2 4 4 23%	2986
	21st to end	Day	24% 18% 5% 11% 5% 3 3 2 2 4 23%	3960
January	1st to 10th	Night	15% 14% 7% 13% 7% 5% 5% 3 4 4 22%	6349
	11th to 20th	Night	11% 15% 6% 15% 8% 7% 5% 4 4 5% 19%	6315
	21st to end	Night	16% 16% 7% 13% 7% 6% 4 3 4 5% 21%	6647
February	1st to 10th	Night	13% 16% 5% 10% 6% 5% 5% 4 6% 6% 24%	2600
	11th to 20th	Night	13% 15% 5% 10% 5% 5% 4 4 4 6% 29%	2533
	21st to end	Night	13% 15% 5% 9% 5% 5% 4 4 5% 6% 29%	1965
March	1st to 10th	Night	19% 12% 4 8% 6% 4 3 3 4 5% 32%	3628
	11th to 20th	Night	17% 15% 4 8% 5% 5% 3 4 5% 6% 26%	3479
	21st to end	Night	15% 10% 4 7% 5% 3 3 3 4 5% 41%	3668
April	1st to 10th	Night	21% 10% 3 7% 4 3 4 3 4 6% 34%	1900
	11th to 20th	Night	20% 8% 3 6% 5% 4 4 3 4 4 38%	1875
	21st to end	Night	19% 11% 3 8% 5% 4 4 4 5% 6% 33%	1799
May	1st to 10th	Night	21% 9% 3 7% 4 4 4 4 6% 6% 32%	2524
	11th to 20th	Night	18% 8% 3 6% 4 4 4 3 5% 6% 38%	2495
	21st to end	Night	13% 6% 2 6% 4 4 4 4 6% 8% 42%	2738
June	1st to 10th	Night	15% 8% 3 7% 6% 5% 6% 4 6% 8% 34%	1520
	11th to 20th	Night	13% 7% 2 6% 4 4 4 4 6% 8% 42%	1520
	21st to end	Night	17% 7% 2 7% 5% 6% 4 4 6% 8% 35%	1520
July	1st to 10th	Night	10% 5% 3 8% 6% 5% 5% 4 7% 9% 38%	2520
	11th to 20th	Night	13% 6% 2 6% 4 4 4 3 5% 8% 46%	2520
	21st to end	Night	11% 6% 2 6% 3 5% 5% 4 6% 7% 45%	2739
August	1st to 10th	Night	13% 6% 2 7% 4 4 4 3 6% 7% 43%	2715
	11th to 20th	Night	14% 7% 3 6% 4 4 4 3 5% 7% 44%	2785
	21st to end	Night	11% 5% 2 7% 5% 5% 5% 5% 7% 8% 42%	3444
September	1st to 10th	Night	12% 6% 2 7% 4 3 3 4 4 9% 46%	1900
	11th to 20th	Night	12% 4 2 4 4 4 4 3 5% 7% 51%	1900
	21st to end	Night	17% 6% 2 6% 4 4 4 3 5% 6% 43%	2167
October	1st to 10th	Night	16% 8% 3 7% 5% 5% 5% 3 5% 6% 39%	2280
	11th to 20th	Night	20% 10% 2 7% 5% 5% 5% 4 6% 6% 31%	2280
	21st to end	Night	23% 11% 3 8% 5% 4 4 3 4 6% 29%	2606
November	1st to 10th	Night	17% 10% 3 7% 4 4 4 3 5% 6% 36%	2557
	11th to 20th	Night	17% 11% 3 8% 5% 5% 5% 4 5% 6% 31%	2800
	21st to end	Night	21% 14% 3 9% 5% 4 5% 4 5% 6% 24%	2800
December	1st to 10th	Night	19% 16% 4 11% 6% 5% 5% 4 5% 6% 17%	4580
	11th to 20th	Night	22% 16% 4 9% 5% 4 4 3 4 5% 24%	5208
	21st to end	Night	26% 17% 4 11% 5% 4 3 3 3 4 20%	6996

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	59% 5% 11% 17% 7% 1	3598
	11th to 20th	Day	65% 6% 10% 12% 7%	3600
	21st to end	Day	67% 5% 7% 10% 9% 1	4305
February	1st to 10th	Day	61% 6% 9% 17% 6% 1	1800
	11th to 20th	Day	59% 4 10% 16% 9% 1	1762
	21st to end	Day	63% 4 10% 11% 11% 1	1583
March	1st to 10th	Day	59% 3 10% 16% 10% 1	3210
	11th to 20th	Day	54% 6% 12% 15% 11% 2	3480
	21st to end	Day	43% 4 7% 26% 16% 4	3964
April	1st to 10th	Day	55% 5% 6% 18% 13% 3	2280
	11th to 20th	Day	49% 5% 7% 21% 16% 2	2254
	21st to end	Day	55% 5% 8% 16% 14% 4	2398
May	1st to 10th	Day	50% 6% 9% 22% 11% 2	4430
	11th to 20th	Day	49% 7% 12% 21% 10% 2	4402
	21st to end	Day	40% 7% 12% 24% 15% 2	4837
June	1st to 10th	Day	51% 8% 9% 19% 12% 1	2660
	11th to 20th	Day	42% 7% 11% 25% 13% 2	2660
	21st to end	Day	48% 7% 13% 19% 12% 1	2660
July	1st to 10th	Day	41% 7% 13% 25% 12% 1	4370
	11th to 20th	Day	36% 8% 15% 31% 10%	4365
	21st to end	Day	38% 9% 12% 30% 12%	4661
August	1st to 10th	Day	46% 7% 13% 22% 11%	4197
	11th to 20th	Day	43% 7% 14% 26% 9% 1	4083
	21st to end	Day	39% 7% 14% 30% 11%	4180
September	1st to 10th	Day	40% 6% 13% 28% 12% 1	2280
	11th to 20th	Day	35% 6% 11% 31% 15% 1	2280
	21st to end	Day	44% 6% 14% 26% 11%	2007
October	1st to 10th	Day	43% 7% 10% 32% 8%	3160
	11th to 20th	Day	45% 6% 13% 25% 11%	3140
	21st to end	Day	50% 6% 15% 22% 7%	3254
November	1st to 10th	Day	48% 6% 15% 21% 8% 1	1740
	11th to 20th	Day	55% 6% 11% 17% 11% 1	1600
	21st to end	Day	63% 8% 12% 9% 8%	1600
December	1st to 10th	Day	67% 7% 14% 8% 3	2600
	11th to 20th	Day	65% 5% 10% 13% 7%	2986
	21st to end	Day	67% 4 7% 15% 7%	3960
January	1st to 10th	Night	65% 5% 11% 14% 6%	6349
	11th to 20th	Night	65% 6% 11% 11% 6%	6360
	21st to end	Night	66% 5% 8% 9% 12% 1	6647
February	1st to 10th	Night	59% 5% 11% 17% 7% 1	2600
	11th to 20th	Night	57% 5% 10% 20% 9% 1	2535
	21st to end	Night	56% 4 10% 19% 10% 1	1965
March	1st to 10th	Night	55% 4 9% 21% 10% 1	3638
	11th to 20th	Night	57% 6% 12% 16% 8% 1	3480
	21st to end	Night	44% 6% 6% 24% 17% 3	3668
April	1st to 10th	Night	51% 4 6% 21% 15% 2	1900
	11th to 20th	Night	49% 5% 8% 20% 18% 1	1875
	21st to end	Night	52% 5% 8% 16% 16% 3	1799
May	1st to 10th	Night	51% 7% 8% 19% 12% 2	2530
	11th to 20th	Night	45% 8% 11% 25% 10% 2	2496
	21st to end	Night	38% 7% 13% 21% 19% 2	2739
June	1st to 10th	Night	47% 8% 11% 21% 11% 2	1520
	11th to 20th	Night	39% 6% 12% 22% 19% 2	1520
	21st to end	Night	46% 7% 13% 20% 12% 1	1520
July	1st to 10th	Night	40% 8% 13% 22% 15% 2	2480
	11th to 20th	Night	37% 7% 13% 34% 10%	2472
	21st to end	Night	36% 8% 14% 26% 14% 1	2651
August	1st to 10th	Night	39% 7% 14% 26% 13% 1	2705
	11th to 20th	Night	39% 6% 14% 31% 9% 1	2812
	21st to end	Night	35% 9% 16% 28% 11% 1	3444
September	1st to 10th	Night	35% 7% 13% 30% 14% 1	1900
	11th to 20th	Night	32% 6% 13% 34% 14% 1	1900
	21st to end	Night	41% 6% 10% 31% 11% 1	2167
October	1st to 10th	Night	39% 6% 11% 28% 16%	3800
	11th to 20th	Night	44% 5% 15% 25% 10%	3779
	21st to end	Night	50% 6% 13% 24% 8%	4292
November	1st to 10th	Night	48% 6% 13% 22% 10% 1	2557
	11th to 20th	Night	53% 6% 10% 20% 10% 2	2800
	21st to end	Night	60% 6% 13% 16% 5%	2800
December	1st to 10th	Night	66% 7% 13% 12% 3	4580
	11th to 20th	Night	62% 6% 9% 14% 9% 1	5208
	21st to end	Night	68% 5% 6% 12% 9%	6996

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	24% 24% 37% 12% 4 1	200
	11th to 20th	Day	34% 17% 31% 15% 3 1	200
	21st to end	Day	24% 25% 33% 14% 3 1	295
February	1st to 10th	Day	34% 26% 29% 10% 1	300
	11th to 20th	Day	30% 28% 36% 5%	300
	21st to end	Day	34% 23% 30% 10% 2	371
March	1st to 10th	Day	27% 21% 34% 14% 4	460
	11th to 20th	Day	27% 23% 33% 14% 4	460
	21st to end	Day	34% 21% 26% 12% 6% 1	506
April	1st to 10th	Day	31% 22% 28% 14% 4 1	460
	11th to 20th	Day	33% 23% 21% 14% 7% 2	452
	21st to end	Day	31% 21% 29% 12% 6% 2	460
May	1st to 10th	Day	27% 15% 32% 17% 7% 2	463
	11th to 20th	Day	19% 17% 35% 18% 9% 2	487
	21st to end	Day	18% 17% 33% 19% 10% 3	529
June	1st to 10th	Day	23% 12% 36% 20% 7% 1	490
	11th to 20th	Day	15% 19% 32% 20% 12% 2	490
	21st to end	Day	21% 14% 32% 22% 8% 2	490
July	1st to 10th	Day	15% 9% 33% 27% 14% 3	485
	11th to 20th	Day	15% 12% 31% 25% 13% 3	484
	21st to end	Day	15% 8% 35% 27% 11% 4	532
August	1st to 10th	Day	15% 8% 32% 27% 14% 4	486
	11th to 20th	Day	15% 8% 29% 27% 16% 6%	479
	21st to end	Day	16% 12% 30% 23% 13% 6%	539
September	1st to 10th	Day	14% 13% 33% 22% 12% 6%	490
	11th to 20th	Day	13% 8% 25% 25% 17% 12%	490
	21st to end	Day	19% 12% 30% 21% 13% 4	490
October	1st to 10th	Day	26% 16% 28% 17% 10% 4	490
	11th to 20th	Day	27% 20% 30% 17% 5% 1	490
	21st to end	Day	29% 20% 28% 17% 5%	486
November	1st to 10th	Day	26% 17% 30% 19% 8%	374
	11th to 20th	Day	28% 20% 33% 13% 5% 3	200
	21st to end	Day	32% 22% 31% 13% 2 1	200
December	1st to 10th	Day	33% 22% 31% 13% 2	200
	11th to 20th	Day	37% 24% 27% 9% 3 1	200
	21st to end	Day	33% 19% 32% 10% 5%	220
January	1st to 10th	Night	28% 21% 31% 18% 4	800
	11th to 20th	Night	28% 18% 31% 18% 5% 1	800
	21st to end	Night	20% 18% 35% 22% 5%	880
February	1st to 10th	Night	23% 21% 35% 19% 2	800
	11th to 20th	Night	23% 20% 37% 16% 3	783
	21st to end	Night	24% 21% 34% 18% 3	647
March	1st to 10th	Night	25% 16% 36% 20% 3	760
	11th to 20th	Night	27% 19% 29% 21% 4 1	760
	21st to end	Night	22% 17% 34% 19% 7% 1	836
April	1st to 10th	Night	28% 17% 31% 20% 3	760
	11th to 20th	Night	25% 21% 29% 18% 7% 1	751
	21st to end	Night	26% 15% 28% 22% 9%	659
May	1st to 10th	Night	25% 11% 25% 27% 10% 2	390
	11th to 20th	Night	16% 10% 36% 31% 7%	374
	21st to end	Night	11% 11% 38% 27% 11%	411
June	1st to 10th	Night	16% 9% 32% 33% 9% 1	380
	11th to 20th	Night	14% 12% 33% 28% 12% 2	380
	21st to end	Night	18% 9% 26% 35% 12%	380
July	1st to 10th	Night	8% 6% 35% 35% 16%	370
	11th to 20th	Night	11% 5% 29% 38% 15% 1	368
	21st to end	Night	10% 6% 30% 42% 12% 1	416
August	1st to 10th	Night	14% 4 28% 34% 20% 1	496
	11th to 20th	Night	12% 5% 24% 35% 22% 2	564
	21st to end	Night	12% 8% 31% 30% 17% 2	817
September	1st to 10th	Night	14% 6% 32% 29% 17% 2	760
	11th to 20th	Night	14% 8% 23% 27% 24% 4	760
	21st to end	Night	20% 11% 23% 28% 17% 2	760
October	1st to 10th	Night	22% 12% 28% 22% 14% 2	760
	11th to 20th	Night	27% 12% 31% 22% 8%	760
	21st to end	Night	29% 15% 29% 21% 6%	836
November	1st to 10th	Night	26% 13% 31% 22% 7%	780
	11th to 20th	Night	26% 16% 33% 17% 8% 1	800
	21st to end	Night	30% 18% 28% 18% 5%	800
December	1st to 10th	Night	29% 19% 31% 18% 3	800
	11th to 20th	Night	27% 19% 33% 17% 3 1	800
	21st to end	Night	34% 16% 30% 17% 3	880

Page generated at 2025-02-22 06:51:33. Version ac07

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