Sandy Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sandy Lake clear sky chart from 2005-11-06 to 2024-02-05.

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	14% 10% 5% 9% 7% 4 6% 6% 6% 7% 28%	77413
	Night	13% 12% 5% 10% 8% 5% 6% 6% 5% 6% 23%	81479
Transparency	Day	55% 6% 12% 19% 8% 1	77094
	Night	61% 5% 10% 17% 6%	81331
Seeing	Day	19% 10% 30% 26% 11% 3	14935
	Night	19% 7% 29% 30% 12% 2	24721

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% 11% 7% 16% 14% 7% 10% 8% 5% 6% 11%	2218
	11th to 20th	Day	5% 9% 5% 16% 15% 7% 8% 8% 8% 6% 12%	2220
	21st to end	Day	12% 18% 8% 16% 8% 4 6% 6% 7% 5% 10%	2442
February	1st to 10th	Day	4 10% 5% 9% 9% 6% 9% 11% 10% 8% 20%	1555
	11th to 20th	Day	5% 10% 5% 8% 7% 5% 8% 10% 8% 9% 25%	1574
	21st to end	Day	4 9% 6% 11% 11% 4 8% 9% 7% 7% 25%	1332
March	1st to 10th	Day	7% 11% 5% 11% 9% 6% 6% 5% 5% 7% 28%	1811
	11th to 20th	Day	12% 11% 5% 8% 7% 4 6% 5% 5% 6% 31%	1980
	21st to end	Day	10% 11% 4 8% 7% 4 6% 6% 5% 6% 32%	2240
April	1st to 10th	Day	10% 11% 4 7% 8% 3 5% 5% 6% 8% 33%	2160
	11th to 20th	Day	12% 10% 4 8% 6% 3 5% 5% 5% 7% 36%	2307
	21st to end	Day	10% 8% 3 7% 6% 3 5% 5% 6% 8% 39%	2470
May	1st to 10th	Day	16% 9% 5% 8% 6% 4 4 5% 6% 7% 31%	2520
	11th to 20th	Day	16% 9% 4 7% 5% 3 4 5% 5% 7% 35%	2566
	21st to end	Day	22% 9% 3 6% 5% 3 5% 4 4 6% 33%	2940
June	1st to 10th	Day	19% 7% 3 6% 6% 3 6% 4 6% 8% 31%	2880
	11th to 20th	Day	18% 7% 3 6% 7% 4 5% 5% 5% 7% 33%	2880
	21st to end	Day	16% 6% 3 6% 7% 4 5% 5% 7% 8% 34%	2880
July	1st to 10th	Day	12% 6% 3 6% 7% 4 6% 7% 6% 7% 36%	2781
	11th to 20th	Day	17% 6% 3 6% 6% 3 5% 6% 6% 8% 34%	2700
	21st to end	Day	15% 5% 2 5% 6% 4 5% 6% 6% 8% 38%	2939
August	1st to 10th	Day	15% 6% 3 5% 6% 4 6% 5% 6% 7% 36%	2561
	11th to 20th	Day	15% 5% 2 6% 6% 3 6% 6% 6% 8% 37%	2394
	21st to end	Day	23% 7% 2 5% 5% 3 5% 5% 6% 7% 31%	2574
September	1st to 10th	Day	19% 9% 4 6% 4 3 5% 5% 5% 6% 34%	2170
	11th to 20th	Day	23% 12% 3 6% 6% 3 4 5% 4 5% 29%	2153
	21st to end	Day	21% 11% 4 6% 5% 3 4 4 4 5% 32%	1883
October	1st to 10th	Day	21% 17% 6% 6% 6% 2 5% 3 4 6% 23%	1800
	11th to 20th	Day	22% 19% 7% 9% 7% 3 3 3 4 5% 18%	1800
	21st to end	Day	20% 26% 8% 9% 6% 3 4 3 4 5% 14%	1652
November	1st to 10th	Day	16% 18% 10% 15% 9% 5% 5% 4 3 3 11%	1487
	11th to 20th	Day	15% 18% 10% 15% 10% 5% 5% 4 3 4 12%	1520
	21st to end	Day	14% 18% 7% 18% 10% 5% 8% 3 4 4 10%	1322
December	1st to 10th	Day	7% 17% 10% 16% 12% 3 6% 8% 5% 5% 11%	1140
	11th to 20th	Day	9% 15% 6% 13% 9% 5% 8% 6% 8% 6% 16%	1436
	21st to end	Day	9% 13% 7% 11% 8% 4 5% 5% 7% 7% 23%	2126
January	1st to 10th	Night	6% 10% 6% 16% 14% 11% 9% 8% 6% 4 10%	4737
	11th to 20th	Night	6% 8% 6% 18% 15% 6% 6% 8% 8% 5% 13%	4750
	21st to end	Night	12% 18% 8% 15% 9% 5% 7% 7% 5% 5% 9%	5225
February	1st to 10th	Night	5% 11% 4 10% 12% 7% 11% 10% 7% 6% 17%	2499
	11th to 20th	Night	5% 10% 5% 10% 8% 6% 10% 10% 9% 6% 20%	2273
	21st to end	Night	4 10% 5% 12% 10% 5% 7% 8% 5% 7% 26%	1924
March	1st to 10th	Night	9% 12% 6% 9% 8% 5% 8% 5% 5% 5% 26%	2150
	11th to 20th	Night	11% 13% 6% 8% 8% 4 7% 5% 5% 5% 28%	1979
	21st to end	Night	10% 11% 4 8% 6% 4 6% 5% 6% 7% 33%	2116
April	1st to 10th	Night	8% 9% 5% 8% 6% 4 4 5% 5% 6% 41%	1800
	11th to 20th	Night	11% 10% 3 7% 6% 4 4 4 5% 6% 39%	1601
	21st to end	Night	8% 12% 4 7% 6% 3 4 4 5% 5% 41%	1490
May	1st to 10th	Night	20% 10% 3 8% 6% 3 3 6% 5% 5% 31%	1440
	11th to 20th	Night	17% 10% 2 5% 5% 2 4 4 5% 7% 38%	1326
	21st to end	Night	23% 8% 3 6% 6% 2 4 3 4 5% 36%	1332
June	1st to 10th	Night	18% 8% 3 6% 7% 4 6% 6% 6% 6% 31%	1080
	11th to 20th	Night	20% 8% 4 7% 7% 3 5% 4 5% 6% 30%	1080
	21st to end	Night	14% 4 3 6% 6% 3 6% 6% 6% 9% 36%	1080
July	1st to 10th	Night	13% 4 2 5% 5% 3 5% 5% 7% 9% 42%	1175
	11th to 20th	Night	16% 6% 3 6% 5% 3 4 5% 6% 9% 37%	1260
	21st to end	Night	13% 6% 2 4 5% 3 5% 5% 5% 9% 42%	1379
August	1st to 10th	Night	12% 5% 2 5% 5% 3 4 5% 6% 8% 45%	1378
	11th to 20th	Night	14% 5% 2 4 5% 3 4 5% 6% 8% 44%	1504
	21st to end	Night	21% 7% 2 5% 5% 3 5% 4 5% 6% 36%	1782
September	1st to 10th	Night	19% 7% 2 5% 5% 3 5% 4 6% 8% 38%	1790
	11th to 20th	Night	22% 10% 3 6% 5% 3 4 3 5% 6% 32%	1804
	21st to end	Night	19% 10% 3 6% 5% 2 4 4 5% 7% 34%	2058
October	1st to 10th	Night	23% 15% 5% 6% 5% 3 4 3 4 5% 26%	2160
	11th to 20th	Night	23% 18% 5% 7% 6% 3 4 4 4 5% 20%	2160
	21st to end	Night	22% 22% 8% 9% 6% 3 4 4 4 4 14%	2703
November	1st to 10th	Night	20% 19% 7% 13% 8% 4 3 3 4 5% 15%	2591
	11th to 20th	Night	16% 17% 9% 15% 11% 6% 6% 3 4 3 13%	2660
	21st to end	Night	12% 20% 10% 16% 12% 5% 6% 4 3 4 7%	2854
December	1st to 10th	Night	8% 15% 8% 16% 13% 7% 8% 6% 4 4 12%	3040
	11th to 20th	Night	8% 14% 7% 12% 11% 6% 9% 7% 6% 6% 14%	3761
	21st to end	Night	7% 14% 7% 14% 9% 5% 7% 4 5% 4 23%	5538

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	72% 6% 10% 10% 2	2219
	11th to 20th	Day	69% 4 12% 11% 3	2220
	21st to end	Day	74% 5% 7% 10% 4	2442
February	1st to 10th	Day	55% 6% 11% 19% 10% 1	1555
	11th to 20th	Day	51% 5% 12% 22% 10%	1583
	21st to end	Day	54% 5% 11% 19% 10% 1	1332
March	1st to 10th	Day	56% 4 13% 17% 10%	1813
	11th to 20th	Day	54% 4 10% 21% 9% 1	1980
	21st to end	Day	52% 5% 12% 22% 8% 2	2240
April	1st to 10th	Day	50% 4 12% 21% 13%	2160
	11th to 20th	Day	49% 4 9% 23% 14% 1	2307
	21st to end	Day	42% 5% 10% 26% 15% 2	2470
May	1st to 10th	Day	51% 5% 11% 21% 11% 1	2520
	11th to 20th	Day	49% 5% 9% 22% 13% 2	2570
	21st to end	Day	52% 5% 9% 19% 14% 1	2940
June	1st to 10th	Day	51% 6% 10% 18% 14%	2880
	11th to 20th	Day	50% 6% 10% 21% 12% 1	2880
	21st to end	Day	47% 7% 13% 20% 13% 1	2880
July	1st to 10th	Day	43% 8% 15% 24% 10%	2707
	11th to 20th	Day	47% 7% 14% 22% 8% 2	2619
	21st to end	Day	43% 9% 17% 27% 5%	2776
August	1st to 10th	Day	45% 9% 18% 24% 4	2544
	11th to 20th	Day	44% 8% 16% 27% 6%	2394
	21st to end	Day	52% 7% 17% 19% 5% 1	2574
September	1st to 10th	Day	50% 7% 16% 19% 7% 1	2170
	11th to 20th	Day	57% 6% 14% 20% 2	2153
	21st to end	Day	55% 5% 14% 21% 5%	1883
October	1st to 10th	Day	63% 5% 12% 15% 4	1800
	11th to 20th	Day	70% 5% 11% 13% 2	1800
	21st to end	Day	75% 6% 9% 9% 2	1652
November	1st to 10th	Day	79% 5% 8% 7% 1	1487
	11th to 20th	Day	77% 5% 7% 9% 2	1520
	21st to end	Day	81% 4 5% 7% 3	1322
December	1st to 10th	Day	75% 3 8% 11% 3	1140
	11th to 20th	Day	66% 4 11% 16% 4	1436
	21st to end	Day	59% 4 9% 19% 9%	2126
January	1st to 10th	Night	76% 5% 7% 10% 2	4737
	11th to 20th	Night	70% 4 10% 13% 3	4750
	21st to end	Night	76% 5% 7% 8% 4	5225
February	1st to 10th	Night	64% 5% 9% 15% 6%	2499
	11th to 20th	Night	58% 6% 10% 19% 7%	2274
	21st to end	Night	55% 4 10% 21% 9% 1	1924
March	1st to 10th	Night	59% 5% 10% 17% 10%	2161
	11th to 20th	Night	58% 4 8% 21% 7% 1	1980
	21st to end	Night	51% 5% 9% 22% 11% 2	2116
April	1st to 10th	Night	43% 4 9% 25% 17% 1	1800
	11th to 20th	Night	45% 4 9% 23% 17% 2	1601
	21st to end	Night	44% 5% 7% 22% 19% 2	1490
May	1st to 10th	Night	53% 5% 8% 21% 12%	1440
	11th to 20th	Night	46% 5% 7% 23% 17% 3	1327
	21st to end	Night	53% 4 5% 20% 16% 1	1332
June	1st to 10th	Night	50% 7% 9% 18% 16%	1080
	11th to 20th	Night	55% 5% 7% 20% 11% 2	1080
	21st to end	Night	43% 7% 15% 20% 14% 1	1080
July	1st to 10th	Night	37% 8% 13% 29% 12% 1	1140
	11th to 20th	Night	43% 8% 14% 24% 10% 1	1218
	21st to end	Night	39% 8% 14% 30% 9%	1302
August	1st to 10th	Night	35% 9% 17% 31% 7%	1371
	11th to 20th	Night	38% 9% 17% 31% 6%	1504
	21st to end	Night	49% 6% 17% 21% 6% 1	1782
September	1st to 10th	Night	45% 6% 18% 23% 7% 1	1790
	11th to 20th	Night	53% 6% 15% 23% 3	1804
	21st to end	Night	50% 7% 16% 21% 6%	2058
October	1st to 10th	Night	62% 5% 11% 17% 5%	2160
	11th to 20th	Night	66% 6% 12% 14% 2	2160
	21st to end	Night	74% 6% 9% 10% 1	2703
November	1st to 10th	Night	74% 5% 10% 8% 2	2591
	11th to 20th	Night	78% 4 8% 7% 2	2660
	21st to end	Night	81% 4 7% 6% 2	2854
December	1st to 10th	Night	76% 4 9% 9% 3	3040
	11th to 20th	Night	70% 5% 9% 13% 4	3760
	21st to end	Night	64% 3 7% 20% 6% 1	5538

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	11% 9% 44% 25% 10% 1	270
	11th to 20th	Day	14% 7% 33% 26% 17% 4	270
	21st to end	Day	16% 8% 33% 30% 10% 3	297
February	1st to 10th	Day	7% 9% 42% 33% 9% 1	252
	11th to 20th	Day	13% 8% 43% 24% 12% 2	240
	21st to end	Day	5% 12% 39% 21% 20% 3	198
March	1st to 10th	Day	12% 8% 36% 26% 10% 7%	240
	11th to 20th	Day	10% 16% 38% 27% 7% 2	240
	21st to end	Day	15% 15% 34% 24% 10% 2	326
April	1st to 10th	Day	15% 10% 31% 29% 13% 2	420
	11th to 20th	Day	17% 10% 32% 26% 12% 2	585
	21st to end	Day	12% 12% 31% 29% 12% 4	600
May	1st to 10th	Day	21% 11% 30% 27% 10% 2	603
	11th to 20th	Day	20% 12% 29% 24% 13% 2	625
	21st to end	Day	22% 14% 31% 23% 9% 2	679
June	1st to 10th	Day	23% 11% 29% 23% 10% 5%	630
	11th to 20th	Day	19% 13% 29% 24% 11% 4	630
	21st to end	Day	19% 10% 29% 26% 12% 5%	630
July	1st to 10th	Day	15% 11% 29% 31% 12% 3	621
	11th to 20th	Day	19% 10% 26% 25% 15% 5%	618
	21st to end	Day	15% 7% 25% 31% 15% 7%	684
August	1st to 10th	Day	18% 7% 23% 32% 16% 4	626
	11th to 20th	Day	15% 10% 22% 30% 17% 6%	615
	21st to end	Day	27% 7% 24% 27% 14% 2	693
September	1st to 10th	Day	24% 9% 33% 27% 7% 1	460
	11th to 20th	Day	28% 10% 26% 30% 6%	443
	21st to end	Day	27% 10% 33% 25% 4	270
October	1st to 10th	Day	28% 12% 30% 22% 7% 2	270
	11th to 20th	Day	28% 12% 28% 24% 6% 2	270
	21st to end	Day	37% 6% 30% 20% 7%	297
November	1st to 10th	Day	21% 15% 33% 24% 6% 1	270
	11th to 20th	Day	19% 18% 32% 19% 8% 4	270
	21st to end	Day	24% 15% 42% 15% 4	224
December	1st to 10th	Day	17% 8% 39% 26% 7% 2	180
	11th to 20th	Day	15% 14% 41% 23% 6% 2	180
	21st to end	Day	15% 7% 34% 25% 16% 3	209
January	1st to 10th	Night	15% 7% 35% 30% 11% 3	950
	11th to 20th	Night	16% 7% 31% 31% 13% 2	950
	21st to end	Night	17% 5% 32% 34% 10% 1	1045
February	1st to 10th	Night	10% 7% 34% 36% 10% 2	923
	11th to 20th	Night	11% 7% 30% 30% 17% 4	879
	21st to end	Night	9% 6% 30% 35% 19% 3	740
March	1st to 10th	Night	15% 7% 28% 34% 14% 1	721
	11th to 20th	Night	17% 12% 31% 27% 12% 1	540
	21st to end	Night	15% 10% 28% 29% 13% 4	594
April	1st to 10th	Night	12% 6% 31% 37% 12% 2	540
	11th to 20th	Night	17% 6% 28% 34% 12% 3	533
	21st to end	Night	14% 10% 27% 36% 12% 2	540
May	1st to 10th	Night	25% 8% 26% 30% 10% 1	540
	11th to 20th	Night	21% 6% 29% 30% 12% 2	531
	21st to end	Night	26% 6% 30% 26% 11% 1	558
June	1st to 10th	Night	21% 6% 23% 32% 16% 1	360
	11th to 20th	Night	25% 6% 24% 31% 13% 2	360
	21st to end	Night	16% 4 25% 38% 17%	360
July	1st to 10th	Night	14% 6% 26% 36% 18%	440
	11th to 20th	Night	19% 6% 26% 31% 15% 2	522
	21st to end	Night	14% 2 23% 36% 21% 4	591
August	1st to 10th	Night	15% 4 19% 42% 18% 1	537
	11th to 20th	Night	18% 5% 19% 36% 20% 1	534
	21st to end	Night	24% 5% 27% 30% 12% 1	594
September	1st to 10th	Night	20% 6% 33% 31% 9%	540
	11th to 20th	Night	29% 8% 23% 30% 10%	540
	21st to end	Night	27% 7% 30% 27% 8% 1	618
October	1st to 10th	Night	33% 8% 30% 22% 6% 1	720
	11th to 20th	Night	32% 10% 22% 25% 9% 2	720
	21st to end	Night	35% 7% 27% 22% 7% 1	931
November	1st to 10th	Night	30% 11% 26% 23% 8% 2	925
	11th to 20th	Night	25% 8% 32% 24% 9% 2	950
	21st to end	Night	22% 13% 33% 23% 9% 1	950
December	1st to 10th	Night	14% 8% 35% 30% 11% 2	950
	11th to 20th	Night	14% 8% 33% 31% 12% 1	950
	21st to end	Night	16% 7% 29% 33% 12% 3	1045

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