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 2026-07-01.

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% 11% 4 10% 6% 5% 5% 4 6% 7% 30%	137964
	Night	11% 12% 5% 12% 7% 6% 6% 5% 6% 5% 24%	134718
Transparency	Day	53% 5% 11% 21% 9% 1	141281
	Night	60% 4 10% 17% 7%	139494
Seeing	Day	19% 11% 31% 26% 11% 3	18310
	Night	19% 8% 30% 30% 12% 2	27893

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	5% 12% 6% 20% 12% 9% 8% 8% 4 4 13%	4124
	11th to 20th	Day	5% 12% 5% 19% 10% 9% 9% 8% 10% 5% 9%	4112
	21st to end	Day	7% 13% 7% 17% 7% 8% 6% 5% 9% 7% 13%	4532
February	1st to 10th	Day	5% 12% 5% 12% 8% 9% 9% 8% 9% 7% 18%	1779
	11th to 20th	Day	5% 10% 5% 9% 7% 7% 9% 7% 8% 8% 25%	1844
	21st to end	Day	3 10% 6% 13% 10% 7% 7% 7% 7% 7% 25%	1557
March	1st to 10th	Day	5% 13% 7% 14% 7% 8% 4 3 4 6% 29%	4641
	11th to 20th	Day	12% 13% 5% 9% 8% 9% 6% 5% 4 5% 23%	5090
	21st to end	Day	6% 13% 4 10% 6% 6% 10% 6% 6% 7% 26%	5761
April	1st to 10th	Day	9% 11% 4 10% 7% 5% 5% 4 6% 7% 34%	2520
	11th to 20th	Day	14% 11% 4 10% 5% 4 5% 4 4 6% 33%	2697
	21st to end	Day	10% 9% 3 8% 5% 5% 5% 4 6% 7% 38%	2882
May	1st to 10th	Day	12% 14% 6% 10% 4 4 4 3 4 6% 34%	8241
	11th to 20th	Day	19% 13% 4 7% 5% 4 5% 4 5% 6% 27%	8517
	21st to end	Day	14% 7% 2 6% 3 3 4 3 4 7% 47%	9761
June	1st to 10th	Day	19% 9% 3 8% 5% 6% 4 3 6% 7% 31%	3360
	11th to 20th	Day	18% 8% 3 7% 6% 5% 5% 4 5% 7% 32%	3360
	21st to end	Day	15% 7% 3 8% 6% 5% 5% 5% 7% 8% 33%	3360
July	1st to 10th	Day	11% 5% 2 6% 5% 5% 5% 5% 6% 8% 41%	6993
	11th to 20th	Day	12% 6% 2 6% 5% 5% 6% 5% 6% 9% 38%	6800
	21st to end	Day	9% 5% 2 6% 5% 5% 5% 4 7% 9% 42%	7406
August	1st to 10th	Day	14% 5% 2 5% 4 5% 5% 4 6% 9% 41%	4645
	11th to 20th	Day	11% 5% 2 5% 4 4 5% 5% 7% 8% 44%	4336
	21st to end	Day	18% 8% 2 6% 4 5% 5% 4 6% 8% 32%	4675
September	1st to 10th	Day	18% 9% 3 8% 4 5% 4 4 5% 6% 34%	2410
	11th to 20th	Day	22% 11% 3 7% 4 4 4 3 4 6% 31%	2391
	21st to end	Day	20% 11% 3 8% 4 4 4 3 4 5% 34%	2091
October	1st to 10th	Day	20% 16% 5% 7% 6% 3 5% 3 5% 7% 23%	2000
	11th to 20th	Day	21% 21% 6% 10% 5% 4 3 2 4 5% 18%	2000
	21st to end	Day	19% 26% 8% 10% 5% 4 4 2 4 5% 14%	1834
November	1st to 10th	Day	16% 19% 9% 16% 8% 6% 4 3 3 4 12%	1647
	11th to 20th	Day	15% 19% 9% 16% 8% 6% 5% 3 4 3 11%	1680
	21st to end	Day	13% 21% 6% 21% 9% 8% 4 2 4 3 9%	1459
December	1st to 10th	Day	6% 15% 10% 19% 12% 10% 8% 4 4 4 8%	2020
	11th to 20th	Day	7% 18% 6% 13% 8% 6% 9% 4 8% 6% 15%	2316
	21st to end	Day	9% 17% 11% 15% 7% 6% 5% 3 6% 6% 16%	3123
January	1st to 10th	Night	6% 13% 6% 18% 10% 10% 8% 6% 6% 5% 12%	8800
	11th to 20th	Night	5% 12% 6% 20% 9% 7% 9% 9% 9% 3 10%	8803
	21st to end	Night	7% 12% 6% 15% 9% 8% 10% 7% 7% 6% 13%	9682
February	1st to 10th	Night	7% 12% 4 12% 10% 9% 10% 7% 7% 5% 17%	2840
	11th to 20th	Night	5% 10% 5% 12% 9% 8% 10% 8% 8% 6% 19%	2663
	21st to end	Night	4 12% 5% 14% 8% 6% 7% 6% 6% 7% 25%	2249
March	1st to 10th	Night	9% 13% 6% 12% 8% 8% 7% 4 5% 5% 24%	5465
	11th to 20th	Night	10% 13% 5% 13% 10% 8% 7% 4 5% 5% 21%	5089
	21st to end	Night	6% 12% 5% 9% 6% 8% 10% 5% 6% 7% 27%	5412
April	1st to 10th	Night	7% 9% 4 9% 6% 5% 4 4 6% 6% 41%	2100
	11th to 20th	Night	13% 11% 4 9% 5% 4 4 3 5% 6% 36%	1871
	21st to end	Night	8% 12% 4 9% 5% 4 5% 3 5% 5% 40%	1738
May	1st to 10th	Night	16% 14% 5% 10% 5% 4 3 3 3 4 33%	4688
	11th to 20th	Night	16% 12% 4 7% 5% 5% 4 3 5% 7% 31%	4372
	21st to end	Night	14% 7% 3 6% 4 3 4 3 5% 6% 47%	4430
June	1st to 10th	Night	19% 8% 3 8% 6% 5% 5% 4 5% 6% 31%	1260
	11th to 20th	Night	20% 10% 2 8% 6% 5% 5% 3 5% 6% 29%	1260
	21st to end	Night	14% 5% 3 8% 5% 5% 5% 5% 6% 8% 36%	1260
July	1st to 10th	Night	11% 3 1 4 4 4 5% 5% 7% 8% 47%	2983
	11th to 20th	Night	13% 6% 2 7% 5% 5% 5% 4 6% 8% 38%	3180
	21st to end	Night	11% 5% 2 5% 5% 5% 5% 4 6% 10% 42%	3469
August	1st to 10th	Night	13% 5% 2 6% 4 3 4 4 7% 8% 44%	2502
	11th to 20th	Night	12% 4 2 4 4 3 4 3 6% 8% 51%	2720
	21st to end	Night	18% 6% 2 6% 4 4 4 4 6% 9% 37%	3234
September	1st to 10th	Night	18% 7% 1 6% 4 5% 5% 3 6% 7% 38%	1990
	11th to 20th	Night	21% 9% 3 7% 4 4 4 3 5% 7% 33%	2005
	21st to end	Night	19% 10% 3 6% 4 4 4 4 5% 7% 35%	2288
October	1st to 10th	Night	22% 15% 4 7% 4 4 5% 3 4 5% 25%	2400
	11th to 20th	Night	21% 19% 5% 8% 4 5% 4 3 4 6% 21%	2400
	21st to end	Night	21% 23% 8% 11% 5% 4 4 3 4 4 15%	3005
November	1st to 10th	Night	18% 19% 7% 15% 6% 4 3 3 4 5% 16%	2871
	11th to 20th	Night	16% 18% 8% 16% 9% 7% 4 3 4 3 12%	2940
	21st to end	Night	11% 22% 10% 18% 10% 7% 4 3 3 3 7%	3155
December	1st to 10th	Night	7% 19% 8% 21% 12% 9% 7% 4 3 3 7%	5390
	11th to 20th	Night	7% 14% 6% 14% 10% 10% 9% 6% 7% 5% 13%	6111
	21st to end	Night	8% 18% 9% 18% 7% 7% 5% 3 4 3 18%	8093

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	74% 4 6% 10% 6%	4125
	11th to 20th	Day	70% 3 8% 14% 4	4140
	21st to end	Day	67% 3 6% 17% 7%	4532
February	1st to 10th	Day	59% 5% 9% 17% 9% 1	1779
	11th to 20th	Day	51% 5% 12% 22% 9%	1853
	21st to end	Day	55% 5% 10% 19% 11% 1	1557
March	1st to 10th	Day	58% 3 9% 16% 14% 1	4643
	11th to 20th	Day	64% 3 7% 14% 11%	5090
	21st to end	Day	55% 4 9% 21% 11% 1	5761
April	1st to 10th	Day	49% 4 11% 23% 13% 1	2520
	11th to 20th	Day	52% 4 8% 22% 13% 1	2697
	21st to end	Day	43% 5% 10% 26% 14% 2	2882
May	1st to 10th	Day	52% 4 10% 24% 10%	8250
	11th to 20th	Day	57% 6% 8% 18% 10% 1	8521
	21st to end	Day	38% 4 10% 25% 20% 4	9761
June	1st to 10th	Day	52% 6% 10% 19% 13%	3360
	11th to 20th	Day	51% 6% 10% 21% 12% 1	3360
	21st to end	Day	47% 7% 13% 21% 12% 1	3360
July	1st to 10th	Day	40% 6% 14% 33% 7%	6920
	11th to 20th	Day	40% 7% 17% 29% 6% 1	6719
	21st to end	Day	35% 8% 17% 35% 5%	7193
August	1st to 10th	Day	38% 7% 15% 33% 7%	4628
	11th to 20th	Day	35% 7% 19% 32% 7%	4378
	21st to end	Day	48% 6% 17% 19% 9%	4674
September	1st to 10th	Day	50% 7% 15% 21% 7%	2410
	11th to 20th	Day	55% 6% 15% 22% 2	2391
	21st to end	Day	53% 5% 14% 22% 6%	2091
October	1st to 10th	Day	57% 6% 13% 16% 7%	3260
	11th to 20th	Day	58% 5% 12% 17% 7%	3240
	21st to end	Day	70% 5% 10% 14% 1	2941
November	1st to 10th	Day	78% 4 9% 8% 2	1647
	11th to 20th	Day	78% 5% 7% 9% 1	1680
	21st to end	Day	82% 4 4 7% 3	1459
December	1st to 10th	Day	79% 3 9% 7% 2	2020
	11th to 20th	Day	67% 3 9% 14% 7%	2316
	21st to end	Day	69% 3 7% 14% 6%	3123
January	1st to 10th	Night	73% 4 6% 10% 7%	8800
	11th to 20th	Night	72% 3 8% 14% 3	8850
	21st to end	Night	70% 4 8% 14% 5%	9682
February	1st to 10th	Night	66% 4 9% 15% 6%	2840
	11th to 20th	Night	59% 6% 11% 18% 7%	2664
	21st to end	Night	56% 4 9% 19% 10% 1	2249
March	1st to 10th	Night	62% 3 8% 14% 12% 1	5476
	11th to 20th	Night	65% 5% 7% 13% 10% 1	5090
	21st to end	Night	56% 4 7% 22% 11% 1	5412
April	1st to 10th	Night	43% 4 9% 26% 17% 1	2100
	11th to 20th	Night	49% 4 9% 21% 15% 1	1871
	21st to end	Night	45% 4 8% 23% 18% 2	1738
May	1st to 10th	Night	56% 3 8% 20% 13%	4695
	11th to 20th	Night	53% 5% 10% 20% 12% 1	4373
	21st to end	Night	39% 4 6% 28% 21% 2	4430
June	1st to 10th	Night	51% 6% 9% 17% 17%	1260
	11th to 20th	Night	56% 5% 7% 19% 12% 2	1260
	21st to end	Night	44% 7% 14% 21% 14% 1	1260
July	1st to 10th	Night	32% 7% 16% 34% 11% 1	2948
	11th to 20th	Night	42% 8% 14% 30% 6% 1	3138
	21st to end	Night	36% 6% 15% 34% 8%	3368
August	1st to 10th	Night	36% 7% 13% 35% 9%	2495
	11th to 20th	Night	30% 7% 20% 36% 8%	2744
	21st to end	Night	44% 6% 22% 22% 5%	3234
September	1st to 10th	Night	45% 6% 18% 24% 6% 1	1990
	11th to 20th	Night	51% 6% 16% 24% 2	2005
	21st to end	Night	49% 7% 16% 22% 6%	2288
October	1st to 10th	Night	62% 6% 12% 16% 5%	3920
	11th to 20th	Night	55% 5% 18% 15% 7%	3899
	21st to end	Night	71% 5% 9% 15% 1	4856
November	1st to 10th	Night	72% 5% 11% 9% 3	2871
	11th to 20th	Night	78% 4 8% 8% 2	2940
	21st to end	Night	83% 4 6% 6% 2	3155
December	1st to 10th	Night	83% 3 7% 5% 2	5390
	11th to 20th	Night	71% 4 9% 12% 5%	6110
	21st to end	Night	71% 3 6% 16% 4	8093

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	12% 10% 41% 26% 10% 1	330
	11th to 20th	Day	13% 8% 36% 25% 15% 4	330
	21st to end	Day	14% 12% 33% 29% 9% 3	363
February	1st to 10th	Day	10% 12% 38% 31% 8% 1	330
	11th to 20th	Day	10% 7% 41% 26% 14% 2	330
	21st to end	Day	5% 12% 40% 23% 17% 2	273
March	1st to 10th	Day	12% 12% 38% 23% 9% 5%	330
	11th to 20th	Day	13% 18% 36% 25% 8% 2	330
	21st to end	Day	13% 15% 35% 25% 10% 2	436
April	1st to 10th	Day	12% 10% 30% 32% 14% 2	540
	11th to 20th	Day	19% 12% 33% 24% 11% 2	735
	21st to end	Day	13% 11% 32% 29% 11% 4	750
May	1st to 10th	Day	22% 11% 32% 25% 9% 1	753
	11th to 20th	Day	22% 12% 30% 22% 11% 2	775
	21st to end	Day	21% 13% 31% 24% 10% 2	844
June	1st to 10th	Day	23% 13% 29% 22% 8% 4	780
	11th to 20th	Day	21% 13% 30% 23% 10% 3	780
	21st to end	Day	18% 11% 27% 26% 13% 6%	780
July	1st to 10th	Day	15% 11% 28% 30% 13% 3	722
	11th to 20th	Day	18% 10% 28% 26% 14% 4	718
	21st to end	Day	14% 8% 26% 31% 14% 6%	794
August	1st to 10th	Day	18% 8% 25% 31% 14% 3	726
	11th to 20th	Day	15% 10% 22% 30% 17% 6%	715
	21st to end	Day	25% 7% 25% 27% 13% 2	803
September	1st to 10th	Day	23% 9% 32% 27% 7% 1	540
	11th to 20th	Day	25% 10% 27% 29% 8% 1	521
	21st to end	Day	26% 11% 33% 24% 5%	330
October	1st to 10th	Day	27% 14% 34% 19% 6% 2	330
	11th to 20th	Day	28% 12% 32% 21% 5% 2	330
	21st to end	Day	36% 8% 30% 19% 7%	363
November	1st to 10th	Day	22% 16% 35% 22% 5% 1	330
	11th to 20th	Day	22% 18% 31% 18% 8% 3	330
	21st to end	Day	23% 18% 41% 15% 4	273
December	1st to 10th	Day	15% 10% 42% 26% 6% 1	220
	11th to 20th	Day	14% 13% 44% 22% 6% 1	220
	21st to end	Day	16% 9% 33% 25% 14% 3	256
January	1st to 10th	Night	14% 9% 35% 30% 11% 2	1050
	11th to 20th	Night	16% 8% 32% 30% 12% 1	1050
	21st to end	Night	16% 6% 33% 34% 10% 1	1155
February	1st to 10th	Night	13% 7% 34% 34% 10% 2	1050
	11th to 20th	Night	10% 7% 30% 33% 17% 4	1029
	21st to end	Night	9% 7% 31% 33% 17% 2	865
March	1st to 10th	Night	15% 9% 30% 32% 13% 1	840
	11th to 20th	Night	16% 12% 33% 27% 12%	630
	21st to end	Night	14% 10% 30% 30% 12% 4	693
April	1st to 10th	Night	11% 6% 32% 38% 12% 2	630
	11th to 20th	Night	18% 8% 28% 32% 11% 3	623
	21st to end	Night	14% 9% 30% 33% 13% 2	630
May	1st to 10th	Night	25% 8% 25% 31% 9% 1	630
	11th to 20th	Night	22% 7% 30% 29% 11% 1	621
	21st to end	Night	25% 6% 29% 29% 10% 1	652
June	1st to 10th	Night	22% 7% 26% 30% 14% 1	420
	11th to 20th	Night	25% 6% 25% 30% 11% 2	420
	21st to end	Night	16% 4 24% 38% 17%	420
July	1st to 10th	Night	13% 6% 26% 37% 17% 1	492
	11th to 20th	Night	18% 6% 26% 33% 14% 2	582
	21st to end	Night	14% 3 23% 36% 21% 4	657
August	1st to 10th	Night	16% 5% 20% 42% 17% 1	597
	11th to 20th	Night	18% 6% 19% 36% 20% 2	594
	21st to end	Night	23% 6% 26% 31% 12% 1	660
September	1st to 10th	Night	20% 7% 34% 31% 9% 1	600
	11th to 20th	Night	27% 8% 23% 31% 10%	600
	21st to end	Night	26% 8% 30% 27% 8% 1	688
October	1st to 10th	Night	32% 10% 31% 21% 5% 1	800
	11th to 20th	Night	30% 11% 24% 25% 9% 2	800
	21st to end	Night	34% 9% 27% 22% 7% 1	1035
November	1st to 10th	Night	29% 12% 28% 22% 8% 2	1025
	11th to 20th	Night	26% 9% 32% 23% 8% 2	1050
	21st to end	Night	21% 14% 34% 22% 8% 1	1050
December	1st to 10th	Night	13% 8% 36% 29% 11% 2	1050
	11th to 20th	Night	14% 9% 34% 31% 11% 1	1050
	21st to end	Night	16% 7% 30% 32% 12% 3	1155

Page generated at 2026-06-28 01:10:44. Version ac07

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