Sheridan Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sheridan Lake clear sky chart from 2005-11-06 to 2026-02-16.

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	8% 11% 4 9% 6% 6% 5% 4 6% 8% 32%	134102
	Night	8% 13% 5% 11% 6% 6% 5% 4 6% 7% 29%	135406
Transparency	Day	47% 9% 15% 19% 8% 1	133810
	Night	51% 9% 15% 17% 7% 1	135277
Seeing	Day	15% 14% 26% 25% 16% 5%	17461
	Night	15% 13% 25% 30% 15% 2	25840

By Month

Percentage Cloud Cover NW (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% 20% 9% 18% 7% 6% 6% 4 5% 6% 13%	4125
	11th to 20th	Day	5% 9% 4 11% 7% 5% 6% 5% 8% 8% 30%	4119
	21st to end	Day	4 13% 5% 13% 7% 7% 6% 4 6% 8% 26%	5104
February	1st to 10th	Day	9% 19% 6% 12% 7% 7% 6% 4 5% 5% 21%	1733
	11th to 20th	Day	7% 17% 7% 10% 6% 5% 5% 4 5% 7% 27%	1801
	21st to end	Day	6% 15% 6% 13% 8% 8% 5% 4 7% 6% 23%	1550
March	1st to 10th	Day	4 13% 6% 13% 8% 7% 7% 5% 6% 8% 23%	4518
	11th to 20th	Day	3 10% 4 11% 7% 6% 7% 6% 8% 9% 29%	4899
	21st to end	Day	7% 13% 5% 12% 7% 7% 6% 4 6% 8% 25%	5810
April	1st to 10th	Day	6% 17% 5% 12% 7% 7% 6% 5% 7% 7% 22%	2400
	11th to 20th	Day	8% 15% 6% 10% 8% 6% 7% 5% 7% 6% 23%	2421
	21st to end	Day	9% 13% 4 10% 8% 6% 6% 4 6% 7% 27%	2800
May	1st to 10th	Day	8% 10% 4 8% 5% 5% 4 4 6% 8% 37%	6320
	11th to 20th	Day	9% 11% 4 10% 7% 8% 6% 5% 8% 9% 22%	6277
	21st to end	Day	12% 13% 3 9% 6% 6% 6% 5% 7% 8% 25%	7279
June	1st to 10th	Day	16% 10% 4 9% 6% 5% 6% 4 6% 7% 28%	3200
	11th to 20th	Day	17% 10% 4 10% 7% 6% 6% 5% 7% 7% 21%	3200
	21st to end	Day	11% 8% 3 9% 7% 6% 6% 4 7% 7% 33%	3200
July	1st to 10th	Day	7% 6% 2 6% 4 4 4 3 5% 8% 51%	7024
	11th to 20th	Day	6% 4 2 6% 4 4 4 4 5% 6% 55%	6780
	21st to end	Day	7% 5% 2 5% 4 4 5% 4 7% 9% 47%	7024
August	1st to 10th	Day	5% 4 2 5% 5% 5% 5% 5% 6% 9% 51%	4541
	11th to 20th	Day	4 4 2 6% 5% 6% 6% 5% 8% 11% 42%	4416
	21st to end	Day	10% 5% 2 6% 4 5% 4 4 7% 9% 43%	4490
September	1st to 10th	Day	11% 5% 2 6% 4 3 4 3 6% 8% 48%	2400
	11th to 20th	Day	12% 7% 2 7% 5% 5% 5% 3 6% 6% 41%	2400
	21st to end	Day	15% 10% 3 8% 5% 4 5% 4 5% 7% 33%	2135
October	1st to 10th	Day	11% 13% 4 9% 5% 5% 5% 4 5% 8% 31%	3280
	11th to 20th	Day	15% 12% 3 8% 4 5% 4 3 5% 6% 34%	3201
	21st to end	Day	10% 12% 5% 10% 6% 6% 6% 4 6% 7% 28%	3178
November	1st to 10th	Day	11% 19% 5% 12% 6% 6% 4 4 7% 5% 21%	1648
	11th to 20th	Day	12% 14% 4 12% 7% 6% 5% 5% 7% 6% 21%	1680
	21st to end	Day	9% 18% 5% 12% 6% 6% 6% 5% 6% 7% 20%	1520
December	1st to 10th	Day	8% 14% 4 13% 8% 7% 6% 5% 6% 6% 22%	2234
	11th to 20th	Day	6% 16% 6% 14% 8% 6% 7% 7% 8% 6% 16%	2322
	21st to end	Day	6% 14% 6% 12% 8% 7% 6% 5% 7% 6% 23%	3073
January	1st to 10th	Night	7% 20% 7% 18% 8% 6% 5% 4 5% 5% 13%	8810
	11th to 20th	Night	4 11% 5% 13% 7% 6% 5% 4 8% 7% 31%	8779
	21st to end	Night	5% 14% 5% 12% 6% 6% 6% 4 5% 7% 29%	9074
February	1st to 10th	Night	7% 20% 6% 13% 7% 6% 5% 3 5% 6% 22%	2884
	11th to 20th	Night	7% 16% 6% 10% 6% 5% 4 4 5% 6% 29%	2597
	21st to end	Night	6% 15% 5% 12% 8% 5% 6% 4 6% 6% 27%	2080
March	1st to 10th	Night	3 13% 6% 11% 5% 6% 7% 6% 8% 9% 26%	5376
	11th to 20th	Night	2 9% 6% 12% 7% 6% 7% 5% 7% 8% 31%	5097
	21st to end	Night	5% 13% 5% 12% 7% 7% 6% 5% 7% 7% 26%	5152
April	1st to 10th	Night	5% 14% 5% 12% 7% 6% 6% 6% 8% 7% 25%	2000
	11th to 20th	Night	6% 14% 4 8% 8% 6% 6% 5% 7% 7% 29%	1925
	21st to end	Night	8% 12% 5% 10% 7% 6% 5% 4 6% 7% 31%	1600
May	1st to 10th	Night	9% 12% 4 10% 6% 5% 4 4 5% 7% 33%	3640
	11th to 20th	Night	14% 11% 4 9% 5% 5% 5% 5% 6% 6% 29%	3616
	21st to end	Night	17% 12% 5% 9% 6% 5% 5% 4 6% 7% 24%	3576
June	1st to 10th	Night	16% 9% 4 11% 5% 6% 5% 4 5% 7% 28%	1200
	11th to 20th	Night	19% 12% 4 9% 8% 5% 5% 4 5% 8% 20%	1200
	21st to end	Night	11% 9% 3 10% 5% 6% 6% 5% 6% 7% 33%	1200
July	1st to 10th	Night	10% 6% 3 5% 3 4 4 3 5% 8% 49%	2919
	11th to 20th	Night	8% 5% 2 5% 4 4 4 4 6% 8% 50%	3180
	21st to end	Night	9% 7% 3 8% 5% 5% 5% 4 5% 8% 41%	3804
August	1st to 10th	Night	5% 5% 3 7% 5% 5% 6% 4 6% 7% 47%	2609
	11th to 20th	Night	6% 7% 3 7% 5% 6% 5% 4 7% 10% 38%	2631
	21st to end	Night	11% 7% 2 8% 5% 5% 5% 4 6% 8% 39%	3424
September	1st to 10th	Night	10% 5% 2 6% 4 4 5% 4 5% 7% 48%	2000
	11th to 20th	Night	10% 8% 2 6% 4 5% 4 4 6% 8% 43%	2000
	21st to end	Night	12% 9% 3 7% 5% 5% 5% 3 6% 7% 38%	2262
October	1st to 10th	Night	14% 12% 4 10% 6% 5% 5% 4 5% 7% 30%	3920
	11th to 20th	Night	11% 10% 3 9% 5% 5% 5% 4 6% 8% 32%	3954
	21st to end	Night	10% 12% 5% 10% 7% 5% 4 4 6% 7% 30%	4620
November	1st to 10th	Night	14% 14% 5% 10% 6% 5% 6% 4 6% 7% 23%	2870
	11th to 20th	Night	10% 15% 4 11% 7% 6% 6% 5% 6% 6% 25%	2940
	21st to end	Night	9% 18% 7% 11% 7% 7% 5% 5% 6% 6% 21%	3077
December	1st to 10th	Night	8% 12% 4 11% 7% 6% 6% 5% 7% 9% 25%	5160
	11th to 20th	Night	8% 20% 7% 15% 7% 6% 5% 5% 5% 6% 16%	6090
	21st to end	Night	4 16% 6% 13% 7% 7% 6% 5% 6% 6% 24%	8140

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% 10% 11% 8% 2	4125
	11th to 20th	Day	47% 8% 21% 13% 6% 4	4140
	21st to end	Day	53% 11% 16% 17% 2	5105
February	1st to 10th	Day	64% 7% 10% 10% 7% 1	1733
	11th to 20th	Day	55% 9% 15% 13% 7% 1	1810
	21st to end	Day	58% 9% 14% 13% 5%	1550
March	1st to 10th	Day	53% 9% 13% 17% 7%	4518
	11th to 20th	Day	45% 9% 16% 22% 8%	4899
	21st to end	Day	54% 10% 11% 17% 8%	5810
April	1st to 10th	Day	57% 11% 12% 15% 5%	2400
	11th to 20th	Day	56% 8% 13% 15% 7% 1	2421
	21st to end	Day	54% 8% 13% 17% 7%	2800
May	1st to 10th	Day	41% 7% 12% 26% 13% 1	6320
	11th to 20th	Day	51% 10% 14% 19% 5%	6280
	21st to end	Day	50% 11% 17% 18% 4	7280
June	1st to 10th	Day	53% 8% 11% 14% 11% 3	3200
	11th to 20th	Day	59% 10% 12% 14% 5%	3200
	21st to end	Day	47% 11% 15% 16% 9% 1	3200
July	1st to 10th	Day	31% 7% 14% 21% 18% 8%	6949
	11th to 20th	Day	29% 6% 14% 27% 19% 5%	6699
	21st to end	Day	30% 8% 18% 28% 13% 4	6827
August	1st to 10th	Day	27% 8% 12% 33% 19% 1	4524
	11th to 20th	Day	30% 11% 21% 28% 9% 1	4458
	21st to end	Day	35% 9% 25% 23% 6% 2	4489
September	1st to 10th	Day	34% 8% 19% 26% 10% 3	2400
	11th to 20th	Day	42% 8% 13% 25% 10% 2	2400
	21st to end	Day	48% 9% 17% 16% 9% 1	2135
October	1st to 10th	Day	48% 9% 20% 17% 5%	3280
	11th to 20th	Day	49% 8% 16% 23% 5%	3201
	21st to end	Day	52% 9% 20% 17% 2	3178
November	1st to 10th	Day	63% 9% 10% 13% 5%	1648
	11th to 20th	Day	58% 12% 15% 12% 3 1	1680
	21st to end	Day	60% 12% 16% 8% 4	1520
December	1st to 10th	Day	61% 9% 18% 10% 2	2234
	11th to 20th	Day	60% 12% 16% 8% 4	2324
	21st to end	Day	57% 11% 14% 15% 3	3073
January	1st to 10th	Night	69% 9% 11% 7% 3	8811
	11th to 20th	Night	48% 8% 17% 18% 6% 3	8820
	21st to end	Night	52% 13% 14% 18% 3	9074
February	1st to 10th	Night	62% 7% 11% 12% 7% 1	2884
	11th to 20th	Night	54% 9% 14% 16% 7% 1	2599
	21st to end	Night	55% 8% 16% 17% 4	2080
March	1st to 10th	Night	48% 11% 13% 18% 10%	5376
	11th to 20th	Night	43% 10% 16% 20% 10%	5098
	21st to end	Night	51% 12% 13% 14% 9%	5152
April	1st to 10th	Night	52% 11% 14% 16% 6%	2000
	11th to 20th	Night	49% 7% 15% 20% 9%	1925
	21st to end	Night	49% 10% 12% 19% 10% 1	1600
May	1st to 10th	Night	47% 7% 10% 23% 12% 1	3637
	11th to 20th	Night	48% 10% 14% 21% 5%	3616
	21st to end	Night	54% 9% 14% 18% 4	3576
June	1st to 10th	Night	52% 8% 10% 18% 9% 3	1200
	11th to 20th	Night	59% 10% 14% 12% 6%	1200
	21st to end	Night	47% 11% 16% 18% 8% 2	1200
July	1st to 10th	Night	32% 7% 13% 22% 17% 9%	2885
	11th to 20th	Night	29% 8% 12% 28% 21% 2	3138
	21st to end	Night	37% 9% 13% 22% 13% 6%	3696
August	1st to 10th	Night	32% 9% 11% 29% 18% 1	2601
	11th to 20th	Night	36% 10% 19% 25% 8% 2	2655
	21st to end	Night	40% 8% 25% 18% 7% 2	3424
September	1st to 10th	Night	33% 9% 16% 25% 15% 2	2000
	11th to 20th	Night	37% 9% 15% 24% 11% 4	2000
	21st to end	Night	44% 8% 17% 19% 10% 1	2262
October	1st to 10th	Night	52% 8% 19% 18% 4	3920
	11th to 20th	Night	47% 7% 16% 24% 5%	3954
	21st to end	Night	52% 7% 19% 19% 4	4620
November	1st to 10th	Night	58% 11% 13% 12% 4 1	2870
	11th to 20th	Night	58% 11% 14% 12% 5% 1	2940
	21st to end	Night	62% 10% 13% 10% 5%	3077
December	1st to 10th	Night	53% 9% 23% 11% 3	5160
	11th to 20th	Night	66% 9% 13% 9% 2	6087
	21st to end	Night	57% 10% 15% 15% 3	8140

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	18% 17% 36% 18% 6% 5%	220
	11th to 20th	Day	10% 21% 29% 23% 14% 3	220
	21st to end	Day	14% 22% 30% 21% 12% 1	242
February	1st to 10th	Day	20% 19% 31% 21% 6% 4	273
	11th to 20th	Day	13% 17% 32% 25% 11% 1	411
	21st to end	Day	12% 19% 34% 21% 12% 3	364
March	1st to 10th	Day	14% 20% 30% 24% 11% 1	500
	11th to 20th	Day	13% 22% 30% 20% 12% 3	500
	21st to end	Day	18% 20% 28% 19% 12% 4	550
April	1st to 10th	Day	16% 22% 28% 22% 9% 3	500
	11th to 20th	Day	13% 24% 27% 21% 10% 5%	492
	21st to end	Day	16% 15% 27% 25% 12% 5%	500
May	1st to 10th	Day	13% 18% 29% 23% 14% 3	503
	11th to 20th	Day	14% 10% 24% 29% 17% 5%	528
	21st to end	Day	17% 12% 23% 27% 17% 4	728
June	1st to 10th	Day	18% 13% 30% 24% 14% 2	930
	11th to 20th	Day	19% 10% 25% 28% 16% 3	930
	21st to end	Day	13% 9% 23% 30% 19% 5%	930
July	1st to 10th	Day	12% 6% 26% 29% 21% 6%	834
	11th to 20th	Day	9% 8% 23% 31% 24% 5%	718
	21st to end	Day	7% 5% 22% 31% 26% 8%	647
August	1st to 10th	Day	7% 6% 17% 30% 28% 11%	527
	11th to 20th	Day	8% 8% 21% 31% 22% 11%	517
	21st to end	Day	13% 8% 21% 24% 21% 13%	583
September	1st to 10th	Day	15% 8% 22% 28% 15% 11%	530
	11th to 20th	Day	15% 12% 20% 26% 19% 8%	530
	21st to end	Day	22% 14% 27% 23% 11% 3	530
October	1st to 10th	Day	22% 12% 25% 21% 15% 7%	530
	11th to 20th	Day	22% 18% 23% 20% 13% 3	495
	21st to end	Day	22% 18% 31% 18% 10% 2	357
November	1st to 10th	Day	22% 25% 29% 15% 7% 2	220
	11th to 20th	Day	22% 18% 26% 21% 10% 2	220
	21st to end	Day	16% 18% 26% 23% 12% 5%	220
December	1st to 10th	Day	13% 13% 29% 22% 18% 5%	220
	11th to 20th	Day	16% 18% 29% 21% 12% 4	220
	21st to end	Day	19% 15% 33% 22% 10% 2	242
January	1st to 10th	Night	21% 13% 33% 24% 8% 1	966
	11th to 20th	Night	15% 14% 27% 31% 12% 1	950
	21st to end	Night	14% 13% 30% 31% 11% 1	938
February	1st to 10th	Night	18% 14% 28% 27% 11% 2	840
	11th to 20th	Night	15% 11% 26% 38% 10% 1	804
	21st to end	Night	14% 13% 24% 30% 16% 2	660
March	1st to 10th	Night	13% 16% 27% 28% 13% 3	800
	11th to 20th	Night	10% 19% 30% 27% 13% 2	800
	21st to end	Night	11% 17% 23% 28% 18% 3	880
April	1st to 10th	Night	11% 13% 27% 30% 16% 3	800
	11th to 20th	Night	12% 11% 30% 31% 15% 2	737
	21st to end	Night	10% 14% 32% 28% 14% 3	400
May	1st to 10th	Night	16% 11% 26% 30% 17% 1	400
	11th to 20th	Night	15% 8% 25% 36% 14% 2	394
	21st to end	Night	17% 6% 24% 27% 23% 2	433
June	1st to 10th	Night	18% 11% 25% 33% 12% 1	400
	11th to 20th	Night	20% 8% 24% 31% 15% 3	400
	21st to end	Night	11% 8% 21% 34% 22% 4	400
July	1st to 10th	Night	15% 4 21% 33% 25% 2	390
	11th to 20th	Night	11% 5% 19% 37% 24% 4	388
	21st to end	Night	9% 4 18% 35% 30% 4	438
August	1st to 10th	Night	8% 3 12% 36% 36% 6%	398
	11th to 20th	Night	8% 6% 11% 36% 33% 5%	424
	21st to end	Night	11% 6% 17% 35% 27% 4	761
September	1st to 10th	Night	13% 6% 17% 35% 25% 5%	800
	11th to 20th	Night	14% 7% 14% 30% 31% 5%	800
	21st to end	Night	18% 12% 23% 30% 14% 3	800
October	1st to 10th	Night	18% 13% 19% 31% 18% 2	800
	11th to 20th	Night	19% 15% 22% 28% 15% 2	800
	21st to end	Night	22% 14% 27% 25% 10% 2	880
November	1st to 10th	Night	23% 18% 25% 26% 7% 1	820
	11th to 20th	Night	21% 19% 25% 25% 10% 1	840
	21st to end	Night	19% 16% 26% 27% 9% 2	977
December	1st to 10th	Night	15% 15% 26% 31% 13% 1	1086
	11th to 20th	Night	18% 16% 27% 29% 9% 1	1160
	21st to end	Night	16% 18% 31% 27% 8%	1276

Page generated at 2026-02-12 22:42:15. Version ac07

Copyright © 2026 Attilla Danko.