Shaw Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Shaw Lake clear sky chart from 2005-11-06 to 2026-09-14.

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	10% 9% 3 9% 6% 5% 5% 4 6% 8% 34%	154425
	Night	8% 10% 4 10% 6% 6% 6% 4 6% 8% 32%	145325
Transparency	Day	47% 6% 17% 23% 7%	154121
	Night	49% 6% 16% 21% 8% 1	145214
Seeing	Day	15% 10% 29% 27% 15% 4	18436
	Night	14% 8% 29% 33% 15% 2	26882

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% 14% 7% 15% 9% 7% 7% 5% 5% 5% 21%	4125
	11th to 20th	Day	4 10% 5% 11% 7% 6% 7% 6% 7% 8% 30%	4119
	21st to end	Day	5% 12% 6% 15% 9% 6% 5% 4 6% 8% 25%	4531
February	1st to 10th	Day	5% 14% 4 13% 7% 6% 6% 5% 7% 7% 24%	1670
	11th to 20th	Day	5% 11% 4 10% 9% 8% 6% 5% 6% 7% 29%	1822
	21st to end	Day	4 13% 5% 10% 9% 8% 7% 6% 7% 8% 23%	1557
March	1st to 10th	Day	5% 9% 4 9% 7% 7% 8% 6% 7% 9% 29%	4607
	11th to 20th	Day	5% 9% 4 11% 7% 6% 6% 4 8% 9% 30%	5109
	21st to end	Day	10% 16% 6% 14% 5% 3 4 3 5% 7% 26%	5607
April	1st to 10th	Day	7% 13% 5% 9% 7% 6% 5% 4 6% 8% 30%	2666
	11th to 20th	Day	11% 13% 4 10% 6% 5% 5% 4 6% 7% 30%	2700
	21st to end	Day	13% 11% 4 9% 5% 5% 5% 4 6% 7% 30%	2803
May	1st to 10th	Day	9% 6% 3 8% 5% 5% 6% 5% 7% 8% 38%	8619
	11th to 20th	Day	17% 12% 3 9% 5% 5% 5% 4 6% 7% 27%	8755
	21st to end	Day	10% 7% 3 7% 6% 6% 6% 4 7% 9% 35%	9649
June	1st to 10th	Day	16% 8% 3 7% 5% 5% 5% 5% 7% 7% 32%	3305
	11th to 20th	Day	19% 10% 3 8% 6% 5% 6% 4 6% 8% 25%	3462
	21st to end	Day	12% 7% 3 7% 6% 5% 5% 5% 7% 10% 33%	3570
July	1st to 10th	Day	10% 6% 2 6% 5% 5% 5% 5% 7% 10% 38%	9084
	11th to 20th	Day	10% 5% 2 7% 4 5% 5% 4 6% 9% 44%	8820
	21st to end	Day	10% 4 2 5% 4 4 5% 4 7% 9% 45%	9569
August	1st to 10th	Day	13% 6% 2 6% 5% 4 5% 4 7% 9% 40%	6910
	11th to 20th	Day	10% 6% 2 7% 4 5% 6% 5% 8% 9% 37%	6066
	21st to end	Day	9% 4 2 6% 4 4 5% 4 6% 10% 46%	6570
September	1st to 10th	Day	13% 6% 2 6% 5% 4 5% 4 5% 8% 41%	2667
	11th to 20th	Day	14% 8% 3 7% 4 5% 4 3 6% 8% 38%	2287
	21st to end	Day	9% 8% 3 6% 5% 4 4 4 6% 8% 43%	2200
October	1st to 10th	Day	9% 13% 4 8% 4 5% 4 4 6% 9% 34%	3283
	11th to 20th	Day	13% 11% 4 8% 5% 4 5% 4 6% 7% 33%	3066
	21st to end	Day	8% 17% 6% 11% 5% 4 5% 4 6% 7% 27%	2983
November	1st to 10th	Day	11% 15% 6% 10% 7% 6% 6% 4 5% 5% 25%	1648
	11th to 20th	Day	8% 13% 6% 13% 6% 7% 5% 5% 6% 7% 24%	1533
	21st to end	Day	5% 12% 6% 13% 9% 6% 6% 4 5% 7% 26%	1457
December	1st to 10th	Day	8% 14% 6% 16% 7% 5% 6% 5% 6% 8% 19%	2020
	11th to 20th	Day	8% 16% 7% 13% 8% 6% 5% 3 6% 5% 23%	2319
	21st to end	Day	3 9% 5% 13% 9% 8% 6% 4 6% 7% 31%	3267
January	1st to 10th	Night	7% 12% 5% 15% 10% 7% 7% 5% 7% 6% 19%	8768
	11th to 20th	Night	3 9% 4 9% 7% 7% 7% 6% 6% 9% 33%	8779
	21st to end	Night	6% 11% 5% 13% 9% 7% 6% 4 6% 7% 28%	9650
February	1st to 10th	Night	6% 11% 5% 12% 8% 7% 6% 6% 7% 7% 25%	2971
	11th to 20th	Night	4 11% 4 12% 8% 6% 5% 5% 7% 7% 31%	2685
	21st to end	Night	3 10% 4 10% 8% 7% 7% 7% 8% 8% 28%	2249
March	1st to 10th	Night	4 9% 4 11% 7% 8% 7% 6% 8% 9% 28%	5503
	11th to 20th	Night	5% 10% 4 10% 6% 5% 6% 4 7% 9% 33%	5110
	21st to end	Night	11% 16% 6% 12% 6% 5% 4 3 5% 7% 26%	5610
April	1st to 10th	Night	8% 11% 4 7% 6% 5% 6% 5% 7% 8% 35%	1950
	11th to 20th	Night	8% 10% 4 10% 7% 6% 6% 5% 7% 7% 31%	1871
	21st to end	Night	11% 13% 4 7% 6% 5% 5% 3 6% 8% 32%	1817
May	1st to 10th	Night	11% 6% 2 6% 4 4 4 4 6% 9% 45%	4306
	11th to 20th	Night	18% 12% 4 8% 5% 6% 5% 4 5% 6% 28%	4105
	21st to end	Night	12% 7% 3 9% 5% 5% 6% 4 7% 8% 34%	4522
June	1st to 10th	Night	16% 9% 2 8% 5% 6% 7% 5% 6% 7% 30%	1313
	11th to 20th	Night	16% 10% 4 9% 6% 6% 5% 4 6% 6% 28%	1151
	21st to end	Night	10% 7% 3 8% 6% 6% 6% 5% 6% 9% 36%	1050
July	1st to 10th	Night	6% 5% 2 5% 4 5% 6% 4 8% 11% 45%	3853
	11th to 20th	Night	7% 5% 3 6% 5% 4 5% 4 7% 8% 46%	4140
	21st to end	Night	11% 5% 2 6% 4 4 5% 3 6% 8% 46%	4499
August	1st to 10th	Night	11% 6% 2 7% 5% 6% 5% 5% 6% 8% 39%	3240
	11th to 20th	Night	11% 6% 2 8% 5% 5% 5% 5% 7% 8% 39%	3991
	21st to end	Night	10% 5% 2 5% 4 4 5% 4 6% 8% 47%	4578
September	1st to 10th	Night	12% 7% 2 6% 3 4 4 4 6% 8% 44%	1952
	11th to 20th	Night	12% 6% 2 6% 4 5% 4 4 6% 9% 43%	2177
	21st to end	Night	10% 6% 2 6% 4 4 5% 4 6% 9% 44%	2200
October	1st to 10th	Night	8% 9% 2 7% 5% 5% 6% 5% 7% 9% 37%	3906
	11th to 20th	Night	11% 9% 3 7% 5% 5% 4 4 7% 8% 37%	4078
	21st to end	Night	10% 10% 6% 11% 6% 4 6% 5% 7% 8% 26%	4785
November	1st to 10th	Night	12% 16% 5% 11% 6% 6% 4 4 5% 5% 25%	2870
	11th to 20th	Night	8% 13% 5% 12% 7% 8% 6% 5% 6% 7% 24%	3085
	21st to end	Night	6% 13% 5% 12% 8% 6% 5% 4 6% 8% 25%	3161
December	1st to 10th	Night	9% 14% 6% 15% 7% 6% 5% 4 6% 6% 20%	5380
	11th to 20th	Night	6% 15% 7% 15% 10% 7% 5% 4 5% 6% 18%	6093
	21st to end	Night	3 9% 4 12% 9% 6% 5% 4 6% 7% 34%	7927

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	65% 4 9% 17% 6%	4125
	11th to 20th	Day	51% 6% 17% 15% 11% 1	4140
	21st to end	Day	58% 6% 19% 11% 7%	4531
February	1st to 10th	Day	57% 6% 13% 14% 10%	1670
	11th to 20th	Day	52% 6% 13% 20% 9%	1831
	21st to end	Day	56% 6% 14% 18% 6%	1557
March	1st to 10th	Day	49% 6% 18% 21% 5%	4607
	11th to 20th	Day	48% 6% 16% 23% 7%	5110
	21st to end	Day	56% 5% 9% 21% 9%	5607
April	1st to 10th	Day	51% 6% 14% 18% 10%	2666
	11th to 20th	Day	53% 5% 12% 19% 11% 1	2700
	21st to end	Day	52% 5% 12% 21% 9%	2803
May	1st to 10th	Day	42% 5% 11% 27% 13% 1	8619
	11th to 20th	Day	54% 5% 8% 25% 7%	8759
	21st to end	Day	42% 8% 18% 22% 9% 1	9650
June	1st to 10th	Day	49% 7% 13% 22% 8% 1	3305
	11th to 20th	Day	56% 7% 13% 19% 5%	3462
	21st to end	Day	45% 8% 17% 22% 7%	3570
July	1st to 10th	Day	40% 8% 23% 25% 5%	9010
	11th to 20th	Day	36% 6% 14% 31% 13%	8739
	21st to end	Day	34% 6% 22% 32% 6%	9362
August	1st to 10th	Day	40% 6% 23% 29% 1	6892
	11th to 20th	Day	39% 8% 26% 22% 4	6106
	21st to end	Day	34% 6% 28% 30% 2	6569
September	1st to 10th	Day	42% 6% 20% 26% 6% 1	2667
	11th to 20th	Day	44% 6% 20% 25% 6%	2287
	21st to end	Day	38% 7% 19% 26% 9% 1	2200
October	1st to 10th	Day	46% 5% 21% 25% 3	3283
	11th to 20th	Day	50% 5% 15% 26% 4	3066
	21st to end	Day	56% 6% 19% 16% 2	2983
November	1st to 10th	Day	60% 5% 12% 18% 4	1648
	11th to 20th	Day	57% 8% 14% 16% 4	1533
	21st to end	Day	57% 8% 13% 17% 4	1457
December	1st to 10th	Day	62% 7% 11% 15% 4	2020
	11th to 20th	Day	62% 5% 15% 16% 3	2320
	21st to end	Day	51% 5% 12% 25% 6% 1	3267
January	1st to 10th	Night	63% 6% 10% 14% 8%	8769
	11th to 20th	Night	47% 5% 16% 20% 11% 1	8820
	21st to end	Night	55% 7% 19% 13% 6%	9650
February	1st to 10th	Night	55% 5% 13% 17% 10%	2971
	11th to 20th	Night	50% 6% 12% 20% 11%	2686
	21st to end	Night	49% 7% 16% 18% 9% 1	2249
March	1st to 10th	Night	49% 6% 17% 22% 7%	5503
	11th to 20th	Night	46% 7% 16% 25% 7%	5110
	21st to end	Night	57% 6% 8% 18% 12%	5610
April	1st to 10th	Night	46% 5% 14% 21% 12% 1	1950
	11th to 20th	Night	50% 6% 11% 19% 11% 3	1871
	21st to end	Night	50% 4 10% 23% 11% 2	1817
May	1st to 10th	Night	35% 5% 10% 32% 17% 2	4306
	11th to 20th	Night	55% 5% 8% 25% 7%	4105
	21st to end	Night	44% 8% 16% 25% 6% 1	4526
June	1st to 10th	Night	50% 7% 13% 20% 9% 1	1313
	11th to 20th	Night	53% 7% 14% 19% 6% 1	1151
	21st to end	Night	42% 9% 16% 23% 7% 1	1050
July	1st to 10th	Night	30% 9% 24% 29% 8%	3818
	11th to 20th	Night	34% 5% 16% 33% 11% 1	4098
	21st to end	Night	35% 6% 22% 31% 5%	4401
August	1st to 10th	Night	40% 7% 23% 27% 1	3233
	11th to 20th	Night	40% 8% 23% 24% 4	4017
	21st to end	Night	34% 5% 23% 35% 3	4578
September	1st to 10th	Night	39% 6% 21% 26% 6% 2	1952
	11th to 20th	Night	38% 6% 18% 29% 9%	2177
	21st to end	Night	36% 7% 17% 29% 10% 2	2200
October	1st to 10th	Night	42% 5% 21% 25% 7%	3906
	11th to 20th	Night	44% 5% 17% 29% 5%	4078
	21st to end	Night	54% 5% 18% 19% 4	4785
November	1st to 10th	Night	60% 5% 11% 19% 5%	2870
	11th to 20th	Night	58% 8% 15% 14% 5%	3085
	21st to end	Night	56% 7% 16% 17% 5%	3161
December	1st to 10th	Night	63% 6% 13% 13% 5% 1	5380
	11th to 20th	Night	67% 5% 14% 11% 3	6091
	21st to end	Night	48% 5% 13% 22% 11% 1	7927

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	7% 9% 29% 37% 16% 2	220
	11th to 20th	Day	15% 10% 30% 29% 12% 3	220
	21st to end	Day	10% 12% 38% 28% 10% 3	242
February	1st to 10th	Day	8% 15% 35% 27% 12% 2	220
	11th to 20th	Day	9% 13% 33% 29% 14% 2	319
	21st to end	Day	8% 16% 33% 29% 10% 5%	273
March	1st to 10th	Day	10% 16% 38% 27% 8% 1	498
	11th to 20th	Day	12% 13% 40% 24% 8% 3	540
	21st to end	Day	17% 12% 33% 27% 9% 2	594
April	1st to 10th	Day	13% 16% 36% 25% 8% 2	540
	11th to 20th	Day	17% 13% 34% 21% 11% 3	532
	21st to end	Day	16% 16% 31% 24% 11% 3	613
May	1st to 10th	Day	13% 16% 26% 27% 14% 5%	753
	11th to 20th	Day	14% 10% 25% 29% 17% 6%	775
	21st to end	Day	18% 8% 25% 27% 19% 4	844
June	1st to 10th	Day	23% 12% 27% 26% 10% 3	780
	11th to 20th	Day	23% 7% 23% 23% 17% 6%	882
	21st to end	Day	13% 6% 23% 31% 20% 7%	990
July	1st to 10th	Day	14% 7% 22% 32% 20% 5%	845
	11th to 20th	Day	13% 6% 26% 29% 20% 6%	768
	21st to end	Day	11% 6% 26% 27% 22% 7%	849
August	1st to 10th	Day	15% 6% 22% 28% 21% 8%	776
	11th to 20th	Day	14% 9% 27% 30% 16% 4	572
	21st to end	Day	12% 7% 26% 28% 21% 6%	627
September	1st to 10th	Day	18% 12% 28% 24% 15% 3	570
	11th to 20th	Day	19% 9% 26% 30% 13% 3	543
	21st to end	Day	14% 15% 34% 24% 12% 2	530
October	1st to 10th	Day	16% 9% 33% 27% 12% 2	343
	11th to 20th	Day	23% 10% 39% 21% 7% 1	330
	21st to end	Day	20% 16% 33% 21% 9% 2	363
November	1st to 10th	Day	22% 9% 32% 25% 9% 2	330
	11th to 20th	Day	16% 12% 48% 17% 7% 1	253
	21st to end	Day	10% 10% 42% 24% 10% 4	220
December	1st to 10th	Day	10% 12% 37% 27% 12% 2	220
	11th to 20th	Day	13% 10% 39% 26% 11%	220
	21st to end	Day	7% 9% 30% 33% 17% 5%	242
January	1st to 10th	Night	12% 9% 32% 33% 12% 2	1050
	11th to 20th	Night	12% 10% 32% 35% 9% 2	1050
	21st to end	Night	14% 12% 34% 28% 9% 2	1155
February	1st to 10th	Night	12% 7% 29% 36% 14% 2	871
	11th to 20th	Night	11% 6% 34% 34% 14% 1	824
	21st to end	Night	7% 7% 29% 37% 18% 3	692
March	1st to 10th	Night	9% 7% 32% 36% 13% 2	840
	11th to 20th	Night	13% 8% 35% 30% 13% 1	840
	21st to end	Night	16% 8% 28% 33% 13% 2	924
April	1st to 10th	Night	12% 8% 28% 36% 14% 2	658
	11th to 20th	Night	12% 9% 34% 29% 15% 1	623
	21st to end	Night	17% 7% 27% 33% 14% 1	630
May	1st to 10th	Night	14% 8% 22% 34% 20% 2	483
	11th to 20th	Night	14% 7% 22% 36% 17% 4	414
	21st to end	Night	17% 5% 20% 33% 22% 2	455
June	1st to 10th	Night	21% 7% 22% 32% 17% 1	420
	11th to 20th	Night	21% 5% 21% 28% 22% 2	420
	21st to end	Night	14% 2 21% 34% 26% 3	420
July	1st to 10th	Night	11% 4 19% 36% 29% 1	410
	11th to 20th	Night	12% 4 20% 40% 22% 2	408
	21st to end	Night	10% 3 18% 39% 25% 5%	460
August	1st to 10th	Night	11% 3 14% 37% 29% 5%	418
	11th to 20th	Night	10% 5% 23% 37% 23% 2	568
	21st to end	Night	13% 4 22% 38% 22% 1	693
September	1st to 10th	Night	17% 6% 21% 32% 21% 2	630
	11th to 20th	Night	13% 6% 21% 41% 19% 1	756
	21st to end	Night	14% 7% 29% 34% 14% 2	800
October	1st to 10th	Night	16% 6% 31% 33% 12% 2	800
	11th to 20th	Night	17% 7% 30% 33% 11% 3	800
	21st to end	Night	18% 11% 32% 28% 8% 1	990
November	1st to 10th	Night	21% 8% 32% 29% 9% 2	1025
	11th to 20th	Night	16% 9% 34% 28% 10% 3	1050
	21st to end	Night	11% 10% 37% 30% 11% 1	1050
December	1st to 10th	Night	13% 9% 33% 29% 12% 3	1050
	11th to 20th	Night	12% 11% 34% 31% 9% 2	1050
	21st to end	Night	10% 6% 33% 33% 16% 3	1155

Page generated at 2026-09-11 02:11:56. Version ac07

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