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 2024-11-02.

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% 33%	102327
	Night	8% 10% 4 10% 6% 6% 6% 5% 6% 8% 32%	96686
Transparency	Day	47% 7% 17% 22% 7%	102068
	Night	48% 7% 16% 22% 7% 1	96591
Seeing	Day	15% 10% 29% 27% 15% 4	15915
	Night	14% 7% 29% 33% 15% 2	24501

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	4 15% 8% 17% 12% 7% 4 3 5% 5% 19%	2219
	11th to 20th	Day	5% 8% 4 10% 7% 8% 10% 9% 9% 7% 23%	2199
	21st to end	Day	6% 11% 5% 15% 9% 6% 5% 4 5% 7% 28%	2442
February	1st to 10th	Day	5% 15% 5% 13% 8% 6% 7% 5% 7% 7% 23%	1510
	11th to 20th	Day	6% 11% 4 11% 8% 7% 6% 5% 7% 7% 28%	1644
	21st to end	Day	4 13% 5% 10% 10% 8% 7% 5% 7% 8% 23%	1413
March	1st to 10th	Day	3 10% 4 9% 7% 7% 8% 6% 7% 9% 29%	3130
	11th to 20th	Day	5% 9% 4 8% 6% 5% 6% 5% 9% 10% 33%	3489
	21st to end	Day	10% 13% 4 14% 6% 4 4 4 6% 7% 28%	3825
April	1st to 10th	Day	7% 14% 4 9% 7% 6% 6% 4 6% 7% 29%	2411
	11th to 20th	Day	12% 13% 4 10% 6% 5% 5% 4 6% 6% 30%	2440
	21st to end	Day	13% 11% 3 9% 5% 6% 5% 4 6% 7% 29%	2536
May	1st to 10th	Day	15% 9% 3 9% 5% 5% 5% 5% 6% 8% 29%	4644
	11th to 20th	Day	16% 12% 3 8% 4 5% 5% 4 6% 7% 31%	4694
	21st to end	Day	12% 8% 3 8% 7% 6% 6% 5% 7% 9% 30%	5161
June	1st to 10th	Day	16% 8% 3 8% 5% 5% 5% 5% 6% 7% 31%	2990
	11th to 20th	Day	19% 10% 3 7% 6% 5% 6% 4 6% 7% 26%	3132
	21st to end	Day	12% 7% 3 7% 7% 5% 5% 5% 7% 10% 33%	3230
July	1st to 10th	Day	9% 6% 2 6% 4 5% 5% 4 6% 9% 43%	4878
	11th to 20th	Day	9% 5% 2 5% 4 4 4 5% 6% 9% 46%	4740
	21st to end	Day	16% 5% 2 5% 4 4 5% 4 6% 9% 40%	5138
August	1st to 10th	Day	12% 7% 3 6% 5% 4 4 4 5% 7% 44%	4720
	11th to 20th	Day	10% 6% 2 6% 4 4 5% 4 8% 9% 41%	4112
	21st to end	Day	10% 4 2 7% 4 4 5% 4 6% 9% 44%	4521
September	1st to 10th	Day	14% 6% 2 7% 5% 4 5% 3 6% 7% 40%	2413
	11th to 20th	Day	15% 9% 3 7% 4 5% 4 3 6% 8% 37%	2138
	21st to end	Day	9% 8% 3 6% 5% 4 4 4 7% 9% 41%	2090
October	1st to 10th	Day	10% 13% 5% 10% 5% 5% 5% 4 5% 7% 32%	1913
	11th to 20th	Day	12% 11% 3 8% 5% 4 5% 4 5% 6% 35%	1792
	21st to end	Day	9% 17% 5% 10% 6% 4 4 4 5% 7% 27%	1758
November	1st to 10th	Day	11% 15% 6% 10% 8% 7% 6% 4 6% 5% 23%	1496
	11th to 20th	Day	9% 13% 6% 13% 6% 7% 5% 5% 6% 6% 24%	1387
	21st to end	Day	5% 13% 6% 13% 9% 5% 6% 4 5% 7% 26%	1319
December	1st to 10th	Day	5% 13% 5% 14% 7% 7% 7% 6% 6% 8% 22%	1140
	11th to 20th	Day	7% 13% 5% 13% 9% 6% 5% 4 7% 6% 26%	1439
	21st to end	Day	3 7% 4 9% 7% 7% 6% 4 7% 8% 39%	2224
January	1st to 10th	Night	5% 12% 6% 18% 11% 8% 7% 4 5% 6% 18%	4726
	11th to 20th	Night	4 10% 4 10% 8% 8% 8% 7% 6% 9% 25%	4699
	21st to end	Night	6% 11% 4 13% 8% 6% 5% 4 7% 7% 30%	5214
February	1st to 10th	Night	6% 11% 5% 12% 9% 7% 6% 6% 6% 7% 25%	2689
	11th to 20th	Night	5% 12% 5% 12% 8% 6% 5% 4 7% 7% 30%	2423
	21st to end	Night	3 9% 4 10% 8% 7% 7% 7% 8% 8% 29%	2041
March	1st to 10th	Night	4 11% 5% 11% 7% 6% 7% 6% 8% 10% 26%	3742
	11th to 20th	Night	5% 9% 3 8% 6% 6% 7% 4 7% 10% 37%	3490
	21st to end	Night	9% 13% 5% 13% 6% 5% 5% 4 6% 7% 27%	3828
April	1st to 10th	Night	8% 11% 4 7% 6% 5% 6% 4 6% 8% 34%	1765
	11th to 20th	Night	8% 10% 4 10% 7% 6% 6% 5% 7% 7% 30%	1691
	21st to end	Night	11% 13% 4 7% 6% 5% 5% 3 6% 8% 32%	1644
May	1st to 10th	Night	16% 8% 2 9% 5% 5% 5% 4 7% 7% 32%	2316
	11th to 20th	Night	17% 10% 3 7% 4 5% 5% 4 6% 7% 34%	2199
	21st to end	Night	13% 8% 3 10% 6% 6% 5% 4 7% 7% 31%	2414
June	1st to 10th	Night	15% 9% 2 8% 5% 6% 7% 5% 6% 7% 30%	1188
	11th to 20th	Night	15% 10% 4 10% 5% 6% 5% 5% 6% 6% 28%	1041
	21st to end	Night	10% 7% 3 8% 6% 5% 6% 5% 5% 10% 36%	950
July	1st to 10th	Night	7% 5% 2 5% 4 4 5% 3 8% 10% 46%	2073
	11th to 20th	Night	6% 4 2 5% 4 4 5% 5% 8% 8% 49%	2220
	21st to end	Night	15% 5% 1 4 3 3 5% 3 6% 9% 45%	2414
August	1st to 10th	Night	11% 5% 2 7% 5% 5% 4 4 5% 7% 43%	2210
	11th to 20th	Night	9% 6% 3 8% 5% 5% 4 5% 7% 9% 40%	2721
	21st to end	Night	11% 5% 2 5% 4 5% 5% 4 6% 8% 45%	3146
September	1st to 10th	Night	13% 7% 2 6% 3 4 4 4 6% 7% 44%	1766
	11th to 20th	Night	12% 6% 2 6% 4 5% 4 4 6% 9% 42%	2039
	21st to end	Night	10% 6% 2 6% 4 4 5% 4 6% 9% 44%	2090
October	1st to 10th	Night	10% 11% 3 8% 5% 5% 5% 4 6% 8% 36%	2266
	11th to 20th	Night	10% 10% 3 7% 4 5% 5% 4 6% 8% 38%	2384
	21st to end	Night	11% 13% 5% 11% 7% 4 5% 5% 5% 6% 29%	2821
November	1st to 10th	Night	12% 16% 5% 11% 6% 6% 4 4 5% 5% 26%	2605
	11th to 20th	Night	8% 13% 5% 12% 7% 8% 6% 5% 6% 7% 23%	2791
	21st to end	Night	6% 14% 5% 12% 8% 6% 5% 5% 6% 8% 26%	2859
December	1st to 10th	Night	7% 12% 5% 11% 7% 7% 5% 5% 6% 7% 27%	3040
	11th to 20th	Night	8% 12% 6% 14% 10% 8% 6% 5% 5% 6% 21%	3753
	21st to end	Night	3 8% 3 9% 6% 6% 6% 4 7% 9% 41%	5428

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	66% 5% 11% 14% 4	2219
	11th to 20th	Day	53% 7% 14% 17% 7% 1	2220
	21st to end	Day	55% 6% 18% 13% 7%	2442
February	1st to 10th	Day	59% 6% 12% 13% 8%	1510
	11th to 20th	Day	54% 6% 14% 19% 7%	1653
	21st to end	Day	57% 5% 13% 17% 7%	1413
March	1st to 10th	Day	49% 8% 19% 21% 4	3130
	11th to 20th	Day	42% 8% 21% 23% 6%	3490
	21st to end	Day	54% 7% 10% 21% 8%	3825
April	1st to 10th	Day	52% 6% 14% 17% 10%	2411
	11th to 20th	Day	53% 5% 12% 19% 10% 1	2440
	21st to end	Day	53% 6% 12% 20% 8% 1	2536
May	1st to 10th	Day	51% 6% 11% 22% 9%	4644
	11th to 20th	Day	50% 7% 10% 23% 10% 1	4698
	21st to end	Day	47% 9% 17% 19% 8%	5162
June	1st to 10th	Day	50% 7% 14% 22% 8%	2990
	11th to 20th	Day	56% 7% 14% 18% 5%	3132
	21st to end	Day	46% 8% 18% 22% 6%	3230
July	1st to 10th	Day	36% 8% 23% 26% 6%	4804
	11th to 20th	Day	33% 7% 18% 30% 12%	4659
	21st to end	Day	41% 6% 23% 25% 6%	4976
August	1st to 10th	Day	40% 6% 20% 32% 1	4702
	11th to 20th	Day	37% 9% 26% 22% 7%	4152
	21st to end	Day	36% 7% 31% 24% 2	4520
September	1st to 10th	Day	43% 6% 19% 25% 6% 1	2413
	11th to 20th	Day	46% 6% 19% 24% 5%	2138
	21st to end	Day	39% 7% 20% 24% 9% 1	2090
October	1st to 10th	Day	50% 6% 19% 21% 5%	1913
	11th to 20th	Day	49% 5% 13% 27% 5%	1792
	21st to end	Day	56% 7% 16% 17% 4	1758
November	1st to 10th	Day	61% 6% 12% 18% 3	1496
	11th to 20th	Day	59% 8% 14% 15% 3	1387
	21st to end	Day	56% 8% 14% 17% 4	1319
December	1st to 10th	Day	57% 7% 10% 18% 6% 1	1140
	11th to 20th	Day	57% 6% 16% 18% 4	1440
	21st to end	Day	41% 6% 12% 31% 9% 1	2224
January	1st to 10th	Night	64% 7% 11% 12% 5% 1	4726
	11th to 20th	Night	53% 6% 13% 20% 6% 1	4740
	21st to end	Night	52% 7% 20% 15% 5%	5214
February	1st to 10th	Night	56% 5% 13% 18% 8%	2689
	11th to 20th	Night	51% 6% 13% 19% 10%	2424
	21st to end	Night	47% 7% 16% 19% 10% 1	2041
March	1st to 10th	Night	49% 7% 15% 24% 6%	3742
	11th to 20th	Night	40% 9% 19% 25% 6%	3490
	21st to end	Night	54% 7% 11% 21% 8%	3828
April	1st to 10th	Night	46% 6% 14% 21% 12% 1	1765
	11th to 20th	Night	51% 6% 10% 19% 10% 3	1691
	21st to end	Night	50% 4 10% 22% 11% 2	1644
May	1st to 10th	Night	48% 6% 9% 26% 10% 1	2316
	11th to 20th	Night	47% 6% 10% 24% 12% 1	2199
	21st to end	Night	47% 10% 15% 20% 7% 1	2414
June	1st to 10th	Night	50% 7% 14% 20% 8% 2	1188
	11th to 20th	Night	54% 7% 14% 19% 6% 1	1041
	21st to end	Night	42% 10% 16% 23% 7% 1	950
July	1st to 10th	Night	30% 9% 25% 27% 8% 1	2038
	11th to 20th	Night	30% 6% 17% 36% 8% 1	2178
	21st to end	Night	35% 6% 23% 29% 6%	2337
August	1st to 10th	Night	39% 6% 19% 34% 1	2203
	11th to 20th	Night	39% 8% 24% 23% 6%	2747
	21st to end	Night	35% 6% 27% 29% 3	3146
September	1st to 10th	Night	39% 5% 21% 26% 7% 2	1766
	11th to 20th	Night	39% 7% 18% 28% 8%	2039
	21st to end	Night	35% 7% 16% 29% 11% 2	2090
October	1st to 10th	Night	45% 6% 16% 24% 9%	2266
	11th to 20th	Night	44% 5% 16% 28% 6%	2384
	21st to end	Night	54% 6% 14% 19% 7%	2821
November	1st to 10th	Night	59% 5% 11% 19% 5%	2605
	11th to 20th	Night	59% 8% 16% 13% 4	2791
	21st to end	Night	55% 7% 17% 16% 4	2859
December	1st to 10th	Night	54% 6% 14% 19% 7% 1	3040
	11th to 20th	Night	64% 6% 13% 12% 5%	3751
	21st to end	Night	39% 6% 15% 24% 14% 2	5428

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% 8% 29% 36% 17% 3	180
	11th to 20th	Day	15% 6% 29% 32% 14% 4	180
	21st to end	Day	9% 9% 38% 30% 11% 4	198
February	1st to 10th	Day	10% 16% 36% 27% 9% 2	180
	11th to 20th	Day	10% 13% 31% 28% 16% 3	261
	21st to end	Day	7% 15% 32% 28% 12% 6%	225
March	1st to 10th	Day	9% 15% 37% 28% 8% 2	422
	11th to 20th	Day	11% 13% 41% 23% 8% 4	460
	21st to end	Day	17% 11% 33% 27% 10% 2	506
April	1st to 10th	Day	13% 17% 35% 24% 7% 3	460
	11th to 20th	Day	18% 12% 32% 22% 12% 4	452
	21st to end	Day	16% 16% 32% 25% 9% 2	526
May	1st to 10th	Day	13% 14% 25% 27% 15% 5%	653
	11th to 20th	Day	12% 9% 26% 30% 17% 6%	675
	21st to end	Day	18% 7% 23% 28% 20% 4	734
June	1st to 10th	Day	23% 10% 27% 27% 10% 3	680
	11th to 20th	Day	24% 8% 24% 22% 17% 6%	772
	21st to end	Day	13% 6% 22% 33% 20% 7%	870
July	1st to 10th	Day	13% 6% 22% 33% 22% 5%	738
	11th to 20th	Day	14% 5% 24% 30% 21% 6%	668
	21st to end	Day	12% 6% 27% 27% 22% 7%	739
August	1st to 10th	Day	15% 6% 21% 28% 21% 9%	676
	11th to 20th	Day	13% 8% 27% 31% 16% 4	490
	21st to end	Day	14% 8% 27% 27% 19% 5%	539
September	1st to 10th	Day	19% 12% 28% 24% 14% 3	490
	11th to 20th	Day	21% 10% 27% 28% 12% 3	490
	21st to end	Day	14% 13% 33% 24% 13% 2	490
October	1st to 10th	Day	17% 9% 32% 27% 13% 3	313
	11th to 20th	Day	22% 9% 40% 22% 7% 1	300
	21st to end	Day	20% 15% 32% 22% 10% 2	330
November	1st to 10th	Day	24% 9% 27% 27% 11% 3	273
	11th to 20th	Day	15% 12% 47% 17% 7% 1	207
	21st to end	Day	10% 12% 42% 23% 9% 4	180
December	1st to 10th	Day	9% 11% 37% 28% 13% 3	180
	11th to 20th	Day	11% 9% 39% 29% 12% 1	180
	21st to end	Day	6% 9% 30% 34% 16% 5%	198
January	1st to 10th	Night	11% 9% 32% 34% 12% 2	950
	11th to 20th	Night	12% 8% 31% 37% 10% 2	950
	21st to end	Night	14% 11% 34% 30% 9% 2	1045
February	1st to 10th	Night	12% 6% 29% 36% 14% 2	789
	11th to 20th	Night	11% 6% 33% 33% 15% 1	744
	21st to end	Night	7% 6% 29% 37% 19% 3	628
March	1st to 10th	Night	10% 7% 31% 36% 14% 2	760
	11th to 20th	Night	13% 7% 35% 29% 14% 1	760
	21st to end	Night	15% 8% 28% 33% 13% 2	836
April	1st to 10th	Night	12% 9% 28% 35% 15% 2	596
	11th to 20th	Night	13% 8% 33% 30% 16% 1	563
	21st to end	Night	17% 8% 28% 32% 14% 1	570
May	1st to 10th	Night	14% 7% 20% 33% 22% 3	437
	11th to 20th	Night	13% 7% 23% 36% 17% 3	374
	21st to end	Night	18% 5% 20% 32% 23% 2	411
June	1st to 10th	Night	20% 6% 22% 34% 17% 1	380
	11th to 20th	Night	20% 6% 22% 28% 22% 2	380
	21st to end	Night	14% 2 21% 33% 26% 3	380
July	1st to 10th	Night	12% 4 18% 35% 30% 1	370
	11th to 20th	Night	12% 4 19% 40% 22% 3	368
	21st to end	Night	11% 3 18% 38% 25% 5%	416
August	1st to 10th	Night	11% 3 14% 37% 29% 6%	378
	11th to 20th	Night	9% 5% 24% 37% 24% 2	514
	21st to end	Night	13% 4 21% 39% 21% 2	627
September	1st to 10th	Night	18% 6% 22% 31% 22% 2	570
	11th to 20th	Night	14% 6% 22% 40% 18% 1	709
	21st to end	Night	14% 7% 28% 35% 14% 2	760
October	1st to 10th	Night	17% 5% 30% 35% 12% 2	760
	11th to 20th	Night	16% 6% 31% 33% 11% 3	760
	21st to end	Night	18% 11% 32% 29% 9% 1	940
November	1st to 10th	Night	20% 6% 33% 30% 9% 2	931
	11th to 20th	Night	16% 8% 34% 28% 11% 3	950
	21st to end	Night	12% 10% 37% 30% 10% 1	950
December	1st to 10th	Night	13% 8% 32% 30% 14% 3	950
	11th to 20th	Night	12% 10% 33% 33% 10% 3	950
	21st to end	Night	9% 5% 32% 34% 17% 3	1045

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