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 2024-03-08.

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% 4 8% 7% 4 6% 6% 6% 8% 32%	78016
	Night	8% 9% 4 9% 8% 5% 6% 6% 6% 8% 32%	81469
Transparency	Day	49% 7% 16% 21% 6%	77717
	Night	49% 7% 15% 21% 8% 1	81348
Seeing	Day	15% 10% 29% 28% 15% 4	14868
	Night	14% 7% 29% 33% 15% 2	23804

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 14% 9% 14% 14% 5% 5% 4 5% 5% 20%	2219
	11th to 20th	Day	5% 8% 4 9% 8% 6% 9% 12% 9% 8% 23%	2199
	21st to end	Day	6% 10% 5% 13% 10% 5% 6% 5% 5% 7% 28%	2442
February	1st to 10th	Day	5% 13% 6% 12% 9% 4 7% 7% 7% 6% 23%	1510
	11th to 20th	Day	6% 11% 5% 10% 10% 5% 7% 7% 6% 7% 28%	1644
	21st to end	Day	4 11% 7% 9% 11% 6% 8% 6% 7% 8% 23%	1413
March	1st to 10th	Day	6% 12% 5% 11% 10% 6% 7% 6% 6% 8% 23%	1859
	11th to 20th	Day	8% 11% 5% 9% 7% 4 5% 5% 5% 8% 32%	1979
	21st to end	Day	9% 13% 6% 10% 7% 3 5% 6% 6% 8% 28%	2178
April	1st to 10th	Day	8% 12% 5% 9% 8% 4 7% 5% 5% 8% 29%	2283
	11th to 20th	Day	12% 12% 4 8% 7% 4 6% 5% 5% 6% 29%	2310
	21st to end	Day	13% 10% 4 8% 6% 4 6% 5% 6% 8% 30%	2402
May	1st to 10th	Day	10% 8% 3 8% 7% 5% 6% 7% 6% 8% 32%	2643
	11th to 20th	Day	10% 6% 2 6% 6% 5% 6% 6% 7% 8% 38%	2654
	21st to end	Day	15% 7% 3 6% 6% 3 5% 5% 6% 8% 37%	2917
June	1st to 10th	Day	16% 8% 3 7% 6% 4 6% 6% 6% 7% 32%	2832
	11th to 20th	Day	19% 9% 4 7% 7% 4 6% 5% 6% 8% 25%	2967
	21st to end	Day	12% 6% 3 6% 7% 3 6% 6% 7% 10% 32%	3060
July	1st to 10th	Day	12% 5% 3 6% 6% 4 6% 6% 6% 9% 38%	2782
	11th to 20th	Day	12% 6% 3 6% 6% 4 5% 5% 7% 10% 36%	2700
	21st to end	Day	10% 6% 2 5% 5% 3 6% 6% 7% 10% 39%	2938
August	1st to 10th	Day	12% 6% 3 5% 6% 3 5% 6% 7% 10% 38%	2686
	11th to 20th	Day	9% 6% 2 5% 5% 3 5% 6% 8% 9% 42%	2359
	21st to end	Day	10% 6% 3 8% 5% 4 5% 5% 7% 9% 39%	2574
September	1st to 10th	Day	14% 6% 2 6% 7% 3 5% 5% 5% 7% 39%	2286
	11th to 20th	Day	15% 8% 4 6% 5% 3 5% 4 6% 8% 37%	2026
	21st to end	Day	9% 7% 3 6% 5% 3 5% 5% 7% 9% 41%	1980
October	1st to 10th	Day	10% 12% 5% 9% 6% 4 4 5% 5% 7% 33%	1813
	11th to 20th	Day	11% 10% 4 8% 6% 3 5% 5% 5% 7% 36%	1698
	21st to end	Day	10% 17% 5% 10% 7% 4 4 5% 5% 7% 27%	1666
November	1st to 10th	Day	11% 14% 7% 9% 9% 5% 7% 6% 5% 5% 23%	1488
	11th to 20th	Day	9% 12% 6% 12% 8% 6% 6% 6% 6% 6% 24%	1387
	21st to end	Day	5% 11% 7% 12% 10% 4 6% 5% 5% 8% 26%	1319
December	1st to 10th	Day	5% 10% 8% 13% 7% 5% 7% 8% 6% 8% 22%	1140
	11th to 20th	Day	7% 13% 5% 10% 11% 5% 5% 5% 6% 7% 26%	1439
	21st to end	Day	3 7% 4 7% 8% 5% 6% 6% 7% 8% 39%	2224
January	1st to 10th	Night	5% 11% 6% 15% 14% 6% 7% 6% 5% 6% 19%	4726
	11th to 20th	Night	4 9% 5% 8% 9% 6% 9% 9% 6% 9% 25%	4699
	21st to end	Night	6% 10% 5% 11% 10% 5% 5% 5% 7% 7% 30%	5214
February	1st to 10th	Night	6% 10% 5% 10% 10% 5% 7% 6% 7% 7% 26%	2689
	11th to 20th	Night	5% 11% 5% 11% 9% 4 5% 5% 7% 7% 30%	2423
	21st to end	Night	4 8% 5% 8% 8% 5% 8% 8% 8% 8% 29%	2041
March	1st to 10th	Night	6% 10% 5% 11% 8% 5% 6% 6% 7% 9% 28%	2261
	11th to 20th	Night	8% 11% 4 8% 6% 3 6% 5% 7% 9% 32%	1980
	21st to end	Night	9% 14% 6% 9% 6% 4 6% 6% 6% 8% 28%	2178
April	1st to 10th	Night	8% 10% 4 6% 6% 4 6% 5% 6% 9% 36%	1673
	11th to 20th	Night	9% 9% 4 9% 8% 4 7% 6% 7% 7% 31%	1601
	21st to end	Night	12% 12% 4 7% 6% 4 5% 4 6% 8% 32%	1558
May	1st to 10th	Night	9% 7% 3 7% 7% 4 5% 5% 6% 7% 40%	1314
	11th to 20th	Night	9% 6% 3 6% 5% 4 5% 5% 6% 7% 44%	1239
	21st to end	Night	16% 8% 4 6% 6% 3 5% 4 7% 7% 35%	1358
June	1st to 10th	Night	16% 7% 2 8% 6% 4 7% 7% 6% 8% 30%	1126
	11th to 20th	Night	15% 9% 5% 9% 5% 4 6% 6% 6% 7% 28%	987
	21st to end	Night	10% 6% 3 6% 8% 5% 6% 6% 6% 9% 36%	900
July	1st to 10th	Night	10% 6% 2 5% 5% 4 4 5% 7% 10% 42%	1169
	11th to 20th	Night	10% 6% 3 4 6% 3 6% 6% 8% 9% 39%	1260
	21st to end	Night	8% 4 3 4 4 2 6% 5% 7% 9% 47%	1379
August	1st to 10th	Night	9% 3 2 6% 6% 4 6% 7% 6% 9% 41%	1253
	11th to 20th	Night	8% 5% 3 5% 5% 4 5% 5% 7% 9% 43%	1538
	21st to end	Night	11% 6% 3 5% 5% 4 6% 5% 5% 8% 42%	1782
September	1st to 10th	Night	13% 7% 2 6% 4 3 4 4 6% 7% 44%	1673
	11th to 20th	Night	12% 5% 2 5% 5% 3 5% 5% 6% 9% 42%	1931
	21st to end	Night	9% 5% 2 5% 5% 3 5% 5% 6% 9% 45%	1980
October	1st to 10th	Night	10% 10% 3 6% 6% 4 5% 5% 6% 8% 36%	2146
	11th to 20th	Night	9% 10% 4 6% 5% 4 5% 5% 6% 8% 39%	2258
	21st to end	Night	11% 12% 5% 9% 8% 3 5% 5% 5% 6% 30%	2672
November	1st to 10th	Night	12% 15% 6% 10% 7% 4 5% 5% 5% 5% 26%	2590
	11th to 20th	Night	8% 13% 5% 11% 9% 6% 7% 6% 5% 7% 23%	2791
	21st to end	Night	7% 13% 6% 10% 9% 4 6% 6% 6% 8% 26%	2859
December	1st to 10th	Night	7% 11% 6% 10% 8% 6% 5% 6% 6% 7% 27%	3040
	11th to 20th	Night	8% 12% 6% 12% 12% 6% 7% 6% 5% 6% 21%	3753
	21st to end	Night	3 7% 3 7% 8% 4 6% 6% 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	58% 7% 17% 14% 4	1859
	11th to 20th	Day	51% 6% 15% 20% 8%	1980
	21st to end	Day	54% 7% 15% 19% 5%	2178
April	1st to 10th	Day	52% 6% 14% 18% 9%	2283
	11th to 20th	Day	54% 5% 12% 19% 9% 1	2310
	21st to end	Day	52% 6% 13% 20% 8% 1	2402
May	1st to 10th	Day	47% 7% 12% 21% 12% 1	2643
	11th to 20th	Day	41% 7% 13% 25% 13% 1	2658
	21st to end	Day	44% 6% 12% 25% 11% 1	2918
June	1st to 10th	Day	49% 7% 14% 22% 7%	2832
	11th to 20th	Day	56% 8% 14% 18% 4	2967
	21st to end	Day	46% 9% 18% 22% 5%	3060
July	1st to 10th	Day	43% 9% 18% 25% 5% 1	2708
	11th to 20th	Day	43% 9% 26% 21% 2	2619
	21st to end	Day	39% 8% 25% 25% 3	2775
August	1st to 10th	Day	41% 9% 24% 24% 2	2668
	11th to 20th	Day	35% 11% 28% 22% 4	2359
	21st to end	Day	40% 9% 24% 24% 3	2574
September	1st to 10th	Day	44% 6% 20% 24% 6% 1	2286
	11th to 20th	Day	46% 6% 19% 24% 5%	2026
	21st to end	Day	38% 8% 19% 25% 9% 1	1980
October	1st to 10th	Day	50% 6% 19% 20% 5%	1813
	11th to 20th	Day	49% 5% 13% 27% 6%	1698
	21st to end	Day	56% 7% 15% 18% 4	1666
November	1st to 10th	Day	62% 6% 11% 18% 3	1488
	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	51% 5% 15% 22% 7%	2261
	11th to 20th	Night	48% 6% 13% 25% 8% 1	1980
	21st to end	Night	53% 6% 14% 19% 7%	2178
April	1st to 10th	Night	45% 6% 15% 22% 12% 1	1673
	11th to 20th	Night	51% 6% 10% 19% 10% 3	1601
	21st to end	Night	50% 4 11% 22% 10% 2	1558
May	1st to 10th	Night	41% 5% 12% 24% 16% 1	1314
	11th to 20th	Night	38% 5% 12% 27% 18% 1	1239
	21st to end	Night	48% 6% 10% 23% 11% 2	1358
June	1st to 10th	Night	50% 7% 14% 19% 9% 2	1126
	11th to 20th	Night	54% 7% 14% 19% 6% 1	987
	21st to end	Night	43% 10% 16% 23% 6% 1	900
July	1st to 10th	Night	34% 9% 22% 26% 7% 1	1134
	11th to 20th	Night	40% 8% 23% 25% 3	1218
	21st to end	Night	30% 9% 27% 31% 3	1302
August	1st to 10th	Night	37% 9% 24% 28% 2	1246
	11th to 20th	Night	35% 8% 27% 24% 6%	1538
	21st to end	Night	40% 6% 18% 31% 5%	1782
September	1st to 10th	Night	40% 6% 22% 24% 6% 2	1673
	11th to 20th	Night	38% 7% 19% 28% 8%	1931
	21st to end	Night	34% 7% 17% 30% 11% 1	1980
October	1st to 10th	Night	46% 6% 15% 23% 9%	2146
	11th to 20th	Night	44% 5% 16% 28% 6%	2258
	21st to end	Night	54% 6% 13% 20% 7%	2672
November	1st to 10th	Night	59% 5% 11% 19% 5%	2590
	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% 16% 36% 29% 8% 2	411
	11th to 20th	Day	12% 12% 41% 23% 8% 4	420
	21st to end	Day	16% 12% 33% 27% 10% 2	462
April	1st to 10th	Day	13% 16% 35% 25% 8% 3	420
	11th to 20th	Day	18% 11% 32% 23% 12% 4	412
	21st to end	Day	16% 16% 33% 24% 9% 2	482
May	1st to 10th	Day	12% 14% 25% 29% 15% 5%	603
	11th to 20th	Day	11% 9% 25% 32% 18% 6%	625
	21st to end	Day	19% 6% 24% 28% 19% 4	679
June	1st to 10th	Day	21% 10% 28% 29% 10% 3	630
	11th to 20th	Day	24% 7% 24% 22% 18% 6%	717
	21st to end	Day	12% 5% 23% 32% 21% 7%	810
July	1st to 10th	Day	14% 6% 22% 32% 22% 4	685
	11th to 20th	Day	15% 6% 24% 30% 20% 5%	618
	21st to end	Day	11% 6% 27% 27% 22% 7%	684
August	1st to 10th	Day	16% 6% 20% 28% 22% 8%	626
	11th to 20th	Day	13% 9% 28% 31% 16% 4	450
	21st to end	Day	14% 7% 26% 28% 20% 5%	495
September	1st to 10th	Day	20% 12% 29% 24% 12% 3	450
	11th to 20th	Day	21% 10% 27% 28% 12% 3	450
	21st to end	Day	14% 12% 33% 25% 14% 2	450
October	1st to 10th	Day	17% 7% 32% 27% 14% 3	283
	11th to 20th	Day	21% 10% 39% 22% 7% 1	270
	21st to end	Day	22% 13% 30% 23% 9% 2	297
November	1st to 10th	Day	24% 9% 27% 27% 10% 2	270
	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	750
	11th to 20th	Night	14% 7% 35% 29% 14% 2	720
	21st to end	Night	15% 8% 28% 33% 14% 3	792
April	1st to 10th	Night	12% 7% 28% 36% 15% 2	565
	11th to 20th	Night	13% 8% 32% 29% 16% 1	533
	21st to end	Night	18% 7% 28% 31% 14% 1	540
May	1st to 10th	Night	14% 7% 20% 34% 22% 3	414
	11th to 20th	Night	11% 7% 24% 37% 18% 4	354
	21st to end	Night	18% 4 21% 32% 23% 2	389
June	1st to 10th	Night	20% 6% 21% 35% 18% 1	360
	11th to 20th	Night	20% 6% 22% 29% 22% 2	360
	21st to end	Night	14% 2 20% 33% 27% 3	360
July	1st to 10th	Night	12% 4 19% 35% 29% 1	350
	11th to 20th	Night	13% 4 20% 41% 21% 3	348
	21st to end	Night	10% 3 18% 39% 26% 5%	394
August	1st to 10th	Night	11% 3 15% 37% 29% 5%	358
	11th to 20th	Night	10% 5% 23% 36% 24% 2	486
	21st to end	Night	13% 4 20% 39% 21% 2	594
September	1st to 10th	Night	18% 6% 22% 30% 22% 2	540
	11th to 20th	Night	14% 6% 22% 40% 18% 1	671
	21st to end	Night	13% 6% 28% 36% 15% 2	720
October	1st to 10th	Night	17% 5% 29% 35% 12% 2	720
	11th to 20th	Night	16% 6% 31% 32% 12% 3	720
	21st to end	Night	19% 11% 31% 29% 9% 1	890
November	1st to 10th	Night	20% 6% 33% 30% 9% 2	925
	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

Page generated at 2024-03-05 05:23:59. Version ac07

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