Watson Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Watson Lake clear sky chart from 2005-11-06 to 2024-01-15.

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% 12% 5% 9% 8% 5% 6% 6% 6% 7% 24%	74418
	Night	11% 15% 6% 11% 8% 5% 6% 5% 5% 6% 21%	75361
Transparency	Day	56% 9% 16% 15% 4	74061
	Night	61% 8% 13% 13% 4	75237
Seeing	Day	16% 7% 20% 28% 21% 7%	16146
	Night	17% 5% 17% 35% 23% 4	23510

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	9% 18% 9% 13% 12% 6% 6% 6% 5% 5% 11%	949
	11th to 20th	Day	13% 19% 8% 12% 11% 5% 8% 4 6% 7% 7%	1016
	21st to end	Day	11% 18% 8% 12% 11% 5% 6% 4 5% 6% 14%	1222
February	1st to 10th	Day	7% 17% 7% 13% 7% 4 9% 6% 6% 6% 17%	1300
	11th to 20th	Day	7% 16% 8% 12% 9% 5% 6% 8% 6% 7% 18%	1400
	21st to end	Day	5% 13% 7% 11% 11% 5% 7% 8% 6% 6% 22%	1315
March	1st to 10th	Day	4 14% 8% 12% 7% 5% 8% 5% 5% 7% 25%	1758
	11th to 20th	Day	4 17% 8% 13% 9% 6% 6% 6% 5% 6% 20%	1926
	21st to end	Day	4 16% 7% 11% 8% 4 5% 5% 4 6% 28%	2258
April	1st to 10th	Day	6% 15% 8% 10% 9% 4 7% 6% 6% 7% 22%	2308
	11th to 20th	Day	6% 15% 6% 9% 8% 3 5% 6% 5% 6% 29%	2308
	21st to end	Day	9% 15% 6% 9% 9% 4 6% 6% 7% 7% 22%	2658
May	1st to 10th	Day	13% 12% 4 9% 7% 4 6% 5% 7% 7% 26%	2700
	11th to 20th	Day	15% 10% 5% 8% 7% 5% 5% 6% 5% 7% 27%	2823
	21st to end	Day	13% 7% 4 8% 7% 4 6% 5% 7% 8% 32%	3305
June	1st to 10th	Day	14% 10% 5% 9% 7% 5% 6% 6% 6% 8% 25%	3060
	11th to 20th	Day	16% 9% 4 9% 9% 5% 7% 6% 6% 8% 22%	3060
	21st to end	Day	14% 8% 4 8% 8% 5% 7% 6% 7% 9% 25%	3060
July	1st to 10th	Day	14% 7% 3 8% 7% 5% 7% 7% 7% 9% 27%	3060
	11th to 20th	Day	13% 7% 4 9% 9% 5% 8% 7% 7% 9% 20%	3060
	21st to end	Day	13% 7% 4 8% 8% 4 6% 6% 7% 7% 30%	3166
August	1st to 10th	Day	10% 8% 4 7% 7% 4 5% 7% 8% 9% 31%	2704
	11th to 20th	Day	16% 8% 4 7% 8% 5% 6% 6% 6% 8% 27%	2594
	21st to end	Day	19% 8% 4 8% 7% 3 5% 6% 7% 8% 25%	2633
September	1st to 10th	Day	17% 8% 3 7% 7% 4 5% 6% 6% 8% 29%	2340
	11th to 20th	Day	11% 7% 4 8% 8% 4 6% 6% 6% 9% 32%	2043
	21st to end	Day	21% 13% 4 8% 7% 3 5% 4 5% 5% 24%	1980
October	1st to 10th	Day	16% 14% 4 7% 7% 5% 5% 5% 5% 5% 26%	1774
	11th to 20th	Day	16% 15% 5% 11% 8% 4 5% 5% 5% 5% 21%	1620
	21st to end	Day	13% 18% 6% 9% 5% 3 5% 6% 6% 6% 24%	1616
November	1st to 10th	Day	12% 21% 8% 11% 8% 5% 5% 5% 5% 5% 14%	1302
	11th to 20th	Day	11% 20% 8% 14% 12% 6% 5% 5% 4 4 11%	1212
	21st to end	Day	8% 21% 7% 13% 10% 7% 7% 3 6% 6% 12%	998
December	1st to 10th	Day	11% 19% 7% 13% 12% 6% 8% 5% 4 4 13%	950
	11th to 20th	Day	7% 20% 8% 10% 11% 6% 7% 6% 5% 8% 12%	1202
	21st to end	Day	9% 20% 6% 13% 11% 6% 7% 6% 5% 4 12%	1738
January	1st to 10th	Night	9% 16% 9% 15% 12% 6% 6% 7% 4 5% 12%	3216
	11th to 20th	Night	14% 22% 8% 12% 6% 4 5% 4 5% 7% 13%	3048
	21st to end	Night	10% 18% 8% 13% 10% 5% 7% 4 4 6% 14%	3133
February	1st to 10th	Night	7% 17% 7% 11% 8% 5% 6% 6% 6% 6% 21%	2660
	11th to 20th	Night	6% 16% 7% 11% 8% 5% 6% 6% 5% 6% 23%	2447
	21st to end	Night	4 13% 9% 11% 9% 4 5% 4 5% 6% 30%	1940
March	1st to 10th	Night	4 14% 8% 10% 9% 5% 6% 5% 5% 6% 28%	2201
	11th to 20th	Night	4 19% 9% 14% 9% 4 5% 5% 5% 6% 19%	2033
	21st to end	Night	6% 14% 6% 11% 9% 4 6% 5% 6% 6% 28%	2097
April	1st to 10th	Night	5% 16% 7% 10% 8% 4 6% 5% 6% 6% 26%	1652
	11th to 20th	Night	6% 13% 5% 9% 8% 4 6% 7% 6% 8% 29%	1601
	21st to end	Night	10% 11% 5% 9% 7% 5% 6% 7% 7% 7% 26%	1301
May	1st to 10th	Night	11% 11% 4 9% 9% 4 5% 5% 5% 9% 27%	1260
	11th to 20th	Night	11% 10% 4 8% 6% 5% 7% 6% 6% 7% 30%	1070
	21st to end	Night	10% 8% 3 7% 6% 5% 6% 6% 7% 9% 34%	970
June	1st to 10th	Night	13% 7% 5% 9% 7% 5% 7% 6% 7% 9% 26%	900
	11th to 20th	Night	14% 7% 5% 9% 9% 5% 7% 8% 5% 8% 21%	900
	21st to end	Night	12% 7% 4 9% 9% 5% 7% 8% 6% 8% 25%	900
July	1st to 10th	Night	14% 7% 3 7% 8% 3 6% 8% 8% 9% 27%	900
	11th to 20th	Night	16% 9% 3 8% 7% 6% 8% 6% 7% 9% 20%	900
	21st to end	Night	13% 8% 4 9% 7% 4 6% 5% 7% 7% 28%	1150
August	1st to 10th	Night	9% 7% 5% 8% 7% 3 5% 5% 7% 10% 33%	1235
	11th to 20th	Night	15% 8% 3 8% 9% 4 6% 6% 7% 7% 27%	1304
	21st to end	Night	19% 11% 4 9% 6% 5% 6% 5% 6% 5% 24%	1723
September	1st to 10th	Night	17% 8% 3 9% 6% 3 6% 6% 6% 6% 30%	1620
	11th to 20th	Night	12% 7% 3 8% 7% 3 7% 6% 7% 8% 31%	1914
	21st to end	Night	21% 14% 6% 10% 6% 4 5% 5% 5% 4 21%	1980
October	1st to 10th	Night	16% 12% 4 9% 6% 3 4 5% 5% 6% 30%	2185
	11th to 20th	Night	17% 17% 6% 9% 7% 3 5% 6% 5% 5% 19%	2340
	21st to end	Night	13% 18% 6% 11% 7% 4 5% 4 5% 6% 22%	2739
November	1st to 10th	Night	13% 18% 8% 12% 7% 4 6% 5% 5% 5% 18%	2776
	11th to 20th	Night	11% 20% 8% 13% 10% 5% 6% 5% 4 4 13%	2949
	21st to end	Night	10% 18% 6% 14% 10% 6% 7% 5% 4 5% 14%	3179
December	1st to 10th	Night	12% 18% 7% 11% 9% 6% 7% 6% 5% 5% 14%	3230
	11th to 20th	Night	7% 20% 7% 13% 10% 6% 5% 5% 4 6% 16%	3990
	21st to end	Night	11% 19% 8% 12% 11% 5% 7% 5% 5% 5% 11%	5918

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% 6% 10% 6% 4	949
	11th to 20th	Day	76% 7% 7% 7% 2	1016
	21st to end	Day	70% 6% 9% 11% 4	1222
February	1st to 10th	Day	63% 7% 12% 11% 7%	1300
	11th to 20th	Day	61% 8% 15% 13% 3	1408
	21st to end	Day	58% 8% 15% 14% 5%	1315
March	1st to 10th	Day	55% 7% 14% 16% 7%	1758
	11th to 20th	Day	62% 8% 14% 13% 3	1926
	21st to end	Day	55% 8% 16% 15% 6% 1	2258
April	1st to 10th	Day	57% 9% 15% 14% 4	2308
	11th to 20th	Day	53% 9% 15% 19% 4	2308
	21st to end	Day	56% 9% 15% 16% 3	2658
May	1st to 10th	Day	54% 9% 18% 16% 3	2700
	11th to 20th	Day	54% 8% 12% 18% 7% 1	2827
	21st to end	Day	48% 8% 13% 21% 8% 1	3306
June	1st to 10th	Day	55% 9% 13% 19% 4	3060
	11th to 20th	Day	58% 10% 14% 13% 5%	3060
	21st to end	Day	51% 11% 20% 15% 4	3060
July	1st to 10th	Day	49% 11% 17% 20% 4	2976
	11th to 20th	Day	55% 13% 20% 11% 1	2967
	21st to end	Day	46% 11% 22% 19% 2	2990
August	1st to 10th	Day	44% 13% 23% 17% 3	2685
	11th to 20th	Day	53% 10% 21% 15% 2	2594
	21st to end	Day	53% 11% 22% 13% 1	2633
September	1st to 10th	Day	51% 10% 20% 16% 3	2340
	11th to 20th	Day	45% 10% 22% 20% 3	2043
	21st to end	Day	61% 8% 13% 17% 2	1980
October	1st to 10th	Day	58% 8% 17% 15% 2	1774
	11th to 20th	Day	64% 8% 14% 13% 1	1620
	21st to end	Day	59% 10% 16% 12% 3	1616
November	1st to 10th	Day	70% 9% 12% 8% 2	1302
	11th to 20th	Day	77% 6% 9% 8% 1	1212
	21st to end	Day	72% 6% 9% 8% 5%	998
December	1st to 10th	Day	75% 7% 9% 7% 1	950
	11th to 20th	Day	66% 8% 10% 14% 2	1204
	21st to end	Day	69% 9% 7% 8% 7%	1738
January	1st to 10th	Night	73% 7% 9% 8% 3	3216
	11th to 20th	Night	71% 7% 8% 8% 4	3048
	21st to end	Night	70% 7% 10% 10% 4	3133
February	1st to 10th	Night	61% 7% 10% 16% 6%	2660
	11th to 20th	Night	59% 9% 15% 14% 3	2450
	21st to end	Night	54% 7% 17% 16% 6%	1940
March	1st to 10th	Night	55% 6% 13% 16% 9% 1	2201
	11th to 20th	Night	64% 7% 13% 11% 4	2034
	21st to end	Night	53% 8% 15% 15% 8%	2097
April	1st to 10th	Night	56% 8% 16% 16% 4 1	1652
	11th to 20th	Night	50% 7% 17% 20% 6%	1601
	21st to end	Night	52% 9% 18% 16% 5%	1301
May	1st to 10th	Night	52% 9% 18% 17% 3	1260
	11th to 20th	Night	49% 9% 15% 19% 8%	1070
	21st to end	Night	44% 10% 15% 20% 10% 1	970
June	1st to 10th	Night	51% 9% 17% 19% 4	900
	11th to 20th	Night	55% 13% 12% 15% 5% 1	900
	21st to end	Night	51% 12% 18% 15% 4	900
July	1st to 10th	Night	48% 11% 17% 19% 5%	875
	11th to 20th	Night	54% 12% 19% 15%	870
	21st to end	Night	51% 10% 18% 19% 2	1086
August	1st to 10th	Night	43% 11% 21% 22% 3	1229
	11th to 20th	Night	52% 11% 18% 17% 2	1304
	21st to end	Night	58% 8% 18% 14% 2	1723
September	1st to 10th	Night	51% 9% 17% 19% 4	1620
	11th to 20th	Night	46% 11% 19% 20% 4	1914
	21st to end	Night	63% 7% 13% 14% 3	1980
October	1st to 10th	Night	54% 8% 17% 17% 4	2185
	11th to 20th	Night	65% 9% 14% 12% 1	2340
	21st to end	Night	61% 9% 14% 14% 2	2739
November	1st to 10th	Night	67% 8% 14% 11% 1	2776
	11th to 20th	Night	72% 9% 11% 8% 1	2949
	21st to end	Night	71% 7% 10% 9% 3	3179
December	1st to 10th	Night	70% 8% 11% 8% 2	3230
	11th to 20th	Night	67% 6% 11% 10% 5%	3987
	21st to end	Night	71% 7% 7% 8% 6%	5918

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	8% 4 14% 41% 22% 12%	180
	11th to 20th	Day	17% 3 9% 32% 29% 10%	168
	21st to end	Day	18% 5% 10% 39% 23% 6%	176
February	1st to 10th	Day	11% 7% 19% 39% 20% 7%	200
	11th to 20th	Day	14% 6% 17% 35% 17% 11%	335
	21st to end	Day	9% 6% 21% 30% 22% 12%	280
March	1st to 10th	Day	9% 7% 21% 28% 23% 12%	340
	11th to 20th	Day	8% 7% 26% 33% 22% 4	396
	21st to end	Day	11% 10% 21% 29% 20% 10%	462
April	1st to 10th	Day	13% 10% 27% 26% 19% 4	420
	11th to 20th	Day	14% 12% 22% 24% 19% 9%	412
	21st to end	Day	17% 13% 28% 23% 15% 5%	599
May	1st to 10th	Day	19% 13% 28% 21% 16% 3	603
	11th to 20th	Day	16% 10% 25% 25% 17% 7%	703
	21st to end	Day	16% 9% 19% 30% 19% 7%	874
June	1st to 10th	Day	17% 8% 21% 26% 24% 5%	810
	11th to 20th	Day	19% 6% 19% 29% 22% 5%	810
	21st to end	Day	17% 7% 19% 29% 22% 7%	810
July	1st to 10th	Day	16% 4 19% 30% 23% 8%	796
	11th to 20th	Day	16% 7% 17% 27% 25% 9%	792
	21st to end	Day	13% 6% 17% 30% 23% 12%	715
August	1st to 10th	Day	12% 5% 18% 26% 25% 13%	626
	11th to 20th	Day	21% 9% 23% 25% 18% 4	615
	21st to end	Day	22% 4 17% 25% 21% 10%	554
September	1st to 10th	Day	21% 7% 21% 22% 22% 8%	450
	11th to 20th	Day	11% 10% 19% 27% 26% 8%	450
	21st to end	Day	25% 12% 23% 22% 14% 4	450
October	1st to 10th	Day	25% 9% 22% 22% 19% 2	418
	11th to 20th	Day	22% 9% 19% 32% 14% 4	360
	21st to end	Day	17% 2 20% 35% 20% 6%	244
November	1st to 10th	Day	20% 3 16% 37% 16% 8%	180
	11th to 20th	Day	18% 4 14% 29% 24% 11%	180
	21st to end	Day	17% 2 16% 42% 16% 8%	180
December	1st to 10th	Day	14% 3 13% 37% 27% 6%	180
	11th to 20th	Day	17% 4 13% 31% 24% 12%	180
	21st to end	Day	10% 3 12% 43% 26% 6%	198
January	1st to 10th	Night	14% 4 12% 39% 25% 6%	1040
	11th to 20th	Night	23% 3 15% 35% 19% 5%	924
	21st to end	Night	18% 4 16% 38% 20% 4	880
February	1st to 10th	Night	12% 6% 14% 42% 23% 3	800
	11th to 20th	Night	13% 3 18% 42% 22% 4	784
	21st to end	Night	9% 4 17% 42% 24% 4	598
March	1st to 10th	Night	8% 5% 22% 38% 20% 7%	720
	11th to 20th	Night	12% 5% 21% 33% 27% 2	720
	21st to end	Night	9% 5% 19% 34% 28% 5%	711
April	1st to 10th	Night	11% 4 22% 33% 26% 4	540
	11th to 20th	Night	12% 5% 17% 36% 24% 6%	533
	21st to end	Night	14% 6% 22% 32% 21% 3	401
May	1st to 10th	Night	14% 4 24% 33% 20% 5%	360
	11th to 20th	Night	16% 6% 22% 31% 23% 3	354
	21st to end	Night	13% 5% 19% 36% 23% 4	389
June	1st to 10th	Night	15% 4 20% 31% 28% 1	360
	11th to 20th	Night	17% 5% 19% 29% 26% 4	360
	21st to end	Night	14% 8% 20% 29% 27% 4	360
July	1st to 10th	Night	14% 5% 17% 35% 27% 2	350
	11th to 20th	Night	17% 4 16% 28% 31% 5%	348
	21st to end	Night	16% 2 18% 28% 30% 6%	394
August	1st to 10th	Night	11% 4 18% 31% 28% 8%	358
	11th to 20th	Night	18% 5% 21% 31% 22% 3	414
	21st to end	Night	25% 3 14% 26% 28% 5%	594
September	1st to 10th	Night	21% 5% 17% 32% 23% 3	540
	11th to 20th	Night	14% 4 19% 32% 27% 4	677
	21st to end	Night	25% 9% 20% 27% 16% 3	720
October	1st to 10th	Night	21% 7% 18% 36% 16% 2	720
	11th to 20th	Night	26% 6% 18% 33% 15% 2	720
	21st to end	Night	21% 5% 17% 35% 17% 4	798
November	1st to 10th	Night	21% 4 14% 35% 22% 4	830
	11th to 20th	Night	16% 5% 14% 34% 23% 7%	949
	21st to end	Night	19% 4 14% 38% 21% 4	1040
December	1st to 10th	Night	20% 4 15% 39% 19% 4	1040
	11th to 20th	Night	16% 4 13% 36% 26% 5%	1040
	21st to end	Night	17% 3 12% 39% 25% 4	1144

Page generated at 2024-01-11 20:33:49. Version ac07

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