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 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	10% 13% 5% 11% 7% 6% 6% 5% 6% 7% 24%	134227
	Night	9% 15% 6% 14% 8% 6% 6% 4 6% 6% 19%	135282
Transparency	Day	54% 8% 16% 16% 5%	133885
	Night	61% 7% 13% 14% 5%	135204
Seeing	Day	15% 8% 20% 29% 21% 8%	18992
	Night	16% 5% 17% 35% 23% 4	26372

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	7% 21% 10% 21% 12% 9% 6% 5% 4 3 4	2929
	11th to 20th	Day	6% 14% 5% 12% 8% 8% 8% 5% 7% 10% 17%	3257
	21st to end	Day	9% 19% 6% 13% 8% 7% 7% 4 5% 6% 17%	3990
February	1st to 10th	Day	6% 18% 6% 14% 7% 6% 8% 4 6% 6% 19%	1517
	11th to 20th	Day	6% 17% 7% 13% 7% 6% 6% 6% 7% 7% 18%	1601
	21st to end	Day	4 13% 6% 13% 9% 7% 7% 6% 6% 6% 21%	1467
March	1st to 10th	Day	3 11% 6% 14% 7% 8% 8% 5% 6% 8% 24%	4406
	11th to 20th	Day	3 16% 6% 18% 11% 8% 6% 4 6% 6% 16%	4862
	21st to end	Day	2 12% 6% 13% 8% 7% 5% 4 5% 7% 32%	5695
April	1st to 10th	Day	5% 15% 6% 12% 8% 6% 6% 5% 7% 7% 22%	2565
	11th to 20th	Day	5% 17% 5% 11% 6% 5% 5% 4 5% 6% 30%	2568
	21st to end	Day	8% 16% 5% 11% 8% 6% 6% 5% 7% 7% 22%	2954
May	1st to 10th	Day	11% 13% 4 11% 6% 5% 5% 4 6% 7% 28%	6780
	11th to 20th	Day	9% 14% 6% 13% 8% 7% 7% 5% 6% 7% 17%	7197
	21st to end	Day	12% 10% 4 10% 7% 7% 6% 5% 7% 8% 24%	8409
June	1st to 10th	Day	13% 11% 4 10% 6% 7% 6% 5% 6% 8% 24%	3400
	11th to 20th	Day	15% 10% 3 10% 7% 7% 7% 5% 7% 9% 22%	3400
	21st to end	Day	13% 9% 3 9% 7% 6% 6% 5% 7% 8% 25%	3400
July	1st to 10th	Day	10% 7% 2 9% 6% 7% 7% 6% 9% 10% 27%	7700
	11th to 20th	Day	10% 8% 3 10% 7% 7% 8% 6% 8% 10% 25%	7700
	21st to end	Day	12% 7% 3 9% 6% 6% 6% 6% 8% 10% 27%	7935
August	1st to 10th	Day	7% 6% 2 7% 4 5% 5% 4 7% 8% 44%	4901
	11th to 20th	Day	11% 7% 2 7% 5% 5% 5% 4 6% 9% 40%	4679
	21st to end	Day	16% 11% 4 10% 6% 5% 5% 4 6% 8% 25%	4768
September	1st to 10th	Day	16% 8% 3 8% 5% 6% 5% 5% 6% 8% 30%	2600
	11th to 20th	Day	11% 8% 4 9% 7% 6% 5% 5% 6% 9% 31%	2269
	21st to end	Day	19% 13% 4 10% 6% 5% 4 4 5% 5% 24%	2200
October	1st to 10th	Day	12% 14% 4 9% 6% 7% 7% 4 7% 7% 22%	3222
	11th to 20th	Day	15% 20% 5% 10% 5% 5% 4 3 5% 5% 23%	2933
	21st to end	Day	12% 19% 7% 12% 5% 4 4 4 5% 5% 25%	2888
November	1st to 10th	Day	11% 23% 8% 13% 7% 6% 6% 3 5% 5% 13%	1442
	11th to 20th	Day	10% 23% 7% 17% 11% 7% 5% 3 4 3 10%	1338
	21st to end	Day	7% 21% 7% 15% 10% 8% 6% 3 6% 5% 12%	1102
December	1st to 10th	Day	13% 21% 6% 13% 9% 10% 6% 5% 5% 4 9%	1680
	11th to 20th	Day	4 22% 10% 18% 8% 7% 5% 5% 5% 6% 11%	1932
	21st to end	Day	8% 21% 6% 18% 12% 9% 6% 4 3 3 9%	2541
January	1st to 10th	Night	7% 16% 10% 25% 12% 8% 6% 4 4 3 5%	9964
	11th to 20th	Night	7% 15% 5% 12% 7% 7% 7% 5% 7% 8% 21%	9698
	21st to end	Night	10% 19% 7% 14% 6% 6% 6% 4 6% 7% 14%	10189
February	1st to 10th	Night	7% 18% 6% 12% 7% 6% 6% 5% 6% 6% 22%	3102
	11th to 20th	Night	5% 17% 6% 13% 7% 6% 6% 5% 5% 7% 24%	2797
	21st to end	Night	4 15% 7% 12% 8% 6% 4 3 5% 6% 30%	2162
March	1st to 10th	Night	2 11% 6% 13% 9% 8% 8% 5% 6% 8% 24%	5467
	11th to 20th	Night	4 18% 6% 17% 9% 6% 6% 5% 6% 6% 15%	5131
	21st to end	Night	3 10% 6% 12% 7% 6% 6% 4 8% 9% 30%	5269
April	1st to 10th	Night	4 17% 6% 11% 7% 6% 5% 4 6% 7% 27%	1835
	11th to 20th	Night	6% 13% 4 10% 7% 5% 5% 5% 6% 7% 31%	1781
	21st to end	Night	9% 13% 4 10% 6% 6% 5% 5% 8% 8% 26%	1445
May	1st to 10th	Night	9% 10% 4 10% 6% 5% 5% 4 6% 9% 33%	3180
	11th to 20th	Night	11% 14% 6% 13% 7% 6% 6% 5% 7% 6% 21%	2696
	21st to end	Night	14% 10% 4 9% 5% 5% 6% 5% 9% 7% 27%	2466
June	1st to 10th	Night	13% 8% 4 10% 6% 6% 6% 4 8% 8% 27%	1000
	11th to 20th	Night	14% 8% 4 11% 8% 6% 7% 7% 7% 8% 21%	1000
	21st to end	Night	12% 9% 3 10% 7% 7% 7% 7% 6% 8% 25%	1000
July	1st to 10th	Night	11% 7% 3 8% 6% 6% 7% 7% 9% 10% 25%	2260
	11th to 20th	Night	13% 8% 3 10% 7% 8% 7% 6% 9% 9% 20%	2260
	21st to end	Night	14% 11% 5% 11% 5% 5% 5% 4 6% 7% 26%	2893
August	1st to 10th	Night	6% 6% 3 8% 4 4 4 3 5% 8% 49%	2249
	11th to 20th	Night	10% 6% 2 7% 6% 6% 5% 4 6% 9% 39%	2370
	21st to end	Night	16% 12% 4 13% 6% 7% 6% 4 6% 5% 19%	3141
September	1st to 10th	Night	16% 8% 3 9% 5% 5% 6% 4 6% 7% 31%	1800
	11th to 20th	Night	12% 8% 3 9% 7% 5% 7% 5% 7% 8% 30%	2128
	21st to end	Night	19% 15% 6% 10% 6% 5% 5% 4 5% 5% 21%	2200
October	1st to 10th	Night	11% 12% 3 9% 5% 5% 6% 5% 7% 9% 29%	3973
	11th to 20th	Night	13% 20% 7% 12% 6% 6% 6% 5% 5% 5% 15%	4215
	21st to end	Night	10% 19% 6% 13% 7% 6% 4 3 5% 6% 21%	4903
November	1st to 10th	Night	11% 21% 6% 12% 6% 6% 5% 4 6% 5% 18%	3076
	11th to 20th	Night	9% 22% 7% 16% 9% 7% 5% 4 4 4 12%	3260
	21st to end	Night	9% 18% 6% 17% 9% 8% 6% 4 5% 5% 14%	3515
December	1st to 10th	Night	15% 22% 6% 10% 6% 6% 7% 6% 8% 5% 10%	5720
	11th to 20th	Night	5% 18% 9% 19% 12% 9% 5% 3 4 5% 11%	6480
	21st to end	Night	10% 20% 9% 18% 10% 7% 6% 3 5% 4 8%	8657

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	82% 5% 5% 4 4	2929
	11th to 20th	Day	59% 7% 15% 13% 6%	3274
	21st to end	Day	65% 8% 9% 15% 3	3991
February	1st to 10th	Day	61% 7% 11% 12% 8% 1	1517
	11th to 20th	Day	59% 8% 17% 13% 3	1609
	21st to end	Day	59% 8% 15% 13% 5%	1467
March	1st to 10th	Day	53% 6% 11% 21% 9%	4406
	11th to 20th	Day	63% 8% 11% 14% 4	4862
	21st to end	Day	48% 8% 16% 22% 5% 1	5695
April	1st to 10th	Day	56% 9% 15% 15% 5%	2565
	11th to 20th	Day	52% 8% 15% 19% 5%	2568
	21st to end	Day	56% 10% 15% 15% 3	2954
May	1st to 10th	Day	49% 9% 13% 18% 10%	6780
	11th to 20th	Day	59% 11% 12% 14% 4	7201
	21st to end	Day	53% 8% 10% 20% 8%	8410
June	1st to 10th	Day	54% 8% 13% 19% 5%	3400
	11th to 20th	Day	57% 10% 15% 14% 4	3400
	21st to end	Day	51% 10% 19% 16% 3	3400
July	1st to 10th	Day	45% 10% 23% 20% 2	7616
	11th to 20th	Day	49% 10% 26% 12% 3	7607
	21st to end	Day	45% 10% 27% 16% 1	7712
August	1st to 10th	Day	35% 9% 16% 27% 10% 3	4882
	11th to 20th	Day	39% 7% 20% 28% 6%	4724
	21st to end	Day	54% 9% 19% 16% 2	4767
September	1st to 10th	Day	48% 10% 21% 18% 3	2600
	11th to 20th	Day	47% 10% 21% 20% 3	2269
	21st to end	Day	60% 7% 13% 18% 2	2200
October	1st to 10th	Day	55% 7% 19% 15% 3	3222
	11th to 20th	Day	62% 6% 14% 17% 2	2933
	21st to end	Day	61% 7% 17% 13% 2	2888
November	1st to 10th	Day	71% 8% 11% 8% 2	1442
	11th to 20th	Day	77% 6% 8% 8% 1	1338
	21st to end	Day	72% 6% 9% 8% 5%	1102
December	1st to 10th	Day	78% 7% 9% 5% 1	1680
	11th to 20th	Day	72% 6% 8% 13% 2	1934
	21st to end	Day	77% 7% 5% 6% 5%	2541
January	1st to 10th	Night	82% 5% 5% 4 3	9965
	11th to 20th	Night	57% 7% 13% 15% 9%	9743
	21st to end	Night	67% 7% 11% 13% 3	10189
February	1st to 10th	Night	60% 7% 11% 16% 7%	3102
	11th to 20th	Night	57% 8% 15% 15% 4	2800
	21st to end	Night	53% 7% 17% 16% 6%	2162
March	1st to 10th	Night	53% 7% 13% 20% 7%	5467
	11th to 20th	Night	63% 8% 12% 11% 6%	5132
	21st to end	Night	44% 9% 18% 21% 8%	5269
April	1st to 10th	Night	54% 8% 16% 18% 5%	1835
	11th to 20th	Night	48% 7% 16% 20% 8%	1781
	21st to end	Night	51% 9% 18% 16% 5%	1445
May	1st to 10th	Night	43% 10% 17% 19% 10%	3177
	11th to 20th	Night	56% 12% 12% 16% 4	2696
	21st to end	Night	50% 8% 13% 19% 10%	2466
June	1st to 10th	Night	50% 9% 16% 20% 5%	1000
	11th to 20th	Night	55% 13% 13% 15% 4 1	1000
	21st to end	Night	52% 11% 17% 16% 4	1000
July	1st to 10th	Night	46% 9% 20% 22% 2	2235
	11th to 20th	Night	53% 11% 22% 13%	2230
	21st to end	Night	54% 8% 23% 14% 1	2811
August	1st to 10th	Night	33% 7% 15% 31% 13% 1	2243
	11th to 20th	Night	40% 8% 17% 28% 7%	2391
	21st to end	Night	63% 7% 15% 13% 2	3141
September	1st to 10th	Night	48% 8% 18% 22% 4	1800
	11th to 20th	Night	47% 10% 18% 20% 4	2128
	21st to end	Night	62% 7% 12% 15% 4	2200
October	1st to 10th	Night	50% 7% 18% 22% 3	3973
	11th to 20th	Night	67% 7% 14% 11% 1	4215
	21st to end	Night	62% 8% 14% 14% 2	4903
November	1st to 10th	Night	65% 8% 13% 12% 1	3076
	11th to 20th	Night	73% 8% 10% 8% 1	3260
	21st to end	Night	71% 7% 11% 9% 3	3515
December	1st to 10th	Night	72% 8% 11% 7% 2	5720
	11th to 20th	Night	75% 5% 9% 7% 4	6477
	21st to end	Night	76% 6% 6% 7% 4	8657

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	9% 5% 13% 39% 24% 12%	220
	11th to 20th	Day	15% 5% 12% 35% 25% 8%	220
	21st to end	Day	14% 6% 12% 42% 21% 5%	242
February	1st to 10th	Day	10% 6% 19% 37% 22% 6%	267
	11th to 20th	Day	12% 6% 18% 34% 19% 12%	411
	21st to end	Day	8% 7% 20% 31% 23% 11%	331
March	1st to 10th	Day	8% 6% 20% 30% 22% 14%	400
	11th to 20th	Day	9% 7% 23% 33% 24% 4	470
	21st to end	Day	10% 9% 21% 28% 22% 10%	550
April	1st to 10th	Day	11% 10% 27% 29% 19% 4	500
	11th to 20th	Day	12% 12% 23% 24% 18% 11%	492
	21st to end	Day	16% 12% 26% 23% 16% 6%	699
May	1st to 10th	Day	18% 15% 29% 20% 15% 3	703
	11th to 20th	Day	15% 10% 25% 26% 18% 7%	813
	21st to end	Day	16% 10% 19% 30% 18% 7%	1006
June	1st to 10th	Day	17% 8% 22% 27% 22% 5%	930
	11th to 20th	Day	18% 6% 17% 30% 23% 6%	930
	21st to end	Day	16% 6% 17% 28% 25% 8%	930
July	1st to 10th	Day	14% 4 20% 32% 23% 7%	916
	11th to 20th	Day	15% 7% 18% 27% 25% 9%	912
	21st to end	Day	13% 6% 17% 29% 23% 13%	827
August	1st to 10th	Day	12% 5% 17% 26% 26% 14%	726
	11th to 20th	Day	20% 8% 24% 25% 18% 5%	715
	21st to end	Day	20% 4 18% 25% 22% 10%	648
September	1st to 10th	Day	18% 7% 21% 24% 23% 8%	530
	11th to 20th	Day	11% 11% 21% 26% 24% 8%	530
	21st to end	Day	22% 12% 24% 24% 15% 4	530
October	1st to 10th	Day	23% 9% 23% 25% 19% 2	490
	11th to 20th	Day	22% 10% 20% 31% 13% 3	420
	21st to end	Day	19% 4 20% 33% 19% 5%	292
November	1st to 10th	Day	19% 4 17% 36% 17% 8%	220
	11th to 20th	Day	16% 4 15% 30% 25% 10%	220
	21st to end	Day	14% 2 13% 42% 21% 8%	220
December	1st to 10th	Day	16% 5% 12% 36% 25% 6%	220
	11th to 20th	Day	15% 4 12% 32% 25% 12%	220
	21st to end	Day	11% 3 10% 40% 27% 8%	242
January	1st to 10th	Night	14% 4 13% 37% 26% 7%	1160
	11th to 20th	Night	21% 5% 17% 36% 18% 4	1065
	21st to end	Night	16% 6% 17% 39% 19% 3	1045
February	1st to 10th	Night	11% 7% 15% 42% 22% 4	950
	11th to 20th	Night	11% 3 18% 41% 22% 5%	909
	21st to end	Night	9% 4 17% 41% 25% 3	667
March	1st to 10th	Night	8% 5% 21% 39% 22% 6%	800
	11th to 20th	Night	12% 5% 21% 33% 27% 2	800
	21st to end	Night	8% 5% 18% 34% 29% 6%	789
April	1st to 10th	Night	10% 5% 21% 35% 26% 3	600
	11th to 20th	Night	11% 5% 17% 37% 25% 6%	593
	21st to end	Night	14% 6% 21% 32% 23% 4	445
May	1st to 10th	Night	13% 5% 24% 34% 19% 5%	400
	11th to 20th	Night	15% 7% 21% 34% 22% 3	394
	21st to end	Night	14% 5% 20% 36% 22% 4	433
June	1st to 10th	Night	15% 6% 22% 31% 26% 1	400
	11th to 20th	Night	16% 5% 18% 31% 27% 4	400
	21st to end	Night	14% 8% 20% 28% 28% 4	400
July	1st to 10th	Night	13% 5% 17% 36% 26% 2	390
	11th to 20th	Night	16% 4 16% 29% 31% 4	388
	21st to end	Night	16% 3 18% 28% 29% 7%	438
August	1st to 10th	Night	11% 4 19% 31% 28% 8%	398
	11th to 20th	Night	17% 5% 21% 32% 22% 3	461
	21st to end	Night	24% 3 14% 26% 28% 5%	660
September	1st to 10th	Night	19% 5% 17% 33% 24% 3	600
	11th to 20th	Night	14% 4 20% 33% 25% 4	753
	21st to end	Night	24% 10% 20% 28% 16% 2	800
October	1st to 10th	Night	21% 8% 17% 35% 17% 2	800
	11th to 20th	Night	26% 6% 18% 34% 14% 2	800
	21st to end	Night	20% 6% 18% 35% 17% 4	888
November	1st to 10th	Night	20% 4 14% 36% 21% 4	930
	11th to 20th	Night	15% 5% 14% 35% 23% 7%	1060
	21st to end	Night	17% 4 14% 38% 23% 4	1160
December	1st to 10th	Night	21% 5% 15% 38% 18% 3	1160
	11th to 20th	Night	15% 4 13% 37% 27% 5%	1160
	21st to end	Night	17% 3 11% 37% 26% 5%	1276

Page generated at 2026-02-12 22:42:13. Version ac07

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