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 2024-11-30.

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% 25%	106378
	Night	10% 16% 6% 13% 7% 6% 6% 4 6% 6% 20%	101777
Transparency	Day	54% 9% 16% 17% 4	106083
	Night	60% 8% 13% 14% 4	101719
Seeing	Day	16% 7% 20% 28% 21% 8%	17443
	Night	16% 5% 17% 35% 23% 4	24594

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	8% 20% 9% 20% 12% 7% 6% 5% 4 4 7%	1579
	11th to 20th	Day	9% 17% 6% 14% 9% 6% 8% 5% 8% 10% 9%	1729
	21st to end	Day	14% 23% 8% 15% 9% 5% 4 2 4 5% 11%	2152
February	1st to 10th	Day	6% 19% 7% 14% 7% 6% 8% 4 6% 6% 17%	1372
	11th to 20th	Day	6% 17% 7% 12% 7% 6% 6% 6% 7% 8% 18%	1480
	21st to end	Day	4 13% 6% 13% 9% 7% 7% 6% 6% 6% 22%	1395
March	1st to 10th	Day	2 10% 5% 15% 8% 9% 8% 6% 6% 9% 22%	3062
	11th to 20th	Day	4 19% 6% 13% 8% 7% 6% 4 5% 7% 21%	3394
	21st to end	Day	2 14% 7% 14% 7% 6% 5% 3 4 6% 31%	3969
April	1st to 10th	Day	6% 16% 6% 12% 8% 6% 6% 4 7% 7% 21%	2437
	11th to 20th	Day	5% 17% 5% 11% 6% 5% 5% 5% 5% 6% 30%	2438
	21st to end	Day	8% 16% 5% 11% 8% 6% 6% 5% 6% 7% 23%	2806
May	1st to 10th	Day	12% 13% 4 11% 6% 5% 5% 4 6% 7% 28%	4740
	11th to 20th	Day	10% 13% 5% 12% 8% 7% 7% 5% 6% 7% 20%	5017
	21st to end	Day	14% 11% 4 9% 7% 6% 5% 4 6% 7% 26%	5857
June	1st to 10th	Day	13% 11% 4 10% 6% 6% 5% 5% 6% 8% 25%	3230
	11th to 20th	Day	15% 10% 3 10% 7% 7% 7% 5% 7% 8% 22%	3230
	21st to end	Day	13% 9% 3 9% 7% 6% 6% 5% 7% 8% 26%	3230
July	1st to 10th	Day	9% 5% 2 8% 6% 6% 7% 6% 9% 10% 33%	5380
	11th to 20th	Day	12% 8% 3 10% 7% 7% 8% 6% 8% 9% 21%	5380
	21st to end	Day	12% 7% 3 9% 7% 6% 6% 5% 8% 9% 28%	5531
August	1st to 10th	Day	7% 6% 2 7% 4 5% 5% 4 7% 8% 45%	4750
	11th to 20th	Day	11% 6% 2 7% 5% 5% 5% 4 6% 9% 40%	4533
	21st to end	Day	16% 11% 4 10% 6% 5% 5% 4 6% 8% 24%	4622
September	1st to 10th	Day	16% 8% 3 9% 5% 6% 5% 5% 6% 8% 29%	2470
	11th to 20th	Day	11% 7% 4 9% 7% 5% 5% 5% 6% 9% 31%	2156
	21st to end	Day	20% 14% 4 10% 6% 4 4 3 5% 5% 24%	2090
October	1st to 10th	Day	13% 14% 4 9% 6% 6% 7% 4 7% 7% 22%	3124
	11th to 20th	Day	16% 20% 5% 10% 5% 5% 4 3 5% 5% 22%	2843
	21st to end	Day	12% 19% 7% 12% 5% 4 4 4 5% 5% 25%	2799
November	1st to 10th	Day	11% 23% 8% 13% 7% 6% 6% 3 5% 5% 13%	1372
	11th to 20th	Day	11% 23% 7% 17% 11% 7% 5% 3 4 3 10%	1275
	21st to end	Day	8% 21% 7% 15% 9% 9% 6% 3 6% 5% 12%	1046
December	1st to 10th	Day	10% 21% 6% 15% 10% 9% 5% 4 3 4 13%	950
	11th to 20th	Day	6% 21% 7% 13% 9% 8% 5% 5% 6% 8% 12%	1202
	21st to end	Day	9% 21% 6% 15% 9% 8% 6% 5% 5% 4 12%	1738
January	1st to 10th	Night	7% 17% 9% 21% 12% 9% 6% 4 4 4 8%	5366
	11th to 20th	Night	9% 18% 5% 14% 7% 7% 7% 5% 7% 7% 13%	5198
	21st to end	Night	14% 25% 7% 15% 7% 6% 5% 3 4 5% 10%	5503
February	1st to 10th	Night	7% 19% 6% 12% 7% 6% 6% 5% 6% 6% 20%	2808
	11th to 20th	Night	6% 18% 6% 12% 7% 7% 5% 5% 5% 7% 24%	2587
	21st to end	Night	4 14% 7% 12% 8% 6% 4 3 5% 6% 30%	2058
March	1st to 10th	Night	2 12% 6% 15% 10% 8% 7% 4 5% 7% 24%	3801
	11th to 20th	Night	6% 22% 7% 13% 7% 6% 5% 5% 6% 6% 17%	3582
	21st to end	Night	4 12% 7% 13% 7% 5% 5% 4 6% 7% 29%	3678
April	1st to 10th	Night	5% 17% 6% 11% 7% 6% 5% 4 6% 6% 25%	1743
	11th to 20th	Night	6% 13% 4 10% 7% 5% 6% 5% 6% 7% 31%	1691
	21st to end	Night	9% 12% 4 10% 6% 6% 5% 5% 8% 8% 26%	1373
May	1st to 10th	Night	10% 11% 4 10% 6% 5% 5% 4 5% 8% 31%	2220
	11th to 20th	Night	12% 13% 4 9% 6% 6% 7% 6% 8% 6% 23%	1876
	21st to end	Night	15% 11% 4 9% 5% 5% 6% 4 8% 7% 27%	1718
June	1st to 10th	Night	13% 8% 4 10% 6% 6% 6% 4 8% 8% 26%	950
	11th to 20th	Night	14% 8% 4 11% 8% 6% 8% 7% 7% 8% 21%	950
	21st to end	Night	11% 9% 3 10% 7% 7% 7% 7% 6% 8% 25%	950
July	1st to 10th	Night	8% 5% 2 7% 6% 6% 7% 7% 10% 12% 30%	1580
	11th to 20th	Night	17% 9% 4 10% 6% 7% 7% 6% 8% 8% 17%	1580
	21st to end	Night	16% 10% 4 11% 6% 5% 5% 5% 6% 6% 25%	2020
August	1st to 10th	Night	6% 5% 3 8% 5% 4 4 3 5% 7% 50%	2180
	11th to 20th	Night	10% 6% 2 7% 6% 5% 5% 4 6% 9% 39%	2297
	21st to end	Night	16% 13% 4 14% 6% 7% 6% 4 6% 5% 18%	3045
September	1st to 10th	Night	17% 9% 3 9% 5% 5% 6% 4 6% 6% 30%	1710
	11th to 20th	Night	12% 8% 3 9% 6% 5% 7% 5% 8% 8% 30%	2021
	21st to end	Night	20% 15% 6% 10% 6% 5% 5% 4 5% 4 21%	2090
October	1st to 10th	Night	11% 12% 3 9% 5% 5% 6% 5% 7% 9% 28%	3851
	11th to 20th	Night	13% 20% 7% 12% 6% 5% 6% 5% 5% 5% 15%	4085
	21st to end	Night	10% 19% 6% 13% 7% 6% 4 3 5% 6% 22%	4750
November	1st to 10th	Night	11% 21% 6% 12% 6% 6% 5% 4 5% 5% 18%	2926
	11th to 20th	Night	9% 23% 7% 15% 9% 7% 6% 4 4 4 12%	3105
	21st to end	Night	10% 18% 6% 16% 9% 8% 6% 4 5% 5% 14%	3347
December	1st to 10th	Night	11% 20% 6% 12% 9% 7% 6% 5% 5% 5% 14%	3230
	11th to 20th	Night	6% 21% 7% 15% 9% 7% 5% 3 4 6% 16%	3990
	21st to end	Night	10% 21% 7% 14% 9% 7% 7% 4 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	78% 7% 7% 5% 3	1579
	11th to 20th	Day	65% 8% 9% 11% 7%	1746
	21st to end	Day	73% 7% 8% 9% 3	2152
February	1st to 10th	Day	63% 8% 11% 11% 7%	1372
	11th to 20th	Day	59% 8% 16% 13% 3	1488
	21st to end	Day	58% 8% 15% 13% 6%	1395
March	1st to 10th	Day	52% 8% 13% 21% 6%	3062
	11th to 20th	Day	56% 11% 13% 16% 4	3394
	21st to end	Day	49% 11% 21% 16% 3	3969
April	1st to 10th	Day	57% 9% 15% 14% 5%	2437
	11th to 20th	Day	52% 9% 15% 19% 5%	2438
	21st to end	Day	56% 10% 16% 16% 3	2806
May	1st to 10th	Day	48% 12% 15% 19% 6%	4740
	11th to 20th	Day	53% 13% 13% 16% 4	5021
	21st to end	Day	52% 10% 12% 18% 7%	5858
June	1st to 10th	Day	54% 9% 13% 19% 5%	3230
	11th to 20th	Day	57% 10% 15% 14% 5%	3230
	21st to end	Day	51% 10% 20% 16% 4	3230
July	1st to 10th	Day	40% 9% 26% 22% 3	5296
	11th to 20th	Day	53% 11% 21% 13% 3	5287
	21st to end	Day	46% 10% 22% 20% 2	5356
August	1st to 10th	Day	34% 9% 16% 28% 10% 3	4731
	11th to 20th	Day	39% 7% 20% 28% 6%	4578
	21st to end	Day	55% 9% 19% 15% 2	4621
September	1st to 10th	Day	50% 10% 20% 17% 3	2470
	11th to 20th	Day	46% 10% 21% 20% 3	2156
	21st to end	Day	60% 8% 13% 18% 2	2090
October	1st to 10th	Day	56% 7% 19% 15% 3	3124
	11th to 20th	Day	62% 6% 14% 16% 1	2843
	21st to end	Day	61% 8% 17% 13% 2	2799
November	1st to 10th	Day	71% 8% 11% 8% 2	1372
	11th to 20th	Day	78% 6% 8% 8% 1	1275
	21st to end	Day	72% 5% 9% 8% 5%	1046
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	78% 7% 6% 6% 2	5366
	11th to 20th	Night	63% 8% 8% 12% 9%	5243
	21st to end	Night	75% 8% 8% 8% 2	5503
February	1st to 10th	Night	61% 7% 11% 16% 6%	2808
	11th to 20th	Night	57% 9% 16% 15% 3	2590
	21st to end	Night	53% 7% 18% 16% 7%	2058
March	1st to 10th	Night	57% 7% 11% 18% 6% 1	3801
	11th to 20th	Night	61% 11% 14% 11% 4	3583
	21st to end	Night	48% 12% 22% 14% 5%	3678
April	1st to 10th	Night	55% 8% 16% 16% 5% 1	1743
	11th to 20th	Night	48% 7% 17% 20% 8%	1691
	21st to end	Night	51% 9% 19% 16% 5%	1373
May	1st to 10th	Night	44% 13% 18% 19% 5%	2220
	11th to 20th	Night	50% 14% 15% 15% 5%	1876
	21st to end	Night	51% 10% 13% 17% 8%	1718
June	1st to 10th	Night	51% 9% 17% 18% 5%	950
	11th to 20th	Night	55% 13% 12% 15% 4 1	950
	21st to end	Night	51% 11% 17% 16% 4	950
July	1st to 10th	Night	38% 11% 23% 26% 3	1555
	11th to 20th	Night	57% 11% 20% 11%	1550
	21st to end	Night	54% 9% 18% 18% 1	1956
August	1st to 10th	Night	32% 7% 14% 31% 14% 1	2174
	11th to 20th	Night	39% 8% 18% 28% 7%	2318
	21st to end	Night	64% 7% 15% 12% 1	3045
September	1st to 10th	Night	50% 9% 17% 20% 4	1710
	11th to 20th	Night	47% 10% 18% 21% 4	2021
	21st to end	Night	62% 7% 12% 14% 4	2090
October	1st to 10th	Night	50% 7% 18% 22% 3	3851
	11th to 20th	Night	68% 7% 14% 11% 1	4085
	21st to end	Night	62% 8% 14% 14% 3	4750
November	1st to 10th	Night	66% 8% 13% 12% 1	2926
	11th to 20th	Night	73% 8% 10% 8% 1	3105
	21st to end	Night	71% 7% 11% 9% 3	3347
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 8% 32% 29% 10%	180
	21st to end	Day	16% 7% 11% 40% 21% 5%	198
February	1st to 10th	Day	10% 6% 21% 36% 21% 6%	222
	11th to 20th	Day	13% 5% 16% 36% 18% 12%	365
	21st to end	Day	8% 7% 21% 30% 22% 12%	307
March	1st to 10th	Day	8% 6% 20% 30% 22% 13%	370
	11th to 20th	Day	9% 7% 24% 34% 22% 4	433
	21st to end	Day	10% 10% 21% 28% 21% 10%	506
April	1st to 10th	Day	12% 10% 27% 28% 19% 4	460
	11th to 20th	Day	12% 11% 21% 23% 19% 12%	452
	21st to end	Day	16% 12% 27% 23% 16% 6%	649
May	1st to 10th	Day	19% 13% 28% 21% 16% 3	653
	11th to 20th	Day	15% 10% 25% 26% 18% 7%	758
	21st to end	Day	16% 9% 19% 30% 19% 7%	940
June	1st to 10th	Day	17% 8% 21% 27% 23% 5%	870
	11th to 20th	Day	18% 6% 18% 29% 23% 6%	870
	21st to end	Day	16% 6% 18% 28% 24% 7%	870
July	1st to 10th	Day	14% 4 19% 32% 23% 8%	856
	11th to 20th	Day	16% 7% 17% 27% 24% 9%	852
	21st to end	Day	12% 6% 17% 30% 23% 11%	771
August	1st to 10th	Day	12% 5% 18% 25% 26% 14%	676
	11th to 20th	Day	20% 8% 24% 26% 18% 5%	665
	21st to end	Day	22% 4 19% 25% 20% 10%	601
September	1st to 10th	Day	19% 7% 22% 23% 22% 8%	490
	11th to 20th	Day	11% 10% 19% 27% 25% 8%	490
	21st to end	Day	23% 12% 23% 22% 15% 4	490
October	1st to 10th	Day	24% 9% 23% 23% 19% 2	454
	11th to 20th	Day	22% 9% 19% 32% 14% 4	390
	21st to end	Day	18% 3 20% 34% 20% 5%	268
November	1st to 10th	Day	20% 3 17% 37% 17% 8%	200
	11th to 20th	Day	18% 4 15% 31% 24% 10%	200
	21st to end	Day	15% 2 14% 41% 20% 8%	199
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	22% 3 15% 36% 19% 5%	955
	21st to end	Night	17% 5% 17% 38% 20% 3	935
February	1st to 10th	Night	11% 7% 15% 41% 23% 3	850
	11th to 20th	Night	12% 3 18% 41% 23% 4	834
	21st to end	Night	9% 4 17% 42% 25% 4	635
March	1st to 10th	Night	8% 5% 21% 39% 21% 6%	760
	11th to 20th	Night	13% 5% 21% 34% 26% 2	760
	21st to end	Night	9% 5% 19% 33% 29% 6%	750
April	1st to 10th	Night	10% 5% 22% 33% 26% 4	570
	11th to 20th	Night	11% 5% 17% 36% 26% 6%	563
	21st to end	Night	14% 7% 22% 32% 22% 4	423
May	1st to 10th	Night	13% 5% 23% 33% 20% 5%	380
	11th to 20th	Night	15% 6% 21% 32% 22% 3	374
	21st to end	Night	14% 5% 19% 35% 22% 4	411
June	1st to 10th	Night	15% 4 21% 31% 27% 1	380
	11th to 20th	Night	17% 4 18% 30% 26% 4	380
	21st to end	Night	13% 7% 19% 28% 28% 4	380
July	1st to 10th	Night	14% 5% 17% 36% 26% 2	370
	11th to 20th	Night	17% 4 16% 28% 31% 5%	368
	21st to end	Night	16% 3 18% 28% 30% 6%	416
August	1st to 10th	Night	11% 3 18% 31% 29% 8%	378
	11th to 20th	Night	17% 5% 21% 32% 21% 3	438
	21st to end	Night	25% 4 14% 26% 27% 5%	627
September	1st to 10th	Night	20% 5% 17% 32% 23% 3	570
	11th to 20th	Night	14% 4 19% 33% 26% 4	715
	21st to end	Night	25% 9% 20% 27% 16% 3	760
October	1st to 10th	Night	21% 8% 18% 35% 17% 2	760
	11th to 20th	Night	26% 6% 18% 34% 14% 2	760
	21st to end	Night	20% 5% 17% 36% 17% 4	843
November	1st to 10th	Night	20% 4 14% 36% 22% 4	880
	11th to 20th	Night	16% 5% 14% 34% 23% 7%	1005
	21st to end	Night	18% 4 14% 38% 23% 4	1100
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 2024-11-27 14:30:50. Version ac07

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