UBC Forest Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the UBC Forest Site 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	29% 10% 3 6% 4 3 3 3 4 5% 30%	105700
	Night	32% 10% 3 6% 3 3 3 2 4 5% 29%	102493
Transparency	Day	57% 6% 11% 16% 8% 1	105450
	Night	60% 5% 11% 15% 8% 2	102389
Seeing	Day	34% 11% 21% 23% 9% 2	15364
	Night	39% 7% 19% 22% 12% 1	23595

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	47% 14% 3 6% 4 4 3 2 3 2 11%	2219
	11th to 20th	Day	32% 13% 4 7% 3 4 2 2 2 3 28%	2208
	21st to end	Day	61% 9% 2 5% 2 2 2 2 2 3 11%	2794
February	1st to 10th	Day	39% 12% 3 7% 4 4 3 3 4 4 17%	1710
	11th to 20th	Day	36% 12% 3 7% 4 4 3 3 4 4 21%	1665
	21st to end	Day	28% 19% 4 7% 5% 4 4 2 4 3 19%	1443
March	1st to 10th	Day	31% 21% 4 7% 4 4 4 2 4 4 15%	3217
	11th to 20th	Day	28% 13% 3 6% 3 3 2 2 3 4 32%	3490
	21st to end	Day	33% 15% 3 7% 5% 3 3 3 3 4 19%	3946
April	1st to 10th	Day	34% 14% 3 8% 6% 5% 4 4 5% 5% 14%	2280
	11th to 20th	Day	28% 13% 3 7% 6% 6% 4 4 4 5% 21%	2325
	21st to end	Day	32% 12% 4 8% 5% 4 4 3 5% 5% 20%	2546
May	1st to 10th	Day	23% 11% 2 5% 4 3 4 3 4 5% 35%	4420
	11th to 20th	Day	20% 9% 2 6% 5% 4 5% 4 6% 8% 31%	4377
	21st to end	Day	35% 12% 3 8% 5% 4 4 3 4 5% 17%	4867
June	1st to 10th	Day	30% 10% 3 6% 5% 4 4 3 5% 6% 24%	2850
	11th to 20th	Day	33% 11% 3 8% 6% 5% 4 3 4 5% 18%	2850
	21st to end	Day	23% 9% 2 6% 4 5% 4 3 5% 6% 32%	2850
July	1st to 10th	Day	11% 4 1 5% 3 3 3 3 4 5% 58%	4740
	11th to 20th	Day	9% 3 1 3 2 2 2 2 3 5% 66%	4740
	21st to end	Day	17% 5% 2 5% 3 3 3 2 5% 7% 48%	4834
August	1st to 10th	Day	9% 4 2 3 2 2 3 2 4 6% 63%	4401
	11th to 20th	Day	20% 7% 2 6% 3 4 4 3 5% 6% 39%	4031
	21st to end	Day	23% 7% 2 6% 4 3 4 3 5% 6% 37%	4398
September	1st to 10th	Day	20% 6% 2 6% 3 3 3 3 4 6% 43%	2280
	11th to 20th	Day	24% 8% 3 6% 4 3 3 2 4 4 37%	2280
	21st to end	Day	30% 8% 2 6% 3 3 3 2 4 5% 33%	2005
October	1st to 10th	Day	30% 8% 3 7% 4 4 4 3 5% 6% 26%	3180
	11th to 20th	Day	42% 6% 2 5% 4 4 4 4 4 5% 21%	3161
	21st to end	Day	39% 13% 4 8% 4 4 4 3 3 5% 14%	3178
November	1st to 10th	Day	45% 10% 3 6% 4 4 4 3 3 3 15%	1568
	11th to 20th	Day	45% 12% 2 6% 3 3 2 1 2 4 21%	1600
	21st to end	Day	44% 12% 3 5% 3 3 3 3 4 4 18%	1595
December	1st to 10th	Day	36% 15% 3 5% 3 2 3 3 3 3 24%	1520
	11th to 20th	Day	43% 15% 3 6% 3 3 3 2 3 3 16%	1690
	21st to end	Day	47% 15% 4 7% 3 3 3 3 3 3 9%	2442
January	1st to 10th	Night	46% 15% 4 7% 3 3 3 2 2 3 13%	4726
	11th to 20th	Night	35% 9% 2 5% 3 3 3 2 4 7% 27%	4687
	21st to end	Night	58% 11% 2 5% 2 2 2 1 2 3 12%	4858
February	1st to 10th	Night	38% 12% 3 6% 4 4 3 3 3 5% 19%	2470
	11th to 20th	Night	33% 15% 3 7% 5% 3 3 2 3 4 22%	2402
	21st to end	Night	32% 12% 3 7% 4 3 3 3 5% 4 24%	2010
March	1st to 10th	Night	31% 19% 3 6% 3 3 3 2 4 4 21%	3657
	11th to 20th	Night	29% 11% 2 5% 3 3 3 2 3 5% 34%	3489
	21st to end	Night	37% 15% 4 7% 3 3 2 2 3 3 20%	3706
April	1st to 10th	Night	31% 13% 3 8% 5% 5% 3 3 5% 6% 20%	1900
	11th to 20th	Night	25% 12% 3 7% 5% 4 4 3 4 5% 26%	1801
	21st to end	Night	30% 11% 3 8% 4 4 4 3 5% 6% 22%	1634
May	1st to 10th	Night	20% 9% 3 6% 4 3 3 2 3 4 44%	2540
	11th to 20th	Night	16% 7% 2 6% 3 4 4 4 6% 7% 42%	2516
	21st to end	Night	32% 12% 3 7% 3 4 3 3 3 5% 25%	2704
June	1st to 10th	Night	26% 10% 2 6% 5% 4 4 3 5% 6% 28%	1330
	11th to 20th	Night	24% 11% 3 8% 5% 5% 4 4 5% 7% 25%	1330
	21st to end	Night	18% 8% 2 5% 4 4 3 4 6% 5% 39%	1330
July	1st to 10th	Night	7% 3 1 3 3 2 3 2 4 5% 65%	2220
	11th to 20th	Night	6% 2 1 3 2 2 1 2 3 4 74%	2220
	21st to end	Night	12% 4 2 4 3 3 4 3 5% 6% 56%	2717
August	1st to 10th	Night	6% 2 1 3 2 1 2 2 5% 7% 68%	2529
	11th to 20th	Night	15% 5% 2 5% 4 3 3 3 5% 7% 48%	2804
	21st to end	Night	19% 6% 2 6% 4 3 4 3 6% 6% 41%	3272
September	1st to 10th	Night	13% 5% 2 4 3 3 4 3 4 6% 52%	1900
	11th to 20th	Night	23% 6% 2 6% 4 4 3 2 3 5% 41%	1900
	21st to end	Night	28% 8% 2 6% 3 4 2 3 4 5% 36%	2170
October	1st to 10th	Night	27% 12% 2 7% 4 4 4 3 4 5% 27%	3800
	11th to 20th	Night	38% 9% 2 5% 3 3 3 3 4 5% 26%	3777
	21st to end	Night	38% 14% 3 7% 3 3 3 2 3 3 21%	4380
November	1st to 10th	Night	46% 9% 3 6% 4 3 3 2 3 4 16%	2730
	11th to 20th	Night	44% 11% 2 5% 3 3 3 2 3 3 21%	2800
	21st to end	Night	42% 11% 3 7% 4 2 4 2 3 3 20%	2800
December	1st to 10th	Night	34% 12% 3 5% 4 3 3 3 4 4 26%	2660
	11th to 20th	Night	49% 14% 3 5% 3 3 2 2 3 3 13%	3510
	21st to end	Night	49% 14% 2 6% 3 3 3 2 2 2 13%	5214

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	80% 5% 6% 6% 2 1	2219
	11th to 20th	Day	64% 3 9% 11% 7% 5%	2229
	21st to end	Day	82% 2 5% 7% 3 1	2794
February	1st to 10th	Day	74% 4 7% 8% 5% 2	1710
	11th to 20th	Day	69% 5% 6% 11% 7% 2	1674
	21st to end	Day	72% 4 8% 10% 5% 2	1443
March	1st to 10th	Day	70% 11% 8% 8% 4	3217
	11th to 20th	Day	58% 6% 8% 22% 5% 1	3490
	21st to end	Day	69% 7% 10% 10% 3	3946
April	1st to 10th	Day	73% 7% 11% 8% 2	2280
	11th to 20th	Day	67% 6% 7% 10% 7% 2	2325
	21st to end	Day	68% 7% 9% 9% 6% 1	2546
May	1st to 10th	Day	51% 7% 13% 22% 6%	4420
	11th to 20th	Day	48% 13% 19% 16% 3	4380
	21st to end	Day	68% 10% 11% 9% 1	4868
June	1st to 10th	Day	62% 7% 13% 12% 5% 2	2850
	11th to 20th	Day	70% 7% 12% 8% 3	2850
	21st to end	Day	54% 7% 14% 16% 7% 1	2850
July	1st to 10th	Day	31% 5% 9% 24% 21% 9%	4666
	11th to 20th	Day	23% 4 11% 40% 21% 1	4659
	21st to end	Day	36% 6% 21% 25% 10% 2	4681
August	1st to 10th	Day	24% 6% 12% 41% 16% 1	4384
	11th to 20th	Day	46% 8% 19% 18% 8% 1	4070
	21st to end	Day	50% 6% 14% 20% 8% 1	4397
September	1st to 10th	Day	44% 6% 12% 22% 12% 4	2280
	11th to 20th	Day	52% 5% 9% 17% 13% 2	2280
	21st to end	Day	55% 7% 13% 15% 9% 2	2005
October	1st to 10th	Day	60% 5% 13% 15% 7%	3180
	11th to 20th	Day	67% 4 10% 12% 6% 1	3161
	21st to end	Day	74% 5% 6% 10% 5% 1	3178
November	1st to 10th	Day	75% 5% 7% 9% 3 1	1568
	11th to 20th	Day	73% 4 7% 8% 6% 2	1600
	21st to end	Day	72% 4 5% 10% 8% 2	1595
December	1st to 10th	Day	67% 5% 6% 10% 11% 1	1520
	11th to 20th	Day	74% 6% 6% 10% 2 2	1693
	21st to end	Day	80% 7% 4 6% 2 1	2442
January	1st to 10th	Night	79% 5% 5% 9% 3 1	4726
	11th to 20th	Night	58% 4 10% 14% 8% 5%	4728
	21st to end	Night	81% 3 4 7% 4 1	4858
February	1st to 10th	Night	71% 5% 9% 8% 5% 3	2470
	11th to 20th	Night	69% 5% 6% 10% 7% 2	2404
	21st to end	Night	65% 4 9% 14% 6% 2	2010
March	1st to 10th	Night	66% 6% 10% 11% 7%	3657
	11th to 20th	Night	55% 7% 11% 20% 7%	3490
	21st to end	Night	70% 6% 12% 9% 2	3706
April	1st to 10th	Night	68% 7% 13% 10% 2	1900
	11th to 20th	Night	61% 6% 9% 14% 7% 2	1801
	21st to end	Night	65% 7% 11% 11% 5% 1	1634
May	1st to 10th	Night	47% 5% 17% 22% 9% 1	2540
	11th to 20th	Night	42% 11% 22% 19% 5%	2516
	21st to end	Night	63% 9% 16% 10% 3	2704
June	1st to 10th	Night	59% 5% 16% 13% 5% 3	1330
	11th to 20th	Night	61% 8% 16% 12% 4	1330
	21st to end	Night	46% 7% 19% 17% 8% 3	1330
July	1st to 10th	Night	23% 5% 10% 34% 19% 9%	2185
	11th to 20th	Night	18% 3 12% 40% 25% 1	2178
	21st to end	Night	29% 6% 14% 30% 18% 3	2631
August	1st to 10th	Night	18% 4 16% 38% 22% 2	2521
	11th to 20th	Night	35% 8% 27% 19% 8% 3	2831
	21st to end	Night	44% 7% 17% 21% 9% 1	3272
September	1st to 10th	Night	36% 8% 14% 23% 15% 5%	1900
	11th to 20th	Night	47% 5% 13% 17% 15% 4	1900
	21st to end	Night	52% 7% 13% 17% 9% 2	2170
October	1st to 10th	Night	61% 6% 14% 13% 6%	3800
	11th to 20th	Night	63% 4 9% 15% 9%	3777
	21st to end	Night	71% 4 6% 12% 6%	4380
November	1st to 10th	Night	73% 5% 7% 10% 4 1	2730
	11th to 20th	Night	72% 4 8% 8% 6% 2	2800
	21st to end	Night	71% 5% 7% 7% 9% 1	2800
December	1st to 10th	Night	64% 5% 8% 12% 9% 2	2660
	11th to 20th	Night	78% 5% 6% 6% 4 2	3506
	21st to end	Night	78% 6% 5% 7% 4 1	5214

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	51% 17% 13% 10% 8% 2	180
	11th to 20th	Day	54% 12% 12% 16% 6% 1	180
	21st to end	Day	55% 8% 16% 16% 5%	198
February	1st to 10th	Day	49% 14% 18% 15% 3 1	370
	11th to 20th	Day	45% 15% 19% 16% 4 1	365
	21st to end	Day	44% 13% 26% 11% 5%	323
March	1st to 10th	Day	46% 13% 17% 18% 6% 1	460
	11th to 20th	Day	43% 12% 17% 20% 8% 1	460
	21st to end	Day	46% 14% 18% 15% 5% 1	506
April	1st to 10th	Day	44% 13% 19% 17% 6% 1	460
	11th to 20th	Day	35% 16% 24% 17% 7% 2	452
	21st to end	Day	37% 16% 23% 17% 7% 1	460
May	1st to 10th	Day	30% 12% 25% 25% 7% 1	463
	11th to 20th	Day	30% 10% 21% 26% 10% 3	488
	21st to end	Day	32% 14% 24% 19% 9% 3	557
June	1st to 10th	Day	33% 12% 23% 23% 8% 1	680
	11th to 20th	Day	35% 15% 22% 20% 6% 2	680
	21st to end	Day	27% 9% 21% 28% 12% 2	680
July	1st to 10th	Day	20% 9% 26% 31% 10% 3	671
	11th to 20th	Day	16% 11% 23% 35% 11% 4	668
	21st to end	Day	13% 8% 23% 38% 12% 6%	562
August	1st to 10th	Day	18% 8% 20% 35% 13% 7%	487
	11th to 20th	Day	15% 5% 23% 34% 18% 5%	477
	21st to end	Day	23% 10% 22% 30% 12% 2	539
September	1st to 10th	Day	24% 11% 23% 27% 12% 2	490
	11th to 20th	Day	31% 9% 19% 26% 14% 2	490
	21st to end	Day	33% 10% 20% 25% 10% 3	490
October	1st to 10th	Day	35% 7% 21% 23% 12% 2	490
	11th to 20th	Day	43% 7% 16% 19% 12% 2	490
	21st to end	Day	45% 10% 19% 15% 8% 2	391
November	1st to 10th	Day	51% 9% 19% 15% 7%	200
	11th to 20th	Day	57% 7% 12% 11% 12% 3	200
	21st to end	Day	53% 10% 15% 8% 10% 5%	199
December	1st to 10th	Day	52% 9% 13% 11% 12% 2	180
	11th to 20th	Day	58% 9% 14% 13% 2 2	180
	21st to end	Day	54% 9% 21% 14% 2 1	198
January	1st to 10th	Night	56% 9% 19% 12% 3	850
	11th to 20th	Night	50% 7% 22% 20% 2	844
	21st to end	Night	50% 8% 21% 17% 4	836
February	1st to 10th	Night	47% 11% 24% 15% 4	760
	11th to 20th	Night	45% 10% 24% 18% 3	744
	21st to end	Night	41% 11% 26% 17% 5%	628
March	1st to 10th	Night	41% 11% 21% 19% 8% 1	760
	11th to 20th	Night	46% 8% 22% 20% 4	760
	21st to end	Night	46% 8% 19% 20% 6%	836
April	1st to 10th	Night	41% 8% 21% 22% 8% 1	760
	11th to 20th	Night	35% 9% 27% 21% 8% 1	673
	21st to end	Night	39% 7% 23% 23% 8% 1	494
May	1st to 10th	Night	28% 5% 19% 30% 18%	380
	11th to 20th	Night	23% 3 13% 36% 22% 2	374
	21st to end	Night	29% 5% 16% 28% 22% 1	411
June	1st to 10th	Night	33% 4 16% 31% 15% 1	380
	11th to 20th	Night	31% 6% 16% 29% 17% 2	380
	21st to end	Night	23% 7% 13% 35% 22% 2	380
July	1st to 10th	Night	14% 5% 11% 35% 31% 4	370
	11th to 20th	Night	13% 4 11% 33% 33% 6%	368
	21st to end	Night	10% 2 8% 34% 42% 4	416
August	1st to 10th	Night	13% 1 7% 26% 47% 7%	378
	11th to 20th	Night	10% 4 7% 35% 39% 6%	556
	21st to end	Night	19% 3 13% 35% 29% 2	701
September	1st to 10th	Night	17% 3 17% 34% 27% 1	760
	11th to 20th	Night	27% 5% 14% 26% 26% 4	760
	21st to end	Night	33% 7% 12% 34% 14% 1	760
October	1st to 10th	Night	32% 7% 19% 27% 14% 1	760
	11th to 20th	Night	43% 6% 19% 22% 10% 1	760
	21st to end	Night	46% 8% 23% 18% 5% 1	836
November	1st to 10th	Night	54% 8% 23% 13% 2	780
	11th to 20th	Night	54% 8% 21% 13% 3 1	800
	21st to end	Night	49% 11% 18% 17% 5%	800
December	1st to 10th	Night	42% 9% 25% 20% 4	760
	11th to 20th	Night	58% 9% 22% 9% 2	845
	21st to end	Night	56% 10% 25% 8% 1	935

Page generated at 2024-11-27 14:30:52. Version ac07

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