Sproat Lake (east)
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sproat Lake (east) clear sky chart from 2005-11-06 to 2024-03-06.

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	23% 12% 4 8% 6% 3 4 4 4 6% 25%	78008
	Night	26% 13% 4 7% 6% 3 4 4 4 5% 23%	81469
Transparency	Day	60% 7% 12% 14% 6% 1	77711
	Night	62% 7% 12% 13% 6% 1	81346
Seeing	Day	26% 11% 23% 24% 12% 4	14691
	Night	28% 7% 20% 26% 16% 2	22936

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	35% 18% 7% 10% 5% 3 3 3 3 4 10%	2219
	11th to 20th	Day	30% 11% 4 9% 11% 4 4 4 5% 6% 12%	2199
	21st to end	Day	49% 18% 5% 6% 4 3 3 2 2 3 6%	2731
February	1st to 10th	Day	29% 16% 5% 9% 7% 3 4 4 4 6% 12%	1710
	11th to 20th	Day	26% 16% 5% 9% 5% 3 5% 4 4 5% 18%	1665
	21st to end	Day	24% 16% 4 7% 7% 4 4 5% 5% 5% 17%	1413
March	1st to 10th	Day	24% 18% 5% 9% 8% 4 5% 4 3 4 15%	1944
	11th to 20th	Day	28% 17% 4 9% 8% 3 5% 3 3 4 17%	1980
	21st to end	Day	30% 16% 5% 8% 7% 3 4 3 3 5% 15%	2178
April	1st to 10th	Day	27% 15% 5% 8% 7% 4 5% 4 4 5% 16%	2153
	11th to 20th	Day	24% 14% 5% 10% 7% 3 5% 4 4 5% 20%	2308
	21st to end	Day	24% 13% 4 8% 7% 3 6% 5% 4 5% 20%	2340
May	1st to 10th	Day	20% 10% 4 7% 7% 4 6% 5% 6% 7% 25%	2492
	11th to 20th	Day	17% 10% 4 9% 8% 3 5% 5% 6% 7% 25%	2477
	21st to end	Day	19% 10% 4 8% 8% 4 5% 5% 6% 7% 26%	2896
June	1st to 10th	Day	24% 10% 4 8% 7% 4 6% 4 5% 6% 23%	2700
	11th to 20th	Day	19% 10% 5% 9% 9% 4 6% 7% 5% 7% 20%	2700
	21st to end	Day	17% 9% 3 8% 6% 4 4 5% 5% 6% 33%	2700
July	1st to 10th	Day	12% 7% 3 7% 6% 4 5% 3 4 7% 41%	2700
	11th to 20th	Day	9% 4 2 4 5% 3 4 6% 6% 9% 47%	2700
	21st to end	Day	7% 4 2 4 4 3 3 4 6% 7% 55%	2905
August	1st to 10th	Day	10% 5% 3 5% 5% 3 4 4 6% 8% 48%	2389
	11th to 20th	Day	7% 4 3 5% 4 2 4 5% 7% 9% 50%	2298
	21st to end	Day	13% 6% 3 6% 6% 3 5% 5% 6% 9% 38%	2574
September	1st to 10th	Day	12% 8% 2 5% 5% 3 4 5% 5% 7% 44%	2174
	11th to 20th	Day	18% 10% 3 6% 5% 3 4 4 4 5% 37%	2062
	21st to end	Day	22% 8% 3 7% 6% 4 4 4 4 6% 33%	1959
October	1st to 10th	Day	25% 11% 3 7% 5% 3 4 4 4 5% 29%	1800
	11th to 20th	Day	31% 10% 5% 7% 7% 3 5% 4 5% 6% 18%	1800
	21st to end	Day	32% 11% 3 7% 6% 3 4 4 5% 6% 20%	1820
November	1st to 10th	Day	35% 16% 5% 10% 7% 3 4 3 3 3 11%	1488
	11th to 20th	Day	35% 13% 5% 7% 6% 3 4 4 4 5% 14%	1520
	21st to end	Day	35% 12% 5% 9% 6% 3 4 3 4 4 15%	1520
December	1st to 10th	Day	28% 15% 6% 10% 6% 3 5% 4 4 4 15%	1367
	11th to 20th	Day	37% 19% 7% 12% 6% 2 3 3 3 2 7%	1685
	21st to end	Day	40% 18% 5% 8% 6% 3 3 3 2 3 9%	2442
January	1st to 10th	Night	35% 19% 5% 9% 7% 4 4 3 3 3 6%	4726
	11th to 20th	Night	31% 13% 5% 8% 7% 4 4 5% 4 5% 16%	4699
	21st to end	Night	47% 22% 5% 6% 3 2 2 2 2 3 7%	4928
February	1st to 10th	Night	29% 18% 5% 7% 6% 3 3 4 4 5% 16%	2470
	11th to 20th	Night	25% 15% 5% 7% 5% 3 4 3 4 5% 24%	2402
	21st to end	Night	22% 16% 3 8% 6% 3 5% 4 4 5% 23%	2041
March	1st to 10th	Night	22% 15% 5% 7% 7% 3 5% 5% 4 5% 21%	2130
	11th to 20th	Night	24% 15% 5% 7% 7% 3 5% 5% 5% 6% 20%	1979
	21st to end	Night	27% 14% 5% 8% 7% 4 6% 4 3 4 17%	2178
April	1st to 10th	Night	24% 12% 4 8% 6% 4 4 5% 5% 7% 22%	1803
	11th to 20th	Night	20% 11% 5% 7% 7% 4 5% 4 6% 7% 23%	1601
	21st to end	Night	24% 10% 3 7% 6% 4 6% 4 6% 6% 24%	1620
May	1st to 10th	Night	14% 9% 3 7% 7% 4 5% 4 5% 7% 37%	1468
	11th to 20th	Night	15% 8% 4 7% 7% 4 7% 6% 7% 8% 28%	1416
	21st to end	Night	16% 7% 3 7% 6% 4 5% 5% 6% 7% 34%	1376
June	1st to 10th	Night	18% 9% 4 8% 6% 3 6% 5% 4 7% 30%	1260
	11th to 20th	Night	14% 8% 3 8% 6% 6% 7% 6% 5% 8% 28%	1260
	21st to end	Night	11% 6% 2 6% 7% 3 5% 6% 7% 8% 38%	1260
July	1st to 10th	Night	12% 5% 2 5% 4 3 5% 5% 5% 8% 47%	1260
	11th to 20th	Night	7% 5% 2 3 5% 3 4 4 6% 9% 53%	1260
	21st to end	Night	7% 4 2 3 4 2 3 4 5% 6% 60%	1410
August	1st to 10th	Night	7% 5% 2 5% 5% 3 4 4 5% 7% 55%	1547
	11th to 20th	Night	5% 3 2 3 4 3 4 4 6% 9% 57%	1602
	21st to end	Night	12% 6% 1 5% 5% 3 4 5% 6% 8% 44%	1782
September	1st to 10th	Night	9% 4 2 4 5% 3 5% 5% 5% 7% 51%	1786
	11th to 20th	Night	16% 8% 3 7% 6% 3 4 6% 4 6% 37%	1896
	21st to end	Night	21% 9% 3 6% 5% 3 3 4 4 5% 37%	2000
October	1st to 10th	Night	20% 9% 3 6% 5% 3 4 4 4 7% 35%	2160
	11th to 20th	Night	29% 11% 3 7% 6% 3 4 5% 4 5% 23%	2160
	21st to end	Night	32% 11% 4 6% 5% 3 3 3 5% 5% 23%	2533
November	1st to 10th	Night	35% 13% 5% 9% 6% 3 4 4 4 5% 14%	2590
	11th to 20th	Night	33% 13% 6% 7% 7% 3 5% 4 4 4 14%	2660
	21st to end	Night	33% 10% 4 9% 8% 4 5% 4 4 5% 15%	2660
December	1st to 10th	Night	27% 14% 6% 9% 6% 4 6% 5% 4 4 15%	2812
	11th to 20th	Night	38% 19% 6% 10% 5% 2 4 3 3 4 7%	3520
	21st to end	Night	40% 19% 5% 8% 5% 2 3 3 3 3 10%	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	78% 6% 6% 7% 2	2219
	11th to 20th	Day	66% 13% 10% 8% 3 1	2220
	21st to end	Day	86% 4 4 4 2	2731
February	1st to 10th	Day	73% 8% 7% 7% 5% 1	1710
	11th to 20th	Day	69% 6% 9% 11% 5% 1	1674
	21st to end	Day	66% 8% 9% 11% 4 2	1413
March	1st to 10th	Day	72% 6% 9% 11% 2	1944
	11th to 20th	Day	73% 4 10% 8% 4 1	1980
	21st to end	Day	73% 6% 11% 9% 1	2178
April	1st to 10th	Day	72% 7% 9% 9% 3	2153
	11th to 20th	Day	68% 5% 9% 10% 6%	2308
	21st to end	Day	68% 5% 11% 11% 5%	2340
May	1st to 10th	Day	57% 9% 16% 14% 5%	2492
	11th to 20th	Day	58% 8% 15% 15% 4	2480
	21st to end	Day	57% 9% 14% 15% 4	2897
June	1st to 10th	Day	63% 7% 13% 10% 5% 1	2700
	11th to 20th	Day	62% 10% 16% 9% 3	2700
	21st to end	Day	51% 7% 17% 17% 7%	2700
July	1st to 10th	Day	44% 8% 16% 20% 10% 1	2626
	11th to 20th	Day	34% 8% 23% 27% 8%	2619
	21st to end	Day	27% 8% 18% 30% 15% 2	2743
August	1st to 10th	Day	34% 8% 20% 24% 13% 2	2372
	11th to 20th	Day	30% 10% 20% 25% 14% 1	2298
	21st to end	Day	43% 9% 20% 22% 6% 1	2574
September	1st to 10th	Day	39% 7% 16% 26% 10% 2	2174
	11th to 20th	Day	49% 6% 12% 16% 15% 1	2062
	21st to end	Day	53% 7% 13% 16% 10% 1	1959
October	1st to 10th	Day	57% 7% 14% 13% 9% 1	1800
	11th to 20th	Day	67% 8% 11% 11% 3	1800
	21st to end	Day	66% 6% 10% 11% 7%	1820
November	1st to 10th	Day	80% 4 7% 5% 4 1	1488
	11th to 20th	Day	72% 6% 9% 7% 6% 1	1520
	21st to end	Day	72% 8% 7% 7% 5% 1	1520
December	1st to 10th	Day	74% 5% 7% 8% 5% 1	1367
	11th to 20th	Day	81% 9% 5% 3 2 1	1688
	21st to end	Day	80% 5% 6% 6% 2 1	2442
January	1st to 10th	Night	79% 9% 6% 4 2	4726
	11th to 20th	Night	63% 12% 9% 11% 4 1	4740
	21st to end	Night	86% 3 4 5% 3	4928
February	1st to 10th	Night	71% 6% 7% 9% 5% 1	2470
	11th to 20th	Night	63% 6% 11% 12% 7% 1	2404
	21st to end	Night	64% 6% 10% 15% 5% 1	2041
March	1st to 10th	Night	63% 6% 13% 14% 5%	2130
	11th to 20th	Night	66% 6% 13% 9% 5% 1	1980
	21st to end	Night	71% 6% 10% 10% 3	2178
April	1st to 10th	Night	62% 8% 12% 13% 4	1803
	11th to 20th	Night	59% 7% 13% 14% 7% 1	1601
	21st to end	Night	61% 8% 10% 14% 6% 1	1620
May	1st to 10th	Night	48% 8% 17% 20% 7%	1468
	11th to 20th	Night	53% 11% 17% 15% 5%	1416
	21st to end	Night	47% 10% 20% 19% 3	1376
June	1st to 10th	Night	54% 6% 22% 11% 5% 2	1260
	11th to 20th	Night	54% 9% 22% 12% 4	1260
	21st to end	Night	42% 10% 23% 17% 7% 1	1260
July	1st to 10th	Night	37% 10% 19% 21% 11% 1	1225
	11th to 20th	Night	28% 9% 26% 28% 9% 1	1218
	21st to end	Night	23% 7% 19% 34% 14% 3	1332
August	1st to 10th	Night	29% 8% 19% 28% 13% 2	1539
	11th to 20th	Night	26% 9% 26% 23% 14% 3	1602
	21st to end	Night	38% 8% 22% 27% 5% 1	1782
September	1st to 10th	Night	32% 8% 19% 27% 12% 2	1786
	11th to 20th	Night	49% 7% 10% 17% 15% 3	1896
	21st to end	Night	49% 7% 14% 18% 10% 2	2000
October	1st to 10th	Night	50% 7% 15% 16% 12% 1	2160
	11th to 20th	Night	62% 6% 12% 14% 6%	2160
	21st to end	Night	64% 5% 10% 13% 7% 1	2533
November	1st to 10th	Night	74% 5% 9% 8% 4 1	2590
	11th to 20th	Night	72% 6% 10% 6% 4 2	2660
	21st to end	Night	69% 7% 9% 8% 5% 1	2660
December	1st to 10th	Night	71% 6% 10% 8% 4 1	2812
	11th to 20th	Night	81% 7% 5% 5% 2 1	3516
	21st to end	Night	80% 4 7% 6% 2	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	42% 9% 19% 18% 7% 4	180
	11th to 20th	Day	43% 13% 14% 18% 11% 2	180
	21st to end	Day	40% 12% 19% 18% 10% 2	309
February	1st to 10th	Day	38% 12% 27% 15% 7% 1	370
	11th to 20th	Day	34% 13% 25% 21% 6% 1	365
	21st to end	Day	35% 20% 23% 15% 6% 2	307
March	1st to 10th	Day	31% 14% 19% 22% 11% 3	414
	11th to 20th	Day	35% 14% 20% 20% 7% 3	420
	21st to end	Day	35% 14% 25% 17% 6% 3	462
April	1st to 10th	Day	39% 14% 23% 17% 7% 1	420
	11th to 20th	Day	30% 16% 26% 14% 11% 3	412
	21st to end	Day	32% 16% 24% 16% 8% 3	420
May	1st to 10th	Day	20% 15% 22% 30% 10% 3	423
	11th to 20th	Day	21% 10% 24% 26% 14% 5%	448
	21st to end	Day	20% 8% 28% 28% 12% 3	658
June	1st to 10th	Day	26% 15% 28% 21% 8% 2	630
	11th to 20th	Day	20% 18% 32% 20% 9% 2	630
	21st to end	Day	18% 10% 25% 30% 12% 4	630
July	1st to 10th	Day	15% 9% 23% 36% 15% 3	621
	11th to 20th	Day	10% 11% 28% 32% 16% 4	618
	21st to end	Day	8% 9% 23% 33% 22% 5%	651
August	1st to 10th	Day	13% 7% 19% 30% 24% 8%	447
	11th to 20th	Day	8% 6% 21% 32% 24% 9%	437
	21st to end	Day	15% 7% 25% 31% 14% 7%	495
September	1st to 10th	Day	19% 7% 26% 30% 13% 5%	450
	11th to 20th	Day	24% 8% 23% 24% 16% 6%	450
	21st to end	Day	26% 10% 24% 20% 16% 3	450
October	1st to 10th	Day	26% 11% 20% 23% 14% 7%	450
	11th to 20th	Day	35% 8% 20% 21% 12% 5%	450
	21st to end	Day	36% 13% 23% 15% 9% 5%	396
November	1st to 10th	Day	41% 12% 12% 21% 12% 2	180
	11th to 20th	Day	39% 9% 14% 17% 15% 4	180
	21st to end	Day	43% 12% 16% 14% 6% 9%	180
December	1st to 10th	Day	33% 12% 19% 18% 12% 6%	180
	11th to 20th	Day	42% 7% 17% 18% 15% 2	180
	21st to end	Day	48% 8% 17% 17% 10% 1	198
January	1st to 10th	Night	45% 10% 19% 16% 8% 2	850
	11th to 20th	Night	41% 7% 18% 21% 12% 1	850
	21st to end	Night	40% 8% 20% 20% 11% 2	906
February	1st to 10th	Night	38% 8% 21% 26% 7% 1	760
	11th to 20th	Night	32% 8% 20% 28% 11%	744
	21st to end	Night	30% 8% 25% 24% 11% 2	628
March	1st to 10th	Night	27% 9% 25% 22% 15% 2	742
	11th to 20th	Night	29% 12% 23% 22% 12% 1	720
	21st to end	Night	33% 9% 20% 26% 10% 2	792
April	1st to 10th	Night	29% 7% 21% 27% 14% 2	712
	11th to 20th	Night	22% 8% 27% 31% 10% 2	533
	21st to end	Night	26% 5% 25% 31% 11% 2	540
May	1st to 10th	Night	15% 6% 18% 38% 22% 1	388
	11th to 20th	Night	18% 5% 18% 34% 23% 3	354
	21st to end	Night	15% 4 19% 40% 22% 1	389
June	1st to 10th	Night	19% 6% 23% 31% 21%	360
	11th to 20th	Night	16% 5% 25% 37% 16% 1	360
	21st to end	Night	13% 5% 23% 36% 21% 4	360
July	1st to 10th	Night	11% 3 15% 37% 31% 2	350
	11th to 20th	Night	8% 4 18% 36% 31% 2	348
	21st to end	Night	6% 4 14% 34% 38% 3	394
August	1st to 10th	Night	10% 3 10% 32% 37% 8%	473
	11th to 20th	Night	6% 3 9% 37% 37% 9%	534
	21st to end	Night	15% 3 17% 29% 32% 4	594
September	1st to 10th	Night	13% 3 16% 35% 27% 6%	706
	11th to 20th	Night	19% 6% 16% 24% 28% 8%	720
	21st to end	Night	24% 7% 20% 25% 20% 4	720
October	1st to 10th	Night	25% 6% 16% 27% 24% 3	720
	11th to 20th	Night	32% 5% 18% 24% 16% 4	720
	21st to end	Night	35% 6% 22% 24% 11% 2	792
November	1st to 10th	Night	39% 9% 20% 25% 6%	740
	11th to 20th	Night	37% 10% 23% 18% 10% 2	760
	21st to end	Night	38% 5% 21% 22% 11% 3	760
December	1st to 10th	Night	32% 10% 19% 23% 13% 2	832
	11th to 20th	Night	42% 7% 22% 21% 7% 1	850
	21st to end	Night	41% 8% 25% 20% 6%	935

Page generated at 2024-03-03 03:28:53. Version ac07

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