Bow Island
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bow Island clear sky chart from 2005-11-06 to 2024-02-10.

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	9% 7% 3 6% 6% 3 5% 5% 6% 8% 42%	77764
	Night	7% 8% 3 7% 6% 3 5% 5% 6% 8% 40%	81220
Transparency	Day	39% 6% 15% 25% 12% 2	77444
	Night	40% 7% 16% 24% 12% 2	81061
Seeing	Day	13% 11% 29% 29% 15% 3	14399
	Night	12% 11% 34% 30% 11% 1	23846

By Month

Percentage Cloud Cover SW (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	4 13% 5% 8% 8% 4 6% 6% 8% 11% 28%	2219
	11th to 20th	Day	5% 8% 5% 10% 7% 4 8% 10% 5% 7% 30%	2220
	21st to end	Day	4 8% 5% 7% 7% 3 5% 5% 5% 6% 44%	2730
February	1st to 10th	Day	8% 12% 6% 10% 8% 5% 6% 5% 6% 7% 27%	1658
	11th to 20th	Day	8% 12% 5% 10% 8% 4 6% 8% 7% 8% 24%	1575
	21st to end	Day	6% 10% 6% 9% 9% 5% 6% 6% 6% 7% 30%	1351
March	1st to 10th	Day	6% 13% 4 8% 8% 4 6% 5% 5% 8% 32%	1868
	11th to 20th	Day	7% 10% 3 8% 7% 4 5% 4 6% 8% 37%	1980
	21st to end	Day	8% 10% 4 8% 6% 4 6% 6% 6% 8% 33%	2178
April	1st to 10th	Day	8% 10% 4 8% 8% 5% 5% 7% 6% 8% 33%	2185
	11th to 20th	Day	11% 11% 4 8% 7% 4 5% 4 5% 7% 32%	2307
	21st to end	Day	11% 9% 3 7% 7% 3 5% 5% 6% 7% 36%	2340
May	1st to 10th	Day	12% 9% 3 7% 6% 4 5% 6% 6% 8% 35%	2448
	11th to 20th	Day	9% 7% 3 5% 6% 3 5% 5% 6% 7% 44%	2560
	21st to end	Day	21% 8% 3 5% 5% 3 4 4 5% 7% 35%	2917
June	1st to 10th	Day	14% 6% 3 5% 6% 3 4 5% 7% 9% 39%	2700
	11th to 20th	Day	17% 6% 3 5% 5% 5% 6% 6% 7% 8% 34%	2700
	21st to end	Day	7% 3 2 4 4 4 5% 5% 7% 9% 51%	2700
July	1st to 10th	Day	5% 3 2 4 4 3 5% 5% 7% 9% 55%	2700
	11th to 20th	Day	7% 4 1 4 4 2 4 4 6% 8% 56%	2700
	21st to end	Day	4 3 1 3 3 2 3 4 4 8% 66%	2938
August	1st to 10th	Day	6% 3 2 4 3 2 3 4 6% 8% 59%	2403
	11th to 20th	Day	7% 4 2 4 3 3 3 5% 6% 9% 55%	2299
	21st to end	Day	8% 3 1 3 3 2 4 3 5% 8% 59%	2574
September	1st to 10th	Day	11% 5% 2 4 4 2 3 3 4 7% 55%	2230
	11th to 20th	Day	13% 5% 2 4 4 2 4 4 5% 7% 50%	1996
	21st to end	Day	9% 5% 2 5% 5% 2 4 4 4 8% 51%	1980
October	1st to 10th	Day	12% 6% 3 6% 4 2 5% 5% 6% 8% 43%	1827
	11th to 20th	Day	8% 8% 4 7% 7% 3 5% 5% 6% 5% 44%	1800
	21st to end	Day	10% 9% 3 7% 5% 3 6% 6% 5% 7% 40%	1774
November	1st to 10th	Day	13% 12% 5% 7% 8% 4 4 4 5% 6% 33%	1488
	11th to 20th	Day	6% 8% 4 9% 8% 4 5% 5% 5% 7% 38%	1520
	21st to end	Day	6% 10% 5% 8% 7% 4 4 4 6% 9% 36%	1442
December	1st to 10th	Day	7% 13% 5% 8% 7% 4 5% 4 5% 8% 33%	1330
	11th to 20th	Day	5% 10% 5% 9% 8% 4 6% 7% 6% 6% 33%	1685
	21st to end	Day	4 8% 3 6% 5% 4 5% 4 6% 6% 50%	2442
January	1st to 10th	Night	3 10% 4 9% 8% 4 5% 5% 7% 9% 35%	4726
	11th to 20th	Night	4 9% 5% 10% 8% 4 6% 6% 6% 8% 34%	4740
	21st to end	Night	3 8% 4 8% 8% 3 5% 5% 7% 8% 40%	4956
February	1st to 10th	Night	9% 11% 5% 8% 8% 5% 6% 5% 6% 7% 31%	2505
	11th to 20th	Night	6% 12% 5% 8% 6% 4 7% 7% 7% 8% 29%	2272
	21st to end	Night	5% 11% 5% 10% 8% 4 6% 5% 5% 9% 33%	1902
March	1st to 10th	Night	6% 9% 4 8% 7% 4 6% 7% 7% 9% 33%	2091
	11th to 20th	Night	8% 9% 4 7% 6% 4 5% 7% 8% 7% 34%	1980
	21st to end	Night	8% 11% 4 9% 5% 3 6% 6% 8% 10% 31%	2178
April	1st to 10th	Night	9% 9% 4 7% 7% 3 6% 4 6% 9% 34%	1771
	11th to 20th	Night	10% 10% 4 7% 6% 4 5% 5% 6% 8% 33%	1601
	21st to end	Night	13% 8% 3 7% 6% 3 5% 6% 7% 7% 35%	1620
May	1st to 10th	Night	12% 8% 3 6% 5% 3 5% 6% 6% 7% 39%	1511
	11th to 20th	Night	8% 5% 3 5% 4 3 6% 5% 5% 7% 48%	1330
	21st to end	Night	18% 7% 3 6% 6% 3 5% 4 6% 8% 35%	1358
June	1st to 10th	Night	15% 6% 2 5% 5% 3 6% 5% 6% 10% 37%	1260
	11th to 20th	Night	13% 5% 2 5% 5% 3 6% 6% 8% 9% 37%	1260
	21st to end	Night	6% 3 1 4 4 3 5% 4 6% 8% 55%	1260
July	1st to 10th	Night	6% 3 1 3 4 2 3 5% 6% 9% 57%	1260
	11th to 20th	Night	6% 4 1 5% 3 3 4 5% 7% 10% 52%	1260
	21st to end	Night	3 2 1 3 3 2 4 4 6% 8% 65%	1379
August	1st to 10th	Night	6% 3 2 4 4 3 4 5% 6% 9% 53%	1533
	11th to 20th	Night	6% 2 1 3 3 2 4 6% 7% 10% 54%	1602
	21st to end	Night	7% 5% 2 4 4 2 4 4 5% 9% 54%	1782
September	1st to 10th	Night	11% 4 2 4 4 3 4 4 5% 7% 52%	1729
	11th to 20th	Night	12% 6% 2 4 3 3 4 4 5% 7% 50%	1962
	21st to end	Night	7% 5% 2 4 5% 3 4 5% 7% 8% 50%	1980
October	1st to 10th	Night	11% 6% 2 5% 5% 3 4 5% 5% 8% 46%	2132
	11th to 20th	Night	8% 7% 3 6% 5% 3 4 4 6% 8% 46%	2160
	21st to end	Night	8% 8% 4 7% 5% 4 5% 6% 6% 8% 39%	2574
November	1st to 10th	Night	12% 12% 4 6% 6% 3 5% 4 5% 7% 36%	2580
	11th to 20th	Night	6% 9% 4 7% 7% 4 5% 6% 6% 7% 40%	2660
	21st to end	Night	6% 10% 4 8% 6% 3 4 5% 6% 8% 39%	2736
December	1st to 10th	Night	6% 11% 5% 9% 7% 3 5% 6% 6% 7% 35%	2850
	11th to 20th	Night	4 10% 5% 8% 6% 5% 6% 5% 6% 9% 36%	3506
	21st to end	Night	5% 7% 3 6% 5% 3 6% 5% 5% 7% 47%	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	48% 8% 17% 21% 5% 1	2219
	11th to 20th	Day	53% 6% 11% 15% 14% 1	2220
	21st to end	Day	38% 8% 21% 28% 5%	2730
February	1st to 10th	Day	55% 6% 14% 16% 8%	1658
	11th to 20th	Day	54% 7% 15% 17% 7%	1584
	21st to end	Day	51% 7% 12% 19% 9% 1	1351
March	1st to 10th	Day	49% 8% 16% 20% 7%	1868
	11th to 20th	Day	43% 8% 18% 23% 8% 1	1980
	21st to end	Day	46% 9% 17% 19% 9%	2178
April	1st to 10th	Day	47% 8% 13% 22% 10% 1	2185
	11th to 20th	Day	51% 5% 10% 24% 8% 1	2310
	21st to end	Day	45% 6% 15% 24% 9% 1	2340
May	1st to 10th	Day	46% 7% 14% 22% 11%	2448
	11th to 20th	Day	37% 6% 15% 28% 13% 1	2564
	21st to end	Day	47% 6% 13% 22% 10% 1	2918
June	1st to 10th	Day	40% 7% 16% 23% 11% 2	2700
	11th to 20th	Day	45% 7% 14% 21% 12% 1	2700
	21st to end	Day	27% 7% 18% 31% 14% 3	2700
July	1st to 10th	Day	23% 7% 18% 31% 17% 4	2626
	11th to 20th	Day	25% 6% 13% 31% 21% 3	2619
	21st to end	Day	17% 5% 13% 33% 26% 6%	2775
August	1st to 10th	Day	23% 5% 15% 31% 21% 5%	2385
	11th to 20th	Day	27% 6% 15% 33% 16% 3	2299
	21st to end	Day	24% 4 14% 30% 23% 4	2574
September	1st to 10th	Day	31% 3 13% 28% 18% 8%	2230
	11th to 20th	Day	33% 6% 12% 31% 16% 3	1996
	21st to end	Day	32% 5% 14% 32% 13% 3	1980
October	1st to 10th	Day	38% 7% 17% 26% 11% 1	1827
	11th to 20th	Day	42% 6% 15% 25% 11% 2	1800
	21st to end	Day	42% 7% 15% 24% 11% 1	1774
November	1st to 10th	Day	50% 7% 15% 18% 7% 2	1488
	11th to 20th	Day	45% 6% 18% 23% 7% 1	1520
	21st to end	Day	45% 6% 19% 21% 7% 1	1442
December	1st to 10th	Day	51% 5% 16% 21% 6% 2	1330
	11th to 20th	Day	48% 7% 18% 23% 4 1	1684
	21st to end	Day	34% 5% 17% 26% 16% 1	2442
January	1st to 10th	Night	44% 8% 20% 23% 5% 1	4726
	11th to 20th	Night	48% 6% 14% 17% 13% 2	4740
	21st to end	Night	40% 8% 19% 26% 7% 1	4956
February	1st to 10th	Night	51% 6% 14% 18% 10% 1	2505
	11th to 20th	Night	49% 8% 15% 18% 10%	2273
	21st to end	Night	48% 6% 14% 20% 10% 2	1902
March	1st to 10th	Night	44% 9% 17% 23% 7%	2091
	11th to 20th	Night	44% 8% 17% 21% 10%	1980
	21st to end	Night	45% 10% 18% 20% 7% 1	2178
April	1st to 10th	Night	45% 6% 15% 23% 10%	1771
	11th to 20th	Night	47% 6% 12% 22% 12% 1	1601
	21st to end	Night	45% 7% 13% 25% 9% 1	1620
May	1st to 10th	Night	41% 7% 13% 24% 14% 1	1511
	11th to 20th	Night	34% 7% 12% 30% 16% 1	1330
	21st to end	Night	48% 5% 12% 24% 9% 1	1358
June	1st to 10th	Night	41% 6% 16% 25% 11% 2	1260
	11th to 20th	Night	38% 9% 14% 25% 12% 2	1260
	21st to end	Night	27% 6% 16% 33% 16% 3	1260
July	1st to 10th	Night	23% 6% 17% 32% 18% 4	1225
	11th to 20th	Night	27% 6% 15% 24% 21% 7%	1218
	21st to end	Night	17% 5% 11% 30% 27% 10%	1302
August	1st to 10th	Night	27% 7% 13% 29% 18% 6%	1526
	11th to 20th	Night	24% 7% 15% 28% 21% 5%	1602
	21st to end	Night	26% 5% 10% 26% 26% 7%	1782
September	1st to 10th	Night	32% 5% 10% 27% 18% 8%	1729
	11th to 20th	Night	33% 5% 11% 28% 16% 6%	1962
	21st to end	Night	30% 6% 13% 31% 16% 3	1980
October	1st to 10th	Night	36% 6% 16% 26% 14% 2	2132
	11th to 20th	Night	37% 6% 15% 27% 13% 2	2160
	21st to end	Night	42% 7% 15% 26% 10% 1	2574
November	1st to 10th	Night	48% 6% 15% 21% 9% 2	2580
	11th to 20th	Night	42% 6% 20% 21% 11%	2660
	21st to end	Night	42% 6% 22% 20% 9% 1	2736
December	1st to 10th	Night	47% 7% 17% 20% 8% 1	2850
	11th to 20th	Night	43% 7% 25% 21% 4 1	3507
	21st to end	Night	35% 6% 14% 25% 16% 3	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	10% 13% 38% 24% 10% 5%	180
	11th to 20th	Day	14% 12% 36% 28% 7% 2	180
	21st to end	Day	11% 14% 39% 29% 5% 3	198
February	1st to 10th	Day	20% 17% 40% 15% 7% 2	246
	11th to 20th	Day	13% 13% 45% 20% 6% 2	240
	21st to end	Day	11% 15% 30% 30% 11% 2	217
March	1st to 10th	Day	12% 18% 38% 21% 9% 2	420
	11th to 20th	Day	11% 14% 38% 24% 10% 3	420
	21st to end	Day	13% 13% 40% 21% 11% 3	462
April	1st to 10th	Day	12% 20% 33% 29% 5% 1	420
	11th to 20th	Day	16% 16% 33% 26% 9%	412
	21st to end	Day	17% 15% 26% 30% 10% 2	420
May	1st to 10th	Day	14% 10% 25% 29% 17% 5%	531
	11th to 20th	Day	16% 7% 24% 30% 20% 4	625
	21st to end	Day	19% 7% 20% 29% 18% 8%	679
June	1st to 10th	Day	16% 10% 23% 32% 16% 3	630
	11th to 20th	Day	19% 11% 31% 27% 11% 1	630
	21st to end	Day	9% 7% 25% 34% 21% 4	630
July	1st to 10th	Day	5% 4 23% 38% 23% 6%	621
	11th to 20th	Day	9% 5% 29% 37% 18% 2	618
	21st to end	Day	4 5% 23% 38% 23% 6%	684
August	1st to 10th	Day	7% 5% 20% 38% 24% 6%	460
	11th to 20th	Day	7% 3 23% 35% 25% 7%	437
	21st to end	Day	8% 7% 25% 30% 24% 6%	495
September	1st to 10th	Day	12% 10% 29% 32% 16% 2	450
	11th to 20th	Day	14% 8% 28% 32% 15% 4	450
	21st to end	Day	15% 11% 30% 28% 11% 4	450
October	1st to 10th	Day	16% 8% 27% 27% 19% 3	297
	11th to 20th	Day	13% 14% 36% 24% 13% 2	270
	21st to end	Day	19% 17% 32% 22% 9% 1	297
November	1st to 10th	Day	24% 13% 35% 21% 6% 1	270
	11th to 20th	Day	13% 20% 38% 22% 6% 1	270
	21st to end	Day	9% 20% 38% 20% 8% 6%	232
December	1st to 10th	Day	10% 21% 40% 20% 8% 1	180
	11th to 20th	Day	10% 24% 39% 21% 6% 1	180
	21st to end	Day	17% 10% 34% 26% 9% 5%	198
January	1st to 10th	Night	10% 15% 40% 25% 9% 1	950
	11th to 20th	Night	13% 14% 39% 25% 9% 1	950
	21st to end	Night	10% 15% 40% 24% 8% 1	891
February	1st to 10th	Night	16% 11% 33% 27% 12% 2	758
	11th to 20th	Night	12% 13% 37% 28% 9%	704
	21st to end	Night	11% 11% 30% 32% 14% 2	592
March	1st to 10th	Night	10% 10% 38% 30% 11% 2	720
	11th to 20th	Night	12% 13% 36% 30% 9% 1	720
	21st to end	Night	13% 12% 37% 28% 9% 1	792
April	1st to 10th	Night	14% 10% 39% 28% 9% 1	594
	11th to 20th	Night	14% 10% 38% 28% 10%	533
	21st to end	Night	18% 9% 31% 34% 8%	540
May	1st to 10th	Night	15% 7% 24% 36% 16% 1	540
	11th to 20th	Night	9% 7% 29% 34% 19% 1	445
	21st to end	Night	19% 7% 25% 30% 17% 2	389
June	1st to 10th	Night	19% 8% 30% 29% 13% 2	360
	11th to 20th	Night	16% 10% 34% 30% 9% 1	360
	21st to end	Night	8% 6% 28% 39% 18% 1	360
July	1st to 10th	Night	6% 5% 26% 41% 21%	350
	11th to 20th	Night	7% 5% 31% 44% 12% 1	348
	21st to end	Night	4 5% 26% 40% 23% 2	394
August	1st to 10th	Night	7% 3 26% 39% 22% 2	474
	11th to 20th	Night	7% 3 22% 43% 24% 1	534
	21st to end	Night	10% 5% 25% 39% 20% 1	594
September	1st to 10th	Night	13% 6% 29% 38% 12% 1	540
	11th to 20th	Night	14% 5% 25% 39% 16% 1	702
	21st to end	Night	9% 8% 35% 31% 14% 2	720
October	1st to 10th	Night	15% 8% 27% 36% 13% 1	720
	11th to 20th	Night	13% 11% 34% 30% 11% 1	720
	21st to end	Night	13% 16% 36% 29% 7%	792
November	1st to 10th	Night	18% 12% 39% 25% 6%	915
	11th to 20th	Night	12% 16% 42% 23% 6% 1	950
	21st to end	Night	11% 14% 41% 27% 7% 1	950
December	1st to 10th	Night	12% 11% 39% 26% 10% 1	950
	11th to 20th	Night	10% 15% 40% 27% 8% 1	950
	21st to end	Night	14% 13% 38% 27% 6% 2	1045

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