Banff
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Banff clear sky chart from 2005-11-06 to 2024-02-25.

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	7% 10% 5% 10% 9% 5% 6% 6% 6% 8% 28%	77896
	Night	3 8% 5% 10% 9% 5% 7% 7% 7% 9% 29%	81353
Transparency	Day	50% 13% 16% 14% 7% 1	77608
	Night	43% 16% 17% 15% 7% 1	81222
Seeing	Day	17% 22% 33% 20% 8% 1	14206
	Night	10% 20% 39% 23% 8% 1	23477

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	1 4 4 17% 16% 7% 7% 8% 9% 10% 17%	2219
	11th to 20th	Day	1 4 4 10% 11% 5% 9% 7% 7% 9% 33%	2361
	21st to end	Day	1 7% 6% 9% 10% 4 8% 8% 8% 11% 28%	2794
February	1st to 10th	Day	2 7% 6% 10% 11% 7% 8% 8% 9% 8% 23%	1520
	11th to 20th	Day	1 8% 5% 14% 10% 5% 8% 8% 7% 9% 25%	1614
	21st to end	Day	1 8% 7% 14% 11% 7% 8% 7% 7% 8% 22%	1521
March	1st to 10th	Day	1 9% 7% 16% 10% 6% 8% 6% 6% 8% 24%	1800
	11th to 20th	Day	1 11% 7% 11% 9% 6% 8% 6% 7% 9% 25%	1902
	21st to end	Day	3 18% 10% 16% 10% 4 5% 5% 5% 6% 17%	2277
April	1st to 10th	Day	5% 15% 9% 15% 12% 5% 6% 5% 4 6% 17%	2160
	11th to 20th	Day	5% 18% 10% 15% 9% 4 6% 5% 5% 6% 19%	2308
	21st to end	Day	8% 20% 8% 12% 6% 4 5% 5% 6% 6% 21%	2340
May	1st to 10th	Day	9% 21% 6% 10% 8% 4 5% 6% 7% 7% 20%	2500
	11th to 20th	Day	11% 14% 4 9% 6% 4 6% 5% 6% 6% 29%	2622
	21st to end	Day	21% 15% 5% 9% 7% 3 6% 4 4 6% 19%	2917
June	1st to 10th	Day	19% 14% 4 9% 7% 3 6% 5% 6% 6% 21%	2700
	11th to 20th	Day	22% 14% 5% 9% 8% 5% 6% 5% 4 5% 17%	2700
	21st to end	Day	12% 10% 4 10% 8% 4 6% 6% 5% 8% 28%	2700
July	1st to 10th	Day	11% 8% 4 8% 8% 4 6% 6% 7% 7% 32%	2700
	11th to 20th	Day	10% 6% 3 7% 8% 3 5% 5% 6% 8% 37%	2700
	21st to end	Day	6% 4 3 5% 6% 4 5% 6% 6% 8% 46%	2794
August	1st to 10th	Day	8% 7% 3 7% 8% 4 6% 6% 6% 7% 37%	2507
	11th to 20th	Day	9% 6% 3 6% 6% 3 5% 5% 6% 8% 43%	2386
	21st to end	Day	11% 7% 3 6% 6% 4 5% 6% 5% 8% 38%	2574
September	1st to 10th	Day	10% 9% 3 7% 8% 3 5% 5% 5% 7% 39%	2174
	11th to 20th	Day	10% 8% 4 7% 6% 5% 5% 4 6% 8% 37%	2016
	21st to end	Day	7% 11% 4 7% 7% 4 6% 5% 6% 8% 35%	1980
October	1st to 10th	Day	9% 12% 5% 7% 8% 4 5% 5% 6% 7% 32%	1929
	11th to 20th	Day	5% 10% 5% 9% 8% 5% 6% 5% 8% 8% 32%	1620
	21st to end	Day	3 11% 5% 8% 8% 4 8% 6% 7% 8% 32%	1782
November	1st to 10th	Day	3 10% 5% 12% 10% 4 6% 6% 7% 10% 27%	1622
	11th to 20th	Day	1 7% 4 8% 8% 5% 8% 7% 11% 10% 31%	1373
	21st to end	Day	2 8% 4 10% 7% 5% 6% 7% 10% 11% 31%	1330
December	1st to 10th	Day	1 5% 5% 10% 11% 6% 6% 8% 8% 10% 31%	1330
	11th to 20th	Day	1 6% 5% 13% 13% 7% 8% 8% 8% 10% 23%	1682
	21st to end	Day	1 7% 5% 9% 9% 7% 8% 7% 8% 10% 29%	2442
January	1st to 10th	Night	1 7% 7% 20% 16% 7% 9% 7% 7% 7% 12%	4726
	11th to 20th	Night	1 4 3 10% 13% 6% 8% 10% 8% 9% 27%	4568
	21st to end	Night	1 10% 7% 13% 13% 7% 8% 7% 7% 8% 20%	4862
February	1st to 10th	Night	2 7% 5% 14% 12% 6% 9% 8% 9% 9% 19%	2660
	11th to 20th	Night	1 8% 6% 14% 9% 6% 8% 7% 8% 9% 25%	2450
	21st to end	Night	1 7% 6% 13% 12% 5% 7% 8% 8% 7% 26%	1829
March	1st to 10th	Night	8% 6% 11% 10% 7% 8% 9% 8% 10% 25%	2160
	11th to 20th	Night	1 9% 6% 9% 7% 4 6% 7% 8% 11% 32%	2057
	21st to end	Night	1 9% 9% 12% 9% 4 6% 7% 8% 9% 26%	2075
April	1st to 10th	Night	4 11% 6% 12% 9% 5% 5% 6% 8% 9% 25%	1800
	11th to 20th	Night	3 12% 6% 10% 8% 4 5% 6% 7% 10% 29%	1602
	21st to end	Night	5% 15% 6% 10% 7% 4 5% 6% 6% 6% 31%	1620
May	1st to 10th	Night	7% 15% 4 10% 6% 4 4 5% 7% 8% 30%	1458
	11th to 20th	Night	7% 8% 3 5% 5% 3 6% 6% 8% 11% 39%	1270
	21st to end	Night	16% 11% 4 7% 6% 2 5% 5% 5% 7% 32%	1358
June	1st to 10th	Night	14% 9% 4 8% 5% 3 4 5% 7% 8% 33%	1260
	11th to 20th	Night	15% 12% 2 7% 7% 3 5% 5% 5% 9% 29%	1260
	21st to end	Night	8% 5% 2 5% 5% 3 4 5% 8% 10% 44%	1260
July	1st to 10th	Night	7% 6% 2 5% 4 3 4 5% 7% 8% 47%	1260
	11th to 20th	Night	6% 6% 3 4 5% 4 5% 5% 7% 7% 47%	1260
	21st to end	Night	4 4 1 4 4 3 3 5% 7% 8% 57%	1519
August	1st to 10th	Night	6% 4 2 6% 6% 3 4 5% 6% 7% 51%	1432
	11th to 20th	Night	8% 4 1 3 4 3 4 5% 6% 10% 51%	1513
	21st to end	Night	7% 6% 2 4 4 3 5% 6% 6% 8% 48%	1782
September	1st to 10th	Night	8% 7% 2 5% 4 3 3 5% 6% 9% 48%	1783
	11th to 20th	Night	9% 8% 4 5% 6% 3 5% 5% 6% 8% 42%	1943
	21st to end	Night	7% 8% 4 4 6% 4 4 5% 6% 9% 45%	1980
October	1st to 10th	Night	7% 10% 4 8% 7% 3 5% 5% 5% 7% 40%	2027
	11th to 20th	Night	4 9% 5% 9% 7% 3 6% 5% 7% 9% 36%	2340
	21st to end	Night	3 12% 6% 10% 8% 5% 5% 7% 7% 9% 30%	2574
November	1st to 10th	Night	2 11% 6% 11% 10% 6% 7% 7% 10% 10% 20%	2437
	11th to 20th	Night	1 7% 5% 11% 10% 6% 10% 8% 8% 10% 24%	2804
	21st to end	Night	1 8% 7% 10% 11% 7% 8% 8% 9% 10% 22%	2850
December	1st to 10th	Night	2 6% 4 10% 10% 6% 9% 8% 11% 13% 22%	2850
	11th to 20th	Night	5% 5% 14% 16% 9% 10% 8% 8% 9% 16%	3510
	21st to end	Night	1 7% 4 11% 13% 8% 10% 8% 7% 9% 22%	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	47% 21% 19% 7% 5% 1	2219
	11th to 20th	Day	44% 13% 14% 12% 14% 4	2384
	21st to end	Day	37% 24% 23% 11% 4	2794
February	1st to 10th	Day	49% 15% 19% 8% 6% 3	1520
	11th to 20th	Day	51% 14% 16% 13% 6% 1	1622
	21st to end	Day	56% 12% 15% 10% 6% 1	1521
March	1st to 10th	Day	55% 14% 16% 10% 5% 1	1800
	11th to 20th	Day	52% 14% 15% 13% 6%	1903
	21st to end	Day	66% 11% 12% 8% 3	2277
April	1st to 10th	Day	67% 10% 14% 7% 2	2160
	11th to 20th	Day	64% 8% 14% 10% 3	2308
	21st to end	Day	62% 10% 13% 13% 2	2340
May	1st to 10th	Day	59% 11% 15% 13% 2	2500
	11th to 20th	Day	53% 10% 17% 15% 5%	2626
	21st to end	Day	65% 8% 12% 11% 3	2918
June	1st to 10th	Day	62% 9% 11% 14% 4 1	2700
	11th to 20th	Day	66% 10% 11% 10% 3	2700
	21st to end	Day	52% 11% 15% 15% 6% 1	2700
July	1st to 10th	Day	47% 10% 14% 17% 10% 2	2626
	11th to 20th	Day	43% 10% 15% 19% 12% 2	2619
	21st to end	Day	33% 9% 13% 27% 16% 2	2639
August	1st to 10th	Day	43% 10% 14% 20% 11% 2	2490
	11th to 20th	Day	36% 10% 17% 24% 12% 1	2386
	21st to end	Day	42% 10% 14% 23% 10% 1	2574
September	1st to 10th	Day	43% 8% 17% 20% 11% 2	2174
	11th to 20th	Day	44% 10% 15% 21% 10% 1	2016
	21st to end	Day	44% 11% 18% 19% 7%	1980
October	1st to 10th	Day	50% 11% 13% 19% 8%	1929
	11th to 20th	Day	44% 14% 19% 18% 5% 1	1620
	21st to end	Day	46% 14% 19% 14% 7%	1782
November	1st to 10th	Day	49% 17% 19% 10% 5%	1622
	11th to 20th	Day	37% 22% 24% 12% 6%	1373
	21st to end	Day	41% 17% 22% 13% 6% 2	1330
December	1st to 10th	Day	42% 18% 19% 14% 6% 1	1330
	11th to 20th	Day	44% 23% 19% 9% 4	1684
	21st to end	Day	36% 17% 18% 15% 12% 2	2442
January	1st to 10th	Night	54% 19% 15% 7% 3 1	4726
	11th to 20th	Night	45% 14% 13% 11% 11% 7%	4607
	21st to end	Night	45% 24% 17% 8% 5% 1	4862
February	1st to 10th	Night	52% 17% 13% 10% 6% 2	2660
	11th to 20th	Night	48% 14% 19% 11% 7% 1	2452
	21st to end	Night	50% 11% 15% 15% 8% 1	1829
March	1st to 10th	Night	45% 16% 19% 13% 6% 1	2160
	11th to 20th	Night	41% 15% 21% 14% 8% 1	2057
	21st to end	Night	49% 15% 17% 13% 5% 1	2075
April	1st to 10th	Night	50% 14% 20% 13% 5%	1800
	11th to 20th	Night	47% 14% 21% 12% 6%	1602
	21st to end	Night	50% 10% 17% 16% 5% 1	1620
May	1st to 10th	Night	51% 11% 16% 17% 6%	1458
	11th to 20th	Night	38% 13% 20% 24% 5%	1270
	21st to end	Night	51% 10% 14% 19% 5%	1358
June	1st to 10th	Night	48% 12% 15% 20% 5%	1260
	11th to 20th	Night	52% 12% 15% 15% 6%	1260
	21st to end	Night	33% 13% 21% 24% 7% 1	1260
July	1st to 10th	Night	31% 13% 19% 23% 12% 2	1225
	11th to 20th	Night	32% 11% 18% 26% 12% 1	1218
	21st to end	Night	23% 10% 15% 33% 18% 1	1435
August	1st to 10th	Night	30% 11% 18% 28% 12% 1	1424
	11th to 20th	Night	27% 10% 21% 34% 9%	1513
	21st to end	Night	29% 12% 19% 28% 11% 1	1782
September	1st to 10th	Night	31% 10% 21% 26% 10% 1	1783
	11th to 20th	Night	35% 13% 20% 21% 10% 1	1943
	21st to end	Night	33% 13% 22% 23% 9%	1980
October	1st to 10th	Night	42% 10% 17% 21% 10%	2027
	11th to 20th	Night	40% 15% 19% 19% 7% 1	2340
	21st to end	Night	46% 15% 18% 16% 5%	2574
November	1st to 10th	Night	49% 19% 16% 10% 5% 1	2437
	11th to 20th	Night	44% 19% 19% 10% 6% 1	2804
	21st to end	Night	45% 18% 18% 11% 5% 3	2850
December	1st to 10th	Night	42% 19% 17% 13% 7% 1	2850
	11th to 20th	Night	48% 23% 17% 8% 4	3507
	21st to end	Night	41% 19% 18% 11% 8% 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	12% 23% 36% 20% 7% 3	180
	11th to 20th	Day	8% 26% 44% 16% 6% 1	180
	21st to end	Day	11% 31% 36% 14% 6% 2	198
February	1st to 10th	Day	24% 24% 33% 12% 6% 2	180
	11th to 20th	Day	12% 20% 41% 21% 4 1	257
	21st to end	Day	14% 27% 33% 20% 5% 1	363
March	1st to 10th	Day	14% 31% 32% 16% 5% 2	420
	11th to 20th	Day	14% 29% 34% 16% 4 3	420
	21st to end	Day	16% 26% 34% 17% 5% 2	462
April	1st to 10th	Day	17% 26% 35% 16% 5%	420
	11th to 20th	Day	16% 26% 31% 19% 6% 1	412
	21st to end	Day	18% 25% 33% 17% 6% 1	420
May	1st to 10th	Day	19% 19% 28% 22% 11% 2	423
	11th to 20th	Day	18% 11% 30% 26% 13% 3	593
	21st to end	Day	24% 12% 24% 27% 11% 1	679
June	1st to 10th	Day	22% 21% 30% 19% 7% 1	630
	11th to 20th	Day	26% 21% 28% 18% 7%	630
	21st to end	Day	14% 18% 33% 22% 12% 2	630
July	1st to 10th	Day	16% 14% 28% 26% 15% 1	621
	11th to 20th	Day	16% 19% 33% 23% 8% 1	618
	21st to end	Day	8% 18% 34% 28% 11% 2	540
August	1st to 10th	Day	13% 18% 34% 25% 9% 1	447
	11th to 20th	Day	11% 19% 38% 23% 8% 1	437
	21st to end	Day	15% 21% 34% 20% 9%	495
September	1st to 10th	Day	19% 24% 33% 16% 8%	450
	11th to 20th	Day	20% 20% 36% 17% 6% 1	450
	21st to end	Day	25% 28% 27% 17% 3 1	450
October	1st to 10th	Day	23% 19% 31% 19% 8% 1	425
	11th to 20th	Day	17% 28% 27% 22% 5% 1	270
	21st to end	Day	19% 27% 36% 14% 3 1	297
November	1st to 10th	Day	14% 35% 34% 13% 3 1	270
	11th to 20th	Day	14% 29% 47% 7% 2	201
	21st to end	Day	16% 28% 29% 14% 9% 4	180
December	1st to 10th	Day	11% 26% 37% 18% 6% 3	180
	11th to 20th	Day	7% 30% 43% 14% 6%	180
	21st to end	Day	8% 28% 38% 22% 3 1	198
January	1st to 10th	Night	9% 27% 48% 14% 2 1	950
	11th to 20th	Night	7% 27% 47% 16% 3 1	869
	21st to end	Night	7% 30% 45% 14% 4	836
February	1st to 10th	Night	11% 22% 40% 20% 7% 1	760
	11th to 20th	Night	8% 21% 46% 21% 5%	744
	21st to end	Night	7% 17% 43% 24% 9% 1	610
March	1st to 10th	Night	6% 19% 47% 22% 6% 1	720
	11th to 20th	Night	8% 21% 45% 19% 6% 1	720
	21st to end	Night	8% 18% 40% 23% 10% 1	792
April	1st to 10th	Night	10% 18% 36% 28% 7% 1	720
	11th to 20th	Night	8% 17% 37% 31% 7% 1	534
	21st to end	Night	12% 17% 37% 26% 8% 1	540
May	1st to 10th	Night	13% 11% 32% 34% 10%	378
	11th to 20th	Night	12% 7% 26% 35% 20%	354
	21st to end	Night	21% 7% 26% 28% 16% 2	389
June	1st to 10th	Night	18% 14% 31% 24% 13% 1	360
	11th to 20th	Night	21% 11% 32% 26% 10%	360
	21st to end	Night	10% 13% 26% 31% 20%	360
July	1st to 10th	Night	10% 8% 25% 39% 17%	350
	11th to 20th	Night	11% 13% 29% 33% 14% 1	348
	21st to end	Night	7% 6% 21% 49% 18% 1	394
August	1st to 10th	Night	8% 7% 20% 44% 22% 1	358
	11th to 20th	Night	10% 10% 22% 38% 19% 1	445
	21st to end	Night	11% 11% 29% 34% 15% 1	594
September	1st to 10th	Night	14% 14% 29% 28% 13% 2	703
	11th to 20th	Night	13% 14% 30% 28% 13% 3	720
	21st to end	Night	14% 20% 35% 22% 9% 1	720
October	1st to 10th	Night	14% 13% 36% 27% 9%	720
	11th to 20th	Night	11% 20% 39% 24% 5% 1	720
	21st to end	Night	11% 23% 42% 20% 4	792
November	1st to 10th	Night	11% 27% 45% 13% 3	772
	11th to 20th	Night	10% 30% 46% 12% 2 1	950
	21st to end	Night	9% 26% 45% 16% 4 1	950
December	1st to 10th	Night	7% 26% 44% 17% 5%	950
	11th to 20th	Night	6% 27% 48% 14% 5%	950
	21st to end	Night	6% 24% 49% 16% 5%	1045

Page generated at 2024-02-22 04:05:47. Version ac07

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