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 2024-10-24.

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% 11% 4 11% 7% 6% 6% 5% 7% 8% 30%	101819
	Night	3 9% 4 11% 8% 7% 6% 5% 7% 8% 30%	97022
Transparency	Day	47% 12% 16% 16% 8% 1	101573
	Night	42% 15% 18% 16% 7% 1	96915
Seeing	Day	17% 22% 32% 20% 8% 1	15231
	Night	10% 20% 39% 23% 8% 1	24194

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 21% 13% 9% 7% 6% 9% 10% 17%	2219
	11th to 20th	Day	1 4 3 13% 9% 8% 8% 5% 7% 9% 33%	2361
	21st to end	Day	8% 5% 10% 8% 6% 8% 7% 8% 11% 27%	2794
February	1st to 10th	Day	2 8% 6% 11% 10% 9% 8% 6% 9% 8% 23%	1520
	11th to 20th	Day	1 9% 4 16% 9% 7% 7% 6% 7% 9% 25%	1614
	21st to end	Day	1 9% 6% 16% 11% 8% 7% 6% 7% 8% 21%	1570
March	1st to 10th	Day	7% 6% 20% 10% 7% 6% 4 5% 7% 28%	3138
	11th to 20th	Day	3 11% 6% 9% 6% 7% 7% 5% 6% 6% 33%	3360
	21st to end	Day	2 22% 10% 17% 8% 5% 4 5% 5% 6% 17%	4001
April	1st to 10th	Day	5% 18% 8% 16% 9% 7% 5% 4 5% 6% 17%	2280
	11th to 20th	Day	4 19% 9% 16% 7% 5% 5% 4 5% 6% 19%	2438
	21st to end	Day	7% 21% 7% 14% 6% 5% 5% 4 6% 6% 20%	2470
May	1st to 10th	Day	12% 24% 6% 9% 6% 4 5% 4 5% 5% 21%	4387
	11th to 20th	Day	11% 16% 4 10% 6% 5% 5% 4 7% 7% 24%	4648
	21st to end	Day	16% 22% 5% 12% 7% 6% 5% 3 4 5% 14%	5161
June	1st to 10th	Day	18% 15% 4 10% 7% 5% 5% 4 6% 6% 21%	2850
	11th to 20th	Day	21% 15% 4 10% 7% 6% 6% 4 4 6% 17%	2850
	21st to end	Day	12% 10% 4 11% 6% 6% 6% 5% 6% 7% 27%	2850
July	1st to 10th	Day	7% 6% 3 7% 6% 5% 5% 5% 6% 6% 45%	4740
	11th to 20th	Day	6% 4 2 6% 6% 5% 5% 5% 7% 8% 46%	4740
	21st to end	Day	4 3 2 6% 5% 6% 6% 5% 9% 9% 45%	4885
August	1st to 10th	Day	6% 5% 3 8% 6% 6% 7% 5% 7% 8% 38%	4401
	11th to 20th	Day	7% 5% 2 7% 5% 5% 6% 6% 8% 10% 37%	4176
	21st to end	Day	8% 6% 3 7% 5% 5% 6% 5% 7% 8% 40%	4521
September	1st to 10th	Day	9% 9% 3 8% 6% 4 4 3 5% 7% 41%	2294
	11th to 20th	Day	10% 9% 4 9% 5% 6% 4 4 6% 8% 37%	2128
	21st to end	Day	7% 11% 3 8% 6% 6% 4 4 6% 8% 36%	2090
October	1st to 10th	Day	9% 12% 4 9% 6% 5% 5% 4 6% 7% 32%	2035
	11th to 20th	Day	5% 10% 4 11% 6% 6% 6% 4 8% 8% 32%	1710
	21st to end	Day	3 12% 4 10% 7% 6% 7% 5% 7% 8% 32%	1809
November	1st to 10th	Day	3 11% 4 14% 8% 6% 5% 5% 7% 10% 27%	1622
	11th to 20th	Day	1 8% 4 9% 7% 7% 7% 6% 12% 9% 31%	1373
	21st to end	Day	1 10% 3 11% 7% 6% 6% 6% 9% 11% 31%	1330
December	1st to 10th	Day	1 6% 4 11% 10% 7% 6% 7% 8% 10% 30%	1330
	11th to 20th	Day	6% 4 16% 11% 9% 7% 6% 8% 9% 23%	1682
	21st to end	Day	1 8% 4 10% 8% 9% 8% 5% 8% 10% 28%	2442
January	1st to 10th	Night	1 8% 6% 23% 13% 9% 8% 6% 7% 6% 12%	4726
	11th to 20th	Night	1 5% 3 12% 11% 8% 8% 8% 8% 9% 27%	4568
	21st to end	Night	1 10% 6% 15% 11% 9% 7% 6% 7% 8% 20%	4862
February	1st to 10th	Night	2 8% 5% 15% 11% 8% 8% 6% 9% 9% 18%	2660
	11th to 20th	Night	1 8% 6% 15% 7% 8% 7% 6% 8% 9% 25%	2450
	21st to end	Night	8% 5% 14% 11% 7% 7% 6% 8% 6% 25%	1884
March	1st to 10th	Night	6% 6% 13% 10% 8% 7% 6% 9% 8% 26%	3736
	11th to 20th	Night	2 10% 5% 9% 5% 6% 8% 6% 7% 9% 34%	3619
	21st to end	Night	2 19% 9% 16% 9% 5% 6% 4 6% 6% 18%	3648
April	1st to 10th	Night	4 14% 5% 12% 8% 7% 5% 5% 7% 9% 25%	1900
	11th to 20th	Night	2 13% 5% 12% 6% 5% 5% 5% 7% 9% 29%	1692
	21st to end	Night	5% 16% 6% 11% 6% 6% 4 5% 6% 6% 30%	1710
May	1st to 10th	Night	11% 22% 5% 10% 4 4 3 3 5% 5% 28%	2572
	11th to 20th	Night	6% 12% 3 8% 6% 5% 6% 4 8% 10% 32%	2244
	21st to end	Night	12% 15% 5% 10% 6% 4 5% 4 6% 7% 27%	2414
June	1st to 10th	Night	13% 12% 3 9% 4 4 5% 4 7% 8% 32%	1330
	11th to 20th	Night	14% 13% 3 7% 6% 5% 4 5% 5% 9% 29%	1330
	21st to end	Night	7% 5% 2 5% 5% 4 5% 5% 8% 11% 44%	1330
July	1st to 10th	Night	4 4 2 5% 4 4 5% 4 6% 7% 54%	2220
	11th to 20th	Night	4 4 2 3 3 4 3 4 6% 8% 59%	2220
	21st to end	Night	2 3 1 5% 5% 4 4 4 5% 7% 60%	2663
August	1st to 10th	Night	7% 7% 3 8% 5% 5% 5% 4 6% 9% 42%	2529
	11th to 20th	Night	6% 4 2 4 4 4 5% 5% 7% 11% 48%	2656
	21st to end	Night	7% 6% 2 5% 4 4 4 4 6% 8% 50%	3146
September	1st to 10th	Night	7% 7% 2 6% 3 4 4 4 6% 9% 49%	1883
	11th to 20th	Night	8% 9% 4 6% 5% 4 5% 4 6% 7% 42%	2051
	21st to end	Night	6% 8% 3 5% 5% 5% 4 4 7% 9% 44%	2090
October	1st to 10th	Night	6% 10% 3 10% 6% 4 5% 4 5% 7% 39%	2141
	11th to 20th	Night	3 9% 4 10% 6% 5% 6% 4 7% 9% 36%	2470
	21st to end	Night	3 12% 6% 12% 7% 6% 5% 5% 7% 9% 30%	2613
November	1st to 10th	Night	2 12% 6% 12% 9% 8% 6% 5% 10% 10% 20%	2437
	11th to 20th	Night	1 7% 5% 12% 9% 9% 9% 6% 8% 10% 24%	2804
	21st to end	Night	10% 5% 12% 10% 9% 7% 6% 9% 9% 22%	2850
December	1st to 10th	Night	2 8% 4 12% 8% 8% 8% 6% 11% 13% 21%	2850
	11th to 20th	Night	5% 4 17% 14% 11% 9% 6% 8% 9% 15%	3510
	21st to end	Night	8% 4 13% 10% 10% 9% 7% 8% 8% 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	1570
March	1st to 10th	Day	50% 13% 15% 11% 11% 1	3138
	11th to 20th	Day	42% 13% 24% 17% 4	3361
	21st to end	Day	62% 13% 11% 8% 5%	4001
April	1st to 10th	Day	66% 10% 14% 8% 2	2280
	11th to 20th	Day	62% 9% 14% 11% 4	2438
	21st to end	Day	62% 10% 13% 13% 2	2470
May	1st to 10th	Day	60% 9% 14% 14% 3	4387
	11th to 20th	Day	51% 12% 17% 16% 4	4652
	21st to end	Day	64% 13% 14% 7% 2	5162
June	1st to 10th	Day	60% 10% 11% 14% 4 1	2850
	11th to 20th	Day	65% 10% 11% 10% 4	2850
	21st to end	Day	51% 11% 15% 15% 7% 1	2850
July	1st to 10th	Day	37% 7% 10% 18% 22% 6%	4666
	11th to 20th	Day	31% 8% 12% 26% 17% 5%	4659
	21st to end	Day	30% 7% 12% 26% 22% 4	4731
August	1st to 10th	Day	38% 9% 14% 27% 12% 1	4384
	11th to 20th	Day	36% 8% 22% 26% 7% 1	4218
	21st to end	Day	35% 8% 24% 25% 8% 1	4520
September	1st to 10th	Day	41% 8% 16% 21% 11% 2	2294
	11th to 20th	Day	43% 10% 14% 22% 10% 1	2128
	21st to end	Day	43% 11% 18% 19% 8% 1	2090
October	1st to 10th	Day	49% 11% 13% 19% 7%	2035
	11th to 20th	Day	42% 14% 20% 18% 6% 1	1710
	21st to end	Day	46% 13% 19% 14% 7%	1809
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	51% 11% 15% 15% 8% 1	1884
March	1st to 10th	Night	41% 19% 19% 12% 9%	3736
	11th to 20th	Night	35% 14% 26% 19% 5%	3619
	21st to end	Night	57% 13% 14% 12% 3	3648
April	1st to 10th	Night	50% 13% 20% 12% 5%	1900
	11th to 20th	Night	47% 14% 21% 13% 6%	1692
	21st to end	Night	51% 10% 17% 16% 5% 1	1710
May	1st to 10th	Night	56% 8% 13% 19% 4	2572
	11th to 20th	Night	40% 15% 19% 23% 4	2244
	21st to end	Night	48% 14% 19% 14% 4	2414
June	1st to 10th	Night	48% 12% 14% 20% 5%	1330
	11th to 20th	Night	52% 11% 15% 15% 7%	1330
	21st to end	Night	33% 12% 21% 24% 9% 1	1330
July	1st to 10th	Night	27% 8% 16% 23% 21% 5%	2185
	11th to 20th	Night	20% 7% 19% 31% 17% 5%	2178
	21st to end	Night	22% 6% 14% 31% 22% 5%	2579
August	1st to 10th	Night	37% 9% 15% 29% 9% 1	2521
	11th to 20th	Night	25% 8% 33% 28% 6%	2680
	21st to end	Night	28% 8% 32% 25% 6%	3146
September	1st to 10th	Night	30% 10% 21% 26% 11% 1	1883
	11th to 20th	Night	36% 13% 19% 22% 10% 1	2051
	21st to end	Night	33% 13% 22% 23% 9%	2090
October	1st to 10th	Night	41% 10% 18% 22% 9%	2141
	11th to 20th	Night	39% 14% 20% 19% 7% 1	2470
	21st to end	Night	46% 15% 18% 17% 5%	2613
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	16% 25% 34% 19% 5% 1	382
March	1st to 10th	Day	15% 31% 32% 16% 5% 2	460
	11th to 20th	Day	13% 29% 35% 17% 4 2	460
	21st to end	Day	16% 26% 34% 17% 5% 2	506
April	1st to 10th	Day	19% 28% 34% 15% 5%	460
	11th to 20th	Day	15% 26% 31% 20% 7% 1	452
	21st to end	Day	17% 26% 32% 18% 6% 1	460
May	1st to 10th	Day	19% 19% 28% 22% 10% 2	463
	11th to 20th	Day	18% 11% 30% 27% 12% 2	642
	21st to end	Day	24% 13% 24% 26% 10% 1	734
June	1st to 10th	Day	23% 20% 31% 19% 7% 1	680
	11th to 20th	Day	26% 21% 28% 18% 7% 1	680
	21st to end	Day	15% 17% 32% 23% 11% 2	680
July	1st to 10th	Day	16% 14% 29% 26% 15% 2	671
	11th to 20th	Day	15% 18% 32% 23% 10% 2	668
	21st to end	Day	9% 17% 35% 27% 10% 2	587
August	1st to 10th	Day	13% 17% 35% 24% 9% 2	487
	11th to 20th	Day	11% 19% 38% 23% 8% 2	477
	21st to end	Day	16% 21% 34% 20% 9% 1	539
September	1st to 10th	Day	18% 23% 32% 16% 9% 1	490
	11th to 20th	Day	19% 20% 37% 17% 6% 1	490
	21st to end	Day	27% 28% 26% 16% 3 1	490
October	1st to 10th	Day	24% 20% 30% 18% 8% 1	463
	11th to 20th	Day	18% 27% 27% 22% 5% 1	300
	21st to end	Day	20% 27% 36% 14% 3 1	306
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	8% 18% 42% 23% 9% 1	628
March	1st to 10th	Night	6% 20% 47% 21% 6% 1	760
	11th to 20th	Night	7% 21% 46% 19% 6% 1	760
	21st to end	Night	8% 18% 39% 24% 10% 1	836
April	1st to 10th	Night	11% 20% 35% 27% 7% 1	760
	11th to 20th	Night	7% 17% 37% 31% 7% 1	564
	21st to end	Night	12% 18% 37% 25% 8% 1	570
May	1st to 10th	Night	14% 11% 32% 33% 10%	399
	11th to 20th	Night	11% 8% 27% 34% 19% 1	374
	21st to end	Night	21% 8% 26% 28% 16% 1	411
June	1st to 10th	Night	18% 13% 32% 23% 12% 1	380
	11th to 20th	Night	22% 11% 31% 26% 10%	380
	21st to end	Night	10% 13% 26% 32% 20%	380
July	1st to 10th	Night	9% 8% 25% 39% 18%	370
	11th to 20th	Night	10% 12% 28% 33% 16% 1	368
	21st to end	Night	6% 6% 21% 49% 18%	416
August	1st to 10th	Night	8% 7% 19% 44% 22% 1	378
	11th to 20th	Night	10% 10% 21% 38% 19% 2	470
	21st to end	Night	11% 11% 29% 33% 15% 1	627
September	1st to 10th	Night	13% 13% 28% 29% 14% 2	743
	11th to 20th	Night	13% 14% 29% 28% 13% 3	760
	21st to end	Night	14% 20% 35% 21% 9% 1	760
October	1st to 10th	Night	15% 13% 36% 27% 8%	760
	11th to 20th	Night	12% 19% 39% 25% 5% 1	760
	21st to end	Night	11% 23% 42% 20% 4	804
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 2024-10-21 00:20:00. Version ac07

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