Crowsnest Pass
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Crowsnest Pass clear sky chart from 2005-11-06 to 2024-09-29.

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	6% 9% 4 9% 6% 6% 6% 5% 7% 8% 35%	101427
	Night	4 9% 4 9% 6% 6% 6% 5% 8% 8% 33%	96875
Transparency	Day	36% 13% 18% 20% 10% 2	101181
	Night	35% 15% 21% 19% 9% 2	96767
Seeing	Day	20% 23% 29% 19% 8% 2	15159
	Night	15% 20% 30% 24% 10% 1	24211

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 6% 6% 13% 10% 8% 7% 8% 11% 9% 20%	2219
	11th to 20th	Day	1 7% 5% 13% 10% 7% 7% 6% 9% 9% 26%	2417
	21st to end	Day	1 11% 4 10% 8% 9% 9% 8% 12% 7% 21%	2794
February	1st to 10th	Day	3 10% 5% 13% 9% 8% 8% 6% 9% 10% 19%	1526
	11th to 20th	Day	2 13% 7% 15% 8% 6% 7% 6% 8% 8% 20%	1677
	21st to end	Day	2 11% 6% 16% 9% 7% 7% 6% 8% 7% 21%	1570
March	1st to 10th	Day	1 7% 5% 16% 8% 8% 6% 5% 10% 7% 28%	3138
	11th to 20th	Day	2 12% 6% 9% 6% 6% 6% 5% 6% 6% 37%	3427
	21st to end	Day	4 20% 8% 16% 8% 6% 5% 4 7% 5% 19%	3907
April	1st to 10th	Day	4 16% 6% 13% 9% 6% 6% 5% 7% 7% 21%	2294
	11th to 20th	Day	6% 17% 6% 13% 7% 5% 6% 5% 7% 6% 23%	2440
	21st to end	Day	9% 16% 5% 9% 6% 6% 5% 5% 6% 7% 27%	2470
May	1st to 10th	Day	13% 21% 4 9% 5% 5% 4 4 5% 5% 24%	4203
	11th to 20th	Day	8% 10% 3 7% 6% 7% 7% 6% 9% 9% 27%	4616
	21st to end	Day	14% 12% 3 8% 7% 7% 7% 6% 8% 9% 20%	5161
June	1st to 10th	Day	15% 10% 4 9% 8% 5% 5% 4 7% 6% 27%	2850
	11th to 20th	Day	15% 10% 3 10% 7% 6% 6% 5% 7% 7% 22%	2850
	21st to end	Day	8% 7% 3 7% 6% 5% 5% 5% 7% 8% 40%	2850
July	1st to 10th	Day	4 4 2 5% 4 5% 5% 4 6% 8% 54%	4740
	11th to 20th	Day	3 3 1 3 3 3 4 3 7% 7% 62%	4740
	21st to end	Day	2 2 1 4 3 4 4 4 6% 8% 63%	4828
August	1st to 10th	Day	8% 6% 2 5% 5% 5% 6% 4 7% 8% 45%	4401
	11th to 20th	Day	5% 4 1 5% 3 4 5% 4 6% 7% 55%	4037
	21st to end	Day	6% 4 1 4 4 4 4 4 6% 7% 55%	4521
September	1st to 10th	Day	9% 8% 2 5% 3 5% 5% 3 6% 7% 48%	2311
	11th to 20th	Day	10% 6% 3 6% 4 4 5% 5% 7% 9% 43%	2090
	21st to end	Day	7% 9% 3 6% 4 5% 6% 3 6% 7% 43%	2069
October	1st to 10th	Day	9% 12% 4 8% 6% 5% 5% 4 6% 7% 35%	1934
	11th to 20th	Day	4 11% 3 10% 7% 7% 5% 4 7% 8% 34%	1662
	21st to end	Day	4 11% 4 9% 6% 7% 7% 5% 8% 9% 30%	1782
November	1st to 10th	Day	6% 12% 5% 12% 8% 7% 6% 6% 7% 8% 23%	1632
	11th to 20th	Day	2 7% 5% 8% 8% 7% 7% 6% 10% 10% 30%	1487
	21st to end	Day	2 10% 4 10% 7% 8% 7% 4 11% 10% 27%	1330
December	1st to 10th	Day	1 8% 5% 10% 7% 10% 7% 8% 11% 9% 25%	1330
	11th to 20th	Day	2 9% 4 10% 8% 8% 7% 7% 13% 11% 20%	1682
	21st to end	Day	1 8% 4 9% 6% 7% 8% 7% 10% 11% 30%	2442
January	1st to 10th	Night	2 7% 6% 13% 9% 9% 10% 8% 12% 9% 16%	4726
	11th to 20th	Night	5% 5% 14% 9% 8% 9% 7% 8% 10% 25%	4510
	21st to end	Night	1 13% 6% 10% 8% 8% 9% 7% 11% 7% 21%	4862
February	1st to 10th	Night	2 10% 6% 11% 9% 7% 8% 7% 9% 9% 22%	2653
	11th to 20th	Night	1 12% 6% 12% 7% 6% 7% 5% 10% 9% 24%	2388
	21st to end	Night	1 10% 4 14% 8% 7% 8% 6% 9% 8% 26%	1884
March	1st to 10th	Night	1 5% 5% 16% 10% 8% 7% 5% 9% 9% 25%	3736
	11th to 20th	Night	2 9% 4 7% 6% 6% 6% 5% 8% 6% 41%	3552
	21st to end	Night	5% 19% 9% 14% 7% 6% 6% 5% 7% 6% 17%	3743
April	1st to 10th	Night	5% 11% 4 9% 5% 5% 7% 5% 9% 9% 30%	1886
	11th to 20th	Night	5% 11% 4 10% 7% 4 5% 5% 8% 9% 32%	1691
	21st to end	Night	6% 14% 4 8% 6% 6% 5% 4 8% 8% 34%	1710
May	1st to 10th	Night	11% 17% 3 9% 6% 5% 6% 4 5% 6% 30%	2749
	11th to 20th	Night	6% 7% 3 6% 4 4 6% 7% 9% 10% 37%	2277
	21st to end	Night	13% 13% 4 8% 4 5% 6% 4 9% 7% 27%	2414
June	1st to 10th	Night	10% 9% 3 8% 5% 6% 6% 6% 8% 7% 32%	1330
	11th to 20th	Night	13% 8% 2 8% 4 6% 7% 5% 7% 8% 30%	1330
	21st to end	Night	4 5% 2 6% 4 3 6% 5% 6% 8% 50%	1330
July	1st to 10th	Night	4 2 1 4 5% 5% 4 3 6% 7% 58%	2220
	11th to 20th	Night	2 3 1 5% 3 2 3 3 5% 6% 65%	2220
	21st to end	Night	2 3 1 3 3 2 3 3 4 6% 70%	2720
August	1st to 10th	Night	9% 10% 2 4 3 3 3 3 4 6% 54%	2529
	11th to 20th	Night	4 3 1 5% 4 4 5% 5% 8% 11% 52%	2802
	21st to end	Night	4 4 1 3 3 4 5% 4 6% 10% 56%	3146
September	1st to 10th	Night	7% 6% 1 4 3 3 4 4 5% 7% 56%	1864
	11th to 20th	Night	7% 7% 2 5% 4 4 5% 4 6% 9% 46%	2090
	21st to end	Night	6% 9% 2 6% 4 4 3 4 7% 9% 45%	2079
October	1st to 10th	Night	9% 9% 2 7% 4 4 4 3 6% 7% 44%	2025
	11th to 20th	Night	4 7% 3 8% 5% 6% 6% 6% 8% 9% 38%	2294
	21st to end	Night	4 9% 4 11% 6% 6% 7% 6% 8% 9% 28%	2574
November	1st to 10th	Night	5% 13% 4 10% 6% 6% 7% 5% 10% 10% 25%	2427
	11th to 20th	Night	2 8% 4 11% 7% 7% 7% 7% 11% 10% 27%	2690
	21st to end	Night	2 9% 3 9% 6% 9% 7% 6% 11% 11% 26%	2850
December	1st to 10th	Night	2 8% 5% 11% 8% 7% 8% 6% 12% 10% 24%	2850
	11th to 20th	Night	1 9% 5% 13% 8% 9% 8% 7% 11% 12% 17%	3510
	21st to end	Night	1 10% 4 10% 7% 8% 7% 7% 11% 9% 27%	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	36% 23% 26% 11% 2 1	2219
	11th to 20th	Day	44% 15% 17% 9% 11% 4	2441
	21st to end	Day	30% 27% 28% 12% 3	2794
February	1st to 10th	Day	42% 21% 19% 11% 5% 1	1526
	11th to 20th	Day	46% 15% 20% 13% 5% 1	1686
	21st to end	Day	45% 15% 20% 13% 5% 2	1570
March	1st to 10th	Day	33% 18% 21% 17% 10% 1	3138
	11th to 20th	Day	31% 16% 29% 20% 4	3428
	21st to end	Day	53% 14% 19% 9% 5%	3907
April	1st to 10th	Day	48% 14% 19% 16% 3	2294
	11th to 20th	Day	50% 12% 18% 16% 4	2440
	21st to end	Day	47% 11% 18% 18% 5% 1	2470
May	1st to 10th	Day	56% 9% 13% 18% 4	4203
	11th to 20th	Day	40% 15% 18% 23% 5%	4620
	21st to end	Day	43% 18% 21% 13% 5%	5162
June	1st to 10th	Day	49% 11% 16% 18% 6%	2850
	11th to 20th	Day	50% 11% 16% 15% 7% 1	2850
	21st to end	Day	34% 10% 18% 23% 13% 1	2850
July	1st to 10th	Day	23% 8% 12% 26% 23% 7%	4666
	11th to 20th	Day	19% 7% 11% 27% 28% 8%	4659
	21st to end	Day	16% 5% 10% 27% 26% 15%	4675
August	1st to 10th	Day	34% 7% 14% 22% 18% 5%	4384
	11th to 20th	Day	25% 7% 19% 34% 13% 2	4076
	21st to end	Day	23% 7% 16% 38% 14% 2	4520
September	1st to 10th	Day	31% 7% 16% 24% 16% 6%	2311
	11th to 20th	Day	33% 9% 17% 26% 14% 2	2090
	21st to end	Day	31% 10% 23% 23% 11% 1	2069
October	1st to 10th	Day	41% 12% 17% 21% 8%	1934
	11th to 20th	Day	35% 14% 23% 18% 10% 1	1662
	21st to end	Day	38% 16% 21% 17% 7% 1	1782
November	1st to 10th	Day	43% 16% 21% 15% 5% 1	1632
	11th to 20th	Day	30% 23% 27% 15% 5%	1487
	21st to end	Day	37% 21% 21% 14% 7% 1	1330
December	1st to 10th	Day	34% 23% 23% 12% 6% 2	1330
	11th to 20th	Day	35% 25% 27% 9% 3	1684
	21st to end	Day	30% 19% 23% 17% 11% 1	2442
January	1st to 10th	Night	38% 23% 25% 10% 3 1	4726
	11th to 20th	Night	41% 16% 19% 10% 8% 6%	4548
	21st to end	Night	32% 27% 24% 12% 4	4862
February	1st to 10th	Night	43% 16% 19% 13% 6% 2	2653
	11th to 20th	Night	41% 17% 23% 14% 6%	2389
	21st to end	Night	42% 15% 19% 18% 5% 2	1884
March	1st to 10th	Night	37% 19% 19% 18% 7%	3736
	11th to 20th	Night	28% 18% 29% 21% 4 1	3552
	21st to end	Night	53% 14% 19% 11% 2	3743
April	1st to 10th	Night	41% 13% 21% 16% 7%	1886
	11th to 20th	Night	41% 11% 20% 24% 4	1691
	21st to end	Night	42% 12% 18% 22% 6% 1	1710
May	1st to 10th	Night	50% 10% 14% 20% 5%	2749
	11th to 20th	Night	30% 13% 22% 27% 8%	2277
	21st to end	Night	42% 17% 20% 16% 6%	2414
June	1st to 10th	Night	41% 11% 23% 19% 5% 1	1330
	11th to 20th	Night	44% 11% 18% 18% 8% 1	1330
	21st to end	Night	25% 10% 21% 29% 13% 2	1330
July	1st to 10th	Night	21% 7% 19% 27% 18% 8%	2185
	11th to 20th	Night	19% 6% 13% 28% 25% 10%	2178
	21st to end	Night	15% 5% 11% 28% 28% 14%	2634
August	1st to 10th	Night	32% 6% 13% 25% 20% 4	2521
	11th to 20th	Night	24% 7% 24% 29% 15% 2	2829
	21st to end	Night	20% 8% 16% 37% 18% 1	3146
September	1st to 10th	Night	25% 7% 15% 31% 16% 6%	1864
	11th to 20th	Night	30% 9% 18% 27% 13% 2	2090
	21st to end	Night	29% 10% 23% 24% 12% 2	2079
October	1st to 10th	Night	33% 13% 18% 23% 11% 1	2025
	11th to 20th	Night	30% 14% 24% 22% 8% 2	2294
	21st to end	Night	38% 17% 21% 18% 6%	2574
November	1st to 10th	Night	40% 19% 20% 14% 5% 1	2427
	11th to 20th	Night	31% 23% 26% 14% 6%	2690
	21st to end	Night	34% 23% 22% 13% 7% 1	2850
December	1st to 10th	Night	34% 23% 22% 13% 6% 1	2850
	11th to 20th	Night	38% 26% 24% 9% 3	3507
	21st to end	Night	35% 18% 23% 15% 7% 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	20% 24% 28% 16% 6% 6%	180
	11th to 20th	Day	18% 21% 36% 19% 4 2	180
	21st to end	Day	14% 39% 32% 9% 5% 2	198
February	1st to 10th	Day	23% 26% 34% 12% 5% 1	184
	11th to 20th	Day	16% 26% 35% 17% 6%	282
	21st to end	Day	21% 29% 34% 12% 3	382
March	1st to 10th	Day	20% 34% 27% 13% 5% 1	460
	11th to 20th	Day	20% 26% 27% 17% 8% 1	460
	21st to end	Day	23% 33% 25% 13% 4 2	506
April	1st to 10th	Day	24% 29% 30% 14% 3	460
	11th to 20th	Day	21% 31% 26% 16% 5% 1	452
	21st to end	Day	25% 28% 26% 13% 7% 2	460
May	1st to 10th	Day	22% 21% 29% 18% 9% 2	463
	11th to 20th	Day	25% 17% 25% 19% 11% 4	623
	21st to end	Day	26% 15% 23% 22% 12% 2	734
June	1st to 10th	Day	20% 25% 27% 19% 8% 2	680
	11th to 20th	Day	28% 23% 23% 17% 8% 1	680
	21st to end	Day	13% 19% 27% 26% 13% 3	680
July	1st to 10th	Day	10% 15% 30% 26% 16% 3	671
	11th to 20th	Day	11% 17% 30% 29% 12% 2	668
	21st to end	Day	8% 17% 37% 25% 10% 3	556
August	1st to 10th	Day	11% 17% 33% 26% 9% 3	487
	11th to 20th	Day	7% 15% 38% 27% 10% 3	477
	21st to end	Day	13% 23% 34% 19% 9% 2	539
September	1st to 10th	Day	19% 24% 27% 20% 9% 2	490
	11th to 20th	Day	21% 18% 33% 18% 9% 1	490
	21st to end	Day	30% 24% 27% 13% 5% 1	483
October	1st to 10th	Day	20% 25% 27% 18% 8% 1	404
	11th to 20th	Day	24% 23% 26% 16% 10% 1	270
	21st to end	Day	28% 25% 26% 15% 5% 1	297
November	1st to 10th	Day	30% 29% 23% 14% 3	270
	11th to 20th	Day	26% 30% 35% 7% 2	255
	21st to end	Day	28% 23% 26% 12% 6% 6%	180
December	1st to 10th	Day	22% 31% 26% 16% 5% 1	180
	11th to 20th	Day	22% 31% 32% 13% 1 1	180
	21st to end	Day	16% 24% 33% 16% 9% 2	198
January	1st to 10th	Night	18% 27% 34% 17% 4	950
	11th to 20th	Night	12% 25% 41% 17% 4	836
	21st to end	Night	11% 30% 37% 17% 5% 2	836
February	1st to 10th	Night	13% 21% 36% 22% 7% 2	760
	11th to 20th	Night	13% 21% 38% 22% 6%	744
	21st to end	Night	14% 19% 33% 24% 9%	628
March	1st to 10th	Night	11% 23% 38% 19% 7% 1	760
	11th to 20th	Night	17% 21% 28% 27% 7% 1	760
	21st to end	Night	16% 19% 26% 28% 8% 2	836
April	1st to 10th	Night	15% 22% 29% 23% 10% 1	746
	11th to 20th	Night	14% 24% 27% 25% 9% 1	563
	21st to end	Night	15% 21% 32% 22% 10% 1	570
May	1st to 10th	Night	18% 15% 26% 26% 14% 1	511
	11th to 20th	Night	17% 10% 23% 29% 20% 2	374
	21st to end	Night	23% 10% 20% 27% 18% 1	411
June	1st to 10th	Night	17% 17% 24% 28% 13% 2	380
	11th to 20th	Night	21% 16% 28% 22% 12% 1	380
	21st to end	Night	7% 13% 24% 37% 19% 1	380
July	1st to 10th	Night	8% 6% 24% 36% 26%	370
	11th to 20th	Night	7% 9% 25% 40% 17% 1	368
	21st to end	Night	8% 8% 22% 37% 23% 1	416
August	1st to 10th	Night	11% 6% 17% 39% 26% 1	378
	11th to 20th	Night	8% 7% 22% 35% 25% 3	555
	21st to end	Night	10% 14% 25% 33% 16% 1	627
September	1st to 10th	Night	14% 10% 21% 31% 20% 4	717
	11th to 20th	Night	16% 12% 23% 28% 17% 5%	760
	21st to end	Night	19% 18% 26% 23% 12% 3	756
October	1st to 10th	Night	20% 15% 20% 32% 13% 1	720
	11th to 20th	Night	14% 21% 26% 28% 10% 1	720
	21st to end	Night	15% 24% 32% 22% 6% 1	792
November	1st to 10th	Night	21% 26% 31% 17% 4	762
	11th to 20th	Night	20% 29% 33% 15% 3 1	950
	21st to end	Night	16% 25% 36% 17% 6% 1	950
December	1st to 10th	Night	12% 25% 35% 20% 7% 1	950
	11th to 20th	Night	13% 26% 40% 18% 3	950
	21st to end	Night	13% 25% 38% 18% 6%	1045

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