Olds
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Olds clear sky chart from 2005-11-06 to 2025-11-18.

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	8% 9% 3 8% 5% 5% 5% 4 6% 8% 36%	131259
	Night	6% 9% 4 10% 6% 5% 5% 4 6% 8% 35%	127764
Transparency	Day	43% 6% 16% 24% 10% 1	130959
	Night	45% 6% 15% 22% 10% 2	127641
Seeing	Day	13% 6% 25% 32% 18% 6%	16734
	Night	11% 5% 30% 36% 15% 2	25723

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	2 10% 6% 14% 7% 7% 7% 4 4 6% 31%	3179
	11th to 20th	Day	3 8% 4 12% 7% 6% 6% 5% 7% 8% 34%	3159
	21st to end	Day	3 8% 3 8% 5% 6% 6% 4 6% 8% 42%	4004
February	1st to 10th	Day	6% 12% 5% 11% 7% 7% 6% 4 6% 8% 27%	1600
	11th to 20th	Day	5% 13% 5% 11% 8% 6% 6% 5% 8% 8% 25%	1720
	21st to end	Day	3 12% 7% 11% 6% 6% 6% 6% 7% 7% 30%	1596
March	1st to 10th	Day	3 10% 4 11% 7% 5% 5% 4 6% 10% 35%	4518
	11th to 20th	Day	5% 11% 5% 11% 5% 5% 4 4 6% 8% 37%	4928
	21st to end	Day	9% 21% 6% 12% 6% 5% 5% 4 6% 5% 21%	5590
April	1st to 10th	Day	8% 13% 4 9% 6% 6% 6% 5% 7% 8% 28%	2460
	11th to 20th	Day	11% 14% 5% 9% 5% 5% 5% 4 6% 8% 27%	2570
	21st to end	Day	12% 12% 4 8% 5% 4 5% 4 6% 9% 31%	2600
May	1st to 10th	Day	13% 10% 3 7% 5% 5% 5% 4 5% 7% 37%	6334
	11th to 20th	Day	12% 12% 4 10% 6% 6% 6% 5% 7% 8% 25%	6734
	21st to end	Day	12% 8% 3 8% 5% 5% 5% 4 6% 7% 36%	7405
June	1st to 10th	Day	15% 8% 3 7% 6% 5% 6% 5% 7% 8% 30%	3000
	11th to 20th	Day	17% 10% 3 8% 6% 6% 6% 5% 7% 7% 25%	3000
	21st to end	Day	8% 6% 2 7% 6% 6% 6% 5% 8% 9% 37%	3000
July	1st to 10th	Day	7% 5% 2 5% 4 4 4 4 7% 10% 47%	6780
	11th to 20th	Day	11% 4 2 5% 4 5% 6% 5% 8% 10% 41%	6780
	21st to end	Day	10% 5% 2 6% 4 4 5% 4 6% 9% 44%	7273
August	1st to 10th	Day	8% 5% 2 7% 5% 5% 6% 5% 7% 9% 40%	4541
	11th to 20th	Day	7% 4 2 6% 4 5% 6% 5% 8% 11% 40%	4236
	21st to end	Day	10% 5% 2 5% 4 4 4 4 7% 8% 49%	4664
September	1st to 10th	Day	11% 6% 2 5% 4 4 4 3 6% 7% 47%	2495
	11th to 20th	Day	15% 7% 2 5% 4 3 4 3 4 7% 46%	2200
	21st to end	Day	8% 8% 3 7% 5% 4 5% 4 6% 7% 43%	2200
October	1st to 10th	Day	7% 7% 3 7% 4 5% 6% 4 7% 9% 41%	3449
	11th to 20th	Day	7% 7% 3 8% 6% 5% 5% 5% 7% 9% 38%	2974
	21st to end	Day	7% 7% 3 8% 5% 6% 5% 3 6% 7% 41%	3200
November	1st to 10th	Day	8% 16% 5% 10% 6% 5% 4 4 6% 7% 29%	1702
	11th to 20th	Day	6% 13% 4 9% 6% 5% 4 5% 6% 7% 35%	1538
	21st to end	Day	5% 13% 4 10% 7% 5% 5% 5% 6% 8% 32%	1400
December	1st to 10th	Day	5% 10% 5% 13% 7% 7% 5% 4 7% 7% 29%	2290
	11th to 20th	Day	4 11% 4 12% 8% 6% 7% 5% 6% 8% 29%	2642
	21st to end	Day	3 9% 4 10% 6% 5% 5% 4 6% 8% 41%	3498
January	1st to 10th	Night	3 13% 6% 14% 8% 7% 7% 5% 6% 7% 24%	6766
	11th to 20th	Night	2 7% 4 13% 7% 6% 7% 6% 7% 7% 33%	6739
	21st to end	Night	2 9% 3 10% 6% 6% 5% 5% 7% 8% 39%	6981
February	1st to 10th	Night	6% 11% 6% 13% 8% 7% 6% 4 6% 7% 27%	2800
	11th to 20th	Night	4 13% 6% 11% 7% 7% 6% 5% 6% 7% 29%	2567
	21st to end	Night	2 11% 5% 10% 6% 7% 6% 4 7% 8% 33%	2030
March	1st to 10th	Night	3 8% 4 12% 7% 7% 6% 5% 7% 8% 33%	5376
	11th to 20th	Night	5% 9% 4 11% 6% 5% 6% 5% 8% 9% 32%	5071
	21st to end	Night	8% 18% 6% 13% 7% 6% 6% 4 6% 6% 21%	5369
April	1st to 10th	Night	7% 12% 4 8% 8% 5% 5% 5% 6% 8% 30%	1940
	11th to 20th	Night	9% 14% 4 10% 7% 5% 5% 5% 6% 7% 28%	1781
	21st to end	Night	12% 10% 3 9% 6% 6% 5% 5% 7% 6% 31%	1800
May	1st to 10th	Night	15% 10% 3 8% 4 4 4 3 5% 7% 37%	3616
	11th to 20th	Night	14% 10% 4 9% 6% 5% 5% 4 7% 9% 28%	3159
	21st to end	Night	11% 9% 3 9% 7% 6% 5% 4 6% 7% 34%	3470
June	1st to 10th	Night	16% 7% 4 8% 4 5% 6% 5% 6% 9% 30%	1400
	11th to 20th	Night	17% 10% 4 8% 6% 7% 6% 5% 6% 9% 23%	1400
	21st to end	Night	9% 6% 2 7% 6% 5% 5% 5% 8% 8% 39%	1400
July	1st to 10th	Night	7% 5% 3 8% 5% 5% 6% 5% 8% 8% 40%	3180
	11th to 20th	Night	8% 5% 2 6% 4 5% 5% 5% 7% 9% 43%	3180
	21st to end	Night	10% 5% 2 5% 4 4 4 4 6% 10% 46%	3555
August	1st to 10th	Night	10% 6% 3 6% 5% 5% 4 4 6% 7% 44%	2609
	11th to 20th	Night	7% 5% 2 8% 5% 5% 6% 4 8% 12% 39%	2807
	21st to end	Night	8% 6% 2 6% 4 4 5% 4 6% 8% 48%	3245
September	1st to 10th	Night	9% 6% 2 5% 4 4 4 4 6% 8% 48%	1902
	11th to 20th	Night	14% 6% 2 5% 4 4 4 4 6% 6% 43%	2200
	21st to end	Night	10% 6% 2 5% 4 4 5% 3 7% 8% 46%	2200
October	1st to 10th	Night	8% 6% 2 6% 4 5% 5% 4 6% 9% 45%	3745
	11th to 20th	Night	6% 7% 3 8% 5% 5% 5% 3 7% 9% 43%	4170
	21st to end	Night	5% 8% 3 7% 5% 5% 6% 5% 6% 8% 41%	4600
November	1st to 10th	Night	7% 14% 5% 10% 5% 5% 5% 5% 6% 7% 32%	2796
	11th to 20th	Night	4 11% 4 10% 6% 6% 4 4 7% 9% 33%	3012
	21st to end	Night	4 11% 4 10% 6% 6% 6% 4 7% 9% 33%	3000
December	1st to 10th	Night	5% 11% 4 12% 7% 6% 7% 5% 7% 8% 28%	4890
	11th to 20th	Night	4 13% 5% 13% 9% 7% 6% 4 6% 7% 25%	5550
	21st to end	Night	2 9% 4 10% 6% 5% 5% 4 6% 8% 42%	7458

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	53% 5% 9% 20% 11% 2	3179
	11th to 20th	Day	46% 6% 10% 16% 19% 3	3180
	21st to end	Day	39% 6% 12% 32% 11% 1	4004
February	1st to 10th	Day	53% 6% 12% 18% 9% 2	1600
	11th to 20th	Day	52% 8% 13% 16% 9% 2	1729
	21st to end	Day	51% 7% 11% 19% 11% 1	1596
March	1st to 10th	Day	42% 5% 15% 23% 14%	4518
	11th to 20th	Day	43% 6% 14% 22% 14% 1	4929
	21st to end	Day	62% 6% 10% 14% 7% 1	5590
April	1st to 10th	Day	50% 8% 17% 17% 8%	2460
	11th to 20th	Day	52% 6% 12% 20% 9% 1	2570
	21st to end	Day	48% 7% 15% 22% 7% 1	2600
May	1st to 10th	Day	46% 5% 9% 23% 15% 2	6334
	11th to 20th	Day	52% 7% 14% 20% 6%	6738
	21st to end	Day	44% 6% 16% 24% 9%	7406
June	1st to 10th	Day	47% 8% 16% 20% 7% 1	3000
	11th to 20th	Day	54% 8% 14% 18% 5% 1	3000
	21st to end	Day	39% 9% 21% 24% 6% 1	3000
July	1st to 10th	Day	30% 5% 19% 31% 12% 2	6706
	11th to 20th	Day	36% 6% 21% 29% 7%	6699
	21st to end	Day	36% 6% 18% 26% 12% 3	7068
August	1st to 10th	Day	38% 7% 18% 30% 7%	4524
	11th to 20th	Day	35% 6% 25% 27% 6% 1	4276
	21st to end	Day	31% 6% 21% 31% 10% 1	4663
September	1st to 10th	Day	34% 5% 20% 25% 11% 4	2495
	11th to 20th	Day	38% 6% 15% 29% 12% 1	2200
	21st to end	Day	37% 6% 17% 26% 12% 3	2200
October	1st to 10th	Day	39% 4 20% 30% 6% 1	3449
	11th to 20th	Day	40% 6% 19% 22% 12% 2	2974
	21st to end	Day	41% 5% 9% 34% 10% 1	3200
November	1st to 10th	Day	53% 6% 11% 19% 9% 2	1702
	11th to 20th	Day	47% 7% 14% 22% 9% 1	1538
	21st to end	Day	48% 7% 15% 19% 9% 2	1400
December	1st to 10th	Day	53% 5% 14% 20% 7% 1	2290
	11th to 20th	Day	51% 6% 18% 19% 5% 1	2644
	21st to end	Day	40% 5% 11% 23% 18% 3	3498
January	1st to 10th	Night	57% 6% 10% 19% 6% 2	6766
	11th to 20th	Night	48% 6% 11% 17% 14% 4	6780
	21st to end	Night	40% 6% 16% 27% 11% 1	6981
February	1st to 10th	Night	54% 6% 10% 18% 11% 2	2800
	11th to 20th	Night	52% 7% 11% 18% 11% 2	2568
	21st to end	Night	46% 5% 12% 22% 13% 2	2030
March	1st to 10th	Night	43% 7% 16% 21% 12% 1	5376
	11th to 20th	Night	43% 9% 15% 20% 12% 1	5071
	21st to end	Night	61% 7% 9% 15% 7% 1	5369
April	1st to 10th	Night	47% 8% 14% 19% 11% 1	1940
	11th to 20th	Night	53% 6% 12% 20% 8% 1	1781
	21st to end	Night	50% 6% 14% 21% 7% 2	1800
May	1st to 10th	Night	47% 5% 10% 22% 14% 3	3613
	11th to 20th	Night	49% 8% 14% 22% 7%	3159
	21st to end	Night	47% 7% 16% 23% 7% 1	3470
June	1st to 10th	Night	47% 10% 14% 18% 9% 1	1400
	11th to 20th	Night	55% 8% 13% 16% 6% 2	1400
	21st to end	Night	39% 8% 21% 24% 7% 1	1400
July	1st to 10th	Night	40% 6% 17% 25% 11% 2	3145
	11th to 20th	Night	34% 6% 21% 30% 6% 3	3138
	21st to end	Night	33% 5% 22% 27% 11% 1	3456
August	1st to 10th	Night	38% 7% 15% 32% 8%	2601
	11th to 20th	Night	36% 6% 25% 27% 5% 1	2832
	21st to end	Night	33% 6% 22% 30% 9% 1	3245
September	1st to 10th	Night	33% 6% 17% 26% 13% 4	1902
	11th to 20th	Night	38% 7% 16% 25% 11% 4	2200
	21st to end	Night	34% 6% 17% 27% 13% 3	2200
October	1st to 10th	Night	35% 4 19% 28% 13% 1	3745
	11th to 20th	Night	38% 5% 17% 27% 11% 2	4170
	21st to end	Night	40% 5% 12% 30% 11% 1	4600
November	1st to 10th	Night	50% 6% 11% 21% 10% 2	2796
	11th to 20th	Night	45% 6% 17% 19% 11% 1	3012
	21st to end	Night	46% 8% 16% 19% 8% 3	3000
December	1st to 10th	Night	53% 5% 16% 18% 6% 2	4890
	11th to 20th	Night	57% 6% 15% 16% 6% 1	5547
	21st to end	Night	39% 5% 10% 25% 17% 4	7458

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	5% 6% 30% 32% 19% 10%	200
	11th to 20th	Day	8% 5% 39% 30% 15% 5%	200
	21st to end	Day	7% 8% 28% 35% 17% 6%	220
February	1st to 10th	Day	10% 11% 25% 35% 14% 7%	200
	11th to 20th	Day	11% 2 34% 37% 13% 3	283
	21st to end	Day	6% 6% 30% 34% 19% 6%	360
March	1st to 10th	Day	9% 6% 34% 31% 17% 5%	500
	11th to 20th	Day	9% 5% 31% 36% 13% 6%	500
	21st to end	Day	13% 8% 29% 32% 13% 5%	550
April	1st to 10th	Day	13% 9% 33% 26% 15% 5%	500
	11th to 20th	Day	17% 11% 25% 28% 15% 4	492
	21st to end	Day	17% 7% 26% 30% 16% 4	500
May	1st to 10th	Day	16% 10% 24% 28% 16% 5%	568
	11th to 20th	Day	14% 7% 22% 33% 19% 5%	725
	21st to end	Day	16% 5% 17% 32% 23% 7%	789
June	1st to 10th	Day	16% 7% 25% 34% 14% 4	730
	11th to 20th	Day	19% 6% 23% 33% 14% 5%	730
	21st to end	Day	10% 5% 23% 30% 22% 9%	730
July	1st to 10th	Day	12% 3 18% 35% 24% 8%	721
	11th to 20th	Day	15% 3 18% 33% 24% 7%	718
	21st to end	Day	9% 4 20% 33% 24% 10%	753
August	1st to 10th	Day	12% 4 21% 31% 22% 9%	527
	11th to 20th	Day	9% 3 23% 35% 23% 7%	517
	21st to end	Day	11% 5% 19% 32% 24% 9%	583
September	1st to 10th	Day	14% 5% 26% 28% 19% 8%	530
	11th to 20th	Day	19% 6% 20% 27% 21% 7%	530
	21st to end	Day	13% 11% 30% 28% 13% 5%	530
October	1st to 10th	Day	14% 7% 27% 31% 16% 6%	444
	11th to 20th	Day	12% 6% 34% 29% 15% 4	330
	21st to end	Day	12% 11% 36% 31% 8% 3	363
November	1st to 10th	Day	18% 5% 28% 32% 12% 4	330
	11th to 20th	Day	13% 10% 32% 31% 13% 2	261
	21st to end	Day	10% 6% 32% 28% 19% 7%	200
December	1st to 10th	Day	12% 5% 31% 31% 15% 7%	200
	11th to 20th	Day	10% 8% 39% 26% 15% 4	200
	21st to end	Day	7% 3 28% 31% 25% 5%	220
January	1st to 10th	Night	9% 7% 36% 34% 13% 2	1000
	11th to 20th	Night	9% 7% 38% 33% 12% 1	1000
	21st to end	Night	11% 7% 35% 34% 11% 2	896
February	1st to 10th	Night	10% 8% 29% 35% 16% 3	800
	11th to 20th	Night	8% 6% 35% 36% 14% 1	784
	21st to end	Night	6% 5% 30% 35% 20% 5%	660
March	1st to 10th	Night	8% 4 31% 37% 15% 4	800
	11th to 20th	Night	8% 4 33% 40% 13% 3	800
	21st to end	Night	13% 4 29% 36% 14% 3	880
April	1st to 10th	Night	11% 6% 31% 34% 16% 2	740
	11th to 20th	Night	15% 6% 33% 35% 10% 1	593
	21st to end	Night	17% 8% 27% 36% 12% 1	600
May	1st to 10th	Night	18% 6% 28% 33% 14%	469
	11th to 20th	Night	13% 4 30% 36% 16% 1	394
	21st to end	Night	21% 4 19% 38% 17% 1	433
June	1st to 10th	Night	18% 6% 24% 37% 13% 2	400
	11th to 20th	Night	20% 4 24% 36% 16% 1	400
	21st to end	Night	12% 5% 21% 38% 23% 2	400
July	1st to 10th	Night	12% 3 15% 44% 25% 1	390
	11th to 20th	Night	13% 3 17% 48% 19% 1	388
	21st to end	Night	9% 3 18% 41% 28% 2	438
August	1st to 10th	Night	11% 3 13% 38% 33% 2	398
	11th to 20th	Night	8% 4 16% 45% 25% 1	536
	21st to end	Night	10% 4 19% 42% 24%	660
September	1st to 10th	Night	13% 3 22% 41% 18% 2	697
	11th to 20th	Night	17% 3 19% 39% 20% 3	800
	21st to end	Night	13% 4 32% 37% 13% 2	800
October	1st to 10th	Night	15% 3 29% 37% 15% 2	800
	11th to 20th	Night	12% 4 32% 37% 14% 2	800
	21st to end	Night	10% 7% 35% 35% 12%	880
November	1st to 10th	Night	15% 8% 37% 28% 11% 2	951
	11th to 20th	Night	10% 7% 41% 30% 11% 2	1036
	21st to end	Night	7% 6% 38% 36% 11% 2	1000
December	1st to 10th	Night	11% 6% 32% 34% 14% 2	1000
	11th to 20th	Night	9% 6% 36% 35% 12% 2	1000
	21st to end	Night	11% 4 34% 35% 14% 2	1100

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