High River
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the High River clear sky chart from 2005-11-06 to 2025-09-19.

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% 8% 3 7% 5% 5% 5% 4 6% 8% 41%	130568
	Night	6% 9% 3 9% 5% 5% 5% 4 6% 8% 39%	127194
Transparency	Day	39% 6% 15% 25% 12% 2	130270
	Night	41% 6% 15% 24% 12% 2	127069
Seeing	Day	13% 13% 30% 27% 13% 4	16517
	Night	11% 9% 31% 34% 13% 2	25514

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 11% 7% 13% 7% 6% 5% 4 7% 7% 31%	3179
	11th to 20th	Day	2 9% 4 10% 6% 5% 5% 5% 8% 7% 40%	3274
	21st to end	Day	2 6% 3 8% 5% 4 5% 4 5% 11% 46%	4004
February	1st to 10th	Day	3 11% 5% 13% 7% 5% 7% 4 8% 8% 30%	1609
	11th to 20th	Day	4 11% 6% 11% 7% 6% 5% 5% 8% 9% 28%	1755
	21st to end	Day	3 10% 6% 11% 7% 6% 5% 4 6% 9% 33%	1610
March	1st to 10th	Day	3 9% 4 10% 6% 5% 5% 3 5% 11% 39%	4518
	11th to 20th	Day	4 9% 4 9% 5% 5% 5% 4 5% 7% 43%	4954
	21st to end	Day	7% 19% 6% 12% 5% 4 5% 4 6% 7% 23%	5546
April	1st to 10th	Day	8% 14% 4 8% 6% 6% 5% 4 7% 7% 31%	2453
	11th to 20th	Day	9% 14% 4 9% 5% 5% 4 4 6% 8% 32%	2570
	21st to end	Day	11% 12% 3 8% 5% 5% 4 5% 7% 8% 34%	2600
May	1st to 10th	Day	14% 11% 3 6% 3 4 4 3 6% 7% 39%	6121
	11th to 20th	Day	12% 9% 4 9% 6% 6% 7% 5% 7% 8% 27%	6734
	21st to end	Day	11% 6% 2 7% 6% 6% 6% 4 6% 7% 38%	7405
June	1st to 10th	Day	15% 7% 3 7% 5% 5% 6% 5% 8% 7% 32%	3000
	11th to 20th	Day	18% 9% 3 7% 5% 5% 5% 4 6% 8% 29%	3000
	21st to end	Day	8% 5% 2 6% 5% 5% 6% 4 8% 9% 43%	3000
July	1st to 10th	Day	7% 4 1 5% 3 4 5% 4 6% 9% 51%	6780
	11th to 20th	Day	9% 4 2 5% 4 4 4 4 7% 10% 49%	6780
	21st to end	Day	7% 5% 2 5% 4 4 4 3 6% 8% 54%	7155
August	1st to 10th	Day	9% 5% 2 5% 3 4 4 5% 7% 11% 44%	4541
	11th to 20th	Day	7% 5% 2 4 4 4 4 6% 7% 9% 48%	4167
	21st to end	Day	8% 3 1 4 3 3 4 3 6% 8% 56%	4664
September	1st to 10th	Day	10% 5% 2 5% 3 4 4 3 5% 7% 52%	2468
	11th to 20th	Day	13% 7% 2 4 3 3 5% 4 5% 8% 46%	2179
	21st to end	Day	8% 8% 2 7% 4 4 4 3 6% 10% 45%	2090
October	1st to 10th	Day	7% 6% 2 7% 5% 4 4 4 6% 10% 45%	3344
	11th to 20th	Day	5% 7% 2 7% 4 4 4 3 8% 11% 45%	2937
	21st to end	Day	6% 8% 3 6% 5% 5% 5% 4 5% 8% 45%	3101
November	1st to 10th	Day	8% 14% 4 9% 5% 5% 5% 4 5% 7% 34%	1649
	11th to 20th	Day	5% 11% 3 8% 5% 5% 5% 4 7% 8% 40%	1551
	21st to end	Day	4 11% 6% 9% 5% 4 4 5% 7% 10% 35%	1400
December	1st to 10th	Day	2 9% 4 12% 6% 6% 5% 4 5% 7% 38%	2290
	11th to 20th	Day	3 9% 5% 10% 7% 6% 6% 4 7% 9% 36%	2642
	21st to end	Day	4 10% 4 9% 5% 5% 5% 4 5% 8% 42%	3498
January	1st to 10th	Night	3 13% 5% 14% 8% 7% 6% 4 6% 7% 27%	6766
	11th to 20th	Night	2 8% 5% 13% 6% 5% 6% 6% 6% 8% 35%	6668
	21st to end	Night	3 8% 4 10% 5% 5% 4 4 6% 8% 43%	6952
February	1st to 10th	Night	4 10% 4 11% 7% 6% 6% 5% 7% 8% 32%	2790
	11th to 20th	Night	4 13% 6% 10% 6% 6% 6% 4 7% 8% 31%	2532
	21st to end	Night	3 10% 5% 11% 9% 6% 5% 4 5% 6% 36%	2015
March	1st to 10th	Night	2 8% 4 12% 7% 6% 6% 5% 6% 10% 34%	5376
	11th to 20th	Night	3 8% 4 10% 6% 5% 5% 4 7% 9% 39%	5044
	21st to end	Night	9% 20% 6% 11% 5% 5% 4 3 6% 7% 23%	5414
April	1st to 10th	Night	8% 14% 4 9% 5% 5% 5% 4 6% 8% 33%	1946
	11th to 20th	Night	9% 13% 4 8% 6% 5% 5% 4 6% 7% 33%	1781
	21st to end	Night	10% 11% 3 8% 6% 5% 6% 4 5% 8% 35%	1800
May	1st to 10th	Night	13% 11% 3 7% 4 4 4 3 4 7% 39%	3846
	11th to 20th	Night	12% 8% 4 9% 5% 5% 6% 5% 7% 10% 30%	3159
	21st to end	Night	11% 6% 3 7% 5% 5% 5% 4 6% 7% 41%	3470
June	1st to 10th	Night	13% 8% 2 8% 5% 3 5% 4 6% 8% 38%	1400
	11th to 20th	Night	18% 7% 3 7% 5% 4 5% 5% 5% 9% 33%	1400
	21st to end	Night	7% 5% 2 5% 3 4 4 5% 8% 9% 47%	1400
July	1st to 10th	Night	6% 5% 2 6% 5% 4 4 4 5% 8% 51%	3180
	11th to 20th	Night	6% 5% 1 5% 3 4 5% 4 8% 9% 50%	3180
	21st to end	Night	11% 5% 2 5% 3 3 3 3 5% 7% 52%	3684
August	1st to 10th	Night	8% 6% 2 6% 5% 5% 5% 5% 7% 8% 44%	2609
	11th to 20th	Night	5% 5% 2 8% 5% 6% 5% 4 6% 9% 45%	2891
	21st to end	Night	8% 3 2 4 2 4 3 3 6% 8% 57%	3245
September	1st to 10th	Night	9% 4 2 5% 4 3 3 3 6% 8% 53%	1929
	11th to 20th	Night	13% 6% 2 5% 3 3 2 3 5% 7% 51%	2178
	21st to end	Night	9% 7% 2 4 3 5% 3 4 6% 8% 48%	2090
October	1st to 10th	Night	6% 5% 2 6% 4 3 5% 4 6% 8% 52%	3631
	11th to 20th	Night	6% 6% 2 5% 4 4 4 4 6% 9% 50%	3988
	21st to end	Night	5% 8% 3 7% 5% 5% 5% 4 6% 7% 47%	4457
November	1st to 10th	Night	7% 13% 4 8% 5% 5% 6% 4 5% 8% 36%	2630
	11th to 20th	Night	4 10% 3 9% 5% 5% 4 4 7% 9% 41%	2845
	21st to end	Night	4 11% 4 8% 6% 4 4 4 6% 10% 38%	3000
December	1st to 10th	Night	3 9% 3 8% 5% 6% 7% 6% 8% 10% 35%	4890
	11th to 20th	Night	2 10% 4 12% 7% 6% 6% 5% 8% 9% 31%	5550
	21st to end	Night	4 10% 4 9% 5% 5% 5% 4 6% 8% 40%	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	50% 5% 11% 22% 9% 2	3179
	11th to 20th	Day	41% 5% 12% 21% 19% 3	3295
	21st to end	Day	32% 5% 13% 34% 14% 1	4004
February	1st to 10th	Day	50% 7% 15% 17% 10% 2	1609
	11th to 20th	Day	50% 7% 13% 20% 8% 2	1764
	21st to end	Day	48% 5% 13% 19% 14% 1	1610
March	1st to 10th	Day	40% 5% 13% 23% 17% 1	4518
	11th to 20th	Day	39% 5% 13% 25% 17% 1	4955
	21st to end	Day	57% 7% 13% 16% 6%	5546
April	1st to 10th	Day	50% 6% 13% 21% 9% 1	2453
	11th to 20th	Day	48% 6% 11% 22% 10% 2	2570
	21st to end	Day	46% 7% 13% 22% 11% 1	2600
May	1st to 10th	Day	43% 5% 10% 22% 17% 3	6121
	11th to 20th	Day	48% 8% 14% 22% 8%	6738
	21st to end	Day	42% 7% 15% 24% 12% 1	7406
June	1st to 10th	Day	46% 8% 15% 19% 10% 2	3000
	11th to 20th	Day	50% 8% 14% 18% 8% 2	3000
	21st to end	Day	34% 8% 19% 26% 11% 2	3000
July	1st to 10th	Day	27% 7% 17% 28% 17% 4	6706
	11th to 20th	Day	30% 6% 20% 30% 12% 2	6699
	21st to end	Day	29% 5% 14% 27% 17% 9%	6953
August	1st to 10th	Day	31% 8% 16% 36% 8% 1	4524
	11th to 20th	Day	29% 8% 24% 30% 8% 1	4206
	21st to end	Day	26% 5% 16% 37% 15% 1	4663
September	1st to 10th	Day	31% 5% 14% 27% 17% 5%	2468
	11th to 20th	Day	36% 5% 13% 28% 14% 2	2179
	21st to end	Day	34% 6% 13% 30% 13% 3	2090
October	1st to 10th	Day	34% 6% 15% 36% 8% 1	3344
	11th to 20th	Day	31% 5% 20% 27% 14% 3	2937
	21st to end	Day	37% 6% 10% 33% 11% 2	3101
November	1st to 10th	Day	49% 6% 12% 19% 12% 2	1649
	11th to 20th	Day	42% 5% 16% 24% 11% 1	1551
	21st to end	Day	43% 6% 17% 22% 10% 3	1400
December	1st to 10th	Day	45% 5% 14% 26% 8% 2	2290
	11th to 20th	Day	44% 6% 21% 20% 7% 1	2644
	21st to end	Day	39% 5% 9% 24% 18% 3	3498
January	1st to 10th	Night	55% 6% 10% 21% 6% 2	6766
	11th to 20th	Night	45% 5% 13% 19% 13% 5%	6709
	21st to end	Night	37% 5% 14% 28% 16% 1	6952
February	1st to 10th	Night	48% 7% 12% 20% 11% 3	2790
	11th to 20th	Night	49% 5% 13% 20% 11% 2	2533
	21st to end	Night	48% 5% 11% 22% 11% 2	2015
March	1st to 10th	Night	43% 6% 17% 20% 12% 2	5376
	11th to 20th	Night	40% 7% 14% 23% 14% 1	5044
	21st to end	Night	59% 6% 13% 13% 8% 1	5414
April	1st to 10th	Night	48% 7% 11% 21% 12% 1	1946
	11th to 20th	Night	49% 6% 12% 22% 10% 1	1781
	21st to end	Night	45% 8% 14% 22% 9% 2	1800
May	1st to 10th	Night	46% 6% 10% 22% 15% 2	3843
	11th to 20th	Night	46% 8% 13% 27% 6% 1	3159
	21st to end	Night	39% 8% 16% 26% 11% 1	3470
June	1st to 10th	Night	42% 7% 15% 23% 12% 1	1400
	11th to 20th	Night	47% 7% 15% 21% 9% 2	1400
	21st to end	Night	29% 8% 21% 28% 13% 1	1400
July	1st to 10th	Night	31% 7% 17% 23% 20% 2	3145
	11th to 20th	Night	28% 7% 21% 32% 9% 2	3138
	21st to end	Night	30% 5% 16% 25% 15% 7%	3581
August	1st to 10th	Night	34% 8% 16% 27% 13% 2	2601
	11th to 20th	Night	33% 7% 21% 27% 10% 1	2918
	21st to end	Night	24% 5% 18% 36% 15% 3	3245
September	1st to 10th	Night	29% 5% 16% 28% 16% 5%	1929
	11th to 20th	Night	32% 6% 15% 28% 15% 5%	2178
	21st to end	Night	33% 4 16% 27% 14% 4	2090
October	1st to 10th	Night	29% 6% 14% 29% 20% 2	3631
	11th to 20th	Night	31% 5% 19% 24% 18% 3	3988
	21st to end	Night	35% 5% 12% 32% 15% 1	4457
November	1st to 10th	Night	47% 6% 12% 21% 12% 2	2630
	11th to 20th	Night	39% 6% 16% 22% 16% 1	2845
	21st to end	Night	41% 6% 16% 22% 11% 4	3000
December	1st to 10th	Night	43% 7% 20% 20% 9% 2	4890
	11th to 20th	Night	47% 7% 21% 18% 7%	5547
	21st to end	Night	40% 4 10% 27% 16% 3	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	3 11% 34% 29% 17% 7%	200
	11th to 20th	Day	9% 14% 32% 30% 12% 4	200
	21st to end	Day	8% 11% 33% 37% 8% 3	220
February	1st to 10th	Day	10% 13% 38% 29% 8% 3	205
	11th to 20th	Day	6% 12% 37% 33% 11% 1	300
	21st to end	Day	9% 16% 36% 27% 11% 1	374
March	1st to 10th	Day	9% 21% 39% 18% 10% 3	500
	11th to 20th	Day	8% 19% 34% 27% 11% 2	500
	21st to end	Day	13% 23% 33% 21% 8% 3	550
April	1st to 10th	Day	18% 20% 34% 19% 8% 1	500
	11th to 20th	Day	16% 17% 33% 22% 9% 2	492
	21st to end	Day	17% 19% 30% 22% 9% 2	500
May	1st to 10th	Day	18% 14% 27% 26% 11% 5%	529
	11th to 20th	Day	18% 10% 25% 26% 16% 4	725
	21st to end	Day	18% 9% 23% 29% 17% 3	789
June	1st to 10th	Day	16% 13% 31% 26% 13% 2	730
	11th to 20th	Day	18% 13% 29% 25% 12% 2	730
	21st to end	Day	10% 9% 28% 31% 17% 5%	730
July	1st to 10th	Day	10% 6% 28% 32% 20% 3	721
	11th to 20th	Day	11% 8% 27% 32% 18% 3	718
	21st to end	Day	7% 8% 31% 31% 19% 4	700
August	1st to 10th	Day	10% 7% 31% 32% 15% 5%	527
	11th to 20th	Day	8% 6% 31% 32% 17% 6%	517
	21st to end	Day	10% 10% 30% 26% 17% 8%	583
September	1st to 10th	Day	11% 11% 29% 27% 15% 8%	530
	11th to 20th	Day	16% 11% 25% 27% 15% 7%	523
	21st to end	Day	14% 18% 27% 27% 11% 3	490
October	1st to 10th	Day	15% 11% 26% 28% 16% 4	409
	11th to 20th	Day	12% 13% 33% 24% 13% 5%	300
	21st to end	Day	12% 17% 35% 25% 8% 3	330
November	1st to 10th	Day	19% 12% 32% 24% 9% 4	300
	11th to 20th	Day	11% 19% 33% 27% 7% 2	275
	21st to end	Day	10% 14% 33% 24% 11% 9%	200
December	1st to 10th	Day	9% 11% 34% 29% 15% 4	200
	11th to 20th	Day	8% 11% 41% 27% 11% 4	200
	21st to end	Day	10% 8% 29% 30% 19% 5%	220
January	1st to 10th	Night	9% 14% 32% 33% 11% 2	1000
	11th to 20th	Night	9% 10% 37% 32% 11% 1	968
	21st to end	Night	10% 11% 33% 36% 10% 1	880
February	1st to 10th	Night	9% 13% 32% 32% 12% 3	800
	11th to 20th	Night	10% 8% 33% 35% 12% 1	784
	21st to end	Night	8% 7% 32% 35% 16% 3	660
March	1st to 10th	Night	9% 8% 35% 31% 14% 3	800
	11th to 20th	Night	8% 13% 35% 32% 10% 1	800
	21st to end	Night	13% 9% 33% 32% 9% 3	880
April	1st to 10th	Night	14% 12% 31% 29% 12% 1	746
	11th to 20th	Night	15% 10% 35% 30% 9%	593
	21st to end	Night	17% 11% 31% 30% 12% 1	600
May	1st to 10th	Night	16% 10% 26% 33% 15%	530
	11th to 20th	Night	14% 10% 22% 33% 20% 2	394
	21st to end	Night	21% 5% 22% 35% 16% 1	433
June	1st to 10th	Night	15% 9% 31% 29% 15% 2	400
	11th to 20th	Night	22% 6% 29% 30% 12% 1	400
	21st to end	Night	9% 6% 21% 42% 21% 2	400
July	1st to 10th	Night	11% 3 20% 41% 25% 1	390
	11th to 20th	Night	10% 4 22% 43% 21% 2	388
	21st to end	Night	8% 5% 23% 40% 22% 3	438
August	1st to 10th	Night	11% 5% 15% 38% 29% 2	398
	11th to 20th	Night	9% 4 21% 44% 21% 1	584
	21st to end	Night	10% 5% 25% 38% 21% 1	660
September	1st to 10th	Night	11% 5% 24% 36% 21% 3	705
	11th to 20th	Night	17% 5% 21% 35% 20% 2	792
	21st to end	Night	11% 8% 33% 34% 11% 3	760
October	1st to 10th	Night	15% 5% 26% 36% 15% 3	760
	11th to 20th	Night	12% 8% 31% 30% 15% 3	760
	21st to end	Night	12% 8% 33% 34% 11% 1	836
November	1st to 10th	Night	14% 11% 37% 29% 8% 1	875
	11th to 20th	Night	10% 16% 38% 29% 6% 1	1000
	21st to end	Night	10% 10% 37% 32% 9% 2	1000
December	1st to 10th	Night	8% 10% 34% 33% 11% 3	1000
	11th to 20th	Night	6% 12% 38% 35% 10% 1	1000
	21st to end	Night	11% 8% 35% 33% 12% 2	1100

Page generated at 2025-09-15 23:49:11. Version ac07

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