Rocky Mountain House
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Rocky Mountain House clear sky chart from 2005-11-06 to 2026-07-01.

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	9% 9% 4 9% 6% 5% 6% 5% 7% 8% 34%	142596
	Night	7% 10% 4 10% 6% 5% 5% 4 6% 8% 33%	138457
Transparency	Day	44% 8% 15% 22% 9% 1	142298
	Night	46% 7% 15% 21% 9% 1	138338
Seeing	Day	13% 8% 27% 30% 16% 5%	17703
	Night	12% 6% 28% 37% 15% 2	26460

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	3 10% 6% 15% 8% 6% 6% 4 6% 8% 28%	4125
	11th to 20th	Day	2 7% 3 10% 6% 6% 6% 5% 6% 8% 41%	4155
	21st to end	Day	3 10% 4 9% 6% 6% 6% 5% 6% 9% 35%	5186
February	1st to 10th	Day	5% 13% 4 11% 8% 6% 6% 5% 7% 7% 29%	1680
	11th to 20th	Day	3 14% 6% 12% 6% 6% 5% 5% 6% 8% 29%	1759
	21st to end	Day	3 9% 6% 12% 9% 8% 7% 5% 6% 7% 28%	1699
March	1st to 10th	Day	2 8% 4 11% 7% 6% 5% 5% 7% 8% 37%	4618
	11th to 20th	Day	4 11% 5% 10% 5% 4 5% 4 7% 9% 35%	4968
	21st to end	Day	9% 20% 7% 11% 5% 5% 5% 4 6% 7% 22%	5819
April	1st to 10th	Day	7% 13% 4 11% 7% 5% 7% 5% 8% 7% 26%	2560
	11th to 20th	Day	10% 15% 4 9% 6% 5% 6% 5% 6% 8% 26%	2700
	21st to end	Day	11% 11% 4 10% 5% 6% 5% 5% 6% 8% 28%	2730
May	1st to 10th	Day	11% 9% 3 8% 5% 5% 6% 4 7% 8% 34%	8356
	11th to 20th	Day	12% 10% 4 10% 6% 6% 6% 5% 8% 9% 23%	8755
	21st to end	Day	13% 8% 3 8% 6% 5% 6% 5% 7% 9% 30%	9649
June	1st to 10th	Day	17% 8% 3 6% 6% 6% 5% 5% 8% 8% 27%	3150
	11th to 20th	Day	17% 10% 3 9% 7% 6% 6% 5% 6% 8% 23%	3165
	21st to end	Day	10% 5% 3 7% 6% 6% 6% 5% 8% 9% 34%	3360
July	1st to 10th	Day	7% 5% 2 6% 4 5% 5% 5% 7% 9% 45%	6790
	11th to 20th	Day	10% 5% 2 6% 5% 5% 5% 5% 7% 10% 39%	6780
	21st to end	Day	10% 6% 2 6% 5% 4 6% 5% 7% 9% 40%	7249
August	1st to 10th	Day	11% 6% 3 6% 4 4 5% 4 6% 9% 43%	4541
	11th to 20th	Day	9% 5% 2 6% 5% 5% 6% 5% 8% 11% 38%	4320
	21st to end	Day	10% 5% 2 6% 4 4 5% 3 6% 9% 43%	4664
September	1st to 10th	Day	12% 6% 3 5% 3 3 4 4 7% 9% 44%	2470
	11th to 20th	Day	14% 8% 2 6% 4 4 4 2 5% 7% 43%	2227
	21st to end	Day	11% 8% 2 6% 4 5% 3 4 7% 8% 41%	2200
October	1st to 10th	Day	8% 8% 3 7% 4 4 4 5% 6% 9% 41%	3458
	11th to 20th	Day	8% 9% 3 8% 6% 5% 6% 4 7% 8% 35%	2932
	21st to end	Day	7% 9% 3 9% 7% 4 5% 4 5% 6% 40%	3200
November	1st to 10th	Day	7% 15% 6% 9% 4 6% 5% 4 6% 8% 30%	1718
	11th to 20th	Day	5% 12% 5% 12% 4 4 4 5% 5% 8% 36%	1496
	21st to end	Day	6% 10% 4 11% 8% 5% 6% 4 5% 9% 32%	1470
December	1st to 10th	Day	4 12% 5% 12% 8% 7% 7% 5% 7% 8% 24%	2360
	11th to 20th	Day	4 11% 4 12% 8% 7% 8% 5% 7% 8% 28%	2712
	21st to end	Day	3 11% 4 11% 6% 5% 6% 4 6% 8% 37%	3575
January	1st to 10th	Night	3 14% 7% 16% 8% 7% 6% 4 6% 6% 23%	8768
	11th to 20th	Night	2 7% 4 12% 7% 6% 5% 5% 6% 7% 38%	8779
	21st to end	Night	3 9% 4 11% 6% 6% 6% 5% 7% 10% 33%	9017
February	1st to 10th	Night	6% 12% 5% 13% 8% 7% 6% 4 6% 8% 26%	2940
	11th to 20th	Night	4 13% 5% 11% 8% 6% 7% 5% 7% 7% 27%	2748
	21st to end	Night	2 12% 5% 11% 6% 6% 7% 4 6% 8% 33%	2105
March	1st to 10th	Night	2 10% 4 12% 6% 6% 6% 4 7% 10% 34%	5496
	11th to 20th	Night	4 13% 5% 10% 5% 5% 5% 5% 8% 10% 29%	5250
	21st to end	Night	8% 17% 6% 13% 6% 5% 5% 4 5% 6% 24%	5397
April	1st to 10th	Night	7% 12% 3 8% 6% 6% 6% 5% 7% 10% 29%	2060
	11th to 20th	Night	10% 13% 5% 10% 6% 6% 5% 4 6% 7% 29%	1871
	21st to end	Night	11% 10% 4 11% 5% 6% 5% 4 5% 7% 33%	1890
May	1st to 10th	Night	15% 11% 4 9% 5% 4 4 3 5% 6% 34%	4558
	11th to 20th	Night	12% 10% 4 9% 6% 6% 6% 5% 8% 8% 27%	4105
	21st to end	Night	11% 8% 3 8% 6% 5% 6% 5% 7% 8% 34%	4522
June	1st to 10th	Night	18% 8% 3 9% 4 4 4 5% 7% 7% 30%	1470
	11th to 20th	Night	16% 9% 3 9% 7% 5% 7% 5% 6% 8% 26%	1444
	21st to end	Night	12% 5% 3 6% 5% 4 5% 5% 8% 8% 38%	1260
July	1st to 10th	Night	9% 7% 3 7% 6% 6% 5% 5% 6% 7% 41%	3152
	11th to 20th	Night	10% 5% 3 6% 5% 4 5% 5% 7% 8% 43%	3180
	21st to end	Night	10% 7% 2 6% 4 4 4 3 5% 9% 45%	3592
August	1st to 10th	Night	13% 6% 2 5% 4 4 5% 3 6% 8% 43%	2609
	11th to 20th	Night	11% 6% 3 7% 5% 4 5% 5% 7% 12% 35%	2732
	21st to end	Night	14% 6% 2 6% 4 3 4 3 5% 7% 46%	3245
September	1st to 10th	Night	12% 6% 2 5% 4 4 5% 4 5% 8% 45%	1928
	11th to 20th	Night	15% 8% 2 6% 3 3 5% 4 6% 7% 42%	2172
	21st to end	Night	10% 7% 3 6% 3 4 4 4 7% 8% 44%	2200
October	1st to 10th	Night	6% 7% 2 8% 5% 5% 6% 4 7% 10% 42%	3735
	11th to 20th	Night	8% 10% 3 7% 5% 5% 4 4 6% 9% 39%	4216
	21st to end	Night	6% 9% 4 8% 6% 5% 6% 4 7% 8% 38%	4600
November	1st to 10th	Night	8% 15% 4 10% 5% 4 5% 4 6% 8% 31%	2780
	11th to 20th	Night	5% 12% 5% 11% 6% 6% 5% 4 6% 8% 31%	3123
	21st to end	Night	4 12% 5% 12% 6% 5% 6% 4 7% 9% 30%	3150
December	1st to 10th	Night	7% 14% 5% 10% 7% 7% 6% 4 6% 7% 27%	5040
	11th to 20th	Night	4 14% 5% 15% 9% 7% 7% 4 6% 7% 22%	5700
	21st to end	Night	3 10% 4 11% 6% 5% 5% 4 6% 7% 38%	7623

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% 10% 18% 13% 2	4125
	11th to 20th	Day	39% 5% 15% 19% 19% 3	4176
	21st to end	Day	42% 7% 14% 29% 8%	5187
February	1st to 10th	Day	51% 7% 12% 18% 10% 3	1680
	11th to 20th	Day	52% 7% 13% 16% 11% 1	1767
	21st to end	Day	52% 7% 12% 19% 9% 1	1699
March	1st to 10th	Day	41% 7% 17% 20% 15% 1	4618
	11th to 20th	Day	41% 7% 14% 21% 16% 1	4969
	21st to end	Day	60% 7% 12% 13% 8%	5819
April	1st to 10th	Day	50% 12% 16% 17% 6% 1	2560
	11th to 20th	Day	52% 9% 13% 18% 8% 1	2700
	21st to end	Day	49% 10% 13% 20% 7% 1	2730
May	1st to 10th	Day	44% 7% 10% 26% 12% 1	8356
	11th to 20th	Day	51% 9% 12% 20% 7% 1	8759
	21st to end	Day	46% 10% 15% 21% 7%	9650
June	1st to 10th	Day	49% 11% 15% 17% 7% 2	3150
	11th to 20th	Day	56% 10% 14% 15% 4 1	3165
	21st to end	Day	40% 12% 19% 21% 6% 1	3360
July	1st to 10th	Day	31% 8% 18% 27% 13% 2	6716
	11th to 20th	Day	37% 8% 19% 30% 6% 1	6699
	21st to end	Day	37% 9% 19% 24% 9% 2	7044
August	1st to 10th	Day	37% 8% 20% 29% 6%	4524
	11th to 20th	Day	36% 10% 21% 24% 8%	4362
	21st to end	Day	35% 8% 23% 27% 7% 1	4663
September	1st to 10th	Day	34% 9% 22% 25% 9% 2	2470
	11th to 20th	Day	40% 8% 14% 28% 10%	2227
	21st to end	Day	38% 7% 16% 24% 12% 2	2200
October	1st to 10th	Day	38% 7% 20% 29% 6% 1	3458
	11th to 20th	Day	44% 6% 16% 20% 13% 2	2932
	21st to end	Day	44% 5% 11% 31% 9% 1	3200
November	1st to 10th	Day	50% 8% 14% 17% 9% 2	1718
	11th to 20th	Day	46% 6% 15% 22% 10% 1	1496
	21st to end	Day	48% 7% 16% 18% 8% 2	1470
December	1st to 10th	Day	56% 6% 16% 15% 6% 1	2360
	11th to 20th	Day	52% 8% 18% 16% 5% 1	2714
	21st to end	Day	42% 6% 10% 21% 17% 3	3575
January	1st to 10th	Night	59% 6% 10% 15% 9% 1	8769
	11th to 20th	Night	43% 5% 15% 19% 14% 4	8820
	21st to end	Night	42% 8% 19% 22% 8% 1	9017
February	1st to 10th	Night	54% 6% 10% 17% 10% 2	2940
	11th to 20th	Night	52% 8% 12% 16% 11% 1	2750
	21st to end	Night	46% 7% 12% 21% 12% 2	2105
March	1st to 10th	Night	42% 9% 17% 21% 11%	5496
	11th to 20th	Night	44% 10% 14% 19% 12% 1	5250
	21st to end	Night	58% 8% 10% 16% 8%	5397
April	1st to 10th	Night	47% 9% 15% 19% 10%	2060
	11th to 20th	Night	52% 6% 14% 19% 8% 1	1871
	21st to end	Night	48% 9% 13% 23% 6% 1	1890
May	1st to 10th	Night	49% 6% 10% 21% 12% 2	4555
	11th to 20th	Night	48% 9% 15% 19% 8%	4105
	21st to end	Night	42% 10% 18% 24% 6% 1	4526
June	1st to 10th	Night	49% 10% 14% 18% 8% 1	1470
	11th to 20th	Night	54% 9% 14% 18% 5% 1	1444
	21st to end	Night	40% 9% 20% 24% 7%	1260
July	1st to 10th	Night	39% 9% 18% 21% 11% 2	3117
	11th to 20th	Night	37% 9% 19% 25% 7% 2	3138
	21st to end	Night	36% 7% 22% 25% 9% 1	3492
August	1st to 10th	Night	37% 9% 19% 29% 6%	2601
	11th to 20th	Night	39% 10% 22% 23% 6% 1	2756
	21st to end	Night	37% 7% 18% 29% 8% 1	3245
September	1st to 10th	Night	36% 8% 17% 26% 11% 2	1928
	11th to 20th	Night	40% 8% 14% 25% 10% 3	2172
	21st to end	Night	35% 8% 17% 25% 13% 3	2200
October	1st to 10th	Night	36% 7% 19% 27% 10% 1	3735
	11th to 20th	Night	40% 7% 15% 28% 9% 1	4216
	21st to end	Night	42% 7% 15% 27% 8%	4600
November	1st to 10th	Night	50% 7% 12% 20% 9% 2	2780
	11th to 20th	Night	48% 7% 15% 18% 11% 1	3123
	21st to end	Night	47% 8% 14% 20% 7% 3	3150
December	1st to 10th	Night	56% 5% 14% 16% 7% 2	5040
	11th to 20th	Night	59% 7% 12% 15% 6% 1	5697
	21st to end	Night	42% 6% 10% 23% 15% 3	7623

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% 5% 32% 29% 19% 10%	220
	11th to 20th	Day	5% 9% 31% 39% 12% 4	220
	21st to end	Day	10% 8% 32% 29% 15% 6%	242
February	1st to 10th	Day	11% 11% 25% 35% 12% 5%	220
	11th to 20th	Day	10% 8% 31% 32% 14% 4	283
	21st to end	Day	6% 8% 33% 35% 17% 2	415
March	1st to 10th	Day	8% 11% 34% 29% 13% 4	540
	11th to 20th	Day	7% 9% 38% 28% 15% 4	540
	21st to end	Day	16% 10% 34% 27% 10% 3	594
April	1st to 10th	Day	11% 16% 33% 25% 10% 4	540
	11th to 20th	Day	15% 12% 30% 24% 14% 4	532
	21st to end	Day	16% 11% 28% 26% 14% 4	540
May	1st to 10th	Day	17% 13% 25% 25% 16% 3	599
	11th to 20th	Day	14% 9% 25% 31% 18% 3	775
	21st to end	Day	18% 8% 22% 29% 18% 5%	844
June	1st to 10th	Day	19% 10% 28% 29% 12% 3	780
	11th to 20th	Day	19% 9% 25% 28% 14% 5%	795
	21st to end	Day	13% 5% 24% 32% 20% 7%	990
July	1st to 10th	Day	13% 4 22% 33% 22% 6%	731
	11th to 20th	Day	16% 5% 20% 33% 22% 5%	718
	21st to end	Day	10% 6% 24% 31% 21% 7%	742
August	1st to 10th	Day	12% 7% 23% 30% 20% 8%	527
	11th to 20th	Day	9% 6% 26% 32% 22% 4	517
	21st to end	Day	12% 7% 24% 29% 21% 7%	583
September	1st to 10th	Day	16% 7% 26% 27% 15% 9%	530
	11th to 20th	Day	17% 6% 20% 32% 18% 7%	530
	21st to end	Day	14% 10% 31% 28% 13% 4	530
October	1st to 10th	Day	15% 7% 25% 30% 17% 6%	467
	11th to 20th	Day	12% 9% 31% 30% 14% 4	330
	21st to end	Day	13% 12% 30% 32% 11% 2	363
November	1st to 10th	Day	17% 7% 28% 31% 16% 2	330
	11th to 20th	Day	13% 9% 28% 36% 11% 3	234
	21st to end	Day	5% 9% 33% 32% 13% 8%	220
December	1st to 10th	Day	9% 9% 28% 32% 17% 4	220
	11th to 20th	Day	9% 15% 35% 24% 14% 5%	220
	21st to end	Day	7% 7% 24% 34% 22% 6%	242
January	1st to 10th	Night	9% 8% 34% 34% 14% 1	1050
	11th to 20th	Night	10% 9% 32% 37% 11% 1	1050
	21st to end	Night	10% 9% 33% 35% 11% 1	934
February	1st to 10th	Night	11% 9% 25% 36% 17% 3	840
	11th to 20th	Night	9% 7% 31% 38% 14% 1	824
	21st to end	Night	7% 5% 27% 42% 16% 4	692
March	1st to 10th	Night	9% 6% 30% 40% 13% 3	840
	11th to 20th	Night	9% 6% 31% 40% 12% 2	840
	21st to end	Night	13% 6% 27% 39% 13% 2	924
April	1st to 10th	Night	13% 8% 30% 35% 14% 2	800
	11th to 20th	Night	16% 6% 32% 35% 10% 1	623
	21st to end	Night	18% 10% 27% 33% 12%	630
May	1st to 10th	Night	19% 8% 24% 33% 14% 2	426
	11th to 20th	Night	14% 6% 24% 39% 16% 1	414
	21st to end	Night	21% 4 24% 32% 18% 1	455
June	1st to 10th	Night	21% 6% 24% 34% 14% 1	420
	11th to 20th	Night	20% 5% 22% 35% 17% 1	420
	21st to end	Night	14% 3 20% 36% 23% 2	420
July	1st to 10th	Night	14% 2 16% 44% 22% 2	390
	11th to 20th	Night	13% 4 21% 40% 20% 1	388
	21st to end	Night	10% 4 16% 42% 27% 2	438
August	1st to 10th	Night	13% 1 16% 36% 31% 3	398
	11th to 20th	Night	14% 4 14% 42% 25% 2	486
	21st to end	Night	12% 2 21% 41% 23% 1	660
September	1st to 10th	Night	15% 2 18% 41% 22% 2	728
	11th to 20th	Night	18% 4 17% 36% 24% 2	800
	21st to end	Night	12% 5% 30% 37% 15% 2	800
October	1st to 10th	Night	15% 3 27% 39% 16% 2	800
	11th to 20th	Night	12% 5% 30% 37% 14% 2	800
	21st to end	Night	10% 11% 30% 38% 10% 1	880
November	1st to 10th	Night	16% 7% 30% 34% 11% 2	935
	11th to 20th	Night	11% 6% 38% 33% 11% 1	1050
	21st to end	Night	9% 7% 34% 36% 12% 2	1050
December	1st to 10th	Night	12% 6% 34% 34% 12% 2	1050
	11th to 20th	Night	8% 8% 34% 38% 11% 1	1050
	21st to end	Night	10% 5% 32% 36% 15% 2	1155

Page generated at 2026-06-28 00:10:48. Version ac07

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