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 2025-02-25.

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%	112434
	Night	7% 10% 4 10% 6% 5% 5% 4 6% 8% 33%	114886
Transparency	Day	44% 9% 16% 22% 9% 1	112180
	Night	46% 8% 14% 21% 9% 2	114786
Seeing	Day	13% 9% 28% 30% 16% 5%	15813
	Night	12% 6% 28% 37% 15% 2	24820

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 11% 6% 14% 8% 5% 6% 4 6% 7% 30%	3179
	11th to 20th	Day	2 8% 4 11% 7% 6% 7% 5% 7% 9% 34%	3181
	21st to end	Day	3 9% 3 9% 6% 6% 6% 5% 7% 9% 37%	4004
February	1st to 10th	Day	5% 14% 4 11% 8% 6% 6% 5% 7% 7% 28%	1600
	11th to 20th	Day	3 14% 6% 13% 7% 6% 5% 5% 6% 7% 27%	1673
	21st to end	Day	3 9% 6% 12% 9% 7% 7% 5% 6% 8% 29%	1581
March	1st to 10th	Day	3 10% 5% 13% 8% 6% 6% 5% 6% 7% 31%	3138
	11th to 20th	Day	5% 10% 3 6% 5% 4 5% 4 7% 10% 40%	3390
	21st to end	Day	6% 20% 7% 12% 5% 4 5% 4 6% 6% 24%	3968
April	1st to 10th	Day	7% 13% 4 11% 7% 5% 7% 5% 8% 7% 26%	2316
	11th to 20th	Day	11% 15% 4 9% 6% 5% 6% 5% 6% 8% 26%	2440
	21st to end	Day	11% 11% 4 9% 5% 6% 6% 5% 7% 8% 28%	2470
May	1st to 10th	Day	16% 12% 4 9% 5% 5% 5% 4 6% 7% 27%	4499
	11th to 20th	Day	10% 10% 4 10% 6% 6% 7% 5% 8% 9% 26%	4694
	21st to end	Day	17% 10% 4 11% 7% 6% 7% 5% 6% 7% 21%	5161
June	1st to 10th	Day	18% 8% 3 6% 6% 6% 6% 6% 8% 8% 26%	2850
	11th to 20th	Day	18% 10% 3 9% 7% 6% 5% 5% 6% 8% 23%	2863
	21st to end	Day	10% 5% 3 7% 6% 6% 6% 5% 8% 9% 34%	3040
July	1st to 10th	Day	8% 5% 2 6% 5% 5% 5% 5% 7% 8% 45%	4749
	11th to 20th	Day	8% 4 2 5% 4 4 5% 5% 7% 10% 46%	4740
	21st to end	Day	8% 5% 2 6% 5% 4 5% 5% 7% 9% 43%	5053
August	1st to 10th	Day	11% 5% 3 6% 4 4 5% 4 6% 9% 43%	4401
	11th to 20th	Day	9% 5% 2 6% 5% 5% 6% 5% 8% 11% 38%	4185
	21st to end	Day	10% 6% 2 7% 4 4 5% 4 6% 9% 42%	4521
September	1st to 10th	Day	13% 6% 3 5% 3 3 4 4 7% 9% 42%	2347
	11th to 20th	Day	14% 9% 3 6% 4 4 4 2 5% 7% 42%	2116
	21st to end	Day	11% 8% 2 6% 4 4 3 4 7% 9% 41%	2090
October	1st to 10th	Day	8% 8% 3 7% 4 4 4 5% 6% 9% 41%	3352
	11th to 20th	Day	8% 9% 3 8% 6% 5% 6% 4 7% 8% 35%	2842
	21st to end	Day	7% 9% 3 9% 7% 5% 5% 4 5% 6% 40%	3101
November	1st to 10th	Day	7% 15% 6% 9% 5% 6% 5% 4 6% 8% 30%	1635
	11th to 20th	Day	5% 12% 5% 13% 4 4 4 4 5% 7% 36%	1425
	21st to end	Day	6% 10% 4 11% 8% 4 6% 4 5% 9% 32%	1400
December	1st to 10th	Day	4 12% 5% 12% 8% 7% 7% 5% 7% 8% 25%	2290
	11th to 20th	Day	5% 11% 4 12% 8% 7% 7% 5% 7% 8% 28%	2642
	21st to end	Day	3 11% 4 11% 6% 5% 6% 4 6% 8% 37%	3498
January	1st to 10th	Night	3 13% 8% 15% 9% 7% 6% 4 6% 6% 25%	6766
	11th to 20th	Night	2 9% 4 14% 8% 6% 5% 5% 6% 7% 33%	6739
	21st to end	Night	3 10% 4 9% 5% 6% 6% 5% 8% 10% 35%	6975
February	1st to 10th	Night	6% 12% 5% 13% 8% 7% 6% 4 6% 8% 26%	2800
	11th to 20th	Night	4 13% 5% 12% 9% 6% 7% 5% 6% 7% 27%	2614
	21st to end	Night	3 12% 5% 11% 6% 6% 7% 4 6% 7% 34%	1965
March	1st to 10th	Night	2 9% 4 14% 8% 7% 7% 5% 7% 10% 27%	3736
	11th to 20th	Night	5% 11% 3 7% 5% 5% 5% 6% 8% 10% 36%	3588
	21st to end	Night	6% 17% 7% 15% 6% 6% 5% 4 6% 7% 21%	3684
April	1st to 10th	Night	7% 12% 3 9% 7% 7% 6% 5% 7% 10% 28%	1864
	11th to 20th	Night	10% 13% 5% 10% 6% 6% 4 4 5% 7% 29%	1691
	21st to end	Night	12% 10% 5% 10% 5% 5% 5% 4 5% 7% 33%	1710
May	1st to 10th	Night	20% 15% 4 9% 5% 4 4 3 4 5% 26%	2456
	11th to 20th	Night	10% 8% 3 9% 6% 6% 6% 5% 9% 9% 30%	2199
	21st to end	Night	16% 11% 4 9% 6% 6% 6% 5% 8% 7% 22%	2414
June	1st to 10th	Night	18% 8% 2 9% 4 4 4 5% 8% 7% 31%	1330
	11th to 20th	Night	16% 9% 3 8% 7% 5% 7% 5% 5% 8% 27%	1306
	21st to end	Night	11% 5% 3 6% 5% 4 5% 5% 8% 8% 39%	1140
July	1st to 10th	Night	10% 8% 3 7% 5% 6% 5% 4 6% 7% 39%	2206
	11th to 20th	Night	7% 4 2 5% 5% 3 5% 5% 7% 8% 49%	2220
	21st to end	Night	7% 6% 2 6% 5% 4 4 4 6% 9% 47%	2497
August	1st to 10th	Night	13% 6% 2 5% 4 4 5% 3 6% 8% 43%	2529
	11th to 20th	Night	11% 6% 3 7% 5% 4 5% 5% 7% 11% 35%	2647
	21st to end	Night	14% 6% 2 6% 4 3 4 3 5% 7% 45%	3146
September	1st to 10th	Night	12% 6% 2 5% 4 4 5% 4 5% 7% 45%	1831
	11th to 20th	Night	15% 8% 2 6% 3 3 5% 4 6% 7% 41%	2063
	21st to end	Night	10% 7% 3 6% 3 4 4 4 7% 8% 44%	2090
October	1st to 10th	Night	6% 7% 2 8% 5% 5% 6% 4 7% 10% 42%	3621
	11th to 20th	Night	8% 9% 3 7% 5% 5% 4 4 6% 9% 39%	4086
	21st to end	Night	6% 9% 4 8% 6% 5% 6% 4 7% 8% 38%	4457
November	1st to 10th	Night	8% 15% 4 10% 5% 4 5% 4 6% 8% 31%	2644
	11th to 20th	Night	5% 12% 5% 11% 6% 6% 5% 4 6% 8% 31%	2974
	21st to end	Night	4 12% 5% 12% 6% 6% 5% 4 7% 8% 30%	3000
December	1st to 10th	Night	7% 14% 5% 10% 7% 7% 6% 4 6% 7% 27%	4890
	11th to 20th	Night	4 14% 5% 15% 9% 7% 6% 4 6% 7% 23%	5550
	21st to end	Night	3 10% 4 11% 6% 5% 5% 4 6% 7% 38%	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	52% 6% 10% 20% 10% 2	3179
	11th to 20th	Day	45% 7% 11% 15% 19% 3	3202
	21st to end	Day	39% 8% 13% 30% 9%	4004
February	1st to 10th	Day	51% 7% 13% 18% 9% 3	1600
	11th to 20th	Day	53% 7% 13% 16% 9% 2	1681
	21st to end	Day	51% 8% 11% 18% 10% 1	1581
March	1st to 10th	Day	49% 9% 15% 15% 12% 1	3138
	11th to 20th	Day	34% 10% 18% 22% 16% 1	3391
	21st to end	Day	57% 8% 14% 13% 7% 1	3968
April	1st to 10th	Day	49% 13% 16% 16% 6%	2316
	11th to 20th	Day	53% 10% 12% 18% 7%	2440
	21st to end	Day	49% 10% 14% 20% 6% 1	2470
May	1st to 10th	Day	52% 10% 11% 22% 6%	4499
	11th to 20th	Day	46% 12% 15% 18% 8%	4698
	21st to end	Day	53% 15% 12% 14% 6% 1	5162
June	1st to 10th	Day	49% 11% 16% 16% 5% 2	2850
	11th to 20th	Day	56% 11% 14% 14% 4 1	2863
	21st to end	Day	39% 13% 19% 20% 7% 1	3040
July	1st to 10th	Day	32% 9% 16% 26% 14% 3	4675
	11th to 20th	Day	30% 8% 19% 35% 7% 1	4659
	21st to end	Day	32% 9% 17% 26% 13% 2	4893
August	1st to 10th	Day	36% 8% 20% 30% 6%	4384
	11th to 20th	Day	35% 10% 21% 25% 9%	4227
	21st to end	Day	36% 8% 23% 26% 6% 1	4520
September	1st to 10th	Day	36% 9% 22% 23% 9% 2	2347
	11th to 20th	Day	41% 8% 14% 27% 10% 1	2116
	21st to end	Day	38% 8% 16% 23% 12% 2	2090
October	1st to 10th	Day	38% 7% 21% 28% 5% 1	3352
	11th to 20th	Day	44% 6% 17% 20% 12% 1	2842
	21st to end	Day	44% 6% 11% 31% 8% 1	3101
November	1st to 10th	Day	51% 8% 14% 16% 9% 2	1635
	11th to 20th	Day	47% 7% 14% 22% 10% 1	1425
	21st to end	Day	48% 8% 16% 18% 8% 2	1400
December	1st to 10th	Day	55% 6% 16% 16% 5% 1	2290
	11th to 20th	Day	52% 8% 19% 16% 5% 1	2644
	21st to end	Day	42% 6% 10% 22% 17% 3	3498
January	1st to 10th	Night	57% 7% 10% 18% 7% 2	6766
	11th to 20th	Night	48% 6% 12% 16% 14% 4	6780
	21st to end	Night	39% 10% 17% 24% 9% 1	6975
February	1st to 10th	Night	55% 6% 10% 18% 10% 2	2800
	11th to 20th	Night	52% 8% 12% 16% 11% 1	2616
	21st to end	Night	45% 7% 12% 21% 12% 2	1965
March	1st to 10th	Night	46% 12% 12% 21% 8%	3736
	11th to 20th	Night	36% 13% 17% 21% 12% 1	3588
	21st to end	Night	58% 11% 11% 14% 5% 1	3684
April	1st to 10th	Night	48% 9% 15% 18% 9%	1864
	11th to 20th	Night	52% 7% 14% 19% 8% 1	1691
	21st to end	Night	48% 9% 14% 22% 6% 1	1710
May	1st to 10th	Night	56% 9% 12% 18% 5%	2456
	11th to 20th	Night	40% 13% 16% 22% 9%	2199
	21st to end	Night	51% 15% 14% 14% 5% 1	2414
June	1st to 10th	Night	48% 10% 15% 19% 8% 1	1330
	11th to 20th	Night	53% 9% 14% 17% 5% 1	1306
	21st to end	Night	40% 9% 20% 23% 7%	1140
July	1st to 10th	Night	40% 10% 14% 21% 12% 3	2171
	11th to 20th	Night	30% 10% 20% 29% 8% 4	2178
	21st to end	Night	33% 7% 16% 30% 13% 1	2418
August	1st to 10th	Night	36% 10% 18% 30% 6%	2521
	11th to 20th	Night	39% 10% 22% 23% 6% 1	2671
	21st to end	Night	38% 7% 19% 28% 8% 1	3146
September	1st to 10th	Night	37% 8% 17% 24% 12% 2	1831
	11th to 20th	Night	41% 8% 14% 24% 9% 3	2063
	21st to end	Night	35% 8% 17% 24% 13% 3	2090
October	1st to 10th	Night	36% 7% 19% 27% 10% 1	3621
	11th to 20th	Night	40% 7% 16% 28% 8% 1	4086
	21st to end	Night	42% 7% 15% 27% 8%	4457
November	1st to 10th	Night	50% 7% 13% 20% 9% 1	2644
	11th to 20th	Night	49% 7% 15% 18% 11% 1	2974
	21st to end	Night	48% 8% 15% 19% 7% 3	3000
December	1st to 10th	Night	55% 5% 14% 17% 7% 2	4890
	11th to 20th	Night	59% 8% 12% 15% 6% 1	5547
	21st to end	Night	42% 6% 10% 23% 15% 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	6% 6% 31% 27% 21% 11%	200
	11th to 20th	Day	6% 8% 31% 39% 14% 4	200
	21st to end	Day	10% 9% 32% 30% 14% 5%	220
February	1st to 10th	Day	12% 13% 27% 33% 12% 5%	200
	11th to 20th	Day	11% 9% 32% 33% 13% 3	257
	21st to end	Day	5% 8% 34% 33% 17% 2	369
March	1st to 10th	Day	9% 13% 36% 28% 11% 3	460
	11th to 20th	Day	8% 9% 38% 26% 15% 4	460
	21st to end	Day	16% 11% 33% 26% 10% 4	506
April	1st to 10th	Day	10% 18% 34% 25% 10% 2	460
	11th to 20th	Day	16% 12% 29% 25% 14% 4	452
	21st to end	Day	17% 11% 30% 27% 12% 3	460
May	1st to 10th	Day	19% 13% 25% 25% 16% 3	513
	11th to 20th	Day	12% 9% 26% 31% 19% 3	675
	21st to end	Day	19% 8% 23% 29% 17% 5%	734
June	1st to 10th	Day	19% 9% 30% 29% 11% 3	680
	11th to 20th	Day	19% 9% 26% 28% 14% 5%	693
	21st to end	Day	13% 5% 25% 33% 19% 5%	870
July	1st to 10th	Day	13% 4 22% 33% 22% 6%	680
	11th to 20th	Day	16% 5% 20% 32% 22% 4	668
	21st to end	Day	9% 6% 25% 32% 21% 7%	690
August	1st to 10th	Day	12% 7% 23% 30% 20% 8%	487
	11th to 20th	Day	9% 6% 26% 32% 22% 5%	477
	21st to end	Day	13% 7% 26% 30% 19% 5%	539
September	1st to 10th	Day	17% 7% 28% 27% 13% 8%	490
	11th to 20th	Day	19% 6% 22% 31% 16% 7%	490
	21st to end	Day	14% 10% 30% 28% 13% 4	490
October	1st to 10th	Day	15% 8% 26% 29% 17% 5%	430
	11th to 20th	Day	12% 10% 31% 29% 14% 4	300
	21st to end	Day	14% 12% 28% 31% 12% 2	330
November	1st to 10th	Day	17% 6% 27% 30% 17% 3	300
	11th to 20th	Day	14% 9% 29% 35% 10% 3	213
	21st to end	Day	5% 8% 35% 32% 12% 9%	200
December	1st to 10th	Day	9% 8% 28% 32% 19% 5%	200
	11th to 20th	Day	9% 15% 33% 24% 15% 6%	200
	21st to end	Day	6% 6% 25% 33% 23% 7%	220
January	1st to 10th	Night	9% 8% 34% 33% 14% 2	1000
	11th to 20th	Night	11% 8% 31% 37% 11% 1	1000
	21st to end	Night	11% 9% 33% 35% 11% 2	890
February	1st to 10th	Night	11% 10% 25% 35% 17% 3	800
	11th to 20th	Night	9% 7% 32% 38% 14% 1	784
	21st to end	Night	7% 5% 25% 42% 17% 4	646
March	1st to 10th	Night	9% 6% 30% 39% 12% 3	760
	11th to 20th	Night	10% 5% 30% 40% 12% 3	760
	21st to end	Night	12% 6% 27% 39% 14% 3	836
April	1st to 10th	Night	12% 8% 30% 35% 13% 2	724
	11th to 20th	Night	16% 7% 32% 34% 11% 1	563
	21st to end	Night	18% 10% 27% 32% 13%	570
May	1st to 10th	Night	19% 9% 25% 31% 14% 2	386
	11th to 20th	Night	14% 5% 24% 40% 17% 1	374
	21st to end	Night	22% 5% 25% 32% 16% 1	411
June	1st to 10th	Night	21% 7% 24% 33% 14% 1	380
	11th to 20th	Night	20% 4 23% 35% 16% 1	380
	21st to end	Night	13% 3 21% 37% 23% 2	380
July	1st to 10th	Night	15% 2 15% 44% 22% 2	370
	11th to 20th	Night	13% 4 21% 42% 20% 1	368
	21st to end	Night	8% 4 17% 43% 26% 2	416
August	1st to 10th	Night	13% 1 16% 36% 31% 3	378
	11th to 20th	Night	14% 4 13% 41% 26% 2	461
	21st to end	Night	13% 2 21% 41% 22% 1	627
September	1st to 10th	Night	16% 2 19% 40% 22% 2	691
	11th to 20th	Night	19% 4 18% 36% 22% 2	760
	21st to end	Night	12% 5% 30% 37% 15% 2	760
October	1st to 10th	Night	15% 3 27% 38% 16% 1	760
	11th to 20th	Night	12% 5% 29% 38% 14% 2	760
	21st to end	Night	11% 11% 28% 38% 11% 1	836
November	1st to 10th	Night	16% 8% 28% 35% 12% 2	889
	11th to 20th	Night	11% 6% 39% 32% 10% 1	1000
	21st to end	Night	9% 7% 35% 36% 12% 2	1000
December	1st to 10th	Night	12% 6% 32% 35% 13% 2	1000
	11th to 20th	Night	8% 8% 33% 39% 12% 2	1000
	21st to end	Night	10% 5% 32% 36% 15% 2	1100

Page generated at 2025-02-22 04:51:35. Version ac07

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