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 2024-02-05.

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	10% 9% 4 7% 7% 4 6% 6% 7% 8% 33%	77876
	Night	7% 10% 4 8% 7% 4 6% 6% 6% 8% 34%	80927
Transparency	Day	45% 10% 16% 20% 8% 1	77580
	Night	45% 9% 14% 20% 9% 2	80803
Seeing	Day	14% 9% 28% 30% 16% 4	14437
	Night	13% 6% 28% 37% 15% 2	23454

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% 7% 13% 8% 3 4 5% 6% 9% 31%	2219
	11th to 20th	Day	3 8% 5% 9% 7% 4 6% 9% 6% 9% 34%	2207
	21st to end	Day	5% 9% 4 8% 8% 5% 5% 6% 7% 9% 35%	2794
February	1st to 10th	Day	6% 14% 4 8% 9% 5% 6% 6% 7% 7% 29%	1472
	11th to 20th	Day	4 14% 7% 10% 8% 5% 5% 6% 6% 8% 26%	1502
	21st to end	Day	4 8% 6% 12% 9% 5% 8% 6% 6% 7% 29%	1453
March	1st to 10th	Day	5% 10% 6% 10% 10% 5% 6% 6% 6% 6% 30%	1800
	11th to 20th	Day	5% 9% 4 8% 8% 3 7% 6% 7% 9% 34%	1919
	21st to end	Day	7% 14% 6% 9% 7% 4 6% 6% 7% 8% 26%	2257
April	1st to 10th	Day	7% 11% 6% 9% 8% 4 7% 7% 8% 7% 25%	2194
	11th to 20th	Day	12% 15% 5% 7% 7% 4 6% 6% 6% 7% 25%	2310
	21st to end	Day	11% 10% 4 8% 6% 5% 6% 7% 6% 9% 29%	2340
May	1st to 10th	Day	13% 11% 4 8% 7% 4 7% 5% 7% 8% 26%	2557
	11th to 20th	Day	9% 7% 3 7% 6% 4 6% 6% 7% 10% 35%	2654
	21st to end	Day	20% 8% 4 6% 6% 4 5% 6% 6% 8% 28%	2917
June	1st to 10th	Day	18% 7% 3 5% 6% 4 7% 7% 8% 8% 26%	2700
	11th to 20th	Day	18% 9% 3 8% 8% 5% 6% 6% 6% 8% 23%	2712
	21st to end	Day	10% 5% 3 6% 6% 4 6% 6% 8% 10% 35%	2880
July	1st to 10th	Day	11% 7% 3 5% 6% 5% 6% 7% 8% 10% 33%	2709
	11th to 20th	Day	11% 5% 3 5% 5% 3 6% 7% 8% 10% 35%	2700
	21st to end	Day	9% 4 3 4 6% 3 6% 7% 8% 9% 42%	2892
August	1st to 10th	Day	11% 5% 3 5% 5% 3 7% 6% 7% 9% 38%	2507
	11th to 20th	Day	10% 4 2 4 6% 4 6% 6% 7% 9% 43%	2395
	21st to end	Day	11% 6% 2 6% 6% 3 6% 5% 6% 9% 41%	2574
September	1st to 10th	Day	13% 6% 3 5% 4 2 4 5% 6% 9% 41%	2224
	11th to 20th	Day	15% 8% 3 6% 5% 2 5% 4 5% 7% 42%	2005
	21st to end	Day	12% 8% 2 6% 5% 3 4 5% 6% 9% 41%	1980
October	1st to 10th	Day	12% 9% 4 6% 5% 3 4 5% 6% 7% 39%	1911
	11th to 20th	Day	10% 9% 3 6% 6% 3 5% 5% 6% 7% 39%	1620
	21st to end	Day	9% 10% 4 8% 8% 3 5% 6% 5% 7% 34%	1782
November	1st to 10th	Day	7% 14% 7% 8% 5% 5% 5% 6% 6% 7% 30%	1552
	11th to 20th	Day	5% 11% 5% 11% 6% 3 4 5% 5% 8% 37%	1354
	21st to end	Day	6% 8% 5% 9% 8% 3 6% 6% 5% 9% 34%	1330
December	1st to 10th	Day	5% 13% 6% 11% 8% 4 7% 6% 5% 7% 29%	1330
	11th to 20th	Day	4 10% 5% 11% 9% 5% 7% 6% 6% 8% 30%	1682
	21st to end	Day	4 10% 4 9% 7% 3 5% 5% 6% 9% 38%	2442
January	1st to 10th	Night	3 12% 7% 12% 9% 5% 7% 6% 6% 7% 27%	4726
	11th to 20th	Night	3 10% 5% 10% 9% 4 5% 7% 7% 7% 31%	4699
	21st to end	Night	4 11% 5% 8% 7% 5% 7% 6% 7% 9% 31%	4885
February	1st to 10th	Night	7% 11% 6% 11% 9% 4 6% 5% 5% 8% 28%	2582
	11th to 20th	Night	4 13% 6% 10% 9% 5% 7% 7% 7% 7% 26%	2345
	21st to end	Night	3 11% 6% 9% 8% 4 8% 5% 5% 7% 35%	1801
March	1st to 10th	Night	4 11% 5% 8% 9% 5% 7% 5% 7% 10% 29%	2160
	11th to 20th	Night	5% 12% 5% 8% 6% 4 5% 7% 8% 10% 31%	2039
	21st to end	Night	6% 13% 6% 9% 7% 4 6% 6% 7% 9% 28%	2098
April	1st to 10th	Night	7% 11% 5% 8% 8% 5% 6% 6% 6% 10% 28%	1766
	11th to 20th	Night	11% 12% 5% 9% 7% 4 5% 4 5% 7% 29%	1601
	21st to end	Night	12% 9% 4 9% 6% 4 6% 5% 5% 6% 34%	1620
May	1st to 10th	Night	14% 12% 4 10% 6% 4 5% 5% 5% 6% 29%	1398
	11th to 20th	Night	11% 6% 3 6% 6% 4 5% 5% 7% 8% 39%	1239
	21st to end	Night	17% 9% 4 6% 5% 3 4 6% 7% 7% 32%	1358
June	1st to 10th	Night	19% 6% 3 8% 5% 3 5% 6% 8% 7% 31%	1260
	11th to 20th	Night	17% 8% 3 8% 7% 4 7% 6% 5% 8% 26%	1238
	21st to end	Night	11% 5% 4 6% 6% 3 5% 7% 8% 8% 39%	1080
July	1st to 10th	Night	12% 6% 2 5% 4 4 6% 6% 8% 9% 37%	1246
	11th to 20th	Night	12% 7% 3 5% 6% 3 5% 6% 7% 8% 39%	1260
	21st to end	Night	7% 4 3 5% 5% 3 5% 6% 6% 8% 49%	1423
August	1st to 10th	Night	12% 5% 2 4 7% 4 6% 5% 7% 9% 39%	1432
	11th to 20th	Night	10% 5% 2 6% 6% 4 4 5% 7% 10% 42%	1504
	21st to end	Night	12% 5% 2 5% 5% 3 4 5% 6% 8% 46%	1782
September	1st to 10th	Night	13% 6% 3 4 5% 3 5% 5% 5% 7% 44%	1734
	11th to 20th	Night	16% 8% 2 5% 4 2 4 5% 5% 7% 42%	1954
	21st to end	Night	10% 7% 3 5% 4 3 4 5% 7% 8% 44%	1980
October	1st to 10th	Night	10% 9% 2 7% 7% 3 4 4 6% 8% 41%	2046
	11th to 20th	Night	10% 9% 3 6% 6% 4 4 5% 6% 9% 37%	2340
	21st to end	Night	7% 11% 5% 8% 7% 4 6% 5% 6% 8% 33%	2574
November	1st to 10th	Night	9% 14% 5% 9% 6% 3 5% 5% 6% 8% 31%	2508
	11th to 20th	Night	6% 11% 5% 10% 6% 4 6% 5% 6% 8% 32%	2825
	21st to end	Night	4 10% 6% 10% 7% 4 6% 6% 7% 8% 31%	2850
December	1st to 10th	Night	7% 10% 5% 9% 8% 5% 6% 5% 5% 7% 33%	2850
	11th to 20th	Night	3 10% 5% 11% 11% 6% 7% 6% 5% 8% 28%	3510
	21st to end	Night	3 10% 4 8% 7% 3 5% 5% 6% 8% 42%	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	48% 6% 12% 22% 9% 2	2219
	11th to 20th	Day	44% 8% 11% 16% 19% 3	2228
	21st to end	Day	40% 10% 14% 28% 7%	2794
February	1st to 10th	Day	50% 7% 13% 19% 8% 3	1472
	11th to 20th	Day	54% 7% 14% 15% 8% 1	1510
	21st to end	Day	52% 7% 12% 18% 10% 1	1453
March	1st to 10th	Day	52% 10% 14% 16% 8% 1	1800
	11th to 20th	Day	42% 10% 14% 21% 12% 1	1920
	21st to end	Day	53% 9% 16% 15% 6% 1	2257
April	1st to 10th	Day	50% 13% 16% 16% 6%	2194
	11th to 20th	Day	54% 10% 11% 18% 7%	2310
	21st to end	Day	49% 10% 14% 20% 6% 2	2340
May	1st to 10th	Day	52% 10% 14% 18% 6%	2557
	11th to 20th	Day	41% 10% 17% 21% 11% 1	2658
	21st to end	Day	50% 10% 13% 19% 7%	2918
June	1st to 10th	Day	50% 11% 17% 17% 5% 1	2700
	11th to 20th	Day	57% 11% 15% 13% 4 1	2712
	21st to end	Day	39% 14% 19% 21% 6% 1	2880
July	1st to 10th	Day	40% 13% 21% 20% 6% 1	2635
	11th to 20th	Day	39% 12% 22% 22% 4	2619
	21st to end	Day	32% 13% 22% 27% 6%	2731
August	1st to 10th	Day	38% 11% 23% 24% 4	2490
	11th to 20th	Day	33% 11% 25% 22% 8% 1	2395
	21st to end	Day	37% 10% 19% 24% 9% 1	2574
September	1st to 10th	Day	37% 9% 22% 23% 7% 1	2224
	11th to 20th	Day	41% 8% 14% 26% 10% 1	2005
	21st to end	Day	39% 8% 17% 22% 12% 2	1980
October	1st to 10th	Day	41% 9% 17% 23% 9% 1	1911
	11th to 20th	Day	42% 7% 17% 21% 12% 1	1620
	21st to end	Day	48% 8% 12% 20% 11% 1	1782
November	1st to 10th	Day	51% 8% 13% 16% 9% 2	1552
	11th to 20th	Day	46% 7% 14% 22% 10% 1	1354
	21st to end	Day	46% 8% 17% 18% 9% 2	1330
December	1st to 10th	Day	53% 7% 12% 16% 9% 2	1330
	11th to 20th	Day	49% 10% 16% 17% 6% 2	1684
	21st to end	Day	39% 8% 11% 20% 18% 4	2442
January	1st to 10th	Night	52% 9% 12% 17% 8% 2	4726
	11th to 20th	Night	48% 7% 10% 15% 14% 6%	4740
	21st to end	Night	43% 12% 15% 21% 8% 1	4885
February	1st to 10th	Night	53% 7% 11% 18% 9% 2	2582
	11th to 20th	Night	53% 9% 12% 16% 9% 1	2347
	21st to end	Night	45% 7% 12% 21% 12% 2	1801
March	1st to 10th	Night	46% 10% 13% 22% 7% 1	2160
	11th to 20th	Night	45% 9% 13% 19% 13% 1	2039
	21st to end	Night	49% 9% 14% 18% 8% 1	2098
April	1st to 10th	Night	49% 9% 15% 18% 9% 1	1766
	11th to 20th	Night	52% 6% 13% 19% 7% 1	1601
	21st to end	Night	48% 9% 14% 23% 6% 1	1620
May	1st to 10th	Night	53% 9% 15% 16% 7%	1398
	11th to 20th	Night	41% 8% 15% 24% 13%	1239
	21st to end	Night	48% 8% 16% 19% 7% 2	1358
June	1st to 10th	Night	48% 11% 15% 19% 7%	1260
	11th to 20th	Night	54% 10% 15% 16% 4 1	1238
	21st to end	Night	40% 10% 19% 24% 7%	1080
July	1st to 10th	Night	38% 13% 20% 24% 5% 1	1211
	11th to 20th	Night	40% 13% 19% 21% 7% 1	1218
	21st to end	Night	30% 11% 22% 28% 8% 1	1344
August	1st to 10th	Night	37% 14% 22% 22% 5%	1424
	11th to 20th	Night	35% 11% 22% 24% 7% 1	1504
	21st to end	Night	35% 9% 18% 25% 12% 1	1782
September	1st to 10th	Night	37% 8% 18% 25% 11% 2	1734
	11th to 20th	Night	41% 8% 14% 25% 9% 3	1954
	21st to end	Night	35% 8% 16% 24% 12% 3	1980
October	1st to 10th	Night	40% 8% 17% 23% 10% 1	2046
	11th to 20th	Night	41% 9% 16% 23% 10% 2	2340
	21st to end	Night	46% 9% 16% 20% 9% 1	2574
November	1st to 10th	Night	50% 7% 12% 19% 10% 2	2508
	11th to 20th	Night	48% 7% 15% 18% 11% 1	2825
	21st to end	Night	47% 9% 15% 19% 7% 3	2850
December	1st to 10th	Night	48% 7% 11% 20% 11% 3	2850
	11th to 20th	Night	51% 10% 13% 20% 6% 1	3507
	21st to end	Night	37% 8% 13% 22% 15% 5%	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	5% 6% 31% 27% 21% 10%	180
	11th to 20th	Day	6% 8% 31% 36% 15% 4	180
	21st to end	Day	11% 7% 33% 30% 13% 6%	198
February	1st to 10th	Day	14% 13% 29% 30% 10% 5%	168
	11th to 20th	Day	14% 10% 31% 34% 10% 1	206
	21st to end	Day	6% 8% 31% 35% 18% 3	319
March	1st to 10th	Day	10% 12% 37% 26% 11% 4	420
	11th to 20th	Day	8% 10% 38% 26% 14% 4	420
	21st to end	Day	16% 12% 33% 26% 10% 4	462
April	1st to 10th	Day	10% 17% 34% 26% 10% 3	420
	11th to 20th	Day	18% 11% 28% 25% 14% 4	412
	21st to end	Day	17% 11% 31% 26% 12% 3	420
May	1st to 10th	Day	17% 14% 25% 24% 16% 3	470
	11th to 20th	Day	13% 8% 25% 32% 20% 3	625
	21st to end	Day	20% 7% 23% 29% 17% 5%	679
June	1st to 10th	Day	20% 7% 29% 30% 11% 3	630
	11th to 20th	Day	20% 9% 26% 28% 14% 4	642
	21st to end	Day	13% 5% 24% 33% 19% 5%	810
July	1st to 10th	Day	13% 4 23% 33% 21% 6%	630
	11th to 20th	Day	16% 5% 22% 32% 21% 3	618
	21st to end	Day	9% 6% 25% 33% 21% 7%	638
August	1st to 10th	Day	13% 7% 23% 30% 19% 7%	447
	11th to 20th	Day	8% 6% 28% 32% 22% 4	437
	21st to end	Day	13% 7% 26% 31% 18% 5%	495
September	1st to 10th	Day	18% 8% 29% 27% 13% 5%	450
	11th to 20th	Day	18% 6% 22% 32% 15% 6%	450
	21st to end	Day	15% 10% 30% 27% 14% 4	450
October	1st to 10th	Day	15% 8% 26% 28% 17% 5%	394
	11th to 20th	Day	13% 10% 31% 27% 14% 4	270
	21st to end	Day	15% 13% 29% 30% 11% 1	297
November	1st to 10th	Day	18% 7% 28% 29% 16% 3	270
	11th to 20th	Day	14% 9% 29% 35% 10% 3	192
	21st to end	Day	4 8% 36% 33% 11% 8%	180
December	1st to 10th	Day	9% 8% 28% 30% 19% 4	180
	11th to 20th	Day	8% 16% 34% 23% 14% 4	180
	21st to end	Day	6% 7% 27% 33% 22% 5%	198
January	1st to 10th	Night	10% 8% 34% 33% 14% 2	950
	11th to 20th	Night	11% 8% 30% 38% 12% 1	950
	21st to end	Night	11% 9% 32% 35% 11% 2	846
February	1st to 10th	Night	12% 10% 26% 34% 16% 2	738
	11th to 20th	Night	10% 8% 32% 37% 13% 1	704
	21st to end	Night	7% 4 24% 43% 17% 5%	592
March	1st to 10th	Night	10% 6% 30% 39% 12% 3	720
	11th to 20th	Night	10% 5% 30% 40% 12% 3	720
	21st to end	Night	12% 5% 27% 39% 14% 3	792
April	1st to 10th	Night	12% 7% 29% 36% 14% 2	686
	11th to 20th	Night	17% 7% 31% 33% 11% 1	533
	21st to end	Night	19% 9% 27% 32% 13%	540
May	1st to 10th	Night	19% 8% 25% 32% 14% 2	366
	11th to 20th	Night	14% 5% 23% 40% 17% 1	354
	21st to end	Night	22% 4 25% 33% 16% 1	389
June	1st to 10th	Night	21% 5% 23% 35% 15% 1	360
	11th to 20th	Night	21% 4 22% 34% 17% 1	360
	21st to end	Night	13% 3 20% 37% 24% 2	360
July	1st to 10th	Night	15% 1 16% 43% 23% 2	350
	11th to 20th	Night	13% 4 21% 42% 18% 1	348
	21st to end	Night	8% 4 16% 44% 26% 2	394
August	1st to 10th	Night	13% 1 16% 36% 31% 3	358
	11th to 20th	Night	13% 4 13% 42% 26% 2	436
	21st to end	Night	12% 2 21% 41% 22% 1	594
September	1st to 10th	Night	17% 2 19% 40% 21% 2	654
	11th to 20th	Night	19% 4 18% 36% 21% 2	720
	21st to end	Night	12% 5% 29% 37% 16% 2	720
October	1st to 10th	Night	16% 3 26% 38% 16% 2	720
	11th to 20th	Night	12% 5% 29% 38% 14% 2	720
	21st to end	Night	11% 11% 30% 37% 11% 1	792
November	1st to 10th	Night	16% 8% 29% 34% 12% 2	843
	11th to 20th	Night	11% 6% 38% 33% 10% 1	950
	21st to end	Night	8% 7% 35% 35% 11% 2	950
December	1st to 10th	Night	12% 6% 32% 34% 13% 2	950
	11th to 20th	Night	7% 7% 33% 39% 12% 2	950
	21st to end	Night	10% 5% 32% 36% 15% 2	1045

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