Valemount
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Valemount clear sky chart from 2005-11-06 to 2025-01-07.

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% 14% 5% 13% 8% 6% 6% 4 6% 6% 24%	108528
	Night	7% 16% 6% 15% 8% 7% 6% 4 5% 6% 19%	109084
Transparency	Day	62% 4 12% 15% 6% 1	108268
	Night	66% 4 11% 13% 5% 1	108991
Seeing	Day	17% 18% 28% 23% 11% 2	16300
	Night	16% 15% 32% 26% 11% 1	24643

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	4 22% 10% 26% 11% 6% 4 4 4 4 6%	1935
	11th to 20th	Day	3 18% 7% 17% 7% 5% 4 3 5% 6% 25%	2179
	21st to end	Day	12% 27% 8% 16% 9% 5% 5% 3 4 4 8%	2771
February	1st to 10th	Day	5% 18% 7% 16% 9% 8% 7% 5% 5% 6% 16%	1520
	11th to 20th	Day	3 13% 7% 16% 10% 7% 6% 5% 6% 6% 19%	1608
	21st to end	Day	2 13% 6% 17% 10% 8% 9% 5% 5% 5% 20%	1513
March	1st to 10th	Day	2 13% 6% 17% 10% 8% 7% 6% 6% 8% 17%	3138
	11th to 20th	Day	3 14% 5% 14% 9% 9% 7% 4 6% 6% 24%	3290
	21st to end	Day	2 15% 7% 16% 8% 6% 6% 5% 6% 6% 21%	4151
April	1st to 10th	Day	5% 20% 6% 16% 10% 8% 7% 5% 6% 5% 11%	2280
	11th to 20th	Day	6% 18% 6% 15% 8% 6% 6% 4 7% 6% 18%	2341
	21st to end	Day	7% 16% 6% 13% 9% 6% 6% 5% 6% 7% 19%	2660
May	1st to 10th	Day	6% 15% 6% 13% 8% 7% 7% 4 5% 6% 22%	4420
	11th to 20th	Day	11% 13% 5% 12% 7% 7% 6% 5% 6% 7% 21%	4472
	21st to end	Day	17% 20% 6% 12% 7% 5% 5% 4 4 5% 16%	5307
June	1st to 10th	Day	18% 14% 4 11% 6% 5% 5% 4 6% 6% 20%	3040
	11th to 20th	Day	20% 16% 5% 11% 8% 6% 5% 5% 4 5% 14%	3040
	21st to end	Day	15% 11% 4 10% 8% 7% 6% 4 6% 6% 23%	3040
July	1st to 10th	Day	9% 8% 3 6% 5% 4 4 4 5% 6% 46%	5060
	11th to 20th	Day	7% 5% 2 6% 4 4 4 3 5% 7% 52%	4978
	21st to end	Day	10% 9% 3 8% 6% 6% 5% 5% 7% 8% 33%	4885
August	1st to 10th	Day	8% 5% 2 6% 4 4 4 4 7% 8% 47%	4401
	11th to 20th	Day	9% 7% 2 8% 6% 6% 7% 6% 8% 8% 33%	4330
	21st to end	Day	13% 9% 3 9% 6% 5% 5% 4 6% 9% 31%	4439
September	1st to 10th	Day	11% 12% 5% 10% 7% 5% 5% 4 5% 6% 31%	2280
	11th to 20th	Day	11% 10% 4 9% 6% 6% 5% 5% 7% 7% 30%	2256
	21st to end	Day	14% 14% 5% 12% 7% 6% 5% 4 5% 6% 21%	2071
October	1st to 10th	Day	10% 11% 5% 14% 8% 9% 7% 5% 7% 6% 17%	3180
	11th to 20th	Day	15% 16% 6% 13% 7% 5% 5% 3 5% 6% 19%	2975
	21st to end	Day	6% 13% 5% 16% 9% 6% 6% 4 6% 8% 21%	3101
November	1st to 10th	Day	8% 19% 7% 17% 9% 8% 6% 4 5% 4 12%	1588
	11th to 20th	Day	4 18% 7% 18% 9% 8% 8% 5% 5% 6% 11%	1457
	21st to end	Day	4 17% 7% 18% 12% 9% 6% 5% 7% 5% 11%	1400
December	1st to 10th	Day	5% 15% 6% 14% 10% 10% 8% 6% 7% 6% 14%	2168
	11th to 20th	Day	3 20% 11% 20% 11% 8% 6% 3 4 5% 9%	2262
	21st to end	Day	3 19% 7% 22% 11% 9% 6% 3 4 6% 9%	2992
January	1st to 10th	Night	5% 23% 11% 23% 9% 7% 4 3 4 3 6%	5143
	11th to 20th	Night	4 18% 7% 15% 8% 7% 7% 5% 5% 5% 19%	4749
	21st to end	Night	12% 30% 9% 16% 8% 6% 4 3 3 3 6%	4884
February	1st to 10th	Night	6% 18% 8% 18% 10% 8% 7% 4 5% 5% 12%	2660
	11th to 20th	Night	4 15% 7% 16% 9% 8% 7% 6% 6% 7% 16%	2456
	21st to end	Night	3 15% 4 14% 10% 10% 7% 5% 7% 6% 19%	1941
March	1st to 10th	Night	2 13% 6% 18% 10% 9% 7% 5% 7% 6% 15%	3736
	11th to 20th	Night	5% 15% 5% 14% 10% 8% 7% 5% 7% 7% 17%	3687
	21st to end	Night	3 16% 6% 15% 8% 5% 6% 5% 7% 8% 21%	3502
April	1st to 10th	Night	3 17% 5% 13% 9% 9% 7% 5% 6% 8% 18%	1900
	11th to 20th	Night	4 15% 5% 12% 8% 7% 7% 6% 7% 8% 24%	1787
	21st to end	Night	9% 12% 4 11% 8% 7% 7% 4 6% 8% 24%	1520
May	1st to 10th	Night	6% 13% 5% 12% 8% 8% 8% 6% 7% 8% 20%	2540
	11th to 20th	Night	11% 13% 4 12% 6% 6% 6% 4 6% 6% 26%	2421
	21st to end	Night	16% 18% 5% 10% 6% 5% 5% 4 5% 6% 20%	2264
June	1st to 10th	Night	16% 11% 4 10% 6% 5% 5% 4 4 5% 30%	1140
	11th to 20th	Night	15% 13% 4 10% 7% 5% 5% 5% 7% 8% 20%	1140
	21st to end	Night	11% 7% 2 7% 6% 7% 8% 5% 7% 8% 32%	1140
July	1st to 10th	Night	9% 7% 2 7% 4 3 3 3 6% 7% 48%	1900
	11th to 20th	Night	5% 6% 2 5% 3 4 3 5% 5% 7% 55%	1980
	21st to end	Night	11% 10% 4 8% 5% 5% 5% 4 6% 6% 36%	2666
August	1st to 10th	Night	5% 5% 2 6% 4 5% 5% 4 7% 11% 47%	2529
	11th to 20th	Night	11% 7% 2 6% 5% 4 5% 5% 8% 9% 37%	2497
	21st to end	Night	11% 9% 3 9% 6% 6% 6% 4 7% 9% 31%	3227
September	1st to 10th	Night	10% 10% 4 9% 6% 5% 5% 5% 5% 6% 35%	1900
	11th to 20th	Night	11% 10% 4 8% 6% 4 4 5% 5% 7% 36%	1924
	21st to end	Night	17% 12% 5% 10% 6% 7% 4 3 5% 6% 24%	2106
October	1st to 10th	Night	9% 14% 5% 13% 8% 6% 7% 5% 6% 7% 20%	3800
	11th to 20th	Night	11% 14% 6% 14% 7% 5% 6% 4 6% 8% 19%	3957
	21st to end	Night	7% 14% 6% 13% 9% 7% 6% 4 5% 7% 22%	4457
November	1st to 10th	Night	12% 23% 7% 17% 8% 6% 5% 4 5% 4 10%	2706
	11th to 20th	Night	6% 19% 7% 21% 10% 7% 6% 5% 5% 4 10%	2922
	21st to end	Night	5% 19% 8% 21% 12% 8% 7% 4 4 4 8%	3000
December	1st to 10th	Night	5% 12% 6% 18% 14% 11% 9% 6% 5% 5% 10%	5009
	11th to 20th	Night	4 20% 11% 21% 11% 8% 6% 3 4 5% 8%	5930
	21st to end	Night	3 23% 9% 23% 10% 8% 6% 3 4 4 6%	7964

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	85% 1 4 8% 2	1935
	11th to 20th	Day	65% 3 6% 11% 8% 7%	2200
	21st to end	Day	83% 2 7% 6% 3	2771
February	1st to 10th	Day	71% 3 9% 8% 9% 1	1520
	11th to 20th	Day	68% 2 12% 11% 6% 1	1617
	21st to end	Day	68% 3 11% 11% 6% 2	1513
March	1st to 10th	Day	69% 1 7% 14% 9%	3138
	11th to 20th	Day	61% 2 13% 20% 3	3290
	21st to end	Day	63% 2 9% 17% 9%	4151
April	1st to 10th	Day	77% 3 9% 8% 3	2280
	11th to 20th	Day	69% 3 11% 13% 4	2341
	21st to end	Day	66% 4 11% 16% 3	2660
May	1st to 10th	Day	61% 2 16% 17% 4	4420
	11th to 20th	Day	63% 2 14% 16% 5%	4475
	21st to end	Day	73% 2 9% 12% 3	5308
June	1st to 10th	Day	68% 3 10% 12% 6% 1	3040
	11th to 20th	Day	74% 4 9% 10% 3	3040
	21st to end	Day	63% 3 13% 15% 5%	3040
July	1st to 10th	Day	40% 5% 8% 22% 23% 1	4981
	11th to 20th	Day	35% 3 13% 31% 17% 1	4891
	21st to end	Day	49% 7% 13% 19% 10% 2	4731
August	1st to 10th	Day	36% 6% 14% 35% 8%	4384
	11th to 20th	Day	45% 9% 19% 22% 4	4372
	21st to end	Day	53% 6% 18% 19% 3	4438
September	1st to 10th	Day	55% 2 17% 18% 6% 1	2280
	11th to 20th	Day	52% 4 17% 19% 7%	2256
	21st to end	Day	64% 5% 10% 15% 6% 1	2071
October	1st to 10th	Day	66% 9% 13% 10% 2	3180
	11th to 20th	Day	68% 5% 17% 10% 1	2975
	21st to end	Day	62% 9% 18% 8% 2	3101
November	1st to 10th	Day	76% 5% 8% 9% 2 1	1588
	11th to 20th	Day	77% 4 8% 7% 4	1457
	21st to end	Day	77% 4 6% 6% 6% 1	1400
December	1st to 10th	Day	74% 8% 8% 7% 2	2168
	11th to 20th	Day	77% 6% 8% 6% 3	2264
	21st to end	Day	75% 4 11% 7% 3	2992
January	1st to 10th	Night	86% 1 4 6% 2 1	5143
	11th to 20th	Night	68% 3 5% 9% 9% 6%	4790
	21st to end	Night	85% 2 4 6% 3	4884
February	1st to 10th	Night	74% 3 7% 8% 8%	2660
	11th to 20th	Night	70% 4 9% 11% 6%	2458
	21st to end	Night	66% 4 9% 13% 6% 2	1941
March	1st to 10th	Night	70% 1 6% 14% 8% 1	3736
	11th to 20th	Night	63% 3 16% 15% 3	3688
	21st to end	Night	61% 3 9% 20% 7%	3502
April	1st to 10th	Night	68% 4 12% 14% 3	1900
	11th to 20th	Night	61% 3 14% 16% 5%	1787
	21st to end	Night	60% 3 13% 20% 5%	1520
May	1st to 10th	Night	56% 3 19% 19% 3	2540
	11th to 20th	Night	58% 3 17% 16% 7%	2421
	21st to end	Night	68% 2 11% 16% 3	2264
June	1st to 10th	Night	58% 3 14% 17% 7% 1	1140
	11th to 20th	Night	65% 4 15% 13% 4	1140
	21st to end	Night	50% 4 20% 21% 5%	1140
July	1st to 10th	Night	36% 3 13% 25% 21%	1870
	11th to 20th	Night	31% 4 15% 33% 16%	1944
	21st to end	Night	48% 6% 13% 20% 11% 2	2582
August	1st to 10th	Night	32% 7% 22% 34% 5%	2521
	11th to 20th	Night	41% 8% 22% 25% 3	2521
	21st to end	Night	52% 6% 24% 14% 4	3227
September	1st to 10th	Night	50% 3 16% 23% 7% 1	1900
	11th to 20th	Night	50% 3 17% 23% 6%	1924
	21st to end	Night	61% 5% 12% 16% 6%	2106
October	1st to 10th	Night	63% 9% 16% 11% 2	3800
	11th to 20th	Night	63% 8% 17% 11% 1	3957
	21st to end	Night	62% 9% 16% 9% 3	4457
November	1st to 10th	Night	81% 3 6% 7% 2	2706
	11th to 20th	Night	79% 3 5% 7% 5%	2922
	21st to end	Night	81% 3 6% 4 5% 1	3000
December	1st to 10th	Night	77% 8% 7% 6% 2	5009
	11th to 20th	Night	81% 6% 5% 6% 2	5927
	21st to end	Night	79% 4 9% 5% 2	7964

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	9% 23% 30% 26% 8% 4	192
	11th to 20th	Day	16% 19% 31% 23% 8% 3	180
	21st to end	Day	17% 22% 32% 19% 9% 2	198
February	1st to 10th	Day	20% 20% 38% 14% 6% 2	180
	11th to 20th	Day	8% 23% 33% 21% 13% 2	309
	21st to end	Day	9% 20% 40% 21% 9% 1	355
March	1st to 10th	Day	12% 26% 30% 21% 9% 2	460
	11th to 20th	Day	14% 24% 31% 19% 11% 2	460
	21st to end	Day	16% 23% 28% 19% 11% 2	506
April	1st to 10th	Day	19% 20% 32% 21% 6% 1	460
	11th to 20th	Day	17% 22% 26% 19% 13% 3	452
	21st to end	Day	19% 22% 25% 20% 11% 3	460
May	1st to 10th	Day	16% 22% 27% 22% 12% 1	463
	11th to 20th	Day	17% 12% 27% 26% 14% 4	544
	21st to end	Day	20% 13% 21% 25% 19% 2	815
June	1st to 10th	Day	21% 18% 28% 24% 8% 1	870
	11th to 20th	Day	25% 16% 25% 23% 10% 1	870
	21st to end	Day	19% 13% 26% 25% 14% 3	870
July	1st to 10th	Day	17% 11% 29% 29% 12% 2	856
	11th to 20th	Day	15% 15% 27% 29% 12% 2	809
	21st to end	Day	12% 13% 32% 26% 14% 3	587
August	1st to 10th	Day	13% 10% 25% 31% 16% 5%	487
	11th to 20th	Day	13% 15% 29% 27% 13% 3	477
	21st to end	Day	16% 18% 30% 22% 11% 3	539
September	1st to 10th	Day	21% 20% 24% 20% 11% 3	490
	11th to 20th	Day	16% 17% 27% 27% 11% 3	490
	21st to end	Day	23% 26% 25% 17% 8% 2	490
October	1st to 10th	Day	21% 19% 27% 18% 12% 3	490
	11th to 20th	Day	20% 23% 30% 15% 9% 2	381
	21st to end	Day	19% 18% 29% 26% 6% 2	330
November	1st to 10th	Day	20% 20% 37% 16% 6% 2	210
	11th to 20th	Day	16% 23% 31% 23% 7% 2	200
	21st to end	Day	12% 25% 32% 21% 7% 5%	200
December	1st to 10th	Day	12% 16% 27% 26% 16% 4	200
	11th to 20th	Day	15% 15% 35% 27% 7% 3	200
	21st to end	Day	6% 14% 38% 25% 13% 3	220
January	1st to 10th	Night	17% 21% 35% 21% 6% 1	1077
	11th to 20th	Night	16% 19% 38% 20% 6% 1	874
	21st to end	Night	15% 21% 39% 19% 6% 1	840
February	1st to 10th	Night	15% 18% 38% 21% 8%	760
	11th to 20th	Night	11% 12% 40% 28% 9%	744
	21st to end	Night	10% 13% 36% 28% 11% 1	628
March	1st to 10th	Night	11% 19% 37% 23% 10% 1	760
	11th to 20th	Night	10% 17% 41% 23% 10% 1	760
	21st to end	Night	11% 15% 36% 26% 9% 2	836
April	1st to 10th	Night	13% 12% 33% 29% 13% 1	760
	11th to 20th	Night	14% 11% 34% 28% 13% 1	659
	21st to end	Night	14% 11% 31% 28% 14% 1	380
May	1st to 10th	Night	11% 10% 30% 32% 17% 1	380
	11th to 20th	Night	14% 7% 23% 39% 17% 1	374
	21st to end	Night	18% 12% 20% 29% 20% 1	411
June	1st to 10th	Night	22% 11% 27% 28% 12% 1	380
	11th to 20th	Night	17% 15% 23% 28% 16% 2	380
	21st to end	Night	14% 6% 26% 32% 20% 2	380
July	1st to 10th	Night	16% 6% 19% 40% 19%	370
	11th to 20th	Night	14% 9% 20% 36% 20% 1	368
	21st to end	Night	13% 6% 17% 40% 23%	416
August	1st to 10th	Night	7% 7% 18% 40% 25% 2	378
	11th to 20th	Night	13% 3 17% 43% 22% 2	376
	21st to end	Night	15% 9% 26% 34% 16%	669
September	1st to 10th	Night	18% 9% 25% 33% 16%	760
	11th to 20th	Night	17% 9% 22% 33% 18% 2	760
	21st to end	Night	25% 15% 25% 22% 11% 1	760
October	1st to 10th	Night	22% 11% 25% 29% 11% 1	760
	11th to 20th	Night	23% 15% 29% 24% 9% 1	760
	21st to end	Night	22% 17% 34% 21% 6%	836
November	1st to 10th	Night	25% 19% 33% 17% 6% 1	780
	11th to 20th	Night	16% 23% 35% 19% 6%	922
	21st to end	Night	16% 20% 37% 21% 5% 1	1000
December	1st to 10th	Night	13% 16% 37% 25% 8%	1035
	11th to 20th	Night	14% 21% 34% 24% 7%	1100
	21st to end	Night	14% 17% 37% 23% 8%	1210

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