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 2024-01-17.

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% 13% 6% 11% 10% 5% 6% 6% 6% 6% 21%	74578
	Night	8% 15% 7% 13% 10% 5% 7% 6% 5% 6% 19%	75244
Transparency	Day	65% 3 12% 14% 5% 1	74255
	Night	67% 3 11% 13% 5%	75086
Seeing	Day	17% 18% 28% 23% 11% 2	14973
	Night	16% 15% 32% 26% 11% 1	23390

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 20% 9% 18% 13% 5% 5% 6% 5% 6% 8%	1139
	11th to 20th	Day	4 18% 9% 14% 11% 6% 7% 6% 6% 7% 12%	1295
	21st to end	Day	4 12% 8% 17% 16% 6% 7% 7% 5% 7% 12%	1575
February	1st to 10th	Day	5% 16% 8% 14% 11% 6% 7% 6% 5% 6% 17%	1440
	11th to 20th	Day	4 12% 8% 15% 12% 6% 7% 6% 6% 6% 18%	1521
	21st to end	Day	2 11% 7% 14% 12% 6% 8% 7% 6% 6% 21%	1426
March	1st to 10th	Day	3 14% 6% 11% 12% 7% 8% 8% 5% 7% 19%	1800
	11th to 20th	Day	4 14% 8% 14% 12% 6% 7% 5% 6% 5% 19%	1858
	21st to end	Day	4 17% 9% 16% 11% 5% 6% 7% 5% 5% 15%	2362
April	1st to 10th	Day	5% 18% 8% 15% 11% 6% 8% 6% 6% 5% 12%	2160
	11th to 20th	Day	7% 16% 8% 13% 9% 5% 6% 6% 7% 6% 17%	2215
	21st to end	Day	8% 14% 7% 12% 10% 4 6% 6% 6% 7% 20%	2520
May	1st to 10th	Day	9% 16% 8% 12% 8% 5% 6% 6% 4 6% 19%	2520
	11th to 20th	Day	12% 12% 5% 9% 7% 4 5% 5% 5% 7% 29%	2530
	21st to end	Day	15% 12% 4 10% 8% 4 5% 6% 5% 7% 24%	2993
June	1st to 10th	Day	19% 13% 4 9% 7% 4 6% 5% 6% 7% 21%	2880
	11th to 20th	Day	21% 15% 7% 10% 9% 5% 6% 5% 4 5% 14%	2880
	21st to end	Day	15% 9% 5% 8% 9% 5% 7% 6% 6% 6% 23%	2880
July	1st to 10th	Day	15% 9% 4 7% 7% 4 5% 6% 6% 8% 30%	2880
	11th to 20th	Day	12% 8% 4 8% 8% 4 6% 5% 6% 7% 31%	2840
	21st to end	Day	10% 7% 3 7% 7% 4 6% 5% 7% 7% 37%	2794
August	1st to 10th	Day	10% 7% 4 8% 8% 5% 6% 6% 7% 7% 32%	2507
	11th to 20th	Day	10% 8% 4 7% 7% 4 6% 6% 7% 8% 33%	2475
	21st to end	Day	13% 10% 5% 10% 9% 4 6% 5% 5% 7% 25%	2531
September	1st to 10th	Day	11% 12% 5% 9% 9% 4 5% 5% 5% 6% 29%	2160
	11th to 20th	Day	11% 10% 5% 7% 8% 4 6% 6% 6% 6% 31%	2138
	21st to end	Day	14% 12% 6% 10% 9% 5% 6% 5% 5% 6% 22%	1962
October	1st to 10th	Day	12% 13% 5% 11% 8% 5% 5% 5% 6% 6% 24%	1800
	11th to 20th	Day	11% 15% 6% 11% 12% 6% 6% 5% 5% 6% 17%	1697
	21st to end	Day	11% 15% 6% 13% 10% 4 6% 6% 5% 5% 19%	1782
November	1st to 10th	Day	9% 18% 8% 16% 12% 5% 7% 5% 5% 4 12%	1507
	11th to 20th	Day	5% 16% 9% 15% 11% 6% 8% 7% 5% 6% 12%	1385
	21st to end	Day	5% 16% 7% 16% 14% 8% 7% 6% 6% 5% 11%	1330
December	1st to 10th	Day	8% 15% 7% 15% 11% 6% 8% 6% 6% 5% 14%	1264
	11th to 20th	Day	5% 22% 12% 17% 12% 5% 7% 4 4 4 9%	1442
	21st to end	Day	4 17% 6% 16% 15% 8% 8% 5% 5% 5% 10%	2090
January	1st to 10th	Night	8% 19% 10% 17% 13% 6% 6% 5% 4 4 8%	3026
	11th to 20th	Night	8% 19% 10% 15% 11% 6% 8% 6% 5% 5% 8%	2826
	21st to end	Night	4 17% 9% 18% 14% 6% 8% 6% 5% 5% 8%	2780
February	1st to 10th	Night	6% 17% 8% 16% 12% 6% 7% 6% 5% 5% 13%	2520
	11th to 20th	Night	5% 15% 7% 13% 12% 6% 7% 8% 6% 7% 14%	2323
	21st to end	Night	3 12% 5% 13% 11% 7% 9% 6% 7% 7% 20%	1830
March	1st to 10th	Night	4 14% 8% 14% 12% 5% 8% 6% 5% 6% 18%	2160
	11th to 20th	Night	3 14% 7% 13% 10% 6% 7% 7% 6% 7% 19%	2099
	21st to end	Night	5% 15% 8% 14% 11% 5% 7% 6% 6% 8% 17%	1994
April	1st to 10th	Night	3 14% 7% 12% 10% 6% 8% 7% 6% 9% 19%	1800
	11th to 20th	Night	4 13% 5% 10% 8% 5% 7% 7% 7% 8% 24%	1693
	21st to end	Night	10% 10% 4 10% 8% 5% 7% 6% 5% 9% 25%	1440
May	1st to 10th	Night	8% 12% 5% 10% 10% 5% 7% 7% 6% 9% 22%	1440
	11th to 20th	Night	10% 9% 2 6% 6% 4 5% 6% 6% 8% 37%	1363
	21st to end	Night	14% 10% 4 6% 6% 5% 6% 5% 7% 8% 29%	1278
June	1st to 10th	Night	16% 10% 4 8% 7% 4 5% 5% 4 6% 31%	1080
	11th to 20th	Night	16% 12% 4 10% 8% 4 6% 6% 6% 8% 19%	1080
	21st to end	Night	12% 6% 3 6% 7% 5% 8% 7% 7% 8% 32%	1080
July	1st to 10th	Night	14% 8% 3 6% 6% 4 4 6% 7% 9% 34%	1080
	11th to 20th	Night	10% 8% 4 7% 5% 4 5% 7% 5% 7% 37%	1118
	21st to end	Night	11% 6% 2 5% 6% 3 5% 6% 6% 8% 44%	1522
August	1st to 10th	Night	8% 6% 2 7% 7% 4 7% 7% 6% 10% 36%	1432
	11th to 20th	Night	11% 5% 2 5% 5% 3 4 5% 7% 9% 44%	1424
	21st to end	Night	12% 6% 3 8% 8% 4 7% 6% 7% 9% 31%	1821
September	1st to 10th	Night	11% 10% 4 9% 7% 4 5% 6% 5% 6% 33%	1800
	11th to 20th	Night	11% 9% 5% 7% 7% 3 5% 6% 5% 6% 36%	1822
	21st to end	Night	17% 11% 5% 9% 7% 5% 5% 4 5% 6% 24%	1995
October	1st to 10th	Night	12% 13% 5% 9% 8% 4 6% 5% 5% 7% 27%	2160
	11th to 20th	Night	14% 14% 6% 11% 10% 4 6% 5% 6% 6% 17%	2263
	21st to end	Night	10% 17% 7% 11% 9% 4 7% 5% 5% 6% 18%	2574
November	1st to 10th	Night	13% 22% 8% 15% 10% 4 6% 5% 4 4 9%	2567
	11th to 20th	Night	6% 17% 8% 19% 12% 5% 7% 6% 5% 5% 10%	2775
	21st to end	Night	5% 18% 10% 19% 13% 6% 8% 5% 5% 4 8%	2850
December	1st to 10th	Night	7% 14% 7% 16% 13% 8% 8% 7% 4 5% 10%	2913
	11th to 20th	Night	4 23% 13% 18% 12% 6% 6% 4 3 4 6%	3750
	21st to end	Night	5% 22% 7% 16% 12% 7% 8% 5% 5% 5% 8%	5566

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	82% 2 7% 6% 2 1	1139
	11th to 20th	Day	74% 4 9% 8% 3 2	1295
	21st to end	Day	75% 2 9% 9% 5%	1575
February	1st to 10th	Day	70% 3 9% 8% 9% 1	1440
	11th to 20th	Day	70% 2 12% 11% 3	1530
	21st to end	Day	67% 3 11% 11% 6% 2	1426
March	1st to 10th	Day	69% 2 11% 11% 8% 1	1800
	11th to 20th	Day	71% 2 9% 14% 4	1858
	21st to end	Day	72% 3 11% 10% 3	2362
April	1st to 10th	Day	77% 3 10% 8% 3	2160
	11th to 20th	Day	69% 3 11% 13% 3	2215
	21st to end	Day	65% 4 12% 16% 3	2520
May	1st to 10th	Day	67% 4 12% 14% 2	2520
	11th to 20th	Day	56% 4 16% 16% 6%	2533
	21st to end	Day	63% 4 15% 14% 4 1	2994
June	1st to 10th	Day	67% 4 10% 11% 6% 1	2880
	11th to 20th	Day	76% 3 9% 10% 3	2880
	21st to end	Day	63% 3 13% 15% 5%	2880
July	1st to 10th	Day	55% 4 11% 19% 9% 1	2801
	11th to 20th	Day	57% 4 12% 19% 7% 1	2753
	21st to end	Day	47% 3 15% 26% 8% 1	2639
August	1st to 10th	Day	51% 5% 17% 20% 7% 1	2490
	11th to 20th	Day	48% 4 20% 20% 7% 1	2475
	21st to end	Day	61% 2 13% 17% 6% 1	2531
September	1st to 10th	Day	58% 2 17% 18% 5% 1	2160
	11th to 20th	Day	52% 3 18% 20% 7%	2138
	21st to end	Day	64% 4 10% 15% 6% 1	1962
October	1st to 10th	Day	60% 3 18% 15% 4	1800
	11th to 20th	Day	70% 2 14% 13% 1	1697
	21st to end	Day	70% 3 11% 12% 4	1782
November	1st to 10th	Day	77% 4 8% 9% 2 1	1507
	11th to 20th	Day	77% 3 8% 7% 4	1385
	21st to end	Day	77% 3 6% 6% 7% 1	1330
December	1st to 10th	Day	75% 3 7% 11% 3 1	1264
	11th to 20th	Day	82% 2 5% 6% 4	1444
	21st to end	Day	73% 3 12% 9% 4	2090
January	1st to 10th	Night	82% 2 6% 7% 3 1	3026
	11th to 20th	Night	78% 4 6% 7% 3 2	2826
	21st to end	Night	79% 3 5% 8% 5%	2780
February	1st to 10th	Night	74% 3 7% 8% 8%	2520
	11th to 20th	Night	72% 4 9% 10% 4	2325
	21st to end	Night	64% 4 9% 14% 7% 2	1830
March	1st to 10th	Night	70% 2 8% 10% 8% 1	2160
	11th to 20th	Night	68% 3 11% 14% 4	2100
	21st to end	Night	69% 5% 12% 10% 3	1994
April	1st to 10th	Night	67% 4 12% 14% 3	1800
	11th to 20th	Night	61% 3 15% 16% 5%	1693
	21st to end	Night	59% 3 14% 20% 5%	1440
May	1st to 10th	Night	60% 5% 15% 17% 3	1440
	11th to 20th	Night	45% 5% 19% 22% 8%	1363
	21st to end	Night	54% 4 17% 20% 4 1	1278
June	1st to 10th	Night	57% 3 15% 18% 7% 1	1080
	11th to 20th	Night	66% 4 15% 12% 3	1080
	21st to end	Night	51% 4 20% 20% 5%	1080
July	1st to 10th	Night	48% 4 18% 21% 8%	1050
	11th to 20th	Night	49% 3 16% 25% 5% 1	1082
	21st to end	Night	41% 4 18% 29% 9%	1438
August	1st to 10th	Night	44% 6% 24% 20% 7%	1424
	11th to 20th	Night	40% 5% 22% 28% 6%	1424
	21st to end	Night	50% 4 20% 19% 7%	1821
September	1st to 10th	Night	52% 3 16% 22% 6% 1	1800
	11th to 20th	Night	50% 3 17% 23% 7%	1822
	21st to end	Night	61% 5% 12% 17% 5%	1995
October	1st to 10th	Night	56% 4 19% 17% 4	2160
	11th to 20th	Night	67% 5% 13% 14% 1	2263
	21st to end	Night	70% 5% 10% 10% 5%	2574
November	1st to 10th	Night	82% 3 6% 7% 2	2567
	11th to 20th	Night	80% 2 5% 7% 5% 1	2775
	21st to end	Night	81% 3 6% 4 5% 1	2850
December	1st to 10th	Night	77% 5% 5% 10% 4	2913
	11th to 20th	Night	87% 2 4 5% 2	3747
	21st to end	Night	76% 2 11% 7% 3	5566

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% 25% 32% 24% 7% 3	180
	11th to 20th	Day	15% 19% 31% 23% 9% 3	172
	21st to end	Day	15% 19% 34% 20% 10% 2	176
February	1st to 10th	Day	21% 21% 38% 14% 5% 1	160
	11th to 20th	Day	9% 25% 33% 21% 10% 1	282
	21st to end	Day	9% 19% 40% 21% 10% 2	322
March	1st to 10th	Day	12% 26% 31% 20% 9% 2	420
	11th to 20th	Day	14% 24% 32% 18% 10% 1	420
	21st to end	Day	18% 24% 27% 19% 11% 2	462
April	1st to 10th	Day	18% 21% 32% 22% 7% 1	420
	11th to 20th	Day	18% 23% 25% 18% 13% 4	412
	21st to end	Day	20% 20% 25% 20% 11% 3	420
May	1st to 10th	Day	17% 22% 27% 22% 12% 1	423
	11th to 20th	Day	18% 10% 27% 27% 14% 4	501
	21st to end	Day	19% 11% 21% 26% 20% 3	755
June	1st to 10th	Day	22% 16% 28% 24% 8% 1	810
	11th to 20th	Day	26% 16% 26% 23% 9% 1	810
	21st to end	Day	19% 13% 25% 25% 14% 3	810
July	1st to 10th	Day	18% 11% 28% 28% 12% 2	796
	11th to 20th	Day	16% 15% 26% 29% 11% 2	752
	21st to end	Day	12% 12% 32% 27% 14% 3	540
August	1st to 10th	Day	14% 11% 24% 32% 15% 4	447
	11th to 20th	Day	14% 16% 30% 26% 12% 3	437
	21st to end	Day	16% 18% 30% 22% 11% 3	495
September	1st to 10th	Day	22% 21% 23% 19% 11% 3	450
	11th to 20th	Day	16% 18% 26% 27% 9% 3	450
	21st to end	Day	22% 24% 26% 18% 8% 2	450
October	1st to 10th	Day	22% 17% 26% 19% 12% 4	450
	11th to 20th	Day	20% 23% 29% 16% 9% 2	347
	21st to end	Day	21% 18% 30% 24% 7% 2	297
November	1st to 10th	Day	21% 18% 37% 15% 6% 2	189
	11th to 20th	Day	16% 22% 32% 22% 7% 1	180
	21st to end	Day	13% 27% 32% 18% 6% 4	180
December	1st to 10th	Day	13% 14% 27% 24% 17% 4	180
	11th to 20th	Day	16% 15% 34% 27% 6% 2	180
	21st to end	Day	6% 14% 38% 27% 13% 2	198
January	1st to 10th	Night	17% 21% 35% 20% 5% 1	1040
	11th to 20th	Night	16% 19% 38% 19% 7% 1	858
	21st to end	Night	13% 20% 40% 20% 6% 1	795
February	1st to 10th	Night	15% 19% 38% 21% 7%	720
	11th to 20th	Night	12% 13% 40% 28% 7%	704
	21st to end	Night	10% 12% 37% 29% 11% 1	592
March	1st to 10th	Night	11% 19% 37% 23% 10% 1	720
	11th to 20th	Night	10% 16% 41% 22% 10% 1	720
	21st to end	Night	12% 15% 36% 26% 9% 2	792
April	1st to 10th	Night	12% 12% 32% 30% 13% 1	720
	11th to 20th	Night	13% 11% 34% 27% 13% 1	625
	21st to end	Night	15% 11% 31% 28% 14% 1	360
May	1st to 10th	Night	11% 10% 29% 32% 17% 1	360
	11th to 20th	Night	14% 5% 23% 39% 18% 1	354
	21st to end	Night	18% 10% 20% 30% 21% 1	389
June	1st to 10th	Night	21% 11% 26% 28% 13% 1	360
	11th to 20th	Night	18% 15% 22% 28% 16% 2	360
	21st to end	Night	14% 6% 25% 33% 20% 2	360
July	1st to 10th	Night	17% 6% 19% 39% 19%	350
	11th to 20th	Night	15% 9% 20% 34% 20% 1	348
	21st to end	Night	13% 5% 16% 41% 24% 1	394
August	1st to 10th	Night	7% 7% 18% 41% 25% 3	358
	11th to 20th	Night	13% 4 17% 43% 21% 2	356
	21st to end	Night	15% 9% 26% 33% 16%	633
September	1st to 10th	Night	18% 9% 25% 31% 16%	720
	11th to 20th	Night	18% 9% 22% 33% 17% 2	720
	21st to end	Night	25% 14% 25% 23% 11% 2	720
October	1st to 10th	Night	23% 10% 24% 30% 12% 1	720
	11th to 20th	Night	23% 15% 29% 24% 9% 1	720
	21st to end	Night	22% 17% 34% 20% 6% 1	792
November	1st to 10th	Night	26% 19% 32% 17% 6% 1	740
	11th to 20th	Night	17% 24% 35% 20% 5%	875
	21st to end	Night	17% 21% 37% 20% 4 1	950
December	1st to 10th	Night	14% 17% 37% 24% 8%	981
	11th to 20th	Night	15% 21% 35% 23% 6%	1040
	21st to end	Night	15% 17% 38% 23% 8%	1144

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