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 2026-05-02.

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	8% 13% 5% 12% 7% 6% 6% 4 6% 7% 25%	135186
	Night	6% 15% 6% 15% 8% 7% 6% 4 5% 6% 21%	135985
Transparency	Day	59% 6% 13% 15% 6% 1	134885
	Night	64% 6% 12% 13% 5%	135866
Seeing	Day	16% 18% 29% 23% 11% 2	18017
	Night	15% 15% 32% 26% 11% 1	26399

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	2 16% 7% 25% 10% 8% 7% 5% 7% 5% 7%	3527
	11th to 20th	Day	2 13% 5% 13% 7% 5% 5% 4 6% 7% 32%	4099
	21st to end	Day	6% 16% 6% 14% 9% 7% 6% 3 5% 7% 20%	5163
February	1st to 10th	Day	4 16% 7% 16% 9% 8% 7% 4 5% 6% 18%	1680
	11th to 20th	Day	3 12% 6% 16% 11% 7% 6% 5% 6% 6% 20%	1782
	21st to end	Day	2 12% 6% 18% 9% 9% 9% 5% 5% 6% 19%	1667
March	1st to 10th	Day	1 13% 6% 16% 9% 8% 8% 6% 6% 8% 19%	4618
	11th to 20th	Day	2 12% 5% 14% 9% 8% 7% 4 7% 7% 23%	4812
	21st to end	Day	4 14% 7% 16% 9% 7% 7% 5% 6% 6% 19%	6086
April	1st to 10th	Day	5% 18% 6% 17% 9% 8% 7% 5% 6% 5% 13%	2520
	11th to 20th	Day	5% 16% 6% 15% 8% 6% 6% 5% 7% 7% 19%	2592
	21st to end	Day	7% 15% 6% 13% 8% 6% 6% 4 6% 7% 22%	2940
May	1st to 10th	Day	6% 13% 5% 12% 7% 6% 6% 4 6% 8% 27%	6335
	11th to 20th	Day	9% 14% 5% 12% 7% 6% 6% 5% 7% 8% 18%	6414
	21st to end	Day	14% 16% 4 10% 6% 5% 5% 4 5% 7% 23%	7607
June	1st to 10th	Day	18% 14% 4 10% 6% 5% 5% 4 6% 7% 22%	3200
	11th to 20th	Day	19% 16% 5% 11% 8% 6% 6% 5% 5% 5% 15%	3200
	21st to end	Day	15% 11% 4 10% 7% 7% 6% 4 7% 6% 23%	3200
July	1st to 10th	Day	8% 8% 3 6% 5% 4 5% 4 6% 7% 45%	7240
	11th to 20th	Day	8% 7% 2 7% 5% 4 4 4 6% 7% 46%	7116
	21st to end	Day	8% 7% 2 7% 5% 5% 5% 5% 7% 9% 39%	7011
August	1st to 10th	Day	8% 6% 2 6% 4 5% 5% 4 7% 8% 46%	4541
	11th to 20th	Day	9% 7% 3 8% 6% 6% 7% 6% 8% 8% 33%	4470
	21st to end	Day	13% 9% 3 9% 6% 5% 5% 4 6% 9% 32%	4579
September	1st to 10th	Day	10% 11% 4 10% 7% 5% 5% 4 5% 6% 33%	2400
	11th to 20th	Day	11% 10% 4 8% 6% 6% 5% 5% 7% 7% 32%	2375
	21st to end	Day	14% 14% 5% 12% 7% 7% 6% 4 5% 6% 21%	2180
October	1st to 10th	Day	10% 11% 6% 14% 8% 9% 7% 5% 6% 6% 17%	3280
	11th to 20th	Day	14% 16% 6% 13% 7% 6% 5% 3 5% 6% 19%	3069
	21st to end	Day	6% 13% 6% 16% 9% 6% 6% 4 6% 8% 21%	3200
November	1st to 10th	Day	9% 19% 7% 17% 9% 7% 6% 4 5% 4 12%	1669
	11th to 20th	Day	5% 18% 7% 17% 10% 8% 7% 5% 6% 6% 12%	1530
	21st to end	Day	4 17% 7% 18% 12% 9% 6% 5% 7% 5% 10%	1470
December	1st to 10th	Day	4 15% 7% 14% 10% 10% 8% 6% 7% 6% 13%	2234
	11th to 20th	Day	3 20% 11% 20% 11% 8% 6% 3 5% 5% 9%	2322
	21st to end	Day	3 19% 7% 22% 11% 9% 6% 3 4 6% 9%	3058
January	1st to 10th	Night	3 19% 10% 26% 10% 8% 6% 4 4 4 6%	9366
	11th to 20th	Night	3 13% 7% 14% 8% 7% 7% 4 5% 7% 27%	8857
	21st to end	Night	7% 19% 7% 14% 9% 7% 6% 4 4 6% 18%	9016
February	1st to 10th	Night	5% 17% 7% 17% 11% 7% 7% 4 6% 5% 14%	2940
	11th to 20th	Night	4 14% 7% 15% 9% 8% 7% 6% 7% 7% 17%	2721
	21st to end	Night	3 15% 5% 15% 10% 10% 7% 4 6% 6% 18%	2138
March	1st to 10th	Night	2 13% 7% 18% 9% 8% 7% 5% 7% 8% 19%	5496
	11th to 20th	Night	4 13% 6% 17% 11% 8% 7% 5% 7% 7% 14%	5392
	21st to end	Night	5% 17% 7% 15% 7% 5% 5% 5% 7% 8% 20%	5131
April	1st to 10th	Night	3 16% 5% 13% 9% 8% 7% 5% 6% 8% 20%	2100
	11th to 20th	Night	3 14% 5% 11% 8% 6% 6% 6% 7% 8% 25%	1976
	21st to end	Night	8% 11% 4 10% 8% 7% 6% 5% 6% 8% 27%	1680
May	1st to 10th	Night	6% 12% 5% 10% 7% 6% 6% 5% 7% 10% 26%	3648
	11th to 20th	Night	10% 14% 4 13% 6% 6% 6% 4 6% 7% 24%	3479
	21st to end	Night	12% 15% 4 9% 6% 5% 5% 4 6% 7% 28%	3250
June	1st to 10th	Night	15% 11% 4 9% 7% 6% 5% 3 4 5% 31%	1200
	11th to 20th	Night	15% 13% 4 10% 7% 5% 5% 5% 7% 9% 20%	1200
	21st to end	Night	12% 7% 2 7% 6% 7% 7% 5% 7% 8% 32%	1200
July	1st to 10th	Night	8% 8% 2 6% 4 3 4 3 5% 7% 49%	2720
	11th to 20th	Night	5% 7% 3 7% 4 5% 5% 5% 6% 7% 46%	2828
	21st to end	Night	9% 8% 3 7% 4 4 4 5% 6% 8% 40%	3831
August	1st to 10th	Night	5% 5% 2 6% 4 5% 5% 4 7% 11% 46%	2609
	11th to 20th	Night	11% 7% 2 6% 5% 4 5% 5% 8% 9% 37%	2577
	21st to end	Night	11% 9% 3 9% 6% 5% 6% 4 7% 8% 33%	3329
September	1st to 10th	Night	10% 9% 4 9% 6% 5% 5% 5% 5% 7% 36%	2000
	11th to 20th	Night	10% 10% 4 8% 6% 4 4 5% 5% 6% 37%	2025
	21st to end	Night	17% 12% 5% 10% 6% 7% 4 3 5% 6% 24%	2217
October	1st to 10th	Night	9% 14% 5% 13% 8% 6% 7% 4 6% 7% 21%	3920
	11th to 20th	Night	11% 14% 6% 14% 7% 5% 6% 4 6% 7% 20%	4083
	21st to end	Night	7% 14% 6% 14% 9% 6% 6% 4 5% 7% 22%	4600
November	1st to 10th	Night	12% 23% 7% 17% 8% 6% 5% 4 5% 4 10%	2845
	11th to 20th	Night	6% 19% 7% 20% 10% 7% 6% 4 6% 5% 10%	3068
	21st to end	Night	5% 19% 8% 21% 12% 8% 7% 4 5% 4 8%	3150
December	1st to 10th	Night	4 12% 6% 18% 14% 11% 8% 6% 5% 5% 10%	5163
	11th to 20th	Night	4 20% 11% 20% 11% 8% 6% 3 4 5% 8%	6090
	21st to end	Night	3 22% 9% 23% 10% 8% 7% 3 4 4 6%	8140

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	77% 9% 4 7% 2	3527
	11th to 20th	Day	51% 7% 16% 16% 6% 4	4120
	21st to end	Day	65% 8% 14% 11% 2	5164
February	1st to 10th	Day	69% 3 8% 9% 10% 1	1680
	11th to 20th	Day	66% 4 12% 12% 5% 1	1791
	21st to end	Day	68% 4 11% 10% 6% 2	1667
March	1st to 10th	Day	66% 4 8% 13% 8%	4618
	11th to 20th	Day	58% 10% 11% 18% 3	4812
	21st to end	Day	63% 6% 8% 15% 7%	6086
April	1st to 10th	Day	75% 3 10% 8% 3	2520
	11th to 20th	Day	67% 4 12% 12% 4	2592
	21st to end	Day	63% 4 12% 17% 5%	2940
May	1st to 10th	Day	55% 5% 17% 20% 4	6335
	11th to 20th	Day	61% 7% 16% 13% 4	6417
	21st to end	Day	61% 8% 16% 12% 2	7608
June	1st to 10th	Day	66% 4 10% 12% 6% 1	3200
	11th to 20th	Day	73% 4 9% 11% 3	3200
	21st to end	Day	62% 4 13% 15% 5%	3200
July	1st to 10th	Day	40% 8% 14% 21% 17% 1	7161
	11th to 20th	Day	40% 7% 13% 27% 12% 1	7029
	21st to end	Day	42% 9% 18% 21% 9% 2	6815
August	1st to 10th	Day	37% 6% 14% 34% 8%	4524
	11th to 20th	Day	45% 9% 20% 22% 4	4512
	21st to end	Day	52% 6% 18% 19% 4 1	4578
September	1st to 10th	Day	53% 3 18% 19% 7% 1	2400
	11th to 20th	Day	51% 5% 17% 20% 7%	2375
	21st to end	Day	64% 5% 11% 14% 5% 1	2180
October	1st to 10th	Day	66% 9% 13% 10% 2	3280
	11th to 20th	Day	67% 5% 16% 10% 1	3069
	21st to end	Day	62% 9% 18% 8% 2	3200
November	1st to 10th	Day	75% 5% 8% 9% 2 1	1669
	11th to 20th	Day	76% 4 9% 7% 4	1530
	21st to end	Day	76% 4 7% 6% 6% 1	1470
December	1st to 10th	Day	75% 8% 8% 7% 2	2234
	11th to 20th	Day	77% 6% 7% 6% 3	2324
	21st to end	Day	74% 4 11% 8% 3	3058
January	1st to 10th	Night	84% 5% 4 6% 2	9367
	11th to 20th	Night	56% 6% 12% 15% 8% 3	8898
	21st to end	Night	67% 5% 12% 11% 4	9016
February	1st to 10th	Night	72% 4 7% 8% 9% 1	2940
	11th to 20th	Night	67% 5% 10% 11% 7%	2723
	21st to end	Night	67% 4 8% 13% 6% 1	2138
March	1st to 10th	Night	64% 4 8% 15% 8%	5496
	11th to 20th	Night	63% 7% 13% 13% 3	5393
	21st to end	Night	60% 6% 9% 18% 7%	5131
April	1st to 10th	Night	66% 4 13% 13% 3	2100
	11th to 20th	Night	59% 4 15% 16% 6%	1976
	21st to end	Night	57% 3 14% 21% 5%	1680
May	1st to 10th	Night	50% 4 22% 19% 4	3645
	11th to 20th	Night	59% 5% 16% 15% 5%	3479
	21st to end	Night	56% 5% 20% 15% 3	3250
June	1st to 10th	Night	57% 3 15% 17% 7% 1	1200
	11th to 20th	Night	64% 4 15% 14% 3	1200
	21st to end	Night	51% 4 20% 21% 5%	1200
July	1st to 10th	Night	37% 5% 17% 24% 17%	2690
	11th to 20th	Night	39% 7% 15% 28% 11%	2792
	21st to end	Night	42% 6% 20% 23% 8% 1	3723
August	1st to 10th	Night	33% 7% 22% 33% 5%	2601
	11th to 20th	Night	41% 9% 22% 24% 3	2601
	21st to end	Night	50% 6% 24% 14% 5% 1	3329
September	1st to 10th	Night	48% 4 17% 24% 7% 1	2000
	11th to 20th	Night	49% 4 17% 24% 6%	2025
	21st to end	Night	61% 5% 12% 16% 5%	2217
October	1st to 10th	Night	62% 9% 16% 11% 2	3920
	11th to 20th	Night	62% 8% 16% 12% 1	4083
	21st to end	Night	62% 9% 16% 9% 3	4600
November	1st to 10th	Night	80% 4 7% 7% 2	2845
	11th to 20th	Night	78% 3 5% 8% 5% 1	3068
	21st to end	Night	80% 4 6% 5% 5% 1	3150
December	1st to 10th	Night	77% 8% 6% 6% 2	5163
	11th to 20th	Night	81% 6% 5% 6% 2	6087
	21st to end	Night	78% 5% 9% 5% 2	8140

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	8% 23% 33% 25% 7% 4	220
	11th to 20th	Day	14% 20% 31% 26% 7% 2	220
	21st to end	Day	14% 19% 35% 21% 9% 2	242
February	1st to 10th	Day	16% 18% 36% 17% 10% 3	220
	11th to 20th	Day	7% 19% 34% 24% 13% 2	363
	21st to end	Day	11% 20% 39% 20% 8% 1	413
March	1st to 10th	Day	12% 26% 31% 21% 8% 2	540
	11th to 20th	Day	14% 25% 30% 19% 11% 1	540
	21st to end	Day	17% 23% 27% 19% 11% 2	594
April	1st to 10th	Day	17% 21% 32% 22% 7% 1	540
	11th to 20th	Day	16% 23% 27% 19% 12% 3	532
	21st to end	Day	18% 21% 24% 22% 12% 3	540
May	1st to 10th	Day	16% 21% 27% 23% 12% 1	508
	11th to 20th	Day	17% 13% 26% 27% 14% 4	587
	21st to end	Day	19% 15% 21% 25% 18% 2	874
June	1st to 10th	Day	20% 18% 29% 24% 8% 1	930
	11th to 20th	Day	24% 15% 26% 24% 10% 1	930
	21st to end	Day	18% 14% 27% 26% 13% 3	930
July	1st to 10th	Day	17% 12% 29% 29% 12% 2	916
	11th to 20th	Day	15% 15% 28% 29% 11% 2	866
	21st to end	Day	12% 13% 32% 26% 15% 3	634
August	1st to 10th	Day	12% 10% 25% 32% 16% 5%	527
	11th to 20th	Day	14% 16% 29% 26% 12% 3	517
	21st to end	Day	15% 17% 28% 22% 13% 5%	583
September	1st to 10th	Day	19% 19% 22% 21% 14% 4	530
	11th to 20th	Day	15% 16% 26% 27% 12% 4	530
	21st to end	Day	23% 25% 26% 16% 7% 2	530
October	1st to 10th	Day	20% 20% 28% 18% 12% 3	530
	11th to 20th	Day	20% 22% 30% 17% 9% 2	415
	21st to end	Day	20% 18% 29% 25% 6% 1	363
November	1st to 10th	Day	20% 20% 36% 16% 5% 2	231
	11th to 20th	Day	15% 22% 33% 21% 7% 2	220
	21st to end	Day	10% 23% 32% 22% 8% 5%	220
December	1st to 10th	Day	11% 18% 29% 24% 15% 4	220
	11th to 20th	Day	14% 17% 34% 27% 6% 2	220
	21st to end	Day	6% 14% 40% 26% 12% 3	242
January	1st to 10th	Night	16% 21% 36% 21% 5% 1	1160
	11th to 20th	Night	15% 19% 40% 20% 6% 1	976
	21st to end	Night	14% 20% 41% 20% 5% 1	928
February	1st to 10th	Night	14% 18% 37% 22% 8%	840
	11th to 20th	Night	10% 11% 41% 30% 8%	824
	21st to end	Night	10% 15% 38% 27% 10% 1	692
March	1st to 10th	Night	11% 19% 38% 22% 10%	840
	11th to 20th	Night	10% 17% 40% 23% 10%	840
	21st to end	Night	10% 16% 36% 27% 9% 2	924
April	1st to 10th	Night	12% 13% 33% 30% 12% 1	840
	11th to 20th	Night	13% 11% 35% 29% 12% 1	728
	21st to end	Night	13% 10% 31% 31% 14% 1	420
May	1st to 10th	Night	11% 10% 31% 32% 16%	402
	11th to 20th	Night	13% 7% 23% 39% 18% 1	394
	21st to end	Night	17% 12% 21% 30% 20% 1	433
June	1st to 10th	Night	21% 11% 27% 29% 12% 1	400
	11th to 20th	Night	16% 15% 23% 28% 16% 2	400
	21st to end	Night	13% 7% 26% 33% 19% 2	400
July	1st to 10th	Night	16% 7% 20% 39% 18%	390
	11th to 20th	Night	14% 9% 22% 35% 19% 1	388
	21st to end	Night	13% 6% 17% 41% 22%	438
August	1st to 10th	Night	7% 7% 18% 41% 24% 2	398
	11th to 20th	Night	13% 4 19% 42% 21% 2	396
	21st to end	Night	14% 9% 25% 34% 18%	705
September	1st to 10th	Night	17% 9% 24% 34% 17%	800
	11th to 20th	Night	16% 9% 21% 34% 18% 2	800
	21st to end	Night	25% 16% 26% 21% 10% 1	800
October	1st to 10th	Night	22% 12% 25% 29% 11% 1	800
	11th to 20th	Night	22% 15% 30% 24% 9% 1	800
	21st to end	Night	21% 18% 34% 21% 6%	880
November	1st to 10th	Night	24% 19% 33% 17% 6% 1	820
	11th to 20th	Night	16% 23% 36% 19% 6%	968
	21st to end	Night	15% 20% 37% 22% 5% 1	1050
December	1st to 10th	Night	13% 17% 38% 25% 8%	1089
	11th to 20th	Night	14% 21% 35% 23% 6%	1160
	21st to end	Night	14% 17% 39% 23% 8%	1276

Page generated at 2026-04-28 23:21:48. Version ac07

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