Val Marie
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Val Marie clear sky chart from 2005-11-06 to 2024-09-29.

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	7% 8% 3 8% 5% 5% 5% 4 6% 8% 42%	101436
	Night	6% 7% 3 8% 5% 5% 5% 4 6% 8% 42%	96970
Transparency	Day	39% 7% 15% 25% 12% 2	101165
	Night	38% 7% 16% 25% 12% 2	96831
Seeing	Day	11% 10% 30% 30% 16% 4	15669
	Night	10% 8% 33% 35% 12% 1	24991

By Month

Percentage Cloud Cover SW (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 12% 4 12% 7% 7% 7% 5% 6% 9% 29%	2219
	11th to 20th	Day	2 8% 5% 11% 9% 7% 8% 5% 7% 9% 29%	2220
	21st to end	Day	4 10% 3 9% 6% 6% 5% 5% 5% 8% 40%	2835
February	1st to 10th	Day	8% 13% 5% 12% 8% 6% 6% 3 7% 7% 26%	1710
	11th to 20th	Day	6% 11% 5% 14% 8% 7% 5% 5% 7% 8% 24%	1665
	21st to end	Day	4 12% 4 11% 8% 8% 7% 6% 6% 7% 26%	1437
March	1st to 10th	Day	4 12% 4 11% 8% 6% 5% 5% 5% 7% 33%	3216
	11th to 20th	Day	6% 8% 3 7% 5% 5% 5% 4 6% 10% 39%	3490
	21st to end	Day	7% 18% 7% 17% 7% 5% 5% 4 5% 6% 20%	3938
April	1st to 10th	Day	8% 9% 3 9% 7% 5% 5% 5% 6% 8% 35%	2280
	11th to 20th	Day	12% 14% 4 8% 5% 5% 5% 4 6% 6% 30%	2331
	21st to end	Day	13% 10% 3 7% 5% 4 4 4 6% 8% 36%	2536
May	1st to 10th	Day	16% 12% 3 8% 5% 4 4 4 5% 6% 32%	4430
	11th to 20th	Day	8% 6% 3 8% 5% 5% 5% 5% 7% 9% 38%	4388
	21st to end	Day	14% 7% 3 8% 6% 5% 6% 5% 7% 9% 31%	4885
June	1st to 10th	Day	14% 6% 2 7% 5% 5% 5% 5% 6% 9% 37%	2850
	11th to 20th	Day	14% 6% 2 7% 5% 5% 6% 4 7% 8% 37%	2850
	21st to end	Day	6% 4 2 5% 5% 5% 5% 4 8% 8% 49%	2850
July	1st to 10th	Day	3 3 1 5% 5% 5% 6% 5% 7% 9% 50%	4740
	11th to 20th	Day	3 2 1 3 3 3 4 3 5% 8% 64%	4740
	21st to end	Day	3 2 1 3 2 2 3 3 4 6% 70%	4865
August	1st to 10th	Day	7% 4 2 4 3 4 4 3 6% 7% 56%	4393
	11th to 20th	Day	4 3 2 4 3 3 4 3 6% 10% 57%	4028
	21st to end	Day	7% 3 1 4 3 3 3 3 5% 7% 61%	4405
September	1st to 10th	Day	9% 6% 2 5% 4 4 4 4 5% 6% 51%	2280
	11th to 20th	Day	11% 6% 2 6% 4 3 4 3 6% 7% 48%	2280
	21st to end	Day	11% 7% 2 5% 3 3 3 3 5% 7% 51%	1983
October	1st to 10th	Day	12% 9% 3 7% 3 3 3 3 5% 7% 44%	1800
	11th to 20th	Day	7% 7% 4 9% 5% 4 6% 4 5% 8% 43%	1800
	21st to end	Day	6% 10% 3 7% 4 5% 5% 5% 7% 7% 41%	1817
November	1st to 10th	Day	9% 13% 4 8% 5% 4 4 3 5% 8% 36%	1488
	11th to 20th	Day	4 8% 4 9% 6% 6% 6% 4 6% 8% 39%	1520
	21st to end	Day	6% 12% 3 9% 5% 5% 5% 4 5% 9% 36%	1520
December	1st to 10th	Day	6% 9% 5% 12% 10% 7% 5% 6% 6% 6% 29%	1520
	11th to 20th	Day	4 10% 6% 12% 6% 7% 5% 4 6% 7% 34%	1685
	21st to end	Day	5% 8% 3 8% 5% 4 4 5% 6% 8% 44%	2442
January	1st to 10th	Night	3 7% 4 10% 7% 7% 7% 6% 9% 9% 32%	4726
	11th to 20th	Night	3 7% 4 13% 8% 7% 6% 7% 9% 7% 29%	4738
	21st to end	Night	3 8% 5% 10% 6% 5% 5% 4 6% 8% 40%	4863
February	1st to 10th	Night	5% 10% 5% 10% 7% 7% 5% 4 6% 8% 33%	2470
	11th to 20th	Night	4 10% 4 11% 7% 6% 6% 5% 7% 9% 31%	2402
	21st to end	Night	4 10% 4 10% 8% 5% 6% 5% 6% 7% 34%	2017
March	1st to 10th	Night	5% 9% 4 11% 8% 6% 6% 5% 7% 9% 30%	3646
	11th to 20th	Night	5% 6% 3 8% 4 4 4 4 7% 12% 43%	3490
	21st to end	Night	8% 15% 6% 17% 7% 6% 5% 5% 5% 6% 19%	3711
April	1st to 10th	Night	7% 8% 3 7% 6% 6% 6% 5% 7% 7% 39%	1900
	11th to 20th	Night	11% 13% 3 7% 5% 5% 5% 5% 6% 8% 34%	1795
	21st to end	Night	9% 9% 4 8% 6% 6% 5% 5% 5% 7% 37%	1644
May	1st to 10th	Night	16% 10% 3 8% 4 4 5% 4 5% 6% 36%	2540
	11th to 20th	Night	9% 6% 2 5% 5% 5% 6% 5% 7% 10% 41%	2517
	21st to end	Night	12% 7% 2 6% 4 4 4 4 7% 9% 40%	2683
June	1st to 10th	Night	12% 6% 2 6% 4 5% 4 4 6% 8% 43%	1330
	11th to 20th	Night	14% 4 2 5% 4 4 5% 5% 7% 8% 44%	1330
	21st to end	Night	5% 3 2 5% 5% 3 5% 3 4 8% 56%	1330
July	1st to 10th	Night	4 2 1 3 3 3 4 4 6% 10% 59%	2220
	11th to 20th	Night	3 3 1 4 3 4 3 3 5% 6% 63%	2220
	21st to end	Night	3 2 1 3 3 4 4 4 6% 8% 63%	2693
August	1st to 10th	Night	7% 4 1 4 3 3 3 3 6% 7% 59%	2543
	11th to 20th	Night	4 3 1 4 3 4 4 4 7% 9% 57%	2811
	21st to end	Night	9% 4 1 5% 3 4 3 3 5% 6% 56%	3261
September	1st to 10th	Night	9% 4 2 4 3 3 3 3 6% 6% 58%	1900
	11th to 20th	Night	9% 7% 2 6% 3 3 4 3 5% 7% 51%	1900
	21st to end	Night	8% 5% 2 4 3 3 3 3 6% 9% 53%	2164
October	1st to 10th	Night	10% 8% 3 5% 4 4 3 3 6% 7% 47%	2160
	11th to 20th	Night	7% 8% 3 6% 4 3 4 4 5% 8% 47%	2160
	21st to end	Night	9% 8% 3 9% 4 4 4 4 6% 8% 40%	2518
November	1st to 10th	Night	11% 10% 4 8% 6% 5% 5% 3 5% 7% 37%	2590
	11th to 20th	Night	4 8% 4 9% 7% 5% 5% 4 7% 8% 40%	2660
	21st to end	Night	5% 9% 4 11% 6% 5% 5% 4 6% 8% 38%	2660
December	1st to 10th	Night	5% 9% 4 12% 9% 7% 6% 5% 6% 8% 29%	2660
	11th to 20th	Night	4 10% 4 11% 5% 5% 5% 5% 7% 8% 35%	3504
	21st to end	Night	4 6% 2 7% 4 4 4 4 5% 7% 53%	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	50% 10% 18% 17% 5%	2219
	11th to 20th	Day	50% 7% 16% 14% 11% 1	2220
	21st to end	Day	42% 8% 21% 23% 6%	2835
February	1st to 10th	Day	56% 7% 13% 16% 8%	1710
	11th to 20th	Day	55% 6% 16% 13% 9% 1	1674
	21st to end	Day	54% 8% 16% 13% 8%	1437
March	1st to 10th	Day	49% 7% 16% 23% 5%	3216
	11th to 20th	Day	39% 7% 23% 25% 6%	3490
	21st to end	Day	64% 9% 13% 11% 3	3938
April	1st to 10th	Day	46% 8% 15% 21% 9%	2280
	11th to 20th	Day	52% 6% 14% 20% 7% 1	2334
	21st to end	Day	45% 6% 14% 25% 8% 1	2536
May	1st to 10th	Day	51% 6% 13% 21% 8% 1	4430
	11th to 20th	Day	37% 8% 15% 27% 13%	4392
	21st to end	Day	43% 10% 16% 23% 8%	4885
June	1st to 10th	Day	42% 9% 17% 22% 10% 1	2850
	11th to 20th	Day	42% 7% 15% 23% 12% 1	2850
	21st to end	Day	30% 7% 16% 34% 13% 1	2850
July	1st to 10th	Day	27% 8% 18% 24% 18% 4	4666
	11th to 20th	Day	18% 5% 13% 34% 23% 6%	4659
	21st to end	Day	15% 3 8% 30% 30% 13%	4711
August	1st to 10th	Day	27% 5% 10% 33% 22% 3	4378
	11th to 20th	Day	23% 5% 17% 35% 17% 2	4067
	21st to end	Day	23% 4 12% 38% 19% 3	4404
September	1st to 10th	Day	32% 5% 11% 29% 17% 6%	2280
	11th to 20th	Day	34% 6% 16% 28% 13% 3	2280
	21st to end	Day	34% 4 13% 31% 16% 2	1983
October	1st to 10th	Day	40% 6% 17% 27% 11%	1800
	11th to 20th	Day	39% 6% 15% 28% 11% 1	1800
	21st to end	Day	39% 7% 19% 26% 9%	1817
November	1st to 10th	Day	47% 6% 16% 22% 8% 1	1488
	11th to 20th	Day	42% 8% 18% 24% 8% 1	1520
	21st to end	Day	44% 8% 20% 21% 7% 1	1520
December	1st to 10th	Day	53% 8% 14% 19% 5% 1	1520
	11th to 20th	Day	47% 7% 22% 20% 4	1684
	21st to end	Day	36% 6% 15% 22% 14% 7%	2442
January	1st to 10th	Night	41% 11% 21% 20% 7% 1	4726
	11th to 20th	Night	48% 6% 15% 17% 13% 1	4738
	21st to end	Night	41% 6% 21% 26% 5%	4863
February	1st to 10th	Night	48% 6% 16% 19% 10% 1	2470
	11th to 20th	Night	47% 8% 17% 17% 10% 1	2403
	21st to end	Night	46% 7% 13% 22% 11% 1	2017
March	1st to 10th	Night	46% 8% 17% 21% 9%	3646
	11th to 20th	Night	33% 6% 27% 26% 8%	3490
	21st to end	Night	64% 8% 11% 12% 4	3711
April	1st to 10th	Night	42% 7% 15% 25% 11% 1	1900
	11th to 20th	Night	47% 7% 11% 22% 10% 2	1795
	21st to end	Night	45% 6% 13% 24% 12%	1644
May	1st to 10th	Night	45% 7% 11% 26% 10% 1	2540
	11th to 20th	Night	34% 9% 16% 27% 13%	2518
	21st to end	Night	37% 10% 17% 28% 8%	2683
June	1st to 10th	Night	38% 7% 16% 24% 13% 1	1330
	11th to 20th	Night	35% 6% 15% 26% 16% 2	1330
	21st to end	Night	26% 6% 18% 31% 17% 2	1330
July	1st to 10th	Night	19% 7% 22% 31% 18% 3	2185
	11th to 20th	Night	21% 4 13% 32% 21% 8%	2178
	21st to end	Night	19% 3 11% 27% 31% 9%	2609
August	1st to 10th	Night	25% 3 10% 33% 25% 4	2535
	11th to 20th	Night	23% 5% 16% 35% 19% 2	2838
	21st to end	Night	28% 5% 11% 34% 18% 4	3261
September	1st to 10th	Night	27% 4 10% 30% 20% 9%	1900
	11th to 20th	Night	33% 5% 12% 28% 18% 5%	1900
	21st to end	Night	28% 5% 12% 32% 21% 3	2164
October	1st to 10th	Night	37% 7% 13% 25% 17% 1	2160
	11th to 20th	Night	35% 6% 14% 29% 15% 1	2160
	21st to end	Night	41% 8% 15% 24% 11% 1	2518
November	1st to 10th	Night	47% 6% 15% 20% 10% 2	2590
	11th to 20th	Night	41% 7% 19% 24% 9% 1	2660
	21st to end	Night	44% 7% 22% 20% 8%	2660
December	1st to 10th	Night	51% 7% 17% 16% 8% 1	2660
	11th to 20th	Night	44% 8% 21% 22% 4 1	3505
	21st to end	Night	31% 5% 13% 28% 17% 6%	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	8% 12% 32% 25% 17% 6%	180
	11th to 20th	Day	6% 12% 34% 27% 19% 2	180
	21st to end	Day	9% 14% 32% 30% 14% 1	297
February	1st to 10th	Day	14% 11% 41% 27% 7% 1	270
	11th to 20th	Day	7% 11% 40% 30% 11% 1	270
	21st to end	Day	8% 8% 34% 37% 9% 4	225
March	1st to 10th	Day	11% 9% 35% 31% 13% 1	317
	11th to 20th	Day	7% 11% 40% 25% 13% 3	460
	21st to end	Day	11% 11% 32% 26% 17% 3	506
April	1st to 10th	Day	11% 15% 38% 28% 7%	460
	11th to 20th	Day	13% 17% 34% 27% 8% 2	452
	21st to end	Day	18% 13% 28% 29% 10% 1	526
May	1st to 10th	Day	15% 11% 25% 27% 18% 3	653
	11th to 20th	Day	12% 8% 26% 29% 19% 5%	675
	21st to end	Day	16% 11% 25% 25% 18% 6%	734
June	1st to 10th	Day	14% 12% 26% 27% 19% 3	680
	11th to 20th	Day	16% 12% 35% 24% 12% 2	680
	21st to end	Day	9% 7% 26% 31% 21% 5%	680
July	1st to 10th	Day	5% 4 25% 39% 22% 5%	671
	11th to 20th	Day	4 6% 28% 38% 20% 5%	668
	21st to end	Day	4 5% 25% 38% 24% 5%	739
August	1st to 10th	Day	8% 5% 22% 37% 21% 7%	671
	11th to 20th	Day	8% 7% 22% 34% 21% 8%	477
	21st to end	Day	7% 8% 25% 36% 19% 6%	539
September	1st to 10th	Day	11% 9% 30% 32% 15% 3	490
	11th to 20th	Day	13% 8% 27% 31% 19% 3	490
	21st to end	Day	15% 11% 27% 27% 16% 3	384
October	1st to 10th	Day	24% 10% 20% 22% 20% 4	270
	11th to 20th	Day	8% 8% 40% 27% 15% 3	270
	21st to end	Day	12% 14% 39% 22% 10% 2	297
November	1st to 10th	Day	18% 15% 33% 26% 8%	270
	11th to 20th	Day	10% 16% 37% 27% 8% 1	270
	21st to end	Day	9% 11% 39% 26% 11% 3	270
December	1st to 10th	Day	10% 8% 41% 29% 10% 2	270
	11th to 20th	Day	7% 16% 38% 31% 7% 2	180
	21st to end	Day	10% 7% 36% 27% 19% 3	198
January	1st to 10th	Night	7% 10% 39% 32% 11% 1	950
	11th to 20th	Night	9% 13% 37% 32% 7% 2	950
	21st to end	Night	8% 13% 39% 30% 10% 1	1035
February	1st to 10th	Night	8% 9% 33% 36% 13% 1	760
	11th to 20th	Night	8% 7% 40% 37% 8% 1	744
	21st to end	Night	6% 8% 32% 35% 17% 2	628
March	1st to 10th	Night	9% 9% 37% 33% 11% 1	760
	11th to 20th	Night	10% 8% 36% 34% 10% 2	760
	21st to end	Night	10% 9% 33% 34% 12% 2	770
April	1st to 10th	Night	9% 7% 37% 36% 9% 1	570
	11th to 20th	Night	19% 8% 34% 31% 8%	563
	21st to end	Night	12% 10% 31% 37% 9%	570
May	1st to 10th	Night	13% 8% 26% 38% 13% 1	570
	11th to 20th	Night	11% 4 30% 38% 15% 1	561
	21st to end	Night	17% 7% 25% 31% 18% 2	577
June	1st to 10th	Night	14% 9% 26% 34% 17% 1	380
	11th to 20th	Night	14% 6% 32% 38% 9%	380
	21st to end	Night	6% 5% 25% 45% 18% 1	380
July	1st to 10th	Night	6% 3 21% 47% 21%	370
	11th to 20th	Night	6% 3 27% 49% 15% 1	368
	21st to end	Night	3 4 26% 48% 18% 1	582
August	1st to 10th	Night	7% 3 26% 45% 18% 2	567
	11th to 20th	Night	7% 3 20% 46% 23% 1	564
	21st to end	Night	9% 5% 24% 42% 19% 1	627
September	1st to 10th	Night	11% 3 26% 41% 19% 1	570
	11th to 20th	Night	11% 6% 27% 38% 17% 1	570
	21st to end	Night	10% 6% 32% 37% 14% 1	742
October	1st to 10th	Night	14% 7% 30% 33% 15% 1	720
	11th to 20th	Night	10% 10% 32% 33% 14% 1	720
	21st to end	Night	13% 10% 38% 32% 6% 1	913
November	1st to 10th	Night	16% 11% 36% 29% 8%	925
	11th to 20th	Night	8% 13% 40% 30% 9% 1	950
	21st to end	Night	9% 10% 42% 31% 8%	950
December	1st to 10th	Night	9% 9% 37% 32% 12% 1	950
	11th to 20th	Night	9% 9% 40% 31% 10%	950
	21st to end	Night	12% 7% 36% 34% 10% 2	1045

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