Vernon
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Vernon clear sky chart from 2005-11-06 to 2024-11-08.

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% 8% 3 8% 6% 6% 5% 4 6% 7% 38%	105686
	Night	8% 11% 4 9% 6% 5% 5% 4 6% 7% 34%	101954
Transparency	Day	42% 12% 16% 19% 9% 2	105444
	Night	46% 12% 16% 17% 8% 1	101842
Seeing	Day	13% 13% 26% 27% 16% 4	15528
	Night	15% 9% 23% 32% 18% 3	23925

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	10% 17% 7% 14% 8% 8% 6% 4 6% 6% 15%	2305
	11th to 20th	Day	9% 15% 4 10% 7% 8% 6% 6% 6% 7% 21%	2516
	21st to end	Day	7% 15% 5% 13% 9% 7% 7% 5% 7% 8% 16%	2794
February	1st to 10th	Day	8% 15% 4 13% 8% 7% 6% 4 6% 4 23%	1534
	11th to 20th	Day	7% 12% 4 11% 7% 6% 5% 4 6% 6% 30%	1665
	21st to end	Day	7% 14% 5% 9% 8% 7% 7% 5% 8% 8% 23%	1555
March	1st to 10th	Day	4 10% 5% 12% 8% 8% 7% 5% 8% 9% 23%	3138
	11th to 20th	Day	5% 7% 3 6% 6% 6% 7% 4 7% 8% 42%	3296
	21st to end	Day	7% 12% 4 10% 7% 6% 6% 5% 7% 8% 28%	4149
April	1st to 10th	Day	9% 14% 5% 9% 7% 6% 6% 4 7% 8% 26%	2280
	11th to 20th	Day	8% 11% 4 9% 7% 6% 5% 5% 7% 7% 31%	2289
	21st to end	Day	9% 11% 3 9% 6% 6% 6% 4 7% 8% 30%	2598
May	1st to 10th	Day	7% 8% 3 8% 5% 5% 6% 4 7% 8% 40%	4420
	11th to 20th	Day	8% 7% 3 8% 5% 5% 5% 5% 7% 10% 37%	4377
	21st to end	Day	14% 11% 4 10% 7% 7% 6% 4 6% 7% 25%	4959
June	1st to 10th	Day	14% 8% 3 8% 7% 5% 5% 4 6% 7% 32%	2889
	11th to 20th	Day	15% 8% 3 8% 6% 6% 7% 6% 6% 6% 29%	3040
	21st to end	Day	9% 6% 2 6% 5% 6% 5% 4 7% 8% 42%	3040
July	1st to 10th	Day	4 3 1 4 3 4 3 3 5% 6% 63%	4938
	11th to 20th	Day	3 2 1 3 3 2 3 3 4 6% 70%	4490
	21st to end	Day	4 3 1 4 3 4 4 3 5% 8% 62%	4790
August	1st to 10th	Day	2 2 1 3 3 4 4 5% 7% 8% 62%	4401
	11th to 20th	Day	3 3 1 4 4 4 5% 5% 7% 9% 56%	4330
	21st to end	Day	7% 4 2 5% 4 5% 4 4 7% 8% 50%	4252
September	1st to 10th	Day	6% 4 1 5% 5% 4 4 3 6% 8% 53%	2280
	11th to 20th	Day	8% 5% 2 6% 5% 5% 5% 4 6% 8% 44%	2252
	21st to end	Day	10% 8% 3 7% 5% 5% 6% 4 6% 9% 38%	2085
October	1st to 10th	Day	7% 8% 3 8% 6% 5% 5% 3 5% 8% 41%	3180
	11th to 20th	Day	16% 9% 3 7% 5% 4 4 3 5% 7% 35%	3035
	21st to end	Day	10% 9% 3 9% 6% 5% 5% 4 7% 7% 35%	3101
November	1st to 10th	Day	13% 13% 4 11% 7% 6% 6% 5% 7% 6% 23%	1646
	11th to 20th	Day	9% 12% 4 11% 8% 6% 6% 6% 6% 6% 26%	1520
	21st to end	Day	10% 14% 4 13% 9% 7% 7% 5% 7% 7% 18%	1348
December	1st to 10th	Day	8% 13% 5% 13% 10% 8% 7% 5% 6% 6% 20%	1330
	11th to 20th	Day	9% 15% 6% 14% 9% 8% 6% 5% 7% 7% 14%	1682
	21st to end	Day	10% 14% 4 14% 9% 9% 7% 5% 6% 7% 16%	2182
January	1st to 10th	Night	11% 22% 7% 15% 8% 6% 6% 4 5% 6% 12%	4647
	11th to 20th	Night	8% 15% 5% 15% 8% 6% 7% 5% 5% 6% 19%	4382
	21st to end	Night	9% 17% 6% 16% 10% 7% 6% 4 5% 6% 14%	4862
February	1st to 10th	Night	11% 17% 5% 11% 8% 6% 6% 5% 6% 6% 20%	2644
	11th to 20th	Night	9% 14% 4 12% 6% 5% 5% 4 5% 7% 30%	2402
	21st to end	Night	8% 16% 5% 11% 7% 5% 5% 5% 6% 6% 27%	1899
March	1st to 10th	Night	6% 10% 4 9% 7% 7% 6% 5% 8% 8% 30%	3736
	11th to 20th	Night	5% 9% 3 6% 5% 4 4 4 5% 8% 47%	3680
	21st to end	Night	7% 11% 4 10% 6% 7% 6% 4 6% 7% 32%	3503
April	1st to 10th	Night	7% 9% 4 7% 6% 6% 4 5% 6% 9% 36%	1900
	11th to 20th	Night	8% 10% 4 9% 7% 7% 6% 6% 7% 6% 32%	1842
	21st to end	Night	9% 8% 4 7% 6% 6% 6% 4 6% 7% 37%	1579
May	1st to 10th	Night	6% 8% 3 10% 7% 6% 6% 4 6% 7% 37%	2540
	11th to 20th	Night	8% 7% 3 6% 5% 5% 5% 4 7% 9% 40%	2516
	21st to end	Night	11% 8% 3 9% 5% 6% 6% 5% 7% 8% 33%	2612
June	1st to 10th	Night	11% 8% 3 6% 6% 4 6% 5% 6% 9% 36%	1287
	11th to 20th	Night	13% 6% 3 8% 6% 5% 5% 5% 8% 8% 33%	1140
	21st to end	Night	5% 6% 2 7% 5% 4 6% 6% 7% 9% 42%	1140
July	1st to 10th	Night	3 3 1 4 4 5% 4 5% 6% 7% 58%	2018
	11th to 20th	Night	2 2 1 3 3 3 3 3 4 6% 71%	2466
	21st to end	Night	4 3 1 3 3 3 4 2 5% 7% 65%	2762
August	1st to 10th	Night	2 1 1 2 2 3 4 3 8% 11% 61%	2529
	11th to 20th	Night	3 2 1 6% 4 4 5% 4 6% 10% 56%	2497
	21st to end	Night	7% 4 2 6% 3 4 5% 4 6% 8% 52%	3422
September	1st to 10th	Night	5% 3 2 5% 4 4 4 3 6% 7% 57%	1900
	11th to 20th	Night	8% 5% 3 4 4 4 4 4 5% 8% 51%	1928
	21st to end	Night	10% 6% 3 8% 4 4 5% 3 4 8% 46%	2093
October	1st to 10th	Night	7% 7% 3 7% 5% 5% 5% 4 6% 7% 44%	3800
	11th to 20th	Night	17% 8% 2 6% 4 4 3 3 5% 7% 41%	3898
	21st to end	Night	9% 10% 3 9% 6% 5% 5% 3 5% 6% 38%	4457
November	1st to 10th	Night	15% 14% 4 9% 6% 5% 5% 4 6% 7% 25%	2589
	11th to 20th	Night	12% 13% 3 11% 8% 7% 6% 5% 5% 5% 25%	2660
	21st to end	Night	11% 16% 5% 12% 7% 6% 6% 5% 6% 7% 20%	2812
December	1st to 10th	Night	9% 16% 5% 12% 8% 6% 6% 5% 7% 6% 22%	2850
	11th to 20th	Night	10% 18% 6% 16% 10% 7% 6% 5% 4 5% 11%	3510
	21st to end	Night	10% 15% 6% 16% 9% 8% 6% 5% 5% 5% 15%	5452

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	63% 22% 11% 3 1	2305
	11th to 20th	Day	56% 13% 17% 10% 1 3	2540
	21st to end	Day	64% 17% 13% 5% 1	2794
February	1st to 10th	Day	62% 12% 13% 9% 4 1	1534
	11th to 20th	Day	53% 14% 16% 12% 5% 1	1674
	21st to end	Day	55% 15% 16% 11% 3	1555
March	1st to 10th	Day	51% 16% 14% 15% 4	3138
	11th to 20th	Day	35% 12% 23% 26% 4	3296
	21st to end	Day	51% 13% 18% 12% 6%	4149
April	1st to 10th	Day	54% 14% 16% 14% 3	2280
	11th to 20th	Day	50% 10% 15% 17% 7% 1	2289
	21st to end	Day	50% 11% 16% 16% 7%	2598
May	1st to 10th	Day	36% 13% 16% 22% 12% 1	4420
	11th to 20th	Day	36% 16% 19% 22% 6%	4380
	21st to end	Day	51% 16% 16% 13% 3	4960
June	1st to 10th	Day	49% 12% 13% 14% 9% 2	2889
	11th to 20th	Day	53% 12% 12% 16% 7% 1	3040
	21st to end	Day	38% 12% 17% 19% 13% 2	3040
July	1st to 10th	Day	21% 8% 11% 22% 25% 14%	4862
	11th to 20th	Day	16% 5% 9% 25% 30% 14%	4412
	21st to end	Day	21% 5% 15% 30% 22% 6%	4639
August	1st to 10th	Day	17% 8% 12% 38% 22% 3	4384
	11th to 20th	Day	23% 8% 26% 30% 11% 2	4372
	21st to end	Day	31% 9% 23% 29% 8% 1	4251
September	1st to 10th	Day	29% 10% 16% 30% 13% 3	2280
	11th to 20th	Day	35% 12% 15% 24% 13% 1	2252
	21st to end	Day	42% 11% 21% 17% 8% 1	2085
October	1st to 10th	Day	42% 8% 24% 22% 4	3180
	11th to 20th	Day	49% 8% 16% 25% 2	3035
	21st to end	Day	45% 11% 25% 16% 3	3101
November	1st to 10th	Day	60% 13% 13% 12% 3	1646
	11th to 20th	Day	58% 14% 15% 8% 3 1	1520
	21st to end	Day	60% 15% 17% 7% 1	1348
December	1st to 10th	Day	61% 14% 12% 12% 1	1330
	11th to 20th	Day	63% 17% 13% 6% 2	1684
	21st to end	Day	59% 15% 16% 9% 1	2182
January	1st to 10th	Night	66% 17% 10% 5% 1	4647
	11th to 20th	Night	62% 10% 16% 8% 3 1	4420
	21st to end	Night	66% 16% 11% 5% 2	4862
February	1st to 10th	Night	61% 11% 13% 10% 4 1	2644
	11th to 20th	Night	53% 10% 15% 16% 5% 1	2404
	21st to end	Night	55% 11% 16% 11% 6%	1899
March	1st to 10th	Night	43% 15% 17% 18% 7%	3736
	11th to 20th	Night	33% 11% 25% 25% 5%	3681
	21st to end	Night	47% 13% 16% 17% 7%	3503
April	1st to 10th	Night	41% 17% 20% 16% 5%	1900
	11th to 20th	Night	49% 11% 14% 18% 7% 1	1842
	21st to end	Night	44% 12% 14% 21% 9%	1579
May	1st to 10th	Night	41% 13% 12% 21% 14%	2540
	11th to 20th	Night	31% 16% 20% 26% 7%	2516
	21st to end	Night	42% 16% 19% 18% 5%	2612
June	1st to 10th	Night	43% 12% 13% 19% 9% 4	1287
	11th to 20th	Night	46% 11% 14% 19% 10%	1140
	21st to end	Night	33% 14% 19% 21% 11% 2	1140
July	1st to 10th	Night	23% 7% 12% 21% 22% 16%	1985
	11th to 20th	Night	16% 5% 10% 21% 34% 14%	2421
	21st to end	Night	19% 5% 12% 33% 21% 11%	2674
August	1st to 10th	Night	16% 6% 12% 37% 25% 4	2521
	11th to 20th	Night	24% 7% 23% 29% 15% 2	2521
	21st to end	Night	29% 8% 24% 26% 12% 1	3422
September	1st to 10th	Night	26% 10% 16% 29% 16% 4	1900
	11th to 20th	Night	31% 11% 15% 23% 18% 3	1928
	21st to end	Night	38% 9% 18% 23% 10% 2	2093
October	1st to 10th	Night	38% 10% 20% 23% 8%	3800
	11th to 20th	Night	44% 8% 18% 24% 6%	3898
	21st to end	Night	47% 8% 18% 24% 3	4457
November	1st to 10th	Night	57% 13% 13% 12% 4	2589
	11th to 20th	Night	58% 15% 12% 10% 5%	2660
	21st to end	Night	60% 14% 15% 8% 3	2812
December	1st to 10th	Night	58% 12% 16% 11% 3	2850
	11th to 20th	Night	68% 15% 10% 5% 1	3507
	21st to end	Night	61% 15% 16% 7% 1	5452

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	16% 13% 26% 24% 13% 8%	180
	11th to 20th	Day	16% 8% 31% 23% 18% 4	180
	21st to end	Day	17% 8% 29% 30% 14% 3	198
February	1st to 10th	Day	16% 21% 35% 21% 6% 1	194
	11th to 20th	Day	13% 18% 31% 27% 9% 2	365
	21st to end	Day	13% 16% 28% 30% 11% 2	375
March	1st to 10th	Day	13% 22% 28% 24% 10% 2	460
	11th to 20th	Day	13% 19% 25% 26% 14% 3	460
	21st to end	Day	17% 20% 26% 18% 16% 2	506
April	1st to 10th	Day	20% 22% 27% 20% 10% 1	460
	11th to 20th	Day	18% 20% 25% 21% 12% 4	452
	21st to end	Day	13% 20% 30% 22% 10% 5%	460
May	1st to 10th	Day	10% 17% 32% 25% 12% 3	463
	11th to 20th	Day	12% 12% 24% 28% 19% 5%	488
	21st to end	Day	15% 12% 22% 28% 18% 5%	610
June	1st to 10th	Day	17% 12% 27% 29% 13% 2	719
	11th to 20th	Day	15% 13% 28% 27% 14% 2	870
	21st to end	Day	11% 11% 25% 29% 20% 4	870
July	1st to 10th	Day	9% 9% 21% 35% 23% 3	789
	11th to 20th	Day	5% 10% 25% 33% 22% 4	525
	21st to end	Day	5% 7% 24% 35% 23% 6%	531
August	1st to 10th	Day	4 8% 21% 35% 23% 9%	487
	11th to 20th	Day	6% 7% 24% 33% 21% 9%	477
	21st to end	Day	10% 9% 25% 30% 19% 7%	539
September	1st to 10th	Day	9% 11% 23% 32% 19% 5%	490
	11th to 20th	Day	11% 11% 26% 28% 21% 3	490
	21st to end	Day	18% 14% 27% 25% 13% 3	490
October	1st to 10th	Day	16% 12% 26% 25% 17% 5%	490
	11th to 20th	Day	18% 15% 26% 23% 15% 3	415
	21st to end	Day	21% 11% 30% 25% 11% 2	330
November	1st to 10th	Day	19% 12% 30% 26% 12% 2	247
	11th to 20th	Day	16% 17% 28% 22% 13% 4	180
	21st to end	Day	16% 12% 29% 23% 14% 6%	180
December	1st to 10th	Day	17% 9% 20% 24% 23% 7%	180
	11th to 20th	Day	17% 9% 32% 23% 13% 5%	180
	21st to end	Day	17% 7% 26% 35% 10% 5%	198
January	1st to 10th	Night	23% 12% 26% 26% 11% 2	837
	11th to 20th	Night	17% 9% 26% 31% 15% 1	760
	21st to end	Night	15% 9% 27% 30% 16% 3	836
February	1st to 10th	Night	21% 11% 25% 30% 12% 2	760
	11th to 20th	Night	16% 9% 25% 35% 13% 1	744
	21st to end	Night	16% 9% 24% 29% 19% 4	628
March	1st to 10th	Night	15% 12% 25% 29% 18% 2	760
	11th to 20th	Night	13% 11% 26% 33% 15% 1	760
	21st to end	Night	13% 9% 27% 31% 17% 3	836
April	1st to 10th	Night	12% 12% 25% 30% 19% 2	760
	11th to 20th	Night	14% 10% 26% 31% 17% 1	714
	21st to end	Night	13% 10% 28% 31% 15% 2	439
May	1st to 10th	Night	13% 9% 19% 36% 21% 1	380
	11th to 20th	Night	12% 5% 20% 38% 23% 2	374
	21st to end	Night	15% 7% 18% 30% 26% 4	411
June	1st to 10th	Night	16% 5% 28% 34% 16% 1	380
	11th to 20th	Night	15% 7% 25% 32% 19% 2	380
	21st to end	Night	8% 6% 22% 38% 23% 3	380
July	1st to 10th	Night	8% 5% 16% 36% 33% 2	370
	11th to 20th	Night	5% 6% 20% 35% 32% 2	368
	21st to end	Night	6% 1 14% 41% 34% 3	416
August	1st to 10th	Night	5% 1 14% 36% 35% 8%	378
	11th to 20th	Night	4 2 13% 40% 35% 6%	376
	21st to end	Night	7% 4 19% 37% 30% 3	786
September	1st to 10th	Night	7% 5% 18% 39% 26% 5%	760
	11th to 20th	Night	11% 5% 16% 28% 33% 7%	760
	21st to end	Night	15% 8% 19% 34% 19% 4	760
October	1st to 10th	Night	13% 6% 20% 35% 23% 3	760
	11th to 20th	Night	18% 9% 20% 30% 21% 2	760
	21st to end	Night	18% 9% 26% 30% 13% 3	836
November	1st to 10th	Night	23% 10% 22% 35% 9% 1	770
	11th to 20th	Night	20% 14% 26% 25% 13% 2	760
	21st to end	Night	18% 11% 25% 30% 13% 3	912
December	1st to 10th	Night	14% 9% 28% 32% 14% 2	950
	11th to 20th	Night	18% 10% 29% 32% 11% 1	950
	21st to end	Night	21% 9% 28% 32% 9% 1	1114

Page generated at 2024-11-05 05:15:48. Version ac07

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