Vernonia
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Vernonia clear sky chart from 2005-11-06 to 2024-01-13.

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	18% 11% 4 7% 6% 3 5% 4 5% 6% 30%	75168
	Night	17% 11% 4 7% 6% 3 5% 4 5% 6% 32%	74580
Transparency	Day	54% 6% 12% 16% 10% 2	74867
	Night	52% 7% 13% 16% 10% 3	74399
Seeing	Day	23% 12% 26% 25% 11% 3	13935
	Night	23% 8% 21% 30% 16% 2	22551

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	29% 18% 5% 11% 7% 4 5% 4 4 2 11%	1519
	11th to 20th	Day	24% 17% 5% 7% 7% 3 3 3 4 4 23%	1456
	21st to end	Day	21% 15% 6% 9% 7% 3 4 4 4 4 22%	1738
February	1st to 10th	Day	24% 17% 5% 10% 7% 4 5% 4 4 5% 15%	1620
	11th to 20th	Day	23% 19% 6% 10% 7% 3 4 4 3 4 18%	1575
	21st to end	Day	22% 17% 6% 11% 8% 5% 4 4 4 5% 14%	1378
March	1st to 10th	Day	23% 18% 5% 10% 6% 4 4 5% 6% 4 16%	1903
	11th to 20th	Day	27% 17% 6% 8% 7% 3 4 3 3 5% 17%	1980
	21st to end	Day	26% 17% 6% 10% 8% 5% 6% 4 4 4 9%	2209
April	1st to 10th	Day	24% 17% 6% 8% 7% 4 5% 4 5% 5% 15%	2160
	11th to 20th	Day	25% 15% 5% 9% 6% 3 5% 4 3 4 19%	2158
	21st to end	Day	22% 13% 4 8% 7% 4 5% 5% 5% 5% 20%	2340
May	1st to 10th	Day	17% 10% 4 8% 6% 3 5% 5% 6% 6% 30%	2470
	11th to 20th	Day	19% 10% 4 8% 7% 4 5% 6% 5% 7% 26%	2477
	21st to end	Day	21% 10% 4 8% 7% 4 6% 6% 5% 6% 23%	2723
June	1st to 10th	Day	22% 10% 4 6% 7% 4 4 5% 5% 6% 27%	2520
	11th to 20th	Day	18% 11% 4 8% 7% 5% 6% 5% 6% 7% 21%	2626
	21st to end	Day	11% 7% 3 5% 5% 3 4 4 5% 8% 43%	2700
July	1st to 10th	Day	8% 6% 3 5% 6% 3 5% 4 5% 6% 50%	2669
	11th to 20th	Day	9% 4 2 4 5% 2 4 4 5% 8% 53%	2520
	21st to end	Day	6% 3 2 3 3 2 3 3 4 6% 65%	2741
August	1st to 10th	Day	6% 5% 3 4 4 2 4 4 5% 8% 55%	2343
	11th to 20th	Day	7% 4 1 4 4 2 3 3 6% 8% 57%	2298
	21st to end	Day	8% 6% 3 5% 6% 3 4 5% 6% 7% 48%	2475
September	1st to 10th	Day	6% 5% 2 4 4 3 5% 5% 5% 7% 54%	2160
	11th to 20th	Day	11% 7% 3 7% 6% 3 5% 5% 5% 7% 40%	2139
	21st to end	Day	15% 9% 3 6% 5% 3 4 4 4 6% 40%	1905
October	1st to 10th	Day	19% 9% 3 6% 6% 4 5% 4 5% 5% 35%	1800
	11th to 20th	Day	19% 8% 3 8% 6% 4 5% 5% 6% 7% 31%	1800
	21st to end	Day	24% 11% 4 8% 6% 3 4 3 3 4 29%	1949
November	1st to 10th	Day	25% 14% 6% 8% 7% 4 6% 6% 5% 6% 15%	1538
	11th to 20th	Day	27% 14% 5% 8% 6% 4 4 3 4 5% 19%	1520
	21st to end	Day	22% 13% 5% 8% 8% 3 5% 5% 4 4 23%	1520
December	1st to 10th	Day	21% 13% 5% 8% 7% 4 7% 5% 4 4 22%	1520
	11th to 20th	Day	23% 15% 5% 10% 7% 5% 5% 4 5% 5% 16%	1925
	21st to end	Day	24% 19% 5% 11% 8% 5% 5% 4 4 4 11%	2794
January	1st to 10th	Night	28% 14% 5% 9% 7% 3 4 4 4 4 16%	2646
	11th to 20th	Night	24% 15% 5% 8% 7% 3 5% 5% 4 5% 19%	2560
	21st to end	Night	22% 14% 5% 9% 7% 3 4 4 4 6% 23%	2614
February	1st to 10th	Night	19% 17% 6% 9% 8% 4 6% 5% 4 4 18%	2340
	11th to 20th	Night	19% 14% 6% 8% 7% 3 5% 4 4 5% 24%	2272
	21st to end	Night	19% 16% 6% 9% 8% 4 5% 4 4 5% 20%	1876
March	1st to 10th	Night	19% 15% 5% 9% 7% 4 6% 4 4 5% 22%	2053
	11th to 20th	Night	22% 13% 5% 9% 7% 3 4 4 5% 6% 22%	1979
	21st to end	Night	21% 16% 6% 10% 7% 4 6% 5% 5% 4 16%	2147
April	1st to 10th	Night	20% 15% 6% 9% 7% 3 6% 4 4 6% 20%	1800
	11th to 20th	Night	17% 13% 4 8% 7% 5% 5% 4 4 7% 25%	1749
	21st to end	Night	18% 11% 4 6% 5% 3 4 5% 5% 8% 30%	1620
May	1st to 10th	Night	11% 10% 4 7% 5% 3 4 4 6% 7% 37%	1490
	11th to 20th	Night	14% 7% 3 6% 5% 4 6% 6% 7% 8% 34%	1416
	21st to end	Night	13% 7% 3 7% 7% 4 7% 6% 6% 8% 32%	1552
June	1st to 10th	Night	15% 7% 5% 7% 7% 3 5% 4 5% 6% 37%	1440
	11th to 20th	Night	11% 10% 5% 7% 5% 2 6% 4 6% 9% 35%	1328
	21st to end	Night	7% 6% 3 4 4 3 3 3 5% 7% 57%	1260
July	1st to 10th	Night	4 3 1 5% 3 3 4 5% 6% 8% 59%	1286
	11th to 20th	Night	4 4 2 4 4 2 3 4 5% 8% 60%	1440
	21st to end	Night	3 2 1 2 2 2 3 3 3 7% 72%	1576
August	1st to 10th	Night	3 2 1 2 3 2 3 4 5% 8% 65%	1593
	11th to 20th	Night	4 3 1 3 2 2 3 3 5% 7% 67%	1602
	21st to end	Night	6% 5% 2 4 4 3 3 4 6% 8% 55%	1880
September	1st to 10th	Night	5% 3 2 4 4 2 3 4 5% 7% 62%	1800
	11th to 20th	Night	9% 4 3 6% 5% 4 5% 4 5% 7% 49%	1818
	21st to end	Night	10% 6% 2 5% 5% 3 4 5% 5% 8% 47%	2054
October	1st to 10th	Night	15% 6% 2 5% 4 4 4 4 5% 6% 44%	2160
	11th to 20th	Night	17% 7% 3 6% 6% 3 4 4 5% 7% 37%	2160
	21st to end	Night	20% 8% 3 7% 5% 4 4 4 5% 5% 35%	2407
November	1st to 10th	Night	24% 12% 4 9% 7% 4 5% 5% 4 5% 22%	2540
	11th to 20th	Night	25% 12% 4 8% 7% 4 6% 4 4 5% 20%	2660
	21st to end	Night	20% 13% 5% 9% 7% 3 5% 5% 4 5% 26%	2660
December	1st to 10th	Night	19% 13% 5% 9% 7% 4 5% 5% 6% 5% 23%	2660
	11th to 20th	Night	21% 16% 5% 10% 8% 5% 5% 4 4 5% 17%	3280
	21st to end	Night	23% 16% 6% 11% 8% 4 5% 4 4 4 16%	4862

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	78% 6% 6% 5% 4 1	1519
	11th to 20th	Day	67% 4 10% 9% 6% 4	1456
	21st to end	Day	66% 6% 8% 11% 8% 1	1738
February	1st to 10th	Day	72% 5% 10% 10% 4	1620
	11th to 20th	Day	71% 6% 8% 10% 5%	1584
	21st to end	Day	73% 4 9% 7% 5% 1	1378
March	1st to 10th	Day	71% 6% 10% 8% 5%	1903
	11th to 20th	Day	71% 5% 8% 13% 3 1	1980
	21st to end	Day	77% 7% 8% 8%	2209
April	1st to 10th	Day	70% 6% 11% 11% 2	2160
	11th to 20th	Day	67% 6% 9% 10% 7% 2	2158
	21st to end	Day	63% 7% 11% 12% 6% 1	2340
May	1st to 10th	Day	51% 6% 16% 19% 7%	2470
	11th to 20th	Day	55% 7% 14% 17% 6% 1	2480
	21st to end	Day	58% 9% 15% 15% 3	2724
June	1st to 10th	Day	56% 6% 16% 13% 7%	2520
	11th to 20th	Day	58% 8% 17% 12% 5%	2626
	21st to end	Day	36% 8% 18% 25% 10% 3	2700
July	1st to 10th	Day	33% 7% 13% 23% 19% 5%	2596
	11th to 20th	Day	27% 5% 12% 28% 22% 5%	2445
	21st to end	Day	16% 5% 12% 34% 29% 5%	2589
August	1st to 10th	Day	25% 6% 17% 29% 19% 4	2326
	11th to 20th	Day	22% 7% 15% 29% 20% 6%	2298
	21st to end	Day	32% 7% 12% 28% 17% 3	2475
September	1st to 10th	Day	28% 6% 13% 25% 19% 9%	2160
	11th to 20th	Day	40% 8% 14% 17% 16% 6%	2139
	21st to end	Day	43% 6% 14% 17% 16% 4	1905
October	1st to 10th	Day	49% 6% 10% 20% 13% 3	1800
	11th to 20th	Day	52% 7% 13% 16% 11% 1	1800
	21st to end	Day	60% 5% 8% 15% 13%	1949
November	1st to 10th	Day	70% 7% 10% 10% 3	1538
	11th to 20th	Day	69% 4 10% 8% 6% 2	1520
	21st to end	Day	65% 6% 7% 9% 12% 1	1520
December	1st to 10th	Day	66% 6% 7% 11% 9% 1	1520
	11th to 20th	Day	70% 5% 11% 11% 2	1928
	21st to end	Day	76% 6% 10% 5% 3	2794
January	1st to 10th	Night	71% 6% 10% 7% 4 2	2646
	11th to 20th	Night	67% 5% 10% 8% 6% 3	2560
	21st to end	Night	64% 5% 9% 13% 9% 1	2614
February	1st to 10th	Night	68% 8% 8% 11% 4	2340
	11th to 20th	Night	62% 6% 12% 12% 6% 2	2274
	21st to end	Night	65% 8% 10% 10% 7% 1	1876
March	1st to 10th	Night	64% 6% 11% 14% 4	2053
	11th to 20th	Night	62% 8% 11% 13% 5% 1	1980
	21st to end	Night	68% 7% 14% 9% 1	2147
April	1st to 10th	Night	65% 5% 13% 12% 5%	1800
	11th to 20th	Night	57% 7% 12% 14% 7% 3	1749
	21st to end	Night	52% 7% 16% 17% 7% 2	1620
May	1st to 10th	Night	43% 7% 18% 22% 9% 1	1490
	11th to 20th	Night	43% 9% 18% 21% 6% 2	1416
	21st to end	Night	46% 11% 18% 19% 6%	1552
June	1st to 10th	Night	46% 6% 18% 23% 6% 1	1440
	11th to 20th	Night	43% 8% 22% 22% 5%	1328
	21st to end	Night	27% 6% 21% 31% 11% 5%	1260
July	1st to 10th	Night	20% 8% 18% 26% 19% 8%	1250
	11th to 20th	Night	19% 5% 15% 28% 25% 7%	1392
	21st to end	Night	9% 4 14% 35% 26% 12%	1488
August	1st to 10th	Night	14% 6% 20% 30% 24% 6%	1585
	11th to 20th	Night	16% 5% 17% 35% 18% 9%	1602
	21st to end	Night	24% 5% 15% 32% 20% 4	1880
September	1st to 10th	Night	22% 5% 14% 28% 20% 11%	1800
	11th to 20th	Night	34% 8% 16% 19% 15% 8%	1818
	21st to end	Night	33% 7% 15% 20% 19% 6%	2054
October	1st to 10th	Night	40% 4 11% 25% 16% 3	2160
	11th to 20th	Night	45% 7% 13% 19% 14% 2	2160
	21st to end	Night	50% 6% 11% 17% 14% 2	2407
November	1st to 10th	Night	63% 7% 10% 13% 6% 1	2540
	11th to 20th	Night	66% 6% 10% 10% 7% 2	2660
	21st to end	Night	60% 6% 9% 10% 13% 2	2660
December	1st to 10th	Night	62% 7% 10% 12% 9% 1	2660
	11th to 20th	Night	69% 7% 9% 9% 6%	3276
	21st to end	Night	70% 7% 13% 8% 2	4862

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	38% 15% 28% 10% 7% 2	180
	11th to 20th	Day	35% 15% 27% 12% 8% 4	164
	21st to end	Day	33% 11% 21% 24% 10% 2	330
February	1st to 10th	Day	41% 13% 19% 17% 9% 1	340
	11th to 20th	Day	40% 14% 26% 15% 4 1	335
	21st to end	Day	37% 19% 22% 17% 4 1	302
March	1st to 10th	Day	35% 16% 27% 14% 7%	420
	11th to 20th	Day	33% 15% 25% 17% 8% 2	420
	21st to end	Day	38% 17% 17% 20% 7% 1	462
April	1st to 10th	Day	37% 14% 22% 15% 9% 3	420
	11th to 20th	Day	33% 15% 24% 17% 7% 3	412
	21st to end	Day	30% 14% 29% 17% 8% 2	420
May	1st to 10th	Day	19% 17% 26% 24% 11% 3	423
	11th to 20th	Day	27% 11% 25% 23% 11% 3	448
	21st to end	Day	22% 11% 27% 24% 13% 4	485
June	1st to 10th	Day	23% 11% 26% 26% 12% 2	450
	11th to 20th	Day	21% 17% 34% 21% 6% 1	556
	21st to end	Day	10% 11% 33% 32% 12% 2	630
July	1st to 10th	Day	9% 7% 33% 36% 10% 3	591
	11th to 20th	Day	8% 10% 31% 35% 12% 3	444
	21st to end	Day	5% 5% 26% 42% 17% 4	487
August	1st to 10th	Day	8% 7% 22% 40% 17% 6%	447
	11th to 20th	Day	6% 4 23% 38% 23% 6%	437
	21st to end	Day	10% 8% 31% 33% 15% 4	495
September	1st to 10th	Day	9% 9% 27% 36% 16% 3	450
	11th to 20th	Day	14% 9% 24% 30% 18% 5%	450
	21st to end	Day	18% 13% 23% 29% 14% 3	450
October	1st to 10th	Day	22% 12% 22% 23% 18% 3	450
	11th to 20th	Day	25% 10% 24% 21% 17% 3	450
	21st to end	Day	32% 12% 23% 19% 10% 4	464
November	1st to 10th	Day	32% 17% 25% 16% 10%	205
	11th to 20th	Day	31% 14% 28% 17% 9% 2	180
	21st to end	Day	24% 18% 28% 21% 8% 1	180
December	1st to 10th	Day	32% 17% 24% 16% 9% 3	180
	11th to 20th	Day	37% 12% 26% 21% 4	180
	21st to end	Day	36% 17% 23% 16% 7% 1	198
January	1st to 10th	Night	37% 12% 21% 17% 11% 2	760
	11th to 20th	Night	35% 11% 18% 18% 16% 2	732
	21st to end	Night	30% 6% 17% 30% 15% 2	792
February	1st to 10th	Night	28% 11% 22% 26% 12% 1	720
	11th to 20th	Night	27% 9% 21% 28% 15%	704
	21st to end	Night	27% 12% 24% 27% 10%	592
March	1st to 10th	Night	28% 10% 22% 25% 14% 1	720
	11th to 20th	Night	29% 10% 19% 29% 13% 1	720
	21st to end	Night	31% 10% 20% 27% 10% 2	792
April	1st to 10th	Night	29% 13% 19% 26% 12% 1	720
	11th to 20th	Night	26% 8% 23% 29% 12% 2	681
	21st to end	Night	24% 8% 22% 31% 15% 1	540
May	1st to 10th	Night	16% 8% 26% 34% 15% 1	410
	11th to 20th	Night	17% 5% 22% 34% 21% 1	354
	21st to end	Night	17% 7% 25% 33% 18%	389
June	1st to 10th	Night	19% 3 26% 39% 12%	360
	11th to 20th	Night	15% 8% 27% 36% 12% 1	360
	21st to end	Night	10% 5% 24% 44% 16% 1	360
July	1st to 10th	Night	4 3 28% 49% 16%	350
	11th to 20th	Night	6% 5% 34% 41% 14% 1	348
	21st to end	Night	3 2 27% 48% 18%	394
August	1st to 10th	Night	5% 3 15% 45% 28% 3	519
	11th to 20th	Night	5% 2 14% 43% 32% 3	534
	21st to end	Night	10% 4 24% 39% 21% 2	692
September	1st to 10th	Night	7% 5% 20% 45% 21% 2	720
	11th to 20th	Night	11% 3 16% 34% 29% 6%	720
	21st to end	Night	14% 6% 18% 38% 23% 2	720
October	1st to 10th	Night	19% 4 18% 36% 20% 2	720
	11th to 20th	Night	21% 6% 17% 28% 23% 4	720
	21st to end	Night	27% 8% 19% 25% 18% 2	792
November	1st to 10th	Night	29% 9% 21% 27% 13% 1	740
	11th to 20th	Night	32% 12% 20% 24% 11% 1	760
	21st to end	Night	26% 11% 22% 27% 13% 1	760
December	1st to 10th	Night	27% 9% 23% 25% 14% 2	760
	11th to 20th	Night	34% 12% 22% 21% 11% 1	760
	21st to end	Night	37% 14% 23% 17% 8% 1	836

Page generated at 2024-01-10 07:16:11. Version ac07

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