Longview
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Longview clear sky chart from 2005-11-06 to 2024-02-15.

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	13% 6% 3 5% 5% 3 4 4 5% 7% 45%	78811
	Night	12% 5% 2 4 4 2 4 4 4 7% 52%	80324
Transparency	Day	37% 6% 11% 21% 19% 6%	78536
	Night	33% 5% 10% 20% 22% 9%	80119
Seeing	Day	14% 8% 21% 27% 22% 7%	14093
	Night	14% 8% 26% 32% 18% 2	24108

By Month

Percentage Cloud Cover SE (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	17% 10% 3 5% 4 2 2 3 3 5% 44%	2847
	11th to 20th	Day	19% 5% 2 4 3 2 2 3 3 6% 51%	2850
	21st to end	Day	23% 9% 3 4 4 2 2 3 2 3 45%	3135
February	1st to 10th	Day	22% 9% 3 5% 5% 2 4 3 3 4 41%	1710
	11th to 20th	Day	23% 8% 3 5% 4 2 3 3 3 5% 41%	1755
	21st to end	Day	24% 7% 3 4 4 2 4 3 3 4 43%	1628
March	1st to 10th	Day	20% 7% 3 6% 4 2 4 4 4 6% 41%	1980
	11th to 20th	Day	18% 8% 3 5% 5% 2 4 4 4 6% 42%	1980
	21st to end	Day	16% 8% 3 4 4 3 4 4 5% 6% 43%	2178
April	1st to 10th	Day	13% 7% 3 5% 4 3 4 3 5% 7% 45%	2011
	11th to 20th	Day	15% 7% 3 4 4 3 5% 5% 6% 7% 41%	2134
	21st to end	Day	13% 5% 3 4 5% 4 4 5% 6% 7% 44%	2160
May	1st to 10th	Day	13% 6% 4 6% 5% 3 4 5% 5% 7% 43%	2250
	11th to 20th	Day	11% 6% 3 6% 5% 4 6% 5% 6% 8% 41%	2302
	21st to end	Day	11% 5% 3 6% 6% 4 6% 5% 6% 9% 38%	2531
June	1st to 10th	Day	6% 5% 2 5% 5% 4 6% 5% 8% 10% 43%	2340
	11th to 20th	Day	5% 3 2 5% 6% 4 7% 6% 7% 11% 45%	2340
	21st to end	Day	5% 4 2 4 6% 3 6% 6% 8% 10% 47%	2340
July	1st to 10th	Day	7% 5% 3 7% 7% 5% 7% 8% 9% 11% 32%	2340
	11th to 20th	Day	4 3 2 4 5% 5% 6% 7% 7% 10% 48%	2340
	21st to end	Day	5% 4 2 5% 5% 4 6% 6% 7% 11% 43%	2546
August	1st to 10th	Day	3 2 2 4 4 3 5% 5% 7% 12% 52%	2328
	11th to 20th	Day	7% 5% 2 5% 5% 3 5% 6% 7% 10% 46%	2230
	21st to end	Day	7% 4 2 5% 7% 4 6% 6% 8% 11% 39%	2376
September	1st to 10th	Day	8% 5% 3 5% 5% 3 5% 5% 5% 8% 48%	2080
	11th to 20th	Day	11% 6% 3 5% 6% 3 5% 4 5% 8% 44%	1980
	21st to end	Day	7% 3 1 3 4 3 5% 4 5% 7% 57%	1980
October	1st to 10th	Day	7% 3 1 4 4 2 4 4 5% 5% 60%	1819
	11th to 20th	Day	14% 5% 2 4 4 2 3 4 4 5% 54%	1800
	21st to end	Day	15% 5% 2 4 4 3 3 3 3 4 55%	1980
November	1st to 10th	Day	12% 5% 3 5% 4 2 4 3 5% 6% 53%	1858
	11th to 20th	Day	10% 5% 3 4 5% 2 3 4 4 5% 54%	1900
	21st to end	Day	18% 8% 3 4 4 2 3 3 4 5% 45%	1777
December	1st to 10th	Day	15% 7% 3 5% 4 3 4 3 5% 5% 47%	1710
	11th to 20th	Day	17% 7% 3 5% 5% 3 4 3 4 6% 43%	2161
	21st to end	Day	16% 9% 3 6% 5% 3 3 3 4 6% 42%	3135
January	1st to 10th	Night	15% 8% 3 5% 4 2 3 3 3 5% 49%	4108
	11th to 20th	Night	18% 6% 2 3 2 2 2 3 3 4 55%	4120
	21st to end	Night	23% 10% 2 4 4 2 2 2 3 4 43%	4532
February	1st to 10th	Night	18% 7% 2 4 4 2 4 3 4 6% 46%	2470
	11th to 20th	Night	20% 7% 3 4 4 2 3 3 3 4 46%	2199
	21st to end	Night	18% 7% 3 5% 4 2 3 4 3 6% 45%	1628
March	1st to 10th	Night	17% 6% 3 5% 4 3 3 3 4 7% 45%	1980
	11th to 20th	Night	15% 7% 3 6% 4 3 4 3 4 6% 45%	1980
	21st to end	Night	13% 6% 2 4 4 2 4 4 4 6% 49%	2178
April	1st to 10th	Night	10% 4 2 4 4 3 5% 5% 5% 8% 50%	1949
	11th to 20th	Night	11% 5% 2 4 6% 3 4 5% 5% 6% 48%	1775
	21st to end	Night	12% 5% 2 4 4 2 3 3 4 8% 52%	1800
May	1st to 10th	Night	8% 5% 2 6% 5% 3 4 4 5% 9% 48%	1706
	11th to 20th	Night	9% 5% 2 4 6% 3 4 4 5% 8% 51%	1593
	21st to end	Night	9% 4 2 5% 5% 3 4 5% 6% 10% 48%	1745
June	1st to 10th	Night	4 3 2 4 4 2 4 5% 7% 11% 55%	1620
	11th to 20th	Night	3 2 2 4 3 2 4 4 6% 9% 61%	1620
	21st to end	Night	5% 3 1 3 4 3 4 6% 7% 9% 57%	1620
July	1st to 10th	Night	5% 3 3 5% 5% 3 5% 5% 6% 10% 49%	1620
	11th to 20th	Night	2 1 1 3 3 3 4 6% 7% 13% 59%	1620
	21st to end	Night	2 2 2 4 5% 3 6% 6% 7% 12% 51%	1772
August	1st to 10th	Night	3 2 1 3 2 2 3 4 5% 9% 66%	1611
	11th to 20th	Night	5% 4 2 5% 5% 2 4 6% 7% 11% 50%	1669
	21st to end	Night	5% 3 2 4 4 3 6% 7% 8% 10% 48%	1980
September	1st to 10th	Night	7% 4 1 5% 4 3 5% 4 5% 7% 55%	1876
	11th to 20th	Night	11% 5% 1 4 4 3 4 4 5% 8% 52%	1980
	21st to end	Night	7% 2 1 3 3 2 4 4 5% 8% 61%	1980
October	1st to 10th	Night	5% 3 1 4 3 2 4 3 4 7% 63%	2121
	11th to 20th	Night	13% 4 2 3 2 2 3 4 3 6% 60%	2160
	21st to end	Night	15% 4 2 4 3 2 2 2 3 5% 57%	2376
November	1st to 10th	Night	10% 5% 2 4 3 2 3 4 4 6% 58%	2220
	11th to 20th	Night	9% 4 3 5% 5% 3 3 3 3 6% 56%	2280
	21st to end	Night	15% 6% 3 4 4 2 3 3 4 5% 49%	2398
December	1st to 10th	Night	15% 6% 2 5% 5% 2 3 4 4 6% 48%	2470
	11th to 20th	Night	15% 7% 2 5% 5% 3 4 3 3 4 49%	3036
	21st to end	Night	16% 7% 3 5% 5% 2 3 2 3 4 49%	4532

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	44% 3 5% 18% 26% 5%	2848
	11th to 20th	Day	36% 4 8% 22% 26% 4	2850
	21st to end	Day	46% 4 4 15% 22% 10%	3135
February	1st to 10th	Day	49% 3 5% 16% 18% 9%	1710
	11th to 20th	Day	48% 3 5% 18% 18% 8%	1765
	21st to end	Day	47% 4 6% 12% 21% 11%	1628
March	1st to 10th	Day	45% 4 8% 16% 18% 10%	1980
	11th to 20th	Day	45% 4 8% 17% 19% 6%	1980
	21st to end	Day	43% 5% 8% 17% 23% 5%	2178
April	1st to 10th	Day	40% 5% 10% 21% 16% 8%	2011
	11th to 20th	Day	40% 6% 10% 17% 19% 7%	2134
	21st to end	Day	38% 6% 10% 21% 22% 4	2160
May	1st to 10th	Day	40% 6% 9% 21% 16% 7%	2250
	11th to 20th	Day	39% 7% 14% 22% 16% 2	2306
	21st to end	Day	41% 8% 14% 21% 14% 1	2531
June	1st to 10th	Day	33% 8% 16% 28% 14% 1	2340
	11th to 20th	Day	30% 8% 17% 27% 15% 2	2340
	21st to end	Day	30% 8% 15% 27% 17% 3	2340
July	1st to 10th	Day	40% 11% 19% 21% 8% 1	2276
	11th to 20th	Day	28% 9% 20% 28% 15%	2271
	21st to end	Day	30% 9% 21% 29% 11%	2405
August	1st to 10th	Day	22% 9% 18% 34% 15% 2	2314
	11th to 20th	Day	31% 9% 15% 27% 16% 2	2230
	21st to end	Day	35% 10% 16% 25% 13% 2	2376
September	1st to 10th	Day	34% 7% 13% 20% 17% 10%	2080
	11th to 20th	Day	38% 7% 12% 18% 18% 7%	1980
	21st to end	Day	25% 6% 10% 22% 25% 11%	1980
October	1st to 10th	Day	25% 5% 11% 22% 23% 15%	1819
	11th to 20th	Day	33% 4 7% 16% 26% 15%	1800
	21st to end	Day	35% 3 6% 16% 27% 14%	1980
November	1st to 10th	Day	33% 4 9% 19% 25% 10%	1858
	11th to 20th	Day	33% 4 7% 18% 27% 11%	1900
	21st to end	Day	43% 4 5% 16% 24% 8%	1777
December	1st to 10th	Day	40% 4 9% 18% 22% 7%	1710
	11th to 20th	Day	43% 3 6% 16% 24% 8%	2159
	21st to end	Day	44% 4 6% 16% 23% 7%	3135
January	1st to 10th	Night	38% 4 6% 14% 31% 7%	4108
	11th to 20th	Night	35% 3 7% 17% 28% 10%	4120
	21st to end	Night	46% 3 6% 14% 22% 9%	4532
February	1st to 10th	Night	40% 4 8% 19% 17% 12%	2470
	11th to 20th	Night	42% 4 6% 17% 23% 9%	2199
	21st to end	Night	43% 4 8% 13% 19% 13%	1628
March	1st to 10th	Night	41% 5% 7% 16% 20% 12%	1980
	11th to 20th	Night	40% 5% 8% 16% 22% 9%	1980
	21st to end	Night	36% 5% 11% 19% 23% 7%	2178
April	1st to 10th	Night	32% 5% 13% 21% 18% 11%	1949
	11th to 20th	Night	35% 6% 9% 19% 19% 12%	1775
	21st to end	Night	32% 4 10% 22% 27% 5%	1800
May	1st to 10th	Night	34% 7% 11% 22% 19% 9%	1706
	11th to 20th	Night	32% 6% 14% 26% 17% 4	1594
	21st to end	Night	31% 7% 16% 26% 19% 2	1746
June	1st to 10th	Night	22% 8% 18% 30% 20% 2	1620
	11th to 20th	Night	19% 6% 18% 33% 21% 4	1620
	21st to end	Night	22% 8% 16% 27% 25% 4	1620
July	1st to 10th	Night	29% 8% 20% 30% 13% 1	1575
	11th to 20th	Night	15% 7% 25% 31% 19% 2	1566
	21st to end	Night	22% 9% 21% 32% 15% 1	1673
August	1st to 10th	Night	15% 6% 21% 35% 21% 2	1601
	11th to 20th	Night	26% 9% 16% 27% 16% 5%	1669
	21st to end	Night	27% 8% 17% 27% 17% 3	1980
September	1st to 10th	Night	28% 7% 13% 23% 20% 9%	1876
	11th to 20th	Night	30% 7% 13% 20% 20% 10%	1980
	21st to end	Night	22% 5% 10% 21% 28% 14%	1980
October	1st to 10th	Night	22% 5% 9% 25% 23% 17%	2121
	11th to 20th	Night	27% 4 7% 15% 27% 20%	2160
	21st to end	Night	31% 3 6% 17% 25% 18%	2376
November	1st to 10th	Night	28% 4 9% 18% 28% 13%	2220
	11th to 20th	Night	30% 4 8% 18% 26% 14%	2280
	21st to end	Night	38% 3 6% 18% 24% 11%	2398
December	1st to 10th	Night	37% 5% 9% 19% 20% 10%	2470
	11th to 20th	Night	40% 4 6% 14% 24% 11%	3037
	21st to end	Night	40% 4 5% 16% 26% 9%	4532

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	24% 16% 37% 17% 6% 1	270
	11th to 20th	Day	26% 19% 34% 16% 4	270
	21st to end	Day	25% 22% 35% 15% 3	297
February	1st to 10th	Day	30% 17% 34% 12% 6%	270
	11th to 20th	Day	34% 19% 33% 12% 1	252
	21st to end	Day	36% 21% 33% 9% 1	198
March	1st to 10th	Day	24% 22% 36% 15% 3	240
	11th to 20th	Day	23% 25% 34% 14% 4	240
	21st to end	Day	21% 21% 34% 19% 5%	264
April	1st to 10th	Day	19% 14% 43% 20% 4	271
	11th to 20th	Day	22% 17% 29% 22% 9% 1	412
	21st to end	Day	17% 15% 34% 23% 8% 2	420
May	1st to 10th	Day	13% 12% 35% 31% 9%	513
	11th to 20th	Day	13% 7% 27% 35% 15% 3	625
	21st to end	Day	13% 5% 24% 36% 17% 5%	679
June	1st to 10th	Day	7% 3 14% 37% 32% 7%	630
	11th to 20th	Day	4 2 16% 40% 32% 7%	630
	21st to end	Day	5% 1 14% 36% 32% 12%	630
July	1st to 10th	Day	7% 2 11% 33% 36% 12%	621
	11th to 20th	Day	3 1 6% 29% 47% 13%	618
	21st to end	Day	6% 2 5% 30% 44% 14%	684
August	1st to 10th	Day	5% 1 5% 28% 47% 14%	626
	11th to 20th	Day	8% 1 4 33% 42% 12%	544
	21st to end	Day	9% 1 6% 22% 41% 21%	495
September	1st to 10th	Day	9% 1 4 27% 43% 15%	370
	11th to 20th	Day	6% 4 9% 31% 36% 15%	270
	21st to end	Day	12% 1 10% 38% 24% 14%	270
October	1st to 10th	Day	6% 3 20% 41% 23% 7%	270
	11th to 20th	Day	13% 8% 29% 32% 14% 4	270
	21st to end	Day	24% 13% 27% 21% 12% 3	297
November	1st to 10th	Day	14% 8% 31% 31% 13% 1	270
	11th to 20th	Day	13% 11% 34% 33% 7% 1	270
	21st to end	Day	22% 18% 30% 20% 9%	270
December	1st to 10th	Day	17% 16% 36% 20% 9% 2	270
	11th to 20th	Day	26% 16% 35% 17% 6% 1	270
	21st to end	Day	22% 19% 39% 15% 5% 1	297
January	1st to 10th	Night	19% 11% 34% 28% 7%	950
	11th to 20th	Night	22% 14% 31% 26% 6%	950
	21st to end	Night	21% 11% 35% 28% 4	1045
February	1st to 10th	Night	22% 12% 35% 26% 5%	950
	11th to 20th	Night	25% 13% 36% 24% 3	768
	21st to end	Night	22% 15% 38% 20% 4	444
March	1st to 10th	Night	20% 10% 34% 30% 6%	540
	11th to 20th	Night	17% 12% 36% 29% 6%	540
	21st to end	Night	15% 12% 39% 27% 6% 1	594
April	1st to 10th	Night	11% 14% 41% 27% 7%	540
	11th to 20th	Night	15% 13% 36% 26% 10% 1	533
	21st to end	Night	12% 9% 40% 26% 11% 1	540
May	1st to 10th	Night	11% 9% 38% 30% 11% 1	540
	11th to 20th	Night	11% 6% 31% 35% 16% 2	531
	21st to end	Night	9% 3 25% 38% 21% 3	584
June	1st to 10th	Night	4 2 10% 44% 37% 3	540
	11th to 20th	Night	3 2 16% 46% 31% 1	540
	21st to end	Night	4 1 15% 36% 38% 7%	540
July	1st to 10th	Night	5% 2 10% 39% 38% 7%	525
	11th to 20th	Night	1 6% 39% 47% 6%	522
	21st to end	Night	2 8% 38% 43% 9%	591
August	1st to 10th	Night	4 1 4 40% 46% 6%	537
	11th to 20th	Night	6% 1 6% 39% 42% 6%	534
	21st to end	Night	7% 1 6% 35% 45% 7%	594
September	1st to 10th	Night	9% 1 7% 32% 45% 7%	540
	11th to 20th	Night	12% 1 7% 31% 40% 7%	540
	21st to end	Night	8% 2 9% 40% 36% 5%	540
October	1st to 10th	Night	7% 2 15% 40% 31% 5%	681
	11th to 20th	Night	15% 5% 25% 35% 18% 3	720
	21st to end	Night	16% 7% 27% 30% 18% 2	792
November	1st to 10th	Night	11% 5% 25% 40% 18% 1	740
	11th to 20th	Night	10% 10% 31% 37% 12% 1	760
	21st to end	Night	17% 12% 31% 26% 12%	878
December	1st to 10th	Night	17% 11% 32% 33% 8%	950
	11th to 20th	Night	22% 10% 29% 33% 6%	950
	21st to end	Night	20% 12% 32% 29% 6%	1045

Page generated at 2024-02-12 05:35:32. Version ac07

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