Yakima
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Yakima clear sky chart from 2003-08-01 to 2005-11-07.

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	10% 6% 5% 7% 49%	8739
	Night	11% 6% 5% 7% 46%	8428
Cloud Cover	Day	8% 5% 5% 7% 48%	8734
	Night	10% 5% 6% 5% 7% 45%	8436
Transparency	Day	19% 18% 30% 22% 8%	5621
	Night	21% 19% 34% 18% 5%	5147
Seeing	Day	19% 26% 27% 22%	569
	Night	8% 23% 38% 26%	2653

By Month

Percentage Cloud Cover
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month		Occurrence of each Forecast	Data Points
January	Day	20% 12% 7% 6% 7% 7% 21%	488
	Night	27% 15% 10% 6% 5% 5% 15%	866
February	Day	12% 5% 7% 5% 7% 41%	528
	Night	8% 7% 5% 5% 5% 52%	725
March	Day	12% 6% 7% 5% 5% 8% 40%	673
	Night	9% 7% 7% 6% 11% 40%	690
April	Day	9% 7% 7% 8% 45%	740
	Night	7% 9% 7% 7% 8% 41%	579
May	Day	15% 5% 5% 5% 7% 5% 10% 32%	866
	Night	8% 8% 5% 6% 9% 38%	488
June	Day	7% 5% 5% 9% 49%	840
	Night	6% 6% 64%	478
July	Day	78%	865
	Night	81%	496
August	Day	6% 70%	1207
	Night	5% 6% 68%	835
September	Day	5% 8% 59%	1013
	Night	6% 5% 7% 63%	922
October	Day	12% 5% 5% 7% 6% 10% 40%	602
	Night	12% 10% 5% 6% 42%	762
November	Day	18% 6% 5% 9% 9% 32%	429
	Night	13% 5% 6% 5% 7% 5% 6% 8% 34%	737
December	Day	17% 10% 6% 5% 8% 6% 29%	488
	Night	25% 9% 6% 5% 6% 6% 25%	850

Percentage Cloud Cover
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month		Occurrence of each Forecast	Data Points
January	Day	18% 12% 9% 6% 6% 7% 5% 19%	488
	Night	26% 15% 12% 6% 5% 15%	866
February	Day	10% 6% 8% 6% 8% 40%	519
	Night	8% 7% 5% 5% 6% 52%	725
March	Day	11% 5% 5% 7% 5% 8% 40%	672
	Night	8% 7% 7% 7% 9% 40%	689
April	Day	8% 7% 8% 10% 42%	741
	Night	5% 8% 7% 7% 9% 40%	579
May	Day	13% 5% 7% 5% 6% 11% 32%	868
	Night	10% 5% 8% 5% 7% 11% 35%	496
June	Day	5% 5% 5% 5% 9% 48%	840
	Night	5% 5% 6% 64%	478
July	Day	78%	856
	Night	81%	496
August	Day	5% 70%	1208
	Night	5% 7% 68%	835
September	Day	5% 7% 60%	1023
	Night	6% 8% 62%	923
October	Day	10% 5% 6% 7% 10% 40%	602
	Night	10% 5% 8% 5% 5% 7% 40%	762
November	Day	17% 6% 5% 6% 7% 9% 32%	429
	Night	12% 5% 5% 5% 6% 7% 5% 5% 8% 34%	737
December	Day	16% 9% 7% 9% 6% 28%	488
	Night	22% 10% 6% 5% 7% 6% 25%	850

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	43% 37% 9% 9%	116
	Night	57% 18% 17% 5%	216
February	Day	29% 28% 34% 6%	279
	Night	26% 14% 46% 12%	426
March	Day	24% 25% 38% 10%	363
	Night	33% 24% 30% 9%	380
April	Day	23% 15% 34% 22%	454
	Night	26% 20% 35% 15%	339
May	Day	31% 23% 33% 10%	448
	Night	33% 15% 37% 12%	258
June	Day	13% 19% 43% 22%	555
	Night	12% 22% 45% 18%	359
July	Day	5% 5% 27% 35% 26%	742
	Night	5% 36% 34% 20%	430
August	Day	7% 11% 23% 40% 16%	980
	Night	6% 11% 30% 36% 15%	673
September	Day	12% 25% 32% 25% 5%	771
	Night	8% 25% 40% 21% 5%	704
October	Day	34% 18% 28% 15%	510
	Night	29% 22% 26% 17%	661
November	Day	36% 34% 22% 5%	222
	Night	29% 24% 38% 7%	421
December	Day	50% 27% 19%	181
	Night	38% 30% 25% 5%	280

Seeing (when cloud cover <= 80%)
Color Meanings: Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month		Occurrence of each Forecast	Data Points
January	Night	15% 23% 38% 20%	207
February	Day	13% 33% 26% 26%	53
	Night	19% 33% 35% 6%	213
March	Day	27% 29% 19% 23%	51
	Night	11% 25% 43% 16%	235
April	Day	29% 29% 27% 9% 5%	55
	Night	9% 26% 39% 23%	214
May	Day	23% 26% 35% 14%	56
	Night	7% 25% 46% 19%	120
June	Day	27% 22% 28% 20%	59
	Night	24% 49% 22%	119
July	Day	10% 33% 28% 18% 8%	59
	Night	24% 49% 22%	122
August	Day	10% 21% 31% 31% 5%	89
	Night	5% 18% 41% 31%	270
September	Day	24% 20% 21% 28% 5%	89
	Night	23% 37% 32%	353
October	Day	15% 25% 32% 22%	58
	Night	11% 22% 32% 27% 6%	352
November	Night	14% 21% 35% 26%	240
December	Night	12% 25% 32% 28%	208

Page generated at 2008-10-12 17:06:08. Version ab11