Yakima
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Yakima clear sky chart from 2005-11-05 to 2008-11-27.

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	6% 5% 5% 7% 49%	12259
	Night	6% 5% 5% 5% 7% 49%	12168
Cloud Cover	Day	6% 5% 5% 5% 5% 7% 46%	12266
	Night	7% 5% 5% 5% 5% 7% 46%	12164
Transparency	Day	9% 18% 29% 20% 6%	9162
	Night	9% 21% 27% 17% 5%	9086
Seeing	Day	21% 30% 23% 17%	739
	Night	7% 21% 42% 20%	3623

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	7% 7% 7% 7% 7% 7% 6% 5% 8% 30%	741
	Night	7% 9% 8% 5% 6% 6% 6% 9% 33%	1298
February	Day	7% 8% 9% 5% 6% 9% 38%	750
	Night	8% 7% 5% 5% 7% 5% 6% 7% 40%	1027
March	Day	6% 6% 5% 6% 10% 7% 8% 9% 31%	1002
	Night	5% 7% 6% 8% 11% 38%	1038
April	Day	5% 6% 6% 5% 6% 9% 42%	1105
	Night	6% 5% 6% 8% 49%	868
May	Day	7% 6% 5% 5% 9% 46%	1302
	Night	6% 5% 6% 7% 52%	744
June	Day	6% 6% 5% 8% 56%	1260
	Night	5% 5% 6% 64%	720
July	Day	5% 75%	1301
	Night	79%	739
August	Day	6% 71%	1201
	Night	6% 76%	834
September	Day	7% 69%	1041
	Night	5% 78%	935
October	Day	5% 5% 5% 6% 7% 53%	892
	Night	5% 5% 9% 55%	1141
November	Day	10% 8% 5% 5% 6% 8% 6% 6% 7% 29%	920
	Night	10% 9% 6% 5% 5% 8% 36%	1523
December	Day	18% 13% 11% 8% 22%	744
	Night	15% 12% 11% 8% 5% 6% 5% 23%	1301

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	8% 10% 7% 11% 5% 7% 6% 9% 25%	742
	Night	10% 8% 7% 6% 5% 6% 7% 8% 30%	1295
February	Day	8% 7% 6% 5% 7% 6% 6% 9% 35%	752
	Night	9% 8% 5% 6% 6% 7% 7% 36%	1026
March	Day	7% 7% 5% 6% 7% 9% 7% 7% 9% 27%	1004
	Night	5% 6% 5% 5% 5% 9% 7% 7% 10% 34%	1036
April	Day	6% 5% 6% 7% 6% 6% 8% 39%	1106
	Night	7% 5% 5% 8% 7% 46%	870
May	Day	7% 5% 6% 5% 7% 10% 42%	1302
	Night	5% 6% 5% 6% 8% 49%	744
June	Day	7% 6% 7% 53%	1260
	Night	5% 6% 6% 61%	720
July	Day	5% 73%	1301
	Night	5% 77%	741
August	Day	6% 69%	1202
	Night	6% 74%	834
September	Day	6% 66%	1039
	Night	6% 75%	935
October	Day	5% 5% 5% 5% 9% 48%	892
	Night	6% 5% 8% 52%	1140
November	Day	12% 9% 6% 8% 7% 6% 6% 7% 26%	922
	Night	12% 10% 5% 8% 5% 5% 7% 34%	1523
December	Day	19% 15% 9% 9% 6% 22%	744
	Night	16% 11% 10% 10% 5% 6% 6% 20%	1300

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	17% 26% 25%	423
	Night	13% 40% 16% 9%	825
February	Day	15% 28% 30% 7%	511
	Night	16% 31% 23% 11%	683
March	Day	18% 26% 26% 5%	663
	Night	12% 30% 32% 7%	700
April	Day	14% 23% 30% 13%	782
	Night	15% 23% 31% 15%	640
May	Day	6% 20% 33% 22%	1000
	Night	5% 20% 36% 21%	595
June	Day	6% 17% 35% 22% 9%	990
	Night	6% 19% 38% 23% 7%	571
July	Day	8% 23% 38% 21%	852
	Night	11% 24% 34% 21%	510
August	Day	5% 31% 36% 12%	1137
	Night	6% 33% 31% 14%	814
September	Day	5% 10% 31% 27% 15%	962
	Night	12% 31% 24% 20%	904
October	Day	7% 21% 29% 16%	809
	Night	11% 14% 29% 21%	1044
November	Day	13% 29% 17%	659
	Night	10% 24% 24% 9%	1116
December	Day	12% 17% 30%	374
	Night	15% 28% 16%	684

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	11% 20% 41% 21%	362
February	Day	19% 31% 34% 13%	73
	Night	10% 23% 43% 17%	303
March	Day	28% 44% 17% 5%	88
	Night	10% 26% 49% 10%	370
April	Day	25% 37% 19% 15%	86
	Night	9% 25% 41% 19%	322
May	Day	29% 28% 20% 16%	92
	Night	24% 45% 23%	180
June	Day	23% 30% 24% 12% 5%	85
	Night	6% 28% 45% 17%	164
July	Day	15% 35% 25% 19%	77
	Night	32% 51% 13%	162
August	Day	17% 20% 20% 29% 11%	89
	Night	18% 39% 26% 9%	266
September	Day	14% 22% 25% 29% 6%	87
	Night	17% 32% 30% 12%	349
October	Day	17% 27% 29% 14%	62
	Night	17% 44% 26%	363
November	Night	10% 19% 39% 16%	434
December	Night	12% 18% 43% 17%	348

Page generated at 2008-11-27 10:47:49. Version ab11