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 2009-12-29.

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% 5% 7% 49%	16466
	Night	6% 6% 5% 7% 49%	16492
Cloud Cover	Day	6% 5% 5% 5% 5% 7% 47%	16473
	Night	7% 6% 5% 5% 5% 7% 46%	16488
Transparency	Day	8% 16% 27% 19% 7%	13368
	Night	9% 19% 26% 16% 5%	13415
Seeing	Day	19% 28% 24% 19%	997
	Night	6% 20% 42% 21%	4952

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% 6% 9% 7% 6% 6% 5% 9% 29%	981
	Night	7% 9% 9% 7% 6% 5% 6% 8% 33%	1716
February	Day	8% 7% 5% 9% 6% 6% 9% 36%	1010
	Night	7% 8% 6% 6% 5% 6% 8% 37%	1383
March	Day	5% 6% 5% 6% 5% 9% 7% 7% 9% 32%	1339
	Night	5% 5% 7% 6% 8% 10% 38%	1383
April	Day	5% 6% 6% 6% 8% 43%	1452
	Night	5% 6% 5% 8% 50%	1148
May	Day	6% 5% 5% 5% 9% 50%	1724
	Night	5% 5% 7% 57%	976
June	Day	5% 6% 5% 7% 55%	1669
	Night	6% 5% 7% 61%	960
July	Day	5% 74%	1719
	Night	78%	971
August	Day	6% 71%	1604
	Night	6% 76%	1113
September	Day	7% 70%	1376
	Night	5% 78%	1227
October	Day	6% 5% 6% 6% 7% 49%	1183
	Night	5% 5% 5% 5% 9% 52%	1510
November	Day	9% 8% 5% 7% 7% 7% 6% 8% 30%	1193
	Night	9% 8% 6% 5% 6% 5% 5% 8% 38%	1976
December	Day	15% 12% 7% 8% 5% 5% 5% 27%	1216
	Night	11% 14% 9% 8% 5% 5% 6% 27%	2129

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% 9% 8% 11% 6% 6% 6% 9% 25%	982
	Night	10% 8% 7% 8% 5% 5% 5% 6% 8% 29%	1713
February	Day	8% 8% 6% 5% 7% 6% 7% 9% 32%	1012
	Night	8% 9% 5% 6% 6% 7% 5% 8% 33%	1382
March	Day	6% 7% 6% 7% 5% 8% 6% 7% 9% 29%	1341
	Night	5% 6% 5% 6% 5% 8% 6% 7% 10% 35%	1381
April	Day	6% 5% 5% 6% 6% 5% 5% 7% 40%	1453
	Night	6% 5% 5% 5% 7% 6% 47%	1150
May	Day	6% 5% 5% 7% 9% 47%	1724
	Night	5% 5% 6% 7% 54%	976
June	Day	6% 5% 6% 7% 52%	1669
	Night	5% 6% 5% 6% 60%	960
July	Day	5% 73%	1719
	Night	5% 77%	973
August	Day	6% 70%	1605
	Night	6% 75%	1113
September	Day	6% 69%	1374
	Night	6% 75%	1227
October	Day	7% 5% 5% 5% 5% 9% 45%	1183
	Night	5% 5% 5% 5% 5% 8% 50%	1509
November	Day	11% 9% 5% 8% 5% 7% 6% 6% 7% 27%	1195
	Night	10% 8% 7% 5% 6% 7% 35%	1976
December	Day	16% 13% 8% 8% 5% 5% 25%	1216
	Night	13% 13% 8% 9% 5% 5% 5% 5% 25%	2128

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	14% 21% 20% 7%	663
	Night	12% 30% 15% 9%	1244
February	Day	15% 28% 22% 6%	771
	Night	14% 28% 21% 9%	1039
March	Day	14% 26% 23% 5%	991
	Night	10% 26% 32% 5%	1045
April	Day	11% 17% 29% 15%	1127
	Night	13% 19% 29% 17%	920
May	Day	6% 17% 33% 23%	1430
	Night	16% 36% 25%	831
June	Day	6% 16% 33% 19% 9%	1399
	Night	7% 17% 36% 22% 6%	811
July	Day	6% 21% 37% 25%	1270
	Night	9% 20% 37% 23%	742
August	Day	6% 30% 35% 12%	1540
	Night	5% 33% 32% 15%	1093
September	Day	9% 31% 30% 14%	1297
	Night	9% 30% 28% 19%	1196
October	Day	7% 19% 27% 14%	1102
	Night	10% 14% 30% 18%	1413
November	Day	14% 25% 16%	932
	Night	11% 23% 23% 8%	1569
December	Day	10% 17% 22% 6%	846
	Night	11% 21% 19%	1512

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	8% 20% 40% 23%	482
February	Day	17% 24% 34% 15%	101
	Night	8% 18% 45% 19%	415
March	Day	28% 39% 15% 7%	119
	Night	10% 26% 45% 12%	494
April	Day	23% 33% 23% 14%	113
	Night	7% 25% 40% 20%	428
May	Day	26% 26% 20% 19%	123
	Night	23% 45% 23%	238
June	Day	20% 25% 28% 17%	115
	Night	28% 43% 18%	222
July	Day	13% 32% 25% 23%	107
	Night	28% 48% 19%	220
August	Day	14% 23% 23% 29% 9%	120
	Night	18% 39% 28% 7%	359
September	Day	13% 24% 23% 31% 6%	116
	Night	17% 34% 32% 10%	461
October	Day	16% 32% 26% 12%	83
	Night	18% 46% 22%	483
November	Night	8% 20% 40% 17%	566
December	Night	8% 15% 44% 20%	584

Page generated at 2009-12-30 02:20:32. Version ab11