A warm Ridge of High pressure that has been building inland over the western U.S. the last 24-hours will get flattened out by a Trof of Low pressure that will be moving across the Northwestern U.S. the next 24-hours.

Very HOT in the Southwestern U.S. on the last day of March 2011……75 in Moab, 79 in Zion, 92 in L.A., 101 in Palm Springs, and hottest was 103 in Death Valley.

Still some clouds coming over the top of that Ridge in a WNW flow over us today, which may cause a few showers over Yellowstone Park and the Teton Mountains, otherwise, just some clouds moving by from time to time today. And warm spring-like temps.

That weather system coming into the Pacific Northwest will bring Jackson Hole some rain on Saturday, by afternoon. A strong cold front will then move through sometime Saturday evening and that will change the rain over to snow at all elevations. Expect dramatically cooler temps by Sunday.

That Low pressure center moves by to the north of us and out into the Dakotas on Sunday. Some moisture remains behind this system in a North to NW flow Sunday & Monday for some light snow.

It now looks like a somewhat moist Westerly flow will be over us Tuesday & Wednesday, with warming temperatures bringing a chance of some valley rain showers and some snow in the mountains.

Text provided by Meteorologist Jim Woodmencey

Graphics by IPS MeteoStar LEADS On-Line

There’s some good news, and some bad news, and some good news again…. about the flow across the Pacific over the next 5 to 7 days.

The first good news is, a Low pressure system this weekend will bring snow Saturday night and Sunday to Jackson Hole.

The bad news is, as we go into the middle and end of next week it looks like a Ridge of High pressure will build over the Western U.S. and Rockies and send storm systems that are lined up out in the Pacific right now to the north of us into Canada and SE Alaska.

The good news about that is….. any radiation that might be in that flow coming across the Pacific from Japan will also get diverted well to the north of Jackson Hole.

Text by Meteorologist Jim Woodmencey
Graphics by IPS MeteoStar, LEADS -OnLine

Concern about radiation particles being carried across the Pacific and into the western U.S. from Japan has become a popular topic.

Despite assurances that radiation amounts will be very low by the time any of that makes it to the West Coast, the flow in the upper levels of the atmosphere is setting up to bring whatever is being emitted over Japan during the course of the next week, directly towards the West Coast.

In the short term, most of the radiation that is already in the atmosphere will be carried over the Aleutian Islands of western Alaska. The rest of Alaska should be missed, as the flow abruptly turns to the southeast across the Gulf of Alaska and gets involved in the Low pressure center that is sitting just off the West Coast.

Top map shows the jet stream position (at 300mb or ~ 30,000-ft.) on Saturday morning March 19.
The middle map shows the wind speeds and flow at 700mb ~ 10,000-ft., which is more representative of the level at which any radiation in the atmosphere would fall out with precipitation.

Strongest winds point at the far western tip of Aleutians, then turn southeast and decrease considerably before turning eastward into the southern half of California.

The bottom map shows the forecasted jet stream position position by the end of next week, which may be more of a concern as the flow straightens out into more of a direct pipeline from west to east across the Pacific.

Not surprisingly, skiers have already inquired about what this radiation might mean for our weather as we go into Spring. “Does it mean more snow or less snow? Or, will it melt the snow that is already on the ground?”

I don’t really know much about the effects of radiation particles in the atmosphere. They are not like volcanic eruptions and their particles, which can actually enhance snowfall by adding more ice nuclei to the atmosphere. It is my understanding that radiation particles attach to dust particles that already exist in the air, and then fallout with precipitation, along with the dust particles.

Even if a nuclear cloud did enhance snowfall, would you really want to rush out and ski that?

Technically, it wouldn’t create a Nuclear Winter, since Spring begins Sunday, March 20, 2011 at 5:30 p.m.

A Nuclear Spring, maybe.

Text by Jim Woodmencey, meteorologist
Graphics from IPS Meteostar, LEADS On-Line