A cool and snowy pattern will be seen into Monday as a strong low pressure moves in just south of us into Oregon. The low will produce heavy snow in the Oregon Cascades, with light snow in the lowlands too.
Some of the Oregon Cascade snow will circulate north into Washington with respectable, high-quality snowfall making for excellent skiing. It will mainly be snowing from The Summit southward. However, Stevens and Baker will get a 1-3 of inches of snow. The Summit, Crystal and White will see 5-10. Snow will continue, but taper off through the day. This is high quality snow with low snow levels. Its a robust storm and wind could be a problem, with visibility or lift closures. In fact, youll see some snow near sea level in the Puget Sound lowlands be careful on the drive, especially south Sound and into the Portland area.
I do not have high confidence as to how far north into Washington the heaviest snowfall will occur. The heaviest snowfall may remain farther south. But the overall the snow will be moving east by later Monday.
Tuesday and Wednesday, a cold upper level low over the region will keep us chilly with low snow levels preserving the new snow in the Cascades, while adding minor new snow at times. Later in the week the coolness will continue and but snowfall may taper off.
Grand Poobah of Powder
How do high and low pressures control our NW weather?
The weather has taken us for quite a ride in the last week. Very cold temperatures with fabulous and abundant new powder last Monday and Tuesday. Then warm spring skiing for Wednesday and especially Thursday. Now we are back in the deep freeze with more quality new snow falling in the Cascades. What drives this sea-saw weather happen?
We live in the mid-latitudes, about 47 degrees north. This where, in winter, the cold of the northern latitudes meets the warmth of the lower latitudes. This great mix provides the mechanism for the variety of weather we see from November through May. The weather is drier and stable in summer as the contrast of temperatures from north to south is not as great as winter so the mix is not dramatic like winter.
The winter weather mix we experience is caused my migrating (generally from west to east) high and low-pressure systems in the mid-latitudes. By tracking and forecasting the highs and lows we can forecast the weather and predict a powder day (like last Tuesday) or a day of warm, spring skiing (like last Thursday).
High pressure is a mountain of air rotating clockwise as the air descends. The descending air slowly warms and dries - so highs are associated with dry weather, and often sunny skies.
Low pressure is a valley air rotating counterclockwise as the air rises. The rising air cools, condenses and produces precipitation with rain in the lowland and snow in the mountains.
Seems simple enough, right? As always, the devil is in the details and there are lots of details. Often our mountains modify the effects of the highs and lows like when our landscapes produce a convergence zone (CZ) of snowfall for Stevens and the Summit. The CZ is formed by airflow around the Olympic Peninsula. The air is split, then converging with rain near Everett, while extending snow into the central Cascades.
Another important detail is the configuration, magnitude, position and duration of the high or low can have profound effects on the impacts of the weather in a region. Also, what part (quadrant) of the high or low is affecting your specific area makes a difference For example, the leading edge of a low can be cloudy, mild and wet. While the back side is often cool with scattered showers and sunbreaks.
This meandering conveyor of highs and lows is what causes our fickle NW weather in fall, winter and spring. Plus, the rapid changes in weather during the spring are often accentuated when stronger sunshine brings increasing warmth.
Its the story of these visiting highs and low which produce a blower powder day, followed by a warm, spring day of skiing like we saw last week.