Rain Returns

It is March 9th and we have not had a drop of rain this month so far.  Drought-worried Northwesterns have begun leaving offerings to Jupiter Pluvius and other appropriate deities.  This weekend I hiked to the top at Mailbox Peak (4800 ft) and my feet never touched snow.

But all will change this week, as a significant shift in the large-scale flow pattern will bring moist, warm southwesterly flow to our region, accompanied by substantial rain in the mountains.

Tonight a ridge of high pressure sits over the West Coast (see map of 500 hPa heights and winds at 8 PM).  It won't last.

By Wednesday at 11 PM, the ridge has deamplified and southwesterly flow will be over us. Expect showers on that day.

A ridge rebuilds temporarily on Thursday afternoon (5 PM shown)

 And then by Saturday morning (5 AM shown), the ridge moves inland exposing us to strong southwesterly flow.

A juicy atmospheric river (a.k.a. pineapple express) will be aimed at us Saturday morning, as indicated by a plot of the vertically integrated water vapor content at that time(see below).

If you were losing sleep because you were worried about filling Seattle's reservoirs, stop worrying.  If you were losing sleep because of concerns about snow conditions for skiing, get a tranquilizer.

You want to know how much rain?  Well, here is the 48h total amount ending 5 PM Thursday.  A modest amount, but useful, particular since the high Olympics could get a few inches.

On the other hand, the 48h totals ending 5 PM Sunday will be enough to make old Pluvius proud, with several inches in all of mountains, 3-4 inches in the north Cascades, with lots of precipitation falling into the watershed of the Columbia River.  Good for irrigation, fish, and power.  Even parched northern California will get a piece of this.

This winter has been a meteorological song on repeat.   With extended warm/dry periods interrupted periodically with warm/wet times.  And the music has not ended.