Let's start with this morning's impressive infrared satellite image (8 AM). A strong Pacific front is immediately offshore (the linear north-south feature) and connects with an occluded front that extends out into the Pacific into a well-defined Pacific low between northern Vancouver Is. and the Queen Charlottes. To the south of the low is a comma cloud, that is associated with upper level disturbance.
There is a very well-defined, strong surface front embedded in the frontal zone and we can watch it approach using our new Langley Hill radar. Here is a sequence of images starting at 4 AM and ending just after 9 AM (you can click on them to blow them up). You see the thin line of enhanced radar reflectivity (reddish or dark yellow)? That is the surface cold front. There is a narrow cold frontal rain band there and if you look carefully you can see that it is corrugated with stronger and weaker segments. A zone of less intense rain follows.
There were big changes as the surface front moved through: pressure rise, temperature fall, wind direction shift. Here is what happened at the Destruction Is. buoy right off the central WA coast for temperature and pressure: big drop in temperature and large rise in pressure. The wind also shifted from southerly to westerly (not shown).
We will get some moderate rain with this front. And then there will be a only some showers until Sunday evening when a stronger front will come through, followed by an even wetter system on Monday. Take a look at the totals for the 72 hours ending Tuesday at 4 AM (graphic below). Many of the mountains areas around here will get 5-10 inches of precipitation. Over 10 inches near the CA/OR border. There will be a lot of snow at higher elevations (particularly above 3500 ft for the first two fronts, but it will be getting warm on Monday and thus the snow level will rise above the lower passes when the precipitation is hardest...sorry. Mt. Baker and Crystal should be able to open. Don't ask about Snoqualmie.
Finally, I hate to mention this, but the latest model runs are suggesting the potential for a major precipitation/flood event on Thursday/Friday. The ground will be saturated from the earlier rains and then a persistent atmosphere river just stays over us. Lots of uncertainty this far out, but here is the 48-h precipitation forecast ending 4 PM on Friday. Over 10 inches in the Olympics.
Take a look at the total precipitation for the next 192 hr (through Sunday at 4 AM) from the National Weather Service GFS model. Unbelievable. 20-25 inches over the Cascades...and this is a low resolution model that will not get the true magnitudes of the mountain precipitation). If you live near any of the major rivers around here, you better stay tuned. FEMA should watch this as well.