Superfront followed by Big Rain

It's the end of November and time for serious storm watching.  And our high-tech observing tools provide a good view  (and lots of warning) about what will occur.  And the latest model runs suggest the next week will be extraordinarily wet.  Perhaps dangerously wet.

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.

Heavy Rains Return to the Northwest

The last two weeks of November are climatologically the wettest period of the entire year.

This year won't disappoint. 

Let me begin by showing you a neat chart never before seen on this blog.  The TOTAL precipitation forecast for the next 8 days from the National Weather Service GFS model.  This model has relatively modest resolution, so it is not capturing the full amounts over our terrain, but you will get the picture.

Very wet from coastal BC down to northern CA (5-10 inches is commonplace, with northwest CA "enjoying" 10-15 inches.  No rain in Arizona and New Mexico and much of the NE U.S. 

Lets take a look what the higher resolution UW WRF model is giving.  Let me first show you the first 72 hr (ending 4 PM on Saturday).  Modest precipitation over western Washington, but the heaviest rain (2-5 inches) over the mountains of NW CA.

But the next 72 hr really opens the skies, particularly over NW CA and western Oregon. Some locations near the CA/OR border are forecast to receive over ten inches of rain.  We are talking about real flood potential.  Notice that even eastern WA is getting wet.

Why so much rain?  A large, cold trough will form over the eastern Pacific, establishing a persistent flow of moist air from the west and southwest (see upper level map for next Monday at 1 PM):

Such heavy precipitation events are inevitably associated with atmospheric rivers--relatively narrow currents of enhanced water vapor.   For this case, the atmospheric river will be coming from the west, not from Hawaii, so don't call it a pineapple express (see graphic).

Teriyaki express?  Will have to work on a good name....

What about snow in the mountains?  

Temperatures will be marginal in the lower passes (Snoqualmie/Stevens), so there should be a mixture of rain and snow there---I doubt they will have enough to open for Thanksgiving.  But higher ski areas (Crystal, Baker) should get substantial amounts (foot plus) and may be able to open by Turkey Day.  Keep tuned.