Quiet Now: But Possible Gorge Ice & Flooding Midweek?

December 14, 2015

A very nice break today…only .02″ of rain in P-Town!  That’s our 14th wet day of course, but far more reasonable.

BMAC Rain Two Day Total

As of this evening we have 10.22″ of rain for the month, the wettest month since November 2006!  The wettest ever recorded at PDX is 13.35″ in December 1996.  I remember that year…we had two ice storms east metro on the 26th and 28th (or 29th?), then warm and wet.  In fact it’s interesting to note that we haven’t seen a big metro ice storm since that time.  As I recall near the end of that event at one point it was 32 at PDX but 55 with a south wind at Hillsboro at the same time!

But I digress…

I think there is a very good chance we are living through what will be PDX’s wettest month ever recorded.  We only need to get 3″ in the next 2+ weeks.  We’ll get at least 2″ of that just by this Saturday at the latest.

MarkHeadlines_FloodPortland

I don’t see a setup for a big flood in the next 7-10 days as the pattern appears to be generally cooler than normal with the jet stream over or south of us at times.  That should keep much of the precipitation above 3,000′ in the form of snow.

We DO have a warm and wet system for Wednesday night and Thursday.  Rainfall totals looks pretty impressive again.  Maybe 1.50-2.50″ precipitation in the metro area with higher amounts in the mountains and southern Oregon.

A new and possibly serious weather event has cropped up today in models:  a complicated and messy Gorge freezing rain/snow event underneath the heavy rain westside during this period.  A setup where we could see flooding issues at the same time a severe winter storm is occurring just 50 miles away.

The problem is that during the day Wednesday a cool airmass near the surface is sliding south through the Rockies.  The approaching low pressure then sucks the cold air right into the Columbia River Gorge just as the precipitation gets going Wednesday evening.

The GFS, WRF-GFS, GEM, and to a lesser extent the ECMWF and our RPM models show this event.  I was hoping it would go away in the evening run of models but it’s actually even more impressive/scary (if you live in the Gorge) now.  The WRF-GFS has at least 8-10 millibars easterly flow (raging east wind) by Thursday morning with tons of precipitation falling through a 4,000′ thick below-freezing airmass in the central/eastern Gorge.  About 2″ liquid precip in the central Gorge would equate to 15″ or more snow and/or a crippling ice storm in the central/western Gorge.  Ice would be thicker than what we went through 2 weeks ago; this is a much wetter system.  The 00z WRF-GFS meteogram for Hood River shows 24 hours of freezing precipitation (snow, then freezing rain).

We’ll keep a very close eye on this event as we get closer; it’s definitely a possibility that models are overdoing the amount of cold air that gets into Eastern Washington and that could mean temperatures far more marginal for frozen precip.  If so, I would expect them to back off quite a bit in the next 48 hours.

Regardless of the total rain we get…we’re going to see more mud & landslide issues over the next 10 days.  Our soils are soaked and don’t want to see another set of downpours late week!

Chief Meteorologist Mark Nelsen

 

 


We’re In The Coldest Weeks of Winter

December 14, 2015

We’ve bottomed out…it’s the coldest day of winter!

Well, one of the coldest. Here in Portland we “bottom out” with an average high/low of 45-35 from December 13th-January 5th. Winter is centered around January 1st in our climate west of the Cascades. Remember these are averages…any year the coldest weather of the winter could occur as late as February in our area. Or it can happen in late November (this year maybe?)…each year is different.

So when someone tries to tell you winter doesn’t start until next week?  Tell them they don’t know what they are talking about weather-wise.  Weather/climate doesn’t follow a calendar!

ColdestDayOfYear

Chief Meteorologist Mark Nelsen