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6pm Wednesday…

Am I getting old, or does it seem like a warm sunshine and temps in the 70s was just a few weeks ago?  Time is flying…

Forget about that warm stuff; it appears that winter is going to move in quickly over the next two weeks in the Pacific Northwest.

First, those weather apps.  This is what Brian MacMillan’s iPhone app showed today

iphone snow JPG

I use the FOX12 Oregon app which does not show lowland snow.  Keep in mind these apps are automated with no human intervention; although that isn’t as shocking as it was just five years ago.  I bet within 10 years most weather forecasting will be automated.  We’re not there yet but computer modeling is getting better.

Weather App Snow Forecasts

So what is going on next week?  I think SOMETHING is up with respect to cold and/or lowland frozen precipitation in the next 10+ days.  But it’s far too early to pin down any sort of details.  Our seven day forecast is snow-free right now, but it’s that time of year to start paying close attention to the forecast.

First, we have beautiful weather for three more days.  East wind keeps us mainly cloud/fog free through Saturday.  A warm upper-level ridge of high pressure keeps storms away and temperatures mild.

ECM_FRI22

By Sunday the flow overhead turns westerly and cools a bit.  Nothing too exciting, but we’ll likely get some light rain out of the first system.

ecm_sun24

But look at the change by next Wednesday!

ecm_wed27

A cold upper-level trough drops in over the western USA.  It’s still there the Saturday after Thanksgiving; the following is from the 18z GFS model.  A warm upper-level ridge into southern Alaska and a cold trough over the Pacific Northwest.  This is a very chilly weather pattern for us; historically a good setup for lowland snow west of the Cascades.

gfs_sat30

Look at the drop in temps the next 10+ days from the ECMWF model.  Forget highs near 60 like today.  Get used to 40s, which is typical mid-winter stuff for us.

ecmwf-operational-KPDX-daily_tmin_tmax_ecmwf-4251200

We have to see a specific placement of surface low pressure, wind direction, and precipitation; but snow CAN make it to sea-level with this setup.  Models have been all over the place the past few days on details.  On Sunday night the ECMWF model produced a snowstorm with 5-15″ snow in the metro area next Wednesday.  Last night the ECMWF brought a deep low into Central Oregon, dumping 2-6″ snow in the south Willamette Valley.  Today’s ECMWF (for example) doesn’t bring any snow west of the Cascades (other than flurries) because it’s much drier.  The latest 18z GFS brings snow into some of the lowlands on Black Friday and Saturday.    You get the idea…

Because of these wild run-to-run gyrations we use “ensemble forecasting”.  The ECMWF model is also run 51 times at a lower resolution.  A graphic showing each of those 51 members (horizontal lines) below shows about 6 of those 51 members produces notable snow (over 1″) in the metro area (Aurora) through Thanksgiving Weekend

ecmwf-ensemble-KUAO-indiv_snow_24-4251200

The GFS has 21 ensemble members, each going out two weeks.  Not much snow there, only 2 of those produce notable snow in the metro area through Thanksgiving Weekend

gfs-ensemble-all-KPDX-indiv_snow_24-4251200

To wrap it up…pay close attention to the forecast as we head toward Thanksgiving and beyond.  It’ll be turning colder.

One thing that’s also obvious, we sure aren’t heading into any sort of real wet/stormy pattern.   Just colder, and a little wetter.

I’m taking an extra day off this “weekend”, so probably no posts until Sunday.

Chief Meteorologist Mark Nelsen

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