Chunky Rain This Evening, and the Long Range Outlook

January 6, 2012

Last night Stephanie and I both mentioned on-air that we’d see sticking snow down to around 1,500′ this evening and a mix lower than that.  Sure enough, models did really well forecasting that snow and rain/snow mix.  The precipitation has mainly passed on to the east now, but at least lots of you on the hills got to see snow, and almost anyone driving passed the “splat test”.  That means you can see the snowflakes attempting to mix in with the rain.

By the way, we can’t forecast snow level (usually) closer than maybe 1,000′ increments.  I see those forecasts each winter elsewhere (other stations in town and sometimes the NWS) and it drives me nuts.  For example, if we know it’ll get down to about 32 at 2,000′, then snow will probably stick 500′ lower than that if the snowflakes are falling lightly.  But if heavier precipitation comes through for 30 minutes, those big fat snowflakes can survive another 500′ or more.  So a forecast snow level of 1,500′ could easily become a snow level of 1,000′ or even a little lower.  Much of the time around here precipitation intensity is far more important for determining the snow level than the actual temp.

Moving on…this weekend looks great.  Clouds to partly cloudy tomorrow, then all sun (after morning fog) Sunday. 

We have one more weak weather system coming through Monday, then upper-level ridging for the rest of the workweek.  Take a look at the WRF-GFS cross section:

The colors are relative humidity, the top of the chart is about 10,000′, the ground is at the bottom.  Time runs from RIGHT to LEFT, opposite what you would expect.  The right side of the chart is Monday PM, the left side is Friday PM.  This model shows low-level moisture clearing out Tuesday morning, then strong easterly low-level flow (lots of Gorge wind!) from later Tuesday through Friday.  If so, lots of sun, temps around average, and a minimum of fog.

Long Range:

A fun ride the last few days with some runs of some models showing a big arctic blast, or set up for snow, or continuing ridging and mild weather.  Some models have shown all three at different times.  So obviously confidence on a pattern change is quite low.  One item DID seem to stick out today.  Models that want to bring cold air south seem to be keying in on sometime in the 8-10 day period (next weekend).  Here’s what I get out of the last 24 hours worth of runs:

ooz GFS Last Night :  Much cooler next Saturday/Sunday, good chance for snow to lower elevations (onshore flow snow).  No arctic air.

06z GFS:  Much colder, but dry next weekend, but no moisture for snow, not incredibly cold, but chilliest so far this season.  Modified arctic air.

12z GFS:  Ridge or split flow through 16 days!  No arctic air.

18z GFS:  Wet snow to lowlands next Friday night and Saturday, then possible transition with ice/snow 13+ days out.  No arctic air.

00z GFS Tonight:  Cool onshore flow a week from Sunday for snow to very low elevations, then warmer and wetter pattern as all the cold air dumps out into the Pacifc.  But stormier/wet pattern beyond at least.  No arctic air.

00z ECMWF: Ridge holds on…No arctic air, no snow or cold either.

12z ECMWF:  Wet snow to lowlands next Friday night and Saturday, then just milder beyond that.  No arctic air.

00z ECMWF Tonight:  Brief cool/wet system (no snow) on Sunday the 15th, then mild. No arctic air.

So I’ll keep an eye on it, but for now I’m not sold on any of these solutions.  Evidence seems to be growing that we’ll see SOME sort of change around next weekend.  Evidence also seems to be growing that we are not in for a big arctic blast.  No model run since last night’s 6z has shown that.  But will it be a brief turn to cooler and wetter or a sudden hit of winter wrath?  We’ll see.

Chief Meteorologist Mark Nelsen