10pm Update: Tough Forecast Still!

January 4, 2011

Tonight’s forecast is one of the most challenging of the past few months, even though it only applies to about the next 8-10 hours of time. 

– I didn’t make any big changes in the forecast, but I think just about all areas north of Salem are going to get something frozen on the ground between now and 5am…then temperatures gradually warm up.  Snow is a possibility, but a wintry mix is most likely.

-So basically I’ve leaned more towards some frozen precipitation for most of us in the Valleys instead of just a few.  Let’s hope we get it out of here before the morning commute.  Or it’ll be a real mess!

I SHOULD point out the most important thing I learned tonight that F5 is the same as “refresh”.  Didn’t know that…thanks kids!

Chief Meteorologist Mark Nelsen


6:30pm Thoughts

January 4, 2011

The plot just keeps thickening.  Isn’t this fun my fellow weather geeks?  All of the metro area at or very near freezing right now.  East wind is pretty much gone, but no south wind up the Valley yet either.  The cold/dry air is here to stay for many hours to come.

Over the last 3 hours I’ve been attempting to convince myself that there’s a good chance we could see a few hours of snow or freezing rain widespread over the Metro area after 10pm.  But a fresh tidbit just arrived; the 00z SLE sounding.  It shows a warm layer that won’t drop below freezing even after the precipitation starts and the temp “wet-bulbs” out.  According to the sounding there’s no way we could see snow over the mid-Valley now, it would have to be freezing rain or sleet.  That warmer air should continue advecting to the north and east, so maybe snow is still not a good possibility.  The layer is from around 1,800-3,000′.  Wouldn’t it be nice if the KPTV Tower Temps went up to 3,000′?  Maybe a little dewpoint sensor too?

Our 00z WRF-RPM is out…same thing…after 10pm freezing rain, then a gradual warming spreading up the Valley after midnight.  It’s slow, but has us around 38 by daybreak.  Not convinced of that, but I’m definitely heading more in the direction of a widespread light freezing rain/sleet event across the entire Metro area, with some snow mixed in possibly?

I have until 9pm, then I’ll change all the forecasts if necessary.  I’ll post again then.

Chief Meteorologist Mark Nelsen


Freezing Rain Update: Midday

January 4, 2011

I told you I’d be looking at more info today…here’s a tidbit that makes it a bit more interesting.  Compare our 12z RPM precipitation-type forecast with the following 18z run (that just came in) for the same time…10pm tonight.

Two very obvious changes…the precipitation is at least 4 hours earlier…arriving to the north and west parts of the metro area by 10pm newstime tonight.  Plus, note the area of freezing rain or ice pellets the model generates.  Models might be playing a bit of catch-up to the chilly airmass over us.  The following frames then warm it above freezing quickly well before sunrise.  

But if the precipitation does rush in that quickly, some spots of freezing rain are definitely possible.  Still don’t think it would affect the Wednesday morning commute, but it’s of meteorological interest overnight tonight.  Still, I’d have to be a moron (no comments please) to not mention that it’s a decent possiblity.  Not a big ice storm, but it only takes about 5 minutes of freezing rain to turn a road to solid ice.

We’ll keep an eye on obs, southerly breezes, and dewpoints this afternoon and evening.

Mark


Tuesday Morning Update

January 4, 2011

Just scanned through things with the morning coffee…just like on the funny promo we run.

-Very strange that the NWS took out the possibility of ZR in the forecast and put snow in???  I don’t understand where that came from…that’s the ONE thing I don’t think is possible, or at least likely.

-Easterly gradient dropping nicely, but still plenty of dry/cold air feeding into the Metro area from the Gorge.  Dewpoint is 21 at Troutdale even though wind has turned light easterly.

-Precipitation still scheduled for sometime around daybreak or just before.

-My other thoughts are the same…once again it’ll be interesting to see how the next 15 hours play out; reality compared to the quickly warming models.

Chief Meteorologist Mark Nelsen