Turning Up the Heat and Dangerous Fire Weather

September 5, 2011

We’ve had 3 days now with high temps in the mid-upper 80s across the Metro area.  Tomorrow should be similar, then the heat is really on for Wednesday and Thursday.

On those two days, the atmosphere warms from 17 to +23 C at about 5,000’/850mb.  Then we add a switch to easterly flow, about as strong as last Saturday’s.   The high temperature forecast is a challenge.  This weekend turned out about like we expected (here at FOX12 at least).  On Friday we forecast 88, 90, 88 for the three days.  It ended up at 87/89/88 at PDX.  My first thought for forecasting Wednesday-Saturday was “don’t go too high!”.  But our RPM model shows 8-9 degrees warming on Wednesday; the NAM shows +6.  Let’s say it goes up 7 from a high tomorrow around 87-88.  That would give you 94 or 95.  So that’s what I did; 95 and 95 for Wednesday and Thursday.  

Has anyone noticed the nearly constant easterly flow for about 72 hours on the models?  Check out the WRF-GFS cross-section:

Click on the image for a good view.  Red lines are temperature in Celsius.  Each flag on the wind barb is 10 kts.  So 2 and a half barbs would be 25 kts.  850 is around 5,000′, 700 is near 10,000′.  The surface is…well…at the bottom.  Probably self-explanatory.  Time goes from right to left.  The image then covers 5pm tonight to 5am Friday. 

Note easterly flow from 5,000′ down to near the surface kicks in around sunset tomorrow.  Then see the easterly flow all the way up to 10,000′ Thursday?  Wow…  It’s not real strong, but I see extreme fire conditions over that Dollar Lake Fire combined with several days of the smoke coming directly up over the Metro area…it’s not going to be pretty around here. 

I checked out the InciWeb update this evening and it sure doesn’t look encouraging for the western part of that fire.  Looks to me like it could easily spread well to the west maybe up and over Lolo Pass.  Obviously I’m not a fire weather expert or burn scientist, but this could end up being the largest fire so close to Portland in years.  That’s IF it gets out of control the next few days.

Weather wise it appears the ridging along the West Coast is here to stay probably through mid-month.  The 00z GFS had NO precipitation in the next 16 days.  The first 8 days are probably correct, but flip a coin in anything beyond that.  The big story is that summer was late, but now it’s here to stay.

Chief Meteorologist Mark Nelsen