Nightmare Forecasting

April 12, 2010

A casual viewer may have noticed the 7 Day forecasts on local TV web sites (and on the air of course) are all over the place the last 3 days.  Combine that with changing numbers just on our 7 Day forecast and a person could easily conclude that we are just throwing darts at a wall.  They wouldn’t be too far off tonight. 

The forecast is a real pain the next 7 days.  The problem?  An upper level trough, a disturbance in the upper-atmosphere, moves down from Canada to just off Oregon by Wednesday.  Then it backs off a bit, links up with another trough moving across the Pacific, and swings some moisture our way at times through early next week.  The issue is that each model and even runs within models themselves each disagree on where the low is at any one time.  If it’s closer to us we get cooler/showery weather.  If it backs off just a bit, much warmer air surges north ahead of it and we can get quite warm.  24 hours ago models were indicating we could hit 80 degrees next weekend as the low moved well off the coastline.  That’s now gone…we’ll see if it reappears.  As forecasters we can’t just follow each model run in patterns like this.  If we did, our 7 Day forecast would have gone from a high of 80-82 next Sunday to 60 just 24 hours later (a good example!).  So we have to make an educated guess (yes, I said that) based on experience and trends in models.  And we also have to avoid what many of you here are familiar with:  Model Riding.  That’s when your forecast and thoughts change with each model run.  Since many models now come out 4 times a day (all arrive at least twice a day), this can give you whiplash from the amount of weather information flying around.

To make it worse…if it was October-February our viewers wouldn’t necessarily care much…really, a 40 degree rainy day or a cloudy 50 degree day?  Most of us stay inside anyway.  But from later March through the summer the public (me too!) has much higher expectations and wants to get outside.  So any forecast of several days of sunshine and warm temperatures is followed closely.  The viewer REALLY wants that to happen…and extreme disappointment is the result if/when we have to put showers/cool weather back into the forecast.  That would include nasty emails and sometimes rough voicemails too.  So some Springs we get through this with just nice fronts and then ridges of high pressure that give us some sunny weather.  Others are dominated by these annoying lows. 

Chief Meteorologist Mark Nelsen


A Few Thunderstorms

April 12, 2010

I don’t want to get Timmy Supercell too excited, but a nice little thunderstorm just popped up near Lowell.  As you can see from the map that’s just southeast of Eugene along that long straight stretch of Highway 58 (on the way to Willamette Pass).  With the nice clearing and warming temps this afternoon, I’d expect a few more to pop up the next few hours.  I just got in about 1/2 hour ago…Stephanie had a pained look on her face as she held the forecast page.  Then I got a headache as I looked over the maps/models too…nightmare spring forecasting ahead the next 7 Days!!!

Chief Meteorologist Mark Nelsen