Thunderstorms; So-So Forecasts, but Lack of Communication

May 27, 2012

What happened the past two days (especially Saturday) is a good example of a growing problem and a dirty little secret in the meteorological world. We often know more about upcoming weather patterns than we share with you in a simplistic “high-low-no rain/rain” forecast.

The slide above is from the Dr. Cliff Mass presentation to our local AMS chapter just 2 weeks ago. I hadn’t really given it much thought until he made it the cornerstone of a push towards using more “uncertainty language” in a forecast.

1. Regional models were clearly showing  the possibility for afternoon showers or thunderstorms somewhere in the western valleys of northern Oregon or SW Washington both Friday and Saturday afternoons.  And the Portland/Vancouver Metro Area seemed to be a good place for that to occur. 

Here are the 12z RPM and WRF-GFS models from Friday morning, showing later Friday afternoon/evening…looks wet to me on both, although the placement was off, especially on the WRF-GFS (2nd image).  We actually did okay with Friday here at FOX-12, mentioning the chance for afternoon rain or thunder.

Now on Saturday morning, our 12z RPM showed almost exactly what occurred just 14 hours later; although it was a few hours earlier than reality in the end:

The WRF-GFS wasn’t quite as good, but it was hinting at some sort of action coming off the Coast Range (not correct):

2. Yet all the forecasts (including mine) downplayed the threat enough Saturday that the thunderstorms were probably a surprise for most of the public.  We didn’t make it abundantly clear that an evening thunderstorm in the city was quite possible.  Yes, a relatively small chance, but the chance was there.  On Friday night at 8/10/11pm I showed our RPM and mentioned that I thought thunderstorms would probably stay on the far east side of the metro area, close to the Cascades.  I thought there would be a slightly shift to more westerly upper-level flow later in the day keeping the developing storms out there.  Clearly location was wrong on that forecast.  But when I saw the skies darken to my northwest and heard a few rumbles, it definitely wasn’t a surprise.  It was more like “I wish I would have included a chance for the entire metro area.”

 The amount of weather information we receive nowadays is incredible, but breaking that down into a forecast that goes just a few minutes on TV (and for a whole state) is a challenge.  Maybe more important, forcing that info into a pretty little cloud/sun/rain graphic is even tricker.  We are sure able to bring uncertainty information verbally into a weathercast and through text on a website.  We need to work harder getting that information out.

Now Dr. Mass also suggested we not show a 7 Day forecast like this:

His point being that we can’t REALLY nail a forecast within a degree or two (regularly) more than a couple days out, so we should be giving temperature ranges instead of specific numbers.  But this ship sailed a long time ago…television 7 day forecasts have specific numbers and that won’t change. 

These 7 Day forecasts also don’t give the public any idea about our confidence in certain patterns either.  For example, models are showing some variance (right now) on Thursday and Friday.  Some are pushing the rain in a bit quicker on Thursday, but others waiting until late Friday.  So I’m quite confident on the Monday-Wednesday forecast, and pretty confident on the general pattern change to wet and cool next weekend.  But in between is a period with significant uncertainty.  You sure don’t see it on the graphic; and there are plenty of numbers, text, and logos on the graphic already.  So where would you show lower confidence on this graphic?  There is no easy way, for now it has to be verbal on television or webcasts. 

Weather forecasts are getting better and better, but we have work to do when conveying that increased forecast accuracy don’t we?

Chief Meteorologist Mark Nelsen


Record Rain; Wettest Hour Ever in May This Evening!

May 26, 2012

History has repeated itself…we just broke the all-time May  rainfall record again on the Saturday night of Memorial Day Weekend.  Remember 2008?  A big thunderstorm on Saturday evening.

Portland Airport reported 1.02″ rainfall from 6:53-7:53pm.  And most of that appears to have fallen in the final 45 minutes of the hour.  Check out the observations here.

The rainfall is in green on the right side.

.97″ of this fell in 36 minutes from 7:17 to 7:53pm!

Compare that to the record sheet here:

http://www.wrh.noaa.gov/pqr/pdxclimate/pg83.pdf

We have broken the all-time one, two, and three  hour rainfall record for May this evening (.93-.95″ on May 24, 2008)

We MAY have broken the all-time one hour rainfall record (1.03″ on September 7, 2010)

The National Weather Service will probably put out a statement after a bit more rain collects in the next hour.  For example, 7:10-8:10pm rainfall could easily be higher than that 1.03″ all time record.

Chief Meteorologist Mark Nelsen


Thunderstorm & Flooding Rain Heading Into Portland

May 26, 2012

A cluster of strong storms is moving through S. Vancouver and N. Portland right now…storms that again came off the S. Washington Cascades.  Lots of cloud to cloud lightning but not too much cloud to ground action…yet.  I can heard almost constant rumbling to my west (I’m home SE of Crown Point).

Vancouver has received 3/4 inch of rain and PDX already 1/2 inch…expect local flooding to spread south into the heart of Portland.  These storms will continue moving very slowly south, then die after sunset.

Follow the latest radar image and loop, go here:

http://www.kptv.com/weather

Then click INTERACTIVE MAP for all the warnings/watches, and looping of the radar…it’s quite a fun tool to track storms with.  In fact it highlights the warnings with colored areas too.  Note you can turn on lightning as well.

Chief Meteorologist Mark Nelsen


250+ Cloud to Ground Strikes In Metro Area

May 25, 2012

Here’s the final lightning map for this evening…

If you take a line from about St. Helens over to Amboy, then count all the strikes from there south to about a Newberg-Canby line, you get a bit over 250 lightning strikes this evening; quite impressive.

More interesting is the location…almost all strikes were west of I-5 & Hwy. 217 in Oregon and north of I-84.  Downtown Portland and areas straight south and east didn’t see any strikes.


All Clear For Fireworks; But Stormy In Salem

May 25, 2012

Rain has ended in most of Portland and the showers continue to head south.  Fireworks viewing (at 9:55pm) will be dry downtown.

But here’s the latest image from the mid-Valley…wet!

These storms will continue to head south and die down over the next hour or so.

Chief Meteorologist Mark Nelsen

 


Heaviest Action Over Hillsboro

May 25, 2012

7:45pm…

Powerful storm over the south side of Hillsboro and moving into Bald Peak…73 dbZ (for the wx geeks).


Thunderstorms Moving In; Take Cover Downtown

May 25, 2012

7:25pm…

Radar shows a burst of storms developing and heading south right into the heart of the Portland Metro area…expect lightning and downpours on the midway down at the Rose Festival soon!

Also, brand new storm spewing lots of strikes in Washington County heading into Hillsboro and Beaverton: