2-3 Days of Weather Action: Thunderstorms Possible

July 16, 2012

Just about anyone in the FOX12 viewing area  could see a thunderstorm during the next 72 hours, but not everyone will; a challenging forecast ahead.  By the way, in case you ever wondered where our signal goes, it’s generally in the blue area.  Some people receive us via satellite outside the blue counties; but these are the counties we “service”.  Specifically, in forecasting weather and severe weather warnings we pay attention to these.

For those just wanting the basics:

1.  Warmer temps today and tomorrow, highs closer to 80 with a mix of sun/clouds.  We won’t see the gruesome clouds/drizzle we had Sunday morning!

2. We can’t (no one can) forecast exactly who or what spot will get thunderstorms or at what time.

3. We do know the best chance appears to be from later today through Tuesday evening. 

4.  Storms that DO develop will move from east to west; the opposite of our normal weather pattern.  They will come from the east (Cascades).

5. Don’t do anything outside that requires 24 hours of dry weather (staining, spraying etc…)…too risky.

 

More Details:

This morning an upper-level low, basically a circulation in the upper atmosphere, is moving south along the Oregon Coast.  It’s near Newport at 11am.   Click for a better view below, map shows the airflow at about 30,000′ or 300mb: Circulation around an area of low pressure is counter-clockwise, which means most of us are on the north and northeast side of the low by later today.  By 11pm tonight it’ll be right on the Oregon/California border.  But look ahead to Thursday afternoon:

Still in the same spot!  That means for the next 3 days we’ll have easterly or southeasterly flow in the upper atmosphere overhead.  This is usually a good setup for getting thunderstorm action west of the Cascades.  Indeed we’ve already seen storms on the north side of the low this morning up in SW Washington:

This is never a guarantee of widespread thunderstorms; I’ve seen this pattern end up with almost nothing over some spots.  But the screaming message is the potential is there for anyone to see a thunderstorm and just about anytime of the day or night the next 72 hours.  Take a look at the Lifted Index forecast for tomorrow afternoon from the NAM, it’s a measure if instability in the atmosphere.  When it gets to zero or below, that’s good: 

Very impressive -4 to -6 over the Cascades of Washington and very close to the Portland Metro area!   Easterly flow could bring storms out over the lowlands west of the Cascades.  Tuesday does appear to have the best dynamics/forcing for stronger storms too; it might be our best bet.  Afternoons/evenings do tend to have more “action” due to the stronger rising motions from daytime heating, but in a pattern like this the action can occur anytime of the day/night as small curls or eddies move around the big upper low setting off storms.

Once this all moves out of here on Friday, models show the hot upper-level ridge over the desert SW pushing closer to us again.  That’ll give us another run at 90 degrees over the weekend or early next week.  The 12z GFS ensemble chart shows above average 850mb temps Saturday and beyond.  The ensemble average generally agrees with the operational model:

The ECMWF is similar:

Chief Meteorologist Mark Nelsen