Tuesday, October 22, 2013

Big Storm System Next Week? It's Possible

While this week will feature a few cold front bringing in shots of cool air, all eyes are on what will happen next week.  I'm really paying attention to the Tuesday-Thursday time period... October 29-31st.  The GFS has been fairly consistent dropping a strong front through the state and the Euro shows a boundary as well.  However, the biggest question that has to be answered pertains to a strong area of low pressure coming out of the southwestern United States.  The GFS pulls this energy out and develops a significant storm system over the southern plains.  This would result in heavy rain/thunderstorms.  The latest run of the Euro shows this piece of energy hanging back over the western United States allowing a front to come through rather harmlessly.  It should be noted previous runs of the Euro looked similar to the GFS.

Check out these maps below explaining the situation.  Remember, this is long term stuff so it's likely to change.

The GFS (Global Forecasting System) shows a large storm system over the mid south.  The red and yellow blobs indicate total precip over the previous 12 hours and it could range up to 1'' or more.  The surface low is just east of the state.  With a counterclockwise surface flow, there's a strong northerly wind developing late Wednesday the 30th of October.  See the blue dashed line?  That's the 540 thickness line.  North of it, it's cold enough to support snow assuming surface temperatures are cold enough.  I wouldn't be surprised to see snow in the TX panhandle into northern OK IF this verifies.  That flow around the surface low should drill cold air south behind it.  The reason why it's developing such a strong storm system has to do with the upper level energy swinging into the region.
This is where the difference between the two models are very noticeable.  The GFS late on the 30th shows a big piece of upper level energy bundled and located across TX and OK.  See that area of red and yellow?  This is why the storm system is much stronger on the GFS compared to the Euro.  (I'm comparing the two model runs from Monday night.)
Now look at the upper level chart from the European model  It keeps the strong area of low pressure aloft over the Pacific Northwest.  HUGE difference.  There's more ridging across the southern plains.  A weak front would be in the area, but it wouldn't result in much expect a few areas of light rain.
The surface chart from the Euro around this time period shows a front coming in with just some rain.  There is no strong low here, but you can see the surface high over N. Dakota bringing in some chilly air.  The front is located from New England southward into southern MO.  The green and yellow blobs surrounding it indicates the presence of some rainfall.  Overall, this is showing a benign storm system.  It should be noted previous runs of the Euro brings the big piece of upper level energy into the region similar to the GFS idea.
In summary, when you're dealing with the long range, there's going to be differences between the modeling.  Many times, both are wrong and it's more of a compromise between the two.  As long as one of the long range models shows this possibility, it must be watched, especially if the upper low gets involved.  We are in our secondary severe weather season so that's on the table. I'm not calling for severe weather at this time, but it's worth watching due to climatology.  One more thought... Look back at the forecast a week in advance for the Race For The Cure.  The GFS was grossly off!  The Euro was wrong too, but was much closer to the idea of some rainfall early that morning.  Stay tuned.

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