Friday, December 17, 2004

- President Franklin Delano Roosevelt

Thank you to all the loyal, supportive readers out there. I enjoy putting the site together as much as I hope you enjoy reading it. I must admit this impeding weather situation is a bigger challenge for forecasters than they would like for the first eastern storm of the season. However, as the event gets closer, the NWS and Accuweather are doing a good job of keeping options on the table in the event the storm shifts in either direction. I fully understand why they are hedging... as it helps to keep hype down while holding everyone's attention at the same time.

The map below will help you understand why it seems I am stubbornly sticking with the forecast, because I am. But just for fun, I will also do a pros and cons summary called the "Powderhounds v. Nervous Nellies" debate. This outlines the reasons for and against this storm, and schools closing or remaining open, in a fun and open-minded way.

This is NOT a waffling, however, as the forecast explained in previous post stands:
(Accumulations by Monday 9 AM)
-Overall 2"+ in Frederick County, 3" in Baltimore County, 4" in Harford, 4-6" in PHL area.
-Higher amounts the farther north and east you go, lesser amounts west.

Now, let's consider the "latest" computer model run and see what it tells us...

The graphic on the left is the GFS 60 hour forecast for about 1AM Monday morning. The graphic on right is the 10 AM Saturday morning forecast. Herein lies the reason why I am sticking to my forecast the way I think the snow will stick when it begins to fall .

1. The Philadelphia and Baltimore NWS admitted earlier today in their discussions that the GFS (Global Forecast System) has been projecting these systems too far east, and then brings them back west with time. That little bluish blob on the right.. WAS NEVER expected to get as close to the coast as it has now done. It has been worrying forecasters all week that it would end up a surprise sideswipe storm for the immediate coast.

2. This means the GFS is showing an EASTWARD bias, indicating that it is predicting storms to be too far out to sea, with a general 50-100 mile error. Accuweather is the one that identified this error, and has adjusted their forecasts accordingly. You can also read evidence of this in your latest "Special Weather Statement" put out by the NWS. Thus, the computer has had to back track the bluish blob up there closer and closer to the coast with each 6 hour run.

3. The third and most critical piece for why I am sticking with my forecast is the continued appearance of the light precip on EAST side of the MD mountains late Sunday night. Notice the big elongated gap in precip between the East coast and the Appalachians. Normally when systems from the west have snow, the mountains squeeze out all the precip, and the coastal plain is left with nothing. Not this time. There appears to be ample dynamics to keep the snow falling in the I-95 corridor after the cold front has passed to our east.

THE CRITICAL COMBINATION OF THE NORTH TRENDING UPPER LEVEL JET STREAM RIGHT OVER THE CHESAPEAKE, (dashed lines) AND THE DELIVERY OF LOW-LEVEL COLD AIR MOVING SOUTH (solid lines) IS A CLASSIC SETUP FOR CONVECTIVE SNOW BURSTS. What this means is a lot of energy is being squeezed together in an already compacted, turbulent area of the atmosphere. The super cold air (-20 C at upper levels), is going to wring out every last drop of precip. That's why the green blob is located where it is... in the zone of greatest enhancement. If there is a 50-100 mile eastward bias in the models, (God forbid, and Marty Bass take note), then move that green blob in the left graphic over just a tad, enhance it with Chesapeake moisture, and PRESTO! you have a surprise 4-5" when everyone else said flurries. One way or another, someone will have egg on their face for breakfast Monday, and someone will have cake. If we get a snowday out of this, I hope to have my cake and eat it too.

There is more to be said, as I think you will find the "Powderhounds v. Nervous Nellies" debate to be a fun read. But Jayla's grandparents are coming Saturday, and I have to help Mrs. Foot get the house ready, I can't just sit here and blog all night or that cake will be quite cold as I'll be eating it outside. :-)

I do have a few microscopic tweaks to the "Hourly Estimates" that I will post later when I get a chance.

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