Monday, March 04, 2013

Brief Update On Wednesday Storm

Last night's modeling showed two distinct camps among the major, quality modeling that's out there. The Euro, Canadian, and UK all show most of the storm's worst impacts from a precipitation standpoint to our south.  The NAM and GFS are waffling and occasionally showing a more northern solution, with the NAM closer to the Euro and the GFS the most northern of the modeling out there.

The northern shift in the GFS is the result of the storm intensifying more rapidly than the other modeling and the lessening of the influence of high pressure aloft over Canada compared to other guidance.  The other models in place keep that high strong enough to keep the worst of precipitation impacts to Philadelphia's south.

IF the GFS is right, precipitation would fall throughout the region...a chunk of it as snow, especially for areas west of I-95 since the precipitation shield would be more expansive.  We're talking a few to perhaps several inches, more snow in higher elevations, with this storm system IF such a scenario played out.  Right now, the GFS stands alone with a more rapid phasing and also a less influenced upper high.

The NAM is still a bit far out to be really reliable -- but it straddles the fence between the Euro and GFS...what is noticeable on both the NAM and Euro is the sharp gradient in precipitation. That will be one thing to watch -- wherever that precip cutoff is will separate very little precipitation from a half inch, perhaps more, over a short distance.  Even if the more amped GFS solution takes hold, there will probably be a sharp cutoff on precipitation somewhere.

Where things are similar, in general, is Shore impact.  Still looking at 40+ mph winds sustained, still looking at the prospect of tidal flooding on Wednesday PM into Thursday AM, with the worst impacts south of Atlantic City down into the Delmarva.  Whether those levels approach Sandy or March 1962 is still to be determined but coastal flooding and beach erosion do look to be pretty bad down there.

Putting all of this together, the most important things to note is that no solution is set in stone yet.  We're leaning, for now, to periods of rain and snow around the region with the best chances of precipitation south of the PA Turnpike, but it's not our "lock" yet in thinking.  If the GFS model gets better support from other guidance we may start looking at a higher potential for snow in the northern and western burbs.  Until we see that, it stands alone.

I'll have more on this later on this evening.