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Coastal storm expected to skirt offshore this weekend

This mornings operations at the forecast desk could almost be mistaken for mid-winter. All kidding aside, forecast models have jumped around over the past several days in regards to the track and intensity of a coastal storm system which is now expected to pass just barely south and east of our area on Friday. The storm itself is forming due to an energetic mid level atmospheric disturbance, which will drive southeastward into the Mid Atlantic states later today and Friday. This will aid in the development of a surface low pressure system, and plenty of atmospheric moisture will help develop precipitation across the Mid Atlantic States.

Perhaps most notable is the fact that this atmospheric energy is undercutting a very fast atmospheric flow to its north, over the Great Lakes and New England. This means that the storm system won’t have much room to move northward — and its development will be shunted to the east instead of expanding northward and westward. Fast northwesterly winds aloft will keep the pattern moving, especially over New England. So the low pressure system at the surface will respond accordingly, developing from the Mid Atlantic and then seaward toward the Western Atlantic Ocean.

Not shockingly, forecast models have jumped around with nearly every aspect of the storm system. Multiple disturbance interacting in the mid levels of the atmosphere almost always wreak havoc on forecast model guidance. The meteorology of the event can give us more clues than the guidance will, especially when inconsistency rules the day. The two main takeaways of the atmospheric pattern are this:

GFS model showing a generally de-amplified atmospheric pattern this weekend, causing the disturbance related to the coastal storm system to stay offshore.

GFS model showing a generally de-amplified atmospheric pattern this weekend, causing the disturbance related to the coastal storm system to stay offshore.

– As noted above, there is a fast flow in the mid and upper levels of the atmosphere over the Great Lakes and New England. There isn’t much high latitude blocking to slow the pattern down, so by nature the storm will remain “progressive”. This makes it more difficult for a coastal storm to come close to the US East Coast.

– In addition, a relatively de-amplified pattern on the West Coast of the United States suggests a more progressive solution. Typically, a mid or upper level atmospheric ridge exists on the West Coast of the United States during our bigger coastal storms. While it’s possible to get a coastal storm without one of these ridges, the atmospheric pattern remains progressive around it — so this time, it hurts the chances of a significant coastal storm.

Watching the forecast evolution of the atmospheric pattern on model guidance lends credence to these ideas. While a last minute mid level disturbance phase or change to the pattern could still cause the storm to come closer to the coast, “close but no cigar” will be the general rule. The best chance for steady rain will remain south of New York City, specifically across Southern NJ and the Mid Atlantic States.

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