NY NJ PA Weather Forecasts

Today’s Technical Forecast Discussion

10/23/08  7:54 AM

TODAY THROUGH SATURDAY:

A strong ridge is in place over the forecast area, which will continue to produce  clear skies and rather cool temperatures over the next 24 hours.  However, the upper level pattern remains volatile and ever changing as we progress through this month!  

A very strong and impressive upper low from the southern branch of the Polar Jet stream is slowly moving through the Plains with heavy rain and strong thunderstorms.  This upper level feature will spawn a low pressure system around the Gulf Coast that will eventually track towards the Ohio Valley by Saturday afternoon.  

The forecast area will remain on the warm side of this low pressure system, which means that surface to 700 MB winds will orient from the southeast beginning late Friday night or early Saturday morning.  Significant MAA from the Atlantic combined with moisture from the Gulf of Mexico will support high water content levels in the atmosphere.  As the upper low is captured by the northern branch of the jet stream on Saturday evening, the surface low will rapidly race towards New England and continue to intensify.  Heavy rain will race through the forecast area Saturday evening through early Sunday morning.  I’m starting to think this rainfall will end faster than model guidance is projecting based on the interactions I am seeing forecasted with this upper low and the northern branch.  So I’m staying below the rainfall amounts seen on the GFS for this period.  

This storm will bomb out over the Canadian Maritimes and produce a strong negative NAO blocking feature while the AO tanks as well.  The upper level pattern will then set up for an interesting disturbance for next week!

SUNDAY THROUGH WEDNESDAY:

A very interesting set up is unfolding for Monday evening and Tuesday, which should be an interesting test for this potential pattern in the winter!  

A strong cold front will race towards the coast on Monday with falling 850 MB temperatures along with crashing heights.  However, because of the blocking, the frontal boundary will stall off the coast on Monday afternoon, establishing an area of weakness between the coastal plain and the Gulf Stream.  Meanwhile, a disturbance will race down from the northern Plains towards the Southeast coast on Monday evening and produce strong divergence/difluence aloft, which will support a complete rising cuplet along the coastal plain.  As a result, a low pressure system will rapidly develop and deepen along the Mid Atlantic coast on Monday night through Tuesday, produce precipitation over the forecast area.  I think based on the 850 temperatures on the GFS, ECMWF, and ensemble guidance, that the GFS MOS may be too warm here so I went below the guidance.  The potential exists as the moisture interacts with the cold air moving into the region, that a mix of snow and rain or even a period of light snow will develop over the interior locations on Tuesday morning.  The areas most likely to see this will be over northeastern Pennsylvania, the Hudson Valley, and interior Connecticut.  

Obviously the forecast is important here, but what I’m keeping an eye on is whether the potential is realized for cyclogenesis and how the blocking features develop.  

As the storm bombs out over the Canadian Maritimes, the trough will remain in place through the end of October making for a chilling Halloween.  The pattern will relax some going into early November, as the NAO can’t stay negative forever.  However, a trough will still linger over the East going into November providing for near normal temperatures.