Thursday, July 26, 2012

Moderate Risk For Severe For City, N/W

Update, 9:30 AM: The Storm Prediction Center has upgraded the Philly metro to a moderate risk of severe weather. This isn't the first time this year we've been in a moderate risk (we were in one back in late May) but pretty much everyone north/west of I-295 in New Jersey, north of the Canal in Delaware, is placed in the risk of severe.  Nothing really has changed in thinking from this morning in terms of timing (mostly late afternoon and evening).

The northern portions of the Delaware Valley are under a moderate risk of severe weather today, generally along and north of a line from New York City to Harrisburg, including the Lehigh Valley & Berks County.  Today is shaping up as a very active weather day from a storm tracking perspective, with the potential for a a couple of nasty lines of storms to develop this afternoon across the Northeast.

This morning already shows that active setup starting to take shape as a MCS is rolling through Upstate New York, triggering a couple of lines of storms -- one across Northeastern into Central PA as of 5 AM, a second line back from Binghamton to near Youngstown, OH.  A batch of storms near Pittsburgh had developed last night near Cincinnati and rolled east slowly through the night to its current position.  All of this will push through during the course of the morning hours and bring an appetizer to the later main course. Not everyone gets thunderstorms over the next several hours but a gusty, loud rumble of thunder is certainly in the realm of possibility through 10, 11 AM around the Delaware Valley as the stuff up above pushes east. Some of it will weaken...we'll see how well it holds together.

The afternoon "main course" fires up generally along the PA/NY border and back near Pittsburgh this afternoon.  Using the higher resolution NAM as a guide, these storms will develop by 4 thoughts on development would be between 1 and 2 PM for the first storms to refire to our northwest.  These will push east-southeast...and these northern storms will probably result in the nastiest of the storms that fire today.  Widespread wind damage is possible...a few tornadoes will be possible...and some hail is not out of the question with the activity across Northern, Central, and Western Pennsylvania this afternoon and evening.

Locally, storms may try to fire near Philadelphia after 4 PM in our heat and humidity.  While these storms won't have the same hail potential as those storms to the north and west will provide, the potential for gusty winds is pretty high with any development locally.  The question is where these storms pop...the NAM from last night suggests development near or just south of Philadelphia, with a general focus on South Jersey with this southern batch of storms, impacting the Shore after 8 PM.  Delaware gets grazed with the southern storms...generally New Castle County would be more "at risk" for anything that were to develop.  We're not in a moderate risk locally (as of the time of this post) as the best dynamics, best indicators for severe are just northwest of us.  Regardless, the potential for nasty weather does exist locally and any storm that does fire in the afternoon down here could easily produce its own share of may not provide as "widespread" a level of nastiness as those farther north.

As a side note, the Euro keeps us dry today in the Philly metro. The GFS brings a threat of storms to us a similar timeframe to the NAM. Both the Euro and GFS keep the worst of the worst to our northwest but the GFS does tip its hat to our region for the possibility of a few localized storms later on.

In timing the threats, we're at risk for afternoon thunderstorms any time after 4 PM in Eastern PA, after 5 PM in New Jersey and Delaware. Again, the best chances of real bad weather will be north and west of us...we do have a shot at some storms though but it's not a lock that things fire locally.

More:  Current Weather Page