Friday, June 07, 2013

Updating Today's Heavy Rainfall

Andrea is in the process of transitioning away from tropical to nontropical this morning -- will likely be "post-tropical" later today as it moves up the East Coast. From a reality perspective, the label in front of Andrea matters very little as it's a rain maker for the East Coast...and the potential of three or more inches of rain is on tap for some of us.

Parts of the region have already picked up over an inch of rain (Western Montgomery and Northern Chester Counties) with half inch totals common through most of the western burbs north into the Lehigh Valley. Those rains are in association with the frontal boundary that's approaching the region and its gradual interaction with moisture being pulled in from the Atlantic from Andrea's circulation.  The storm is moving up the East Coast, with heavy rains likely to kick in later today.  Radar shows those heavier rains in the Carolinas, moving into Virginia, as the system moves northeast.  Those rains will move in here by midday, continuing through the afternoon and into the evening hours.

The worst of worst sets up in a eight hour window from around 2 PM until 10 PM tonight.  Rains of varying intensity, heavy at times, will push in and work through the whole of the region.  The frontal boundary that's to our west will act as a conduit for additional moisture to squeeze out along and west of the Fall Line.  That will yield some higher than three inch rainfall totals. High resolution modeling has waffled a bit on the placement of that axis of heavier rainfall but generally has it just west of the city...although the newest guidance from the NAM that hit at 5 AM shows it from Bucks down through Lower Montco, Delco, and into Southwest Jersey...a notch east of last night.

Essentially, it would not shock if there were a 20 mile stripe where three or more inches of rain fell. Whether that falls between Pottstown and Plymouth Meeting...or between Norristown and Huntington Valley, remains to be seen.  However, those in the immediate western burbs (Conshy, Lafayette Hill, Drexel Hill) probably will see some of the heaviest totals overall once today's rains are done.

That isn't to diminish the impacts elsewhere -- most everyone gets at least one inch of rain and many will see two inches. There will be some varying amounts of flooding on the usual suspect roads, streams, and places that typically flood easily will likely do so today.

Again, the worst impacts shape up between 2 PM and 10 PM -- that's when we'll probably see the heaviest rains.  Winds will likely not be an issue -- probably some gusty conditions along the coast where winds could hit 30 mph in a gust or two but the region should generally not see much wind from this as stronger winds with Andrea's leftovers will be out over the water and not onshore.

More: Current Weather Page