Friday, June 01, 2012

Updating This Evening's Storms

Track tonight's storms on our current weather page.

Update, 10 PM:  The line of severe weather out to our west has weakened a little bit but is still formidable in spots as it moves eastward.  It has crossed the Harrisburg area and is working into Lancaster County from the west.   Flood warnings and advisories are out for portions of the region as rainfall continues to fall on saturated ground...the lion's share of warnings and advisories are north and west of the city.

The earlier tornado warning in Lower Montco and Central Bucks expired at 9:30 as the storm weakened as it tracked northward.  Wind will remain a potential issue over the next few hours as the squall line to the west moves towards the region.  Heavy rain does remain an issue through the night, regardless of wind or not.

Update, 9 PM:  The first of a couple of batches of rain and thunder are lifting northeast through the northern half of the city, with the main course still out to the west.  A squall line of rain and wind lines up from Williamsport south to near Harrisburg and York, moving east and northeast.  That line is still a good two to three hours away from the city...if it holds together...and will bring wind and rain with it as it marches through.  The question, now that we're after sunset, is how well these thunderstorms hold together but given the dynamics with the system there should not be much tapering off of the activity for the next few hours.

Locally, the cell just north of Philadelphia has shown signs of rotation within the storm itself...enough to warrant a tornado warning for Central Bucks and Lower Montco until 9:30 PM this evening.

Philly will have a bit of a break...albeit brief...for the next bit before more rain down to the south lifts back into the city.  It's going to be on and off for the next couple of hours before that line works through the region towards 11 PM-Midnight...and later east of the city.

Update, 8 PM:  Tornado Watch has been issued until 2 AM for Eastern and Southern PA, South Jersey, and Delaware due to the potential of an isolated tornado or two this evening with the storm system approaching.  While the storm's bigger calling card for many of us will be rain...and a good bit of isolated tornado cannot be ruled out.  A watch does not mean any one of us will get a tornado but it does mean it is possible.

Update, 7 PM:  Radar shows the main batch of rain and thunder to our west in two lines -- one from Central PA on south through Baltimore to just east of DC, the second farther west over the Appalachians.  You can click on the radar image to see it in better detail.  As of 7 PM, no further watches have been issued locally although a tornado watch was issued for Central and Northern Pennsylvania until Midnight (Schuylkill County on west and north).  The Storm Prediction Center is continuing to monitor the region for the potential of severe weather and it's possible a tornado or severe thunderstorm watch get issued in the next couple of hours for portions of the region as the 9 PM watch in Maryland and South Central PA expires.  Here, the main brunt of activity is still to our west and we will see conditions drop downhill through the course of the evening although there will be an occasional lull in the rain and thunder over the next couple of hours despite off and on showers pushing through the city and the immediate western burbs.  After 8:30 and 9 PM is when the activity will really start to crank up locally.

An active night ahead of us as we currently have a flash flood watch out for the Delaware Valley, Lehigh Valley, and Poconos for tonight...mainly for the isolated possibility of stream and creek flooding due to heavy rain in short fashion from storms that are beginning to move into Pennsylvania from Maryland.   Odds don't lean towards widespread heavy rainfall across the region but some places, especially west of the city and perhaps north, could pick up a couple of inches of rain in a quick hour or two...which would result in localized stream and road flooding.  Given the heavier rainfall of late, a watch definitely makes sense in the Poconos and Lehigh Valley given they are a bit more susceptible to flooding.

A tornado watch is out until 9 for South Central Pennsylvania, Berks County, and Maryland...and the Storm Prediction Center is hinting at the possibility of a watch being issued for parts of Southeast PA, Delaware, and perhaps South Jersey later on.  Watch does not mean tornadoes are imminent but that the possibility of a tornado may drop from these thunderstorms that are moving up from the southwest.   The storms pack a wallop and mean business...having dropped tornadoes in Virginia and Maryland earlier this evening.

Locally, the city should be ok for the next three hours or so.  These storms that are west of the city will pass west of town and weaken somewhat as the atmosphere is slightly less favorable for severe weather as they trek northeast.  The storms down by Washington and points south of there will track towards the Philly metro after 8 PM, moving in from the southwest.  At minimum, gusty winds and locally heavy rainfall is expected.  A tornado can't be ruled out but is not likely for most locations -- the "best" chances for any tornadic activity remain south through west of Philadelphia -- especially towards Dover through Lancaster.  That said, a tornado can't be ruled out completely.   Rainfall should average out to about an inch or so for most locations west of the NJ Turnpike and Route 1 in Delaware, with slightly lower amounts possible at the Shore.   The brunt of activity will occur between 9 and 2 tonight, tapering off from southwest to northeast late, late tonight.