Second Heat Event Of Summer Looms

We're a couple of days away from the beginning of our second heat event of the year. Whether it makes it to a heat wave by hitting on 90 remains to be seen but we will get two hot to very hot days, perhaps three, this week before we enter a more unsettled pattern for the weekend as a front stalls out nearby.   The combination of surface high pressure off of the Carolinas and very warm temperatures aloft will allow the heat that brought 100 degree temperatures to Texas and Louisiana the past couple of days to work its way northeast and torch us.

Computer modeling suggests Thursday is the hottest of the upcoming stretch as high temperatures could approach record levels in Philadelphia.   The record for Thursday is 98 and we're predicting 96 in our forecast for Thursday.  Whether it hits or not is not important...the combination of heat and dewpoints in the 60's will bring heat index values close to 100 to the region, which is rather nasty regardless of whether the surface temperature is 95, 96, or 98 as it's gonna be hot.   Heat will even impact the Shore pre sea breeze in the afternoon as the surface winds will generally be west and west-southwest.  Expect highs in the 80's Wednesday-Friday at the Shore Points each day, with temperatures quickly reaching 90 as you get a mile or two inland.

A cool front will try to slide through the region -- whether that occurs early in the day Friday or on Friday afternoon remains to be seen but the front's bigger story is its predicted stalling out over the Mid Atlantic.  Assuming the front does stall out, an unsettled weekend with scattered thunderstorms looms for both Saturday and Sunday.   The one thing the front should be able to do is bring an end to the heat.   Unfortunately, the potential price to pay is a less than stellar weekend but after reaching the 90's for two to three days, some may be willing to pay that price.   Thunder will not occur all weekend long but neither day looks completely dry and thunderstorms will be scattered about more numerous in the afternoon both days this coming weekend.

Like A Traffic Jam On The Schuylkill...

...so goes the latest cold front to approach the region. Yeah, another one of these slow-to-approach and slow-to-cross cold fronts is inching towards Philadelphia and will have us in the warm sector until the wee hours of Wednesday morning.   The slow march, then stall, and then a final move of the front as it waits for low pressure to develop and lift northeast along the front means we'll coax one warm day out of the coming week, with temperatures hitting or exceeding 80 in Philly tomorrow afternoon.   All the while, a chance for showers and storms will exist across Western and Central Pennsylvania tonight, with Western Pennsylvania seeing more thunderstorm activity develop tomorrow afternoon as the low lifts north and agitates the front.

Until Tuesday night, Southeastern Pennsylvania is poised to remain dry -- although a shower or two can't be ruled out as close as the northern and western burbs as an area of showers moves through this evening.   The NAM, GFS, and most computer guidance keep the showers away from Philadelphia until Tuesday night.

The front will gradually approach on Tuesday evening, working east as low pressure rides along the front to the northeast.   Showers and thunderstorms develop along the front and lift northeast as the front marches east, with the potential for some severe thunderstorms in parts of Central Pennsylvania tomorrow afternoon, possibly into Eastern Pennsylvania tomorrow night depending on how the front moves.  The northern and western suburbs, along with Central Pennsylvania, are under a slight risk for severe weather for Tuesday and Tuesday night.  Gusty winds and heavy rains are possible with any thunderstorms that develop.   The threat for flooding around here is low but some stream rises can't be ruled out if heavier thunderstorms track into the region.

Most of the activity is poised to move through the region Tuesday night and midday Wednesday, first as possible thunderstorms across Central into Eastern PA, secondly followed by an area of steadier showers or rain that may lift through the region during the morning hours.

Philly Rides The Coaster

It wouldn't be April in Philadelphia without having temperature forecasting headaches -- and hangovers -- from the afterglow of an 80 degree day in the city.   Temperatures have been on an impressive roller coaster ride -- jumping 25 degrees from Tuesday to Wednesday in Philadelphia, only to see the "official" daytime high drop another 15 degrees from yesterday to 1 AM this morning in Philadelphia.   Philly has been the home to impressive swings in temperature as of late -- we've shown larger bounces just a week ago.   However, unlike last week this week's bounces were really the most significant in Philadelphia.

Allentown and Reading had smaller, less impressive, hikes in temperature between Tuesday and Wednesday -- Reading bouncing up 21 degrees, Allentown just 16 as cooler air held much later in the afternoon in the Lehigh Valley and Berks and prevented larger temperature climbs from taking place.   Likewise, Millville climbed 14 degrees between Tuesday and Wednesday as they were able to avoid showers for a longer period of time on Tuesday and were in the warm sector for a while before winds nudged off of the Atlantic and cooled them off.

If anything, this pattern shows how fickle frontal boundaries can be at this time in the year as winter chill gasps for its last signs of life and the strengthening of the Southeast ridge can help negate cold air pushes...or stall them out into fickle boundaries that can screw up forecasts and cause large day-to-day temperature fluctuations.

Afternoon Showers & Thunder

Radar this morning is showing showers and thunderstorms in Ohio and Indiana with a disturbance that will track east along a frontal boundary that stalled out across the region this morning.   The front separates 40's to the north of the front from 60's in Delaware and Extreme South Jersey and by this afternoon will separate 50's  north of the city from 70's to the south.   The aforementioned showers will move east and east-northeast during the day today, generally bringing rain and thunder chances to the city and points north after midday today.

We're not expected severe weather today from these showers or thundershowers -- the disturbance has enough pop though to drop a quarter inch to half inch of rain for areas north of the city later on as it works through.  

Showers and thundershowers could linger around into the evening before gradually pulling north and east as the frontal boundary begins to push northward as a warm front.  Check out the Phils Gamecast for tonight's thoughts on the game (as of this morning).

More:   Current Weather Page

Showers, Mainly South?

Showers may spread in late tonight, especially south of the city, but periods of rain are more likely on Friday from Philadelphia on south as a disturbance tracks east along a stalled frontal boundary that lies to our south. The challenge for forecasters and computer modeling is determining how far north that rain shield gets -- the NAM, for example, essentially shuts the rain shield off at Philadelphia and along 422 to the northwest, with increasing totals of rain to the city's south.  Some parts of the Delmarva may pick up over a half inch from this event -- it's just a question of how far north the northern extent gets.   The NAM is the most south of that extent, with the GFS and EURO painting rain farther to the north...perhaps even into the Poconos.

The high resolution modeling from the Storm Prediction Center shows the potential for some rain on Friday evening across Pennsylvania.   During Friday, most of the rain stays south of the city across Delaware but by dinner time the chances for some precipitation near Philadelphia increases.  It is in the "southern" camp to an extent but does suggest that the northern blob of rain in Pennsylvania could track through Friday evening and overnight.

Regardless, the best chances for the most rain are south of the city, with areas north of Philadelphia on the fence to get little more than just showers.  In fact, it could be dry if the NAM is right outright.

We'll update the weather outlook in the morning.