Potential For Strong Storms Tomorrow

With a frontal boundary working east tomorrow into our region, warmth and humidity will provide the spark necessary for thunderstorm development during the afternoon and evening hours. Questions linger regarding how much rain is possible but there is some potential for heavy rain around the region as these storms develop tomorrow and march east.

Modeling is indecisive about the exact location of heavy rainfall -- the NAM (see below) places the heaviest and strongest thunderstorm activity to our north while the GFS places it to our south. The Euro doesn't give any one spot overly heavy rainfall but plants a general swath of half inch rains from tomorrow's thunderstorms. Predicting exactly where summertime thunder drops heavy rain is a low confidence prediction more often than not but noting that more computer models than not are showing the threat for heavy rainfall tomorrow afternoon and evening is worth bringing up.   Some spots could see an inch plus of rain -- if it is Philly or south, the rain will be quite welcome as things locally have been a bit dry of late.

We could see thunderstorms locally as early as later tonight as a warm front associated with this system lifts northeast up the coast. Thunder could break out this afternoon to our south in Virginia and lift northeast slowly this evening along the coast or across New Jersey.    However, the main burst of activity should be later tomorrow with the front crossing the region.

Some of tomorrow's storms could potentially go severe, especially north/west of the city.   Odds don't favor a widespread outbreak of severe as dynamics with the front aren't all that great but with a humid atmosphere and temperatures in the mid and upper 80's the potential does exist for some stronger thunderstorms in the afternoon hours.

Foggy Start Gives Way To Northern Thunder Threat

A foggy...and showery in some spots...morning in the Delaware Valley as a frontal boundary lies about across the region.  It is a warm, summer-like morning that has many birds chirping up a storm at 5 AM as temperatures are in the 60's in many locations.   The frontal boundary lurks between the northern burbs and South Jersey, snaking across the Philadelphia area along where a few showers are falling this morning.   Those showers will exit over the next couple of hours and the fog will lift later on this morning, leading to a mix of sun and clouds and a humid April day as temperatures warm to around 80 or just above that in the city and across inland areas in the Delaware Valley, with 70's across the Lehigh Valley this afternoon.

The warming coincides with a northward advance of that frontal boundary, with said boundary acting as a trigger for thunderstorm activity in spots this afternoon and evening.   Best chances for storms will be dinner through 11 PM to the west and northwest of the city.   The Storm Prediction Center has much of Central Pennsylvania under a slight risk for severe weather, with that slight risk grazing the western suburbs.  Higher resolution radar below shows the thunderstorm potential this evening mainly west of Philly, with the NAM and  GFS in general agreement that the thunder threat stays out west.

The front will lift north and provide us one relatively thunder-free day in the coming warm stretch -- Tuesday looks to be the nicest overall day as temperatures get into the 80's again away from the coast.   We say "relatively" thunder free as there is still a chance for thunderstorms to our west in Central PA...odds favor Tuesday's storms staying west, which means warmth and more sun than none for us.

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Maybe Some Storms Later...

It's a warm and borderline muggy afternoon in the region -- temperatures are in the low and mid 80's in many locations and with a stiff southwest wind it feels a bit summery outside today.   While the cold front that will put the brakes on the warmth is still out across Western Pennsylvania, a few thunderstorms have tried to pop up ahead of the front.   However, a lack of upper dynamics plus limited instability is keeping thunderstorms from blossoming into full blown severe storms and even weakened the complex of storms that is currently near Scranton on the radar.

Most of the organized severe weather is farther southwest, setting up with an upper level disturbance back in the Ohio Valley.  This system will organize a low pressure center that will track through here on Tuesday afternoon and night, bringing us consistent and steadier showers or period of rain as well as colder temperatures due to the low tracking to our south and the cold front slipping past us early tomorrow morning. A few rumbles of thunder and a period of rain are likely later on tonight with the cold front itself (look back by Pittsburgh for the smattering of thunderstorms and rain) but the odds for severe weather are decreasing.   The Storm Prediction Center still has Pennsylvania under a slight risk for severe weather and one can't rule out a strong gust of wind with any thunderstorms that do pop in the next few hours.     However, the threat is relatively limited overall.

Enjoy the warmth though -- the one day surge into the mid 80's will be quickly replaced by a cool down tomorrow!

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Freaky Friday

The morning radar and temperature overlay is showing a "lull" between rounds -- this looks like a three round event at play as round one has lifted through most of the city and is about to lift through Bucks and the eastern suburbs, and round two is approaching us from the west in Central Pennsylvania.   In the interim, a couple of "dry" hours except for spray on the roads.    Temperatures this morning are pretty much in line with what we thought as a warm front lurks just to our south -- 40's in place around town this morning, with 50's in Lower Delaware, and 30's in the Poconos where icy rain has fallen for much of the evening.

The radar look on the left shows a bit of a wider view of the incoming storm and the other two rounds.   Round two is the batch in Central Pennsylvania in association with surface low pressure that will ride east-northeast through the state today.  As this moves through later this morning, expect a round of rain to come back in (probably after 7, 8 AM) and for some of that rain to be heavy in the northern suburbs.  Farther south, showery rain will dash through.   Around midday, this second round of rain clears the coast and we enter a dry slot between this and the upper level energy that lurks back in Ohio (you can see a break in Eastern Ohio on the left edge of the map).   Winds will shift to the west-southwest and increase to 15-25 mph, with some clearing possible for a couple of hours as those west-southwest winds 'dry' out the lower atmosphere.    As that upper energy works east and pulls cold air in, thunderstorms or gusty showers could break out along the leading edge of the colder air.   Those showers/storms will work through between 3 and 5 PM and could bring a brief, heavy shower but more importantly, bring the strongest winds of the day to those areas they impact assuming they develop.   Winds could gust to 60 mph, perhaps higher in those gusty showers/storms.   By definition, that's severe criteria so it's possible we could see a few rogue warnings this afternoon across Southeastern Pennsylvania, Maryland, New Jersey.

Temperature-wise, it's going to be a bouncy day.  Around Philadelphia, temperatures will stay in the 40's until late morning before they begin to spike in the dryslot.  We could get into the 60's for a time south of the city but could approach that mark around the city for a couple of hours if we get some sun.   As the front/gusty showers work in towards dinner we will see temperatures drop off after 5 PM through the 50's and 40's over the course of the evening, leading to a cool and windy night.

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