Severe Thunderstorms marching east

If you haven't been outside yet today, the unusually cool weather of the past few days is gone.  Ahead of a strong cold front, warm and humid air is surging into the region along gusty southwesterly winds.  If you have a relative who gets pain in their joints as the pressure falls, I don't need to tell you that change is once again on the way.  A strong cold front currently draped across Western Pennsylvania is heading east, and thunderstorms are popping up along and ahead of the front this afternoon in the warm, unstable air across the Keystone State.  The Storm Prediction Center has maintained their slight risk for severe thunderstorms this afternoon across our entire coverage area (the map above shows the probability of wind gusts of at least 50 knots, or 58 mph, anywhere within 25 miles of a point -- 30%, which is fairly high).

Right now, it looks like the time frame for these storms would be anywhere between 5 and 10pm.  Obviously, with such a soupy atmosphere, thunderstorms can develop at anytime, but the primary line associated with the cold front should hold off until mid- to late-evening.  A severe thunderstorm watch is already up for most of Central PA through this evening, and will likely be expanded further east over the next few hours.  The storms that have already popped up across the Appalachian ridges south of State College have a fairly dangerous characteristic -- they all seem to be producing large, damaging hail, at least according to radar.  That may be the biggest threat for the next few hours, but as the storms move east, the threat for damaging straight-line winds will increase, and that will likely be our biggest threat this evening.

Of course, tune to local media for the latest updates, and follow out Twitter account for updates as well.
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Well Blow Me Down!

Southeastern Pennsylvania was rocked by strong wind gusts, usually reserved for March, for hours-on-end Saturday afternoon and evening.  The end result was numerous reports of downed trees, power outages, and several dozen lost lawn ornaments.  Even at this late hour, at least 4,000 PECO residents are still without electricity in the Philadelphia metro area.  Peak wind gusts registered by area weather stations easily exceeded 40 mph in most areas, with some even above 50 mph.  Below are official peak wind gusts at observing sites from around the area on Saturday:

Observing Site	Peak Wind Gust
Philadelphia (International Airport)	55 mph
Northeast Philadelphia	51 mph
Allentown (International Airport)	50 mph
Willow Grove	47 mph
Reading	47 mph
Doylestown	47 mph
Allentown (Queen City Airport)	45 mph
Blue Bell	43 mph
Coatesville	41 mph
Pottstown	40 mph

So, what's the deal?  An area of low pressure, which dragged a cold front through the region earlier this morning, rapidly deepened today as it moved through Northern New England.  The corresponding difference in pressure, or gradient, between the deepening low and a high pressure moving east into the Ohio Valley led to the strong winds.  Short of giving you an exhaustive meteorology lesson -- many of the details I've probably forgotten since graduation -- know that a strong, or tight, pressure gradient = strong winds.  Luckily for those tired of swerving around road debris in their cars, the gradient is lessening, and wind speeds will be lower for Mother's Day.  However, as daytime heating commences with the pressure continuing to rise, stronger-than-normal wind gusts can be expected during the day on Sunday, but probably not to the tune of 50 mph again.

One thing you're also going to notice is the drastically cooler weather now that the cold front is history.  Hope you bought mom a sweatshirt or a new coat for Sunday as high temperatures across the area will struggle to reach the upper 50s, in fact we'll probably be in the 40s for much of the morning (breakfast in bed rather than a brunch out?).  A taste of Winter will come by nightfall, with temperatures plummeting into the 30s by early Monday morning.  There is even the potential for a hard freeze across the usually colder areas overnight Sunday, so keep mom's flowers inside.  Similarly cool weather can be expected for Monday and Monday night.

A special shout-out to the moms on their special day.  Maybe you'll get a Snuggie tomorrow.
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Odds & Ends: Recent Storms, Gulf Oil Spill, Cooler Weather

It's been a while since our last blog post, and a lot of meaningful weather has occurred.  The first real taste of Summer heat and humidity roasted the region this past weekend.  While it wasn't the first time many of us saw temperatures eclipsing the 90-degree mark (see early April), humidity reared it's ugly head over the weekend, creating that classic, sweaty combo and drawing to mind that classic comment: "It's not the heat, it's the HUMIDITY!"

March of the Storms:
Luckily for those of us longing for drier, cooler air -- or those who wish not to hear that cliche repeated every few minutes -- relief came Sunday night in the form of showers and strong thunderstorms.  Those showers and thunderstorms brought locally heavy rainfall, gusty winds and some localized storm damage, which could've been worse had the storms not weakened as they moved into our area.

The storms on Sunday night were associated with the first of several frontal boundaries that have been marching through the region over the past 48 hours.  The cold front that finally brought relief in the humidity department arrived on Monday afternoon with gusty showers.  Yet another surface trough feature pushed through today, again associated with a thunderstorm, which many felt the effects of even without receiving a single drop of rain.  An outflow boundary, or strong gust front that is generated by a thunderstorm and then pushes out well ahead of it (see the Wikipedia article), swept through most of Bucks and Montgomery counties between 4 and 5pm today.  It was even detected on the reflectivity mode of radar (see image to the right), which normally only detects precipitation.  Check out that thin, blue line as it pushes out well ahead of the parent thundershower.  As it moved through, we saw calm, warm conditions turn suddenly into cooler, gustier conditions.  For example, at Doylestown, just outside of our coverage area, temperatures fell from 75 to 63 in an hour (presumably a matter of minutes between observations) on a wind shift from west to northwest with only 0.01" of rain.

If you're yearning for an afternoon of weather that won't be interrupted by sudden showers and wind shifts and outflow boundaries, you'll be in luck... but just for a day.  Wednesday will feature bright, sunny skies and temperatures into the lower 80s.  Additional frontal boundaries, similar to those we've been experiencing the past few days from what are called "shortwaves," will continue to affect us toward the end of the week.  A stronger cold front will usher in unseasonably cool weather by next weekend, but more about that later.

Gulf Oil Spill:
I'm sure by now you've heard about the tremendous disaster occurring in the Gulf of Mexico with the explosion of a BP oil rig and subsequent, significant discharge of oil that is still ongoing.  What you may not know is that NOAA, the parent government agency behind the National Weather Service, is largely responsible for tracking and forecasting the trajectory of the 150-mile wide swath of oil.  Dubbed "Deepwater Horizon Incident," NOAA's website portal for the disaster is constantly being updated with new information about the disaster as 210,000 gallons of oil continues to be released into the Gulf every day.

While Louisiana and Florida are most imminently under the threat of environmental impacts from the growing oil spill, there are growing concerns that even those with interests along and off the Atlantic East coast could soon have to deal with oil contamination.  Strong northwesterly winds, which are expected later this week, could force some of the oil further to the southwest of its release point and into the Loop Current, a swift underwater current that would drive the oil southeast toward the Florida Keys.  At this point, it would come in contact with the Gulf Stream and potentially traverse up offshore of the East Coast.  Of course this is all theoretical, and dependent on many factors including steering winds, precipitation, and whether or not BP is finally able to shut off that insufferable valve.

Cooler Weather this Weekend:

As the Montreal Canadiens head into town to face the Flyers this week, another un-welcomed Canadian guest may not be far behind.  Behind a strong cold front which is expected to move through early Saturday, cooler-than-normal Canadian air will usher into the area for the beginning of next week.  After our low temperatures a few days ago barely edged below 80 degrees, some of us may struggle to reach 60 for a high on Sunday.  The image to the right shows the Climate Prediction Center's temperature outlook for early next week, and there's plenty of blue/below normal across the Northeast.

As always, continue to follow our Twitter account, @TheWeatherWord, for more frequent updates you won't always see here on the blog.
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