June 10th, 2008 Severe Weather Discussion
4:45 PM Discussion: Some pretty explosive development taking place along the I-81 corridor. Would not be surprised to see a severe thunderstorm watch issued for a chunk of our region within the next hour or so. Take a look at the radar below you can see the storm development that has taken place over the last hour northwest of the city.
3:00 PM: Severe Thunderstorm Watch until 10 PM in Central PA, basically Lancaster on west. Watch also includes DC, Baltimore, Scranton, and Upstate New York.
2:45 PM Update: The first storm is popping up in Northeast Maryland and far southern Chester County. This first storm is moving northeast to the west of Philadelphia. As of 4 PM that storm fell apart as the cap is holding in place over Philadelphia. However, more storms are farther west over Central and Western PA. Those may impact our region later tonight.
1 PM Update: Moderate Risk for severe weather extended down to Washington DC area and continues to run along and west of I-95. Storm Prediction Center discussion continues to outline the potential for scattered storm development later this afternoon.
Looking at the composite index data at the Storm Prediction Center website the best chance for "supercell" development in our region as of noon is around Lancaster and York. Given the upper pattern aloft, these storms would migrate east-northeast and northeast, which could push them essentially along and just south of 222.
11 AM Update: A tornado watch is out over Northeast PA and Upstate New York, in an area where the most severe weather will take place later today. Our area is definitely prime for severe weather but we may not see a squall line of storms sweep across Philadelphia -- the storm activity is more likely to be scattered storms or a broken line of storms and some of those storms are definitely going to bring a wallop to them. One of the reasons for storms likely being more scattered than in a line is a "cap" in the atmosphere which prevents air from rising and cloud formation to take place. Anywhere where this cap is broken is where the best chances for storm development will take place. Calling that is the tough part, but given that we have had four days of 90 degree weather some areas will get some nasty weather later this afternoon.
The most recent runs of the NAM support the potential for some strong to severe storms later this evening across our region (after 5 or 6 PM).
With the hot weather in place over the Delaware Valley it's not going to take much of a front or trough to set off showers and thunderstorms. We will have a weak "cold" front moving east through the Great Lakes and into the Northeast over the next 12-18 hours and will be trying to nudge this heat and humidity out of the way.
Given that we will have four days of non-stop heat over much of the region with little in the way of thunderstorm activity in the Delaware Valley itself there is plenty of instability in place and most severe weather parameters support the potential for strong and severe thunderstorms to develop Tuesday afternoon across Central PA. These storms will move east and through the Delaware Valley during the late afternoon and early evening hours. As a result a moderate risk for severe weather is out for today west of Philadelphia, with a slight risk for Philadelphia and points south & east.
Storm development should take place between 2 and 4 across Central PA, impacting the Delaware Valley probably after 5 PM in the afternoon from west to east. Storm development looks to be scattered the farther south one goes but storms may tend to organize into a squall line of sorts as one travels farther north as upper level support is stronger. The strongest threat from these storms will be straight line-winds, followed by hail, but an isolated tornado cannot be ruled out in the region.
The price paid in the form of possible strong and severe weather on Tuesday will result in less humid and cooler weather starting Wednesday as temperatures will be in the 80's. While still above average (which is around 80), temperatures will feel a whole lot less abrasive compared to the sauna of the last few days.
There will be a couple of updates through the day today on the weather situation (heat, severe weather) warrant an occasional update or two through the day. Radar is posted below and you can click on it to see the radar in full size imagery.
3:00 PM: Severe Thunderstorm Watch until 10 PM in Central PA, basically Lancaster on west. Watch also includes DC, Baltimore, Scranton, and Upstate New York.
1 PM Update: Moderate Risk for severe weather extended down to Washington DC area and continues to run along and west of I-95. Storm Prediction Center discussion continues to outline the potential for scattered storm development later this afternoon.
Looking at the composite index data at the Storm Prediction Center website the best chance for "supercell" development in our region as of noon is around Lancaster and York. Given the upper pattern aloft, these storms would migrate east-northeast and northeast, which could push them essentially along and just south of 222.
11 AM Update: A tornado watch is out over Northeast PA and Upstate New York, in an area where the most severe weather will take place later today. Our area is definitely prime for severe weather but we may not see a squall line of storms sweep across Philadelphia -- the storm activity is more likely to be scattered storms or a broken line of storms and some of those storms are definitely going to bring a wallop to them. One of the reasons for storms likely being more scattered than in a line is a "cap" in the atmosphere which prevents air from rising and cloud formation to take place. Anywhere where this cap is broken is where the best chances for storm development will take place. Calling that is the tough part, but given that we have had four days of 90 degree weather some areas will get some nasty weather later this afternoon.
The most recent runs of the NAM support the potential for some strong to severe storms later this evening across our region (after 5 or 6 PM).
With the hot weather in place over the Delaware Valley it's not going to take much of a front or trough to set off showers and thunderstorms. We will have a weak "cold" front moving east through the Great Lakes and into the Northeast over the next 12-18 hours and will be trying to nudge this heat and humidity out of the way.
Given that we will have four days of non-stop heat over much of the region with little in the way of thunderstorm activity in the Delaware Valley itself there is plenty of instability in place and most severe weather parameters support the potential for strong and severe thunderstorms to develop Tuesday afternoon across Central PA. These storms will move east and through the Delaware Valley during the late afternoon and early evening hours. As a result a moderate risk for severe weather is out for today west of Philadelphia, with a slight risk for Philadelphia and points south & east.
Storm development should take place between 2 and 4 across Central PA, impacting the Delaware Valley probably after 5 PM in the afternoon from west to east. Storm development looks to be scattered the farther south one goes but storms may tend to organize into a squall line of sorts as one travels farther north as upper level support is stronger. The strongest threat from these storms will be straight line-winds, followed by hail, but an isolated tornado cannot be ruled out in the region.
The price paid in the form of possible strong and severe weather on Tuesday will result in less humid and cooler weather starting Wednesday as temperatures will be in the 80's. While still above average (which is around 80), temperatures will feel a whole lot less abrasive compared to the sauna of the last few days.
There will be a couple of updates through the day today on the weather situation (heat, severe weather) warrant an occasional update or two through the day. Radar is posted below and you can click on it to see the radar in full size imagery.
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