From the ABC 7 Weather team

Severe weather outbreak possible Friday

May 30, 2012 - 09:53 PM
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The severe weather season in the District and surrounding areas back to the Shenandoah Valley has revved up quickly this past week. The icing on the cake could be with a strong frontal passage Friday.

All the ingredients could be coming together for a large scale severe weather outbreak in the region late Friday. As a matter of fact, some of the factors are falling in line with a past episode of severe weather that occurred at almost exactly the same time of the year back in 1998.

First of all, at the surface, a strong cold front separating warm, humid air from much cooler, drier air will be a driving mechanism for storms to build across western Pennsylvania and carry over the mountains into the District. All the forecast models agree the timing of the storms to be during and just after the warmest part of the day; mainly between 4 p.m. and 10 p.m. This could significantly impact the evening commute.

FrontForecast

(This image shows an average model solution for Friday evening. The front noted with the edged line likely moves through before Midnight. The bright yellow blobs show where the best potential for severe storms would be along the front.)

The front has significant upper-level support. Aloft, winds will be diverging allowing air at the surface to rise. The storms will easily be able to tap strong winds aloft around 50 mph. Significant updrafts going well into the atmosphere, bypassing the freezing level at 10,000 feet will be enough to support large hail. Additionally, winds turning with height (or changing direction) could be enough to generate a few tornadoes.

The threat is great enough that the Storm Prediction Center has much of the East Coast in a slight risk for severe weather two days out already.

Ironically, the forecast for severe weather on Friday, June 1st comes within 24 hours of the 14-year anniversary of the major outbreak on June 2, 1998 across the Mid-Atlantic. A similar situation happened with a strong cold front plowing east from the Ohio Valley. Very warm temperatures ahead of the front were replaced by much cooler, breezy weather in the 1998 set up.

Notice the similarities in the weather map from the morning of June 2, 1998 (below) and where the forecast models show a similar strong front this Friday morning (second image below). The low pressure is forecast to be only 250 miles southeast of the June 2nd outbreak.

1998surfacemap

(Archived weather map from 8 a.m. June 2, 1998)

ModelForecast

(Long-term GFS forecast model shows the placement of the cold front on Friday morning)

The wind profile from Dulles International late on June 2, 1998 is seen below. The winds up to 5,000 feet in this sounding are 29 knots with mid-level winds (on the same horizontal line as the number 50 on the diagram) are 46 knots. The strength of the wind field through the atmosphere between the June 2, 1998 outbreak and what is forecast for Friday afternoon (second image below) is very similar as well.

IADSounding(The wind profile from Dulles International on the evening of June 2, 1998. Courtesy of the National Weather Service in Sterling, Va.)

 

ForecastSounding(The forecast wind profile for Friday afternoon)

The June 2, 1998 outbreak produced Maryland’s first F4 tornado (before the Fujita Scale was renamed to the Enhanced Fujita Scale) in a small western Maryland town of Frostburg. In total, 7 tornadoes touched down in the Baltimore-Washington Forecast Office’s area of responsibility on that day.

All-in-all with a severe weather outbreak possible Friday, you should stay tuned to ABC7 Weather Team and WTOP for the latest forecasts and any watches and warnings that could be issued on Friday.

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