Friday, July 6, 2012

July 6, 2012 Severe Weather Discussion

There is a slight risk of severe weather over the Mid Atlantic into the Northeast, with two 'See Text' areas placed over the Southeast and South Central Plains.

Short range guidance indicates a cold front will be moving south, igniting showers and thunderstorms in the Mid Atlantic region, progressing southward as the day goes on. As this cold front moves southward, it will encounter roughly 5000 j/kg of instability based on NAM sounding. 12z NAM sounding forecast indicates the likelihood of a capping inversion over southern Pennsylvania into the severe weather region being watched tomorrow. Should this capping inversion be present, there is the potential that some of the storms will be unable to form. It will depend on the strength of the cold front to force air upwards, past the cap and into the 4000-5000 j/kg of instability across the area being monitored.


Temperatures to Moderate for Next Week

Temperatures are expected to moderate across the country over the next week, as a series of cold fronts move south and drop temperatures into the 80s across many areas that have touched or broken 100 in the past few days.

Short range guidance for Sunday evening by the Hydrometeorological Prediction Center (HPC) shows a few low pressure systems affecting the midsection of the US, igniting some showers and storms in the Mid Atlantic. Behind those systems is a long cold front, which will be draped over much of the US and deliver relief to areas that have seen numerous records smashed over the past week or more.

Monday evening brings the main cold front to a stationary position while a Canadian low pressure system drops another cooling air mass into the upper Midwest. Temperatures will only continue to drop in those areas, while places below that second cold front will keep temperatures at around seasonal levels.

The National Centers for Environmental Prediction Ensemble System is projecting the Madden-Julian Oscillation to make a quick turn around from a very close brush with Phase 3, which would increase precipitation across much of the northern US. However, the ensembles are indicating that a switch into a weak Phase 2 and eventually a strong Phase 1 would indicate a cooling trend across the Eastern US for the duration of Phase 2 and a slight warming trend going into Phase 1, which does appear to be the thinking of National Weather Service forecasts.

The ECMWF Ensemble Prediction System is indicating that the MJO will instead move into an early Phase 3 before looping back into a weak Phase 2 and 1 before once again looping around and strengthening in Phase 2, which would keep the nation on a cool trend. Eventually, it looks to come down to when the MJO decides to switch back into Phase 2 and 1, and just how early this switch may happen.