Sunday, July 15, 2012

Forecast for Sunday, July 16, 2012

A weak trough is currently producing some scattered showers and thunderstorms across our region. Any thunderstorms into tonight have the potential to produce a few inches of rain in a short period of time and could cause isolated flash flooding. Some thunderstorms may also contain some strong wind gusts. An earlier thunderstorm in South-Central Pennsylvania had some rotation with it and any stronger storms across our region may rotate a bit as well. The overall threat for severe weather is minimal with the Storm Prediction Center giving us a 5% chance of damaging winds or large hail within 25 miles of a point, below the slight risk threshold of 15%. 

Hot weather begins Monday with excessive heat expected starting on Tuesday as a Bermuda High Pressure area sets up shop in the Atlantic and pumps in a hot, southerly flow of air. Temperatures should top out into the mid nineties on Monday. By Tuesday and Wednesday, oppressive conditions are expected with high temperatures in the upper nineties. A 100 degree reading cannot be ruled out. Heat Index Values between 100 and 108 should be expected during Tuesday and Wednesday, particularly in the afternoon and early evening hours. For Monday and Tuesday, minimal thunderstorm activity is expected at this moment. There could be an isolated thunderstorm on Monday with a weak cold front. However, our eyes need to be focused out to our west for any potential MCS development. An MCS is very difficult to forecast for and may head our way with little notice or at least send leftover cloud debris. An Excessive Heat Warning is in effect for Tuesday and Wednesday for Philadelphia and surrounding urban areas.

On Wednesday, severe thunderstorms look very likely as a strong cold front, with plenty of moisture coincides with daytime heating and moves through in the early evening hours. Damaging winds with some areas of large hail are the primary threats at this moment. Just like the past few thunderstorm events to take place during extreme heat outbreaks, these thunderstorms should have the access to strong instability that allows some of them to produce significant damaging wind gusts. Some relief is anticipated behind the front with another round of warming temperatures and humidity late in the forecast period.