Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 305 AM EDT Tue Sep 10 2013 Valid 12Z Tue Sep 10 2013 - 12Z Thu Sep 12 2013 ...Strong to severe thunderstorms possible from the Great Lakes into northern New England... ...Heat and humidity will be on the increase across the Ohio Valley...Northeast...and Mid-Atlantic states through midweek... ...Heavy showers and thunderstorms will persist over the Southwest...promoting additional concerns for flash flooding... Multiple surface waves of low pressure tracking northeastward across the Great Lakes region and into the Saint Lawrence River Valley over the next couple of days will help to focus multiple clusters of moderate to locally heavy showers and thunderstorms. While gradually the main focus for the activity will be tending to shift north into southeastern Canada, expect the Great Lakes region and especially northern areas of New England to see multiple rounds of showers and thunderstorms today through Wednesday, and especially as a warm front crosses the region. Some of the thunderstorms will be strong to severe. By Wednesday night and Thursday, a cold front will be dropping southeast, which will bring a renewed band of showers and thunderstorms to the region. South of the aforementioned warm front, the airmass will be quite hot and humid, and this airmass which has already be in entrenched over the Midwest and the South will be advancing up across the Ohio Valley and into the Mid-Atlantic and Northeast by Wednesday. Thus, expect temperatures the the next couple of days to be well above normal. Meanwhile a front attendant to the aforementioned waves of low pressure crossing the Great Lakes region will be trailing southwest down into the Central Plains where it will be stalled out. The front should act as a focus for some scattered showers and thunderstorms throughout the Midwest. By Thursday, cool high pressure settling south from Canada will push the front southeast as a cold front through the Midwest and into the Ohio Valley and Lower Great Lakes region. This will bring an end to the aforementioned heat and humidity, and this will ultimately push into the Mid-Atlantic and Northeast just beyond this period. Across the South, heat and humidity will be the story, but it will be considerably more unsettled back into the Southwest U.S. for the balance of the week. Deep and very moist monsoonal flow will persist and become entrenched over the region from the Desert Southwest northeast into the Central Rockies and immediate High Plains near the Front Range. A weak upper level trough of low pressure over the Southwest is expected to interact with this moist monsoonal fetch and support widespread showers and thunderstorms across the region. Given the anomalous amount of moisture in place, expect heavy rainfall amounts with an elevated risk of flash flooding, especially over and near areas of higher terrain. The remainder of the South will tend to be dry, with the exception of southern Texas and southern Florida where moist easterly flow will support some scattered showers and thunderstorms. Orrison Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_wbg.php