Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 330 AM EDT Mon May 04 2015 Valid 12Z Mon May 04 2015 - 12Z Wed May 06 2015 ...Severe thunderstorms possible across portions of the central U.S. today and Tuesday... ...Flash flooding possible across portions of the south central U.S. today and Tuesday... ...Above average temperatures to continue through Tuesday for much of the contiguous U.S... The weather pattern across the contiguous U.S. will become increasingly active through the short range forecast period. An upper-level low will move onshore in California today and will move eastward into the Four Corners region by early Tuesday. Upper-level energy associated with this feature will promote the development of widespread showers and thunderstorms across much of the central U.S. over the next couple days. At the surface a stationary frontal boundary will provide a focus for shower and thunderstorms development across the central plains today as southerly winds south of the front transport moist and unstable air northward and lift it across the boundary. This frontal boundary will begin to lift northward as a warm front on Tuesday. Farther south, a surface trough/dry line will serve as a focus for shower and thunderstorm development across the southern plains as several upper-level disturbances pass over the region. Heavy rain and flash flooding are possible in this area today and Tuesday. The Storm Prediction Center is also forecasting a slight risk of severe thunderstorms across much of the central and southern plains. Please refer to the Convective Outlook products issued by the SPC for further details on the severe weather threat. A cold front will move eastward across the Lower Great Lakes today and into the Northeast and Mid-Atlantic tonight. Showers and thunderstorms will be possible across these areas in association with the frontal boundary. A Pacific low pressure system will move onshore in the Northwest this afternoon. Rain showers and high elevation snow showers will be possible in the onshore flow behind the front late today through Tuesday. This low pressure system will cross the Intermountain West on Tuesday and will move into the northern plains Tuesday night into early Wednesday. An upper-level low over eastern Gulf of Mexico will drift eastward to the Bahamas over the next couple days before turning northward. This system will increase chances for showers and thunderstorms across southern Florida on Tuesday. Above average temperatures will continue across much of the U.S. over the next couple days. Afternoon high temperatures today will be 10 to 20 degrees above average across much of the Mid-Atlantic and Northeast, reaching into the 80s in many areas. Temperatures will be below average in portions of the southern and central plains where clouds and precipitation will keep temperatures cooler. Ryan Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_wbg.php