Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 253 AM EDT Thu Oct 20 2016 Valid 12Z Thu Oct 20 2016 - 12Z Sat Oct 22 2016 ...Heavy rain possible for for portions of the central Appalachians and Northeast... ...Cooler temperatures across the central U.S. today spreading to the East Friday and Saturday... A developing area of low pressure along a frontal boundary will bring showers and thunderstorms from the lower Mississippi valley to the Great Lakes and portions of the Northeast today. On Friday the system will continue to strengthen as it crosses the Appalachians, eventually evolving into a low pressure system off the southern New England coast by Friday evening. Widespread rain is expected to continue from the Appalachians and portions of the Mid-Atlantic to the Northeast on Friday. This system could produce heavy rainfall both today and Friday anywhere from the eastern Ohio valley and central Appalachians to the Northeast. As the low pressure system moves north along the coast of Maine by Saturday morning, colder air wrapping around the western side of the system could cause rain to mix with snow across the higher elevations of interior Mid-Atlantic and Northeast. Behind the cold front associated with the strengthening eastern U.S. low pressure system, a cool Canadian air mass with below average temperatures will overspread the central and eastern U.S. High temperatures today are forecast to be 5 to 10 degrees below average from the southern plains to the Upper Midwest. The cool temperatures will spread east on Friday and Saturday, with high temperatures 5 to 15 degrees below average across the Great Lakes and Ohio valley on Friday, reaching the Eastern Seaboard by Saturday. The Pacific Northwest will see occasional periods of rain through the next few days as a series of relatively weak frontal systems move into the region. The first frontal boundary will move onshore today, with showers expected from the Pacific Northwest into the northern Intermountain Region. Precipitation will taper off somewhat tonight into Friday morning before another round of showers arrives with a weakening frontal boundary by Friday afternoon. Showers will once again taper off Friday night before another system begins to approach by Saturday. With each of these, precipitation will fall as rain at all but the highest elevations, where snow will be possible. Ryan Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_wbg.php