Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 119 PM EST Fri Dec 20 2019 Valid 00Z Sat Dec 21 2019 - 00Z Mon Dec 23 2019 ...Heavy rain and mountain snow for the Pacific Northwest and rain returns to the Gulf Coast region in time for the weekend... Heavy rain and high elevation snow will continue to make weather headlines from northern California to western Washington as an atmospheric river advects deep Pacific moisture inland across the region. This pattern will be supported by an active jet stream pivoting around a large and slow moving low pressure system over the northeast Pacific, spawning multiple waves of low pressure along a slow moving cold front. Extended periods of moderate to heavy rain could result in additional rainfall amounts on the order of 3 to 6 inches over portions of western Oregon and northwest California through Saturday evening. Over the higher elevations of the Cascades and Olympic Mountains, heavy snow is expected with accumulations of 1 to 3 feet possible. An upper level low crossing the southern Plains today is forecast to reach the Gulf Coast region by Sunday morning. A strong shortwave impulse associated with this will result in the development of a surface low over the northern Gulf of Mexico by Saturday morning. Increasing cloudiness followed by widespread rain is forecast from the central Gulf Coast eastward to South Carolina as copious moisture surges northward. Further development of this low is expected beyond this forecast period. In terms of temperatures, conditions will be gradually moderating through the weekend across the East Coast region after a couple days of very cold weather. In contrast, warmer than normal temperatures are expected across the Plains, and this should expand eastward to the Great Lakes, Ohio Valley and the Southeast by the weekend. D. Hamrick Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php