Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 401 PM EST Thu Dec 19 2013 Valid 00Z Fri Dec 20 2013 - 00Z Sun Dec 22 2013 ...Heavy rain possible over the Lower/Middle Mississippi Valley into parts of the Ohio Valley... ...Heavy precipitation possible over the Cascades... ...Temperatures will be 15 to 20 degrees below average for the Northern/Central Plains ... in contrast temperatures will be 15 to 20 degrees above average for parts of the Lower/Middle Mississippi Valley into parts of the Tennessee and Ohio Valleys... A quasi-stationary front will extend from the Northeast to the Southern Plains through Saturday. A storm over the Southwest/Northern Mexico will move eastward to the Southern Plains, merging with the quasi-stationary front by Saturday morning. A wave of low pressure along the boundary over the Lower Missouri Valley will move northeastward along the quasi-stationary boundary to Northern New England by Saturday. The system will produce rain over parts of the Middle Mississippi Valley into parts of the Ohio Valley with a small ribbon of rain/freezing rain over parts of the Middle Missouri Valley on Thursday evening. The rain will move eastward into the Ohio Valley and Northern New England by Saturday morning. Snow will develop over parts of the Northern Plains into parts of the Upper Great Lakes that will move into the Great Lakes and parts of Northern New England, also by Saturday. Along the rain/snow line, pockets of rain/freezing rain will develop Thursday into Saturday. Meanwhile, a closed upper-level low over Southern California/Northern Mexico will move eastward to the Southern High Plain/North-Central Mexico by Saturday. The storm will produce higher elevation snow/lower elevation rain over parts of the Southwest/Southern California ending over California by Friday morning. The snow will end over parts of the Southwest overnight Friday, with the rain tapering off to scattered rain by Saturday morning. As the upper-low moves closer to the Southern Plains, moisture from the Gulf of Mexico will move northward into the Western Gulf Coast/Lower Mississippi Valley by Saturday morning. The moisture will overrun the associated front producing light to moderate rain over parts of the Southern Plains on Friday. The rain will expand into parts of the Ohio and Middle Mississippi Valleys, while increasing in intensity to moderate to heavy rain by Saturday. Showers and thunderstorms will also start to develop over parts of the Lower/Middle Mississippi Valley on Friday evening. Likewise, the showers and thunderstorms will expand into the Tennessee Valley/Southern Ohio Valley while increasing to moderate to heavy rain by Saturday morning. Additionally, an area of rain/freezing rain will develop over parts of the Central Plains into the Middle Mississippi Valley on Saturday morning. In the meantime, upper-level energy will move onshore over the Pacific Northwest early Friday morning moving to the Northern/Central Rockies by Saturday. A plume of Pacific moisture will accompany the energy, producing coastal rain and snow at relatively low elevation on Friday morning. The snow levels will rise through Friday into Saturday morning. Snow will also develop over parts of the Northern Rockies/Northern Intermountain Region by Friday evening, expanding into parts of the Central Rockies/Great Basin by Saturday morning. Ziegenfelder Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_wbg.php